uu.seUppsala University Publications
Change search
Refine search result
12 1 - 50 of 58
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Aihara, Aya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Uzunoğlu, Bahri
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Florida State Univ, Dept Math, Tallahassee, FL, USA.
    Vortex induced vibration energy extraction modeling via forced versus free vibration2017In: Proceedings Of Oceans 2017 - Aberdeen, IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    Vortex induced vibrations (VIV) for energy extraction have been revisited in last years by both marine power and wind power communities. Even though vortex induced vibrations have been focus of research for many years, energy extraction from vortex induced vibrations is relevantly new field which needs more detailed investigation and modeling. To this end, there has been recent experimental and modeling parametric studies where VIV was modeled by solution of one-degree-of-freedom ordinary differential equation spring system where engineering modeling of vortex induced vibration for energy extraction has been investigated based on a spring system with the forces defined from forced oscillation experiments where full coupling of free oscillations were not taken into account. Herein a Computational Fluid Dynamics (CFD) modeling of a circular cylinder will be studied to compare forced and free vibrations in the context of vortex-induced energy extraction. The model is essentially solved by partial differential isothermal incompressible Navier-Stokes equations to model fully mathematical model of the fluid-structure interaction of vortex induced vibration. The comparison between forced and free oscillation response studies of this paper will serve to improve the scientific knowledge where vortex induced vibration modeling are comparatively more limited. The preliminary results are presented herein for forced and free oscillations for the Reynolds number regimes Re = 100 and Re = 3800 in two dimensions for combinations of amplitudes and frequency of oscillations in the context of energy extraction modeling.

  • 2.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saury, Didier
    Univ Poitiers, ENSMA, CNRS, Inst PPRIME, BP 40109, F-86961 Futuroscope, France.
    Temperature and velocity measurements in a buoyant flow induced by a heat source array on a vertical plate2017In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 88, p. 234-245Article in journal (Refereed)
    Abstract [en]

    Heat source arrays are common in engineering applications. Natural convection is a reliable and silent cooling strategy. Therefore, an array of flush-mounted heat sources has been studied under conjugate conduction and natural convection condition. This studies was performed for a system with relatively large dimensions, typical for power electronics, and a modified Rayleigh number up to 2 . 10(10) A modular set of heaters was designed to vary the distribution of heat sources on the plate and investigate the influence of the spacing. Velocity and temperature were measured in the convective flow with particle image velocimetry and micro-thermocouple. The velocity field was analyzed with proper orthogonal decomposition. The first instabilities of the convective flows were described. The results gave abetter understanding of the heat transfers in these configurations and are valuable for model validation.

  • 3.
    Berglund, Albin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evolution of Cavity Tip Vortices in High-Pressure Turbines2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This degree project in applied physics studies the tip gap flows over the rotor blades of a high-pressure turbine. The rotor blade used in the study has an improved design that utilizes both a cavity tip and an uneven profiling to reduce turbine loss. The designed rotor blade is shown to admit a 21% lower leakage mass flow rate across the tip gap than a reference rotor blade with a flat tip. By studying the designed rotor blade using transient CFD, the flow field of the tip gap region has been studied through one blade passage. The flow field characteristics of particular interest are the leakage mass flow rate across the tip gap region, which is proportional to turbine loss, and the characteristic vortices that reside within the cavity tip. By using post-processing scripts, the leakage mass flow rate has been calculated for every time step across one blade passage, showing a strong time dependence. The characteristic vortices are found using two different vortex detection algorithms, and their respective vorticity magnitude is shown to depend on the leakage mass flow rate. The simulation shows that the vorticity magnitude is increasing above a threshold of leakage mass flow rate, and that it is decreasing under this threshold. This effect is shown to destabilize the leakage mass flow rate, increasing its amplitude over its period of one blade passage.

  • 4. Birken, Philipp
    et al.
    Bull, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Jameson, Antony
    A study of multigrid smoothers used in compressible CFD based on the convection diffusion equation2016In: Proc. 7th ECCOMAS Congress, European Community on Computional Methods in Applied Sciences (ECCOMAS), 2016, p. 2648-2663Conference paper (Refereed)
  • 5. Birken, Philipp
    et al.
    Bull, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Jameson, Antony
    Preconditioned smoothers for the Full Approximation Scheme for the RANS equations2019In: Journal of Scientific Computing, ISSN 0885-7474, E-ISSN 1573-7691, Vol. 78, p. 995-1022Article in journal (Refereed)
  • 6.
    Blomström, Hanna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Effektiviseringspotential inom industrisektorn: Energibesparing vid frekvensstyrning av centrifugalpumpar – en fallstudie2013Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The project was performed at Siemens

    Industry Drive Technologies with the

    objective to provide actual values for

    the energy savings potential within

    Siemens scope of practice.

    In Sweden the electrical drives stand

    for about 30 % of the total electricity

    consumption and about 60 % of the

    electricity consumption within the

    industry. During the pre-study phase

    electrical drives with pump applications

    were identified as large energy users.

    Because of this a case study at one of

    Siemens customers, Stora Enso Fors was

    performed. The system that was evaluated

    during the case study was a throttled

    system with a centrifugal pump for

    pumping pulp.

    The results yielded that a saving of

    over 50 % could be achieved by replacing

    the throttle valve with a variable speed

    drive, a frequency converter. The

    payback period was two years and two

    months and the present value for the

    total life cycle cost of the variable

    speed system was 662.566 SEK lower than

    for the throttled system. As a

    consequence, Stora Enso Fors is advised

    to invest in a frequency converter for

    regulation of the system.

    The general conclusion is that a focus

    on system efficiency is the most

    important factor in energy efficiency

    projects and that the system regulation

    method has a large impact on the overall

    system losses and hence its efficiency.

    Energy efficiency potential for

    throttled systems with centrifugal pumps

    is large and significant economical

    savings can be made through investments

    with short payback time.

  • 7.
    Bull, Jonathan
    et al.
    Stanford University.
    Jameson, Antony
    High-Order Flux Reconstruction Schemes for LES on Tetrahedral Meshes2014In: Progress in Hybrid RANS-LES Modelling: Volume 130 of the series Notes on Numerical Fluid Mechanics and Multidisciplinary Design / [ed] Sharath Girimaji, Werner Haase, Shia-Hui Peng, Dieter Schwamborn, 2014Conference paper (Refereed)
    Abstract [en]

    The use of the high-order Flux Reconstruction (FR) spatial discretization scheme for LES on unstructured meshes is investigated. Simulations of the compressible Taylor-Green vortex at Re=1,600 demonstrate that the FR scheme has low numerical dissipation and accurately reproduces the turbulent energy cascade at low resolution, making it ideal for high-order LES. To permit the use of subgrid-scale models incorporating explicit filtering on tetrahedral meshes, a high-order filter acting on the modal form of the solution (i.e. the Dubiner basis functions) is developed. The WALE-Similarity mixed (WSM) model using this filter is employed for LES of the flow over a square cylinder at Re=21,400, obtaining reasonable agreement with experiments. Future research will be directed at improved SGS models and filters and at developing high-order hybrid RANS/LES methods.

  • 8.
    Bull, Jonathan
    et al.
    Applied Modelling and Computation Group, Department of Earth Science and Engineering, Imperial College London, London, UK.
    Piggott, Matthew
    Imperial College London.
    Pain, Christopher
    Imperial College London.
    A finite element LES methodology for anisotropic inhomogeneous meshes2012In: Proceedings of the Seventh International Symposium On Turbulence, Heat and Mass Transfer Palermo, Italy, 24-27 September, 2012, Begell House, 2012Conference paper (Refereed)
    Abstract [en]

    Large eddy simulation techniques offer a wealth of valuable information for engineering design purposes, but in many cases the required mesh resolution is prohibitive. Combining the dynamic LES procedure with unstructured mesh adaptivity offers a robust and efficient way of capturing the inhomogeneity and anisotropy of complex turbulent flows. However, this may result in a non-vanishing commutation error due to the filter employed. The inverse Helmholtz filter is used here with a tensor definition of filter width related to the local element size and shape. The formulation, verification and validation of a finite element methodology, designed to yield maximal accuracy from moderate mesh resolution with minimal ad hoc procedures, is described. Results for the 3D backward facing step obtained using the open source CFD code Fluidity are presented. Using adaptive meshing, closer agreement to DNS was obtained compared to fixed meshes while using 60% fewer nodes.

  • 9.
    Burman, Jan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Swedish Def Res Agcy, FOI, Div CBRN Def & Secur, S-90182 Umea, Sweden.
    Jonsson, Lage
    Swedish Def Res Agcy, FOI, Div CBRN Def & Secur, S-90182 Umea, Sweden;Royal Inst Technol, KTH, S-10044 Stockholm, Sweden.
    Rutgersson, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    On possibilities to estimate local concentration variations with CFD-LES in real urban environments2019In: Environmental Fluid Mechanics, ISSN 1567-7419, E-ISSN 1573-1510, Vol. 19, no 3, p. 719-750Article in journal (Refereed)
    Abstract [en]

    Applied studies with Large Eddy Simulation (LES) of hazardous gas dispersion around buildings in cities have become increasingly feasible due to rapid advancements in computing technology. However, there is little extant literature investigating how each model's results compare with others, as well as their ability to predict near-field dispersion in a real city. In this study, three typical LES sub-grid-scale models are used to simulate gas dispersion, utilizing alternatively constant values and synthetic turbulence at inflow boundaries. The results are compared with data from the Joint Urban 2003 Atmospheric Dispersion Study in Oklahoma City. Flow and turbulence statistics of the simulation is presented at two probe locations, one inside the city-core and one outside. In addition, comparisons with the measured mean concentration and maximum concentration values are conducted. It was found that in the core of the city, simulated turbulence is mainly determined by buildings and their configurations, and is only weakly affected by model type and assumed turbulence at the inflow boundaries. On the other hand, outside and upwind the city center the turbulence set at the inflow boundaries is very important if realistic turbulence statistics is to be achieved. Downstream of the source, all tested models produce similar predictions of maximum concentration values, which in turn are similar to the experimental data. Thus, the results indicate that it could be better to use the LES calculated maximum-concentration instead of the calculated mean-concentration when developing methods for hazard area estimation.

  • 10.
    Chang, Bo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Shah, Ali
    Aalto University.
    Zhou, Quan
    Aalto University.
    Ras, Robin
    Aalto University.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Self-transport and self-alignment of microchips using microscopic rain2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 14966Article in journal (Refereed)
    Abstract [en]

    Alignment of microchips with receptors is an important process step in the construction of integrated micro- and nanosystems for emerging technologies, and facilitating alignment by spontaneous self-assembly processes is highly desired. Previously, capillary self-alignment of microchips driven by surface tension effects on patterned surfaces has been reported, where it was essential for microchips to have sufficient overlap with receptor sites. Here we demonstrate for the first time capillary self-transport and self-alignment of microchips, where microchips are initially placed outside the corresponding receptor sites and can be self-transported by capillary force to the receptor sites followed by self-alignment. The surface consists of hydrophilic silicon receptor sites surrounded by superhydrophobic black silicon. Rain-induced microscopic droplets are used to form the meniscus for the self-transport and self-alignment. The boundary conditions for the self-transport have been explored by modeling and confirmed experimentally. The maximum permitted gap between a microchip and a receptor site is determined by the volume of the liquid and by the wetting contrast between receptor site and substrate. Microscopic rain applied on hydrophilic-superhydrophobic patterned surfaces greatly improves the capability, reliability and error-tolerance of the process, avoiding the need for accurate initial placement of microchips, and thereby greatly simplifying the alignment process.

  • 11.
    Chang, Bo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Zhou, Quan
    Aalto University, Finland.
    Ras, Robin
    Aalto University, Finland.
    Shah, Ali
    Aalto University, Finland.
    Wu, Zhigang
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Sliding droplets on hydrophilic/superhydrophobic patterned surfaces for liquid deposition2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, no 15, article id 154102Article in journal (Refereed)
    Abstract [en]

    A facile gravity-induced sliding droplets method is reported for deposition of nanoliter sized droplets on hydrophilic/superhydrophobic patterned surface. The deposition process is parallel where multiple different liquids can be deposited simultaneously. The process is also high-throughput, having a great potential to be scaled up by increasing the size of the substrate.

  • 12.
    Cruz, F. Javier
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    High pressure inertial focusing: integration in parallel and series2018Conference paper (Other academic)
  • 13.
    Deglaire, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analytical Aerodynamic Simulation Tools for Vertical Axis Wind Turbines2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wind power is a renewable energy source that is today the fastest growing solution to reduce CO2 emissions in the electric energy mix. Upwind horizontal axis wind turbine with three blades has been the preferred technical choice for more than two decades. This horizontal axis concept is today widely leading the market. The current PhD thesis will cover an alternative type of wind turbine with straight blades and rotating along the vertical axis. A brief overview of the main differences between the horizontal and vertical axis concept has been made. However the main focus of this thesis is the aerodynamics of the wind turbine blades.

    Making aerodynamically efficient turbines starts with efficient blades. Making efficient blades requires a good understanding of the physical phenomena and effective simulations tools to model them. The specific aerodynamics for straight bladed vertical axis turbine flow are reviewed together with the standard aerodynamic simulations tools that have been used in the past by blade and rotor designer. A reasonably fast (regarding computer power) and accurate (regarding comparison with experimental results) simulation method was still lacking in the field prior to the current work. This thesis aims at designing such a method.

    Analytical methods can be used to model complex flow if the geometry is simple. Therefore, a conformal mapping method is derived to transform any set of section into a set of standard circles. Then analytical procedures are generalized to simulate moving multibody sections in the complex vertical flows and forces experienced by the blades. Finally the fast semi analytical aerodynamic algorithm boosted by fast multipole methods to handle high number of vortices is coupled with a simple structural model of the rotor to investigate potential aeroelastic instabilities.

    Together with these advanced simulation tools, a standard double multiple streamtube model has been developed and used to design several straight bladed rotor ranging from 2 kW to 20 kW.

    List of papers
    1. Conformal mapping and efficient boundary element method without, boundary elements for fast vortex particle simulations
    Open this publication in new window or tab >>Conformal mapping and efficient boundary element method without, boundary elements for fast vortex particle simulations
    2008 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 27, no 2, p. 150-176Article in journal (Refereed) Published
    Abstract [en]

    In this paper, a revitalization of conformal mapping methods applied to fluid flows in two dimensions is proposed. The present work addresses several important issues concerning their application for vortex particle flow solvers. Difficulties of past conformal based method are reviewed. One difficulty concerns the ability of a mapping procedure to represent complicated shapes. The present paper improves past algorithms to be able to map new shapes, including multiply connected domains. A new fast procedure allows transferring a set of points in the mapped simplified plane to the complicated domain and vice versa. After a mapping construction, it is demonstrated how basic exact solutions to potential flow problems with vortices can be put in a new form which provides a faster and more accurate computation than with distributed singularity methods.

    Keywords
    conformal mapping, Laurent's series expansion, fast imaging
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-110478 (URN)10.1016/j.euromechflu.2007.03.005 (DOI)000254116800005 ()
    Available from: 2009-11-16 Created: 2009-11-16 Last updated: 2017-12-12Bibliographically approved
    2. Analytical solutions for a single blade in vertical axis turbine motion in two dimensions
    Open this publication in new window or tab >>Analytical solutions for a single blade in vertical axis turbine motion in two dimensions
    2009 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 28, p. 506-520Article in journal (Refereed) Published
    National Category
    Computational Mathematics Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-88420 (URN)10.1016/j.euromechflu.2008.11.004 (DOI)000267179900004 ()
    Available from: 2009-02-01 Created: 2009-02-01 Last updated: 2018-11-12Bibliographically approved
    3. A Multi-Body Vortex Method Applied to Vertical Axis Wind Turbines
    Open this publication in new window or tab >>A Multi-Body Vortex Method Applied to Vertical Axis Wind Turbines
    2010 (English)Article in journal (Refereed) Accepted
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-131981 (URN)
    Available from: 2010-10-12 Created: 2010-10-12 Last updated: 2014-12-10Bibliographically approved
    4. Fast aeroelastic model for straight bladed vertical axis wind and hydro turbines
    Open this publication in new window or tab >>Fast aeroelastic model for straight bladed vertical axis wind and hydro turbines
    2010 (English)In: Wind Engineering, ISSN 0309-524XArticle in journal (Refereed) Accepted
    Place, publisher, year, edition, pages
    Multi Science Publishing, 2010
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-131987 (URN)
    Available from: 2010-10-12 Created: 2010-10-12 Last updated: 2014-12-10Bibliographically approved
    5. Matching a permanent magnet synchronous generator to a fixed pitch vertical axis turbine for marine current energy conversion
    Open this publication in new window or tab >>Matching a permanent magnet synchronous generator to a fixed pitch vertical axis turbine for marine current energy conversion
    Show others...
    2009 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 34, no 1, p. 24-31Article in journal (Refereed) Published
    Abstract [en]

    Extracting energy from a free-flow marine current using a vertical axis fixed pitch turbine requires a generator that can handle varying speeds and loads, since such a turbine gives maximum power capture for a fixed tip speed ratio. A prototype of such a generator has been designed and constructed. In this paper, its variable speed and load operation is evaluated, both in terms of how the constructed generator performs in relation to simulations, and in terms of how the generator could perform with three different fixed pitch turbines. Measurements of root mean square (RMS) voltage and current differ 10% from simulations. Performance analysis with example turbines shows that the generator can match fixed tip speed ratio operation of several turbines for current speeds between 0.5 and 2.5 m/s.

    Keywords
    Fixed tip speed ratio operation, permanent magnet generators, tidal power generation, variable speed generator, vertical axis turbine
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-96617 (URN)10.1109/JOE.2008.2010658 (DOI)000264618000003 ()
    Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2017-12-14Bibliographically approved
    6. Design of a 12kW vertical axis wind turbine equipped with a direct driven PM synchronous generator
    Open this publication in new window or tab >>Design of a 12kW vertical axis wind turbine equipped with a direct driven PM synchronous generator
    Show others...
    2006 (English)In: EWEC 2006 - European Wind Energy Conference & Exhibition, Athens, GreeceArticle in journal (Refereed) Published
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97452 (URN)
    Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2016-07-12Bibliographically approved
    7. Experimental results from a 12 kW vertical axis wind turbine with a direct driven PM synchronous generator
    Open this publication in new window or tab >>Experimental results from a 12 kW vertical axis wind turbine with a direct driven PM synchronous generator
    2007 (English)Conference paper, Published paper (Other academic)
    Abstract [en]

    Experimental results from a three bladed vertical axis wind turbine with a direct driven PM synchronous generatorare presented. The H-rotor turbine, independent of wind direction, does not require any yaw mechanism.Furthermore, the variable speed, stall regulated turbine does not require pitch mechanism. The specifically designeddirectly driven generator eliminates the need for a gearbox. All electrical equipment, including generator, are placedon the ground. This reduces the weight that has to be supported by the structure and simplifies maintenance. Thus, theoverall strength of this concept is simplicity.The H-rotor has five meter long blades that are tapered at the tips. The aerodynamic torque is transferred to thegenerator via a 5.4 meter long drive shaft supported by a tower. A universal joint connects the drive shaft to thegenerator shaft, cancelling any transverse bending moments from the turbine on the generator. The generator acts as amotor to start up the turbine using a separate auxiliary winding. The turbine has a swept area of 30 m2 and is rated at12 kW in 12 m/s winds for 127 rpm.The turbine has been placed on a site where the wind resources have been extensively documented. The wind datarecord is more then ten years and includes data from various heights giving an accurate wind mapping of the area.The experimental aerodynamic power curve in turbulent wind conditions is presented. Considering the highlyturbulent wind conditions and the small size of the wind turbine these results are encouraging.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97453 (URN)
    Conference
    EWEC 2007 - European Wind Energy Conference & Exhibition, Milan, Italy, May. 7-10, 2007
    Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2018-05-30Bibliographically approved
    8. Progress of control system and measurement techniques for a 12 kW vertical axis wind turbine
    Open this publication in new window or tab >>Progress of control system and measurement techniques for a 12 kW vertical axis wind turbine
    Show others...
    2008 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97454 (URN)
    Conference
    ??
    Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2016-04-12Bibliographically approved
  • 14.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Properties of the energy transport for plane-parallel polychromatic surface gravity waves in waters of arbitrary depthIn: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691Article in journal (Other academic)
  • 15. Ge, Zhouyang
    et al.
    Holmgren, Hanna
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Kronbichler, Martin
    Brandt, Luca
    Kreiss, Gunilla
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Effective slip over partially filled microcavities and its possible failure2017Report (Other academic)
  • 16. Ge, Zhouyang
    et al.
    Holmgren, Hanna
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Kronbichler, Martin
    Brandt, Luca
    Kreiss, Gunilla
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Effective slip over partially filled microcavities and its possible failure2018In: Physical Review Fluids, E-ISSN 2469-990X, Vol. 3, p. 054201:1-17, article id 054201Article in journal (Refereed)
  • 17.
    Goude, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engblom, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computational Science.
    A general high order two-dimensional panel method2018In: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, Vol. 60, p. 1-17Article in journal (Refereed)
  • 18.
    Goude, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Staffan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Forces on a marine current turbine during runaway2017In: International Journal of Marine Energy, ISSN 2214-1669, Vol. 19, p. 345-356Article in journal (Refereed)
    Abstract [en]

    A runaway marine current turbine will typically overshoot the runaway speed significantly before it settles at that speed. Numerical simulations of an experimental turbine indicate that the peak forces experienced by the turbine during runaway are up to 2.7 times those seen during nominal operation, and 2.1 times those at asymptotic runaway speed, making peak runaway force an important consideration in turbine design. The main contribution to the force increase is found to originate from the increased rotational speed, but a significant part is also due to the temporal lag in turbine wake development. A parameter study further shows that turbines with low inertia, turbines that have low losses, and turbines designed for low tip speed ratios will experience larger increases in forces.

  • 19.
    Gravråkmo, Halvar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Buoy Geometry, Size and Hydrodynamics for Power Take Off Device for Point Absorber Linear Wave Energy Converter2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wave energy converters of point absorber type have been developed and constructed. Full scale experiments have been carried out at sea and electricity has been successfully delivered. Linear permanent magnet generators together with a subsea substation and buoys of various geometric shapes have been investigated theoretically and experimentally. The design has in large extent an electronic approach, keeping the mechanical part of it as simple as possible, due to the long life span and reliability of electric components.

    Because of the nature of a linear generator, the internal translator with permanent magnets has a limited stroke length which will be reached when the buoy is exposed to large wave heights. Internal springs at the top and bottom of the generator prevent the translator from hitting the generator hull. Inertial forces due to the mass and velocity of the translator and the buoy and its heave added mass compresses the spring. The added mass is a rather large part of the total moving mass. Simulations of a converter with a vertical cylindrical buoy and with a toroidal buoy were conducted, as well as real sea experiments with converters with cylindrical buoys of two different sizes and a toroidal buoy. The overloads are likely to affect the design and service life of the generator, the buoy and the wire which interconnects them.

    Buoy shapes with as much excitation force as possible and as little heave added mass as possible were sought. A toroidal buoy caused less overloads on the generator at sea states with short wave periods and relatively large wave height, but for sea states with very long wave periods or extremely high waves, the magnitude of the overloads was mainly determined by the maximum displacement of the buoy.

    Snap loads on the interconnecting wire, as the slack wire tensed up after a very deep wave trough, were found to be greater but of the same order of magnitude as forces during the rest of the wave cycle.

    During a 4 day period at various wave conditions, two converters with cylindrical buoys proved efficiency between 11.1 % and 24.4 %. The larger buoy had 78 % larger water plane area than the other buoy which resulted in 11 % more power production. Short wave period was beneficial for the power production.

    Infinite frequency heave added mass was measured for a cylindrical buoy at real sea and found to be greater than the linearly calculated theoretical added mass.

    List of papers
    1. The Lysekil Wave Power Project: Status Update
    Open this publication in new window or tab >>The Lysekil Wave Power Project: Status Update
    Show others...
    2008 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97846 (URN)
    Available from: 2008-11-21 Created: 2008-11-21 Last updated: 2014-04-29Bibliographically approved
    2. Tracking a Wave Power Buoy Using a Network Camera: System Analysis and First Results
    Open this publication in new window or tab >>Tracking a Wave Power Buoy Using a Network Camera: System Analysis and First Results
    2009 (English)In: Volume 4: Ocean Engineering; Ocean Renewable Energy; Ocean Space Utilization, Parts A and B, Honolulu, Hawaii, 2009, p. 799-807Conference paper, Published paper (Refereed)
    Abstract [en]

    Anobservation system has been set up on a small isleton the Swedish west coast. The purpose of the systemis to monitor the wave buoys in The Lysekil Project.The project is an attempt to harvest wave energy usinglinear generators and point absorbing buoys. The observation system isself-sufficient and uses a network camera to follow the buoymotions. The first results from the camera, which has beenoperating since July 2008, have been analyzed to examine themotion tracking capabilities of the system. The motion tracking wouldwork as a complement to the other measurements that arebeing done on the buoy. The method for extracting motiondata from the two-dimensional pictures is presented. The results aregraphs of translative buoy motion in two dimensions, and rotationalmotion about two different axes. The vertical buoy motion forthe studied sequence is in the range of ±0.5 m.

    Place, publisher, year, edition, pages
    Honolulu, Hawaii: , 2009
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-113302 (URN)10.1115/OMAE2009-79121 (DOI)
    Conference
    ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2009) May 31–June 5, 2009 , Honolulu, Hawaii, USA
    Available from: 2010-01-26 Created: 2010-01-26 Last updated: 2014-04-29Bibliographically approved
    3. Design proposal of electrical system for linear generator wave power plants
    Open this publication in new window or tab >>Design proposal of electrical system for linear generator wave power plants
    Show others...
    2009 (English)In: 35TH ANNUAL CONFERENCE OF IEEE INDUSTRIAL ELECTRONICS, IEEE , 2009, p. 4180-4185Conference paper, Published paper (Refereed)
    Abstract [en]

    This paper describes an electrical system layout for a wave power plant connecting linear generators to the grid. The electrical power out from the wave energy converters must be converted before they can be connected to the grid. The conversion is carried out in marine substations that will be placed on the seabed.

    The paper presents experimental power data from a wave energy converter that has been in operation at the Lysekil research site since March 2006. Moreover, results and analyses from experiments and simulations from tests with the generator connected to a rectifier and filter are presented. A simulation is made to show the difference between having the generator connected to a linear load and a nonlinear load, which would be the case when the generator is connected to the grid.

    Place, publisher, year, edition, pages
    IEEE, 2009
    Keywords
    electrical system layout, linear generator wave power plants, marine substations, wave energy converters
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112956 (URN)10.1109/IECON.2009.5414903 (DOI)000280762001321 ()978-1-4244-4648-3 (ISBN)978-1-4244-4650-6 (ISBN)
    Conference
    35th Annual Conference of the IEEE-Industrial-Electronics-Society (IECON 2009), Porto, PORTUGAL, NOV 03-05, 2009
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2016-04-14Bibliographically approved
    4. Description of a torus shaped buoy for wave energy point absorber
    Open this publication in new window or tab >>Description of a torus shaped buoy for wave energy point absorber
    Show others...
    2010 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-142504 (URN)
    Conference
    Renewable Energy 2010, 27 June - 2 July, Pacifico Yokohama, Japan
    Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2015-01-07Bibliographically approved
    5. Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
    Open this publication in new window or tab >>Catch the wave to electricity: The Conversion of Wave Motions to Electricity Using a Grid-Oriented Approach
    Show others...
    2009 (English)In: IEEE Power and Energy Magazine, ISSN 1540-7977, Vol. 7, no 1, p. 50-54Article in journal (Refereed) Published
    Abstract [en]

    The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-112949 (URN)10.1109/MPE.2008.930658 (DOI)000262015100004 ()
    Available from: 2010-01-22 Created: 2010-01-22 Last updated: 2017-01-25Bibliographically approved
    6. Lysekil Research Site, Sweden: A status update
    Open this publication in new window or tab >>Lysekil Research Site, Sweden: A status update
    Show others...
    2011 (English)In: 9th European Wave and Tidal Energy Conference, Southampton, UK, 2011, 2011Conference paper, Published paper (Refereed)
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-160039 (URN)
    Conference
    9th European Wave and Tidal Energy Conference, Southampton, UK, 5-9 September 2011
    Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2017-01-25
    7. Theory and Simulations of an End Stop Solution in a Linear Wave Power Generator
    Open this publication in new window or tab >>Theory and Simulations of an End Stop Solution in a Linear Wave Power Generator
    (English)Manuscript (preprint) (Other academic)
    National Category
    Other Civil Engineering
    Identifiers
    urn:nbn:se:uu:diva-207205 (URN)
    Available from: 2013-09-10 Created: 2013-09-10 Last updated: 2014-09-18Bibliographically approved
    8. Toroidal Buoy for Point Absorver WEC with Focus on Added Mass and Overloads
    Open this publication in new window or tab >>Toroidal Buoy for Point Absorver WEC with Focus on Added Mass and Overloads
    Show others...
    (English)In: Article in journal (Refereed) Submitted
    Abstract [en]

    In order for a wave energy converter (WEC) to produce electricity at competitive prices, the generator must not be over dimensioned in order to save money on production, transport and installation, but the WEC, in this case a point absorber, must also be dimensioned to withstand harsh sea states. High added mass will in some cases create severe inertia forces on the generator and might shorten the service life of the system. The magnitude of the overload forces can be reduced by choosing a buoy geometry with small added mass. Measurements of snap loads produced by a toroidal buoy and calculations of buoy intertia forces causing overloads on a generator with a toroidal buoy and an equal generator with a cylindrical buoy are investigated in order to compare the two shapes numerically. A toroidal buoy was found to have less added mass than a vertical cylindrical buoy with similar excitation force, which caused reduced overloads at short wave periods, thus reducing the overloads on the generator. Snap loads were found to not cause much greater loads than other forces found during operation.

    Keywords
    WEC, point absorber, toroidal, torus; buoy, overload, survivability, wave, energy, converter
    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-220341 (URN)
    Available from: 2014-03-13 Created: 2014-03-13 Last updated: 2014-09-18
    9. Power Production by Linear Wave Energy Converters of Point Absorber Type with Vertical Cylindrical Buoys during Various Sea States
    Open this publication in new window or tab >>Power Production by Linear Wave Energy Converters of Point Absorber Type with Vertical Cylindrical Buoys during Various Sea States
    Show others...
    (English)In: Article in journal (Refereed) Submitted
    Abstract [en]

    Two wave energy converters (WEC) were deployed near the city of Lysekil as part of Uppsala University's wave energy project. The converters were electrically identical and mechanically very similar. The converters were installed on the seabed at 25 m depth at the same site and believed to be exposed to very similar wave conditions. They utilized permanent magnets oscillating vertically due to surface buoys actuating the generators. The buoys were vertical cylinders excitated by ocean waves, with different diameters but with equal volume. The power production from the converters and the sea states were measured and comparison of power production between the two converters during various sea states was conducted. Also wind and tidal oscillations were considered and were found to influence the power production directly or indirectly, as did also significant wave height and energy period. The only difference between the two converters were the buoys, as the generators and electric loads were equal. During a 4 day period of various wave climates, the WEC with the buoy with 78 % larger water plane area than the WEC with the more narrow buoy with a water plane area of 7.07 m2 was found to produce 11 % more power.

    Keywords
    wave power, point absorber, WEC, experiment, efficiency, energy, buoy
    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-220342 (URN)
    Available from: 2014-03-13 Created: 2014-03-13 Last updated: 2014-12-11
    10. Measurements of Extreme Forces on a Wave Energy Converter of Point Absorber Type and Estimation of Added Mass of Cylindrical Buoy
    Open this publication in new window or tab >>Measurements of Extreme Forces on a Wave Energy Converter of Point Absorber Type and Estimation of Added Mass of Cylindrical Buoy
    Show others...
    2014 (English)In: 33Rd International Conference On Ocean, Offshore And Arctic Engineering, 2014, Vol 9B: Ocean Renewable Energy, ASME Press, 2014Conference paper, Published paper (Refereed)
    Abstract [en]

    A wave energy converter (WEC) of point absorber type is tested at the west coast of Sweden. The buoy is a vertical cylinder. The linear generator on the seabed has limited stroke length. Large waves cause the generator to reach its maximum stroke length. As this happen, a spring in the generator is compressed, causing the buoy to instantly come to rest. During this process the force between the buoy and the generator is measured. Also the acceleration of the buoy is measured. This process and the extreme forces on the generator hull is described and the study shows that the magnitude of this force is greatly influenced by the added mass of the buoy and thus the buoy geometry. The ratio between the extreme forces on the hull and the forces during normal operation will affect the dimensioning and economy of the WEC. Force acting between generator and buoy were measured during various events as the WEC was operating. Added mass was estimated from the measurements

    Place, publisher, year, edition, pages
    ASME Press, 2014
    Keywords
    added mass, buoy, wave, energy, converter, point, absorber, cylindrical, heave
    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-220343 (URN)000363499100037 (DOI)978-0-7918-4554-7 (ISBN)
    Conference
    33rd International Conference on Ocean, Offshore and Arctic Engineering
    Available from: 2014-03-13 Created: 2014-03-13 Last updated: 2016-01-12Bibliographically approved
  • 20.
    Guimarães da Silva, Jôse Lorena
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Computational sound propagation models: An analysis of the models Nord2000, CONCAWE, and ISO 9613-2 for sound propagation from a wind farm2017Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The recent goals from some countries to become renewable energy based and reduce carbon dioxide emissions have caused the wind industry to grow. Together, the size of the wind farms and the noise emission have grown, while the noise emission regulations have to be fulfilled. Numerical simulations based on engineering approaches are in many cases a fast alternative that may supplement actual sound measurements at the site on question. However, the sound propagation models have many assumptions and estimations, as different variants can affect the resulting sound propagation. The accuracy of the sound propagation models Nord2000, CONCAWE, and ISO 9613-2 are investigated in this research by comparing the predicted to the measured sound pressure levels from a wind farm in northern Sweden.

    Different parameters were investigated in each model, as wind speed and direction, roughness length, ground class, temperature gradient, and receiver height. The computational calculations were run on SoundPLAN software for a single point, the nearby dwelling. For the different parameters investigated, the settings were defined and inputted in the software, and the calculations were run. The equivalent sound pressure level results from the computational models were compared to the equivalent sound pressure level of the sound measurements filtered from background noise.

    The results indicate that the model ISO 9613-2 did not perform well for the specific site conditions at the wind farm. On the other hand, the CONCAWE and Nord2000 showed high accuracy, for downwind conditions at 8 m/s. For upwind conditions at 8 m/s, Nord2000 is more accurate, as the refraction of the sound rays are better calculated on this model. For the variants investigated on the Nord2000 model, the results that better approximate to the sound levels of the sound measurements are the roughness length 0.3, ground class D, and temperature gradient  0.05 K/m. Thus, these settings would be recommended for calculations with Nord2000 for noise assessment in a permit process.

  • 21.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Interaction distance for scattered and radiated waves in large wave energy parks2015Conference paper (Refereed)
  • 22.
    Göteman, Malin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Engström, Jens
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Methods of reducing power fluctuations in wave energy parks2014In: Journal of Renewable and Sustainable Energy, ISSN 1941-7012, E-ISSN 1941-7012, Vol. 6, p. 043103-Article in journal (Refereed)
    Abstract [en]

    One of the major challenges in constructing effective and economically viable wave energy parks is to reduce the large fluctuations in power output. In this paper, we study different methods of reducing the fluctuations and improve the output power quality. The parameters studied include the number of devices, the separating distance between units, the global and local geometries of the array, sea state and incoming wave direction, and the impact of including buoys of different radii in an array. Our results show that, e. g., the fluctuations as well as power per device decrease strictly with the number of interacting units, when the separating distance is kept constant. However, including more devices in a park with fixed area will not necessarily result in lowered power fluctuations. We also show that varying the distance between units affects the power fluctuations to a much larger extent than it affects the magnitude of the absorbed power. The fluctuations are slightly lower in more realistic, randomized geometries where the buoys tend to drift slightly off their mean positions, and significantly lower in semi-circular geometries as opposed to rectangular geometries. 

  • 23.
    Ivanell, Stefan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Carlen, Ingemar
    Nilsson, Karl
    Sarmast, Sasan
    Odemark, Ylva
    Andersen, Sören Juhl
    Tenneler, Görkem
    Eriksson, Ola
    Breton, Simon-Philippe
    Åkervik, Espen
    Gravdahl, Arne
    Fransson, Jens
    Mikkelsen, Robert
    Sörensen, Jens
    Henningson, Dan
    Optimization of Large Wind Farms, The Nordic Consortium, Activity report 2009-2012: Elforsk rapport 13:122013Report (Other academic)
  • 24.
    Johansson, Linda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
    Acoustic Manipulation of Particles and Fluids in Microfluidic Systems2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The downscaling and integration of biomedical analyses onto a single chip offers several advantages in speed, cost, parallelism and de-centralization. Acoustic radiation forces are attractive to use in these applications since they are strong, long-range and gentle. Lab-on-a-chip operations such as cell trapping, particle fluorescence activated cell sorting, fluid mixing and particle sorting performed by acoustic radiation forces are exploited in this thesis. Two different platforms are designed, manufactured and evaluated.

    List of papers
    1. An Evaluation of the Temperature Increase from PZT Micro-Transducers for Acoustic Trapping
    Open this publication in new window or tab >>An Evaluation of the Temperature Increase from PZT Micro-Transducers for Acoustic Trapping
    Show others...
    2005 (English)In: 2005 IEEE Ultrasonics Symposium, 2005, p. 1614-1617Conference paper, Published paper (Refereed)
    Identifiers
    urn:nbn:se:uu:diva-100674 (URN)0-7803-9382-1 (ISBN)
    Available from: 2009-04-06 Created: 2009-04-05 Last updated: 2009-04-06Bibliographically approved
    2. Noninvasive acoustic cell trapping in a microfluidic perfusion system for online bioassays
    Open this publication in new window or tab >>Noninvasive acoustic cell trapping in a microfluidic perfusion system for online bioassays
    Show others...
    2007 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 79, no 7, p. 2984-2991Article in journal (Refereed) Published
    Abstract [en]

    Techniques for manipulating, separating, and trapping particles and cells are highly desired in today's bioanalytical and biomedical field. The microfluidic chip-based acoustic noncontact trapping method earlier developed within the group now provides a flexible platform for performing cell- and particle-based assays in continuous flow microsystems. An acoustic standing wave is generated in etched glass channels (600x61 microm2) by miniature ultrasonic transducers (550x550x200 microm3). Particles or cells passing the transducer will be retained and levitated in the center of the channel without any contact with the channel walls. The maximum trapping force was calculated to be 430+/-135 pN by measuring the drag force exerted on a single particle levitated in the standing wave. The temperature increase in the channel was characterized by fluorescence measurements using rhodamine B, and levels of moderate temperature increase were noted. Neural stem cells were acoustically trapped and shown to be viable after 15 min. Further evidence of the mild cell handling conditions was demonstrated as yeast cells were successfully cultured for 6 h in the acoustic trap while being perfused by the cell medium at a flowrate of 1 microL/min. The acoustic microchip method facilitates trapping of single cells as well as larger cell clusters. The noncontact mode of cell handling is especially important when studies on nonadherent cells are performed, e.g., stem cells, yeast cells, or blood cells, as mechanical stress and surface interaction are minimized. The demonstrated acoustic trapping of cells and particles enables cell- or particle-based bioassays to be performed in a continuous flow format.

    Keywords
    Perfusion, Blood, Rhodamine, Fluorescence spectrometry, Transducer, Glass, Acoustic wave, Continuous flow method, Chemical analysis, Acoustic method, System on a chip, Biochemical analysis, Biological indicator, Bioassay, On line, Microfluidics, Trapping
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-100675 (URN)10.1021/ac061576v (DOI)000245304300047 ()17313183 (PubMedID)
    Available from: 2009-04-06 Created: 2009-04-05 Last updated: 2017-12-13Bibliographically approved
    3. Temperature control and resonance mode analysis of an acoustic trap for μTAS
    Open this publication in new window or tab >>Temperature control and resonance mode analysis of an acoustic trap for μTAS
    Show others...
    (English)Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-100678 (URN)
    Available from: 2009-04-08 Created: 2009-04-05 Last updated: 2009-04-08Bibliographically approved
    4.
    The record could not be found. The reason may be that the record is no longer available or you may have typed in a wrong id in the address field.
    5. On-chip fluorescence activated cell sorting by an integrated miniaturized ultrasonic transducer
    Open this publication in new window or tab >>On-chip fluorescence activated cell sorting by an integrated miniaturized ultrasonic transducer
    2009 (English)In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 81, no 13, p. 5188-5196Article in journal (Refereed) Published
    Abstract [en]

    An acoustic microfluidic system for miniaturized fluorescence-activated   cell sorting (mu FACS) is presented. By excitation of a miniaturized   piezoelectric transducer at 10 MHz in the microfluidic channel bottom, an acoustic standing wave is formed in the channel. The acoustic   radiation force acting on a density interface causes fluidic movement, and the particles or cells on either side of the fluid interface are displaced in a direction perpendicular to the standing wave direction. The small size of the transducer enables individual manipulation of   cells passing the transducer surface. At constant transducer activation   the system was shown to accomplish up to 700 mu m sideways displacement   of 10 mu m beads in a 1 mm wide channel. This is much larger than if   utilizing the acoustic radiation force acting directly on particles, where the limitation in maximum displacement is between a node and an antinode which at 10 MHz is 35 mu m. In the automatic sorting setup,   the system was demonstrated to successfully sort single cells of E-GFP expressing beta-cells.

    National Category
    Chemical Sciences Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-100677 (URN)10.1021/ac802681r (DOI)000267609500014 ()
    Available from: 2009-04-08 Created: 2009-04-05 Last updated: 2017-12-13Bibliographically approved
    6. Surface Acoustic Wave-induced particle sorting with node-position flexibility
    Open this publication in new window or tab >>Surface Acoustic Wave-induced particle sorting with node-position flexibility
    (English)In: Lab on a Chip, ISSN 1473-0197, E-ISSN 1473-0189Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-100812 (URN)
    Available from: 2009-04-07 Created: 2009-04-07 Last updated: 2017-12-13Bibliographically approved
    7. Surface Acoustic Wave-induced particle manipulation in a glass microfluidic channel
    Open this publication in new window or tab >>Surface Acoustic Wave-induced particle manipulation in a glass microfluidic channel
    (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439Article in journal (Refereed) Submitted
    Keywords
    surface avoustic wave, manipulation, acoustic
    Identifiers
    urn:nbn:se:uu:diva-100904 (URN)
    Available from: 2009-04-10 Created: 2009-04-10 Last updated: 2017-12-13Bibliographically approved
    8. Acoustic manipulation of sub-micrometer particles by interface waves in microfluidic channels
    Open this publication in new window or tab >>Acoustic manipulation of sub-micrometer particles by interface waves in microfluidic channels
    Show others...
    (English)In: Lab on a Chip, ISSN 1473-0197, E-ISSN 1473-0189Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-100905 (URN)
    Available from: 2009-04-10 Created: 2009-04-10 Last updated: 2017-12-13Bibliographically approved
  • 25.
    Jonsson, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Edqvist, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
    Kratz, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Almqvist, Monica
    Electrical Measurements, Lund University.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Simulation, manufacturing, and evaluation of a sonar for a miniaturized submersible explorer2010In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 57, no 2, p. 490-495Article in journal (Refereed)
    Abstract [en]

    Single-beam side-scan sonar elements, to be fitted on a miniaturized submersible, are here simulated, manufactured, and evaluated. Finite element analysis simulations are compared with measurements, and an overall observation is that the agreement between simulations and measurements deviates from the measured values of 1.5 to 2°, for the narrow lobe angle, by less than 10% for most models. An overall finding is that the lobe width along the track direction can be accurately simulated and, hence, the resolution of the sonars can be predicted. This paper presents, to the authors’ knowledge, the world’s smallest side-scan sonars.

  • 26.
    Jonsson, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Lekholm, Ville
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Kratz, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Monica, Almqvist
    Dept of Measurement Technology and Industrial Electrical Engineering, Lund University.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Enclosure-Induced Interference Effects in a Miniaturized Sidescan Sonar2012In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 37, no 2, p. 236-243Article in journal (Refereed)
    Abstract [en]

    On, for instance, the miniaturized submersible explorer, Deeper Access, Deeper Understanding (DADU), only 20 cm in length and 5 cm in diameter, the sidescan sonar needs to be tightly mounted in the hull. Finite element analysis (FEA) as well as physical measurements were used to investigate the effects of beam interaction with acoustically nearby rigid boundaries. Computer simulations showed the first major dip in the beam shape to vary in strength, size, and position with the enclosure wall height, from a position of 47° at 0.0-mm wall height to 32° at 3.0-mm wall height. Hydrophonic measurements on the manufactured test device confirmed these values to within 9%, varying between 47° and 29°. In addition, Schlieren imaging was proposed and used as a noninvasive means of qualitative beam shape characterization. A field test was performed with the enclosure height set to 0 and 3 mm. With the latter height, a dark band, corresponding to a sonar sensitivity dip at about 30° in the beam, appeared in the sonar image. It was found that the beam shape is sensitive to small mounting errors, in this case where the wavelength of the sonar is on the same size scale as the enclosure. Furthermore, it was found that FEA models can be used to accurately predict enclosure effects on sonar beam shapes, and Schlieren imaging can be used to visually detect the shape deformations in mounted sonar devices.

  • 27.
    Kleusberg, E.
    et al.
    Royal Inst Technol, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish E Sci Res Ctr SeRC, KTH Mech, SE-10044 Stockholm, Sweden.
    Mikkelsen, R. F.
    Tech Univ Denmark, DTU Wind Energy, DK-2800 Lyngby, Denmark.
    Schlatter, P.
    Royal Inst Technol, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish E Sci Res Ctr SeRC, KTH Mech, SE-10044 Stockholm, Sweden.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Royal Inst Technol, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish E Sci Res Ctr SeRC, KTH Mech, SE-10044 Stockholm, Sweden.
    Henningson, D. S.
    Royal Inst Technol, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish E Sci Res Ctr SeRC, KTH Mech, SE-10044 Stockholm, Sweden.
    High-Order Numerical Simulations of Wind Turbine Wakes2017In: WAKE CONFERENCE 2017, IOP PUBLISHING LTD , 2017, article id 012025Conference paper (Refereed)
    Abstract [en]

    Previous attempts to describe the structure of wind turbine wakes and their mutual interaction were mostly limited to large-eddy and Reynolds-averaged Navier Stokes simulations using finite volume solvers. We employ the higher-order spectral-element code Nek5000 to study the influence of numerical aspects on the prediction of the wind turbine wake structure and the wake interaction between two turbines. The spectral-element method enables an accurate representation of the vortical structures, with lower numerical dissipation than the more commonly used finite-volume codes. The wind-turbine blades are modeled as body forces using the actuator-line method (ACL) in the incompressible Navier Stokes equations. Both tower and nacelle are represented with appropriate body forces. An inflow boundary condition is used which emulates homogeneous isotropic turbulence of wind-tunnel flows. We validate the implementation with results from experimental campaigns undertaken at the Norwegian University of Science and Technology (NTNU Blind Tests), investigate parametric influences and compare computational aspects with existing numerical simulations. In general the results show good agreement between the experiments and the numerical simulations both for a single turbine setup as well as a two-turbine setup where the turbines are offset in the spanwise direction. A shift in the wake center caused by the tower wake is detected similar to experiments. The additional velocity deficit caused by the tower agrees well with the experimental data. The wake is captured well by Nek5000 in comparison with experiments both for the single wind turbine and in the two-turbine setup. The blade loading however shows large discrepancies for the high-turbulence, two-turbine case. While the experiments predicted higher thrust for the downstream turbine than for the upstream turbine, the opposite case was observed in Nek5000.

  • 28.
    Kleusberg, E.
    et al.
    Royal Inst Technol, KTH Mech, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish ESci Res Ctr SeRC, SE-10044 Stockholm, Sweden.
    Sarmast, Sasan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Schlatter, P.
    Royal Inst Technol, KTH Mech, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish ESci Res Ctr SeRC, SE-10044 Stockholm, Sweden.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Royal Inst Technol, KTH Mech, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish ESci Res Ctr SeRC, SE-10044 Stockholm, Sweden.
    Henningson, D. S.
    Royal Inst Technol, KTH Mech, Linne FLOW Ctr, SE-10044 Stockholm, Sweden;Royal Inst Technol, Swedish ESci Res Ctr SeRC, SE-10044 Stockholm, Sweden.
    Actuator line simulations of a Joukowsky and Tjaereborg rotor using spectral element and finite volume methods2016In: SCIENCE OF MAKING TORQUE FROM WIND (TORQUE 2016), 2016, article id 082011Conference paper (Refereed)
    Abstract [en]

    The wake structure behind a wind turbine, generated by the spectral element code Nek5000, is compared with that from the finite volume code EllipSys3D. The wind turbine blades are modeled using the actuator line method. We conduct the comparison on two different setups. One is based on an idealized rotor approximation with constant circulation imposed along the blades corresponding to Glauert's optimal operating condition, and the other is the Tjareborg wind turbine. The focus lies on analyzing the differences in the wake structures entailed by the different codes and corresponding setups. The comparisons show good agreement for the defining parameters of the wake such as the wake expansion, helix pitch and circulation of the helical vortices. Differences can be related to the lower numerical dissipation in Nek5000 and to the domain differences at the rotor center. At comparable resolution Nek5000 yields more accurate results. It is observed that in the spectral element method the helical vortices, both at the tip and root of the actuator lines, retain their initial swirl velocity distribution for a longer distance in the near wake. This results in a lower vortex core growth and larger maximum vorticity along the wake. Additionally, it is observed that the break down process of the spiral tip vortices is significantly different between the two methods, with vortex merging occurring immediately after the onset of instability in the finite volume code, while Nek5000 simulations exhibit a 2-3 radii period of vortex pairing before merging.

  • 29. Lei, Q
    et al.
    Latham, J-P
    Xiang, J
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Role of natural fractures in damage evolution around tunnel excavation in fractured rocks2017In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 231, p. 100-113Article in journal (Refereed)
    Abstract [en]

    This paper studies the role of pre-existing fractures in the damage evolution around tunnel excavation in fractured rocks. The length distribution of natural fractures can be described by a power law model, whose exponent a defines the relative proportion of large and small fractures in the system. The larger a is, the higher proportion of small fractures is. A series of two-dimensional discrete fracture networks (DENs) associated with different length exponent a and fracture intensity P-21 is generated to represent various scenarios of distributed preexisting fractures in the rock. The geomechanical behaviour of the fractured rock embedded with DFN geometry in response to isotropic/anisotropic in-situ stress conditions and excavation-induced perturbations is simulated using the hybrid finite-discrete element method (FEMDEM), which can capture the deformation of intact rocks, the interaction of matrix blocks, the displacement of natural fractures, and the propagation of new cracks. An excavation damaged zone (EDZ) develops around the man-made opening as a result of reactivation of preexisting fractures and propagation of wing cracks. The simulation results show that when a is small, the system which is dominated by large fractures can remain stable after excavation given that P-21 is not very high; however, intensive structurally-governed kinematic instability can occur if P-21 is sufficiently high and the fracture spacing is much smaller than the tunnel size. With the increase of a, the system becomes more dominated by small fractures, and the EDZ is mainly created by the coalescence of small fractures near the tunnel boundary. The results of this study have important implications for designing stable underground openings for radioactive waste repositories as well as other engineering facilities that are intended to generate minimal damage in the host rock mass.

  • 30.
    Lekholm, Ville
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Palmer, Kristoffer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ericson, Fredric
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ceramic cold gas microthruster with integrated flow sensor2011In: PowerMEMS 2011 Technical digest: The 11th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications / [ed] Young-Ho Cho, Daejeon, Republic of Korea: Cell Bench Research Center, KAIST , 2011, p. 167-170Conference paper (Refereed)
    Abstract [en]

    For aggressive environments, the material properties of silicon become a limitation. Macroscopically, ceramics are as common for high-temperature applications as is silicon in miniaturized systems, but this group of materials has been little exploited for MEMS components. This paper describes the  design, manufacturing and characterization of a ceramic, heated cold-gas microthruster with integrated flow sensor, using HTCC processing and silicon tools. The calorimetric flow sensor is integrated in the structure, and heaters are embedded in the stagnation chamber of the nozzle. The heater was shown to improve the efficiency of the thruster, as confirmed by measurements of the flow rate. Flow rate changes were seen as changes in resistance of the fabricated flow sensor. The choice of yttria stabilized zirconia as material for the components make them robust and capable of withstanding  very high temperatures. Samples have been shown  capable of achieving temperatures locally exceeding 1000ºC.

  • 31.
    Liu, Lei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. China Acad Engn, Inst Fluid Phys, Natl Key Lab Shock Wave & Detonat Phys, Mianyang 621900, Peoples R China;Uppsala Univ, Dept Earth Sci, SE-75236 Uppsala, Sweden.
    Bi, Yan
    China Acad Engn, Inst Fluid Phys, Natl Key Lab Shock Wave & Detonat Phys, Mianyang 621900, Peoples R China.
    How far away are accurate equations of state determinations?: Some issues on pressure scales and non-hydrostaticity in diamond anvil cells2016In: MATTER AND RADIATION AT EXTREMES, ISSN 2468-2047, Vol. 1, no 4, p. 224-236Article in journal (Refereed)
    Abstract [en]

    The equations of state (EOSs) of materials are the cornerstone of condensed matter physics, material science, and geophysics. However, acquiring an accurate EOS in diamond anvil cell (DAC) experiments continues to prove problematic because the current lack of an accurate pressure scale with clarified sources of uncertainty makes it difficult to determine a precise pressure value at high pressure, and non-hydrostaticity affects both the volume and pressure determination. This study will discuss the advantages and drawbacks of various pressure scales, and propose an absolute pressure scale and correction methods for the effects of non-hydrostaticity. At the end of this paper, we analyze the accuracy of the determined EOS in the DAC experiments we can achieve to date. Copyright (C) 2016 Science and Technology Information Center, China Academy of Engineering Physics. Production and hosting by Elsevier B.V.

  • 32.
    Magnusson, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Flödesmätning i smörjoljesystem med bärbar ultraljudsmätare: Underlag till en arbetsinstruktion2016Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

     This thesis was conducted at Siemens

    Industrial Turbomachinery (SIT) under a period

    of ten weeks. Siemens service department at

    this company takes care of the aftermarket of

    the turbines and provides inspection, spare

    parts and measures to increase the efficiency of

    the machines. SIT provides also oil lubrication

    systems. Because the turbomachines have a

    variety of pipe systems and flows, it may need

    to perform flow measurements for

    troubleshooting, optimization and detection of

    oil leaks. Through the years, SIT has gathered

    data from flow measurements that may suggest

    that a tubomachine system is operating at over

    or under the designed capacity. However, SIT

    does not have enough knowledge about proper

    flow measurements, evaluation of the test

    results and necessary measures to be taken,

    therefor no clear work instruction has been

    established. The goal of this work is therefore to

    provide a document about applicable flow

    measurement methods, based on which the

    company at a later phase can establish

    necessary work instruction.

    In order to write this document, necessary

    theory was gathered in order to understand

    how oil lubrication systems and flow

    measurement systems work. The author and

    some of SIT employees attended a training

    course in portable ultrasound measurement

    system provided by PEMA Control AB in

    Gothenburg. After the course, practical data

    collection and a summary of the entire flow

    measurement process was documented. This

    process was later tested in two experiments.

    The experiment results, as well as the practical

    measurement steps were then analyzed and

    discussed. After the analysis and evaluation a

    proposal of measurement procedure was

    compiled.

    Conclusions of the report include

    recommendations for improvement of the

    measurement process. The recommendations

    include necessary information about what the

    staff should think about before-, during- and

    after the measurement. This is to make the

    measurement as efficient as possible and to

    minimize the risk of engine failure and personal

    injuries. Other recommendations were to add

    necessary equipment to the existing flow

    measurement bag.

  • 33.
    Markendahl, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing.
    Finite volume simulation of fast transients in a pipe system2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The MUSCL-Hancock finite volume method with different slope limiters has been analyzed in the context of a fast transient flow problem. A derivation and analysis of the axial forces inside a pipe system due to a flow transient is also performed. 

    The following slope limiters were implemented and compared: MC, van Leer, van Albada, Minmod and Superbee. The comparison was based on the method's ability to calculate the forces due to a flow transient inside a pipe system.

    The tests and comparisons in this thesis show that the MC, van Leer, van Albada and Minmod limiters behave very much the same for the flow transient problem. If one would rank these four limiters with respect to the numerical error, the order would be the one presented above, the MC limiter being the most accurate. The error the four limiters produce is mainly of diffusive nature and it is just the magnitude of the diffusion that seems to differ between the methods. One should also note that the workload rank of the four limiters is the same as the order presented above. The MC limiter being the least efficient of the four and the Minmod limiter the most efficient.

    In most of the tests performed the Superbee limiter display a rather negative unpredictable behavior. For some relatively simple cases this particular approach shows big difficulties maintaining the dynamical properties of the force. However, the upside of the Superbee limiter is its remarkable ability to maintain the maximum value of the forces present in the pipe system, preventing underestimation of the maximum magnitude of the force.

  • 34.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bachant, Peter
    WindESCo Inc, Boston, MA USA.
    Ferreira, Carlos
    Delft Univ Technol, Wind Energy Res Inst, TU Delft, Delft, Netherlands.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Near-Wake Flow Simulation of a Vertical Axis Turbine Using an Actuator Line Model2019In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 2, p. 171-188Article in journal (Refereed)
    Abstract [en]

    In the present work, the near‐wake generated for a vertical axis wind turbine (VAWT) was simulated using an actuator line model (ALM) in order to validate and evaluate its accuracy. The sensitivity of the model to the variation of the spatial and temporal discretization was studied and showed a bigger response to the variation in the mesh size as compared with the temporal discretization. The large eddy simulation (LES) approach was used to predict the turbulence effects. The performance of Smagorinsky, dynamic k‐equation, and dynamic Lagrangian turbulence models was tested, showing very little relevant differences between them. Generally, predicted results agree well with experimental data for velocity and vorticity fields in representative sections. The presented ALM was able to characterize the main phenomena involved in the flow pattern using a relatively low computational cost without stability concerns, identified the general wake structure (qualitatively and quantitatively), and the contribution from the blade tips and motion on it. Additionally, the effects of the tower and struts were investigated with respect to the overall structure of the wake, showing no significant modification. Similarities and discrepancies between numerical and experimental results are discussed. The obtained results from the various simulations carried out here can be used as a practical reference guideline for choosing parameters in VAWTs simulations using the ALM.

  • 35.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chaudhari, Ashvinkumar
    Lappeenranta Univ Technol, Sch Engn Sci, CEID, Lappeenranta, Finland.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Performance and wake comparison of horizontal and vertical axis wind turbines under varying surface roughness conditions2019In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 4, p. 458-472Article in journal (Refereed)
    Abstract [en]

    A numerical study of both a horizontal axis wind turbine (HAWT) and a vertical axis wind turbine (VAWT) with similar size and power rating is presented. These large scale turbines have been tested when operating stand-alone at their optimal tip speed ratio (TSR) within a neutrally stratified atmospheric boundary layer (ABL). The impact of three different surface roughness lengths on the turbine performance is studied for the both turbines. The turbines performance, the response to the variation in the surface roughness of terrain, and the most relevant phenomena involved on the resulting wake were investigated. The main goal was to evaluate the differences and similarities of these two different types of turbine when they operate under the same atmospheric flow conditions. An actuator line model (ALM) was used together with the large eddy simulation (LES) approach for predicting wake effects, and it was implemented using the open-source computational fluid dynamics (CFD) library OpenFOAM to solve the governing equations and to compute the resulting flow fields. This model was first validated using wind tunnel measurements of power coefficients and wake of interacting HAWTs, and then employed to study the wake structure of both full scale turbines. A preliminary study test comparing the forces on a VAWT blades against measurements was also investigated. These obtained results showed a better performance and shorter wake (faster recovery) for an HAWT compared with a VAWT for the same atmospheric conditions.

  • 36.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Improving farm efficiency of interacting vertical‐axis wind turbines through wake deflection using pitched struts2019In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 4, p. 538-546Article in journal (Refereed)
    Abstract [en]

    This work presents a numerical study of the obtained performance and the resulting flow field between two interacting large scale vertical-axis wind turbines (VAWTs), under the influence of a deflected wake through the struts pitching of the upwind turbine. The configuration consists of two VAWTs aligned in the direction of the incoming flow in which a wide range of fixed struts pitching angles in the upwind turbine have been investigated. The main goal is to evaluate the influence of the wake deflection on the turbines performance while they are operating at their optimal tip speed ratio (TSR), and to reproduce the most relevant phenomena involved in the flow pattern of the interacting wake. Arrangements with cross-stream offsets have also been tested for quantifying the contribution of this modification into the overall performance. For this purpose, an actuator line model (ALM) has been implemented using the open-source CFD library OpenFOAM in order to solve the governing equations and to calculate the resulting flow. The Large eddy simulation (LES) approach is considered to reproduce the turbulence flow effects. A preliminary study to identify the optimal TSR of the interacting downwind turbine has been investigated.

  • 37.
    Mukha, Timofey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Johansson, Mattias
    Liefvendahl, Mattias
    Effect of wall-stress model and mesh-cell topology on the predictive accuracy of LES for wall-bounded flows2018In: Proc. 7th European Conference on Computational Fluid Dynamics, European Community on Computional Methods in Applied Sciences (ECCOMAS), 2018Conference paper (Refereed)
  • 38.
    Mukha, Timofey
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Rezaeiravesh, Saleh
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Liefvendahl, Mattias
    A library for wall-modelled large-eddy simulation based on OpenFOAM technology2019In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 239, p. 204-224Article in journal (Refereed)
  • 39.
    Nguyen, Minh-Thao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Balduzzi, Francesco
    Univ Firenze, Dept Ind Engn DIEF, I-50139 Florence, Italy.
    Bianchini, Alessandro
    Univ Firenze, Dept Ind Engn DIEF, I-50139 Florence, Italy.
    Ferrara, Giovanni
    Univ Firenze, Dept Ind Engn DIEF, I-50139 Florence, Italy.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Evaluation of the unsteady aerodynamic forces acting on a vertical-axis turbine by means of numerical simulations and open site experiments2020In: Journal of Wind Engineering and Industrial Aerodynamics, ISSN 0167-6105, E-ISSN 1872-8197, Vol. 198, article id 104093Article in journal (Refereed)
    Abstract [en]

    An increasing number of vertical-axis wind turbine prototypes have reached the step in which the theoretically predicted performance needs to be validated in order to move to the next steps of a real commercial project. This step often faces the significant challenges posed by their airfoil aerodynamics that are more complex than those of conventional horizontal-axis wind turbines, and it has also to deal with the lack of fundamental experimental data for robust validation. In this context, an accurate prediction of the real turbine operation is important and the use of computational fluid dynamics (CFD) is imposing itself as the most suitable tool to characterize the unsteady phenomena that are difficult to detect by means of experimental measurements. In the current work, two-dimensional numerical simulations of an H-type three-blade Darrieus turbine have been performed in a wide range of tip-speed ratios (TSRs) from TSR = 1.8 to TSR = 5.0. Unsteady CFD simulations were compared with unique experimental data collected in the field in terms of normal aerodynamic forces acing on the blades during the revolution. Generally, nice agreement was found between simulations and experiments, especially at medium-high tip-speed ratios. The influence of operating conditions on the performance prediction capability of the numerical model was also discussed. This is one of the key points of study since the lack of detailed experimental data often makes numerical analyses doubtful or scarcely effective. Finally, the simulation results were exploited in order to analyze the phenomena occurring during the revolution and to correlate them with the experimental findings.

  • 40.
    Nguyen, Van Dang
    et al.
    KTH Royal Inst Technol, Sch Comp Sci & Commun, Dept Computat Sci & Technol, Stockholm, Sweden.
    Jansson, Johan
    KTH Royal Inst Technol, Sch Comp Sci & Commun, Dept Computat Sci & Technol, Stockholm, Sweden; Basque Ctr Appl Math, Bilbao, Spain.
    Leoni, Massimiliano
    Basque Ctr Appl Math, Bilbao, Spain.
    Janssen, Barbel
    KTH Royal Inst Technol, Sch Comp Sci & Commun, Dept Computat Sci & Technol, Stockholm, Sweden.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hoffman, Johan
    KTH Royal Inst Technol, Sch Comp Sci & Commun, Dept Computat Sci & Technol, Stockholm, Sweden.
    Modelling Of Rotating Vertical Axis Turbines Using A Multiphase Finite Element Method2017In: VII International Conference on Computational Methods in Marine Engineering (MARINE 2017) / [ed] Visonneau, Michael; Queutey, Patrick & Le Touzé, David, International Center for Numerical Methods in Engineering (CIMNE) , 2017, p. 950-959Conference paper (Refereed)
    Abstract [en]

    We combine the unified continuum fluid-structure interaction method with a multiphase flow model to simulate turbulent flow and fluid-structure interaction of rotating vertical axis turbines in offshore environments. This work is part of a project funded by the Swedish Energy Agency, which focuses on energy systems combining ecological sustainability, competitiveness and reliability of supply. The numerical methods used comprise the Galerkin least-squares finite element method, coupled with the arbitrary Lagrangian-Eulerian method, in order to compute weak solutions of the Navier-Stokes equations for high Reynolds numbers on moving meshes. Mesh smoothing methods help to improve the mesh quality when the mesh undergoes large deformations. The simulations have been performed using the Unicorn solver in the FEniCS-HPC framework, which runs on supercomputers with near optimal weak and strong scaling up to thousands of cores.

  • 41.
    Ogden, Sam
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Bodén, Roger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Do-Quang, Minh
    KTH.
    Wu, Zhigang
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Amberg, Gustav
    KTH.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Fluid behavior of supercritical carbon dioxide with water in a double-Y-channel microfluidic chip2014In: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 17, no 6, p. 1105-1112Article in journal (Refereed)
    Abstract [en]

    The use of supercritical carbon dioxide (scCO2) as an apolar solvent has been known for decades. It offers a greener approach than, e.g., hexane or chloroform, when such solvents are needed. The use of scCO2 in microsystems, however, has only recently started to attract attention. In microfluidics, the flow characteristics need to be known to be able to successfully design such components and systems. As supercritical fluids exhibit the exciting combination of low viscosity, high density, and high diffusion rates, the fluidic behavior is not directly transferrable from aqueous systems. In this paper, three flow regimes in the scCO2–liquid water two-phase microfluidic system have been mapped. The effect of both total flow rate and relative flow rate on the flow regime is evaluated. Furthermore, the droplet dynamics at the bifurcating exit channel are analyzed at different flow rates. Due to the low viscosity of scCO2, segmented flows were observed even at fairly high flow rates. Furthermore, the carbon dioxide droplet behavior exhibited a clear dependence on both flow rate and droplet length.

  • 42.
    Olivares-Espinosa, Hugo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Ecole Technol Super, Dept Mech Engn, 1100 Notre Dame Ouest, Montreal, PQ H3C 1K3, Canada.
    Breton, Simon-Philippe
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Nergica, 70 Rue Bolduc, Gaspe, PQ G4X 1G2, Canada.
    Nilsson, Karl
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Masson, Christian
    Ecole Technol Super, Dept Mech Engn, 1100 Notre Dame Ouest, Montreal, PQ H3C 1K3, Canada.
    Dufresne, Louis
    Ecole Technol Super, Dept Mech Engn, 1100 Notre Dame Ouest, Montreal, PQ H3C 1K3, Canada.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Assessment of Turbulence Modelling in the Wake of an Actuator Disk with a Decaying Turbulence Inflow2018In: Applied Sciences, E-ISSN 2076-3417, Vol. 8, no 9, article id 1530Article in journal (Refereed)
    Abstract [en]

    The characteristics of the turbulence field in the wake produced by a wind turbine model are studied. To this aim, a methodology is developed and applied to replicate wake measurements obtained in a decaying homogeneous turbulence inflow produced by a wind tunnel. In this method, a synthetic turbulence field is generated to be employed as an inflow of Large-Eddy Simulations performed to model the flow development of the decaying turbulence as well as the wake flow behind an actuator disk. The implementation is carried out on the OpenFOAM platform, resembling a well-documented procedure used for wake flow simulations. The proposed methodology is validated by comparing with experimental results, for two levels of turbulence at inflow and disks with two different porosities. It is found that mean velocities and turbulent kinetic energy behind the disk are well estimated. The development of turbulence lengthscales behind the disk resembles what is observed in the free flow, predicting the ambient turbulence lengthscales to dominate across the wake, with little effect of shear from the wake envelope. However, observations of the power spectra confirm that shear yields a boost to the turbulence energy within the wake noticeable only in the low turbulence case. The results obtained show that the present implementation can successfully be used in the modelling and analysis of turbulence in wake flows.

  • 43.
    Rezaeiravesh, Saleh
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Application of Uncertainty Quantification Techniques to Studies of Wall-Bounded Turbulent Flows2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wall-bounded turbulent flows occur in many engineering applications. The quantities of interest (QoIs) of these flows can be accurately obtained through experimental measurements and scale-resolving numerical approaches, such as large eddy simulation (LES). However, due to the prohibitive computational costs imposed by the turbulent boundary layers (TBL) involved in these flows, the use of a standard wall-resolving (WR)LES is limited to low Reynolds (Re-) numbers. As an alternative, wall-modeled (WM)LES can be employed, in which the near-wall region of the TBL is modeled.

    This thesis evaluates the uncertainties involved in the measured QoIs of a set of experiments on TBLs, and also, investigates the predictive accuracy and sensitivity of LES, both wall-resolving and wall-modeled. For these purposes, different uncertainty quantification (UQ) techniques are employed.

    In particular, such techniques are applied to the forward (uncertainty propagation) and inverse (parameter estimation) problems involved in the measurement of mean velocity and wall shear stress using hot-wire anemometry and oil-film interferometry, respectively. The possibility of reducing epistemic uncertainties by a more detailed analysis is demonstrated. The metamodels constructed by combining non-intrusive generalized polynomial chaos expansion with the stochastic-collocation method are employed to investigate the sensitivity of WRLES of turbulent channel flow to grid resolution. This research further provides a set of recommendations for grid resolution. Through the use of a systematic simulation campaign, the predictive accuracy and sensitivity of WMLES of the same flow is investigated with respect to several influential factors. The metamodel technique is also used to explore the sensitivity to the grid anisotropy and wall model parameters. Based on this study, a set of best practice guidelines is obtained for WMLES of turbulent channel flow, the validity of which is confirmed in a wide range of Re-numbers. For all the UQ-based studies, variance-based sensitivity analysis is also performed.

    For WMLES, this thesis also introduces several developments in wall-stress modeling. The performance of algebraic wall-stress models is investigated in an a-priori framework, using accurate WRLES data. Two novel approaches based on integrating the wall model and dynamically adjusting its parameters are proposed and tested. This thesis also contributes to the development of an open-source library for WMLES based on OpenFOAM, which is used in the afore-mentioned systematic study for channel flow.

    List of papers
    1. Assessment of uncertainties in hot-wire anemometry and oil-film interferometry measurements for wall-bounded turbulent flows
    Open this publication in new window or tab >>Assessment of uncertainties in hot-wire anemometry and oil-film interferometry measurements for wall-bounded turbulent flows
    2018 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 72, p. 57-73Article in journal (Refereed) Published
    National Category
    Fluid Mechanics and Acoustics Computational Mathematics
    Identifiers
    urn:nbn:se:uu:diva-351476 (URN)10.1016/j.euromechflu.2018.04.012 (DOI)000447570200005 ()
    Available from: 2018-05-03 Created: 2018-05-25 Last updated: 2018-12-13Bibliographically approved
    2. Effect of grid resolution on large eddy simulation of wall-bounded turbulence
    Open this publication in new window or tab >>Effect of grid resolution on large eddy simulation of wall-bounded turbulence
    2018 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 30, p. 055106:1-22, article id 055106Article in journal (Refereed) Published
    National Category
    Computational Mathematics Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-351478 (URN)10.1063/1.5025131 (DOI)000433958400032 ()
    Available from: 2018-05-21 Created: 2018-05-25 Last updated: 2018-11-21Bibliographically approved
    3. On grid resolution requirements for LES of wall-bounded flows
    Open this publication in new window or tab >>On grid resolution requirements for LES of wall-bounded flows
    2016 (English)In: Proc. 7th ECCOMAS Congress, European Community on Computional Methods in Applied Sciences (ECCOMAS), 2016, p. 7454-7465Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    European Community on Computional Methods in Applied Sciences (ECCOMAS), 2016
    National Category
    Fluid Mechanics and Acoustics Computational Mathematics
    Identifiers
    urn:nbn:se:uu:diva-294353 (URN)10.7712/100016.2345.7105 (DOI)978-618-82844-0-1 (ISBN)
    Conference
    ECCOMAS Congress 2016, June 5–10, Crete, Greece
    Projects
    eSSENCE
    Available from: 2016-06-07 Created: 2016-05-18 Last updated: 2018-10-07Bibliographically approved
    4. A-priori study of wall modeling in large eddy simulation
    Open this publication in new window or tab >>A-priori study of wall modeling in large eddy simulation
    2018 (English)In: Proc. 7th European Conference on Computational Fluid Dynamics, European Community on Computional Methods in Applied Sciences (ECCOMAS), 2018Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    European Community on Computional Methods in Applied Sciences (ECCOMAS), 2018
    National Category
    Fluid Mechanics and Acoustics Computational Mathematics
    Identifiers
    urn:nbn:se:uu:diva-356045 (URN)
    Conference
    ECFD 2018, June 11–15, Glasgow, UK
    Available from: 2018-06-12 Created: 2018-07-12 Last updated: 2018-10-07Bibliographically approved
    5. A library for wall-modelled large-eddy simulation based on OpenFOAM technology
    Open this publication in new window or tab >>A library for wall-modelled large-eddy simulation based on OpenFOAM technology
    2019 (English)In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 239, p. 204-224Article in journal (Refereed) Published
    National Category
    Fluid Mechanics and Acoustics Computational Mathematics
    Identifiers
    urn:nbn:se:uu:diva-356462 (URN)10.1016/j.cpc.2019.01.016 (DOI)000466248000019 ()
    Available from: 2019-02-02 Created: 2018-07-27 Last updated: 2019-06-19Bibliographically approved
    6. Systematic study of accuracy of wall-modeled large eddy simulation using uncertainty quantification techniques
    Open this publication in new window or tab >>Systematic study of accuracy of wall-modeled large eddy simulation using uncertainty quantification techniques
    2019 (English)In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 185, p. 34-58Article in journal (Refereed) Published
    National Category
    Fluid Mechanics and Acoustics Computational Mathematics
    Identifiers
    urn:nbn:se:uu:diva-362563 (URN)10.1016/j.compfluid.2019.03.025 (DOI)000467508800004 ()
    Available from: 2019-03-29 Created: 2018-10-07 Last updated: 2019-06-24Bibliographically approved
  • 44.
    Rezaeiravesh, Saleh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Liefvendahl, Mattias
    Effect of grid resolution on large eddy simulation of wall-bounded turbulence2018In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 30, p. 055106:1-22, article id 055106Article in journal (Refereed)
  • 45.
    Rezaeiravesh, Saleh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Liefvendahl, Mattias
    Swedish Defence Research Agency.
    Fureby, Christer
    On grid resolution requirements for LES of wall-bounded flows2016In: Proc. 7th ECCOMAS Congress, European Community on Computional Methods in Applied Sciences (ECCOMAS), 2016, p. 7454-7465Conference paper (Refereed)
  • 46.
    Rezaeiravesh, Saleh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Mukha, Timofey
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Liefvendahl, Mattias
    A-priori study of wall modeling in large eddy simulation2018In: Proc. 7th European Conference on Computational Fluid Dynamics, European Community on Computional Methods in Applied Sciences (ECCOMAS), 2018Conference paper (Refereed)
  • 47.
    Rezaeiravesh, Saleh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Mukha, Timofey
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Liefvendahl, Mattias
    Systematic study of accuracy of wall-modeled large eddy simulation using uncertainty quantification techniques2019In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 185, p. 34-58Article in journal (Refereed)
  • 48.
    Rezaeiravesh, Saleh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Vinuesa, Ricardo
    Liefvendahl, Mattias
    Schlatter, Philipp
    Assessment of uncertainties in hot-wire anemometry and oil-film interferometry measurements for wall-bounded turbulent flows2018In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 72, p. 57-73Article in journal (Refereed)
  • 49.
    Sarmast, Sasan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Shen, W. Z.
    Tech Univ Denmark, Wind Energy Dept, DK-2800 Lyngby, Denmark.
    Zhu, W. J.
    Tech Univ Denmark, Wind Energy Dept, DK-2800 Lyngby, Denmark.
    Mikkelsen, R. F.
    Tech Univ Denmark, Wind Energy Dept, DK-2800 Lyngby, Denmark.
    Breton, Simon-Philippe
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. KTH Mech, S-10044 Stockholm, Sweden.
    Validation of the actuator line and disc techniques using the New MEXICO measurements2016In: SCIENCE OF MAKING TORQUE FROM WIND (TORQUE 2016), 2016, article id 032026Conference paper (Refereed)
    Abstract [en]

    Actuator line and disc techniques are employed to analyse the wake obtained in the New MEXICO wind turbine experiment. The New MEXICO measurement campaign done in 2014 is a follow-up to the MEXICO campaign, which was completed in 2006. Three flow configurations in axial flow condition are simulated and both computed loads and velocity fields around the rotor are compared with detailed PIV measurements. The comparisons show that the computed loadings are generally in agreement with the measurements under the rotor's design condition. Both actuator approaches under-predicted the loading in the inboard part of blade in stall condition as only 2D airfoil data were used in the simulations. The predicted wake velocities generally agree well with the PIV measurements. In the experiment, PIV measurements are also provided close to the hub and nacelle. To study the effect of hub and nacelle, numerical simulations are performed both in the presence and absence of the hub geometry. This study shows that the large hub used in the experiment has only small effects on overall wake behaviour.

  • 50.
    Segalini, Antonio
    et al.
    KTH Mech, Linne FLOW Ctr, S-10044 Stockholm, Sweden..
    Arnqvist, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    A spectral model for stably stratified turbulence2015In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 781, p. 330-352Article in journal (Refereed)
    Abstract [en]

    A solution of the inviscid rapid distortion equations for a stratified flow with homogeneous shear is proposed, extending the work of Hanazaki & Hunt (J. Fluid Mech., vol. 507, 2004, pp. 1-42) to the two horizontal velocity components. The analytical solution allows for the determination of the spectral tensor evolution at any given time starting from a known initial condition. By following the same approach as that adopted by Mann (J. Fluid Mech., vol. 273, 1994, pp. 141-168), a model for the spectral velocity tensor in the atmospheric boundary layer is obtained, where the spectral tensor, assumed to be isotropic at the initial time, evolves until the breakup time where the spectral tensor is supposed to achieve its final state observed in the boundary layer. The model predictions are compared with atmospheric measurements obtained over a forested area, giving the opportunity to calibrate the model parameters, and further validation is provided by additional low-roughness data. Characteristic values of the model coefficients and their dependence on the Richardson number are proposed and discussed.

12 1 - 50 of 58
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf