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Stable and Accurate Artificial Dissipation
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys. (Waves and Fluids)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys. (Waves and Fluids)
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Avdelningen för teknisk databehandling. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Matematisk-datavetenskapliga sektionen, Institutionen för informationsteknologi, Numerisk analys. (Waves and Fluids)
2004 (engelsk)Inngår i: Journal of Scientific Computing, ISSN 0885-7474, E-ISSN 1573-7691, Vol. 21, s. 57-79Artikkel i tidsskrift (Fagfellevurdert) Published
sted, utgiver, år, opplag, sider
2004. Vol. 21, s. 57-79
HSV kategori
Identifikatorer
URN: urn:nbn:se:uu:diva-71152DOI: 10.1023/B:JOMP.0000027955.75872.3fOAI: oai:DiVA.org:uu-71152DiVA, id: diva2:99063
Tilgjengelig fra: 2007-01-26 Laget: 2007-01-26 Sist oppdatert: 2018-01-10bibliografisk kontrollert
Inngår i avhandling
1. Summation-by-Parts Operators for High Order Finite Difference Methods
Åpne denne publikasjonen i ny fane eller vindu >>Summation-by-Parts Operators for High Order Finite Difference Methods
2003 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

High order accurate finite difference methods for hyperbolic and parabolic initial boundary value problems (IBVPs) are considered. Particular focus is on time dependent wave propagating problems in complex domains. Typical applications are acoustic and electromagnetic wave propagation and fluid dynamics. To solve such problems efficiently a strictly stable, high order accurate method is required.

Our recipe to obtain such schemes is to: i) Approximate the (first and second) derivatives of the IBVPs with central finite difference operators, that satisfy a summation by parts (SBP) formula. ii) Use specific procedures for implementation of boundary conditions, that preserve the SBP property. iii) Add artificial dissipation. iv) Employ a multi block structure.

Stable schemes for weakly nonlinear IBVPs require artificial dissipation to absorb the energy of the unresolved modes. This led to the construction of accurate and efficient artificial dissipation operators of SBP type, that preserve the energy and error estimate of the original problem.

To solve problems on complex geometries, the computational domain is broken up into a number of smooth and structured meshes, in a multi block fashion. A stable and high order accurate approximation is obtained by discretizing each subdomain using SBP operators and using the Simultaneous Approximation Term (SAT) procedure for both the (external) boundary and the (internal) interface conditions.

Steady and transient aerodynamic calculations around an airfoil were performed, where the first derivative SBP operators and the new artificial dissipation operators were combined to construct high order accurate upwind schemes. The computations showed that for time dependent problems and fine structures, high order methods are necessary to accurately compute the solution, on reasonably fine grids.

The construction of high order accurate SBP operators for the second derivative is one of the considerations in this thesis. It was shown that the second derivative operators could be closed with two order less accuracy at the boundaries and still yield design order of accuracy, if an energy estimate could be obtained.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2003. s. 23
Serie
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 828
Emneord
finite difference methods, accuracy, stability, dissipation
HSV kategori
Forskningsprogram
Numerisk analys
Identifikatorer
urn:nbn:se:uu:diva-3434 (URN)91-554-5596-4 (ISBN)
Disputas
2003-05-09, Room 2146, Polacksbacken, Uppsala University, Uppsala, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2003-04-17 Laget: 2003-04-17 Sist oppdatert: 2011-10-27bibliografisk kontrollert
2. Stable High-Order Finite Difference Methods for Aerodynamics
Åpne denne publikasjonen i ny fane eller vindu >>Stable High-Order Finite Difference Methods for Aerodynamics
2004 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Alternativ tittel[sv]
Stabila högordnings finita differensmetoder för aerodynamik
Abstract [en]

In this thesis, the numerical solution of time-dependent partial differential equations (PDE) is studied. In particular high-order finite difference methods on Summation-by-parts (SBP) form are analysed and applied to model problems as well as the PDEs governing aerodynamics. The SBP property together with an implementation of boundary conditions called SAT (Simultaneous Approximation Term), yields stability by energy estimates.

The first derivative SBP operators were originally derived for Cartesian grids. Since aerodynamic computations are the ultimate goal, the scheme must also be stable on curvilinear grids. We prove that stability on curvilinear grids is only achieved for a subclass of the SBP operators. Furthermore, aerodynamics often requires addition of artificial dissipation and we derive an SBP version.

With the SBP-SAT technique it is possible to split the computational domain into a multi-block structure which simplifies grid generation and more complex geometries can be resolved. To resolve extremely complex geometries an unstructured discretisation method must be used. Hence, we have studied a finite volume approximation of the Laplacian. It can be shown to be on SBP form and a new boundary treatment is derived. Based on the Laplacian scheme, we also derive an SBP artificial dissipation for finite volume schemes.

We derive a new set of boundary conditions that leads to an energy estimate for the linearised three-dimensional Navier-Stokes equations. The new boundary conditions will be used to construct a stable SBP-SAT discretisation. To obtain an energy estimate for the discrete equation, it is necessary to discretise all the second derivatives by using the first derivative approximation twice. According to previous theory that would imply a degradation of formal accuracy but we present a proof that this is not the case.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2004. s. 25
Serie
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1026
Emneord
finite difference methods, high-order accuracy, summation-by-parts, stability, energy estimates, finite volume methods
HSV kategori
Forskningsprogram
Numerisk analys
Identifikatorer
urn:nbn:se:uu:diva-4621 (URN)91-554-6063-1 (ISBN)
Disputas
2004-11-12, Room 1211, Polacksbacken, Lägerhyddsvägen 2F, Uppsala, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2004-10-22 Laget: 2004-10-22 Sist oppdatert: 2011-10-27bibliografisk kontrollert

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