Numero
Veckobladet om forskning,
undervisning och
administration, m.m.
Nummer 42· 16 December 2004 · Årgång 34      
NADA

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Prefekten bortrest

Under tiden 18-23 december är Stefan Arnborg
ställföreträdande prefekt. Jag övertar ansvaret på julafon.

Ingrid

 

Delfis öppettider under Jul & Nyår

20/12-10/1 10.00-11.00
23/12 STÄNGT
5/1 STÄNGT

Vid allvarliga driftstörningar då Delfi är stängt kan systemgruppens journummer användas. Detta återfinns i Nadas telefon- och adresslista.

Studentexpeditionens öppetider
under jul och nyår

Studentexpeditionen har stängt mellan den 23 december och den 7 januari. Mellan 10-14/1 januari är det endast öppet mellan kl. 10.00-11.00.

Jonas/Delfi

 

 



Teknologie doktorsexamen i numerisk analys:

Aspects of the recursive projection method applied to flow calculations
Respondent: Joakim Möller
Opponent: TeknD Per Weinerfelt, SAAB
Huvudhandledare: Prof Jesper Oppelstrup

Torsdagen den 20 januari 2005 kl. 10.15
Seminarierum L1, Kungl. Tekniska Högskolan, Drottning Kristinas väg 30, Stockholm

Abstract:
In this thesis, we have investigated the Recursive Projection Method, RPM, as an accelerator for computations of both steady and unsteady flows, and as a stabilizer in a bifurcation analysis.
The criterion of basis extraction is discussed. It can be interpreted as a tolerance for the accuracy of the eigenspace spanned by the identified basis, alternatively it can beviewed as a criterion when the approximative Krylov sequence becomes numerically rank deficient.

Steady state calculations were performed on two different turbulent test-cases; a 2D supersonic nozzle flow with the Spalart-Allmaras 1-equation model and a 2D sub-sonic airfoil simulation using the $k-\epsilon$ model. RPM accelerated the test-cases with a factor between 2 and 5.

In multi-scale problems, it is often of interest to model the macro-scale behavior, still retaining the essential features of the full systems. The ``coarse time stepper’’ is a heuristic approach for circumventing the analytical derivation of models. The system studied here is a linear lattice of non-linear reaction sites coupled by diffusion. After reformulation of the time-evolution equation as a fixed-point scheme, RPM coupled with arc-length continuation is used to calculate the bifurcation diagrams of the effective (but analytically unavailable) equation.

Within the frame-work of dual time-stepping, a common approach in unsteady CFD-simulation, RPM is used to accelerate the convergence. Two test-cases were investigated; the von Karman vortex-street behind a cylinder at $Re=100$, and the periodic shock oscillation of a symmetric airfoil at $M_{\infty}=0.76$ with a Reynolds number $Re=11 \times 10^6$.

It was believed that once a basis had been identified, it could be retained for several steps. The simulations usually showed that the basis could only be retained for one step.

The need for updating the basis motivates the use of Krylov methods. The most common method is the (Block-) Arnoldi algorithm. As the iteration proceeds, Krylov methods become increasingly expensive and restart is required. Two different restart algorithm were tested. The first is that of Lehoucq and Maschhoff, which uses a shifted QR iteration, the second is a block extension of the single-vector Arnoldi method due to Stewart. A flexible hybrid algorithm is derived combining the best features of the two.

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Numero

önskar

alla läsare

God Jul

&

Gott Nytt År

 

Numero är institutionstidningen vid Nada - institutionen för numerisk analys och datalogi, KTH. Numero utkommer normalt på torsdags-förmiddagar under teminstid. Manus måste lämnas in före kl.12 på onsdagar.Manus, tips, förslag och andra bidrag till Numero kan lämnas på något av följande sätt:

Bidrag för artiklar och notiser bör i största möjliga mån vara färdigformulerade och korrekturlästa. Varje Numeronummer utkommer i två former:

Numeroredaktionen består av Maria Engström. Ansvarig utgivare är Ingrid Melinder. Numeros innehåll uttrycker inte institutionens officiella ståndpunkt annat än då detta anges.

 

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Kalendarium
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16 December

14:15-15

A compiler for variational forms Anders Logg, i D4523


16-17 December



Grid Computing and Beyond A symposium and a gala dinner in celebration of
Professor S. Lennart Johnsson’s 60th birthday


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17 december

kl 14.00

kl 17.30

Doctoral thesis, Aspects of Viscous Shocks, Malin Siklosi, Kollegiesalen,
Administrationsbyggnaden, KTH

Frescati Rösters jubileumskonsert i Sveaplans aula


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  20 januari 2005   kl. 10.15   Teknologie doktorsexamen: Aspects of the recursive projection method applied to flow calculations, Joakim Möller, Seminarierum L1, KTH, Drottning Kristinas väg 30

 
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21 januari 2005

kl 14.00

Doctoral Thesis, Video Based Analysis and Visualization of Human
Action
, MARTIN ERIKSSON, i Kollegiesalen


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tomtar på rad illustration
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