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Institut fürInformatik
Scientific Computing in Computer Science
Practical Course SC & VTime Discretisation
Dr. Miriam Mehl
Time Discretisation
• Euler step for momentum equations
• pressure ensures mass conservation
– poisson equation
– correction of velocities
Time Step – Stability
• small reynolds number: dt < dx2
• high reynolds number: dt < dx
Algorithm (One Time Step)
(1) compute time step dt
(2) set boundary values
(3) compute preliminary velocities
(4) solve pressure equation
(5) compute final velocities
Debugging
• simple setup:
– one(!!!) time step
– external forces zero
• test preliminary velocities at boundaries
• test residual of the pressure equation
Debugging
• enhanced setup:
– initialize velocities constant butwith nonzero boundary values
• test preliminary velocities
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