Index

Transient iterative parameters

Ver: 1
 

DESCRIPTION

Assigns data for the time-marching scheme for time-dependent tasks.
Polyflow makes use of an implicit time-marching scheme of the predictor-corrector type for all variables (velocities, pressure, positions, ...).

In a linear analysis, these schemes are unconditionally stable; the time step is limited by accuracy rather than stability. The time step is dynamically adapted, starting from an initial time step dtinit, in order to keep the error between the predictor step and the corrector step at a prescribed level.

  OPTIONS
 
   -1 
 Upper level menu
 1
 Modify the initial time value
tinit is the value of t corresponding to the initial condition.
The first solution will be evaluated at tinit + dtinit.
Default : tinit = 0
2 
 Modify the upper time limit
tfinal is the value of t corresponding to the final condition.
Default : tfinal = 1
3 
 Modify the initial value of the time-step
dtinit is the value of delta-t at the first step.
After the first step, dt is dynamically adapted as a function of the difference between the predictor and corrector step, and the tolerance (see option 8). The initial time step can be estimated on the basis of the Courant number dt*V/H; dtinit should lead to Courant numbers between 1 and 10.
Default : dtinit = 0.01
4
 Modify the min value of the time-step
dtmin is the minimum allowable time-step.
Default : dtmin = 0.0001
5
 Modify the max value of the time-step
dtmax is the maximum allowable time-step.
Default : dtmin = 0.25
6
 Modify the tolerance
epsilon is a relative tolerance, to be compared with the difference between the predictor and corrector steps.
Default : epsilon = 0.001
7
 Modify the max number of successful steps
Default : 20
# 
 Use of the 0-order method
Not available
9
 Use of the implicit Euler method
First order time-marching scheme based on :
Explicit Euler (pred.) - Implicit Euler(corr.).
This is the default scheme.
10
 Use of the Galerkin method
First order time-marching scheme based on :
Explicit Euler (pred.) -
    (1/3 Expl. Euler + 2/3 Impl. Euler) (corr.)
11
 Use of the Crank-Nicholson method
Second order time-marching scheme based on :
Adams Bashforth (pred.) - Trapezoidal rule (corr.)
12
 Disable prediction of velocity field
In any transient simulation including contact detection, the abrupt change of the velocity field that occurs when the fluid enters into contact with the solid part annihilates the advantages of the prediction scheme. For such problem, it is highly recommended to disable the prediction of velocity field.
SEE ALSO