[Hemishmistry04]

Hello,

I want to make an Expression in CFX,which depends on Simulation time.

Time Duration-
Total time = 6000 [s]

Timesteps Adaption=
Maximum Timestep= _______ Expression


How can I relate both,


I have done following,


1) User Function Interpolation

MaxTotalTimeSteps

time [s] Maximum Timesteps [s]
5E-11 - 0.00075
1 - 0.00075
6 - 0.00075
8 - 0.0008
20 - 0.06
…
60 - 0.005


2) Expression

Expression 5 = MaxTotalTimeSteps(t)


can be seen in figure

3) Connection in Analysis Setting


Getting error


Parameter 'Maximum Timestep' in object '/FLOW:Flow Analysis 1/ANALYSIS TYPE/TIME STEPS/TIMESTEP ADAPTION' is not allowed to be assigned an expression value that depends on variables. It must be assigned a numeric value, or an expression that resolves to a constant value.




How can call this Expression in Maximum timesptes?

[urosgrivc]

I think you did everything fine, it's just that...

Parameter 'Maximum Timestep' is not allowed to be assigned an expression value that depends on variables.

[ghorrocks]

Have you misunderstood the purpose of the variables on the adaptive timestepping page?

Time duration/total time = the total amount of simulated time the simulation will run for.

Timestep Adaption/Maximum Timestep = the largest time step size you allow the solver to use.

You can't change the maximum timestep during a run. If you did then what is the point of adaptive time stepping? You might as well just define the time step size yourself manually and forget about adaptive time stepping.