Use data from previous timestep

m_mehrdad · January 4, 2020, 01:15

Dear All;
I want to simulate a dynamic body with remeshing in CFX19.1. Everything is fine But in simulate the motion of the body, I want to use this eq:

delta_y=0.5*acceleration_y*deltat^2+ VelocityY0*deltat

and

VelocityY=acceleration_y*deltat + VelocityY0

In this eq the VelocityY0 is the previous time step VelocityY.
Because the body motions are the y_translate and x_Rotation around the variable point, I can't read the VelocityY0 from (Mesh Velocity y) variable.

How can I use the previous data VARIABLE OR Monitoring at the new time?

AtoHM · January 4, 2020, 04:01

afaik you cannot access the values from previous timesteps without using user-fortran.

m_mehrdad · January 4, 2020, 04:11

Quote:

Originally Posted by AtoHM

afaik you cannot access the values from previous timesteps without using user-fortran.

Thanks for your response. I don't know how to use user-Fortran. Can you help me?

What is setup in cfx-pre?
Thanks a lot.

ghorrocks · January 4, 2020, 05:35

Can you explain why the built-in rigid body solvers and immersed solid solvers are not suitable for this task? You should use the built-in capability if it is suitable.

User fortran is described in the CFX documentation. There are examples in the documentation and more are available on the ANSYS customer webpage.

You can access variable values from previous time steps without user fortran, but it is not a released feature, so it is not reliable and does not work in all cases. Do a search on the forum for TRANS_LOOP. I would not recommend a beginner in CFX try this approach, you might get unexpected behaviour.

January 4, 2020, 01:15	Use data from previous timestep	#1
m_mehrdad New Member Mehrdad Join Date: Apr 2014 Posts: 11 Rep Power: 12	Dear All; I want to simulate a dynamic body with remeshing in CFX19.1. Everything is fine But in simulate the motion of the body, I want to use this eq: delta_y=0.5acceleration_ydeltat^2+ VelocityY0deltat and VelocityY=acceleration_ydeltat + VelocityY0 In this eq the VelocityY0 is the previous time step VelocityY. Because the body motions are the y_translate and x_Rotation around the variable point, I can't read the VelocityY0 from (Mesh Velocity y) variable. How can I use the previous data VARIABLE OR Monitoring at the new time?

January 4, 2020, 05:35		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Can you explain why the built-in rigid body solvers and immersed solid solvers are not suitable for this task? You should use the built-in capability if it is suitable. User fortran is described in the CFX documentation. There are examples in the documentation and more are available on the ANSYS customer webpage. You can access variable values from previous time steps without user fortran, but it is not a released feature, so it is not reliable and does not work in all cases. Do a search on the forum for TRANS_LOOP. I would not recommend a beginner in CFX try this approach, you might get unexpected behaviour. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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January 4, 2020, 04:01		#2
AtoHM Senior Member M Join Date: Dec 2017 Posts: 642 Rep Power: 12	afaik you cannot access the values from previous timesteps without using user-fortran.