Fluid Structure Interaction. Tut 20 like Problem

 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 2, 2005, 08:20 Fluid Structure Interaction. Tut 20 like Problem #1 Aziz Guest   Posts: n/a Hi, I have been trying to simulate geometry with Moving Wall boundary condition, the equations are similar like the FSI Tutorial 20 in CFX. the Problem which i am facing is that i cannot model these equation using Expression editor because you cant define variable dependent on Time, i was wondering if some one has developed a Fortran Routine for case like tutorial 20. For reference i can post these equation too. F1=known; Fopp=0 (First Time Step); V1=Known; FNEW=F1; V2=(FNEW-Fopp)*DeltaT/mball; FNEW=F1-Fopp; Unfortunetly i dont have any idea with Fortran in CFX other wise these equation wouldnt be a problem to program it........ What i feel Thanks Aziz

 May 2, 2005, 13:36 Re: Fluid Structure Interaction. Tut 20 like Probl #2 SteveR Guest   Posts: n/a Hi Aziz, The FSI tutorial demonstrates how simple FSI cases involving solid body dynamics w/o deformation can be solved in CFX. If you want to simulate structural deformations, you'll need to process loads on a per-element basis, rather than the per-body or per-boudary condition basis that is used in the tutorial. This will require extensive UserCEL or User FORTRAN... or you could order the licenses that are required to take advantage of the new two-way 'MFX' coupling between CFX and ANSYS in their upcoming release, 10.0. What sort of application do you have in mind? Regards, SteveR

 May 2, 2005, 18:54 Re: Fluid Structure Interaction. Tut 20 like Probl #3 Glenn Horrocks Guest   Posts: n/a Hi Aziz, Can you clarify what you mean by "the Problem which i am facing is that i cannot model these equation using Expression editor because you cant define variable dependent on Time"? Do you mean the motion is a function of the flow and other parameters and therefore the simulation determines the motion; or do you do know the motion of the object but you cannot get CFX to use an expression as a function of time? I say this as you can define mesh deformation motions as functions of time, and if it does not work for you then you have done something wrong. Just checking. Regards, Glenn

 May 3, 2005, 04:08 Re: Fluid Structure Interaction. Tut 20 like Probl #4 Aziz Guest   Posts: n/a Hi SteveR, You are right, the best way to model Fluid Structure together would be to use 2 way coupling with CFX and ANSYS together, but to know the basic phenonmenon i need to do it as simple as possible. My requirement is to simple model Impulse Equation and for that i know the initial velocity with that a ball is moved inside let say Water and produces a local increase in pressure which tends to deccelerate the ball and now ball moves with new velocity untill it is stoped and moves backward. Thats what i only need to model. With equation editor it is not easy as you cant store the velocity from the last time step or we can i dont know exactly...... This is equation which i need to model V1=Vo-DeltaF*DeltaT/mass So here i need Vo from last time step and after calculating V1 i need to store it again as Vo. Do you know i have model it on Excel sheet by my own but with CFX it seems that i must use Fortran which i dont really want to go in. Thanks Aziz

 May 3, 2005, 04:29 Re: Fluid Structure Interaction. Tut 20 like Probl #5 Aziz Guest   Posts: n/a Hi Glenn, Actually if you need the values from last time to be used for calculating new values you cant store them using Expression editor. Have a look on the equation perhaps you will understand better V1=Vo-DeltaF*DeltaT/mass So here i need Vo from last time step and after calculating V1 i need to store it again as Vo. Do you know i have model it on Excel sheet by my own but with CFX it seems that i must use Fortran which i dont really want to go in. If it would have possible using Expression editor that you could define variables as a function of time then things were very easy for me. thanks Aziz

 May 3, 2005, 08:42 Re: Fluid Structure Interaction. Tut 20 like Probl #6 SteveR Guest   Posts: n/a Hello Aziz, In the documented tutorial, there is a CEL expression something like velBallOld=areaAve(Mesh Velocity v)@Ball. I suspect that this is what you are looking for... Mesh updates/motion occurs as a pre-processing step at the start of a time step, and the areaAve call back is last evaluated at the end of the previous time step --- This, and other callbacks, are *not* updated during mesh motion; They are only updated during the coefficient iterations within the timestep. Thus, during the mesh update at time n+1, the value of velBallOld is constant, and corresponds to the mesh velocity at time n. In your equation, V0 would be evaluated as velBallOld above, and V1 would be evaluated as V1=(disp1-disp0)/dt where disp1 is the displacement you apply to the mesh at time n+1 and disp 0 is evaluated using another areaAve callback. Hope it helps... SteveR

 May 4, 2005, 09:34 Re: Fluid Structure Interaction. Tut 20 like Probl #7 Aziz Guest   Posts: n/a Thanks SteveR for your reply, i have tried your way but still not succeed, infact i know intial velocity Vo and V1 can be calculate using Vo but the problem is now to store new V1 into Vo as Vo is already been defined as initial values. Regards, Aziz

 May 4, 2005, 19:24 Re: Fluid Structure Interaction. Tut 20 like Probl #8 Glenn Horrocks Guest   Posts: n/a Hi, There is no way of storing a variable for use in the next timestep in CEL. Steve's described method works fine and I have used it many times. Glenn Horrocks

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post jnattia Main CFD Forum 25 May 21, 2015 09:16 Amol CFX 4 April 4, 2011 12:18 Amol CFX 2 February 23, 2011 11:26 Haree FLUENT 2 August 7, 2010 02:56 ken Main CFD Forum 0 March 9, 2004 20:10

All times are GMT -4. The time now is 15:12.