"solidDisplacementFoam" solver usage

Vlad Miryaha · November 12, 2012, 18:46

Hello,
in the paper http://powerlab.fsb.hr/ped/kturbo/op...tresspaper.pdf
it`s written, that
"The initial condition consists of specified distribution of u and du/dt at time zero."
I think that the paper authors use "solidDisplacementFoam" solver.

Does anybody know how to set initial du/dt distribution???

TIA

Hisham · November 12, 2012, 19:43

Hi Vlad,

The solver in question is to my understanding solidDisplacementFoam as you mentioned. Currently, I think it is not possible to introduce initial velocity. I am not aware of the initial version where that was possible. Nevertheless, you can introduce a new volVectorField called initialVelocity that is read from a dictionary and add a term to the equilibrium equation that is fvc::ddt(initialVelocity) ... I do not know if this is a proper way for your application but if you can explain more about your problem maybe you can get better help!

Best regards,
Hisham

Vlad Miryaha · November 13, 2012, 06:21

Thank you for your answer, Hisham!
At this moment I`m doing some test computations of transient wave propagation in a cube (1m*1m*1m).
At time zero initial displacement at one side is set. (I want to see a compression plane wave propagetion and a reflection from opposite side).
Wave propagates and it`s reflected, but it becomes smearing.
Wave becomes smearing even before it reachs opposite side.
I had rectangle mesh 40*40*40.
Boundary conditions are set to zeroGradient (I tried symmetryPlane too).
The value of "relTol" and "nCorrectors" in fvSolution file are set to 0.01 and 10 respectively.
Approximation orders in fvScheme file are set to cubic/fourth for spatial derivatives.

I can`t understand the reason of such significant smearing.

I hope that if I set initial velocity instead of displacement result becomes better.

Hisham · November 13, 2012, 08:21

Dear Vlad

I do not think you need to change the way of input. What I think could be the problem is the mesh size ... if the mesh is relatively coarse, it could cause dampening of waves. Try to increase the density of your mesh to the point where it does not significantly affect wave reflection as you expect it.

Best regards
Hisham

November 12, 2012, 18:46	"solidDisplacementFoam" solver usage	#1
Vlad Miryaha New Member Vlad Miryaha Join Date: Nov 2012 Posts: 2 Rep Power: 0	Hello, in the paper http://powerlab.fsb.hr/ped/kturbo/op...tresspaper.pdf it`s written, that "The initial condition consists of specified distribution of u and du/dt at time zero." I think that the paper authors use "solidDisplacementFoam" solver. Does anybody know how to set initial du/dt distribution??? TIA

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November 12, 2012, 19:43		#2
Hisham Senior Member Hisham Elsafti Join Date: Apr 2011 Location: Braunschweig, Germany Posts: 257 Blog Entries: 10 Rep Power: 17	Hi Vlad, The solver in question is to my understanding solidDisplacementFoam as you mentioned. Currently, I think it is not possible to introduce initial velocity. I am not aware of the initial version where that was possible. Nevertheless, you can introduce a new volVectorField called initialVelocity that is read from a dictionary and add a term to the equilibrium equation that is fvc::ddt(initialVelocity) ... I do not know if this is a proper way for your application but if you can explain more about your problem maybe you can get better help! Best regards, Hisham

November 13, 2012, 06:21		#3
Vlad Miryaha New Member Vlad Miryaha Join Date: Nov 2012 Posts: 2 Rep Power: 0	Thank you for your answer, Hisham! At this moment I`m doing some test computations of transient wave propagation in a cube (1m1m1m). At time zero initial displacement at one side is set. (I want to see a compression plane wave propagetion and a reflection from opposite side). Wave propagates and it`s reflected, but it becomes smearing. Wave becomes smearing even before it reachs opposite side. I had rectangle mesh 404040. Boundary conditions are set to zeroGradient (I tried symmetryPlane too). The value of "relTol" and "nCorrectors" in fvSolution file are set to 0.01 and 10 respectively. Approximation orders in fvScheme file are set to cubic/fourth for spatial derivatives. I can`t understand the reason of such significant smearing. I hope that if I set initial velocity instead of displacement result becomes better.

November 13, 2012, 08:21		#4
Hisham Senior Member Hisham Elsafti Join Date: Apr 2011 Location: Braunschweig, Germany Posts: 257 Blog Entries: 10 Rep Power: 17	Dear Vlad I do not think you need to change the way of input. What I think could be the problem is the mesh size ... if the mesh is relatively coarse, it could cause dampening of waves. Try to increase the density of your mesh to the point where it does not significantly affect wave reflection as you expect it. Best regards Hisham