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2D Axisymmetric simulation with morphing boundary 

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September 6, 2018, 13:37 
2D Axisymmetric simulation with morphing boundary

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Hi there, I am hoping to get some help on 2d axisymmetric simulation in ccm+. Been stuck on this for a few days now so any suggestions would be appreciated...
I am trying to run a 2d axisymmetric simulation with moving boundary using the mesh morpher solver. My set up involves a square domain with the right boundary set as the axis of symmetry. The top boundary is a pressure outlet at 100kPa and 300K (also initial conditions). The lhs boundary is a stationary wall (fixed boundary plane specification) and the bottom wall (radial axis) is moving according to a grid velocity. I specify the grid velocity using a field function x(r,t)  which is a combination of an exponential function and a cosine. The grid velocity therefore changes as a function of time and radial position r. I generate a trimmed cell mesh with prism layers on the moving boundary to capture the high gradients in this region. The models that I am using are: Axisymmetric, Gradients, IF97 Water (compressible), implicit unsteady, laminar, segregated flow, and segregated fluid temperature. Here goes my problem: I initialize the problem and so far all looks good (or as I think it should). Upon trying to step the simulation, the following error comes up: Nonzero radial coordinate found on axis boundary rhs Maximum error was :0 Repair boundary using "Project to Axis...". Command: StepSimulation error: Server Error I am surprised by this since I set up the domain/mesh as described in the userguide for axisymmetric meshes, i.e. i) in Z=0 plane ii) with the axis of symmetry on the xaxis iii) mesh above y=0. Anyway, I have tried using Project Axis but it still does not work. Instead, a floating point error comes up: A floating point exception has occurred: floating point exception [Invalid operation]. The specific cause cannot be identified. Please refer to the troubleshooting section of the User's Guide. Command: Unknown Command error: Server Error I think that the problem lies in my field function for the Grid Velocity. I have tried running the exact same thing but with a constant velocity i.e. I specify a constant value directly rather than as a function of exp and cos and it works. I have tried increasing the complexity of the function step by step by introducing the cos and exp function separately. The cos function works but not the exp. An interesting thing I noticed is that the exponential function contains the dependence on the radial coordinate r i.e. e^br where b is a constant. cos is expressed in terms of time. Please help.... I do not think this should be that difficult to set up and run 

September 6, 2018, 22:22 
Hi..Just a doubt!

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Siddharth
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Quote:


September 7, 2018, 04:39 

#3 
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Hi Ubuntu,
No it will not have a variable area inlet in 3D...I am trying to model an ultrasonic cleaning tank. I want the boundary motion in my simulation to account for the acoustic wave in the tank filled with water...So if I revolve my axisymmetric geometry to get 3D this would look just like a cylinder (or pipe) but with one end closed (moving wall) and the other end open to atmosphere (pressure outlet)...hope this clarifies 

September 7, 2018, 09:25 
Hi again

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Siddharth
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Does the attachment look like what you wanted? more or less?
https://we.tl/t9YMy02OVyQ I had some free time. 

September 7, 2018, 10:01 
oscillatory boundary motion as function of time and position

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Hello again Ubuntu,
Thanks for your reply. Yes looks close enough to what I am trying to do. The main difference I notice is that in the attached video the oscillation seems to be varying only with time. In my case I need the oscillation to also be varying with position..mainly because I want the motion at the left wall (r=0.06m) to be fixed and the maximum motion to take place at the axis of symmetry (r=0).. in fact that is why i am using an exponential function of the form exp^(br) in my field function...r is the radial position and b is a constant. At r = 0 the mesh displacement would be maximum and minimum at r=0.06m (left boundary) the mesh displacement would be zero. Can you explain how you did your simulation in CCM+ and any suggestions for my case? That would be very helpful for me, thanks in advance! 

September 8, 2018, 00:36 

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Siddharth
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I used the same boundary conditions as you described in your post (see attachment) except that I used laminar, without energy equation terms. In my case, the axis boundary was along the Xaxis, and the mesh was on the XY plane above y =0. I am not sure why it happens to you though you followed all these. Regarding the morphing motion, I created a simple Field Function which looks like, sin(2*$Time) In your case, it will be like exp($$Position[1])*sin(2*$Time) The location of lab coordinate system is important when you use $$Position[]. Hope this helps you. 

September 8, 2018, 08:25 

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I really appreciate you trying to help out!
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[((($$Position[1] <= 0.06) && ($$Position[0] <= 3e4) ) ? (( (2*3.1416*33e3)*(0.2e6) * (cos(2*3.1416*33e3*${Time}))*(exp(pow((2e8)*$$Position[1],6))))) : 0 ),0,0] I have also tried replacing $$Position[1] with $RadialCoordinate but still won't work. It does work if I get rid of the exp(pow((2e8)*$$Position[1],6)) bit however 1) In your field function, do you use some kind of condition or do you specify the velocity as a vector directly, i.e. [x,y,z] components? 2) What mesh morpher solver conditions are you using? In my case, I'm using Morph from Zero and Recompute Interfaces 3) I was using a Fixed Boundary Plane Specification on my left boundary. I tried it using Floating as in your case but I keep getting this error: SIGSEGV: memory access exception Command: StepSimulation Processor: 0 Recoverability: Nonrecoverable ServerStack: [ libStarNeo.so: SignalHandler::signalHandlerFunction(int, siginfo*, void*), libpthread.so.0(+0xf6d0), libMorpherModel.so(+0x1534d6), libMorpherModel.so(+0x1591ce), libMorpherModel.so(+0x159af6), libMorpherModel.so: ProMorpher::update(int const&, double const&), libMorpherModel.so: ProMorpherMap::run(int, double), libMorpherModel.so: MovingMeshSolverBase::updateThisTimeStep(FvReprese ntation const&), libMorpherModel.so: MovingMeshSolverBase::commonTimeStepUpdate(unsigne d int const&), libStarSolve.so: ImplicitUnsteadySolver:: preStep(), libStarSolve.so: ImplicitUnsteadySolver::step(), libStarSolve.so: SimulationIterator::startSimulation(RunnableSolver *, int, SimulationIterator::RunMode, bool), libStarSolve.so(+0x1e6357), libStarNeo.so: Controller::executeCommand(Command&, Properties const&, Properties&), libStarNeo.so: Controller:: processCommands(), libStarMachine.so: CommandController::SerialMasterCommandLoop::start( ), libStarMachine.so: CommandController:: processCommands(), libStarMachine.so: Machine::startServerHost(int, char**, std::map<std::string, unsigned int, std::less<std::string>, std::allocator<std: pair<std::string const, unsigned int> > >&), libStarMachine.so: Machine::main(int, char**)] Signal: SIGSEGV: memory access exception error: Server Error I am running on 16GB ram so again surprised to have this come up. I am running out of ideas to try make this work Your help is very much appreciated, at least I know I am on the right track Look forward to your reply! 

September 8, 2018, 21:26 

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Siddharth
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2. I didn't change any solver settings of morpher (default). I went to respective boundaries and specified morpher conditions for each of them. 3. I am not sure why. What is the equation you wish to put as field function? I wonder if that conditional statement in your field function is really necessary. May be placing a new coordinate system will help, I think. Also I made some changes in the field function (Fig3) and did it again. Check if this looks more like what you want. https://we.tl/tVvft7y2mOc 

September 11, 2018, 05:19 
Motion field function

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Hello again Ubuntu,
Thank for your reply and apologies for the delay in reply Quote:
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The equation I am using is of the form: const*exp(const*$$Position)*cos(const*${Time}) After lots of trial and error I figured that the memory access exception error was in fact coming from the field function. I eliminated the condition and declared the two functions, i.e. trigonometric and exponential, as two separate field functions. I create a third field function in which I reference the trig and exp function as vector components. Still curious as to why it wouldn't work by simply putting the whole definition in a single field function, but I'm glad I finally managed to get the desired motion on the boundary Hope this helps anyone having the same problem in the future. Thanks a lot Ubuntu for your help 

September 11, 2018, 06:50 

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Siddharth
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Glad to know that you solved it.


Tags 
axisymmetric, field function, floating point exception, grid velocity, morphing 
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