# dynamic mesh motion (angularOscillatingDisplacement) in OF1.6

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 May 12, 2010, 11:29 dynamic mesh motion (angularOscillatingDisplacement) in OF1.6 #1 New Member   Tamás Baksa Join Date: Dec 2009 Location: Budapest, Hungary Posts: 2 Rep Power: 0 Dear Foamers, I'd like to simulate the flow around an oscillating cross-section. The shape is very simple it is almost like a rectangle. I had to define very fine boundary layer resolution in order to stay below y+<1. The chord length of my shape is 1 [m] and the first cell next to the wall is 0.04e-3 [m]. My constant/dynamicMeshDict looks like: Code: ```dynamicFvMesh dynamicMotionSolverFvMesh; solver displacementLaplacian; motionSolverLibs ("libfvMotionSolvers.so"); diffusivity quadratic inverseDistance 1(fixedWalls); // **************************************** //``` I have defined 0/pointDisplacement like the following: Code: ```... boundaryField { [inlet, outlet, frontAndBack description] fixedWalls { type angularOscillatingDisplacement; // angle = angle0_ + amplitude_*sin(omega_*t.value()); axis (0 0 1); // direction origin (0 0 0); angle0 0; amplitude 0.17453; // 10 deg in rad omega 6.2832; // 1Hz * (2pi) value uniform (0 0 0); // ??? } } // ********************************************* //``` Using this configuration and moveDynamicMesh utililty severely non-orthogonal faces appear at angle = 0.59° and runs until the following error at angle = 1.83°: Code: ```Mesh non-orthogonality Max: 179.989 average: 7.45988 *Number of severely non-orthogonal faces: 318. ***Number of non-orthogonality errors: 50. ***Error in face pyramids: 204 faces are incorrectly oriented.``` In the next timestep OF exits and the mesh looks like in the following figure. The boundary layer mesh should remain parallel to the wall during the whole cycle. http://img526.imageshack.us/img526/7...edmesha183.png Do you have any idea how to avoid this? 1) Maybe using different diffusivity fields? According to Jasak and Tukovic paper [1] I should try diffusivity proportional to the distortion energy. But none of the available diffusivity keywords sound like dist. energy in OF1.6: Code: ```10 ( uniform quadratic file motionDirectional inverseDistance inversePointDistance inverseFaceDistance directional inverseVolume exponential )``` 2) Shall I define different sets for near field (BL mesh) and far field then rotate the near field set rigidly? I have found a similar case [2] but it was used in OF1.3. There is no subsetMotionSolverFvMesh in dynamicFvMesh keyword list in OF1.6: Code: ```5 ( dynamicMotionSolverFvMesh // I'm using this one solidBodyMotionFvMesh dynamicRefineFvMesh dynamicInkJetFvMesh staticFvMesh // mesh has no motion )``` Any idea is appreciated! Thanks in advance. ps: my time step is sufficiently small, I think: 2e-4 [1] http://powerlab.fsb.hr/ped/kturbo/Op...tionFAMENA.pdf [2] http://www.aero.lr.tudelft.nl/~frank/index.php?id=research/cfd/problems/2D_movingmesh_wing

 May 13, 2010, 05:43 #2 Senior Member     Eric Paterson Join Date: Mar 2009 Location: Blacksburg, VA Posts: 198 Blog Entries: 1 Rep Power: 10 Why not look at 1.5-dev? subsetMotionSolverFvMesh is there for you to use, or at least learn what to do and then re-implement in 1.6.

 May 13, 2010, 10:53 #3 Senior Member   Kevin Smith Join Date: Mar 2009 Posts: 104 Rep Power: 9 If you can conform your mesh around the body to a circle, you could use GGI to oscillate the body, which would avoid mesh deformation. Take a look at the mixerGGI example and code, it is fairly easy to change the driving function to a cosine signal. If you don't want to change your mesh or simply cannot conform the mesh surrounding the body to a circle, I would look into the subset motion as Eric mentioned or RBF mesh motion.

 May 13, 2010, 11:16 #4 Senior Member     Eric Paterson Join Date: Mar 2009 Location: Blacksburg, VA Posts: 198 Blog Entries: 1 Rep Power: 10 But Kevin, GGI is only in 1.5-dev, and the OP is using 1.6....

 May 13, 2010, 12:22 #5 Senior Member   Kevin Smith Join Date: Mar 2009 Posts: 104 Rep Power: 9 Ah, you are correct.

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