Learning Forum

[nvspronsen]

Hello everyone,nnI want to perform a simulation with an overset mesh, where the background mesh contains a certain flow profile, and the component mesh (in 2D a circle, and in 3D a sphere), follows that flow profile. nRight now I am a bit confused on how to handle this problem. First I was thinking about using 6DOF, however, than I will create forces which will act on the component mesh whereas I want the component to follow the background mesh.nIs there anyone who has an idea on how to tackle this problem or has some tips?n

[Stephen Orlando]

Hi, nCan you provide some further details on the flow profile that you mentioned including images of the mesh and the Fluent setup? Is this flow profile imposed on a boundary only? It sounds like 6dof is what is needed, but more info is needed to say for sure.nThanks,nSteven

[nvspronsen]

Yes of course. First I will show you the mesh I created before and after hybrid initialization. For the intialization, I turned off the overlap minimizaton, to increase the overlap, because I thought this would increase the accuracy and prevent errors during simulation.nnFor my Fluent set-up I used: Transient, pressure-base, absolute, planar. With the following model and boundary conditions. About the boundary conditions of the component wall, I doubted whether to use 'no slip' or 'specified shear' and than setting the shear stress to 0, so I tried both, but it did not give any difference in outcome.nAfterwards I compiled the following SDOF, where I only entered the mass and inertia IZZ. And enabled Dynamic mesh: Six DOF and implicit Update. nBelow are the methods that I used and the calculations settings. nSo actually when I enabled the 'write history motion', my overset grid went down (I believe) because CG_Y started at 2.5 and ended at 2.4789, and this happened in 0.161 seconds. However, after that moment the error occured that a negative cells volume was detected. I have attached a photo where the negative cell volums are encircled. So basically my question still remains, whether is the right approach? So assiging the mass and inertia through a udf - SDOF and than applying a pressure or flow filed in Fluent. And if this is the case, than how will I remove the error of negative cell volume? Should I reduce the time step size or maybe make the cells, that cause problems, smaller?nThank you in advance!n