velocity difference between moving boundary and fluid
I'm reproducing 2D lid-driven cavity flow problem and set the velocity of lid to 1 m/s. I'm quite curious why the particle velocity at the top is not equal to 1 m/s. Can anyone explain why it is the case?
Comments
Increase ViscoBound, try 100 just to see that it works.
Kind regards
I've always felt that there are some problems with the code when it comes to tangential forces (specifically friction, whether fluid-solid or solid-solid interaction), and I'm still trying to understand how it's implemented and Verify if there is really a problem.
There is not a problem with the code as such, it is just that you cannot accurately model tangential forces using DBC. It is a limitation of the theory, since water particles can never touch the actual surface.
So if you need tangential forces between objects you should use the Chrono library, since it is solving for (friction) tangential forces through linear FEM.
If you need tangential forces between water and object, then mDBC, with possibility of varying speed at surface would be of use - you will have to wait for that.
Kind regards
@Asalih3d Thanks for your reply!
Regarding the interaction between different objects (solid-solid interaction), using the Chrono library, I found that the code mainly uses DVI, and the fixed point iteration method is used in the solution process to solve the equation. This method brings another problem. The calculation speed is relatively slow. It takes me a day to calculate 33 particles (a total of more than 6000 particle points, although particle counts have little effect on Chrono's computation time, since his contact detection is based on geometry). If you use the DEM that comes with the code to perform the calculation, it may only take ten minutes to complete the calculation, but the calculation result is not very ideal.
I am not sure what you are simulating, but particle count should have no direct effect on Chrono. It only has an effect on the fluid dynamics. I.e. if you are getting fluid dynamics wrong, your tangential force will probably be wrong too. Chrono as far as I know use particle distance to determine the distance between colliding objects, if the particle count is very low it will of course go wrong.
Maybe you need specific settings for DEM to work properly, I rarely use it anymore - I prefer Chrono.