Moment Calculation

Hi,

So, I have a floating body (2D) for which I would like to evaluate moment about its centre. Since it is not fixed, the centre of gravity will move. To take that into account, I am doing this

  1. Evaluate the (x,y,z) coordinates of the centre of gravity for each time step.
  2. Compute moment about that point for each timestep n about centre (xn,yn,zn)

- %computeforces% -dirin %diroutdata% -onlymk:60 -momentaxis:xn:xn:yn:zn:xn:-yn:zn -first:n -last:n -savecsv %dirout2%/_FloatingForce_1

This was the process I followed to get the moment. Recently, I asked a question about how to get the forces and moments from Chrono. I applied it to get the moment from Chrono as well.

When I compare these two moments, the one evaluated from computeforces is around 5x larger compared to the moment evaluated by chrono


If I compare the forces in x and z directions, the values are similar order of magnitude, though not same. ( I have scaled up the force values here)


I expected that they will be in the same order of magnitude. But did not expect this difference. Is there any reason why this difference might be occurring? Is it my moment computation or my understanding?

@Alex @Asalih3d

Comments

  • Additionally, I could not find the source code for ComputeForces in either Github or the /src folder on my downloaded version. Could you please let me know where that is available so that I can look at how the moment is being computed.

  • I have not yet tried what you are doing, but I will try to keep this post in mind for the future.

    One question I have though is; was collisions enabled in Chrono? Perhaps the interaction between bodies means that the moment is different than what you observe from looking at the fluid-solid interaction only.

    Another option you can try is to export the particle force values to Paraview (i.e. computeforces with vtk output), which should give you each particle and force in x,y,z direction. Then you can calculate moment for this and see if it matches DualSPHysics own moment calculation at least.

    Kind regards

  • Perhaps you should a more direct comparison in 3D....

    Chrono works in 3D, while the simulation is 2D


    Regards

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