Hydrodynamic coefficients for swaying

edited November 2014 in Old versions
Hi,

I am trying to simulate swaying motion by oscillating rectangular box which I'm comparing to experimental data. I am trying to validate my model by comparing the total pressure acted on the body which is the combination of added mass and damping.

It seems that my 2D model has a very high damping coefficient compared to the experiment. I've calculate the total pressure and its 4times bigger than the experimental result. I've tried to reduce the damping by lower viscosity (artificial), varying coef. speed of sound (10-30), using 0 value of 'eps' in XSPH and extending the a bigger dimension (20m in length).

However, nothing seems to work plus I experience numerical instability on the right hand side of the tank. I am pretty sure the model is sensitive to some parameters in the XML file which I cant relate to.

I've kept my particle spacing around 0.010m with 0.4mx0.4m oscillating rectangular box. I've run cases in 2D and find similar results over an over damped system.

And I realized force calculated by pressure integration over line of boundary particles (N/m) and force calculated directly from acceleration (N) have different outcomes. Have you got any idea what the cause of this 2D issue.

Any help that anyone may have would be extremely helpful.

Comments

  • In other posts we have explained how you can compute forces. Try to take a look to them. If you can not find that information, please email us to dualsphysics@gmail.com.

    Force can not be computed starting from pressure values, not correct. Values of pressure of boundary particles are not physically correct and pressure of fluids close to the boundary are slightly corrupted by previous fact. The best way to compute forces is using the ACE values of boundary particles which are the forces exerted by the fluid on those boundaries.

    If you want we check your XML, please send it to our email contact.

    Regards

    Alex
  • Hi,

    Thank you again for your explanation. I will send my XML asap.

    In that case, why the boundary pressure is not physically correct and what is the significant of computing boundary pressure values from PartVTK.

    I got experimental data which the force is in N/m. So, by computing force out from ace, eventually I will obtain force in N and need to do something from the experimental data in order to make a compatible comparison ??

    And could you please tell me the different between acepos and aceneg for the boundary acceleration values ??

    Regards,
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