# Force computations

edited July 2017
Hi

In the examples of floating bodies, I have noticed that for computing the force, ALL of the particles of that floating bodies are used. Why only the boundary particles are not used?

Thanks

• In ComputeForces you can specify the particles of the object you want to compute the force exerted on it by.... id, type, mk....
In those examples onlytype:floating is used!!!
• Thanks!
I know it. I mean that for a specified floating body, when we want to compute the applied force to it, we consider all the particles of that body, and NOT only the particles that are located on its boundary.
This is my question.
Regards
• if you specify onlymk:20, then force is computed for all particles of mk:20...
• edited July 2017
Is the force computed has units Newton and is it in global coordinates in x, y and z directions of the geometry we have created?..
or is it converted to a unitless quantity and/ or is it in another coordinate system?

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UPDATE 1 day later:

I am now just taking the force computed as PER UNIT DEPTH, seems to work better IS ıt so? Now, I just ask for confirmation, so it is not Newton, but Newton per unit depth in 2D problems? no matter the depth I have given still got same result..

Thank you!
• units in 2D are N/m
units in 3D are N

Regards
• @SUMMER how were you able to specify a specific depth in 2D problem? As far as I know the calculation of depth in 2D by ComputeForces is done by:

depth = 2*h*(1+h0)

As seen in the picture at "Dinter" - h is smoothing length, but h0 I am unsure of.

• Just a note to my comment above (23th of September) - DualSPHysics does not use arbitrary depth in 2D simulations like FVM programs do. Instead it outputs units for an example force as N/m.