Q: Do you have any guidance on modelling a specific ground bearing strength?


A: The ground-point mechanism does not attempt to model actual force vs. penetration functions which you might find in real life. It just gives you a means of setting a relatively stiff barrier to incr easing penetration which you can adjust to match observed conditions. The default setting is usually acceptable. Note that it behaves as a spring (though nonlinear), meaning that when you push down on it then let up to the same position you have the same force -- which is unlike real ground. Real ground would tend to be compacted or displaced as you press down and return much less force when you let
up. Therefore you should set up your grounded condition with the compacting/displacing of the ground already done. If some of the penetration has been into the ship by deforming the hull, you could lo
cate the ground point inside the modeled hull surface. Otherwise it should be on the hull surface or appendage -- wherever the ship is or will be in contact with the ground.

The adjustment for ground hardness is set by the optional ddm (maximum penetration) parameter which is not about penetration in any absolute sense, but rather the penetration which you would have if th e entire fixed weight of the ship (i.e. excluding tank loads) were supported on that point without any other support. This is supposed to give you an intuitive handle for setting it. If the weight were
equally shared by four ground points and you wanted the penetration to be p for each one, the ddm value to use would be p/4.

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