[MBDyn-users] Applicability to Marine Hydrodynamics

Pierangelo Masarati pierangelo.masarati at polimi.it
Fri Dec 1 07:55:20 CET 2017

On 11/28/2017 05:16 PM, Patrick Marleaux wrote:
> Dear MBdyn Users,
> I am considering to use MBdyn in combination with a nonlinear Boundary 
> Element Method for the analysis of multiple rigid marine floaters, 
> that are linked to each other via  certain constraints. Excitation 
> forces from water waves as well as radiation and diffraction forces 
> will be calculated by the BEM whereas the equation of motion of the 
> coupled system shall be solved  by MBdyn.
> What are the experiences regarding motion calculation in the fields of 
> hydrodynamics?  From my experience solving for the motions of a 
> floating body often turns out to be unstable since hydrodynamic forces 
> highly depend on the accelerations of the body, leading to a higher 
> order differential equation. A common approach addressing this problem 
> is to subtract this acceleration dependent part  from the forces 
> (based on some estimation) and add it to the inertia term 
> (hydrodynamic added mass). It would then be necessary to change the 
> inertia of bodies during the simulation. Is that possible using the 
> Python or C++ API? Or are there any other solution strategies?
> Thank you in advance for your answers. If you have any other concerns 
> or suggestions about the usage of MBdyn for this application please 
> let me know.
In addition to Richard Crozier's suggestions, MBDyn supports variable 
inertia bodies, i.e. rigid bodies whose inertia properties (mass, CM 
location and inertia tensor with respect to the CM) can change during 
the simulation.  Those values are defined through "drive callers".  See 
the "variable mass" variant of the "body" element.

You can define the drive callers that describe the inertia properties 
from an external solver by means of a "stream" file driver.  See the 
"stream" variant of the "drivers" section and the "file drive" variant 
of the "Drive and drive callers" section.

Sincerely, p.

Pierangelo Masarati
Dipartimento di Scienze e Tecnologie Aerospaziali
Politecnico di Milano

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