[MBDyn-users] Applicability to Marine Hydrodynamics

Richard Crozier r.crozier at ed.ac.uk
Wed Nov 29 09:54:58 CET 2017

Hi Patrick,

I have developed an open source Matlab based model which used mbdyn for 
wave energy converter simulation whihc you might find interesting. It 
should also work in Octave (https://www.gnu.org/software/octave/), but 
some testing is needed.

It consists of the following system:

* A Matlab based preprocessor for the NEMOH open source boundary element 
solver to determine hydrodynamic coefficients

* An object oriented MBDyn preprocessor for Matlab (so the MBDyn system 
can be described using Matlab code, and the mbdyn input file is 
generated by the preprocessor)

* A mex interface to the MBDyn MBC library to facilitate communication 
with the mbdyn solver) during simulation. Force communication is done 
using the MBDyn's external structural force element and achieved using 

* A hydrodynamic force solver derived from WEC-Sim (see 
http://wec-sim.github.io/WEC-Sim/index.html, developed by USE DOE and 
Sandia National labs). This solves the hydrostatic, excitation and 
radiation forces in the time domain. I have removed the dependancy on 
Simulink and Simmechanics by replacing them with MBDyn and extracting 
the Simulink hydrodynamics code so the system is pure matlab.

* Modification to MBDyn so that it can be easily compiled to run on 
Windows (though I prefer Linux myself). The entire system is cross-platform.

Currently code can be found as part of the RenewNet Foundry here:


Here it is mixed in with lots of other stuff, however we (The University 
of Edinburgh) plan to split into packages and make a release, with 
documentation (one main area where the code is lacking) early in 2018.

Feel free to contact me if you would like to learn more, or be informed 
of the release.


Richard Crozier
Institute for Energy Systems -- The University of Edinburgh

On 28/11/17 16:16, 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.
> Best regards
> Patrick
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