Change in stiffness matrix when selecting plots parameter in solveEquilibrium about moorpy HOT 2 CLOSED

Hi Ahirvoas,

Thanks for reaching out. It's very exciting to see the code being used by more people! Apologies for the delayed response.

In general, MoorPy is still very much in a "development" phase and the documentation is still very much in progress.

It seems like your approach and logic are all correct, but I'll offer some suggestions to get things working:

• I'm not sure which branch you are using, but the "master" branch has not been updated in a while. The "dev" branch is the most up-to-date.

• The System.solveEquilibrium() method is very out-of-date. We have been using the System.solveEquilibrium3() method for all of our equilibrium solves

• I just pushed an update to the dev branch that comments out the solveEquilibrium() method, renames the solveEquilibrium3() method to solveEquilibrium(), and adds in another solveEquilibrium3() method to call the new solveEquilibrium() method to account for our other dependencies. So for now, keep calling solveEquilibrium().

• I am slightly confused because I don't see the getSystemStiffness() method calling any solveEquilibrium() method

  • getSystemStiffness finds the stiffness maxtrix of all "DOFtype" DOFs without equilibrating
  • getCoupledStiffness finds the stiffness matrix of all coupled DOFs while equilibrating the free DOFs
  • getSystemStiffnessA finds the stiffness matrix of all "DOFtype" DOFs using a purely analytical approach without equilibrating anything

• Here are my suggestions of what you should do to produce the stiffness matrix of the OC3 spar:

ms = mp.System('NRELOffshrBsline5MW_OC3Hywind_MoorDyn.dat', depth=320)
ms.initialize(plots=0)
print(ms.bodyList[0].type)

If the above printed line is 0, then the body is a free body. If it's 1, it's fixed. If it's -1, it's coupled

ms.solveEquilibrium(DOFtype="free", plots=0, rmsTol=10, maxIter=200)

This call to solveEquilibrium (see the recent commit) will not change anything if the body type is 1 or -1, since there are no free points to equilibrate
If the body type is 0, then the body will want to balance forces, which include weight/buoyancy (see the Body class)

Now that the system is equilibrated, we can calculate the stiffness matrix
If the body type is 0, I would recommend

K_mooring1 = ms.getSystemStiffness(DOFtype="free", dx = 0.1, dth = 0.1, solveOption=1, plots=0)

If the body is -1, I would recommend

K_mooring2 = ms.getCoupledStiffness(any optional inputs you want)

Regardless of the body type, I would still recommend running

K_mooringA = ms.getSystemStiffnessA(options)

And comparing this to any of the other system stiffness matrices, especially in terms of run time (it's a much more efficient method)

Hopefully this clears up any issues between solveEquilibrium and any system stiffness method.

Stein

from moorpy.

Presumably resolve, so closing this issue.

from moorpy.