NWTC

Hi Paul, You're correct -- when I say that the line "t" outputs should give an accurate representation of the peak tension along a line if the discretization is fine enough, I mean that other terms can be neglected. Other terms includes the "c" output, as well as inertial loads, ...

Hi Paul, To start with, I must admit that I wrote most of the current MoorDyn module in OpenFAST years ago as a side project during my PhD, and I did a hasty job with the optional outputs. Most of the refinements I made since then were to the standalone/C++ version, and it's only since I joined NREL...

Dear Ioannis, MoorDyn doesn't model a floating platform itself, so it isn't set up to run purely independently. However, it is common to use a script to "drive" the fairlead motions in MoorDyn's for a simplified analysis focused on the mooring system. The specified fairlead motions can eve...

Dear Abhinay, We traced this problem with the tensions back to how the time variable is stored in MoorDyn. It seems that the existing single-precision float causes problems with the interpolation/extrapolation of fairlead kinematics when the simulation time reaches a certain point (in this case 512 ...

Dear Abhinay, I appreciate you bringing this up and sharing the illustrative plots. This has come up before, and it's tricky because I can't think of anything in MoorDyn that would cause a change in behavior partway through a simulation. Other instances of this are documented in these threads: https...

Dear Abnhinay, The results you're seeing are as I'd expect. My understanding was you were only concerned with simulating the results of a line failure on the floater itself. You'll see the code I helped you with simply zeroes the forces of the failed line on the platform; it does not do anything to ...

Dear Abhinay, It looks like your code is zeroing out the X-component force for the fairleads and anchors of all lines. DoLineRHS is called separately for each line, and the three entries of the FairFtot array correspond to the X, Y, and Z force components. FairFtot corresponds to forces at the fairl...

Dear Abhinay, You're on the right track, but I think you'll need to study more about FORTRAN coding, and figure out more about the MoorDyn code, before you'll be able to succeed. Here are a couple tips: - To set a value to zero, you can use "=0.0_ReKi", for example: m%ConnectList(m%FairIdL...

Regarding a portion of the lines being out of the water, it looks like this is occurring because the lines being modeled are buoyant and have enough slack to float up to the water surface. This version of MoorDyn doesn't distinguish the water surface, so the buoyancy is modeled even as the lines ris...

Hi Abhinay, MoorDyn requires a time step small enough to resolve vibrations of individual line segments in order for its calculations to be convergent. Because you are modeling a relatively light and stiff line with quite small segment lengths, the natural frequency of segment vibration will be quit...

Dear Krishnaveni, MoorDyn is not set up to handle non-uniform seabed depths at this time. You can specify different anchor depths, but only one depth (specified by WtrDpth) will be used to model lines resting on the seabed. Positioning a line end below the seabed depth, as you do in your MoorDyn inp...

Hi Francisco, Thanks for providing the plots that show the problem, and also checking with the similar problem noted by a user last year. What you're showing isn't a behavior I'm familiar with, and I haven't been able to think of what could cause it within the MoorDyn model. To help eliminate possib...

Sorry to not have responded sooner. Here are some answers: (1) Yes, this is the right way to compile it. (2) You would need to share with me the specifics of the outputs you are looking at and what their values are for me to be able to offer a suggestion about this. (3) If you would like to use this...

This is an interesting problem that I haven't figured out yet. I see that you're using the standard OC4-DeepCwind mooring system description and it was a surprise to me that the simulation was unstable (the NaN value errors). These errors don't occur in MoorDyn v1.01.00 but do occur in v1.01.01, whi...

Hi Francisco, The frequency of those tension oscillations could be affected by hydrodynamic drag as well as the internal damping that you mentioned, so I'd double check drag coefficients just to be safe. That said, because the oscillations seem to decay more rapidly than the pitch motion, I wonder i...