Search found 29 matches

by Matt.Hall
Tue Dec 01, 2020 6:29 pm
Forum: Computer-Aided Engineering Software Tools
Topic: Line tension output from MoorDyn
Replies: 4
Views: 246

Re: Line tension output from MoorDyn

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, ...
by Matt.Hall
Mon Nov 30, 2020 10:54 am
Forum: Computer-Aided Engineering Software Tools
Topic: Line tension output from MoorDyn
Replies: 4
Views: 246

Re: Line tension output from MoorDyn

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...
by Matt.Hall
Mon Aug 31, 2020 7:15 am
Forum: General
Topic: Moordyn
Replies: 9
Views: 2223

Re: Moordyn

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...
by Matt.Hall
Thu Jul 02, 2020 3:25 pm
Forum: Computer-Aided Engineering Software Tools
Topic: DTU 10-MW Reference Wind Turbine
Replies: 65
Views: 36473

Re: DTU 10-MW Reference Wind Turbine

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 ...
by Matt.Hall
Tue Jun 30, 2020 10:09 pm
Forum: Computer-Aided Engineering Software Tools
Topic: DTU 10-MW Reference Wind Turbine
Replies: 65
Views: 36473

Re: DTU 10-MW Reference Wind Turbine

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...
by Matt.Hall
Fri Jun 26, 2020 9:30 am
Forum: Computer-Aided Engineering Software Tools
Topic: Tendon failure in FAST modeling
Replies: 47
Views: 13620

Re: Tendon failure in FAST modeling

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 ...
by Matt.Hall
Fri Jun 19, 2020 9:27 am
Forum: Computer-Aided Engineering Software Tools
Topic: Tendon failure in FAST modeling
Replies: 47
Views: 13620

Re: Tendon failure in FAST modeling

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...
by Matt.Hall
Fri Jun 12, 2020 9:19 am
Forum: Computer-Aided Engineering Software Tools
Topic: Tendon failure in FAST modeling
Replies: 47
Views: 13620

Re: Tendon failure in FAST modeling

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...
by Matt.Hall
Fri May 15, 2020 9:27 am
Forum: General
Topic: Taut leg mooring synthetic ropes
Replies: 9
Views: 5690

Re: Taut leg mooring synthetic ropes

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...
by Matt.Hall
Fri May 15, 2020 9:15 am
Forum: General
Topic: Taut leg mooring synthetic ropes
Replies: 9
Views: 5690

Re: Taut leg mooring synthetic ropes

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...
by Matt.Hall
Thu Feb 20, 2020 10:52 am
Forum: General
Topic: Moordyn
Replies: 9
Views: 2223

Re: Moordyn

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...
by Matt.Hall
Fri Aug 30, 2019 10:44 am
Forum: Structural Analysis
Topic: Response in Long term simulations and different MoorDyn time step
Replies: 5
Views: 2206

Re: Response in Long term simulations and different MoorDyn time step

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...
by Matt.Hall
Fri Aug 23, 2019 4:29 pm
Forum: Computer-Aided Engineering Software Tools
Topic: Compile MoorDyn C++ source files in Linux and some error of calculations
Replies: 1
Views: 891

Re: Compile MoorDyn C++ source files in Linux and some error of calculations

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...
by Matt.Hall
Fri Aug 23, 2019 4:13 pm
Forum: Computer-Aided Engineering Software Tools
Topic: Steps to compile MoorDyn
Replies: 4
Views: 1471

Re: Steps to compile MoorDyn

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...
by Matt.Hall
Fri Aug 23, 2019 10:27 am
Forum: Structural Analysis
Topic: MoorDyn Response in Pitch/Roll
Replies: 2
Views: 1723

Re: MoorDyn Response in Pitch/Roll

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...

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