Function Request: Simulate Seaweed Effects on Subsurface Mooring Line

[EnochBadu]

Dear all,

I humbly write to request for a function within MoorDyn to simulate the hydrodynamic effects of seaweed (or a feature to mimic seaweed) attached to a subsurface mooring line.
The function should model additional drag and inertia forces caused by seaweed, modifying the line’s dynamic response.

The function could use the Morrison equation to calculate hydrodynamic forces on the mooring line segments with seaweed attached.
Seaweed introduces extra drag and inertia loads, altering the line tension and motion.
The model could incorporate seaweed properties such as effective diameter increase, drag coefficient, and added mass coefficient.

Input may include :

Mooring line segment properties (length, diameter, position, velocity, acceleration)
Seaweed parameters like effective diameter increase, drag coefficient (Cd), added mass coefficient (Ca), seaweed density if needed

Output:
Updated hydrodynamic forces (drag and inertia) on each mooring line segment considering seaweed effects

I hope to hear from you soon.

Kind regards
Enoch Badu.

[RyanDavies19]

Hi Enoch,

We don't have any current projects focused on developing a marine growth model specifically for MoorDyn. Typically we model marine growth exactly as you described, by changing the mooring line diameter, linear mass density, and hydrodynamic coefficients in the MoorDyn input file. We do have a tool for this, FAModel, that we use for setting up MoorDyn simulations. The theory behind that model's marine growth module is here: https://github.com/FloatingArrayDesign/FAModel/tree/main/famodel/mooring#marine-growth-modeling

[EnochBadu]

Thanks @RyanDavies19 for this information.

Considering the length of kelp plants grown on subsurface lines, I have a suggestion.

How about attaching free hanging lines (long enough to mimic kelp plants. example 2m ) on the nodes of the main subsurface MoorDyn line between 2 floats.
Then the FAModel can be applied on the hanging lines to mimic growth as the parameters of the lines are increased.
This is more realistic and represents/mimics kelp plants well.

Is this possible in MoorDyn?

Thanks.

[RyanDavies19]

What you proposed certainly is possible in MoorDyn, though I'm not sure it would give the most realistic results. MoorDyn line elements are cylindrical, so the hydrodynamics might not match kelp exactly. Also, I should have been more clear about FAModel. It is a tool that can help you generate the input files for MoorDyn, one part of which is looking at a line with marine growth. Once a MoorDyn simulation is started, the hydrodynamic coefficients can't be changed. We generally think of marine growth happening on longer time scales than any MoorDyn simulation.

[EnochBadu]

Thank you very much for the information. Concerning the input file for MoorDyn, I have a question which I will ask on the WEC-Sim github discussions page. I realized you are active there and my question might benefit other users. kind regards

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On Wed, Aug 13, 2025 at 10:14 AM Ryan Davies ***@***.***> wrote: *RyanDavies19* left a comment (FloatingArrayDesign/MoorDyn#322) <#322 (comment)> What you proposed certainly is possible in MoorDyn, though I'm not sure it would give the most realistic results. MoorDyn line elements are cylindrical, so the hydrodynamics might not match kelp exactly. Also, I should have been more clear about FAModel. It is a tool that can help you generate the input files for MoorDyn, one part of which is looking at a line with marine growth. Once a MoorDyn simulation is started, the hydrodynamic coefficient can't be changed. We generally think of marine growth happening on longer time scales than any MoorDyn simulation. — Reply to this email directly, view it on GitHub <#322 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AU4IXDPB2YWGHIS6ZUL2U3D3NNB6BAVCNFSM6AAAAACDSN24QOVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTCOBUGEYTGNZUHA> . You are receiving this because you authored the thread.Message ID: ***@***.***>