Is it possible to model the loss of a pre-tension cable in SubDyn, by using the Controlled pre-tension cable] capability?

I noticed the Controlled pre-tension cable capability available in SubDyn, and I have the following question.

  1. As far as I understood, it is possible to describe a change in cable length in function of time (only in the direction of cable shortening). First question: is there an example file on how this is implemented?

  2. Second point: in theory, it should be possible to prescribe a reduction in length of the cable such that the pretension goes to zero, which would be the same as losing that pretension cable. Could this be implemented?

  3. I suppose the eigenmodes/eigenfrequencies derived by SubDyn at the beginning depend on the pre-tension in the cables. SO, if I change the tension in the cable, should not these change?

These questions arise from the fact that I would like to simulate the IEC 61400-3-2 DLCs where there is a loss of a line (9.1, 10.1), but at the moment the only way I see is to:
A. Run the simulation with all the cables intact, up to the time t = T_loss
B. Copy the state at time t = T_loss of all the DOFs which can be specified in ElastoDyn.dat as INITIAL CONDITIONS
C. Run a separate simulation, removing the cable lost, and running the simulation (although I would not know how to say to OpenFAST how to resume from the wind speeds and wave elevatoin time histories at
time t = T_loss).

Maybe there is a better way?

Kind Regards

Dear @Maurizio.Collu,

I agree that due to SubDyn’s assumption of linearity, the change eigenmodes/eigenfrequencies associated with the change in pretension is not captured by SubDyn if you are applying active control of cable pretensioning.

I know that NREL has tested the capability to actively control cable pretensioning, but I’m not aware of a model available in the public domain that demonstrates that.

Regarding the simulation of mooring line or tendon loss in the stationkeeping system for simulating DLC 9.1 and 10.1, we discussed that recently in a different forum topic: How to simulate IEC 61400-3-2 DLC 9.1 (10.1) in OpenFAST. (The easiest approach is to make a small change to the source code.) That said, I know NREL has plans to add the ability to simulate line loss directly within MoorDyn in an upcoming release (but I’m not sure exactly when yet).

Best regards,