Time step in hydrodyn vs time step in Elastodyn vs time step in fst file

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Dear @Jason.Jonkman ,

Hope you are doing well.

I wanna ask whether the time step in Hydrodyn is different from elastodyn ?
For the first glimpse, i thought that the time step is the same due to the fact that OpenFast is a hydro-elastic tool.

Moreover, what is the difference between the time step in the fst file and the time step present in elastoDyn ?

Furthermore, in the expression of irregular long crested wave appears a variable x. I don’t remember where i read (maybe in your thesis !) that x is the undisplaced position of the platform (x=0 for OC3 Hywind ?), is that right ?

BR

Riad

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Dear @Riad.Elhamoud,

OpenFAST presently requires that all modules communicate with each other at the same rate–as regulated by the OpenFAST driver/glue code–which is the time step (DT) specified in the OpenFAST primary (.fst) input file.

Each module also has its own time integrator based on a time step that is specified at the module level, e.g., DT in ElastoDyn and RdtnDT in HydroDyn. You can specify these time steps at the module-level as “DEFAULT” if you want to use the same time step as the driver/glue code.

OpenFAST currently supports subcycling, which means the module-level time steps can be smaller than the driver/glue code, but does not support oversampling. Moreover, if you have subcycling, OpenFAST currently requires that the module-level time steps be integer divisors of the driver/glue code time step.

I’m not sure I understand your last question; can you share a link to the expression you are referring to?

Best regards,

1 Like
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Dear @Jason.Jonkman ,

Sorry for the late reply.

Thank you so much for clarifying the different time steps.

I am so sorry for my question whichis related to the variable x in the expression of irregular wave. I was misconfused. So, if i get it, the variable x in the expression of irregular waves generated by HydroDyn is the position of the floater at each time step. right ?

Thank you

BR

Riad

4

Dear @Riad.Elhamoud,

I’m still not sure I understand what expression you are referring too. Can you share a link or identify the source of the expression you are referring to?

Best regards,