Dear @Nikhil.Mathews,
I only briefly looked at your HydroDyn input file and see that the Echo line is on line 4 when it should be on line 3. See the HydroDyn model I shared above for an example.
Best regards,
dear @Jason.Jonkman ,
Good day,
Noted and i made the changes. I am encountering a problem as attached regarding the modified Wamit data.I have cross checked with the HydroDyn model you have shared above as an example and could not find any differences. Awaiting your feedback. Wamit files can be found in the below link
Regards
Nikhil
Dear @Nikhil.Mathews,
The error message is saying that your .1 and .3 files do not have the same frequency components. Have you confirmed that they do? Other than infinite (-1) and zero (0) periods, your .1 file is ordered from highest (5.026548E+02 s) to lowest (1.570792E+00 s) period (lowest to highest frequency). Does your .3 file have the same period/frequency discretization? I took a quick look at your files and noticed that the periods are not sorted from highest to lowest in your .3 file. HydroDyn should be able to resort this data, but perhaps there is a bug in the sorting algorithm? Perhaps try sorting your .3 file from highest to lowest period?
Best regards,
Dear Jaison,
It worked when .3 file was sorted from highest to lowest period.
Many thanks for your support and guidance.
Best Regards
Nikhil
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I asked Lu Wang of NREL, who has been making improvements to HydroDyn recently and he noted the following:
I took a quick look at the code. It looks like HydroDyn requires the period ordering in the .1 and .3 files to be the same (which would be the case if they are generated from the same WAMIT run), so the same sorting can be applied to both. In the forum post, the .1 and .3 files have different ordering of the period/frequency, which caused the error.
Best regards,
Hi Jason,
I have a doubt regarding the Hydrodyn output channel created as per attached. i have made the output channel based on the example given by you. Do we need the other output channels except the “Wave1Elev” which is the output channel in general used for standard reference platform.
Dear @Nikhil.Mathews,
Presumably you are referring to WavesF1xi and WavesF2xi, etc.? These should be named B1WvsF1xi and B1WvsF2xi, etc. in the version of HydroDyn that supports multiple WAMIT bodies.
Best regards,
Hello Jason,
In the output file generated , for all the 4 bodies it was seen to have same values of surge,sway,heave, pitch , roll and yaw. Can all the 4 bodies give same response values or can this be explained somehow. Even though value changes for each time series for a particular wind speed ,but the other 3 bodies show exactly same values as the platform for each time step
regards
Nikhil
Dear @Nikhil.Mathews,
I would generally expect different potential-flow bodies in HydroDyn to have different motion if the bodies are located at different positions within the floater, especially if the floater is considered as a structurally flexible in SubDyn. What model are you are referring to where all 4 bodies have the same motion?
Best regards,
Attached is sketch of hybrid platform with 3 no OWC placed at the Centre of Volturn US-S floater, IEA 15MW wind turbine
Dear @Nikhil.Mathews,
The motions of each of your potential-flow bodies are identical because their reference locations are identical according to your HydroDyn input file and WAMIT output file. But this does not seem to match your figure, where it looks like each of the OWC are offset from the platform centerline a bit (if I understand your figure correctly).
Best regards
Hi Jason,
Yes…it is correct and thanks for the clarification. I would also like to clarify if the output values from ElastoDyn module for platform motions like heave, yaw considers combined effects for the all 4 bodies or can we consider it as the response of the hybrid system since next to computing structural loads ElastoDyn also receives the loads calculated by HydroDyn . Or will it have the same values of B1 body in the Hydrodyn output file for 4 body case considered here
Dear @Nikhil.Mathews,
If SubDyn is not enabled, meaning the floating substructure is characterized by the rigid-body properties set within ElastoDyn, then the floater will be treated rigidly and all HydroDyn bodies will follow the same rigid-body motion as the platform in ElastoDyn (different potential-flow bodies may have different motion only if their reference points are offset from the platform reference point in ElastoDyn, based on rigid-body kinematics).
Best regards,
Hi Jason,
Thanks for the above clarification .
Reason for having the same reference point for OWC is that because they are considered as a very thin flat piston that has relative motion in heave DoF only.