Dear all
I am using WaceMod = 6 in Hydrodyn for my calculations.
In the process of using it, I found that I need to provide input files containing Vxi, Vyi, Vzi, Axi, Ayi, Azi, DynP, Elev.
My questions are:
I didn’t find the file for water depth input. Where is the file for water depth input. The Hydrodyn file only let me input the parameter file and horizontal coordinate position, but there should be parameter of different water depth for calculating the floating body force, right?
How to select the coordinate points (up to 9 points) in the input file to make the structure calculation more accurate?
Thank you!
Shunhang Lu
Here are my answers to your questions, which I presume were in reference to WaveMod = 6 (not WaceMod):
With WaveMod = 6, the columns in each of the wave velocity, wave acceleration, and dynamic pressure files correspond to the internal HydroDyn analysis nodes–as determined by the strip-theory member input definitions–corresponding exactly those written to the HydroDyn summary file.
Presumably you are referring to HydroDyn inputs NWaveElev, WaveElevxi, and WaveElevzi. You can set these arbitrarily at up to 9 locations; they will not impact the solution accuracy. It is the number of strip-theory hydrodynamic analysis nodes that will impact the solution accuracy, not the number of wave elevation outputs.
Dear @Jason.Jonkman
Thank you for answering my question. First of all, I’m sorry for the spelling mistake.
With WaveMod=6, what I understand is that the number of columns in the input file is related to NWaveElev. In my understanding, if NWaveElev=5, then the input file .Vxi, .Vyi, .Vzi, .Axi, .Ayi, .Azi, .DynP each has five columns of data. But in your answer, it means that if n computing nodes are set up in strip-theory, then the input file has n columns, and the data of each column corresponds to different water depth positions in turn, right?
2.If the NwaveElev is greater than one, do I need to enter multiple file names on the WvKinFile line of the HydroDyn file? What’s the distinction between different file names, spaces or commas? Multiple quoted strings separated by spaces？
3.Can the location of the computing node of strip-theory be modified by the user? Could you please tell me how to modify the computing node of strip-theory? Or can you tell me where there are WaveMod=6 tutorials so I can study them.
As a beginner, I’m sorry to ask so many basic questions. Thank you again for your answer.
The number of columns in the .Elev file is NWaveElev. The number of columns in the .Vxi, .Vyi, .Vzi, .Axi, .Ayi, .Azi, and .DynP files is the number of internal hydrodynamic analysis nodes.
No, there is only one .Elev file, with the number of columns equaling NWaveElev.
Yes. The internal hydrodynamic analysis nodes are dictated by the joints, members, and member discretization (NDivSize) in the definition of the strip-theory members. The exact location of each internal hydrodynamic analysis node is given in the HydroDyn summary file.
Dear @Jason.Jonkman
I have some more questions about WaveMod = 5 and 6. It seems hard to investigate the breaking wave effect on the monopile-based wind turbine by the present FAST version. Based on the latest research, I found that the wave nonlinearity could induce significant dynamic response comparing to the linear wave. Here are my questions:
1. With WaveMod = 5, if I input a time history of breaking wave which has high-order component, more than second order, can I obtain the dynamic response of the structure accurately. I have read the HydroDyn manual carefully, and I found that HydroDyn will compute an FFT of the provided wave elevation time series to the amplitudes and phases of each frequency component. But I also found that using higher order wave data may produce erroneous results.
2. Based on WaveMod = 5 cannot obtain reasonable results, I’m trying to use WaveMod = 6. Firstly, I want to make a validation. The period and wave height is set as T = 10s and H = 6m, respectively. I obtain the time history of velocity (Vxi, Vyi, Vzi), acceleration (Axi, Ayi, Azi) and the dynamic pressure (DynP) at the analysis nodes based on the linear wave theory. However, the results of Wave1Elev and Vxi at SWL are not good as show below. I have searched in the forum and tried to change the input file format. But still I cannot handle it.
The WaveMod = 5 option of HydroDyn assumes that the user-specified wave elevation can be derived by a superposition of linear regular waves. If your wave elevation considers higher-order components (such as breaking waves), these would not be captured properly by HydroDyn. Normally, we’d band-pass filter the wave-elevation time series so as to only capture the linear wave-frequency range of wave components when using WaveMod = 5.
The WaveMod = 6 option of HydroDyn should allow you to specify your own wave kinematics, including nonlinear components, but I’m not sure I understand what is happening in your case. It appears that your user-specified wave kinematics data is not being interpreted properly by HydroDyn. I would suggest reviewing your user-specified wave kinematics data and step through how HydroDyn is reading in this data with a debugger.
The HydroDyn module of OpenFAST does not currently consider breaking wave loads. Even if you user-specify wave kinematics that properly include the effects of breaking waves with WaveMod = 6, the hydrodynamic load computed by the strip-theory solution of HydroDyn will only include standard terms from Morison’s equation such as fluid-inertia and viscous drag, with no special consideration for breaking loads such as slap loads.
