Your files look fine. A few things I noticed:
*For load case 4.5, I suggest disabling AeroDyn instead of setting the wind speed to zero, which was the intent of that load case.
*Likewise, you can disable ServoDyn instead of turning off all of the control options within ServoDyn.
*Load case 4.5 calls for a simulation that is 3600-s long, however, I only see that you’ve set-up a 90-s simulation. A longer simulation will be important to establish statistical significance for an irregular sea state.
Yes, B59Ax is equivalent to M5N1FKZe in this SubDyn model of the OC4-jacket.
I would tend to compare PSDs using [kN^2/Hz]; I’m not sure why that figure is labeled as [dB/Hz]. Perhaps its a typo or perhaps the PSD has been normalized by some reference value and computed as a base-10 log. You should be able to check by integrating the PSD across the frequency range, which should equal the variance of the signal if the units are [kN^2/Hz].
Dear Jason
I have sloved my question with your help.
In other Load Case 2.3a and 3.2, I want to get a good agreement with other research team.
I have attached the simulation file, could you please take a look at it?
Load Case 2.3a
Enabled DOF: None
Wind Conditon: No air
Wave Condition: Regular Airy: H=6m, T=10s
Is tower blockage effect equal to tower shadow effect?
Load Case 3.2
Enabled DOF: All, Rotor speed and blade pitch via controller
Wind Conditon: Steady, uniform, no shear: Vhub=8m/s
Wave Condition: No water
For load-case 2.3a, I see that you’ve disabled all of the DOFs in ElastoDyn, but kept SubDyn enabled. This will not result in proper simulation results. As described in Section 5.4 of the SubDyn User’s Guide and Theory Manual (wind.nrel.gov/nwtc/docs/SubDyn_Manual.pdf), when SubDyn is coupled to FAST, the 6 DOFs of the platform in ElastoDyn must be enabled to couple loads and displacements between the turbine and the substructure. Unfortunately, load-case 2.3a calls for a completely rigid structure, which is not really possible in FAST v8 with SubDyn. Alternatively, you could probably increase the stiffness of the SubDyn model to make it act more rigidly, or you could run HydroDyn in standalone mode (resulting in no hydro-elastics) for this case.
For load-case 3.2, I see that you’ve kept using the OC4-jacket model (with HydroDyn disabled) instead of using the land-based turbine, which is what this load case calls for (the load case calls for the land-based turbine to sit atop a short rigid cylinder, instead of the turbine atop the OC4-jacket). That said, it may not matter what the support structure is if you are not looking at responses (loads/deflections) in the support structure. I also suggest that you enable the unsteady aerodynamics model (change STEADY to BEDDOES), enable tangential induction (change WAKE to SWIRL), and disable the tower shadow (change TwrShadow from True to False) in AeroDyn for this case. The term “tower shadow” refers to the downwind wake of the tower (important for the loading of downwind rotors), whereas the term “tower influence” or “tower blockage” refers to the upwind “bow wake” (important for the loading of upwind rotors).
I am using FAST v8.10.00a-bjj and I would like to ask if it is now possible for someone to define the wave parameters (height, velocity, acceleration) for the OC4 semi-submersible platform.
Without customization to the source code, the current release of HydroDyn within FAST v8.10.00a-bjj allows the following incident wave kinematics model (WaveMod) options:
0: none = still water
1: regular (periodic) waves
1P#: regular (periodic) waves with user-specified phase, for example 1P20.0 for regular waves with a 20˚ phase (without P#, the phase will be random, based on WaveSeed); 0˚ phase represents a cosine function, starting at the peak and decreasing in time
2: Irregular (stochastic) waves based on the JONSWAP or Pierson-Moskowitz frequency spectrum
3: Irregular (stochastic) waves based on a white-noise frequency spectrum
4: Irregular (stochastic) waves based on a user-defined frequency spectrum from routine UserWaveSpctrm()
We are working on an update to HydroDyn that allows user-define wave kinematics time histories – that is, it allows the user to fully prescribe the wave kinematics (velocities, accelerations, dynamic pressures) at each hydrodynamic analysis node as a function of time. This will be available in the next release of HydroDyn in June.
I am analysing a floating support structure for a wind turbine for the load cases listed in IEC 61400-3 and for this I need the joint probability of wind speed at hub height and significant wave height and peak spectral period for the specific installation site. I have chosen to use the same geographic location as that of your report, “Dynamics Modeling and Loads Analysis of an Offshore Floating Wind Turbine”.
Are the data plotted in figure 3-15 on page 77 available?
When selecting the peak spectral period for a given hub height wind speed, is it in general necessary to analyse any period between the upper or lower bound or is there some way of selecting a relevant period based on the upper and lower bound of the peak spectral period?
In general, the IEC -3 standard would call for using the Tp that results in the highest loads. For most floating systems, we haven’t noticed a strong sensitivity to Tp, and so, a coarse resolution of the Tp range may be satisfactory. In the report you reference, the range of Tp associated with each Hs was split uniformly into three bins and was considered in the loads analysis by running three sets of simulations with discrete values of Tp centered within those bins.
I am performing a preliminary design of a mooring system using the guidelines in DNV-OS-E301, where a combination of a wind with a 100-year recurrence period, a significant wave height with a recurrence period of 100 years and a sea current with a recurrence period of 10 years. In your PhD-thesis, you have calculated the wind speed at hub height and the significant wave height for a 50 year recurrence period. I was wondering if it is possible to get the 100 year recurrence period from your data also?
In my PhD thesis, we used the Waveclimate.com service to identify the extreme significant wave heights at the reference site for various return periods. But while this may have been available through the service, we did not obtain results for the 100-year return period. Sorry.
From the AeroDyn15 manual, I came to know that we could determine the Dynamic pressure at different nodes along the tower nodes. I switched to AeroDyn15 to do so, but I am getting invalid in my SUM file for the dynamic pressure. I was testing the modified blade file (AeroDyn v15.04) while using the default Aerodyn15 input file.
I am using the following input file for the blade.
While using the default file for the blade I was receiving an error message stating “no valid value of phi”, but switching to modified blade file helped in that regard.
Could you please suggest what I should be doing to see the dynamic pressure output?
Yes, upgrading from AeroDyn v15.03 to v15.04 should improve the robustness of the BEM solution and eliminate errors regarding “no valid value of phi”, as has been discussed several times on this forum.
However, I’m not sure i understand you question regarding “invalid in my SUM file for the dynamic pressure”…please clarify your question.
Sorry for making my problem unclear.
I am not getting the values for dynamic pressure while running the simulation. When I check my .SUM file, I see “INVALID” in TwN1DynP.
Is there anything I might be lacking behind in order to get the result for dynamic pressure along the tower nodes?
I was having that result because of my NTwOuts parameter, it was 0 as default and forgotten to change before running the simulation.
I can now get the value for TwN1DynP.
Dear Jason,
Is there any interval to be considered between wave seed (1) and wave seed (2) within multiple simulations with the same sea states in order to reach a statistical convergence? For instance, if wave seed (1) is set to 123456789 must the wave seed (2) be an integer greater than first seed value ?
If a range set between two wave seeds for the first simulation,shall it be the same range for the other simulations or not ? For example,for the first attempt wave seed(1)=1234567890(billion) and wave seed (2)=1534678346(billion as well).For the next simulation,should it be something like wave seed(1)=1234785937(billion again) wave seed (2)= an integer greater than first seed in billion size ??
Or, it is not different whether a same range is designated or not ? As an instance,
[]1st. sim. Wave seed(1)=1234567890,wave seed (2)=1534678346
[]2nd. sim. Wave seed(1)=10, wave seed (2)=1234590,
[*]3rd. sim. Wave seed(2)=10067, wave seed (2)=569, and so on.
Your guidance would be the best as always.
Best regards,
Arsalan
The selection of WaveSeed can be random. When running many simulations, normally we set a counter in our script that increments the WaveSeed by a small fixed amount between separate simulations.
Dear Jason,
Firstly, thank you so much for the answer and appreciate for spending your time to answer me.But by script herein,do you mean the source code of the FAST or you mean the hydrodyn input file ?! Would the counter be same for the Turbsim random seed ?
Best regards,
Arsalan
By script, I mean a custom batch script used to run many FAST simulations (not FAST source code). This script would e.g. change the WaveSeed and wave height and period in the HydroDyn input file based on a master file (and other input files) and run the FAST simulation and repeat with other WaveSeeds and wave heights and periods.
Yes, the same answer applies to the seeds in TurbSim (these seeds can be selected randomly or incrementally between separate simulations).
