CALM buoys, mooring chains and underbuoy, or submarine, hoses are modelled in the time domain with OrcaFlex.
Scaling up by 1pt5 HydroDyn_HD_Summary scaling up by 1pt5 HydroDyn_HD_Summary.PNG (38.94 KiB) Viewed 9368 times OC4_DeepCwind_HydroDyn_HD_summary OC4_DeepCwind_HydroDyn_HD_summary.PNG (38.STA specializes in the dynamic analysis of single point moorings. The attached is the HydroDyn summary file for both OC4DeepCwind and the scaled up model. If the BouyMyi is not a problem, what else can cause this problem in your perspective? Any suggestions would be greatly appreciated! Does the scaling method I used for these parameters make sense? 2: the term AddCLin as you discussed in the topic AddCLin for OC4 Semisubmersible, it is added because of the ballast water. the size of the side columns and FillFSLoc, which are scaled up by λ. But if it was, I think of two terms that are related to internal buoyancy, 1. I am not sure if this will cause my trouble. I checked the HydroDyn summary file and compared it with OC4-Semi HydroDyn summary file, all the volume terms and buoyancy terms are reasonable based on the scaling factor except the internal BuoyMyi term, which is caused by filled members (ballast water). With all the work done above, I run the simulation again and the results are still the same as I posted before. And also neither 2nd order wave nor current are considered in my study. The assumptions made in my work is that both transverse and axial hydrodynamic coefficients for viscous drag, added mass, and dynamic pressure Modifications are assumed to be same as OC4-DeepCwind. AddCLin for terms (4,4) and (5,5) are scaled up by λ^4 And also member outer diameter, PropD are scaled up by λ, however the thickness of the members are assumed to be same as OC4-Semi. In HydroDyn input file, change PtfmVol0 according to WAMIT output and set PtfmCOBxt=PFtmCOByt=0. Then run WAMIT to get the hydrodynamic coefficients and excitation forces (.1.3 and.hst) with wave frequency range from 0.02 ran/sec to 5 rad/secģ. To avoid double calculating teh restoring terms in WAMIT, the VCG in WAMIT is set to be 0. In ElastoDyn input file, scaled up the platform mass by λ^3 and inertia by λ^5. Scaled up the platform geometry model in Multi-surf in x,y,z directions by factor λĢ. In summary, here are what I did to build this scaled up platform model (λ is the scaling factor):ġ. I go through the HydroDyn manual and double checked my model. I will check with the latest version(V8.10) later to see if there is any difference. I am using FAST V8.09 for my work,not the latest one. The document you provided is really helpful! Heave Motion 2.png (16.87 KiB) Viewed 9380 times Surge Motion 1.png (20.38 KiB) Viewed 9380 times Please find attached the figures for surge and heave motions.ĭo you know happen to know a particular reason for this behavior? Also the surge motion does not seem to converge.
the platform is tending to rise up above the MSL to height of 85m. Heave motion tends grows up to a very high "positive" value (~ 85m) i.e. The simulation results for the 6 motions seem to be incorrect.
ORCAFLEX MANUAL ADDED MASS COEFFICIENTS OF MOORING CHAIN FREE
I studied the files that Marco had shared and created my own input files for my scaled up platform to run the free decay simulation (I mainly disabled the aerodyanamic loads, set wind speed=0.0, wave mode=0 and set initial heave motion to 0.2). We are trying to optimize the size of the platform to support the larger wind turbine properly and we first carried out the free-decay simulation to check the static stability of the new system. A divergence problem came up when I am trying to run the free-decay simulation for the global system. I am working on a larger wind turbine (compared to NREL 5MW) mounted on a scaled-up OC4-semi submersible platform now.
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