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
![orcaflex oc4 semi-submersible orcaflex oc4 semi-submersible](https://ars.els-cdn.com/content/image/1-s2.0-S2092678216304848-gr16.jpg)
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.
#Orcaflex oc4 semi submersible manual
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 9368 times Surge Motion 1.png (20.38 KiB) Viewed 9368 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 oc4 semi submersible 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. An increased design environmental loads need to be considered to achieve a further reduction in the failure probability.I am working on a larger wind turbine (compared to NREL 5MW) mounted on a scaled-up OC4-semi submersible platform now.
![orcaflex oc4 semi-submersible orcaflex oc4 semi-submersible](https://ars.els-cdn.com/content/image/1-s2.0-S2092678218303765-gr17.jpg)
Sensitivity analysis results indicate that the annual failure probability of the WT for the considered offshore locations is greater than 10 -3 if the site-specific 50-year return period values of the annual maximum wind speed and significant wave height are used for the design and without additional load factor. The component failure analysis also shows that the failure probability is dominated by the tower buckling, followed by the platform overturning. The results indicate that the failure probability of the considered WT is greater than the optimal value suggested in the literature, showing that the TC risk of such a WT could be very high if it is installed at offshore locations near the coastline of mainland China. The overall procedure is illustrated for the reliability evaluation of an offshore semi-submersible WT placed at four potential locations near the coastline of mainland China. The proposed procedure can take into account the dependent TC induced wind and wave loads to estimate failure probability by considering multiple performance limits of various components. The construction of the databases and their use for reliability analysis are described. The procedure relies on establishing the synthetic databases of TC track, TC wind and wave fields, and structural response. In the present study, an overall simulation-based procedure to assess the fragility and reliability of offshore wind turbines (WTs) subjected to tropical cyclone (TC) hazard is presented.