RyanDavies19
commented
1 month ago Hi @HANloading,
1) Seabed stiffness, damping, and friction are all user inputs in MoorDyn. Their default values are listed in the docs here: https://moordyn.readthedocs.io/en/latest/inputs.html#id4. The theory behind the seabed contact can be found here: https://iopscience.iop.org/article/10.1088/1742-6596/2362/1/012018 2) dtIC and ThreshIC are parameters that control the initial condition generation for MoorDyn. Before the simulation begins, MoorDyn attempts to find the system steady state with no external loads by letting the lines 'fall' into place. It does this by running the system with no external forces until the fairlead tensions are constant as defined by dtIC and ThreshIC. ThreshIC is the error threshold for tensions to be considered steady. dtIC is the amount of time the tensions need to be within ThreshIC to be considered stationary. There are other parameter like TmaxIC, which controls the max time this initialization runs for before giving up, and CDscaleIC, which scales the drag coefficients to find equilibrium faster. 3) The impact of the seabed contact values on anchor loads depends on your system. In general though you can leave them as the default if you don't know site conditions. The impact of the initial condition solver parameters does not impact accuracy. If a steady state solution is not found before the simulation begins, then the first couple seconds of the simulation will likely show the system moving towards its equilibrium state, while under the influence of external forces. 4) Nothing needs to be modified for surface piercing lines and/or rods in MoorDyn. For rods it calculates the submergence of each segment. For lines it assumes they are fully submerged, it is a work in progress to add partial submergence. It can handle attachment points above the water line.
Dear All： I have some questions about moordyn's input file (1) Are bottom stiffness and bottom damping determined by the anchor chain data, and if so, how is this value derived? Does it require some anchor chain data to calculate it? (2) What determines dtIC and threshIC? How do I arrive at these two figures? (3) Do the four values mentioned above have a significant effect on the anchor chain load? Is the derived anchor chain load accurate if these four data are inaccurate? (4) If the guide hole for the anchor chain line is located above the water surface, i.e. at the top position of the platform, can I still use moordyn for the anchor chain load calculation? If so, is there data in the moordyn file that needs to be modified accordingly? Or what data is affected?