Mooring Dynamics: Computer Models and Experiments at a Sixty Foot Scale.

Abstract

Ihree cases from the experiment conducted in the hydroballistics tank of the Naval Surface Weapons Center in 1976 are compared to the SNAPLOAD and SEADYN computer models. Two of theruns simulate the anchor-last deployment of a mooring; the third shows the relaxation of a mooring displaced laterally, then released. The quality of the experimental data is evaluated by comparing each case to the static, elastic catenary equations at the start and finish of each run. The measured positions of points along the static catenaries are found typically to agree with the catenary calculations within 1 to 2 percent of the cable length. Tension measured at the fixed end typically agrees with the calculated value within about 12 percent. The SEADYN and SNAPLOAD computer models are found to reproduce all the significant motion and forces observed in the experiment. The "handbook" drag coefficients programmed in these models allow the cable motion sometimes to lead the data, sometimes to lag behind. More specific coefficients must be used when the rate of the dynamic motion is critical. Neither model included elastic hysteresis. The SEADYN program gave somewhat erratic tension values in the mooring line because tension waves were not damped by hysteresis. The SNAPLOAD model eliminated the tension variation through artificial damping. wie A lieC un.e Uq I. .°. .... . UNCLASSIFIED SgCURITY CLASSIPICATION OF 'MIS P446Mlhen Onto tntofed) 12