LIFTBOAT DYNAMIC ANALYSIS
Available from Stewart Technology Associates
STA LIFTBOAT is a software package used by designers and also by the US Coast Guard for evaluating liftboat design submissions. The purpose of STA LIFTBOAT is to calculate the structural response and pad reactions of liftboats in the elevated mode, subject to environmental and gravity loads. The program accounts for wind loading on exposed sections of legs in the air gap and above the hull, as well as on the hull and superstructure, including the crane. Wave and current loads are calculated on the legs below the still water level and in the splash zone. Shallow water wave theory is used, as embodied in the ABS MODU Rules and the legs are modeled as equivalent cylinders with the correct equivalent diameter, drag coefficient and inertias which represent the full leg (with rack). The drag coefficient varies with wave attack angle, being strongly influenced by the rack (or racks) on each leg. A graph of drag coefficient with wave attack angle is produced by the program once the user has input the rack geometry.
Leg stresses typically limit liftboat operational envelopes. STA LIFTBOAT computes unity stress checks based upon both ABS MODU Rules & DnV. The US Coast Guard will accept any of these unity stress checks, subject to certain conditions.
STA LIFTBOAT also evaluates leg stresses induced by vessel roll and heave motions (plus lateral wind loads) in transit.