Assessment of One Company’s Regulations for Offshore Lifting Operations

摘要

During subsea lifting/lowering operations, offshore operatorsrntypically utilize published regulations or recommendedrnpractice (e.g. Ref 1 & 2) for calculating key parameters suchrnas maximum and minimum crane wire tension duringrndeployment through the splash zone and through the waterrncolumn. First hand observations by the authors has revealedrnshortcomings of accepted practice in key areas such as:rn1. Over-prediction of wire tension and snap loads, leading tornlesser weight being liftedrn2. Under-prediction of underwater heave motion of modulernwhile being loweredrnThese issues are discussed in light of the fact that added massrnof the module changes with submergence. Model tests andrnnumerical simulations using DNV’s software SESAM arernused to evaluate the added mass of cylindrical and rectangularrnmodules and to gain an understanding of heave motionsrnexperienced by the modules in moderate wave conditions.rnSample calculations are used to show areas where existingrnregulations are inadequate.