FPSO COLLISION LOCAL DAMAGE AND ULTIMATE LONGITUDINAL BENDING STRENGTH ANALYSES

Abstract

IN OFFSHORE OIL &GAS PRODUCTION THERE IS A LARGE CONCENTRATION OF PLATFORMS IN A LIMITED AREA OF THE SEA, WITH THE CONSEQUENT INCREASE OF VESSEL TRAFFIC IN THE REGION. PLATFORM SUPPLY VESSELS (PSVS), SHUTTLE TANKERS AND MAINTENANCE AND SAFETY UNITS OPERATE VERY CLOSE TO THESE PRODUCTION PLATFORMS, CREATING A PROPITIOUS SCENARIO FOR COLLISIONS. THUS, THE RISK OF COLLISION BETWEEN VESSELS AND PLATFORMS HAS SIGNIFICANTLY INCREASED, CAUSING CONCERN FROM THE POINT OF VIEW OF LIFE LOSS, MATERIAL DAMAGE AND MARINE ENVIRONMENT DEGRADATION. IT IS IMPORTANT TO ADEQUATELY DESIGN THE STRUCTURES AND TO PREDICT THE EFFECTS OF ACCIDENTS ON THE INVOLVED VESSELS. IN THE STRUCTURAL ANALYSIS OF COLLISION, GEOMETRIC AND MATERIAL NONLINEARITIES MUST BE CONSIDERED, AS WELL AS THE STRIKING SHIP VELOCITY, THE VESSELS DRAFT DIFFERENCE, AMONG OTHER VARIABLES. IN THIS WORK, THE COLLISION OF A PLATFORM SUPPLY VESSEL WITH A SINGLE-HULL FLOATING PRODUCTION STORAGE AND OFFLOADING (FPSO) PLATFORM IS STUDIED THROUGH NUMERICAL SIMULATION USING THE ANSYS LS-DYNA COMPUTATIONAL SYSTEM. DAMAGE IS LOCALLY CHARACTERIZED BY THE COLLISION FORCE ON THE FPSO HULL AND THE DEPTH OF PENETRATION (DISPLACEMENT). IN ADDITION, IT IS ALSO SHOWN THE ENERGY ABSORPTION CAPACITY OF EACH TYPE OF STRUCTURAL ELEMENT FOR THE COLLISION SCENARIOS STUDIED AND A CRITERION IS PROPOSED TO DETERMINE WHICH STRUCTURAL ELEMENT GROUP SHOULD RECEIVE MORE ATTENTION IN THE DESIGN PHASE IN ORDER TO REDUCE THE EFFECTS OF A COLLISION. BOTH THE LONGITUDINAL STRENGTHS OF THE INTACT FPSO AS WELL AS THE REMAINDER AFTER COLLISION ARE EVALUATED BY ASSESSING THE BENDING MOMENT VERSUS CURVATURE CURVES. IT IS OBSERVED THAT A SINGLE-HULL FPSO PLATFORM WITH THE THICKNESSES OF THE STRUCTURAL ELEMENTS MAINTAINED UNCHANGED IN THE CONVERSION OF THE ORIGINAL OIL TANKER (VLCC) SHOWS A SIGNIFICANT ULTIMATE LONGITUDINAL STRENGTH EVEN AFTER COLLISION OF A LARGER SUPPORT VESSEL AT HIGHER VELOCITY THAN RECOMMENDED BY THE IACS RULE.