Structural analysis of floating offshore remote terminal for deep sea fishing

Abstract

Productivity of offshore fishing can increase if there are offshore terminals providing services such as fish unloading and repair of crafts and gears to the fishing fleets. This research proposed the use of FORT (fishing offshore remote terminal) as a very large floating structure (VLFS). Structural analysis is key in the design of VLFS. The research developed an adaptable framework to simulate FORT's hydroelastic interaction and motion using Newtonian's harmonic method. The governing partial differential equation of motion including the effect of deformation and torsional inertia was expressed in a dimensionless form. A finite difference algorithm was employed to transform the differential equations into linear algebraic equations. Linear and nonlinear dynamic responses was obtained using Hamilton principle with modal superposition coupled with finite element methods. Sensitivity tests are performed to quanti$z the effect of changing numerical parameter. Variety of plate models is investigated. Techno-economic model is also developed. The solution for a selected load condition has been presented. The result on hydroelastic response for several wavelength q (0.12, 0.23 and 0.43) to structural length ratios (l:1,2:r and 4:1) revealed longish F9RT experiences higher elastic deformations as comparc a square FORT for higher wavelength. In continuous springing freeboard reaction, the safe margin decreases from 4m to below 2m at higher wavelength ratio. At small wave length the hydroelastic response is the smallest for the lower ratio orientation. It is found that hydroelastic response is minimal as aspect ratio close to 1. Resultant stress on FORT stiffness when aspect ratio approaches 1 amplifies response amplitude by 35%. Sensitivity test indicates, for full load condition, larger structure will experience larger deformation stress (0.928 MN/m2 for 250m, 1.035MN/m2 for 500m, 1.035MN/m2 for 1000m). Permanent plastic deformation starts occurr ing at 20o and worsen at 45o causing higher shear force and moment. Maximum torsional force exceeds 51.25N/m2. For long crest of 0.43 maximum torsional deflection measured are250m(19.32N/m2 for 250m), 500m (27.55N/m2 for 500m), and 1000m 1za.o:\Vm2 for 1000m). Net present value of F9RT is NPV of 146mil, internal rate of return of 22.94% overl5 years. FORT as a new concept is thus techno economically feasible. The analytical model developed is a comprehensive tool for FORT designers.