Fluid-structures interaction research to predict fatigue life of offshore platforms. Determine structural response properties (such as natural frequencies, damping and modal shapes) from field data. Predict the dynamic response of structures to wave and ground excitation. Project No. 36 is an adjunct project to this investigation.
Complete. Two high resolution spectral estimators were applied to assess the amount of structural damping: maximum likelihood spectral analysis (MLM) (to locate frequency bands of energy) and maximum entropy analysis (MEM) (to assess energy levels in the various bands). Results indicate lower damping than commonly believed. The MEM damping estimators were compared to results measured by Shell and agreed to within confidence bounds. Multiple channel MEM techniques were investigated to identify modal shapes. The research applied unique relationships between linear wave forces and wave radiation damping and revealed additional useful relationships between nonlinear drag forces and viscous hydrodynamic damping.