Comparative evaluation of PML technique for hydrodynamic impact loading on spar-type floating platform

The structural dynamic stability of spar-type floating platform for offshore wind turbine subject to hydrodynamic impact is numerically investigated by the dynamic response analysis. The unbounded flow domain of sea water is truncated to a bounded finite domain and the reflection of out-going hydrodynamic impact wave at the artificial boundary of truncated domain is minimized by the perfectly matched layer (PML) technique. The generalized transport equations governing the non-viscous compressible water flow is split into three PML equations by introducing the direction-wise absorption coefficients and the state variables. The coupled fluid-structure interaction problem is approximated by the iterative Eulerian FVM-Lagrangian FEM with the Euler-Lagrange coupling scheme. The impact-induced hydrodynamic pressure is calculated by the JWL equation of state and the mixture of un-reacted explosive and reaction products is defined by the reacted volume fraction. It is confirmed from the numerical experiments that the wave reflection phenomenon at the artificial boundary is substantially reduced when compared with the case without using the PML technique. And, the remarkable amplitude difference and the fluctuation with several subsequent peaks in the time responses of rigid body motion and effective stress of the floating platform are successfully suppressed when PML layers are used.