Modelling Wave Energy Converter (WEC) pointer absorbers using AMR
techniques with both subcycling and non-subcycling
Abstract
Wave energy has received significant attention in both academic and
industrial areas during the past few decades. Among all of Wave Energy
Devices (WEC) devices, many researchers focus on modeling the point
absorber since it can provide a large amount of power in a small simple
device when compared with other technologies. In this present work, we
developed an efficient Structured Adaptive Mesh Refinement (SAMR)
framework to model the interactions between the wave and pointer
absorber by directly solving the Naiver-Stokes equation in a
conservative manner. In particular, the level set function is used to
capture the air-water interface, and re-initialization across different
levels is applied. The Discrete Immersed Boundary Method (DIBM) is
applied to describe geometry of the pointer absorber and include its
effects on the incoming wave, which is generated in the inlet and
absorbed by using a sponger layer closed to the outlet. To save
computational cost, meshes are only refined near the air-water interface
and surface of point absorber. Specially, both non-subcycling, where a
uniform time step is employed for all variables on composite levels, and
subcycling, in which variables on different levels advance via different
time steps, are embedded in the SAMR framework. Cases about wave
generation and fluid-structure interaction are obtained to validate the
above proposed algorithm. Results show that subcycling takes
significantly less CPU hours than non-subcycling to model the wave and
pointer absorber interaction. Heave motions under different wave inputs
are compared with previous experiments as well as results from potential
flow theory, which shows viscous effects are important in this process.
Future work including coupling AMR with Turbulent Models (e.g. RANS or
LES) are also listed as an extension.