Offshore Wind Turbine Interaction with Floating Freshwater Ice on the Great Lakes.

Abstract

Developing offshore wind energy has become more and more serious worldwide in recent years. Many of the promising offshore wind farm locations are in cold regions that may have ice cover during wintertime. The challenge of possible ice loads on off- shore wind turbines raises the demand of modeling capacity of dynamic wind turbine response under the joint action of ice, wind, wave and current. The simulation software FAST is an open source CAE package maintained by the National Renewable Energy Laboratory. In this thesis, a new module of FAST for assessing the dynamic response of offshore wind turbines subjected to ice forcing is presented.

In the ice module, six models are included which involve both prescribed forcing and coupled response. The division of ice models is based on different ice failure modes and ice-structure interaction characteristics. Among these six models, two new analytical models of ice loading are presented. One is a new analytical model to simulate time-dependent ice forces limited by ice failure with the ice considered to fail in multiple zones non-simultaneously. The other model generates time-dependent ice forces on sloping structures due to bending failure.

Besides ice loading models, since ice thickness is an important input parameter when predicting ice loads, several analytical models that predict ice thickness change over time as a function of air temperatures are also presented in this thesis.