應用於離岸風電套管式支撐結構頻域法疲勞分析之代表性環境的選擇

Abstract

本研究以台灣福海風場水域為例應用OC4 5 MW套管式離岸風電進行時域與頻域疲勞分析，符合國際標準估算離岸風電運行二十年的疲勞損傷累積值。利用SACS軟體設置波浪環境的有義波高與與週期資訊，對結構進行動態響應分析，取出觀察接點的FA、IPB、OPB三種結構響應訊號考量應力集中係數後，將其應力訊號自相關後傅立葉轉換成功率頻譜密度函數，總能量以Dirlik method進行譜疲勞分析，搭配T-curve S-N曲線估算在離岸風電作用的二十年間的疲勞損傷值。本研究以台灣海峽海況環境為例，比較各種代表性海況的組合方式所受的損傷與真實情況共一百二十個環境狀況的損傷總合，探討是否能以少數的環境組合去近似真實情況。頻域疲勞分析因為線性系統的假設，使響應的能量譜相互疊加，相對於時域法即可大幅減少90 %的分析時長，本研究再提出利用代表性環境組合的方法，可大幅減少所需分析數量，推薦選用前九大出現機率海況(不考慮較低波高)的組合方式，只需原本花費時長的1/12，即可使損傷比例平均值達60.3 %，變異係數37.7 %。

This paper is to perform frequency-domain analysis of the jacket support structure for OC4 5MW offshore wind turbine in Fuhai Offshore in 50m of water under Taiwan’s local environmental sea state, and estimate the cumulative fatigue damage values of 20 year lifetime. SACA software is employed to analyze the dynamic response at each significant wave height and time period of the wave environment. After extracting the FA, IPB, and OPB structures response of the observation joints and multiplying the stress concentration factors, we Fourier transform the autocorrelated strss signal into a power spectral density, then apply the spectral fatigue analysis by Dirlik method. Palmgren-Miner rule is employed to evaluate the fatigue life under the consideration of 20 year lifetime. This paper takes the sea conditions of the Taiwan Strait as an example, and compares the damage caused by the combination of various representative sea conditions with the actual damage of 120 environmental conditions, then explore whether it is possible to approximate the real situation with a less number of environmental combinations. Because of the assumption of the linear system, frequency domain fatigue analysis can be greatly reduced by 90% compared with the time domain method. This study proposes a method of using a representative environment combination, which can greatly reduce the analysis quantity, it is recommended to use the combination of the top nine probability sea conditions (not considering the lower wave height), only need to spend 1/12 of the original time, the average damage ratio can reach 60.3 %, and the coefficient of variation is 37.7 %.