Analysis and Design Optimization of Offshore Wind Turbine Support Structures

Analyse og designoptimering af et offshore vindmøllefundament

Jørgensen, Jeppe Bjørn ; Nissen, Christian Fløe

4. term

Design of Mechanical Systems, Master

2013

2013-06-04

111

Dette speciale undersøger, hvordan støttestrukturer til havvindmøller (jacket-understel) kan gøres lettere uden at gå på kompromis med udmattelsesstyrken, dvs. den gradvise skade fra mange lastcykler. Med en generisk jacket-model og et givet lasttilfælde er målet at minimere massen under udmattelsesbegrænsninger ved hjælp af gradientbaseret optimering. Hovedfokus er en analytisk designfølsomhedsanalyse (DSA) for udmattelsesbetingelser under ikke-proportionale lastespektre, altså belastninger der ændrer størrelse og retning over tid. Et 3D finite element-program (FEM) i MATLAB er udviklet til at analysere strukturen og beregne den akkumulerede skade. Små benchmark-eksempler blev brugt til at vurdere og vælge metoder til skadeestimering, optimering og den analytiske DSA. DSA er udført både numerisk og analytisk ved brug af adjoint- og direkte differentiering for at bestemme gradienter, som beskriver, hvordan udmattelsesbetingelserne ændrer sig med designændringer. Parametristudier og optimeringer er gennemført med de valgte metoder. En SLP-algoritme er anvendt, og en adaptiv move limit-strategi (begrænsning af trinstørrelse) er udviklet for at opnå gode resultater. Metoderne fungerede godt for jacket-strukturen og har stort potentiale i strukturel optimering, og optimering samt analytisk DSA med fokus på udmattelse viser lovende perspektiver for fremtidigt arbejde.

This thesis examines how to make offshore wind turbine support structures (jacket frames) lighter while still resisting fatigue, the gradual damage caused by many load cycles. Using a provided generic jacket model and a defined load case, the goal is to minimize mass subject to fatigue constraints with gradient-based optimization. The main focus is an analytical design sensitivity analysis (DSA) for fatigue constraints under non-proportional load spectra, meaning loads that change in magnitude and direction over time. A 3D finite element program in MATLAB was developed to analyze the structure and compute accumulated fatigue damage. Small benchmark examples were used to assess and select methods for damage estimation, optimization, and the analytical DSA. The DSA was carried out both numerically and analytically using adjoint and direct differentiation to obtain gradients that show how fatigue constraints change with design modifications. Parametric studies and optimization runs were then performed with the selected methods. An SLP algorithm was applied, and an adaptive move limit strategy was developed to obtain successful results. The methods worked well for the jacket case and show strong potential for structural optimization; the fatigue-focused optimization and analytical DSA also show promise for future work.

[This abstract was generated with the help of AI]

Optimering ; Udmattelse ; Design Sensitivity Analysis

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