Semi-submersible topside conceptual design: Transition piece

Vidal Puche, Fernando

4. term

Structural and Civil Engineering, Master

2014

88

This thesis investigates the fatigue life of the transition piece in a semi-submersible floating foundation for offshore wind at the conceptual design stage. The core question is how to reliably assess fatigue early in design by consistently transferring hydrodynamic loads into a mechanical model to obtain stress time series under irregular sea states. The work comprises: (1) validation of CAE tools by comparing ASAS with ROSAP on a jacket structure; (2) development of a hydrodynamic model in ANSYS AQWA based on a design basis that addresses site conditions, ballast, mooring system, heave plates, and cross-bracing; and (3) creation of a mechanical model of the topside, transition piece, and main columns together with a load-transfer procedure from AQWA to ASAS. Wind and wave loading are treated in the time domain using NREL FAST/TurbSim, producing stress histories evaluated via the effective hotspot stress approach with submodelling and rainflow counting to estimate fatigue damage. Several semi-submersible configurations are examined (with and without reinforcement bracing, and with tapered or uniform box girders), and mechanical design recommendations are provided. While no quantitative results are reported in this excerpt, the thesis delivers a validated hydrodynamic model, a tested load-transfer workflow, and guidance that enable a systematic fatigue assessment of the transition piece.

Dette speciale undersøger træthedslivet for transitionstykket i en semi-submersibel flydende offshore-vindfundament på konceptniveau. Hovedspørgsmålet er, hvordan træthed kan vurderes pålideligt tidligt i designet ved at koble hydrodynamiske laster til en mekanisk model og dermed få konsistente spændingstidsserier i uregelmæssige søtilstande. Arbejdet omfatter 1) validering af CAE-værktøjer ved at sammenligne ASAS med ROSAP på en jaketstruktur, 2) opbygning af en hydrodynamisk model i ANSYS AQWA efter et designgrundlag, der tager højde for placering, ballast, fortøjningssystem, heave-plader samt tværstivheder, og 3) udvikling af en mekanisk model af topside, transitionstykke og hovedkolonner samt en metode til lastoverførsel fra AQWA til ASAS. Vind- og bølgelaster behandles i tidsdomænet med brug af NREL FAST/TurbSim og resulterer i spændingstidsserier, som evalueres med effektiv hotspot-spænding, submodellering og rainflow-tælling for at estimere træthedsskade. Der afprøves forskellige semi-submersible-konfigurationer (med/uden forstærkende afstivning samt konisk eller ensartet kassedrager), og der gives anbefalinger til den mekaniske udformning. Ud fra det foreliggende uddrag rapporteres ingen kvantitative resultater, men afhandlingen leverer en valideret hydrodynamisk model, en gennemprøvet lastoverførselsmetode og designanvisninger, som muliggør en systematisk træthedsvurdering af transitionstykket.

[This apstract has been generated with the help of AI directly from the project full text]

Semi-submersible ; AQWA ; ASAS ; FOWT ; FAST ; Offshore wind ; Fatigue life ; Transition piece ; Floating foundation ; Load transfer

Download PDF
View record in AAU Student Projects