Study of fatigue design on marine current turbine support structure, Bali-Indonesia

Abstract

Clean Green energy is being desired all over the globe. It gives cleaner world and healthier environment to live. Most of the green energy resources such as tidal and wave are freely available in large amount and also sustainable. On the other hand, the energy demand is increasing along with population growth. Therefore, researchers are developing the technology of energy converter from these resources to support human activities, business and leisure. Indonesia an archipelago country with plenty of narrow strait and surrounded by two oceans makes this tidal energy extraction looks promising. A pioneer study in Bali Strait as the reference site is selected among other prospective sites. Bali strait has relatively shallow water depth, high current density and high energy demand to support Bali Island and its tourism board. As the equipment of tidal energy converter is placed in severe condition for relatively long period, hence it has to be strength resistance and fatigue resistance. Fatigue failure will cause integrity failure which mostly occurs in the joint connections and at the base of support structure. Therefore, Fatigue design plays an important role in the development of tidal energy converter. Fatigue analysis on MCT support structure is based on experience and engineering judgement. Two established industries, oil and gas exploration and offshore wind turbine, are tailored into marine current turbine development. In addition, a range of representative cases is selected in this dissertation. To conclude, the fatigue service life for MCT support structure located in Bali strait has fulfil the minimum required of 80 years (20 years service life with factor of safety 4.0) with various alternatives. Contrary to the offshore wind turbine (OWT) with natural period at soft-soft range, the recommended natural period range for MCT is placed at soft-stiff range. This because of the MCT support structure requires stiffer and more compact structure as they are exposed to more severe loading compare to OWT. However, another analysis should be conducted such as strength resistance and accidental limit stress in order to have a complete design. On the other hand, Environment Impact Assessment should be prepared as well. In addition, this study might be the first study of fatigue assessment in MCT support structure and should be considered as an opening to a further renewable energy development.