Design Of Nacelle Structure Of Horizontal Axis Tidal Turbine Against Different Failure Modes

Nacelle of a horizontal axis tidal turbine (HATT) is a watertight envelope underwater which contains transmission system and blade-hub assembly is also connected to it. Its strength is important due to the reason that it has to withstand both static and dynamicloading. Nacelle of HATT is cylindrical shell structure with conical shell ends. In thisregard, a detailed literature survey was carried out on shell structure theories anddifferent design rules. The current research work is aimed at providing a design of aHATT nacelle against different failure modes with structural view point.In this context a finite element model of the structure was prepared using ANSYS(a popular Finite Element Analysis software) built-in programming language calledAPDL (ANSYS Parametric Design Language). The power of this language is that itprovides greater flexibility in the model generation and analysis process. Furthermore itresults in greater time saving when many design iterations are needed which requirechanges in parameters of the model.Optimization module of ANSYS software was used to optimize the thickness of thenacelle structure by minimizing its weight and using Von Mises yield criterion. Dynamicresponse of the structure was examined by performing stress free and pre-stressed modalanalyses. Modal analysis was also performed on symmetrical model. Simplified fatigueanalysis was performed at hot spot locations of the structure using the guidelines ofDNV rules.Finally, the stability of nacelle against buckling was studied as it is also one of theimportant failure modes for shell structures. Eigen buckling and nonlinear bucklinganalyses were performed for cylindrical nacelle and its conical ends. Buckling loadswere also calculated with analytical formulations for validation purpose.