Assessment of the dynamic response of the Bergsøysund Bridge in the frequency domain
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The Norwegian Public Roads Administration is currently both planning and building a new coastal highway, along the fjord-dense Norwegian west coast. In that concern, dynamic response of floating structures exposed to wave loads is of high importance. This kind of problem can be solved in the frequency or the time domain. In time domain analyses, the stochastic load must be estimated using Monte Carlo simulations, and long time series run to find confident results for the stochastic response. For linear problems, calculations in the frequency domain are therefore often favourable. The accuracy of the well-established linear frequency domain methods was studied, for stochastic problems, in this thesis. In particular, the Bersøysund Bridge was considered. A program was developed in Matlab for calculations of structures on floating elements, where DNV HydroD Wadam analyses of the floating elements and an Abaqus/CAE model of the frame of the structure are prerequisites. Using state space form and iteration, the complex and non-linear modal eigenvalue problem of the system was also solved. The findings of this thesis involve that the results agree well with similar analyses performed in the time domain. 20 modes resulted in near-converged results for the model of the Bergsøysund Bridge exposed to white noise loading. When estimated sea load was enforced, approximately 30 included modes were needed for convergence. The findings supported the credibility of the methods used, and indicated adequate accuracy.