Dynamic Analysis of Mooring Cables with Application to Floating Offshore Wind Turbines

Floating offshore wind turbines are recently being considered widely for adoption in the wind power industry, attracting interest of several researchers and calling for the development of appropriate computational models and techniques. In the present work, a nonlinear finite-element formulation is proposed and applied to the static and dynamic analysis of mooring cables. Numerical examples are presented, and in particular, a mooring cable typically used for floating offshore wind turbines is analyzed. Hydrodynamic effects on the cable are accounted for using the Morison approach. A key enabling development here is an algorithmic tangent stiffness operator including hydrodynamic coupling. Numerical results also suggest that previous empirical hydrodynamic coefficients could be obtained by fully coupled fluid–structure interaction. Convergence-rate and energy-balance calculations have been used to demonstrate the accuracy of computed solutions. The introduction of the developed cable model in a framework for the study of the global behavior of floating offshore wind turbines is the subject of the current work. Source code developed for this work is available as online supplemental material with the paper

Minimum cost performance-based seismic design of reinforced concrete frames with pushover and nonlinear response-history analysis

Previous studies compare results of pushover and nonlinear response-history analysis of predesigned reinforced concrete frames. The present study employs nonlinear response-history analysis and pushover analysis with the N2 method in a computational framework for the optimum performancebased seismic design of reinforced concrete frames according to the fib Model Code 2010 methodology and compares their obtained design solutions in terms of cost and structural performance. It is found that the minimum costs of pushover-based designs are similar to the costs from response-history analysis for regular frames but the pushover-based designs can be more expensive for irregular frames. Furthermore, the pushover-based designs are not guaranteed to satisfy performance objectives when subjected to response-history analysis even when more than one lateral load distributions are applied

Direct damage controlled seismic design of plane steel degrading frames

A new method for seismic design of plane steel moment resisting framed structures is developed. This method is able to control damage at all levels of performance in a direct manner. More specifically, the method: (a) can determine damage in any member or the whole of a designed structure under any given seismic load, (b) can dimension a structure for a given seismic load and desired level of damage and (c) can determine the maximum seismic load a designed structure can sustain in order to exhibit a desired level of damage. In order to accomplish these things, an appropriate seismic damage index is used that takes into account the interaction between axial force and bending moment at a section, strength and stiffness degradation as well as low cycle fatigue. Then, damage scales are constructed on the basis of extensive parametric studies involving a large number of frames exhibiting cyclic strength and stiffness degradation and a large number of seismic motions and using the above damage index for damage determination. Some numerical examples are presented to illustrate the proposed method and demonstrate its advantages against other methods of seismic design. © 2014, Springer Science+Business Media Dordrecht