Dynamic Response Analysis Methods Research Of Structures Under Random Wind And Wave Load

With the rapid development of China's economy, more and more ocean engineering structures are built. For example, many cross-sea bridges such as the East Sea Bridge, the Hangzhou Bay Bridge and the Qingdao Bay Bridge have been built recently. In addition, the Qiongzhou Strait Bridge, the Bohai Strait Bridge and the Taiwan Strait Bridge are also in planning. The over-strait bridge not only has a long span, but also locates in deep water. Its environment factors such as wave, climatic, hydrology, geology and earthquake are exceedingly complicated. The wind and wave have great power. Moreover, they have complicated relationship in intensity, direction, frequency spectrum and so on. The action on the over-strait bridge has intensive dynamic characteristic, randomness and coupling. Under many circumstances, the transient strong wind and wave excitation are regarded as equivalent static loads. But for the over-strait bridge, wind and wave have distinctive dynamic characteristic and coupling effect. It's significant to considering the actual dynamic characteristic of wind and wave for the design and construction of the over-strait bridge. Therefore, it is important to develop an appropriate method for the random response of structures under wind and wave loads.A numerical method for the dynamic response analysis of the structures mentioned above subjected to wind and wave loads is developed in this article, and it includes:First, based on the designing wave method, the dynamic response analysis of a pier and a bridge tower is fulfilled by using ANSYS. The pier and tower are modeled by the PIPE59 element. Two different wave theories, i.e., the Airy wave theory and the fifth Stokes wave theory are used for comparison.Second, a Fortran Program is developed for obtaining the wave load spectrum of a cylinder from the wave spectrum. The wave load spectrum is then used in ANSYS for random vibration analysis of structures. This method is verified through a simple example. Moreover, it is used to obtain the response spectrum and mean square deviation of a pier and a bridge tower under JONSWAP wave spectrum and P-M wave spectrum. A random vibration method is developed for the response of structures under wave loads based on pseudo-excitation method. The corresponding program is developed in the structural analysis program DDJ-W of Dalian University of Technology. The random responses of a pier and a tower are implemented and compared with those obtained by ANSYS. Third, a random vibration method for analyzing the random responses of structures under wind and wave loads is developed. The wind and wave are taken as random loads while their spectra are regarded as basic inputs. This method is based on the pseudo-excitation method. The wave loads which are computed by Morison equation is translated to node loads by the projection area method. The nonlinear dynamic water damping is handled iteratively based on Borgman assumption. The non-orthogonal damping matrix can be dealt with precisely. This method can consider wind and wave which spread along arbitrary directions. Based on the structural analysis software DDJ-W of Dalian University of Technology, a program is developed to analyze dynamic responses of structures under random wind and wave loads. Finally, a pier and a bridge tower are analyzed to make a preliminary verification of the proposed method.