The Nonlinear Dynamics And Galloping Analysis Of The Offshore Platform Structures Subjected To Ice And Wind Excitation

In this paper,the nonlinear dynamical theories are used to study the problems of birfurcation and complex dynamical behavior of offshore platform system with the ice and wind exitation. The work of this paper includes the following aspects:(1)A new model of ice—induced vibrations of strctures is established. The effect of ice on structure presents in two steps, i.e., the ice deformation and its crushing, which has discontinuous nonlinear characteristics. Taking into account the characteristics, we, using the nonlinear methods of analysis, developed a nonlinear dynamical model of ice—structure interaction, explicated in theory that the ice—induced vibrations of flexible structures is a system of multiple frequencies interfernece, self—excitement and forced oscillations, and investigated "locking"' principle observed in experiments. The formulas to compute ice forces given in this paper can be applied to structural design and computation in ocean engineering.(2) The hysteretic nonlinearity is studied. Using Davidenkov's model, we described the hysteretic nonlinearity of material and obtained some new dynamical behaviors of the system by means of the singularity theory. This work provides the theoretical basis for dynamic control of this kind of system.(3) The partial defferential dynamical equations of platform structure with four legs is established. Based on the Hamilton principle, the nonlinear dynamical model of the large system is obtained in consideration of the influence of ice. Through the Lapace transform, the model shapes of the torsional vibration is given. The model provides a close approach for the understanding of the dynamic characteristics of the ice—induced platform.(4) The nonlinear dynamical phenomena of ice—induced offshore platform is studied. The perturbation analyse indicates that the system exibites multiple kinds of combination resonances and that its natural frequencies accord with the testing results of the model-platform. Under the condition of the primary resonance, we discussed the nonlinear dynamical phenomena of self—excited,...