RESPONSE STATISTICS OF OCEAN STRUCTURES TO NONLINEAR HYDRODYNAMIC LOADING .1. GAUSSIAN OCEAN WAVES

This paper presents an analytical approach based on the stochastic ave raging of the energy envelope to treat the dynamic behavior of single- degree-of-freedom elastic ocean structures. Such systems are usually s ubjected to a narrow-band random process which may be modelled as the output of a shaping filter. The response co-ordinates of the system an d filter experience slow and fast variations with respect to time, res pectively. For this class of problems, the method of stochastic averag ing is used to establish stochastic Ito differential equations for the process of slow variation. This approach has not previously been used for non-linear mechanical problems. Three different shaping filters ( including those possessing a Pierson-Moskowitz spectrum) are employed to model Gaussian random sea waves. The response statistics of the str ucture are estimated in terms of the excitation spectrum for different levels of non-linear hydrodynamic drag force. It is found that the hy drodynamic drag reduces the system response energy and consequently su ppresses the motion of the structure. In addition, the response probab ility density deviates from normality as the non-linear hydrodynamic d rag parameter increases. The case of non-Gaussian random sea waves wil l be considered in Part II. (C) 1995 Academic Press Limited