6. If the process can be inverted into a vector Markov process by state-space trans- 
formations, sometimes the solution of Fokker—Planck equations can be used to estimate 
the joint probability distribution function, from which many probability characteristics of 
the original process can be derived, even for nonlinear oscillations. 
7. Recently, a few applications of this approach have appeared in seakeeping 
studies. However, the Fokker—Planck equations have been solved only for some limited 
cases, and are not so familiar to engineers. More studies are necessary for naval architects 
to become familiar to the application of this method. 
8. Some efforts have been made to expand the model fitting method to the nonlin- 
ear process. The threshold autoregressive model, the exponential autoregressive model, 
and the nonlinear threshold model are examples of expanded models. Some of these mod- 
els look promising and some are under active development, but we will have to wait until 
they are more fully formulated to accumulate experience in application to practical 
problems. 
As was mentioned in the Foreword, the contents of this report were summarized at 
the time of this author’s oral presentation at DTRC in July 1985, reflecting the state of the 
art up to 1984, though the written version was completed in August 1987. After these 
dates, the state of the art has made considerable progress, especially in the field treated 
here in Part III, and this author finds the ‘review,’ and this conclusion, to be insufficient 
because of the recent works of several researchers. In order to update the report, this 
author added a Supplement of References 101 through 124, listing publications that have 
appeared since 1984, together with some other publications that were not referred to in 
the original manuscript. 
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