The Implementation Of The 20-Year Hindcast Wave Data In The Design And Operation Of Marine Structures
Authors: Chen H.H. , Hoffman D.H. 
Published: October 2008

Following the initial success in verifying the hindcast spectra obtained from the Spectral Ocean Wave Model (SOWM) at Fleet Numerical Weather Central (FNWC) as reported in our 1978 OTC paper, the present paper represents a continuation of the development effort aimed at the full utilization of the directional hindcast spectra as a long term wave data source in the design and operation of marine structures.

The paper summarizes the current status of the 20 year hindcast project and discusses in length the extensive statistical validation of the data. Comparisons with measured data from a variety of sources such as weather ships, buoys and fixed offshore towers are given. The applicability of the hindcast data as a primary source of long term wave statistics such as spectral families, persistance and exceedance probabilities and extrapolated design wave heights are illustrated through examples in assessing the short term responses and long term operability of various floating structures in specific offshore locations. An outline of a general procedure for calculating the long term wave induced response based on the vessel's mission profile is also given.

Due to the sheer volume and large geographical coverage of the data base, suggestions of some practical steps for implementing such vast data sources are given, including a complete data base management, processing procedures and standard outputs for the design and operation of marine systems.

INTRODUCTION

The design and evaluation of marine structures in terms of their structural integrity and their dynamic, behavior requires as input in addition to the response characteristics of the vessel, an adequate representation of the ocean environment at the intended area of operation. The need to obtain more reliable and comprehensive environmental data became increasingly urgent with the advent of offshore structures into more distant and hostile seas for oil exploration and as ships become subjected to more strict pollution control regulations as well as more strict operational margins due to economical and technological constraints. The search for sources of wave data in an adequate format and sufficiently large quantities as a basis for design and evaluation of marine structures has been of major concern to the maritime industry for some time.

Observed wave data has traditionally been regarded as the most common source of wave data in terms of its coverage, since wave observations along major shipping lanes have been recorded for over a century. Such data is least suited for design and analysis of marine structures due to the lack of spectral details and very often its biased nature. Measured wave spectra is naturally more suited for use in the design and evaluation of marine systems since it describes completely and realistically the distribution of wave energy both in the frequency domain and somewhere in the directional domain. Unfortunately, reliable wave measurements are costly and time consuming to obtain and as a result, are very scarce.