Prediction Of Maximum Wave Height From Historical Data
Authors: Durning Paul J. 
Published: October 2008

The designer of offshore facilities usually is faced with the problem of-using historical weather data gathered during a few years to make an estimate of the conditions that will exist during the future life of an offshore facility. Usually, he realizes that he cannot design equipment to withstand the worst possible conditions, but that he must design for conditions that have a small probability of occurrence. This paper describes a method that simulates the occurrence of storms and their intensities. The statistical properties of ocean waves, the statistical properties of storm occurrence, and historical data are used to determine an estimate of a total population of storms. Then a Monte Carlo method is used to simulate a large number of storms. The distributions of maximum waves in these storms can be used to develop design specifications. The method is explained by applying it to an example in a form useful to structural engineers.

INTRODUCTION

Engineers for most construction projects face the problem of selection of proper design criteria. The task of selecting realistic criteria can be exceedingly difficult when the design involves facilities for which weather (wind and waves) generates the primary design loads. Offshore oil facilities certainly fall within this category of structures, and the selection ofrealistic design criteria for these structures is exceedingly difficult. First, sea conditions are highly variable and seemingly unpredictable. Second, little basic data are available in many locations. This paper describes a statistical approach for selecting design conditions in which the variability of the sea is accounted for and its behavior can be predicted. The method permits us to make maximum use of the small amount of data that may be available. The method could be used for any kind of weather phenomena that can be described in terms of probability functions. This paper speaks in terms of sea waves for clarity and conciseness.

The method described in the paper takes account of the following things:the height of significant waves during a storm can be assumed to follow a Rayleigh distribution;the time duration of storms at a particular location can be described by a different statistical distribution;the wave frequency, or period, for significant waves of a specified height can be described by another statistical distribution; andfinally, that the height of the maximum waves for a specified significant wave height caI1 be described by a statistical distribution.

Various previous authors, notably, Longget Higgins2, Neumann and Pierson5, and Ippen6 as editor, discuss several statistical distributions that can be used to describe these individual parts of a storm. But the problem the offshore designer faces involves the entire storm. He needs not a relationship between significant wave height and maximum wave-height, not a distribution of significant wave heights, but instead he needs to know the probability of occurrence of a specified maximum wave during a specified lifetime for an offshore structure. This occurrence involves a combination of all of these probabilities.