Hindcasting Hurricane Waves in the Gulf of Mexico

An estimate of wave heights is needed for risk and venture analysis, for platform design, and for operational planning. Very little reliable data on hurricane waves have been available for a number of years. The present hindcast system uses a moving, two-dimensional wind field to generates and propagate waves to a location of interest. The propagate waves to a location of interest. The wind-wave model is based on work reported in the literature by Wilson. Wave Program I uses a synoptic wind field based on measurements or observations. Wave Program II generates its own wind field based on the track, the time history of the radius to maximum Winds, and the barometric pressure of the storm. Wave Program III also pressure of the storm. Wave Program III also generates its own wind fields, but the storm is moved along a predetermined path. The results of all three hindcast methods have been compared with data gathered from Hurricane Carla. Other hurricanes have also been studied and each of the programs gives comparable results. programs gives comparable results Introduction The most critical environmental factor in deepwater platform design is the selection of wave heights to which the platform will be subjected. Regardless of the design theory, wave loading contributes a major portion of the environmental force on a deep-water platform. To date there has been little sound historical evidence of the magnitude of wave heights that could occur in the Gulf of Mexico. To overcome this problem the offshore oil industry has sought an answer by two related methods. The first method consists of several measuring programs to gather both wave force and wave height information. Since reliable measuring techniques have existed for only a short time, the second method consists of developing techniques to predict historical waves that probably occurred in the Gulf of Mexico. The purpose of this paper is to document Shell's efforts in hindcasting paper is to document Shell's efforts in hindcasting waves for hurricanes that have passed through the Gulf since 1900. In order to hindcast waves, it was necessary to find a mathematical simulation model that would generate waves from a moving wind field. Such wind fields may be taken from synoptic charts or developed from empirical equations based on hurricane data such as radius to maximum winds, central pressure, and forward speed. WAVES FROM A MOVING WIND FIELDTHE BASIC WILSON MODEL Wilson, a consultant in the field of oceanography, has developed a mathematical model that would generate and propagate waves based on a moving wind field. We shall discuss the basic equations for this technique, but shall not go into detail concerning how the equations were developed. INITIATION OF THE WAVE The first wave height generated by a moving wind field can be calculated from Eq. 1 below (1) H1 = 0 .0636U In the above equation Ui is the wind vector in the direction of propagation at time zero and location (x1) where the wave is to start. The distance x1 over which the wave will move is described in Eq. 2. (2) = 0 .761 x1 is the distance the wave travels in nautical miles before it is to be modified by another value of wind velocity. The celerity is defined by Eq. 3. (3) C1 = 2 .498 Finally, the period and wave length of this initial wave are described below. (4) T1 = C1/3 (5)1 2L1 = 5 .12T SPEJ P. 321