| Summary: | In minimal-time ship routing there are two main problems: 1. The computation of wavecharts from windcharts. 2. The determination of the least time track for a ship given these wavecharts and a polar velocity diagram. The second problem has been treated in the foregoing report (Bijlsma en Van Rietschote, 1972 I, II en III). In this report the first problem is dealt with. Hereby we assume that the problem of (forecasting and) converting pressure charts into wind charts has been solved. In practice this is a delicate problem depending mainly on the accuracy with which the pressure charts are given. The computation of waves from windfields goes back to the second part of the nineteenth century when some empirical formulas were derived in order to descrive the wave-wing relation (for a review of some of these relationships one is referred to Sverdrup, Johnson and Fleming (1942) and Defant (1961)). The first theoretical attempt however was made by Sverdrup and Munk (1947), when the outbreak of world war II made it necessary to have sea and swell forecasts at one's disposal. Although in later years applications of the developments in statistical analysis made the foundations on which their theory (revised by Brettschneider (1952)) was based, very disputable, it is nevertheless still in rather wide use. In this report (section 1) a brief outline is given of a wave forecasting method due to Pierson (1952). In his theory the forecast of ocean waves is considered as an application of the theory the stochastic processes. In this section, moreover, some elementary aspects of nonlinear wave interaction are given. Based on results of the last mentioned theory a computerprogram has been constructed for the computation of wave fields on the North Atlantic. Applications are given and compared with results of manual treatment (section 3). The computerprogram and a flow diagram of it are added.
|
|---|