ON THE USE OF A WIND-WAVE MODEL IN THE PREDICTION OF OPERATIONAL PERFORMANCE OF MARINE STRUCTURES

Article type: Research Article

Authors: Claessens, E.J. | Pinkster, H.J.M. | Dallinga, R.P.

Affiliations: Current affiliation: RIZA (Institute for Inland Water Management and Waste Water Treatment), The Netherlands | Current affiliation: PTS Software, The Netherlands | Maritime Research Institute Netherlands, The Netherlands

Abstract: The quantification of the performance of ships and marine structures is multidisciplinary in character. It requires input from the areas of ship hydrodynamics (for the resistance, the inherent motion characteristics and mean environmental forces), the area of ship-operations (for an operational scenario that describes the master's reactions on the anticipated and encountered behaviour with related criteria for tolerable behaviour) and oceanography (for a description of the interacting wind and waves). The most complete description of the operational performance up to now is based on a statistical approach, using long-term wind and wave statistics for the operational area or route. In this approach it is not possible to account for spatial variations of the wave characteristics along coastal routes, the coherence of wind speed, wind direction and their persistence on one hand and the characteristics of the generated waves (height, period, spectral characteristics) on the other. Regarding the predicted performance statistical methods have difficulties in accounting for complex operational scenarios and the effects of wind and wave persistence on the performance at the mission level. A method that is currently under development is based on time domain "scenario simulations". The wind and wave input for these simulations (several years of hourly characteristics of wind and waves) is obtained through a hindcast for the operational area. This hindcast accounts for the natural evolution of the spectral shape (thus accounting for separate wind-driven and swell-wave components), the directional spread and coastal effects (such as current and sheltering) on wave growth and decay. The performance is established by evaluating the progress on a mission in time; simulating a large number of missions yields the performance statistics at a mission level. The present paper describes the techniques underlying this method. The paper focuses on the wave input for the scenario simulations. Based on results of sample simulations it is concluded that wind-wave models provide a practical basis for a performance analysis. It is also shown that the variable spectral shape as accounted for in these simulations can have a considerable influence on the performance prediction.

Keywords: hindcasts, scenario simulations, seakeeping, ship behaviour, wind-wave climate, wind-wave model, validation, operational performance of marine structures

Journal: International Shipbuilding Progress, vol. 52, no. 4, pp. 297-323, 2005