Real Time Estimation of Ship Motions in Short Crested Seas

Abstract

The presented research is part of the development of an onboard wave and motion estimation system that aims to predict wave elevation and vessel motions some 60–120 s ahead, using wave elevation measurements by means of X-band radar. In order to validate the prediction model, scale experiments have been carried out in short crested waves for 3 different sea states with varying directional spreading, during which wave elevation and vessel motions were measured. To compare predicted and measured wave elevation, three wave probes were used at different distances from a large set of wave probes that was used as input to the model. At one of the prediction locations, also tests were performed to measure vessel motions. This setup allowed validation of a method that was used for initializing the linear wave prediction and ship motion prediction model. Various observations and conclusions are presented concerning optimal combinations of prediction model parameters, probe set-up and sea state.

Wave energy converter control by wave prediction and dynamic programming

“…This requirement has been a bottleneck for the development of suitable optimal control strategies for WECs. However, the developments in deterministic sea wave modeling techniques have made real time sea wave prediction for a short time period realizable, [12e19, 26,28]. A key finding from this work is that the prediction horizons required are considerably smaller than those resulting from the previous studies [43e45].…”

“…In this paper, the constrained optimal control problem is solved using fundamental principles from optimal control theory [48e50], see Section 3, and real time deterministic sea wave prediction [12e19, 26,28]. We demonstrate that a nearly optimal control is of bangebang type, meaning that the control input f is always at one edge of the allowed range, see Subsection 3.2.…”

“…It will be shown that (as [9e11] demonstrated in the 1970s) methods for achieving the maximum power output are inevitably non-causal and require prediction of the shape of the incident waves. The recent development of deterministic sea wave prediction (DSWP) as a scientific discipline [12e28], particularly real time DSWP [12e19, 26,28] now makes such an approach realistic. For a variety of reasons high accuracy real time DSWP is very demanding.…”

On dispersion of directional surface gravity waves

“…The 10×10 array was fixed to a carriage which could be positioned at any location in the basin. The wave fields were repeatable, see Naaijen et al (2009). Spatio-temporal measurements were achieved by positioning the carriage at different locations in repetitions of the same wave field.…”

Prediction for Irregular Ocean Wave and Floating Body Motion by Regularization: Part 1. Irregular Wave Prediction

“…In addition, due to the dispersive characteristic of the ocean wave -phase velocity is directly proportional to wave length -the measured wave elevation does not accurately reach the floating body. It is for this reason that an algorithm for ocean wave prediction is needed, and there are several similar studies (Naaijen and Hujismans [7], Clauss et al [8], Naaijen et al [9], Wu [10], Blondel [11]). While the above theses share a commonality of calculating the wave phase to predict ship motion, Clauss et al [8] and Kosleck [12] calculate the phases of the real and imaginary parts using the FFT on the wave elevation map, and Naaijen and Hujismans [13] use singular value decomposition to calculate the phases of waves.…”