Session: 12-01-02 Wave theories II
Paper Number: 125405
125405 - Optimization of Segmented Wave-Maker Control to Generate Spatially Uniform Regular Waves in a Wave Basin by Parallel Simulated Annealing Algorithm
In order to ensure the accuracy of seakeeping tests, it is essential that the spatial distribution of regular wave heights generated in a basin is uniform. However, it is known that the spatial distribution of wave heights of regular waves generated by a segmented wave maker based on the “snake motion” principle is not uniform. One of the major causes of such spatial non-uniformity is the cylindrical propagation property of the waves generated by the wave maker, which has a limited width relative to the basin.
A method has been proposed to determine the operating amplitude of each wave-maker segment that minimizes the mean squared error between the target wave height and the observed wave height at a reference grid arranged on the basin using the least-squares method. However, when the authors preliminarily optimized the wave-maker amplitude using the above method, the authors obtained a physically unreasonable solution with a large difference in amplitude between adjacent wave makers. In an actual basin, it is not possible to command such an operating amplitude to wave makers because of the mechanical limitations.
Therefore, in this study, the authors propose a method to find a solution with a small difference in amplitude between adjacent wave makers. Specifically, the authors proposed that the amplitude of each wave-maker segment according to the snake motion principle multiplied by amplification coefficients that align on a Bezier curve. Furthermore, the authors set the mean squared error of wave heights as the objective function and the control points of the Bezier curve as variables, and aimed to find the optimal variables that minimize the objective function using “Temperature Parallel Simulated Annealing (TPSA)”. Generally in the iteration of SA, variables that worsen the objective function could be accepted with certain probabilities. Ordinary SA requires “temperature scheduling” to determine how to reduce the probability of accepting worse variables with the progress of its iterations, and temperature scheduling significantly affects the optimization performance. Therefore, in order to eliminate such an effect, the authors adopted TPSA, which can automate temperature scheduling.
The authors validate the proposed method numerically by comparing the spatial distribution of wave heights based on the snake motion principle with the optimized ones for several wave conditions regarding the actual sea model basin (80 m long, 40 m wide, and 4.5 m deep with 382 flap type wave-makers arranged all around the perimeter) at the National Maritime Research Institute.
Presenting Author: Daichi Ota National Maritime Research Institute, National Institute of Maritime, Port and Aviation Technology
Presenting Author Biography: Daichi Ota is a researcher of National Maritime Research Institute in Japan. His work focuses on the experiments and numerical calculations of hull motion in waves related to the second generation intact stability criteria. In particular, he is interested in the development of methods to generate the expected wave field in a basin.
Authors:
Daichi Ota National Maritime Research Institute, National Institute of Maritime, Port and Aviation TechnologyHidetaka Houtani The University of Tokyo
Optimization of Segmented Wave-Maker Control to Generate Spatially Uniform Regular Waves in a Wave Basin by Parallel Simulated Annealing Algorithm
Submission Type
Technical Paper Publication