Realistic and real-time simulation of mixed sea using base spectrum-based wave systems

Abstract

The sea has a very wide, irregular, and continuously changing surface and is usually a mixed sea composed of several wave systems. Each wave system is generated from different locations and conditions and has its own characteristics. The Fourier domain approach using sea wave spectra is an effective technique for realistic simulation of sea surfaces in real time, but the conventional Fourier domain approach can not independently simulate the characteristics of each wave system. Existing studies have also focused only on the visual realism of the sea surface and lack physical realism, which is one of the important factors in the training simulator. Particularly, it is a major limitation that the low frequency and high frequency wave components of the mixed sea can not be properly simulated respectively. In this study, I propose a realistic and real-time simulation method of the mixed sea using base spectrum-based wave systems for maritime simulators. The proposed method recognizes the importance of the visual and physical contributions of each wave system and faithfully reproduce all wave systems in the mixed sea. In order to simulate the mixed sea, I generate and combine realistic spectrum-based wave systems using adaptive spectral sampling of the separated spectrum of multi-peaked spectrum. The unique characteristics of each wave system can be set independently through spectral parameters, sampling number and range, wave direction and spread, and the shape factor of waves. The proposed method can also simulate the smooth transition between different sea states that each wave system can have, as well as between wind sea, swell, and mixed sea in real time. Since the conventional Fourier domain approach takes a long time to sample, it is very difficult to simulate sea state change in real time. The proposed base spectrum based sea simulation enables fast and smooth sea state change simulation even in the presence of multiple wave systems. The base spectrum always has a constant energy distribution regardless of sea state changes, and is sampled only once during simulation preparation. The components of the sampled base spectrum can be transformed into the spectral components of the target sea state in a very short time, and the target sea state can be reproduced without additional sampling. Through the experiments, it is verified that the proposed method effectively reflects sea wave spectra and the reproduced sea shows very similar statistical characteristics to the actual sea. Experimental results also show that the proposed method realistically simulates both high frequency wind sea and low frequency swells in the mixed sea and reproduces various sea states and changes between them very fast and smoothly.