Spectral analysis of ship waves in deep water from accurate measurements of the free surface elevation by optical methods

Abstract

This paper details the spectral analysis of the waves generated from an experimental study of the water surface elevation around a ship model in a towing tank. The wave pattern is measured with accurate optical methods in deep-water conditions for various Froude numbers. These optical methods allow the entire wave field around the model with a high spatial resolution to be obtained. The quality of the measured surface elevation around the ship model enables us to perform a spectral analysis of the waves generated by a ship. To validate this approach, the experimental spectrum is compared to the fundamental theoretical dispersion relation of the waves generated by a moving perturbation in calm deep water. In a second step, a fundamental decomposition of the wave system is achieved, from which the contribution of the near field, the local flow disturbance, and the contribution of the far field that corresponds to the Kelvin wake system are computed. In addition, the experimental extraction of the dispersion relation provides an estimate of the angle of the cone of the Kelvin wake in the spectral space.

Wake Features of Moving Submerged Bodies and Motion State Inversion of Submarines

“…The image brightness corresponds to the power spectral intensity. The far-field Kelvin wake is seen as a distinct ''X'' component in the power spectrum [29], [30]:…”

Virtual Replica of a Towing Tank Experiment to Determine the Kelvin Half-Angle of a Ship in Restricted Water

“…In this section, the method devised by Caplier et al [20] and Gomit et al [22] is briefly examined. This method has previously been used to determine a ship's speed via satellite imagery [46,47].…”

“…Therefore, the validation of numerical ship-generated waves is of high importance. In this respect, the work Caplier et al [20], Fourdrinoy et al [21], and Gomit et al [22] is important to mention. The authors of the aforementioned references systematically developed and implemented a technique to capture and analyse ship-generated waves from a model experiment.…”

Large-scale free surface measurement for the analysis of ship waves in a towing tank

“…In the last part of the paper, the large-scale results are compared with measurements taken by Gomit et al (2014) in a smaller towing tank around the same ship model at scale 1/77.5. The free surface at the two scales is compared.…”

“…In the case of wave measurements in towing tanks, the surface is smoother and artificial patterns need to be created to identify the free surface. For application in towing tanks, two techniques based on the correlation of images recorded with stereoscopic systems are used by Gomit et al (2014). The first technique was based on the use of particles floating on the surface , and the second was based on volumic seeding using neutrally buoyant PIV particles (Gomit et al 2013).…”