Chi-Chao Tung

A unified two-parameter wave spectral model for a general sea state

Based on theoretical analysis and laboratory data, we proposed a unified two-parameter wave spectral model as

Interactions between Steady Won-Uniform Currents and Gravity Waves with Applications for Current Measurements

\phi(n) = \frac{\beta g^2}{n^m n_0^{5-m}} {\rm exp} \left\{-\frac{m}{4}\left(\frac{n_0}{n}\right)^4\right\}

The local properties of ocean surface waves by the phase-time method

with β and m as functions of the internal parameter, the significant slope η of the wave field which is defined as

Statistical Characteristics of Breaking Waves

\sect = \frac{(\overline{\zeta^2})^{\frac{}1{2}}}{\lambda_0},

Peak and trough distributions of nonlinear waves

where

An Analytical Model for Oceanic Whitecap Coverage

\overline{\zeta^2}

The influence of the directional energy distribution on the nonlinear dispersion relation in a random gravity wave field

is the mean squared surface elevation, and λ 0 , n 0 are the wavelength and frequency of the waves at the spectral peak. This spectral model is independent of local wind. Because the spectral model depends only on internal parameters, it contains information about fluid-dynamical processes. For example, it maintains a variable bandwidth as a function of the significant slope which measures the nonlinearity of the wave field. And it also contains the exact total energy of the true spectrum. Comparisons of this spectral model with the JONSWAP model and field data show excellent agreements. Thus we established an alternative approach for spectral models. Future research efforts should concentrate on relating the internal parameters to the external environmental variables.

Reflection of oblique waves by currents: analytical solutions and their application to numerical computations

Abstract Interactions between steady non-uniform currents and gravity waves are generalized to include the case of a random gravity wave field. The Kitaigorodskii-Pierson-Moskowitz frequency spectrum is used as the basic spectral form for zero current condition. Modified spectral functions in both wavenumber and frequency spaces under the influence of current are found by using energy conservation and kinematic wave conservation laws. The relative importance of the current-wave interaction was measured by the nondimensional parameter U/C0, with U as the current speed and C0 the phase speed of a wave under no current. As a result of the current-wave interaction, the magnitude and the location of the energy peak in the spectrum is altered. Since the phase speed of gravity waves is a monotonically decreasing function of wavenumber and frequency, the influence of current will be predominant at the higher wavenumber range. Furthermore, the contribution from the higher wavenumber range dominates the surface slo...

Application of hermite polynomial to wave and wave force statistics

Traditionally, investigation of statistical properties of ocean waves has been limited largely to global quantities related to elevation and amplitude such as the power spectral and various probability density functions. Although these properties give valuable information about the wave field, the results cannot be related directly to any portion of the time data from which it was derived. We present a new approach using phase information to view and study the properties of frequency modulation, wave group structures, and wave breaking. We apply the method here to ocean wave time series data and identify a new type of wave group (containing the large “rogue” waves), but the method also has the capability of broad applications in the analysis of time series data in general.

A non-Gaussian statistical model for surface elevation of nonlinear random wave fields

The modification of the shape of the wave spectrum in the high-frequency range and the amount of energy loss, due to wave breaking are examined. The original waves are assumed to be Gaussian, stationary, and of finite bandwidth. Breaking is assumed to occur when the vertical acceleration at any point on the surface reaches g/2. Based on the wave breaking model, an approximate but accurate spectrum of breaking waves and an exact expression of the amount of energy loss due to wave breaking are derived. It is shown that the spectrum which corresponds to minimum rate of energy loss has an upper limit proportional to in the high-frequency range.