Dynamic Interaction of Parallel Moving Ships in Close Proximity

Nowadays,there are many studies conducted in the field of marine hydrodynamics which focus on two vessels traveling and floating in sufficiently close proximity to experience significant interactions.The hydrodynamic behavior of parallel moving ships in waves is an interesting and important topic of late.A numerical investigation has been carried out for the prediction of wave exciting forces and motion responses of parallel moving ships in regular waves.The numerical solution was based on 3D distribution technique and using the linear wave theory to determine the exciting forces and ship＇s motion.The speed effects have been considered in the Green function for more realistic results.The numerical computations of wave exciting forces and motion responses were carried out for a Mariner and Series 60 for the purpose of discovering different Froude numbers and different separation distances in head sea conditions.Based on the numerical computations,it was revealed that the sway,roll and yaw have a significant effect due to hydrodynamic interaction.

Wave Trapping by Dual Porous Barriers Near a Wall in the Presence of Bottom Undulation

Trapping of oblique surface gravity waves by dual porous barriers near a wall is studied in the presence of step type varying bottom bed that is connected on both sides by water of uniform depths. The porous barriers are assumed to be fixed at a certain distance in front of a vertical rigid wall. Using linear water wave theory and Darcy's law for flow past porous structure, the physical problem is converted into a boundary value problem. Using eigenfunction expansion in the uniform bottom bed region and modified mild-slope equation in the varying bottom bed region, the mathematical problem is handled for solution. Moreover, certain jump conditions are used to account for mass conservation at slope discontinuities in the bottom bed profile. To understand the effect of dual porous barriers in creating tranquility zone and minimum load on the sea wall, reflection coefficient, wave forces acting on the barrier and the wall, and surface wave elevation are computed and analyzed for different values of depth ratio, porous-effect parameter, incident wave angle, gap between the barriers and wall and slope length of undulated bottom. The study reveals that with moderate porosity and suitable gap between barriers and sea wall, using dual barriers an effective wave trapping system can be developed which will exert less wave force on the barriers and the rigid wall. The proposed wave trapping system is likely to be of immense help for protecting various facilities/infrastructures in coastal environment.

Numerical Simulation of Water Wave Propagation and Transformation

A numerical approach was performed to predict the propagation and transformation of nonlinear water waves. A numerical wave flume was developed based on the non-periodic high-order spectral (HOS) method. The flume was applied to analyze the effect of wave steepness and wavelength on the propagation of nonlinear waves. The results show that for waves of low steepness, the wave profile and the wave energy spectrum are stable, and that the propagation can be predicted by the linear wave theory. For waves of moderate steepness and steep waves, the effects associated with the interactions between waves in a wave group become significant and a train of initially sinusoidal waves may drastically change its form within a short distance from its original position.

Estimation of Wave Forces on Large Compliant Platforms

Compliant offshore structures such as spars,tension leg platforms(TLPs) and semi-submersibles have been dramatically improved in recent years due to their capability for deep water operation. Waves are the most important environmental phenomenon affecting these offshore structures. Estimation of wave forces is vital in offshore structure design. For large compliant offshore platforms,Morrison's equation is not valid anymore and usually diffraction theory is used. In this research,by using the finite difference method,a detailed analysis of the first-order diffraction of monochromatic waves on a large cylinder as a structural element is performed to solve the radiation and diffraction potentials. The results showed that the developed model is a reliable tool to estimate the wave forces and hydrodynamic coefficients on large structure elements when wave diffraction and radiation are considered.

Wave Drift Forces on Two Floating Bodies Arranged Side by Side

An innovative hydrodynamic theory and numerical model were developed to help improve the efficiency, accuracy, and convergence of the numerical prediction of wave drift forces on two side-by-side deepwater floating bodies. The wave drift forces were expressed by the double integration of source strength and the corresponding Green function on the body surface, which is consistent with the far field formula based on momentum conservation and sharing the advantage of near field calculations providing the drift force on each body. Numerical results were validated through comparing the general far field model and pressure integral model, as well as the middle field model developed usin^z the software HydroStar.

Theoretical and experimental investigation on nonlinear interaction among wave groups

Wave group is important in ocean wave theory and applications. In the past, nonlinear interaction among wave groups has been studied on the basis of the nonlinear Sehrrdinger equation. Using this theoretical approach, we found that the nonlinear interaction among wave groups causes asymmetry in the shape of the wave envelope （steeper in the front of the curve of the envelope）. An important consequence of this asymmetry is that the highest wave in a wave group appears one individual wave length ahead of the center of the wave group. Further results show that the degree of envelope asymmetry increases with increasing spectral width and the wave steepness. This theoretical analysis has been supplemented by a systematic experimental study of wind waves. Laboratory and some open sea wave data were analyzed. The results show that the shape of the wind wave envelope of wind waves has the same asymmetry predicted by the theoretical approach. The observed degree of deformation of the envelope also increases with increasing spectral width and the wave steepness as predicted by theory. These conclusions have important ramifications for practical applications of ocean wave theory.

A unified theory for elastic wave propagation through porous media containing cracks-An extension of Biot's poroelastic wave theory

Rocks in earth＇s crust usually contain both pores and cracks. This phenomenon significantly affects the propagation of elastic waves in earth. This study describes a unified elastic wave theory for porous rock media containing cracks. The new theory extends the classic Biot＇s poroelastic wave theory to include the effects of cracks. The effect of cracks on rock＇s elastic prop- erty is introduced using a crack-dependent dry bulk modulus. Another important frequency-dependent effect is the ＂squirt flow＂ phenomenon in the cracked porous rock. The analytical results of the new theory demonstrate not only reduction of elas- tic moduli due to cracks but also significant elastic wave attenuation and dispersion due to squirt flow. The theory shows that the effects of cracks are controlled by two most important parameters of a cracked solid： crack density and aspect ratio. An appealing feature of the new theory is its maintenance of the main characteristics of Biot＇s theory, predicting the characteristics of Blot＇s slow wave and the effects of permeability on elastic wave propagation. As an application example, the theory cor- rectly simulates the change of elastic wave velocity with gas saturation in a field data set. Compared to Biot theory, the new theory has a broader application scope in the measurement of rock properties of earth＇s shallow crust using seismic/acoustic waves.

Improvements to the statistical theoretical model for wave breaking based on the ratio of breaking wave kinetic and potential energy

An improvement was proposed for the statistical theory of breaking erttrainment depth and surface whitecap coverage of real sea waves in this study. The ratio of the kinetic and potential energy was estimated on a theoretical level, and optimal constants were determined to improve the statistical theory model for wave breaking. We also performed a sensitivity test to the model constants. A comparison between the model and in situ observations indicated that the level of agreement was better than has been achieved in previous studies.

A discussion on the double wave theory and its applications to description of radiation atoms

The double wave theory (DWT), sometimes called the“non_statistical quantum mechanics” by its proposer, describes the state of each single particle in an ensemble with two wave functions which have a parameter corresponding to the particle. However the basic postulates of the DWT show that this theory can hardly describe any quantum rules of the microscopic world. In the double wave descriptions, the wave feature of the behavior of microscopic particles and the discontinuity characteristic of energy almost disappear. The discussions on several problems of the radiation atoms made by the DWT's proposer on the basis of this theory are either mathematically incorrect or inconsistent with experiments and the usual theory.

Asymptotic Calculation of Wave Period Statistics in Non-Gaussian Mixed Sea

This article concerns the calculation of the wave period probability densities in non-Gaussiau mixed sea states. The calculations are carried out by incorporating a second order nonlinear wave model into an asymptotic analysis method which is a novel approach to the calculation of wave period probability densities. Since all of the calculations are performed in the probability domain, the approach avoids long time-domain sinmlations. The accuracy and efficiency of the asymptotic analysis method for calculating the wave period probability densities are validated by comparing the results predicted using the method with those predicted by using the Monte-Carlo simulation （MCS） method.

An acoustic-wave theory for casing bond evaluation using viscoelastic slip boundary modeling

Slip boundary condition is commonly utilized to model elastic wave propagation through layered earth media. The same approach is used here to characterize acoustic wave propagation along a cased borehole with various cement bond conditions. By modeling the cement layer between casing and formation as a viscoelastic slip interface with complex coupling rigidity parameters, one can not only reduce the complexity in the classical elastic wave modeling of the problem, but also efficiently model various complicated wave phenomena that are difficult for the existing modeling. More specifically, the new theory can well describe the effect of the cement bond condition change and the location of the change(i.e., whether it is in the first interface between casing and cement, or the second interface between cement and formation) on the acoustic waves,demonstrating the good modeling capability and predicting power. Application of the theory to field data shows that the theory can correctly model the acoustic wave characteristics and interpret the cement bond condition, thus providing a useful fundament theory for casing bond evaluation using acoustic logging.