Applications of improved 2-D numerical wave tanks in wave breaking

Song and Banner (2002, henceforth referred to as SB02) used a numerical wave tank (developed by Drimer and Agnon, and further refined by Segre, henceforth referred to as DAS) to study the wave breaking in the deep water, and proposed a dimensionless breaking threshold that based on the behaviour of the wave energy modulation and focusing during the evolution of the wave group. In this paper, two modified DAS models are used to further test the SB02's results, the first one (referred to MDAS1) corrected many integral calculation errors appeared in the DAS code, and the second one (referred to MDAS2) replaced the linear boundary element approximation of DAS into the cubic element on the free surface. Researches show that the results of MDAS1 are the same with those of DAS for the simulations of deep water wave breaking, but, the different values of the wavemaker amplitude, the breaking time and the maximum local average energy growth rate delta(max) for the marginal breaking cases are founded by MDAS2 and MDAS1. However, MDAS2 still satisfies the SB02' s breaking threshold. Furthermore, MDAS1 is utilized to study the marginal breaking case in the intermediate water depth when wave passes over a submerged slope, where the slope is given by 1 : 500, 1 : 300, 1 : 150 or 1 : 100. It is found that the maximum local energy density U increases significantly if the slope becomes steeper, and the delta(max) decreases weakly and increases intensively for the marginal recurrence case and marginal breaking case respectively. SB02's breaking threshold is still valid for the wave passing over a submerged slope gentler than 1 : 100 in the intermediate water depth.

阿尔文涨落与地球磁层亚暴

本文讨论了一种地球磁层的亚暴机制。当行星际磁场有大的南向分量时,磁层的位形可由基本闭式转变为开式。磁鞘中的阿尔文波可以携带超过10~(18)尔格/秒的能流传入磁层尾部,并将能量耗散于等离子体片中。等离子体片中的粒子被加热和加速后,注入近地空间,产生环电流和极区亚暴。计算了剪切流场中阿尔文波的传播过程,以及磁层中阿尔文波的耗散。将本文的结算与[4]中的结果合在一起,可以说明当行星际磁场转向南时,容易发生地球磁层亚暴,但这两者并非一一对应的关系,行星际磁场没有南向分量时也可以发生地球磁层亚暴。

A New Model for Sediment Transport

The problem of predicting sediment transportation by water waves is treated analytically with the rate of wave energy dissipation or wave damping. With resorting to the theory of shallow water waves and the basis of Yamamoto’s Coulomb-damped poroelastic model, the Boussinesq-type equation has been derived over a variation depth bed. For convenience Cnoidal wave is just discussed, The Cnoidal wave with complex wave length and wave velocity, which are as a function of wave frequency, water depth, permeability, Poisson’s ratio and complex elastic moduli of bed soil, is applied to analyse the rate of sediment transportation. Considering the sediment transportation depended on the shear stress near-bed or the horizontal velocity, the conclusion of Yamamoto’s experiment in clay bed has been extended to general situation. It could be figured out that the model should provide a method to avoid the undistinguishable factors during sediment transport processes and relate mass transport with the sediment peculiarities.

Effects of volumetric allocation on heave response of semisubmersible in deep sea

The configuration of semisubmersibles consisting of pontoons and columns and their corresponding heave motion response in incident progressive waves are examined. The purpose of the present study is to provide a theoretical approach to estimating the effects of volumetric allocation on natural period and response amplitude operator (RAO) in heave motion. We conclude that the amplitude of heave motion response can be considerably suppressed by appropriately adjusting volumetric allocation so that the natural heave period keeps away from the range of wave energy. The theoretical formulae are found in good agreement with the corresponding computational results by WAMIT.

Short-pulse laser absorption in very steep plasma density gradients

An analytical fluid model for resonance absorption during the oblique incidence by femtosecond laser pulses on a small-scale-length density plasma [k(0)L is an element of(0.1,10)] is proposed. The physics of resonance absorption is analyzed more clearly as we separate the electric field into an electromagnetic part and an electrostatic part. It is found that the characteristics of the physical quantities (fractional absorption, optimum angle, etc.) in a small-scale-length plasma are quite different from the predictions of classical theory. Absorption processes are generally dependent on the density scale length. For shorter scale length or higher laser intensity, vacuum heating tends to be dominant. It is shown that the electrons being pulled out and then returned to the plasma at the interface layer by the wave field can lead to a phenomenon like wave breaking. This can lead to heating of the plasma at the expanse of the wave energy. It is found that the optimum angle is independent of the laser intensity while the absorption rate increases with the laser intensity, and the absorption rate can reach as high as 25%. (c) 2006 American Institute of Physics.

Vacuum heating in the interaction of ultrashort, relativistically strong laser pulses with solid targets

An analytical fluid model for vacuum heating during the oblique incidence by an ultrashort ultraintense p-polarized laser on a solid-density plasma is proposed. The steepening of an originally smooth electron density profile as the electrons are pushed inward by the laser is included self-consistently. It is shown that the electrons being pulled out and then returned to the plasma at the interface layer by the wave field can lead to a phenomenon like wave breaking since the front part of the returning electrons always move slower than the trailing part. This can lead to heating of the plasma at the expense of the wave energy. An estimate for the efficiency of laser energy absorption by the vacuum heating is given. It is also found that for the incident laser intensity parameter, a(L)> 0.5, the absorption rate peaks at an incident angle 45 degrees-52 degrees and it reaches a maximum of 30% at a(L)approximate to 1.5.

Electronic states of InAs/GaAs tyre-shape quantum ring

In the framework of the effective mass theory, this paper calculates the electron energy levels of an InAs/GaAs tyre-shape quantum ring (TSQR) by using the plane wave basis. The results show that the electron energy levels are sensitively dependent on the TSQR's section thickness d, and insensitively dependent on TSQR's section inner radius R-1 and TSQR's inner radius R-2. The model and results provide useful information for the design and fabrication of InAs/GaAs TSQRs.

中国海洋能专利研究

专利是除论文外的又一非常重要的科技成果。目前专利申请工作并未得到足够重视，并且文献中对专利技术成果的反映甚少。文章对中国国家知识产权局（SIPO）专利数据库中海洋能专利授权情况进行了分类统计。介绍了波浪能、潮汐能、温差能的最新专利，并指出了该领域专利申请的热点和空白领域。最后根据统计数据从专利的角度分析了中国海洋能研究的进展和前景。

The effects of random surface waves on the steady Ekman current solutions

The response of near-surface current profiles to wind and random surface waves are studied based on the approach of Jenkins [1989. The use of a wave prediction model for driving a near surface current model. Dtsch. Hydrogr. Z. 42,134-149] and Tang et al. [2007. Observation and modeling of surface currents on the Grand Banks: a study of the wave effects on surface currents. J. Geophys. Res. 112, C10025, doi:10.1029/2006JC004028]. Analytic steady solutions are presented for wave-modified Ekman equations resulting from Stokes drift, wind input and wave dissipation for a depth-independent constant eddy viscosity coefficient and one that varies linearly with depth. The parameters involved in the solutions can be determined by the two-dimensional wavenumber spectrum of ocean waves, wind speed, the Coriolis parameter and the densities of air and water, and the solutions reduce to those of Lewis and Belcher [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans. 37, 313-351] when only the effects of Stokes drift are included. As illustrative examples, for a fully developed wind-generated sea with different wind speeds, wave-modified current profiles are calculated and compared with the classical Ekman theory and Lewis and Belcher's [2004. Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift. Dyn. Atmos. Oceans 37, 313-351] modification by using the Donelan and Pierson [1987. Radar scattering and equilibrium ranges in wind-generated waves with application to scatterometry. J. Geophys. Res. 92, 4971-5029] wavenumber spectrum, the WAM wave model formulation for wind input energy to waves, and wave energy dissipation converted to currents. Illustrative examples for a fully developed sea and the comparisons between observations and the theoretical predictions demonstrate that the effects of the random surface waves on the classical Ekman current are important, as they change qualitatively the nature of the Ekman layer. But the effects of the wind input and wave dissipation on surface current are small, relative to the impact of the Stokes drift. (C) 2008 Elsevier Ltd. All rights reserved.

基于多种群遗传算法的波能装置的优化设计及分析

作为可再生能源,波浪能的吸收和利用一直是国内外热点研究内容之一。本文提出一种新的基于惯性摆结构的波浪能吸收转换方法,对这种结构在波浪力作用下的频域响应进行了分析,建立了其最优化能量获取模型,提出采用多种群遗传算法对其结构进行优化设计,并针对系统所受波浪力(矩)随载体半径改变而改变,且求取困难的问题,采用最小二乘法对波浪力(矩)与载体半径变化的关系进行了拟和。通过优化结果找出影响结构获取波浪能量的因素,仿真结果表明了方法的先进性,为进一步的应用研究和频域波能获取研究奠定了基础。

基于惯性摆的波能系统研究

提出了一种基于惯性摆结构的波浪能吸收转换方法,并对采用此结构构成的水中载体所受到的波浪力及水动力进行了理论分析,建立了实验模型,对其进行了运动学、动力学仿真实验,仿真结果证明了方案的可行性。

基于惯性摆的波浪能获取机理与方法研究

随着陆地战略资源日益短缺以及经济的全球化进展，海洋资源的开发利用已成为沿海各国的重要发展战略之一，也成为地球资源保护与开发的关注热点。 海洋资源开发和利用能力对于一个国家的科研、经济实力具有重大的影响及意义。由于海洋资源开发利用和地球环境监测的迫切需求，促进了水下机器人、水下潜器等无人水中移动载体技术的发展。能源供给技术是水中移动载体系统的关键技术，能源技术对海洋人工系统的生存、作业、自主能力提升具有重要意义。目前海洋移动人工系统主要依赖自携带能源形式，针对水中移动载体的能量自补给技术研究还处于探索阶段。 地球表面有70%的面积被海水所覆盖，海水中蕴藏巨大的波浪能。具有环保、再生特色的波浪能开发利用技术长期以来一直受到国内外科研人员的关注。随着海洋战略地位的提升，海洋自主人工系统已成为海洋科学技术的重点发展内容。利用波浪能为海洋人工移动载体进行能量补给，是对于海洋波浪能利用的一种新的方法和思路。这对于提高海洋人工系统的自主生存、续航能力，提高人类在海洋资源与环境的探测、开发利用等方面的技术能力无疑具有重大意义。因而研究面向海洋人工系统的波浪能利用机理和系统实现技术无疑具有广泛的应用前景。 本文针对海洋人工移动载体自主能量获取利用这一重大科学技术需求，依托中国科学院基地创新基金项目“基于惯性摆原理的无源系统研究”，探索基于惯性摆机理的移动载体波浪能自主获取的机理，研究相关设计理论和技术方法。 由于目前尚无基于惯性摆机理的海洋移动载体能量自补给技术的相关研究成果。因而本论文的研究主要从理论分析和实验方法两个方面开展。重点分析了惯性摆的外激励能量获取机理，基于惯性摆的波浪机械能获取理论的可行性；开展了惯性摆载体的水动力学建模，原理样机的仿真，频域下的能量建模和优化，非线性波浪条件模拟，惯性摆载体的能量获取结构优化等研究工作。主要研究工作如下： 1.针对基于惯性摆机理的移动载体随机波能获取研究方案，分析了相关单摆及惯性摆机械能量转换机理，采用动量及动量矩定理，构建了惯性摆载体的六自由度运动学和动力学方程。 2．进行了相关水动力系数获取方法研究，获得了水动力系数数学描述。同时，采用虚拟样机方法进行惯性摆载体能量获取的研究，证明了基于惯性摆的波能自主获取方法的可行性及有效性。 3.针对虚拟样机方法建模的复杂性及容易产生错误等问题，进行了基于BP神经网络方法的惯性摆能量吸收效率的建模研究。并研究了基于该模型的不同波向角及波浪频率、载体外形尺寸、质量等的虚拟样机的波浪能吸收效率问题，为载体机构的改进及设计提供了较好的理论模型和基础。 4.开展了频域下惯性摆能量吸收效率研究。研究了基于频域的单惯性摆载体的动力学建模方法以及载体结构优化方法，提出采用多种群遗传算法进行载体结构的优化设计方法。通过仿真实验证明了相关算法的有效性，为系统的优化设计研究提供了理论基础。 5.以能量吸收效率最大为目标，进行了多种惯性摆形式的能量获取最大化分析研究，提出了包括单摆在内的多种可行的形式，给出了对比研究结果，可根据不同的提取形式而确定采用的惯性摆的形式。 6.采用PM谱对非线性波浪进行了模拟，研究了单惯性摆结构在非线性波浪力下的能量获取情况，仿真结果表明，在非线性条件下获取的惯性摆能量要更多，而其他波向角、频率等优化条件均与线性条件下的研究结果相同。

Perpendicular-electric-field dependence of exciton binding energy studied by continuous-wave photoluminescence

The reduction of exciton binding energy induced by a perpendicular electric field in a stepped quantum well is studied. From continuous-wave photoluminescence spectra at 77 K we have observed an obvious blueshift of the exciton peak due to a spatially direct-to-indirect transition of excitons. A simple method is used to calculate the exciton binding energy while the inhomogeneous broadening is taken into account in a simple manner. The calculated result reproduces remarkably well the experimental observation.