Higher order Boussinesq equations

A new form of Boussinesq-type equations accurate to the third order are derived in this paper to improve the linear dispersion and nonlinearity characteristics in deeper water. Fourth spatial derivatives in the third order terms of the equations are transformed into second derivatives and present no difficulty in numerical computations. With the increase in accuracy of the equations, the nonlinear and dispersion characteristics of the equations are of one order of magnitude higher accuracy than those of the classical Boussinesq equations. The equations can serve as a fully nonlinear model for shallow water waves. The shoaling property of the equations is also of high accuracy through shallow water to deep water by introducing an extra source term into the second order continuity equation. An approach to increase the accuracy of the nonlinear characteristics of the new equations is introduced. The expression for the vertical distribution of the horizontal velocities is a fourth order polynomial.     

三阶非线性海浪波面斜率的联合概率统计分布

从Longuet-Higgins于1963年建立的非线性随机海浪模型出发,对各向同性波面斜率的联台概率统计分布进行了理论研究.结果表明,在三阶近似下,波面斜率联合概率统计分有为截断的Gram-Charlier级数,截断的项数取决于非线性近似的阶数,每一阶近似均对前一阶近似结果有所修正如果不考虑非线性耦合相互作用的影响,则分布蜕化为高斯分布.     

基于时间分解的多波束常梯度声线跟踪方法

针对多波束常梯度声线跟踪计算耗时和声速剖面简化导致计算精度下降的问题,在对多波束常梯度声线跟踪理论进行分析的基础上,提出了一种基于时间分解的常梯度声线跟踪方法。将波束在层内的传播时间分解为与波束入射角无关的固定项和有关的变化项,固定项对于每个声速剖面仅需计算一次,对变化项采用麦克劳林公式展开得到其一阶近似,简化了层内传播时间和水平位移的计算;同时仅对变化项应用简化的声速剖面,降低剩余传播时间计算误差。实验结果证明当波束角小于50°、层间距小于50 m或上下层声速差小于20 m/s时,近似模型与常梯度算法精度相当,时间分解法在声速剖面层间距增大时能显著提高声线跟踪的精度。     

Measurements and estimation of flow velocity in mobile bed rills

Rills are primary sediment sources and hillslope water/sediment runoff transport channels. Water flow velocities in rills are easily affected by bed condition over eroding and non-eroding slopes, which is an important hydrodynamic process in soil erosion research. This research is done to demonstrate the poorly understood “feedback mechanism” related to slope independence of flow velocity to slope gradient. A series of experiments were done on silt loam soil slopes to measure water flow velocity...     

基于形态学的海洋锋形态特征提取

根据形态学梯度理论:不同尺寸的结构元素适合不同空间尺度的特征提取,结构元素尺寸的过大或者过小都会达不到最佳的特征边缘提取效果,从结构元素的尺寸δ与海洋锋横断面宽度γ和海流流幅的空间尺度λ的理论关系图推导中,提出δ,γ和λ的最佳定量关系:δ=γ/2,且δ<=λ/2,旨在对海洋锋形态特征进行提取。最后,以黑潮和墨西哥湾流为实验数据,进行海洋锋形态特征的自动提取,实验结果表明该定量关系的正确性和有效性。     

Derivation and application of new equations for radiation stress and volume flux

In this paper, new expressions of radiation stress and volume flux for long waves have been analytically derived by inclusion of higher-order surface elevations up to the sixth-order. To quantify these expressions, surface elevations along a beach are first simulated using the fully nonlinear Boussinesq-type model COULWAVE. Then, based on the large amount of numerical data, new equations for radiation stress and volume flux are statistically formulated. The research unveils the essential roles of the Ursell parameter, Irribarren number and wave steepness described by the local wave height, wave length and bottom slope. The study shows the importance of nonlinear wave properties in wave-induced currents and mean water levels (set-up/down). The higher-order formulations produce lower values for radiation stress and volume flux than calculated from the lower-order and linear waves. Case studies suggest that the new formulations produce an accurate estimation for mean water level. However, improvement on the computed current profiles is marginal for some cases. This implies that the accurate prediction of the current profile would require more than just the proposed improvement of the radiation stress and volume flux.     

大板金矿物探解译分析及成矿远景预测

大板金矿位于医巫闾造山带中段,为韧性剪切带型金矿,经 1999年度普查资料证实其有一定资源潜力,成矿远景较好,尤其是电法及高精度磁测工作为掩盖区地质填图及地下深部矿体分布提供了透视性信息,为 2000年大板金矿勘查工作奠定了良好的工作基础。经本次对物探资料解译分析,提出大板金矿东部及南部以及白土沟一带为主要成矿远景区。     

一类三阶非线性微分方程组的全局稳定性条件

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