波浪计算可视化的研究

文章讨论了波浪场可视化实现过程中的一些关键的算法。文中针对表示波浪面的数据集的特性,采用了一种简单的节点法矢量算法。绘制结果表明,用这种简单算法取代二维和三维的数据场节点法矢量的常用算法,能够保持波浪场三维图形的光照效果。利用层次模型算法进行波浪的动态演示,比较了相同面积的波浪场在不同网格密度情况下图形的显示质量,提出波浪场图形质量有与特征波长相匹配的最佳经验网格密度。     

Introduction of accumulation-dispersal coefficient of marine organisms

Avoiding the subject for fish accumulation, the traditional view in fish population dynamics has ascribed immigration and emigration of fish to dispersal of fish. The main purpose of this paper is to find a quantity that represents the time rate of accumulation-dispersal of marine organisms, and also has some relation to the horizontal convergence of current velocity of the surrounding water. For this, the accumulation-dispersal coefficient is introduced not in the form of diffusion, but in the same form as the convergence. Since the accumulation-dispersal of organisms is a factor that changes its distribution density, all factors causing the change are first classified to locate the position occupied by the accumulation dispersal. Each factor corresponds to each coefficient appearing in a linearized equation describing the rate of change in the density, averaged over a region or a group. The immigration-emigration coefficient is divided into three coefficients of passage, accumulation dispersal and diffusion velocity. For the organisms ranging in a nearly horizontal layer, the accumulation-dispersal coefficient is shown to equal the area-averaged horizontal convergence of organismal velocity relative to land, which is the sum of the area-averaged horizontal convergences of swimming velocity relative to water and of current velocity. However, the area-averaged convergence of current velocity associated with the accumulation-dispersal coefficient for a region is shown to be somewhat different from the usual one.     

贝叶斯统计方法在海浪方向谱研究中的应用

较详细介绍了贝叶斯统计方法在海浪方向谱估计中的应用,指出先验分布的不同对估计结果没有影响,由于均匀分布与最大熵原则相对应,使其具有某种特殊性.数值模拟表明贝叶斯方法对双峰方向分布估计的有效性,将其应用于黑海实测资料,证明双峰方向分布的出现依赖于估计方法分辨力的大小,而用最大似然法得到的双峰方向分布值得怀疑.最后给出出现双峰方向分布的一种可能物理解释.     

国际eLoran发展现状与我国罗兰C现代化的技术分析

讨论并分析了在目前GNSS广泛应用的背景下,罗兰系统所面对的挑战和机遇。对增强罗兰技术的国际现状作了一定的介绍和分析,并对我国罗兰C系统进行现代化改造的需求和可行性进行了简单分析。结论表明,罗兰C系统作为GNSS的备份增强系统进行改造和建设是必要可行的。     

Mechanism of the formation of volcanic chains of French Polynesia

A possible mechanism of the formation of chains of intraplate seamounts and islands alternative to the “hot spot” hypothesis is considered. It is related to the appearance of additional stresses in the lithospheric plate when it ascends over a mantle inhomogeneity and descends from it. The magnitude of these stresses (～600 bar) is sufficient for formation of deep fracture zones. In the paper, schemes of formation of volcanic chains are described. The formation of the “faults-volcanoes-volcanic chains” sequence may follow two different ways. The first is controlled by the fracture zones formed along the direction of the plate movement. In this case, feeding channels are localized along the boundary of the rise. If the chain is gradually formed simultaneously with the plate motion, the age of the volcanoes along the chain may change in a more or less regular way. The second type is formed by fractures orthogonal to the movement direction. They may be formed when the plate ascends over a mantle inhomogeneity and/or descends from it. In this case, adjacent volcanoes may have similar ages. A combination of these two variants may also be encountered. The mechanism posed allowed us to explain selected facts referring to the volcanic chains of French Polynesia and may be applied to other regions of the Pacific Ocean.     

Improved prediction of the threshold of surf-riding of a ship in steep following seas

An extended version of Melnikov's method is implemented in order to predict more accurately the threshold of global surf-riding for a ship operating in steep following seas. The key advantage of the proposed method is that it overcomes the limitation of small damping and/or small forcing that are intrinsic to the implementation of the standard Melnikov's method. A reference ITTC ship is used here by way of example and the result is compared to that obtained from standard analysis as well as numerical simulations. Because of the primary drawback of the extended Melnikov's method is the inability to arrive at a closed form equation, in this work the authors arrive at a “best fit” approximation to the extended Melnikov numerically predicted result.     

水流作用下渔网养殖空间变化的计算方法

渔网的动力分析是养殖网箱设计和优化的基础。通过把一系列杆相互铰接在一起,建立网的模型,模拟网在来流作用下的变形。作用在杆上的水动力可以通过Morison公式来计算,采用有限单元的离散方法,并利用网目合并的方法来减少总的自由度数目。模型的计算结果同试验成果做了对比,计算与试验在柔性网的变形方面,结果吻合良好。     

Significance of relative velocity in the estimation of drag force of a tethered spherical float

In the present study, a tethered spherical float undergoing oscillatory motion in regular waves is analysed. Float velocity is computed through dynamical equation of motion and particle velocity using linear wave theory. The results show that variation of particle velocity with respect to wave period, wave height or water depth is small compared to the variation of float velocity with respect to the same parameters. The results further indicate that the difference between float velocity and particle velocity is considerable and, in such cases, the relative velocity instead of the particle velocity has to be considered for drag force or drag power estimation. However, it is suggested that float velocity must be higher than the particle velocity in order to use relative velocity in drag force or drag power estimation.     

流场散度的误差估计

按照误差传递原理,推导出流场散度的误差估计式,并将其应用于赤道中东太平洋上升流区域水平散度误差的估计。应用结果表明:赤道中东太平洋上升流区多年平均流场的散度稳定,平均散度约为3.0×10-7s-1;和通常采用的误差估计公式相比,该估计公式降低了散度误差,从而提高了散度的可信度。     

Spin-up and spin-down processes of the large cold water mass of the Kuroshio south of Japan

Time variation of the cold water mass of the Kuroshio south of Japan, which was formed in August 1975 and disappeared in August 1980, is studied. Its lifecycle includes several repetitions of spin-down and spin-up processes. The spin-down (or the spin-up) process is accompanied by warming (cooling) of the cold water mass and descending (ascending) motion of the inner water. Expansion of the cold water area is also associated with the spin-up period while shrinking occurs in the spin-down period. The rate of spin-down of the cold water mass is approximately equal to that of the Gulf Stream rings. The spin-up process is not observed in the Gulf Stream rings and the longer lifetime of the cold water mass off Japan, in comparison with the Gulf Stream rings, is due to the existence of the spin-up periods. The spin-up process tends to occur in late spring to summer, and it seems to be related to the seasonal variation in intensity of the Kuroshio.     

On the formation of sand banks of finite extent

We consider a model where the fluid depth depends on both horizontal coordinates, quasi-steady depth-uniform non-divergent fluid flow is governed by inertial, pressure and bottom-frictional forces, sand transport is proportional to the cube of the instantaneous current but augmented by a down-slope component and by wind-wave action, and sand is conserved.It is found that low parallel banks grow fastest, so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate. The inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump. A small bump can evolve to an equilibrium bank (typically after an initial rapid extension across the tidal currents) provided that sand is sufficiently restricted and particularly if some wind-wave action prevents growth up to the sea surface. Sand banks are likely to be in a late stage of evolution, when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition. The equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents, or when sand is abundant.     

有机质对海底沉积物中粘土矿物X射线衍射分析结果的影响

X射线衍射法广泛应用于分析粘土矿物的含量和结晶特征,由于粘土矿物易与有机质结合形成有机-粘土复合体,是否去除有机质对分析结果有很大影响,实验结果表明影响最大的是伊-蒙混层矿物(含蒙脱石)和伊利石的含量,为得到可靠实验数据,必须重视对样品的前处理工作,对不同批次样品应该保持一致的处理程序。     

Tikhonov正则化法在重力场最小二乘配置逼近理论中的应用

最小二乘配置法由于其能融合不同种类重力观测数据进行局部重力场逼近的特性而受到广泛关注,但最小二乘配置结果的不稳定严重影响该方法的推广应用。 基于对重力观测量协方差矩阵的谱分解,分析出该协方差矩阵存在病态性,协方差矩阵的求逆过程是信号放大的非平稳过程,微小的观测误差会被协方差矩阵的小奇异值放大,从而导致配置结果的不稳定且精度偏低。 引入 Tikhonov 正则化算法,通过 L 曲线法选择正则化参数,利用正则化参数修正重力观测量协方差矩阵的小奇异值,能抑制其对观测误差的放大影响。 通过以 EGM2008 重力场模型分别计算的山区、丘陵和海域重力异常作为基础数据确定相应区域大地水准面的实验,验证了本文算法的有效性。     

Implications of gas content for predicting the stability of submarine slopes

Abstract

The behavior of gas‐laden, soft submarine soils subjected to changes in mean normal and shearing stresses is discussed. Information developed for partially saturated soils is extended to soft sediments. Calculations indicating that gas‐laden submarine soils generally have degrees of saturation in situ that exceed ～ 90% are presented. Therefore, it is suggested that insignificant error is introduced in predicting the effective stresses of soft sediments using the standard effective stress equation and neglecting the pore‐gas pressure.

The presence of gas is shown to permit volume changes of soft sediments under wave loadings. The compressibility of the gaswater pore fluid is quantified. The pore‐pressure response, related to the ratio of the compressibility of the pore fluid and soil structure, is shown to be similar to that of fully saturated soils. The relevance of “undrained”; shipboard tests to the prediction of slope stability is discussed. It is concluded that the presence of gas leads to undrained strengths, as measured on recovered samples, which are lower than those that occur in situ. The use of these measured strengths in stability calculations leads to conservative predictions of submarine slope stability.     

水雷作战效能海洋环境影响评估

提出并定性分析了海洋环境对水雷作战效能的影响,提出了构造模糊隶属函数,归一量化描述不同环境参数;采用层次分析法构建水雷作战效能指标参数,建立水雷作战效能与海洋环境参数之间的关联和层次结构,构造环境参数到水雷效能的训练样本;采用机器学习方法对海洋环境影响下水雷作战效能进行评估。通过实例,给出了水雷作战效能量化评估过程。     

Sediment movement characteristics of coast and analysis of seabed evolution

The rotary ring flume is used to study the silty sand movement in a periodic alternating current.Characteristics of sediment movement of different coasts in the tidal current are summarized.More detailed analysis of erosion-sedimentation function in a numerical simulation is made.The equilibrium sediment concentration is advanced.Based on the equilibrium sediment concentration,the seabed erosion-sedimentation index is derived and the seabed erosion-sedimentation calculation is analyzed.The seabed erosion-sedimentation index is used to calculate the seabed evolution of Yangshan sea area and a good agreement with field measurements is obtained.     

水下滑翔器主体外形优化设计

对水下滑翔器主体外形的优化设计问题进行研究.首先,在考虑内部机械结构限制的条件下,建立了主体外形优化数学模型,并采用CFX计算了若干主体形状的绕流阻力.在此基础上建立了映射主体外形的尺寸参数与绕流阻力的BP神经网络.然后将建立的神经网络作为优化设计问题的目标函数,采用坐标轮换法对滑翔器主体外形进行了优化设计,确定了尺寸参数的最优解.     

Influence of non-linearities on the limits of stability of ships rolling in head seas

The present paper describes an investigation on parametric resonance in head seas in which a new third-order coupled mathematical model is considered. The restored modes of heave, roll and pitch are contemplated. The discussion is illustrated for the case of a transom stern fishing vessel at different speeds. It is pointed out that numerical simulations employing the new model are successfully compared to experimental results previously obtained for the vessel.Considering that analyticity is an important tool when handling complex stability issues, some theoretical dynamic characteristics of the equations are discussed. By means of the analysis of the coupled linear variational equation derived from an extended third-order model, the appearance of super-harmonics and increased rigidity proportional to wave amplitude squared due to third-order terms is demonstrated.In the present paper, an important tool is explored, that is the analysis of the limits of stability obtained from the new model. Limits of stability are a well-known and practical way of looking into the problem of parametric resonance. New limits of stability are derived and compared to the more conventional Strut diagram. Dynamic characteristics associated with the new limits of stability are discussed. The influence of different parameters is investigated, including vessel speed, damping and tuning. Consistent and revealing results are obtained through the analysis of the new limits of stability for different speeds and damping.     

Investigation of scour effect on tensile capacity of suction caissons considering stress history of sand

Abstract

Since the pull-out response of upwind caissons governs the design of multi-caisson foundations, it is worthwhile to study scour effect on the tensile capacity of suction caissons. The tensile capacity of suction caissons after scour is relevant to the scour depth and the pressure under the caisson lid: the tensile capacity decreases dramatically with increasing scour depth; the smaller the pressure, the stronger the weakening effect of scour. Moreover, the scour effect is investigated in two cases: ignoring stress history and considering stress history. The results show that tensile capacity after scour is larger when the stress history is considered, so ignoring the stress history leads to a conservative design. In order to quantitatively evaluate the effect of scour depth and pressure, an empirical formula for the tensile capacity of suction caissons after scour is proposed based on multiple regression analysis.     

Application of polypyrrole actuators: feasibility of variable camber foils

A decade of research into electroactive polymer actuators is leading to the exploration of applications. These technologies are not ready to compete with the internal combustion engine and electric motors in high power propulsion systems but are suitable for intermittent or aperiodic applications with moderate cycle life requirements, providing an alternative to solenoids and direct drive electric motors. Polypyrrole, an emerging actuator material, is applied to drive hydrodynamic control surfaces and in particular to change the camber of a foil. The foil is intended for use in the propeller blade of an autonomous underwater vehicle. A scaled prototype is constructed which employs polypyrrole actuators imbedded within the blade itself to vary camber. The kinematics required to generate camber change are demonstrated, with >30/spl deg/ deflections of the trailing edge being observed from both bending bilayer and linear actuator designs. Forces developed in still conditions are five times lower than the 3.5 N estimated to be required to implement variable camber. The observed 70 kJ/m/sup 3/ polypyrrole work density however is more than sufficient to produce the desired actuation from within the limited blade volume, enabling an application that is not feasible using direct drive electric motors. A key challenge with the polypyrrole actuators is to increase force without sacrificing speed of actuation.