Calculation of the initial elevation at the tsunami source using analytical solutions

We have obtained an analytical solution to the problem of determining the initial elevation at the tsunami source, which was formed by small residual deformations of a flat sloping bottom. This solution, which is newly derived, is compared with the known analytical solution of an equivalent problem over a horizontal bottom. It is shown that applying an analytical solution over a horizontal bottom for calculating the initial perturbations in the sources of realistic tsunami provides sufficient accuracy.     

On the relationships between the radial tidal current field and the radial sand ridges in the southern Yellow Sea: a numerical simulation

The origin of the radial sand ridges (RSRs) in the southern Yellow Sea has been a controversial problem since they were discovered in the early 1960s. To resolve the problem, two key questions need to be answered: (1) was the radial tidal current field in the RSR area generated by the submarine topography, or (2) did it exist before the RSRs occurred? In this study, the M₂ tide and tidal currents in the RSR area were simulated with a two-dimensional tidal model using a flat bottom and a shelving slope topography, the results being then compared with the field data. It is demonstrated that the radial tidal current field in the southern Yellow Sea is independent of bottom topography, and may thus be the controlling factor generating the RSRs. The radial tidal current field probably existed before the RSRs were formed.     

Self-Weight Penetration Characteristics of the Suction Foundation with Different Diameters in Sand

During the self-weight penetration process of the suction foundation on the dense sand seabed, due to the shallow penetration depth, the excess seepage seawater from the outside to the inside of the foundation may cause the negative pressure penetration process failure. Increasing the self-weight penetration depth has become an important problem for the safe construction of the suction foundation. The new suction anchor foundation has been proposed, and the self-weight penetration characteristics of the traditional suction foundation and the new suction anchor foundation are studied and compared through laboratory experiments and analysis. For the above two foundation types, by considering five foundation diameters and two bottom shapes, 20 models are tested with the same penetration energy. The effects of different foundation diameters on the penetration depth, the soil plug characteristics, and the surrounding sand layer are studied. The results show that the penetration depth of the new suction foundation is smaller than that of the traditional suction foundation. With the same penetration energy, the penetration depth of the suction foundation becomes shallower as the diameter increases. The smaller the diameter of the suction foundation, the more likely it is to be fully plugged, and the smaller the height of the soil plug will be. In the stage of self-weight penetration, the impact cavity appears around the foundation, which may affect the stability of the suction foundation.

     

Experimental and numerical study of the effect of variable bathymetry on the slow-drift wave response of floating bodies

An experimental campaign is reported on the slow-drift motion of a rectangular barge moored at different positions along an inclined beach, at waterdepths ranging from 54 cm to 21 cm, and submitted to irregular beam seas. The beach is achieved by inclining the 24 m long false bottom of the tank at a slope of 5%, from a depth of 1.05 m. The slow-drift component of the measured sway motion is first compared with state-of-the-art calculations based on Newman’s approximation. At 54 cm depth a good agreement is obtained between calculations and measurements. At 21 cm depth the Newman calculations exceed the measured values. When the flat bottom setdown contribution is added up, the calculated values become 2 to 3 times larger than the measured ones. A second-order model is proposed to predict the shoaling of a bichromatic sea-state propagating in varying water-depth. This model is validated through comparisons with an extension of Schäffer’s model for a straight beach [Schäffer HA. Infragravity waves induced by short-wave groups. J Fluid Mech 1993;247:551-88] and with a fully nonlinear Boussinesq model. It appears that the long wave amplitude is much less than predicted by the flat bottom model, and that its phase difference with the short wave envelope also deviates from the flat bottom model prediction. As a result of this phase shift the actual second-order wave loads can be lower than predicted by Newman’s approximation alone. Application of the shoaling model to the barge tests yields a notably better agreement between numerical and experimental values of its slow-drift sway motion.     

桐花树红树林潮滩近底层悬沙浓度垂向剖面变化特征分析*

观测红树林潮滩在波浪和潮流作用下的近底层垂向剖面悬沙浓度变化过程, 对理解海岸带植被的消能促淤机制和滨海湿地生态修复工程有着重要作用。本文以北部湾七星岛岛尾桐花树红树林潮滩为例, 基于剖面流速仪HR、声学多普勒单点流速仪ADV、浪潮仪T-wave及剖面浊度仪ASM, 获取了研究区域2019年夏季大潮连续3天的水文数据, 同时结合桐花树典型植株实测参数, 分析了潮周期内红树林潮滩近底层垂向剖面悬沙响应波浪、潮流作用及桐花树空间结构的运动过程。结果表明: 1) 桐花树潮滩近底层悬沙浓度和悬沙通量具有涨潮明显大于落潮的潮汐不对称现象, 剖面垂向高悬沙浓度区域在涨潮初期—涨急由距底部0.1~0.37m转变为距底部0.5~0.67m, 落急—落潮末期则由上部转变为下部; 2) 潮周期内悬沙起动和再悬浮阶段发生在以波浪作用主导的涨潮初期和落潮末期, 平流和沉降发生在以潮流作用为主的涨急至落急整个阶段; 3) 涨潮阶段桐花树冠层的茂密枝叶通过减缓流速拦截多于冠层上部40%以上的悬沙, 落潮水体则挟沙自陆向海经过桐花树群落, 使得悬沙浓度下降超过71%。该不对称涨、落潮动力沉积机制有利于悬沙向岸输运, 促进潮滩扩张过程。     

黏土中桩靴底部吸附力产生机理研究

在海洋工程中,移动钻井平台在作业结束后需要转场时,经常会遇到拔桩困难的问题,桩靴底部的吸附力是上拔力的重要组成部分,明确其产生机理及发展规律对于上拔力计算与缓解上拔困难问题有重要意义。通过室内模型试验研究了黏土中桩靴底部真空度对桩靴吸附力产生机理的影响,试验结果表明,桩靴底部真空度的变化对上拔力的影响显著,而桩靴贯入深度和上拔速率会对真空度产生影响。当真空度达到峰值时,桩靴底部吸附力与上拔力几乎同时达到峰值,因此可以通过减小桩靴底部真空度的措施来减小上拔力。根据试验结果,提出了运用真空吸盘理论来计算桩靴底部吸附力的计算公式。所述吸附力计算方法与试验结果进行对比,其误差较小,对工程实践具有一定的参考意义。     

浙江健跳港动力沉积过程及冲淤平衡机理

根据浙江健跳港实测水文泥沙和港道底部高程资料,分析了健跳港动力沉积过程及其港道的冲淤平衡机理。健跳港受潮流动力作用,大潮冲刷,小潮淤积,港道底部冲刷,湖滩淤积,随着空间上的冲淤变化,岸坡逐渐变陡,最终失去平衡,发生滑塌,形成潮滩与港道底部之间的动态平衡。     

声波在水-多孔介质海底界面上的反射与透射

声波在海底界面的反射和透射是海底散射、海底混响、海底目标探测的重要问题。利用Biot多孔介质声传播理论对声波在水-多孔海底界面上的反射和透射进行了分析,具体给出反射声波的反射系数,3种透射声波的透射系数以及声能透射系数随入射波入射角和频率(10~40 kHz)的变化关系,分析了各种透射波对透射声能的贡献。多孔海底介质参数分别采用Stoll和Chotiros给出的2组参数进行理论计算。     

砂土中吸力式导管架基础沉贯试验研究

吸力式导管架基础具备高承载力、高施工效率、高环境友好度、低造价等特点,使用其作为海上风电底部支撑结构有利于产业的规模化发展,实现上述愿景的前提在于使筒型基础顺利安装以满足设计要求。基于此,在不同初始施加泵压下,对吸力式导管架的沉贯效率特征值、基础内外围渗流变化、筒裙端部土压力特点进行探究。通过抱桩器使吸力式导管架在吸力安装过程中仅具备竖向自由度,从而进行纯沉贯试验。结果表明：初始泵压2 kPa时沉贯效率特征值最高;沉贯过程中基础外围渗流水压小于基础内围渗流水压;筒裙外侧所受土压要大于筒壁内侧所受土压力。     

On the stability of fronts near shelfbreak

Using a two-dimensional semi-geostrophic model. the stability of fronts near shelf break (shelfbreak font, western boundary current front) and its mechanism are studied. We find that the stability of the front is related to the frontal structure. In general, the increase of the lower layer depth lowers the unstable growth rate (a1). (1) The shelfbreak front is baroclinically unstable and ai increases with the increase of the bottom slope, different from the conclusion of Flagg and Beardsley (1978). (2) A western boundary current front with uniform vorticity in the upper layer is barotropically unstable, due to the strong horizontal shear of the mean current. The unstable growth rate of this front for a realistic topography is only one seventh of that of the flat bottom case. (3) For a western boundary current front with hyperbolic tangent structure, we find its wave propagation speed to be about 0. 5 m/s, in agreement with the observed values. The front is baroclinically unstable. (4)The unstable growth     

A Numerical Study on the Structure and Dynamics of Turbulence in Oscillatory Bottom Layer Flow over A Flat or Rippled Bed

1 .IntroductionUnder the influence of surface waves ,sandripples often appear on beaches . Whenthe amplitudeof water oscillationis sufficientlylarge ,vortices are formed onthe lee of every sand ripple crest . A-mongthese vortices ,the most important are t…     

The bottom currents in the area of abyssal hills in the north-east tropical Pacific Ocean

The results of simultaneous measurements of the bottom (6.25 and 35 m above the bottom) currents, deep currents, and surface currents made at three points in the north-east tropical Pacific Ocean are given. The bottom intensification of the current velocity is revealed in a layer of 35–25 m above the bottom. The estimation of the thickness of the bottom boundary layer (BBL) indicates that the velocity intensification is observed over the boundary layer upper border. A 10-day long benthic storm with a maximum measured velocity of 13 cm/s was revealed 6 m above the bottom. As was found, the origin of the benthic storm is associated with the penetration of an anticyclonic eddy down to the bottom.Translated by Mikhail M. Trufanov.     

Behavior of a Large Cylinder in Free-Fall Through Water

This paper presents results of experimental deployment of a large instrumented cylinder of variable nose geometry and center of mass offset (CMO) in free-fall in realistic environment. Data on four tests series in the Gulf of Mexico are presented and analyzed statistically. The stochastic nature of the problem of the cylinder free-falling through water is outlined and described as an input to the subsequent impact burial prediction package. Significance of the CMO on the behavior of the cylinder is underlined. Influence of the release conditions on trajectory is discussed and found to affect the behavior of the cylinders only in the first 3.5 m of free-fall in water. Beyond this depth, quasi-stable (in the mean sense) conditions are achieved. Effects of three different nose shapes-blunt, hemispherical, and chamfered-on cylinder behavior are analyzed and found to have a pronounced influence on the fall trajectory. The blunt nose shape appears to be hydrodynamically most stable in free-fall. Apparent periodicity in motions of all cylinders were noted and were found to be the function of the CMO and nose shape primarily. Implications of these and other findings on modeling and impact burial predictions are discussed.     

Eigen solutions of internal waves over subcritical topography

Diapycnal mixing plays an important role in the ocean circulation.Internal waves are a kind of bridge relating the diapycnal mixing to external sources of mechanical energy.Difficulty in obtaining eigen solutions of internal waves over curved topography is a limitation for further theoretical study on the generation problem and scattering process.In this study,a kind of transform method is put forward to derive the eigen solutions of internal waves over subcritical topography in twodimensional and linear framework.The transform converts the curved topography in physical space to flat bottom in transform space while the governing equation of internal waves is still hyperbolic if proper transform function is selected.Thus,one can obtain eigen solutions of internal waves in the transform space.Several examples of transform functions,which convert the linear slope,the convex slope,and the concave slope to flat bottom,and the corresponding eigen solutions are illustrated.A method,using a polynomial to approximate the transform function and least squares method to estimate the undetermined coefficients in the polynomial,is introduced to calculate the approximate expression of the transform function for the given subcritical topography.     

半球形多向波聚合波道振荡水柱气室优化设计

为了解决振动水柱式波浪能转换装置收集多向波浪问题,本文设计了半球形多向聚合波道振荡水柱气室结构,以适合远海单点波浪能采集和发电。在规则波正向入射条件下,基于流体仿真分析软件(FLUENT)、流体动力学连续性假设和粘性不可压缩流体动量守恒的运动方程(Navier-Stokes方程)建立半球形振荡气室和三维数值波浪水槽模型。仿真结果表明:增设气室后壁,合理设计波道开口角度实现多向迎波捕获波浪能,优化前壁形状可降低波浪触底反射带来的能量耗散,同时提高了气室内空气压强和出气口速度,有效提升波浪能俘获效率,为后续发电的二次能量转换提供高效的空气动力。     

Modelling of the barotropic processes in the Bohai Sea

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Wave parameter gradients along the wave ray

Computer methods have been used to track selected deep-water waves along their orthogonals to the surf zone. Three bottom orbital parameters were computed at each step: diameter, maximum velocity and acceleration. These three parameters were then plotted along the several wave rays, thereby providing shoreward gradients.The three gradients have essentially the same geometry, so that any one can be taken as an indicator of the other two. Bottom slope changes are responsible for departure of the gradients from linearity. The bottom orbital gradients are quite different from gradients of wave height and wave length. These results from coasting waves cannot be applied directly to the case of forced, or wind-driven, waves.The non-linear nature of the bottom orbital gradients indicates that the near-shore bottom should exhibit a crude banding, more-or-less parallel with the coast, with different sediment transport and ripple-mark geometry from band to band.     

潜堤上规则波辐射应力的数值研究

在近岸波浪相关研究中,辐射应力是波动在水体中引起的剩余动量流,是波浪运动的重要物理量.在波浪从深水逐渐传向浅水的过程中,波浪的非线性逐渐增强,甚至会发生破碎等剧烈变形,引起辐射应力的强烈变化,对次重力波生成等有重要贡献.应用OpenFOAM精细模拟波浪在潜堤上的传播,得出波浪运动的详细流场信息,计算了有波浪破碎情况下潜...     

Study on the currents in Lake Biwa (I)

Some numerical experiments by the barotropic nonlinear two dimensional models are performed to study the water circulations in Lake Biwa, especially to study the large anticlockwise gyre in the north basin. The wind fields used in the experiments have no rotational component. This gyre is induced by the southerly wind and is approximately on the geostrophic balance. The vorticity of this gyre is contributed from the vertical stretching of the vortex tube by the variable bottom topography and the inertia term. But the latter term does not become effective if the bottom profile of the basin is flat. Therefore the horizontal circulation in the barotropic closed basin is the “topographic gyres”. The bottom stress has a little contribution to the vorticity balance of the gyre.