Laboratory investigations on impulsive waves caused by underwater landslide

Laboratory investigations have been performed on the submarine landslide generated waves by performing 120 laboratory tests. Both rigid and deforming-slide masses are considered. The effects of bed slope angle, initial submergence, slide geometry, shape and deformation on impulse wave characteristics have been inspected. Impulse wave amplitude, period, energy and nonlinearity are studied in this work. The effects of bed slope angle on energy conversion from slide into wave are also investigated. Laboratory-based prediction equations are presented for impulse wave amplitude and period in near and far-field and are successfully verified using the available data in previous laboratory and numerical works.     

Numerical simulation of tsunami waves generated by deformable submarine landslides

This paper presents a new submarine landslide model based on the non-hydrostatic wave model NHWAVE of Ma et al. (2012). The landslide is modeled as a water–sediment mixture. The dense plume is driven by baroclinic pressure forcing introduced by spatial density variations. The model is validated using laboratory measurements of turbidity currents and of water wave generation by a granular landslide. The model is then utilized to study the dependence of landslide motion and associated tsunami wave generation on parameters including sediment settling velocity, initial depth of the landslide and slide density. Model results show that the slide motion and water waves which it generates are both sensitive to these parameters. The relative tsunamigenic response to rigid and deformable landslides of equal initial geometry and density is also examined. It is found that the wave energy is mostly concentrated on a narrow band of the dominant slide direction for the waves generated by rigid landslides, while directional spreading is more significant for waves generated by deformable landslides. The deformable landslide has larger speed and acceleration at the early stage of landslide, resulting in larger surface waves. The numerical results indicate that the model is capable of reasonably simulating tsunami wave generation by submarine landslides.     

实验室造波条件对内孤立波发展影响的直接数值模拟

内孤立波具有振幅尺度大、能量集中的特点,其引起流场和密度场的迅速变化可能对海洋工程结构物以及水下潜体造成严重威胁。因此研究不同造波条件下生成的内孤立波运动的流场特征具有重要的学术意义和实际应用价值。采用直接数值模拟方法和给定的初始密度场密度跃迁函数,对重力塌陷激发内孤立波的运动过程进行研究,探讨了不同造波条件下,激发产生的内孤立波波型、涡度、振幅和水平速度等流场特征。结果表明:(1)直接模拟数值方法能够模拟内孤立波传播过程中的密度界面波型反转现象;(2)从定性和定量的角度,证实了不稳定内孤立波传播过程中存在能量的向后传递;(3)对于相同的台阶深度(水闸两侧初始密度界面的高度差),初始涡流保持相同,但是随着上下层水深比的减小,其强度下降显著;(4)台阶深度对初始涡流的垂直结构的影响要大于上下层水深比,且台阶深度对内孤立波的振幅、水平速度的影响显著。     

Analysis and Design Implications on Stability of Cofferdam Subjected to Water Wave Action

Based on Power-Law nonlinear failure criterion and the upper bound theorem of limit analysis, a numerical solution was developed to analyze the shape of collapsing block and landslide thrust of cofferdam subjected to residual pore pressure which was caused by longstanding water wave action. In the upper bound analysis, the effect of water pressure assumed to be a work rate of external force was considered. To evaluate the validity of the present method, the results were compared with previous findings. The good agreement between the present results and the previous findings indicated that the proposed method was valid to assess the shape of collapsing block and landslide thrust of cofferdam subjected to residual pore pressure. As for the influence of the factors on the shape of collapsing block and landslide thrust, a parametric study was conducted. This parametric study was carried out to optimize the design of cofferdam supporting structures and improve analysis of the stability of cofferdam subjected to water wave action.     

Numerical Modeling of Sediment Mass Sliding and Tsunami Generation: The Case of February 7, 1963, in Corinth Gulf,Greece

Numerical modeling of a landslide process at the continental slope by taking into account slope parameters is performed for the tsunami event of February 7, 1963, reported in the Corinth Gulf, central Greece. A layered sediment structure was considered, and an initial external dynamic action at the landslide process was introduced. The results obtained were quite consistent with the observational runup data as well as with the results arrived at by conventional rigid-body and viscous-fluid models. However, this approach permits to describe in detail the formation of several wave groups and particular tsunami characteristics that are strongly dependent on the landslide model.     

Numerical Modeling of Sediment Mass Sliding and Tsunami Generation: The Case of February 7, 1963, in Corinth Gulf, Greece

Numerical modeling of a landslide process at the continental slope by taking into account slope parameters is performed for the tsunami event of February 7, 1963, reported in the Corinth Gulf, central Greece. A layered sediment structure was considered, and an initial external dynamic action at the landslide process was introduced. The results obtained were quite consistent with the observational runup data as well as with the results arrived at by conventional rigid-body and viscous-fluid models. However, this approach permits to describe in detail the formation of several wave groups and particular tsunami characteristics that are strongly dependent on the landslide model.     

The evaluation method of total damage to ship in underwater explosion

Whipping response will happen when a ship is subjected to underwater explosion bubble load. In that condition, the hull would be broken, and even the survivability will be completely lost. A calculation method on the dynamic bending moment of bubble has been put forward in this paper to evaluate the impact of underwater explosion bubble load on the longitudinal strength of surface ships. Meanwhile the prediction equation of bubble dynamic bending moment has been concluded with the results of numerical simulation. With wave effect taken into consideration, the evaluation method of the total damage of a ship has been established. The precision of this evaluation method has been proved through the comparison with calculation results. In order to verify the validity of the calculation results, experimental data of real ship explosion is applied. Prediction equation and evaluation method proposed in this paper are to be used in ship structure design, especially in the preliminary prediction of the ultimate withstanding capability of underwater explosion damage for the integrated ship in preliminary design phase.     

潜堤后高阶自由谐波的研究

基于高阶边界元方法的完全非线性数值水槽模型模拟潜堤地形上波浪的传播变形,通过与实验值进行比较,考察数学模型的正确性.采用两点法分离得到堤后高倍频自由波来研究入射波参数、水深对堤后高倍频自由波的影响.研究发现:基频波、二阶和三阶自由波幅值分别与入射波波幅成线性、二次和三次函数关系,基频波幅值基本不随波浪周期变化,而二阶和...     

Wave-in-deck loads on coastal bridges and the role of air

Recent failures of coastal bridges during extreme storm events have focused attention on the need for research on wave loading of coastal structures suspended above the still water level. This paper presents findings from large-scale experimental work carried out in the wave basin of the Yokohama Port and Airport Technical Investigation Office. Measurements from physical model tests are used to gain insights on the dynamics of wave-loading of coastal bridges and to derive an “ad-hoc” prediction method for both quasi-static and impulsive wave loads. The effect of openings in the bridge deck is also discussed, and guidance derived for design purpose.     

Modeling the generation and gravity-capillary waves using an underwater sound source

This is an experimental study of the acoustic method of surface-wave excitation using an underwater source of high-frequency (950 kHz) sound. The surface waves are excited at the sound-beam modulation frequency (3–55 Hz). For a normal fall onto the free surface, the modulated sound beam efficiently generates waves in the gravity-capillary range. This provides flexible electronic control of the main wave parameters (frequency and amplitude) in the packet and continuous modes. The amplitude-frequency characteristics of the process of surface-wave generation were obtained by numerical calculations (based on equations for the rate of acoustic flux and propagation of gravity-capillary surface waves) and by experiments (based on surface wave measurements by optical and contact methods). Both values are very consistent: on the background of a similar monotonic attenuation with frequency, they have a local dip near the minimum of the phase velocity and oscillation in the frequency range above 20 Hz. The experiments on the excitation of wave packets by single acoustic messages with varying lengths and powers, as well as by falling water drops, indicated that, in all cases, the phase characteristics are satisfactorily consistent with one another and the time needed for the signal to arrive at the measurement point is determined by the group velocity.     

滑坡监测系统在北长山岛山后村山体滑坡监测中的应用

为有效地监测海岛山体滑坡,找到滑坡的诱发因素,以达到海岛地区防灾减灾的目的。本文以北长山岛为例,针对采石引起的滑坡,利用GPS、三维激光扫描、无人机遥感、位移传感器4种滑坡监测方法,联合建立了北长山岛山后村山体滑坡监测系统。通过对比分析这4种方法发现,在三维激光扫描点云数据密集的滑坡体中、下部选择三维激光扫描获取的滑坡体形态数据,在点云数据稀疏的滑坡体上部选择无人机遥测获取的滑坡体形态数据,精确获取了不同时期滑坡体的挖方量、滑移量;位移传感器获取的实时位移监测数据可得到滑坡体的实时滑移动态,发现在其监测数据突变时滑坡存在滑动的风险。研究还发现采石和降雨是引起山后村滑坡体滑移的两个最重要因素,采石导致滑坡体体积整体减小,降雨导致滑坡体上部拉张加速并引起碎石滑塌。由于监测区环境条件的限制,该系统只能进行滑坡体的表面变形监测。研究成果可为其他海岛滑坡的监测乃至预警提供借鉴和参考。     

On the evolution and run-up of breaking solitary waves on a mild sloping beach

This paper presents new laboratory experiments carried out in a supertank (300 m × 5 m × 5.2 m) of breaking solitary waves evolution on a 1:60 plane beach. The measured data are employed to re-examine existing formulae that include breaking criterion, amplitude evolution and run-up height. The properties of shoreline motion, underwater particle velocity and scale effect on run-up height are briefly discussed. Based on our analyses, it is evidently found that there exist five zones during a wave amplitude evolution course on the present mild slope. A simple formula which is capable of predicting maximum run-up height for a breaking solitary wave on a uniform beach with a wide range of beach slope (1:15–1:60) is also proposed. The calculated results from the present model agree favorably with available laboratory data, indicating that our method is compatible with other predictive models.     

复杂海况下水下拖缆数值分析研究

为了解复杂海况下风浪对水下拖缆的影响进行了动力学仿真研究。以P-M谱作为海浪谱密度公式,计算一组不同频率的组成波,采用线性波浪叠加法,计算由波浪引起的空间流场速度及加速度,推导叠加波的干扰力,将不规则波引入水下拖缆动力学模型中,采用四阶龙格库塔积分法对动力学模型进行数值求解,讨论拖缆在不同海况下的动力特性。结果表明,随着海况等级的提高,叠加波的频率范围逐渐降低,拖缆的垂向偏移量以及拖点处张力均会产生明显增加及波动,且其波动周期接近叠加波的平均周期;在不同浪向角的作用下,拖缆波动规律与规则波作用下类似,但也具有一些不规则波的特点。     

海水对海洋平台声发射传播特性影响研究

针对海洋平台水下钢结构无损检测的需要,研究在空气、淡水和海水作为耦合介质的情况下,声发射波在钢结构传播过程中幅值和能量的变化趋势,以及幅值和能量损失的原因。基于声发射波反射原理,分析声发射波在钢结构中传播的多径效应及波形转换特性,并解释了时域波形发生分离的原因。根据实验结果,分析了盐度对声发射波传播特性的影响。该项研究为提高海洋平台声发射检测中故障源的精确定位提供了实验依据。     

Wave effects on ascending and descending motions of the autonomous underwater vehicle

In the paper, a hydrodynamic model including the characteristics of maneuvering and seakeeping is developed to simulate the six-degree of freedom motions of the underwater vehicle steering near the sea surface. The corresponding wave exciting forces on the underwater vehicle moving in waves are calculated by the strip theory, which is based on the source distribution method. With the hydrodynamic coefficients relevant to the maneuvering and seakeeping, the fourth-order Runge–Kutta numerical method is adopted to solve the equations of motions and six-degrees of freedom of the motions for the underwater vehicle steering near the free surface can be obtained. The wave effect on the corresponding motions of the underwater vehicle is investigated and some interesting phenomena with respect to different wave frequencies and headings are observed. The hydrodynamic numerical model developed here can be served as a valuable tool for analyzing the ascending and descending behaviors of the underwater vehicle near the sea surface.     

Hydrodynamic Modeling with Grey-Box Method of A Foil-Like Underwater Vehicle

In this study, a dynamic modeling method for foil-like underwater vehicles is introduced and experimentally verified in different sea tests of the Hadal ARV. The dumping force of a foil-like underwater vehicle is sensitive to swing motion. Some foil-like underwater vehicles swing periodically when performing a free-fall dive task in experiments. Models using conventional modeling methods yield solutions with asymptotic stability, which cannot simulate the self-sustained swing motion. By improving the ridge regression optimization algorithm, a grey-box modeling method based on 378 viscous drag coefficients using the Taylor series expansion is proposed in this study. The method is optimized for over-fitting and convergence problems caused by large parameter matrices. Instead of the PMM test data, the unsteady computational fluid dynamics calculation results are used in modeling. The obtained model can better simulate the swing motion of the underwater vehicle. Simulation and experimental results show a good consistency in free-fall tests during sea trials, as well as a prediction of the dive speed in the swing state.     

水下压力阵列的测波方法

本文介绍了ＨＤＬ—２１７６底压式测波仪的基本特性，给出了水下压力阵列进行波浪方向谱估计的数据计算方法。     

Experimental investigation on a two-part underwater towed system

An experimental set-up is developed and proved to be effective for laboratory study of an underwater towed system. The experimental technique gives a practical method for monitoring the kinematic and dynamic performance of an underwater towed system in a ship towing tank. Both the theoretical and experimental results in the investigation indicate that the hydrodynamic response of a towed vehicle to the wave induced motion of a towing ship can be significantly reduced by applying a two-part tow method. A comparison of the numerical and experimental results in the investigation demonstrates that the numerical simulation results are close to the experimental data, overall agreement between experimental and theoretical results is satisfactory. The results qualitatively verify the mathematical model of a two-part underwater towed system proposed by Wu and Chwang [Wu, J., Chwang, A.T., 2000. A hydrodynamic model of a two-part underwater towed system. Ocean Engineering 27 (5), 455–472].     

Numerical and experimental study on seakeeping performance of a SWATH vehicle in head waves

The seakeeping characteristics of a Small Waterplane Area Twin Hull (SWATH) vehicle equipped with fixed stabilizing fins was investigated by experimental and numerical methods The calculation methods range from viscous CFD simulation based on an unsteady RANS approach to Boundary Element Method (BEM) based on Three Dimensional Translating-pulsating Source Green Function (3DTP). Responses of ship motions in head regular waves and nonlinear effects on motion responses with increasing wave amplitude were analyzed. Numerical simulations have been validated by comparisons with experimental tests. The results indicate that the heave and pitch transfer functions depict two peaks with the increase of wave length. Comparisons amongst experimental data and different numerical calculations illustrate that the RANS method predicts ship motions with higher accuracy and allows the detection of nonlinear effects. The heave and pitch transfer functions see a downward trend with the increasing wave amplitude in the resonant zone at low speed.     

波浪作用下浮泥悬扬浓度特性研究

为研究不同波浪环境下,水底浮泥层产生泥沙悬扬后其浓度的分布特性,使用浊度计测定浊度的方法确定水体中泥沙的浓度,并在水槽实验中改变水深、浮泥厚度及造波机的频率和振幅,观察水槽中悬浮泥沙浓度的变化情况,获得水深、波浪频率、波幅以及浮泥厚度对底床泥沙悬扬的影响,分析泥沙浓度的垂向分布特征等。实验结果显示,水深对底床泥沙悬扬的影响最为显著,其他实验参数的影响均不十分显著。同时,通过垂向输沙平衡的分析,得到一个可描述泥沙垂向浓度分布的理论公式,并利用水槽实验结果进行验证。对比结果显示,理论公式所得曲线与实验结果曲线变化趋势一致,部分工况下,理论值稍稍偏大。