Wave impacts on structures with rectangular geometries: Part 1. Seawalls

This paper considers steep wave impact on seawalls of various geometries. A simple analytical model for the pressure impulse due to a wave of idealized geometry and dynamics is developed and applied to the following geometries: (a) vertical seawall with a berm, (b) vertical seawall with a ditch at its base and (c) vertical seawall with a block missing (damaged condition).The method uses eigenfunction expansions in each of the rectangular regions that satisfy some of the rigid surface conditions and a simplified free-surface condition. Their unknown coefficients are determined from the impact boundary condition, rigid wall conditions and by matching the values and the horizontal derivatives of the solutions in each rectangular region at their mutual boundary. The method yields the pressure impulse throughout the entire region. The overall impulse and moment impulse on the seawall and a simple model for the uprush of the spray jet after the impact are also presented. The effects of different impact regions and different geometries can therefore be quickly estimated and used to show trends in the results. It is shown that berms generally have a beneficial effect on reducing the impulse, moment impulse and uprush, but not the maximum pressure impulse on the seawall, whereas ditches are generally and sometimes strongly detrimental for all effects except uprush. A missing block in the seawall gives an almost constant or linearly decreasing value inside the gap (depending on the boundary condition applied at the rear of the gap being hard or soft respectively); the soft case can affect the pressure impulse on the front face of the seawall, thereby affecting the impulse and moment impulse.     

Wave impact pressure and its effect upon bodies lying on the sea bed

This paper is concerned with the very large, sudden pressures produced by water-wave impact on a vertical wall. Numerical and theoretical models are briefly described and we show that there are significant pressure gradients along an impermeable sea bed, away from the wall. This aspect of wave impact pressure has not previously been noted. The effects of such transient pressure gradients on bodies lying on the bed are examined in the light of pressure impulse theory. Our theoretical results indicate that bodies may be displaced by these pressure gradients when ordinary fluid drag is insufficient to move them. We discuss the impulse and the speed imparted to a rigid body lying within a region of pressure impulse which has constant horizontal gradient, and we show that the impulse is related to the body's volume, and shape. Analytic results are given for a hemi-ellipsoidal “boulder”, which is free to translate in a direction perpendicular to the wall. The analysis for the hemi-ellipsoid encompasses the special cases of a semi-circular cylinder and a semi-circular disc. The case of a circular cylinder which touches the bed is also discussed, and it is shown that there is a significant vertical impulse on the body in addition to the horizontal component of the impulse.     

Wall effect of underwater explosion load based on wave motion theories

Owing to the existence of the flow field boundary, the shock wave load near the boundary is different from the freefield shock wave load. In the present paper, the hull plate load subjected to underwater shock wave is investigated based onwave motion theories; in addition, the experimental study of the hull plate load is carried out. According to the theoreticalanalysis of the hull plate pressure, we find that the hull plate pressure oscillates repeatedly and decays rapidly with timepassing, the maximum hull plate pressure is 2/（1＋n） times the maximum free field pressure, where n is the ratio ofimpedance, and the impulse is much smaller than the free field impulse. Compared with the experimental study, thetheoretical results agree well with the experimental data.     

Numerical Simulation on the Impact of A Liquid Square on Rigid Plate and Liquid Layer

Fluids and structures impact is one of the common phenomena in nature, and it widely exists in engineering practice,including ship hydrodynamic slamming, wave impact on offshore platforms, plunging wave on coastal structures,emergency landing of aircrafts at sea as well as impact of ultra-cold droplets and ice lumps under aviation conditions.In this paper, a two dimensional (2-D) solver for Navier-Stokes equations is developed and applied in the numerical simulation of the impact on a rigid plate by a liquid square. The computational domain is discretized by Finite Volume Method (FVM). The Volume of Fluid (VOF) technique is used to track the free surface and the PiecewiseLinear Interface Construction (PLIC) is used for reconstruction. The Continuum Surface Force (CSF) model is used to account for the surface tension. The convective term and the diffusive term are upwind and centrally differenced respectively. The Inner Doubly Iterative Efficient Algorithm for Linked Equations (IDEAL) is used to decouple the pressure and velocity. Based on the proposed techniques, collapse of water column is simulated and convergence study is performed for the validation of the numerical solver. Then the impact of a free falling liquid body is simulated, and the effect of volume and initial height of the liquid body is analyzed. In addition, the impact on a plate with a liquid layer is also simulated to study the effect of falling height on a liquid floor.     

Three-dimensional liquid sloshing in a tank with baffles

A numerical model has been developed to study three-dimensional (3D) liquid sloshing in a tank with baffles. The numerical model solves the spatially averaged Navier-Stokes equations, which are constructed on a non-inertial reference frame having six degree-of-freedom (DOF) of motions. The large-eddy-simulation (LES) approach is employed to model turbulence by using the Smagorinsky sub-grid scale (SGS) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate volume-of-fluid (VOF) method is used to track the distorted and broken free surface. The baffles in the tank are modeled by the concept of virtual boundary force (VBF) method. The numerical model is first validated against the available analytical solution and experimental data for two-dimensional (2D) liquid sloshing in a tank without baffles. The 2D liquid sloshing in tanks with baffles is then investigated. The numerical results are compared with other results from available literatures. Good agreement is obtained. Finally, the model is used to study 3D liquid sloshing in a tank with vertical baffles. The effect of the baffle is investigated and discussed.     

Large Amplitude Magnetic Anomalies in the Northern Sector of the Powell Basin,NE Antarctic Peninsula

Magnetic profiles obtained during the Hesant 92/93 cruise with the R/V Hesperides show large amplitude anomalies (up to 1000 nT) along a 100 km wide band in the northern margin of the Powell Basin. The anomalies, which are also locally identified in the eastern and western margins, are attributed to the continuation of the two branches of the Antarctic Peninsula Pacific Margin Anomaly (PMA). Interactive modelling of two-dimensional bodies in four profiles oriented NNW-SSE allows us to determine the main features of the magnetic source bodies within the continental crust. These are elongated in a N60/degE trend, and their base is located at a depth exceeding 15 km. Equivalent magnetic susceptibilities mostly between 0.07 and 0.1 (SI) are obtained. These values are consistent with the hypothesis that remanent magnetisation of the magnetic source bodies is sub-parallel to the present geomagnetic field (norÍmally magnetised). The general trends of the bathymetry a nd the geometry of the acoustic basement on multichannel seismic profiles are consistent with the upper surface of magnetic bodies. In order to match the observed anomalies it is also necessary to consider a second tabular shaped body with induced magnetisation in almost all the profiles, which could represent layers 2 and 3 of the oceanic crust of the Powell Basin. Three different geometries of connection between the anomalies in the Powell Basin margins and the PMA branches are discussed. The most plausible one is the occurrence of two branches, although they are closer together than in the Bransfield Strait. The northern branch would continue along the fragments of continental crust of the South Scotia Ridge located at the northern boundary of the Powell Basin, whereas the southern branch would be located only in the eastern and western passive margins of the Powell Basin. The apparent splitting of the southern branch of the anomalous body indicates that it was emplaced before Oligo cene times, when the opening of this basin occurred, and that it was subsequently fragmented during the Cenozoic. A possible time of formation of the PMA body would be during the long Cretaceous normal polarity interval, which also coincides with a peak in magmatic activity along the Antarctic Peninsula.     

Application of a 2D harmonic polynomial cell (HPC) method to singular flows and lifting problems

Further developments and applications of the 2D harmonic polynomial cell (HPC) method proposed by Shao and Faltinsen [22] are presented. First, a local potential flow solution coupled with the HPC method and based on the domain decomposition strategy is proposed to cope with singular potential flow characteristics at sharp corners fully submerged in a fluid. The results are verified by comparing them with the analytical added mass of a double-wedge in infinite fluid. The effect of the singular potential flow is not dominant for added mass and damping, but the error is non-negligible when calculating mean wave loads using direct pressure integration. Then, the double-layer nodes technique is used to simulate a thin free shear layer shed from lifting bodies, across which the velocity potential is discontinuous. The results are verified by comparing them with analytical results for steady and unsteady lifting problems of a flat plate in infinite fluid. The latter includes the Wagner problem and the Theodorsen functions. Satisfactory agreement with other numerical results is documented for steady linear flow past a foil and beneath the free surface.     

The pressure impulse in a fluid saturated crack in a sea wall

When a wave breaks against a sea wall containing a crack, such as might exist within the blockwork, pressure pulses can travel through the fluid and propagate into the crack. This can cause high stresses to act on the sides and roof of the crack and may even cause the constituent blocks to move. The Pressure Impulse, P, is used to model the effect of wave impact against a wall in which there is a fluid filled crack. A two-dimensional field equation is derived for P that is applicable in plane cracks of non-uniform, narrow width. This is solved for several geometries relating to cracks between constituent blocks of sea walls, in order to compare the impulsive forces with the gravitational force on a block. It is shown that a large block can be lifted due to the impulse exerted by the fluid in a crack beneath it.     

An efficient hybrid integral-equation method for point-absorber wave energy converters with a vertical axis of symmetry

To assist in the prototyping and controller design of point-absorber wave energy converters (WECs), an easy-to-implement hybrid integral-equation method is presented for computing the frequency-domain hydrodynamic properties of bodies with a vertical axis of symmetry in waves. The current hybrid method decomposes the flow domain into two parts: an inner domain containing the body and an outer domain extending to infinity. The solution in the inner domain is computed using the boundary-element method, and the outer-domain solution is expressed using eigenfunctions. Proper matching at the domain boundary is achieved by enforcing continuity of velocity potential and its normal derivative. Body symmetry allows efficient computation using ring sources in the inner domain. The current method is successfully applied to three different body geometries including a vertical truncated floating cylinder, the McIver toroid, and the coaxial-cylinder WEC being developed in the authors’ laboratory. In particular, the current results indicate that, by replacing the flat bottom of the coaxial-cylinder WEC with the Berkeley-Wedge (BW) shape, viscous effect can be significantly reduced with only minor negative impact on wave-exciting force, thus increasing WEC efficiency. Finally, by comparing to experimental measurements, the current method is demonstrated to accurately predict the heave added mass and wave-exciting force on the coaxial-cylinder WEC with BW geometry. If a viscous damping correction factor is used, the heave motion amplitude can also be accurately computed.     

Elastic response of catamaran wetdeck to liquid impact

The impact of an elastic plate onto the compressible fluid without free surface deformation is considered. The ability of the liquid volume to be deformed is geometrically limited which leads to severe impact conditions. The present analysis is focused on the stresses in the plate and the hydrodynamic loads under the impact. The motivation for this research comes from ship hydrodynamics, where the hulls of a catamaran restrict the liquid outflow and the water impacts onto the wetdeck. The influence of the air on the impact process is investigated. The analysis did not reveal any great advantage of utilizing the air-cushion effect or ejection of air into the water near the impact region to prevent high stresses in the elastic plate. It was found that in the problem considered, the stress peaks far from the plate centre and the one-mode approximation does not provide correct information about the stress level.     

虚拟海洋场景构建与技术研究

随着传统GIS应用向三维立体方向发展,三维虚拟场景在信息认知、空间规划管理、时空挖掘与分析等方面的应用逐渐成为研究热点。本文基于Skyline平台集成遥感影像数据、地形数据、纹理特征数据、倾斜摄影测量数据、三维全景数据和三维模型数据,构建了集虚拟海岛海岸带模型、虚拟海底地形模型和虚拟水体模型于一体的虚拟海洋场景,并针对场景构建中涉及的多源影像数据集成技术、多尺度影像实时切片技术和基于OGC服务的数据集成技术开展了研究。构建形成的虚拟海洋场景在海洋应用服务系统中开展了实践应用。     

Wave impacts on structures with rectangular geometries: Part 2 decks,baffles and seawalls with impermeable or porous surfaces

This paper considers wave impacts on baffles, on baffles or decks adjacent to a vertical wall, and on porous seawalls and/or sea beds. For seawalls and vertical baffles, impacts can occur in steep waves, whilst a deck can be struck from below by a rising wave crest either in open sea or in a tank with standing waves (sloshing). A simple analytical model for the pressure impulse, P, due to a wave of idealized geometry and dynamics is developed and applied to the following geometries with impermeable surfaces:

• •horizontal wave impact onto a vertical wall with a deck at the waterline,
• •vertical wave impact under a deck in the same configuration (equivalent to vertical water impact of a horizontal plate),
• •horizontal wave impact onto a surface-piercing vertical baffle in open sea,
• •as for 3. but with the baffle in front of a wall,
• •as for 4. but with a deck extending from the vertical wall to the baffle,
• •bottom-mounted baffle in front of a wall with impact occurring on the wall.

We also consider cases that complement part 1 of this paper to include the effect on impacts on a seawall with a porous sea bed and/or sea wall with/without a berm. Finally we reconsider case 3) above but with a porous baffle.The method uses eigenfunction expansions in each of the rectangular regions that satisfy some of the impermeable or porous surface conditions, and a simplified free-surface condition. Their unknown coefficients are determined from the impact boundary condition, impermeable or porous boundary conditions and by matching the solutions, in any two neighbouring rectangles, along their common boundary. Although the fluid motion is treated rather crudely, the method yields the pressure impulse throughout the entire region. Impulses, I, and moment impulses, M, on all or parts of the structure are also presented.     

Modelling a spade rudder as a hollow two-way tapered Kirchhoff’s plate : free dry and wet vibration study with numerical verification

A semi-analytical approach to free dry and wet vibration of a trapezoidal, 2-way tapered, pivoted hollow spade rudder is presented. The rudder is modeled as a hollow Kirchhoff’s plate, with a NACA0018 profile chord section. The rudder pivot is modeled as a combination of a translational spring and a rotational spring. The span-wise and chord-wise non-uniform beam vibration is first analyzed by the Rayleigh-Ritz method, to establish the non-uniform beam modeshapes, which act as admissible functions to the Galerkin’s method for plate vibration. Eigenvalue analysis generates the plate natural frequencies and the plate modeshapes. Alternately, uniform beam modeshapes themselves are used as admissible functions into the Galerkin’s method. Frequencies are analyzed for various pivot positions, taper ratios, and NACA sections. For the wet vibration, constant strength source distribution technique is used to generate the added mass of a 2D aerofoil. Also, 3D panel method is used to generate the modal added masses, and hence the wet natural frequencies. The added mass coefficient is generated for various aerofoil fineness ratios, pivot fixities, taper ratios, aspect ratios.     

河道砂岩体地震反射特征分析

按河道形态,河流分为４类：（１）顺直河;（２）曲流河;（３）辫状河;（４）网状河。根据河道砂岩体主体的宽（ｗ）与（ｈ）高之比,河道砂岩体分为带状砂岩体（ｗ∶ｈ小于１５）和席状砂岩体（ｗ∶ｈ大于１５）。在参考前人资料的基础上,总结了在横切河道的地震剖面上河道砂岩体的反射形态、结构及振幅变化。重点介绍了曲流河内侧沙洲地震勘探,以及三维地震勘探技术在寻找河道砂岩体方面的应用。并强调指出,在河道砂岩体地震勘探中,应当加强地震资料与钻井资料、测井资料的结合。     

Desorption of Hydrophobic Organic Chemicals from Fragment-Type Microplastics

Microplastics provide an important medium for hydrophobic organic chemicals (HOCs), and the desorption of HOCs from microplastics is an important process for the dynamics of HOCs associated with microplastics. Although desorption kinetics has been studied for microplastics with ideal geometries, most of the microplastics isolated from the environment are irregular fragment-type microplastics. This study investigated the desorption of six model HOCs from polyethylene (PE) and polypropylene (PP) fragments to artificial seawater and compared the results with those predicted assuming ideal geometries (e.g., sphere and infinitely flat sheet) of microplastics. The experimental desorption was explained well by the model predictions with the characteristic radius for a sphere and the thickness for a plate estimated from visual imaging. The mass fraction remaining at the later stage of desorption was higher than the model simulation assuming a single characteristic length, likely due to the heterogeneity of the particle size distribution. Although there are inevitable uncertainties, it would be useful to assign a single length dimension in desorption modeling for even fragment-type microplastics, especially for the estimation of desorption half-life.     

Free fall water entry of a wedge tank into calm water in three degrees of freedom

The hydrodynamic problem of a two dimensional wedge tank filled with liquid entering a calm water surface is analysed based on the incompressible velocity potential theory. The motion effect of inner liquid on the entry process is investigated through comparison with the result containing equivalent solid mass or the liquid being frozen. The problem is solved through the boundary element method in the time domain. Two separated computational regions are constructed. One is the inner domain for the internal liquid, and the other is the outer open domain for the open water. The former is solved in the physical coordinate system, and the latter is solved in a stretched coordinate system. The solutions of two separated domains are connected through the motion of the body. The auxiliary function method is extended to decouple the nonlinear mutual dependence between fluid loads from two separated domains and the body motion. Detailed results for wedge motion, external impact pressure and free surface, and for internal pressure, free surface deformation and liquid motion are provided. Through comparison with the results of a wedge tank with frozen ice, in-depth discussion on the effect of the inner liquid is provided.     

Numerical Analysis of the Behavior of A New Aeronautical Alloy (Ti555-03) Under the Effect of A High-Speed Water Jet

In this paper, we present a numerical simulation of a water jet impacting a new aeronautical material Ti555-03 plate.The Computational Fluid Dynamics(CFD) behavior of the jet is investigated using a FV(Finite Volume) method.The Fluid–Structure Interaction(FSI) is studied using a coupled SPH(Smoothed Particle Hydrodynamics)-FE(Finite Element) method. The jets hit the metal sheet with an initial velocity 500 m/s. Two configurations which differ from each other by the position(angle of inclination) of the plate relatively to the axis of revolution of the jet inlet are investigated in this study. The objective of this study is to predict the impact of the fluid produced at high pressure and high speed especially at the first moment of impact. Numerical simulations are carried out under ABAQUS. We have shown in this study that the inclination of the titanium alloy plate by 45° stimulates the phenomenon of recirculation of water. This affects the velocity profile, turbulence and boundary layers in the impact zone. The stagnation zone and the phenomenon of water recirculation are strongly influenced by the slope of the plate which gives a pressure gradient and displacement very important between the two configurations. Fluctuations of physical variables(displacement and pressure) prove the need for a noise and vibratory study. These predictions will subsequently be used for the modeling of the problem of an orthogonal cut in a high-speed machining process assisted by high-pressure water jet.     

Wave types of landslide generated impulse waves

Subaerial landslide generated impulse waves were investigated in a prismatic wave channel. Seven governing parameters, namely the still water depth, slide impact velocity, slide thickness, bulk slide volume, bulk slide density, slide impact angle, and grain diameter, were systematically varied. The generated impulse waves are nonlinear, intermediate- to shallow-water waves involving a small to considerable fluid mass transport. The Stokes wave, cnoidal wave, solitary wave, and bore theories were applied to describe the observed maximum waves. The theoretical and observed features of these four wave types are highlighted. A diagram allows to predict the wave type directly as a function of the slide parameters, the slide impact angle, and the still water depth.     

Multi-vessel seakeeping computations with linear potential theory

The wave-induced motion of two vessels in close proximity is studied using traditional two-dimensional (2D) and three-dimensional (3D) boundary element methods. Added mass, damping, and the behavior of the free surface between the vessels are examined in some detail. As expected based on previous work, the response of the water between the vessels is found to have a profound effect on the hydrodynamic forces. At “critical frequencies” corresponding to standing waves between the hulls, the hydrodynamic forces undergo significant drastic changes. The 2D and 3D results are compared, and the effects of a skew angle between the vessels are examined. Some of the consequences of the behavior at the critical frequencies for simulations in the time domain are examined, the most significant of which is a very lightly damped impulse response.     

Effect of a submerged plate on the near-bed dynamics underincoming waves in deep water conditions

It is well known that wave induced bottom oscillations become more and more negligible when the water depth exceeds half the wavelength of the surface gravity wave. However, it was experimentally demonstrated for regular waves that the bottom pressure oscillations at both first and second wave harmonic frequencies could be significant even for incoming waves propagating in deep water condition in the presence of a submerged plate [16]. For a water depth h of about the wavelength of the wave, measurements under the plate (depth immersion of top of plate h/6, length h/2) have shown bottom pressure variations at the wave frequency, up to thirty times larger than the pressure expected in the absence of the plate. In this paper, not only regular but also irregular wave are studied together with wave following current conditions. This behavior is numerically verified by use of a classical linear theory of waves. The wave bottom effect is explained through the role of evanescent modes and horizontally oscillating water column under the plate which still exist whatever the water depth. Such a model, which allows the calculation of the velocity fields, has shown that not only the bottom pressure but also the near bed fluid velocity are enhanced. Two maxima are observed on both sides of the location of the plate, at a distance of the plate increasing with the water depth. The possible impact of such near bed dynamics is then discussed for field conditions thanks to a scaling based on a Froude similarity. It is demonstrated that these structures may have a significant impact at the sea bed even in very deep water conditions, possibly enhanced in the presence of current.