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1.
The problem of a two-dimensional finite-width wedge entering water near a freely floating body is considered through the velocity potential theory for the incompressible liquid with the fully nonlinear boundary conditions on the free surface. The problem is solved by using the boundary element method in the time domain. The numerical process is divided into two phases based on whether the interaction between the wedge and floating body is significant. In the first phase, when the single wedge enters water at initial stage, only a small part near its tip is in the fluid, the problem is studied in a stretched coordinate system and the presence of the floating body has no major effect. In the second phase, the disturbance by water entry of the wedge has reached the floating body, and both are considered together in the physical system. The auxiliary function method is adopted to decouple the nonlinear mutual dependence between the motions of the wedge and floating body, both in three degrees of freedom, and the fluid flow, as well as the interaction effects between them. Case studies are undertaken for a wedge entering water in forced or free fall motion, vertically or obliquely. Results are provided for the accelerations, velocities, pressure distribution and free surface deformation, and the interaction effects are discussed. 相似文献
2.
A two-dimensional finite wedge entering water obliquely in freefall with three degrees of freedom is considered through the velocity potential theory for the incompressible liquid. The problem is solved by using the boundary element method in the time domain. The scheme of the stretched coordinate system is adopted at the initial stages when only a small part of the wedge near its tip has entered water. The auxiliary function method is adopted to decouple the nonlinear mutual dependence between the body motions in three degrees of freedom and the fluid flow. When the liquid has detached from the knuckle of the wedge, the free jet is treated through the momentum equation. The developed method is verified through existing results for one degree of freedom in vertical motion. Various case studies are undertaken for a wedge entering water vertically, obliquely and with rotational angles. Results are provided the accelerations, velocities, pressure distribution and free surface deformation, and the physical implications are discussed. 相似文献
3.
We studied the structure of the surface perturbations generated by a stratified flow of an ideal fluid of finite depth around underwater obstacles. We consider a cylinder modeled by a point dipole localized near the density interface both above and below the interface. It is shown that density jumps characteristic of the marine medium significantly influence the formation and variability of the structure of the surface perturbations generated during a fluid??s flowing around an underwater obstacle. The results are compared with the data of the previous model calculations made by the authors for an infinite flow around an obstacle [4]. Significant differences between them are revealed, which should be taken into account in the solution of practical problems, for example, monitoring of coastal marine basins. 相似文献
4.
The interaction of a linear water wave in a channel of constant depth impinging on a vertical thin porous breakwater with a semi-submerged and fixed rectangular obstacle in front of it is investigated. The water follows conventional assumptions as an irrotational, incompressible, and inviscid fluid flow. The solid skeleton of the porous breakwater is assumed to be rigid and thin. We get the general solution by applying the eigenfunction expansion method and solve it with a numerical matrix solver. In order to verify the correctness of the general solution, wave flume experiments are conducted. Two asymptotic solutions for long and short incoming waves are also obtained. Both experiments and asymptotic solutions show good agreement with the general solution at proper limits. Finally, the effect of the fixed obstacle on the porous breakwater is discussed, and a general guide of how to obtain better energy trapping is delivered. 相似文献
5.
The effects of chaotic advection in a three-layer ocean model 总被引：1，自引：0，他引：1
A three-layer model of an inviscid incompressible fluid is considered in a quasigeostrophic approximation within the concept
of background currents. A singular topographic obstacle yields the formation of a vortical motion in the layers. It is always
present in the lower layer, while in the upper and middle layers it can be observed only at certain velocities of the external
flows. Three current functions describing a singular topographic flow in the lower layer and two regular flows in the upper
layer are obtained. In case of a nonstationary harmonic perturbation of the external flow, chaotic particle transport is possible
in these flows. This paper analyzes the chaotic properties of this model. Depending on the type of unperturbed frequency curves
of the fluid particle revolution is determined by the model parameters (stratification) and the incident flow, the patterns
of the chaotic transport will substantially differ. Two of the limiting dependences of the revolution frequency are determined,
namely, the dependence for a singular vortex and that for a regular vortex with the smallest area. Other dependences are intermediate
ones. Two limiting types of revolution frequencies determine the two different scenarios of chaotic advection. 相似文献
6.
《Coastal Engineering》2005,52(3):257-283
Vortex generation and evolution due to flow separation around a submerged rectangular obstacle under incoming cnoidal waves is investigated both experimentally and numerically. The Particle Image Velocimetry (PIV) technique is used in the measurement. Based on the PIV data, a characteristic velocity, phrased in terms of incoming wave height, phase speed, dimension of the obstacle, and a local Reynolds number are proposed to describe the intensity of vortex. The numerical model, which solves the two dimensional Reynolds Averaged Navier Stokes (RANS) equations, is used to further study the effects of wave period on the vortex intensity. Measurements for the mean and turbulent velocity fields further indicate that the time history of the intensity of fluid turbulence is closely related to that of the vortex intensity. 相似文献
7.
We study the interactions between a non-breaking solitary wave and a submerged permeable breakwater experimentally and numerically. The particle image velocimetry (PIV) technique is employed to measure instantaneous free surface displacements and velocity fields in the vicinity of a porous dike. The porous medium, consisting of uniform glass spheres, is mounted on the seafloor. Due to the limited size of each field of view (FOV) for high spatial resolution purposes, four FOVs are set in order to form a continuous flow field around the structure. Quantitative mean properties are obtained by ensemble averaging 30 repeated instantaneous measurements. The Reynolds decomposition method is then adopted to separate the velocity fluctuations for each trial to estimate the turbulent kinetic energy. In addition, a highly accurate two-dimensional model with the volume of fluid interface tracking technique is used to simulate an idealized volume-averaged porous medium. The model is based on the Volume-Averaged Reynolds Averaged Navier–Stokes equations coupled with the non-linear k–ε turbulence closure solver. Comparisons are performed between measurements and numerical results for the time histories of the free surface elevation recorded by wave gauges and the spatial distributions of free surface displacement with the corresponding velocity and turbulent kinetic energy around the permeable object imaged by the PIV system. Fairly good agreements are obtained. It is found that the measured and modeled turbulent intensities on the weather side are much larger than those on the lee side of the object, and that the magnitude of the turbulent intensity increases with increasing wave height of a solitary wave at a constant water depth. The verified numerical model is then used to estimate the energy reflection, transmission and dissipation using the energy integral method by varying the aspect ratio and the grain size of the permeable obstacle. 相似文献
8.
Experiments and numerical methods are developed to investigate the water entry of a freefall wedge with a focus on the evolution of the pressure on the impact sides (the side contacting water) and the top side (the dry side on the top of the wedge), evolution of the global hydrodynamic loads, evolution of the air–water interface, and wedge motion. It is found that a typical water entry of a freefall wedge can be divided into slamming, transition, collapse and post-closure stages. A single-fluid numerical model is presented to simulate the first three stages. The results are compared to experiments and good agreements are obtained. A two-fluid BEM is proposed to investigate the influence of the air flow before the closure of the cavity created on the top of the wedge. It is found that for the closure of the 2D cavity, the air flow starts to play an important role just before closure but due to the short duration, the influence of air flow on the body velocity and configuration of the air–water interface is limited. 相似文献
9.
《Coastal Engineering》2001,44(1):13-36
Interactions between a solitary wave and a submerged rectangular obstacle are investigated both experimentally and numerically. The Particle Image Velocimetry (PIV) technique is used to measure the velocity field in the vicinity of the obstacle. The generation and evolution of vortices due to flow separation at the corners of the obstacle are recorded and analyzed. It is found that although the size of the vortex at the weatherside of the obstacle is smaller than that at the leeside, the turbulence intensity is, however, stronger. A numerical model, based on the Reynolds Averaged Navier–Stokes (RANS) equations with a k–ϵ turbulence model, is first verified with the measurements. Overall, the agreement between the numerical results and laboratory velocity measurements is good. Using the RANS model, a series of additional numerical experiments with different wave heights and different heights of the rectangular obstacle are then performed to test the importance of the energy dissipation due to the generation of vortices. The corresponding wave transmission coefficient, the wave reflection coefficient and the energy dissipation coefficient are calculated and compared with solutions based on the potential flow theory. As the height of the obstacle increases to D/h=0.7, the energy dissipation inside the vortices can reach nearly 15% of the incoming wave energy. 相似文献
10.
We study wave perturbations appearing at the surface of a two-layer fluid flowing around an underwater obstacle in the lower layer of the fluid. The obstacle is modeled as a point source. A class of asymptotic solutions was obtained that demonstrate that realistic conditions of the open sea and the given parameters of the source in the neighborhood of the source of hydrodynamic perturbations allow for the formation of two types of surface waves. The waves of the first type only slightly depend on the stratification, and, in the conditions of the real sea, they are almost not observed. The characteristics of the second type of waves were repeatedly recorded in field experiments during radar and optical monitoring of the sea surface. 相似文献
11.
Impact problems associated with water entry have important applications in various aspects of naval architecture and ocean engineering. Estimation of hydrodynamic impact forces especially during the first instances after the impact is very important and is of interest. Since the estimation of hydrodynamic impact load plays an important role in safe design and also in evaluation of structural weight and costs, it is better to use a reliable and accurate prediction method instead of a simple estimation resulted by analyzing methods. In landing of flying boats, some phenomena such as weather conditions and strong winds can cause asymmetric instead of symmetric descent. In this paper, a numerical simulation of the asymmetric impact of a wedge, as the step of a flying boat, considering dynamic equations in two-phase flow is taken into account. The dynamic motion of the wedge in two-phase flow is solved based on finite volume method with volume of fluid (VOF) scheme considering dynamic equations. Then the effects of different angles of impact and water depth on the velocity change and slamming forces in an asymmetric impact are investigated. The comparison between the simulation results and experimental data verifies the accuracy of the method applied in the present study. 相似文献
12.
M. S. Permyakov V. I. Semykin N. P. Malikova 《Izvestiya Atmospheric and Oceanic Physics》2018,54(5):423-429
The generalized two-dimensional vortex equation is derived for an incompressible viscous fluid in a rotating system for a vertically averaged flow taking into account the variability of the boundary layer characteristics. The resulting equation contains parameters and their spatial derivatives determined by the second moments of functions describing the vertical profiles of the flow components. Numerical experiments demonstrate the influence of the boundary-layer horizontal inhomogeneity on the evolution of the vorticity field of a pair of atmospheric vortices. 相似文献
13.
O. A. Druzhinin V. V. Papko D. A. Sergeev Yu. I. Troitskaya 《Izvestiya Atmospheric and Oceanic Physics》2006,42(5):615-626
The far-wake flow past a sphere towed in a fluid with high Reynolds and Froude numbers and with a pycnocline-form salt-density stratification is studied in a laboratory experiment based on particle image velocimetry and in numerical and theoretical modeling. In the configuration under consideration, the axis of sphere towing is located under a pycnocline. Flow parameters, the profiles of density and average velocity, and the initial field of velocity fluctuation in numerical modeling are specified from the data of the laboratory experiment. The fields of fluid velocity at different times and the time dependences of integral parameters of wake flow, such as the average velocity at the axis and the transverse width of the flow, are obtained. The results of numerical modeling are in good qualitative and quantitative agreement with the data of the laboratory experiment. The results of the laboratory experiment and numerical modeling are compared to the predictions of a quasi-linear and quasi-two-dimensional theoretical model. The time evolution of both the average velocity at the axis and the transverse width of the wake is obtained with the model and is in good agreement with the experimental data. The results of numerical modeling also show that, under the effect of velocity fluctuation in the wake, internal waves whose spatial period is equal to the characteristic period of the wake’s vortex structure are excited efficiently in the pycnocline. 相似文献
14.
Wedge entry into initially calm water 总被引：2，自引：0，他引：2
Martin Greenhow 《Applied Ocean Research》1987,9(4):214-223
This paper presents results of calculations based on the Cauchy's theorem method of Vinje and Brevig1 for the two-dimensional entry of wedges of various angles into initially calm water. The problem has a long history which is briefly reviewed in the introduction, and significant progress has been made with both linear theories (valid for low entry speed) and with theories which treat the free surface conditions exactly but with the assumptions of zero gravity and constant speed of entry. This simplifies the problem to one which is self-similar in dimensionless space variables ξ = x/vt and η = y/vt and this has a number of consequences. For wedges with half-angles up to about 45° and with high entry speeds, the numerical approach, which includes gravity, validates these assumptions and the agreement between both free surface displacements and pressure distributions on the wetted wedge surface is excellent except in the region of the jet of fluid which rises up the side of the wedge. Because the potential flow initial value problem is singular at the intersection of the free surface and wedge surface, exact numerical resolution of the jet is not possible. Nevertheless, the rest of the fluid motion is insensitive to the treatment of the jet, which itself may be calculated quite realistically. Of particular interest (but little practical relevance) is the pressure on the upper part of the wedge surface (in the jet region) which according to self-similar theories is very small but positive, but which is calculated to be small but negative by the numerical scheme. This effect, which is enhanced when gravity is included, is insensitive to the numerical resolution of the jet and suggests that the jet may separate from the wedge surface, the new intersection point being where the pressure vanishes on the wedge surface. A modified numerical scheme allows this to happen and the results are in qualitative agreement with the experiments by Greenhow and Lin.2
The numerical method presented here is extremely versatile and a number of other effects may be explored. Examples of transient motion, non-constant speed of entry, oblique entry and complete penetration of the surface so that a cavity is formed behind the wedge are presented. 相似文献
15.
We studied the surface perturbations of a two-layer ideal fluid induced by a flow past a submerged obstacle (simulated by
a point dipole) in the vicinity of the density-jump layer. It is shown that the formation of two different types of surface
waves is possible behind the flowed past obstacle in the real conditions of the open sea. The comparison of the amplitudes
of the surface perturbations induced by the obstacle located above and below the density jump revealed their significant differences,
which seems to be important for the use of this effect in practical problems. 相似文献
16.
《Coastal Engineering》2006,53(5-6):441-462
The structure of large-scale turbulence under a broken solitary wave on a 1 in 50 plane slope was studied. Three-component velocity measurements were taken at different heights above a smooth bed in the middle surf zone using an acoustic Doppler velocimeter. The measured data showed that turbulent velocity components were well correlated in the middle part of the water column. The velocity correlations could be produced by an oblique vortex similar to the obliquely descending eddy observed previously by other investigators. The vertical distributions of the relative values of the components of the Reynolds stress tensor showed that the structure of turbulence evolved continuously between the free surface and the bottom. The evolution was related to transition from two-dimensional to three-dimensional flow structures and the effect of the solid bottom on flow structures. Time histories of measured turbulent kinetic energy and turbulence stresses showed episodic turbulent events near the free surface but more sporadic turbulence in the lower layer. Large or intense turbulent events were found to have short duration and time lag relative to the wave crest point. These events also maintained good correlations between the turbulence velocity components close to the bottom.Instantaneous turbulent velocity fields were measured near the bottom at the same cross-shore location by using a stereoscopic particle image velocimetry system. These measurements showed that the near-bed flow field was characterized by large-scale, coherent flow structures that were the sources of most of the turbulent kinetic energy and turbulence stresses. The types of organized flow structures observed included vortices and downbursts of turbulence descending directly from above, lateral spreading of turbulent fluid along the bed, and formation of vortices in shear layers between fluid streams. A common feature of the organized flow structures near the bed was the large turbulence velocities in the longitudinal and transverse directions, which reflected the influence of a solid bottom on the breaking-wave-generated turbulence arriving at the bed. 相似文献
17.
Waldemar Magda 《Ocean Engineering》1997,24(6):551-576
A two-dimensional finite-element simulation of the wave-induced hydrodynamic uplift force acting on a submarine pipeline buried in sandy seabed sediments subject to continuous loading of sinusoidal surface waves is presented. Neglecting inertia forces, a linear-elastic stress-strain relationship for the soil and Darcy's law for the flow of pore fluid are assumed. The model takes into account the compressibility of both components (i.e., pore fluid and soil skeleton) of the two-phase medium.The results of numerical analysis are presented and discussed with respect to soil and pore fluid parameters where special attention is paid to the question of soil saturation conditions. The meaning of the results is also related to surface wave conditions. As a general conclusion, the practical, engineering recommendation is given in order to make a realistic, safe and economic estimation of the wave-induced uplift force acting on a buried submarine pipeline. 相似文献
18.
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. 相似文献
19.
Naga fold thrust belt is an emerging destination for petroleum exploration in eastern India. It is a thin skinned FTB where new initiatives are being taken after a long gap of initial discoveries. In absence of sufficient drilling or quality seismic data in the southern part of the fold thrust belt, fluid pressure regimes remain largely speculative. Using the concept and the formulation for efficient coefficient of basal friction, we have revisited the method and concept of pressure-dependent Coulomb wedge theory for thin skinned thrust belts for deriving the fluid pressure ratio in Naga fold thrust belt. The efficient coefficient of basal friction on the decollement and the fluid ratio of Naga fold thrust belt are estimated to be 0.22 and 0.85 respectively. This indicates an overpressure situation in the wedge. This method of estimating basal friction and fluid pressure is more case-specific and can be obtained from the data of thrust initiation angle and thrust spacing. 相似文献
20.
Kiriaki Haralambidou Georgios SylaiosVassilios A. Tsihrintzis 《Estuarine, Coastal and Shelf Science》2010
The dynamics of a seasonally formed salt-wedge propagating along the micro-tidal channel of Strymon River estuary, Northern Greece, and its consequences on river water quality, are thoroughly studied through intensive sampling campaigns. The wedge is developed at the downstream river part, under the summer limited freshwater discharge conditions (Q < 30 m3/s). The geometric features of the wedge (length and thickness) appeared directly related to Strymon River discharge. A maximum intrusion length of 4.7 km along Strymon River estuary was observed under minimum river discharge of almost 6 m3/s. Relations produced from in situ data illustrate that limited river flow expands the wedge horizontally, reducing its vertical dimension, while higher flows lead to increased wedge thickness. Estuarine flushing time ranges between 0.2 and 1.5 days, exponentially dependent on Strymon River discharge. Wedge velocities depicted tidal asymmetry between tidal phases, with consistent inward motion, even under the ebb tidal stage. Strong vertical stratification prevails throughout the tidal cycle, proving the limited vertical mixing between the two layers, although higher interfacial stresses are produced in ebb. Bottom topography plays an interesting role in wedge propagation, as the presence of an underwater sill either prevents saline intrusion during flood or isolates the front of the wedge from its core at the ebb. Ecological consequences of salt-wedge propagation in Strymon River estuary are the frequent evidence of bottom hypoxic conditions and the increased TSS levels, leading to the occurrence of a turbidity maximum at the tip of the salt-wedge. Higher BOD and ammonium levels were mostly observed at the river end, associated to point and non-point pollution sources. Nitrates and silicates were found associated with freshwater fluxes, while ammonia levels were related to saline intrusions. The reduced phosphorus freshwater fluxes, resulting from phosphorus uptake at the upstream reservoir (Kerkini Lake) and the increased bottom turbidity induced by the salt-wedge seem responsible for the limited chlorophyll-a levels along Strymon River estuary. 相似文献