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1.
A nonlinear liquid sloshing inside a partially filled rectangular tank has been investigated. The fluid is assumed to be homogeneous, isotropic, viscous, Newtonian and exhibit only limited compressibility. The tank is forced to move harmonically along a vertical curve with rolling motion to simulate the actual tank excitation. The volume of fluid technique is used to track the free surface. The model solves the complete Navier–Stokes equations in primitive variables by use of the finite difference approximations. At each time step, a donor–acceptor method is used to transport the volume of fluid function and hence the locations of the free surface. In order to assess the accuracy of the method used, computations are verified through convergence tests and compared with the theoretical solutions and experimental results. 相似文献
2.
Three-dimensional fully nonlinear waves generated by moving disturbances with steady forward speed without motions are solved using a mixed Eulerian–Lagrangian method in terms of an indirect boundary integral method and a Runge–Kutta time marching approach which integrates the fully nonlinear free surface boundary conditions with respect to time.A moving computational window is used in the computations by truncating the fluid domain (the free surface) into a computational domain. The computational window maintains the computational domain and tracks the free surface profile by a node-shifting scheme applied within it. An implicit implement of far field condition is enforced automatically at the truncation boundary of the computational window.Numerical computations are applied to free surface waves generated by Wigley and Series 60 hulls for the steady problem. The present numerical results are presented and compared with existing linear theory, experimental measurements, and other numerical nonlinear computations. The comparisons show satisfactory agreements for these hydrodynamic problems. 相似文献
3.
In the present study, three-dimensional sloshing phenomena occurring in liquid cargo tanks are numerically simulated. The Navier-Stokes equations and continuity equation are used for the governing equations, and solved with a finite difference method in a rectangular fixed staggered mesh system. The positions of free surface are defined by the Marker density method satisfying the free-surface boundary conditions, and the flows of the gas and liquid regions are simulated simultaneously. The irregular leg length and star method is employed on the cells near the free surface for the computations of pressure. The computation results are compared with other experimental results to verify the consistency of the present numerical method, and the agreements are reasonably good. Furthermore, the flow characteristics inside a partially filled liquid tank of a real sized ship oscillating regularly and irregularly are computed to verify the possibility of practical application of the present method. 相似文献
4.
We perform the numerical analysis of the influence of variations of the geometric characteristics of an annular basin of variable depth on the space structure of wave motions generated by the oscillations of atmospheric pressure periodic as functions of time. Within the framework of the linear theory of long waves, we determine (with regard for the action of the Coriolis force) the ranges of periods inside which the free surface of liquid has a fixed number of nodes. The dependence of these ranges on the parameters of the basin is established and the shapes of the free-surface profiles are compared for circular and axisymmetric waves.Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 14–23, September–October, 2004.This revised version was published online in May 2005 with corrections to cover date. 相似文献
5.
A three-dimensional numerical model is developed in this study to investigate the problem of wave–current–body interaction. The model solves the spatially averaged Navier–Stokes equations. Turbulence effects are modeled by a subgrid-scale (SGS) model using the concept of large eddy simulation (LES). The model is employed to study the wave–current interaction with a square cylinder that is mounted on the bottom and vertically pierces the free surface. The force analysis demonstrates that the presence of waves can reduce both the strength and frequency of vortex shedding induced by a uniform current due to the nonlinear wave–current interaction. The free surface elevation, strain rates of the mean flow, and eddy viscosity are found to closely correlate with the mechanism of vortex shedding. It is also shown that when the vortex shedding is neglected in the calculation such as by the potential flow approach, one may significantly underestimate the magnitude of in-line force. The energy spectral analysis reveals that there exist initiating, growing, and decaying regions for shedding vortices around the cylinder. In the vortex initiating region, both coherent and turbulent structures are nearly two-dimensional that become three-dimensional in the vortex growing region. The kinetic energy of both coherent and turbulent motions is dissipated in the vortex decaying region, within which the mean flow gradually returns back to two-dimensional. 相似文献
6.
In this paper, a numerical model is established for simulating the wave forces on a submarine pipeline. A set of two-dimensional Navier–Stokes equations is discretized numerically with a finite volume method in a moving mesh system. After each time step, the mesh is modified according to the changed wave surface boundary. The deffered correction second-order upwind scheme (SUDC) is adopted here to discretize the convective fluxes. The effects of the clearance between the pipeline and the seabed, water depth and wave height on wave forces are studied, respectively. The results by the numerical simulation agree well with the experimental data and theory value. 相似文献
7.
Unsteady nonlinear wave motions on the free surface in shallow water and over slopes of various geometries are numerically simulated using a finite difference method in rectangular grid system. Two-dimensional Navier–Stokes equations and the continuity equation are used for the computations. Irregular leg lengths and stars are employed near the boundaries of body and free surface to satisfy the boundary conditions. Also, the free surface which consists of markers or segments is determined every time step with the satisfaction of kinematic and dynamic free surface conditions. Moreover, marker-density method is also adopted to allow plunging jets impinging on the free surface. Either linear or Stokes wave theory is employed for the generation of waves on the inflow boundary. For the simulation of wave breaking phenomena, the computations are carried out with various wave periods and sea bottom slopes in surf zone. The results are compared with other existing computational and experimental results. Agreement between the experimental data and the computation results is good. 相似文献
8.
The problem of wave propagation in a fully nonlinear numerical wave tank is studied using desingularized boundary integral equation method coupled with mixed Eulerian–Lagrangian formulation. The present method is employed to solve the potential flow boundary value problem at each time step. The fourth-order predictor–corrector Adams–Bashforth–Moulton scheme is used for the time-stepping integration of the free surface boundary conditions. A damping layer near the end-wall of wave tank is added to absorb the outgoing waves with as little wave reflection back into the wave tank as possible. The saw-tooth instability is overcome via a five-point Chebyshev smoothing scheme. The model is applied to several wave propagations including solitary, irregular and random incident waves. 相似文献
9.
The extent to which marine organic matter is associated with surfaces and the consequences of such associations for organic matter remineralization are the focus of considerable attention. Since extracellular enzymes operating outside microbial cells are required to hydrolyze organic macromolecules to sizes sufficiently small for substrate uptake, the effects of surface interactions–on enzymes as well as on substrates–for hydrolytic activity also require investigation. We used a simplified laboratory system consisting of a free (dissolved) polysaccharide (pullulan) and the same polysaccharide tethered to agarose beads to restrict mobility, plus the corresponding free enzyme (pullulanase) and the same enzyme sorbed to montmorillonite (Mte), to investigate systematically the consequences of surface associations of enzymes and of substrates on hydrolytic activity. Changes in substrate molecular weight were monitored with time to measure the course of enzymatic hydrolysis. Although hydrolysis of free substrate was nearly complete after 2 min incubation with the free enzymes, the sorbed enzymes also effectively hydrolyzed free substrate, and the data suggest that they retained activity longer in solution compared to the free enzymes. Sorbed enzymes progressively hydrolyzed the free substrate from > 50 kD to lower molecular weights during a 24 h incubation, with a final product distribution on average showing only 1.4% and 10.3% of substrate still in the > 50 kD and 10 kD size classes, while 46.6%, 29.3%, and 12.5% of substrate was in the 4 kD, monomer, and free tag size classes, respectively. This product distribution was very similar to that of the free substrate/free enzyme experiment. Tethering the substrate to agarose beads led to lower substrate release (2–3% of total substrate after 98 h incubation) into solution compared to the free substrate case. For tethered substrates, the state of the enzyme (free or sorbed) measurably affected the molecular weight distribution of the hydrolysis products, with free enzymes producing a higher fraction of high molecular weight hydrolysis products (28.7 ± 5.4% of substrate > 50 kD at the end of the incubation) compared to sorbed enzymes (11.6 ± 2.8% of substrate > 50 kD at the end of the incubation.) Tethered substrates were also hydrolyzed in a sediment slurry from surface sediments from Cape Lookout Bight, North Carolina; 0.1% of total substrate was released by enzymes naturally present in 1 cm3 of sediment after 144 h incubation, demonstrating that the enzymes naturally present in marine sediments are also capable of accessing tethered substrates. These investigations suggest that surface associations of enzymes in marine systems may extend the active lifetime of such enzymes, providing an opportunity for hydrolysis over longer periods of time and producing a different size spectrum of hydrolysis products relative to free enzymes. Furthermore, in well-mixed systems, surface-associated enzymes can hydrolyze substrates whose mobility is restricted, highlighting the importance of processes such as resuspension and bioturbation on organic matter remineralization. 相似文献
10.
In this paper methods are given of the IR radiometric determination of the temperature of the radiating oceanic layer,T
s, and the determination on its basis of the temperature drop in the skin layer,dt, from on board a ship underway, which allows for the emissivity of the sea surface and the contribution of the atmosphere to the upward radiation of the sea surface. The seawater temperatureT
w was registered by a contact sensor towed along the ship at a depth of 0.1–0.4 m. The valuedt=T
s–T
w was found to be within the limits of 0.07 to –0.85 K, being on average 0.33 K. The near-surface wind speedv (v=1–13 m s–1) had the best relationship withdt;dt=–0.66+0.06v. The empirical values ofdt were compared with the model ones obtained by the well-known formulae for the conditions of forced and free convection of the surface layer.Translated by Mikhail M. Trufanov. 相似文献
11.
A new three-dimensional, non-hydrostatic free surface flow model is presented. For simulating water wave motions over uneven bottoms, the model employs an explicit project method on a Cartesian the staggered gird system to solve the complete three-dimensional Navier–Stokes equations. A bi-conjugated gradient method with a pre-conditioning procedure is used to solve the resulting matrix system. The model is capable of resolving non-hydrostatic pressure by incorporating the integral method of the top-layer pressure treatment, and predicting wave propagation and interaction over irregular bottom by including a partial bottom-cell treatment. Four examples of surface wave propagation are used to demonstrate the capability of the model. Using a small of vertical layers (e.g. 2–3 layers), it is shown that the model could effectively and accurately resolve wave shoaling, non-linearity, dispersion, fission, refraction, and diffraction phenomena. 相似文献
12.
In this paper, a numerical wave model based on the incompressible Reynolds-averaged Navier–Stokes (RANS) and k–ε equations is used to estimate the impact of a solitary wave on an idealized beachfront house located at different elevations on a plane beach. The locations of the free surface are reconstructed by volume of fluid (VOF) method. The model is satisfactorily tested against the experimental data of wave runup, and the analytical solution of wave forces on vertical walls. The time histories of wave profiles, forces, and overturning moments on the idealized house are demonstrated and analyzed. The variations of wave forces and overturning moments with the elevation of the idealized beachfront house are also investigated. 相似文献
13.
Based on Green–Naghdi equation this work studies unsteady ship waves in shallow water of varying depth. A moving ship is regarded as a moving pressure disturbance on free surface. The moving pressure is incorporated into the Green–Naghdi equation to formulate forcing of ship waves in shallow water. The frequency dispersion term of the Green–Naghdi equation accounts for the effects of finite water depth on ship waves. A wave equation model and the finite element method (WE/FEM) are adopted to solve the Green–Naghdi equation. The numerical examples of a Series 60 (CB=0.6) ship moving in shallow water are presented. Three-dimensional ship wave profiles and wave resistance are given when the ship moves in shallow water with a bed bump (or a trench). The numerical results indicate that the wave resistance increases first, then decreases, and finally returns to normal value as the ship passes a bed bump. A comparison between the numerical results predicted by the Green–Naghdi equation and the shallow water equations is made. It is found that the wave resistance predicted by the Green–Naghdi equation is larger than that predicted by the shallow water equations in subcritical flow
, and the Green–Naghdi equation and the shallow water equations predict almost the same wave resistance when
, the frequency dispersion can be neglected in supercritical flows. 相似文献
14.
A time-independent finite-difference method and a fifth-order Runge–Kutta–Felhberg scheme were used to analyze the dynamic responses of sea-wave-induced fully non-linear sloshing fluid in a floating tank. The interaction effect between the fully non-linear sloshing fluid and the floating tank associated with coupled surge, heave and pitch motions of the tank are analyzed for the first time in the present pilot study. For the analysis of fluid motion in the tank, the coordinate system is moving (translating and rotating) with tank motion. The time-dependent water surface of the sloshing fluid is transformed to a horizontal plane and the flow field is mapped on to a rectangular region. The Euler equations as well as the fully non-linear kinematic free surface condition were used in the analysis of the sloshing fluid. The strip theory for linearized harmonic sea-wave loading was adopted to evaluate the regular encounter wave force. In addition, the dynamic coefficients used in the dynamic equations of tank motion were also derived based on strip theory and a harmonic motion of the tank. The characteristics of free and forced tank motions with and without the sloshing effect are studied. By the damping effect, the response of free oscillation will damp out and that of forced oscillation will approach a steady state. Without sea-wave action, the contribution of the sloshing load would enlarge the angular response of tank motion as well as the rise of free surface and the sloshing effect will delay the damping effect on angular displacement. On the contrary, under sea-wave action, the sloshing effect will decrease the dynamic response of tank motion and rise of free surface. The interaction, sloshing and coupling effects are found to be significant and should be considered in the analysis and design of floating tanks. 相似文献
15.
The effect of the shear and normal stress free surface boundary conditions on the laminar flow induced by wave propagation is discussed. The approximate form of the boundary conditions, as used by (Lin, P., Zhang, W., 2008. Numerical simulation of wave-induced laminar boundary layers. Coast. Eng. 55, 400–408), is valid only when the free surface slope is mild. 相似文献
16.
A two-equation k– turbulence model is used in this paper to simulate the propagation of cnoidal waves over a submerged bar, where the free surface is handled by the volume-of-fluid (VOF) method. Using a VOF partial-cell variable and a donor–acceptor method, the model is capable of treating irregular boundaries, including arbitrary bottom topography and internal obstacles, where the no-slip condition is satisfied. The model also allows the viscous sublayer to be modeled by a wall function approximation implemented in the grid nodes that are immediately adjacent to a wall boundary. The numerical model applied to the propagation of cnoidal waves over a submerged bar can produce results that are in general agreement with some laboratory measurements. Some remarks arising from the comparison between the computational and experimental results are presented. 相似文献
17.
Heat and salt balances in the Seto Inland Sea 总被引：1，自引：0，他引：1
Seasonal variations of heat and salt balances are estimated in the Seto Inland Sea with the use of a numerical experiment.The surface effect is dominant with respect to the heat balance. In spring, however, the effect of the horizontal heat transport is the same as or greater than that of the surface heating (or cooling). Annual mean heat transport is 85 cal cm–2 day–1 (356 J cm–2 day–1) which is supplied from the open ocean and lost through the sea surface in the Inland Sea as a whole. Because of the shallow water depth, heat is supplied through the surface and carried out by the horizontal heat transport in Hiuchi- and Bingo-nada in the annual mean. The heat transport has the opposite sense to that in the whole Seto Inland Sea and annual mean transport is negative (–10 cal cm–2 day–1,i.e., –42 J cm–2 day–1).The salt balance is primarily controlled by the river discharge and the surface effect (precipitation) in June and July. In the other months, the effects of horizontal salt transport, of river inflow and of sea surface exchange (especially of the evaporation in autumn) are comparable to each other. In the Bungo Channel the river effect is relatively small. Osaka Bay and the Kii Channel are characterized by a smaller surface effect.Contribution No. 446 from Tohoku Regional Fisheries Research Laboratory. 相似文献
18.
Artificial cavitation, or ventilation, is produced by releasing gas into the liquid flow. One of the objectives of creating this multiphase flow is to reduce frictional and sometimes wave resistance of a marine vehicle completely or partially immersed in the water. Flows around surface ships moving along the water–air boundary are considered in this paper. It is favorable to achieve a negative cavitation number in the developed cavitating flow under the vessel’s bottom in order to generate additional lift. Cavities, formed in the flow, have limiting parameters that are affected by propulsion and lift-enhancing devices. Methods for calculating these influences and the results of a parametric study are reported. 相似文献
19.
Information coming from fishery monitoring, surveys and experimental fishing with participation of fishers was employed to determine the impact of an artisanal gear, ‘boliche’, on the biodiversity of the Ciénaga Grande de Santa Marta (CGSM), an estuarine lagoon on the Caribbean coast of Colombia. Fishery monitoring (catch data) included landings before (1968 and 1978) and after (1994–1996) the introduction of the boliche in the CGSM (1985), whereas surveys were conducted seasonally during 1993–1994. Fishing experiments involved evaluating different mesh sizes and the short-term effect of physical disturbance by the boliche. Monitoring suggested potential trophic effects of this fishing gear: the catch of large, long-lived, carnivorous species declined after the introduction of the boliche in the CGSM, whereas catch rates of smaller, shorter-lived, and lower trophic level species increased. Surveys revealed that the boliche retained 41 species. The by-catch made up 62% of the total catch and the remaining 38% involved the three target species Eugerres plumieri, Mugil incilis and Cathorops spixii. Selectivity experiments showed that 2.5 in. stretched mesh size gill nets caught more species than the 3.0-in. mesh. The smaller mesh also increased the risk of a critical reduction in the spawning stock of target species (notably E. plumieri); a situation that could affect the fish community if mesh sizes lower than 2.5 in. were intensively used. Suspended particulate matter significantly increased after fishing activity, with higher resuspension on mud-shells and mud substrata, whereas dissolved oxygen showed no appreciable changes after fishing operations. Notwithstanding, the activity of the boliche would generate sediment resuspension between 382 and 470 t day−1, which could lead to potential cascade impacts on water quality. We propose a framework of redundancy in management measures in order to simultaneously reach management and conservation goals. 相似文献
20.
Shipboard data from seven cruises covering April 1988–October 1990 are analyzed to follow the dynamical evolution of a persistent warm core eddy located to the southeast of Cyprus. The eddt is characterized by an isothermal, isohaline lens of water wedged between the seasonal and permanent thermoclines. In the winter, this thermostad extends from the surface to a depth of nearly 400 m, while in other seasons it lies in the layer from 200 to 400 m. The data indicate that the temperature and salinity of the core of the eddy remained constant throughout most of 1989 and then increased abruptly (with a slight increase in σφ) in the winter of 1989–1990. The velocity jet usually appears between the surface and 200 m at a mean distance of 35 km from the center of the eddy. Speeds in the jets typically exceed 25 cm s−1 and occasionally reach 50 cm s−1. During 1989 the eddy spins down as indicated by a loss of kinetic energy. This weakening permits an abrupt renewal or exchange of core water during the winter of 1989–1990. The remnants of the previous core are apparently forced to sink into the permanent thermocline where the water may be free to spread laterally if the cross-isopycnal gradient of potential vorticity is weak. This process could explain the cycle of Levantine Intermediate Water formation in the centers of warm core eddies and its eventual lateral spreading. Finally the eddy slowly begins to spin up again in 1990. 相似文献