NUMERICAL SIMULATION OF IRREGULAR WAVE-SIMULATING IRREGULAR WAVE TRAIN

In real sea states, damage incidents on offshore floating structures are not due to the whole time series of wave elevation characterized as statistical one but due to few extreme waves or wave groups in irregular wave train. So, using CFD tools to precisely simulate predetermined irregular wave train will lay sound basis for understanding the local characteristic of the flow field and impact loads on offshore floating structures when damage incidents occur. In this article, the generation of single extreme wave is investigated in a numerical wave tank. First, experimental irregular wave train is decomposed into certain number of small-amplitude waves. The Fourier series expansion is performed to determine the amplitude and initial phase angle of each wave component. A hydrodynamic transfer function is used to calculate the amplitude of wave-maker motion associated with each wave component. Then superposition is carried out on all of the wave-maker motion components to get the final wave-maker motion. With the wave-maker motion as input, simulation of the single extreme irregular wave train is modeled successfully. Then the method is applied to simulating a much more complicated irregular wave train. Once again main features of the complicated irregular wave train are reproduced compared with experiment carried out in the new deepwater experimental basin at Shanghai Jiao Tong University. In the simulation, dynamic mesh method is enabled to model the piston-type wave-maker, the Volume Of Fluid (VOF) method is employed to capture the free surface and a dissipation zone is introduced to deal with wave reflection.     

NUMERICAL MODELLING OF THE WATER AIR TWO PHASE JET INTO A PLUNGE POOL

１．　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｆｌｏｗｆｉｅｌｄａｎｄｅｎｅｒｇｙｄｉｓｓｉｐａｔｉｏｎｉｎｐｌｕｎｇｅｐｏｏｌａｒｅｏｆｐｒａｃｔｉｃａｌｉｍｐｏｒｔａｎｃｅｆｏｒｄａｍｅｎｇｉｎｅｅｒｉｎｇ．Ｔｈｅａｒｅａｔｉｏｎｈａｓｉｍｐｏｒｔａｎｔｅｆｆｅｃｔｓｏｎｔｈｅｆｌｏｗｉｎｐｌｕｎｇｅｐｏｏｌ［１］　．Ｉｎｔｈｅｃｏｎｖｅｎｔｉｏｎａｌｍａｔｈｅｍａｔｉｃａｌｍｏｄｅｌｓｏｆｗａｔｅｒｆｌｏｗｉｎｈｙｄｒａｕｌｉｃｅｎｇｉｎｅｅｒｉｎｇ，ｔｈｅａｒｅ…     

NUMERICAL SIMULATION OF TWO-PHASE GRAVITY CURRENTS OVER A POROUS SUBSTRATE

1 .　INTRODUCTIONGravitycurrentsoccurinmanysituationsaris inginbothindustrialandnaturalsettings[1 2 ] .Commonlythecurrentisdrivenbycompositionalortemperaturedifference ,toleadtoahomoge nouscurrent ,orbysuspended particulatematter ,toleadtoaparticle drivencurrent.Combinationsbybothparticleandcompositionalortemperaturedifferencecanalsooccur[3] .Mostoftheresearchesareconcentratedonthesituationswherethecur rentsflowaboveanimpermeableboundary .How evertherearemanyimportantcaseswheregravitycurr…     

THREE-DIMENSIONAL MODELLING FOR LUBRICATION WITH REFERENCE TO HUMAN JOINTS

ＴＨＲＥＥ－ＤＩＭＥＮＳＩＯＮＡＬＭＯＤＥＬＬＩＮＧＦＯＲＬＵＢＲＩＣＡＴＩＯＮＷＩＴＨＲＥＦＥＲＥＮＣＥＴＯＨＵＭＡＮＪＯＩＮＴＳＺｈａｎＪｉｅ－ｍｉｎ（ＤｅｐａｒｔｍｅｎｔｏｆＡｐｐｌｉｅｄＭｅｃｈａｎｉｃｓａｎｄＥｎｇｉｎｅｅｒｉｎｇ，Ｚｈｏｎ...     

THREE-DIMENSIONAL NUMERICAL MODELING OF SECONDARY FLOWS IN A WIDE CURVED CHANNEL

Most natural rivers are curved channels, where the turbulent flows have a complex helical pattern, as has been extensively studied both numerically and experimentally. The helical flow structure in curved channels has an important bearing on sediment transport, riverbed evolution, and pollutant transport study. In this article, different turbulence closure schemes i.e., the mixing-length model and the k – ? model with different pressure solution techniques i. e., hydrostatic assumptions and dynamic pressure treatments are applied to study the helical secondary flows in an experiment curved channel. The agreements of vertically-averaged velocities between the simulated results obtained by using different turbulence models with different pressure solution techniques and the measured data are satisfactory. Their discrepancies with respect to surface elevations, superelevations and secondary flow patterns are discussed.     

NUMERICAL STUDY ON THE THREE-DIMENSIONAL CHARACTERISTICS OF THE TIDAL CURRENT AROUND HARBOR ENTRANCE

A three-dimensional (3-D) numerical model is established to investigate the tidal current motion characteristics around the harbor entrance. Computational approaches consist of the finite difference method, time-splitting technique, C-grid, and a high-order turbulence closure model. The Ocean General Circulation Model (OGCM) inundation scheme is incorporated in the model. An engineering application, Lianyungang Harbor, China, is used as a real-life case. The model is validated by showing that the simulated results agree well with the field data. In the approach channel, the tidal current shows a deflection effect especially in the bottom layer. As for Lianyungang Harbor, a jet flow forms at the tip of the northern breakwater, which drives a circulation flow at the inner side of the harbor entrance. In the vertical, the flow is significantly stratified at the entrance section within the channel, where the flow direction varies between layers and the speed distribution is quite uniform. These 3-D features become less evident to the offshore. Additionally, the sensitivity analysis shows that the flow deflection is related to the channel depth. Simulation results also imply that the siltation rate at the entrance section of the approach channel tends to be more uniform by the 3-D flow motion feature, and could be more significant with the increase of the channel depth.     

THREE-DIMENSIONAL NUMERICAL MODELLING OF SUBMERGED DIKE ALIGNMENT IN CURVED ESTUARINE CHANNEL

1.INTRODUCTIONSubmerged dikes are frequently built in curveriver and estuarine channels to i mprove navigational conditions and/or to protect banks.Manefforts have been made to study flow characteristics around a dike in a straight channel experi mentally and numerically(Rajaratnamet al.1983;Liet al.1994;Mayerle et al.1995;Tominaga et al1997;Peng et al.1997).However,few studiehave investigated overall flowpatterns around submerged dikes in curved estuarine channels.Although many researc…     

THREE-DIMENSIONAL NUMERICAL SIMULATION OF TIDES AND CURRENTS IN FUSHAN BAY, QINGDAO

The three-dimensional Princeton Ocean Model (POM) was employed to simulate the tide and current simultanuously for the first time in the Fushan Bay, Qingdao, China By adopting the elevation condition that was combined with the tides M2, $2, K1 and O1 at the open boundary and by choosing the proper value of bottom roughness, the horizontal and vertical distributions of the tidal current and water level variations in the bay were computed. The results agree well with the field observation data, indicating that this model can be used to predict accurately the variation of tides and currents in the Fushan Bay and other costal regions in the future.Our study also provides useful information and a data base for the Olympic Projects that will be conducted in the Fushan Bay in 2008.     

THREE-DIMENSIONAL NUMERICAL MODEL FOR WINDING TIDAL RIVER WITH BRANCHES

Natural rivers are usually winding with branches and shoals,which are difficult to be simulated with rectangular grids. A 3-D current numerical model was established based on the orthogonal curvilinear coordinate system and vertical σ coordinate system. The equations were discretisized using a semi-implicit scheme. The “predictor” and “corrector” steps were applied for the horizontal momentum equations to meet the basic requirement that the depth-integrated currents obtained from the equations for 2-D and 3-D modes have identical values. And a modification of traditional method of dry/wet discriminance was proposed to determine accurately the boundary and ensure the continuity of variable boundary in the simulation. This model was verified with the data measured in a winding tidal river with branches in April,2004. The simulated data of water levels and velocities agree well with the measured ones,and the computed results reveal well the practical flow characteristics,including the vertical secondary flow in a winding reach.     

NUMERICAL MODELLING OF THE QUASI-GLOBAL OCEAN CIRCULATION BASED ON POM

A free surface quasi-global ocean circulation model, Princeton Ocean Model (POM), was adopted to simulate the climatological circulation. The horizontal resolution of the model was 1/2~X 1/2~ with 16 vertical sigma layers. The initial temperature and salinity fields of the model were interpolated from the Levitus data, and the COADS(Comprehensive Ocean-Atmosphere Data Set ) monthly mean SST and wind fields were used as the surface forcing. The integral time length is 6a. The main general circulation components such as the equatorial current, the equatorial undercurrent, the south and north equatorial currents, the Antarctic Circumpolar Current (ACC), the Kuroshio and the Gulf Stream were well reconstructed. The volume transports of PN section and ACC agree well with the estimations on field survey. Up to now there is no global or quasi-global circulation model results using POM in literature. Our results demonstrate that POM has sound ability to simulate the coastal circulation as well as the general ocean circulation. And this result can provide open boundary conditions for fine resolution regional ocean circulation models.     

NUMERICAL MODELLING OF NATURAL RIVER NETWORK

ＮＵＭＥＲＩＣＡＬＭＯＤＥＬＬＩＮＧＯＦＮＡＴＵＲＡＬＲＩＶＥＲＮＥＴＷＯＲＫ￥ＺｅｎｇＰｉｎｇ；ＬｉＹｕ－ｃｈｅｎｇ（ＤａｌｉａｎＵｎｉｖｅｒｓｉｔｙｏｆＴｅｃｈｎｏｌｏｇｙ，Ｄａｌｉａｎ１１６０２３，Ｐ．Ｒ．Ｃｈｉｎａ）ＺｈａｏＷｅｎ－ｑｉａｎ（...     

NUMERICAL STUDY ON THE PURIFICATION PERFORMANCE OF RIVERBANK

During the rain time, the runoff infiltrates into the riverbank through the collecting gutter and slope surface. The city runoff is generally polluted by organic, oil, heavy metal particulates, etc. The pollutants moving with the water through the riverbank experience advection, dispersion, diffusion, adsorption, biochemical reaction and plant uptaking processes. In this article, a mathematical model was developed to simulate the performance of pollutant removal of the riverbank. The model took those main mechanisms into account. The modified Richards equation was used in simulating flow field. The mass balance law was employed in deriving the equation for pollutant transport, where the diffusion and dispersion were described with the Fick-type law, the adsorption was macroscopically expressed as form isotherm, and the bio-chemical degradation process was assumed to follow the Monod kinetics. The NH3-N and TP were considered in the present model. The mathematical model was descritized with a finite element numerical model, which was applied to two types of model riverbanks. In the model test, the hydraulic loading was assumed to have the intermittent pattern simulating the storm runoff of certain return period, and the values of the rainfall runoff and concentrations of the NH3-N and TP were taken from the model test. The computed overall removal rates for the NH3-N and TP in 6 cases are in the range of 88%-98%, 87%-97%, respectively. The differences between the computed and tested overall removal rates for the NH3-N and TP are less than 5%. The time-varying oscillation pattern of the concentrations of the NH3-N and TP were rationally simulated, which shows that the model presented in this article can be used to assess the purification performance of the riverbank constructed with sand or soil.     

THREE-DIMENSIONAL NUMERICAL SIMULATION OF WIND-INDUCED CIRCULATION IN LAKE TAIHU

1 .　INTRODUCTIONHydrodynamicshassignificanteffectsoneutroph icationinshallowlakesbecausewavesandcurrentscanleadtosedimentresuspensionresultinginnutrientre lease,highturbidityandre distributionofnutrientsandSuspendedParticulateMatter (SPM ) .Asare sult ,therecoveryofthelimnicecosystemismorethanlikelytobepreventedespeciallyinshallowlakes[1 3] ,whichiswhyhydrodynamicsandsedimentdynamicshavereceivedgreatattentioninthelakeecosystemre searchandothershallowwaterareas[4 8] .Asthethirdlargestf…     

THREE-DIMENSIONAL TURBULENCE NUMERICAL SIMULATION OF A STEPPED SPILLWAY OVERFLOW

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅａｐｐｌｉｃａｔｉｏｎｏｆｔｈｅｓｔｅｐｐｅｄｓｐｉｌｌｗａｙｈａｓｈａｄａｌｏｎｇｈｉｓｔｏｒｙ .Ｔｈｅ ｐｈｙｓｉｃａｌｍｏｄｅｌｔｅｓｔｓｔｕｄｙｏｆｔｈｅｓｔｅｐｐｅｄｓｐｉｌｌｗａｙｈａｓｂｅｅｎ ｐｅｒｆｏｒｍ     

2-D NUMERICAL SIMULATION OF RADIONUCLIDE TRANSPORT IN THE LOWER YANGTZE RIVER

The assessment of the radiological impact of the liquid discharges from nuclear power plants is a major issue for the environmental protection. In this study, a numerical model for the radionuclide transport in the aquatic environment is built, based on the hydrodynamic equations, including the complete set of Saint-Venant equations, the sediment transport equations, with consideration of several different particle sizes and the deposition and erosion of the suspended sediments, and the radionuclide transport equations. The exchanges of radionuclides between water, suspended matter and bed sediments are described in terms of kinetic transfer coefficients. The model is used to simulate the transport of the radionuclides discharged from a planned nuclear power plant project to be sited along the lower Yangtze River. From the model results, one may see the detailed temporal-spatial evolution of the radionuclide contamination in the solution, in the suspended matter and in the bed sediments. The model can be used as a basic tool for studying the environmental impacts of the liquid discharges from nuclear facilities on a river system.     

THREE-DIMENSIONAL TURBULENCE NUMERICAL SIMULATION OF A STEPPED SPILLWAY OVERFLOW

In this paper, the κ-ε two-equation turbulence model was used to simulate the three-dimensional turbulent flow of the stepped spillway at the Yubeishan reservoir. In order to solve the curved free water surface and to handle the complex boundary conditions, the fractional Volume Of Fluid (VOF) model that is applicable to the solution of the stratified two-phase flow was intorduced to the κ-ε turbulence model and the unstructured grid was used for the discretization of the irregular simulation domain. By these methods, the turbulent flow field of the stepped spillway was simulated successfully.The location of the free surface along the spillway, the magnitude and distribution of the velocity, the pressure distribution on the step surface, the turbulence kinetic energy and turbulence dissipation rate were obtained by simulation. The changes and distributions of these characteristics along the width of the spillway were also obtained. The energy dissipation ratio of the stepped spillway was calculated according to the upstream and downstream water depth and velocities.     

NUMERICAL INVESTIGATION OF THREE-DIMENSIONAL FLOW AND BED SHEAR STRESS DISTRIBUTION AROUND THE SPAN SHOULDER OF PIPELINE

1 .　INTRODUCTIONWhena pipelineis placedonanerodibleseabed ,freespanmaydevelopastheresultoflocalscourunderthepipeline .Oneofthemostimpor tantissuesinpipelinestabilitydesignistheevalua tionofthefreespanlengthandtherateatwhichthefreespandevelopsalongthespandirectionduetothescour .Bothfreespanlengthandtherateofscourdevelopmentdependonflowconditionsaroundthespanshoulders.Sincemostofthescourinvestigationsintheopenliteraturewereonthescourdepthorscourdevelopmentinthe perpendiculardirectionofpipe…     

THE STATISTIC CHARACTERISTICS OF IRREGULAR BREAKING WAVE FORCES ON VERTICAL WALLS

ＴＨＥＳＴＡＴＩＳＴＩＣＣＨＡＲＡＣＴＥＲＩＳＴＩＣＳＯＦＩＲＲＥＧＵＬＡＲＢＲＥＡＫＩＮＧＷＡＶＥＦＯＲＣＥＳＯＮＶＥＲＴＩＣＡＬＷＡＬＬＳ￥ＬｉＹｕ－ｃｈｅｎｇ；ＬｉｕＤａ－ｚｈｏｎｇ（Ｄｅｐｔ．ｏｆＣｉｖｉｌＥｎｇｉｎｅｅｒｉｎｇ，Ｄａｌｉａｎ...     

NUMERICAL SIMULATION OF SCOURING PROCESS UNDER SPILLWAY

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｆｒｅｅｊｅｔｄｉｓｓｉｐａｔｏｒｓｈａｖｅｂｅｅｎｆｒｅｑｕｅｎｔｌｙｕｓｅｄｉｎｈｉｇｈｄａｍｓｔｏｄｉｓｓｉｐａｔｅｔｈｅｈｕｇｅｅｎｅｒｇｙｃｏｎｔａｉｎｅｄｂｙｄｉｓｃｈａｒｇｉｎｇｆｌｏｏｄｗａｔｅｒ .Ｆｏｒｈｉｇｈｄａｍｓｉｎｒｅｍｏｔｅｍｏｕｎｔａｉｎｓａｎｄｇｏｒｇｅｓ,ｗｉｔｈｔｈｅｈｅａｄｓａｓｈｉｇｈａｓ 2 0 0～30 0ｍｅｔｅｒｓ ,ｆｒｅｅｊｅｔｄｉｓｓｉｐａｔｏｒｓａｒｅｓｔｉｌｌｅｆｆｅｃｔｉｖｅ ;ｂｕｔｊｅｔｓｍａｙｓｔｒｉｋｅｇｒｅ…     

3-D VARIABLE PARAMETER NUMERICAL MODEL FOR EVALUATION OF THE PLANNED EXPLOITABLE GROUNDWATER RESOURCE IN RE-GIONAL UNCONSOLIDATED SEDIMENTS

In order to correctly evaluate the exploitable groundwater resource in regional complex,thick Quaternary unconsolidated sediments,the whole Quaternary unconsolidated sediments are considered as a unified hydrogeological unit and a 3-D unsteady groundwater flow numerical model is adopted.Meanwhile,with the consideration of the dynamic changes of the porosity,the hydraulic conductivity and the specific storage with the groundwater level dropping during the exploitation process,an improved composite element seepage matrix adjustment method is applied to solve the unsteady flow problem of free surface.In order to eva-luate the exploitable groundwater resource in Cangzhou,Hebei Province,the hydrogeological conceptual model of Cangzhou is generalized to establish,a 3-D variable parameter numerical model of Cangzhou.Based on the prediction of the present groundwater exploitation,and by adjusting the groundwater exploitation layout,the exploitable groundwater resource is predicted.The model enjoys features like good convergence,good stability and high precision.