Showing papers in "Journal of Hydrodynamics in 2000"

Diagnosis and Identification of Vibration Accident for Hydrogenerator Unit

Abstract: Vibration is the main accident that affects the normal function of hydrogenerator unit and endangers the life span of hydrogenerator unit To eliminate the vibration accident of the unit, it is necessary to detect the causes that lead to the vibration of the unit This paper intends to discuss the causes resulting in the vibration of the unit, revealed by some characteristics of the unit vibration For the sake of simplifying the program, the interaction of the factors causing the vibration of the unit was not considered in this paper However, it is helpful for the analysis of the main reasons of the unit vibration

Nonlinear Dynamical Modeling of Fluid-Structure Interaction of Fluid-Conveying Pipes

Abstract: A nonlinear 4 equation model, including full coupling mechanisms of fluid structure interaction of fluid conveying pipe, was developed by use of Hamilton′s variational principle and equations of momentum and continuity of internal flows in deformable moving control volume in this paper. The vibrations were described with a set of 4 partial differential equations in which 4 dependent variables, axial and lateral displacements of pipe motion, and flow velocity and pressure, are involved for a flexible pipe conveying fluid. The equations of motion were then compared with those already in existence, for the save of clarifying the derivations, the validity, and the completeness. The findings obtained by comparisons are the model given in this paper is a more complelete one. [WT5HZ]

Study on Starting Velocity of Cohesive Sediment

Abstract: In this paper, the formulas of starting velocity on cohesive sedimentation are discussed, combined with experiments of natural cohesive sedimentation in Lang ya Mountain Pumped Storage Power Station. Based on the research results of the theory and the test about turbulence in open channel, author proposes an assumption concerning the starting mechanism and starting velocity of cohesive sediment and gives a formula to determine the starting velocity of compact clay. The paper also points out that the fluctuating stress of flow is a main factor on the starting of sedimentation. And the component and the structure of cohesive sediment are also affecting factors to the starting. Consequently, by means of modern results of soil mechanics, clay mineralogy and fluid mechanics to investigate this kind of problem is avaiable for engineering. [WT5HZ]

Studies on Numerical Modeling of Water Environment in the Yangtze Estuary-Numerical Simulation of Hydrodynamic Flows

Abstract: Based on the depth integrated 2 dimensional mathematical model, the numerical simulation of the effect of a deep water navigation channel project on the hydrodynamic flows is presented in this paper. The calibration and validation showed that the model is fairly stable and applicable for studying regulation projects in the Yangtze estuary. The computed results show that the flow field in the estuary changes significantly due to the project.

Review of FSI analysis of fluid-conveying pipes

Abstract: WT5”BZ]Pipes are widely used in industry and play a quite important role. A Coupling vibration induced by a fluid surge may attack a working pipe which exhibits complicated dynamical behavior. For many years, this subject has been extensively studied in both the linear and the non linear analysis in the academic and the engineering communities, and a lot of results have been reported. In this paper, the typical achievements in the research field were introduced and reviewed. [WT5HZ]

Study of Low-frequency Noise Induced by Marine Propeller

Abstract: The low frequency noise of propeller has constituted the main part of radiated noise of middle or high speed marine. The low frequency discrete noise of the propeller is induced by the interaction between blades of the propeller and wake of the marine, and the low frequency broadband noise of the propeller is produced by the interaction of blades and turbulent field of the marine stern. Using a combination method of the lifting surface theory and acoustic technique, the effects of different diameters, skews and rakes on the discrete noise of the propeller are studied by the numerical method and some useful results for engineering are presented in this paper. According to mechanism of low frequency broadband noise of the propeller, theoretical analysis method is given and numerical calculation of the noise is worked out as well. The methods will not only make a key tool for noise prediction, but also play a role for noise control of the propeller in engineering project.[WT5HZ]

Application of a numerical model for shallow water waves

Abstract: Several existing numerical models for shallow water waves based on different wave theories were reviewed. Some wave energy conservation models for the forecasting of shallow water waves were analyzed, in which, the SWAN model, which makes use of the most advanced achievements of wave study and has been applied to several academic and realistic problems, was introduced here. The characteristics, capability, finite difference scheme of action balance equation of the SWAN model and its source term computing method were detailedly described. The model was applied to the problem of the wave propagation in a following and opposing current. Finally, the model was employed in the Haian bay area to simulating the wave heights and wave periods there, and the numerical results were compared with the observations.

Numerical Simulation for Concrete Rockfill Dam Failure

Abstract: By making use of the model test and b ased on the analysis for the characteristics and mechanism of the concrete rockf ill dam failures a method of numerical simulation for concrete rockfill dam fail ure is presented in the paper. It is shown that the computed results by the meth od agree with the date measured in the Gou Hou dam failure.

Two-Dimensional Time Domain Dynamic Analysis for the General Buoy-Cable-Body System

Abstract: A two-dimensional time domain met ho d is presented for the analysis of dynamic behaviour of the ocean cable system i n wind, wave and current. The ocean cable system consists of a surface buoy, con necting cable and intermediate bodies. The equations which model the motions of the various components of the cable system are deduced. Numerical results are gi ven for a typical sonosystem.

ALE Finite Volume Computations of Fluid-Structure Interaction Problems

Abstract: A computational procedure is develop ed to analyze the fluid-structure interaction problems The Navier-Stokes equati ons and the equation of the motion of the structure are coupled and solved by a predictor-corrector method The Newmark scheme is employed to solve the equ ation of structure The spatial discretization of the N-S equation is achieved by the finite volume method using non-staggered grid in a curvilinear coordina te system, while the time derivatives are approached by a second-order backward scheme The Arbitrary-Lagangian-Eulerian method is employed to incorporate th e interface conditions between the structure and fluid Extensive studies are ca rried out with the present method to analyze the vibrations of a single circular cylinder in a viscous fluid filling a circular domain Four different types of fluid, including air, water, mineral oil and silicon oil,are selected as the flu id media in the computation The added mass and damping coefficients obtained fr om time history of displacement are compared with the analytical solutions Good agreement shows that the fluid forces acting on the cylinder are accurately pre dicted Furthermore, the present method can be also used to explore the similar problem with large vibrating amplitude and eccentric cylinder, of which the anal ytical solutions are unavailable

Bjerknes force during bubbles collapse

Abstract: A formula for the Bjerknes force in bubble motion is drived on the basis of the Bjerknes force theory and bubble dynamics, and the Bjerknes forces during bubbles collapse are calculated and analyzed. [WT5HZ]

Effect of Abrasive Parameters on Cutting Efficiency of Collimated Abrasive Water Jet

Abstract: The effect of the diameter of particles and feed rate of abrasive on the speed of the particles in collimated abrasive water jet (CAWJ) is analyzed by calculational methods for the multiphase fluid with energy loss in the collimated pipe. Theoretical and experimental results show that the particle speed increases with decreasing feed rate, and not striking as abrasive concentration is less than 9.5%. There is an optimal relationship between the length of the collimated pipe and feed rate of abrasive. The smaller the size of particles is the higher the speed of particles is. They also show that the cutting efficiency of CAWJ is dependent on the speed and diameter of particles, and larger size abrasive is better than smaller size ones. [WT5HZ]

Study on Turbulence Closure of Dynamics Model for Marine Plankton Ecosystem

Abstract: The basic processes of turbulence cl osure and its practicable simplification were summarized from the basic equation s of geophysics and thermodynamics, which was generalized to processes of closin g the equation set of ecosystem dynamics model. The second order closure of equa tions in the dynamics model for marine plankton ecosystems was formulated and it s simple formulation that second order relative terms were expresses by eight sy stems of two algebra equations was suggested thereby. Several problems in simpli fication of second order turbulence closure were discussed.

Large Eddy Simulation of Turbulent Flows in Smooth a nd Rough Open Channels

Abstract: In this paper, the turbulent flows in smooth and rough open channels are studied by the large eddy simulation meth od combined with the Smagorinsky subgrid scale model. The Reynolds numbers based on the bulk velocity and depth of channels are selected as 3000, 22800 and 10 -5 respectively. The numerical algorithm is the finite volume method. The rigi d lid assumption is used for the free surface, and the wall function for the sol id wall. Good results are achieved in this prediction by comparison with the dir ect numerical simulation at low Reynolds number and physical experiments. The es timated macroscale of turbulence by the large eddy simulation reveals the limita tion of the Taylor hypothesis near the wall.

Simulation of Propagation, Reflection and Diffraction of Bores Caused by Sudden and Full Destruction of a Dam

Abstract: Two 1D nonlinear hyperbolic conservation equations are derived by decoupling and splitting the 2D shallow water equations and solved by using the hybrid TVD scheme with flux limiters And the propagation, reflection and diffraction of dam break waves induced by the sudden and full destruction of a dam are numerically simulated The complex flow characteristics of the bores are demonstrated, which provides scientific basis for the analysis and prevention of disaster caused by dam destruction

Numerical calculation of three-dimensional boundary layers over moving wavy wall

Abstract: WT5”BZ]The Arbitrary Lagrangian Eulerian (ALE) method was applied to a numerical simulation of two and three dimensional flow over a moving wavy wall in this paper. Special attention was in paid to analysing the dynamical behavior of flow fields, such as the velocity, vorticity and pressure. The efficient effect of drag reduction was proved. A mesh system which might exactly the moving boundary was designed, which took the advantage of ALE rezoning ability. The results show that the ALE method together with the moving mesh system is effective in simulating flows over moving wavy walls. [WT5HZ]

Experimental Research of Hydrodynamic Performance of Flexible Scull

Abstract: In a circulating water channel, the h ydrodynamic performance of typical flexible scull for rowing was tested at diff erent inclinations, angles of attack and entering-water depths of scull. The a ppropriate depth of scull in water was thus given. And it is found that the inc lination of a scull should be as small as possible.

Numerical solution of Boussinesq equations with finite element method

Abstract: It this paper, a numerical model for solving the improved Boussinesq equations derived by Beji and Nadaoka [4] is presented. The finite element method was used to discretize the spatial derivatives. Quadrilateral elements with linear interpolating functions were employed for the two horizontal velocity components and the water surface elevation. The time integration was performed using the Adams Bashforth Moulton predictor corrector method. Test cases for which either theoretical solutions or laboratory results are available were used to test the proposed scheme. The model is capable of giving satisfactory predictions in the cases.

Study of airflow characteristics at surface of a van-body truck

Abstract: In this paper, the surface airflow characteristics of a van body truck were investigated by means of the 3 D numerical simulation combined with wind tunnel experiments for the first time. The relationship between airflow characteristics and aerodynamic drag and the variation of aerodynamic drag with basic structural parameters were obtained. The research results can render important reference for aerodynamic shape designing of van body truck.

The research of vortex precaution in intake

Abstract: A vertical vortex arised from intake of hydroulic structure does harm largely to water resources and hydro electrical project. Vortex can be suppressed by reliable design, improving the boundary condition, building and installing specific structure. For the finished intake, intake, it can be done by suitable operating way. When design engineering sturcture, that rational in economic, simple in structure and easy to control must be considered overall according to topographic features around the intake, in order to choose best scheme of vortex precaution and suppressing. The methods of vortex precaution and suppressing in the following can be studied and adopted in design by similar engineering structure.

Water Wave Dynamics in the Ocean High-Tech for the New Century

Abstract: Water wave dynamics and its enginee ri ng application become one of the frontier research fields drawing great attentio n recently A state of the art review on the progress in the investigation of wa ter waves and the interaction between wave and ocean structures is made in the p resent paper and some brief comments are given for the potential research develo pments in the near future

Head advancement of turbulent gravity current: numerical solution

Abstract: The head front location as the function of time for the turbulent gravity current of lock release type was firstly derived by CFD approach in this paper The adopted Renormalization Group (RNG) k e model for Reynolds stress closure proved to be seccessful in characterizing the time dependant current with transitional and highly localized turbulence Consistent with well known experimental observations, the numerical results show that the gravity current passes through two phases, an initial slumping phase in which the current head advances steadily, and a second self similar phase in which the front velocity decreases in the form of negative third power of the time after release [WT5HZ]

Development of environmental decision support system for tidal river networks and its application to the Pearl River Delta

Abstract: WT5”BZ]The environmental decision support system (EDSS) was developed as the outcome of a collaborative research program which had the objective of developing a comprehensive, easy to use decision suppot system for water pollution control in tidal river networks in general and for that in the Pearl River Delta in particular. Its purpose was to provide a practical tool which could assist government agencies in decision making for the efficient management of water resources in terms of both quantity and quality. By combining the capabilities of geographical information system (GIS), database management system(DBMS), model management system(MMS), optimization procedure and expert system, the quality of decision making was thus improved in an area which has the most complicated tidal river network patterns as well as the fastest economic development in the world. This paper outlines the basic concepts and philosophy adopted in developing the EDSS. Thereafter, the system architecture, design features, implementation techniques and major facilities provided are described briefly. Finally, potential applications of the system and directions for further research are also outlined. [WT5HZ]

A method for determination of the potential pressure distribution parameter C_h in a influx header

Abstract: It is pointed out in this paper that in a influx header through the relationship between the C h in infinitesimal control unit momentum conservation equations and momentum transfer coefficient K and the expressions of local resistant coefficient for straight runs in a tee junction, the potential pressure distribution parameter C h in a influx header can be derived as C hi =1-(0.55ω i+ω i+1 )/(ω i+ω i+1 ). It is also derived that when equally influxed, expression of C hei  is that C hei =(0.45-0.45x i/L)/(2-1/n-2x i/L).

Theoretical Study on Liquefied Natural Gas Rollover

Abstract: There is an instability phenomenon ca lled rollover during the storage process of liquefied natural gas (LNG). This ph enomenon affects the safety and economy of the LNG tank, therefore it is necessa ry to correctly understand the mechanism and parameters governing the phenomenen . Based on the double-diffusive convection model, this paper theoretically anal yses the stability of the interface between the layers, heat and mass transfer c haracteristics of the interface and the mixing across a density interface.

Tests and calculations of water impact characteristics of a recovery module

Abstract: WT5”BZ]The water impact loads and water entry depth when a recovery module landing on a seaplane are obtained by similarity tests in the present paper. The theoretical method is also utilized to calculate the impact loads and depthes, the results are in good agreement with the experiments. [WT5HZ]

Monte Carlo Method with Irregular Random Walk Grid

Abstract: A new Monte Carlo method with irreg ula r random walk grid is presented for solving hydrodynamic problems in this paper. The method is used to study an example. The result by Monte Carlo method agree well with the result by the finite element method. The new method is adapted to the problems with complex boundary condition.

Influences of diffuser length on buoyant jets in cross flows

Abstract: Using the hybrid finite analytic method and staggered grid, the authors treated numerically the line buoyant jets in cross flows and simulated the phenomena and development of end vortices successfully. The influences of diffuser length on turbulent buoyant jets were analyzed.