NUMERICAL AND EXPERIMENTAL STUDIES OF INFLUENCE OF THE CAUDAL FIN SHAPE ON THE PROPULSION PERFORMANCE OF A FLAPPING CAUDAL FIN

This article presents a comprehensive study of the effects of the caudal fin shape on the propulsion performance of a candal fin in harmonic heaving and pitching.A numerical simulation based on an unsteady panel method was carried out to analyze the hydrodynamic performance of flapping caudal fins of three shapes(the whale caudal fin with the largest projected area,the dolphin caudal fin with the median projected area,and the tuna caudal fin with the smallest projected area).Then,a series of hydrodynamic ex...     

NUMERICAL PREDICTION OF SUBMARINE HYDRODYNAMIC COEFFICIENTS USING CFD SIMULATION

The submarine Hydrodynamic coefficients are predicted by numerical simulations.Steady and unsteady Reynolds Averaged Navier-Stokes(RANS) simulations are carried out to numerically simulate the oblique towing experiment and the Planar Motion Mechanism(PMM) experiment performed on the SUBOFF submarine model.The dynamic mesh method is adopted to simulate the maneuvering motions of pure heaving,pure swaying,pure pitching and pure yawing.The hydrodynamic forces and moments acting on the maneuvering submarine are obtained.Consequently,by analyzing these results,the hydrodynamic coefficients of the submarine maneuvering motions can be determined.The computational results are verified by comparison with experimental data,which show that this method can be used to estimate the hydrodynamic derivatives of a fully appended submarine.     

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.     

FINITE ELEMENT NUMERICAL SIMULATION FOR THE HYDRODYNAMIC FIELD EVOLUTION OF GEOTHERMAL WATER IN THE NANWENQUAN ANTICLINE IN CHONGQING IN CHINA

1. INTRODUCTION The Nanwenquan anticline is the drape storing geothermal water. The anticline extends from north to south in Chongqing, the Nanwenquan and Xiaoquan in the middle of the anticline [1]. The two hot springs, and geothermal water in the other …     

HYDRODYNAMIC ANALYSIS AND SIMULATION OF A SWIMMING BIONIC ROBOT TUNA

A dynamic model for undulatory locomotion was proposed to study the swimming mechanism of a developed bionic robot tuna. On the basis of inviscid hydrodynamics and rigid-body dynamics, the momentum and propulsive force required for propelling the swimming robot tuna’s flexible body was calculated. By solving the established dynamic equations and efficiency formula, the swimming velocity and propulsive efficiency of the bionic robot tuna were obtained. The relationship between the kinematic parameters of the robot tuna’s body curve and the hydrodynamic performances was established and discussed after hydrodynamic simulations. The results presented in this article can be used to increase the swimming speed, propulsive thrust, and the efficiency of underwater vehicles effectively.     

NUMERICAL SIMULATION OF SCALE EFFECT ON SHIP STERN FLOW AND HYDRODYNAMIC PERFORMANCE

ＮＵＭＥＲＩＣＡＬＳＩＭＵＬＡＴＩＯＮＯＦＳＣＡＬＥＥＦＦＥＣＴＯＮＳＨＩＰＳＴＥＲＮＦＬＯＷＡＮＤＨＹＤＲＯＤＹＮＡＭＩＣＰＥＲＦＯＲＭＡＮＣＥ￥ＧａｏＱｉｕ－ｘｉｎ；ＺｈｏｕＬｉａｒ－ｄｉ（ＣｈｉｎａＳｈｉｐＳｃｉｅｎｔｉｆｉｃＲｅｓｅａｒｃｈＣ...     

NUMERICAL SIMULATION OF ARTIFICIAL VENTILATED CAVITY

1. INTRODUCTION The cavitation phenomenon[1,2] has already been paid high attention as a primary characteristic in the process of underwater body’s manufacture and exploitation. For a long time, the purpose of cavitation research is to prevent the occurr…     

EXPERIMENT ON THE CHARACTERISTICS OF 3-D VORTEX RING BEHIND A FLEXIBLE OSCILLATING CAUDAL FIN

A test for the wake vortex of a flexible oscillating caudal fin is carried out with Digital Particle Image Velocimetry (DPIV), and the variation of vortex distance and the vorticity in the range of oscillating frequency from 0.704 Hz to 1.17 Hz are analyzed. It is found that with the increase of the oscillating frequency, the vortex distance decreases and the peak of the vorticity increases, When the Strouhal number is smaller than 0.49, a larger thrust component is obtained. The distribution of the velocity circulation and the vortex distance in the different spanwise section of the caudal fin are given, and then the dimension of the vortex ring is determined. The radius of the vortex ring is 79.3 mm and the average velocity circulation is 28152.9 mm²/s at the oscillating frequency of 0.835 Hz. The model of 3-D vortex ring chain of flexible oscillating caudal fin is constructed based on the information of wake vortex field. Finally, an effective analysis method is provided for establishing the relationship of oscillating parameters for the caudal fin and the wake structure and the intrinsic mechanism of efficient fish swimming is investigated.     

NUMERICAL INVESTIGATION ON THE HYDRODYNAMIC PERFORMANCES OF A NEW SPAR CONCEPT

Recently, the spar platform concept develops quickly in the offshore oil and gas exploitations, especially in deep and ultra-deep water, owing to its benign motion performance, excellent stability and adaptation to wide range of water depth. Many new spar concepts have been put forward with the purpose of reducing fabrication difficulty and cost, while meeting the requirements of exploitation in the meantime. Based on the aims mentioned above, a new spar concept was presented in this article and its hydrodynamics both in operating and survival conditions was studied by means of numerical simulation. Basic model tests were also conducted to calibrate the numerical approach. Following aspects are highlighted: (1) new spar concept, (2) global performance of the spar concept and (3) mooring line analysis.     

NUMERICAL STUDIES ON THE PROPULSION AND WAKE STRUCTURES OF FINITE-SPAN FLAPPING WINGS WITH DIFFERENT ASPECT RATIOS

An immersed-boundary method is used to investigate the flapping wings with different aspect ratios ranging from 1 to 5. The numerical results on wake structures and the performance of the propulsion are given. Unlike the case of the two-dimensional flapping foil, the wing-tip vortices appear for the flow past a three-dimensional flapping wing, which makes the wake vortex structures much different. The results show that the leading edge vortex merges into the trailing edge vortex, connects with the wing tip vortices and then sheds from the wing. A vortex ring forms in the wake, and exhibits different patterns for different foil aspect ratios. Analysis of hydrodynamic performances shows that both thrust coefficient and efficiency of the flapping wing increase with increasing aspect ratio.     

NUMERICAL MODELING PURIFICATION PERFORMANCE OF POT TEST

A three-dimensional mathematical model was developed to simulate the pollutant removal efficiency of the soil and plants in the pot test. The advection, dispersion, diffusion, adsorption, biochemical reaction and plant uptake processes were taken into account in the model. The three-dimensional 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 mathematical model was descretized by the finite element numerical method. In the pot test, the hydraulic loading was assumed to have the intermittent pattern simulating the rainfall duration and the occurrence of frequency, and the concentrations of pollutants in the influent and effluent were measured. The computed overall removal rates for the COD_Cr and TN in four cases are in the range of 90.62% ? 95.43% and 85.01% ? 96.46%, respectively. The differences between the computed and tested overall removal rates for the COD_Cr and TN are smaller than 5%. The time-varying oscillation pattern of the concentrations of the COD_Cr and TN were rationally simulated, which showed that the model presented in this article could be used to assess the pollutant removal efficiency of the soil and plants in related cases.     

NUMERICAL SIMULATION OF THE TURBULENT FLUID FLOW AND PREDICTION OF INCIPIENT CAVITATION NUMBER ON ISOLATED SURFACE TRIANGULAR PROTRUSION

ＮＵＭＥＲＩＣＡＬＳＩＭＵＬＡＴＩＯＮＯＦＴＨＥＴＵＲＢＵＬＥＮＴＦＬＵＩＤＦＬＯＷＡＮＤＰＲＥＤＩＣＴＩＯＮＯＦＩＮＣＩＰＩＥＮＴＣＡＶＩＴＡＴＩＯＮＮＵＭＢＥＲＯＮＩＳＯＬＡＴＥＤＳＵＲＦＡＣＥＴＲＩＡＮＧＵＬＡＲＰＲＯＴＲＵＳＩＯＮ￥ＲｅｎＢｉ...     

NUMERICAL SIMULATION OF THE EFFECTS OF WEIGHT SYSTEM ON THE HYDRODYNAMIC BEHAVIOR OF 3-D NET OF GRAVITY CAGE IN CURRENT

In this article, a model of 3-D net is set up by using lumped mass method. Model test results made by Lader and Enerhaug are cited to verify the numerical model. The aim of this paper is to investigate the effects of weight system on the hydrodynamic behavior of 3-D net of gravity cage in current. Using the 3-D net model, with different styles and masses of weight system, hydrodynamic behavior of gravity cage net in current is simulated. In this article, two styles of common weight system are used, which include: (1) sinker system , (2) bottom collar-sinker system. Under each style, three different masses of weight system are adopted. The numerical results indicate that the bottom collar-sinker system is practically feasible in improving the cage net volume deformation. Results of this study will give references for better knowledge of hydrodynamic behavior of gravity cage.     

THE HYDRODYNAMIC CHARACTERISTICS OF FREE VARIABLEPITCH VERTICAL AXIS TIDAL TURBINE

The hydrodynamic characteristics of free variable-pitch vertical axis tidal turbine are investigated by combining experime-ntal and numerical simulations.The variations of hydrodynamics are obtained based on testing the kinematics and the dynamics of the turbine under different flow and structural conditions.Through analyzing the movement of the turbine and the characteristics of the flow field by numerical simulations,it is shown how the turbine’s performance is improved.     

EXPERIMENTAL AND NUMERICAL STUDY FOR HYDRODYNAMIC CHARACTERISTICS OF AN OSCILLATING HYDROFOIL

The present article reports the experimental Particle Image Velocimetry （PIV） investigation and the corresponding numerical simulation results about the water flow over the oscillating hydrofoil and its unsteady dynamic characters. The experimental study focuses on the effect of mean angles of attack. The comparison between the PIV results and numerical prediction about the flow field using Fluent well demonstrates the capability of CFD on the simulation of the water flow around the pitching hydrofoil. The numerical results indicate that the forced oscillating frequencies have evident effects on the flow separation and vortex shedding. The simulations about the hydrodynamic drag and lift coefficients were also performed.     

NUMERICAL SIMULATION OF PARTICLE SEPARATION IN AN OIL-SAND SEPARATOR

ＮＯＴＡＴＩＯＮＳＡ　Ａｒｅａｏｆｉｎｌｅｔ ,ｍ2ａ　Ｃｅｎｔｒｉｆｕｇａｌａｃｃｅｌｅｒａｔｉｏｎ ,ｍ2 /ｓｉ　Ｇｒｉｄｏｆａｘｉａｌｄｉｒｅｃｔｉｏｎｍｌ 　ＭａｘｉｍｕｍｇｒｉｄｎｕｍｂｅｒｏｆｒａｄｉａｌｄｉｒｅｃｔｉｏｎＱ　Ｆｌｕｉｄｍａｓｓｒａｔｅ ,ｍ3/ｓＲｃ 　Ｍａｘｉｍｕｍｒａｄｉｕｓｏｆｃｙｃｌｏｎｅ ,ｍＲｅ　Ｒｅｙｎｏｌｄｓｎｕｍｂｅｒｒ　Ｄｉｍｅｎｓｉｏｎｌｅｓｓｒａｄｉａｌｄｉｓｔａｎｃｅｔ　Ｄｉｍｅｎｓｉｏｎｌｅｓｓｔｉｍｅｕ　Ｄｉｍｅｎｓｉｏｎｌｅｓｓａｘｉａｌｖｅｌｏｃ…     

NUMERICAL SIMULATION OF REYNOLDS NUMBER EFFECT ON EFFETIVE WAKE FIELD AND HYDRODYNAMIC PERFORMANCE OF PROPELLER BEHIND SHIP

1.INTRODUCTIONTheaccuratepredictionofeffectivewakefieldisofgreatslgnlflcancenolonlyindesigningpropellersforstudyofshipvibrationandnoisereduction.hulalsoinunderstandingflowphenomenanandcapturingflowstructureintheinteractionbetweentheshiphullandprerpeller.Theshipsternflowdrivenbyoperatingpropellersismuchmorecomplexthantheshipsternflowwithoutpropellers.Withoperatingpropellerstheaxialvelocityinfrontofpro-pellersisacceleratedgraduallyduetothecontractioneffectofI)ropellersandthecontractioneffec…     

THE NUMERICAL SIMULATION OF TWO-DIMENSIONAL OPEN CHANNEL TURBULENCE

A numerical simulation on 2-D open channel turbulence using the two-equationturbulent model(k-e model) is made.The diseretization equations of depth-averaged 2-D differ-ential equation are obtained by the control-volume formulation.Some examples including theflows in straight open channel,symmetry sudden expansion and one-side sudden expansion arecalculated by using the SIMPLE algorithm.The distributions of the flow velocity u,the kineticturbulent energy k,and the turbulent viscosity μ,etc.are obtained.The numerical calculationsindicate a good agreement with experimental data and other turbulent models calulations.     

NUMERICAL SIMULATION OF THE FLOW PATTERNS OF YUQIAO RESERVOIR

In this paper the slot method is used in the computation of 2-dimensional flow withtransient boundary.The slot located inside the computation zone is placed in each space grid,parallel to both X and Y axes.Combined with the operator splitting method,the numerical simu-lation of the flow patterns of Yuqiao Reservior is made.The calculated results are in good agree-ment with observed data.     

NUMERICAL SIMULATION OF TRANSIENT FLOW AROUND A SHIP IN UNSTEADY BERTHING MOTION

Ship berthing is a specific maneuver operation. The flow around a berthing ship and the forces acting on the hull are quite different from those for a ship in normal navigation. By solving the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations, the transient flow field around a ship undergoing unsteady lateral motion is simulated and the varying lateral hydrodynamic force acting on the hull is evaluated in this article. The numerical results obtained with different turbulence models are analyzed and compared with experimental results and other numerical results published in literature, and a turbulence model more suitable for simulation of the viscous flow around a ship undergoing unsteady berthing is determined.