江浙沪地区风暴潮的特征与预测

风暴潮的运行规律,可以用流体力学的湍流方程组进行描述,实质上它是一种非线性的湍流现象。动力数值计算法,是风暴潮预报的发展方向。

CFD prediction of local scour hole around bridge piers

In order to predict the local scour hole and its evaluation around a cylindrical bridge pier, the computational fluid dynamics （CFD） and theories of sediment movement and transport were employed to carry out numerical simulations. In the numerical method, the time-averaged Reynolds Navier-Stokes equations and the standard k-e model were first used to simulate the three-dimensional flow field around a bridge pier fixed on river bed. The transient shear stress on river bed was treated as a crucial hydrodynamic mechanism when handling sediment incipience and transport. Then, river-bed volumetric sediment transport was calculated, followed by the modification of the river bed altitude and configuration. Boundary adaptive mesh technique was employed to modify the grid system with changed river-bed boundary. The evolution of local scour around a cylindrical bridge pier was presented. The numerical results represent the flow pattern and mechanism during the pier scouring, with a good prediction of the maximum scour hole depth compared with test results.

Riser VIV and its numerical simulation

This paper summarizes some of the typical riser vortex-induced vibration （VIV） problems in subsea oil and gas developments, and presents the corresponding computational fluid dynamics （CFD） time domain simula- tion results to address these problems. First, the CFD time domain simulation approach was applied to analyze the wake field behind a stationary cylinder and a vibrating cylinder. Then a vertical riser VIV response under uniform current was studied. The VIV response time histories revealed some valuable clues that could lead to explanation of the higher harmonics. After that, a vertical riser VIV response under shear current was investigated. A 3 000 ft （1 ft=-0.304 8 m） water depth top tensioned riser was sized, and its VIV responses under uniform and shear current were studied. Then this paper continues to discuss one catenary flexible riser VIV response during normal lay. Last, the time domain simulation approach was applied to a partially submerged flexible jumper, to study the jumper VIV behavior, and dynamic motion envelopes. It was demonstrated that the time domain simulation ap- proach is able to disclose details of the flow field, vortex shedding pattern, and riser dynamic behavior, and han- dle different tvoes of risers under different Woe of currents.

Time Collocation Method for Structural Dynamic Problems

In order to achieve highly accurate and efficient numerical calculations of structural dynamics, time collocation method is presented. For a given time interval, the numerical solution of the method is approximated by a polynomial. The polynomial coefficients are evaluated by solving algebraic equation. Once the polynomial coefficients are evaluated, the numerical solutions at any time in the interval can be easily calculated. New formulae are derived for the polynomial coefficients,which are more practical and succinct than those previously given. Two structural dynamic equations are calculated by the proposed method. The numerical solutions are compared with the traditional fourth-order Runge-Kutta method. The results show that the method proposed is highly accurate and computationally efficient. In addition, an important advantage of the method is the simplicity in software programming.

Dynamic mathematical model and numerical calculation method on spontaneous combustion of loose coal

Through the experiment of coal spontaneous combustion and relationship particle size with oxidation character of loose coal, some calculation formula of characteristic parameters is got in the process of coal spontaneous combustion. According to these theories of porous medium hydrodynamics, mass transfer and heat transfer, mathematical models of air leak field, oxygen concentration field and temperature field are set up. Through experimental and theoretical analysis, 3 D dynamic mathematical model of coal spontaneous combustion is set up. The method of ascertaining boundary condition of model is analyzed, and finite difference method is adopted to solve 2 D mathematical model.

Crosswind stability of high-speed trains in special cuts

Analysis of the aerodynamic performance of high-speed trains in special cuts would provide references for the critical overturning velocity and complement the operation safety management under strong winds.This work was conducted to investigate the flow structure around trains under different cut depths,slope angles using computational fluid dynamics(CFD).The high-speed train was considered with bogies and inter-carriage gaps.And the accuracy of the numerical method was validated by combining with the experimental data of wind tunnel tests.Then,the variations of aerodynamic forces and surface pressure distribution of the train were mainly analyzed.The results show that the surroundings of cuts along the railway line have a great effect on the crosswind stability of trains.With the slope angle and depth of the cut increasing,the coefficients of aerodynamic forces tend to reduce.An angle of 75°is chosen as the optimum one for the follow-up research.Under different depth conditions,the reasonable cut depth for high-speed trains to run safely is 3 m lower than that of the conventional cut whose slope ratio is 1:1.5.Furthermore,the windward slope angle is more important than the leeward one for the train aerodynamic performance.Due to the shield of appropriate cuts,the train body is in a minor positive pressure environment.Thus,designing a suitable cut can contribute to improving the operation safety of high-speed trains.

Numerical simulation of a direct internal reforming solid oxide fuel cell using computational fluid dynamics method

A detailed mathematical model of a direct internal reforming solid oxide fuel cell(DIR-SOFC) incorporating with simulation of chemical and physical processes in the fuel cell is presented. The model is developed based on the reforming and electrochemical reaction mechanisms,mass and energy conservation,and heat transfer. A computational fluid dynamics(CFD) method is used for solving the complicated multiple partial differential equations(PDEs) to obtain the numerical approximations. The resulting distributions of chemical species concentrations,temperature and current density in a cross-flow DIR-SOFC are given and analyzed in detail. Further,the influence between distributions of chemical species concentrations,temperature and current density during the simulation is illustrated and discussed. The heat and mass transfer,and the kinetics of reforming and electrochemical reactions have significant effects on the parameter distributions within the cell. The results show the particular characteristics of the DIR-SOFC among fuel cells,and can aid in stack design and control.

Separation Processes of Granular Materials by Sizes at the Sieve Classifiers

A mathematical model of the kinetics of thin-layer separation of granular materials by size stacked sieve classifiers based on the theory of Markov processes is constructed. The probability of screening in a cell in the shape and size of the holes and particle sieve material shared with the influence of the relative speed of their movement was determined. Residues on whole meal with sieves were identified by a kinetic model and numerical calculations, the efficacy of separation.

Investigation on high angle of attack characteristics of hypersonic space vehicle

The high angle of attack characteristics play an important role in the aerodynamic performances of the hypersonic space vehicle. The three-dimensional Reynolds Averaged Navier-Stokes (RANS) equations and the two-equation RNG k-? turbulence model have been employed to investigate the influence of the high angle of attack on the lift-to-drag ratio and the flow field characteristics of the hypersonic space vehicle, and the contributions of each component to the aerodynamic forces of the vehicle have been discussed as well. At the same time, in order to validate the numerical method, the predicted results have been compared with the available experimental data of a hypersonic slender vehicle, and the grid independency has been analyzed. The obtained results show that the predicted lift-to-drag ratio and pitching moment coefficient show very good agreement with the experimental data in the open literature, and the grid system makes only a slight difference to the numerical results. There exists an optimal angle of attack for the aerodynamic performance of the hypersonic space vehicle, and its value is 20°. When the angle of attack is 20°, the high pressure does not leak from around the leading edge to the upper surface. With the further increasing of the angle of attack, the high pressure spreads from the wing tips to the central area of the vehicle, and overflows from the leading edge again. Further, the head plays an important role in the drag performance of the vehicle, and the lift percentage of the flaperon is larger than that of the rudderevator. This illustrates that the optimization of the flaperon configuration is a great work for the improvement of the aerodynamic performance of the hypersonic space vehicle, especially for a high lift-to-drag ratio.

Effect of Tip Flange on Tip Leakage Flow of Small Axial Flow Fans

Aerodynamic performance of an axial flow fan is closely related to its tip clearance leakage flow. In this paper, the hot-wire anemometer is used to measure the three dimensional mean velocity near the blade tips. Moreover, the filtered N-S equations with finite volume method and RNG k-s turbulence model are adopted to carry out the steady simulation calculation of several fans that differ only in tip flange shape and number. The large eddy simulation and the FW-H noise models are adopted to carry out the unsteady numerical calculation and aerodynamic noise prediction. The results of simulation calculation agree roughly with that of tests, which proves the numerical calculation method is feasible.The effects of tip flange shapes and numbers on the blade tip vortex structure and the characteristics are analyzed. The results show that tip flange of the fan has a certain influence on the characteristics of the fan. The maximum efficiencies for the fans with tip flanges are shifted towards partial flow with respect to the design point of the dattun fan. Furthermore, the noise characteristics for the fans with tip flanges have become more deteriorated than that for the datum fan. Tip flange contributes to forming tip vortex shedding and the effect of the half-cylinder tip flange on tip vortex shedding is obvious. There is a distinct rela- tionship between the characteristics of the fan and tip vortex shedding.The research results provide the profitable reference for the internal flow mechanism of the performance optimization of small axial flow fans.

Numerical method of static aeroelastic correction and jig-shape design for large airliners

In this paper,a coupled CFD-CSD method based on N-S equations is described for static aeroelastic correction and jig-shape design of large airliners.The wing structural flexibility matrix is analyzed by a finite element method with a double-beam model.The viscous multi-block structured grid is used in aerodynamic calculations.Flexibility matrix interpolation is fulfilled by use of a surface spline method.The load distributions on wing surface are evaluated by solving N-S equations with a parallel algorithm.A flexibility approach is employed to calculate the structural deformations.By successive iterations between steady aerodynamic forces and structural deformations,a coupled CFD-CSD method is achieved for the static aeroelastic correction and jig-shape design of a large airliner.The present method is applied to the static aeroelastic analysis and jig-shape design for a typical large airliner with engine nacelle and winglet.The numerical results indicate that calculations of static aeroelastic correction should employ tightly coupled CFD-CSD iterations,and that on a given cruise shape only one round of iterative design is needed to obtain the jig-shape meeting design requirements.

Design of a new tandem wings hybrid airship

It is scientifically important science value and engineering promising to develop the buoyancy-lift integrated hybrid airship for high attitude platform.Through the numerical method,a new tandem wings hybrid airship with both higher utility value and economy efficiency was obtained and its total performance and technical parameters were analyzed in detail.In order to further improve the lift-drag characteristics,we implemented the optimization design for aerodynamic configuration of tandem wings hybrid airship via the response surface method.The results indicate that the tandem wings hybrid airship has considerable volume efficiency and higher aerodynamic characteristics.After optimization,the lift-drag ratio of this hybrid airship was increased by 6.08%.In a given gross lift condition,tandem wings hybrid airship may provide more payload and specific productivity.Furthermore,the size of tandem airship is smaller so the demand for skin flexible materials can be reduced.Results of this study could serve as a new approach to designing buoyancy-lifting integrated hybrid airship.

Approximating Stationary Statistical Properties

It is well-known that physical laws for large chaotic dynamical systems are revealed statistically.Many times these statistical properties of the system must be approximated numerically.The main contribution of this manuscript is to provide simple and natural criterions on numerical methods (temporal and spatial discretization) that are able to capture the stationary statistical properties of the underlying dissipative chaotic dynamical systems asymptotically.The result on temporal approximation is a recent finding of the author,and the result on spatial approximation is a new one.Applications to the infinite Prandtl number model for convection and the barotropic quasi-geostrophic model are also discussed.