The objective of this study is to get into physical insights to the unsteady force and the relevant mechanisms in forward flight of insects. Unsteady force in the forward flight was studied, based on a virtual model problem of a foil with oscillating translation and rotation in a uniform flow, by solving the two-dimensional incompressible Navier-Stokes equations with a finite element method. The effects of typical parameters, including the advance ratio, the inclined angle of stroke plane, the stroke amplitude, and the amplitude of pitching angle of attack, on the forces and the flow structures were analyzed....

A set of constrained Newton methods were developed for static traffic assignment problems.The Newton formula uses the gradient of the objective function to determine an improved feasible direction scaled by the second-order derivatives of the objective function.The column generation produces the active paths necessary for each odgin-destlnation pair.These methods then select an optimal step size or make an orthogonal projection to achieve fast,accurate convergence.These Newton methods based on the constrained Newton formula utilize path information to explicitly implement Wardrop's principle in the transport network modelling and complement the traffic assignment algodthms.Numedcal examples are presented to compare the performance with all possible Newton methods.The computational results show that the optimal-step Newton methods have much better convergence than the fixed-step ones,while the Newton method with the unit step size is not always efficient for traffic assignment problems.Furthermore,the optimal-step Newton methods are relatively robust for all three of the tested benchmark networks of traffic assignment problems....

The dynamic responses of two pontoons while connected with each other in irregular waves are calculated by means of three-dimensional (3-0) potential flow theory. The computation is to find the optimal status for connection at a certain sea state. On the basis of the relative motion of two pontoons in irregular waves, Visual FORTRAN programming language, as well as OpenGL (Open Graphics Library), is used to develop a set of virtual reality system of the relative motion of two pontoons, which is fully interactive with realistic effect. The transfinite interpolation scheme is applied for the mesh generation of wave surface, and the wave motion is simulated by surface elevation and calculated by 3-D potential flow theory....

In lost foam casting (LFC),the distribution of polymer beads during the bead filling process is not uniform,and the collision between polymer beads determines the distribution of two-phase flow of gas and solid.The interaction between the gas and solid phases reveals as coupling effect of the force that gas exerts on particles or vice versa,or that among particles.The gas-solid flow in filling process is nonlinearity,which makes the coupling effect an essential point to carry out a simulation properly.Therefore,information of each particle's motion is important for acquiring the law of filling process.In bead filling process,compressed air is pressed into mold cavity,and discharged from gas vent,creating a pressure difference between outer and inner space near the gas vent.This pressure difference directly changes the spatial distribution and motion trace of gas and solid phases.In this paper,Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) are employed to simulate the fluid dynamic character based on Newton's Third Law of Motion.The simulation results of some casting products such as pressure plate and valve handle are compared with the result obtained from practical experiment in order to test the feasibility of DEM.The comparison shows that this DEM method can be a very promising tool in the mould filling simulation of beads' movement....

Two mathematical models are built to study the effects of the fluid flow on thermal distributions of the gas tungsten arc welding(GTAW) process. One model is based on the heat conductivity equation, which doesn' t take the effects of the fluid flow into account, and the other couples the laminar heat transfer and fluid flow in the weld pool, which is called laminar fluid flow model in short. The simulated results of the two models show that the pattern and velocity of the fluid flow play a critical role in determining the thermal distribution and the weld pool shape. For the laminar fluid flow model, its highest temperature is 400 K lower than that calculated with the other model and the depth of its weld pool is shallower too, which is mainly caused by the main vortex of the flow in the weld pool....

From the viewpoint of systems energy conservation, the influences of material flow on its energy consumption in a steel manufacturing process is an important subject. The quantitative analysis of the relationship between material flow and the energy intensity is useful to save energy in steel industry. Based on the concept of standard material flow diagram, all possible situations of ferric material flow in steel manufacturing process are analyzed. The expressions of the influence of material flow deviated from standard material flow diagram on energy consumption are put forward....

Based on the continuum equation, momentum conservation and energy conservation equations, the numerical model of turbulent flow filling was introduced; the 3-D free surface vof method was improved. Whether or not the numerical simulation results are reasonable, it needs corresponding experimental validations. General experimental techniques for casting fluid flow process include: thermocouple tracking location method, hydraulic simulating method, heat-resistant glass window method and X-ray observation etc. The hydraulic analogue experiment with DPIV technique is arranged to validate the fluent flow program for low-pressure casting with 0.1×105 Pa and 0.6×105 Pa pressure visually. By comparing the flow head, liquid surface, flow velocity, it is found that the filling pressure value influences the flow state strongly. With the increase of the filling pressure, the fluid flow state becomes unstable, the flow head becomes higher, and the filling time is reduced. The simulated results are accordant with the observed results approximately, which can prove the reasonability of our numerical program for filling process further....

The solution algorithm (SOLA) method was used to solve the velocity and pressure field of the thermal flow filling process, and the volume of fluid (VOF) method for the free surface problem. Since the "donor-acceptor" rule often results in the free interface vague, the explicit difference method was adopted, and a method describing the free surface state at 0＜F＜1 was proposed to deal with this problem. In order to raise the computation efficiency, such algorithms were investigated and invalidated as: 1) internal and external area separation simplification algorithm; 2) the reducing necessary search area method. With the improved algorithms, the filling processes of the valve cover castings with gravity cast and an up cylinder block casting with low-pressure cast were simulated, the simulation results are believable and the computation efficiency is greatly improved. The SOLA-VOF model and its difference method for thermal fluid flow filling process were introduced....

Filtration and flow process of molten metals was analyzed by water simulation experiments. Fluid dynamic phenomena of molten metal cells through a foam ceramic filter was described and calculated by ERGOR equation as well. The results show that the filter is most useful for stable molten metals and the filtered flow is laminar, so that inclusions can be removed more effectively....

In the rill erosion process,run-on water and sediment from upslope areas,and rill flow hydraulic parameters have significant effects on sediment detachment and transport.However,there is a lack of data to quantify the effects of run-on water and sediment and rill flow hydraulic parameters on rill erosion process at steep hillslopes,especially in the Loess Plateau of China.A dual-box system,consisting of a 2-m-long feeder box and a 5-m-long test box with 26.8% slope gradient was used to quantify the effects of upslope runoff and sediment,and of rill flow hydraulic parameters on the rill erosion process.The results showed that detachment-transport was dominated in rill erosion processes; upslope runoff always caused the net rill detachment at the downslope rill flow channel,and the net rill detachment caused by upslope runoff increased with a decrease of runoff sediment concentration from the feeder box or an increase of rainfall intensity.Upslope runoff discharging into the rill flow channel or an increase of rainfall intensity caused the rill flow to shift from a stratum flow into a turbulent flow.Upslope runoff had an important effect on rill flow hydraulic parameters,such as rill flow velocity,hydraulic radius,Reynolds number,Froude number and the Darcy-Weisbach resistance coefficient.The net rill detachment caused by upslope runoff increased as the relative increments of rill flow velocity,Reynolds number and Froude number caused by upslope runoff increased.In contrast,the net rill detachment decreased with an increase of the relative decrement of the Darcy-Weisbach resistance coefficient caused by upslope runoff.These findings will help to improve the understanding of the effects of run-on water and sediment on the erosion process and to find control strategies to minimize the impact of run-on water....

The mass of the embedded systems are driven by second batteries, not by wired power supply. So saving energy is one of the main design goals for embedded system. In this paper we present a new technique for modelling and solving the dynamic power management (DPM) problem for embedded systems with complex behavioural characteristics. First we model a power-managed embedded computing system as a controllable Flow Chart. Then we use the Poisson process for optimisation, and give the power management algorithm by the help of Dynamic Voltage Scaling (DVS) technology. At last we built the experimental model using the PXA 255 Processors. The experimental results showed that the proposed technique can achieve more than12％ power saving compared to other existing DPM techniques....

Stability condition and quality evaluation formula of layerlike backfilling roof, Q≥C, where Q denotes is quality index depending on allowable compressive or tensile strength and integrity of backfilling, and C is the technical index depending on mining method and backfilling technology, were inferred according to simply supported beam theorem. Technical treatment measures for instable backfilling roof, including optimum of appropriate filling materials and dosage for excellent flow property and reduction of backfill cost. It is proved that slope equation of backfill slurry in a stope to be filled is y=hexp[-x2/(2σ)2)], where h is height of cone and σ2 is mean square, and that optimum drainage point of backfill slurry can be determined by the equation and sizes of stope. Case study indicates that the results can give a theoretical support for quality evaluation and control of layerlike backfilling....

Hydraulic transport of sand is one of the key processes in river, lake, harbor and waterway dredging engineering. Understanding the flow resistance, solid distribution, flow stratification, transport economy, etc., in the two-phase flow of sand-water mixture through a pipeline is crucial to the design and operation of power drives of a dredger, and to the construction of a dredging project. This paper presents the intensive laboratory experimental data and physical and numerical analyses on the highly concentrated slurry flow under an extended large range of slurry mean velocities for three narrow-graded sands of different sizes. The investigation indicates that the solids concentration and particle size strongly affect the slurry flow characteristics....

The problem of hydrate blockage of pipelines in offshore production is becoming ever-increasing severe because oil fields in ever-increasing unusual environments have been brought in production.HCFC-141b and THF were selected as the substitutes to study the flow assurance of the hydrates in pipelines.There are critical hydrate volume concentrations for these two slurries.Hydrate slurries behave like Bingham fluids and have high agglomerating tendency when the hydrate volume concentrations are larger than the critical ones.Based on theological behaviors of these two hydrates,a non-dimensional parameter is proposed through studying the driving forces of agglomeration among hydrate particles,which shows the agglomerating probability of hydrate particles in pipeline and can be used to judge the safety of the pipeline.Moreover,a safe model to judge the safely flow hydrate slurries was presented and verified with the experimental data,which demonstrates that the model is effective to judge whether the pipeline can be run safely or not....

分析拓扑优化中的密度惩罚函数插值法SIMP（Solid isotropic material with penalization model）,将结构力学中的拓扑优化方法应用到渗流问题的拓扑优化设计中,用有限元的方法建立了简单的理想状态下的渗流问题的拓扑优化数学模型,并采用基于剃度法的数值解法-优化准则法（OC系列算法）,以设计具有最小能量损耗情况下的流体最佳流动路径的拓扑分布。以一组二维渗流问题为例,说明了该模型的有效性,为渗流问题的优化设计提供了一种有效的新思路和方法。...

Volumetric fraction distribution measurement is a constituent part of process tomography system in oil-water-gas mulfiphase flow. With the technological development of nuclear radial inspection, dual-energy γ-ray techniques make it possible to investigate the concentration of the different components on the cross-section of oil-water-gas multiphase pipe-flow. The dual-energy gamma-ray technique is based on materials attenuation coefficients measurement comprised of two radioactive isotopes of 241Am and 241Cs which have emission energies at 59.5 keV and 662 keV in this project. Nuclear instruments and data acquisition system were designed to measure the material's attenuation dose rate and a number of static tests were conducted at the Multiphase Laboratory, Institute of Mechanics, Chinese Academy of Sciences. Three phases of oil-water-gas media were investigated for their possible use to simulate different media volumetric fraction distributions in experimental vessels. Attenuation intensities were measured, and the arithmetic of linear attenuation coefficients and the equations of volumetric fractions were studied. Investigation of an unexpected measurement error from attenuation equations revealed that a modified arithmetic was involved and finally the system achieved acceptable accuracy in experimental research....

The knowledge of flow regimes is very important in the study of a two-phase flow system. A new flow regime identification method based on a Probability Density Function (PDF) and a neural network is proposed in this paper. The instantaneous differential pressure signals of a horizontal flow were acquired with a differential pressure sensor. The characters of differential pressure signals for different flow regimes are analyzed with the PDF. Then, four characteristic parameters of the PDF curves are defined, the peak number (K1), the maximum peak value (K2), the peak position (K3) and the PDF variance (K4). The characteristic vectors which consist of the four characteristic parameters as the input vectors train the neural network to classify the flow regimes. Experimental results show that this novel method for identifying air-water two-phase flow regimes has the advantages with a high accuracy and a fast response. The results clearly demonstrate that this new method could provide an accurate identification of flow regimes....

This paper gives an overview of the recent development of modeling and simulation of chemically reacting flows in gas-solid catalytic and non-catalytic processes.General methodology has been focused on the Eulerian-Lagrangian description of particulate flows.where the particles behave as the catalysts or the reactant materials.For the strong interaction between the transport phenomena(i.e.,momentum.heat and mass transfer)and the chemical teactions at the particle scale.a cross-scale modeling approach.i.e., CFD-DEM or CFD-DPM.is established for describing a wide variety of complex reacting flows in multiphase reactors.Representative processes,including fluid catalytic cracking(FCC).catalytic conversion of syngas to methane.and coal pyrolysis to acetylene in thermal plasma.are chosen as case studies to demonstrate the unique advantages of the theoretical scheme based on the integrated particle-scale information with clear physical meanings.This type of modeling approach provides a solid basis for understanding the multiphase reacting flow problems in general....

The measurement of void fraction is of importance to the oil industry and chemical industry. In this article,the principle and mathematical method of determining the void fraction of horizontal gas-liquid flow by using a single-energy γ-ray system is described. The γ-ray source is the radioactive isotope of 241Am with γ-ray energy of 59.5 keV. The time-averaged value of the void fraction in a 50.0-mm i.d. transparent horizontal pipeline is measured under various combinations of the liquid flow and gas flow. It is found that increasing the gas flow rate at a fixed liquid flow rate would increase the void fraction. Test data are compared with the predictions of the correlations and a good agreement is found. The result shows that the designed γ-ray system can be used for measuring the void fraction in a horizontal gas-liquid two-phase flow with high accuracy....

Current modelling techniques for the prediction of conveying line pressure drop in low velocity dense phase pneumatic conveying are largely based on steady state analyses.Work in this area has been on-going for many years with only marginal improvements in the accuracy of prediction being achieved.Experimental and theoretical investigations undertaken by the authors suggest that the flow mechanisms involved in dense phase conveying are dominated by transient effects rather than those of steady state and are possibly the principal reasons for the limited improvement in accuracy.This paper reports on investigations on the pressure fluctuation behaviour in dense phase pneumatic conveying of powders.The pressure behaviour of the gas flow in the top section of the pipeline was found to exhibit pulsatile oscillations.In particular,the pulse velocity showed variation in magnitude while the frequency of the oscillations rarely exceeded 5 Hz.A wavelet analysis using the Daubechie 4 wavelet found that the amplitude of the oscillations increased along the pipeline.Furthermore,there was significant variation in gas pulse amplitude for different types of particulate material....

Dense gas-particle flows are encountered in a variety of industrially important processes for large scale production of fuels, fertilizers and base chemicals. The scale-up of these processes is often problematic and is related to the intrinsic complexities of these flows which are unfortunately not yet fully understood despite significant efforts made in both academic and industrial research laboratories. In dense gas-particle flows both (effective) fluid-particle and (dissipative) particle-particle interactions need to be accounted for because these phenomena to a large extent govern the prevailing flow phenomena, i.e. the formation and evolution of heterogeneous structures. These structures have significant impact on the quality of the gas-solid contact and as a direct consequence thereof strongly affect the performance of the process. Due to the inherent complexity of dense gas-particles flows, we have adopted a multi-scale modeling approach in which both fluid-particle and particle-particle interactions can be properly accounted for. The idea is essentially that fundamental models, taking into account the relevant details of fluid-particle (lattice Boltzmann model) and particle-particle (discrete particle model) interactions, are used to develop closure laws to feed continuum models which can be used to compute the flow structures on a much larger (industrial) scale. Our multi-scale approach (see Fig. 1 ) involves the lattice Boltzmann model, the discrete particle model, the continuum model based on the kinetic theory of granular flow,and the discrete bubble model. In this paper we give an overview of the multi-scale modeling strategy, accompanied by illustrative computational results for bubble formation. In addition, areas which need substantial further attention will be highlighted....

n this paper,we study a free boundary value problem for two-phase liquidgas model with mass-depcndent viscosity coefficient when both the initial liquid and gas masses connect to vacuum continuously.The gas is assumed to be polytropic whereas the liquid is treated as an incompressible fluid.We give the proof of the global existence and uniqueness of weak solutions when β ∈ (0,1),which have improved the result of Evje and Karlsen,and we obtain the regularity of the solutions by energy method....

Heat transfer between gas-solid multiphase flow and tubes occurs in m a ny industry processes, such as circulating fluidized bed process, pneumatic conv eying process, chemical process, drying process, etc. This paper focuses on the influence of the presence of particles on the heat transfer between a tube and g as-solid suspension. The presence of particles causes positive enhancement of h e at transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the case of very low solid loading ratio (Ms of les s than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle s ize and flow Reynolds number was derived from experimental data. In addition, th e k-ε two-equation model and the Fluctuation-Spectrum- Random-Trajecto ry Model ( FSRT Model) are used to simulate the flow field and heat transfer of the gas-ph a se and the solid-phase, respectively. Through coupling of the two phases the mo d el can predict the local and total heat transfer characteristics of tube in gas - solid cross flow. For the total heat transfer enhancement due to particles loadi ng the model predictions agreed well with experimental data....

This article proposes a new model for calculating the gas-well liquid loading capacity,which is critical to an accurate prediction of gas well production.Based on analysis of flow regime during the gas well production with water,which is regarded as many single particles in the model,with the shape of particles being assumed as disk-like ellipsoid instead of traditional sphere and changing according to the forces exerted on them,the influences of non-Darcy flow,compressibility,and non-sphere shape on friction factor are analyzed.The differences between the new model and other models are discussed and a new formula for calculating the critical flow rate is obtained.The calculation results and a comparison with other two models show that the new model is more consistent with the actual situation and is practical....