考虑预估驾驶行为的跟驰模型及其稳定性分析

在OV模型的基础上,进一步考虑预估驾驶行为对车流的影响,提出一个新的跟驰模型以获得预估驾驶行为与交通拥堵的关系。通过对新模型进行稳定性分析得到了系统的临界稳定条件。数值仿真结果表明：新模型能够模拟诸如时停时走、系统临界相变等实际交通现象,较OV模型更贴近于实际。同时,预估驾驶行为增强了交通流稳定性能,提高了车流陷入交通阻塞状态的阈值。最后以车速的平滑度和波动幅度最小为评价指标得到了新模型中预估参数的最优取值范围。     

Microscopic Traffic Simulation Mathematic Model Based on Cellular Automata

This paper presents a model for freeway traffic flow simulation and prediction. The model uses cellular automation theory to model complex traffic behavior. The advantage of the cellular automata approach is that the roadway to be modeled is quantized into simple homogeneous cells, time is quanitzed into discrete steps, and physical quantities take on a finite set of values. Also, the state of the cells is updated at each discrete timestep by using a vehicle update algorithm that combines a few vehicle motion models, governed by a relatively small set of parameters. Then vehicles just move one or several cells at each discrete timestep according to the self-defined rule. This approach makes the computer operation feasible. At last, the paper puts forward a suppose that if the simulation system is equiped with the self-study system of NN (neural network) module according to the statistical data from the transducer fixed on the freeway, it can predict the traffic status ahead of 10 minutes.     

An Unsteady Flow Analysis in Gas Transmission Pipeline Based on Theory of Functional Analysis

Branch -like pipeline is a common structure in gas transmission pipeline. In the light of the constituent properties of natural gas branch - like pipeline system, the system can be divided into fundamental constituent units. This paper presents a realistic unsteady flow model consisting of simple models of pipeline units and connecting conditions, boundary conditions and initial condition associated with units by using system analysis method. The solutions in wide sense are obtained by theory of functional analysis and operator series method, Such a method has the properties of both analytical solution and numerical solution methods. When the divided pipeline unit is larger, an intuitive approximate analytical solution may be obtained; while the one is smaller, a more accurate numerical solution may be acquired. Based on this, a general computer program has been developed for this model and solutions have been used successfully in a local natural gas transmission network in Sichuan. It is proved that the model and algorithm proposed in this paper are of the advantages of convenient calculation, high precision, time saving and wide application range by way of analysis and application.     

Simulation of thermocapillary flow in a two dimensional cavity with lattice Boltzmann method

Thermocapillary flow driven by an unbalanced surface tension plays the most important role for mass and heat transport in floating zone melt crystal growth under microgravity. The authors develop both a serial and a parallel codes with lattice Bhatnagar-Gross-Krook(BGK) model using two distribution functions, and numerically study the thermocapillary flow in a two dimensional square cavity with a single free surface under microgravity condition. The serial code is developed by combining collision and propagation step, using a temporary array to continuously read distribution functions, and its performance is improved two times faster than the code with separating the collision and propagation step. The MPI parallel code is proposed utilizing one dimensional partitioning and non-blocking communication. The accurate and reliable results are achieved with both the serial and parallel codes by comparing with CFD results simulated by the finite volume method; the MPI parallel code has high performance.     

POD analysis of flow structures in thermally stratified flow in a confined space with the effects of horizontal wind

PIV measurements are carried out on the thermally stratified flows under different horizontal shear intensities in a confined space. Proper orthogonal decomposition (POD) is used to analyze the structures of these thermally stratified flows. Results show that, at the conditions without forced horizontal airflow, the low-order POD mode constitutes a high proportion of the total energy of the flow, and the horizontal flow is the dominant flow structure. The horizontal shear drives the energy to dissipate from large structure to smaller structures. Relative to the conditions without forced horizontal airflow, the ratios of vertical kinetic energy to horizontal kinetic energy become higher for each order of POD mode in the conditions with forced horizontal airflow. This indicates that horizontal shear can result in stratification instability and enhance the mass exchange in the vertical direction.     

Investigation on the flow field in the connection sectionbetween two heat exchangers of a condensate gas water heater

This paper investigates a new type of condensate gas water heater,which consisted of a burner,a high temperature heater exchanger (i.e.rut exchanger) and a low temperature heater exchanger (i.e.subjoin exchanger or condensate exchanger).These components are set vertically one by one with a same rare plane.The subjoin exchanger is set at top and smaller in width than the rut exchanger and burner.A lean plane with some holes is set in the connect channel between the two exchangers aslant.As the flue gas flow crows the subjoin heater exchanger,the gas temperature will be below the dew point,and the same steam in the gas condensed into water.These blobs drip to the lean plane and are collected through the holes on the plane.The flow field of the connect channel and subjoin exchanger affected by the dip angle and holes distribution of the lean plane is investigated with CFD.The results show that there is a suitable configuration about the dip anger,hole's diameter and distribution of the lean plane.With that configuration,the flue gas can wash the tubes of the subjoin heat exchanger homogeneously in a higher velocity than the rut exchanger does.     

Water model study on flow optimization of five streams L-type tundish

In this paper, the water model method is used to optimize the flow behavior of asymmetrical five streams L-type tundish in a steelmaking plant. The results show that the optimization plan is set up with turbulence suppressor T+ vice guide wall D2+ main guide wall with three holes (D1a) which consists of top two holes with 25° inclination and one hole with 30° inclination below. With this plan, the time which the colorants reach to the outlets increases, the difference of response time in all outlets decreases, the peak concentration of the RTD reduces, the existence time of high concentration liquid steel extends, and the ratio of dead zone in each streams reduces.     

Numerical Simulation on Confluence of the Two Rivers in Chongqing City

Flows of the confluence of Yangtze River and Jialing River in the city of Chongqing are numerically simulated by using Delft3D Model with staggered grids and ADI integral method. The water level, flow velocity and drogue trace are studied. Comparing the numerical results with observed data shows good agreement. Therefore the computational model and the simplified parameters are of good accuracy and have practical meaning. The results show that the contamination will linger near the Caiyuanba area and drift to Chaotianmen and the right bank of Yangtze River upstream. The results can be used to forecast flood, inspect contamination and management of riverway in the city.     

Conversion of flow pattern in the slender crucible by detached solidification

When the top surface is non-slip solid and the ratio between height and radius of crucible equals 2, the finite-difference method is adopted to carry on three-dimensional numerical simulation on the thermocapillary convection in detached solidification under microgravity. The distributions of velocity and temperature in the melt are obtained as the width of gap in crucible is selected as 0.1, 0.075 and 0.05, respectively. The results show that when the Marangoni number is small, there is one steady toroidal roll cell near the lower free surface, and the flow of melt is steady and weak. With the increase of Marangoni number, the flow is expanded toward the inner part of melt gradually and the velocity of flow on the lower free surface increases. When the Marangoni number exceeds the critical value, the flow of melt becomes unstable.     

Analysis of plastic flow characteristics based on bridge steel 16Mn ratcheting

Abstract:The analysis of the plastic flow characteristics on the basis of the ratcheting experimental results for the bridge steel 16Mn are carried out by calculatig the plastic modulus H and the angle θ between the backstress rate deviator and the plastic flowdirection. The different mechanisms causing uniaxial andmultiaxial non proportional ratchetting are illustrated, that is, the starting and evolution of uniaxial ratchetting is due to the different values of the plastic modulus H at the symmetric loading points with respect to the mean stress. On the other hand, the staring and evolution of multiaxial non proportional ratcheting is driven by H and θ variations. The influence of loading history on ratchetting is the result of the influence of loading history on the angle θ.     

The developing of the potential flow modelling of the burden flow in a blast furnace

Potential flow theory is an alternative theory to simulate burden flow in a blast furnace. But a contour line of the flow function defined to solve the old potential flow model isn’t a stream line. In this paper, the old potential flow model is first developed to a three-equation model which should include the equations of motion and continuity, and it is proved that the contour lines of the flow function defined to solve this three-equation model are stream lines. Second, an equation capable of calculating the distribution of diameter of burden particles in blast furnace is derived from an assumption that all burden particles on a stream line has the same diameter. Finally, the developed potential flow model and the derived equation are used to simulate a final reduction reactor producing hot metal containing Cr, together with other needed transportation equations. These works would play an important improving and exemplary role in the application of potential flow theory to simulate blast furnace process and other iron-making process.     

Similar experiments of the flow field in cavity construction period of underground energy storage

A similar model experimental platform of flow field in construction period of salt caverns is established based on the similar theory of “selected laws of physics”. The movement rule of flow field in cavity construction period is analyzed by systematic experiments with staining. It finds that the brine migration in reverse circulation of cavity construction can be divided into 6 role zones: buoyant plume zone, convection diffusion zone, buffer diffusion zone, saturated precipitation zone, border dissolution zone and waterfall flow zone. The increase of water injection flow rate accelerates its influence scope and spread speed, but the brine’s movement trend cannot be changed. The change of tube pitch and its spatial location changes the influence scope of water injection flow. Promoting the tube pitch makes the influence scope of fresh water upward, which accelerates the dissolution of upper salt rock. Interlayer changes not only the state of water injection flow, but also the state of boundary mass flow. The more the number of sandwich, the more complex the motion state and the concentration distribution of brine are. With the expansion of the cavity, the relative influence scope of the injection flow and the boundary mass flow become small, and injection water flow’s influence scope gradually goes upward.     

Analysis on Simulation Meteorological Data Under Climate Change

Climate has a determining influence on building energy consumption. Since 1980s, the global climate has appeared excessive warming, which inevitably causes the change of building energy consumption. The climatic simulation was used to forecast meteorological data from 2021 to 2050 for five cities in China. The five cities represent five different climate types in China. According to the Analysis of Energy Efficient Meteorological Year (AEEMY), model of meteorological data for building energy simulation based on TMY2 was presented. At the same time, meteorological data for DOES was also made from 1971 to 2000. A high residential building was respectively simulated in five cities under two kinds of meteorological data by using DOE2 software. The model of simulation was proved by the simulation result.     

Design and numerical simulation for flow deflector in the gas flue of selective catalytic reduction denitrification system

Four design schemes of flow deflector in the gas flue of selective catalytic reduction (SCR) denitrification system are simulated based on K ε turbulence model and 2D model by Fluent. By analyzing the speed profile and pressure drop of the import and export, the effects of the flow deflector on the import and export speed profile, pressure drop, and energy dissipation are studied. It can be concluded that flow field distribution could be significantly improved by putting the flow deflector into the gas flue. Reasonable flow deflector design can not only make the flow field distribution uniform but also reduce the pressure drop and the energy dissipation. With the increase of flow deflector dimensions, the flow field distribution will be more uniform. The pressure drop and the energy dissipation will increase because of the increase of resistance caused by flow deflector. The research results are helpful for designing selective catalytic reduction denitrification system.      

Modeling of the Break Simulation for Both Single and Two Phase Conditions

Based on the Moody model and complied with the modular modeling ideology and principle,a general break simulation model has been proposed for both single and two phase conditions in a thermal liquid pipe.This model now is used to develop the training simulator a power plant.     

发动机用平板型空滤器流动阻力特性分析和改进

为减小平板型空滤器流动阻力以增大进气量,对平板型空滤器流动阻力特性开展了实验研究,获得了空滤器流动阻力随流量变化的规律和阻力构成成分。阻力随流量的增大而加速增大,滤芯阻力约占整个空滤器阻力的一半,入口流量为120 m 3/h时,总阻力为915.3 Pa,滤芯阻力为426.4 Pa。在实验获得滤芯阻力参数的基础上,提出采用多孔介质跃升模型对平板型空滤器内部流场开展三维数值仿真分析,结果表明,仿真结果与实验结果比较吻合,最大误差为5.67%。滤芯阻力同样约占整个阻力的一半,另一半阻力主要为出口处阻力,其余壁面阻力约占15%。最后,在实验和仿真分析的基础上,提出了改进模型并进行了仿真分析。结果表明,改进模型阻力有较大程度的下降,入口流量为120 m 3/h时,总阻力为588.2 Pa,较原始模型下降了32.2%;增大空滤器流通横截面积是减小阻力以增大进气量的有效手段,改进空滤器壁面的平滑性是补充措施。     

Aeroacoustics numerical simulation of flow past tow dimensional two circular cylinders in Tandem arrangements

The flow mechanism of flowing over two circular cylinders in tandem arrangements is numerically investigated. First, the unsteady incompressible Navier Stokes equation is solved using two dimensional large eddy simulation (LES) model in order to capture the flow instantaneous source data. Then both the FW H equation and its integral solutions based on Lighthill’s acoustic analogy are employed to compute the noise generated by fluid flow. Different flow velocity, circle cylinder diameter and spacing ratios are compared. The result shows that the SPL augments with the increase of flow velocity or circle cylinder diameter. The frequency of vortices shedding is raised with the increase of flow velocity. Different spacing ratios impact the vortices shedding at a certain extent, and as a result impact the acoustic noise. There is the largest SPL near the critical spacing and the direction of acoustic fields is obvious.     

Modelling and Simulation of Anoxic Biofilter for Municipal Wastewater Treatment

For a further understanding of biofilter, a mathematical model is developed based on the analysis of the main effects on the up flow anaerobic biofilter(UFAB), which can characterize not only the substrate removal dynamics but also the gradual biofilter clogging. The model considers three aspects: the biological reaction, deep filtration and hydrodynamics, and consists of flow rate of UFAB, the substrate and suspend solid concentration in the influent, and diameter, surface area, porosity of support medium. By applying the model to the experimental UFAB, and contrasting the simulated and experimental data, the authors prove the model can simulate availably the performance of the biofilter, which is operated on different loading and environment. The model can be used as an effective tool for the wastewater treatment plants operation management and the biofilter optimizing design accurately.