高速列车设备舱通风散热数值模拟

为研究格栅通风口位置和类型对设备舱通风散热性能的影响,建立包含车底设备舱和转向架等结构的高速列车空气动力学模型.基于三维非定常不可压缩N S方程和k ε两方程湍流模型,用FLUENT进行速度为350 km/h的高速列车设备舱通风散热数值模拟.结果表明,合理设置通风口位置能够有效提升设备舱通风散热性能;采用竖向格栅通风口设备舱的通风散热性能优于采用横向格栅通风口的设备舱;设备舱内发热量较大设备应置于一位端靠近出风口处,其他设备应置于设备舱二位端靠近进风口处.     

格栅对高速列车设备舱散热性能的影响

为研究在裙板不同位置增加格栅对高速列车设备舱散热的影响,建立3种不同设备舱的高速列车空气动力学模型,分别包括原始设备舱、裙板中间增加格栅的设备舱和裙板两端增加格栅的设备舱.基于三维不可压缩N-S方程和k-ε两方程湍流模型,利用FLUENT对250 km/h高速列车设备舱的温度场和流场进行模拟.对列车上行和下行时设备舱的流场与温度场进行分析,比较在不同位置增加格栅时设备舱内温度的变化.结果表明:在裙板不同位置增加格栅对设备舱内的温度场影响较大,在裙板中间增加格栅对头车和中间车设备舱的散热不利,建议在裙板两端增加格栅以更有利于设备舱散热.     

DCS分布式处理单元及其散热风扇供电设计优化

分布式处理单元是DCS系统中最重要的组成部分,其供电可靠性的设计直接影响到DCS系统的安全稳定运行。主要分析了某核电厂1、2号机组非安全级DCS控制柜内分布式处理单元与散热风扇不满足单一故障准则,并结合现场项目建设进展,通过对目前控制柜内分布式处理单元及散热风扇供电设计进行分析,从可靠性、机组安全性和经济性角度对原有设计提出优化方案,并推动该方案在1、2号机组完成改造实现,为后续核电机组DCS系统提供参考和借鉴。     

基于三维模型的通风系统优化调控模拟分析

以某矿为研究对象,利用VENTSIM三维通风动态仿真模拟系统构建了矿井通风系统真实三维模型,在获取可靠通风基础参数的基础上,对该矿通风系统优化调控方案进行了准确模拟。现场实际测量结果与模拟结果较为吻合,误差很小,验证了基于三维模型的通风系统优化调控方案的可靠性。     

神经网络预测及电力主变室多参数优化控制

针对变压器室通风散热这类多变量、非线性和时变的复杂控制系统,采用神经网络作为优化反馈控制器求解优化反馈解;利用预测控制的滚动优化具有克服室外温度干扰和不确定性影响的优势,通过滚动优化算法训练神经网络模型,同时对控制系统中负荷电流变化也采用神经网络进行预测,以实现被控对象的实时预测;利用该方法对变压器室通风散热系统进行理论分析和仿真,仿真结果表明系统具有较强的鲁棒性;最后应用于变压器室智能通风散热系统实际工程中,获得较好降温的效果。     

矿井局部通风智能调控系统及关键技术研究

目前矿井局部通风自动控制方式采用手动调节通风机频率,且风筒参数依靠人工采集,缺少准确、可靠的监测方法来反映通风状态,无法为准确调节风量提供依据。针对矿井局部通风智能化建设需求,提出了矿井局部通风智能调控系统,从系统组成、原理、功能等方面详细介绍了系统总体设计方案。根据多传感器实时监测数据,提出了局部通风参数计算方法及通风系统功耗分析方法,通过分析风筒阻力动态分布对风筒阻力和功耗异常进行研判和快速定位,结合监测参数对风量进行超前模拟,以确定最佳供需匹配调控方案。根据工作面瓦斯涌出规律,提出了基于瓦斯涌出量监测和通风机变频调风稀释瓦斯的智能调风方案,制定了5种局部通风机变频调控规则,实现了局部通风智能化供需匹配。采用贝叶斯网络算法对局部通风机和传感器设备健康状况进行诊断,利用粗糙集和遗传算法提取局部通风正常供风和故障状态的特征样本和前兆信息,基于支持向量机建立局部通风故障决策规则,建立局部通风异常研判和预警模型,实现了对局部通风状态及发展态势的研判及预警。以某矿掘进工作面局部通风为例验证了该系统通风参数计算方法,为局部通风异常研判与预警提供了基础数据。     

某型导弹电子舱地面数据采集分析系统实现

针对脱离弹体后的电子舱无法进行实时数据采集分析的这一问题,提出使用VI和FPGA配合的独立模拟测试平台方案,利用FPGA模拟各类故障检测信号并且使用直接注入至电子舱的方法,用以解决在保证使电子舱加电正常运转的前提下使用VI技术实现独立采集和检测电子舱各类参数和性能指标目的;经实际检测结果验证,该数据采集分析系统能够独立地完成电子舱各类故障模拟并且能实时采集、记录、分析和显示电子舱的若干相应信号,为电子舱的性能分析、评价和故障定位分析等提供了重要的数据参考。     

Ventsim三维通风仿真系统在四台矿的应用

针对四台矿通风系统复杂、管理难度大、通风系统调整主要依靠经验等问题,应用Ventsim三维通风仿真系统构建三维立体通风网络模型,可真实反映四台矿通风系统状况,实现通风模拟、污染物模拟、热模拟、火灾模拟、经济性模拟等功能,为通风系统管理和优化提供辅助决策依据。     

红外导弹目标模系统的实现

红外导弹采用探测目标红外热源实现对目标的追踪,追踪过程中利用红外导引头自身的目标识别功能排除环境干扰和人工干扰.为完成导弹的测试,建立了一套红外目标模拟系统,制定了详细的定性和定量校准方案,实现了红外目标和人工诱饵干扰的动态模拟.系统具有精度高、覆盖性广、通用性强和全程自动化测试的特点,为控制舱的性能研究、设计改进和生产交付提供了一个良好的目标模拟平台.     

多彩DLP390A电源

随着电脑功率的不断提升,用户对电脑的散热要求也越来越高。传统的风冷散热系统,要提高散热能力,要么必须提供更高的散热器转速,要么让通风面积更大(即用叶面更大的风扇)。但提升转速带来的直接问题就是风扇噪音明显加大,这与用户需要的健康环保电脑显然格格不入,因此大叶面风扇的设计成了越来越多厂商的选择这款多彩DLP390A电源采用的就是大叶面散热设计,而且还是超过一般12cm电源散热器的14cm大叶面散热器,这样的页面设计使多彩DLP390A电源的通风面积比12cm散右为采用14cm散热器的多彩390A电源,左为12cm散热器电源热器电源大了36%。相…     

Simulations of the wind field in Athens with the nonhydrostatic mesoscale model MEMO

MEMO is a fully vectorized nonhydrostatic mesoscale model using terrain-following coordinates. The numerical solution is based on second-order discretization applied on a staggered grid which is allowed to be non-equidistant in all directions. Special care is taken that conservative propeprties are preserved within the discrete model equations. The discrete pressure equation is solved with a direct elliptic solver in conjuction with a generalized conjugate gradient method. Advective terms are treated with an explicit, monotonicity-preserving discretization scheme with only small implicit diffusion. Turbulent diffusion is described using an one-equation turbulence model, while at roughness height similarity theory is applied. An efficient scheme is applied to calculate radiative transfer. The algebraic surface heat budget equation and an one dimensional heat conduction equation are solved to obtain the surface temperature over land and the soil temperature. In the frame of the APSIS exercise A the model MEMO was used to simulate the mesoscale flow in the Athens basin on May 25, 1990. Being in satisfactory agreement with observations, the results indicate that weak pressure gradients accompanied by warm advection aloft may lead to stagnant conditions and thus to severe air pollution episodes in Athens.     

Large eddy simulation of turbulent heat transport in the Strait of Gibraltar

We develop a numerical model for large eddy simulation of turbulent heat transport in the Strait of Gibraltar. The flow equations are the incompressible Navier–Stokes equations including Coriolis forces and density variation through the Boussinesq approximation. The turbulence effects are incorporated in the system by considering the Smagorinsky model. As a numerical solver we propose a finite element semi-Lagrangian method. The solution procedure consists of combining a non-oscillatory semi-Lagrangian scheme for time discretization with the finite element method for space discretization. Numerical results illustrate a buoyancy-driven circulations along the Strait of Gibraltar and the sea-surface temperature is flushed out and move to northeast coast. The Ocean discharge and the temperature difference are shown to control the plume structure.     

An Asymptotic Preserving Scheme for the ES-BGK Model of the Boltzmann Equation

In this paper, we study a time discrete scheme for the initial value problem of the ES-BGK kinetic equation. Numerically solving these equations are challenging due to the nonlinear stiff collision (source) terms induced by small mean free or relaxation time. We study an implicit-explicit (IMEX) time discretization in which the convection is explicit while the relaxation term is implicit to overcome the stiffness. We first show how the implicit relaxation can be solved explicitly, and then prove asymptotically that this time discretization drives the density distribution toward the local Maxwellian when the mean free time goes to zero while the numerical time step is held fixed. This naturally imposes an asymptotic-preserving scheme in the Euler limit. The scheme so designed does not need any nonlinear iterative solver for the implicit relaxation term. Moreover, it can capture the macroscopic fluid dynamic (Euler) limit even if the small scale determined by the Knudsen number is not numerically resolved. We also show that it is consistent to the compressible Navier-Stokes equations if the viscosity and heat conductivity are numerically resolved. Several numerical examples, in both one and two space dimensions, are used to demonstrate the desired behavior of this scheme.     

Asymptotic properties of the space–time adaptive numerical solution of a nonlinear heat equation

We consider the fully adaptive space–time discretization of a class of nonlinear heat equations by Rothe’s method. Space discretization is based on adaptive polynomial collocation which relies on equidistribution of the defect of the numerical solution, and the time propagation is realized by an adaptive backward Euler scheme. From the known scaling laws, we infer theoretically the optimal grids implying error equidistribution, and verify that our adaptive procedure closely approaches these optimal grids.     

汽车换热器风室试验台的CFD分析

为给汽车前端和发动机舱内气流数值计算提供参考依据,基于FLUENT对某汽车换热器风室试验台进行建模和数值模拟;分析风室内部空气流动状况,针对流动特征,给出风室计算流体力学（Computational Fluid Dynamics,CFD）校核的评价．网格采用四面体结构,模型中采用三维不可压的雷诺平均N．S方程,速度压力耦舍采用SIMPLE方法．空间离散格式为2阶迎风格式,时间离散格式为2阶隐式．选用realizable k-ε占模型模拟风室内部空气的湍流流动．固体壁面采用无滑移边界条件和非平衡壁面函数边界条件．模型进口采用速度入口来给定风量,出口采用压力出口．比较计算结果与试验设计标准,喷嘴压差的相对偏差范围在5％以内,基本达到对设备的精度要求,对风室设计有一定指导意义．     

A subgrid stabilization finite element method for incompressible magnetohydrodynamics

This paper studies a numerical scheme for approximating solutions of incompressible magnetohydrodynamic (MHD) equations that uses eddy viscosity stabilization only on the small scales of the fluid flow. This stabilization scheme for MHD equations uses a Galerkin finite element spatial discretization with Scott-Vogelius mixed finite elements and semi-implicit backward Euler temporal discretization. We prove its unconditional stability and prove how the coarse mesh can be chosen so that optimal convergence can be achieved. We also provide numerical experiments to confirm the theory and demonstrate the effectiveness of the scheme on a test problem for MHD channel flow.     

Electromagnetic modeling of high magnetic contrast media using Calderón preconditioning

In this contribution, we present a Calderón preconditioner for a novel single-source equation to efficiently model electromagnetic scattering problems involving high magnetic contrasts. Through analysis of the spectral properties of the system matrix after discretization, it is shown that this formulation does not break down when high permeabilities are present, which was an unresolved problem of the Calderón preconditioned Poggio–Miller–Chan–Harrington–Wu–Tsai method. The adopted discretization scheme, which involves Rao–Wilton–Glisson and Buffa–Christiansen basis functions, allows for an easy integration in existing commercial Method of Moments software. The efficiency and accuracy of the presented method is corroborated by numerical examples.     

Parameter-uniform hybrid numerical scheme for time-dependent convection-dominated initial-boundary-value problems

In this paper, we propose a numerical scheme which is almost second-order spatial accurate for a one-dimensional singularly perturbed parabolic convection-diffusion problem exhibiting a regular boundary layer. The proposed numerical scheme consists of classical backward-Euler method for the time discretization and a hybrid finite difference scheme for the spatial discretization. We analyze the scheme on a piecewise-uniform Shishkin mesh for the spatial discretization to establish uniform convergence with respect to the perturbation parameter. Numerical results are presented to validate the theoretical results.     

Energy Stability Analysis of Some Fully Discrete Numerical Schemes for Incompressible Navier–Stokes Equations on Staggered Grids

In this paper we consider the energy stability estimates for some fully discrete schemes which both consider time and spatial discretizations for the incompressible Navier–Stokes equations. We focus on three kinds of fully discrete schemes, i.e., the linear implicit scheme for time discretization with the finite difference method (FDM) on staggered grids for spatial discretization, pressure-correction schemes for time discretization with the FDM on staggered grids for the solutions of the decoupled velocity and pressure equations, and pressure-stabilization schemes for time discretization with the FDM on staggered grids for the solutions of the decoupled velocity and pressure equations. The energy stability estimates are obtained for the above each fully discrete scheme. The upwind scheme is used in the discretization of the convection term which plays an important role in the design of unconditionally stable discrete schemes. Numerical results are given to verify the theoretical analysis.     

An energy-preserving algorithm for nonlinear Hamiltonian wave equations with Neumann boundary conditions

In this paper, a novel energy-preserving numerical scheme for nonlinear Hamiltonian wave equations with Neumann boundary conditions is proposed and analyzed based on the blend of spatial discretization by finite element method (FEM) and time discretization by Average Vector Field (AVF) approach. We first use the finite element discretization in space, which leads to a system of Hamiltonian ODEs whose Hamiltonian can be thought of as the semi-discrete energy of the original continuous system. The stability of the semi-discrete finite element scheme is analyzed. We then apply the AVF approach to the Hamiltonian ODEs to yield a new and efficient fully discrete scheme, which can preserve exactly (machine precision) the semi-discrete energy. The blend of FEM and AVF approach derives a new and efficient numerical scheme for nonlinear Hamiltonian wave equations. The numerical results on a single-soliton problem and a sine-Gordon equation are presented to demonstrate the remarkable energy-preserving property of the proposed numerical scheme.