燃料电池工作电流对热力特性的仿真研究

碳酸熔融盐燃料电池热力特性的研究对改善电池性能和提高电池寿命起着至关重要的作用.重点分析了电池工作电流对电池热力特性的影响.基于Matlab/Simulink的仿真环境,分析了燃料电池的工作过程,由能量和物质守恒对电极-电解质、燃料流、氧化剂流和隔板的热力特性进行研究并建立MCFC温度和电流的仿真模型.仿真结果表明燃料电池内部各点的温度分布和电流分布都存在较大的差异,随着燃料和氧化剂流量的增加,电极-电解质的温度和电流显著增加,工作电流对电池的热力特性有显著的影响.计算中的有关数据来自上海交通大学燃料电池研究所1.5kW级熔融碳酸盐燃料电池.     

多物理场耦合界面数据传递的仿真研究

高超声速飞行器的系统仿真是一个气动流场、结构应力场以及结构温度场的高度耦合过程,仿真过程中,需要在耦合界面上完成数据的迭代交换,传递的内容主要包括位移、速度、压力、温度等耦合数据,主要作用就是完成各个耦合场的方程之间参数的传递,在统一的仿真时间内实现仿真的迭代.耦合界面数据传递的技术难点在于要保证耦合界面处的总功守恒以及多物理场耦合仿真的精度[1].目前大多采用以插值为主的局部数据传递方法针对二元耦合开展研究与应用[1,3],局部插值的缺点在于全局精度偏低,偏差较大,计算速度不高.采用径向基函数法(RBF),对界面数据交换方法的仿真应用进行了研究,验证结果表明,计算精度满足仿真要求,求解方程的速度较快,工程应用效果较好.     

基于FBG传感的电子式互感器温度场监测研究

基于光纤Bragg光栅(FBG)测温原理,对电子式互感器内部温度从其工作时间为12h和24h两个时间段进行数据采集,并运用ANSYS仿真软件对内部采集的温度数据进行仿真分析,得出温度场分布云图,可知,电子式互感器上部沿着外壳边缘为温度最高处,中部两侧温度次之,下部温度最低,此时电子式互感器热点温度位于上部.随着电子式互感器工作时间延长,工作达到稳定状态,由于向外部环境散热,电子式互感器工作12h时整体温度比工作24h时高,两个时间段最热点温度分别为90.836,79.764℃.电子式互感器中部导体温度为电子式互感器整体最高.     

城市蒸汽管网水力热力耦合系统及其应用

本文建立了蒸汽管网水力热力耦合计算模型,通过迭代校正管段流量、管段平均密度和定压比热的方式,采用管网水力模型与热力模型相关联的节点方程法求解节点温度与节点压力.基于该耦合模型,以数据库技术、仿真技术和可视化技术为支撑,成功开发出蒸汽管网水力热力计算分析系统,实现了管网动态仿真数字化与模块化.以济南市典型蒸汽供热管网为例,对管网的水力和热力的工况进行了模拟计算,其计算结果与实际运行结果比较表明:该系统可用于蒸汽管网的设计计算、运行调节及其数值模拟.     

火灾后型钢混凝土十字形柱的敏感性分析

为准确分析型钢混凝土柱的抗火灾行为,采用Abaqus软件对型钢混凝土十字形柱进行顺序热力耦合分析,将十字形柱的截面温度分布、温度-时间关系、火灾后的破坏模式以及载荷-位移关系的模拟结果与试验结果进行对比,验证有限元模型的有效性。讨论十字形柱模型的参数敏感性,选择最优混凝土材料属性、建模单元和材料的热膨胀系数,为型钢混凝土组合结构模拟提供更精确的参考依据。     

自动武器抽壳过程仿真及抽壳力相关研究

自动武器的抽壳是一个瞬态动力学过程,其中耦合了许多复杂因素,仅用理论的力学分析很难得到较为精确的抽壳力数值,这使得传统的自动武器抽壳机构设计只能依赖估算和经验.为了更加准确和简便地得到抽壳力数值,采用有限元方法对某自动武器的抽壳过程进行了计算机仿真.给出了抽壳力随时间变化的曲线,可用于指导抽壳机构设计.并用理论和仿真数据相结合分析了初始间隙和弹膛壁厚对抽壳力的影响,用仿真数据分析了摩擦系数对抽壳力的影响.分析表明初始间隙与抽壳力近似成线性负相关关系,弹膛壁厚与抽壳力近似成反比例关系,摩擦系数与抽壳力近似成线性正相关关系.     

巷道热流蔓延及阻滞的分块耦合LBM仿真

为了掌握地下矿火灾发生后遇到易燃物蔓延、障碍物阻滞的规律,提出用分块耦合格子Boltzmann方法(LBM)进行巷道热流蔓延与阻滞的仿真方法.该方法使用分块耦合算法将巷道分为若干相对规则的块,并应用速度-温度双分布LBM对巷道热流蔓延及阻滞过程进行仿真.仿真时,在巷道随机设置多处易燃物,当热流流经巷道时采用热流蔓延模型使得易燃物在一定条件下被引燃,产生热流与原有热流共同传播;在巷道随机设置障碍物,采用热流阻滞模型分析热流遇到障碍物后其方向和温度变化状况.仿真结果表明,该仿真方法可得到关于热流流动速度、热流温度和压力的详细数据,获得关于巷道热流流态的直观信息,从而为制定有效的规避热流的方案提供依据.     

细长柔性空间结构几种动力学模型的比较

对于自由-自由边界的大型柔性梁式空间结构在轨搬运过程中,其大范围刚体运动和柔性振动会相互耦合,是一类典型的刚柔耦合动力学问题.建立相对准确的动力学模型是设计良好控制系统的前提,但现有文献在研究该问题时却采用了忽略刚柔耦合作用的动力学模型并依此设计控制器,因此有必要建立耦合模型,并探讨其与非耦合模型之间的区别和适用性.首先针对结构自身运动特点选择以瞬时质心为原点的浮动坐标系作为辅助坐标系,将结构两类不同的运动形式进行分解,并利用其产生的附加约束条件简化虚功表达式;其次选择Euler-Bernoulli梁变形形式描述结构变形并采用假设模态法对变形进行变量分离;基于虚功原理推导得到结构大范围运动的刚柔耦合动力学模型;通过仿真算例1对非耦合模型、零次近似模型和一次近似模型进行了对比,验证了非耦合模型的不合理性及零次近似简化模型的准确性和有效性;通过仿真算例2对零次近似简化模型和一次近似模型的对比,说明了二者的使用范围;仿真对比为后续的运动控制系统设计和振动抑制研究提供了依据.     

真空退火炉的建模与优化

真空退火炉中工件温度的精确控制是一个典型的非线性、大时滞、强耦合的复杂控制问题.为实现工件温度的精确控制,通过对退火炉工作机理的分析,以现场实际采集的数据为基础,采用神经网络建立对象模型并利用遗传算法对神经网络的权值、阈值进行优化,提出一种真空退火炉工件温度精确控制的优化数学模型.经仿真研究并将其成果应用于实际控制中,取得了令人满意的效果.     

发动机排气歧管流固耦合仿真

应用AVL-fire软件和Abaqus软件对某发动机排气歧管进行流固耦合仿真.对排气歧管材料进行各温度下的材料试验,得到准确的材料在不同温度下的属性曲线.由AVL-fire软件和Abaqus软件进行流固耦合仿真得到排气歧管的温度场分布,并进行排气歧管应力和应变分析.仿真结果与试验结果的对比表明,塑性应变高的区域正是发生开裂的区域.     

Maintaining large time steps in explicit finite element simulations using shape matching

We present a novel hybrid method to allow large time steps in explicit integrations for the simulation of deformable objects. In explicit integration schemes, the time step is typically limited by the size and the shape of the discretization elements as well as by the material parameters. We propose a two-step strategy to enable large time steps for meshes with elements potentially destabilizing the integration. First, the necessary time step for a stable computation is identified per element using modal analysis. This allows determining which elements have to be handled specially given a desired simulation time step. The identified critical elements are treated by a geometric deformation model, while the remaining ones are simulated with a standard deformation model (in our case, a corotational linear Finite Element Method). In order to achieve a valid deformation behavior, we propose a strategy to determine appropriate parameters for the geometric model. Our hybrid method allows taking much larger time steps than using an explicit Finite Element Method alone. The total computational costs per second are significantly lowered. The proposed scheme is especially useful for simulations requiring interactive mesh updates, such as for instance cutting in surgical simulations.     

基于快速多极边界元法的沥青混凝土弹性模量预测

由于对沥青混凝土材料的研究无论是试验法还是经验法均建立在宏观层面上,无法与其细观结构建立本质的联系,因此利用快速多极边界元法(Fast Multipole Boundary Element Method,FMBEM),结合数字图像处理技术,实现沥青混凝土二维几何建模及弹性模量预测.通过数字图像处理技术识别拍摄得到的原始...     

Error analysis of a stochastic immersed boundary method incorporating thermal fluctuations

A stochastic numerical scheme for an extended immersed boundary method which incorporates thermal fluctuations for the simulation of microscopic biological systems consisting of fluid and immersed elastica was introduced in reference [2]. The numerical scheme uses techniques from stochastic calculus to overcome stability and accuracy issues associated with standard finite difference methods. The numerical scheme handles a range of time steps in a unified manner, including time steps which are greater than the smallest time scales of the system. The time step regimes we shall investigate can be classified as small, intermediate, or large relative to the time scales of the fluid dynamics of the system. Small time steps resolve in a computationally explicit manner the dynamics of all the degrees of freedom of the system. Large time steps resolve in a computationally explicit manner only the degrees of freedom of the immersed elastica, with the contributions of the dynamics of the fluid degrees of freedom accounted for in only a statistical manner over a time step. Intermediate time steps resolve in a computationally explicit manner only some degrees of freedom of the fluid with the remaining degrees of freedom accounted for statistically over a time step. In this paper, uniform bounds are established for the strong error of the stochastic numerical method for each of the time step regimes. The scaling of the numerical errors with respect to the parameters of the method is then discussed.     

Simulation analysis of thermal stress of RCC dams using 3-D finite element relocating mesh method

The 3-D finite element relocating mesh method is developed for simulation analysis of temperature and thermal stress distribution in a roller compacted concrete dam during the construction period. According to the relation between specific properties and age of concrete, some meshes are merged into a larger mesh or a few larger meshes when the age of the concrete is appropriate. Using this method, the total number of elements and nodes were remarkably reduced when the dam height was increased. When the change in elastic modulus, creeps and hydration heat is within the limits permitted by design criteria, the relocating of mesh will start. Using this method, a 3 D simulation analysis of thermal stress in a roller compacted concrete (RCC) high dam can be realized by microcomputer and appeared at the construction site. On the basis of real factors during the construction period, an engineer can predict the distribution of temperature and thermal stress in the RCC dam. Therefore, engineers can take appropriate measures to control the concrete temperature to reduce the thermal stress and avoid crack development within the dam.     

Implicit Integration for Particle‐based Simulation of Elasto‐Plastic Solids

We present a novel particle‐based method for stable simulation of elasto‐plastic materials. The main contribution of our method is an implicit numerical integrator, using a physically‐based model, for computing particles that undergo both elastic and plastic deformations. The main advantage of our implicit integrator is that it allows the use of large time steps while still preserving stable and physically plausible simulation results. As a key component of our algorithm, at each time step we compute the particle positions and velocities based on a sparse linear system, which we solve efficiently on the graphics hardware. Compared to existing techniques, our method allows for a much wider range of stiffness and plasticity settings. In addition, our method can significantly reduce the computation cost for certain range of material types. We demonstrate fast and stable simulations for a variety of elasto‐plastic materials, ranging from highly stiffelastic materials to highly plastic ones.     

Elastic mesh technique for 3D BIM simulation with an application to underwater explosion bubble dynamics

The proposed elastic mesh technique (EMT) is a mesh regulation technique, which is based on the assumption that the segments of a mesh are elastic. EMT can be employed in conjunction with the boundary integral method (BIM) for the simulation of three-dimension bubble dynamics in which problems relating to severe mesh distortion as the bubble evolves are a common occurrence. With EMT, the mesh is advanced not by the material velocity, but the optimum shift velocity obtained by minimizing the total elastic energy stored in every segment of the mesh at each time step. In doing so, the prohibitively small time stepping associated with small meshes without EMT in order to maintain numerical stability is mitigated to a large extent. An important feature is that the EMT scheme accords the user the flexibility to implement a non-uniform optimum constitutive relation governing the elastic behavior of mesh segment and which can be further varied with time. Tests were performed for an underwater explosion bubble exhibiting the dynamics of strong jet development with and without EMT for comparison, and the consideration of incorporating EMT as a hybrid system serving as an alternative to the required mesh refinement which is computationally intensive. A full three-dimension simulation of explosion bubble(s) and in the presence of the free surface were further carried out to elucidate the associated flow physics.     

DACAPO-III: Parallel multilevel hardware simulation on transputers

Digital simulators are widely used in the design of digital integrated circuits. The complexity of these circuits is increasing, leading to higher simulation times. One strategy to increase simulation speed is parallel processing. In this paper the implementation of the DACAPO-III simulation system is described in two steps. In the first step this system was implemented on one transputer and in a second step, on multiple transputers. For synchronization between the processors the 'time warp' method was chosen. Problems and results in using parallel processing for distributed simulation are discussed.     

An atomistic-continuum inhomogeneous material model for the elastic bending of metal nanocantilevers

The equivalent elastic modulus of nanocantilever can be obtained using atomistic simulation. However, the use of this modulus to predict the bending of nanocantilever results in significant error compared with direct atomistic simulation. The error originates from the surface effect. In our current work, the nanocantilever is considered as an inhomogeneous continuum material. The distributions of materials parameters at the cross-section, such as atomistic elastic constants, are calculated from atomistic simulations. These atomistic-information-based materials parameters are used as inputs to continuum model. A numerical example case validates the presented model and methodology. To correctly predict the structure-property relations of elemental nano-structures are very important for the design of nano-devices. Our continuum model includes nano-effects and provides another way to study nanomechanics.     

Stress analysis of an elastic plate with an opening or notches under tension based on the concept of general systems

The paper presents a method of calculation dealing with plane stress problems, based on the concept of general systems theory. The first part makes a proposal for calculating the stresses and the stress concentration factor of an elastic plate with a circular hole under tension. The remainder describes its application to similar problems, such as an elastic plate with an elliptical hole, an oval hole and semi-circular notches under tension. The stresses at any point in a plate are calculated from the effect of the stresses on the boundaries. General systems theory suggests state object evolves at discrete times. The deformation of the plate is supposed to take a few steps along the time axis, though the real deformation finishes at one step. The results were compared with analytical solutions and/or experimental results.     

A robust automatic crack detection method from noisy concrete surfaces

In maintenance of concrete structures, crack detection is important for the inspection and diagnosis of concrete structures. However, it is difficult to detect cracks automatically. In this paper, we propose a robust automatic crack-detection method from noisy concrete surface images. The proposed method includes two preprocessing steps and two detection steps. The first preprocessing step is a subtraction process using the median filter to remove slight variations like shadings from concrete surface images; only an original image is used in the preprocessing. In the second preprocessing step, a multi-scale line filter with the Hessian matrix is used both to emphasize cracks against blebs or stains and to adapt the width variation of cracks. After the preprocessing, probabilistic relaxation is used to detect cracks coarsely and to prevent noises. It is unnecessary to optimize any parameters in probabilistic relaxation. Finally, using the results from the relaxation process, a locally adaptive thresholding is performed to detect cracks more finely. We evaluate robustness and accuracy of the proposed method quantitatively using 60 actual noisy concrete surface images.