供热系统输配网络模型简化方法研究

该文以供热系统枝状网这种特殊拓扑结构的流体网络系统为研究对象,阐述了网络模型的简化原则,提出了相应的网络简化的方法。讨论的基准有两点：一是保证简化前后网络的温度延迟时间一致;二是保证简化前后工质的流动阻力保持不变。简化的网络模型,在动态性能损失不大的情况下,计算负荷大大降低。这种简化,对于掌握网络的热动态以及供热系统优化运行具有重要的意义。     

基于简化模型的T型微反应器设计

分析T型微反应器内流体混合程度和反应产物收率的常用方法:是建立计算流体动态模型,也就是CFD模型,可是这种模型不适用于微反应器的优化设计,因为利用CFD模型进行优化计算需要的大量的计算时间。本研究开发了一个描述T型微反应器流体流动状态的简化模型,通过假设边界条件和假设扩散系数的设定来计算微反应器内反应产物收率。其中假设边界条件用来描述强混合效果在反应通道入口处的流动状态,假设扩散系数用来描述混合效果在流动路径上的变化。本研究依据此简化模型,确立了一种优化设计方法:,用来设计具有最优尺寸的T型微反应器。优化问题的目标函数是最大反应产物收率,优化约束包括反应通道尺寸约束和操作压力约束。在求解过程中,首先建立尺寸约束边界条件下的CFD模型,然后依据CFD模型计算结果:,求解简化模型中的未知参数。将建好的简化模型作为优化问题的等式约束,最后求出最优的T型微反应器。简化模型和优化设计方法:的有效性通过一个快速平行串联反应在微反应器中的反应过程来验证。简化模型的优化设计结果:和CFD模型验证结果:高度一致。     

基于特征保持的三角形折叠网格简化算法

针对模型简化过程中出现的特征细节丢失、简化结果过于均匀等问题,文中基于特征保持提出一种改进的三角形折叠网格简化算法。简化前对原始模型中的三角形预分类,简化中以二次误差测度度量简化过程,以三角形狭长度、局部区域面积以及局部区域尖锐度控制三角形简化顺序,对边界三角形和内部三角形采取不同的简化策略,以此保持模型特征和降低算法复杂度。本算法在Visual c＋＋6．0开发环境下,结合OpenGL编程语言实现。实验结果表明,改进算法采用延迟简化特征区域及形状好的三角形的方法,有效地保持了模型原始特征,且简化速度较快。     

ANSYS二次开发在PIM充模流动模拟中的应用

论文介绍了ANSYS所具有的针对不同需求、特点和应用范围的多种二次开发技术;根据PIM充模喂料流体的幂律模型,基于ANSYS用户可编程特性中对其FLOTRAN模块流体特性中的粘度模型进行了二次开发,用所开发的幂律模型对I型拉伸试样的PIM充模二维流动进行了数值模拟,模拟结果与实验结果吻合很好;并将二次开发的方法推广到PIM喂料的密度、导热系数、比热等的修改,为将ANSYS强大的计算流体力学功能广泛应用于PIM充模流动模拟的研究奠定了基础。     

“节流装置设计计算软件”(LGY-l.0-94版)

为贯彻国家标准GB/T2624—93《流量测量节流装置用孔板喷嘴和文丘利管测量充满圆管的流体流量》,负责起草亥标准的单位——机械部上海工业自动化仪表研究所本着为行业服务、方便用户的精神,以优惠的价格向广大用户提供“节流装置设计计算软件”(LGY-1.0-94版).该软件能用于标准中所有取压方式、所有节流件的节流装置设计计算,也可用于标准之外,当前常用节流件的节流装置设计计算,亦即能用于任何条件下,测量任何流体的节流件的节流装置设计计算.     

“节流装置设计计算软件”(LGY-1.0-94版)问世

为了更好地贯彻国家标准GB/T2624-93《流量测量节流装置用孔板喷嘴和文丘里管测量充满圆管的流体流量》,负责起草国家标准的单位——机械工业部上海工业自动化仪表研究所根据标准的要求,编制了“节流装置设计计算软件”(LGY-1.0-94版)。 该软件能用于标准中所有取压方式、所有节流件的节流装置设计计算,也可用于标准之外,当前常用节流件的节流装置设计计算,简言之,能用于任何条件下,测量任何流体的节流件的节流装置设计计算。     

电导式相关流量测量传感器

在油水两相流条件下,水为连续相时,电导式传感器利用油相分布的离散性所造成的流体阻抗的随机变化检测流体流动噪声,通过对传感器中的上、下游传感器所检测出的流体流动噪声进行互相关运算,得到和流体流量相关的渡越时间,该传感器用于井下油水两相流量测量。文中给出了相关流量测量用电导式传感器检测流体流动噪声的原理、传感器中敏感器的结构及设计原则,同时给出了传感器激励源及信号处理电路的设计原则,文中最后给出了电导传感器在多相流模拟井上的流量测量实验及分析。     

乙烯裂解炉反应管数学模拟新方法

综述了不同类型的乙烯裂解炉反应管数学模型，分析了各类模型的缺点。为此提出了一种进行反应管数学模拟的新方法。即应用CFD方法对反应管内流体流动、传热、传质及裂解反应过程，不经任何简化直接进行数值求解，得到了管内的流场、温度场和浓度场等详细信息。模拟计算得到了反应管长度方向上的温度、速度、压力和组分浓度的变化规律；在反应管径向上存在着明显的速度和温度分布，而组分浓度变化程度不如速度和温度明显；计算结果为提出结焦抑制方法提供了依据。     

用计算奇异值摄动方法简化复杂化学反应动力学模型

介绍了用于简化化学反应动力模型的计算奇异值摄动方法(CSP),给出了其基本思想与具体计算方法,然后用该方法来对一氧化碳／氢气在空气中燃烧的化学反应、激波管中甲烷的点火燃烧反应实例进行了简化。从计算结果看,CSP方法是一种比较有效的化学反应模型简化方法,用该方法简化得出的简化模型不仅减少了微分求解的组分数目,而且保持了较高的计算精度,能有效提高计算效率,具有较强的工程实际价值。     

作用于大数据处理的级联分类器泛化设计

针对级联分类器的设计主要集中于分类器组合优化等方面，有关自动化设计研究相对较少。为了简化设计流程，设计一种方法以自动设计具有理想性能的级联分类器。这种方法不需要分别考虑每个可能的级联长度并通过最终数值优化来进一步确定每个级联长度的次优参数，而是向能够设置级联的泛化边界方向来研究，探讨如何简化级联分类器的设计流程，实现自动化设计。     

Relative Flow Estimates for Shot Boundary Detection

This paper proposes a simple approach based on Relative Flow Estimates (RFE) for shot cut detection. The property of Relative flow estimates can be used for abrupt cut detection and a correction mechanism for gradual camera-shot transition detection (e.g., fade-in and fade-out, dissolves, wipes). The exacted feature vector in each frame can be mapped into a 3-D space along the continuous time axis, and these feature data can be treated as a virtually constructed pipe with fluid flowing in the 3-D axis. Compared with existing approaches, the new RFE-based algorithm can directly detect shot cut. A wide range of test videos are used to evaluate the performance of the proposed method. The experimental results show that the new scheme can produce promising results.     

On rheological characteristics of non-Newtonian nanofluids in the material forming process

In this paper, the material forming process (such as that of the functionally graded materials) of adding nanoparticles into non-Newtonian fluids is considered. By adding nanoparticles to a non-Newtonian fluid, a new non-Newtonian fluid is created. Thus, the rheological characteristics of the original fluid matrix have been changed. This research attempts to consider the influence of the rheological characteristics combined with the Brownian diffusion, and the thermophoresis diffusion, the distribution of nano-sized particles, the heat transfer, and the pressure drop on the process of material formation. The configuration of material treatment process is an H-height horizontal parallel plate channel with laminar forced convection nanofluids-based non-Newtonian fluids flowing through. The channel is separated by three different boundary conditions: heating, cooling, and isolated, to simulate the melting, the freezing, and the flowing processes of materials in liquid form. The non-Newtonian behaviour of nanofluids is described by the power-law model. To highlight the rheological factors of power-law nanofluids which are not the same as those of the base non-Newtonian fluids, they are assumed to vary with the quantity of the added nanoparticles in the fluid matrix, that is to say, both the consistency coefficient \(m\) and the power-law index \(n\) are considered as functions of particle loading parameter \(\phi\). Two sets of different functions of consistency coefficient \(m\) and power-law index \(n\) are used and compared in the later calculation. Method of finite element is adopted to solve the coupled momentum, energy and concentration equations, and conquer the difficulties arsing in the iteration of calculation. It is found that whether the rheological factors of non-Newtonian nanofluids are considered changeable or not would lead to very different results of the mass transfer. Also, as the parameter \(N_{\text{T}}\) (depicting the thermophoresis diffusion) increases, both temperature and concentration profiles rise, while volume fraction of particles and temperature both fall as \(N_{\text{B}}\) number (presenting the Brownian diffusion) increases. Furthermore, when two models are compared, different rheological models may possess different change rule of power-law index, but in both rheological models, the diversification of power-law index is so large that it cannot be ignored in calculation. Above all, the detailed information of velocity, temperature, and pressure drop obtained by rheological models highlights the necessity of studying the impact of rheological characteristics of non-Newtonian fluids in elaborate industrial requirements.     

Energy-efficient real-time scheduling for two-type heterogeneous multiprocessors

We propose three novel mathematical optimization formulations that solve the same two-type heterogeneous multiprocessor scheduling problem for a real-time taskset with hard constraints. Our formulations are based on a global scheduling scheme and a fluid model. The first formulation is a mixed-integer nonlinear program, since the scheduling problem is intuitively considered as an assignment problem. However, by changing the scheduling problem to first determine a task workload partition and then to find the execution order of all tasks, the computation time can be significantly reduced. Specifically, the workload partitioning problem can be formulated as a continuous nonlinear program for a system with continuous operating frequency, and as a continuous linear program for a practical system with a discrete speed level set. The latter problem can therefore be solved by an interior point method to any accuracy in polynomial time. The task ordering problem can be solved by an algorithm with a complexity that is linear in the total number of tasks. The work is evaluated against existing global energy/feasibility optimal workload allocation formulations. The results illustrate that our algorithms are both feasibility optimal and energy optimal for both implicit and constrained deadline tasksets. Specifically, our algorithm can achieve up to 40% energy saving for some simulated tasksets with constrained deadlines. The benefit of our formulation compared with existing work is that our algorithms can solve a more general class of scheduling problems due to incorporating a scheduling dynamic model in the formulations and allowing for a time-varying speed profile.     

On the disturbance model in the robustification of explicit predictive control

This article deals with the predictive control for linear systems, described in a explicit form as piecewise affine (PWA) state feedback laws. The main goal is to reduce the sensitivity of these schemes with respect to the model uncertainties. This objective can be attained by considering worst-case (min–max) formulations, optimisation over the control policies or tube predictive control. Such comprehensive approaches may lead to fastidious on-line optimisation, thus reducing the range of application. In the present note, a two-stage predictive strategy is proposed, which in the first place synthesises an analytical (continuous and piecewise linear) control law based on the nominal model and secondly robustifies the control law in the neighbourhood of the equilibrium point (the feedback gain obtained for the unconstrained control problem – most often assimilated to the LQR gain). How the disturbance model corresponding to the unconstrained control robustification can be used to improve the robustness of the PWA control law is also shown.     

基于流场的流动水体仿真

为了逼真地模拟自然河道中的流动水体,提出了一种基于流场的流动水体仿真方法.应用流体力学原理,实时计算稳定水流的速度,构建河流的流场,然后运用流场驱动并约束满足泊松碟分布的块状纹理在河道内移动,通过对块状纹理进行混合与渲染,构成了一种自然水体的动态流动效果.水面渲染采用GLSL (opengl shading language)着色器进行渲染,实际运用GPU可编程渲染管线进行图形计算,减少了CPU的实时运算量,提高程序的整体效率,实践表明,应用以上方法可以有效地模拟流域内的动态流动水体.     

基于流速修正的单直管CMF密度测量方法

科氏流量计(CMF)可以直接测量流体密度,目前单直管CMF的密度测量均未考虑流体流速的影响,密度测量精度受到限制.本文通过力学建模分析,得出了流体流速对单直管CMF密度测量的影响规律,推导了考虑流速影响的单直管CMF密度测量公式,并利用ANSYS Workbench进行了仿真验证.仿真结果表明:当流体流动时,与不考虑流速影响的单直管CMF密度测量结果相比,本文考虑流速影响得到的密度测量值与实际密度值更加吻合.     

Particle streaming and separation using dielectrophoresis through discrete periodic microelectrode array

This study presents a particle manipulation and separation technique based on dielectrophoresis principle by employing an array of isosceles triangular microelectrodes on the bottom plate and a continuous electrode on the top plate. These electrodes generate non-uniform electric fields transversely across the microchannel. The particles within the flowing fluid experience a dielectrophoretic force perpendicular to the fluid flow direction due to the non-uniform electric fields. The isosceles triangular microelectrodes were designed to continuously exert a small dielectrophoretic force on the particles. Particles experiencing a larger dielectrophoretic force would move further in the perpendicular direction to the fluid flow as they traveled past each microelectrode. Polystyrene microspheres were used as the model particles, with particles of ∅20 μm employed for studying the basic characteristics of this technique. Particle separation was subsequently demonstrated on ∅10 and ∅15 μm microspheres. Using an applied sinusoidal voltage of 20 V_pp and frequency of 1 MHz, a mean separation distance of 0.765 mm between them was achieved at a flow rate of 3 μl/min (~1 mm/s), an important consideration for high throughput separation capability in a micro-scale technology device. This unique isosceles triangular microelectrodes design allows heterogeneous particle populations to be separated into multiple streams in a single continuous operation.     

Topological derivatives applied to fluid flow channel design optimization problems

Topology optimization methods application for viscous flow problems is currently an active area of research. A general approach to deal with shape and topology optimization design is based on the topological derivative. This relatively new concept represents the first term of the asymptotic expansion of a given shape functional with respect to the small parameter which measures the size of singular domain perturbations, such as holes and inclusions. In previous topological derivative-based formulations for viscous fluid flow problems, the topology is obtained by nucleating and removing holes in the fluid domain which creates numerical difficulties to deal with the boundary conditions for these holes. Thus, we propose a topological derivative formulation for fluid flow channel design based on the concept of traditional topology optimization formulations in which solid or fluid material is distributed at each point of the domain to optimize the cost function subjected to some constraints. By using this idea, the problem of dealing with the hole boundary conditions during the optimization process is solved because the asymptotic expansion is performed with respect to the nucleation of inclusions – which mimic solid or fluid phases – instead of inserting or removing holes in the fluid domain, which allows for working in a fixed computational domain. To evaluate the formulation, an optimization problem which consists in minimizing the energy dissipation in fluid flow channels is implemented. Results from considering Stokes and Navier-Stokes are presented and compared, as well as two- (2D) and three-dimensional (3D) designs. The topologies can be obtained in a few iterations with well defined boundaries.     

Non-newtonian laminar flow machine rotor design by using topology optimization

Flow machines are widely used in industry through devices such as hydraulic turbines and pumps. Most part of these devices work with newtonian fluids, however, there are some specific devices dedicated to work with non-newtonian fluids, such as blood pumps. The main function of a blood pump is to have a suitable hydraulic performance while maintaining good haematological compatibility which consists of avoiding hemolysis (release of hemoglobin from red blood cells) and thrombosis (clotting). However, the challenge of improving the performance of these non-newtonian fluid machines requires the solution of an inverse-based design optimization problem, in which an oriented search must be conducted to obtain the optimized design. The rotor is a main component in the non-newtonian pump and the design of rotor topology can play an important role in the pump performance and its haematological conditions. Thus, performance improvement of these devices can be achieved by using topology optimization techniques. The optimization of pump hydraulic performance can be achieved by minimizing dissipative energy and power consumption and for the improvement of the haematological conditions, it is proposed to minimize the vorticity. Thus, in this work, topology optimization techniques are applied for designing the rotor pump such that the energy dissipation, vorticity, and power consumption are minimized considering non-Newtonian fluid. A two-dimensional finite element derived for a rotating frame is applied to model the rotor flow behavior. The modeling predicts the flow field between relative two blades of a rotor without considering the influence of the volute. A modified Cross model is adopted for the non-Newtonian fluid modeling. It is assumed that the fluid is flowing an idealized porous medium subjected to a friction force, which is proportional to the fluid velocity and the inverse local permeability. A porous flow model is considered with a continuous (gray) permeability design variable for each element that defines the local permeability of the medium and allows the transition between fluid and solid property. The design optimization problem is solved by using the method of moving asymptotes (MMA). Numerical examples are presented to illustrate this methodology aiming blood pump applications. A comparison among designs obtained by considering newtonian and non-newtonian fluid is included. Finally, it is verified that an improvement of the hemolysis index can be achieved by minimizing the vorticity in the rotor.     

Eigenvalue inverse formulation for optimising vibratory behaviour of truss and continuous structures

This paper presents formulations for inverse optimisation of vibration behaviour of finite element models of both truss and continuous structures. The proposed algorithms determine the required modifications on truss and continuous structures to achieve specified natural frequencies. The modification can be carried out globally or locally on the structures stiffness and matrices and the formulation can also be used to add new structural members to achieve the desired response. Numerical examples and finite element implementation of the developed method are provided to demonstrate the feasibility of the formulations.