动态压差控制阀流场及流量控制特性研究

针对变流量加热及冷却系统水力和热力失调的问题,设计一种动态压差控制阀.基于计算流体力学(CFD)方法,建立不同阀芯开度下动态压差控制阀三维流道模型.对比研究了不同阀芯开度下阀内流场分布以及流量变化,得出了动态压差控制阀在不同阀芯开度下阀内压降曲线的变化规律、阀芯节流口处速度曲线及湍动能曲线的分布规律,拟合了阀门出口流量...     

An elastic-plastic constitutive equation for transversely isotropic materials and its application to the bending of perforated circular plates

Extending Hencky's interpretation for Mises' yield condition to anisotropic materials, it is first assumed that the plastic deformation occurs when the elastic distortion energy attains to a certain constant value. Then, the shearing stress and the shearing strain intensities are defined in terms of the elastic and the plastic distortion energy. By assuming the deformation theory of plasticity along with the hydrostatic pressure insensitivity of material response, trigonometric representations of stress and strain are derived in order to formulate an elastic-plastic constitutive equation for transversely isotropic materials. Yield conditions and the corresponding yield loci for the relevant materials are also discussed. As an application of the resulting constitutive equation, elastic-plastic bending of perforated circular plates is analysed by modelling them by equivalent homogeneous transversely isotropic plates.     

模糊控制在低压铸造中的应用

低压铸造是目前广泛应用的铸造成型工艺。该针对铝合金车轮的铸造工艺要求,采用模糊控制技术实现低压铸造过程中对气体压力的快速准确跟踪。实际应用表明,所研究的模糊控制器具有良好的性能。     

气相色谱电子流量/压力控制模块研制和应用

为了提高气相色谱仪气路控制自动化水平,研制了电子流量/压力控制模块.该模块在基于闭环控制的方式上,通过小流量比例电磁阀、小流量和压力传感器、微型可调限流装置、颗粒过滤网、集成流路块体的优化设计,以放大基准电路、A/D转换、单片机控制系统PID、D/A转换、功率驱动电路来达到控制气体流量/压力的目的.再以单气路控制为最小...     

迷宫式最小流量调节阀的设计及应用

论述了迷宫式最小流量调节阀的结构特点、工作原理和主要部件的设计。     

DCS在药液配送控制系统中的应用

从工程实际出发简要介绍了药液配送系统的功能与作用,结合系统的特点,设计了以PLC为基础的DCS控制系统,详细阐述了整个系统控制结构设计及其软件实现.     

On-line measurement of particle size distribution and mass flow rate of particles in a pneumatic suspension using combined imaging and electrostatic sensors

This paper presents a novel instrumentation system that uses a combination of electrostatic and digital imaging sensors. An inferential approach is adopted for the mass flow measurement of particles, velocity and volumetric concentration of particles being measured independently. The velocity of particles is determined by cross correlating two signals derived from a pair of electrostatic sensors and the volumetric concentration of particles is obtained using a novel digital imaging sensor, which also provides particle size distribution data. The basic principles and limits of operation of the imaging sensor are discussed and explained. Results obtained from a pneumatic conveyor are presented which demonstrate good performance of the measurement system for both mass flow metering (accurate to about ±6%) and particle sizing (reliable to around ±2.5%). Particle size distribution results are also included and the insensitivity of particle sizing to changes in velocity and concentration is assessed. In addition, on-line sizing results are compared to off-line results, measured using an accepted laser diffraction based instrument, and good agreement is observed. In general, the results obtained are encouraging and the system shows great promise.     

PID控制在CMF系统恒流量产水中的应用

文章从理论入手，分析PID控制的原理，并描述了其内容，以连续膜过滤系统（CMF）为例，介绍恒流量产水方案的方法，设计了离散系统的计算机控制模型，并运用西门子S7-200PLC实现预先设计的算法，达到了变频调速以实现恒流量产水的目的。     

A numerical study on the characteristics of transient flow in a pressure regulator resulting from closure of the pressure control valve

This study investigates characteristics of transient flow and the possibility of freezing in a pressure regulator and the rear connecting pipe of the pressure regulator during the closing process of the pressure control valve (PCV), which is an essential element in the operation of a natural gas pipeline network. For this purpose, the study develops a numerical model for the PCV and its rear connecting pipe by applying computational fluid dynamics method. The analysis is conducted in each of two cases: (1) a steady-state analysis in the case of normal operation and (2) an unsteady-state analysis in the case of emergency closure in problematic situations. First, we closely examine characteristics of internal flow in the pressure regulator and the rear connecting pipe when the PCV operates regularly with a 50% opening ratio in a steady state. Afterwards, unsteady-state analysis examines characteristics of transient flow, such as lowered pressure and temperature, velocity change, etc., of rear flow in the pressure regulator when the PCV is closed because of trouble in the pressure control system.     

Investigation on characteristics of pressure fluctuation in a centrifugal pump with clearance flow

Journal of Mechanical Science and Technology - Clearance flow has great impact on pressure fluctuation of centrifugal pumps. Numerical calculations are performed to study the pressure fluctuation...     

The plastic bending of clamped polygonal plates with an application to radial buckling in milk bottle tops

Solutions for the plastic bending of clamped polygonal plates are investigated. For an isosceles triangular plate, and for a truncated isosceles triangular plate, minima exist for plastic work of formation with respect to angles of the triangle, and location of the apex of the deformed pyramid shape. A characteristic number of radial buckles is formed when the foil circular top of British one-pint milk bottles is pushed in and material drawn over the rim of the bottle on opening. The plastic bending analysis provides an approximate means of predicting the number of buckles.     

On the influence of the characteristics of flow on pressure distribution around building models with a view to simulating the minimum height of the atmospheric boundary layer

Results of an investigation of the influence of the characteristics of flow on pressure distribution around building models are reported. The influence of the mean velocity profile, turbulence intensity, percentage boundary layer immersion ratio and the building model's aspect ratio on the pressure distribution was studied with the view of simulating the minimum height of the atmospheric boundary layer in a wind tunnel for building aerodynamics investigations. It is cautiously suggested that atmospheric boundary layer height of at least three times the building height should be simulated in the wind tunnel. Turbulence characteristics exercise primary influence on the flow around models and shear exercises secondary influence on the flow. Finally, it is imperative to simulate the correct turbulence intensity and scale in the simulated turbulent boundary layer. However, further tests should be carried out to study these problems in closer detail.     

Pressure drop and flow distribution characteristics of single and parallel serpentine flow fields for polymer electrolyte membrane fuel cells

This study numerically investigates pressure drop and flow distribution characteristics of serpentine flow fields (SFFs) that are designed for polymer electrolyte membrane fuel cells, which consider the Poiseuille flow with secondary pressure drop in the gas channel (GC) and the Darcy flow in the porous gas diffusion layer (GDL). The numerical results for a conventional SFF agreed well with those obtained via computational fluid dynamics simulations, thus proving the validity of the present flow network model. This model is employed to characterize various single and parallel SFFs, including multi-pass serpentine flow fields (MPSFFs). Findings reveal that under-rib convection (convective flow through GDL under an interconnector rib) is an important transport process for conventional SFFs, with its intensity being significantly enhanced as GDL permeability increases. The results also indicate that under-rib convection can be significantly improved by employing MPSFFs as the reactant flow field, because of the closely interlaced structure of GC regions that have different path-lengths from the inlet. However, reactant flow rate through GCs proportionally decreases as under-rib convection intensity increases, suggesting that proper optimization is required between the flow velocity in GCs and the under-rib convection intensity in GDLs.     

Demonstration of robust micromachined jet technology and its application to realistic flow control problems

This paper describes the demonstration of successful fabrication and initial characterization of micromachined pressure sensors and micromachined jets (microjets) fabricated for use in macro flow control and other applications. In this work, the microfabrication technology was investigated to create a micromachined fluidic control system with a goal of application in practical fluids problems, such as UAV (Unmanned Aerial Vehicle) -scale aerodynamic control. Approaches of this work include: (1) the development of suitable micromachined synthetic jets (microjets) as actuators, which obviate the need to physically extend micromachined structures into an external flow; and (2) a non-silicon alternative micromachining fabrication technology based on metallic substrates and lamination (in addition to traditional MEMS technologies) which will allow the realization of larger scale, more robust structures and larger array active areas for fluidic systems. As an initial study, an array of MEMS pressure sensors and an array of MEMS modulators for orifice-based control of microjets have been fabricated, and characterized. Both pressure sensors and modulators have been built using stainless steel as a substrate and a combination of lamination and traditional micromachining processes as fabrication technologies.     

模糊控制在变频调速恒压供水系统中的应用研究

分析研究了供水系统特性,建立了供水系统数学模型,应用模糊数学原理设计了一种自调整修正因子Fuzzy-PID控制器,详细说明了供水控制策略,并运用MATLAB/SIMULINK工具分别对采用数字PID、模糊控制和自调整修正因子Fuzzy-PID控制器的供水系统进行了仿真,仿真结果说明采用Fuzzy-PID控制方法控制效果明显优于另外两种控制方法.     

Flow measurement and instrumentation flow control characteristics of throttling venturi valve with adjustable area

In this study, a throttling venturi valve with adjustable area was designed to control the thrust of a monopropellant thruster using hydrogen peroxide. The flow rate control characteristics of the throttling venturi valve were investigated based on the pintle stroke and upstream pressure of the venturi. Three kinds of experiments were conducted: pressure and flow rate measurement according to pintle stroke and venturi upstream pressure, determination of critical pressure ratios under various conditions, flow rate control performance through open-loop control and feedback control of an actuator. The pressures were measured at the upstream, throat, and downstream of the venturi. It was observed that the flow rate changed in proportion to the stroke and upstream pressure. Below a stroke of 10 mm, the critical pressure ratio gradually decreased as the stroke and upstream decreased. However, above a stroke of 10 mm, the critical pressure ratio converged to a value between 0.7 and 0.8 regardless of the upstream pressure. The results of automatic flow rate control tests using open-loop control and feedback control showed that the measured flow rate satisfactorily followed the target flow rate profile.     

高炉炉顶余压透平发电控制研究与应用

为了实现高炉炼铁工序的节能降耗,介绍了现代钢铁厂回收能量的最新技术一高炉炉顶余压透平发电(TRT).分析和研究了TRT系统工艺流程和控制过程,给出了顶压调节、转速调节、升功率控制等关键技术内容.实践结果表明:该系统能极大改善高炉炉顶压力稳定性,基本上消除了减压阀组的噪音污染,可实现日均发电量为60 000 kW·h.     

Test bed for vehicle longitudinal control using chassis dynamometer and virtual reality: An application to adaptive cruise control

In this study, a test bed for vehicle longitudinal control is developed using a chassis dynamometer and real time 3-D graphics. The proposed test bed system consist of a chassis dynamometer on which test vehicle can run longitudinally, a video system that shows virtual driver view, and computer that control the test vehicle and realize the real time 3-D graphics. The purpose of the proposed system is to test vehicle longitudinal control and warning algorithms such as Adaptive Cruise Control (ACC), stop and go systems, and collision warning systems. For acceleration and deceleration situations which only need throttle movements, a vehicle longitudinal spacing control algorithm has been tested on the test bed. The spacing control algorithm has been designed based on sliding mode control and road grade estimation scheme which utilizes the vehicle engine torque map and gear shift information.     

主被动隔振法在金刚石刀具研磨压力控制中的应用

主被动隔振能够有效改善系统全频带隔振能力,有助于金刚石刀具研磨过程中稳定控制刀具刃口所受到的研磨压力.在应用主被动隔振法控制刀具研磨压力时,需要根据刀具刃磨机床进给轴的控制能力,合理设计柔性调压平台Z向支承刚度,通过调压平台的支承刚度抑制高频振动,同时还要确保位移控制量的输出频率和调压平台固有频率之间的匹配关系,通过主动控制削弱调压平台的谐振峰,以达到稳定刀具研磨压力的目的.     

Numerical simulation of fully developed flow and heat transfer characteristics in a curved tube with pulsating pressure gradient

Characteristics of fluid flow and convective heat transfer of a pulsating flow in a curved tube have been investigated numerically. The tube wall is assumed to be maintained at a uniform temperature peripherally in a fully developed pulsating flow region. The temperature and flow distributions over a cross-section of a curved tube with the associated velocity field need to be studied in detail. This problem is of particular interest in the design of Stirling engine heat exchangers and in understanding the blood flow in the aorta. The time-dependent, elliptic governing equations are solved, employing finite volume technique. The periodic steady state results are obtained for various governing dimensionless parameters, such as Womersley number, pulsation amplitude ration, curvature ratio and Reynolds number. The numerical results indicate that the phase difference between the pressure gradient and averaged axial velocity increases gradually up to π/2 as Womersley number increases. However, this phase difference is almost independent of the amplitude ratio of pulsation. It is also found that the secondary flow patterns are strongly affected by the curvature ratio and Reynolds number. These, in turn, give a strong influence on the convective heat transfer from the pipe wall to the pulsating flow. The results obtained lead to a better understanding of the underlying physical process and also provide input that may be used to design the relevant system. The numerical approach is discussed in detail, and the aspects that must be included for an accurate simulation are discussed.