Use of a higher order Heydemann–Welch model to characterize a controlled clearance piston gauge

We present a new method for characterizing a controlled-clearance piston gauge as a primary pressure standard. This method requires operating the piston gauge to jacket pressures of over 80% of the system pressure. We present measurements on a hydraulic piston gauge with a 290 MPa maximum pressure and a nominal piston diameter of 3.27 mm. Measurements showed that the cylinder becomes stiffer as the jacket pressure increases, and that non-linear models of the Heydemann–Welch parameters improve the determination of the effective area. The relative standard uncertainty in the effective area of the piston gauge ranges from 16.0 × 10⁻⁶ to 17.6 × 10⁻⁶, and the agreement to the present NIST pressure scale is within the standard uncertainty.     

Computer simulation of a 1.0 GPa piston–cylinder assembly using finite element analysis (FEA)

The paper reports a preliminary study of the behavior of a high performance controlled-clearance piston gauge (CCPG) in the pressure range up to 1 GPa through finite elemental analysis (FEA). The details of the experimental characterization of this CCPG has already been published (Yadav et al., 2007 [1]). We have already pointed out that the use of Heydemann–Welch (HW) model for the characterization of any CCPG, has some limitation due to the fact that the linear extrapolation of the cube root of the fall rate versus jacket pressure (v^1/3–p_j) curve is assumed to be independent of the rheological properties of the pressure transmitting fluids. The FEA technique addresses this problem through simulation and optimization with a standard ANSYS program where the material properties of the piston and cylinder, pressure dependent density and viscosity of the pressure transmitting fluid etc. are to be used as the input parameters. Thus it provides characterization of a pressure balance in terms of effective area and distortion coefficient of the piston and cylinder. The present paper describes the results obtained on systematic studies carried out on the effect of gap profile between piston and cylinder of this controlled-clearance piston gauge, under the influence of applied pressure (p) from 100 MPa to 1000 MPa, on the pressure distortion coefficient (λ) of the assembly. The gap profile is also studied at different applied jacket pressure (p_j) such that p_j/p varied from 0.3, 0.4 and 0.5.     

Nonlinear modeling and identification of the electro-hydraulic control system of an excavator arm using BONL model

Electro-hydraulic control systems are nonlinear in nature and their mathematic models have unknown parameters. Existing research of modeling and identification of the electro-hydraulic control system is mainly based on theoretical state space model, and the parameters identification is hard due to its demand on internal states measurement. Moreover, there are also some hard-to-model nonlinearities in theoretical model, which needs to be overcome. Modeling and identification of the electro-hydraulic control system of an excavator arm based on block-oriented nonlinear（BONL） models is investigated. The nonlinear state space model of the system is built first, and field tests are carried out to reveal the nonlinear characteristics of the system. Based on the physic insight into the system, three BONL models are adopted to describe the highly nonlinear system. The Hammerstein model is composed of a two-segment polynomial nonlinearity followed by a linear dynamic subsystem. The Hammerstein-Wiener（H-W） model is represented by the Hammerstein model in cascade with another single polynomial nonlinearity. A novel Pseudo-Hammerstein-Wiener（P-H-W） model is developed by replacing the single polynomial of the H-W model by a non-smooth backlash function. The key term separation principle is applied to simplify the BONL models into linear-in-parameters struc~tres. Then, a modified recursive least square algorithm（MRLSA） with iterative estimation of internal variables is developed to identify the all the parameters simultaneously. The identification results demonstrate that the BONL models with two-segment polynomial nonlinearities are able to capture the system behavior, and the P-H-W model has the best prediction accuracy. Comparison experiments show that the velocity prediction error of the P-H-W model is reduced by 14%, 30% and 75% to the H-W model, Hammerstein model, and extended auto-regressive （ARX） model, respectively. This research is helpful in controller design, system monitoring and diagnosis.     

超低温弹簧蓄能密封圈动密封性能有限元分析与优化设计*

为进一步探究超低温工况下弹簧蓄能密封圈系统的动密封性能,建立弹簧蓄能密封圈系统的等效二维轴对称有限元模型;对密封圈轴向装配以及径向装配2种典型数值装配过程进行模拟、分析与比较,利用稳定装配后的构型计算在常温与超低温下密封圈在不同介质压力下的密封特性,并分析密封圈在不同工况下的动密封特性。基于数值模拟试验结果,对弹簧蓄能密封圈内唇表面结构、底座宽度以及弹簧刚度进行优化,并对3种优化策略进行评估验证。结果表明：在室温与超低温下,轴滑动的摩擦力都随介质压力的增大而增加;在超低温环境下夹套材料由于收缩而增大了对轴的压力,轴滑动时的摩擦力比常温下更大;随着介质压力增大,低温与室温下摩擦力差异减小。提出的3种优化方案都可在对密封性影响较小的前提下减小轴在工作过程中摩擦力,其中蓄能弹簧刚度的优化对于改善密封圈性能最为有效。     

Tool-path generation for sheet metal incremental forming based on STL model with defects

Tool-path generation is a key issue in sheet metal incremental forming process, and existing approaches either are prone to computationally expensive or cannot be applied to stereolithography (STL) model including defects. Thus, a new tool-path generation method is presented by adopting the thought of generating cutter-location (CL) data directly from corresponding cutter-contact (CC) data. By analyzing the interference characteristics between fillet-end tool and model surface and considering tangential case and intersection case comprehensively, a discrete computational model is proposed to calculate single-layer interference-free CL contour, instead of computing a precise CL point by checking potential interferences from candidate facet, vertices, and edges, respectively. So this method is more efficient and easier for program implementation. Additionally, a fast recursive search algorithm is developed to identify and extract flat area features, and an efficient 2D invalid loops removal algorithm based on decomposition thought is presented to obtain valid CC contours and CL contours with a near linear time-complexity. Implementation tests prove that the new method is effective and robust for STL model with defects, and tool-path achieved is highly precise. It is also applicable to various tool shapes and suitable for planning various types of tool-paths to meet different SMIF process requirements.     

Application of variable area cavitating venturi as a dynamic flow controller

The variable area cavitating venturi is an effective means to throttle the mass flow rate of liquid. The mass flow rate is a function of the upstream pressure, the pintle stroke, the density and saturation pressure of the liquid, independent of the downstream pressure. In this paper, a variable area cavitating venturi is designed and four different sets of experiments are conducted to investigate the performance of the variable area cavitating venturi. In these experiments, the mass flow rates are examined under different pintle positions, upstream pressures, downstream pressures and dynamic motions of the pintle. The experimental results indicate that the mass flow rate is independent of the downstream pressure when the ratio of the downstream pressure to upstream pressure is less than 0.8. The mass flow rate is almost linearly dependent on the pintle stroke for a constant upstream pressure. The discharge coefficient is a function of the pintle stroke, whereas the upstream and downstream pressures have rare influence on the discharge coefficient. The variable area cavitating venturi can control and measure the mass flow rate dynamically by determining the pintle stroke and the upstream pressure.     

超低温弹簧蓄能密封圈密封性能及试验研究

为研究往复运动弹簧蓄能密封圈的低温特性,通过构建等效弹簧建立二维轴对称模型,采用ANSYS分析弹簧蓄能密封圈在常温环境下装配和介质加压、由常温到低温过程中及低温加压过程中夹套的应力和摩擦力的变化。结果表明:常温和低温下夹套内外唇口为主要承压区,内外唇口的应力、接触压力、接触宽度和摩擦力随压力升高而增大;低温下的接触压力比常温下大,但接触宽度比常温下小,且摩擦力是常温下的2～3倍。仿真结果表明弹簧蓄能密封圈在常温和低温下具有良好的密封性能,通过常温氦气、低温液氮下的密封性能试验,验证了仿真分析结果的正确性,同时也验证了该弹簧蓄能内密封圈在常温和低温下良好的工作性能。     

还原炉挠性夹套的焊接残余应力有限元模拟

夹套是广泛运用在化工、医药等行业设备上的加热冷却装置,夹套焊缝是常常发生开裂泄漏的失效部位,焊接残余应力是导致开裂泄漏的重要因素之一。利用有限元技术对一种新型多晶硅还原炉挠性冷却夹套的焊接过程的温度场、残余应力和塑性应变场进行了数值模拟。借助ANSYS的APDL编程和单元生死技术,采用热-结构直接耦合法,传热分析采用含高斯热源的瞬态过程、应力分析为稳态,材料本构为随温度变化的双线性随动强化弹塑性模型。通过模拟获得焊缝区域残余应力和塑性应变的分布规律,为同类夹套的焊接强度评定提供了有效方法。     

旋转配流激振控制阀开槽参数的交互作用试验研究

提出一种旋转配流激振控制阀,为研究阀芯开槽参数交互作用对激振控制阀输出压力的影响,基于Fluent多参考系滑移网格方法,对激振控制阀的输出压力进行仿真,利用试验测定方法对仿真结果进行验证;采用二次回归正交试验法、中心复合试验法,建立开槽参数与输出压力的显著不失拟回归模型,通过方差分析得到开槽参数影响输出压力的显著性差异...     

Simplified Modeling of Deflagration in Vessels

A simplified method that models the deflagration process occurring in closed or vented vessels is described. When combustion occurs within the spherical or cylindrical vessels, the flame moves spherically or segmentally to the vessel periphery. The volume and area of each element along the propagating flame front are calculated by using simple geometrical rules. For instabilities and turbulence resulting in enhanced burning rates, a simple analysis results in reasonable agreement with the experimental pressure transients when two burning rates (a laminar burning rate prior to the onset of instability and an enhanced burning rate) were used. Pressure reduction caused by a vent opening at predetermined pressure was modeled. Parameters examined in the modeling include ignition location, mixture concentration, vented area, and vent opening pressure. It was found that venting was effective in reducing the peak pressure experienced in vessels. The model can be expected to estimate reasonable peak pressures and flame front distances by modeling the enhanced burning rates, that is, turbulent enhancement factor.     

Developing an optimal valve closing rule curve for real-time pressure control in pipes

Sudden valve closure in pipeline systems can cause high pressures that may lead to serious damages. Using an optimal valve closing rule can play an important role in managing extreme pressures in sudden valve closure. In this paper, an optimal closing rule curve is developed using a multi-objective optimization model and Bayesian networks (BNs) for controlling water pressure in valve closure instead of traditional step functions or single linear functions. The method of characteristics is used to simulate transient flow caused by valve closure. Non-dominated sorting genetic algorithms-II is also used to develop a Pareto front among three objectives related to maximum and minimum water pressures, and the amount of water passes through the valve during the valve-closing process. Simulation and optimization processes are usually time-consuming, thus results of the optimization model are used for training the BN. The trained BN is capable of determining optimal real-time closing rules without running costly simulation and optimization models. To demonstrate its efficiency, the proposed methodology is applied to a reservoir-pipe-valve system and the optimal closing rule curve is calculated for the valve. The results of the linear and BN-based valve closure rules show that the latter can significantly reduce the range of variations in water hammer pressures.     

低温液体罐车外壳加强圈削边后的稳定性计算

低温液体罐车的外壳（也即外筒体）为真空容器，外设多个加强圈以增强其抗失稳能力，但为了提高装载量并且不突破罐车的宽度限制，往往对加强圈两侧进行削边处理。由于削边后结构不规则，无法再按照 GB 150—2011《压力容器》进行失稳临界压力或许用外压计算。为此，提出了加强圈刚度削弱系数的概念，并在有限元分析的基础上，拟合出了加强圈刚度削弱系数表达式。有了该系数，就可以在按照 GB 150—2011进行常规设计的基础上，解决低温液体罐车外壳加强圈削边后的失稳临界压力计算问题。     

基于SimulationX的外齿轮泵输出特性的研究

外啮合齿轮泵是液压系统中应用最广泛的动力源,具有良好的性能和较低的制造成本。基于SimulationX软件构建了考虑流量压力脉动的齿轮泵模型,基于泵的可变孔口、可变容积及间隙区域（均为角位移的函数）建立了流体动态模型。仿真获取了典型工况流量及压力的变化结果,并与实验数据进行了时域和频域的对比分析,对外啮合齿轮泵的输出特性预测方法进行研究。结果表明,仿真结果可以预测齿间容腔内达到的最大和最小压力,有助于防止气蚀以及减少泵噪声的研究;同时,在给定系统条件时,能够对泵的输出特性进行模拟预测。为外部齿轮泵的设计和开发提供工具,具有一定的工程领域应用价值。     

Mathematical modeling of pressure characteristics of the deflector-jet pilot stage considering boundary layer flow

The performance of a deflector-jet servo valve significantly depends on the pressure characteristics of its pilot stage. The complex flow field within the deflector-jet pilot stage presents enormous difficulty and challenge in establishing its mathematical model. In this work, according to the energy conversion characteristics of the flow field, the flow process within the pilot stage is divided into five phases for modeling: inside-pipe flow, first jet, first pressure recovery, secondary jet, and secondary pressure recovery. To better reveal the intrinsic operating mechanism of a deflector-jet pilot stage, the boundary layer is introduced into the model. Computational fluid dynamic (CFD) simulation and experiment are conducted to validate the developed mathematical model at different supply pressures. The result demonstrates that the velocity distribution of the jets and the pressure characteristics of the pilot stage are significantly influenced by the boundary layer. The boundary layer flow within the V-groove has a greater impact on the pressure characteristics than that within the nozzle. Verified by the CFD simulation and experiment, the developed model can accurately predict the velocity distribution of the jets and pressure characteristics. At different supply pressures, the maximum relative error between the theoretical and experimental results of the dimensionless pressure characteristic is 5.36%.     

FEA calculation of pressure distortion coefficients of gas-operated pressure balances – EURAMET project 1039

Finite element analysis methods were developed and applied to gas piston–cylinder units (PCUs) of piston- and cylinder-floating configuration (2, 5, 10 and 20) cm² nominal effective area, operated in gauge and absolute mode at pressures (0.06–7.5) MPa to determine their zero pressure and pressure-dependent effective areas, as well as pressure distortion coefficients (λ) with associated uncertainties. Real dimensional properties of the PCUs were used. λ were found to be independent of gas (ideal, N₂, He) within the viscous flow model, but strongly dependent on the gap shape, operation mode and elastic properties. Results demonstrate good agreement for λ, with its uncertainty for different PCUs varying between (0.03 and 0.21) × 10⁻⁶ MPa⁻¹ corresponding to maximum relative uncertainties in pressure of (0.07–0.34) × 10⁻⁶.     

Measurement of mass flow rate and evaluation of heat transfer coefficient for high-pressure pneumatic components during charge and discharge processes

Both the mass flow rate and heat transfer characteristics are significant factors to the flow behavior of the high-pressure air; however, they are not easy to be obtained by analytical model during discharge and charge processes. In this paper, the mass flow rate characteristics of high-pressure pneumatic components (HPPC) are measured by a compounding approach; two components under test with the same geometry and dimension are needed to be connected in series. Both the effective cross-section area and critical pressure ratio of HPPC are determined accurately, and only the pressure variation and the steady-state temperature of air in the chamber are utilized. The compared results between experimental and simulation data show that the accuracy of the measured effective cross-section area and critical pressure ratio of the HPPC is high when the sonic and adiabatic releasing time is less than 2 s. And then, a new combined method of calculating the heat transfer coefficient during discharging and charging processes for the high-pressure air is proposed. The computational fluid dynamics (CFD) method is used to illustrate the intensity of heat exchange between the high-pressure air inside the chamber and outer atmosphere. The dynamic flow behavior is analyzed based on the tested flow rate characteristics of HPPC, mixed heat transfer theory and numerical results. The results show that the heat-transfer coefficient during charge process is much greater than discharge process, and the forced convection heat exchange happened owing to the strong “air agitation” during the charge process. The experimental results also validate that the proposed method of calculating the transient heat transfer coefficient is more reasonable to describe the heat transfer behavior. The findings may also have general implication in the development of the design and analysis of the high-pressure pneumatic system.     

基于遗传算法的海洋平台损伤诊断

海洋平台结构在环境因素下可能出现局部破损,提出一种快速诊断结构损伤的损伤探测方法,而遗传算法因其方法简单及较强的鲁棒性成为近年来发展较快的一种全局优化方法。以海洋平台实测的固有频率和振型为诊断依据,将海洋结构的损伤诊断归结为优化问题,采用遗传算法进行优化搜索。考虑到平台结构刚度的方向性,针对测量噪声和海洋平台模态的特点,提出了一种修正的目标函数作为遗传算法进行损伤诊断的适应度函数。数值模拟和物理模型试验结果表明,该方法能够准确地诊断出导管架海洋平台结构的损伤,改进了进化搜索的鲁棒性,提高了海洋平台结构损伤诊断的可靠性。     

Centrifugal pump transient characteristics and analysis using the method of characteristics

A theoretical and experimental study has been carried out on the transient characteristics of a centrifugal pump during starting and stopping periods. Experiments have been conducted on a volute pump with different valve openings to study the dynamic behaviour of the pump during normal start up and stopping, when a small length of discharge pipe line is connected to discharge flange of the pump. Similar experiments have also been conducted when the test pump was part of a hydraulic system to study the system effect on the transient characteristics. Instantaneous rotational speed, flowrate, and delivery and suction pressures of the pump are recorded and it is observed in all the tested cases that the change of pump behaviour during the transient period is quasi-steady. The dynamic characteristics of the pump have been analysed by a numerical model using the method of characteristics. The model is presented and the results are compared with the experimental data. As the model contains speed acceleration and unsteady discharge terms, the model can be applied for analyses of purely unsteady cases where the pump dynamic characteristics show considerable departure from their steady-state characteristics.     

Assessment of cement introduction and pressurization techniques

The objective of this study was to measure the medullary pressures generated during bone cement injection, pressurization and femoral prosthesis insertion. The measurements were recorded throughout the length of an in vitro femoral model while implanting a series of prosthetic hip stems using different pressurization techniques. The prostheses used were a Charnley 40 flanged stem (Johnson & Johnson DePuy International Limited), an Exeter No. 3 stem (Stryker Howmedica Osteonics, Howmedica International Limited), and a customized femoral component (Johnson & Johnson DePuy International Limited). The following parameters were derived from the pressure data recorded: peak pressure, decay pressure and duration above optimum pressure of 76 kPa to predict adequate penetration. The custom and Exeter stems generated cement pressures throughout the length of the cavity model that were predicted to achieve adequate bone cement interdigitation into cancellous bone. For all the conditions investigated in this study, when using the Charnley femoral component, an adequate level of cement pressurization was generated in the medial-distal portion of the femoral cavity. It is postulated that this could result in reduced integration of the cement mantle with bone and less effective transmission of functional loads applied during a patient's normal activity, postoperatively.     

Calibration models for high enthalpy calorimetric probes

The accuracy of gas-aspirated liquid-cooled calorimetric probes used for measuring the enthalpy of high-temperature gas streams is studied. The error in the differential temperature measurements caused by internal and external heat transfer interactions is considered and quantified by mathematical models. The analysis suggests calibration methods for the evaluation of dimensionless heat transfer parameters in the models, which then can give a more accurate value for the enthalpy of the sample. Calibration models for four types of calorimeters are applied to results from the literature and from our own experiments: a circular slit calorimeter developed by the author, single-cooling jacket probe, double-cooling jacket probe, and split-flow cooling jacket probe. The results show that the models are useful for describing and correcting the temperature measurements.