Gap Flow Simulation Methods in High Pressure Variable Displacement Axial Piston Pumps

High pressure variable displacement axial piston pumps are subject to complex dynamic phenomena. Their analysis is difficult, additionally complicated by leakage of the working fluid. Analytically gap flow is calculated with the Reynolds equation which describes the pressure distribution in a thin lubricating layer. The paper presents various approaches to analyze gap flow both in traditional axial piston pump and novel type of hydraulic pump, designed at the Polish Gdansk Institute of Technology. Because of large aspect ratio between the height of the gap and the size of pump elements, the authors present the numerical simulation approach using a local model to define a lubrication gap, linked to a global model of a pump from which boundary conditions were imported. User defined functions implemented in Fluent and Excel were used to calculate the pressure and velocity fields and assess the fluid flow rate.     

考虑汽蚀影响的给水泵仿真建模及实现

该文根据蒸汽动力装置模拟器的研制需求,讨论了考虑汽蚀影响的给水泵仿真建模和实现方法。蒸汽动力装置中使用的给水泵动态特性变化很大,给水泵作为变转速泵的特性模拟在整个蒸汽动力装置热工水力特性模拟中占有非常重要的地位。由于给水泵性能受汽蚀影响很大,因此考虑汽蚀对给水泵性能的影响对于提高模拟器在正常工况和事故工况下的仿真精度有很大意义。该文构建的模型形式简单,计算精度高,覆盖的给水泵运行工况宽。该文提出的仿真模型和数值方法对于同类型泵的仿真建模和计算分析具有一定的参考价值。     

航空发动机燃油柱塞泵计算机辅助设计方法

针对现有航空燃油柱塞泵实验设计方法的不足,给出了一种计算机辅助设计方法。首先采用坐标互换法建立燃油柱塞泵的二元运动模型;然后使用AMESim仿真软件建立柱塞泵的模块化仿真模型;最后进行了柱塞泵的运动仿真分析和性能仿真分析。通过某型航空燃油柱塞泵的试验和仿真对比研究表明:性能仿真数据与试验数据十分吻合,能够反映柱塞泵实际工作性能。说明辅助设计方法是可行的、有效的。     

挖掘机高压轴向柱塞泵的虚拟样机

为利用虚拟样机技术预测挖掘机高压轴向柱塞泵的各项性能,基于AMESim和Virtual.Lab开展液压系统建模、一维与三维刚柔耦合联合仿真建模、缸体的系统级疲劳分析以及柱塞泵的辐射噪声分析,得到流量和压力特性曲线、缸体疲劳损伤结果以及各场点的声压曲线,为开展优化设计提供参考.     

Simulation algorithm for piston ring dynamics

Piston ring dynamics play important roles on the lubricant characteristic of reciprocating engines which lead to the consequences of engine wear and vast amount of lubricating oil consumption. Due to the complexity of motion, a study of motions and effects of the piston ring is mostly conducted in a simulation program. This paper shows a theoretical work and a new simulation algorithm of the 3D piston ring motions. The simulation concept is to determine the positions of the piston ring, which are the solutions of the Newton and Euler equations. Well known models like mixed lubrication model, asperity contact model, and blow-by/blow-back flow model were used in this study. The new simulation algorithm consists of four processes: construction of calculation nodes, use of finite different method, determination of the non-linear equation system, use of parallel computational technique.Two sets of the experimental studies were conducted for simulation verification. First, the gas flows through the static rectangular piston ring pack. Second, the blow-by/blow-back gas flow through the piston ring pack of a single cylinder diesel engine. The good agreement between the experimental and simulation results indicates that the developed simulation program can illustrate the piston ring motions and blow-by/blow-back flow. Since there is no algebraic equation in the ring profile, the presented simulation technique is suitable for the complicated surface of the piston and piston rings.     

A novel approach for predicting the operation of external gear pumps under cavitating conditions

This paper addresses the problem of predicting the effects of gas cavitation in fluid power components, accounting for the dynamic features of gas (including free air and vapour) release and adsorption. Several approaches to evaluate fluid properties under cavitating conditions have been proposed in the past, but those suitable to model hydraulic components with the classic lumped parameter approach do not consider the dynamic nature of the gas cavitation process. Cavitation can have a relevant impact on component operation, particularly for positive displacement machines directly connected to the oil reservoir. With the goal of studying the cavitation effects in hydrostatic units, in this paper a novel model to describe fluid properties – which utilizes a simplified formulation of the Full Cavitation Model – was integrated in an existing lumped parameter model for external gear machines previously developed by the authors’ research team. While the basic formulation of the new fluid model was previously validated for a single closed fluid chamber, the present study extends its formulation for the case of complete systems in which multiple chambers with variable volume are connected to each other. A proper experimental set-up was developed to permit the validation of the proposed model for the case of external gear pumps. Comparisons between measured and simulated instantaneous internal tooth space pressures as well as the outlet flow rates are presented. The significance of the proposed model is highlighted by comparing its predictions with those obtained using classic models of fluid properties, which cannot predict with accuracy the effects of cavitation.     

基于斜盘交错角的柱塞泵流量脉动研究

为了减小液压系统的噪声排放,必须减小来自泵源处的流量脉动。采用斜盘交错角的柱塞泵结构可以有效降低柱塞泵出口的流量脉动。交错角通过改变柱塞在轴向方向上的运动规律来影响柱塞在三角槽过渡区的压缩体积。通过分析发现交错角每增加1°,过渡区压缩体积增加0.084mL。使用PumpLinx软件计算不同交错角下的单柱塞腔出口流量。发现交错角越大,柱塞腔内的倒灌流量越小,但会增加柱塞腔内的压力超调量。最后通过PumpLinx软件计算交错角柱塞泵在不同转速、压力下的出口流量,得出合适的交错角大小。     

基于键合图法的活塞泵建模与仿真

基于由荷兰Twente大学控制工程系研发的机电一体化建模软件20-sim,提出利用键合图法实现活塞泵的建模与仿真。在实例模型中,首先实现了单向阀的20-sim模块构造,继而在20-sim环境中建立了活塞泵的键合图模型,仿真结果理想地显示了概念设计阶段的控制效果。     

A novel adaptive convolutional neural network for fault diagnosis of hydraulic piston pump with acoustic images

As an essential part of hydraulic transmission systems, hydraulic piston pumps have a significant role in many state-of-the-art industries. Thus, it is important to implement accurate and effective fault diagnosis of hydraulic piston pumps. Owing to the heavy reliance of shallow machine learning models on the expertise and experience of engineers, fault diagnosis based on deep models has attracted significant attention from academia and industry. To construct a deep model with good performance, it is necessary and challenging to tune the hyperparameters (HPs). Since many existing methods focus on manual tuning and use common search algorithms, it is meaningful to explore more intelligent algorithms that can automatically optimize the HPs. In this paper, Bayesian optimization (BO) is employed for adaptive HP learning, and an improved convolutional neural network (CNN) is established for fault feature extraction and classification in a hydraulic piston pump. First, acoustic signals are transformed into time–frequency distributions by a continuous wavelet transform. Second, a preliminary CNN model is built by setting initial HPs. The range of each HP to be optimized is identified. Third, BO is employed to select the optimal combination of HPs. An improved model called CNN-BO is constructed. Finally, the diagnostic efficiency of CNN-BO is analyzed using a confusion matrix and t-distributed stochastic neighbor embedding. The classification performance of different models is compared. It is found that CNN-BO has a higher accuracy and better robustness in fault diagnosis for a hydraulic piston pump. This research will provide a basis for ensuring the reliability and safety of the hydraulic pump.     

柱塞泵故障实时检测系统的设计

电厂除灰系统中柱塞泵的工作条件恶劣,非常容易发生泄漏。通过对柱塞泵正常工作和泄漏时声音信号的特征量的对比分析,设计了频域和时域相结合的方法检测故障,设计中利用功率谱、短时能量、自相关函数等特征量来判断柱塞泵工作状态,并提供了采用工程简化实现实时检测的方案。     

Performance analysis of a new energy-efficient variable supply pressure electro-hydraulic motion control method

Electro-hydraulic actuation is used in many motion control applications due to its high power density, excellent dynamic response and good durability. However fluid power actuation has been shown to be very energy inefficient, with an average efficiency for fluid power systems across all industries of 22% in the USA. This is a very significant problem, given that 3% of the energy used by mankind is transmitted in this way.The key challenge for researchers is to reduce energy losses in hydraulic actuation systems without increasing weight, size, and noise, and without reducing speed of response. Conventional high performance electro-hydraulic motion control systems use a fixed supply pressure with valve-controlled actuators (FPVC). This is inherently inefficient due to the need to use a valve to throttle the flow required by each actuator in the system down to match its load pressure. In this paper, a new load-prediction based method is proposed, in which the supply pressure is varied to track the pressure required by any actuator branch. By implementing this model-based approach using a high response servomotor-driven pump, it is shown that the dynamic response remains excellent. The load model not only allows feedforward control for servomotor speed based on the motion demand, but also feedforward for the control valves to supplement conventional proportional-integral feedback control.The new variable supply pressure valve-controlled (VPVC) method is investigated in simulation and experimentally using a two-axis hydraulic robot arm supplied by an axial piston pump. The performance has been rigorously compared with the same robot arm using a fixed supply pressure and proportional-integral joint position control. Experimental results showed that up to 70% hydraulic power saving was achieved, and that the dynamic tracking errors for VPVC were about half that for FPVC as a result of using feedforward control.     

基于树莓派的空化检测设备研制及控制系统优化

为研究表面织构的形状、大小、位置、排列与空化现象发生的关系,结合流体动力学和摩擦学等理论,拟设计以活塞裙部-缸套为模型建立检测表面织构在摩擦时发生空化现象的装置;由于空化泡发生的瞬时性,设计一种基于Raspberry Pi树莓派微型计算机的空化设备控制系统,降低系统的延时性,准确地采集到数据进而分析得出结论;采用TLC549CP A/D数据采集器、膜盒式传感器、OSG030-815UM超高速工业摄像机组成检测系统,分别对温度、压力、图像的输出参数进行采集;通过Java语言开发的空化参数采集平台对空化现象发生参数进行实时计算并显示;与树莓派原系统相比,优化后的系统可以准确地采集到空化发生时的参数,并且有低延时性和优异的稳定性,能够降低延时到1.73ms,降低了约81%。     

隔膜泵曲轴连杆连接松动动力学建模与分析

将隔膜泵曲轴连杆连接处连接松动按照磨损故障来考虑,采用碰撞-分离两状态接触力模型建立了相应的隔膜泵十字头滑块的动力学模型,在此基础上采用Runge-Kutta法进行了数值仿真,给出了不同参数下,即不同曲柄转速、不同磨损量、不同液体压力下的十字头滑块的位移-速度动态响应,并得出以下结论:隔膜泵曲轴连杆连接松动的动态响应受到曲柄转速的影响较大,与磨损量和活塞表面的液体压力也有一定的关系。     

面向航天任务综合仿真的想定生成系统研究

设计和实现了一个面向航天任务综合仿真的想定生成系统。目前,多数的想定生成系统都是为军事战术仿真服务,而所描述的想定系统,则是建立在航天任务综合仿真的基础上。航天任务综合仿真的想定生成系统有如下特点;首先,它支持同一概念模型向不同仿真模型的映射;其次,由于想定模型种类多样,模型之间关系复杂,想定生成系统在对多粒度模型支持以及想定的描述方法等方面也异于一般想定生成系统。首先定义了航天任务综合仿真的想定的内涵,并阐述了想定生成系统的特点。接下来给出了系统的组成结构,最后是系统实现方案及运行流程。     

基于 AMESim 的航空燃油柱塞泵特性仿真

针对柱塞倾斜安装的某型航空燃油柱塞泵进行运动学分析,首先基于坐标互换法建立柱塞运动方程,然后采用 AMESim 软件构建柱塞泵模型,最后仿真分析柱塞倾角和转子转速对柱塞泵运动特性、流量特性及压力特性的影响。仿真结果表明,相同工况下柱塞倾角对流量的影响小于转子转速,但斜柱塞结构能增大柱塞行程,增加泵的供油量,适度改善柱塞泵的流量脉动情况。     

基于小波能量熵和邻域粗糙集的电磁阀故障诊断研究

液体电磁阀是航空变量柱塞泵系统的关键控制元件，准确诊断电磁阀的故障类型是系统安全运行的重要保证；为了对航空变量柱塞泵系统中电磁阀进行检测与诊断，提出了一种基于小波能量熵和邻域粗糙集相结合的方法；研究了液体电磁阀驱动端的电流故障特征；采用AMEsim多学科领域仿真软件建立仿真模型，分析驱动端电流与阀体位移的关系，搭建实验系统，采集正常状态和故障状态的电流信号，分析不同状态的电流特性；然后利用小波包分解重构信号，提取对应的频带能量作为特征向量；最后，引入变精度模糊邻域粗集约简算法简化数值属性，提高了系统的效率；简化的属性集用于构建决策树，经过迭代训练，该模型诊断准确率达90%，达到了预期效果，实现了对液体电磁阀的快速诊断。     

Micro-hydrodynamics of immiscible displacement inside two-dimensional porous media

In this paper, a Boolean lattice-gas model based on field mediators proposed by Santos and Philippi (Phys Rev E 65:046305, 2002) is used for the simulation of fluid–fluid interface displacement inside two-dimensional simplified porous media. A new procedure is introduced to allow the simulation of different viscosity ratios on the framework of lattice-gas models. The model is verified by simulating the spreading of a liquid drop on a solid surface and by comparing the simulation results with experimental spreading data. Some important basic physical mechanisms occurring at the pore scale are simulated and compared qualitatively with experimental visualizations. The break-off phenomenon of the fluid–fluid interface is observed in bifurcations, when a wetting (or non-wetting) fluid is displacing a non-wetting (or wetting) fluid. The role of break-off is shown to be different in imbibition and drainage processes in agreement with experimental results. Finally, the influence of wettability on the displacement efficiency is investigated in two-dimensional random arrays of disks.     

Gerotor pump cavitation monitoring and fault diagnosis using vibration analysis through the employment of auto-regressive-moving-average technique

Gerotor pumps, as well known, are widely used in lubrication circuits of internal combustion engines for their simplicity, high efficiency and low costs.In this paper an experimental characterization of a Gerotor pump is shown. The research is a collaboration between the Hydraulic Power Research Group (HPRG) of the University of Naples “Federico II” and the Istituto Motori of CNR.The aim of this research is to investigate the possibility of using simple data to acquire, as vibrational data, on the pump under investigation to detect possible cavitation problem by implementing a proper mathematical procedure to this aim. As been demonstrated that these pumps are particularly subject to cavitation.The gerotor pumps are much subject to cavitate than expected, especially under particular operating conditions of the engine. Cavitation is also correlate to vehicle dynamics particularly with the recent tendency to reduce the mass of oil in the sump. Therefore, the research to avoid cavitation is crucial nowadays. Consequently this study has been firstly performed with an experimentation on the pump by monitoring the delivered oil flow-rate and the adsorbed torque on the pump shaft. An accurate analysis of the pressure oscillations in cavitation conditions, has been, also, conducted. Then, an accelerometer sensor has been properly located to study the cavitation with a fault diagnosis system based on vibration detection.The experimental tests have been performed on a test bench of the Hydraulic Laboratory of the University of Naples “Federico II” in Italy. The bench allows testing the pump working by varying the shaft speed, the oil temperature, the suction and the delivery pressure. The main measured parameters are shaft torque, oil flow rate, mean suction and delivery pressure and the instantaneous suction and delivery pressure.As expected, tests revealed the high influence of the suction pressure on the delivered oil flow rate, while no significant influence has been noted on the adsorbed torque. Furthermore, the pressure oscillations in the pump delivery are highly influenced by the suction pressure.A non intrusive accelerometer has been installed during the experimentation on the oil pump. Since the vibration due to cavitation is the main concern of this study, the accelerometer has been mounted at the suction port in the radial direction.More precisely, the paper presents a fault diagnosis system based on vibration detection. Firstly, a Fast Fourier Transform of the vibration signal has been computed. The investigation has been made with and without the presence of cavitation varying the pump rotation speeds. Limitations due to the detecting of the on line cavitation problems by monitoring the FFT vibration spectra have been overcame by implementing an alternative method based on stochastic approach.This diagnosis method of accelerometer time series analysis based on an Auto Regressive and Moving Average (ARMA) method has been used to determine the pump failure. The diagnosis results have demonstrated the ability of the proposed mathematical technique in the identification of cavitation phenomena proving that the proposed approach is a useful methodology to detect the presence of fault. The approach can predict, with good accuracy, pump failure in real time operation. In addition, a threshold vibration level in decibel scale is also fixed.     

Investigation of the discharge process in a shadow‐mask PDP cell using fluid models

Abstract— Two fluid models, LFA (local field approximation) and EME (electron mean energy), were applied to simulate the discharge process of a novel PDP with a shadow mask. In order to consider the variation of the secondary electron emission coefficient under different electric‐field and gas content, the secondary electron emission coefficient was calculated as a function of the energy of incident ions. The variation of the mean density of different particles as a function of time, electron temperature, and their space distributions in the discharge cell will be presented. And the simulation results of these two models are also compared in this paper. Then the EME model was used to investigate the relation between the discharge efficiency and the structure of the shadow mask, the xenon concentration, and the pressure.