Impact of Typical Steady-state Conditions and Transient Conditions on Flow Ripple and Its Test Accuracy for Axial Piston Pump

The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated working conditions. However, the pump usually has to work in large-scale and time-variant working conditions. Therefore, the flow ripple characteristics of pump and analysis for its test accuracy with respect to variant steady-state conditions and transient conditions in a wide range of operating parameters are focused in this paper. First, a simulation model has been constructed, which takes the kinematics of oil film within friction pairs into account for higher accuracy. Afterwards, a test bed which adopts Secondary Source Method is built to verify the model. The simulation and tests results show that the angular position of the piston, corresponding to the position where the peak flow ripple is produced, varies with the different pressure. The pulsating amplitude and pulsation rate of flow ripple increase with the rise of pressure and the variation rate of pressure. For the pump working at a constant speed, the flow pulsation rate decreases dramatically with the increasing speed when the speed is less than 27.78% of the maximum speed, subsequently presents a small decrease tendency with the speed further increasing. With the rise of the variation rate of speed, the pulsating amplitude and pulsation rate of flow ripple increase. As the swash plate angle augments, the pulsating amplitude of flow ripple increases, nevertheless the flow pulsation rate decreases. In contrast with the effect of the variation of pressure, the test accuracy of flow ripple is more sensitive to the variation of speed. It makes the test accuracy above 96.20% available for the pulsating amplitude of pressure deviating within a range of ~6% from the mean pressure. However, with a variation of speed deviating within a range of ±2% from the mean speed, the attainable test accuracy of flow ripple is above 93.07%. The model constructed in this research proposes a method to determine the flow ripple characteristics of pump and its attainable test accuracy under the large-scale and time-variant working conditions. Meanwhile, a discussion about the variation of flow ripple and its obtainable test accuracy with the conditions of the pump working in wide operating ranges is given as well.

Moisture Absorption, Mass Loss and Evaporative Resistance of Clothing in Transient Condition

The water vapour resistance of clothing ensembles is not as commonly determined as dry thermal insulation. The measurement techniques are more complicated and the measurement values differ among laboratories. Due to complicated moisture transfer process through clothing ensemble, the moisture absorbed and evaporated varies in transient and steady state phases depending on properties, thickness of clothing, and environmental conditions. The purpose of this study was to measure moisture gain inside hygroscopic underwear, and hydrophobic and permeable outer wear as a function of time, to investigate mass loss from ＂skin＂ as well as from the manikin, to quantify evaporative heat loss and total heat loss from the manikin, and to determine water vaponr resistance of clothing. Manikin Tore was used by wearing wet ＂skin＂ to simulate sweating condition. Moisture content in the inner garment gain shows an exponential relation against time. Moisture in the outer permeable layer shows little gain. On the contrary, mass loss directly from the wet skin decreases exponentially. The mass loss from the manikin is relatively stable throughout three test phases. The evaporative heat loss is about 2/3 of the total heat loss from the sweating manikin. While measuring the evaporative resistance of clothing ensembles with hygroscopic inner garment and permeable outer garment, unlike to measure ensembles with impermeable outer layer, one hour measurement time is enough to get relatively stable results. The variation between the 1^rt hour and the 3^nd hour is less than 5%. The length of transient period and measurement time is dependent on the permeability, thickness of clothing ensembles and environmental conditions.

A novel approach for predicting inlet pressure of aircraft hydraulic pumps under transient conditions

Cavitation caused by insufficient suction is a major factor that influences the life of aircraft pumps. Currently, pressurizing the tank can solve the cavitation problem under steady largeflow conditions. However, this method is not always effective under transient conditions(from zero flow to full flow in a very short time). Moreover, to apply and design other measures, such as a boost impeller, the suction dynamics during the transient period must be investigated. In this paper,a novel approach based on the pressure wave propagation theory is proposed for predicting the inlet pressure of an aircraft pump under transient conditions. First, a dynamic model of a typical aircraft pump is established in the form of differential equations. Then, the transient flow model of the inlet line is described using momentum and continuity equations, and the governing equations are discretized by the method of characteristics and the finite difference method. The simulated results are in good agreement with the results from verification tests. Further simulation analysis indicates that the wave velocity and transient time may influence the inlet and reservoir pressure as well as the size of the inlet line. Finally, solutions for upgrading the inlet pressure are discussed. These solutions provide guidelines for designing inlet installations.

空调器压缩机启停瞬间管路应变分析及结构优化

某型定速单冷窗机压缩机停机时管路应变超标,本文通过模态分析和启停瞬态分析相结合的方法,利用仿真数据对优化方案进行可行性预判,并进行试验验证,结果表明,同一位置仿真应变值与实测应变值差异在4%左右,仿真结果在偏差范围内。可见,应用瞬态分析技术对空调器压缩机停机时管路应变进行辅助分析能够提高空调器的开发效率。

External Characteristics and Internal Flow Features of a Centrifugal Pump during Rapid Startup

Centrifugal pumps always work under steady conditions,and many researches focus on the steady operation.But transient conditions,such as sudden startup and shutdown,are inevitable.The researches on the inner flow of centrifugal pumps under transient conditions have been done,and they show that the transient operation is different from the steady operation.In order to research the evolution of unsteady flow in a centrifugal pump under transient conditions,and to investigate the mechanism of transient effects by analyzing the unsteady flow in a centrifugal pump,the external characteristic experiment and the internal flow numerical calculation of the centrifugal pump with an open impeller during startup is presented.The relationships of the rotation speed,capacity and head between start-time are obtained by the external characteristics experiment.The numerical calculations under startup process are carried out by using the k-e model and N-S equation.The distribution of velocity and pressure in the inner channel of the tested pump was obtained by choosing fourteen start-time points and twelve geometrical points in the impeller channel during startup.The calculation results show that the velocity and the pressure increase linearly with the start-time before rotation＇s speed gets steady,then changes almost horizontally after rotation speed becomes steady,then fluctuates until being steady.The internal flow characteristics are in good agreement with the external characteristic experimental results and numerical calculation.The simulation methods and results make the basis for the diagnosis and optimization of under flow in the centrifugal pump during transient operation.

一拖三变频空调系统建模方法及控制研究

一拖多变频空调系统由于各蒸发器状态参数间的相互影响,使得系统的控制特性相当复杂,也增加了对系统进行动态建模的难度。为此,本文以一拖三系统为例,采用集总参数法,建立起系统的动态热力学模型;同时提出了系统中变频压缩机和电子膨胀阀的控制策略,引入了吸气压力控制和以电子膨胀阀直接控制室温的思路;制定了带有调整因子的模糊控制方法;利用系统热力学模型对控制策略和方法进行仿真研究,仿真结果表明所提出的控制策略和方法是有效可行的,能取得满意的控制效果。

双联变频空调系统的动态特性研究

通过引入空泡系数模型方程 ,应用守恒原理 ,建立起以蒸发器、电子膨胀阀、压缩机为一体的双联空调系统的动态分布参数数学模型 ;通过仿真计算对一拖二系统随变频压缩机转速、电子膨胀阀开度以及回风风机转速改变的动态特性进行研究分析 ;为系统的实时控制打下基础。

面向配电网接地故障暂稳态协同调控的UPQC优化运行方法

针对现有有源消弧装置存在稳态时直流侧取电难、直流电容难以稳压,暂态时接地故障瞬时过电压等问题,充分解析了接地故障全过程中统一电能质量调节器(unified powerqualityconditioner,UPQC)主动参与调控的潜力,提出一种面向配电网接地故障暂稳态协同调控的UPQC优化运行方法。将使用此方法的装置简称为具备消弧功能的统一电能质量调节器(arcsuppression-unifiedpowerquality conditioner,AS-UPQC)。首先,通过分析消弧稳态模式下AS-UPQC系统的功率流向,提出一种适用于AS-UPQC的能量主动平衡方法,通过控制AS-UPQC串联侧从电网吸收一定的有功来补偿并联侧消弧时消耗的有功。该方法在无需额外储能设备的前提下,有效保证了消弧装置直流侧电容能量平衡。其次,对接地故障的暂态模式进行分析,提出一种暂态响应优化的控制方法。在发生接地故障瞬间,控制串联侧从电网中吸收的有功,其等效增大系统阻尼,加快暂态过渡过程,从而抑制瞬态过电压的幅值。最后,通过仿真和实验验证了所提调控方法的有效性与可行性。

基于瞬态特性的手征媒质参数反演研究

电磁脉冲垂直投射到金属衬底的手征媒质,其反射信号一定也是脉冲,利用时域与频域的关系,换算得到频域的反射系数,结合本文推导得到的反射系数理论值构造优化目标函数,对该目标函数的优化处理实现了手征媒质参数的反演。文中给出了全部反演过程并进行了计算机模拟,得到了比较理想的结果,为实现手征媒质参数的反演提供了一条新的途径。

空调器非稳态制热量测量方法探讨

分析空调器非稳态制热量测量的特点和常规焓差法在非稳态制热量测量方面的欠缺。提出一种基于焓差法的改进型空调器非稳态制热量测量方法,即前置式测量空调器出风温度的方法,并对这种方法进行试验验证。结果表明,这种方法能够有效排除出风与受风室之间非稳态换热量对测量结果的影响,提高测试精度。

关于一种低温制热量的测量方法探讨

分析了焓差法测量空调低温制热量的特点。提出了一种基于焓差法的改进型空调低温制热量测量方法,即前置式测量空调出风温度的方法。通过试验验证,这种方法能有效排除出风空气和受风室之间非稳态换热量对测量的影响,提高测试精度。

瞬时受体电位离子通道3在糖尿病肾病小鼠的表达及意义

目的:研究瞬时受体电位离子通道3(TRPM3)在2型糖尿病肾病模型db/db小鼠肾组织的表达,以及高糖对人肾小管上皮细胞(HK2)和小鼠足细胞(MPC)TRPM3表达的影响。方法:(1)将20只雄性5周龄db/db小鼠随机分为两组,各10只。同窝出生的db/m小鼠作为正常对照组(n=20)。待db/db小鼠生长至10周龄和18周龄后取血、尿标本测定相关生化指标,留取肾组织。利用Western blot、实时荧光定量PCR(qRT-PCR)和免疫组织化学方法,检测正常对照组(db/m小鼠)及不同周龄(10周、18周)db/db小鼠肾组织中TRPM3的表达水平及分布情况。(2)体外培养HK2和条件永生化MPC,分别按以下处理分组:对照组(D-葡萄糖5.6 mmol/L);甘露醇组(D-葡萄糖5.6 mmol/L+甘露醇24.4 mmol/L);高糖组(D-葡萄糖30 mmol/L),培养24h、48h、72h收获细胞,用Western blot和qRT-PCR检测细胞中TRPM3的表达。结果:(1)与db/m小鼠相比,db/db小鼠肾组织肾小管和肾小球中TRPM3的表达增多,差异有统计学意义(P<0.05);(2)与正常对照组相比,高糖组HK2和MPC中TRPM3的表达均增多,差异有统计学意义(P<0.05);结论:TRPM3可表达于糖尿病肾病小鼠肾脏组织的肾小管和肾小球中,且高血糖可诱导TRPM3在HK2细胞和MPC细胞的高表达;TRPM3可能参与了糖尿病肾病的发生发展。

房间空调器热泵运行时的瞬态仿真

通过对房间空调器的热力学、传热学和流体力学分析，建立了制冷系统瞬态仿真的数学模型，得出了一台房间空调器在热泵运行时制冷系统的参数以及房间温度变化的曲线。

房间空调器制冷运行时的瞬态仿真

利用所建立的房间空调器制冷系统瞬态仿真的数学模型，对一台房间空调器的制冷运行进行了数值计算，得出了制冷系统的参数变化曲线和房间温度的变化曲线，结果较为满意。

铁路功率调节器过渡态出力配置及控制策略研究

针对电力机车过渡态(驶入–制动–启动)运行情况下负荷的功率特性,该文首次研究电气化铁路功率调节器过渡态的出力配置及控制策略。传统的电气化铁路功率调节器通常采用最大容量配置,其控制方式也是针对电力机车的稳定运行状态。而文中提出的出力配置及控制方式兼容电力机车过渡态运行时的电能质量、容量配置及出力需求,充分发挥了铁路功率调节器的并联特性,有效提高其利用率。首先,文章通过分析牵引机车过渡态负荷功率及电流特性,可知牵引机车负荷功率及电流呈现波动性。然后,根据电力机车过渡态的运行特性,分配电气化铁路功率调节器容量配置与出力,以满足其电能质量需求。在此基础上,创新性的研究机车过渡态下的铁路功率调节器最大出力控制策略,进而得到合理的电气化铁路功率调节器指令电流及容量配置区域,解决传统控制方式易出现过流保护而退出的问题,有效满足机车加速等过渡态下电流、功率波动的运行环境,实现电力机车牵引变电能质量、电气化铁路功率调节器容量配置及出力的有机统一。最后,通过Matlab仿真和实验平台验证算法的有效性和合理性。

变频空调室外机启动异常噪音分析及改善

为了解决变频压缩机启动过程产生的异常撞击噪音,本文对变频压缩机的驱动力矩与负载力矩的特性进行分析,得出压缩机启动过程的振动响应与自身的转动惯量、转矩常数和驱动开环电流都有相关性。进一步对压缩机-管路系统进行瞬态启动分析,得出基脚最大位移为2.1 mm,超出设计间隙,导致压缩机启动时基脚不断撞击定位螺栓。最后通过优化压缩机基脚的安装间隙,使得定位螺栓的振动响应从原来的2.3 g,降低至0.3 g,从而彻底消除了结构碰撞的异响噪音,显著改善压缩机启动过程的音质。

有限元法在空调器结构动力分析中的应用

应用有限元法对空调器整机及其钣金件、管道系统进行了模态分析 ,并与试验结果进行对比 ,吻合情况较好 ,可以满足工程需要。通过研究解决了空调器整机及其部件分析所需的约束条件。此项研究为今后在产品设计中应用有限元技术奠定了基础。

基于改进的ISO 7637-2评价方法解决驻车空调浪涌问题的研究

驻车空调是近年来兴起的一种新兴车用电器,因其高能效、长续航、舒适性而广泛应用在重卡前后装领域。随着卡车司机对驻车空调的使用场景深入,行车使用及燃油发电机加装越来越普遍,由此引发的浪涌失效越来越多。文章基于普遍采用的浪涌失效评价标准ISO 7637-2进行失效研究,通过对实验方法的改进及电路设计的的优化解决抗浪涌失效问题,建立了新的评价方法,明确了浪涌可靠性设计应在不同系统下采用差异化的电路设计。