共查询到20条相似文献，搜索用时 718 毫秒
1.
A molecular dynamics simulation model is established based on the well-known Lennard-Jones 12-6 potential function to determine the surface tension of a Lennard-Jones liquid-vapor interface.The simulation is carried out with argon as the working fluid of a given molecular number at different temperature and different truncated radius.It is found that the surface tension of a Lennard-Jones fluid is likely to be bigger for a bigger truncated radius,and tends to be constant after the truncated radius increased to a certain value.It is also found that the surface tension becomes smaller as the temperature increases. 相似文献
2.
The flame structure of gasoline engine is complicated and has the characteristic of fractal geometry. A fractal combustion model was used to simulate the engine working cycle. Based on this model, the fractal dimension and laminar flame surface area of turbulent premixed flames were studied under different working conditions. The experimental system mainly includes an optical engine and a set of photography equipment used to shoot the images of turbulent flame of spark-ignition engine. The difference box-counting method was used to process 2D combustion images. In contrast to the experimental results, the computational results show that the fractal combustion model is an effective method of simulating the engine combustion process. The study provides a better understanding for flame structure and its propagation. 相似文献
3.
The major aim of power quality （PQ） enhancing techniques is to maintain a specified voltage magnitude at a desired frequency for sensitive loads irrespective of faults on the power distribution network. The dynamic voltage restorer （DVR） is a device used to mitigate voltage sags to regulate load voltage. This paper presents a mathematical model for leading series voltage injection to mitigate sags thereby achieving the improvement of the utility power factor as well as power sharing between the DVR and utility. The power sharing will be as per requirement to compensate the sags considering the available distributed generation （DG）. The approach of mitigating voltage sags using the concept of leading series voltage injection is suitable for those locations where phase shift in the voltage will not cause any problem. The MATLAB/SIMULINK SimPowerSystem toolbox has been used to obtain simulation results to verify the proposed mathematical model. 相似文献
4.
Dielectric elastomer actuators （DEAs） are an emerging class of polymer actuation devices and have extensive application prospect in the field of robotics because of their light weight, high efficiency and large deformation. A cone DEA is manufactured and its working principle is analyzed. To obtain the deformation of elastomer and movement of DEA in advance, a finite element method （FEM） simulation is performed first. According to the working principle, two working equilibrium points of DEA, corresponding to the displacements of DEA with voltage off and on, are obtained and validated by experiments, thus work output in a workcycle is computed. Experiments show that the actuator can respond quickly when voltage is applied and can return to its original position rapidly when voltage is released. Simulation results agree well with experimental ones and the feasibility of DEA simulation is proved, and causes for the small difference between them in displacement output are analyzed. The performance of the actuator is improved from the aspects of both displacement and force output. A diamond four-bar linkage mechanism is used as the preload part and a displacement output of 17 mm is obtained. The force output of one actuating unit is about 1.77 N, so three actuating units are assembled in parallel and the force output is heightened to as high as 5.07 N. 相似文献
5.
The influence of water on protein conformation was investigated by simulating the molecular dynamics of a model protein lysozyme in different water systems.The lysozyme-water system with TIP3P water model and lysozyme-water cluster system with six-ring water model were evaluated.In addition,the radial distribution function of solvent around lysozyme was calculated.It is found that the distribution of water molecules around lysozyme is similar to that of water clusters.The analyses of dihedral angles and disulfide bonds of lysozyme show that the conformation of lysozyme is severely damaged in the lysozyme-water cluster system compared with that in the lysozyme-water system.This difference can be attributed to the formation of larger number of intermolecular hydrogen bonds between lysozyme and water cluster.It is in agreement with the analysis that water clusters can change the degree of denaturation in the process of heat denaturation of lysozyme. 相似文献
6.
This paper discusses dynamic characteristics of proton exchange membrane fuel cell (PEMFC) under rapid fluctuation of power demand. Wavelet neural network is adopted in the identification of the characteristic curve to predict the voltage. The system control scheme of the voltage and power is introduced. The corresponding schemes for voltage and power control are studied. MATLAB is used to simulate the control system. The results reveal that the adopted control schemes can produce expected effects. Corresponding anti-disturbance and robustness simulation are also carried out. The simulation results show that the implemented control schemes have better robustness and adaptability. 相似文献
7.
Simulation and analysis of resin flow in injection machine screw 总被引：1，自引：0，他引：1
Ling-feng LI Samir MEKID 《浙江大学学报(A卷英文版)》2008,9(3):338-345
A method with simulation and analysis of the resin flow in a screw is presented to ease the control of some problems that may affect the efficiency and the quality of the product among existing screws in an injection machine. The physical model of a screw is established to represent the stress, the strain, the relationship between velocity and stress, and the temperature of the cells. In this paper, a working case is considered where the velocity and the temperature distributions at any section of the flow are obtained. The analysis of the computational results shows an ability to master various parameters depending on the specifications. 相似文献
8.
Passive worms can passively propagate through embedding themselves into some sharing files, which can result in significant damage to unstructured P2P networks. To study the passive worm behaviors, this paper firstly analyzes and obtains the average delay for all peers in the whole transmitting process due to the limitation of network throughput, and then proposes a mathematical model for the propagation of passive worms over the unstructured P2P networks. The model mainly takes the effect of the network throughput into account, and applies a new healthy files dissemination-based defense strategy according to the file popularity which follows the Zipf distribution. The simulation results show that the propagation of passive worms is mainly governed by the number of hops, initially infected files and uninfected files. The larger the number of hops, the more rapidly the passive worms propagate. If the number of the initially infected files is increased by the attackers, the propagation speed of passive worms increases obviously. A larger size of the uninfected file results in a better attack performance. However, the number of files generated by passive worms is not an important factor governing the propagation of passive worms. The effectiveness of healthy files dissemination strategy is verified. This model can provide a guideline in the control of unstructured P2P networks as well as passive worm defense. 相似文献
9.
To ensure that limited resources are allocated more effectively to reduce marine risks, formal safety assessment (FSA), a proactive method, is introduced in planning a vessel traffic system (VTS). Based on the data of Wuhan port, some new solutions based on risk-indices are put forward. The weighted number of traffic accidents is predicted after the future weighted vessel traffic volume is estimated by analyzing the trend of trade development. To analyze risk acceptability, the as-low-as-reasonably-practicable (ALARP) matrix is transformed into a new model containing two parameters: the future weighted vessel traffic volume and the future weighted number of traffic accidents. The new risk control options (RCOs)can be identified by a revised Domino model with several feedback loops from all system levels to close a limited window of accident opportunity. The results indicate that the four most beneficial RCOs are a wider sub-area 1 channel, a VTS bridges area, a dredging sub-area 2 main route, and a VTS QSX anchorage to the 3rd bridge. The FSA is a method that is effective in evaluating the rationality, necessity and cost-effectiveness of VTS projects. 相似文献
10.
Modeling of D-STATCOM in distribution systems load flow 总被引：1，自引：0，他引：1
HOSSEINI Mehdi SHAYANFAR Heidar Ali FOTUHI-FIRUZABAD Mahmud 《浙江大学学报(A卷英文版)》2007,8(10):1532-1542
This paper presents modeling of Distribution STATCOM (D-STATCOM) in load flow calculations for the steady- state voltage compensation. An accurate model for D-STATCOM is derived to use in load flow calculations. The rating of this device as well as the direction of required reactive power injection for voltage compensation in the desired value (1 p.u.) is de- rived and discussed analytically and mathematically by the phasor diagram method. Furthermore, an efficient method for node and line identification used in load flow calculations is presented. The validity of the proposed model is examined by using two standard distribution systems consisting of 33 and 69 nodes, respectively. The best location of D-STATCOM for under voltage problem mitigation approach in the distribution networks is determined. The results validate the proposed model for D- STATCOM in large distribution systems. 相似文献
11.
通过对电除尘器工作原理的分析,建立了电除尘器高压电源供电数学模型。以这些数学模型为基础,采用免疫遗传算法对电除尘器高压电源进行优化控制的仿真研究。仿真结果表明,只要合理调节各级电场的工作电压、尽量减少无效电流和低效电流的发生机会,可使电除尘器高压电源的控制性能达到最佳状态。 相似文献
12.
An improved automatic voltage coordination control strategy(AVCCS) based on automatic voltage control(AVC) and battery energy storage control(BESC) is proposed for photovoltaic grid-connected system(PVGS) to mitigate the voltage fluctuations caused by environmental disturbances.Only AVC is used when small environmental disturbances happen,while BESC is incorporated with AVC to restrain the voltage fluctuations when large disturbances happen.An adjustable parameter determining the allowed amplitudes of voltage fluctuations is introduced to realize the above switching process.A benchmark low voltage distribution system including PVGS is established by using the commercial software DIg SILENT.Simulation results show that the voltage under AVCCS satisfies the IEEE Standard 1547,and the installed battery capacity is also reduced.Meanwhile,the battery’s service life is extended by avoiding frequent charges/discharges in the control process. 相似文献
13.
采用晶闸管三相全控桥式整流电路,能使电除尘三相高压电源输出电压平稳,提高功率因数、二次电压和有效电晕功率;采用综合降低电压振打技术,可以使电晕线和收尘板更清洁,减少发生反电晕现象,提高粉尘荷电率;通过采用32位DSP为核心的控制器．配置火花优化控制、实时充电比优化控制、无效电流和低效电流处理等软件,可实现电除尘器电源的最优控制功能。实践表明,综合上述技术的新型三相高压电源和单相电源比较,电能转换效率提高了12％、功率因素提高了24％,成为目前大型电除尘器配套电源和单相工频SCR整流电源的更新换代产品。 相似文献
14.
郭晓霞 《深圳职业技术学院学报》2013,12(3):27-30
电火花沉积工艺（ESD）是一种微弧焊工艺,电极材料沉积到基体表面,并于基体呈冶金结合．本文以冷作模具钢Cr12MoV为基体材料,利用电火花沉积对局部区域进行修复．研究了影响沉积层质量和沉积率的工艺参数,其中包括电容、电压和保护气．实验结果显示,虽然随着电容和电压的增大,沉积率提高,但同时也会使沉积层中的微裂纹和孔洞增加．因此,只有合理选择沉积工艺参数,才能达到一定沉积率的同时保证沉积层的质量． 相似文献
15.
针对电网电压出现频率偏移时,传统锁相环精度差、响应速度慢等问题,提出一种基于双二阶广义积分器正交信号发生器的新型锁相环,分析了新型锁相环工作原理,并建立基于新型锁相环的三相三电平电压型SVPWM整流器模型.通过MATLAB/Simulink对模型进行分析验证,结果表明：该新型锁相环能够在频率突变情况下实现频率跟踪,实现有功、无功分量独立控制以及较高功率因数运行. 相似文献
16.
针对中央空调系统运行管理中实际存在的启动时段内运行一台冷水机组、二台冷冻水泵和二台冷却水泵的现象（称为“一机多水泵运行”）,根据现场测试获得的中央空调系统运行数据,从冷冻水流量、冷水机组能效、冷冻泵效率、冷冻水侧能效和冷冻站能效等多个角度对该运行管理方式进行了分析和评价,指出应改变现有的运行管理方式,使空调系统保持良好的运行性能模式. 相似文献
17.
陈德淑 《重庆大学学报(英文版)》2003,2(2)
1. Introduction At present, it is necessary to use fertilizer to ensure the stable and high agricultural productivity. However, as we all know, the fertilizer not only decreases the self-fertility of soil, but also is accompanied with pesticide. Food poisoning caused by remnant pesticide in fruits and vegetables is often reported, and in such cases, chronic poisoning is the majority. The remnant pesticide accumulates in body gradually, and then induces kinds of disease. As reported, the Miyu… 相似文献
18.
提出一种基于双蓄电池储能系统的电压分层协调控制策略,以储能系统为主体协调控制母线电压稳定。根据母线电压的变化范围将系统的动态调节过程划分为稳态阶段与暂态阶段。稳态阶段下,采用双蓄电池组共同协调工作方式,解决了负载突变导致单组蓄电池充放电电流过大,易引起过流故障的问题;暂态阶段下,采用基于改进下垂控制的双蓄电池组轮换协调工作方式,解决了单组蓄电池荷电状态(State of Charge,SOC)达到上、下限后,出现过充或过放情况引起的蓄电池损坏问题。利用Matlab/Simulink平台分别对系统的两种动态调节过程进行仿真,验证各阶段下所提出的工作方式的有效性,并通过单、双蓄电池组的对比,验证所提出控制策略的合理性与优越性。 相似文献
19.
电子测量系统工频干扰与接地问题的研究 总被引：1，自引：0，他引：1
在工频干扰模型基础上,通过对示波器和毫伏表的电源变压器漏电阻和等效漏电压典型值的测量,估算了工频干扰电压的幅度,从而说明电子测量系统各设备间共地连接的必要性,并介绍了共地方式在交流电桥等实践中的应用实例. 相似文献
20.
以美国NI公司的Lab Windows/CVI软件为开发平台,配合电阻分压器、信号调理模块和高速数据采集卡等,设计研究了一套基于虚拟仪器的点火控制器性能检测系统。该系统突破了传统检测方法的局限性,实现了对点火控制器工作电压、工作电流、点火电压、吸合电压、维持电压、放电能量等性能的检测。 相似文献