单相流负压排水系统在于坝村污水收集中的应用

文章针对农村污水重力排水收集系统存在的施工空间小、施工困难,矛盾多等诸多问题,在南通市海安市大公镇于坝村采用单相流负压排水系统,284户农户生活污水进行收集,优化了于坝村污水收集模式,确定了单相流负压排水系统的设计方案,并在工程施工难度、施工周期、运行效果等方面与重力排水系统进行了比较。研究结果表明,单相流负压排水系统优势较为明显,可以有效降低施工难度,缩短施工周期,提高农村污水收集率,在河网密集的农村地区具有良好的应用推广价值。

对87型雨水斗排水系统设计流态的几点思考

87型雨水斗的构造有别于重力式雨水斗,现行《建筑给水排水设计规范》(GB50015-2003,2009年版)采用重力流设计方法,《建筑与小区雨水利用工程技术规范》(GB50400-2006)采用半有压流设计方法,两者存在不同点,重力流方法在技术和经济上存在着缺陷。

直读式瞬时流量表的研究

用阀孔节流原理探讨了纯机械的直读式瞬时流量表的理论模型；并以ＳＬ－４５／４型瞬时流量表为例，阐述了理论模型的实际应用。

一类等熵欧拉方程组的流近似

研究了一类带有流扰动的一般压力等熵欧拉方程组的黎曼问题,获得了包含5种不同结构的黎曼解.证明了当包含压力的3-参数流扰动消失时,任何包含2个激波的黎曼解收敛于零压流系统的狄拉克激波解;任何包含2个稀疏波的黎曼解收敛于零压流系统的真空解.还证明了当包含压力的2-参数流扰动消失时,任何满足一定初值条件的2-激波黎曼解收敛于一类Chaplygin型气体方程组的狄拉克激波解.最后,对狄拉克激波和真空状态的形成过程进行了数值模拟.

汽轮机纯液调系统的自动升速控制

分析了汽轮机纯液压调速系统的特点 ,建立了汽轮机升速阶段的数学模型。采用矢量控制电机驱动 ,在仿真的基础上 ,实现了汽轮机转速的全程控制。

塔机液压顶升系统模拟带载试验装置

塔机液压顶升系统模拟带载试验装置刘铁钧，高平，李景升（北京市建工机械厂）自从自升式塔机诞生以来，塔机的升高与降落这一工况就一直由液压顶升系统来完成。塔机在这一工况下对安全性、可靠性要求有绝对的保证，如果液压顶升系统在使用中出现故障，那么排除比较困难，...

Modern Travelling Wave Based Fault Location Techniques for HVDC Transmission Lines

The modern travelling wave based fault location principles for transmission lines are analyzed.In order to apply the travelling wave principles to HVDC transmission lines,the special technical problems are studied.Based on this,a fault locating system for HVDC transmission lines is developed.The system can support modern double ended and single ended travelling wave princi- ples simultaneously,and it is composed of three different parts:travelling wave data acquisition and processing system,communication network and PC based master station.In the system,the fault generated transients are induced from the ground leads of the over-voltage suppression capacitors of an HVDC line through specially developed travelling wave couplers.The system was applied to 500 kV Gezhouba-Nanqiao(Shanghai)HVDC transmission line in China.Some field operation experiences are summarized,showing that the system has very high reliability and accuracy,and the maximum location error is about 3 km(not more than 0.3%of the total line length). Obviously,the application of the system is successful,and the fault location problem has finally been solved completely since the line operation.

Adaptive controller design based on input-output signal selection for voltage source converter high voltage direct current systems to improve power system stability

An input-output signal selection based on Phillips-Heffron model of a parallel high voltage alternative current/high voltage direct current(HVAC/HVDC) power system is presented to study power system stability. It is well known that appropriate coupling of inputs-outputs signals in the multivariable HVDC-HVAC system can improve the performance of designed supplemetary controller. In this work, different analysis techniques are used to measure controllability and observability of electromechanical oscillation mode. Also inputs–outputs interactions are considered and suggestions are drawn to select the best signal pair through the system inputs-outputs. In addition, a supplementary online adaptive controller for nonlinear HVDC to damp low frequency oscillations in a weakly connected system is proposed. The results obtained using MATLAB software show that the best output-input for damping controller design is rotor speed deviation as out put and phase angle of rectifier as in put. Also response of system equipped with adaptive damping controller based on HVDC system has appropriate performance when it is faced with faults and disturbance.

Influence of Negative Pressure Gradient on Pressure Distribution and Gas-Solid Flow Pattern of Solid Feed Systems

A series of experiments on a solid feed system was performed to investigate the effect of negative pressure gradient on the gas-solid flow pattern and hydrodynamic characteristics.Based on the non-fluidized gas-solid two phase flow and particulate mechanics in the standpipe,a method for predicting the pressure of the air passing through the recycle chamber and the pressure drop through the loop seal slit in these systems is also presented.The predicted pressure profile along the negative pressure gradient from the proposed model exhibits a good agreement with the experimental data.The experimental data show that the gas flow in the standpipe is always upward in the negative pressure gradients,while the direction ofthe superficial gas velocity through the recycle chamber of the loop seal does not affect the pressure drop in standpipe.It increases with an increasing negative pressure gradient.

Effect of phase-shift angle on 12-pulse star connection transformer system

Based on the study of the harmonic suppression on DC side of the multi-pulse rectification system,a software platform is established in Matlab environment.The phase-shift angle is studied from the aspects of system stability and economy,analyzing the effects of phase-shift angle on the input-side line current,the output-side voltage ripple,the equivalent capacity of autotransformer and other auxiliary devices in 12-pulse rectifier system.The software platform can complete the analysis only by inputting the initial conditions,eliminating the derivation of the intermediate formula and reducing the complexity of the system analysis,and have good scalability.The simulation results show that the system can effectively analyze the influence of phase angle on 12-pulse star-connected transformer.

A multi-objective gravitational search algorithm based approach of power system stability enhancement with UPFC

On the basis of the theoretical analysis of a single-machine infinite-bus （SMIB）, using the modified linearized Phil- lips-Heffron model installed with unified power flow controller （UPFC）, the potential of the UPFC supplementary controller to enhance the dynamic stability of a power system is evaluated by measuring the electromechanical controllability through singular value decomposition （SVD） analysis. This controller is tuned to simultaneously shift the undamped electromeehanical modes to a prescribed zone in the s-plane. The problem of robust UPFC based damping controller is formulated as an optimization problem according to the eigenvalue-based multi-objective function comprising the damping factor, and the damping ratio of the undamped electromechanical modes to be solved using gravitational search algorithm （GSA） that has a strong ability to find the most optimistic results. The different loading conditions are simulated on a SMIB system and the rotor speed deviation, internal voltage deviation, DC voltage deviation and electrical power deviation responses are studied with the effect of this flexible AC transmission systems （FACTS） controller. The results reveal that the tuned GSA based UPFC controller using the proposed multi-objective function has an excellent capability in damping power system with low frequency oscillations and greatly enhances the dynamic stability of the power systems.

Numerical Simulation on a Throttle Governing System with Hydraulic Butterfly Valves in a Marine Environment

Hydraulic butterfly valves have been widely applied in marine engineering because of their large switching torque, low pressure loss and suitability for large and medium diameter pipelines. Due to control problems resulting from switching angular speeds of the hydraulic butterfly valve, a throttle-governing control mode has been widely adopted, and detailed analysis has been carried out worldwide on the structural principle concerning speed-regulation and the load torque on the shaft while opening or closing a hydraulic butterfly valve. However relevant reports have yet been published on the change law, the error and the influencing factors of the rotational angular velocity of the hydraulic butterfly valve while opening and closing. In this article, research was based on some common specifications of a hydraulic butterfly valve with a symmetrical valve flap existing in a marine environment. The throttle governing system supplied by the accumulator to achieve the switching of the hydraulic control valve was adopted, and the mathematical models of the system were established in the actual conditions while the numerical simulations took place. The simulation results and analysis show that the rotational angular velocity and the error of the hydraulic butterfly valve while switching is influenced greatly by the drainage amount of the accumulator, resulting in pressure loss in the pipeline, the temperature of hydraulic medium and the load of the hydraulic butterfly valve. The simulation results and analysis provide a theoretical basis for the choice of the total capacity of the accumulator and pipeline diameters in a throttle governing system with a hydraulic butterfly valve.It also determines the type and specification of the hydraulic butterfly valve and the design of motion parameters of the transported fluid.

The Effect of Hydrostatic Pressure Fields on the Dispersion Characteristics of Fluid-shell Coupled System

The effect of hydrostatic pressure on the vibration dispersion characteristics of fluid-shell coupled structures was studied.Both fluid-loaded cylindrical shells and fluid-filled cylindrical shells were considered.Numerical analysis was applied to solve the dispersion equations for shells filled with or loaded with fluid at various hydrostatic pressures.The results for external pressure showed that non-dimensional axial wave numbers are nearly independent when the pressure is below the critical level.The influence of internal pressure on wave numbers was found significant for the real branch s=1 and the complex branches of dispersion curves.The presence of internal pressure increased the cut on frequencies for the branch s=1 for high order wave modes.

Flow Pattern and Pressure Fluctuation of Severe Slugging in Pipeline-riser System

During the exploitation of offshore oil and gas,it is easy to form severe slugging which can cause great harm in the riser connecting wellheads and offshore platform preprocessing system.The flow pattern and pressure fluctuation of severe slugging were studied in an experimental simulation system with inner diameter of 0.051 m.It is found that severe slugging can be divided into three severe slugging regimes：regime I at low gas and liquid flow rates with large pressure fluctuation,intermittent flow of liquid and gas in the riser,and apparent cutoff of liquid phase,regime II at high gas flow rate with non-periodic fluctuation and discontinuous liquid outflow and no gas cutoff,regime III at high liquid flow rate with degenerative pressure fluctuation in form of relatively stable bubbly or plug flow.The results indicate that severe slugging still occurs when the declination angle of pipeline is 0,and there are mainly two kinds of regimes：regime I and regime II.As the angle increases,the formation ranges of regime I and regime III increase slightly while that of regime II is not affected.With the increase of gas superficial velocity and liquid superficial velocity,the pressure fluctuation at the bottom of riser increases initially and then decreases.The maximum value of pressure fluctuation occurs at the transition boundary of regimes I and II.

Damping controller design based on FO-PID-EMA in VSC HVDC system to improve stability of hybrid power system

Wind energy sources have different structures and functions from conventional power plants in the power system.These resources can affect the exchange of active and reactive power of the network.Therefore,power system stability will be affected by the performance of wind power plants,especially in the event of a fault.In this paper,the improvement of the dynamic stability in power system equipped by wind farm is examined through the supplementary controller design in the high voltage direct current(HVDC)based on voltage source converter(VSC)transmission system.In this regard,impacts of the VSC HVDC system and wind farm on the improvement of system stability are considered.Also,an algorithm based on controllability(observability)concept is proposed to select most appropriate and effective coupling between inputs-outputs(IO)signals of system in different work conditions.The selected coupling is used to apply damping controller signal.Finally,a fractional order PID controller(FO-PID)based on exchange market algorithm(EMA)is designed as damping controller.The analysis of the results shows that the wind farm does not directly contribute to the improvement of the dynamic stability of power system.However,it can increase the controllability of the oscillatory mode and improve the performance of the supplementary controller.

某特殊造型屋顶雨水排放设计比较

结合北京师范大学珠海理工校区音乐厅屋顶的特点,探讨不同暴雨重现期、雨水排水方式、设计参数的比选,以保证屋面雨水排水安全。当屋面面积较小、坡度较大且屋面雨水斗的数量相同时,选择半有压流排水系统会比虹吸式雨水系统更经济、实用。

地铁车辆段大型屋面的排水工程设计

屋面雨水排水系统按雨水在管道内的流态分为压力流雨水排水系统、重力半有压雨水排水系统和重力流雨水排水系统,文章以厦门市地铁车辆段运用库、检修库等大型屋面的排水实例,比较压力流雨水排水系统、重力半有压流雨水排水系统、重力流雨水排水系统的优势和适用性,结果表明,排水工程采用压力流、半有压力流,还是重力流,应根据该工程的特点,通过技术经济比较,因地制宜,选择合宜的排水方案。

Electromagnetic Fields and Induced Voltages on Underground Pipeline in the Vicinity of AC Traction System

Various regulations, aimed at the protection of human beings and electrical equipment against possible adverse effects resulting from exposure to electromagnetic fields, have been issued in many countries. Most of them are based on safety guidelines published by international expert groups. In this paper, electric and magnetic fields are calculated in the vicinity of 25 kV traction line supplying railway traction systems. Calculation results are compared to exposure limits specified by safety guidelines and regulations. Possible countermeasures for reduction of electromagnetic fields are proposed. Also, this paper presents a method for calculation of the induced voltages to an underground gas pipeline from a neighbouring 25 kV electric traction overhead line in case of short circuit. Calculations are performed with EMTP-ATP software. Possible countermeasures for reduction of induced voltages are proposed.

Research on Common Grounding Electrode Technique in HVDC

This paper discusses the characteristics of DC transmission common system ground electrode type and shared ground electrode, established the mathematical model of two circuit DC systems share ground electrode, analyze effects of the shared loop ground DC transmission system electrode on the operation of HVDC system size under different operation modes, and compare with the independent ground electrode, ground electrode impact on environment under different operation mode, and the paper finally puts forward some solving measures for the influence of the shared ground electrode on the environment and public ground electrode effects on DC system operation problems.

On Simultaneous Exact Controllability

We consider a mixed problem for a system describing the evolution of sound in a compressible fluid. We describe how to treat a simultaneous exact boundary controllability problem in the sense proposed by J.L. Lions as well as D. Russell. By using convenient modified multipliers we obtain an observability inequality provided suitable geometric condition on the domain is valid and the speed velocity of the models are related.