科创中国

Existing researches on no-moving part valves in valve-less piezoelectric pumps mainly concentrate on pipeline valves and chamber bottom valves,which leads to the complex structure and manufacturing process of pump channel and chamber bottom.Furthermore,position fixed valves with respect to the inlet and outlet also makes the adjustability and controllability of flow rate worse.In order to overcome these shortcomings,this paper puts forward a novel implantable structure of valve-less piezoelectric pump with hemisphere-segments in the pump chamber.Based on the theory of flow around bluff-body,the flow resistance on the spherical and round surface of hemisphere-segment is different when fluid flows through,and the macroscopic flow resistance differences thus formed are also different.A novel valve-less piezoelectric pump with hemisphere-segment bluff-body(HSBB)is presented and designed.HSBB is the no-moving part valve.By the method of volume and momentum comparison,the stress on the bluff-body in the pump chamber is analyzed.The essential reason of unidirectional fluid pumping is expounded,and the flow rate formula is obtained.To verify the theory,a prototype is produced.By using the prototype,experimental research on the relationship between flow rate,pressure difference,voltage,and frequency has been carried out,which proves the correctness of the above theory.This prototype has six hemisphere-segments in the chamber filled with water,and the effective diameter of the piezoelectric bimorph is 30mm.The experiment result shows that the flow rate can reach 0.50 mL/s at the frequency of 6 Hz and the voltage of 110 V.Besides,the pressure difference can reach 26.2 mm H2O at the frequency of 6 Hz and the voltage of 160 V.This research proposes a valve-less piezoelectric pump with hemisphere-segment bluff-body,and its validity and feasibility is verified through theoretical analysis and experiment.

In the mixed-flow pump design,the shape of the flow passage can directly affect the flow capacity and the internal flow,thus influencing hydraulic performance,cavitation performance and operation stability of the mixed-flow pump.However,there is currently a lack of experimental research on the influence mechanism.Therefore,in order to analyze the effects of subtle variations of the flow passage on the mixed-flow pump performance,the frustum cone surface of the end part of inlet contraction flow passage of the mixed-flow pump is processed into a cylindrical surface and a test rig is built to carry out the hydraulic performance experiment.In this experiment,parameters,such as the head,the efficiency,and the shaft power,are measured,and the pressure fluctuation and the noise signal are also collected.The research results suggest that after processing the inlet flow passage,the head of the mixed-flow pump significantly goes down;the best efficiency of the mixed-flow pump drops by approximately 1.5%,the efficiency decreases more significantly under the large flow rate;the shaft power slightly increases under the large flow rate,slightly decreases under the small flow rate.In addition,the pressure fluctuation amplitudes on both the impeller inlet and the diffuser outlet increase significantly with more drastic pressure fluctuations and significantly lower stability of the internal flow of the mixed-flow pump.At the same time,the noise dramatically increases.Overall speaking,the subtle variation of the inlet flow passage leads to a significant change of the mixed-flow pump performance,thus suggesting a special attention to the optimization of flow passage.This paper investigates the influence of the flow passage variation on the mixed-flow pump performance by experiment,which will benefit the optimal design of the flow passage of the mixed-flow pump.

Direct drive servovalves are mostly restricted to low flow rate and low bandwidth applications due to the considerable flow forces.Current studies mainly focus on enhancing the driving force,which in turn is limited to the development of the magnetic material.Aiming at reducing the flow forces,a novel rotary direct drive servovalve(RDDV)is introduced in this paper.This RDDV servovalve is designed in a rotating structure and its axially symmetric spool rotates within a certain angle range in the valve chamber.The servovalve orifices are formed by the matching between the square wave shaped land on the spool and the rectangular ports on the sleeve.In order to study the RDDV servovalve performance,flow rate model and mechanical model are established,wherein flow rates and flow induced torques at different spool rotation angles or spool radiuses are obtained.The model analysis shows that the driving torque can be alleviated due to the proposed valve structure.Computational fluid dynamics(CFD)analysis using ANSYS/FLUENT is applied to evaluate and validate the theoretical analysis.In addition,experiments on the flow rate and the mechanical characteristic of the RDDV servovalve are carried out.Both simulation and experimental results conform to the results of the theoretical model analysis,which proves that this novel and innovative structure for direct drive servovalves can reduce the flow force on the spool and improve valve frequency response characteristics.This research proposes a novel rotary direct drive servovalve,which can reduce the flow forces effectively.

为研究5个水稻品种对美国稻瘟病小种IB-1、IE-1k和IG-1的抗性遗传,于2008-2009年在美国阿肯色大学潘布拉夫分校和水稻研究推广中心,用中国水稻品种特青和4个美国水稻品种Katy、Mars、LaGrue和Newbonnet组成完全双列杂交.一代、杂交二代和亲本在温室,用美国稻瘟病(Magna porthegrisea)3个主要菌原小种IB-1、IE 1k和IG-1进行接种鉴定,进行完全双列杂交遗传分析研究.结果表明:特青抗所有的小种;Katy抗IB-1和IG-1,但感IE-1k; Mars抗IE-1k和IG-1,但感IB 1;LaGrue感所有小种;Newbonnet抗IG-1,但感IB-1和IE-1k.抗病品种特青与感病品种Newbonnet对小种IB-1,抗病品种特青与抗病品种Mars对IE-1k,抗病品种特青与抗病品种Katy,抗病品种特青与抗病品种Newbonnet对IG-1,其正反交二代抗病植株与感病植株的比例为63:1,说明,这些抗病品种对相应的IB-1、IE-1k和IG-1分别存在3对独立遗传的显性抗病基因,出现重叠作用的遗传关系.抗病品种特青与抗病品种Katy,抗病品种特青与感病品种LaGrue,抗病品种Katy与感病品种Newbonnet对IB-1,抗病品种特青与感病品种Mars 和感病品种Lagure,抗病品种Katy与感病品种Mars和感病品种Lagure对IG-1,其正反交杂交二代抗病植 株与感病植株的分离比例符合15:1的比例,说明,这些抗病品种对相应稻瘟病小种存在两对独立遗传的显 性抗性基因,出现重叠作用的遗传关系.抗病品种Mars与感病品种Katy、感病品种Lagure和感病品种Newbonnet对IE-1k,其杂交一代表现感病,正反交杂交二代抗病植株和感病植株的分离符合7抗:9感的比例,说明,品种Mars存在两对隐性抗病基因,感病品种Katy、Lagure和Newbonnet与抗病品种Mars的后代出现两对显性感病基因互补作用的遗传关系.抗病品种特青与感病品种Mars,抗病品种Katy与感病品种Mars及LaGrue对IB-1,抗病品种特青与感病品种Katy、LaGrue和Newbonnet对IE-1k,抗病品种Katy、Mars和Newbonnet与感病品种LaGrue对IG-1,其正反交二代的抗病植株与感病植株的比例为3:1,说明,这些品种对IB-1、IE-1k和IG-1的抗性分别存在1对显隐性基因遗传关系.感病品种Mars、La-Grue、Newbonnet对IB-1和感病品种Katy、LaGrue、Newbonnet对IE-1k,其正反交二代全为感病植株,说明,这些感病品种分别对IB-1、IE-1k的感病基因是等位的.

南水北调中线天津干线采用全箱涵无压接有压自流输水方案,调节池是实现无压流和有压流平稳过渡的重要控制性建筑物.经多方案比选,斜坡式调节池结构安全稳定,水力条件好,实现了上下游流态的平稳衔接.

The transient behavior of centrifugal pumps during transient operating periods,such as startup and stopping,has drawn more and more attention recently because of urgent needs in engineering.Up to now,almost all the existing studies on this behavior are limited to using water as working fluid.The study on the transient behavior related to solid-liquid two-phase flow has not been seen yet.In order to explore the transient characteristics of a high specific-speed centrifugal pump during startup period delivering the pure water and solid-liquid two-phase flow,the transient flows inside the pump are numerically simulated using the dynamic mesh method.The variable rotational speed and flow rate with time obtained from experiment are best fitted as the function of time,and are written into computational fluid dynamics(CFD)code-FLUENT by using a user defined function.The predicted heads are compared with experimental results when pumping pure water.The results show that the difference in the transient performance during startup period is very obvious between water and solid-liquid two-phase flow during the later stage of startup process.Moreover,the time for the solid-liquid two-phase flow to achieve a stable condition is longer than that for water.The solid-liquid two-phase flow results in a higher impeller shaft power,a larger dynamic reaction force,a more violent fluctuation in pressure and a reduced stable pressure rise comparing with water.The research may be useful to understanding on the transient behavior of a centrifugal pump under a solid-liquid two-phase flow during startup period.

To improve the performance of the positive displacement blower,it is imperative to understand the detailed internal flow characteristics or enable a visualization of flow status.However,the existing two-dimensional unsteady,three-dimensional steady or quasi-unsteady numerical simulation and theoretical analysis cannot provide the detailed flow information,which is unfavorable to improve the performance of positive displacement blower.Therefore,the unsteady flow characteristics in a three-lobe positive displacement blower are numerically investigated by solving the three-dimensional,unsteady,compressible Navier-Stokes equations coupled with RNG k-εturbulent model.In the numerical simulation,the dynamic mesh technique and overset mesh updating method are adopted.Due to the air being compressed in the process of the rotors rotating,the variation of the temperature field in the positive displacement blower is considered.By comparing the experimental measurements and the numerical results on the variation of flow rate with the outlet pressure,the maximum relative error of the flow rate is less than 2.15%even at the maximum outlet pressure condition,which means that the calculation model and numerical computational method used are effective.The numerical results show that in the intake region,the fluctuations of the inlet flow are greatly affected by the direction of the velocity vectors.In the exhaust region,the temperature changes significantly,which leads to the increase of the airflow pulsation.Through analysis on the velocity,pressure and temperature fields obtained from the numerical simulations,three-dimensional unsteady flow characteristics in the positive displacement blower are revealed.The studied results will provide useful reference for improving the performance and empirical correction in the design of the positive displacement blower.

With the increasing noise pollution,low noise optimization of centrifugal pimps has become a hot topic.However,experimental study on this problem is unacceptable for industrial applications due to unsustainable cost.A hybrid method that couples computational fluid dynamics(CFD)with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects.Under Langthjem's assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps,the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software.The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency(BPF)noise,and the sound pressure level(SPL)reached peaks near the cutoff that corresponded with the pressure pulsation in this region.An experiment is performed to validate this prediction.Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model.The simulation results for the noise are analyzed and compared with the experimental results.The variation in the calculated noise with changes in the flow agreed well with the experimental results.When the flow rate was increased,the SPL first decreased and reached the minimum near the best efficient point(BEP);it then increased when the flow rate was further increased.The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps.The noise simulation method in current study has a good feasibility and suitability,which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.

声学多普勒水流剖面仪是目前较先进的河道测流设备.按《规范》要求,利用该仪器前,需要对该仪器与流速仪测流的实测流量进行对比实验,计算其换算系数.在分析ADCP测流原理的基础上,利用引黄干渠张二庄水文站实测流量资料,对两种测流方法测量结果进行对比分析.根据最小二乘法原理,建立回归直线,并对其进行检验.对回归直线进行拟合优度检验,拟合优度系数为0.982;对回归直线用F检验法进行截距检验,回归效果显著.在该断面用ADCP测流时,流量换算系数为0.9911.

针对互联网中常见的VoIP应用类型,重点从分类特征的选取出发,提出了一种基于C4.5决策树算法的VoIP流量识别方法,并分别利用模拟数据和真实网络数据对其进行了测试.结果表明,该方法识别准确率高,对含有不同协议种类VoIP的网络数据具有较强的适应能力