科创中国

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.

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.

根据预期假说,本文对我国利率期限结构的远期利率预测作用进行了经验分析.结果表明,我国利率期限结构存在明显的时变溢价特征,这可以解释利率期限结构中的"预期之谜".经期限溢价修正后,利率期限结构所隐含的远期利率包含了大量未来即期利率变化的信息,而且无法拒绝预期理论.这对中央银行观察金融市场对经济的预期和未来利率走势,判断实际货币政策态势,具有重要的参考价值,并为我国推进利率市场化、实现通过利率价格工具调整开展间接调控的货币政策模式转型,提供了可靠的理论依据.

Blade vibration failure is one of the main failure modes of compressor wheel of turbocharger for vehicle application.The existing models for evaluating the reliability of blade vibration of compressor wheel are static,and can not reflect the relationship between the reliability of compressor wheel with blade vibration failure mode and the life parameter.For the blade vibration failure mode of compressor wheel of turbocharger,the reliability evaluation method is studied.Taking a compressor wheel of turbocharger for vehicle application as an example,the blade vibration characteristics and how they change with the operating parameters of turbocharger are analyzed.The failure criterion for blade vibration mode of compressor wheel is built with the Campbell diagram,and taking the effect of the dispersity of blade natural vibration frequency and randomness of turbocharger operating speed into account,time-dependent reliability models of compressor wheel with blade vibration failure mode are derived,which embody the parameters of blade natural vibration frequency,turbocharger operating speed,the blade number of compressor wheel,life index and minimum number of resonance,etc.Finally,the rule governing the reliability and failure rate of compressor wheel and the method for determining the reliable life of compressor with blade vibration is presented.A method is proposed to evaluate the reliability of compressor wheel with blade vibration failure mode time-dependently.

The existing researches of the evaluation method of ride comfort of vehicle mainly focus on the level of human feelings to vibration. The level of human feelings to vibration is influenced by many factors, however, the ride comfort according to the common principle of probability and statistics and simple binary logic is unable to reflect these uncertainties. The random fuzzy evaluation model from people subjective response to vibration is adopted in the paper, these uncertainties are analyzed from the angle of psychological physics. Discussing the traditional evaluation of ride comfort during vehicle vibration, a fuzzily random evaluation model on the basis of annoyance rate is proposed for the human body's subjective response to vibration, with relevant fuzzy membership function and probability distribution given. A half-car four degrees of freedom suspension vibration model is described, subject to irregular excitations from the road surface, with the aid of software Matlab/Simulink. A new kind of evaluation method for ride comfort of vehicles is proposed in the paper, i.e., the annoyance rate evaluation method. The genetic algorithm and neural network control theory are used to control the system. Simulation results are obtained, such as the comparison of comfort reaction to vibration environments between before and after control, relationship of annoyance rate to vibration frequency and weighted acceleration, based on ISO2631/1(1982), ISO 2631–1(1997) and annoyance rate evaluation method, respectively. Simulated assessment results indicate that the proposed active suspension systems prove to be effective in the vibration isolation of the suspension system, and the subjective response of human being can be promoted from very uncomfortable to a little uncomfortable. Furthermore, the novel evaluation method based on annoyance rate can further estimate quantitatively the number of passengers who feel discomfort due to vibration. A new analysis method of vehicle comfort is presented.

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.

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.

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.

针对NRA算法和BPA算法查询效率不高、重复访问数据的问题,提出了一种基于三维分档布鲁姆过滤器表(TF)的Top-κ查询算法(TKBFP).该算法使用TF对数据进行处理,以较低的误判率获得较高的访问效率并降低了内存消耗,利用最优位置索引策略,避免重复访问数据对象.对TKBFP算法进行了严格的语义定义,推导出每一维BF中需要的哈希函数个数;以自主开发的Java程序为仿真平台,对TKBFP算法进行了试验,并对算法执行效率和存储性能进行评价.试验结果表明,该算法能够避免重复访问数据对象,并能以较低的误判率实现大规模数据的高效查询处理.与NRA和BPA相比,当属性列表超过4个时,开销明显降低,适合面向大规模数据的查询处理应用.