科创中国

现对水工混凝土各种养护的方法进行汇总,对养护剂的机理、历史、发展、应用详细分析,提出适合水工混凝土的养护方式及注意事项,对养护剂的优点和种类范围做了重点阐述,总结出较为经济实用的水工混凝土养护方式,提高混凝土的质量.

The existing research of the electro-hydraulic vibrator mainly focuses on system stability,working frequency width and output waveform distortion.However,this high frequency performance of the electro-hydraulic vibrator is difficult to be improved greatly due to fast insufficiently frequency response of the servo valve itself and limited compensation capability of the control structure in the vibrator system.In this paper,to realize high frequency vibration,an improved two-dimensional valve(here within defined as a2D valve)as a main control component is adopted to the parallel connection with a servo valve to control the electro-hydraulic vibrator.Because the output waveforms of this electro-hydraulic vibrator are incapable to be verified through timely feedback as in the conventional electro-hydraulic servo system,the analysis to the output waveform becomes crucial to the design and control of the electro-hydraulic vibrator.The mathematical models of hydraulic actuation mechanism and the orifice area of the parallel valves connection are established first.And then the vibration process is divided into two sections in terms of the direction of the flow,the analytical expression of the excited waveform is solved.Based on the analytical results,the vibration boundary positions and the relationships exist between working states and the control parameters are derived.Finally an experimental system was built to validate the theoretical analysis.It is verified that this electro-hydraulic vibration system could achieve high working frequency,up to 2 000 Hz.The excited waveform is similar to the sinusoidal waveform.And the ascent and decent slopes of the waveforms are somewhat asymmetrical.This asymmetry is not only caused by the change of the direction of the elastic force but also dependent on the bias position of the vibration.Consequently the distortion of effective working waveform is less than 10%.This electro-hydraulic vibrator controlled by the multiple valves could not only greatly enhance the working frequency but also precisely control the vibration characteristic variables such as waveform shape.

The aerodynamic braking is a clean and non-adhesion braking, and can be used to provide extra braking force during high-speed emergency braking. The research of aerodynamic braking has attracted more and more attentions in recent years. However, most researchers in this field focus on aerodynamic effects and seldom on issues of position control of the aerodynamic braking board. The purpose of this paper is to explore position control optimization of the braking board in an aerodynamic braking prototype. The mathematical models of the hydraulic drive unit in the aerodynamic braking system are analyzed in detail, and the simulation models are established. Three control functions-constant, linear, and quadratic-are explored. Two kinds of criteria, including the position steady-state error and the acceleration of the piston rod, are used to evaluate system performance. Simulation results show that the position steady state-error is reduced from around 12–2 mm by applying a linear instead of a constant function, while the acceleration is reduced from 25.71–3.70 m/s2 with a quadratic control function. Use of the quadratic control function is shown to improve system performance. Experimental results obtained by measuring the position response of the piston rod on a test-bench also suggest a reduced position error and smooth movement of the piston rod. This implies that the acceleration is smaller when using the quadratic function, thus verifying the effectiveness of control schemes to improve to system performance. This paper proposes an effective and easily implemented control scheme that improves the position response of hydraulic cylinders during position control.

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.

The strain distributions near the interface when the elbow steel fiber is pulled out from the half-mould concrete matrix are directly measured using a combined method of single fiber pull-out test and digital image correlation. Meanwhile, the real-time processes of the bonding, debonding and sliding at the interface are observed. The micro-mechanism of the strain localization in the failure process of interface when debonding occurs and the strengthening mechanism at the imbedded fiber are discussed. The experimental results show that the meso-scale strain localization gives rise to the localization of shear damage near the fiber interface. This strain localization characterized by the debonding process near the interface occurs, develops and moves gradually at an apparently regular interval. At the elbow part of the imbedded fiber, the peak value of the shearing stress occurs. But the primary debonding does not occur at this place because the strength of the shear damage is increased at the local area of the elbow part in the concrete, displaying an apparent reinforced effect at the end of the fiber.

简述中小型三相同步水轮发电机无刷励磁的工作原理,介绍交流励磁机中重要部件-旋转整流装置的两种结构形式、原理特点及应用效果.

水泥混凝土路面具有良好的抗冲击、抗冻、抗裂性能,有利于延长路面使用寿命、能有效减小路面截面厚度等优点.结合2010年度新沂河整治水泥混凝土路面防汛道路工程,介绍混凝土路面工程结构及施工特点,并对施工质量控制具体措施、混凝土路面质量检测及评定方法进行探讨,旨在为水泥混凝土路面在水利堤防配套防汛道路工程中的推广及应用提供借鉴.

通过对抗冲耐磨混凝土原材料、拌和工艺等方面的质量控制管理,糯扎渡水电站溢洪道工程抗冲耐磨混凝土拌和物工作性能、混凝土强度、耐久性、抗冲耐磨强度均满足设计规范要求,为保证糯扎渡工程高流速溢洪道工程质量奠定了基础.

钻芯法作为结构混凝土抗压强度现场检测方法,在建筑、水利、水运(港口)、公路等建设领域应用广泛,各相关规程对芯样试件抗压强度试验前的养护条件差异较大.试验研究结果表明,不同直径、不同强度等级的芯样经泡水至饱和时,抗压强度相对于自然干燥时均有所降低,直径较小、本身强度等级较低的芯样混凝土降低更多.因此,要正确理解被检工程,运用好钻芯法检测技术规程,才能准确把握工程的结构混凝土强度.

基于室内标定试验得到的混凝土内部温湿度对于钢筋锈蚀速率的影响关系以及现场混凝土内部温湿度的实时监测数据,提出了一种用于实时监测混凝土内钢筋锈蚀速率的新方法,并设计了相关试验进行验证.结果表明:通过该监测方法得到的钢筋锈蚀速率数据能较为可靠地计算钢筋锈蚀量.