科创中国

The methods of improving the dynamic performance of high speed on/off solenoid valve include increasing the magnetic force of armature and the slew rate of coil current, decreasing the mass and stroke of moving parts. The increase of magnetic force usually leads to the decrease of current slew rate, which could increase the delay time of the dynamic response of solenoid valve. Using a high voltage to drive coil can solve this contradiction, but a high driving voltage can also lead to more cost and a decrease of safety and reliability. In this paper, a new scheme of parallel coils is investigated, in which the single coil of solenoid is replaced by parallel coils with same ampere turns. Based on the mathematic model of high speed solenoid valve, the theoretical formula for the delay time of solenoid valve is deduced. Both the theoretical analysis and the dynamic simulation show that the effect of dividing a single coil into N parallel sub-coils is close to that of driving the single coil with N times of the original driving voltage as far as the delay time of solenoid valve is concerned. A specific test bench is designed to measure the dynamic performance of high speed on/off solenoid valve. The experimental results also prove that both the delay time and switching time of the solenoid valves can be decreased greatly by adopting the parallel coil scheme. This research presents a simple and practical method to improve the dynamic performance of high speed on/off solenoid valve.

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.

对1000MW机组低压II转子高速动平衡过程进行了分析,并对动平衡所用设备及转子的平衡方法进行介绍,为今后国内相关百万超超临界机组转子平衡提供参考和借鉴.

Cavitation of centrifugal blood pump is a serious problem accompany with the blocking failure of short inlet cannula.However,hardly any work has been seen in published literature on this complex cavitation phenomenon caused by the coupling effect of inlet cannula blocking and pumps suction.Even for cavitation studies on ordinary centrifugal pumps,similar researches on this issue are rare.In this paper,the roles of throttling,rotation speed and fluid viscosity on bubble inception and intensity in a centrifugal blood pump are studied,on the basis of experimental observations.An adjustable throttle valve installed just upstream blood pump inlet is used to simulate the throttling effect of the narrowed inlet cannula.The rotation speed is adjusted from 2 600 r/min to 3 200 r/min.Glycerin water solutions are used to investigate the influences of kinetic viscosity.Bubbles are recorded with a high-speed video camera.Direct observation shows that different from cavitation in industrial centrifugal pumps,gas nuclei appears at the nearby of vane leading edges while throttling is light,then moves upstream to the joint position of inlet pipe and pump with the closing of the valve.It's found that the critical inlet pressure,obtained when bubbles are first observed,decreases linearly with viscosity and the slope is independent with rotation speeds;the critical inlet pressure and the inlet extreme pressure which is obtained when the throttle valve is nearly closed,fall linearly with rotation speed respectively and the relative pressure between them is independent with rotation speed and fluid viscosity.This paper studies experimentally on cavitation in centrifugal blood pump that caused by the failure of assembled short inlet cannula,which may beneficial the design of centrifugal blood pump with inlet cannula.

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 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 mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 ℃ to 650 ℃ for 90 min and at 550 ℃ for different time were investigated by tensile test, micro hardness test, and Transmission Electron Microscope (TEM). The steel was strengthened when it got annealed at temperatures ranging from 100 ℃ to 550 ℃, while it was softened when it got annealed at temperatures ranging from 550 ℃ to 650 ℃. Annealing temperature had stronger effect on mechanical properties than annealing time. TEM observations showed that nano-sized precipitates formed when the steel was annealed at 150 ℃ for 90 min, but the size and density of precipitates had no noticeable change with annealing temperature and time. Recrystallization occurred when the steel was annealed at temperatures above 550 ℃ for 90 min, and its scale increased with annealing temperature. Nano-sized annealing twins were observed. The mechanisms that controlled the mechanical behaviors of the steel were discussed.

The competition of surface and subsurface crack initiation induced failure is critical to understand very high cycle fatigue(VHCF)behavior,which necessitates the elucidation of the underlying mechanisms for the transition of crack initiation from surface to interior defects.Crack initiation potential in materials containing defects is investigated numerically by focusing on defect types,size,shape,location,and residual stress influences.Results show that the crack initiation potency is higher in case of serious property mismatching between matrix and defects,and higher strength materials are more sensitive to soft inclusions(elastic modulus lower than the matrix).The stress localization around inclusions are correlated to interior crack initiation mechanisms in the VHCF regime such as inclusion-matrix debonding at soft inclusions and inclusion-cracking for hard inclusions(elastic modulus higher than the matrix).It is easier to emanate cracks from the subsurface pores with the depth 0.7 times as large as their diameter.There exists an inclusion size independent region for crack incubation,outside which crack initiation will transfer from the subsurface soft inclusion to the interior larger one.As for elliptical inclusions,reducing the short-axis length can decrease the crack nucleation potential and promote the interior crack formation,whereas the long-axis length controls the site of peak stress concentration.The compressive residual stress at surface is helpful to shift crack initiation from surface to interior inclusions.Some relaxation of residual stress can not change the inherent crack initiation from interior inclusions in the VHCF regime.The work reveals the crack initiation potential and the transition among various defects under the influences of both intrinsic and extrinsic factors in the VHCF regime,and is helpful to understand the failure mechanism of materials containing defects under long-term cyclic loadings.

The remanufacturing blanks with cracks were considered as irreparable. With utilization of detour effect and Joule heating of pulsed current, a technique to arrest the crack in martensitic stainless steel FV520B is developed. According to finite element theory, the finite element(FE) model of the cracked rectangular specimen is established firstly. Then, based on electro-thermo-structure coupled theory, the distributions of current density, temperature field, and stress field are calculated for the instant of energizing. Furthermore, the simulation results are verified by some corresponding experiments performed on high pulsed current discharge device of type HCPD-I. Morphology and microstructure around the crack tip before and after electro pulsing treatment are observed by optical microscope(OM) and scanning electron microscope(SEM), and then the diameters of fusion zone and heat affected zone(HAZ) are measured in order to contrast with numerical calculation results. Element distribution, nano-indentation hardness and residual stress in the vicinity of the crack tip are surveyed by energy dispersive spectrometer(EDS), scanning probe microscopy(SPM) and X-ray stress gauge, respectively. The results show that the obvious partition and refined grain around the crack tip can be observed due to the violent temperature change. The contents of carbon and oxygen in fusion zone and HAZ are higher than those in matrix, and however the hardness around the crack tip decreases. Large residual compressive stress is induced in the vicinity of the crack tip and it has the same order of magnitude for measured results and numerical calculation results that is 100 MPa. The relational curves between discharge energies and diameters of the fusion zone and HAZ are obtained by experiments. The difference of diameter of fusion zone between measured and calculated results is less than 18.3%. Numerical calculation is very useful to define the experimental parameters. An effective method to prevent further extension of the crack is presented and can provide a reference for the compressor rotor blade remanufacturing.

Current researches show that mechanical deformation of seal ring face makes fluid film clearance decrease at high pressure side, thus a divergent clearance is formed and face wear occurs more seriously at the high pressure side than that on the low pressure side. However, there is still lack of published experimental works enough to prove the theoretical results. In this paper, a spiral groove dry gas seal at high pressures is experimentally investigated so as to prove the face wear happened at the high pressure side of seal faces due to the face mechanical deformation, and the wear behavior affected by seal ring structure is also studied. The experimental results show that face wear would occur at the high pressure side of seal faces due to the deformation, thus the leakage and face temperature increase, which all satisfies the theoretical predictions. When sealed pressure is not less than 5 MPa, the pressure can provide enough opening force to separate the seal faces. The seal ring sizes have obvious influence on face wear. Face wear, leakage and face temperature of a dry gas seal with the smaller cross sectional area of seal ring are less than that of a dry gas seal with bigger one, and the difference of leakage rate between these two sizes of seal face width is in the range of 24%–25%. Compared with the effect of seal ring sizes, the effect of secondary O-ring seal position on face deformation and face wear is less. The differences between these two types of dry gas seals with different secondary O-ring seal positions are less than 5.9% when the rotational speed varies from 0 to 600 r/min. By linking face wear and sealing performance changes to the shift in mechanical deformation of seal ring, this research presents an important experimental method to study face deformation of a dry gas seal at high pressures.