Optimal arrangement for pressure measurement points in working chamber of earth pressure balance shield

In order to exactly provide scientific basis for pressure dynamic balance control of working chamber of earth pressure balance shield (EPBS),study on optimal arrangement of pressure measurement points in working chamber was conducted. Based on mathematical description of optimal arrangement for pressure measurement points,fuzzy clustering analysis and discriminant analysis were used to divide pressure regions of nodes on bulkhead. Finally,the selection method of optimal measurement points was proposed,and by selecting d6.28 m EPBS as study object,the case study was conducted. By contrast,based on optimal arrangement scheme of pressure measurement points,through adopting weighted algorithm,the absolute error mean of equivalent pressure of working chamber is the smallest. In addition,pressure curve of optimal arrangement points presents parabola,and it can show the state of pressure distribution on bulkhead truly. It is concluded that the optimal arrangement method of pressure measurement points in working chamber is effective and feasible,and the method can provide basis for realizing high precision pressure control of EPBS.

Numerical simulation of flow field characteristics and the improvement of pressure oscillation of rotating detonation engine

Due to the inherent working mode of rotating detonation engine(RDE),the detonation flow field has the characteristics of pressure oscillation and axial kinetic energy loss,which makes it difficult to design nozzle and improve propulsion performance.Therefore,in order to improve the characteristics of detonation flow field,the three-dimensional numerical simulation of annular chamber and hollow chamber is carried out with premixed hydrogen/air as fuel in this paper,and then tries to combine the two chambers to weaken the oscillation characteristics of detonation flow field through the interaction of detonation flow field,which is a new method to regulate the detonation flow field.The results show that there are four states of velocity vectors at the outlet of annular chamber and hollow chamber,which makes RDE be affected by rolling moment and results in the loss of axial kinetic energy.In the external flow field of combined chamber,the phenomenon of cyclic reflection of expansion wave and compression wave on the free boundary is observed,which results in Mach disk structure.Moreover,the pressure monitoring points are set at the external flow field.The pressure signal shows that the high-frequency pressure oscillation at the external flow field of the combined chamber has been greatly weakened.Compared to the annular chamber,the relative standard deviation(RSD) has been reduced from 14.6% to5.6%.The results thus demonstrate that this method is feasible to adjust the pressure oscillation characteristics of the detonation flow field,and is of great significance to promote the potential of RDE and nozzle design.

Pressure Changes in Patients with Chronic Renal Failure Undergoing Hemodialysis

Purpose: To determine the effects of hemodialysis on intraocular pressure (IOP) and to evaluate the correlation of IOP changes with anterior chamber angle anatomy. Patients and Methods: The study included 80 eyes of 40 patients with chronic renal failure (CRF) undergoing hemodialysis at the High Technology Medical Center between October 2018 and October 2021. Hemodialysis (HD) was performed 3 times a week and the duration of the procedure was 3 - 5 hours. The enrolled patients were grouped according to the width of the anterior chamber angle. IOP was evaluated at three different times during HD. Intraocular pressure was measured in both eyes in an upright sitting position with iCare tonometer. Results: According to the study results, there was no statistically significant difference in the axial length between the three measurements (p = 0.232). In patients with normal anterior chamber depth, IOP decreased significantly (68.75%) or did not show any changes in their IOP during or after the session. In patients with moderate narrow-angle (22.5%), IOP revealed no statistically significant differences. In patients with narrow-angle (8.75%), there was a marked increase in IOP. Changes in intraocular pressure were correlated with the anatomy of the anterior chamber angle. Loss in body weight as a result of hemodialysis was statistically important (p Conclusion: A significant increase in mean was revealed during and after hemodialysis in patients with extremely narrow-angle in comparison to eyes with wide or moderately anterior chamber angle. Eyes with shallow anterior chambers are at risk of having impaired aqueous humor outflow facilities and, as a result, significantly increase IOP during HD. Because of the high prevalence of narrow angles in the Caucasian population, it is of clinical importance to investigate the IOP changes in patients on HD. The results of our study support the idea that iridocorneal angle anatomy is affecting IOP fluctuation occurring in patients with ESRD undergoing HD.

Star Grain Regression Analysis under Spin Effect and Chamber Pressure Effect

The angular acceleration due to the spin effect increases the burning rate of solid propellant and changes the motor performance by increasing the operating pressure and decreasing the burning time. So it is important to know the grain regression taken place in the solid propellant rocket motor in the acceleration field. This study represents the grain regression analysis of two-dimensional axis-symmetric star grain configuration of the solid propellant rocket motor with spin induced acceleration effect and pressure effect on burn rate using geometrical and numerical analysis. While the rocket is spinning, the burn rates on each point of the propellant surface are different with its radial distance, acceleration vector angle and surface slope. With the different burn rates on the propellant surface, we analyze the propellant surface perimeter and port area, and these results are compared with those of constant burn rate and burn rate affected by the chamber pressure.

Measurement of Sound Pressure Levels in Anechoic Chamber and a Noisy Environment Experimentally

In real life, when a noise problem occurs, it is important to identify the cause and measure the noise of the source, since it may affect human beings or other constructions due to vibration generated from noise, so it is necessary to determine the noise related to a specific source like a machine in the presence of other sources which is a very important approach in noise control engineering. In this article a full experiment was executed to measure the sound pressure levels of various sources (stationary and non-stationary), in both an anechoic chamber and a non-ideal noisy environment. The sound pressure level was extracted for different sources and compared for both ideal and non-ideal environment. The results showed that acoustical free field of the space is the best field to do measurements to avoid reflection, on the other hand the difference between the source and the background should be more than 3 dB to get better results.

Producing ultra-high-speed nitrogen jets by arc heating in a low-pressure chamber

Pure nitrogen gas was heated with direct current arc, at input powers from several hundred Watt to over 5 kW, and then injected through a nozzle into a chamber at 1 or 10 Pa pressure, with the purpose of accelerating the gas to very high speed around 7 km/s. Various structures of the arc generator and gas expansion nozzle were examined. Results show that bypass exhausting of the boundary layer before it enters the nozzle divergent section can greatly increase flow speed of the jet, thus it might be possible to use nitrogen as a working gas in high speed gas dynamic test facilities.

Elimination of phosphorus vaporizing from molten silicon at finite reduced pressure

Elimination of phosphorus vaporizing from silicon was investigated. Si-P alloy made from electronic grade silicon was used. All the samples were analyzed by GD-MS. Theory calculation determines that phosphorus evaporates from molten silicon as gas species P and P2 at a finite reduced pressure. The experimental results show that phosphorus mass fraction can be decreased from 0.046% （460ppmw） to around 0.001% （10ppmw） under the condition of temperature 1 873 K, chamber pressure 0.6-0.8 Pa, holding time 1 h. Both experimental data and calculation results agree that at high phosphorus concentration, phosphorus removal is quite dependent on high chamber pressure while it becomes independent on low chamber pressure. The reason is that phosphorus evaporates from molten silicon as gas species P2 at a relatively high phosphorus concentration, while gas species P will be dominated in its vapour at low phosphorus content.

Modeling approaches to pressure balance dynamic system in shield tunneling

In order to deal with modeling problem of a pressure balance system with time-delay, nonlinear, time-varying and uncertain characteristics, an intelligent modeling procedure is proposed, which is based on artificial neural network(ANN) and input-output data of the system during shield tunneling and can overcome the precision problem in mechanistic modeling(MM) approach. The computational results show that the training algorithm with Gauss-Newton optimization has fast convergent speed. The experimental investigation indicates that, compared with mechanistic modeling approach, intelligent modeling procedure can obviously increase the precision in both soil pressure fitting and forecasting period. The effectiveness and accuracy of proposed intelligent modeling procedure are verified in laboratory tests.

The Pressure Gradient Elastic Wave： Energy Transfer Process for Compressible Fluids with Pressure Gradient

The temperature separation was discovered inside the short vortex chamber （H/D = 0.18）. Experiments revealed that the highest temperature of the periphery was 465 ℃, and the lowest temperature of the central zone was -45 ℃ （the compressed air was pumped into the chamber at room temperature）. The objective of this paper is to proof that this temperature separation effect cannot be explained by conventional heat transfer processes. To explain this phenomenon, the concept of PGEW （Pressure Gradient Elastic Waves） is proposed. PGEW are kind of elastic waves, which operate in compressible fluids with pressure gradients and density fluctuations. The result of PGEW propagation is a heat transfer from area of low pressure to high pressure zone. The physical model of a gas in a strong field of mass forces is proposed to substantiate the PGEW existence. This physical model is intended for the construction of a theory of PGEW. Understanding the processes associated with the PGEW permits the possibility of creating new devices for energy saving and low potential heat utilization, which have unique properties.

Paracentesis following intravitreal drug injections in maintaining physiologic ocular perfusion pressure

A retrospective analysis was performed of patients who received a paracentesis immediately following an intravitreal injection of bevacizumab or triamcinolone acetonide.These patients were previously diagnosed as having glaucoma,ocular hypertension,or had responded previously with sustained elevated intraocular pressure.Of 1661 procedures were performed.Totally 219（13%） of the injections were on phakic patients.A median（SD） of 210 μL（40 μL） of aqueous was removed during each paracentesis.There were no reported incidences of any complications.We propose performing a paracentesis immediately following intravitreal injections for patients at risk for ocular hypertension,glaucoma,and retinal vein or artery occlusion.

Effect of low dose laser cycloplasty on deepening anterior chamber in chronic angle-closure glaucoma

AIM:To describe the outcome of using low-dose laser cycloplasty(LCP)in chronic angle-closure glaucoma(CACG).METHODS:A retrospective case series.Medical charts of CACG patients who underwent LCP in the Eye Hospital of Wenzhou Medical University were reviewed.The main outcomes included intraocular pressure(IOP),the number of glaucoma medication,anterior segment parameters and surgery-related complications.RESULTS:A total of 7 eyes of 7 CACG patients(age 38.9±11.0y)underwent LCP with a mean follow-up of 27.1±13.7mo(range 16-48mo).Following LCP,mean IOP and glaucoma medications decreased from 26.1±6.1 mm Hg with 3.1±1.1 glaucoma medications pre-treatment to 14.9±3.1 mm Hg(P=0.027)with 0.4±1.1 glaucoma medications(P=0.001)at final follow-up.The anterior chamber depth(ACD),angle opening distance500 and trabecular-iris angle increased from 1.65±0.33 mm,0.05 mm(range 0-0.30 mm)and 5.1°(range,0-31.97°)at baseline to 1.98±0.43 mm(P=0.073),0.53 mm(range 0.42-0.91 mm,P=0.015),45.9°(range,40.2°-59.4°),(P=0.015)in the long-term follow-up,respectively.The deepening of ACD and reopening of anterior chamber angle(ACA)was observed in 6 eyes(85.7%).CONCLUSION:LCP is a promising treatment option for patients with CACG via reducing IOP and glaucoma medication without serious complications.In addition,LCP can bring a significant deepening in ACD and reopening of ACA.

Dynamic calibration method of capacitive pressure measuring device

This paper presents working principle,structure and a dynamic calibration method of capacitive pressure measuring device.Using this method,placing calibrated capacitive electronic pressure measuring device and three standard sensors in simulation chamber pressure generator is proper and the data generated by them are analyzed and compared.This calibration method realizes dynamic calibration of capacitive electronic pressure measuring device under actual working pressure;pressure signal and frequency spectrum are analyzed.The experimental results show that simulation chamber pressure calibration method is feasible.

Pressure impact characteristic of vane type continuous rotary motor under different buffer structures

In order to solve the problem of pressure shock on the continuous rotary electro-hydraulic servo motor,the mathematical models of pressure gradient under the structure of pre-compressed chamber and U-shaped groove were established.The optimal structure dimensions of the pre-compressed chamber and the U-shaped groove were determined.The fluid models were established by Solidworks under the four structures of triangular groove,triangular groove with pre-compression chamber,U-shaped groove and U-shaped groove with pre-compression chamber.Simulation analysis of depressurization process of fluid models was performed based on FLUENT.The pressure nephograms of different buffer structures were compared and analyzed,and the pressure change curves and pressure gradient change curves in the process of depressurization were obtained.The results show that the optimal edge length of the pre-compressed chamber of continuous rotary electro-hydraulic servo motor is 20 mm in the process of decompression.The pressure reduction effect is the best when the width of the U-shaped groove is 1.5 mm and the depth is 1.65 mm.The U-shaped groove structure with pre-compression chamber is more conducive to alleviate the pressure shock phenomenon of the motor compared with different combine buffer structures.

Spectral characteristics of underwater laser-induced breakdown spectroscopy under high-pressure conditions

Laser-induced breakdown spectroscopy(LIBS) has been proven to be an attractive technique for in situ oceanic applications.However,when applying LIBS into deep-sea,the pressure effect caused by different ocean depths is inescapable and could have great influence on the LIBS signals.In this work,spectral characteristics of underwater LIBS were investigated as a function of pressure in the range of 0.1-45 MPa.A high-pressure chamber built in the laboratory was used to simulate the high-pressure deep-sea environment.Optimal laser energy and detection delay were first determined under different pressure conditions and were shown to be independent of the external pressure.The increase in pressure has a significant impact both on the peak intensity and line broadening of the observed spectra.The peak intensity of Na,Li and K lines increases with the increasing pressure until a maximum intensity is reached at 12.5 MPa.Above this value,the peak intensity decreases gradually up to 45 MPa.For Ca line,the maximum intensity was observed at 30 MPa.The line broadening keeps constant at low pressures from 0.1-10 MPa,while it increases linearly at higher pressures,indicating a higher electron density caused by the compression effect of the high external pressure.We also compared the spectral data obtained from the high-pressure chamber and from the field sea trials,and the good consistency between the laboratory data and sea-trial data suggested the key role of pressure effect on underwater LIBS signals for practical deep-sea applications.

An Experimental Determination of the Supply and Exhaust Pressures in an Electro-Pneumatic Clutch Actuation System

Inlet and outlet orifices in an actuation chamber are sources through which the supply and exhaust pressures pass during the actuation process in clutch systems. They are key ingredients in an actuation chamber and are very phenomenal in heavy-duty vehicle operation. It is these pressures that initiate linear or rotary motions in drive systems. The pressure actions are processed in an enclosure termed an actuation chamber. Oftentimes, the forces or pressures produced in an actuation chamber are unknown and immeasurable owing to a lack of precise instruments to accomplish them. This challenge can only be approached via an improvised technique that requires experimentation. This is precisely what this presentation is all about. The knowledge of these parameters is important in the study of the actuation process in electro-pneumatic clutch systems of heavy-duty vehicles. The study was done with a Mercedes Benz Actros Truck Model MP 2, 2031 Actuator chamber. An empirical and analytical approach was adopted. Meter rule, Venire Callipers and Mass Spring Balance were deployed for the experiments. Piston coil or spring, clutch distance in the actuator, the cross-sectional diameter of the actuator, and displacement in the free lengths of the coils among others were measured. The results of the experiments were analysed and used to determine the values of the supply (inlet) and exhaust (outlet) pressures which results stood at 9.61 bars and 11.299 bars, respectively.

太阳成像仪镜筒舱内压力控制技术研究

文章阐述了太阳成像仪镜筒舱内压力控制技术研究,主要包括限流小孔机械尺寸理论分析、慢速泄压阀设计、镜筒压力控制模拟测试等内容。目前,所研制的慢速泄压阀已顺利交付使用,并随46.5 nm极紫外太阳成像仪在中科院空间新技术试验卫星上进行了搭载,实现了在轨顺利开机,验证了太阳成像仪镜筒舱内压力控制手段的正确性。

基于深度学习的盾构机土舱压力场预测方法

土舱压力是盾构机受力状态和掌子面稳定等核心问题中的关键因素。土舱压力具有显著的空间变异性,其形成演化机制源于装备与岩土之间的复杂耦合作用,与地质特征、掘进参数等多源参数相关。然而,现有土舱压力预测方法一般未考虑空间分布特征或地质参数影响。针对该问题,提出了一种基于空间分布物理特征函数导引深度学习的盾构机土舱压力场预测方法。该方法构建物理特征函数用于解耦土舱压力空间分布特征,采用卷积神经网络和门控循环单元分别提取多源参数历史信息的空间特征和特征系数的时序特征,结合多源参数实时信息对特征系数进行预测,从而实现土舱压力场的预测。以长沙地铁四号线某区段为案例,利用该方法准确预测了土舱压力空间分布实测数据,准确率高达0.98,验证了所提方法的有效性。敏感性分析表明,不同地层中土舱压力空间分布特征系数的主要敏感参数基本一致,但其敏感度随地层地质条件的变化规律差异显著,可为复杂地层盾构机土舱压力精细化调控提供参考。

某枪弹在三种典型大气环境长期贮存后的性能变化研究

目的摸清某枪弹长期贮存后的性能底数,支撑新研枪弹及发射药设计与改进、长贮寿命指标考核与验证。方法采集湿热海洋气候、暖湿酸雨气候、寒冷气候3种典型大气环境下贮存13 a某枪弹的外观、膛压、射击密集度等性能数据,分析研究该型枪弹在不同贮存环境下的性能变化,以及环境影响的差异。结果该枪弹在完好的包装状态下,在3种典型大气环境库房贮存13 a后,枪弹长度、全形、质量、底火、密封性均满足验收规范的规定,无明显变化,而在热带海洋气候贮存的枪弹,最大膛压略超出设计指标要求。结论影响枪弹长贮性能的主要环境因素为温度,拔弹力、最大膛压、射击密集度等指标,与贮存环境温度强相关,温度越高,拔弹力越大,最大膛压值越大,射击密集度越低。

高压氧舱恒湿平压系统的设计

目的:设计一种高压氧舱恒湿平压系统,以消除舱内静电火花造成的危害,保证氧舱的安全运行。方法:该系统的硬件主要由加湿装置、除湿装置、平压装置、主控制器、压力传感器、温湿度传感器等组成。其中,加湿装置主体为经过特殊加工后的防爆过滤瓶;除湿装置采用工业级风机过滤单元(fan filter unit,FFU),由蒸发器、冷凝器、风轮3个部分组成;平压装置主要由电磁阀和减压管路组成;主控制器选用EX3G-C系列PLC触摸屏一体机,温湿度传感器选用NWSF-1AT型号温湿度传感器,压力传感器选用TXYS-G1K2HN3型变送器。系统的软件控制程序采用指令表语言编程,通过PID(proportional-integral-derivative)控制算法实现整体控制。结果:经过测试,该系统可使高压氧舱内相对湿度恒定在70%,使舱内极难产生静电。结论:该系统能够调节氧舱内的湿度、减少静电火花产生,保证舱内治疗的安全。

土压盾构非满舱掘进时压缩空气与地层适应性分析

针对气压辅助工法应用越来越多工程实践,基于Geostudio Air/w建立的气-水-固耦合数值计算模型,探讨了不同盾构隧道顶部埋深、上覆闭气层厚度、地层性质以及盾构压力舱空舱高度对开挖面渗气量的影响。结果表明:分析广州地铁21号线某区间土压盾构气压辅助工法的应用案例,压缩空气渗气量控制在1.2 m^(3)·min^(-1)内,在开挖面建立稳定的支护压力,确保盾构掘进达到微扰动控制水平;闭气能力强的粉质黏土和黏土地层土压盾构掘进时,通过向压力舱注入少量压缩空气可以更好的保持开挖面支护压力的稳定;渗透系数较大、地质分布不均的砂卵石、上软下硬地层,难以进行满舱掘进时,可根据隧道埋深和上覆闭气层厚度来选择合适的空舱高度,确保压缩空气逃逸量小于产气量;土压盾构穿越渗透性地层,上覆闭气层厚度在10.0 m以上、或埋深大于28.0 m时,压缩空气逃逸量较少,也不易发生压缩空气逃逸冒顶。