Influence of air pressure on mechanical effect of laser plasma shock wave

The influence of air pressure on mechanical effect of laser plasma shock wave in a vacuum chamber produced by a Nd：YAG laser has been studied. The laser pulses with pulse width of 10ns and pulse energy of about 320mJ at 1.06μm wavelength is focused on the aluminium target mounted on a ballistic pendulum, and the air pressure in the chamber changes from 2.8 × 10^ 3 to 1.01 × 10^5pa. The experimental results show that the impulse coupling coefficient changes as the air pressure and the distance of the target from focus change. The mechanical effects of the plasma shock wave on the target are analysed at different distances from focus and the air pressure.

Minimum wall pressure coefficient of orifice plate energy dissipater

Orifice plate energy dissipaters have been successfully used in large-scale hydropower projects due to their simple structure, convenient construction procedure, and high energy dissipation ratio. The minimum wall pressure coefficient of an orifice plate can indirectly reflect its cavitation characteristics： the lower the minimum wall pressure coefficient is, the better the ability of the orifice plate to resist cavitation damage is. Thus, it is important to study the minimum wall pressure coefficient of the orifice plate. In this study, this coefficient and related parameters, such as the contraction ratio, defined as the ratio of the orifice plate diameter to the flood-discharging tunnel diameter; the relative thickness, defined as the ratio of the orifice plate thickness to the tunnel diameter; and the Reynolds number of the flow through the orifice plate, were theoretically analyzed, and their relationships were obtained through physical model experiments. It can be concluded that the minimum wall pressure coefficient is mainly dominated by the contraction ratio and relative thickness. The lower the contraction ratio and relative thickness are, the larger the minimum wall pressure coefficient is. The effects of the Reynolds number on the minimum wall pressure coefficient can be neglected when it is larger than 10^5. An emoirical expression was presented to calculate the minimum wall oressure coefficient in this study.

Experimental Study on the Performance of Twin Plate Breakwater

The wave transmission characteristics and wave induced pressures on twin plate breakwater are investigated experimentally in regular and random waves. A total of twenty pressure transducers are fixed on four surfaces of twin plate to measure the wave induced dynamic pressures. The spatial distribution of dynamic wave pressure is given along the surface of the twin plate. The uplift wave force obtained by integrating the hydrodynamic pressure along the structure is presented. Discussed are the influence of different incident wave parameters including the relative plate width B/L, relative wave height Hi / a and relative submergence depth s / a on the non-dimensional dynamic wave pressures and total wave forces. From the investigation, it is found that the optimum transmission coefficient, Kt occurs around B/L = 0.41 - 0.43, and the twin plate breakwater is more effective in different water depths. The maximum of pressure ratio decreases from 1.8 to 1.1 when the relative submergence depth of top plate is increased from -0.8 to ＋0.8.

Numerical simulation of heat transfer and flow of cooling air in triangular wavy fin channels

Numerical computation models of air cooling heat transfer and flow behaviors in triangular wavy fin channels(TWFC) were established with structural parameters of fins considered.The air side properties of heat transfer coefficient and pressure drop are displayed with variable structural parameters of fins and inlet velocities of cooling air.Within the range of simulation,TWFC has the best comprehensive performance when inlet velocity vin=4-10 m/s.Compared with those of straight fins,the simulation results reveal that the triangular wavy fin channels are of higher heat transfer performances especially with the fin structural parameters of fin-height Fh=9.0 mm,fin-pitch Fp=2.5-3.0 mm,fin-wavelength λ=14.0-17.5 mm and fin-wave-amplitude A=1.0-1.2 mm.The correlations of both heat transfer factor and friction factor are presented,and the deviations from the experimental measurements are within 20%.

On the Relationship between Climatic Variables and Pressure Systems over Saudi Arabia in the Winter Season

The synoptic circulation over Saudi Arabia is complicated and frequently governed by the effect of large-scale pressure systems. In this work, we used NCEP–NCAR global data to illustrate the relationship between climatic variables and the main pressure systems that affect the weather and climate of Saudi Arabia, and also to investigate the influence of these pressure systems on surface air temperature（SAT） and rainfall over the region in the winter season. It was found that there are two primary patterns of pressure that influence the weather and climate of Saudi Arabia. The first occurs in cases of a strengthening Subtropical High（Sub H）, a weakening Siberian High（Sib H）, a deepening of the Icelandic Low（Ice L）, or a weakening of the Sudanese Low（Sud L）. During this pattern, the Sub H combines with the Sib H and an obvious increase of sea level pressure（SLP） occurs over southern European, the Mediterranean, North Africa, and the Middle East. This belt of high pressure prevents interaction between midlatitude and extratropical systems, which leads to a decrease in the SAT,relative humidity（RH） and rainfall over Saudi Arabia. The second pattern occurs in association with a weakening of the Sub H, a strengthening of the Sib H, a weakening of the Ice L, or a deepening of the Sud L. The pattern arising in this case leads to an interaction between two different air masses： the first（cold moist） air mass is associated with the Mediterranean depression travelling from west to east, while the second（warm moist） air mass is associated with the northward oscillation of the Sud L and its inverted V-shape trough. The interaction between these two air masses increases the SAT, RH and the probability of rainfall over Saudi Arabia, especially over the northwest and northeast regions.

Cylinder Pressure Prediction of An HCCI Engine Using Deep Learning

Engine tests are both costly and time consuming in developing a new internal combustion engine.Therefore,it is of great importance to predict engine characteristics with high accuracy using artificial intelligence.Thus,it is possible to reduce engine testing costs and speed up the engine development process.Deep Learning is an effective artificial intelligence method that shows high performance in many research areas through its ability to learn high-level hidden features in data samples.The present paper describes a method to predict the cylinder pressure of a Homogeneous Charge Compression Ignition(HCCI)engine for various excess air coefficients by using Deep Neural Network,which is one of the Deep Learning methods and is based on the Artificial Neural Network(ANN).The Deep Learning results were compared with the ANN and experimental results.The results show that the difference between experimental and the Deep Neural Network(DNN)results were less than 1%.The best results were obtained by Deep Learning method.The cylinder pressure was predicted with a maximum accuracy of 97.83%of the experimental value by using ANN.On the other hand,the accuracy value was increased up to 99.84%using DNN.These results show that the DNN method can be used effectively to predict cylinder pressures of internal combustion engines.

Study of the Flow Mechanism of Wind Turbine Blades in the Yawed Condition

The computational fluid dynamics method was used to simulate the flow field around a wind turbine at the yaw angles of 0°,15°,30°,and 45°.The angle of attack and the relative velocity of the spanwise sections of the blade were extracted with the reference points method.By analyzing the pressure distribution and the flow characteristics of the blade surface,the flow mechanism of the blade surface in the yawed condition was discussed.The results showed that the variations of the angle of attack and the relative velocity were related to the azimuth angle and the radius in the yawed condition.The larger the yaw angle was,the larger the variation was.The pressure distribution in the spanwise sections was affected by both the angle of attack and the relative velocity.The angle of attack was more influential than the relative velocity.At the same yaw angle,when the angle of attack decreased,the c_(p)∼x/c curve shrunk inward and the lift force decreased.The larger the yaw angle was,the more obvious the shrink was.The effect of the yaw on the blade root region was higher than its effect on the blade tip region.

油田注汽锅炉产汽单耗的计算方法与影响因素分析

为有效降低油田注汽锅炉产汽单耗,通过系统分析油田注汽锅炉生产工艺、生产设备、能耗水平及产汽单耗的计算方法,确定影响产汽单耗水平的关键因素包括温度、压力、干度、过热度、运行管理水平、锅炉热效率等,对各项因素的影响效果进行了分析验证。采用实际测试结果与理论计算数据对比的方法,得出了常见工况下油田注汽锅炉产汽单耗的变化规律,在此基础上明确了注汽锅炉节能提效的重点方向和技术措施,分析各项措施提效降耗的基本效果,对油田注汽锅炉的节能提效、降低产汽单耗和企业生产成本提供了良好借鉴。

空气罐在高扬程泵站水锤防护中的应用及影响

以甘肃某大型供水工程为研究背景,泵站供水管线起伏明显,泵站扬程高、流量大,事故停泵后管线负压严重,通过增设空气阀无法将负压消除。基于特征线法采用HAMMER软件对该泵站在采用二阶段关闭液控偏心半球阀及空气罐的组合下进行了事故停泵水力过渡过程仿真分析,另分析了空气罐的主要参数对水力过渡过程的影响。计算结果表明:设置空气罐后管线负压明显得到解决;空气罐容积越大、水头损失比率越高、水箱进水口直径相对偏小一点,其水锤防护效果越好;空气罐初次向管道补水和吸收管道水在水锤防护过程发挥重要作用;不同参数下空气罐首次向管道补水的时间几乎相同。

单叶风阀调节性能试验研究

文章主要研究了不同规格的单叶风阀在不同开度或风量下的调节性能。本文在保持风量不变的情况下,通过改变风阀的开度,测试了风管内部压力、风速、阻力等参数,以及在开度不变的情况下改变风量,测试了不同开度下风管内部压力、风速、阻力等参数。找到了不同工况下,风管内部气流从距离阀门6倍管径处开始稳定,以及风阀阻力、风速随风阀开度变化的规律基本呈“指数型”,风阀阻力随风量变化的规律基本呈“线性”,风阀调节对管路影响的不敏感区处于0°~45°,敏感区域处于45°~80°。以上结论在200×200 mm与300×300 mm规格的方形风管与阀门中均成立。

气压差变化及环氧树脂层对混凝土气体渗透性的影响

基于Cembureau法测量不同气压差下混凝土气体渗透系数,研究气压差变化及环氧树脂层对混凝土气体渗透性的影响。研究结果表明,在一定范围内,混凝土气体渗透系数随气压差的增大呈减小趋势;环氧树脂层可有效减小混凝土气体渗透系数。

列车制动系统开关型电空阀控制方法研究

轨道交通车辆制动系统通过对电空阀的开关控制来调节制动缸压力的输出值,满足列车安全快速停车的需求。针对制动缸压力调节过程中电磁阀动作频繁的问题,考虑气动系统容积室气压变化的滞后性,提出一种开关型电空阀控制方法,引入平均气压变化值和滞后系数对充风和排风的过程进行控制,试验结果表明所提出的控制策略能够有效降低电磁阀的动作频率。

Meteorological Features at 6523 m of Mt.Qomolangma(Everest)between 1 May and 22 July 2005

Mt. Qomolangma （Everest）, the highest mountain peak in the world, has little been studied extensively from a meteorological perspective, mostly because of the remoteness of the region and the resultant lack of meteorological data. An automatic weather station （AWS）, the highest in the world, was set up on 27 April 2005 at the Ruopula Pass （6523 m asl） on the northern slope of Mt. Qomolangma by the team of integrated scientific expedition to Mt. Qomolangma. Here its meteorological characteristics were analyzed according to the lo-minute-averaged and 24-hour records of air temperature, relative humidity, air pressure and wind from 1 May to 22 July 2005. It is shown that at 6523 m of Mt. Qomolangma, these meteorological elements display very obvious diurnal variations, and the character of averaged diurnal variation is one-peak-and-one-vale for air temperature, one-vale for relative humidity, two-peak-and-two-vale for air pressure, and one-peak with day-night asymmetry for wind speed. In the 83 days, all the air temperature, relative humidity and air pressure increased with some different fluctuations, while wind speed decreased gradually and wind direction turned from north to south. The variations of relative humidity had great fluctuations and obvious local differences. Then the paper discusses the reason for the characters of diurnal and daily variations. Compared with the corresponding records in May 1960, 5-day-averaged maximums, minimums and diurnal variations of air temperature in May 2005 were apparently lower.

The Effect of Non-equilibrium Condensation on the Drag Coefficient in a Transonic Airfoil Flow

In this study, a transonic flow past NACA0012 profile at angle of attack α=0^0 whose aspect ratio AR is 1.0 with non-equilibrium condensation is analyzed by numerical analysis using a TVD scheme and is investigated using an intermittent indraft type supersonic wind tunnel. Transonic flows of 0.78-0.90 in free stream Mach number with the variations of the stagnation relative humidity（φ0） are tested. For the same free stream Mach number, the increase in φ0 causes decrease in the drag coefficient of profile which is composed of the drag components of form, viscous and wave. In the case of the same Moo and To, for more than φ0=30%, despite the irreversibility of process in non-equilibrium condensation, the drag by shock wave decreases considerably with the increase of φ0. On the other hand, it shows that the effect of condensation on the drag coefficients of form and viscous is negligible. As an example, the decreasing rate in the drag coefficient of profile caused by the influence of non-equilibrium condensation for the case of M∞=0.9 and φ0 =50% amounts to 34%. Also, it were turned out that the size of supersonic bubble （that is, the maximum height of supersonic zone） and the deviation of pressure coefficient from the value for M=1 decrease with the increase of φ0 for the same M∞.

Modeling of Soybean Plant Sap Flow

Soybean (Glycine max. (L.) Merr.) sap flow during the growth stages in relation to soil moisture, nutrition, and weather conditions determine the plant development. Modeling this process helps to better understand the plant water-nutrition uptake and improve the decisions of efficient irrigation management and other inputs for effective soybean production. Field studies of soybean sap flow took place in 2017-2021 at Marianna, Arkansas using heat balance stem flow gauges to measure the sap flow during the reproductive growth stages R3-R7. Plant water uptake was measured using the lysimeter-container method. The uniform sap flow-based hydraulic system in the soil-root-stem-leaf pathway created negative water tensions with osmotic processes and water surface tensions in stomata cells as water evaporation layers increase are the mechanism of the plant water uptake. Any changes the factors like soil water tension, solar radiation, or air relative humidity immediately, within a few seconds, affect the system’s balance and cause simultaneously appropriate reactions in different parts of the system. The plant water use model was created from plant emergence, vegetative to final reproductive growth stages depending on soil-weather conditions, plant morphology, and biomass. The main factors of the model include solar radiation, air temperature, and air relative humidity. The effective sap flow uptake occurs around 0.8 KPa VPD. Further research is needed to optimize the model’s factors to increase the plant growth dynamics and yield productivity.

Determination of gamma-ray parameters for polyethylene glycol of different molecular weights

Mass attenuation coefficient(μ_m) for polyethylene glycol(PEG) of different molecular weights was determined by using NaI(Tl) scintillator and Win Xcom mixture rule at gamma energies of 59.5, 302.9, 356.0, 661.7, 1173.2 and 1332.5 keV. The total atomic, molecular and electronic cross sections, half-value layer, effective atomic and electron numbers, mass energy-absorption coefficients and kerma relative to air are calculated. The energy and compositional dependence of μ_m values, and the related radiation absorption parameters, are evaluated and discussed. The experimental results agree well with the theoretical ones, within an uncertainty of 1% in the effective atomic number for all PEG samples at the designated energies.

土工织物顶压蠕变特性与折减系数研究

常规土工合成材料蠕变特性仅考虑筋材拉伸状态。随着土工合成材料应用愈加广泛,其受力条件也愈加复杂。为研究土工织物在受到顶压力作用下的蠕变特性,研制了顶压蠕变试验装置。采用该装置对Mirafi PET 1300土工织物进行了CBR圆形顶破试验以及40%、50%和60%三种荷载水平下的2400 h圆形顶压蠕变试验,计算了5、10、60和120 a设计年限在不同顶压面积应变下的顶压蠕变折减系数,并与常规拉伸蠕变折减系数对比,建立了顶压蠕变折减系数、设计年限与顶压面积应变三者的量化关系式,以预测顶压蠕变折减系数。结果表明,对于试验土工织物,顶压蠕变折减系数比常规拉伸蠕变折减系数大65.340%~148.496%;随设计年限的增加,顶压蠕变折减系数变化不大;在不同设计年限下,随顶压面积应变的增加,顶压蠕变折减系数保持平稳。为提升工程结构的安全性和耐久性,在土工合成材料受顶压作用情况下,建议设计采用顶压蠕变折减系数。

上肢加压治疗在预防无运动能力患者经外周静脉穿刺的中心静脉导管相关血栓形成中的作用

目的观察上肢加压治疗在预防无运动能力患者经外周静脉穿刺的中心静脉导管(PICC)相关血栓形成中的作用。方法选取2020年1月至2022年8月在西安交通大学第二附属医院行上肢PICC置管术并进行导管维护的无运动能力患者84例,采用随机数字表法将其分为对照组和加压组,各42例。对照组采用被动活动干预,加压组使用空气压力波加压干预。应用彩色多普勒超声监测两组干预前和干预30 min后腋静脉和锁骨下静脉血流速度;于置管前、置管2周后,检测两组纤维蛋白原、凝血酶原时间、D-二聚体。记录两组PICC相关血栓发生情况。结果干预30 min后,两组腋静脉和锁骨下静脉血流速度均快于干预前,且加压组快于对照组,差异有统计学意义(P<0.05)。置管2周后,对照组纤维蛋白原、凝血酶原时间、D-二聚体水平高于本组置管前,且高于加压组,差异有统计学意义(P<0.05)。加压组置管前、置管2周后纤维蛋白原、凝血酶原时间、D-二聚体比较,差异无统计学意义(P>0.05)。在2周的观察期内,加压组PICC相关血栓发生率低于对照组,差异有统计学意义(P<0.05)。结论空气压力波治疗仪通过增加置管侧静脉血流速度,能有效预防无运动能力患者上肢PICC相关血栓形成。

环境参数对回热空气制冷系统COP及能效最优压缩比的影响分析

为配合加强基加利修正案中氢氟碳化物的管控,环境友好型制冷空调系统的研究成为热点。针对以空气为工质的制冷系统,为研究系统性能系数(COP)及其达峰的最优压缩比,本文建立了回热直流高压空气制冷系统COP计算模型,探讨分析了环境温度、压力及相对湿度等参数对系统COP与能效最优压缩比的影响。结果表明:降低环境温度、增大环境压力可降低系统的能效最优压缩比并提高制冷COP,且环境压力升高可显著减少膨胀过程的凝冰量;环境空气相对湿度对能效最优压缩比及系统制冷COP影响较小。

气压短时扰动对常熟台伸缩仪影响频段的分析

利用小波变换、相关分析和回归分析等方法,在时域和频域内研究气压短时扰动对常熟台伸缩仪观测的影响特征和机制。结果表明,影响频段主要集中在8-256 min;8 min以下气压影响较弱;8-32 min伸缩仪测量值与气压的相关系数、气压影响系数均由正值变为负值;32 min以上伸缩仪测量值与气压的相关系数的平均值大于0.7,气压影响系数呈高值且变化较为平稳。气压对NS分量的影响大约是EW分量的2.5-3倍。最后,使用小波分解与重构方法实现气压短时干扰的有效排除。