Experimental Analysis of the Flow Characteristics of an Adjustable Critical-Flow Venturi Nozzle

The response of an adjustable critical-flow Venturi nozzle is investigated through a set indoor experiments aimed to determine the related critical flow rate,critical pressure ratio,and discharge coefficient.The effect of a variation in the cone displacement and liquid content on the critical flow characteristics is examined in detail and it is shown that the former can be used to effectively adjust the critical flow rate.The critical pressure ratio of the considered nozzle is above 0.85,and the critical flow control deviation of the gas flow is within±3%.Liquid flow can reduce the gas critical mass flow rate accordingly,especially for the cases with larger liquid volume and lower inlet pressure.The set of results and conclusions provided are intended to support the optimization of steam injection techniques in the context of heavy oil recovery processes.

Elasto-Plasticity Critical Corrosive Ratio Model for RC Structure Corrosive Expanding Crack

The parameter of filling expanding ratio n, plasticity factor k1 and deformation parameter k2 is raised, and then the elasto-plasticity critical corrosive ratio model for RC structure corrosive expanding crack based on elasto-plasticity theory is constructed in this paper. The influences of parameters such as filling expansion ratio n, plasticity factor kl, deformation parameter k2, Poisson ratio of concrete v, diameter of reinforced bar d and protective layer thickness c on the critical corrosive ratio are researched by theory analysis and experiments. The experimental results validate the accuracy of the model. According to the experimental study, the least squares solution is calculated as n = 1.8 ,k1 =0.61 ,k2 =0.5.

Factors Affecting the Relation of Fracture Toughness V_(GC) with Critical Void Growth Ratio R_C/R_O

The relationship between fracture toughness VGC and critical void growth RC/RO was studied for ten kinds of Steel. The macroscopic fracture toughness VGC was determined by using notched tensile specimens. and the microscopic parameters of critical void growth ratio RC/RO were quantitatively measured under SEM. Then, the coefhcient C in the relation VGC = C In(RC/RO) proposed in author's past work was specifically explored. The correlation of C with tensile proderty parameter φ=σyδ/(Eφn) was presented for the Steel investigated, and the effects of low temperature on C were also discussed. Results show that the coefficient C is linearly related to the parameter and insensitive to low temperature.

Seasonal shifts in the solute ion ratios of vadose zone rock moisture from the Eel River Critical Zone Observatory

One of the greatest challenges in critical zone studies is to document the moisture dynamics, water flux,and solute chemistry of the unsaturated, fractured and weathered bedrock that lies between the soil and groundwater table. The central impediment to quantifying this component of the subsurface is the difficulty associated with direct observations. Here, we report solute chemistry as a function of depth collected over a full year across the shale-derived vadose zone of the Eel River Critical Zone Observatory using a set of novel sub-horizontal wellbores,referred to as the vadose zone monitoring system. The results of this first geochemical glimpse into the deep vadose zone indicate a dynamic temporal and depth-resolved structure. Major cation concentrations reflect seasonal changes in precipitation and water saturation, and normalized ratios span the full range of values reported for the world's largest rivers.

Critical Cyclic Stress Ratio of Undisturbed Saturated Soft Clay in the Yangtze Estuary under Complex Stress Conditions

There exists a critical cyclic stress ratio when sand or clay is subjected to cyclic loading. It is an index dis-tinguishing stable state or failure state. The soil static and dynamic universal triaxial and torsional shear apparatus de-veloped by Dalian University of Technology in China was employed to perform different types of tests on saturated soft marine clay in the Yangtze estuary. Undisturbed samples were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consoli-dation parameters. The effects of initial orientation angle of major principal stress, initial ratio of deviatoric stress,initial coefficient of intermediate principal stress and stress mode of cyclic shear on the critical cyclic stress ratio wereinvestigated. It is found that the critical cyclic stress ratio decreases significantly with increasing initial orientation angle of major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientationangle of major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate prin-cipal stress is less evident. Under the same consolidation condition, the critical cyclic stress ratio from the cyclic cou-pling shear test is lower than that from the cyclic torsional shear test, indicating that the stress mode of cyclic shear has an obvious effect on the critical cyclic stress ratio. The main reason is that the continuous rotation in principal stressdirections during cyclic coupling shear damages the original structure of soil more than the cyclic torsional shear does.

Effect of fiber-reinforcement on the mechanical behavior of sand approaching the critical state

Several types of ground improvement methods that employ fiber-reinforcement have been developed in recent years.A series of consolidated drained triaxial compression tests has been conducted here to examine the effect of short fibers on the mechanical properties of Toyoura sand.Sand with 0%,0.2%,0.4%,and 1%fiber contents,prepared to yield random distribution,was sheared under several confining pressures and controlled via their initial relative densities.The test results showed that the maximum and residual deviatoric stresses increased,whereas the volumetric expansion decreased with an increase in fiber content.Although the stress ratio h(=q/p′)and specific volume changed depending on the fiber content and confining pressure with shear progression,they each reached the same values for a definite fiber content at the end of shearing,independent of initial relative density.In other words,the unique critical state line can be found for a definite fiber content.Moreover,the greater the fiber content,the larger the slope of the critical state line at the end of shearing.Additionally,as the length of fibers shortened with the same percentage of fiber inclusions in sand,the deviatoric stress and the stress ratio decreased,approaching the shear-strain-volumetric response of unreinforced sand.

Modeling for critical state line of granular soil with evolution of grain size distribution due to particle breakage

Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.

Determination of the Critical Value of Deflection for Embedded Cylindrical Structures

An embedded cylinder is a large-diameter cylinder embedded in a soil foundation. The state of failure of such an embedded cylindrical structure shows large deflection instead of slide and overturn of the traditional gravity type of structure placed on a rubble base or foundation base. The critical value of deflection of the embedded cylindrical structure, which is the maximum allowable deflection for stability calculation of the cylinder, is a vital control value. Through investigation on deflection and soil pressures on an embedded cylinder by model experiments, the variations of the angle of rotation θ of a cylinder with effective anti-overturning ratio η and moment MH of thrust are discussed. On the basis of experimental study, the critical value of deflection of the cylindrical structure is proposed in the paper. Meanwhile, the formulas for calculating deflection of cylinders are derived.

Critical weight on bit of double-driven bottomhole assembly during vertical and fast drilling

It is difficult to determine the optimal weight on bit (WOB) of the double-driven bottomhole assembly (DD-BHA, with double stabilizers and a bent housing positive displacement motor (PDM)) which is employed during vertical and fast drilling. High WOB leads to well deviation out of control, and low WOB leads to low rate of penetration (ROP). So considering the rock physical properties, the anisotropy index function of polycrystalline diamond compact (PDC) bit was derived with the structure and cutting performance parameters of the bit, and the effect of natural hole deviation tendencies on the performance of DD-BHA resisting deviation was represented. The concept of elliptic deformation ratio was used to characterize the performance of DD-BHA resisting deviation. Eventually, a model calculating the critical WOB was established. By comparing the model predictions with the measured hole angle changes in the field, the results show that the model predictions are accurate with error less than 5.8%, which can meet the operational requirements in the projects. Furthermore, the model was adopted to justify and guide the operating conditions and parameters during drilling, which shows that the optimum WOB predicted by the model can not only control deviation but also improve ROP effectively. The model is independent on the formation characteristics of blocks, so it can be expanded widely to other oilfields.

基于CRITIC法和转换比率法的公立医院医师需求测算研究

医师人力资源是医院核心资源,科学测算医院医师人力资源需求有助于合理配置医师人力资源,提升公立医院可持续发展能力,实现高质量发展。以某高校附属医院为例,分别运用文献法、专家咨询法、CRITIC赋权法和转换比率法确定测算指标,设置指标权重,计算科室医师理论需求人数,探索完善公立医院医师人力资源需求测算方法,提出科学制定引人计划、加强人才梯队建设、健全人力资源管理规划的建议,为科学配置医师人力资源提供参考。

沿面放电光脉冲发展特征与临界击穿判据研究

绝缘沿面放电是引起高压开关柜中滑闪及电弧击穿的主要原因和前期阶段,准确有效地对绝缘异常爬电进行监测、跟踪和预警对保障设备安全运行非常关键。该文通过试验研究强垂直分量绝缘爬电的光脉冲阶段特征,并提出基于多波段光谱辐射强度信息的放电发展阶段划分方法和临界击穿判据,从而建立基于多波段光谱强度比值的放电跟踪预警方法。首先,搭建多波段单光子试验系统,采用自制多波段光学传感装置对沿面放电发展全过程跟踪测量,获得表征放电发展过程光谱比率的统计参量;其次,借助模糊聚类算法和支持向量机,构建放电发展临界特征空间边界,并对放电严重程度进行量化评估,结果表明该方法对放电阶段的正判率达到96.9%以上;最后,确立基于光谱比率的放电危险性主动预警逻辑,并开发了放电光脉冲跟踪预警系统,为开关柜放电和弧光监测的创新应用提供了参考。

油气管道焊缝凹陷韧性损伤研究

针对含焊缝凹陷管道的失效问题,以X80管线钢为研究对象,采用临界空穴扩张比韧性失效准则与数值模拟相结合的方法对管道焊缝凹陷损伤程度进行了研究,探讨了焊接残余应力应变、焊缝余高、凹陷深度、压头尺寸、内压和偏移距离对焊缝凹陷损伤的影响。结果表明:焊接残余应力应变和焊缝余高使管道焊缝凹陷损伤值增大;焊缝凹陷损伤值随凹陷深度的增加而增大;随着内压的增加,损伤值增幅最大值点在凹陷侧部;压头与管道接触面积越小,焊缝凹陷损伤值越大;凹陷偏移达到一定距离时,凹陷附近的损伤值超过焊缝附近的损伤值,此时凹陷可以视作普通凹陷。

砂-粉混合料颗粒接触状态的临界条件确定

砂-粉混合料被广泛应用于高速铁路路基、人工筑岛及海底沉管隧道垫层等重大工程,如何科学地表征砂-粉混合料复杂的颗粒接触状态及连续演变的力学行为特征,并深入揭示其对混合料静/动力学特性的影响已是一项紧迫的基础性科学研究任务。本文基于代表性砂-粉混合料的基本物理性能指标及力学特性指标试验数据,验证Rahman等提出的区分“细粒填充砂粒”和“砂粒悬浮细粒”的阈值细粒含量FCth半经验公式预测能力。基于理想二元介质材料的理论最小孔隙比计算方法,提出确定中间性态土颗粒接触状态临界条件参量FC_(in-min)和FC_(in-max)的方法,分析各参数对FC_(in-min)和FC_(in-max)的影响规律,建立基于基本物理性能指标的FC_(in-min)和FC_(in-max)预测方法,最终提出全FC范围(FC=0~100%)的砂-粉混合料各颗粒接触状态临界条件参量的有效评价方法。

地下连续墙受力变形光纤监测与数值模拟研究

地下连续墙是一种常见的深基坑支护方式,具有刚度大、防渗性能好、适应范围广等优点,但其受力变形规律较为复杂。基于超弱光纤光栅感测技术,对某地铁车站基坑地下连续墙水平位移进行实时监测。将监测数据与数值模拟结果进行对比,验证了数值分析模型选取的合理性,并基于该数值分析模型研究了不同厚度软土层中,地下连续墙水平位移的变化规律,通过墙体位移梯度(D_(w))和软土位移梯度(D_(r))进行临界厚度比计算。研究结果显示:水平位移随软土厚度的变化呈“凸肚”状,沿深度方向划分为相对稳定区、线性增长区、最大变形区和线性下降区。利用D_(w)和D_(r)标定出临界厚度比为0.24;土压力变化在基坑前四步开挖过程中较为稳定,而在第五步开挖与施工后40 d变化显著。上述研究结果为类似工程的设计、施工和监测方案的制定提供了重要参考。

喷嘴距及混合室喉部长度对喷射器性能综合影响研究

在实际环境条件下,采用变几何喷射器是提高喷射器性能的重要途径。基于喷嘴距可调式的喷射器实验测试平台,采用实验和数值分析相结合的方法,研究不同无量纲混合室喉部长度下,无量纲喷嘴距对喷射器的性能及不可逆性影响。结果表明:在测试范围内,喷射器的临界喷射系数随着喷嘴距的增加先增加后减小,当达到最佳无量纲喷嘴距5.83时,临界喷射系数达到最大值0.45,合理的喷嘴距应避免激波链出现在混合室收缩段;喷射器的临界冷凝压力随喷嘴距的增加逐渐下降,当无量纲混合室喉部长度为4时,其临界冷凝压力下降7.36%,下降速度最慢,原因是较大的射流冲量提高了扩压室的压力恢复能力,使流体动能衰减速度有所减缓;当无量纲混合室喉部长度为4,无量纲喷嘴距为5.83时,热力学完善度达到最大值0.21;由喷嘴距引起的喷射器熵产主要来源于两股入口流在混合室收敛段的混合和第二冲击波向扩压室出口的移动,提高扩压室的压力恢复能力能有效避免熵产的急剧增加。研究结果对喷射器的结构及综合性能进行多目标优化,以减小喷射器不可逆性提供重要参考。

AHP-CRITIC混合加权法优选风湿痹痛膏提取工艺

目的确定指标权重,优选风湿痹痛膏的最佳提取工艺。方法以出膏率及芍药苷、单酯型乌头碱含量为考察指标,采用层次分析法(AHP)、基于指标相关性的权重确定方法(CRITIC)、AHP-CRITIC混合加权法确定权重系数,结合正交试验优选风湿痹痛膏复方提取工艺最佳参数。结果采用AHP-CRITIC混合加权法确定的权重系数更符合实际,按该权重系数进行综合评分,优选的最佳提取工艺为:加6倍量的水,提取1.5 h,提取2次。结论AHP-CRITIC混合加权法较单一方法更全面、合理,所确定的提取工艺稳定可行,可为风湿痹痛膏的研制开发提供参考依据。

冠心病临界病变患者残余胆固醇/高密度脂蛋白胆固醇比值水平与冠脉CT血流储备分数的相关性

【目的】探讨冠状动脉粥样硬化性心脏病(冠心病)临界病变患者残余胆固醇/高密度脂蛋白胆固醇比值水平对冠脉CT血流储备分数(FFRct)的影响。【方法】本研究回顾性分析2022年1月1日-2022年12月31日中山大学附属第三医院心内科收治住院并行CCTA显示存在冠状动脉临界病变(管腔狭窄50%~70%)的219例患者为研究对象,其中临界病变血管304条。对以上纳入的冠脉临界病变血管行FFRct检查。FFRct以0.8为界,分为缺血组(FFRct≤0.8,N=108例)与非缺血组(FFRct>0.8,N=111例)。采用多因素Logistic回归分析探究冠心病临界病变患者FFRct≤0.8的影响因素;绘制受试者工作特征(ROC)曲线评估RC/HDL-C对FFRct≤0.8的预测价值;并通过Pear-son相关分析评估RC/HDL-C与FFRct之间是否存在相关性。【结果】缺血组中有糖尿病病史患者比例显著增高(P<0.001)。与非缺血组相比,缺血组患者RC、RC/HDL-C比值、Non-HDL-C、APOB、HbA1c、FPG水平显著增高(P<0.05)。Pearson相关性分析显示,RC/HDL-C比值、RC、Non-HDL-C、TC、TG、LDL-C、HDL-C、LP(a)、HbA1c、FPG均与FFRct值呈显著负相关(P<0.05)。单因素Logistic回归分析结果显示,糖尿病、RC、RC/HDL-C比值、Non-HDL-C、TG、LP(a)、HbA1c、FPG均与FFRct≤0.8均呈显著相关(P<0.05)。多因素Logistic回归分析表明,RC/HDL-C比值是FFRct≤0.80的预测因子(OR=4.682,95%CI 1.197~18.316,P<0.05)。【结论】冠状动脉粥样硬化性心脏病临界病变患者RC/HDL-C比值水平与FFRct≤0.8独立相关,RC/HDL-C比值可能成为评估冠状功能性缺血的潜在指标。

DEM investigation of strength and critical state behaviours of granular materials under true triaxial loadings

This paper investigates the strength and critical state(CS)behaviours of granular materials via DEM simulations of true triaxial drained tests under three different loading modes including constant b(in-termediate stress ratio)tests with constantσ'1(major principal stress),constant p(mean pressure)and constantσ'3(minor principal stress)respectively.To this end,a series of samples are generated with the same particle size distribution,and with the confining stresses ranging from 100 kPa to 900 kPa.The CS is achieved for all samples.Both the macroscopic behaviours and the microscopic behaviours are examined and compared considering different loading modes,confining stresses and intermediate stress ratios(b).The critical state lines(CSLs)are found to be unique and independent of the loading modes,but dependent on the b values.The CSLs with b=0 and b=1 form the two boundaries of CSLs respectively beyond which CSLs under all other b tests cannot go beyond.Six different strength criteria are examined and compared in terms of both peak and CS failures.The Mohr-Coulomb strength criterion is found to be only suitable for axisymmetric loading conditions.The Lade-Duncan criterion is only suitable for describing peak strengths,which is dependent on the loading modes and confining stresses.The Satake criterion and Matsuoka-Nakai criterion are the more appropriate strength criteria for describing CS failures,indicating that the CS values of both the Satake parameter and the Matsuoka-Nakai parameter describe an inherent property that characterizes the CS failure for a given type of soil.The CS mechanical coordination number is fitted by a curved line for a given b value,which is unique regardless of the loading modes.The peak and CS values of both major and minor principal fabric tensors decrease with increasing b values,while they increase with increasing b values for the intermediate principal fabric tensor.

最低工资标准测算实证研究——基于CRITIC-熵权法客观赋权的动态组合测算

科学合理的测算方法是最低工资标准制定及其制度有效施行并切实发挥权益保障效应的关键。本研究以上海市2007-2016年相关统计数据作为研究样本,分别采用比重法、恩格尔系数法、国际收入比例法、因子测算模型和ELES模型等5种方法实证测算最低工资标准,进而构建基于CRITIC-熵权法进行客观赋权的组合测算模型,并以灰色关联分析所得主要影响因子作为参考依据进行动态调整。研究结果发现:(1)5种单一算法中比重法和恩格尔系数法所得理论最低工资标准整体水平偏低,国际收入比例法所得温饱线与执行标准较接近而发展线则显著偏高,因子测算模型和ELES模型测算结果总体较为理想;(2)构建所得最低工资标准组合测算模型的模拟结果与实际执行标准拟合度较高,表明上海市近10年来最低工资标准制定含金量较高,相应标准已基本满足低收入劳动者生存和温饱需求,尤其近年来相关情况已得到显著改善;(3)深入分析来看,上海市最低工资标准仍普遍低于发展线需求,且与最低生活保障标准、人均GDP和职工平均工资等主要影响指标的比率关系并不协调,表明上海市最低工资标准制定及相应配套体制仍有较大提升改善空间。

配置抗冲切钢筋的RC板柱节点受冲切承载力计算

为计算配有常用抗冲切钢筋(箍筋和栓钉)的钢筋混凝土(RC)板柱节点的受冲切承载力,结合梁斜拉破坏机理和修正压力场理论(MCFT)提出一种配有抗冲切钢筋的RC板柱节点的受冲切承载计算方法.首先根据MCFT推导出配有抗冲切钢筋的RC板柱节点的临界斜裂缝倾角计算式;然后,假定冲切破坏时临界截面周长范围内的抗冲切钢筋达到屈服强度,将临界斜裂缝倾角代入MCFT推导出板柱节点的受冲切承载力计算方法;最后,使用该方法和美国规范(ACI 318-19)方法计算62个配有抗冲切钢筋的RC板柱节点试验的冲切承载力,并分析了混凝土强度、板有效厚度、柱截面边长、抗弯钢筋配筋率及抗冲切钢筋配筋率对节点抗冲切承载力的影响.结果表明:由MCFT推导出的节点受冲切承载力计算值与试验值吻合较好,均值为0.96,变异系数为0.20;节点的冲切承载力与上述影响因素呈非线性正相关.该方法可用于配有抗冲切钢筋的RC板柱节点的受冲切承载力计算.