A photogrammetric approach for quantifying the evolution of rock joint void geometry under varying contact states

Accurate measurement of the evolution of rock joint void geometry is essential for comprehending the distribution characteristics of asperities responsible for shear and seepage behaviors.However,existing techniques often require specialized equipment and skilled operators,posing practical challenges.In this study,a cost-effective photogrammetric approach is proposed.Particularly,local coordinate systems are established to facilitate the alignment and precise quantification of the relative position between two halves of a rock joint.Push/pull tests are conducted on rock joints with varying roughness levels to induce different contact states.A high-precision laser scanner serves as a benchmark for evaluating the photogrammetry method.Despite certain deviations exist,the measured evolution of void geometry is generally consistent with the qualitative findings of previous studies.The photogrammetric measurements yield comparable accuracy to laser scanning,with maximum errors of 13.2%for aperture and 14.4%for void volume.Most joint matching coefficient(JMC)measurement errors are below 20%.Larger measurement errors occur primarily in highly mismatched rock joints with JMC values below 0.2,but even in cases where measurement errors exceed 80%,the maximum JMC error is only 0.0434.Thus,the proposed photogrammetric approach holds promise for widespread application in void geometry measurements in rock joints.

A Novel Method for Determining the Void Fraction in Gas-Liquid Multi-Phase Systems Using a Dynamic Conductivity Probe

Conventional conductivity methods for measuring the void fraction in gas-liquid multiphase systems are typically affected by accuracy problems due to the presence of fluid flow and salinity.This study presents a novel approach for determining the void fraction based on a reciprocating dynamic conductivity probe used to measure the liquid film thickness under forced annular-flow conditions.The measurement system comprises a cyclone,a conductivity probe,a probe reciprocating device,and a data acquisition and processing system.This method ensures that the flow pattern is adjusted to a forced annular flow,thereby minimizing the influence of complex and variable gas-liquid flow patterns on the measurement results;Moreover,it determines the liquid film thickness solely according to circuit connectivity rather than specific conductivity values,thereby mitigating the impact of salinity.The reliability of the measurement system is demonstrated through laboratory experiments.The experimental results indicate that,in a range of gas phase superficial velocities 5–20 m/s and liquid phase superficial velocities 0.079–0.48 m/s,the maximum measurement deviation for the void fraction is 4.23%.

Molecular Dynamics Simulation of Shock Response of CL-20 Co-crystals Containing Void Defects

To investigate the effect of void defects on the shock response of hexanitrohexaazaisowurtzitane(CL-20)co-crystals,shock responses of CL-20 co-crystals with energetic materials ligands trinitrotoluene(TNT),1,3-dinitrobenzene(DNB),solvents ligands dimethyl carbonate(DMC) and gamma-butyrolactone(GBL)with void were simulated,using molecular dynamics method and reactive force field.It is found that the CL-20 co-crystals with void defects will form hot spots when impacted,significantly affecting the decomposition of molecules around the void.The degree of molecular fragmentation is relatively low under the reflection velocity of 2 km/s,and the main reactions are the formation of dimer and the shedding of nitro groups.The existence of voids reduces the safety of CL-20 co-crystals,which induced the sensitivity of energetic co-crystals CL-20/TNT and CL-20/DNB to increase more significantly.Detonation has occurred under the reflection velocity of 4 km/s,energetic co-crystals are easier to polymerize than solvent co-crystals,and are not obviously affected by voids.The results show that the energy of the wave decreases after sweeping over the void,which reduces the chemical reaction frequency downstream of the void and affects the detonation performance,especially the solvent co-crystals.

Mechanism of cross-level settlements and void accumulation of wide and conventional sleepers in railway ballast

The cross-level and twist irregularities are the most dangerous irregularity types that could cause wheel unloading with the risk of derailments and additional maintenance expenses.However,the mechanism of the irregularities initiation and development is unclear.The motivation of the present study was the previous experimental studies on the application of wide sleepers in the ballasted track.The long-term track geometry measurements with wide sleepers show an enormous reduction of the vertical longitudinal irregularities compared to the conventional track.However,wide sleepers had higher twist and cross-section level irregularities.The present paper aims to explain the phenomenon by discrete element method(DEM)modeling the development process of sleeper inhomogeneous support at cross-level depending on the sleeper form.The DEM simulations show that the maximal settlement intensity is up to 3.5 times lower for a wide sleeper in comparison with the conventional one.Nevertheless,the cross-level differential settlements are almost the same for both sleepers.The particle loading distribution after all loading cycles is concentrated on the smaller area,up to the half sleeper length,with fully unloaded zones under sleeper ends.Ballast flow limitation under the central part of the sleeper could improve the resilience of wide sleepers to the development of cross-level irregularities.The mechanism of initiation of the cross-level irregularity is proposed,which assumes the loss of sleeper support under sleeper ends.The further growth of inhomogeneous settlements along the sleeper is assumed as a result of the interaction of two processes:ballast flow due to dynamic impact during void closing and on the other side high pressure due to the concentration of the pressure under the middle part of the sleeper.The DEM simulation results support the assumption of the mechanism and agree with the experimental studies.

层裂损伤早期微孔洞分布特征的变化规律

构建耦合材料微介观结构信息的物理模型是损伤力学的发展趋势,同时也能不断促进数值计算方法、实验技术以及理论研究的发展.因缺乏微介观尺度孔洞分布特征的演化信息,目前的层裂损伤模型不仅在极端加载条件下的应用受到制约,同时也无法有效提供一些工程中十分关注的材料损伤与最后材料破碎颗粒度之间的关联信息,因而迫切需要发展反映损伤材料内部微介观孔洞分布特征变化规律的层裂损伤模型.通过对孔洞成核过程中各种影响因素的分析,结合孔洞早期增长的特点,同时考虑到解析求解方便,本文给出了基于余弦函数形式的孔洞成核概率分布函数,采用新的孔洞成核概率函数的解析计算结果不仅与分子动力学计算的孔洞数随时间变化结果相符,而且与损伤发展早期的金属钽层裂实验结果也符合得很好,也就是说,采用新的孔洞成核概率函数可以在一定程度上反映层裂损伤早期微孔洞分布特征的变化规律.

基于三轴不排水有效应力路径的结构性剑桥模型的修正研究

室内外试验和工程实践都表明天然沉积黏土具有一定的结构性,因此建立结构性本构模型对准确预测天然黏土的力学响应和解决实际岩土工程问题具有重要意义。首先,基于结构性黏土的三轴固结不排水试验的有效应力路径对结构性剑桥(SCC)模型进行了两点改进:(1)对附加孔隙比Δe的计算公式进行了修正,可以准确模拟结构性黏土超过临界状态线后的有效应力路径;(2)考虑了屈服面内的塑性即亚屈服特性,可以较好地模拟屈服面内的有效应力路径然后,利用修正结构性剑桥(MSCC)模型对结构性黏土的侧限压缩试验、三轴固结不排水和三轴固结排水试验进行了模拟计算,并与试验结果和SCC模型的计算结果进行了对比分析,结果表明MSCC模型可以更好地模拟结构性黏土的三轴不排水有效应力路径以及侧限压缩和三轴固结排水试验的应力应变曲线。最后,对MSCC模型中的参数β(屈服面内塑性变形参数)、p'_(yi)(初始结构屈服应力)、Δe_(i)(初始附加孔隙比)、b(结构破损速率)、γ(剪切引起结构破损的参数)和ω(反映结构性对塑性流动准则的影响)进行了参数敏感性分析,结果表明参数β影响结构性黏土屈服面内的有效应力路径,参数p'_(yi)影响峰值强度,参数Δe_(i)影响残余强度,参数b和γ影响峰值后的强度衰减速率,参数ω影响强度开始衰减时的偏应变大小。

爆破挤淤法中炸药埋深对土体参数影响的模型试验研究

爆破挤淤法是厚度15 m以上的软弱土地基有效处理方法之一。为了研究炸药埋深对该方法处理效果的影响,开展了淤泥中爆破的模型试验,利用全自动十字剪切板进行了不排水抗剪强度测试,探讨了炸药埋深对淤泥的不排水抗剪强度、含水率等影响,并利用扫描电镜分别观测了不同炸药埋深下爆破前后土体的微观结构。研究结果表明:爆破会破坏爆点附近的土结构,导致孔隙率增加,不排水抗剪强度骤降,形成爆破扰动区;扰动区以外土体受到挤压导致不排水抗剪强度增加,形成爆破挤密区。爆破后土体含水率下降,爆心距越大下降越显著。炸药埋深为0.3倍淤泥厚度的爆后不排水抗剪强度减小最显著,约27%,扰动区范围最大,约为19.2 d(d为爆点直径),爆破效果最显著。因此,存在爆点最佳埋深,使得爆破效果最好,扰动土体的范围最大;可通过不排水抗剪强度确定爆破扰动范围。研究结果可为相关工程中炸药埋深设计提供技术支持和参考。

某电厂低硬度P91钢力学性能及微观组织研究

为探究在役P91钢的组织损伤对力学性能的影响,对已服役3.3×10^(4)h的P91钢的力学性能进行了测试,并使用金相显微镜、扫描电镜等对断口、微观组织特征进行了表征。结果表明:早期服役历史使P91钢中的析出相发生粗化,应力与局部应变进一步促进了粗化相附近孔洞的形核和粗化。析出相粗化造成材料硬度及强度下降,孔洞的形核与粗化会促进孔洞连接形成微裂纹。组织损伤对短期蠕变强度未造成明显影响,对长期蠕变强度可能有一定的负面影响。

基于紫外光谱的油气两相流含气率检测研究

发动机润滑油系统中油气两相流含气率的检测对工业过程的安全运行有重要意义,准确和快速地测量出含气率对监控发动机的运行状态尤为重要。鉴于传统含气率检测方法的局限性,提出一种紫外光谱结合建模算法预测含气率的方法。首先,在波长为185~430 nm的光谱范围内,在5个不同两相流温度、3个不同两相流流速下共15个工况下,分别采集31组含气率范围在0.9%~3%的吸收光谱数据,光谱波长变量为1799个。对光谱数据采用光谱-理化值共生距离算法(SPXY)将数据集划分为21组校正集,10组测试集,对不同含气率工况进行偏最小二乘(PLS)建模,得到测试集决定系数(R^(2))范围为0.63~0.91。针对不同工况预测效果差别过大的问题,采用中心化(center)、标准化(autoscaling)、SG卷积平滑、多元散射校正(MSC)、标准正态变量变换(SNV)、去趋势算法(Detrend)、OPLS正交信号校正等数据预处理矫正方法优化模型,得到Detrend-center-PLS模型预测效果最好,其中R^(2)由0.9032提高到0.9557。针对光谱波长变量过多的问题,选取竞争性自适应加权算法(CARS)、蒙特卡洛无信息变量消除算法(MCUVE)和遗传算法(GA)三种方法进行波段降维,对降维后的光谱数据分别进行多元线性回归(MLR)、偏最小二乘和最小二乘支持向量机(LS-SVM)建模,得到预测结果最优为Detrend-center-CARS-PLS模型,与全波段模型比较,R^(2)从0.9557提升到0.9598。由于优化效果并不显著,对三种降维方法取交集,重新进行建模,R^(2)从0.9598提升到0.9671,优化效果有所提升。考虑到温度和流速对预测模型的影响,建立多工况含气率预测模型,采用与单工况相同的建模流程,得到autoscaling为最优预处理方法,且autoscaling-PLS模型的R^(2)为0.9488,波段降维方法将1799波长变量消减到400~500个变量,降维效果明显。针对不同的建模方法,得到autoscaling-MCUVE-LS-SVM模型为多工况最佳预测模型,R^(2)达到0.9926。最后,通过对比单工况预测模型和多工况预测模型,得知多工况预测模型含气率预测效果优于单工况模型,能改善模型预测效果。结果表明,采用光谱分析法结合建模算法预测油气两相流含气率是具备可行性的,为发动机的安全运行提供了有效的监控方法。

水泥路面脱空区域含水状态对面板剩余寿命的影响分析

【目标】针对水泥路面脱空病害不可避免又缺乏有效结构承载力评价方法的问题,研究水泥路面板底脱空含水状态对面板承载力和剩余寿命的影响规律。采用Abaqus构建了水泥路面的三维有限元模型。【方法】以充气脱空为对象,分析了脱空区域连续性、脱空尺寸等参数对路面应力和位移的影响;根据脱空含水区域的物理特征,提出了降低弹性模量和提高材料泊松比的含水脱空区域数字模拟方法,建立了高中低3种状态的脱空含水区域,分析了脱空含水对路面承载力的影响。在此基础上,以实际路面为对象,结合仿真结果和疲劳寿命分析方法,分析了含水与不含水脱空区域的剩余疲劳寿命。【结果】脱空尺寸和脱空含水是影响路面结构安全性的主要因素,路面的应力和位移随脱空尺寸的增大而增大,而含水会进一步增大轴载作用下脱空区域的应力及位移;脱空区域含水程度越高,路面的应力及位移增长越快,路面的应力及位移与轴载呈线性增加的关系;脱空区域含水时的路面剩余寿命远小于充气脱空路面剩余寿命,证明了充水脱空对路面的结构安全性危害更大。【结论】路面剩余疲劳寿命与脱空半径成负相关,脱空半径越大,剩余寿命越短;当脱空半径达到0.4 m时,路面剩余寿命不足1 a,需立即修复。【应用】研究结果为分析路面结构安全性和路面养护提供了科学依据。

使用光谱分析实现弯管中两相流含气率的预测

空气被夹带进入发动机润滑油系统形成油气两相流后,会严重影响润滑系统的正常运行。因此实现发动机润滑油系统中油气两相流含气率的准确和快速测量具有十分重要的意义。基于光谱匹配方法,对发动机润滑油系统在弯管处的油气两相流含气率进行了测量研究。首先使用近红外、可见光和紫外光谱仪获取油气两相流在2个流速、5个温度工况下0.10%~1.00%含气率范围(间隔0.06%)的吸光度数据并进行分析,确认油气两相流在三个波段下均有吸收,且吸收强度与含气率有关;其次提出将数据预处理结合光谱相似性测度方法并应用于弯管含气率光谱分析中,显著降低了基于原始光谱的含气率预测的最大相对误差。在近红外波段通过使用数据增强方法如中心化(center)和标准化(autoscaling)并结合光谱角余弦方法,得出新润滑油的含气率最大相对误差相对于原始光谱得到的数值从48%降低到36%。利用该方法分别在三个波段进行含气率预测,试验工况包括2个流速、5个温度,分析了两相流的温度和流速对含气率预测的影响。温度30.0℃,流速5.1 m·min^(-1)下,含气率信息在紫外波段(193.5~413.8 nm)与光谱向量的方向或形状差异的联系更为紧密,含气率预测的最大相对误差仅为6%。在近红外和可见光波段,流速或温度一定时,最大相对误差随着温度或流速的增加均有减小趋势。紫外波段下温度对含气率预测效果没有特定的影响规律,随着两相流的流速增加,含气率预测的最大相对误差有增大趋势。结果表明对于透光性较好的新润滑油,使用紫外光谱仪进行含气率数据的采集,含气率的预测选用标准化预处理结合光谱角余弦方法,得到的含气率预测最大相对误差最小。

Void defect detection in BGA solder joints using mathematical morphology

Voids are one of the major defects in ball grid array （BGA） solder joints due to a large amount of outgassing flux that gets entrapped during reflow. X-ray nondestructive machines are used to make voids visible as lighter areas inside the solder joints in X-ray images for detection However, it has always been difficult to analyze this problem automatically because of some challenges such as noise, inconsistent lighting and void-like artifacts. This study realized accurate extraction and automatic a-nalysis of void defects in solder joints by adopting a technical proposal, in which Otsu algorithm was used to segment solder balls and void defects were extracted through opening and closing operations and top-hat transformation in mathematical mor-phology. Experimental results show that the technical proposal mentioned here has good robustness and can be applied in the detection of voids in BGA solder joints.

A Model on the Void Fraction in Liquid Slugs for Vertical Slug Flow

Aim To develop a hydrodynamic model on the void fraction in liquid slugs for gas liquid slug flow in vertical tubes. Methods Developing the model by considering the gas exchange between the Taylor bubble and the following liquid slug. Results Some experimental data are obtained to check the model. In comparison with previous published results, the predictions from this model are better and in good agreement with the experimental data. The error is within ±20%. Conclusion The proposed model can correctly predict the void fraction in liquid slugs for gas liquid two phase slug flow in vertical tubes.

掺杂剂种类对大直径直拉硅单晶中void微缺陷的影响

研究了掺杂剂原子种类及快速热处理技术对大直径直拉硅单晶中空洞型微缺陷密度的影响.实验结果发现,掺入半径较大杂质原子的硅片,空洞型微缺陷密度相对较高,掺入半径较小杂质原子的硅片,空洞型微缺陷的密度相对较低.高温快速热处理后,硅片中FPD s的密度都有很大程度降低,而A r气氛退火对vo id微缺陷密度的影响要优于N2气氛.轻掺B硅片在O2气氛退火后FPD s密度下降最多,而重掺Sb硅片在O2气氛退火后FPD s密度下降最少.

完全性脊髓横断后排尿次数对神经源性膀胱模型大鼠成模率的影响

背景:脊髓损伤常导致逼尿肌反射亢进型神经源性膀胱,目前对其发病机制和治疗缺乏明确认识,建立稳定可靠的动物模型对揭示疾病的病理机制和探索治疗方法具有重要影响。目的:探究完全性脊髓横断术后辅助排尿次数对神经源性膀胱模型大鼠的影响,以提高神经源性膀胱模型大鼠术后生存率及成模率。方法:从46只雌性SD大鼠中按随机数字表法抽取6只为假手术组,剩余40只大鼠完全性脊髓横断造模后随机分为每日排尿0,1,3,5次组,每组10只。术后19 d内每隔3 d测量残余尿量,术后第19天时观察存活及成模情况,进行尿流动力学检测及离体逼尿肌肌条收缩实验。结果与结论:①存活率及成模率:每日排尿0次组存活率10%,成模率10%;每日排尿1次组存活率20%,成模率10%;每日排尿3,5次组存活率70%,成模率70%;②残余尿量:与假手术组相比,术后第3,6,9,12,15天,每日排尿3,5次组的残余尿量显著增加(P<0.01);术后第18天,每日排尿3,5次组的残余尿量增多(P<0.05);与每日排尿3次组相比,术后第6天,每日排尿5次组的残余尿量减少(P<0.05),术后第3,9,12,15,18天,每日排尿5次组的残余尿量无统计学差异;③尿流动力学:与假手术组相比,每日排尿3,5次组大鼠的漏尿点压差明显减小(P<0.01),膀胱最大容量显著增大(P<0.01);与每日排尿3次组相比,每日排尿5次组的漏尿点压差和膀胱最大容量均无统计学差异;④离体逼尿肌肌条收缩实验:与假手术组相比,每日排尿3,5次组逼尿肌肌条收缩幅度和频率显著减少(P<0.01);与每日排尿3次组相比,每日排尿5次组的逼尿肌肌条收缩幅度和频率均无统计学差异。结果表明:辅助排尿是成功构建逼尿肌反射亢进型神经源性膀胱模型的影响因素之一,每日排尿3次或5次无明显差异,结合实际工作量和成模率,建议每日排尿频率至少3次及以上。

浅谈C/C++中的void

对C语言中void关键字的含义进行了解释,并详述了void及void指针类型的使用方法和技巧．

基于地表沉陷数据反演的采动覆岩空隙时空演化规律

为明确采动覆岩空隙演化与地表下沉规律,采用现场实测和数值模拟方法,分析相似工作面的地表沉陷与覆岩空隙实测数据,标定研究工作面离散元数值模型参数,分析采动覆岩空隙时空演化规律。结果表明:42106浅埋工作面的地表下沉过程为开始—快速—缓慢—稳定,测点地表下沉速度呈现先增加后减小的几字形。充分采动前覆岩走向空隙率随推进距离增加而增大,充分采动后覆岩走向与倾向空隙率随工作面推进距离增加而减小。

沥青混合料施工温度确定方法

选择两种不同的温拌剂Evotherm、Sasobit制备温拌沥青并进行了黏温曲线测试,同时测试不同压实温度下温拌沥青混合料的空隙率及混合料的路用性能。研究结果表明:Evotherm/SBS I-D(E-SBS I-D)温拌改性沥青及Sasobit/SBS I-D(S-SBS I-D)温拌改性沥青较SBS I-D原样沥青分别可以降低约25℃及20℃的施工温度;通过黏温曲线可以准确确定不同类型改性沥青的施工温度;基于体积参数及路用性能评价指标可以直观地判定施工温度的合理性;对原样沥青及温拌沥青进行黏温曲线的测定,确定原样沥青所对应的规范规定的最低拌和温度的黏度,再选取温拌沥青相应黏度所对应的温度,即为最低拌和温度。

Effects of binder strength and aggregate size on the compressive strength and void ratio of porous concrete

To test the influence of binder strength, porous concretes with 4 binder strengths between 30.0-135.0 MPa and 5 void ratios between 15%-35% were tested. The results indicated that for the same aggregate, the rates of strength reduction due to the increases in void ratio were the same for binders with different strengths. To study the influence of aggregate size, 3 single size aggregates with nominal sizes of 5.0, 13.0 and 20.0 mm （Nos. 7, 6 and 5 according to JIS A 5001） were used to make porous concrete. The strengths of porous concrete are found to be dependent on aggregate size. The rate of strength reduction of porous concrete with small aggregate size is found to be higher than that with larger aggregate size. At the same void ratio, the strength of porous concrete with large aggregate is larger than that with small aggregate. The general equations for porous concrete are related to compressive strength and void ratio for different binder strengths and aggregate sizes.

A theoretical analysis of the electromigration-induced void morphological evolution under high current density

In this work, analysis of electromigration-induced void morphological evolution in solder interconnects is performed based on mass diffusion theory. The analysis is conducted for three typical experimentally observed void shapes: circular, ellipse, and cardioid. Void morphological evolution is governed by the competition between the electric field and surface capillary force. In the developed model, both the electric field and capillary force on the void's surface are solved analytically. Based on the mass conversation principle, the normal velocity on the void surface during diffusion is obtained. The void morphological evolution behavior is investigated, and a physical model is developed to predict void collapse to a crack or to split into sub-voids under electric current. It is noted that when the electric current is being applied from the horizontal direction, a circular void may either move stably along the electric current direction or collapse to a finger shape, depending on the relative magnitude of the electric current and surface capillary force. However, the elliptical-shaped void will elongate along the electric current direction and finally collapse to the finger shape. On the other hand, the cardioid-shaped void could bifurcate into two sub-voids when the electric current reaches a critical value. The theoretical predictions agree well with the experimental observations.