Generalized polynomial chaos expansion by reanalysis using static condensation based on substructuring

This paper presents a new computational method for forward uncertainty quantification(UQ)analyses on large-scale structural systems in the presence of arbitrary and dependent random inputs.The method consists of a generalized polynomial chaos expansion(GPCE)for statistical moment and reliability analyses associated with the stochastic output and a static reanalysis method to generate the input-output data set.In the reanalysis,we employ substructuring for a structure to isolate its local regions that vary due to random inputs.This allows for avoiding repeated computations of invariant substructures while generating the input-output data set.Combining substructuring with static condensation further improves the computational efficiency of the reanalysis without losing accuracy.Consequently,the GPCE with the static reanalysis method can achieve significant computational saving,thus mitigating the curse of dimensionality to some degree for UQ under high-dimensional inputs.The numerical results obtained from a simple structure indicate that the proposed method for UQ produces accurate solutions more efficiently than the GPCE using full finite element analyses(FEAs).We also demonstrate the efficiency and scalability of the proposed method by executing UQ for a large-scale wing-box structure under ten-dimensional(all-dependent)random inputs.

Experimental study on expansion and cracking properties of static cracking agents in different assembly states

Rolled static cracking agent(RSCA)can solve the intractable problem of traditional bulk static cracking agent(BSCA)in engineering applications.This paper innovatively studies the rational water-cement ratio of BSCA and the immersion soaking time of RSCA under the condition of controlling temperature.Through the expansion and cracking performance experiments,the development characteristics of expansion pressure,the cracking effect of the single-hole specimen and the performance of hole spraying prevention under the action of BSCA and RSCA were compared and analyzed.The results show that:(1)The volume growth rate of static cracking agent decreases with the increase of water-cement ratio,and the fluidity increases with the increase of water-cement ratio.The rational water-cement ratio for BSCA application is 0.3,and the rational immersion time of RSCA is 2-2.5 min;(2)Under the bore diameters of 30,35,40 and 45 mm,the expansion pressure of BSCA with a water-cement ratio of 0.3 is 38.2,52.3,61.5 and 68 MPa,and the expansion pressure of RSCA immersed in water for 2.5 min is 43.5,58.8,69.5 and 75.1 MPa,respectively.Among them,the development speed of expansion pressure of BSCA is higher than that of RSCA,and the arrival time of the peak expansion pressure of RSCA is 1.7 times that of BSCA;(3)The crack initiation speed of single-hole specimen under the action of RSCA is 10.3%lower than that under the action of BSCA,but the cracking speed of the former is 72.6%higher than that of the latter;(4)The hole spraying occurs in BSCA under the bore diameter of 50,55 and 60 mm,while the hole spraying occurs in RSCA under the bore diameter of 60 mm.In terms of bore diameter,the hole spraying prevention of the RSCA is better than that of BSCA.The research results enrich the static blasting technology and provide data support and theoretical reference for field application.

Static response analysis of structures with interval parameters using the second-order Taylor series expansion and the DCA for QB

In this paper, based on the second-order Taylor series expansion and the difference of convex functions algo- rithm for quadratic problems with box constraints （the DCA for QB）, a new method is proposed to solve the static response problem of structures with fairly large uncertainties in interval parameters. Although current methods are effective for solving the static response problem of structures with interval parameters with small uncertainties, these methods may fail to estimate the region of the static response of uncertain structures if the uncertainties in the parameters are fairly large. To resolve this problem, first, the general expression of the static response of structures in terms of structural parameters is derived based on the second-order Taylor series expansion. Then the problem of determining the bounds of the static response of uncertain structures is transformed into a series of quadratic problems with box constraints. These quadratic problems with box constraints can be solved using the DCA approach effectively. The numerical examples are given to illustrate the accuracy and the efficiency of the proposed method when comparing with other existing methods.

An improved outer pipe method for expansive pressure measurement of static cracking agents

Static cracking agent(SCA)is actively investigated as an alternative to explosive blasting for rock breakage due to its immense expansion property.SCA can eliminate the negative effects of shock,noise and harmful gases encountered in explosive blasting processes.Accurate measurement and deep understanding of the expansive properties of SCAs are important in their industrial application.An improved outer pipe method(OPM),termed the upper end surface method(UESM),is proposed in this paper to overcome the shortcomings of the OPM in the expansive pressure measurement of SCAs.Numerical simulation is used to proof the concept and a mathematical model established to relate the internal pressure and the radial strains at different positions in the upper end surface method test equipment.The new equipment is calibrated using oil pressure and strain measurements.The calibrated equipment is then used to measure the expansion pressure of SCA at three different water contents to proof its potential.The differences in the measurements with OPM and UESM at three different moisture contents are less than 4%.The experimental results confirm the accuracy and applicability of the more user friendly and less expensive UESM in the measurement of the expansive pressures of SCAs.

西方经济学方法论及其展开方式

经济学已然成为显学,学习者甚众。西方经济学初学者有两个感觉:一是难度大,二是容易忘。究其原因,教学中“重知识轻方法”是最大的弊病,对西方经济学方法及其层级关系不甚明了,教师就无法用方法论“红线”将知识点串起来,学生学习的困难就可想而知了。该文阐述西方经济学的主要方法,指出其之间的层级关系,并例证经济学方法的展开过程,提醒在教和学之中要注意方法论的学习,旨在提高经济学的教学水平。

基于HSCA静力破岩的金属矿山遗留矿柱安全低损回采试验研究

针对采用爆破破岩方式对金属矿山遗留矿柱进行回采存在安全性差与矿石损失率高的局限性,将具有无振动特征的高效静态破碎剂(High Range Static Cracking Agent,HSCA)引入遗留矿柱回采中。通过设计HSCA膨胀压应力测试试验与静力破岩试验,分析了HSCA径向膨胀压应力大小及其分布规律与水灰比的关系。分别从膨胀压应力分布特征、主裂纹定向控制方法与破岩时效性3个方面,论证了通过HSCA静力破岩实现金属矿山遗留矿柱安全低损回采的可行性。研究结果表明:当水灰比大于理论最优水灰比时,膨胀压应力随着水灰比的增大而减小。对于上向倾斜装药孔膨胀压应力沿孔底至孔口方向呈增大趋势,对于下向倾斜装药孔膨胀压应力则呈减小趋势。采用HSCA静力破岩对遗留矿柱进行回采,遗留矿柱主裂纹走向可通过对装药孔进行预切槽、增设诱导片或新增诱导孔等方式进行定向控制,进而有效降低非破岩区矿岩的再损伤。因此,对于不宜采用爆破破岩方式对遗留矿柱进行回采的区域,HSCA静力破岩不仅有利于保障遗留矿柱回采安全,而且可提高遗留矿柱回收率。研究成果可为进一步探索金属矿山遗留矿柱回采破岩新理论与新技术提供参考。

润宏煤业1305工作面静态膨胀剂致裂顶板卸压技术研究

以润宏煤业1305工作面地质条件为工程背景,采用静态膨胀技术对运输巷顶板切顶卸压,避免煤柱侧应力集中。通过理论分析、实验室测试、现场工程试验等方法,分析和测试了静态膨胀剂的膨胀力性能,计算分析了静态膨胀剂作用下切顶卸压的钻孔参数,设计了详细的施工工艺。研究结果表明,静态膨胀剂的最大膨胀力可达到70 MPa,且持续时间长,完全可以用于煤岩致裂工程。钻孔间距、钻孔直径以及钻孔角度是影响静态膨胀剂致裂效果的主要参数。钻孔内产生的静态膨胀压力作用到孔壁,且能一直保持到顶板进入采空区后,在矿压、自重及静态膨胀力的作用下,顶板会出现裂缝、裂缝扩展、顶板致裂垮落3个过程。根据现场具体工程条件,在多组成排钻孔共同膨胀作用下,可形成膨胀应力的叠加,能够起到更好的致裂效果。研究为探索和推广煤矿非爆破式顶板致裂技术提供了借鉴。

非爆破机械钻进联合静力膨胀裂切技术应用研究

采用钻爆法进行非煤矿山巷道掘进的过程中,往往会产生诸多安全隐患。随着机械装备的快速发展,非爆破机械采矿逐渐成为非煤矿山开采的主流研究方向。为解决某矿山下向进路充填采矿时,首采层采场回采难度大、回采周期长、支护难度高和作业安全性差等问题,提出非爆破机械钻进联合静力膨胀裂切的技术思路。首先,通过数值模拟的方式进行机械钻进静态裂切孔网参数优化,确定裂切孔网方案,然后进行现场试验检验技术效果。结果表明,非爆破机械钻进联合静力膨胀裂切技术应用良好,能够切实解决矿山面临的生产难题。

基于响应面法优化静态致裂剂施工参数

静态致裂技术主要是利用生石灰与水发生水合反应,引起体系体积膨胀,致裂机理主要可分为物质转移理论、固体体积扩展理论和孔隙体积增长理论。致裂剂在水化反应过程中体积增长率与水化反应速率成正比,与孔隙体积率成反比。为了实现静态致裂效果的最大化,提高资源利用率,丰富致裂剂的实用价值,基于静态致裂机理,在单因素实验的基础上,以静态致裂剂的自由膨胀率为响应值,采用响应面法对影响静态致裂剂体积膨胀率的因素进行优化,研究了不同影响因子对体积膨胀率的作用效果。结果表明:水灰比为0.27∶1,温度为35℃,药剂量为105 g时,静态致裂剂的体积膨胀率最大,该研究对致裂剂的现场应用具有指导意义。

冻土膨胀对管道及法兰连接应力变化影响分析

冻土膨胀会使燃气管道产生应力集中,导致高压燃气管道极易发生失效甚至破裂,从而引发爆炸事故。为了研究冻土膨胀对管道及法兰连接应力变化影响,使用Workbench对管道及法兰连接进行分析。以位移载荷20 mm为例,观察管道及法兰连接的应力分布情况,并研究其在0~30 mm位移情况下的应力变化。结果表明:管道最大应力出现在管道弯头处;法兰盘最大应力出现在法兰盘与管道焊接处;管道的应力变化随着位移的增加变化最大,法兰盘次之,螺栓的应力平稳增加。

冷轧钢带双头开卷机的设计与分析

为解决目前单侧上卷冷轧开卷机工作效率低等问题,设计了一种新型的双头开卷机,由引导机构、支撑机构、胀紧固定机构、开卷机主体等构成。为代替人工手动引卷,在开卷机一侧安装了引导机构,通过调整引导直板可以自动完成引卷;针对主轴长期承受压应力易发生应力疲劳,在主轴下侧安装了支撑机构,可以转移部分钢卷的压应力从而提高主轴工作稳定性;针对现有开卷机效率低,在支撑主轴两侧分别安装了固定机构,两侧固定机构通过联动控制可以实现开卷与上卷同步进行。利用CATIA建立了开卷机各机构模型,并完成了整机装配,对开卷机进行了运动干涉检查,结果表明开卷机运动无干涉。对开卷过程进行了静力学分析,应力云图显示固定机构的最大应力为830.837 kPa,未超过材料许用应力。

高瓦斯综放面开切眼架前膨胀预裂坚硬顶板切顶技术研究

针对高瓦斯坚硬顶板综放工作面初采期来压步距大及顶煤损失的问题,提出代替火药爆破的开切眼架前及两顺槽煤柱侧静态膨胀预裂切顶技术;采用数值模拟方法确定了静态膨胀预裂切顶的关键参数,设计了切顶方案及工艺,并通过现场工程应用验证了静态膨胀预裂切顶技术的有效性。结果表明:综放工作面初采前在开切眼架前及两顺槽煤柱侧实施静态膨胀预裂切顶,既保证了开切眼设备安装期间的安全性,又可在后续采动应力的作用下顶板及时破断,减小坚硬顶板初次来压步距和强度;当综放工作面初采推进至开切眼宽度时发生初次来压,人工减跨效果良好,不仅提前回收了工作面的顶煤资源,而且还消除了坚硬顶板大面积悬顶带来的诸多重大安全隐患,研究成果可在类似条件下代替炸药爆破进行推广应用。

分级侧向膨胀型锚杆结构力学性能及锚固机理

为了更好地应对传统锚杆在边坡、隧道灾害防治领域锚固性能的不足,研发了一种具有分级侧向膨胀性能的锚杆结构。首先,基于弹性力学理论与物理圆环模型,得到了分级侧向膨胀锚杆径向承载变形的本构关系与极限抗拉拔力公式;然后,通过静态拉拔试验,揭示了锚杆的承载力传递规律与承载变形机理;最后,通过对分级侧向膨胀锚杆与NPR锚杆的结构特性进行对比,发现分级侧向膨胀锚杆不仅在抗剪切、扭转和吸能等方面具有更优异的性能,且相比较NPR锚杆的单次膨胀特性,其分级膨胀与可控变形的特性在提高围岩整体稳定性,释放围岩变形能方面更具优势。结果表明,分级侧向膨胀锚杆的特性更加适合稳定性较差的地质环境,为灾害防治工程提供了新的解决方案。

膨胀静力在灌注桩桩头破除工程中的应用

桥梁桩基破除桩头施工一直是施工技术难点,施工时经常会破坏桩头钢筋,从而影响桩基质量,并且桩头破除工程费时费力。以赣南大道快速路某桩基破除桩头施工为例,采用静力膨胀法破除桥梁灌注桩桩头,运用该工艺桩头能够有效实现截桩面部位出现微观水平裂缝,有利于桩头整体破除,桩头部位钢筋洁净无损伤,施工过程中无扬尘、无噪声,绿色环保,经济低碳,可以有效节约施工成本,提高施工效率。

巴万高速典型边坡危岩分析与处治方法研究

随着国民经济的快速发展,跨山区的高速交通愈发受到重视,而山区地质灾害频发,边坡危岩属于山区的典型地质灾害,因此,山区高速公路尤其需要做好边坡危岩的处治工作。基于此,本文对边坡危岩的失稳方式进行了讨论,并根据巴万高速某边坡危岩工程实例,提出采用柔性主动防护网技术与静态膨胀破碎法相结合的施工方案进行边坡危岩处治,并对该方案的工艺流程进行了介绍,为同种类型的边坡危岩处治提供了思路。

基于Aspen Hysys模拟100万m^(3)/d的液化厂二级氮膨胀液化工艺

本设计中天然气处理量为100万m^(3)/d,处理量较小,属于调峰型天然气液化厂,常采用小型LNG液化流程。液化厂中小型液化装置流程主要有以下两大类:单混合制冷剂流程和各类膨胀流程,如二级氮膨胀液化流程、N_(2)-CH_(4)膨胀液化流程、开式膨胀液化流程。二级氮膨胀液化流程简单、设备数量少,本设计主要利用Aspen Hysys搭建出二级氮膨胀液化静态模拟流程,并基于Matlab工具箱中的遗传算法对液化流程的能耗、液化率进行优化。经过130次迭代,模拟计算出优化变量最优值,流程优化前比功耗0.7041,液化率为0.9515,优化后比功耗0.5403,液化率为0.9515,优化前后比功耗降低28.37%。

近距离煤层切顶卸压沿空留巷技术及应用研究

针对开采近距离煤层时上煤层回采结束,底板受到破坏,采空区矸石垮落使得下煤层顶板结构及应力环境愈加复杂,下煤层巷道顶板的完整性及稳定性受到影响,为下煤层巷道围岩控制带来诸多难点,以龙门塔煤业近距离煤层工作面沿空留巷为研究背景,通过理论计算得到了切顶的具体参数,提出了静态胀裂切顶技术,优化了支护形式,实现了近距离下煤层工作面无煤柱切顶卸压沿空留巷。经现场实践检验,下煤层巷道受采动影响较小,留巷效果较好。

Static and Dynamic Pull-In Instability of Nano-Beams Resting on Elastic Foundation Based on the Nonlocal Elasticity Theory

This paper provides the static and dynamic pullin behavior of nano-beams resting on the elastic foundation based on the nonlocal theory which is able to capture the size effects for structures in micron and sub-micron scales. For this purpose, the governing equation of motion and the boundary conditions are driven using a variational approach. This formulation includes the influences of fringing field and intermolecular forces such as Casimir and van der Waals forces. The differential quadrature （DQ） method is employed as a high-order approximation to discretize the governing nonlinear differential equation, yielding more accurate results with a Considerably smaller number of grid points. In addition, a powerful analytical method called parameter expansion method （PEM） is utilized to compute the dynamic solution and frequency-amplitude relationship. It is illustrated that the first two terms in series expansions are sufficient to produce an acceptable solution of the mentioned structure. Finally, the effects of basic parameters on static and dynamic pull-in insta- bility and natural frequency are studied.

异形孔在膨胀荷载作用下的定向致裂机制

基于室内相似材料应变试验,对带有尖角的异形孔如正三角孔、等腰直角三角孔、120°顶角的等腰三角孔在膨胀压力作用下的裂岩机理展开讨论.在此基础上,使用颗粒流模拟进一步研究了单向致裂效果的最佳角度、双孔的最佳作用间距以及岩石强度对压裂效果的影响.结果表明,异形孔作用下试样的起裂和破碎时间均短于圆形孔,并且其裂纹的发展是可控的,总是沿着尖角角平分线延长线方向进行.根据应变的变化,可将试验分为三个阶段.平稳发展阶段,各个方向的应变增长速率几乎没有差别;快速增长阶段,新的破裂面广泛形成且具备一定的方向性;衰弱阶段,断裂不断出现导致能量消散,应变急剧下降.数值模拟结果表明,双正三角孔间距为7倍正三角形边长时定向效果最佳,岩石强度和致裂效果呈乘幂关系.

基于三角孔应力集中效应的岩桥破断机制研究

确定三角孔与软岩裂隙间的合理距离及夹角,对提高静力膨胀法破裂软岩的效率有重要意义。通过对三角孔带单裂隙的类软岩试样进行静力膨胀试验及数值模拟,详细分析了预制裂隙与三角孔之间不同间距、不同走向条件下贯通岩桥后的试样断裂程度。结果表明:试样只沿三角孔的角平分线方向发育3条主裂纹;45°~90°范围走向的预制裂隙试样破裂后的裂纹数量比0°~30°范围的裂纹数量增加了30.4%~44.2%;0°走向试样的分形维数和断裂密度远低于45°和90°走向试样的分形维数和断裂密度;45°~90°走向的预制裂隙有利于试样的破裂,裂隙与孔之间的距离对破碎试样的效果影响较小;在0°~30°走向范围内,预制裂隙起着屏蔽作用,阻碍着试样的断裂,在2倍等效半径内,屏蔽作用明显,大于2倍等效半径时屏蔽作用基本消失。