Mobility and dynamic erosion process of granular flow:insights from numerical investigation using material point method

In order to understand the dynamics of granular flow on an erodible base soil,in this paper,a series of material point method-based granular column collapse tests were conducted to investigate numerically the mobility and dynamic erosion process of granular flow subjected to the complex settings,i.e.,the aspect ratio,granular mass,friction and dilatancy resistance,gravity and presence of water.A set of power scaling laws were proposed to describe the final deposit characteristics of granular flow by the relations of the normalized run-out distance and the normalized final height of granular flow against the aspect ratio,being greatly affected by the complex geological settings,e.g.,granular mass,the friction and dilatancy resistance of granular soil,and presence of water in granular flow.An index of the coefficient of friction of granular soil was defined as a ratio of the target coefficient of friction over the initial coefficient of friction to quantify the scaling extent of friction change(i.e.,friction strengthening or weakening).There is a characteristic aspect ratio of granular column corresponding to the maximum mobility of granular flow with the minimum index of the apparent coefficient of friction.The index of the repose coefficient of friction of granular flow decreased gradually with the increase in aspect ratio because higher potential energy of granular column at a larger aspect ratio causes a larger kinetic energy of granular soil to weaken the friction of granular soil as a kind of velocity-related friction weakening.An increase in granular mass reduces gradually the indexes of the apparent and repose coefficients of friction of granular soil to enhance the mobility of granular flow.The mobility of granular flow increases gradually with the decrease in friction angle or increase in dilatancy angle of granular soil.However,the increase of gravity accelerates granular flow but showing the same final deposit profile without any dependence on gravity.The mobility of granular flow increases gradually by lowering the indexes of the apparent and repose coefficients of friction of granular flow while changing the surroundings,in turn,the dry soil,submerged soil and saturated soil,implying a gradually increased excessive mobility of granular flow with the friction weakening of granular soil.Presence of water in granular flow may be a potential catalyzer to yield a long run-out granular flow,as revealed in comparison of water-absent and water-present granular flows.In addition,the dynamic erosion and entrainment of based soil induced by granular flow subjected to the complex geological settings,i.e.,the aspect ratio,granular mass,gravity,friction and dilatancy resistance,and presence of water,were comprehensively investigated as well.

Axial Compression Behavior and Analytical Method of L-Shaped Column Composed of Concrete-Filled Square Steel Tubes

Based on the characteristics of an L-shaped column composed of concrete-filled square steel tubes, the axial compression experiment and nonlinear finite element analysis were carried out to study the mechanical property of the L-shaped column. The load-displacement curve for the L-shaped column, the deflection and load-strain curves for the mono columns were obtained by the axial compression experiment. The results show that the L-shaped column exhibits a flexural-torsional buckling failure mode. The numerical simulation by the finite element analysis shows that the bearing capacity and failure mode are in accordance with those of the axial compression experiment and the feasi- bility of the finite element analysis is proved. For the calculation of the bearing capacity of the L-shaped column com- posed of concrete-filled square steel tubes, an analytical method is proposed based on the theory of the elastic stability and spatial truss model. The results of the analytical method are in good agreement with those of the axial compression experiment and the finite element analysis.

Shortcut Method of Design and Energy-Saving Analysis of Sargent Dividing Wall Column

The Sargent dividing wall column can implement four products separation sequences in one column based on Fully Thermally Coupled Distillation Column. The initial design parameters are required for the design optimization or dynamic control of the Sargent dividing wall column, and in order to make the rigorous simulation of the Sargent dividing wall column more conducive to convergence, a ten column model for complex Sargent column is established in this paper,and the shortcut design method of this model is proposed. The internal minimum vapor and liquid flow are obtained by the Underwood equations and the mass balance method and the V-min method. The separation for a 4-component shortcut mixture of pentane, hexane, heptane and octane was considered, while the initial values of design parameters and the ratio of vapor-liquid distribution of each column were calculated by using the shortcut design method of a ten column model. And by comparing the shortcut calculations with rigorous simulation results, the practicality and reliability of shortcut calculations were verified. The reason for energy saving was analyzed based on back-mixing. A virtual heat exchanger is proposed to make the Sargent dividing wall column more energy efficient.

Responses of bacterial community to potential heap construction methods of fine-grained copper tailings in column bioleaching system

The column bioleaching of copper flotation tailings was comparatively investigated using layered heap construction method(LM),agglomerate heap construction method(AM),and pellets-sintering heap construction method(PM).The bacterial communities of free,attached,weakly-attached,and strongly-attached microbes in the later bioleaching stage were investigated.In AM group,the addition of lump sulphide ore resulted in the low leachate pH,high ferric iron concentration,and rapid microbial adsorption,which obtained the maximum copper extraction(60.1%)compared with LM(54.6%)and PM(43.9%)groups.The relative abundance of dominant genera and microbial communities of different microbiota underwent changes in three heap construction methods.The alpha-diversity indexes of attached,weakly-attached,and strongly-attached microbes were different,while no significant change was observed in free bacteria.The variation of whole bacterial community was significantly associated with solution pH,total iron,and ferric iron concentrations.Pearson correlation analysis and partial least square path model both indicated that attached bacteria made larger contribution to the copper extraction of tailings.

Preparation of λ-MnO_2 by Column Method and Its Ion-Sieve Property

MnO 2 was prepared by column method from normal spinel LiMn 2O 4 with purity of 99.38%.The influence of LiMn 2O 4 grain size and acidity of leaching solution on the lithium leaching process was studied.The results show that the appropriate range of LiMn 2O 4 grain size was 60-160 meshes and the concentration of leaching solution HCl was 0.1 mol·L -1.The adsorption capacity Q of λ-MnO 2 for lithium increased with the increase of pH and changed markedly at pH 6.0-10.0.It was 3.80mmol/g at pH 12.0.The distribution coefficients K d of Li + and Na + were 3.406×10 4 and 2.300 respectively,and the separation coefficient α Li Na was 1.481×10 4 at pH 6.5.As a result,λ-MnO 2 is a high performance ion-sieve material for lithium ion.

Finding the buckling load of non-uniform columns using the iteration perturbation method

The aim of this study is to calculate the critical load of variable inertia columns. The example studied in this paper can be used as a paradigm for other non-uniform columns. The wavelength of equivalent vibratory system is used to calculate the critical load of the trigonometrically varied inertia column. In doing so, the equilibrium equation of the column is theoretically studied using the perturbation method. Accuracy of the calculated results is evaluated by comparing the solution with numerical results. Effect of improving the initial guess on the solution accuracy is investigated. Effects of varying parameters of the trigonometrically varied inertia and the uniformly tapered columns on their stability behavior are studied. Finally, using the so-called ＂perfectibility＂ parameter, two design goals, i.e., being lightweight and being strong, are studied for the discussed columns.

A New Method for Predicting the UL of Circular CFST Columns

Concrete filled steel tube structures have gained booming development in recent decades, especially in China. Simplified methods have been proposed in design codes, such as the Eurocode 4 (EC4) and the China engineering and construction specification (CECS). In EC4, the confinement effect is reasonably related to slenderness and load eccentricity. The CECS method is much straight forward in that the slenderness ratio and load eccentricity are treated as independent reduction factors. To make use of the advantages of both the CECS and the EC4 methods, the CECS method is modified to consider the confinement effect associated with slenderness and load eccentricity. It is shown that the proposed method can predict well the ultimate load capacity of circular section concrete filled steel tube columns.

Development of simple HPLC/UV with a column-switching method for the determination of nicotine and cotinine in hair samples

Nicotine and cotinine in hair are good biomarkers for assessing long-term exposure to smoking. However, analytical devices such as GC/MS are associated with high cost and are not widely used. HPLC/UV is used widely in laboratories, but is unsuitable for measurement of minor constituents, except when using the column-switching method. Thus, we aimed to establish a simple, inexpensive and sensitive method based on HPLC/UV with column switching for measuring nicotine and cotinine in hair. First, we compared the presence and absence of a column selection unit. We then measured amounts of nicotine and cotinine in hair samples collected from the general population, and compared both the corresponding levels and the detection limits with those in previous studies. Finally, initial and running costs of HPLC/UV were compared with other analytical methods. As one of the results, the areas of nicotine and cotinine measured by HPLC/UV with column-switching method were 12.9 and 16.9 times greater, respectively, than those without the column-switching method. The amount of nicotine and cotinine in hair was significantly correlated to number of cigarettes smoked per day (r = 0.228, p = 0.040). In addition, the HPLC/UV method showed similar sensitivity and detection limit (nicotine, 0.10 ng/mg;cotinine, 0.08 ng/mg) as reported in previous studies. The cost of the HPLC/UV method is lower than that of other analytical methods. We were able to establish a low-cost method with good sensitivity for measuring nicotine and cotinine in hair. The HPLC/UV with a column-switching method will be useful as a first step in screening surveys in order to better understand the effects of smoking exposure.

On the Convergence of the Column-Updating Method

In this paper, we prove the local and Supcrlinear convergence theorem of the column-updating method for n>2. This is an oped problem for the convergene theory of the column-updating method given by Martinez in the Intcrnational Conference of the NATO-ASI (Italy, 1994).

黄土地区洞桩法地铁车站边桩和中柱的受力变形机理

[目的]为了确保黄土地区洞桩法车站施工过程中重要竖向承重构件的稳定性,需要对施工过程中边桩和中柱的受力变形机理进行研究,并对最不利受力阶段边桩和中柱提出变形控制措施。[方法]以西安地铁2号线何家营站为研究背景,通过数值模拟与现场监测的方法,对施工过程中边桩的水平位移、钢筋内力、水平土压力及中柱应变展开研究。[结果及结论]扣拱施作以及站厅层和站台层土体开挖是边桩水平位移最不利的三个阶段,在这些关键阶段施工时,应在结构内部架设钢支撑并适当加固已扰动的地层;在桩梁和扣拱施作中,边桩主筋承受轴向压力,而在站内剩余土方施工阶段,边桩背土侧的钢筋由轴向压力逐渐转化为轴向拉力,且随着边桩埋深的增大,钢筋的轴向拉压力增长变缓;在扣拱初期支护施作中,土压力在边桩埋深6.6 m处达到最大值34.5 kPa,且随着边桩埋置深度增大,边桩的桩侧压力增长速率显著,因此车站内侧的土方开挖是控制边桩迎土侧土压力大小的关键阶段,必要时对桩后土体进行注浆加固有利于提高桩基的承载力;中跨扣拱施工时,中柱的应变呈现出先减小、后增大的趋势。

新型钢管混凝土梁柱节点力学性能试验研究

为研究内加强环式圆钢管混凝土柱与矩形钢管混凝土梁这种新型连接节点的力学性能,设计了缩尺钢管混凝土梁柱节点试件,开展了相同梁柱节点试件的静力加载试验和低周往复加载试验。通过研究该节点试件的破坏模式、荷载-位移曲线以及拟静力加载试验的骨架曲线、核心区剪切变形等,分析了节点试件的承载能力、延性和耗能能力,全面考察了同一梁柱节点在静力加载和低周往复加载两种工况下的受力性能和破坏模式。结果表明:钢管混凝土梁柱节点试件核心区强度较强,破坏模式主要为梁端破坏,低周往复加载试验时试件梁柱连接处附近的梁端钢板发生拉裂破坏和钢板鼓曲,静力加载试验时试件梁端焊缝发生拉裂破坏;试件延性较好,加载过程中经历了弹性、弹塑性和塑性发展阶段。最后提出了该类钢管混凝土梁柱节点核心区的抗剪强度计算公式。

工作面内地质异常无线电磁波透视规律研究

为了掌握煤(岩)层及地质异常体对电磁波透视的影响规律,采用三维数值模拟方法,研究全空间条件下环形天线发射电磁波在煤(岩)层中传播时,遇到不同地质异常体(断层、陷落柱)时的传播特征。结果表明:异常体充填空气较多时,电磁波损耗小,磁场强度等值线外凸;若异常体充填水较多时,电磁波能量损耗较大,曲线内凹;充填其他介质时,电磁波损耗介于两者之间,可通过实测场强曲线、等值线变化,判断异常区电性特征。异常体形态和规模不同,磁场强度分布也不相同;异常区为圆形或似圆形时,磁场强度在异常体内产生畸变,远离异常体后逐渐恢复正常分布,识别较为困难;故异常体直径越小,离接收点越远,识别越困难;当异常区为条状断层分布时,断层走向与巷道交角越小,受影响的测点较多,识别较容易;若断层走向与巷道交角变大,受影响的测点变少,则识别较困难,据此可大致判断断层走向。正常情况下,场强曲线呈左右对称的抛物线形态,中间大、两侧递减;异常体所处位置、形态及充填物质不同,曲线形态亦不相同;当异常体规模较大时,曲线呈对称或不对称的“M”形。因此,在数据处理初期,由于场强曲线获取较快,可以通过识别曲线形态初步定性判别异常体的某些特性,但无法准确定位射线上不同区段的异常特征,可进一步结合层析成像分析,得到正确合理的认识。

林区桥梁墩柱加固虚拟仿真实验教学探索与实践

以林区桥梁墩柱加固为例,基于现代教学理念以及虚拟仿真技术设计桥梁墩柱加固虚拟仿真资源,并实现在线共享。实验解决了土木类大型实验经费高、周期长、存在一定安全隐患的难题。结合虚拟教研室的建设,采取浸入式、自主式、交互式、探究式、反馈式教学方法相结合,探索开展虚拟综合性实验设计、实施以及教学评估,构建了混合教学模式下虚拟仿真实验教学体系。教学实践证明,通过虚拟仿真实验教学有利于混合式教学模式下学生的自主探究以及创新实践,全方面地提升了学生综合素质。

CFRP布加固RC柱细观力学分析模型及抗扭分析

为了探究配纤率、截面形状、截面尺寸、轴压比对碳纤维增强复合材料(carbon fiber reinforced polymer,CFRP)加固钢筋混凝土(reinforced concrete,RC)柱抗扭性能的影响,采用了可以同时考虑混凝土材料非均质性、钢筋与混凝土间黏结-滑移关系、CFRP布与混凝土间界面关系的细观力学分析方法。首先,建立了用于CFRP布加固RC柱抗扭性能分析的三维数值模型;进而,将基于该模型的数值模拟结果与试验结果对比,验证了模型中加载方式、外贴CFRP布方法的合理性及材料参数的准确性;最后,基于建立的细观力学分析模型,探讨了配纤率、截面形状、截面尺寸、轴压比对扭转作用下CFRP布加固RC柱破坏模式和力学性能的影响机制。分析结果表明:CFRP布加固RC柱抗扭承载力随配纤率增大而提高,但提高幅度随配纤率增大而降低;受到围压分布的影响,圆形截面的有效约束面积大于方形截面,使得CFRP布对圆柱的约束效果好于方柱;CFRP布加固RC柱的名义扭转强度存在尺寸效应;轴压比的增大使其抗扭承载力先增大后减小,在轴压比为0.4时达到最大值。进一步,采用叠加规范公式方法提出了FRP布加固RC构件抗扭承载力计算公式,与数值模拟结果对比发现,该公式可给出安全储备冗余度30.2%的设计值,可初步用于CFRP布加固RC柱抗扭承载力的安全设计。

微柱-酶法在不规则抗体筛查中的应用研究

目的研究传统微柱凝胶法与微柱-酶法在不规则抗体筛查中的敏感度及特异度,为提高不规则抗体筛查检出率提供循证依据。方法选择2022年11月至2023年12月在玉林市第一人民医院就诊的输血不良反应患者60例为研究对象,分别用传统微柱凝胶法及微柱-酶法进行不规则抗体筛查的对比研究,比较两种筛查方法的不规则抗体检出率、不规则抗体效价;同时采用倍比稀释法检查两种方法测试不规则抗体的最高滴度,采用excel表格AVERAGE函数公式计算平均滴度;另外选取同时期在该院体检中健康人群60名作为不规则抗体筛查阴性对照组,分别评价两种方法对不规则抗体检查的敏感度及特异度。结果微柱-酶法对不规则抗体检出率高于传统微柱凝胶法[8(13.3%)vs.18(30.0%),P<0.05],微柱-酶法平均滴度高于传统微柱凝胶法[(1∶18)vs.(1∶42),P<0.05]。传统微柱凝胶法及微柱-酶法敏感度差异无统计学意义(89.5%vs.90.8%,P>0.05);传统微柱凝胶法及微柱-酶法特异度(78.9%vs.80.2%,P>0.05)。结论微柱-酶法对不规则抗体有更高的检出滴度,传统酶法及微柱-酶法对不规则抗体检测敏感度及特异度无统计学差异,均能满足临床输血对于不规则抗体的检测需求。

基于割线模量的散体材料桩复合地基沉降计算

基于土体侧限条件下的应力-应变关系曲线均为双曲线的现象,且应用割线模量计算土体的竖向应变更有助于实现程序计算,首先利用土体割线模量与压缩指数和压缩模量的关系,得到桩周土体割线模量的确定方法.在此基础上,基于等应变假设条件得到考虑土体非线性压缩的桩土应力比,并提出改进的应力修正法和复合模量法,以实现散体材料桩复合地基非线性沉降计算.最后结合模型试验和实际工程算例,对2个改进的沉降计算方法开展验证分析.研究结果表明:室内模型试验中,改进的应力修正法和复合模量法的沉降计算值与试验值误差均小于1.00 mm,表明改进的沉降计算方法具有一定的可靠性;实际工程算例中,改进的复合模量法计算值与实测值间误差为8.70%,远小于JGJ 79—2012《建筑地基处理技术规范》中规定的复合模量法误差(55.06%),改进的应力修正法计算值与实测值误差为8.73%,远小于JGJ 79—2012中规定的应力修正法误差(55.11%).对比分析表明,改进的沉降计算方法优于JGJ 79—2012中的复合模量法和应力修正法,且改进方法计算值更接近实测值,说明改进方法具有更好的可靠性和适用性.

圆钢管型钢再生混凝土组合柱水平承载力计算方法研究

通过对11个圆钢管型钢再生混凝土组合柱进行低周反复荷载试验,分析再生粗骨料取代率、型钢截面形式、轴压比、型钢配钢率及圆钢管壁厚参数对组合柱水平承载力的影响规律;观察了组合柱的破坏形态及特征,研究了圆钢管、型钢翼缘及腹板应变的发展规律,分析了组合柱的地震破坏特征。研究表明,在水平地震作用下组合柱发生典型的压弯塑性铰破坏。在此基础上,结合现有规范提出了基于叠加原理的圆钢管型钢再生混凝土组合柱水平承载力计算方法。计算结果表明,其水平承载力计算值与试验值吻合度较好,能较为准确地预测组合柱的水平承载力。

外置耗能角钢的摇摆-自复位桥梁双柱墩地震易损性分析

为评估设置耗能角钢的摇摆-自复位桥梁双柱墩的抗震能力,本文建立该结构的有限元分析模型,分别定义和量化双柱墩不同损伤状态和损伤指标。本文从太平洋地震工程研究中心选取16条近断层地震动,基于增量动力分析,得到该结构的地震响应。基于最小二乘法,对得到的增量动力分析曲线进行对数回归分析,计算结构不同损伤状态的超越概率及易损性曲线。研究表明:当地面峰值加速度为0.1 g时,外置耗能角钢与耗能钢筋屈服的超越概率分别为34%和22%;当峰值加速度为0.4 g时,外置耗能角钢与耗能钢筋失效的超越概率分别为6%和11%,而预应力筋未屈服;当峰值加速度为1.0 g时,外置耗能角钢和耗能钢筋失效的概率分别达到85%和91%,桥墩发生倒塌的概率为46%。

装配式建筑梁柱节点疲劳损伤检测方法研究

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