Calculation mode of side friction for large open caisson

To overcome the problems in design methodologies and construction control measures for the large open caisson, systematic research was conducted on the side friction calculation mode of the large open caisson. Based on the field monitoring data of lateral soil pressure on the side wall of the open caisson for the southern anchorage of the Maanshan Yangtze River Highway Bridge, the statistical result of the side friction under different buried depths of the cutting edge of the open caisson was back-analyzed; and the side friction distribution of the large open caisson was underlined. The analysis results indicate that when the buried depth of the cutting edge is smaller than a certain depth H0, the side friction linearly increases with the increase in the buffed depth. However, as the buffed depth of the cutting edge is larger than H0, the side friction shows a distribution with small at both ends and large in the middle. The top of the distribution can be regarded as a linear curve, while the bottom as a hyperbolic curve. As the buffed depth of cutting edge increases continuously, the peak value of the side friction linearly increases and the location of the peak value gradually moves down. Based on the aforementioned conclusions, a revised calculation mode of the large open caisson is presented. Then, the calculated results are compared with the field monitoring data, which verifies the feasibility of the proposed revised calculation mode.

Range of applicability of real mode superposition approximation method for seismic response calculation of non-classically damped industrial buildings

An industrial building is a non-classically damped system due to the different damping properties of the primary structure and equipment.The objective of this paper is to quantify the range of applicability of the real model superposition approximation method to the seismic response calculation of industrial buildings.The analysis using lumped mass-and-shear spring models indicates that for the equipment-to-structure frequency ratiosγf>1.1 orγf<0.9,the non-classical damping effect is limited,and the real mode superposition approximation method provides accurate estimates.For 0.9<γf<1.1,the system may have a pair of closely spaced frequency modes,and the non-zero off-diagonal damping terms have a non-negligible effect on the damping ratios and mode shape vectors of these modes.For 0.9<γf<1.1 and the equipment-to-structure mass ratiosγm<0.07,the real mode superposition approximation method results in large errors,while the approximation method can provide an accurate estimation for 0.9<γf<1.1 andγm>0.07.Furthermore,extensive parametric analyses are conducted,where both steel structures and reinforced concrete structures with equipment with various damping ratios are considered.Finally,the finite element analysis of a five-story industrial building is adopted to validate the proposed range of applicability.

Determine the Stress Calculating Mode of Sliding Failure of Soil Mass under the Push-Extend Multi-under-Reamed Pile

Through the analysis of the sliding failure form of soil mass under the bearing push-extend reamed of Push-extend Multi-under-reamed Pile, in the paper, the law of coulomb-Mohr is used to establish a stress function and the theory of the sliding line is used to establish Prandtl regional stress field, which determines the stress calculating mode of soil mass and provides a theoretical basis for a further study of this type of pile ultimate bearing capacity of soil mass.

CALCULATION OF FUEL SLOSHING AND ITS COUPLING VIBRATION WITH A TANK

The response of fuel-tank-sloshing to aircraft maneuver is a difficult mathematical problem to be solved. Beginning with setting up the mechanical model and the respective mathematical model, this paper uses both F.E. and B.E.M. to imitate the sloshing process. The paper has developed some special techniques to deal with strong nonlinear characteristics, and provided satisfactory numerical results of displacements and stress for low frequency, resonance, high frequency and fuel tank dynamic response characteristics. The program not only assures convergence and stability of the solution, but also has the function of graphic display. It is a valuable technique to deal with the strong nonlinear oscillation of fuel tank with large amplitude and moving boundary condition on free surface.

A NEW MODEL FOR CALCULATING PROPAGATION PRESSURE AND INITIATION PRESSURE OF PIPELINES WITH A LOCAL DENT

An analytical model of a ring with six yield hinges and two deformable arc segments is presented for. the prediction of the buckle propagation pressure and initiation pressure in offshore pipelines. The configuration of a fully collapsed ring is considered as a real dumbbell shape with a line touch between two 'bells', instead of the dumbbell shape with a point touch of two diametrically opposite points. Calculations are performed assuming that the dominant effect on the plastic energy dissipation has the circumferential bending mode. For the linear strain-hardening materials it is found that theoretical predictions based on the above model for both propagation pressure and initiation nressure are in good agreement with experimental results of Kyriakides et al.

间断焊接包管加固圆钢管构件轴压极限承载力研究

为研究间断焊接包管加固杆件的轴心受压性能,设计了13组试件进行单调加载静力试验。对试件极限承载力、破坏模式、荷载-位移曲线和截面应变发展规律进行分析,对比了负载加固与非负载加固对试件极限承载力的影响。结果表明:包管构件的破坏模式可分为整体失稳破坏和内管外伸段强度破坏;包管构件内外管协同工作、共同受力,内管和外管都在屈服后发生整体失稳破坏;负载加固与非负载加固试件的极限承载力基本一致,相差2.2%,非负载加固试件与未加固试件相比,极限承载力最大提高了479.9%。根据试验结果对包管构件的ABAQUS有限元模型进行修正,并用该模型分析了各主要影响因素对包管构件极限承载力的影响规律。提出了包管构件极限承载力经验计算公式,且公式计算结果与试验结果吻合较好。

基坑坑底抗隆起稳定性研究现状与展望

基坑坑底抗隆起稳定安全系数是基坑工程设计的重要指标之一,但在实践中,现有计算方法较难满足工程需要,经常导致基坑设计造价过高。为了推动基坑坑底抗隆起稳定分析方法研究,讨论了经典方法、我国现行规范方法及其规定的安全系数限值所存在的问题,并总结了近年来各类稳定性验算方法在考虑土体强度不均匀性,支护结构嵌固深度、刚度和抗弯强度等影响因素下的改进与发展。常规基坑坑底抗隆起稳定性验算方法并未考虑基坑宽度效应的影响,因此,进一步总结了地铁车站和综合管廊等需要考虑基坑宽度效应的窄基坑抗隆起稳定性的研究进展,主要对基于地基承载力模式和圆弧滑动模式改进的窄基坑坑底隆起破坏模式和稳定性验算方法进行了讨论,以期为基坑坑底抗隆起稳定性验算方法向着科学性、合理性、准确性方向发展提供参考。

火灾中钢筋混凝土两端固结梁破坏模式变化规律

为了研究火灾过程中钢筋混凝土两端固结梁破坏模式的变化规律,利用有限元分析软件对梁内部的温度场进行分析,确定其不同耐火时刻的分布规律,利用承载力简化计算公式对火灾过程中钢筋混凝土梁不同时刻的极限承载力进行计算分析。并对上侧纵筋配筋面积、混凝土保护层厚度和混凝土强度为变换因素的三组固结梁试件进行理论分析,讨论了火灾过程中不同参数对钢筋混凝土固结梁破坏模式临界点ξ变化规律的影响。结果表明:上侧纵筋配筋面积越大,ξ点对应受火时间T越提前;混凝土保护层厚度越大,混凝土强度越高,ξ点对应受火时间T越滞后。在理论计算的基础上,为保证梁在受火两小时内发生弯曲破坏,对梁的防火设计提供了思路。本研究方法可以简化分析钢筋混凝土梁高温中破坏模式的变化规律,为火灾中构件的设计计算提供参考。

分析化学教学中引入动态缓冲容量“去公式化”计算的新策略

缓冲容量是分析化学重要内容。目前教材中缓冲容量计算没有考虑缓冲溶液与样品溶液混合时体积的变化,这种不考虑体积变化的缓冲容量被称为“静态”缓冲容量。而在实际应用中,往往缓冲溶液与样品溶液混合后的体积远远大于缓冲溶液的原始体积,此时需要考虑“动态”缓冲溶液。这里提出了一种“动态”缓冲容量问题的“去公式化”解决方案,它完全基于学科思想的底层逻辑,不会增加学生学习的记忆负担。

RC梁柱节点抗剪机理及承载力计算方法综述

对国内外关于框架结构中梁柱节点抗震性能研究成果进行总结归纳,分析了加载过程中节点的破坏形态及其抗剪机理,总结了典型的梁柱节点抗剪承载力计算模型,并基于各国规范对比了现有的抗剪承载力计算模型的适用性。对比了美国规范ACI 318-19、欧洲规范EC2的抗剪承载力计算的差异,指出了《混凝土结构设计规范》(GB 50010—2010)(2015年版)建议的梁柱节点抗剪承载力计算结果相对保守。建议适量增加节点核心区配箍率,从而提高钢筋与核心区混凝土的粘结性能,减少纵筋的粘结滑移现象。

亮氨酸与异亮氨酸太赫兹光谱的振动模式分析

氨基酸是含有碱性氨基和酸性羧基的有机化合物,是构成蛋白质的基本单位,其种类,数量和排列直接影响蛋白质的生物功能,对维持机体功能有重要意义。氨基酸分子间振动模式(扭转,氢键和集体振动)大部分处于太赫兹(THz)波段,表现出独特的吸收特征,因此,对氨基酸进行THz光谱研究,能够更全面了解生物特性。总结前人实测的亮氨酸与异亮氨酸位于0.2~2.6 THz波段的吸收谱,同时,利用量子化学计算方法解释其形成机理。使用Gaussian09软件对单分子构型模拟计算,模拟方法为半经验法(PM6),从头计算法(HF,MP2)和密度泛函理论(B3LYP,M06-2X)结合6-311+G(d,p)高斯型基组;使用Materials Studio 2019软件对晶胞构型模拟计算,模拟方法为广义梯度近似的PBE,PBEsol,RPBE和WC等四种密度泛函结合平面波基组。结果表明:单分子构型模拟均缺少吸收峰位,不同方法对同一振动模式的峰位计算不同,因此,对分子间相互作用较强的结构,进行单一方法的该构型模拟,很大程度不能正确匹配振动模式,且受原子轨道线性组合方法影响,与输入结构相比,输出结构由COO^(-)和NH_(3)^(+)基团变为COOH和NH_(2),无法体现实际振动模式;晶胞构型模拟对分子内和分子间振动模式描述,吸收峰位与实测值匹配较好,不存在质子转移情况,较好指认实测峰位的振动模式。亮氨酸与异亮氨酸使用PBEsol泛函计算结果最接近实测值,说明模拟计算需充分考虑结构与泛函的匹配性,即对结构交换关联能的描述,也说明同一泛函对异构体的普适性,此外,不能以结构优化后差异作为判断泛函是否适用的标准。晶胞构型计算结果包含分子间振动模式,是单分子构型无法得到的结果,且数据进行半峰全宽拟合,导致两种构型结果在某一实测峰位处的振动模式存在差异。

采用自复位U形连接件的装配式钢框架-复合墙结构性能研究

对于内填RC墙的框架结构,为有效减小结构的损伤,改善结构力学性能,本文研究了一种在框架与墙之间设置开缝并安装耗能连接件,能够耗散能量从而有效地保护主体结构。采用ABAQUS分析了不同类型耗能连接件的内力特性以及节点的受力破坏模式。通过在两侧开缝的密肋复合墙-钢框架结构中设置可滑移连接,实现了节点的耗能作用。研究结构表明:U形连接件水平段长度对连接件极限位移影响较大,可以通过双折线理想弹塑性荷载-位移曲线描述U形连接件在竖向压力与水平剪切作用下的荷载-位移关系。采用耗能连接件的结构在加载前期残余变形小,具有一定的自复位能力,并且能满足结构的大变形要求。通过以上分析,本文基于承载能力极限状态提出了耗能连接件的设计公式。

基于cosRMC的聚变堆输运-活化内耦合方法研究

在聚变反应堆运行过程中,中子活化会导致大量放射性核素的产生,因此活化计算在反应堆的屏蔽设计和辐射安全分析中具有重要作用。本文基于蒙特卡罗粒子输运程序cosRMC的内置燃耗求解器Depth,开发了固定源模式下的内耦合输运-活化耦合计算功能。将该程序应用于中国聚变工程试验堆(Chinese Fusion EngineeringTestingReactor,CFETR)的第一壁(First-wall,FW)材料钢和面向等离子体部件(Plasma-facing Component,PFC)材料钨,分别使用连续能量截面和多群截面进行活化计算,并与活化程序ALARA进行对比验证,发现cosRMC的计算结果与ALARA计算的结果符合良好,初步验证了开发的cosRMC程序输运-活化内耦合计算功能的正确性。与传统蒙特卡罗-活化计算程序的外耦合方式相比,内耦合方式蒙特卡罗不需要把中子能谱传给外部活化程序,而是在蒙特卡罗中子输运过程中嵌入计算活化相关的核素单群反应截面,动态更新中子能谱和材料信息,同时可以使用连续能量截面进行反应率计算,得到与实际问题的几何、能谱相关的反应截面,从而精确地考虑了共振区核截面的影响。

某型号运载火箭发射场模态试验技术

目的在取消传统的自由-自由状态全箭模态试验的前提下,通过发射场自由-固支状态模态试验获取某型号运载火箭的模态参数,为火箭总体设计提供依据。方法基于成熟型号相同部段的仿真模型和模态试验数据基础,建立高精度的全箭三维动力学模型,预示结构模态参数,为发射场模态试验的激励方案和测量方案等提供指导。通过多点全相干步进正弦激励模态试验方法,运用测试得到的“伪频响函数”进行参数识别,从而获取结构的模态参数。结果获得了发射场竖立状态下全箭前4阶弯曲模态和1阶扭转模态,基于“伪频响函数”的识别结果与真实频响函数的识别结果频率最大偏差为0.82%,阻尼比最大偏差为1.89%。结论某型号运载火箭的发射场模态试验为火箭总体设计提供了关键参数,型号首飞成功验证了该技术的可靠性,也为获取火箭模态参数开辟了一条新的路径。

基于拓展传输线理论的高压交流电缆输入阻抗和金属护套电压计算分析

基于电缆外部精确电磁场分析方法,提出了一种拓展传输线理论,能够计及广义大地参数和电磁暂态仿真的影响计算电缆输入阻抗。采用电磁暂态仿真程序EMTP-RV,利用拓展传输线理论对典型高压交流电缆开展输入阻抗和金属护套电压特性研究,研究当合闸于空载电缆时的金属护套暂态电压特性;通过对正序激励下的电缆输入阻抗模值-频率响应进行研究,分析由三相金属护套交叉互联产生的多种传播模态。采用拓展传输线理论计算的结果与使用基于矩量法的改进数值电磁场分析方法(method of moments-surface admittanceoperator,MoM-SO)的计算结果基本拟合,与现有电磁暂态仿真软件中(ATP-EMTP、PSCAD/EMTDC和EMTP-RV)的CableConstants子程序计算结果出现显著性差异。当合闸于空载电缆线路时,受大地电阻率影响,采用Cable Constants子程序计算出的电缆金属护套最大暂态电压与采用拓展传输线理论所得出的结果相比,计算偏差位于1.8%至135%之间。考虑输入阻抗计算和暂态仿真的关键性差异,研究内容对今后开展高压交流电缆参数计算、模态分析、电磁暂态仿真、过电压研究具有参考意义。

全轻页岩陶粒混凝土与钢筋的极限粘接强度影响研究

全轻页岩陶粒混凝土和钢筋之间的粘接作用较为复杂,粘接强度受钢筋类型、锚固长度、混凝土强度等因素影响,通常采用中心拉拔试验方法分析全轻页岩陶粒混凝土的粘接效果。对此,采用该方法进行了12组不同标准的全轻页岩陶粒钢筋混凝土试件粘接强度测试试验,分析了试件拉拔破坏和劈裂破坏二种破坏形态,对比了不同钢筋直径、钢筋类型和混凝土强度等级下试件的粘接强度变化,并提出了更加合理的极限粘接强度计算方式。以期促进全轻页岩陶粒混凝土的深入研究和在建筑行业的广泛应用。

钢桁腹-混凝土组合箱梁局部外接节点静载试验及极限承载力计算研究

为了解钢桁腹-混凝土组合箱梁(顶、底板为混凝土结构,腹杆为钢结构)外接节点在水平荷载作用下的受力性能,以某钢桁腹-混凝土组合箱梁桥方案为背景,选取钢腹杆轴力最大节点设计、制作缩尺比为1∶3的钢桁腹-混凝土组合箱梁局部外接节点试件(由混凝土弦杆、方形钢腹杆、节点板组成,原混凝土板简化为混凝土弦杆)并开展静载试验,分析外接节点试件静载试验现象及破坏模式、荷载~位移曲线,以及混凝土弦杆、节点板和钢腹杆的应力分布规律,并基于有效宽度法及撕裂面法与最大强度准则提出外接节点极限承载力计算方法。结果表明:外接节点试件的破坏模式为节点板拉剪断裂失效,极限承载力为设计荷载的5.71倍,承载能力满足要求;混凝土弦杆压应力沿加载方向逐渐减小,沿竖直方向从上往下逐渐增大;节点板应力沿加载方向总体上先增后减,外露节点板是节点受力的关键构件;外接节点极限承载力由节点板和钢腹杆中较弱者控制,采用所提出的计算方法得到的外接节点极限承载力计算值与试验结果相差小于6%。

露天矿山生态修复后碳汇调查及计算方法研究

为了推动“双碳”目标下矿山生态修复及碳汇研究,以江苏省长江沿线废弃露天矿山为对象展开相关研究。文章总结了矿山生态修复现状,分析了固碳机制与碳库类型,确定了现场调查模式,结合地形因素提出了矿山修复后的碳汇量计算方法。文章提出的矿山碳汇调查模式及碳汇量计算方法,旨在为修复矿山的碳汇研究提供参考与依据,从生态固碳角度为废弃矿山的土壤重构和植被恢复工作提供思路。

基于动力学模态分解的空化水射流非定常流场演化分析

空化水射流具有流速高、湍流强等特点,其空化流动结构十分复杂。因此,准确、快速地从非定常流场的海量数据中提取关键信息,并分析空化水射流的流动特性十分必要。基于FBDCM模型对RNG模型的湍流黏度进行修正,并考虑剪切应力对空泡形成的影响,对空化模型进行修正,与试验结果进行对比;采用动力学模态分解(DMD)方法对空化流场的空泡体积分数场进行模态分解。结果发现:1阶模态为平均流场,是流场的主要结构;2阶模态与空化云周期性脱落、溃灭的动力学行为有关;3、4阶模态表现出流场的高频行为;随着进口压力的增大,空泡脱落与溃灭的演变程度越来越剧烈,空泡尺寸与空穴长度逐渐增加,而2阶模态的频率逐渐降低,使得空化射流的流动周期变长。最后,将DMD重构流场与真实流场进行对比发现,随着进口压力的增加,DMD重构流场的误差增大,不过重构流场的最大误差仍低于1%,表明DMD方法能够准确地提取空化流场的流动特征。

Research on the influence of flexible wheelset rotation effect on wheel rail contact force

Purpose-Under the high-speed operating conditions,the effects of wheelset elastic deformation on the wheel rail dynamic forces will become more notable compared to the low-speed condition.In order to meet different analysis requirements and selecting appropriate models to analyzing the wheel rail interaction,it is crucial to understand the influence of wheelset flexibility on the wheel-rail dynamics under different speeds and track excitations condition.Design/methodology/approach-The wheel rail contact points solving method and vehicle dynamics equations considering wheelset flexibility in the trajectory body coordinate system were investigated in this paper.As for the wheel-rail contact forces,which is a particular force element in vehicle multibody system,a method for calculating the Jacobian matrix of the wheel-rail contact force is proposed to better couple the wheel-rail contact force calculation with the vehicle dynamics response calculation.Based on the flexible wheelset modeling approach in this paper,two vehicle dynamic models considering the wheelset as both elastic and rigid bodies are established,two kinds of track excitations,namely normal measured track irregularities and short-wave irregularities are used,wheel-rail geometric contact characteristic and wheel-rail contact forces in both time and frequency domains are compared with the two models in order to study the influence of flexible wheelset rotation effect on wheel rail contact force.Findings-Under normal track irregularity excitations,the amplitudes of vertical,longitudinal and lateral forces computed by the flexible wheelset model are smaller than those of the rigid wheelset model,and the virtual penetration and equivalent contact patch are also slightly smaller.For the flexible wheelset model,the wheel rail longitudinal and lateral creepages will also decrease.The higher the vehicle speed,the larger the differences in wheel-rail forces computed by the flexible and rigid wheelset model.Under track short-wave irregularity excitations,the vertical force amplitude computed by the flexible wheelset is also smaller than that of the rigid wheelset.However,unlike the excitation case of measured track irregularity,under short-wave excitations,for the speed within the range of 200 to 350 km/h,the difference in the amplitude of the vertical force between the flexible and rigid wheelset models gradually decreases as the speed increase.This is partly due to the contribution of wheelset's elastic vibration under short-wave excitations.For low-frequency wheel-rail force analysis problems at speeds of 350 km/h and above,as well as high-frequency wheel-rail interaction analysis problems under various speed conditions,the flexible wheelset model will give results agrees better with the reality.Originality/value-This study provides reference for the modeling method of the flexible wheelset and the coupling method of wheel-rail contact force to the vehicle multibody dynamics system.Furthermore,by comparative research,the influence of wheelset flexibility and rotation on wheel-rail dynamic behavior are obtained,which is useful to the application scope of rigid and flexible wheelset models.