Experimental Study on Damage Properties of Rocks Under Dynamic Loading

The damage properties of two types of rocks under dynamic loading are studied. The shock induced experiments are done using planar impact technique on the one? stage light gas gun, and the ultrasonic tests on the damaged rocks have been made by use of the ultrasonic pulse? transmission method. The shock induced damage of rock is related to the shock speed and the attenuation coefficient of sonic wave, and the latter reflects the damage degree in rock fairly well. The attenuation coefficient α can be used as main damage parameter for constructing damage model of rock under dynamic loading.

Test and numerical investigations on static and dynamic characteristics of extra-wide concrete self-anchored suspension bridge under vehicle loads

The present work is aimed at studying the mechanic properties of the extra-wide concrete self-anchored suspension bridge under static and dynamic vehicle loads. Based on the field test using 12 heavy trucks and finite element simulations, the static deformations of different components, stress increments and distributions of the girder, as well as the vibration characteristics and damping ratio of the Hunan Road Bridge were analyzed, which is the widest self-anchored suspension bridge in China at present. The dynamic responses were calculated using the Newmark-β integration method assisted by the simulation models of bridge and vehicles, the influences on the dynamic impact coefficient(DIC) brought by the vehicle parameters, girder width, eccentricity travel and deck flatness were also researched. The spatial effect of the girder is obvious due to the extra width, which performs as the stress increments distribute unevenly along the transverse direction, and the girder deflections and stress increments of the upper plate change as a "V" and "M" shape respectively under the symmetrical vehicle loads affected by the shear lag effect, cross slope and local effect of the wheels, the maximum of stress increments are located in the junctions with the inner webs. The obvious girder torsional deformation and the apparent unevenness of the hanger forces between the two cable planes under the eccentric vehicle loads, together with the mode shapes such as the girder transverse bending and torsion which appear relatively earlier, all reflect the weakened torsional rigidity of the extra-wide girder. The transverse displacements of towers are more obvious than the longitudinal ones. As for the influences on the DIC, the static effect of the heavier vehicles plays a major role when pass through with a higher speed and the changes of vehicle suspension stiffness generate greater impacts than the suspension damp. The values of DIC in the vehicle-running side during the eccentric travel, affected by the restricts from the static effects of the eccentric moving trucks, are significantly smaller than the vehicle-free side, the increase in the road roughness is the most sensitive one among the above influential factors. The results could provide references for the design, static and dynamic response analysis of the similar extra-wide suspension bridges.

Dynamic behavior of single-layer latticed cylindrical shells subjected to seismic loading

The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of single-layer latticed cylindrical shells are analyzed by the finite element method using ANSYS software.In the numerical study,where hundreds of cases were analyzed,the parameters considered included rise-span ratio,length-span ratio,surface load and member section size.Moreover,to better define the actual behavior of single-layer latticed shells,the study is focused on the dynamic stress response to both axial forces and bending moments.Based on the numerical results,the effects of the parameters considered on the stresses are discussed and a modified seismic force coefficient method is suggested.In addition,some advice based on these research results is presented to help in the future design of such structures.

Study on dynamic response of multi-degree-of-freedom explosion vessel system under impact load

In order to study the dynamic response and calculate the axial dynamic coefficient of the monolayer cylindrical explosion vessel,the wall of vessel is simplified as a multi-degree-of-freedom(MDoF) undamped elastic foundation beam.Decoupling the coupled motion equation and using Duhamel's integrals,the solutions in generalized coordinates of the equations under exponentially decaying loads,square wave loads and triangular wave loads are calculated.These solutions are consistent in form with the solutions of single-degree-of-freedom(SDoF) undamped forced vibration simplified model.Based on the model,equivalent MDoF design method(also called MDoF dynamic coefficient method) of cylindrical explosion vessel is proposed.The traditional method can only predict the dynamic coefficient of torus portion around the explosion center,but this method can predict that of the vessel wall at any axial n dividing point position.It is verified that the prediction accuracy of this model is greatly improved compared with the SDoF model by comparing the results of this model with SDoF model and numerical simulation in different working conditions.However,the prediction accuracy decreases as the scaled distance decreases and approaches the end of the vessel,which is related to the accuracy of the empirical formula of the implosion load,the simplification of the explosion load direction,the boundary conditions,and the loading time difference.

欧洲规范铁路桥梁动力分析竖向荷载取值研究

为有助于推动海外工程顺利实施,解决海外工程结构设计中的部分问题,开展国外标准规范系统研究是十分必要的,进而吸收与借鉴国际标准的先进经验,同时增强国际竞争力。针对铁路桥梁动力分析中欧洲规范竖向荷载的相关规定进行了详细研究,探讨分析了其规定差异性,提出了对国际工程设计咨询具有指导价值的结论。有助于解决涉外工程结构分析中荷载计算问题,有利于我国结构设计行业对外交流,为进一步推动海外工程的顺利实施奠定基础。

Effect of friction coefficients on the dynamic response of gear systems

The inevitable deterioration of the lubrication conditions in a gearbox in service can change the tribological properties of the meshing teeth. In turn, such changes can significantly affect the dynamic responses and running status of gear systems. This paper investigates such an effect by utilizing virtual prototype technology to model and simulate the dynamics of a wind turbine gearbox system. The change in the lubrication conditions is modeled by the changes in the friction coefficients, thereby indicating that poor lubrication causes not only increased frictional losses but also significant changes in the dynamic responses. These results are further demon-strated by the mean and root mean square values calculated by the simulated responses under different friction coefficients. In addition, the spectrum exhibits significant changes in the first, second, and third harmonics of the meshing components. The findings and simulation method of this study provide theoretical bases for the development of accurate diagnostic techniques.

Effects of fragments on W-DLC films properties under boundary lubrication condition in the friction system

Abstract Effects of film fragments in the friction system on friction and wear properties of tungsten doped diamond-like carbon films （W-DLC） were studied in the condition of boundary lubrication. It could be observed that the average friction coefficient was increased after introducing film fragments into the friction system, where these film fragments can accelerate the breaking of the extreme thin oil film which could separate two friction surfaces when the system is under boundary lubrication conditions. The increasing friction load can accelerate the friction ehenfieal reaction on the friction interface and lead to the crushing effect on film fragments, which decreased the friction coefficient of friction system. It was also found that the wear width, depth, and volume of the film increased by introducing film fragments and applying great load.

高速铁路无砟轨道车辆荷载传递特性研究

为进一步探讨无砟轨道荷载设计参数取值,为我国时速400 km及以上高速铁路建设提供重要理论支撑,通过开展无砟轨道静力分析以及钢轨焊缝、车轮扁疤激励下车辆-轨道动力相互作用,揭示列车静、动力载荷特征及传递规律;同时根据轨道承载特点和无砟轨道设计原理,提出车辆竖向设计荷载取值建议。研究结果表明:(1)高速列车车轮扁疤和钢轨焊缝不平顺将造成显著的轮轨冲击,其轮载动载系数最大可达5.79,远高于现行规范取值;扣件系统对扁疤和焊缝不平顺引起的轮轨力高频成分衰减作用明显,扣件支反力的动载系数最大为2.64;(2)钢轨焊缝不平顺引起的轮轨冲击力随着车速提高以及焊缝不平顺幅值的增大而迅速增大,建议500 km/h及以下高速铁路的钢轨焊缝平直度标准取0.2 mm/m;(3)列车轮载通过扣件支反力作用于轨道板,从传递特性的角度来说,以扣件支反力作为轨道板竖向设计荷载更为合理,其动载系数可取3.0,且能满足400 km/h及以上高速铁路的行车需求。

近地面大长宽比跟踪式光伏阵列风洞试验研究

为明确近地面风场对跟踪式光伏结构风荷载取值的影响,本文基于风洞试验和计算流体力学(CFD)模拟对单排光伏组件的倾角、风向角、离地高度展开分析,并在此基础上研究了多排光伏阵列在不同风向角下,其遮挡效应对体型系数取值的影响.结果表明:单排光伏组件的表面风压符合梯形分布方式;多排光伏阵列中上游组件对下游的遮挡程度会随倾角的增大而增长,且后排光伏组件体型系数随着前排遮挡的增多逐渐趋于稳定;离地高度对光伏组件及阵列的体型系数存在一定的影响.

计及恒定减载桨距角控制的风电高占比电力系统频率动态特性分析

在新型电力系统中,风电主动参与电网频率调节已成为必然,如何评估风电参与调频对频率动态特性的影响也成为了研究热点。围绕现有的风电调频措施,提出一种可以在额定风速前减少变桨动作次数的恒定减载桨距角的改进风电机组变桨控制,推导出该控制下风电机组参与一次调频的调差系数表达式。基于此构建了含恒定减载桨距角控制的电力系统频率响应模型。推导出频率动态特性指标的解析表达式,揭示了风速、初始桨距角等对风电机组调差系数及频率动态特性的影响机理。通过改进的IEEE三机九节点系统验证了所构建频率等值模型的准确性以及所提调频方法的有效性和可行性。

重载与中强地震联合作用下的曲线独柱墩桥梁倾覆性分析

为探讨移动车辆和中强地震联合作用对曲线梁桥的抗倾覆影响,建立车-桥-地震分析模型,提出考虑地震作用的曲线梁桥车-桥耦合振动分析方法。以多跨曲线连续梁桥为研究对象,对比分析中强地震和重载车辆偏载组合作用下的支座反力和主梁倾覆时整体转角大小。研究地震动类型、峰值、车辆关键参数等因素对曲线梁桥倾覆稳定性的影响。结果表明:不同车辆和地震荷载组合会改变桥梁的受力情况,纵向间隔2 m的3辆100 t车辆以3 m/s速度行驶时,三跨曲线梁桥的倾覆最明显;综合考虑重载及地震联合作用,对抗倾覆性规范中的稳定系数计算公式进行了修正;分析了五跨曲线梁桥中墩支座偏心距对抗倾覆稳定系数的影响,计算结果表明中墩两相邻支座设置偏心时曲线桥最大抗倾覆系数为1.55。

强夯动荷载作用方向对黄土边坡稳定性的影响分析

为进一步研究强夯对周边黄土边坡稳定性的影响,采用极限平衡圆弧条分法对强夯作用下的边坡安全系数进行推导计算。结合工程实例,使用TC-4850爆破测振仪对现场监测点进行加速度测试。考虑高程差和测点距离的共同影响,采用MATLAB编程对现场数据进行多元回归分析,求出强夯作用下边坡质点振动加速度解析式。在求得最小安全系数的基础上,研究不同强夯动荷载方向对黄土边坡稳定性的影响。研究结果表明:在相同荷载作用下,强夯动荷载方向与水平轴正方向夹角为0°、45°、60°、270°、315°、330°、360°时,安全系数均小于等于1.00,且随着拟静力系数不断增大,安全系数越来越小。强夯动荷载方向与水平轴正方向夹角为90°、135°、150°、180°、225°、240°时,安全系数均大于1.05。随着拟静力系数不断增大,安全系数也随之增大。该方法简单易行,便于计算,可用于黄土边坡实际工程。

考虑瓦块子结构的可倾瓦轴承广义完整动特性系数研究

针对因忽略瓦块子结构动力学特性而导致常规8系数无法分析瓦块摆振特性及其稳定性的问题,提出考虑瓦块子结构的可倾瓦轴承广义完整动特性系数表征方法。以瓦间承载的四瓦可倾瓦轴承为研究对象,采用差分概念法计算了其广义完整动特性系数,利用线性和非线性方法计算得到的小扰动响应对比验证了计算模型的正确性,研究了轴承结构参数和运行工况对可倾瓦轴承动特性系数的影响规律。研究结果表明:承载瓦的稳定性高于非承载瓦;重载工况下非承载瓦易发生失稳故障;转速过高会降低转子轴承系统的减振能力;存在一个最佳支点系数可以使各瓦块的角刚度最大;增大长径比、预载荷系数和瓦包角,减小轴承间隙比可以提高轴承的刚度系数、阻尼系数以及各瓦块的角刚度系数、角阻尼系数,轴承间隙对动特性系数的影响最显著。

爆炸荷载线性强化抗力模型梁构件动力系数研究

目前梁构件抗爆设计动力系数计算常采用理想弹塑性抗力模型,制约着塑性强化抗力构件的精细化抗爆设计。为解决线性强化抗力类型梁构件的爆炸作用动力系数计算问题,由抗力强化系数和阻尼比数值大小关系,分三种情况推导了柔性和刚性两类构件关于延性比的动力系数解析解。有限元分析及规范对比算例表明,本文推导理论公式精度较高,与抗爆设计规范公式计算结果趋势相似;延性比为1时,抗力强化系数与动力系数无关;延性比大于1且抗力强化系数小于0.01时,可忽略抗力强化系数的影响;延性比大于2时,需考虑阻尼参数后完成抗爆设计分析;延性比大于3时且抗力强化系数大于0.1时,线性强化抗力模型具有较好经济效益。

偏心误差对分扭-并车齿轮传动系统均载性能的影响

为研究分扭-并车齿轮传动系统中不同级齿轮偏心误差对各支路均载性能的影响,对其不均载成因进行了分析。采用集中质量法建立含偏心误差的弯扭耦合动力学模型,利用Newmark-β法求解动力学方程,计算了各分支均载系数,对比了有无偏心误差时动态均载系数的变化;通过两组数值仿真,探究了不同级齿轮偏心误差对各支路均载系数的影响情况。结果表明,齿轮偏心误差加剧了系统各支路均载系数的幅值波动,且闭环布置的分扭-并车齿轮传动系统右支路均载系数小于左支路;各级齿轮偏心误差单独作用时,偏心误差对含误差的齿轮级所在支路均载性能影响更大;各级偏心误差共同作用时,传动系统并车级均载性能的稳定性劣于分扭级,表明动力传递过程中误差具有累积效应。研究结果为选择性减小不同级齿轮偏心误差、有效改善传动系统各支路的均载性能提供了依据。

飞机着陆数值仿真及机场道面动载特性研究

为研究飞机着陆滑跑过程民用机场道面动荷载特性,以Boeing737-800机型为例,基于动力学仿真软件VI-Aircraft,建立了机身、起落架及轮胎三维数值仿真模型,根据某机场道面实测平整度数据创建道面仿真模型,形成了一套考虑气动力变化特性的飞机着陆冲击仿真方法,并通过相关起落架系统落震试验以及飞机-地面运动学理论解析两方面验证了仿真方法的可靠性。此外,系统讨论了各类着陆状态参数对道面动载特性的影响,明确了不同着陆状态参数影响下道面动载系数量化取值范围,揭示了各着陆状态参数对道面动载响应的影响规律及影响机理。研究结果表明:随着陆质量、接地速度及滚转角增大,道面动载响应显著增强;随着陆航向速度增大,道面动载响应明显减小;而随俯仰角增大,道面动载响应整体呈现波动减小的趋势。飞机着陆过程中道面动载系数敏感性因素从大到小依次为:航向速度、着陆质量、接地速度、滚转角与俯仰角,充分考虑各着陆状态参数影响,一般情况下道面动载系数DIM分布区间为1.18~1.80。研究成果可进一步拓展用于飞机着陆跑道桥的分析研究。

行星传动系统均载与动载系数试验测量改进设计

试验测量行星传动系统均载与动载系数的精准度是评价系统动态性能的基础。针对现有行星传动系统均载与动载系数测量方法存在灵敏度与精度欠佳、系数测试算法缺失、测试应力点存误等问题,本文提出了一种方便、实用且具有高精度的行星传动系统均载与动载系数测试方法,定义了系统系数的测试算法与概念,明确了精确应力测试位置点及不同位置间差异性,采用应变片电桥传感器串并联设计,实现了拉压应力叠加、温度补偿以及繁琐标定免除等优点,为精准测取行星传动系统均载与动载性能提供了重要的理论基础和技术手段。

强对流天气下输电塔-线体系倒塌破坏与风雨组合系数研究

极端气象灾害给输电线路的安全运行带来了严重威胁,相对低电压等级的角钢输电塔出现了较高频次的倒塌破坏事故。基于现象学非线性滞回模型,开展了输电塔-线体系在强对流天气下的倒塌破坏研究,总结了雨荷载对输电塔响应的影响规律;基于风雨气象记录,进行了风雨组合分析并提出了风雨组合系数。结果表明,在极端强对流天气中,所研究输电塔的薄弱部位主要为第3、4节段,该部位的大量斜材和少量主材陆续屈曲是造成输电塔倒塌的主要原因,极端风雨气象条件下有必要考虑雨荷载对输电塔-线体系响应的影响。不同重现期下风速和雨量的组合值均小于其相应的标准值,该地区50 a重现期下风速和雨量的组合系数建议值分别为1.0和0.7。

某上承式箱形拱桥荷载试验研究

为探究某评定标度为4类桥的上承式箱形拱桥的实际承载力,确定该桥的实际受力状况,为后期的加固研究和监控提供科学依据。本文采用现场荷载试验结合有限元分析的方法获取实测值和理论值,静动载试验分别测量挠度、应变和自振特性、冲击系数等参数,再引入静力荷载试验效率和校验系数等参数判定结构特性是否仍满足荷载为公路Ⅰ级的要求。结果表明:部分工况挠度校验系数和应变校验系数不满足规范中0.50<η≤1.00和0.50<η<0.90,但都满足不大于1的要求,表明结构刚度尚有富余;且相对残余挠度和相对残余应变都在20.0%以内,表明结构尚处于弹性范围工作;脉动、跑车和跳车试验结果显示结构的整体刚度优于理论,动力性能良好,且行车平顺。

高墩大跨连续刚构桥的荷载试验研究

为探明某高墩大跨连续刚构桥在正常运营状态及最不利受力状态下的动静态荷载特性,基于成桥荷载试验方法,开展不同车辆位置、车速等条件下大跨连续刚构桥动静荷载现场试验。试验主要包括正载及偏载两种情况,静荷载试验测试了这两种情况下的主梁应变与挠度,动荷载试验分别在20、30、40 km/h车速下,通过无障碍行车试验和刹车试验,测试了桥梁的冲击系数、自振频率及动应变。在采集处理完现场数据后,将其与有限元软件的理论计算结果进行对比分析。研究结果表明:该连续刚构桥在正载及偏载两个工况下,挠度和应变实测值均小于理论计算值,相对残余应变最大值为18.8%,相对残余挠度最大值为11.71%,均不超过20%;在动载试验中,主桥一、二、三阶竖向实测振动频率均大于理论计算值;该连续刚构桥承载能力满足要求。