ANALYSIS OF THE LARGE DEFLECTION DYNAMIC PLASTIC RESPONSE OF SIMPLY-SUPPORTED CIRCULAR PLATES BY THE“MEMBRANE FACTOR METHOD”

Based on energy equilibrium,a new procedure called the Membrane Factor Method is devel- oped to analyze the dynamic plastic response of plates with deflections in the range where both bending mo- ments and membrane forces are important.The final deflection of a simply -supported circular rigid-plastic plate loaded by a uniformly distributed impulse is obtained.In comparison with other approximate solutions, the present results are found to be simpler and in better agreement with the corresponding experimental values reoorded by Florence.

Dynamic Characteristics Analysis of Ice-Adhesion Transmission Tower-Line System under Effect of Wind-Induced Ice Shedding

The tower line system will be in an unsafe status due to uniform or uneven fall of ice coating which is attached to the surface of tower and lines.The fall of ice could be caused by wind action or thermal force.In order to study the dynamic characteristics of the self-failure of the transmission line under the action of dynamicwind load,a finite elementmodel of the two-span transmission tower line system was established.The birth and death element methods are used to simulate the icing and shedding of the line.Tensile failure strength is the shedding criterion for ice coating.The fluctuating wind speed time history of the tower line systemis first simulated,and then the fluctuating wind and the average wind are superimposed to generate the instantaneous wind speed and converted into wind load.The dynamic response of the transmission tower line systemunder iced coupling with different wind speeds and different thicknesses of ice coating was studied.This is the first attempt that the coupling dynamic response of the icing shedding and wind load for the transmission tower-line system is discussed in this paper.In addition,the dynamic characteristics of wind are included.In particular,the limiting mechanical conditions are considered.According to the simulation results,it is found:because of the ice shedding,the stress of the conductor changes obviously in the first 20 seconds,and the ground wire changes sharply in the first two seconds;the icing of the conductor(ground)wire is gradually deicing under the action of wind vibration;the displacement of tower top increases with the increase of wind speed and icing thickness.

Dynamic plastic response of clamped stiffened plates with large deflection

Study on the dynamic response, and especially the nonlinear dynamic response of stiffened plates is complicated by their discontinuity and inhomogeneity. The finite element method (FEM) and the finite strip method are usually adopted in their analysis. Although many useful conclusions have been obtained, the computational cost is enormous. Based on some assumptions, the dynamic plastic response of clamped stiffened plates with large deflections was theoretically investigated herein by a singly symmetric beam model. Firstly, the deflection conditions that a plastic string must satisfy were obtained by the linearized moment-axial force interaction curve for singly symmetric cross sections and the associated plastic flow rule. Secondly, the possible motion mechanisms of the beam under different load intensity were analysed in detail. For structures with plastic deformations, a simplified method was then given that the arbitrary impact load can be replaced equivalently by a rectangular pulse. Finally, to confirm the validity of the proposed method, the dynamic plastic response of a one-way stiffened plate with four fully clamped edges was calculated. The theoretical results were in good agreement with those of FEM. It indicates that the present calculation model is easy and feasible, and the equivalent substitution of load almost has no influence on the final deflection.

ANALYSIS OF THE LARGE DEFLECTION DYNAMIC RESPONSE OF RIGID-PLASTIC CIRCULAR PLATE RESTING ON FLUID

A study is presented for the large deflection dynamic response of rigid- plastic circular plate resting on potential fluid under a rectangular pressure pulse load. By virtue of Hankel integral transform technique,this interaction problem is reduced to a problem of dynamic plastic response of the plate in vacuum.The closed-form solutions are derived for both middle and high pressure loads by solving the equations of motion with the large deflection in the range where both bending moments and membrane forces are important.Some numerical results are given.

Deflection amplification factor for estimating seismic lateral deformations of RC frames

Different values have been assigned to the ratio of the defl ection amplifi cation factor(Cd) to the response modifi cation factor(R) for a specifi ed force-resisting system in the seismic design provisions while the same application is defi ned for it. An analytical study of the seismic responses of several reinforced concrete frames subjected to a suite of earthquake records performed in this research indicate that the stories’ overstrength and stiffness distribution along the structural height can affect local defl ections more than global ones. Therefore, the Cd/R ratio is calculated based on the ratio of both maximum inelastic to maximum elastic displacements and interstory drifts. Due to damage concentration in some specifi c stories, the defl ection amplifi cation factor calculated based on inelastic interstory drifts was larger than that of the inelastic displacements. Consequently, a minimum value of 1.0 is recommended for the Cd/R ratio in order to estimate maximum inelastic drifts. The ratio of inelastic to elastic displacement was generally found to increase slightly along the structural height for the studied RC models. In addition, it was detected that the story damage indices of the studied RC frames decrease when the inverted value of inelastic interstory drift ratios are increased through a(negative) power form.

Experimental investigation of the dynamic behavior of railway track with sleeper voids

The deterioration of the sleeper support on the ballasted track begins with the accumulation of sleeper voids.The increased dynamic loading in the voided zone and the ballast contact conditions cause the accelerated growth of the settlements in the voided zones,which results in the appearance of local instabilities like ballast breakdown,white spots,subgrade defects,etc.The recent detection and quantification of the sleeper voids with track-side and onboard monitoring can help to avoid or delay the development of local instabilities.The present paper is devoted to the study of the dynamic behavior of railway track with sleeper voids in the ballast breakdown zone.The result of the experimental track-side measurements of rail acceleration and deflection is presented.The analysis shows the existence of the dynamic impact during wheel entry in the voided zone.However,the measured dynamic impact is subjected to the bias of the track-side measurement method.Both the mechanism of the impact and the measurement aspects are explained by using the one-beam model on viscoelastic foundation.The void features in the dynamic behavior are analyzed for the purpose of track-side and onboard monitoring.A practical method of the void parameter quantification is proposed.

Observation and modeling of tide- and wind-induced surface currents in Galway Bay

A high-frequency radar system has been deployed in Galway Bay, a semi-enclosed bay on the west coast of Ireland. The system provides surface currents with fine spatial resolution every hour. Prior to its use for model validation, the accuracy of the radar data was verified through comparison with measurements from acoustic Doppler current profilers （ADCPs） and a good correlation between time series of surface current speeds and directions obtained from radar data and ADCP data. Since Galway Bay is located on the coast of the Atlantic Ocean, it is subject to relatively windy conditions, and surface currents are therefore strongly wind-driven. With a view to assimilating the radar data for forecasting purposes, a three-dimensional numerical model of Galway Bay, the Environmental Fluid Dynamics Code （EFDC）, was developed based on a terrain-following vertical （sigma） coordinate system. This study shows that the performance and accuracy of the numerical model, particularly with regard to tide- and wind-induced surface currents, are sensitive to the vertical layer structure. Results of five models with different layer structures are presented and compared with radar measurements. A variable vertical structure with thin layers at the bottom and the surface and thicker layers in the middle of the water column was found to be the optimal layer structure for reproduction of tideand wind-induced surface currents. This structure ensures that wind shear can properly propagate from the surface layer to the sub-surface layers, thereby ensuring that wind forcing is not overdamped by tidal forcing. The vertical layer structure affects not only the velocities at the surface layer but also the velocities further down in the water column.

Study of the Dynamic Characteristics of A Cone-Shaped Recovery System on Submarines for Recovering Autonomous Underwater Vehicle

National navies equip their submarines with Autonomous Underwater Vehicle(AUV)technology.It has become an important component of submarine development in technologically-advanced countries.Employing advanced and reliable recovery systems directly improves the safety and operational efficiency of submarines equipped with AUVs.In this paper,based on aerial refueling technology,a cone-shaped recovery system with two different guiding covers(closed structure and frame structure)is applied to the submarine.By taking the Suboff model as the research object,STAR-CCM was used to study the influence of the installation position of the recovery system,and the length of the rigid rod,on the Suboff model.It was found that when the recovery system is installed in the middle and rear of the Suboff model at the same velocity and the same length of the rigid rod,the Suboff model has the good stability and less drag.It experiences the largest drag when being installed in the front of the rigid rod.Moreover,when the recovery system is installed in the front and middle of the rigid rod,the drag increases as its length increases,and the lift decreases as its length increases.Compared with the closed structure guiding cover,the Suboff model will have less drag and better stability when the recovery system uses the frame structure guiding cover.Besides,the deflection and vibration of the rigid rod were also analyzed via mathematical theory.

Influence of tool deflection on micro channel pattern of 6:4 brass with rectangular tool

Machining experiment of micro channel structure with 6:4 brass was carried out by shaping process using a single crystal diamond tool. FEM simulation using solid cantilever beam model was analyzed. In result of experiment, tool deflection is observed as machining characteristics through result of experiments such as surface roughness, cutting force and burr formations. And the influence of tool deflection is experimentally proved.

结构刚塑性动力解的弹性补偿

近年来,我国学者以膜力因子法和饱和分析方法相结合为理论工具,对梁、板等结构件在脉冲载荷作用下的塑性大变形行为作了全面深入的研究,为脉冲加载下结构的最终挠度提供了优于历史上各种刚塑性近似解的最佳刚塑性预测公式。然而,由于实际工程应用中金属结构弹塑性动力响应的复杂性和数值模拟的局限性,与考虑材料弹性效应的结果相比,刚塑性解对脉冲加载下结构所预测的最终挠度的误差有多大,是一个亟待解决的关键问题。对这个问题的首阶段研究成果厘清了材料弹性对脉冲加载下结构塑性动态大变形的影响,定量评估了由最佳刚塑性理论解与弹塑性数值模拟得到的最终挠度预测结果之间的差异。在此基础上,提出了补偿弹性效应的策略和方法,即:在已有的最佳刚塑性解预测的挠度基础上添加一个补偿项,将补偿项表达为脉冲载荷强度的效应与结构自身刚度的效应分离的变量函数,并尽量减少待定系数/指数的数量,以求表达式的简洁;根据这些原则在金属结构的主要工程应用领域内选定结构刚度和外载参数的变化范围,对固支梁和固支方板的案例实施拟合与补偿,最后得到了对梁和板增添补偿项后的简单而实用的最终挠度预测公式,其相对误差在3%的范围之内,很适合工程设计应用。文末列表给出了符号与公式的一览,并对梁和方板的结果作了综合和比较。

不同冲击载荷下典型路面结构的动态弯沉响应

为研究不同冲击载荷下典型路面结构的动态弯沉响应数值规律,开展试验勘测等级公路信息,分析实测数据并归纳出等级公路承载能力与路面结构的相关关系,基于统计规律构建了承载力维度下的典型路面结构。建立包含塑性损伤的多层连续道路结构模型,通过比对仿真结果与试验数据验证模型的有效性,研究模型大小对不同冲击载荷作用下路面弯沉仿真结果的影响。开展不同冲击载荷下典型路面结构的弯沉响应规律研究,计算出冲击载荷作用下路面峰值沉降与残余沉降数值,揭示不同冲击载荷下典型路面结构弯沉响应内在规律。研究结果表明:包含塑性损伤的多层连续道路结构模型能够准确反映冲击载荷下路面真实动态弯沉响应;不同冲击载荷下,路面沉降中塑性沉降量占比与冲击载荷幅值满足双指数方程;百吨级范围内,路面沉降中弹性回弹部分随冲击载荷幅值增大而增大,塑性沉降部分与载荷幅值呈指数正相关关系;百吨级以上,路面沉降中弹性回弹量达到上限1.2~1.3 mm,路面塑性沉降量与载荷幅值呈线性关系。开展的不同冲击载荷下模型大小对仿真结果的影响规律研究可为有限元仿真中确定合适的仿真模型尺度提供参考。

面向齿廓变位的圆柱直齿轮啮合动态特性研究

为研究齿廓变位的直齿轮传动系统啮合特性,建立了变位直齿圆柱齿轮传动分析模型。该模型考虑了赫兹接触刚度、弯曲刚度、剪切刚度、轴压刚度和圆角基础刚度,给出了两种不同的齿廓变位的几何设计。在此基础上采用数值模拟方法研究了齿廓变位对时变啮合刚度(TVMS)和动态特性的影响。对于单个齿廓变位,正变位虽然增加了齿轮的厚度,但降低了齿轮的轮齿刚度以及齿轮副的接触比,从而加剧齿轮系统的振动。相反,负变位可以提高齿轮的轮齿刚度,增加齿轮的接触比,使得齿轮系统的传动更平稳。对于复合变位,负复合变位的S齿轮传动会导致TVMS升高,并显著降低振动,而s_(0)齿轮变位对时变啮合刚度(TVMS)影响较小,但对动态特性影响较大。

考虑挠度的宽温域陶瓷轴承转子系统动态特性分析

宽温域下陶瓷轴承外圈与轴承座之间配合间隙发生变化,同时转子质量对轴特别是细长轴会产生挠度影响,导致轴与轴承接触处力的边界条件发生变化,对轴承性能有很大影响。建立一种考虑挠度变化对宽温域内轴承转子系统影响的动力学模型,将轴承座与陶瓷轴承的热变形分别计算,并将不同温度下配合间隙作为边界条件,最后引入挠度因素改变轴与轴承接触处力的边界条件,来对全陶瓷球轴承动态特性进行求解。考虑轴承工作温度以及转轴挠度变化,对全陶瓷球轴承外圈振动情况展开参数化研究,并结合试验手段对模型精度加以验证。结果表明,挠度的产生使宽温域内全陶瓷轴承径向竖直正方向振动幅值减小,导致系统运行不稳定。研究结果对全陶瓷轴承动力学分析提供参考,并为提高陶瓷轴承转子系统稳定性提供理论依据。

半刚构-连续箱梁桥动静载试验研究

桥梁动静载试验是检测桥梁结构安全的重要方法,可准确评价桥梁结构的受力性能和实际工作状态。文中依据JTG/T J21-01—2015《公路桥梁荷载试验规程》,对陶赖昭特大桥主桥进行动静载试验,测试桥梁结构的挠度、应变及动力特性,并与理论值进行对比分析。结果表明,桥梁处于弹性受力状态,强度及刚度满足设计要求,动力响应及动力特性良好。

毫米波雷达在桥梁智慧化监测中的应用研究

文章利用毫米波雷达技术对某系杆拱桥的动挠度、基频进行运营期智慧化在线监测,并与现有其他非在线测量结果进行比对分析,验证毫米波雷达在桥梁监测中应用的可靠性。通过对比毫米波雷达与光电挠度仪的动挠度测试结果,与加速度传感器的基频测试结果,表明毫米波雷达在桥梁动挠度、基频监测的测试结果是可靠的,研究成果可为类似工程提供参考。

自动机曲柄连杆机构柔性冲击研究

由于自动机曲柄连杆机构的质心在纵向不断运动,在高低过载交替发生的情况下,曲柄和连杆受到交替时变惯性载荷作用,产生动挠度,引起自动机柔性冲击;对柔性冲击的成因、特点进行分析,根据达朗伯原理中对惯性载荷的定义,在有限元分析中作为边界条件引入惯性载荷;在马蒙托夫时变规律火药气体作用条件下,对曲柄连杆机构进行运动仿真分析,得到了曲柄和连杆过载、跃度变化规律;再用有限元法对曲柄连杆进行了惯性载荷作用下动挠度(形变量)分析,结果表明,连杆在过载大于25 000 m/s2时成为振动的主要根源,降低转动副中心距和质心附近质量分布,可以降低动挠度,进而降低柔性冲击。

架空线路风偏计算的多刚体动力学模型及其分析

为准确高效地计算架空线路动态风偏位移响应,进而预防风偏闪络事故发生,结合架空线路风偏摆动的运动特征,考虑绝缘子串中各个绝缘子的相对运动,采用多个刚杆与扭转弹簧相互连接模拟架空导线,根据风偏变形的力学关系与能量守恒原则,建立了连续档架空线路风偏位移响应的多刚体模型与动力学方程;通过量纲分析与相似理论构建物理仿真模型的风洞实验,验证多刚体模型的准确性;通过对工程实例进行数值仿真分析,并比较多刚体模型与通用软件有限元模型的运算时间,验证多刚体模型的高效性。研究结果表明:连续档架空线路的风偏多刚体动力学模型可以有效展现各个绝缘子串与各档导线的动态风偏响应规律,计算精度能够满足工程使用需求,计算效率优于有限元模型。

山区峡谷风袭击下绝缘子串风偏特性研究

为了掌握山区峡谷风袭击下输电线路绝缘子串风偏特性,提出了一种山区输电线路峡谷风场模拟方法.首先以峡谷风变化规律和信息为目标,基于Davenport风功率谱,通过待定系数法修正风功率谱,采用谐波叠加法构建了山区输电线路峡谷风场,分析了模拟风场与峡谷实测风场的相关性;然后建立山区输电塔线体系有限元模型,研究了峡谷风袭击下绝缘子串风偏特性,分析了降雨条件和风攻角对绝缘子动态风偏的影响,探索了峡谷风增大效应,给出了峡谷风袭击下的绝缘子串风偏角计算公式.结果表明:通过待定系数法修正Davenport风功率谱,可实现山区输电线路峡谷风场模拟;峡谷风袭击下的绝缘子串动态风偏角呈现上下波动趋势,且服从正态分布.降雨强度和风攻角越大,绝缘子串的风偏越大.建议峡谷风作用的绝缘子串采用修正的刚体直杆法计算.计算峡谷风袭击下绝缘子串的风偏角时,建议考虑峡谷风动力增大效应.

鸭舵式迫击炮弹气动特性研究

可动双翼鸭舵式新型迫击炮弹的气动布局区别于传统固定鸭舵式修正迫弹,表现出不同的气动特性。基于计算流体动力学方法,采用气动分析软件对某新型迫弹进行气动仿真计算,获得不同条件下弹丸的阻力系数、升力系数和俯仰力矩系数变化规律及舵翼的受力情况。数值模拟结果表明:弹丸的阻力系数、升力系数和俯仰力矩系数随攻角和马赫数的增加而增大;舵翼力随舵偏角和马赫数的增加而增大;双翼鸭舵式迫弹整体气动特性良好。计算结果对可动舵翼修正弹的研究及设计具有一定的参考价值。

基于模糊PID算法的磁流变悬架系统的控制仿真研究

为了改善车辆的行驶平顺性,选择车速为30 m/s、路面激励为C级的工况条件,对被动控制、模糊控制和模糊PID控制的磁流变悬架系统进行MATLAB仿真,并选取车身垂向加速度、悬架动挠度和轮胎动载荷作为行驶平顺性的评价指标。结果表明:与被动控制的悬架系统比较,模糊PID控制与模糊控制的磁流变悬架系统的垂向加速度均方根值分别为28.02%、9.40%,峰值改善率分别为24.68%、2.49%;模糊PID控制与模糊控制的磁流变悬架系统的悬架动挠度均方根值分别为20%、10%,峰值改善率分别为13.58%、13.58%;模糊PID控制与模糊控制的磁流变悬架系统的轮胎动载荷均方根值分别为0.18%、0.003%,峰值改善率分别为3.79%、2.64%。