Review on dynamic analysis of road pavements under moving vehicles and plane strain conditions

This paper reviews works on the dynamic analysis of flexible and rigid pavements under moving vehicles on the basis of continuum-based plane strain models and linear theories.The purpose of this review is to provide in-formation about the existing works on the subject,critically discuss them and make suggestions for further research.The reviewed papers are presented on the basis of the various models for pavement-vehicle systems and the various methods for dynamically analyzing these systems.Flexible pavements are modeled by a homogeneous or layered half-plane with isotropic or anisotropic and linear elastic,viscoelastic or poroelastic material behavior.Rigid pavements are modeled by a beam or plate on a homogeneous or layered half-plane with material properties like the ones for flexible pavements.The vehicles are modeled as concentrated or distributed over a finite area loads moving with constant or time dependent speed.The above pavement-vehicle models are dynamically analyzed by analytical,analytical/numerical or purely numerical methods working in the time or frequency domain.Representative examples are presented to illustrate the models and methods of analysis,demonstrate their merits and assess the effects of the various parameters on pavement response.The paper closes with con-clusions and suggestions for further research in the area.The significance of this research effort has to do with the presentation of the existing literature on the subject in a critical and easy to understand way with the aid of representative examples and the identification of new research areas.

Regional Finite-Fault Source Model for Development of Ground Motion Attenuation Relationship in Sichuan, China

The attenuation relationship of ground motion based on seismology has always been a front subject of engineering earthquake.Among them,the regional finite-fault source model is very important.In view of this point,the general characteristics of regional seism-tectonics,including the dip and depth of the fault plane,are emphasized.According to the statistics of regional seism-tectonics and focal mechanisms in Sichuan,China,and the sensitivity of estimated peak ground acceleration(PGA)attenuation is analyzed,and the dip angle is taken as an average of 70°.Based the statistics of the upper crustal structure and the focal depth of regional earthquakes,the bottom boundary of the sedimentary cover can be used as the upper limit for estimating the depth of upper-edge.The analysis shows that this value is sensitive to PGA.Based on the analysis of geometric relations,the corresponding calculation formula is used,and a set of concepts and steps for building the regional finite-fault source model is proposed.The estimation of source parameters takes into account the uncertainty,the geometric relationship among parameters and the total energy conservation.Meanwhile,a set of reasonable models is developed,which lay a foundation for the further study of regional ground motion attenuation based on seismology.

Prediction of high-speed train induced ground vibration based on train-track-ground system model

The development of analysis on train-induced ground vibration is briefly summarized. A train-track- ground integrated dynamic model is introduced in the paper to predict the ground vibration induced by high-speed trains. Representative dynamic responses of the train-track-ground system predicted by the model are presented. Some major results measured from two field tests on the ground vibration induced by two high-speed trains are reported. Numerical prediction with the proposed train-track-ground model is validated by the high-speed train running experiments. Research results show that the wheel/rail dynamic interaction caused by track irregularities has a significant influence on the ground acceleration and little influence on the ground displacement. The main frequencies of the ground vibration induced by high-speed trains are usually below 80 Hz. Compared with the ballasted track, the ballastless track structure can produce much larger train-induced ground vibration at frequencies above 40 Hz. The vertical ground vibration is much larger than the lateral and longitudinal components.

Influence of dynamic pressure on deep underground soft rock roadway support and its application

Due to high ground stress and mining disturbance, the deformation and failure of deep soft rock roadway is serious, and invalidation of the anchor net-anchor cable supporting structure occurs. The failure characteristics of roadways revealed with the help of the ground pressure monitoring. Theoretical analysis was adopted to analyze the influence of mining disturbance on stress distribution in surrounding rock,and the change of stress was also calculated. Considering the change of stress in surrounding rock of bottom extraction roadway, the displacement, plastic zone and distribution law of principal stress difference under different support schemes were studied by means of FLAC3D. The supporting scheme of U-shaped steel was proposed for bottom extraction roadway that underwent mining disturbance. We carried out a similarity model test to verify the effect of support in dynamic pressure. Monitoring results demonstrated the change rules of deformation and stress of surrounding rock in different supporting schemes. The supporting scheme of U-shaped steel had an effective control on deformation of surrounding rock. The scheme was successfully applied in underground engineering practice, and achieved good technical and economic benefits.

Mechanical behavior of underground pipe gallery structure considering ground fissure

The mechanical behavior of underground pipe gallery is a key research issue due to the static/dynamic states which exist in a ground fissure area.This study took an underground pipe gallery project in Xi’an,China as the research object.We analyzed the stress/strain characteristics of the pipe gallery structure and surrounding soil under static/dynamic conditions by the numerical simulation methods in detail.Based on the results,we proposed a theoretical calculation model for the pipe gallery structure considering the influence of the ground fissure,and combined with engineering examples for calculation and discussion.Subsequent results showed that:(1)the effective activity range of ground fissure on the deformation of the pipe gallery structure was mainly from 0.0 m(horizontal direction of ground fissure)to 32.0 m.In activity range,the pipe gallery structure is prone to failure,owing to the large soil deformation in the vertical direction;(2)with the increase of ground fissure settlement,a stress reduction area near the ground fissure appeared at the bottom of the hanging wall of the pipe gallery structure,and a local void phenomenon was revealed.The length of the local void is 6.0 m to 8.0 m under the maximum settlement(0.8 m)of the ground fissure;(3)Compared with the static conditions,the vertical and horizontal displacements of the pipe gallery structure and surrounding soil under the seismic action were little,and there were tensioncompression and torsion-shear effects in corner of the square pipe gallery structure(with a stress concentration phenomenon).The deformation law of pipe gallery structure and surrounding soil considering ground fissure and the theoretical model of pipe gallery structure established in this paper can provide reference for practical engineering.

IN-PLANE WAVE MOTION IN FINITE ELEMENT MODEL

The analysis method of lattice dynamics in classical physics is extended to study the properties of in-plane wave motion in the hybrid-mass finite element model in this paper. The dispersion equations of P and SV waves in the discrete model are first obtained by means of separating the characteristic equation of the motion equation, and then used to analyse the properties of P-and SV-homogeneous, inhomogeneous waves and other types of motion in the model. The dispersion characters, cut-off frequencies of P and SV waves, the polarization drift and appendent anisotropic property of wave motion caused by the discretization are finally discussed.

Simulating Coupled Longitudinal, Pitch and Bounce Dynamics of Trucks with Flexible Frames

Simulating the dynamic response of trucks requires that a model be constructed and subjected to road inputs. Inclusion or omission of flexible frame effects is often based on intuition or assumption. If frame vibration is assumed to be significant, it is typically incorporated in one of two ways. Either a complex finite element model of the frame is used, or a simplified linear modal expansion model (which assumes small motions) is employed. The typical low-order modal expansion model, while computationally efficient and easier to use, is limited by the fact that 1) large rigid body motions and road grade changes are not supported, and 2) longitudinal dynamics are not coupled to vertical and bounce dynamics. In this paper, a bond graph model is presented which includes coupled pitch and bounce motions, longitudinal dynamics, and transverse frame vibration. Large rigid body motions are allowed, onto which small flexible vibrations are superimposed. Frame flexibility is incorporated using modal expansion of a free-free beam. The model allows for a complete pitch-plane representation in which motive forces can propel the truck forward over varying terrain, including hills. The effect of frame flexibility on vehicle dynamics can then be studied. This is an extension of the typical half-car model in which suspension motion is assumed vertical, pitch angles are small, and longitudinal dynamics are completely decoupled or omitted. Model output shows the effect of frame flexibility on vehicle responses such as forward velocity, pitch angle, and payload acceleration. Participation of individual modes can be seen to increase as road input approaches their natural frequency. The bond graph formalism allows for any or all flexible frame modes to be easily removed from the model if their effects are negligible, and for inclusion of more complex submodels for components such as suspension and engine if desired.

The New Formula of Seismic Rigidity Method

This publication is a revised version of the previous article. Seismic rigidity method despite its widespread use is the object of harsh criticism from scientists who oppose it to the methodology and results of seismological registration of earthquakes and microseisms. The article substantiates the original approach based on the solution of the direct problem of seismic microzonation for the model of real soil thickness. A new formula of the seismic rigidity method is proposed, taking into account the lithological, hydrogeological and spectral features of the soil mass, as well as the position of the new seismic scale of the SSI. The formula was tested on the example of the correct description of the features of macroseismic effects on the territory of Leninakan at the Spitak earthquake in 1988. Linear estimates according to the formula of seismic rigidity in the seismic microzoning area represent changes in seismic intensity in the most contrast way. It is shown that the real estimates of seismic intensity under strong seismic effects (by I > VII degree) will not exceed those given by the formula of the seismic rigidity method.

Real-time modular dynamic modeling for compression system of altitude ground test facilities

Modeling of a centrifugal compressor is of great significance to surge characteristics and fluid dynamics in the Altitude Ground Test Facilities(AGTF).Real-time Modular Dynamic System Greitzer(MDSG)modeling for dynamic response and simulation of the compression system is introduced.The centrifugal compressor,pipeline network,and valve are divided into pressure output type and mass flow output type for module modeling,and the two types of components alternate when the system is established.The pressure loss and thermodynamics of the system are considered.An air supply compression system of AGTF is modeled and simulated by the MDSG model.The simulation results of mass flow,pressure,and temperature are compared with the experimental results,and the error is less than 5%,which demonstrates the reliability,practicability,and universality of the MDSG model.

基于增量动力地震易损性分析的高层结构抗震加固研究

由于承重结构构件分布不均匀,导致高层建筑框架承重构件间的距离不相等。在地震时,这种不规则分布可能引起加速度共振效应,从而导致建筑失稳。为此,以地震动强度、地震动速度峰值、最大层间位移角为参数指标,分析高层建筑的极限状态,提出基于增量动力地震易损性分析的高层结构抗震加固研究。以某实际工程为试验对象,运用ABAQUS软件构造高层建筑框架结构三维模型,选取多条地震波以及符合场地条件的地震动记录进行验证,绘制地震易损性曲线。结果表明:在高层建筑框架结构中安装阻尼器,可增强结构中各构件的承载力,改善高层建筑抗震性能;增加钢板厚度可提高结构抗震水平,降低极限状态下框架结构IO、LS与CP的超越概率;提高混凝土强度,可改善框架结构抗倒塌性能。高层结构完成抗震加固后,抗震能力由0.91提升至1.01。由此证明,以增量动力分析得到的结构易损性为基础,对建筑易损性较大的地方进行加固、完善,能够改善高层建筑框架结构地震易损性,减少地震灾害损失。

Civil 3D在某砂石料场运输道路设计中的应用

为提高道路的设计质量及工作效率,依据现场实测高程数据及相关资料,针对性地研究了Civil 3d在道路设计中的应用。获取实测高程数据建立原始地形曲面,直观地表达了现场地形的变化情况。通过Civil 3D软件的横、纵断面设计功能,建立了道路的三维模型。利用Civil 3D参数化设计对象联动的功能,对道路进行动态调整,提高了设计效率,对比不同设计方案下的开挖量情况,对方案进行迭代优化。

Dynamics of freezing/thawing indices and frozen ground from 1900 to 2017 in the upper Brahmaputra River Basin, Tibetan Plateau

Dynamics of the frozen ground are key to understand the changes of eco-environment in cold regions,especially for areas with limited field observations.In this study,we analyzed the spatial and temporal variations of the ground surface freezing and thawing indices from 1900 to 2017 for the upper Brahmaputra River(also called the Yarlung Zangbo River in China)Basin(UBRB),southwestern Tibetan Plateau,with the air freezing and thawing indices using the University of Delaware(UDEL)monthly gridded air temperature dataset.The abrupt change years for air freezing index(AH)and ground surface freezing index(GH)were detected in 1999 and 2002,respectively,and for both air thawing index(ATI)and ground surface thawing index(GTI)were 2009.With the air temperature rising at a rate of 0.006℃ per year over 1900-2017,the AH and GH decreased at a rate of-0.1℃ d per year,while the ATI and GTI increased at rates of 0.3 and 0.5℃ d per year before the abrupt change year,respectively;all changing trends of freezing/thawing indices increased after the abrupt year,which was-2.9,-0.8,7.3,and 21.7℃ d per year for the AH,GFI,ATI,and GTI,respectively.We utilized the surface frost number model to obtain the dynamics of the frozen ground over the UBRB.When the empirical coefficient of E was assigned to 1.2,the simulated frozen ground occupied about 53.2%of the whole UBRB in the 1990s,which agreed well with the existing permafrost map published in 1996.The area of frozen ground accounts for 51.5%-54.5%of the UBRB during 1900-2017.This result may facilitate further studies of the multi-interactions among the frozen ground and relevant eco-environment,such as the air-ground surface energy exchange,hydrological cycles,and changes of the active layer thickness over the UBRB.

空间多体绳系编队动力学与控制研究综述

针对空间多体绳系编队的构型进行了分类,分析了国内外对绳系编队动力学模型的研究现状,并总结了常用于绳系系统动力学模型建立的三种系绳模型。此外,对绳系编队全流程控制,包括绳系编队构型形成、构型稳定保持以及刚体姿态机动控制进行了梳理和分析,同时对现有的地面试验装置及方法进行了概括。最后针对目前绳系编队的动力学建模与控制、地面试验装置研究中存在的不足进行了总结,对未来的发展方向提出了建议。

顺倾层状碎裂结构岩质边坡地震动力响应及破坏模式分析

顺倾层状边坡沿软弱带剪切方式破坏是滑坡的主要类型之一。采用块体砌筑斜坡振动台模型,在多维多参数地震动作用下,考虑斜坡不同工况下力学参数弱化的过程,研究了层状碎裂结构岩质边坡的地震动力响应和失稳破坏模式。结果表明:斜坡地震动特性和斜坡地质结构是决定斜坡地震动力稳定性以及破坏模式的决定因素;斜坡水平动力响应具有明显的高程和坡表放大效应,高程对斜坡的垂直动力响应影响较小,地震动放大效应与结构面力学强度、地震波波形、频谱特性等均有一定的关系,正弦波较天然波对坡体放大效应影响更为显著;坡体裂纹依托优势结构面在最弱部位起裂萌生扩展,并向节理面追踪形成蠕滑段和锁固段,节理面强度参数在外界地质营力作用下发生弱化,使潜在滑带出现由后缘向前端搭接贯通的前进式破坏模式和由前端向后缘的后退式破坏模式的分化,滑体也由高位剪出向溃散破坏演变。

基于路侧激光雷达的障碍物目标检测方法

针对现有障碍物检测方法在复杂道路场景下存在地面分割欠精准、计算量大以及不同距离下的目标聚类困难问题,提出了一种基于路侧激光雷达的障碍物检测方法。在地平面分割方面,提出基于圆柱坐标系的改进扇形栅格模型以及最低点代表法优化种子点的选取,采用多地平面模型并通过随机采样一致性算法(RANSAC)实现地面拟合及分割。在障碍物聚类方面,构建KDTree加速聚类过程,提出划分区域及阈值自适应的方式改进欧氏聚类算法。实验结果表明,该方法在4种典型道路场景下对地面点的分割准确率均达到86%以上,且针对不同距离下的障碍物目标聚类准确率提升明显。

平面滚珠丝杠副多结合面建模与动态特性分析

为了提高平面运输设备的传送效率与定位精度,针对x‑y轴平面滚珠丝杠副的多机械装配界面,应用吉村允效法确定螺栓联接界面的法向压缩刚度和切向运动刚度,采用赫兹接触理论确定丝杠螺母、轴承和导轨内接触界面的径向或法向压缩刚度。基于ABAQUS软件建立x‑y直线进给系统的动力学模型,通过锤击法模态试验和文献对比研究,证明了所提理论模型以及结合面刚度计算的正确性。数值仿真了工作台质量、滑块间距及导轨间距对于系统动态行为的影响,并给出设计建议值。通过医疗剪刀毛坯平面进给机床设计试验,验证了所获得动态系统设计规律的有效性。

地埋管换热器动态热负荷下地层温度场的解析解

垂直地埋管换热器(borehole heat exchanger,BHE)是利用浅层地热能的主要换热装置,如何确定合理的地埋管间距对地源热泵系统(ground source heat pump system,GSHPs)的传热性能与经济性影响很大。以往工程应用中未考虑地埋管热负荷的动态变化,常采用最大延米热/冷负荷(即最不利情况下)的影响半径作为设计依据,使设计参数趋于保守,很难实现地源热泵系统的技术和经济优化,而考虑负荷变化的数值模拟方法耗时复杂,不便于工程应用。文章提出了一种在地埋管实际热冷负荷动态变化条件下,计算地埋管换热器影响半径的简单数学方法。该法首先推导了地埋管换热器在周期性热流边界条件下,井筒周围地层温度场的解析解,在此基础上将地面建筑物全年周期下的实际波动热冷负荷进行傅里叶级数近似展开,最后通过线性叠加每个周期函数对应的解析解,得到建筑物实际动态热冷负荷下的地层温度动态分布。提出的解析解实时耦合了地面建筑动态热冷负荷,计算结果接近实际应用,具有计算精度高、简单方便快捷的优点,便于在工程实际中推广应用。

波流作用下高桩码头动力响应试验研究

针对外海工程地质环境,以高桩码头为研究对象,设计波流作用下水槽试验方案,开展波流作用下高桩码头动力响应的试验研究,还原了高桩码头真实的使用环境,探讨高桩码头桩身内部响应差异,分析自由场与桩周土孔压和加速度的响应关系。结果表明:1)高桩码头各桩响应差异明显,顺波流方向桩身所受动水压力逐渐减小,桩身弯矩前排桩大于后排桩,中间桩大于两侧桩;2)面板位移和加速度呈周期性变化,扭转随波流作用逐渐减小;3)土层加速度和孔压随波流传播和埋深增加逐渐减小,群桩的存在会增大土层加速度、减小孔压;4)高桩码头设计时,应适当提高中间桩的强度,重视对表层海床土的加固。研究成果可为高桩码头的设计和维护提供一定的参考与借鉴。

城市环境下基于A*算法和DWA算法的无人机路径规划方法研究

为解决城市环境下无人机在全局最优路径的基础上实现动态避障的路径规划需求,提出一种将改进A*算法和动态窗口算法(DWA)结合的算法。首先,利用无人机的起点和目标点构成一个二维平面与建筑障碍物的高度关系进行坐标转化,将三维城市地图转换成二维平面地图,改善路径规划过程中耗时长和计算速度慢的问题。其次,针对传统A*算法得到的路径存在过多的转角、不利于无人机飞行的问题,利用弗洛伊德(Floyd)法对全局路径进行平滑处理。最后,提取平滑处理后的路径父节点作为DWA算法的中间目标点,实现局部规划。实验结果表明,在不同类型的环境下,提出的融合算法既能保证更平滑和距离更短的全局最优路径,又能有效地躲避环境中出现的动态障碍物。