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.

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.

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.

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.

Modeling of Roll-Heave-Pitch Motions of a Ram Wing Translating over Non-uniform Surface

Ground-effect vehicles flying close to water or ground often employ ram wings which generate aerodynamic lift primarily on their lower surfaces.The subject of this paper is the 3-DOF modeling of roll,heave,and pitch motions of such a wing in the presence of surface waves and other ground non-uniformities.The potential-flow extreme-ground-effect theory is applied for calculating unsteady pressure distribution under the wing which defines instantaneous lift force and moments.Dynamic simulations of a selected ramwing configuration are carried out in the presence of surface waves of various headings and wavelengths,as well as for transient flights over a ground obstacle.The largest amplitudes of the vehicle motions are observed in beam waves when the periods of the encounter are long.Nonlinear effects are more pronounced for pitch angles than for roll and heave.The present method can be adapted for modeling of air-supported lifting surfaces on fast marine vehicles.

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.

Verification of Seismic Performance of Pile Foundation in Composite Ground through Experimental and Numerical Methods

A new construction method of pile foundation in composite ground, in which, prior to installing piles, the ground is improved around the heads of the piles in soft ground or ground subject to liquefaction, which is introduced in this paper. This construction method uses a combination of pile foundation construction together with common ground improvement methods, including deep mixing, preloading and sand compaction piling, and it is referred to as the composite ground pile method. Since an artificial ground with relatively high rigidity comparing with that of the original ground was formed around the pile in this method, and the seismic performance has not been made clear, thus the seismic performance of piles in composite ground was systematically analyzed through a series of centrifuge model tests and numerical analyses by using dynamic nonlinear finite element method, and a verification method for the seismic performance of piles in composite ground was proposed on the basis of the experimental and numerical results.

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.

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。

空降车辆着陆缓冲过程仿真分析与模型验证

围绕空降车辆在着陆缓冲过程中的冲击载荷,建立空降车辆-缓冲气囊耦合有限元模型并开展着陆缓冲过程仿真.开展典型垂直降落工况地面跌落模拟试验,对比仿真数据与试验实测数据,验证仿真模型的准确性.对垂直降落工况和水平向速度的着陆缓冲过程开展仿真分析,校核车辆冲击载荷、反弹速度、气囊内压等着陆缓冲响应.仿真结果表明,对于某空降车辆,目前的空降车辆-缓冲气囊设计方案在多种工况下的冲击载荷满足使用要求.此种方法可以较好满足空降车辆方案优化和着陆缓冲性能预测.

Ground-state and dynamical properties of a spin-S Heisenberg star

We generalize the Heisenberg star consisting of a spin-1/2 central spin and a homogeneously coupled spin bath modeled by the XXX ring[Richter J and Voigt A 1994 J.Phys.A:Math.Gen.271139-1149]to the case of arbitrary central-spin size S<N/2,where N is the number of bath spins.We describe how to block-diagonalize the model based on the Bethe ansatz solution of the XXX ring,with the dimension of each block Hamiltonian≤2 S+1.We obtain all the eigenenergies and explicit expressions of the sub-ground states in each l-subspace with l being the total angular momentum of the bath.Both the eigenenergies and the sub-ground states have distinct structures depending whether S≤l or l<S.The absolute ground-state energy and the corresponding l as functions of the intrabath coupling are numerically calculated for N=16 and S=1,2,…,7 and their behaviors are quantitatively explained in the weak and strong intrabath coupling limits.We then study the dynamics of the antiferromagnetic order within an XXX bath prepared in the Néel state.Effects of the initial state of the central spin,the value of S,and the system-bath coupling strength on the staggered magnetization dynamics are investigated.By including a Zeeman term for the central spin and the anisotropy in the intrabath coupling,we also study the polarization dynamics of the central spin for a bath prepared in the spin coherent state.Under the resonant condition and at the isotropic point of the bath,the polarization dynamics for S>1/2 exhibit collapse-revival behaviors with fine structures.However,the collapserevival phenomena are found to be fragile with respect to the anisotropy of the intrabath coupling.

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。

空间绳网系统展开动力学特性分析

空间绳网系统是一种新型轻质空间柔性结构,具有很大的应用价值。针对地面环境和太空环境下的不同受力特性,推导空间绳网动力学模型;通过地面试验验证仿真模型的可信度;基于展开面积、飞行距离等性能参数,仿真分析空间绳网展开过程中的绳网位形、应力分布以及能量变化等动力学特性,分析轨道高度、捕获方向和发射参数对展开效果的影响。

边坡动力特性与动力响应的大型振动台模型试验研究

设计并完成了1∶10比尺的边坡大型振动台模型试验。试验模型尺寸为2.15 m×3.5 m×1.5 m(高×长×厚),坡角约为38°,采用土体材料制备。通过输入不同类型、幅值、频率的地震波和白噪声激励,探讨地震作用下模型边坡的动力特性与动力响应规律,以及地震动参数对动力特性和动力响应的影响。试验结果表明,随着振动次数的增加,模型边坡自振频率逐渐降低,阻尼比逐渐增大。自振频率降低的幅度随振幅的增大而加大。边坡土体对输入地震波具有明显的放大作用,沿坡面向上,加速度峰值放大系数呈现递增趋势,在坡肩附近急剧增大。在不同地震波作用下,坡面加速度响应具有明显的差异。当输入地震动卓越频率与模型边坡自振频率接近时,坡面加速度峰值放大效应显著增强。随着输入地震动幅值的增加,坡面加速度峰值放大系数呈现明显的递减趋势。边坡土体对输入波的低频部分存在放大作用,对高频部分存在滤波作用。随着输入地震动幅值的加大,土体表现出更强的滤波作用。试验结果有助于揭示边坡在地震作用下的失稳机制,为边坡工程的抗震设计提供有益的参考。

空间飞网发射动力学建模仿真研究与地面试验

空间飞网是近来提出的一个创新的空间系统概念,在空间碎片处理和在轨服务方面具有独特的应用潜力。针对飞网系统的发射过程,利用建模仿真和地面试验两种手段进行了研究,建立了飞网发射的集中质量模型,设计了基于燃气助推质量块的飞网发射地面试验装置,开展了多次飞网发射试验。地面试验结果与模型仿真结果基本吻合,说明所建立的动力学模型可用于空间飞网系统设计。

1976年M_S7.8唐山地震断层动态破裂及近断层强地面运动特征

采用美国南加州地震委员会(SCEC)Steven Day博士提供的三维有限差分断层瞬态破裂动力学模型(3DFDM),以1976年唐山Ms 7.8地震为例,从简化的断层双侧破裂模式出发,对该地震发震断层的动态破裂过程及近断层地表运动特征进行了仿真模拟和计算.研究区域为围绕发震断层200 km×140 km×40 km(深度)的长方形块体组成,模拟计算的空间分辨率和时间分辨率分别为200 m和0.012 s,形成的空间网格节点数为1051×701×201.在DELL小型工作站上,我们实现了对源程序的移植和并行计算.同时,通过引进计算机可视化技术,对模拟数据进行了3D/4D解释分析.另外,在对源程序修改过程中,实现了对京津唐地区三维地壳速度结构的嵌入,在一定程度上增强了对地震波传播以及地面运动模拟的真实性,并讨论了地震破裂的方向性对近断层地表运动的影响.最后根据初步研究结果结合京津唐地区活动断层构造特征,对唐山M_S7.8级主震后随之而来的1976滦县M_S7.1级余震及宁河Ms6.9级余震的动态触发机制提出了新的解释.由于受主震破裂方向性作用的影响,使得主震对后续两个较大余震产生的动态应力变化的峰值在断层的走滑方向上较大,为2～3 MPa,在逆冲方向上较小,为0.1～0.2 MPa.即唐山主震的发生使得其周边的应力场有一个瞬态的应力调整,唐山主震对后续余震的发生有促发作用.