Dynamic response analysis of liquefiable ground due to sinusoidal waves of different frequencies of shield construction

Vibration induced by shield construction can lead to liquefaction of saturated sand.Based on FLAC3D software,a numerical model of tunnel excavation is established and sinusoidal velocity loads with different frequencies are applied to the excavation face.The pattern of the excess pore pressure ratio with frequency,as well as the dynamic response of soil mass under different frequency loads before excavation,is analyzed.When the velocity sinusoidal wave acts on the excavation surface of the shield tunnel with a single sand layer,soil liquefaction occurs.However,the ranges and locations of soil liquefaction are different at different frequencies,which proves that the vibration frequency influences the liquefaction location of the stratum.For sand-clay composite strata with liquefiable layers,the influence of frequency on the liquefaction range is different from that of a single stratum.In the frequency range of 5-30 Hz,the liquefaction area and surface subsidence decrease with an increase in vibration frequency.The research results in this study can be used as a reference in engineering practice for tunneling liquefiable strata with a shield tunneling machine.

An experimental study on dynamic response for MICP strengthening liquefiable sands

The technology of bio-gronting is a new technique for soft ground improvement. Many researchers have carried out a large number of experiments and study on this topic. However, few studies have been carried out on the dynamic response of solidified sand samples, such reducing liquefaction in sand. To study this characteristic of microbial-strengthened liquefiable sandy foundation, a microorganism formula and grouting scheme is applied. After grouting, the solidified samples are tested via dynamic triaxial testing to examine the cyclic performance of solidified sand samples. The results indicate that the solidified sand samples with various strengths can be obtained to meet different engineering requirements, the use of bacteria solution and nutritive salt is reduced, and solidified time is shortened to 1-2 days. Most importantly, in the study of the dynamic response, it is found that the MICP grouting scheme is effective in improving liquefiable sand characteristic, such as liquefaction resistance.

Discrete Element with Flexible Connector for Dynamic Analysis of 3-D Beam Structures

Combined multi-body dynamics with structural dynamics, a new discrete element with flexible connector, which is applicable for 3-D beam structures, is developed in this paper. Both the generalized elastic coefficient matrix of the flexible connector and the mass matrix of discrete element may be off-diagonal in a general case. The zero-length rigid element is introduced to simulate the node at which multiple elements are jointed together. It may also be effective when the axes of adjacent elements are not in the same line. The examples for eigenvalue calculation show that the model is successful. It can be extended to the geometric nonlinear response analysis.

Dynamics and Stability of Blind Grasping of a 3-Dimensional Object under Non-holonomic Constraints

A mathematical model expressing the motion of a pair of multi-DOF robot fingers with hemi-spherical ends, grasping a 3-D rigid object with parallel fiat surfaces, is derived, together with non-holonomic constraints. By referring to the fact that humans grasp an object in the form of precision prehension, dynamically and stably by opposable forces, between the thumb and another finger （index or middle finger）, a simple control signal constructed from finger-thumb opposition is proposed, and shown to realize stable grasping in a dynamic sense without using object information or external sensing （this is called ＂blind grasp＂ in this paper）. The stability of grasping with force/torque balance under non-holonomic constraints is analyzed on the basis of a new concept named ＂stability on a manifold＂. Preliminary simulation results are shown to verify the validity of the theoretical results.

Dynamic Responses of Pontoons Connecting Process of Mobile Offshore Base

The dynamic responses of two pontoons while connected with each other in irregular waves are calculated by means of three-dimensional （3-D） potential flow theory. The computation is to find the optimal status for connection at a certain sea state. On the basis of the relative motion of two pontoons in irregular waves, Visual FORTRAN programming language, as well as OpenGL （Open Graphics Library）, is used to develop a set of virtual reality system of the relative motion of two pontoons, which is fully interactive with realistic effect. The transfinite interpolation scheme is applied for the mesh generation of wave surface, and the wave motion is simulated by surface elevation and calculated by 3-D potential flow theory.

3-D Simulation Study on Seismic Response of Bridge Piles in Landslide

The anti-slide support structure is widely used in the anti-seismic reinforcement of bridge foundations,but related experimental research was processing slowly. Based on the prototype of the Jiuzhaigou bridge at the Chengdu-Lanzhou Railway,a 3-D simulation model was established on the basis of the shaking table model test,and the rationality of the dynamic analysis model was verified by indicators such as the bending moment of the bridge piles,peak soil pressure,and PGA amplification factors. The results show that the inertia force of the bridge pier has an important influence on the deformation of the pile foundation. The bending moment and shearing force are larger in lateral bridge piles,and the maximum value is near the pile top. The PGA amplification factor is stronger in the back of the rear anti-slide piles and so is it in front of the bridge pier,and the soil is prone to slip and damage. The bedrock is rigid and the dynamic response is maintained at a low level. The anti-slide piles in the rear row play a major role in the anti-seismic reinforcement design,and the anti-slide piles in the front row can be used as an auxiliary support structure.

基于3m波长地铁钢轨焊缝接头不平顺的轮轨响应分析

相对于1 m弦测值的焊缝接头动力学评估与管理,基于3 m波长范围的焊缝接头不平顺轮轨响应分析对其服役状态评估与管理具有重要意义。首先,基于车辆-轨道垂向耦合动力学理论建立车辆-轨道垂向耦合模型;然后,借助基于一弦N点弦测法研制的钢轨短波不平顺测量小车,对地铁线路焊缝接头不平顺进行精确测量,并根据传统弦测理论得到1 m弦测值;接着,将实测3 m波长焊缝接头不平顺和1 m弦测值作为车辆-轨道垂向耦合模型的不平顺激励输入,对比3 m波长焊缝接头不平顺和1 m弦测值激扰下的轮轨响应;最后,研究了车速和焊缝位置对轮轨动力响应的影响。结果表明:相比1 m弦测值激扰下的轮轨动力响应结果,3 m波长焊缝接头不平顺激扰下的轮轨力幅值变化不明显,轮重减载率幅值增大11.52%,钢轨加速度幅值增大54.05%,轮对振动加速度幅值增大37.67%;车速提高会导致轮轨力和轮重减载率幅值增大;焊缝中心与轨枕间的距离增加,轮轨力幅值先增加后减小,当焊缝中心距离轨枕0.1 m时,轮轨力幅值最大。

THE ANALYSIS OF DYNAMIC STRESS INTENSITY FACTOR FOR SEMI-CIRCULAR SURFACE CRACK USING TIME-DOMAIN BEM FORMULATION

The time-domain BEM was developed to analyze the dynamic stress intensity factor ( DSIF) of 3-D elastodynamic crack problems. To simulate the stress singularity along the front of a crack, eight-node isoparametric singular elements were used, and the DSIF for a semi-circular surface crack was firstly calculated based on displacement equation using the time-domain BEM formulation. The new scheme to determine the time step was brought forward. By the dynamic analysis program of time-domain BEM compiled by its, several numerical examples are presented, which demonstrate the unconditional stability and high accuracy of time-domain BEM applied to 3-D elastodynamic crack problems.

Thre-dimensional topographic responses in MT using finite diference method

In this paper, the magnetotelluric response to 3-D earth topography was studied using the finite difference method for rectangular cells. Three numerical modeling calculations were carried out; the results indicate that the finite difference method is applicable to the magnetotelluric problem in estimating the 3-D topographic responses.

In-situ three-dimensional visualization of dynamic tension deformation in ferrite stainless steels

An improved three-dimensional （3-D） experimental visualization methodology is presented tor evaluating the fracture mechanisms of ferritic stainless steels by in-situ tensile testing with an environmental scanning electron microscope （ESEM）. The samples were machined with a radial notched shape and a sloped surface. Both planar surface deformation and sloping surface deformation-induced microvoids were observed during dynamic tension experiments, where a greater amount of information could be obtained from the sloping surface. The results showed that microvoids formed at the grain boundaries of highly elongated large grains. The microvoids nucleated in the severely deformed regions grew nearly parallel to the tensile axis, predominantly along the grain boundaries. The microvoids nucleated at the interface of particles and the matrix did not propagate due to the high plasticity of the matrix. The large microvoids propagated and showed a zigzag shape along the grain boundaries,seemingly a consequence of the fracture of the slip bands caused by dislocation pile-ups. The final failure took place due to the reduction of the load-beating area.

3-D Fracture Network Modelling in Hydropower Engineering Based on Optimal Monte Carlo Simulation

Effectively and accurately modelling the spatial relation of fracture surfaces is crucial in the design and construction of large hydropower dams having a complex underlying geology. However, fracture surfaces are randomly formed and vary greatly with respect to their spatial distribution, which makes the construction of accurate 3-D models challenging. In this study, we use an optimal Monte Carlo simulation and dynamic conditioning to construct a fracture network model. We found the optimal Monte Carlo simulation to effectively reduce the error associated with the Monte Carlo method and use dynamic conditioning to ensure the consistency of the model with the actual distribution of fractures on the excavation faces and outcrops. We applied this novel approach to a hydropower station on the Jinshajiang River, China. The simulation results matched the real sampled values well, confirming that the model is capable of effectively and accurately simulating the spatial relations in a fracture network.

Dynamic phase transition of ferroelectric nanotube described by a spin-1/2 transverse Ising model

The dynamic phase transition properties for ferroelectric nanotube under a spin-1/2 transverse Ising model are studied under the effective field theory(EFT)with correlations.The temperature effects on the pseudo-spin systems are unveiled in three-dimensional(3-D)and two-dimensional(2-D)phase diagrams.Moreover,the dynamic behaviors of exchange interactions on the 3-D and 2-D phase transitions under high temperature are exhibited.The results present that it is hard to obtain pure ferroelectric phase under high temperature;that is,the vibration of orderly pseudo-spins cannot be eliminated completely.

3-D Modelling of the Confederation Bridge Using Data of Full Scale Tests

Long-span bridges are special structures that require advanced analysis techniques to examine their performance. This paper presents a procedure developed to model the Confederation Bridge using 3-D beam elements. The model was validated using the data collected before the opening of the bridge to the public. The bridge was instrumented to conduct fullscale static and dynamic tests. The static tests were to measure the deflection of the bridge pier while the dynamic tests to measure the free vibrations of the pier due to a sudden release of the static load. Confederation Bridge is one of the longest reinforced concrete bridges in the world. It connects the province of Prince Edward Island and the province of New Brunswick in Canada. Due to its strategic location and vital role as a transportation link between these two provinces, it was designed using higher safety factors than those for typical highway bridges. After validating the present numerical model, a procedure was developed to evaluate the performance of similar bridges subjected to traffic and seismic loads. It is of interest to note that the foundation stiffness and the modulus of elasticity of the concrete have significant effects on the structural responses of the Confederation Bridge.

A Comparative Study between Pseudo-static and Dynamic Analyses of Keddara Dam

The numerical analysis of static and dynamic performance of embankment dams using the finite difference approach is a complex procedure that takes into account material behavior,soil-dam foundation interaction,hydraulic conditions,and saturation effects.In this study,a numerical analysis using the finite difference method(FLAC 3D)is used to conduct a static and dynamic analysis of the Keddara earthen dam in the Boumerdes region of Algeria,with the goal of defining its behaviour in terms of settlement,deformation,and pore pressure variation during construction and operation.There are two steps to consider:dam construction and water filling.For the static analysis,two mathematical models are considered:the elastic model and the Mohr-Coulomb model.An actual earthquake record is used to conduct a coupled dynamic analysis,and the interaction between the fluid and solid phases is taken into account.Maximum displacement,acceleration,and pore pressure remain inconsequential for dam instability;horizontal and vertical displacements increase with distance from the dam body’s base to the top.

高功率双包层Er^(3+)/Yb^(3+)共掺光纤放大器的动态响应(英文)

基于速率方程的离散算法,分析了双包层Er3+/Yb3+共掺光纤放大器的动态响应,显示了输出功率和增益的动态特征。当单个脉冲注入放大器时,输出脉冲的峰值功率不仅依赖于输入脉冲的峰值功率,而且依赖于泵浦功率;当脉冲序列注入时,输出脉冲的功率和增益最终将收敛于它们的稳态值。在双信道情况下,输入脉冲重叠时的输出功率和增益变得更陡峭。在连续波泵浦下,反向自发辐射输出功率(ASE-)首先快速地增加到峰值功率,然后单调下降到稳态值;在脉冲波泵浦下,反向自发辐射输出功率(ASE+)与光纤长度成反比,而ASE-与光纤长度成正比。

3-D simulation of transient flow patterns in a corridor-shaped air-cushion surge chamber based on computational fluid dynamics

The 3-D characteristics of the water-air flow patterns in a corridor-shaped air-cushion surge chamber during hydraulic transients need to be considered in the shape optimization. To verify the reliability of the water-air two-phase model, namely, the volume of fluid model, the process of charging water into a closed air chamber is successfully simulated. Using the model, the 3-D flow characteristics under the load rejection and acceptance conditions within the air-cushion surge chamber of a specific hydro- power station are studied. The free surface waves, the flow patterns, and the pressure changes during the surge wave process are analyzed in detail. The longitudinal flow of water in the long corridor-shaped surge chamber is similar to the open channel flow with respect to the wave propagation, reflection and superposition characteristics. The lumped parameters of the 3-D numerical simulation agree with the results of a 1-D calculation of hydraulic transients in the whole water conveying system, which validates the 3-D method. The 3-D flow structures obtained can be applied to the shape optimization of the chamber.

脉冲泵浦下Er^(3+)，Yb^(3+)的动态响应研究

针对光纤通信中泵浦源故障引起的时续时断问题,采用矩形脉冲进行处理。基于速率方程,分析了不同脉宽泵浦下,Er^(3+)/Yb^(3+)共掺晶系中Er^(3+)、Yb^(3+)上能级粒子数的变化。结果表明:不同的脉宽对上能级Er^(3+),Yb^(3+)的影响具有不同的特点。在决定Yb^(3+)到Er^(3+)的能量转换的动态特性和效果方面,Yb^(3+)吸收的饱和与非均匀加宽的Yb^(3+)吸收谱线所引起的烧孔效应是影响Er^(3+)上能级粒子数动态的最主要因素。

基于三维数字图像相关方法的水下冲击载荷作用下铝板动力学响应研究

基于数字图像相关(DIC)方法搭建了三维动态DIC方法测试系统,利用冲击加载实验设备,对喷涂散斑的铝靶板进行冲击加载实验,获得了靶板的实时离面位移场;并利用安装在水靶舱壁面的压力传感器,测取了水中冲击波压力时程曲线;建立了针对冲击实验的二维轴对称仿真模型,分析了水靶舱内冲击波的形成与传播过程以及靶板的动态响应变形进程。研究结果表明,靶板的变形是由边界向中心呈环形扩展的,而且靶板极容易在法兰约束边界处出现剪裂现象。靶板实时变形与测点压力时程的实验值与仿真值具有良好的一致性,这表明结合三维动态DIC方法测试系统与等效加载设备可以实现对结构的水下冲击响应分析研究工作。

大型复杂钢结构厂房的抗震性能的有限元分析

利用通用有限元程序ANSYS建立了某大型复杂钢结构厂房的三维空间有限元模型,完成了其整体结构的动力学特性分析,还根据现有7级地震记录对其施加了横向、纵向和斜向地震激励,分别做时间历程分析,并对计算结果做了相应的对比.最后结合结构抗震规范的相关条文,对该钢结构厂房的抗震性能进行了综合评定,结果表明其满足7级抗震要求.分析结果可为工程师们设计类似结构提供相应的依据.

地下水位上升对上海软土场地地震反应的影响

根据工程地质勘探和室内外试验建立上海软土场地计算模型,采用Biot动力固结理论,结合弹塑性边界面模型,研究三向地震作用下地下水位上升对场地土层地震反应的影响。利用具有水平和垂直三向完整加速度记录的Taft波构造基岩输入地震动时程曲线,分析三向地震作用下地下水位上升对土层竖向和水平加速度放大效应、竖向与水平加速度峰值比、地表加速度和反应谱特征以及沿土层深度最大孔隙水压力和孔压比的影响。计算分析表明:地下水位上升对水平向和竖向峰值加速度的放大效应影响差异显著,同时对地表加速度及其反应谱特征具有重要影响。地下水位的上升,地表水平峰值加速度放大效应增大,竖向峰值加速度放大效应减小;竖向与水平向加速度峰值比减小;土层高频滤波作用增强,长周期成分放大效应增大;近地表液化土层范围增大,加剧砂土液化危害性。