Simulation of near-fault bedrock strong ground-motion field by explicit finite element method

Based on presumed active fault and corresponding model, this paper predicted the near-fault ground motion filed of a scenario earthquake （Mw=6 3/4 ） in an active fault by the explicit finite element method in combination with the source time function with improved transmitting artificial boundary and with high-frequency vibration contained. The results indicate that the improved artificial boundary is stable in numerical computation and the predicted strong ground motion has a consistent characteristic with the observed motion.

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.

Analysis on effect of surface fault to site ground motion using finite element method

Dynamic contact theory is applied to simulate the sliding of surface fault. Finite element method is used to analyze the effect of surface fault to site ground motions. Calculated results indicate that amplification effect is obvious in the area near surface fault, especially on the site that is in the downside fault. The results show that the effect of surface fault should be considered when important structure is constructed in the site with surface fault.

Kinematic source model for simulation of near-fault ground motion field using explicit finite element method

This paper briefly reviews the characteristics and major processes of the explicit finite element method in modeling the near-fault ground motion field. The emphasis is on the finite element-related problems in the finite fault source modeling. A modified kinematic source model is presented, in which vibration with some high frequency components is introduced into the traditional slip time function to ensure that the source and ground motion include sufficient high frequency components. The model presented is verified through a simple modeling example. It is shown that the predicted near-fault ground motion field exhibits similar characteristics to those observed in strong motion records, such as the hanging wall effect, vertical effect, fling step effect and velocity pulse effect, etc.

Finite element simulation of steady state SH wave motion

A discrete local transmitting boundary is combined with a lumped-mass finite element technique for simulating steady SH wave motion in a layered and unbounded medium.The combination decouples any node of the finite element model from the others except those in its neighborhood,and an effective algorithm of the Gauss elimination in implementation of the method is then devised to reduce the main memory and computing time.The method and its accuracy are first analysed via simulating steady SH wave motion in layered elastic media,the effective algorithm is then introduced and illustrated by simple examples.

The Finite-Element Modeling of Dynamic Motions of a Constraint Wind Turbine and the System Diagnosis for the Safety Control

The aim of this paper is to present a finite element modeling of the dynamic motion of a turbine rotor and its controller design with the mass unbalance under a crack on a rotating shaft. This process is an advanced method to the mathematical description of a system including an influence of a mass unbalance and a crack on the rotor shaft. As the first step, the shaft is physically modeled with a finite element method and the dynamic mathematical model is derived by using the Hamilton principle;thus, the system is represented by various subsystems. The equation of motion of a shaft with a mass unbalance and a crack is established by adapting the local mass unbalance and stiffness change through breathing and gaping from the existence of a crack. This is a reference system for the given system. Based on a fictitious model for transient behavior induced from vibration phenomena measured at the bearings, an elementary estimator is designed for the safety control and detection of a mass unbalance on the shaft. Using the state estimator, a bank of an estimator is established to get the diagnosis and the system data for a controller.

Apply of Explicit Finite Element in Seismic Ground Motion Computation

In this paper, we will use the explicit finite element to compute ground motion due to Tangshan earthquake. The explicit finite-element method uses one integration point and an hourglass control scheme. We implement the coarse-grain method in a structured finite-element mesh straightforwardly. At the same time, we also apply the coarse-grain method to a widely used, slightly unstructured finite-element mesh, where unstructured finite elements are only used in the vertical velocity transition zones. By the finite-element methods, we can compute the ground velocity with some distance to the seismogenic fault in Tangshan earthquake. Through the computation, we can find the main character of ground motion for the strike slip earthquake events and the high frequency vibration motion of ground motion.

FE Dynamic Analysis Using Moving Support Element on Multi-Span Beams Subjected to Support Motions

In the present study, finite element dynamic analysis or time history analysis of two-span beams subjected to asynchronous multi-support motions is carried out by using the moving support finite element. The elemental equation of the element is based on total displacements and is derived under the concept of the quasi-static displacement decomposition. The use of moving support element shows that the element is very simple and convenient to represent continuous beam moving, deforming and vibrating simultaneously due to support motions. The comparison between the numerical results and analytical solutions indicates that the FE result agrees with the analytical solution.

海管抛填装备重载偏心行走机构稳性优化设计

为了研制新型高效自动化的海底管道悬空治理抛投导向装备,保证大型重载抛投导向装备工作运动行走时的准确性、平衡性、可靠性和安全性,设计一种具有高度调节功能的重载偏心平衡轮组机构。根据抛投机构水平运动的相对位置调节轮组高度,平衡抛投偏心力矩和优化轮组负载受力分布,同时利用有限元软件计算分析新型的偏心平衡轮组机构关键零部件的强度。结果表明:轮轴关键部位的受力应力均比平衡前下降了61%,轮轴变形量减少了57%,在减少抛投机构因应力集中而损坏的风险的同时,验证了偏心运动平衡装置的有效性和安全性。研究成果可为新型高效自动化海底管道悬空治理抛投导向装备的研制提供理论和技术支撑。

Parallel Computing of Discrete Element Method on GPU

General purpose computing on GPU for scientific computing has been rapidly growing in recent years. We investigate the applicability of GPU to discrete element method (DEM) often used in particle motion simulation. NVIDIA provides a sample code for this type of simulation, which obtained superior performance than CPU in computational time. A computational model of the contact force in NVIDIA’s sample code is, however, too simple to use in practice. This paper modifies the NVIDIA’s simple model by replacing it with the practical model. The computing speed of the practical model on GPU is compared with the simple one on GPU and with the practical one on CPU in numerical experiments. The result shows that the practical model on GPU obtains the computing speed 6 times faster than the practical one on CPU while 7 times slower than that of the simple one on GPU. The effects of the GPU architectures on the computing speed are analyzed.

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅱ): with saturated poroelastic soil layers

As the continuation study on amplification of in-plane seismic ground motion by underground group cavities in layered half-space, this study extends to the case of poroelastic half-space with dry poroelastic and saturated poroelastic soil layers. The influence of poroelastic layers on the amplification of seismic ground motion is studied both in frequency domain and time domain using indirect boundary element method （IBEM）. It is shown that for the example of a saturated poroelastic site in Tianjin under the excitation of Taft wave and E1 Centro wave, the amplification of seismic ground motion in poroelastic case is slightly smaller than that in the elastic case, and the amplification of PGA （peak ground acceleration） and its PRS （peak response spectrum）.. can be increased up to 38.8% and 64.6%; the predominant period of response spectra in poroelastic case becomes shorter to some extent compared with that in the elastic case. It is suggested that the effect of underground group cavities in poroelastic half-space on design seismic ground motion should be considered.

A varying time-step explicit numerical inte-gration algorithm for solving motion equa-tion

If a traditional explicit numerical integration algorithm is used to solve motion equation in the finite element simulation of wave motion, the time-step used by numerical integration is the smallest time-step restricted by the stability criterion in computational region. However, the excessively small time-step is usually unnecessary for a large portion of computational region. In this paper, a varying time-step explicit numerical integration algorithm is introduced, and its basic idea is to use different time-step restricted by the stability criterion in different computational region. Finally, the feasibility of the algorithm and its effect on calculating precision are verified by numerical test.

基于振动台试验的鱼线固定梅瓶文物响应规律性研究

为了探索鱼线固定梅瓶文物在实际博物馆的地震响应以及抗震效果,首先选取了典型梅瓶文物,并在三层钢筋混凝土框架结构中开展了24种地震工况的振动台试验,然后建立了上述试验所用梅瓶文物的有限元模型,验证了有限元模型的准确性,最后采用增量动力分析法分析了该文物在两种常见直径鱼线保护措施下的运动响应。结果表明:鱼线固定梅瓶文物在地震作用下会产生滑移、摇摆、倾覆以及鱼线断裂等现象;不同楼层下的文物响应差别较大,尤其在大震作用下,高楼层的鱼线固定梅瓶文物易发生倾覆和鱼线断裂破坏,要重视高楼层文物的震前保护措施;在较强的地震作用下,仅依靠增大鱼线直径有时对控制文物的倾覆情况起不到关键性决定作用,需要进一步采取其它措施对文物进行保护。

A SELF－ADAPTIVE FINITE ELEMENT METHOD FOR SOLVING 2－D EULER EQUATIONS ON THE UNSTRUCTURED MESHES

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A procedure to predict the precise seismic response of arch dams in time domain using boundary element formulation

In this context,a new boundary element algorithm based on the time-convoluted traction kernels is employed to evaluate the spatially varying earthquake ground motions of the Pacoima dam in the USA subjected to SH,SV and P incident waves.An accurate three-dimensional (3D) model of the dam canyon is implemented into the computer code BEMSA to investigate the seismic response of the dam.The analyses are performed in time domain with a linearly elastic constitutive model for the medium.This modeling procedure has been validated by the results reported in the existing literature.According to the results of this study,the response of the dam to earthquake waves is generally influenced by predominant frequency of the incident motion,surface topography,relative distance of observation points,and type of the incident seismic wave.For the cases considered,the incident SV wave has led to the maximum amplification of incident motions,especially at the left side of the dam.The results indicate that the proposed procedure can be employed for accurate prediction of a dam response during an earthquake.

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅰ)

Amplification of in-plane seismic ground motion by underground group cavities in layered half-space is studied both in frequency domain and time domain by using indirect boundary element method （IBEM）, and the effect of cavity interval and spectrum of incident waves on the amplification are studied by numerical examples. It is shown that there may be large interaction between cavities, and group cavities with certain intervals may have significant amplification to seismic ground motion. The amplification of PGA （peak ground acceleration） and its PRS （peak response spectrum） can be increased up to 45.2% and 84.4%, for an example site in Tianjin, under the excitation of Taft wave and E1 Centro wave; and group cavities may also affect the spectra of the seismic ground motion. It is suggested that the effect of underground group cavities on design seismic ground motion should be considered.

An Integrated Dynamic Model of Ocean Mining System and Fast Simulation of Its Longitudinal Reciprocating Motion

An integrated dynamic model of China＇s deep ocean mining system is developed and the fast simulation analysis of its longitudinal reciprocating motion operation processes is achieved. The seafloor tracked miner is built as a three-dimensional single-body model with six-degree-of-freedom. The track-terrain interaction is modeled by partitioning the track-terrain interface into a certain number of mesh elements with three mutually perpendicular forces, including the normal force, the longitudinal shear force and the lateral shear force, acting on the center point of each mesh element. The hydrodynamic force of the miner is considered and applied. By considering the operational safety and collection efficiency, two new mining paths for the miner on the seafloor are proposed, which can be simulated with the established single-body dynamic model of the miner. The pipeline subsystem is built as a three-dimensional multi-body discrete element model, which is divided into rigid elements linked by flexible connectors. The flexible connector without mass is represented by six spring-damper elements. The external hydrodynamic forces of the ocean current from the longitudinal and lateral directions are both considered and modeled based on the Morison formula and applied to the mass center of each corresponding discrete rigid element. The mining ship is simplified and represented by a general kinematic point, whose heave motion induced by the ocean waves and the longitudinal and lateral towing motions are considered and applied. By integrating the single-body dynamic model of the miner and the multi-body discrete element dynamic model of the pipeline, and defining the kinematic equations of the mining ship, the integrated dynamic model of the total deep ocean mining system is formed. The longitudinal reciprocating motion operation modes of the total mining system, which combine the active straight-line and turning motions of the miner and the ship, and the passive towed motions of the pipeline, are proposed and simulated with the developed 3D dynamic model. Some critical simulation results are obtained and analyzed, such as the motion trajectories of key subsystems, the velocities of the buoyancy modules and the interaction forces between subsystems, which in a way can provide important theoretical basis and useful technical reference for the practical deep ocean mining system analysis, operation and control.

基于Ansys的曲柄滑块机构的运动学分析在教学课程中的应用

在机械原理的教学中,曲柄滑块机构的设计原理与方法是重点和难点问题,传统的实物实验对曲柄滑块机构的种类、复杂性都有很大的限制,不利于学生对曲柄滑块系统运行规律的掌握。基于此,利用Ansys中的workbench建立了曲柄滑块机构运动仿真模型,通过对模型进行分析设置,对典型曲柄滑块机构进行运动仿真,得出了曲柄滑块机构的位移及应力、应变的分析结果,为机械结构仿真教学提供了有效的方法。

一种基于根管预备的绳驱机器人设计与分析

该文设计一种应用于根管预备手术中绳驱机器人构型。电机转动输出连接软轴,软轴与绳索滚筒采用锥度插孔相连,可以实现输出轴方便快捷的拆卸,便于末端机构的高温消毒程序。采用绳索驱动实现驱动元件与执行元件的相对远距离布置,保证末端执行部件的较小尺寸,便于在口腔狭小空间中进行动作。对末端执行机构根管锉软轴进行变形分析,并利用相邻关节间绳索的反向拉缩进行运动的补偿,保证关节间运动的解耦。最后进行样机的制作并验证其基本运动与运动补偿具备可行性。

Prediction of ash content of unloaded coal based on a discrete element simulation

Based on analysis of regularity of stacking coal,discrete element simultaneous simulation is adopted to predict the process of unloading coal,which is proved to be effcient in the prediction of ash content.The results show that the altitude of new irregular coal is equal to the income coal volume divided by area of cabin.The distribution of infnitesimal flow velocity helps to induce the motion equation of infnitesimal element,which provides the mathematical model for computer simulation.Swarm,a computer programming language,is utilized in this study.Adaptive infnitesimal stacking algorithm helps settle the diffculties in attainment of infnitesimal elements.The result of simulation is similar to the actual situation,which can accurately predict the ash contents of current time and cumulative time.Coal movement in the cabin is a new project,the result of which can also be applied to other solid particles and the widespread of the result will be highly valued.