The use of the node-based smoothed finite element method to estimate static and seismic bearing capacities of shallow strip footings

The node-based smoothed finite element method(NS-FEM)is shortly presented for calculations of the static and seismic bearing capacities of shallow strip footings.A series of computations has been performed to assess variations in seismic bearing capacity factors with both horizontal and vertical seismic accelerations.Numerical results obtained agree very well with those using the slip-line method,revealing that the magnitude of the seismic bearing capacity is highly dependent upon the combinations of various directions of both components of the seismic acceleration.An upward vertical seismic acceleration reduces the seismic bearing capacity compared to the downward vertical seismic acceleration in calculations.In addition,particular emphasis is placed on a separate estimation of the effects of soil and superstructure inertia on each seismic bearing capacity component.While the effect of inertia forces arising in the soil on the seismic bearing capacity is non-trivial,and the superstructure inertia is the major contributor to reductions in the seismic bearing capacity.Both tables and charts are given for practical application to the seismic design of the foundations.

DYNAMIC RESPONSE OF PLATES DUE TO MOVING VEHICLES USING FINITE STRIP METHOD

Dynamic response of beam-like structures to moving vehicles has been extensively studied. However, the study on dynamic response of plates to moving vehicles has so far received but scant attention. A plate-vehicle strip for simulating the interaction between a rectangular plate and moving vehicles was described. For the portion of strips that are in direct contact with the moving vehicles, the plate-vehicle strips were employed. Conventional plate finite strips were used to model the portion of strips that are not directly under the action of moving vehicles. In the analysis, each moving vehicle is idealized as a one-foot dynamic system with tire unsprung mass and sprund mass interconnected by a spring and a dashpot. The numerical results obtained from the proposed method agree well with available results.

A dynamic large-deformation particle finite element method for geotechnical applications based on Abaqus

In this paper,the application of Abaqus-based particle finite element method(PFEM)is extended from static to dynamic large deformation.The PFEM is based on periodic mesh regeneration with Delaunay triangulation to avoid mesh distortion.Additional mesh smoothing and boundary node smoothing techniques are incorporated to improve the mesh quality and solution accuracy.The field variables are mapped from the old to the new mesh using the closest point projection method to minimize the mapping error.The procedures of the proposed Abaqus-based dynamic PFEM(Abaqus-DPFEM)analysis and its implementation in Abaqus are detailed.The accuracy and robustness of the proposed approach are examined via four illustrative numerical examples.The numerical results show a satisfactory agreement with published results and further confirm the applicability of the Abaqus-DPFEM to solving dynamic large-deformation problems in geotechnical engineering.

Finite Element Analysis of the Influence of Artificial Cementation on the Strength Parameters and Bearing Capacity of Sandy Soil under a Strip Footing

Artificial cementation is a method commonly used to enhance and improve soil properties. This paper investigates the effect of using different amounts of cement on soil strength parameters and soil bearing capacity, using the finite element method. Experimental tests are conducted on soil samples with different amounts of Portland cement. A 2-D numerical model is created and validated using the numerical modelling software, COMSOL Multiphysics 5.6 software. The study finds that the cohesion, and the angle of the internal friction of the soil samples increase significantly as a result of adding 1%, 2%, and 4% of Portland cement. The results demonstrate that the stresses and strain under the strip footing proposed decrease by 3.24% and 7.42%. Moreover, the maximum displacement also decreases by 1.47% and 2.97%, as a result of adding cements of 2% and 4%. The bearing capacity values obtained are therefore excellent, especially when using the 2% and 4% cement. The increase identified is due to the increased values of the bearing capacity factors. It is concluded that from an economic viewpoint, using 2% cement is the best option.

基于监控理论的EFSM设计方法

随着扩展有限状态机(EFSM)模型在计算机科学和工程领域的广泛应用,EFSM的设计逐渐成为一个重要的问题。目前EFSM的设计仍然主要依赖于个人经验,缺乏理论基础。由于EFSM中每个转移的谓词可以看作此转移的一个监控器,所以可以用离散事件系统的监控理论为EFSM设计提供理论基础。首先定义了有限状态机(FSM)导出的EFSM及其产生的语言。然后,基于监控理论中的受控对象和监控器,提出了一种设计EFSM的方法,用离散事件系统监控理论为EFSM设计提供理论依据。最后用两个实际例子说明了提出方法的可用性和有用性。

连续退火机组带钢瓢曲临界张力影响因素研究

带钢连续退火过程中张力是影响带钢瓢曲的关键参数之一,合理的张力对确保带钢高效、稳定运行至关重要。为获得带钢发生瓢曲的临界张力,制定抑制带钢瓢曲的有效工艺措施,采用有限元软件ABAQUS建立“两辊一带”有限元模型,模拟计算不同传送辊凸度、辊面平台区长度、摩擦系数和带钢宽度下带钢瓢曲的临界张力;结合带钢表面应力分布、横向压缩应力分布,分析传送辊凸度、辊面平台区长度、摩擦系数及带钢宽度对带钢瓢曲临界张力的影响规律。结果表明:随传送辊凸度、摩擦系数、带钢宽度的增加,带钢瓢曲临界张力呈现下降的变化趋势;但随传送辊平台区长度的增加,带钢瓢曲临界张力上升,其中传送辊凸度对带钢瓢曲临界张力的影响最大。实际生产中,为保障带钢高速通板的稳定性,建议综合考虑传送辊凸度、辊面平台区长度、摩擦系数和带钢宽度等因素协同优化工艺,确保各参数在最优范围。本文建立的带钢通板“两辊一带”模型已成功应用于宝钢冷轧退火生产线,本文研究可为生产现场退火机组传送辊的选型优化、带钢实际张力制定及瓢曲问题的解决提供切实可行的技术指导。

Numerical Simulation of Temperature Field and Thermal Stress Field of Work Roll During Hot Strip Rolling

Based on the thermal conduction equations, the three-dimensional （3D） temperature field of a work roll was investigated using finite element method （FEM）. The variations in the surface temperature of the work roll during hot strip rolling were described, and the thermal stress field of the work roll was also analyzed. The results showed that the highest roll surface temperature is 593 ℃, and the difference between the minimum and maximum values of thermal stress of the work roll surface is 145.7 MPa. Furthermore, the results of this analysis indicate that temperature and thermal stress are useful parameters for the investigation of roll thermal fatigue and also for improving the quality of strip during rolling.

Three-Di mensional Model for Strip Hot Rolling

A three-dimensional model for strip hot rolling was developed, in which the plastic deformation of strip, the thermal crown of rolls, roll deflection and flattening were calculated by rigid-plastic finite element method, finite difference method, influential function method and elastic finite element method respectively. The roll wear was taken into consideration. The model can provide detailed information such as rolling pressure distribution, contact pressure distribution between backup rolls and work rolls, deflection and flattening of work rolls, lateral distribution of strip thickness, and lateral distribution of front and back tensions. The finish rolling on a 1 450 mm hot strip mill was simulated.

Re-reddening on Strip Surface After Water Cooling

After water cooling, there is a big temperature difference between the center and the surface of strip, which leads to the heat transfer from the center to the surface, and the surface temperature can rise in a short time. The finite element method was used to simulate the phenomena of re-reddening on the surface of strip and to analyze the temperature field of hot roiled strip during laminar cooling, and the periodical variation curve of the cooling rate was obtained during water cooling and subsequent re-reddening. The results show that the critical line of the cooling rate is at 1/3 of the half-thickness from the strip surface. The regression model of the relation of rereddening temperature, time, and distance from the surface was obtained in the re-reddening region. Re-reddening regularity on the surface of strip under the condition of different thickness and cooling rate was also studied.

Multi-scale Simulation on Bonding Mechanism of Solid-Liquid Cast-Rolling of Cu/Al Cladding Strip based on FEM and MD

To explore the complex thermal-mechanical-chemical behavior in the solid-liquid cast-roll bonding(SLCRB) of Cu/Al cladding strip, numerical simulations were conducted from both macro and micro scales. In macro-scale, with birth and death element method, a thermo-mechanical coupled finite element model(FEM) was set up to explore the temperature and contact pressure distribution at the Cu/Al bonding interface in the SLCRB process. Taking these macro-scale simulation results as boundary conditions, we simulated the atom diffusion law of the bonding interface by molecular dynamics(MD) in micro-scale. The results indicate that the temperature in Cu/Al bonding interface deceases from 700 to 320 ℃ from the entrance to the exit of caster, and the peak of contact pressure reaches up to 140 MPa. The interfacial diffusion thickness depends on temperature and rolling reduction, higher temperature results in larger thickness, and the rolling reduction below kiss point leads to significant elongation deformation of cladding strip which yields more newborn interface with fresh metal and make the diffusion layer thinner. The surface roughness of Cu strip was found to be benefit to atoms diffusion in the Cu/Al bonding interface. Meanwhile, combined with the SEM-EDS observation on the microstructure and composition in the bonding interface of the experimental samples acquired from the castrolling bite, it is revealed that the rolling reduction and severe elongation deformation in the solid-solid contact zone below kiss point guarantee the satisfactory metallurgical bonding with thin and smooth diffusion layer. The bonding mechanisms of reactive diffusion, mechanical interlocking and crack bonding are proved to coexist in the SLCRB process.

Transverse Distributions of Front and Back Tension Stresses in Cold Strip Rolling

In this paper,such a new lateral displacement function is proposed that the lateral flow velocity is con- tinuous at the entry and the exit of deformation zone.A new kind of finite strip method—the third power B-spline finite strip method—is put forward to simulate strip rolling process.Front and back tension stresses are formulated.The computed results of the transverse distributions of the front and back tension stresses are close to the experimental results.The paper lays a foundation for further analysing the three-dimensional stresses and deformations of strip rolling.

Analysis model for deformation mechanism of strip foundation of building:Considering shear effect of down-crossing tunnel under excavation

When the tunnel underpasses through the building,it will cause deformation and even damage to the buildings above,and the deformation of building foundation is the key to building safety.Based on the engineering case,the theoretical analysis was employed to evaluate the influence of shield tunnel underpass construction on the stability of the building,and the optimal tunneling parameters in the field construction have been obtained through the verified theoretical model and parameter analysis.First,the strip foundation of the building was simplified to the Timoshenko beam,which was taken into account the shear effect,and then the deformation displacement of the soil at the same place of strip foundation was applied to the simplified Timoshenko beam.Finally,the numerical solution of the displacement of the strip foundation was obtained by using the finite element method and verified its reliability using Euler-Bernoulli beam theoretical model,field monitoring data,and numerical simulation.Parameters analysis for the deformation and internal force of strip foundation under different types of shield machine tunneling parameters showed that the influence of the pressure of shield excavation chamber,thrust of shield,and driving speed played an important role in the deformation of the building’s strip foundation and internal force.

Effect of roller shapes on strip buckling in a continuous annealing furnace

The effect of roller shapes on strip buckling in a continuous annealing furnace was focused on. The tensile stress distribution, the transverse compressive stress, and the critical buckling stress of the strip were studied by the finite element method （FEM） when the flat roller, crown roller, single taper roller, and double taper roller were used, respectively. Simulation results show that strip buckling is most likely to occur with the crown roller, then the double taper roller, and finally the single taper roller. Also, strip buckling can not occur when the flat roller is used. Considering strip snaking, the single taper roller and double taper roller are suggested in the continuous annealing fur-nace. The double taper roller with a better strip snaking-prevention ability should be applied in the sections with high strip temperature, and the single taper roller with a better buckling-prevention ability should be used in the sections with low strip temperature.

Analysis of the thermal profile of work rolls in the hot strip rolling process

A 2-dimension axisymmetric model was developed by the finite-differencemethod, which can be used to predict the transient temperature field and thermal profile of workrolls in the hot strip rolling process. To demonstrate the accuracy and reliability of the solutiondeveloped, the calculation results were compared with the production data of a 1700 mm hot striprolling mill and good agreement was found between them. The effect of strip width and roll shiftingon the thermal expansion of the work rolls was studied. It is found that the strip width has markedeffect on the efficient thermal crown. Initially, when the rolling strip changes from narrow towide, a bigger efficient thermal crown can be quickly achieved; afterwards, when the rolling stripchanges from wide to narrow, not only the influence of uneven wear can be reduced but also theexcessive efficient thermal crown can be avoided. It is also found that the work roll shifting has adeterminate but not obvious effect on the reduction of the efficient thermal crown, and will makethe strip shape unstable without being used properly.

基于改进FSM的RBAC测试集约简方法

使用完备的有限状态机生成一致性测试集虽然有效,但数量庞大。针对该问题,考虑一般系统访问控制的基本需求,提出6种探索式方法对有限状态机(FSM)进行约简,有效避免状态爆炸的现象发生,简化了生成的一致性测试集大小。对基于FSM生成树进行实验,结果表明,改进FSM对缩小基于角色的访问控制系统一致性测试集是有效的。

Powell's optimal identification of material constants of thin-walled box girders based on Fibonacci series search method

A dynamic Bayesian error function of material constants of the structure is developed for thin-walled curve box girders. Combined with the automatic search scheme with an optimal step length for the one-dimensional Fibonacci series, Powell＇s optimization theory is used to perform the stochastic identification of material constants of the thin-walled curve box. Then, the steps in the parameter identification are presented. Powell＇s identification procedure for material constants of the thin-walled curve box is compiled, in which the mechanical analysis of the thin-walled curve box is completed based on the finite curve strip element （FCSE） method. Some classical examples show that Powell＇s identification is numerically stable and convergent, indicating that the present method and the compiled procedure are correct and reliable. During the parameter iterative processes, Powell＇s theory is irrelevant with the calculation of the FCSE partial differentiation, which proves the high computation efficiency of the studied methods. The stochastic performances of the system parameters and responses axe simultaneously considered in the dynamic Bayesian error function. The one-dimensional optimization problem of the optimal step length is solved by adopting the Fibonacci series search method without the need of determining the region, in which the optimized step length lies.

Stress concentration factor expression for tension strip with eccentric elliptical hole

Two explicit expressions of the stress concentration factor for a tension finite-width strip with a central elliptical hole and an eccentric elliptical hole, respectively, are formulated by using a semi-analytical and semi-empiricai method. Accuracy of the results obtained from these expressions is better, and application scope is wider, than the results of Durelli＇s photo-elastic experiment and Isida＇s formula. When eccentricity of the elliptical hole is within a certain range, the error is less than 8%. Based on the relation between the stress concentration factor and the stress intensity factor, a stress intensity factor expression for tension strips with a center or an eccentric crack is derived with the obtained stress concentration factor expressions. Compared with the existing formulae and the finite element analysis, this stress intensity factor expression also has sufficient accuracy.

Comparison of methods for vibration analysis of electrostatic precipitators

The paper presents two methods for the formulation of free vibration analysis of collecting electrodes of precipitators.The first,called the hybrid finite element method, combines the finit element method used for calculations of spring deformations with the rigid finite element method used to reflect mass and geometrical features,which is called the hybrid finite element method.As a result,a model with a diagonal mass matrix is obtained.Due to a specific geometry of the electrodes,which are long plates of complicated shapes,the second method proposed is the strip method which is a semi-analytical method.The strip method allows us to formulate the equations of motion with a considerably smaller number of generalized coordinates.Results of numerical calculations obtained by both methods are compared with those obtained using commercial software like ANSYS and ABAQUS.Good compatibility of results is achieved.

薄壁杆件屈曲模态分析的力特征约束有限条法

整体、畸变、局部等基本变形模式的划分是条理化开展薄壁杆件工程计算的必要手段。薄壁杆件的基本变形模式传统上基于简化应力-应变关系,采用变形、应变等几何特征进行定义,不利于因应复杂化应力-应变关系。提出一套完全基于力特征和正交完备性原则的基本模式定义。与广义梁理论和约束有限条法相比,提出的整体、畸变、局部3种基本变形模式关于刚度严格正交,且完整覆盖薄壁杆件全变形域。基于该定义实现了针对薄壁杆件有限条模型的屈曲模态分解和识别。算例表明,提出的基本模式定义和屈曲模态分析方法具有开、闭口和折、曲线形截面的一致适应能力,剪应变和横向伸缩的影响在基本屈曲模式中得到合理表达,曲线形截面薄壁构件具有与多边形截面薄壁构件一致的整体、畸变和局部屈曲机理。

基于传递有限条薄壁构件弹性屈曲分析

目的为研究薄壁构件的弹性屈曲问题,提高其计算效率。方法根据有限条传递矩阵法的相关理论知识编写了基于传递有限条程序(简称TFSM)。该程序不需要建立整体刚度矩阵,降低了系统矩阵的阶数,通过输入相应的截面参数和材料参数便能对薄壁构件进行弹性屈曲分析,大大提高了计算效率。结果为验证程序的可行性,首先对划分不同条形单元数的薄板构件进行屈曲分析,将计算结果与理论值进行对比,考察不同条形单元数对计算精度的影响。然后采用精度较高的条形单元划分方法对冷弯薄壁型钢构件弹性畸变屈曲进行了研究,并与有限元方法和经典有限条法的计算结果进行了对比。数据表明TFSM程序具有较高的精度。结论TFSM程序可以应用于冷弯薄壁构件的弹性屈曲分析。