Time Domain Backcalculation of Pavement Structure Material Properties Using 3D FEM with Ritz Vectors

The three‐dimensional finite element (3D FE) methods have been used increasingly to evaluate the bearing capacity of pavement structures. In this evaluation, layer moduli are backcalculated from measured surface deflections of the pavement structure. However, backcalculation requires repetitive computation to improve the parameter values in an iterative manner, and thus it is time consuming when 3D finite elements are used for the analysis. In this article, an effective method is developed to estimate layer moduli and damping coefficients in the time domain. The pavement is modeled using 3D finite elements. Gauss‐Newton and singular value decomposition methods are employed to backcalculate the unknown parameters. Ritz vectors are used to reduce the size of the matrices required for the analysis. Numerical simulations verify the effectiveness and accuracy of the Ritz vector method.     

Comparison of methods for calculating the influence of asymmetry in strip and plate rolling

The effect of different work roll diameters, different circumferential speeds of work rolls, and different friction for top and bottom side on roll parameters, especially on curvature of outgoing material, is investigated. Three methods, which are all based on the theorem of the upper bound of total power, are discussed. Their results are compared with experimental data of Juretzek. They differ in the kind of velocity field for the material flow in the roll gap. The first makes use of a polynomial global velocity field. The second employs bilinear quadrilateral finite elements, which are fixed to space, while the stationary rigid plastic material flow goes through (stationary FEM). The third field consists of rigid triangles which can slide along their contact lines. The last method produces a formation of shear lines, which is in good coincidence with that of the zones of high strain rate, given by stationary FEM. Results of parameter studies using stationary FEM are shown as relationship between dimensionless characteristic numbers. At last a comparative analysis of the effectiveness of the different methods is given.     

模拟热轧板带三维变形的条层法及仿真实例

提出一种模拟板带轧制过程三维变形的新的数值方法———条层法。首先沿高向将变形区均匀地划分为若干层 ,然后再沿着金属的流动轨迹将变形区内的每层带材划分为若干流线条元 ,为了方便分析和计算 ,又将流线条元映射为矩形条元。横向位移的纵向分布被构造为四次曲线 ,横向分布用三次样条插值函数表示 ,高向分布用二次曲线拟合。根据塑性力学流动理论 ,分析推导了变形区三维变形和应力的数学模型。与本文作者曾经提出的流线条元法相比 ,考虑了应力与变形沿高向的不均匀分布 ,实现了精确的三维分析和计算。关于热带钢连轧和厚板轧制的仿真实例表明 ,提出的方法和模型符合实际 ,为板带轧制过程的三维力学仿真提供了一个新的实用工程数值方法。     

Developments in Coarse-Grain Modeling of Transient Heat-Flow in Buildings

The note reports on recent developments to the coarse-grain method (CGM) of modeling transient heat flow in buildings. CGM was originally developed as an alternative to conventional fine-grain modeling techniques [such as the finite-difference method (FDM) and finite-element method (FEM)] to increase simulation speed to a degree that facilitates three-dimensional modeling, and to ease the tasks of model development and experimentation. Earlier work has shown that CGM can provide reasonably accurate simulations at a processing speed several orders of magnitude faster than FDM or FEM. This note describes and demonstrates refinements to the CGM approach that increase its modeling accuracy to a level comparable to FEM, while doubling its processing speed. These refinements are: (1) the use of a hybrid linear regression model with an artificial neural network (ANN) to represent each coarse-grain modeling element (the hybridization of the ANN effectively halves its complexity); and (2) a linear calibration of the ANN-based coarse-grain modeling elements to account for an observed positive bias in their predictions. The improved approach is demonstrated for a two-dimensional model of a bay in a research building located at the University of Florida. The note concludes with some suggestions for continuing research.     

Single strand continuous caster tundish furniture comparison for optimal performance

Abstract

Analysis of a single strand 36 t thin slab caster tundish has been conducted with different sets of furniture using a three-dimensional computation fluid dynamics model taking heat losses into account. Five distinct and optimised cases and a base case were used for simulation. The cases were built considering tundish furniture that is readily and economically available and provides ease of maintenance, thus targeting an optimal set of furniture. The performance of different sets of furniture was assessed based on residence time parameters like plug volume fraction, mixed volume fraction, dead volume fraction, etc. Other performance indicators used in the analysis were temperature distribution, observing cold spot, surface velocity and nature of flow in the tundish. Insight from the base case reveals the desired flow characteristics that help to achieve the target performance. Inferred results suggested the use of a turbulence inhibitor in combination with a dam as the optimal set of furniture. Use of a non-isothermal model is important, as it was found that even a small change in temperature (2·3°C) plays a vital role in the fluid flow inside the tundish.     

中厚板轧制过程中轧制力变化有限元模拟

采用动态显式有限元法对中厚板轧制过程进行了分析.分析了轧制过程稳定阶段接触区中厚板单元数、轧辊单元尺寸以及中厚板初始速度选择对有限元分析计算结果的影响,得出了合理的轧制过程有限元模拟参数,并对某中厚板厂15道次轧制过程轧制力变化规律进行了分析,稳定阶段轧制力计算结果与实测结果非常接近.该结果对中厚板轧制过程模拟具有一定的参考意义.     

Numerical simulation of the UOE forming process based on MSC. Marc secondary development technology

U-ing-O-ing-Expanding (UOE),the main process for making longitudinal submerged arc welded pipe(LSAW) with steel plate,is famous for its superior quality and reliability.Based on the famous non-linear finite element analysis (FEA) software MSC.Marc,a finite element model (FEM) has been established to simulate the whole UOE forming process by using the secondary development technology with the Python language.Research has also been conducted systematically on the crimping,U-ing,O-ing and mechanical expanding processes.The practice has shown that the simulation calculation is in close conformity with the actual site production data.The FEM has been successfully applied in the UOE production at Baosteel.     

Physical parameters and boundary conditions for the numerical simulation of hot forming processes

Exact simulation of hot-forming processes using the finite element method requires the most precise possible specification of the material parameters and physical boundary conditions prevailing in each case. The report presents a method to supply all the necessary data. New experimental concepts have been developed and applied, particularly for the more complex boundary conditions, which are virtually undocumented in literature. These techniques permit analysis of the real workpiece/interlayer/die combination, supplying reliable data for an FEM simulation.     

Separation and Recovery of Copper,Nickel and Cobalt from the Copper Converter Slag by Solvent Extraction

An attempt has been made to develop a simple SX flowsheet to recover Ni, Cu and Co separately using alkyl phosphonic acid PC 88A diluted with kerosene. Process parameters such as phase ratio. pH of the feed solution and number of stages for extraction, scrubbing and stripping have been optimised. A computer program in FORTRAN has been developed to determine the process parameters for producing pure solutions of Ni. Cu and Co simultaneously in a counter-current set up. Conventional approach of separating individual metals in the order of their extraction affinities has also been studied. Both the processes have been found to yield Co, Cu and Ni sulphate solutions of purities required for downstream metal winning steps. This paper presents the salient data collected along with the optimised flowsheets.     

Design of hydroforming process for an automobile subframe by FEM and experiment

Tube hydroforming technology has shown the attention of the automotive industry due to its advantages over conventional stamping and welding methods.In this study,the tube hydroforming process including tube bending,preforming and hydroforming process for an automobile subframe is analyzed and designed by the simulation software AutoForm of a finite element method (FEM) program.A parametric study is carried out to obtain the effect of the forming parameters such as initial tube size and loading path on the forming results.The simulation results are also compared with experiment results.The research indicates that the multiple forming operation of the tube hydroforming process can be simulated accurately by using the implicit code AutoForm,and the formability of tube hydroforming can be improved by designing suitable forming parameters.     

有限元法分析带钢在拉弯矫直过程中的能耗值

依据国内某钢厂带钢拉弯矫直机的结构参数及工艺参数,用ANSYS／LS-DYNA建立了拉弯矫直过程的有限元分析模型,经加载计算后将计算得到的塑性变形能与实际生产中的电机功率进行对比,得到两者误差为6．19％,从而验证了此拉弯矫直有限元模型具有较高的精度,也为后续分析实际生产中的拉弯矫直过程提供了较为可靠的参考数据。     

Fast Algorithms for the Simulation of Electromagnetic Metal Forming

Despite the comprehensive understanding of the modelling and numerical simulation of electromagnetic metal forming that has recently been gained, the simulation of real forming situations is still a challenging task due to the large computational resources required. A bottleneck is the computation of the electromagnetic fields, since 100 000 up to several million unknowns are required to represent the geometry of a typical forming device. The purpose of this article is to present new techniques to speed up the simulation of electromagnetic metal forming with particular emphasis on the computation of the electromagnetic fields. An acceleration of the electromagnetic field computation is a significant step towards a virtual design of electromagnetic forming processes.     

Numerical Simulation and Sensitivity Analysis of Parameters for Multistand Roll Forming of Channel Section With Outer Edge

 Cold roll forming is a high production but complex metal forming process under the conditions of coupled effects with multi factor. A new booting finite element method (FEM) model using the updated Lagrangian (UL) method for multistand roll forming process is developed and validated. Compared with most of the literatures related to roll forming simulation, the new model can take the roll rotation into account and is well suited for simulating multistand roll forming. Based on the model, the process of a channel section with outer edge formed with twelve passes is simulated and the sensitivity analysis of parameters is conducted with orthogonal design combined FEM model. It is found that the multistand roll forming process can be efficiently analyzed by the new booting model, and sensitivity analysis shows that the yield strength plays an important role in controlling the quality of the products.     

Simulation of macroscopic solidification with an incorporated one-dimensional microsegregation model coupled to thermodynamic software

In this article, a numerical model is presented which predicts phase distributions and dendrite arm spacings for a realistic casting within suitable CPU time. Three software components are coupled to perform calculations: (1) an FEM simulation package for the macroscopic temperature field, (2) an FDM code for the microstructure parameters, and (3) a thermodynamic software package for equilibrium calculations at the interfaces. The macrosoftware provides the micromodule with the present temperature at each node of a finite-element grid. At each such node, the micromodule calculates the dendrite arm spacings, the phase amounts, and the diffusion-controlled segregation profiles for the current time-step using equilibrium information from the thermodynamic software. A change of solid fraction and of the phase concentrations results in the release of latent heat and in the change of the heat capacity. These values are used as input parameters in the macrosoftware for the temperature calculation in the next time-step. Simulations have been performed for the ternary alloy AlCu4Mg1 and the results have been compared to “traditional” temperature calculations and to experimentally determined phase fractions and dendrite arm spacings. Measurements have been done by means of an interactive image analysis system over the entire breadth of an ingot casting at four different heights as well as at three different longitudinal cuts.     

Computational aspects of finite element modeling in EEG source localization

A comparison is made of two different implementations of the finite element method (FEM) for calculating the potential due to dipole sources in electroencephalography (EEG). In one formulation (the direct method) the total potential is the unknown that is solved for and the dipole source is directly incorporated into the model. In the second formulation (the subtraction method) the unknown is the difference between the total potential and the potential due to the same dipole in an infinite region of homogeneous conductivity, corresponding to the region where the dipole is located. Both methods have the same FEM system matrix. However, the subtraction method requires an additional calculation of flux integrations along the edges of the elements in the computation of the right-hand side (RHS) vector. It is shown that the subtraction method is usually more accurate in the forward modeling, provided the flux integrations are computed accurately. Errors in calculating the flux integrations may result in large errors in the forward solution due to the ill-conditioned nature of the FEM system matrix caused by the Neumann boundary condition. To minimize the errors, closed-form expressions for the flux integrations are used for both linear and quadratic triangular elements. It is also found that FEM forward modeling errors may cause false extrema in the least-square objective function obtained from the boundary potential, near boundaries between media of differing conductivity. Multiple initial guesses help eliminate the possibility of the solution getting trapped in these false extrema.     

Relationships between process parameters and temperature field of roll casting for wide sheet made of AZ61 magnesium alloy: Finite element method

In recent years, wide sheet made of AZ61 wrought magnesium alloys has been widely studied and applied in industry. Thin roll-casting technology for the new wrought magnesium alloy can provide acceptable quality wide and thin sheet made of AZ61 magnesium alloy. To study the influences of roll-casting process parameters on temperature field for wide and thin sheet made of AZ61 magnesium alloy plates, some simplification and assumptions have been done by characteristics of magnesium alloy. Two-dimensional FEM model for roll-casting has been established along casting direction. Simulations of temperature fields of the plates have been done by using finite element analysis ANSYS software. A series of researches on the temperature distributions under different process parameters (pouring temperature, heat-transfer coefficients and casting speeds) have been done. The simulation results and the literature about the casting process of the relevant theory are the same. The simulation results show that the process parameters of rapid-casting process for AZ61 magnesium alloy are mutual influenced on the temperature fields of wide sheet made of AZ61 magnesium alloy.     

GCr15棒线材粗轧过程的隐式静力和隐式动力算法有限元模拟

借助大型商用有限元软件MSC.Marc,采用隐式静力和隐式动力有限元算法,对GCr15棒线材的粗轧过程进行了热力耦合有限元模拟,模拟采用生产实际中的轧制参数.2种算法的出辊速度、温度场和平均轧制力模拟结果基本一致,温度场模拟值与实测值的比较证明了这2种算法的可靠性.实际模拟时,隐式动力学算法计算时间少于隐式静力学算法,效率较高.     

中厚板轧制过程的有限元仿真研究

本文采用了MSC MARC2005有限元分析软件包建立了中厚板轧制的有限元仿真模型,通过接触分析的方法对中厚板的轧制过程进行了三维模拟仿真,并对不同压下量轧件轧后变形及应力分布做了分析,结果表明与实际轧制参数基本一致。     

斜轧螺纹过程的数值模拟

对螺旋孔型斜轧螺纹过程进行了非线性有限元分析，得到了轧件内部应力－应变分布情况，为模具的设计和工艺参数的确定提供了重要依据。