Discrete 3D model as complimentary numerical testing for anisotropic damage

It is proposed to use a discrete particle model as a complimentary “numerical testing machine” to identify the hydrostatic elasticity-damage coupling and the corresponding sensitivity to hydrostatic stresses parameter. Experimental tri-axial tensile testing is difficult to perform on concrete material, and numerical testing proves then its efficiency. The discrete model used for this purpose is based on a Voronoi assembly that naturally takes into account heterogeneity. Tri-tension tests on a cube specimen, based on a damage growth control, are presented. A successful identification of the hydrostatic sensitivity function of a phenomenological anisotropic damage model is obtained.     

A 3D numerical model for computing non-breaking wave forces on slender piles

In this paper a numerical model for water-wave-body interaction is validated by comparing the numerical results with laboratory data. The numerical model is based on Euler’s equation without considering the effects of energy dissipation. The Euler equations are solved by a two-step projection finite-volume scheme and the free-surface displacements are tracked by the volume-of-fluid method. The numerical model is used to simulate solitary waves as well as periodic waves and their interaction with a vertical slender pile. A very good agreement between the experimental data and numerical results is observed for the time history of free-surface displacement, fluid-particle velocity, and dynamic pressure on the pile.     

三维连通网络陶瓷电磁参数的改性

以水玻璃为溶胶、以SiO2气溶胶粉末和磁性γ-Fe2O3粉末为填料,通过浸渍挂浆、凝胶、无机化等步骤,对三维连通网络陶瓷的介电常数和磁导率进行了改性．结果表明,填加SiO2气溶胶粉末可以有效降低网络陶瓷的介电常数,控制SiO2气溶胶的填加量可以实现网络陶瓷介电常数的连续可调．填加磁性材料亦可以在一定范围内改变网络陶瓷的磁导率．在水玻璃溶胶浆料中加入不高于10％(质量分数)的SiO2气溶胶粉末,可使网络陶瓷的抗压性能显著提高;SiO2气溶胶粉末的填加量大于10％后,溶胶在网络陶瓷骨架表面及Si02颗粒之间难以形成连续结合而使网络陶瓷的抗压强度下降．     

Development of numerical phantoms by MRI for RF electromagnetic dosimetry: a female model

Numerical human models for electromagnetic dosimetry are commonly obtained by segmentation of CT or MRI images and complex permittivity values are ascribed to each issue according to literature values. The aim of this study is to provide an alternative semi-automatic method by which non-segmented images, obtained by a MRI tomographer, can be automatically related to the complex permittivity values through two frequency dependent transfer functions. In this way permittivity and conductivity vary with continuity--even in the same tissue--reflecting the intrinsic realistic spatial dispersion of such parameters. A female human model impinged by a plane wave is tested using finite-difference time-domain algorithm and the results of the total body and layer-averaged specific absorption rate are reported.     

Comparison between 3D, 2D finite element methods and analyticalcalculations for electromagnetic problems

A study is carried out to determine when 2D modeling is sufficient for a 3D problem. Numerical and analytical errors are identified for different solved problems and the effect of disregarding the length of the system is studied (i.e. regarding it as infinite). A minimum length is determined for which the 2D results are better than the 3D results     

Study on numerical approaches for the evaluation of J-Integral Results in 3D problems

For numerical analyses of fracture mechanics problems often a combination of the finite element method with a post processor program for the evaluation of J-integral values is used. Instead of calculating a line integral as originally proposed by RICE it is reasonable to evaluate surface or volume integrals (for two or three dimensional calculations, respectively) in this case. In this paper 3D-formulations proposed by DE LORENZI and ATLURI are considered and several possibilities of the numerical realisation of these formulations are described. While the De Lorenzi proposal is contained as subroutines in the GRS-version of the standard finite element program ADINA, the Atluri formulation is used in separate post-processing programs developed by GRS. As a first application three-dimensional calculations of a compact-tension-shear specimen are considered.     

U型电磁超声换能器三维仿真研究

针对U型电磁超声表面波换能器(electromagnetic acoustic transducer,EMAT)换能效率低的问题,提出一种基于三维仿真的研究方法。首先,在Maxwell软件中建立U型电磁超声无损检测激发探头三维有限元模型并进行仿真分析,研究电磁超声换能器中线圈间距、截面积以及提离距离和磁铁类型及几何参数对换能效率的影响。结果表明:在使用蛇形线圈和U型磁铁作为电磁超声表面波换能器的情况下,减小线圈的提离距离、线圈截面积,适当增大线圈间距可以提高EMAT换能效率;此外,正交方差分析法对U型永磁铁的几何参数研究表明,U型永磁铁的宽度对换能效率的影响显著。     

基于Maxwell 3D的汽车空调压缩机电磁离合器电磁力仿真研究

以SEBX15汽车空调压缩机为设计原型,应用Ansoft Maxwell对基于三维静磁场的汽车空调压缩机电磁离合器的电磁力进行仿真计算,旨在研究线圈安匝数、气隙、吸盘隔磁槽槽宽、间距和内圈半径等几个因素对电磁离合器所产生的电磁力的影响,为汽车空调压缩机电磁离合器的设计和选配工作提供理论依据。     

3D numerical model of snow deformation without failure and its application to cold room mechanical tests

A three-dimensional model developed for the slow deformation, without macroscopic failure, of a stratified snow cover has been used to simulate laboratory mechanical tests performed on sieved snow. The model is based on a non-linear visco-elastic constitutive law for snow whose parameters depend on the snow temperature and density. Snow densification is derived from the bulk viscous strain. The model has been implemented in the Flac3D finite-difference code. The experimental device is a convergent channel in which snow is forced at a constant velocity in the range 1–100 μm s^− 1. Although snow is compressed under plane strain conditions, the channel geometry allows obtaining a multi-axial stress-state. Since the testing conditions involve ranges of variation of both the snow density and the strain-rate wider than those encountered for a natural snowpack, the constitutive relations of the model had to be modified. In this paper we present the constitutive model for snow, some details about its implementation into the Flac3D code, and its application to the numerical simulation of the mechanical tests. The comparison of the model and experimental results shows a relatively good agreement, although snow microstructure is accounted for only through its density. However, the treatment of the non-linearity of the viscosity must be improved. This 3D numerical model can be regarded as an interesting tool for assessing a constitutive law for snow on the basis of cold-room experiments, as well as for studying natural snow covers.     

3D numerical simulations of thermodiffusion experiment for a ternary mixture on-board foton

The phenomenon of mass flux in a mixture due to a temperature gradient is known as the Soret effect. Accurate experimental and theoretical models are needed for a better understanding and effective characterisation of situations involving coupled transport processes as in hydrocarbon reservoirs. This requires precise knowledge of the transport coefficients particularly the Fick and Soret diffusion coefficients. We have investigated the effect of residual-g and (very) low-frequency g-jitters encountered on-board spacecraft FOTON on mass-thermo-fluid dynamics in the presence of Soret effect. Results revealed that the diffusion process is slightly affected by the g-jitter on board the FOTON platform, which indicates that FOTON is a good platform to conduct near perfect microgravity environment.     

A numerical method for determining electromagnetic fields in cracked metals

We improve the numerical algorithm of the solution of a three-dimensional hypersingular integral equation of first kind based on the collocation method. The efficiency of the developed approach is shown. We also give some numerical results and their interpretation. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 2, pp. 85–93, March–April, 2007.     

An electromagnetic model for eddy-current imaging

In this paper, a model is presented for the interaction between an eddy-current probe system and a localized flaw in a test piece. The model is expressed in terms of the electromagnetic fields generated by the probe in the absence of the flaw, which are evaluated on an imaging surface near or on the surface of the test piece. Assuming that the quasistatic fields scattered by the flaw are proportional to immittance coefficients that are independent of the probe position, explicit expressions for the point-spread functions of the probe are derived. Knowledge of these functions permits one to optimize probe design and identify appropriate image-processing techniques. In contrast with optical image processing, it is shown that more than one point-spread function may be required to characterize a flaw image produced by an eddy-current probe.     

A plasticity concrete material model for DYNA3D

Lagrangian finite element codes with explicit time integration are extensively used for the analysis of structures subjected to explosive loading. Within these codes, numerous material models have been implemented. However, the development of a realistic but efficient concrete material model has proven complex and challenging.

The plasticity concrete material model in the Lagrangian finite element code DYNA3D was assessed and enhanced. The main modifications include the implementation of a third, independent yield failure surface; removal of the tensile cutoff and extension of the plasticity model in tension; shift of the pressure cutoff; implementation of a three invariant formulation for the failure surfaces; determination of the triaxial extension to triaxial compression ratio as a function of pressure; shear modulus correction; and implementation of a radial path strain rate enhancement. These modifications insure that the response follows experimental observations for standard uniaxial, biaxial and triaxial tests in both tension and compression, as shown via single element analyses. The radial path strain rate enhancement insures constant enhancement for all those tests. As a full scale example, a standard dividing wall subjected to a blast load is analyzed and the effects of the modifications assessed.     

Design of couplers for traveling wave RF structures using 3D electromagnetic codes in the frequency domain

In this paper, a simple equivalent circuit model of a traveling wave RF structure with input and output couplers is introduced. A few properties related to evaluating the reflection coefficient of the single coupler are then obtained and discussed. From these properties, a general procedure to design couplers for traveling wave structures using 3D electromagnetic codes in the frequency domain is derived. Finally, an example of coupler design for a 2π/3 X band accelerating structure is illustrated.     

Analytical and numerical analysis of 3D grid-reinforced orthotropic composite structures

A comprehensive micromechanical investigation of 3D periodic composite structures reinforced with a grid of orthotropic reinforcements is undertaken. Two different modeling techniques are presented; one is based on the asymptotic homogenization method and the other is a numerical model based on the finite element technique. The asymptotic homogenization model transforms the original boundary value problem into a simpler one characterized by effective coefficients which are shown to depend only on the geometric and material parameters of a periodicity cell. The model is applied to various 3D grid-reinforced structures with generally orthotropic constituent materials. Analytical formula for the effective elastic coefficients are derived, and it is shown that they converge to earlier published results in much simpler case of 2D grid reinforced structures with isotropic constituent materials. A finite element model is subsequently developed and used to examine the aforementioned periodic grid-reinforced orthotropic structures. The deformations from the finite element simulations are used to extract the elastic and shear moduli of the structures. The results of the asymptotic homogenization analysis are compared to those pertaining to their finite element counterparts and a very good agreement is shown between these two approaches. A comparison of the two modeling techniques readily reveals that the asymptotic homogenization model is appreciably faster in its implementation (without a significant loss of accuracy) and thus is readily amenable to preliminary design of a given 3D grid-reinforced composite structure. The finite element model however, is more accurate and predicts all of the effective elastic coefficients. Thus, the engineer facing a particular design application, could perform a preliminary design (selection of type, number and spatial orientation of the reinforcements) and then fine tune the final structure by using the finite element model.     

3D discrete numerical modelling of ridge keel punch through tests

Ridge keel punch through tests were simulated in 3D. In simulations unconsolidated ridge keel was modelled as a rubble pile of loose ice blocks. Combined finite–discrete element method (FEM–DEM) with rigid discrete elements representing ice blocks was used. Simulations were run in full scale. In total 47 simulations were run with various friction coefficients and keel depths. The failure process of simulated rubble piles was analysed and the shear strength of the rubble pile was derived from results. The effect of rubble porosity, keel depth and friction on shear strength of the pile was also analysed. The simulation results were compared to laboratory and full-scale punch through tests of unconsolidated ice rubble. Shear strength values achieved from simulations were in range for experimental results. Failure process was observed to be similar to laboratory experiments.     

Comparison of experimental AA6063 extrusion trials to 3D numerical simulations, using a general solute-dependent constitutive model

In this paper, laboratory scale extrusion experiments carried out on AA6063 billets are compared to numerical simulations. The numerical simulations are performed with a general solute-dependent elasto-viscoplastic constitutive model based on a hyperbolic sine law, allowing for the quantification of pressure levels, strain rates and stresses. The parameters for the material model were determined with compression tests. The extrusion trials were performed isothermally at temperatures of 623 and 723 K and with two distinct material conditions. The results of the numerical simulations show good agreement with the experimental results. It turns out that local high strain rates (>40 s⁻¹) have a significant influence on the extrusion pressure. However adequate test methods to provide constitutive data at these strain rates are very limited. At high temperatures the difference between material conditions had a considerably smaller influence on the extrusion experiments compared to the simulations. It is argued that this effect can be attributed to dynamic precipitation that occurred during the experiments under high temperature, high strain rate conditions.