Dimensional precision simulation of the formed picture tube panel

In the forming process of picture tube panel, the accumulated residual stresses cause the formed part to shrink, and the thermal and mechanical loads cause the mold blocks to deform. These two factors result in large deviations on the dimensions of the formed panel, which are both modeled and simulated in this paper. For residual stresses analysis, a thermo-rheologically simple viscoelastic material model is introduced to consider the stresses relaxation effect and to describe the mechanical behavior according to the temperature change. The shrinkage of formed parts induced by the residual stresses is calculated based on the theory of shells, represented as an assembly of flat elements formed by combining the constant strain and the discrete Kirchhoff triangular elements. A thermoelastic model is presented to predict the deformation of the mold blocks during pressing, which is based on the steady mold temperature field and thermoelastic boundary element method. The integrated simulation results suggest the amounts that the mold cavity should be machined by, and have been verified by comparing the dimensional precision of the panels produced by the mold considering a uniform part shrinkage and mold expansion or the mold considering the predicted ununiform part shrinkage and mold deformation.     

A thermoelastic analysis of shrink-fit type constructions by boundary element method

In this paper a boundary element method for the analysis of shrink fits is presented. The contact stresses created at the interference layer of the mating bodies and all over boundaries can be accurately evaluated. The shrinkage is usually generated or relieved by thermal expansions or by inertia forces and thus a thermoelastic bodyforce analysis is performed. The method is straightforward. Only the boundaries of the mating bodies are required to be discretized. Examples are shown to verify the accuracy of the analysis.     

Boundary point method for linear elasticity using constant and quadratic moving elements

Based on the boundary integral equations and stimulated by the work of Young et al. [J Comput Phys 2005;209:290–321], the boundary point method (BPM) is a newly developed boundary-type meshless method enjoying the favorable features of both the method of fundamental solution (MFS) and the boundary element method (BEM). The present paper extends the BPM to the numerical analysis of linear elasticity. In addition to the constant moving elements, the quadratic moving elements are introduced to improve the accuracy of the stresses near the boundaries in the post processing and to enhance the analysis for thin-wall structures. Numerical tests of the BPM are carried out by benchmark examples in the two- and three-dimensional elasticity. Good agreement is observed between the numerical and the exact solutions.     

Feedforward control of glass mold colling

In the manufacture of glass containers, good temperature regulation of the forming molds is essential for a high production yield. However daily and hourly temperature fluctuations of the cooling air, drawn from outside the glass plant, upsets the temperature stability. A 1°F change in the cooling air results in a 1.4°F change in the formed glass if air flow is unchanged. Since continuous mold or glass temperature measurements are impractical under production conditions, a feedforward control system, based upon a mathematical model of mold cooling and supported by experimentation, was designed to modulate the air flow to maintain mold cooling conditions. The design is implemented using a pressure controller manipulating a valve (or blower louver), with the controller setpoint computed from the air temperature. If the computed pressure exceeds a preset limit, due to temperature extremes, an override control function changes the glass feeder temperature controller setpoint and/or the machine speed instead of pressure. In the first installation, the feedforward control system paid for itself in several days. Since then, two years of operation at one plant has shown that two containers with production yields previously at 80–82% increased an average 7.6% and six containers with production yields at 90–92% increased an average 2.3%.     

Direct numerical simulation of the transitional boundary-layer flow induced by an isolated hemispherical roughness element

The joint application of direct numerical simulation (DNS) and a combined multiple-direct forcing and immersed boundary method (MDF/IBM) is proposed to investigate the transitional boundary-layer flow induced by three-dimensional roughness elements. The multi-direct forcing technique is used to calculate the interacting force between the solid surface of roughness elements and the fluid, and let the no-slip boundary conditions be satisfied. In order to validate the efficiency of these numerical methods, a flow past an isolated three-dimensional hemispherical roughness element mounted on a flat plate is simulated. The evolutional process of the discrete hairpin vortex and the formation of two kinds of secondary vortex structures are captured. The comparisons of profiles of streamwise mean velocity and velocity fluctuation between the simulated results and the experimental ones show great quantitative agreement. The evolution of disturbances and the growth of steady disturbance energy prove the transient growth mechanisms underlying the transitional flow induced by moderate-amplitude isolated three-dimensional roughness elements. Numerical methods used in this investigation can be extended to the simulation of the transitional boundary-layer flows induced by randomly distributed three-dimensional roughness elements.     

Study on the replication quality of micro-structures in the injection molding process with dynamical tool tempering systems

The injection molding of micro-structures is a promising mass-production method for a broad range of materials. However, the replication quality of these structures depends significantly on the heat flow during the filling stage. In this paper, the filling and heat transfer of v-groove and random structures below 5 μm is investigated with the help of an AFM (atomic force microscope) and thermo couples. A numerical model is developed to predict the filling of surface structures during the filling and packing stage. The model implies the use of simple fully developed flow models taking the power-law material model into account. This permits investigation into which ways several processing parameters affect the polymer flow in the surface structures. The mold wall temperature, which has significant effects on the polymer flow, is varied by using a variothermal mold temperature control system to validate the model proposed.     

Adaptive meshing for two-dimensional thermoelastic problems using Hermite boundary elements

In the present work, error indicators for the potential and elastostatic problems are used in a combined fashion to implement an adaptive meshing scheme for the solution of two-dimensional steady-state thermoelastic problems using the Boundary Element Method. These error indicators exploit in their formulation the possibility of generating two different numerical solutions from just one analysis using Hermite elements. The first solution is the standard one obtained from an analysis using Hermite elements. The second is a “reduced” solution obtained representing the field variables inside an element using some of the degrees of freedom of the Hermite element together with Lagrangian shape functions. The basic idea behind the computation of the error indicator is to compare these two solutions, on an element by element basis, to obtain an estimate of the magnitude of the error in the numerical solution corresponding to the Hermite elements. In this sense, it is assumed that the bigger the difference between these two solutions, the bigger the error in the original solution with Hermite elements. Since the thermoelastic problem in its uncoupled fashion is considered, the former approach is applied to both problems, heat conduction and thermoelastic. Since both numerical solutions for each one of these problems are obtained from just one analysis, the computational cost of the proposed error indicators is very low.     

Finite element stress analysis of a reinforced high-strength concrete column in severe fires

The objective of this study is to quantify the development of thermal stress states that account for the occurrence of moisture-induced explosive spalling of reinforced high-strength concrete structures under rapid heating conditions. Obtained from finite difference models of simulating coupled heat and mass transport phenomena in heated reinforced concrete elements, transient temperature profiles are used as prescribed boundary conditions for subsequent finite element thermo-elastic stress analysis. A computational methodology using the theory of mixtures (volume averaging) is presented to compute thermally induced effective stresses that are potentially associated with thermal spalling of high-strength concrete.     

Heating and melting deformable models

We develop physically-based graphics models of non-rigid objects capable of heat conduction, thermoelasticity, melting and fluid-like behaviour in the molten state. These deformable models feature non-rigid dynamics governed by Lagrangian equations of motion and conductive heat transfer governed by the heat equation for non-homogeneous, non-isotropic media. In its solid state, the discretized model is an assembly of hexahedral finite elements in which thermoelastic units interconnect particles situated in a lattice. The stiffness of a thermoelastic unit decreases as its temperature increases, and the unit fuses when its temperature exceeds the melting point. The molten state of the model involves a molecular dynamics simulation in which ‘fluid’ particles that have broken free from the lattice interact through long-range attraction forces and short-range repulsion forces. We present a physically-based animation of a thermoelastic model in a simulated physical world populated by hot constraint surfaces.     

空调车室气流流场和温度场的数值模拟

空调车室气流流场和温度场研究是空调车室内气流组织设计及车室内舒适环境评价与研究的基础。空调车室的空气流场数值计算是一复杂热边界条件、气固耦合的传热数值计算问题。该文介绍了空调车室内空气流动的数学模型及复杂边界条件的处理，阐述了车室气流流场和温度场数值模拟采用整体求解法所应注意的问题，SIMPLE和SIMPLER算法的比较，以及通用微分方程中各项的处理方式。最后通过ANSYS／FLOYRAN软件对二维的车室内气流流场和温度场进行模拟，论证了此有限元软件在空调车室数值模拟上的可行性。     

Boundary element analysis of nonlinear transient heat conduction problems

This paper is concerned with a boundary element formulation and its numerical implementation for the nonlinear transient heat conduction problems with temperature-dependent material properties. By using the Kirchhoff transformation for the material properties a set of pseudo-linear integral equations is obtained in space and time for the fully three-dimensional nonlinear problems under consideration. The resulting boundary integral equations are solved by means of the usual boundary element method. Emphasis is placed on the numerical solution procedure employing constant elements with respect to time. It is shown that in this case there is no need to evaluate the domain integrals resulting from the nonlinearity of the problem. Finally, the powerful usefulness of the proposed method is demonstrated through the numerical computation of several sample problems.     

Thermoplastic Forming of Bulk Metallic Glass— A Technology for MEMS and Microstructure Fabrication

A technology for microelectromechanical systems (MEMS) and microstructure fabrication is introduced where the bulk metallic glass (BMG) is formed at a temperature where the BMG exist as a viscous liquid under an applied pressure into a mold. This thermoplastic forming is carried out under comparable forming pressure and temperatures that are used for plastics. The range of possible sizes in all three dimensions of this technology allows the replication of high strength features ranging from about 30 nm to centimeters with aspect ratios of 20 to 1, which are homogeneous and isotropic and free of stresses and porosity. Our processing method includes a hot-cutting technique that enables a clean planar separation of the parts from the BMG reservoir. It also allows to net-shape three-dimensional parts on the micron scale. The technology can be implemented into conventional MEMS fabrication processes. The properties of BMG as well as the thermoplastic formability enable new applications and performance improvements of existing MEMS devices and nanostructures     

Elastic–plastic thermal stress analysis in a thermoplastic composite disc applied linear temperature loads via FEM

The aim of this study is to obtain thermal stresses in a thermoplastic composite disc unidirectionally reinforced by steel fibers. Finite element method was used to calculate the thermal elastic and elastic–plastic stress distributions within the composite disc. Therefore, the solution was carried out using the ANSYS software. The temperature loading was chosen so as to vary linearly from inner surface to outer surface along the radial sections of the disc. Linear thermal loads were selected as to differ from each other. They were also adjusted from 90 to 130 °C. Thermal stresses were formed within the disc by the linear temperature loads due to its having different thermal expansion coefficients in radial and tangential directions. In line with the thermal analysis results, the magnitudes of the tangential stress components for both elastic and elastic–plastic solutions were above the radial stress components. In addition, the residual stress components were also calculated using both elastic and elastic–plastic solution results. The results obtained pointed out that the magnitudes and distributions of the thermal stresses and residual stresses were greatly influenced by the increase in linear temperature loads.     

Application of Mathematical Modeling to Determine the Thermoelastic Characteristics of Nano-Reinforced Composites

A two-level mathematical model is constructed to describe the thermomechanical interaction between structural elements of a composite (nanoclusters formed by randomly distributed anisotropic single-walled carbon nanotubes and matrix particles) and an isotropic medium possessing the desired thermoelastic characteristics. This model was first employed to obtain the thermoelastic properties of a nanocluster by the self-consistency method and then the same technique was used to describe the thermomechanical interaction of nanoclusters with an isotropic matrix of the composite. A comparative analysis of the calculated dependences for the elastic moduli of the composite and its thermal coefficient of linear expansion was carried out with two-sided estimates of these characteristics based on the dual variational formulation of the thermoelasticity problem. For comparison, the results of a numerical experiment are also used. The presented relationships make it possible to predict the thermoelastic properties of promising composites reinforced by nanoclusters.     

An optimal solution for magnetohydrodynamic nanofluid flow over a stretching surface with constant heat flux and zero nanoparticles flux

This article examines the hydromagnetic three-dimensional flow of viscous nanoliquid. A bidirectional linear stretching surface has been used to create the flow. Novel features regarding Brownian motion and thermophoresis have been studied by employing Buongiorno model to examine the slip velocity of nanoparticle. Viscous liquid is electrically conducting subject to uniform applied magnetic field. Problem formulation in boundary-layer region is performed for low magnetic Reynolds number. Simultaneous effects of constant heat flux and zero nanoparticles flux conditions are utilized at boundary. Appropriate transformations correspond to the strongly nonlinear ordinary differential expressions. The resulting nonlinear systems have been solved through the optimal homotopy analysis method. Graphs have been sketched in order to analyze that how the temperature and concentration profiles are affected by various physical parameters. Further the coefficients of skin-friction and heat transfer rate have been numerically computed and discussed. Our findings show that the temperature distribution has a direct relationship with the magnetic parameter. Moreover, the temperature distribution and thermal boundary-layer thickness are higher for hydromagnetic flow in comparison with the hydrodynamic flow.

     

Solid-to-shell transition elements for the computation of interlaminar stresses

This paper presents an accurate and practical technique for coupling shell element models to three-dimensional continuum finite element models. The compatibility between these two types of formulations is enforced by degenerating a continuum element through kinematic constraints compatible with shell deformations. Two formulations of two-dimensional/three-dimensional transition elements are presented. The first and simplest formulation is based on the Mindlin-Reissner plate assumptions, and is found to perform well in a variety of problems involving the analysis of geometrically linear/non-linear laminated structures. The second formulation is based on a higher-order shell theory that allows stretching in the through-the-thickness direction. This additional freedom virtually eliminates the interlaminar normal stress boundary layer that can form in lower-order transition elements. Finally, the coupling of two-dimensional to three-dimensional subdomains is enriched with the use of an interface element, which can be used in conjunction with either transition formulation. The interface element improves the efficiency of the solid-to-shell transition modeling scheme by allowing the independent selection of optimal mesh sizes in the shell and the three-dimensional regions of the model.     

Microforming of three-dimensional microstructures from thin-film metallic glass

Thin-film metallic glasses (TFMGs) are characterized by an absence of size effect, high strength and high elastic limit due to their amorphous nature. As such, these materials are considered to be ideal candidates for microelectromechanical systems (MEMS). Furthermore, the TFMGs soften and show viscous flow within a certain temperature range called the supercooled liquid region (SCLR), which allows the TFMGs to be easily formed into three-dimensional (3-D) microstructures. The viscous flow in the SCLR is also useful for annealing and relaxing inner residual stresses of TFMGs. In the present paper, TFMG microcantilevers are fabricated by surface micromachining techniques. In order to heat and form the cantilevers, a local laser heating and microforming system is introduced, and the conditions of laser power and heating time that can not only form the cantilevers but also can maintain the amorphous nature of the TFMG are examined. Finally, based on the results of these investigations, microcantilevers having a 90/spl deg/ bend and a 90/spl deg/ twist, respectively, are successfully fabricated.     

Estimation of residual stresses in weldments using adaptive grids

Residual stress is a critical determining factor for the strength and service life of welded structures. Owing to its importance, a number of researchers have worked to estimate the residual stresses in the weldments. In the present work the residual stresses in butt welds were estimated using an elasto-plastic nonlinear finite element model. The temperature distribution was calculated by a finite element model using adaptive grid techniques. The temperature dependent mechanical properties were considered. The results were compared with the experimental results available in the literature.     

An efficient 3D stochastic finite element method for failure probability analysis of high temperature components

The loadings on high temperature components are generally complex and the discreteness of the material strength is usually great. Therefore, the two-dimensional (2D) failure probability analysis model and the deterministic finite element method (DFEM) cannot be applied to evaluate the failure probability of asymmetrical three-dimensional (3D) components. To overcome the drawbacks of the 2D model and the DFEM, an efficient 3D stochastic finite element method (SFEM) is proposed in this paper. With this method, the failure probability of components subjected to complex loadings can be estimated by using the statistical analysis of the Von Mises stresses of element nodes. Meanwhile, ANSYS and MATLAB were employed to carry out 3D parametric modeling, solving and statistical analysis. The proposed method is efficient, as is verified for two cases, and it can also be easily applied in practical engineering.