bluuebunny/crossref_metadata_2025 huggingface dataset:
Valve-Plate Design for an Axial Piston Pump Operating at Low Displacements
Authors: Manring Noah D.
Published: March 2003

The objectives of this research are to investigate the principal advantages of using various valve-plate slot geometries within an axial piston pump. In particular, three types of geometries are considered: a constant area slot geometry, a linearly varying slot geometry, and a quadratically varying slot geometry. By analyzing the pressure transients that are associated with each design at low pump displacements, it is shown that the magnitude of the pressure transition itself and the maximum pressure time rate-of-change may be specified for each design. In conclusion, it is shown that the constant area slot design exhibits the principal advantage of minimizing the required discharge area of the slot, the linearly varying slot design exhibits the principal advantage of utilizing the shortest slot length, while the quadratically varying slot design exhibits no principal advantage over either of the other two designs. The results of this research suggest that the use of quadratically varying slot geometry is not justified since it offers no obvious performance improvement.
A Fit-and-Merge Algorithm for Range-Image Segmentation and Model Reconstruction
Authors: Djebali M. , Melkemi M. , Sapidis N.
Published: March 2003

A segmentation and model-reconstruction algorithm is proposed based on polynomial approximation and on a new version of the “region growing” methodology. First, an initial partition is calculated on the basis of differential-geometric properties of the range image. Then, the first merging procedure is applied (“merge with constraints”) aiming at correctly identifying principal surfaces of the model. It examines all possible mergers of regions and selects those satisfying strict compatibility constraints. The second merging procedure relaxes these constraints to produce the “extended” regions and surfaces of the final segmentation. Theoretical work is presented proving the consistency of these merging procedures. Finally, application of the algorithm on industrial data is presented demonstrating the efficiency of the proposed methodology.
A CAD/CAM Representation Model Applied to Tolerance Transfer Methods
Authors: Desrochers Alain
Published: March 2003

This paper presents the adaptation of tolerance transfer techniques to a model called TTRS for Technologically and Topologically Related Surfaces. According to this model, any three-dimensional part can be represented as a succession of surface associations forming a tree. Additional tolerancing information can be associated to each surface association represented as a node on the tree. This information includes dimensional tolerances as well as tolerance chart values. Rules are then established to infer tolerance chains or stack up along with tolerance charts directly from the graph. This way it becomes possible to combine traditional one dimensional tolerance transfer techniques with a powerful three-dimensional representation model providing high technological contents.
Feasible Motion Solutions for Serial Manipulators at Singular Configurations
Authors: Fang Yuefa , Tsai Lung-Wen
Published: March 2003

When a serial manipulator is at a singular configuration, the Jacobian matrix will lose its full rank causing the manipulator to lose one or more degrees of freedom. This paper presents a novel approach to model the manipulator kinematics and solve for feasible motions of a manipulator at singular configurations such that the precise path tracking of a manipulator at such configurations is possible. The joint screw linear dependency is determined by using known line varieties so that not only the singular configurations of a manipulator can be identified but also the dependent joint screws can be determined. Feasible motions in Cartesian space are identified by using the theory of reciprocal screws and the resulting equations of constraint. The manipulator first-order kinematics is then modeled by isolating the linearly dependent columns and rows of the Jacobian matrix such that the mapping between the feasible motions in Cartesian space and the joint space motions can be uniquely determined. Finally, a numerical example is used to demonstrate the feasibility of the approach. The simulation results show that a PUMA-type robot can successfully track a path that is singular at all times.
Design Optimization of a Cartesian Parallel Manipulator
Authors: Kim Han Sung , Tsai Lung-Wen
Published: March 2003

This paper introduces a 3-DOF translational parallel manipulator called Cartesian Parallel Manipulator (CPM). The manipulator consists of a moving platform that is connected to a fixed base by three limbs. Each limb is made up of one prismatic and three revolute joints and all joint axes are parallel to one another. In this way, each limb provides two rotational constraints to the moving platform and the combined effects of the three limbs lead to an over-constrained mechanism with three translational degrees of freedom. The manipulator behaves like a conventional X-Y-Z Cartesian machine due to the orthogonal arrangement of the three limbs. Two actuation methods are analyzed. However, the rotary actuation method is discarded because of the existence of singularities within the workspace. For the linear actuation method, there exists a one-to-one correspondence between the input and output displacements of the manipulator. The effects of misalignment of linear actuators on the motion of the moving platform are discussed. Each limb structure is exposed to a bending moment induced by external forces exerted on the moving platform. In order to minimize the deflection at the joints caused by the bending moment, a method to maximize the stiffness is suggested. A numerical example of the optimal design is presented.
Multidisciplinary Robust Design Optimization of an Internal Combustion Engine
Authors: McAllister Charles D. , Simpson Timothy W.
Published: March 2003

In this paper, we introduce a multidisciplinary robust design optimization formulation to evaluate uncertainty encountered in the design process. The formulation is a combination of the bi-level Collaborative Optimization framework and the multiobjective approach of the compromise Decision Support Problem. To demonstrate the proposed framework, the design of a combustion chamber of an internal combustion engine containing two subsystem analyses is presented. The results indicate that the proposed Collaborative Optimization framework for multidisciplinary robust design optimization effectively attains solutions that are robust to variations in design variables and environmental conditions.
The FEM Analysis of Dry Contact in the Variable Torque Slipping Clutch With Skewed Rollers by Using Weighted Simplex and BFGS Methods
Authors: Feng Ming , Ono Kyosuke , Mimura Kenji
Published: March 2003

This paper describes an investigation of the dry contact problem in the variable torque slipping clutch with skewed rollers. The FEM based discretization of the integral equation of the Boussinesq solution is utilized in order to consider the spatial finite curve contact between the roller and the races. The non-Hertzian contact pressures are calculated by the method which is improved from what Conry and Seireg proposed. It is found that the additional time-consuming iterations arising from the modification of the entry rules can be completely avoided if the entering and leaving variables are properly weighted. The experience of calculations has shown that this improved method is very efficient, stable and robust for solving the present contact problem. In principle, the method is suitable for both 2-dimensional and 3-dimensional contact problems and it’s free from the continuous and disconnect surfaces. To obtain the contact pressure, a set of nonlinear equilibrium equations which govern the equilibrium of the elements of the clutch are solved by the BFGS (Broyden-Fletcher-Goldfarb-Shanno) method. The objective function is constructed such that it has the value of the square summation of these equilibrium equations. The unknown variables, including the roller attitudes and the angular velocities of the cage and the roller, are then obtained from the minimization of the objective function. To reduce the computational time, an algorithm of making the full use of the gradient information to calculate the optimal step is developed. In addition, the effects of various roller generator corrections on the contact pressure distribution are investigated. It helps to lengthen the raceway life by reducing the pressure concentrations occurring at the roller ends.
Contact Stress for Toroidal Drive
Authors: Xu Lizhong , Huang Zhen , Yang Yulin
Published: March 2003

Considering the elastic deformation of the rotor and the periodic change of the mesh teeth pair number, the calculation equations of the load distribution for the toroidal drive are presented. Based on the equations, the formulas for calculation of the contact stresses among stator and worm are introduced. By using the above-mentioned formulas, the contact stress distributions for the drive are obtained. The optimal parameters providing for equal contact strength of the stator and worm are determined. These results are useful in manufacture and design of the drive.
On Stress-Focusing Effect in a Uniformly Heated Solid Sphere
Authors: Ding H. J. , Wang H. M. , Chen W. Q.
Published: March 2003

By using the separation of variables technique, the dynamic thermal stress responses in an isotropic solid sphere subjected to uniform temperature rise all over the sphere and a sudden constant pressure at the external surface are performed successfully. The analytical solutions of the radial and hoop dynamic stresses at the center are also obtained. By means of the present method, integral transform can be avoided. Numerical results denote that a very high dynamic stress peak appears periodically at the center of the isotropic solid sphere subjected to uniform temperature rise all over the sphere and a sudden constant pressure at the external surface.
Rocking Vibration of Rotating Disk and Spindle Systems With Asymmetric Bearings
Authors: Park J. S. , Shen I. Y. , Ku C.-P. R.
Published: March 2003

This note presents how bearing asymmetry affects natural frequencies and mode shapes of a rotating disk/spindle system through a perturbation analysis. The analysis will focus on rocking motion of the disk/spindle system that consists of rigid-body rocking of the spindle, one-nodal-diameter modes of each disk, and deformation of spindle bearings.
On the Nonlinear Generalized Maxwell Fluid Model
Authors: Hu H.
Published: March 2003

An equation describing a nonlinear generalized Maxwell fluid model is presented. Model behavior, for constant rate elongations, is investigated. A comparison of the results in this study with those in the literature has been given. The conclusion of Corr et al. that the model has two solutions is questionable.
On Global Energy Release Rate of a Permeable Crack in a Piezoelectric Ceramic
Authors: Li S.
Published: March 2003

A permeable crack model is proposed to analyze crack growth in a piezoelectric ceramic. In this model, a permeable crack is modeled as a vanishing thin, finite dimension, rectangular slit with dielectric medium inside. A first-order approximation solution is derived in terms of the slit height, h0. The main contribution of this paper is that the newly proposed permeable crack model reveals that there exists a realistic leaky mode for electrical field, which allows applied electric field passing through the dielectric medium inside a crack. By taking into account the leaky mode effect, a correct estimation of electrical and mechanical fields in front of a crack tip in a piezoelectric ceramic is obtained. To demonstrate this new finding, a closed-form solution is obtained for a mode III permeable crack under both mechanical as well electrical loads. Both local and global energy release rates are calculated based on the permeable crack solution obtained. It is found that the global energy release rate derived for a permeable crack is in a broad agreement with some known experimental observations. It may be served as a fracture criterion for piezoelectric materials. This contribution reconciles the outstanding discrepancy between experimental observation and theoretical analysis on crack growth problem in piezoelectric materials.
Vibration of Thick Circular Disks and Shells of Revolution
Authors: Singh A. V. , Subramaniam L.
Published: March 2003

A fully numerical and consistent method using the three-dimensional theory of elasticity is presented in this paper to study the free vibrations of an axially symmetric solid. The solid is defined in the cylindrical coordinates r,θ,z by a quadrilateral cross section in the r-z plane bounded by four straight and/or curved edges. The cross section is then mapped using the natural coordinates (ξ,η) to simplify the mathematics of the problem. The displacement fields are expressed in terms of the product of two simple algebraic polynomials in ξ and η, respectively. Boundary conditions are enforced in the later part of the solution by simply controlling coefficients of the polynomials. The procedure setup in this paper is such that it was possible to investigate the free axisymmetric and asymmetric vibrations of a wide range of problems, namely; circular disks, cylinders, cones, and spheres with considerable success. The numerical cases include circular disks of uniform as well as varying thickness, conical/cylindrical shells and finally a spherical shell of uniform thickness. Convergence study is also done to examine the accuracy of the results rendered by the present method. The results are compared with the finite element method using the eight-node isoparametric element for the solids of revolution and published data by other researchers.
An Acoustic-Microwave Method for the Study of the Mechanical Influence of Moisture Content in Materials
Authors: Bacon C. , Guilliorit E. , Hosten B.
Published: March 2003

A one-dimensional theoretical model is developed to predict the acoustic waves generated by rapid thermal expansion caused by electromagnetic microwave absorption in viscoelastic rods. The theoretical acceleration at the end of the irradiated rod is predicted. The comparison between the experimental and the theoretical accelerations leads to the evaluation of viscoelastic characteristics. Parameters related to the electromagnetic absorption can be also obtained. A procedure to find approximate values of the different parameters is developed. Since it is considered in the model that the distribution of the temperature rise along the rod is exponential, very absorbing materials can be tested. Consequently, the influence of the moisture content on viscoelastic properties of a porous material can be investigated. The method is applied to study the influence of the moisture content on viscoelastic characteristics of medium density fiberboard materials.
Determination of the Local Stress-Strain Response of Foams
Authors: Wierzbicki T. , Doyoyo M.
Published: March 2003

A new specimen for determining the local stress-strain response of foams under uniaxial compression is presented along with the corresponding theory. The drawback of using conventional cubic specimens is that average stresses and strains are calculated, which introduces size effects due to structural and material inhomogeneities of commercial foams. Under compression, foam cubes develop unstable regimes, which involve localized deformation. The instabilities cause difficulties in establishing the correct stress-strain response of the material. Tapering specimens can enable controlled motion of the boundary separating the unstable and stable regimes. This concept is exploited in the present paper in experiments on closed-cell aluminum foam trapezoids. A crushing front propagates down the tapered specimen during compression, while the deformed region develops a new lateral shape. The experimental results are used along with several assumptions to extract a more representative stress-strain response of foam. The response is characterized by the initial plateau stress, shape exponent and densification strain. The significant effect of the variable Poisson’s ratio during crushing is also introduced. The results provide a basis for developing local constitutive behavior of foams.
Three-Dimensional Green’s Functions in Anisotropic Elastic Bimaterials With Imperfect Interfaces
Authors: Pan E.
Published: March 2003

In this paper, three-dimensional Green’s functions in anisotropic elastic bimaterials with imperfect interface conditions are derived based on the extended Stroh formalism and the Mindlin’s superposition method. Four different interface models are considered: perfect-bond, smooth-bond, dislocation-like, and force-like. While the first one is for a perfect interface, other three models are for imperfect ones. By introducing certain modified eigenmatrices, it is shown that the bimaterial Green’s functions for the three imperfect interface conditions have mathematically similar concise expressions as those for the perfect-bond interface. That is, the physical-domain bimaterial Green’s functions can be obtained as a sum of a homogeneous full-space Green’s function in an explicit form and a complementary part in terms of simple line-integrals over [0,π] suitable for standard numerical integration. Furthermore, the corresponding two-dimensional bimaterial Green’s functions have been also derived analytically for the three imperfect interface conditions. Based on the bimaterial Green’s functions, the effects of different interface conditions on the displacement and stress fields are discussed. It is shown that only the complementary part of the solution contributes to the difference of the displacement and stress fields due to different interface conditions. Numerical examples are given for the Green’s functions in the bimaterials made of two anisotropic half-spaces. It is observed that different interface conditions can produce substantially different results for some Green’s stress components in the vicinity of the interface, which should be of great interest to the design of interface. Finally, we remark that these bimaterial Green’s functions can be implemented into the boundary integral formulation for the analysis of layered structures where imperfect bond may exist.
The Bending of Curved Pipes With Variable Wall Thickness
Authors: Cherniy V. P.
Published: March 2003

A general solution is presented for the in-plane bending of short-radius curved pipes (pipe bends) which have variable wall thickness. Using the elastic thin-shell theory, the actual radius of curvature of the pipe’s longitudinal fibers and displacement of the neutral line of the cross section under bending are taken into account. The pipe’s wall thickness is assumed to vary smoothly along the contour of the pipe’s cross section, and is a function of an angular coordinate. The solution uses the minimization of the total energy, and is compared to our previous solution for curved pipes with constant wall thickness.
Forced Vibration of Cylindrical Helical Rods Subjected to Impulsive Loads
Authors: Temel B. , C¸alim F. F.
Published: March 2003

In this study, the forced vibration of cylindrical helical rods subjected to impulsive loads is theoretically investigated in the Laplace domain. The free vibration is then taken into account as a special case of forced vibration. The governing equations for naturally twisted and curved space rods obtained using Timoshenko beam theory are rewritten for cylindrical helical rods. The material of the rod is assumed to be homogeneous, linear elastic, and isotropic. The axial and shear deformations are also taken into account in the formulation. Ordinary differential equations in scalar form obtained in the Laplace domain are solved numerically using the complementary functions method to calculate exactly the dynamic stiffness matrix of the problem. The desired accuracy is obtained by taking only a few elements. The solutions obtained are transformed to the real space using the Durbin’s numerical inverse Laplace transform method. The free and forced vibrations of cylindrical helical rods are analyzed through various example. The results obtained in this study are found to be in a good agreement with those available in the literature.
Indentation Problems of Two-Dimensional Anisotropic Thermoelasticity With Perturbed Boundaries
Authors: Chao C.-K. , Gao B.
Published: March 2003

Complex variable representations in the Stroh formalism are used to analyze the problem of rigid stamp indentation on an irregularly shaped surface of an anisotropic thermoelastic body. The shape of boundary surface considered in this work includes a cosine wave-shaped surface and a triangular hole that are assumed to be slightly different from a straight line and an ellipse, respectively, for which the exact solutions exist. Based on a perturbation technique, an approximate solution for the punch problem of rigid stamp indentation on a wave-shaped surface or a triangular hole that is viewed as being perturbed from a straight line or an elliptical hole is provided. First-order perturbation solutions for both temperature and stress functions are given explicitly. Numerical results of contact stress under the punch face are discussed in detail and shown in graphic form.
Constraint-Based Design of Optimal Transport Elements
Authors: Drumheller Michael
Published: March 2003

A large aircraft contains thousands of transport elements, such as tubes, ducts, and wires. Their shape is subject to many constraints, some extrinsic (e.g., obstacle clearance) and others intrinsic (e.g., legal bend angles). A key problem is to design a feasible route that is optimal (e.g., as short as possible). We present an algorithm specialized for metal tubing that allows the user to sketch a route using constraint objects. The user arranges the constraint objects and the system fills in an optimal tube. Trade-offs can be explored rapidly, in terms of quantities of direct engineering interest. This effectively automates a tedious manual design process, saving time and money and producing superior designs. The algorithm has been implemented and tested in a production environment.
A Collaborative Framework for Integrated Part and Assembly Modeling
Authors: Bidarra Rafael , Kranendonk Niels , Noort Alex , Bronsvoort Willem F.
Published: March 2003

An ideal product modeling system should support both part modeling and assembly modeling, instead of just either of them as is the case in most current CAD systems. A good basis for such integration is multiple-view feature modeling, as it allows focusing on different aspects of the product, while at the same time maintaining consistency of all model views. This paper presents a framework that supports synchronous collaborative sessions via Internet, among members of a distributed development team, with such a modeling system. The framework provides facilities for creating a hierarchical product structure, with single and compound components, and meanwhile assigning tasks to team members. The actual design of a single component is supported by a web-client specialized in part design, whereas the specification of assembly relations among components is supported by a web-client specialized in assembly design. All clients make use of the same server, which runs a multiple-view feature modeling system and maintains the complete product model, guaranteeing consistency of the part design and the assembly design views.
Topological Framework for Part Families
Authors: Raghothama Srinivas , Shapiro Vadim
Published: March 2003

One of the fundamental unsolved problems in geometric design of mechanical solids has been the lack of a proper notion of family or class. Numerous heuristic and often incompatible definitions are used throughout the CAD industry, and it is usually not clear how to generate members of a family or, to decide if a given object belongs to an assumed family. Until these difficulties are resolved, no guarantees or standards for parametric modeling are possible, and all efforts to allow exchange of parametric representations between different CAD systems are likely to remain futile. Standardizing on a particular definition may be difficult, because parametric families depend intrinsically not only on shape but also on its representation. We classify families into parameter-space and representation-space, and show that both types are representation-induced families. We propose a formal framework for families based on the notion of topological categories. Every parametric family is defined by the representation-induced topological space of solids that are closed under the continuous maps in the assumed topology. We illustrate several well defined families and formally define a special but important case of CSG-induced family that generalizes to the more general case of feature-induced families.
Process-Planning for Layered Manufacturing of Heterogeneous Objects Using Direct Metal Deposition
Authors: Shin Ki-Hoon , Dutta Debasish
Published: March 2003

Layered manufacturing (LM) is emerging as a new technology that enables the fabrication of three-dimensional heterogeneous objects such as multimaterials and functionally gradient materials (FGMs). The necessary steps for LM fabrication of heterogeneous objects include representation and process planning of material information inside an object. This paper introduces a new processing planning method that takes into account the processing of material information. The detailed tasks are pre-processing (discretization), orientation (build direction selection), and adaptive slicing of heterogeneous objects. In particular, this paper focuses on the discretization process that converts all of the material information inside a heterogeneous object into material features like geometric features. It is thus possible to choose an optimal build direction among various preselected ones by approximately estimating build time. This is because total build time depends on the complexity of features. This discretization process also allows adaptive slicing of heterogeneous objects to minimize surface finish and material composition error. In addition, tool path planning can be simplified into fill pattern generation. Examples are shown to illustrate the overall procedure.
Dual-Primal Mesh Optimization for Polygonized Implicit Surfaces With Sharp Features
Authors: Ohtake Yutaka , Belyaev Alexander G.
Published: March 2003

A new method for improving polygonizations of implicit surfaces with sharp features is proposed. The method is based on the observation that, given an implicit surface with sharp features, a triangle mesh whose triangles are tangent to the implicit surface at certain inner triangle points gives a better approximation of the implicit surface than the standard Marching Cubes mesh [Lorensen, W.E., and Cline, H.E., 1987, Computer Graphics (Proceedings of SIGGRAPH ’87), 21(3), pp. 163–169] (in our experiments we use VTK Marching Cubes [Schroeder, W., Martin, K., and Lorensen, W., 1998, The Visualization Toolkit: An Object-Oriented Approach to 3-D Graphics, Prentice Hall]). First, given an initial triangle mesh, its dual mesh composed of the triangle centroids is considered. Then the dual mesh is modified such that its vertices are placed on the implicit surface and the mesh dual to the modified dual mesh is considered. Finally the vertex positions of that “double dual” mesh are optimized by minimizing a quadratic energy measuring a deviation of the mesh normals from the implicit surface normals computed at the vertices of the modified dual mesh. In order to achieve an accurate approximation of fine surface features, these basic steps are combined with adaptive mesh subdivision and curvature-weighted vertex resampling. The proposed method outperforms approaches based on the mesh evolution paradigm in speed and accuracy.
Handling Tool Holder Collision in Optimal Tool Sequence Selection for 2.5-D Pocket Machining
Authors: D’Souza Roshan M. , Wright Paul K. , Se´quin Carlo
Published: March 2003

Significant cycle time saving can be achieved in 2.5-D milling by intelligently selecting tool sequences. The problem of finding the optimal tool sequence was formulated as finding the shortest path in a single-source single-sink directed acyclic graph. The nodes in the graph represented the state of the stock after the tool named in the node was done machining and the edges represented the cost of machining. In this paper a novel method for handling tool holder collision in the graph-based algorithm for optimal tool sequence selection has been developed. The method consists of iteratively solving the graph for the shortest path, validating the solution by checking for tool holder collisions and eliminating problematic edges in the graph. Also described is a method to reduce the complexity of building the tool sequence graph in case there are tool holder collisions.
A Generic Approach to Free Form Surface Generation
Authors: Cotrina-Navau J. , Pla-Garcia N. , Vigo-Anglada M.
Published: March 2003

A theoretical approach to construct free form surfaces is presented. We develop the concepts that arise when a free form surface is generated by tracing a mesh, using differentiable manifold theory, and generalizing the B-spline scheme. This approach allows us to define a family of practical schemes. Four different applications of the generic approach are also presented in this paper.
Hybrid Cellular-functional Modeling of Heterogeneous Objects
Authors: Adzhiev Valery , Kartasheva Elena , Kunii Tosiyasu , Pasko Alexander , Schmitt Benjamin
Published: March 2003

An approach to modeling heterogeneous objects as multidimensional point sets with multiple attributes (hypervolumes) is presented. Attributes given at each point represent object properties of arbitrary nature (material, physical, etc.). A proposed theoretical framework is based on a hybrid model of geometry and attributes combining a cellular representation and a functionally based constructive representation of dimensionally non-homogeneous entities. Hypervolume model components such as objects, operations and relations are introduced and outlined. We present examples of modeling a multi-layer geological structure with cavities and wells, time-dependent adaptive mesh generation, and conversion of a 3D implicit complex to the cellular representation.
Application of Haptic Navigation to Modify Free-Form Surfaces Through Specified Points and Curves
Authors: Higashi Masatake , Aoki Nobuaki , Kaneko Takanobu
Published: March 2003

In this paper, we propose a method which modifies free-form surfaces to pass through not only specified points, but also specified curves with the assistance of haptic navigation. Using the method, designers of aesthetic shapes, such as a car body, can manipulate the model of the shape in real-time looking at its stereoscopic image and feeling its haptic sensation as if there were a clay model. The haptic navigation helps designers, letting them capture and recognize the object easily and constraining their operation to the appropriate direction or along the specified geometric element. In addition, the designers can get force feedback proportional to the modification quantity. To obtain a smoothly modified shape, we introduce correction functions to the given surface equations. A correction function distributes the effect of the change over the whole shape or the specified region according to the distance of the point in the normal direction of the given surface. The values of the correction function are 1 at the indicated point and 0 at the boundaries, and the shape is modified to keep the original smoothness. The correction values of the functions at the indicated points are determined to pass through all of them by solving a linear equation. To apply this to the specified curves including boundaries of a trimmed surface, we treat points composing the curve similarly to the point specification by representing them with a Cardinal spline. We have confirmed that the system is effective to manipulate a shape with its feeling and that smooth surfaces are obtained in real time as designers want.
Hierarchical Iso-Surface Extraction
Authors: Labsik Ulf , Hormann Kai , Meister Martin , Greiner Gu¨nther
Published: March 2003

The extraction and display of iso-surfaces is a standard method for the visualization of volume data sets. In this paper we present a novel approach that utilizes a hierarchy on both the input and the output data. For the generation of a coarse base mesh, we construct a hierarchy of volumes and extract an iso-surface from the coarsest resolution with a standard Marching Cubes algorithm. We additionally apply a simple mesh decimation algorithm to improve the shape of the triangles. We iteratively fit this mesh to the iso-surface at the finer volume levels. To be able to reconstruct fine detail of the iso-surface we thereby adaptively subdivide the mesh. To evenly distribute the vertices of the triangle mesh over the iso-surface and generate a triangle mesh with evenly shaped triangles, we have integrated a mesh smoothing algorithm into the fitting process. The advantage of this approach is that it generates a mesh with subdivision connectivity which can be utilized by several multiresolution algorithms such as compression and progressive transmission. As applications of our method we show how to reconstruct the surface of archeological artifacts and the reconstruction of the brain surface for the simulation of the brain shift phenomenon.
Conjugate Heat Transfer and Effects of Interfacial Heat Flux During the Solidification Process of Continuous Castings
Authors: Amin M. Ruhul , Gawas Nikhil L.
Published: March 2003

Multiphase fluid flow involving solidification is common in many industrial processes such as extrusion, continuous casting, drawing, etc. The present study concentrates on the study of air gap formation due to metal shrinkage on the interfacial heat transfer of a continuous casting mold. Enthalpy method was employed to model the solidification of continuously moving metal. The effect of basic process parameters mainly superheat, withdrawal velocity, mold cooling rate and the post mold cooling rate on the heat transfer was studied. The results of cases run with air gap formation were also compared with those without air gap formation to understand the phenomenon comprehensively. The current study shows that there exists a limiting value of Pe above which the effect of air gap formation on the overall heat transfer is negligible.
Estimation of Surface Temperature and Heat Flux Using Inverse Solution for One-Dimensional Heat Conduction
Authors: Monde Masanori , Arima Hirofumi , Mitsutake Yuhichi
Published: March 2003

An analytical method has been developed for the inverse heat conduction problem using the Laplace transform technique when the temperatures are known at two positions within a finite body. On the basis of these known temperatures, a closed form to the inverse solution can be obtained to predict surface conditions. The method first approximates the measured temperatures with a half polynomial power series of time as well as a time lag, which takes for a monitor to sense the temperature change at the point. The expressions for the surface temperature and the surface heat flux are explicitly obtained in the form of the power series of time. The surface temperature and heat flux calculated for some representative problems show agreement with the known values. The method can be applied to the case where an initial temperature distribution exists.
An Adaptive Angular Quadrature for the Discrete Transfer Method Based on Error Estimation
Authors: Versteeg Hendrik K. , Henson Jonathan C. , Malalasekera Weeratunge
Published: March 2003

The ray effect is a serious problem in radiative heat transfer computations. Continuously varying radiation fields are approximated numerically by sampling a limited number of angular directions. The discrete transfer method (DTM) is a conceptually simple technique suitable for general-purpose calculations of thermal radiation in complex geometries. Over the years a large variety of quadratures based on fixed ray firing patterns has been suggested for use in conjunction with the DTM. Arguably, in absence of a comprehensive error analysis, the efficacy of all these quadratures has only been proved for limited collections of radiation problems. Recently, sharp error bounds for the heat flux integral in the DTM have been established for irradiation distributions of three different continuity classes: smooth fields, fields with discontinuous angular derivatives and piecewise constant fields. The resulting error formulas have paved the way for a new adaptive quadrature strategy. Results are presented of its application to an idealized jet flame and to radiative exchanges inside a cube-shaped enclosure, along with brief comments on the viability of this approach in general-purpose CFD/radiation computations. In this paper, the following capabilities of the new adaptive angular quadrature are demonstrated: Evaluation of DTM heat flux integrals to a pre-specified tolerance for any intensity distribution; Excellent accuracy with very low ray numbers for irradiation due to small view factor sources; and Good heat flux estimates for piecewise constant sources, provided that the starting mesh is selected carefully.
Shape Identification by Inverse Heat Transfer Method
Authors: Cheng Chin-Hsiang , Chang Mei-Hsia
Published: March 2003

The aim of this study is to investigate the performance of the inverse heat transfer method in application to the shape identification problem. The approach is constructed by combining the curvilinear grid generation scheme, the direct problem solver, the conjugate gradient optimization method, and the redistribution method. A number of practical cases are considered, in which shape identification for an inner void within a solid body based on the data of the outer surface temperature of the solid body is performed. These cases are divided into five kinds of geometrical configurations. Results show that the profile of the inner void can be identified by using the inverse heat transfer approach, and the accuracy of the shape identification is dependent on the uncertainty of the outer surface temperature data, the Biot number, size of the inner void, and the geometrical configuration as well.
Effectiveness-NTU Relations for Heat Exchangers With Streams Having Significant Kinetic Energy Variation
Authors: Nellis Gregory F.
Published: March 2003

Effectiveness-NTU equations are derived for counter and parallel-flow heat exchangers with fluids having high velocities. In this case, the change in the kinetic energy occurring within the heat exchanger will significantly affect the temperature profiles. The effectiveness is found to depend on the usual non-dimensional variables that compare the heat exchanger conductance to the hot- and cold-side capacity rates and on four additional nondimensional quantities that reflect the magnitude and distribution of the kinetic energy on the hot and cold-sides of the heat exchanger. The governing differential equations are derived, nondimensionalized, and solved analytically for the case of an exponentially distributed kinetic energy. Graphical solutions are presented and interpreted for several cases. The solutions are applied to a particular case involving high velocities within a counter-flow heat exchanger used to produce cryogenic temperatures.
Temperature and Volumetric Fraction Measurements in a Hot Gas Laden With Water Droplets
Authors: Ruffino Paolo , di Marzo Marino
Published: March 2003

Two temperatures can be detected in a hot gas laden with water droplets. The lower one is the temperature read by a sensor immersed in the flow. This measurement is affected by significant evaporative cooling resulting in readings much below the real gas temperature. The higher one is the temperature of the gas. The difference between these two temperatures is proportional to the water volumetric fraction in the flow. On this basis, a new technique for the measurement of the water volumetric fraction is proposed. The results are compared with a conventional measurement technique based on optical methods. A novel approach to the gas temperature measurement is also introduced. The sensing device is kept at temperatures exceeding the Leidenfrost transition and therefore it is insensitive to the presence of the water droplets. Independent measurement techniques developed at the Evaporative Cooling Sensor Accuracy Test (ECSAT) facility provide the data to validate the measurements obtained with the Above Leidenfrost Temperature and Evaporative Cooling (ALTEC) sensor.
Three-Dimensional Investigation of a Laminar Impinging Square Jet Interaction With Cross-Flow
Authors: Aldabbagh L. B. Y. , Sezai I. , Mohamad A. A.
Published: March 2003

The flow and heat transfer characteristics of an impinging laminar square jet through cross-flow have been investigated numerically by using the three-dimensional Navier-Stokes and energy equations in steady state. The simulations have been carried out for jet to cross-flow velocity ratios between 0.5 and 10 and for nozzle exit to plate distances between 1D and 6D, where D is the jet width. The complex nature of the flow field featuring a horseshoe vortex has been investigated. The calculated results show that the flow structure is strongly affected by the jet-to-plate distance. In addition, for jet-to-plate spacing of one jet width and for jet to cross-flow velocity ratios less than 2.5 an additional peak occurs at about three-dimensional downstream of the jet impingement point. For high jet to cross-flow ratios two horseshoe vortices form around the jet in the case of small jet-to-plate spacings.
An Experimental Investigation on Flow Boiling of Ethylene-Glycol/Water Mixtures
Authors: Kandlikar Satish G. , Bulut Murat
Published: March 2003

Mixtures of ethylene glycol and water are used in cooling the engines in automotive applications. Heat is transferred essentially under subcooled flow boiling conditions as the mixture flows over the hot surfaces, which are at temperatures well above the local saturation temperature of the mixture. Very little information is available in the literature on the subcooled flow boiling characteristics of this mixture. The present work focuses on obtaining experimental heat transfer data for water and its mixtures containing ethylene-glycol (0 to 40 percent mass fraction, limited by the maximum allowable temperature in the present setup) in the subcooled flow boiling region. The experimental setup is designed to obtain local heat transfer coefficients over a small circular aluminum heater surface, 9.5-mm in diameter, placed at the bottom 40-mm wide wall of a rectangular channel 3-mm×40-mm in cross-section. Available models for (a) subcooled flow boiling of pure liquids and (b) saturated flow boiling of binary mixtures are extended to model the subcooled flow boiling of binary mixtures.
The Approximate Deconvolution Model for Large-Eddy Simulation of Compressible Flows With Finite Volume Schemes
Authors: von Kaenel R. , Adams N. A. , Kleiser L. , Vos J. B.
Published: March 2003

The approximate deconvolution model for large-eddy simulation is formulated for a second-order finite volume scheme. With the approximate deconvolution model, an approximation of the unfiltered solution is obtained by repeated filtering, and given a good approximation of the unfiltered solution, the nonlinear terms of the Navier-Stokes equations are computed directly. The effect of scales not represented on the numerical grid is modeled by a relaxation regularization involving a secondary filter operation. A turbulent channel flow at a Mach number of M=1.5 and a Reynolds number based on bulk quantities of Re=3000 is selected for validation of the approximate deconvolution model implementation in a finite volume code. A direct numerical simulation of this configuration has been computed by Coleman et al. Overall, our large-eddy simulation results show good agreement with our filtered direct numerical simulation data. For this rather simple configuration and the low-order spatial discretization, differences between approximate deconvolution model and a no-model computation are found to be small.
Identification of artifacts in Auger electron spectroscopy due to surface topography
Authors: Gelsthorpe A. , El-Gomati M. M.
Published: March 2003

The application of Auger electron spectroscopy to sharp topographies, such as microfabricated field emitters, leads to two analysis artifacts; edge enhancement and shadowing. As a result, the detected Auger electron peak heights can change by more than 100%; potentially giving rise to the wrong conclusions being drawn about the elemental surface concentrations. A single-pass cylindrical mirror analyzer has been modified for use in the rapid identification of such artifacts. The modifications comprises a multichannel electron detector divided into six segments spanning 360° of azimuth and an electrostatic lens that passes electrons to the electron detector along the same exit trajectory independently of their energy. Preliminary results of the use of the instrument in the analysis of a tungsten coated volcano-shaped silicon field-emitter structure are reported. The analysis simultaneously shows two different edge artifacts in the six spectra due to edge enhancement and shadowing. The experiment demonstrated here shows a rapid method for identifying these artifacts and avoids the need to repeat the experiment using a different angle of incidence, as was conventionally the case.
Design of a shallow thermally stable ohmic contact to p-type InGaSb
Authors: Wang S. H. , Mohney S. E. , Hull B. A. , Bennett B. R.
Published: March 2003

Ohmic contacts to p-type InGaSb have been investigated. The factors that influence the contact resistance, thermal stability, and shallowness of the contacts are examined. The most desirable contact studied in this work employs three layers. A very thin layer of palladium is deposited on the p-InGaSb first and is found to lower the resistance at the metal/semiconductor interface. The next layer is W, which is predicted to be in thermodynamic equilibrium with InGaSb and which serves as a diffusion barrier to protect the semiconductor from the reaction with the final capping layer. The final capping layer is a 100 or 150 nm Au layer. The Au lowers the metal sheet resistance, which we have found both experimentally and through modeling to influence the contact resistance measurements, and the Au layer provides a contact surface that does not oxidize. The contact resistance of the as-deposited Pd/W/Au (5/50/145 nm) contact is 0.08 Ω mm (corresponding to a specific contact resistance of <3×10−7 Ω cm2), while the more thermally stable Pd/W/Au (5/145/100 nm) contact exhibits a contact resistance of 0.08 Ω mm only after annealing at 250 °C for 3 h, in both cases on a p-In0.25Ga0.75Sb layer with a semiconductor sheet resistance of approximately 300 Ω/□. The thermal stability of the Pd/W/Au contacts was also examined. The Pd/W/Au (5/145/100 nm) contacts remained shallow and exhibited no measurable electrical degradation when aged at 250 °C in N2 for 100 h, while they survived at 250 °C for 14 days in sealed, evacuated, quartz tubes.