bluuebunny/crossref_metadata_2025 huggingface dataset:
A Closure Model for Transient Heat Conduction in Porous Media
Authors: Hsu C. T.
Published: February 2008

Equations governing the transient heat conduction in porous materials consisting of solids and fluids of different thermal properties were derived with a volumetric average scheme under the assumption of nonthermal equilibrium. The derivation leads to a macroscopic two-equation system which requires the closure modeling of new unknown terms due to interfacial transport, namely, the tortuosity term and the interfacial heat transfer term. Closure relations were obtained from the microscopic equations for temperature fluctuation under quasi-steady assumption. The closure coefficients appeared in the closure relations then depend on the media geometry as well as thermal properties. To demonstrate these dependencies, the closure coefficient for the thermal tortuosity is evaluated based on the effective stagnant thermal conductivity model proposed by Hsu et al. (1995) for periodically packed cubes, and the coefficient for interfacial heat transfer based on a quasi-steady heat conduction of dispersed spheres immersed in fluids. The salient features as well as the applicability and limitation of the newly proposed transient heat conduction model were discussed.
Enhanced Heat Transfer Characteristics of Viscous Liquid Flows in a Chevron Plate Heat Exchanger
Authors: Muley A. , Manglik R. M. , Metwally H. M.
Published: February 2008

Steady-state heat transfer and pressure drop data for single-phase viscous fluid flows (2 ≤ Re ≤ 400) in a single-pass U-type counterflow plate heat exchanger (PHE) with chevron plates are presented. With vegetable oil as test fluid (130 < Pr < 290), three different plate arrangements are employed: two symmetric (β = 30 deg/30 deg and 60 deg/60 deg) and one mixed (β = 30 deg/60 deg). The effects of chevron angle β, corrugation aspect ratio γ, and flow conditions (Re, Pr, μ/μw on Nu and f characteristics of the PHE are delineated. The results show a rather complex influence of plate surface corrugations on the enhanced thermal-hydraulic behavior. Relative to the performance of equivalent flat-plate packs, chevron plates sustain up to 2.9 times higher heat transfer rates on a fixed geometry and constant pumping power basis, and require up to 48 percent less surface area for the fixed heat load and pressure drop constraint.
Performance of Dehumidifying Heat Exchangers With and Without Wetting Coatings
Authors: Hong K. , Webb R. L.
Published: February 2008

Limited previous work has shown that use of special hydrophilic coatings will provide lower air pressure drop in finned tube heat exchangers operated under dehumidifying conditions. However, no detailed work has been reported on the effect of different coating types, or different fin surface geometries on the wet pressure drop. In this study, wind tunnel tests were performed on three different fin geometries (wavy, lanced, and louver) under wet and dry conditions. All dehumidification tests were done for fully wet surface conditions. For each geometry, the tests were performed on uncoated and coated heat exchangers. For all three fin geometries, the wet-to-dry pressure drop ratio was 1.2 at 2.5 m/s frontal air velocity. The coatings have no influence on the wet or dry heat transfer coefficient. However, the wet surface heat transfer coefficient was 10 to 30 percent less than the dry heat transfer coefficient, depending on the particular fin geometry. The effect of the fin press oil on wet pressure drop was also studied. If the oil contains a surfactant, good temporary wetting can be obtained on an uncoated surface; however, this effect is quickly degraded as the oil is washed from the surface during wet operation. This work also provides a critical assessment of data reduction methods for wet surface operation, including calculation of the fin efficiency.
Turbulent Convection in a Czochralski Silicon Melt
Authors: Zhang T. , Ladeinde F. , Prasad V.
Published: February 2008

The individual and combined effects of buoyancy, crystal rotation, and crucible rotation are reported in this paper for axisymmetrically averaged melt convection in a large Czochralski crystal growth system for silicon. These body force effects are characterized by the respective parameters of Grashof number, Gr, rotational Reynolds number, Rer, and the Marangoni number, Ma. The range investigated consists of 108 ≤ Gr ≤ 1010, 103 ≤ Re ≤ 3 × 104, and 103 ≤ Ma ≤ 104, which is appropriate for the real Czochralski system. The studies are based on a multizone, adaptive, finite volume calculation. Validations of the numerical procedures are presented, including a grid convergence study. The effects of buoyancy and rotation on melt convection are discussed in detail. When the crystal and crucible both rotate at the same speed, but in opposite directions, without buoyancy, the effect of the crucible rotation is stronger. The rotation induces turbulence, contrary to what the literature suggests. For the combined effects, the intensity of turbulence and the average Nusselt number at the crucible wall are largest when buoyancy is slightly dominant over rotation. High rotation rates generate temperature oscillations in the presence of high Grashof numbers. Because of the consequence of oscillation for crystal quality, a dynamic adjustment of the rotation rate might be necessary in order to obtain desirable growth conditions.
Nusselt Numbers in Rectangular Ducts With Laminar Viscous Dissipation
Authors: Morini G. L. , Spiga M.
Published: February 2008

In this paper, the steady temperature distribution and the Nusselt numbers are analytically determined for a Newtonian incompressible fluid in a rectangular duct, in fully developed laminar flow with viscous dissipation, for any combination of heated and adiabatic sides of the duct, in H1 boundary condition, and neglecting the axial heat conduction in the fluid. The Navier-Stokes and the energy balance equations are solved using the technique of the finite integral transforms. For a duct with four uniformly heated sides (4 version), the temperature distribution and the Nusselt numbers are obtained as a function of the aspect ratio and of the Brinkman number and presented in graphs and tables. Finally it is proved that the temperature field in a fully developed T boundary condition can be obtained as a particular case of the H1 problem and that the corresponding Nusselt numbers do not depend on the Brinkman number.
Effect of Aperture Geometry on Heat Transfer in Tilted Partially Open Cavities
Authors: Elsayed M. M. , Chakroun W.
Published: February 2008

Free convection from a square, tilted partially open cavity was investigated experimentally. The experiment was carried out to study the effect of the aperture geometry on the heat transfer between the cavity and the surrounding air. Four different geometrical arrangements for the opening were investigated: (1) high wall slit, (2) low wall slit, (3) centered wall slit, and (4) uniform wall slots. Each opening arrangement was studied at opening ratios (i.e., ratio of opening height to cavity height) of 0.25, 0.5, and 0.75. The average heat transfer coefficient between the cavity and the surrounding air was estimated for each geometrical arrangement for tilt angles ranging from −90 deg to +90 deg with increments of 15 deg and at a constant heat flux Grashof number of 5.5 × 108. The results showed that for tilt angles between 90 and 75 deg, the heat transfer coefficient has a small value that is independent of the geometrical arrangement of the opening. The value of the heat transfer coefficient increases sharply with decreasing tilt angle until an angle value of zero degrees is reached. The increase in the heat transfer coefficient continues in the negative range of tilt angle but not in the same rate as in the positive range of the tilt angle. The uniform slot arrangement gave in general higher heat transfer coefficient than the other three arrangements of the opening. Large differences in the heat transfer coefficient were observed between the high and the low wall slits where the high wall slit is found to transfer more heat to the surroundings than the low wall slit. Correlations were developed to predict the average Nusselt number of the cavity in terms of the opening ratio and the cavity tilt angle for cavities with high wall slit, low wall slit, centered wall slit, and the uniform wall slots.
Far-Infrared Transmittance and Reflectance of YBa2Cu3O7-δ Films on Si Substrates
Authors: Kumar A. R. , Zhang Z. M. , Boychev V. A. , Tanner D. B. , Vale L. R. , Rudman D. A.
Published: February 2008

The transmittance and reflectance of superconductive YBa2Cu307-δ (YBCO) thin films deposited on Si substrates have been measured in the far-infrared frequency region from 10 to 100 cm−1 (wavelength from 1000 to 100 μm) at temperatures between 10 and 300 K. The effects of interference, optical resonance, and antireflection on the radiative properties of high-temperature superconducting (HTSC) films are observed and quantitatively analyzed. Furthermore, we have measured the reflectance of the HTSC film-substrate composites for radiation incident on the substrate side (backside reflectance) for the first time. The backside reflectance increases significantly from the normal state to the superconducting state at certain frequencies; this experimentally demonstrates that HTSC films can be used to build far-infrared intensity modulators. The complex refractive index of the YBCO films is determined from the measured transmittance using the Drude model in the normal state and a two-fluid model in the superconducting state. The complex refractive index obtained from this study is useful for various applications of YBCO films, including radiation modulators, detectors, and Fabry-Perot resonators.
Forced Convection Condensation on a Horizontal Tube: Influence of Turbulence in the Vapor and Liquid Phases
Authors: Homescu D. , Panday P. K.
Published: February 2008

An implicit finite difference scheme is used to solve the problem of condensation of pure vapors flowing vertically downwards around a horizontal tube. The incompressible flow equations coupled at the interface for the liquid and vapor phases are solved. The pressure gradient, inertia, and enthalpy convection terms are retained in this analysis, and the influence of turbulence in the two phases is considered. The calculated results for laminar flow and those from different mixing length turbulence models are compared with experimental results for condensation of steam and R113. The results presented show that the average condensation heat transfer coefficients obtained using Kato’s turbulence model in the condensate film and Pletcher’s model in the vapor phase, are in good agreement with the experimental data.
Complete Condensation of Forced Convection Two-Phase Flow in a Miniature Tube
Authors: Begg E. , Khrustalev D. , Faghri A.
Published: February 2008

A physical and mathematical model of annular film condensation in a miniature tube has been developed. In the model the liquid flow has been coupled with the vapor flow along the liquid-vapor interface through the interfacial temperature, heat flux, shear stress, and pressure jump conditions due to surface tension effects. The model predicts the shape of the liquid-vapor interface along the condenser and the length of the two-phase flow region. The numerical results show that complete condensation of the incoming vapor is possible at comparatively low heat loads. Observations from a flow visualization experiment of water vapor condensing in a horizontal glass tube confirm the existence and qualitative features of annular film condensation leading to the complete condensation phenomenon in small diameter (d < 3.5 mm) circular tubes.
Experimental Study of Dispersed Droplets in High-Pressure Annular Flows
Authors: Trabold T. A. , Kumar R. , Vassallo P. F.
Published: February 2008

Local measurements were made in a droplet-laden vapor core in upward R-134a annular flow in a high aspect ratio vertical duct. These detailed measurements are unique in that they were performed at high pressures and low liquid-to-vapor density ratios. Using a gamma densitometer, hot-film anemometer and laser Doppler velocimeter, profiles of void fraction, liquid droplet frequency, and droplet velocity were acquired across the narrow test section dimension. At relatively high flows, the measured void fraction was highest near the wall, due to the thinning of the liquid film. The dip in the void fraction in the vapor core at these flows suggests significant droplet entrainment. The entrainment fractions for these refrigerant flows fall in the range measured for pressurized steam-water systems. The average drop size, calculated from direct measurements of void fraction, droplet velocity, and frequency, compares favorably with previous experimental results from the literature. These data are useful for developing an improved understanding of practical two-phase flows, and for assessment of advanced two-fluid computer codes.
On the Prediction of Local Ice Formation in Pipes in the Presence of Natural Convection
Authors: Keary A. C. , Bowen R. J.
Published: February 2008

Pipe freezing is a pipeline maintenance technique which is used to isolate sections of a liquid-filled pipeline by freezing the contents to form a solid pressure-resistant plug. This paper describes the development of a numerical model of natural convection and solidification in a vertical water-filled pipe. The natural convection-driven flows are examined in detail and the interaction with the forming ice plug is studied. The results are compared with experimental data. The numerical approach is contrasted with a simpler one-dimensional analytical method and criteria are proposed to aid the choice of modeling technique under different conditions.
Optical Measurement of Thermal Contact Conductance Between Wafer-Like Thin Solid Samples
Authors: Ohsone Y. , Wu G. , Dryden J. , Zok F. , Majumdar A.
Published: February 2008

This paper presents a noncontact optical technique for measuring the thermal contact conductance between wafer-like thin solid samples. The technique is based on heating one solid surface by a modulated laser beam and monitoring the corresponding temperature modulation of the other solid surface across the interface using the reflectance of a probe laser beam. The phase lag between the two laser signals is independent of the optical properties of the samples as well as the laser intensities, and can be related to the thermal contact conductance. A detailed theoretical analysis is presented to estimate the thermal contact conductance as well as the thermophysical properties of the solids from the phase lag measured as a function of the modulation frequency. Closed-form solutions in the high-frequency limit are derived in order to provide a simple estimation procedure. The effect of misalignment of the two lasers is studied and the conditions for robust measurements are suggested. As a benchmark for this technique, the thermal conductivity of a single crystal silicon sample was measured to within two percent of reported values. The thermal contact conductance was measured for Al-Si samples, each about 0.22 mm thick, in the pressure range of 0.8–10 MPa. In contrast to traditional contact conductance measurement techniques that require steady-state operation and insertion of thermocouples in thick solid samples, the noncontact dynamic optical technique requires much less time and is particularly well suited for electronic packaging materials that are typically in the thickness range of 0.1–5 mm. In addition, localized conductance measurements are now possible with a spatial resolution of about four times the thickness of the solid and can be used to detect interfacial voids and defects.
Energy Dissipation in Sheared Granular Flows
Authors: Karion A. , Hunt M. L.
Published: February 2008

Using a two-dimensional discrete element computer simulation of a bounded, gravity-free Couette flow of particles, the heat dissipation rate per unit area is calculated as a function of position in the flow as well as overall solid fraction. The computation results compare favorably with the kinetic theory analysis for rough disks. The heat dissipation rate is also measured for binary mixtures of particles for different small to large solid fraction ratios, and for diameter ratios of ten, five, and two. The dissipation rates increase significantly with overall solid fraction as well as local strain rates and granular temperatures. The thermal energy equation is solved for a Couette flow with one adiabatic wall and one at constant temperature. Solutions use the simulation measurements of the heat dissipation rate, solid fraction, and granular temperature to show that the thermodynamic temperature increases with solid fraction and decreases with particle conductivity. In mixtures, both the dissipation rate and the thermodynamic temperature increase with size ratio and with decreasing ratio of small to large particles.
Three-Dimensional Study of Combined Conduction, Radiation, and Natural Convection From Discrete Heat Sources in a Horizontal Narrow-Aspect-Ratio Enclosure
Authors: Adams V. H. , Joshi Y. , Blackburn D. L.
Published: February 2008

Three-dimensional natural convection flow and heat transfer were numerically studied for a three-by-three array of discrete protruding heat sources on a horizontal substrate in an air-filled, rectangular, narrow-aspect-ratio enclosure with length, width, and height ratio of 6:6:1. The governing equations for natural convection in air, coupled with conjugate conduction and radiation within the enclosure were solved using a finite volume method. The study examines the complex thermal interactions between the heat sources, substrate, and enclosure walls as affected by the thermal conductance of the walls and substrate with the intent of determining which physical effects and level of detail are necessary to accurately predict thermal behavior of discretely heated enclosures. The influence of radiation on the overall heat transfer is given particular attention. The three-dimensionality of the problem was evident in the overall flow characteristics and in the convective heat transfer edge effects on the heat source surfaces. Excellent agreement between temperature predictions on the heat sources and substrate and experimental measurements was obtained for modified Rayleigh numbers in the range of 9.7 × 105 to 1.6 × 107.
Kinematic Synthesis of Deployable-Foldable Truss Structures Using Graph Theory, Part 1: Graph Generation
Authors: Warnaar D. B. , Chew M.
Published: February 2008

Kinematic structural synthesis has been relatively successful when applied to the conceptual design of mechanisms. The approach presented in this paper, however, views the design process from an initial standpoint of a truss structure. First, graphs are generated that represent truss structures with a given number of nodes and links. Each graph is then modified by designating certain edges in the graph to represent links in the structure that incorporate additional degrees of freedom. In so doing, the graph of a structure is transformed into one representing a mechanism. A procedure is presented that enables the exhaustive generation of these graphs for deployable structures of any given number of nodes and links. From these graphs, it is then possible to obtain enumerable novel deployable truss structures as well as those that have been reported in the literature.
A Derivation of the Pole Curve Equations in the Projective Plane
Authors: Brady M. , Peterson S.
Published: February 2008

Traditional four-position mechanism synthesis focuses on the poles corresponding to four displacements of a rigid body. From these poles equations for the center-point and circle-point curves are developed. However, if a pole is infinite (the associated displacement is a pure translation), the established derivations for the pole curve equation break down. One can eliminate this problem by expressing the pole curve equation in the projective plane, because all points, including points at infinity, have finite homogeneous coordinates. In this paper, the pole curve equation is derived in the projective plane. This projection derivation is an analytic expression of Alt’s graphical construction of the pole curve. The pole curve is the intersection of a pair of projective pencils of circles (one pencil for opposite sides of the opposite-pole quadrilateral) which are defined by the homogeneous coordinates of the poles. The resulting equations are applied to several problems in the synthesis of four-bar linkages. In addition the rotation curves, the locus of displacement poles for a four-bar linkage, are computed for linkages with sliding joints.
Burmester Theory for Four-Bar-Band Mechanisms
Authors: Luck K. , Modler K.-H.
Published: February 2008

A band mechanism includes inter alia a flexible band and a disk profile. Such a mechanism can be used for path generation better than a four-bar linkage. Also several plane positions can be realized. This paper investigates the synthesis of four-bar-band mechanisms by using complex vector algebra. Several technical tasks demonstrate the flexible application of such mechanisms. These tasks are formulated according to the well-known Burmester Theory, but with higher claims and a solution achieved by analytical methods. Furthermore, this paper demonstrates that a four-bar linkage is a special case of a four-bar-band mechanism.
Band-Drive Suspension Mechanism Design for Ground-Based Testing of Flexible Space Structures
Authors: Yang Li-Farn , Chew Meng-Sang , Juang Jer-Nan
Published: February 2008

A suspension system based on a band mechanism is investigated to provide the free-free conditions for ground-based validation testing of flexible space structures. The band mechanism consists of a noncircular disk with a convex profile, preloaded by torsional springs at its center of rotation so that static equilibrium of the test structure is maintained at any vertical location; gravitational force will be directly counteracted during dynamic testing of the space structure. This noncircular disk within the suspension system can be configured to remain unchanged for test articles with different weights as long as the torsional spring is replaced to maintain the originally designed frequency parameter of W/ks Simulations of test articles which are modelled as lumped-parameter as well as continuous parameter systems are also presented.
A Computer-Aided Design Technique for Semi-Automated Infinite Point Coupler Curve Synthesis of Four-Bar Linkages
Authors: Unruh V. , Krishnaswami P.
Published: February 2008

At the present time, there are no satisfactory computer-aided solution schemes for solving the infinite point coupler curve synthesis problem (i.e., the problem of synthesizing a four-bar linkage whose coupler curve best approximates a fully specified closed trajectory). In order to develop a programmable solution process for this class of problems, it is necessary to devise a way of storing a catalog of coupler curves in a computer database. In addition, comparison procedures must be developed for detecting geometric similarities between curves; these procedures must be capable of observing similarities in the shapes of curves which may be scaled or oriented differently. In this paper, a data representation scheme based on uniform periodic B-splines is proposed as a viable means of storing coupler curves in a database. Automated procedures for fitting B-splines to coupler cures or other closed curves are also developed. The paper also presents a set of algorithms for comparing the shapes of curves based on the control polygons of their B-spline approximations. These algorithms are implemented in a computer program that is an effective tool for semi-automated computer-aided solution of the infinite point coupler curve synthesis problem. Example problems solved using this program are discussed, along with some suggestions for further work on this topic.
Parametric Deflection Approximations for End-Loaded, Large-Deflection Beams in Compliant Mechanisms
Authors: Howell L. L. , Midha A.
Published: February 2008

Geometric nonlinearities often complicate the analysis of systems containing large-deflection members. The time and resources required to develop closed-form or numerical solutions have inspired the development of a simple method of approximating the deflection path of end-loaded, large-deflection cantilever beams. The path coordinates are parameterized in a single parameter called the pseudo-rigid-body angle. The approximations are accurate to within 0.5 percent of the closed-form elliptic integral solutions. A physical model is associated with the method, and may be used to simplify complex problems. The method proves to be particularly useful in the analysis and design of compliant mechanisms.
Design and Development of a Two-Axis Passive Line-of-Sight Stabilization System
Authors: Poo A. N. , Teo C. L. , Loh M. K. , Tay S. L.
Published: February 2008

The line-of-sight (LOS) stabilization system is basically a system that has the capability of maintaining the sightline—for example, of an optical sensor—fixed in inertial space even when the system is subjected to an external vibrational environment. This paper examines and presents the feasibility of using a passive LOS stabilization system to maintain the sightline stability to within 1 mrad when it is subjected to linear and angular vibrations and other disturbances. Equations of motion of the system as well as the vibrational response equations are presented. From these equations, design parameters that affect the vibrational response of the system are established. A prototype of the LOS stabilization system has been built. The pointing stability of this prototype with different values of the design parameters is evaluated and compared with simulation results. Initial test results on the prototype are encouraging, with pointing stability of less than 1 mrad on both axes, which is within the original design objective.
Computational Issues Associated with Gear Rattle Analysis
Authors: Padmanabhan C. , Barlow R. C. , Rook T. E. , Singh R.
Published: February 2008

This paper proposes a new procedure for formulating the gear rattle type problem analytically before attempting a numerical solution. It also outlines appropriate evaluation criteria for direct time domain integration algorithms used to solve such problems. The procedure is necessary due to the non-analytical nature of the mathematical formulation describing vibro-impacts, which can lead to numerical “stiffness” problems. The method is essentially an “intelligent” pre-processing stage and is based on our experience in simulating such systems. Important concepts such as model order reduction, gear or clutch stiffness contact ratio, appropriate choice of non-dimensionalization parameters are illustrated through examples. Several case studies of increasing complexity are solved using various well known numerical algorithms; solutions are compared qualitatively and quantitatively using the proposed evaluation criteria, and specific numerical problems are identified. Some of the simulation models have also been validated by comparing predictions with experimental data.
Comparative Fatigue Resistance of Fiber Reinforced Nylon 6 Gears
Authors: Crippa G. , Davoli P.
Published: February 2008

The fatigue-life diagrams of injection-molded nylon 6 gears with different reinforcements are shown for various lubrication modes (dry, grease, splash oil lubrication) and for different meshing combinations (plastic/plastic and steel/plastic gears). Tests using a suitably designed back-to-back rig have been carried out, and the results compared with previous experiments, performed using unreinforced nylon 6 gears. 232 gears (70 in unreinforced and 162 in differently filled nylon) were tested. More than 700 · 106 cycles have been totalled. From test data, and from the “matrix” of the gear/pinion material combination, the capabilities of differently reinforced nylon 6 gears in terms of fatigue and wear resistance have been outlined. These capabilities are the basis for a proper material selection in plastic gear design.
On the Metrics of Rigid Body Displacements for Infinite and Finite Bodies
Authors: Martinez J. M. R. , Duffy J.
Published: February 2008

This paper presents a critical analysis of the metric of rigid body displacements obtained from the so-called kinematic mapping. It is shown that this metric is not suitable for finite rigid bodies. The paper also addresses the metrics obtained for the planar group, as it can be regarded as a subgroup of the group of all rigid body displacements, which is denoted here as the Euclidean group. Finally, the paper proposes some metrics for the set of spatial and planar displacements for a finite rigid body, undergoing a finite displacement.
A Recursive Method for Finding Revolute-Jointed Manipulator Singularities
Authors: Burdick J. W.
Published: February 2008

A geometric application of screw theory is used to develop a recursive algorithm for computing all singular configurations of revolute-jointed manipulators with arbitrary link geometries and an arbitrary number of joints. The depth of the recursion is linear in the number of joints, n, while the computational burden is proportional to 2n−2. This method does not require explicit construction of the Jacobian matrix elements or a determinant operation. The method is also robust with respect to the bifurcations that occur for industrial robot geometries. Further, the screw axis of the singular motion is determined at no additional cost.
Polynomial Solution of the Spatial Burmester Problem
Authors: Innocenti C.
Published: February 2008

This paper presents a new method for the dimensional synthesis of the spatial guidance linkage that features the guided body connected to the base by the interposition of five rods having spherical joints at both extremities. The linkage is required to index the guided body through seven arbitrarily-chosen rigid-body positions. Core of the proposed method is an original algebraic elimination procedure that allows five unknowns to be dropped from a set of six second-order algebraic equations in six unknowns. As a result, a final univariate polynomial equation of twentieth order is obtained whose twenty roots, in the complex domain, represent as many possible placements for a connecting rod. A numerical example is reported.
Analysis of Overconstrained Mechanisms
Authors: Mavroidis C. , Roth B.
Published: February 2008

This paper presents a new systematic method for dealing with overconstrained mechanisms. With this one method we are able to verify all previously known overconstrained mechanisms. In addition, this method yields the input-output equations of any single-loop overconstrained mechanism. Two numerical examples and one set of input-output curves are presented.
New and Revised Overconstrained Mechanisms
Authors: Mavroidis C. , Roth B.
Published: February 2008

In this paper we use a new general method which allows us to verify all known overconstrained mechanism classes, and to correct errors in several previously published overconstraint conditions. Also, we present a general classification of overconstrained mechanisms, and use our methodology to discover new overconstrained mechanisms. Examples of the input-output curves for the new mechanisms are presented.
Automated Formation of Closed Form Kinematic Displacement Polynomials for Open Loop Planar and Spatial Chains
Authors: Jen S. C. , Kohli D.
Published: February 2008

A new numerical approach for determining inverse kinematic polynomials of manipulators is presented in this paper. Let the inverse kinematic polynomial of a manipulator in one revolute joint variable θi be represented by gnTn + gn-1Tn-1 + gn-2Tn-2 + • + g1T + go = 0. T = tanθi/2 and go, g1...gn are polynomial type functions of hand position variables. The coefficients g are expressed in terms of undetermined coefficients and hand position variables. Then the undetermined coefficients are evaluated by using direct kinematics and the solutions of sets of linear equations, thus determining coefficients g and the inverse kinematic polynomial. The method is general and may be applied for determining inverse kinematic polynomials of any manipulator. However, the number of linear equations required in determining coefficients g become significantly larger as the number of links and the degrees of the manipulator increase. Numerical examples of 2R planar and 3R spatial manipulator are presented for illustration.
Design and Analysis of Explosively Actuated Valves: The Interaction of the Plunger and the Housing
Authors: Emery A. F. , Deckers S. , Jones B. K.
Published: February 2008

Explosive values are generally composed of a tapered plunger which is explosively driven along the bore of a cylindrical housing and forced to stop at a location designed to alter a particular fluid flow configuration. The stopping point of the plunger is determined primarily by the friction between the plunger and the housing and the axial forces exerted on the taper. One way of calculating these forces is to model the valve as a series of thin disks and to assume an interference fit between the disks of the plunger and the disks of the housing. A previous paper described the modification necessary to account for plastic deformations and strain hardening of nontapered plungers. These modifications are not sufficient when considering tapered hollow plungers. This paper compares the disk model predictions with measured performances and shows that the differences are primarily due to the unusually high pressures developed at the interface between the plunger and the housing. These high pressures are shown to be the result of axial stresses induced by bending of the housing. Likewise, it is shown that the axial stresses induced by the bending of the hollow plunger walls has a significant effect upon the value of the coefficient of friction needed to achieve acceptable simulations.
A Strain-Based Fatigue Reliability Analysis Method
Authors: Baldwin J. D. , Thacker J. G.
Published: February 2008

A new fatigue reliability technique has been developed using a strain-based analysis. A probabilistic strain-life curve, where the variability in cycles to failure at constant strain range has been modeled with a three-parameter Weibull distribution, has been incorporated into the strain-based fatigue analysis. This formulation, which includes a notch strain analysis, rainflow cycle counting and damage accumulation according to Miner’s rule, is used to estimate fatigue life to crack initiation for notched components using smooth specimen laboratory data. Unlike other probabilistic fatigue models, the technique developed here does not include a distribution model for stress peaks such as the commonly-used stationary narrow band Gaussian random process assumption but rather uses strain histories directly. Using this model, techniques have been developed to estimate the number of cycles to failure at a specified reliability and to predict the reliability and failure rate at a specified time in the analysis.
An Extended Model for the Analysis of the Dynamic Behavior of Planetary Trains
Authors: Saada A. , Velex P.
Published: February 2008

An extended model for determining critical frequencies for tooth loading on spur and helical gear planetary trains is proposed. Torsional, flexural and axial generalized displacements of all the components are considered and a finite element procedure is used for generality. In order to avoid modulations between meshing pulsations and the carrier angular velocity, equations are written relative to rotating frames fixed to planet centers. Depending on their architectures, complex drives are broken down in basic 12 degree of freedom elements, namely: external gear element (sun gear-planet element); internal gear element (ring gear-planet element); pin-carrier element; classical elements for shafts, bearings, couplings, etc. Details are given for elementary stiffness matrices. Due to contact conditions between mating teeth, these matrices are full and torsional, bending and traction effects are coupled. State equations point to parametrically excited differential systems with gyroscopic contributions. A first application of the model is conducted on a 3 planet epicyclic drive whose gyroscopic terms are neglected. Potentially dangerous frequencies for sun gear-planet and planet-ring gear contacts are determined and contributions of some components of the planetary train are discussed.
Fault Detection of Helicopter Gearboxes Using the Multi-Valued Influence Matrix Method
Authors: Chin H. , Danai K. , Lewicki D. G.
Published: February 2008

Fault detection of a helicopter gearbox by pattern classification is discussed. The detection system is composed of two components, a quantization matrix to flag the measurements, and a multi-valued influence matrix (MVIM) that represents the behavior of measurements during normal operation and at fault instances. Both the quantization matrix and the influence matrix are tuned during a training session so as to minimize the error in detection. This detection system was applied to vibration measurements collected from a helicopter gearbox test stand during accelerated fatigue tests and at various fault instances. The results indicate that the MVIM method provides accurate detection when the full range of faults effects on the measurements are included in the training set. Furthermore, the fixed structure of MVIM allows evaluation of individual measurements. This feature was utilized to select a subset of measurements crucial to detection.
Computerized Simulation of Transmission Errors and Shift of Bearing Contact for Face-Milled Hypoid Gear Drive
Authors: Litvin F. L. , Chen Jui-Sheng , Sep T. M. , Wang Jyh-Chiang
Published: February 2008

A computerized investigation of the influence of alignment errors on the transmission errors and the shift of the bearing contact is performed. The investigation is performed for an imaginary hypoid gear drive with conjugate tooth surfaces. The transmission error functions caused by misalignment are shown to be periodic discontinuous almost linear functions with the frequency of the cycle of meshing. The above functions can be totally absorbed by a predesigned parabolic function. The shift of the bearing contact caused by misalignment has been determined as well. The investigation is based on computerized simulation of meshing and contact of gear tooth surfaces. The machine-tool settings for the generation of the designed gear drive have been determined. A numerical example that illustrates the developed theory is given.
Computational Kinematic Analysis of Higher Pairs with Multiple Contacts
Authors: Sacks E. , Joskowicz L.
Published: February 2008

We present a computational kinematic theory of higher pairs with multiple contacts, including simultaneous contacts, intermittent contacts, and changing contacts. The theory systematizes single- and multiple-contact kinematic analysis by mapping it into geometric computation in configuration space. It derives the contact conditions, contact functions, and relations between contacts from the shapes and degrees of freedom of the parts. It helps identify common design flaws, such as undercutting, interference, and jamming, that cannot be systematically identified with current methods. We describe a program for the most common pairs: planar higher pairs with two degrees of freedom.
Forward Position Analysis of Two 3-R Robots Manipulating a Planar Linkage Payload
Authors: Pennock G. R. , Mattson K. G.
Published: February 2008

This paper presents the forward position analysis of two planar three degree-of-freedom robots, with all revolute joints, manipulating a single degree-of-freedom closed-loop linkage payload. Kinematic constraint relations are developed which provide geometric insight into the cooperating robot-payload system and are important in the control of the two robots. For illustrative purposes, the payload that is considered here is a planar four-bar linkage. The paper shows that the orientation of a specified link in the payload can be described by a sixth-order polynomial. This polynomial is an important contribution, not only to the kinematics of the cooperating robots, but to the multiple-input closed-loop nine-bar linkage formed by the two robots and the payload. The polynomial contains important information regarding the assembly configurations and the stationary configurations of the system. The paper shows that zero, two, four, or six assembly configurations are possible and that each configuration corresponds to a different circuit of the system. Graphical methods are utilized to provide geometric insight into the assembly and stationary configurations and to check the results obtained from the sixth-order polynomial. A numerical example is included which demonstrates the importance of the polynomial in solving the forward position problem, and in determining the number of assembly configurations.
A Synthesis Algorithm for Three-Revolute Manipulators by Using an Algebraic Formulation of Workspace Boundary
Authors: Ceccarelli M.
Published: February 2008

A new synthesis algorithm for general three-revolute open chain manipulators is proposed making use of an algebraic formulation for the workspace boundary. This algebraic form of a synthesis model is used to formulate design equations and to discuss the number and the type of the multiple solutions.
An Improved Shape Annealing Algorithm For Truss Topology Generation
Authors: Reddy G. , Cagan J.
Published: February 2008

An improved shape annealing algorithm for truss topology generation and optimization, based on the techniques of shape grammars and simulated annealing, is introduced. The algorithm features a shape optimization method using only simulated annealing with a shape grammar move set; while no traditional gradient-based techniques are employed, the algorithm demonstrates more consistent convergence characteristics. By penalizing the objective function for violated constraints, the algorithm incorporates geometric constraints to avoid obstacles. The improved algorithm is illustrated on various structural examples taking into account stress, Euler buckling and geometric constraints, generating a variety of solutions based on a simple grammar.
Computational Geometry for Optimal Workpiece Orientation
Authors: Haghpassand K. , Oliver J. H.
Published: February 2008

Workpiece orientation is formulated as an optimal design problem based on a discrete approximation of design surface geometry, the kinematic capabilities of the process machine tool, and processing cost. The primary process application addressed is three-and four-axis numerically controlled (NC) milling, although the techniques presented may be applied to machines with more general articulation. Recent developments in applied spherical geometry are employed to formulate a constrained problem, and furthermore, a nonlinear optimization problem. For three-axis milling applications, a weight is assigned to each surface normal of the discrete model corresponding to the actual area it represents. Workpiece/machine orientation is optimized such that the angle between the weighted normals and the milling tool axis is minimized. This formulation is augmented, for four-axis milling, to incorporate limitations of the rotational degree of freedom, into the optimization formulation. The influence of tool geometry is also discussed and incorporated within constrained orientation algorithm.
Fabrication and Analysis of a Novel 3 DOF Parallel Wrist Mechanism
Authors: Agrawal S. K. , Desmier Glen , Li Siyan
Published: February 2008

This paper describes a three-degrees-of-freedom parallel-actuated wrist mechanism developed at Ohio University. This mechanism is capable of pointing an axis within a cone from the nominal position. The mechanism allows unlimited rotation about the pointing axis. Experiments were conducted to validate the kinematic model of the designed wrist.
Design of Ball Wheel Mechanisms for Omnidirectional Vehicles With Full Mobility and Invariant Kinematics
Authors: West M. , Asada H.
Published: February 2008

A new ball wheel design for fully mobile omnidirectional vehicles is presented. This ball wheel mechanism yields a unique vehicle design that is not only omnidirectional with no kinematic singularity but is configuration-invariant in kinematic behavior. Invariant kinematics greatly simplifies the control of smooth and precise vehicle motion. Multiple displacement sensors are easily incorporated into each ball wheel mechanism to enhance the accuracy of vehicle motion control. Two fundamental requirements of functioning ball wheel designs are established: one is the translational form closure requirement for holding a spherical tire, and the other is the non-overconstraint requirement to allow each ball to rotate in two directions. It is proved that a class of mechanisms in which a ball is held by rollers whose axes are fixed directly to the vehicle chassis cannot satisfy the fundamental requirements. A class of modified mechanisms are then analyzed and the necessary and sufficient conditions for the modified mechanisms the fundamental requirements are obtained. For this class of ball wheels (Class 1), conditions for configuration-invariant kinematics are found and two possible actuation schemes are discussed. Two prototype vehicles have been built: both have three Class 1 ball wheels but each uses a different actuation scheme. Performance data of the two prototypes are compared. Both achieve smooth motion and precise dead reckoning.
Surface Contact Analysis for a Spatial Cam Mechanism
Authors: Wang W. H. , Tseng C. H. , Tsay C. B.
Published: February 2008

This paper proposes and analyzes a new meshing condition between a modified hyperboloidal roller follower and a spatial cam surface. This new geometrical model can be utilized to avoid the edge contact phenomenon between a cylindrical roller follower and its mating cam surface. In the new model a modified hyperboloidal roller follower is selected to replace the original cylindrical roller follower. Once the new spatial cam mechanism is modeled by means of surface contact analysis (SCA), the contact condition between the modified hyperboloidal roller follower and the cam surface is clearly derived. Errors in the displacement function and the contact path arising from assembly errors are also analyzed. This study assists the manufacture and assembly of more accurate and higher quality spatial cam mechanisms.
Enumerating Possible Design Options for Integral Attachment Using a Hierarchical Classification Scheme
Authors: Genc S. , Messler R. W. , Bonenberger P. R. , Gabriele G. A.
Published: February 2008

The proliferation of plastic in parts, and the ability to mold such parts of great complexity at little cost penalty, has resulted in the growing use of integral attachment in the form of snap-fit features in designs. Heretofore, the great diversity in geometry of mating parts and of available integral attachment snap-fit features (e.g., cantilever hooks, compression traps, bayonet-fingers, etc.) has made it appear that assembly design possibilities may be unbounded, and that attempts at optimization might be intractable. This paper enumerates all possible assembly design options using a hierarchical classification scheme. In so doing, it guides new designers and validates choices for experienced ones. The result is great order and simplicity that facilitates better understanding of this assembly joining method, better communication, development of design aids, and improved and extended attachment performance.