bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Limitations in Applying Classical EHD Film Thickness Formulas to a High-Speed Bearing
Authors: Coy J. J. , Zaretsky E. V.
Published: March 2013

Elastohydrodynamic film thickness was measured for a 20-mm ball bearing using the capacitance technique. The bearing was thrust loaded to 90, 448, and 778 N (20, 100, and 175 lb). The corresponding maximum stresses on the inner race were 1.28, 2.09, and 2.45 GPa (185,000, 303,000, and 356,000 psi). Test speeds ranged from 400 to 14,000 rpm. Film thickness measurements were taken with four different lubricants: (a) synthetic paraffinic, (b) synthetic paraffinic with additives, (c) neopentylpolyol (tetra) ester meeting MIL-L-23699A specifications, and (d) synthetic cycloaliphatic hydrocarbon traction fluid. The test bearing was mist lubricated. Test temperatures were 300, 338, and 393 K. The measured results were compared to theoretical predictions using the formulae of Grubin, Archard and Cowking, Dowson and Higginson, and Hamrock and Dowson. There was good agreement with theory at low dimensionless speed, but the film was much smaller than theory predicts at higher speeds. This was due to kinematic starvation and inlet shear heating effects. Comparisons with Chiu’s theory on starvation and Cheng’s theory on inlet shear heating were made.
Thermal Effects on Traction in EHD Lubrication
Authors: Conry T. F.
Published: March 2013

The effects of heat generation and the resulting temperature profiles on the traction coefficient for two rollers in EHD contact are determined. An exact solution for the velocity profile through the film thickness is obtained to simultaneously satisfy the momentum balance and the nonlinear Maxwell model where the viscous term follows the Eyring “sinh” law. These results are coupled with the heat diffusion equation to yield simultaneous solutions for temperature and shear stress distributions in the film. Several cases are investigated for LVI 260 lubricant and are compared with experimental observations. The thermal theory is in good agreement with the experimental data. It is shown that the thermal theory predicts a maximum traction while the isothermal theory predicts increasing traction with increasing sliding speed.
The Isothermal Elastohydrodynamic Lubrication of Spheres
Authors: Evans H. P. , Snidle R. W.
Published: March 2013

The paper describes a numerical procedure for solving the point-contact elastohydrodynamic lubrication problem under isothermal conditions at moderate loads. Results are presented showing the shape of the film and variation of hydrodynamic pressure. Analysis of results for a range of operating conditions gives the following approximate formulas for minimum and central film thickness, repsectively: Hm = 1.9 M−0.17 L0.34 and Ho = 1.7 M−0.026 L0.40 where H, M, and L are the Moes and Bosma nondimensional groups. In common with earlier solutions based upon the forward-iterative method the solution breaks down under moderately heavily loaded conditions. Ways of extending the solution to heavier loads using the authors’ inverse solution of Reynolds’ equation under point-contact elastohydrodynamic conditions are discussed.
Hydrodynamic Lubrication in Wavy Contacting Face Seals—A Two Dimensional Model
Authors: Lebeck A. O.
Published: March 2013

The role of circumferential surface waviness in contacting mechanical face seals is examined. First, a two dimensional model is developed. The model considers waviness amplitude, surface roughness, asperity contact, hydrodynamic and hydrostatic pressures, and fluid cavitation. Given waviness, roughness, number of waves, geometry, and sealed fluid, the model predicts the fraction of load supported by fluid pressure, the relative wear rate, friction coefficient, and leakage rate. A numerical method for solving this problem is presented. Using this model, the effects of waviness amplitude, roughness, number of waves, face width, and sealed pressure on seal performance are examined. Based on these results, certain conclusions are reached concerning the role of waviness in commercial face seals. Finally, using the model, it is shown how waviness can be applied to advantage to reduce seal friction and wear rates.
Leakage Flow-Induced Vibration of an Eccentric Tube-in-Tube Slip
Joint
Authors: Mulcahy T. M.
Published: March 2013

Eccentricity of a specific slip-joint design separating two cantilevered telescoping tubes did not create any self-excited lateral vibrations that had not been observed for a concentric slip joint. In fact, the eccentricity made instabilities less likely to occur, but only marginally. Most importantly, design rules previously established to avoid instabilities for the concentric slip joint remain valid for the eccentric slip joint.
On the Deformation of the Pipe Wall During Propagation of a Ductile
Crack in a High-Pressure Gas Pipeline
Authors: Abbassian F. , Calladine C. R.
Published: March 2013

Long-running ductile fractures have been observed in high-pressure gas pipelines. These fractures propagate at nearly constant speeds and are accompanied by a large amount of plastic deformation of the pipe wall. In particular, the pipe wall displacement is large, and of the order of one pipe radius. The phenomenon of ductile fracture propagation is very complex. In consequence, most of the existing theoretical investigations into ductile fracture propagation have used an energy balance method as a first approach. Various energies involved in the fracture propagation process depend strongly on the mode of pipe wall deformation and in particular on the geometry of the deformed pipe wall. The major theme of this paper is a proper consideration of the pipe wall deformation during the propagation of a constant-velocity ductile crack. Axial stretching is considered to be the prime mode of deformation of the pipe wall. It is shown that the mode of deformation can be adequately described by two parameters which define the pattern of the pipe wall mid-surface stretching. A shell theory approach is then used to obtain the deformed geometry of the pipe wall in terms of these two parameters; and physical models of the deformed pipe wall are constructed in order to study the large displacement of the pipe wall.
Stochastic Stress Analysis of Assembled Structures
Authors: Nakagiri S. , Hisada T. , Nagasaki T.
Published: March 2013

Intrinsic stress caused by uncertain members in an assembled structure is analyzed by means of the stochastic finite element method. Use is made of the second-order perturbation technique in the formulation of the stochastic finite element method, which is able to deal with uncertainties involved in the stiffness equation. The expectation and variance of the initial stresses in closed ring and portal frame are successfully estimated when the covariance matrix is given for uncertain fluctuation in the dimensions of the curved beam and quasi-straight beam members.
Nonlinear Analysis of Axisymmetric Layered Pressure Vessels—Part 1:
Theory
Authors: Blandford G. E. , Tauchert T. R. , Leigh D. C.
Published: March 2013

A finite element formulation for the nonlinear heat conduction and thermoelastic analyses of orthotropic, axisymmetric layered pressure vessels is presented. Nonlinearities include temperature-dependent material properties and stress-dependent layer interface conditions. Solution of the nonlinear heat conduction equations is iteratively obtained using a modified Newton-Raphson scheme. Direct iteration between heat conduction and stress analyses is employed when stress-dependent interface thermal resistance is considered. A modified time integration scheme to reduce oscillatory noise is introduced, and the stability and accuracy of the time integration scheme are discussed. Numerical results for various vessel designs and loadings are presented in Part 2 of the paper.
Nonlinear Analysis of Axisymmetric Layered Pressure Vessels—Part 2:
Steady-State Applications
Authors: Leigh D. C. , Tauchert T. R. , Blandford G. E.
Published: March 2013

Steady-state applications of the theory in Part 1 of the paper are made to a particular layered pressure vessel design subjected to a typical set of pressure and thermal loadings. Results are compared for several analyses: elastic analysis, linear thermoelastic analysis for a solid-wall vessel, nonlinear analysis for solid-wall, and nonlinear analysis for a layered vessel. Due to the thermal resistance between layers, the maximum circumferential stress is, for the nonlinear analysis, about 35 percent greater for the layered vessel than it is for the solid-wall vessel.
Membrane Theory for Anisotropic Laminated Shells of
Revolution
Authors: Logan D. L. , Widera G. E. O.
Published: March 2013

The present paper discusses the derivation and application of the membrane theory equations governing the small deformation of laminated, anisotropic, elastic shells of revolution. The equations are derived by use of the Hellinger-Reissner variational principle in conjunction with the asymptotic expansion technique. They are then used to analyze specific shells under loadings of practical interest.
Micromechanical Analysis of the Elastoplastic Response of Metal
Matrix Composites
Authors: Pindera M.-J. , Lin M. W.
Published: March 2013

The micromechanics model proposed by Aboudi is employed to predict the response of two types of metal matrix unidirectional composites characterized by different microstructures; namely, boron/aluminum and graphite/aluminum. The analytical predictions are compared with experimental data obtained from tension and compression tests. It is illustrated that the elastoplastic response of boron/aluminum is modelled with good accuracy by the micromechanics model. In the case of graphite/aluminum, however, the nonlinear response in compression is affected by secondary dissipative mechanisms which, in turn, result in differences in the experimental/analytical correlation for compressive loading. These differences are discussed in terms of the microstructure of the graphite/aluminum system.
Nonlinear Buckling Analysis of Pipelines Subjected to Creep of
Supporting Soil
Authors: Vinogradov A. M.
Published: March 2013

The paper deals with the nonlinear buckling analysis of pipelines supported by frozen soil and subjected to differential soil movements. The adopted structural model affords a parametric examination of various loading factors generated by the overburden soil pressure, restrained thermal expansion of heated pipelines and possible load imperfections. The influence of time and temperature effects induced by the mechanical properties of supporting soil is examined. Based on the obtained analytical solution, the critical condition for the pipelines is formulated, and the post-buckling response of the pipeline-soil system is examined in detail. The results of the nonlinear analysis are compared with those derived from the linear approach yielding an assessment of the small deformation theory.
Application of Static Condensation Method to Vibration Analysis of
Thin Cylindrical Shells
Authors: Tokuda N. , Sakata Y.
Published: March 2013

A simple formula is proposed, by which the error in the natural frequencies introduced by using the static condensation method can be evaluated prior to the numerical computation, though its effective applicability is found in simple structures such as plates and shells. The effectiveness of the proposed formula is examined in the vibration analysis of thin cylindrical shells having freely supported ends by using various reduction patterns. Not only the accuracy of natural frequencies, but also that of modal displacements and the corresponding modal stresses are investigated by comparing with the results obtained without reduction and with the exact analytical solutions given by Arnold and Warburton.
Nonsymmetric Buckling of Plate-End Pressure Vessels
Authors: Teng J. G. , Rotter J. M.
Published: March 2013

Small cylindrical pressure vessels are often constructed with a circular flat plate end closure. The end-plate undergoes large deformations under working loads. High local stresses develop at the junction between the cylinder and end-plate, causing yield under proof loading. The compressive circumferential stresses at the junction may lead to bifurcation into a nonsymmetric deformation mode. This study explores the geometrically nonlinear elastic-plastic behavior of plate-end pressure vessels. The form of the axisymmetric prebuckling path is investigated, showing the strongly stiffening nature of the response. Bifurcation of the closure into a nonsymmetric mode is then studied.
A Study of the Impact Dynamics of Loosely Supported Heat Exchanger
Tubes
Authors: Goyder H. G. D. , Teh C. E.
Published: March 2013

Heat exchanger tube bundles may be damaged by vibration induced from the cross flow. This damage generally occurs at the tube supports where the tube is only loosely supported. The loose support results in the tube motion being strongly nonlinear with very complicated dynamics. Some theoretical equations for the tube dynamics and wear rates are investigated by using dimensional analysis, physical modeling and numerical simulations. From the analysis of these equations, some simple formulas are developed which show the influence of excitation level and tube-to-support clearance on the tube response.
Dynamic Instability of a High-Speed Rotor Containing a Partitioned
Cavity Filled With Two Kinds of Liquids
Authors: Jinnouchi Y. , Araki Y. , Inoue J. , Kubo S.
Published: March 2013

This paper is concerned with the dynamic instability of a high-speed rotor containing a partitioned cavity filled with two kinds of liquids of different density. The system considered simulates a centrifuge of two liquids type, in which the cylindrical cavity is divided into fan-shaped compartments in order to suppress asynchronous whirling motions induced by waves in the liquids traveling around the cavity. Assuming rotor vibrations to be small, liquids inviscid, and external damping negligible, perturbed motions of the liquid-rotor system are analyzed. The theory shows that the rotor containing a partitioned cavity can still exhibit unstable behavior, similar to that observed for a rotor system equipped with centrifugal pendula, in the region where the rotor speed is nearly equal to the sum of the critical speed of the system and the natural frequency of the liquids. The theory has been verified by the experiments. The dependence of the unstable region on the main system parameters is also discussed.
Vibration of Tube Bundles in Two-Phase Cross-Flow: Part
1—Hydrodynamic Mass and Damping
Authors: Pettigrew M. J. , Taylor C. E. , Kim B. S.
Published: March 2013

Two-phase cross-flow exists in many shell-and-tube heat exchangers, such as condensers, reboilers and nuclear steam generators. An understanding of damping and of flow-induced vibration excitation mechanisms is necessary to avoid problems due to excessive tube vibration. Accordingly, we have undertaken an extensive program to study the vibration behavior of tube bundles subjected to two-phase cross-flow. In this paper we present the results of experiments on four tube bundle configurations; namely, normal triangular of pitch over diameter ratio, p/d, of 1.32 and 1.47, and parallel triangular and normal square of p/d of 1.47. The bundles were subjected to air-water mixtures to simulate realistic mass fluxes and vapor qualities corresponding to void fractions from 5 to 99 percent. Hydrodynamic mass and damping are discussed in Part 1 of this series of three papers. We found that hydrodynamic mass is roughly related to the homogeneous mixture density. The damping characteristics of all tube bundles are generally similar. Damping is maximum between 40 and 80 percent void fraction where the damping ratio reaches about 4 percent. The effect of mass flux is generally weak. Design guidelines are proposed for hydrodynamic mass and for damping.
The Quasi-Steady Design of a Compressor or Pump Stage for Minimum Fluctuating Lift
Authors: Gearhart W. S. , Henderson R. E. , McMahon J. F. , Horlock J. H.
Published: March 2013

This paper is intended for the designer of rotating turbomachinery who is concerned with the fluctuating forces generated in a turbomachine. The analysis presented is a quasi-steady analysis and its use is justified by a recent paper by Horlock. This analysis indicates that a time-dependent analysis and a quasi-steady analysis for the minimization of fluctuating lift on an isolated airfoil requires identical airfoil geometries. Assuming this agreement holds for a cascade of airfoils, this paper presents the cascade geometry required to minimize fluctuating lift as predicted by the quasi-steady analysis.
Convective Heat Transfer in a Gas-Fired Pulsating Combustor
Authors: Hanby V. I.
Published: March 2013

The effect of longitudinal combustion-driven oscillations on convective heat transfer rates was studied using a tubular, propane-fired combustor which resonated as a quarter-wavelength organ pipe at a frequency of 100 cps. The combustor was provided with damping tubes of variable length which enabled the amplitude of the oscillations to be varied, to the extent of damping them out completely. Heat transfer coefficients were measured with and without the presence of combustion-driven oscillations. It was found that heat transfer coefficients were highest at a position of maximum velocity amplitude, where improvements of over 100 percent were obtained. Satisfactory prediction of the effects of the oscillations was obtained by using the quasisteady-state theory.
Burning Rate Development in a Closed Vessel of Arbitrary Shape and Variable Volume, for Variable but Uniform Pressure
Authors: Bascunana J. L.
Published: March 2013

An expression is derived to compute the mass burning rate in a closed vessel for which the variable volume and pressure during the process of combustion are known. The solution presented will be satisfactory for applications where the effects of heat transfer and variable chemical reaction during the combustion process can be neglected, and may serve as a basis of comparison for more complete numerical solutions.
Impingement Cooling of Concave Surfaces With Lines of Circular Air Jets
Authors: Metzger D. E. , Yamashita T. , Jenkins C. W.
Published: March 2013

An experimental study of the heat transfer characteristics between single lines of circular jets and concave cylindrical surfaces is presented. It is intended to model a practically important class of impingement cooling configurations for which existing heat transfer correlations are not obviously applicable. The results clarify the present uncertain position with regard to the optimum spacing between the jet nozzle and the heat transfer surface and with regard to the center-to-center spacing between the jets. Some limited results for a two-dimensional jet impinging on the concave surfaces are also presented.
The Determination of Thermal Diffusivities of Thermal Energy Storage Materials: Part II—Molten Salts Beyond the Melting Point
Authors: Sreenivasan K. , Altman M.
Published: March 2013

A quasisteady method for measuring the thermal diffusivity of molten salts at temperatures above their melting point is described. Essentially, the difference between the temperature at the surface and at the center of a cylindrical container is measured for a constant rate of surface temperature rise. The liquid, whose thermal diffusivity is to be measured, is contained in a narrow annular groove concentric with the surface. The advantages of this method are: (a) no heat flux measurements are needed; (b) no liquid temperature need be measured; (c) theoretically assumed boundary conditions can be experimentally realized; (d) absence of convection can be experimentally verified. Results of measurements are reported for liquid lithium fluoride and sodium nitrate. The results for sodium nitrate agree with previously published results. The thermal conductivity of lithium fluoride can be empirically expressed in terms of the melting point, the molecular weight and the density, as k=0.9Tm1/2ρm2/3M−7/6
Wall Temperature and Prandtl Number Effects on Turbulent Boundary Layer Thicknesses and Shape Factors for Subsonic Compressible Gas Flow Over a Flat Plate
Authors: Kelnhofer W. J.
Published: March 2013

Based on n-power velocity and temperature profiles a method of computing various turbulent boundary layer thicknesses and shape factors affected by wall temperature and Prandtl number for fully developed subsonic gas flow over a flat plate is presented. Density variation in the boundary layer is given main consideration. Numerical computations include both heating and cooling of the gas. Boundary layer thicknesses and shape factors are shown to be significantly affected by wall temperature and to a lesser degree by Prandtl number. An experiment is described which involved air flow up to 30 m/sec over a flat plate maintained at constant wall temperatures up to 250 C. Comparisons between theory and experiment are good.
Thermal Stress Analysis of Nonuniformly Heated Cylindrical Shell and Its Application to a Steam Generator Membrane Wall
Authors: Bijlaard P. P. , Dohrmann R. J. , Duke J. M.
Published: March 2013

A method has been developed which accurately predicts the thermal stresses and deformations in a nonuniformly heated cylindrical shell and has been applied to a steam generator membrane wall. The analysis is based on the theory of thermoelasticity and treats the membrane wall as a repetitive geometry. The tube and membrane are treated separately and are later joined, satisfying continuity. The analysis is also applicable to drums, nozzles, shells, and other cylindrical vessels as long as the temperture is steady and independent of the longitudinal axis of the geometry. Through the use of this method the thermal stresses can readily be calculated and thus assist in the establishment of flow rates, heat input or flux levels, circuit configuration, and material selection. In addition it provides the information to evaluate the effects of the inside heat transfer coefficient and variations in tube and web geometries on the thermal stresses.
An Analytical and Experimental Study of Air-Lift Pump Performance
Authors: Stenning A. H. , Martin C. B.
Published: March 2013

A one-dimensional analysis of air-lift pump performance in shallow water has been developed which includes the effects of friction and slip between the gas and the liquid. The theory predicts the performance characteristics of these devices successfully, and explains the empirical design rules recommended in earlier publications.
Shell Theory Solution for Asymmetric Balanced Radial Loads on Long Cylinders
Authors: Melworm R. F. , Patel P. D. , Berman I.
Published: March 2013

The elastic behavior of a long cylinder subjected to equilibrated radial loads is considered. The problem is formulated by the use of shell theory equations. Although numerical results are available for simply supported cylinders, these results do not apply to long cylinders. The simply supported results were calculated, by Bijlaard, on the basis of equations formulated by Timoshenko and the use of a double Fourier series. The Bijlaard work uses some assumptions which limit the length of the cylinder. In the current work, the more complete equations derived by Flu¨gge and by Biezeno and Grammel are used as transformed by Kempner with the added simplification that the square of the thickness to mean radius ratio is negligible as compared to unity. Solutions for equal and opposite balanced uniformly distributed radial line loads of an any angle are obtained. The solution is carried out by means of a Fourier integral, Fourier series product. All the results are given by a single expression with tabulated coefficients. The infinite cylinder stress and deflection results are presented in graphical form for the parameters of axial position, circumferential position, angle of loading, and mean radius to thickness ratio of the cylinder. The results were checked with axisymmetric thin shell theory.
Measuring Abrasiveness of Solid Fuels and Other Materials by a Radiochemical Method
Authors: Goddard C. W. , Duzy A. F.
Published: March 2013

A new method for predicting pulverizer grinding element wear has been developed. This paper describes a laboratory model, ball-and-race, grinding machine, and a radioactive tracer technique used to determine the relative abrasiveness of solid fuels. A procedure for determination of the quartz content of coals was developed, and its relationship to abrasiveness is discussed. Results of testing the abrasiveness of numerous coals and some materials other than coal are presented. A comparison of laboratory abrasion results with actual field wear data is given. Included is a method of application of the experimental wear data to design considerations for new units and also in anticipating wear rates of milling equipment in use.
The Distribution and Stability of Flow in a Rotating Channel
Authors: Fowler H. S.
Published: March 2013

The importance of flow distribution and stability leaving the impeller of a centrifugal compressor is discussed. Experiments on the flow in converging, parallel, and diffusing channels, representative of sections of impeller channels, are reported and discussed. The convergent or divergent character of the channel appears to have less influence on the flow pattern than on the stability. Change of Reynolds number appears to change the degree of nonuniformity of distribution in the channel, but change of rotation number appears to affect the distribution of the nonuniformity more. It appears that the influence of adjacent channels, and of the downstream flow-field in general, has a large effect on the flow within the rotating channel, particularly as regards detachment from the suction channel wall. “No man is an island unto himself,” and no element in an aerodynamic system can be divorced from its upstream or downstream neighbors.
Axial Cascade Technology and Application to Flow Path Designs. Part I—Axial Cascade Technology
Authors: Balje´ O. E.
Published: March 2013

Using established cascade criteria, such as the aerodynamic blade loading coefficient and the blade surface diffusion ratio, generalized relations for the losses in cascades of axial turbomachines are formulated. These relations have been evaluated numerically for incompressible media, assuming conventional Reynolds numbers. The results are presented in forms of diagrams showing profile, endwall, and clearance loss coefficients. The calculated data are compared with test data, revealing fair agreement, with the possible exception of “impulse” cascades. Extension of the “single cascade” data to “multiple row cascades” shows the operating regime where substantial performance improvements can be obtained by multiple row cascades.
U. S. Navy’s Marine Gas Turbines
Authors: Brockett W. A. , Graves G. L. , Hauschildt M. R. , Sawyer J. W.
Published: March 2013

The development, progress, and sea experience of marine gas turbines in the U. S. Navy are reviewed. Practical problems encountered with engine components, installation arrangements, forward area support, and the marine environment are outlined. Development programs in progress with simple and regenerative open-cycle engines are presented. Development efforts of the future are postulated. Shipbuilding programs involving gas turbines are described. Gas turbines are now being considered for naval service over a wide range of power (40–25,000 hp per engine); the gas turbine should be further developed to meet projected needs; it, like any other prime mover, is to be treated as a component of an overall ship system and judged on the basis of lifetime cost, system reliability, maintainability, operability, performance, and personnel requirements. The authors suggest that specific weight and fuel rate, although significant features of any power source, have been overemphasized in the transfer of gas-turbine technology from aircraft to general marine use.
Facilities and Instrumentation for Aircraft Engine Noise Studies
Authors: Gorton R. E.
Published: March 2013

This paper describes the special facilities and instrumentation developed and used in the study of aircraft turbine-engine noise at Pratt & Whitney Aircraft. Studies of jet-exhaust noise and compressor-blade noise have required extensive use of the experimental method to obtain basic understanding and to provide design data. Both model-scale and full-scale facilities are described, as well as instrumentation systems for recording and analyzing the acoustic data.
Perspectives for the Liquid Phase Compression Gas Turbine
Authors: Angelino G.
Published: March 2013

The possibility of performing a liquid phase compression in closed cycle gas turbine through the use of particular working fluids is discussed. From the results of calculations carried out for different fluids there is evidence that efficiency of the resulting cycle is considerably higher than that of regenerative Brayton cycles and comparable with that of regenerative Rankine cycles. The working fluid selection is recognized as the major problem in view of practical applications. Available data strongly support the conclusion that fluids meeting the needed requirements, at least for moderate temperature operation, can be found. Nuclear power stations appear to be one of the most promising fields of application of the liquid phase compression cycle.
A Comparison of Measured and Calculated Stresses in Pressure Vessels
Authors: Kraus H.
Published: March 2013

Stresses as calculated by two available computer programs for the analysis of pressure vessels are compared to photoelastic data obtained for a series of pressure vessels with hemispherical and torispherical heads. Of these, one program is based upon Love’s first approximation to the theory of thin elastic shells and the other is based upon a higher-order theory of shells. The comparison shows that programs based on either theory can be used with equal confidence in the calculation of stresses in pressure vessels.
Recent Blade Vibration Techniques
Authors: Armstrong E. K.
Published: March 2013

The methods which have been used recently to predict the amplitudes of vibration of compressor blades are explained. Examples for resonances with maldistributions in the intake flow and downstream blockages are given. Two techniques of obtaining blade vibration data from the HP shaft of a two-shaft jet engine are described. By comparing the measured amplitudes with the fatigue properties of blading, a parameter has been established which is used in assessing the seriousness of a vibration when considering its service life.
The Off-Design Analysis of Axial-Flow Compressors
Authors: Jansen W. , Moffatt W. C.
Published: March 2013

This paper describes in some detail the methods used for generation of a computer program for analyzing the off-design performance of axial compressors. The purpose of the study was to predict such axial-compressor characteristics as pressure rise and efficiency as a junction of mass flow and rotor speed when only the mechanical geometry of the annulus and blades are given. The aerodynamic analysis is divided into two basic parts. The first part of the analysis involves the numerical solution of the equations of motion in the compressor to find the flow field, temperature and pressure rise, and efficiency of the compressor. The second part concerns the analysis of the blade elements, in particular their performance at various angles of attack. Several effects are included that have a bearing on this performance. The relative Mach number and the axial-velocity ratio across the blade element, together with the shape of the blade and its configuration in the compressor, affect the flow discharging from the blade. Therefore, an elaborate study has been included to find the flow angle at the blade discharge and the pressure losses of the flow passing through the blade row. The calculation procedures have been tested by applying them to a number of compressors for which sufficient experimental data were available. A one-stage, a two-stage transonic, and a 13-stage axial compressor have been investigated and good agreement with experiments has been found provided the correct boundary layer displacement thickness along the annulus wall is used.
Comparison of Neutron Diffraction Measurements of Residual Stress of Steel Butt Welds With Current Fitness-for-Purpose Assessments
Authors: Paradowska Anna M. , Price John W. H. , Finlayson Trevor R. , Rogge Ronald B. , Donaberger Ronald L. , Ibrahim Raafat
Published: March 2013

In this research, the neutron diffraction technique was used to investigate the residual stress distributions in constrained carbon steel welds. Two full penetration welds were studied using (a) the stringer bead and (b) the temper bead weld techniques in 25 mm thick plate. The welds were not post-weld heat treated. The focus of the measurements is on the values of the subsurface and through-thickness strain/stress variation near the middle of the weld and the toe. The experimental results showed that both processes had high residual stresses particularly through the thickness. The measurements were compared with current fitness-for-purpose approaches, such as BS7910 and R6. It was found that the residual stress distribution in the temper bead welded specimen was not as favorable as suspected and post-weld heat treatment should be recommended to reduce residual tensile stresses in this type of steel welds.
A New Class of Damage Variables in Continuum Damage Mechanics
Authors: Voyiadjis George Z. , Kattan Peter I.
Published: March 2013

In this work various new proposed damage variables are introduced, examined and compared. Only the scalar case pertaining to isotropic damage is investigated here. Several types of new damage variables are proposed as follows: (1) damage variables that are defined in terms of cross-sectional area, (2) damage variables that are defined in terms of the elastic modulus or stiffness, and (3) composite damage variables that are defined in terms of two parameters relating to both cross-sectional area and stiffness. However, the generalization to tensors and general states of deformation and damage may be a straightforward process but is beyond the scope of this work. The damage variables introduced in this work can be applied to elastic materials including homogeneous materials like metals and heterogeneous materials like composite laminates. In the second part of this work, higher-order strain energy forms are proposed. It is seen that a specific nonlinear stress-strain relationship is associated with each higher-order strain energy form. These higher order strain energy forms along with some of the proposed damage variables are used in trying to lay the theoretical groundwork for the design of undamageable materials, i.e., materials that cannot be damaged where the value of the damage variable remains zero throughout the deformation process.
Experimental and Theoretical Study of Liquid Desiccant Dehumidification System by Using the Effectiveness Model
Authors: Pahlavanzadeh Hassan , Nooriasl Parisa
Published: March 2013

Desiccant evaporation cooling technology is compatible with the environment and can be used as an air conditioner in the indoor environment of the buildings. The characteristics of dehumidification column of the liquid desiccant evaporation cooling air conditioning system (LDCS) are introduced in this paper. This system was designed and manufactured for this purpose. Lithium chloride (LiCl), as liquid desiccant, and a packed bed column were used for the dehumidification. The described system includes a part for processed air simulation in various temperatures, humidities, and flow rates. The effectiveness model, based on heat and mass transfer equations, is considered for predicting performance of the lithium chloride dehumidification system. For validation purpose, a comparison was performed between experimental outlet data of the system and the corresponding results of the experimental model that showed a satisfactory correlation i.e., increase in the mass transfer unit number (NTU) leads to a better performance of the dehumidification system. In addition, factors leading to increase in NTUs are also investigated.
Mini Twist: A Study of Long-Range Linear Drive by String Twisting
Authors: Guzek James J. , Petersen Conrad , Constantin Stephane , Lipson Hod
Published: March 2013

Published methods of linear actuation via string transmission are discussed. A novel twisting string actuator design named Mini Twist is introduced. The design and components of the Mini Twist are thoroughly explained, and a theoretical model for its transmission method is discussed. The experimental set-up is defined. Experimental data regarding the relationship between string diameter, string tension, strand count, and strand type is presented, and analysis of the data is provided. The features of the actuator and the validity of the theoretical model are summarized.
Mechanism Synthesis of a Foldable Stair
Authors: Zhao Jing-Shan , Wang Jian-Yi , Chu Fulei , Feng Zhi-Jing , Dai Jian S.
Published: March 2013

This paper proposes a foldable stair that is easily deployed for use and folded for storage. It consists of a number of identical deployable scissor-like elements which form the staircases when expanded. In addition to use, the folded stair can be used for hanging clothes and acting as a decoration. The mechanism of the stair is first synthesized in line with the common stairs between two horizontal levels. The actuating mechanism is then synthesized in accordance with two extreme positions of the stair, folded, and unfolded. Because the stair can be folded after use, it is convenient in use and will witness a wide application both indoors and outdoors where there is no enough space for a fixed stair. In addition, this deployable stair is also particularly useful in evacuating people from a building when the disasters such as earthquakes occur.
Experimental Validation of the Tactile Exploration by a Manipulator With Joint Backlash
Authors: Mazzini Francesco , Dubowsky Steven
Published: March 2013

This research investigates using a manipulator to tactilely explore objects and environments when significant backlash affects its joint’s positions. A typical application is the exploration of rough environments, such as oil wells, where the harsh conditions dictate the use of tactile exploration. These conditions can result in large, unknown, and variable backlash in the manipulator’s transmissions, which strongly affects the measurement precision. Here, a method is developed to simultaneously map the unknown surface and identify the joint backlash. The robot probes the surface and uses its encoder readings to construct a partial map of the environment as a combination of geometric primitives. While the surface is built, the same data are also used to estimate backlash in the joints and to correct the surface measurements for backlash error. The effectiveness of the approach is demonstrated in simulation case studies and laboratory experiments.
An Analytical Study of Diffusion, Chemical Reaction and Voltage Loss in High-Temperature Solid Oxide Fuel Cells
Authors: Young John B.
Published: March 2013

The paper describes a mathematical analysis of multi-component diffusion with chemical reaction in the porous materials of high-temperature solid oxide fuel cells. The objectives are to clarify the underlying physics, to investigate different modeling approaches and to establish expressions for the cell voltage loss. The description proceeds from the simplest non-reactive binary diffusion process, through a multi-component analysis with non-reactive diluent gases present, to diffusion in the presence of the water-gas shift chemical reaction. Using a single average diffusion coefficient, an analytical solution can be found, not only for the limiting cases of frozen and equilibrium water-gas shift chemistry but also for the general non-equilibrium situation. A Damköhler number is identified and it is shown that shift equilibrium is not necessarily preserved in the anode flow. The non-equilibrium analysis also reveals unusual behavior whereby the molar fluxes become discontinuous in the equilibrium limit while the mole fractions and cell voltage loss approach the limit continuously. A physically more realistic model based on two diffusion coefficients provides a more detailed description for frozen and equilibrium chemistry but does not yield an explicit non-equilibrium solution. In all, the analysis provides fundamental insight and quantitative predictions for many of the flow phenomena occurring in the porous materials of SOFCs.
Experimental and Numerical Heat Transfer Analysis of an Air-Based Cavity-Receiver for Solar Trough Concentrators
Authors: Bader R. , Pedretti A. , Steinfeld A.
Published: March 2013

We report on the field testing of a 42 m-long full-scale solar receiver prototype installed on a 9 m-aperture solar trough concentrator. The solar receiver consists of a cylindrical cavity containing a tubular absorber with air as the heat transfer fluid (HTF). Experimental results are used to validate a heat transfer model based on Monte Carlo ray-tracing and finite-volume techniques. Performance predictions obtained with the validated model yield the following results for the receiver. At summer solstice solar noon, with HTF inlet temperature of 120 °C and HTF outlet temperature in the range 250–450 °C, the receiver efficiency ranges from 45% to 29% for a solar power input of 280 kW. One third of the solar radiation incident on the receiver is lost by spillage at the aperture and reflection inside the cavity. Other heat losses are due to natural convection (9.9–9.7% of solar power input) and re-radiation (6.1–17.6%) through the cavity aperture and by natural convection from the cavity insulation (5.6–9.1%). The energy penalty associated with the HTF pumping work represents 0.6–24.4% of the power generated.
Optimized Thermoelectric Module-Heat Sink Assemblies for Precision Temperature Control
Authors: Zhang Rui , Hodes Marc , Brooks David A. , Manno Vincent P.
Published: March 2013

Robust precision temperature control of heat-dissipating photonics components is achieved by mounting them on thermoelectric modules (TEMs), which are in turn mounted on heat sinks. However, the power consumption of such TEMs is high. Indeed, it may exceed that of the component. This problem is exacerbated when the ambient temperature and/or component heat load vary as is normally the case. In the usual packaging configuration, a TEM is mounted on an air-cooled heat sink of specified thermal resistance. However, heat sinks of negligible thermal resistance minimize TEM power for sufficiently high ambient temperatures and/or heat loads. Conversely, a relatively high thermal resistance heat sink minimizes TEM power for sufficiently low ambient temperatures and heat loads. In the problem considered, total footprint of thermoelectric material in a TEM, thermoelectric material properties, component operating temperature, relevant component-side thermal resistances, and ambient temperature range are prescribed. Moreover, the minimum and maximum rates of heat dissipation by the component are zero and a prescribed value, respectively. Provided is an algorithm to compute the combination of the height of the pellets in a TEM and the thermal resistance of the heat sink attached to it, which minimizes the maximum sum of the component and TEM powers for permissible operating conditions. It is further shown that the maximum value of this sum asymptotically decreases as the total footprint of thermoelectric material in a TEM increases. Implementation of the algorithm maximizes the fraction of the power budget in an optoelectronics circuit pack available for other uses. Use of the algorithm is demonstrated through an example for a typical set of conditions.
Characterization of Metallically Bonded Carbon Nanotube-Based Thermal Interface Materials Using a High Accuracy 1D Steady-State Technique
Authors: Wasniewski Joseph R. , Altman David H. , Hodson Stephen L. , Fisher Timothy S. , Bulusu Anuradha , Graham Samuel , Cola Baratunde A.
Published: March 2013

The next generation of thermal interface materials (TIMs) are currently being developed to meet the increasing demands of high-powered semiconductor devices. In particular, a variety of nanostructured materials, such as carbon nanotubes (CNTs), are interesting due to their ability to provide low resistance heat transport from device-to-spreader and compliance between materials with dissimilar coefficients of thermal expansion (CTEs), but few application-ready configurations have been produced and tested. Recently, we have undertaken major efforts to develop functional nanothermal interface materials (nTIMs) based on short, vertically aligned CNTs grown on both sides of a thin interposer foil and interfaced with substrate materials via metallic bonding. A high-precision 1D steady-state test facility has been utilized to measure the performance of nTIM samples, and more importantly, to correlate performance to the controllable parameters. In this paper, we describe our material structures and the myriad permutations of parameters that have been investigated in their design. We report these nTIM thermal performance results, which include a best to-date thermal interface resistance measurement of 3.5 mm2 K/W, independent of applied pressure. This value is significantly better than a variety of commercially available, high-performance thermal pads and greases we tested, and compares favorably with the best results reported for CNT-based materials in an application-representative setting.
Evaluation of Joining Strength of Silicon-Resin Interface at a Vertex in a Three-Dimensional Joint Structure
Authors: Koguchi Hideo , Hoshi Kazuhisa
Published: March 2013

Portable electric devices such as mobile phones and portable music players have become compact and improved their performance. High-density packaging technology such as chip size package (CSP) and stacked-CSP is used for improving the performance of devices. CSP has a bonded structure composed of materials with different properties. A mismatch of material properties may cause a stress singularity, which leads to the failure of the bonding part in structures. In the present paper, stress analysis using the boundary element method and an eigenvalue analysis using the finite element method are used for evaluating the intensity of a singularity at a vertex in three-dimensional joints. A three-dimensional boundary element program based on the fundamental solution for two-phase isotropic materials is used for calculating the stress distribution in a three-dimensional joint. Angular function in the singular stress field at the vertex in the three-dimensional joint is calculated using an eigenvector determined from the eigenvalue analysis. The joining strength of interface in several kinds of sillicon-resin specimen with different triangular bonding areas is investigated analytically and experimentally. An experiment for debonding the interface in the joints is firstly carried out. Stress singularity analysis for the three-dimensional joints subjected to an external force for debonding the joints is secondly conducted. Combining results of the experiment and the analysis yields a final stress distribution for evaluating the strength of interface. Finally, a relationship of force for delamination in joints with different bonding areas is derived, and a critical value of the 3D intensity of the singularity is determined.