bluuebunny/crossref_metadata_2025 huggingface dataset:
Two Thermodynamic Optima in the Design of Sensible Heat Units for Energy Storage
Authors: Bejan A.
Published: November 2010

The paper presents a treatment of sensible heat energy storage units as systems intended to store useful work. An analysis of the thermodynamic irreversibilities associated with storing energy from a hot gas source as sensible heat in huge liquid baths points out two important trade-offs: 1. There exists an optimum, well-defined quantity of hot gas to be used in order to maximize the useful work stored in the liquid bath. Using more than this optimum quantity in the hope of maximizing the amount of thermal energy stored as sensible heat leads to severe thermodynamics losses. 2. There exists an optimum relationship among the gas-liquid heat exchanger design parameters which minimizes the system irreversibility while maximizing its capability of storing useful work. This relationship provides a procedure for estimating the heat exchanger optimum number of transfer units (Ntu). Increasing the Ntu above the optimum in order to upgrade the heat exchanger effectiveness and the thermal energy storage capability leads to prohibitive losses due to fluid friction in the heat exchanger channels. The existence of the two optima demonstrates that designing sensible heat units for maximum thermal energy storage does not necessarily amount to thermodynamically optimizing such systems.
Laminar Free Convection Heat Transfer through Horizontal Duct Connecting Two Fluid Reservoirs at Different Temperatures
Authors: Bejan A. , Tien C. L.
Published: November 2010

This technical note develops an analytical result for heat transfer by laminar free convection in a long horizontal parallel-plate channel connecting two reservoirs containing the same fluid but kept at different temperatures. The analysis is based on the integral method. The Nusselt number result is presented in chart form in terms of the Rayleigh number based on height, Ra, and the height/length aspect ratio, h/L.
Unsteady Mixed Convection Heat Transfer from a Horizontal Circular Cylinder
Authors: Jain P. C. , Lohar B. L.
Published: November 2010

A numerical investigation of an unsteady mixed convection from a horizontal circular cylinder is presented. The coupled basic equations of motion and energy are solved for two cases 1) Re = 100, Gr = 104 and 2) Re = 200, Gr = 5 × 104. The velocity field and the temperature field around the cylinder are exhibited by streamlines and isotherms at different times. The Strouhal number for the shedding of vortices in the wake of the cylinder is calculated. Figures have been drawn to show the variations of the local and the mean Nusselt numbers with time. The effects of the presence of free convection are discussed.
Convective Heat Transfer Augmentation in Thermal Entrance Regions by means of Thermal Instability
Authors: Kamotani Y. , Ostrach S. , Miao H.
Published: November 2010

The effects of thermal instability on a liminar thermally developing entrance flow between two horizontal plates heated from below are studied experimentally. The experiments cover a range of Rayleigh numbers between 2.2 × 104 and 2.1 × 105, and Reynolds numbers between 50 and 300 using air. Results for the heat transfer rate and entrance length show that they are influenced not only by the Rayleigh number but also by the ratio Re2/Gr. The heat transfer rate is increased as much as 4.4 times due to thermal instability. The flow visualization experiments show that the critical wavelength is determined by the channel height, not by the thermal boundary layer thickness.
Calculation of Mean Temperature Difference in Air-Cooled Cross-Flow Heat Exchangers
Authors: Roetzel W. , Neubert J.
Published: November 2010

An approximate explicit equation together with empirical coefficients is presented for the fast calculation of the mean temperature difference of eight cross-flow arrangements. The mean temperature difference is calculated from the effectiveness of the process stream and the number of transfer units on the air side.
A Variational Analysis of Freezing or Melting in a Finite Medium Subject to Radiation and Convection
Authors: Yeh L. T. , Chung B. T. F.
Published: November 2010

The objective of this work is to develop an approximate analytical solution for the heat transfer in a finite medium with a change in phase. The medium is subjected to radiative and aerodynamic cooling (or heating) at one side and is thermally insulated at the other side. Furthermore, the initial temperature is different from the fusion (or melting) temperature. It is assumed that all the physical properties are constant for each phase but may be different (except density) for different phases. In this analysis, Biot’s variational method is employed. With this technique, the complicated nonlinear problem is reduced to an initial value problem which is then solved by the Runge Kutta method. The calculated temperature histories at both surfaces and the time variant fusion (or melting) line are in terms of dimensionless parameters such as radiation number, Biot’s number, Stefan number, ratio of freezing (or melting) to initial temperatures and the thermal properties ratios in both phases. Some limiting solutions of the present work are found to agree with the earlier analysis.
Flow in a Toroidal Thermosyphon with Angular Displacement of Heated and Cooled Sections
Authors: Damerell P. S. , Schoenhals R. J.
Published: November 2010

A toroidal thermosyphon consisting of a fluid-filled torus located in a vertical plane was studied analytically and experimentally. Good agreement was obtained between analytical predictions and measurements for large values of the angular displacement of the heated and cooled sections. For smaller angular displacements, the analytical predictions of steady state flow rates were found to exceed the corresponding experimentally observed values. The discrepancies were attributed to a reverse flow phenomenon. Some analytically predicted flows were not physically achievable. In these situations the flow would either reach a steady condition in the opposite direction, or it would oscillate indefinitely.
Analysis of Diffuse-Specular Axisymmetric Surfaces with Application to Parabolic Reflectors
Authors: Mahan J. R. , Kingsolver J. B. , Mears D. T.
Published: November 2010

Presented is an exact numerical technique for radiative analysis of diffusely emitting axisymmetric enclosures, passages, and cavities having both diffuse and specular components of reflectivity. The specular components of the required exchange factors are synthesized by chaining together partial exchange factors, defined as the fraction of diffusely distributed radiation leaving one surface and arriving at another after one intervening specular reflection with a reflectivity of unity. The technique is employed to predict the temperature distributions on parabolic reflectors in radiative equilibrium with sources located at their foci. It is demonstrated that, at least for this important geometry, an accurate representation of the exchange factors can be obtained by considering only low order chains.
Friction-Induced Heating in Axially Loaded Ball Bearings
Authors: Schwartz J. I.
Published: November 2010

This paper compares theoretical and experimental results on the friction-induced heating in thrust-loaded ball bearings at constant speed. Heat transfer and friction heat-generation models are developed for the bearings using computer techniques. The comparisons indicate that the models are reasonable since the predictions are within ±10 percent of the measured values. More work is needed, however, before a more accurate prediction technique will be available.
The Axial Load-Carrying Capacity of Radial Cylindrical Roller Bearings
Authors: Korrenn H.
Published: November 2010

Thrust load transmission at the contact areas of roller ends and flanges occurs under conditions of pure sliding. Recent theoretical and experimental investigations showed that with adequately designed roller ends and flanges and with a satisfactory lubricant high thrust loads can be accommodated over a wide speed range with fully hydrodynamic lubrication. The conventional methods used for the determination of the safe thrust load should be revised and supplemented. Oil viscosity should be introduced as an important parameter. Contrary to present opinion the hydrodynamic load-carrying capacity at the flange increases with increasing speed. This new knowledge broadens the application range of radial cylindrical roller bearings.
High-Speed Performance of Tapered Roller Thrust Bearings With Various Lubricating Systems
Authors: Naik V. V. , Keim E. L. , Neifert H. R.
Published: November 2010

Using high oil-flow rates, 6-in-bore tapered roller thrust bearings were operated in a speed range of 3600 fpm to 10800 fpm with loads up to 70,000 lb. Bearing operating temperature is considered to be the principal criterion of operation. The effect of lubricating systems, speed, load, oil-flow rates, lubricant viscosity, and oil-inlet temperature on the operating temperature is demonstrated. The test-rig results are generalized by means of dimensional analysis enabling the designer to predict operating temperature for various operating conditions of speed, load, oil-flow rates, and oil-inlet viscosity.
On Controlling the Film Thickness in Self-Acting Foil
Bearings
Authors: Eshel A.
Published: November 2010

Some factors useful in overcoming excessive air gaps in foil bearings are investigated. Since the gaps of interest are small, the foil bearing equations are modified to include the effects of the molecular mean free path. It is shown that by small corners in the solid wall, one can reduce the air film thickness considerably. A change in curvature with continuous slope has also a marked effect on the film thickness. Theoretical prediction curves allowing the calculation of the air gap as a function of corner angle, change in radius of curvature, and the molecular mean free path are presented.
The Optimum One-Dimensional Hydrodynamic Gas Rayleigh Step Bearing
Authors: Wylie G. M. , Maday C. J.
Published: November 2010

The optimum Rayleigh gas slider bearing is determined for a range of bearing numbers. Numerical methods are used to calculate step location, step pressure, and load capacity for given values of step height ratio, bearing number, and flow parameter. These methods are used to determine as many data points as desired so that it is possible to obtain the optimum configuration dimensions to a very high degree of accuracy. An inherent feature of this analytical experiment is the acquisition of data pertaining to the near-optimum bearings and such data are presented for bearings with load capacities ranging down to seven-tenths of the load associated with the optimum Rayleigh bearing. At low bearing numbers it is found that the optimum Rayleigh bearing has only slightly lower load-carrying capability than the optimum gas slider bearing. For bearing numbers of 50, 100, and 500 the optimum Rayleigh slider bearings were, respectively, 5.8, 8.3, and 15.3 percent lower in load-carrying capability than the corresponding optimum bearings.
Effects of Heat Generation in an Air Hydrostatic Journal Bearing
Authors: Baker R. E. , Hornung K. G.
Published: November 2010

A rather complete heat transfer analysis is carried out for a specific air hydrostatic bearing. The effects of viscosity variation and thermal deformations are included. The result is a prediction of film temperature of the bearing at high speed. Torque and temperature measurements are made on the subject bearing and show fair correlation with the theory.
Investigation of the Spherical Hydrostatic Gas Bearing for Two-Axis Gyros
Authors: Rood L.
Published: November 2010

Investigation shows that spherical hydrostatic gas bearings can be manufactured by coining of precision dimensions in aluminum die castings. The paper also shows that the goals of low competitive costs and high reliability can be achieved with commercial balls, filters, and gas cartridges. Load support of a spherical hydrostatic gas bearing can be 40 percent of the supply pressure times the projected ball area. Gas consumption for a bearing ball size of 1.0-2.0 in. can be low (1.0 SCFM). Bearing noise can be less than 5.0 dyne-cm. These observations are from work on a family of two-axis gyros and a two-axis wind tunnel model pivot.
The Development of a Three-Micron Absolute Main Oil Filter for the T53 Gas Turbine
Authors: Lynch C. W. , Cooper R. B.
Published: November 2010

This paper describes the development of the first known successful three-micron absolute main oil filter for an aircraft gas turbine lubrication system, replacing the 40-micron nominal filter on the Avco Lycoming T53 engines. The new disposable elements, running approximately 300 hours without clogging, provide a much cleaner lubrication system and have eliminated requirements for 25 hour filter inspections and 100 hour oil drains. Despite past filter experience, the clean pressure drop through the new filter is close to that of the 40-micron unit. Two benefits of the new elements are described. The first is prevention of the wear caused by the abrasive action of oil containing fine one to five-micron particles. Once these particles are removed, the system stays clean for hundreds of hours. This period is not shortened unless lube system component failures, engine teardowns and rebuilds, or frequent oil changes occur. The second benefit is the marked absence of oil degradation with clean oil over long drain intervals. The paper describes the design of the filter assembly and indicator system, bench testing, and the 6000 hours of engine testing of the filter prior to its proposed incorporation into the production engines.
Flow Instability Induced by Viscosity Variation in High Pressure Two-Dimensional Laminar Flow Between Parallel Plates
Authors: Gould P.
Published: November 2010

This paper presents the results of an analysis of fluid flow in high pressure hydrostatic bearings and seals which can be modeled as infinitely long, closely spaced, rigid parallel plates. The flow is laminar and at low Reynolds number. The fluid is Newtonian with a viscosity which is an exponential function of temperature and pressure. The effect of the temperature variation across the fluid film is found to be extremely significant, and limits the application of the integrated adiabatic energy equation to a narrow range of the parameters.
Isothermal Elastohydrodynamic Theory for the Full Range of Pressure-Viscosity Coefficient
Authors: Cheng H. S.
Published: November 2010

The isothermal, elastohydrodynamic (EHD) solutions in the inlet region of line contacts are extended to cover the full range of pressure-viscosity parameter, G, and the region of extremely heavy loads. The effect of a composite exponential model for the pressure-viscosity dependence on the film thickness is also studied. Results of the film thickness are compared with those based on work by Grubin, Dowson-Higginson, Bell and Kannel, and Herrebrugh. Comparison is also made between the theoretical results with the recently obtained X-ray film thickness measurements.
Lubrication Mechanism of Hip Joint Replacement Prostheses
Authors: Weightman B. , Simon S. , Paul I. , Rose R. , Radin E.
Published: November 2010

A laboratory study has been made of the lubrication and friction characteristics of a plastic on metal (Charnley-Muller) and a metal on metal (McKee-Farrar) total hip joint replacement prostheses. The results show the effect of lubricant, speed, and load on the performance of the joints. Under a 560 lb load the coefficient of friction of the plastic to metal joint was lower than that of the metal to metal at speeds up to the equivalent of fast walking. Bovine serum and synovial fluid, as well as human serum albumin were found to be good lubricants of both types of prostheses. The frictional force produced by the metal on metal prosthesis increased linearly with load, in both the dry and lubricated states. This was not the case with the plastic to metal joint. The results show that at low physiological loads the effort required to articulate the prostheses are comparable while at higher loads the friction force of the metal to plastic is significantly lower. Friction readings taken with no lubricant indicate the serious damage which would result in the human body if a metal to metal prosthesis became devoid of liquid. The load and speed behavior of the prostheses require different interpretation of the data than presently postulated.
Reduction of Electrical Runout to Improve the Accuracy of Eddy Current Probe Sensing of Turbomachinery Vibration
Authors: Schanzenbach G. P.
Published: November 2010

The objective of the work reported in this paper is to reduce the effect of electrical runout in order to improve accuracy of eddy current probe sensing of turbomachinery vibration. Results of a combined analytical study and test program indicate that electrical runout effect can be reduced by configuration changes such as probe coil diameter, operating air gap, and operating frequency.
Squeeze Films in Porous Metal Bearings
Authors: Prakash J. , Vij S. K.
Published: November 2010

Squeeze films in an axially undefined porous journal bearing with a full film of lubricant are analyzed to determine their performance. The expressions for pressure distribution and load capacity are given in closed form. The time-height relation is obtained by numerical integration. The results are shown graphically. It is found that the time required for the film to reduce in thickness is significantly less as compared to a nonporous bearing.
A Study of the Thermohydrodynamic Performance of Finite Slider Bearings
Authors: Ezzat H. A. , Rohde S. M.
Published: November 2010

The thermohydrodynamic (THD) performance of finite inclined-plane slider bearings is studied. The fluid film momentum, continuity, and energy equations are coupled to the heat-conduction equations for the bearing solids, and solved numerically. The effect of bearing geometry, oil type, and inlet temperature on bearing performance is shown. The manner in which environmental temperature and heat transfer considerations influence the fluid film behavior is studied.
Comparison of the Bearing Performance of Normal and Artificial Human Joints
Authors: Walker P. S. , Gold B. L.
Published: November 2010

A comparison is made between the lubrication mechanisms believed to occur in normal human hip joints, and artificial hip joints. A review of the literature and some new experimental data is used to highlight many of the characteristics of human joint lubrication. Specimens of artificial joints removed from patients after various periods of service were studied, and deductions made about the modes of lubrication and wear. Both metal-on-metal and metal-on-plastic joints were considered. It was concluded that human joints operated mainly by fluid film lubrication while artificial joints displayed principally boundary lubrication.
Elastomer Inertia Effects in Compliant Surface Bearings
Authors: Pirvics J. , Castelli V.
Published: November 2010

A bearing system using a compliant surface may be so constructed that the lubricant pressure distribution is either stationary or in motion relative to the elastomer. In the latter case the motion of the deformation in the elastomer introduces inertial effects which can be important at high enough bearing velocities. This paper is concerned with the assessment of these effects. Steady state operating conditions are computed and analytical techniques presented for the infinite width slider and infinite length journal bearing.
Analytical Investigation of the Spiral Groove Face Seal
Authors: Sneck H. J. , McGovern J. F.
Published: November 2010

An analytical investigation of both a simplified and a comprehensive mathematical model of a spiral groove face seal, using the “narrow seal” approximation. The sealing fluid is assumed to be incompressible and Newtonian. The inertial effects associated with seal curvature are incorporated in the comprehensive model. The results of the analysis are programmed for computer computation in order to facilitate their application in parametric design studies. Performance characteristics are calculated for some particular seal designs.
Performance of Plain Journal Bearings Operating Under Vortex Flow Conditions
Authors: Freˆne J. , Godet M.
Published: November 2010

An experimental program conducted on an original device was undertaken to study the performance of plain bearings operating at sufficiently high Reynolds number to introduce Taylor vortices. Curves of relative eccentricity, attitude angle, and friction torque were obtained versus speed and load. Experimental results conducted for Reynolds number smaller than 1100 indicate that both laminar and Taylor vortex regimes are encountered. The occurrence of the vortices is identified by a break in the slope of the friction torque versus speed curves. The position of the break is in good agreement with the theoretical predictions of Di Prima and Ritchie. From the practical point of view, the data show that for constant viscosity the occurence of Taylor vortices does not alter the curves of eccentricity versus either speed or load but modifies the attitude angle and frictional torque. In turn, the increase in frictional torque, and subsequently of temperature may cause a decrease in viscosity and thus a drop in load carrying capacity for fluids such as oils whose variations of viscosity with temperature is large.
Solution for the Pressure and Temperature in Thrust Bearings Operating in the Thermohydrodynamic Turbulent Regime
Authors: Huebner K. H.
Published: November 2010

A numerical solution is developed for the equations governing the turbulent thermohydrodynamic flow in a sector shaped thrust bearing. The lubricant viscosity is taken as a function of the three-dimensional temperature distribution in the fluid-film. Three-dimensional heat transfer between the lubricant and both the moving and stationary solids is included in the analysis. Isotropy of the turbulent mixing process is assumed. The “law of the wall” for turbulent shear flows is used to define an eddy viscosity based on the local wall shear stress and the viscosity within the film. A modified Reynolds analogy is assumed to relate the turbulent transport of heat and momentum. According to the Ng-Pan theory the momentum transport equations are linearized by assuming the nonplanar flow is a small perturbation of turbulent Couette flow. Thermal effects are shown to be less pronounced in turbulent flow than in laminar flow.
Application of Energy Model of Turbulence to Calculation of Lubricant Flows
Authors: Ho Mein-Kai , Vohr J. H.
Published: November 2010

A turbulent energy model for determination of turbulent stresses is used to calculate velocity profiles in lubricant films. The results agree very well with the predictions of the previously established turbulent lubrication theory of Elrod, Ng, and Pan. The present turbulent analysis can be readily extended to lubricant flows in which mean flow convective effects are significant.
Analysis of Externally Pressurized Gas Porous Bearings
Authors: Murti P. R. K.
Published: November 2010

An analytical solution is presented to predict the performance of an externally pressurized porous gas thrust bearing. When the wall thickness of the pad is small compared to its radius, the expressions for the bearing characteristics can be given in a closed form. The bearing number Λ—a dimensionless design variable—can adequately describe the performance of the bearing. The load capacity and mass flow rate progressively increase with the bearing number; the static stiffness increases with the bearing number up to Λ ∼ 4.0 and then gradually decreases. The decisive influence of permeability of the pad material in controlling the performance of the bearing is discussed and the interesting behaviour of the static stiffness as the film thickness is reduced is pointed out. It is found that there is near perfect agreement between the predicted performance of the bearing and the one experimentally evaluated. The characteristics are plotted over a wide range for the bearing number (.01 ≤ Λ ≤ 2500) in such a way that the information is of direct use to designers and applications engineers. Also, the results are given in tabular form to facilitate interpolation of the values as required.
The Effects of Elastohydrodynamic Traction Behavior on Cage Slip in Roller Bearings
Authors: Ford R. A. J. , Foord C. A.
Published: November 2010

A simple theoretical model of a bearing and measured traction curves are used to explain the different types of experimentally observed cage behavior which result from different lubricants. Traction curves with a pronounced peak are shown to produce unstable cage slip behavior, although bearings can operate steadily in the high slip region. The instability occurred in tests with a high traction fluid but not with ester-type gas turbine lubricants. A bench-top roller bearing rig of the type used in these experiments provides an effective method of assessing the tractive properties of lubricants, using a 25-ml sample.
A New Model of Articular Cartilage in Human Joints
Authors: Ling F. F.
Published: November 2010

A new model of the fluid-filled articular cartilage in human joints is introduced. It is a composite which can imbibe and exudate across the surface and offers resistance in tension and compression, while preserving the essential nonlinearity. The model makes tractable transient static or moving contact problems whose solutions are paramount in the study of failure criteria associated with arthritic conditions. In two examples, indentation—time characteristics and friction coefficient, based on deformation theory, are found and they agree with measured values. Moreover, a third example illustrates the mutual inclusiveness of the two leading theories: the weeping and boosted lubrication theories.
Externally Pressurized Compliant Air Bearing Operating on a Rough Moving Surface
Authors: Lau H. , Harman C. M.
Published: November 2010

An externally pressurized compliant air bearing with potential for operation on surfaces of moderate unevenness or roughness such as might be encountered in vehicle guideways is considered. Analytical results are presented which show the effect on load carrying capacity, flow requirement, and center of pressure location of variation of bearing compliance, surface roughness, bearing speed, and bearing slope.
Drift Analysis of a Spherical Ball Bearing Gyro
Authors: Gu A.
Published: November 2010

The drift torque produced in a spherical ball bearing supporting a directional gyro is obtained. The analysis is based on static load balance and Coulomb friction. The effects of preload and wear track on drift torque are also studied. It is found that the drift rate of the gyro due to this drift torque is significant.
The Measurement and Analysis of Ball Motion in High Speed Deep Groove Ball Bearings
Authors: Boness R. J. , Chapman J. J.
Published: November 2010

This paper reports on a study of ball motion, including the measurement of ball rolling axis, in deep groove bearings operating at high speeds under thrust load conditions. The technique employed relies on viewing the test bearing, operating in the conventional fixed outer ring mode, through a rotating prism which eliminates optically the gross rotation of the separator. Videotape recordings of a selected ball, distinctively marked and illuminated stroboscopically, allows a complete analysis of ball bearing kinematics. Experimental results of separator speed, ball speed and rolling axis together with separator slip, ball slip and spin velocities at both the inner and outer raceway contacts are presented for a wide range of loads and shaft speeds up to 12,000 rev/min. These results are compared with the existing theory of Jones. Discrepancies between predicted and actual ball motion are due to the assumption made by Jones in neglecting bearing element slip. A further analysis of the experimental results including both gyroscopic torques and slip based on elastohydrodynamic traction values for the test lubricant explains actual ball motion more fully.
Tribological Properties of Self-Lubricating Fluoride-Metal Composites to 900 Deg C (1650 Deg F)—A Review and Some New Developments
Authors: Sliney H. E. , Graham J. W.
Published: November 2010

This paper summarizes the friction and wear behavior of some fluoride-metal, self-lubricating composites. Fluoride-infiltrated sintered nickel alloy composites and plasma-sprayed, co-deposited fluoride-nickel alloy composites are described. The importance of proper surface-conditioning of the composites is stressed. Performance of fluoride-metal composites in some machine application evaluations is discussed.
Analysis of Noncircular Gas Journal Bearings
Authors: Pinkus O.
Published: November 2010

The compressible Reynolds Equation under isothermal conditions was solved for finite elliptical and 3-lobe bearings with the load vector acting in any arbitrary direction over the full range of 360 deg. Envelopes of minimum and maximum eccentricity for a given set of operating conditions are provided, the first to yield maximum load capacity, and the second to assist stability by a choice of the highest possible ε. Some values of the spring and damping forces are also given and it is shown that in comparison with conventional bearings, the non-circular designs offer a significant advance in stiffness, particularly for low ε, when instability is most often encountered.
Short Bearing Analysis Applied to Rotor Dynamics—Part I: Theory
Authors: Kirk R. G. , Gunter E. J.
Published: November 2010

A derivation of the Reynolds equation is presented in fixed Cartesian coordinates which allows rapid solution of the fluid-film bearing forces using the short bearing approximation. The solution for the fluid-film pressure profile is given in terms of the instantaneous position and velocities expressed in the fixed reference frame. The effects of cavitation are approximated by deleting subambient pressures when integrating the pressure profile. The equations for the instantaneous whirl rate and curvature are presented and discussed in relation to journal bearing behavior. Three-dimensional plots of the pressure profile for selected dynamic conditions give a vivid picture of the fluid pressure field. Dimensionless plots of the stiffness and damping coefficients for the short bearing are presented. The results of a linearized stability analysis are presented and compared to other published results. Results of transient response analysis will be presented in Part 2.
Experimental Parametric Study of a Squeeze Film Bearing
Authors: Tonnesen J.
Published: November 2010

The paper presents the results of an experimental investigation in which the damping coefficients of a squeeze-film bearing are obtained from impedance measurements. For various force levels, and for frequencies up to 200 Hz, the bearing length, radial clearance, and viscosity are varied and both the concentric and the eccentric case are investigated. Good correlation is found with a simplified linearized theory for moderate force levels, and for higher force levels the correlation is satisfactory when the oil supply pressure is increased sufficiently.
Two-Fluid Flow Between Rotating Annular Disks
Authors: Zweig J. E. , Sneck H. J.
Published: November 2010

The general hydrodynamic behavior at small clearance Reynolds numbers of two fluids of different density and viscosity occupying the finite annular space between a rotating and stationary disk is explored using a simplified version of the Navier-Stokes equations which retains only the centrifugal force portion of the inertia terms. A criterion for selecting the annular flow fields that are compatible with physical reservoirs is established and then used to determine the conditions under which two-fluid flows in the annulus might be expected for specific fluid combinations.
The Lubrication of Lightly Loaded Cylinders in Combined Rolling, Sliding, and Normal Motion—Part II: Experimental
Authors: Markho P. H. , Dowson D.
Published: November 2010

This paper forms part of a wider investigation which includes the theoretical analysis given in Part I in addition to a study of the outlet cavitation boundary, using high-speed cine photography, reported elsewhere [4]. Pressure and some load measurements are presented which show good agreement with the theoretical predictions despite the well-known shortcomings of the Swift-Stieber boundary condition used in the analysis. Two sets of results have been included to cover the pure squeeze-film problem in addition to that of combined rolling, sliding and “normal” motion.
Endurance and Failure Characteristic of Main-Shaft Jet Engine Bearing at 3 × 106 DN
Authors: Bamberger E. N. , Zaretsky E. V. , Signer H.
Published: November 2010

Groups of thirty 120-mm bore angular-contact ball bearings were endurance tested at a speed of 12 000 and 25 000 rpm (1.44 × 106 and 3.0 × 106 DN) and a thrust load of 66 721 N (5000 lb). The bearings were manufactured from a single heat of VIM-VAR AISI M-50 steel. At 1.44 × 106 and 3.0 × 106 DN, 84 483 and 74 800 bearing test hours were accumulated, respectively. Test results were compared with similar bearings made from CVM AISI M-50 steel run under the same conditions. Bearing lives at speeds of 3 × 106 DN with the VIM-VAR AISI M-50 steel were nearly equivalent to those obtained at lower speeds. A combined processing and material life factor of 44 was found for VIM-VAR AISI M-50 steel. Continuous running after a spall has occurred at 3.0 × 106 DN can result in a destructive fracture of the bearing inner race.
Design and Evaluation of a 3 Million DN Series-Hybrid Thrust Bearing
Authors: Scibbe H. W. , Winn L. W. , Eusepi M.
Published: November 2010

The design and experimental evaluation of a series-hybrid thrust bearing, consisting of a 150-mm ball bearing and a centrifugally actuated, conical, fluid-film bearing, is presented. Tests were conducted up to 16 000 rpm and at this speed an axial load of 15 600 N (3500 lb) was safely supported by the hybrid bearing system. Through the series-hybrid bearing principle, the effective ball bearing speed was reduced to approximately one-half of the shaft speed. A speed reduction of this magnitude would result in a tenfold increase in the ball bearing fatigue life. A successful evaluation of fluid-film bearing lubricant supply failure was performed repeatedly at an operating speed of 10 000 rpm. A complete and smooth changeover to full-scale ball bearing operation was effected when the oil supply to the fluid-film bearing was cut off. Reactivation of the fluid-film oil supply system produced a flawless return to the original mode of hybrid operation.
Pressure Distribution for Patchlike Contact in Seals With Frictional Heating, Thermal Expansion, and Wear
Authors: Kilaparti S. R. , Burton R. A.
Published: November 2010

Sliding contact in seals is known to change at high sliding speed from initially uniform pressure to a deformed state where contact is restricted to small patches of the surface. An earlier analysis of such contact was based upon the assumption of uniform pressure on the small patches. The present study draws upon a thermoelastic influence function to provide simultaneous equations for pressure on subdivisions of the patches. The final result is that at high wear rate (and, consequently, high traversal speed of the patch along the surface of the more conductive body of the contacting pair) the pressure distribution becomes roughly triangular with the maximum pressure toward the leading edge of the patch.
Load Capacity and Stiffness Considerations for Hydrostatic Journal Bearings
Authors: Ghai R. C. , Singh D. V. , Sinhasan R.
Published: November 2010

A theoretical solution, using finite element method, to predict performance characteristics of a capillary compensated hydrostatic oil journal bearing has been presented. Load capacity curves for two load directions of a typical bearing with four pockets are given for various design parameters and eccentricity ratios, and the four fluid film stiffness coefficients are computed. The effect of the feeding system on bearing load capacity and stiffness is discussed. Without using the flow approximations of Raimondi and Boyd [1] and Kher and Cowley [2], which are essentially valid for small eccentricity ratios and small circumferential land widths, the bearing flow has been computed both as the sum of nodal flows on the external boundary and as the inflow to the pockets.
Eccentric Operation of the Squeeze-Film Damper
Authors: Pan Coda H. T. , Tonnesen Jorgen
Published: November 2010

The squeeze-film damper, undergoing a whirl orbit as may be caused by rotor unbalance, resists eccentricity of the whirl orbit with a static stiffness which is proportional to the dynamic force carried by the squeeze-film. In addition, the fluid film force would develop nonsynchronous components. The short bearing analysis is applied to treat this problem. Implications regarding the unbalance dynamics of a rigid rotor in the presence of a static load are examined.
Nonaxisymmetric Incompressible Hydrostatic Pressure Effects in Radial Face Seals
Authors: Etsion Izhak
Published: November 2010

A flat seal having an angular misalignment is analyzed, taking into account the radial variations in seal clearance. An analytical solution for axial force, tilting moment, and leakage is presented that covers the whole range from zero to full angular misalignment (surfaces in contact). It is shown that nonaxisymmetric hydrostatic pressures due to the radial variations in the film thickness have a considerable effect on seal stability. When the high pressure is on the outer periphery of the seal, both the axial force and the tilting moment are nonrestoring. This causes the seal surfaces to wear at the outer diameter. Instability and wear at the inner diameter can occur when angular misalignment is combined with radial distortions and the high pressure is on the inner periphery. The case of high-pressure seals, where cavitation is eliminated, is discussed, and the possibility of dynamic instability is pointed out.
Light-Scattering Study of the Glass Transition in Lubricants
Authors: Alsaad M. A. , Winer W. O. , Medina F. D. , O’Shea D. C.
Published: November 2010

The sound velocity of four lubricants has been measured as a function of temperature and pressure using Brillouin scattering. A change in slope of the velocity as a function of temperature or pressure allowed the determination of the glass transition temperature and pressure. The glass transition data were used to construct a phase diagram for each lubricant. The data indicate that Tg increased with pressure at a rate which ranged from 120 to 200 C/GPa. The maximum pressure attained was 0.69 GPa and the temperature range was from 25 to 100 C.
Interferometric Deformation Measurement of Elastohydrodynamically Loaded Surfaces
Authors: Jakobsen J. , Larsen P. C.
Published: November 2010

A method of determining deformations of elastohydrodynamic point and line contacts under actual operating conditions is presented. An optical interference of two beams is applied. The method appears to give a high degree of accuracy and thereby offers the possibility of determining pressure profiles over the contact area with sufficient precision for viscometric purposes.
Numerical Solution of Reynolds Equation With Slip Boundary Conditions for Cases of Large Bearing Number (Λ > 300)
Authors: Sereny A. , Castelli V.
Published: November 2010

The behavior of two numerical discretizations for the solution of Reynolds equation with slip boundary conditions for cases of large bearing number is described. The narrow boundary layer caused by the large bearing number is well handled by a variable grid spacing. The performance of these methods is compared against exact solutions for the ∞-wide case. It is clearly demonstrated that discretization which satisfies integral conservation is preferable to the differential procedure of finite differencing.
Seizure Resistance of Cast Aluminum Alloys Containing Dispersed Graphite Particles of Different Sizes
Authors: Rohatgi P. K. , Pai B. C.
Published: November 2010

Seizure resistance of the cast graphite particle-aluminum composite alloys, containing graphite particles of varying sizes has been studied using a Hohman wear tester. The size of the spheroidal graphite particles was varied from 30 μm to 400 μm, and in one case 80 μm size flake graphite was used to observe the effect of shape of graphite. When the graphite content of graphitic aluminum alloys is more than 2 percent, these alloys can be self-mated under condition of boundary lubrication without seizing. The size and shape of the graphite particles had no significant effect on the seizure resistance of these alloys, in the range of conditions investigated in this study. This is attributed to the extensive deformation and fragmentation of graphite due to the low yield strength of the aluminum matrix and the low flow stress of the graphite particles. During wear, the deforming aluminum matrix accentuates the deformation and fragmentation of subsurface graphite particles and causes them to come to the mating surface, thus providing continuous lubrication and preventing seizure. Even after a short run-in period, a continuous layer of graphite is observed on the mating surfaces of graphite particle-aluminum composite alloys. This layer persists even after extensive wear deformation.
Seizure of Eccentrically Loaded Journal Bearings and Sealing Rings
Authors: Heckmann S. R. , Burton R. A.
Published: November 2010

Thermal and elastic deformations are derived for a ring receiving heat input over a limited part of its inner circumference. This is applied to the problem of seizure of journal bearings or radial seals operating with dry or boundary lubricated contact. It is found that when the ratio of outer to inner radius for the ring is less than 1.715, seizure will not occur as a result of the mode of distortion studied. For thicker bearing/housing bodies there is always some load-speed combination which will lead to seizure, and this may occur in the range of common speeds and loads encountered in engineering applications.
Observation of Self-Excited Wobble in Face Seals
Authors: Etsion I. , Burton R. A.
Published: November 2010

A face seal model consisting of a rigidly mounted rotor and a flexibly mounted stator was tested under conditions of eccentric loading. Self-excited oscillations in the form of combined precession and nutation of the stator were observed. The nature of the motion and its frequency are dependent on rotational speed, seal clearance, and external tilting moment. It is possible that some unexplained seal failures and waviness of seal faces are the result of such self excited wobble.
Transient Analysis of a Permeable Thermal Barrier System
Authors: Cheng L. C. , Bowyer J. M.
Published: November 2010

A permeable thermal barrier system lines the walls of certain enclosures and pipes within the High Temperature Gas-Cooled Reactor (HTGR). This system protects the Prestressed Concrete Reactor Vessel (PCRV) from the otherwise damaging effects of heat transfer from the high-temperature helium working fluid. A one-dimensional transient model of this system has been developed to study the response of this system and its associated supporting structure when it is subjected to a rapid depressurization. The analytical model is normalized, and the dimensionless parameters which characterize the system response are extensively studied. The results of this study will provide both the qualitative and quantitative knowledge required for a rational design of thermal barrier system in the High Temperature Gas-Cooled Reactors.
Comparison of Some Optimal Control Methods for the Design of Turbine Blades
Authors: de Silva B. M. E. , Grant G. N. C.
Published: November 2010

This paper attempts a comparative study of some numerical methods for the optimal control design of turbine blades whose vibration characteristics are approximated by Timoshenko beam idealizations with shear and incorporating simple boundary conditions. The blade was synthesized using the following methods (1) conjugate gradient minimization of the system Hamiltonian in function space incorporating penalty function transformations (2) projection operator methods in a function space which includes the frequencies of vibration and the control function (3) ε-technique penalty function transformation resulting in a highly nonlinear programming problem (4) finite difference discretization of the state equations again resulting in a nonlinear program (5) second variation methods with complex state differential equations to include damping effects resulting in systems of inhomogeneous matrix Riccatti equations some of which are stiff (6) quasi-linear methods based on iterative linearization of the state and adjoint equation. The paper includes a discussion of some substantial computational difficulties encountered in the implementation of these techniques together with a resume of work presently in progress using a differential dynamic programming approach.
Fatigue Life Prediction of Complex Structures
Authors: Leis B. N.
Published: November 2010

Because of the complex nature of the fatigue process, it is only recently that reasonably effective analysis procedures for predicting finite-fatigue life for simple notched coupons have evolved. One of the more vexing problems in adapting these procedures to making life predictions for complex components and structures is that of the multiplicity of crack initiation sites and mechanisms which determine the fatigue life of such structures. It has been observed that which of the many potential initiation sites and mechanisms controls failure depends on the service environment and the magnitude and character of the service loading. The present paper critically examines available technology for fatigue analysis of complex structures in which the multiplicity of initiation sites and mechanisms control the structure’s life. It was concluded after this critique that those techniques most likely to yield accurate predictions were based on the critical location concept. Thereafter, the complexities in the use of this concept in fatigue analysis of components and structures were detailed and the concept illustrated by its application to the fatigue analysis of a component configuration which simulates a joint in an airframe. Finally, the use of the critical location concept as an aid to understanding the mechanisms of fatigue improvement fasteners was discussed.
An Analytic Study of the Energy Dissipation of Turbomachinery Bladed-Disk Assemblies Due to Inter-Shroud Segment Rubbing
Authors: Bielawa R. L.
Published: November 2010

A novel computational method is presented for analytically studying the energy dissipative characteristics of turbomachinery bladed-disk assemblies due to inter-shroud segment rubbing. Coulomb friction, as the dissipative mechanism, is utilized in this method with broader generality than that in other similar studies heretofore. The immediate objectives of this study were 1) to obtain an understanding of the general slippage characteristics of the shroud segment interfaces in the presence of both steady normal (to the shroud segment interfaces) lock-up stresses and stresses due to modal vibration, and 2) to incorporate these characteristics in a calculation of the minimum modal deflection required for incipient slipping as well as an estimation of the energy dissipation (damping) due to subsequent rubbing. The utlimate applications of this knowledge are for more accurate calculations of flutter stability margins and dynamic magnifications of stresses, and for a more rigorous formulation of the shroud boundary conditions used in the calculation of natural frequencies and mode shapes. As a result of this preliminary investigation it is concluded that the energy dissipation due to inter-shroud segment rubbing tends to an amplitude squared dependency and is thus similar to classic structural damping.