bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of temperature rise in oil due to compression
Authors: Imado K , Kido Y , Miyagawa H , Hirano F
Published: October 2002

Temperature rises of various oils were measured in both impact tests and quasi-adiabatic compression tests. A steel ball impacted against an oiled sapphire glass in the impact test. It was found that the maximum temperature rise was 45 °C in impact tests. A close relationship between temperature rise and α amax was found for oils of relatively low viscosity, where α was the pressure-viscosity coefficient and amax was the maximum acceleration of the hammer during impact; namely, the temperature increased with each increase in the product of the contact force and the pressure-viscosity coefficient. In the compression tests, the temperature increased almost linearly with increase in the volumetric strain regardless of the type of oil. The order of the temperature rise for the corresponding oil in each experiment was reversed; i.e. a higher temperature increase was observed for an oil of smaller pressure-viscosity coefficient in the compression test. On the contrary, a higher temperature rise was noted in the case of a larger pressure-viscosity coefficient in the impact test. As far as the temperature rise is concerned for entrapped oil in the impact tests, there exists an optimum combination of viscosity and pressure-viscosity coefficient.
Computational aspects of tribology in metal machining
Authors: Maekawa K
Published: October 2002

The present paper reviews tribological phenomena in metal machining from computational aspects. Emphasis is laid on the interaction between the mechanical aspects of tribology and the characteristics of the cutting process. Firstly, the fundamentals of the mechanics and physics of cutting processes are outlined. This is extended to friction and lubrication at the tool-workpiece interface and tool wear. On the basis of this quantitative knowledge, the interaction of tribology with a cutting process is demonstrated by means of computer simulation including machinability of free-cutting steels, cutting fluid action and prediction of tool wear. Finally, concluding remarks are devoted to the interaction of tribology with wider aspects of cutting towards the goal of ‘better machining‘.
The influence of fluid inertia forces on the sudden unbalance responses of squeeze-film damper supported rotors
Authors: Meng G , Guo Y-C , Hahn E. J.
Published: October 2002

The influence of fluid inertia on the sudden unbalance response of a flexible rotor supported on centralized and uncentralized squeeze-film dampers is investigated. Whether the rotor is at constant speed or accelerating, it was generally found that fluid inertia shortens the transient process and decreases the transient vibration amplitude. Qualitatively, the effect of fluid inertia is similar to increased damping.
Numerical analysis for the influence of water film on adhesion between rail and wheel
Authors: Chen H , Yoshimura A , Ohyama T
Published: October 2002

The adhesion force between rail and wheel is one of the important factors for proceeding towards the realization of high-speed railway. On the other hand, it is supposed that the water film formed between the rail and wheel has a remarkable influence on the adhesion force under rainy condition at higher speeds. In this paper, taking Bett and Cappi's viscosity values of water, which show quite a different behaviour from the viscosity of oil, the influence has been investigated of important factors such as rolling speed, contact pressure and temperature on water film thickness for a smooth surface by applying elastohydrodynamic lubrication theory. Based on the numerical solutions, an empirical equation has been developed for water film thickness relating to rolling speed, load and material parameter by using a linear regression method and comparing it with other authors' works on a lower material parameter or elastic-isoviscous contact. Furthermore, in order to understand the influence of the above factors and the surface roughness on the adhesion force, adhesion coefficients have been calculated on a trial basis in the case of rough surface contact under limited conditions, and the theoretical results have been compared with the measured values of the tests on Japanese Shinkansen vehicles in the field.
Sliding wear and friction of Si3N4-SiC-based ceramic composites containing hexagonal boron nitride
Authors: Westergård R , Åhlin A , Axén N , Hogmark S
Published: October 2002

The friction and wear behaviour of a series of new Si3N4-SiC-based ceramic composites, intended for face seal applications, has been investigated with cylinder-on-disc equipment. In particular, the influence of water and vapour on the friction, wear and tribo-film formation has been studied. The ceramics consisted of Sis3N4 and SiC in the proportions 7:3, to which 0, 4 or 8 wt% of hexagonal boron nitride was added as a solid lubricant. All specimens were produced by hot isostatic pressing. X-ray diffraction and scanning electron microscopy were used to reveal the phase composition and microstructure respectively. The hardness was assessed using Vickers indentation. The chemical composition of the tribo-films was studied with X-ray photoelectron spectroscopy.

The major results are that both friction and wear showed distinct low and high levels. The high friction level corresponded to friction coefficients between 0.4 and 0.9 and wear rates between 104 and 105 μm3/Nm. The low level corresponded to friction coefficients between 0.02 and 0.1, and wear rates between 10 and 103 μm3/Nm. When water or saturated vapour was present in the tribo-system, both friction and wear were low. All surfaces produced in the low level were smooth, covered by a thin well-adhering tribo-film while the high level resulted in strongly oxidized and patchy tribo-film covered by wear particles.
The influence of surface conditions in hot forming determined by ring upsetting: A numerical and experimental investigation
Authors: Fletcher J. D. , Li Y. H. , Beynon J. H. , Sellars C. M.
Published: October 2002

Compression of rings is now an established technique for hot friction testing. However, there are subtleties that the investigator needs to be aware of in order to interpret results correctly. The significance of oxides and lubricants in terms of insulation levels and surface mechanics is investigated. Deformation profiles of the rings arising from the constrained plastic flow give a direct indication of the sensitivity of parameters describing the interface conditions. Fully coupled finite element modelling is used to simulate the experimental work on a comparative basis and is then extended to explore the influencing parameters on the physics of the process and examination of either continuous or step changes in friction. Both experimental and analytical work show that complex relations exist between heat exchange and surface traction and that these also depend upon parameters such as reduction, scale thickness and initial temperature. The conclusion is that the scale thickness with its mix of oxides is the dominant index in establishing predictive relations between the surface shear, contact pressure, temperature gradients and modes of lubrication.
A comparative thermal analysis of the static performance of different fixed profile bore plain bearings
Authors: Ma M-T , Taylor C. M.
Published: October 2002

Profile bore bearings are important components in high-speed rotating machinery. In order to provide bearing designers with some useful information on the performances of different bearing profiles, this paper presents a theoretical evaluation of five commonly used types of bearing through a comparison of their steady state performance characteristics. The bearings investigated were two-lobe circular, elliptical (lemon-bore), offset-half, three-lobe and four-lobe types. Their operating characteristics, including the minimum film thickness, maximum temperature, power loss and flowrate, have been calculated using a computerized detailed thermohydrodynamic model developed by the authors. The influences of the shaft speed, specific load, bearing pre-load ratio and lubricant viscosity index on the performance of the bearings have been investigated. In addition, the effect of oil groove angle and load orientation on a four-lobe bearing is briefly examined. Results show that, in general, the performance of the non-circular bearings is inferior to that of the circular bearing; of the non-circular types, the offset-half and elliptical bearings have better overall performances. Also, it is shown that reasonably increasing the angular size of an oil groove has a favourable effect on the static performance of a multi-lobe bearing.
Development of a grease lubrication system for an expendable small turbomachine
Authors: Kim K
Published: October 2002

The feasibility of operating a mainshaft ball bearing on a small high-speed turbomachine with grease lubrication has been demonstrated at high speeds. Angular contact ball bearings of 8 mm bore were used with a 137 N axial load. In order to examine the reliability of grease lubrication at very high speeds, the bearings have been subjected to a variety of hostile tests. From the tests, it was found that the bearings could be operated up to a speed parameter of 0.87 × 106 DN with grease lubrication, and the life of the grease lubricated bearing at 100000 r/min should be limited to 10 h without replenishment of grease.
Physical models, theory and fundamental improvement to self-acting spiral-grooved gas bearings and visco-seals
Authors: Yemelyanov A V , Yemelyanov I A
Published: October 2002

A model of a self-acting gas bearing and a visco-seal with congruent spiral grooves of different depths on both bearing surfaces is introduced. A new model general theory, consisting of the well-known Whipple—Pan—Vohr—Malanoski theory of conventional spiral-grooved gas bearings as a special case, is outlined. Problems of geometry parameter optimization with respect to the load capacity, the stiffness and the pressure above atmospheric pressure are then solved. It is proved that the optimum geometry is identical spiral grooves on both bearing surfaces. A model with this geometry was termed a binary model. It is shown that the power characteristics of a binary self-acting gas bearing and visco-seals are 60 per cent as effective as the best world-wide analogues of other types, while their viscous torque is lower by not less than 5 per cent.
The behaviour of low-amplitude surface roughness under line contacts
Authors: Hooke C J
Published: October 2002

A method of analysis is presented for low-amplitude roughness in line contacts. The technique deals with two-dimensional sinusoidal profiles where the roughness may be moving relative to the contact and shows that the non-linear two-dimensional time-varying problem can be reduced to the solution of a linear one-dimensional steady state equation. This removes many of the computational problems associated with rough elastohydrodynamic lubrication and enables solutions for a wide variety of operating conditions and surface profiles to be obtained rapidly. A number of examples are given to illustrate the method.
Thin films in elastohydrodynamic lubrication: The contribution of experiment
Authors: Spikes H. A.
Published: October 2002

This paper reviews the various experimental techniques that have contributed to an understanding of elastohydrodynamic (EHD) lubrication. After a brief historical overview, attention focuses on the main methods for studying the behaviour of lubricant films in lubro, within EHD contacts, in particular ultra thin film interferometry, film thickness mapping, in-contact infrared and Raman spectroscopy, fluorescence and temperature/shear stress mapping. From this review, the important role of the experimentalist in the study of EHD lubrication is identified and appreciated.
Experimental study on microelastohydrodynamic lubrication
Authors: Kaneta M , Nishikawa H
Published: October 2002

The effects of surface irregularities on rolling and/or sliding point contact elastohydrodynamic lubrication (EHL) have been surveyed on the basis of direct observations using the duo-chromatic optical interferometry technique. A local fluctuation in film thickness caused by surface irregularities depends strongly on shear flow dominating the EHL conjunction and side leakage. The influence of pressure flow has been examined in relation to the local entrapment at asperities due to pure squeeze motion. In reciprocating motion with a small length of the stroke, EHL films are affected not only by surface irregularities but also by air bubbles produced in the previous stroke. The effects of thickener lumps and groove on grease EHL have also been discussed.
Thin-film grease lubrication
Authors: Cann P. M. E.
Published: October 2002

One of the most important examples of the thin-film regime is in the grease lubrication of rolling element bearings. Grease lubrication is not usually considered in this context and yet there is considerable evidence that many bearings operate under starved conditions where the film thickness drops to a fraction of the fully flooded value. Thus it is the mechanisms of lubricant supply and film formation in the starved regime that are important in ensuring the successful operation of a bearing. The aim of this paper, therefore, was to explore grease lubrication from a thin-film perspective and to examine the many factors that could influence starved film formation. Much of the current understanding in this area is derived from studies of starved fluid film lubrication and this provides a convenient starting point for the discussion. Grease lubrication is considered as a replenishment problem and recent experimental work is presented illustrating some of the aspects discussed in the text. The effect of grease properties, bearing operation and design on film formation is examined. Grease lubrication in the thin-film regime is a complex problem. It includes aspects of non-Newtonian rheology, surface chemistry, capillary flow and starved elastohydrodynamic lubrication (EHL). All of these aspects need to be resolved in any future model that will be capable of explaining and predicting grease lubricating behaviour in bearings.
Development of a wear-resistant surface layer for a tool to be used for high-temperature stainless steel rolling
Authors: Tsubouchi K , Akiyama M , Tsumura M , Amano S
Published: October 2002

A new method for a tool surface reinforcing coating was presented to prolong the tool life for hot stainless steel rolling above 1473 K. It is basically by welding a Co-based matrix powder mixed with an NbC powder on the surface of a medium-carbon steel using plasma transferred arc (PTA) welding technology. The new tool covers the region where the PTA welded tool for hot stainless steel rolling reinforced by BS 316S12 and NbC powders developed by the present authors fails to show as good a performance as for the rolling under 1473 K. In the laboratory tests, the new tool showed an excellent performance among the trial combinations of matrix and carbide powders, and its superiority was verified through a test rolling by an elongator in a Mannesmann plug mill line.
A simple method of stress intensity factor calculation for inclined surface-breaking cracks with crack face friction under contact loading
Authors: Fletcher D. I. , Beynon J. H.
Published: October 2002

A simple method has been developed for the calculation of stress intensity factors for cracks growing by a shear mechanism under contact loading (typical of rolling contacts) which includes the consideration of friction between the crack faces. The results compare well with the existing data from more complex models.
Pole tip recession in linear tape heads: Measurement technique and influence of head materials, tape speed and tape tension
Authors: Scott W. W. , Bhushan B
Published: October 2002

Pole tip recession (PTR) in linear tape heads causes an increase in spacing and consequently an increase in signal loss. In this study, PTR in linear tape drives is analysed. Functional drive tests are conducted using thin-film Al2O3-TiC and Ni-Zn ferrite heads sliding against metal particle tape. Atomic force microscopy is used to measure PTR and the recession of the overcoat material used in the construction of the head. In measuring PTR, care must be taken in correctly orienting the stand-alone atomic force microscope tip with respect to the head sample. Care must also be taken in post-processing the raw stand-alone atomic force microscopy data. Based on PTR data with Al2O3-TiC and Ni-Zn ferrite heads, no significant differences exist in the PTR of Al2O3-TiC heads compared with Ni-Zn ferrite heads. In the case of the Ni-Zn ferrite head, the softer Ni-Zn ferrite substrate has mechanical properties close to those of the poles, suggesting that PTR growth should be low. However, additional third-body wear particles from the ferrite substrate result in additional pole tip wear. No significant difference is seen in the wear of Co-Zr-Ta poles and Ni-Fe poles, as they have comparable mechanical properties. No strong conclusion may be drawn about the effect of tape speed on PTR. An increase in tape tension leads to an increase in PTR. This is a result of an increase in the normal force, which causes an increase in the abrasive wear. An increase in interface contamination also leads to an increase in PTR.
Mixed lubrication in mechanical face seals with plain faces
Authors: Lebeck A. O.
Published: October 2002

For the purposes of design and analysis of plain-face contacting mechanical face seals, it is necessary to predict the seal leakage and the friction power as functions of the face profile and the operating conditions. Thus a model of mixed friction behaviour for face seals is required. A complete model is presented. Load support is based on the sum of three components of pressure: hydrostatic, hydrodynamic and contact. Prediction of the hydrostatic pressure is straightforward. Empirical data are developed for the prediction of hydrodynamic load support. Both a plastic and an elastic model for contact pressure are presented. Complete equations are given for load support, load support equilibrium and friction. It is shown how the model is used to predict the film thickness and leakage for any combination of fluids and operating conditions. Predictions from the model are compared with some test data and agreement is encouraging. While the model is currently used as a practical tool to predict the seal performance, the weaknesses of the model are discussed, and it is shown where further research is needed.
Turbine forced response prediction using an integrated non-linear analysis
Authors: Sayma A I , Vahdati M , Imregun M
Published: October 2002

The forced response due to flow defects caused by the upstream blade rows is predicted for two turbines: intermediate pressure (IP) and low pressure (LP). The prediction method is based on an advanced numerical tool where the compressible viscous flow field is modelled by solving Favre-averaged Navier-Stokes equations with the Baldwin and Barth turbulence model. The flow solution is coupled to a modal model of the structure and information is exchanged every time step between the fluid and the structural domains. The hybrid unstructured mesh is moved at each time step to follow the structural motion using a spring analogy. For the IP turbine, the method was used to rank two different designs of nozzle guide vanes. For the LP turbine, special emphasis was placed on predicting vibration amplitudes due to high and low engine order excitations. Predictions and measurements were found to be in good agreement for both turbines. Due to insufficient experimental data, it was difficult to assess the accuracy of the low engine order computations, although it was shown that the model was capable of undertaking such a task.
Dynamic response and optimization for suspension systems with non-linear viscous damping
Authors: Sun T C , Luo A C J , Hamidzadeh H R
Published: October 2002

The design sensitivity and optimization of vehicle suspension parameters under excitation caused by road roughness are investigated by the finite element method with non-linear viscous damping taken into consideration. A numerical approach for vehicle dynamics is developed to determine the non-linear dynamic response, enabling design sensitivity analysis and optimization to be carried out for vibration reduction. For verification of this approach, a four-wheel independent suspension is modelled for linear and non-linear viscous damping, and this model can be applied to road irregularities. The non-optimized and optimized acceleration responses for the two damping cases are illustrated. The optimized suspension systems give a 60 per cent reduction in acceleration at the design point.
Three seconds in two days: A theoretical and practical model for teaching basic dynamics analysis
Authors: Dixon J C , Martin J K
Published: October 2002

A procedure for dynamics analysis is given that provides a stepped approach to dynamics problems in undergraduate level Engineering courses. Also described is a dynamics teaching project that uses the procedure in the analysis and design of model dragsters on an instrumented test track. Both form part of a distance learning course in Engineering Mechanics.
Forward kinematic analysis of a 6-3 type Stewart platform mechanism
Authors: Ku D-M
Published: October 2002

The Stewart platform mechanism is one example of a fully parallel, six-degrees-of-freedom manipulator. Its forward kinematic analysis, i.e. finding the position and orientation of the top platform when a set of link lengths is given, has been extensively studied in the past. Study results have shown that if the closed-form solving procedure is performed, then this analysis could finally lead to a 16th-order polynomial equation in one unknown from which 16 different positions and orientations of the top platform can be determined. However, obtaining the solutions from such a high-order polynomial equation is quite an arduous task which is both computationally complex and time consuming. Relative to the closed-form solving procedure, the purpose of this paper is to propose an alternative numerical algorithm based upon the Newton-Raphson method in order to work out the forward kinematic analysis of a 6-3 type Stewart platform mechanism. The numerical results show that the present solutions could be obtained within a few iteration steps and are in excellent agreement with the published literature.
Dynamic analysis of an articulated interurban train by means of a symbolic-numerical method for closed-loop mechanisms
Authors: Plöchl M , Heinzl Ph , Mack W , Lugner P
Published: October 2002

A specific articulated interurban train consists of two railcars connected with joints to an intermediate passenger cabin without bogies. It is modelled by a plane three-body linkage mechanism guided at two points along a given trajectory with a prescribed velocity of the front point, resulting in a closed-loop multi-body system. The problem is analysed by means of a symbolic-numerical method leading to ordinary differential equations in minimal coordinates. This approach proves advantageous particularly for trajectories with discontinuities of curvature.
Complete shaking force and partial shaking moment balancing of planar four-bar linkages
Authors: Arakelian V H , Dahan M , Smith M R
Published: October 2002

This paper deals with a solution to the problem of shaking force and shaking moment balancing of planar four-bar linkages. The conditions for balancing are formulated by the minimization of the root mean square (r.m.s.) value of the shaking moment. The method is based on displacements of the axes of rotation of the counterweights connected to the crank and rocker. The efficiency of the suggested method is illustrated by a numerical example in which a reduction in the shaking moment of 76 per cent is achieved.
On machining dynamics of flexible parts
Authors: Abrari F , Elbestawi M A , Spence A D
Published: October 2002

Solid modellers are now well established for computer aided design of mechanical parts. Machining applications, however, remain limited to geometric tool path planning. The physical aspects of the process are largely ignored. Success in actual machining, however, depends on consideration of cutting forces, torques, part and tool deflection, chatter, tool breakage and wear. This paper reports research progress towards a comprehensive simulation of the physical machining process of thin flexible parts. The system is based on extensions to a commercially available solid modeller. Cutting tool location data (CL-DATA) files along with an initial solid model of the workpiece are inputs. Each tool motion is segmented into short steps along the path and angular increments of spindle rotation. At each simulation step, immersion of the cutting tool teeth with the part is calculated. This information is then used by a machining process model to calculate cutting forces and tool/workpiece deflection. Up to five-axis motion is supported using a sweep representation of the tool swept volume. Flexible tools are modelled as cantilevers; flexible parts are created as solid models, are meshed and are dynamically solved using finite element analysis. The mesh is updated as material is machined away from the part.
Hamilton equation based symplectic finite element modelling of flexible multi-bodies undergoing large overall motions
Authors: Han R P S , Mao S G
Published: October 2002

In this paper, Hamilton equation based finite elements for the dynamic analysis of flexible beams undergoing large overall motions are formulated. A symplectic algorithm is then employed to integrate the resulting equations. Explicit expressions for the various mass matrices and the symplectic iteration equations are provided. Three examples are solved to demonstrate the procedure. Also, no blow-up of solutions is observed despite the use of fairly large time steps in the long-term dynamic simulation runs. Thus, it appears that the proposed symplectic finite element approach is capable of producing an accurate and robust algorithm for the modelling of a non-linear flexible multi-body system.
Full control modes of three-wheeled vehicles with zero body sideslip angle and zero body motions
Authors: Yu C-C , Liu T
Published: October 2002

By using the full control concept, zero body sideslip angle and zero body motions can be achieved. In this study, firstly, the governing equations for the six-degree-of-freedom three-wheeled vehicle model, with either two wheels on the front axle or two wheels on the rear axle are developed. With six properly chosen control inputs, there are nine full control modes for the zero body sideslip angle and zero body motion control. The sum of tractive forces, cornering forces or active suspension forces is set as the criterion for evaluating these full control modes. These control modes are compared and discussed for typical driving scenarios, and conclusions are drawn about preferable modes.
Stability and vibration of a non-linear vehicle and passenger system
Authors: Yu K , Luo A C J , He Y
Published: October 2002

A non-linear dynamic model to predict the passenger's response in a vehicle travelling on a rough pavement surface (or a rough terrain) is developed. The corresponding equilibrium and stability are investigated through the non-linear equations of motion for a vehicle and passenger system with impacts. The stability with respect to the torsional spring stiffness of safety belts is illustrated. Based on such a stability condition, the dynamic responses for the vehicle and passenger system with and without impacts are simulated numerically. This investigation shows that a strong torsional spring is required in order to reduce the vibration amplitudes of passengers and to avoid impacts between the vehicle and passenger.
Design of welded structures working under random loading
Authors: Kouta R , Gungad M , Play D
Published: October 2002

This paper presents a design method for prediciting the fatigue life of T-joint assemblies loaded by random loads, based on a statistical analysis of tests. This sduty was on the correclation between the types of loading observed in practive and test results obtained for fatigue life determination. The work follows three steps: analysis tof the statistical distributions of random loads that illustrate extremen value from Markov matrix representations; statistical analysis of lifetimes obtained when the specimens are sbumitted to random loads defined earlier; design of a set of endurance curves [stress-number of cycles to failure ( S-N) curves], called ‘random’ S-N curves. These SN curves. These S-N curves are shifted compared with that obtained under sinusoidal loading. Random S-N curve positions in the S-N plane are obtimized depending on the lifetime able to take into account the damege due to the small cycles that are often present in actual loading. The use of random S-N curves for fatigue life calculations gives results matching with theral fatigue lifetime obtained with a T-joint assembly of a bogie chassis used for railway applications. Different analyses show the robustness of the proposed approach.
Accuracy issues of parallel kinematic machine tools
Authors: Weck M , Staimer D
Published: October 2002

Parallel kinematic machines (PKMs) have been attracting attention in research institutes as well as in the machine tool industry because of their structural rigidity due to their closed kinematic loops and their conceptual capabilities in high dimensional accuracy. During performance evaluation of the first prototypes of parallel machine tools, it turned out that their accuracy has not yet reached industrial application level. Against this background, the accuracy behaviour of a hexapod milling machine, located at the Laboratory for Machine Tools and Production Engineering (WZL) at Aachen University of Technology, and accuracy-related design issues have been extensively studied. Based on these investigations, strategies for kinematic calibration and error compensation have been developed.
Dynamic stability of flexible cam follower systems
Authors: Hamidzadeh H R , Dehghani M
Published: October 2002

Dynamic stability of a flexible cam-follower system is considered. The shaft-cam-follower assembly is modelled by a single degree-of-freedom system. In the analysis, transverse and rotational flexibility of the camshaft along with flexibility and damping of the follower are taken into consideration. The governing equation of motion for the follower is given by a linear, second-order, ordinary differential equation with time dependent coefficients. In general, this class of equation is known as a second-order Hill's equation. The time responses of the cam-follower system for an eccentric circular cam for different rotational speeds are determined. In addition, stability analysis based on Hill's infinite determinant is performed, and the effects of operational speed and damping on the stability are determined. For the special case of the cam-follower system that has been considered, it has been found that the system is stable for low values of the angular speed of the cam. As the speed is increased gradually, a few unstable regions occur. In general, damping shows a significant effect on stabilizing the cam-follower system.
BEAST—a rolling bearing simulation tool
Authors: Stacke L-E , Fritzson D , Nordling P
Published: October 2002

Rolling bearings are high-precision, low-cost machine elements used in all kinds of rotating machinery. Dynamic simulations of rolling bearings bring increased understanding of their dynamic behaviour and shorten product development time. Owing to the high demands on contact geometry description and contact force calculations (including traction), simulations are computationally intensive and cannot generally be done with traditional multibody dynamic programs. A rolling bearing simulation model called BEAST (BEAring Simulation Tool) has been developed by SKF. It is used daily by SKF engineers to improve their understanding of bearings and, as a consequence, improve the bearings themselves. A few typical examples of BEAST usage are presented.
Multi-mass rotating shaft analysis and identification
Authors: Aleyaasin M , Ebrahimi M , Whalley R
Published: October 2002

The frequency response function of a multi-mass rotor system, modelled as a series of interconnected, distributed and lumped elements is considered. The system comprises a number of rigid disc elements mounted on a flexible-distributed shaft. The characteristic determinant of the system model is computed and the overall transfer matrix of the model is derived. The damped natural frequency of the system is established by computation of complex roots of the irrational characteristic determinant of the system, using Nedler and Mead's simplex optimization method. Thereafter, by decomposition of the transfer matrix and considering boundary conditions associated with the bearings, a flexibility matrix is introduced, enabling frequency response functions of the rotor to be computed. The overall system is approximated by a linear multivariable model with second-order transfer function elements. It is shown that an accurate reduced-order model can be obtained by this method, enabling new strategies for vibration control of rotating machinery to be achieved.
Vehicle dynamics and control for improving handling and active safety: From four-wheel steering to direct yaw moment control
Authors: Abe M
Published: October 2002

Recent trends of vehicle chassis control are reviewed, paying attention to the basic nature of the vehicle dynamics, tyre characteristics and the effectiveness and limit of four-wheel steering (4WS) and direct yaw moment control (DYC). It is pointed out that, taking the non-linear characteristics of tyre and vehicle dynamics into consideration, change in chassis control from 4WS to DYC inevitably improves handling performance and active safety in vehicle motion with larger slip angles and/or higher lateral accelerations. Emphasis is placed on the need to propose a control strategy based on thorough observation and understanding of the tyre and vehicle dynamics. A side slip model following DYC by sliding control is introduced and the effects of the control are discussed.
Preparation and tribology of ultrafine and amorphous strontium borate
Authors: Chen G X , Hu Z S , Nai R , Wang L G , Peng Y , Dong J X
Published: October 2002

Ultrafine amorphous strontium borate was prepared using an ethanol supercritical fluid drying (ESFD) technique and characterized using transmission electron microscopy (TEM), X-ray diffractometry (XRD), small angle X-ray scattering (SAXS) and nitrogen physical adsorption. Its tribological properties, as an antiwear additive of lubricating oil, were evaluated with four-ball and block-on-ring tribotester. The wear scar was characterized using scanning electron microscopy (SEM). Results indicated that strontium borate prepared in this way possessed a porous structure with a pore size below 20 nm. The wear resistance and load-carrying capacity of lubricating oil were improved by the strontium borate and the friction coefficient was also slightly decreased. The improvement of lubricating oil tribological properties resulted from the deposition of strontium borate and its tribo-chemical reaction product containing boron.
A probability density function method for turbulent mixing and combustion on three-dimensional unstructured deforming meshes
Authors: Subramaniam S , Haworth D. C.
Published: October 2002

A hybrid Lagrangian-Eulerian methodology is developed for numerical simulation of turbulent mixing and combustion in arbitrary three-dimensional time-dependent geometric configurations. The context is a probability density function (PDF) based approach intended for modelling in cylinder processes in reciprocating piston internal combustion (IC) engines. Issues addressed include mean estimation, particle tracking and particle number-density control on three-dimensional unstructured deforming meshes. The suitability of the methodology for statistically time-dependent three-dimensional turbulent flow with large density variations is demonstrated via simulations of turbulent freon vapour/air mixing on an unstructured deforming mesh representing an idealized IC engine [13]. Computed profiles of mean and r.m.s. freon mole fractions show good quantitative agreement with measurements. Moreover, inherent advantages of the Lagrangian-Eulerian PDF approach are demonstrated, compared to Eulerian finite volume solutions of an (approximately) equivalent set of moment equations. The new approach is, by design, compatible with existing computational fluid dynamics codes that are used for multidimensional modelling of in-cylinder thermal fluids processes. This work broadens the accessibility of PDF methods for practical turbulent combustion systems.
Subgrid combustion modelling for large-eddy simulations
Authors: Menon S
Published: October 2002

Next-generation gas turbine and internal combustion engines are required to reduce pollutant emissions significantly and also to be fuel efficient. Accurate prediction of pollutant formation requires proper resolution of the spatio-temporal evolution of the unsteady mixing and combustion processes. Since conventional steady state methods are not able to deal with these features, methodology based on large-eddy simulations (LESs) is becoming a viable choice to study unsteady reacting flows. This paper describes a new LES methodology developed recently that has demonstrated a capability to simulate reacting turbulent flows accurately. A key feature of this new approach is the manner in which small-scale turbulent mixing and combustion processes are simulated. This feature allows proper characterization of the effects of both large-scale convection and small-scale mixing on the scalar processes, thereby providing a more accurate prediction of chemical reaction effects. LESs of high Reynolds number premixed flames in the flamelet regime and in the distributed reaction regime are used to describe the ability of the new subgrid combustion model.
Computational fluid dynamics modelling of non-premixed combustion in direct injection diesel engines
Authors: Barths H , Hasse C , Peters N
Published: October 2002

An overview over flamelet modelling for turbulent non-premixed combustion is given. A short review of previous contributions to simulations of direct injection (DI) diesel engine combustion using the representative interactive flamelet concept is presented. A surrogate fuel consisting of 70 per cent (liquid volume) n-decane and 30 per cent α-methyl-naphthalene is experimentally compared to real diesel fuel. The resemblance of their physical and chemical properties is shown to result in very similar combustion and pollutant formation for both fuels.

In order to account for variations of the scalar dissipation rate within the computational domain, a method using multiple flamelets, called the Eulerian particle flamelet model, is used. A strategy is described for subdividing the computational domain and assigning the resulting subdomains to different flamelet histories represented by Eulerian marker particles. Experiments conducted with an Audi DI diesel engine and diesel fuel are compared to simulations using the surrogate fuel. The use of multiple flamelets, each having a different history, significantly improves the description of the ignition phase, leading to a better prediction of pressure, heat release and exhaust emissions of soot and NOx. The effect of the number of flamelet particles on the predictions is discussed.
Modelling superheated fuel sprays and vaproization
Authors: Zuo B , Gomes A M , Rutland C J
Published: October 2002

One of the major challenges to the gasoline direct injection (GDI) engine design is to understand the behaviour of fuel atomization and vaporization at a variety of chamber conditions and injection strategies. As gasoline is a volatile fuel, it is often unintentionally superheated before injection in GDI engines. This can cause significant changes in the fuel spray distribution and fuel-air mixing. To account for these situations, this paper presents a comprehensive superheat fuel spray and vaporization model. In the model, it is assumed that, under superheat conditions, a hollow cone spray sheet still forms from a pressure-swirl atomizer. The sheet flash boiling is considered to be constrained by the transient heat conduction process inside the sheet with an effective thermal conductivity. Hydrodynamic instability, cavitation and bubble growth inside the sheet eventually break up the sheet to form droplets. Models of the subsequent droplet vaporization account for heat transfer under both flash boiling and sub-boiling conditions. Simulation results have been compared with Mie scattering images of the spray in an optical engine and good agreement is found at all the operating conditions considered. Finally, changes in the spray characteristics, evolution and vaporization behaviour under superheat conditions are explored with GDI applications in mind.
Gas sampling analysis of combustion processes in a homogeneous charge compression ignition engine
Authors: Tsurushima T , Shimazaki N , Asaumi Y
Published: October 2002

In-cylinder gas sampling experiments were conducted to clarify the chemical reaction processes of homogeneous charge compression ignition (HCCI) combustion. To study the differences in ignition processes by the ignitability of fuels, three kinds of straight-chain saturated hydrocarbons, such as n-pentane, n-hexane and n-heptane, were used as the fuels. Also, to study specific differences in the ignition processes between a single-component fuel and a dual-component fuel, n-pentane was used as the single-component fuel and n-hexane and ethylene, with compositions adjusted in order to have the same ignitability as n-pentane, were used as the dual-component fuel. The results show that the chemical processes in the low-temperature oxidation range, from 700 to 900 K, need to be controlled for the ignition timing control of HCCI combustion. Controlling ignition timing by dual fuel means controlling the oxidation starting time by the ignitability of a high cetane number fuel and controlling the low-temperature oxidation rate by varying the composition of the high and low cetane number fuels.
Approaches to extremely low emissions and efficient diesel combustion with oxygenated fuels
Authors: Miyamoto N , Ogawa H , Nabi M. N.
Published: October 2002

Significant improvements in smoke, particulate matter, NOx, THC, engine output and thermal efficiency were simultaneously achieved with highly oxygenated liquid fuels. Engine noise was also remarkably reduced for oxygenates with higher ignitability. The improvements in exhaust emissions and thermal efficiency depended almost entirely on the oxygen content in the fuels regardless of the oxygenate-diesel fuel blending ratio or type of oxygenate. Smoke emission decreased sharply and linearly with an increase in oxygen content and disappeared entirely at an oxygen content above 38 wt %, even at stoichiometric conditions. Smoke-free, low NOx diesel combustion with oxygenated fuels was achieved at stoichiometric conditions with the adoption of very high exhaust gas recirculation (EGR). NOx, THC and CO emissions were almost completely removed with a combination of high EGR and a three-way catalyst over a wide range of brake mean effective pressure (b.m.e.p.). The maximum b.m.e.p. with the highly oxygenated fuels was significantly higher than that with the conventional diesel fuel because b.m.e.p. was released from the smoke limits.
The internal flow of diesel fuel injector nozzles: A review
Authors: Schmidt D. P. , Corradini M. L.
Published: October 2002

Diesel fuel injector nozzles have a significant effect on the quality of spray and charge preparation. However, the mechanism and degree of this effect is unclear. The complexity of the internal nozzle flow has hindered the study of the fuel injection process. Diesel fuel injector nozzle flows are highly turbulent and usually two-phase. Several experiments have shown the presence of cavitation in the nozzles to be a dominating effect. Recent experimental work has revealed new qualitative details about the cavitation in fuel injector nozzles. The cavity tends to be smooth near the inlet, transitioning to a more ruffled appearance downstream. These flows are also strongly asymmetric in realistic geometries. Additionally, photographs have shown string cavitation inside the sac volume extending into the nozzles. The strings appear to be a form of stratified two-phase flow, like the cavities near the inlet corner. Like the cavities, the strings break down into bubbly flow near the exit of the nozzle. Future experiments in this field should address the exact nature of the two-phase flow at the exit.

In spite of these difficulties, useful models for the flow in fuel injector nozzles have been developed. Analytical models work very well for the steady state behaviour of axisymmetric nozzles. Multi-dimensional models have proved to be useful for more general geometries and attempt to predict transient behaviour. There is currently no consensus on the basic physics behind the multi-dimensional models. Despite this controversy, there are several models available that have succeeded in predicting gross cavitation behaviour. The implications of the recent experimental investigations are that future cavitation models should include the ability to simulate more than one kind of cavitation. Typically, a model assumes that the cavitation is either a smooth cavity or a bubbly mixture. In general, the ideal cavitation model must capture either kind of behaviour.
Computation of flamefront NO emissions from spark ignition engines
Authors: Narayan S , Rajan S
Published: October 2002

Flamefront NO emissions from spark ignition engines are estimated in this work using a two-zone thermo-dynamic combustion model, an unsteady engine flame model, the wrinkled laminar flame model of Bray and Moss, the k-ε theory and simplified flamefront NO chemistry which has been verified in steady laminar premixed flames. The results show that as much as 230 ppm of flamefront NO may be formed under stoichiometric engine operating conditions. The present approach is an alternative to the empirical correlations used to compute engine flamefront NO which are based on highly extrapolated data.
Comparison of 2-ethylhexyl nitrate and fuel composition induced changes in the diesel spray ignition process
Authors: Higgins B. S. , Siebers D. L. , Aradi A. A.
Published: October 2002

The autoignition processes of three fuels under quiescent, direct injection, heavy-duty diesel engine conditions were investigated and compared. Two of the fuels were blended from three single component fuels to have cetane numbers (CN) of 45 and 55. The third fuel was made by adding 2-ethylhexyl nitrate to the CN-45 fuel blend to give a second CN-55 fuel. The results indicate that cool-flame, first-stage ignition chemistry induces a significant temperature rise in the igniting region of the spray. For longer ignition delay conditions (i.e. cold-start and light-load), this thermal boost (up to 300 K), coupled with hot air entrainment, is critical for driving the ignition process into the high-temperature chemistry, second stage of ignition. Increases in CN cause an earlier start of the first stage and thus an earlier thermal boost and faster ignition. For shorter ignition delay conditions (i.e. high-load), the ignition chemistry develops very fast and the ignition period becomes dominated by physical processes. Consequently, differences in ignition due to CN become less significant at higher load conditions. The results also show that the two fuels with a CN of 55 have different ignition processes, indicating that fuels with the same CN do not necessarily follow the same path to ignition. The first stage of ignition for the CN-55 fuel containing 2-ethylhexyl nitrate mirrored that of the parent CN-45 fuel, except that it was shifted earlier in time. The 2-ethylhexyl nitrate results support previous observations indicating that 2-ethylhexyl nitrate provides radicals early in the ignition process, but does not change the basic ignition chemistry of the parent fuel.