bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stiffness and damping coefficients of air rings with a chamber feeding system
Authors: Czolczyñski K , Kapitaniak T , Marynowski K 
Published: October 2002

When, during the operation of rotors supported in gas bearings, their rotational velocity reaches a sufficiently high value, loss of steady state stability occurs. This instability is caused by the loss of damping properties of the gas film, which leads to self-excited vibrations. These vibrations are the basic obstacle to a widespread application of gas bearings. The phenomenon of self-excited vibrations can be avoided by introducing an elastic supporting structure between the bearing bushes and the casing, characterized by properly selected stiffness and damping coefficients. In practice, such a structure can have the form of an externally pressurized gas ring. In this paper, on the basis of selected examples, those ranges of the values of stiffness and damping coefficients of the gas ring that make it possible to retain steady state stability at practically any rotational velocity of the rotor are demonstrated. A design of the ring structure, especially of its feeding system, is also shown, which ensures the required values of stiffness and damping coefficients (with regard to the stability). These investigations have been carried out by means of a numerical simulation method with the use of a mathematical model of the gas bearing, which has already been verified many times.
Surface roughness modification in elastohydrodynamic line contacts operating in the elastic piezoviscous regime
Authors: Hooke C. J. 
Published: October 2002

In heavily loaded elastohydrodynamic (EHD) lubrication contacts operating in the piezoviscous regime, the original surface roughness is largely flattened as it enters the conjunction and is replaced by an inlet generated clearance variation. This clearance variation is convected through the contact at the entrainment velocity. It has a spatial distribution that differs (except for rolling without slip) from the original surface and a different amplitude. This amplitude may be smaller or greater than that of the original profile. An analytical solution of this behaviour is presented for contacts operating well inside the elastic piezoviscous regime for the situation where the roughness is relatively small compared with the film thickness. This solution allows the main features of surface roughness modification to be understood and produces results that compare well with the few numerical solutions available.
Performance study of a back-depression mechanical dry gas seal
Authors: Stolarski T. A. , Xue Y 
Published: October 2002

An aerostatic mechanical dry gas seal is described in this paper. The seal has shallow depression grooves (compensators) on the back and annular grooves on one of the working faces. With the help of the back depression grooves, a hydrostatic pressure and thereby a separating force with satisfactory stiffness are produced within the sealing gap. A model which takes surface roughness into account was used to predict the performance of the seal. Relationships between the control parameters (the recess position, rG, the nominal film thickness, h0, the depth, hv, of depression grooves and the surface roughness parameter, a) are investigated against various pressure ratios, pe/ pi. The analysis provides a simple optimum design procedure. A finite element analysis was carried out to account for the effect of face deformation during operation of the seal. Experiments for various speeds, pressures and roughness parameters were carried out and the results from the experiments were used to validate the analysis performed. Analysis and experiment revealed the importance of the surface roughness and deformation of the faces for the creation and retention of the gap.
The inclusion of lubricant shear thinning in the short bearing approximation
Authors: Taylor R. I. 
Published: October 2002

For short journal bearings (defined as those where L/D < 0.5, where L is the length and D is the diameter), such as those used in modern automotive engines, the 'short bearing approximation' is an attractive fast tool for bearing designers to use as a first approximation. The essence of the approximation is that the pressure variation across the width of the bearing is much greater than that around the circumference of the bearing. With this approximation, it is possible to neglect certain terms in the Reynolds equation, and an analytical expression for the pressure variation around the bearing can be written down. By integrating the pressure around the bearing, an analytical expression relating the load, W, to the eccentricity ratio, ε, may be obtained. The standard ‘short bearing approximation’ assumes that the lubricant is Newtonian, and so any variation in the lubricant viscosity with the shear rate is neglected. In this paper, an isothermal analysis is made which uses the short bearing approximation but allows for the possibility of lubricant shear thinning. The variation in the lubricant viscosity with the shear rate is assumed to be as described by the Cross equation, which has previously been shown to give a good fit to measured flow curves. A detailed description of the analysis is given, together with results obtained when the model was applied to a modern automotive con-rod bearing. (Note that the effects of pressure on lubricant viscosity have been neglected.)
Elastohydrodynamic lubrication: A lubricant industry perspective
Authors: Bovington C 
Published: October 2002

The twin challenges facing the automotive and lubricants industries as we approach the millennium are: how to reduce the levels of gaseous emissions and how to achieve increased durability. Improved durability is necessary in order to maintain low levels of emissions. The lubricant has an important part to play in both the improvement in durability by way of improved wear and in the reduction of emissions and conservation of non-renewable energy resources by way of the reduction of friction levels in engines. Examples are shown of how the application of electrohydrodynamic lubrication (EHL) equations permit the calculation of the oil film distribution between cam and follower contacts as a function of cam angle, cam speed and oil viscosity. The results are compared to post-engine test cam wear patterns. The position with of maximum wear can thus be predicted and critical operating conditions identified. The development of optical methods for studying EHL behaviour and simple, reliable, methods for measuring traction under EHL conditions represents a major advance and allows the development of lubricants that offer high levels of wear protection together with high levels of fuel efficiency. This paper shows the importance of selection of both base oils and additive packages to achieve these ends. The relationships between ambient pressure viscosity, pressure coefficient of viscosity, EHL film thicknesses and EHL traction coefficients are discussed. The use of such data in the prediction of fuel economy performance in industry engine tests is also discussed.
Limiting speeds and operating temperatures of fixed preload large bore angular contact ball bearings for machine tools
Authors: Lacey S. J. , Kemble A 
Published: October 2002

Because of the ability of angular contact ball bearings to support both radial and axial loads and operate at high speeds, they are used widely to support machine tool spindles. The limiting speed of angular contact bearings depends on a number of factors including the type of bearing arrangement, preload, lubrication and bearing spacing. Preloaded back-to-back angular contact ball bearings are commonly used and in this paper the limiting speed of such an arrangement is considered together with a simple method for estimating speed factors which is shown to agree with actual experience. Also, little information is available on the operating temperatures of large angular contact bearings and so the effect of lubrication conditions on the limiting speed of angular contact bearings of 200 mm bore are investigated. In particular the design of the lubrication nozzle is shown to have a significant influence on the bearing operating temperature.
Valve-train dynamics: A simplified tribo-elasto-multi-body analysis
Authors: Kushwaha M , Rahnejat H , Jin Z M 
Published: October 2002

This paper presents a model of a cycloidal cam-flat follower pair. The model incorporates the inertial elements, the assembly constraint functions and the sources of compliance in the valve train. The sources of compliance include the valve spring characteristics, including the spring surge effect under dynamic conditions, as well as the contact compliance between the cam and the flat follower. The contact domain is treated as a counterformal concentrated lubricated region subjected to an elasto-hydrodynamic regime of lubrication (EHL). The prevailing contact geometry is one of finite line contact. The paper presents the results of simultaneous solution of the Lagrangian dynamics for the non-linear constrained system, together with an approximate quasi-static elastohydrodynamic solution of the lubricated contact conjunction at each time step by an extrapolated oil-film thickness formula for combined entraining and squeeze film action. The effect of spring surge on the contact separation and residual vibrations of the system are investigated, as well as the lubricant pressure distribution and film thickness, including during start-up and acceleration.
Dynamic response of adhesively bonded single-lap joints with a void subjected to harmonic peeling loads
Authors: Vaziri A , Hamidzadeh H R , Nayeb-Hashemi H 
Published: October 2002

The only viable method to join some components is by using adhesives. These components are often subjected to dynamic loading, which may cause initiation and propagation of failure in the joint. In order to ensure the reliability of these structures, their dynamic response and its variation with the presence of defects in the bonded area must be understood. The dynamic response of a single-lap joint subjected to an out-of-plane harmonic force is evaluated. The bonded joint is modelled as a Euler-Bernoulli beam joined with an adhesive and constrained at one end and subjected to a harmonic force at the free end. The results show that the system response is not sensitive to a range of adhesive loss factor of 0-1. Furthermore, the system response is little affected by the presence of void in the bond area. The system response seems to be more sensitive to the void location than to its size. Peel and shear stresses in the bond area are obtained and found to be confined to the edge of the overlap. For the adhesive and adherent properties and geometries investigated the maximum peel and shear stresses in the bond area are little affected by the presence of a central void, covering up to 60 per cent of the overlap length for all applied loading frequencies. However, when the frequency of the applied load is close to the natural frequencies of the structure, a void may increase or decrease both the maximum peel and shear stresses.
Practical considerations for the static balancing of mechanisms of parallel architecture
Authors: Ebert-Uphoff I , Johnson K 
Published: October 2002

This paper discusses the development of statically balanced spatial parallel platform mechanisms. A mechanism is statically balanced if its potential energy is constant for all possible configurations. This property is very convenient for robotic manipulators with large constant payloads, since it means that the mechanism is statically stable for any configuration, i.e., zero actuator torques are required whenever the manipulator is at rest. Furthermore, only inertial forces and moments have to be sustained while the manipulator is moving. This makes it possible to create passive devices that can assist humans to manipulate a heavy load, and to create robotic manipulators that require smaller actuators and/or consume less energy. Furthermore, by retrofitting existing machine tools, static deflection problems due to gravitational loads may be reduced. This paper (1) summarizes how static balancing can be implemented in a parallel manipulator with six degrees of freedom, (2) presents the design of a small-scale prototype, and (3) discusses general implementation issues.
Effects of exhaust gas recirculation in homogeneous charge compression ignition engines
Authors: Nakano M , Mandokoro Y , Kubo S , Yamazaki S 
Published: October 2002

Ignition control is an important issue in homogeneous charge compression ignition (HCCI) engines, which have the advantages of low NOx emission and high thermal efficiency. In this study, the effect of the exhaust gas recirculation (EGR) on the ignition control of HCCI engines is discussed using an engine cycle simulation in which a homogeneous mixture is assumed. Auto-ignition of 65 per cent iso-octane + 25 per cent toluene + 10 per cent n-heptane, which is used as a fuel to evaluate the characteristics of a gasoline-like fuel, is represented by a detailed reaction model. The dilution by EGR delays the ignition timing when the charged gas temperature is not changed by EGR. The temperature rise of the charged gas promotes auto-ignition. Based on these characteristics, it was suggested that the ignition timing could be controlled by EGR with temperature control, when the amount of fuel supply is constant. This control method can also be applied to control of the air-fuel ratio (A/F) in the cylinder while maintaining the optimum ignition timing. In spite of the difference in the A/F and the EGR ratios, no significant difference was found in the pressure rise rate at combustion and the NOx emission when the ignition timing was the same.
Investigation on exhaust emissions of a common rail high-speed direct injection diesel engine running with dimethyl ether
Authors: Maroteaux F , Descombes G , Sauton F , Jullien J 
Published: October 2002

This research investigates engine performance and the potential to reduce exhaust emissions by using dimethyl ether (DME) as an alternative fuel to diesel for compression ignition engines. The main objective of this study it to evaluate on a test-bed the performance and emissions reduction potential of a four-cylinder passenger car HSDI common rail turbocharged diesel engine running with DME in the absence of specific modifications to the engine itself but some modifications to the fuel injection system. The results obtained from this engine running with DME using diesel fuel as reference are encouraging. In the next phase of this study the injection rate will be adapted to DME operation and to the geometric and thermodynamic conditions of the combustion process. A study of combustion reaction is also necessary in order to optimize the turbocharging system for exclusive DME operation.
Development of a liquid natural gas pump and its application to direct injection liquid natural gas engines
Authors: Goto Y 
Published: October 2002

Direct injection gas engines operated with liquid natural gas (LNG) look promising because the energy density-volume ratio of LNG is three times higher than that of compressed natural gas (CNG) and pressurization of LNG to injection pressures is much easier and expends less energy. Based on these considerations, a prototype of an LNG high-pressure pump, which can achieve a pressure as high as 20 MPa, was developed and tested using nitrogen instead of LNG. It was confirmed that the energy consumption of the LNG pump to pressurize an amount of natural gas is one-eighth the energy consumption of the corresponding CNG pump. A direct injection natural gas engine having a 108 mm bore and a compression ratio of 12 was developed for the evaluation of its performance and emissions. The result of the engine experiment made it clear that the indicated thermal efficiency of the gas engine is approximately 44 per cent over a medium and high load range, which is equivalent to that of the corresponding diesel engine. Since the energy required for pressurizing LNG to 15 MPa is 2–3 per cent of the indicated power of the engine, the LNG engine proposed is considered to have the same level of brake thermal efficiency as the corresponding diesel engine. If a truck vehicle is powered by the direct injection LNG engine and carries an LNG tank with a capacity 1.5 times larger than that of gas oil, the cruising distance of the vehicle could be the same as that of a diesel truck.
Engine thermomanagement with electrical components for fuel consumption reduction
Authors: Cortona E , Onder C. H. , Guzzella L 
Published: October 2002

This paper proposes a solution for advanced temperature control of the relevant temperature of a combustion engine. It analyses the possibility of reducing vehicle fuel consumption by improving engine thermomanagement. In conventional applications, combustion engine cooling systems are designed to guarantee sufficient heat removal at full load. The cooling pump is belt-driven by the combustion engine crankshaft, resulting in a direct coupling of engine and cooling pump speeds. It is dimensioned such that it can guarantee adequate performance over the full engine speed range. This causes an excessive flow of cooling fluid at part-load conditions and at engine cold-start. This negatively affects the engine efficiency and, as a consequence, the overall fuel consumption. Moreover, state-of-the-art cooling systems allow the control of the coolant temperature only by expansion thermostats (solid-to-liquid phase wax actuators). The resulting coolant temperature does not permit engine efficiency to be optimized. In this paper, active control of the coolant flow as well as of the coolant temperature has been realized using an electrical cooling pump and an electrically driven valve which controls the flow distribution between the radiator and its bypass. For this purpose, a control-oriented model of the whole cooling system has been derived. Model-based feedforward and feedback controls of coolant temperature and flow have been designed and tested. With the additional actuators and the model-based control scheme, a good performance in terms of fast heat-up and small temperature overshoot has been achieved. The improvements in fuel consumption obtained with the proposed configuration have been verified on a dynamic testbench. Both engine cold-start under stationary engine operation and the European driving cycle MVEG-A with engine cold-start were tested. The fuel consumption reductions achieved during these tests vary between 2.8 and 4.5 per cent, depending on the engine operating conditions. Compared to vehicle mass reduction or internal engine improvements, engine thermomanagement is a simple, flexible and cost efficient solution for improving system performance, i.e. fuel consumption.
Role of spatial and temporal variations in the computation of radiative forcing due to sulphate aerosols: A regional study
Authors: Myhre Gunnar , Jonson Jan E. , Bartnicki Jerzy , Stordal Frode , Shine Keith P. 
Published: October 2002

AbstractA high‐resolution regional model for sulphate aerosols is used to investigate the effects of spatial and temporal averaging of radiative forcing. Mie theory is used to calculate the aerosol optical properties. The strong hygroscopic growth with increasing relative humidity is taken into account. The results for the regional area selected in our study (Europe and much of the North Atlantic) show that earlier global studies may have underestimated the magnitude of the radiative forcing due to sulphate aerosols by up to 30–40% due to coarse spatial and/or temporal resolution, at least over certain regions. This underestimation in global models of the water uptake is important for all strongly scattering hygroscopic aerosols. Our results imply that representation of relative humidity at even higher spatial resolution than used in this study may be of importance. This could be incorporated in models using subgrid‐scale parametrizations of the relative humidity. Copyright © 2002 Royal Meteorological Society.
Third‐order transport due to internal waves and non‐local turbulence in the stably stratified surface layer
Authors: Zilitinkevich Sergej S. 
Published: October 2002

AbstractUntil recently the concern of the traditional theory of the atmospheric stable boundary layer (SBL) was, almost without exception, the nocturnal SBL developing after sunset on the background of a neutral or slightly stable residual layer. In the nocturnal SBLs the nature of turbulence is basically local. Its lower portion is well described by the classical Monin–Obukhov surface‐layer similarity theory. Things are different in long‐lived SBLs situated immediately below the stably stratified free flow. Here, the surface‐layer turbulence is affected by the free‐flow Brunt–Väisälä frequency, N. The surface layer represents approximately one‐tenth of the SBL, so that it is separated from the free atmosphere by the upper nine‐tenths of the SBL comprising hundreds of metres. Traditional concepts fail to explain such distant links. Zilitinkevich and Calanca extended the traditional Monin–Obukhov similarity theory by including N in the surface‐layer scaling, and provided experimental evidence in support of this extension. In the present paper, physical mechanisms responsible for non‐local features of the long‐lived SBL turbulence are identified as: radiation of internal waves from the SBL upper boundary to the free atmosphere, and the internal‐wave transport of the squared fluctuations of velocity and potential temperature. The third‐order wave‐induced fluxes are included in an advanced turbulence‐closure model to correct the wind and temperature profiles in the surface layer. The model explains why developed turbulence in the surface layer can exist at much larger Richardson numbers than the classical theory predicts. Results from the new model are in good agreement with the extended similarity theory and experimental data. Copyright © 2002 Royal Meteorological Society.
Infrasound Pressure Meter and Examples of Measuring Data
Authors: Iwahashi Kiyokatsu , Ochiai Hiroaki 
Published: October 2002

Recently, complaints about low frequency noise are increasing in Japan. In Inter-Noise ′99, Ochiai has reported the following three kinds of evaluation methods for effects caused by infra and low frequency noise. An evaluation for rattling of doors or windows. An evaluation for psychological and sleep effects An evaluation for oppressive or vibratory sensation. We have developed a measuring instrument corresponding to the above evaluation methods. In this report, an outline of the instrument and examples of infra and low frequency noise data are introduced.
A Numerical Approach of Self-Sustained Tone Generation and Reduction in Ducts
Authors: Coiret A. , Guerin S. , Sakout A. , Henry R. 
Published: October 2002

Starting from numerical models which are used in engineering, it is shown that it is possible to bring to light the main features which are responsible for the generation of self-sustained tones in turbulent flows. The numerical study is based on our experimental results. The set-up consists of two diaphragms in tandem in a duct, leading to self-sustained tones up to 150 dB. The modelled flow is assumed to be incompressible. It does not allow estimation of noise levels. However the calculation of the flow field exhibits the necessary conditions for the conversion of the kinetic energy towards the acoustical field. An initial stationary model shows the location of the acoustical source. A second non-stationary L.E.S. model describes the dynamics of the detachment and impingement of the coherent structures. An experimental noise reduction method is performed. The numerical approach contributes an explanation of the noise reduction mechanism.