bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of lean-burn control technology on the fuel economy and NOx emission of gasoline engines
Authors: Ye Z-M , Li Z-J
Published: May 2010

Lean-burn engines operate at a very lean air-to-fuel (A/F) ratio under light-load and part-load regions. Because of better combustion in the lean mixture, fuel economy enhancement is the major merit. Lean-burn technologies also give rise to high engine performance and low emission levels (hydrocarbons and carbon monoxide). In the full-load region, the engine operates in the stoichiometric or rich mode. The drawback of the lean-burn engine is its higher nitrogen oxide (NO x) emission level. The three-way catalyst acts as a suitable device near stoichiometry; however, it is inefficient when the A/F ratio is far from stoichiometry. Hence, advanced catalysts are needed to carry out the NO x storage (oxidation) and purge (reduction) operations. This article is concerned with the lean-burn control applications on gasoline engines, which can also be expanded to other types of engine. Case studies on port fuel injection (PFI) and gasoline direct-injection (GDI) engines have been conducted from different points of view. The experimental investigation on a quasi-homogeneous lean-burn PFI engine has been studied from a fuel economy and NO x reduction viewpoint. The modelling and control approaches are also presented for GDI engines to achieve ultra-lean mixtures for fuel economy enhancement and NO x emission reduction.
Enhancement of automotive exhaust heat recovery by thermoelectric devices
Authors: Ibrahim E A , Szybist J P , Parks J E
Published: May 2010

In an effort to improve automobile fuel economy, an experimental study was undertaken to explore the practical aspects of implementing thermoelectric devices for exhaust gas energy recovery. An experimental apparatus consisting of a hot-side (exhaust gas) rectangular duct and a cold-side (coolant liquid) rectangular duct enclosing six thermoelectric elements has been built and instrumented. Measurements of the thermoelectric voltage output, fluid and surface temperatures, and flowrates were acquired and analysed to investigate the power generation and heat transfer properties of the apparatus. The effects of inserting aluminium wool packing material inside the hot-side duct on augmentation of the heat transfer from the gas stream to duct walls were studied. Data were collected for both the unpacked and the packed cases to allow for deduction of the packing influence on the flow and surface temperatures. The effects of variations in the gas inlet temperature (300°C, 320°C, 340°C, 360°C, 380°C, and 400°C), coolant inlet temperature (40°C, 50°C, 70°C, and 90°C), and gas flowrate (40sl/min, 60sl/min, and 80sl/min) on the thermoelectric power output were examined. The results indicate that thermoelectric power production is increased at higher gas inlet temperatures or flowrates at a fixed coolant temperature. However, thermoelectric power generation decreases with a higher coolant temperature as a consequence of the reduced temperature differential between the hot side and the cold side. For the unpacked hot-side duct, a large temperature difference of up to 140°C existed between the gas and solid surface temperatures owing to poor heat transfer through the gaseous medium. Adding the packing material inside the exhaust duct enhanced heat transfer and hence raised the hot-side duct surface temperature by as much as 30°C and thermoelectric power by up to twofold, compared with the unpacked duct, particularly where the gas-to-surface temperature differential is highest. Therefore, it is recommended that packing of the exhaust duct becomes common practice in thermoelectric waste-energy-harvesting applications.
Improvements in the performance and pollutant emissions for stoichiometric diesel combustion engines using a two-spray-angle nozzle
Authors: Kim J-H , Reitz R D , Park S W
Published: May 2010

An experimental and numerical study was conducted to investigate the effect of the nozzle layout on the combustion and emission characteristics for stoichiometric diesel combustion. In order to improve fuel—air mixing, a new concept of nozzle layout was studied. The nozzle has two spray angles, one heading for the bowl and the other targeting the squish area (two-spray-angle nozzle (2SAN)). The spray included angles of the nozzle layout are 150° (upper holes) and 70° (lower holes), and the start-of-injection timings were swept from −33° to −9° after top dead centre. The results of the 2SAN were compared with those of a well-characterized baseline single-hole nozzle (SHN) with a 130° spray included angle.

The experimental results showed that the engine performance and carbon monoxide emissions were reduced significantly by using the 2SAN instead of the SHN with stoichiometric diesel combustion. However, hydrocarbon emissions were increased owing to fuel-film formation. In addition, the range of optimal injection timings for reduced fuel consumption for the 2SAN is wider than that of the SHN because the upper spray of the 2SAN utilizes oxygen in the squish area more efficiently.
An investigation into the use of neural networks for the semi-active control of a magnetorheologically damped vehicle suspension
Authors: Metered H , Bonello P , Oyadiji S O
Published: May 2010

Neural networks are highly useful for the modelling and control of magnetorheological (MR) dampers. A damper controller based on a recurrent neural network (RNN) of the inverse dynamics of an MR damper potentially offers significant advantages over conventional controllers in terms of reliability and cost through the minimal use of sensors. This paper introduces a neural-network-based MR damper controller for use in conjunction with the system controller of a semi-active vehicle suspension. A mathematical model of a semi-active quarter-vehicle suspension using an MR damper is derived. Control performance criteria are evaluated in the time and frequency domains in order to quantify the suspension effectiveness under bump and random road disturbance. Studies using the modified Bouc—Wen model for the MR damper as well as an actual damper fitted in a hardware-in-the-loop simulation (HILS) both showed that the inverse RNN damper controller potentially offers a significantly superior ride comfort and vehicle stability over a conventional MR damper controller based on continuous-state control. The neural network controller produces a smoother and lower input voltage to the MR damper coil, ensuring extended damper life and lower power requirement respectively. Further studies performed using an RNN model of the forward dynamics of the MR damper showed that it is a reliable substitute for HILS for validating multi-damper control applications.
A cumulative-summation-based stochastic knock controller
Authors: Jones J C Peyton , Frey J , Muske K R , Scholl D J
Published: May 2010

In this paper, an analysis of knock signals suggests that the knock intensity is a cyclically uncorrelated random process, and that it is therefore not possible to control individual cycles to a specified knock intensity in a deterministic manner. A new knock control algorithm is therefore developed on the basis of a stochastic interpretation of the knock signal, and on the basis of a control objective specified as a certain percentage of knocking cycles. Unlike traditional controllers, the new algorithm does not respond to knock events provided that these are occurring within a specified tolerance of the target knock rate. The new controller uses the cumulative summation of knock events to make this determination, thereby avoiding the slow transient response times sometimes associated with ‘stochastic’ knock controllers. When a spark adjustment is deemed necessary, the magnitude of the control action is scaled according to the likelihood ratio of the observed events since the last spark adjustment was made. A theoretical analysis of the new controller is presented and a simulation tool which is closely based on experimental data is used to assess its performance. The results show that the new controller is able to achieve the same target knock rate as a traditional controller while operating at a more advanced mean spark angle. There is also less cyclic variance about this mean and the regulatory response is significantly improved. The transient response to overly advanced or retarded conditions is similar to the traditional controller. These results suggest that the new controller will deliver increased torque and engine efficiency under knock-limited conditions without increasing the risk of engine damage.
Potential-Field-Based Evolutionary Route Planner for the Control of Multiple Unmanned Aerial Vehicles
Authors: Lin C-L , Li Y-H , Aouf N
Published: May 2010

A novel flight route planning design technique is proposed for a group of unmanned aerial vehicles (UAVs) autonomous navigation based on the combination of evolutionary algorithms and modified artificial potential field methods. In this framework, the individual candidate route is capable of avoiding threats by introducing a virtual potential field while taking into account a variety of flight constraints. The candidate flight route is divided into several sections whose lengths are calculated individually such that the corresponding speed of each UAV can be evaluated to ensure that each member arrives at the desired termination simultaneously. The flight route planner has been tested under a variety of scenarios and proven to be effective in achieving the rendezvous of UAVs.
Supersonic inlet buzz margin control of ducted rockets
Authors: Shi X , Chang J-T , Bao W , Yu D , Li B
Published: May 2010

The maximum performance of a supersonic inlet will be achieved when operating as close as possible to its buzz boundary. In order to maintain high performance without crossing the buzz boundary, an active buzz margin predictor and controller is necessary. The goal of a control system is to acquire inlet buzz margin and maintain it as the designated value and predict inlet buzz before it occurs and then take some measures to buzz mitigation or inlet restart. The inlet buzz boundary and the margin of ducted rockets were first discussed and analysed. Then the dynamic mathematical model of a gas flow control system was established. Lastly, the inlet buzz margin controller of a ducted rocket was designed. Simulation results show that there exist anti-regulation characteristics for gas flow control for ducted rockets, and it leads to the particularity of inlet buzz margin control for ducted rockets in contrast to liquid ramjet. The designed inlet buzz margin has to be bigger to avoid the appearing of inlet buzz because of anti-regulation characteristics; otherwise, the inlet buzz phenomenon probably appears. If the inlet buzz of the ducted rocket appears, the command of decreasing fuel flow could not be given immediately; otherwise, the inlet buzz will aggravate.
Development of a three-dimensional collision risk model tool to assess safety in high density en-route airspaces
Authors: Sáez Nieto F J , Arnaldo Valdés R , García González E J , McAuley G , Izquierdo M I
Published: May 2010

A three-dimensional collision risk model (CRM) is being developed by the Technical University of Madrid and INECO for the European Organization for the Safety of Air Navigation (EUROCONTROL) as a method of assessing the European en-route risk, due to all causes and across all dimensions within the airspace. This model provides a method for assessing the level of safety in en-route airspaces, where controllers monitor air traffic by means of radar and provide tactical instructions to aircraft, and also provides safety metrics required to understand these results.

The three-dimensional CRM is based on the analysis of recorded aircraft tracks from radar data processing systems in order to identify and analyse automatically all proximate events within a time span and a given volume of airspace. The three-dimensional collision risk analytical model is backed up by a modular software tool developed to analyse radar data samples and to support the different processes that need to be addressed to obtain the required three-dimensional CRM outcome.

The main purpose of this research is to show how the three-dimensional CRM software prototype performs an in-depth analysis of radar data, in order to provide robust information on air traffic factors and safety metrics.
Aircraft stability and control model using wavelet transforms
Authors: Mohammadi S J , Sabzeparvar M , Karrari M
Published: May 2010

In contrast to the conventional aerodynamic and high-order Taylor series models, the model of wavelet transform is defined. This model is a black box model and has a better efficiency in comparison to the conventional models. The wavelet model can be used as a function of high-order aerodynamic derivatives to estimate the aerodynamic behaviour of an aircraft. Different wavelet aerodynamic model structures are made and evaluated. The results show that these non-parametric models are efficient models, and in comparison to high-order Taylor aerodynamic derivatives, the number of terms and the complexity of the model are reduced.
Modelling, simulation, and optimization of a hot pressurization system for a liquid propellant space engine and comparison with experimental results
Authors: Zanj A , Kalabkhani A , Abdous M A , Karimi H
Published: May 2010

The main objective of this paper is to optimize the performance of a gas generator (GGO) in order to reduce propellant consumption, flyweight, and contamination. Hence, the periodic operation of a GGO is offered. For this purpose, a non-linear modelling and dynamic simulation of a hot pressurization system is developed in order to predict the history of pressure, temperature, and mass flowrate of pressurant and propellant during the expulsion of the propellant from a tank. This model calculates the change in ullage volume owing to expulsion of the propellant. It also considers the net heat transfer in the ullage space. The new approach is validated using experimental results. It is noticeable that despite other modelling approaches, the present pressurization system modelling is not decoupled from the turbopump system. It means that the interaction is observed between these two systems. Finally, the periodic operation of a GGO is compared with its normal performance, and acceptable results are obtained.
Passive magnetic attitude stabilization system of the EduSAT microsatellite
Authors: Battagliere M L , Santoni F , Piergentili F , Ovchinnikov M , Graziani F
Published: May 2010

Passive magnetic attitude stabilization systems are simple, easy to realize, cheap, and do not require software development and on-board energy consumption. Owing to these features, passive magnetic attitude stabilization systems were selected for the EduSAT (Educational Satellite) microsatellite, a student-built satellite funded by the Italian Space Agency, scheduled to be launched in the last quarter year of 2010. The passive magnetic attitude stabilization system is based on a permanent magnet, which provides a restoring torque to align an oriented axis of the satellite with the Earth's magnetic field direction, and an energy dissipation system, which can consist of a set of permeable rods magnetized by the oscillation of the geomagnetic field along their axis.

UNISAT-3 attitude determination results after 1 year from its launch demonstrated the necessity of an accurate design and manufacturing process of soft magnetic strips. Predicting system performance in orbit and evaluating the obtainable accuracy are not trivial: the main problem is knowing the effective magnetization of the permeable rods.

The paper deals with sizing, choice of material, manufacturing process, and arrangement of a set of permeable rods on board the EduSAT microsatellite on the basis of previous flight experience.
Detection of Delamination in Carbon-Fibre-Reinforced Polymers with Lock-In Thermography
Authors: Meola C , Carlomagno G M , Annicchiarico D , Giordano M , Zarrelli M
Published: May 2010

Attention of this paper is devoted to testing and evaluation of carbon-fibre-reinforced polymer specimens with lock-in thermography. Several specimens were prepared by a vacuum infusion technique using a low-viscosity epoxy system; delaminated areas were simulated by the insertion of thin Kapton® diskettes at a given depth through the thickness. Artificial defects had different shapes (circular or elliptical) and dimensions. Inserts were located at different depths and, in some cases, by overlapping more than one Kapton®-shaped layer (i.e. two or more concentric discs, each of different diameter). A preliminary test campaign was performed by differential scanning calorimetry and rheometry to find optimal processing parameters to achieve fully cured state of matrix and to avoid the formation of defects in accordance with aerospace standards for composites manufacturing. Specimens were non-destructively inspected with optical lock-in thermography; results were presented in terms of phase images. All inserts were discovered and also well outlined under difficult conditions such as in the case of thin overlapped foils.
Spiral landing guidance law design for unmanned aerial vehicle net-recovery
Authors: Yoon S , Kim H J , Kim Y
Published: May 2010

A spiral landing guidance law is proposed for a net-recovery landing of a fixed-wing unmanned aerial vehicle (UAV). In this study, the net-recovery landing is divided into two phases: a spiral descent phase and a final approach phase. In the spiral descent phase, a spiral descending path is designed from any initial position to a final approaching waypoint. The flight path angle of the UAV is controlled to align with the approaching direction at the end of the spiral descent. In the final approach phase, the aircraft is directly guided from the approaching waypoint to the recovery net by a pseudo pursuit guidance law. Sequential imaginary landing and approaching points are generated using a cubic polynomial in the pseudo pursuit guidance law. Therefore, the UAV at a high altitude with an arbitrary heading angle spirals down towards the recovery net without loitering and flies into the recovery net along a desired approaching path. Six-degree-of-freedom numerical simulation is performed to verify the performance of the spiral descent and final approach guidance laws.
New visions in experimental investigations of a supersonic under-expanded jet into a high subsonic crossflow
Authors: Hojaji M , Soltani M R , Taeibi-Rahni M
Published: May 2010

A series of experiments was performed to investigate the interaction of an under-expanded axisymmetric supersonic jet exhausted from a flat plate with a high subsonic crossflow. The goal was to study the effect of boundary layer thickness (δ) and jet to freestream dynamic pressure ratio ( J) on flow field pressure distributions. The resulting measurements upstream of the jet showed that with increasing boundary layer thickness, the magnitude of the pressure coefficient decreases, whereas downstream of the jet, the recovery of the back-pressure moved closer to the nozzle exit. Flow field measurements indicated that with increasing boundary layer thickness, the jet plume dissipation rate increased, whereas the strength of the counter-rotating vortex pair (CRVP) did not vary significantly. In addition, it was clearly observed that with increasing J, the CRVP penetrated into the crossflow and the magnitude of the pressure coefficient on the surface upstream and downstream of the jet increased.
Wing Flutter Simulations Using an Aeroelastic Solver Based on the Predictor—Corrector Scheme
Authors: Xiao J , Gu C
Published: May 2010

An integrated computational fluid dynamics (CFD) and computational structural dynamics (CSD) method is developed here for the calculation and analysis of wing flutter in the time domain. The CFD solver is based on an unsteady multi-grid finite-volume algorithm for the Euler/Navier—Stokes equations on a multi-block structured grid. The CSD solver adopts a linear multi-step method to integrate the aeroelastic governing equations expressed in the modal space. A grid deformation method employing a radial basis function approach is introduced here to generate a dynamically moving grid. The solving procedure of an aeroelastic system is implemented with a predictor—corrector scheme in the physical time. By extrapolating the aerodynamic force, the hybrid predictor—corrector scheme is introduced to save the flow calculation right before the correcting step. The coupled CFD—CSD method is used to simulate wing flutter problems in the time domain in order to predict the stability of an aeroelastic system, which, in this paper, is fulfilled by finding the flutter boundaries. The calculation of the Isogai wing finds an S-shaped flutter boundary, which has been predicted by other studies. The obtained flutter boundary of the AGARD 445.6 wing shows a distinct transonic dip, which agrees well with the experiment result. Computational efficiency and accuracy using two predictor—corrector algorithms and a strong coupling algorithm are also compared.
Analytical Landing Trajectories for Embedded Autonomy
Authors: Li M D , Macdonald M , McInnes C R , Jing W X
Published: May 2010

This paper considers an optimal guidance law for the initial braking phase of a soft landing mission on a celestial body without atmosphere in which boundary conditions on height and velocity are specified. The optimal lander attitude for the minimum fuel landing problem is found. An analytic optimal trajectory is achieved by expanding the thrust acceleration, gravitational acceleration and the cosine of the vertical attitude angle to a high-order polynomial. Coefficients of these polynomials are obtained from the boundary conditions. A fixed gain control law and a direct adaptive control (DAC) law are then developed to track the analytical reference trajectory. Finally, a mission scenario is presented to illustrate the accuracy of the analytical trajectory and validity of the control laws developed. The use of DAC for embedded autonomy will be directly contrasted against a traditional fixed gain controller, using a Lunar landing scenario. The advantage of the DAC approach is that it does not require system monitoring to detect thruster failure and can adjust its gain automatically. As such, DAC combined with the developed analytical solution enables autonomy to be embedded within the lander guidance and control system. In addition, it is shown that DAC increases the probability of lander survival through faster transient response and stability than a traditional fixed gain controller with system level failure detection and recovery.
Nuclear Power Sources: A Key Enabling Technology for Planetary Exploration
Authors: Summerer L , Stephenson K
Published: May 2010

Nuclear power sources for space (NPS) are, according to current physics knowledge, the only power source option for some classes of space missions. Europe has successfully used NPS exploration missions (e.g. Huygens lander on Titan and Ulysses spacecraft). Although some small-scale study and development efforts have been undertaken at the national level during the past 40 years, these did not go beyond study and early prototyping level.

The present paper introduces the European situation with respect to the development and use of NPS.
Sliding mode-based pure pursuit guidance for unmanned aerial vehicle rendezvous and chase with a cooperative aircraft
Authors: Yamasaki T , Balakrishnan S N
Published: May 2010

This article introduces a high-performance pure pursuit guidance method via sliding mode approach for an unmanned aerial vehicle's (UAV) rendezvous with a cooperative aircraft. A guidance method for rendezvous should orient the UAV to a predicted rendezvous position and a specified heading constraint that enables the UAV to continue to follow a cooperative aircraft at a desired distance. For the guidance scheme to accomplish these objectives, a chosen waypoint is used to guide the UAV to a rendezvous point with an allowable heading error. Furthermore, the UAV has to reach the proposed rendezvous point at an admissible time of arrival and has to have the aircraft's velocity. To this end, a dynamic inversion (DI)-based velocity controller is introduced. The proposed pure pursuit guidance, in conjunction with a waypoint setting methodology, and the DI-based velocity controller are discussed in this article. Some simulation results are also provided to demonstrate and analyse the performance of the proposed scheme.
Non-Linear Indentation Law for Lightweight Sandwich Beam
Authors: Sadighi M , Saadati M
Published: May 2010

Indentation law is the relationship between force and deflection under the load on a sandwich beam in a fully backed state (on rigid ground). In the classical method, the Winkler model, which is based on analysing a beam on elastic foundation, is used for verifying the indentation law and for measuring core compression yielding load. This load is assumed to be the same as the one in the three-point bending (3PB) state. The typical formula of indentation is F= Kα n, where K and n are determined by an indentation test and α is the sandwich compression. In the present article, the sandwich beam is analysed by the higher order sandwich panel theory (HOSPT), and the indentation law is determined for fully backed and 3PB states separately. The effect of contact width on non-linearity of the indentation law is investigated, and the contact width is determined for cylindrical indentors. Foam, laminate, and sandwich beam contact pressure profiles are presented, and the indentation law is obtained in accordance to the radius of the indentor and contact width. It presents an analytical solution for the factors K and n in the indentation problem for simply supported and fully backed states. It is shown that the core compression in the 3PB state is lower than fully backed indentation. However, the classical theory predicts lower value for it than experimental value. It is shown that K increases as the indentor radius increases in the indentation law. Results are compared with the Winkler foundation method, ANSYS FEM software, and the previous article. Good agreements are found between HOSPT, ANSYS, and the previous work.
Analysis of Choked Viscous Flows through a Constant Area Duct
Authors: Lijo V , Kim H D , Setoguchi T
Published: May 2010

The phenomenon of choked flow has been recognized and understood for many decades. These flows also have a variety of practical applications, such as pneumatic systems, oil and gas well blowouts, and vents in high-pressure systems, among others. According to some recent experiment data carried out in a straight pipe, the flow Mach number exceeds unity at the exit of pipe. This conflicts the Fanno flow theory that has long been applied to the one-dimensional gas dynamics area. At present, it is not clear whether this comes from experimental errors or any other reasoning that was not yet disclosed. There may be a suspected possibility of boundary layer thinning near the duct exit, which accounts for a divergent flow passage. The main objective of the present effort is to understand the flow mechanism by which the main flow Mach number exceeds unity near the exit of a straight duct. Both computational and theoretical analyses have been performed to investigate the detailed choking phenomenon at the vicinity of duct exit. The results obtained show that boundary layer thinning is produced by the flow at the vicinity of duct exit, with subsonic inlet conditions, consequently leading to the divergent flow passage. The sonic conductance is analysed in terms of pressure loss and boundary layer blockage with different duct sizes.
Tribological properties of PA6-filled maleic anhydride-grafted polypropylene composite
Authors: Li J
Published: May 2010

Blending polypropylene (PP) to recycled polyamide (PA)-6 industrial wastes with and without compatibilizer was produced in a co-rotating twin-screw extruder, in which PP acts as the polymer matrix and PA as the dispersed phase. Friction and wear behaviours of PA6-filled PP composites were investigated on block-on-wheel model friction and wear tester. In order to further understand the wear mechanisms, worn surfaces and scraps of samples were analysed by a scanning electron microscope.
Lubricant ageing effects on the friction characteristics of wet clutches
Authors: Berglund K , Marklund P , Larsson R
Published: May 2010

The friction characteristics and performance of wet clutches have been investigated by several authors. Studies have also been made to understand the frictional performance during the service life of the clutch system. However, most lifetime studies have been conducted for systems with paper-based friction material so that systems using sintered bronze friction material remain largely unexplored. To study the friction performance of how these systems can vary over time, the friction characteristics for a clutch system using lubricants aged in three different ways were compared. The effects on friction characteristics resulting from oxidation of the lubricant, reduced additive concentration, and ageing under real operating conditions in a wet clutch test rig were studied.

The oxidation effects on friction characteristics were examined using a modified waterless turbine oil oxidation stability test on a fully formulated lubricant. Five oxidation time periods from 48 to 408 h were investigated. For each period of oxidation, a friction performance test was run using a pin-on-disc machine.

The ageing carried out in a wet clutch test rig is a standard test of a wet clutch systems manufacturer which is used in order to verify that an oil-friction disc combination will last the full service life of the specific application. This test gives a realistic ageing process similar to that in a wet clutch in a field test.

Under boundary-lubricated conditions, additives are vital to the performance of wet clutches. Therefore, the effect of reducing the additive concentration in the oil was also studied, in the range of 10 to 100 per cent of the original additive package used in the fully formulated wet clutch lubricant.

Results showed that a general friction increase can be observed for oxidation, additive reduction, and test rig ageing. It was also concluded that different methods of simulating the wet clutch ageing process differ and cannot be directly correlated with each other.
Model-based virtual surface texturing for concentrated conformal-contact lubrication
Authors: Zhu D , Nanbu T , Ren N , Yasuda Y , Wang Q J
Published: May 2010

A model-based virtual texturing approach has been developed and applied to design, generate, ‘test’, and evaluate textured surfaces through numerical simulations. A series of studies on the numerical generation and performance evaluation of textured surfaces in a lubricated concentrated contact has been conducted, which includes (a) numerical generation of a large variety of textures considering possible geometric imperfections that exist in reality due to tooling design considerations and fabrication errors; (b) determination of texture depth, size, and area density; (c) texture distribution pattern selection; (d) bottom shape comparison and design optimization; (e) investigation of the influence of surface relative motion; (f) prediction of performance deviation caused by texture shape imperfections; and (g) evaluation of the effect of originally machined roughness. The present study was conducted using the deterministic mixed elastohydrodynamic lubrication (EHL) model recently developed, modified, and validated, which appears to be useful for surface texture design based on comparative performance evaluation in a wide range of operating conditions.
On the effects of sliding velocity and operating pressure differential in rotary O-ring seals
Authors: Lingerkar K , Khonsari M M
Published: May 2010

An experimental study is conducted to investigate the effect of sliding velocity and pressure differential across an O-ring seal. Of specific interest are the power loss, friction torque and temperatures at the interface between the O-ring and rotating shaft. Nitrile butadiene rubber of circular cross-section with 70 Shore A hardness is used as a test specimen. The O-ring power loss and temperatures at a distance of 0.61 mm away from the O-ring tip are measured during the tests. In order to analyze the temperature at the interface, a two-dimensional axisymmetric computational fluid dynamics (CFD) model is preprocessed in GAMBIT and thermal heat transfer analysis is carried out using a commercial CFD package, FLUENT. Variations of frictional torque, O-ring friction power loss and interfacial temperatures with changes in sliding velocity and operating pressure differential are presented. Results reveal that the O-ring power loss increases in an approximately linear fashion with sliding velocity. Further, it is found that the friction power significantly increases with relatively higher pressure differentials across an O-ring. Friction torque is found to drop with an increase in shaft speed and it rises at relatively higher pressure differentials. Moreover, the interfacial temperatures are found to increase with increase in sliding speed and operating pressure differentials. The physical and practical usefulness of these results are discussed.
Tribofilm formation in biotribocorrosion – does it regulate ion release in metal-on-metal artificial hip joints?
Authors: Yan Y , Neville A , Dowson D , Williams S , Fisher J
Published: May 2010

Metal-on-metal prostheses have been considered as alternatives to the well-established metal-on-polyethylene implants due to polyethylene wear debris-induced osteolysis. The release of metal ions from metallic components of metal-on-metal joint implants is of great concern to patients and surgeons. Clinical studies have shown that the level of ions in blood and urine samples of patients does not increase linearly with time. Understanding the processes of metallic ion release from the bearing surfaces of metal-on-metal implants is urgent, as more and more younger and active patients demand longer-lasting joint prostheses. In this study, a hip joint simulator with a novel integrated corrosion cell was used. The diameter of the hip joint head was 36 mm. In situ electrochemical measurements were carried out to investigate the interactions between the tribological contacts and corrosion (ion release) processes in simulated biological environments. The role of the tribofilm on the bearing surfaces is discussed. As a conclusion, the complex organometallic tribofilm once formed can protect the bearing surface from further ion release and act to control the level of overall damage from the implant.
Lubrication mechanisms with laser-surface-textured surfaces in elastohydrodynamic regime
Authors: Mourier L , Mazuyer D , Ninove F-P , Lubrecht A A
Published: May 2010

Micro-texturing is very efficient to make surfaces super-hydrophobic according to a physical process known as ‘lotus effect’. In the recent past, tribologists have also investigated surface texturing because it could be a promising way to increase the lifetime of contacts or to make its working conditions more severe. Moreover, significant friction coefficient reductions have been obtained with textured surfaces in different lubrication regimes. In this presentation, transient lubrication phenomena induced by laser-made circular dimples passing through an elastohydrodynamic lubrication point contact are analysed both experimentally and numerically. Under rolling—sliding conditions, the passage of an isolated dimple modifies the film thickness distribution. Deep dimples induce an oil film failure. On the contrary, a shallow dimple locally generates a large increase in the film thickness. Dimples geometry and the slide/roll ratio modify the pressure distribution and then control the level and extension of the local film reinforcement. Experiments are simulated numerically with a two-dimensional multi-grid solver. This allows one to have a better understanding of the lubrication mechanism with a textured surface as a function of dimple geometry, entrainment speed, and contact pressure. The key point is the control of tribological conditions to maintain the viscosity of the lubricant high enough inside the dimple in order that the shearing can expel it to locally enhance the film thickness.
Impact of a rigid sphere on a highly compressible porous layer imbibed with a Newtonian liquid
Authors: Pascovici M D , Popescu C S , Marian V G
Published: May 2010

The process of liquid flow takes place inside a highly compressible porous layer (HCPL) many times. In these cases, elastic forces of the HCPL solid phase are negligible, compared with hydrodynamic (HD) forces. Such processes were named ex-poro-HD (XPHD). A study of the impact process under XPHD conditions for circular and rectangular aligned plates was recently performed and presented by the authors. The impact of a rigid sphere on an HCPL, imbibed with a Newtonian liquid, under XPHD conditions, is analysed in the present paper. The Kozeny—Carman equation was used to compute the permeability variation as a function of compacticity/porosity. The Bowden and Tabor model for squeeze under impact was extended for XPHD conditions. The obtained model gives the impact pressure and force variations as the layer thickness decreases, so the damping capacity of the HCPL was evaluated. The maximum value of the absorbed energy, given by the optimal compacticity/porosity of the HCPL, is established. A comparison with the impact of a rigid sphere on a Newtonian liquid film under HD conditions is also done, keeping the same geometry and same kinematic and dynamic parameters, inherited from the XPHD model. The damping capacity of an HCPL is several orders of magnitude greater than that of the Newtonian liquid layer. The theoretical model was validated by two experiments, in which the HCPL is impacted by free falling ball tests.
Wear prediction of clearance joint by integrating multi-body kinematics with finite-element method
Authors: Su Y , Chen W , Tong Y , Xie Y
Published: May 2010

A numerical approach of wear prediction integrating with system kinematics is proposed to investigate the interaction between wear of joint with clearance and kinematics in multi-body systems. The coupling between wear of joint and system kinematics is modelled by integrating wear prediction process with finite-element-based iterative scheme. Kinematical behaviours of a machine with a kinematical model of imperfect joint are progressively changed throughout joint wear process. The massless link model for clearance joint with the assumption of continuous contacts is used. Results from predictions and tests show that both wear zones and wear depth are different for the pin and bushing.
Micro-geometry effects on the sliding friction transition in elastohydrodynamic lubrication
Authors: Morales-Espejel G E , Wemekamp A W , Félix-Quiñonez A
Published: May 2010

An engineering scheme is proposed to calculate the effects of deterministic micro-geometry in sliding friction for the transition between full-film elastohydrodynamic and boundary lubrication regimes. The method combines the concepts of micro-geometry deformation from lubricated and/or dry contact conditions. Pressures are calculated from the elasto-plastic displacements and the load sharing between lubricant and contacts is resolved iteratively in the classical way, i.e. flow balance. Thus, by varying the lubricant entrainment speed in the contact for known values of boundary and full-film friction coefficients, it is then possible to calculate the Stribeck curve. The scheme is semi-analytical and the use of fast Fourier techniques makes it attractive for engineering applications. Theoretical predictions are compared with numerical solutions from the literature and with in-house measurements for different surface topographies and the results are in reasonable agreement with the model.
Effects of non-Newtonian micropolar fluids on the squeeze-film characteristics between a sphere and a plate surface
Authors: Lin J-R , Liang L-J , Chu L-M
Published: May 2010

On the basis of the Eringen's micro-continuum theory, this study is mainly concerned with the effects of non-Newtonian micropolar-fluid rheology on the squeeze-film characteristics between a sphere and a plate surface. To account for the micro-rotational effects and the micro-rotational inertia of the fluid elements arising from the lubricant blended with additives, the non-Newtonian Reynolds-type squeeze-film equation is derived using the continuity equation and the linear momentum equations coupled with the angular momentum equations. A closed-form solution for the film pressure, the load-carrying capacity and the time—height relationship is obtained for engineering applications. According to the results, the effects of non-Newtonian micropolar fluids provide an increase in the load capacity, and therefore lengthen the response time to prevent the contact of sphere with plate. Furthermore, the non-Newtonian effects on the squeeze-film characteristics are more emphasized under lower squeeze-film heights with larger coupling numbers and smaller interacting parameters. As the value of the coupling number tends to zero or the value of the interacting parameter approaches infinity, the presented derivation provides a close agreement with the Newtonian sphere-plate systems by Conway and Lee [1].
Hydrodynamic force and moment in pure rolling lubricated contacts. Part 1: Line contacts
Authors: Biboulet N , Houpert L
Published: May 2010

Hydrodynamic rolling force and moments in line contact have been studied in detail using isoviscousrigid (IVR) and elastohydrodynamic (EHL) models. Using fully flooded assumptions, curve-fitted relationships are suggested for calculating the IVR and EHL hydrodynamic rolling force per unit length. At high speed and light load, EHL numerical results converge towards IVR results so that a single curve-fitted relationship has been derived for covering the full range of operating conditions with a rapid transition from IVR to EHL regime of lubrication.

Results obtained are often close to published results (especially in the IVR regime). The EHL hydrodynamic rolling force per unit length is found to be load independent, while load exponents ranging from 0.01 to 0.37 can be found in the literature. A single relationship for both lubrication regimes (IVR and EHL) is given for deriving a starvation factor function of the ratio between the film thickness at the inlet meniscus and the fully flooded minimum film thickness.

Finally, the calculation of the total power loss per unit length has also been conducted by integrating through the film and along the rolling direction the power loss per unit volume (defined as the product shear stress time shear rate). Results obtained are consistent with the calculation of the rolling force per unit length.
Hydrodynamic force and moment in pure rolling lubricated contacts. Part 2: Point contacts
Authors: Biboulet N , Houpert L
Published: May 2010

Hydrodynamic rolling force and moments in point contact have been studied in detail using isoviscousrigid (IVR) and elastohydrodynamic (EHL) models. Using fully flooded assumptions, curve-fitted relationships are given for calculating the IVR and EHL hydrodynamic rolling forces. Both are proportional (or almost proportional in the IVR case) to 2 a, the Hertzian contact length being perpendicular to the rolling direction, and are also functions of the dimensionless speed parameter. A single curve-fitted relationship has been derived to cover the full range of operating conditions with a smooth transition from IVR to EHL regime of lubrication. The results obtained are slightly higher than those previously published (the ratio being of the order of 1.5 for usual operating conditions).

Point contact and line contact (with a contact length £ being equal to the point contact length 2 a) hydrodynamic rolling forces have also been compared. The point contact forces are about 26 per cent larger than those obtained using line contact relationship (published in part 1) because of a larger domain of integration in the lateral direction.

By limiting the width of the integration domain to £ (roller length or ball diameter), the effect of 2 a/£ on the hydrodynamic rolling force has been studied, leading to the derivation of a truncation factor C. As the load increases, 2 a increases and the truncation factor decreases until reaching a limit when ellipse truncation starts because 2 a/£ is equal to or larger than one. Using the truncation factor and limiting the 2 a/£ ratio to one, it was found that point contact and line contact hydrodynamic forces are the same within a few per cent. A single point contact relationship can therefore be suggested, covering the IVR to EHL operating conditions with a smooth transition between these lubrication regimes, and also a smooth transition from point contact to line contact as the load increases and contact ellipse truncation occurs.

Finally, calculations of power losses due to the Poiseuille flow in the rolling direction x and in the perpendicular direction z show that the power loss in the z direction is usually very small for wide elliptical contacts and that most of the power is dissipated in the inlet and outlet, with a 26 per cent contribution of the integration domain defined out the range − a < z < a. This result is in line with the truncation factor defined previously.
The role of the coefficient of restitution on impact problems in multi-body dynamics
Authors: Seifried R , Schiehlen W , Eberhard P
Published: May 2010

This review article presents methods for treatment of impact problems in multi-body dynamics with a special focus on the coefficient of restitution. The impact modelling in multi-body systems is presented, including the impact kinematics, different definitions of the coefficient of restitution, the instantaneous impact modelling, and the continuous impact modelling. A main topic is the multi-scale simulation approach for the numerical evaluation of the coefficient of restitution using additional simulations on a fast time scale. Different models on the fast time scale are proposed and techniques for experimental validation of the models are given. Many numerical and experimental results for impacts of two and more bodies are presented. Thereby the efficiency and accuracy of the multi-scale simulation approach are verified; the influence of physical parameters on the impact process as well as the agreement of the instantaneous and continuous impact modelling are demonstrated. Finally, the extension of the presented methods to particle systems consisting of thousands of impacting bodies is briefly reviewed.
Elasto-multi-body dynamics of internal combustion engines with tribological conjunctions
Authors: Perera M S M , Theodossiades S , Rahnejat H
Published: May 2010

Reduction of frictional losses and NVH (Noise, Vibration, and Harshness) refinement constitute the key customer-focussed aims in internal combustion engine development. Numerical predictive tools have progressively become an important part of achieving these aims. However, the interactions and sometimes the conflicting requirements of the aforementioned objectives call for the inclusion of many phenomena in realistic models of practical significance. These phenomena occur at varying physics of scale, from micro-scale tribological conjunctions to small scale vibrations and onto large scale inertial dynamics. At the same time, the inclusion of many disciplines for a cohesive analysis will be required, such as rigid body dynamics and elastodynamics, as well as tribology. While the inclusion of such a multi-disciplinary approach is deemed essential, the use of analytical rather than numerical models, as far as possible, would render realistic predictions within the usual tight industrial timescales. This article presents an experimentally validated model of the engine piston assembly, which is based on the multi-physics, multi-scale nature of the interacting components. Furthermore, it provides predictions of some current development trends in engines such as the high output power to weight ratio and offset crankshaft. The emphasis of this article is on the integration of the kinetic reactions arising from the tribological conjunction of the dynamics of engine subsystems, piston, and crankshaft.