Academic literature on the topic 'Internal friction model'

Temperature dependence of internal friction on silicon nitride ceramics with yttria and alumina sintering aids was discussed using 4-elements visco-elastic model. It is known that the internal friction of this ceramic material shows a characteristic peak at around 1040 oC and an exponential increase over 1200 oC. This temperature dependence of internal friction was well approximated with using parallel Maxwell model. The parameters for this model and the relaxation time on this model were obtained. The relaxation time was very short, compared to the transient creep deformation of this ceramics. The analyzed results on internal friction could not be related with the creep deformation.

AbstractAdhesion is one of essences with respect to rubber friction because the magnitude of the friction force is closely related to the magnitude of adhesion on a real contact area. However, the real contact area during sliding depends on the state and history of the contact surface. Therefore, the friction force occasionally exhibits rate-, state-, and pressure dependency. In this study, to rationally describe friction and simulate boundary value problems, a rate-, state-, and pressure-dependent friction model based on the elastoplastic theory was formulated. First, the evolution law for the friction coefficient was prescribed. Next, a nonlinear sliding surface (frictional criterion) was adopted, and several other evolution laws for internal state variables were prescribed. Subsequently, the typical response characteristics of the proposed friction model were demonstrated, and its validity was verified by comparing the obtained results with those of experiments conducted considering the contact surface between a rough rubber hemisphere and smooth acrylic plate.

Abstract The article presents the determination of an exemplary measure in the assessment of the technical state of sets of mechanical objects at the stage of manufacture, use and maintenance. The technical state of the assemblies is influenced by the quality of the friction-cooperating elements, the quality of basic functions, the surroundings and the diameter clearance of kinematic node components. Energy wasted to overcome the frictional resistance is a significant part of the energy supplied, which is why current friction losses are minimized. The article includes analysis of the phenomena occurring in the cylindrical pairs in the presence of static and kinetic friction. The many factors affecting the course and values of friction force between cylindrical elements performing relative reciprocating motion have been indicated. The subject of the article is the method of measuring the friction force between a fixed and movable cylindrical element of the mechanical object. The gradual increase of the friction force component takes place by means of easily accessible force. The results of experimental tests of the friction force in different laboratory conditions under are also included. The effect on the measured friction force was investigated: of friction elements geometry and the surface condition after manufacture and/or operation. Scatter results of static friction force depending on the geometry and surface state can be significant. Examples of surface state images are shown. A friction force model was also developed depending on factors affecting its value.

This paper describes the influence of pump operating conditions, such as operating pressures, pump speeds, and oil temperatures, on the friction torque characteristics of internal gear pumps for automobiles. Additionally, it presents a new mathematical model reflecting the influence of the oil temperature on the friction torque. In an internal gear pump, the friction torque was affected by oil temperature as well as operating pressure and pump speed. When the operating pressure was high, the influence of oil temperature on friction torque at a pump speed of less than 1000 r/min was contrary to that at a pump speed of greater than 1000 r/min. It was considered that the friction torque is fundamentally composed of three components: the component dependent on the operating pressure, dependent on the pump speed, and independent of both the operating pressure and the pump speed. However, the component dependent on the operating pressure was affected significantly by not only the pump speed but also the oil temperature. In addition, another factor besides the viscosity of the oil existed in the component dependent on the pump speed. A mathematical model for the friction torque characteristic of the internal gear pump was newly established by adding factors including the oil temperature to the Wilson’s model. The new model was able to represent with accuracy the experimental friction torque characteristic in the internal gear pump under various pump operating conditions.

[ES] Con el aumento de la demanda de soluciones más amigables con el medio ambiente en la industria de la automoción, el motor de combustión interna alternativo (MCIA) enfrenta actualmente grandes desafíos para minimizar su consumo de recursos no renovables y especialmente, para reducir sus emisiones contaminantes. Debido a que el aporte de los MCIAs es fundamental para cubrir las necesidades de movilidad y de generación de energía alrededor de todo el mundo, y el hecho de que diferentes alternativas, como los motores eléctricos e hibrido, están y continuaran enfrentado múltiples obstáculos para su implementación masiva en el futuro cercano, la investigación continua en MCIA es fundamental para cumplir con los propósitos de reducción de emisiones. En este aspecto, una aproximación para el aumento de la eficiencia del motor y la reducción del consumo de combustible es mediante la implementación de alternativas dirigidas a reducir las pérdidas mecánicas por fricción. Estas alternativas tribológicas incluyen aquellas que requieren modificaciones en los componentes del motor, como materiales y acabados superficiales, y el uso de formulaciones de aceite lubricante de menor viscosidad o aditivos que mejoren las condiciones de lubricación del motor. Con la contante evolución y mejoras en el MCIA y las condiciones de trabajo cada vez más severas, también surgen nuevas alternativas tribológicas para enfrentar los nuevos desafíos del motor, y por tanto se requiere de investigaciones adicionales en este tema. Durante el desarrollo de esta Tesis, uno de los objetivos consistió en contribuir a la investigación del uso de aceites de baja viscosidad para el ahorro de combustible como un efecto conjunto con las condiciones de conducción del vehículo. Para llevar a cabo este objetivo, se desarrollaron ensayos experimentales bajo condiciones estacionarias en un banco de motor con formulaciones de aceite de diferente viscosidad HTHS, algunas de ellos con aditivo modificador de fricción para expandir el rango de reducción de fricción a condiciones de lubricación más severas. Los mapas de consumo de combustible resultantes de estos ensayos fueron utilizados en un modelo de simulación del vehículo para estimar su consumo de combustible como función del aceite y las condiciones de trabajo de tres ciclos de conducción. Con el objetivo de expandir los conocimientos en los fundamentos de lubricación de los MCIAs y tener la capacidad de evaluar otras alternativas para reducir las pérdidas por fricción, se consideró necesario enfocar la investigación en el conjunto pistón-camisa, que es el par tribológico con mayor aporte a las perdidas por fricción. Para conseguir este objetivo, durante esta Tesis se desarrolló una maqueta específica para el ensamble pistón-camisa, y un modelo teórico para simular la lubricación del segmento de compresión. Para la primera parte, la maqueta se desarrolló basada en el método de camisa flotante, en el cual la camisa fue aislada del resto del motor y la fuerza de fricción generada en la interfaz pistón-camisa pudo ser medida mediante sensores de fuerza. En esta instalación se desarrollaron diferentes ensayos los cuales permitieron llevar a cabo un análisis exhaustivo de los fundamentos de lubricación de este par tribológico como función de diferentes parámetros que tiene impacto en las condiciones de lubricación. Este estudio se complementó con el desarrollo de un modelo de lubricación para el segmento de compresión basado en el método de diferencias finitas. Finalmente, se llevó a cabo una comparativa de resultados experimentales y teóricos para el segmento de compresión, lo cual permitió validar los ensayos experimentales en la maqueta de camisa flotante, así como el modelo de simulación desde el punto de vista de datos de entrada, condiciones de contorno y supuestos.
[CA] Amb l'augment de la demanda de solucions més amigables amb el medi ambient en la indústria de l'automoció, el motor de combustió interna alternatiu (MCIA) s'enfronta actualment a grans desafiaments per minimitzar el seu consum de recursos no renovables i especialment, per reduir les seves emissions contaminants . Tenint en compte que l'aportació dels MCIA és fonamental per a cobrir les necessitats de mobilitat i generació d'energia arreu de tot el món, i el fet que diferents alternatives, com els motors elèctrics i híbrids, estan i continuaran enfrontat múltiples obstacles per a la seva implementació massiva al proper futur, la investigació contínua en MCIA és fonamental per complir amb els propòsits de reducció d'emissions. En aquest aspecte, una aproximació per a l'augment de l'eficiència del motor i la reducció de consum de combustible és mitjançant la implementació d'alternatives dirigides a reduir les pèrdues mecàniques per fricció. Aquestes alternatives tribològiques inclouen aquelles que requereixen modificacions de components del motor, com materials i acabats superficials, i l'ús de formulacions d'oli lubricant de menor viscositat o additius que milloren les condicions de lubricació del motor. Amb la constant evolució i millores en el MCIA i les condicions de treball cada vegada més severes, també sorgeixen noves alternatives tribològiques per enfrontar els nous desafiaments del motor, i per tant es requereix d'investigacions addicionals en aquest tema. Durant el desenvolupament d'aquesta Tesi, un dels objectius va consistir a contribuir a la investigació de l'ús d'olis de baixa viscositat per a l'estalvi de combustible com un efecte conjunt amb les condicions de conducció de vehicle. Per dur a terme aquest objectiu, es van desenvolupar assajos experimentals sota condicions estacionàries en un banc de motor amb formulacions d'oli de diferent viscositat HTHS, algunes d'elles amb additiu modificador de fricció per expandir el rang de reducció de fricció a condicions de lubricació més severes . Els mapes de consum de combustible resultants d'aquests assajos van ser utilitzats en un model de simulació del vehicle per estimar el seu consum de combustible com a funció de l'oli i les condicions de treball de tres cicles de conducció. Amb l'objectiu d'expandir els coneixements en els fonaments de lubricació dels MCIAs i tenir la capacitat d'avaluar altres alternatives per reduir les pèrdues per fricció, es va considerar necessari enfocar la recerca al conjunt pistó-camisa, que és el parell tribològic amb major aportació a les perdudes per fricció. Per aconseguir aquest objectiu, durant aquesta Tesi es va desenvolupar una maqueta específica per al acoblament pistó-camisa, i un model teòric per simular la lubricació del segment de compressió. Per a la primera part, la maqueta es va desenvolupar basada en el mètode de camisa flotant, en el qual la camisa va ser aïllada de la resta del motor i la força de fricció generada en la interfície pistó-camisa va poder ser mesurada mitjançant sensors de força. En aquesta instal·lació es van desenvolupar diferents assajos els quals van permetre dur a terme una anàlisi exhaustiva dels fonaments de lubricació d'aquest parell tribològic com a funció de diferents paràmetres que tenen impacte en les condicions de lubricació. Aquest estudi es va complementar amb el desenvolupament d'un model de lubricació per al segment de compressió basat en el mètode de diferències finites. Finalment, es va dur a terme una comparativa de resultats experimentals i teòrics per al segment de compressió, la qual cosa va permetre validar els assajos experimentals a la maqueta de camisa flotant, així com el model de simulació des del punt de vista de dades d'entrada, condicions de contorn i hipòtesis.
[EN] With the increasing demand for greener solutions in the automotive industry, the ICE is currently facing great challenges to minimize the consumption of nonrenewable resources and specially to reduce its harmful emissions. Given that the contribution of the ICE is fundamental to cover the actual mobility and power generation needs worldwide, and the fact that different power-train alternatives, such as electric and hybrid vehicles, are and will continue facing multiple obstacles for their large-scale implementation in the near future, the continuous research on the ICE is fundamental in order to meet the emissions reduction targets. In this regard, one approach to increase the engine efficiency and reduce the fuel consumption, is through the implementation of alternatives aimed to reduce the friction mechanical losses. These tribological alternatives include those that require modifications to the engine components, such as materials and surface finishes, and the use of lubricant oil formulation of lower viscosity or additives that improve the lubrication performance of the engine. With the ongoing evolution and improvement of the ICE and the increasingly severe working conditions, new tribological solutions also emerge to face the new challenges in the ICE, and therefore further research is required on this subject. During the development of this Thesis, one of the objectives was to contribute to the research on low viscosity engine oils for fuel economy as a joint effect with the driving conditions of the vehicle. To accomplish this, experimental tests were performed under stationary conditions in an engine bench test for oil formulations of different HTHS viscosity, some of them with friction modifier additive to expand the friction reduction effect to more severe lubrication conditions. The resultant fuel consumption maps were then employed in a vehicle model to estimate the fuel consumption of the vehicle as function of the oil formulation and the working conditions of the three driving cycles. With the aim of expanding the knowledge on the lubrication fundamentals of the engine and to have the capability to assess other alternatives to further reduce the friction mechanical losses, it was deemed necessary to focus the research on the piston-cylinder liner assembly, the tribo-pair of major friction share. In order to achieve this objective, a test rig was developed in this Thesis specific for the piston-liner assembly, and a theoretical model to estimate the lubrication of the piston compression ring. For the first part, the test rig was designed based on the floating liner method, where the cylinder liner was isolated from the rest of the engine and the friction force generated in the piston-liner conjunction could be measured by means of force sensors. Different tests were developed in this test rig which allowed a comprehensive analysis of the piston lubrication fundamentals as function of different parameters having an impact on the lubrication performance of this assembly. This study was complemented with the development of a piston compression ring lubrication model based on the finite differences method. A comparison of experimental and theoretical results was performed for the piston compression ring that helped to validate both the experimental tests in the floating liner and the simulation model from the point of view of input data, boundary conditions and assumptions.
Bastidas Moncayo, KS. (2021). Experimental and analytical study of the mechanical friction losses in the piston-cylinder liner tribological pair in internal combustion engines (ICE) [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172188
TESIS

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Os projetos de carrocerias veiculares atuais procuram desenvolver estruturas leves, seja para reduzir o consumo de combustível, no caso dos motores de combustão interna, seja para maior autonomia de bateria, no caso dos veículos elétricos e híbridos. Redução no consumo de combustível significa redução na emissão de poluentes. As estruturas precisam ser leves, mas cada vez mais resistentes e rígidas a fim de proporcionar máximo conforto e segurança aos ocupantes. Estas premissas têm levado ao contínuo desenvolvimento dos materiais. No caso dos aços, um dos processos que tem permitido a melhora significativa das propriedades mecânicas é a estampagem a quente. Nos últimos anos, as peças estampadas a quente têm ocupado lugar de destaque na estrutura das carrocerias veiculares por estarem em sintonia com as demandas mencionadas. Há muitas pesquisas em curso para esta tecnologia, seja nos materiais, nos meios de produção, nos revestimentos e em aplicações. O aço mais utilizado neste processo, 22MnB5, também apresenta o chamado efeito bake hardening; a tensão de escoamento é aumentada após tratamento térmico realizado em temperaturas próximas a 200 °C. Neste trabalho, visando à melhoria nas propriedades mecânicas, amostras foram tratadas termicamente na faixa de temperatura supracitada. Após isso, dados obtidos de ensaios mecânicos foram inseridos em programas de simulação de impacto lateral cujo resultado foi a redução na intrusão na célula de sobrevivência. O efeito bake hardening também propiciou um aumento na absorção da energia de impacto em teste estático feito com barras de proteção lateral. O mecanismo metalúrgico envolvido no fenômeno, devido à difusão de intersticiais foi evidenciado no ensaio de atrito interno.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

AbstractIn machining, high mechanical and thermal loads are exerted on a small area of the tool where it interacts with the workpiece. Despite limited interaction space, extensive use of cutting fluids (CFs) is inefficiently used to improve the machining process and increase productivity. In order to minimize CFs’ negative impact on health, environment and financial burden, various strategies have been developed and studied to optimize their use including minimum quantity lubrication. In this research, initial period of chip formation (IPCF), that occurs during a narrow window of space and time at the beginning of the cut, is closely investigated in an orthogonal machining setup. During IPCF, low mechanical loads were observed. The existence of IPCF is further investigated under interrupted cutting process at prescribed intervals in order to sustain its positive effects. In addition, 2D numerical chip formation friction model is proposed. The numerical model comprises a friction criterion dependent on tool temperature that is observed to be associated with a transient friction regime.

A comprehensive piston skirt lubrication and secondary motion model that can be used for piston friction simulations was developed based on Greenwood and Tripp’s surface asperity contact model and Patir and Cheng’s modified Reynolds equation with surface flow factors. Oil flow between the skirt-liner clearances was modeled and hydrodynamic and asperity contact pressures around the skirt were calculated. Reynolds boundary conditions were applied to determine the film rupture boundaries and wetted areas. Surface roughness and roughness orientation were included in the model. Due to its important effect on pressure development in the oil film, change in the skirt profile due to elastic deformations was taken into account. Change of the skirt profile due to piston thermal expansion is also calculated using the steady-state temperature distribution of the piston corresponding to the investigated engine running conditions. A piston stiffness matrix obtained by finite element analysis was used to determine the elastic deformations of the piston skirt under the calculated oil film pressures. A two-degree-of-freedom system is formed with the forces and moments calculated by the lubrication model. These forces and moments require a coupled solution with piston position. This is achieved by applying an iterative numerical procedure based on Broyden’s scheme which seeks force and moment balance at each iteration phase making use of time step variation. The effects of various engine operating conditions and piston design parameters on piston secondary motion were investigated. Piston skirt friction force due to hydrodynamic shear forces and metal-to-metal contact is calculated.

The atomistic mechanisms are proposed for the origin of the static and the dynamic friction forces. The mechanism for the origin of the static friction force resembles the mechanical locking mechanism in a surface roughness model. The origin of the dynamic friction force is formulated as a problem of how the given translational kinetic energy dissipates into the internal relative motions of constituent atoms of bodies during sliding. From studying that the available phase space volume of the translational motion becomes negligible small for a large system size, compared with that of the internal motions, it is concluded that the energy dissipation occurs irreversibly from the translational motion to the internal motions. A phenomenon of superlubricity, where two solid bodies move relatively with no resistance, is discussed.

This paper presents two piston ring and cylinder liner lubrication models and compares the friction predictions against the experimental results from a corresponding bench test. The first model aims to solve the average Reynolds equation with corrective flow factors, which describe the influence of surface irregularities on the lubricant flow under mixed lubrication condition. The second model takes account of the lubricant film rupture and cavitation. Meanwhile, a stochastic rough contact sub-model quantifies the relation between contact pressure and mean surface separation in both cases. Numerical results on the top compression ring simulation show that both models capture hydrodynamic, mixed, and boundary lubrication regimes, which depend on the real surface topographies of the piston ring and the cylinder liner. Whenever hydrodynamic action is insufficient to maintain the equilibrium position of the ring, the restoring force will be augmented by multi-asperity contacts lubricated by a thin boundary film. Total friction will originate mainly from shearing of viscous lubricant and shearing of asperity conjunctions. The purpose of this modeling effort is to compare both lubrication models to data from an experimental test-rig. This test rig eliminates many of the factors that can make analysis of predictions for real engine operating conditions difficult.

Wedge-type piezoelectric motor is easily subject to disturbance such as friction, preload and temperature change, which influences the performance significantly and reduces the positioning accuracy and reliability. In this study, Exponentially Weighted Moving Average (EWMA) method is considered to use for the velocity-feedback loop, which is included in an Internal Model Control (IMC) to achieve a Run-to-Run IMC (RtR-IMC) control structure. Such control scheme is able to adapt the control command following a changing system dynamics so that it can improve the tracking accuracy and robustness. Friction is also a problem of generating dead-zone area and causes serious nonlinear phenomenon especially while moving direction is changed. A feedforward controller is designed based on the friction model. Moreover, temperature increase appears in long-time operation, which is another factor influential to piezoelectric motor’ performance. Instead of using the Single EWMA method, which cannot efficiently deal with such environmental drift problem, a Double EWMA algorithm is developed. Practical experiment is carried out to verify the performance by using these proposed methods. It concludes that the Double EWMA associated with the friction-model-based feedforward controller is superior to the other methods.

The influence of piston ring lubrication on internal combustion engine performance has received considerable attention for over half-century. Studies show that hydrodynamic lubrication prevails through most of engine cycles, and asperity contact only occurs near the vicinity of dead centers [1][2]. In order to solve the governing equation of lubricant, appropriate velocity and pressure boundary conditions should be incorporated into the lubrication equation - Reynolds equation. While lubricant obeys the no-slip velocity boundary condition, the pressure boundaries at the leading and trail edge of piston ring are related to the chamber and the inter-ring crevice gas pressures. A complete lubrication analysis of piston ring requires an inter-ring gas flow model. In most of existing lubrication models, an isentropic orifice flow model is adopted and the gas flow is assumed to an ideal gas passing through the piston ring end gaps with a constant discharge coefficient [2][3][4][5]. In additional to the flow path of piston ring end gaps, gas also flows through the side-clearance between piston ring and flank groove [6][7][8][9][10]. In this paper, a quasi-Rayleigh narrow-channel gas flow model is proposed by consideration of temperature gradient along radial direction of piston assembly. Piston ring friction force is estimated by a test-rig verified mixed lubrication model [11]. Numerical simulation shows that piston ring friction force and ring axial motion are sensitive to inter-ring gas flow model. The instantaneous indicated mean effective pressure (IMEP) method was adopted here to measure the piston friction during motoring condition. Experimental and numerical results indicate that top ring could contribute about 10% of total power cylinder friction loss.

A numerical model has been developed to investigate the effects of surface modifications on the lubrication condition and frictional loss at the interface between a piston ring and cylinder liner. The effects of boundary and mixed lubrication conditions were included through the use of a fully deterministic mixed lubrication model, which provides detailed information of the rough contact zone throughout the stroke. The effects of non-Gaussian surface characteristics (e.g. skewness) on the cycle-average frictional performance are discussed. Surface modifications in the form of circular profile dimples were added to the cylinder liner and their effects were investigated. The modified cylinder liner was shown to reduce the cycle-average coefficient of friction by 55–65%, while total energy loss per cycle was reduced by 20–40%.

This paper presents enhancements to a previously developed mixed-lubrication ring-pack model that has been used extensively in the automotive industry in predicting piston-ring/liner oil film thickness, friction and oil-transport processes along the liner. The previous model considers three lubrication regimes, shear thinning of the lubricant, and the unsteady wetting conditions of the rings at the leading and trailing edges. The model incorporates the effects of surface roughness by using Patir and Cheng’s average flow model and the Greenwood and Tripp statistical asperity contact model, assuming a Gaussian distribution of surface roughness. However, as a result of the methods used to machine a cylinder liner and the wear-in process observed in engines, the cylinder liner finish is highly non-Gaussian. The purpose of this current study is to understand the effects of additional surface parameters other than Gaussian root-mean-square surface roughness on piston ring-pack friction in the context of a natural gas reciprocating engine ring/liner interface. In general, the surface roughness of a cylinder liner is negatively skewed. Applying similar methodology published in the literature, a wide variety of non-Gaussian probability density functions were generated in terms of the skewness of the cylinder liner surface. These probability density functions were implemented into the Greenwood and Tripp asperity contact model, and subsequently into the traditional MIT ring-pack friction model. The effects of surface skewness on flow were approximated using Gaussian flow factors and a simple truncation method. The enhanced model was studied in conjunction with results from an existing ring-pack dynamic model that provided the dynamic twists of the rings relative to the liner and inter-ring pressures. In this manner, a detailed analysis of the effects of engineered cylinder liner finish on reducing friction losses was performed.

Abstract This paper presents the static analysis of general spherical nR simple open or closed kinematic chains with joint friction. The internal loading on each link is found to consist of a bending moment and a torsional moment. The goal of this analysis is to determine these moments which are then used in designing the link. The moment and force balance equations for each link yields a linear system of equations which define the internal moments of the mechanism and the output torque on the driven crank for a given input torque. A Coulomb model of joint friction is used to determine the friction torque along the axis of a joint. The joint friction model requires an iterative solution. The purpose of this algorithm is to provide a means of computing the complete internal and external loading on the members of spherical chains while including frictional effects in order to facilitate the design of a functional spherical mechanisms.

Friction from the power cylinder represents a significant contribution to the total mechanical losses in internal combustion engines. A reduction in piston ring friction would therefore result in higher efficiency, lower fuel consumption, and reduced emissions. In this study, models incorporating piston ring dynamics and piston secondary motion with elastic skirt deformation were applied to a Waukesha natural gas power generation engine to identify the main contributors to friction within the piston and ring pack system. Based on model predictions, specific areas for friction reduction were targeted and low-friction design strategies were devised. The most significant contributors to friction were identified as the top ring, the oil control ring, and the piston skirt. Model predictions indicated that the top ring friction could be reduced by implementing a skewed barrel profile design or an upward piston groove tilt design, and oil control ring friction could be reduced by decreasing ring tension. Piston design parameters such as skirt profile, piston-to-liner clearance, and piston surface characteristics were found to have significant potential for the reduction of piston skirt friction. Designs were also developed to mitigate any adverse effects that were predicted to occur as a result of implementation of the low-friction design strategies. Specifically, an increase in wear was predicted to occur with the upward piston groove tilt design, which was eliminated by the introduction of a positive static twist on the top ring. The increase in oil consumption resulting form the reduction in the oil control ring tension was mitigated by the introduction of a negative static twist on the second ring. Overall, the low-friction design strategies were predicted to have potential to reduce piston ring friction by 35% and piston friction by up to 50%. This would translate to an improvement in brake thermal efficiency of up to 2%, which would result in a significant improvement in fuel economy and a substantial reduction in emissions over the life of the engine.

Abstract An attempt was made as part of this work to acquire on-engine measurements to identify how closely current Finite Element Analysis (FEA) models replicate actual on-engine exhaust manifold behavior. Further correlation study with FEA models was performed to understand and eliminate the gaps to improve the overall FEA process. Dry cast iron exhaust manifolds experience thermo-mechanical fatigue (TMF) during engine operation. This is one of the critical failure modes. Literature is available to perform TMF assessment of exhaust manifold e.g. [1–6]. However, it is difficult to accurately predict TMF life of exhaust manifold in FEA due to dependency on multiple factors such as non-linear material behavior [3], temperature dependent material behavior, oxidation effect, creep effect, accuracy in prediction of metal temperatures and joint friction effects. Typically, non-linear material models, creep effects and oxidation effects are accounted by advanced fatigue processing software. Non-linear material models account for material and for temperature dependent non-linearity [4]. These non-linear material model and fatigue parameters are often developed using uniaxial specimen level testing. These doesn’t account for all the complexity during on-engine test due to factors such as friction and bolt loads that can influence manifold behavior. FEA processes for exhaust manifolds are seldom calibrated with on-engine measurements due to the complexity of obtaining these measurements in an environment that has severe temperatures and vibrations. The correlation study highlighted that exhaust manifold was over constrained by excessive clamping in FEA. This raised question on the gasket coefficient of friction (COF) and working preloads. These settings were investigated to get better correlation. Using reduced COF and non-linear material model for manifold capscrews, helped to achieve better correlation. Replacing material properties of manifold capscrews with nonlinear data provided capability to simulate localized yielding of capscrews and hence the corresponding load loss. Using these new settings for few other case studies also showed improvement in correlation of manifold warpage and thermal fatigue life prediction. Outcome of this work was a refined FEA approach which showed better FEA to Test correlation for exhaust manifold subject to thermal loading.

Recent concerns regarding global warming and energy security have accelerated research and developmental efforts to produce biofuels from agricultural and forestry residues, and energy crops. Anaerobic digestion is a promising process for producing biogas-biofuel from biomass feedstocks. However, there is a need for new reactor designs and operating considerations to process fibrous biomass feedstocks. In this research project, the multiphase flow behavior of biomass particles was investigated. The objective was accomplished through both simulation and experimentation. The simulations included both particle-level and bulk flow simulations. Successful computational fluid dynamics (CFD) simulation of multiphase flow in the digester is dependent on the accuracy of constitutive models which describe (1) the particle phase stress due to particle interactions, (2) the particle phase dissipation due to inelastic interactions between particles and (3) the drag force between the fibres and the digester fluid. Discrete Element Method (DEM) simulations of Homogeneous Cooling Systems (HCS) were used to develop a particle phase dissipation rate model for non-spherical particle systems that was incorporated in a two-fluid CFDmultiphase flow model framework. Two types of frictionless, elongated particle models were compared in the HCS simulations: glued-sphere and true cylinder. A new model for drag for elongated fibres was developed which depends on Reynolds number, solids fraction, and fibre aspect ratio. Schulze shear test results could be used to calibrate particle-particle friction for DEM simulations. Several experimental measurements were taken for biomass particles like olive pulp, orange peels, wheat straw, semolina, and wheat grains. Using a compression tester, the breakage force, breakage energy, yield force, elastic stiffness and Young’s modulus were measured. Measurements were made in a shear tester to determine unconfined yield stress, major principal stress, effective angle of internal friction and internal friction angle. A liquid fludized bed system was used to determine critical velocity of fluidization for these materials. Transport measurements for pneumatic conveying were also assessed. Anaerobic digestion experiments were conducted using orange peel waste, olive pulp and wheat straw. Orange peel waste and olive pulp could be anaerobically digested to produce high methane yields. Wheat straw was not digestible. In a packed bed reactor, anaerobic digestion was not initiated above bulk densities of 100 kg/m³ for peel waste and 75 kg/m³ for olive pulp. Interestingly, after the digestion has been initiated and balanced methanogenesis established, the decomposing biomass could be packed to higher densities and successfully digested. These observations provided useful insights for high throughput reactor designs. Another outcome from this project was the development of low cost devices to measure methane content of biogas for off-line (US$37), field (US$50), and online (US$107) applications.

Vibration compaction is the most effective way of compacting coarse-grained materials. The effects of vibration frequency and amplitude on the compaction density of different backfill materials commonly used by INDOT (No. 4 natural sand, No. 24 stone sand, and No. 5, No. 8, No. 43 aggregates) were studied in this research. The test materials were characterized based on the particle sizes and morphology parameters using digital image analysis technique. Small-scale laboratory compaction tests were carried out with variable frequency and amplitude of vibrations using vibratory hammer and vibratory table. The results show an increase in density with the increase in amplitude and frequency of vibration. However, the increase in density with the increase in amplitude of vibration is more pronounced for the coarse aggregates than for the sands. A comparison of the maximum dry densities of different test materials shows that the dry densities obtained after compaction using the vibratory hammer are greater than those obtained after compaction using the vibratory table when both tools were used at the highest amplitude and frequency of vibration available. Large-scale vibratory roller compaction tests were performed in the field for No. 30 backfill soil to observe the effect of vibration frequency and number of passes on the compaction density. Accelerometer sensors were attached to the roller drum (Caterpillar, model CS56B) to measure the frequency of vibration for the two different vibration settings available to the roller. For this roller and soil tested, the results show that the higher vibration setting is more effective. Direct shear tests and direct interface shear tests were performed to study the impact of particle characteristics of the coarse-grained backfill materials on interface shear resistance. The more angular the particles, the greater the shear resistance measured in the direct shear tests. A unique relationship was found between the normalized surface roughness and the ratio of critical-state interface friction angle between sand-gravel mixture with steel to the internal critical-state friction angle of the sand-gravel mixture.

The paper considers a New Keynesian framework in which agents form expectations based on a combination of autoregressive mis-specified forecasts and myopia. The proposed expectations formation process is shown to be consistent with all three empirical facts on consensus inflation forecasts. However, while mis-specified forecasts can be both sufficient and necessary to match all three facts, myopia alone is neither. The paper then derives the general equilibrium solution consistent with the proposed expectations formation process and estimates the model with likelihood-based Bayesian methods, yielding three novel results: (i) macroeconomic data strongly prefer a combination of autoregressive mis-specified forecasting rules - of the VAR(1) or AR(1) type - and myopia over other alternatives; (ii) no strong evidence is found in favor of VAR(1) forecasts over simple AR(1) rules; and (iii) frictions such as habit in consumption, which are typically necessary for models with full-information rational expectations, are significantly less important, because the proposed expectations generate substantial internal persistence and amplification to exogenous shocks. Simulated inflation expectations data from the estimated general equilibrium model reflect the three empirical facts on forecasting data.