Surface texturing for enhanced tribological performance

Surface texturing for enhanced tribological performanc

Psychoacoustic analysis of high frequency elasto-acoustic emissions from hollow driveshaft tubes

Lightly damped non-linear systems such as vehicular drivelines undergo a plethora of Noise, Vibration and Harshness (NVH) problems. The clonk phenomenon is one concern which occurs as the result of impulsive torque input in the form of sudden clutch actuation or throttle tip-in and back-out. The resulting impact of meshing gear pairs propagate structural waves down the driveline. With lightly damped thin-walled tubes having high modal density, elasto-acoustic coupling occurs. High frequency noise emission is of metallic nature and quite disconcerting to vehicle occupants as well as passers-by. It is perceived as structural failure and/or poor-quality build. Therefore, the occurrence of the phenomenon is a concern to vehicle manufacturers and progressively constitutes a warranty concern. This paper investigates the clonk phenomenon through use of a long-wheel base rear drive light truck test rig. The investigation uses psychoacoustic metrics to establish the severity of clonk noise in different maneuvers. This is an attempt to quantify the effect of transient clonk event which is usually ascertained through subjective evaluation ratings in a customer/jury clinic in industry. Alternatively, detailed numerical analysis is carried out with parametric studies to quantify different clonk events, a very time consuming approach which is not usually correlated with occupants’ perception of the event. Therefore, the experimental NVH monitoring-psycho-acoustic approach is new for the case of clonk and not hitherto reported in literature. The study corroborates the results and conclusions of previous work, pointing to the loudness and sharpness of high frequency short-lived “metallic” response, which is attuned to human aural perception. The psychoacoustic analysis has shown this to be as the result of short duration hard impact (accelerative period). This hard impact duration accounts for the bulk loudness and sharpness of the overall event. Therefore, effective palliation should focus on the attenuation of particular frequency bands, which carry the main contribution to loudness and sharpness

Integrated thermal and dynamic analysis of dry automotive clutch linings

Optimum operation of clutch systems is dictated by their dynamic as well as thermal performance. Both of these aspects are closely related to the interfacial frictional characteristics of the clutch lining material, which also affects the noise, vibration and harshness response of the entire vehicular powertrain system. Severe operating conditions such as interfacial clutch slip and increased contact pressures occur during clutch engagement, leading to generation of contact heat, and higher clutch system temperature. Therefore, any undesired oscillatory responses, generated during clutch engagement, such as take-up judder phenomenon can exacerbate generated heat due to stick-slip motion. The paper presents an integrated thermal, and 9-DOF dynamic model of a rear wheel drive light truck powertrain system. The model also includes experimentally measured clutch lining frictional variations with interfacial slip speed, non-linear contact pressure profile and generated surface flash temperature. It is shown that severe torsional oscillations known as take-up judder lead to an increased overall clutch temperature. It also shows that ageing of clutch lining material alters its dynamic and thermal performance

Lubricated loaded tooth contact analysis and non-newtonian thermoelastohydrodynamics of high-performance spur gear transmission systems

Energy efficiency and functional reliability are the two key requirements in the design of high-performance transmissions. Therefore, a representative analysis replicating real operating conditions is essential. This paper presents the thermoelastohydrodynamic lubrication (TEHL) of meshing spur gear teeth of high-performance racing transmission systems, where high generated contact pressures and lubricant shear lead to non-Newtonian traction. The determination of the input contact geometry of meshing pairs as well as contact kinematics are essential steps for representative TEHL. These are incorporated in the current analysis through the use of Lubricated Loaded Tooth Contact Analysis (LLTCA), which is far more realistic than the traditional Tooth Contact Analysis (TCA). In addition, the effects of lubricant and flash surface temperature rise of contacting pairs, leading to the thermal thinning of lubricant, are taken into account using a thermal network model. Furthermore, high-speed contact kinematics lead to shear thinning of the lubricant and reduce the film thickness under non-Newtonian traction. This comprehensive approach based on established TEHL analysis, particularly including the effect of LLTCA on the TEHL of spur gears, has not hitherto been reported in literature

Numerical heat transfer modelling of staggered array impinging jets

A numerical study of flow field and heat transfer rate in external flow of a novel heat exchanger (Anglia Ruskin University, 2001) was conducted. The design comprises of confined impinging jets from a staggered bundle of tubes in which the fluid flows in an opposite staggered arrangement array after impingement. The RNG k-ε model and enhanced wall treatment near wall turbulence modelling was applied to model a three-dimensional computational domain. The accuracy of the model was validated in two- and three-dimensional cases for single impinging jets with available experimental results. The arrangement of the staggered array was fixed Sn/D=2.1 and Sp/D=1.6 where Sn and Sp are the distances between tubes transverse and parallel to fluid flow respectively and D was the hydraulic diameter of tubes. The dimensionless tubes to impinging surface distance (H/D) were in the range of 0.2, 0.5, 1.0, and 2.0 and the Reynolds number based on the tubes’ hydraulic diameter and average fluid velocity at the exit of tubes in the range of 1000, 5000, and 20000 were studied. The global heat transfer rate on both impinging and confinement plates increased with decreasing of H/D and increasing of Reynolds number; however, the slope of increasing Reynolds number was sharper in low H/Ds. The friction factor increased with a decreasing H/D and an increasing of the Reynolds number. The local Nusselt number was studied on both impinging and confinement plates. The temperature contours and velocity vectors are also presented. Keywords: bundle of impinging jets, jet to jet interaction, RNG k-ε, enhanced wall treatment

Lubricant-surface system characterisation for high performance transmissions

Lubricant-surface system characterisation for high performance transmission

The Effect of Hemispheric Dominance on Learning Vocabulary Strategies among Iranian EFL Learners

Vocabulary is one of the skills that students need for success in their studies and as some teachers believe, the students have different vocabulary skills and they use different strategies when they try to recall new vocabularies. The purpose of the study is to investigate the variable impact of two types of vocabulary instruction including context clues, and word parts on adult students' competence in the first place and studying the relationship between the effect of left or right hemispheric dominance on teaching vocabulary leaning strategies. Ninety students from six intact classes were selected for the purpose of this study. The participants consist of female Iranian EFL learners at intermediate level. Each intact class was randomly selected as an experimental group and a control group. Their level of English proficiency was determined on the basis of their scores on the TOEFL proficiency test. After hemispheric dominance questionnaire was administered, the learners in experimental group were divided into right-hemisphere and left-hemisphere group. The experimental group were taught context clue and word part vocabulary strategy while it was not the case for the control group. The results showed that teaching vocabulary strategies play a significant role in developing the level of the learners’ vocabulary knowledge. Furthermore, left-dominant learners had better performance in learning vocabulary after they were taught vocabulary strategies, in comparison to right-dominant learners. As a conclusion, it can be said that investigating hemispheric dominance and learning styles from the aspects of curriculum, teaching process and teachers will contribute significantly to the Iranian Education

The Effect of Hemispheric Dominance on Learning Vocabulary Strategies among Iranian EFL Learners

Vocabulary is one of the skills that students need for success in their studies and as some teachers believe, the students have different vocabulary skills and they use different strategies when they try to recall new vocabularies. The purpose of the study is to investigate the variable impact of two types of vocabulary instruction including context clues, and word parts on adult students' competence in the first place and studying the relationship between the effect of left or right hemispheric dominance on teaching vocabulary leaning strategies. Ninety students from six intact classes were selected for the purpose of this study. The participants consist of female Iranian EFL learners at intermediate level. Each intact class was randomly selected as an experimental group and a control group. Their level of English proficiency was determined on the basis of their scores on the TOEFL proficiency test. After hemispheric dominance questionnaire was administered, the learners in experimental group were divided into right-hemisphere and left-hemisphere group. The experimental group were taught context clue and word part vocabulary strategy while it was not the case for the control group. The results showed that teaching vocabulary strategies play a significant role in developing the level of the learners’ vocabulary knowledge. Furthermore, left-dominant learners had better performance in learning vocabulary after they were taught vocabulary strategies, in comparison to right-dominant learners. As a conclusion, it can be said that investigating hemispheric dominance and learning styles from the aspects of curriculum, teaching process and teachers will contribute significantly to the Iranian Education

Lubricant-surface system characterisation for high performance transmissions abstract

Lubricant-surface system characterisation for high performance transmissions abstrac