Nirmal Kumar Mandal

Vibration power flow: A critical review

Prediction and measurement of vibration power flow in structures are both important for locating vibration sources and sinks and for confirming vibration propagating paths. From the point of view of noise and vibration control in industries, the method is very important for practical reasons. Consequently, it is essential to address the state of the art of the method, its effectiveness and limitations. Vibration power flow methods or structural intensity techniques are reviewed and compared in this paper. There is a particular focus on flexural waves, but in-plane waves are also considered. Both experimental and numerical methods are put forward. Likely future trends of structural intensity are also discussed. The anticipated areas of interest include complex structures such as build-up edges, stiffeners, and modified geometry of beams and plates.

Development of a unified railway track stability management tool to enhance track safety

Track buckling is a serious problem for railways. High longitudinal rail stresses contribute to problems such as track buckling, rail joint failure, rail breakage and failure of turnouts. The direct and indirect costs of track buckling problems are very high. The influences of rail temperature, stress-free temperature (SFT) and lateral misalignment of track on track buckling need comprehensive investigation. In this paper, an experimental design comprising strain gauges, thermocouples and rail stress sensors has been implemented on the Queensland Rail heavy haul 60 kg/m rail network. A new creep measurement technique using internal rail stress has been developed. The changes in rail neutral temperature due to the variation of actual rail temperature and the occurrence of rail creep in straight and curved track is quantified. Modes of differences of SFT in the two rails at a location, and of SFT in straight track and in curved track are discussed. The relationship of SFT to rail temperature is also presented. Daily variation in rail temperature due to ambient air temperature is presented. Field trials showed that SFT can vary by 2–3 ℃ during the day. Based on this finding and the derivation of an equation for change of SFT, an improvement in utilising rail creep measurements for assessing track condition has resulted. This finding suggests that it is possible to determine the SFT throughout a day rather than just a single SFT value. This paper also presents a simple track stability management tool that is based on two major parameters, namely rail stress and track resistance. Each parameter in the tool has been given three levels of value to determine the required preventive measures. Overall, the tool decides the need for speed restriction during hot weather based on the quantified parameters from the field trials and rail standards.

Prediction of Structure-Borne Sound in Orthotropic Plates for Far-Field Conditions:

Structural intensity method is used to formulate vibration power flow model in naturally orthotropic plates in the frequency domain for far-field conditions considering bending waves. Dimensionless parameters are used in classical orthotropic plate equations to get this power. Techniques of Fourier transform and finite difference approximation are used in the formulation. Shear force components of vibration power transmission in x-direction and y-direction are obtained separately. Total power is obtained from the idea of far-field conditions. Cross-spectral density functions of field signal are used to facilitate the estimation of power transmission. Structural intensity is formulated, which is similar to that of the conventional two-transducer method. A transducer array of two points is required to get an intensity vector in one direction of a point in the plates. A new bending wave number and a modified Laplace operator are also proposed.

Ratchetting damage of railhead material of gapped rail joints with reference to free rail end effects

Free ends of insulated rail joints occur because gaps between the rails and endposts can be created due to pull-apart problems as the rails contract longitudinally in winter and by degradation of railhead material. Dynamic behaviour of gapped rail joints changes adversely compared to that of insulated rail joints. Thus, material degradation and damage of gapped rail joint components such as rail ends, joint bars, etc. are accelerated. Only limited literatures are available addressing the free end of rail effects at rail joints, targeting stress and pressure distributions in the vicinity of the rail joints. To understand clearly the material degradation and delamination process of gapped rail joints, a thorough analysis of failure of both insulated rail joints and gapped rail joints and subsequent damage of the railhead material is necessary to improve the service life of these joints. A new three-dimensional finite element analysis is carried out in this paper to assess damage to railhead material when gapped rail joints form. Both narrow (5 mm) and wide (10 mm) gaps are considered, using a peak vertical pressure load of 2500 MPa applied cyclically at one rail end, forming vertical impacts. Stress distributions and plastic deformations in the vicinity of gapped rail joints are quantified using finite element analysis data and compared with that of the insulated rail joints to show the effects of free rail ends. Residual stress and strain distributions indicate the damage to the railhead material. Equivalent plastic strain (PEEQ) quantifies the progressive damage to the railhead material at the rail ends. The free end of rail effects can be further illustrated by comparing PEEQ for insulated rail joints and gapped rail joints. The railhead material of 5 and 10 mm gapped rail joints is more sensitive to permanent deformation compared to that of the corresponding insulated rail joints. Therefore, free rail end joints pose an increased potential threat to rail operations in relation to crack initiation, damage and premature failure of railhead material.

Finite element analysis of the mechanical behaviour of insulated rail joints due to impact loadings

Insulated rail joints (IRJs) are safety-critical components in the signalling system of rail corridors. They are subjected to dynamic loads generated by heavy rolling-stock/track- system interactions and degrade faster than the other components of the rail track. Degraded IRJs diminish the reliability of the signalling system, thus posing a serious threat to the safety of rail operations. Therefore, there is a pressing need to closely examine the failure mechanisms of the end posts made of insulated material and inserted into the discontinuity in the rail at IRJs with a view to improving their service life, reliability and efficiency. Only a limited literature is available that examines different materials for IRJ end posts, and these primarily focus on contact pressure and contact stress distributions in the vicinity of the end post, disregarding the damage to the rail ends and end post materials. In this paper, a detailed three-dimensional finite element analysis procedure is carried out to quantify plastic deformation and material damage to the end post and railhead materials of IRJs due to a wheel load above that of the shakedown limit of rail steel. A modified Hertzian contact pressure distribution is considered in this simulation. A 5 mm thickness of an end post is considered at the discontinuity in the rail, which is required to form the six-bolt IRJ. Three popular IRJ end post materials are considered in this study: fibreglass, polyhexamethylene adipamide, and polytetrafluoroethylene. A total of 2000 cycles of a 174 kN dynamic wheel load (in pressure format over the wheel/rail contact patch) are applied on the top of the rail’s surface in the vicinity of the IRJ. Equivalent plastic deformations along with vertical and longitudinal plastic strains for unloaded conditions are presented. The strain plots depict damage of end post materials and ratchetting failure of rail ends. The ratchetting failure modes follow the established trend of decay in ratchetting rate in successive wheel load cycles. Comparisons of strain and stress on the railhead surface and in the railhead sub-surface considering all three different end post materials are put forward. Out of the three end post materials, fibreglass is the optimal material considering the ratchetting mode for the damage of the railhead material.

Structure-Borne Power Transmission in Thin Naturally Orthotropic Plates: General Case

The structural intensity technique is usually used to estimate vibration power flow in structures. This method is used to determine vibration power flow in thin naturally orthotropic plates. The bending wave is considered to find general vibration power transmission in the frequency domain that is not approximated by far field conditions. This intensity formulation defines power flow per unit width of the plates (W m−1) similar to that of the conventional idea. Power flow estimation is formulated using cross-spectra of field signals, facilitating the use of a fast Fourier transform analyzer.

Student satisfaction – What it means to teaching and learning of undergraduate engineering units

This paper describes teaching enhancements the author used to improve student satisfaction ratings in three higher year undergraduate Mechanical Engineering units. Improvements to student satisfaction and feedback rates were obtained by applying Central Queensland University’s seven principles of good teaching and the author’s new innovative teaching approach, called the ‘4-point teaching and learning strategy’ to make red units green and good units excellent. The research question is to analyse how effective is the author’s 4-point teaching and learning strategy to student satisfaction and their learning journey. Student satisfaction ratings and attrition rates, as well as student grades are compared over a few years to identify trends. These approaches were presented to other engineering colleagues, some of whom employed them with an overall improvement in student learning being noticed in recent terms. This paper deals with the Scholarship of Teaching where an instructor uses a systematic approach and a rational framework employing the new 4-point strategy to make changes to unit delivery to improve student learning and satisfaction, as well as to reduce attrition.

Importance of student feedback in improving mechanical engineering courses

The purpose of this study is to review and analyse the importance of responding to feedback from students attending my courses on their learning outcomes and their satisfaction with various elements of my courses: one traditional course titled Solid Mechanics and Computational Analysis and a learner-centred course titled Fluid and Electrical Drive Systems. Central Queensland University utilises online evaluations for each course in each term of the year through a student experience survey. With careful consideration and evaluation of these data using a new student feedback evaluation framework developed by the author, some appropriate teaching interventions are developed and implemented during each term. The research question is to analyse the effectiveness of this framework by collecting the same data through subsequent student experience surveys. The student experience survey data for my courses showed that student satisfaction was increasing gradually for best managed courses, indicating that proactive implementation of appropriate responses to student feedback on their learning journey is effective in improving both student satisfaction and learning.

Emerging rail vehicle design and simulation in train operational environment

Design and operation of rail vehicles are multidisciplinary and multidimensional tasks that require a wide range of knowledge. Conventional rail vehicle design and numerical assessment procedures separate the objective vehicle from its train operational environment. Meanwhile, conventional train operational studies could not consider the specific details of rail vehicle designs. These limitations are mainly due to the high cost of train operational tests and challenges from complex modelling and time-consuming simulations. The necessity of considering the train operational environment in the rail vehicle design process and computer simulations is evident from industry reports and academic publications. Advancements in computing techniques and simulation methods now allow rail vehicle design and simulations to take account of various characteristics of the train operational environment. These advancements also allow train operational simulations to consider the details of rail vehicle designs. These details can be modelled in mechanical systems, mechatronic systems and electrical systems. The emerging design procedure implies both vehicle details and train operational environment. This special issue called for relevant ideas and studies from experts in academia and industry. Six papers are presented in this special issue. Bosomworth et al. used parallel computing techniques to handle large-scale simulation tasks, using which to investigate the influence of train dynamics on rail foot heat transfer. Both Bosso et al. and Wang et al. studied the interaction between vehicles and infrastructures; the former was for railway vehicles while the latter was for maglev vehicles. Two papers were presented for to topic of Longitudinal Train Dynamics. The one by Oprea was about train starting while the one by Wei et al. was about train braking. Zou et al. studied the influence of wheel diameter differences on locomotive wheel–rail interface in train operational environment. The guest editors would like to thank all publishing authors for their time and knowledge contributions to this special issue. We also thank the authors whose papers were not accepted for their time spent on preparing the manuscripts. Acknowledgement is also made to the chief editors of the journal for their support and guidance during the organisation of this special issue.

Far-Field Power Transmissions in Orthotropic Plates: A New Approach

The structural intensity (SI) technique is an essential tool for locating and ranking vibration sources and sinks on structures. It can quantify vibration fields by plotting a vector map of energy transmission on the structures. In this paper, a different strategy, changing coordinate systems of plate equations, is used to develop an intensity equation from shear force components in both x and y directions. The formulation is carried out in the frequency domain considering flexural waves. Orthotropic plate theory, far-field conditions, Fourier transform, and finite difference approximation are considered. The same intensity definition is obtained using this different strategy. A dual-channel FFT analyser is essential for data acquisition to get an intensity vector in a particular direction for far-field conditions.