Wear transitions in a wear coefficient model

The frictional-work wear model has been used popularly for the prediction of wear phenomena such as rail corrugation. The accuracy of such models depends on the value chosen for the empirical wear coefficient in this wear model. Experimental results have widely shown that this wear coefficient is strongly dependent upon the type of wear process involved. The wear coefficient in the frictional-work wear model under two-disc contact and dry friction conditions proposed is a multi-step function of the friction power density corresponding to three types of wear. However, at present there is no clear means of predicting the transitions between wear types. This paper investigates wear transitions between the wear types are predicted using analytical models based on the wear mechanics involved

A method of predicting variable speed rail corrugation growth using standard statistical moments

Wear-type rail corrugation is a significant problem in the railway transport industry. Some recent work has suggested that speed control can be used as an effective tool to minimize the rate of corrugation growth. This has brought about the need to model corrugation growth under variable passing speed. Variable speed rail corrugation growth modelling normally consists of either numerical simulation of a sequence of varied speed wheel passes or direct integration of a probabilistic passing speed distribution function; both of which are computationally expensive. This paper investigates the use of the statistical moments of the speed probability density function to greatly improve the computational speed of variable speed corrugation growth models and compares results of changing standard deviation and skewness to numerical integration models. It also identifies the effects of individual statistical moments on corrugation growth to provide better insight into control methods. The new modelling method correlated well with the numerical integration models for small standard deviations in speed (less than 10%) and highlighted a need to consider kurtosis in predicting the performance of speed control based corrugation mitigation schemes. For larger standard deviations in speed, higher than 4th order effects need to be considered

Probabilistic Prediction of Wheel Squeal under Field Humidity Variation

This research examines the effect of changes in coefficient of friction due to humidity on the likelihood of wheel squeal events occurring in practice. Theoretical mechanics based modeling is developed and compared to a database of field measurements of wheel squeal occurrences at a field site in Australia. In particular, a relatively simplified model of wheel squeal is developed based on existing literature but notably incorporates probabilistic mechanics to account for field parameter variations and hence allows direct comparisons with field data. The model is then tuned to field site conditions at which over 2 million wheel passes have been monitored for a period of 3 years. The comparison indicates that field measured trends for the effect of relative humidity on coefficient of friction and hence the occurrences of wheel squeal have been able to be predicted using the very efficient model

Implicit finite element study of non-steady effects in cold roll forming

The ability of ABAQUS Standard to obtain a non-steady implicit solution to the problem of cold roll forming a channel section is investigated. A solution can be found with careful selection of parameters, but solutions are unacceptably slow for commercial use. The implicit solutions show buckling on the first pass that does not develop into an edge wave, in contrast to a published explicit solution. Faster solutions to steady rolling can be obtained using ALE models that permit convection of stress in the direction of rolling

Longwall shearer cutting force estimation

Longwall mining is an underground coal mining method that is widely used. A shearer traverses the coal panel to cut coal that falls to a conveyor. Operation of the longwall can benefit from knowledge of the cutting forces at the coal/shearer interface, particularly in detecting pick failures and to determine when the shearer may be cutting outside of the coal seam. It is not possible to reliably measure the cutting forces directly. This paper develops a method to estimate the cutting forces from indirect measurements that are practical to make. The structure of the estimator is an extended Kalman filter with augmented states whose associated dynamics encode the character of the cutting forces. The methodology is demonstrated using a simulation of a longwall shearer and the results suggest this is a viable approach for estimating the cutting forces. The contributions of the paper are a formulation of the problem that includes: the development of a dynamic model of the longwall shearer that is suitable for forcing input estimation, the identification of practicable measurements that could be made for implementation and, by numerical simulation, verification of the efficacy of the approach. Inter alia, the paper illustrates the importance of considering the internal model principle of control theory when designing an augmented-state Kalman filter for input estimation

The effects of passing speed distribution on rail corrugation growth rate

The transportation phenomenon known as wear-type rail corrugation is a significant problem in railway engineering, which manifests as a periodic wear pattern developing on the surface of the wheel and rail with use. Some field studies and recent theoretical results by the current authors have suggested that uniformity in pass speed causes an increase in corrugation growth rate. This paper presents the predicted change in corrugation growth rate and dominant wavelengths with change in passing speed distribution, based on state of the art cornering growth modelling techniques

The effect of non-uniform train speed distribution on rail corrugation growth in curves/corners

Rail corrugation is a significant problem in railway engineering, manifesting as an oscillatory wear pattern on the rail head. These profile variations induce unwanted vibrations, excessive noise and other associated problems. Constant train speed for consecutive train passes has been shown to accelerate corrugation growth while widening the probabilistic speed distribution can be shown to mitigate the phenomena. This paper extends this research by investigating the effect of non-uniformity (or asymmetry) in speed distribution on corrugation growth on curved track/corners. To this end, an efficient corrugation growth prediction model is further developed to include quasistatic bogie cornering dynamics and investigated under non-uniform speed distribution conditions. The results indicate that under typical cornering conditions, the rate of corrugation growth is increased (or decreased) when the mean or skewness of the distributed set of passing speeds is biased to higher (or lower) speeds. In particular, for the conditions investigated, controlling (or not controlling) skewness could achieve a further 12% (or −20%) in corrugation growth rate reduction from a nominal 41% reduction due to symmetric speed variation. Hence, non-uniform speed distribution could cause up to a 50% reduction in predicted effectiveness of widened speed distribution control to reduce corrugation growth rate

The Ionization Fraction in Dense Molecular Gas II: Massive Cores

We present an observational and theoretical study of the ionization fraction in several massive cores located in regions that are currently forming stellar clusters. Maps of the emission from the J = 1-> O transitions of C18O, DCO+, N2H+, and H13CO+, as well as the J = 2 -> 1 and J = 3 -> 2 transitions of CS, were obtained for each core. Core densities are determined via a large velocity gradient analysis with values typically 10^5 cm^-3. With the use of observations to constrain variables in the chemical calculations we derive electron fractions for our overall sample of 5 cores directly associated with star formation and 2 apparently starless cores. The electron abundances are found to lie within a small range, -6.9 < log10(x_e) < -7.3, and are consistent with previous work. We find no difference in the amount of ionization fraction between cores with and without associated star formation activity, nor is any difference found in electron abundances between the edge and center of the emission region. Thus our models are in agreement with the standard picture of cosmic rays as the primary source of ionization for molecular ions. With the addition of previously determined electron abundances for low mass cores, and even more massive cores associated with O and B clusters, we systematically examine the ionization fraction as a function of star formation activity. This analysis demonstrates that the most massive sources stand out as having the lowest electron abundances (x_e < 10^-8).Comment: 35 pages (8 figures), using aaspp4.sty, to be published in Astrophysical Journa

A review: Aedes-borne arboviral infections, controls and Wolbachia-based strategies

Arthropod-borne viruses (Arboviruses) continue to generate significant health and economic burdens for people living in endemic regions. Of these viruses, some of the most important (e.g., dengue, Zika, chikungunya, and yellow fever virus), are transmitted mainly by Aedes mosquitoes. Over the years, viral infection control has targeted vector population reduction and inhibition of arboviral replication and transmission. This control includes the vector control methods which are classified into chemical, environmental, and biological methods. Some of these control methods may be largely experimental (both field and laboratory investigations) or widely practised. Perceptively, one of the biological methods of vector control, in particular, Wolbachia-based control, shows a promising control strategy for eradicating Aedes-borne arboviruses. This can either be through the artificial introduction of Wolbachia, a naturally present bacterium that impedes viral growth in mosquitoes into heterologous Aedes aegypti mosquito vectors (vectors that are not natural hosts of Wolbachia) thereby limiting arboviral transmission or via Aedes albopictus mosquitoes, which naturally harbour Wolbachia infection. These strategies are potentially undermined by the tendency of mosquitoes to lose Wolbachia infection in unfavourable weather conditions (e.g., high temperature) and the inhibitory competitive dynamics among co-circulating Wolbachia strains. The main objective of this review was to critically appraise published articles on vector control strategies and specifically highlight the use of Wolbachia-based control to suppress vector population growth or disrupt viral transmission. We retrieved studies on the control strategies for arboviral transmissions via arthropod vectors and discussed the use of Wolbachia control strategies for eradicating arboviral diseases to identify literature gaps that will be instrumental in developing models to estimate the impact of these control strategies and, in essence, the use of different Wolbachia strains and feature