abstract / Mechanical Engineering / Master / Master of Philosophy

M.Ing. / Sound pressure levels exceeding acceptable limits are being generated by trains travelling on the 1000 m radius curved railway line past the town of Elands Bay. Unacceptable sound levels are attributed mainly to top of rail wheel squeal. Top of rail wheel squeal belongs to the family of selfinduced vibrations and originates from frictional instability in curves between the wheel and the rail under predominantly saturated lateral creep conditions. In small radius curves, saturated lateral creep conditions occur due to the steering of railway wheelsets with large angles of attack. Given the large curve radius and the utilisation of self-steering bogies on the Sishen-Saldanha Iron Ore railway line, curve squeal is a highly unexpected result for the 1000 m radius curved railway line. This is because curving of bogies in large radius curves are achieved without high wheelset angles of attack leading to saturated creep conditions. An experimental and analytical investigation was carried out to identify the mechanisms influencing the generation of wheel squeal in large radius curves. Simultaneous measurement of sound pressure and lateral wheel-rail forces were made during regular train service in one of the two 1000 m radius curves at Elands Bay to characterise the bogie curving behaviour for tonal noise due to wheel squeal occurring in the large radius curve. The lateral force curving signature not only reveals the levels of lateral wheel-rail forces required for bogie curving, but also whether the bogie is curving by means of the creep forces generated at the wheel-rail interface only or if contact is necessitated between the wheel flange and rail gauge corner to help steer the bogie around the curve. The test set-up consisted of two free field microphones radially aligned at equivalent distances towards the in – and outside of the curve in line with a set a strain gauge bridges configured and calibrated to measure the lateral and vertical forces on the inner and outer rail of the curve. This test set-up allowed the squealing wheel to be identified from the magnitude difference of the sound pressures recorded by the inner and outer microphones in combination with comparing the point of frequency shift of the squeal event due to the Doppler Effect with the force signals of the radially aligned strain gauge bridges. From the experimental phase of the investigation, it was found that wheel squeal occurring in the 1000 m radius curve at Elands Bay is characteristic of empty wagons and is strongly related to the squealing wheel’s flange/flange throat being in contact with the gauge corner of the rail. Here high levels of spin creepage associated with high contact angles in the gauge corner lead to high levels of associated lateral creepage necessary for squeal generation. This is in contrast to lateral creepage due to high wheelset angles of attack being the key kinematic parameter influencing squeal generation in small radius curves. Furthermore, the amplitude of wheel squeal originating from the passing of empty wagons was found to be inversely proportional to the level of flange rubbing on the squealing wheel i.e. increased flange contact on the squealing wheel brings about a positive effect on squeal control. Contrary to the empty wagons which are characterised by tonal curve squeal, loaded 4 wagons requiring contact between the wheel flange and rail gauge corner in the 1000 m curve was characterised by broadband flanging noise. It was concluded from measurements that flange contact occurring under high lateral forces for steady state curving of loaded wagons provides the complete damping necessary for squeal control. The curve squeal noise that originated from the passing of empty wagons in the Elands Bay curve could further be classified according to the frequency at which the squeal event manifested itself in the curve, i.e. low frequency audible (0 – 10 kHz), high frequency audible (10 – 20 kHz) and ultrasonic squeal (> 20 kHz). The vast majority of low frequency audible squeal events recorded in the 1000 m Elands Bay curve occurred at approximately 4 kHz and originated from the low rail/trailing inner wheel interface, whilst the vast majority of high frequency audible squeal events occurred in the frequency range between 15 and 20 kHz and originated from both the high rail/leading outer wheel and low rail/trailing inner wheel interfaces.

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Mass transit vehicles in formal rail service frequently attain speeds which can excited carbody oscillations (primary hunting), as well as sustained lateral oscillations of the trucks (secondary hunting). The carbody motions have been shown to generate passenger discomfort and sustained truck hunting can lead to derailment. This thesis developed approximate equations which predict the carbody hunting frequencies, as well as the hunting speed of an articulated frame truck. The linear equations of motion are derived from a simplified model of a railway vehicle. A comparison indicates the results obtained using the approximate truck hunting equation presented here are within ten percent of the results obtained from more rigorous approaches reported by others.

Severe railcar responses can result from crosslevel and vertical rail inputs. At low speeds rail joint excitation can coincide with the roll natural frequency of a vehicle. At high speeds, dynamic effects can cause high wheel loads and harsh ride for sensitive cargos. Computer simulation of these and other vertical dynamic effects cans assist in design selections of vehicle components and diagnosis of troublesome vehicle responses. Many dynamic models available today lack the complexity to analyze accurately some of the important dynamic effects. In this report a 28-degree-of-freedom railcar model has been developed to analyze the vertical dynamic responses of railcars subjected to random and deterministic track inputs. This model features carbody vertical bending and torsional modes, multiple component trucks and suspensions, and rail irregularity inputs at each of the eight wheels. Simulation results for a 100-ton vehicle operating on harmonic track inputs compare favorably with the AAR Flexible Carbody Model. Other simulations on random track evaluate the influence of auxiliary viscous stabilizers and increased payloads on railcar responses. These simulations demonstrate the effectiveness of the computer simulation as a design and analysis tool. / M.S.

Finite element models of four design configurations of a proposed composite aluminum-steel high-side coal gondola rail car were developed. The designs were analyzed for compliance with the loadings set forth by the Association of American Railroads. Each of the first three designs were analyzed to check design concepts and alternatives with the fourth design being the final design planned for a prototype car. The results of the finite element analyses indicate that the final design is acceptable. However, two areas exist where results taken literally indicate a negative margin of safety. These areas are in the end sill to draftsill connection and in the draftsill casting. These conditions appear to be inconsequential since in the end sill case, the high stress is apparently caused by modeling constraints and the draftsill casting is a traditional design and is in common use on current cars and therefore should not cause any service problems. Step-by-step application of the finite element method to this design process is presented along with discussion of some significant element formulation assumptions and modeling methods. / Master of Science

In this thesis, a computer program for graphically displaying finite element beam stresses is discussed. Beam elements are represented as thick lines with colored stress contours along the length. Stress gradients through the beam thickness are not displayed. Many program options are available to aid in creating a clear view of stress distributions in complex models. The front, right, top, and isometric views are preprogrammed views, or a rotated view of the model can be specified. Also, specific portions of the model can be magnified. A region may be defined for showing cut sections of the model. Contour options are available to help enhance stress representation. Node locations may be marked, and beam line widths modified. Finally, any view that has been developed can be saved in a file to be redisplayed at a later time. The program also has the capability of displaying resultant beam forces and moments. Beam stress displays for two train car models are used to demonstrate the usefulness of the program as both a presentation and modeling diagnostic tool. Stress gradients and high-stress regions are easily seen. With these displays some model discrepancies were uncovered and some highly stressed locations were observed that had not been discovered in the prior research. / Master of Science

This paper presents a static three-dimensional finite element analysis and redesign of a railroad hopper car draftsill. The purpose of the work was to modify the current draftsill structure to minimize its weight without compromising its current capabilities and foundry production specifications. The intuitive optimization procedure used both linear and parabolic isoparametric solid finite element models to check for solution convergence. In order to intuitively optimize the models, a composite plotting program was developed to display only the highest stresses at each node from all loading cases. This allowed for an overall visualization of low stressed regions for potential weight reduction. An additional study investigated the possibility of tapering the front and rear draftlugs for a better stress distribution in the draftsill's structure under loading. It was determined that a tapered relief of 0.025 - 0.050 in.(0.0635 - 0.127 cm) from the center of the draftlug to its outer edge would more effectively distribute the stresses created, and also reduce the maximum stress levels generated by at least 20 percent. All loading and geometry specifications used in this research were based on data provided by the Norfolk Southern Corporation. If both the redesign and tapered relief are adopted, then the final redesign will produce a draftsill that is approximately 106 lb(471.5 N) or 9.6 percent lighter than its original weight with maximum stresses reduced by 20 percent. / Master of Science

Thesis: M.S., Massachusetts Institute of Technology, Department of Civil Engineering, 1978 / Includes bibliographical references. / M.S. / M.S. Massachusetts Institute of Technology, Department of Civil Engineering