Ali Tajaddini

A Machine Vision System for Automated Joint Bar Inspection From a Moving Rail Vehicle

Broken joint bars have been identified as one of the major causes of main line derailments in the US. On October 2006, the US Federal Railroad Administration issued a federal regulation that mandates periodic inspections to detect cracks and other indications of potential failures in CWR joints [1]. The rule requires periodic on-foot inspection or an approved alternative procedure providing equivalent or higher level of safety. This paper describes a new machine vision-based system for joint bars inspection at speeds up to 70 mph. Four line-scan cameras mounted on a hi-railer or full size rail vehicle continuously capture high resolution images from both sides of each rail. An on-board computer system analyzes these images in real time to detect the joint bars. Each joint bar image is automatically saved and analyzed for visible fatigue cracks. The images can also be analyzed for missing bolts and other defects. When a potential defect is detected, the system provides audio warning, tags the image with GPS position, and displays the joint bar image with highlighted defects on the screen. The operator may confirm or reject defects. At the end of the survey, the operator can generate a survey report with the joint bar GPS location and types of all defects. This new system improves productivity and workers safety, inspecting joint bars from a moving vehicle instead of having to walk along highly transited tracks. It also allows the railroads to reduce the time between inspections, preventing defects to develop into hazards. Several tests have been performed on different rail roads showing system defect detection capabilities on both CWR and jointed track.Copyright

Wheel-Rail Contact Characteristics on a Tangent Track Vs a Roller Rig

This study derives explicit analytical expressions for comparing contact patch dimensions and Kalker’s coefficients for a wheel moving on a roller and compares the results with a tangent track arrangement. The expressions suggest that full size roller rig will underpredict Kalker’s traction coefficients (creepage forces per unit creepage) by a factor that depends on the roller radius.Studying rail-wheel contact mechanics and dynamics in the field conditions can prove to be challenging due to the difficulties in adequately controlling the test conditions that can significantly affect the results, such as track irregularities, rail surface condition, etc. Roller rigs can prove to be a useful tool for such studies. One, however, must be careful when interpreting roller rig test results because of the differences in wheel-rail contact mechanics and dynamics between the track and the roller. The findings of this study, which are consistent with other studies’ conclusions, will allow researchers to relate results with field testing.Copyright

Vehicle Track Interaction Safety Standards

Vehicle/Track Interaction (VTI) Safety Standards aim to reduce the risk of derailments and other accidents attributable to the dynamic interaction between moving vehicles and the track over which they operate. On March 13, 2013, the Federal Railroad Administration (FRA) published a final rule titled “Vehicle/Track Interaction Safety Standards; High-Speed and High Cant Deficiency Operations” which amended the Track Safety Standards (49 CFR Part213) and the Passenger Equipment Safety Standards (49 CFR Part 238) in order to promote VTI safety under a variety of conditions at speeds up to 220 mph. Among its main accomplishments, the final rule revises standards for track geometry and enhances qualification procedures for demonstrating vehicle trackworthiness to take advantage of computer modeling.The Track Safety Standards provide safety limits for maximum allowable track geometry variations for all nine FRA Track Classes — i.e., safety “minimums.” These limits serve to identify conditions that require immediate attention because they may pose or create a potential safety hazard. While these conditions are generally infrequent, they define the worst conditions that can exist before a vehicle is required to slow down. To promote the safe interaction of rail vehicles with the track over which they operate (i.e. wheels stay on track, and vehicle dynamics do not overload the track structure, vehicle itself, or cause injury to passengers), these conditions must be considered in the design of suspension systems. In particular, rail vehicle suspensions must be designed to control the dynamic response such that wheel/rail forces and vehicle accelerations remain within prescribed thresholds (VTI safety limits) when traversing these more demanding track geometry conditions at all allowable speeds associated with at particular track class.To help understand the differences in performance requirements (design constraints) being placed on the design of passenger equipment suspensions throughout the world, comparisons have been made between FRA safety standards and similar standards used internationally (Europe, Japan, and China) in terms of both allowable track geometry deviations and the criteria that define acceptable vehicle performance (VTI safety limits). While the various factors that have influenced the development of each of the standards are not readily available or fully understood at this time (e.g., economic considerations, provide safety for unique operating conditions, promote interoperability by providing a railway infrastructure that supports a wide variety of rail vehicle types, etc.), this comparative study helps to explain in part why, in certain circumstances, equipment that has been designed for operation in other parts of the world has performed poorly, and in some cases had derailment problems when imported to the U.S. Furthermore, for specific equipment that is not specifically designed for operation in the U.S., it helps to identify areas that may need to be addressed with other appropriate action(s) to mitigate potential safety concerns, such as by ensuring that the track over which the equipment is operating is maintained to standards appropriate for the specific equipment type, or by placing operational restrictions on the equipment, or both.In addition to these comparisons, an overview of the new FRA qualification procedures which are used for demonstrating vehicle trackworthiness is provided in this paper. These procedures, which include use of simulations to demonstrate dynamic performance, are intended to give guidance to vehicle designers and provide a more comprehensive tool for safety assessment and verification of the suitability of a particular equipment design for the track conditions found in the U.S.© 2014 ASME

ENGINEERING STUDIES ON JOINT BAR INTEGRITY, PART I: FIELD SURVEYS AND OBSERVED FAILURE MODES

This paper is the first of a two-part series describing a research project, sponsored by the Federal Railroad Administration (FRA), to study the structural integrity of joint bars. In Part I of this series, observations from field surveys conducted on revenue service track are presented. Automated and visual inspections of rail joints were conducted to identify defective joint bars. Detailed information and measurements were collected at various joint locations. The survey team consisted of personnel from ENSCO, Inc. and Transportation Technology Center, Inc. (TTCI), working in cooperation with staff from participating railroads. Part II of this series describes the development of finite element analyses of jointed rail, which is being carried out by the Volpe National Transportation Systems Center (Volpe Center).

EXAMINATION OF VEHICLE PERFORMANCE AT HIGH SPEED AND HIGH CANT DEFICIENCY

In the US, increasing passenger speeds to improve trip time usually involves increasing speeds through curves. Increasing speeds through curves will increase the lateral force exerted on track during curving, thus requiring more intensive track maintenance to maintain safety. These issues and other performance requirements including ride quality and vehicle stability, can be addressed through careful truck design. Existing high-speed rail equipment, and in particular their bogies, are better suited to track conditions in Europe or Japan, in which premium tracks with little curvature are dedicated for high-speed service. The Federal Railroad Administration has been conducting parametric simulation studies that examine the performance of rail vehicles at high speeds (greater than 90 mph) and at high cant deficiency (greater than 5 inches). The purpose of these analyses is to evaluate the performance of representative vehicle designs subject to different combinations of track geometry variations, such as short warp and alinement.

Optimizing Wheel/Rail Performance on High Speed, Mixed Traffic Corridors

Between 2001 and 2009, a series of field, laboratory and theoretical studies were conducted with FRA sponsorship to better understand the wheel/rail interaction on Amtrak’s multi-user Northeast Corridor. The development of a new wheel profile, optimized rail profiles, friction management practices and a grinding strategy were key aspects of the program. The experience gathered over an eight year period, including many lessons learned, has been collected and provides a template for how optimization of the wheel/rail interaction can be undertaken on high speed, shared use railway corridors.Copyright

A Nonlinear Rail Vehicle Dynamics Computer Program SAMS/Rail: Part 3—Applications to Predict Railroad Vehicle-Track Interaction Performance

The dynamic response of a railroad vehicle traveling at speed over track deviations can be predicted by using multibody simulation codes. In this case, the solution of nonlinear equations of motion and extensive calculations based on the suspension characteristics of the vehicle are required. Recently, the Federal Railroad Administration, Office of Research and Development has sponsored a project to develop a general multibody simulation code that uses an online nonlinear three-dimensional wheel-rail contact element to simulate contact forces between wheel and rail. In this paper, several applications to examine such issues as critical speed, curving performance at varying cant deficiencies, and wheel load equalization are presented to demonstrate the use of the multibody code. In addition, the application of the multibody code can be extended to train a neural network system. Neural network technology has the ability to learn relationships between a mechanical system input and output, and, once learned, give quick outputs for given input. The neural network can be combined with the use of a nonlinear multibody code to predict the performance of multiple railroad vehicle types in real time. In this paper, this system is briefly presented to shed light on the optimum use of the multibody code to prevent derailment.Copyright

A Nonlinear Rail Vehicle Dynamics Computer Program SAMS/Rail: Part 2—Preliminary Validation of BETA Release

The Federal Railroad Administration is sponsoring a research project at the University of Illinois at Chicago (UIC) to develop state of the art modeling and simulation capabilities for railroad vehicle systems. This involves the development of a general purpose code for the dynamic simulation and performance evaluation of railroad vehicle systems. During development of the beta version, SAMS/Rail (Systematic Analysis of Multibody Systems/Rail), a number of simplified models have been constructed to validate the program. These examples include single wheelset models, truck models, full vehicle models and industry recognized benchmarks. In each of these cases, comparisons have been made to available solutions. These results are described in this paper.Copyright

A Nonlinear Rail Vehicle Dynamics Computer Program SAMS/Rail: Part 1—Theory and Formulations

Accurate prediction of railroad vehicle performance requires detailed formulations of wheel-rail contact models. In the past, most dynamic simulation tools used an offline wheel-rail contact element based on look-up tables that are used by the main simulation solver. Nowadays, the use of an online nonlinear three-dimensional wheel-rail contact element is necessary in order to accurately predict the dynamic performance of high speed trains. Recently, the Federal Railroad Administration, Office of Research and Development has sponsored a project to develop a general multibody simulation code that uses an online nonlinear three-dimensional wheel-rail contact element to predict the contact forces between wheel and rail. In this paper, several nonlinear wheel-rail contact formulations are presented, each using the online three-dimensional approach. The methods presented are divided into two contact approaches. In the first Constraint Approach, the wheel is assumed to remain in contact with the rail. In this approach, the normal contact forces are determined by using the technique of Lagrange multipliers. In the second Elastic Approach, wheel/rail separation and penetration are allowed, and the normal contact forces are determined by using Hertz’s Theory. The advantages and disadvantages of each method are presented in this paper. In addition, this paper discusses future developments and improvements for the multibody system code. Some of these improvements are currently being implemented by the University of Illinois at Chicago (UIC). In the accompanying “Part 2” and “Part 3” to this paper, numerical examples are presented in order to demonstrate the results obtained from this research.Copyright

Using a Multibody Dynamic Simulation Code With Neural Network Technology to Predict Railroad Vehicle-Track Interaction Performance in Real Time

Recently, there has been a large demand for predicting, in real time, the performance of multiple railroad vehicle types traversing existing track as the geometry of the track is being measured. To accurately predict a railroad vehicle’s response over a specified track requires the solution of nonlinear equations of motion and extensive calculations based on the suspension characteristics of the vehicle. To realize the real time goal, codes are being implemented that use linear approximations to the fully nonlinear equations of motion to reduce computation time at the expense of accuracy. Alternatively, neural network technology has the ability to learn relationships between a mechanical system input and output, and, once learned, give quick outputs for given input. The training process can be done using measured data or using simulation data. In general, measured data is very expensive to gather due to the instrumentation requirements and is most often not available. In this paper, the use of multibody simulation code as a training tool for a neural network is presented. The example results estimate the vertical and lateral forces at the wheel-to-rail interface as a function of the geometry of the track and the suspension characteristics of the vehicle type by using a multibody code with neural network technique.Copyright