Michael Craft

Magneto-rheological fluid behavior in squeeze mode

Little published data exists on the behavior of MR fluids in squeeze mode. Many of the basic properties of MR fluids in squeeze mode are still unknown. In squeeze mode, MR fluids can generate a large range of force associated with a small displacement. As a result, squeeze mode has recently received more attention. This research focuses on modeling and testing MR fluids in squeeze mode. A novel squeeze mode rheometer is designed and built. MR fluid is tested in squeeze mode to evaluate its performance and behavior. The rheometer can test MR fluid under different conditions (gap size, magnetic field density, speed, etc). It utilizes a Gauss meter for direct measurement of the magnetic field density. MR fluid squeeze test results show that MR fluid can deliver a large range of force that is comparable in magnitude to the force in shear mode. The tests also indicate a clumping effect of the fluid when tested in repeated cycles that does not appear to have been documented previously. This paper describes, in detail, the clumping effect and provides possible reasons for this phenomenon. A non-dimensional mathematical model is developed and validated experimentally. The non-dimensional model directly compares the squeeze mode force to the shear mode force. The results indicate that MR fluid in squeeze mode can be used in many applications requiring a large range of controllable force in envelopes that can only accommodate small strokes.

Experimental Investigation of MR Squeeze Mounts

Based on results obtained from testing MR fluid in a squeeze mode rheometer, a novel compression-adjustable element has been fabricated and tested, which utilizes MR fluid in the squeeze mode. While shear and valve modes have been used exclusively for MR fluid damping applications, recent modeling and testing with MR fluid has revealed that much larger adjustment ranges are achievable in the squeeze mode. Utilizing the squeeze mode, an MR squeeze mount was developed and tested. Test results show that the device was capable of varying the compression force from less than 8 lb 35.6 N to greater than 800 lb 3560 N, when the pole plates were 0.050 in. 1.3 mm apart. Test results showed that the mount tends to achieve higher forces after each repeat of test. This behavior, called ‘clumping’, was studied and solutions to minimize this effect are discussed.

Dynamic Testing and Modeling of an MR Squeeze Mount

MR fluid squeeze mode investigations at CVeSS have shown that MR fluids show large force capabilities in squeeze mode. It was found that MR fluids in squeeze mode may be used in a wide range of applications such as engine mounts and impact dampers. In these applications, MR fluid is flowing in a dynamic environment due to the transient nature of inputs and system characteristics. The research presented in this article undertakes the problem of dynamic testing and modeling of MR fluid squeeze mounts. Dynamic tests of an MR mount are studied for different applied currents, initial gaps, frequencies, and excitation amplitudes. An effective mathematical model of the MR squeeze mount for steady-state testing was built which includes the effect of the inertia of the fluid. The results show that the compression force and the area of the hysteresis loop increase with the increase of excitation amplitude or applied current and it will decrease with the increase of frequency or initial gap. Also, the inertia effect becomes more significant for higher displacement frequencies. The mathematical model agrees with the test data very well during the compression process and it can be used for the dynamics analysis and the real-time control.

On the Application of Roller Rigs for Studying Rail Vehicle Systems

The primary intent of this study is to highlight the advantages and disadvantages of using roller rigs for engineering issues of importance to the railroad industry. Roller rigs have been in existence for more than a century for studying railway vehicle behavior. In contrast to field testing, roller rigs offer a controlled laboratory environment that can provide a successful path for obtaining data on the mechanics and dynamics of railway systems for a variety of operating conditions. Their use, however, imposes discrepancies from the field environment due to the nature of the commonly-used roller design. This study describes different rig configurations, including scaled and full-scale rigs. It includes the potential advantages and limitations of various rigs for conducting a wide range of studies concerning the dynamic stability of railcars, wheel–rail adhesion, wear and fatigue mechanisms, braking systems, and locomotive power.Copyright

Modeling of a Roller Rig for Evaluation of Wheel/Rail Contact Mechanics

This paper provides a detailed dynamic model of the electromechanical system for a scaled roller rig that is under construction at the Railway Technology Laboratory of Virginia Tech (RTL) for accurate study of the mechanics and dynamics at wheel-rail interface in railway vehicles. Roller rigs are critical laboratory test equipment for studying rail vehicle dynamics, either as a full railcar or single component. The controlled laboratory environment will provide a successful path for obtaining data on the mechanics and dynamics of the system, including creepage and creep forces at the wheel-rail interface under various conditions. The single-wheel scaled rig under development at RTL includes a wheel that is placed on a roller with similar profile as a U.S. 136 weight rail. The test setup allows for adjusting the wheel load, the wheel angle of attack, the rail cant, and the lateral position of the wheel with respect to the rail (including flanging). The roller and the wheel are each powered independently by two AC motors that enable controlling their relative speed to a high degree of precision, i.e., 0.1 RPM, in order for precisely controlling and simulating various creep conditions that occur in practice. An essential step for the successful design and development of the test rig is modeling the motors and the roller/wheel drivelines. The model includes the electromagnetic dynamics of the AC motors, the compliances and damping of the drivelines, the inertial properties of the motors, shafts, couplers, and the rotating wheels, in a multi-domain (electrical, magnetic, and mechanical) lumped-parameter model. The model is used to determine the damped natural frequencies of the coupled system. The results of the study indicate that the compliances of the driveline mechanics is the most critical element in maintaining a prescribed speed at the driven wheel, and also controlling the relative creep between the wheel and the simulated (round) rail.Copyright

Evaluation of LIDAR Track Measurement Systems in Car Body and Truck-Mounted Configurations

This study presents track alignment and curvature measurement results from a Doppler LIDAR (light detection and ranging) speed measurement system, a non-contact speed and distance measurement system comparable to encoders found on research geometry cars. The system has multiple mounting capabilities with the primary implementations being body-mounted and truck-mounted. Track speed is measured using the individual rails as reference targets, producing two speed signals. Curvature data is obtained from the measured speed differential as the train navigates tangent and curved track. The different dynamic behaviors of the truck and car body influence the motion of the LIDAR system, and thus the results vary depending on the mounting configuration. The curvature, speed, and distance data obtained from the LIDAR system has been compared with results from a geometry car and manual track measurements. The results indicate the LIDAR system has strong potential in serving as a highly precise, non-contact speed, distance, and curvature measurement device suitable for implementation in rail geometry applications.Copyright

Multifunction LIDAR Sensors for Non-Contact Speed Measurement in Rail Vehicles: Part I — System Installation and Implementation

This study presents speed measurement system using Light detection And Ranging (LIDAR) technology is successfully tested on moving railway cars. The system has multiple mounting capabilities that allow it to attach to various locations on the railcar. Using lasers to measure train speed off of each rail individually, the system determines curvature characteristics of the track based on known track geometry and speed differentials measured by the system. The LIDAR speed measurement system offers a non-contact form of measurement that eliminates noise and unwanted disturbances originating from contact sensors such as wheel-mounted encoders. The results of the study indicate that, with an ability to operate at speeds from 0.5mph and upwards of 100mph, the LIDAR system proves to be a highly versatile and precise measurement device useful in rail geometry measurement applications.Copyright

Multifunction LIDAR Sensors for Non-Contact Speed Measurement in Rail Vehicles: Part 2 — Data Collection and Analysis

The application of Doppler based, LIght Detection And Ranging (LIDAR or lidar) technology for measuring true ground speed in a non-contacting manner is investigated, as a replacement to wheel tachometers that are commonly used for such measurements. Measuring track speed and distance traveled is an essential part of rail geometry measurement systems. Wheel tachometer measurement accuracy can often be adversely affected by wheel vibrations, change in wheel diameter, and wheel slip in high traction conditions. LIDAR is a non-contact measurement device that uses the Doppler technology to accurately determine speed. Two LIDAR sensors are attached to the underside of a track geometry car with the sensors’ Class I laser beams facing the gauge corner of each rail. The LIDAR sensors measure the absolute ground speed for each rail, allowing for the determination of forward speed and track curvature. The results of the tests show high accuracy in LIDAR speed, distance, and track curvature measurements when compared with other conventional means that are used in the railroad industry and ground truth measurements. With further development, LIDAR sensors can replace wheel tachometers that are commonly used for speed and distance measurement, therefore eliminating the problems with mechanical reliability and the need for periodic calibration of wheel tachometers.© 2013 ASME

Active vibration control with optimized modified acceleration feedback equipped with adaptive line enhancer

Modified acceleration feedback (MAF) control, an active vibration control method that uses collocated piezoelectric actuator actuators and sensors is improved using an optimal controller. The controller consists of two main parts: 1) Frequency adaptation that uses Adaptive Line Enhancer (ALE), and 2) an optimal controller. Frequency adaptation tracks the frequency of vibrations using ALE. The obtained frequency is then fed to MPPF compensators and the optimal controller. This provides a unique feature for MAF, by extending its domain of capabilities from controlling tonal vibrations to broad band disturbances. The optimal controller consists of a set of optimal gains for wide range of frequencies that is provided, related to the characteristics of the system. Based on the tracked frequency, the optimal control system decides to use which set of gains for the MAF controller. The gains are optimal for the frequencies close to the tracked frequency. The numerical results show that the frequency tracking method that is derived has worked quite well. In addition, the frequency tracking is fast enough to be used in real-time controller. The results also indicate that the MAF can provide significant vibration reduction using the optimal controller.