Defect detection in freight railcar tapered-roller bearings using vibration techniques

Currently,there are two types of defect detection systems used to monitor the health of freight railcar bearings in service:wayside hot-box detection systems and trackside acoustic detection systems.These systems have proven to be inefficient in accurately determining bearing health,especially in the early stages of defect development.To that end,a prototype onboard bearing condition monitoring system has been developed and validated through extensive laboratory testing and a designated field test in 2015 at the Transportation Technology Center,Inc.in Pueblo,CO.The devised system can accurately and reliably characterize the health of bearings based on developed vibration thresholds and can identify defective taperedroller bearing components with defect areas smaller than 12.9 cm2 while in service.

Nonlinear Vibration Induced by the Water-film Whirl and Whip in a Sliding Bearing Rotor System

Many industrial applications and experiments have shown that sliding bearings often experience fluid film whip due to nonlinear fluid film forces which can cause rotor-stator rub-impact failures. The oil-film whips have attracted many studies while the water-film whips in the water lubricated sliding bearing have been little researched with the mechanism still an open problem. The dynamic fluid film forces in a water sliding bearing are investigated numerically with rotational, whirling and squeezing motions of the journal using a nonlinear model to identify the relationships between the three motions. Rotor speed-up and slow-down experiments are then conducted with the rotor system supported by a water lubricated sliding bearing to induce the water-film whirl/whip and verify the relationship. The experimental results show that the vibrations of the journal alternated between increasing and decreasing rather than continuously increasing as the rotational speed increased to twice the first critical speed, which can be explained well by the nonlinear model. The radial growth rate of the whirl motion greatly affects the whirl frequency of the journal and is responsible for the frequency lock in the water-film whip. Further analysis shows that increasing the lubricating water flow rate changes the water-film whirl/whip characteristics, reduces the first critical speed, advances the time when significant water-film whirling motion occurs, and also increases the vibration amplitude at the bearing center which may lead to the rotor-stator rub-impact. The study gives the insight into the water-film whirl and whip in the water lubricated sliding bearing.

Investigations for vibration and friction torque behaviors of thrust ball bearing with self-driven textured guiding surface

In order to improve the starved lubrication condition of rolling bearings,three kinds of textures,namely dimple,groove texture,and gradient groove texture,were developed on the guiding surface of thrust ball bearings in this study.The results show that gradient groove texture has the one-way self-driving function of liquid droplets.The root mean square(RMS)value of vibration acceleration of gradient groove textured bearing(GGB)decreased by 49.1% and the kurtosis decreased by 24.6% compared with non-textured bearing(NB)due to the directional spreading effect of gradient groove textures on oil.The frequency domain analysis showed that the textures mainly suppressed the medium and high-frequency energy of bearing vibration,and the GGB was reduced the most with 65.3% and 48%,respectively.In addition,whether the grease is sufficiently sheared has a large impact on the oil guiding effect,and the friction torque of GGB could decrease by 10.5% compared with NB in the sufficiently sheared condition.Therefore,the gradient groove texture with oil self-driven effect on the guiding surface of rolling bearing can effectively improve the lubrication condition of the bearing and thus reduce the bearing vibration and friction torque,which has a promising application prospect.

Hybrid fiber Bragg grating sensor for vibration and temperature monitoring of a train bearing

We report a fiber Bragg grating（FBG）-based sensor for the simultaneous measurement of a train bearing’s vibration and temperature. A pre-stretched optical fiber with an FBG and a mass is designed for axial vibration sensing. Another multiplexed FBG is embedded in a selected copper-based alloy with a high thermal expansion to detect temperature. Experiments show that the sensor possesses a high resonant frequency of 970 Hz, an acceleration sensitivity of 27.28 pm/g, and a high temperature sensitivity of 35.165 pm/℃. A resonant excitation test is also carried out that demonstrates the robustness and reliability of the sensor.

Analysis and Testing of Microvibrations Produced by Momentum Wheel Assemblies

The microvibrations produced by momentum wheel assemblies（MWA） can degrade the performance of instruments with high pointing precision and stability on spacecraft.This paper concentrates on analyzing and testing the microvibrations produced by MWA.We analyze the disturbance sources produced by mass imbalance,structural mode,bearing irregularity and nonlinear stiffness,and random noise;then,test a well-balanced MWA by a highly sensitive measurement system consisting of a Kistler table and an optical tabletop.The results show that the test system has a resolution of less than 0.003 N in the frequency range of 3-300 Hz.The dynamic imbalance of the MWA cannot excite the radial rocking mode,but there are dynamic amplifications when the poly-harmonic disturbances intersect with the structural modes.Especially at high rotational speed（〉3 000 rev/min）,the main disturbance sources of the MWA come from the bearing irregularity interacting with radial translation mode in the high frequency range.Thus,bearing noise deserves more attention for the well-balanced MWA,and alternative of high quality bearings are proposed to reduce the microvibrations.

Flow-pipe-soil coupling mechanisms and predictions for submarine pipeline instability

The stability of a submarine pipeline on the seabed concerns the flow-pipe-soil coupling, with influential factors related to the ocean waves and/or currents, the pipeline and the surrounding soils. A flow-pipe-soil coupling system generally has various instability modes, including the vertical and lateral on-bottom instabilities, the tunnel-erosion of the underlying soil and the subsequent vortex-induced vibrations（VIVs） of free-spanning pipelines. This paper reviews the recent advances of the slip-line field solutions to the bearing capacity, the flow-pipe-soil coupling mechanism and the prediction for the lateral instability, the multi-physical coupling analysis of the tunnel-erosion, and the coupling mechanics between the VIVs and the local scour. It is revealed that the mechanism competition always exists among various instability modes, e.g., the competition between the lateral-instability and the tunnel-erosion. Finally, the prospects and scientific challenges for predicting the instability of a long-distance submarine pipeline are discussed in the context of the deep-water oil and gas exploitations.

Nonlinear identification of electro-magnetic force model

Conventional attractive magnetic force models (proportional to the coil current squared and inversely proportional to the gap squared) cannot simulate the nonlinear responses of magnetic bearings in the presence of electromagnetic losses,flux leakage or saturation of iron.In this paper,based on results from an experimental set-up designed to study magnetic force,a novel parametric model is presented in the form of a nonlinear polynomial with unknown coefficients.The parameters of the proposed model are identified using the weighted residual method.Validations of the model identified were performed by comparing the results in time and frequency domains.The results show a good correlation between experiments and numerical simulations.