Field Measurements of Vibration on the Car Body-Suspended Equipment for High-Speed Rail Vehicles

The vibrations in the flexible car bodies of the high-speed electric multiple units (EMUs) and their coupling effects with the bogies and other types of equipment vibrating have lead issues for railway operators and gained interest for researchers. Other than a numerical investigation, field measurements on the vibrating characteristics of the car body (CB) and its suspended equipment (CBSE) for a high-speed railway vehicle were performed to elaborate the vibrating characteristics on the CB and its CBSE. In this long-term tracking test, the running stability of vehicle and wheel-rail interaction were also examined with the increase of operation distance (OD), a total of 2,400,000 km. The test configuration and arrangements are introduced first, followed by the data analysis in time and frequency domains. It is seen that the wheelset conicity increases 0.008 per 10,000 km, which increases approximately linearly with the OD from 0.10 to 0.40. Two types of wheel treads, S1002CN and LMB10, have different ranges in conicity and reprofiling cycles. The lateral accelerations on CB in a downward-running case (0.5 g) are much greater than that in upward-running case (0.2 g) corresponding to the vehicle stability differences. The 15 Hz low-pass filtered acceleration on CB experiences a maximum of 0.10 g and an averaged amplitude around 0.05 g, whereas the frequency spectrum has peaks of 0.01 g on CB and 0.1 g on CBSE. It states that an elastic suspension between the CBSE and the CB prevents the high-frequency vibration from the CB

Research on Low-Frequency Swaying Mechanism of Metro Vehicles Based on Wheel-Rail Relationship

For the worn state of the wheel, metro vehicles often suffer a serious carbody swaying issue, which causes the lateral stability of the vehicle to exceed the limit and affects the ride comfort. An experimental test was carried out on this investigation to study the carbody swaying of the metro vehicle. The field results show that the vehicle system vibrates at around 2.5 Hz in the lateral direction, which leads to the low-frequency swaying on the carbody. In order to explore the formation mechanism of the carbody low-frequency swaying and its relationship with the geometry matching of wheel-rail contact, measured rail and wheel profiles are employed to present a comparative analysis with respect to the initial contact geometry. A multibody dynamic railway vehicle system is established further. Time-domain simulations state that the 2.5 Hz vibration on the carbody belongs to the natural frequency of the vehicle, and the amplitude is larger for the measured wheels than that of the standard wheel profiles. By using the root-locus method, it can be determined that the 2.5 Hz vibration corresponds to the upper swaying mode of the carbody. With the increase in the wheel-rail equivalent conicity, the hunting frequency of bogie increases gradually, which converts frequency with the upper swaying frequency of carbody and leads to carbody low-frequency swaying

Low-Frequency Carbody Sway Modelling Based on Low Wheel-Rail Contact Conicity Analysis

Low-frequency carbody swaying on China’s high-speed trains is not only an impediment to ride comfort but it may also be an operational risk under some extreme situations. To study the mechanism and mitigate the carbody swaying problem for high-speed trains, a multibody dynamics model was established based on both linear and nonlinear analyses. Whilst it is generally assumed that carbody swaying is predominantly caused by carbody hunting motion, the results in this paper has shown that, under certain boundary conditions, bogie-hunting motion can also lead to low-frequency carbody swaying. This low-frequency swaying phenomenon was also found to be caused by the excessively low wheel-rail contact or mismatched suspension parameters. Parametric optimization analysis was accordingly conducted from the perspective of the wheel-rail contact relationship and the suspension system. The analysis indicated that although optimizing the suspension parameters can meet the requirement of vehicle stability, bogie's vibration worsen when the wheel profiles wear over time. Overall, while rail reprofiling was found to be one of the fundamental solutions to mitigate carbody swaying, it is cost prohibitive for most routine operational applications. Thus, for economic considerations and the fact that low wheel-rail contact conicity is also a contributing factor to carbody swaying, vehicles with worn wheels can also be operated on the rail line, which was successfully verified by the field data presented in this paper

INTEGRATION OF GEOMETRY AND ANALYSIS FOR THE STUDY OF LIQUID SLOSHING IN RAILROAD VEHICLE DYNAMICS

A new continuum-based liquid sloshing approach that accounts for the effect of complex fluid and tank-car geometry on railroad vehicle dynamics is developed in this investigation. A unified geometry/analysis mesh is used from the outset to examine the effect of liquid sloshing on railroad vehicle dynamics during curve negotiation and during the application of electronically controlled pneumatic (ECP) brakes that produce braking forces uniformly and simultaneously across all cars. Using a non-modal approach, the geometry of the tank-car and fluid is accurately defined, a continuum-based fluid constitutive model is employed, and a fluid-tank contact algorithm is developed. The liquid sloshing model is integrated with a three-dimensional multibody system (MBS) railroad vehicle algorithm which accounts for the nonlinear wheel/rail contact. The three-dimensional wheel/rail contact force formulation used in this study accounts for the longitudinal, lateral, and spin creep forces that influence the vehicle stability. In order to examine the effect of the liquid sloshing on the railroad vehicle dynamics during curve negotiation, a general and precise definition of the outward inertia force is defined, and in order to correctly capture the fluid and tank-car geometry, the absolute nodal coordinate formulation (ANCF) is used. The balance speed and centrifugal effects in the case of tank-car partially filled with liquid are studied and compared with the equivalent rigid body model in curve negotiation and braking scenarios. In particular, the results obtained in the case of the ECP brake application of two freight car model are compared with the results obtained when using conventional braking. The traction analysis shows that liquid sloshing has a significant effect on the load distribution between the front and rear trucks. A larger coupler force develops when using conventional braking compared with ECP braking, and the liquid sloshing contributes to amplifying the coupler force in the ECP braking case compared to the equivalent rigid body model which does not capture the fluid nonlinear inertia effects. Furthermore, the results obtained in this study show that liquid sloshing can exacerbate the unbalance effects when the rail vehicle negotiates a curve at a velocity higher than the balance speed

Hypothermia protects the brain from transient global ischemia/reperfusion by attenuating endoplasmic reticulum response-induced apoptosis through CHOP.

Endoplasmic reticulum (ER) stress has been implicated in the pathology of cerebral ischemia. Apoptotic cell death occurs during prolonged period of stress or when the adaptive response fails. Hypothermia blocked the TNF or Fas-mediated extrinsic apoptosis pathway and the mitochondria pathway of apoptosis, however, whether hypothermia can block endoplasmic reticulum mediated apoptosis is never known. This study aimed to elucidate whether hypothermia attenuates brain cerebral ischemia/reperfusion (I/R) damage by suppressing ER stress-induced apoptosis. A 15 min global cerebral ischemia rat model was used in this study. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) positive cells in hippocampus CA1 were assessed after reperfusion of the brain. The expressions of C/EBP-homologous protein (CHOP) and glucose-regulated protein 78 (GRP78) in ischemic hippocampus CA1 were measured at 6, 12, 24 and 48 h after reperfusion. The results showed that hypothermia significantly attenuated brain I/R injury, as shown by reduction in cell apoptosis, CHOP expression, and increase in GRP78 expression. These results suggest that hypothermia could protect brain from I/R injury by suppressing ER stress-induced apoptosis

Neuronal apoptosis in CA1 region of hippocampus induced by global cerebral ischemia.

<p>Detection of apoptosis in hippocampus CA1 pyramidal neurons was carried out using Tunel staing. The sham group showed a large number of neurons and almost no TUNEL-positive cells (5.1±1.2) (A). In ischemia (C) and hypothermia (B) groups, the number of neurons were decreased and substantial TUNEL-positive cells were detected. The number of TUNEL-positive cells in hypothermia group (34.4±4.2) (B) is more than in ischemia group (40.5±5.7) (C), /400×visual field.</p

Expression of chop in hippocampus CA1.

<p>(a) Immunohistochemistry showed the chop was barely detected in sham group (A).The expression of chop in hypothermia group (B) is much weaker than that in ischemia group (C) at reperfusion 24 hours. /400×visual field (b) Western blot analysis showed that the chop was barely detected in sham group. In brains of ischemia group, it was increased 6 hour after 15 minutes of ischemia and gradually decreased thereafter; however, the degree of increase was much smaller in the hypothermia brains. (c) Quantitative analysis of Western blotting showed that hypothermia after ischemia significantly decreased chop after 15 minutes of ischemia (P<0.05 compared with ischemia brains at the same time points. 6 rats from each group at every time points were used for analysis).</p