scholarly journals Numerical Analysis of Vibration Responses in High-Speed Railways considering Mud Pumping Defect

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Ting Li ◽  
Qian Su ◽  
Kang Shao ◽  
Jie Liu
Keyword(s):  
High Speed ◽  
Coupled Model ◽  
Test Results ◽  
External Excitation ◽  
Slab Track ◽  
Vibration Responses ◽  
Track Irregularity ◽  
Mud Pumping ◽  
Element Theory ◽  
Good Agreement

As a newly appeared defect under slab tracks in high-speed railways, mud pumping weakens the support ability of the subgrade to slab track, bringing about deviations on the vibration responses of the vehicle, slab track, and subgrade. Therefore, this paper proposes a vehicle-slab track-subgrade coupled model based on the multibody simulation principle and the finite element theory to highlight the influences of mud pumping defect. As an external excitation to this model, random track irregularity is considered. In order to simulate the mud pumping defect, the contact between the concrete base and subgrade is described as a spring-damper system. This model is validated by field test results and other simulation results, and a very good agreement is found. The vibration responses of the vehicle, slab track, and subgrade under different mud pumping lengths and train speeds are studied firstly. The deviations of vibration responses in high-speed railways induced by mud pumping are then obtained, and the limited mud pumping length is put forward finally to provide a recommendation for maintenance works of high-speed railways in practice.

scholarly journals The Influence of an Integration Time Step on Dynamic Calculation of a Vehicle-Track-Bridge under High-Speed Railway

Mathematics ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 431
Author(s):  
Junjie Ye ◽  
Hao Sun
Keyword(s):  
High Speed ◽  
Coupled Model ◽  
Short Wave ◽  
Integration Time ◽  
Vertical Acceleration ◽  
Dynamic Calculation ◽  
Time Step ◽  
High Speed Railway ◽  
Track Irregularity ◽  
Track Bridge

In order to study the influence of an integration time step on dynamic calculation of a vehicle-track-bridge under high-speed railway, a vehicle-track-bridge (VTB) coupled model is established. The influence of the integration time step on calculation accuracy and calculation stability under different speeds or different track regularity states is studied. The influence of the track irregularity on the integration time step is further analyzed by using the spectral characteristic of sensitive wavelength. According to the results, the disparity among the effect of the integration time step on the calculation accuracy of the VTB coupled model at different speeds is very small. Higher speed requires a smaller integration time step to keep the calculation results stable. The effect of the integration time step on the calculation stability of the maximum vertical acceleration of each component at different speeds is somewhat different, and the mechanism of the effect of the integration time step on the calculation stability of the vehicle-track-bridge coupled system is that corresponding displacement at the integration time step is different. The calculation deviation of the maximum vertical acceleration of the car body, wheel-sets and bridge under the track short wave irregularity state are greatly increased compared with that without track irregularity. The maximum vertical acceleration of wheel-sets, rails, track slabs and the bridge under the track short wave irregularity state all show a significant declining trend. The larger the vibration frequency is, the smaller the range of integration time step is for dynamic calculation.

scholarly journals Deformation Law and Control Limit of CRTSIII Slab Track under Subgrade Frost Heave

2021 ◽  
Vol 11 (8) ◽  
pp. 3520
Author(s):  
Xiaopei Cai ◽  
Qian Zhang ◽  
Yanrong Zhang ◽  
Qihao Wang ◽  
Bicheng Luo ◽  
...  
Keyword(s):  
High Speed ◽  
Base Plate ◽  
Element Model ◽  
Middle Part ◽  
Railway Track ◽  
Frost Heave ◽  
Track Structure ◽  
Slab Track ◽  
Plastic Damage ◽  
Track Irregularity

In order to find out the influence of subgrade frost heave on the deformation of track structure and track irregularity of high-speed railways, a nonlinear damage finite element model for China Railway Track System III (CRTSIII) slab track subgrade was established based on the constitutive theory of concrete plastic damage. The analysis of track structure deformation under different subgrade frost heave conditions was focused on, and amplitude the limit of subgrade frost heave was put forward according to the characteristics of interlayer seams. This work is expected to provide guidance for design and construction. Subgrade frost heave was found to cause cosine-type irregularities of rails and the interlayer seams in the track structure, and the displacement in lower foundation mapping to rail surfaces increased. When frost heave occured in the middle part of the track slab, it caused the greatest amount of track irregularity, resulting in a longer and higher seam. Along with the increase in frost heave amplitude, the length of the seam increased linearly whilst its height increased nonlinearly. When the frost heave amplitude reached 35 mm, cracks appeared along the transverse direction of the upper concrete surface on the base plate due to plastic damage; consequently, the base plate started to bend, which reduced interlayer seams. Based on the critical value of track structures’ interlayer seams under different frost heave conditions, four control limits of subgrade frost heave at different levels of frost heave amplitude/wavelength were obtained.

scholarly journals Geometric Effects Analysis and Verification of V-Shaped Support Interference on Blended Wing Body Aircraft

2020 ◽  
Vol 10 (5) ◽  
pp. 1596
Author(s):  
Xin Xu ◽  
Qiang Li ◽  
Dawei Liu ◽  
Keming Cheng ◽  
Dehua Chen
Keyword(s):  
Wind Tunnel ◽  
High Speed ◽  
Pitching Moment ◽  
Straight Section ◽  
Test Results ◽  
Wind Tunnel Tests ◽  
Blended Wing Body ◽  
Support Interference ◽  
Geometric Effects ◽  
Good Agreement

A special V-shaped support for blended wing body aircraft was designed and applied in high-speed wind tunnel tests. In order to reduce the support interference and explore the design criteria of the V-shaped support, interference characteristics and geometric parameter effects of V-shaped support on blended wing body aircraft were numerically studied. According to the numerical results, the corresponding dummy V-shaped supports were designed and manufactured, and verification tests was conducted in a 2.4 m × 2.4 m transonic wind tunnel. The test results were in good agreement with the numerical simulation. Results indicated that pitching moment of blended wing body aircraft is quite sensitive to the V-shaped support geometric parameters, and the influence of the inflection angle is the most serious. To minimize the pitching moment interference, the straight-section diameter and inflection angle should be increased while the straight-section length should be shortened. The results could be used to design special V-shaped support for blended wing body aircraft in wind tunnel tests, reduce support interference, and improve the accuracy of test results.

Design of a 33-Knot Aluminum Catamaran Ferry

2000 ◽  
Vol 37 (02) ◽  
pp. 88-99
Author(s):  
R. G. Latorre ◽  
P. D. Herrington
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
High Speed ◽  
Frame Structure ◽  
Test Results ◽  
Finite Element Analyses ◽  
The Finite Element Method ◽  
Floating Frame ◽  
Good Agreement ◽  
Panel Design

This paper presents the results of an investigation on the suitability of using hull panels with alternating fixed and floating frames for a 30–40 knot aluminum catamaran ferry. A prototype 4.6 m × 1.8 m bottom hull panel with alternating frames is analyzed numerically and physically tested. The corresponding finite-element analyses and test results are in good agreement. The results show that the floating frame hull panel design is a feasible structure for an aluminum catamaran. The floating frame structure was then used for a 33-knot, 250-passenger aluminum catamaran ferry designed to meet the ABS High Speed Craft rules. A midship section of the catamaran hull was analyzed using the finite-element method. Catamaran weight estimates, heave and pitch motions, and powering estimates are also provided. The results show that the alternating floating frame structure was within the ABS rules stress allowables.

Influence of static preload on vibration reduction effect of floating slab tracks

2018 ◽  
Vol 25 (6) ◽  
pp. 1148-1163 ◽  
Author(s):  
Minghang Li ◽  
Meng Ma ◽  
Weining Liu ◽  
Bolong Jiang
Keyword(s):  
Vibration Reduction ◽  
Coupled Model ◽  
Mitigation Measures ◽  
Vehicle Body ◽  
Reference Case ◽  
Slab Track ◽  
Vibration Responses ◽  
Reduction Effect ◽  
Impact Vibration

To effectively reduce the railway vibration and its environmental impact, vibration mitigation measures are increasingly used. The vibration reduction effect of railway tracks is described quantitatively by insertion loss (IL). ILs obtained from in situ measurements under moving train loads and laboratory tests under artificial excitation differ significantly due to the different track loading state between these two methods. The differences of track loading state are induced by the moving effect of train passages and the preloads effect of vehicle masses, the latter of which is a significant factor to discuss in this paper. In order to study the static preload by vehicle masses influence on the vibration reduction effect in isolated tracks, the steel spring floating slab track and regular slab track, as a reference case, were compared. First, a theoretical simplified model was constructed, following which a finite–infinite element coupled model was built, which was calibrated by experimental test results. Impact loads were applied to both tracks with preloads using unsprung wheelsets or sprung vehicle-body masses, with the total mass varying from 0 t to 30 t. The results demonstrate that the increase in preload of unsprung mass makes the natural frequencies further reduced, and the peak IL value increased from 39 dB to 48 dB. The increase in preload has a significant effect on vibration responses below 5 Hz, and the application of the preload has different effects on the reduction effect in different frequency ranges.

scholarly journals Analysis of Influencing Mechanism of Subgrade Frost Heave on Vehicle-Track Dynamic System

2020 ◽  
Vol 10 (22) ◽  
pp. 8097
Author(s):  
Liang Gao ◽  
Wenqiang Zhao ◽  
Bowen Hou ◽  
Yanglong Zhong
Keyword(s):  
Dynamic System ◽  
High Speed ◽  
Frost Heave ◽  
Leverage Effect ◽  
Cold Regions ◽  
Severe Problem ◽  
Slab Track ◽  
Influencing Mechanism ◽  
Track System ◽  
Track Irregularity

Uneven subgrade frost heave has been a severe problem for the operation of high-speed railways in cold regions. In order to reveal the influencing mechanism of frost heave on the vehicle-track system, a novel FEM (finite element method) model based on an explicit algorithm was proposed. In the novel model, the existence of the leverage effect in slab track, which was caused by frost heave, was realistically reproduced at first, and then the vehicle model started running for evaluating the influence of the frost heave on the whole dynamic system. Results show that the leverage effect plays a key role in analyzing the influence of frost heave on the vehicle-track system, besides for track irregularity and contact loss. Specifically, the leverage effect decreases the stability of the slab track and causes an increase in dynamic irregularity. The roles of the track irregularity and the contact loss in the influencing mechanism were also revealed. With the ratio of wavelength to amplitude increasing, the track irregularity is gradually dominant in the influence mechanism of frost heave on the vehicle-track system. The research could provide a reference for the management and maintenance of the slab track in cold regions.

Hydrodynamic Air-Riding in Leaf Seals

2013 ◽  
Author(s):  
Ingo H. J. Jahn ◽  
David Gillespie ◽  
Paul Cooper
Keyword(s):  
High Speed ◽  
Lift Force ◽  
Coupled Model ◽  
Hydrodynamic Effect ◽  
Fluid Structure Interactions ◽  
Static Structure ◽  
Speed Test ◽  
Full Picture ◽  
Mode A ◽  
Good Agreement

Leaf seals are filament seals for use at static to rotating interfaces in rotating machinery. They are capable of withstanding significant pressure differences while minimising leakage. One of their advantages over comparable filament seals is the ability of the leaves to generate significant hydrodynamic lift at their tips. If this force is sufficient to lift the leaf tip away from the rotor, leaf wear is eliminated and an infinite life seal is created. In order to design seals that are capable of operating in this mode, a good understanding of the hydrodynamic effect and how it interacts with the seal is required. This paper presents a detailed theoretical and experimental investigation into hydrodynamic air-riding in leaf seals. First the hydrodynamic lift is investigated by analysing the flow field and forces generated between a static structure resembling the leaf tip geometry and a moving surface resembling the rotor. This allows the fundamental effects behind air-riding to be identified and quantified. Next a coupled model is presented, which captures the interactions between the lift force and the leaf tip movements. This gives a full picture of the steady-state fluid-structure interactions controlling air-riding in leaf seals. Based on these results several guidelines for obtaining air-riding are extracted. Finally the predictions from the coupled model are compared to results from a high speed test campaign using a prototype leaf seal. Good agreement is found, confirming the presence of hydrodynamic air-riding in leaf seals and demonstrating the accuracy of the presented coupled model.

Theoretical and Experimental Comparisons for Rotordynamic Coefficients of a High-Speed, High-Pressure, Orifice-Compensated Hybrid Bearing

1995 ◽  
Vol 117 (2) ◽  
pp. 285-290 ◽  
Author(s):  
Nancy M. Franchek ◽  
Dara W. Childs ◽  
Luis San Andres
Keyword(s):  
High Pressure ◽  
High Speed ◽  
Discharge Coefficient ◽  
Test Fluid ◽  
Test Results ◽  
Rotordynamic Coefficients ◽  
Hybrid Bearing ◽  
San Andres ◽  
Experimental Comparisons ◽  
Good Agreement

Comparisons are presented between measurements and predictions for a 76.2 mm diameter, high-speed (24,600 rpm), high-pressure (7.0 MPa), hybrid bearings using warm (54°C) water as a test fluid. “Hybrid” refers to combined hydrostatic and hydrodynamic action. Test results are presented for an orifice-fed, square-recess configuration with five recesses. Data are provided for rotordynamic coefficients including direct and cross-coupled stiffness, direct damping, direct added-mass coefficients, and the whirl-frequency ratio. Experimental results are compared to predictions from an analysis by San Andres (1990a), which accounts for both temporal and convective acceleration terms in the fluid film. San Andres’ development uses an orifice discharge coefficient to model the pressure drop from supply pressure to recess pressure. With experimentally determined discharge-coefficient values as input, good agreement is obtained between theory and experiment. However, predictions are sensitive to changes in the orifice discharge coefficients.

scholarly journals Behavior and Control of the Ballastless Track-Subgrade Vibration Induced by High-Speed Trains Moving on the Subgrade Bed with Mud Pumping

2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Junjie Huang ◽  
Qian Su ◽  
Ting Liu ◽  
Wei Wang
Keyword(s):  
High Speed ◽  
Visual Observation ◽  
Vertical Vibration ◽  
Track Structure ◽  
Test Results ◽  
Low Viscosity ◽  
Ballastless Track ◽  
High Speed Trains ◽  
Mud Pumping ◽  
And Control

This paper investigates behavior and control of the ballastless track-subgrade vibration induced by high-speed trains under mud pumping occurring in the subgrade bed. The characteristics of mud pumping occurring in the subgrade bed under the ballastless track structure are analyzed by visual observation and nondestructive testing. Then, based on the injection of the low-viscosity epoxy resin (LVER), the repair procedures for the mud pumping are proposed. A variety of on-site tests are performed on the ballastless track-subgrade with and without mud pumping and also after mud pumping reinforcement to analyze the vibration of the ballastless track-subgrade under the high-speed trains. The test results show that mud pumping can significantly increase the vertical vibration acceleration and displacement of the ballastless track structure and slightly decrease the vibration of subgrade surface. After mud pumping reinforcement, the abnormal vibration of the ballastless track-subgrade can be effectively controlled to make the vibration close to normal. In addition, the vibration ratio of the subgrade surface to the concrete base is proposed as a way to evaluate the effectiveness of the reinforcement of the mud pumping using the LVER, based on the vibration attenuation feature of the ballastless track-subgrade.

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