Contact Force Fluctuation Research Articles

Rapid Adaptation for Active Pantograph Control in High-Speed Railway via Deep Meta Reinforcement Learning.

Active pantograph control is the most promising technique for reducing contact force (CF) fluctuation and improving the train's current collection quality. Existing solutions, however, suffer from two significant limitations: 1) they are incapable of dealing with the various pantograph types, catenary line operating conditions, changing operating speeds, and contingencies well and 2) it is challenging to implement in practical systems due to the lack of rapid adaptability to a new pantograph-catenary system (PCS) operating conditions and environmental disturbances. In this work, we alleviate these problems by developing a revolutionary context-based deep meta-reinforcement learning (CB-DMRL) algorithm. The proposed CB-DMRL algorithm combines Bayesian optimization (BO) with deep reinforcement learning (DRL), allowing the general agent to adapt to new tasks quickly and efficiently. We evaluated the CB-DMRL algorithm's performance on a proven PCS model. The experimental results demonstrate that meta-training DRL policies with latent space swiftly adapt to new operating conditions and unknown perturbations. The meta-agent adapts quickly after two iterations with a high reward, which require only ten spans, approximately equal to 0.5 km of PCS interaction data. Compared with state-of-the-art DRL algorithms and traditional solutions, the proposed method can promptly traverse scenario changes and reduce CF fluctuations, resulting in an excellent performance.

A Reinforcement Learning-Based Pantograph Control Strategy for Improving Current Collection Quality in High-Speed Railways.

In high-speed railways, the pantograph-catenary system (PCS) is a critical subsystem of the train power supply system. In particular, when the double-PCS (DPCS) is in operation, the passing of the leading pantograph (LP) causes the contact force of the trailing pantograph (TP) to fluctuate violently, affecting the power collection quality of the electric multiple units (EMUs). The actively controlled pantograph is the most promising technique for reducing the pantograph-catenary contact force (PCCF) fluctuation and improving the current collection quality. Based on the Nash equilibrium framework, this study proposes a multiagent reinforcement learning (MARL) algorithm for active pantograph control called cooperative proximity policy optimization (Coo-PPO). In the algorithm implementation, the heterogeneous agents play a unique role in a cooperative environment guided by the global value function. Then, a novel reward propagation channel is proposed to reveal implicit associations between agents. Furthermore, a curriculum learning approach is adopted to strike a balance between reward maximization and rational movement patterns. An existing MARL algorithm and a traditional control strategy are compared in the same scenario to validate the proposed control strategy's performance. The experimental results show that the Coo-PPO algorithm obtains more rewards, significantly suppresses the fluctuation in PCCF (up to 41.55%), and dramatically decreases the TP's offline rate (up to 10.77%). This study adopts MARL technology for the first time to address the coordinated control of double pantographs in DPCS.

Active vibration control in robotic grinding using six-axis acceleration feedback

Industrial robots endure severe vibrations in the grinding process due to factors such as joint flexibility, low damping, and contact force fluctuations. Additionally, the motion control of the robot primarily relies on feedback signals from the motor-side encoders, while lacking motion state feedback from the load side. This exacerbates the robot vibrations, severely compromising the surface quality of the workpieces. To address this problem, an active damping control method for robotic grinding using six-axis acceleration feedback is proposed. This method realizes a simple, reliable, and efficient active vibration control without altering the robot body. A multi-sensor fusion Cartesian space six-axis accelerometer is designed and integrated into the robot end effector, achieving accurate feedback on the robot load side vibration state. The strategy of six-axis acceleration decoupling and principle of the vibration suppression with the acceleration feedback are explained. Compared with conventional sensing schemes, this reduces joint acceleration approximation errors and end vibrations. The robotic grinding experiments are carried out on aeronautic structural parts. Extensive case studies demonstrate that the proposed approach can effectively control the vibration caused by joint flexibility in the robot grinding process, and greatly improve the surface quality of workpieces. This method has great potential application in vibration suppression during robotic grinding and polishing.

Study on the effect of different structural parameters on the wear mechanism in the anchor-segment joint of the rigid overhead catenary

Abnormal wear can occur at the anchor joint section of a rigid catenary in metro vehicles. This study aims to compare the impact of the contact wire distance at the anchor joint section on the wear mechanism between the contact wires and the carbon skateboard. The findings indicate that contact pairs with a reduced center distance of contact wires exhibited lower contact stress and displayed minimal fluctuations in the dynamic contact force, and the coefficient of friction increased after decreasing. The wear rate demonstrates an inverse correlation with the center distance of the contact wires. Furthermore, the electrical contact resistance continuously increases as the slip distance increases.

Sensitivity Analysis and Optimisation of Key Parameters for Railway Rigid Overhead System and Pantograph

This paper aims to enhance the speed of rigid overhead systems by investigating the impact of important parameters of the overhead system and pantograph on the interaction performance, specifically the contact force between the panhead of the pantograph and the contact wire of the overhead system. To accomplish this, this paper first builds a rigid overhead system model based on the finite element method. The pantograph–contact wire interaction simulation is achieved by including a three-stage lumped mass pantograph model. The Sobol sensitivity analysis method is utilised to determine the contribution of different parameters to the contact force standard deviation. Subsequently, an optimisation approach is used to minimise the contact standard deviation at various speeds by adopting five crucial parameters. The sensitivity analysis of 13 variables indicates that the span length, bending stiffness, and linear density of the conductor rail, and the masses of the pantograph head and upper frame are the most relevant variables for the contact force standard deviation. The quantification of each parameter’s contribution reveals that the increase in bending stiffness generally has a positive effect in reducing the contact force fluctuation, while the decreases in other variables are preferred. The optimisation analysis shows that the optimised contact force standard deviation decreases by 39.18%, 66.77%, and 61.02% at speeds of 90 km/h, 120 km/h, and 150 km/h, respectively, compared to the original values.

Experimental Investigation on the Arc Damage and Fatigue Crack Initiation Risk of Copper-Silver Contact Wires

Contact wires are subjected to both mechanical and electrical interactions while electrical energy is transmitted to the trains by overhead lines and train pantographs. Particularly, an increase in the speed of trains can result in greater contact force fluctuations and more intense pantograph arcs, therefore, these mechanical and electrical interactions have potential to drive failure of Overhead Line Equipment (OLE) conductors. In this paper, the effect on fatigue crack initiation risk of material ablation from the contact wire surface due to arc discharge is experimentally investigated under laboratory conditions. Fatigue life, crack propagation directions and crack initiation locations in arc-exposed copper silver contact wire samples are compared with those in comparable arc-free samples. The results show that under the conditions of having arc damage on the contact wire surface could result in 50% shorter fatigue life compared to arc-free contact wires. It is often considered that wear rather than fatigue cracking defines the life of the contact wires, but under some conditions with the combination of arcing, the fatigue life in the contact wire can become the controlling failure risk. Therefore, in determining system life and maintenance requirements the fatigue life of the contact wire should be taken into consideration at locations where the arc discharge is likely.

Armature Design Recommendations Based on Action Parameters

Force resolution over a C-armature reveals a large Lorentz force that acts to push the armature into rails. Large contact forces lead to a multitude of problems and efficiency losses. This article introduces a set of new parameters called action parameters (APs): armature action and action constant. These parameters optimize armature–rail (A/R) contact force to desired levels and improve muzzle velocity and launcher efficiency. The kinetic energy increases by 7.56 times for the case considered in this article. However, issues regarding loss of compliance and contact force fluctuations arising from optimizing C-armature unveil the need to develop a new armature design. It is recommended that the new armature should have a monolithic design, mechanical load carrying capacity, compliance, and a short current path. Such a hybrid armature design is proposed, and the design process is described.

Static and Dynamic Analysis of Conductor Rail with Large Cross-Sectional Moment of Inertia in Rigid Catenary Systems

The rigid catenary system is widely used in tunnels to power electric trains via contact with a pantograph. Due to gravity, the contact wire normally has a sag that may affect the dynamic interaction performance with a pantograph. To reduce the contact wire sag, the most efficient measure is to improve the moment of inertia of the conductor rail, which is used to clamp the contact wire. Six new types of conductor rail with large moments of inertia are developed based on a conventional conductor rail. Then both the static and dynamic analyses are conducted to investigate the performance of the new types of conductor rail with a big moment of inertia. The conductor rail’s 3D solid finite element model is built using a finite element approach. The vertical deflection and the stress distribution are comparatively analyzed among different types of conductor rail. The analysis results indicate that the vertical deflection and maximum stress are significantly reduced when using the conductor rail with a large moment of inertia. The best performance is observed when the conductor rail of case 1 is used. The maximum sag is reduced by 28.37%, and the maximum stress is decreased by 27.76% compared with the conventional conductor. Finally, a pantograph model is included to evaluate the dynamic performance of the conductor rail with large moments of inertia. The results indicate that contact force fluctuation is significantly reduced after the conductor rails with large moments of inertia are presented. The conductor rail of case 1 shows the best performance, which can reduce the contact force standard deviation by 32% and 27% at speeds of 160 km/h and 200 km/h.

Deep Reinforcement Learning Based Active Pantograph Control Strategy in High-Speed Railway

The pantograph-catenary system (PCS) is the essential power supply system in the high-speed railway, but its coupling performance is influenced significantly by the rapidly increasing train speed. The actively controlled pantograph is one of the promising technologies to suppress the fluctuation of the pantograph-catenary contact force (PCCF). In this paper, we propose a novel pantograph control strategy based on deep reinforcement learning (DRL) to overcome the complex time-varying characteristic of PCS, which distorts the system identification of the classical control methods. First, a non-linear pantograph-catenary system model is established based on the finite element and multi-body dynamics theory as the simulation environment in DRL. Then, the state space, action space, and reward in DRL are redesigned to train the agent, which is suitable for PCS. Finally, the effectiveness and robustness of our proposed method are verified under various working conditions and parameter disturbances. The experiment results show that our control strategy can reduce the PCCF fluctuation up to 40% and reject parametric perturbation while achieving state-of-the-art performance on the benchmarks.

Disturbance Observer-Based Sliding Mode Controller for Regulating Pantograph–Catenary Contact Force

For most electrified railways, pantographs play a vital role in transmitting energy from overhead line to vehicles, and therefore a stable and continuous contact behavior is required. This paper proposes a disturbance observer-based sliding mode controller (DO-SMC) for the problem of pantograph–catenary contact force regulation. The simulation results show that the DO-SMC with a chattering alleviation approach can effectively reduce contact force fluctuation through a reasonable control input.

An Experimental Study on Friction Contact Between Chamfered Labyrinth Fin and High Speed Rotor

Abstract This study reports an experimental work on friction contact between the chamfered labyrinth fin and high speed rotor at different incursion rates, final incursion depths, and sliding velocities. The small (original design case) and large specimens were selected to quantify the geometrical impact on the mass loss, plastic deformation, wear pattern, contact forces, and frictional temperature variations in the chamfered labyrinth fins. The results show that the contact-separations and contact force fluctuations are generated in rubbing events, which significantly affect the wear characteristics, contact forces, and temperature distributions for the small and large specimens. The abrasive and oxidation wears have pronounced influence on the wear behaviors of the tested specimen. At the same incursion condition, the mass loss percentages for the large specimen and small specimen are almost identical. As the sliding velocity increases from 55 m/s to 110 m/s, the mass loss percentage is decreased by 12–36%. For the large specimen, the mushrooming damage is mainly generated in the fin tip. The averaged frictional coefficient is 0.08–0.17, and the maximum temperature in the contact region is 640–700 °C. For the small specimen, the combined mushrooming and bending damage is generated in the labyrinth fin tip. The averaged frictional coefficient is 0.13–0.25, and the maximum temperature is 560–600 °C in the contact region. Due to the increased elasticity for the small specimen, the temperature fluctuation in the rubbing event is not as significant as the large one.

Integration of a dissipative contact force model into vehicle–track dynamics for analysing wheel–rail dynamic interaction under short-wavelength irregularity

Wheel–rail dynamic interaction under short-wavelength irregularity which has a detrimental effect on the service life of vehicle and track components, is of crucial importance to be estimated accurately. Aiming at this, dissipative contact force models are integrated into a validated vehicle–track coupled dynamics model, which enables to consider the energy dissipation at the wheel–rail interface. Wheel–rail interactions for different dissipative contact force models are evaluated, and the Hu–Guo model is selected as the most suitable one for wheel–rail interaction analysis. The wheel–rail interactions for the Hu–Guo model and Hertz theory are analysed under different track irregularities including sinusoidal rail corrugation and rail welded joints. The simulation results indicate that the Hu–Guo model has little effect on the normal interaction at low frequencies, but reduces the contact force fluctuation amplitude obviously at high frequencies above 600 Hz, with a more significant reduction at the resonance peak of high frequency range. The Hu–Guo model has an obvious contact force phase lead compared with the Hertz theory at higher frequencies above 1250 Hz. The Hu–Guo dissipative contact force model is needed for the wheel–rail interaction analysis at high frequencies above 600 Hz.

Fluctuation of particles during funnel flow discharge from flat‐bottomed silos

AbstractAlthough resonant motion of particles during mass flow discharge from silos has been extensively investigated by earlier researchers, the appearance of such phenomenon during funnel flow discharge has not been emphasized. In this work, the flow behavior of particles during funnel flow discharge from flat‐bottomed silos has been investigated by conducting three‐dimensional Discrete Element Method (DEM) simulations. It is found that particles in the upper part of flowing zone move collectively, manifested by the oscillatory fluctuations of the velocity and the non‐Gaussian characteristics of the fluctuations of individual velocity around the average. Correlation analysis and discrete Fourier transform have been performed to characterize the emission and propagation of velocity fluctuation. It is found that the observed resonant motion of particles is induced by the regular fluctuation of contact force between particles, and there exists an intermediate region in the converging part of the flowing zone. The bottom boundary of this region corresponds to the emission source from which the velocity wave propagates upward and downward. Its upper boundary coincides with that of the converging part of the flowing zone and is featured by the most violent fluctuation of contact force. The simulation results thus suggest that the discharge of granular assembly seems to be determined by the rheological behavior of particles in this intermediate region.

Study on the effect of the fastener support structure on rail corrugation in metros based on the friction-induce vibration

Rail corrugation is very serious in Cologne egg fastener track; effective control measures are still lacking. The cause of the corrugation wear on a curved metro track is analyzed based on the friction-induced vibration theory. A finite element model is established to study the frequency domain and time domain features of the friction-induced oscillation of this system. The influences of the fastener spacing and the fastener support length on the corrugation wear are investigated to develop countermeasures. The simulation results show that the friction-induced vibration of the wheel-track system is the wavelength-fixed mechanism of the corrugation wear of rail of the curved Cologne egg fastener track. There are two reasons why the low rail corrugation wear is more serious. The contact resultant force between the low rail and the wheel is obviously bigger than that between the wheel and the high rail, resulting in a higher wear rate of the low rail. The contact force fluctuation of the low rail caused by the friction-induced vibration is more severe, resulting in a higher corrugation wear evolution speed on the low rail. The friction-induced oscillation cannot be eliminated only by adjusting the fastener support length and spacing. However, the long-wavelength corrugation wear instead of the more harmful short-wavelength corrugation wear can be produced by adjusting the fastener support length and the fastener spacing to alleviate the influence of corrugation wear on the vehicle-track system.

Evaluation of the influence of the speed, preload and span length on the contact forces in the interaction between the pantograph and the overhead conductor rail

The Overhead Conductor Rail is one of the methods to transmit energy to a moving train. This power feeding system has some advantages compared to the conventional overhead catenary system. However, its use is still mainly limited to underground and tunnel train infrastructures, probably due to a lack of knowledge of the performance of this method in some operating conditions. This work is devoted to the study of the influence of the speed, preload, and span length on the contact forces in the interaction between the pantograph and the overhead conductor rail. Three different lumped-element models of commercially available pantographs and a finite element model of the overhead conductor rail have been used to carry out the simulations. The contact forces between each pantograph and the catenary have been obtained in all cases. The analysis of the results reveals that the higher the speed and span length are the higher the contact force fluctuations are. On the contrary, the increase in the preload leads to lower contact force oscillations provided no resonance effects are present.

A multi-center experience of ablation index for evaluating lesion delivery in typical atrial flutter.

Anatomical studies demonstrate significant variation in cavotricuspid isthmus (CTI) architecture. Thirty-eight patients underwent CTI ablation at two tertiary centers. Operators delivered 682 lesions with a target ablation index (AI) of 600 Wgs. Ablation parameters were recorded every 10-20ms. Post hoc, Visitags were trisected according to CTI position: inferior vena cava (IVC), middle (Mid), or ventricular (V) lesions. There were no complications. 92.1% of patients (n=35) remained in sinus rhythm after 14.6 ± 3.4 months. For the whole CTI, peak AI correlated with mean impedance drop (ID) (R2 =0.89, p<.0001). However, analysis by anatomical site demonstrated a non-linear relationship Mid CTI (R2 =0.15, p=.21). Accordingly, while mean AI was highest Mid CTI (IVC: 473.1 ± 122.1 Wgs, Mid: 539.6 ± 103.5 Wgs, V: 486.2 ± 111.8 Wgs, ANOVA p<.0001), mean ID was lower (IVC: 10.7 ± 7.5Ω, Mid: 9.0 ± 6.5Ω, V: 10.9 ± 7.3Ω, p=.011), and rate of ID was slower (IVC: 0.37 ± 0.05 Ω/s, Mid: 0.18 ± 0.08 Ω/s, V: 0.29 ± 0.06 Ω/s, p<.0001). Mean contact force was similar at all sites; however, temporal fluctuations in contact force (IVC: 19.3 ± 12.0mg/s, Mid: 188.8 ± 92.1mg/s, V: 102.8 ± 32.3mg/s, p<.0001) and catheter angle (IVC: 0.42°/s, Mid: 3.4°/s, V: 0.28°/s, p<.0001) were greatest Mid CTI. Use of a long sheath attenuated these fluctuations and improved energy delivery. Ablation characteristics vary across the CTI. At the Mid CTI, higher AI values do not necessarily deliver more effective ablation; this may reflect localized fluctuations in catheter angle and contact force.

Dynamic characteristics and growth curve of rail corrugation at saturation stage

Rail corrugation, which causes the vibration and the noise, is a phenomenon in which roughness patterns of approximately regular wavelengths are formed on the rail running surface by trains running. In the previous paper, we have already explained the growth mechanism and the wavelength determination mechanism of the rail corrugation from the dynamic point of view and that there are three stages in the evolution process of the corrugation: formation, growth and saturation. In this paper, we analyze the dynamic characteristics of the track and vehicle in the saturation stage, propose a growth curve of corrugation, and verify them based on measured data obtained on commercial lines. As a result, it is confirmed that when the roughness amplitude grows and exceeds the critical roughness amplitude, there are two characteristics: the significant increase of the contact force fluctuation and the acceleration of the rail and wheel, formation of higher-order roughness components of the corrugation. The growth curve of the corrugation can be approximated by a logistic function.

Rheology and scaling behavior of cascading granular flows in rotating drums

Mixing, agglomerating, and milling of granular materials within a rotating drum is often performed in the cascading flow regime; however, the scaling behavior of these industrial applications remains poorly understood. It involves both centrifugal forces and an inertial surface flow with a curved profile. By means of discrete element simulations, we investigate the rheology of cascading flows in rotating drums as a function of drum size, rotation speed, and filling degree. We find that the surface profile, described by the ratio between the steepest descent slope and an average slope, is strongly correlated with flow variables such as active layer thickness, contact force variability, and wall slip. We show that the flow variables cannot be scaled by Froude number alone but are instead nicely scaled by a dimensionless parameter that combines the Froude number with other system parameters. This scaling works even for small drums and low filling degrees where finite-size effects prevail and the slippage of particles at the drum wall considerably affects the cascading flow at the free surface. The observed correlation between this parameter and contact force fluctuations suggests that it may also be a relevant upscaling parameter for milling and agglomeration in rotating drums.

On the dynamics of a lubricated roller contact

This study proposes a dynamic model of a lubricated roller contact, focusing on the excitation of surface pit/defect. The fluctuation of contact force caused by periodic surface topography variation is used to determine the dynamic displacements and velocities of contact bodies. These responses, in turn, affect the thickness and flow of lubrication film, impacting contact pressure, and consequently contact force that is required in the dynamic analysis. It is shown, as the pit size grows, the acceleration increment escalates, therefore, can be used as an effective indicator for pitting failure occurrence. Additionally, a comparison of contact pressure between dynamic simulation and its quasi-static counterpart points to the importance of dynamic responses in tribological behavior description.

Reduction of Contact Force Fluctuation for Rotary Wear Test Apparatus

In electric railway systems, wear of current collector devices leads to high maintenance cost. To develop a cost reduction methodology, the wear behavior of current collector materials needs to be fully investigated. However, the wear test apparatuses currently in use cannot control the contact force between materials, and the contact force fluctuates. It is difficult to classify accurate conditions of a wear transition under contact force fluctuation. To solve this problem, we propose a force control system with acceleration and velocity feedbacks to suppress the force fluctuation. The positive feedback of acceleration compensates the periodic force fluctuation at frequencies according to the sliding velocity of rubbing surfaces. The velocity feedback compensates the force fluctuation caused by resonance. The proposed control system is validated by experiments using a prototype of a rotary wear test apparatus.