Low Adhesion Conditions Research Articles

Twin disc evaluation of third body materials in the wheel/rail interface

ABSTRACT Twin disc instruments are an essential tool for evaluating third body materials in the wheel/rail interface. Twin disc testing results (from two different scale instruments) were proven to correlate exceptionally well with field performance of Top of Rail products and Gauge Face greases. Furthermore, the twin disc instrument was utilized to evaluate the friction characteristics (creep curve) and Rolling Contact Fatigue (RCF) propagation potential of the TOR materials. Common environmental contaminants (leaves, clay, iron oxides) were studied for their potential to cause low adhesion conditions in presence of water. A correlation between material hardness and resultant friction levels was determined.

Assessing the effectiveness of traction gels using full-scale and field testing

Leaf fall during the autumn season creates low adhesion problems on the railways. Traction gels are used to prevent low adhesion, but very little testing has been carried out to assess their performance. Views on their effectiveness vary and their usage is inconsistent across the UK network as a result. This work developed a range of full-scale laboratory and field tests that can be used to assess traction gel performance. The outcomes can lead to increased industry confidence in their ability to mitigate low adhesion, as well as in future product development. It was shown that as a wheel passes over a puddle of traction gel on a rail head, that the gel element is squeezed away leaving the solid particles behind, pick-up on the wheel of particles was also evident. Traction gels were shown to increase traction in full-scale laboratory friction tests in dry and low adhesion conditions. Field brake tests showed that braking was effective in low adhesion and dry conditions with traction gel applied, matching the laboratory test results. The traction gel was also shown to remove a leaf layer, artificially produced by running a DMU over leaf material on a test track. Subsequent work should validate the results on a working railway line during the autumn season.

Wheel/rail dynamic interaction induced by polygonal wear of locomotive wheels

ABSTRACT Serious wheel polygonal wear usually causes drastic wheel/rail interactions, which threats the running safety of railway vehicles. This paper presents an investigation into the effect of polygonal wear of heavy-haul locomotive wheels on the dynamic performance and wheel/rail interactions through extensive on-site tests and numerical simulations, in which a special attention is paid to locomotive vibrations and dynamic wheel/rail tangential forces. The measured results conducted on two objective locomotives were firstly compared, including the characteristics of wheel polygonal wear and locomotive vibrations in vertical, longitudinal and lateral directions. A 3D heavy-haul train-track coupled dynamic model was then formulated to investigate wheel/rail dynamic interaction induced by polygonal wear of locomotive wheels. A low adhesion zone (LAZ) and a PI-based anti-slip control algorithm were embedded into the dynamic model to analyse the effects of wheel polygonal wear on wheel/rail longitudinal and lateral interactions under normal and low adhesion conditions. The results show that the severe wheel polygonal wear affects not only the vertical but also the longitudinal performance of the wheel/rail system notably. The wheel high-order polygonal wear has a conspicuous effect on longitudinal, lateral and vertical vibrations of locomotive system components.

Microencapsulation of cellular aggregates composed of differentiated insulin and glucagon-producing cells from human mesenchymal stem cells derived from adipose tissue

BackgroundIn type I diabetes mellitus (T1DM) pancreatic β cells are destroyed. Treatment entails exogenous insulin administration and strict diet control, yet optimal glycemic control is hardly attainable. Islet transplant could be an alternative in patients with poor glycemic control, but inefficient islet purification and autoimmune response of patients is still a challenge. For these reasons, it is necessary to explore new cellular sources and immunological isolation methods oriented to develop T1DM cell-based therapies.AimsWe postulate human adipose-derived stem cell (hASC) as an adequate source to generate pancreatic islet cells in vitro, and to produce islet-like structures. Furthermore, we propose microencapsulation of these aggregates as an immunological isolation strategy.MethodshASC obtained from lipoaspirated fat tissue from human donors were differentiated in vitro to insulin (Ins) and glucagon (Gcg) producing cells. Then, insulin producing cells (IPC) and glucagon producing cells (GPC) were cocultured in low adhesion conditions to form cellular aggregates, and later encapsulated in a sodium alginate polymer. Expression of pancreatic lineage markers and secretion of insulin or glucagon in vitro were analyzed.ResultsThe results show that multipotent hASC efficiently differentiate to IPC and GPC, and express pancreatic markers, including insulin or glucagon hormones which they secrete upon stimulation (fivefold for insulin in IPC, and fourfold for glucagon, compared to undifferentiated cells). In turn, calculation of the Feret diameter and area of cellular aggregates revealed mean diameters of ~ 80 µm, and 65% of the aggregates reached 4000 µm2 at 72 h of formation. IPC/GPC aggregates were then microencapsulated in sodium-alginate polymer microgels, which were found to be more stable when stabilized with Ba2+, yielding average diameters of ~ 300 µm. Interestingly, Ba2+-microencapsulated aggregates respond to high external glucose with insulin secretion.ConclusionsThe IPC/GPC differentiation process from hASC, followed by the generation of cellular aggregates that are later microencapsulated, could represent a possible treatment for T1DM.

Modelling and Simulation of an Anti-skid Braking System for Rail Vehicles

Pneumatic braking systems are widely used on rail vehicles. Anti-skid control systems are equipped to prevent wheels from locking and ensure braking distances in low adhesion conditions. To model and simulate an anti-skid pneumatic braking system, a concise modelling method was proposed. By dividing the pneumatic braking control unit into two parts, the complex model was simplified according to its working principle. The pneumatic model, kinematic model, adhesion force model and controller model were established and simulated with MATLAB/Simulink and AMESim. The results show that this method is suitable for anti-skid control modelling and simulation and can be used for controller development and verification.

A Chemically Defined Serum-Free Culture System for Spontaneous Human Mesenchymal Stem Cell Spheroid Formation.

Mesenchymal stem cells (MSCs) possess promising potential in tissue engineering and regenerative medicine. Previous studies demonstrated that spheroid formation of MSCs exhibited improved stemness maintenance and therapeutic potential compared with monolayer culture. To date, various spheroid culture systems have been developed but most of them required low adhesion conditions or special equipment. In this study, we demonstrated that inoculation of dissociated MSCs in TeSR-E8 medium could induce self-assemble spheroid formation in conventional tissue culture polystyrene dishes. Compared with monolayer culture, adipose-derived stem cell (ADSC) spheroids enhanced the proliferation and osteogenic capability of ADSCs compared with monolayer culture. When reseeded in normal serum-containing medium, the expression level of stemness biomarkers was even higher in spheroid-derived ADSCs than monolayer culture. Importantly, spheroid ADSCs could effectively promote the M2 polarization of macrophages both in vitro and in vivo. After transplantation into mouse, spheroid ADSCs improved the survival rate and significantly decreased serum levels of proinflammatory factors IL-1β and TNF-α following LPS challenge. In summary, we developed a 3D spheroid culture system through TeSR-E8 medium without the involvement of low adhesion conditions and special equipment, which provided a practical and convenient method for spheroid formation of MSCs with great potential for stem cell clinical therapy.

Multi-Objective Optimization Study of Regenerative Braking Control Strategy for Range-Extended Electric Vehicle

Currently, the researches on the regenerative braking system (RBS) of the range-extended electric vehicle (R-EEV) are inadequate, especially on the comparison and analysis of the multi-objective optimization (MOO) problem. Actually, the results of the MOO problem should be mutually independent and balanced. With the aim of guaranteeing comprehensive regenerative braking performance (CRBP), a revised regenerative braking control strategy (RRBCS) is introduced, and a method of the MOO algorithm for RRBCS is proposed to balance the braking performance (BP), regenerative braking loss efficiency (RBLE), and battery capacity loss rate (BCLR). Firstly, the models of the main components related to the RBS of the R-EEV for the calculation of optimization objectives are built in MATLAB/Simulink and AVL/Cruise. The BP, RBLE, and BCLR are selected as the optimization objectives. The non-dominated sorting genetic algorithm (NSGA-II) is applied in RRBCS to solve the MOO problem, and a group of the non-inferior Pareto solution sets are obtained. The simulation results show a clear conflict that three optimization objectives cannot be optimal at the same time. Then, we evaluate the performance of the proposed method by taking the individual with the optimal CRBP as the final optimal solution. The comparation among BP, RBLE, BCLR, and CRBP before and after optimization are analyzed and discussed. The results illustrate that characteristic parameters of RRBCS is crucial to optimization objectives. After parameters optimization, regenerative braking torque works early to increase braking energy recovery on low tire-road adhesion condition, and to reduce the battery capacity loss rate at the expense of small braking energy recovery on the medium tire-road adhesion condition. In addition, the results of the sensitivity analysis show that after parameter optimization, RRBCS is proved to perform better road adaptability regarding the distribution of solutions. These results thoroughly validate the proposed approach for multi-objective optimization of RRBCS and have a strong directive to optimize the control strategy parameters of RBS.

Improved modelling of trains braking under low adhesion conditions

ABSTRACT Predicting the behaviour of trains when braking under low adhesion conditions presents considerable challenges. This paper describes an approach to the problem using a model of the full train braking system known as LABRADOR (Low Adhesion Braking Dynamic Optimization for Rolling Stock) and an improved method for representing the creep force–creepage behaviour when low adhesion is presently known as WILAC (Water Induced Low Adhesion Creep Force Model). The development of these models and their integration are summarized and a number of test cases are presented to demonstrate the improvements which can be gained from this approach. A number of suggestions are made for future enhancements with the aim of providing brake engineers and systems integrators with reliable simulation tools for optimizing train braking performance when low adhesion is present.

Double-Drum Test Bench for Variable Load Transfer Simulation by Electromechanical Inertia Compensation.

To improve the accuracy and actual road equivalence of vehicle performance testing using test benches, a double-drum test bench that meets the test requirements of vehicle control system prototypes and in-use vehicles was designed. Dynamic models of the single-wheel test bench and the vehicle test bench were established, and mechanisms were theoretically analyzed for single-wheel variable adhesion and vehicle load transfer for equivalent testing using the variable placement angle. The mechanism of electromechanical inertia compensation was studied to realize stepless simulation of vehicle inertia and simulate dynamic load while braking. The simulation model of the vehicle test bench system was established based on MATLAB/Simulink. Simulations were carried out to verify the anti-lock braking system (ABS) performance test functionality of the test bench under high adhesion, bisectional, and low adhesion conditions. Referring to the simulation conditions, ABS tests under actual test bench and road conditions were carried out. Results demonstrated that the mechanism of variable load transfer simulation by electromechanical inertia compensation improves the equivalent accuracy compared to that of its road test equivalent, verifying the feasibility of the simulation mechanism. This study could help further improve the accuracy and reduce the cost of vehicle performance testing, thus greatly benefitting the vehicle development and testing industry.

Considerations on longitudinal dynamics of passenger trains with blocked wheelsets during braking

The aim of the study is to highlight the fact that, besides the other well-known aspects, wheelsets blocking during braking actions performed in poor wheel/rail adhesion conditions has important influence on the longitudinal dynamics of the train. The study is based on MATLAB numerical simulations, performed for passenger trains consisting of four vehicles. There were considered the possible operational situations specific in low adhesion condition braking, determined by the pitch effect, i.e. the possible blocking of one up to all wheelsets of the vehicle. The results presented in the paper cover two situations: train set composed of identical vehicles, considering only the braking forces and, respective, classical configuration train hauled by a locomotive with a larger weight compared to each coach, resistances being also taken into account in simulations in that case. The outcomes indicate important dynamic effects in the train body, highlighting the importance of using performant wheel slide protection devices, essential not only for traffic safety reasons, but also useful in terms of in-train level of forces. It is to mention that these results represent the initial step of a more comprehensive ongoing study.

A novel anti-lock braking strategy for high speed light weight dual-motor electric drive tracked vehicles

Anti-lock braking strategies are of great importance in improving manoeuvrability of vehicles. However, studies on that of tracked vehicles are rare compared with wheeled vehicles due to their complicated drivetrain and the sluggish of their braking system. Dual-motor electric drive tracked vehicles (DDTVs), whose drivetrain differs significantly from the traditional ones, have drawn a lot of attention in the trends of hybridization and electrification for tracked vehicles, and made it practical to apply advanced braking control strategies with the application of permanent magnet synchronous motors (PMSMs). This paper develops a novel anti-lock braking strategy with a sliding mode controller and a rule based braking torque allocating method to enhance the braking stability. Simulations are conducted under a typical low adhesion condition to compare the control performances of the proposed strategy with normal full braking strategy and traditional anti-lock braking strategy transplanted from wheeled vehicles. Simulation results show that the proposed control strategy performs better than the other two strategies in reducing stopping distances while still has the ability of regenerate braking energy.

Particle characterisation of rail sands for understanding tribological behaviour

Low adhesion between a train’s wheel and the rail can cause performance and safety issues, costing the UK rail industry ~£345 m/annum. Sand is applied to the wheel/rail interface to increase traction when low adhesion conditions are present. In order to improve performance, an understanding of how particles are entrained into and act within the interface is needed. This paper outlines a particle characterisation framework and applies it to sands used in the rail industry: Leighton Buzzard (LB), Central European (CE), and Derbyshire Youlgreave (DY) sand. The largest difference found in this framework was between the sand’s particle size, LB being largest, then CE, then DY. A high pressure torsion rig measured traction when the sands were applied to dry, wet, and leaf extract contaminated conditions, the latter two representing low adhesion conditions. All sands had no impact on wheel/rail adhesion in dry conditions; in low adhesion conditions DY had little influence, whereas LB and CE were found to increase traction. Particles in dry conditions had no effect on test specimen surface roughness, whereas roughness increased when sand was applied in low adhesion conditions. The developed characterisation framework provides a platform for assessing prospective adhesion enhancing particles.

Wheel–rail low adhesion issues and its effect on wheel–rail material damage at high speed under different interfacial contaminations

The objective of this paper is to ascertain the wheel–rail low adhesion mechanism using a high-speed wheel–rail rolling contact test rig under different interfacial contaminations. Based on the experimental results, a numerical method was proposed to investigate the wheel–rail wear and rolling contact fatigue due to low adhesion issues. The experimental results indicated that the wheel–rail low adhesion phenomena can happen under interfacial liquid contaminations, especially at high-speed running condition. Preliminary numerical investigations showed that the low adhesion condition can easily lead to sliding hence serious wear, especially at the speed between 160 km/h and 200 km/h. The temperature rise within the contact patch can be significantly more severe once wheel and rail are in full slip, causing rolling contact fatigue due to material softening.

Blood-brain-barrier organoids for investigating the permeability of CNS therapeutics.

In vitro models of the blood-brain barrier (BBB) are critical tools for the study of BBB transport and the development of drugs that can reach the CNS. Brain endothelial cells grown in culture are often used to model the BBB; however, it is challenging to maintain reproducible BBB properties and function. 'BBB organoids' are obtained following coculture of endothelial cells, pericytes and astrocytes under low-adhesion conditions. These organoids reproduce many features of the BBB, including the expression of tight junctions, molecular transporters and drug efflux pumps, and hence can be used to model drug transport across the BBB. This protocol provides a comprehensive description of the techniques required to culture and maintain BBB organoids. We also describe two separate detection approaches that can be used to analyze drug penetration into the organoids: confocal fluorescence microscopy and mass spectrometry imaging. Using our protocol, BBB organoids can be established within 2-3 d. An additional day is required to analyze drug permeability. The BBB organoid platform represents an accurate, versatile and cost-effective in vitro tool. It can easily be scaled to a high-throughput format, offering a tool for BBB modeling that could accelerate therapeutic discovery for the treatment of various neuropathologies.

Modelling and simulation of the train brake system in low adhesion conditions

This paper describes the current version of the Low Adhesion Braking Dynamic Optimisation for Rolling Stock (LABRADOR) simulation tool that can predict the train brake system performance and support decision-making in the design and optimisation of the braking system including wheel slide protection, sanders and the blending and control of friction and dynamic brakes in low adhesion conditions. The model has been developed in MATLAB/Simulink and is intended to mimic the braking performance of both older and newer generations of multiple unit passenger trains. LABRADOR models have been initially validated by comparing simulation results for a single car train (Class 153) and two-car train (Class 158) in dry conditions with experimental tests, for tare and crush laden vehicles. This project is supported by RSSB and a technical steering group composed of railway braking experts, suppliers and train operators and manufacturers.

Near real-time monitor of rail way track adhesion conditions

In this paper we examine the possibilities of using sensor data from trains in service to develop a real-time monitor of the adhesion conditions of the rail. In everyday railway operations, low adhesion conditions of the track are an important challenge for railway operators, since these may result in a loss of punctuality, an increase in wear of both wheel and rail, and in an increase of the risk for red signal passage in situations where trains are unable to stop in time. At the same time, prudent driving behavior while the adhesion conditions returned to normal, results in unnecessary train delays. A central issue here is that rail adhesion conditions vary across space and time. To date it is a challenge to give accurate real-time information to both train drivers and infrastructure managers. With real-time monitoring of the adhesion conditions, the drivers can adjust their (de)acceleration control to local adhesion conditions and thereby minimize wear, and the infrastructure managers could improve the track conditions by taking friction enhancing measures. To monitor the adhesion conditions of the track, we used real-time sensor data from ~20 trains. We designed an algorithm that can diagnose track sections as having either slippery or normal adhesion conditions. Specifically, we trained a logistic classifier on a data set that contained reported rail adhesion conditions as well as sensor data from trains in service, such as information about traction, velocity, excessive wheel slip-/sliding detection, and weight. We then assessed the performance of this classifier using an independent test data set. This first assessment shows a classification accuracy of approximately 77%, with a ~23% false positive rate and a ~23% false negative rate, when compared to the drivers reporting. Several improvements are proposed to increase the sensitivity, which outline the directions of our future research towards the implementation of a real-time monitor of railway track adhesion conditions.

Re-adhesion control strategy based on the optimal slip velocity seeking method

In the railway industry, re-adhesion control plays an important role in attenuating the slip occurrence due to the low adhesion condition in the wheel–rail interaction. Braking and traction forces depend on the normal force and adhesion coefficient at the wheel–rail contact area. Due to the restrictions on controlling normal force, the only way to increase the tractive or braking effect is to maximize the adhesion coefficient. Through efficient utilization of adhesion, it is also possible to avoid wheel–rail wear and minimize the energy consumption. The adhesion between wheel and rail is a highly nonlinear function of many parameters like environmental conditions, railway vehicle speed and slip velocity. To estimate these unknown parameters accurately is a very hard and competitive challenge. The robust adaptive control strategy presented in this paper is not only able to suppress the wheel slip in time, but also maximize the adhesion utilization performance after re-adhesion process even if the wheel–rail contact mechanism exhibits significant adhesion uncertainties and/or nonlinearities. Using an optimal slip velocity seeking algorithm, the proposed strategy provides a satisfactory slip velocity tracking ability, which was demonstrated able to realize the desired slip velocity without experiencing any instability problem. The control torque of the traction motor was regulated continuously to drive the railway vehicle in the neighborhood of the optimal adhesion point and guarantee the best traction capacity after re-adhesion process by making the railway vehicle operate away from the unstable region. The results obtained from the adaptive approach based on the second-order sliding mode observer have been confirmed through theoretical analysis and numerical simulation conducted in MATLAB and Simulink with a full traction model under various wheel–rail conditions.

Intervention criterion and control research for active front steering with consideration of road adhesion

ABSTRACTA multi-objective active front steering (AFS) control system considering the road adhesion constraint on vehicle stability is developed using the sliding mode control (SMC) method. First, an identification function combined with the relationship between the yaw rate and the steering angle is developed to determine whether the tyre state is linear or nonlinear. On this basis, an intervention criterion for the AFS system is proposed to improve vehicle handling and stability in emergent conditions. A sideslip angle stability domain enveloped by the upper, lower, left, and right boundaries, as well as the constraint of road adhesion coefficient, is constructed based on the phase-plane method. A dynamic weighting coefficient to coordinate the control of yaw rate and sideslip angle, and a control strategy that considers changing control objectives based on the desired yaw rate, the desired sideslip angle, and their proportional weights, are proposed for the SMC controller. Because road adhesion has a significant effect on vehicle stability and to meet the control algorithm's requirement of real-time access to vehicle states, a unscented Kalman filter-based state observer is proposed to estimate the adhesion coefficient and the required states. Finally, simulations are performed using high and low road adhesion conditions in a Matlab/Simulink environment, and the results show that the proposed AFS control system promptly intervenes according to the intervention criterion, effectively improving vehicle handling and stability.

Optimisation of a Railway Sanding System: Adhesion Tests

Contamination on the railhead such as crushed leaves, oxide formation or even changes in atmospheric conditions can cause adhesion loss between the wheel and the rail. In these situations, trains can lose some or all of their braking capacity leading to vehicles coming within dangerously close proximity to one another. Low adhesion situations are traditionally combatted by firing sand directly into the wheel/rail contact from on-board the train. Previous testing has been carried out to investigate the optimum sanding system set-up which delivers the most amount of sand to the wheel/rail interface. The testing presented in this paper is a continuation of the previous set-up tests and focuses on adhesion differences when sand enters the contact under low adhesion conditions. A full-scale test facility was used for these tests. Firstly, tests were undertaken which investigated the effect of sand density on the rail head and how this affects adhesion restoration. A second set of tests looked at how adhesion was restored when sand was fired into the contact using the ideal sanding system set-up found in previous testing.

Analysis of Wheel-Rail Contact under partial slip and low speed conditions

The paper analyzes applicability of rolling contact simulation in low speed and adhesion conditions. Additionally, transition zone of the coefficient of friction is implemented. Efffects of the friction coefficient are examined to the forces which are normal and tangential components. Various comparative studies are also computed and differences between numerical results with results of the comparative studies are observed for validation. The results show that outputs of developed FEM model are compatible with comparative studies. Transition zone of the coefficient of friction directly affects the traction force at low speed conditions.DOI: http://dx.doi.org/10.5755/j01.mech.23.1.13779