Monitoring the condition of railway tracks effectively increases the safety of regional railways. A system that uses a compact on-board sensing device was previously developed for monitoring the track condition of regional railways. However, this system does not consider the running speed of the vehicle. In this study, we propose two new methods for diagnosing the condition of tracks considering the travelling speed of the vehicle: one based on the Mahalanobis distance and the other that uses Gaussian process regression. After conducting a test study to verify the effectiveness of the proposed methods, the results showed that both approaches can provide an accurate diagnosis when considering the influence of speed.
When railway vehicles run on sharp curves, the coefficient of friction (COF) between the outer rail and the leading-outside wheel flange of a bogie is an important value related to problems such as wheel/rail severe wear, squeak noise arising from wheel/rail contact, and running safety against flange-climb derailment. In general, it is difficult to grasp the actual state of COF, which changes from moment to moment during commercial operations. From the viewpoint of running safety and maintenance, it is desirable to detect curved tracks with relatively high COF from the entire service line. The monitoring bogie, which can measure wheel/rail contact forces during commercial operations, has realized a long-term observation of wheel/rail contact forces. For further applications of the monitoring bogie, the simulation-based estimation method of COF at the wheel flange have been proposed in the author’s previous paper. Furthermore, an investigation based on roller-rig tests have been conducted. However, the probability of the flange wear progress cannot be determined only by COF at the wheel flange, and other factors should be involved. The wear number is used to assess rolling contact fatigue and wheel/rail wear progress. In the present paper, on the basis of a multi-body dynamics simulation model of the roller-rig equipment, the difference of the wear number among four lubrication conditions on the bogie is clarified. The estimation method of COF is extended to estimate the wear number simultaneously. The extended method is applied to the roller-rig test and the wear number is estimated. The estimated wear number shows qualitative agreement with the amount of wear debris, which is observed in the roller-rig test conducted in previous research.
This paper presents a frequency-domain analytic solution of mathematical expectation for bogie-track dynamic interaction problems in which a random roughness on the railhead is considered. To achieve this, the Floquet transformation is applied to the coupling system consisting of a bogie and an infinite track. Due to the periodicity of the sleeper spacing, the present problem is reduced to that in a representative track unit. Transformed solutions are expressed by Fourier series in the unit cell. The unknown Fourier coefficients are then obtained from infinite simultaneous equations. In the present formulation the vibration reaction due to the roughness is described in terms of the response function of the bogie-track coupling system and the power spectrum density (PSD) of rail roughness. The track dynamic nature which is independent of the roughness is represented by the former. To validate the derived solution, comparison with time-domain numerical solution is carried out. Furthermore, based on the developed frequency-domain method, two kind of pad damping model given by a constant loss factor and viscous damping are compared through evaluation of the expected value of energy spectrum density (ESD) of rail vibration and the PSD of wheel acceleration. Finally, influence of track structure such as the dynamic equivalent stiffness of rail pad and that of under-sleeper pad on the expectation of ESD of rail vibration and the PSD of wheel acceleration is examined.
A “personalized guidance system” has been gathering attention as a service for railroad users that utilizes information and communication technology to guide passengers to the most appropriate train to board. In addition to commuters, there are also some private users who are willing to accept a delay in arrival at their destination if they can avoid congestion, and especially in recent years when infectious diseases are spreading, there are passengers who strongly desire to avoid congestion. The purpose of the individual guidance system proposed in this study is to provide individual guidance that meets the individual requirements of each passenger by classifying passengers into matrix groups according to their disutility for early and late arrival and for congestion, and by reflecting the behavioral characteristics of individual passengers in the guidance. Authors compared the results of two methods used by the system to assign trains to passengers: the “incremental assignment method,” in which passengers are assigned to trains one by one in a certain order, and the “user equilibrium method,” in which all passengers choose the best route for themselves. Authors also proposed an index to quantify passengers’ trust in individual guidance systems, and evaluated the passenger disutility and distrust caused by the guidance systems through an urban rail model. The results showed that when the order in which passengers are assigned to trains is random, both the overall disutility of passengers and their distrust of the guidance system are reduced, and that the disutility of passengers who are assigned to trains earlier is greater. This study confirmed that a guidance method that is easy to implement in society can reduce both overall disutility and individual trust to some extent, but it also revealed that passengers who make decisions early in the process can suffer greater disutility.
The timetable of urban rail greatly affects its daily energy consumption. To improve the utilization of renewable energy between trains using timetabling has become an effective way to reduce energy consumption. Previous studies ignore or simplify the modelling of traction power supply network, which failed to accurately describe the flow of energy between trains through the power network. This paper proposed an optimisation method of energy efficiency timetabling considering the power flow of traction power supply network. First, an urban rail transit DC traction network model is established, and the current-vector iterative method is used to characterize the energy consumption. Then, a train timetable optimisation model is proposed to minimize the total energy consumption of the traction network system by adjusting the dwell time and section running time. The genetic algorithm is used to solve the optimisation problem. Finally, simulation result shows that the proposed method can accurately characterize the energy flow and effectively reduce the total energy consumption of the urban rail transit.
The effect of electropulsing on the extrusion due to persistent slip bands (PSBs) and the defects in PSBs was investigated. To extend the service life and improve structural safety, technology is needed to repair fatigue damage such as cracks and dislocations directly. It has been shown that electropulsing of damaged metallic materials delays fatigue crack initiation and extends fatigue life, but the detailed mechanism of this has not been explained. When cyclic strain is localized into a PSB, the PSB forms lamella, thin walls that contain rich dislocation, and thick channels that contain poor dislocation. The cyclic plastic strain within a PSB causes extrusions and intrusions, called persistent slip markings, to appear on the surface. Cracking is initiated at the tip of the intrusion. Fatigue tests were performed using an electromagnetic force fatigue testing system while applying electropulsing every 2000 cycles to polycrystalline copper. The extrusion height before and after electropulsing was observed through atomic force microscopy. The resulting extrusion growth was slowed by the electropulsing. Polák’s model was applied to examine the effect of electropulsing on the extrusion growth. When the vacancy concentration reaches a steady state in the channel and electropulsing is performed, the vacancies migrate and are assumed to be annihilated at the matrix or walls. Therefore, the vacancy concentration in the PSB decreases with electropulsing. The decrease in vacancy concentration in the PSB is thought to suppress the extrusion growth until the vacancy concentration reaches a steady state again.
The influence evaluation against projectile impacts has attracted much attention for the safety assessment of nuclear-facility buildings subjected to projectiles, such as tornado missiles or aircraft. Many experimental studies have been reported on the impact resistance of reinforced concrete (RC) structures. Based on these results, many empirical formulas for penetration depth, scabbing limit thickness, and perforation-limit thickness have been proposed for the local damage evaluation. However, most formulas were derived from impact tests based on normal impact to target structures using rigid projectiles that do not deform during impact. Therefore, this study develops a local damage evaluation method considering the rigidity of projectiles and oblique impacts that should be considered in realistic projectile impact phenomena. Specifically, we focused on scabbing, defined as the peeling off the back face of the target opposite the impact face, and conducted impact tests on RC panels to clarify the scabbing limit by changing the impact velocity in an oblique impact. The effects of the projectile rigidity and oblique impact on the scabbing limit were investigated based on the test results. This work presents the test conditions, equipment, results, and the scabbing limit on the local damage to RC panels subjected to oblique impacts.
Dump trucks are widely used in the construction industry. When sand is discharged from a dump truck bed, the friction with the bed causes sand to remain on the bed. Therefore, it is desirable to develop a technology to adhere low-friction fluororesin to the steel plates of a truck bed. This study develops a technique for directly joining dissimilar materials, namely steel and polytetrafluoroethylene (PTFE), using one-sided seam welding and investigates the effects of heat input and pressure conditions on joining quality. The joining conditions that affect joining quality are examined. The results show that tensile shear strength tends to increase with increasing heat input. Furthermore, it is found that the amount of PTFE deformation and the fracture morphology during tensile testing change with roller pressurization. For a one-sided seam welding machine, the anchor effect occurs between the electrodes with roller pressurization but does not occur without roller pressurization. It is also found that the type of anchor effect (dense or dispersed) depends on whether roller pressure is applied. Furthermore, it is suggested that the amount of deformation of PTFE during tensile testing is different caused by the different form of occurrence of the anchor effect. It was assumed that the fracture morphology of PTFE changed as the amount of deformation increased during the tensile test, approaching the elongation limit of PTFE. Furthermore, when the rollers were cooled to increase the cooling function of the rollers, the number of anchors was found to be lower than when the rollers were not cooled. This result suggested that the thermal contraction of the PTFE during cooling causes the PTFE in the concave area to peel off. From these results, it is assumed that the reason for the dispersed anchor effect is due to the influence of heat removal by the roller pressurization.
In this study, we aim to investigate the effect of galvanic corrosion on the mechanical properties of aluminum-CFRP adhesive joints. Aluminum-CFRP, aluminum-aluminum, and CFRP-CFRP adhesive joint specimens were prepared. Subsequently, the specimens were subjected to accelerated aging treatment in a salt spray environment, and the tensile shear adhesive strength, the transition of the failure surface and the deposition state and the components of corrosion products with aging time were quantitatively evaluated. As a result, in aluminum-CFRP adhesive joints under the salt spray, galvanic corrosion of the aluminum substrate occurred within 24 hours, and the adhesive-adherend interfacial strength decreased significantly compared to aluminum-aluminum and CFRP-CFRP adhesive joints. In addition, the failure mode of aluminum-CFRP adhesive joints changed from the mixed failure of interfacial failure, cohesive failure, and fiber tear failure to interfacial failure. Furthermore, it was found that the deposition amount of Al2O3 increased under the influence of the salt spray environment.
A “Stroke” is a neurological disease due to poor blood flowing to the brain, resulting in body cell death. It is ranked second as the most common cause of death globally. The “World Health Organization” estimates that about 15 million people suffer a stroke annually. Most stroke survivors have gait disorders, and most patients cannot walk without assistance. Physiotherapy is crucial for stroke patients to recover and maintain their mobility, functionality, and well-being. In the last 20 years, the replacement of physiotherapists with wearable robotics has become essential due to the developing technology, the need for economic growth, and the challenging health circumstances around the world, such as the COVID-19 pandemic recently. Lower Limb Exoskeleton (LLE) represents the solution for stroke patients under such circumstances, though its performance is a critical challenge paid attention to in the industry. This challenge has motivated the researchers to investigate the application of gait rehabilitation. This review presents and discusses the developments in the control system of LLE over the last decade. It also explores the limitations, new directions, and recommendations in LLE development according to the literature.
In this study, we proposed a structural health monitoring and diagnostic method for layered structures using the force identification of approach. This method belongs to the primary diagnosis one, and its purpose is to identify the location of abnormality quickly after abnormality detection. A feature of this method is that the displacement change caused by an abnormality in the structure is considered by applying additional force to the normal structure. In the early stage of abnormality, the stiffness of a certain layer will change, so the local additional force is identified, and the accuracy of the reconstructed displacement change is estimated. In the diagnosis of an actual structure, the actual vibration characteristics may differ from those obtained by the mathematical model. We also proposed a method for predicting the frequency response function in the abnormal state based on the difference between the actual measurement and the mathematical model in the normal state. First, we considered a five-layered structure as a numerical example and validated the proposed method. When we applied the method to three types of abnormal conditions, we found that the abnormality could be diagnosed correctly. Next, we constructed an experimental model of a five-layered structure and verified the applicability of the proposed method. We created a type of abnormal condition and showed that the abnormality could be diagnosed correctly. As described above, the validity and applicability of the proposed method were clarified.
This study proposes a parallel parametric analysis approach, in which parametric analysis for a local shape, such as a hole, is automated and parallelized. For the automation, the present approach is based on an s-version FEM, namely, the coupling-matrix-free iterative s-version FEM. In this method, the hole can be detached from the mesh of the global structure. This feature overcomes a difficulty in generating a mesh with a hole, particularly together with a crack for fracture mechanics analysis. Moreover, the parallelization is implemented by Message Passing Interface (MPI). In the present approach, a large number of analyses for different hole positions are performed in parallel. In each analysis, the hole position is changed using the s-version FEM. Then, this approach was applied to numerical examples of stationary crack problems, namely, a plate with an edge crack and a V-bending die with a circular surface crack. Both examples had a hole, the position of which was the parameter of the parametric analysis. In each numerical example, changes in stress intensity factor of the crack for different hole positions were investigated. It was numerically demonstrated that some hole positions decreased the stress intensity factor of the crack. Moreover, our approach achieved high speedup and parallel efficiency in a strong scaling test.
This paper describes the visualization of defect regions in a structure via hammering test that employs the level set type topology optimization based on the concept of the phase-field method. In this study, the residual between the calculated displacement and the observed displacement is defined as the performance function, with the identification problem of defect regions being formulated based on the adjoint variable and finite element methods. Numerical experiments were performed to investigate the effect of the regularization parameter, the number of observation point, the evaluation equation of convergence and the application of the weighted gradient. Consequently, it was found that the number, position and size of defect can be adjusted using the regularization parameter τ. In addition, it was seen that if the number of observation points and the evaluation equation in the iterative computation of topology update are appropriately given, the identified defect topology is close to the exact defect topology. Furthermore, it was found that defect topologies can be more accurately identified by applying weighted sensitivities.
Cam contour fitting is greatly affected by data segmentation errors. Yet traditional segmentation methods are susceptible to data noise and not able to cope with contour of multiple curve type. Therefore, a new method is proposed based on Generalized Cross Product (GCP), and the segmentation of arc cam contour is taken as examples. Regarding the contour as a series of arc fragments, circular features of each fragment are transformed to a GCP norm by vector mapping. Based on the robustness of GCP, the disturbances of data noises on the GCP norms of a segmented arc are suppressed while those on its adjacent arc are amplified in the mapping. Then there is a sharp contrast in between the GCP norms, i.e. the differences of the features of 2 adjacent arcs are exhibited distinctly. Thus the dividing point between 2 segments can be easily identified. By this way, the cam contour is segmented accurately. Most importantly, the accuracy can be greatly improved through comparing the vector mappings of different mapping parameters. It is validated by experiments that the method can apply to cam contour of various curve type, including spline curves, and has strong robustness against data noise.
This study demonstrates that the robustness of friction dampers can be enhanced by using the positive velocity dependence of the kinetic friction force. First, we show that the kinetic friction coefficient can be reduced under extremely low sliding velocity conditions by using oleyl acid phosphate (OLAP) as an additive to the lubricant on the sliding surfaces between bronze-filled polytetrafluoroethylene (PTFE) and steel. Next, based on the results of the numerical simulations, we show that the use of a sliding surface with a positive velocity dependence of the friction coefficient is effective in improving the vibration reduction ability of the friction dampers. Finally, our findings are demonstrated through a simplified experiment.
Semi-trailers have the advantage that the maximum load capacity is large. However, there are some problems that high driving skill is required because it is necessary to perform unique steering during turning or backward driving. This paper proposes a path planning and tracking algorithm for autonomous parking of semi-trailers. The path planner determines the parking path to the target parking position in accordance with the given parking environment including obstacles. Furthermore, the steering control system is desinged to handle the path tracking and stabilize the hitch angle. The proposed path planning method and tracking control are both unique in that it focuses on the vehicle’s terminal state at the target parking position, and finds the solution in the time-inverse order of the actual driving sequence. The parking simulations is performed and the effectiveness of the proposed method is verified.
Vapor cooling shield is a key technology for long-term cryogenic propellant storage in space. Cooling channels with a triply periodic minimal surface embedded inside are expected to improve its cooling performance. Herein, a cooling channel with a triangle cross-section embedded gyroid structure, a type of the triply periodic minimal surface structure, was additively manufactured. The pressure drop and heat transfer performances of the channel were experimentally measured using liquid nitrogen vapor. Furthermore, in addition to the gyroid-embedded channel, three channels with different cross-sections were fabricated for comparison: circular, triangle, and triangle with a step/groove on the bottom. The gyroid-embedded channel exhibited unique characteristics, with a thermal conductance that was approximately 40% higher than that of the channel with a simple triangle cross-section, but an excessive pressure drop of approximately 50 times higher than that of the other cross-sections. This denotes that strong vortex and turbulence and the flow separation cause excess pressure drop in the gyroidembedded channel. The pressure drop characteristic of the gyroid-embedded channel against the Reynolds number completely differed from that of the other channels, and the pressure drop of the gyroid-embedded channel can be estimated assuming analogy with particle packed beds.