Net Traction Research Articles

Cooperative optimal train operation algorithm for utilizing regenerative braking energy

The efficient use of regenerative braking energy between trains can significantly reduce the net traction energy consumption in urban rail transit systems, and has attracted considerable attention in recent years. An effective way of using regenerative braking energy is to adjust the train's coasting or cruising phase to an acceleration phase to match the braking phase of a nearby train within the same substation. This paper formulates the train driving phase adjustment problem as a cooperative optimal control problem, where a novel energy constraint is introduced to ensure efficient use of regenerative braking energy during the adjusted phase with optimal traction effort. By applying the control parameterisation method and elaborate handling of the energy constraint and the non-smooth control bound constraint, we transform the formulated problem into a nonlinear programming problem. We then use the sequential quadratic programming algorithm to solve the resulting problem, with the gradients of the cost and constraint functions computed using the sensitivity method. Numerical examples based on real-world data for a subway line show the effectiveness of the proposed method and its advantages over a genetic algorithm in terms of energy savings and computational efficiency.

Assessment of Tractor Tires Used in Forest Conditions in Terms of Traction Performance and Impact on Ground

This paper presents the assessment of selected tractor tires used in forest conditions. The first element of this assessment is related to tractive properties, while the second part concerns the potential negative impact of the tires on the ground. The research was conducted on the skid trail located in a lowland pine stand in Poland (Lower Silesian District). The 9.5-24, 400/55-22.5 and 11.2R24 tires were used for the experiment, and the following tractive parameters were analyzed: traction force, pulling force and rolling resistance. These parameters were determined during the experiment using special measure stand mounted on a 3-point linkage of the tractor. In addition to the traction properties, the impact of the wheel on the ground was determined – this evaluation included measurements of footprint areas and calculation of contact pressures. Based on the obtained results, it was shown that the increase of the vertical load and reduction of the inflation pressure of tires can cause an increase in net traction force of as much as 35% and 16%, respectively. The analysis of contact areas and pressures showed that the widest tire (400/55-22.5) had the least negative impact on the ground. The reducing of inflation pressure allowed to obtain higher traction force, higher contact area and smaller contact pressures.

Development and Experimental Validation of an Agricultural Robotic Platform with High Traction and Low Compaction

Some researchers expect that future agriculture will be automated by swarms of small machines. However, small and light robots have some disadvantages. They have problems generating interaction forces high enough to modify the environment (lift a stone, cultivate the soil, or transport high loads). Additionally, they have limited range and terrain mobility. One option to change this paradigm is to use spikes instead of wheels, which enter the soil to create traction. This allows high interaction forces with the soil, and the process is not limited by the weight of the vehicle. We designed a prototype for mechanical soil cultivation and weeding in agricultural fields and evaluated its efficiency. A static and dynamic test was performed to compare the energy input of the electrical motor with precise measurements of the forces on the attached tool. The results indicate that the prototype can create interaction forces of up to 2082 N with a robot weight of 90 kg. A net traction ratio of 2.31 was reached. The dynamic performance experiment generated pull forces of up to 1335 N for a sustained net traction ratio of 1.48. The overall energy efficiency ratio for the machine reached values of up to 0.54 based on the created draft force and the measured input energy consumption.

Design of a special rigid wheel for traversing loose soil

Wheels play an important role in mobile robotics, wheelchairs and vehicles and represent an ideal solution for traversing rigid ground due to higher efficiency. Through traversing loose soil, the rigid wheels lose traction because of sinking and higher slip ratios. Therefore, the study suggests a new rigid wheel with a distinguished perimeter to increase mobility demands to overcome the previous inevitable concerns and clarifies its full detailed design. The lateral undulation locomotion of snakes inspired the author to introduce a new simple and affordable wheel design. The optimum values of the limbless creature movement on the sand are reflected in the geometrical parameters of the wheel, amplitude to wavelength ratio. In addition, the experimental work assessed the traveling performance of the fabricated wheel on the rigid ground and the sandy soil. The attained net traction and slip ratios approach the values of more complicated, expensive and heavier wheels that were used in farming and planetary exploration. Consequently, the wheel enables the wheeled locomotive to do missions on sandy soil with no trouble.

ACDRL: An actor–critic deep reinforcement learning approach for solving the energy-aimed train timetable rescheduling problem under random disturbances

In recent years, large-scale and high-density operations have caused a dramatic increase in the energy consumption of metro systems. For overcrowded metro systems, the original energy-optimized timetable is no longer optimal after unexpected dwell disturbances occur. In this paper, we propose an actor–critic deep reinforcement learning (ACDRL) approach for solving the energy-aimed train schedule rescheduling (ETTR) problem in a real-time and energy-efficient manner. The proposed ACDRL approach can reduce metro systems’ net traction energy consumption by rearranging trains in millisecond time after the occurrence of unpredictable dwell disturbances. The simulation experimental results show that the average response time of ACDRL under unpredictable disturbances is only 0.0009 s and 0.0016 s in two-train and five-train metro systems, which can save energy by 4.73% and 6.95% on average, respectively. This means that a lot of energy can be saved.

Tire mobility numbers and vehicles performance evaluation based on empirical approaches

The wheel mobility number is a dimension less parameter that has a great and effective influence on prediction the off-road wheeled vehicle’s performance. The wheel mobility number is affected by soil strength, vehicle’s weight, and tires geometry. Different types of published wheel mobility numbers were collected and theoretically investigated to compare their vehicle performance. The major goal of this paper is to investigate the impact of tires parameters on vehicle mobility. For this, the tire geometry was measured using experimental testing at various tires inflation pressures. A theoretical comparison is carried out to the investigate the effect of soil cone index, tire geometry and vehicle weight on mobility numbers. The theoretical results are arranged in three worked zones and the vehicle performance in terms of net traction and tractive efficiency using empirical approaches were predicted. A comparison between predicted results and published results gives a good correlation.

Unified Power-Based Analysis of Combustion Engine and Battery Electric Vehicle Energy Consumption

<div class="section abstract"><div class="htmlview paragraph">The previously developed power-based fuel consumption theory for Internal Combustion Engine Vehicles (ICEV) is extended to Battery Electric Vehicles (BEV). The main difference between the BEV model structure and the ICEV is the bi-directional character of traction motors and batteries. A traction motor model was developed as a bi-linear function of positive and negative traction power. Another difference is that the accessories and cabin heating are powered directly from the battery, and not from the powertrain. The resulting unified model for ICEV and BEV energy consumption has linear terms proportional to positive and negative traction power, accessory power, and overhead, in varying proportions. Compared to the ICEV, the BEV powertrain has a high marginal efficiency and low overhead. As a result, BEV energy consumption data under a wide range of driving conditions are mainly proportional to net traction power, with only a small offset. Powertrain ‘bottom-up’ data and vehicle ‘top-down’ data are well described by the model. The observed powertrain transfer function can be used to estimate the energy consumption changes when it is used in different vehicle variants or under different driving conditions. Analytically derived range estimates are then possible for variants of a base BEV, just as analytically derived fuel economy can be estimated for ICEV variants.</div></div>

Coordinated tractions increase the size of a collectively moving pack in a cell monolayer

Cells in an epithelial monolayer coordinate motion with their neighbors giving rise to collectively moving packs of sizes spanning multiple cell diameters. The physical mechanism controlling the pack size, however, remains unclear. A potential mechanism comes from assuming that cell–substrate traction forces persist over some time scale: with large enough persistence time, collective cell packs emerge. To test this hypothesis, we measured the velocity and net traction of each cell. The data showed that in addition to having some temporal persistence, tractions were spatially correlated, suggesting that cells coordinate with their neighbors to apply tractions in the same direction. Chemical inhibitors and activators of actomyosin contraction were used to determine effects of altering the traction persistence and alignment. Numerical simulations based on the self-propelled Voronoi model, augmented to include both traction persistence and alignment and calibrated against the experimental data, matched the experimentally measured pack size. The model identified that if there were no alignment of traction between neighboring cells, the size of the collective pack would be substantially smaller than observed in the experiments. Hence, combining experiments and a simple mechanical model, this study confirms the long-standing assumption of traction persistence and adds the notion of traction alignment between neighbors. Together, persistence and alignment are two factors controlling the size of a collectively moving cell pack.

Design and Development of a Mobile Platform Mimicking Skating With Continuous Contact

Abstract This paper describes skating locomotion in a straight line based on continuous contact of rollers with the surface. Two skates traverse in and out while changing their orientation. Net traction force is generated because of no-slip conditions of rollers at the contact. The two skates are in continuous contact with the surface and therefore the balancing problem is circumvented. Different designs are developed and evaluated in order to replicate the desired motion. A heuristic-based architecture is developed to move the robot in a straight line.

Energy-saving optimization strategy of multi-train metro timetable based on dual decision variables: A case study of Shanghai Metro line one

In metro systems, reducing traction energy consumption and increasing the use of regenerative braking energy (RBE) are two important methods of energy-saving optimization, which are closely related to the driving strategy and timetable of the trains. In order to minimize the net traction energy consumption (i.e., the difference between traction energy and feedback energy) of trains in a metro system, an energy-saving optimization strategy of multi-train metro timetable based on double decision variables is proposed. Considering the actual situation of the short distance between the stations of the Shanghai Metro Line One (SML1) pilot network, at the driving strategy level, two optimized driving strategies of acceleration-cruising-braking (ACRB) and acceleration-coasting-braking (ACOB) are considered respectively. At the timetable level, genetic algorithm (GA) is used to optimize the decision variables of the trains. The optimization of driving strategy and timetable balances the traction energy consumption and feedback energy to minimize the net traction energy consumption of the metro system. Finally, simulation experiments were conducted based on the pilot network of the SML1. The results show that the energy consumption of the proposed strategy can be reduced by 23.28%.

Uticaj sadržaja vlage zemljišta, dinamičkog opterećenja, klizanja točkova kod određivanja sile vuče u uslovima laboratorije

A study was conducted to determine the effect of soil moisture content, dynamic load and wheel slippage in measuring traction. A single wheel test rig was developed to enable fundamental research on traction studies on tropical soil at the department of Agricultural and Environmental Engineering of Federal University of Technology, Akure. This facility consists of a moving carriage with a trolley that moves in either forward or reverse directions on rails well above a soil bin powered by 2.2 kW, three phase induction motor. The present facility set up was able to operate in either towing test mode for tire motion resistance studies or driving test mode for tire net traction and tractive efficiency studies. The test tire on the moving carriage was powered to rotate by a motor with additional pull provided by a cable-pulley mechanism connected to a tower with hanging dead weights. All controls on the moving carriage were activated from the main control console. The developed facility was successfully tested to determine tractive efficiency for narrow wheels at a particular inflation pressure on clay soil. The single wheel test rig facility worked well and the research indicates that wheel load, wheel slippage, soil moisture content and inflation pressure has great effect on traction efficiency. Traction efficiency decreased as the wheel load and wheel slippage increased. The developed single wheel testing facility can perform traction tests in controlled soil conditions to study the effect of soil, tire and moisture parameters on the performance of the system.

A Real-Time Train Timetable Rescheduling Method Based on Deep Learning for Metro Systems Energy Optimization under Random Disturbances

Considering that uncertain dwell disturbances often occur at metro stations, researchers have proposed many methods for solving the train timetable rescheduling (TTR) problem. This paper proposes a Modified Genetic Algorithm-Gate Recurrent Unit (MGA-GRU) method, which is a real-time TTR method based on deep learning. The proposed method takes the Gate Recurrent Unit (GRU) network as the decision network and uses the results produced by the Modified Genetic Algorithm (MGA) as the training set of the decision network. A well-trained decision network can provide effective solutions in real time after random disturbances occur, in order to optimize the net traction energy consumption of trains in metro systems. Based on the Shanghai Metro Line One (SML1) pilot network, this paper establishes a comprehensive model of the metro system as a training and testing environment to verify the energy-saving effect and real-time performance of the proposed method in solving the TTR problem. The experimental results show that in the two-train metro system, the three-train metro system, and the five-train metro system, the MGA-GRU method can save an average of energy by 4.45%, 6.16%, and 7.19%, while the average decision time is only 0.15 s, 0.27 s, and 0.33 s, respectively.

Tractive performance analysis of a lugged wheel by open-source 3D DEM software

Open-source software (OSS) is free to use and has accessible source codes, thus, it can be modified by various users. By using OSS, it is possible to easily and economically develop a target program for interaction studies in terramechanics. Yet Another Dynamic Engine (YADE) is an OSS for the 3D discrete element method (DEM), but its applicability to various contact interaction problems in terramechanics is not well-known. To investigate the applicability of YADE in terramechanics, the tractive performance of a lugged wheel was analyzed in this study. An idea of a proportional-integral-differential control model was applied to realize the constant rotation of the wheel in YADE. Our previous experiments on the locomotion of a small lugged wheel on a lunar-soil simulant were analyzed by YADE, and the results were found to be qualitatively similar to the obtained experimental results when considering the effects of the lug height, lug thickness, lug number, and wheel diameter. By applying a quasi-2D analysis with the same soil bin width and wheel width, the computational load of 3D DEM by YADE can be reduced up to 36.8% with similar net traction behavior against the wheel slip in a 3D analysis.

Estrogen Receptors Differentially Regulate the Overall Contractility of Human Airway Smooth Muscle

PurposeEpidemiological evidences suggest higher incidence and severity of asthma in pre‐menopausal women and aging men, indicating the role of sex steroids, especially estrogen. Our recent studies demonstrated that airway smooth muscle (ASM) cells from both male and female expresses estrogen receptors (ERα and β) and these receptors differentially regulate intracellular calcium ([Ca2+]i) which is a key role player in contraction. The degree of force for contraction can also be altered in a Ca2+‐independent manner via RhoA. Both Ca2+‐dependent and Ca2+‐independent pathways in ASM thus together contribute towards the airway contractility. In this study, we hypothesized that the ERs differentially regulate cyclic adenosine monophosphate (cAMP) and RhoA mechanisms, thereby affecting the overall contractility of human ASM cells.MethodsAsthmatic and non‐asthmatic primary human ASM cells (isolated from lung tissue, Mayo Clinic, IRB‐approved) were seeded and grown to 70% confluence. After serum‐deprivation, cells were exposed to 1nM 17β‐estradiol (E2), 10nM PPT (ERα agonist) or WAY (ERβ agonist) for 24hr. IBMX (10μM) was used as phosphodiesterase inhibitor and Isoproterol (100nM for 10min) served as a positive control group for estimation of cAMP. In parallel studies, phosphorylation of myosin light chain (MLC20) and myosin phosphatase targeting subunit‐1 (MYPT1) was assessed through Western analyses. Activated RhoA and cAMP measurements were done through ELISA kits. Cell contraction was accessed through traction force microscopy (TFM) using softgel plates coated with collagen and fluorescent beads. Upon treatments, phase‐contrast and fluorescent images were captured before, during and after 10μM histamine exposure and net traction force was calculated using advanced software.ResultsProlonged (24h) activation of ERβ significantly increased the baseline cAMP levels whereas ERα activation decreased it. This effect was more profound in asthmatic ASM cells compared to non‐asthmatics. Furthermore, ERβ activation lowered the active RhoA levels in non‐asthmatic human ASM cells. The phosphorylation of MLC20 and MYPT1 was significantly attenuated with ERβ activation compared to vehicle. TFM studies demonstrated reduced traction force in non‐asthmatic ASM cells treated with ERβ agonist compared to the vehicle, whereas ERα activation did not show any significant changes.ConclusionOur findings highlight the crucial role of divergent ER signaling in regulating Ca2+‐dependent and Ca2+‐independent pathways, which together govern the contractile function of ASM. Particularly, ERβ activation (and not ERα) mediates ASM relaxation by increasing the cAMP, reducing active RhoA and decreasing phosphorylation of MLC20/MYPT1. Thus, ERβ activation might serve as a novel target to manage the increased ASM contractility in asthma.Support or Funding InformationAcknowledgementSupported by NIH grants R01‐HL0123494 (Venkatachalem), R01‐HL 088029 (Prakash) and R01‐HL142061 (Pabelick, Prakash).

Net traction force/slip behaviour of tractor tyres - practical oriented measurement and simulation with the Hohenheim Machine Model

Within investigations on the fuel consumption of agricultural process chains, a simulation model for tractors is being developed which enables the calculation of time-related fuel consumption of static operating points. The transmission of forces between tyre and soil in longitudinal direction is mapped by a regression model, which however is based on outdated data. The current status of tyre size and technology can thus only be simulated inadequately. Based on the development and discussion of a suitable measurement methodology to determine the net traction force/slip-curves of modern tyres of larger dimensions, measurements with different tyre sizes are carried out and the results are presented. The introduction of correction factors in the empirical regression equations opens a way to update the tyre-soil model, which is done on the basis of the measured curves. Investigations on the influence of different parameters on the traction behaviour of standard tractors up to 300 kW nominal power are possible with the updated model and are presented as results.

Development of a Variable-Diameter Cage Wheel for Walking Tractor and Its Performance Evaluation in Soil Bin (Simulating Wetland)

Cage wheel is commonly used with walking tractors, but its diameter suitable for getting maximum tractive performance needs to be studied. Hence, an open-lug-type variable-diameter cage wheel to fit with a walking tractor was designed using SOLIDWORKS 2016 software. After verifying its dimensions by using finite element analysis, an actual wheel was fabricated with provision to vary its diameter from 620 to 710 mm using a manually operated hydraulic jack. Its performance in terms of tractive efficiency (TE) and net traction ratio (NTR) was evaluated in the soil bin under flooded condition at a normal load of 145 kg and forward speed of 1 km/h by varying the pull and diameter. The input torque and pull were measured with a torque transducer and a load cell, respectively. The NTR was found to increase with the increase in wheel slip until it reached a maximum value at around 45% slip. With the increase in diameter of wheel from 620 to 710 mm, both drawbar pull and TE were increased by 48–75% and 40–64%, respectively, at wheel slip of 20–40%. Both diameter and slip of wheel were found to have significant effect on NTE and TE.

Parametric study and design guidelines for rigid wheels for planetary rovers

This paper addresses the design of rigid wheels for planetary rovers in loose, granular soil. Wheel surface features, such as grousers, are known to improve tractive capability in planetary-relevant soils. However there are no comprehensive design guidelines for these wheel features. In this research, a series of intensive and extensive parametric studies were carried out in full-scale vehicle slope experiments and single-wheel tests that assess the influence of grouser count, height, orientation, and end-cap in various longitudinal and lateral slip conditions. This work also investigates the traction process of grousers based on a soil flow imaging technique. The soil motion analysis reveals that grousers reduce forward soil flow/motion resistance and increase net traction. A grouser design formula is derived from the soil flow observation, and design guidelines of rigid wheels of planetary rovers for loose soil are proposed based on these results. The proposed guidelines are applied to the modification of grouser design of the Mars Science Laboratory rover to improve tractive performance on loose terrain.

Mobility Enhancement of Heavy-Duty Tracked Vehicles Under Load Using Real-Time Terrain Characterization, Traction Control, and a Towing Winch

This paper presents a generalized, multibody dynamics model for a tracked vehicle equipped with a towing winch and control strategies that enhance vehicle mobility by regulating track slip based on real-time terrain characterization and automating winch use. The vehicle model is validated under conditions where no action is taken by the winch. Thereafter, two mobility enhancing control strategies are outlined. The first strategy regulates track slip to a real-time estimated value that generates maximum net traction. This is done by computing state-force estimates from a Kalman filter that are compared to terrain traction models using a Bayesian hypothesis selection approach. If the vehicle is traction limited and the first strategy fails, a second strategy that automates winch use is activated. Simulation results are shown for both scenarios.

Use of explicit finite-element formulation to predict the rolling radius and slip of an agricultural tire during travel over loose soil

Theoretically, there is zero slip between two bodies when there is no relative motion in their contact points. In the contact between a wheel and a surface, zero slip can be obtained only in the case of a single contact point. In this case, the wheel and the surface must be rigid. The theoretical zero-slip condition can’t be obtained in the contact between tire and terrain surface. In much of the scientific literature, two alternatives are suggested for a practical definition of the zero-slip condition: the point at which the gross traction force is equal to zero, or the point at which the net traction force is equal to zero. In the ASABE (2013), there is still no unique definition for the practical zero-slip condition. According to the definition of zero-slip condition, the rolling radius is not constant and depends on the slip.A detailed finite-element model using Lagrangian elements was built for each tire, taking into account the effect of all tire materials and their arrangement, lug shape, and inflation pressure. The soil model was built with Eulerian elements, which allow a large degree of deformation and flow of the soil. The initial verification experiments of the tire models were conducted by pressing the tires against a rigid plane. Each tire was examined under several different inflation pressures. Very good correlations were obtained between the experimental and model results. The verification test for the gross and net traction forces was performed in the soil-bin laboratory at the Technion. Special equipment was built, including a heavy dragging platform and a cell to hook the tire. This equipment allows control of the tire slip. The net traction force, gross traction force, and vertical load were measured in each test. Good correlations were obtained between the experimental and model results.Using the FEM model developed, some definitions for zero-slip condition were examined. The results indicate that the best criterion for zero-slip condition is definition of the point at which the gross traction force is equal to zero.

Integrated Steering Systems to Enhance Manoeuvrability: Technical Note

Most vehicles today employ conventional steering system where the front wheels are solely responsible for steering the vehicle, due to this the rear wheels remain dependent of the front wheels in the dynamic condition which is not allowing the vehicle to reach its maximum potential. On the other hand, in a four-wheel steering system the rear wheels along with the front wheels steer the vehicle improving its manoeuvrability. Four wheels steering also produces better acceleration as power is distributed to all the four-wheels enhancing the net traction and reducing the overall rolling resistance. Vehicles today are designed to under-steer a little with a steering ratio ranging between 14 and 22, this phenomenon fails in few scenarios where it takes longer to manoeuvre a vehicle in case of lane emergencies. Implementing in-phase and counter-phase steering mechanisms in a vehicle allow sharper turn, reduces tire wear and improves the overall manoeuvrability of the vehicle. Factors like steering torque, turning angle and velocity of the vehicle are taken into consideration for devising a proper method to shift between different steering modes. The input from steering angle and torque at a certain speed, allows the vehicle to choose between the crabs, parallel or counter steering mechanism during a turn for best performance. Thereby, integrating these mechanisms in a single vehicle would invariably stabilize and provide a better control to the driver in high as well as slow speed conditions.