Hunting Velocity Research Articles

Effect of Dynamic Creep Coefficients and External Load on Hunting Velocity in a Railway Vehicle

Effect of Dynamic Creep Coefficients and External Load on Hunting Velocity in a Railway Vehicle

Modelling and evaluation of the hunting behaviour of a high-speed railway vehicle on curved track

Nowadays, rail transport is a very important part of the transportation network for any countries. The demand for high operational speed makes hunting a very common instability problem in railway vehicles. Hunting leads to discomfort and causes physical damage to carriage components, such as wheels, rails, etc. The causes of instability and derailment should be identified and eliminated at the designing stage of a train to ensure its safe operation. In most of the earlier studies on hunting behaviour, a simplified model with a lower degree of freedom were considered, which resulted in incorrect results in some instances. In this study, a complete bond graph model of a railway vehicle with 31 degrees of freedom is presented to determine the response of a high-speed railway vehicle. For this purpose, two wheel–rail contacts grounded on a flange contact and Kalker’s linear creep theory are implemented. The model is simulated to observe the effects of suspension elements on the vehicle’s critical hunting velocity. It is observed that the critical hunting speed is extremely sensitive to the primary longitudinal and lateral springs. Other primary and secondary springs and dampers also affect the critical speed to some extent. However, the critical hunting velocity is insensitive to vertical suspension elements for both the primary and secondary suspensions. Also, the critical speed is found to be inversely related to the conicity of the wheel.

Dynamic Response of Railway Bogie Due to Change in Vertical Primary Suspension Stiffness Parameters

A mathematical model of a railway carriage moving on tangent tracks is constructed by deriving the equations of motion concerning the model in which single-point and two-point wheel-rail contact is considered. The presented railway carriage model comprises of carbody and front and rear simple conventional bogie with two leading and trailing wheelets attached to each bogie. The railway carriage is modeled by 31 degrees of freedom which govern vertical displacement, lateral displacement, roll angle and yaw angle dynamic response of wheelset whereas vertical displacement, lateral displacement, roll angle, pitch angle and yaw angle dynamic response of carbody and each of the two bogies. Linear stiffness and damping parameters of longitudinal, lateral and vertical primary and secondary suspensions are provided to the railway carriage model. Combination of linear Kalker's theory and nonlinear Heuristic model is adopted to calculate the creep forces in which introduced at wheel and rail contact patch area. Computer aided-simulation is constructed to solve the governing differential equations of the mathematical model using Runge-Kutta fourth order method. Principle of limit cycle and phase plane approach is applied to realize the stability and to evaluate the concerning critical hunting velocity at which railway carriage starts to hunt. Numerical simulation model is used to study the dynamic responses of a railway carriage bogie subjected to specific parameters of wheel conicity and primary suspension characteristics. A comparison to study the sensitivity of railway carriage bogie to dynamic responses is also presented at different vertical primary suspension stiffness parameters.

Railway carriage simulation model to study the influence of vertical secondary suspension stiffness on ride comfort of railway carbody

A mathematical model of a railway carriage moving on tangent tracks is constructed by deriving the equations of motion concern the model in which single-point and two-point wheel–rail contacts are considered. The presented railway carriage model comprises front and rear simple conventional bogies with two leading and trailing wheelsets attached to each bogie. The railway carriage is modeled using 31 degrees of freedom which govern vertical displacement, lateral displacement, roll angle, and yaw angle dynamic response of wheelset, whereas vertical displacement, lateral displacement, roll angle, pitch angle, and yaw angle dynamic response carbody and each of the two bogies were also studied. Linear stiffness and damping parameters of longitudinal, lateral, and vertical primary and secondary suspensions are provided to the railway carriage model. Combination of linear Kalker’s theory and non-linear Heuristic model is adopted to calculate the creep forces introduced at wheel and rail contact patch area. Computer-aided simulation is constructed to solve the governing differential equations of the mathematical model using Runge–Kutta fourth-order method. Principle of limit cycle and phase plane approach is applied to realize the stability and evaluate the concerning critical hunting velocity at which the railway carriage starts to hunt. The numerical simulation model is used to study the influence of vertical secondary suspension spring stiffness on the ride passenger comfort of railway carbody at speeds below and at critical hunting velocity. High magnitudes of vertical secondary spring stiffness suspension introduce undesirable roll and yaw dynamic responses in which affect ride passenger comfort at critical hunting velocity.

Railway Carriage Model to Study the Influence of Vertical Secondary Stiffness on Ride Comfort of Railway Carbody Running on Curved Tracks

A mathematical model of a railway carriage running on curved tracks is constructed by deriving the equations of motion concerning the model in which single-point and two-point wheel-rail contact is considered. The presented railway carriage model comprises of front and rear simple conventional bogies with two leading and trailing wheelets attached to each bogie. The railway carriage is modeled by 31 degrees of freedom which govern vertical displacement, lateral displacement, roll angle and yaw angle dynamic response of wheelset whereas vertical displacement, lateral displacement, roll angle, pitch angle and yaw angle dynamic response of carbody and each of the two bogies. Linear stiffness and damping parameters of longitudinal, lateral and vertical primary and secondary suspensions are provided to the railway carriage model. Combination of linear Kalker's theory and nonlinear Heuristic model is adopted to calculate the creep forces in which introduced at wheel and rail contact patch area. Computer aided-simulation is constructed to solve the governing differential equations of the mathematical model using Runge-Kutta fourth order method. Principle of limit cycle and phase plane approach is applied to realize the stability and evaluate the concerning critical hunting velocity at which railway carriage starts to hunt. The numerical simulation model is used to study the influence of vertical secondary suspension spring stiffness on the ride passenger comfort of railway carbody running with speeds under and at critical hunting velocity. High magnitudes of vertical secondary spring stiffness suspension introduce undesirable roll and yaw dynamic response in which affect ride passenger comfort at critical hunting velocity. Low critical hunting velocity with railway carriage running on curved tracks can be represented.

A Fundamental Study on Fine Unevenness and Tangent Force on Wheel Tread of Railway Vehicle (Relations between Environmental Condition and Tangent Force Characteristics with a Two-Disk Rolling Machine)

This paper presents the laboratory experimental results in relation to tangent force between a wheel and a rail under different environmental conditions. In the experiments, we used two types of cylindrical test specimens (with / without fine unevenness on contact surface) assuming actual wheels, and investigated the relation of tangent force to the cases of with / without fine unevenness on contact surface under the conditions of different environmental temperature and relative humidity. Consequently, under the conditions of without fine unevenness on the contact surface of a test specimen, it showed that there is a tendency in the tangent force which turned out low whence relative humidity is over 60%, regardless of environmental temperature. However, on the conditions which have fine unevenness on the contact surface of a test specimen, we could not observe the effect of environmental temperature and relative humidity on the tangent force. In addition, running stability analysis of railway vehicle was carried out for the cases of with / without fine unevenness on wheel tread of railway vehicle under the condition of different relative humidity. As a result, it was shown that the critical hunting velocity under the condition of without fine unevenness becomes low while increasing relative humidity.

EMPIRICAL TESTS OF HUNTER–COVEY INTERFACE MODELS

Quail hunting consists of a complex set of behaviors that involve humans, pointing dogs, and wild birds. The recent development of models known as Hunter–Covey Interface (HCI) theory provides an opportunity to analyze how we perceive, understand, and manage quail hunting. There are 2 groups of HCI models: static and dynamic. The static HCI model predicts daily hunting mortality based on the velocity of the hunt and area covered during a hunt. The dynamic HCI models estimate the probability of flushing a covey given a set of circumstances that revolve around the potential rate of which quail learn to avoid hunters. We quantified the variables required to test whether the static and dynamic models of HCI theory provide meaningful results. We used spatial data on hunting velocity and area covered during >100 quail hunts, along with estimates of quail population density, mortality, and movements from 2 areas in south Texas, to evaluate output from HCI models. The static model predicted average daily harvest rates that ranged from 5 to 50 birds. This average is within the range of average daily bag of south Texas quail hunters in groups of 2–4. Output from the dynamic models suggested that quail populations on our study areas were subjected to relatively low hunting intensities with a corresponding low avoidance behavior and learning rate, which is a scenario that matched 1 of 4 predictions by Guthery (2002). We found it difficult to meet basic assumptions of HCI theory. For example, hunting pressure was potentially redundant, coveys were not always randomly distributed in space, and the extent to which quail are naive at the beginning of a hunting season was unknown. However, both the static and dynamic HCI models appeared robust to violation of these assumptions. Application of HCI theory may provide meaningful results that can be used to manage quail hunting pressure, optimize harvest, and sustain populations.

Stability Analysis of High-Speed Truck Having New Conception Steering and Z-N Link Suspension Device Mechanism.

It is empirically known that a railway vehicle is by nature, characterized by contra-dictory behaviors on a tangent track and on curves. Hence, it becomes clear that the Z-link-equipped vehicle, which is intended to improve the passing performance on curves, has a slight forward expansion of the unstable region of body hunting in comparison with traditional vehicles. In order to improve this hunting unstability, the steering truck with a unique mechanism, Z-N-link suspension device mechanism, has been developed, which contributes to enhancement of good running performance both on the tangent track and on curves. On the basis of the theoretical analysis, it is recognized that adequate supporting stiffness at the point of connection between N-links is an effective means of increasing the hunting velocity, and that there exist two limit cycles, that is, one is an unstable limit cycle and the other is a stable one. In this paper, a new concept of the steering truck is given, which provides guidelines of future design of high-speed trucks.

An analysis of running stability for high speed railway vehicles connected in series with elastic and frictional forces against truck turning. (3rd report Stability criteria for vehicle hunting)

In this paper, we analysed theoretically the hunting stability of a high speed railway vehicle which has at least seven degrees of freedom with respect to lateral motion when elastic and frictional forces are connected in series against truck turning. According to the theoretical results, it was found that the stability criteria of the hunting, so-called, lower-center rolling, upper-center rolling and yawing of a car body, and the front and rear trucks depended on the lower hunting velocity was an unstable limit cycle, while the upper limit cycle changed into either a stable limit cycle or an unstable one corresponding to the magnitude of the angular amplitude. As the amplitude increased, the unstable region between the lower and upper limit cycles increased larger. Further, as the angular amplitude increased, the truck hunting phenomena of a bogie car connected with the damping of a suspension device between the car body and the trucks, the magnitude of the angular amplitude between the front and rear trucks, phase angle and others are made clear.

Analysis of running stability for high speed railway vehicles connected in series against truck turning with spring and friction (1st reoport, Truck hunting having small clearance between truck frame and bolster anchor)

In this paper, we analysed, ed theoretically the hunting stability of a bogie truck having a small clearance in the connecting position between the truck frame and the bolster anchor when the spring and friction are connected in series against truck turning. According to the theoretical analysis, we suggest that the exclusion of clearance is extremely important for securing the running stability of high speed railway vehicles, because the hunting velocity may be reduced due to the influence of clearance. Then, the fact that the limit cycle corresponding with the hunting velocity is an unstable limit cycle when there is no clearance is examined. However, on the contrary, there appears to be either a stable limit cycle or an unstable one corresponding to the magnitude of the angular amplitude of the truck frame if there is cleamance in the connecting position between the truck frame and bolster anchor. In the practical analysis, we investigated truck hunting which occurred in an actual car during a SHlNKANSEN running test carried out by the JNR.

An analysis of running stability for high speed railway vehicles connected in series against truck turning with spring and friction. 2nd report Body hunting having small clearance between truck frame and bolster anchor.

In this paper, we analysed theoretically the hunting stability of a high speed vehicle having a small clearance in the connecting position between the truck frame and the bolster anchor when the spring and friction are connected in series against truck turning. According to the theoretical analysis, it was found that the stability of hunting depends on the angular amplitude of the truck. And the limit cycle corresponding with the hunting velocity is a stable limit cycle when the amplitude is small, while the limit cycle is an unstable one when the amplitude is large. Then, the fact that the body hunting ceases to exist in the range between both amplitudes is made clear. Further, the analysis revealed that the stability of hunting is affected by various factors : the stiffness of the bolster anchor, the friction force acting on the side bearer, the clearance in the connecting position between the truck frame and bolster anchor, the damping coefficient of truck turning and the damping coefficient of body suspension and so on.