Hunting Stability Research Articles

Wheel nominal rolling radius difference on hunting stability of railway vehicle system under a speed-dependent nonlinear creep model

This study presents the hunting stability of a railway vehicle system in a speed-dependent nonlinear creep model with varying wheel conicity and nominal rolling radius. Integrating Kalker’s linear theory, Hertz contact theory, and the heuristic nonlinear creep model, the speed-dependent nonlinear creep model, including the semi-axis lengths and nonconstant creep coefficients with the varying vehicle speed, is investigated. Modeling and dynamic analysis are performed in the 28 degrees-of-freedom railway vehicle system. Lyapunov’s indirect method is used to calculate critical hunting speed of a railway vehicle system. The effects of suspension system parameters, various wheel conicities, and nominal rolling radii on the hunting stability are illustrated and compared. Critical hunting speeds calculated for the original design wheel are consistently better than those obtained from worn wheels with differences in wheel conicity and wheel rolling radius. Notably, critical hunting speeds calculated for a softer stiffness and damping decrease as wheel nominal rolling radius difference increases. Furthermore, the critical hunting speed calculated by the harder stiffness and damping increase as wheel nominal rolling radius difference increases. Analysis of hunting stability further shows that vehicle running speed must be considered when the wheel nominal rolling radius is less than the origin design wheel radius. Therefore, the effects of various wheel nominal rolling radius differences on hunting stability is an important research issue.

The effect of wheel set gyroscopic action on the hunting stability of high-speed trains

ABSTRACTThis study explores the effects of wheel set gyroscopic action on hunting stability by calculating linear and nonlinear critical speeds. First, a dynamic model for a high-speed vehicle with 23 degrees of freedom is developed by considering wheel set gyroscopic action. The linear and nonlinear critical speeds are calculated by eigenvalue analysis and drawing a bifurcation map, respectively. Two computer programs for linear and nonlinear stability analysis are developed. Second, based on an actual high-speed vehicle in China, the effects of wheel set gyroscopic action on hunting stability are quantitatively investigated using computer simulation. Furthermore, the difference between the effects of gyroscopic moments about the x-axis and z-axis is discussed. The results show that the moment about the x-axis is harmful to hunting stability, but the moment about the z-axis is beneficial to hunting stability. However, the integrated effect of these two moments can enhance the critical speeds and suppress the hunting motion.

Hunting stability of high-speed railway vehicles on a curved track considering the effects of steady aerodynamic loads

Aerodynamic loads may have effects on the hunting stability, and the factor of curved track makes it more complicated. Therefore, considering the steady aerodynamic loads generated by crosswind and airflow in the opposite advancing direction of train, the hunting stability of high-speed railway vehicle on a curved track is studied in this paper. The changes of gravitational restoring force and creep coefficients which are caused by aerodynamic loads are considered, and the change of equilibrium position due to aerodynamic loads, centrifugal force and the factor of curved track is also in consideration. A mathematical model of a high-speed railway vehicle during curve negotiation with aerodynamic loads is set up. A program based on the model is written and verified. Using this program, the linear critical speed considering the effects of aerodynamic loads is determined by the eigenvalue analysis. This paper investigates the critical speeds in three aerodynamic conditions. Considering the aerodynamic loads, the dependence of critical speed on curve radius and super-elevation is analyzed, and the impact of aerodynamic loads on instability mode is analyzed as well. In addition, this paper obtains the dominant factors affecting critical speed and the variation tendency of critical speed with primary longitudinal stiffness by orthogonal experiments. The results show that the critical speed decreases or increases while the wind is blowing to outer rail or inner rail respectively. The aerodynamic loads produce obvious effects on the instability mode. The variation tendency of critical speed dependence on curve radius in the conditions with aerodynamic loads keeps consistent with the case without aerodynamic loads. It is seen from the orthogonal experiments that, aerodynamic loads and curve radius are the dominant factors affecting linear critical speed of vehicle on a curved track, and the linear critical speed decreases with the increasing of primary longitudinal stiffness.

Experimental investigation on vibration behaviour of a CRH train at speed of 350 km/h

The objective of the article is to investigate the vibration characteristic and the long-term service performance of a China Railway High-speed (CRH) train at operation speed of 350 km/h through on-track field tests. The article first introduces the test method and system as well as the field conditions including the main parameters of the test train and track. A CRH electric multiple unit (EMU), called the CRH2C, is chosen for the experiment. A duration test lasting for about 2 months is carried out to acquire the data of vehicle vibration acceleration and the wheel profile wear. Based on the test data, the article presents the vibration behaviours of car body, bogie frame and axle box as well as the lateral hunting stability of the train operating at speed of 350 km/h, and the evolution of the train dynamic performance under long-term operation condition. Results show that the vibration accelerations of vehicle components are in a low level when the train runs on a non-ballasted track at the speed of 350 km/h, indicating that both the ride comfort and the running stability are acceptable. Through wheel re-profiling, it is possible to effectively reduce the vibrations of the axle box, the bogie frame and the car body, and thus the train dynamic performance can be kept in an excellent condition in a long period.

Influences of aerodynamic loads on hunting stability of high-speed railway vehicles and parameter studies

The influences of steady aerodynamic loads on hunting stability of high-speed railway vehicles were investigated in this study. A mechanism is suggested to explain the change of hunting behavior due to actions of aerodynamic loads: the aerodynamic loads can change the position of vehicle system (consequently the contact relations), the wheel/rail normal contact forces, the gravitational restoring forces/moments and the creep forces/moments. A mathematical model for hunting stability incorporating such influences was developed. A computer program capable of incorporating the effects of aerodynamic loads based on the model was written, and the critical speeds were calculated using this program. The dependences of linear and nonlinear critical speeds on suspension parameters considering aerodynamic loads were analyzed by using the orthogonal test method, the results were also compared with the situations without aerodynamic loads. It is shown that the most dominant factors affecting linear and nonlinear critical speeds are different whether the aerodynamic loads considered or not. The damping of yaw damper is the most dominant influencing factor for linear critical speeds, while the damping of lateral damper is most dominant for nonlinear ones. When the influences of aerodynamic loads are considered, the linear critical speeds decrease with the rise of crosswind velocity, whereas it is not the case for the nonlinear critical speeds. The variation trends of critical speeds with suspension parameters can be significantly changed by aerodynamic loads. Combined actions of aerodynamic loads and suspension parameters also affect the critical speeds. The effects of such joint action are more obvious for nonlinear critical speeds.

Carbody hunting investigation of a high speed passenger car

This paper describes the low frequency carbody hunting problem of a high speed passenger car emerged in the process of tests and service operations. It causes a significant deterioration of lateral comfort. First, the vehicle model is established as a multiple rigid body system. Using root locus analysis, the effect of system parameters on the carbody hunting stability has been studied. It shows that carbody hunting instability has something to do with suspension parameters and wheel/rail conditions. To find the causes of this carbody hunting problem, component tests have been carried out. Based on the theoretical hunting stability analysis and component tests, solutions are proposed and then validated in the field test.

Hunting Stability Test for Railway Vehicles by Hardware-In-the-Loop Simulation with Actual Yaw Damper (Development and Qualitative Verification of Test Equipment)

Hunting stability is one of the most essential characteristics of high speed trains, and it has been investigated by roller rig testing at a testing bench and numerical simulation. Those ways have their own drawbacks in their accuracy, cost and flexibility. We propose a new approach, Hardware-In-the-Loop Simulation (HILS), to test hunting stability of railway vehicles. HILS is a kind of simulation that uses some actual devices, and it enables us to increase simulation accuracy, keeping its cost-effectiveness and flexibility high. In this paper, we demonstrated hunting stability tests by HILS, which showed that the tests worked properly. Furthermore, we also exhibited how excitation device responsiveness affects quantitative analysis of hunting stability through simulation studies.

Lateral Stability Analysis of Heavy-Haul Vehicle on Curved Track Based on Wheel/Rail Coupled Dynamics

Being viewed from the standpoint of whole system, the hunting stability of a heavy-haul railway vehicle on a curved track is investigated in this paper. First, a model to simulate dynamic performance of the heavy-haul vehicle on the elastic track is developed. Secondly, the reason of the hunting motion is analyzed, and a bifurcation diagram for the vehicle on the curved track is put forward to simulate the nonlinear critical speed. Results show that the hunting motion of the heavy-haul vehicle will appear due to the larger conicity, the initial lateral shift and the wheelset angle of attack. With the hunting motion appearing, the lateral shift and force of the wheelset are changed sharply and periodically with a wave of circa 3.6 m. There is obvious difference in the bifurcation diagram between on a curved track and on a tangent track. Relative to the centerline of the track, each vehicle body on the curved track has two stable cycles. As for the curved track with a radius of 600 m and a superelevation of 55 mm, the nonlinear critical speed of the heavy-haul vehicle is 76.4 km/h.

A parametric dynamic study on hunting stability of full dual-bogie railway vehicle

Analysis is performed on the hunting stability of a full railway vehicle system composed of a vehicle body, two bogie frames, and two wheelsets for each bogie frame. Incorporated into this analysis are the nonlinear heuristic creep and flange-rail contact models. The results show that the hunting speed is most sensitive to the primary longitudinal and lateral stiffnesses, and the nonlinear heuristic creep model plays a key role in confining the hunting speed within a physically reasonable range. Eigenanalysis is performed to investigate the dynamic behavior of the vehicle in the vicinity of the hunting speed. The results reveal that there exists not only the most dominant pair of complex conjugate roots, but also its shadowed roots. The roles of these two principal pairs of eigensolutions in the hunting motion are thoroughly explored via numerical studies using bifurcation analysis and an orbital representation. It is shown that the nonlinear hunting motions before the modal transition speed mainly refer to the principal mode, and those after the critical speed refer not only to the principal mode, but also to its shadowed mode, which supports the necessity of the dual-bogie railway vehicle model in the hunting analysis.

3404 逆踏面式輪軸が有する蛇行動特性の実験解析(OS2-4 蛇行動に関するダイナミクス,OS2 交通・物流システムのダイナミクス,オーガナイズド・セッション(OS))

In order to increase self steering ability of independently rotating wheelset (IRW), the new-type of IRW with inverse tread conicity is presented. In previous study, it is confirmed by experiment and simulation that the presented wheelset have higher self steering ability than conventional IRW, whereas the hunting stability of the new wheelset have never been researched by experiment. Therefore, experimental equipments are developed to verify the validity of constructed theory of simulation model for the new wheelset. Furthermore, the hunting characteristics and the effectiveness of longitudinal suspension for running stability is investigated with the identified simulation model.

Dynamics of Independently Rotating Wheel System in the Analysis of Multibody Railroad Vehicles

In this investigation, dynamic characteristics of independently rotating wheel systems are discussed. To this end, a multibody independently rotating wheelset (IRW) model is developed using the method of velocity transformation. The linear stability analysis of a two-axle IRW truck is performed, the hunting stability and vibration characteristics of IRW truck are investigated, and the results are compared with those obtained using the multibody dynamics model. Good agreement is obtained in hunting frequencies and critical speeds. It is shown using the linear IRW equations that since a constant forward speed is assumed for IRW, the longitudinal slip can occur due to the change in the wheel rolling radius. This leads to longitudinal creep forces even in the case of IRW and it contributes to a coupling of the lateral, yaw, and pitch motions of IRW. Furthermore, it is observed in several numerical examples that, due to small self-centering forces of IRW, continuous flange contact occurs on tangent track, while in curve negotiation, flange contacts on outer wheel of the front axle, as well as that on inner wheel of the rear axle, occur. Such an effect can be more significant when sharp curve negotiation is considered as encountered in light rail vehicle applications.

Lateral Hunting Stability of Railway Vehicles Running on Elastic Track Structures

Considering the viscoelastic property of railway track structure, it is suggested in this paper to include the influence of track dynamics in calculation of lateral stability of railway vehicles running on tracks. A direct numerical method based on the stability of time histories of vehicle components is proposed to ascertain the nonlinear critical hunting speed of railway vehicles. The time histories of the vehicle system are calculated by use of the three-dimensional vehicle-track coupled models, which are capable of taking into account the influence of dynamic properties of track structures on vehicle dynamics. The effect of track system properties such as the rail fastener stiffness and the rail profile on the lateral hunting stability of the vehicle is investigated. Differences of the critical hunting speeds of vehicles on rigid track model and on elastic track model are found out. Generally, the rigid track model overestimates the critical hunting speed by 5–10% for different types of vehicles, which implies that the classical vehicle dynamics predicts higher lateral stability of a vehicle than the vehicle-track coupled dynamics does. This conclusion is of significance to the safety design of railway vehicles and should be taken notice in the design stage. The reason that causes the differences is discussed. A full-scale field experiment was carried out to investigate the hunting behavior of a freight car with three-piece bogies on a straight track. Very obvious hunting motion was observed in the experiment when the unloaded vehicle ran at the speed of 75 km/h, which verified the theoretical calculation results.

Object-Oriented Modeling and Simulation of Railway Vehicle Systems

An object-oriented modeling method was proposed to develop a simulation software package named GVDS which could be used to predict some aspects of dynamic behavior of railway vehicle. The package based on multi-body dynamics mainly consists of three parts, an interactive pre-processor, the solver and an interactive post-processor. With UML, demands and structure of the software package are represented. By modeling of the geometry and behavior of each object, virtual prototype of railway vehicle is formed and by the simulation, the critical speed of hunting stability, wheel-rail contact forces and so on can be determined and the hunting stability, curving behavior and ride comfort can be analyzed and evaluated. Finally, some cases are simulated. The simulation results show the effectiveness of the proposed method.

Modeling and nonlinear hunting stability analysis of high-speed railway vehicle moving on curved tracks

A heuristic nonlinear creep model is used to derive the nonlinear coupled differential equations of motion of a high-speed railway vehicle traveling on a curved track. The vehicle dynamics are modeled using a 21 degree-of-freedom (21-DOF) system which takes account of the lateral displacement and yaw angle of each wheelset, the lateral displacement, vertical displacement, roll angle and yaw angle of the truck frames, and the lateral displacement, vertical displacement, roll angle, pitch angle and yaw angle of the car body. To analyze the respective effects of the major system parameters on the vehicle dynamics, the 21-DOF system is reduced to 20-DOF, 14-DOF and 6-DOF models, respectively, by excluding designated subsets of the system parameters. The validity of the analytical models and the numerical solution procedure is confirmed by comparing the result obtained using the 6-DOF model for the critical velocity of a railway vehicle traveling on a tangent track with the solution presented in the literature. In general, the results obtained in this study show that the critical hunting speed derived using the 6-DOF or 14-DOF model is generally higher than that evaluated using the 20-DOF model. In addition, the critical hunting speed evaluated via the heuristic nonlinear creep model is lower than that derived using a linear creep model.

3303 独立回転輪軸の縦クリープ力が車両運動に及ぼす影響(OS4-1:接触問題,OS4:接触問題とトライボロジ,オーガナイズド・セッション(OS),第18回交通・物流部門大会(TRANSLOG2009))

In this investigation, dynamic characteristics of independently rotating wheel systems (IRW) are discussed. To this end, a multibody IRW model is developed using the method of velocity transformation. The linear stability analysis of a two-axle IRW truck is first performed, and the hunting stability and vibration characteristics of IRW truck are investigated and the results are compared with those obtained using the multibody dynamics model. It is presented that the longitudinal creep force is not ideally equal to zero in tight curve negotiation and special care need to be exercised when a simplified IRW model developed by specifying zero longitudinal creepages is used.

362401 ANALYSIS ON CURVING PERFORMANCE AND HUNTING STABILITY OF ACTIVE-BOGIE-STEERING TRUCK WITH VARIOUS WHEEL TREADS(Bogie,Technical Session)

Railway truck is necessary to have excellent curving performance as well as high speed hunting stability, but generally they are contrary to each other. In order to realize the compatibility, many trucks with passive steering mechanism have been studied. In order to realize further improvement of bogie steering ability on sharp curved track, active steering control can give effective performance. The truck treated here has simple but effective mechanism: Actuators are attached between the car body and bogie frames. If the truck frame is steered by actuators toward "radial steering position of the truck", the curving performance of the truck can be improved. This is the concept of active-bogie-steering (ABS) truck. In this paper, more detailed study and evaluation for ABS truck will be presented. Validity tests were carried out with the bogie on rolling test stand in NTSEL, which can simulate curving condition. Bogie parameters and steering actuator characteristics are elaborately identified in order to compare the experimental results with multi-body dynamics simulation. According to the test results and numerical simulation, the effectiveness of the proposed bogie mechanism and control are proved.

11802 鉄道車両ボギー角アクティブ操舵台車のアクチュエータ特性を考慮した走行性能の解析(車両と構造物の解析技術,OS.3 マルチボディダイナミクスによるシミュレーション技術の新展開)

Railway truck is necessary to have excellent curving performance as well as high speed hunting stability, but generally they are contrary to each other. "Active-bogie-steering (ABS) Bogie", is one of the methods to realize the compatibility between curving performance and hunting stability. ABS bogie has active steering mechanism only between car body and, bogie frame, and bogie frame is steered by actuators toward "radial steering position", which realizes no "bogie angle shortage". In this paper, the actuator consists of AC servo controlled motor and mechanism with friction is modeled to realize ideal response and tracking ability for desired actuator force. The effective control which compensates actuator friction is proposed and is investigated in experiment. Moreover, calculation of hunting stability for ABS truck by using half body model was compared with other truck model.

Influences of the vertical and the roll motions of frames on the hunting stability of trucks moving on curved tracks

Based on the heuristic nonlinear creep model, the nonlinear coupled differential equations of the motion for the truck modeled by a eight-degrees of freedom system moving on curved tracks, considering the lateral displacement and the yaw angle of the each wheelset and the lateral displacement, the vertical displacement, the roll angle and the yaw angle of the truck frame, are derived. The accuracy of the present analysis is verified by comparing the limiting case and the current numerical results with the findings available in published literature. The influences of the vertical and the roll motions of frames on the critical hunting speed of trucks are studied and evaluated via the linear and the nonlinear creep models. It is shown that the critical hunting speeds evaluated using the eight-degrees of freedom system differ significantly from those calculated using a system with six-degrees of freedom. In addition, the influences of the physical parameters, including those missing in the six-degrees of freedom system, on the critical hunting speed of trucks are also examined.

Nonlinear Analysis on Hunting Stability for High-Speed Railway Vehicle Trucks on Curved Tracks

Based on the heuristic nonlinear creep model, the nonlinear coupled differential equations of the motion of a ten-degree-of-freedom truck system, considering the lateral displacement, the vertical displacement, the roll and yaw angles of the each wheelset, and the lateral displacement and yaw angle of the truck frame, moving on curved tracks, are derived in completeness. To illustrate the accuracy of the analysis, the limiting cases are examined. The influences of the suspension parameters, including those losing in the six-degree-of-freedom system, on the critical hunting speeds evaluated via the linear and nonlinear creep models, respectively, are studied and compared.

A102 RESEARCH AND DEVELOPMENT OF ACTIVE-BOGIE-STEERING TRUCK : 1st report

In this paper we introduce "active-bogie-steering (ABS) truck", that is one of the methods to realize the compatibility between curving performance and hunting stability. The ABS truck has active steering mechanism only between car body and truck frame, and truck flame is steered by actuators toward "radial steering position", which realizes no "bogie angle shortage". Validity tests were carried out on the truck rolling test stand in NTSEL, which can simulate curve-running condition. According to the test results, 1) "lateral contact force of front/outside wheel" in curving is proportional to "bogie angle shortage", 2) "bogie angle shortage" is proportionally reduced by bogie-steering actuator force. So the lateral force of the front/outside wheel in curving can be reduced by active-bogie-steering, and it is possible to realize zero lateral force even in sharp curve.