Multiobjective Optimization of a Railway Vehicle Dampers Using Genetic Algorithm

An articulated railway vehicle (ARV) experienced an abnormal vibration on car body which deteriorates its riding comfort significantly. On-track experiments were conducted considering the wheel-rail interaction, the vibration transmission of primary and secondary suspensions, to locate the vibration sources and find a solution. Compared to the existing dynamics tests performed on a railway vehicle, the modes of car body motions were further recorded as well as its structural modes when the vehicle was operated on track. Furtherly, the lateral motion of the wheelset and car body were recorded by a video surveillance on-board to check the modes of motion of the vehicle system for the first time. The tests performed in this work extends the field measurement techniques and can be used on track for the railway vehicle dynamics analysis. It is shown that measured wheel profiles have a small radius difference which lead to a low equivalent conicity of wheelset, which in turn introduces a low-frequency hunting motion of wheelset in case of a soft steering. The yaw motion of the car body was excited by the wheelset hunting and then the coupled vibration between the wheelset and car body deteriorates the ride comforts of ARV. A solution of this low frequency vibration on vehicle system is to increase the wheelset conicity and has been verified on-track. Additionally, reduce the stiffness of the anti-yaw damper can improve the ride comfort in case of a low conicity.

To make the superconducting magnetically levitated (maglev) transport system more attractive, it has been important to enhance the ride comfort by controlling vehicle vibration. We have reduced maglev vehicle vibration by controlling only the secondary suspension between the car bodies and bogies. However, by doing so, it has been difficult to reduce vibration for the characteristic and relatively high frequencies of the primary suspension. Recently, we have directed our attention to primary suspension control, using power collection coils of the distributed-type linear generator system, which we are testing as an onboard power source. Because this type of vibration control can apply damping directly to the primary suspension, we consider it to be optimal for reducing vibrations at high frequencies. We have used maglev vehicle models that focus on lateral, vertical, rolling, and pitching motions to describe the effectiveness of reducing vibrations by using linear generator system damping force control in the primary suspension and linear quadratic (LQ) control of the actuators in the secondary suspension.

This paper presents performance analysis of semi-active railway vehicle suspension system using MR damper. In order to achieve this goal, a mathematical dynamic model of railway vehicle is derived by integrating car body, bogie frame and wheel-set which can be able to represent lateral, yaw and roll motion. Based on this model, the dynamic range of MR damper at the railway secondary suspension system and design parameters of MR damper are calculated. Subsequently, control performances of railway vehicle including car body lateral motion and acceleration of MR damper are evaluated through computer simulations. Then, the MR damper is manufactured to be retrofitted with the real railway vehicle and its characteristics are experimentally measured. Experimental performance of MR damper is assessed using test rig which is composed of a car body and two bogies.

Achieving higher operation speeds safely and comfortably is yet a significant challenge in the railway industry. The rail irregularities and wheel-rail interactions in a train running at high speeds may result in large-amplitude vibration in the train’s car body and affect passengers by reducing ride comfort. The train suspension systems have a crucial role in reducing the vibration and improving ride comfort to an acceptable level. In this context, an exclusive semi-active magneto-rheological (MR) damper with a favorable dynamic range was designed and fabricated. The MR dampers were installed in a high-speed train’s secondary lateral suspension system in replacement of original passive hydraulic dampers, with intent to mitigate vibration of the car body and keep the ride comfort in a proper level at low and high running speeds. A unique full-scale experimental investigation on the high-speed train equipped with MR dampers was carried out to evaluate the MR damper functionality in a real operating situation. The full-scale roller experiments were conducted in a vast range of speeds from 80 to 350 km/hr. At each speed, different currents were applied to the MR dampers. The car body dynamic responses were collected to evaluate the ride quality of the train. Ride comfort indices under various train operating conditions are calculated through Sperling and UIC513 rules. This study reveals that the designed MR dampers effectively reduce the car body’s rolling motion. According to Sperling ride comfort index, the car body vibration was “clearly noticeable” at some running speeds when adopting the MR dampers, but it was not unpleasant. Besides, a “very good comfort” was achieved according to the UIC513 criterion. Also, no train instability was whatsoever observed at high speeds. This experimental investigation bears out the capability of the devised MR damper to achieve desirable ride comfort under high running speeds.

A multibody system is one of the complex mechatronic system whose dynamic performance is influenced by its connected components and the mechanical structure. However, during the service life, the system is subjected to degradation of different components whose conditions may greatly impact the vehicles running characteristics like stability and reliability. The suspension system is one of the key systems which ensures that better and reliable running behaviors are achieved and hence any uncertain changes in its performance characteristics becomes of significant interest and must be treated with utmost attention. This research presents a relevant study on how suspension system degradation affects the dynamic performance and reliability of multibody rail vehicles and provides a model which can be applied to evaluate the performance of the vehicle at various levels of suspension design parameters. The vehicle is modelled using SIMPACK dynamic software, incorporated with track irregularities from maintenance data and using matlab to estimate various levels suspension design parameters. The dynamic performance of the vehicle is evaluated by using dynamic indexes like derailment coefficient and vibration sensitivity to assess the level of reliability and sensitivity of the vehicle. The results showed that the running safety reliability is more sensitive at low values of damping and stiffness of the primary suspension and stability is achieved as they increase while vibration sensitivity increases with increase in damping and stiffness values of both primary and secondary suspension. Furthermore, secondary suspension damping and stiffness greatly influence vibration sensitivity as opposed to primary suspension damping and stiffness which exhibits little influence on vibration sensitivity hence secondary suspension damping exhibits the greatest influence on vibration sensitivity while primary suspension stiffness exhibits the least influence on vibration sensitivity.

Primary suspension is the term used for suspension components connecting the wheel assemblies of a vehicle to the frame of the vehicle (Fig.1). This is in contrast to the suspension components connecting the frame and body of the vehicle, or those components located directly at the vehicle’s seat, commonly called the secondary suspension. Usually a vehicle contains both primary and secondary suspension system but primary suspension is chosen for control. There are two basic types of elements in conventional suspension systems. These elements are springs and dampers. The role of the spring in a vehicle’s suspension system is to support the static weight of the vehicle. The role of the damper is to dissipate vibrational energy and control the input from the road that is transmitted to the vehicle. Primary suspensions are divided into passive, active and semi active systems [Miller 1990], as will be discussed next, within the context of this study.

(1977). Variation of Contact Wheel-Rail Forces After Overreaching Creep-Slip Adhesion Boundary. Vehicle System Dynamics: Vol. 6, No. 2-3, pp. 92-95.

완화곡선구간은 직선과 곡선사이에 설치되는 구간이며, 곡선반경 및 캔트 등의 선형변화에 따라 차량의 횡방향 가속도, 횡방향 저크 및 롤속도의 변화가 발생하여 차량주행안전성 및 승차감 측면에서 취약구간이 된다. 본 논문에서는 철도차량의 차체횡가속도와 롤속도의 계측결과를 이용하여 완화곡선 구간의 승차감을 정량적으로 산정하였으며, 승차감 평가기법은 EN규격에서 제시하는 완화곡선 구간의 승차감 평가방법을 사용하였다. 평가결과로 부터 통하여 국내 일반철도 노선의 완화곡선구간 승차감의 분포특성을 조사하였으며, 곡선반경 크기와 차량 속도가 완화곡선 구간의 승차감에 미치는 영향을 분석하였다. 마지막으로, 캔트 시간변화율과 완화곡선 승차감의 관계를 분석하였다. Transition curves are located between curve and straight section in railway. These transition curves are vulnerable to the ride comfort of passengers and safety of a vehicle because lateral acceleration, lateral jerk and roll velocity increase as curvature and cant change along the transition curves. In this paper, ride comfort on the transition curve was calculated on the basis of lateral acceleration and roll velocity measurements. The evaluation of ride comfort was conducted according to the methodology specified in European Standard. The distribution characteristics of the comfort index were investigated for the korean conventional line from the evaluation results. The influence of the curve radius and the vehicle speed on the ride comfort index was also investigated. Finally, the relationship between ride comfort and the rate of cant changes on transition curves was analyzed.

To make the superconducting magnetically levitated transport (maglev) system more attractive, it has been important to enhance the ride comfort by controlling vehicle vibration. Maglev vehicle vibrations have been reduced in previous experiments by controlling only the secondary suspension between the car bodies and bogies. However, by doing so, it has been difficult to reduce vibration for the characteristic and relatively high frequencies of the primary suspension between the bogies and guideway. Recently, control of the primary suspension is being considered. Power collecting coils of a linear generator system, which is being tested as an onboard power source, can also generate additional forces that can be used to control vibrations. Because this type of vibration control can apply damping directly to the primary suspension, it can reduce vibrations of relatively higher frequencies that are difficult to reduce by controlling only the secondary suspension. A maglev vehicle model that focuses on vertical and pitching motions is used to examine the effectiveness of reducing vibrations by using a linear generator damping force control in the primary suspension and linear quadratic (LQ) control of the actuators in the secondary suspension. Experimental results using the linear generator on a full-scale maglev vehicle on the Yamanashi Maglev Test Line are described.

In realistic working conditions, a vibratory roller operates and moves on various kinds of soil ground and when it does vibration excitation sources, such as soil ground, drum and engine are transmitted to the driver through the isolation systems of the cab and seat, which has direct influence on the driver’s health and their working efficiency. Thus, in order to evaluate the riding comfort of a vibratory roller under the different soil grounds, a nonlinear dynamics model of a single drum vibratory roller was established in this paper, based on the analysis of the contact physics of the wheel with different soil grounds. In order to describe the vertical excitation force acting on the front frame generated by a vibratory drum with elastic-plastic soil, a 3-DOF vibration model which describes vibratory drum operating is developed in this study, based on Adam D. and Kopf F’s elastic-plastic soil model. Using Bekker’s hypothesis of the soft soil ground, the tire- deformation soil surface contact model was established to analyze the vertical excitation force acting on the rear frame. Matlab/Simulink software was used to simulate the nonlinear dynamic models and calculate the values of the vertical weighted r.m.s acceleration responses of driver’s seat and cab. The nonlinear dynamics model of the whole vehicle was analyzed according to the ISO 2631: 1997 (E) standard, the influence of noise and vibration to human health which evaluates the influence of the different road conditions, operating conditions, and vehicle speeds on the driver’s ride comfort. The results showed that the rigid road surface roughness level has a greater influence on vibratory roller ride comfort that a driver subjectively feels is very uncomfortable when the vehicle moves on a poor road surface roughness. The deformation of the road surfaces dominate cab sloshing when a vehicle moves on relatively soft soil road surface. And in a low frequency region, vehicle ride comfort becomes worse when there are vibratory compacts and moves on elastic-plastic soil. The study can provide a reference for vibration roller ride comfort design.

In this paper, the ride comfort obtained from computer simulation was compared to that of physical experiment. To measure ride comfort of a passenger car, acceleration data was obtained from the floor and seat during highway running with different speeds. The measured acceleration components were multiplied by weighting functions, and then summed together to calculate overall ride values. For the computer simulation, MADYMO software was employed. To enhance ride comfort, several air cells are installed in the seat cushion to adjust the stiffness of seat by changing the air pressure in the cells. For the ride comforts, SEAT (Seat Effective Amplitude Transmissibility) was compared. To choose optimum air pressure in the cell, several test drivers with different weights were tested on several vehicle speeds.

In this work, control performance of a semi-active railway vehicle suspension system featuring MR damper is evaluated. Firstly, a mathematical model for railway vehicle which contains car body, bogie frame and wheel-set is derived to represent lateral, yaw and roll motions. From this model, design parameters of MR damper are optimally determined. And then, MR dampers which can generate proper damping force to control the unwanted vibration of the railway vehicle are manufactured and evaluated experimentally. In order to attenuate the vibration of railway vehicle, in this work, skyhook controller is designed and implemented. Control performances of MR damper for railway vehicle including car body lateral motion and acceleration of MR damper are evaluated using test rig composed of a car body and two bogies.

It is a commonly held view that semi-actively (S/A) controlled dampers can significantly improve the behaviour of a road and railway vehicles. Although simulation results published to date indicate potential improvements in railway vehicle ride comfort, this has not been sufficiently verified in real operation. This paper therefore investigates the effectiveness of S/A suspension control using magnetorheological (MR) dampers in improving the ride comfort of railway vehicle in real-world conditions. Field tests were carried out on a electric multiple unit , in which the conventional (passive) vertical and lateral dampers in the secondary suspension were replaced by MR dampers. These experiments were realized on three different railway lines that varied in terms of track alignment, maximum speed and quality. The results demonstrate that S/A control significantly improves ride comfort, especially at higher speeds and on poor-quality tracks. On standard lines, the mean comfort index N MV decreased by an average of 25%. The greatest benefit was achieved at the natural frequency of the vehicle body motion, where the vibration level is reduced by an average of 35%. Despite some challenges, this paper highlights the potential of S/A damping control to improve passenger comfort and makes a recommendations to further optimise its performance.

One of the well-known methods for improving the lateral stability of a vehicle is to utilize an active steering controller. Common active steering systems use feedback signals from a yaw rate sensor and side-slip angle estimation. However, in some driving conditions, skilled drivers can prevent vehicle rollover using the steering angle of the vehicle. Hence, the effect of an active front-steering controller on the roll angle of the vehicle is studied in this paper. For this study, a three-degree-of-freedom linear model of a vehicle which has the lateral motion, the yaw motion and the roll motion as the degrees of freedom is derived. The effectiveness of the active steering controller on the roll stability of the vehicle is examined by simulations in a wide range of longitudinal velocities of the vehicle using a linear quadratic regulator controller. The results obtained indicate that the active steering controller increases the roll stability of the vehicle only at low vehicle speeds and also that consideration of the roll degree of freedom in the design of the active steering controller is not effective at high vehicle speeds. Therefore a two-degree-of-freedom bicycle model is sufficient for active steering controller design. Another part of this paper is dedicated to designing a practical active steering controller for a vehicle with time-varying and uncertain parameters. In fact, designing a controller which guarantees the stability of the vehicle with simultaneous uncertainties in the cornering stiffnesses of the tyres and in the time-varying velocity is the main goal of this paper. Another important advantage of the proposed controller is its simplicity and static structure. In fact, this controller design is carried out offline and can be implemented for use in a real vehicle. This simple and powerful controller is a robust linear quadratic regulator controller. For designing a robust linear quadratic regulator controller, a polytopic model of the two-degree-of-freedom vehicle is obtained, which considers the uncertainty in the parameters. In addition, a linear matrix inequality is used to design a linear quadratic regulator controller for an uncertain or parameter-varying system. Finally, the performance of the designed robust linear quadratic regulator controller was studied by simulating the vehicle responses in some manoeuvres. A sport utility vehicle model is used for simulation purposes. This non-linear vehicle model has eight degrees of freedom and its tyres are assumed to be both linear and non-linear. The performance of the robust linear quadratic regulator controller was studied for vehicles with both linear and non-linear Pacejka tyres. The proposed controller guarantees robust stability of the closed-loop system in the presence of 50% variation in the vehicle speed and 20% uncertainty in the stiffnesses of the tyres.

This paper presents the optimization of suspension characteristics under the condition of curved track railway vehicles. Reducing lateral acceleration on curved track is an issue for high-speed railway vehicles. In terms of curved track running environments, reducing the lateral vibration of railway vehicles is critical to safety and curving performance. The properties of lateral damping and stiffness of both primary and secondary suspension show effect on wheel-set, bogie and car-body. Analysis for reducing the lateral vibration of rail vehicles with respect to the characteristics of both primary and secondary suspension has been developed using ADAMS/Rail. Response Surface Method has been chosen for the purpose of verifying correlation effects among design parameters. Also, this paper suggests the method for designing optimal suspension of railway vehicles on curved track. The optimization result indicates decrement of lateral acceleration on wheel-set by 3% and bogie by 1% on curved track. Finally, this paper comes to the conclusion that suspension system of railway vehicle (KTX I) is properly designed when regarding lateral vibration of railway vehicle on diverse curved track condition.