Hyung-Suk Han

Simulation of Train Crashes in Three Dimensions

Summary It is important to predict the crash behavior of trains to improve their crashworthiness. This paper investigates the simulation of high-speed train crashes in three dimensions using multibody dynamics. At present, little is known about three-dimensional crash simulations. This study shows that it is possible to simulate overriding, derailment and lateral buckling, including results from one-dimensional or two-dimensional simulations. Several factors, however, such as computational time and large deformation of structures, need further investigation.

Effects of the guideway's vibrational characteristics on the dynamics of a Maglev vehicle

The levitation control system in an electromagnetically levitated vehicle controls the voltage in its winding to maintain the air gap, which is the clearance between the electromagnet and the guideway, within an allowable range of variation, while strongly interacting with the flexible guideway. Thus, the vibrational characteristics of the guideway play an important role in the dynamics of Maglev (magnetically levitated) vehicles that utilise an active electromagnetic suspension system. In this study, the effects of the guideways vibrational characteristics, such as natural frequency and damping, on the dynamics of the Maglev vehicle UTM-02 are numerically and experimentally analysed. From these analyses, the coupled equations of motion of the simplified vehicle–guideway model with three degrees of freedom are derived. Eigenvalues are calculated and frequency response analysis is also performed, in order to obtain a clear understanding of the dynamic characteristics resulting from the guideways vibrational characteristics. To verify the numerical results, air gap tests of the urban Maglev vehicle UTM-02 are also carried out. These results lead us to recommend that the natural frequency of the guideway be decreased by increasing mass density rather than by decreasing rigidity, and that its damping ratio be increased in the Maglev vehicle UTM-02 employing a five-state feedback control law as a levitation control law.

Curving performance simulation of an EMS-type Maglev vehicle

For electromagnetic suspension (EMS) type urban Maglev vehicles using a U-shaped electromagnet, the levitation and guidance forces are generated by only one electromagnet. Although the levitation force is actively controlled by changing the voltage of the electromagnet, the guidance force is passively determined by the levitation force. In addition, the curve negotiation performance of EMS-type urban Maglev vehicles using a U-shaped electromagnet must be considered, because an urban guideway may have some curves with shorter radii. It is, therefore, necessary to predict the curving performance with the greatest accuracy possible, in order to improve electromagnetic suspension and establish guideway design specifications. The objective is to establish a new dynamic modelling technique, so as to achieve more realistic curving simulation and thus to more accurately evaluate the curving performance of an EMS-type Maglev vehicle. The use of a full vehicle multibody dynamic model is proposed, and is applied to the evaluation of curving performance. Design changes are also investigated to obtain the bogie design directions for minimising variation in the lateral air gap, which is a criterion for curving performance.

Coupled vibration analysis of Maglev vehicle-guideway while standing still or moving at low speeds

Dynamic instability, that is, resonance, may occur on an electromagnetic suspension-type Maglev that runs over the elevated guideway, particularly at very low speeds, due to the flexibility of the guideway. An analysis of the dynamic interaction between the vehicle and guideway is required at the design stage to investigate such instability, setting slender guideway in design direction for reducing construction costs. In addition, it is essential to design an effective control algorithm to solve the problem of instability. In this article, a more detailed model for the dynamic interaction of vehicle/guideway is proposed. The proposed model incorporates a 3D full vehicle model based on virtual prototyping, flexible guideway by a modal superposition method and levitation electromagnets including feedback controller into an integrated model. By applying the proposed model to an urban Maglev vehicle newly developed for commercial application, an analysis of the instability phenomenon and an investigation of air gap control performance are carried out through a simulation.

Prediction of ride quality of a Maglev vehicle using a full vehicle multi-body dynamic model

In magnetically levitated (Maglev) transportation systems, especially in electromagnetic suspension system (EMS) type Maglev systems, highly accurate prediction of ride quality is very important in order to reasonably relax guideway construction tolerances or constraints and stiffness while meeting the specification for ride comfort, thereby reducing guideway construction and maintenance costs. A full vehicle multi-body dynamic model is proposed, to facilitate a rigorous ride quality prediction of an EMS-type Maglev vehicle. Using the more realistic dynamic model proposed in this paper, the effects of guideway deflection limits, surface roughness, and levitation control system parameters on ride quality are studied numerically. The results obtained from the simulation studies are then used to facilitate a discussion of the trade-off between guideway smoothness and vehicle suspension. It can be expected that these studies could suggest cost-effective specifications for guideway construction tolerances and stiffness and EMS.

Design and Validation of a Slender Guideway for Maglev Vehicle by Simulation and Experiment

ABSTRACT Normally, Maglev (magnetic levitation) vehicles run on elevated guideways. The elevated guideway must satisfy various load conditions of the vehicle, and has to be designed to ensure ride quality, while ensuring that the levitation stability of the vehicle is not affected by the deflection of the guideway. However, because the elevated guideways of Maglev vehicles in South Korea and other countries fabricated so far have been based on over-conservative design criteria, the size of the structures has increased. Further, from the cost perspective, they are unfavourable when compared with other light rail transits such as monorail, rubber wheel, and steel wheel automatic guided transit. Therefore, a slender guideway that does have an adverse effect on the levitation stability of the vehicle is required through optimisation of design criteria. In this study, to predict the effect of various design parameters of the guideway on the dynamic behaviour of the vehicle, simulations were carried out using a dynamics model similar to the actual vehicle and guideway, and a limiting value of deflection ratio of the slender guideway to ensure levitation control is proposed. A guideway that meets the requirement as per the proposed limit for deflection ratio was designed and fabricated, and through a driving test of the vehicle, the validity of the slender guideway was verified. From the results, it was confirmed that although some increase in airgap and cabin acceleration was observed with the proposed slender guideway when compared with the conventional guideway, there was no notable adverse effect on the levitation stability and ride quality of the vehicle. Therefore, it can be inferred that the results of this study will become the basis for establishing design criteria for slender guideways of Maglev vehicles in future.

Effect of Lateral Deformations of Guideway on Guidance Characteristics of Maglev Train

A slender guideway is essential in improving aesthetically and reducing its construction cost which accounts for about 70% of overall investment for maglev system. As the slender guideway, however, may increase its deformation, its effect on levitation stability and guidance performance needs to be analyzed. The purpose of this study is to analyze the effect on guidance characteristics of maglev due to the lateral deformation of the guideway girder and lateral irregularity of guiderail. For doing this, 3D model considering lateral deformation of girder and irregularity of rail of the guideway is developed. Using the dynamic interaction model integrated with the proposed guideway and maglev vehicle including electromagnetics and its controller, guidance characteristics of maglev are analyzed. It is analyzed that the effect on lateral deformation of girder is relatively small compared to deformation on the lateral irregularities of guiderail.

Magnetic Levitation Control through the Introduction of Bogie Pitch Motion into a Control Law

The uneven reaction surface profile facing the lift magnets in attractive Maglev vehicles naturally brings about pitch motion of the bogie. In particular, in the placement configuration of the long stator of the linear synchronous motor (LSM) on the track for high-speed propulsion, surface irregularities and the offsets between the stator packs create measurable airgaps, i.e., the clearance between the magnet and the stator, with discontinuously extreme values, resulting in bogie pitch motion. This occurs because the airgap velocities and accelerations derived by the differentiations of the measured air-gaps are used to determine the voltages applied to the magnets. This paper incorporates bogie pitch motion into a control law for each magnet controller to reduce the variations in both the airgap and the pitch angle. The effectiveness of the proposed method is analyzed using a full-scale Maglev vehicle running over a test track.

Yaw Motion Control of Electromagnetic Guidance System for High-Speed Maglev Vehicles

In an attractive-type high-speed magnetic levitation (maglev) train, separate electromagnets are used for lateral guidance. For the guidance system, a U-shaped electromagnet that uses transverse flux has been designed and analyzed. Electromagnets counterbalance centrifugal forces during curving as well as under all operating conditions so that the clearances between on-board magnets and the guideway surface can be maintained within an allowable range. Because of the rigidity of the bogie, coupling effects exist among the magnets that are controlled independently. This study incorporates bogie yaw motion into control law for adjusting the voltages applied to magnets to provide constant clearance control. The effects of bogie yaw motion on guidance control performance are investigated experimentally using a full-scale vehicle.