• Journal of the Korean Society for Railway
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• v.10 no.3 s.40
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• pp.257-263
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• 2007

The critical speed above which the vehicle become unstable is one of the items that should be verified in the development of a new train. In the case of a high speed tilting train, which requires both higher critical speed and higher curving speed, the critical speed should be more carefully treated because the both requirements are in conflict with each other in the conventional train design. The main purpose of the present work is to estimate the linear and non-linear critical speeds of 200km/h Korean Tilting Train 'Hanbit200' under development. The newly developed self-steering mechanism was attached to the tilting train to ensure that the critical speed falls under the lower yaw stiffness which is needed to secure higher curving performance. The simulation for predicting the critical speed was done by a commercially available vehicle dynamics software. A full scale roller rig test was carried out to validate the numerical results and to verify the effectiveness of the self-steering mechanism.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.2
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• pp.127-134
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• 2021

This study presents an overhang-type rail traction system using dual brushless AC (BLAC) motors with hall sensors. For an accurate position and moving length control of the designed rail traction system, instantaneous position controller using speed reference model and modified disturbance observer for BLAC motor with hall sensor are proposed. The presented speed reference model is designed to satisfy the required performance of 200 mm/s with proper acceleration and deceleration slopes to reduce mechanical vibration. Through the instantaneous speed reference model, instantaneous position and speed errors can be compensated together. Furthermore, the modified disturbance observer for BLAC motors with low-resolution hall sensors can improve the torque and speed control performance. The proposed disturbance observer is based on an actual motor speed. However, the feedback speed information of the hall sensor is not enough for use in the low-speed region. The practical adopted disturbance observer uses an activation speed band to the actual torque controller of the designed rail traction system. The proposed position control scheme is verified by the MATLAB-Simulink model and a practical manufactured traction system. In the computer simulation and experiments, the proposed position control scheme shows advanced control performance.

• Structural Engineering and Mechanics
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• v.77 no.5
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• pp.627-635
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• 2021

The speed of rail vehicles become higher and higher over two decades, and China has unveiled a prototype high-speed train in October 2020 that has been able to reach 400 km/h. At such high speeds, wheel-rail force items that had previously been ignored in common computational model should be reevaluated and reconsidered. Aiming at this problem, a new model for investigating the vehicle-bridge interaction at high moving speed is proposed. Comparing with the common model, the new model was more accurate and applicable, because it additionally considers the second-order pseudo-inertia forces effect and its modeling equilibrium position was based on the initial deformed curve of bridge, which could include the influences of temperature, pre-camber, shrinkage and creep deformation, and pier uneven settlement, etc. Taking 5 km/h as the speed interval, the dynamic responses of the classical vehicle-bridge system in the speed range of 5 km/h to 400 km/h are studied. The results show that ignoring the second-order pseudo-inertia force will underestimate the dynamic response of vehicle-bridge system and make the high-speed railway bridge structure design unsafe.

• Advances in Computational Design
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• v.8 no.1
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• pp.1-12
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• 2023

To consider the effects of the increasing speed of next-generation high-speed trains, the existing traffic safety code for railway bridges needs to be improved. This study suggests a numerical method of evaluating the new effects of this increasing speed on railway bridges. A prestressed concrete (PSC) box bridge with a 40 m span length on the Gyeongbu track sector is selected as a representative example of high-speed railway bridges in Korea. Numerical models considering the inertial mass forces of a 38-degree-of-freedom train and the interaction forces with the bridge as well as track irregularities are presented in detail. The vertical deflections and accelerations of the deck are calculated and compared to find the new effects on the bridge arising with increasing speed under simply and continuously supported boundary conditions. The ratios between the static and dynamic responses are calculated as the dynamic amplification factors (DAFs) under different running speeds to evaluate the traffic safety. The maximum deflection and acceleration caused by the running speed are indicated, and regression equations for predicting these quantities based on the speed are also proposed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.4
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• pp.269-275
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• 2022

In ideal configuration, elapsed-time method can measure the exact reaction wheel speed. But in real configuration, the speed measurement error exists due to tacho pulse non-uniformity. In this research, we study the method which overcome the non-uniformity effects. First, we introduce the method which spin the wheel at the specific speed and measure the non-uniformity. Then, we propose the real-time measurement error correction method which uses the obtained non-uniformity information. This method calculate the speed candidates from the elapsed-time method's counts and non-uniformity information, and choose the closest speed to the real speed. Through simulation, we show that proposed method measure the exact speed regardless of non-uniformity, and fast wheel speed control is possible.

• Wind and Structures
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• v.37 no.4
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• pp.275-287
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• 2023

Subgrade differential settlement of high-speed railways was a pivotal issue that could increase the risk of trains operation. The risk will be further increased when trains in the subsidence zone are affected by crosswinds. In this paper, the computational fluid dynamics (CFD) model and finite element (FE) model were established, and the data transmission interface of the two models was established by fluid-solid interaction (FSI) method to form a systematic crosswind-train-track-subgrade dynamic model. The risk of high-speed train encountering crosswind in settlement area was analyzed. The results showed that the aerodynamic force of the trains increased significantly with the increase in crosswind speed. The aerodynamic force of the trains could reach 125.14 kN, significantly increasing the risk of derailment and overturning. Considering the influence of crosswind, the risk of train operation could be greatly increased. The safety indices and the wheel-rail force both increased with the increase of the wind speed. For the high-speed train running at 350 km/h, the warning value of wind speed was 10.2 m /s under the condition of subgrade settlement with wavelength of 20 m and amplitude of 15 mm.

• Journal of Korean Society of Transportation
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• v.35 no.4
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• pp.261-277
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• 2017

This study defines influencing sections as the part of the road section where passing vehicles are traveling with the lower speed compared to speed limit due to speed humps. The influencing section was divided into 3 parts; influencing section before the speed hump, interval section, and influencing section after the speed hump. This analysis focused on the changes of each part depending on installation types, vehicle types, and daytime or nighttime. For the interval section, especially, the ratio of distance traveled with lower speed than speed limit to interval section is defined as effective influencing section ratio to be analyzed. Vehicle speed profiles were collected with a speed gun to extract influencing section lengths. The survival analysis was applied and estimated survival functions are compared with each other by several statistical tests. As a consequence, the average length of influencing section on the 50m sequential speed humps was 75.3% longer during the deceleration than that of isolated speed hump, and 18.9% during the acceleration. The effective influencing section ratio for the 30m and 50m sequential speed humps had a small difference of 81.0% and 76.0% while the absolute values of the section that passing speed were less than the speed limit were longer on 50m sequential speed humps, each being 24.3m and 38.0m. Using the log rank test, it was evident that sequential speed humps were more effective to increase the length of influencing sections compared to the isolated speed hump. Vehicle type was the strong factor for influencing section length on the isolated speed hump, but daytime or nighttime was not the effective one. This research result can be used for improving the efficiency selecting the installation point of speed humps for road safety and estimating the standard of the distance between sequential speed humps.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.92-99
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• 2016

A wind turbine is controlled for the purpose of obtaining the maximum power below its rated wind speed. Among the methods of obtaining the maximum power, TSR (Tip Speed Ratio) optimal control and P&O (Perturbation and Observation) control are widely used. The P&O control algorithm using the turbine power and rotational speed is simple, but its slow response is a weak point. Whereas TSR control's response is fast, it requires the precise wind speed. A method of measuring or estimating the wind speed is used to obtain a precise value. However, estimation methods are mostly used, because it is difficult to avoid the blade interference when measuring the wind speed near the blades. Neural networks and various numerical methods have been applied for estimating the wind speed, because it involves an inverse problem. However, estimating the wind speed is still a difficult problem, even with these methods. In this paper, a new method is introduced to estimate the wind speed in the wind-power graph by using the turbine power and rotational speed. Matlab/Simulink is used to confirm that the proposed method can estimate the wind speed properly to obtain the maximum power.

• Journal of Korean Society of Transportation
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• v.26 no.3
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• pp.85-95
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• 2008

The purpose of this study is to reduce a high speed driving, it is a large scale traffic accident as the most dangerous fact on the highway. So traffic accidents related to high speed driving, a number of automated speed enforcement system has been established up to now. At present automated speed enforcement system in Korea control overspeed vehicle only in the specific spot. Because the drivers generally recognize the previous stated fact. therefore, we need speed control by new system. it is necessary to establish the automated traffic enforcement system based on the travel time speed. In conclusion, we obtain the desired results about automated traffic enforcement system based on the travel time speed. it is important that the number of traffic accidents has decreased and try to secure the safety of traffic.

• Wind and Structures
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• v.26 no.3
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• pp.129-146
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• 2018

Extreme wind speed analysis has been carried out conventionally by assuming the extreme series data is stationary. However, time-varying trends of the extreme wind speed series could be detected at many surface meteorological stations in China. Two main reasons, exposure change and climate change, were provided to explain the temporal trends of daily maximum wind speed and annual maximum wind speed series data, recorded at Hangzhou (China) meteorological station. After making a correction on wind speed series for time varying exposure, it is necessary to perform non-stationary statistical modeling on the corrected extreme wind speed data series in addition to the classical extreme value analysis. The generalized extreme value (GEV) distribution with time-dependent location and scale parameters was selected as a non-stationary model to describe the corrected extreme wind speed series. The obtained non-stationary extreme value models were then used to estimate the non-stationary extreme wind speed quantiles with various mean recurrence intervals (MRIs) considering changing climate, and compared to the corresponding stationary ones with various MRIs for the Hangzhou area in China. The results indicate that the non-stationary property or dependence of extreme wind speed data should be carefully evaluated and reflected in the determination of design wind speeds.