• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.6
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• pp.620-627
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• 2009

Shaking table test was carried out to obtain dynamic characteristics of TLCDs with uniform and non-uniform sections for both horizontal and vertical tubes. The input to the table is harmonic acceleration with constant magnitude. The output is horizontal dynamic force which is measured by load cell installed below the TLCD. Transfer functions are experimentally obtained using the ratio of input and output. Natural frequency, the most important design factor, is compared to that by theoretical equation for TLCDs with five different water levels. System identification process is performed for experimentally obtained transfer functions to find the dynamic characteristics of head loss coefficient and effective mass of TLCDs. It is found that their magnitudes are larger for a TLCD with non-uniform section than with uniform section and natural frequencies are close to theoretical ones.

• Structural Engineering and Mechanics
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• v.31 no.5
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• pp.545-566
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• 2009

Bridge columns are subjected to combined actions of axial force, shear force and bending moment during earthquakes, caused by spatially-complex earthquake motions, features of structural configurations and the interaction between input and response characteristics. Combined actions can have significant effects on the force and deformation capacity of RC columns, resulting in unexpected large deformations and extensive damage that in turn influences the performance of bridges as vital components of transportation systems. This paper evaluates the seismic response of three prototype reinforced concrete bridges using comprehensive numerical models that are capable of simulating the complex soil-structural interaction effects and nonlinear behavior of columns. An analytical approach that can capture the shear-flexural interacting behavior is developed to model the realistic nonlinear behavior of RC columns, including the pinching behavior, strength deterioration and stiffness softening due to combined actions of shear force, axial force and bending moment. Seismic response analyses were conducted on the prototype bridges under suites of ground motions. Response quantities of bridges (e.g., drift, acceleration, section force and section moment etc.) are compared and evaluated to identify the effects of vertical motion, structural characteristics and the shear-flexural interaction on seismic demand of bridges.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.6
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• pp.496-503
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• 2003

SFC system has come to be used as drive large synchronous machine in many industry applications. Many papers have been presented on the control algorithm of SFC system, not the acceleration and start-up but the rated speed operation with line connection and the braking operation with regeneration which is used in the industry. This paper presents the whole section control algorithm for a large synchronous machine using SFC system. The results of experiment show that the proposed algorithm is proper and effective.

• Journal of the Korea Institute of Military Science and Technology
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• v.25 no.2
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• pp.169-176
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• 2022

Laser ablation propulsion(LAP) is the method to create impulse by laser ablation. It can be used to deorbit the space debris(SD), as its long-range property and versatility on any material. In this paper, we find out several requirements of the LAP system(LAPS) to deorbit the SD by simple numerical calculations of the SD orbit and laser beam flux. As a result, minimum operable altitude angle turned out to be a crucial variable to the LAPS. Moreover, if minimum operable altitude angle is 10°, and if the minimum distance between the LAPS and the SD is below 450 km, 1 m/s² is sufficient to deorbit the SD by once. With 18 kJ/3 ns pulsed laser and cube shaped 100 kg SD, 1 m/s² acceleration can be achieved by increasing the pulse repetition rate over 34~53 Hz, depending on the size of the SD. This capability could compare with the conceptual design of the Japan Establishment for a Power-laser Community Harvest(J-EPoCH) facility, which include 8 kJ, 5 PW@100 Hz laser.

• 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.

• International Journal of Highway Engineering
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• v.14 no.4
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• pp.149-162
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• 2012

PURPOSES : The causes of traffic accidents can be classified into the factors of highway users, vehicles, and driving environments. Traffic accidents result from the deficiency in single or combination of these three factors. The objective of this study is to define the "potentially hazardous sections of highway" in terms of traffic safety considering these three factors. METHODS : The test drivers performed repeated driving on these highway sections. The drivers and passengers recorded the sections on which the driving was uncomfortable, and the speeds on the sections excluding the uncomfortable sections were used for the development of the model. RESULTS : The model is composed of three sub-models for each of the horizontal curve, tangent, and the section where the curve starts/ends. The safe driving behavior coefficients by the horizontal curvature were derived by comparing the maximum operating speeds at which the vehicle may slide or deviate and the speeds at which the drivers feel comfort. The safety speeds on tangent were derived by the length of tangent section considering the driver's desired speeds under the traffic condition on which the drivers hardly influenced by the other vehicles. For the sections where the curve starts/ends, the driving behaviors were classified by the distances between the curves, and the safe acceleration/deceleration speeds were derived on which the drivers enter/exit the curve sections safely. CONCLUSIONS : Safety speed could then be regarded that the model suggested in this study may be useful to define the potentially hazardous highway section and contribute the improvement of highway safety.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.6
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• pp.891-898
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• 2012

The study for the passenger's comfortableness of vehicles and the arousal of car drivers has been done widely. On the other hand, there are few studies for the locomotive engineers. Human error means that the mistakes made by human, recently it receives attention in the field of safety engineering and human engineering. Comparing the operating condition of train with car, because of the simplification of the visual stimulus, the arousal level on the train goes down easily. The arousal level down makes judgement down, the accident risk from human error is getting bigger. In this study, we measured bio-signals(ECG, EDA, PPG, respiration and EEG) from 6 locomotive engineers to evaluate their arousal state while they operated the train. Also we recorded the 3 axes acceleration signal showing the vibration state of train. Also, the existence of tunnels were simultaneously measured. At the station section where the train speed goes down, the size of vector's sum decreases because of reduced vibration. Beta component in EEG tends to increase at the entering point of each station and tunnel. It is due to the arousal reaction and tension growth. The mean SCR(skin conductance response) was more increased in neutral section. As the button control movement (body movement) increases in the neutral section, it is appeared that SCR increase. RR interval tends to gradually increase during train operation for 1 hour 40 minutes. However, It tends to sharply decrease at the stop station because strong concentration needed to stop train on the exact point. The engineer's arousal reaction can be checked through analysing the bio-signal change during train operation. Therefore, if this analysing result is adopted to the sleepiness prevention caution system, it will be useful for the safety train operation.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.4
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• pp.47-55
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• 2009

The purpose of this study is to verify the transfer function of input acceleration and output control force by linearizing a velocity-dependent damping term of Liquid Column Vibration Absorber (LCVA). Analytical and experimental research is conducted to identify natural frequency, damping ratio and participated mass ratio of LCVA with various section ratios of vertical and horizontal areas. Findings obtained experimentally by the shaking table test are compared with analytical findings using optimization technique with constraints. The results indicate that the level of liquid and section ratio of LCVA affect the characteristics of damping ratio and mass ratio. Damping and mass ratio increase as the section of vertical column of LCVA decreases, due to turbulence in the elbow of LCVA.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.7
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• pp.921-929
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• 2011

We measured experimentally the properties of fluid dynamics, velocity fields, and the pressure, around stenotic obstruction located inside a circular channel structure. Particle image velocimetry system was employed to obtain velocity fields at the central section of the circular channel in the streamwise direction. The stenosis model used was made of acrylic material with different stenotic aspect ratios. The working fluid was water and it was returned by a centrifugal pump system. Pressure measurements were carried out to validate the effect of a narrow passageway. Results showed that the acceleration of gap flow through stenotic obstruction and the pressure drop in the recirculation regime behind the stenosis model can be observed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.04a
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• pp.191-198
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• 1994

The nonlinear dynamic behaviors of guardrail established on the local or high way have been investigated using BARRIER Ⅶ program with respect to four design variables such as section type of beams and posts, impact angle, impact velocity and vehicle weight. Computer simulation programs are sophisticated analytical models for analyzing dynamic vehicle/barrier interactions and provide a relatively inexpensive alternative to full scale crash testing. This study has been focused on the structural adequacy, occupant risk, and vehicle trajectory. For this purpose, the maximum deflection and impact force have been calculated to design the clear zone and to analyze effect of impact attenuation. Also, the acceleration of vehicle and exit angle after collision have been computed to estimate the occupant risk. From this study, it is suggested that we should strengthen the design criteria of guradrail to prevent from disastrous traffic accidents.