• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6D
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• pp.905-913
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• 2008

Recently, concrete tracks are introduced into high-speed railroads as an alternative to ballast tracks. Concrete tracks are superior to ballast tracks in the aspect of durability, maintenance and safety. However, deteriorated stiffness of railroad bed and settlement of soft ground induced by trapped or seepage water lead to problems in safety of train operation. In this research, flexural rigidity of concrete tracks was employed as an index of track displacement and a new seismic technique called FRACTAL (Flexural-Rigidity Assessment of Concrete Tracks by Antisymmetric Lamb Waves) method was proposed to delineate flexural rigidity of concrete tracks in a 2-D image. In this paper, to establish theoretical background, parametric research was performed using numerical simulations of stress-wave tests at concrete tracks. Feasibility of the FRACTAL technique was proved at a real concrete track for Korean high-speed trains. Validity of the FRACTAL technique was also verified by comparing the results of impulse-response tests performed at the same measurement array and the results of DC resistivity survey performed at a shoulder nearby the track.

• Progress in Medical Physics
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• v.17 no.3
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• pp.159-166
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• 2006

The nonlinearity of hemodynamic response in the somatosensory cortex was investigated with vibrotactile stimulation. The stimuli consisted of a train of 25 Hz, each tasting five different duration periods, 2 s, 4 s, 8 s 12 s, or 16 s with 20 sec periods of no vibration in a pseudo-random order. In order to understand the linearity on the change of stimulus duration for somatosensory cortex, two different tests- checking the linearity of system and finding the impulse response function from gamma-variate function were applied to analyze the hemodynamic response functions. They have produced nearly same results. The BOLD response in the somatosensory cortex Is nonlinear for stimuli of less than 8 seconds, but nearly linear for stimuli greater than 8 seconds. The amplitude, area, TTP, and FWHM as functions of the stimulus duration were calculated and showed a significant downward trend with Increasing stimulus duration for the amplitude and the area. It supports the ranges of nonlinearity are less than 8 seconds.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.101-102
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• 2002

Indicial response characteristics of a rotor supported by a gas-lubricated, spiral-grooved proceeding bearing are studied theoretically to develop a fundamental investigation for the bearing design with considering NRRO characteristics. The trajectory of rotor movement is calculated by applying the non-linear orbit scheme against a prescribed impulse load, then two characteristic quantities are introduced to evaluate the indicial response performance of the bearing, i.e., 'maximum deviation of rotor center' and 'integrated rotor center deviation'. The effects of some design parameters of spiral grooves to these representative quantities are studied so that 'robust' design against impulse load is discussed.

• International Journal of Automotive Technology
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• v.7 no.7
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• pp.769-776
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• 2006

A mathematical model is developed in this paper to define the interaction between the occupant and vehicle passenger compartment and to predict the occupant dynamic response during a sudden impulse load. Two different types of occupants are considered in this study, child and adult occupants. The occupants are considered as lumped masses connected to the child seat and vehicle's body masses by means of restraint systems. In addition, the occupant restraint characteristics of seat belt and airbag are represented by stiffness and damping elements. To obtain the dynamic response of the occupant, the equations of motion of the occupants during vehicle collisions are developed and analytically solved. The occupant's acceleration and relative displacement are used as injury criteria to interpret the results. It is demonstrated from the numerical simulations that the dynamic response and injury criteria are easily captured and analyzed. It is also shown that the mathematical models are flexible, useful in optimization studies and it can be used at initial design stage.

• Proceedings of the KIEE Conference
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• 1987.07b
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• pp.1252-1255
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• 1987

In this paper an approach for the analysis of the transient field response of radially symmetric transducer due to a wideband ultrasonic pulse is presented, which is based on a development of Green's function and applies the linear system theory to obtain an analytic expression for the impulse response of an annulus with a planar or spherical geometry. For the focused annular array, the impulse responses of the indivisual annuli are convolved with the delayed excitation pulse, and then summed to obtain the resultant response of the array. This process is very effective in the study of the various focusing abilities of the annular array. For illustration, the field distribution of a five element annular array is treated in detail for several focusing system.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.883-888
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• 2001

The theoretical method is developed to investigate the effects of ring stiffeners on free vibration characteristics and transient response for the ring stiffened composite cylindrical shells subjected to the impulse pressure loading. In the theoretical procedure, the Love's thin shell theory combined with the discrete stiffener theory to consider the ring stiffening effect is adopted to formulate the theoretical model. The concentric or eccentric ring stiffeners are laminated with composite and have the uniform rectangular cross section. The modal analysis technique is used to develop the analytical solutions of the transient problem. The analysis is based on an expansion of the loads, displacements in the double Fourier series that satisfy the boundary conditions. The effect of stiffener's eccentricity, number, size, and position on transient response of the shells is examined. The theoretical results are verified by comparison with FEM results.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.2132-2134
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• 2000

Since surge arresters are recommended to protect the electric power system from the lighting surge, the impulse current is generally used to verify this requirement at the test labotaries. Recently, the international standard(IEC 60060-2) related to the impulse current techniques revised requiring a traceability of measuring system for impulse current measurements. In this paper, a shunt for impulse current is developed satisfing the revised IEC standard and the possibility of application has been investigated using step response.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.12
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• pp.777-784
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• 1999

Since the ultra-high voltage power apparatus are recommended to withstand switching surge generated from the electric power system, the switching impulse voltage is generally used to verify this requirement at the testing laboratories. Recently, the international standard(IEC 60060-2) related to the high voltage measurement techniques is revised requiring a traceability of measuring system for high voltage measurements. In this paper, a reference divider for switching impulse voltage is developed satisfying the revised. IEC standard and the possibility of applications has been investigated. Therefore, the characteristics of the high and low voltage side resistor and the shielding ring have been analyzed including the step response characteristics of the prototype divider. Throughout various efforts, it is confirmed that our measuring device has shown compatible characteristics as a reference divider.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2149-2151
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• 1999

This paper describes the impulse response characteristics of the grounding systems in power utility system. Several regulations regarding to electric power equipments, services and managements require that the groundings of class 1 ($E_1$) and class 2 ($E_2$) must be connected at the common point in grounding systems. In addition, the grounding for arrester ($E_{LA}$), which belongs to the grounding of class 1, should be connected at the same point. However, there is no method and position of common-connection at anywhere. In this work, when the impulse current was injected through the grounding conductor for arrester, the investigations measuring and analyzing potential rises induced at the common connection point and other grounding conductors were conducted. The experiments were carried out in the conditions of the grounding conductor of 25m long and the near or remote common connection from ground electrode. The lightning impulse current was applied so as to simulate the on-set of arrester due to lightning and/or switching surges.

• Journal of Electrical Engineering and Technology
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• v.7 no.6
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• pp.876-883
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• 2012

The paper investigates three types of transfer function methods for detecting displacements of winding in a model transformer. To acquire these transfer functions, the measuring method of input voltage, current and its response is used in impulse method. The applied impulse voltages had three rising times, which were short rising time (less than 0.6 ${\mu}s$), medium rising time (about 0.8 ${\mu}s$) and long rising time (about 1 ${\mu}s$) in front waves. Every 10 measurements of voltage and current waves were averaged from 50 measurements of voltage and current waves. These transfer functions were tested in normal, 24mm elevated and 48mm elevated windings conditions and were analyzed with correlation coefficients and spectrum deviations. In the analysis, the results depend on the types of transfer functions and the rising times of input voltages.