• Earthquakes and Structures
• /
• v.20 no.4
• /
• pp.457-471
• /
• 2021

This study aims at providing a simple and effective methodology to define a meaningful characteristic period for special class of earthquake records named "pulse-like ground motions". In the proposed method, continuous wavelet transform is employed to extract the large pulse of ground motions. Then, Fourier amplitude spectra obtained from the original ground motion and the residual motion is simply compared. This comparison permits to define a threshold pulse-period (Tp∗) as the threshold period above which the pulse component has negligible contributions to the Fourier amplitude spectrum. The effect of pulse on frequency content of motions was discussed on the light of this definition. The advantage and superior features of the new definition were related to the inelastic displacement ratio (IDR) for single-degree-of-freedom systems with period equal to one half of the threshold period. Analyses performed for the proposed period at three ductility levels u=2,4,6 were compared with the results obtained at half of pulse period derived from wavelet analysis, peak-point method and the peak of product of the velocity and the displacement response spectra (Sv x Sd). According to the results, pulse effects on inelastic displacement ratio seem to be more important when $\frac{T_p^*}{T}=2$ (T is the fundamental vibration period of system). The results showed that utilizing of the proposed definition could facilitate an enhanced understanding of pulse-like records features.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2002.03a
• /
• pp.51-58
• /
• 2002

The relative site amplification factors in southern Korea were determined from coda waves using coda normalization method. The seismograms of 15 events at 79 stations were used in this study. Seismogram envelopes were obtained by the Hilbert transform of bandpass-filtered velocity seismograms with frequency bands at 1-2Hz, 2-4Hz, 4-8Hz, 8-l6Hz and 16-32Hz. The envelopes were stabilized by application of moving-average scheme with time window of 1 second. The relative amplitudes of seismogram envelope were computed by dividing the amplitude of seismogram envelope at one site by the amplitude of seismogram envelope at reference site. The relative site amplification factors were obtained by taking averages of the relative amplitude. Values of relative site amplification factors in southern Korea are generally low in western area and high in eastern area.

• Journal of the Korean Society of Safety
• /
• v.16 no.1
• /
• pp.31-36
• /
• 2001

Surface crack growth characteristics and influence of the stress amplitude in rotary bending fatigue test were evaluated for annealed S35C steel, and than fractal dimensions of fatigue crack paths estimated using the box counting method. The following results that will be helpful to understand the fatigue crack growth mechanism were obtained. (1) Crack growth rate ds/dN and db/dN (s : half crack length at the surface crack, b : crack depth) depended on stress amplitude (${\Delta}{\sigma}/2$), stress intensity factor range (${\Delta}K_A, {\Delta}K_C$) and crack length. (2) At the effect area of 0.3 mm hole notch (s＜0.5 mm) crack growth rate did not depend on these factors. (3) The fractal dimensions (D) increased with stress amplitude (${\Delta}{\sigma}/2$) but decreased with cyclic number.

• Journal of Power Electronics
• /
• v.16 no.4
• /
• pp.1407-1414
• /
• 2016

Unlike existing pulse-width modulation (PWM) techniques, such as sinusoidal PWM and random PWM, the wavelet PWM (WPWM) technique based on a Harr wavelet function can achieve a high fundamental component for the output voltage, low total harmonic distortion, and simple digital implementation. However, the original WPWM method lacks output voltage control. Thus, the practical application of the WPWM technique is limited. This study proposes an improved WPWM technique that can regulate output voltage amplitude with the addition of a parameter. The relationship between the additional parameter and the output voltage amplitude is analyzed in detail. Experimental results verify that the improved WPWM exhibits output voltage control in addition to all the merits of the WPWM technique.

• Earthquakes and Structures
• /
• v.4 no.2
• /
• pp.181-202
• /
• 2013

It is well known that the properties of the soil deposits, especially the damping, depend on both frequency and strain amplitude. Therefore it is important to consider both dependencies to calculate the soil response against earthquakes in order to estimate input motions to buildings. However, it has been difficult to calculate the seismic response of the soil considering both dependencies directly. The author has studied the time domain evaluation of the frequency dependent dynamic stiffness, and proposed a simple hysteretic damping model that satisfies the causality condition. In this paper, this model was applied to nonlinear analyses considering the effects of the strain amplitude dependency of the soil. The basic characteristics of the proposed method were studied using a two layered soil model. The response behavior was compared with the conventional model e.g. the Ramberg-Osgood model and the SHAKE model. The characteristics of the proposed model were studied with regard to the effects of element divisions and the frequency dependency that is a key feature of the model. The efficiency of the model was confirmed by these studies.

• Journal of the Korea Computer Industry Society
• /
• v.5 no.3
• /
• pp.355-362
• /
• 2004

This paper presents the common and different results between the galloping cable and torsional oscillations in suspension bridge. Numerical results of the galloping cable and torsional oscillations in suspension bridge are presented by using the second-order Runge Kutta method under the initial conditions. This paper shows that large amplitude solution can coexist with the small amplitude one as the frequency and amplitude of the oscillation change. The differences in symmetry and transient effects are presented.

• Journal of the Korea Concrete Institute
• /
• v.12 no.3
• /
• pp.77-85
• /
• 2000

Various concretes are used for construction works depending on the types of structure, building element and method of construction. An internal vibration work is one of the important processes for adequately pouring various concrete into a certain form. This study was undertaken to find out the effects of internal vibration on flowability of fresh concrete by concrete flow test under eight conditions of vibration. Presumable equation models also were created to show all vibration effects without regard to kinds of concrete. As the results of this study, the degree of vibration effects were varied according to the properties of concrete. Acceleration amplitude of vibration that applied to fresh concrete was effective value of the properties of vibration in a viewpoint of flowability. Moreover, This research presents the presumed equation models including variables created by acceleration amplitude and measuring value of vibrated concrete flow test. These models are presumable methods of vibration effects regardless of kinds of concrete.

• Journal of The Korean Astronomical Society
• /
• v.42 no.6
• /
• pp.155-159
• /
• 2009

In order to determine color excess in the $uvby\beta$ color system for high amplitude $\delta$ Scuti stars, reddening free $[m_1]$, $[c_1]$, and $\beta$ indices data were obtained from the existing literature for 21 stars. Then, the three intrinsic relations of $(b-y)_0$ - $[m_1]$, $(b-y)_0$ - $[c_1]$, and $(b-y)_0$ - $\beta$ were investigated. Among these, it was shown that the $(b-y)_0$-$[c_1]$ relation is the most useful. By establishing intrinsic $(b-y)_0$-$[c_1]$ relations for six reddening calibration stars, color excesses of other stars were determined.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.4
• /
• pp.428-439
• /
• 1998

Fluid flow and heat transfer have been numerically investigated for an oscillating flow in a tube with a regenerator. The regenerator is placed between hot and cold spaces which are heated and cooled at uniform temperature. An oscillating flow is generated by the piston motion at both ends of a tube. The time dependent, two-dimensional Navier-Stokes equations and energy equation are solved by using the finite-volume and moving grid method. The regenerator is adopted as Brinkmann-Forchheimer extended Darcy model. Numerical results are obtained for the flow and temperature fields, and described the effects of the oscillating frequency and amplitude ratio by the piston motion as well as the aspect ratio. The numerical results obtained indicate that the heat transfer between the tube wall and oscillating flow is increased as the oscillating frequency, amplitude ratio and the aspect ratio are increased.

• Journal of Power System Engineering
• /
• v.4 no.4
• /
• pp.70-77
• /
• 2000

On the dynamic behavior of a simple beam the influences of the velocities and distance of two moving masses have been studied by numerical method. The instant amplitude of a simple beam is calculated and analyzed for each position of the moving masses represented by the time functions. As increasing the velocties of two moving masses on the simple beam, the amplitude of the transverse vibration of the simple beam is decreased and the frequency of the transverse vibration of the simple beam is increased. As the distance between two moving masses increase, the transverse displacement of the simple beam is decrease. The simple beam is very stable in second mode at $\bar{a}=0.5$ and in third mode at $\bar{a}=0.3$.