• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.61-68
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• 1999

In the nonlinear dynamic structural analysis the given ground excitation as an input should be well defined. Because of the lack of recorded accelerograms in Korea it is required to generate an artificial earthquake by a stochastic model of ground excitation with various dynamic properties rather than recorded accelerograms. It is well known that earthquake motions are generally non-stationary with time-varying intensity and frequency content. Many researchers have proposed non-stationary random process models. Yeh and Wen (1990) proposed a non-stationary modulation function and a power spectral density function to describe such non-stationary characteristics. Satio and Wen(1994) proposed a non-stationary stochastic process model to generate earthquake ground motions which are compatible with design reponse spectrum at sites in Japan. this paper shows the process to modify power spectrum compatible with target design response spectrum for generating of nonstationary artificial earthquake ground motions. Target reponse spectrum is chosen by ATC14 to calibrate the response spectrum according to a give recurrence period.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.257-259
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• 2008

Acceleration time history (ATH) used in the seismic analysis should envelop a target power spectral density (PSD) function in addition to the design response spectrum in order to have sufficient energy at each frequency for the purpose of ensuring adequate load. Even though design regulations require the ATH used in seismic analysis to meet a target PSD function, the reason that ATHs meet to a target PSD function is not described. Thus, artificial ATHs for high PSD function and artificial ATHs for low PSD function are generated. And then elastic and inelastic single-degree-of-freedom (SDOF) systems are loaded with these artificial time histories as the earthquake load. As a result, linear response and inelastic response of SDOF systems are affected by PSD function.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.416-421
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• 2013

In this paper, the design concept of the transport of defense equipment and processes were established. And the transport of large radar equipment design were investigated. Detailed design of moving equipment with reference to the U.S. military standard was performed.Damping system of the moving equipment by using a simulation designed to predict In order to minimize shock and vibration in the vehicle due to the irregular road surface is transmitted through. Analysis of the damping system was verified using the driving test.

• Journal of Institute of Convergence Technology
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• v.13 no.1
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• pp.35-40
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• 2023

편대 비행중인 선행 항공기에서 발생한 후류는 후행 항공기의 공력특성 및 비행 안정성에 영향을 준다. 최근에는 편대 비행 하는 무인기에서 발생하는 후류의 거동에 대한 연구가 활발히 진행되고 있다. 본 연구에서는 푸리에-스펙트럴법을 이용하여 편대 비행 중인 XQ-58A 무인기에서 발생한 후류의 거동에 대한 연구를 수행하였다. 3개의 무인기 사이의 수직/수평 거리를 조절하여 편대 비행 대형을 바꾸어가며 와 거동을 계산하였다. 항공기 날개 간 수직/수평 이격 거리 매우 근접하는 경우 와들이 날개에서 멀리 떨어지지 못하고 주변에서 거동하였으며, 상대적으로 날개 사이 거리가 멀 경우 빠르게 와들이 하강하였다. 추후 연구에서는 와 거동과 항공기의 날개에 공력 특성 사이의 관계에 대한 연구를 수행하고자 한다.

• Geomechanics and Engineering
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• v.16 no.4
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• pp.435-448
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• 2018

In order to make reliable earthquake-resistant design of civil engineering structures, one of the most important considerations in a region with high seismicity is to pay attention to the local soil condition of regions. It is aimed in the current study at specifying dynamic soil characteristics of Kirikkale city center conducting the 1-D equivalent linear and non-linear site response analyses. Due to high vulnerability and seismicity of the city center of Kirikkale surrounded by active many faults, such as the North Anatolian Fault (NAF), the city of Kirikkale is classified as highly earthquake-prone city. The first effort to determine critical site response parameter is to perform the seismic hazard analyses of the region through the earthquake record catalogues. The moment magnitude of the city center is obtained as $M_w=7.0$ according to the recorded probability of exceedance of 10% in the last 50 years. Using the data from site tests, the 1-D equivalent linear (EL) and nonlinear site response analyses (NL) are performed with respect to the shear modulus reduction and damping ratio models proposed in literature. The important engineering parameters of the amplification ratio, predominant site period, peak ground acceleration (PGA) and spectral acceleration values are predicted. Except for the periods between the period of T=0.2-1.0 s, the results from the NL are obtained to be similar to the EL results. Lower spectral acceleration values are estimated in the locations of the city where the higher amplification ratio is attained or vice-versa. Construction of high-rise buildings with modal periods higher than T=1.0 s are obtained to be suitable for the city of Kirikkale. The buildings at the city center are recommended to be assessed with street survey rapid structural evaluation methods so as to mitigate seismic damages. The obtained contour maps in this study are estimated to be effective for visually characterizing the city in terms of the considered parameters.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.2
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• pp.216-233
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• 2013

Conventional optimization designs of wireless networks mainly focus on spectral efficiency (SE) as a performance metric. However, as diverse media services are emerging, a green wireless network, which not only meets the quality of experience (QoE) requirements for users and also improves energy efficiency (EE), is the most appropriate solution. In this paper, we firstly propose the unit QoE per Watt, which is termed QoE efficiency (QEE), as a user-oriented metric to evaluate EE for wireless networks. We then analyze which is the kind of wireless resource given priority to use under different scenarios to obtain an acceptable QEE. Particularly, power, delay and data-rate related to QoE are separately addressed for several typical services, such as file download, video stream and web browsing services. Next, the fundamental tradeoffs are investigated between QEE and SE for wireless networks. Our analytical results are helpful for network design and optimization to strike a good balance between the users perceived QoE and energy consumption.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.9
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• pp.1939-1946
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• 2011

Expander graphs are useful in the design and analysis of communication networks. Mukhopadhyay et. al introduced a method to generate a family of expander graphs based on nongroup two predecessor single attractor CA(Cellular Automata). In this paper we propose a method to generate a family of expander graphs based on 60/102 Null boundary CA(NBCA) which is a group CA. The spectral gap generated by our method is larger than that of Mukhopadhyay et. al [12]. As an application we give an algorithm which generate one-way functions whose security lies on the combinatorial properties of our expander graphs. the one-way function using d-regular graph generated by the 60/102 NBCA is based on the Goldreich's construction [5].

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.29-34
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• 2001

In this paper, we designed an LSF coefficient quantizer of the wideband speech codec that can produce high quality speech service. For the efficient LSF coefficient quantizer, the interframe correlation was used. Also we separately quantized the LSF coefficients with high and low interframe correlation. Predictive pyramid vector quantizer (PVQ) was used for quantizing the LSF coefficients with high interframe correlation, and PVQ was used for quantizing the LSF coefficients with low interframe correlation. Experiments show that the proposed UF quantizer can quantize LSF information in 40 bits/frame, with an average spectral distortion (SD) of 1 dB and less than 3.87% frames having SD greater than 2 dB.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.1
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• pp.1-4
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• 2001

We have fabricated and evaluated a new Si pin photodetector for APF optical link. The fabricated device has the $p^{+}$-guard ring around the metal-semiconductor contact and the web patterned $p^{+}$-shallow diffused region in the light absorbing area. From the measurements of electo-optical characteristics under the bias of -5 V, the junction capacitance of 4 pF and the dark current of 180 pA were obtained. The optical signal current of 1.22 $\mu$A and the responsivity of 0.55 A/W were obtained when the 2.2 $\mu$W optical power with peak wavelength of 670 nm was incident on the device. The fabricated device showed the maximum spectral response in a spectrum of 650-700 nm. It is expected that the fabricated device can be very useful for detecting the optical signal in the application of red light optics.

• Smart Structures and Systems
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• v.13 no.4
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• pp.587-614
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• 2014

In recent years the interest in online monitoring of lightweight structures with ultrasonic guided waves is steadily growing. Especially the aircraft industry is a driving force in the development of structural health monitoring (SHM) systems. In order to optimally design SHM systems powerful and efficient numerical simulation tools to predict the behaviour of ultrasonic elastic waves in thin-walled structures are required. It has been shown that in real industrial applications, such as airplane wings or fuselages, conventional linear and quadratic pure displacement finite elements commonly used to model ultrasonic elastic waves quickly reach their limits. The required mesh density, to obtain good quality solutions, results in enormous computational costs when solving the wave propagation problem in the time domain. To resolve this problem different possibilities are available. Analytical methods and higher order finite element method approaches (HO-FEM), like p-FEM, spectral elements, spectral analysis and isogeometric analysis, are among them. Although analytical approaches offer fast and accurate results, they are limited to rather simple geometries. On the other hand, the application of higher order finite element schemes is a computationally demanding task. The drawbacks of both methods can be circumvented if regions of complex geometry are modelled using a HO-FEM approach while the response of the remaining structure is computed utilizing an analytical approach. The objective of the paper is to present an efficient method to couple different HO-FEM schemes with an analytical description of an undisturbed region. Using this hybrid formulation the numerical effort can be drastically reduced. The functionality of the proposed scheme is demonstrated by studying the propagation of ultrasonic guided waves in plates, excited by a piezoelectric patch actuator. The actuator is modelled utilizing higher order coupled field finite elements, whereas the homogenous, isotropic plate is described analytically. The results of this "semi-analytical" approach highlight the opportunities to reduce the numerical effort if closed-form solutions are partially available.