• Earthquakes and Structures
• /
• 제3권2호
• /
• pp.169-180
• /
• 2012

The performance of pure friction isolation system with respect to the frequency bandwidth of excitation and the predominant frequency is investigated. A set of earthquake ground motions (artificial as well as recorded [with different combinations of magnitude-distance and local site geology]) is considered for investigating effectiveness of pure friction isolators. The results indicate the performance of pure friction base isolated system does not only depend upon coefficient of friction and mass ratio but the stick-slip behaviour depends upon the frequency content of the excitation as well. Slippage prevails if the excitation frequency lies in a suitable frequency range. This range widens with increasing mass ratio. For larger mass ratios, the sliding effect is more pronounced and the maximum acceleration response is further reduced in the neighbourhood of frequency ratio (${\omega}/{\omega}_n$) of unity. The pure friction isolation system is effective in the case of broadband excitations only and that too, in the acceleration sensitive range of periods. The pure friction system is not effective for protection against narrow band motions for which the system response is quasi-periodic.

• 전자공학회논문지
• /
• 제51권5호
• /
• pp.106-113
• /
• 2014

최근 반도체 업계에서 주요 관심사로 떠오르고 있는 SOC(System-on-a-chip) 테스트는 비용 및 시간 절감을 위해 여러 종류의 FDR(Frequency-directed run-length) 기술이 제안되었다. 기존의 FDR보다 압축률을 향상시키는 EFDR(Extended-FDR)과 SAFDR(Shifted-Alternate-FDR), VPDFDR(Variable Prefix Dual-FDR)이 있다. 본 논문에서는 제안한 Frequency-ordered 방식은 FDR, EFDR, SAFDR, VPDFDR에 적용시켜 상당한 압축률 개선을 보인다. 본 기술을 사용하면 압축률을 극대화할 수 있고, 결과적으로 전체적인 양산 테스트 비용 및 시간을 크게 절감할 수 있게 한다.

• Geomechanics and Engineering
• /
• 제1권3호
• /
• pp.219-239
• /
• 2009

Vertical vibration tests were conducted using model footings of different size and mass resting on the surface of finite sand layer with different height to width ratios and underlain by either rigid concrete base or natural red-earth base. A comparative study of the ratio of predicted and observed natural frequency ratio of the finite sand stratum was made using the calculated values of equivalent stiffness suggested by Gazetas (1983) and Baidya and Muralikrishna (2001). Comparison of results between model footings resting on finite sand stratum underlain by the rigid concrete base and the natural red-earth base showed that, the presence of a finite base of higher rigidity increases the resonant frequency significantly. With increase in H/B ratio beyond 2.0, the influence of both the rigid concrete and natural red-earth base decreases. Increase in the contact area of the footing increases the resonant frequency of the model footings resting on finite sand stratum underlain by both the types of finite bases. Both the predicted and the observed resonant frequency ratio decreases with increase in force rating and height to width ratio for a given series of model footing.

• 전기전자학회논문지
• /
• 제22권4호
• /
• pp.1158-1162
• /
• 2018

안티-하모닉락 기능을 가지는 고속-락킹 MDLL 기반의 디지털 클락 주파수 증배기를 소개한다. 제안하는 디지털 주파수 증배기는 하모닉락 문제 없이 빠른 락킹 시간을 구현하기 위하여 새로운 MSB-구간 검색 알고리즘을 사용한다. 제안하는 디지털 MDLL 주파수 증배기는 65nm CMOS 공정으로 설계되었으며, 1 GHz ~ 3 GHz의 출력 동작주파수 영역을 가진다. 제안하는 디지털 MDLL은 프로그래머블한 N/M (N=1, 4, 5, 8, 10, M=1, 2, 3)의 분수배 주파수 증배 기능을 제공한다. 제안하는 MDLL은 1GHz에서 3.52 mW의 전력을 소모하고, 14.07 ps의 피크-투-피크 (p-p) 지터를 갖는다.

• 한국소음진동공학회논문집
• /
• 제12권4호
• /
• pp.261-271
• /
• 2002

The fluid-elastic instability analysis of the U-tube bundle inside the steam generator is very important not only for detailed design stage of the SG but also for the change of operating condition of the nuclear powerplant. However the calculation procedure for the fluid-elastic instability was so complicated that the consolidated computer program has not been developed until now. In this study, the numerical calculation procedure and the computer program to obtain the stability ratio were developed. The thermal-hydraulic data in the region of secondary side of steam generator was obtained from executing the ATHOS3 code. The distribution of the fluid density can be calculated by using the void fraction, enthalpy, and operating pressure. The effective mass distribution along the U-tube was required to calculate natural frequency and dynamic mode shape using the ANSYS ver. 5.6 code. Finally, stability ratios for selected tubes of the CE type steam generator were computed. We considered the YGN 3.4 nuclear powerplant as the model plant, and stability ratios were investigated at the flow exit region of the U-tube. From our results, stability ratios at the central and the outside region of the tube bundle are much higher than those of other region.

• Smart Structures and Systems
• /
• 제19권6호
• /
• pp.653-663
• /
• 2017

The modal parameters of the deck of Runyang Suspension Bridge (RSB) as well as their relationships with wind and temperature are studied based on the data recorded by its Structural Health Monitoring System (SHMS). Firstly, frequency analysis on the vertical responses at the two sides of the deck is carried out to distinguish the vertical and torsional vibration modes. Then, the vertical, torsional and lateral modal parameters of the deck of RSB are identified using Hilbert-Huang Transform (HHT) and validated by the identified results before RSB was opened to traffic. On the basis of this, the modal frequencies and damping ratios of RSB during the whole process of Typhoon Masta are obtained. And the correlation analysis on the modal parameters and wind environmental factors is then conducted. Results show that the HHT can achieve an accurate modal identification of RSB and the damping ratios show an obvious decay trend as the frequencies increase. Besides, compared to frequencies, the damping ratios are more sensitive to the environmental factors, in particular, the wind speed. Further study on configuring the variation law of modal parameters related with environmental factors should be continued.

• Bulletin of the Korean Chemical Society
• /
• 제32권9호
• /
• pp.3395-3399
• /
• 2011

Copper oxide thin films were synthesized by reactive radio frequency magnetron sputtering at different oxygen gas ratios. The chemical and physical properties of the thin films were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). XPS results revealed that the dominant oxidation states of Cu were $Cu^0$ and $Cu^+$ at 0% oxygen ratio. When the oxygen ratios increased above 5%, Cu was oxidized as CuO as detected by X-ray induced Auger electron spectroscopy and the $Cu(OH)_2$ phase was confirmed independent of the oxygen ratio. The valence band maxima were $1.19{\pm}0.09$ eV and an increase in the density of states was confirmed after formation of CuO. The thickness and roughness of copper oxide thin films decreased with increasing oxygen ratio. The crystallinity of the copper oxide films changed from cubic Cu through cubic $Cu_2O$ to monoclinic CuO with mean crystallite sizes of 8.8 nm (Cu) and 16.9 nm (CuO) at the 10% oxygen ratio level.

• Composites Research
• /
• 제12권5호
• /
• pp.65-79
• /
• 1999

본 논문은 단순지지된 복합재료 사각판과 원통쉘이 결합된 구조물의 자유진동해석을 위한 해석적 방법에 대하여 기술하였다. 결합전 단순지시된 사각판과 원통쉘의 응답을 얻기 위하여 고전적 판이론과 Love의 얇은 쉘이론에 기초한 에너지법을 적용하였다. 결합구조물의 해석에는 동적응답법을 적용하였고, 길이방향 판과 쉘의 결합부에서의 동적 주기 하중과 모멘트는 Dirac 델타 함수와 정현 함수를 사용하였을 때 연속조건을 만족함을 보였다. 또한 원통쉘의 기하하적 매개변수인 쉘의 길이 대 반경비와 반경 대 두께비에 따른 진동특성의 변화를 고찰하였고, 복합재료의 섬유 방향각과 직교이방성 매개변수가 결합 원통쉘의 기본 진동수에 미치는 영향에 미치는 영향에 대하여 연구하였다.

• 한국물환경학회지
• /
• 제23권4호
• /
• pp.551-560
• /
• 2007

The present study analyzed noise reduction and long/short-term components for discharge, TOC concentration, and TOC load data in order to understand the data characteristics better. For the purpose, wavelet transform which can reduce noise from raw data and has flexible resolution in time and frequency domain was applied and the theory of nonlinear dynamics was also used to determine the last decomposition level for wavelet transform. Wavelet function of 'db10' and the 7th level for the last decomposition of wavelet transform were applied for the all data in the present study. Also the results revealed that the energy ratios of approximation components with 187-hour periodicity decomposed from 7th level of wavelet transform were 94.71% (discharge), 99.00% (TOC concentration), and 93.84% (TOC load), respectively. In addition, the energy ratios of detail components showed the range between 1.00% and 6.17%, which were extremely small comparing to the energy ratios of approximation components, therefore, the first and second detail components might be considered as noise components included in the raw data.

• 비파괴검사학회지
• /
• 제34권6호
• /
• pp.419-427
• /
• 2014

Nonlinear features of ultrasonic waves are more sensitive to the presence of a fatigue crack than their linear counterparts are. For this reason, the use of nonlinear ultrasonic techniques to detect a fatigue crack at its early stage has been widely investigated. Of the different proposed techniques, laser nonlinear wave modulation spectroscopy (LNWMS) is unique because a pulse laser is used to exert a single broadband input and a noncontact measurement can be performed. Broadband excitation causes a nonlinear source to exhibit modulation at multiple spectral peaks owing to interactions among various input frequency components. A feature called maximum sideband peak count difference (MSPCD), which is extracted from the spectral plot, measures the degree of crack-induced material nonlinearity. First, the ratios of spectral peaks whose amplitudes are above a moving threshold to the total number of peaks are computed for spectral signals obtained from the pristine and the current state of a target structure. Then, the difference of these ratios are computed as a function of the moving threshold. Finally, the MSPCD is defined as the maximum difference between these ratios. The basic premise is that the MSPCD will increase as the nonlinearity of the material increases. This technique has been used successfully for localizing fatigue cracks in metallic plates.