• Steel and Composite Structures
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• 제9권2호
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• pp.119-130
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• 2009

This paper reports results of the structural response of empty steel tanks under vertical ground motions. The tanks are modeled using a finite element discretization using shell elements, and the vertical motion is applied and analyzed using nonlinear dynamics. Several excitation frequencies are considered, with emphasis on those that may lead to resonance of the roof. The computational results illustrate that as the base motion frequency is tuned with the frequency of the first roof-mode of the tank, the system displays large-amplitude displacements. For frequencies away from such mode, small amplitude displacements are obtained. The effect of the height of the cylinder on the dynamic response of the tank to vertical ground motion has also been investigated. The vertical acceleration of the ground motion that induces significant changes in the stiffness of the tank was found to be almost constant regardless of the height of the cylinder.

• Wind and Structures
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• 제17권1호
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• pp.21-41
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• 2013

Wind-induced vibrations of mast arms of cantilever traffic signal structures can lead to fatigue failure. Two such structures were instrumented each with a sonic anemometer and a camera that records the motions of the tip of the arm. It was observed throughout this experiment that large amplitude vertical vibrations of mast arms with signals with backplates occur for the most part at low wind speed ranges, between 2 to 7 m/s, and as the wind speed increases the amplitude of the vertical vibrations decreases. The results of these experiments contradict the generally accepted belief that vortex shedding does not cause significant vibrations of mast arms that could lead to fatigue failure, which have been attributed to galloping in the past. Two damping devices were tested with mixed results.

• Journal of Magnetics
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• 제3권1호
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• pp.21-30
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• 1998

An artificially modulated magnetic Co/Pd multilayer is one of the promising candidates for high density magneto-optic (MO) recording media, due to large Kerr rotation angle in the wavelength of a blue laser beam. however, since multilayer structure, as well as amorphous structure, is a non-equilibrium state in terms of free energy and MO recording is a kind of thermal recording which is conducted aound Curie temperature (Tc) of the recording media, when the multilayer is used for the MO recording media, changes in the multilayer structure are occurred as the amorphous structure do. Therefore, the assessment of the structural stability in the Co/Pd multilayer is crucially important both for basic research and applications. As the parameter of the structural stability in this research, modulation amplitude and particle size of the Co/Pd multilayer are measured in terms of Ar sputtering pressure and heat treatment temperature. From the results of the research, we find out that the magnetic exchange energy in the structural changes of a magnetic multilayer structure and suggest the operating temperature range for MO recording in the Co/Pd multilayer for the basic research and applications, respectively.

• 한국정보통신학회논문지
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• 제4권1호
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• pp.283-288
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• 2000

본 논문은 마이크로프로세서를 이용하여 구현하는 전파브리지 인버터의 새로운 PWM 제어 방법을 제안한다. 이 방법은 단방향 전파 브리지 인버터의 한 주기를 주파수 변조비로 등간격 분할하고 기준 기본파와 인버터의 출력 기본파의 진폭을 비교하는 PWM 제어 방법이다. 이 방법을 이용하면 각 간격의 turn-on time 계산이 매우 용이하여 마이크로프로세서 구현에 매우 적합하다. 그리고, 고조파 해석에 있어서 주파수 변조비가 크면 모든 고조파를 무시할 수 있음을 보여준다 시뮬레이션과 실험을 통하여 타당성을 입증하였다.

• Advances in nano research
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• 제13권1호
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• pp.63-75
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• 2022

The nonlinear dynamic behavior of a nonuniform small-scale nonlocal beam is investigated in this work. The nanobeam is theoretically modeled using the nonlocal Eringen theory, as well as a few of Von-nonlinear Kármán's theories and the classical beam theory. The Hamilton principle extracts partial differential equations (PDE) of an axially functionally graded (AFG) nano-scale beam consisting of SUS304 and Si₃N₄ throughout its length, and an elastic Winkler-Pasternak substrate supports the tapered AFG nanobeam. The beam thickness is a function of beam length, and it constantly varies throughout the length of the beam. The numerical solution strategy employs an iteration methodology connected with the generalized differential quadratic method (GDQM) to calculate the nonlinear outcomes. The nonlinear numerical results are presented in detail to examine the impact of various parameters such as nonlinear amplitude, nonlocal parameter, the component of the elastic foundation, rate of cross-section change, and volume fraction parameter on the linear and nonlinear free vibration characteristics of AFG nanobeam.

• Journal of Information Processing Systems
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• 제18권1호
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• pp.48-58
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• 2022

Blind restoration for motion-blurred images is always the research hotspot, and the key for the blind restoration is the accurate blur kernel (BK) estimation. Therefore, to achieve high-quality blind image restoration, this thesis presents a novel windowed-total-variation method. The proposed method is based on the spatial scale of edges but not amplitude, and the proposed method thus can extract useful image edges for accurate BK estimation, and then recover high-quality clear images. A large number of experiments prove the superiority.

• 한국정밀공학회지
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• 제3권2호
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• pp.91-101
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• 1986

This paper deals with the effect of static and dynamic cuttig force and the behaviour of drill life in drilling process. The experiments are performed with cemented carbide drills and high speed steel drills of 10mm in diameter and in an annealed SM45C. The conclusions are as follows (1) Dynamic cutting force is varied with the dept of hole. (2) Dynamic cutting forces of torque and thrust are increase with the increase in feed and cutting speed. (3) Chipping influence the dynamic cutting force of thrust than torque, and in the case of thrust, the amplitude is 3-7 times large than ordinary cutting state. (4) Prediction of drill life can be obtained from more easily the amplitude of static cutting force than that of dynamic cutting force.

• 대한조선학회논문집
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• 제47권3호
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• pp.410-420
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• 2010

When ships are sailing with large motions in rough waves, the slamming phenomenon occurs and the ships suffer from impulsive pressure loadings. Recently, ships are becoming lager and faster than before and it becomes more possible that the ships experience larger impacts on their bows and sterns. Many researchers have been performing the investigations on slamming experimentally and theoretically for a long time. Most of the research reported in the open literature focused on how to accurately estimate the amplitude of the peak pressure of slamming. According to the results of a recently published work, not only the amplitude of peak pressure but also the width of the peak may play an important role in predicting the extents of damage of impacted structures. The uncertainty of impulsive pressure loadings due to slamming has been indicated by many researchers. However, probabilistic treatments of the impulsive pressure loadings are few. In this study, drop tests were conducted on wedges having dead-rise angles of $0^{\circ}$ and $10^{\circ}$. Not only the amplitude of peak pressure but also the width of peak pressure were measured. Furthermore, the variations of those values are also provided for the probabilistic approach of the slamming problem.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2005년도 공동학술대회 논문집
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• pp.261-266
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• 2005

인공위성 측지학의 발달로 최근 들어 정밀도와 해상도가 높아진 중력포텐셜 모델들이 공개되었다. 근래에 가장 많이 사용되는 EGM96과 CHAMP, GRACE 등의 저고도 위성자료를 기반으로 하는 가장 최근의 EIGEN-CG01C 모델을 이용하여 한반도와 인근지역을 포함하는 $123^{\circ}{\sim}132^{\circ}$ E, $33^{\circ}{\sim}43^{\circ}$ N의 연구지역에서 지오이드와 중력이상을 계산하고, 비교 검토하였다. 두 모델은 지오이드와 중력이상에서 0.90이상의 매우 높은 상관관계를 가지고 있으나, Amplitude 분석에서 EIGEN-CG01C 모델이 고주파영역이 우세한 것으로 나타났다. 두 모델을 통해 계산된 중력이상에서 북한지역 및 황해 연안 일부에서 다소 차이를 보인다. Power spectrum 분석을 통하여 대규모 지구조나 지하자원 탐사에 유용하게 활용될 수 있는 잔여이상을 계산하였다.

• 대한기계학회논문집B
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• 제25권1호
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• pp.18-28
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• 2001

The present study investigates flow dynamics between two dimensional compliant plates under sinusoidal flow conditions in order to understand influence of wall motion, impedance phase angle (time delay between pressure and flow waveforms), and non-Newtonian fluid on wall shear stress using computational fluid dynamics. The results showed that wall motion induced additional terms in the streamwise velocity profile and the pressure gradient. These additional terms due to wall motion reduced the amplitude of wall shear stress and also changed the mean wall shear stress. The trend of the changes was very different depending on the impedance phase angle. As the impedance phase angle was changed to more negative values, the mean wall shear stress decreased while the amplitude of wall shear stress increased. As the phase angle was reduced from 0°to -90°under $\pm$4% wall motion, the mean wall shear stress decreased by 12% and the amplitude of wall shear stress increased by 9%. Therefore, for hypertensive patients who have large negative phase angles, the ratio of amplitude and mean of the wall shear stress is raised resulting in a more vulnerable state to atherosclerosis according to the low and oscillatory shear stress theory. We also found that non-Newtonian characteristics of the blood protect atherosclerosis by decreasing the oscillatory shear index.