• Earthquakes and Structures
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• 제20권4호
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• pp.457-471
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• 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.

• Smart Structures and Systems
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• 제30권2호
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• pp.183-193
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• 2022

Structural health monitoring and structural vibration control are multidisciplinary and frontier research directions of civil engineering. As intelligent materials that integrate sensing and actuation capabilities, shape memory alloys (SMAs) exhibit multiple excellent characteristics, such as shape memory effect, superelasticity, corrosion resistance, fatigue resistance, and high energy density. Moreover, SMAs possess excellent resistance sensing properties and large deformation ability. Superfine NiTi SMA wires have potential applications in structural health monitoring and micro-drive system. In this study, the mechanical properties and electrical resistance sensing characteristics of superfine NiTi SMA wires were experimentally investigated. The mechanical parameters such as residual strain, hysteretic energy, secant stiffness, and equivalent damping ratio were analyzed at different training strain amplitudes and numbers of loading-unloading cycles. The results demonstrate that the detwinning process shortened with increasing training amplitude, while austenitic mechanical properties were not affected. In addition, superfine SMA wires showed good strain-resistance linear correlation, and the loading rate had little effect on their mechanical properties and electrical resistance sensing characteristics. This study aims to provide an experimental basis for the application of superfine SMA wires in engineering.

• Smart Structures and Systems
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• 제31권6호
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• pp.585-599
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• 2023

Field monitoring techniques offer an attractive approach for understanding bridge behavior under in-service loads. However, the investigations on bridge behavior under high-speed train load using field monitoring data are limited. The focus of this study is to explore the structural behavior of an in-service long-span steel truss arch bridge based on field monitoring data. First, the natural frequencies of the structure, as well as the train driving frequencies, are extracted. Then, the train-induced bearing displacement and structural strain are explored to identify the effects of train loads and bearings. Subsequently, a sensitivity analysis is performed for the impact factor of strain responses with respect to the train speed, train weight, and temperature to identify the fundamental issues affecting these responses. Additionally, a similar sensitivity analysis is conducted for the peak acceleration. The results indicate that the friction force in bearings provides residual deformations when two consecutive trains are in opposite directions. In addition, the impact factor and peak acceleration are primarily affected by train speed, particularly near train speeds that result in the resonance of the bridge response. The results can provide additional insight into the behavior of the long-span steel truss bridges under in-service high-speed train loads.

• 항공우주시스템공학회지
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• 제13권3호
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• pp.23-31
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• 2019

현대의 위성들의 설계요구조건은 운용되는 목적에 따라 다양해진다. 기존 중/대형 위성과는 달리 저궤도에서 운용되는 소형위성의 경우 군사적인 목적을 나타내기도 한다. 그렇기 때문에 고해상도의 사진 및 영상 수요가 증가하며 다표적 관측이 중요하게 된다. 이에 다표적 관측을 하기 위해서 위성의 기동성은 중요한 설계변수이다. 기동성이 증가하기 위해서 소형화가 되면 전체 질량관성모멘트가 감소하기 때문에 위성의 강성을 높여야한다. 본체에 비해서 강성이 낮은 태양전지판의 경우 진동이 발생하기 때문에 영상획득에 큰 영향을 미친다. 이러한 진동특성을 확인하기 위하여 본 연구에서는 위성을 축소모델로 제작하여 자세기동을 모사하기 위한 실험 치구를 도입하였고, 위성의 강성을 모사하기 위한 모사장치를 제시하였다. 또한 실험방식은 스텝모터를 이용하여 와이어의 감는 길이에 따라 위성의 기동각을 모사하였으며, 기동실험 시 발생되는 위성의 본체 및 태양전지판에 대하여 진동특성을 실험적으로 검증하고자 한다.

• 대한기계학회논문집A
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• 제29권5호
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• pp.777-785
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• 2005

The swing motion control problem of a container hanging on the trolly is considered in the paper. In the container crane control problem, suppressing the residual swing motion of the container at the end of acceleration, deceleration or the case of that the unexpected disturbance input exists is main issue. For this problem, in general, many trolley motion control strategies are introduced and applied. In this paper, we introduce and synthesize a swing motion control system in which a small auxiliary mass is installed on the spreader made by ourselves. In this control system, the actuator reacting against the auxiliary mass applies inertial control forces to the container to reduce the swing motion in the desired manner. In many studies, the controllers used to suppress the vibration have been synthesized for the given mathematical model of plants. And, the designers have not been able to utilize the degree of freedom to adjust the structural parameters for the control object. To overcome this problem, so called 'Structure/control Simultaneous Method' is used. In this paper, the simultaneous design method is used to determine the optimum weight of moving mass such that the optimal system performance would be achieved. And the experimental result shows that the proposed control strategy is useful to the case of that the controlled system is exposed to the uncertainties and, robust to the unexpected disturbance inputs.

• Structural Engineering and Mechanics
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• 제74권6호
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• pp.789-807
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• 2020

Multiple earthquakes that occur during short seismic intervals affect the inelastic behavior of the structures. Sequential ground motions against the single earthquake event cause the building structure to face loss in stiffness and its strength. Although, numerous research studies had been conducted in this research area but still significant limitations exist such as: 1) use of traditional design procedure which usually considers single seismic excitation; 2) selecting a seismic excitation data based on earthquake events occurred at another place and time. Therefore, it is important to study the effects of successive ground motions on the framed structures. The objective of this study is to overcome the aforementioned limitations through testing a two storey RC building structural model scaled down to 1/10 ratio through a similitude relation. The scaled model is examined using a shaking table. Thereafter, the experimental model results are validated with simulated results using ETABS software. The test framed specimen is subjected to sequential five artificial and four real-time earthquake motions. Dynamic response history analysis has been conducted to investigate the i) observed response and crack pattern; ii) maximum displacement; iii) residual displacement; iv) Interstorey drift ratio and damage limitation. The results of the study conclude that the low-rise building model has ability to resist successive artificial ground motion from its strength. Sequential artificial ground motions cause the framed structure to displace each storey twice in correlation with vary first artificial seismic vibration. The displacement parameters showed that real-time successive ground motions have a limited impact on the low-rise reinforced concrete model. The finding shows that traditional seismic design EC8 requires to reconsider the traditional design procedure.

• 대한토목학회논문집
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• 제6권1호
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• pp.61-68
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• 1986

본(本) 연구(硏究)에서는 포텐셜에너지 이론(理論)을 바탕으로 탄성정력학적(彈性靜力學的) 문제(問題)에 대한 재차 Euler 방정식(方程式)을 완벽히 만족(滿足)하는 새로운 형태(形態)의 형상함수(形狀函數)를 제안(提案)하였다. Shear locking 현상(現像)을 피하기 위한 함차적분(咸差積分)이 필요(必要)없는 이 형상함수(形狀函數)를 사용(使用)한 보 유한요소(有限要素)를 Galerkin 가중잔차법(加重殘差法)으로 유도(誘導)하여 보의 자유진동(自由振動)과 정력학적(靜力學的) 문제(問題)를 해석(解析)하여 이 형상함수(形狀函數)의 효율성(効率性)과 정확도(正確度)를 고찰(考察)하였다. 본(本) 연구(硏究)에서 제안(提案)된 형상함수(形狀函數)를 이용(利用)한 유한요소해(有限要素解)는 보의 靜的解析의 경우 정확해(正確解)와 완벽히 일치(一致)하였으며 자유진동해석(自由振動解析)의 경우에도 월등(越等)한 정확도(正確度)를 보여주었다. 따라서 본(本) 연구(硏究)에서 제안(提案)된 형상함수(形狀函數)의 개념(槪念)은 모든 탄성정력학적(彈性靜力學的) 문제(問題) 유한요소해(有限要素解)를 구하는데 적용(適用)될 수 있다고 사료된다.

• 대한기계학회논문집A
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• 제34권7호
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• pp.867-872
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• 2010

자연계에 존재하지만 사용되지 못 하고 버려지는 에너지를 효과적으로 채집하여 배터리를 충전하거나 전기 장치에 전기 에너지를 공급하는 에너지 하베스팅에 대한 연구를 수행하였다. 압전재료는 물체의 움직임이나 진동으로부터 에너지를 채집하는 주요한 재료로 널리 연구되고 있다. 본 논문에서는 기존의 PZT 압전 특성을 개량하고자 압전-복합재료 발전소자(Piezo-Composite Generating Element, 이하 PCGE)를 도입하여 성능 예측모델을 제안하고 이를 실험적으로 검증하였다. PCGE는 탄소/에폭시, PZT, 유리/에폭시 층으로 구성된다. 제작 과정에서 적층된 PCGE는 오토클레이브 안에서 $177^{\circ}C$의 온도에서 성형되는데, 이때 PCGE 내부에 초기잔류응력이 발생하게 되어 압전재료의 성능이 변화하게 된다. 세 종류의 PCGE를 제작한 후 에너지 채집 실험을 수행하여 제안된 성능 예측모델의 타당성과 기계적 진동을 전기적 에너지로 변환되는 성능을 검증하였다. 실험 결과 이론적인 성능 예측모델이 실험 결과와 잘 일치함을 확인하였다.

• 한국해양공학회지
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• 제19권3호
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• pp.66-73
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• 2005

The sway motion control problem of a container hanging on the trolley is considered in this paper. In the container crane control problem, the main issue involves suppressing the residual swing motion of the container at the end of acceleration, during deceleration, or for an unexpected disturbance input. For this problem, in general, many trolley motion control strategies are introduced and applied. In this paper, we introduce and synthesize a swing motion control system, in which a small auxiliary mass is installed on the spreader. In this control system, the actuator reacting against the auxiliary mass applies inertial control forces to the container to reduce the swing motion in the desired manner. In many studies, the controllers used to suppress the vibration have been synthesized for the given mathematical model of plants. In many cases, the designers have not been able to utilize the degree of freedom to adjust the structural parameters for the control object. To overcome this problem, so called "Structure/Control Simultaneous Method" is used. From this, in this paper the simultaneous design method is used to achieve optimal system performance. And the experimental result shows that the proposed control strategy is useful, to the case of that the controlled system is exposed to the uncertainties and, robust to disturbances like wind.

• 한국지반공학회지:지반
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• 제9권2호
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• pp.5-14
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• 1993

화강풍화토는 한국에서 대부분을 차지하고 있는 대표적인 토질이다. 본 연구는 화강풍화토의 동역학적 특성치와 침하특성을 실험적으로 연구함으로써 화강풍화토에 기초를 둔 구조물의 동역학적 해석에 기여하고자 한다. 입도가 서로 다른 두종류의 화강풍화토를 상대밀도 80~90% 범위의 공시체를 성형하여 진동 삼축압축시험을 실시하였다. 시험을 통하여 전단탄성계수와 감쇠계수를 시료의 상대밀도와 구속응력을 달리하여 구하고 이를 전단 변형률의 크기에 따라 표시하였다. 대표적인 결과로서, 전단탄성계수는 화강풍화토를 구성하는 입도분포에 따라 구속응력, 시료의 상대밀도 및 전단변형률과 관련하여 큰 변화를 나타내었다. 모래성분이 많은 화강풍화토의 동적특성치는 Seed와 Idriss에 의하여 정리된 모래의 값 보다 다소 큰 값이 측정되었다. 또한 잘다져진 화강풍화토에 대하여 진동하중에 의한 잔류침하는 거의 일어나지 않았다.