• Wind and Structures
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• 제12권5호
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• pp.413-424
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• 2009

A series of wind tunnel free-decay sectional model dynamic tests were conducted to examine the effects of torsional-to-vertical natural frequency ratio of 2DOF bridge dynamic systems on the aerodynamic and dynamic properties of bridge decks. The natural frequency ratios tested were around 2.2:1 and 1.2:1 respectively, with the fundamental vertical natural frequency of the system held constant for all the tests. Three 2.9 m long twin-deck bridge sectional models, with a zero, 16% (intermediate gap) and 35% (large gap) gap-to-width ratio, respectively, were tested to determine whether the effects of frequency ratio are dependent on bridge deck cross-section shapes. The results of wind tunnel tests suggest that for the model with a zero gap-width, a model to approximate a thin flat plate, the flutter derivatives, and consequently the aerodynamic forces, are relatively independent of the torsional-to-vertical frequency ratio for a relatively large range of reduced wind velocities, while for the models with an intermediate gap-width (around 16%) and a large gap-width (around 35%), some of the flutter derivatives, and therefore the aerodynamic forces, are evidently dependent on the frequency ratio for most of the tested reduced velocities. A comparison of the modal damping ratios also suggests that the torsional damping ratio is much more sensitive to the frequency ratio, especially for the two models with nonzero gap (16% and 35% gap-width). The test results clearly show that the effects of the frequency ratio on the flutter derivatives and the aerodynamic forces were dependent on the aerodynamic cross-section shape of the bridge deck.

• Smart Structures and Systems
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• 제22권1호
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• pp.41-55
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• 2018

Damping ratio and frequency have influence on dynamic serviceability or instability such as vortex-induced vibration and displacement amplification due to earthquake and critical flutter velocity, and it is thus important to make determination of damping ratio and frequency accurate. As bridges are getting longer, small scale model test considering similitude law must be conducted to evaluate damping ratio and frequency. Analysis conditions modified by similitude law are applied to experimental test considering different scale ratios. Generally, Nyquist frequency condition based on natural frequency modified by similitude law has been used to determine sampling rate for different scale ratios, and total time length has been determined by users arbitrarily or by considering similitude law with respect to time for different scale ratios. However, Nyquist frequency condition is not suitable for multimode system with noisy signals. In addition, there is no specified criteria for determination of total time length. Those analysis conditions severely affect accuracy of damping ratio. The focus of this study is made on the determination of minimum analysis conditions for different scale ratios. Influence of signal to noise ratio is studied according to the level of noise level. Free initial value problem is proposed to resolve the condition that is difficult to know original initial value for free vibration. Ambient and free vibration tests were used to analyze the dynamic properties of a system using data collected from tests with a two degree-of-freedom section model and performed on full bridge 3D models of cable stayed bridges. The free decay is estimated with the stochastic subspace identification method that uses displacement data to measure damping ratios under noisy conditions, and the iterative least squares method that adopts low pass filtering and fourth order central differencing. Reasonable results were yielded in numerical and experimental tests.

• 한국전산구조공학회논문집
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• 제30권1호
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• pp.7-15
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• 2017

본 논문에서는 온실 구조물의 구조 성능 검토 시 적합한 모델링 방법을 제시하기 위해 대상 온실 구조물을 선정하고 지점 및 접합부 조건 그리고 케이블 요소의 단면적을 변화시켜 가며 파라메트릭 스터디를 수행하였으며, 이들 파라메터의 변화에 따른 대상 구조물의 주요 모드 형상 및 고유진동수 변화를 조사하였다. 또한 대상 구조물에 대해 현장 가속도계 측정법을 이용하여 상시진동을 계측하여 주요 모드 형상 및 고유진동수를 측정하여 해석 결과와 비교하였다. 이들 비교 결과로부터 대상 온실 구조물의 해석에 적합한 모델링 기법을 제시하였다.

• 한국ITS학회 논문지
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• 제10권5호
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• pp.14-22
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• 2011

본 연구는 버스정보시스템(BIS)의 운행데이터를 이용하여 신호교차로에서의 지체시간을 추정하기 위한 연구이다. 기존의 버스시스템에 첨단정보통신 기술을 접목한 BIS는 많은 지방자치단체에서 구축하여 운영 중에 있다. 그러나 기존에 구축된 BIS의 운영을 통해 실시간으로 수집되고 있는 운행데이터의 활용은 활발히 이루어지지 못하고 있다. 본 연구에서는 BIS 운행데이터를 이용하여 실시간으로 지체시간을 산정하여 도시교통관리, 교통정보를 제공에 활용하기 위한 기초적인 연구를 수행하고자 하였다. VISSIM 5.20을 활용하여 시뮬레이션 모형을 구축하였으며 버스정류장에서의 서비스 시간을 제외한 버스 통행시간과 일반차량 지체시간 간의 상관관계가 유의한 것으로 분석되어 거시적 통계모형인 회귀모형으로 구축하여 분석한 결과 직선회귀모형의 결정계수가 0.826으로 가장 높게 나타났다. 구축된 모형을 통계적으로 검증하기 위하여 현장조사 값과 모형추정 값으로 T-test를 실시한 결과 95% 신뢰수준에서 통계적으로 유의한 것으로 분석되었다.

• Smart Structures and Systems
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• 제19권4호
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• pp.341-350
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• 2017

Based on the super elastic properties of the shape memory alloy (SMA) and the inverse piezoelectric effect of piezoelectric (PZT) ceramics, a kind of hybrid semi-active control device was designed and made, its mechanical properties test was done under different frequency and different voltage. The local search ability of genetic algorithm is poor, which would fall into the defect of prematurity easily. A kind of adaptive immune memory cloning algorithm(AIMCA) was proposed based on the simulation of clone selection and immune memory process. It can adjust the mutation probability and clone scale adaptively through the way of introducing memory cell and antibody incentive degrees. And performance indicator based on the modal controllable degree was taken as antigen-antibody affinity function, the optimization analysis of damper layout in a space truss structure was done. The structural seismic response was analyzed by applying the neural network prediction model and T-S fuzzy logic. Results show that SMA and PZT friction composite damper has a good energy dissipation capacity and stable performance, the bigger voltage, the better energy dissipation ability. Compared with genetic algorithm, the adaptive immune memory clone algorithm overcomes the problem of prematurity effectively. Besides, it has stronger global searching ability, better population diversity and faster convergence speed, makes the damper has a better arrangement position in structural dampers optimization leading to the better damping effect.

• 한국정밀공학회지
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• 제27권5호
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• pp.56-62
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• 2010

This paper presents the development process of roof carrier assembly using a one side release system for a vehicle. An RV(Recreational Vehicle) or SUV(Sports Utility Vehicle) has a roof carrier system on an upper surface of a roof panel for loading large or long size baggage. Such a roof carrier system is comprised of a roof rack longitudinally mounted on a roof panel and cross bar perpendicularly installed in the horizontal direction. Several locking mechanisms used in most vehicle roof carrier systems are composed with both side releasable locking ones. The obvious drawback to this arrangement is that when the user desires to reposition the cross bar, first one of the locking members must be unlocked and then the user must walk around to the opposite side of the vehicle to unlock the other member. In this paper, we proposed a newly locking mechanism, which allows a user simultaneously place both locking members of the roof carrier in locked and unlocked positions. In order to estimate design compatibility, structural and modal analysis is performed. Furthermore, a prototype based on the proposed design has been made, and then durability test carried out. From the simulation and experimental results, the proposed roof carrier system is proved effective and safe.

• 한국정밀공학회지
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• 제22권10호
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• pp.114-120
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• 2005

Urethane is a high polymeric and elastic material useful in designing mechanic parts that cannot be molded with rubber or plastic material. In particular, urethane is high in mechanical strength and anti-abrasive. Hereby, a urethane coated aluminum wheel is used to support of the OHT vehicle moving back and forth to transport products. For the sake of verifying the safety of the vehicle, structural safety fur applied maximum dynamic load on a urethane wheel must be examined carefully while driving. Therefore, we performed a dynamic simulation on the OHT vehicle model and we determined the driving load. The area definition of applied load may be obtained from the previous study of Hertzian and Non-Hertzian contact force model having exact properties of contact material. But the static analysis is simulated after we have performed the actual contact area test for each load since the proper material properties of urethane have not been guaranteed. In this study, the method of distributing loads for each node is included. Finally, in coMParison with the results of analysis and load-displacement curve obtained from the compression test, we have defined the material properties of urethane. In the analysis, we verified the safety of the wheel. Finally, we performed a mode analysis using the obtained material properties. With these results, we presented a reliable finite element model.

• 한국항공우주학회지
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• 제33권8호
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• pp.99-104
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• 2005

인공위성에서 구조체의 역할은 발사환경 및 궤도상의 모든 발생 가능한 환경에서 위성체를 안전하게 지지하는 것이다. 인공위성의 개발단계에서 구조 및 열 개발모델은 유한요소모델 보정 및 구조강도/특성 확인 등의 구조적인 특징과 열평형시험을 통한 열적 안정성의 확인을 그 목적으로 한다. 이때 얻어진 결과는 실제 비행모델의 개발 시 구조 및 열적 안정성 검증 등의 중요한 자료로써 활용된다. 본 논문에서는 고정밀 지구관측위성의 구조 및 열 개발모델에 대해 구조 관점에서의 설계/해석에 대해 기술하고 또한 모달 시험을 통한 시험결과와 유한요소해석과의 비교에 대해 기술한다.

• 한국음향학회지
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• 제39권4호
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• pp.371-377
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• 2020

종횡비(Length/Diameter, L/D)가 크고, 실린더-슬롯형 그레인을 적용한 고체로켓모터의 연소시험에서 연소불안정 현상이 발생하였다. 압력섭동을 스펙트럼 분석한 결과 중심축 길이방향 주파수가 지배적임이 확인되어, 음향노드와의 일치를 해소하기 위해 실린더 파트의 길이를 증가시켰다. 또한 고체로켓모터에서 발생하는 유동 구조에 의한 불안정성 발생 원인을 분석하기 위하여 음향모드해석과 유동해석을 수행하였다. 설계 변경 전후 그레인 형상을 이용하여 연소실 내 압력 진동 크기 및 주파수에 대해 정량적 비교를 통해 연소불안정이 저감됨을 확인하였다. 최종적으로 연소시험을 수행하여 해석결과와 같이 연소불안정 현상이 사라짐을 확인하였다.

• Wind and Structures
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• 제10권5호
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• pp.463-479
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• 2007

A series of wind tunnel sectional model dynamic tests of a twin-deck bridge were conducted at the CLP Power Wind/Wave Tunnel Facility (WWTF) of The Hong Kong University of Science and Technology (HKUST) to investigate the effects of gap-width on the self-excited vibrations and the dynamic and aerodynamic characteristics of the bridge. Five 2.9 m long models with different gap-widths were fabricated and suspended in the wind tunnel to simulate a two-degrees-of-freedom (2DOF) bridge dynamic system, free to vibrate in both vertical and torsional directions. The mass, vertical frequency, and the torsional-to-vertical frequency ratio of the 2DOF systems were fixed to emphasize the effects of gap-width. A free-vibration test methodology was employed and the Eigensystem Realization Algorithm (ERA) was utilized to extract the eight flutter derivatives and the modal parameters from the coupled free-decay responses. The results of the zero gap-width configuration were in reasonable agreement with the theoretical values for an ideal thin flat plate in smooth flow and the published results of models with similar cross-sections, thus validating the experimental and analytical techniques utilized in this study. The methodology was further verified by the comparison between the measured and predicted free-decay responses. A comparison of results for different gap-widths revealed that variations of the gap-width mainly affect the torsional damping property, and that the configurations with greater gap-widths show a higher torsional damping ratio and hence stronger aerodynamic stability of the bridge.