• 한국기계가공학회지
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• 제18권12호
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• pp.104-110
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• 2019

A nanosatellite designed by the Korea Microgravity Science Laboratory (KMSL) is currently under development. The KMSL nanosatellite is designed to perform two different scientific missions in space. To successfully complete missions, a variety of tests must be conducted to verify the performance of the designed satellite before launch. As part of the qualification test campaign, the KMSL nanosatellite underwent high level vibrational tests (to comply with Falcon 9 qualification level) to demonstrate the integrity of the system. The purpose of this study is to demonstrate that the primary structure and all electronic and mechanical components can withstand the vibrations and the loads experienced during the launch period. To this end, the KMSL nanosatellite was exposed to static and dynamic loads and various types of vibrations that are inevitably produced during the space vehicle launch period. The vibration test results clearly demonstrated that all avionics and mechanical components can withstand the vibrations and the loads applied to the KMSL nanosatellite's body through a Pico-satellite Orbital Deployer (POD).

• Structural Engineering and Mechanics
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• 제29권6호
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• pp.603-622
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• 2008

This work deals with the design optimization of tuned mass damper (TMD) devices used for mitigating vibrations in high-rise towers subjected to seismic accelerations. A stochastic approach is developed and the excitation is represented by a stationary filtered stochastic process. The effectiveness of the vibration control strategy is evaluated by expressing the objective function as the reduction factor of the structural response in terms of displacement and absolute acceleration. The mechanical characteristics of the tuned mass damper represent the design variables. Analyses of sensitivities are carried out by varying the input and structural parameters in order to assess the efficiency of the TMD strategy. Variations between two different criteria are also evaluated.

• Smart Structures and Systems
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• 제10권1호
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• pp.15-31
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• 2012

This study proposes an active control method to suppress beam-rotating machinery system vibrations. The present control method is a combination of the fuzzy input estimation method (FIEM) and linear quadratic Gaussian problem (LQG) algorithms. The FIEM can estimate the unknown input and optimal states by measuring the dynamic displacement, the optimal estimated states into the feedback control; thereby obtaining the optimal control force for a random linear system. Active vibration control of a beam-rotating machinery system is performed to verify the feasibility and effectiveness of the proposed algorithm. The simulation results demonstrate that the proposed method can suppress vibrations in a beam-machine system more efficiently than the conventional LQG method.

• 항공우주시스템공학회지
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• 제15권4호
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• pp.40-46
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• 2021

At launch, satellites are exposed to various types of structural loads, such as quasi-static loads, sinusoidal vibrations, acoustic/random vibrations, and shocks. The launch environment test is aimed at verifying the structural stability of the test object against the launch environment. Various types of launch environments are simulated by simple vibration, acoustic, and shock tests considering possible test conditions in ground. However, the difference between the launch environment and the test environment is one of the causes of excessive testing. To prevent overtesting, a notching technique that adjusts the frequency range and the input load considering the design load is applied. For notching, specific procedures are established considering the satellite development concept, selected launch vehicle, higher system requirements, and test target level. In this study, the notching method, established procedure, and development of a notching toolkit for efficient testing are described.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.717-720
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• 2005

Acoustic loads generated by a rocket propulsion system cause severe random vibrations on payloads. In developing a new launch vehicle, a random vibration level must be specified before the detailed design of payloads or electronic equipments. This paper deals with prediction procedures of a random vibration level on payload section of KSLV-I. The prediction is based on statistical energy analysis. In order to verify the prediction methodology, test and analysis on a sub-scale payload section are performed. The predicted results subject to very high level of acoustic loads show a good agreement with the test results performed in the high intensity acoustic chamber. The predicted random vibration level on payload section of KSLV-I is also presented in this paper.

• Structural Engineering and Mechanics
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• 제63권5호
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• pp.659-667
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• 2017

Rail support failure is inevitably subjected to track geometric deformations. Due to the randomness and evolvements of track irregularities, it is naturally a hard work to grasp the trajectories of dynamic responses of railway systems. This work studies the influence of rail fastener failure on dynamic behaviours of wheel/rail interactions and the railway tracks by jointly considering the effects of track random irregularities. The failure of rail fastener is simulated by setting the stiffness and damping of rail fasteners to be zeroes in the compiled vehicle-track coupled model. While track random irregularities will be transformed from the PSD functions using a developed probabilistic method. The novelty of this work lays on providing a method to completely reveal the possible responses of railway systems under jointly excitation of track random irregularities and rail support failure. The numerical results show that rail fastener failure has a great influence on both the wheel/rail interactions and the track vibrations if the number of rail fastener failure is over three. Besides, the full views of time-dependent amplitudes and probabilities of dynamic indices can be clearly presented against different failing status.

• 한국전자파학회논문지
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• 제19권12호
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• pp.1394-1401
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• 2008

본 논문은 800 MHz 대역의 CDMA 이동 통신 기지국의 안테나에서 보편적으로 발생되고 있는 수동 상호 변조 왜곡 특성에 대하여 조명해 보고 진동이 수동 상호 변조 왜곡에 미치는 영향을 분석하여 그에 대한 개선 방안을 연구하였다. 이동 통신 기지국은 대부분 건물 옥상이나 철탑 등 고지대에 위치하게 된다. 그렇기 때문에 비, 바람 등 자연 환경적인 요인이나 차량 등 생활 환경적인 요인에 의해 미세한 흔들림 곧, 진동이라는 영향을 수없이 받고 있다. 이에 착안하여 이동 통신 안테나가 진동에 의해 영향을 받고 있다는 것을 실험을 통해 입증해 냄으로써 실제 이동 통신 운용 필드에서 진동이라는 요인에 의해 안테나의 수동 상호 변조 왜곡 특성이 쉽게 열화된다는 것을 증명해 보였다. 또한, 진동에 잘 견딜 수 있는 안테나 구조에 대한 개선 방안을 제시하였고, 구조 개선 전후 안테나의 수동 상호 변조 왜곡 특성을 실험적으로 비교함으로써 그 열화 정도를 35 dB 이상 향상시킬 수 있었다.

• 대한음성언어의학회:학술대회논문집
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• 대한음성언어의학회 1998년도 제10회 학술대회 심포지움
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• pp.208-209
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• 1998

It is generally known that many cases of pathological rough voice are characterized not by simple random perturbations but by quasi-periodic perturbations in the speech wave. However, there are few studies on the characteristics of perturbations in vocal fold vibrations associated with this type of voice. We have been conducting studies of pathological vocal fold vibration using a high-speed digital image recording system developed by our institute, Compared to the ordinary high-speed-motion picture system, the present system is compact and simple to operate and thus, it suited for pathological data collection. (omitted)

• Structural Engineering and Mechanics
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• 제6권5호
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• pp.473-484
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• 1998

The first and second moments of response variables for SDOF systems with hysteretic nonlinearity are obtained by a direct linearization procedure. This adaptation in the implementation of well-known statistical linearization methods, provides concise, model-independent linearization coefficients that are well-suited for numerical solution. The method may be applied to systems which incorporate any hysteresis model governed by a differential constitutive equation, and may be used for zero or non-zero mean random vibration. The implementation eliminates the effort of analytically deriving specific linearization coefficients for new hysteresis models. In doing so, the procedure of stochastic analysis is made independent from the task of physical modeling of hysteretic systems. In this study, systems with three different hysteresis models are analyzed under various zero and non-zero mean Gaussian White noise inputs. Results are shown to be in agreement with previous linearization studies and Monte Carlo Simulation.

• 마이크로전자및패키징학회지
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• 제20권3호
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• pp.59-62
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• 2013

Plastic ball grid array (PBGA)에 대한 강력한 임의 진동에서의 신뢰성을 실험적으로 검증하였다. 실험시편을 만들기 위해 데이지 체인이 형성된 PCB에 칩을 실장시킨 후 그중 절반은 underfill 공정을 거쳤다. 임의 진동 프로파일은 인공위성 전자장비의 신뢰성 검증에서 사용되는 두 종류의 진동 수준, 즉 판정시험 (acceptance level) 및 합격시험(qualification level)을 사용하였으며 각각의 power spectrum density는 22.7 Grms와 32.1 Grms였다. 실험후 underfill과 관계없이 모든 샘플에서 솔더의 균열이 발생되지 않았으며, 차후 항공 및 우주용 전자장비를 대치할 수 있는 패키징 구조의 가능성을 보여 줬다.