• 항공우주기술
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• 제6권1호
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• pp.114-119
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• 2007

본 연구는 KSLV-I 페이로드 페어링을 제외한 2단 구조부에 대한 모드시험 결과를 기술하고 있다. 2단부는 크게 위성 분리부, 탑재부, 킥모터 지지부, 킥모터로 구성되어 있다. 번지코드를 이용하여 자유경계단 조건을 모사하였고 가진은 대형 가진 망치를 사용하였다. 이러한 모드시험 결과를 통하여 모드변수를 추출할 수 있고, 2단부 구조체의 동특성을 파악할 수 있다. 시험 결과는 TDAS를 사용하여 분석하였고, 100Hz 이하의 모드변수 및 모드형상을 추출하였다.

• 한국생산제조학회지
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• 제23권3호
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• pp.223-229
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• 2014

In this paper, the natural frequency and damping ratio are analyzed with the acceleration signal of an Euler-Bernoulli beam using the impact hammer test. The results are presented according to crack depth and position using the recursive least squares method. The results are compared and investigated with FEM analysis of CATIA. Both methods agree well with each other regarding the natural mode characteristics. The captured acceleration can be used for the calculation of the natural frequency and damping ratio using time series methods that are based on the measured acceleration. Using these data, a recursive time series model with the acceleration signal was configured and the behaviors of the natural frequency and damping ratio were investigated and analyzed. Finally, the results can be used for the prediction of crack position and depth under different crack conditions for an Euler-Bernoulli beam.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.2011-2014
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• 2005

The purpose of this study is to compare the modal parameters of a newly developed soft golf club prototype, which is designed to be lighter than regular golf clubs, with those of a regular commercial golf club. The modal tests were performed with two kinds of boundary conditions. The first condition was free-free condition and the second was fixed-free condition. An impact hammer and a Fast Fourier Transform analyzer were used to obtain modal data. From the results, it was found out that the modal characteristics of the soft golf club prototype were close to those of the regular golf club although the weight of the soft club was lighter. Therefore, the soft golf club is expected to be able to convey similar feel to the golfers even with lighter weight. This would enable elderly golfers to swing easily with the soft golf club with same skill which they acquired with regular golf clubs but with reduced load to their muscles.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.457-462
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• 2006

This paper is concerned with the active vibration control experiment on cylindrical shell equipped with Macro Fiber Composite(MFC) actuators. The MFC actuators were glued to the cylindrical shell in circumferential directions. To verify the theoretical result, vibration test using impact hammer and accelerometer was carried out. It was found from experiments that theoretical result predicts experimental result to some extent. The positive position feedback controllers were designed and applied to the test article. It was observed that the resonant amplitude of the fundamental mode was reduced by 20dB thus achieving active vibration control. The active vibration control of the response subject to non resonant excitation has been of interest. We developed the combination of the positive position feedback controller which can cope with the fundamental mode and the positive position feedback controller which can counteract the external disturbance with non resonant frequency. It was found from experiments that the hybrid controller can suppress the vibration amplitude successfully.

• 한국정밀공학회지
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• 제33권10호
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• pp.805-811
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• 2016

Prior to installation in a navy ship, shipboard equipment should be qualified by shock test requirements. The multi-function console mounted on the elastic platform of the ship should also withstand given shock loads. In this study, both real shock test methods, as well as numerical computer simulations using the finite element method were used to verify structural durability under shock load conditions. First, we used domestic test facilities to perform possible shock tests, including an impact hammer test, a drop table test and a shaker shock test. Full model tests satisfying the shock response spectrum level were performed. Thereafter, an analytical model of the complex console structure was built by the finite element method. Finally, numerical results were verified by modal test results of the real product and an FEA analysis was also performed with a full model transient response analysis.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2004년도 학술대회지
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• pp.186-194
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• 2004

Experiments were conducted to determine the structural static and dynamic characteristics of air foil bearings. The housing of the bearing on the journal was driven by an impact hammer which was used to simulate dynamic forces acting on the bump loll with various leading condition. Two different bump foils (Cu-coated bump and viscoelastic bump) were tested and the static and dynamic coefficients of two bump foils compared, based on the experimental measurements for a wide range of operating conditions. The static and dynamic characteristics of air foil bearings were extracted 0rpm the frequency response function by least square method and IV(Instrumental Variable) method. The experiment was tested at 0rpm and $10,000\~16,000rpm$, and loaded on $50\~150N$. From the test results, the possibility of the application of high load and high speed condition is suggested.

• Geomechanics and Engineering
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• 제8권3호
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• pp.415-440
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• 2015

In the present case study, High Strain Dynamic Testing of piles is conducted at 3 different locations of Kolkata city of India. The raw field data acquired is analyzed using Pile Driving Analyzer (PDA) and CAPWAP (Case Pile Wave Analysis Programme) computer software and load settlement curves along with variation of force and velocity with time is obtained. A finite difference based numerical software FLAC3D has been used for simulating the field conditions by simulating similar soil-pile models for each case. The net pile displacement and ultimate pile capacity determined from the field tests and estimated by using numerical analyses are compared. It is seen that the ultimate capacity of the pile computed using FLAC3D differs from the field test results by around 9%, thereby indicating the efficiency of FLAC3D as reliable numerical software for analyzing pile foundations subjected to impact loading. Moreover, various parameters like top layers of cohesive soil varying from soft to stiff consistency, pile length, pile diameter, pile impedance and critical height of fall of the hammer have been found to influence both pile displacement and net pile capacity substantially. It may, therefore, be suggested to include the test in relevant IS code of practice.

• Computers and Concrete
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• 제17권4호
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• pp.455-475
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• 2016

Dynamic characteristics, named as natural frequencies, damping ratios and mode shapes, affect the dynamic behavior of buildings and they vary depending on the construction stages. It is aimed to present the effects of construction stages on the dynamic characteristics of reinforced concrete (RC) buildings considering theoretical and experimental investigations. For this purpose, a three-storey RC building model with a 1/2 scale was constructed in the laboratory of Civil Engineering Department at Karadeniz Technical University. The modal testing measurements were performed by using Operational Modal Analysis (OMA) method for the bare frame, brick walled and coated cases of the building model. Randomly generated loads by impact hammer were used to vibrate the building model; the responses were measured by uni-axial seismic accelerometers as acceleration. The building's modal parameters at these construction stages were extracted from the processed signals using the Enhanced Frequency Domain Decomposition (EFDD) technique. Also, the finite element models of each case were developed and modal analyses were performed. It was observed from the experimental and theoretical investigations that the natural frequencies of the building model varied depending on the construction stages considerably.

• 한국산학기술학회논문지
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• 제7권4호
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• pp.671-678
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• 2006

진동해머를 이용한 널말뚝 시공은 소음에 민감한 도심지 굴착 공사에 유용하다. 그러나 널말뚝의 진동-항타 시공시 항타관입성에 대한 연구는 거의 수행된 적이 없다. 이 연구에서는 국내에서 많이 사용되고 있는 U형 널말뚝을 진동해머를 이용하여 시공할 때 여러 가지 조건에 따른 항타관입성을 WEAP 프로그램을 이용하여 분석하였다. 해석결과 널말뚝의 관입속도는 N값이 클수록 느려지며, 20m 이내로 시공되는 경우 단면적이 클수록 느려지는 것으로 나타났다.

• 한국추진공학회지
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• 제3권1호
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• pp.104-117
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• 1999

복합재료는 비강성과 비강도의 우수성 때문에 첨단 산업분야에서 사용되고 있으며, 특히 낮은 비중으로 인한 중량감소 효과와 접착과 주조 둥에 의한 부품수의 감소효과 때문에 항공기와 수송기계분야에 널리 이용되고 있다. 복합재료의 이러한 장점들을 이용하여 항공기용 동력전달축과 자동차용 추진축에서 연구와 활용이 이뤄지고 있다. 본 연구에서는 우수한 진동 안정성을 갖는 복합재료 추진축을 설계하고 해석하였으며 이를 증명하기 위해 충격망치를 이용한 FFT해석기와 회전장비를 이용하는 두 가지 실험을 수행하였다.