• 한국소음진동공학회논문집
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• 제22권1호
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• pp.29-37
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• 2012

This paper is concerned with the natural vibration characteristics of a rectangular plate with a rectangular hole in contact with the water. The addressed problem was solved by using the Rayleigh-Ritz method combined with the Green function method. This study presents the numerical approach, numerical results and experimental results. In addition, the validity of the approximate formula which mainly depends on the so-called non-dimensionalized added virtual mass incremental factor and the natural mode shape change due to the presence of the water were investigated. Experiments were also carried out to validate theoretical results. The theoretical results are in good agreement with the experimental results. It was found that the effect of a square hole on the natural frequencies of the square plate in contact with water is different from the effect of a square hole on the natural frequencies of the square plate in air and the approximate formula can predict lower natural frequencies in water with a good accuracy.

• Structural Engineering and Mechanics
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• 제21권2호
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• pp.169-184
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• 2005

This study deals with the free vibration of a circular plate in contact with a fluid; submerged in fluid, beneath fluid or on fluid. An analytical method based on the finite Fourier-Bessel series expansion and Rayleigh-Ritz method is suggested. The proposed method is verified by the finite element analysis using commercial program with a good accuracy. The normalized natural frequencies are obtained in order to estimate the relative added mass effect of fluid on each vibration mode of the plate. Also, the location of plate coupled with fluid and the cases of free and bounded fluid surface are studied for the effect on the vibration characteristics.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.101-105
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• 2008

A flexible structure submerged in acoustic fluid is affected by its surrounding fluid. In transient response of a submerged structure, the coupled effect between structures and surrounding fluid emerges as damping and added mass at early and late time, respectively. Therefore, the characteristics of submerged structure such as natural frequencies and damping coefficients are changed by its surrounding fluid. In this paper, the analytic modal equation of a spherical shell surrounded by water and air is dealt with. Through the example, the damping coefficients and natural frequencies of flexible structures are studied for various external acoustic fluid and structures.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2002년도 ICCAS
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• pp.97.3-97
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• 2002

This paper presents the vibration characteristics of an intelligent cantilever beam in contact with a fluid using a PZT actuator and PVDF film. The dynamic behaviors of a flexible beam-water interaction system are examined. The effect of the liquid level on free vibration of the composite beam in a partially liquid-filled circular cylinder is investigated. The coupled system is subject to an undisturbed boundary condition in the fluid domain. It was found that the coupled natural frequencies decreased with the fluid level for the identical composite beam due to added mass effect. In case of the free-free boundary condition, the natural frequency gently decreased at fluid water level betw...

• 대한기계학회논문집A
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• 제32권2호
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• pp.127-134
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• 2008

The aerodynamically excited vibration and natural frequency of rotating disks are analytically studied in this paper. The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and drag forces. The explicit expressions on natural frequencies of the air coupled disk are obtained as functions of the aerodynamic coefficients. for the three cases where the disk rotates in three different cases (in vacuum, in open air without enclosure, and close to rigid wall). The theoretical results give that the natural frequencies of rotating disks in air are smaller than those in vacuum, because the effect of the added fluid mass decreases the frequencies. This paper also proposes an analytical method to predict the flutter speed of a rotating disk.

• 한국기계가공학회지
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• 제16권4호
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• pp.62-68
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• 2017

Since the aircraft parts industry is a high-value-added industry, mass production order production, and the hundreds of thousands. Therefore, parts produced However, since these parts require high reliability and stability, a high degree of precision is required. In Korea, there on the roughness of the machined surface in cutting process. However, research on the surface roughness characteristic obtained by which is widely used for aircraft parts is still insufficient in Korea. The purpose of this study is to investigate the effect of turning tool rotation speed and X axis feed rate on the surface roughness of cutting tools in CNC lathes during cutting of aluminum alloy 7075.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1994년도 추계학술대회 논문집
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• pp.975-979
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• 1994

The experimental and finite element studies of a coaxial cylindrical shell filled with liquid in the annular gap were performed to understand its vibration characteristics. Finite element analysis was achieved by using ANSYS code. Form the investigation of the changing trend of natural frequencies for the change of annular gap we know that the natural frequency of the coaxial cylindrical shell varies according to the mode shape. that is, in case of in-phase mode the natural frequency decrease as annular gap increase, but in case of out-of-phase mode the natural frequency increase. Finite element analysis results show the excellent agreement with the experimental results both in air and in water case, so that analysis on other cases with be possible without experiment.

• 설비공학논문집
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• 제11권6호
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• pp.740-748
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• 1999

This research was concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different vertical tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare inner surface, groove inner surface, corrugated inner surface and spring inserted inner surface tubes. The additive concentration was about 0.08 mass%. The heat transfer coefficient was measured as a function of film Reynolds number in the range of 20~200. Experiments were tarried out at higher cooling water temperature of $35^{\circ}C$ to simulate an air cooling condition for several kinds of absorber testing tubes. The experimental results were compared with cases without surfactant. The enhancement of heat transfer by Marangoni convection effect which was generated by addition of the surfactant is observed in each test tube. Especially, it is clarified that the tube with an inserted spring has the highest enhancement effect.

• 대한영양사협회학술지
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• 제13권3호
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• pp.240-249
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• 2007

The objective of this study was to investigate the relation of serum calcium level, body mass index(BMI) with bone status expressed as broadband ultrasound attenuation(BUA) measured by quantitative ultrasound (QUS) and the occurrence of osteopenia among adult men and women. Two hundred eleven(63 male and 148 female) workers who worked in 4 different battery factories were recruited from March 2005 to October 2005. BUA was used as a surrogate of bone mineral density and measured at left calcaneous bone area. The BUA value transformed into T-score by WHO standard conversion criteria to determine osteopenia (-2.5

• 한국식품과학회지
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• 제29권1호
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• pp.51-56
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• 1997

겨자의 항균성 및 식품보존제로의 이용가능성을 조사하기 위하여 겨자의 첨가에 따른 냉면육수의 보존 중 그 효과를 조사하고, 대장균의 형태변화를 현미경으로 관찰한 결과는 다음과 같다. 겨자를 첨가시킨 냉면육수의 적정산도는 처음에 겨자 무첨가 육수에 비하여 높았으나 24시간 보존 후에는 겨자 무첨가 육수보다 낮게 나타났으며, 겨자 첨가 냉면육수의 생균수 및 대장균수는 처음에 겨자 무첨가시보다 감소하였으며, 겨자 첨가농도가 높을수록 감소하는 폭이 크게 나타났고, VBN 함량은 보존기간이 지남에 따라 증가하였고, 겨자가 첨가된 냉면육수가 겨자 무첨가보다 낮게 나타났으며, 겨자첨가 농도가 높을수록 더욱 낮게 나타났다. 겨자 물추출물로 처리한 대장균을 전자현미경으로 관찰한 결과 균체표면이 수축되고 표층구조가 허물어져 심한 형태학적 변화를 나타내었다.