• 비파괴검사학회지
• /
• 제31권2호
• /
• pp.174-180
• /
• 2011

본 연구에서는 초음파원자현미경을 이용하여 비파괴적인 표면탄성이미지 분석과 나노표면에서의 기계적 물성 평가를 연구하였다. 이를 위해 접촉역학 특성에 따른 캔틸레버의 공진주파수 변화를 이론적으로 해석하고 실험적으로 측정하였다. 스프링-질량 모델과 Herzian 이론을 이용하여 계산한 이론적인 접촉공천주파수는 초음파원자현미경 캔틸레버의 실험적인 접촉 공진주파수의 변화와 매우 유사하였다. 결과적으로, 초음파원자현미경의 표면 높이 이미지와 진폭이미지를 성공적으로 얻을 수 있었고 진폭신호를 통하여 시료표면에서의 탄성특성을 정성적으로 평가하였다.

• 한국정보기술응용학회:학술대회논문집
• /
• 한국정보기술응용학회 2005년도 6th 2005 International Conference on Computers, Communications and System
• /
• pp.233-235
• /
• 2005

Non-contact power supply (NCPS), as a clean and safe energy supply concept has been applying wildly. Comparing with the conventional transformer the non-contact transformer has a large air gap between the long primary winding and the secondary winding. Due to it, the non-contact transformer has increased leakage inductance and reduced magnetizing inductance. So the high frequency series resonant converter has been widly used on the non-contact power supply system for transferring the primary power to the secondary one, from what a high influence voltage can be gained on the secondry coil even though the large air gap exists. However, it still has the disadvantages of the load sensitive voltage gain characteristics when load is changing. In this paper, we propose a fuzzy logic controller to adjust the frequency of the inverter to track the resonat which is changing when the load is change.

• 한국산학기술학회논문지
• /
• 제22권3호
• /
• pp.339-351
• /
• 2021

본 연구에서는 초, 중, 고 학생의 부모-자녀 간 대화 빈도에 대한 인식 차이에 따른 차별적인 특징을 갖는 유형을 탐색하고, 탐색된 유형에 따라 초, 중, 고 학생의 진로개발역량과 학업적 특성에 차이가 있는지 검증하였다. 이를 위해 초·중등 진로 교육 현황조사(2018) 자료를 활용하였으며, 잠재프로파일분석 방법을 사용하였다. 분석 결과, 초, 중, 고 학생의 부모-자녀 간 대화 빈도에 대한 인식 차이는 초등학생 6개 잠재계층(자녀 학교생활 대화 상, 자녀 상-부모 학교 생활 대화 상, 자녀 하-부모 하, 자녀 상-부모 상, 자녀-부모 학교생활 대화 상, 자녀 하-부모 중), 중학생 6개 잠재계층(자녀 하-부모 하, 자녀 중-부모 중, 자녀 상-부모 하, 자녀 상-부모 중상, 자녀 하-부모 상, 자녀 최상-부모 최상), 고등학생 7개 잠재계층(자녀-부모 학교생활 대화 상, 자녀 상-부모 하, 자녀 중-부모 중, 자녀 중-부모 상, 자녀 하-부모 하, 자녀 상-부모 중상, 자녀 최상-부모 최상)이 존재하는 것으로 확인되었다. 그리고 초, 중, 고 모두 잠재계층에 따라 진로개발역량(자기이해와 사회성, 직업이해, 진로탐색, 진로설계와준비도)과 학업적 특성(자율적 학습 동기, 자기주도학습)에 차이가 있는 것으로 나타났으며, 대체로 부모-자녀 모두 대화 빈도가 높다고 인식한 집단과 부모보다 자녀가 인식한 대화 빈도 수준이 높은 집단의 진로개발역량과 학업적 특성 점수가 높은 것으로 확인되었다. 본 연구는 초, 중, 고 학생은 부모와의 대화 빈도를 부모와 다르게 인식할 수 있으며, 이와 같은 인식의 차이가 진로개발역량과 학업적 특성에 영향을 미칠 수 있음을 시사한다.

• Journal of Biosystems Engineering
• /
• 제35권3호
• /
• pp.189-196
• /
• 2010

This study was conducted to develop an non-contact ultrasonic transducer for measurement of fruit firmness. The center frequency of non-contact ultrasonic transducer was 500 kHz. As an active element of non-contact ultrasonic transducer, the 1-3 piezoelectric composite material was selected. That material has high piezoelectric properties such as electro-mechanical coupling factor, $k_t$ and piezoelectric voltage constant, $d_{33}$ and also that material has low acoustical impedance which enables to matching the acoustical impedances between piezoelectric material and air. As a front matching material between 1-3 piezoelectric composite material and air, various kinds of paper with different thickness were tested. To control the dead-zone of the fabricated non-contact ultrasonic transducer, the backing material composed of epoxy resin and tungsten powder were made and evaluated. The fabricated non-contact ultrasonic transducer for fruit showed that the cneter frequency, bandwidth and beamwidth were approximately 480 kHz, 30 % and 12 mm, respectively. It was concluded that non-contact measurement of apple firmness would be possible by using the fabricated non-contact ultrasonic transducer.

• 한국음향학회지
• /
• 제41권6호
• /
• pp.691-697
• /
• 2022

직류 계전기는 전기자동차의 하나의 부품으로 간헐적으로 고주파수 소음이 710 Hz ~ 730 Hz의 주파수 범위에서 전기적 부하에 의해 발생한다. 고정접점과 가동접점 사이에서 발생하는 전자 반발력이 가동접점과 접압 스프링을 진동시키고, 그 진동으로 가동접점과 접압 스프링에 공진이 발생하여 고주파수 소음이 발생한다. 본 논문에서는 수치해석 및 실험을 통하여 고주파수 소음의 원인을 규명하고, 소음을 제거하는 방안을 제시하였다. 710 Hz ~ 730 Hz의 주파수 범위에서 가동접점은 고정접점과의 2개의 접촉점을 기준으로 회전하는 공진모드가 발생한다. 따라서 해당 여기서 제안한 방법은 공진모드를 제거하기 위해 가동접점의 구조를 2점 접촉구조 방식에서 3점 접촉구조 방식으로 변경하는 것이다. 3점 접촉구조를 적용함에 따라 공진모드가 제거되는 것을 수치해석으로 확인하였고, 실험적으로도 고주파수 소음이 발생하지 않는 것을 확인하였다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2012년도 춘계학술대회 논문집
• /
• pp.505-506
• /
• 2012

• Structural Engineering and Mechanics
• /
• 제62권1호
• /
• pp.113-123
• /
• 2017

The bi-material elastic system consisting of the circular hollow cylinder and the infinite elastic medium surrounding this cylinder is considered and it is assumed that on the inner free face of the cylinder a point-located axisymmetric time harmonic force, with respect to the cylinder's axis and which is uniformly distributed in the circumferential direction, acts. The shear-spring type imperfect contact conditions on the interface between the constituents are satisfied. The mathematical formulation of the problem is made within the scope of the exact equations of linear elastodynamics. The focus is on the frequency-response of the interface normal and shear stresses and the influence of the problem parameters, such as the ratio of modulus of elasticity, the ratio of the cylinder thickness to the cylinder radius, and the shear-spring type parameter which characterizes the degree of the contact imperfectness, on these responses. Corresponding numerical results are presented and discussed. In particular, it is established that the character of the influence of the contact imperfection on the frequency response of the interface stresses depends on the values of the vibration frequency of the external forces.

• 가정과삶의질연구
• /
• 제22권3호
• /
• pp.23-34
• /
• 2004

This study was conducted to identify the characteristics of paternal and maternal grandmothers' social support, and to investigate the relationship between paternal and maternal grandmothers' social support and their school-aged grandchildren's psychological adaptation. The participants of this study were 215 students in the 5th and 6th grades and their mothers residing in Daegu. Collected data were analyzed using t-test, paired t-test, ANOV A, Scheffe's test, and hierarchical multiple regression. Findings of this study are as follows: 1. School-aged children perceived that their maternal grandmothers rendered more emotional and informational support than their paternal grandmothers. 2. Paternal grandmother's social support as perceived by the grandchild varied significantly with the frequency of face-to-face contact, the frequency of phone contact, and the friendship between the paternal grandmother and the mother. Maternal grandmother's social support as perceived by the grandchild, on the other hand, varied significantly by the level of grandmother's education, the frequency of face-to-face contact, and the frequency of phone contact. 3. Perceived paternal and maternal grandmothers' social support had indirect impacts on grandchildren's depression, which was mediated by their mothers' parenting.

• 한국자동차공학회논문집
• /
• 제11권6호
• /
• pp.171-182
• /
• 2003

Tire vibration modes are known to play a key role in vehicle ride and comfort characteristics. Inputs to the tire such as impacts, rough road surface, tire nonuniformities, and tread patterns can potentially excite tire vibration. In this study, experimental modal analysis on the tire in ground contact are performed by a 3-D impact at the center of contact patch to investigate which modes of tire influence the vibration of wheel and axle. Through the experiment, the vibration transmission properties from tire to axle are examined. And we have compared the influential tire modes when the tire is excited by a vertical impact with those when excited by the 3-D impact. Additionally, the modes of ground contact tire are compared with those of the suspended tire.

• 한국생산제조학회지
• /
• 제23권4호
• /
• pp.368-373
• /
• 2014

This paper presents the dynamic modeling and analysis results for a spindle supported by angular contact ball bearings (ACBBs) subjected to angular misalignment. Although ACBBs are widely used in spindle systems, their characteristics in regard to angular misalignment have rarely been investigated. A simulation program was developed to calculate the dynamic characteristics of a simple spindle model that is supported by angular contact ball bearings subjected to angular misalignment. Angular misalignment is shown to introduce anisotropy into the angular contact ball bearings and then split the natural frequencies in spindles. Simulations were also performed to show the possibility of evaluating bearing misalignment using natural frequency measurements.