• Coupled systems mechanics
• /
• 제13권2호
• /
• pp.133-151
• /
• 2024

In this paper, an improved theoretical interfacial stress analysis is presented for simply supported composite aluminum- sandwich honeycomb beam strengthened by imperfect FGM plateusing linear elastic theory. The adherend shear deformations have been included in the present theoretical analyses by assuming a linear shear stress through the thickness of the adherends, while all existing solutions neglect this effect. Remarkable effect of shear deformations of adherends has been noted in the results.It is shown that both the sliding and the shear stress at the interface are influenced by the material and geometry parameters of the composite beam. This new solution is intended for applicationto composite beams made of all kinds of materials bonded with a thin plate. Finally, numerical comparisons between the existing solutions and the present new solution enable a clear appreciation of the effects of various parameters.

• 한국학교보건학회지
• /
• 제14권2호
• /
• pp.279-288
• /
• 2001

This study investigates the effect of adolescent dining habits on their physical development. We selected 200 students from the three high schools in Taejon, and surveyed with a questionnaire and collected data concerning physique from school health records. The results obtained from this study were as follows: 1. A point of intersection of two development trends of male and female students' heights was between sixth grade of elementary school and first grade of middle school. Two development trends of weights didn't have a point of intersection and male students' development trend of weights was a little higher than that of female students. 2. There were significant differences in the weight and BMI of male students. The 'regular dining' group had heavier weight and higher BMI than the other group, and the 'Eating only favorite food' group had lower weight and BMI than the other group. In female, heights of 'three meals a day' group were higher than that of 'two meals a day' group and the more snacks per day, the higher students' height was. 3. The 'regular exercise' group had significantly heavier weight and higher BMI than the other group amount females. 4. 'Regular dining' and 'Eating habits' had a positive linear relationship with male students' weight and BMI. 'Number of times of snacking' has a positive linear relationships with female students' height and a negative linear relationship with female students' BMI. Since dining habits of adolescents have not only an effect on their development but also later adults' health, to develop good habits of health and dining is a critical issue.

• 한국전자파학회논문지
• /
• 제29권4호
• /
• pp.308-315
• /
• 2018

본 논문에서는 두 표적 간의 거리차를 정밀하게 계측할 수 있는 S-band 고 분해능 레이다 개발을 위한 시스템 기본 설계 및 구현 결과를 제시한다. 3.5 GHz LFM(Linear Frequency Modulation) 레이다 기본 설계를 위하여 제안하는 시스템 요구조건은 거리 분해능 1 m, 최대 계측 거리 2 km이며 레이다 방정식을 통해 각 모듈의 사양을 결정하였다. 최종적으로 150 MHz 대역폭, 송신 출력 43 dBm 전력 증폭기, 이득 26 dBi 안테나, 잡음 지수 8 dB 이하, RCS $1m^2$일 때, 표적과 레이다의 최대거리 2 km 기준 SNR이 30 dB 이상이 나올 수 있음을 확인할 수 있었다. 시뮬레이션 결과를 토대로 하드웨어 설계를 하였으며, SDR(Software Defined Radar) 장비를 이용한 LFM 레이다 설계 이론과 방법 그리고 야외 시험 결과를 보여주고 요구조건을 만족하는 레이다 시스템 설계가 가능함을 입증하였다.

• 문화기술의 융합
• /
• 제8권2호
• /
• pp.315-319
• /
• 2022

본 연구는 선형 혼합 모형을 활용하여 쓰기 능력이 장기적으로 어떻게 발전되어 가는지를 통사적 복잡성(syntactic complexity) 측면에서 4명의 사례 연구자들이 작성한 에세이를 활용하여 분석하였다. 사례 연구자들은 자발적으로 Criterion 이라는 자동 쓰기 평가 프로그램의 피드백을 받아 초안과 수정본을 교실 밖에서 매달 한 개 씩 일 년 동안 작성했다. 총 48개 초안 에세이가 본 연구의 분석 대상이고, 통사적 복잡성은 Syntactic Complexity Analyzer의 14개 지표 중에서 추출하여 분석하였다. 선형 혼합 모형 분석 결과를 살펴보면 다음과 같다. 시간과 T-unit의 평균길이 간에는 통계적으로 유의미한 선형 관계가 있었으며, 이는 연구 참여자들이 시간이 지날수록 길이가 긴 T-uni을 포함한 에세이를 작성했음을 보여준다. 또한 시간과 의존절과 독립절 간의 비율 간에도 통계적으로 유의미한 선형 관계가 있었는데, 이는 연구 참여자들이 일 년 동안 높은 비율의 의존절이 포함된 에세이를 작성했음을 시사한다.

• 한국정밀공학회지
• /
• 제33권4호
• /
• pp.303-307
• /
• 2016

The fiber optical temperature sensing device was developed by using a Fiber Bragg Grading (FBG) sensor and a linear transmittance optical filter. The temperature change causes change in the FBG sensor reflectance wavelength and the reflectance wavelength from FBG sensor is transmitted to a linear transmittance filter so that the optical signal value is determined by the wavelength. The temperature can be measured by the optical signal value by passing FBG reflectance wavelength to the linear transmittance filter. Using the developed system, temperature ranges from $10^{\circ}C$ to $50^{\circ}C$ were measured and the measured data were almost linear.

• 전기학회논문지
• /
• 제59권6호
• /
• pp.1059-1063
• /
• 2010

Shimming is an important technique in development of nuclear magnetic resonance (NMR) magnets where image resolution is highly dependent on magnetic field homogeneity. Classically, shimming may be categorized into two types: 1) active shimming that incorporates with extra coils and precise tuning of their currents; and 2)passive shimming that incorporates with pieces of steel placed in a bore of a main magnet and their uniform magnetization under homogeneous external fields. Additional magnetic fields, produced by the coils and/or the steel sheets, compensate original magnetic field from the main magnet in such a way that the total field becomes more homogeneous. In this paper, we developed a passive shimming method based on linear programming optimization. Linear programming is well known to be highly efficient to find a global minimum in various linear problems. We firstly confirmed the linearity of magnetization of ferromagnetic pieces under a presence of external magnetic fields. Then, we adopted the linear programming to find optimized allocation of the steel pieces in the inner bore of a main magnet to improve field homogeneity.

• 한국초전도ㆍ저온공학회논문지
• /
• 제17권3호
• /
• pp.51-56
• /
• 2015

Cryogenic cooling system for HTS electric power devices requires a reliable and efficient high-capacity cryocooler. A Striling cryocooler with a linear compressor can be a good candidate. It has advantages of low vibration and long maintenance cycle compared with a kinematic-driven Stirling cryocooler. In this study, we developed dual-opposed linear compressor of 12 kW electric input power with two 6 kW linear motors. Electrical performance of fabricated linear compressor is verified by experimental measurement of thrust constant. The developed Stirling cryocooler has gamma-type configuration. Piston and displacer are supported with flexure spring. A slit-type heat exchanger is adopted for cold and warm-end, and the generated heat is rejected by cooling water. In cooling performance test, waveforms of voltage, current, displacement and pressure are obtained and their amplitude and phase difference are analysed. Moreover, temperatures of cooling water, housing and linear motor are recorded and electric power parameters of driving circuit are also obtained. The developed Stirling cryocooler reaches to 47.8 K within 23.4 min. with no-load. From heat load tests, it shows cooling capacity of 440 W at 78.1 K with 6.45 kW of electric input power and 19.4 of % Carnot COP.

• 한국실천공학교육학회논문지
• /
• 제4권1호
• /
• pp.57-64
• /
• 2012

전기기기 설계는 전통적이고 고전적인 방식을 이용하여 자기회로를 고려한 기기의 크기를 결정하고 권선방식과 권선을 정하고 해석프로그람을 이용하여 자속밀도와 토크를 계산하는 절차로 진행된다. 그러나 전기기기는 형상이 복잡하여 학생들이 설계하는 절차를 이해하고 해석하는데 많은 어려움을 겪고 있어 교육매체 개발이 매우 필요하다. 본 논문에서는 비교적 형상이 단순하여 자기회로 계산이 복잡하지 않고 전자기적 크기에 의한 추력의 발생과 해석을 쉽게 이해할 수 있는 Linear Force motor를 이용하여 설계절차를 설명하고 각 부위의 자속밀도를 설계 프로그람을 이용하여 도시함으로써 쉽게 이해할 수 있도록 하였다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2003년도 춘계학술대회 논문집
• /
• pp.343-346
• /
• 2003

In order to discuss the availability of the hydrostatic guideway driven by the coreless linear motor to ultra precision machine tools, a prototype of guideway is designed and tested in this research. A coreless linear DC motor with the continuous force of 156 N and a laser scale with the resulution of 10 nm are used as the feeding system. The experiments are performed on the static stiffness. motion accuracy, positioning accuracy. microstep response and variation of velocity. The guideway has the infinite axial stiffness within 50 N of applied load, and has 0.08 ${\mu}{\textrm}{m}$ of linear motion error and 0.1 arcsec of angular motion error. It also has 0.21 ${\mu}{\textrm}{m}$ of positioning error and 0.09 ${\mu}{\textrm}{m}$ of repeatability, and it shows the stable response against the 10 nm resolution step command. The velocity variation of feeding system is less than 5%. From these results, it is confirmed that the hydrostatic guideway driven by the coreless linear motor is very useful for the ultra precision machine tools.

• International Journal of Precision Engineering and Manufacturing
• /
• 제6권2호
• /
• pp.55-60
• /
• 2005

In order to develop the hydrostatic guideways driven by a core less linear motor for ultra precision machine tools, a prototype of guideway is designed and tested. A coreless linear DC motor with a continuous force of 156 N and a laser scale with a resolution of 0.01 ㎛ are used in the system. Experimental analysis on the static stiffness, motion errors, positioning error and its repeatability, micro step response and velocity variation of the guideway are performed. The guideway shows infinite stiffness within 50 N applied load in the feed direction, and by the motion error compensation method using the Active Controlled Capillary, 0.08 ㎛ linear motion error and 0.1 arcsec angular motion error are acquired. The guideway also reveals 0.21 ㎛ positioning error and 0.09 ㎛ repeatability, and it shows stable responses following a 0.01 ㎛ resolution step command. The velocity variation of feeding system is less than 0.6 ％. From these results, it is estimated that the hydrostatic guideway driven by a coreless linear motor is very useful for the ultra precision machine tools.