• EDISON SW 활용 경진대회 논문집
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• 제6회(2017년)
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• pp.317-323
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• 2017

Due to the unique characteristic of auxetic material, negative poisson's ratio, it has a variety of distinctive properties compared to conventional materials. Numerous researches have been conducted on the auxetic material in order to find out how to make auxetics. In this study, we analyzed triangular and rectangular patterned rotating rigid units using finite element method. Our purpose is to investigate the mechanical properties of the rotating rigid units and to show their auxetic behaviors. We studied the Poisson's ratio and the bulk modulus of the rotating rigid units depending on their unit cell sizes. The Poisson's ratio and the bulk modulus decreased as the number of unit cells increased. Also, when the geometry of the unit cell was changed, the tendency of the Poisson's ratio and the bulk modulus was also different from the previous case. The results of the Poisson's ratio and the bulk modulus referred that they were critically affected by the number of unit cells and the shape of unit cell.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.300-303
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• 2006

The rotor blade of a helicopter is the key structural units and provides three components such as vertical lifting force, horizontal propulsive force and control force. With advancements in aerospace technology, composite materials have been widely used in lightweight structures. In addition, composites show great potential on the design of rotor blades due to the advantages of strength, durability and weight of the materials. In the operational condition of a helicopter, it is required the vibration characteristics of the rotating blades for avoiding resonance and analysis of efficient performance prediction et al. In this study, the CAMRAD-II is used for analyzing the vibration characteristics of rotating composite blades. The effects of rotating speed and collective angles are investigated. Also, the numerical results are compared with experimental data.

• 한국직업건강간호학회지
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• 제9권2호
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• pp.86-93
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• 2000

This study was conducted to find out the degree of tiredness, accumulated tendencies of fatigues in accordance with 3 types of circadian rhythms and 3 types of perceived fatigue signs such as physical, psychological and neurosensory aspects in before and after work at night. Samples were chosen from the 217 intensive care units nurses working in 13 general hospitals which had 3 shift rotating systems, Data were collected from November to December in 1999. Two hundreds seventeen respondents were classified by 3 circadian types such as 59 morning, 110 middle and 48 evening. Circadian type was measured by the circadian type scale which was designed by ${\ddot{O}}stberg$ and Home (1976). in order to estimate the level of tiredness, the investigator used the fatigue checklist designed by the Labor and Health Institute of Japan(1970). Analysis was done by frequency a percentages, ${\chi}^2$ test and repeated measures ANOVA test. The result of this study were as follow: 1. In the general characteristics of the subjects circadian types, moderate type had the large proportion at 50.7% and morning type had 27.2% and evening type had 22.1%. 2. According to the 3 types of fatigue signs, the highest general tendency was 'General weakness' and 'Feeling of headsore' for physically perceived sign, 'Drowsiness' for psychological sign, and 'Uncomfortableness in sight seeing' for neurosensory sign. 3. The most frequently complained fatigue were observed in physical symptoms among physical, mental, and neurosensual symptoms. The percentage of complained was higher after night work than before the work started. 4. There was not any statistical significant difference between the circadian type and the degree of physical, mental, neurosensory fatigue. 5. There was not any statistical significant difference in regarding to each date of night shift except difference between 1st and 2nd days of fatigue perceived physically. Therefore, the study concluded that the fatigue perceived by night shift nurses might be related with shift working condition rather than circadian types.

• Journal of Biosystems Engineering
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• 제7권1호
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• pp.17-32
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• 1982

The binders introduced in Korea were originally designed to be used for Japonica-type varieties which have relatively long stem and are highly resistant to shattering. In order to use it for Tongil varieties which are short and easy to be shattered, mechanical modifications are necessary to reduce a grain loss incurred during binder operation. This study was intended to investigate analytically and experimentally the major sources of grain losses caused by three kinds of binders now introduced in Korea. Actual modification for each of three binders was done and experimentally compared to see if any improvement on grain loss was achieved. The results obtained in this study are summarized as follows; 1. It was required that the power transmission of binder should have a shifting mechanism so that velocities of pick-up and traveling units could be changed independently as desired according to the Japonica-type and Tongil varieties. In other words, the desired velocity of traveling unit should be obtained by shifting the transmission and the velocity of pick-up unit should be selected by reaping clutch according to the variety independent of the velocity of traveling unit as shown in Fig. 6. 2. To reduce grain loss it was desired that the moving parts of the pick-up unit should have the lowest possible velocities in harvesting Tongil varieties, unless the reduction of the speed be hindered the conveyance of the material. Based on the study, it was concluded that the velocities of pick-up unit be reduced by about 35% of those of the existing units. 3. It was found that the lug at the upper rotating section of pick-up case gave a severe impact on the ears of rice to increase grain loss. The optimum design of pick-up case to protect the ears from the protruding part of the lug was recommended by the result of analysis of the trajectory of the end-point of lug at the position. 4. It was proved analytically and experimentally that pick-up unit at the lower-rotating part was the other important source of grain loss in pick-up and divider assembly. In order to reduce a grain loss incurred by lugs at their lower-rotating section, it was suggested to improve it by (1) widening the space between right and left lower-rotating section, (2) shortening the length of lugs, (3) enlargement of the angle between the pick-up case and ground-level, and (4) attaching guard to right and left dividers so that the rotating lug could not give a high impact to the paddy hill. 5. Pick-up and divider assembly of the original binder of three models studied was modified according to the suggestions that were given by the preliminary study. Field test showed that the modified binders were able to reduce grain losses by about 0.4-0.7 percentage points compared to those without modification.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1425-1429
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• 2007

Consumer's product selection measures are being shifted from the units' operational performance to overall performance. Low noise, low vibration, and low power consumption rate, etc. which used to be additional quality indices, now become vital performance factors. Especially, noise and vibration characteristics are being considered as equivalent to/or even more critical than operational performance in certain products such as office machines and home entertainment systems, which share the same space with human being's daily life. Therefore, noise reduction and sound quality improvement technology becomes an inevitable design issue for those applications. Qualitative noise characteristics of rotating polygonal disk applied to digital printer systems are presented. Overall sound pressure level change and tonal noise variation with respect to the geometrical properties of polygonal disk, operational speed, and others are briefly discussed based on experimental results.

• 한국소음진동공학회논문집
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• 제18권6호
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• pp.606-611
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• 2008

Consumer's product selection measures are being shifted from the units' operational performance to overall performance. Low noise, low vibration, and low power consumption rate, etc. which used to be additional quality indices, now become vital performance factors. Especially, noise and vibration characteristics are being considered as equivalent to/or even more critical than operational performance in certain products such as office machines and home entertainment systems, which share the same space with human being's daily life. Therefore, noise reduction and sound quality improvement technology becomes an inevitable design issue for those applications. Qualitative noise characteristics of rotating polygonal disk applied to digital printer systems are presented. Overall sound pressure level change and tonal noise variation with respect to the geometrical properties of polygonal disk, operational speed, and others are briefly discussed based on experimental results.

• 한국지능시스템학회논문지
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• 제24권2호
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• pp.123-128
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• 2014

본 논문은 상하 회전형 차동 구동부를 이용한 자기 유도 무인운반차에 대한 연구이다. 기존의 자기 유도 무인운반차는 주행 정보를 얻기 위해 자기 위치측정 센서 외에 랜드마크 및 이를 인식하기 위한 추가적인 센서가 필요하다. 또한, 일반적으로 사용되는 고정형 차동 구동부를 사용할 경우 자기 유도 무인운반차의 무게 불균형으로 인해 위치측정 오차의 증가 및 제어에 어려움이 존재하므로 2개 이상의 구동부를 필요로 한다. 이러한 단점들을 해결하기 위해 본 논문에서는 상하 회전형 차동 구동부를 이용한 자기 유도 무인운반차를 제안한다. 제안된 무인운반차는 주행 경로상에 자석의 양극으로 패턴을 구성하고 자기 위치측정 센서로 주행 정보를 획득하며, 하나의 상하 회전형 차동 구동부를 이용하여 후진 주행을 제어한다. 또한, 위치측정 오차의 감소를 위해 KF(Kalman filter)를 적용하여 무인운반차의 위치측정 정밀도를 향상시킨다. 제안된 방법의 성능을 확인하기 위하여 직접 제작한 자기 유도 무인운반차를 이용하여 실험하였다. 실험 결과, 제안된 방법의 패턴 인식 및 무인운반차의 후진 주행 성능을 확인할 수 있었으며, 기존의 방법보다 위치측정 정밀도의 RMSE가 더 감소된 것을 확인하였다.

• 천문학회보
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• 제45권1호
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• pp.52.4-53
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• 2020

It is less well known that the properties, especially the mass accretion rate, of accretion flow are affected by the angular momentum of accreting gas. Park (2009) found that the mass accretion rate \dot{m}, mass accretion rate in units of Bondi accretion rate, is inversely proportional to the angular momentum of gas λ, at the Bondi radius where gas sound speed is equal to the free-fall velocity and proportional to the viscosity parameter α, and also Narayan & Fabian (2011) found a similar relation, but the dependence of the mass accretion rate of the gas angular momentum is much weaker. In this work, we investigate the global solutions for the rotating Bondi flow, i.e., polytropic flow accreting via viscosity, for various accretion parameters and the dependence of the mass accretion rate on the physical characteristics of gas. We set the outer boundary at various radius r_{out}=10^3~10^5 r_{Sch}, where r_{Sch} is the Schwarzschild radius of the black hole. For a small Bondi radius, the mass accretion rate changes steeply, as the angular momentum changes, and for a large Bondi radius, the mass accretion rate changes gradually. When the accreting gas has a near or super Keplerian rotation, we confirm that the relation between the mass accretion rate and angular momentum is roughly independent of Bondi radius as shown in Park (2009). We find that \dot{m} is determined by the gas angular momentum at the Bondi radius in units of r_{Sch}c. We also investigate the solution for the rotating Bondi flow with the outflow. The outflow affects the determination of the mass accretion rate at the outer boundary. We find that the relation between the mass accretion and the gas angular momentum becomes shallower as the outflow strengthens.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.141-148
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• 2003

This paper presents a rotating ann test for assessment of an underwater hybrid navigation system for a semi-autonomous underwater vehicle. The navigation system consists of an inertial measurement unit (IMU), an ultra-short baseline (USBL) acoustic navigation sensor and a doppler velocity log (DVL) accompanying a magnetic compass. The errors of inertial measurement units increase with time due to the bias errors of gyros and accelerometers. A navigational system model is derived to include the error model of the USBL acoustic navigation sensor and the scale effect and bias errors of the DVL, of which the state equation composed of the navigation states and sensor parameters is 25 in the order. The conventional extended Kalman filter was used to propagate the error covariance, update the measurement errors and correct the state equation when the measurements are available. The rotating ann tests are conducted in the Ocean Engineering Basin of KRISO, KORDI to generate circular motion in laboratory, where the USBL system was absent in the basin. The hybrid underwater navigation system shows good tracking performance against the circular planar motion. Additionally this paper checked the effects of the sampling ratio of the navigation system and the possibility of the dead reckoning with the DVL and the magnetic compass to estimate the position of the vehicle.

• 한국정밀공학회지
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• 제28권3호
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• pp.265-274
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• 2011

This paper presents current state of the prediction simulator of structural characteristics of machinery equipment accuracy. Developed accuracy prediction simulator proceeds and estimates the structural analysis between the designer and simulator through the internet for convenience of designer. 3D CAD model which is input to the accuracy prediction simulator would simplified by the process of removing the small hole, fillet and chamfer. And the structural surface joints would be presented as the spring elements and damping elements for the structural analysis. The structural analysis of machinery equipment joints, containing rotary motion unit, linear motion unit, mounting device and bolted joint, are presented using Finite Element Method and their experiment. Finally, a general method is presented to tune the static stiffness at a rotation joint considering the whole machinery equipment system by interactive use of Finite Element Method and static load experiment.