• 대한기계학회논문집A
• /
• 제34권10호
• /
• pp.1549-1554
• /
• 2010

플라스틱 나사는 경량성, 내식성, 열 및 전기절연성이 우수하여 최근 금속나사 대체용도로 사용 되고 있다. 플라스틱 나사는 사출성형에 의해 제작되며 성형과정에서 수축이 발생하여 형상정밀도가 저하된다. 특히 소형 정밀나사의 경우 마이크로미터 단위의 정밀도를 요구하는 관계로 소성가공에 의해 제작되는 금속나사를 대체하기 위해서는 많은 어려움이 따른다. 본 연구에서는 사출성형 공정의 수치해석을 통해 금형설계 인자를 결정하였고, 실험계획법을 적용하여 변형량을 최소화하기 위한 성형조건을 도출함으로써 플라스틱 나사의 형상정밀도 향상을 위한 연구를 수행하였다.

• 한국도로학회논문집
• /
• 제13권1호
• /
• pp.33-40
• /
• 2011

국내에서 일반적으로 보조기층재료로 사용되고 있는 보조기층 다짐재료의 역학적 특성을 반영한 실내 회복탄성계수는 역학적-경험적 포장설계법에서 적용하는 설계 인자이다. 따라서, 역학적-경험적 포장설계법의 보조기층 현장에서 실시하여야 하는 다짐관리는 다짐 후 측정된 현장 탄성계수가 설계에 적용된 실내 회복탄성계수를 만족하는지 여부를 확인하여야 할 것이다. 이를 위하여 본 연구에서는 기존 다짐관리 시험인 들밀도 시험과 평판재하시험(PBT)의 시험결과와 현장탄성계수와의 상관성을 분석하였고, 현장에서 탄성계수를 측정할 수 있는 소형 충격 재하시험(LFWD)을 통한 현장탄성계수와 실내 회복탄성계수와의 상관관계식과 시험간격을 제안하였다. 또한 제안된 상관관계를 이용하여 현장시험을 통한 보조기층의 다짐관리방안을 제안하였다.

• Tribology and Lubricants
• /
• 제30권1호
• /
• pp.9-14
• /
• 2014

In this Part II study, rotordynamic stability analyses were carried out to confirm improvements to the stability of a process high-speed lightweight centrifugal compressor, depending on the effects of tilting pad journal bearing designs. The bearing design variables considered were the clearances, LBPs, LOPs, and preloads. The results showed that the rotordynamic stability of the subject compressor rotor-bearing system improves exactly in accordance with the effects of the bearing design variables, which were determined in the preceding Part I study, owing to reduced bearing stiffnesses. Specifically, it was confirmed that the stability of the rotor system can be greatly improved by increasing both the machined and assembled bearing clearances, but there were no stability improvements by simply changing from an LBP to an LOP design. In addition, it was confirmed that for given fixed machined bearing clearances, the stability can be additionally improved by decreasing the preloads, i.e., by increasing the assembled clearances. In conclusion, it may be necessary to improve the designs of the original tilting pad bearings to obtain a sufficient margin of rotordynamic stability against a possible aerodynamic cross-coupled stiffness in a process high-speed centrifugal compressor. Thus, increasing the machined and assembled bearing clearances and decreasing the preload could be effective solutions.

• Transactions on Control, Automation and Systems Engineering
• /
• 제3권3호
• /
• pp.181-189
• /
• 2001

The software components of embedded control systems get extremely complex as they are designed into distributed systems get extremely complex as they are designed into distributed systems consisting of a large number of inexpensive microcontrollers interconnected by low-bandwidth real-time networks such as the controller area network (CAN). While recently emerging middleware technologies such as CORBA and DCOM address the complexity of distributed programming, they cannot be directly applied to distributed control system design due to their excessive resource demand and inadequate communication models. In this paper, we propose a CORBA-based middleware design for CAN-based distributed embedded control systems. Our design goal is to minimize its resource need and make it support group communication without losing the IDL (interface definition language) level compliance to the OMG standards. To achieve this, we develop a transport protocol on the CAN and a group communication scheme based on the well-known publisher/subscriber model. The protocol effectively realizes subject-based addressing and supports anonymous publisher/subscriber communication. We also customize the method invocation and message passing protocol, referred to as the general inter-ORB protocol (GIOP), of CORBA so that CORBA method invocations are efficiently serviced on a low-bandwidth network such as the CAN. This customization includes packed data encoding and variable-length integer encoding for compact representation of IDL data types. We have implemented our CORBA-based middleware on the mArx real-time operating system we have developed at Seoul National University. Our experiments clearly demonstrate that it is feasible to use CORBA in developing distributed embedded control systems possessing severe resource limitations. Our design clearly demonstrates that it is feasible to use a CORBA-based middleware in developing distributed embedded systems on real-time networks possessing severe resource limitations.

• Structural Engineering and Mechanics
• /
• 제5권4호
• /
• pp.399-414
• /
• 1997

This paper presents an investigation into the seismic response characteristics of a proposed ligh-weight pedestrian cable-stayed bridge made entirely from Glass Fiber Reinforced Plastics(GFRP). The study employs three dimensional finite element models to study and compare the dynamic characteristics and the seismic response of the GFRP bridge to a conventional Steel-Concrete (SC) cable-stayed bridge alternative. The two bridges were subjected to three synthetic earthquakes that differ in the frequency content characteristics. The performance of the GFRP bridge was compared to that of the SC bridge by normalizing the live load and the seismic internal forces with respect to the dead load internal forces. The normalized seismically induced internal forces were compared to the normalized live load internal forces for each design alternative. The study shows that the design alternatives have different dynamic characteristics. The light GFRP alternative has more flexible deck motion in the lateral direction than the heavier SC alternative. While the SC alternative has more vertical deck modes than the GFRP alternative, it has less lateral deck modes than the GFRP alternative in the studied frequency range. The GFRP towers are more flexible in the lateral direction than the SC towers. The GFRP bridge tower attracted less normalized base shear force than the SC bridge towers. However, earthquakes, with peak acceleration of only 0.1 g, and with a variety of frequency content could induce high enough seismic internal forces at the tower bases of the GFRP cable-stayed bridge to govern the structural design of such bridge. Careful seismic analysis, design, and detailing of the tower connections are required to achieve satisfactory seismic performance of GFRP long span bridges.

• 토지주택연구
• /
• 제4권2호
• /
• pp.185-192
• /
• 2013

이 논문에서는 저층 경량건물을 대상으로 고성능 내진을 구현하기 위하여 적용된 복합면진시스템의 적용효과가 비선형해석과 현장실험을 통하여 제시되었다. 이 연구에서 적용된 복합면진시스템은 슬라이딩베어링(sliding bearing)과 적층고무베어링(laminated rubber bearing)을 혼용하는 방법으로 전체 면진시스템의 고유주기를 신장시키는데 있어서 적층고무베어링이 지니는 한계를 극복하기 위한 것이다. 비선형해석결과, 복합면진시스템을 채용하여 설계된 면진건물은 아주 드물게 발생하는 강진에 대해서도 최대응답변위가 허용설계변위 이내이며, 최대응답전단력이 설계지진력 이하이므로 안전하게 유지될 수 있음을 알 수 있었다. 또한 현장실험결과, 면진층의 강성은 설계 등가강성 값의 약 95.8%에 해당하는 값을 나타내 전체 면진시스템의 실제 특성이 설계값과 잘 일치하고 있음을 확인할 수 있었다.

• 한국항공우주학회지
• /
• 제46권2호
• /
• pp.159-166
• /
• 2018

본 연구에서는 소형민수헬기(Light Civil Helicopter, LCH)의 풍동시험에 필요한 축소 로터 블레이드에 대해 내부 구조설계와 동특성 및 하중해석을 수행하였다. 축소로터 풍동시험은 로터 시스템의 공력성능과 소음 특성을 평가하기 위해 수행되므로, 실제 크기의 로터시스템과 동일한 공력 특성을 모사할 수 있도록 축소 블레이드 설계 시 마하 스케일(Mach-scale) 기법을 적용하였다. 마하 스케일 블레이드는 실물 블레이드의 끝단속도(blade tip speed)와 동일한 값을 유지할 수 있도록 로터의 회전속도를 증가시켜야 하며, 블레이드 중량, 단면강성 및 고유진동수 등은 특정한 축소계수(${\lambda}$, scaling factor)를 통해 조정된다. 블레이드 내부의 주요 구성품인 스킨, 스파, 토션박스 등을 설계하기 위해 탄소섬유와 유리섬유 계열의 복합소재를 적용하였으며, 국내에서 수급이 가능한 프리프레그(prepreg) 형태의 복합소재를 적용하였다. 내부구조 설계가 완료된 블레이드에 대해 단면강성을 평가하기 위해 KSec2D 프로그램을 사용하였으며, 회전익 항공기의 통합해석 프로그램인 CAMRADII를 이용하여 축소 블레이드의 하중 분포와 동역학적 특성을 검토하였다.

• Child Health Nursing Research
• /
• 제4권2호
• /
• pp.159-176
• /
• 1998

In effort to conduct comparative study on the caregiving environment of Neonatal Intensive Care Unit(NICU) in both U. S and Korea, this study was been conducted first in the U.S. Purpose : The purpose of this study is to identify the physical environment and direct caregiving practices to lowbirth weight infants in NICU in the US. It also aims to examine the NICU outcome status and behavioral reponses of lowbirth weight infants. Methods : A study design using descriptive and inferential statistics was been conducted through an observational, field method. A sample of 15 preform infants admitted to NICU were recruited for the study. The subjects were those with birth weight between 1,000 gm to 1,500 gm, born at the gestation period of 27 to 33 weeks, and without any chromosomal or other genetic anomalies, major congenital infections, or maternal illness. Thirty minutes observation(three times of ten minutes of continuous observation)of the infant's behavior and physiological status, and an four-hour observation of the physical environment and direct care giving procedures were been conducted on the 3rd and 10th day after birth, and on the day of discharge from the NICU or at 34weeks postconception. The data to be collected were in four areas : the demograghic characteristics of the infants, the physical environment and care giving procedures, the frequency of the infant's designated behavior and physiological response, and NICU outcome variables. A descriptive analysis and Kruskal-Wallis, Pearson r were been applied according to variable characteristics. Results : 1. Mother's mean age was 29.47. The sample consisted of 6 males and 9 females. Mean gestational ages were 29.17 weeks. Mean birth weight was 1236.33g. Mean Apgar scores at one minute were 6.6, and 7.8 at five minutes. 2. The location for the incubator was in the distance from the light, X-ray screens and nursing station, in proximity to side-lamp, telephone and faucet on the third day after birth. The location for the incubator was in the distance from the light and radio on the tenth day and in proximity to nursing station on the day of dischage from the NICU or at 34weeks postconception. 3. Nesting was the most applying aids to the infants. And foot roll, shielding and plastic frame were frequently using by nurses for facilitating well modulated restful posture. 4. There were statistically significant changes in the patterns of physical environment included locating the infant's incubator and bedding, specific aids to self regulation on the 3rd and 10th day after birth, and on the day of discharge from the NICU or at 34weeks postconception. 5. Statistically significant changes were not appeared in the patterns of direct caregiving procedure to the infants included stress inducing or reducing manipulations on the 3rd and 10th day after birth, and on the day of discharge from the NICU or at 34weeks postconception. 6. The stress response of the infants in NICU were significantly reduced as the infants grow older. 7. There were not statistically significant correlation between the physical envronment and the stress responses of the infants in NICU. 8. There were statistically significant correlation between the direct caregiving procedure to the infants and the stress response of the infants in NICU in the second and third observation on the day three. 9. Average weight gain per day from birth to discharge was 38.73g, number of days in the hospital was 42.60, number of days before bottle feeding was 3.6. Postconception age starting bottle feed ing was 31/sup +5/ weeks. Number of days on mechanical ventilator was average 7.64, 11.42 was an average number of days of oxygen need. Conclusion : It, thus, appears that to minimize the sensorymotor stimulation for the low birthweight preterm infant in NICU, manipulation of care giving practices to the babies whatever the stress inducing or reducing procedures, have to be limited in the immediate early stage after birth. And it needed to be reexamine to identify the appropriate and specific physical environment and the patterns of direct caregiving to the low birthweight preform infant as the infants grow older in NICU.

• 한국정밀공학회지
• /
• 제25권10호
• /
• pp.77-83
• /
• 2008

In terms of saving costs, energy and materials, the weight of cars has been gradually reduced by optimizing design of structure, which also gives us good performance. In compliance with this, it should satisfy the lifetime of cars for 25 years under the operation. The purpose of this study is to evaluate the strength of fatigue using date from strain gauges attached carbody and bogie frame. This dynamic stress can be evaluated using S-N curve based on stress amplitude. Modified S-N curve by CORTON-DOLAN is used for more conservative and substantial evaluation. In addition, !he loadings itself of carbody and bogie frame are considered by calculating the rate of the differences which are occurred between empty car and fuiiy occupied car with passengers. Rainflow cycle counting method is applied to arrange the stress data for the modified S-N curve to predict lifetime of the materials. Conclusively the cumulative damages are not only calculated by Miner's Rule, but the safety factors are also determined by Goodman diagram.

• 한국의류학회지
• /
• 제35권8호
• /
• pp.968-981
• /
• 2011

This study examines the effect of the structure of Intarsia and Jacquard knit on mechanical properties of knit fabrics to suggest data for knit design. Intarsia and 7 types of Color Jacquard (Floating Jacquard, Normal Jacquard, Bird's eye Jacquard, Tubular Jacquard, Ladder's back Jacquard, Blister Jacquard, and Transfer Jacquard) were used. The samples with a gauge of 14 were knitted using 100% wool 2/48's yarn by Shima Seiki SIG computer knitting machine. The Objective Hand was measured by KES-FB system and HV and THV were calculated by the formula of KN-402-KT and KN-301-winter respectively. The results showed that Intarsia and Floating Jacquard are thin, flexible and light, Bird's eye Jacquard is slick, flat and slim, Tubular Jacquard is stiff and undrapable, Ladder's back Jacquard is difficult in shearing deformation and relatively bulky, Blister Jacquard is thickest and transfer jacquard is uneven in surface contour. The selection of proper structure is important for the knit apparel production since the thickness and weight of knit determine the amount of yarn needed and consequently the production cost. The hands of Ladder's back Jacquard and Tubular Jacquard are superior to those of other structures. Intarsia and Floating Jacquard which are thin, light and flexible seem to be good structures for designs showing a body silhouette whereas, Bird's eye Jacquard, Tubular Jacquard and Blister Jacquard (which are thick, heavy, and stiff) are suitable for a boxy silhouette.