• International Journal of Automotive Technology
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• 제2권1호
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• pp.1-7
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• 2001

This paper presents further investigation into the effect of over-expansion cycle in a spark-ignition engine. On the basis of the results obtained in previous studies, several combinations of late-closing (LC) of intake valve and expansion ratio were tested using a single-cylinder production engine. A large volume of intake capacity was inserted into the intake manifold to simulate multi-cylinder engines. With the large capacity volume, LC can decrease the pumping loss and then increase the mechanical efficiency. Increasing the expansion ratio from 11 to 23.9 with LC application can produce about 13% improvement of thermal efficiency which was suggested to be caused by the increased cycle efficiency. The decrease of compression ratio from 11 to 5.5 gives little effect on the thermal efficiency if the expansion ratio could be kept constant. Thus, the expansion ratio is revealed to be a determining factor for cycle efficiency, while compression ratio is no more important, which suggests the usefulness of controlling the intake charge with intake valve closure timing. These were successfully explained by simple thermodynamic calculation and thus the mechanism could be verified by the estimation.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제37회 추계학술대회논문집
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• pp.985-987
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• 2011

본 논문은 파생형엔진의 설계를 위해 시동시간 예측모델을 개발하는 경우를 다루었다. 파생형엔진 설계를 위해 압축기/터빈의 특성맵을 새로 제안한 Modified Pump Scaling Law(MPS)방법을 사용하여 시동모델링에 필요한 아이들 이하 회전수(sub idle rpm) 영역으로 확장시켰고, 기준엔진의 손실특성에서 압력/온도와 엔진별 특성차이를 고려한 파생형엔진의 손실모델을 도출하였다. 이러한 특성을 반영한 파생형엔진의 시동시간 예측모델은 시험결과와 비교하여 비교적 양호한 결과를 나타내었다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.951-956
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• 2008

Development of a silencer to Reduce Noise of Cross Talking in Apartment & Stores and air conditioning to fan Composite silencer application a specific of resonant type and expansion type, design possibility at reduction frequency. This silencer test result develop reduce 20dB of specification frequency. Pressure loss 2mmAq. This silencer is special of brief structure and possibility disjoint and joint, simple installation and maintenance.

• 소음진동
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• 제3권3호
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• pp.271-278
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• 1993

Acoustic characteristics of silencer system are affected by various geometric parameters such as cross sectional geometry, size of chamber, and location of inlet-outlet port. It is impossible to obtain exact solutions of the equations of acoustic wave propagation except few simple cases. So, we resort to numerical techniques to analyze performance of acoustic system. In this work, finite element formulation has been obtained to predict transmission loss of an arbitrary 3-dimensional muffler in the presence of mean flow of low mach number. The effect of the degree of the ellipticity of expansion chambers on the transmission loss has been studied using the resulting finite element equation.

• 한국농공학회지
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• 제34권E호
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• pp.60-69
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• 1992

The research significance of the paper is to identify the major properties of synthetic lightweight concrete that are affected by ASR expansion and to determine the extent and magnitude of the loss in these properties. Emphasis is also given to the use of non-destructive testing techniques ; Such as dynamic modulus of elasticity and ultrasonic pulse velocity, to examine whether these methods could be used to identify the initiation of expansion and the internal structural damage caused by ASR.

• 정보처리학회논문지C
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• 제9C권4호
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• pp.531-542
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• 2002

입력과 출력에 버퍼를 갖는 ATM 교환기의 셀 폐기 방법은 기존의 귀환(Backpressure)모드와 손실(Queueloss)모드가 있으며, 최근에는 두 모드의 단점을 보완한 하이브리드(Hybrid)모드가 제안되었다. 하이브리드모드는 목적하는 출력 버퍼와 입력 버퍼가 모두 포화일 경우에만 셀을 폐기하는 방식이다. 본 논문에서는 유니폼 트래픽하에서 Output-port expansion 기법을 사용한 귀환 손실 모드 및 하이브리드모드 하에서의 셀 손실률과 셀 지연을 성능 비교 분석한다 Output-port expansion 기법은, 한 타임 슬롯동안에 입력포트 당 하나의 셀만 교환되며, 만약 하나 이상의 셀들이 같은 출력포트로 향하고자 하면, 최대 교환되는 셀 수를 K(Output-port expansion ratio)개로 제한하는 방식이다. 셀 손실률을 비교 분석한 결과, 이전의 연구에서와는 달리 로드 0.9를 기점으로. 0.9이하의 로드에서는 하이브리드 모드가, 0.9 이상의 로드에서는 손실모드가 가장 낮은 셀 손실률을 보인다. 셀 지연을 비교 분석한 결과, 한 개의 교환기 성능 분석에서는 셀 손실로 인한 재전송(retransmission)을 고려하지 않는 관계로, 예상한 바와 같이, 로드가 많아질수록 셀 손실률이 높은 귀환모드가 K를 높일수록 다른 모드에 비해 낮은 셀 지연을 보였다.

• 대한치과교정학회지
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• 제53권4호
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• pp.264-275
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• 2023

Objective: To investigate the effects of maxillary orthodontic expansion on the alveolar bone tissue in adult patients treated with aligners by using cone-beam computed tomography. Methods: Thirty patients (22 females and 8 males; mean age: 36.3 years) were treated with Invisalign^® aligners. Cone-beam computed tomography and digital models were obtained before (T0) and after (T1) upper arch expansion. The bone thicknesses in the cervical, middle, and apical areas of the incisors, canines, premolar, and first molars were buccally and palatally measured, totaling 96 areas and 2,880 measurements. The buccolingual inclinations and transverse measurements of the teeth were obtained from digital models to correlate them with the bone changes. The statistical tests used were Student's t-test, analysis of variance, and Pearson's correlation tests (p < 0.05). Results: From the 96 areas evaluated, 84 revealed an increase or stability in the alveolar bone thickness and twelve displayed significant bone loss. Bone changes did not correlate with the tooth inclination and transverse measurements. Conclusions: Within the limitation of the present study, mild levels of upper arch expansion obtained with Invisalign^® aligners in adult patients did not result in any clinically significant loss of alveolar bone thickness.

• 콘크리트학회논문집
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• 제13권3호
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• pp.213-220
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• 2001

콘크리트에 폐유리의 사용은 알칼리 실리카 반응(ASR)의 팽창으로 균열과 강도저하를 일으킬 수 있다. 본 연구에서는 폐유리의 혼입률과 색상(갈색, 녹색) 및 폐유리로 인해 발생되는 ASR팽창을 저감시키기 위해 섬유의 종류(강섬유, 폴리프로필렌섬유)와 섬유혼입률에 따른 ASR팽창과 강도특성을 분석하였다. 연구결과 녹색의 폐유리가 팽창량이 비교적 작기 때문에 갈색의 폐유리보다 더욱 유용하며, ASTNM C 1260의 시험에 있어서 폐유리의 혼입으로 인한 퍼시멈(pessimum)량은 발견되지 않았다. 또한, 폐유리와 함께 섬유의 혼입은 폐유리의 실리카와 시멘트 페이스트의 알칼리 사이의 ASR로 인한 팽창과 강도 저하를 저감시키는데 효과적인 것으로 나타났다. 특히 폐유리 혼입률 20%에 대해서 강섬유를 1.5vol.% 혼입하였을 경우 팽창은 40%까지 감소하였으며 휨강도는 폐유리만을 혼입한 것(8$0^{\circ}C$ $H_2O$ 양생)에 비해 110%의 강도발현을 나타내었다.

• Journal of Advanced Marine Engineering and Technology
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• 제23권6호
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• pp.748-754
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• 1999

The acoustic performance of reactive type single expansion chamber can be calculated theoretically by plane wave theory. But higher order modes should be considered to widen the frequency range. Munjal has suggested the method for analyzing the acoustic properties of simple expansion chamber with taking into consideration of higher order mode of inlet/outlet. But his method cannot predict the acoustic properties exactly when the dimensions of inlet/outlet and expansion chamber have not integer multiples. In this paper the new method was suggested to overcome the shortcomings of Munjal's method The predictions by this method were also compared with those by the finite element method.

• 설비공학논문집
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• 제13권2호
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• pp.96-105
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• 2001

R410a which is one of HFC refrigerants is being considered to be a promising replacement for R22 widely used in domestic air conditioners. The rolling piston type rotary compressors for R410a have lower energy efficiency than those for R22 because of the high pressure difference between a suction chamber and a discharge chamber in the compression mechanism. in addition, the re-expansion gas loss of the rotary compressor for R410a which occurs a ta clearance volume in a discharge port becomes larger than that for R22 due to high density of R410a refrigerant. Therefore, Pressure-Volume analyses for various design parameters of a discharge system were carried out to improve efficiency of a R410a rotary compressor. The results such as performance dta, over-compression loss, and re-expansion loss were acquired by P-V analyses and analyzed quantitatively. As a conclusion, the optimal specifications of several design parameters of a discharge system were obtained by analyzing P-V diagrams.