• 제목/요약/키워드: Direct expansion

검색결과 401건 처리시간 0.026초

직접 수치 모사법을 이용한 섬유 강화 복합재료의 열팽창계수 예측 (Prediction of Thermal Expansion Coefficients for Fiber-Reinforced Composites by Direct Numerical Simulation)

  • 남윤식;오민환;김광식;조진연
    • 한국항공우주학회지
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    • 제35권9호
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    • pp.771-777
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    • 2007
  • 본 논문에서는 직접 수치 모사 기법을 이용해 섬유 강화 복합재료의 열팽창계수를 예측하였다. 직접 수치 모사 기법을 통해 구한 열팽창계수 예측치와 실험치의 비교를 통해 본 논문에서 제안한 직접 수치 모사 기법을 이용하면 인위적인 가정을 최소화하면서 기존의 방법과 유사하게 복합재료 열팽창계수를 예측할 수 있음을 확인하였다. 또한 섬유 체적비 변화에 따른 열팽창계수의 변화를 예측하고 그 경향성을 고찰하였다.

B-spline 곡선을 power 기저형태의 구간별 다항식으로 바꾸는 Direct Expansion 알고리듬 (A Direct Expansion Algorithm for Transforming B-spline Curve into a Piecewise Polynomial Curve in a Power Form.)

  • 김덕수;류중현;이현찬;신하용;장태범
    • 한국CDE학회논문집
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    • 제5권3호
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    • pp.276-284
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    • 2000
  • Usual practice of the transformation of a B-spline curve into a set of piecewise polynomial curves in a power form is done by either a knot refinement followed by basis conversions or applying a Taylor expansion on the B-spline curve for each knot span. Presented in this paper is a new algorithm, called a direct expansion algorithm, for the problem. The algorithm first locates the coefficients of all the linear terms that make up the basis functions in a knot span, and then the algorithm directly obtains the power form representation of basis functions by expanding the summation of products of appropriate linear terms. Then, a polynomial segment of a knot span can be easily obtained by the summation of products of the basis functions within the knot span with corresponding control points. Repeating this operation for each knot span, all of the polynomials of the B-spline curve can be transformed into a power form. The algorithm has been applied to both static and dynamic curves. It turns out that the proposed algorithm outperforms the existing algorithms for the conversion for both types of curves. Especially, the proposed algorithm shows significantly fast performance for the dynamic curves.

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Direct position tracking method for non-circular signals with distributed passive arrays via first-order approximation

  • Jinke Cao;Xiaofei Zhang;Honghao Hao
    • ETRI Journal
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    • 제46권3호
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    • pp.421-431
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    • 2024
  • In this study, a direct position tracking method for non-circular (NC) signals using distributed passive arrays is proposed. First, we calculate the initial positions of sources using a direct position determination (DPD) approach; next, we transform the tracking into a compensation problem. The offsets of the adjacent time positions are calculated using a first-order Taylor expansion. The fusion calculation of the noise subspace is performed according to the NC characteristics. Because the proposed method uses the signal information from the previous iteration, it can realize automatic data associations. Compared with traditional DPD and two-step localization methods, our novel process has lower computational complexity and provides higher accuracy. Moreover, its performance is better than that of the traditional tracking methods. Numerous simulation results support the superiority of our proposed method.

뉴우먼 확장법에 의한 3차원 트러스의 확률유한요소해석 (Stochastic Finite Element Aalysis of Space Truss by Neumann Expansion Method)

  • 정영수;김기정
    • 한국전산구조공학회:학술대회논문집
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    • 한국전산구조공학회 1993년도 봄 학술발표회논문집
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    • pp.117-124
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    • 1993
  • The Neumann Expansion method has been used for evaluating the response variability of three dimensional truss structure resulting from the spatial variability of material properties with the aid of the finite element method, and in conjunction with the direct Monte Carlo simulation methods. The spatial variabilites are modeled as three-dimensional stochastic field. Yamazaki 〔1〕 has extended the Neumann Expansion method to the plane-strain problem to obtain the response variability of 2 dimensional stochastic systems. This paper presents the extension of the Neumann Expansion method to 3 dimensional stochastic systems. The results by the NEM are compared with those by the deterministic finite element analysis and by the direct Monte Carlo simulation method

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대형 CNG기관의 직접분사화에 의한 희박한계확장 (A study on expansion of lean burn limit with direct injection of the heavy-duty CNG engine)

  • 박정일;정찬문;노기철;이종태
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2007년도 춘계학술대회B
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    • pp.3282-3287
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    • 2007
  • Lean combustion is one of the most promising method for increasing engine efficiency and reducing the exhaust emission from SI gas engines. Due to the possibility of partial burn and misfire, however, under lean burn operation, stable flame kernel formation and fast burn rate are needed to guarantee a successful subsequent combustion. Experiment data were obtained on a single-cylinder CNG fueled SI engine to investigate the effect of direct injection, spark timing and variation of injection timing. Experimental results show that lean burn limit is ${\lambda}$=1.3 with port injection, and expansion of lean burn limit ${\lambda}$=1.4 with direct injection method, due to increase of turbulence intensity in cylinder and stratified charge. Combustion duration in lean region is improved by using the variation of injection timing.

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LNG냉열발전시스템에 있어서 직접팽창 및 유기랭킨사이클의 운전성능평가 (Performance Analysis of Direct Expansion and Organic Rankine Cycle for a LNG Cold Power Generation System)

  • 조은비;정문;황인주;강춘형
    • 대한기계학회논문집 C: 기술과 교육
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    • 제3권1호
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    • pp.55-62
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    • 2015
  • 국내에서는 천연가스 공급국가와 수입국가의 거리, 공급시설 투자, 국가 간 협력 등 여러 가지 제약에 따라 액화천연가스를 수입하고 있다. 수입한 액화천연가스를 수요처로 공급하기 위해 해수를 이용한 기화과정에서 냉열이 낭비되고 있다. 본 연구에서는 이러한 냉열을 효율적으로 활용하는 냉열발전시스템에서 직접팽창과 유기랭킨사이클 방식의 운전성능을 비교 연구하였다. 시뮬레이션은 Aspen HYSYS를 이용하여 수행하였으며, 운전성능 분석은 T-S 선도 및 시스템 성능 해석을 토대로 비교분석하였다. 시뮬레이션 결과로부터 발전시스템의 운전 측면에서는 유기랭킨사이클 방식이 유리한 것을 확인하였다.

직접시공 확대의 영향 분석 및 직접시공의무제도 적용을 위한 대응방안 제언 (Analysis of the Impact of the Expansion of Direct Construction Works and Suggestions on the Application)

  • 이미성;김시연;유일한;한주연;손정욱
    • 한국건설관리학회논문집
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    • 제22권6호
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    • pp.15-23
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    • 2021
  • 건설산업 혁신방안의 일환으로 건설생산체계가 개편됨에 따라 직접시공이 확대되고 있는 추세이다. 본 연구는 이러한 추세에 따라 직접시공 확대의 영향 및 문제점을 건축관련 업계의 입장과 외국 사례 조사를 통하여 분석하고 직접시공 확대 조치에 따른 영향을 다양한 측면에서 진단하여 직접시공의무제도를 바람직하게 적용하기 위한 대응방안을 제언하였다. 또한, 각 대안에 대하여 정책/행정 및 건축 분야 전문가 인터뷰를 통하여 효과 및 문제점을 평가하였다. 본 연구에서 도출된 직접시공의무제도 확대 및 효율화를 위한 대응방안은 발주자의 재량권 부여, 공사규모에 따른 차별화, 건설보증시스템 활용, 탄력적 작업반장제 도입의 4가지로, 전문가 인터뷰 결과 모두 직접시공 확대에 직간접적으로 긍정적 영향을 줄 것으로 평가되었다. 본 연구는 직접시공 현황을 조사하여 직접시공의무제도 적용에 있어 기초자료를 제공하며 또한 적절한 직접시공의무제도 적용을 위한 대응방안 도출과 이에 대한 전문가 평가를 통하여 직접시공 확대를 위한 방향을 제시함으로써 결과적으로 합리적 직접시공의무제도 운영을 통한 건설기업과 현장의 생산성 향상 및 효율화에 기여할 것으로 기대된다.

직접순환식 수직밀폐형 지열원 열펌프의 연간 운전성능 평가 (Evaluation of the Annual Performance of the Direct Expansion Vertical Closed-Loop Ground Source Heat Pump)

  • 김민성;우정선;백영진;장재철;김지영;라호상
    • 한국태양에너지학회:학술대회논문집
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    • 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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    • pp.534-542
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    • 2012
  • Vertical closed-loop ground source heat pump systems(GSHP) have been installed widely in Korea since it can extract moderate temperature level of geothermal heat in a small area. As a ground heat exchanger, a vertical closed-loop type with brine circulation is mostly preferred since it is simple and less harmful to ground environment. However, it requires a secondary heat exchange loop between the refrigerant in a heat pump and the brine. By adding a geothermal heat exchanger in the secondary heat exchange loop, circulation pumps should be attached and the temperature difference between refrigerant and ground is increased, which are important parts of performance degradation. In this paper, annual and seasonal performances of direct expansion(DX) geothermal heat pump were estimated mathematically as an alternative of classical indirect geothermal heat pump based on the annual performance evaluation. As a result, DX geothermal heat pump showed 43% higher annual performance than the classical U-tube geothermal heat pump.

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주거용 직접순환식 수직밀폐형 지열원 열펌프의 연간 운전성능 평가 (Annual Performance Evaluation of Direct Expansion Vertical Closed-Loop Ground Source Heat Pump for Residential Application)

  • 김민성;백영진;라호상
    • 한국태양에너지학회 논문집
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    • 제32권3호
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    • pp.114-122
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    • 2012
  • Vertical closed-loop ground source heat pump systems(GSHP) have been installed widely in Korea since it can extract moderate temperature level of geothermal heat in a small area. As a ground heat exchanger, a vertical closed -loop type with brine circulation is mostly preferred since it is simple and less harmful to ground environment. However, it requires a secondary heat exchange loop between the refrigerant in a heat pump and the brine. By adding a geothermal heat exchanger in the secondary heat exchange loop, circulation pumps should be attached and the temperature difference between refrigerant and ground is increased, which are important parts of performance degradation. In this paper, annual and seasonal performances of direct expansion(DX) geothermal heat pump were estimated mathematically as an alternative of classical indirect geothermal heat pump based on the annual performance evaluation. As results, DX geothermal heat pump showed 43% higher annual performance than the classical U-tube geothermal heat pump.