• 한국강구조학회 논문집
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• 제17권6호통권79호
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• pp.717-726
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• 2005

본 연구에서는 중심 축하중을 받는 H형강 기둥의 베이스플레이트의 지압응력의 분포와 설계에 대하여 조사하였다. 일반적으로 강구조 기둥의 베이스플레이트는 지압응력이 등분포하다고 가정하고 그 크기와 두께를 결정한다. 그러나 중심 축하중이 적으면 베이스플레이트의 크기도 작아지고 두께도 얇아지며 지압응력은 등분포하게 되지 않으며 기둥단면의 하부에 집중된다. 본 연구에서는 실험적 방법과 해석적 방법으로 지압응력의 분포에 대하여 조사하고 그 결과를 이용하여 설계법을 검토하였다. 7개의 H형강 기둥 베이스플레이트 시험체를 제작하여 실험을 수행하였다. 또한 유한요소해석프로그램인 ANSYS를 이용하여 베이스플레이트의 지압응력의 분포를 해석하였다. 연구결과 지압응력은 기둥단면의 하부에 집중되고 등분포하지 않아 강구조 한계상태 설계기준에서의 등분포한 지압응력의 가정은 적정치 않았다.

• 정보과학회 논문지
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• 제41권10호
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• pp.762-773
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• 2014

시맨틱 웹상에서 RDFS로 표현된 데이터의 사용 증가로 인하여, 대용량 데이터의 추론에 대한 많은 요구가 생겨나고 있다. 많은 연구자들은 대용량 온톨로지 추론을 수행하기 위해서 하둡과 같은 고가의 분산 프레임워크를 활용한다. 그러나, 적절한 사이즈의 RDFS 트리플 추론을 위해서는 굳이 고가의 분산 환경 시스템을 사용하지 않고 단일 머신에서도 논리적 프로그래밍을 이용하면 분산 환경과 유사한 추론 성능을 얻을 수 있다. 본 논문에서는 단일 머신에 논리적 프로그래밍 방식을 적용한 대용량 RDFS 추론 기법을 제안하였고 다중 머신을 기반으로 한 분산 환경 시스템과 비교하여 2억개 정도의 트리플에 대한 RDFS 추론 시스템을 적용한 경우 분산환경과 비슷한 성능을 보이는 것을 실험적으로 증명하였다. 효율적인 추론을 위해 온톨로지 모델을 세부적으로 분리한 메타데이터 구조와 대용량 트리플의 색인 방안을 제안하고 이를 위해서 전체 트리플을 하나의 모델로 로딩하는 것이 아니라 각각 온톨로지 추론 규칙에 따라 적절한 트리플 집합을 선택하였다. 또한 논리 프로그래밍이 제공하는 Unification 알고리즘 기반의 트리플 매칭, 검색, Conjunctive 질의어 처리 기반을 활용하는 온톨로지 추론 방식을 제안한다. 제안된 기법이 적용된 추론 엔진을 LUBM1500(트리플 수 2억개) 에 대해서 실험한 결과 166K/sec의 추론 성능을 얻었는데 이는 8개의 노드(8 코아/노드)환경에서 맵-리듀스로 수행한 WebPIE의 185K/sec의 추론 속도와 유사함을 실험적으로 증명하였다. 따라서 단일 머신에서 수행되는 본 연구 결과는 트리플의 수가 2억개 정도까지는 분산환경시스템을 활용하지 않고도 분산환경 시스템과 비교해서 비슷한 성능을 보이는 것을 확인할 수 있었다.

• 한국산학기술학회논문지
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• 제21권6호
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• pp.35-40
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• 2020

도상 자갈층은 열차하중을 분산하고 지지하는 중요한 역할을 수행하나, 큰 공극으로 인하여 열차 동하중 작용시 침하가 발생하여 지속적인 유지보수가 필요하다. 본 논문에서는 특정한 형상의 인공자갈 3종류 (정사각 형상, 테트라 포드 형상, 육각 형상) 를 혼합한 도상 자갈층을 2 차원 개별 요소 해석법을 이용하여 모델링하고, 열차 동하중에 의한 도상 층의 침하 특성을 평가하기 위하여 침목에 의한 반복 재하 시험을 실시하였다. 동 해석 결과 침목 하부에서 작은 힘의 전달경로가 형성된 테트라 포드형의 인공 자갈이 포함된 도상 층에서 침하가 가장 작게 발생하였다. 또한, 도상층 내 접촉력 분포로부터 오목 형상을 갖는 테트라 포드 형상을 포함한 인공 자갈 혼합 도상에서 힘의 다중 전달 경로를 형성하기 쉬우며, 이를 통하여 도상 층으로 전달된 열차 하중이 보다 다양한 경로로 균등하게 분산될 수 있는 것을 확인하였다. 이와 같은 결과로부터 반복 열차 하중 재하 시 오목 형상의 인공 자갈이 혼합된 도상 층에서 훨씬 효과적으로 침하 발생을 저감시킬 수 있다는 것을 알 수 있었다. 도상 층에서의 이와 같은 침하 저감 효과는 유지보수를 절감할 수 있는 자갈궤도 구조에 대한 가능성을 보여준다.

• Structural Engineering and Mechanics
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• 제7권5호
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• pp.513-525
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• 1999

This paper presents exact close form solutions of plastic limit loads of a clamped circular plate under uniformly distributed load with different loading radii. A unified yield criterion, which includes a family of piecewise linear yield criteria and the commonly adopted yield criteria such as the Tresca criterion and the maximum principal deviatoric stress criterion or the twin shear stress criterion that are its special cases, and the Mises criterion can be approximated by it, is employed in the analysis. The plastic limit loads, moment fields and velocity fields of the clamped circular plate are calculated based on the unified yield criterion. The influences of the yield criteria, the edge effects and the loading radius on the plastic limits of the clamped circular plate are investigated. Analytical results are calculated and compared. The exact close form solutions presented in this paper provide efficient approaches for obtaining plastic limit loads and the corresponding moments and velocities of the clamped circular plates. The previously derived solutions based on the Tresca and the Mises criteria are its special cases.

• The Korean Journal of Ecology
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• 제19권5호
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• pp.487-496
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• 1996

This study was conducted to investigate pollutant loading, were quality and plant distribution of 8 streams which are tributaries of the Youngsan River. The nitrate reductase activity (NRA) and nutrient removall capacity of the most frequently occurring aquatic plants on streamside were also determined. As a result, the pollutant loading appeared to be correlated with the area of watershed, while the water quality was related to the land use pattern of each steam. The aquatic plants were distributed differently among the streams; Hydrilla verticillata - Potamogeton crispus, Numphoides peltata - Hydrocharis dubia and Polygonum thunbergii - Phragmites japonica were dominant at the Orye Chon, Jungan Chon, Whangryong River and Jiseok Chon, while potamogeton crispus - Lemma paucicostata, Zizania latifolia - Phragmites communis were dominant at the Youngam Chon and Munpyeong Chon. Persicaria hydropiper and Echinochloa crus-galli var. oryzicola were dominant at Kwangju Chon which was polluted with domestic wastewater. >From the measurement of leaf NRA for dominant species, the highest value of NRA was shown by the Polygonum thunbergii, followed by Oenanthe javanica > Phragmites communis > Zizania latifolia > Lemma paucicostata. The highest nitrogen and phosphorus removal capacity was found in Phragmites communis.

• 대한치과기공학회지
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• 제31권1호
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• pp.7-15
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• 2009

Purpose: This study was to propose the clear understanding for stress distribution of supporting bone by use of staggered buccal offset tripodal placement of fixtures of posterior 3 crown implant partial dentures. We realized posterior 3 crown implant fixed partial dentures through finite element modeling and analysed stress effect of implant arrangement location to supporting bone under external load using finite element method. Method: To understand stress distribution of 3 crown implant fixed partial dentures which have 2 different arrangement by finite element analysis. In each model, for loading condition, we applied $45^{\circ}$ oblique load to occlusal surface of crown and applied 100 N for 3 crown individually(total 300 N) for imitating possible oral loading condition. at this time, we calculated Von Mises stress distribution in supporting bone through finite element method. Result: When apply $45^{\circ}$ oblique load to in-line arrangement model, maximum stress result for 100 N for each 3 crown 47.566MPa. In tripodal placement, result for 1mm buccal offset tripodal placement implant model was maximum distributed load 51.418MPa, so result was higher than in-line arrangement model. Conclusion: In stress distribution result by placement of implant fixture, the most effective structure was in-line arrangement. The tripodal placement does not effective for stress distribution, gap cause more damage to supporting bone.

• 대한기계학회논문집B
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• 제20권7호
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• pp.2337-2346
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• 1996

One of the most useful method for increasing combustion loading of premixed flame is to strengthen the turbulent intensity of unburned mixture. It produces an important information to a design of efficient combustion equipment that analysing microstructure of strong turbulence premixed flame. The flame structure and characteristics are depend on the turbulence of unburned mixture. Therefore, to strengthen the turbulent intensity of unburned mixture make flame scale small and accomplish efficient combustion. We measured the velocity of local flame front movements, local eddy radius and local reaction zone thickness quantitatively with increasing turbulent intensity of unburned mixture. We researched the microstructure of flame using ion currents that react sensitively in the reaction zone. Consequently, the velocity of local flame front movements is depend on the velocity of unburned mixture and local eddy scale is to be small with increasing turbulent intensity. But there is no change in local reaction zone thickness with turbulence.

• Steel and Composite Structures
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• 제36권2호
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• pp.229-247
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• 2020

This study analyzed stresses in concrete and its reinforcement, computing the additional loading transferred by concrete creep. The loading varied from zero, structure exclusively under its self-weight, up to the critical buckling load. The studied structure was a real, tapered, reinforced concrete pole. As concrete is a composite material, homogenizing techniques were used in the calculations. Due to the static indetermination for determining the normal forces acting on concrete and reinforcement, equations that considered the balance of forces and compatibility of displacement on cross-sections were employed. In the mathematical solution used to define the critical buckling load, all the elements of the structural dynamics present in the system were considered, including the column self-weight. The structural imperfections were linearized using the geometric stiffness, the proprieties of the concrete were considered according to the guidelines of the American Concrete Institute (ACI 209R), and the ground was modeled as a set of distributed springs along the foundation length. Critical buckling loads were computed at different time intervals after the structure was loaded. Finite element method results were also obtained for comparison. For an interval of 5000 days, the modulus of elasticity and critical buckling load reduced by 36% and 27%, respectively, compared to an interval of zero days. During this time interval, stress on the reinforcement steel reached within 5% of the steel yield strength. The computed strains in that interval stayed below the normative limit.

• Structural Engineering and Mechanics
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• 제32권4호
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• pp.549-561
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• 2009

As it is known, laminated composite materials are increasingly used in many technological applications, and in some instance, cutouts must be made into laminated panels for practical reasons, changing the stress distribution. The present study deals with the determination of the stress concentration factor that holes of square shape cause in an orthotropic plate subjected to distributed in - plane loading. Square holes of rounded corners in a rectangular plate are considered, and the effect of different combinations of axial and tangential forces applied to its middle plane at the external edges, is studied. The mutually perpendicular axes, which define the principal axes of orthotropy, are assumed in many different directions referred to the sides of the plate. Numerical experiments by means of a finite element code is performed, evaluating the influence of the fiber orientation with respect to the edges of the plate and the characteristics of the orthotropic materials since such structures do not exhibit easily predictable behavior.

• 대한기계학회논문집B
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• 제27권6호
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• pp.701-713
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• 2003

The BEM is a highly efficient method in the sense of economical computation. However, boundary integration is not easy for the complex geometry and moving surface, e.g. a rotating blade. Thus, Kirchhoff surface is designed in an effort to overcome the difficulty resulting from complex boundary conditions. A Kirchhoff surface is a fictitious surface which envelopes acoustic sources of main concern. Acoustic sources may be distributed on each Kirchhoff surface element according to their acoustic characteristics. In this study, an axial fan is assumed to have unsteady loading noise as a dominant source. Dipole sources can be modeled to solve the FW-H equation. Acoustic field is then computed by determining Kirchhoff surface on which near-field is implemented, to analyze the effect of Kirchhoff surface on it. The optimal shape and the location of Kirchhoff surface are discussed by comparing with experimental data acquired in an anechoic chamber.