• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.864-869
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• 2003

The purpose of this paper is to investigate the free vibration characteristics of tapered beams with translational and rotational springs and point masses at the ends. The beam model is based on the classical Bernoulli-Euler beam theory which neglects the effects of rotatory inertia and shear deformation. The governing differential equation for the free vibrations of linearly tapered beams is solved numerically using the corresponding boundary conditions. Numerical results are compared with existing solutions by other methods for cases in which they are available. The lowest four natural frequencies are calculated over a range of non-dimensional system parameters.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3495-3501
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• 2013

The cross-sections of continuous multi-span beams are sometimes suddenly increased or stepped at the interior supports of continuous beams to resist high negative moments. This paper investigates inelastic lateral-torsional buckling of monosymmetric stepped I-beams subjected to pure bending. A three-dimensional finite-element program ABAQUS and a regression program were used to analytically develop new design equation. The flange thickness ratio, flange width ratio and stepped length ratio were considered as parameters of this study. The combined effects of residual stresses and geometric imperfection on inelastic lateral-torsional buckling of beams are considered. The proposed solution can be easily used to calculation for inelastic lateral torsional buckling strengths of monosymmetric beams with doubly stepped cross sections and to develop new design equations for inelastic lateral-torsional buckling resistances of stepped beams.

• Journal of Korean Society of Forest Science
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• v.84 no.2
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• pp.186-197
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• 1995

Site-specific allometric equations relating aboveground tree component biomass and leaf area to tree diameter, basal area, sapwood cross-sectional area and sapwood volume were developed using the destructive harvesting method for Pinus rigida Mill., Larix leptolepis Gordon, and Quercus serrata Thunb. stands in Yangpyeong, Kyonggi Province. There were significantly strong correlations between aboveground tree component biomass or leaf area and diameter at breast height (DBH), basal area, sapwood area and sapwood volume. For a similar diameter tree, the three species had a similar stem wood biomass. However, carbon allocation patterns to stem bark, foliage, branch and total aboveground biomass differed among the three species. Specific leaf area and the ratio of leaf area to sapwood cross-sectional area of the three species were significantly different. Allometric equations seemed To be related to leaf habit or leaf longevity. To elucidate the effect of leaf habit or leaf longevity on allometry and canopy characteristics clearly, more intensive studies are needed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.5
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• pp.1020-1025
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• 2009

This study investigates elastic lateral-torsional buckling(LTB) of monosymmetric doubly stepped I-beams subjected to pure bending based on finite element analysis(FEA). The results from the FEA are used for new design stepped equation, Cst. The equations are compared with the results from the FEA. The comparison indicates that the new equation provides a good relation with the FEA results. The maximum difference between two results is of 11%. The new equation could be easily used to calculate the elastic lateral-torsional buckling moment resistance of monosymmetric stepped I-beams and to expand the new equation for developing LTB equations of monosymmetric stepped beams subjected to general loading conditions such as a concentrated load, distributed load, or a seres of concentrated load.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.79-86
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• 2005

This paper deals with the static optimal shapes of simple beams which are subjected to a vertical point load. The area and second moment of inertia of the regular polygon cross-section of the tapered beams are determined, which have always same volume and same length for the parabolic taper. The differential equation governing the elastic curve is derived using the small deflection theory and solved numerically. By using the numerical results of deflections, rotations and bending stresses of such beams, the optimal shapes, namely, optimal section ratios, of the beams subjected to a single point load according to variation of load position parameters are determined and presented in the figures. Examples of the static optimal shapes for beams with a single load and multiple loads are reported. The design process of this study can be used directly for the minimum weight design of simple beams.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.3
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• pp.223-233
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• 2012

This paper deals with free vibrations of the tapered Timoshenko beam with constant volume, in which both the rotatory inertia and shear deformation are included. The cross section of the tapered beam is chosen as the regular polygon cross section whose depth is varied with the parabolic function. The ordinary differential equations governing free vibrations of such beam are derived based on the Timoshenko beam theory by decomposing the displacements. Governing equations are solved for determining the natural frequencies corresponding with their mode shapes. In the numerical examples, three end constraints of the hinged-hinged, hinged-clamped and clamped-clamped ends are considered. The effects of various beam parameters on natural frequencies are extensively discussed. The mode shapes of both the deflections and stress resultants are presented, in which the composing rates due to bending rotation and shear deformation are determined.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.2
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• pp.111-117
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• 2017

In this paper, a local deformation effect in thin-walled box beams is investigated via a finite element modal analysis. The analysis is carried out for single-cell and multi-cell box beam configurations. The single-cell box beam with and without a neck, which mimics a simple wind-turbine blade, is analyzed first. The results obtained by shell elements are compared to those of one-dimensional(1D) beam elements. It is observed that the wall thickness plays a crucial role in the natural frequencies of the beam. The 1D beam analysis deviates from the shell analysis when the wall thickness is either thin or thick. The shell modes(local deformations) are dominant as it becomes thin, whereas the shear deformation effects are significant as it does thick. The analysis is extended to the single-cell box beam with a neck, in which the shell modes are confined to near the neck. Finally the multi-cell box beam with a taper, which is quite similar to real wind-turbine blade configuration, is considered to investigate the local deformation effect. The results reveal that the 1D beam analysis cannot match with the shell analysis due to the local deformation, especially for the lagwise frequencies. There are approximately 5~7% errors even if the number of segments is increased.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.2033-2037
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• 2009

호소내의 흐름은 중력의 영향을 받는 하천의 흐름과는 달리 열수지에 의한 밀도류 및 바람 등에 영향을 크게 받아 특유의 유동특성을 나타낸다. 본 연구에서는 EFDC(Environmental fluid Dynamics Code, 미국 버지니아 해양연구소 개발) 모델을 이용하여 호소 내 수치모의를 실시하였다. 복잡한 지형을 형성하고 있는 호수 내의 유동특성의 정밀도를 향상시키기 위해서는, 흐름특성을 고려한 grid작성이 중요하다. 본 연구에서는 1:3000, 1:5000 축척의 수치지도를 이용하여 장흥호의 하상단면 값을 추정하였으며, GIS를 이용하여 (${\Delta}x$, ${\Delta}y$)=100m로 DEM을 생성하였다. 그리고 구성된 DEM값을 이용하여 정밀도가 높은 최종 Cartesian grid(active cell=706)를 구축하였다. EFDC를 이용한 장흥호의 수치모의 결과 호수내의 흐름은 수면을 통한 열 교환에 의한 수온 밀도류를 형성하고 있으며, 수온성층의 형성과 파괴가 호수 흐름을 형성하는 큰 인자로 작용한다는 것을 확인할 수 있었다. 그리고, 호에 유입되는 하천부분에서는 유입되는 수온에 따라 흐름특성이 변하며, 유입수온에 따라 호수 내 관입위치가 변하여 표면흐름, 내부흐름, 저부흐름 등의 흐름특성을 보인다 이상과 같이, 호수내의 흐름특성을 열수지, 외력에 의해서 크게 변동하며 해석대상역의 지역특성을 반영한 수리현상의 정확한 재현 없이는, 이 유동해석결과를 입력치로 하는 수질모델링 결과는 신뢰도에 심각한 문제를 발생시킨다고 할 수 있다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.612-620
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• 2019

The increasing use of curved beams in buildings, vehicles, ships, and aircraft has results in considerable effort being directed toward developing an accurate method for analyzing the dynamic behavior of such structures. The stability behavior of elastic curved beams has been the subject of a large number of investigations. Solutions of the relevant differential equations have traditionally been obtained by the standard finite difference. These techniques require a great deal of computer time as the number of discrete nodes becomes relatively large under conditions of complex geometry and loading. One of the efficient procedures for the solution of partial differential equations is the method of differential quadrature. The differential quadrature method(DQM) has been applied to a large number of cases to overcome the difficulties of the complex algorithms of programming for the computer, as well as excessive use of storage due to conditions of complex geometry and loading. In this study, the in-plane extensional vibration for asymmetric curved beams with linearly varying cross-section is analyzed using the DQM. Fundamental frequency parameters are calculated for the member with various parameter ratios, boundary conditions, and opening angles. The results are compared with the result by other methods for cases in which they are available. According to the analysis of the solutions, the DQM, used only a limited number of grid points, gives results which agree very well with the exact ones.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.690-690
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• 2012

효율적인 수자원 관리를 위한 하천정비기본계획과 유역치수계획의 수립은 정확한 홍수량을 산정을 통해여 이루어지며, 이러한 첨두홍수량에 대한 계산이 좀 더 정밀해져야 할 필요성이 있다. 흐름해석에서 중요한 요소인 조도계수는 원래 하상재료의 조도(roughness)를 나타내는 척도로서 하상재료 및 하상표면의 특성에 의해 결정되어지는 값이지만, 실제 흐름계산에서는 식생, 하천 구조물, 사행도, 단면형태 단면 변화양상 등 하도의 상황뿐만 아니라 유량이나 수위에 의해서도 변화기 때문에(Frech, 1985) 이론적으로 조도계수를 정확하게 계산하는 것은 거의 불가능하다. 내륙부와는 매우 특이한 유출 형태를 보이고 있는 제주도의 하천은 평시는 대부분이 건천이지만 집중호우나 태풍 내습시에는 하천변의 침수와 범람 등의 재해가 발생하기도 한다. 지금까지 하천정비기본계획에서 제주도 하천의 조도계수는 자연형 하천에 적용되는 계수만을 전 구간에 일률적으로 사용하여 왔으나, 제주도의 하천은 대부분 15km내외의 짧은 구간에 산지와 농 목축업 및 도심하천이 혼재하고 있고 또한, 하상재료는 자갈 및 호박돌, 전석 등이 산재해 있어 구간별 조도분포도 매우 복잡하며 큰 변화를 보이고 있다. 하지만 하천현장에 대한 실측 조도계수의 조사나 측정은 전무한 실정이다. 한천의 하상재료의 입경을 이용한 방법으로 연구대상인 한천의 구간은 11.5km이며, 조도계수 산정구간을 10구간으로 세분화하고 각 구간마다 좌안, 중앙, 우안마다 100개씩 하상재료를 채취하였으며, 총 3000개의 채취한 하상재료를 이용하여 대표입경을 선정하고 입도분석 실시하였다. 지당 총 100개 이상의 자갈 입자를 선택하고 중경(intermediate axis)을 측정하도록 하고 있다. 그 결과를 기존의 조도계수 경험식에 대입하여 조도계수를 산정하였으며, 기존의 하천정비기본계획에 제시된 조도계수와 비교 분석하였다. 이러한 실측 조도계수을 이용한다면 보다 정확한 홍수량 산정과 하천실무에 적용 및 활용성이 기대된다.