• Structural Engineering and Mechanics
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• 제13권5호
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• pp.557-568
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• 2002

For the evaluation of the capability of a tubular member of an offshore structure to absorb the collision energy, a simple method can be employed for the collision analysis without performing the detailed analysis. The most common simple method is the rigid-plastic method. However, in this method any characteristics for horizontal movement and rotation at the ends of the corresponding tubular member are not included. In a real structural system of an offshore structure, tubular members sustain a certain degree of elastic support from the adjacent structure. End fixity has influences in the behaviors of a tubular member. Three-dimensional FEM analysis can include the effect of end fixity fully, however in viewpoints of the inherent computational complexities of the 3-D approach, this is not the recommendable analysis at the initial design stage. In this paper, influence of end fixity on the behaviors of a tubular member is investigated, through a new approach and other approaches. A new analysis approach that includes the flexibility of the boundary points of the member is developed here. The flexibility at the ends of a tubular element is extracted using the rational reduction of the modeling characteristics. The property reduction is based on the static condensation of the related global stiffness matrix of a model to end nodal points of the tubular element. The load-displacement relation at the collision point of the tubular member with and without the end flexibility is obtained and compared. The new method lies between the rigid-plastic method and the 3-demensional analysis. It is self-evident that the rigid-plastic method gives high strengthening membrane effect of the member during global deformation, resulting in a steeper slope than the present method. On the while, full 3-D analysis gives less strengthening membrane effect on the member, resulting in a slow going load-displacement curve. Comparison of the load-displacement curves by the new approach with those by conventional methods gives the figures of the influence of end fixity on post-yielding behaviors of the relevant tubular member. One of the main contributions of this investigation is the development of an analytical rational procedure to figure out the post-yielding behaviors of a tubular member in offshore structures.

• 대한원격탐사학회지
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• 제21권5호
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• pp.405-415
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• 2005

It is difficult to classify tidal flat surface that is composed of a mixture of mud, sand, water and microphytobenthos. We used a Linear Spectral Unmixing (LSU) method for effectively classifying the tidal flat surface characteristics within a pixel. This study aims at 1) detecting algal mat using LSU in the Saemangeum tidal flats, 2) determining a suitable end-member selection method in tidal flats, and 3) find out a habitual characteristics of algal mat. Two types of end-member were built; one is a reference end-member derived from field spectrometer measurements and the other image end-member. A field spectrometer was used to measure spectral reflectance, and a spectral library was accomplished by shape difference of spectra, r.m.s. difference of spectra, continuum removal and Mann-Whitney U-test. Reference end-members were extracted from the spectral library. Image end-members were obtained by applying Principle Component Analysis (PCA) to an image. The LSU method was effective to detect microphytobenthos, and successfully classified the intertidal zone into algal mat, sediment, and water body components. The reference end-member was slightly more effective than the image end-member for the classification. Fine grained upper tidal flat is generally considered as a rich habitat for algal mat. We also identified unusual microphytobenthos that inhabited coarse grained lower tidal flats.

• 한국지형학회지
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• 제23권1호
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• pp.77-85
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• 2016

To understand the difference of runoff discharge processes between Gwangneung deciduous and coniferous forest catchments, we collected hydrological data (e.g., precipitation, soil moisture, runoff discharge) and conducted hydrochemical analyses in the deciduous and coniferous forest catchments in Gwangneung National Arboretum in the northwest part of South Korea. Based on the end-member mixing analysis of the three storm events during the summer monsoon in 2005, the hillslope runoff in the deciduous forest catchment was higher 20% than the coniferousforest catchment during the firststorm event. Howerver, hillslope runoff increased from the second storm event in the coniferous catchment. We conclude that low soil water contents and topographical gradient characteristics highly influence runoff in the coniferous forest catchment during the first storm events. In general, coniferous forests are shown high interception loss and low soil moisture compared to the deciduous forests. It may also be more likely to be a reduction in soil porosity development when artificial coniferous forests reduced soil biodiversity. The forest soil porosity is an important indicator to determine the water recharge of the forest. Therefore, in order to secure the water resources, it should be managed coniferous forests for improving soil biodiversity and porosity.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.54-58
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• 2001

In recent years, hydroforming technology has been one of the most important technology in automotive industry in the points of weight saving, cost reduction and qualify improvement. However, compared with traditional metal forming technology, hydroforming has much fewer information in experience and empirical knowledge. But we don't have my sufficient time and money to produce hydroforming products using real blank directly Therefore Simulation is essential in hydrofonrung technology development. In this paper, we simulate the side member as the tubular hydroforming technology. The manufacturing process of side member' consists of pre_bending, pre_forming, and hydroforming of a thin tube. Variables such as internal pressure, end feeding, and tool geometry are optimized to improve the forming safety. And we simulate side member according to several lubricant conditions. from those simulations, we find that strain distributions can be reduced well by internal pressure and end feeding control, and lubrication is the most important thing in hydroforming process.

• 한국정밀공학회지
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• 제18권7호
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• pp.120-126
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• 2001

The widely used spot welded section members of vehicles are structures which absorb most of the energy in a front-end collision. In front-end collision, sufficiently absorbed in the front parts, the impact energy does not reach the passengers. Simultaneously, the frame gets less damaged. This structures have to be very stiff, but collapse progressively to absorb the kinetic energy as expected. In the view of stiffness, the double-hat shaped section member is stiffer than the hat shaped section member. In progress of collapse, the hat shaped section member is collapsing progressively, but the double-hat shaped section member does not due to stiffness. An analysis on the hat shaped section member was previously completed. This paper concerns the collapse characteristic of the double-hat shaped section member. In the program system presented in this study, an explicit finite element code, LS-DYNA3D is adopted for simulating complicate collapse behavior of double hat shaped section members with respect to spot weld pitches. And comparing with the results from the quasi-static and impact experiment, the simulation has been verified.

• 한국강구조학회 논문집
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• 제15권2호
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• pp.159-165
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• 2003

단부에 관통 가셋트판이 부착된 강관부재의 좌굴거동은 단부의 형상 및 상태에 따라 구속정도가 상이하게되며 단부요소는 세 장비에 따라 탄성 및 비탄성 거동 특성을 보임에 따라 이론적 좌굴내력을 도출하는 것은 사실상 불가능하다. 본 연구에서는 탄성좌굴의 이론적 접근을 바탕으로 세장비($\lambda$), 강성비($\beta$), 지지길이비(G), 강관크기, 부재의 초기변형 등을 고려하여 비탄성 유한요소 해석을 수행하여 각각의 영향요소가 좌굴하중에 미치는 영향을 살펴보았다. 또한 유한요소 모델링시 세장비($\lambda$), 강성비($\beta$), 지지길이비(G), 강관크기 등의 매개변수 분석을 통하여 강도식을 도출하였다.

• Steel and Composite Structures
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• 제5권6호
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• pp.443-458
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• 2005

Steel angles are widely used in roof trusses as web and chord members and in lattice towers. Very often angle members are connected eccentrically. As a result, not only an angle member is under an axial force, but it is also subject to a pair of end eccentric moments. Moreover, the connection at each end provides some fixity so neither pinned nor the fixed end represents the reality. Many national design codes allow for the effects due to eccentricities by modifying the slenderness ratio and reducing the compressive strength of the member. However, in practice, it is difficult to determine accurately the effective length. The concept behind this method is inconsistent with strength design of members of other cross-sectional types such as I or box sections of which the buckling strength is controlled by the Perry constant or the initial imperfection parameters. This paper proposes a method for design of angle frames and trusses by the second-order analysis. The equivalent initial imperfection-to-length ratios for equal and unequal angles to compensate the negligence of initial curvatures, load eccentricities and residual stresses are determined in this paper. From the obtained results, the values of imperfection-to-length ratios are suggested for design and analysis of angle steel trusses allowing for member buckling strength based on the Perry-Robertson formula.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.252-255
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• 2004

Design modification of the stamping die for the upper member of a front end module carrier is carried out in order to improve the feeling qualify of the final product. The small inferiority induced by wrinkling near the wall of the FEM upper member has been inspected after the draw-forming process. The finite element simulation shows that the excess metal is developed by the irregular contact of the blank the tool and it remains after the final stroke. This paper proposes two guidelines for the modification: one is to add the draw-bead; and the other is to modify the tool shape such as the forming shape at the wall. Simulation results show that the proposed guidelines both guarantee the improved feeling quality.

• 한국자동차공학회논문집
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• 제21권5호
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• pp.97-103
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• 2013

Crash performance of the straight member was studied by FE analysis. One end of model was fixed and the other end was impacted by 1,000kg rigid mass with velocity of 16.0m/sec. The maximum and mean load were discussed to compare crash performance. The members with various section shapes were analyzed and the flange location was changed. Also, spot weld points were added in the initial buckling region to investigate its effect. Final rectangular section model which has flanges at the center and reinforcement in initial buckling region showed high enhancement in crash performance.

• 한국자동차공학회논문집
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• 제22권2호
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• pp.52-59
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• 2014

Front impacted SUV vehicle shows that the front parts of side members are collapsed by the bending due to the transverse load exerted at the end of side members. Side member models were impacted with various angles in order to study the crash performance according to the impact angle. Even for the small impact angle of $10^{\circ}$, crash performance seriously deteriorated and the deformations for impact angle $15^{\circ}$ were similar to those from the front body impact analysis. In addition, the angled front impact analysis for the straight member with hat section was carried out and the effects of inner reinforcement shape on crash performance was investigated.