• 한국강구조학회 논문집
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• 제12권4호통권47호
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• pp.417-428
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• 2000

최근 복합재료는 토목뿐만 아니라 건축, 항공, 선박산업분야에서 널리 사용되고 있다. 두 가지 이상의 다른 재료들로 구성된 복합재료는 역학적 특성에서 단일재료보다 매우 유리한 장점을 가지고 있다. 쉘 구조물은 직선구조물과 비교해 볼 때 곡선형상 때문에 하중에 효과적으로 저항하는 이점이 있다. 이러한 쉘 구조물에 복합재료를 사용함으로서 보다 높은 강성과 낮은 중량을 가진 경제적인 쉘 구조물을 설계할 수 있다. 본 논문의 목적은 전단변형효과를 고려한 원뿔형 쉘을 해석하여 복합재료의 이점을 규명하고 자유경계의 효과를 고찰하는데 있다. 본 논문은 원뿔형 쉘의 미분방정식을 해결하기 위해서 유한 차분법을 사용하였다.

• 한국주조공학회지
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• 제23권5호
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• pp.257-267
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• 2003

In early solidification during the continuous casting of steel slabs, the formation of oscillation marks on the surface of slabs was mainly affected by carbon contents and casting conditions. The control of oscillation mark is required for the HCR(Hot Charged Rolling) process because the deep oscillation marks seriously deteriorate the surface qualities of steel slabs. The metallographic study has revealed that the oscillation mark can be classified principally according to the presence or absence of a small 'subsurface hook' and the depth of the oscillation marks in the subsurface structure at the basis of individual oscillation marks. The subsurface hook of oscillation marks was either straight or curved. When the amount of overflow was small and the subsurface hook was formed in the top of oscillation marks, the subsurface hook was straight and the oscillation mark was shallow. The oscillation marks without subsurface hook have small early solidification shell and were formed wide. The actual negative strip time$(t_N)$ was changed by the effect of meniscus level fluctuation Therefore irregular early solidification shell and oscillation mark were formed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2664-2669
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• 2008

Feedwater heaters of many nuclear power plants have recently experienced severe wall thinning damange, which will increase as operating time progresses. Several nuclear power plants in Korea have experienced wall thinning damage in the area around the impingement baffle-installed downstream of the high pressure turbine extraction stream line- inside number 5A and 5B feedwater heaters. At that point, the extracted steam from the high pressure turbine is two phase fluid at high temperature, high pressure, and high speed. Since it flows in reverse direction after impinging the impingement baffle, the shell wall of the number 5 high pressure feedwater heater may be affected by flow-accelerated corrosion. This paper describes operation of experience and numerical analysis composed similar condition with real high pressure feedwater heater. This study applied squared, curved and new type impingement baffle plates to feedwater heater same as previous study. In addition, it shows difference of pressure distribution and value between single phase and two phase based on experience and numerical analysis.

• 대한기계학회논문집A
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• 제30권1호
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• pp.76-83
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• 2006

This paper addresses the method for the shape design sensitivity analysis of the buckling load in the continuous elastic body. The sensitivity formula for critical load is analytically derived and expressed in terms of shape variation, based on the continuum formulation of the stability problem. Though the buckling problem is more efficiently solved by the structural elements such as beam and shell, the elastic solids are considered in this paper because the solid elements can be used in general for any kind of structures whether they are thick or thin. The initial stress and buckling analysis is carried out by the commercial analysis code ANSYS. The sensitivity is computed by using the mathematical package MATLAB using the results of ANSYS. Several problems including straight and curved beams under compressive load, ring under pressure load, thin-walled section and bottle shaped column are chosen to illustrate the efficiency of the presented method.

• 한국안전학회지
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• 제22권5호
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• pp.41-49
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• 2007

In general, the curved structures have the engineering efficiency as well as a fine view compared with straight member. Also, composite materials are composed of two or more different materials to produce desirable properties for structural strength as compared to single ones. Shell structures with composite materials have many advantages in strength and weight reduction. Therefore, composite laminated conical shells are analyzed in this study. To solve differential equations of conical shells, this paper used finite difference method. Various parametric study according to the change of radius ratio, vertex angle and subtended angle are examined. The change of radius ratio, vertex angle and subtended angle mean the change from conical shells to cylindrical shells, conical shells to circular plates and open shells closed shells, respectively.

• The Journal of the Acoustical Society of Korea
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• 제21권3E호
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• pp.132-139
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• 2002

Swaging technique is frequently used to stiffen thin panels for reducing the vibration levels of the machine or vehicle structure. Because the internal constraints imposed by swages can distort the mode shapes of panels, they affect the sound radiation characteristics. In this paper, the radiated sound field generated by the idealized and baffled finite swaged panel is studied, in which the curved swage section is modeled as an incomplete cylindrical shell. The modal radiation efficiencies are predicted using the transfer matrix concept and compared with those of flat panels. It is observed that the radiation efficiencies of the swaged vibrational modes can increase slightly for frequencies below the critical frequency, while increase of radiation efficiency depends on the mode shapes and other related structural parameters.

• 한국공간정보시스템학회:학술대회논문집
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• 한국공간정보시스템학회 2004년도 춘계 학술발표회 논문집 제1권1호(통권1호)
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• pp.222-229
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• 2004

This study purports to analyze equally stressed surfaces in tension-membrane structures through a geometrically nonlinear approach. It adopts the formulation of a 4-node quadrilateral isoparametric plane stress element considering the orthotropic characteristic of membrane textures. Tension structures, which include cables and tension membranes, such as a cable dome initially exhibit unstable conditions because no initial internal stiffness such as bending stiffness is present. Such a structural system requires prestressing to the tension members to attain a stable state. A tension-membrane structure retains a stable three dimensional curved surface as a structural shape. This analytical process for finding the geometry is referred to as Shape Finding Analysis. In order to assess the validity of this study, we examine equally stressed surfaces of saddle and catenary shape shell structures and carry out pertinent stress analyses

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.841-846
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• 2006

This paper addresses the method for the shape design sensitivity analysis of the buckling load in the continuous elastic body. The sensitivity formula for critical load is analytically derived and expressed in terms of shape variation, based on the continuum formulation of the stability problem. Though the buckling problem is more efficiently solved by the structural elements such as beam and shell, the elastic solids are considered in this paper because the solid elements can be used in general for any kind of structures whether they are thick or thin. The initial stress and buckling analysis is carried out by the commercial analysis code ANSYS. The sensitivity is computed by using the mathematical package MATLAB using the results of ANSYS. Several problems including straight and curved beams under compressive load, ring under pressure load, thin-walled section are chosen to illustrate the efficiency of the presented method.

• 한국공간구조학회논문집
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• 제1권1호
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• pp.157-166
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• 2001

In general, the cutting pattern of the membrane structures is determined by dividing the complicated curved 3-D surface into several 2-D plane strip by using flattening technique. In this procedure, however, some discrepancies ore occurred between actual stresses of equilibrated state and designed uniform stresses because the material properties are not considered. These deviations can cause the critical structural problems, wrinkling or overstress, and thus a optimization process should be considered. In this paper, a new analytical method for determining an optimum cutting pattern considering material properties is presented. Here, iterative procedure is introduced to decrease the errors caused in numerical process. The optimization method proposed can diminish the deviations occurred by material properties and numerical errors, simultaneously. As a results, it is shown that the final stress distributions for the HP shell model are sufficiently near to design stress distributions, and it can be concluded that this method can be used to obtain the optimized cutting pattern of membrane structures.

• Structural Engineering and Mechanics
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• 제13권5호
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• pp.533-542
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• 2002

This paper considers the buckling and post-buckling behavior of empty metal storage tanks under wind load. The structures of such tanks may be idealized as cantilever cylindrical shells, and the structural response is investigated using a computational model. The modeling employs a doubly curved finite element based on a theory by Simo and coworkers, which is capable of handling large displacements and plasticity. Buckling results for tanks with four different geometric relations are presented to consider the influence of the ratios between the radius and the height of the shell (R/L), and between the radius and the thickness (R/t). The studies aim to clarify the differences in the shells regarding their imperfection-sensitivity. The results show that thin-walled short tanks, with R/L = 3, display high imperfection sensitivity, while tanks with R/L = 0.5 are almost insensitive to imperfections. Changes in the total potential energy of tanks that would buckle under the same high wind pressures are also considered.