• Structural Engineering and Mechanics
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• 제67권6호
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• pp.565-578
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• 2018

This research article reported the nonlinear finite solutions of the nonlinear flexural strength and stress behaviour of nano sandwich graded structural shell panel under the combined thermomechanical loading. The nanotube sandwich structural model is derived mathematically using the higher-order displacement polynomial including the full geometrical nonlinear strain-displacement equations via Green-Lagrange relations. The face sheets of the sandwich panel are assumed to be carbon nanotube-reinforced polymer composite with temperature dependent material properties. Additionally, the numerical model included different types of nanotube distribution patterns for the sandwich face sheets for the sake of variable strength. The required equilibrium equation of the graded carbon nanotube sandwich structural panel is derived by minimizing the total potential energy expression. The energy expression is further solved to obtain the deflection values (linear and nonlinear) via the direct iterative method in conjunction with finite element steps. A computer code is prepared (MATLAB environment) based on the current higher-order nonlinear model for the numerical analysis purpose. The stability of the numerical solution and the validity are verified by comparing the published deflection and stress values. Finally, the nonlinear model is utilized to explore the deflection and the stresses of the nanotube-reinforced (volume fraction and distribution patterns of carbon nanotube) sandwich structure (different core to face thickness ratios) for the variable type of structural parameter (thickness ratio, aspect ratio, geometrical configurations, constraints at the edges and curvature ratio) and unlike temperature loading.

• 한국염색가공학회지
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• 제17권6호
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• pp.27-35
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• 2005

Conventional pad- dry-cure(thermo-fixation) process usually produces functional performance on both sides of a fabric. UV curing technique was applied to impart water- and oil-repellent finish effective only on the face of a PET knitted fabric. The preferential one-side coating, by virtue of the limited penetration of UV light, was achieved by W curing after padding of a fluorocarbon agent without special coating or printing equipments. The difference in the functional property of face and back sides was examined by measuring water and oil repellency at each side of the treated fabric. The influence of pre/post-irradiation dose and agent concentration on the performance of the finished fabrics were investigated. While increase in both resin concentration and post-irradiation did not have significant effect on the finish, UV pre-irradiation of PET fabrics caused remarkable influence presumably due to appropriate surface modification of PET fabrics required for facile wetting of the resin. The dimensional stability and color change of the UV cured fabrics measured by FAST and reflectance spectrophotometry showed significantly decreased color difference and increased percent extension compared with the samples pre-irradiated without agent application.

• Structural Engineering and Mechanics
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• 제52권2호
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• pp.323-349
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• 2014

In this paper, linear buckling analysis of a curved sandwich beam with a flexible core is investigated. Derivation of equations for face sheets is accomplished via the classical theory of curved beam, whereas for the flexible core, the elasticity equations in polar coordinates are implemented. Employing the von-Karman type geometrical non-linearity in strain-displacement relations, nonlinear governing equations are resulted. Linear pre-buckling analysis is performed neglecting the rotation effects in pre-buckling state. Stability equations are concluded based on the adjacent equilibrium criterion. Considering the movable simply supported type of boundary conditions, suitable trigonometric solutions are adopted which satisfy the assumed edge conditions. The critical uniform load of the beam is obtained as a closed-form expression. Numerical results cover the effects of various parameters on the critical buckling load of the curved beam. It is shown that, face thickness, core thickness, core module, fiber angle of faces, stacking sequence of faces and openin angle of the beam all affect greatly on the buckling pressure of the beam and its buckled shape.

• 한국항해학회지
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• 제7권1호
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• pp.63-81
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• 1983

A vessel encountered heavy weather is face to two kinds of danger ; the danger of upset due to the lack of stability and the lack of the longitudinal strength. Generally a small vessel is face to the former and the large vessel to the latter. Most of people do not consider the danger of upset by the latter but the former. But many ships missed at sea, the exact causes being not known. This pper investigated and analyzed the causes of accidents. The result was that the lohgitudinal strength of the hull is not enough to cope with heavy weather, and the particular cautions are needed to handle a ship in heavy weather.

• 한국대기환경학회지
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• 제20권3호
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• pp.361-369
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• 2004

A metal fiber bed has seldom been applied to the practical filtration process despite its excellent mechanical and chemical stability. The filter-bed used in this work was highly porous with open structure, of which apparent porosity was 80 ∼ 90%. Although pressure loss across the filter-bed was very low, separation efficiency was found to be quite high. This paper focuses on the basic filtration mechanisms of a metal filter-bed and a thin ceramic filter from fly ash for reference. The experimental parameters were face velocity, dust loading and porosity of filter-bed. Pressure drop increased with increasing face velocity and dust feeding load for both filters. It also showed that dust particles deposited in the deep flow path, finally resulting in clogging the pore channels. It thereby indicates that the dominating mechanism of the metal filter-bed would be depth filtration. Meanwhile, the thin fly ash composite filters trapped the aerated dust mainly on the surface of the filter medium, so that the instantaneously formed dust layer might cause a steep increase of pressure drop across the filtration system.

• Steel and Composite Structures
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• 제41권6호
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• pp.821-829
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• 2021

Nonlinear dynamic response of a sandwich beam considering porous core and nano-composite face sheet on nonlinear viscoelastic foundation with temperature-variable material properties is investigated in this research. The Hamilton's principle and beam theory are used to drive the equations of motion. The nonlinear differential equations of sandwich beam respect to time are obtained to solve nonlinear differential equations by Homotopy perturbation method (HPM). The effects of various parameters such as linear and nonlinear damping coefficient, linear and nonlinear spring constant, shear constant of Pasternak type for elastic foundation, temperature variation, volume fraction of carbon nanotube, porosity distribution and porosity coefficient on nonlinear dynamic response of sandwich beam are presented. The results of this paper could be used to analysis of dynamic modeling for a flexible structure in many industries such as automobiles, Shipbuilding, aircrafts and spacecraft with solar easured at current time step and the velocity and displacement were estimated through linear integration.

• 대한지질공학회:학술대회논문집
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• 대한지질공학회 2002년도 정기총회 및 학술발표회
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• pp.61-73
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• 2002

울산광역시 울주군 두동면 천전리 306번지 일대에 건설되는 대곡댐은 높이 52m, 길이 190m의 표면차수벽형 석괴댐이다. 대곡댐 건설사업과 관련하여 여수로 좌안사면 굴착공사를 시행 중 2000. 7. 23 13:00~7. 24. 04:00 67.0mm의 강우가 있은 후 Sta. No. 1~2, EL. 137~134m 지점에 균열이 발생하였다. 안정대책을 수립하고자 지표지질조사 및 평사투영법에 의한 안정성을 검토하고 굴착 후 예상되는 불안정 요소를 고려하여 사면의 부분적인 추가절취 및 Pre-stress가 가능한 SSL PC Anchoring에 의한 억지공법을 수립, 시공하였다.

• 센서학회지
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• 제31권1호
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• pp.57-63
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• 2022

This study describes a system that monitors the tool and cutting state of automatic beveling operation in real time. As a signal for cutting state monitoring, a motor current detected from the spindle drive system of the automatic beveling machine is used to monitor abnormal state. Because automatic beveling is processed using a face milling cutter, the cutting force mechanism is the same as the milling process. The predicted cutting torque is obtained using a cutting force model based on specific cutting resistance. Then, the predicted cutting torque is converted into the spindle motor current value, and cutting state stability is diagnosed by comparing it with the motor current value detected during beveling operation. The experimental results show that the spindle motor current can detect abnormal cutting state such as overload and tool wear during beveling operation, and can diagnose the cutting stability using the proposed equip-current line diagram.

• 대한치과교정학회지
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• 제36권5호
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• pp.369-379
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• 2006

본 연구는 수직적 안모유형에 따른 치료 후 교합평면 변화양상을 조사하여 향후 적절한 치료계획과 기전의 설정에 도움이 되고자 시행하였다. 골격성 I급 부정교합으로 진단되어 비발치로 치료받은 성민 60명(남자 28명, 여자 32명)을 대상으로 하였으며, Ricketts법의 facial axis, facial depth, mandibular plane angle, lower face height, mandibular arc의 5개 항목을 이용하여 한국 성인의 정상교합자 통계치의 기준에 따라 short face type (1군), average face type (2군), long face type (3군)으로 분류하였다. 각 군의 치료 전, 치료 종료, 종료 후 1년의 측모두부 방사선사진 계측치를 비교 분석하였다. 1군은 치료 종료 시와 비교하여 유지기간에 일반적 교합평면각, 기능적 교합 평면각, L6/L1, MP-L6 항목이 유의하게 감소하였고(p < 0.01) L1-FOP 항목은 유의하게 증가하였다(p < 0.001). 2군은 유지기간에 유의한 변화를 보이지 않았으며 3군은 유지기간에 기능적 교합평면각이 유의하게 증가하였다(p < 0.05). 기능적 교합평면각의 치료 후 변화량은 각 군 간에 유의한 차이를 보였으며 특히, 1군과 3군 간에 매우 큰 유의성을 보였다. 따라서 치아의 압하, 정출 및 치료 후 전치부 피개 등에 있어 유지기간 중 교합평면각 변화의 고려가 필요하다고 생각된다.

• 한국터널지하공간학회 논문집
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• 제6권4호
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• pp.327-343
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• 2004

터널 시공 도중이나 터널 굴착 직후 주지보재에 의한 보강 전에 터널막장 전방에 존재하는 연약암반 혹은 단층파쇄대로 인해 유발되는 터널막장의 붕괴사고가 빈번이 일어나고 있다. 기존의 지반탐사방법으로는 터널막장부근에 있는 연약암반이나 단층파쇄대를 찾기 어렵다. 본 연구에서는 이러한 문제점들을 극복하고 기존의 탐사방법들을 보완하기 위해 전자기파를 이용한 터널전방 예측방법을 제안하였다. 전기장의 특성을 고려한 Coulomb 및 Gauss 법칙을 이용하여 절리를 가지는 암반에서의 전기장을 해석하였다. 이를 바탕으로 터널막장 전방에 구형연약암반과 단층파쇄대가 존재하는 경우에 대하여 각각 전기장해석을 수행하여 이론식을 도출하였다. 또한 개발된 해석기법을 작용하여 터널 전방에 구형연약이역과 단층파쇄대가 존재하는 경우에 대하여 예제해석을 수행하였다. 해석결과는 터널 전방에 부착된 몇 개의 전극에서 측정된 암반의 저항으로부터 역함수기법을 이용하여 터널 전방에 존재하는 연약지역의 등가 크기, 위치 및 성질을 정확하게 예측할 수 있음을 보여주었다. 암반에서의 전기저항 가탐심도는 터널막장의 크기, 자연전위 및 기타 전기적 신호에 의해 영향을 받음을 알 수 있었다. 제시된 해석기법은 실내시험을 통하여 검증하였다. 가로, 세로, 높이가 각각 5cm인 콘크리트 블록 1800여 개를 가지고서 3방향 절리를 가진 암반상태를 구현하였고 터널 전방에 전기전도도가 콘크리트 블록보다 상대적으로 높은 물질을 이용하여 연약지반을 구현하였다. 모델링을 통한 실험결과는 해석결과와 거의 일치함을 보여주었다.