• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.22 no.1
• /
• pp.38-45
• /
• 2012

In this paper, flow-induced flutter instability of a cantilever carbon nanotube conveying fluid and modelled as a thin-walled beam is investigated. Analytically nonlocal effect, transverse shear and rotary inertia are incorporated in this study. The governing equations and the boundary conditions are derived through Hamilton's principle. Numerical analysis is performed by using extended Galerkin method which enables us to obtain more exact solutions compared with conventional Galerkin method. Variation of critical flow velocity of carbon nanopipes based on three different models such as analytically nonlocal model, partially nonlocal model, and local model are investigated and pertinent conclusion is outlined.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.5
• /
• pp.1104-1111
• /
• 1990

A method to identify nonlinear elements position of a nonlinear system is presented. Nonlinear elements position can be identified by an equivalent error damping and stiffness matrices which are based on the equivalent linearization technique. The procedures of this technique are: (1) Obtain input force and system response. (2) Define error between the actual and linearized restoring forces. (3) Calculate linearized damping and stiffness coefficients to minimize the square error sum. Several examples are tested and found that these methods are very effective not only to locate the nonlinear elements position but also to identify the degree of nonlinearity qualitatively. Nonlinear type can be qualitatively identified by examining the plots of restoring force vs equivalent state values.

• Journal of Korea Ship Safrty Technology Authority
• /
• no.7 s.25
• /
• pp.47-63
• /
• 2008

저항성능 측면에서 한국 어선선형의 특성을 파악하기 위하여, 본 연구에서는 한국과 일본에서 건조되어진 대표적인 어선을 한 척씩 선정하여 두 어선의 선형적 특성을 비교하였다. 또한 한국 어선의 선형적 특성들, 즉 일부 대표적인 선형요소들과 이를 제외한 기타의 국부적 선형특성들을 일본어선의 선형을 참고로 보정함으로써 우리나라 어선들의 저항성능을 향상시킬 수 있는 방안에 대하여 연구하였다. 한국어선과 일본어선은 해양환경과 어업의 종류가 다를 뿐만 아니라 관습적인 이유 등으로 선형의 차이가 있게 되며, 이것은 한국 어선이 일본 어선에 비하여 같은 배수량을 가지더라도 배 길이가 짧은 반면 폭이 넓으며 흘수가 얕은 대표적인 선형요소들의 차이로 확인할 수 있다. 이러한 차이를 고려하여, 일본어선들에 대한 유효마력 추정프로그램을 한국어선들에 맞게 보정.개발하는 과정을 통하여 양국 어선의 저항성능 차이를 확인할 수 있었으며, 보정된 프로그램을 이용하여 연구대상의 한국어선에 대한 저항저감효과를 줄 수 있는 선형요소들을 도출함으로써 선형요소들의 변화에 따른 저항성능 효과를 확인할 수 있었다. 그러나 선형요소들의 보정에도 불구하고 한국어선의 저항성능은 여전히 일본어선의 그것보다 떨어짐을 확인하여, 본 연구에서는 대표적인 선형요소들뿐만 아니라 국부적 선형특성 즉, 선수부에서 차인선(chine line) 경사도, 용골의 형상, 선미길이(용골 끝에서 선미단까지의 거리)를 각각 보정해 봄으로써 보다 더 큰 저항성능의 개선효과를 확인하였다. 본 연구결과는 앞으로 저항성능이 우수하면서도 실용 가능한 개량된 한국 어선선형의 개발에 기초적인 자료로서 활용이 가능할 것으로 사료된다.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.3
• /
• pp.1346-1351
• /
• 2012

In order to evaluate the local scour around offsshore wind foundation, mono pile and jacket foundation were simulated by using FLOW-3D. Numerical analysis results show that local increases of velocity around mono pile and jacket foundation was developed but velocity decreases in backward of pile and leg due to the wake vortex was observed. Local increases of velocity around foundation and scouring of jacket is more significant than that of mono pile, since jacket is the complex structure and has the interference effect with legs. Therefore, in order to evaluate the scour and design the scour protection method, the form and shape of substructures of offshore wind should be considered.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.23 no.4
• /
• pp.324-331
• /
• 2013

In this paper, static and oscillatory instability of a nanotube conveying fluid and modeled as a thin-walled beam is investigated. Analytically nonlocal effect, effects of boundary conditions, transverse shear and rotary inertia are incorporated in this study. The governing equations and boundary conditions are derived through Hamilton's principle. Numerical analysis is performed by using extended Galerkin method which enables us to obtain more accurate results compared with conventional Galerkin method. Variations of critical flow velocity of carbon nanopipes with two different boundary conditions based on the analytically nonlocal theory and partially nonlocal theory are investigated and pertinent conclusions are outlined.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.1
• /
• pp.71-81
• /
• 2009

In this study, the seismic performance of the Buckling Restrained Knee Bracing (BRKB) system was evaluated through a pin-connected one-bay, one-story frame. The BRKB system developed in this study was composed of a steel plate as a load-resisting core member and two channel sections to restrain local and global buckling of the core plate. The main purpose of the BRKB system is to restrengthen/rehabilitate old low- and mid-rise RC buildings, which, it is assumed, were designed with non-seismic designs and details. The main variables for the test specimens were the size of the core plates and the stiffeners, and the condition of the end plates. The test results showed that the size of the core plate, which was the main element of the load-resisting member, was the most important parameter in achieving a ductile behavior under tension as well as compression until the maximum displacement exceeds twice the design drift limit.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.3
• /
• pp.211-219
• /
• 2008

A three-dimensional inviscid flow solver has been developed based on unstructured meshes for the investigation of the effect of the external stores on the tail surfaces of a generic fighter aircraft. The numerical method is based on a vertex-centered finite-volume discretization and an implicit point Gauss-Seidel time integration. The calculations were made for a steady flow and the computed results were compared with experimental data to validate the flow solver. An unsteady time-accurate computation of the generic fighter aircraft with external stores at transonic flight conditions showed that the external stores cause unsteady loading on the horizontal tail surface due to the mutual interference between their wake and the horizontal tail surface. It was shown that downward deflection of the trailing edge flap significantly reduces the undesirable interference effect.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.27 no.1
• /
• pp.24-34
• /
• 1990

In this paper, the formulation of a new simplified finite element is made to analyze the ultimate strength of damaged tubular members subjected to combined axial force and end moment. A damaged tubular member that has the bending deformation and the local dent is modeled by beam elements. Tangent elastic stiffness matrix of a beam element which contains the effect of the geometric nonlinearity is derived by using the updated Lagrangian approach. Here the contribution of the stiffness in the dented area is neglected since its resistance against the external loads is considered to be small. A fully plastic interaction curve of the element under combined loads taking account of the local dent effect is selected as a yielding criterion at each nodal point. Also tangent elasto-plastic stiffness matrix of the element is formulated by plastic node method. Comparison with the present solution and the existing experimental results is made showing that the present method gives quite an accurate solution.

• Journal of Korean Society of Steel Construction
• /
• v.17 no.6 s.79
• /
• pp.707-715
• /
• 2005

Corrugated webs have been used for composite prestressed concrete box girder bridges. Innovative steel plate girders using corrugated webs have been proposed. It has been found that analytical and experimental researches conducted to determine the strength of trapezoidally corrugated webs can fail with respect to three different buckling modes: local, global, and interactive shear buckling. Shear buckling capacity equations based on classical and orthotropic plate buckling theories have been proposed,but these equations show some differences. In this paper, geometric parameters that influence interactive shear buckling behavior with interaction effects are identified via extensive bifurcation buckling analysis using the finite element meth.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.402-402
• /
• 2011

본 연구에서는 결정질 태양전지 제작에 있어 재료비 절감과 기존의 Screen Printing 공정 기술에서의 단점을 보완하기 위한 방안으로 후면 passivation 구조와 레이저를 이용한 국부적 후면 전극 형성(Laser Fired Contact) 방법에 대한 실험을 진행하였다. 후면 passivation 층으로 SiO2/ SiNx/SiO2 삼중막 구조와 SiNx 단일막 구조를 형성시킨 후 anneal 온도에 따른 소수캐리어의 lifetime 변화를 비교하였다. LFC 형성은 2 ${\mu}m$ 두께의 Al이 증착된 기판 후면에 1,064 nm 파장의 레이저를 통해 diameter와 dot pitch 등의 파라미터를 가변 하여 실시하였다. 실험 결과 800$^{\circ}C$의 고온 열처리 후 ONO 삼중막에서의 lifetime 향상이 우세하여 SiNx 단일 막 보다 열적 안정성이 우수함을 확인하였다. LFC 결과 diameter가 40, 50, 60 ${\mu}m$로 가변된 조건에서는 40 ${\mu}m$ 일 경우와 dot pitch가 200, 500, 1,000 ${\mu}m$로 가변된 조건에서는 1,000 ${\mu}m$일 경우 610 mV의 Voc 값을 보였다. 이는 레이저를 통해 국부적으로 Al-Si 간 alloy를 형성시킴으로써 접촉 면적이 최소화됨에 따라 후면에서의 캐리어의 재결합속도를 감소시키고, passivation 효과를 극대화시키기 때문이다.