• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.79-87
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• 1991

An efficient numerical procedure for material and geometric nonlinear analysis of reinforced concrete shells under monotonically increasing loads through their elastic, inelastic and ultimate load ranges is developed by using the finite element method. The 8-node Serendipity isoparametric element developed by the degeneration approach including the transverse shear deformation is used. A layered approach is used to represent the steel reinforcement and to discretize the concrete behavior through the thickness. The total Lagrangian formulation based upon the simplified Von Karman strain expressions is used to take into account the geometric nonlinearity of the structure. The material nonlinearities are taken into account by comprising the tension, compression, and shear models of cracked concrete and a model for reinforcement in the concrete; and also a so-called smeared crack model is incorporated. The steel reinforcement is assumed to be in a uniaxial stress state and is modelled as a smeared layer of equivalent thickness. This method will be verified a useful tool to account for geometric and material nonlinearities in detailed analysis of reinforced concrete concrete shells of general form through numerical examples of the sequential paper( ).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.10
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• pp.843-852
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• 2016

The autorotative flight of maple seeds(Acer palmatum) is numerically simulated based on the 3D geometry and the motion parameters of real seeds. The nominal values of the motion parameters are 1.26 m/s for descent velocity, 133.6 rad/s (1,276 rpm) for spinning rate, $19.4^{\circ}$ for coning angle, and $-1.5^{\circ}$ for pitch angle. A compact leading-edge vortex (LEV) positioned at the inner span of the seed blade causes a large suction pressure on its leeward surface. The suction pressure peaks occur near the leading region of inner span sections. The flow pattern characterized by the prominent LEV and the values of aerodynamic force coefficients obtained in the present study are in good agreement with experimental data measured for a dynamically-scaled robot maple seeds. A spiraling vortex developed in the leeward region advances toward the seed tip and merges with the tip-passing flow, which is considered to be a mechanism of maintaining stable and attached LEV for the autorotating maple seeds.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.6
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• pp.649-654
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• 2010

A three-dimensional numerical study of the WIG-effect vehicle with a direct-underside-pressurization (DUP) system and a propeller is performed to analyze the aerodynamic forces and moments acting on the vehicle. The computational model includes all the compartments of a WIG-effect vehicle, including a propeller in the middle of the fuselage and an air chamber under the fuselage. The DUP system and propeller help considerably reduce the take-off speed and minimize the effect of the hump drag when the vehicle accelerates to take off on water. The airflow is accelerated by a propeller, and the air then enters the air chamber through a channel in the middle of the fuselage, this air helps increase the lift since the dynamic pressure of air is converted to static pressure. However, the air accelerated by the propeller produces excessive drag and creates yawing moment. It is found that the effect of yawing and rolling moments on static stability is negligible.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.2
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• pp.70-76
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• 2000

A numerical study on the viscous flow around a 2-dimensional circulation control foil is carried out for application on the field of naval architecture and ocean engineering. The governing equations are the RANS and the continuity equations. The equations are discretized by finite difference method and MAC method and the pressure poisson equation is calculate by a SOR method and an O-type non-staggered boundary fitted coordinate system which is overlapped near the slot is used to improve the numerical accuracy. Turbulence is approximated by a modified Baldwin-Lomax turbulence model. In the present paper, the Coanda effect on a 2-dimensional foil of a 20% thickness ellipse with modified rounded trailing edge has been numerically studied. The change in drag and lift of the foil with various jet momentums are calculated and compared to the experimental results to show good agreements.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.2
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• pp.62-70
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• 2001

As the ship hull is a compound-curved structure, plate bending process is indispensible. The process includes press bending process for forming major 1st curvature and heating process for forming the rest curvature. Especially the heating process that is above 50 percents of entire bending work is carried out exclusively by skillful workers. Many researches have been made to automate the heating process but most of these are about line heating process and researches for triangle heating process are rare. This study is a fundamental study to develop a efficient analysis method for triangle heating and focused on clarifying the deformation characteristics of plate by triangle heating. In this paper, we carried out heating experiments and analysed the deformation characteristics of plate to explain the deformation characteristics of plates rationally by showing the phase transformed high temperature region. Also we investigated the heating effect on the hull material properties by mechanical tests.

• Journal of the Korean Institute of Gas
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• v.12 no.4
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• pp.21-28
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• 2008

A numerical analysis is achieved to elucidate the behavior of lifted flames and characteristics of flow near flame zone according to the exit velocity of triple flame, Poiseuille and uniform distribution. For the cases of Poiseuille and uniform nozzle exit velocity, we reviewed previous results with the present numerical results and investigated characteristics of the flame structure near the flame zone comparing with liftoff height generalized by momentum flux. In addition, a close inquiry into the combustion flow characteristics near flame zone was made with the characteristics of velocity, pressure, temperature and chemical reaction. From nozzle to flame zone, center line velocity profile traced well with the velocity profile of typical cold jet flow, but very near the flame zone, this study examined phenomenon that flow velocity decreases very quickly before the flame zone and then increases very quickly after the flame zone. Because flame zone acts as a barrier at the flow region which is before the flame zone and accelerate the flow velocity when it pass through the flame zone. This phenomenon was not clarified previous cold jet flow.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.6
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• pp.169-174
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• 2019

Flexure joints are recently used in the ultra-precision mechanism for a telecommunication mirror stage. Flexure joints have several advantages coming from their monolithic characteristics. They can be used to reduce the size of manipulators or to increase the precision of motion. In our research, 6 dof(degree of freedom) mechanism is suggested for micrometer repeatability using a flexure mechanism. To design the 6-dof motion, the 2-dof planar mechanism are designed and assembled to make the 6-dof motion. To achieve a certain performance, it is necessary to define the performance of mechanism that quantifies the characteristics of flexure joints. This paper addresses the analysis and design of the 6-dof parallel manipulator with a flexure joint using a finite element analysis tool. To obtain experimental result, CCD laser displacement sensor is used for the total displacement and the stiffness for the 6-dof flexure mechanism.

• Journal of Industrial Technology
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• v.26 no.A
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• pp.29-38
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• 2006

Efficiency and universality which was the spirit of the modern age, had also an enfluence on our living environment. Various types of individual housing unit were developed and mass-produced. However, the exterior space in our city is a place for our social life and intermediate place to connect the private life of each individual to our society. For the people to adapt themselves well to their environment, it should be well organized which means it is clearly divided and integrated in a hierarchical order. To realize these conditions, adequate boundaries to divide each territory and entrances to connect each territory are two essential elements. One of the possible methods to realize these conditions can be found in korean traditional architecture where the exterior space has the same figural quality like buildings and is the center of the whole composition. Buildings, walls and colonnades are the elements to define space. Gates, pavilions, gabs between buildings and posts are the elements to symbolize the entrance connecting each space. Each exterior space is integrated to a whole composition. One is the gradual differentiation along the axis which is unique in korean traditional architecture. The other is the rectangular connection which is also found in the other area in the world. The results of this thesis are as follows. The exterior space in the housing area should have the figural quality. The elements to make boundaries defining exterior space are classified into horizontal elements such as low buildings and walls, and vertical elements such as tower-shape buildings which define space in a different way. The position of openings in a housing block affects the characteristic and openness of a exterior space. Various types of gates are used to decide the relationship between spaces.

• Journal of Advanced Navigation Technology
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• v.16 no.2
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• pp.179-189
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• 2012

The aim of this paper is to research the change in the turbulent flow and the AOA(Angle Of Attack) occurred by $40^{\circ}$ crosswind to the direction of runway through the three-dimensional numerical analysis and to predict the take-off and landing flight stability. As a result, the maximum amplitude of AOA variation on runway reached $2^{\circ}$ within 3 second because of the wake formed by the constructions in the vicinity of the airport, and the overall effects appeared as an irregular aperiodic forms. Additionally, it was observed that the layout and shape of the buildings effected on the strength of turbulence directly, and the rapid flow generated between the buildings changed into stronger wake and eventually expected that the flow raises serious take-off and landing flight instability.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.43-43
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• 2011

최근 컴퓨터 기술의 발전으로 수심방향으로 완전한 운동방정식인 Navier-Stokes 방정식을 이용하는 3차원 수치모형에 의한 연구가 기초과학 분야인 수학에서부터 공학은 물론 의학 분야까지 광범위하게 진행되고 있다. 3차원 수치모형을 이용한 연구는 이론적으로 매우 우수하긴 하나 정확도 높은 결과를 얻기 위해서는 매우 조밀한 격자를 필요로 하기 때문에 아직까지 막대한 계산시간이 필요하다는 단점이 있으나 근래의 컴퓨터 기술이 엄청난 속도로 발전하고 있는 점을 감안할 때 적용 가능성은 계속 높아지고 있다. 이러한 흐름에 따라 해안공학 분야에서도 3차원 수치모형을 이용한 다양한 연구가 시도되고 있다. 복잡한 해안구조물로 인한 파랑변형 및 구조물의 안전성 등을 검토할 때 기존의 평면 2차원 수치모형이나 연직 2차원 수치모형으로는 재현이 힘들어 상대적으로 수치모형을 활용한 연구의 효용성이 낮았던 것에 비해 3차원 수치모형을 활용할 경우 복잡한 지형 및 구조물의 형상을 재현할 수 있기 때문에 좀 더 유용하게 사용될 수 있다. 한편, 파랑변형을 다루는 수치모형실험을 수행할 때 외부조파를 사용할 경우 구조물이나 지형에 의해 반사되어 나온 파랑이 조파지점에 도달할 때 실험영역으로 재 반사되는 문제가 발생한다. 이를 해결하기 위해 내부조파기법의 개발에 대한 연구가 필수적이었으며, 2차원 수치모형을 중심으로 그 연구가 매우 활발하게 진행되어 왔으나 Navier-Stokes 방정식 모형의 경우 상대적으로 연구가 미흡하였다. 본 연구에서는 3차원 Navier-Stokes 방정식 모형에서 내부조파기법을 도입하여 목표 파랑을 조파하였다. 수치모형은 Navier-Stokes 방정식을 엇갈림 격자체계에서 계산하는 유한차분모형으로 자유수면 추적에는 2차 정확도의 VOF(volume-of-fluid) 기법을 사용한다. 수치모형실험 결과를 일정한 수심을 전파하는 정현파의 해석해와 비교하였으며, 수치모형실험 결과가 비교적 정확하게 목표 파랑을 조파할 수 있음을 검증하였다.