• Journal of the Earthquake Engineering Society of Korea
• /
• v.7 no.4
• /
• pp.1-13
• /
• 2003

For spatial free vibration of non-symmetric thin-walled curved beams with shear deformation, an improved formulation is proposed in the present study. The elastic strain and the kinetic energies are first derived by considering constant curvature and shear deformation effects due to shear forces and restrained warping torsion. Next equilibrium equations and force-deformation relations are obtained using a stationary condition of total potential energy. And the finite element procedures are developed by using isoparametric curved beam element with arbitray thin-walled sections. Particularly not only shear deformation and thickness-curvature effects on vibration behaviors of curved beams but also mode transition and crossover phenomena with change in curvatures of beams are parametrically investigated. In order to illustrate the accuracy and the reliability of this study, various numerical solutions for spatial free vibration are compared with results by available references and ABAQUS's shell element.

• Journal of Internet Computing and Services
• /
• v.17 no.4
• /
• pp.35-42
• /
• 2016

Recently many researches have been focused on the use of the markerless augmented reality system using face, foot, and hand of user's body to alleviate many disadvantages of the marker based augmented reality system. In addition, most existing augmented reality systems have been utilized rigid objects since they just desire to insert and to basic interaction with virtual object in the augmented reality system. In this paper, unlike restricted marker based augmented reality system with rigid objects that is based in display, we designed and implemented the markerless augmented reality system using deformable objects to apply various fields for interactive situations with a user. Generally, deformable objects can be implemented with mass-spring modeling and the finite element modeling. Mass-spring model can provide a real time simulation and finite element model can achieve more accurate simulation result in physical and mathematical view. In this paper, the proposed markerless augmented reality system utilize the mass-spring model using tetraheadron structure to provide real-time simulation result. To provide plausible simulated interaction result with deformable objects, the proposed method detects and tracks users hand with Kinect SDK and calculates the external force which is applied to the object on hand based on the position change of hand. Based on these force, 4th order Runge-Kutta Integration is applied to compute the next position of the deformable object. In addition, to prevent the generation of excessive external force by hand movement that can provide the natural behavior of deformable object, we set up the threshold value and applied this value when the hand movement is over this threshold. Each experimental test has been repeated 5 times and we analyzed the experimental result based on the computational cost of simulation. We believe that the proposed markerless augmented reality system with deformable objects can overcome the weakness of traditional marker based augmented reality system with rigid object that are not suitable to apply to other various fields including healthcare and education area.

• Journal of the Korean Geotechnical Society
• /
• v.29 no.6
• /
• pp.77-86
• /
• 2013

Embankments on soft ground experience significant deformation during time-dependent consolidation settlement, as well as an initial undrained settlement. Since infinitesimal strain theory assumes no configuration change and minute strain during deformation, finite strain analysis is required for better prediction of geotechnical problems involving large strain and geometric change induced by imposed loadings. Updated Lagrangian formulation is developed for time-dependent consolidation combining both force equilibrium and mass conservation of fluid, and mechanical constitutive equation is written in Janumann stress rate. Numerical convergence during Newton's iteration in large deformation analysis is improved by Nagtegaal's approach of considering the effect of rotation in mechanical constitutive relationship. Numerical simulations are conducted to discuss numerical reliability and applicability of developed numerical code: deformation of cantilever beam, two-dimensional consolidation. The numerical results show that developed formulation can efficiently describe large deformation problems. Proposed formulation is expected to facilitate the upgrading of a numerical code based on infinitesimal strain theory to that based on finite strain analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.10a
• /
• pp.273-273
• /
• 2003

나노인덴테이션은 압자를 수 $\mu\textrm{N}$의 힘으로 시편에 압입을 시켜 재료의 경도나 탄성계수와 같은 기계적 특성을 평가하는 압입경도 시험법이다. 압입 변위를 나노미터범위로 조절할 수 있어 기존에 접근할 수 없었던 박막의 기계적 특성을 평가하는데 응용이 넓어지고 있다. 본 연구에서는 나노인덴테이션에서 제공되는 하중-변위곡선과 유한요소해석의 결과를 비교하여 유한요소해석의 신뢰성을 검증하고, 유한요소해석에서 여러 가지 재료의 특성에 따른 파일업과 싱크인 현상을 규명 하고자 한다.

• The Optical Journal
• /
• s.151
• /
• pp.33-45
• /
• 2014

대구경 비구면 거울은 대형 천체 망원경이나 고해상도 위성 카메라 등에 사용하는 핵심부품이다. 일반적인 디지털 카메라와 비교하면 매우 크므로 설계 및 제작이 같은 크기의 구면보다 훨씬 어렵다. 특히 경량화가 많이 될수록 중력이나 온도변화와 같은 외부의 힘에 의한 변형이 쉽게 발생하기 때문에 이러한 효과를 줄여주는 광기계 설계 및 해석이 더욱 중요해진다. 지상용과 우주용은 사용 환경에 차이가 있어서 설계 요구조건이 달라지고 이에 따라 지지구조물이나 반사경의 경량화 모양 등에 많은 차이가 있다. 본 논문에서는 대구경 비구면 광학기술가운데 가장 어려운 광기계 설계에 관하여 지상용과 우주용으로 나누어 자세히 설명하고자 한다.

• Journal of Korean Society of Steel Construction
• /
• v.8 no.4 s.29
• /
• pp.51-58
• /
• 1996

연직하중을 받는 적층보에서 박리좌굴하중을 산정하는 방법을 제시하였다. 재료역학적 방법에 근거하여 박리된 보의 변위함수를 설정하였으며 힘과 변위의 적합조건을 이용하여 연직하중과 박리좌굴하중과의 관계식을 유도하였다. 또한 박리의 진전을 판단하기 위한 변형도에너지 방출율(release rate)을 산정하였다. FRP로 보강된 GLULAM보에 대한 실험과 비교한 이론해는 정확한 결과를 보여 주었으며 연직하중을 받는 적층보의 박리 진전현상은 축하중을 받는 보와는 다른 거동을 보였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1997.04a
• /
• pp.247-252
• /
• 1997

축어긋남이 있는 회전체-볼베어링계의 진동을 묘사할 수 있는 모델을 개발하였다. 이 모델은 축어긋남의 효과로서 커플링과 베어링에 작용하는 힘과 모멘트, 그리고 이에 의한 변형을 고려하였으며, 실험과 수치해석 결과로부터 모델의 타당성을 검증하였다. 그 결과는 각축어긋남이 심해짐에 따라 타원 형태의 선회궤적을 보여주며, 어긋남방향의 회전체 고유진동수와 베어링 강성계수가 크게 증가하는 것으로 나타났다. 그리고 이러한 현상은 어긋남 방향의 베어링 모멘트 강성증가에 의한 것으로 밝혀졌다.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2009.04a
• /
• pp.93-96
• /
• 2009

바퀴동력계는 차량에 지면으로부터 전달되는 힘과 모멘트를 측정하는 로드셀이다. 본 연구에서 개발한 바퀴동력계는 스트레인 게이지식 로드셀로써 이러한 로드셀을 설계하는데 있어서 몇가지 고려해야 하는 사항이 있다. 우선 스트레인 게이지를 부착하기 쉬운 구조가 되어야 하고 조립시의 오차를 줄이기 위하여 한 몸체로 제작되어야 한다. 이와 동시에 가장 중요하게 고려되어야 하는 인자로 감도를 위해 재료가 허용하는 응력내에서 되도록 큰 변형률이 발생해야 하고 상호 간섭 오차가 발생하지 말아야 한다. 본 연구에서는 수식을 이용하여 이론적으로 상호 간섭 오차를 0으로 만들 수 있었다. 또한 설계 변수 및 재료 물성치의 산포를 고려한 신뢰성 기반 최적설계 기법을 사용하였으며, 이를 통해 허용 응력하에서 최대의 변형률이 발생하는 바퀴동력계를 설계하였다.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.8 no.4
• /
• pp.177-185
• /
• 2000

The deformation characteristics is one of the major factors to resume the crash configuration in collision accident reconstruction. Crash analysis are carried out using finite element method and body stiffness equations representing force-deformation relationship are derived, Two different crash conditions : 1) frontal barrier impact 2) frontal impact between cars are given for the derivation of the equations. The stiffness coefficient of equation by method 2) is larger than that by method. 1). Crash analysis between two vehicles is accomplished with three crash angles and three velocities for each angle condition. The deformations are measured for six selected points and deformation energies are calculated using the derived equations. Equation by method 2) results in better estimation of deformation energy than that by method 1) for all crush configurations. The estimated energies can be utilized as one of indices to identify the type of the collision accident result.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.13 no.4
• /
• pp.308-316
• /
• 2003

Terfenol-D is one of magnetostrictive materials which have the property of converting the energy in magnetic fields into mechanical movement and vice versa. We designed and fabricated a linear magnetostrictive actuator using Terfenol-D. It has 25 mm diameter and 100 mm long. To grasp the characteristics of it, a series of tests were performed in the range of 50 Hz below. Induced-strain actuation displacements of the actuator measured by test and predicted by magnetic analysis agreed well. And blocked forces according to the input currents were estimated from the testing results. Modelling method representing the exerting force of a linear magnetostrictive actuator was confirmed through some testing results.