• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2009.06a
• /
• pp.525-526
• /
• 2009

• Journal of the Korea Computer Graphics Society
• /
• v.6 no.1
• /
• pp.1-9
• /
• 2000

This paper proposes a novel 3D representation of a plenoptic function that uses cylindrical maps placed on a circle. The proposed representation has an advantage over the previous one, concentric mosaics, in that it can render an object looking inward as well as looking outward of an environment. We also present an effective rendering technique for the representation that fully utilizes the depth information estimated or given for the cylindrical maps. This technique allows us to render more accurate images with novel views than point sampling or bilinear interpolation, which has been used for concentric mosaics.

• Journal of Aerospace System Engineering
• /
• v.17 no.4
• /
• pp.43-57
• /
• 2023

The hypervelocity impact simulations of space objects and structures are performed using LS-DYNA. Space objects with spherical, conical, and hollow cylindrical shapes are modeled using the Smoothed Particle Hydrodynamics (SPH). The direct and indirect impact zones of a space structure are modeled using the SPH and finite element methods, respectively. The Johnson-Cook material model and Mie-Grüneisen Equation of State are used to represent the nonlinear behavior of metallic materials in hypervelocity impact. In the hypervelocity impact simulations, various impact conditions are considered, such as the shape of the space object, the thickness of the space structure, the impact angle, and the impact velocity. The shapes of debris clouds are quantitatively classified based on the geometric parameters. Conical space objects provide the worst debris clouds for all impact conditions.

• The Journal of the Acoustical Society of Korea
• /
• v.33 no.1
• /
• pp.10-20
• /
• 2014

To study the water-entry impact noise, on-board experiment using a small launcher firing various objects was performed in the Yellow Sea. As the launcher fires a cylindrical object from the ship vertically, generated noise is measured with a hydrophone on the starboard of Chung-hae, Marine surveyor. Three types of cylindrical objects, which have noses of flat-faced, conical, and hemisphere, were used during the experiment. The measured noise exhibits a time-dependency which can be divided into three phases: (1) initial impact phase, (2) open cavity flow phase, (3) cavity collapse and bubble oscillation phase. In most cases, the waveform of bubble oscillation phase is dominant rather than that of initial impact phase. Pinch-off time, where a cavity begins to collapse, occurs at 0.18 ~ 0.2 second and the average lasting time of bubble was 0.9 ~ 1.3 second. The energy of water-entry impact noise is focused in the frequency region lower than 100 Hz, and the generated noise is influenced by the nose shapes, object mass, and launching velocity. As a result, energy spectral density on the bubble frequency is higher in the order of flat-faced, conical, hemisphere nose, and the increase of initial energy raises the energy spectral density on the bubble frequency in the cylinder body of same shape. Finally, we compare the measurements with the simulated signals and spectrum based on the bubble explosion physics, and obtain satisfactory agreements between them.

• Proceedings of the Korea Multimedia Society Conference
• /
• 2003.05b
• /
• pp.546-549
• /
• 2003

본 논문은 사용자가 가상환경 내에서 가상 물체의 무게를 인지하기 위한 힘을 적용시키는 장치(device)에 관해 연구하였다. 이 장치는 3-DOF를 갖는 장치로 원통형 플라스틱 스틱에 4개의 스트레인 게이지를 부착시켜 사용자가 원하는 방향으로 스틱을 밀거나 당기거나 누르면 스틱의 인장 강도에 따른 변화량을 스트레인 게이지를 통하여 측정되도록 설계하였다. 이 장치의 사용성을 평가하기 위해 무게가 다른 5개의 상자를 현실세계와 가상환경에 위치시킨 후에 피실험자로 하여금 정량적, 정성적인 평가를 하였다 그 결과 본 논문을 통하여 제작한 장치를 가상환경에 응용하였을 때, 사용자로 하여금 가상 물체에 대한 힘을 인지하게 함으로써 가상환경에서 현실감과 몰입감을 효과적으로 중대시킴을 확인할 수 있었다.

• Geophysics and Geophysical Exploration
• /
• v.5 no.3
• /
• pp.206-216
• /
• 2002

The finite element method (FEM), a powerful numerical modeling tool for solving various engineering problems, is frequently applied to three-dimensional (3-D) modeling thanks to its capability of discretizing and simulating the shape of model with finite number of elements. Considering the accuracy of the solution and computing time in modeling of engineering problems, it is preferable to construct physical continuity and simplify mesh system. Although there exist systematic mesh generation systems for arbitrary shaped model, it is hard to model a simple cylinder in terms of 3-D coordinate system especially in the vicinity of the central axis. In this study I adopt cylindrical coordinate system for modeling the 3-D model space and define the origin of the coordinates with mathematically clear coordinate transformation. Since we can simulate the whole space with hexahedral elements, the cylindrical coordinate system is effective in handling the 3-D model structure. The 3-D do resistivity modeling scheme developed in this study provides basie principle for borehole-to-surface resistivity survey, which can be a useful tool for the application to environmental problem.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.10
• /
• pp.843-849
• /
• 2016

It has been shown that the adaptive grasp feature can be implemented by underactuated robotic hands with a minimal number of actuators. Following this approach, a new design of prosthetic hand is presented. A method is proposed for evaluating grasp performance using cylinders, spheres, and square bars of various sizes. The effects of the major design parameters were investigated experimentally and an improved design is proposed.

• 한국전산유체공학회:학술대회논문집
• /
• 1999.05a
• /
• pp.73-78
• /
• 1999

극초음속 유동장의 정확한 해석을 위해 AUSMPW+ 수치기법과 충격파 포착시 생기는 수치오차를 제거하기 위해 충격파 정렬 기법(Shock-Aligned Grid Technique)을 개발하였다. AUSMPW+ 수치기법은 자체 수치점성이 적은 수치기법으로 점성 경계층 계산시 정확한 계산결과를 보여주며 기존의 AUSM 계열이 가지는 문제점인 물성치의 진동 현상을 제거한 수치기법이다. 원통형과 무딘 물체 주위의 극초음속 유동장 해석을 통해 공력이 진동현상 없이 정확하게 계산됨을 확인하였다. 그리고 충격파 정렬 기법의 특성을 파악하기 위해 충격파 반사문제와 충격파-충격파 상호작용 문제를 해석하여 수치오차 없이 충격파를 포착할 수 있음을 보였다. 또한 화학적 평형 비평형 유동 영역까지 충격파 정렬 격자 기법을 확장하였다.

• Journal of Sensor Science and Technology
• /
• v.10 no.6
• /
• pp.286-294
• /
• 2001

In this study, 3-D underwater object recognition using the self-made 3-3 type composite ultrasonic transducer and modified SOFM(Self Organizing Feature Map) neural network are investigated. Properties of the self-made 3-3 type composite specimens are satisfied considerably with requirements as an underwater ultrasonic transducer's materials. 3-D underwater all object's recognition rates obtained from both the training data and testing data in different objects, such as a rectangular block, regular triangular block, square block and cylinderical block, were 100% and 94.0%, respectively. All object's recognition rates are obtained by utilizing the self-made 3-3 type composite transducer and SOFM neural network. From the object recognition rates, it could be seen that an ultrasonic transducer fabricated with the self-made 3-3 type composite resonator will be able to have application for the underwater object recognition.

• Journal of Biomedical Engineering Research
• /
• v.18 no.4
• /
• pp.447-456
• /
• 1997

When the disabled is operating a rehabilitation assisting system with a joystick by himself, unlike in the case of a normal person, tremor with joystick control or instant miscontrol can often occur. If these misoperations should be directly relayed to the system, shaking or malfunction of the mobile rehabilitation assisting system might be the result. The safety of the disabled is of prime concern. To solve this problem, that is, to prevent the miscontrol of the disabled operator and avoid crashes into his or her surroundings, we propose the force-reflection locomotion algorithm with the joystick. This method uses ultrasonic sensors to measure the distance between the object and mobile robot. Based on the reception of sensory data, the necessary torque is applied via the joystick to the attatched motor. To confirm the effectiveness of the proposed method, the subjects on the reflected force by the dynamic characteristics of the joystick and the reflected force by the distance information are tested Even though there are some differences in human dexterity, we confirmed the fact that the information from the obstacles was relayed to the operator via the joystick and resulted in an improved operational performance and safety level with regard to those obstacles.