• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.33 no.7
• /
• pp.495-505
• /
• 2009

A two-dimensional circular cylinder freely falling in a channel has been simulated by using immersed boundary - lattice Boltzmann method (IB-LBM) in order to analyze the characteristics of motion originated by the interaction between the fluid flow and the cylinder. The wide range of the solid/fluid density ratio has been considered to identify the effect of the solid/fluid density ratio on the motion characteristics such as the falling time, the transverse force and the trajectory in the streamwise and transverse directions. In addition, the effect of the gap between the cylinder and the wall on the motion of a two-dimensional freely falling circular cylinder has been revealed by taking into account a various range of the gap size. As the cylinder is close to the wall at the initial dropping position, vortex shedding in the wake occurs early since the shear flow formed in the spacing between the cylinder and the wall drives flow instabilities from the initial stage of freely falling. In order to consider the characteristics of transverse motion of the cylinder in the initial stage of freely falling, quantitative information about the cylinder motion variables such as the transverse force, trajectory and settling time has been investigate.

• Proceedings of the Korean Society of Computer Information Conference
• /
• 2011.01a
• /
• pp.63-64
• /
• 2011

포물체란 중력이 작용하는 환경에서 어떤 속도로 던져진 물체를 뜻합니다. 예를 들자면, 박찬호 선수가 포수를 향하여 던진 야구공이라든지, 박세리 선수의 스윙으로 그린을 향하여 날아가고 있는 골프공, 그리고 목표물을 향하여 날아가고 있는 포탄은 모두 포물체입니다. 이 물체는 수직방향으로는 중력의 영향을 받고 공기의 저항을 무시한다면 수평방향으로는 힘을 받지 않기 때문에 포물선운동을 한다. 본 논문에서는 포물체의 운동을 이용하여 도로의 일부가 유실되어 없어진 곳을 실험 대상을 한다. 여기에서 속도가 일정하게 달리던 자동차가 유실된 도로의 가장자리를 넘어갔을 때 도로의 가장자리로에서 얼마나 멀리 가서 떨어지는지를 나타내었다.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.1
• /
• pp.853-859
• /
• 2015

1-DOF shear building was designed, built and tested to investigate the interactions between the shear building and the shaking table excited harmonically by the electro-magnetic forces. In the experiments horizontal accelerations of the shaking table and the shear building were measured. To understand the experimental results experimental setting was modeled as an unconstrained 2-DOF system under the hormonic forces. The responses of the shear building and the shaking table of the unconstrained 2-DOF system were found with the equations of motions. The magnification factors of the table and the shear building with respect to the amplitude of the harmonic forces and the transmission of the shear building with respect to the table excitations were found and compared with the experimental results.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.6C
• /
• pp.249-257
• /
• 2012

The reinforced earth method is financially viable. Furthermore, it overcomes environmental limitations and is therefore employed in retaining walls, slopes, foundations, roads, embankments, and other structures. However, in some cases, reinforced retaining walls are not strong enough in the curved sections and can collapse. Such mishaps are believed to occur because of an unsatisfactory analysis of the curved sections of a reinforced retaining wall. Accordingly, with the aim of investigating the workability and structural safety of curved sections of various types, this study investigates the differences in the estimated horizontal displacements of curved sections of various types and subsequently uses this information to study and analyze preliminary data so that appropriate measures can be taken to resolve alignment issues. The results of an experiment reveal that when a load is applied to curved sections of both concave and convex types, the largest horizontal displacement occurs at the center of the section. In the concave form, the earth pressure force is directed inward, whereas in the convex form, this force is directed outward. As a result, the horizontal displacement in convex forms is larger than that in concave forms. Convex reinforced earth structures are subjected to earth pressures as well as lateral earth pressure, therefore horizontal displacements in convex curved sections is larger than that of concave curved sections.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.13 no.6
• /
• pp.431-450
• /
• 2011

When a circular vertical shaft is constructed below the groundwater level, additional forces caused by groundwater flow besides horizontal effective stresses will act on the wall. The inward direction of the groundwater flow will be inclined to the vertical wall and its direction will change depending on the wall depth. In this paper, to figure out the effect of seepage forces acting on the circular vertical shaft, the slope of the inclined flow varying with the depth is divided into vertical and horizontal components to derive the coefficient of earth pressure considering the seepage pressure and to obtain the vertical stress by taking the seepage pressure into account. The control volume in this study is assumed to be the same with that of the dry ground condition within which the earth pressure is acting on the wall by the creation of the plastic zone during shaft excavation. An example study shows that the vertical stress increases by about 1.4 times and the horizontal earth pressure increases up to 2.5 times compared to the dry ground condition. The estimated values from the proposed equation considering seepage forces and the calculated values from numerical analysis with "effective stress plus seepage force" show similar values, which verifies appropriateness of the proposed equation to estimate the earth pressure under the seepage condition.

• Journal of The Korean Association For Science Education
• /
• v.19 no.1
• /
• pp.8-18
• /
• 1999

The purpose of this study is to investigate middle school student's conceptual change about Force and Motion by the courseware based on constructivism. It is well known to science educators that misconcrptions about physics concepts are hardly changed into scientific ones. So as to change student's misconceptions about force and motion, the courseware was developed through the analysis of students' conceptions. 20 students were tested before and after learning through the courseware. One of the questions was about the direction of force acting on the ball thrown in the air when it is rising, at the top, and falling. The other was about the magnitudes and directions of forces acting on a car when it is accelerating, in uniform velocity, and decelerating. The results are as follows: In case of vertical motion, all students had misconceptions before learning, but after learning 5 students(25%) have changed their ideas into scientific ones. In case of horizontal motion, 9(45%) out of 20 students who had misconceptions about force and motion have changed their ideas into scientific ones.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.41 no.4
• /
• pp.277-283
• /
• 2017

In this study, we investigated how a jumping strategy changes with an increase in the vertical jump height for a resultant ground reaction force (GRF) vector. We expected that the resultant force vector between two sequential motion phases (i.e., countermovement and push-off) of the countermovement jump would significantly change with the vertical jump height to take advantage of the resulting supportive force (i.e., an initial push-off force larger than the body weight) through the countermovement phase. Nine healthy young subjects were instructed to jump straight up to five different height levels ranging from 191 cm to 221 cm, and the kinematic and kinetic data were obtained in regular trials. The results showed that a lower center of mass position and larger resultant force vector were clearly observed in a higher jump, implying that the countermovement strategy changed with the vertical jump height to prepare for sufficient joint deviation and obtain a force advantage for larger push-off work.

• Tribology and Lubricants
• /
• v.29 no.2
• /
• pp.91-97
• /
• 2013

Quantifying the nanoscale force between the atomic force microscopy (AFM) probe of a force-sensing cantilever and the sample is one of the challenges faced by AFM researchers. The normal force calibration is straightforward; however, the lateral force is complicated due to the twisting motion of the cantilever. Force measurement in a liquid environment is often needed for biological applications; however, calibrating the force of the AFM probes for those applications is more difficult owing to the limitations of conventional calibration methods. In this work, an accurate nondestructive lateral force calibration method using multiple pivot loading was proposed for liquid environment. The torque sensitivity at the location of the integrated probe was extrapolated based on accurately measured torque sensitivities across the cantilever width along a few cantilever lengths. The uncertainty of the torque sensitivity at the location of the integrated tip was about 13%, which is significantly smaller than those for other calibration methods in a liquid environment.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.10 no.5
• /
• pp.350-355
• /
• 2000

The fabrication of sapphire wafer in C plane has been developed by horizontal Bridgeman method and GaN based semiconductor epitaxial growth has been carried out in metal organic chemical vapour deposition. The single crystalline ingot of sapphire has been utilized for 2 inch sapphire wafers and wafer slicing and lapping machines were designed. These several steps of lapping processes provided the mirror-like surface of sapphire wafer. The measurements of the surface flatness and the roughness were carried out by the atomic force microscope. The GaN thin film growth on the developed wafer was confirmed the wafer quality and applicability to blue light emitting devices.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2010.10a
• /
• pp.337-338
• /
• 2010

Projectile is said that objects thrown on the ground of the atmosphere. This objects exercises the parabolic motion because of the fact under the influence of gravity in the direction perpendicular and it does not include the horizontal force neglecting air resistance. In this paper, the experiment target is where subsidence occurred by that some of the road is lost to a certain depth using projectile motion. It says how far away and falling from the edge of the road when you have gone over the edge of depressed road that a car was driving at a constant speed.