• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.7 no.2
• /
• pp.60-65
• /
• 2008

The high-technology industries including a semi-conductor and an information communication need an ultra-precision technology from the technological points of view. Nano technology based on an ultra-precision technology is being studied to overcome the delicate technology that may occur in the semi-conductor fields. Then, the transferring equipment with high resolution and long displacement becomes an important technology. The goal of this study is to analyze the displacement magnification mechanism driven by piezoelectric actuator which has high resolution and fast response characteristics using flexure hinge with the merits of soft displacement, negligible back-lash and stick-slip, and no-lubrication. The analyses to reduce the magnification losses occurred during the magnification process are performed using ANSYS software based on FEM. The five design variables such as arm thickness, thickness of hinge, radius of hinge, length of input side at the 1st lever and magnification ratio of 1st lever are optimized to induce the maximum magnification ratio using Taguchi method.

• Solar Energy
• /
• v.17 no.3
• /
• pp.59-66
• /
• 1997

The present study adopted the PTV method for the velocity acquisition. The system consists of an image grabber built-in a personal computer and a laser-based sheet light projector and particle identification softwares. Velocity vectors are obtained, by PTV and they are used as velocity components for Poisson equation for pressure. Related boundary conditions and no-slip condition at solid wall and the linear velocity extrapolation on the upper side of cavity are well examined for the present study. For calculation of pressure, resolution of grid is basically $40{\times}40$ and 2-dimensional uniform mesh using MAC staggered grid is adopted. The result of experiment reveal that, newly suggested measuring method is capable of estimating pressure and velocity distribution of flow field reasonably.

• Proceedings of the SAREK Conference
• /
• 2009.06a
• /
• pp.154-158
• /
• 2009

The vortex ventilation system (VV) which uses a rotating finned swirler installed coaxially with the exhaust duct is a very effective local ventilator. VV can enhance the capture depth by a factor of 3-5 compared to the conventional exhaust hood, in the absence of any solid walls nearby. In real situations there may exist ceiling, side wall and floor, all of which can affect the flow field and suction performance by way of the no-slip condition on the walls. 3D CFD simulation was performed in order to see the effect of the floor on the capture performance of the VV. The presence of floor reduced suction flow velocity, and increased the critical rotational speed which is the rotational speed required for stable vortex formation. Flow velocity profile along the axis could be well approximated by a universal functional form when the distance from the exhaust inlet is non-dimensionalized by the distance to the floor. Capture depth, define by the distance from the exhaust inlet to a point of velocity decreased to 10% of that at the inlet, is reduced by about 10% when the floor distance is 6 times the exhaust hood diameter.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.8 s.227
• /
• pp.1125-1134
• /
• 2004

This paper presents a mathematical model which is about the dynamics of not only a two wheel steering vehicle but a four wheel steering vehicle. A sliding mode ABS control strategy and PID rear wheel control logic are developed to improve the brake and cornering performances, and enhance the stability during emergency maneuvers. The performances of the controllers are evaluated under the various driving road conditions and driving situations. The numerical study shows that the proposed full car model is sufficient to accurately predict the vehicle response. The proposed ABS controller reduces the stopping distance and increases the vehicle stability. The results also prove that the ABS controller can be employed to a four wheel steering vehicle and improves its performance. The four wheel steering vehicle with PID rear wheel controller shows increase of stability when a vehicle speed is high and sharp cornering maneuver when a vehicle speed is low compared to that of a two wheel steer vehicle.

• Journal of computational fluids engineering
• /
• v.18 no.4
• /
• pp.17-24
• /
• 2013

In this study, we consider the characteristics of channel flow in the presence of an infinite streamwise array of equispaced identical rotating circular cylinders. This flow configuration can be regarded as a model representing a micro channel or an internal heat exchanger with cylindrical vortex generators. A numerical parametric study has been carried out by varying Reynolds number based on the bulk mean velocity and the cylinder diameter, and the gap between the cylinders and the channel wall for some selected angular speeds. An immersed boundary method was employed to facilitate implementing the cylinders on a Cartesian grid system. No-slip condition is employed at all solid boundaries including the cylinders, and the flow is assumed to be periodic in the streamwise direction. The presence of the rotating circular cylinders arranged periodically in the streamwise direction causes a significant topological change of the flow, leading to increase of mean friction on the channel walls. More quantitative results as well as qualitative physical explanations are presented to justify the effectiveness of rotating cylinders to modify flow topology, which might be used to enhance heat transfer on the channel walls.

• Tribology and Lubricants
• /
• v.10 no.1
• /
• pp.14-26
• /
• 1994

The minimum oil film thickness(MOFT) in the connecting-rod bearing of a 1.5 liter, L-4, gasoline engine is measured up to 5500 rpm and calculated to study the dynamically loaded engine bearing. Short bearing approximation and Mobility method are used for theoretical analysis of oil film characteristics. And cylinder pressure, crank-pin surface temperature and bearing temperature are measured as the input data of theoretical analysis. The MOFT are measured by the total capacitance method(TCM). To improve the reliability of the test results, a reasonable determination method of bearing clearance is introduced and used, and the effects of cavitation and aeration on the test results are neglected. The crankshaft is grounded by means of a slip ring. A scissor type linkage system was developed to measure the MOFT and bearing temperature. The effects of engine speed, load and oil viscosity on the measured and calculated minimum oil film thicknesses are investigated at 1500 to 5500 rpm. From the comparison between the measured and calculated MOFT, it is found that a qualitative similarity exists between them, but in all cases, the measured MOFT are smaller than those calculated.

• 한국가시화정보학회:학술대회논문집
• /
• 2004.12a
• /
• pp.119-124
• /
• 2004

Experimental study was conducted to characterize the flow effect of particle migration in a microchannel which can be used to deliver small amount of liquids, drugs, biological agents and particles in microfluidic devices. Fluorescent particles of $1\{mu}m$ diameter were used to obtain velocity profiles of the fluid in which large particles of $10\{mu}m$ diameter were suspended at different volume fraction of 0.6 and $0.8\%$. Measurements were obtained by using micro-PIV system which contains a Nd:YAG laser with a light of 532-nm wavelength, an inverted epi-fluorescent microscope and a cooled CCD camera to record particle images. The volume fraction of $\phi$ and the particle Reynolds number $Re_p$Rep were used as a parameter to assess the influence of the velocity profile of the suspensions. To expect the slip velocity between the particle and fluids, experiments were carried out at low volume fraction. It was shown that the velocity profile was not influenced by Rep but influenced by the volume fraction, which is in similar trend with the previous study.

• Annals of Clinical Neurophysiology
• /
• v.1 no.2
• /
• pp.173-181
• /
• 1999

Eye movements serve vision by placing the image of an object on the fovea of each retina, and by preventing slippage of images on the retina. The brain employs two modes of ocular motor control, fast eye movements (saccades) and smooth eye movements. Saccades bring the fovea to a target, and smooth eye movements prevent retinal image slip. Smooth eye movements comprise smooth pursuit, the optokinetic reflex, the vestibulo-ocular reflex (VOR), vergence, and fixation. Saccades achieve rapid refixation of targets that fall on the extrafoveal retina by moving the eyes at peak velocities that can exceed $700^{\circ}/s$. Various brain lesions can affect saccadic latency, velocity, or accuracy. Smooth pursuit maintains fixation of a slowly moving target. The pursuit system responds to slippage of an image near the fovea in order to accelerate the eyes to a velocity that matches that of the target. When smooth eye movements velocity fails to match target velocity, catch-up saccades are used to compensate for limited smooth pursuit velocities. The VOR subserves vision by generating conjugate eye movements that are equal and opposite to head movements. If the VOR gain (the ratio of eye velocity to head velocity) is too high or too low, the target image is off the fovea, and head motion causes oscillopsia, an illusory to-and-fro movement of the environment.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.5 no.1
• /
• pp.110-119
• /
• 1997

Four wheel steering(4WS) systems which can control the lateral and yaw motions of vehicles by steering front and rear wheels simultaneously, have been regarded as effective for improving the stability and handing performance of vehicles. However, since the 4WS systems depend only on the lateral force of tire, they have some limitation due to the nonlinear characteristics of tire related with the saturation phenomenon of lateral force to the slip angle of tire in a near-limit-performance maneuvering range. In this study, in other to evaluate the effect of nonlinear characteristics of tire on the dynamic performance of vehicles, a new concept for driving the cornering stiffness of nonlinear tire by using the "Magic Formula" tire model is proposed. In addition, the nonlinear 4WS vehicle model is constructed based on the proposed cornering stiffness of nonlinear tire. It is noted from simulation that the nonlinear characteristics of tire affect greatly on the 4WS vehicle performance.rformance.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1999.10a
• /
• pp.387-394
• /
• 1999

Artificial Neural Network (ANN) is a computational model inspired by the structure and operations of the brain. It is massively parallel system consisting of a large number of highly interconnected and simple processing units. The purpose of this paper is to verify the applicability of ANN to predict experimental results through the use of measured experimental data. Although there have been accumulated data based on hysteretic characteristics of structural element with cyclic loading tests, it is difficult to directly apply them for the analysis of elastic and plastic response. Thus, simple models with mathematical formula such as Bi-Linear Model, Ramberg-Osgood Model, Degrading Tri Model, Takeda Model, Slip type Model, and etc, have been used. To verify the practicality and capability of this study, ANN is adapted to several models with mathematical formula using numerical data To show the efficiency of ANN in nonlinear analysis, it is important to determine the adequate input and output variables of hysteretic models and to minimize an error in ANN process. The application example is Beam-Column joint test using the ANN in modeling of the linear and nonlinear hysteretic behavior of structure.