• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1173-1176
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• 2004

In a previous work we reported the bistable property by doping a chiral material in a splay cell. The bistable states are the splay state and the metastable 180$^{\circ}$twist state. The retention time of the metastable state can be changed by the variation of d/p (cell gap over pitch), cell gap, pretilt angle, azimuthal anchoring force, liquid crystal material, and so on. In this paper we will present uniform bend transition and twist retention time improvement in a multi-domain BCSN LC cell by using the multi cell gap method.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1147-1150
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• 2004

We studied on an electro-optical (EO) hysteresis, coming from the in-plane modulation of the molecular reorientation, in highly twisted nematic liquid crystal devices. Varying a ratio d/$P_0$ of the cell thickness d to the natural pitch $P_0$, the EO hysteresis and the twisted angle transition were observed and analyzed in terms of the periodicity of the in-plane modulation within the continuum theory.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.93-100
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• 2007

Post swirl stator is an energy saving device to recover rotational energy of the propeller. To optimize the performance of post swirl stator in container vessels, computational fluid dynamics using body force method was introduced. A commercial code Fluent was used in conjunction with body force distributed on the surface of actuator disk which is located in the propeller plane to optimize pitch angle of the post swirl stator blade. This study showed that CFD is an important tool to simulate flow behind ship with propeller, rudder and post swirl stator.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.16 no.3
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• pp.1-6
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• 2008

The stalling speed flight test of light airplane, ChangGong-91, was performed to acquire the certification. With power-off engine condition, the wings level stall flight tests were conducted at the aircraft configuration of various flap angle - clean, 20degree, and full flap, respectively. They were performed considering with the combination of the maximum and minimum test weight, and forward and afterward center of gravity. The stalling speeds and the minimum speeds of light airplane were determined from the results of flight test. Also, the appropriateness of stall warning speeds are evaluated through the flight test measures. The airplane is recoverable only with pitch control and engine throttle from stall state without exceptional operation.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.316-321
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• 2001

The optical storage device has recently experienced significant improvement, especially for the aspects of high capacity and fast transfer rate. However, it is necessary to study a new shape of air bearing surface for the rotary type actuator because the optical storage device has the lower access time than that of HDD (Hard Disk Drives). In this study, we proposed the air bearing shape by using SA (Simulated Annealing) algorithm which is very effective to achieve the global optimum instead of many local optimums. The objective of optimization is to minimize the deviation in flying height from a target value 100nm. In addition, the pitch and roll angle should be maintained within the operation limits.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.319-328
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• 2000

This paper presents a new design method of the 1 generation wheel bearing unit using a numerical optimization technique in order to increase bearing fatigue life. For calculating the fatigue life, a method of load analysis is studied on the automotive wheel bearing system. The design variables selected are ball size, initial contact angle, number of balls, pitch diameter, pre-load, and distance between ball centers. The method of feasible directions in ADS (Automated Design Synthesis) is utilized to automatically find the optimum design variables. To validate the design method, a computer program is developed and applied to a practical passenger car model. The optimum design results demonstrated the effectiveness of the proposed design method showing that the system life of the optimally designed wheel bearing unit is enhanced in comparison with that of the initial ones within the given available design space.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.8
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• pp.711-717
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• 2007

Shape optimization of a staggered herringbone groove micromixer using three-dimensional Navier-Stokes analysis has been carried using Kriging model. The analysis of the degree of mixing is performed by the calculation of spatial data statistics. The calculation of the variance of the mass fraction at various nodes on a plane in the channel is used to quantify mixing. A numerical optimization technique with Kriging model is applied to optimize the shape of the grooves on a single wall of the channel. Three design variables, namely, the ratio of groove width to groove pitch, the ratio of the groove depth to channel height ratio and the angle of the groove, are selected for optimization. A mixing index is used as the objective function. The results of the optimization show that the mixing is very sensitive to the shape of the groove which can be used in controlling mixing in microdevices.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.1
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• pp.20-29
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• 2009

There are concerns about the influence of the gust wind caused by helicopters affecting the moving vehicles while hovering over the road during rescue activities. For the understanding of such complicated flow. numerical simulation of a rotor hovering above the ground has been carried out, changing the rotor/ground clearances. The rotor thrust is kept constant. and the rotor control is determined by trim adjustments incorporated into the CFD algorithm. Collective pitch angle and the required power decreases with the rotor/ground clearance which agrees with experience. Changes of the flowfield near the rotor with regard to the rotor height are investigated based on the calculated results.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.3
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• pp.271-277
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• 2011

This study presents a nondestructive test for underwater PVC pipes. To use guided ultrasonic waves, specially denoted by cylindrical Lamb waves, a test setup was made in a water tank using the pitch and catch mode and specimens were made to give artificial cutouts located in the circumferential direction of the pipes. Total three states of damaged levels were considered to see how the guided waves interact with the defects. For the experimental adjustments, three different pipe diameters (60, 90, 114 mm) were tested, and two factors - incident angle (10 and $40^{\circ}$) and distance (50 and 200 mm) - were tried. From the results, regardless of the diameters and two experimental factors, it is shown that the degrees of defects were recognized through amplitude and arrived time of the very first part of the received cylindrical Lamb waves. Between amplitude and arrived time, it is found that the amplitude gives more sensitive results.

• Journal of KSNVE
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• v.8 no.6
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• pp.1015-1022
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• 1998

This paper addresses the results of an experimental and analytical research of a helical coil spring subjected to dynamic behavior using space curve vector after considering elongation rate. Vibrations in helical coil spring can be divided into 3 modes such as vibrations of coil spring center axis' vertical direction. axis' horizontal direction, direction about center axis. However. these 3 modes are dependent one another and are characterized as coupled. The dependency was proved through both theoretically and experimentally analyzing the results of dynamic characteristics of coil spring center axis' vertical direction vibration by transfer matrix method using the governing equation of static equilibrium. Also this paper shows that pitch angle and active coils in coil spring affect the dynamic spring characteristics of the above 3 modes and are especially sensitive to the mode for vibration of axis' horizontal direction which most affects especially on dynamo stability of helical coil spring.