• 대기
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• 제17권3호
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• pp.231-240
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• 2007

The flow regimes of continuously stratified flow over a double mountain and the effects of a double mountain on wave breaking, upstream blocking, and severe downslope windstorms are investigated using a mesoscale numerical model (ARPS). According to the occurrence or non-occurrence of wave breaking and upstream blocking, three different flow regimes are identified over a double mountain. Higher critical Froude numbers are required for wave breaking and upstream blocking initiation for a double mountain than for an isolated mountain. This means that the nonlinearity and blocking effect for a double mountain is larger than that for an isolated mountain. As the separation distance between two mountains decreases, the degree of flow nonlinearity increases, while the blocking effect decreases. A rapid increase of the surface horizontal velocity downwind of each mountain near the critical mountain height for wave breaking initiation indicates that severe downslope windstorms are enhanced by wave breaking. For the flow with wave breaking, the numerically calculated surface drag is much larger than theoretically calculated one because the region with the maximum negative perturbation pressure moves from the top to the downwind slope of each mountain as the internal jump propagating downwind occurs.

• 한국컴퓨터정보학회논문지
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• 제10권5호
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• pp.109-114
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• 2005

Twofish 암호알고리즘은 AES인 Rijndael 암호알고리즘에 비하여 알고리즘 자체가 간결하며, 구현의 용이성이 좋지만 처리속도가 느린 단점을 가진다. 그러므로 본 논문은 Twofish 암호알고리즘의 속도를 향상시키기 위하여 개선된 MDS 블록을 설계하였다. 기존 MDS 블록은 Twofish 암호시스템의 critical path를 점유하게 되는 블록으로서 처리속도의 병목현상으로 인한 속도저하의 문제점이 존재하였다. MDS 블록에서 연산자로 사용되는 곱셈연산을 감소시키기 위하여 본 논문은 LUT 연산과 modul-2o연산을 사용하여 MDS자체에 대한 속도저하 및 병목현상을 제거하였다 이러한 결과로 새롭게 설계된 MDS블록을 포함하는 Twofish 암호시스템은 기존 Twofish 암호시스템에 비하여 10$\%$정도 처리속도의 향상을 가져옴을 확인하였다.

• 소성∙가공
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• 제22권3호
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• pp.143-149
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• 2013

A new finite element model for the hydrostatic extrusion of a biaxial bar is introduced. In this model, a penalty contact algorithm, which is adopted to replace the traction boundary conditions due to the fluid in the container of the extruder, is incorporated into a consistent penalty finite element formulation for the viscoplastic deformation of a work piece during hydrostatic extrusion. Two parameters, introduced in the penalty contact algorithm in this study, a critical penalty contact pressure $P_0$ and a critical penalty contact distance $D_c$, are carefully examined for various process conditions. The proposed finite element model is applied to the hydrostatic extrusion of a Cu-clad Al bar. The extrusion loads and thickness ratios of the clad materials by the proposed model are compared in detail to values from experiments reported in the literature. Finally, it is concluded that the proposed finite element model is useful in practical implementations.

• 중환자간호학회지
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• 제4권1호
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• pp.65-73
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• 2011

Purpose: This study was to develop and evaluate stability and effects of an early exercise program for patients with open heart surgery. Methods: The subjects of this study were 30 patients who had either a coronary bypass surgery or a valvular heart surgery at a tertiary hospital in Seoul. The data was collected by observation and measurement from October 1, 2004 to November 15, 2004. Results: The early exercise program developed for this study consisted of range of motion exercise and walking. Intensity of walking was 1~3 METs and increased progressively to daily target distance. During exercise, the subjects were monitored heart rate, blood pressure and RPE (Rating of Perceived Exertion). The mean FIM (Functional Independent Measurements) score of subjects was significantly improved after the early exercise program. However, several complaints such as dizziness or pain were also reported. Most complaints were associated with chest tube and RPE. Conclusion: The early exercise program can help to recover patients' physical activities after surgery, and can be applied to most patients. Patients' RPE, dizziness and pain was possible limitations, therefore, active pain control and prevention of accidents for patients would be needed.

• Progress in Superconductivity
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• 제13권3호
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• pp.184-188
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• 2012

$MgB_2$ superconducting sheets have been fabricated by powder rolling method using mixture of Mg and B powders. Sheet-type $MgB_2$ bulk samples of ~10 mm width and 50-100 mm long were squeezed out after compacted by two rotating rolls of 130 mm diameter with gap distance of 0.5 mm and speed of ~40 cm/min (~1 rpm). The nominal composition of Mg, which is ductile metal, was added up to 30% to facilitate forming the $MgB_2$ sheets. The annealed samples at $900^{\circ}C$ and 3 hrs showed superconducting transition temperature of ~32 K and critical current densities at zero fields were ${\sim}10^5A/cm^2$ at 5 K and ${\sim}5{\times}10^4A/cm^2$ at 20 K.

• 대한기계학회논문집
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• 제17권11호
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• pp.2762-2772
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• 1993

The paper deals with the flutter of a cantilevered beam subjected to a rocket thrust generated by a solid rocket motor. It is saaumed that the rocket thrust is to be a constant follower thrust, and produced by the installation of a solid rocket motor to the tip end of the cantilevered beam. The rocket motor is considered to be a rigid body having finite sizes, but not a mass point as it has been assumed so far. Governing equations are derived through the extended Hamilton's principle, and finite element method is applied to obtain the theoretical prediction for critical follower thrust. The maximum follower thrust is also calculated through the change of shear deformation parameter of the beam in the numerical simulation. The theoretical prediction for flutter or stability is verified by experiment. The experimental results show that critical follower thrust in theory agrees well with the experimental value taking account of the magnitude, rotary inertia of the rocket motor and the distance from the tip end of the beam to the center of gravity of the rocket motor.

• Journal of Advanced Marine Engineering and Technology
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• 제38권10호
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• pp.1263-1268
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• 2014

In this study, the variations of swirl center according to evaluating position have been investigated in a steady flow bench of SI engine. For the experiments, two engine heads with different intake valve angles ($11^{\circ}$ and $26^{\circ}$) were tested in the flow bench by varying the evaluating position (1.75~6.0B) and valve lift (2~10 mm). Particle image velocimetry was used to measure the velocity field inside the engine cylinder. The swirl center position is found with a critical point theory and the intensity of turbulence is calculated from PIV velocity data. The results show that the center of swirl is located closer to the center of cylinder and turbulence intensity is lower, when the intake valve angle is the smaller. It is conventional to evaluate the swirl ratio at 1.75B position in the steady flow bench of SI engine. At this position, however, the distance of swirl center from the cylinder center scatters significantly for the variation of valve lift, and the turbulence intensity is much stronger regardless of the valve angle. Thus, to estimate the flow at the end of compression stroke in a real engine from the data in the steady flow experiments, the evaluation position should be moved further downstream more than 4.5B.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.274-279
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• 2004

Currently, carbon-fiber reinforced plastics(CFRP) are widely used in both space and civil aircraft due to their superior stiffness and strength to weight ratios compared to conventional metallic materials. This paper is to study the effects of curvature and stacking sequence on the penetration characteristics of composite laminated shell. And were performed to investigate the penetration characteristics of composite laminated shells by the oblique impact. They are stacked to [0$_3$/90$_3$]s, [90$_3$/0$_3$]s and [0$_2$/90$_3$/0]s, [90$_2$/0$_3$/90]s their interlaminar number two and fore. They are manufactured to varied curvature radius (R=100, 150, 200mm and $\infty$). When the specimen is subjected to transverse impact by a steel ball, the velocity of the steel ball was measured both before and after impact by determining the time for it to pass two ballistics-screen sensor located a known distance apart. In general, the critical penetration energy interface decrease and slope angle on the impact surface increased. [0$_3$/90$_3$]s and [0$_2$/90$_3$]s specimens higher than [90$_3$/0$_3$]s and [90$_2$/0$_3$/90]s specimens.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2009년도 IWAIT
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• pp.390-395
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• 2009

The robustness of audio fingerprinting system in a noisy environment is a principal challenge in the area of content-based audio retrieval. The selected feature for the audio fingerprints must be robust in a noisy environment and the computational complexity of the searching algorithm must be low enough to be executed in real-time. The audio fingerprint proposed by Philips uses expanded hash table lookup to compensate errors introduced by noise. The expanded hash table lookup increases the searching complexity by a factor of 33 times the degree of expansion defined by the hamming distance. We propose a new method to improve noise robustness of audio fingerprinting in noise environment using predominant pitch which reduces the bit error of created hash values. The sub-fingerprint of our approach method is computed in each time frames of audio. The time frame is transformed into the frequency domain using FFT. The obtained audio spectrum is divided into 33 critical bands. Finally, the 32-bit hash value is computed by difference of each bands of energy. And only store bits near predominant pitch. Predominant pitches are extracted in each time frames of audio. The extraction process consists of harmonic enhancement, harmonic summation and selecting a band among critical bands.

• Wind and Structures
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• 제14권1호
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• pp.55-70
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• 2011

This study investigates the design criteria required for wind barriers to protect vehicles running on an expressway under a high side wind. At the first stage of this study, the lateral deviations of vehicles in crosswinds were computed from the commercial software, CarSim and TruckSim, and the critical wind speeds for a car accident were then evaluated from a predefined car accident index. The critical wind speeds for driving stability were found to be 35 m/s for a small passenger car, yet 30 m/s for a truck and a bus. From the wind tunnel tests, the minimum height of a wind barrier required to reduce the wind speed by 50% was found to be 12.5% of the road width. In the case of parallel bridges, the placement of two edge wind barriers plus one wind barrier at center was recommended for a separation distance larger than 20 m (four lanes) and 10 m (six lanes) respectively, otherwise two wind barriers were recommended.