• The Journal of the Acoustical Society of Korea
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• 제15권1E호
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• pp.39-44
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• 1996

Matched field localization schemes often show a high sensitivity to acoustic variabilities due to mismatch between assumed and actual environments. In this paper, we focus on the effect of source motion or Doppler on matched field processing (MEP). to accomplish this, MFP is extended to treat a moving source problem with normal mode description of the sound field. the extension involves both the temporally nonstationary and spatially inhomogeneous nature of the sound field generated by a time-harmonic point source moving uniformly in a stratified oceanic waveguide. It is demonstrated that the impact of source motion can be significant to MEP although the velocity of a moving source is much smaller than the sound velocity of the oceanic waveguide. In addition, a criteria for minimizing the effect of Doppler on MFP is discussed.

• 한국분무공학회지
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• 제22권3호
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• pp.129-136
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• 2017

Effects of collision angle on heat transfer characteristics of a liquid droplet impinging on a heated wall above the Leidenfrost point temperature were experimentally investigated. The heated wall and droplet temperatures were $506^{\circ}C$ and $100^{\circ}C$, respectively, and the impact angle varied from $20^{\circ}$ to $90^{\circ}$ while the normal collision velocity was constant at 0.27 m/s. The droplet collision behaviors and the surface temperature distribution were measured using synchronized high-speed video and infrared cameras. The major physical parameters influencing upon droplet-wall collision heat transfer, such as residence time, wall heat flux, effective heat transfer area, heat transfer amount, were analyzed. It was found at the constant normal collision velocity that the residence time, wall heat flux and effective heat transfer area were hardly not changed, resulting in the almost constant heat transfer amount.

• 해양환경안전학회지
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• 제28권6호
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• pp.890-898
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• 2022

해상공사에서 발생하는 부유사는 해수의 탁도를 증가시키고 광량을 감소시켜 해양생물에 악영향을 미치므로 해양환경영향평가에서 중요한 요소이다. 하지만 평가에 적용되는 인자에 대한 공식적인 자료의 부족과 평가자의 능력에 따라 그 영향이 달리 평가되고 있다. 따라서 본 연구에서는 해역이용영향평가센터에서 검토한 3년간(2012-2014)의 매립, 준설, 외곽시설물 설치 등 총 58건 사업에 대한 부유사 확산 평가에 대한 실태를 진단하고 개선방안을 제시하였다. 개선방안 제시를 위해 4가지의 평가지표(격자체계의 적정성, 원단위의 적정성, 대표입경 및 침강속도의 적정성)를 적용하였다. 각 항목별 신뢰도에 평균점수 분석결과, 격자체계는 25점, 원단위는 60점, 대표입경은 34점 그리고 침강속도는 17점으로 평가항목에 대한 개선방안이 필요한 것으로 나타났다. 본 연구에서는 부유사 확산 평가상태에 대한 진단 및 신뢰도 평가 결과를 활용하여 부유사 확산예측에 대한 개선방안을 제안하였다. 먼저, 부유사 발생원단위 및 대표입경별 침강속도에 대한 공신력 있는 값이 가이드라인을 통해 제공해야 한다. 그리고 실무에선 신뢰성 향상을 위해 격자체계의 적정성과 결과의 검증을 철저히 해야 한다.

• 한국지반공학회논문집
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• 제29권5호
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• pp.19-27
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• 2013

여름철 강우로 인한 산사태는 대부분 토석류의 형태로 나타난다. 토석류는 빠른 이동속도와 체적 때문에 경제적 손실 뿐만 아니라 많은 인명피해를 일으킨다. 토석류 해석 프로그램인 FLO-2D를 사용하여 유동학적 인자인 점성과 항복응력에 따른 토석류의 이동과 퇴적 특성을 분석하였다. 수치해석을 수행한 결과, 점성이 증가할수록 토석류 입자간의 응집력이 증가하여 토석류의 퇴적거리와 속도가 감소한다. 그에 따라 유동심은 증가하고 충격력은 감소하였다. 항복응력은 토석류의 발생과 퇴적에 큰 영향을 미치는 요인이다. 항복응력이 증가할수록 충격력은 증가하였다. 수치 해석 결과에 의하면, 토석류의 이동속도는 주로 점성에 의존하나 토석류의 퇴적 특성(퇴적거리, 퇴적 폭, 퇴적면적)은 점성과 항복응력에 의존한다.

• Bulletin of the Korean Chemical Society
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• 제32권6호
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• pp.2027-2031
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• 2011

Molecular dynamics simulation is used to study the binary collisions of nanometer-sized droplets of argon in the presence of a surrounding gas. By systematically varying the droplet size, the impact parameter and the velocity of collision, the outcome of such collisions were examined and they can be classified into coalescence, separation and shattering. If one of the colliding droplets is half or less than the other in diameter, a shattering is not possible to occur. The threshold of impact parameter for a given separation was studied by adjusting the Weber number. Overall nanoscale droplets were more likely to coalesce than the macroscopic sized ones due to their high surface-to-volume ratio.

• Journal of Mechanical Science and Technology
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• 제15권2호
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• pp.180-191
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• 2001

The widely used spot welded sections of automobiles(hat and double hat shaped section members) absorb most of the energy in a front-end collision. The sections were tested with respect to axial static(10mm/min) and quasi-static(1000mm/min) loads. Based on these test results, specimens with various thicknesses, width ratios and spot weld pitches on the flange were tested at high impact velocity(7.19m/sec and 7.94m/sec) which simulates an actual car crash. Characteristics of collapse have been reviewed and structures for optimal energy absorbing capacity is suggested.

• 반도체디스플레이기술학회지
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• 제6권1호
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• pp.37-41
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• 2007

Recently PZT is used in ultra precision mechanism field. PZT has a small motion range although it has a high resolution. Many methods, such as inchworm, impact driving, etc., have been applied for the expansion of the motion range.? In this study, the new actuating mechanism for rotational motion with two PZT actuators is proposed. The ultra precision rotational actuator which is made by proposed mechanism is able to operate both coarse and fine motion. The design parameters of the proposed mechanism are considered to improve the performance of the system. The rotational stage which is applied by the proposed mechanism is fabricated. The resolution and velocity for fabricated rotational stage are measured by laser interferometer.

• 한국철도학회논문집
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• 제6권1호
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• pp.15-20
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• 2003

The computer simulation techniques were adopted to evaluate the effects of seating positions of passenger under various accident scenarios. The baseline of computer simulation model was tuned by the sled impact tests which conducted under the upright and standard seating positions. This study shows the effect of relative velocity between occupant and struck vehicle while occupant is impacted to a front seat's seatback. Although, base on the current accident scenarios, The KHST is performed well enough to protect average adult male occupants. However, Results from the tests indicate small size occupant or higher impact speed may cause sever neck and femur injuries.

• 한국운동역학회지
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• 제13권1호
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• pp.173-184
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• 2003

The purpose of this study was to investigate the batting characteristics in elite baseball players. Seven skilled collegiate players hit the ball which was thrown by a pitching machine linearly and strongly to the center of the field. Time, velocity, angle and pound reaction force variables were measured by using high-speed video cameras and pound reaction force analyzer. The results were as follows: 1. The elite players finished their stride performance in a short time and they stayed longer in a swing phase. The increases in the range of trunk rotation were associated with the delay of the swing phase. 2. The 'take-back' phenomenon in the trunk was showed after the stride phase. 3. The down swing demonstrated powerful line drives. 4. Equivalent body weights were placed on both feet during the ready phase. 95% of the body weights were moved to the rear foot during the stride phase, whereas the body weights were driven to the front foot during the swing phase. 95% of the body weights were placed on the front foot at impact.

• 대한기계학회논문집A
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• 제26권5호
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• pp.939-951
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• 2002

We propose a new multiscale Galerkin method based on interpolation wavelets for two-dimensional Poisson's and plane elasticity problems. The major contributions of the present work are: 1) full multiresolution numerical analysis is carried out, 2) general boundaries are handled by a fictitious domain method without using a penalty term or the Lagrange multiplier, 3) no special integration rule is necessary unlike in the (bi-)orthogonal wavelet-based methods, and 4) an efficient adaptive scheme is easy to incorporate. Several benchmark-type problems are considered to show the effectiveness and the potentials of the present approach. is 1-2m/s and impact deformation of the electrode depends on the strain rate at that velocity, the dynamic behavior of the sinter-forged Cu-Cr is a key to investigate the impact characteristics of the electrodes. The dynamic response of the material at the high strain rate is obtained from the split Hopkinson pressure bar test using disc-type specimens. Experimental results from both quasi-static and dynamic compressive tests are Interpolated to construct the Johnson-Cook model as the constitutive relation that should be applied to simulation of the dynamic behavior of the electrodes. The impact characteristics of a vacuum interrupter are investigated with computer simulations by changing the value of five parameters such as the initial velocity of a movable electrode, the added mass of a movable electrode, the wipe spring constant, initial offset of a wipe spring and the virtual fixed spring constant.