• Proceeding of EDISON Challenge
• /
• 2016.11a
• /
• pp.74-77
• /
• 2016

본 연구에서는 Scream Jet Intake에 발생하는 충격파 경계층에서 속도를 Supersonic에서 Subsonic으로 줄였을 때의 상호작용을 EDISON_CFD로 해석하기로 한다. 이상적인 공기 유동에서 충격파 경계층의 각도를 $15^{\circ}{\sim}20^{\circ}$, $25^{\circ}{\sim}30^{\circ}$, $15^{\circ}{\sim}40^{\circ}$, $25^{\circ}{\sim}50^{\circ}$와 같이 두 개($5^{\circ}$, $25^{\circ}$)의 각도 차이를 두어 이중압축램프에서의 유동현상을 EDISON_CFD로 수행하고 분석하였다.

• Tunnel and Underground Space
• /
• v.13 no.3
• /
• pp.215-224
• /
• 2003

Weathering in nature was simulated by freeze-thaw cyclic test which represents mechanical weathering. Measured physical properties were elastic wave velocities, absorption rate, volume change and weight change. Uniaxial compression tests were also conducted before and after the weathering tests. The change in weight and volume of the specimens were not clearly related to the weathering process, but P, S wave velocities, uniaxial compression strength and Young's modulus were clearly decreased as weathering progresses. Test result can be used for the assessment of long-term stability of rock slopes.

• The Journal of the Acoustical Society of Korea
• /
• v.9 no.6
• /
• pp.81-90
• /
• 1990

유체 동역학에서, 난류에 의해 수중 구조물에 가해지는 압력과 전단력의 측정은 중요한 문제이 다. 이러한 유체의 흐름에 의한 압력과 전단력, 나아가 유체의 흐름방향까지 시간과 거리의 함수로 측정 할 수 있는 새로운 탄성표면파 센서가 개발되었다. 센서는 압축 인장형 전단력을 받는 두 개의 표면파 와 흐르는 유체 속의 표면파의 속도차는 또한 유체흐름에 의해 가해지는 압력에 비례한다. 정지류 속의 표면파와 흐르는 유체 속의 표면파의 속도차는 또한 유체흐름에 의해 가해지는 압력에 비례한다. 이 센 서를 응력 로젯과 같이 배열하면 유체의 진행방향도 함께 측정할 수 있다. 표면파 센서는 넓은 주파수 대역에 걸쳐 사용이 가능하므로, 적절히 설계하면 유체의 흐름에 의한 표면력과 유체의 진행방향을 동 시에 거리와 시간의 함수로서 국부적으로, 광역적으로 측정할 수 있다.

• Explosives and Blasting
• /
• v.28 no.2
• /
• pp.59-68
• /
• 2010

Building demolition and blasting work in urban areas has a possibility which has an effect on the structural stability of nearby structures. In this study, the compressive strength and chemical composition of decrepit concrete materials were estimated by Schmidt rebound test and XRD phase analysis. The damage index of the concrete materials was calculated by measured P-wave velocities. It was revealed that the constituents of the concrete materials affect on the compressive strength. The damage index decreases with increasing compressive strength and decreasing impact energy.

• Journal of the KSME
• /
• v.29 no.4
• /
• pp.376-384
• /
• 1989

압축성 유동은 유동의 속도(Mach 수)에 따라, 아음속에서 초음속으로 바뀜에 따라 지배 방정 식의 형태가 바뀜은 물론이고 천음속에서는 아음속과 초음속이 공존하므로 지배방정식 자체도 두 가지 형태가 공존하는 어려움이 앞선다. 또한 압축성 유동장에서는 비압축성 유동장에서는 없는 충격파를 전후하여 유동변수들의 큰 불연속이 존재하게 되고, 이러한 불연속선을 유한한 크기의 계산격차를 사용하여 정확하게 해석한다는 것이 그렇게 쉬운 일이 아니다. 또한 저속의 비압 축성 유동에 비하여 일반적으로 보다 많은 독립변수들을 동시에 다루어야 하므로 대형컴 퓨터 용량과 빠른 계산속도를 요구하게 되며 국내에서는 2∼3년 전까지만 하더라도 실질적인 연구가 매우 어려운 실정이었다. 따라서 본 글에서는 최근 들어 대학실험실에 고성능 퍼스널 컴퓨터의 도입과 더불어 활발하게 진행되고 있는 압축성 유동의 수치해석 연구에 대하여 그 동 안의 국내연구 결과들을 모아 분류, 정리해 보고 앞으로의 연구에 대하여 간단히 언급해 보고자 한다.

• Proceedings of the KIPE Conference
• /
• 2010.11a
• /
• pp.316-317
• /
• 2010

본 논문은 압축기용 영구자석 동기전동기의 효율 개선을 위한 새로운 운전 제어 방법에 대해 제안한다, 일반적으로 냉장고용 압축기는 종래에 고정속도로 운전되는 유도기를 많이 적용해 왔으나 최근 고효율화, 고성능화의 요구증대로 영구자석 동기전동기를 적용하여 가변속 제어가 가능하도록 구성한다. 최근 냉장고의 경우 대용량화 고효율화의 요구로 인해 더 넓은 운전 범위 운전 특성이 요구되고 있는 실정이다. 이에 따라 본 논문에서 제안하는 제어 방법은 넓은 운전 제어 및 고효율 운전이 가능하도록 운전 속도에 따라 구형파 제어 및 정현파 제어가 전환이 되어 속도 및 부하조건에 따라 최적 제어가 이루어지는 방법을 제안한다.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.10 no.4 s.50
• /
• pp.1-13
• /
• 2006

Soil and rock dynamic properties such as shear wave velocity $(V_s)$, compressional wave velocity $(V_p)$ and corresponding Poisson's ratio (v) are very important geotechnical parameters in predicting deformational behavior of structures as well as practicing seismic design and performance evaluation. In an effort to measure the parameter efficiently and accurately, various bore-hole seismic testing techniques have been, thus, developed and used during past several decades. In this study, cross-hole seismic testing technique which is known as the most reliable seismic method was adopted for obtaining geotechnical dynamic properties. To perform successfully the cross-hole test for rock as well as soil layers regardless of the ground water level, spring-loaded source which impact laterally a subsurface ground in vertical bore-hole was developed and applied at three study areas, which contain four sites composed of two existing port sites and two new LNG storage facility sites. The geotechnical dynamic properties such as $V_s,\;V_p$ and v with depth from the soil surface to the engineering and seismic bedrock were efficiently determined from the laterally impacted cross-hole seismic tests at study sites, and were provided as the fundamental parameters for the seismic performance evaluation of the existing ports and the seismic design of the LNG storage facilities.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2005.09a
• /
• pp.155-175
• /
• 2005

Soil and rock dynamic properties such as shear wave velocity (VS), compressional wave velocity (VP) and corresponding Poisson's ratio ( v ) are very important geotechnical parameters in predicting deformational behavior of structures as well as practicing seismic design and performance evaluation. In an effort to measure the parameter efficiently and accurately, various bore-hole seismic testing techniques have been, thus, developed and used during past several decades. In this study, cross-hole seismic testing technique which is known as the most reliable seismic method was adopted for obtaining geotechnical dynamic properties. To perform successfully the cross-hole test for rock as well as soil layers regardless of the ground water level, spring-loaded source which impact laterally a subsurface ground in vertical bore-hole was developed and applied at three study areas, which contain four sites composed of two existing port sites and two new LNG storage facility sites. The geotechnical dynamic properties such as VS, VP and v with depth were efficiently determined from the laterally impacted cross-hole seismic tests at study sites, and were provided as the fundamental parameters for the seismic performance evaluation of the existing ports and the seismic design of the LNG storage facilities.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.26 no.5
• /
• pp.291-296
• /
• 2006

The residual stress in shot-peened Al 7075 alloy was evaluated using surface acoustic wave (SAW). Shot peening was conducted to produce a variation in the residual stress with the depth below the surface under a shot velocity of 30 m/s. The SAW velocity was measured from the V(z) curve using a scanning acoustic microscopy (SAM). The Vickers hardness profile from the surface showed a significant work hardening near the surface layer with a thickness of about 0.25 mm. As the residual stress became more compressive, the SAW velocity increased, whereas as the residual stress became more tensile, the SAW velocity decreased. The variation in the SAW velocity through the shot peened surface layer was in good agreement with the distribution of the residual stress measured by X-ray diffraction technique.

• Geophysics and Geophysical Exploration
• /
• v.9 no.1
• /
• pp.108-113
• /
• 2006

Urban conditions, such as existing underground facilities and ambient noise due to cultural activity, restrict the general application of conventional geophysical techniques. At a tunnelling site in an urban area along an existing railroad, we used the refraction microtremor (REMI) technique (Louie, 2001) as an alternative way to get geotechnical information. The REMI method uses ambient noise recorded by standard refraction equipment and a linear geophone array to derive a shear-wave velocity profile. In the inversion procedure, the Rayleigh wave dispersion curve is picked from a wavefield transformation, and iteratively modelled to get the S-wave velocity structure. The REMI survey was carried out along the line of the planned railway tunnel. At this site vibrations from trains and cars provided strong seismic sources that allowed REMI to be very effective. The objective of the survey was to evaluate the rock mass rating (RMR), using shear-wave velocity information from REMI. First, the relation between uniaxial compressive strength, which is a component of the RMR, and shear-wave velocity from laboratory tests was studied to learn whether shear-wave velocity and RMR are closely related. Then Suspension PS (SPS) logging was performed in selected boreholes along the profile, in order to draw out the quantitative relation between the shear-wave velocity from SPS logging and the RMR determined from inspection of core from the same boreholes. In these tests, shear-wave velocity showed fairly good correlation with RMR. A good relation between shear-wave velocity from REMI and RMR could be obtained, so it is possible to estimate the RMR of the entire profile for use in design of the underground tunnel.