• 한국공작기계학회논문집
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• 제10권6호
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• pp.95-101
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• 2001

This work is concerned with construction of the intelligence stress predictor far compression strength evaluation using neural network-ultrasonic waves. The contact pressure in jointed plates was measured by using ultrasonic technique. Neural network is used to evaluate and predict contact pressure from the results of the calibration curves. The organized neural system was leaned with the accuracy of 99%, as a result of learning the ultrasonic echo ratio to the contact pressure measurement between SM45C and STS410 materials. And it could be evaluated and predicted with the accuracy of 90% in the evaluation of ultrasonic echo ratio difference in the same surface roughness and contact pressure, and 85% in the prediction of virtual ultrasonic echo ratio. Thus the proposed stress predictor is very useful for the evaluation and prediction of the contact pressure between SM45C and STS410 materials.

• 한국음향학회지
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• 제7권4호
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• pp.117-126
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• 1988

산란된 파동의 형태는 그 산란체의 기하학적 형상 및 위치에 따라 변한다. 본 논문에서는 매질 내에 임피던스를 가지는 무한 실린더가 있는 경우 평면 입사파에 대한 산란된 파동을 유도하였고 그 결과로부터 산란된 파동의 방향성을 나타내는 지표로서 전방 산란파의 peak 값에 대해 산란파의 크기가 반으로 떨어지는 각도를 구하였다. 이 각도를 검토해 본 결과 입사파의 주파수 및 거리에 따라 그 각의 변화가 뚜렷함을 볼 수 있었다. 따라서 매질 내에 어떠한 산란체가 있는 경우 이 각도가 산란체의 위치 및 형상을 추정하는데 유용하게 적용될 수 있을 것이라 생각된다.

• International Journal of Fluid Machinery and Systems
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• 제1권1호
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• pp.140-147
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• 2008

An experiment setup was introduced to study dynamic behaviour of different types of check valves and the effects of air entrainment on the check valve performance under pressure transient condition. The experiment results show that the check valves with low inertia, assisted by springs or small traveling distance/angle gave better performance under pressure transient condition than check valves without these features. Air entrainment was found to affect both wave speed and reverse velocity. With the increase of the initial air void fraction in pipeline, the experiment results show that the wave speed was reduced, the reverse velocity was increased. The first peak pressure increased initially and then decreased with the increase of the initial air void fraction, the pressure surge periods were increased proportionally with air void fraction due to the greatly reduced wave speed. The study can be applied to help choosing suitable check valves for a particular pumping system.

• 한국산업융합학회 논문집
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• 제2권2호
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• pp.115-124
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• 1999

The interaction of weak normal shock wave with turbulent boundary layer in a supersonic nozzle was investigated experimentally by wall static pressure measurements and by schlieren optical observations. The lime-mean flow in the interaction region was classified into four patterns according to the ratio of the pressure $p_k$ at the first kink point in the pressure distribution of the interaction region to the pressure $p_1$ just upstream of the shock. It is shown for any flow pattern that the wall static pressure rise near the shock foot can be described by the "free interaction" which is defined by Chapman et al. The ratio of the triple point height $h_t$ of the bifurcated shock to the undisturbed boundary layer thickness ${\delta}_1$ upstream of the interaction increases with the upstream Mach number $M_1$, and for a fixed $M_1$, the normalized triple point height $h_t/{\delta}_1$ decreases with increasing ${\delta}_1/h$, where h is the duct half-height.

• 한국철도학회논문집
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• 제7권3호
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• pp.193-199
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• 2004

Numerical analysis of aerodynamic characteristics was differently performed according to the running situation of the Korean Tilting Train eXpress(TTX) that would be introduced for an improvement in efficiency of the used railroad track. Fluent 6.0 was used for the analysis of Non-tilting case, Tilting case and Passing-by case with the model of TTX. As a result, the aerodynamic drag had little difference between Tilting and Non-tilting case. However, pressure contour under the train of Tilting case was not symmetry because the gap between a train and the ground was different at both sides. In Passing-by case attraction and counterattraction occurred alternately and affected to the opposite train. When two trains were side by side, the maximum attraction was generated especially. Through an analysis of pressure wave in tunnel a large variation of pressure was generated by the bluff nose of TTX. The results in this study would be good data for the aerodynamic characteristic on TTX and provide important information to judgment of running safety.

• 상하수도학회지
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• 제35권1호
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• pp.15-25
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• 2021

In this study, a method of leakage detection was proposed to locate leak position for a reservoir pipeline valve system using wavelet coherence analysis for an injected pressure wave. An unsteady flow analyzer handled nonlinear valve maneuver and corresponding experimental result were compared. Time series of pressure head were analyzed through wavelet coherence analysis both for no leak and leak conditions. The leak information can be obtained through either time domain reflectometry or the difference in wavelet coherence level, which provide predictions in terms of leak location. The reconstructed pressure signal facilitates the identification of leak presence comparing with existing wavelet coherence analysis.

• 한국군사과학기술학회지
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• 제24권6호
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• pp.619-628
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• 2021

In order to compare numerical analyses made by Song and Kim needed for predicting gas and water filling with experimental results we conducted an experiment to recover a test projectile (43.7 kg with a 155 mm diameter) at a velocity of 775 m/s in a soft recovery system with a length of 179 m using pressurized gas and filled water. The soft recovery system consisting of a series of pressure tubes had a diaphragm, piston, and water plug for filling the pressurized gas and water. We installed a continuous wave Doppler radar system for velocity measurements of the test projectile travelling in the pressure tubes and pressure transducers for measuring the pressure in the soft recovery system. Continuous wave Doppler radar has the advantage of achieving real-time measurements of the velocity of a test projectile. The velocity-time curve of the test projectile, measured using the continuous wave Doppler radar, and the pressure profile were compared with the numerical analysis results. The experiment results show good agreement with the numerical analysis results based on the one-dimensional Euler equation with an HLL Riemann solver.

• 한국자기학회지
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• 제20권3호
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• pp.106-113
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• 2010

비가압 상태에서 혈압 및 맥박을 정확하게 측정한 값를 얻기 위하여 안정시 휴대성과 소형화가 가능한 자성 홀소자를 이용한 손목 착용형 맥진기의 시제품을 개발하였다. 본 시제품을 이용하여 맥진파를 분석한 13명의 임상시험 데이터로 상관인자를 정하여 혈압추정 알고리즘의 회귀식을 구하였다. 5초간 비가압 맥진기로 맥진파를 수집한 혈압추정값과 전자혈압계나 수은혈압계로 측정한 혈압값을 비교하였다. 비가압 맥진기로 추정한 최고혈압과 최저혈압의 표준편차는 혈압국제규격 허용치 범위 안에 있는 12.1과 5.9로 각각 나타났다.

• 한국전산유체공학회지
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• 제17권1호
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• pp.36-43
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• 2012

When a high-speed train passes an underground station, large pressure waves are generated due to the piston effect. These pressure waves can cause the problems of vibration and noise as well as the ear discomfort of passengers at the underground station. This work numerically analyzed the pressure wave generation and propagation in an high-speed railway underground station, and the optimal location for vent shafts was studied to improve the passenger comfort by reducing the magnitude of the pressure wave and its rate of change. The evolution of pressure field in the underground station was calculated using a CFD(Computational Fluid Dynamics) software(Fluent), where the axis-symmetric two-dimensional model verified by Wu was used. And this study is applied to modelling of the underground station and the tunnel from Daegok station A-line of GTX(Great Train Express). From the result, we can have a conclusion that the role of vent shafts respectively were different according to the position in and out the underground station. Also Vent shaft in the underground station widely reduced pressure magnitude. And vent shaft out underground station reduced initial pressure peak value. Double vent shafts installed at tunnel toward station entrance and inside of the tunnel are the most efficient to reduce pressure. and pressure reduction increases according to the number of vent shaft.

• 한국지진공학회논문집
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• 제11권2호
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• pp.81-94
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• 2007

지진시 발생하는 지반 액상화 현상은 지진피해예측시 가장 중용하게 평가해야 하는 항목으로 실내에서 액상화 현상을 시뮬레이션하는 경우, 불규칙성의 지진을 제어하기 어려운 이유로 등가반복형태의 정현파 또는 쐐기파를 이용하는 것이 통상적이었다. 그러나, 90년대 이후 컴퓨터의 발달과 함께한 신호처리 및 제어기술의 급속한 발전은 동역학분야에서의 실험연구에 큰 도움을 주었으며 지반진동분야의 경우, 진동대 및 원심모형기와 같은 대형지진모의시험에서 실지진하중을 이용한 연구사례들이 증가되고 있는 실정이다. 국내에서도 실지진하중재하가 가능한 요소시험결과에 대한 연구사례가 발표되는 등 이에 관한 연구가 활발하게 진행되고 있으며 특히, 실지진하중 시험결과로부터 실지진하중하에서의 과잉간극수압의 변화가 정현하중시험에서의 결과와 큰 차이를 보이고 있다는 분석결과가 발표되어 현재까지 지반동역학분야에서 지진하중의 불규칙성을 크게 고려하지 않았던 통상적 가정사항들이 문제점으로 대두되어 관심을 집중시키고 있다. 본 연구에서는 등가의 정현파 및 쐐기파와 증가형태의 쐐기파, 그리고 실지진파 등 다양한 진동하중을 재하할 수 있는 삼축압축시험기를 이용하여 기존의 유효응력개념에서 사용하는 과잉간극수압관련 매개변수인 소성일, 전단소성 변형률 상각궤도, 그리고 액상화 상태전환선의 기울기를 비교분석하였으며 하중변화에 따른 토립자의 변형과 간극수압의 변화를 상세분석하였다. 연구결과, 토립자의 변형, 간극수의 동적흐름, 동적흐름 속도수두의 압력수두로의 전환, 그리고 과잉간극수압의 증가로 표현되는 새로운 개념의 액상화 발생이론을 제안하였으며 그 타당성 검토를 위해 과잉간극수압과 동적흐름의 압력수두(흐름속도의 제곱값)와의 상관관계를 비교하였다.