• Journal of Advanced Marine Engineering and Technology
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• 제33권4호
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• pp.466-475
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• 2009

A numerical analysis of reactive flow in a liftoff flame is accomplished to elucidate the characteristics of flame propagation velocity and volume integral of reaction rate with the variation of fuel injection velocity at the fuel rich region, fuel lean region and diffusion flame region. The increase of fuel injection velocity enhances flame propagation velocity, but its effect on the flame propagation velocity is not much greater under 4%. The increase of fuel injection velocity affects directly and linearly on the flame surface area in the fuel rich region and so enhances volume integral of reaction rate to accommodate the increment of fuel.

• Journal of Information Processing Systems
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• 제15권4호
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• pp.820-832
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• 2019

Estimation of accurate blood volume flow in ultrasound Doppler blood flow spectrograms is extremely important for clinical diagnostic purposes. Blood volume flow measurements require the assessment of both the velocity distribution and the cross-sectional area of the vessel. Unfortunately, the existing volume flow estimation algorithms by ultrasound lack the velocity space distribution information in cross-sections of a vessel and have the problems of low accuracy and poor stability. In this paper, a new robust ultrasound volume flow estimation method based on multigate (RMG) is proposed and the multigate technology provides detail information on the local velocity distribution. In this method, an accurate double iterative flow velocity estimation algorithm (DIV) is used to estimate the mean velocity and it has been tested on in vivo data from carotid. The results from experiments indicate a mean standard deviation of less than 6% in flow velocities when estimated for a range of SNR levels. The RMG method is validated in a custom-designed experimental setup, Doppler phantom and imitation blood flow control system. In vitro experimental results show that the mean error of the RMG algorithm is 4.81%. Low errors in blood volume flow estimation make the prospect of using the RMG algorithm for real-time blood volume flow estimation possible.

• 한국자기학회지
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• 제26권4호
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• pp.142-148
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• 2016

자기공명영상에서 위상대조(phase contrast; PC) 기법으로 혈류 속도와 혈류량을 정량적으로 측정하기 위해 VENC(150 cm/s)에서 숙임각의 변화에 따른 혈류 속도와 혈류량을 측정하였다. 1.5T MRI로 지원자 17명(여: 8, 남: 9, 평균연령 $57.9{\pm}15.4$)을 대상으로 non-breath holding 기법을 적용하여 상행대동맥에서 VENC(150 cm/s)로 숙임각을 $20^{\circ}$, $30^{\circ}$, $40^{\circ}$ 변화하여 측정하였다. 혈류는 average velocity, peak velocity, net forward volume, net forward volume/body surface area를 획득하였다. 상행대동맥에서 AV(average velocity)의 평균값은 숙임각 $20^{\circ}$(9.87 cm/s), $30^{\circ}$(9.6 cm/s), $40^{\circ}$(10.05 cm/s)로 측정되었다. 숙임각을 $20^{\circ}$, $30^{\circ}$, $40^{\circ}$에서 peak velocity, average velocity, net forward volume, net forward volume/body surface area는 통계적인 유의한 차이가 없었다(p > .05). 혈류속도와 혈류량 측정은 매개변수를 조정하여 적용하면 심장혈관 질환의 진단 및 치료에 중요한 정보가 되는 혈류량을 정확히 계산하고, 혈류량 측정에 관한 연구에 도움을 줄 수 있다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.461-464
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• 2003

A new control volume finite element method is proposed for three dimensional analysis of polymer flow. Tetrahedral finite element is employed and co-located interpolation procedure for pressure and velocity is implemented. Inclusion of pressure gradient term in the velocity shape functions prevents the checkerboard pressure field from being developed. Vectorial nature of pressure gradient is considered in the velocity shape function so that velocity profile in the limit of very small Reynolds number becomes physically meaningful. The proposed method was verified through three dimensional simulation of pipe flow problem for Newtonian and power-law fluid. Calculated pressure and velocity field showed an excellent agreement with analytic solutions for pressure and velocity. Driven-cavity problem, which is reported to yield checkerboard pressure filed when conventional finite element method is applied, could be solved without yielding checkerboard pressure field when the proposed control volume finite element method was applied. The proposed method could be successfully applied to the three dimensional mold filling problem.

• Computers and Concrete
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• 제5권6호
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• pp.509-524
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• 2008

Containment structures not only are leak-tight barriers, but also may be subjected to impacts caused by tornado-generated projectiles, aircraft crashes or the fragments of missile warhead. This paper presents the results of an experimental study of the impact resistance of steel fiber-reinforced concrete against 45 g projectiles at velocity around 2500 m/s. An explosively formed projectile (EFP) was designed to generate an equivalent missile fragment. The formation and velocity of EFP are measured by flash x-ray. A switch made of double-layered thin copper sheets controlled the exposure time of each flash x-ray. The influence of the fiber volume fraction on the crater diameter of concrete slab and the residual velocity of the projectile were studied. The residual velocity of the projectile decreased as the fiber volume fractions increased. In this work, the residual velocity of the projectile was to 44% that of plain concrete when the fiber volume fraction exceeded 1.5%. Based on the present finding, steel fiber reinforced concrete with the fiber volume fraction exceeding 1.5% appear to be more efficient in protection against high velocity fragment impact.

• 소음진동
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• 제9권5호
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• pp.943-948
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• 1999

This paper proposes a feasible and effective method for measuring the mechanical-acoustic transfer function by the application of equivalent area and velocity transfer function, a manifestation of the vibro-acoustical reciprocity principle. On the contrary to the volume velocity used in traditional method, the equivalent area is a peculiar raidation characteristics of sound sources and not influenced by any input signal for driving sound source. This invariant property of equivalent area can get rid of boresome works to measure the volume velocity of a sound source every time the driving signal is changed. Moreover, this method has a remarkable advantage to use a general loudspeaker as an accoustic exciter without the assumption of point source and can be applied to all kinds of sound sources even if they are not omni-directional sources.

• 한국해양공학회지
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• 제17권1호
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• pp.55-60
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• 2003

The effect of size and volume fraction of ceramic particles, with sliding velocity on the wear properties were investigated for the metal matrix composites fabricated by the pressureless infiltration process. The metal matrix composites exhibited about 5.5 - 6 times the wear resistance compared with AC8A alloy at high sliding velocity, and by increasing the particle size and decreasing the volume fraction, the wear resistance was improved. The wear resistance of metal matrix composites and AC8A alloy exhibited different aspects. Wear loss of AC8A alloy increased with sliding velocity, linearly : whereas, metal matrix composites indicated more wear loss than AC8A alloy at the slow velocity region. However, a transition point of wear loss was found at the middle velocity region, which shows the minimum wear loss. Further, wear loss at the high velocity region exhibited nearly the same value as the slow velocity region. In terms of wear mechanism, the metal matrix composites generally exhibited abrasive wear at slow to high sliding velocity； however, AC8A alloy showed abrasive wear at low sliding velocity and adhesive and melt wear at high sliding velocity.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 추계학술대회 논문집
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• pp.379-384
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• 2002

The effect of size and volume fraction of ceramic particles with sliding velocity on the wear properties were investigated for the metal matrix composites fabricated by pressureless infiltration process. The particulate metal matrix composites exhibited about 5.5 - 6 times of excellent wear resistance compared with AC8A alloy at high sliding velocity, and as increasing the particle size and decreasing the volume fraction the wear resistance was improved. The wear resistance of metal matrix composites and AC8A alloy exhibited different aspects. Wear loss of AC8A alloy increased with sliding velocity linearly. whereas metal matrix composites indicated more wear loss than AC8A alloy at slow velocity region, however a transition point of wear loss was found at middle velocity region which show the minimum wear loss, and wear loss at high velocity region exhibited nearly same value with slow velocity region. In terms of wear mechanism, the metal matrix composites exhibited the abrasive wear at slow to high sliding velocity generally, however AC8A alloy showed abrasive wear at low sliding velocity and adhesive and melt wear at high sliding velocity.

• 한국자동차공학회논문집
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• 제7권9호
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• pp.158-164
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• 1999

In this paper a simple measurement technique for mechanical-acoustic transfer functions is proposed . The mechanical-acoustic transfer functions, generally , are measured through mechanical excitations ; impact hammers or shakers. Recently , by virtue of vibro-acoustical reciprocity principle, they are measured through acoustic excitations : loudspeakers. This kind of test needs to measure the volume velocity , the radiation characteristics of a sound source. Because the volume velocity of the sound source is changed by driving signal , it is difficult to measure it. However , the new method in this paper needs not to measure the volume velocity of a sound source by combination of mechanical and acoustic excitations. Moreover, this method has the methodological advantages, such as usage of a general loudspeaker for the reciprocal excitation, no sptatial limitations for measurements of mechanical-acoustic transfer functions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.712-716
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• 2003

In the present study, the gas injection system based on air-water model was designed to investigate the behavior characteristics of bubbles injected into a ladle. The parameters such as gas volume fraction and bubble rise velocity were exprementally measured in a gas-liquid flow region. To measure gas volume fraction, an electo-conductivity probe was used and bubble rise velocity was obtained by a high speed CCD camera. Gas volume fraction was symmetric to the axis of nozzle secured on the bottom of a ladle. The bubble rise velocity was calculated for two different experimental conditions. That is, gas flow conditions were following two case: 1) Q = $0.63{\times}10^{-4}$ $m^{3}/s$, 2) $1.26{\times}10^{-4}$ $m^{3}/s$. As a gas injected into the liquid ladle, the liquid-phase region is circulated by bubbles' behavior. The bubble rise velocity was influenced of the circulation flow of liquid phase. As a result, the bubble rise velocity was appeared higher middle region of ladle than near the nozzle.