• 한국ITS학회 논문지
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• 제11권4호
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• pp.51-62
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• 2012

Lighthill과 Whitham의 충격파모형에 따르면 동일한 속도를 유지하는 교통류 흐름상태에서도 충격파가 존재하며, 이는 라디오 전파처럼 보이지도 않고 관측할 수도 없다고 하였다. 최근의 한 논문은 이 문제에 대해 새로운 접근방법을 통해 위와 같은 모순이 어떻게 발생하였는지를 보여주었고, 이를 개선하기 위해 점근적 충격파모형 (asymptotical shock wave model) 을 제시하였다. 점근적 충격파모형은 동일한 속도로 이동하는 균일한 교통류에서 라디오 전파와 같은 관측 불가능한 충격파가 존재하지 않는 것을 증명하였다. 그러나 상기 논문은 모형의 유도와 증명에 치중하였고 모형으로서의 해석이나 구체적인 수치를 적용한 모형의 검증은 아직 실행된 적이 없다. 본 논문은 점근적 충격파모형의 내포된 의미를 해석하고, 구체적인 수치를 바탕으로 한 시나리오를 통해 모형의 성능을 시험하였다. 그 결과 점근적 충격파모형은 기존 모형에 비해 수식상의 큰 차이는 없었지만, 유일한 차이인 등식의 세 번째 항목이 모형 결과에 결정적인 차이를 나타냄을 확인하였다. 새 모형에 도입된 파라메터는 적용된 수치의 대소에 따라 그 결과가 다르게 나타났다. 이는 기존의 충격파모형에는 없는 특징으로서, 적절한 수치를 선정한다면 다양한 교통흐름에 신축적으로 모형을 적용할 수 있을 것으로 판단된다. 또한 구체적인 수치를 적용한 점근적모형의 시나리오별 시험 결과 동일한 조건에서 새로운 모형은 기존 모형에 비해 충격파가 교통류의 하류 측으로 더 진행됨을 확인하였다. 양 모형간의 이러한 차이는 통계적 유의성 검토에서도 확인되었으며, 향후 현장 자료를 적용한 추가적 비교연구가 필요한 것으로 사료된다.

• 한국음향학회지
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• 제25권1호
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• pp.43-48
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• 2006

압전식 충격파 쇄석기를 사용하여 대상물을 파쇄하는 과정에서 발생하는 음의 특성을 조사한 결과, 대상물이 파쇄됨에 따라 방사음이 더욱 저주파대로 이동한다는 실험적인 결과가 발표되었고(2), 이 결과를 입증하기 위하여 실제의 대상물이 파쇄되어가는 과정을 모델링하여 제작한 대상물을 사용한 실험에서도 동일한 결과가 관측되었다. 본 논문에서는 이와 같이 실험적으로 밝혀진 연구결과를 이론적으로 확인하고자 한다. 따라서, 유한요소법을 이용한 수치 시뮬레이션을 실험과 유사하게 모델링한 대상물에 실행하였고, 시뮬레이션에서 관측된 결과를 제시하여 실험적으로 관측된 결과가 이론적으로도 유효하다는 것을 입증하였다.

• 소음진동
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• 제11권2호
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• pp.285-291
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• 2001

The impingement of a weak shock wane discharged from the open end of a shock tube upon a flat plate was investigated using shock tube experiments and numerical simulations. Harten-Yee Total Variation Diminishing method was used to solve axisymmetric, unsteady, compressible flow governing equations. Experiments were carried out to validate the present computations. The effects of the flat plate and baffle plate sizes on the impinging flow field over the flat plate were investigated. Shock Mach number was varied in the range from 1.05 to 1.20. The distance between the plate and shock tube was changed to investigate the effect on the peak pressure. From both the results of experiments and computations we obtained a good empirical equation to predict the peak pressure on the flat plate.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.792-797
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• 2003

A helical vane is applied to reduce the magnitude of the impulse wave discharged from the exit of a duct. A shock tube with an open end is used to investigate the effect of the helical vanes on the impulse wave magnitude. Four different types of helical vanes are installed into the low-pressure tube of shock tube. The magnitude of the incident shock wave is varied below 1.25, and the magnitude of impulse wave is measured using a pressure transducer mounted on a wedge probe. Instant images of the impulse wave are obtained by means of the Schlieren optical method. The present experimental results show that the helical vane considerably reduces the magnitude of the impulse wave and the vane effects are more remarkable for stronger incident shock wave.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.86-89
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• 2005

2단식 경가스총으로 부터 발사된 발사체의 공기역학적 특성을 연구하기 위해 이동 경계 수치계산법을 축대칭 비정상 압축성 오일러 방정식에 적용하였다. 본 연구로 얻어진 결과는 초음속으로 발사된 발사체로 인한 충격파와 폭발파사이 간섭현상, 와류와 barrel 충격파사이의 간섭현상, 정상 부족팽창 제트을 관찰할 수 있었으며, 발사체 질량 변화에 따른 발사체의 속도, 가속도, 항력 선도를 예측하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1742-1747
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• 2003

When a shock wave is discharged from the exit of a duct, complicated flow is formed near the duct exit. The flow field is much more complicated under the ground effects or any other objects near the exit of a duct, such as the circumstance near the exit of the high-speed railway tunnel. The resulting flow is essentially three-dimensional unsteady with the effects of strong compressibility. In the current study, three-dimensional flow fields of the weak shock wave which is discharged from the exit of a duct are numerically investigated using a CFD method. Computations are performed for the weak shock wave in the range below 1.5. The results obtained show that the directivity and magnitude of the weak shock discharged strongly depend upon the Mach number of initial shock wave and are significantly influenced by the ground effects.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.355-360
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• 2001

This study addresses a computational work of the impulsive wave which is discharged from the open end of a pipe. An initial compression wave inside the pipe is assumed to propagate toward atmosphere. The over pressure and wave-length of the initial compression wave are changed to investigate the characteristic values of the impulsive wave. The second order total variation diminishing (TVD) scheme is employed to solve the axisymmetric, compressible, unsteady Euler equations. The relationship between the initial compression wave form and impulsive wave is characterized in terms of the peak pressure of the impulsive wave and its directivity. The results obtained show that for the initial compression wave of a large wave-length the peak pressure of the impulsive wave does not depend on the over pressure of the initial compression wave, but for the initial compression wave of a very short wave-length, like a shock wave, the peak pressure of the impulsive wave is increased with an increase in the over pressure of the initial compression wave. The directivity of the impulsive wave to the pipe axis becomes significant with a decrease in the wave-length of the initial compression wave.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.317-322
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• 2001

This study depicts an experimental work of the impulsive wave discharged from the open end of several kinds of right-angle bend pipes, which are attached to the open end of a simple shock tube. The weak normal shock wave with its magnitude of Mach number from 1.03 to 1.20 is employed to obtain the impulsive wave propagating outside the open end of the bend pipes. The experimental data of the magnitude of the impulsive wave and its propagation directivity are analyzed to characterize the impulsive waves discharged from the right-angle bend pipes and compared with those from a straight pipe. The results obtained show that a right-angle miter bend considerably reduces the magnitude of the impulsive wave and its directivity toward to the pipe axis, compared with the straight pipe. It is believed that the right angle miter bend pipe can playa role of passive control against the impulsive wave.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.151-154
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• 2002

The twin impulse wave leads to very complicated flow fields, such as Mach stem, spherical waves, and vortex ring. The twin impulse wave discharged from the exits of the two tubes placed in parallel is investigated to understand detailed flow physics associated with the twin impulse wave, compared with those in a single impulse wave. In the current study, the merging phenomena and propagation characteristics of the impulse waves are investigated using a shock tube experiment and by numerical computations. The Harten-Yee's total variation diminishing (TVD) scheme is used to solve the unsteady, two-dimensional, compressible, Euler equations. The Mach number $M_{s}$, of incident shock wave is changed below 1.5 and the distance between two-parallel tubes, L/d, is changed from 1.2 to 4.0. In the shock tube experiment, the twin impulse waves are visualized by a Schlieren optical system for the purpose of validation of computational work. The results obtained show that on the symmetric axis between two parallel tubes, the peak pressure produced by the twin-impulse waves and its location strongly depend upon the distance between two parallel tubes, L/d and the incident shock Mach number, $M_{s}$. The predicted Schlieren images represent the measured twin-impulse wave with a good accuracy.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.432-437
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• 2001

A computational work of the impulse wave which is discharged from the open end of a pipe is compared to the Lighthill's aeroacoustics theory. The second-order total variation diminishing(TVD) scheme is employed to solve the axisymmetric, compressible, unsteady Euler equations. The relationship between the initial compressure wave form and the resulting impulse wave is characterized in terms of the peak pressure. The overpressure, pressure gradient and wavelength of the initial compression wave are changed to investigate the influence of the initial compressure wave form on the peak pressure of impulse wave. The results obtained show that for the initial compression wave of a large wavelength and small pressure gradient the peak pressure of the impulse wave depends upon the wavelength and pressure gradient of compression wave, but for the initial compression wave of a short wavelength and large pressure gradient the peak pressure of the impulse wave is almost constant regardless of the wavelength and pressure gradient of compression wave. The peak pressure of the impulse wave is increased with an increase in the overpressure of the initial compression wave. The results from the numerical analysis are well compared to the results from the aeroacoutics theory with a good agreement.