• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.92-97
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• 2003

By using a centerbody injection, an effort to reduce shock assoicated noise is made in an underexpanded sonic nozzle with an exit diameter of 10mm. The centerbody or micro nozzle, aligned with the axis of the main jet has an o.d. of 2mm and i.d. of 1.5mm. When measured at 90$^{\circ}$ relative to the main jet the farfield noise spectra showed that the screech tones and broadband shock associated noise can be significantly reduced simply by varying the length of the centerbody and/or mass fraction of the microjet. The maximum reduction in overall sound pressure level (OASPL) was as much as 9 and 4 ㏈ at fully expanded jet Mach numbers Mi of 1.3 and 1.5, respectively, when the length of the centerbody was varied from 0 to 4 main nozzle diameters without blowing. With the aid of the blowing, the maximum reduction in OASPL increased to 12 and 7 ㏈ at M$\sub$j/=1.3 and 1.5, respectively. The impact pressure field in the main jet plume strongly suggested that the reduced periodic pressure distribution in the shear layers and/or centerline is responsible for the reduced screech and broadband shock associated noise. Therefore, the steady blowing by a micro centerbody is a promising technique for shock noise reduction in a supersonic jet.

• 소음진동
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• 제9권1호
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• pp.113-120
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• 1999

A perforated tube nozzle as an exhaust noise suppressor of a high-speed civil transport(HSCT) is proposed. The experimental results for the near and far field sound. the visualization of jet structures and the static pressure distributions in the jet passing through a perforated tube are presented and discussed in comparison with those for a simple tube. It is shown that the perforated tube has an excellent performance to greatly reduce the shock-associated noise and that also the turbulent mixing noise is reduced in the range of a limited jet pressure ratio. This considerable noise reduction is due to the pressure relief caused by the through-flow through the perforated holes. Such a pressure relief results in the transformation of normal shock waves into weak Mach waves of X -type and increases the thrust force of the perforated tube nozzle.

• 대한기계학회논문집B
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• 제24권1호
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• pp.132-142
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• 2000

The objective of this study is to experimentally investigate the noise propagating characteristics, the noise reduction mechanism and the performance of a slotted tube attached at the exit plane of a circular convergent nozzle. The experiment is performed through the systematic change of the jet pressure ratio and the slot length under the condition of two kinds of open area ratios, 25% and 51%. The open area ratio calculated by the tube length equivalent for the slot length is defined as the ratio of the total slot area to the surface area of a slotted tube. The experimental results for the near and far field sound, the visualization of jet structures and the static pressure distributions in the jet passing through a slotted tube are presented and explained in comparison with those for a simple tube. The propagating characteristics of supersonic jet noises from the slotted tube is closely connected with the slot length rather than the open area ratio, and its propagating pattern is similar to the simple tube. It is shown that the slotted tube has a good performance to suppress the shock-associated noise as well as the turbulent mixing noise in the range of a limited jet pressure and slot dimension. The considerable suppression of the shock‘associated noise is mainly due to the pressure relief caused by the high-speed jets passing through the slots on the tube. Both the strength of shock waves and the interval between them in a jet plume are decreased by the pressure relief. Moreover, the pressure relief is divided into the gradual and the sudden relief depending upon the open area ratio of the slotted tube. Consequently, the shock waves in a jet plume are also changed by the type of pressure relief. The gradual pressure relief caused by the slotted tube with the open area ratio 25% generates the weak oblique shock waves. On the contrary, the weak normal shock waves appear due to the sudden pressure relief caused by the slotted tube with the open area ratio 51%.

• 한국음향학회:학술대회논문집
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• 한국음향학회 2001년도 추계학술발표대회 논문집 제20권 2호
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• pp.389-392
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• 2001

To investigate the generation mechanism of the shock-associated noise, an underexpanded supersonic jet from an axisymmetic nozzle is simulated under the conditions of the Nozzle exit Mach number of 2 and the exit pressure ratio of Pe/Pe =1.5. The present simulation is performed based on the high-order accuracy and high-resolution ENO (Essentially Non-Oscillatory) scheme to capture the time-dependent flow structure representing the sound source. It was found that the shock-associated noise is generated by the weak interaction between the downstream propagating large turbulence structures of the jet flow and the quasi-periodic shock cell structure during the one is passing through the other. The directivity of propagating waves to the upstream is clearly shown in the visualization of pressure field. It is shown that the present calculation of the centerline pressure distribution is in fare agreement with the experimental data at the location of first shock cell.

• 한국안전학회지
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• 제17권3호
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• pp.1-6
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• 2002

A dynamic characteristics of shock absorber in the various excitation is investigated experimentally. Work diagrams and characteristic curves are used as a experimental standard. The various excitation conditions temperature and noise are very important factors in associated with the reduction of damping force. It is found that the heat occurrence from shock absorber, the gas shock absorber is much higher than oil shock absorber and increased in high speed. As to the variation of damping force, there are no change when the speed is low but we fixed amount of variation by increasing speed and change of new and old decrease. The sound pressure of the swash noise from cycle of shock absorber, we compared with theory sound pressure by experiment.

• 한국항공우주학회지
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• 제35권1호
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• pp.27-32
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• 2007

본 논문에서는 초음속 제트로부터 유발되는 소음의 특성을 실험적으로 분석하고, 기존의 소음예측식을 사용하여 비교해 봄으로서 예측식의 적용가능 범위를 살펴보았다. 실험을 위하여 제작된 초음속제트 발생장치의 출구마하수를 측정하기 위하여 정체실의 온도, 압력과 함께 피토 튜브를 이용하였고, 결과를 쉐도우 그래프 가시화 방법을 사용하여 얻은 결과와 비교하였다. 제트소음의 스펙트럼을 관찰한 결과, 불완전 팽창의 제트 유동에서 발생하는 충격파 관련 소음인 광대역 소음과 스크리치 톤 소음의 경향이 나타는 것을 확인 할 수 있었다. 아음속 조건에서는 큰 난류 구조에 의해 발생되는 난류 혼합 소음에 의하여 흐름방향으로 강한 방향성을 나타내었고, 초음속 조건에서는 충격파 관련 소음이 흐름의 상류 방향으로도 강하게 전파됨을 확인 하였다. 그리고 제트 엔진의 소음 예측 프로그램인 ARP876D 코드를 이용하여 실험에서 측정한 스펙트럼과 비교해 본 결과 아음속 영역에서보다는 초음속 영역에서 더 좋은 결과를 보였다.

• 한국소음진동공학회논문집
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• 제11권7호
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• pp.239-246
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• 2001

The present study addresses the open correction associated with the reflection and discharge phenomena of a weak shock wave from an open end of a duct. The open correction of the weak shock wave is investigated experimentally and by numerical computation. An experiment is made using a simple shock tube with an open end. and computaion is performed to simulate the experimental flow field using the unsteady, axisymmetric compressible. flow governing equations. The results obtained show the an open correction should be involved for shock wave discharge and reflection problems generated from the exit of the duct with an open baffle plate. With a baffle plate less than three times the duct diameter, it is found that the open end correction is a function of both the diameter of the baffle plate and normal shock wave magnitude However, for a baffle plate larger than three the duct diameter it is independent of the baffle plate diametre, The present computations predict the results of shock tube experiment with good accuracy. A new empirical equation for prediction of the open correction is found for the weak shock reflection and discharge phenomena occurring at the open of the duct with and without a baffle plate.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 춘계학술대회 논문집
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• pp.545-547
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• 2014

The scope of ISO/TC 108/SC 6, revised in accordance with Doc. ISO/TC 108/SC 6 N 35, September 1997, is as follows: Standardization in the field of vibration and shock generating systems, for test purposes (including environment, seismic and dynamic testing, calibration and diagnostics) as well as auxiliary equipment and instrumentation normally associated with it. Vibration and shock generating systems as an object of standardization within ISO/TC 108/SC 6 are only those systems that are used during vibration/shock testing to determine properties of a specimen. Vibration and shock systems being used in such processes as transportation, milling, compacting, metal working, etc., as parts of vibration control systems or household appliances and in health services, are not covered by ISO/TC 108/SC 6.

• Journal of Mechanical Science and Technology
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• 제15권8호
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• pp.1174-1180
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• 2001

Various experimental data, including mixing areas, cross correlation factors, surface flow patterns on nozzle walls, and far field noise spectra, was used to draw a noise control mechanism in a supersonic jet. In the underexpanded case, mixing of the jet air with ambient air was significantly enhanced as presented before, and mixing noise was also dramatically reduced. Screech tones, in the overexpanded case, were effectively suppressed by trailing edge modifications, although mixing enhancement was not noticeable. From mixing and noise performance of nozzles with modified trailing edges, enhancing mixing through streamwise vortices seems an effective way to reduce mixing noise in the underexpanded flow regime. However, screech tones in the overespanded flow regime is well controlled or suppressed by making shock cells and/or spanwise large scale structures irregular and/or less organized by a proper selection of trailing edges. The noise field in the overexpanded flow regime was greatly affected by the symmetricity of the nozzle exit geometry. In the underexpanded flow regime, the effects of the symmetricity of the nozzle exit on mixing were negligible.

• 한국소음진동공학회논문집
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• 제14권4호
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• pp.287-294
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• 2004

Dynamic Load/unload (L/UL) mechanism is an alternative to the contact start stop (CSS) technology which eliminates striction and wear failure modes associated with CSS. Inertia latch mechanism becomes important for mobile disk drives because of non operating shock performance. Various types of latch designs have been introduced in hard disk drives to limit a rotary actuator from sudden uncontrolled motion. In this paper, a single spring inertia latch is introduced for a small form optical disk drive, which uses a rotary actuator for moving an optical pick-up. A new small inertia latch with sin91e spring is designed to ensure both feasible and small size. The shock performance of the new inertia latch is experimentally verified.