• 한국음향학회지
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• 제28권4호
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• pp.356-362
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• 2009

현대 사회에서는 세계 인구의 대부분이 도시에 몰려 있기 때문에, 도심의 소리는 중요한 의미를 가진다. 그 중 교통음은 가장 대표적인 도심소리 중에 하나이다. 일반적으로 도심 교통음은 환경소음으로, 대표적인 자연의 소리인 숲, 폭포소리등은 사람에게 긍정적인 효과를 주는 소리로 분류한다. 본 연구에서는 자연의 소리가 포함하는 백색잡음에 다양한 형태의 FFT보정 필터를 적용시켜, 사람이 가장 선호하는 형태의 백색잡음 주파수 특성을 발견하고 자연 소리와의 상관관계를 확인하였다. 그리고 여러 형태의 도심 교통음과 숲소리의 파형, 스펙트럼 비교를 통한 분석을 진행하였다. 분석 결과 도심 교통음이 숲소리에 비해 특정 주파수대역과 시점에 집중된 소리 에너지 특징이 있음을 발견하였으며, 이러한 특징이 사람에게 미칠 수 있는 부정적인 요소들을 확인하였다. 마지막으로 전극법 뇌파 실험을 통하여, 도심 교통음과 자연의 숲, 폭포소리를 직접 피실험자들에게 들려주어, 알파파와 베타파의 에너지 분포를 측정하였다. 측정결과 도심 교통음은 자연의 소리보다 현저하게 많은 양의 베타파를 발생 시켰으며, 반대로 자연의 소리는 많은 양의 알파파를 발생 시켰다. 이러한 결과를 통해 도심 교통음이 사람에게 미치는 부정적인 영향과 자연 소리의 긍정적인 영향을 직접적으로 확인하였다.

• 한국음향학회지
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• 제43권2호
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• pp.214-224
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• 2024

소노부이는 수중에서 음파를 활용하여 정보 수집을 수행하는 장치로, 엔진 소음이나 다양한 음향 특성을 감지하여 수중 표적을 정확하게 탐지하는 대잠전에 효과적인 탐지체계이다. 다중상태 시스템에서의 기존 소노부이 배치 방식은 고정된 패턴이나 휴리스틱 기반의 규칙에 의존하므로, 예측하기 힘든 수중 표적의 기동으로 인해 소노부이 투하 개수 및 작전 소요 시간 측면에서 효율적인 배치를 보장하지는 못한다. 본 논문에서는 기존 소노부이 배치 방식의 한계를 극복하기 위해, 수중 표적의 이동을 고려한 시뮬레이션 기반의 실험 환경에서 강화학습을 이용한 무인항공기의 소노부이 최적 배치를 제안한다. 제안한 방법은 Unity ML-Agents를 통해 Proximal Policy Optimization(PPO) 알고리즘을 이용하여 가상 작전환경과 실시간 상호작용하며 무인항공기를 학습한다. 소노부이 투하 개수 및 음원 및 수신기 간의 비용을 고려한 보상 함수를 설계하여 효과적인 학습이 가능하게 한다. 동일한 실험 환경에서 강화학습을 적용한 배치 방식과 기존 소노부이 배치 방식을 비교한 결과, 탐지 성공률, 투하된 소노부이 개수, 작전 소요 시간 측면에서 강화학습을 적용한 배치 방식이 가장 우수한 성능을 보였다.

• 동력기계공학회지
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• 제6권3호
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• pp.57-63
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• 2002

This paper describes the acoustic analysis of mid duty truck. The focus of the analysis is on structure borne engine noise with major contributions of 2nd order. It has been previously recognized that the noise contribution of each transfer path of structure borne noise can be varied with the charateristics of each mounts and vibro acoustic sensitivity of car body. The structure of car body will be split up into three major sub components, which are modeled separately, the engine, the frame and the cab. The acoustic performance is evaluated on three levels: engine to frame transfer, frame to cab transfer, and panel contribution from cab to driver. In order to perform these analyses, analytical models are created for the engine, frame, cab and acoustic cavity. The models are linked through a coupled fluid structure calculation, and through FRF Based Substructuring for the structural couplings. Based on the structural coupling calculations, a transfer path analysis is performed to identify the most important transfer paths. These paths are then the focussing points for applying modifications to the structure or the mount system. Finally, a number of modification are proposed and their effect is quantified.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa$-$\omega$ turbulence model. The flow field is observed to oscillate in the shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}-{\varepsilon}$ turbulence model. The flow field is observed to oscillate in the "shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• 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.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.993-998
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• 1997

The advanced technology of micro-machining is starting to penetrate our lives. This technology, with which it is possible to make micro-structures by means of processing on the order of nm (micrometer = 1/1,000 mm) or less, is realizing machines that were only part of our wildest imagination. However, the fact is that many issues remain in the quest for a variety of applications. With the advent of computing technologies, information technologies, and telecommunications technologies, we foresee the need for new approaches in design, process, and the use of materials, technologies, and people in a globalized manufacturing enterprise. A new thinking paradigm is needed to focus on quality of service on the products we design and manufacture. Factories in different regions need to be co-ordinated through use of the state-of-the-art information on productivity, diagnostics, and service evaluation of manufacturing systems could be shared among different locations and partners. In this research, We develope the internet based Diagnosis system for micro machining and evaluate its characteristics by using mechatronic sensor like Dynamometer, acoustic emission, Acceleration sensor, micro phone, vision, infra-red thermometer.

• 대한기계학회논문집
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• 제18권10호
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• pp.2686-2697
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• 1994

When a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel, which causes an impulsive noise. In order to estimate the magnitudes of the noises and to effectively minimize them, the characteristics of the compression wave propagating in a tunnel must be understood. In the present paper, the experimental and analytical investigations on the attenuation and distortion of the propagating compression waves were carried out using a model tunnel. This facility is a kind of open-ended shock tube with a fast-opening gate valve instead of a general diaphragm. One-dimensional flow model employed in the present study could appropriately predict the strength of the compression wave, Mach number and flow velocity induced by the compression wave. The experimental results show that the strength of a compression wave decreases with the distance from the tunnel entrance. The decreasing rate of the wave strength and pressure gradient in the wave is strongly dependent on the strength of the initial compression wave at the tunnel entrance.

• 한국군사과학기술학회지
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• 제21권3호
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• pp.288-294
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• 2018

Recently, as the speed and performance of the launcher and the missile have been improved, it is necessary to consider the acoustic load of launching and flight in initial design step. In this paper, an experimental study on acoustic absorption and transmission characteristics of aluminium vs. sandwich composite structures were conducted. The overall noise reduction was evaluated by performing an acoustic test in the reverberation room, and the acoustic absorption and transmission loss of the structures were analyzed by conducting the sound absorption test inside the structure.

• 한국정밀공학회지
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• 제34권4호
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• pp.287-292
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• 2017

A gas turbine is the main equipment used in a combined heat and power plant. It generates a high sound pressure noise level. To reduce the noise level, an enclosure is installed around the turbine. The sound insulation performance of the enclosure affects the amount of external noise reduction. In this study, a sound transmission loss analysis is performed using the boundary element method to predict sound insulation performance according to the numbers and shapes of the supporter. Radiated noise analysis is also performed for the main external points of the enclosure using ray-acoustics. The results of these analyses are presented and a design plan is proposed that reduces the sound pressure noise level of the enclosure.