• Proceedings of the Korea Water Resources Association Conference
• /
• 2020.06a
• /
• pp.45-45
• /
• 2020

하천 횡단구조물 하류부에서는 고유속 및 ±압력에 의해 하상재료가 유실되는 세굴현상이 발생한다. 이러한 세굴을 방지하기 위해 횡단구조물 하류부에는 석재, 콘크리트 및 콘크리트 블록 등을 설치 및 포설하여 하상보호공을 설치한다. 하상보호공을 설치하면 설치된 부분은 세굴이 방지 되지만, 하상보호공 끝단 이후에는 지반이 노출되어 있어 노출된 지반에서 고유속 흐름 및 압력변화에 의한 세굴이 발생하는 경우가 많다. 이에 본 연구에서는 하상보호공 끝단 즉, 하상이 노출된 지반에서 압력변화에 따라 하상재료가 유실되므로 압력에너지를 감쇄시키기 위한 하상보호장치를 개발하였다. 개발한 하상보호장치는 본래 다수개가 열을 지어 메트릭스 형태로 설치되도록 하여야 하지만 실험 여건상 단일체로 수리실험을 진행하였다. 하상보호장치는 상판과 하판이 조립된 형태이며 상판과 하판 사이에 이격공간이 구비되어있다. 하상보호장치 검증을 위해 상판과 하판에 쓰이는 판은 수로재질과 같은 아크릴로 제작하였으며, 하상재료의 공극률을 반영하여 다공성 판으로 제작하였다. 다공판의 전체 구멍 면적 대비 판 면적은 35 % 로 동일하다. 상판 구멍 지름 15.0 mm, 4.5 mm 2가지로 제작하였으며, 하판 구멍 지름 3.0 mm 으로 동일하다. 압력변화가 큰 곳에서 작은 곳으로 물이 이동하게 되므로 고유속 수리조건에서 상판과 하판 사이에서의 압력변화를 측정하기 위해 판 중간에 압력계를 설치하였다. 하상보호장치 설치지점 앞 0.3 m 부근에 PIV를 설치하여 유속을 측정하였다. 실험결과 상판의 구멍 직경(15.0 mm)이 클 경우 상판부 압력이 하판부로 전달되어 하판에서 측정되는 압력이 증폭 되었으며, 상판의 다공성 구멍 직경(4.5 mm)이 작을 경우 상판부에서 하판부로 전달되는 압력이 감소하여 하판에서 측정되는 압력이 감소하였다. 상판과 하판의 다공성 구멍의 직경을 적절한 사이즈로 조절하면 상판부의 압력이 하판부로 전달되는 것을 막고 압력에 의해 하상에서 흡출되는 유사를 막을 수 있는 것으로 판단되며 추후 상판과 하판의 다공성판 구멍 직경의 상대적 차이에 따른 압력 감소효율에 관한 연구가 필요하다고 판단된다.

• Journal of the Korean Society for Railway
• /
• v.12 no.5
• /
• pp.806-810
• /
• 2009

The air conditioner system that is used in large structure, such as hospital, hotel, railway platform and train generate a high level noise generally. A chamber with sound absorbing materials, such as glass wool and polyurethane foam, are installed in this system to reduce the noise. However, these chambers cause environmental problems owing to the sound absorbing materials recently. Therefore, we develop noise chamber a built-in perforated panel resonance system as eco-friendly chamber to solve this problems. This noise chambers show the same noise reduction performance as the current chambers in the range above 500Hz. But, it reduces the noise up to 8dB(A) comparison to the current chambers in the range 200Hz~400Hz.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11b
• /
• pp.896-901
• /
• 2002

The sound absorption coefficients for multiple layer perforated plate systems containing several compartments with airspaces and porous absorbing materials are estimated using the transfer matrix method developed in the previous paper. The absorption coefficients from transfer matrix method agree well with the values measured by the two-microphone impedance tube method for various combinations of perforated plates, airspaces or porous materials. Based on these results, a guidance for the design of multiple layer perforated plate systems combined with airspaces and porous absorbing materials is discussed in detail.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11a
• /
• pp.388.1-388
• /
• 2002

The sound absorption coefficients for multiple layer perforated plate systems containing several companments with airspaces and porous absorbing materials are estimated using the transfer matrix method developed in the previous paper. The absorption coefficients from transfer matrix method agree well with the values measured by the two-microphone impedance tube method fur various combinations of perforated Plates, airspaces or porous materials. (omitted)

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.13 no.3
• /
• pp.180-185
• /
• 2003

The equivalent electroacoustic circuit approach has been conventionally used for the analysis of the multiple layer perforated plate system. However, it is found that an analogy error has been involved in the equivalent electroacoustic approach proposed by previous researchers for the element of straight pipe. Although the pipe between the perforated layers is a distributed element in the analogy, it has been treated as a parallel element by previous investigators. The analogy error is demonstrated by comparing the calculated absorption coefficients based on the parallel circuit and the distributed circuit, respectively, with the measured values by the two-microphone impedance tube method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.1209-1211
• /
• 2006

This paper introduces an experimental study for the noise reduction of a ventilating fan system. For the purpose of noise reduction, conventionally an absorptive duct silencer filled with a glass fiber has been utilized. However, a glass fiber has some disadvantages like hygiene and secondary pollution problems. In order to overcome these problems, in this paper, a perforated duct silencer has been applied to the ventilating fan system. For the designing of a perforated duct silencer, the transmission losses for various perforated panel systems are measured and compared with its noise reduction performance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.65-70
• /
• 2004

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11b
• /
• pp.902-907
• /
• 2002

An equivalent electroacoustic circuit approach of estimating the sound absorption coefficient for parallel perforated plate system is proposed. The proposed approach is validated by comparing the calculated absorption coefficients of a parallel single layer perforated plate system with the values measured by the two-microphone impedance tube method for various porosity and the number of perforated plate. The sound absorbing performances of parallel and series perforated plate systems are compared and discussed from a standpoint of frequency bandwidth with sound absorption. The proposed approach is further extended to the parallel double layer perforated plate system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.11b
• /
• pp.890-895
• /
• 2002

The equivalent electroacoustic circuit approach has been conventionally used for estimating the absorption coefficient of a single layer perforated plate system. When the single layer system is extended to the multiple layer ones, however, it is found that an analogy error has been involved in the equivalent electroacoustic parallel circuit approach proposed by previous investigators. The analogy error is demonstrated by the corrected equivalent electroacoustic circuit approach in this study.

• The KSFM Journal of Fluid Machinery
• /
• v.17 no.3
• /
• pp.65-70
• /
• 2014

The effectiveness of a perforated plate installed additionally at butterfly valve to reduce cavitation which can cause vibration, noise, erosion, and flow path blockage has been investigated using CFD. Rayleigh-Plesset equation was applied to simulate cavitation phenomena. 3D flow simulations have been performed for 6 cases to consider the occurrence of cavitation at the downstream of the valve. From the present results, the perforated plate was thought to be very effective to suppress the cavitation inside of the pipe.