• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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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).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.9
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• pp.645-651
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• 2008

For a high speed train driving at 300 km/h, aero-acoustic noise is a dominant component among various noise sources. The aeroacoustic noise is mainly due to inter-coach spacings because discontinuities in the train surface significantly disturb turbulent flows. This often leads to the uncomfortableness of passengers. Interestingly, the aero-acoustic noise reduces with decreasing the mud-flap spacing of the inter-couch spacing. We perform numerical simulations to investigate flow characteristics around the inter-coach spacing. We model the inter-coach spacing as a simple 2-D cavity with flaps, and calculate the velocity and pressure field using two equation turbulence models, varying the flap spacing. The results show that a wider flap spacing develops a higher inflection point in mean velocity profiles over the cavity. It is likely that large eddies generated near the inflection point persist longer in the downstream since they are less affected by the wall. This probably induces the more aero-acoustic noises. The wider spacing also results in the larger pressure difference between the inside and outside of the cavity. This is also responsible for the increased noise since the large difference would cause a strong flow oscillations in and out of the cavity.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.81-89
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• 1999

The major source of noise in the process of transporting liquids is related to the cavitation phenomenon. The control valve noise is mostly dominated by bubble dynamics under cavitating conditions. In this investigation, an orifice configuration is set-up to correlate its flow-field and acoustic signatures with those from a control valve device. The performance and noise characteristics form the orifice configuration in anechoic surroundings were measured to reveal the noise sources depending on pressure differences across the orifice configuration. The sound powers from the orifice configuration are effectively normalized using proposed scaling parameters. Flow-excited dynamic systems for which there is no strong coupling between the flow and the system response can be described using a linear source-filter model. On this assumption, the normalized sound powers can be decomposed of noise source function and a response function. To find noise sources, pressure spectra measured over a range of pressure differences are transformed into the product of two non-dimensional frequency function : $P_{ss}(He,f_{ca},x/D) = F(f_{ca})\;G(He,x/D)$. This scheme of finding noise sources is shown to be applicable to the cavitation noise from the control valve effectively Two kinds of cavitating modes based on our experimental data are found and discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.2
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• pp.183-190
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• 2015

An ejector is a type of non-powered pump that is used to supply a secondary flow via the ejection of a primary flow. It is utilized in many industrial fields, and is used for fueling the vehicle because of less failures and simple structure. Since most of ejectors in industry are gas-to-gas and liquid to gas ejector, many research activities have been reported in optimization of gas ejector. On the other hand, the liquid ejector is also applied in many industry but few research has been reported. The liquid ejector occurs cavitation, and it causes damage of parts. Cavitation has bees observed at the nozzle throat at the specified pressure. In this study, a two-dimensional axisymmetric simulation of a liquid-liquid ejector was carried out using five different parameters. The angle of the nozzle plays an important role in the cavitation of a liquid ejector, and the performance characteristics of the flow ratio showed that an angle of $35^{\circ}$ was the most advantageous. The simulation results showed that the performance of the liquid ejector and the cavitation effect have to be considered simultaneously.

• The Korean Journal of Air & Space Law and Policy
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• v.4
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• pp.167-176
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• 1992

1957년에 서명된 로마조약(條約)을 처음 개정한 단일(單一)유럽법(法)이 1987년 7월 1일에 발효(發效)되었을 때 유럽공동체(共同體) 12개 회원국(會員國)들은 공동정책(共同政策)에 의거 상업(商業), 농업(農業), 운송(運送), 금융(金融) 및 기타 관련부분에 있어 단일역내시장(單一域內市場)을 형성하기로 약속했다. 물론 완전한 역내공동시장(域內共同市場)은 자유로운 운송시장(運送市場)을 전제로 한다. 따라서 EC조약(條約)은 모든 회원국(會員國)들이 서어비스의 자유에 근거하여 공동운송정책(共同運送政策)을 따를 것을 강제하고 있다. 항공운송(航空運送)에 있어서의 목표도 역시 다른 모든 경제활동의 목표와 마찬가지로 로마조약(條約)이 적용되는 공동운송정책(共同運送政策)의 일부를 구성하고 있다. 종합적인 공동체항공정책(共同體航空政策)의 작업에는 운임(運賃), 공급량(供給量), 시장진출(市場進出) 및 경쟁상(競爭上)의 일괄적인 자유화 조치 이상의 것을 내포하고 있다. 그것은 국가장벽으로 방해되지 않는 공동체(共同體)의 항공운송망(航空運送網)의 개발과 확장뿐만 아니라 경제(經濟), 안전(安全), 환경(環境) 및 사회적(社會的) 요인(要因)들 간에 합리적인 균형을 이루는 공동체항공운송정책(共同體航空運送政策)의 개발을 위한 공동항공운송정책(共同航空運送政策)의 공식화(公式化)를 요한다. 1987년의 항공(航空)에 관한 일괄입법조치, 1989년의 제 2 차 항공(航空)에 관한 일괄입법조치 및 1992년 이후로 예정된 제 3 차 일괄입법조치에 따라 EC는 초국가적(超國家的)인 항공운송(航空運送) 분야에 있어서의 개방적인 국제경쟁(國際競爭)을 본격적으로 추구하고 있다. 결국 이러한 일괄규칙은 EC와 제(第) 3 국(國)들간의 관계에 중대한 의미를 가지게 될 것이다. EC항공운송정책(航空運送政策)이 아시아 항공산업(航空産業)의 상업운선(商業運船)에 어떠한 영향을 미칠 것인가는 모든 아시아 국가들이 알아야 할 중요한 문제이다. 이론적으로 말해서, 역내공동체(域內共同體) 항공운송(航空運送)의 자유화는 아시아 국가들에 대한 치외법권적(治外法權的) 효과를 일으킬 수 있는 로마조약(條約)과 유럽사법재판소(司法裁判所)에 의해 형성된 원칙들에 필연적으로 영향을 미칠 것이다. 이와 관련하여 아시아 항공산업(航空産業)은 무차별원칙(無差別原則), 설립(設立)의 자유(自由), 서어비스의 자유(自由) 및 EEC 경쟁법(競爭法)과 같은 제(第) 3 국(國)의 국제항공운송에 영향을 미치는 일련의 새로운 원칙과 법률의 출현에 큰 관심을 갖고 있다. 실무적인 관점에서, 1992년 이후의 종합적인 공동체항공운송정책(共同體航空運送政策)의 작업에는 항공운화(航空運貨), 시장진출(市場進出), 제(第)3 및 제(第)4의 운륜자유권(運輪自由權), 복수지정(複數指定), 제(第)5의 자유(自由), 캐보타지(cabotage), 손상(損傷)(derogation), 공급량(供給量), 편수(便數), 불정기운항(不定期運航) 및 기타 부문항공기소음(部門航空機騷音), 최저(最低) 안전(安全) 및 사회적(社會的) 조치(措置), 항공종사자면허(航空從事者免許), 감항증명(堪航證明), 운항시간제도(運航時間制度), 컴퓨터 예약제도(豫約制度), 탑승거절보상의 공동최저기준(共同最低基準), 공중혼잡(空中混雜), 공항이착륙시간할당법(空港離着陸時間割當法), 공항시설(空港施設), 정부지원(政府支援 등). 이와 같은 모든 공동체항공운송정책(共同體航空運送政策)의 주요문제들은 아시아 항공산업(航空産業)에 여러 각도로 영향을 미치게 될 것이다. 위와 같은 문제들 가운데, 제(第) 3국(國) 항공사(航空社)들의 역내공동체(域內共同體) 항로(航路)의 접근, 공급량(供給量), 운임(運賃), 제(第)5의 자유(自由) 및 캐보타지가 아시아 항공산업(航空産業)에 관심이 큰 문제가 되고 있다. 아시아 항공사(航空社)들의 EEC시장(市場)에로의 상업운항(商業運航)이 다소 영향을 받게 될 것이다. 첫째, 복수(複數) 목적지(目的地) 문제이다. 둘째, 항공(航空)서어비스의 운임(運賃) 및 료솔(料率)문제이다. 셋째, 항공운송구역(航空運送區域)에서의 사업에 대한 경쟁원칙의 적용 문제이다. 넷째, 제(第)5 자유(自由) 운륜권(運輪權) 문제이다. 다섯째, 캐보타지(cabotage)문제이다. 끝으로, 유럽 항공사(航空社)들간의 합병(合倂)의 문제이다. 결론적으로 유럽공동체항공운송(共同體航空運送)의 자유화는 1993년까지 공동체(共同體) 역내(域內)와 역외(域外)의 항공운송법제(航空運送法制)의 현재의 모습을 극적으로 바꾸어 놓을 정도로 가속화(加速化)되고 있다. 한편 항공운송(航空運送)의 자유화(自由化)에 대한 EC의 제의는 대담하고 급진적이다. 반면에 그것이 아시아 항공산업(航空産業)에 미칠 영향 또한 중대하다. 의심할 여지없이 항공사(航空社)와 고객들의 이익면에서 EEC와 비(非)EEC국가들의 항공운송산업(航空運送産業)에서 더욱 경제적으로 경쟁적이 되도록 할 필요가 있다. 전세계 항공운송산업(航空運送産業) 운영(運營)의 대부분을 정부가 소유하거나 통제하는 것은 정말로 국제항공운송(國際航空運送)의 발전에 불필요한 장애를 일으킨다. 따라서 國內航空社와 전세계 항공사(航空社)들간의 이해관계의 조화를 협상하는 것이 중요하다. 아마도 아시아 항공사(航空社)들간의 지역적 협조가 미국(美國)뿐만 아니라 유럽으로 부터의 압력 증가에 대해 균형을 이루는 힘이 될 수 있을 것이다.

• Journal of the Korean housing association
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• v.24 no.2
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• pp.97-104
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• 2013

This study involves 2 newly built apartment houses which are A with 23 floors as 150 mm slab width and B with 16 floors as 180 mm slab width. The impact was added by tapping and bang machine at the middle floor level of these 2 apartments and the test was arranged in terms of the characteristic of vibration and sound level which transferred to upper or down floors. As a result, impact floor shows the highest value in terms of both sound and vibration level and followed was at down floor of the Impact floor. Also, blocking function for the lightweight and heavyweight floor impact sound level was tested for each room of the apartment A and B including living room, main room, room 1 and 2. As a result, sound blocking function of B apartment was better than that of A and the function was getting worse when the room size is getting smaller.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.4
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• pp.291-298
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• 2015

In this study, the reverberation time of apartment living room was measured and distribution of the reverberation time was analyzed. In addition, sound field characteristics of mock-up test room similar with living room and timber structured bedroom was investigated with addition of furniture and sound absorption material. Average reverberation time of unfurnished apartment unit was 1.11 s, and reverberation time in 630 Hz~2000 Hz bands were longer than 1.2 s. It was found that from the field measurement results, reverberation time characteristic of furnished apartment living room was uniform in most of frequency bands. Averaged reverberation time of furnished living room was 0.48 s and the reverberation time of bedroom was 0.44 s. Standardized sound pressure level correction values were calculated from the average reverberation time of furnished and unfurnished apartment units. The correction value of unfurnished living room was −3.4 dB and that of furnished living room was 0.2 dB. Measured reverberation time of furnished and unfurnished apartment units indicated that reference reverberation time; 0.5 s, in KS and ISO standards is reasonable also in Korean residential environment.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.288-290
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• 2010

국산자동차의 품질이 비약적으로 발전하였으나, 주행시나 정차시의 정숙성은 세계최고의 자동차에 비해서는 여전히 취약한 실정이며, 특히 자동차 트렁크에서 발생한 소음과 자동차 하체에서 발생한 소음이 트렁크를 타고 내부에 전달되는 문제가 발생되어 그 해결책이 요구되고 있다. 본 연구에서는 흡 차음이 높은 자동차 트렁크 매트를 개발하는데 목적이 있다. 연구방법으로는 공동연구기업에서 제공한 완제품 형식의 자동차 트렁크 시트와 성형하기 전에 플라스틱판(Board)과 부직포를 이용하여 트렁크 매트의 흡음 및 차음성능을 테스트하였으며, 부직포와 시트의 면밀도를 증가시켜 흡음률과 투과손실의 변화를 살펴보았다. 흡 차음 성능이 높은 자동차트렁크 매트를 개발하기 위하여 부직포와 시트 사이에 다공층을 형성하는 설계를 통하여 매트를 제작하였으며, 개발된 매트의 흡/차음성의 변화를 살펴본 결과 흡음률과 차음도가 기존 제품보다 우수한 것을 확인하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1152-1155
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• 2007

Lately concerns about structure have been increased by advantages of floor impact noise, poilitical induction and changeability. Hence, Flat Plate Structure has been constructed increasingly. This study shows the comparison of the performance of sound insulation of Flat Plate Structure System and the existing Wall Structure. For this study, taking the same level organization of Daelim Architectural Environmental Research Center, I found the performance of sound insulation between the upper and lower floors about Wall Structure and Flat Plate Structure. Consequently, the performance of sound insulation between upper and lower floors of Flat Plate Structure was 3-5dB higher was approximately 3-5dB higher than one of Wall Structure. Especially, the performance of sound insulation on the upper floor was 1-3dB higher than on the lower floor. In addition, as the result of comparing radiation sound which radiates from the wall of lower floors with each structure system, Flat Plate Structure was about 4dB higher with Rw than Wall Structure. As we see totally, the performance of sound insulation of Flat Plate Structure is highter than one of the Wall Structure. It is 3-5dB higher and the main reason for this result depends on the existence of the wall which can radiate sound and nonexistence.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.12
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• pp.1250-1256
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• 2012

Resilient materials are used to reduce the floor impact sound in apartment buildings. Since an on-dol layer is installed in the resilient materials' upper part, thickness deformation can be occur in the resilient material. It is necessary to check a thickness deformation grade for a long period of time. In this research, we measured thickness deformation over 400th day to the resilient materials(EPP, EPS, EVA) which is used in Korea. Although there was a difference according to the kind of measurement test specimens, it became clear that thickness was decreases as to time increased. The thickness deformation grade of ten years after was calculated based on the thickness measurement result. Compare with the calculated result and result of ISO 20392. Larger thickness deformation occurred in the measurement result of these research findings compare with the ISO standard.