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전산 소음 해석 기법을 이용한 잠수함 표면 처리에 따른 소음 효과 관찰
김승기(Seunggi Kim),유재영(Jaiyoung Ryu) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.4
Submarine has been performed for national defense activities representatively as a multi-purpose underwater vehicle. Underwater Radiated Noise (URN) which emitted during underwater vehicle operation is directly related to the survivability of the underwater vehicle. This study focused on examining the effects of surface treatment on noise aspects in whole submarine body for the first time. Prior to the acoustic analysis on the submarine model, the acoustic analysis procedure using commercial CFD software was verified using a 2D cylinder model. Acoustic analysis on submarine model was conducted for two cases: smooth surface as a reference case, and a few micrometers of V-type applied riblet case. To solve the incompressible fluid flow passing the submarine, the Reynolds-averaged Navier-Stokes (RANS) equation coupled with the k-ω SST turbulence model was used. For acoustic analysis, the Ffowcs Williams and Hawkings acoustic analogy, which calculates flow-induced noise by designating a physical wall as a noise source, was used. The noise effects according to the surface treatment on submarine shape were examined by comparing overall sound pressure level (OASPL) between smooth and riblet case and the results indicate that noise around submarine shape was reduced about 4.3 dB in maximum on surface-treated area. However, when calculating OASPL excluding noise below 20 Hz, which is a frequency range where noise does not propagate, the noise tends to increased due to riblet shape. This study provides established procedure in acoustic analysis on whole submarine body and a new perspective that underwater radiation noise should be considered when designing surface treatment on submarine.
Seo, Seunggi,Yeo, Byung Chul,Han, Sang Soo,Yoon, Chang Mo,Yang, Joon Young,Yoon, Jonggeun,Yoo, Choongkeun,Kim, Ho-jin,Lee, Yong-baek,Lee, Su Jeong,Myoung, Jae-Min,Lee, Han-Bo-Ram,Kim, Woo-Hee,Oh, Il-K American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.47
<P>The reaction mechanism of area-selective atomic layer deposition (AS-ALD) of Al2O3 thin films using self-assembled monolayers (SAMs) was systematically investigated by theoretical and experimental studies. Trimethylaluminum (TMA) and H2O were used as the precursor and oxidant, respectively, with octadecylphosphonic acid (ODPA) as an SAM to block Al2O3 film formation. However, Al2O3 layers began to form on the ODPA SAMs after several cycles, despite reports that CH3-tenninated SAMs cannot react with TMA. We showed that TMA does not react chemically with the SAM but is physically adsorbed, acting as a nucleation site for Al2O3 film growth. Moreover, the amount of physisorbed TMA was affected by the partial pressure. By controlling it, we developed a new AS-ALD Al2O3 process with high selectivity, which produces films of similar to 60 nm thickness over 370 cycles. The successful deposition of Al2O3 thin film patterns using this process is a breakthrough technique in the field of nanotechnology.</P>
전산 해석을 통한 유선 방향 미세 구조 적용 SUBOFF 모델에 나타나는 항력 효과 관찰
김승기(Seunggi Kim),장경식(Kyoungsik Chang),이상욱(Sang-Wook Lee),김민재(Minjae Kim),윤재문(Jaemoon Yoon),유재영(Jaiyoung Ryu) 대한기계학회 2024 大韓機械學會論文集B Vol.48 No.7
수중 운동체는 국방의 목적뿐만 아니라, 해저 탐사 등의 목적으로도 사용되고 있는 다목적 운동체이다. 본 연구에서는 수동적인 항력 감소 효과가 있다고 알려진 V자형 미세 구조를, SUBOFF 모델에 유선 방향으로 적용했을 때 어떠한 항력 효과가 있는지 확인해 보고자 한다. 기존의 미세 구조를 적용하지 않은 매끄러운 표면의 SUBOFF 모델과 총 여섯 가지 경우의 마이크로미터 크기 미세 구조(h = 50, 100, 200, 250, 400, 500 μm), 총 일곱 가지의 모델에 대하여 전산 해석을 진행했다. 결과적으로 h가 100 μm인 경우에서는 총 항력이 약 3% 감소했지만, 항력 효과 임계점을 지난 h가 500 μm인 경우에서는 총 항력이 약 3% 증가했다. 본 연구를 통해, 수중 운동체에 V자형 미세구조를 적용할 때 유동 특성 및 미세구조의 크기 등을 종합적으로 고려한 설계가 필요하다는 관점을 제시한다. The drag reduction techniques for underwater vehicles(UWVs) are vital for their long-term longevity in oceans. The UWVs with V-type riblet structures, recognized for passive drag reduction, were investigated in this study. This study focused on examining the effects of streamwise riblet structures on hydrodynamic drag using an UWV scaled SUBOFF model for the first time. Seven models were compared: a smooth surface and riblets with a micrometer-scale (h = 50, 100, 200, 250, 400, 500 μm) in the streamwise direction. To solve the incompressible fluid flow passing through the UWV, the Reynolds-averaged Navier–Stokes (RANS) equation coupled with an SST k-ω turbulence model was used. The total drag reduced by approximately 3% at a certain point; however, a critical point shifted the drag of the riblet UWV to a maximum of approximately 3% increase. This study establishes a procedure for analyzing submarine-wide hydrodynamics with spatially evolving flow, highlighting the riblet design impact on the UWV efficiency.
Dong Hyun Kim,Seunggi Min,Hyun Joo Lee,Hee-June Kim,Hoseok Lee,Jong Pil Yoon 대한견주관절의학회 2019 대한견주관절학회지 Vol.22 No.1
A 73-year-old woman presented with a recurrent cystic mass around her left olecranon. She had a history of 8 steroid injections due to elbow pain beginning 3 years ago and twice had undergone aspiration of olecranon bursitis that developed two months prior to presentation. She had been taking medications for hypertension and diabetes with no pertinent past history. On magnetic resonance imaging (MRI), there were multiple nodules in the olecranon bursa, which were isointense to muscle on T1-weighted images and hyperintense to muscle on T2-weighted images. Our initial diagnosis was synovial chondromatosis. On bursoscopy, masses of gray-white colored nodules were observed in the bursa. Finally, synovial chondromatosis and non-tuberculous mycobacterial infection were concurrently diagnosed. In conclusion, uncalcified synovial chondromatosis and rice bodies can have similar visual and MRI characteristics; therefore, we suggest that clinicians should be aware of the possibility of other infections in cases of this type.