• 한국농공학회논문집
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• 제46권3호
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• pp.3-14
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• 2004

A two-dimensional numerical model based on a finite volume method was formulated to solve the shallow water equations and applied for evaluating drainage characteristics at large-sized paddy fields. Manning roughness coefficient was calibrated using the observed inundating depths at drainage tests, and used for validating the model with the results from another drainage test. The simulated results were in good agreement with the observed inundating depths. The result of surface drainage showed that the longer width of the outlet was or the more the number of drainage outlet was, the shorter the drainage time was taken, and the larger the size of the field become, the longer the drainage time was taken, and the field shape had little effect on drainage time. To reduce the drainage time to 24 hours, the outlet is located lower than the elevation of the basin and small drainage ditch is constructed at the field. The results showed that the drainage time was taken short as the small drainage ditch was constructed. The comparison of drainage time as to the size of field constructed small drainage ditch showed the field, 100m ${\times}$ 200 m, can be drained in 24 hours.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2012년도 학술발표회
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• pp.576-580
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• 2012

하도내 수리구조물 건설과 준설로 인해 발생되는 급격한 수리특성의 변화와 편수위로 야기될 수 있는 제방의 파괴 및 침식을 검토하기 위해서는 다차원 모형의 검토가 필요하다. 본 연구에서는 HEC-RAS로 산정한 조도계수를 다차원 모형에 적용하여 수리거동을 분석하였다. 낙동강 수계에 대해 2003년, 2004년, 2006년 그리고 2007년 태풍 사상에 대해 적용하였으며 HEC-RAS 모형의 조도계수를 0.01부터 0.04까지 0.001씩 증가하여 HEC-RAS 모형에 적용하였고 부정류 흐름모의를 수행하여 RMSE와 NRMSE를 이용해 관측 값과 비교하였다. 공간단위 다차원 모형은 격자크기, 만곡도, 난류 등으로 인한 손실이 추가적으로 반영되기 때문에 선단위 1차원 모형에서 산정된 조도계수를 적용할 경우 실측 관측 수위보다 큰 값이 산정되었다. 따라서, 1차원 수치모형에 의해 산정된 조도계수를 다차원 모형에 그대로 적용할 경우 과대한 수위를 산정할 수 있기 때문에 모형 차원에 따른 별도의 보정을 수행하여 얻어진 조도계수를 적용해야 할 것으로 판단된다.

• 한국식생활문화학회지
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• 제30권1호
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• pp.86-96
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• 2015

Onions contain antioxidant flavonoids and bioactive sulfur compounds. These substances are more abundant in the peel than in onion flesh. For this reason, whole onions including peels were added to soy milk to produce soy milk with whole onions (SWO), whereas peeled onions were added to soy milk to produce soy milk with peeled onions (SPO). The functional and antioxidant properties of these two kinds of soy milk were then analyzed and compared. Compared to control soy milk (CS) without onion powder, treated samples (to which freeze dried onion powder was added at 1.4, 1.6, 1.8, and 2.0%, respectively) showed significantly increased amounts of quercetin, isoflavone, and total phenol (p=0.05). The magnitude of the increase rose as the amount of added onion powder increased and when onion powder contained onion peels. With regards to antioxidant activity (DPPH and ABTS), SWO showed a greater value than SPO. The sensory evaluation scores of SWO and SPO were lower than CS for roughness and swallowing, as adding onion powder increased solid contents and viscosities. However, higher overall acceptability were obtained 1.8SPO and 1.8SWO.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1069-1074
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• 2019

A novel fabrication method of oxide dispersion strengthened (ODS) steel cladding tubes for advanced fast reactors has been investigated using the cold spray powder-based materials deposition process. Cold spraying has the potential advantage for rapidly fabricating ODS cladding tubes in comparison with the conventional multi-step extrusion process. A gas atomized spherical 14YWT (Fe-14%Cr, 3%W, 0.4%Ti, 0.2% Y, 0.01%O) powder was sprayed on a rotating cylindrical 6061-T6 aluminum mandrel using nitrogen as the propellant gas. The powder lacked the oxygen content needed to precipitate the nanoclusters in ODS steel, therefore this work was intended to serve as a proof-of-concept study to demonstrate that free-standing steel cladding tubes with prototypical ODS composition could be manufactured using the cold spray process. The spray process produced an approximately 1-mm thick, dense 14YWT deposit on the aluminum-alloy tube. After surface polishing of the 14YWT deposit to obtain desired cladding thickness and surface roughness, the aluminum-alloy mandrel was dissolved in an alkaline medium to leave behind a free-standing ODS tube. The as-fabricated cladding tube was annealed at $1000^{\circ}C$ for 1 h in an argon atmosphere to improve the overall mechanical properties of the cladding.

• 한국분무공학회지
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• 제25권4호
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• pp.154-161
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• 2020

A single spray plume is the basic unit of the entire spray plume and is an important factor in understanding the spray characteristics. However, since the multi-hole GDI injector has a narrow spray angle, the superposition of the spray plumes occurs severely. Therefore, the spray uniformity and the spray atomization characteristics of a single spray plume were analyzed in this study using a single-hole GDI injector. Five single-hole GDI injectors with different nozzle hole diameters were used in the experiment. The uniformity of the spray was evaluated through the analysis of the spray pattern images. In addition, the atomization characteristics were compared using the diameter distribution of the spray droplets obtained using PDPA. As a result, the larger diameter of the nozzle hole, the less uniformity of the spray, and the injection pressure did not have a significant effect on the spray uniformity. It is judged that the surface roughness of the injector has a greater effect on spray uniformity than the diameter of the nozzle hole. Also, the size of the spray droplets increased sharply when the diameter of the nozzle hole was 230 ㎛.

• Advances in aircraft and spacecraft science
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• 제9권2호
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• pp.131-148
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• 2022

The paper presents the surface-modified NACA 2412 airfoil performance with variable cavity characteristics such as size, shape and orientation, by numerically investigated with the pre-validation study. The study attempts to improve the airfoil aerodynamic performance at 30 m/s with a variable angle of attack (AOA) ranging from 0° to 20° under Reynolds number (R_e) 4.4×10⁵. Through passive surface control techniques, a boundary layer control strategy has been enhanced to improve flow performance. An intense background survey has been carried out over the modifier orientation, shape, and numbers to differentiate the sub-critical and post-critical flow regimes. The wall-bounded flows along with its governing equations are investigated using Reynolds Average Navier Strokes (RANS) solver coupled with one-equational transport Spalart Allmaras model. It was observed that the aerodynamic efficiency of cavity airfoil had been improved by enhancing maximum lift to drag ratio ((l/d) max) with delayed flow separation by keeping the flow attached beyond 0.25C even at a higher angle of attack. Detailed investigation on the cavity distribution pattern reveals that cavity depth and width are essential in degrading the early flow separation characteristics. In this study, overall general performance comparison, all the cavity airfoil models have delayed stalling compared to the original airfoil.

• 대한토목학회논문집
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• 제43권6호
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• pp.749-762
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• 2023

천수 방정식 흐름률 계산에 근사 Riemann 해법을 채택한 수심 적분 모형을 도수 실험에 적용하였다. 도수 때문에 단일 수로에서 서로 다른 흐름 양상이 동시에 나타나므로 흐름 저항에 대해 수심이나 유속에 무관한 Manning 조도 계수보다는 흐름 조건을 반영할 수 있는 Weisbach 저항 계수를 채택하였다. 모의 결과는 실험 결과에 잘 부합되었으며, Weisbach 계수로부터 환산한 Manning 계수는 사류 구간과 상류 구간에서 각 각 적절하게 설정되고 있음을 확인하였다. 도수 실험과 비교에서 정수압 가정에 기반한 천수 방정식의 한계가 드러나 비정수압 천수 흐름 모형 도입의 필요성이 높아졌다.

• 한국전자파학회논문지
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• 제25권12호
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• pp.1219-1227
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• 2014

펄스 레이저 증착(Pulsed laser Deposition: PLD) 및 RF 스퍼터링 증착(Sputtering Deposition)의 단계적 적용을 통해, 표면탄성파 대역 통과 필터(Surface Acoustic Wave Bandpass Filter: SAW-BPF)용 ZnO 박막을 성장시켰다. PLD 방법으로 성장된 ZnO 박막위에 RF sputtering 방법을 사용하여 ZnO 박막을 재증착시켰으며, 성장된 ZnO 박막의 물성을 분석하기 위하여 XRD, SEM 및 AFM 분석장비를 사용하였다. 두 가지 증착 방법이 단계적으로 적용되어 성장된 ZnO 박막의 경우, 결정성과 배향성이 우수하게 유지되면서 표면거칠기가 향상되었다. 분석 결과, ${\omega}$-scan의 반치폭과 표면거칠기의 RMS 값은 각각 $0.79^{\circ}$와 1.108 nm였다. 그리고 성장된 양질의 ZnO 박막을 사용하여 SAW-BPF를 제작하여 측정한 결과는 응답 특성의 중심주파수가 260.8 MHz, 대역폭은 2.98 MHz, 그리고 삽입손실은 36.5 dB이었다.

• The Journal of Advanced Prosthodontics
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• 제5권4호
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• pp.485-493
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• 2013

PURPOSE. To evaluate the effects of surface treatments on shear bond strength (SBS) between microwave and conventionally sintered zirconia core/veneers. MATERIALS AND METHODS. 96 disc shaped Noritake Alliance zirconia specimens were fabricated using YenaDent CAM unit and were divided in 2 groups with respect to microwave or conventional methods (n=48/group). Surface roughness (Ra) evaluation was made with a profilometer on randomly selected microwave (n=10) and conventionally sintered (n=10) cores. Specimens were then assessed into 4 subgroups according to surface treatments applied (n=12/group). Groups for microwave (M) and conventionally (C) sintered core specimens were as follows; $M_C$,$C_C$: untreated (control group), $M_1,C_1:Al_2O_3$ sandblasting, $M_2,C_2$:liner, $M_3,C_3:Al_2O_3$ sandblasting followed by liner. Veneer ceramic was fired on zirconia cores and specimens were thermocycled (6000 cycles between $5^{\circ}-55^{\circ}C$). All specimens were subjected to SBS test using a universal testing machine at 0.5 mm/min, failure were evaluated under an optical microscope. Data were statistically analyzed using Shapiro Wilk, Levene, Post-hoc Tukey HSD and Student's t tests, Two-Way-Variance- Analysis and One-Way-Variance-Analysis (${\alpha}$=.05). RESULTS. Conventionally sintered specimens ($1.06{\pm}0.32{\mu}m$) showed rougher surfaces compared to microwave sintered ones ($0.76{\pm}0.32{\mu}m$)(P=.046), however, no correlation was found between SBS and surface roughness (r=-0.109, P=.658). The statistical comparison of the shear bond strengths of $C_3$ and $C_1$ group (P=.015); $C_C$ and $M_C$ group (P=.004) and $C_3$ and $M_3$ group presented statistically higher (P=.005) values. While adhesive failure was not seen in any of the groups, cohesive and combined patterns were seen in all groups. CONCLUSION. Based on the results of this in-vitro study, $Al_2O_{3-}$ sandblasting followed by liner application on conventionally sintered zirconia cores may be preferred to enhance bond strength.

• 한국해안·해양공학회논문집
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• 제31권6호
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• pp.335-343
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• 2019

본 연구에서는 수리모형실험을 통해 낮은 마운드 높이에 높은 상치구조물을 갖는 경사식 호안(LMHW 호안)의 월파량에 관해 검토하였다. 상치구조물의 형식은 직립식, Flare 식 및 Bullnose 식을 적용하였으며, 호안 전면사면의 소파공은 테트라포드(2층적)와 아크로포드(1층적)를 적용하였다. 수리모형실험 결과는 EurOtop에서 제시하는 경사식 및 직립식 호안의 월파량 산정식과 비교하였다. LMHW 호안에 대해 경사식 호안의 월파량 산정식을 적용할 때 전면 소파공에 따른 조도영향계수(γ_f)로 EurOtop Manual에서 제시하는 계수를 적용할 경우 월파량이 과소평가 되었으나, 상치구조물 대비 마루높이 영향계수(γ_AR)를 곱한 수정조도계수를 적용한 경우에는 실험결과와 비교적 일치하였다. Flare 및 Bullnose 상치의 효과를 검토하기 위해 EurOtop Manual에서 제시하는 직립구조물 상부에 설치된 반파공의 효과(Kortenhaus et al., 2003; Pearson et al., 2004a)와 매끄러운 사면에 설치된 반파공의 효과(Van Doorslaer et al., 2015)를 적용하였다. 검토 결과 매끄러운 사면에 설치된 반파공의 효과가 낮은 마운드 높이에 높은 상치구조물을 갖는 경사식 호안에 보다 타당한 결과를 보였다.