• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.1-11
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• 2021

Performance of a NACA 63₄-021 hydrofoil in motion under and in close proximity of a free surface for a large range of angles of attack is studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally, for 0° ≤ AoA ≤ 30° at a Reynolds number of 10⁵. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high angles of attack close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. In comparing with a baseline case, results suggest a 55% increase in maximum lift coefficient and 90% average improvement in performance for, based on the lift-to-drag ratio, but it is also observed significant decrease of lift-to-drag ratio at lower angles of attack. Flow details obtained from combined finite volume and volume of fluid numerical methods provide insight into the underlying enhancement mechanism, involving interaction between the hydrofoil and the free surface.

• 한국농촌건축학회논문집
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• 제16권3호
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• pp.45-52
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• 2014

Recently, Korean people are more interested in leisure time as the Korean economy has enjoyed the economic growth on a continual basis. Along with it, the disabled people's demand for enjoying the beach is growing. To meet the disabled people's demand for enjoy the beaches, it is important to prepare the convenient facilities where the disabled people in the wheel chair can use comfortably, including the handicapped parking area, toilet for the disabled, shower stall room and am bathhouse. On the backdrop of this, the study has been made on the obstacles which keep the disabled people from using the convenient facilities installed on 12 beaches in the southern coat of Korea from the perspective of barrier free design. This study showed that half of the beaches in question did not have the handicapped parking places. The parking space was also so narrow that it was difficult for handicapped people to access the parking lot with their vehicles. There were also 3 beaches which did not have the toilet for the disabled. Even the beaches which have the toilet for the disabled, the size of entrance door and floor space was so narrow and there were a lot of physical obstacles such as no handles for the disabled people that it was really hard for the disabled people in wheelchair to use them.

• 한국정보통신학회논문지
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• 제15권6호
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• pp.1355-1362
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• 2011

본 논문에서는 IEEE 802.11n 무선 랜 표준에 규정된 3가지 블록길이(648, 1296, 1944)와 4가지 부호율(1/2, 2/3, 3/4, 5/6)을 지원하는 LDPC 복호기를 최소합 알고리듬과 layered 복호방식을 적용하여 설계하였다. 검사노드 값과 패리티 검사 행렬 정보의 효율적인 저장방법을 통해 메모리 용량을 최소화하였으며, 또한 효율적인 검사노드 메모리 어드레싱 방법을 적용하여 stall 없이 메모리 읽기/쓰기가 가능하도록 하였다. 설계된 회로는 FPGA 구현을 통해 하드웨어 동작을 검증하였으며, $0.18-{\mu}m$ CMOS 셀 라이브러리로 합성한 결과 219,100 게이트와 45,036 비트의 메모리로 구현되었고, 50 MHz@2.5V로 동작하여 164～212 Mbps의 성능을 갖는 것으로 평가되었다.

• International Journal of Aeronautical and Space Sciences
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• 제10권2호
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• pp.23-33
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• 2009

The inherent aeromechanical complexity of a rotor system necessitated the comprehensive analysis code for helicopter rotor system. In the present study, an aerodynamic analysis module has been developed as a part of rotorcraft comprehensive program. Aerodynamic analysis module is largely classified into airload calculation routine and inflow analysis routine. For airload calculation, quasi-steady analysis model is employed based on the blade element method with the correction of unsteady aerodynamic effects. In order to take unsteady effects - body motion effects and dynamic stall - into account, aerodynamic coefficients are corrected by considering Leishman-Beddoes's unsteady model. Various inflow models and vortex wake models are implemented in the aerodynamic module to consider wake induced inflow. Specifically, linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot's induced inflow distribution and sectional normal force coefficients of AH-1G. In order to validate unsteady aerodynamic model, 2-D unsteady model for NACA0012 airfoil is validated against aerodynamic coefficients of McAlister's experimental data.

• 한국전산유체공학회지
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• 제10권2호
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• pp.60-68
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• 2005

For study on the unsteady wall interference effect, flows around a forced oscillating airfoil in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The Spalart-Allmaras one-equation model is employed for the turbulence effect. The computed results of the oscillating airfoil having a thin wake showed that the lift curve slope is increased and the magnitude of hysteresis loop is reduced by the interference effects. Since the vortex around the airfoil is generated and convected downstream faster than the free-air condition, the phase of lift, drag and pitching moment coefficients was shifted. The pressure on the test section wall shows harmonic terms having the oscillating frequency contained in the wail effect.

• Animal Bioscience
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• 제37권6호
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• pp.1110-1120
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• 2024

Objective: This study was conducted to evaluate the effect of offering (OSF) or not (NSF) supplemental feed at milking on temperament (TS), udder hygiene (UHS) and body condition (BCS) scores, and milk yield per milking (MYM), milk quality traits, and profitability of primiparous Anatolian buffalo cows at 90 days of lactation confined in closed-tied (CB) or semi-open free-stall (OB) barns. Methods: In Experiment I, 108 cows were selected to encompass four treatments (OBOSF, OB-NSF, CB-OSF, and CB-NSF) of 27 cows, considering barn type (OB and CB) and supplementary feed (OSF and NSF) at milking. In Experiment II, 60 OB cows were selected to encompass one of five groups of 12 cows each: i) no supplemental feed (CON), ii) commercial concentrate (CC), iii) CC + corn silage (CCS), iv) CCS + alfalfa hay (CSA), or v) CC + ryegrass silage (CRS) at milking. Results: The TS and UHS of the OB and OSF cows were lower (better) than those of the CB and NSF cows, respectively. The OSF increased milk protein, lactose, and solids-not-fat but decreased milk freezing point and electrical conductivity compared with the NSF. The MYM and milk fat of the OB-OSF cows were higher than those of the OB-NSF and CBNSF cows. The TS and UHS of the cows negatively correlated with MYM and some milk chemicals (fat, protein, and solids-not-fat), but BCS correlated positively. The TS and milk electrical conductivity of the CCS, CSA, and CRS cows were lower than those of the CON and CC cows, but BCS, MYM, and milk fat were higher. Partial budget analysis identified a higher net profit for supplemental feed-offered groups (OB-OSF, CCS, CSA, and CRS). Conclusion: Offering roughage with concentrates at milking for indoor primiparous buffalo cows is more conducive to well-being, milk yield, milk quality, and economy.

• Advances in aircraft and spacecraft science
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• 제10권4호
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• pp.303-315
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• 2023

The primary goal of this research is to investigate flow separation phenomena using various turbulence models. Also investigated are the effects of free-stream turbulence intensity on the flow over a NACA 0018 airfoil. The flow field around a NACA 0018 airfoil has been numerically simulated using RANS at Reynolds numbers ranging from 100,000 to 200,000 and angles of attack (AoA) ranging from 0° to 18° with various inflow conditions. A parametric study is conducted over a range of chord Reynolds numbers for free-stream turbulence intensities from 0.1 % to 0.5 % to understand the effects of each parameter on the suction side laminar separation bubble. The results showed that increasing the free-stream turbulence intensity reduces the length of the separation bubble formed over the suction side of the airfoil, as well as the flow prediction accuracy of each model. These models were used to compare the modeling accuracy and processing time improvements. The K- SST performs well in this simulation for estimating lift coefficients, with only small deviations at larger angles of attack. However, a stall was not predicted by the transition k-kl-omega. When predicting the location of flow reattachment over the airfoil, the transition k-kl-omega model also made some over-predictions. The Cp plots showed that the model generated results more in line with the experimental findings.

• 한국가축번식학회지
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• 제26권3호
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• pp.291-298
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• 2002

본 연구는 경상북도 영주지역의 한우 사육농가를 대상으로 사육규모와 형태, 사양관리 방법 등 번식우의 사양관리 형태와 번식우의 번식장애 발생률을 조사하였으며, 번식장애우에 대하여 proge-sterone제재인 control internal drug releasing for cattle(CIDR)를 처리하여 치료효과를 구명하기 위하여 수행하였다 번식장애우에 대한 CIDR 처리는 7일간 질내에 삽입하였으며, 제거 하루 전에 PGF$_2$$\alpha$를 투여하여 황체를 퇴행 발정을 유기하고 발정 확인 후 10시간 간격으로 인공수정을 실시 임신의 유무로 치료 판정한 결과는 다음과 같다. 1. 경북 영주지방의 127호의 한우 사육농가에서 사육하는 총 1,061두의 번식우의 번식상황을 조사한 결과 번식장애우는 209두로서 발생률은 19.7%이었다. 사육규모별 번식장애 발생율은 10두 이하, 10~20두 및 20두 이상 농가에서 각각 37.5, 14.7 및 13.6%로서 사육규모가 커질수록 발생률이 유의적으로(P<0.05) 낮아지는 경 향이 었다. 2. 번식우의 농가 사육형태별 번식장애 발생률은 계류사육이 30.4%로서 군사의 14.7%보다 유의 적으로(P<0.05) 발생률이 높았으며, 군사의 경우 두당 사육면적이 넓을수록 번식장애 발생률이 낮아지는 경향이었다. 3. 번식장애우의 산차별 분포를 보면 미경산우가 50.7%로 가장 많았으며 산차가 증가할수록 번식장애우에서 차지하는 비율이 감소하는 경향이었다. 4. 번식장애우의 요인별 분포는 무발정이 65.1%, 미약발정 29.2%, 난소낭종 4.3% 그리고 기타1.4%의 순으로 많이 분포되었다. 5. 209두의 번식장애우에 CIDR를 처리하고 인공 수정한 결과 157두가 임신되어 75.1%의 치료효과를 얻었다. 번식장애우의 신체충실 지수별 치료효과는 신체충실 지수가 1, 2 및 3인 경우 수태 율이 각각 85.7, 84.9 및 86.8%로서 유의 적으로(P<0.05) 높았으며, 전체적으로 다소 야윈 경우가 과비된 경우에 비하여 치료 효과가 좋았다. 본 연구결과를 종합하면, 한우 사육농가의 번식장애 발생률은 19.7%로서 사육규모가 커서 농가의 관심도가 높을수록 또한 계류보다는 넓은 면적에서 군사하는 경우가 번식장애 발생률이 낮았으며, 요인별로는 발정과 관련된 장애가 많았다. 이러한 번식장애우도 농가에서 손쉽게 이용할 수 있는 progesterone 제재인 CIDR를 처리함으로서 75.1%를 치료할 수 있으며 치료 효과를 높이기 위해서는 신체충실지수를 1, 2 및 3으로 유지하기 위한 적정 사양관리가 필요하다고 사료된다.

• 대한조선학회지
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• 제38권3호
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• pp.88-92
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• 2001

H. Kim, B.K. Lee and C.K. Rheem have been experimentally studied to clarified the mechanism of thrust force generated by sculling motion for the propulsion of Korean small boats. The experimental investigations have been conducted under the bollard condition by installing a scull at the end of a trimming tank of towing tank. The sculling motion produced by the skilful fisherman and the resultant venerated forces have been measured in respect to the Cartesian coordinate fitted to the pivot point of the scull. ("An Experimental Study on the Propulsive Characteristics of Sculls". J. of the Soc. of Naval Arch. of Korea, Vol. 26, No. 3, 1989, pp.13-24) Through these experiments the trajectory of the blade tip and the angular displacement of the blade section have been measured as shown in Fig. 1 and 2 of this paper. And at the same time the resultant hydrodynamic force components are expressed in Fig. 3 and 4. These three dimensional data of sculling motion and generated real time force components are the unique experimental information which could clarify the thrust force generating mechanism of sculling motion. The experimental results have been reanalyzed by focusing the relation between instantaneous attack angle of blade section and the resultants real time force components. Through these investigation it is found out that the conventional imagination that the 7cull motion should be effective in generating lift force must be reconsidered because the attack angle of scull blade are too great to free from stall phenomena during the sculling operation.

• Asian-Australasian Journal of Animal Sciences
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• 제26권8호
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• pp.1111-1118
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• 2013

The objective of this study was to determine the effects of whole linseed supplementation on performances and milk fatty acid composition of dairy cows. Thirty six Holstein Friesian crossbred lactating dairy cows were blocked by milking days first and then stratified random balanced for milk yields and body weight into three groups of 12 cows each. The control group received 300 g of palm oil. The second group was supplemented with 344 g/d of top-dressed whole linseed plus 150 g of palm oil and the third group was supplemented with 688 g/d of top-dressed whole linseed. All cows also received ad libitum grass silage (Brachiaria ruziziensis), had free access to clean water and were individually housed in a free-stall unit and individually fed according to treatments. Residual feeds were collected on 2 consecutive days weekly and at the end of the experiment. Feed samples were pooled to make representative samples for proximate and detergent analyses. Daily milk yields were recorded. Milk samples were collected on 2 consecutive days weekly. Live weights were recorded at the start and at the end of the experiment. Milk samples were taken on d 56 of the experiment and subjected to milk fatty acid composition. The results showed no statistical significant differences in intakes, live weight change, milk yields and milk compositions, however, C18:1, C18:3 and unsaturated FAs were increased while saturated FAs were reduced by whole linseed supplementation. It is recommended that the addition of 300 g/d oil from whole linseed could be beneficial to lactating dairy cows in early lactation.