• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.311-318
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• 2010

본 연구에서는 팁 형상이 가스터빈 블레이드의 팁 열전달에 미치는 영향을 알아보기 위하여 선형 캐스케이드의 블레이드에 설치된 평면 팁, 스퀼러 팁, Groove 팁들에 대하여 열전달 계수가 측정되었다. 블레이드 팁에서의 열전달 계수는 색상검출방식에 기반을 둔 천이액정법을 이용하여 측정되었으며 각각의 팁 형상에 대하여 팁 간극은 블레이드 스팬의 1.5%와 2.3%로 변경 하에 실험을 수행하였다. 캐스케이드 출구 속도와 블레이드 코드길이에 기초를 둔 Reynolds 수는 $2.48{\times}10^5$ 이다. Groove 팁 표면에서의 열전달 계수는 평면 팁보다 낮게 측정되었으며, 특히 흡입면을 따라 경사진 홈이 파인 팁에서는 스퀼러 팁보다 낮은 열전달 계수가 측정되었다.

• Wind and Structures
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• 제23권3호
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• pp.211-229
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• 2016

In recent years, the frequency and duration of supply interruption in electric power transmission system due to flashover increase yearly in China. Flashover is usually associated with inadequate electric clearance and often takes place in extreme weathers, such as downbursts, typhoons and hurricanes. The present study focuses on the wind-induced oscillation of conductor during the process when a downburst is passing by or across a specified transmission line. Based on a revised analytical model recently developed for stationary downburst, transient three-dimensional wind fields of moving downbursts are successfully simulated. In the simulations, the downbursts travel along various motion paths according to the certain initial locations and directions of motion assumed in advance. Then, an eight-span section, extracted from a practical 500 kV ultra-high-voltage transmission line, is chosen. After performing a non-linear transient analysis, the transient displacements of the conductors could be obtained. Also, an extensive study on suspension insulator strings' rotation angles is conducted, and the electric clearances at different strings could be compared directly. The results show that both the variation trends of the transient responses and the corresponding peak values vary seriously with the motion paths of downburst. Accordingly, the location of the specified string, which is in the most disadvantageous situation along the studied line section, is picked out. And a representative motion path is concluded for reference in the calculation of each string's oscillation for the precaution of wind-induced flashover under downburst.

• International Journal of Naval Architecture and Ocean Engineering
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• 제4권2호
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• pp.151-161
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• 2012

The present study numerically investigates the aerodynamic characteristics of two-dimensional wings in the vicinity of the ground by solving two-dimensional steady incompressible Navier-Stokes equations with the turbulence closure model of the realizable k-${\varepsilon}$ model. Numerical simulations are performed at a wide range of the normalized ground clearance by the chord length ($0.1{\leq}h/C{\leq}1.25$) for the angles of attack ($0^{\circ}{\leq}{\alpha}{\leq}10^{\circ}$) in the prestall regime at a Reynolds number (Re) of $2{\times}10^6$ based on free stream velocity $U_{\infty}$ and the chord length. As the physical model of this study, a cambered airfoil of NACA 4406 has been selected by a performance test for various airfoils. The maximum lift-to-drag ratio is achieved at ${\alpha}=4^{\circ}$ and h / C = 0.1. Under the conditions of ${\alpha}=4^{\circ}$ and h / C = 0.1, the effect of the Reynolds number on the aerodynamic characteristics of NACA 4406 is investigated in the range of $2{\times}10^5{\leq}Re{\leq}2{\times}10^9$. As Re increases, $C_l$ and $C_d$ augments and decreases, respectively, and the lift-to-drag ratio increases linearly.

• Tribology and Lubricants
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• 제35권3호
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• pp.158-168
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• 2019

This paper presents the investigation of two types of rotordynamic modeling issues for 2.2 kW-class, rated speed of 1,800 rpm, squirrel-cage type induction motors. These issues include the lamination structure of rotor cores, and the radial clearance of ball bearings that support the shaft of the motor. Firstly, we focus on identifying the effects of rotor core lamination on the rotordynamic analysis via a 2D prediction model. The influence of lamination is considered as the change in the elastic modulus of the rotor core, which is determined by a modification factor ranging from 0 to 1.0. The analysis results show that the unbalanced response of the rotor-bearing system significantly varies depending on the value of the modification factor. Through modal testing of the system, the modification factor of 0.079 is proven to be appropriate to consider the effects of lamination. Next, we investigate the influence of ball bearing clearance on the rotordynamic analysis by establishing a bearing analysis model based on Hertz's contact theory. The analysis results indicate that negative clearance greatly changes the bearing static behavior. Rotordynamic analysis using predicted bearing stiffness with various clearances from -0.005 mm to 0.010 mm reveals that variations in clearance result in a slight difference in the displacement of the system up to 18.18. Thus, considering lamination in rotordynamic analysis is necessary as it can cause serious analysis errors in unbalanced response. However, considering the effect of the bearing clearance is optional because of its relatively weak impact.

• International Journal of Computer Science & Network Security
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• 제22권11호
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• pp.213-221
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• 2022

Intelligent Character Recognition System for Account Payable (ICRS AP) Automation represents the process of capturing text from scanned invoices and extracting the key fields from invoices and storing the captured fields into properly structured document format. ICRS plays a very critical role in invoice data streamlining, we are interested in data like Vendor Name, Purchase Order Number, Due Date, Total Amount, Payee Name, etc. As companies attempt to cut costs and upgrade their processes, accounts payable (A/P) is an example of a paper-intensive procedure. Invoice processing is a possible candidate for digitization. Most of the companies dealing with an enormous number of invoices, these manual invoice matching procedures start to show their limitations. Receiving a paper invoice and matching it to a purchase order (PO) and general ledger (GL) code can be difficult for businesses. Lack of automation leads to more serious company issues such as accruals for financial close, excessive labor costs, and a lack of insight into corporate expenditures. The proposed system offers tighter control on their invoice processing to make a better and more appropriate decision. AP automation solutions provide tighter controls, quicker clearances, smart payments, and real-time access to transactional data, allowing financial managers to make better and wiser decisions for the bottom line of their organizations. An Intelligent Character Recognition System for AP Automation is a process of extricating fields like Vendor Name, Purchase Order Number, Due Date, Total Amount, Payee Name, etc. based on their x-axis and y-axis position coordinates.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 봄 학술논문 발표대회
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• pp.12-13
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• 2021

Methods for the manufacture, erection, and assembly of heavy frame modules were proposed. Interferences among precast members were prevented by using bolted metal plates for dry precast beam-to-column joints during assembly with a clearance for tolerance implementing grouted concrete filler plates instead of metal filler plates. Clearances for tolerances were provided to avoid conflictions among components during erection phases. These gaps were, then, grouted by high-strength mortar. The constructability of new connections of a beam-to-column joint using bolted metal plates for precast structures was examined using a full-scale assembly test in which practical observations indicated that members could be aligned and placed accurately in both horizontal and vertical directions, leading to a fast and convenient assembling. Bolt holes of the endplate were properly aligned using couplers with 30 mm fastened length embedded in the columns. The assembly test demonstrated the erection safety and structural stability of the proposed joints that were without filler plates when they were subjected to heavy loads at the time of their erection. The facile and rapid assembly of precast beam-to-column connections with a 30 mm tolerance was observed. The proposed assembly method is rapid, sustainable, and resilient, replacing the conventional methods of concrete frame construction, offering a connection that can be used in constructing infrastructure, such as buildings and pipe-rack frames.

• 소성∙가공
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• 제32권2호
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• pp.81-86
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• 2023

The hot stamping process is widely used for high strength of vehicle parts, with heating 900 ℃ or higher in a furnace and in-die quenching to achieve strength above 1.5 GPa of the quenchable boron alloyed steel 22MnB5. First of all, the hot stamping process consisted of heating, forming, quenching and trimming. In the trimming process case, the laser method has been conventionally adopted. For laser trimming process, it has the problems pertaining to low productivity and high cost while the hot stamping process, accordingly the trimming process need to investigate the research for alternative method. In order to overcome these issues, many research groups have studied the mechanical trim solution on the hot stamped parts at high temperature. In this study, the mechanical piercing was performed during the hot stamping process at the high temperature for overcome the disadvantages of laser cutting. Also, the process parameters such as piercing time after die closing, clearances of between die and punch were controlled for obtaining the reasonable shear characteristics.

• Design & Manufacturing
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• 제17권3호
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• pp.15-20
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• 2023

In the fine blanking process, which is a press operation known for producing parts with narrow clearances and high precision through the application of high pressure, die roll often occurs during the shearing process when the punch penetrates the material. This die roll phenomenon can significantly reduce the functional surface of the parts, leading to decreased product performance, strength, and fatigue life. In this research, we conducted an in-depth analysis of the factors influencing die roll in the curvature area of the fine blanking process and identified its root causes. Subsequently, we designed and experimentally verified a die roll reduction process specifically tailored for the door latch manufacturing process. Our findings indicate that die roll tends to increase as the curvature radius decreases, primarily due to the heightened bending moment resulting from reduced shape width-length. Additionally, die roll is triggered by the absorption of initial punch energy by scrap material during the early shearing phase, resulting in lower speed compared to the product area. To mitigate the occurrence of die roll, we strategically selected the Shaving process and carefully determined the shaving direction and clearance area length. Our experiments demonstrated a promising trend of up to 75% reduction in die roll when applying the Shaving process in the opposite direction of pre-cutting, with the minimum die roll observed at a clearance area length of 0.2 mm. Furthermore, we successfully implemented this approach in the production of door latch products, confirming a significant reduction in die roll. This research contributes valuable insights and practical solutions for addressing die roll issues in fine blanking processes.

• 한국해양학회지:바다
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• 제24권4호
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• pp.495-508
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• 2019

조석현상이 뚜렷한 연안에서 항해, 연안 구조물 설계, 해양영토 획정, 침수범람 예보 등을 위하여 여러 조위 기준면들(tidal datums)이 사용된다. 우리나라 수로학 분야와 해안공학 분야에서는 수심을 측량하는 기본 수준면(datum level)으로 약최저저조위(ALLW)를 사용하고, 해안선과 안전수직높이(vertical clearances) 기준면으로는 약최고고조위(AHHW)를 사용하고 있다. 그러나 최근에 미국, 호주, 영국을 포함하여 국제적으로는 최저 천문조위(LAT)와 최고 천문조위(HAT)를 기본 수준면과 안전수직높이의 기준면으로 사용하고 있다. 이 연구에서는 서해안과 남해안 9개 조위 관측소에서 19년(1999-2017년) 동안 1시간 간격으로 관측한 해수면 높이 자료를 '19년 벡터평균 분석', '19년 연속 분석', '1년 연속 분석' 방법으로 각각 1분 간격으로 19년간 예측한 조위로부터 LAT와 HAT를 계산하였다. 이 연구에서는 19년 연속 관측자료의 조석 조화분해와 19년 연속 조석 예측에 모두 적합한 UTide 프로그램을 사용하였다. 각 조위 관측소에서 '19년 벡터평균 분석'과 '19년 연속 분석' 방법으로 각각 계산한 LAT 또는 HAT 값들의 차이는 대부분 ±1 cm 미만으로 큰 차이를 보이지 않았으며, 이 두 방법은 서로 거의 일치하는 결과를 생산하였다. 반면에 각 조위 관측소에서 19년간 연속 관측한 자료를 연별로 19개로 나누어 각각 1년 자료씩 조석 조화분해한 후 각각 19년간 조위를 예측한 '1년 연속 분석' 방법은 서로 크게 다른 19개의 LAT와 HAT 값들을 산출하였으며, 그 19개들의 표준편차는 3~7 cm이었다. '1년 연속 분석' 방법으로 구한 이들 값들은 '19년 연속 분석' 방법으로 산출 값과 비교하면 서해안과 남해안에서 LAT는 -16.4~10.7 cm의 차이를 보였으며, HAT는 -8.2~14.3 cm의 차이를 보였다. 계산된 LAT와 HAT를 ALLW와 AHHW와 정량적으로 비교했을 때, 서해안과 남해안에서 LAT는 ALLW보다 평균적으로 46.2 cm 더 낮았으며, HAT는 AHHW보다 평균적으로 33.6 cm 더 높았다. 이러한 차이에 가장 크게 기여하는 분조는 ALLW와 AHHW 계산에 고려되지 않은 진폭이 비교적 큰 S_a와 N₂ 분조이었다. 또한 천해분조가 강하게 발달한 내만에서는 M₄와 MS₄ 분조가 추가적으로 그 차이에 상당히 기여하였다. LAT와 ALLW 간 차이와 HAT와 AHHW 간 차이가 같지 않은 이유는 ALLW와 AHHW를 계산할 때는 주요 4대 분조의 진폭만을 사용하지만 LAT와 HAT를 계산할 때는 실질적으로 67개 분조의 진폭뿐만 아니라 지각도 사용하기 때문이다.

• The Korean Journal of Physiology
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• 제23권2호
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• pp.363-375
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• 1989

It has been well known that peripheral infusion of angiotensin II results in an increase of blood pressure, and an elevation of aldosterone secretion, and an inhibition of renin relase. However, the direct effect of angiotensin II on renal function has not been clearly established. In the present study, to investigate the effect of angiotensin II on renal function and renin release, angiotensin II (0.3, 3 and 10 ng/kg/min) was infused into a unilateral renal artery of the unanesthetized rabbit and changes in renal function and active and inactive renin secretion rate (ARSR, IRSR) were measured. In addition, to determine the relationship between the renal effect of angiotensin II and adenosine, the angiotensin II effect was evaluated in the presence of simultaneously infused 8-phenyltheophylline (8-PT, 30 nmole/min), adenosine A 1 receptor antagonist. Angiotensin II infusion at dose less than 10 ng/kg/min decreased urine flow, clearances of para-amino-hippuric acid and creatinine, and urinary excretion of electrolytes in dose-dependent manner. The changes in urine flow and sodium excretion were significantly correlated with the change in renal hemodynamics. Infusion of angiotensin II at 10 ng/kg/min also decreased ARSR, but it has no significant effect on IRSR. The change in ARSR was inversely correlated with the change in IRSR. The plasma concentration of catecholamine was not altered by an intarenal infusion of angiotensin II. In the presence of 8-PT in the infusate, the effect of angiotensin II on renal function was significantly attenuated, but that on renin secretion was not modified. These results suggest that the reduction in urine flow and Na excretion during intrarenal infusion of angiotensin II was not due to direct inhibitions of renal tubular transport systems, but to alterations of renal hemodynamics which may partly be mediated by the adenosine receptor.