• 한국유체기계학회 논문집
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• 제13권6호
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• pp.30-35
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• 2010

The aerodynamic performance of axial flow fans for outdoor unit of air-conditioner is investigated by numerical and experimental approaches in this study. The pressure drop and volumetric flow rate are compared each other in several different conditions and fan speeds. It is shown that the predicted fan performances are quite well matched with the experimental results. It is also shown that the curvature of the fan arc and hub height have significant influences on the flow distribution after hub. By the results of this study, it can be suggested that several ways to improve the aerodynamic performance of the axial flow fan can be found using the numerical analysis.

• Journal of Welding and Joining
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• 제31권1호
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• pp.21-25
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• 2013

Aluminum alloy, Al5083-O, is one of candidate materials for the LNG storage tank, because of its excellent weldability, cryogenic characteristics, and corrosion resistance. The good weldability of Al5083-O is very important in LNG storage tank manufacturing. In this study, high current metal inert gas(MIG) welding process was used to get one pass welding of thick plate aluminum alloy. Bead on plate(BOP) welding was performed to evaluate the effect of welding conditions on the height of bead and depth of penetration. The optimum welding conditions were derived to get one pass welding of the thickness of 14.5mm. The mechanical properties of the welded joint were evaluated. The cross-sectional macro test, tensile test, and bending test satisfied the class rule.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2005년도 학술발표논문집
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• pp.399-403
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• 2005

Slope angle, ground water table and thickness of soils are the key factors affecting landslide stability. However examining the factors such as thickness of soils; geological structure, slope angle, and height, in order to use the global landslide susceptibility forecasting analysis is very expensive and time consuming effort. So most researchers prefer to use the simplest methods such as the C strata and the USGS methods. In this research thickness of soils was calculated using these two methods and stability analysis was performed with the thickness of soils calculated by the two methods at the SINMAP based on ArcView 3.2. The two safety factor maps were compared with the past landslide records. The thickness of soils calculated by USGS method showed more unstable safety factors.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.286-289
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• 2009

This paper deals with the experimental investigation of the steel cord straightening during the stranding process. The over-twisting and roller straightening process are essential to improve the product quality during the stranding process. To investigate the effectiveness of two processes, four experimental cases are constructed according to the use of an over-twister and two roller straighteners. Three assessment items, such as the residual torsion, the arc-height and the preforming ratio, are measured in each experimental case for the quantitative evaluation of a steel cord. The steel cord shape is also measured to investigate the variation of the straightness efficiently after passing through each process. Finally, the effectiveness of the over-twisting and the roller straightening process is explained based on the experimental results.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2005년도 춘계학술대회 논문집
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• pp.191-196
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• 2005

The effects of shot peening on the fatigue strength of SK-5M steel is investigated by experiment. The shot peening process is investigated optimum peening condition by changing impeller speed and exposure time. Bending fatigue test is accomplished to investigate the effect of optimum peening condition on the fatigue characteristics. As exposure time is increased, fatigue life in high stress is increased in early stage, become the maximum from 60 to 100 seconds, and then is decreased. Observing fracture surface through SEM after fatigue test, we can see clear configuration of cracks and peening layer.

• Restorative Dentistry and Endodontics
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• 제41권4호
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• pp.271-277
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• 2016

Objectives: In this study, we evaluated the influence of different radiant exposures provided by single-peak and polywave light-curing units (LCUs) on the degree of conversion (DC) and the mechanical properties of resin cements. Materials and Methods: Six experimental groups were established for each cement (RelyX ARC, 3M ESPE; LuxaCore Dual, Ivoclar Vivadent; Variolink, DMG), according to the different radiant exposures (5, 10, and $20J/cm^2$) and two LCUs (single-peak and polywave). The specimens were made (7 mm in length ${\times}$ 2 mm in width ${\times}$ 1 mm in height) using silicone molds. After 24 hours of preparation, DC measurement was performed using Fourier transform infrared spectrometry. The same specimens were used for the evaluation of mechanical properties (flexural strength, FS; elastic modulus, E) by a three-point bending test. Data were assessed for normality, after which two-way analysis of variance (ANOVA) and post hoc Tukey's test were performed. Results: No properties of the Variolink cement were influenced by any of the considered experimental conditions. In the case of the RelyX ARC cement, DC was higher when polywave LCU was used; FS and E were not influenced by the conditions evaluated. The LuxaCore cement showed greater sensitivity to the different protocols. Conclusions: On the basis of these results, both the spectrum of light emitted and the radiant exposure used could affect the properties of resin cements. However, the influence was material-dependent.

• 대한치과기공학회지
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• 제42권3호
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• pp.281-289
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• 2020

Purpose: This study analyzes the self-efficacy and CAD/CAM practice of dental technology students with the aim of providing data that will be useful for improving CAD/CAM education. Methods: A questionnaire survey on self-efficacy and CAD/CAM practice was given to students who participated in face-to-face classes in the Department of Dental Technology at a college in Daegu and Gyeongsangnam-do. The survey period was two weeks long (June 15, 2020 to July 2, 2020), and 84 students completed the questionnaire. Results: The higher the self-efficacy, the fewer difficulties or mistakes students made in CAD/CAM practice. The most difficult parts of the scanning process were the top and bottom arc operation and the bite match arc insertion. The most difficult part of the design work was the use of (multiple) tools. The difference between the degree of difficulty and the degree of mistakes during the practical course was shown as the margin line setting in the design work. Setting the margin line was not difficult, but the degree of mistakes was nonetheless high. In the CAM process, height control was the most difficult part, but the degree of mistakes did not differ according to students' self-efficacy. Conclusion: Given that higher self-efficacy correlated with fewer difficulties or mistakes in CAD/CAM practice, students should be encouraged to enhance their self-efficacy. This may be done by improving their satisfaction with their major course of study, forming friendly relations with their colleagues, and increasing the ratio of performance rather than observation in CAD/CAM practice.

• 대한치과보철학회지
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• 제41권3호
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• pp.379-386
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• 2003

Statement of problem. Resin cements are widely used in adhesive dentistry specially on all ceramic restorations. It is needed to find out adequate bonding strength between different porcelain surface treatments, commercially available porcelains, and different resin cement systems. Purpose. The purpose of this study was to evaluate shear bond strength of resin cements bonded to porcelains in three different modalities; 5 different porcelain surface treatments, 3 different resin cement systems and 3 different commercially available pressable porcelains. Material and Method. This study consisted of 3 parts. Part I examined the effect of five different surface treatments on the pressable porcelain. Fifty discs (5 mm in diameter and 3 mm in height) of Authentic porcelain were randomly divided into 5 groups (n = 10). The specimens were sanded with 320 grit SiC paper followed by 600 grit SiC paper. The specimens were treated as follow: Group 1-Sandblasting (aluminum oxide) only, Group 2 - sandblasting/ silane, Group 3 - sandblasting/ acid etching/ silane, Group 4 - acid etching only, Group 5 - acid etching/ silane. Part II examined the shear bond strength of 3 different resin cement systems (Duolink, Variolink II, Rely X ARC) on acid etching/ silane treated Authentic pressable porcelain. Part 3 examined the shear bond strength of Duolink resin cement on 3 different pressable porcelains (Authentic, Empress I, Finesse). All cemented specimens were stored in distilled water for 2 hours and tested with Ultradent shear bond strength test jig under Universal Instron machine until fracture. An analysis of variance(ANOVA) test was used to evaluate differences in shear bond strength. Result. The shear bond strength test resulted in the following: (1) Acid etched porcelains recorded greater shear bond strength values to the sandblasted porcelains. (2) Silane treated porcelains recorded greater shear bond strength values to non-silane treated porcelains. (3) There was no significant difference between sandblasting/ acid etching/ silane treated and acid etching/ silane treated porcelains. However those values were much higher than other three groups. (4) The shear bond strength with Variolink II was lower than the value of Duolink or Rely X ARC. (5) The shear bond strength of Finesse was lower than the value of Authentic or Empress I.

• Steel and Composite Structures
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• 제32권5호
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• pp.571-582
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• 2019

This study aimed to assess the feasibility on the wide and long 9%Ni steel plate for use in the LNG storage inner tank shell. First, 5-m-wide and 15-m-long 9%Ni steel plates were test manufactured from a steel mill and specimens taken from the plates were tested for strength, toughness, and flatness to verify their performance based on international standards and design specifications. Second, plates with a thickness of 10 mm and 25 mm, a width of 4.8~5.0 m, and a length of 15 m were test fabricated by subjecting to pretreatment, beveling, and roll bending resulting in a final width of 4.5~4.8 m and a length of 14.8m with fabrication errors identical to conventional plates. Third, welded specimens obtained via shield metal arc welding used for vertical welding of inner tank shell and submerged arc welding used for horizontal welding were also tested for strength, toughness and ductility. Fourth, verification of shell plate material and fabrication was followed by test erection using two 25-mm-thick, 4.5-m-wide and 14.8-m-long 9%Ni steel plates. No undesirable welding failure or deformation was found. Finally, parametric design using wide and long 9%Ni steel plates was carried out, and a simplified design method to determine the plate thickness along the shell height was proposed. The cost analysis based on the parametric design resulted in about 2% increase of steel weight; however, the construction cost was reduced about 6% due to large reduction in welding work.

• 한국지리정보학회지
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• 제19권4호
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• pp.92-105
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• 2016

본 연구는 CCTV(Closed Circuit Television) 촬영범위에 영향을 주는 카메라 사양 및 위치 등 설치 요인에 대한 변수를 고려한 3차원 시뮬레이션 개발을 목적으로 한다. 현재 각 지자체는 방범, 교통, 산불감시와 같은 다양한 공공분야에서 CCTV를 운영하고 있다. 그러나 현재로서 CCTV의 설치는 신규입지의 선정을 위한 분석적 기법의 활용보다는 결정권자의 경험에 의존하여 최종 입지가 선정되고 있는 실정이다. 또한 최근에는 여러 기관이 운영하는 개별 CCTV의 다목적 또는 공동 활용의 중요성이 강조되고 있다. 위에 제시된 상황을 해결하기 위한 방법 중 하나로 이용 목적에 적합한 CCTV 사양 선택 및 최적입지분석 방법론의 필요성이 커지고 있는 실정이다. 이에 본 연구는 기존 연구들의 CCTV 입지점 선정 및 촬영범위 구현 방법의 장단점을 분석하여 이를 보완한 3차원 시뮬레이션 기법을 개발하고자 하였다. 이를 위하여 본 연구에서는 CCTV 촬영범위 산정을 위해 기존 연구의 단점을 보완할 수 있는 요인을 도출하고, GIS기법을 활용하여 도출 요인을 적용한 3차원 촬영범위 분석을 하였다. 도출된 요인은 카메라의 화각에 영향을 주는 촬상소자의 크기와 초점거리, 촬영범위에 관련된 설치 높이 및 설치각 등 총 8개이었다. 위 요인들을 적용한 3차원 시뮬레이션 기법을 ArcObject와 Visual C#을 이용하여 자동화하였다. 이를 이용하여 CCTV 사양에 따른 촬영범위를 시뮬레이션 할 수 있었으며, 신규 설치 시 최적 배분된 입지점의 도출 또한 가능하였다. 이에 본 연구의 결과는 CCTV의 사양 선택 및 입지점 도출을 위해 결정권자의 합리적인 의사결정을 제공할 수 있을 것이다.