디스크 회전각에 따른 버터플라이 밸브 하류에서의 유동특성

조대환,Cho, Dae-Hwan 해양환경안전학회 2006 해양환경안전학회지 Vol.12 No.4

버터플라이 밸브는 선박에서 냉각수와 유류 계통 등에 범용으로 널리 사용되고 있다. 이 연구에서는 유량조정에 따른 배관계통의 버터플라이밸브 후류 유동특성을 규명하기 위하여 입자영상 유속측정장치를 이용하여 밸브개도에 따른 유선과 속도벡터 분포에 관한 정량적인 데이터를 확보하였다. 또한 밸브 주위 유동장의 압력성분을 고찰하기 위하여 개폐각도를 6가지 경우로 변화시켜 정압을 측정하였다. 그 결과 실험관 벽면에서 측정된 압력의 분포는 디스크가 전개 상태인 $0^{\circ}$에서 $45^{\circ}$까지는 입구 압력은 일정한 상태로 거의 변화하지 않았으나 약 $60^{\circ}$ 이상에서부터 압력 상승과 점차 급격한 변동현상이 나타났다. 특히, $75^{\circ}$ 부근에서는 상류에서 급격한 압력 상승 경향을 보인 반면 하류 측은 압력변동이 적게 나타났다. Butterfly valves have been used for shut-off and throttling-control application in many industrial fields. Recently, they are frequently used for cooling water, oil system and ballast piping system of many larger vessels. They are especially suited for flow throttling control of heat exchangers in engine room. Measurement by the PIV(Particle Image Velocimetry) was conducted to investigate the flow characteristics of butterfly valve inserted within circular pipe. Flow behaviors such as instantaneous and time-mean velocity vectors are investigated. Furthermore, to reveal systematic performance of the butterfly valve, wall pressure was measured at 6 points along the pipe by digital manometer. As the valve position moves to the closed side, flow separation increases and persists its tendency downstream until smoothly uniform flow developed. The pressure loss is found to be about zero for the disk open angles less than 45 degrees, but is substantially increased for those larger than 60 degrees.

고속카메라를 이용한 멀티필라멘트사의 인터레이싱 거동 분석

조대환,정영진,Cho Dae-Hwan,Jeong Young-Jin 한국섬유공학회 2006 한국섬유공학회지 Vol.43 No.2

An attempt is carried out to make the knots in multifilament yarns with conventional interlacer that is controlled to investigate the relationship between the interlacing results and processing conditions. In order to analyze the multifilament movements in interlacer, images of multifilament yams in real time using high speed camera are captured. The physical properties of interlaced yarn are measured to evaluate the influences of two processing conditions, namely, air pressure and yarn tension. Interlacing properties that are caused by the changes of process conditions based on the captured images are analyzed. The mechanism of interlacing in interlacer with the captured images of consecutive multifilament movements were inferred. The movements are classified into several stages according to the status of knot formation which is mainly dependent on the process conditions. Experimental results can be utilized in producing the optimum interlaced yarns for end-use application.

Wear Evaluation of Technical Polyethylene Terephthalate Yarn for Seat Belt Fabric

조대환,Cho, Dae-Hwan The Korean Fiber Society 2011 한국섬유공학회지 Vol.48 No.6

Friction is an important characteristic of the technical yarn. An understanding of this phenomenon is essential for controlling the properties of yarn in a manufacturing process. In order, to evaluate its wear behavior, the mechanical property and the friction coefficient of the yarn used in the seat belt fabric were measured. Different types of technical polyethylene terephthalate(PET) yarns were prepared by varying the yarn denier and the diameter of constituent filaments in the yarn (commonly used as denier per filament or DPF). This was done using a conventional spin-draw melt spinning machine. The yarn of a low DPF showed a higher friction coefficient than that of a high DPF. In a wear test of yarn-to-metal, the low denier yarns lost less strength than high denier yarns. To enhance the wear performance of the seat belt fabric on the basis of the yarn property, the mechanical strength and the wear property of the yarn were coincidently evaluated. As the strength of the seat belt fabric was estimated by using the results of the strength retention ratio after the wear test, a yarn type may be optimally suggested for better wear performance of the seat belt fabric.

이미지 프로세싱을 이용한 배너용 편직물 외관의 객관적 평가

조대환,정영진,Cho, Dae-Hwan,Jeong, Young-Jin 한국섬유공학회 2008 한국섬유공학회지 Vol.45 No.1

The performance of warp knitted fabrics as banner application is influenced by the structure of the fabric. Especially, the level of visibility of a banner fabric is dependent on the evenness of the fabric, which is also influenced by the characters of the component yarns. Until now, the status of fabric surface has been subjectively determined by human, which gives us inconsistent results. Thus, we try to study an objective method using image processing which characterizes the surface status of banner fabric. To do this, we prepare six different samples and extract parameters defining the surface status with image technology. Using the parameters, we analyze the relation between the surface status and yarn characters.

수중 장애물의 하부틈새 크기가 하류 유동장에 미치는 영향

조대환,Cho, Dae-Hwan 해양환경안전학회 2008 해양환경안전학회지 Vol.14 No.4

해안 지역은 해수의 운동에너지의 대부분은 해안에서 소산되며 이 과정에서 해안의 토사 등이 유실된다. 수면에 돌출된 방파제에 비해 수중구조물은 해수의 유통을 가능하게 하고 해안선을 따라 해수순환을 가능케 한다. 이 연구에서는 해안 침식을 방지 기능을 갖는 수중구조물을 하부틈새를 갖는 수중장애물로 형상화 하고 후방의 흐름특성을 규명하였다. 실험은 Re =$1.2{\times}10^4$ 조건에서 2프레임 입자영상유속계를 이용하여 속도장을 계측하여 고찰하였다. 측정된 시간평균 속도분포를 분석한 결과 유선의 곡률 효과가 현저히 나타났으며 전단층 주위 유체의 유입 등의 영향으로 박리 전단층 내에서 커다란 와구조가 연속적으로 발생하였다. 또한 하부틈새의 크기가 증가할수록 재순환 영역의 중심이 후류로 이동하고 재순환영역의 강도도 약해지는 결과를 보였다. The coastal zone is a delicate and dynamic area in which the majority of a water kinetic energy is dissipated. These processes are subsequent to the transport of the beach materials. In comparison to emerged breakwaters, submerged structures permit the passage of some wave energy and in turn allow for circulation along the shoreline zone. This research aims to examine the beach erosion prevention capability of submerged structure by laboratory model. The flow characteristics behind a submerged obstacle with bottom gap were experimentally investigated at Re = $1.2{\times}10^4$ using the two-frame PIV(CACTUS 2000) system. Streamline curvature field behind the obstacle has been obtained by using the data of time-averaged mean velocity information. And the large eddy structure in the separated shear layer seems to have signification influence on the development of the separated shear layer. As bottom gap size increases, the recirculation occurring behind the obstacle moves toward downstream and its strength is weakened.

구동류를 갖는 계단 캐비티의 PIV계측

조대환(Dae-Hwan Cho),김진구(Jin-Gu Kim),이영호(Young-Ho Lee) 한국해양공학회 1998 韓國海洋工學會誌 Vol.12 No.1

An experimental study was carried out in a three-dimensional cubic cavity driven by 2-dimensional plane Poiseuille flow for three kinds of Reynolds number, 10⁴, 3 × 10⁴ and 5 × 10⁴ based on the cavity width and cavity inlet mean flow velocity. Instant simultaneous velocity vectors at whole field were measured by 2-D PIY system. Laser based illumination and two-frame grey-level cross correlation algorithm are adopted. Severe unsteady flow fluctuation within the cavity are remarkable at above Re=3 × 10⁴ Reynolds numbers and sheared mixing layer phenomena are also found at the region where inlet driving Poiseuille flow is collided with the clock-wise rotating main primary vortex at upper center area. Instant velocity profiles reveal that deformed forced vortex formation is observed throughout the separate two areas.

전단 유한요소해석을 이용한 초고장력 강판 피어싱 공정의 펀치 형상에 따른 내구성 평가 연구

조대환(Dae-hwan Cho),박준홍(Jun-hong Park) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4

최근 자동차 업계는 친환경 정책과 연비 향상을 위해 차량 경량화에 많은 노력을 기울이고 있다. 외부의 충격에서 탑승자를 보호하는 가장 중요한 수단인 차량 프레임 관련 부품 제작에는 고강도 및 경량화에 초점을 맞춘 UHSS(초고장력 강판) 소재가 주로 사용되며, 측면 충돌 시 안전 확보에 중요한 역할을 하는 B-pillar 제작 시 적극 사용을 권하는 추세이다. 하지만, UHSS 소재는 고가의 소재이기 때문에 큰 충격으로 인해 소재 자체가 파괴되는 경우를 제외하면 수리를 통해 재사용 하는 경우가 대부분이다. 현재 리벳팅 된 부품을 분리하기 위해 사용되는 펀치 공구에 관한 연구가 활발히 진행되고 있으며, 본 연구에서는 UHSS 급의 CP1180 판재에 관하여 전단 유한요소해석을 통해 펀치의 형상에 따른 펀치 부하 응력 값을 측정하고, 측정된 응력을 기반으로 한 피로해석을 수행하여 형상에 따른 펀치의 수명에 관하여 분석하였다. In recent years, the automotive industry is putting a lot of effort into lighter vehicles to improve eco-friendly policies and fuel economy. In order to achieve weight lightening with high strength of the vehicle frame parts, there is a trend to actively use UHSS(Ultra High Strength Steel) as proper materials. In particular, because of its high strength property, it is commonly supposed to manufacture the vehicle frame parts like the B-pillar that related to safety from automotive side collision. But, UHSS occurs the high cost in manufacturing, it is necessary to apply the disassembly and bonding of parts to the GPa material of the piercing punch to enable repair. In this study, the fatigue analysis is performed to analysis the fatigue life of punch according to punch shape in the piercing process of the UHSS grade CP1180 sheet through finite element method. The shear shape and the stress on the tool were investigated for the shear analysis about angle difference of the punch using DEFORM program which is a commercial forming analysis software and an ANSYS-based user-defined auxiliary program was created, verified and created. As a result, it was confirmed that the optimized angle of the punch considered the appropriate load, fatigue life and material properties of tools. and it will be used in the evaluation of the suitability for the piercing process of GPa grade material sheet through numerical analysis in the future.

구성원의 조직정체성과 이미지 지각이 조직동일시 및 지식공유에 미치는 영향 연구

조대환 ( Dae Hwan Cho ),장용선 ( Yong Sun Chang ) 한국생산성학회 2015 生産性論集 Vol.29 No.3

The purpose of this study is to find out the relationships among organizational identity and perceived organizational image, organizational identification and knowledge sharing. Organizational identification is an important concept that plays a vital role in promoting organization members`` sense of belonging to their organization, their job satisfaction, and the organizational effectiveness. Organizational identity that distinguishes members of his own organization and other organizations, most important and lasting characteristics. In addition, external point of view of the organization, has had a significant impact on the recognition of the organization``s members. This study made the research model based on the theoretical arrangement to explain these relationships between constructs. Using the collected data from 676 members at 53 organizations in South Korea, we tested and confirmed the construct validity and internal consistency by exploratory and confirmatory factor analysis, reliability by Cronbach``s alpha. And we used regression analysis to test hypothesized relationship. This research came to the conclusions to as follows: First, organizational identity and perceived organizational image had the positive effect on organizational identification. Second, organizational identification had the positive effect on knowledge sharing. Third, The organizational identification``s mediating effect among organizational identity and perceived organizational image, knowledge sharing behavior was confirmed in this research. The findings suggest that organizational identity is meaningful variable to understand individual attitude and behavior.

Ni-Ti-Co 계 형상기억합금 코일 스프링의 온도 변화에 따른 동적 특성 연구

조대환(Dae Hwan Cho),김성은(Seong Eun Kim),정한현(Han Hyun Jeong),최주호(Ju Ho Choi),김재일(Jae Il Kim),박준홍(Joon Hong Park) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.5

가습기 살균제 참사와 관련된 당시 생활화학물질 관리 법령에 대한 비판적 고찰

조대환(Dae Hwan Cho),조경이(Kyung Ehi Zoh),박태현(Taehyun Park),최예용(Yeyong Choi),박동욱(Dong-Uk Park) 한국환경보건학회 2022 한국환경보건학회지 Vol.48 No.3

Background: No study has examined the regulatory factors associated with fatal health problems due to the use of humidified disinfectants (HD) in South Korea. Objectives: This study aimed to identify and discuss the deficiencies and limitations found in the Toxic Chemical Control Acts (TCCA) that failed to prevent the health risk of chemicals in HD products. Methods: The South Korean TCCA was reviewed focusing on acts in operation from 1994 through the end of 2011, the period when HD was allowed in manufacturing and marketing. Results: The TCCA was the act intended to regulate the toxicity of chemicals in HD products. We found the TCCA to lack three key legal clauses which would have been essential to controlling the health risk of HD. First, there was the exemption of toxic and hazard testing for existing chemicals, including chloromethylisothiazolinone (CMIT), methylisothiazolinone (MIT), and benzalkonium chloride (BKC). Secondly, there were no articles requiring industry to provide animal inhalation test result for polymers such as polyhexamethylene guanidine (PHMG) and Oligo(2-)ethoxyethoxyethyl guanidine chloride (PGH). Finally, there was a lack of articles on examining the risk of products as well as on addressing changes in the usage of products. These articles were found to be generally provided in the US Toxic Substance Chemical Act (TSCA) and the EU Registration, Evaluation and Authorization of Chemicals (REACH). Conclusions: In conclusion, the Ministry of Environment of South Korea had not updated key articles for regulating hazardous chemicals, causing large-scale health problems due to HD which had been fundamentally addressed in chemical-related acts in other countries.