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Aerodynamic effects of canopy inflation in paragliding
Seokbong Chae,Jeonghan Shin,신이수,Seongyun Hwang,박정목,Ginseok Song,김주하 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.4
In this study, the aerodynamic effects of the inflation of a paraglider wing (canopy) are investigated at the maximum chord Reynolds number of 330000. The aerodynamic forces and surface flow patterns were compared between the inflated and uninflated canopy models in a wide range of angles of attack. The stall angle and maximum lift coefficient of the inflated model are approximately 80 % and 38 % greater than those of the uninflated model. Before stall, dot- and line-shaped separation bubbles are formed on the inflated and uninflated models, respectively. The dot-shaped separation bubbles remain to a much higher angle of attack than the line-shaped one, with little change in the size and location. For the inflated model near stall, the flow is partially separated in the spanwise center, and the separation bubbles remaining are distorted. After stall, the canopy inflation has little effect on aerodynamic performance as the flow is fully separated.
예비변형률 효과를 고려한 차체용 박판의 동적 물성 특성 연구
김석봉(Seokbong Kim),임지호(Jiho Lim),허훈(Hoon Huh) 한국자동차공학회 2003 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Most parts of auto-body are produced through the sheet metal forming process, and during this process they have change of thickness and residual stress and strain remain. In this paper, to specify dynamic material properties considering this pre-strain effect, materials SPCEN, SPRC45E and SPRC35R were selected and were imposed 5, 10% pre-strains. After that using the high speed material testing machine, materials were tested at given strain rates of between 0.003 and 50 s^-¹. It was found from experimental results that in case of SPCEN and SPRC35R, the yield stress and ultimate stress were increased due to pre-strain effect at strain of over 10 s^-¹ but SPRC45E was not affected by pre-strain effect.
김석봉(Seokbong Kim),안광현(Kwanghyun Ahn),하지웅(Jiwoong Ha),허훈(Hoon Huh),복현호(Hyunho Bok) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
This paper deals with the formability of CQ and DP590 steel sheets in relation to the strain rate. The high speed forming limit tests were performed using the high speed crash testing machine and high speed forming jig. Compared with the static FLC, the high-speed FLC of CQ is higher in a simple tension region and lower in a biaxial stretch forming region. The high-speed FLC for DP590 decreases in relation to the static FLC throughout the entire region. The elongation at fracture appears to be closely related to the simple tension region of the FLC. The decrease of the high-speed FLC in the biaxial stretch forming region is due to the shear fracture in fracture surfaces. Three theoretical (Hill?Swift, Jun and M?K models) approaches and two empirical (Keeler?Brazier and Raghavan models) approaches were discussed to predict the FLC of sheet metals. The theoretical models are found to be very conservative, especially at plane strain region in FLC. Among the various prediction models, the Raghavan model with NADDRG curve gives better prediction at plane strain region.
승용차 센터페시아의 버튼 각도에 따른 버튼 조작 힘과 만족도 평가
박석봉(Seokbong Park),장준호(Joonho Chang),정기효(Kihyo Jung) 대한인간공학회 2020 大韓人間工學會誌 Vol.39 No.4
Objective: This study examined the angular effects of a button on the center fascia of vehicle in terms of push force and satisfaction score. Background: The angle of buttons on the center fascia may influence usability and user experience. However, a comprehensive study to investigate the angular effects of a button has been lacking. Method: This study measured push forces and satisfaction scores for six angles (0°, 10° 20°, 30°, 40°, and 50°) of a button for 25 male participants. Push forces applied on a button with the right index finger were recorded using a force sensitive resistor, which was placed on a button. Subjective satisfaction scores were observed using a 5-point scale (1 = very dissatisfied, 3 = neutral, 5 = very satisfied). Results: Mean push forces at button angles 0~30° (mean ± SE; 3.31±0.06N) were significantly higher than the other angles (3.10±0.05N). Similarly, peak push forces at button angles 0~20° (4.43±0.04N) were higher than the other angles (4.28±0.04N). Satisfaction scores at button angles 10~30° (3.86±0.18) were higher than the other angles (2.50±0.18). The debriefing on experiment results revealed that participants preferred button angles 10~30° since it improved button usability and visibility than the other angles. Conclusion: The button angles 10~30° can help effective force transmission and improve subjective satisfaction. Application: The angular effects of a button identified in this study can be applied in ergonomic design of buttons on the center fascia of vehicle.
김석봉(Seokbong Kim),허훈(Hoon Huh),임지호(Jiho Lim),김기풍(Keepoong Kim) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.11_3
An important challenging issue in the automotive industry is the light-weight, safe design and enhancement of crash response of an auto-body structures. These objectives lead to increasing adoption of TRIP-type and DP-type steel sheets for an inner part of auto-body members. This study evaluates the dynamic tensile characteristics of TRIP60. TRIP80, DP60 and DP80 at the range of strain rate from 0.003/sec to 200/sec. The tensile tests acquire stress-strain relation and fracture elongation of each material. The experimental results show that the flow stress is increased as strain rate increases and elongation is not decreased even when the strain rate increases. In order to investigate the pre-strain effect at high strain rate, TRIP60 and DP60 were deformed with 5, 10% pre-strain at 0.003/sec strain rate. Then dynamic tensile test was carried out at the strain rate of 0.003, 1, 10, 100/sec. The results demonstrate that the material properties are noticeably influenced by the pre-strain at the high strain rate. The ultimate tensile strength as well as the yield stress is increased due to the pre-strain.
김석봉(Seokbong Kim),이경호(Kyungho Lee),허훈(Hoon Huh),유정수(Jungsu Yoo),이문용(Munyong Lee) 한국자동차공학회 2006 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
This study deals with the crashworthiness of aluminum crash box for an auto-body with the various types of cross section. For the aluminum alloy, Al7003-T7, the dynamic tensile test was carried out to apply for crash analysis at the range of strain rate from 0.003/sec to 200/sec. The crash analysis was carried out for four cross sections, square and hexagonal with and without ribs. The analysis result shows that the absorbed internal energy and the reaction force of crash box with rib are higher than that of crash box without rib. This result is due to the interaction between member and rib and the collapse of rib with the buckling mode. And the energy absorption is also affected by the cross section shape. Hexagonal cross section shows higher energy absorption and reaction force than square cross section.
예비변형률 효과를 고려한 고변형률 속도에서의 차체용 강판의 물성 특성
김석봉(Seokbong Kim),임지호(Jiho Lim),허훈(Hoon Huh),임종대(Jongdae Lim) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Most auto-body members fabricated by the sheet metal forming process. During this process the thickness and material properties of the sheet metal are changed with the residual stress and plastic strain. This paper deals with the material properties of the sheet metal at the high strain rate considering the pre-strain effect. Specimens are selected from sheet metals for outer panels and inner members, such as SPCEN, SPRC45E, SPRC35R and EZNCD. The specimens are prepared with the prestrain of 2, 5 and 10 % by tensile elongation in Instron 5583, which could be equivalent to the plastic strain in sheet metal forming, High speed tensile tests are then carried out with the pre-stained specimens at the strain rate of 1 to 100 /sec. The experimental result informs that the material properties are noticeably influenced by the pre-strain when the yield stress of the specimens is moderate as SPCEN, SPRC35R and EZNCD. The result also demonstrates that the ultimate tensile strength as well as the yield stress is increased as the amount of the pre-strain is increased.