• 한국정밀공학회지
• /
• 제16권11호
• /
• pp.122-132
• /
• 1999

This study describes a dynamic model of the hydroforming process which is used for precision forming of sheet metals. To help the controller design for the control of the forming pressure needed for this process as well as to investigate the effect of system parameters on the dynamic behavior, dynamic modeling is performed with emphasis on hydraulic servo system which actuates the forming machine. Since the model contains several unknown parameters, these were estimated via a least square parameter identification method. Based upon the identified model, a series of simulations were performed for various operating conditions. The results were compared with those of the experiments to verify the validity of the proposed model. The comparison study shows that the proposed dynamic model can describe dynamic behavior of the forming pressure of the hydroforming process to desirable accuracy.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 추계학술대회
• /
• pp.1810-1815
• /
• 2003

Tube hydroforming provides a number of advantages over conventional stamping process, including fewer secondary operation, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength and stiffness. In this study, the effect of the heat treatment on the hydro-formability has been investigated. By using the mild steel tube bulging test is performed at various heat treatment conditions to evaluate the hydro-formability.

• Molecules and Cells
• /
• 제24권3호
• /
• pp.424-430
• /
• 2007

The biological effects of low-dose radiation have been investigated and debated for more than a century, but its cellular effects and regulatory mechanisms remain poorly understood. This study shows the human cellular responses to low-dose radiation in CCD-18 Lu cells, which are derived from normal human lung fibroblasts. We examined a colony-forming assay for cell survival by ionizing radiation. Live cell counting and cell cycle analysis were measured for cell proliferation and cell cycle progression following low-dose irradiation. We examined Raf and Akt phosphorylation to determine the proliferation mechanism resulting from low-dose radiation. We also observed that p53 and p21 were related to cell cycle response. We found that 0.05 Gy of ionizing radiation enhanced cell proliferation and did not change the progression of the cell cycle. In addition, 0.05 Gy of ionizing radiation transiently activated Raf and Akt, but did not change phospho-p53, p53 and p21 in CCD-18 Lu cells. However, 2 Gy of ionizing radiation induced cell cycle arrest, phosphorylation of p53, and expression of p53 and p21. The phosphorylation of Raf and Akt proteins induced by 0.05 Gy of ionizing radiation was abolished by pre-treatment with an EGFR inhibitor, AG1478, or a PI3k inhibitor, LY294002. Cell proliferation stimulated by 0.05 Gy of ionizing radiation was blocked by the suppression of Raf and Akt phosphorylation with these inhibitors. These results suggest that 0.05 Gy of ionizing radiation stimulates cell proliferation through the transient activation of Raf and Akt in CCD-18 Lu cells.

• 소성∙가공
• /
• 제17권3호
• /
• pp.218-224
• /
• 2008

A recent trend in automotive parts has been an integration of sub-assemblies with unified shapes. Tube structures also have been integrated to one body structure by using a near net shape forming instead of adopting welding. A cylindrical elastomer-forming process can be utilized to form a steel tube compressed in a radial direction. This process has some advantages compared to a hydro-forming or a swaging process in the viewpoint of a lower investment and a higher productivity. In order to predict a feasible specification of products within a work capability of the elastomer-forming equipment developed previously, effects of geometrical parameters of a tube on its shape accuracy are examined. Two characteristic parameters to account for the shape accuracy are chosen. One is the curvature radius at the corner part and the other is the straight ratio of the formed region. Careful examination of two parameters has led that the shape accuracy can be easily predicted by the regression equation obtained from the response surface method.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2010년도 춘계학술대회 논문집
• /
• pp.1105-1106
• /
• 2010

• 한국산학기술학회논문지
• /
• 제18권10호
• /
• pp.675-680
• /
• 2017

국내 대다수의 하수처리장 방류수로는 2.0 m 미만의 낙차를 형성하고 있고 유량이 지속적이며 변동이 크지 않다는 점을 고려할 때, 저낙차 조건에서도 안정적인 전력 생산과 효율을 유지할 수 있는 소수력 발전장치 개발이 시급히 요구된다. 본 연구에서는 저유속 조건에서 소수력 에너지 생산 효율 증진을 위한 항력식 수직축 수차를 개발하기 위하여 전산 유체 동역학(CFD) 기법을 이용하여 수치해석을 수행하였다. 즉, 2.0 m/s 미만의 유속 조건에서 수차 블레이드의 타공 유무에 따른 블레이드 압력변화와 내부유동을 분석하였다. 수치해석 결과, 수차 블레이드의 타공 유무에 따른 압력분포는 타공이 있는 수차 블레이드에 발생하는 압력이 타공이 없는 수차 블레이드보다 약 5.1 % 감소되는 것으로 나타났다. 수조와 수차 블레이드 주변의 내부유동을 분석한 결과, 벡터의 분포로부터 유동속도가 변화하는 것을 알 수 있었으며, 타공이 있는 수차 블레이드의 유속이 타공이 없는 수차 블레이드의 유속보다 5.6 % 감소하는 것으로 밝혀졌다. 따라서 수차 블레이드에 타공을 형성하는 것이 구조안전성 측면에서 도움이 될 것으로 판단된다.

• 한국정밀공학회지
• /
• 제23권5호
• /
• pp.51-58
• /
• 2006

The necessities for heightening fuel efficiency as well as lightweight design, lead to an increase of the use of aluminum alloys in the automobile industry. Extruded aluminum profile channels are used widely for the design of frame parts as lightweight assemblies, especially if a high stiffness is needed. While many applications can be realized with forming of hollow square-sectioned extruded profiles such as a stretch bending and a hydro-forming, some applications demand the use of a press bending which can be hardly found in the previous study. In this study, by introducing the use of a press bending into car sub-frames, the demands for higher accuracy as well as higher flexible method than the conventional methods will be satisfied. With respect to the design of sub-frames, the process planning was performed from the shape of a sub-frame product. The designed processes were analyzed by the commercial FEM code, DEFORM-3D. Forming dies for the each process were designed and prototypes of sub-frames were manufactured by the verified farming process. In addition, some of the important features of design parameters in the press bending were reviewed.

• 한국태양에너지학회 논문집
• /
• 제40권4호
• /
• pp.23-33
• /
• 2020

The loss in photovoltaic power due to hailstorms has been highlighted as a major issue in the sustained growth of the PV power plant industry. This study investigates the safety of a solar module by conducting a numerical analysis of a hail test according to the IEC 61215 standard. Our study aims to elucidate the detailed behavior between the ice and solar modules and the micro-cracks forming on solar modules during hailstorms. To analyze the impact of hail, we used the ANSYS AUTODYN software to evaluate the impact characteristics on a solar module with different front glass thicknesses. The simulations show that a solar module with a glass thickness of 4.0 mm results in excellent durability against hail. The results indicate the feasibility of using simulations to analyze and predict micro-cracks on solar modules tailored to various conditions, which can be used to develop new solar modules.

• 한국수자원학회논문집
• /
• 제51권3호
• /
• pp.183-193
• /
• 2018

본 연구에서는 내성천의 영주댐 하류 구간에서의 안정하도 단면 평가를 수행하기 위해 하도형성유량을 산정하였으며 이를 기준으로 용혈지점에서의 안정하도 경사, 수심, 하폭에 대한 평가를 수행하였다. 하도형성유량과 안정하도 평가를 수행하기 위해 사용된 자료는 용혈지점에서 영주댐 건설 전에 수집된 자료이다. 특정 재현기간별 유량, 유효유량, 만제유량을 산정하여 비교 검토를 통해 최종적으로 만제유량인 $260m^3/s$을 하도형성유량으로 채택하였다. 또한 안정하도 설계 프로그램(SCAD)을 활용하여 Ackers and White, Brownlie, Engelund and Hansen, Yang 공식을 각각 적용하여 대상단면의 안정하도를 평가하였다. 그 결과, 모든 유사이송공식이 현재 하도의 하상경사인 0.00177보다 완만한 경사를 제시하는 것으로 나타났으며 하도의 바닥 폭을 설계구속인자로 고려할 경우 Ackers and White 공식을 적용하여 안정하도를 계산했을 때 안정하도의 수심이 현재 단면의 수심과 가장 근접한 것을 알 수 있었다.

• 소성∙가공
• /
• 제10권7호
• /
• pp.534-542
• /
• 2001

Tubular hydroforming has attracted increased attention in the automotive industry recently. In this study, a professional finite element program for analysis and design of tube hydroforming processes, has been developed, called HydroFORM-3D, which is based on a rigid-plastic model. With the developed program HydroFORM-3D, the hydroforming process for an automobile lower arm is analyzed and designed. The manufacturing process for a lower arm consists of tube bending, preforming, and final hydroforming. To accomplish successful hydroforming process design, thorough investigation on proper combination of process parameters such as internal hydraulic pressure, axial feeding, and tool geometry is required. This paper describes the influences of forming conditions on the hydroforming of a lower arm by using simulation to predict strain and tube shape during bending, preforming, and final hydroforming processes.