• 한국항공우주학회지
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• 제36권7호
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• pp.621-627
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• 2008

풍동에서 측정된 공력자료에는 풍동벽면의 영향으로 인하여 불가항력적인 오차가 포함되어 있다. 벽면영향이 없는 공력자료를 얻기 위해서는 이러한 원하지 않는 벽면효과를 제거 하여야 한다. 유선곡률 효과는 풍동벽면의 영향으로 유선의 곡률이 자유 흐름의 것과 다르기 때문에 발생한다. 고정익 항공기에 사용되고 있는 전통적인 유선곡률 효과를 보정방법인 Glauert의 보정방법은 회전익 항공기에 적용이 적절하지 않다. 본 논문에서는 로터에 적절한 후류모델을 사용하는 Heyson의 보정방법을 사용하여 로터축 기울어짐 각과 동압을 보정하였다. Heyson 보정방법의 결과를 Glauert 보정방법의 결과와 비교하였다.

• Design & Manufacturing
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• 제12권3호
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• pp.31-35
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• 2018

In this paper, the method of improving the flatness and perpendicularity for a corner fixing bracket of the large display frame is studied through experiments. Three specimens were tested, one specimen not subjected to bending line before bending, and two specimens with a straight groove with 0.2 mm and 0.5 mm depth. Experimental results show that the flatness of bracket becomes worse with deeper depth. When there is no straight groove, the perpendicularity becomes worse. For the flatness correction, a restriking process was added. The twist of bracket was corrected by performing the restriking with a curvature larger than the twist amount in the direction opposite to the deformed direction. We also found that the perpendicularity is maintained regardless of the amount of curvature with the restriking process.

• 산업기술연구
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• 제20권A호
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• pp.169-178
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• 2000

The 4-point bending tests have been performed In order to estimate the effect of TIG-dressing on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strengths of as-welded specimens have satisfied the grade of fatigue strength prescribed in specifications of korea, AASHTO and JSSC. Fatigue strength at 2 million cycles of TIG-dressing specimens have increased compared with as-welded specimens. As the result of beachmark tests, fatigue cracks occurred at several points, where the radius of curvature and flank angle in the weld bead toes were low, and grew as semi-elliptical cracks, then approached to fracture. As a result of finite element analysis, stress concentration factor in weld bead toes has closely related to the flank angle and radius of curvature, and between these, the radius of curvature has more largely affected in stress concentration factor than flank angle. As a result of fracture mechanics approaches, the crack correction factor of test specimens has largely affected on stress gradient correction factor in case a/t is below 0.4. From the relations between stress intensity factor range estimated from FEM analysis and fatigue crack growth rate, fatigue life has been correctly calculated.

• 한국지구과학회지
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• 제28권7호
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• pp.825-837
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• 2007

한국 국립해양조사원의 수심자료와 미국 NIMA((National Imagery and Happing Agency)의 수치지형자료를 바탕으로 우리나라 일원에서 측정한 중력의 지형보정을 위한 위도 및 경도 간격이 각각 $3"{\times}3"$)인 지형자료를 재편집하였다. 이 자료를 바탕으로 지구 곡률을 고려한 정밀 지형보정값을 계산하기 위한 알고리즘을 개발하였고, 중력측정점으로부터 반지름 166.735 km인 원 내부에 대한 지형보정값을 계산하는 Fortran프로그램을 작성하였다. 이 알고리즘 및 프로그램을 이용하여 남한 전역에 대한 지형보정값을 계산하였다. 그 결과 최대값은 56.508 mGal 이고 평균값은 4.539 mGU이다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1987년도 한국자동제어학술회의논문집; 한국과학기술대학, 충남; 16-17 Oct. 1987
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• pp.249-254
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• 1987

This paper presents a new method for generating smooth free-form surface by local correction. B-spline surface is used for its convenience of local correction, and the direction of surface correction is fixed to the average-surface-normal direction. The surface to be corrected is approximated into a uniform cubic B-spline surface. Then, the smoothness (curvature arrows, iso-parametric lines) of the approximated surface is displayed with B-spline control points. When a control point near the region that needs correction is selected, a new point 1 mm higher than the original control point in the direction of the average surface normal is displayed. And the surface is corrected by giving the amount of control point movement interactively. Since the direction of correction is given by the program and the amount of correction is selected by the user, the method is called semiautomatic. sufficiently smooth surface can be obtained by this method. Examples are given to illustrate the method.

• Current Optics and Photonics
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• 제1권4호
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• pp.378-388
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• 2017

We present a graphical method for determining a pair of optical materials and powers to design an achromatic and athermal lens system with corrected Petzval curvature. To graphically obtain the solutions, a three-dimensional (3D) glass chart is proposed. Even if a particular material combination is unavailable, we can select an element suitable for a specific lens and continuously change the element powers of an equivalent single lens for aberrations correction. Thus, we can iteratively identify the materials and powers on a 3D glass chart. By designing a fisheye lens using this method, an achromatic and athermal system with flat Petzval curvature is obtained, over the specified waveband and temperature ranges.

• 복식문화연구
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• 제24권3호
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• pp.358-366
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• 2016

This study was performed to measure the posture correction effect of wearing ergonomic experimental clothing. Two types of experimental clothing (A, B) were developed. Both of them reinforced the muscles surrounding the spine. Experimental clothing A was developed by reflecting the shape and position of the pectoralis major muscle, abdominal muscle, and latissimus dorsi muscle. Experiment clothing B was developed by reflecting the integrated form of those muscles. Subjects were males in their 20s~30s (n=32). They were divided into two groups based on their acromion distance (AD): the turtle neck syndrome group (n=16, AD=3.81cm) and the normal group (n=16, AD=1.27cm). The correction of body posture was detected by three index values: change of the cervical curvature angle, horizontal distance between the seventh cervical vertebra and tragion, and AD. The comfort and tightness of the clothing were also measured. The results showed that both types of experimental clothing corrected body posture and that turtle neck syndrome can be prevented by wearing these types of posture correcting clothing. Two index values were decreased: cervical curvature angle ($0.31{\sim}1.32^{\circ}$) and horizontal distance between seventh cervical vertebra and tragion (0.22~0.31cm). The chest was also stretched. The comfort was rated as good for both types of experimental clothing. These results indicate that the experimental clothing had a posture correction effect without any discomfort for daily living.

• 혜화의학회지
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• 제24권2호
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• pp.1-16
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• 2016

Objectives : This study was designed to evaluate various tools including C-spine X-ray for estimating cervical curvature and identify the effect of wooden pillow on patients diagnosed with straightening of cervical curvature. Methods : This study was carried out on 51 subjects who were encountered traffic accident suffering cervical pain and diagnosed with straightening of cervical curvature by X-ray. 51 subjects were divided into wooden pillow(experimental) group and conservative therapy(control) group. Visual analogue scale, neck disability index and lateral pictures were used and compared after treatment. C-spine AP., Lat. X-ray were used on admission day to calculate cervical curvature and scoliosis by various ways. Results : 4 different measurements of cervical curvature didn't show common results. Both wooden pillow(experimental) group and conservative therapy(control) group showed significant improvement in the visual analogue scale(VAS) and neck disability index(NDI) after hospital treatment. Comparison between center line pictured by lateral view and C-spine Lat. pictured by X-ray showed significant difference in cervical curvature. Lateral deviation of cervical vertebra showed lengthened distance between mastoid process and spinous process of C7. Conclusion : As a result of this research, I found out that various tools for calculating cervical lordosis could derive different results and C-spine AP., Lat X-ray could cause artificial cervical lordosis. According to visual analogue scale(VAS) and neck disability index(NDI) wooden pillow was not effective to reduce pain & disability caused by straightening of cervical curvature. Futhermore, correction effect of straightening of cervical curvature and scoliosis by wooden pillow was weak.

• Wind and Structures
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• 제34권1호
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• pp.43-58
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• 2022

The BARC flow is studied via Direct Numerical Simulation at a relatively low turbulent Reynolds number, with focus on the geometrical representation of the leading-edge (LE) corners. The study contributes to further our understanding of the discrepancies between existing numerical and experimental BARC data. In a first part, rounded LE corners with small curvature radii are considered. Results show that a small amount of rounding does not lead to abrupt changes of the mean fields, but that the effects increase with the curvature radius. The shear layer separates from the rounded LE at a lower angle, which reduces the size of the main recirculating region over the cylinder side. In contrast, the longitudinal size of the recirculating region behind the trailing edge (TE) increases, as the TE shear layer is accelerated. The effect of the curvature radii on the turbulent kinetic energy and on its production, dissipation and transport are addressed. The present results should be contrasted with the recent work of Rocchio et al. (2020), who found via implicit Large-Eddy Simulations at larger Reynolds numbers that even a small curvature radius leads to significant changes of the mean flow. In a second part, the LE corners are fully sharp and the exact analytical solution of the Stokes problem in the neighbourhood of the corners is used to locally restore the solution accuracy degraded by the singularity. Changes in the mean flow reveal that the analytical correction leads to streamlines that better follow the corners. The flow separates from the LE with a lower angle, resulting in a slightly smaller recirculating region. The corner-correction approach is valuable in general, and is expected to help developing high-quality numerical simulations at the high Reynolds numbers typical of the experiments with reasonable meshing requirements.

• 한국정밀공학회지
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• 제21권8호
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• pp.157-163
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• 2004

Scoliosis is a complex musculoskeletal dieses requiring 3-D treatment with surgical instrumentation. To investigate the effects of correction surgery, a finite element model of personalized model of the scoliotic spine that will allow the design of clinical test providing optimal estimation of the post-operation results was developed. Three dimensional skeletal parts, such as vertebrae, clavicle and scapular were modeled as rigid bodies with keeping their morphologies. Kinematical joints and spring elements were adapted to represent the inter-vertebral disc and ligaments respectively. With this model, two types of surgery procedure, distraction procedure with Harrington device and rod derotation procedure with pedicle screw and rod system had been carried out. The obtained simulation results were comparatively corresponding to the post operational outcomes and successfully demonstrated qualitative analysis of surgical effectiveness. From this analysis, it has been found that the preparing of appropriate rod curvature and its insertion was more important than just performing the excessive derotation for scoliosis correction.