10 research outputs found

    Elastohydrodynamics of turning a page

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    ํ•™์œ„๋…ผ๋ฌธ(์„์‚ฌ)--์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› :๊ณต๊ณผ๋Œ€ํ•™ ๊ธฐ๊ณ„ํ•ญ๊ณต๊ณตํ•™๋ถ€,2019. 8. ๊น€ํ˜ธ์˜.ํŽ˜์ด์ง€๋ฅผ ๋„˜๊ธฐ๋Š” ์ผ์ƒ์ ์ธ ํ™œ๋™์€ ๋…์„œ๋ฟ๋งŒ ์•„๋‹ˆ๋ผ ์ข…์ด์™€ ์ง๋ฌผ์„ ์ด์šฉํ•˜๋Š” ์ œํ’ˆ ์ƒ์‚ฐ ๊ณผ์ •์—์„œ๋„ ์ฐพ์•„๋ณผ ์ˆ˜ ์žˆ๋‹ค. ์šฐ๋ฆฌ๋Š” ์ฑ…์˜ ํŽ˜์ด์ง€๋ฅผ ๋„˜๊ธฐ๋Š” ๊ณผ์ •์„ ์ดํ•ดํ•˜๊ธฐ ์œ„ํ•ด ์ฑ…์˜ ์ข…์ž‡์žฅ์„ ์–‡์€ ํƒ„์„ฑ ์‹œํŠธ๋กœ ๊ฐ„์ฃผํ•˜๊ณ , ์‹œํŠธ๊ฐ€ ๋ณ€ํ˜•๋˜์–ด ์žˆ๋‹ค๊ฐ€ ํ•œ์ชฝ ๋์ด ๋†“์—ฌ์ ธ ์šด๋™์„ ํ•˜๊ฒŒ ๋˜๋Š” ํ˜„์ƒ์„ ์ •์ -๋™์  ๋‹จ๊ณ„๋กœ ๋‚˜๋ˆ„์–ด ๋ถ„์„ํ•˜์˜€๋‹ค. ์šฐ์„ , ์ •์  ๋‹จ๊ณ„์—์„œ๋Š” ์–‘์ชฝ ๊ฒฝ๊ณ„๊ฐ€ ์ง€๋ฉด์— ๋Œ€ํ•ด ํŠน์ • ๊ฐ๋„๋ฅผ ๊ฐ€์ง€๊ณ  ํŠน์ • ๊ฐ„๊ฒฉ์œผ๋กœ clamped๋œ ํƒ„์„ฑ ์‹œํŠธ์˜ ๋ชจ์–‘์„ Euler Elastica๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ด๋ก ์ ์œผ๋กœ ์˜ˆ์ธกํ•˜์˜€๋‹ค. ๋™์  ๋‹จ๊ณ„์—์„œ๋Š” ํ•œ์ชฝ ๊ฒฝ๊ณ„์˜ clamped๋ฅผ ํ’€์–ด์ฃผ์—ˆ์„ ๋•Œ ๋ฒ„ํด๋ง ๋˜์–ด์žˆ๋˜ ์‹œํŠธ๊ฐ€ ๋ณ€ํ˜•์„ ํšŒ๋ณตํ•˜๋ฉด์„œ ํ•ญ๋ ฅ, ์ค‘๋ ฅ์„ ๋ฐ›์•„ ์ขŒ์šฐ๋กœ ๋ฐ˜๋ณต ์šด๋™์„ ํ•˜๊ฒŒ ๋œ๋‹ค. ๊ทธ๋ฆฌ๊ณ  ๋ฐ˜๋ณต ์šด๋™์˜ ์ค‘์‹ฌ์ถ•์ด ์™ผ์ชฝ์ด๋‚˜ ์˜ค๋ฅธ์ชฝ์œผ๋กœ ์น˜์šฐ์ณ์ง€๋ฉด์„œ ์‹œํŠธ๊ฐ€ ์–ด๋Š ํ•œ์ชฝ์œผ๋กœ ๋„˜์–ด๊ฐ€๊ฒŒ ๋˜๋Š” ๋‘ ๊ฐ€์ง€ flipping ํ˜„์ƒ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ๋‹ค. ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š”, ์ •์  ๋‹จ๊ณ„์—์„œ fixed end์— ์ž‘์šฉํ•˜๋Š” ๋ชจ๋ฉ˜ํŠธ๋“ค์˜ ํฌ๊ธฐ๋ฅผ ๋น„๊ตํ•˜์—ฌ ์‹œํŠธ๊ฐ€ ์ตœ์ข…์ ์œผ๋กœ ๋„˜์–ด๊ฐ€๋Š” ๋ฐฉํ–ฅ์„ ์˜ˆ์ธกํ•  ์ˆ˜ ์žˆ๋Š” ๋ฐฉ๋ฒ•์„ ์ œ์‹œํ•˜์˜€๋‹ค. ๋‹ค์–‘ํ•œ ์ง€์˜ค๋ฉ”ํŠธ๋ฆฌ์™€ ์žฌ๋ฃŒ์˜ ํƒ„์„ฑ ์‹œํŠธ๋ฅผ ์ด์šฉํ•œ ์‹คํ—˜์œผ๋กœ ์šฐ๋ฆฌ์˜ ์˜ˆ์ธก์„ ํ™•์ธํ•˜์˜€๋‹ค. ์ถ”๊ฐ€๋กœ, ์‹ค์ œ ์ฑ…์„ ๋„˜๊ธฐ๋Š” ํ™œ๋™์—์„œ๋„ flipping ์–‘์ƒ์„ ๊ฒฐ์ •ํ•˜๋Š” ๊ฒฝ๊ณ„๊ฐ€ ์กด์žฌํ•จ์„ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ์ ์šฉํ•˜์—ฌ ์„ค๋ช…ํ•จ์œผ๋กœ์จ ์ข…์ด๋ฅผ ์ง‘์–ด ํŽ˜์ด์ง€๋ฅผ ๋„˜๊ธฐ๋Š” ์ตœ์ ์˜ ๊ฒฝ๋กœ๋ฅผ ์„ค๋ช…ํ•˜์˜€๋‹ค. ๋ณธ ์—ฐ๊ตฌ ๊ฒฐ๊ณผ๋Š” ๋…์ž์™€ ํšจ์œจ์ ์ธ ์ œ์กฐ ๋กœ๋ด‡์„ ์œ„ํ•ด ํŽ˜์ด์ง€๋ฅผ ๋„˜๊ธฐ๋Š” ์†๊ฐ€๋ฝ์˜ ์ตœ๋‹จ ๊ฒฝ๋กœ๋ฅผ ํŒŒ์•…ํ•˜๋Š”๋ฐ ๊ธฐ์—ฌํ•  ์ˆ˜ ์žˆ๋‹ค.A mundane activity of turning a page arises not only in reading, but also in product production with paper or textile. Here we analyze the shape and stability of a thin paper, bound to a book in one side and compressed from the other side, to gain mechanical understanding of the page turning. Page turning can be divided into a static phase and a dynamic phase. We start with describing the static shape of a sheet that is buckled between the bound end and gripping fingers, using the Euler Elastica. After releasing one end clamped with fingers, the buckled sheet restores the deformation receiving drag and gravity, and it makes vibrating motion to the left and right. Then, the central axis of the vibrating motion is biased to the left or right, and two flipping phenomena are observed, in which the sheet moves to one side. In this study, we proposed a method of predicting the final direction of the sheet after external load is removed by comparing the magnitudes of the moments acting on the fixed end in the static phase. We have confirmed our predictions by experiments using elastic sheets of various geometries and materials. By explaining the existence of a boundary that determines the flipping way of a page, we describe the shortest path for turning a page. This study can contribute to suggest an optimal path for both readers and efficient manufacturing robots.๊ตญ๋ฌธ์ดˆ๋ก i ๋ชฉ์ฐจ iii List of Figures v List of Tables vii ๊ธฐํ˜ธ์„ค๋ช… viii 1. ์„œ๋ก  1 2. ์‹คํ—˜์žฅ์น˜ ๋ฐ ์‹คํ—˜๋ฐฉ๋ฒ• 3 2.1 ์‹คํ—˜์žฅ์น˜ 3 2.2 ์‹คํ—˜๋ฐฉ๋ฒ• 5 3. ์ด๋ก ์  ๋ชจ๋ธ๋ง 10 3.1 Statics 10 3.2 Dynamics 14 4. ๊ฐ„์†Œํ™” ์ด๋ก ์  ๋ชจ๋ธ๋ง 16 4.1 Flipping moment vs. Restoring moment 16 4.2 ํ†ตํ•ฉ ๋ชจ๋ธ ๋ฐ ๊ฒ€์ฆ 20 5. ์‹ค์ƒํ™œ ์ ์šฉ(practical implications) 24 6. ๊ฒฐ๋ก  26 ๋ถ€๋ก A.1 Measuring material properties 27 ์ฐธ๊ณ ๋ฌธํ—Œ 30 Abstract (์˜๋ฌธ์ดˆ๋ก) 33Maste

    ํฐ ์ง„ํญ ์ง„๋™์˜ ์œ ์ฒด-๊ตฌ์กฐ๋ฌผ ์ƒํ˜ธ ์ž‘์šฉ๊ณผ ์ˆ˜๋™ ์ œ์–ด

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    ํ•™์œ„๋…ผ๋ฌธ (๋ฐ•์‚ฌ)-- ์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› ๊ณต๊ณผ๋Œ€ํ•™ ๊ธฐ๊ณ„ํ•ญ๊ณต๊ณตํ•™๋ถ€, 2017. 8. ์ตœํ•ด์ฒœ.๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ๊ณ ์ฒด์™€ ์œ ์ฒด์˜ ์ €๋ฐ€๋„ ๋น„(ฯ)์—์„œ ์œ ์ฒด-๊ตฌ์กฐ๋ฌผ ์ƒํ˜ธ์ž‘์šฉ์„ ์œ„ํ•œ ์•ฝํ•œ ๊ฒฐํ•ฉ๋ฒ•์„ ์ œ์‹œํ•˜๊ณ  ๋‹ค์Œ์˜ ๊ตฌ์กฐ๋ฌผ ์ฃผ์œ„ ์œ ๋™์— ๋Œ€ํ•œ ๋น„์ •์ƒ 3์ฐจ์› ์‹œ๋ฎฌ๋ ˆ์ด์…˜์„ ์ˆ˜ํ–‰ํ•œ๋‹ค. ๊ตฌ์กฐ๋ฌผ์€ ํƒ„์„ฑ ๊ฐ•์ฒด ์›ํ˜• ์‹ค๋ฆฐ๋”์™€ ๋‚˜์„ ํ˜• ๋น„ํ‹€๋ฆผ ํƒ€์›(HTE) ์‹ค๋ฆฐ๋”, ์ง์„ ํ˜• ์ „๋‹จ๋ฅ˜์—์„œ์˜ ์œ ์—ฐ ์›ํ˜• ๋ฐ HTE ์‹ค๋ฆฐ๋”, ๊ทธ๋ฆฌ๊ณ  ํƒ€์ฝ”๋งˆ ๋ธŒ๋ฆฟ์ง€์ด๋‹ค. ์•ฝํ•œ ๊ฒฐํ•ฉ๋ฒ•์—์„œ ์ •ํ™•ํ•˜๊ณ  ์•ˆ์ •์ ์ธ ํ•ด๋ฅผ ์–ป๊ธฐ ์œ„ํ•ด ๊ฐ ์‹œ๊ฐ„ ๋‹จ๊ณ„์—์„œ ์œ ์ฒด-๊ตฌ์กฐ๋ฌผ ๊ฒฝ๊ณ„์˜ ์ž„์‹œ ์†๋„์™€ ์œ„์น˜๋ฅผ ์˜ˆ์ธกํ•˜๋Š” ์˜ˆ์ธก๊ธฐ(๋ช…์‹œ์  2๋‹จ๊ณ„ ๋ฐฉ๋ฒ• ๋ฐ ์ž„์‹œ์  ์˜ค์ผ๋Ÿฌ ๋ฐฉ๋ฒ•)๋ฅผ ๋„์ž…ํ•œ๋‹ค. ๋น„์••์ถ•์„ฑ ๋‚˜๋น„์—-์Šคํ† ํฌ์Šค ๋ฐฉ์ •์‹์€ ์œ ์ฒด-๊ตฌ์กฐ๋ฌผ ๊ฒฝ๊ณ„๋ฉด์—์„œ์˜ ์ž„์‹œ ์†๋„ ๋ฐ ์œ„์น˜์™€ ์—‡๊ฐˆ๋ฆผ ๊ฒฉ์ž์—์„œ ๊ฐ€์ƒ ๊ฒฝ๊ณ„ ๋ฐฉ๋ฒ• ๋ฐ ์œ ํ•œ ์ฒด์  ๋ฐฉ๋ฒ•์„ ์‚ฌ์šฉํ•˜์—ฌ ์˜ค์ผ๋Ÿฌ ์ขŒํ‘œ๋กœ ํ’€๋ฆฐ๋‹ค. ์œ ์ฒด ๋ฐ ๊ตฌ์กฐ๋ฌผ์— ๋Œ€ํ•œ ๊ฐ ์ง€๋ฐฐ๋ฐฉ์ •์‹์€ 2์ฐจ ์‹œ๊ฐ„ ์ ๋ถ„๊ธฐ๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ž„์‹œ์ ์œผ๋กœ ํ•ด๊ฒฐ๋œ๋‹ค. ์ „๋ฐ˜์ ์ธ 2์ฐจ ์‹œ๊ฐ„ ์ •ํ™•๋„๋Š” ๋‚ฎ์€ ์ •ํ™•๋„์˜ ์˜ˆ์ธก๊ธฐ๋ฅผ ์‚ฌ์šฉํ•˜๋”๋ผ๋„ ๋ณด์กด๋œ๋‹ค. ๋˜ํ•œ ์„ ํ˜• ์•ˆ์ •์„ฑ ๋ถ„์„์€ ๊ฐ€์žฅ ๋‚ฎ์€ ๋ฐ€๋„ ๋น„๋กœ ์•ˆ์ •์ ์ธ ํ•ด๋ฅผ ์ œ๊ณตํ•˜๋Š” ์ตœ์ ์˜ ๋ช…์‹œ์  2๋‹จ๊ณ„ ๋ฐฉ๋ฒ•์„ ์ฐพ๊ธฐ ์œ„ํ•œ ์ด์ƒ์ ์ธ ๊ฒฝ์šฐ์— ๋Œ€ํ•ด ์ˆ˜ํ–‰๋˜์—ˆ๋‹ค. ํ˜„์žฌ์˜ ์•ฝํ•œ ๊ฒฐํ•ฉ๋ฒ•์œผ๋กœ 3๊ฐ€์ง€ ๋‹ค๋ฅธ ์œ ์ฒด-๊ตฌ์กฐ๋ฌผ ์ƒํ˜ธ ์ž‘์šฉ ๋ฌธ์ œ์— ๋Œ€ํ•ด ์‹œ๋ฎฌ๋ ˆ์ด์…˜์„ ํ•˜์˜€๋‹ค. ํƒ„์„ฑ ๊ฐ•์ฒด ์›ํ˜• ์‹ค๋ฆฐ๋”, ๊ณ ์ •๋œ ์›ํ˜• ์‹ค๋ฆฐ๋”์˜ ๋ฒ ์ด์Šค์— ๋ถ€์ฐฉ๋œ ํƒ„์„ฑ ๋น”, ๊ทธ๋ฆฌ๊ณ  ์œ ์—ฐ ํ”Œ๋ ˆ์ดํŠธ(ฯ = 0.678) ์ฃผ์œ„ ์œ ๋™์ด๋‹ค. ์•ˆ์ •๋œ ํ•ด๋ฅผ ์ œ๊ณตํ•˜๋Š” ์ตœ์ € ๋ฐ€๋„ ๋น„๋Š” ์ฒ˜์Œ ๋‘ ๊ฐ€์ง€ ๋ฌธ์ œ์— ๋Œ€ํ•ด ํƒ์ƒ‰๋˜๋ฉฐ 1๋ณด๋‹ค ํ›จ์”ฌ ๋‚ฎ๋‹ค(๊ฐ๊ฐ ฯmin = 0.21๊ณผ 0.31). ์‹œ๋ฎฌ๋ ˆ์ด์…˜ ๊ฒฐ๊ณผ๋Š” ์ œ์•ˆ๋œ ๊ฐ•ํ•œ ๊ฒฐํ•ฉ๋ฒ•๊ณผ ์ด์ „์˜ ์ˆ˜์น˜ ๋ฐ ์‹คํ—˜ ์—ฐ๊ตฌ ๊ฒฐ๊ณผ์™€ ์ž˜ ์ผ์น˜ํ•˜๋ฉฐ ํ˜„์žฌ์˜ ์•ฝํ•œ ๊ฒฐํ•ฉ๋ฒ•์˜ ํšจ์œจ์„ฑ๊ณผ ์ •ํ™•๋„๋ฅผ ๋‚˜ํƒ€๋‚ธ๋‹ค. ํƒ„์„ฑ ๊ฐ•์ฒด ์›ํ˜• ์‹ค๋ฆฐ๋” ์ฃผ์œ„ ์œ ๋™ ์‹œ๋ฎฌ๋ ˆ์ด์…˜์€ 2์˜ ์งˆ๋Ÿ‰๋น„, 6์˜ ํ™˜์‚ฐ ์†๋„, 0์˜ ๊ฐ์‡ ๋น„ ๋ฐ 4200์˜ ๋ ˆ์ด๋†€์ฆˆ ์ˆ˜๋ฅผ ๊ฐ–๋Š”๋‹ค. 1.19D์˜ ํšก ๋ฐฉํ–ฅ ๋ณ€์œ„ ์ง„ํญ์„ ๊ฐ–๋Š” ์ง„๋™์€ ์›ํ˜• ์‹ค๋ฆฐ๋”์˜ ํšก ๋ฐฉํ–ฅ ๋‘ ๋ฉด์—์„œ์˜ ํฐ ์••๋ ฅ์ฐจ์— ์˜ํ•ด ์œ ๋„๋œ๋‹ค. ์—ฌ๊ธฐ์„œ D๋Š” ์›ํ˜• ์‹ค๋ฆฐ๋”์˜ ์ง๊ฒฝ ๋˜๋Š” HTE ์‹ค๋ฆฐ๋”์˜ ์žฅ์ถ•๊ณผ ๋‹จ์ถ•์˜ ๊ธธ์ด ๊ณฑ์˜ ์ œ๊ณฑ๊ทผ์ด๋‹ค. ์ „๋ฐฉ ๋ฐ ํ›„๋ฐฉ์—์„œ ๋ฐœ์ƒ๋œ ์ „๋‹จ์ธต์—์„œ ์ƒ์„ฑ๋œ ์‹œ์ž‘ ์™€๋ฅ˜์— ์˜ํ•ด ์œ ๋„๋œ ์œ ๋™์ด ์›ํ˜• ์‹ค๋ฆฐ๋”์˜ ํšก๋ฐฉํ–ฅ ๋ฉด์— ์ถฉ๋Œํ•จ์œผ๋กœ ์ธํ•ด ์‹ค๋ฆฐ๋”์˜ ํšก ๋ฐฉํ–ฅ ์ด๋™๊ณผ ๋ฐ˜๋Œ€๋˜๋Š” ๋ฉด์—์„œ ์••๋ ฅ์ด ๋†’๊ณ  ๋‹ค๋ฅธ ๋ฉด์€ ์œ ๋™ ๊ฐ€์†๊ณผ ๋ฐ•๋ฆฌ ์ง€์—ฐ์œผ๋กœ ์ธํ•ด ์••๋ ฅ์ด ๋‚ฎ๋‹ค. ํ•œํŽธ, ํฐ ์ง„ํญ ์ง„๋™์„ ์–ต์ œํ•˜๊ธฐ ์œ„ํ•ด ํƒ„์„ฑ ๊ฐ•์ฒด HTE ์‹ค๋ฆฐ๋”์˜ ํŒŒ์žฅ(ฮปH) ๋ฐ ์ข…ํšก๋น„(ARH)์— ๋Œ€ํ•œ ๋งค๊ฐœ ๋ณ€์ˆ˜ ์—ฐ๊ตฌ๊ฐ€ ์ˆ˜ํ–‰๋œ๋‹ค. ARH = 2.6 ๋ฐ ฮปH = 10D์„ ๊ฐ€์ง€๋Š” ํƒ„์„ฑ ๊ฐ•์ฒด HTE ์‹ค๋ฆฐ๋”์˜ ๊ฒฝ์šฐ ์œ ๋™์— ์˜ํ•œ ์ง„๋™์ด ์™„์ „ํžˆ ์–ต์ œ๋˜๊ณ  ํ‰๊ท  ํ•ญ๋ ฅ ๊ณ„์ˆ˜๋Š” ํƒ„์„ฑ ๊ฐ•์ฒด ์›ํ˜• ์‹ค๋ฆฐ๋”์— ๋น„ํ•ด ํ˜„์ €ํžˆ ๊ฐ์†Œํ•˜์ง€๋งŒ ๊ณ ์ • ์›ํ˜• ์‹ค๋ฆฐ๋” ๋ณด๋‹ค๋Š” ์•ฝ๊ฐ„ ๋” ํฌ๋‹ค. ์œ ์—ฐํ•œ ์›ํ˜• ์‹ค๋ฆฐ๋” ์ฃผ์œ„ ์œ ๋™ ์‹œ๋ฎฌ๋ ˆ์ด์…˜์€ 7.64์˜ ์งˆ๋Ÿ‰๋น„, 4.55์˜ ์ธ์žฅ ๊ณ„์ˆ˜, 9.09์˜ ๊ตฝํž˜ ๊ณ„์ˆ˜, 3.67์˜ ์ตœ์†Œ ์†๋„์— ๋Œ€ํ•œ ์ตœ๋Œ€ ์†๋„์˜ ๋น„, 200์˜ ์ง๊ฒฝ์— ๋Œ€ํ•œ ๊ธธ์ด์˜ ๋น„, ์„ ํ˜• ์ „๋‹จ๋ฅ˜ ์œ ์ž…์—์„œ์˜ ์ตœ๋Œ€ ์†๋„์— ๊ธฐ๋ฐ˜ํ•œ ๋ ˆ์ด๋†€์ฆˆ ์ˆ˜ 330์„ ๊ฐ–๋Š”๋‹ค. ๋ฝ์ธ ํ˜„์ƒ์€ ๊ณ ์† ์˜์—ญ์—์„œ 0.148, 0.162 ๋ฐ 0.174์˜ ์„ธ ๊ฐ€์ง€ ์ฃผํŒŒ์ˆ˜์— ๋Œ€ํ•ด ๋ฐœ์ƒํ•˜๋ฉฐ, ์ด๋Š” ๋‹ค์ค‘ ๋ชจ๋“œ ์‘๋‹ต์„ ์œ ๋„ํ•˜๊ณ  ๊ณ ์† ์˜์—ญ์—์„œ ์ €์† ์˜์—ญ์œผ๋กœ ์ „ํŒŒํ•˜๋Š” ์ง„ํ–‰ํŒŒ๋ฅผ ์œ ๋„ํ•œ๋‹ค. ํšก ๋ฐฉํ–ฅ ๋ณ€์œ„ ์ง„ํญ์€ 1D๋ณด๋‹ค ์ž‘์œผ๋ฉฐ ์ •์ƒํŒŒ์™€ ์ง„ํ–‰ํŒŒ๊ฐ€ ๊ด€์ฐฐ๋œ๋‹ค. ํ›„๋ฅ˜์—์„œ๋Š” ์ฃผ๊ธฐ ๋‹น 2๊ฐœ์˜ ๋‹จ์ผ ์™€๋ฅ˜๊ฐ€ ์ƒ์„ฑ๋œ๋‹ค(2S ๋ชจ๋“œ). ํ•œํŽธ, ์œ ์—ฐํ•œ ์›ํ˜• ์‹ค๋ฆฐ๋” ์ฃผ์œ„ ์œ ๋™ ์‹œ๋ฎฌ๋ ˆ์ด์…˜์€ 2.55์˜ ์งˆ๋Ÿ‰๋น„, 5์˜ ์ธ์žฅ ๊ณ„์ˆ˜, 10์˜ ๊ตฝํž˜ ๊ณ„์ˆ˜, 9์˜ ์ตœ์†Œ ์†๋„์— ๋Œ€ํ•œ ์ตœ๋Œ€ ์†๋„์˜ ๋น„, ์„ ํ˜• ์ „๋‹จ๋ฅ˜์—์„œ์˜ ์ตœ๋Œ€ ์†๋„์— ๊ธฐ๋ฐ˜ํ•œ ๋ ˆ์ด๋†€์ฆˆ ์ˆ˜ 4000์„ ๊ฐ–๋Š”๋‹ค. ์œ ์—ฐํ•œ ์›ํ˜• ์‹ค๋ฆฐ๋”๋Š” ๊ธธ์ด์˜ 2๋ฐฐ ํŒŒ์žฅ์œผ๋กœ ์ง„๋™ํ•œ๋‹ค(mode 1). ํšก๋ฐฉํ–ฅ ๋ณ€์œ„ ์ง„ํญ์€ 2D๋ณด๋‹ค ํฌ๊ณ  ์œ ๋™ ๋ฐฉํ–ฅ ๋ณ€์œ„๋Š” ์œ ์—ฐํ•œ ์›ํ˜•์‹ค๋ฆฐ๋” ์ค‘๊ฐ„ ๋ถ€๊ทผ์—์„œ ์‹ฌํ•˜๊ฒŒ ๋ณ€๋™ํ•œ๋‹ค. ์ „๋‹จ์ธต์œผ๋กœ๋ถ€ํ„ฐ ๊ฐ•ํ•œ ์‹œ์ž‘ ์™€๋ฅ˜๊ฐ€ ๋ฐœ์ƒํ•˜๊ณ  ์‹ค๋ฆฐ๋”์˜ ์ด๋™ ๋ฐฉํ–ฅ์˜ ๋ฐ˜๋Œ€์ชฝ ๊ทผ์ฒ˜์— ์œ„์น˜ํ•œ๋‹ค. ๋‹ค์ค‘ ๋ชจ๋“œ ๋ฐ ๋‹จ์ผ ๋ชจ๋“œ ์‘๋‹ต์˜ ๊ฒฝ์šฐ ๋ชจ๋‘, ARH = 2.6 ๋ฐ ฮปH = 10D์ธ ์œ ์—ฐํ•œ HTE ์‹ค๋ฆฐ๋”๋Š” ์œ ๋™์œผ๋กœ ์ธํ•œ ์ง„๋™์„ ์™„์ „ํžˆ ์–ต์ œํ•˜๊ณ  ํ๋ฆ„ ๋ฐฉํ–ฅ์œผ๋กœ์˜ ์ฒ˜์ง์„ ๊ฐ์†Œ์‹œํ‚จ๋‹ค. ํƒ€์ฝ”๋งˆ ๋ธŒ๋ฆฟ์ง€ ์ฃผ์œ„ ์œ ๋™์€ ๊ฐ‘ํŒ ๋†’์ด๋ฅผ ๊ธฐ์ค€์œผ๋กœ ๋ ˆ์ด๋†€์ฆˆ 300์—์„œ ์‹œ๋ฎฌ๋ ˆ์ด์…˜๋œ๋‹ค. ํƒ€์ฝ”๋งˆ ๋ธŒ๋ฆฟ์ง€๊ฐ€ ๊ธธ์ด์˜ 1๋ฐฐ ํŒŒ์žฅ์œผ๋กœ ๋น„ํ‹€๋ฆผ ์ง„๋™ํ•  ๋•Œ ํƒ€์ฝ”๋งˆ ๋ธŒ๋ฆฟ์ง€ ๋’ค์˜ ์™€๋ฅ˜ ํ˜๋ฆผ์€ ์ŠคํŒฌ ๋ฐฉํ–ฅ ๋ฐ ํšก ๋ฐฉํ–ฅ์„ ๋”ฐ๋ผ ๋ฒˆ๊ฐˆ์•„ ์ƒ์„ฑ๋œ๋‹ค. ํƒ€์ฝ”๋งˆ ๋ธŒ๋ฆฟ์ง€์˜ ๋น„ํ‹€๋ฆผ ์ง„๋™์€ ์„ ๋‹จ ์†Œ์šฉ๋Œ์ด์™€ ์ƒํ˜ธ ์ž‘์šฉํ•œ๋‹ค. ๊ฐ‘ํŒ ๋‹จ๋ฉด์˜ ๋” ๋†’์€ ๋ฐ›์Œ๊ฐ์œผ๋กœ ์ธํ•ด ์„ ๋‹จ ์†Œ์šฉ๋Œ์ด๊ฐ€ ๊ฐ•ํ•ด์ง€๊ณ  ์„ ๋‹จ ์†Œ์šฉ๋Œ์ด๊ฐ€ ๊ฐ•ํ•ด์ง€๋ฉด ๋ฐํฌ์—์„œ ๋” ๋†’์€ ๋ชจ๋ฉ˜ํŠธ๊ฐ€ ๋ฐœ์ƒํ•œ๋‹ค. ๋น„ํ‹€๋ฆผ ์ง„๋™์„ ๊ฒช๊ณ  ์žˆ๋Š” ํƒ€์ฝ”๋งˆ ๋ธŒ๋ฆฟ์ง€ ํ›„๋ฅ˜์—์„œ์˜ ์™€๋ฅ˜ ๋ฐฉ์ถœ ์ฃผํŒŒ์ˆ˜๋Š” ์ •์ง€๋œ ํƒ€์ฝ”๋งˆ ๋ธŒ๋ฆฟ์ง€ ํ›„๋ฅ˜์—์„œ์˜ ์™€๋ฅ˜ ๋ฐฉ์ถœ ์ฃผํŒŒ์ˆ˜ ๋ณด๋‹ค๋Š” ํ›จ์”ฌ ๋‚ฎ์€ ๋ฐ˜๋ฉด ์ผ€์ด๋ธ”์— ์˜ํ•ด ์œ ๋„๋œ ๋น„ํ‹€๋ฆผ ๊ณ ์œ  ์ฃผํŒŒ์ˆ˜์™€๋Š” ์ž˜ ์ผ์น˜ํ•œ๋‹ค.In the present study, we present a weak coupling approach for fluid-structure interaction with low density ratio (ฯ) of solid to fluid and conduct unsteady three-dimensional simulations of flows around structures: elastically mounted rigid circular cylinder and helically twisted elliptic (HTE) cylinders in the super-upper branch, flexible circular and HTE cylinders in a linearly sheared flow, and the Tacoma Narrows Bridge. For accurate and stable solutions in a weak coupling approach, we introduce predictors, an explicit two-step method and the implicit Euler method, to obtain provisional velocity and position of fluid-structure interface at each time step, respectively. The incompressible Navier-Stokes equations, together with these provisional velocity and position at the fluid-structure interface, are solved in an Eulerian coordinate using an immersed-boundary finite-volume method on a staggered mesh. The dynamic equation of an elastic solid-body motion, together with the hydrodynamic force at the provisional position of the interface, is solved in a Lagrangian coordinate using a finite element method. Each governing equation for fluid and structure is implicitly solved using second-order time integrators. The overall second-order temporal accuracy is preserved even with the use of lower-order predictors. A linear stability analysis is also conducted for an ideal case to find the optimal explicit two-step method that provides stable solutions down to the lowest density ratio. With the present weak coupling, three different fluid-structure interaction problems were simulated: flows around an elastically mounted rigid circular cylinder, an elastic beam attached to the base of a stationary circular cylinder, and a flexible plate (ฯ = 0.678), respectively. The lowest density ratios providing stable solutions are searched for the first two problems and they are much lower than 1 (ฯmin = 0.21 and 0.31, respectively). The simulation results agree well with those from strong coupling suggested here and also from previous numerical and experimental studies, indicating the efficiency and accuracy of the present weak coupling. Flow around an elastically mounted rigid circular cylinder is simulated at the mass ratio of 2, the reduced velocity of 6, the damping ratio of 0, and the Reynolds number of 4200. Vibration with the transverse displacement amplitude of 1.19D is induced by large pressure difference between the upper and lower sides, where D is the diameter of a circular cylinder or square root of the product of the lengths of the major and minor axes of the HTE cylinder: pressure is high on the opposite side to the moving direction of the cylinder due to the impingement of flow induced by starting vortices in the shear layers evolved from the front and rear sides but low on the other side due to the flow acceleration and separation delay. To suppress large amplitude vibration, a parametric study is conducted for the wavelength (ฮปH) and apsect ratio (ARH) of an elastically mounted rigid HTE cylinder. For the elastically mounted rigid HTE cylinder with ARH = 2.6 and ฮปH = 10D, flow-induced vibration is completely suppressed, and the mean drag coefficient is significantly decreased compared to that for an elastically mounted rigid circular cylinder but slightly higher than for a stationary circular cylinder. Flow around a flexible circular cylinder is simulated at the mass ratio of 7.64, tension coefficient of 4.55, bending coefficient of 9.09, the ratio of the maximum to minimum velocity of 3.67, the ratio of length to diameter of 200, and the Reynolds number of 330 based on the maximum velocity in a linearly sheared inflow. Lock-in occurs for three frequencies of 0.148, 0.162, and 0.174 in the high velocity region, which induces multi-mode response and traveling waves propagating from the high velocity region to low velocity region. The transverse displacement amplitude is less than 1D and standing waves as well as traveling waves are observed. In the wake, two single vortices shed per cycle (2S mode). Flow around a flexible circular cylinder is simulated at the mass ratio of 2.55, tension coefficient of 9, the Reynolds number of 4000 based on the maximum velocity in a linearly sheared inflow. A flexible circular cylinder vibrates with the wavelength two times the spanwise domain size (mode 1). The transverse displacement amplitude is greater than 2D and streamwise displacement severely fluctuates near the middle of a flexible circular cylinder. Strong starting vortices are generated from the shear layers and located near the side opposite to the moving direction of the cylinder. For both cases of multi-mode and single-mode responses, the flexible HTE cylinder with ARH = 2.6 and ฮปH = 10D completely suppresses flow-induced vibration and reduces the deflection in the streamwise direction. Flow around the Tacoma Narrows Bridge is simulated at the Reynolds number of 300 based on the height of the deck. Vortex shedding behind the Tacoma Narrows Bridge is alternatively generated along the spanwise and transverse directions when the Tacoma Narrows Bridge torsionally vibrates with the wavelength of LT, where LT is the length of the Tacoma Narrows Bridge. Torsional vibration of the Tacoma Narrows Bridge interacts with leading edge vortices: higher angle of attack of the cross section of the deck induces a stronger leading edge vortex, and again stronger leading edge vortices generate higher moment on the deck. The vortex shedding frequency matches well with the torsional natural frequency induced by the cables although the matched frequency is much lower than the frequency of vortex shedding for flow around a stationary Tacoma Narrows Bridge because a leading edge vortex stays longer near the leading edge as the angle of attack of the cross section of the deck is higher.1 Introduction 1 2 A weak-coupling immersed boundary method for fluid-structure interaction with low density ratio of solid to fluid 4 2.1 Motivations and objectives 4 2.2 Numerical method 8 2.2.1 Weak coupling vs. strong coupling 8 2.2.2 Numerical method for fluid flow 9 2.2.3 Numerical method for the motions of rigid and elastic bodies 11 2.2.4 Predictors for the motion of fluid-solid interface and their numerical stability 13 2.2.5 Strong coupling algorithm 18 2.3 Numerical examples 21 2.3.1 Vortex-induced vibration of a rigid circular cylinder 21 2.3.2 Vortex-induced vibration of an elastic beam 25 2.3.3 Bending of a flexible plate 27 2.4 Summary 31 3 Vortex-induced vibrations of an elastically mounted rigid circular cylinder and flexible circular cylinder, and controls for them 45 3.1 An elastically mounted rigid cylinder in a uniform current 45 3.1.1 Motivations and objectives 45 3.1.2 Computational details 48 3.1.3 Vortex-induced vibration of an elastically mounted rigid circular cylinder at the super-upper branch 50 3.1.4 Flow over the elastically mounted rigid helically twisted elliptic cylinder 53 3.2 A flexible cylinder in a linearly sheared current 57 3.2.1 Motivations and objectives 57 3.2.2 Computational details 59 3.2.3 Multi-mode response of a flexible circular cylinder and its control 61 3.2.4 Single-mode response of a flexible circular cylinder and its control 67 3.3 Summary 69 4 Collapse of the Tacoma Narrows Bridge 106 4.1 Objectives 106 4.2 Computational details 107 4.3 Flow-induced vibration of the Tacoma Narrows Bridge 112 4.4 Summary 115 References 122Docto

    Um algoritmo com preditor monolรญtico para problemas do tipo interaรงรฃo fluido-estrutura

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    Orientador: Prof. Dr. Yuan Jin YunDissertaรงรฃo (mestrado) - Universidade Federal do Paranรก, Setor de Ciรชncias Exatas, Programa de Pรณs-Graduaรงรฃo em Matemรกtica. Defesa : Curitiba, 05/02/2020Inclui referรชncias: p. 69-72Resumo: O objetivo deste trabalho e desenvolver um novo algoritmo para a solucao de equacoes diferenciais parciais que modelam problemas do tipo Interacao Fluido-Estrutura. Apresentamos, inicialmente, como essas equacoes sao obtidas, a partir da versao das equacoes de Navier-Stokes em sua formulacao Lagrangeana-Euleriana Arbitraria, acoplada a uma estrutura hiperelastica generica. Revisamos, como motivacao para nosso metodo, alguns metodos de Elementos Finitos da literatura desenvolvidos para estes sistemas de equacoes, enfatizando sua classificacao em metodos particionados e monoliticos. Nosso metodo e entao apresentado como um meio-termo entre essas duas classes. Descrevemos duas versoes para ele, dependendo das condicoes de contorno que consideramos no preditor monolitico: condicoes de Dirichlet constantes ou dependentes do tempo. Por fim, reportamos alguns resultados numericos, de modo a comparar nosso metodo com condicoes constantes de Dirichlet com um metodo monolitico e um metodo particionado. Palavras-chave: Interacao fluido-estrutura. Formulacao Lagrangeana-Euleriana Arbitraria. Metodo de Elementos Finitos. Preditor monolitico.Abstract: In this work, we develop a new algorithm for the solution of the systems of partial differential equations that model Fluid-Structure Interaction problems. We first present how these equations are obtained, through an Arbitrary Lagrangian-Eulerian version of the Navier-Stokes equations, coupled with a generic hyperelastic structure. We then review some Finite Element methods already available to solve such system of equations, emphasizing the rough classification between monolithic and partitioned methods. This motivates the presentation of our method, which stands somewhat in between those alternatives. Two flavors of our algorithm are described, which depend on the Dirichlet conditions imposed on the monolithic predictor: one uses constant conditions and the other uses time-dependent ones. Lastly, we report numerical results that compare our method with constant Dirichlet conditions with a monolithic and a partitioned method. Keywords: Fluid-Structure Interaction. Arbitrary Lagrangian-Eulerian formulation. Finite Element Method. Monolithic predictor

    Splitting schemes and unfitted mesh methods for the coupling of an incompressible fluid with a thin-walled structure

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    International audienceTwo unfitted mesh methods for a linear incompressible fluid/thin-walled structure interaction problem are introduced and analyzed. The spatial discretization is based on different variants of Nitsche's method with cut elements. The degree of fluid-solid splitting (semi-implicit or explicit) is given by the order in which the space and time discretizations are performed.The a priori stability and error analysis shows that strong coupling is avoided without compromising stability and accuracy. Numerical experiments in a benchmark illustrate the accuracy of the different methods proposed

    modeling and optimization

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    ํ•™์œ„๋…ผ๋ฌธ(๋ฐ•์‚ฌ)--์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› :๊ณต๊ณผ๋Œ€ํ•™ ๊ธฐ๊ณ„ํ•ญ๊ณต๊ณตํ•™๋ถ€(๋ฉ€ํ‹ฐ์Šค์ผ€์ผ ๊ธฐ๊ณ„์„ค๊ณ„์ „๊ณต),2020. 2. ์ตœํ•ด์ฒœ.The aerodynamic characteristics of a hovering rhinoceros beetle are numerically and theoretically investigated. Its wing kinematics is measured using high speed cameras and used for numerical simulation of flow around a flapping rhinoceros beetle in hovering flight. The numerical results show that the aerodynamic forces generated (especially for lift) and power required by the hind wing during a quasi-periodic state are quite different from those during the first stroke. This indicates that the wing-wake interaction significantly affects the aerodynamic performance of the hind wing during the quasi-periodic state. Also, twisting of the hind wing along the wing span direction does not much contribute to total force generation as compared to that of the flat wing, and the role of elytron and body on the aerodynamic performance is quite small at least for the present hovering flight. Based on a previous model (Wang et al., J. Fluid Mech., vol. 800, 2016, pp. 688-719), we suggest an improved predictive aerodynamic model without any ad hoc model constants for a rigid and flat hind wing by considering the effect of the wing-wake interaction in hovering flight. In this model, we treat the wake as a steady or unsteady non-uniform downwash motion and obtain its magnitude by combining a quasi-steady blade element theory with an inviscid momentum theory. The lift and drag forces and aerodynamic power consumption predicted by this model are in excellent agreements with those obtained from numerical simulations. Based on the developed quasi-steady aerodynamic model, the optimal planform shapes and motions of the hind wing of the hovering beetle for minimum power consumption are investigated. First, we optimize wing motions with the measured wing planform shape for minimum aerodynamic and positive mechanical power consumptions, respectively. We also optimize wing planform shapes with the measured wing motion, as done for the optimization of the wing motion. We find that the measured wing shape is not optimal in terms of aerodynamic power consumption and the optimal wing shape and motion minimizing positive mechanical power consumption are close to the measured ones. For minimum aerodynamic power consumption, the pitching axis of the wing should be located between the 1/4-chord and the mid-chord points, together with the radius of the first moment of wing area of around 0.5. For minimum positive mechanical power consumption, the wing area should be concentrated near the wing root rather than the aerodynamically optimal wing shape, and the pitching axis is between the leading edge and the 1/4-chord point.์ •์ง€ ๋น„ํ–‰ํ•˜๋Š” ์žฅ์ˆ˜ํ’๋Ž…์ด์˜ ๊ณต๊ธฐ ์—ญํ•™์  ํŠน์„ฑ์„ ์ˆ˜์น˜์ -์ด๋ก ์ ์œผ๋กœ ์กฐ์‚ฌํ•˜์˜€๋‹ค. ๋‚ ๊ฐฏ์ง“์€ ๊ณ ์† ์นด๋ฉ”๋ผ๋ฅผ ํ†ตํ•ด ์ธก์ •๋˜์—ˆ์œผ๋ฉฐ, ์ •์ง€ ๋น„ํ–‰ํ•˜๋Š” ์žฅ์ˆ˜ํ’๋Ž…์ด ์ฃผ๋ณ€์˜ ์œ ๋™์„ ์ˆ˜์น˜ํ•ด์„ํ•˜๋Š” ๋ฐ ์‚ฌ์šฉ๋˜์—ˆ๋‹ค. ์ˆ˜์น˜ํ•ด์„ ๊ฒฐ๊ณผ๋Š” ์ค€์ฃผ๊ธฐ์  ์ƒํƒœ์ผ ๋•Œ ์†๋‚ ๊ฐœ๋กœ๋ถ€ํ„ฐ ๋ฐœ์ƒ๋˜๋Š” ํž˜(ํŠนํžˆ ์–‘๋ ฅ)๊ณผ ๊ณต๊ธฐ ์—ญํ•™์  ์š”๊ตฌ์ „๋ ฅ์ด ์ฒซ ๋ฒˆ์งธ ๋‚ ๊ฐฏ์ง“ ๋™์•ˆ์˜ ํž˜ ๋ฐ ๊ณต๊ธฐ ์—ญํ•™์  ์š”๊ตฌ์ „๋ ฅ๊ณผ ์ƒ๋‹นํžˆ ๋‹ค๋ฅด๋‹ค๋Š” ๊ฒƒ์„ ๋ณด์—ฌ์ค€๋‹ค. ์ด๋Š” ๋‚ ๊ฐœ-ํ›„๋ฅ˜ ๊ฐ„ ์ƒํ˜ธ์ž‘์šฉ์ด ์ค€์ฃผ๊ธฐ์  ์ƒํƒœ๋™์•ˆ ์†๋‚ ๊ฐœ์˜ ๊ณต๋ ฅ ํŠน์„ฑ์— ํฌ๊ฒŒ ์˜ํ–ฅ์„ ๋ฏธ์นœ๋‹ค๋Š” ๊ฒƒ์„ ๋‚˜ํƒ€๋‚ธ๋‹ค. ๋˜ํ•œ ์†๋‚ ๊ฐœ์˜ ๋‚ ๊ฐœ ๊ธธ์ด ๋ฐฉํ–ฅ์— ๋”ฐ๋ฅธ ๋น„ํ‹€๋ฆผ์€ ํŽธํ‰ํ•œ ์†๋‚ ๊ฐœ์™€ ๋น„๊ตํ•  ๋•Œ ์ „์ฒด ํž˜ ์ƒ์„ฑ์— ํฌ๊ฒŒ ๊ธฐ์—ฌํ•˜์ง€ ์•Š์œผ๋ฉฐ ๊ณต๊ธฐ ์—ญํ•™์  ์„ฑ๋Šฅ์— ๋Œ€ํ•œ ๊ฒ‰๋‚ ๊ฐœ์™€ ๋ชธํ†ต์˜ ์—ญํ• ์€ ์ ์–ด๋„ ํ˜„์žฌ์˜ ์ •์ง€ ๋น„ํ–‰์— ๋Œ€ํ•ด ๋งค์šฐ ์ž‘์Œ์„ ํ™•์ธํ•˜์˜€๋‹ค. ๊ธฐ์กด์˜ ๊ณต๋ ฅ ๋ชจ๋ธ์„ ๋ฐ”ํƒ•์œผ๋กœ ๋‚ ๊ฐœ-ํ›„๋ฅ˜ ๊ฐ„ ์ƒํ˜ธ์ž‘์šฉ์˜ ํšจ๊ณผ๋ฅผ ๊ณ ๋ คํ•˜์—ฌ ์ •์ง€ ๋น„ํ–‰ํ•˜๋Š” ํŽธํ‰ํ•œ ์†๋‚ ๊ฐœ์— ๋Œ€ํ•ด ์–ด๋– ํ•œ ๋ชจ๋ธ ์ƒ์ˆ˜๋„ ์—†๋Š” ๊ฐœ์„ ๋œ ์˜ˆ์ธก์  ๊ณต๋ ฅ ๋ชจ๋ธ์„ ์ œ์•ˆํ•˜์˜€๋‹ค. ์ด ๊ณต๋ ฅ ๋ชจ๋ธ์—์„œ ํ›„๋ฅ˜๋ฅผ ๋น„๊ท ์ผ์˜ ์ •์ƒ ๋˜๋Š” ๋น„์ •์ƒ ํ•˜๊ฐ•๊ธฐ๋ฅ˜๋กœ ๊ฐ„์ฃผํ•˜๊ณ , ์ค€์ •์ƒ ๋ธ”๋ ˆ์ด๋“œ ์š”์†Œ ์ด๋ก ๊ณผ ๋น„์ ์„ฑ ์šด๋™๋Ÿ‰ ์ด๋ก ์„ ๊ฒฐํ•ฉํ•˜์—ฌ ํ›„๋ฅ˜์˜ ์„ธ๊ธฐ๋ฅผ ๊ตฌํ•˜์˜€๋‹ค. ํ˜„์žฌ์˜ ๊ณต๋ ฅ ๋ชจ๋ธ๋กœ ์˜ˆ์ธก๋œ ์–‘, ํ•ญ๋ ฅ ๋ฐ ๊ณต๊ธฐ ์—ญํ•™์  ์š”๊ตฌ์ „๋ ฅ์€ ์ˆ˜์น˜ํ•ด์„์œผ๋กœ๋ถ€ํ„ฐ ์–ป์–ด์ง„ ๊ฒฐ๊ณผ์™€ ๋งค์šฐ ์ž˜ ์ผ์น˜ํ•˜์˜€๋‹ค. ๊ฐœ๋ฐœ๋œ ์ค€์ •์ƒ ๊ณต๋ ฅ ๋ชจ๋ธ์„ ๊ธฐ๋ฐ˜์œผ๋กœ, ์ตœ์†Œ ์ „๋ ฅ ์†Œ๋น„๋ฅผ ์œ„ํ•œ ์ •์ง€ ๋น„ํ–‰ํ•˜๋Š” ์žฅ์ˆ˜ํ’๋Ž…์ด ์†๋‚ ๊ฐœ์˜ ์ตœ์  ํ‰๋ฉด ํ˜•์ƒ ๋ฐ ์›€์ง์ž„์„ ์กฐ์‚ฌํ•˜์˜€๋‹ค. ๋จผ์ €, ์ตœ์†Œ ๊ณต๊ธฐ ์—ญํ•™์  ๋ฐ ์–‘์˜ ๊ธฐ๊ณ„์  ์ „๋ ฅ ์†Œ๋น„๋ฅผ ์œ„ํ•ด ์ธก์ •๋œ ๋‚ ๊ฐœ ํ‰๋ฉด ํ˜•์ƒ์œผ๋กœ ๋‚ ๊ฐœ ์›€์ง์ž„์„ ์ตœ์ ํ™”ํ•˜์˜€๋‹ค. ๋˜ํ•œ ๋‚ ๊ฐœ ์›€์ง์ž„์˜ ์ตœ์ ํ™”๋ฅผ ์œ„ํ•ด ์ˆ˜ํ–‰๋œ ๊ฒƒ ์ฒ˜๋Ÿผ ์ธก์ •๋œ ๋‚ ๊ฐœ ์›€์ง์ž„์œผ๋กœ ๋‚ ๊ฐœ ํ‰๋ฉด ํ˜•์ƒ์„ ์ตœ์ ํ™”ํ•˜์˜€๋‹ค. ์ตœ์ ํ™” ๊ฒฐ๊ณผ๋กœ๋ถ€ํ„ฐ ์ธก์ •๋œ ๋‚ ๊ฐœ ํ˜•์ƒ์€ ๊ณต๊ธฐ ์—ญํ•™์  ์š”๊ตฌ์ „๋ ฅ ์ธก๋ฉด์—์„œ ์ตœ์ ์ด ์•„๋‹ˆ๋ฉฐ, ์–‘์˜ ๊ธฐ๊ณ„์  ์ „๋ ฅ ์†Œ๋น„๋ฅผ ์ตœ์†Œํ™”ํ•˜๋Š” ๋‚ ๊ฐœ ๋ชจ์–‘๊ณผ ์›€์ง์ž„์ด ์ธก์ •๋œ ๊ฒƒ๋“ค์— ๊ฐ€๊น๋‹ค๋Š” ๊ฒƒ์„ ํ™•์ธํ•˜์˜€๋‹ค. ์ตœ์†Œ ๊ณต๊ธฐ ์—ญํ•™์  ์ „๋ ฅ ์†Œ๋น„๋ฅผ ์œ„ํ•ด์„œ๋Š” ๋‚ ๊ฐœ ๋ฉด์ ์˜ ์ฒซ ๋ฒˆ์งธ ๋ชจ๋ฉ˜ํŠธ์˜ ๋ฐ˜๊ฒฝ์€ ์•ฝ 0.5์ด๋ฉฐ, ๋‚ ๊ฐœ์˜ ํ”ผ์นญ ์ถ•์ด ์‹œ์œ„ ๊ธธ์ด์˜ 1/4 ์ง€์ ๊ณผ 1/2 ์ง€์  ์‚ฌ์ด์— ์žˆ์–ด์•ผํ•จ์„ ํ™•์ธํ•˜์˜€๋‹ค. ์ตœ์†Œ ์–‘์˜ ๊ธฐ๊ณ„์  ์ „๋ ฅ ์†Œ๋น„๋ฅผ ์œ„ํ•ด์„œ๋Š” ์ตœ์†Œ ๊ณต๊ธฐ ์—ญํ•™์  ์ „๋ ฅ ์†Œ๋น„๋ฅผ ์œ„ํ•œ ๋‚ ๊ฐœ๋ณด๋‹ค ๋‚ ๊ฐœ ๋ฉด์ ์ด ๋‚ ๊ฐœ ๋ฟŒ๋ฆฌ ๊ทผ์ฒ˜์— ๋ชจ์—ฌ์žˆ์–ด์•ผํ•˜๋ฉฐ, ํ”ผ์นญ ์ถ•์€ ์„ ๋‹จ๊ณผ ์‹œ์œ„ ๊ธธ์ด์˜ 1/4 ์ง€์  ์‚ฌ์ด์— ์žˆ์–ด์•ผํ•จ์„ ํ™•์ธํ•˜์˜€๋‹ค.Part I A numerical and theoretical study of the aerodynamic performance of a hovering rhinoceros beetle (Trypoxylus dichotomus) 1 1 Introduction: Why rhinoceros beetle? 2 2 Wing kinematics and morphological parameters 7 2.1. Measurement of the wing kinematics 7 2.2. Measured wing kinematic and morphological parameters 8 3 Numerical details 17 4 Simulation results 23 5 Quasi-steady aerodynamic model of a flapping wing in hover 35 5.1. Quasi-steady blade element theory 36 5.2. Estimation of induced downwash motion 43 6 Model validation and discussions 50 7 Further consideration on the induced downwash motion 62 8 Conclusions 68 Part II Optimal wing geometry and kinematics of a hovering rhinoceros beetle for minimum power consumption 71 1 Introduction 72 2 Models for a hovering flight of a rhinoceros beetle 75 2.1. Wing motion and shape 76 2.2. Aerodynamic force and power expenditure 79 3 Optimization 84 4 Results and discussion 88 4.1. Optimal wing motions for the measured wing shape 88 4.2. Optimal wing shapes for the measured wing motion 90 4.3. Numerical simulation on the optimal wing motions and shapes 92 5 Conclusion 104 References 106 Appendix 114 A A predictive model of the drag coefficient for a revolving wing at low Reynolds number 114 A.1. Introduction 114 A.2. An improved model of the drag coefficient 117 A.3. Results and discussion 122 A.4. Conclusion 123 Abstract (in Korean) 128Docto

    Platelet Activation in Artificial Heart Valves

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    A numerical framework is developed to perform multi-scale (hinge-to valve-scale) flow simulation and quantify the thrombogenic performance of prosthetic heart valves. This aim is achieved by 1) developing a parallel dynamic overset grid and combining it with the curvilinear immersed boundary (overset-CURVIB) method to reduce the computational cost; and 2) developing a framework for evaluating the thrombogenic performance of heart valves in terms of platelet activation. The dynamic overset grids are used to locally increase the grid resolution near immersed bodies, which are handled using a sharp interface immersed boundary method, undergoing large movements as well as arbitrary relative motions. The new framework extends the previous overset-CURVIB method with fixed overset grids and a sequential grid assembly to moving overset grids with an efficient parallel grid assembly. In addition, a new method for the interpolation of variables at the grid boundaries is developed which can drastically decrease the execution time and increase the parallel efficiency. This overset grid framework is integrated with a framework to quantify the platelet activation which is developed using a Eulerian frame of reference which calculates the activation over the whole computational domain (contrary to Largrangian methods which use limited number of particles). The new framework is verified and validated against experimental data, and analytical/benchmark solutions. This framework is used to compare the role of systole phase in the poor performance of bileaflet mechanical heart (BMHV) valve by using the bioprothtetic heart valve as a control. The results show that the activation in the bulk flow during the systole phase might play an essential role in poor hemodynamic performance of BMHVs. In addition, the contribution of bulk and hinge flows to the activation of platelets in BMHVs is quantified for the first time by performing simulations of the flow through a BMHV and resolving the hinge by overset grids. The total activation by the bulk flow is found to be several folds higher than that by the hinge/leakage flow. This is mainly due to the higher flow rate of the bulk flow which exposes much more platelets to shear stress than the leakage flow. For the future work, this framework is going to be applied for thrombogenic optimization of new designs of mechanical heart valves including trileaflet ones as well as patient-specific hemodynamic analysis of heart valves using fluid-structure interaction in more realistic geometries extracted from the medical images such as echocardiography
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