열에너지 저장용 암반 공동의 최적 종횡비 결정을 위한 역학적 안정성 해석

박도현(Dohyun Park),류동우(Dongwoo Ryu),최병희(Byung-Hee Choi),선우춘(Choon Sunwoo),한공창(Kong-Chang Han) 한국암반공학회 2013 터널과지하공간 Vol.23 No.2

일반적으로 열저장소의 종횡비(폭에 대한 높이의 비)가 커짐에 따라 저장된 열에너지의 성층화가 높게 유지될 수 있는 것으로 알려져 있다. 따라서 열저장소의 열적 성능을 높이기 위해서는 저장소 종횡비를 크게 설정하는 것이 유리할 것이다. 그러나 종횡비의 증가에 따라 저장소의 폭에 비해 높이가 커지고, 이는 열저장소의 구조적 안정성 측면에서 불리하게 작용할 수 있으므로 저장소의 최적 종횡비 결정시 열적 성능 분석과 더불어 역학적 안정성에 대한 정량적인 분석이 수행되어야 할 것이다. 본 연구에서는 지하 열에너지 저장을 위한 사일로 형 암반공동의 종횡비 변화에 따른 역학적 안정성을 수치해석적으로 조사하였다. 적용한 종횡비는 1-6의 범위이었고, 전단강도 감소기법에 의한 안전율을 토대로 암반공동의 역학적 안정성을 평가하였다. 종횡비별 안정성 분석 결과, 암반공동의 종횡비가 증가함에 따라 안전율이 감소하는 경향을 보였으며, 주변 암반의 측압계수가 안정성에 미치는 영향이 큰 것으로 분석되었다. 또한 동일한 암반특성 및 종횡비 조건에서 암반공동의 규모(저장 용량)가 줄어듦에 따라 안정성이 향상되는 것으로 나타나, 큰 규모의 단일 암반공동을 소규모의 다중 암반공동으로 분할함으로써 높은 종횡비의 암반공동 설계가 가능한 것을 알 수 있었다. It is generally well known that the stratification of thermal energy in heat stores can be improved by increasing the aspect ratio (the height-to-width ratio) of the stores. Accordingly, it will be desirable to apply a high aspect ratio so as to demonstrate the good thermal performance of heat stores. However, as the aspect ratio of a store increases, the height of the store become larger compared to its width, which may be unfavorable for the structural stability of the store. Therefore, to determine an optimum aspect ratio of heat stores, a quantitative mechanical stability assessment should be performed in addition to thermal performance evaluations. In the present study, we numerically investigated the mechanical stability of silo-shaped rock caverns for underground thermal energy storage at different aspect ratios. The applied aspect ratios ranged from 1 to 6 and the mechanical stability was examined based on factor of safety using a shear strength reduction method. The results from the present study showed that the factor of safety of rock caverns tended to decrease with the increase in aspect ratio and the stress ratio of the surrounding rock mass was influential to the stability of the caverns. In addition, the numerical results demonstrated that under the same conditions of rock mass properties and aspect ratio, mechanical stability could be improved by the reduction in cavern size (storage volume), which indicates that one can design high-aspect-ratio rock caverns by dividing a single large cavern into multiple small caverns.

모바일 디바이스 세로형 비디오 화면비율에 관한 연구 - 프레임 속 배우 표현 방법을 중심으로 -

이태규 한국연기예술학회 2019 연기예술연구 Vol.14 No.1

모바일 시장의 활성화로 인해 이미 대중들은 영상 미디어를 스마트폰을 활용하여 접하고 있다. 영상 의 표현방식에 있어 현재까지는 영화, TV 프로그램, 동영상의 화면비율(screen aspect ratio)은 1.78:1, 1.85:1 또는 2.35:1인 가로 방향으로 긴 직사각형의 비율이 주를 이루고 있다. 그러나 모바일 미디어의 사 용행태에 있어 스마트폰을 이용하는 많은 사람들은 영상물을 보기위해 90도를 회전하여 시청하는 가로 형태와 함께 세로형태의 시청을 하고 있다. 이는 모바일 미디어 사용행태에 있어, 기존 가로 콘텐츠를 우선적으로 소비했던 ‘가로 먼저(Horizontal First)’에서 ‘세로로만(Vertical Only)’의 소비행태로 변화하게 되었고, 스마트폰을 중심으로 한 모바일 디 바이스의 활성화로 인해 9:16 또는 9:18의 종횡비를 가진 세로형 콘텐츠의 제작이 활발히 이루어지고 있 다. 이를 바탕으로 다양한 화면 구성과 기존 가로형태의 영상비율과는 다른 방식의 구도적 접근이 필요 해 지기도 한다. 이에 세로형 콘텐츠의 화면비율 구성에 있어 구도에 대한 분석과 화면분할을 활용한 콘텐츠 제작에 관한 측면으로 본 논고에서는 모바일 디바이스 중 스마트폰을 중심으로 한 세로형 콘텐츠 제작에 필요한 화면 구도, 공간적 표현(Space), 움직임(movement)의 측면으로 세로형 비디오의 효율적인 사용을 위한 제작적 측면을 살펴보고자 한다. 또한, 세로형 비디오 형식의 프레임(Frame) 속에서 표현되는 상하 개념의 화면공간(Space)을 활용한 이미지 표현방식의 측면과, 피사체(인물)의 표현에 있어 가로형 비디오 보다 상대적으로 배우의 비중이 많이 차지하게 되는 프레임의 구조에서 배우의 연기적 표현 방법에 있어 살펴보고자 한다. As a mobile device market is established and revitalized, a lot of people watch video contents using that especially smartphone. From the beginning of the first film to now, screen aspect ratio is settled in Horizon first. For instance, films and TV programs have 1.78: 1, 1.85: 1, or 2.35: 1 screen aspect ratio. A meaning of today’s video is related with people. People make the best use of video as a record in the beginning era. However, today people use video as an art, entertainment, even if a way to express one’s life. Rate of smartphone supply rate is almost 90% in Korea. It means mass of people use smartphone, and they also enjoy watching video contents through using various platform. Lots of people using smartphone do not rotate 90 degrees to view the horizontal video. They hold their device in vertical form like using cellphone calling. It can be represented that consumer prefer vertical only first but horizontal first. Due to the use of vertical first spread, vertical screen aspect ratio is also expanded rapidly. Naturally, advent of 9:16 or 9:18 vertical screen aspect ratio video contents are produced. In this respect, actors and producers need to study of vertical film focused on a aspect fo video image framing, camera and acting movement, and express way to space. In this paper, I discuss a vertical screen aspect ratio not only as a producer’s point of view but also a actor’s point of view when making video contents. Moreover, I discuss also an express way to show image space more efficiently using top and bottom shape frame. It is not familiar with people who habituated to horizontal screen aspect ratio, but it can be expressed fresh, exotic and more creative ways. In addition, in this paper, I also discuss what is the more efficient way to show actor’s acting in a vertical screen aspect ratio. Actors are focused on more deeply and intensively compare to horizontal screeb saoect ratio. Their acting is restricted by narrow left and right width. Therefore, I treat what a preparation of acting on vertical screen aspect ratio.

열교환기 내부 유로 종횡비 변화에 따른 국소 열/물질전달 특성 고찰

장인혁,황상동,조형희 대한설비공학회 2005 설비공학 논문집 Vol.17 No.6

The present study investigates the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger. The effects of duct aspect ratio and flow velocity on the heat/mass transfer are investigated. Local heat/mass transfer coefficients on the corrugated duct sidewall are determined using a naphthalene sublimation technique. The aspect ratios of the wavy duct are 7.3, 4.7 and 1.8 with the corrugation angle of 145 . The Reynolds numbers, based on the duct hydraulic diameter, vary from 300 to 3,000. The results show that at the low Re(Re 1000) the secondary vortices called Taylor-Gortler vortices perpendicular to the main flow direction are generated due to effect of duct curvature. By these secondary vortices, non-uniform heat/mass transfer coefficients distributions appear. As the aspect ratio decreases, the number of cells formed by secondary vortices are reduced and secondary vortices and corner vortices mix due to decreased aspect ratio at Re 1000. At Re>1000, the effects of corner vortices become stronger. The average Sh for the aspect ratio of 7.3 and 4.7 are almost same. But at the small aspect ratio of 1.8, the average Sh decreases due to decreased aspect ratio. More pumping power (pressure loss) is required for the larger aspect ratio due to the higher flow instability.

고종횡비를 갖는 용액기반 원통형 마이크로렌즈 제조

전경준,이진영,박종운,Jeon, Kyungjun,Lee, Jinyoung,Park, Jongwoon 한국반도체디스플레이기술학회 2021 반도체디스플레이기술학회지 Vol.20 No.1

A cylindrical microlens (CML) has been widely used as an optical element for organic light-emitting diodes (OLEDs), light diffusers, image sensors, 3D imaging, etc. To fabricate high-performance optoelectronic devices, the CML with high aspect ratio is demanded. In this work, we report on facile solution-based processes (i.e., slot-die and needle coatings) to fabricate the CML using poly(methyl methacrylate) (PMMA). It is found that compared with needle coating, slot-die coating provides the CML with lower aspect ratio due to the wide spread of solution along the hydrophilic head lip. Although needle coating provides the CML with high aspect ratio, it requires a high precision needle array module. To demonstrate that the aspect ratio of CML can be enhanced using slot-die coating, we have varied the molecular weight of PMMA. We can achieve the CML with higher aspect ratio using PMMA with lower molecular weight at a fixed viscosity because of the higher concentration of PMMA solute in the solution. We have also shown that the aspect ratio of CML can be further boosted by coating it repeatedly. With this scheme, we have fabricated the CML with the width of 252 ㎛ and the thickness of 5.95 ㎛ (aspect ratio=0.024). To visualize its light diffusion property, we have irradiated a laser beam to the CML and observed that the laser beam spreads widely in the vertical direction of the CML.

날개의 종횡비가 날개 짓 운동의 공기역학적 특성에 미치는 영향

오현택(Hyun-Taek Oh),최항철(Hang-Cheol Choi),김광호(Kwang-Ho Kim),정진택(Jin Taek Chung) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-

The lift and drag forces produced by a wing of a given cross-sectional profile are dependent on the wing planform and the angle of attack. Aspect ratio is the ratio of the wing span to the average chord. For conventional fixed wing aircrafts, high aspect ratio wings produce a higher lift to drag ratio than low ones for flight at subsonic speeds. Therefore, high aspect ratio wings are used on aircraft intended for long endurance. However, birds and insects flap their wings to fly in the air and they can change their wing motions. Their wing motions are made up of translation and rotation. Therefore, we tested flapping motions with parameters which affect rotational motion such as the angle of attack and the wing beat frequency. The half elliptic shaped wings were designed with the variation of aspect ratio from 4 to 11. The flapping device was operated in the water to reduce the wing beat frequency according to Reynolds similarity. In this study, the aerodynamic forces, the time-averaged force coefficients and the lift to drag ratio were measured at Reynolds number 15,000 to explore the aerodynamic characteristics with the variation of aspect ratio. The maximum lift coefficient was turned up at AR=8. The mean drag coefficients were almost same values at angle of attack from 10° to 40° regardless of aspect ratio, and the mean drag coefficients above angle of attack 50° were decreased according to the increase of aspect ratio. For flapping motion the maximum mean lift to drag ratio appeared at AR=8.

Effects of cross-sectional aspect ratio of V-shaped ribs and blockage ratio on heat transfer in a channel at a low Reynolds number

안준,김무선,장성일 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.11

V-shaped ribs were investigated with the objective of enhancing heat transfer at the high-temperature side of a fin-plate type heat exchanger used in a railway vehicle compressor. The high-temperature side supplied with compressed air has a Reynolds number of approximately 4000, which is not sufficiently high to generate strong turbulence. When a 3D printer is used to fabricate a heat exchanger, the cross-sectional aspect ratio or blockage ratio of the ribs should be greater than the optimum value in order to attain a certain value of strength. In this study, a series of numerical analyses were conducted to investigate whether increasing the aspect ratio or the blockage ratio was more advantageous for achieving high heat transfer. Ribs with cross-sectional aspect ratios ranging from 0.3 to 5 were investigated. The investigated blocking ratios were 0.1 and 0.3. The results of computational fluid dynamics calculations were used to investigate the influences of flow separation–reattachment, secondary flow, and turbulence on heat transfer. The results demonstrated that the introduction of V-shaped ribs with a high blockage ratio into the channel at a low Reynolds number resulted in greater heat transfer enhancement compared with the effect of introducing ribs with a high cross-sectional aspect ratio.

토카막에서 Aspect Ratio가 n이 1인 자기유체동역학적 한계 에 미치는 영향

권오진 한국물리학회 2019 새물리 Vol.69 No.3

We have numerically investigated the dependence of the n = 1 global beta limit without wall stabilization on the aspect ratio in tokamaks. For all aspect ratios, the maximum stable values generally increase as the safety factor at the magnetic axis increases. The maximum t and maximum N increase considerably as the aspect ratio becomes tighter while the maximum p does not change much. The maximum depends on the profile of the plasma current density such that it increases with increasing internal inductance. This behavior is dominant for large aspect ratios and for low plasma currents, but becomes negligible for tight aspect ratios. As the plasma current increases, the maximum p and the maximum N decrease, while the maximum t increases. 본 연구에서는 토카막의 외관비 A가 플라즈마 전류가 일정하고 도체 벽의 안정효과를 무시하였을 때 n 이 1인 자기유체역학적 모드에 대해 안정한 의 최대값에 미치는 영향에 대하여 수치적으로 조사하였다. 모든 A에 대하여 최대 값은 일반적으로 q0 가 증가할수록 커진다. 최대 p 는 A에 따라 별로 변하지않지만, 최대 t 와 최대 N 은 A가 감소하여 구형 토카막에 가까워지면서 상당히 증가한다. 최대 값은플라즈마 전류밀도의 형태에 의존하는데, 내부 인덕턴스가 증가함에 따라 최대값도 증가한다. 이러한경향은 A가 크거나 플라즈마 전류가 작을 때 현저하게 나타나고, A가 1에 접근함에 따라 거의 사라진다. 전체 플라즈마 전류가 커지면 최대 t 는 증가하지만 최대 p 와 최대 N 은 감소한다.

A technique to avoid aspect-ratio locking in QUAD8 element for extremely large aspect-ratios

S. Rajendran 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.6

This paper investigates the aspect-ratio locking of the isoparametric 8-node quadrilateral (QUAD8) element. An important finding is that, if finite element solution is carried out with in exact arithmetic (i.e., with no truncation and round off errors), the locking tendency of the element is completely avoided even for aspect-ratios as high as 100000. The current finite element codes mostly use floating point arithmetic. Thus, they can only avoid this locking for aspect-ratios up to 100 or 1000. A novel method is proposed in the paper to avoid aspect-ratio locking in floating point computations. In this method, the offending terms of the strain-displacement matrix (i.e., B-matrix) are multiplied by suitable scaling factors to avoid ill-conditioning of stiffness matrix. Numerical examples are presented to demonstrate the efficacy of the method. The examples reveal that aspect-ratio locking is avoided even for aspect-ratios as high as 100000.

A technique to avoid aspect-ratio locking in QUAD8 element for extremely large aspect-ratios

Rajendran, S. Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.37 No.6

This paper investigates the aspect-ratio locking of the isoparametric 8-node quadrilateral (QUAD8) element. An important finding is that, if finite element solution is carried out with in exact arithmetic (i.e., with no truncation and round off errors), the locking tendency of the element is completely avoided even for aspect-ratios as high as 100000. The current finite element codes mostly use floating point arithmetic. Thus, they can only avoid this locking for aspect-ratios up to 100 or 1000. A novel method is proposed in the paper to avoid aspect-ratio locking in floating point computations. In this method, the offending terms of the strain-displacement matrix (i.e., $\mathbf{B}$-matrix) are multiplied by suitable scaling factors to avoid ill-conditioning of stiffness matrix. Numerical examples are presented to demonstrate the efficacy of the method. The examples reveal that aspect-ratio locking is avoided even for aspect-ratios as high as 100000.

Investigation of electromagnetic interference shielding effectiveness and electrical percolation of carbon nanotube polymer composites with various aspect ratios

Lee Dong-Kwan,Yoo Jongchan,Kim Hyunwoo,Park Sung-Hoon 한국탄소학회 2024 Carbon Letters Vol.34 No.1

Metals are recognized as electromagnetic interference (EMI) shielding materials owing to their high electrical conductivity. However, the need for light and flexible EMI shielding materials has emerged, owing to the heavyweight and inflexible nature of metals. Carbon nanotube (CNT)/polymer composites have been studied as promising flexible EMI shielding materials because of their lightweight nature due to the low density of CNTs and their high electrical conductivity. CNTs evenly dispersed in the polymer form an electrically conductive network, and the aspect ratio of the CNTs, which are one-dimensional nanofillers, is an important factor affecting electrical conductivity. In this study, we prepared three types of multi-walled carbon nanotubes (MWNTs) with different aspect ratios and fabricated polydimethylsiloxane (PDMS)/MWNT composites. Subsequently, the electrical conductivities and electrical percolation thresholds of the three PDMS/MWNT composites with different MWNT aspect ratios were measured to analyze the behavior of electrically conducting network formation according to the aspect ratio. Furthermore, the total EMI shielding effectiveness of each composite was determined to evaluate the effect of the MWNT aspect ratio on the EMI shielding. Reflection and absorption of electromagnetic wave were measured for the PDMS/MWNT composite with the largest aspect ratio to analyze the EMI shielding mechanism of the composite. Additionally, the effects of the MWNT content on the conductivity and EMI shielding performance were examined. The results provide valuable guidance for designing polymer MWNT composites with good electrical conductivity and EMI shielding performance under different aspect ratios of MWNTs.