Experimental investigation of the stress-strain behavior of FRP confined concrete prisms

Hosseinpour, F.,Abbasnia, R. Techno-Press 2014 Advances in concrete construction Vol.2 No.3

One of the main applications of FRP composites is confining concrete columns. Hence identifying the cyclic and monotonic stress-strain behavior of confined concrete columns and the parameters influencing this behavior is inevitable. Two significant parameters affecting the stress-strain behavior are aspect ratio and corner radius. The present study aims to scrutinize the effects of corner radius and aspect ratio on different aspects of stress-strain behavior of FRP confined concrete specimens (rectangular, square and circular). Hence 44 FRP confined concrete specimens were tested and the results of the tests were investigated. The findings indicated that for specimens with different aspect ratios, the relationship between the ultimate stress and the corner radius is linear and the variations of the ultimate stress versus the corner radius decreases as a result of an increase in aspect ratio. It was also observed that increase of the corner radius results in increase of the compressive strength and ultimate axial strain and increase of the aspect ratio causes an increase of the ultimate axial strain but a decrease of the compressive strength. Investigation of the ultimate condition showed that the FRP hoop rupture strain is smaller in comparison with the one obtained from the tensile coupon test and also the ultimate axial strain and confined concrete strength are smaller when a prism is under monotonic loading. Other important results of this study were, an increase in the axial strain during the early stage of unloading paths and increase of the confining effect of FRP jacket with the increase and decrease of the corner radius and aspect ratio respectively, a decrease in the slope of reloading branches with cycle repetitions and the independence of this trend from the variations of the aspect ratio and corner radius and also quadric relationship between the number of each cycle and the plastic strain of the same cycle as well as the independence of this relationship from the aspect ratio and corner radius.

스파이럴 그루브 가스시일의 저ㆍ고속 성능특성 해석

이안성(An Sung Lee),양재훈(Jae-Hun Yang),최동훈(Dong-Hoon Choi) 한국트라이볼로지학회 2004 한국트라이볼로지학회 학술대회 Vol.38 No.-

Applying a general Galerkin FE lubrication analysis method to spiral groove dry gas seals, this study analyzes in detail the effects of groove design parameters, such as a number of groove, spiral angle, groove width ratio, groove radius ratio, groove depth ratio. and groove taper ratio, on the lubrication performances of an opening force, leakage, axial stiffness and damping, and angular stiffness and damping at low and high rotating speeds: 3,600 and 15.000 rpm. Results show that, for the primary design consideration performances such as the opening force and axial and angular stiffnesses, a large number of groove, spiral angle of 25°, groove width ratio of 0.46, groove radius ratio of 1.1, groove depth ratio of 1.0, and groove taper ratio of 0.0 are preferred. Where the recommended relatively low values of groove depth and taper ratios are to keep the axial and angular dampings positive or higher than 0 particularly at the high rotating speed.

반경비 및 각속도의 변화에 따른 Taylor 유동에 관한 연구

배강열(K. Y. Bae),김형범(H. B. Kim),정희택(H. T. Chung) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-

This paper represents the numerical study on Taylor flow according to the radius ratio and the angular velocity for flow between tow cylinder. The numerical model is consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8 mm, the numerical parameters are angular velocity and radius ratio. The numerical method is compared with the experimental results by Wereley, and the results are very good agreement. The critical Taylor number is calculated by theoretical and numerical analysis, and the results is showed the difference about 土10 %. As Re/Rec is increased, Taylor vortex is changed to wary vortex, and then the wave number for azimuthal direction is increased. Azimuthal wave according to the radius ratio is showed high amplitude and low frequence in case of small radius ratio, and is showed low amplitude and high frequence in case of large radius ratio.

Rotor profile design in a hypogerotor pump

권순만,Han Sung Kang,신중호 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.12

A geometric approach for the outer-rotor profile as a conjugate to the inner-rotor in a hypotrochoidal rotor pump (hypogerotor pump) is proposed by means of the principle of the instantaneous center and the homogeneous coordinate transformation. The inner-rotor profile is defined by the combination of two circular arcs. Next, the radius of curvature of the outer-rotor is derived with the relationships of the trochoid ratio and the inner-rotor tooth size ratio. Then by examining the minimum radius of curvature of the extended hypotrochoidal outer-rotor profile on the convex section, an explicit formula to avoid undercutting in the hypogerotor pump is proposed. It is found that undercut or selfintersection does not occur so long as the minimum value of the radius of curvature on the convex section is not less than zero. Design examples are presented to simulate the operation and to demonstrate the feasibility of the approaches using a computer-aided design program developed on C++ language. A geometric approach for the outer-rotor profile as a conjugate to the inner-rotor in a hypotrochoidal rotor pump (hypogerotor pump) is proposed by means of the principle of the instantaneous center and the homogeneous coordinate transformation. The inner-rotor profile is defined by the combination of two circular arcs. Next, the radius of curvature of the outer-rotor is derived with the relationships of the trochoid ratio and the inner-rotor tooth size ratio. Then by examining the minimum radius of curvature of the extended hypotrochoidal outer-rotor profile on the convex section, an explicit formula to avoid undercutting in the hypogerotor pump is proposed. It is found that undercut or selfintersection does not occur so long as the minimum value of the radius of curvature on the convex section is not less than zero. Design examples are presented to simulate the operation and to demonstrate the feasibility of the approaches using a computer-aided design program developed on C++ language.

회전하는 하나의 내부 원통에서 서로 다른 반경비가 Taylor-Couette 유동에 미치는 영향

승삼선(Samsun Seung),김상일(Sangil Kim) 대한기계학회 2018 大韓機械學會論文集B Vol.42 No.12

회전하는 하나의 내부 원통이 서로 다른 반경비를 갖는 경우에 Taylor vortex형성에 미치는 영향에 대해 수치해석을 수행하였다. 서로 다른 반경비는 내부 원통 중앙을 기준으로 동일한 폭에 깊이를 달리한 것으로 먼저 반경비가 0.83인 매끈한 내부 원통에 대한 수치계산 결과를 기존의 실험결과와 비교하여, 타당성을 검토하였다. 그런 다음, 내부 원통 중앙에 동일한 홈의 폭에 깊이를 각각 3, 6, 9, 12 mm 달리한 내부 원통에 회전수 25, 100 rpm인 경우의 수치계산 결과와 비교하였다. 그 결과, Taylor vortex는 층류인 경우 내부 원통 양끝에서 생성되기 시작하지만 홈이 있는 경우에는 홈 모서리에서도 이루어짐을 확인하였다. 홈의 깊이와 내부 원통의 회전수에 따라 쌍으로 이루어진 Taylor vortex셀의 폭이 달라졌으며, 회전수가 큰 경우에는 작은 경우보다 Taylor vortex 셀의 폭이 넓어져 개수가 감소하였다. 또한 각각의 Taylor vortex 쌍의 vortex 중심은 이웃하고 있는 vortex 쌍 사이의 vortex 중심보다 더 가깝게 자리하고 있음을 확인하였다. The Taylor-Couette flow in a rotating inner cylinder with different radius ratios has been studied numerically to show the effects of Taylor vortices formation, where different radius ratios refer to the varied depths having the same width based on the center of the inner cylinder. The numerical calculations results are compared with those of the straight inner cylinder. In order to examine the feasibility of the numerical calculations, the numerical results are compared with existing experimental results for a straight inner cylinder. Then, we compare the numerical results in the case of inner cylinders with different radius ratios. Initially, laminar Taylor vortices form at the end walls and corners of the groove. Results show that the widths of pairs of Taylor vortex cells are varied according to the depth and rotational speed of the inner cylinder. In the case involving a higher rotational speed of inner cylinder widths, and the number of pairs of Taylor vortex cells are wide and decreasing than low rotational speed of it. In addition, the vortex centers of each Taylor vortex pair are closer together than the vortex centers between neighboring vortex pairs.

A study on the bending stress of the hollow sun gear in a planetary gear train

고경은,임도형,김판영,박진수 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.1

Generally, planetary gear type traveling reduction gear is composed of multiple planetary gear stages and has a hollow sun gear in the last stage planetary gear. In designing reduction gear, it is important to evaluate accurately the bending stress at the tooth root of the sun gear as the sun gear is the weakest component in the reduction gear system. Although bending stress can be calculated easily using gear standard codes such as the American Gear Manufacturers Association (AGMA) and International Organization for Standardization (ISO)6336 for almost all gears, meticulous calculation is needed for the hollow sun gear because of its low backup ratio (rim thickness divided by tooth height) and comparatively large root fillet radius. In this study, a finite element analysis (FEA) is carried out to investigate the effect of rim thickness and root fillet radius on bending stress at the tooth root of the hollow sun gear. In standard codes, bending stress at the tooth root is calculated linearly with a constant slope for the backup ratio below 1.2. However, the effect of the rim thickness on bending stress is more complex in the planetary gear system. Bending stresses calculated by FEA with various backup ratios and root filler radii are compared with the bending stresses calculated by the standard codes.

내부회전실린더를 가진 동심환형관에서 반경비의 영향에 관한 수치해석적 연구

배강열(Kang-Youl Bae),김형범(Hyoung-Bum Kim),이상혁(Sang-Hyuk Lee) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-

This paper represents the numerical analysis on effects of radius ratio in a concentric annulus with a rotating inner cylinder. The numerical model consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8mm, the numerical parameters are angular velocity and radius ratio. Also, the whole walls of numerical model have no-slip and the working fluid is used water at 20℃. The numerical analysis is assumed the transient state to observe the flow variations by time and the 3-D cylindrical coordinate system. The calculation grid adopted a non-constant grid for dense arrangement near the wall side of cylinder, the standard k-ω high Reynolds number model to consider the effect of turbulence flow and wall, the fully implicit method for time term and the quick scheme for momentum equation. The numerical method is compared with the experimental results by Wereley and Lueptow, and the results are very good agreement. As the results, TVF isn't appeared when Re is small because of the initial flow instability is disappear by effect of the centrifugal force and viscosity. The vortex size is from 0.8 to 1.1 for TVF at various η, and the traveling distance for wavy vortex have the critical traveling distance for each case.

실린더 내부 유동에서 반경비 및 각속도의 변화에 따른 임계수에 관한 수치해석

배강열(Kang-Youl Bae),김형범(Hyoung-Bum Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

This paper represents the numerical analysis on critical Taylor number according to the variation of radius ratio and angular velocity on flow in cylinder. The numerical model consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8mm, the numerical parameters are angular velocity and radius ratio. The numerical method is compared with the experimental results by Wereley, and the results are very good agreement. As the results, the vortex size is from 0.8 to 1.1 for TVF at various  , and the traveling distance for wavy vortex have the critical traveling distance for each case. Also, the critical Taylor number is calculated by theoretical and numerical analysis, and the results is showed the difference about ±2~3%.

Thermal Analysis on Triple-Passage Heat Exchangers for a Continuous Hot-Steel Tube Cooling System

Ko, Bong-Hwan,Park, Seung-Ho The Society of Air-Conditioning and Refrigerating 2002 International Journal Of Air-Conditioning and Refr Vol.10 No.1

The objective of present study is to analyze a concentric triple-passage heat exchanger for an optimal design of a continuous hot steel-tube cooling system, where a hot-steel tube line is passing through an antioxidant gas with a constant speed. Velocities and temperatures of the inert gas flowing between inner and outer tubes are calculated theoretically for laminar and numerically for turbulent flow regimes. From their profiles Nusselt numbers and friction factors are calculated (or various ratios of inner/outer tube radii and relative velocities. With these Nusselt numbers triple-passage heat exchangers are investigated for their thermal characteristics. It is shown that heat transfer coefficients based on ratios of average heat fluxes from inner and outer tubes might result in great errors for the temperature distributions of the flows, since local heat transfer coefficients for flows through an annulus are dependent on local wall heat flux ratios.

PRESSURE DROP AND HEAT TRANSFER INSIDE THE COILED FLOW CHANNEL OF SMOOTH TUBES AND INTERNALLY HELICAL-GROOVED TUBES

NORIHIRO INOUE,SHINITSU IKU,KAZUHIDE WATANABE 대한설비공학회 2012 International Journal Of Air-Conditioning and Refr Vol.20 No.4

In this study, we investigated ways of improving the performance of heat exchangers, which are the heat pumps for use in hot-water supply systems on the hot-water supply side. Therefore, we verified experimentally the pressure drop and the heat transfer characteristics within the coiled flow channel. Five smooth copper tubes and five internally helical-grooved copper tubes with an outside diameter of 12.7mm and coil diameters of 100 mm, 120 mm, 140 mm, 160mm and 180mm were used as the heat-transfer coiled tubes in the experiments. Experiments were conducted under conditions of constant isothermal heating and fluid flow inside coiled tubes with an inlet temperature of 20℃, and the flow rates of the fluid flow inside the coiled tubes were adjusted and varied to change the Reynolds number within the range of 900 to 25,000. Based on the experimental values, we proposed prediction equations to systematically calculate the friction factor and the heat transfer coefficient for different curvature radius ratios.