• Title/Summary/Keyword: critical inclination

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Wind tunnel study of wind structure at a mountainous bridge location

  • Yan, Lei;Guo, Zhen S.;Zhu, Le D.;Flay, Richard G.J.
    • Wind and Structures
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    • v.23 no.3
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    • pp.191-209
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    • 2016
  • Wind tunnel tests of a 1/2200-scale mountainous terrain model have been carried out to investigate local wind characteristics at a bridge location in southeast Tibet, China. Flows at five key locations on the bridge at deck level were measured for 26 directions. It was observed that wind characteristics (including mean wind velocity and overall turbulence intensity) vary significantly depending on the approaching wind direction and measurement position. The wind inclination angle measured in the study fluctuated between $-18^{\circ}$ and $+16^{\circ}$ and the ratio of mean wind velocity to reference wind velocity was small when the wind inclination angles were large, especially for positive wind inclination angles. The design standard wind speed and the minimum critical wind speed for flutter rely on the wind inclination angle and should be determined from the results of such tests. The variation of wind speed with wind inclination angles should be of the asymmetry step type. The turbulence characteristics of the wind were found to be similar to real atmospheric flows.

Determination of inclination of strut and shear strength using variable angle truss model for shear-critical RC beams

  • Li, Bing;Tran, Cao Thanh Ngoc
    • Structural Engineering and Mechanics
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    • v.41 no.4
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    • pp.459-477
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    • 2012
  • This paper attempts to determine the inclination of the compression strut within variable angle truss models for RC beams loaded in shear-flexure through a proposed semi-analytical approach. A truss unit is used to analyze a reinforced concrete beam, by the principle of virtual work under the truss analogy. The inclination of the compression strut is then theoretically derived. The concrete contribution is addressed by utilizing the compatibility condition within each truss unit. Comparisons are made between the predicted and published experimental results of the seventy one RC beams with respect to the shear strength and the inclined angle of the compression strut at this state to investigate the adequacy of the proposed semi-analytical approach.

Failure Characteristics of Foundation System Reinforced with Stone Columns (쇄석말뚝으로 보강된 기초시스템의 파괴 거동)

  • Shin, Bang Woong;Bae, Woo Seok
    • Journal of the Korean GEO-environmental Society
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    • v.2 no.3
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    • pp.71-80
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    • 2001
  • The quantitative analysis of bearing capacity with stone column-mat is not ease because the bearing capacity of stone column is affected by so many parameters. The bearing capacity of stone column is mainly governed by horizontal resistance along the interface with soil. Also, this foundation system is affected by geometric factors such as column spacing, embedment ratio and failure surface inclination. Therefore, in this study, critical length and the effect of failure surface inclination was studied with single and group end bearing stone columns by loading tests. Results of model tests are compared to the present theoretical methods and are examined with FEM analysis.

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Design of an Elliptical Orbit for High-Resolution Optical Observation at a Very Low Altitude over the Korean Peninsula

  • Dongwoo Kim;Taejin Chung
    • Journal of Astronomy and Space Sciences
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    • v.40 no.1
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    • pp.35-44
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    • 2023
  • Surveillance and reconnaissance intelligence in the space domain will become increasingly important in future battlefield environments. Moreover, to assimilate the military provocations and trends of hostile countries, imagery intelligence of the highest possible resolution is required. There are many methods for improving the resolution of optical satellites when observing the ground, such as designing satellite optical systems with a larger diameter and lowering the operating altitude. In this paper, we propose a method for improving ground observation resolution by using an optical system for a previously designed low orbit satellite and lowering the operating altitude of the satellite. When the altitude of a satellite is reduced in a circular orbit, a large amount of thrust fuel is required to maintain altitude because the satellite's altitude can decrease rapidly due to atmospheric drag. However, by using the critical inclination, which can fix the position of the perigee in an elliptical orbit to the observation area, the operating altitude of the satellite can be reduced using less fuel compared to a circular orbit. This method makes it possible to obtain a similar observational resolution of a medium-sized satellite with the same weight and volume as a small satellite. In addition, this method has the advantage of reducing development and launch costs to that of a small-sized satellite. As a result, we designed an elliptical orbit. The perigee of the orbit is 300 km, the apogee is 8,366.52 km, and the critical inclination is 116.56°. This orbit remains at its lowest altitude to the Korean peninsula constantly with much less orbit maintenance fuel compared to the 300 km circular orbit.

Effect of Inclination Angle and Size of Heated Surface on Pool Boiling CHF

  • Yang, Soo-Hyung;Baek, Won-Pil;Chang, Soon-Heung
    • Proceedings of the Korean Nuclear Society Conference
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    • 1999.05a
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    • pp.155-155
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    • 1999
  • Pool boiling critical heat flux (CHF) have been investigated using plate type test sections with different widths (3 cm & 4 cm) and lengths (10 cm, IS cm & 20 cm) under various incli- nation angles. As the inclination angle increases from $0^{\circ}$ (horizontally facing downward plate) to $30^{\circ}$, CHF sharply increases. After that angle, CHF gradually increases with the increase of the inclination angle. There must be a transition angle between $0^{\circ}$ and $30^{\circ}$, at which the CHF increase rate remarkably changes. According to the comparison of present and previous ex- periments, the transition angle may be affected by heater size and increase with the increase of heater size. The size effect of heated surface on CHF is noticeable in the L15 & L20 series and W4 series; however, it seems to be difficult to find the size effect in L10 series and W3 series.

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Yaw wind effect on flutter instability of four typical bridge decks

  • Zhu, Le-Dong;Xu, You-Lin;Guo, Zhenshan;Chang, Guang-Zhao;Tan, Xiao
    • Wind and Structures
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    • v.17 no.3
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    • pp.317-343
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    • 2013
  • When evaluating flutter instability, it is often assumed that incident wind is normal to the longitudinal axis of a bridge and the flutter critical wind speed estimated from this direction is most unfavorable. However, the results obtained in this study via oblique sectional model tests of four typical types of bridge decks show that the lowest flutter critical wind speeds often occur in the yaw wind cases. The four types of bridge decks tested include a flat single-box deck, a flat ${\Pi}$-shaped thin-wall deck, a flat twin side-girder deck, and a truss-stiffened deck with and without a narrow central gap. The yaw wind effect could reduce the critical wind speed by about 6%, 2%, 8%, 7%, respectively, for the above four types of decks within a wind inclination angle range between $-3^{\circ}$ and $3^{\circ}$, and the yaw wind angles corresponding to the minimal critical wind speeds are between $4^{\circ}$ and $15^{\circ}$. It was also found that the flutter critical wind speed varies in an undulate manner with the increase of yaw angle, and the variation pattern is largely dependent on both deck shape and wind inclination angle. Therefore, the cosine rule based on the mean wind decomposition is generally inapplicable to the estimation of flutter critical wind speed of long-span bridges under skew winds. The unfavorable effect of yaw wind on the flutter instability of long-span bridges should be taken into consideration seriously in the future practice, especially for supper-long span bridges in strong wind regions.

Comprehensive experimental investigation on mechanical behavior for types of reinforced concrete Haunched beam

  • Albegmprli, Hasan M.;Gulsan, M. Eren;Cevik, Abdulkadir
    • Advances in concrete construction
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    • v.7 no.1
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    • pp.39-50
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    • 2019
  • This study presents a comprehensive experimental investigation on mostly encountered types of Reinforced Concrete Haunched Beams (RCHBs) where three modes of RCHBs investigated; the diversity of studied beams makes it a pioneer in this topic. The experimental study consists of twenty RCHBs and four prismatic beams. Effects of important parameters including beam type, the inclination angle, flexure and compressive reinforcement, shear reinforcement on mechanical behavior and failure mode of each mode of RCHBs were examined in detail. Furthermore crack propagation at certain load levels were inspected and visualized for each RCHB mode. The results confirm that RCHBs have different behavior in shear as compared to the prismatic beams. At the same time, different mechanical behavior was observed between the modes of RCHBs. Therefore, RCHBs were classified into three modes according to the inclination shape and mode of failure (Modes A, B and C). However, it was observed that there is no significant difference between RCHBs and prismatic beams regarding flexural behavior. Moreover, a new and unified formula was proposed to predict the critical effective depth of all modes of RCHBs that is very useful to predict the critical section for failure.

Prediction of the Critical Stress for the Inclined Crack in Orthotropic Materials under Biaxial load (2축하중을 받는 직교이방성 경사균열에서 임계응력의 예측)

  • Lim, Won-Kyun;Cho, Hyung-Suk;Jeong, Woo-Kil;Lee, Ill-Soo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.11 s.254
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    • pp.1384-1391
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    • 2006
  • The problem of an infinite anisotropic material with a crack inclined with respect to the principal material axes is analyzed. The material is subjected to uniform biaxial load along its boundary. It is assumed that the material is homogeneous, but anisotropic. By considering the effect of the horizontal load, the distribution of stresses at the crack tip is analyzed. The problem of predicting critical stress in anisotropic solids which is a subject of considerable practical importance is examined and the effect of load biaxiality is made explicitly. The present results based on the normal stress ratio theory show significant effects of biaxial load, crack inclination angle and fiber orientation on the critical stress. The analysis is performed for a wide range of the crack angles and biaxial loads.

The wave stability of the nonparallel natural convection flows adjacent to an inclined isothermal surface submerged in water at $4degC$ ($4degC$ 물에 잠겨있는 경사진 등온 벽주위 비평행 자연대류의 파형 안정성)

  • 황영규;장명륜
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.2
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    • pp.644-653
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    • 1991
  • A wave instability problem is formulated for natural convection flows adjacent to a inclined isothermal surface in pure water near the density extremum. It accounts for the nonparallelism of the basic flow and temperature fields. Numerical solutions of the hydrodynamic stability equations constitute a two-point boundary value problem which are accurately solved using a computer code COLSYS. Neutral stability results for Prandtl number of 11.6 are obtained for various angles of inclination of a surface in the range from-10 to 30 deg. The neutral stability curves are systematically shifted toward modified Grashof number G=0 as one proceeds from downward-facing inclined plate(.gamma.<0.deg.) to upward-facing inclined plate (.gamma.>0.deg.). Namely, an increase in the positive angle of inclination always cause the flows to be significantly more unstable. The present results are compared with the results for the parallel flow model. The nonparallel flow model has, in general, a higher critical Grashof number than does the parallel flow model. But the neutral stability curves retain their characteristic shapes.

Ability to Maintain Postural Control while Standing on Perturbed Surfaces (바닥면의 교란에 따른 자세균형능력의 변화)

  • Park, Sung-Ha;Lee, Seung-Won
    • Journal of Korean Society of Industrial and Systems Engineering
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    • v.31 no.4
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    • pp.146-152
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    • 2008
  • This study was aimed to understand the effects of perturbed floor surface on human postural stability while standing. Ten subjects were asked to stand quietly on the surface with two angles of inclination ($0^{\circ}$ and $5^{\circ}$), two contamination conditions (dry and oil-contaminated), and three commercial floor materials (ceramic tile, coated wood, and vinyl tile). During each trial, a force plate with data acquisition systems was used to collect subject's center of pressure (COP) position. Measured COPs were then converted into the length of postural sway path in both subject's anterior-posterior (AP) and medio-lateral (ML) axis. Results showed that the length of sway path in ML axis was significantly affected by the angle of inclination and the type of floor material. The sway length was increased significantly at the inclination angle of $5^{\circ}$ and on the vinyl tile, respectively. The contamination condition, however, did not significantly affect the postural sway length in both AP and ML axis. The results imply that a proper treatment of floor surface and material is critical to preserving postural balance while standing.