• Journal of the Korea Concrete Institute
• /
• v.22 no.3
• /
• pp.357-366
• /
• 2010

This paper presents experimental results about shear wall with various lateral reinforcement details in boundary elements. The research objective is to study the structural behavior of shear wall with boundary column confined by rectangular spiral hoops and headed cross ties developed to improve workability in the fabrication of boundary columns. These two details can be fabricated in a factory and put together on-site after being delivered so that the construction work may be reduced. Main parameters in the experimental study were the types of hoop and cross tie: rectangular spiral hoop and headed cross tie vs. standard hoop and cross tie with hook. Four half scaled shear wall specimens with babel shape were made and tested by applying horizontal cyclic load under constant axial force, 10% of nominal compressive strength of concrete. Based on the test result, it was shown that the shear wall with rectangular spiral hoop and headed cross tie in boundary columns has structural capacity compatible with conventional shear wall. The specimen SW-Hh which has bigger hoop bar and higher volumetric ratio of transverse reinforcements than other showed improved energy dissipating characteristic but it presented a rapid reduction of strength after peak point. The results indicates that, it is necessary to consider volumetric ratio of transverse reinforcements as well as hoop space in designing of shear wall with boundary columns for improved strength and ductility.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.12
• /
• pp.924-930
• /
• 2008

Immersed boundary method (IBM) is the most effective method to overcome the disadvantage of LBM (Lattice Boltzmann Method) related to the limitation of the grid shape. IBM also make LBM possible to simulate flow over complex shape of obstacle without any treatment on the curved boundary. In the research, IBLBM was used to perform LBM simulation of a flow over a moving circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of IBLBM on the moving obstacle near the wall, it was first simulated for the case of the flow over a fixed circular cylinder in a channel and the results were compared against the solution of moving cylinder in the channel using IBLBM. The simulations were performed in a moderate range of Reynolds number at each moving cylinder to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag and lift coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical Reynolds number for vortex shedding is Re=50 and the result is the same as the case of fixed cylinder. As the cylinder approaching to a wall (${\gamma}<2.5$), the 2nd vortex is developed by interacting with the wall boundary-layer vorticity. When the cylinder is very closed to the wall, ${\gamma}<0.6$, the cylinder acts like blockage to block the flow between the cylinder and wall so that the vortex developed on the upper cylinder elongated and time averaged lifting and drag coefficients abruptly increase.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2731-2736
• /
• 2007

In this paper, incompressible flow over a cylinder near a plane wall using the Immersed Boundary. Finite Difference Lattice Boltzmann Method (IB-FDLBM) is implemented. In this present method, FDLBM is mixed with IBM by using the equilibrium velocity. We introduce IBM so that we can easy to simulate bluff-bodies. With this numerical procedure, the flow past a circular cylinder near a wall is simulated. We calculated the flow patterns about various Reynolds numbers and gap ratios between a circular cylinder and plane wall. So these are enabled to observe for vortex shedding. The numerical results are found to be in good agreement with those of previous studies.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.652-657
• /
• 2001

Computational work using the axisymmetric, compressible, Navier-Stokes Equations is carried out to predict the discharge coefficient of mass flow through a micro-critical nozzle. Several kinds of turbulence models and wall functions are employed to validate the computational predictions. The computed results are compared with the previous experimented ones. The present computations predict the experimental discharge coefficients with a reasonable accuracy. It is found that the standard $k-\varepsilon$ turbulence model with the standard wall function gives a best prediction of the discharge coefficients. The displacement thickness of the nozzle wall boundary layer is evaluated at the nozzle throat and is well compared to a prediction obtained by an empirical equation. The resulting displacement thickness of the wall boundary layer is about 2% to 0.6% of the diameter of the nozzle throat for the Reynolds numbers of 2000 to 20000.

• 한국연소학회:학술대회논문집
• /
• 2006.04a
• /
• pp.32-38
• /
• 2006

A premixed flame propagating in a tube suffers strong variation in its shape and structure depending on boundary conditions. The effects of thermal boundary conditions and flow fields on flame propagation are numerically investigated. Navier-Stokes equations and species equations are solved with a one-step irreversible global reaction model of methane-air mixture. Finite volume method using an adaptive grid method is applied to investigate the flame structure. In the case of an adiabatic wall, friction force on the wall significantly affected the flame structure while in the case of an isothermal wall, local quenching near the wall dominated flame shapes and propagation. In both cases, variations of flow fields occurred not only in the near field of the flame but also within the flame itself, which affected propagation velocities. This study provides an overview of the characteristics of flames in small tubes at a steady state.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.9 no.2
• /
• pp.181-189
• /
• 1985

The effect of the Coriolis force on the 2-D turbulent boundary layer which is developed in the side wall of the rotating rectangular flow channel was investigated. In this study, we measured mean velocities, turbulent velocity components(axial as well as lateral ones) and Reynolds stresses of the turbulent boundary layer. For high Reynolds number flows, the turbulent boundary layer without pressure gradient is hardly affected by the rotation. For low Reynolds number flows, however, the shearing stress at suction side decreases. Consequently, the velocity near the wall become slower so that the thickness of the viscous sublayer expands. On the other hand, the velocity near the wall at pressure side turns out increased.

• Computers and Concrete
• /
• v.2 no.2
• /
• pp.111-123
• /
• 2005

The ductility of reinforced concrete bearing walls subjected to high axial loading and moment can be enhanced by improving the deformability of the compression zone or by reducing the neutral axis depth. The current state-of-the-art procedure evaluating the confinement effect prompts a consideration of the spaces between the transverse and longitudinal reinforcing bars, and a provision of tie bars. At the same time, consideration must also be given to the thickness of the walls. However, such considerations indicate that the confinement effect cannot be expected with the current practice of detailing wall ends in Korea. As an alternative, a comprehensive method for dimensioning boundary elements is proposed so that the entire section of a boundary element can stay within the compression zone when the full flexural strength of the wall is developed. In this comprehensive method, the once predominant code approach for determining the compression zone has been advanced by considering the rectangular stress block parameters varying with the extreme compression fiber strain. Moreover, the size of boundary elements can also be determined in relation to the architectural requirement.

• Earthquakes and Structures
• /
• v.18 no.3
• /
• pp.379-390
• /
• 2020

Four full-scaled partially confined and unconfined masonry panels were tested with monotonic lateral loads. To study the effects of vertical force and boundary columns, two specimens with no boundary columns were subjected to different vertical forces, while two wing-wall specimens had the column placed eccentrically and in the middle, respectively. The specimens with no boundary columns exhibited ductile rocking behavior, where the lateral strength increased with increasing vertical compression. The wing-wall specimens with columns behaved as strut-and-tie systems. The column-panel interaction resulted in greater strength, lower deformation capacity and differences in failure modes. A comparison with analytical models showed that rocking strength can be accurately estimated using vertical force and the panel aspect ratio for panels with no boundary columns. The estimation for lateral strength on the basis of a panel section area indicated scattered error for wing-wall specimens.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.6
• /
• pp.802-813
• /
• 2000

This paper represents numerical computations of the interaction between the longitudinal vortex and a flat plate 3-D turbulent boundary layer. In the present study, the main interest is in the behavior of longitudinal vortices introduced in turbulent boundary layers. The flow field behind vortex generator is modeled by the information that is available from studies on the delta winglet. Also, the Reynolds-averaged Navier-Stoke equations for three-dimensional turbulent flows, together with a two-layer turbulence model to resolve the near-wall flow, is solved by the method of pseudo compressibility. The present results show that the boundary layer is thinned in the regions where the secondary flow is directed toward the wall and thickened where it is directed away from the wall, and have a good agreement with the experimental data.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.11 s.242
• /
• pp.1189-1198
• /
• 2005

Direct numerical simulations were performed to investigate the physics of a spatially developing turbulent boundary layer flow subjected to spanwise oscillating electromagnetic forces in the near wall region. A fully implicit fractional step method was employed to simulate the flow. The mean flow properties and the Reynolds stresses were obtained to analyze the near-wall turbulent structure. It is found that skin friction and turbulent kinetic energy can be reduced by the electromagnetic forces. The decrease in production is responsible fur the reduction of turbulent kinetic energy. Instantaneous flow visualization techniques were used to observe the response of streamwise vortices and streak structures to spanwise oscillating forces. The near-wall vortical structures are affected by spanwise oscillating electromagnetic forces. Following the stopping of the electromagnetic force, the flow eventually relaxes back to a two-dimensional equilibrium boundary layer.