• Journal of the Korean Society of Safety
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• v.24 no.4
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• pp.74-81
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• 2009

In this study, the seismic performance of RC school buildings which were not designed according to earthquake-resistance design code were evaluated by using response spectrum and push-over analyses. The torsional amplification effect due to plan irregularity is considered and then the efficiency of seismic retrofitting methods such as RC shear wall, steel frame, RC frame and PC wing wall was investigated. The analysis result indicate that the inter-story drift concentrated in the first floor and most plastic hinge forms at the column of the first story. Among the retrofitting methods, the PC wing wall has the highest seismic performance in strength and story drift aspect. Especially, it can make building ductile behavior due to the concentrated inter-story drift at the first column hinge is distributed overall stories. The axial force, shear force and moment magnitude of existing elements significantly decreased after retrofitting. However, the axial and shear force of the elements connected to the additional retrofitting elements increased, and especially the boundary columns at the end of the retrofitting shear wall should be reinforced for assuring the enhancement of seismic performance.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.2
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• pp.162-168
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• 2009

In this study, numerical analysis is performed to investigate the sound radiation characteristics of an apartment house according to the type of the slab system. In order to satisfy the boundary condition of the apartment house, the whole floor is modelled with FEM model for three different structural system: wall, RC, flat slab system. From the analytical results, it is shown that heavy weight floor impact noise of wall type slab is larger than that of the other slab systems and the noise radiated from the wall have great effect on the sound pressure level. The results also show that the vibration energy of RC or flat slab system is widely distributed over the whole slab, which is main reason that the noise induced by the slab systems is reduced in comparison with wall slab system.

• Structural Engineering and Mechanics
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• v.86 no.1
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• pp.49-68
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• 2023

This study investigates the static and dynamic structural analysis of symmetrical and asymmetrical coupled shear walls using the continuous and modified transfer matrix methods by idealizing the coupled shear wall as a three-field CTB-type replacement beam. The coupled shear wall is modeled as a continuous structure consisting of the parallel coupling of a Timoshenko beam in tension (with axial extensibility in the shear walls) and a shear beam (replacing the beam coupling effect between the shear walls). The variational method using the Hamilton principle is used to obtain the coupled differential equations and the boundary conditions associated with the model. Using the continuous method, closed-form analytical solutions to the differential equation for the coupled shear wall with uniform properties along the height are derived and a numerical solution using the modified transfer matrix is proposed to overcome the difficulty of coupled shear walls with non-uniform properties along height. The computational advantage of the modified transfer matrix method compared to the classical method is shown. The results of the numerical examples and the parametric analysis show that the proposed analytical and numerical model and method is accurate, reliable and involves reduced processing time for generalized static and dynamic structural analysis of coupled shear walls at a preliminary stage and can used as a verification method in the final stage of the project.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2315-2325
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• 1996

A compression wave is attenuated or distorted as it propagates in a tube. The present study investigated the propagation characteristics of the compression waves which are generated by a train in a high-speed railway tunnel. A Total Variation Diminishing (TVD) difference scheme was applied to one-dimensional, unsteady viscous compressible flow. The numerical calculation involved the effects of wall friction, heat transfer and energy loss due to the friction heat in the boundary layer behind the propagating compression wave, and compared with the measurement results of a shock tube and a real tunnel. The present results show that attenuation of the compression wave in turbulent boundary layer is stronger than in laminar boundary layer, but nonlinear effect of the compression wave is greater in the laminar boundary layer. The energy loss due to the frictional heat had not influence on attenuation and distortion of the propagating compression waves.

• Journal of the Korean Society of Visualization
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• v.1 no.1
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• pp.64-74
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• 2003

An experimental study was carried out to investigate the effect of periodic blowing and suction on a turbulent boundary layer. Particle image velocimetry (PIV) was used to probe the characteristics of the flow. The local forcing was introduced to the boundary layer via a sinusoidally-oscillating jet issuing from a thin spanwise slot. Three forcing frequencies (f$^{+}$=0.044, 0.066 and 0.088) with a fixed forcing amplitude (A$^{+}$=0.6) were employed at $Re_{=690. The effect of the forcing angles ($\alpha$=60$^{\circ}$ , 90$^{\circ}$ and 120$^{\circ}$ ) was investigated under the fixed forcing frequency (f$^{+}$=0.088). The PIV results showed that the wall region velocity decreases on imposition of the local forcing. Inspection of phase-averaged velocity profiles revealed that spanwise large-scale vortices were generated in the downstream of the slot and persist further downstream. The highest reduction in skin friction was achieved at highest forcing frequency (f$^{+}$=0.088) and a forcing angle of $\alpha$=120$^{\circ}$. The spatial fraction of the vortices was examined to analyze the skin friction reduction.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.463-466
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• 2002

In order to examine the possibility of using a cavity as a passive device for reduction of skin friction and heat transfer, an intensive parametric study over a broad range of the cavity depth and length at different Reynolds numbers is performed for both laminar and turbulent boundary layers in the present study. Direct and large eddy simulation techniques are used for turbulent boundary layers at low and moderate Reynolds numbers, respectively. for both laminar and turbulent boundary layers over a cavity, a flow oscillation occurs due to the shear layer instability when the cavity depth and length are sufficiently large and it plays an important role in the determination of drag and heat-transfer increase or decrease. For a cavity sufficiently small to suppress the flow oscillation, both the total drag and heat transfer are reduced. Therefore, the applicability of a cavity as a passive device for reduction of drag and heat transfer is fully confirmed in the present study. Scaling based on the wall shear rate of the incoming boundary layer is also proposed and it is found to be valid in steady flow over a cavity.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.472-478
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• 2000

An experimental study is performed to analyze flow structures behind a local suction/blowing in a flat-plate turbulent boundary layer, The local forcing is given to the boundary layer flow by means of a sinusoidally oscillating jet issuing from a thin spanwise slot at the wall. The Reynolds number based on the momentum thickness is about $Re_{\theta}=1700$. The effects of local forcing are scrutinized by altering the forcing frequency $(0.011{\leq}f^+{\leq}0.044)$. The forcing amplitude is fixed at $A_0=0.4$. It is found that a small local forcing reduces the skin friction, and this reduction increases with the forcing frequency. A phase-averaging technique is employed to capture the coherent structures. Velocity signals are decomposed into a periodic part and a fluctuating part. An organized spanwise vortical structure is generated by the local forcing. The larger reduction of skin friction for the higher forcing frequencies is attributed to the diminished adverse effect of the secondary vortex. An investigation of the random fluctuation components reveals that turbulent energy is concentrated near the center of vortical structures.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.2
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• pp.18-25
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• 2007

Computational study on the passive control of the oblique shock-wave/turbulent boundary-layer interaction utilizing slotted plates over a cavity has been carried out. The numerical boundary layer profile upstream of the interaction follows the compressible turbulent boundary-layer theory reasonably well, and the other results also show good agreements with the experimental observations, such as the wall surface pressures and Schlieren flow visualizations. Further, the effects of various slot configuration including number, location and angle of the slots on the characteristics of the interactions, such as the variation of the total pressures, the boundary-layer characteristics downstream of the interaction and the recirculating mass flux through the slots, are also tested and compared.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.3
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• pp.25-32
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• 2001

A passive control method of the interaction between a weak normal shock-wave and a turbulent boundary-layer was simulated using two-dimensional Navier-Stokes computations. The inflow Mach number just upstream of the normal shock wave was 1.33. A porous plate wall having a cavity underneath was used to control the shock-wave/turbulent boundary-layer interaction. The flows through the porous holes and inside the cavity were investigated to get a better understanding of the flow physics involved in this kind of passive control method. The present computations were validated by some recent wind tunnel tests. The results showed that downstream of the rear leg of the $\lambda$-shock wave the main stream inflows into the cavity, but upstream of the rear leg of the $\lambda$-shock wave the flow proceeds from the cavity toward to the main stream. The flow through the porous holes did not choke fur the present shock/boundary layer interaction.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.10 no.3
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• pp.125-131
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• 1998

The paper deals with the application of Boundary-Fitted Coordinate System (BFCS) to the two wave models of parabolic and hyperbolic types developed on a rectangular grid system. Since the BFCS conforms the boundaries of the region in such wary that boundary conditions or calculation process can be accurately represented, improvement in predicting the wave fields can be achieved. The numerical results show a good agreement with the analytical results for either waves propagating or reflecting along a circular channel of constant depth. Simulation of reflecting waves in a parabolic wave model is accomplished by the backward calculation as if waves approached at the cross wall take a turn in the opposite direction and propagate against a channel.