• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.1
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• pp.9-17
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• 2020

The stochastic point-source model has been widely used in generating artificial ground motions, which can be used to develop a ground motion prediction equation and to evaluate the seismic risk of structures. This model mainly consists of three different functions representing source, path, and site effects. The path effect is used to emulate decay in ground motion in accordance with distance from the source. In the stochastic point-source model, the path attenuation effect is taken into account by using the geometrical attenuation effect and the inelastic attenuation effect. The aim of this study is to develop accurate equations of ground motion attenuation in the Korean peninsula. In this study, attenuation was estimated and validated by using a stochastic point source model and observed ground motion recordings for the Korean peninsula.

• Earthquakes and Structures
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• v.17 no.6
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• pp.557-566
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• 2019

The evaluation of the seismic hazard for a given site is to estimate the seismic ground motion at the surface. This is the result of the combination of the action of the seismic source, which generates seismic waves, the propagation of these waves between the source and the site, and site local conditions. The aim of this work is to evaluate the sensitivity of dynamic response of extended structures to spatial variable ground motions (SVGM). All factors of spatial variability of ground motion are considered, especially local site effect. In this paper, a method is presented to simulate spatially varying earthquake ground motions. The scheme for generating spatially varying ground motions is established for spatial locations on the ground surface with varying site conditions. In this proposed method, two steps are necessary. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi-Kanai power spectral density function. An empirical coherency loss model is used to define spatial variable seismic ground motions at the base rock. In the second step, power spectral density function of ground motion on surface is derived by considering site amplification effect based on the one dimensional seismic wave propagation theory. Several dynamics analysis of a curved viaduct to various cases of spatially varying seismic ground motions are performed. For comparison, responses to uniform ground motion, to spatial ground motions without considering local site effect, to spatial ground motions with considering coherency loss, phase delay and local site effects are also calculated. The results showed that the generated seismic signals are strongly conditioned by the local site effect. In the same sense, the dynamic response of the viaduct is very sensitive of the variation of local geological conditions of the site. The effect of neglecting local site effect in dynamic analysis gives rise to a significant underestimation of the seismic demand of the structure.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.84-90
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• 2000

Ground effect of three-dimensional wing is studied. LU-factored Implicit upwind TVD scheme and Baldwin-Lomax turbulence model are used for this calculation. To investigate ground effect, NACA 4415 wing at M=0.5 calculated. Two different angles of attack and three cases of flight height are calculated. As increasing angle of attack, the ground effect becomes strong. In case of NACA 4415 wing in ground effect, strength of wing tip vortex becomes stronger than that of free flight.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.427-430
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• 2006

The ground effect on tilt-rotor UAV is analyzed by simulating the hovering UAV for various altitudes. Ground effect increases pressure beneath the UAV body and generates additional lifting force. The ground effect diminishes at altitude 3m and hovering UAV generates constant lifting force above 3m.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.193-198
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• 2006

It takes a lot of time and effort to generate grids for numerical analysis of problems with ground effect because the relative attitude and height of airfoil should be maintained to the ground as well as the inflow. A low Mach number preconditioned turbulent flow solver using the overlap grid technique has been developed and applied to the ground effect simulation. It has been validated that the present method using the multi-block grid gives us highly accurate solutions comparing with the experimental data of the RAE 101 airfoil in an unbounded condition. Present numerical method has been extended to simulate ground effect problems by using the overlapped grid system to avoid tedious work in generating multi-block grid system. An extended method using the overlapped grid has been verified and validated by comparing with results of multi-block method and experimental data as well. Consequently, the overlapped grid method can provide not only sufficiently accurate solutions but also the efficiency to simulate ground effect problems. It is shown that the pressure and aerodynamic centers move backward by the ground effect as the airfoil approaches to the ground.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.674-681
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• 2005

The unsteady evolution of trailing vortex sheets behind wings in close formation flight near the ground is simulated using a discrete vortex method. The ground effect is included by an image method. The method is validated by comparing computed results with other numerical results. For a lifting line with an elliptic loading, the ground has an effect of moving wingtip vortices laterally outward and suppressing the development of vortex evolution. The gap between wings in close formation flight has an effect of moving up wingtip vortices facing each other. For wings flying in parallel, the ground effect causes the wingtip vortices facing each other to move up, and it makes the opposite wing tip vortices to move laterally outward. When there is a relative height between the wings in ground effect, right-hand side wingtip vortices from a mothership move laterally inward.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.670-676
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• 2007

A comparative study on ground boundary conditions for the airfoil in ground effect has been carried out. The objective of the present study is to clarify effects of the ground boundary conditions so that it will be helpful to analyse results of wind tunnel tests using the fixed ground board or the image method. A low Mach number preconditioned Navier-Stokes solver using the overlap grid method has been applied. It has been turned out that results with the symmetric boundary condition are almost the same to those with the moving boundary condition. Results with the fixed ground boundary show discrepancy to those with the moving boundary condition when flow separation on the ground board takes place.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.397-404
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• 2001

Sand pile is one of the widely used ground improvement methods. Sand pile improved ground will have composite ground effects, even though the primary purpose is the accelerated consolidation. However, the consolidation of sand pile improved ground as a composite ground is substantially under developed. This study investigate the effect of composite ground for relatively low volume displacement sand piles. Plate bearing tests and earth pressure cell measurements are performed. It turned out that the contribution of sand pile as a load bearing mechanism is not substantial. However the bearing capacity of the surrounding clayey soil is increased by sixty percent, and it cause the stiffness change during consolidation. Therefore it is expected that, the effect of increased stiffness of sand pile improved ground is influenced by change of ground stiffness.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.2
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• pp.209-217
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• 2016

Unlike conventional airplane, a WIG craft experiences righting moment and adverse yaw moment in banked turning in ground effect. Numerical simulations are carried out to study the aerodynamics of banked wing in ground effect. Configurations of rectangular wing and delta wing are considered, and performance of endplates and ailerons during banking are also studied. The study shows that righting moment increase nonlinearly with heeling angle, and endplates enhance the righting. The asymmetric aerodynamic distribution along span of wing with heeling angle introduces adverse yaw moment. Heeling in ground effect with small ground clearance increases the vertical aerodynamic force and makes WIG craft climb. Deflections of ailerons introduce lift decrease and a light pitching motion. Delta wing shows advantage in banked turning for smaller righting moment and adverse yaw moment during banking.

• Journal of computational fluids engineering
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• v.11 no.4 s.35
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• pp.81-89
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• 2006

Two dimensional turbulent flow simulations on the low Mach number - high Reynolds number flow about the NACA 4412 airfoil are carried out as the airfoil approaches a ground. It has turned out that angle of attack between 2 and 8 degrees is recommended for the airfoil to utilize the benefit of ground effect. For the large angle of attack, the increment of lift due to the ground effect is faded away and negative aerodynamic effect such as destabilizing aspect in static longitudinal stability occurs and the separation point moves to forward as the airfoil approaches a ground.