• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.5
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• pp.408-415
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• 2011

The moon landing is composed of the de-orbit descent phase, powered descent phase, and the powered descent phase is divide into 3-sub phase of the braking, approach, final landing phase. In this paper, the lunar lander perform landing control using 3-sub phase of optimal trajectory. First, generate the reference trajectory using gauss pseudo-spectral method. Thereafter generate PID controller using altitude and velocity error in each direction. Finally the lunar lander landing system constitute using the Simulink of Matlab, and perform simulation.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.62-67
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• 2001

Velocities of leaky surface acoustic waves (LSAW/sub s/) were measured by using a line-focus polyvinylidene fluoride (PVDF) transducer and compared with theoretically calculated ones. Isotropic materials of Cu, Al, fused quartz, and anisotropic one of Z-cut α-quartz crystal were used as specimens. The velocities were obtained by the separation time between wave components reflected directly from the surface of specimen and LSAW components according to the defocusing distance. The measured velocities well agree with the theoretical results within 1％ error, and it was shown that the leaky pseudo-surface acoustic wave (LPSAW) as well as the LSAW propagates with the typical 6-fold anisotropy on the (0,0,1) surface of α-quartz.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.211-221
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• 2003

The response displacement method is the most frequently used method for seismic design of underground structures. This method is pseudo-static method, and the evaluations of velocity response spectrum of seismic base and response displacement of surrounding soil are the most important steps. In this study, the evaluation of velocity response spectrum of seismic base according to the Korean seismic design guide and the simple method of calculating the response displacement were studied. It was found that velocity response spectrum of seismic base can be estimated by directly integrating the ground-surface acceleration response spectrum of soil type S$_A$, and the evaluation of the response displacement using double cosine method assuming two layers of soil profile shows the advantages in the seismic design.

• The KSFM Journal of Fluid Machinery
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• v.6 no.1 s.18
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• pp.44-50
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• 2003

Flow through a turbine flow meter is simulated by solving the incompressible Navier-Stokes equations. The solution method is based on the pseudo-compressibility approach and uses an implicit-upwind differencing scheme together with the Gauss-Seidel line relaxation method. The equations are solved steadily in rotating reference frames, and the centrifugal force and the Coriolis force are added to the equation of motion. The standard $k-{\epsilon}$model is employed to evaluate turbulent viscosity. Computational results yield quantitative as well as qualitative information on the design of turbine flow meters by showing the distributions of pressure and velocity around the turbine blades.

• Communications of the Korean Mathematical Society
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• v.33 no.2
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• pp.571-580
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• 2018

The object of the present paper is to prove the non-existence of pseudo projective Ricci symmetric spacetimes $(PW\;RS)_4$ with different types of energy momentum tensor. We also discuss whether a fluid $(PW\;RS)_4$ spacetime with the basic vector field as the velocity vector field of the fluid can admit heat flux. Next we consider perfect fluid and dust fluid $(PW\;RS)_4$ spacetimes respectively. Finally we construct an example of a $(PW\;RS)_4$ spacetime.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1624-1629
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• 2008

The governing equations in generalized curvilinear coordinates for a 3D pulsatile flow are the Incompressible Navier-Stokes (INS) equations with the artificial dissipative terms and continuity equation discretized using a second-order accurate, finite volume method on the nonstaggered computational grid. This method adopts a dual or pseudo time-stepping Artificial Compressibility (AC) method integrated in pseudo-time. The computational technique implements the implicit approximate factorization method of the Beam and Warming method (1978), which is the extension of the Alternate Direction Implicit (ADI) method. The algorithm yields practically identical velocity profiles and secondary flows that are in excellent overall agreement with an experimental measurement (Rindt & Steenhoven, 1991).

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1392-1396
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• 2007

The governing equations in generalized curvilinear coordinates for 3D laminar flow are the Incompressible Navier-Stokes (INS) equations with the artificial dissipative terms. and continuity equation discretized using a second-order accurate, finite volume method on the nonstaggered computational grid. This method adopts a dual or pseudo time-stepping Artificial Compressibility (AC) method integrated in pseudo-time. Multigrid methods are also applied because solving the equations on the coarse grids requires much less computational effort per iteration than on the fine grid. The algorithm yields practically identical velocity profiles and secondary flows that are in excellent overall agreement with an experimental measurement (Humphrey et al., 1977).

• Structural Engineering and Mechanics
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• v.20 no.6
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• pp.655-672
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• 2005

Seismic random responses due to the wave passage effect are extensively investigated by using the pseudo excitation method (PEM). Two examples are used. The first is very simple but also very informative, while the second is a realistic suspension bridge. Numerical results show that the seismic responses vary significantly with wave speed, especially for low velocity or large span. Such variations are not monotonic, especially for flexible structures. The contributions of the dynamic and quasi-static components depend heavily on the seismic wave velocity and the natural frequencies of structures. For the lower natural frequency cases, the dynamic component has significant effects on the dynamic responses of the structure, whereas the quasi-static component dominates for higher natural frequencies unless the wave speed is also high. It is concluded that if insufficient data on local seismic wave velocity is available, it is advisable to select several possible velocity values in the seismic analysis and to choose the most conservative of the results thus obtained as the basis for design.

• Journal of Environmental Science International
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• v.18 no.3
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• pp.333-343
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• 2009

This study presents the analysis of an atmospheric flow around a single-doppler radar located in a pseudo-site. The use of a doppler radar in meteorological field of wind engineering has become widespread over the last several decades, but it has generally been recognized that the single-Doppler radar yields only one single velocity component - the radial velocity($V_r$) so that some additional hypotheses or simplifications must be necessary to get proper wind forecast. Therefore, in order to get an accurate radial velocity($V_r$) in this study, the existing methods such as VAD(Velocity Azimuth Display) and VARD(Velocity Area Display) are reformulated and applied to match the previous study(Waldteufel and Corbin), which have been an important indicator for retrieving a radar velocity. The results presented in this study include the results from different assessment methods in a peudo-site of different wind fields. Unless the existing method can consider the proper decomposition of radial velocity in the real site, then authors suggest an appropriate curve-fitting to decrease the uncertainty errors by changing a grid adaptation rate or applying a weighting function with respect to the wind angle. It is concluded that provided properly formulated fitting function are used, the wind retrieval from the Doppler radar using VAD and VARD methods can be a viable tool for use in wind engineering problems searching for the wind resources.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.5-12
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• 2013

The critical velocity effect on railway trackbed means the amplification of vibration energy when the train running-speed and group velocity of ground surface wave are superimposed. It is called a pseudo-resonance phenomenon of time domain. In the past, it was not issued because the train speed was low and the ground group velocity was higher. But since the high-speed train is introduced, critical velocity reported causing a track irregularity. So far, theoretical analysis has been performed because of the complexity of formation process. However it requires reasonable consideration which is similar to actual track and trackbed conditions. In the present paper, finite element analysis to verify the critical velocity effect is performed considering each track structure and trackbed supporting stiffness. As a result, the deformation amplification caused by the critical velocity effect is verified to analyze each supporting stiffness and track system.