• Geophysics and Geophysical Exploration
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• v.11 no.1
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• pp.41-51
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• 2008

To construct in situ velocity-porosity relationships for oceanic basalt, considering crack features, P- and S-wave velocity measurements on basaltic samples obtained from the eastern flank of the Juan de Fuca Ridge were carried out under confining pressures up to 40 MPa. Assuming that the changes in velocities with confining pressures are originated by micro-crack closure, we estimated micro-crack aspect ratio spectra using the Kuster-$Toks{\ddot{o}}z$ theory. The result demonstrates that the normalised aspect ratio spectra of the different samples have similar characteristics. From the normalised aspect ratio spectrum, we then constructed theoretical velocity-porosity relationships by calculating an aspect ratio spectrum for each porosity. In addition, by considering micro-crack closure due to confining pressure, a velocity-porosity relationship as a function of confining pressure could be obtained. The theoretical relationships that take into account the aspect ratio spectra are consistent with the observed relationships for over 100 discrete samples measured at atmospheric pressure, and the commonly observed pressure dependent relationships for a wide porosity range. The agreement between the laboratory-derived data and theoretically estimated values demonstrates that the velocity-porosity relationships of the basaltic samples obtained from the eastern flank of the Juan de Fuca Ridge, and their pressure dependence, can be described by the crack features (i.e. normalised aspect ratio spectra) and crack closure.

• Journal of Korean Ophthalmic Optics Society
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• v.6 no.1
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• pp.13-29
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• 2001

A mathematical model was proposed to analyze the vibration of diaphragm, such as the contact lenses fitted on the eyes, being subjected to the external sinusoidal pressure. The model incorporates the differential equations and their numerical solution program, based on the wave equations. Turbo-C and graphic software, formulated to describe the dependence of the various parameters involved in the vibration. The model predicts the radial distribution of amplitude, frequency dependence of both average displacement amplitude and the power of diaphragm whose edge is being either simply supported or rigidly clamped in vibration. The effect of variables such as thickness, radius, damping coefficients on the vibration characteristics was illustrated by the computer simulation of the derived program. As the frequency of driving pressure increases above the certain value determined by the boundary conditions and parameters the wave shape or pattern changes from simple arc to belly or loops having double antinode. It seems that the effect of outer antinode progressively increases as the frequency increases. If this kind of phenomena occurs to the contact lens on the cornea in vivo, it may cause an abnormal correction power in the lenses or pull off the eye due the increased rise of outer part of the lens.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.3
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• pp.575-583
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• 2017

Various types of flow patterns around the stepped weir and spillway, such as the skimming flow over such structures and the wave-type flow with a standing undular hydraulic jump and roller downstream of the structures, are developed in open channels. Unsteady three-dimensional numerical simulations are carried out using a hybrid RANS-LES turbulence modeling approach and the volume of fluid method for resolving free surface fluctuations to represent the turbulent flow including the skimming flow and wave-type flow over a stepped weir installed in a rectangular channel. The comparison of numerical results with an existing experimental measurement reveals that the present numerical simulations reasonably well reproduce the turbulent flow passing the stepped weir, in terms of time-averaged velocity profiles at selected locations downstream of the weir, flow topology characterized by the wave-type and skimming flows, the maximum height and length of the standing wave and the length of reattachment of recirculating zone. The numerical result further elucidates the distinct flow behaviors of the wave-type and skimming flow by presenting instantaneous intense variations of free surface and velocity vectors, the distributions of Reynolds shear stress and turbulent kinetic energy and three-dimensional complex features of coherent structures and total pressure distribution.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.3
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• pp.116-129
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• 2000

The interaction of incident monochromatic waves with a tensioned, flexible, circular membrane submerged horizontally below free surface is investigated in the frame of three-dimensional linear hydro-elastic theory. The velocity potential is split into two parts i.e. the diffraction potential representing the scattering of incident waves by a rigid circular disk and the radiation potential describing motion induced waves by elastic responses of flexible membrane. The fluid domain is divided into three regions, and the diffraction and radiation potentials in each region are expressed by the Fourier Bessel series. The displacement of circular membrane is expanded with a set of natural functions, which satisfy the membrane equation of motion and boundary conditions. The unknown coefficients in each region are determined by applying the continuity of pressure and normal velocity at the matching boundaries. The results show that various types of wave focusing are possible by controlling the size, submergence depth, and tension of membrane.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.5
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• pp.671-679
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• 2022

Harmful factors such as shock waves and fragments are generated at domestic ammunition testing sites and military shell shooting training sites due to frequent shooting and explosion tests. As a result, complaints from local residents are rapidly increasing, and there is a high risk of damage to facilities and human life. The recently constructed ammunition test site built a test facility for firing artillery and rocket propulsion in a narrow area with a radius of 300 m due to site restrictions, but damage to the facility is accumulating because there is no adequate protective structure. Therefore, in this study, quantitative data on harmful factors such as noise, vibration, shock wave, and thermal effect generated between artillery firing and rocket propulsion tests were measured, and explosion pressure characteristics were analyzed to design a protective structure, and use Autodyn to protect performance. to perform verification.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.3
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• pp.161-167
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• 1992

We consider the preparation of long finite amplitude nondispersive waves over a step bottom between two regions of finite different depths. Two dimensional motion is assumed. with the wave crests parallel to the step, and irrotational flow in the inviscid fluid is considered. To describe the transformation of finite amplitude waves we use the finite-amplitude shallow-water equations, the conditions of mass flow conservation and pressure continuity at the cut above the step in Riemann's variables. The equations define four families of curves-characteristics on which the values of the Riemann's invariants remain constant and a system of two nonlinear equations that relates the amplitudes of incident reflected and transmitted waves. The system obtained is difficult to analyze in common form. Thus we consider some special cases having practical usage for tsunami waves. The results obtained are compared with the long wave theory and significant nonlinear effects are found even for quite small amplitude waves.

• Journal of computational fluids engineering
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• v.17 no.4
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• pp.49-55
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• 2012

Research has importance in proposing the design of a tunnel with a vertical vent to secure passengers in a comfortable environment and safe against pressure. Using several analysis methods, the magnitude of the pressure induced by the vertical vent in the tunnel can be analyzed. In addition to the 3-dimensional method, the 2-dimensional method and the 2-dimensional axis-symmetric method are also used to analyze the strong and weak points of each so that the optimum analysis method can be obtained. As a result, it appears that the 2-dimensional axis-symmetric method is the most suitable in analyzing tunnel pressure consider to accuracy and time effective aspect. Also, the 3-dimensional method is disadvantageous in that it takes longer in calculating results, but is more effective in predicting phenomena around the vertical vent in the tunnel.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.1
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• pp.9-17
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• 2013

A considerable deal of work has been carried out to get an insight into the gas-solid suspension flows and to specify the particle motion and its influence on the gas flow field. In this paper an attempt is made to develop an analytical model to study the effect of nozzle inlet/exit pressure ratio, particle/gas loading and the particle diameter effect on gas-solid suspension flow. The effect of the particle/gas loading on the mass flow, Mach number, thrust coefficient and static pressure variation through the nozzle is analyzed. The results obtained show that the presence of particles seems to reduce the strength of the shock wave. It is also found that smaller the particle diameter is, bigger will be the velocity as bigger particle will have larger slip velocity. The suspension flow of smaller diameter particles has almost same trend as that of single phase flow with ideal gas as working fluid. Depending on the ambient pressure, the thrust coefficient is found to be higher for larger particle/gas loading or back pressure ratio.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.61-71
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• 1993

The stress waves generated by the mechanical energies by impact or the chemical energies by the explosions are transmitted through medium. The wave propagation process through medium is a very complicated procedure due to the reflections and refractions of the waves at the free surfaces and interfaces. In this study the pressure independent Von-Mises model is employed for the wave propagation analysis in the layered systems. Governing equations of this study are conservation equations of momentum and mass in Lagrangian coordinate system which is fixed to the material. Due to the shock-front which violates the continuity assumptions inherent in the differential equations numerical artificial viscosity is used to spread the shock front over several computational zones. These equations are solved by Finite Difference Method with discretized time and space coordinates. The associate normality flow rule as a plastic theory is implemented to find the plastic strains.

• Journal of the Korean GEO-environmental Society
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• v.16 no.5
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• pp.55-66
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• 2015

Big tidal differences, which range from 3.0 m to 8.0 m, exist with regional locations at south and west shores of Korea. Under this ocean circumstance, since a large scour may occur due to multi-directional tidal current and transverse stress of the wind, the scour surrounding the wind turbine structure can make instability of the system due to unexpected system vibration. The hydraulic resistance capacity of soils consolidated under different pressures are evaluated by Erosion Function Apparatus (EFA) under unidirectional and bi-directional flows in this study. It was found that the flow direction change affects significantly on the sour rate and critical shear stress, regardless of soil types while the consolidation pressure affects mainly cohesive soil. Among geotechnical parameters, the undrained shear strength can be well-correlated with the hydraulic resistance capacity, regardless soil type while the shear wave velocity shows the proportional relationships with the hydraulic resistance capacities of fine grained soil and coarse grained soil, respectively.