• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.2 no.2
• /
• pp.67-74
• /
• 1990

A numerical model is developed to predict the shoreline change by the coastal structures constructed. In order to describe the wave deformation at the shadow zone of the structure, the present model employs the mild-slope equation in steady state and the wave ray method using the coefficients of wave refraction, diffraction and shoaling. In the model results of shoreline changes for the various structures. it showed a qualitative agreement with the findings observed in the field such as tombolo, and the response of this model was found to be very sensitive to the longshore distribution of wave heights. It was also applied to a field area. From the results of the application this model is proved to be useful around the complex coastal structures and bottom topography.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.11 no.2
• /
• pp.77-89
• /
• 1991

Based on Boussinesq equation, the parabolic approximation equation is used to analyse the propagation of shallow water waves with currents over slowly varying depth. Rip currents (jet-like) occur mainly in shallow waters where the Ursell parameter significatly exceeds the range of application of Stokes wave theory. We employ the nonlinear parabolic approximation equation which is valid for waves of large Ursell parameters and small scale currents. Two types of currents are considered; relatively strong and relatively weak currents. The wave propagating over rip currents on a sloping bottom experiences a shoaling due to the variations of depth and current velocity as well as refraction and diffraction due to the vorticity of currents. Numerical analyses for a nonlinear theory are valid before the breaking point.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.7
• /
• pp.149-159
• /
• 1998

The importance of soundness and safety evaluation in weld zone using by the ultrasonic wave has been recently increased rapidly because of the collapses of huge structures and safety accidents. Especially, the ultrasonic method that has been often used for a major non-destructive testing(NDT) technique in many engineering fields plays an important role as a volume test method. Hence, the defecting any defects of weld Bone in austenitic stainless steel type 304 using by ultrasonic wave and neural network is explored in this paper. In order to detect defects, a distance amplitude curve on standard scan sensitivity and preliminary scan sensitivity represented of the relation between ultrasonic probe, instrument, and materials was drawn based on a quantitative standard. Also, a total of 93％ of defect types by testing 30 defect patterns after organizing neural network system, which is learned with an accuracy of 99％, based on ultrasonic evaluation is distinguished in order to classify defects such as holes or notches in experimental results. Thus, the proposed ultrasonic wave and neural network is useful for defect detection and Ultrasonic Non-Destructive Evaluation(UNDE) of weld zone in austenitic stainless steel 304.

• Water for future
• /
• v.27 no.2
• /
• pp.73-83
• /
• 1994

The unproper development of the nearshore zone can enhance the diffusion of pollutant in the nearshore zone resulting in unbalanced sediment budget of beach which causes alteration of beach topography. Therefore, it is required to predict the effects of the envirnmental change quantitatively. In this paper, the depth-averaged and time-averaged energy balance equation is selected to acount for the wave transformation such as refraction, shoaling effect, the surf zone energy disipation, wave breaking index and bore, due to wave breaking in the shore region.(Numerical solutions are obtained by a finite difference method, ADI and Upwind. For the calculation of the wave-induced current, the unsteady nonlinear depth-averaged and time-averaged governing equation is derived based on the continuity and momentum equation for imcompressible fluid.) Numerical solutions are obtained by finite difference method considering influences of factors such as lateral mixing coefficient, bed shear stress, wave direction angle, wave steepness, wave period and bottom slope. The model is applied to the computation of wave transformation, wave-induced current and variation of mean water leel on a uniformly sloping beach.

• Journal of the Korea Society of Computer and Information
• /
• v.27 no.11
• /
• pp.81-87
• /
• 2022

In this paper, we propose diffraction-based sound control method to improve sound immersion in a virtual environment. The proposed technique can express the wave and flow of sound in a physical environment and a pattern similar to diffraction in real-time. Our approach determines whether there is an obstacle from the location of the sound source and then calculates the position of the new sound reflected and diffracted by the obstacle. Based on ray tracing, it determines whether or not it collides with an obstacle, and predicts the sound level of the agent behind the obstacle by using the vector reflected and refraction by the collision. In this process, the sound attenuation according to the distance/material is modeled by attenuating the size of the sound according to the number of reflected/refracted rays. As a result, the diffraction pattern expressed in the physics-based approach was expressed in real time, and it shows that the diffraction pattern also changes as the position of the obstacle is changed, thereby showing the result of naturally spreading the size of the sound. The proposed method restores the diffusion and diffraction characteristics of sound expressed in real life almost similarly.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.4 no.1
• /
• pp.18-25
• /
• 1992

A discrete spectral model for generation, propagation and dissipation of wind waves for arbitrary depth and current is presented. This model incorporates wave current interaction, including changes of absolute frequencies due to unsteadiness of depth and currents. The numerical scheme for propagation if basically second-order accurate, and effects of refraction and frequency shills due to unsteadiness of depth and current are calculated on a fixed grid, also using second-order scheme.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
• /
• 1996.10a
• /
• pp.109-114
• /
• 1996

In a linear dispersive system, the combined effect of water wave frnnsformations such as refraction, diffraction, shoaling, and reflection can be predicted by the mild-slope equation which was developed by Berkhoff (1972) using the Galerkin-eigenfunction method. In the derivation of the equation, he assumed a mild slope of the bottom $\nabla$h/kh << 1 (where $\nabla$ is the horizontal gradient operator, k is the wavenumber, and h is the water depth) and thus neglected second-order bottom effect terms proportional to O($\nabla$h)$^2$ and O($\nabla$$^2$h). (omitted)

• Journal of Welding and Joining
• /
• v.15 no.3
• /
• pp.109-117
• /
• 1997

The temperature gradient in weldment changes the transit time and distorts the direction of the ultrasound beam to the higher temperature regions due to the lower sound speed in the hotter regions of the weldment. This paper describes a ray-tracing method for calculating the effects of temperature gradients on ultrasonic propagation in fillet arc weldig. In the method, weldment is conceptually devided into a number of layers and the refraction and sound speed at each layer is calculated using the temperature which calculated from analytical solution. Calculating the time and location of echoes arrived from various interfaces around a molten weld pool determines the optimum location of ultrasonic transducers and the correct position of flaws.

• ETRI Journal
• /
• v.31 no.2
• /
• pp.225-227
• /
• 2009

A new planar metamaterial (MTM) with simultaneous negative values of permittivity (${\varepsilon}$) and permeability (${\mu}$) is proposed. Our MTM is composed of two identical copper patterns etched on both sides of dielectric laminate, which is very thin and easy to fabricate. Unlike conventional MTMs, the proposed structure shows a negative refractive index (NRI) behavior with respect to a normally incident wave. To explain the underlying principle of the NRI characteristics, an equivalent resonant circuit model based on surface current density distribution is investigated. An eigenmode analysis and a three-dimensional wave simulation for the stacked MTM prism are also performed to verify the existence of negative refraction. The experimental results from the transmission and reflection measurement ensure the validity of our design approach and show good agreement with the theoretically predicted effective medium parameters.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.6 no.3
• /
• pp.260-265
• /
• 1994

A new set of elliptic wave equations describing the deformations of irregular waves on a large-scale current field in water of irregular depth is given, and using finite difference scheme an efficient numerical method is also presented. The elliptic equations are solved in a similar way to Initial value problem. This method is extensively used for the calculation of wave spectral transformation. and computation results agree very well with experimental data (Hiraishi, 1991). Finally numerical examples are presented concerning the interactions between waves and currents over a mildly sloping beach and also over a mound.