• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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• pp.205-211
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• 2005

In this study, a new numerical procedure for the generation of a nonlinear tailored group of waves is presented. The procedure is based on the transient wave group technique. In order to integrate the nonlinearity during the wave propagation in the computational method, the Navier-Stokes equations are applied as governing equations. The governing equations are discretized by finite volume approximation. The deformation of the free water surface in each time step is pursued with a moving grid. A two-dimensional, numerical wave tank for the simulation of the wave propagation is developed and tested in detail. The numeric results are compared first with analytical wave theories and with measurements, in order to examine the correctness of the numerical wave tank. Wave surface elevation and associated fields of velocity and pressure are numerically computed and compared with measurements. Very good agreements show up.

• Geomechanics and Engineering
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• v.13 no.5
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• pp.775-791
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• 2017

Surface wave techniques are widely used as non-invasive method for geotechnical site characterization. Field surface wave data are collected and analyzed using different processing techniques to generate the dispersion curves, which are further used to extract the shear wave velocity profile by inverse problem solution. Characteristics of a dispersion curve depend on the subsurface layering information of a vertically heterogeneous medium. Sometimes soft layer can be found between two stiff layers in the vertically heterogeneous media, and it can affect the wave propagation dramatically. Now most of the surface wave techniques use the fundamental mode Rayleigh wave propagation during the inversion, but this may not be the actual scenario when a soft layer is present in a vertically layered medium. This paper presents a detailed and comprehensive study using finite element method to examine the effect of soft layers which sometimes get trapped between two high velocity layers. Determination of the presence of a soft layer is quite important for proper mechanical characterization of a soil deposit. Present analysis shows that the thickness and position of the trapped soft layer highly influence the dispersion of Rayleigh waves while the higher modes also contribute in the resulting wave propagation.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.04a
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• pp.537-543
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• 1997

A new procedure for the advanced one-side measurement of longitudinal wave and surface wave velocities in concrete is presented in this paper. Stress waves are generated in a consistent fashion with a DC solenoid. Two piezoelectric accelerometers are mounted on the surface of a specimen as receivers. Stress waves propagate along the surface of the specimen and are detected by the receivers. In order to reduce the large incoherent noise levels of the signals, signals are collected and manipulated by a computer program for each velocity measurement. For a known distance between the two receivers and using the measured flight times, the velocities of the longitudinal wave and the surface wave are measured. The velocities of the longitudinal wave determined by this method are compared with those measured by conventional methods on concrete, PMMA and steel.

• Journal of Navigation and Port Research
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• v.37 no.3
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• pp.283-289
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• 2013

Wave profiles coming with oblique angle to trapezoidal submerged breakwater on the porous seabed are computed numerically by using a boundary element method. The analysis method is based on the wave pressure function with the continuity in the analytical region including fluid and structure. When compared with the existing results on the oblique incident wave, the results of this study show good agreement. The fluctuation of wave profiles is increased in the rear of the submerged breakwater due to the increase of the transmission coefficient, as the incident angle increases. In addition, in the case of the wave profiles passing over the submerged breakwater on porous seabed, it is able to verify that the attenuation of wave height occurs more significantly due to the wave energy dissipation than that of passing over the submerged breakwater on the impermeable seabed. The results indicate that wave profile own high dependability regarding the change of oblique incident waves and porous seabed. Therefore, the results of this study are estimated to be applied as an accurate numerical analysis referring to oblique incident waves and porous seabed in real sea environment.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.4
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• pp.18-24
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• 1999

The design method of a wave absorber for a perfectly conducting sphere is presented. The backscattered field from a coated sphere can be represented as the sum of the reflected field and the creeping wave. The wave absorber for a curved surface has been designed from that the reflection coefficient of the reflected field is zero. For the design of wave absorber for a small sized conducting sphere, the creeping wave should be considered as well as the reflected field. The perfect absorbing conditions are numerically searched using the Newton-Raphson method from the backscattered field of the eigenfunction series solution from a coated sphere. The wave absorber designed by this method exhibits a superior performance of absorption to that designed from the plate type absorbing condition.

• Journal of the Korean Chemical Society
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• v.5 no.1
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• pp.84-87
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• 1961

A polarographic method for rapid determination of Uranium in the presence of foreign ions was proposed. The method is based on the measurement of polarogram in the sulfuric acid as supporting electrolyte. In this medium Uranyl ions give well defined reduction waves, and half-wave potentials are -0.19V vs. S.C.E. as first wave, and uncertain volt. vs. S.C.E. as second wave in $2.4 N-H_2SO_4.$ The first wave has a linear relationship between the concentration of Uranyl ion and wave height. The author also studied a method for rapid determination of Uranium in Korean monazite sand without eliminating the foreign ions. The Korean monazite sands were analyzed by this method and satisfactory result were obtained.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.1
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• pp.95-104
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• 2011

As sea state harsher in the ocean space, more large motion and wave loads occurs on ships hull by non-linear phenomena. To consider nonlinear effect on ships hull in the structural design verification, the direct calculation method with numerical approach is used rather than rule values for the reliable accuracy. In this paper, the non-linear wave loads analysis in time domain is performed by using a Rankine Panel Method together with numerical schemes. Linear calculations have been carried out based on DNV CSA-2 notation to generate the motion responses and wave loads of large ships. By short and long term analysis, the design wave amplitudes are selected for the nonlinear analysis. The maximum wave induced bending moment in hogging and sagging conditions are calculated in the nonlinear analysis. Also, the green water effect on the wave induced vertical bending moment was investigated. The results show the vertical bending moments are more influenced by green water in sagging condition than in hogging condition due to green water loading.

• Journal of the Korean Geophysical Society
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• v.5 no.4
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• pp.321-328
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• 2002

Difficulties encountered in downhole S-wave (shear wave) surveys include the precise determination of shear wave travel times and determination of geophone orientation relative to the direction of polarization caused by the seismic source. In this study an S-wave enhancing and a principal component analysis method were adopted as a tool for determination of S-wave arrivals and the direction of polarization from downhole S-wave survey data. An S-wave enhancing method can almost double the amplitudes of S-waves, and the angle between direction of polarization and a geophone axis can be obtained by a principal component analysis. Once the angle is obtained data recorded by two horizontal geophones are transformed to principal axes, yielding so called scores. The scores gathered along depth are all in-phase, consequently, the accuracy of S-wave arrival picking could be remarkably improved. Applying this processing method to the field data reveals that the test site consists of a layered ground earth structure.

• Journal of Korea Society of Digital Industry and Information Management
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• v.13 no.4
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• pp.91-98
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• 2017

Previous works for detecting arrhythmia have mostly used nonlinear method such as artificial neural network, fuzzy theory, support vector machine to increase classification accuracy. Most methods require higher computational cost and larger processing time. Therefore it is necessary to design efficient algorithm that classifies PVC(premature ventricular contraction) and decreases computational cost by accurately detecting minimal feature point based on only R peak through optimal R wave. We propose an optimal R wave detection and PVC classification method through extracting minimal feature point in IoT environment. For this purpose, we detected R wave through optimal threshold value and extracted RR interval and R peak pattern from noise-free ECG signal through the preprocessing method. Also, we classified PVC in realtime through RR interval and R peak pattern. The performance of R wave detection and PVC classification is evaluated by using record of MIT-BIH arrhythmia database. The achieved scores indicate the average of 99.758% in R wave detection and the rate of 93.94% in PVC classification.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.3
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• pp.209-218
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• 1995

Nonlinear interaction between directional wave components is theoretically analyzed in deep water. The perturbed solution for an irregular wave is derived accurate up to the third order of the wave steepness and it is shown that the wave characteristics are modulated due to the nonlinear interaction. The convergence rate of the perturbed solution depends on not only wave steepness but also wavelength ratio between wave components. The long-wave component of the perturbed solution converges rapidly. while the short-wave solution converges slowly or diverges. The short wave properties in a broad-band wave spectrum cannot accurately be obtained by the conventional wave-mode method because it fails to properly describe the modulation of short-wave frequency caused by the nonlinear interaction with much longer wave.