• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.382-388
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• 2017

This study performed an OpenFOAM-based numerical modeling for simulating performance of wave reduction by a floating vertical plate. Based on the Waves2FOAM library, an internal wave generation and energy dissipation with sponge layers schemes were further implemented. The performance of wave generation and dissipation was first tested with a simple two-dimensional analysis. Then, numerical simulation was carried out with the experimental data of Briggs et al. (2001) for the two regular wave cases. In general, the modeling results agreed well with the experimental data, showing better agreement than the numerical analysis by WAMIT that is included in Briggs et al. (2001).

• Clinics in Shoulder and Elbow
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• v.7 no.1
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• pp.35-40
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• 2004

Purpose: The aim of this study was to investigate effects of calcific lesion on shockwave therapy of the tennis elbow. Materials and Methods: twenty-four patients with refractory tennis elbow were treated with shock waves. The patients were evaluated by assessment of pain using visual analog scale (VAS) and simple elbow test (SET). Comparision of clinical outcomes for the patients with and without calcification in the extensor tendon and/or cortical irregularity of lateral condyle was tried to determine if this could be a possible prognostic factor in clinical settings. Overall clinical outcomes were evaluated by Roles and Maudsley score at 12 months after ESWT. Results: Significant improvement of symptoms were observed in 20 (83 %) patients at 12 months follow up according to Roles and Maudesley scores. The patients with calcification and/or cortical irregularity improved significantly better, when compared to the patients without calcification and/or cortical irregularity at follow up. Conclusion: This study suggests that shock waves therapy could be considered as effective and noninvasive treatment modality for refractory tennis elbow. Also calcific deposit in extensor tendon and/or cortical irregularity of the lateral epicondyle was seem to be good prognostic factor for shock wave therapy for tennis elbow

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.6
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• pp.578-586
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• 2010

This paper describes a theoretical model and acoustic analysis of hysteresis of contacting surfaces subject to compression pressure. Contacting surfaces known to be nonlinear and hysteretic is considered as a simple spring that has a complex stiffness connecting discontinuous displacements between two solid contact boundaries. Mathematical formulation for 1-D interfacial wave propagation between two contacting solids is developed using the complex spring model to derive the dispersion relation between the interface wave speed and the complex interfacial stiffness. Existence of the interface wave propagating along the hysteretic interface is studied in theory and discussed by investigating the solution to the dispersion equation. Unlike the linear interface without hysteresis, there can exist only one distinct mode of interface waves for the hysteretic interface, which is anti-symmetric motion. The anti-symmetric mode of interface wave propagates with the velocity faster than the Rayleigh surface wave but less than the shear wave depending on the interfacial stiffness. If the contacting surfaces are compressed so much that the linear interfacial stiffness is very high, the hysteretic stiffness does not affect the interface wave velocity. However, it has an effect on the speed of interface wave for a loosely contact surfaces with a relatively low linear stiffness. It is also found that the phase velocity of anti-symmetric wave mode converges to the shear wave velocity in despite of the linear stiffness value if the hysteretic stiffness approaches 0.5.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.8-15
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• 2005

Wave energy has been considered to be one of the most promising energy resources for the future, as it is pollution-free and an abundant natural resource. However, since it has drawbacks of non-stationary energy density, it is necessary to change the wave energy into a simple concentrated energy. Progressive waves in a coastal area can be amplified, swashed, and overtopped by a wave overtopping control structure. By conserving the quantity of overflow in a reservoir, the kinetic energy of the waves can be converted to the potential energy with a hydraulic head above the mean sea level. The potential energy in the form of a hydraulic head can be utilized to produce electric power, similar to hydro-electric power generation. This study aims to find the most optimal shape of wave overtopping structure for maximum overtopping volume of sea water; for this purpose, we carried out the wave overtopping experiment in a wave tank, under both regular and irregular wave conditions.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.1
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• pp.72-79
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• 2011

Typical results obtained by a newly developed, nonlinear time domain hybrid method for simulating large amplitude motions of ships advancing with constant forward speed in waves are presented. The method is hybrid in the way of combining a time-domain transient Green function method and a Rankine source method. The present approach employs a simple double integration algorithm with respect to time to simulate the free-surface boundary condition. During the simulation, the diffraction and radiation forces are computed by pressure integration over the mean wetted surface, whereas the incident wave and hydrostatic restoring forces/moments are calculated on the instantaneously wetted surface of the hull. Typical numerical results of application of the method to the seakeeping performance of a standard containership, namely the ITTC S175, are herein presented. Comparisons have been made between the results from the present method, the frequency domain 3D panel method (NEWDRIFT) of NTUA-SDL and available experimental data and good agreement has been observed for all studied cases between the results of the present method and comparable other data.

• Journal of Korean Port Research
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• v.15 no.1
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• pp.47-56
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• 2001

A numerical model for practical use based on the 1-line theory is presented to simulate shoreline changes due to construction of offshore structures. The shoreline change model calculates the longshore sediment transport rate using breaking waves. Before the shoreline change model execution, a wave model, adopting the modified Boussinesq equation including the breaking parameters and bottom friction term, was used to provide the longshore distribution of the breaking waves. The contents of present model are outlined first. Then to examine the characteristics of this model, the effects of the parameters contained in this model are clarified through the calculations of shoreline changes for simple cases. Finally, as the guides for practical application of this model, several comments are made on the parameters used in the model, such as transport parameter, average beach slope, breaking height variation alongshore, depth of closure, etc. with the presentation of typical examples of 3-dimensional movable bed experimental results for application of this model. Here, beach change behind the offshore structures is represented by the movement of the shoreline position. Analysis gives that the transport parameters should be taken as site specific parameters in terms of time scale for the shoreline change and adjusted to achieve the best agreement between the calculated and the observed near the structures.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.1 s.116
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• pp.76-81
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• 2007

In this paper, we analyzed the vulnerability of information leakage due to the leakage electromagnetic waves of a PC keyboard. First, we reviewed the keyboard protocol and hardware structure, we analyzed the correlation between the data signal, which is transmitted from the keyboard to the main body, and the leakage signal on the power cable. With the result, we grasped the cause of the Conducted Emission of a PC keyboard. Also, we compared the limit level of the CISPR 22 standard with the amplitude of the keyboard leakage electromagnetic waves we calculated. By analyzing the signal on the power cable of the PC main body through the simple experiment, we show that it is possible to extract the contents of the PC key. Therefore it is verified that the secret information of the PC user could leak out.

• Transactions on Electrical and Electronic Materials
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• v.9 no.5
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• pp.181-185
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• 2008

Using the extensional vibration mode of PZT ring, a piezopump is successfully made. The PZT ring is polarized with thickness direction. The traveling extensional wave along the circumference of the ring is obtained by dividing two standing waves which are temporally and spatially phase shifted by 90 degrees from each other. The proposed piezopump is consisted of coaxial cylindrical shells that are bonded piezoelectric ceramic ring. The pump takes an unobtrusive operation into the simple displacing mechanism using peristaltic traveling waves without the physical moving parts. The finite elements analysis on the proposed pump model is carried out to verify its operation principle and design by the commercial FEM software. Components of piezopump were made, assembled, and tested to validate the concepts of the proposed pump and confirm the simulation results. The performance of the proposed piezopump is about 580 ${\mu}l/min$ in flow rate with the highest pressure level of 0.85 kPa, when the driving voltage is 150 $V_p$, 57 kHz.

• Transactions on Electrical and Electronic Materials
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• v.9 no.5
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• pp.213-219
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• 2008

Pulse waves continuously change with respect to the characteristics and status of the cardiovascular system and in relation to the blood pressure (BP) and the pulse wave velocity (PWV). Monitoring the vascular condition by analyzing the variations in pulse waveforms has been used to diagnose vascular disorders and in drug treatment of arteriosclerosis and peripheral circulatory obstruction. In this paper, we investigated the vascular characteristic index with regard to the BP and classified by pulse wave signals. The pressure pulse wave and photoplethysmography (PPG) were measured simultaneously while subjects exercised, producing changes in the BP, to analyze the variation in the vascular characteristic index. We investigated the correlation between the BP and vascular characteristic index with regard to the classification methods of the pulse wave. The reflection index (RI) and vascular stiffness index were correlated with the diastolic BP, but no correlation was found between these parameters and the systolic BP. These results suggest the possibility of estimating BP through simple measurements of pulse waves.

• Journal of the Korea Society of Computer and Information
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• v.23 no.11
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• pp.129-135
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• 2018

In this study, we designed a model that can measure the level of user's concentration by measuring and analyzing EEG data of the subjects who are performing Continuous Performance Test based on visual stimulus. This study focused on alpha and beta waves, which are closely related to concentration in various brain waves. There are a lot of research and services to enhance not only concentration but also brain activity. However, there are formidable barriers to ordinary people for using routinely because of high cost and complex procedures. Therefore, this study designed the model using the portable EEG measurement device with reasonable cost and Visual Continuous Performance Test which we developed as a simplified version of the existing CPT. This study aims to measure the concentration level of the subject objectively through simple and affordable way, EEG analysis. Concentration is also closely related to various brain diseases such as dementia, depression, and ADHD. Therefore, we believe that our proposed model can be useful not only for improving concentration but also brain disease prediction and monitoring research. In addition, the combination of this model and the Brain Computer Interface technology can create greater synergy in various fields.