• Journal of Navigation and Port Research
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• v.33 no.1
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• pp.65-70
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• 2009

The hybrid numerical model is developed by combining BEM that can calculate the wave motion rapidly under the potential theory and CADMAS-SURF that solves Navier-Stokes equations for the free surface variation near the structure, In the hybrid model the calculation of wave motion in a wide field of wave reflection for deep water area is conducted by BEM but for shallow water area by CADMAS-SURF. Especially the hybrid model can calculate random wave motions for long term period more rapidly with almost similar accuracy than the calculation of wave motion which was carried out by CADMAS-SURF only. In this study the coupling model was applied to the calculation of the strong nonlinear wave motion such as wave runup and overtopping at the coastal structure on the mild-slope bottom and the results of numerical model were compared with the Toyosima's experiments of regular wave runup and Goda's design diagram of ramdom wave overtopping, respectively.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.6
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• pp.233-246
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• 2022

The design and the construction were carried out by installing new caissons on the back or the front of existing caissons to increase the structural stability of caisson breakwaters. In this study, we used the ANSYS AQWA program to analyze the wave forces acting on individual caissons according to the effects of wave-structure interaction when new caissons were additionally installed on existing caisson breakwaters. The wave force characteristics acting on the individual caisson were analyzed according to the distance among caissons in frequency domain analysis. In addition, the dynamic wave force characteristics were closely examined on the basis of the frequency at which the unusual distribution of wave forces occurs in irregular wave conditions using time domain analysis.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.5
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• pp.203-216
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• 2021

Analyzing various wave interactions with oscillating wave surge converters (OWSC) is essential because they must be operated efficiently under a wide range of wave conditions and designed to extract optimal wave energy. In the conceptual design and development stage of OWSC, numerical analysis can be a good alternative as a design tool. This study performed a numerical analysis on the behavioral characteristics of the inverted triangle flap against the incident waves using open source CFD to examine the essential behavioral attributes of OWSC. Specifically, the behavioral characteristics of the structure were studied by calculating the free water surface displacement and the flap rotation angle near the inverted triangular flap according to the change of the period under the regular wave conditions. By comparing and examining the numerical analysis results with the hydraulic model experiments, the validity of the analysis performed and the applicability in analyzing the wave-structure interactions related to OWSC was verified. The numerical analysis result confirmed that the hydrodynamic behavior characteristic due to the interactions of the wave and the inverted triangle flap was well reproduced.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.3
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• pp.151-158
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• 2003

The study of velocity fields and vortex generation around the submerged breakwater can be utilized as materials related to understanding of wave dissipation mechanism, sediment transport, and stability of structure. In the present study, two-dimensional numerical wave flume, based on the VOF method to trace free surface, developed by Kim et al.(2001, 2002) was used to numerically simulate velocity fields and vortex generation around the impermeable submerged breakwater installed at the uniform bottom. Especially, the characteristics of vortex generation due to the geometry of the structure and incident wave conditions are examined through the analysis of averaged-velocity fields around the impermeable submerged breakwater. From the numerical simulations, it is confirmed that a counter clockwise vortex is formed in front of the structure and a clockwise vortex develops behind the structure. Also, incident wave height and period have an sensitive effect on the strength of vortex.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.1
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• pp.111-117
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• 2010

A three-dimensional numerical model is employed to investigate wave deformation due to a submerged structure. The three-dimensional numerical model solves the spatially averaged Navier-Stokes equations for two-phase flows. The LES(large-eddy-simulation) approach is adopted to model the turbulence effect by using the Smagorinsky SGS(sub-grid scale) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate VOF(volume-of-fluid) method is used to track the distorted and broken free surface. A simple linear wave is generated on a constant depth and compared with analytical solutions. The model is then applied to study wave deformation due to a submerged structure and the predicted results are compared with available laboratory measurements.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.12
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• pp.1259-1263
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• 2004

In this paper, the optimum design of ultrasonic dry cleaning head was investigated. The transducer instead of mechanical dynamic structure was used to generate ultrasonic wave and the horn-shape amplifier was utilized to solve the energy decaying problem of ultrasonic wave with propagating it through the media. The analyses of ultrasonic wave and a fluid for the selected structure of a cleaning head were carried out using SYSNOISE and ANSYS simulators, respectively. Based on simulator results, the distance between a horn and the substrate of 4 mm and the horn diameter of 10 mm were determined to maximize the energy of ultrasonic waves. The cooling structure was also considered to reduce the heat from the transducer and the horn. The equivalent circuit for the fabricated horn was deduced from HP4194A impedance/gain/phase analyzer and the frequency of an ultrasonic wave of 20.25 kHz was confirmed using the parameters of the equivalent circuit.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.2
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• pp.146-151
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• 2016

This study concentrates on the design of floater for 15kW-class wave energy converter that extracts the ocean energy by oscillating vertically along the wave motion. The floater connects to a arm structure that connects to a hydraulic cylinder, which drives a hydraulic generator. The study mainly focuses on the structural analysis of the floater. Previous studies have been conducted using a miniature model; however, this study focuses on the size selection of the floater for a full scale model. Static structural analysis is conducted using fine numerical grids. Due to the complexity of the whole model, it is analyzed as a separate component. There are several load cases for each floater size, and they are analyzed thoroughly for stress (von-mises, shear, and normal) and deformation. The initial design was conducted by scaling up from the miniature model of the previous study, and the final design has been redesigned by changing the thickness and internal support structure shape.

• Journal of the Korean Society of Visualization
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• v.22 no.1
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• pp.18-27
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• 2024

A series of shock wave pulses with Mach number 2.2 of 100, 200, and 300 shocks were applied to lead sulfide (PbS) nanomaterials at intervals of 5 sec per shock pulse. To investigate the crystallographic, electronic, and magnetic phase stabilities, powder X-ray diffractometry (XRD), diffused reflectance spectroscopy (DRS), and vibrating-sample magnetometry (VSM) were employed. The material exhibited a rock salt structure (NaCl-type structure); XRD results indicated that material is monoclinic with space group C121 (5). Further, XRD results showed shifts due to lattice contraction and expansion when material was subjected to shock wave pulses, indicating stable material structure. Based on the data obtained, we believe that the PbS material is a good choice for high-pressure, high-temperature, and aerospace applications due to its superior shock resistance characteristics.

• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.43-47
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• 2009

This paper compares theoretical wave profile and particle kinematics with experimental results generated by a 2 D wave tank. Particle velocity fields of compound waves were acquired using a PIV technique. Synchronization was applied to acquire images of the wave fields, and the time gap between these images was controlled by the user. This technique was applied to investigate the wave breaking mechanism, and the wave profile and velocity distribution in a wave breaking field was obtained.

• Journal of Biosystems Engineering
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• v.23 no.6
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• pp.615-620
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• 1998

The nondestructive internal quality evaluation of agricultural products has been strongly required from the needs for individual inspection. In recent, ultrasonic wave has been considered as a solution for this problem. It transmit well through most materials and can handle safely and easily. However, specially in a watermelon, it is known that general frequency band (higher than 20kHz) ultrasonic waves do not transmitted well due to severe attenuation. The objectives of this study were to find out the proper waveform and frequency of the ultrasonic waves that transmit well inside the watermelon, and to analyze the transmitted waveform in order to make clear the structure of wave propagation in watermelon. The result of several experiments showed that 2kHz shear wave was the most suitable for the detection of internal cavity in the watermelon. Also, it was found that the surface wave did not influence the directly transmitted bulk wave. These results could be a basis of application of ultrasonic wave on the evaluation of internal quality of the watermelon.