• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.09b
• /
• pp.958-960
• /
• 2005

• Journal of Ocean Engineering and Technology
• /
• v.32 no.5
• /
• pp.393-401
• /
• 2018

This paper reports a novel mobile-type wave energy harvesting system. The proposed system adopts a wave glider's propulsion mechanism. A wave glider's blades were mounted on a circular layout and generated a rotational motion. Combining the wave converting system with the wave glider, a mobile floating-type robotic buoy system was developed. It enabled the relocation of the buoy position, as well as station-keeping for long term operation. It had a small size and could efficiently harvest wave energy. A feasibility study and modeling were carried out, and a prototype system was constructed. Various tank tests were performed to optimize the proposed wave energy harvesting system.

• Geophysics and Geophysical Exploration
• /
• v.26 no.3
• /
• pp.114-125
• /
• 2023

The physics-informed neural network (PINN) has been proposed to overcome the limitations of various numerical methods used to solve partial differential equations (PDEs) and the drawbacks of purely data-driven machine learning. The PINN directly applies PDEs to the construction of the loss function, introducing physical constraints to machine learning training. This technique can also be applied to wave equation modeling. However, to solve the wave equation using the PINN, second-order differentiations with respect to input data must be performed during neural network training, and the resulting wavefields contain complex dynamical phenomena, requiring careful strategies. This tutorial elucidates the fundamental concepts of the PINN and discusses considerations for wave equation modeling using the PINN approach. These considerations include spatial coordinate normalization, the selection of activation functions, and strategies for incorporating physics loss. Our experimental results demonstrated that normalizing the spatial coordinates of the training data leads to a more accurate reflection of initial conditions in neural network training for wave equation modeling. Furthermore, the characteristics of various functions were compared to select an appropriate activation function for wavefield prediction using neural networks. These comparisons focused on their differentiation with respect to input data and their convergence properties. Finally, the results of two scenarios for incorporating physics loss into the loss function during neural network training were compared. Through numerical experiments, a curriculum-based learning strategy, applying physics loss after the initial training steps, was more effective than utilizing physics loss from the early training steps. In addition, the effectiveness of the PINN technique was confirmed by comparing these results with those of training without any use of physics loss.

• 한국방재학회:학술대회논문집
• /
• 2007.02a
• /
• pp.137-139
• /
• 2007

To enhance capability on discerning local and regional seismic phases, such as, Pn, Pg, Sn, Rg, etc, within the crust, 2-D numerical forward modeling will be applied to the data obtained from local seismic stations by simulating almost all waves including not only body wave but also surface wave generated without having to explicitly include them under consideration of Q factor. In this study, after getting rid of instrumental response by deconvolution, pseudo-spectral method instead of relying on typical numerical methods, such as, FEM(Finite Element Method) and FDM(Finite Difference Method), will be implemented for 2-D numerical forward modeling by considering velocities of P-wave and S-wave, density, and Q factors. Ultimately, the Power of reaching the enhanced capability on discerning local and regional seismic phases will make it easier for us to identify the seismic source, whether it is originated from man-made explosion or pure earthquake.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.28 no.6
• /
• pp.383-396
• /
• 2016

In this study, wave model was conducted on the presence or absence of water level changes and currents effects in coastal waters coexisting with waves and currents, then the results were compared. The flow field applied the results of the RIAMOM model and the wave model applied the SWAN model. Among ECMWF, NCEP and JMA, wind data applied JMA data sets which agreed well with the observed data comparatively. Numerical simulation was conducted for 8 months from January to August 2016. For each case, the deviation of wave height was calculated for the high wave of more than 2.5 m for comparison with observed data. As a result, the deviation of wave height was not significant both considering water level changes and currents effects or not at wave observation stations installed in deep waters. However, a significant deviation of wave height of 5~10% was obtained depending on water level changes and currents effects at the comparison point in shallow waters.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.7 no.1
• /
• pp.70-86
• /
• 2015

Short crested waves play an important role for planning and design of harbours. In this context a numerical simulation is carried out to evaluate wave tranquility inside a real harbour located in east coast of India. The annual offshore wave climate proximity to harbour site is established using Wave Model (WAM) hindcast wave data. The deep water waves are transformed to harbour front using a Near Shore spectral Wave model (NSW). A directional analysis is carried out to determine the probable incident wave directions towards the harbour. Most critical threshold wave height and wave period is chosen for normal operating conditions using exceedence probability analysis. Irregular random waves from various directions are generated confirming to Pierson Moskowitz spectrum at 20m water depth. Wave incident into inner harbor through harbor entrance is performed using Boussinesq Wave model (BW). Wave disturbance experienced inside the harbour and at various berths are analysed. The paper discusses the progresses took place in short wave modeling and it demonstrates application of wave climate for the evaluation of harbor tranquility using various types of wave models.

• Journal of Korea Water Resources Association
• /
• v.54 no.11
• /
• pp.943-953
• /
• 2021

The propagation of impact wave induced by landslide and debris flow occurred on the slope of lake, reservoir and bays is a three-dimensional natural phenomenon associated with strong interaction of debris flow and water flow in complex geometrical environments. We carried out 3D numerical modeling of such impact wave in a bay using a multiphase turbulence flow model and a rheology model for non-Newtonian debris flow. Numerical results are compared with previous experimental result to evaluate the performance of present numerical approach. The results underscore that the reasonable predictions of both thickness and speed of debris flow head penetrating below the water surface are crucial to accurately reproduce the maximum peak height and free surface profiles of impact wave. Two predictions computed using different initial debris flow thicknesses become different from the instant when the peaks of impact waves fall due to the gravity. Numerical modeling using relatively thick initial debris flow thickness appears to well reproduce the water surface profile of impact wave propagating across the bay as well as wave run-up on the opposite slope. The results show that the maximum run-up height on the opposite slope is not sensitive to the initial thickness of debris flows of same total volume. Meanwhile, appropriate rheology model for debris flow consisting of inviscid particle only should be employed to more accurately reproduce the debris flow propagating along the channel bottom.

• The Journal of the Acoustical Society of Korea
• /
• v.26 no.2E
• /
• pp.44-49
• /
• 2007

Donghae City - Ulleung Island Line (DC-UI Line) is a representative line for underwater and geoacoustic modeling in the middle western East Sea. In this line, an integrated model of P-wave velocity is proposed for a low-frequency range target (<200 Hz), based on high-resolution seismic profiles (2 - 7 kHz sonar and air-gun), shallow and deep cores (grab, piston, and Portable Remote Operated Drilling), and outcrop geology (Tertiary rocks and the basement on land). The basement comprises 3 geoacoustic layers of P-wave velocity ranging from 3750 to 5550 m/s. The overlying sediments consist of 7 layers of P-wave velocities ranging from 1500 to 1900 m/s. The bottom model shows that the structure is very irregular and the velocity is also variable with both vertical and lateral extension. In this area, seabed and underwater acousticians should consider that low-frequency acoustic modeling is very range-dependent and a detailed geoacoustic model is necessary for better modeling of acoustic propagation such as long-range surveillance of submarines and monitoring of currents.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2012.05a
• /
• pp.80-82
• /
• 2012

In this paper, we present electromagnetic modeling to design unclonable PUFs with frequency-dependant materials corresponding to Debye dispersion. To demonstrate FDTD calculations consider that 1-D problem of pulsed plane wave traveling in free space normally incident on air-silicon material interface. The pulse traveling wave at a vacuum-medium interface were reflected, and transmitted wave were dissipated. As a result, 1-D PUF with Debye dispersion material structure can be applied and FDTD calculation for PUF modeling is a good approximation.

• 한국전산유체공학회:학술대회논문집
• /
• 1998.05a
• /
• pp.117-122
• /
• 1998

A numerical study is carried out to investigate the transient process of combustion phenomena associated with hypersonic propulsion devices. Reynolds averaged Navier-Stokes equations for reactive flows are used as governing equations with a detailed chemistry mechanism of hydrogen-air mixture and two-equation SST turbulence modeling. The governing equations are discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit time accurate method. At first, oscillating shock-induced combustion is analyzed and the comparison with experimental result gives the validity of present computational modeling. Secondly, the model ram accelerator experiment was simulated and the results show the detailed transient combustion mechanisms. Thirdly, the evolution of oblique detonation wave is simulated and the result shows transient and final steady state behavior at off-stability condition. Finally, shock wave/boundary layer interaction in combustible mixture is studied and the criterion of boundary layer flame and oblique detonation wave is identified.