• Journal of Korea Water Resources Association
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• v.47 no.11
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• pp.1051-1060
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• 2014

This study is attempted to realize an improved computation performance by combining the MPI (Message Passing Interface) Technique, a standard model of the parallel programming in the distributed memory environment, with the DHM(Diffusion Hydrodynamic Model), a inundation analysis model. With parallelizing inundation model, it compared with the existing calculation method about the results of applications to complicate and required long computing time problems. In addition, it attempted to prove the capability to estimate inundation extent, depth and speed-up computing time due to the flooding in protected lowlands and to validate the applicability of the parallel model to the actual flooding analysis by simulating based on various inundation scenarios. To verify the model developed in this study, it was applied to a hypothetical two-dimensional protected land and a real flooding case, and then actually verified the applicability of this model. As a result of this application, this model shows that the improvement effectiveness of calculation time is better up to the maximum of about 41% to 48% in using multi cores than a single core based on the same accuracy. The flood analysis model using the parallel technique in this study can be used for calculating flooding water depth, flooding areas, propagation speed of flooding waves, etc. with a shorter runtime with applying multi cores, and is expected to be actually used for promptly predicting real time flood forecasting and for drawing flood risk maps etc.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.5
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• pp.505-511
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• 2023

In the present study, a deep learning model was established to predict the motion response of small fishing vessels. Hydrodynamic performances were evaluated for two small fishing vessels for the dataset of deep learning model. The deep learning model of the Long Short-Term Memory (LSTM) which is one of the recurrent neural network was utilized. The input data of LSTM model consisted of time series of six(6) degrees of freedom motions and wave height and the output label was selected as the time series data of six(6) degrees of freedom motions. The hyperparameter and input window length studies were performed to optimize LSTM model. The time series motion response according to different wave direction was predicted by establised LSTM. The predicted time series motion response showed good overall agreement with the analysis results. As the length of the time series increased, differences between the predicted values and analysis results were increased, which is due to the reduced influence of long-term data in the training process. The overall error of the predicted data indicated that more than 85% of the data showed an error within 10%. The established LSTM model is expected to be utilized in monitoring and alarm systems for small fishing vessels.

• Journal of Navigation and Port Research
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• v.38 no.4
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• pp.335-341
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• 2014

Faced with global agenda of greenhouse abatement program including regulations and $CO_2$ emission trading scheme, shipping companies are enforced to a high level of efficiency in fuel consumption. Accordingly shipbuilding companies worldwide are required to develop fuel-efficient ships which otherwise traditionally consume a great amount of fossil fuels. In this dissertation, relevant to the improvement of fuel efficiency for commercial ships, design methodology through the numerical simulations are intensively described. This work consists of derivation of effective hydrodynamic design practice based on the application of longitudinal grooves to effectively improve the pressure distribution around ship hull. The primary objective of the present study is to improve ship resistance performance using longitudinal grooves which originate from long strips on the abdomen of humpback whale. Several groove shapes have been extensively investigated and the proposed shape efficiently controlled the variation of pressure distributions acting on the hull surface.

• Journal of Korean Society on Water Environment
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• v.26 no.2
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• pp.231-242
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• 2010

The objective of study was to determine an optimal location of a float-type curtain weir in Daecheong Reservoir and to assess its effectiveness for the control of algal blooms in the reservoir. CE-QUAL-W2, a laterally averaged two-dimensional hydrodynamic and eutrophication model, was modified to accommodate vertical displacement of the weir according to water surface fluctuation and applied to simulate the reservoir hydrodynamics and water quality changes for the reservoir. The model calibrated in a previous study was updated and validated for different hydrological conditions representing drought year (2008) and normal year (2006) for the study, and adequately simulated the temporal and spatial variations of water temperature, nutrients and algal (Chl-a) concentrations. The effectiveness of curtain weir on the control of algal bloom was evaluated by applying the validated model to 2001 and 2006 assuming 9 scenarios for different installation locations. The reduction rates of algal concentration were placed in the range of 11.2~40.3% and 20.3~56.7% for 2001 and 2006, respectively. Although, the performance of curtain weir was slightly varied for different locations and different hydrological years, overall, the performance was improved as the weir was installed further downstream.

• Journal of the Korean Society for Marine Environment & Energy
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• v.20 no.2
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• pp.91-99
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• 2017

The parametric study was performed for performance enhancement of wave energy converter(WEC) using a submerged pendulum plate. The wave exciting moment and hydrodynamic moment were obtained by means of eigenfunction expansion method based on the linear potential theory, and then the roll response of a pendulum plate and time averaged extracted power were investigated. The optimal PTO damping coefficient was suggested to give optimal extracted power. The peak value of optimal extracted power occurs at the resonant frequency. The resonant peak and it's width increase, as the height and thickness of a pendulum plate increase. The mooring line installed at the end of the pendulum plate is effective for extracting wave energy because it can not only induce the resonance with the waves of the installation site but also increase the restoring moment in case of PTO-on. The WEC using a rolling pendulum plate suitable for the shallow water acts as breakwater as well as energy extraction device.

• Particle and aerosol research
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• v.9 no.4
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• pp.261-269
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• 2013

The chemical mechanical polishing (CMP) process is widely used in semiconductor manufacturing process for planarization of various materials and structures. Point-of-use (POU) filters are used in most of the CMP processes in order to reduce the unwanted micro-scratches which may result in defects. The performance of the POU filter is depends on type and size of the abrasives used during cleaning process. For this reason, there is a need to evaluate POU filters for their filtration efficiency (FE) with different types of abrasives. In this study, we developed filter test system to evaluate the FE of POU using ceria and silica abrasives (slurry). The POU filter is roll type capsule filter with retention size of 0.2 ${\mu}m$. Two POU filters of different make are evaluated for FE. We observed that both POU filters show similar filtration efficiency for silica and ceria slurry. Results reveal that the ceria slurry and the colloidal silica particle are removed not only by mechanical way but also hydrodynamic and electrostatic interaction way.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.4
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• pp.82-91
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• 2003

Experiments to investigate the mixing performance of unlike doublet impinging jets are conducted. Reynolds number of simulants used in this study rages from 1.0 to 1.5 Cold flow test is performed to investigate the hydrodynamic effect and spray of the impinging jets are collected locally and calculated by using Rupe's mixing efficiency equation. Momentum exchanges and relative velocity ratio between two jets are taken as the main parameter to represent the effect of enlargement of the orifice diameter. As diameter ratio increases, the corresponding momentum ratio where maximum mixing efficiency occurs and relative velocity at the maximum mixing efficiency ranges 0.6 to 0.7, respectively. Penetration depth can be taken as a prominent parameter to estimate the mixing efficiency.

• Tribology and Lubricants
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• v.36 no.4
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• pp.193-198
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• 2020

Fluid film bearings are among the best devices used for overcoming friction and reducing wear. Surface texturing is a new surface treatment technique used for processing grooves and dimples on the lubricated surface, and it helps to minimize friction further and improve the wear resistance. In several studies, parallel surfaces, such as thrust bearings and mechanical face seals, have been investigated, but most sliding bearings have a convergent film shape. This paper presents the third part of a recent study and focuses on the effect of the groove shape on the lubrication performance of inclined slider bearings, following the two previous papers on the effects of the groove position and depth. We adopted the continuity and Navier - Stokes equations to conduct numerical analyses using FLUENT, which is a commercial computational fluid dynamics code. The groove shape adopted in the numerical analysis is rectangular and triangular, and its depth is varied. The results show that the streamlines, pressure distributions, and groove shape significantly influence the lubrication performance of the inclined slider bearing. For both shapes, the load-carrying capacity (LCC) is maximum near the groove depth, where vortices occur. In the shallow grooves, the LCC of the rectangular shape is higher, but in deeper grooves, that of the triangular shape is higher. The deeper the rectangular groove, the higher the decrease in the frictional force. The results of this study can be used as design data for various sliding bearings.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.11
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• pp.1868-1878
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• 2016

This paper proposes a novel velocity estimator for long-term underwater navigation of autonomous underwater vehicles(AUVs). Provided that an external position fix is not given, a viable goal in designing a underwater navigation algorithm is to reduce the divergence rate of position error only using the sporadic velocity information obtained from Doppler velocity log(DVL). For such case, the performance of underwater navigation eventually depends on accuracy and reliability of external velocity information. This motivates us to devise a velocity estimator which can drastically enhance the navigation performance even when the DVL measurement is unavailable. Incorporating the Gertler-Hagen hydrodynamics model of an AUV with the measurement models of velocity and depth sensors, the velocity estimator design problem is resolved using the extended Kalman filter. Different from the existing methods in which an AUV simulator is regarded as a virtual sensor, our approach is less sensitive to the model uncertainty often encountered in practice. This is because our velocity filter estimates the simulator errors with sensor aids and furthermore compensates these errors based on the indirect feedforward manner. Through the simulations for typical AUV navigation scenarios, the effectiveness of the proposed scheme is demonstrated.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.3
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• pp.345-352
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• 2009

The purpose of inlet baffle is to distribute the flow uniformly over the entire cross-sectional area of the sedimentation basin. The goal when designing this baffle is to achieve some head loss while keeping the velocity gradients through the ports equal to the velocity gradient in the end of the flocculator, so as to not break up the flocs. Sedimentation tank performance is strongly influenced by hydrodynamic and physical effects such as inlet design. This study was conducted to evaluate the effect of open ratio of the inlet baffle on hydraulic behavior within a rectangular sedimentation basin using CFD simulation and ADV technique. In order to verify the CFD simulation, we measured the factual velocity at 18 points in the full-scale sedimentation basin at Y water treatment plant. Good agreement was obtained between the CFD predictions and the experimentally measured data. From the simulation results of the existing basin with 7.4 % open ratio, it was investigated that extreme decrease in velocity occurred in the middle of basin. Since then, flow features was unstable. The region which the velocity decrease rapidly moved forward to the flow direction in proportion to the increase of inflow velocity. Also, it was investigated that the flow characteristic of 6.0 % open ratio was significantly different from 7.4 % open ratio at the same configuration condition. These results are a clear indication that inflow momentum and open ratio are the parameters affecting the characteristics of hydraulic patterns. The influence of these parameters on the sedimentation performance requires further study.