• Journal of Advanced Marine Engineering and Technology
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• v.36 no.5
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• pp.627-634
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• 2012

This study includes results of basin test for hydrodynamic performance evaluation with a developed inflatable kayak. Inclining experiment and turning trial experiment of the developed inflatable kayak and an abroad product were carried out in the Ocean engineering Basin. Resistance test was carried out by using downscale model in the circulating water channel. Through method of following performance evaluation, advantage and disadvantage of the developed inflatable kayak were compared with those of the abroad product.

• Journal of Ocean Engineering and Technology
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• v.25 no.1
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• pp.8-13
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• 2011

A compact array system of small buoys is used for wave energy extraction. To evaluate the performance of this system, hydrodynamic analysis is carried out in regular waves using the higher order boundary element method. The motion response of each buoy is calculated considering hydrodynamic interactions caused by other buoys. The effect of energy extraction device is modeled as a linear damping load. The efficiencies of energy conversion are compared using the various sizes and arrangements of the array system and the damping coefficients for energy extraction. The increase in size or the packing ratio of the system gives better efficiency. However, the wave condition and the cost for the system should be considered to optimize performance from the perspective of engineering and economics. The proposed nondimensionalized damping coefficient for energy extraction is 0.1~0.5.

• Journal of Ship and Ocean Technology
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• v.8 no.1
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• pp.31-41
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• 2004

A ducted marine propulsor has been widely used for the thruster of underwater vehicles for protecting collision damage, increasing propulsive efficiency, and reducing cavitation. Since a single-stage ducted propulsor contains a set of rotor and stator inside an annular duct, the numerical analysis becomes extremely complex and computationally expensive. However, the accurate prediction of viscous flow past a ducted marine propulsor is essential for determining hydrodynamic forces and the propulsive performances. To analyze a ducted propulsor having rotor-stator Interaction, the present work has solved 3D incompressible RANS equations on the sliding multiblocked grid. The flow of a single stage turbine flow was simulated for code validation and time averaged pressure coefficients were compared with experiments. Good agreement was obtained. The hydrodynamic performance coefficients were also computed.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.98-103
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• 2004

This paper presents modeling and simulation of the bump foil bearings with consideration of the elastic behavior of the foil and gas compressibility. Heshmat had originally introduced the simple compliance model to estimate the EHL(elasto-hydrodynamic lubrication) performance. But this approach can not consider the deflection of top foil at the edge of bearing, so model is insufficient to analyze in case that the eccentricity ratio is greater than I. So the top foil is considered as a simple beam model supported by linear spring elements, and the bump foil deflection can be simple compliance model. The EHL calculations are performed for convention rigid type, classical foil type, variable pitch type and double bump type toil bearings. This paper presents that 2nd or 3rd generation bearings have excellent performance in every speeds.

• Advances in aircraft and spacecraft science
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• v.7 no.4
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• pp.309-333
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• 2020

The proposed study aims to numerically investigate the performance of hydrofoils in the context of amphibious aircraft application. In particular, we also study the effectiveness of a slotted hydrofoil in minimizing the cavitation phenomenon, to improve the overall water take-off performance of an amphibious aircraft. We use the ICON A5 as a base model for this study. First, we propose an approach to estimate the required hydrofoil surface area and to select the most suitable airfoil shape that can minimize cavitation, thus improving the hydrodynamic efficiency. Once the hydrofoil is selected, we perform 2D numerical studies of the hydrodynamic and cavitating characteristics of a non-slotted hydrofoil on ANSYS Fluent. In this work, we also propose to use a slotted hydrofoil to be a passive method to control the cavitation performance through the boundary layer control. Numerical results of several slotted configurations demonstrate notable improvement on the cavitation performance. We then perform a multiobjective optimization with a response surface model to simultaneously minimize the cavitation and maximize the hydrodynamic efficiency of the hydrofoil. The optimization takes the slot geometry, including the slot angle and lengths, as the design variables. In addition, a global sensitivity study has been carried and it shows that the slot widths are the more dominant factors.

• Journal of Ocean Engineering and Technology
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• v.20 no.6 s.73
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• pp.24-34
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• 2006

Hydrodynamic coefficients strongly affect the dynamic performance of an AUV. Thus, it is important to know the true values of these coefficients, in order to accurately simulate the AUV's dynamic performance. Although these coefficients are generally obtained experimentally, such as through the PMM test, the measured values are not completely reliable because of experimental difficulties and errors. Another approach, by which these coefficients can be obtained, is the observer method, in which a model-based estimation algorithm estimates the coefficients. In this paper, the hydrodynamic coefficients are estimated using two nonlinear observers: a sliding mode observer and an extended Kalman filter. Their performances are evaluated in Matlab simulations, by comparing the estimated coefficients obtained from the two observer methods, with the experimental values as determined from the PMM test. A sliding mode controller is constructed for the diving and steering maneuver by using the estimated coefficients. It is demonstrated that the controller, applied with the estimated values, maintains the desired depth and path with sufficient accuracy.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.10
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• pp.1017-1022
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• 2015

Specific hydrodynamic characteristic of pump-turbine during the start and load rejection process of generating mode causes anomalous increase of water pressure, along with large machine vibration, called "S" characteristic. The aim of this study is to understand and explain the hydrodynamic performance of pump-turbine at "S" characteristic region by using a model of pump-turbine system. The operation in the condition of runway and low discharge in a typical "S" characteristic curve may become unstable and complex flow appears at the passage of guide vane and impeller. Therefore, velocity and pressure distribution are investigated to give an all-sided explanation of the formation and phenomenon of this characteristic, with the assistance of velocity triangle analysis at the impeller inlet. From this study, the internal flow and pressure fluctuation at the normal, runway and low discharge points are explored, giving a deep description of hydrodynamic characteristic when the pump-turbine system operates with "S" characteristic.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.6
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• pp.995-1006
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• 2015

Underwater glider, as a new kind of autonomous underwater vehicles, has many merits such as long-range, extended-duration and low costs. The shape of underwater glider is an important factor in determining the hydrodynamic efficiency. In this paper, a high lift to drag ratio configuration, the Blended-Wing-Body (BWB), is used to design a small civilian under water glider. In the parametric geometric model of the BWB underwater glider, the planform is defined with Bezier curve and linear line, and the section is defined with symmetrical airfoil NACA 0012. Computational investigations are carried out to study the hydrodynamic performance of the glider using the commercial Computational Fluid Dynamics (CFD) code Fluent. The Kriging-based genetic algorithm, called Efficient Global Optimization (EGO), is applied to hydrodynamic design optimization. The result demonstrates that the BWB underwater glider has excellent hydrodynamic performance, and the lift to drag ratio of initial design is increased by 7% in the EGO process.

• Journal of Korean Society on Water Environment
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• v.27 no.4
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• pp.413-424
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• 2011

The study was aimed to evaluate the applicability of a three-dimensional (3D) hydrodynamic and water quality model, ELCOM-CAEDYM for Yongdam Reservoir, Korea. The model was applied for the simulations of hydrodynamics, thermal stratification processes, stream density flow propagation, and water quality parameters including dissolved oxygen, nutrients, organic materials, and algal biomass (chl-a) for the period of June to December, 2006. The field data observed at four monitoring stations (ST1~ST4) within the reservoir were used to validate the models performance. The model showed reasonable performance nevertheless low frequency boundary forcing data were provided, and well replicated the physical, chemical, and biological processes of the system. Simulated spatial and temporal variations of water temperature, nutrients, and chl-a concentrations were moderately consistent with the field observations. In particular, the model rationally reproduced the succession of different algal species; i.e., diatom dominant during spring and early summer, after then cyanobacteria dominant under warm and stratified conditions. ELCOM-CAEDYM is recommendable as a suitable coupled 3D hydrodynamic and water quality model that can be effectively used for the advanced water quality management of large stratified reservoirs in Korea.

• Earthquakes and Structures
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• v.14 no.2
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• pp.167-178
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• 2018

A roller compacted concrete (RCC) dam should be analyzed under seismic ground motions for different conditions such as empty reservoir and full reservoir conditions. This study presents three-dimensional earthquake response and performance of a RCC dam considering materially non-linearity. For this purpose, Cine RCC dam constructed in Aydın, Turkey, is selected in applications. The three-dimensional finite element model of Cine RCC dam is obtained using ANSYS software. The Drucker-Prager material model is considered in the materially nonlinear time history analyses for concrete and foundation rock. Furthermore, hydrodynamic effect was investigated in linear and non-linear dynamic analyses. Researchers observe that how the tensile and compressive stresses change by hydrodynamic pressure effect. The hydrodynamic pressure of the reservoir water is modeled with the fluid finite elements based on the Lagrangian approach. In this study, dam body and foundation are modeled with welded contact. The displacements and principle stress components obtained from the linear and non-linear analyses with and without reservoir water are compared each other. Principle stresses during earthquake were obtained at the most critical point in the upstream face of dam body. Besides, the change of displacements and stresses by crest length were investigated. Moreover demand-capacity ratio criteria were also studied under linear dynamic and nonlinear analysis. Earthquake performance analyses were carried out for different cases and evaluated. According to linear and nonlinear analysis, hydrodynamic water effect is obvious in full reservoir situation. On the other hand, higher tensile stresses were observed in linear analyses and then non-linear analyses were performed and compared with each other.