• Journal of the Korea Computer Graphics Society
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• v.24 no.4
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• pp.21-27
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• 2018

In this paper, we propose a real-time interaction method using user's mouth wind in mobile device. In mobile and virtual reality, user interaction technology is important, but various user interface methods is still lacking. Most of the interaction technologies are hand touch screen touch or motion recognition. In this study, we propose an interface technology that can interact with real time using user's mouth wind. The direction of the wind is determined by using the angle and the position between the user and the mobile device, and the size of the wind is calculated by using the magnitude of user's mouth wind. To show the superiority of the proposed technique, we show the result of visualizing the flow of the vector field in real time by integrating the mouth-wind interface into the Navier-Stokes equations. We show the results of the paper on mobile devices, but can be applied in the Agumented reality(AR) and Virtual reality(VR) fields requiring interface technology.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.127-138
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• 1999

In this study steady state solutions of cavity flows driven by two moving walls are studied. The north and east walls of the cavity are movable where as the remaining two walls are fixed in space. Numerical experiments for three different driving schemes for moving walls are done at two different Reynolds numbers of Re=40 and 400. The first scheme is to accelerate north and east walls simultaneously. In the second one, the north wall is started first and the east wall is accelerated later. In the third one the east wall starts first. It is usually expected that all these three cases yield the same steady state solution after sufficiently long time. However, present numerical experiments show that such a usual belief is valid only when the Reynolds number is low enough (Re=40). At higher Reynolds number (Re=400), the flow develops to three different steady states depending on the history of the boundary condition change.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.4
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• pp.281-289
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• 2016

Accurate prediction of the trajectory and time of a time-varying mass parachute system remains essential in the mission requiring a precision airdrop to the ground. In this study, we investigate the altitude-varying behavior of a cross-type parachute system designed to deliver a time-varying mass object like flare. The dynamics of the descending parachute system was analyzed based on the Runge-Kutta method of the ordinary differential system. The drag coefficients of the cross-type parachute and flare were calculated by a CFD code based on the incompressible Navier-Stokes equation. Finally, by using a simplified gust wind model in troposphere, the combined effects of gust wind and time-varying mass were examined in detail.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.28-40
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• 2002

Turbulent flows around two-dimensional wing sections in ground effect are analysed by incompressible RANS equations and a finite difference method. The Baldwin-Lomax algebraic turbulence model is used to simulate high Reynolds number flows. The main purpose of this study is to clarify the two-dimensional ground effect and its flow characteristics due to different ground boundary conditions, i.e., moving and fixed bottom boundary. As a first step, to validate the present numerical code, the computational result of Clark-Y(t/C 11.7%) is compared with published numerical results and experimental data. Then, NACA4412 section in ground effect is calculated for various ground clearances with two bottom boundary conditions. According to the computational results, the difference in the lift and moment simulated with the two bottom boundary conditions is negligible, but the drag force simulated by the fixed bottom is to some extent smaller than that by the moving bottom. Therefore, it can be concluded that the drag force measured in a wind tunnel with the fixed bottom could be smaller than that with the moving bottom.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.12
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• pp.579-587
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• 2014

This paper deals with precise analytical state equation modeling of a variable speed refrigeration system (VSRS) for optimum control in state space. The VSRS is described as multi-input and multi-output (MIMO) system, which has two controlled variables and two control inputs. First, the Navier-Stokes equation and mass flow rate were applied to each component of the basic refrigeration cycle to build a dynamic model. The dynamic model, represented by a differential equation, was transformed into the state equation formula. Next, a full-order state observer was built to estimate all of the state variables to compose an optimum control system. Then, an optimum controller was designed to minimize an evaluation function that has input energy and control error. Finally, simulations and experiments were conducted to verify the validity of the proposed modeling and designed optimum controller to regulate target temperature and superheat in a 1RT oil cooler system. The results show that the proposed method, state equation modeling and optimum control, is efficient to ensure optimal control performance of the VSRS.

• The Journal of the Acoustical Society of Korea
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• v.36 no.6
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• pp.371-377
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• 2017

The performance of an air conditioner is closely related to the cooling performance of a split-type outdoor unit so that, in most of the relevant preceding studies, the independent performance of an axial fan in an outdoor unit has been studied. However, there is a lack of research on the effects of other components in an outdoor units was rarely investigated. Therefore, in this paper, the effects of the fan orifice among other parts on the flow performance of the outdoor unit was numerically investigated. A virtual fan tester consisting of 18 million grids was developed for highly resolved flow simulation. The unsteady RANS (Reynolds-averaged Navier-Stokes) equations are numerically solved by using finite-volume CFD (Computational Fluid Dynamics) techniques. In order to verify the validity of the numerical methods, the predicted P-Q curve of the cooling fan in a full outdoor unit is compared with the measured one. Optimization of orifice shape was carried out for maximum flow performance of the outdoor unit using the validated numerical method.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.314-320
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• 2017

A pressure relief valve is generally used to prevent piping systems from being broken due to high pressure gas flows. However, the sudden pressure drop caused by the pressure relief valve produces high acoustic energy which propagates in the form of compressible acoustic waves in the pipe and sometimes causes severe vibration of the pipe structure, thereby resulting in its failure. In this study, internal aerodynamic noise due to valve flow is estimated for a simple contraction-expansion pipe by combining the LES (Large-Eddy Simulation) technique with the wavenumber-frequency analysis, which allows the decomposition of fluctuating pressure into incompressible hydrodynamic pressure and compressible acoustic pressure. In order to increase the convergence, the steady Reynolds-Averaged Navier-Stokes equations are numerically solved. And then, for the unsteady flow analysis with high accuracy, the unsteady LES is performed with the steady result as the initial value. The wavenumber-frequency analysis is finally performed using the unsteady flow simulation results. The wavenumber-frequency analysis is shown to separate the compressible pressure fluctuation in the flow field from the incompressible one. This result can provide the accurate information for the source causing so-called acoustic-induced-vibration of a piping system.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.369-381
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• 2017

It has been presumed that highly nonlinear skewed waves frequently observed in a surf zone could significantly influence the transmission behaviour via a porous wave breaker due to its larger inertia force than its nonlinear counterparts of zero skewness [Cnoidal waves]. In this study, in order to confirm this perception, a numerical simulation has been implemented for 6 waves the skewness of that range from 1.02 to 1.032. A numerical simulation are based on the Tool Box called as the ihFoam that has its roots on the OpenFoam. Skewed waves are guided by the shoal of 1:30 slope, and the flow in the porous media are analyzed by adding the additional damping term into the RANS (Reynolds Averaged Navier-Stokes equation). Numerical results show that the highly nonlinear skewed waves are of higher transmitted ratio than its counterparts due to its stronger inertia force. In this study, in order to see whether or not the damping at the porous structure has an effect on the wave celerity, we also derived the dispersive relationships of Nonlinear Shallow Water Eq. [NSW] with damping at the porous structure being accounted. The newly derived dispersive relationships shows that the phase lag between the damping friction and the free surface elevation due to waves significantly influence the wave celerity.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.4
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• pp.401-412
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• 2008

Simulations of three-dimensional numerical wave tank are performed to investigate wave force acting on a large cylindrical structure and consequent wave deformation, which are induced by bore after breaking waves. The numerical model is based on the three-dimensional Navier-Stokes equations with a finite-difference method combined with a volume of fluid(VOF) method, which is capable of tracking the complex free surface, including wave breaking. In order to promote wave breaking of the incident wave, the approach slope was built seaward of the structure with a constant slope and a large cylindrical structure was installed on a flat bed. The incident waves were broken on the approach slope or flat bed by its wave height. In the present study, all waves acting on the large cylindrical structure were limited to breaking bore after wave breaking. The effects of the position of the structure and the incident wave height on the wave force and wave transformations were mainly investigated with the concern of wave breaking. Further, the relations between the variation of wave energy by wave propagation after wave breaking and wave force acting on the structure were discussed to give the understanding of the full-linear wave-structure interactions in three-dimensional wave fields.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.3
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• pp.189-197
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• 2006

The influence of leodo Ocean Research Station structure to surrounding atmospheric flow is carefully investigated using CFD techniques. Moreover, the validation works of computational results are performed by the comparison with the observed data of leodo Ocean Research station. In this paper, we performed 3-dimensional CAD modelling of the station, generated the grid system for numerical analysis and carried out flow analyses using Navier-Stokes equations coupled with two-equation turbulence model. For suitable free stream conditions of wind speed and direction, the interference of the research station structure on the flow field is predicted. Beside, the computational results are benchmarked by observed data to confirm the accuracy of measured date and reliable data range of each measuring position according to the wind direction. Through the results of this research, now the quantitative evaluation of the error range of interfered gauge data is possible, which is expected to be applied to provide base data of accurate sea surface wind around research stations.