• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.1-1
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• 2009

In this presentation, I talk about various fluid simulation methods that have been developed for computer graphics special effects since 1996. They are all based on CFD but sacrifice physical reality for visual plausability and time. But as the speed of computer increases rapidly and the capability of GPU (graphics processing unit) improves, methods for more physical realism have been tried. In this talk, I will focus on four aspects of fluid simulation methods for computer graphics: (1) particle level-set methods, (2) particle-based simulation, (3) methods for exact satisfaction of incompressibility constraint, and (4) GPU-based simulation. (1) Particle level-set methods evolve the surface of fluid by means of the zero-level set and a band of massless marker particles on both sides of it. The evolution of the zero-level set captures the surface in an approximate manner and the evolution of marker particles captures the fine details of the surface, and the zero-level set is modified based on the particle positions in each step of evolution. (2) Recently the particle-based Lagrangian approach to fluid simulation gains some popularity, because it automatically respects mass conservation and the difficulty of tracking the surface geometry has been somewhat addressed. (3) Until recently fluid simulation algorithm was dominated by approximate fractional step methods. They split the Navier-Stoke equation into two, so that the first one solves the equation without considering the incompressibility constraint and the second finds the pressure which satisfies the constraint. In this approach, the first step introduces error inevitably, producing numerical diffusion in solution. But recently exact fractional step methods without error have been developed by fluid mechanics scholars), and another method was introduced which satisfies the incompressibility constraint by formulating fluid in terms of vorticity field rather than velocity field (by computer graphics scholars). (4) Finally, I want to mention GPU implementation of fluid simulation, which takes advantage of the fact that discrete fluid equations can be solved in parallel.

• Journal of the Korean Magnetic Resonance Society
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• v.10 no.1
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• pp.46-58
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• 2006

With a simple pulse sequence ($\pi/2$-{gradient, duration T}-acquisition) in solution NMR, detected signal has slowly grown up to percents of the equilibrium magnetization. The source of this unusual resurrection of dephased magnetization after a crushed gradient is cross-correlated effects of radiation damping and the distant dipolar field, which has been demonstrated by a numerical simulation and theoretical analysis.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.199-201
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• 2011

NACA0012 Airfoil was simulated with Computational Fluid Dynamics(CFD) and the aerodynamic characteristics was analyzed for various far-field boundary distances ranging from 10 airfoil chord to 50 chord Drag coefficient distribution was dependent on the far-field distance and circulation, integrated along the loop inside the flow region, was also dependent. It was turned out that some corrections based on the circulation should be added to the far-field boundary condition for accurate airfoil simulation.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.289-294
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• 2012

In this paper, the three-dimensional magnetic field created by non-periodic magnet arrays is calculated analytically. The analytical expression of the magnetic field is derived by using a magnetic charge model. The influence of ferromagnetic boundaries is formulated with an image method. Finally, we compare the results determined by analytical calculations to those from a finite element simulation.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1418-1419
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• 2007

In order to check the electric field distribution of polymer line post insulator, we performed electric field simulation according to state of water drops. Sea water is used to the contaminant. Electric field analysis is performed with change of contact angle, number and distance of water drops.

• Journal of the Korea Safety Management & Science
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• v.5 no.4
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• pp.87-95
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• 2003

The purpose of this paper is analyses about in 12kV/50kA vacuum interrupter with an axial magnetic field type electrode system through the studies of electromagnetic phenomena for the possess of Safety break. Vacuum interrupter is important in electric safety part. In this paper, we performed analysis of electric field, magnetic field, current density in AMF electrode using the Maxwell 3D simulation.

• Wind and Structures
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• v.24 no.1
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• pp.1-24
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• 2017

Wind environment in urban residential areas is an important index to consider when evaluating the living environment. However, due to the complexity of the flow field in residential areas, it is difficult to specify the correct inflow boundary conditions in the large eddy simulation (LES). In this paper, the weighted amplitude wave superposition (WAWS) is adopted to simulate the fluctuating velocity data, which satisfies the desired target wind field. The fluctuating velocity data are given to the inlet boundary of the LES by developing an UDF script, which is implemented into the FLUENT. Then, two numerical models - the empty numerical wind tunnel model and the numerical wind tunnel model with spires and roughness elements are established based on the wind tunnel experiment to verify the present method. Finally, the turbulence generation approach presented in this paper is used to carry out a numerical simulation on the wind environment in an urban residential area in Lisbon. The computational results are compared with the wind tunnel experimental data, showing that the numerical results in the LES have a good agreement with the experimental results, and the simulated flow field with the inlet fluctuations can generate a reasonable turbulent wind field. It also shows that strong wind velocities and turbulent kinetic energy occur at the passageways, which may affect the comfort of people in the residential neighborhood, and the small wind velocities and vortexes appear at the leeward corners of buildings, which may affect the spreading of the pollutants.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6453-6457
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• 2015

In this paper, the theoretical analysis for a solenoid with a finite length was verified by the finite element simulation. The solenoids are widely being used in the field of mechanical, industrial, medical industry due to their simple structure and fast responses. Solenoid actuators use an electromagnetic force. A magnetic field is formed around the solenoid coil when a current is applied. The magnetic force generated by the magnetic field enables an inside plunger to move linearly. The axial and radial magnetic fields (magnetic flux density, B) at a certain point were calculated from the Biot-Savart's law and compared with the simulation analysis from the ANSYS-Magnetostatic S/W. Comparison result, an error exists in the error range, and could therefore verify the accuracy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.964-969
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• 2006

The soundscape is a novel attempt to offer comfortable sound environments at the urban public spaces by adding pleasant sounds and removing unagreeable ones. Most important factors to be considered therein are to determine what kind of sounds to offer and how to adjust them to the changing circumstances. But nowadays, the audio system provided in the almost every urban public spaces is just only a PA system with CD player or radio broadcasting music, the provided sound is only intended by the operator. Furthermore, providing the soundscape which fits to the situation and the atmospheric conditions needs enormous effort and time, it is almost impossible with the existing PA systems which installed in the public spaces nowadays. Thus, the new sounds cape reproduction system was developed on the basis of the prior VAFSS(Virtual Acoustic Field Simulation System) systems, which has the artificial intelligence to read out the mood of the field and select the appropriate soundscape to reproduce. In this new system, various environmental sensors with standard voltage, current or resistance output are available simultaneously, and the monitoring with video and sound became available via the TCP/IP communication protocol. The update and control of this system can be very convenient, so the money, time and the effort of maintaining and providing soundscape on the public spaces can be enormously saved. This new soundscape reproducing system was named as Virtual Acoustic Field Simulation System II (V AFSS II).

• Journal of Biosystems Engineering
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• v.16 no.4
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• pp.346-354
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• 1991

Turning behavior of tractor-trailer system was studied to guide the tractor and trailer. Based upon kinematic relationship between the tractor and the trailer, a mathematical model was developed and analyzed by computer simulation. A field test was carried out to verify the mathematical model. Following conclusions were drawn from this study. 1. A mathematical model and a simulation program for turning behavior of tractor-trailer system were developed. 2. The results of the field tests showed that the RMS errors were less than 0.33m and the mathematical model based upon kinematic relationship can be used for mapping guidance system for tractor and trailer. 3. As the steering angle was increased, the turning radius was decreased. When the tractor travelled at the low speed, the travel speed of the tractor did not affect turning radius but did affect running time and stability for steering. 4. When the tractor travelled under the critical velocity, the towed trailer followed smoothly. When the the tractor travelled faster than the critical velocity, the towed trailer oscillated. The critical velocity was determined from the specification of the tractor and the trailer.