• Wind and Structures
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• v.27 no.3
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• pp.187-197
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• 2018

In this study, aerodynamic characteristics of a horizontal axis wind turbine (HAWT) were evaluated and discussed in terms of measured data in existing onshore wind farm. Five wind turbines (T1, T2, T3, T4 and T5) were selected, and hub-height wind speed, $U_D$, wind turbine power output, P and turbine rotational speed, ${\Omega}$ data measured from these turbines were used for evaluation. In order to obtain characteristics of axial flow induction factor, a, power coefficient, $C_p$, thrust force coefficient, $C_T$, thrust force, T and tangential flow induction factor, a', Blade Element Momentum (BEM) theory was used. According to the results obtained, during a year, probability density of turbines at a rotational speed of 16.1 rpm was determined as approximately 45%. Optimum tip speed ratio was calculated to be 7.12 for most efficient wind turbine. Maximum $C_p$ was found to be 30% corresponding to this tip speed ratio.

• Fire Science and Engineering
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• v.11 no.4
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• pp.3-14
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• 1997

The smoke filling process for the atrium space containing a fire source is simulated using two types of deterministic fire model : Zone model and Field model. The zone model used is the CFAST(version 1.6) model developed at the Building and Fire Research Laboratories, NIST in the USA. The field model is a self-developed frie field model based on Computational Fluid Dynamic (CFD) theories. This article is focused on finding out the smoke movement and temperature distribution in atrium space which is cubic in shape. For solving the liked set of velocity and pressure equation, the PISO algorithm, which strengthened the velocity-pressure coupling, was used. Since PISO algorithm is a time-marching procedure, computing time si very fast. A computational procedure for predicting velocity and temperature distribution in fire-induced flow is based on the solution, in finite volume method and non-staggered grid system, of 3-dimensional equations for the conservation of mass, momentum, energy, species and so forth. The fire model i.e Zone model and Field model predicted similar results for clear heights and the smoke layer temperature.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.5
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• pp.522-526
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• 2008

In this paper, we propose a system to convert a video motion into cartoon-style animation automatically. Our system is a new video cartoon stylization method that can apply natural transformation with satisfying physical constraints. It applies physically reasonable transformation to a selected video object with considering physical information such as momentum, movement direction and force. We construct several deformation scenarios which correspond with traditional animation techniques, then a scenario can be easily selected to apply the effects. Finally, this system gene-rates a dynamic cartoon-style video by timing control and a cartoon rendering technique.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1423-1430
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• 1993

One of the most important parameters for explosive welding is flyer velocity $V_p$, which principally depends on momentum caused by detonation of explosive. And close dependency with other parameters such as detonation velocity $V_D$, dynamic angle $\beta$, charge ratio R, flyer thickness $t_f$ and stand-off distance d, should be taken accounts for welding design. This paper describes, as a result of experiment, an empirical equation related to relation between $V_p$/$V_D$ and R. The flyer velocity which is estimated by $V_{p}=0.284{\times}R^{0.593}$or $V_{p}=\sqrt[0.2]{2E_G}{\times}R^{0.593}$ can be used in ordinary experiments. And the calculated values of the flyer velocity exhibit better accuracy than those of other investigators.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.6
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• pp.543-552
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• 2011

Control Moment Gyro(CMG) is one of the most efficient momentum exchange devices for satellite attitude control and CMG is very essential device for agile satellite. In this study, the essential dynamic equation for the design of gimbal motor and wheel motor is summarized. The development process of SGCMG hardware for agile small satellite system, the description of developed hardware and its performance test results are presented. Test result shows that the developed hardware model can produce an output torque more than 1.2Nm as designed. Other test items are max. torque, gimbal bandwidth, minimum torque, torque error, gimbal rate error.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.3-17
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• 2007

This paper provides an introduction to life-span simulation and numerical approach to support the performance design processes of reinforced concrete structures. An integrated computational system is proposed for life-span simulation of reinforced concrete. Conservation of moisture, carbon dioxide, oxygen, chloride, calcium and momentum is solved with hydration, carbonation, corrosion, ion dissolution. damage evolution and their thermodynamic/mechanical equilibrium. Coupled analysis of mass transport and damage mechanics associated with steel corrosion is presented for structural performance assessment of reinforced concrete. Multi-scale modeling of micro-pore formation and transport phenomena of moisture and ions are mutually linked for predicting the corrosion of reinforcement and volumetric changes. The interaction of crack propagation with corroded gel migration can also be simulated. Two finite element codes. multi-chemo physical simulation code (DuCOM) and nonlinear dynamic code of structural reinforced concrete (COM3) were combined together to form the integrated simulation system. This computational system was verified by the laboratory scale and large scale experiments of damaged reinforced concrete members under static loads, and has been applied to safety and serviceability assessment of existing structures. Based on the damage details predicted by the nonlinear finite element analytical system, the life-span-cost of RC structures including the original construction costs and the repairing costs for possible damage during the service life can be evaluated for design purpose.

• STI Policy Review
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• v.1 no.1
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• pp.93-109
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• 2010

Over the last decade, some Korean enterprises have emerged to become global players in their specialized products. How have they achieved such tremendous technological progress in a short period of time? This paper explores that question by examining the characteristics of technological innovation activities at major Korean enterprises. The paper begins with a brief review of the stages of economic growth and science and technology development in Korea. Then, the existing literature, explaining the Korean innovation model, is analyzed in order to establish a new framework for the Korean innovation model. Specifically, Korean firms have experienced three sequential phases, and thus, the Korean model, at the firm level, can be coined as "path-following," "path-revealing," and "path-creating." Then, the stylized facts in the first phase (path-following) and the second phase (path-revealing) are discussed, in the context of empirical evidence from the areas of memory chips, automobiles, shipbuilding, and steel. In terms of technology development, the Korean model has evolved as "collective learning" in the first phase, "collective recombination" of existing knowledge and technology in the second phase, and is assumed as "collective creativity" in the third phase. Ultimately, all three can be classified as "collective creation". Korean firms now face a transition in the modes of technological innovation in order to efficiently implement the third phase. To achieve remarkable progress again, as they did in the past, and to sustain the growth momentum, Korean firms should challenge new dimensions such as creative technological ideas, distinctive technological capabilities, and unique innovation systems -- all of which connote 'uniqueness'. Finally, some lessons from the Korean technological innovation experience are addressed.

• Structural Engineering and Mechanics
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• v.56 no.6
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• pp.1021-1040
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• 2015

An effective method to calculate aerodynamic loads and aeroelastic responses of large wind turbine tower-blade coupled structures in yaw condition is proposed. By a case study on a 5 MW large wind turbine, the finite element model of the wind turbine tower-blade coupled structure is established to obtain the modal information. The harmonic superposition method and modified blade-element momentum theory are used to calculate aerodynamic loads in yaw condition, in which the wind shear, tower shadow, tower-blade modal and aerodynamic interactions, and rotational effects are fully taken into account. The mode superposition method is used to calculate kinetic equation of wind turbine tower-blade coupled structure in time domain. The induced velocity and dynamic loads are updated through iterative loop, and the aeroelastic responses of large wind turbine tower-blade coupled system are then obtained. For completeness, the yaw effect and aeroelastic effect on aerodynamic loads and wind-induced responses are discussed in detail based on the calculating results.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.6
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• pp.9-13
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• 2009

In the three axis control of Low Earth Orbit (LEO) satellite by using reaction wheel and gyro, a reaction wheel produces the control torque by the wheel speed or momentum, and a gyro carries out measuring of the attitude angle and the attitude angular velocity. In this paper, the dynamic modelling of LEO is consisted of the one from the rotational motion of the satellite with basic rigid body model and a flexible model, in addition to the reaction wheel model. A robust controller $(H_\infty)$ is designed to stabilize the rigid body and the flexible body of satellite, which can be perturbed due to disturbance, etc. The result obtained by $H_\infty$ controller is compared with that of the PI (Proportional and Integration) controller, which has been traditionally using for the stabilizing LEO satellite.

• Journal of ILASS-Korea
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• v.16 no.3
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• pp.140-145
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• 2011

Gelled propellants are non-Newtonian fluids in which the viscosity is a function of the shear rate, and they have a high dynamic shear viscosity which depends on the amount of gelling agent contents. The present study has focused on the breakup process, wave development of ligament and liquid sheets formed by impinging jets with various gelling agent contents. The breakup process of like-on-like doublet impinging jets are experimentally characterized using non-Newtonian liquids. The spray shape with elliptical pattern is distributed in a perpendicular direction to the momentum vectors of the jets. Gelled propellant simulants with high viscosity jets are more stable and produce less pronounced surface waves than low viscosity jets. Gelled propellant simulants from like-on-like doublet impinging jets have the spray shape of closed rim patterns at low pressure. As the injection pressure increased, rimless patterns which were composed of ligament sheets and small droplets emerged due to the effect of the aerodynamic action.