• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.95-104
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• 2007

A new design approach of complex geometries such as wing/body configuration is arranged by using overset mesh techniques under large scale computing environment. For an in-depth study of the flow physics and highly accurate design, several special overlapped structured blocks such as collar grid, tip-cap grid, and etc. which are commonly used in refined drag prediction are adopted to consider the applicability of the present design tools to practical problems. Various pre- and post-processing techniques for overset flow analysis and sensitivity analysis are devised or implemented to resolve overset mesh techniques into the design optimization problem based on Gradient Based Optimization Method (GBOM). In the pre-processing, the convergence characteristics of the flow solver and sensitivity analysis are improved by overlap optimization method. Moreover, a new post-processing method, Spline-Boundary Intersecting Grid (S-BIG) scheme, is proposed by considering the ratio of cell area for more refined prediction of aerodynamic coefficients and efficient evaluation of their sensitivities under parallel computing environment. With respect to the sensitivity analysis, discrete adjoint formulations for overset boundary conditions are derived by a full hand-differentiation. A smooth geometric modification on the overlapped surface boundaries and evaluation of grid sensitivities can be performed by mapping from planform coordinate to the surface meshes with Hicks-Henne function. Careful design works for the drag minimization problems of a transonic wing and a wing/body configuration are performed by using the newly-developed and -applied overset mesh techniques. The results from design applications demonstrate the capability of the present design approach successfully.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.233-240
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• 2017

The flowfield around transonic wing-body configuration was simulated using in-house CFD code and compared with the experimental data to understand the influence of several features of CFD(Computational Fluid Dynamics) ; grid dependency, turbulence models, spatial discretization, and viscosity. The wing-body configuration consists of a simple planform RAE Wing 'A' with an RAE 101 airfoil section and an axisymmetric body. The in-house CFD code is a compressible Euler/Navier-Stokes solver based on unstructured grid. For the turbulence model, the $k-{\omega}$ model, the Spalart-Allmaras model, and the $k-{\omega}$ SST model were applied. For the spatial discretization method, the central differencing scheme with Jameson's artificial viscosity and Roe's upwind differencing scheme were applied. The results calculated were generally in good agreement with experimental data. However, it was shown that the pressure distribution and shock-wave position were slightly affected by the turbulence models and the spatial discretization methods. It was known that the turbulent viscous effect should be considered in order to predict the accurate shock wave position.

• The Mathematical Education
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• v.58 no.4
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• pp.519-530
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• 2019

According to previous studies, meta-affect based on the interaction between cognitive and affective elements in mathematics learning activities maintains a close mechanical relationship with the learner's mathematical ability in a similar way to meta-cognition. In this study, in order to grasp these characteristics phenomenologically, small group problem-solving cases of 5th grade elementary mathematically gifted children were analyzed from a meta-affective perspective. As a result, the two types of problem-solving cases of mathematically gifted children were relatively frequent in the types of meta-affect in which cognitive element related to the cognitive characteristics of mathematically gifted children appeared first. Meta-affects were actively acted as the meta-function of evaluation and attitude types. In the case of successful problem-solving, it was largely biased by the meta-function of evaluation type. In the case of unsuccessful problem-solving, it was largely biased by the meta-function of the monitoring type. It could be seen that the cognitive and affective characteristics of mathematically gifted children appear in problem solving activities through meta-affective activities. In particular, it was found that the affective competence of the problem solver acted on problem-solving activities by meta-affect in the form of emotion or attitude. The meta-affecive characteristics of mathematically gifted children and their working principles will provide implications in terms of emotions and attitudes related to mathematics learning.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.11
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• pp.1531-1541
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• 2002

The NOx emission characteristics of C$H_4$-Air coflow jet flames were numerically and experimentally investigated. NOx was measured using a chemiluminescent detection and calculated by the parabolic -type equation solver with a detatiled NOx chemistry. The fuel flow rate( $Q_{F}$), the diameter of mixture nozzle and the equivalence rate(Ф) were varied to discuss the EINOx of each flames at the various combustion conditions. The NOx emission index(EINOx) was introduced to quantify the NOx emission from the parametrically varied flames. The results show that Prompt EINOx increases on a logarithmic profile with increasing ${\Phi}$ and keeps nearly constant for the variation of $Q_{F}$. Thermal EINOx reaches the maximum value at around ${\Phi}$ =1.5 and then slowly decrease for ${\Phi}$ >1.5. In addition, Thermal EINOx increases with increasing $Q_{F}$, but nearly indifferent to the variation of the mixture nozzle diameter. Total EINOx also shows a peak at around ${\Phi}$ =1.5, followed by a relatively sharp decrease for 1.5< ${\Phi}$ <2.5 and increase slowly for 2.5 < ${\Phi}$ < $\infty$ The present Total EINOx trend is well explained by a combination of above Thermal and Prompt EINOx trend with the variation of ${\Phi}$ n of ${\Phi}$.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.5
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• pp.42-49
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• 2015

In this study, the multi-disk of a high-pressure drop control valve is designed and manufactured. Then, the flow rate and high-pressure drop of fluids flowing in the high-pressure drop control valve is CAE/CFD. This study involves numerical analysis for the Zambil offshore project of a high-pressure drop control valve. ANSYS used a solver for offshore structures analysis. A high-pressure drop control valve, which transforms the power transfer of a system by reducing the inlet pressure of 345bar to the outlet pressure of 112bar, is a fundamental component in the offshore process. This study not only analyzes the relation between pressure drop and fluid velocity in a trim by using fluid analysis, but also examines the possibility of cavitation in a valve in addition to the plot for the extension of lifespan. It is demonstrated that the pressure drop from 345bar to 112bar is more feasible in the presence of the trim, which can induce a continuous and diminutive pressure drop in order to prevent cavitation in a high-pressure drop control valve.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.7
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• pp.679-688
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• 2010

The major objective of the present study is to extend the applications of inverse analysis to more realistic engineering fields with a complex combustion process rather than the traditional simple heat-transfer problems. In order to do this, the unknown initial mass fractions of $CH_4/O_2$ are estimated from the temperature measurement data by inverse analysis in the practical diffusion-controlled turbulent combustion problem. In order to ensure efficient inverse analysis, the repulsive particle swarm optimization (RPSO) method, which belongs to the class of stochastic evolutionary global optimization methods, is implemented as an inverse solver. Based on this study, it is expected that useful information can be obtained when inverse analysis is used in the diagnosis, design, or optimization of real combustion systems involving unknown parameters.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.9
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• pp.843-850
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• 2010

This In this paper, we describe the performance characteristics of a turbo blower as a function of the shape of the volute casing: expansion diameter and width of the volute casing. The turbo blower considered in the present study is mainly used in a refuse collection system. The flow characteristics inside the turbo blower were analyzed by a three-dimensional Navier-Stokes solver and compared with experimental results. The distributions of pressure and efficiency obtained by numerical simulation were in good agreement with those determined experimentally. Throughout the numerical simulation of the turbo blower, the blower performance was enhanced by decreasing the local losses in the blade passage and the outlet flow. The efficiency and pressure for the design flow condition were enhanced by about 3% and 2%, respectively, compared to the efficiency and pressure of the reference blower. Detailed flow analysis was performed using the results of the numerical simulation

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.4
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• pp.1-12
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• 2003

In this study, a regime where independent treatment of SETs in transient simulations is valid has been identified quantitatively. It is found that as in the steady-state case, each SET can be treated independently even in the transient case when the interconnection capacitance is large enough. However, the value of the load capacitance $C_{L}$of the interconnections for the independent treatment of SETs is approximately 10 times larger than that of the steady state case. A compact SET transient model is developed for transient circuit simulation by SPICE. The developed model is based on a linearized equivalent circuit and the solution of master equation is done by the programming capabilities of the SmartSpice. Exact delineation of several simulation time scales and the physics-based compact model make it possible to accurately simulate hybrid circuits in the time scales down to several tens of pico seconds. The simulation time is also shown to depend on the complexity level of the transient model.l.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.2
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• pp.38-45
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• 1997

In this paper, the three-dimensional stress effect of thermal oxide is simulated. We developed a three-dimensional finite element numerical simulator including three-dimensional adaptive mesh generator that is able to refine and eliminate nearby moving boundary of oxide, and oxidation solver with stress model. To investigate the behavior of thermal oxidation the simulations of thermal oxidation for island and hole structures are carried out assuming silicon wafer of <100> direction, temperature of $1000^{\circ}C$, oxidation time of 60min, wet ambient, initial oxide thickness of $300\AA$, and nitride thickness of $2, 000\AA$. The main effect of deformation at the corner area of oxide is due to distribution of oxidant, but the deformation of oxide is affected by the stressin theoxide. In the island structure which is the structure mostly covered with nitride and a coner is opended to oxidation, oxidation is reduced at the coner by compressive stress. In the hole structure which is the structure mostly opedned to oxide and a coner is convered with nitride, however, oxidation is increased at the coner by tensile stress.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.29-41
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• 2008

The present paper provides a CFD analysis of diffraction problem for a ship with forward speed using an unsteady RANS simulation method, a WAVIS code. The WAVIS viscous solver adopting a finite volume method has second order accuracy in time and field discretizaions for the RANS equations. A two phase level-set method and a realizable ${\kappa}-{\varepsilon}$ turbulence model are adopted to compute the free surface and to meet the turbulence closure, respectively. To validate the capability of the present numerical methods for the simulation of an unsteady progressive regular wave, computations are performed for three grid sets with refinement ratio of ${\sqrt{2}}$. The main simulation is performed for a DTMB5512 model with a forward speed in a regular head sea condition. Validation of the present numerical method is carried out by comparing the present CFD results with available unsteady experimental data published in the 2005 Tokyo CFD Workshop: resistance, heave force, pitch moment, unsteady free surface elevations and velocity fields.