• Journal of the Society of Naval Architects of Korea
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• v.52 no.5
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• pp.372-379
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• 2015

The blade root fillets which have strong influences on the performance of propellers in the both structural and hydrodynamic points of view, are mechanical parts for smooth connection surface with a blade and a hub. A few related researches (Sabol, 1983; Kennedy, 1997) have noted that 3T-T/3 double radius section design would be suitable for reducing Stress Concentration Factor(SCF) and increasing Cavitation Inception Speed(CIS). In this paper, it is confirmed that this compound cross-section design has come close to the optimum solution in the shape optimization standpoint so that it could protect the propeller blade under the frequent and various loading cases. On that basis, we suggest the definite and simple fillet design methodology that has the cross-section with nT-T/n compound radius and elliptic shape which could sustain the given derivatives information as well as the offsets at the boundary and all inner region of the fillet surface. In addition, the result of design is presented in form of IGES file format in order to connect with NC machine seamlessly.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.37.2-37.2
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• 2017

The gravitational radiation capture between unequal mass black holes without spins is investigated with numerical relativistic simulations, and compared with the Post-Newtonian approximations. The parabolic approximation which assumes that the gravitational radiation from a weakly hyperbolic orbit is the same as that from the parabolic orbit is adopted. Using the radiated energies from the parabolic orbit simulations, we have obtained the impact parameters (b) of the gravitational radiation captures for weakly hyperbolic orbits with respect to the initial energy. The most energetic encounters occur around the boundary between the direct merging and the fly-by orbits, and we find that several percent of the total ADM initial energy can be emitted at the peak. The equal mass BHs emit more energies than unequal mass BHs at the same initial orbital angular momentum in the case of the fly-by orbits. The impact parameters obtained with numerical relativity deviate from those in Post-Newtonian when the encounter is very strong ($b{\leq}100M$), and the deviations are more conspicuous at the high mass ratio.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.111-121
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• 1997

The spectral energy balance model is composed and the nonlinear interaction is approximated by the discrete interaction parameterization as in WAM model. The numerical results of durational limited growth test agree very well with those of the exact model, EXACT-NL. The response of a wave spectrum to a change in wind direction is investigated numerically for a sequence of direction changes 30$^{\circ}$ , 45$^{\circ}$ , 60$^{\circ}$ , 90$^{\circ}$ . The high frequency components relax more repidly to the new wind direction than the low frequency components and the relaxation process also depends on the wave age. For wind direction changes less than 60$^{\circ}$ , the coupling by nonlinear interaction is so strong that the secondary peak in input source distribution is counteracted by the negative lobe of the nonlinear interaction. For wind direction changes grater than 60$^{\circ}$ , a second independent wind-sea spectrum is generated in the new wind direction, while the old spectrum gradually decays as swell.

• Journal of applied mathematics & informatics
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• v.7 no.3
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• pp.787-800
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• 2000

In this paper we consider an optimal control system described by n-dimensional heat equation with a thermal source. Thus problem is to find an optimal control which puts the system in a finite time T, into a stationary regime and to minimize a general objective function. Here we assume there is no constraints on control. This problem is reduced to a moment problem. We modify the moment problem into one consisting of the minimization of a positive linear functional over a set of Radon measures and we show that there is an optimal measure corresponding to the optimal control. The above optimal measure approximated by a finite combination of atomic measures. This construction gives rise to a finite dimensional linear programming problem, where its solution can be used to determine the optimal combination of atomic measures. Then by using the solution of the above linear programming problem we find a piecewise-constant optimal control function which is an approximate control for the original optimal control problem. Finally we obtain piecewise-constant optimal control for two examples of heat equations with a thermal source in one-dimensional.

• Journal of applied mathematics & informatics
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• v.29 no.3_4
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• pp.621-639
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• 2011

The purpose of this paper is to introduce a general iterative process by viscosity approximation method with parallel method to ap-proximate a common element of the set of solutions of a mixed equilibrium problem and of the set of common fixed points of a finite family of $k_i$-strict pseudo-contractions in a Hilbert space. We obtain a strong convergence theorem of the proposed iterative method for a finite family of $k_i$-strict pseudo-contractions to the unique solution of variational inequality which is the optimality condition for a minimization problem under some mild conditions imposed on parameters. The results obtained in this paper improve and extend the corresponding results announced by Liu (2009), Plubtieng-Panpaeng (2007), Takahashi-Takahashi (2007), Peng et al. (2009) and some well-known results in the literature.

• Journal of computational fluids engineering
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• v.11 no.1 s.32
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• pp.57-66
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• 2006

An optimal shape design approach is presented for a subsonic S-shaped intake using aerodynamic sensitivity analysis. Two-equation turbulence model is employed to capture strong counter vortices in the S-shaped duct more precisely. Sensitivity analysis is performed for the three-dimensional Navier-Stokes equations coupled with two-equation turbulence models using a discrete adjoint method For code validation, the result of the flow solver is compared with experiment data and other computational results of bench marking test. To study the influence oj turbulence models and grid refinement on the duct flow analysis, the results from several turbulence models are compared with one another and the minimum number of grid points, which can yield an accurate solution is investigated The adjoint variable code is validated by comparing the complex step derivative results. To realize a sufficient and flexible design space, NURBS equations are introduced as a geometric representation and a new grid modification technique, Least Square NURBS Grid Approximation is applied With the verified flow solver, the sensitivity analysis code and the geometric modification technique, the optimization of S-shaped intake is carried out and the enhancement of overall intake performance is achieved The designed S-shaped duct is tested in several off-design conditions to confirm the robustness of the current design approach. As a result, the capability and the efficiency of the present design tools are successfully demonstrated in three-dimensional highly turbulent internal flow design and off-design conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.11
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• pp.1907-1916
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• 2003

During decades, there has been much progress in understanding of the inelastic behavior of the materials and numerous inelastic constitutive equations have been developed. The complexity of these constitutive equations generally requires a stable and accurate numerical method. To obtain the increment of state variable, its evolution laws are linearized by several approximation methods, such as general midpoint rule(GMR) or general trapezoidal rule(GTR). In this investigation, semi-implicit integration schemes using GTR and GMR were developed and implemented into ABAQUS by means of UMAT subroutine. The comparison of integration schemes was conducted on the simple tension case, and simple shear case and nonproportional loading case. The fully implicit integration(FI) was the most stable but amplified the truncation error when the nonlinearity of state variable is strong. The semi-implicit integration using GTR gave the most accurate results at tension and shear problem. The numerical solutions with refined time increment were always placed between results of GTR and those of FI. GTR integration with adjusting midpoint parameter can be recommended as the best integration method for viscoplastic equation considering nonlinear kinematic hardening.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.435-435
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• 2011

The electronic structure and various physical properties of CeO2, Ce2O3, PrO2, and Pr2O3 have been studied from the framework of Ab-initio by the all-electron projector-augmented-wave (PAW) method, as implemented VASP (Vienna Ab-initio Simulation Package). The generalized gradient approximation (GGA) with effective U (Ueff) has been used to explain the strong on-site Coulomb repulsion among the localized Ce 4f electrons. The dependence of selected observables of these materials on the Ueff parameter has been scrutinized. The studied properties contain lattice constants, density of states, and reaction energies of CeO2, Ce2O3, PrO2, and Pr2O3. For CeO2 and PrO2, the GGA(PBE)+U results are in good agreement with experimental data whereas for the computational calculationally more demanding Ce2O3 and Pr2O3 both approaches give comparable accuracy. This results represent that by choosing an appropriate Ueff it is possible to reliably describe structural and electronic properties of CeO2, Ce2O3, PrO2, and Pr2O3, which enables modeling of oxygen reduction reaction processes involving ceria-based materials.

• ETRI Journal
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• v.27 no.6
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• pp.747-758
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• 2005

The problem of selection among competing models has been a fundamental issue in statistical data analysis. Good fits to data can be misleading since they can result from properties of the model that have nothing to do with it being a close approximation to the source distribution of interest (for example, overfitting). In this study we focus on the preference among models from a family of polynomial regressors. Three decades of research has spawned a number of plausible techniques for the selection of models, namely, Akaike's Finite Prediction Error (FPE) and Information Criterion (AIC), Schwartz's criterion (SCH), Generalized Cross Validation (GCV), Wallace's Minimum Message Length (MML), Minimum Description Length (MDL), and Vapnik's Structural Risk Minimization (SRM). The fundamental similarity between all these principles is their attempt to define an appropriate balance between the complexity of models and their ability to explain the data. This paper presents an empirical study of the above principles in the context of model selection, where the models under consideration are univariate polynomials. The paper includes a detailed empirical evaluation of the model selection methods on six target functions, with varying sample sizes and added Gaussian noise. The results from the study appear to provide strong evidence in support of the MML- and SRM- based methods over the other standard approaches (FPE, AIC, SCH and GCV).

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2001.05a
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• pp.126-130
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• 2001

In this paper, we propose the design methodology of target tracking system using fuzzy basis function expansion (FBFE) based on virus evolutionary genetic algorithm(VEGA). In general, the objective of target tracking is to estimate the future trajectory of the target based on the past position of the target obtained from the sensor. In the conventional and mathematical nonlinear filtering method such as extended Kalman filter (EKF), the performance of the system may be deteriorated in highly nonlinear situation. To resolve these problems of nonlinear filtering technique, by appling artificial intelligent technique to the tracking control of moving targets, we combine the advantages of both traditional and intelligent control technique. In the proposed method, after composing training datum from the parameters of extended Kalman filter, by combining FBFE, which has the strong ability for the approximation, with VEGA, which prevent GA from converging prematurely in the case of lack of genetic diversity of population, and by identifying the parameters and rule numbers of fuzzy basis function simultaneously, we can reduce the tracking error of EKF. Finally, the proposed method is applied to three dimensional tracking problem, and the simulation results shows that the tracking performance is improved by the proposed method.