• Journal of computational fluids engineering
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• v.14 no.1
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• pp.53-61
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• 2009

The objective of this research is to design blade planform to reduce high speed impulsive(HSI) noise from a non-lifting helicopter rotor using CFD method and optimization techniques. As for the aero-acoustic analysis, CFD technique for aerodynamic analysis and Kirchhoff's method for the acoustic analysis were used. As for the optimization method, Kriging-based genetic algorithm(GA) model as a high-fidelity optimization method was chosen. Design variables and constraints are determined for arbitrary blade planform. The result shows that the optimized blade planform with high swept-back and taper ratio can reduce HSI noise by suppressing generation of the strong shock wave on blade surface and propagation of the noise to the farfield flow region.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.641-645
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• 2002

In case of aluminum-cased battery, The ratio of height and base of square is generally above the ten times, square-shaped and problem of non-axis symmetry. It is typical model to set up the analysis method of finite element. The reliable analysis of finite element method is suggested, which is used to investigate the possibility that multi-stage deep drawing and ironing used currently is replaced by backward impact extrusion favorable in the respect of cost production and productivity. The influence of parameter was analyzed and compared, which was considered to analyze the process of large deformation plasticity such as extrusion. Die and billet was made as the same shape of finite element model. The results of experiment show good forming without the rupture and wrinkles with the optimum velocity 100mm/sec obtained by analysis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2001.11a
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• pp.50-53
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• 2001

Flame propagation during the initial stages of ignition in a non-premixed swirl, having some of characteristics of the primary zone of an aero gas turbine combustor, has been investigated. Nd:YAG laser was adopted as the principal ignition source to allow arbitrary placing of the ignition site i subsequent flame development was monitored using a natural light high speed filming technique for many ignition site at two different swirl ratios and an overall equivalence ratio of 0.9. For ignition offset from the burner centreline, buoyancy force associated with radial pressure gradient produced a strong inward movement of the flame kernel. At the burner exit. flame kernels invariably developed into cylindrical form and a 'radial confinement /axia expansion' (RCAE) process was observed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.04a
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• pp.34-41
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• 2001

Most of the eigenvalue analysis methods for the undamped or proportionally damped systems use the well-known Sturm sequence property to check the missed eigenvalues when only a set of the lowest modes is to be used for large structures. However, in the case of the non-proportionally damped systems such as the soil-structure interaction system, the structural control system and the composite structures, no counterpart of the Sturm sequence property for undamped systems has been developed yet. Hence, when some important modes are missed for those systems, it may leads to poor results in dynamic analysis. In this paper, a technique for calculating the number of eigenvalues inside the open disk of arbitrary radius for the eigenproblem with the damping matrix is proposed by applying Chen's algorithm and Gleyse's theorem. To verify the applicability of the proposed method, two numerical examples are considered.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.10a
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• pp.267-274
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• 1999

An understanding of the natural frequencies of a beam is virtually a prerequisite to the understanding of its response in forced vibration due to shock, ground acceleration or moving loads. Contrary to the frequencies of the prismatic bars with arbitrary boundary conditions, those of a tapered bar are hard to determine when one employs convevtional neutral equilibrium or energy method. In this paper, finite element method is adopted to determine the fundamental frequencies of the non-symmetrically tapered bars. The bars assume the shapes of straight lines along the axis. The parameters considered in this study are sectional parameter, m,n and taper parameter, $\alpha$ For the structural engineer's convenience, the results by finite element method are expressed by simple algebraic equations, by which first mode frequencies are easily estimated. And they agree fairy well with those by F.E.M in most cases.

• Structural Engineering and Mechanics
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• v.26 no.3
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• pp.297-313
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• 2007

A preliminary performance-based seismic design methodology is proposed. The top yield displacement of the system is computed from these of the components, which are assumed constant. Besides, a simple procedure to evaluate the top yield displacement of frames is developed. Seismic demands are represented in the form of yield point spectra. The methodology is general, conceptually transparent, uses simple calculations based on first principles and is applicable to asymmetric systems. To consider a specific situation two earthquake levels, occasional and rare are considered. The advantage of an arbitrary assignment of strength to the different components to reduce eccentricities and improved the torsional response of the system is addressed. The methodology is applied to an asymmetric five story building, and the results are verified by push-over analysis and non linear dynamic analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.6
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• pp.981-987
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• 1997

Modern helicopter rotor blades with non-homogeneous cross section composed of anisotropic material rquire highly sophisticated structural analysis. Variation in cross section geometry makes this task of analysis more complicated. Since rotor blades generally are much longer than their lateral dimensions, one-dimensional models seem feasible, at least from a computational point of view. Therefore determination of the principal coordinate system is very important to remove the structural coupling for one-dimensional beam modelling. In this study, shear center, and principal direction. The method will be verified by comparing the results with confirmed experimental results.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.505-511
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• 2002

In the present study, we visualize the linkage framework between geometric modeling and shell finite element based on B-spline representation. For the development of a consistent shell element, geometrically exact shell elements based on general curvilinear coordinates is provided. The NUBS(Non Uniform B-Spline) is used to generate the general free form shell surfaces. Employment of NUBS makes shell finite element handle the arbitrary geometry of the smooth shell surfaces. The proposed shell finite element .model linked with NUBS surface representation provides efficiency for the integrated design and analysis of shell surface structures. The linkage framework can potentially provide efficient integrated approach to the shape topological design optimizations for shell structures.

• Journal of the Korean Data and Information Science Society
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• v.22 no.6
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• pp.1265-1273
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• 2011

This article deals with the problem of testing the equality of the location parameters in the half-normal distributions. We propose Bayesian hypothesis testing procedures for the equality of the location parameters under the noninformative prior. The non-informative prior is usually improper which yields a calibration problem that makes the Bayes factor to be defined up to arbitrary constants. This problem can be deal with the use of the fractional Bayes factor or intrinsic Bayes factor. So we propose the default Bayesian hypothesis testing procedures based on the fractional Bayes factor and the intrinsic Bayes factors under the reference priors. Simulation study and an example are provided.

• Communications of the Korean Mathematical Society
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• v.9 no.4
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• pp.961-973
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• 1994

A stochastics process $X = {X(t) : t \in T}$, with an index set T, is said to be infinitely divisible (ID) if its finite dimensional distributions are all ID. An ID process X is said to be a stochastic integral process if $X = {X(t) : t \in T} =^D {\int f_td\Lambda : t \in T}$ where $f : T \times S \to R$ is a deterministic function and $\Lambda$ is an ID random measure on a $\delta$-ring S of subsets of an arbitrary non-empty set S with the property; there exists an increasing sequence ${S_n}$ of sets in S with $U_n S_n = S$. Here $=^D$ denotes equality in all finite dimensional distributions.