• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.66-71
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• 1998

A study of treatment effects on laser surface melted Ni-base alloy 600, especially on precipitation behavior ad chemical composition changes on the grain boundary were conducted with microscopic equipments. Long-term aging treatment at 40$0^{\circ}C$ caused no considerable effects on the grain boundary properties. Cr-rich M$_2$$_3$C$_{6}$ and Cr$_{7}$C$_3$ carbides were precipitated and the resultant Cr depletion below 12 wt pct on some high angle grain boundaries was occurred by heat treatment at $600^{\circ}C$ for 24 hours. These results can imply that the resistance of intergranular stress corrosion cracking of heat treated alloy 600 might not be changed considerably in comparion with the as-LSM one.e.e.

• Structural Engineering and Mechanics
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• v.47 no.3
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• pp.345-359
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• 2013

For the purpose of investigating the free vibration response of the spatial curved beams, the governing equations are derived in matrix formats, considering the variable curvature and torsion. The theory includes all the effects of rotary inertia, shear and axial deformations. Frobenius' scheme and the dynamic stiffness method are then applied to solve these equations. A computer program is coded in Mathematica according to the proposed method. As a special case, the dynamic stiffness and further the natural frequencies of a cylindrical helical spring under fixed-fixed boundary condition are carried out. Comparison of the present results with the FEM results using body elements in I-DEAS shows good accuracy in computation and validity of the model. Further, the present model is used for reciprocal spiral rods with different boundary conditions, and the comparison with FEM results shows that only a limited number of terms in the resultant provide a relatively accurate solution.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1186-1193
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• 1996

The analytic solution of the stress field at creep crack in the presence of grain boundary caviation is to be obtained by solving the governing equation which was derived through the previous paper. The complex integral technique is used to slove the singular integral equation. under the help of the information about stress behaviors at the ends of integral region know by numerical solution. The resultant stress disstribution obtained shows the relaxed crack-tip singularity of $r^{1/2+\theta}$ due to the intervention of cavitation effect, otherwise, it should assumed to be $r^{1/2}$ singularity of linear elastic fracture mechanics with no cavitation.

• Steel and Composite Structures
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• v.42 no.3
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• pp.389-396
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• 2022

This investigation in fluid mechanics surrounds around the variety of flow problems for different fluids along the stretching cylinder. Numerical procedure is carried out for the obtained resultant equations by Keller-Box technique. Numerical study of laminar, steady, viscous and incompressible two dimensional boundary layer flow of effects of suction and blowing on boundary layer slip flow of Casson fluid along permeable exponentially stretching cylinder has been carried out in the present draft. physical parameters i.e., Nusselt number and skin friction coefficient, suction parameter and the local Reynold number are investigated on velocity profile and elaborated through proper graphs and table.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.24-29
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• 2011

Immersed boundary lattice Boltzmann method has been applied to analyze the characteristics of the self-propelled fish motion swimming robot. The airfoil NACA0012 with caudal fin stroke model was considered to examine the characteristics. The foil in steady forward motion and a combination of steady-state harmonic deformation produces thrust through the formation of a flow downstream from the trailing edge. The harmonic motion of the foil causes unsteady shedding of vorticity from the trailing edge, while forming the vortices at the leading edge as well. The resultant thrust is developed by the pressure difference formed on the upper and lower surface of the airfoil. and the time averaged thrust coefficient increases as Re increase in the region of $Re{\leqq}700$. The suggested numerical method is suitable to develop the fish-motion model to control the swimming robot, however It would need to extend in 3D analysis to examine the higher Re and to determine the more detail mechanism of thrust production.

• Wind and Structures
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• v.13 no.2
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• pp.145-167
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• 2010

By using the 'failure' model approach, the effects of wind direction on the flight of sheathing panels from the roof of a model house in extreme winds was investigated. A complex relationship between the initial conditions, failure velocities, flight trajectories and speeds was observed. It was found that the local flow field above the roof and in the wake of the house have important effects on the flight of the panels. For example, when the initial panel location is oblique to the wind direction and in the region of separated flow near the roof edge, the panels do not fly from the roof since the resultant aerodynamic forces are small, even though the pressure coefficients at failure are high. For panels that do fly, wake effects from the building are a source of significant variation of flight trajectories and speeds. It was observed that the horizontal velocities of the panels span a range of about 20% - 95% of the roof height gust speed at failure. Numerical calculations assuming uniform, smooth flow appear to be useful for determining panel speeds; in particular, using the mean roof height, 3 sec gust speed provides a useful upper bound for determining panel speeds for the configuration examined. However, there are significant challenges for estimating trajectories using this method.

• Advances in Computational Design
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• v.3 no.3
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• pp.213-232
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• 2018

First time, an exact solution for free vibration of the Levy-type rectangular laminated plate is developed considering the most efficient Zig-Zag theory (ZIGT) and third order theory (TOT). The plate is subjected to hard simply supported boundary condition (Levy-type) along x axis. Using the equilibrium equations and the plate constitutive relations, a set of 12 m first order differential homogenous equations are obtained, containing displacements and stress resultant as primary variables. The natural frequencies of a single-layer isotropic, multi-layer composites and sandwich plates are tabulated for three values of length-to-thickness ratio (S) and five set of boundary conditions and further assessed by comparing with existing literature and recently developed 3D EKM (extended Kantorovich method) solution. It is found that for the symmetric composite plate, TOT produces better results than ZIGT. For antisymmetric and sandwich plates, ZIGT predicts the frequency for different boundary conditions within 3% error with respect to 3D elasticity solution while TOT gives 10% error. But, ZIGT gives better predictions than the TOT concerning the displacement and stress variables.

• Advances in aircraft and spacecraft science
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• v.7 no.4
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• pp.353-369
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• 2020

This paper presents the flutter analysis and optimum design of axially functionally graded box beam cantilever wing section by considering various geometric and material parameters. The coupled dynamic equations of the continuous model of wing system in terms of material and cross-sectional properties are formulated based on extended Hamilton's principle. By expressing the lift and pitching moment in terms of plunge and pitch displacements, the resultant two continuous equations are simplified using Galerkin's reduced order model. The flutter velocity is predicted from the solution of resultant damped eigenvalue problem. Parametric studies are conducted to know the effects of geometric factors such as taper ratio, thickness, sweep angle as well as material volume fractions and functional grading index on the flutter velocity. A generalized surrogate model is constructed by training the radial basis function network with the parametric data. The optimized material and geometric parameters of the section are predicted by solving the constrained optimal problem using firefly metaheuristics algorithm that employs the developed surrogate model for the function evaluations. The trapezoidal hollow box beam section design with axial functional grading concept is illustrated with combination of aluminium alloy and aluminium with silicon carbide particulates. A good improvement in flutter velocity is noticed by the optimization.

• Nuclear Engineering and Technology
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• v.17 no.2
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• pp.116-128
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• 1985

Considering vacancy generation and migration in grain and sink at grain boundary, a mechanistic densification model which is dependent on UO$_2$ temperature and microstructure has been developed. This densification model is a function of time, fission rate, temperature, density, pore size distribution and grain size. The resultant equation derived in this model which is different from Assmann and Stehle's resultant equations for four temperature regions, can be applied directly for all the pellet temperatures. The predictions of the present densification model very well agreed with the experimental data. This model well predicts absolute magnitude and trend in comparison with the empirical algorithm used in KFEDA code.

• Structural Engineering and Mechanics
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• v.18 no.2
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• pp.247-262
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• 2004

In the earlier application of the spline finite strip method(FSM), the uniform B3-spline functions were used in the longitudinal direction while the conventional interpolation functions were used in the transverse direction to construct the displacement filed in a strip. To overcome the shortcoming of the uniform B3-spline, non-periodic B-spline was developed as the displacement function. The use of non-periodic B3-spline function requires no tangential vectors at both ends to interpolate the geometry of shell and the Kronecker delta property is also satisfied at the end boundaries. Recently, non-periodic spline FSM which was modified to have a multiple knots at the boundary was developed for the shell analysis and applied to the analysis of bridges. In the formulation of a non-symmetric spline finite strip method, the concepts of non-periodic B3-spline and a stress-resultant finite strip with drilling degrees of freedom for a shell are used. The introduction of non-symmetrically spaced knots in the longitudinal direction allows the selective local refinement to improve the accuracy of solution at the connections or at the location of concentrated load. A number of numerical tests were performed to prove the accuracy and efficiency of the present study.