• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.529-534
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• 2002

The receptance method was applied for the analysis of a cylindrical shell with a curvaturated plate attached at the top of the shell. The boundary conditions of the shell considered here were clamped at the bottom and free at the top of the shell. Before the analysis of the shell/plate combined structure, the natural frequencies of the plate and the shell were calculated separately and then they were used in the calculation of the frequencies of the combined structure by the receptance method. The frequency equation of the combined structure was derived from the continuity condition at the junction of the shell and the plate. The frequencies for various curvature factors of the plate were presented and compared with those from ANSYS to show its validity of the present method.

• Structural Engineering and Mechanics
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• v.65 no.6
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• pp.731-739
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• 2018

This paper presents an optimal pattern for distributing stiffness along a framed tube structure through an analytic equation, which may be used during the preliminary design stage. Most studies in this field are computationally intensive and time consuming, while a hand-calculation method, as presented here, is a more suitable tool for sensitivity analyses and parametric studies. Approach in development of the analytic model is to minimize the mean compliance (external work) for a given volume of material. A variational statement of the problem is made, and a specified deformation-profile is obtained as the necessary condition for a minimum; enforcing this condition, stiffness is then computed. Due to some near-zero values for stiffness, the problem is modified by considering a lower bound constraint. To deal with this constraint, the design domain is assumed to be divided into two zones of constant stiffness and constant curvature; and the problem is restated in terms of these concepts. It will be shown that this methodology allows for easy computation of stiffness through an analytic and dimensionless equation, valid in any system of units. To show practicality of the proposed method, a tubed-system structure with uniform stiffness distribution is redesigned using the proposed model. Comparative analyses of the results reveal that in addition to simplicity of the proposed method, it provides a rather high degree of accuracy for real-world problems.

• Special Issue of the Society of Naval Architects of Korea
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• 2017.10a
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• pp.8-13
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• 2017

The rolled carbon steel plate has anisotropic property in Z-direction(thickness direction). This is induced by cooling rate difference of Z-direction and sulfur which make non-metallic inclusion(MnS) at center line of thickness direction. Z-directional mechanical properties of normal steel plate are not generally specified and it is defined for Z-Quality steel only through tensile test in Z-direction. If Z-quality steel is not applied for cruciform joint, the lamella tearing will be occurred by tensile stress after welding & during operation of the structure. In this research, one equation estimating Z-directional(orthogonal to plate) stress was developed to prevent lamella tearing by welding. This equation deals with plate thickness & joint configuration(eccentricity, angle and curvature). Analyses were done by strain boundary method using sectional FE modeling and FE 3D models are also used for some cases. Designers can predict the possibility of lamella tearing by adequately applying the result and can appropriately minimize the application of Z-quality steel by revising welding design to some extent.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.18-21
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• 1999

In this study in order to make doubly-curved sheet metal effectively a sheet metal forming process has been developed by adopting the flexibility of the incremental forming process and the principle of bending deformation which causes slight deformation to thickness The developed process is an unconstrained forming process with no holder. For this study the experimental equipment is set up with the punch-set which consists of two pairs of lower support-punches and one upper center-punch. In the experiments using aluminum sheet it is found that the curvature of the formed sheet metal is determined by controlling the distance between supporting punches in pairs and the forming depth of the center-punch. and the edge-forming method is proposed for forming the sheet metal into the balanced shape. The equation using process variables such as the distance between supporting punches in pairs and the forming depth of the center-punch is proposed for the prediction of the radii of curvatures of the formed shape and it is corrected by the experimental results and the FEM simulation results about whether springback takes place. It is found that according o the simulation there is a certain set of the distance between a pair of supporting punches and the forming depth of the center-punch which causes a little springback. It is thus shown that the radii of curvatures of the formed sheet metal can be predicated by the corrected equation unless significant springback occurs.

• Water for future
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• v.28 no.4
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• pp.205-213
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• 1995

Flow in meandering channel is a great concern to civil engineers and may further be characterized as one of the key problems in river morphology. It is difficult to state generalized criteria for channel improvement applicable to any particular river. But it is important to provide some principles and quidelines for the design engineer. The objective of this experimental study is to suggest riprap size, principles and quidelines for the design engineer by the hydraulic model test. For the sake of effective uses for the bank stabilization, hydraulic model tests about riprap weight and size are performed and examing thoroughly. Riprap weight for the upstream of the curvature appex can be computed by U.S.B.R. and Brahms' equation, and the size by Mavis and Laushey's equation. Those for the downstream can be computed using Brahms' and Steinberg's equations, respectively.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.150-159
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• 2014

A simplified method for the calculation of buckling and vibrational characteristics of initially stressed rectangular plate and antisymmetric angle-ply laminated plates is presented in this paper using the natural frequencies under unloading state. The equation of motion of rectangular plate with two opposite edges simply supported is investigated on the basis of Rayleigh-Ritz method and Mindlin plate theory with effect of the curvature term. The relationships of the non-dimensional natural frequencies with initial stresses the coeffcients of critical buckling and the boundaries of the dynamic principal instability region can be characterized by the non-dimensional natureal frequencies under unloading state. Numerical examples are presented to verify the simplified equations and to illustrate potential applications of the analysis.

• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3805-3809
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• 2012

Results for molecular dynamics simulation method of small liquid drops of argon (N = 1200-14400 molecules) at 94.4 K through a Lennard-Jones intermolecular potential are presented in this paper as a preliminary study of drop systems. We have calculated the density profiles ${\rho}(r)$, and from which the liquid and gas densities ${\rho}_l$ and ${\rho}_g$, the position of the Gibbs' dividing surface $R_o$, the thickness of the interface d, and the radius of equimolar surface $R_e$ can be obtained. Next we have calculated the normal and transverse pressure tensor ${\rho}_N(r)$ and ${\rho}_T(r)$ using Irving-Kirkwood method, and from which the liquid and gas pressures ${\rho}_l$ and ${\rho}_g$, the surface tension ${\gamma}_s$, the surface of tension $R_s$, and Tolman's length ${\delta}$ can be obtained. The variation of these properties with N is applied for the validity of Laplace's equation for the pressure change and Tolman's equation for the effect of curvature on surface tension through two routes, thermodynamic and mechanical.

• Journal of Korea Water Resources Association
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• v.39 no.12 s.173
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• pp.1023-1030
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• 2006

The characteristics of the longitudinal velocity in a $180^{\circ}$ constant-radius, recirculating laboratory channel were investigated. Three-dimensional velocity fields were measured using a side-looking ADV. The shortcomings of existing equations for longitudinal velocity are discussed. An eddy viscosity model is adopted in the downstream momentum equation. A mathematical equation was developed to describe the vertical distribution of longitudinal velocity. The comparisons of the longitudinal velocity show generally good agreement. It is found that the curvature change in the curved channel affects the vertical location of maximum velocity and the vertical profile of longitudinal velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.471-478
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• 2008

Detached Eddy Simulation (DES) is performed for developing turbulent flow of the $270^{\circ}$ curved duct at a Reynolds number of 56,690. The curvature ratio on the basis of a centric radius $R_c$ and a duct height H is 3.357. Turbulence models adopted are k-$\omega$ model for Reynolds Average Navier-Stokes (RANS) equation Simulation and Shear Stress Transport (SST) model for DES. DES is used as the hybrid computation technique combined with RANS-SST and Large Eddy Simulation (LES). Predicted results are compared with measured results including the distributions of Reynolds stresses and the flow characteristics on the symmetric plane of curved duct are presented. Judging from the comparison between the predicted and the measured results, the DES approach is applicable to calculate the developing turbulent flow in a $270^{\circ}$ curved duct.

• Journal of Power System Engineering
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• v.22 no.6
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• pp.58-66
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• 2018

The use of external gear pumps is an effective way to achieve adequate performance at low cost when composing hydraulic systems. The biggest drawback, on the other hand, is the accompanying noise. Gears of continuous contact shape are actively used for the pump recently. The continuous contact shape must be the helical type due to the nature of the gear pump that is driven only by the drive gear. In this paper the theoretical shape of continuous contact gear is analyzed using simple rack shape of straight lines and two circular arcs. Using such geometry, the theoretical equation will be developed by envelope curves according to the conjugate gear shape rules. After checking the validity of the theory by the shape of gear rules, the grinding shape was also developed. The 3D shapes using equation can be also drawn. It was also shown that contact ratio and radius of curvature are easily developed by the theoretical equations.