• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.354-362
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• 1995

The finite element modeling is used to study the buckling and postbuckling behavior of composite laminates with an embedded delamination. Degenerated shell element and rigid beam element are utilized for the finite element modeling. In the nonlinear finite element formulation, the updated Lagrangian description method based on the second Piola-Kirchhoff stress tensor and the Green strain tensor is used. The buckling and postbuckling behavior of composite laminates with a delamination are investigated for various delamination sizes, stacking sequences, and boundary conditions. It is shown that the buckling load and postbuckling behavior of composite laminates depend on the buckling model which is determined by the delamination size, stacking sequence and boundary condition. Also, results show that introduction of couplings can reduce greatly the buckling load.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.11
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• pp.1029-1035
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• 2011

Pressure pulsation of exciting sources that generally occurs on the piping system connected to the discharge of BFP(boiler feed water pump) in power plants causes wave reflection, wave interference, resonance, standing wave and so on. But if the operating speed of the pump is changed, the state of the noise and vibration can be done because characteristics of the exciting source are changed. This paper is to investigate the cause of the noise and vibration occurring on the piping system when the operating speed of BFP is down in accordance with lowering of the power generation. It is approached to two points of view ; Firstly, it is examined whether the pulsation source impacts on the shell mode vibration that vibrates radially across the cross-section of the pipe. But it doesn't affect the shell mode as much as the resonance occurs. Secondly, to find the relation between the pulsation source and the acoustic mode of the piping system, analysis for the piping system by indirect BEM(boundary element method) is carried out. Therefore it is investigated that the mechanism of the noise and vibration relates with acoustic mode of the piping system.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.04a
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• pp.17-27
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• 1995

For the post-buckling and elasto-plastic analysis of shell structures, the total Lagrangian formulation is presented based upon the degenerated shell element. Geometrically correct formulation is developed by updating the direction of normal vectors in the iteration process and evaluating the total Green-Lagrange stain corresponding U total displacements. In the calculation of the stiffness matrix, the element formulation takes into account the effect of finite rotation increments by retaining second order rotation terms in the incremental displacement field. The selective or reduced integration scheme using the heterosis element is applied in order to overcome both shear locking phenomena and the zero energy mode. The load/displacement incremental scheme is adopted for geometric non-linear F .E. analysis. Based on such methodology, the computer program is developed and numerical examples to demonstrate the accuracy and the effectiveness of the proposed shell element are presented and compared with references's results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1321-1324
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• 2007

In this paper, the in-plane end vibration of a cylindrical shell has been analyzed. The theoretical result has showed that the strong in-plane vibration at the ends of the cylindrical shell can be generated by the evanescent wave field, which is excited along about half the length of the shell. This has been also observed from experimental result. The evanescent waves are generated due to mode conversion of elastic waves at the ends of the cylindrical shells. The results show that the strong in-plane end vibration can be generated in cylindrical shells.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.1
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• pp.36-42
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• 2017

Helical gear excitation is transmitted to a gearbox through the shafts and bearings and the vibration of the gearbox radiates the noise in the air. Therefore gearbox modeling is essential to evaluate the gear noise. This work deals with vibration and acoustic analysis of a cylindrical shell-type gearbox with/without holes excited by helical gears and focuses on the development of the simple gearbox model. To do so, helical gears and bearing forces are calculated. Gearbox with/without holes is modeled by the aluminum end plates and PMMA cylindrical shell body. The vibration mode and the forced harmonic response were calculated by the commercial FE software and the end plate of the gearbox is more contributed to vibration than the body. Acoustic analysis was also conducted by the commercial acoustic software and a cylindrical shell type gearbox with/without holes has the similar vibro-acoustic characteristics.

• Particle and aerosol research
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• v.14 no.3
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• pp.49-63
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• 2018

During the last decade, electrospray (ES) techniques have been used as potential methods for preparing of core-shell materials. Depending on the architecture of nozzle and design of devices, the ES techniques includes monoaxial, coaxial, multiple coaxial nozzle ES and microfluidic ES devices. ES operates based on a basic principle, in which a spray of monodisperse droplets is formed by dispensing an electrically conductive liquid through a capillary charged to a sufficiently high potential. In review of many recent research papers, we take a closer look at ES techniques and their applications for fabrication of core-shell materials. Several advantages of ES technique compared with other methods were emphasized and it may be regarded as a potential tool for fabrication of core-shell materials current and near future.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.10
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• pp.767-776
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• 2003

The theoretical method is developed to Investigate the nitration characteristics of the combined cylindrical shells with an annular plate joined to the shell at any arbitrary axial position. The structural coupling between shell and plate is simulated using two types of artificial springs a translational spring is introduced for translational coupling and a rotational spring is used for rotational coupling. The springs are continuously distributed along circumferential direction. Using the Rayleigh-Ritz method the natural frequencies and mode shapes of the combined shell with an annular plate examine. The effect of Inner-to-outer radius ratio, axial position of annular plate and length-to-radius ratio of shell on vibration characteristics of combined cylindrical shells is studied. The theoretical results are verified by comparison with FEM results.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.57-64
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• 2001

For the dynamic nonlinear analysis of stiffened plate and shell structures, total Lagrangian formulation is presented based upon the degenerated shell element considering finite rotation effects. Assumed strain concept is adopted in order to overcome shear locking phenomena and to eliminate spurious zero energy mode. In the elasto-plastic analysis, the return mapping algorithm based on the consistent elasto-plastic tangent modulus is applied to collapse analysis of shell structures. Newmark integration method is used for dynamic nonlinear analysis of shell structures under dynamic forces.

• Bulletin of the Society of Naval Architects of Korea
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• v.24 no.1
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• pp.42-50
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• 1987

The energy expressions are formulated for the axially stiffened shell treating the stiffeners as discrete elements. The principle of minimum potential energy is employed to formulate the buckling equations for a simply supported, axially stiffened shell under uniform axial compression. The displacement functions are expended into double trigonometric series. The mode assuming method employed in this paper makes it possible to reduce the matrix size of the eigenvalue problem considerably. Effects are made to investigate the transition from overall buckling to local buckling and to verify the existence of the minimum stiffness ratio of stiffener as in the case of stiffened plate. The results of the calculation show that the critical stiffener size increase linearly as the length of the shell increases. The results also show that the overall buckling load decreases and the local buckling load has a nearly constant value as the length of the shell increases. The results show very good agreements with other computational available.

• Structural Engineering and Mechanics
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• v.8 no.6
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• pp.591-605
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• 1999

An accurate and efficient shell element is presented. The stiffness of the shell element is decomposed into two parts with one part corresponding to stretching and bending deformation and the other part corresponding to shear deformation of the shell. Both parts of the stiffness are calculated with reduced integration rules, thereby improving computational efficiency. Shear strains are averaged on the reference surface such that neither locking phenomena nor any zero energy mode can occur. The satisfactory behaviour of the element is demonstrated in several numerical examples.