• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2334-2343
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• 2000

This paper proposes an efficient beam-shell modeling technique for the free vibration analysis of a T-joint thin-walled beam structure. Except a small portion of a T-joint which is modeled by shell elements, the structure is modeled by thin-walled beam elements that can describe warping and distortion. In order to match the shell and thin-walled beam elements at the interface of the dissimilar elements, a technique based on a pseudo inverse matrix is formulated. This paper also examines the role of the thin-walled element taking into account the distortion and warping deformation degrees of freedom in predicting accurately the dynamic characteristics of a T-joint thin-walled structure.

• Advances in materials Research
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• v.7 no.3
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• pp.185-194
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• 2018

The mechanism of biological materials structure is very complex and has optimal properties compared to engineering materials. Top Neck mollusks shells, as an example of biological materials, have hierarchical structure, which 95 percent of its structure is Aragonite and 5 percent organic materials. This article detected mechanical properties of the Top Neck mollusks shell as a Nano composite using Nano-indentation method in different situations. Research findings indicate that mechanical properties of the Top Neck mollusks shell including elastic modulus and hardness are higher than a fresh one preserved in -50 centigrade and also a Top Neck mollusks shell preserved in environmental conditions. Nano-indentation test results are so close in range, overall, that hardness degree is 3900 to 5200 MPa and elastic modulus is 70 to 85 GPa.

• Structural Engineering and Mechanics
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• v.20 no.2
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• pp.241-257
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• 2005

A numerical approach combining the finite element method with two different stability criteria namely the Budiansky and the phase-plane buckling criteria is used to study the dynamic buckling phenomena of plate and shell structures subjected to sudden applied loading. In the finite element analysis an explicit time integration scheme is used and the two criteria are implemented in the Finite Element analysis. The dynamic responses of the plate and shell structures have been investigated for different values of the plate and shell imperfection factors. The results indicate that the dynamic buckling time, which is normally considered in predicting elasto-plastic buckling behavior, should be taken into consideration with the buckling criteria for elastic buckling analysis of plate and shell structures. By selecting proper control variables and incorporating them with two dynamic buckling criteria, the unique dynamic buckling load can be obtained and the problems of ambiguity and contradiction of dynamic buckling load of plate and shell structure can be resolved.

• Journal of Sensor Science and Technology
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• v.21 no.6
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• pp.456-460
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• 2012

Au/$SnO_2$ core-shell structure nanoparticles (NPs) were synthesized by microwave hydrothermal method, and the effect of working temperature on sensitivity of Au/$SnO_2$ core-shell NPs for CO gas was investigated. The $SnO_2$ shell layer was consisted of $SnO_2$ primary particles with 4.5 nm diameter. The response of Au/$SnO_2$ core-shell NPs for CO gas was maximized at the working temperature of $350^{\circ}C$ while the sensitivity increased with decreasing the working temperature due to the low grain size effect of $SnO_2$ NPs on the response of CO gas.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.3
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• pp.225-231
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• 2003

A new three-dimensional thin shell element for a structure containing an integrated distributed piezoelectric sensor and actuator is Proposed. The assumed strain formulation and the bubble function are introduced to improve the performance of the shell element. A finite element formulation gives a general tool that can predict the static or dynamic responses of the shell with piezoelectric sensor/actuator. The verification through the calculation of the static response for the piezoelectric bimorph beam shows that the results agree with those from the theoretical analysis very well. Dynamic response of a shell shows that the reduction of vibration is possible with the introduction of the piezoelectric shell sensor and actuator. However. the curvature of sensor/actuator is an obstacle for application, since the flexible PVDF is not strong enough and the PZT with curvature should be made specially.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1848-1862
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• 2006

As a basic study on the fluid-structure interaction of the shell structure, a theoretical formulation has been suggested on the free vibration of a thin-walled conical frustum shell filled with an ideal fluid, where the shell is assumed to be fixed at both ends. The motion of fluid coupled with the shell is determined by means of the velocity potential flow theory. In order to calculate the normalized natural frequencies that represent the fluid effect on a fluid-coupled system, finite element analyses for a fluid-filled conical frustum shell are carried out. Also, the effect of apex angle on the frequencies is investigated.

• Structural Engineering and Mechanics
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• v.36 no.6
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• pp.729-744
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• 2010

There is world wide concern for safety of nuclear power installations after the terrorist attack on World Trade Center in 2001 and several other civilian structures in the last decade. The nuclear containment structure in many countries is a double shell structure (outer shell a RCC and inner a prestressed concrete). The outer reinforced concrete shell protects the inner shell and is designed for external loading like impact and blast. A comparative study of non-linear response of reinforced concrete nuclear containment cylindrical shell subjected to impact of an aircraft (Phantom) and explosion of different amounts of blast charges have been presented here. A material model which takes into account the strain rate sensitivity in dynamic loading situations, plastic and visco-plastic behavior in three dimensional stress state and cracking in tension has been developed earlier and implemented into a finite element code which has been validated with published literature. The analysis has been made using the developed software. Significant conclusions have been drawn for dissimilarity in response (deflections, stresses, cracks etc.) of the shell for impact and blast loading.

• Current Optics and Photonics
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• v.7 no.5
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• pp.496-503
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• 2023

We present a detailed analysis of the light extraction efficiency (LEE) of a core-shell nanorod light emitting diode (LED) using finite-difference time-domain (FDTD) simulations. We found that the LEE has a deep dependence on source positions and polarization directions based on the calculated LEE results for every x and z position inside the core-shell nanorod structure. The LEEs are different for the upper part (pyramid) and the lower part (sidewall) of the core-shell nanorod owing to total internal reflection (TIR) and the generated optical modes in the structure. As a result, the LEE of sidewall is much larger than that of pyramid. The averaged LEE of the core-shell nanorod LED is also investigated with variable p-GaN thickness, n-GaN thickness, and height for the design guidelines for the optimized LEE of core-shell nanorod LEDs.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.27-34
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• 2020

Use of axisymmetric shell element for the structure increases the efficiency and accuracy in finite element analysis of the interaction between the ground and the structure. This paper derived the force balance equation and the moment balance equation for an axisymmetric shell element based on Kirchhoff's theory. The governing equation for the axial deformation used the isoparametric shape function in the Galerkin formulation, and the governing equation for the shell bending used the higher-order shape function. The developed axisymmetric shell element was combined with Geo-COUS, a geotechnical finite element program for the coupled analysis with the ground. The accuracy of the developed element was confirmed through the example analyses of the circular plate and the liquid storage tank. And the energy balance equation for the axisymmetric shell element is presented.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.154-157
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• 2000

Distributed piezoelectric sensor and actuator system has been designed for the active vibration control of shell structure. PVDF is used for the materials of sensor/actuator. To prevent the adverse effect of spillover, distributed modal sensor/actuator system is established. Although shell structure is three-dimensional structure, the PVDF sensor/actuator system can be treated as two-dimensional Finite element programs are developed to consider curved structures having PVDF modal sensor/actuator. The nine-node Mindlin shell element with five nodal degree of freedoms is used for finite element discretization. The electrode patterns and lamination angle of PVDF sensor/actuator are optimized to design the modal sensor/actuator system Genetic algorithm is used for optimization. Sensor is designed to minimize the observation spillover, and actuator is designed to minimize the system energy of the control modes under a given initial condition. Modal sensor/actuator for the first and second modes of singly curved cantilevered shell structure are designed using mentioned methods. Discrete LQG method is used as a control law. Experimental demonstrations of the active vibration control with designed sensor/actuator system have been performed successfully.