• Journal of the Korean Society for Precision Engineering
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• v.24 no.8 s.197
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• pp.108-115
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• 2007

3D nano-scale manufacturing is an important aspect of advanced manufacturing technology. A key element in ability to view, fabricate, and in some cases operate micro-devices is the availability of tightly focused particle beams, particularly of photons, electrons, and ions. The use of ions is the only way to fabricate directly micro-/ nano-scale structures. It has been utilized as a direct-write method for lithography, implantation, and milling of functional devices. The simulation of ion beam induced physical and chemical phenomena based on sound mathematical models associated with simulation methods is presented for 3D micro-/nanofabrication. The results obtained from experimental investigation and characteristics of ion beam induced direct fabrication will be discussed.

• Journal of Mechanical Science and Technology
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• v.20 no.10
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• pp.1646-1652
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• 2006

A model of mechanical behavior of microcantilever due to intrinsic strain during deposition of MEMS structures is derived. A linear ordinary differential equation is derived for the beam deflection as a function of the thickness of the deposited layer. Closed-form solutions are not possible, but numerical solutions are plotted for various dimensionless ratios of the beam stiffness, the intrinsic strain, and the elastic moduli of the substrate and deposited layer. This model predicts the deflection of the cantilever as a function of the deposited layer thickness and the residual stress distribution during deposition. The usefulness of these equations is that they are indicative of the real time behavior of the structures, i.e. it predicts the deflection of the beam continuously during deposition process.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1684-1689
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• 2003

This paper concerns the analytical modeling and dynamic analysis of advanced cantilevered blade structure implemented by a dual approach based on structural tailoring and viscoelastic materials technology. Whereas structural tailoring uses the directionality properties of advanced composite materials, the passive materials technology exploits the damping capabilities of viscoelastic material(VEM) embedded into the host structure. The structure is modeled as a composite thin-walled beam incorporating a number of nonclassical features such as transverse shear, secondary warping, anisotropy of constituent materials, and rotary inertias. The case of VEM spreaded over the entire span of the structure is considered. The displayed numerical results provide a comprehensive picture of the synergisitic implications of the application of both techniques, namely, the tailoring and damping technology on vibration response of thin-walled beam structure exposed to external time-dependent excitations.

• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.2
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• pp.159-167
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• 2020

In actual battlefield environment, IFF radar plays an important role in distinguishing friend or foe targets and assigning unique identification code to management. Performance of IFF radar is greatly affected by radio environment including atmosphere and terrain, target maneuvering and operation mode. In this paper, M&S tool is consisted of interrogator(IFF radar) and answering machine(target) for radar performance analysis. The wave propagation model using APM(Advanced Propagation Model) and radar actuator system were modeled by considering beam waveform of individual operation beam mode. Using this tool, IFF radar performance was analyzed through two experimental results. As a result, it is expected that performance of IFF radar can be predicted in the operational environment by considering target maneuvering and operation beam mode.

• KCI Concrete Journal
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• v.11 no.3
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• pp.115-126
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• 1999

An analytical method based on the nonlinear layered finite element method is developed to simulate an overall load-deflection behavior of strengthened beams. The developed model distinguishes itself by its capability to trace residual flexural behavior of a beam after the fracture of brittle strengthening materials at peak load. The model. which uses a rather advanced numerical technique for iterative convergence to equilibrium, can be regarded as superior to the two models based on load control and displacement control The model predictions were compared with the experimental results and it was observed that there was good agreement between them.

• Structural Engineering and Mechanics
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• v.74 no.2
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• pp.175-187
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• 2020

The theories having been developed thus far account for higher-order variation of transverse shear strain through the depth of the beam and satisfy the stress-free boundary conditions on the top and bottom surfaces of the beam. A shear correction factor, therefore, is not required. In this paper, the effect of surface on the axial buckling and free vibration of nanobeams is studied using various refined higher-order shear deformation beam theories. Furthermore, these theories have strong similarities with Euler-Bernoulli beam theory in aspects such as equations of motion, boundary conditions, and expressions of the resultant stress. The equations of motion and boundary conditions were derived from Hamilton's principle. The resultant system of ordinary differential equations was solved analytically. The effects of the nanobeam length-to-thickness ratio, thickness, and modes on the buckling and free vibration of the nanobeams were also investigated. Finally, it was found that the buckling and free vibration behavior of a nanobeam is size-dependent and that surface effects and surface energy produce significant effects by increasing the ratio of surface area to bulk at nano-scale. The results indicated that surface effects influence the buckling and free vibration performance of nanobeams and that increasing the length-to-thickness increases the buckling and free vibration in various higher-order shear deformation beam theories. This study can assist in measuring the mechanical properties of nanobeams accurately and designing nanobeam-based devices and systems.

• Advances in nano research
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• v.13 no.4
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• pp.351-368
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• 2022

Recently, promising structural technologies like multi-function, ultra-load bearing capacity and tailored structures have been put up for discussions. Finite Element (FE) modelling is probably the best-known option capable of treating these superior properties and multi-domain behavior structures. However, advanced materials such as Functionally Graded Material (FGM) and nanocomposites suffer from problems resulting from variable material properties, reinforcement aggregation and mesh generation. Motivated by these factors, this research proposes a unified shape function for FGM, nanocomposites, graded nanocomposites, in addition to traditional isotropic and orthotropic structural materials. It depends not only on element length but also on the beam's material properties and geometric characteristics. The systematic mathematical theory and FE formulations are based on the Timoshenko beam theory for beam structure. Furthermore, the introduced element achieves C1 degree of continuity. The model is proved to be convergent and free-off shear locking. Moreover, numerical results for static and free vibration analysis support the model accuracy and capabilities by validation with different references. The proposed technique overcomes the issue of continuous properties modelling of these promising materials without discarding older ones. Therefore, introduced benchmark improvements on the FE old concept could be extended to help the development of new software features to confront the rapid progress of structural materials.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.467-470
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• 1999

An analytical method based on the nonlinear layered finite element method is developed to simulate overall load-deflection behavior of bonded and unbonded prestressed concrete beams. The model which uses rather advanced numerical technique for iterative convergence to equilibrium can be regarded as superior one compared to the models mainly based on either load control or displacement control methods. Model predictions were compared with preceding experimental results and it was observed that there were good agreements between them.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2696-2707
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• 2021

The purpose of this study is to investigate the efficiency of various structural modeling schemes for evaluating seismic performances and fragility of the reactor containment building (RCB) structure in the advanced power reactor 1400 (APR1400) nuclear power plant (NPP). Four structural modeling schemes, i.e. lumped-mass stick model (LMSM), solid-based finite element model (Solid FEM), multi-layer shell model (MLSM), and beam-truss model (BTM), are developed to simulate the seismic behaviors of the containment structure. A full three-dimensional finite element model (full 3D FEM) is additionally constructed to verify the previous numerical models. A set of input ground motions with response spectra matching to the US NRC 1.60 design spectrum is generated to perform linear and nonlinear time-history analyses. Floor response spectra (FRS) and floor displacements are obtained at the different elevations of the structure since they are critical outputs for evaluating the seismic vulnerability of RCB and secondary components. The results show that the difference in seismic responses between linear and nonlinear analyses gets larger as an earthquake intensity increases. It is observed that the linear analysis underestimates floor displacements while it overestimates floor accelerations. Moreover, a systematic assessment of the capability and efficiency of each structural model is presented thoroughly. MLSM can be an alternative approach to a full 3D FEM, which is complicated in modeling and extremely time-consuming in dynamic analyses. Specifically, BTM is recommended as the optimal model for evaluating the nonlinear seismic performance of NPP structures. Thereafter, linear and nonlinear BTM are employed in a series of time-history analyses to develop fragility curves of RCB for different damage states. It is shown that the linear analysis underestimates the probability of damage of RCB at a given earthquake intensity when compared to the nonlinear analysis. The nonlinear analysis approach is highly suggested for assessing the vulnerability of NPP structures.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.3
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• pp.396-404
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• 1998

A numerical analysis is presented for the transient behavior of a rotating turbines blades. The response due to partial admission during start-up and resonance pass is considered, Modal analysis and numerical integation method are used for solving the problems A theory for determining the material and aerodynamic damping values of turbine blades is presented. The damping values of the various modeling of blaes-uniform beam and tapered twisted beam-are calculated and the influence on blades response is investigated. The effect of angular velocity on transient response are also shown.