• Structural Engineering and Mechanics
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• v.35 no.3
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• pp.335-348
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• 2010

Cutouts are often provided in structural and aircraft components for ventilation, for access, inspection, electric lines and fuel lines or sometimes to lighten the structure. This paper addresses the effects of cutout shape (i.e., circular, square, diamond, elliptical-vertical and elliptical-horizontal) and size on buckling and postbuckling response of quasi-isotropic (i.e., $(+45/-45/0/90)_{2s}$) composite laminate under uni-axial compression. The finite element method is used to carry out the investigation. The formulation is based on first order shear deformation theory and von Karman's assumptions are used to incorporate geometric nonlinearity. The 3-D Tsai-Hill criterion is used to predict the failure of a lamina while the onset of delamination is predicted by the interlaminar failure criterion. It is observed that for the smaller size cutout area there is no significant effect of cutout shape on load-deflection response of the laminate. It is also concluded that the cutout size has substantial influence on the buckling and postbuckling response of the laminate with elliptical-horizontal cutout, while this effect is observed to be the least in case of laminate with elliptical-vertical cutout.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.9-12
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• 2000

The importance of the role of plastic spin in the rate-dependent response of materials at large deformations is the main objective of this work. After a brief presentation of a general consitutive framework for visco-rigid plasticity at large strains an isotropic/kinematic hardening and a visco-rigid plastic model are used to analyze the stress-strain response under simple shear. A clear understanding of the role of plastic spin is achieved by obtaining numerical analyzed results for different stress values in which the plastic spin consititutive parameters interrelaste with the strain rate and other more conventional model constants, Especially this paper is concerned with introducing behaviors of Al7075

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.47-51
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• 2005

If a structure is founded on the ground saturated with pore water, then the ground should be modeled as a saturated two-phase porous medium for accurate earthquake response analysis. In this study, an axisymmetric transmitting boundary hyperelement is developed for modeling of far field of the ground using u-U formulation for water-saturated transversely isotropic layered stratum. The developed hyperelement is verified by comparing the dynamic stiffness of rigid circular foundation on water-saturated isotropic layered stratum with the case of using equivalent single-phase medium model.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2396-2400
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• 2008

The motion of small heavy particles in homogeneous isotropic turbulence in the present of gravity is investigated using Direct Numerical Simulations (DNS) at moderate Reynolds number. The Lagrangian velocity and acceleration statistics of particles and of flow for a wide range of Stokes number, defined as the ratio of the particle response time to Kolmogorov time scale of turbulence, were obtained for the direction of the gravity and normal direction, respectively. It is found that particles lose their correction faster than the case without gravity. Then, a significant increase in the average settling velocity was observed for a certain range of Stokes number. Our focus is placed on gravitational effect on very small particles. Our simulations show that as the Stokes number reduces to zero, their mean settling velocity approaches the terminal velocity in still fluid.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.345-350
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• 2006

If a structure is founded on the ground saturated with pore water, then the ground should be modeled as a saturated two-phase porous medium for accurate earthquake response analysis. In this study, a 3-dimensional transmitting boundary is developed for modeling of far field using u-U formulation for water-saturated transversely isotropic layered stratum. The developed transmitting boundary is verified by comparing the dynamic stiffness of rigid square foundation on water-saturated isotropic layered stratum with the case of using equivalent single-phase medium model.

• Geomechanics and Engineering
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• v.29 no.1
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• pp.53-63
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• 2022

Simplified analytical solutions are developed for the dynamic analyses of an axially loaded pile foundation embedded in a transverse-isotropic, fluid-filled, poro-visco-elastic soil with rigid substratum. The pile is modeled as a viscoelastic Rayleigh-Love rod, while the surrounding soil is regarded as a transversely isotropic, liquid-saturated, viscoelastic, porous medium of which the mechanical behavior is represented by the Boer's poroelastic media model and the fractional derivative model. Upon the separation of variables, the frequency-domain responses for the impedance function of the pile top, and the vertical displacement and the axial force along the pile shaft are gained. Then by virtue of the convolution theorem and the inverse Fourier transform, the time-domain velocity response of the pile head is derived. The presented solutions are validated, compared to the existing solution, the finite element model (FEM) results, and the field test data. Parametric analyses are made to show the effect of the soil anisotropy and the excitation frequency on the pile-soil dynamic responses.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1993.10a
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• pp.207-215
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• 1993

With the aid of finite element method, this paper deals with the problem of structural response variability of transmission tower subjected to the spatial variability of material properties, Young's modulus herein. The spatial variability of material property are modeled as two-dimensional stochastic field which has an isotropic auto-correlation function. Response variability has been computed based on two numerical techniques, such as the Neumann expansion method in conjunction with the Monte Carlo simulation method. The results by these numerical methods are compared with those by the deterministic approach.

• Journal of KSNVE
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• v.3 no.1
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• pp.57-63
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• 1993

The dynamic response of stiffened rectangular plate subjected to a concentrated force or mass moving at constant speed is analyzed by using finite- element method. Stiffened plates are modelled as an assembly of isotropic thin plate elements and equivalent Euler beam ones, in which the beam elements represent the stiffener effects concentrated at the attached lines of stiffeners to the plates. The Newmark's time integration method is used to obtain the dynamic response of stiffened plates. Numerical examples are given to verify the validity of the presented method and also to investigate the effects of speed and moving mass on the dynamic characteristics of stiffened plates.

• Tribology and Lubricants
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• v.39 no.6
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• pp.221-227
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• 2023

A rotordynamic system consists of components that undergo rotational motion. These components include shafts, impellers, thrust collars, and components that support rotation, such as bearings and seals. The motion of this type of rotating system can be modeled as two-dimensional motion and, accordingly, the equation of motion for the rotordynamic system can be represented using complex coordinates. The directional frequency response function (dFRF) can be derived from this complex coordinate system and used as an effective analytical tool for rotating machinery. However, the dFRF is not widely used in the field because most previous studies and commercial software are based on real coordinate systems. The objective of the current study is to introduce the dFRF and show that it can be an effective tool in rotordynamic analysis. In this study, the normal frequency response function (nFRF) and dFRF are compared under rotordynamic analysis for isotropic and unisotropic rotors. Results show that in the nFRF, the magnitude of the response is the same for both positive and negative frequencies, and the response is similar under all modes. Consequently, the severity of the mode cannot be identified. However, in the dFRF, the forward and backward modes are clearly distinguishable in the frequency domain of the isotropic rotor, and the severity of the mode can be identified for the unisotropic rotor.