• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.2
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• pp.76-83
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• 2014

This paper deals with the numerical method of calculating the frequency-dependent impedances of grounding electrodes. The proposed electromagnetic field approach is based on the solutions to Maxwell's equations obtained from the method of moment in the frequency domain. In order to evaluate the quality of the proposed simulation method, the frequency-dependent impedances of horizontally-buried ground electrodes were presented. The program for calculating the current distributions and impedances of grounding electrodes was implemented in MATLAB. The grounding impedances of two 10m and 50m long horizontal ground electrodes were measured and simulated in the frequency range from 100Hz to 10MHz for easy analysis and comparison. Also the simulated results were compared with those calculated from a sophisticated computer program CDEGS (HIFREQ module). As a result, the resultant results of frequency-dependent impedances obtained by using the numerical simulation method proposed in this work are in good agreement with experimental data. The validity of the approach techniques was confirmed.

• Advances in aircraft and spacecraft science
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• v.4 no.4
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• pp.449-465
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• 2017

The aim of the present work is to present a computational study of the non-linear aero-elastic behavior of a multi-layered Thermal Protection System (TPS). The severity of atmospheric re-entry conditions is due to the combination of high temperatures, high pressures and high velocities, and thus the aero-elastic behavior of flexible structures can be difficult to assess. In order to validate the specific computational model and the overall strategy for structural and aerodynamics analyses of flexible structures, the simplified TPS sample tested in the 8' High Temperature Tunnel (HTT) at NASA LaRC has been selected as a baseline for the validation of the present work. The von $K{\acute{a}}rm{\acute{a}}n^{\prime}s$ three dimensional large deflection theory for the structure and a hybrid Raleigh-Ritz-Galerkin approach, combined with the first order Piston Theory to describe the aerodynamic flow, have been used to derive the equations of motion. The paper shows that a good description of the physical behavior of the fabric is possible with the proposed approach. The model is further applied to investigate structural and aero-elastic influence of the number of the layers and the stitching pattern.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.4
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• pp.550-563
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• 1999

A wavelet-Galerkin scheme based on the time-dependent Maxwell's equations is presented. Daubechies wavelet with two vanishing wavelet moments is expanded for basis function in spatial domain and Yee's leap-frog approach is applied. The shifted interpolation property of Daubechies wavelet family leads to the simplified formulations for inhomogeneous media without the additional matrices for the integral or material operator. The stability condition is formulated. The dispersion characteristics are analyzed and compared with those of finite difference time domain and multiresolution time domain methods. The analyses show the excellent trade-off between the regularity and the support width of the basis function. Although the basis function has only two vanishing wavelet moments, it is enough to provide negligible dispersive error in the numerical analysis and its compact support enables only several involved terms per nodes. The storage effectiveness, execution time reduction and accuracy of this scheme are demonstrated by calculating the resonant frequencies of the homogeneous and inhomogeneous cavities.

• Journal of the Korean Society of Industry Convergence
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• v.3 no.1
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• pp.43-51
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• 2000

The response statistics of a hinged-clamped beam under broad-band random excitation is investigated. The random excitation is applied at the nodal point of the second mode. By using Galerkin's method the governing equation is reduced to a system of nonautonomous nonlinear ordinary differential equations. A method based upon the Markov vector approach is used to generate a general first-order differential equation in the dynamic moment of response coordinates. By means of the Gaussian and non-Gaussian closure methods the dynamic moment equations for the random responses of the system are reduced to a system of autonomous ordinary differential equations. The case of two mode interaction is considered in order to compare it with the case of three mode interaction. The analytical results for two and three mode interactions are also compared with results obtained by Monte Carlo simulation.

• Water Engineering Research
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• v.2 no.3
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• pp.161-169
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• 2001

Present study deals with the development of a numerical model for the estimation of net annual recharge by coupling the Galerkin's finite element flow simulationl model with the Gauss-Newton-Marquardt optimization technique. The developed coupled numerical model is applied for estimating net annual recharge for Mahi Right Bank Canal (MRBC) project the norms of Groundwater Resources Estimation committee (1984, 1997) and Indian Agricultural research Institute(1983). It is observed that the estimated net recharge by inverse modeling is closer to the net recharge estimated using the water balance approach. Further it is observed that the computed head distribution from the estimated recharge agree closely with the observed head distribution. The study concludes that the developed model for inverse modeling can be successfully applied to large groundwater system involving regional aquifers where reliable recharge estimation always requires considerable time and financial resources.

• Structural Engineering and Mechanics
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• v.67 no.2
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• pp.143-153
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• 2018

Thermal buckling of nonlocal flexoelectric nanoplates incorporating surface effects is analyzed for the first time. Coupling of strain gradients and electrical polarizations is introduced by flexoelectricity. It is assumed that flexoelectric nanoplate is subjected to uniform and linear temperature distributions. Long range interaction between atoms of nanoplate is modeled via nonlocal elasticity theory. The residual surface stresses which are usually neglected in modeling of flexoelectric nanoplates are incorporated into nonlocal elasticity to provide better understanding of the physic of problem. A Galerkin-based approach is implemented to solve the governing equations derived from Hamilton's principle are solved. The verification of obtained results is performed by comparing buckling loads of flexoelectric nanoplate with previous data. It is shown that buckling loads of flexoelectric nanoplate are significantly affected by thermal loading type, temperature change, nonlocal parameter, surface effect, plate thickness and boundary conditions.

• Advances in nano research
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• v.8 no.1
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• pp.49-58
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• 2020

This paper investigates the vibration characteristics of flexoelectric nanobeams resting on viscoelastic foundation and subjected to magneto-electro-viscoelastic-hygro-thermal (MEVHT) loading. In this regard, the Nonlocal strain gradient elasticity theory (NSGET) is employed. The proposed formulation accommodates the nonlocal stress and strain gradient parameter along with the flexoelectric coefficient to accurately predict the frequencies. Further, with the aid of Hamilton's principle the governing differential equations are derived which are then solved through Galerkin-based approach. The variation of the natural frequency of MEVHT nanobeams under the influence of various parameters such as the nonlocal strain gradient parameter, different field loads, power-law exponent and slenderness ratio are also investigated.

• Advances in concrete construction
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• v.14 no.1
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• pp.35-43
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• 2022

Based on novel Galerkin's technique, the theoretical study gives a prediction to estimate the vibrations of FG rotating cylindrical shell. Terms of ring supports have been introduced by a polynomial function. Three different laws of volume fraction are utilized for the vibration of cylindrical shells. Variation frequencies with the locations of ring supports have been analyzed and these ring supports are placed round the circumferential direction. The base of this approach is an approximate estimation of eigenvalues of proper functions which are the results of solutions of vibrating equation. Each longitudinal wave number corresponds to a particular boundary condition. The results are given in tabular and graphical forms. By increasing different value of height-to-radius ratio, the resulting backward and forward frequencies increase and frequencies decrease on increasing length-to-radius ratio. There is a new form of frequencies is obtained for different positions of ring supports, which is bell shaped. Moreover, on increasing the rotating speed, the backward frequencies increases and forward frequencies decreases.

• Advances in nano research
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• v.17 no.4
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• pp.315-321
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• 2024

Here, vibration of double walled carbon nanotubes is evaluated using Euler-Bernoulli beam model. These tubes are placed on Winkler elastic foundation. A simple Galerkin's approach is presented to solve the tube governing equations and for extracting of vibration eigen-frequencies of double walled carbon nanotubes. The procedure is easy for computer programming with various combinations of boundary conditions. The frequency influence is observed with different parameters. Effects of Winkler foundation versus frequencies with varying lengths is examined for a number of boundary conditions. It is noticed that the frequencies are lower for higher length on increasing the Winkler foundation. The frequencies of clamped-clamped are higher than that of clamped simply supported end condition. The obtained results are compared with some experimental ones.

• Steel and Composite Structures
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• v.42 no.3
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• pp.375-388
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• 2022

In this work, limit elastic speed analysis of functionally graded porous rotating disks has been reported. The work proposes an effective approach for modeling the mechanical properties of a porous functionally graded rotating disk. Four different types of porosity models namely: uniform, symmetric, inner maximum, and outer maximum distribution are considered. The approach used is the variational principle, and the solution has been achieved using Galerkin's error minimization theory. The study aims to investigate the effect of grading indices, aspect ratio, porosity volume fraction, and porosity types on limit angular speed for uniform and variable disk geometries of constant mass. To validate the current study, finite element analysis has been used, and there is good agreement between the two methods. The study yielded a decrease in limit speed as grading indices and aspect ratio increase. The porosity volume fraction is found to be more significant than the aspect ratio effect. The research demonstrates a range of operable speeds for porous and non-porous disk profiles that can be used in industries as design data. The results show a significant increase in limit speed for an exponential disk when compared to other disk profiles, and thus, the study demonstrates a range of FG-based structures for applications in industries that will not only save material (lightweight structures) but also improve overall performance.