• Steel and Composite Structures
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• v.20 no.5
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• pp.1119-1131
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• 2016

As a first attempt, an inverse hybrid numerical method for small scale parameter estimation of functionally graded (FG) nanobeams using measured frequencies is presented. The governing equations are obtained with the Eringen's nonlocal elasticity assumptions and the first-order shear deformation theory (FSDT). The equations are discretized by using the differential quadrature method (DQM). The discretized equations are transferred from temporal domain to frequency domain and frequencies of the nanobeam are obtained. By applying random error to these frequencies, measured frequencies are generated. The measured frequencies are considered as input data and inversely, the small scale parameter of the beam is obtained by minimizing a defined functional. The functional is defined as root mean square error between the measured frequencies and calculated frequencies by the DQM. Then, the conjugate gradient (CG) optimization method is employed to minimize the functional and the small scale parameter is obtained. Efficiency, convergence and accuracy of the presented hybrid method for small scale parameter estimation of the beams for different applied random error, boundary conditions, length-to-thickness ratio and volume fraction coefficients are demonstrated.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.4
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• pp.641-647
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• 2004

By most sensorless speed control schemes for induction motor. the control performances in high speed range are good, but it is difficult to obtain satisfactory results in low speed region. This paper proposes a new method controlling the low and the high speed regions separately to attain the stable operation in the overall range. The current error compensation method, in which the controlled stator voltage is applied to the induction motor so that the error between stator currents of the numerical model and the actual motor can be forced to decay to zero as time proceeds. is used in the low speed region In the high speed region. the method with adaptive observer is utilized. This control strategy contains an adaptive state observer for flux estimation. The rotor speed can be calculated from the rotor flux and the motor currents. The experimental results indicate good speed and load responses from the very low speed range to the high, and also show accurate speed changing performance between the low and the high speed range.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.973-983
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• 2003

The suitability of high-order accurate, centered and upwind-biased compact difference schemes is evaluated for large eddy simulation of turbulent flow. Two turbulent flows are considered: turbulent channel flow at Re = 23000 and flow over a circular cylinder at Re = 3900. The effects of numerical dissipation on the finite differencing and aliasing errors and the subgrid-scale stress are investigated. It is shown through the simulations that compact upwind schemes are not suitable for LES, whereas the fourth order-compact centered scheme is a good candidate for LES provided that proper dealiasing of nonlinear terms is performed. The classical issue on the aliasing error and the treatment of nonlinear terms is revisited with compact difference schemes.

• Journal of the Korean Mathematical Society
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• v.48 no.3
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• pp.529-550
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• 2011

In this work, a numerical solution of the incompressible Navier-Stokes equations is proposed. The method suggested is based on an algorithm of discretization by mixed finite elements with a posteriori error estimation of the computed solutions. In order to evaluate the performance of the method, the numerical results are compared with some previously published works or with others coming from commercial code like Adina system.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.24 no.2
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• pp.143-159
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• 2020

We propose a consistent numerical method for elliptic interface problems with nonhomogeneous jumps. We modify the discontinuous bubble immersed finite element method (DB-IFEM) introduced in (Chang et al. 2011), by adding a consistency term to the bilinear form. We prove optimal error estimates in L² and energy like norm for this new scheme. One of the important technique in this proof is the Bramble-Hilbert type of interpolation error estimate for discontinuous functions. We believe this is a first time to deal with interpolation error estimate for discontinuous functions. Numerical examples with various interfaces are provided. We observe optimal convergence rates for all the examples, while the performance of early DB-IFEM deteriorates for some examples. Thus, the modification of the bilinear form is meaningful to enhance the performance.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.615-622
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• 2002

In this paper, the modification of double projection method for the adaptive analysis of Element-free Galerkin(EFG) method were proposed. As results of the double projection method, the smoothed error profile that is adequate for adaptive analysis was obtained by re-projection of error that means the differences of EFG stress and projected stress. However, it was found that the efficiency of double projection method is degraded as increase of the numerical integration order. Since, the iterative refinement to single step error estimation made the same effect as increasing of integration order, the application of the iterative refinement base on double projection method could be produced the inadequately refined analysis model. To overcome this defect, a modified scheme of double projection were proposed. In the numerical example, the results did not show degradation of double projection effect in iterative refinement and the efficiency of proposed scheme were proved.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.3
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• pp.113-119
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• 1998

In this paper, the error sidelobe level and signal to noise loss from the numerical analysis using the modelling of quadrature coherent detector in the case that the channel imbalance and with local oscillator leakage is considered. From the numerical results, the error sidelobe level and signal to noise loss that with the gain and phase imbalance(0.8(dB)J5(dog)) is (-21.322[dB], -0.0071[dB]), (-11.6839[dB], -0.0059[dB]) in the case that the channel imbalance and with local oscillator leakage is considered.

• Geomechanics and Engineering
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• v.33 no.4
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• pp.353-367
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• 2023

The construction of a protective embankment is a suitable strategy to stop and control high-energy rock blocks' impacts during the rockfall phenomenon. In this paper, based on the discrete element numerical method, by modeling an existing embankment reinforced with geogrid, its stability status under the impact of a rock block with two types of low and high kinetic energy, namely 2402 and 4180 kJ, respectively, has been investigated. The modeling results show that the use of geogrid has caused the displacement in the front and back of the embankment to decrease by more than 30%. In this case, the reinforced embankment has stopped the rock block earlier. The displacements obtained from the DEM modeling are compared with the displacements measured from an actual practical experiment to evaluate the results' validity. Comparison between the results shows that the displacement values are close together, while the maximum percentage error in previous studies by an analytical method and the finite element method was 76.4% and 36.6%, respectively. Therefore, the obtained results indicate the discrete numerical method's high ability compared to other numerical and analytical methods to simulate and design the geogrid-reinforced soil embankment under natural disasters such as rockfall with a minor error.

• Journal of applied mathematics & informatics
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• v.17 no.1_2_3
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• pp.615-622
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• 2005

In this paper, we discuss the average case errors of some numerical quadratures, namely Trapezoidal and Simpson's, in the numerical integration problem. Our integrands are r-fold Wiener functions from the interval [0,1] and only at finite number of points the function values are evaluated. We study average case errors of these quadratures theoretically and then compare it with our practical (a posteriori) researches. Monte-Carlo simulation is used to perform these empirical researches. Finally we empirically compute the error bounds of studied quadratures for the higher degrees of Wiener functions.

• Journal of applied mathematics & informatics
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• v.31 no.5_6
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• pp.609-621
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• 2013

At present, research on providing new methods to solve nonlinear integral equations for minimizing the error in the numerical calculations is in progress. In this paper, necessary conditions for existence and uniqueness of solution for nonlinear 2D Fredholm integral equations are given. Then, two different numerical solutions are presented for this kind of equations using 2D shifted Legendre polynomials. Moreover, some results concerning the error analysis of the best approximation are obtained. Finally, illustrative examples are included to demonstrate the validity and applicability of the new techniques.