• Journal of electromagnetic engineering and science
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• v.8 no.3
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• pp.100-109
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• 2008

The finite volume time domain(FVTD) technique faces serious limitations in simulating electromagnetic scattering at high frequencies due to requirements related to discretization. A modified FVTD method is proposed for electrically large, perfectly conducting scatterers by partially incorporating a time-domain physical optics(PO) approximation for the surface current. Dominant specular returns in the modified FVTD method are modeled using a PO approximation of the surface current allowing for a much coarser discretization at high electrical sizes compared to the original FVTD scheme. This coarse discretization can be based on the minimum surface resolution required for a satisfactory numerical evaluation of the PO integral for the scattered far-field. Non-uniform discretization and spatial accuracy can also be used in the context of the modified FVTD method. The modified FVTD method is aimed at simulating electromagnetic scattering from geometries containing long smooth illuminated sections with respect to the incident wave. The computational efficiency of the modified FVTD method for higher electrical sizes are shown by solving two-dimensional test cases involving electromagnetic scattering from a circular cylinder and a symmetric airfoil.

• Computational Structural Engineering
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• v.5 no.2
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• pp.119-127
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• 1992

The entire nonlinear behavior of reinforced concrete frames up to collapse, is analyzed by the displacement control method and the combined layered and nonlayered method. All of the rigidities of section are calculated approximately by a sum over all the layers for the layered method, are used the integral values over the cross section area for the nonlayered method. The spurious sensitivity to the chosen element size in the result of analysis by finite element method for the materials with strain-softening can be overcome by modifying the strain distribution based on the concept of fracture energy at plastic hinge considering the applied axial load.

• Geophysics and Geophysical Exploration
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• v.26 no.1
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• pp.1-7
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• 2023

This study derives the expressions of vector gravity and gravity gradient tensor due to an elliptical cylinder. The vector gravity for an arbitrary three-dimensional (3D) body is obtained by differentiating the gravitational potential, including the triple integral, according to the shape of the body in each axis direction. The vector gravity of the 3D body with axial symmetry is integrated along the axial direction and reduced to a double integral. The complex Green's theorem using complex conjugates subsequently converts the double integral into a one-dimensional (1D) closed-line integral. Finally, the vector gravity due to the elliptical cylinder is derived using 1D numerical integration by parameterizing a boundary of the elliptical cross-section as a closed line. Similarly, the gravity gradient tensor due to the elliptical cylinder is second-order differentiated from the gravitational potential, including the triple integral, and integrated along the vertical axis direction reducing it to a double integral. Consequently, all the components of the gravity gradient tensor due to an elliptical cylinder are derived using complex Green's theorem as used in the case of vector gravity.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.2 no.3
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• pp.26-31
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• 1991

The scattering property of TMz illuminated a elliptic dielectric cylinders with arbitrary cross section are analyzed by the boundary element techniques. The boundary element equations are for- mulated via Maxwell's equations, weighted residual of Green's theorem, and the boundary conditions. The unknown surface fields on the boundaries are then calculated by the boundary element integral equations. Once the surface fields are found, the scattered fields in far-zone and scattering widths (SW) are readily determined. To show the validity and usefulness of this formulation, computations are compared with those obtained using analytical method and one layer circular cylinder. As exten- sion to arbitrary cross-sectioned cylinders, plane wave scattering from a elliptic dielectric cylinders are numerically analyzed. A general computer program has been developed using the quadratic ele- ments(Higher order borndary elements) and the Gaussian quadrature.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.12
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• pp.65-73
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• 1995

In this paper, new algorithm which calculates transmission coefficient of electromagnetic wave by numerical analysis of scattered field by conductors with arbitrary cross-sections in parallel-plate waveguide is proposed. Proposed algorithm assumes magnetic current distribution on the boundary of scattering conductors, and applies Image theorem to perfect conductor surfaces of parallel-plate waveguide. Integral equations for fictitious magnetic currents on conducting boundary are set up. Magnetic current distributions on conducting boundary are expanded as exponential basis function, and using Galerkin method matrix equations are set wp. To compute matrix elements this method utilizes Fourier transform which is faster than numerical integration. Finally, frequency and incidence-angle characteristic of transmission coefficient are calculated and compared with experimental results.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.715-731
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• 2021

Uncertainties are calculated for pressurized water reactor (PWR) spent nuclear fuel (SNF) characteristics. The deterministic code STREAM is currently being used as an SNF analysis tool to obtain isotopic inventory, radioactivity, decay heat, neutron and gamma source strengths. The SNF analysis capability of STREAM was recently validated. However, the uncertainty analysis is yet to be conducted. To estimate the uncertainty due to nuclear data, STREAM is used to perturb nuclear cross section (XS) and resonance integral (RI) libraries produced by NJOY99. The perturbation of XS and RI involves the stochastic sampling of ENDF/B-VII.1 covariance data. To estimate the uncertainty due to modeling parameters (fuel design and irradiation history), surrogate models are built based on polynomial chaos expansion (PCE) and variance-based sensitivity indices (i.e., Sobol' indices) are employed to perform global sensitivity analysis (GSA). The calculation results indicate that uncertainty of SNF due to modeling parameters are also very important and as a result can contribute significantly to the difference of uncertainties due to nuclear data and modeling parameters. In addition, the surrogate model offers a computationally efficient approach with significantly reduced computation time, to accurately evaluate uncertainties of SNF integral characteristics.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1775-1782
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• 2023

Several reactor physics commissioning experiments were conducted to obtain the neutronic parameters at the beginning of the G.A. Siwabessy Multi-purpose Reactor (RSG-GAS) operation. These parameters are essential for the reactor to safety operate. Leveraging the experimental data, this study evaluated the calculated core reactivity, control rod reactivity worth, integral control rod reactivity curve, and fuel reactivity. Calculations were carried out with Serpent 2 code using the latest neutron cross-section data ENDF/B-VIII.0. The criticality calculations were carried out for the RSG-GAS first core up to the third core configuration, which has been done experimentally during these commissioning periods. The excess reactivity for the second and third cores showed a difference of 510.97 pcm and 253.23 pcm to the experiment data. The calculated integral reactivity of the control rod has an error of less than 1.0% compared to the experimental data. The calculated fuel reactivity value is consistent with the measured data, with a maximum error of 2.12%. Therefore, it can be concluded that the RSG-GAS reactor core model is in good agreement to reproduce excess reactivity, control rod worth, and fuel element reactivity.

• Nuclear Engineering and Technology
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• v.47 no.7
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• pp.791-803
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• 2015

The effective cross sections (XSs) in the direct whole core calculation code nTRACER are evaluated by the equivalence theory-based resonance-integral-table method using the WIMS-based library as an alternative to the subgroup method. The background XSs, as well as the Dancoff correction factors, were evaluated by the enhanced neutron-current method. A method, with pointwise microscopic XSs on a union-lethargy grid, was used for the generation of resonance-interference factors (RIFs) for mixed resonant absorbers. This method was modified by the intermediate-resonance approximation by replacing the potential XSs for the non-absorbing moderator nuclides with the background XSs and neglecting the resonance-elastic scattering. The resonance-escape probability was implemented to incorporate the energy self-shielding effect in the spectrum. The XSs were improved using the proposed method as compared to the narrow resonance infinite massbased method. The RIFs were improved by 1% in $^{235}U$, 7% in $^{239}Pu$, and >2% in $^{240}Pu$. To account for thermal feedback, a new feature was incorporated with the interpolation of pre-generated RIFs at the multigroup level and the results compared with the conventional resonance-interference model. This method provided adequate results in terms of XSs and k-eff. The results were verified first by the comparison of RIFs with the exact RIFs, and then comparing the XSs with the McCARD calculations for the homogeneous configurations, with burned fuel containing a mixture of resonant nuclides at different burnups and temperatures. The RIFs and XSs for the mixture showed good agreement, which verified the accuracy of the RIF evaluation using the proposed method. The method was then verified by comparing the XSs for the virtual environment for reactor applicationbenchmark pin-cell problem, as well as the heterogeneous pin cell containing burned fuel with McCARD. The method works well for homogeneous, as well as heterogeneous configurations.

• The korean journal of orthodontics
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• v.30 no.5 s.82
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• pp.625-642
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• 2000

The purpose of this study is to evaluate the effects of mechanical and thermal fatigue stress on the shear, tensile and shear-tensile combined bond strengths(SBS, TBS, CBS) in various orthodontic brackets bonded to human premolars with chemically cured adhesive(Ortho-one, Bisco, USA). Five types of commercially available metal brackets with various bracket base configurations of Photoetched base(Tomy, Japan), Non-Etched Foil Mesh base(Dentaurum, Germany), Micro-Etched Foil Mesh base(Ortho Organizers, USA), Chessboard base(Daesung, Korea), and Integral base(3M Unitek, USA) were used. Samples were divided into 3 groups, the first group was acted with shear-tensile combined loads($45^{\circ}$) of 200g for 4 weeks(mechanical fatigue stress), the second group was subjected to the 5,000 thermocycles of 15 second dwell time each in $5^{\circ}C\;and\;55^{\circ}C$ baths(thermal fatigue stress), and the third group was the control. Bond strengths were measured at the crosshead speed of 0.5mm/min. The cross-section of bracket base/adhesive interface and the fracture surface were examined with the stereoscope and the scanning electron microscope. The resin remnant on bracket base surface was assessed by ART(Adhesive Remnant Index). The obtained results were summarized as follows, 1. In static bond strength, Photoetched base bracket showed the maximum bond strength and Integral base bracket showed the minimum bond strength(p<0.05). In all brackets, shear bond strength(SBS) was in the greatest value and shear-tensile combined strength(CBS) was in the least value(p<0.05). 2. After mechanical fatigue test, Photoetched base bracket showed the maximum bond strength and Integral base bracket showed the minimum bond strength(p<0.05). In Photoetched base bracket and Micro-Etched Foil Mesh base bracket, shear bond strength(SBS), tensile bond strength(TBS) and shear-tensile combined strength(CBS) were decreased after mechanical fatigue test(p

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.12
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• pp.2468-2478
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• 1994

A hybrid finite element method is presented for a characterization of scattering an radiation properties of microstrip patch and arrays residing in a cavity recessed in a ground plane. The technique combines the finite element and boundary integral methods to formulate a system for the solution of fields at the aperture and the scattering field and radar cross sections at free space. By virture of the finite element method, the proposed technique is applicable to patch antennas and arrays residing on or embeded in a layered dielectric loss/lossless substrate and is also capable of treating various feed configuration. Several numerical results are presented demonstrating the validity, efficiency and capability of the technique.