• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.8
• /
• pp.1971-1979
• /
• 1993

In this paper, a new method to estimate stress status in metal nondestructively by using nonlinear dependency of sound speed on stress is proposed. For the purpose, equivalent nonlinear elastic constants up to fourth-order are introduced and a new characteristic parameter given as a function of these constants is presented. And a concrete system to measure the characteristic parameter is constructed by electromagnetic pumping wave and ultrasonic probing wave system. Some experimental results for Al alloy showed that the estimation of stress status in metal is possible by the proposed method.

• Journal of Mechanical Science and Technology
• /
• v.20 no.9
• /
• pp.1323-1338
• /
• 2006

An analytical method to estimate the coupled frequencies of the circular plate submerged in fluid is developed using the finite Fourier-Bessel series expansion and Rayleigh-Ritz method. To verify the validity of the analytical method developed, finite element method is used and the frequency comparisons between them are found to be in good agreement. For the perforated plate submerged in fluid, it is almost impossible to develop a finite element model due to the necessity of the fine meshing of the plate and the fluid at the same time. This necessitates the use of solid plate with equivalent material properties. Unfortunately the effective elastic constants suggested by the ASME code are found to be not valid for the modal analysis. Therefore in this study the equivalent material properties of perforated plate are suggested by performing several finite element analyses with respect to the ligament efficiencies.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.13 no.1
• /
• pp.51-61
• /
• 2000

This paper discusses the homogenization method to determine effective average elastic constants of a linear structure by considering its microstructure. A detailed description on the homogenization method is given for the linear elastic material and then the finite element approximation is performed for an investigation of elastic properties. An asymptotic expansion is carried out in the cross-section area, or in the unit cell. Two and three lay-up structures made up of individual isotropic constituents are chosen for numerical examples to check discrepancies between results generated by this theoretical development and the conventional approach. Asymptotic characteristics of the process in extracting the stiffness of structure locally formed by spatial repetitions yield underestimated values of stiffness. These discrepancies are detected by the asymptotic corrective term which is ascribed to considerations of microscopic perturbations and proved in the finite element formulation. The asymptotic analysis is the more reasonable in analysing the composite material, rather than the conventional approach to calculate the macroscopic average for elastic properties.

• Journal of electromagnetic engineering and science
• /
• v.2 no.1
• /
• pp.16-21
• /
• 2002

On the contrary to the progress of the electronic industry and radio communication technologies, many social problems such as EMI, due to unnecessary electromagnetic(EM) wave are serious with the increased use of EM wave. It is required that the absorbing capability of an EM wave absorber is more than 20 dB, the bandwidth of which is required from 30 MHz to 18 GHz to satisfy the international standard about an anechoic chamber for EMI/EMS measurement$^{[1]}$TEX>. However, the absorbing frequency band of the conventional EM wave absorbers satisfying more than 20 dB is very narrow, for examples, from 30 MHz to 400 MHz in ferrite tile type and from 30 MHz to 870 MHz in ferrite grid type, respectively. In this paper, we proposed and designed a new tripe absorber with broadband characteristics covering the frequency band from 30 MHz to 10 GHz by use of the equivalent material constants method (EMCM)$^{[2]~[4]}$TEX>.

• The Journal of the Acoustical Society of Korea
• /
• v.30 no.7
• /
• pp.368-376
• /
• 2011

Piezoelectric composites have been widely used in broadband acoustic transducers because of their lower acoustic impedance and higher electro-mechanical coupling factor. However, their complex structure has placed many limitations on the design of various transducers. This paper suggests the methodology to substitute the 1-3 piezocomposites by a single-phased material that has properties equivalent to those of the piezocomposites. The resonant method and finite element analysis (FEA) are used to derive the equivalent properties that can accurately depict resonant properties at various vibration modes of the piezocomposites. Validity of the suggested method is confirmed by comparing frequency characteristics of fabricated 1-3 piezocomposite specimens and FEA models. Further, accuracy of the derived material constants is checked by applying the equivalent properties to FEA models of the single phase material for various resonant modes.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 1994.04a
• /
• pp.43-48
• /
• 1994

A wide band design method of an electromagnetic wave absorber using exponentially tapered ferrite which has very wide band frequency characteristics is proposed and discussed. The wide band electromagnetic wave absorber can be designed by the proposed equivalent material constants method for the regions varying spatially in the shape of ferrite. Furthemore the wide band ferrite electromagnetic wave absorbers with taper which have not only excellent reflectivity frequency characteristics but also the band width of 30MHz to 2150 or 2450MHz under the tolerance limits of -20dB reflectivity were designed.

• Journal of the Korean Institute of Navigation
• /
• v.18 no.2
• /
• pp.151-158
• /
• 1994

A wide band design method of an electromagnetic wave absorber using exponentially tapered ferrite, which has very wide band frequency characteristics, is proposed and discussed. The wide band electroma-gnetic wave absorber can be designed by the proposed equivalent material constants method for the re-gions varying spatially in the shape of ferrite. Futhermore, the wide band ferrite electromagnetic wave absorber with taper, which have not only exce-llent reflectivity frequency characteristics but also the band width of 30MHz to 2150 or 2450MHz under the tolerance limits of -20dB reflectivity, were designed.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 1994.10a
• /
• pp.59-68
• /
• 1994

A wide band design method of an double layerred electromagnetic wave absorber sintered ferrite which has a flat and an anti-grid shape layers is proposed and discussed. The wide band electomagnetic wave absorber can be designed by the equivalent material constants method for the each layer, As a result the wide band ferrite electonmagnetic wave absorber with the band width of 30MHz to 3670, 3680 or 3690MHz were designed under the tolerance limits of -20dB reflectivity.

• Journal of the Korean Institute of Navigation
• /
• v.19 no.4
• /
• pp.93-102
• /
• 1995

A design method of an electromagnetic wave absorber with ferrite fins in the second layer, which has very wide band frequency characteristics, is proposed and discussed. A theoretical model using the equivalent material constants method is adopted, assessed for its accuracy by comparision with the Hashin-Shtrikman formulas and compared with the conventional absorbers. Based on the model, a wide band electromagnetic wave absorber with excellent reflectivity frequency characteristics in frequency range of 30MHZ to 3530MHZ has been designed.

• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.34D no.4
• /
• pp.8-16
• /
• 1997

A wide band design method of an electromagnetic wave absorber with using exponentially tapered ferritic is proposed and discussed. A theoretical model using the equivalent material constants method is also proposed to analyze the regions varying sptially in the shape of ferrite. Based on the developed model, wide band electromagnetic wave absorbers with excellent reflectivity frequency charaateristics in the freqency rang eof 30MHz to 2,150MHz or 2,430MHz were designed.