• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.627-634
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• 2002

To facilitate a drilling plan for grouting in fractured rock, an algorithm of practical use associated with a new term “fracture density distribution”or“fracture tomogram”is developed. It is well known that Televiewer data(amplitude and traveltime image) provide detailed information about not only dip and dip direction of each fracture but also its aperture size estimated by an appropriate evaluation algorithm. A selected plane section of medium around a borehole or the cross section between two boreholes is discretized into a two dimensional grid of cells(rectangular elements). As each elongated(straight) fracture passes through the cells, the corresponding aperture size value is successively summed up in each cell, depending on the fracture length segment. In this, the fracture lines can be determined by intersecting of each fracture plane with the selected plane section. If the fracture line does not pass through a particular grid element, the segment length is set to zero. The final value(aperture size value of each cell) derived from all the detected fractures constitutes the fracture density distribution of the selected plane section, Field examples are illustrated, which will prove the benefit of the suggested algorithm for several kinds of grouting works.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.585-592
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• 2005

In this paper, we present the principle of virtual work, from which the exact non-linear equations of motion of a rotating ring can be derived, by using the theory of finite deformation For a thin ring of which the effect of variation in curvature across the cross-section is neglected, the radial displacement and the extensional stress are determined from the principle of virtual work at the steady state where the ring is rotating with a constant angular velocity. And also we formulate systematically the governing equations concerned to the in-plane vibrations and the out-of-plane vibrations at the disturbed state by using the principle of virtual work which is expressed with the disturbed displacements about the steady state. The formulated governing equations are classified by four models along the cases of considering or neglecting all or partly the secondary effects of flexural shear, rotary inertia, circumferential extension, and twist inertia. The natural vibrations of thin rings are analyzed, and its results are compared and discussed.

• Steel and Composite Structures
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• v.3 no.4
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• pp.261-275
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• 2003

Truss members built-up with double angles back-to-back have monosymmetric cross-section and twisting always accompanies flexion upon the onset of buckling about the axis of symmetry. Approximate formulae for calculating the buckling capacity are presented in this paper for routine design purpose. For a member susceptible only to flexural buckling, its optimal cross-section should consist of slender plate elements so as to get larger radius of gyration. But, occurrence of twisting changes the situation owing to the weakness of thin plates in resisting torsion. Criteria for limiting the leg slenderness are discussed herein. Truss web members in compression are usually considered as hinged at both ends for out-of-plane buckling. In case one (or both) end of member is not supported laterally by bracing member, its adjoining members have to provide an elastic support of adequate stiffness in order not to underdesign the member. The stiffness provided by either compression or tension chords in different cases is analyzed, and the effect of initial crookedness of compression chord is taken into account. Formulae are presented to compute the required stiffness of chord member and to determine the effective length factor for inadequately constrained compressive diagonals.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.66.2-66.2
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• 2016

KASI and NAOJ are making collaborating efforts to implement faster mapping capability into the new 275-500 GHz Atacama Submillimeter Telescope Experiment focal plane array (FPA). Feed horn antenna is one of critical parts of the FPA. Required fractional bandwidth is almost 60 % while that of traditional conical horn is less than 50 %. Therefore, to achieve this wideband performance, we adopted a horn of which the corrugation depths have a longitudinal profile. A profiled horn has features not only of wide bandwidth but also of shorter length compared to a linear-tapered corrugated horn, and lower cost fabrication with less error can be feasible. In our design process the flare region is represented by a cubic splined curve with several parameters. Parameters of the flare region and each dimension of the throat region are optimized by a differential evolution algorithm to keep >20 dB return loss and >30 dB maximum cross-polarization level over the operation bandwidth. To evaluate RF performance of the horn generated by the optimizer, we used a commercial mode matching software, WASP-NET. Also, Gaussian beam (GB) masks to far fields were applied to give better GB behavior over frequencies. The optimized design shows >23 dB return loss and >33 dB maximum cross-polarization level over the whole band. Gaussicity of the horn is over 96.6 %. The length of the horn is 12.5 mm which is just 57 % of the ALMA band 8 feed horn (21.96 mm).

• Journal of the Korean Society for Precision Engineering
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• v.33 no.1
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• pp.69-75
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• 2016

Polydimethylsiloxane (PDMS) is used as a scaffold for cell culture. Because both the stress and strain acting on the substrate and the hemodynamic environment are important for studying mechano-transduction of cellular function, the traction force of the surface of a substrate has been measured using fluorescence images of particle distribution. In this study, deformation of the cross-sectional plane of a PDMS block was measured by correlating particle image distributions to validate the particle image strain measurement technique. Deformation was induced by a cone indentor and a shearing parallel plate. Measured deformations from particle image distributions were in agreement with the results of a computational structure analysis using the finite-element method. This study demonstrates that the particle image correlation method facilitates measurement of deformation of a polymer scaffold in the cross-sectional plane.

• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.106-113
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• 2004

Recently, a new issue in designing spot welded structures such as automobile and train car bodies is to predict an economical fatigue design criterion. One of the most typical and traditional methods is to use a ΔP-N$\sub$f/ curve. However, since the fatigue data on the ΔP-N$\sub$f/ curve vary according to the welding conditions, materials, geometry of joint and fatigue loading conditions, it is necessary to perform the additional fatigue tests for determining a new fatigue design criterion of spot-welded lap joint having specific dimension and geometry. In this study, the stress distributions around spot welds of various spot welded lap joints such as in-plane bending type (IB type), tension shea. type (TS type) and cross tension type (CT type) were numerically analyzed. Using these results, the ΔP-N$\sub$f/ curves Previously obtained from the fatigue tests for each type were rearranged into the Δ$\sigma$-N$\sub$f/ relations with the maximum stresses at the nugget edge of the spot weld.

• Imaging Science in Dentistry
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• v.35 no.2
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• pp.83-86
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• 2005

Purpose : To evaluate the effect of deviation of mandibular positioning, by changing the mandibular plane inclination, on the measured height and width of mandible in spiral conventional tomography. Materials and Methods : By means of the Scanora multifunctional unit, cross-sectional tomograms were taken from two human dried mandibles at the mandibular angulations: -15 degree, -10 degree, -5 degree, and 0 degree. Twenty-eight sites in two dried mandibles were imaged. One examiner measured the bone heights and widths at selected sites on the images and the actual bone heights were recorded. Results : The bone heights at the four mandibular inclinations overestimated real bone heights and the mean difference between actual heights and image heights on 0 degrees was the smallest (P<0.01). The bone widths on -15 degrees were narrowest and there were significant differences between bone widths measured at the four mandibular inclinations (P<0.001). We found statistically significant differences between both bone heights and widths as measured according to the mandibular plane angle for the posterior region (P<0.01). Conclusion : The use of different mandibular positioning may result in discrepancies in heights and widths when measured from the cross-sectional tomographic images. It is suggested that the mandibular positioning may play a significant role in the measurement of mandibular heights and widths.

• 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.

• Steel and Composite Structures
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• v.10 no.4
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• pp.297-315
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• 2010

This paper is concerned with free vibration characteristics and natural frequency of horizontally curved composite plate girder bridges. Three-dimensional finite element models are developed for the girders using the software package LUSAS and analyses carried out on the models. The validity of the finite element models is first established through comparison with the corresponding results published by other researchers. Studies are then carried out to investigate the effects of total number of girders, number of cross-frames and curvature on the free vibration response of horizontally curved composite plate girder bridges. The results confirm the fact that bending modes are always coupled with torsional modes for horizontally curved bridge girder systems. The results show that the first bending mode is influenced by composite action between the concrete deck and steel beam at low subtended angle but, on the girders with larger subtended angle at the centre of curvature such influence is non-existence. The increase in the number of girders results in higher natural frequency but at a decreasing rate. The in-plane modes viz. longitudinal and arching modes are significantly influenced by composite action and number of girders. If no composite action is taken into account the number of girders has no significant effect for the in-plane modes.

• Wind and Structures
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• v.27 no.6
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• pp.417-430
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• 2018

The concentration fields in the proximities of a local gas emission source are experimentally analyzed in several combinations of wind incidences and source emissions. These conditions are determined by the plume buoyancy, emission velocity and incident flow wind speed. Concentration measurements are performed by an aspirating probe in a boundary layer wind tunnel. The analysis included the mean concentration values and the intensity of concentration fluctuations in a neutral atmospheric boundary layer flow. Different configurations are tested: an isolated stack in a homogeneous terrain and a stack with a bluff body in close proximity, located windward and leeward from the emission source. The experimental mean concentration values are contrasted with Gaussian profiles and the dilution factor is analyzed with respect to the empirical curves of the minimum dilution. Finally, a study on the plume intermittency is performed in a cross-sectional plane near the emission source. It is possible to highlight the following observations: a) plume vertical asymmetry in the case of an isolated emission source, b) significant differences in the dispersion process related to the relative location of the emission source and bluff body effects, and c) different probabilistic behavior of the concentration fluctuation data in a cross-sectional measurement plane inside the plume.