• International Journal of Aeronautical and Space Sciences
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• v.14 no.4
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• pp.310-323
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• 2013

In this paper, the aeroelastic static response of flexible wings with arbitrary cross-section geometry via a coupled CUF-XFLR5 approach is presented. Refined structural one-dimensional (1D) models, with a variable order of expansion for the displacement field, are developed on the basis of the Carrera Unified Formulation (CUF), taking into account cross-sectional deformability. A three-dimensional (3D) Panel Method is employed for the aerodynamic analysis, providing more accuracy with respect to the Vortex Lattice Method (VLM). A straight wing with an airfoil cross-section is modeled as a clamped beam, by means of the finite element method (FEM). Numerical results present the variation of wing aerodynamic parameters, and the equilibrium aeroelastic response is evaluated in terms of displacements and in-plane cross-section deformation. Aeroelastic coupled analyses are based on an iterative procedure, as well as a linear coupling approach for different free stream velocities. A convergent trend of displacements and aerodynamic coefficients is achieved as the structural model accuracy increases. Comparisons with 3D finite element solutions prove that an accurate description of the in-plane cross-section deformation is provided by the proposed 1D CUF model, through a significant reduction in computational cost.

• Journal of KSNVE
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• v.2 no.4
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• pp.305-315
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• 1992

In order to investigate the effects of layer-wise in-plane displacements on vibration and damping characteristics of composite laminated plates, the finite element method based on the generalized laminated plate theory(GLPT) has been formulated. Specific damping capacity of each mode was obtained by modal strain energy method. To see the effect of transverse shear on deformation, the strain energy of stress components was computed. The accuracy of this study was examined for the cylindrical bending vibration of cross-ply plate strip. The results were very accurate compared with 3-D solutions. The numerical results show that through-thickness variation of in-plane displacements has not so much influence on the natural frequency, but has a great influence on the damping of composite plates, especially on the damping of thick composite plates since the damping is affected by local behavior while the natural frequency is affected by global behavior.

• Journal of Periodontal and Implant Science
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• v.32 no.2
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• pp.379-388
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• 2002

For the success of dental implant, accurate radiographic evaluation is prerequisite for planning the location of the osseointegrated implants and avoiding injury to vital structures. CT/MPR(computed tomography/multiplanar reformation) shows improved visualization of inferior alveolar canal. In order to obtain cross-sectional images parallel to the teeth, the occlusal plane is used to orientate for the axial plane. If the direction of axial plane is not parallel to the occlusal plane, the reformatted cross-sectional scans will be oblique to the planned fixture direction and will not show the actual dimension of the planned fixture's location. If the available bone height which measured in the cross-sectional view is much greater than the actual available bone height, penetration of canal may occur. The aim of this study is to assess the effect of the axial plane to measurement of available bone height for dental implant in computed tomography of the mandible. 40 patients who had made radiographic stents and had taken CT were selected. The sites that were included in the study were 45 molar regions. In the central panoramic scan, the length from alveolar crest to superior border of inferior alveolar canal(available bone height, ABH) was measured in direction of reformatted cross-sectional plane(uncorrected ABH). Then, length from alveolar crest to superior border of canal was measured in direction of stent(corrected ABH). The angle between uncorrected ABH and corrected ABH was measured. From each ABH, available fixture length was decided by $Br{{\aa}}nemark$ system. The results were following ; the difference between two ABHs was statistically significant in both first and second molar(p< 0.01). The percentage of difference more than 1 mm was 8.7% in first molar and 15.5% in second molar. The percentage of difference more than 2 mm was 2.0% in first molar and 6.6% in second molar. The maximum value of difference was 2.5 mm in first molar and 2.2 mm in second molar. The correlations between difference of 2 ABHs and angle was positive correlations in both first and second molar. The correlation coefficient was 0.534 in first molar and 0.728 in second molar. The second molar has a stronger positive correlation. The percentage of disagreement between 2 fixture lengths from two ABHs was 24.4% in first molar and 28.9% in second molar.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.5
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• pp.389-395
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• 2016

In this paper, vibration characteristics in terms of the airfoil cross-sectional shape was examined by using the EDISON co-rotational plane beam-transient analysis. Co-Rotational plane beam analysis is appropriate for large rotation and small strain. Assuming aircraft wing as a cantilevered beam, natural frequencies of each airfoil cross-sectional shape were estimated using VABS program and fast Fourier transformation(FFT). VABS conducts finite element analysis on the cross-section including the detailed geometry and material distribution to estimate the beam sectional properties. Under the same airfoil geometric configuration and material selection, variation of material induced difference in the deflection and natural frequencies. It was observed that variation of the natural frequency was dependent on variation of the airfoil shape and material.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.203-208
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• 2016

In this paper, vibration characteristics in terms of the airfoil cross-sectional shape was examined by using the EDISON co-rotational plane beam-transient analysis. Assuming aircraft wing as a cantilevered beam with a constant cross-sectional shape, natural frequencies of each airfoil shape was compared while varying airfoil maximum thickness and maximum camber length, using Fast Fourier Transformation(FFT). When the airfoil maximum thickness was varied, natural frequency showed peak value at 18% chord, and decreased afterwards. When the airfoil maximum camber length was varied, natural frequency either increased or decreased at 6% chord, while at 8% the natural frequency showed its maximum. Applying such trends to B-737 wing airfoil, an improved B-737_mod airfoil shape was obtained with regard to the vibration characteristics.

• Journal of Welding and Joining
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• v.17 no.2
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• pp.66-75
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• 1999

Weld bead quality in tailored blank(TB) is critically affected by edge preparation of sheets. The edge quality of prepared sheets for TB can be classified into straightness and the cross section quality of sheared plane such as a ratio of shear face, shear plane angle, etc. In order to have a good edg quality for butt-welding sheets, precision shearing will be recommended. In this paper, the feasibility of a conventional mechanical shearing as the edge preparation for tailored blanks is studyied. It reveals that fine shearing may not be the unique solution as it is generally accepted. To obtain the good shearing condition with a conventional mechanical shearing, experiments were carried out using Tahuchi method. The major parameters affecting a sheared contour are the clearance between upper blade and lower blade, and shear angle. The optimal shearing condition yields a very good straightness along the entire length of the cut, which gives a butt joint gap less than 10% of the base material thickness. The good cross section of sheared plane is also achieved in the optimal shearing condition such as a ratio of the shear face above 65%, a cross section's shear plane angle above 85%, little burr, which is providing finally good weld beads.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.2
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• pp.183-192
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• 2013

This paper presents formation reconfiguration using impulsive control input for spacecraft formation flying. Spacecraft in a formation should change the formation size and/or geometry according to the mission requirements and space environment. To modify the formation radius and geometry with respect to the leader spacecraft, the follower spacecraft generates additional control inputs; the two impulsive control inputs are general control type of the spacecraft system. For the impulsive control input, Lambert's problem is modified to construct the transfer orbit in relative motion, given two position vectors at the initial and final time. Moreover, the numerical simulation results show the transfer trajectories to resize the formation radius in the radial/along-track plane formation and in the along-track/cross-track plane formation. In addition, the maneuver characteristics are described by comparing the differential orbital elements between the reference orbit and transfer orbit in the radial/along-track plane formation and along-track/cross-track plane formation.

• Tunnel and Underground Space
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• v.22 no.1
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• pp.43-53
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• 2012

Stability of cut-slope, the orientation and dimension of which are gradually changed, has been analyzed by employing the cross-section method capable of comprehensibly considering the lithological, structural and mechanical characteristics of slope rock. Lithological fragility is investigated by inspecting the drilled core logs and BIPS image has been taken to delineate the rock structure. Engineering properties of drilled-core including the joint shear strength have been also measured. Potential failure modes of cut-slope and failure-induced joints are identified by performing the stereographic projection analysis. Traces of potential failure-induced joints are drawn on the cross-section which depicts the excavated geometry of cut-slope. Considering the distribution of potential plane failure-induced joint traces blocks of plane failure mode are hypothetically formed. The stabilities and required reinforcements of plane failure blocks located at the different excavation depth have been calculated to confirm the applicability of the cross-section method for the optimum cut-slope design.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.4
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• pp.300-306
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• 2019

Transmission cross section(TCS) is described analytically as $2G{\lambda}^2/4{\pi}$ irrespective of the aperture shapes for various transmission resonant apertures, such as small ridged circular or H-shaped, U-shaped, or Jerusalem cross-shaped apertures in an infinite thin conducting plane. The proposed expression is validated by comparison with the numerical results obtained from the method of moments(MOM). The TCS characteristics of the transmission resonant cavity structure in a thick conducting plane are also studied and the equivalence between the two small aperture structures is reported from the viewpoint of transmission efficiency.

• Journal of KSNVE
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• v.7 no.5
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• pp.747-756
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• 1997

Wigner-Ville distribution which is a time-frequency analysis has a fatal drawback, when the signal has multiple components. This is the cross-talk and often causes a neagative value in the distribution. Wingner-Ville distriution is an expression of power, therefore the cross-talk must be avoided. Smoothing the Wigner-Ville distribution by convoluting it with a window, is most commonly used to reduce the cross-talk. There can be infinite number of distributions depending on the windows. But, the smoothing reduces resolution in time-frequency plane; this motives to design a more effective window in reducing cross-talk while remaining resolution. The domain in which the cross-talk and legitimate components can be easily distinguished, is the ambiguity function. In the ambiguity function domain, the legitimate components appear as linear lines passing through the orgine. But, the cross-talk is widely distributes in the ambiguity function plane. Based on the relative distributions of cross-talk and legitimate components, rotating window can be designed to minimize cross-talk. Applying the rotating window to the ambiguity function corresponds to smoothing the Wigner-Ville distribution. Therefore, the effects of rotating window is estimated in terms of the bias error due to smooting the Wigner-Ville distribution. By applying the rotating window, not only the Wigner-Ville distribution but also its properties are changed. The properties of the new distribution are checked, in order to complete analyzing the rotating window.