• Journal of the Korean Ceramic Society
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• v.47 no.4
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• pp.290-295
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• 2010

This study has been focused on properties of mirror surface grinding technology by ELID(Electrolytic In-process Dressing) for structural ceramics using in high precision structural parts as like semi-conductor manufacturing processes. The experimental studies have been carried out to get mirror surface for grinding of structural ceramics, SiC, $Al_2O_3$ and AlN. Grinding process of the ceramics is carried out with varying mesh type, depth of cut and feed rate using diamond wheel. The machining result of the surface roughness and condition of ground surface, have been analyzed by use of surface roughness tester, SEM, AFM and three dimensional surface profiler measurement system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.48-59
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• 2019

In recent years, the type of bridge where cables such as suspension bridge and cable-stayed bridge are the main factors in the construction of long-range bridges has been soaring. The effects of cables on these structures are very large, and for structural analysis, it is necessary to study the cable and the structural changes according to the mode characteristics of the cables. In particular, cables are directly connected to camber adjustment, which conveys load effects on girders to tower, and are important components in the overall structure, and since the initial tension on the construction is compared with the tension over time, this study was conducted to help identify the condition of the bridge's aging and abnormalities. Therefore, in this study, the characteristics of the mode from the mode analysis through the impact hammer to the mass of the cable and the change in the length of the cable are analyzed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.365-370
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• 2000

A sliding mode fuzzy control (SMFC) algorithm is applied to design a controller for a benchmark problem on a wind- excited building. The structure is a 76-story concrete office tower with a height of 306 meters, hence the wind resistance characteristics are very important for the serviceability as well as the safety. A control system with an active tuned mass damper is assumed to be installed on the top floor. Since the structural acceleration is measured only at ,limited number of locations without measurement of the wind force, the structure of the conventional continuous sliding mode control may have the feed-back loop only. So, an adaptive least mean squares (LMS) filter is employed in the SMFC algorithm to generate a fictitious feed-forward loop. The adaptive LMS filter is designed based on the information of the stochastic characteristics of the wind velocity along the structure. A numerical study is carried out. and the performance of the present SMFC with the ,adaptive LMS filter is investigated in comparison with those of' other control, of algorithms such as linear quadratic Gaussian control, frequency domain optimal control, quadratic stability control, continuous sliding mode control, and H/sub ∞///sub μ/, control, which were reported by other researchers. The effectiveness of the adaptive LMS filter is also examined. The results indicate that the present algorithm is very efficient .

• Structural Engineering and Mechanics
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• v.21 no.3
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• pp.351-367
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• 2005

Multi-span beams carrying multiple point masses are widely used in engineering applications, but the literature for free vibration analysis of such structural systems is much less than that of single-span beams. The complexity of analytical expressions should be one of the main reasons for the last phenomenon. The purpose of this paper is to utilize the numerical assembly method (NAM) to determine the exact natural frequencies and mode shapes of a multi-span uniform beam carrying multiple point masses. First, the coefficient matrices for an intermediate pinned support, an intermediate point mass, left-end support and right-end support of a uniform beam are derived. Next, the overall coefficient matrix for the whole structural system is obtained using the numerical assembly technique of the finite element method. Finally, the natural frequencies and the associated mode shapes of the vibrating system are determined by equating the determinant of the last overall coefficient matrix to zero and substituting the corresponding values of integration constants into the related eigenfunctions respectively. The effects of in-span pinned supports and point masses on the free vibration characteristics of the beam are also studied.

• Composites Research
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• v.23 no.1
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• pp.37-43
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• 2010

In this paper, we present the result of an experimental investigation pertaining to the structural behavior of bolted lap-joint connection of pultruded fiber reinforced plastic structural shapes. In the experimental investigation, in order to find the mechanical property of the material, tension and shear tests on the pultruded structural composite specimen are conducted prior to the investigation on the structural behavior of bolted lap-joint connection of the member. Based on the result, number of bolts, type of placement and location of bolt are determined to be a test variable. Three different types of experimental specimens are prepared. Tensile load is applied through the center of the specimen with lap-joint connection and the structural behavior and failure mode of the test specimens with respect to the tensile load increment are investigated. As a result, it is found that most of the failure mode at the lap-joint connection is shear failure mode. Consequently, it is also found that the data obtained through this experimental program could be used for the structure connection design as a basis.

• Ocean Systems Engineering
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• v.2 no.2
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• pp.137-145
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• 2012

Recent developments in underwater image recognition methods have received large attention by the ocean engineering researchers. In this paper, an improved bi-dimensional empirical mode decomposition (BEMD) approach is employed to decompose the given underwater image into intrinsic mode functions (IMFs) and residual. We developed a joint algorithm based on BEMD and Canny operator to extract multi-pixel edge features at multiple scales in IMFs sub-images. So the multiple pixel edge extraction is an advantage of our approach; the other contribution of this method is the realization of the bi-dimensional sifting process, which is realized utilizing regional-based operators to detect local extreme points and constructing radial basis function for curve surface interpolation. The performance of the multi-pixel edge extraction algorithm for processing underwater image is demonstrated in the contrast experiment with both the proposed method and the phase congruency edge detection.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1994.10a
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• pp.38-45
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• 1994

P-version finite element model for the computation of stress intensity factors in two dimensional cracked panels by J-integral method is presented. The proposed model is based on high order theory and hierarchical shape function. The displacements fields are defined by integrals of Legendre polynomials which can be classified into three part such as basic mode, side mode, integral mode. The stress intensity factors are computed by J-integral method. The example models for validating the proposed p-version model are centrally cracked panel, single and double edged crack in a rectangular panel under pure Mode I. And the analysis results are compared with those by the h-version of FEM and empirical solutions in literatures. Very good agreement with the existing solution are shown.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.335-342
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• 2005

Using higher order Mindlin plates and piezoelectric materials, eigenvalue problems are considered. Since piezoelectric crystal resonators produce a proper amount of electric signal for a thickness-shear frequency, the objective is to decouple the thickness-shear mode from the others. Design variables are the bulk material densities corresponding to the mass of masking plates for electrodes. The design sensitivity expressions for the thickness-shear frequency and mode shape vector are derived using direct differentiation method(DDM). Using the developed design sensitivity analysis (DSA) method, we formulate a topology optimization problem whose objective function is to maximize the thickness-shear component of strain energy density at the thickness-shear mode. Constraints are the allowable volume and area of masking plate. Numerical examples show that the optimal design yields an improved mode shape and thickness-shear energy.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.163-166
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• 2000

Fiber Bra99 grating (FBG) sensor, one of the fiber optic sensor (FOS) offers lots of advantages for structural health monitoring due to its multiplexing capability. Also, it is proper to measure the structural vibration with no mass concentration effect. In this paper, we constructed two sensor arrays composed of 9 FBG sensors for the vibration and mode sensing of a composites beam. For an accurate measurement of wavelength shift, a signal processing board with an electric circuit based on time-interval counting was developed. This sensor system showed a good resolution of dynamic strain (<10${\mu}{\varepsilon}$). Using this sensor system, dynamic strains at 9 points of composite beam was measured and strain measured mode shape of the beam was calculated from the acquired strains and compared with numerical results by ABAQUS.

• Structural Engineering and Mechanics
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• v.26 no.4
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• pp.377-392
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• 2007

A discrete sliding mode control (SMC) method based on hybrid model of neural network and nominal model is proposed to reduce the vibration of flexible structures, which is a robust active controller developed by using a sliding manifold approach. Since the thick boundary layer will reduce the virtue of SMC, the multilayer feed-forward neural network is adopted to model the uncertainty part. The neural network is trained by Levenberg-Marquardt backpropagation. The design objective of the sliding mode surface is based on the quadratic optimal cost function. In course of running, the input signal of SMC come from the hybrid model of the nominal model and the neural network. The simulation shows that the proposed control scheme is very effective for large uncertainty systems.