• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.132-139
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• 1992

This paper presents geometrically nonlinear formulation of shell problems using the three-dimensional curved shell element, which includs large displacements and large rotations. Formulations of the geometrically nonlinear problems can be derived in a variety of ways, but most of them have been obtained by assuming that nodal rotations are small. Hence, the tangent stiffness matrix is derived under the assumptions that rotational increments are infinitesimal and the effect of finite rotational increments have to be considered during the equilibrium iterations. To study the large displacement and large rotation problems, the restrictions are removed and the formulations of the curved shell element including the effect of large rotational increments are developed in this paper. The displacement based finite element method using this improved formulation are applied to the analyses of the geometrically nonlinear behaviors of the single and double curved shells, which are compared with the results by others.

• Computational Structural Engineering
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• v.11 no.1
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• pp.205-216
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• 1998

A solution method is presented to solve the eigenvalue problem arising in the dynamic analysis of nonclassicary damped structural systems with multiple eigenvalues. The proposed method is obtained by applying the modified Newton-Raphson technique and the orthonormal condition of the eigenvectors to the linear eigenproblem through matrix augmentation of the quadratic eigenvalue problem. In the iteration methods such as the inverse iteration method and the subspace iteration method, singularity may be occurred during the factorizing process when the shift value is close to an eigenvalue of the system. However, even though the shift value is an eigenvalue of the system, the proposed method provides nonsingularity, and that is analytically proved. Since the modified Newton-Raphson technique is adopted to the proposed method, initial values are need. Because the Lanczos method effectively produces better initial values than other methods, the results of the Lanczos method are taken as the initial values of the proposed method. Two numerical examples are presented to demonstrate the effectiveness of the proposed method and the results are compared with those of the well-known subspace iteration method and the Lanczos method.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.509-523
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• 1998

A consistent finite element formulation and analytic solutions are presented for stability of thin-walled circular arch. The total potential energy is derived by applying the principle of linearized virtual work and including second order terms of finite semitangential rotations. As a result, the energy functional corresponding to the semitangential moment is newly derived. Analytic solutions for the out-of-plane buckling of symmetric thin-walled curved beam subjected to pure bending or uniform compression with simply supported boundary conditions are obtained. For finite element analysis, the cubic Hermitian polynomials are utilized as shape functions and $16{\times}16$ stiffness matrix for curved beam elements and $14{\times}14$ stiffness matrix for straight beam elements are evaluated, respectively. In order to illustrate the accuracy of this study, analytical and numerical results for lateral buckling problems of circular arch are presented and compared with available analytical solutions.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.1
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• pp.41-54
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• 1999

For free vibration of non-symmetric thin-walled circular arches including restrained warping effect, the elastic strain and kinetic energy is derived by introducing displacement fields of circular arches in which all displacement parameters are defined at the centroid axis. The cubic Hermitian polynomials are utilized as shape functions for development of the curved thin-walled beam element having eight degrees of freedom. Analytical solution for in-plane free vibration behaviors of simply supported thin-walled curved beams with monosymmetric cross-sections is newly derived. Also, a finite element formulation using two noded curved beams element is presented by evaluating elastic stiffness and mass matrices. In order to illustrate the accuracy and practical usefulness of this study, analytical and numerical solutions for free vibration of circular arches are presented and compared with solutions analyzed by the straight beam element and the ABAQUS's shell element.

• Computational Structural Engineering
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• v.10 no.1
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• pp.201-211
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• 1997

A clearly consistent finite element formulation for geometrically non-linear analysis of space frames is presented by applying incremental equilibrium equations based on the updated Lagrangian formulation and introducing Vlasov's assumption. The improved displacement field for symmetric cross sections is introduced based on inclusion of second order terms of finite rotations, and the potential energy corresponding to the semitangential rotations and moments is consistently derived. For finite element analysis, elastic and geometric stiffness matrices of the space frame element are derived by using the Hermitian polynomials as shape functions. A co-rotational formulation in order to evaluate the unbalanced loads is presented by separating the rigid body rotations and pure deformations from incremental displacements and evaluating the updated direction cosines of the frame element due to rigid body rotations and incremental member forces from pure deformaions. Finite element solutions for the spatial buckling and post-buckling analysis of space frames are compared with available solutions and other researcher's results.

• Journal of the Korean Geophysical Society
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• v.6 no.4
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• pp.277-294
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• 2003

Structures show the phenomena of deformation and lowering of function with time-lapse by artificial environments and changes of geotechnical conditions or accumulation of initial deformation elements. This study aims the structural assessment of cultural property, Chum-Sung-Dae, located in Kyeongjucity, Korea. It was built about 1,300 years ago, and has undergone deformation and ground-subsidence with time-lapse. Non-destructive evaluation techniques were applied to the Chum-Sung-Dae, to protect it from survey. Because of this reason, 3D precise laser scanning surveying system was applied to measure the exact size of Chum-Sung-Dae, displacement and declining angles. Geophysical exploration also was applied to study the subsurface distribution of geotechnical parameters or physical properties. Natural frequencies were measured from real and model of Chum-Sung-Dae to study the dynamic characteristics of vibration and/or earthquake load and stiffness of structures.

• Journal of the Korea Concrete Institute
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• v.24 no.2
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• pp.205-214
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• 2012

Crack widths play an important role in the serviceability limit state. When crack widths are controlled sufficiently, the reinforcement corrosion can be reduced using only existing concrete cover thickness due to low permeability in the region of finely distributed hair-cracks. Thus, the knowledge about the tensile crack opening is essential in designing more durable concrete structures. Therefore, numerous researches related to the topic have been performed. Nevertheless accurate measurement of a crack width is not a simple task due to several reasons such as unknown potential crack formation location and crack opening damaging strain gages. In order to overcome these difficulties and measure precise crack widths, a displacement measurement system was developed using digital image correlation. Accuracy calibration tests gave an average measurement error of 0.069 pixels and a standard deviation of 0.050 pixels. Direct tensile test was performed using ultra high performance concrete specimens. Crack widths at both notched and unnotched locations were measured and compared with clip-in gages at various loading steps to obtain crack opening profile. Tensile deformation characteristics of concrete were well visualized using displacement vectors and full-field displacement contour maps. The proposed technique made it possible to measure crack widths at arbitrary locations, which is difficult with conventional gages such as clip-in gages or displacement transducers.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.22 no.1
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• pp.63-71
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• 2004

This research is to reconstruction of railway alignment using GPS data, an investigation is made on the method of optimum simplification for reduction of unnecessary linear data, improve the accuracy by using four simplification algorithms among the methods. By applying two measured of displacement between observed data and it's simplification methods have been evaluated. The results showed that the complexities of lines is not practical to investigate simplification algorithms, the Douglas-Peucker method produced a little displacement between observed data and it's simplification. Its by using the Douglas-Peucker method to observed linear GPS data in railway track, design elements of horizontal alignment have been calculated. Then we could know that obtain the good results fur reconstruction of alignment elements through the methods and algorithns of this study.

• The Journal of the Acoustical Society of Korea
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• v.18 no.2
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• pp.83-89
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• 1999

The forced vibration of a finite cylindrical shell has been analyzed from an elastic wave viewpoint. The displacement vector is used to formulate the vibration field, that is regarded as a superposition of disturbances due to elastic waves propagating on the shell. The reflection matrix is also used in the formulation of the vibration field, that is easily derived in the present approach. It allows one to easily identify the wave conversion of elastic waves at the ends of the shell. The present approach is used to predict the vibration field of the cylindrical shell with free-free boundary conditions. The contribution of each type of elastic waves into the vibration field was identified, and the wave conversion at the ends of the shell was observed. Those results showed that the present approach can be effectively used to analyze the forced vibration of the cylindrical shell from an elastic wave viewpoint.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4A
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• pp.371-382
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• 2002

A camera model with optical axes parallel has been widely used for stereo vision applications. A pair of input ages are obtained from a convergent-looking stereo camera model based on the human visual system in this per, and each image is divided into quadrant regions with respect to the fixation point. The reasoning of quadrant partitions is based on the human visual system and is proven by a geometrical method. Image patches : constructed from the right and left stereo images. A modified cepstrum filter is applied to the patches and disparity vectors are determined by peak detection algorithm. The three-dimensional information for synthetic ages is obtained from the measured disparity and the convergent stereo camera model. It is shown that the experimental results of the proposed method for various stereo images are accurate around the fixation point like the human visual system.