• Steel and Composite Structures
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• v.47 no.5
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• pp.551-568
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• 2023

In this research, a new two-dimensional (2D) and quasi three-dimensional (quasi-3D) higher order shear deformation theory is devised to address the bending problem of functionally graded plates resting on an elastic foundation. The displacement field of the suggested theories takes into account a parabolic transverse shear deformation shape function and satisfies shear stress free boundary conditions on the plate surfaces. It is expressed as a combination of trigonometric and exponential shear shape functions. The Pasternak mathematical model is considered for the elastic foundation. The material properties vary constantly across the FG plate thickness using different distributions as power-law, exponential and Mori-Tanaka model. By using the virtual works principle and Navier's technique, the governing equations of FG plates exposed to sinusoidal and evenly distributed loads are developed. The effects of material composition, geometrical parameters, stretching effect and foundation parameters on deflection, axial displacements and stresses are discussed in detail in this work. The obtained results are compared with those reported in earlier works to show the precision and simplicity of the current formulations. A very good agreement is found between the predicted results and the available solutions of other higher order theories. Future mechanical analyses of three-dimensionally FG plate structures can use the study's findings as benchmarks.

• Structural Engineering and Mechanics
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• v.52 no.2
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• pp.323-349
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• 2014

In this paper, linear buckling analysis of a curved sandwich beam with a flexible core is investigated. Derivation of equations for face sheets is accomplished via the classical theory of curved beam, whereas for the flexible core, the elasticity equations in polar coordinates are implemented. Employing the von-Karman type geometrical non-linearity in strain-displacement relations, nonlinear governing equations are resulted. Linear pre-buckling analysis is performed neglecting the rotation effects in pre-buckling state. Stability equations are concluded based on the adjacent equilibrium criterion. Considering the movable simply supported type of boundary conditions, suitable trigonometric solutions are adopted which satisfy the assumed edge conditions. The critical uniform load of the beam is obtained as a closed-form expression. Numerical results cover the effects of various parameters on the critical buckling load of the curved beam. It is shown that, face thickness, core thickness, core module, fiber angle of faces, stacking sequence of faces and openin angle of the beam all affect greatly on the buckling pressure of the beam and its buckled shape.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.10a
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• pp.43-48
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• 2003

This study presents the detailed methods for university facilities mapping using GPS and totalstation. In the control survey by GPS network adjustment, the level of significance for the height value of fourth order triangulation stations was estimated about loom. The accuracy analysis of height determination by totalstation for the traverse points showed that the RMSE came out 9mm to the basis of direct leveling, so it indicated that trigonometric leveling by totalstation was correct comparatively. For GPS/RTK method, the result of accuracy analysis about traverse points showed that the RMSE came out 33㎜ in horizontal location to the basis of totalstation's outcome and 15㎜ in height value to the basis of direct leveling. In the construction survey, GPS/RTK surveying is quicker and more economical than totalstation surveying in the feasible areas of GPS surveying, but there were many impossible areas lot GPS/RTK surveying by the obstacles like a building.

• Smart Structures and Systems
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• v.13 no.1
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• pp.111-135
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• 2014

Based on the Reissner mixed variational theorem (RMVT), finite rectangular layer methods (FRLMs) are developed for the three-dimensional (3D) linear buckling analysis of simply-supported, fiber-reinforced composite material (FRCM) and functionally graded material (FGM) sandwich plates subjected to bi-axial compressive loads. In this work, the material properties of the FGM layers are assumed to obey the power-law distributions of the volume fractions of the constituents through the thickness, and the plate is divided into a number of finite rectangular layers, in which the trigonometric functions and Lagrange polynomials are used to interpolate the in- and out-of-plane variations of the field variables of each individual layer, respectively, and an h-refinement process is adopted to yield the convergent solutions. The accuracy and convergence of the RMVT-based FRLMs with various orders used for expansions of each field variables through the thickness are assessed by comparing their solutions with the exact 3D and accurate two-dimensional ones available in the literature.

• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.4
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• pp.17-23
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• 1984

A model analysis of pattern shift in the epitaxial growth of silicon on (111) substrates was performed. The growth rate anisotropy was considered as the most important affecting factor of pattern shift, and for the model establishment the off angle of the substrate and the process temperature were taken as the variables. We derived a theoretical equation of pattern shift by assuming the growth rate anisotropy as the trigonometric sine function of the off angle of the substrate and defining the growth rate anisotropy factor related to the process temperature. The pattern shift ratio calculated by this model had the same tendency with the experimental ones, which, however, were about twice greater than those. It was supposed that this discrepailcy was due to the second order affecting factor such as facetting and step broadening which had been exluded in model establishment.

• Journal of KSNVE
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• v.8 no.3
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• pp.467-476
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• 1998

The free vibration analysis and design optimization of the rotating composite cylindrical shells with a rectangular cutout are investigated by theoretical method. The Love's thin shell theory is used to derive the frequency equation. The theoretical results are obtained by application of the energy method employing the Rayleigh-Ritz procedure. The used circumferential vibration modes are trigonometric functions, the axial modes are the beam modal functions chosen to satisfy the prescribed boundary conditions. To check the validity, the theoretical results are compared with experimental, FEM and other theoretical results.

• Korean Journal of Remote Sensing
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• v.19 no.5
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• pp.381-392
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• 2003

Multi-temporal approaches using sequential data acquired over multiple years are essential for satisfactory discrimination between many land-cover classes whose signatures exhibit seasonal trends. At any particular time, the response of several classes may be indistinguishable. A harmonic model that can represent seasonal variability is characterized by four components: mean level, frequency, phase and amplitude. The trigonometric components of the harmonic function inherently contain temporal information about changes in land-cover characteristics. Using the estimates which are obtained from sequential images through spectral analysis, seasonal periodicity can be incorporates into multi-temporal classification. The Normalized Difference Vegetation Index (NDVI) was computed for one week composites of the Advanced Very High Resolution Radiometer (AVHRR) imagery over the Korean peninsula for 1996 ～ 2000 using a dynamic technique. Land-cover types were then classified both with the estimated harmonic components using an unsupervised classification approach based on a hierarchical clustering algorithm. The results of the classification using the harmonic components show that the new approach is potentially very effective for identifying land-cover types by the analysis of its multi-temporal behavior.

• Smart Structures and Systems
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• v.16 no.1
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• pp.195-211
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• 2015

This paper presents nonlinear analysis of a functionally graded square plate integrated with two functionally graded piezoelectric layers resting on the Winkler-Pasternak foundation. Geometric nonlinearity was considered in the strain-displacement relation based on the Von-Karman assumption. All the mechanical and electrical properties except Poisson's ratio can vary continuously along the thickness of the plate based on a power function. Electric potential was assumed as a quadratic function along the thickness direction and trigonometric function along the planar coordinate. The effect of non homogeneous index was investigated on the responses of the system. Furthermore, a comprehensive investigation has been performed for studying the effect of two parameters of assumed foundation on the mechanical and electrical components. A comparison between linear and nonlinear responses of the system presents necessity of this study.

• Structural Engineering and Mechanics
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• v.87 no.2
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• pp.165-172
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• 2023

This paper presents a novel method for modeling elastic wave propagation in long beams. The proposed method derives a solution for the transient transverse displacement of the beam's neutral axis without assuming the separation of variables (SV). By mapping the governing equation from the space domain to the frequency domain using Fourier transformation (FT), the transverse displacement function is determined as a convolution integral of external loading functions and a combination of trigonometric and Fresnel functions. This method determines the beam's response to general loading conditions as a linear combination of the analytical response of a beam subjected to an abrupt localized loading. The proposed solution method is verified through finite element analysis (FEA) and wave propagation patterns are derived for tone burst loading with specific frequency contents. The results demonstrate that the proposed solution method accurately models wave dispersion, reduces computational cost, and yields accurate results even for high-frequency loading.

• Steel and Composite Structures
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• v.52 no.5
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• pp.595-608
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• 2024

This study presents a static analysis of thin shallow cylindrical and spherical panels, as well as plates (which are a special case of shells), under Levy-type mixed boundary conditions and various loading conditions. The study utilizes the boundary discontinuous double Fourier series method, where displacements are expressed as trigonometric functions, to analyze the system of partial differential equations. The panels are subjected to a simply supported type 3 (SS3) boundary condition on two opposite edges, while the remaining two edges are subjected to clamped type 3 (C3) boundary conditions. The study presents comprehensive tabular and graphical results that demonstrate the effects of curvature on the deflections and moments of thin shallow shells made from symmetric and antisymmetric cross-ply laminated composites, as well as isotropic steel materials. The proposed model is validated through comparison with existing literature, and the convergence characteristics are demonstrated. The changing trends of displacements and moments are explained in detail by investigating the effect of various parameters, such as stacking lamination, material types, curvature, and loading conditions.