• Structural Engineering and Mechanics
• /
• v.15 no.2
• /
• pp.199-223
• /
• 2003

The formulation of a non-linear shear deformable shell element is presented for the solution of stability problems of stiffened plates and shells. The formulation of the geometrical stiffness presented here is exactly defined on the midsurface and is efficient for analyzing stability problems of thick plates and shells by incorporating bending moment and transverse shear resultant force. As a result of the explicit integration of the tangent stiffness matrix, this formulation is computationally very efficient in incremental nonlinear analysis. The element is free of both membrane and shear locking behaviour by using the assumed strain method such that the element performs very well in the thin shells. By using six degrees of freedom per node, the present element can model stiffened plate and shell structures. The formulation includes large displacement effects and elasto-plastic material behaviour. The material is assumed to be isotropic and elasto-plastic obeying Von Mises's yield condition and its associated flow rules. The results showed good agreement with references and computational efficiency.

• Structural Engineering and Mechanics
• /
• v.69 no.5
• /
• pp.479-486
• /
• 2019

Based on the displacement general solution of a pre-twisted Euler-Bernoulli beam, the shape function and stiffness matrix are deduced, and a new finite element model is proposed. Comparison analyses are made between the new proposed numerical model based on displacement general solution and the ANSYS solution by Beam188 element based on infinite approach. The results show that developed numerical model is available for the pre-twisted Euler-Bernoulli beam, and that also provide an accuracy finite element model for the numerical analysis. The effects of pre-twisted angle and flexural stiffness ratio on the mechanical property are also investigated.

• Composites Research
• /
• v.32 no.4
• /
• pp.191-198
• /
• 2019

The basic mechanical properties of helicopter rotor blade are important parameters for the analysis of helicopter performance. However, it is difficult to estimate these properties because the most of rotor blades consist of various materials such as composite materials and metals, etc. In this paper, the bending/torsional stiffness for composite rotor blade of unmanned helicopter were evaluated through experimental and analytical studies. In finite element analysis, the bending/torsional stiffness were evaluated through the relationship of load-displacement and element stiffness matrix. The evaluated stiffness from the measured strains and displacements in bending and torsional test agreed well with the derived results of FEA.

• Journal of KSNVE
• /
• v.7 no.4
• /
• pp.571-578
• /
• 1997

Recently, many general-purpose packages for fluid-structure interaction problems have been announced. However, they have a lot of limitations to model structures in the fluid-structure interaction problems reasonably. Utilizing general-purpose packages such as MSC/NASTRAN and SYSNOISE, in this paper, a method to slove the radiation scattering problems with some accuracy in the fluid-structure interaction problems was developed. Using a simple model, the results from the presented method here are compared with those from SYSNOISE. The result shows quite a good agreement between the two methods. The problems, which could not be solved by SYSNOISE, were tried to solve with the presented method and results were presented. It was proved that this method could be safely used to solve fluid-structure interaction problems.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.29 no.12 s.243
• /
• pp.1574-1585
• /
• 2005

In this paper, a spectral element model is developed for the uniform straight pipelines conveying internal unsteady fluid. Four coupled pipe-dynamics equations are derived first by using the Hamilton's principle and the principles of fluid mechanics. The transverse displacement, the axial displacement, the fluid pressure and the fluid velocity are all considered as the dependent variables. The coupled pipe-dynamics equations are then linearized about the steady state values of the fluid pressure and velocity. As the final step, the spectral element model represented by the exact dynamic stiffness matrix, which is often called spectral element matrix, is formulated by using the frequency-domain solutions of the linearized pipe-dynamics equations. The FFT-based spectral dynamic analyses are conducted to evaluate the accuracy of the present spectral element model and also to investigate the structural dynamic characteristics and the internal fluid transients of an example pipeline system.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.10
• /
• pp.1653-1660
• /
• 2003

The use of frequency-dependent spectral element matrix (or exact dynamic stiffness matrix) in structural dynamics is known to provide very accurate solutions, while reducing the number of degrees-of-freedom to resolve the computational and cost problems. Thus, in the present paper, the spectral element model is formulated for the axially moving Timoshenko beam under a uniform axial tension. The high accuracy of the present spectral element is then verified by comparing its solutions with the conventional finite element solutions and exact analytical solutions. The effects of the moving speed and axial tension on the vibration characteristics, the dispersion relation, and the stability of a moving Timoshenko beam are investigated, analytically and numerically.

• Architectural research
• /
• v.16 no.3
• /
• pp.121-129
• /
• 2014

A plate element is developed by using isogeometric approach in order to determine natural frequencies of laminated composite plates. Reissner-Mindlin (RM) assumptions is adopted to consider the shear deformation and rotatory inertia effect. All terms required in isogeometric element formulation are consistently derived by using Non-uniform rational B-spline surface (NURBS) definition. Gauss quadrature rule is used to form the element stiffness matrix and separately Lobatto quadrature rule is used to calculate element mass matrix. The capability of the present plate element is demonstrated by using numerical examples. From numerical tests, the present isogeometric element produces reliable numerical results for both thin and thick plate situations.

• Proceedings of the KSR Conference
• /
• 2007.05a
• /
• pp.1598-1606
• /
• 2007

In this paper, we present a thin circular beam finite element for the out-of-plane vibration analysis of curved beams. The element stiffness matrix and the element mass matrix are derived respectively from the strain energy and the kinetic energy by using the natural shape functions which are obtained from an integration of the differential equations of the finite element in static equilibrium. The matrices are formulated with respect to the local polar coordinate system or to the global Cartesian coordinate system in consideration of the effects of shear deformation and rotary inertias. Some example problems are analysed. The FEM results are compared with the theoretical ones to show that the presented finite element can describe quite efficiently and accurately the out-of-plane motion of thin curved beams.

• Wind and Structures
• /
• v.25 no.5
• /
• pp.459-474
• /
• 2017

In this study an analytical expression is derived for the natural frequency of the wind turbine towers supported on flexible foundation. The derivation is based on a Euler-Bernoulli beam model where the foundation is represented by a stiffness matrix. Previously the natural frequency of such a model is obtained from numerical or empirical method. The new expression is based on pure physical parameters and thus can be used for a quick assessment of the natural frequencies of both the real turbines and the small-scale models. Furthermore, a relationship between the diagonal and non-diagonal element in the stiffness matrix is introduced, so that the foundation stiffness can be obtained from either the p-y analysis or the loading test. The results of the proposed expression are compared with the measured frequencies of six real or model turbines reported in the literature. The comparison shows that the proposed analytical expression predicts the natural frequency with reasonable accuracy. For two of the model turbines, some errors were observed which might be attributed to the difference between the dynamic and static modulus of saturated soils. The proposed analytical solution is quite simple to use, and it is shown to be more reasonable than the analytical and the empirical formulas available in the literature.

• Structural Engineering and Mechanics
• /
• v.19 no.5
• /
• pp.551-566
• /
• 2005

Using two different, but related approaches, an exact dynamic stiffness matrix for a two-part beam-mass system is developed from the free vibration theory of a Bernoulli-Euler beam. The first approach is based on matrix transformation while the second one is a direct approach in which the kinematical conditions at the interfaces of the two-part beam-mass system are satisfied. Both procedures allow an exact free vibration analysis of structures such as a plane or a space frame, consisting of one or more two-part beam-mass systems. The two-part beam-mass system described in this paper is essentially a structural member consisting of two different beam segments between which there is a rigid mass element that may have rotatory inertia. Numerical checks to show that the two methods generate identical dynamic stiffness matrices were performed for a wide range of frequency values. Once the dynamic stiffness matrix is obtained using any of the two methods, the Wittrick-Williams algorithm is applied to compute the natural frequencies of some frameworks consisting of two-part beam-mass systems. Numerical results are discussed and the paper concludes with some remarks.