• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.887-902
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• 1994

Within the framework of anisotropic thermoelasticity, the problem of an interlaminar crack in a laminated fiber-reinforced composite subjected to a uniform heat flow is investigated. Under a state of generalized plane deformation, dissimilar anisotropic half-spaces with different fiber orientations are considered to be bound together by a matrix interlayer containing the crack. The interlayer models the matrix-rich interlaminar region of the fibrous composite laminate. Based on the flexibility/stiffness matrix approach, formulation of the current crack problem results in having to solve two sets of singular integral equations for temperature and thermal stress analyses. Numerical results are obtained, illustrating the parametric effects of laminate stacking sequence, relative crack size, crack location, crack surface partial insulation, and fiber volume fraction on the values of mixed mode thermal stress intensity factors.

• Advanced Composite Materials
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• v.18 no.2
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• pp.105-119
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• 2009

In this work, the structural response of thin-walled composite beams with pretwist angle is investigated by using a mixed beam approach that combines the stiffness and flexibility methods in a unified manner. The Reissner's semi-complimentary energy functional is used to derive the stiffness matrix that approximates the beam in an Euler-Bernoulli level for extension and bending and Vlasov level for torsion. The bending and torsion-related warpings induced by the pretwist effects are derived in a closed form. The developed theory is validated with available literature and detailed finite element structural analysis results using the MSC/NASTRAN. Pretwisted composite beams with rectangular solid and thin-walled box sections are illustrated to validate the current approach. Acceptable correlation has been achieved for cases considered in this study. The effects of pretwist and fiber orientation angles on the static behavior of pretwisted composite beams are also studied.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.221-226
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• 2005

In this paper, a dynamic model for the rotor shaft-coupling-blade system is developed. The blades are attached to a disk and driven by an electric motor shaft which is flexible in torsion. We assumed that the shaft torsional flexibility is lumped in the flexible coupling which is usually adopted in rotor systems. The Lagrangian approach with the small deformation theory for both blade-bending and shaft-torsional deformations is employed for developing the equation of the motion. The assumed modes method is used for estimating the blade transverse deflection. The numerical results highlight the effects of both structural damping of the system and the torsional stiffness of the flexible coupling to the dynamic response of the blade. The results showed strong coupling between the blade bending and shaft torsional vibrations in the form of inertial nonlinearif, stiffness hardening and softening.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.9 s.102
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• pp.1023-1029
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• 2005

In this paper, a dynamic model for the rotor shaft-coupling-blade system was developed. The blades are attached to a disk and driven by an electric motor shaft which is flexible in torsion. We assumed that the shaft torsional flexibility was lumped in the flexible coupling which is usually adopted in rotor systems. The Lagrangian approach with the small deformation theory for both blade-bending and shaft-torsional deformations was employed for developing the equation of the motion. The Assumed Modes Method was used for estimating the blade transverse deflection. The numerical results highlight the effects of both structural damping of the system and the torsional stiffness of the flexible coupling to the dynamic response of the blade. The results showed strong coupling between the blade bending and shaft torsional vibrations in the form of inertial nonlinearity, stiffness hardening and softening.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.125-135
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• 2011

The latest study for formulation of finite element method and computation techniques has progressed widely. The classical method in the formulation of frame elements for geometrically nonlinear analysis derives the geometric stiffness directly from the governing differential equation for bending with axial force. From the computational viewpoint of this paper, the most common approach is the finite element method. Commonly, the formulation of frame elements for geometrically nonlinear structures is based on appropriate interpolation functions for the transverse and axial displacements of the member. The formulation of flexibility-based elements, on the other hand, is based on interpolation functions for the internal forces. In this paper, a new method is used to suppose that interpolation functions for the displacements from the curvatures is Lagrangian interpolation. This paper derives flexibility matrix from that displacement functions and is considered the application of it. Using the flexibility matrix, this paper apply the program considered geometrically nonlinear analysis to common problems.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2241-2251
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• 1992

This work is concerned with the investigation of end effects of a cylinder on a structure where a circular plate is attached to a solid circular cylinder. Three-dimensional elasticity solutions are used in a cylinder whereas the classical thin plate theory is employed for a plate. The end effect of the cylinder on the flexibility and the structural response is demonstrated by several numerical examples.

• Structural Engineering and Mechanics
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• v.13 no.5
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• pp.557-568
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• 2002

For the evaluation of the capability of a tubular member of an offshore structure to absorb the collision energy, a simple method can be employed for the collision analysis without performing the detailed analysis. The most common simple method is the rigid-plastic method. However, in this method any characteristics for horizontal movement and rotation at the ends of the corresponding tubular member are not included. In a real structural system of an offshore structure, tubular members sustain a certain degree of elastic support from the adjacent structure. End fixity has influences in the behaviors of a tubular member. Three-dimensional FEM analysis can include the effect of end fixity fully, however in viewpoints of the inherent computational complexities of the 3-D approach, this is not the recommendable analysis at the initial design stage. In this paper, influence of end fixity on the behaviors of a tubular member is investigated, through a new approach and other approaches. A new analysis approach that includes the flexibility of the boundary points of the member is developed here. The flexibility at the ends of a tubular element is extracted using the rational reduction of the modeling characteristics. The property reduction is based on the static condensation of the related global stiffness matrix of a model to end nodal points of the tubular element. The load-displacement relation at the collision point of the tubular member with and without the end flexibility is obtained and compared. The new method lies between the rigid-plastic method and the 3-demensional analysis. It is self-evident that the rigid-plastic method gives high strengthening membrane effect of the member during global deformation, resulting in a steeper slope than the present method. On the while, full 3-D analysis gives less strengthening membrane effect on the member, resulting in a slow going load-displacement curve. Comparison of the load-displacement curves by the new approach with those by conventional methods gives the figures of the influence of end fixity on post-yielding behaviors of the relevant tubular member. One of the main contributions of this investigation is the development of an analytical rational procedure to figure out the post-yielding behaviors of a tubular member in offshore structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.2
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• pp.137-144
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• 1983

Core walls for tall building is one of the structures to support lateral load. Since most structural elements used for resisting which ate relatively weak against torsion, it is important to investigate tosional effects in the analysis and design of tall buildings. Rutenberg proposed a more refined theory on the torsional analysis of core walls which can be used when the stiffness of lintel beams are small or large. In this paper a more refined method to analysis the torsion of core wall structures with variable cross sections and being subjected to arbitrarilly distributed load was suggested. To reduce complex and a great number of calculations and to enhance the generality and flexibility of application of this method, the discrete method using transfer matrix formulation was used. Then this method can be easily applied to irregular and variational sections, has no necessity to get particular solution for each of loading conditions, and the maximum size of matrix calculated is $4{\times}4$, which makes this approach more appropriate for design office calculations using comuters of any sizes or even desk calculators.