Vibration of open cylindrical shells: A three-dimensional elasticity approach

The three-dimensional elastic analysis of the vibration of open cylindrical shells are presented. Transverse normal stress usually neglected in plate and shell higher-order theories has been considered. The natural frequencies and vibration mode shapes have been obtained via a three-dimensional displacement-based extremum energy principle. Excessive requirements for memory and computational effort have been overcome, without sacrificing numerical accuracy, by (i) decoupling the three-dimensional displacements into the product of a set of beam and shell shape functions; and (ii) classifying the vibration modes. The effects of subtended angle and aspect ratio have been concluded for shells with various boundary conditions. Typical vibration mode shapes demonstrating the dependence of vibration characteristics on boundary constraints are presented. ©1998 Acoustical Society of America.published_or_final_versio

Nonlinear free vibration of shear deformable sandwich beam with a functionally graded porous core

The nonlinear free vibration behavior of shear deformable sandwich porous beam is investigated in this paper within the context of Timoshenko beam theory. The proposed beam is composed of two face layers and a functionally graded porous core which contains internal pores following different porosity distributions. Two non-uniform functionally graded distributions are considered in this paper based on the equivalent beam mass, associated with a uniform distribution for purpose of comparison. The elastic moduli and mass density are assumed to vary along the thickness direction in terms of the coefficients of porosity and mass density, whose relationship" is determined by employing the typical mechanical characteristic of an open-cell metal foam. The Ritz method and von Karman type nonlinear strain-displacement relationships are applied to derive the equation system, which governs the nonlinear vibration behavior of sandwich porous beams under hinged or clamped end supports. A direct iterative algorithm is then used to solve the governing equation system to predict the linear and nonlinear frequencies which are presented by a detailed numerical study to discuss the effects of porosity coefficient, slenderness ratio, thickness ratio and to compare the varying porosity distributions and boundary conditions, providing a feasible way to improve the vibration behavior of sandwich porous beams

Numerical Simulation of Structural Behaviour of Transmission Towers

Transmission towers are a vital component and management needs to assess the reliability and safety of these towers to minimise the risk of disruption to power supply that may result from in-service tower failure. Latticed transmission towers are constructed using angle section members which are eccentrically connected. Towers are widely regarded as one of the most difficult form of lattice structure to analyse. Factors such as fabrication errors, inadequate joint details and variation of material properties are difficult to quantify. Consequently, proof-loading or full-scale testing of towers has traditionally formed an integral part of the tower design. Stress calculations in the tower are normally obtained from a linear elastic analysis where members are assumed to be axially loaded and, in the majority of cases to have pinned connections. In practice, such conditions do not exist and members are detailed to minimize bending stresses. Despite this, results from full-scale tower test often indicated that bending stresses in members could be as high as axial stresses. EPRI (1986) compared data from full-scale tests with predicted results using current techniques and concluded that the behaviour of transmission towers under complex loading condition cannot be consistently predicted using the present techniques. They found that almost 25% of the towers tested failed below the design loads and often at unexpected locations. Furthermore, available test data showed considerable discrepancies between member forces computed from linear elastic truss analysis and the measured values from full-scale tests. The paper describes a nonlinear analytical technique to simulate and assess the ultimate structural response of latticed transmission towers. The technique may be used to verify new tower design and reduce or eliminate the need for full-scale tower testing. The method can also be used to assess the strength of existing towers, or to upgrade old and aging towers. The method has been calibrated with results from full-scale tower tests with good accuracy both in terms of the failure load and the failure mode. The method has been employed by electricity utilities in Australia and other countries to: (a) verify new tower design; (b) strengthen existing towers, and (c) upgrade old and aging towers

Recursos electrònics en història de la ciència

Màster oficial en història de la ciència: ciència, història, societa

Bending Analysis of Folded Laminated Plates by the FSDT Meshfree Method

AbstractA meshfree method is developed in this paper to study the flexure behavior of folded laminated plates. A folded laminated plate is considered as an assembly of laminates. Based on the first-order shear deformation theory (FSDT) and the moving-least square approximation, the stiffness equations of the laminates are derived. A treatment is implemented to modify the equations, and the equations are then superposed to obtain the governing equation of the entire folded laminated plate. No mesh is required in the determination of the stiffness equations of the laminates, and therefore the proposed method is more flexible than the finite element methods. The convergence and accuracy of the proposed method are examined by computing several numerical examples, and good agreement is observed between the present results and those given by ANSYS