Sharif Digital Repository

In this paper application of Functionally Graded Materials (FGMs) in suspension bridge structures for the purpose of vertical vibration improvement is investigated. Functionally graded materials are inhomogeneous composites, which are usually made from a mixture of metal and ceramic. Initially the classical equation of motion is modified based on the FGM model and natural frequencies of structure are extracted by Galerkin method. The material properties of structure vary continuously in the longitude direction according to power law form. In this regard, combination of materials is structured in such a way that the desired frequencies of the bridge are achieved by designing the proper power... 

In this paper axial and torsional vibrations of a drillstring are studied using cylindrical superelement. Drillstring vibration equation is derived by calculating kinetic and potential energy and work done by external forces on drillstring, and utilizing Hamilton's principle. The model is analyzed by implementing finite element technique with consideration drillstring weight, centrifugal force due to rotation of drillstring, axial force resulting from bit with the formation contact and torsional torque caused by the stick-slip phenomenon. To calculate the vibrational response of drillstring, a computational finite element scheme was developed. For a typical case of oil well drillstring, the... 

This paper presents a nonlinear model to illustrate the effect of contact stress in the vibration behavior of mechanical components, especially rotating systems. The problem is considered in the case of the vertical vibration of a sphere on a plate. The Hertzian contact theory is used to obtain the relationship between contact force and the deflection of the mass center of the sphere. Modeling the system by a mass and a nonlinear spring, the vibration equation of the mass center of the sphere is derived. The method of LindstedtPoincar is implemented to solve the equation of motion, and obtain vibration characteristics under a compressive preload. The dependency of frequency on several...