Sharif Digital Repository

The dry friction and its effect on the dynamics and vibrations of structures have always been one of the remarkable engineering issues. In the structures of engineering, dry friction mostly exists at the joints of structures and substrates and dry friction can lead to the nonlinearity and even chaos in the vibration of structures. There are different theories for the friction modeling and the most famous theory is the relation between the proportional ratio of the force of friction and perpendicular force to the surface. The main characteristic of friction as a damper force is the change of direction along with change in the direction of velocity. In the present study, at first, the nature... 

Because the structural stability is directly related with structural damage, it is considered one of the most important issues in the industry. One of the applied cases in the stability issue discuss about the stability of the beam under follower loads. Follower loads obtained from aerodynamic pressure, rocket’s thrust, dry friction of the rotating disk, drilling and etc. Because the follower loads are always perpendicular to the beam cross section, thus with changing the angle of their location, their directions are changed. Spatial dependence makes a non-conservative and dynamic problem. So these loads causes dynamic instability that say flutter. In this study, the stability of a... 

In this thesis, effects of bending and torsional elasticity of a flapping wing on its average lift and input power are studied, using a semi-analytic method. Bending stiffness and torsional rigidity of wing spar, wing mass ratio and chordwise and spanwise center of gravity, also spar location are considered as variables for controlling elastic behavior of the wing.Governing integral equation is derived using Hamilton principle via modified quasi aerodynamic and linear Green-Lagrange strain tensor. Also an idealized flapping pattern is used to maximize average acceleration during each cycle. Next, integral equation is converted to a set of ordinary differential equations by means of Galerkin... 

In this study, an analytical investigation of the hydrodynamic damping due to vertical baffles in circular cylindrical storage tanks is investigated. A lot of research about damping characteristics of different types of baffles has been done but because of specific applications of vertical baffles, studies are limited in this case. For analytical approach the average rate of energy dissipation is obtained with using the solution of Laplace’s equation by estimation the rate of the work done by baffles drag force to the oscillatory flow. The analytical solution validate by a series of experiments that conducted at the Langley Research Center of the National Aeronautics and Space... 

Long thin rectangular beams are used in many industrial engineering including railways, aerospace and etc. Beam subjected to moving mass is one of the classic problems in mechanics and vibrations of beams and have been studied by many researchers. In most of done works, the moving mass was assumed to be small compared to beam mass and only acceleration effect of mass was considered. Also in many of researches only bending of beams was studied. Moving mass imposes 2 type of force in the supporting beam, first one is weight and the other is due to motion of mass and contains lateral, coriolis and centrifugal acceleration effects. In addition, due to the particular geometry considered (narrow...