چكيده به لاتين
Today, according to the design criteria, if the components of a mechanical system are subjected to in-plane compressive loads, the most important threat to their normal performance is the issue of instability or loss of stiffness and load capacity. The purpose of this thesis is to investigate the dynamic instability of a three-layer composite smart beam with an electrorheological fluid core, under two-layer boundary conditions and cosine compressive external axial force. For this purpose, Hamilton's principle is first used to obtain the governing equations of the problem. Then, using the variable separation method, the governing equation of the system is reduced to two equations only in time and only in space. The obtained time equation is known as Mathieu's equation and it determines whether the system is stable or not. In the following, the analytical-approximate method of parameter steering is used in order to determine the limits of dynamic instability in the form of algebraic equations. Subsequently, with the mentioned method, the dynamic response of this system will be obtained for excitations whose characteristics are exactly on the boundaries of instability. Also, for other excitations whose characteristics are not exactly on the boundaries of the unstable regions, the fourth order Runge–Kutta numerical method has been used. In the following, using the electrorheological fluid layer in the core of the beam, an active control system based on sliding mode control is designed and implemented. Considering the numerical results and graphs obtained in uncontrolled and controlled mode, it is shown to what extent the use of the controller can reduce the transient response time and improve the system performance in reducing the area of instability areas and transferring this Areas will help towards larger loading frequencies and amplitudes. It is worth mentioning that in the future works, adding non-linear supports, applying extensive transverse load, adding visco - elastic bed can be investigated.
