جستجوی مقالات مرتبط با کلیدواژه "vibrations" در نشریات گروه "ریاضی"

In the present paper, the impacts of viscous dampers on controlling the vibrations imposed on seismic vibrations are evaluated using descriptive methods. To this end, the library method and other research related to viscous dampers and their impacts on controlling external excitation such as earthquakes have been used. ETABS software was used for modelling the structures. Also, nonlinear dynamic analysis was used for seismic analysis of the structures. Based on the findings, using viscous dampers are effective to improve seismic parameters of structure and to decrease displacement, speed, base shear, and velocity. On the other hand, viscous fluid dampers can strengthen the structure and its performance during severe earthquakes and can be applied in newly constructed structures. The impact of a passive viscous damper on reducing the seismic response of the structures is found significant at the confidence level of 90%. Reduction of energy of structure hysteresis because of the nonlinear behaviour of members using dampers is proved to be significant at the confidence level of 80%. The results reveal that the lateral resistance of an EBF with a short joint can be 4/5 to 9 times more than the lateral resistance of an MRF, that the behaviour coefficient of fifteen-story EBF considered 6/5-7/75, concluded that the length of the bray does not have an impact on the behaviour coefficient of these frames.

This paper attempts to study the vibration characteristics of a simply supported nth order rectangular nanoplate using the modified couple stress theory. The modified couple stress theory, which has only one length scale parameter, has been used to consider the small-scale effects. The basic and auxiliary equations of the nanoplate are obtained after determining the strain energy, kinetic energy, and external work and substituting them into Hamilton’s equation. Then, the vibrations of the simply supported nth order rectangular nanoplate with a thickness of h are investigated by substituting the boundary and force conditions into the governing equations. Navier’s method is used for the solution. The results indicate that the frequencies of the different modes of the nth order nanoplate decrease with an increase in the length-to-thickness ratio of the nanoplate. Furthermore, the frequency is the smallest when the effect of the size parameter is not considered (classical theory), and it increases with an increase in the size effect. In addition, the frequency is smallest for the first mode and increases for the subsequent modes. Also, the vibrational frequency increases with an increase in the order of the nanoplate.

This paper studies the dynamics of a non-smooth vibrating system of the Filippov type. The main focus is on investigating the stability and bifurcation of a simple harmonic oscillator subjected to a non-smooth velocity-dependent damping force. In this way, we can analyze the effects of damping on the system's vibrations. For this purpose, we will find a parametric region for the existence of generalized Hopf bifurcation, in order to compute a branch of periodic orbits for the system. The tool for our purpose is the theoretical results about generalized Hopf bifurcation for planar Filippov systems. Some numerical simulations as examples are given to illustrate our theoretical results. Our theoretical and numerical findings indicate that the harmonic oscillator can experience different kinds of vibrations, in the presence of a non-smooth damping.

This paper is devoted to study of a partial differential equation governing panel motion in supersonic flow. This PDE can be transformed to an ODE by means of a Galerkin method. Here by using a criterion which is closely related to the Routh-Hurwitz criterion, we investigate the mentioned transformed ODE from Hopf bifurcation point of view. In fact we obtain a region for existence of simple Hopf bifurcation for it. With the aid of computer language Matlab and Hopf bifurcation tool, flutter and limit cycle oscillations of panel are verified. Moreover, Hopf bifurcation theory is used to analyse the flutter speed of the system.