pouya sarvi

In the analysis of many offshore structures such as oil columns and structures, oil rig abutments and towers surrounded by water, the single-beam model is usually used. These models usually bear the weight of a concentrated mass, and the response amplitude of these structures is of particular importance during design.In this paper, a nonlinear beam immersed in a fluid with a concentrated mass under the effects of the harmonic flow of water has been studied. Using the harmonic balancing method, the response of a nonlinear beam with three nonlinear terms is determined in the first four modes. Examination of the frequency response by analytical solution and numerical simulation shows that the jump phenomenon occurs in the triple response zone between the bifurcation points. The jump phenomenon is hardening in the first mode and softening in the second to fourth modes. Each of the nonlinear sentences has different effects on the vibrational behavior of the system and the jump phenomenon. The behavior of the beam in the state space along with the time response and Poincaré mapping shows that the path of the phase curve has different stability points. Finally, the phenomenon of chaos in the nonlinear beam was studied. At the bifurcation points, the behavior of the system is chaos, and the geometric nonlinear sentence has the most effective effect on the response disorder.

Nowadays, there is a high demand for great structural implementation and multifunctionality with excellent mechanical properties. The porous structures reinforced by graphene platelet (GPLs) having valuable properties, such as heat resistance, lightweight, and excellent energy absorption, have been considerably used in different engineering implementations. However, stiffness of porous structures reduces significantly, due to the internal cavities, by adding GPLs into porous medium, effective mechanical properties of porous structure considerably enhances. To boost the efficiency and capability of structures, functionally graded (FG) porous structures reinforced by GPLs have been suggested in the literature. Therefore, some researchers tried to figure out the fantastic characteristics of these structures and research activities in this emerging area have been rapidly increasing. The present paper (a) briefly reviews the mechanical properties of functionally graded porous composites reinforced by GPLs and discusses the existing micromechanics model for the prediction of effective mechanical properties; (b) presents a comprehensive review on the mechanical analyses of these structures; (c) discuses the challenges and possible future works.

For the modelling of marine structures, such as the oil columns and structures, the terminal and base of oil platforms and the towers surrounded by water usually a cantilever beam or rod is used. These models are subjected to random excitation and the response amplitude of these structures is of particular importance during design. In this paper, a nonlinear cantilever beam immersed in a fluid with a concentrated mass under a narrow band random excitation has been studied and its response has been analyzed. With the development of the harmonic balance method, the variance of the random system response has been determined and the phenomenon of jumping and random jumping has been investigated. The analytical solution and the numerical simulations show that in comparison with the deterministic response, the random excitation increases the amplitude of the random response between the bifurcation points of the beam. As the intensity of the random excitation increases, the steady response changes from a circular to a cyclic state. The results also show that the random jump phenomenon occurs in the area where there are three states for the system. Finally, the results of analytical and numerical modeling indicate that there is a very good agreement between the data and the results of these two methods.