Analyse des vibrations propres des risers tendus par la méthode de segmentation-Dans le but de l'évaluation des vibrations des risers induites par vortex (VIV), les vibrations modales d'un riser uniforme tendu en eau profonde sont considérées. Du fait de la faible rigidité des risers, les vibrations du type câble et poutre sont analysées. Les solutions exactes et asymptotiques de l'équation différentielle de câble sont présentées. Les vibrations de la poutre sont déterminées en modifiant la solution câble pour chaque demi-longueur d'onde du mode propre. La procédure analytique simplifiée est vérifiée par la méthode des éléments finis. Les conclusions utiles sur le comportement dynamique des risers dans le domaine des hautes et basses fréquences sont présentées.

In this paper, a finite strip for vibration analysis of rotating toroidal shells subjected to internal pressure is developed. The expressions for strain and kinetic energies are formulated in a previous paper in which vibrations of a toroidal shell with a closed cross section are analyzed using the Rayleigh–Ritz method (RRM) and Fourier series. In this paper, however, the variation of displacements u, v, and w with the meridional coordinate is modeled through a discretization with a number of finite strips. The variation of the displacements with the circumferential coordinate is taken into account exactly by using simple sine and cosine functions of the circumferential coordinate. A unique argument nφ+ω t is used in order to be able to capture traveling modes due to the shell rotation. The finite strip properties, i.e., the stiffness matrix, the geometric stiffness matrix, and the mass matrices, are defined by employing bar and beam shape functions, and by minimizing the strain and kinetic energies. In order to improve the convergence of the results, also a strip of a higher-order is developed. The application of the finite strip method is illustrated in cases of toroidal shells with closed and open cross sections. The obtained results are compared with those determined by the RRM and the finite element method (FEM).

In the present thick plate vibration theory, governing equations of force-displacement relations and equilibrium of forces are reduced to the system of three partial differential equations of motion with total deflection, which consists of bending and shear contribution, and angles of rotation as the basic unknown functions. The system is starting one for the application of any analytical or numerical method. Most of the analytical methods deal with those three equations, some of them with two (total and bending deflection), and recently a solution based on one equation related to total deflection has been proposed. In this paper, a system of three equations is reduced to one equation with bending deflection acting as a potential function. Method of separation of variables is applied and analytical solution of differential equation is obtained in closed form. Any combination of boundary conditions can be considered. However, the exact solution of boundary value problem is achieved for a plate with two opposite simply supported edges, while for mixed boundary conditions, an approximate solution is derived. Numerical results of illustrative examples are compared with those known in the literature, and very good agreement is achieved.

The significant growth of renewable energy production in the past decades is present mainly due to the global depletion of fossil fuel reserves. One of interesting and well developed renewable energy technologies are wind turbines which are mainly built onshore. Due to more favorable wind characteristics at sea, off shore wind power plants are an interesting and challenging option for meeting future energy demands. In particular, less turbulent wind with higher average velocity enhances energy production and reduces structural fatigue of wind energy structures. In this study, benefits and drawbacks of off shore wind turbine units and power plants are pointed out. Based on the available climate data, sea depths and existing sea traffic routes, two possible wind power plants, i.e. one with fixed and another with floating turbines, are proposed for installation in the Croatian part of the Adriatic Sea. Benefits for the Croatian shipbuilding industry and its economy are pointed out.