No abstract

No abstract

For more complex nonlinear systems, where the amplitude of excitation can vary in time or where time-dependent external disturbances appear, an analysis based on the frequency response curve may be insufficient. In this paper, a new tool to analyze nonlinear dynamical systems is proposed as an extension to the frequency response curve. A new tool can be defined as the chart of bistability areas and area of unstable solutions of the analyzed system. In the paper, this tool is discussed on the basis of the classic Duffing equation. The numerical approach was used, and two systems were tested. Both systems are softening, but the values of the coefficient of nonlinearity are significantly different. Relationships between both considered systems are presented, and problems of the nonlinearity coefficient and damping influence are discussed.

The paper deals with the problem of prediction of the rolling period. A special emphasis is put on the practical application of the new method for rolling period prediction with regard to non-linearity of the GZ curve. The one degree-of-freedom rolling equation is applied with using the non-linear stiffness moment and linear damping moment formulas. A number of ships are considered to research the discrepancies between the pending GM-based IMO--recommended method and the results of conducted numerical simulations performed for a wide range of operational loading conditions. Since the research shows some drawbacks of the IMO formula for the ship rolling period, a new formula is worked out and proposed instead.

One of the significant problems in the safe operation of vessels is the behavior of the ship on the wave. Of all degrees of freedom, the greatest threat to the safety of a ship is associated with excessive rolling. One of the best methods to improve the safety of a ship in this field is to carry out experiments on the ship model, performed at her design stage. The problem is that the model tests are costly. An alternative is to conduct simulation tests based on numerical models. The primary goal of the article is to present the results of the simulation regarding the determination of parameters describing the risk areas of chaotic rolling for the ship designed for transporting liquefied natural gas (LNG carrier) and offshore support vessel (OSV). The first discusses the state of knowledge on mathematical modeling of oscillations. Then, the theory of nonlinear differential equations is presented, and the mathematical model of ship rolling is described. This model is used to prepare and conduct a numerical simulation in the Mathematica package. The results of these studies and their discussion constitute the central part of the article. Finally, the conclusions are presented.