A method of determination of drive functions of slewing of a mobile crane's upper structure is presented in the paper. The purpose of their determination is to reduce load oscillations at the end of the motion. Drive functions for selected angles and durations of slewing have been calculated using a simple model of the crane and dynamic optimisation. Drive functions for intermediate angles have been determined by means of interpolation. Res ul ts of numerical simulations executed for the model of the crane are presented, taking into consideration flexibilities and damping in the cranes subsystems. Results obtained for drive functions determined using optimisation and interpolation algorithms are compared. An attempt to determine sensitivity of load positioning to selected operating parameters is also presented. Introduction of the notion of a positioning quality coefficient is proposed.

The peculiarity of offshore cranes, i. e. cranes based on ships or drilling platforms, is not only a significant motion of their base, but also the taut-slack phenomenon. Under some circumstances a rope can temporarily go completely slack, while a moment later, the force in the rope can increase to nominal or even higher value. Periodic occurrence of such phenomena can be damaging to the supporting structure of the crane and its driver. In the paper, mathematical models of offshore cranes that allow for analysis of the taut-slack phenomenon are presented. Results of numerical calculations show that the method of load stabilization proposed by the authors in their earlier works can eliminate this problem.

In offshore pedestal cranes one may distinguish three components of considerable length: a pedestal, a boom and a frame present in some designs. It is often necessary in dynamical analyses to take into account their flexibility. A convenient and efficient method for modelling them is the rigid finite element method in a modified form. The rigid finite element method allows us to take into account the flexibility of the beam system in selected directions while introducing a relatively small number of additional degrees of freedom to the system. This paper presents a method for modelling the pedestal, the frame and the boom of an offshore column crane, treating each of these components in a slightly different way. A custom approach is applied to the pedestal, using rigid finite elements of variable length. Results of sample numeric computations are included.

The paper presents the mathematical model of a pipelay spread. In the model, elasto-plastic deflections of the pipe, its large deformations and contact problems are considered. The modification of the rigid finite element method (REFM) is used to discretise the pipe. The problem is analyzed in two stages. First, the quasi-static problem is considered. The tip of the pipe is pulled from the reel to the tensioner. Then, dynamic analysis (during ordinary work) of the pipelay spread is carried out. Some results of numerical calculations are presented.

The paper presents the numerical model of a supply vessel-load-crane-offshore vessel system for simulation of heave motion and dynamic analysis of the system during critical phases of the handling operation: taking the load off from and lowering it to a moving base. The model enables extreme forces in elements and deflection of the structure to be determined. Different operating and emergency conditions can be simulated (e.g. horizontal motion of a supply vessel). The elaborated software can be applied also for determination of derated load charts and ultimate crane capacity (sequence of failure).

The paper presents the dynamic model of an A-frame, which is a kind of an offshore crane with a portal construction. The rigid finite element method (RFEM) has been used in discretization of the flexible substructure. An application of optimisation methods to define the drive function course of the hoisting winch is presented. The goal of the optimisation is to ensure stabilization of the load’s position. In order to achieve appropriate numerical effectiveness, the optimisation problem has been solved for a simplified model of an A-frame. Comparison of numerical results obtained for different types of objective functions and types of drive functions is presented in the paper as well.