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# Analysis of movement of the bop crane under sea weaving conditions

JOURNAL OF THEORETICAL AND APPLIED MECHANICS 01/2010; 48(3):677-701.

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**ABSTRACT:**A one-dimensional finite-element lumped-mass model of a vertically tethered caged ROV system subject to surface excitation is presented. Data acquired during normal operation at sea are used with a least-squares technique to estimate the coefficients required by the model. The model correctly predicts: (a) the motion of the cage and the tension in the tether at the ship; (b) the spectrum of cage acceleration in the wave-band; (c) the transfer function between the vertical motion of the ship and cage; and (d) the natural frequency of the system and its harmonics. A simple model of the wake of the cage was added to the model simulation and this reduced the error in the calculated motion and tension by almost a factor of two and brought the calculated transfer function within the 95% confidence interval of the measurements. By increasing ship motion slightly, the model accurately reproduced eight snap loads and their non-linear characteristics—a regularly spaced series of rapid increases in the records of the acceleration of the cage and tension at the ship—that occurred during the measurements used for validation.Applied Ocean Research 06/2000; · 1.26 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**In the authors' earlier work, a concept called a mechanical filter was introduced and investigated for suppressing non-linear, planar crane–load oscillations on floating platforms. To implement this concept, the pivot point about which the load oscillations occur was constrained to follow a circular track. In the current effort, the geometry of the planar mechanical filter is generalized, and the corresponding non-linear dynamical system is derived and presented. On the basis of a Lyapunov function, analytical results are obtained to aid the choice of the filter geometry and the control law. For weak harmonic disturbances, the method of multiple scales is used to study non-linear oscillations of the system with a circular filter. The results of the perturbation analysis demonstrate the occurrence of cyclic-fold bifurcations in the system with the passive filter and suppression of crane–load oscillations in the system with the active filter. The analytical results are found to be in agreement with the associated numerical results. For large magnitude harmonic and aperiodic disturbances, numerical results demonstrate the effectiveness of the active filter in suppressing “large” crane–load oscillations. Tailoring of the response suppression bandwidth by using the active filter is also discussed.Journal of Sound and Vibration 11/2001; 247(4):633-653. · 1.61 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Dynamic analysis of offshore systems mounted on platforms or vessels is especially difficult since it is necessary to consider phenomena connected with a sea waves [1]. The waving causes additional impulse forces in the system which should be taken into account in design process. The suitable description of dynamic behavior of the system allows its using in design of control systems. The algorithm for generating the equations of motion of the gantry crane using homogenous transformations and joints coordinates is presented in the paper [2,3]. The Lagrange equations of the second order are used to derive the equations of motion.12/2008: pages 49-59;

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