Analysis of movement of the bop crane under sea weaving conditions


ABSTRACT In the paper, mathematical models for dynamic analysis of a BOP crane un-der sea weaving conditions are presented. The BOP crane is a kind of gantry crane. It is installed on drilling platforms and used for transportation of the Blowout Preventor (BOP). The most important features characterising its dynamics are: motion of the crane base caused by sea weaving, clearance in the supporting system (between the support and rails), impacts of the load into guides and a significant weight of the load. In order to investigate dy-namics of the system, its mathematical model taking into consideration all these features has been formulated. Equations of motions have been derived using homogenous transformations. In order to improve numerical effecti-veness of the model, the equations have been transformed to an explicit form. The input in the drive of the travel system has been modelled in two ways: the kinematic input via a spring-damping element and the force input. Exemplary results of numerical calculations are presented.

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    ABSTRACT: The nonlinear dynamics of a floating crane is investigated. The motion of the system – consisting of the hull with the crane, the load and a nonlinear mooring system – was found to exhibit various nonlinear phenomena. Operating conditions, in which the motion of the vessel or the load is highly dependent on the initial conditions or disturbances are of special interest. Bifurcations in which a small change of a parameter value causes a large qualitative change of the dynamics often limit the range of save operation.For a floating crane which is periodically forced by waves, different mathematical tools are used to investigate resonances and subharmonic motions. The multiple-scales method allows for the analysis in frequency domain and path following algorithms are applied for a numerical bifurcation analysis. The results of both methods agree very well with each other and both offer tools that could help for the evaluation of operating conditions of crane vessels.
    Multibody System Dynamics 04/2003; 9(4):377-387. · 2.02 Impact Factor
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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. 01/2000;
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    ABSTRACT: In this article, results obtained through analytical and numerical investigations into the control of planar, large-amplitude crane-load oscillations are presented. A novel concept called a mechanical filter is proposed and described. In the context of ship crane-load oscillations, this concept is implemented on the basis of the premise that by controlling the pivot point about which the load oscillates, one can effectively suppress crane-load oscillations. Ship-roll-induced load oscillations are considered and a “mechanical filter” is introduced at the pivot to control these oscillations. The pivot is constrained to follow a circular track in the considered filter. The governing non-linear dynamical systems for the cases with and without the filter are presented. Transfer functions are determined for the linearized dynamical systems and the filter performance characteristics are discussed. The non-linear dynamics of the systems with and without the filter is studied with respect to quasi-static variation of different scalar control parameters. Static feedback laws for actively controlling the pivot motions are also considered and the dynamics in the controlled cases is compared with the dynamics in the corresponding uncontrolled cases. It is shown that the presence of the filter helps in eliminating some of the subcritical bifurcations that may arise in the crane-load response during periodic ship-roll excitations. The presence of feedback control also allows us to effectively suppress transient crane-load oscillations.
    Journal of Sound and Vibration 01/1999; 228(3):651-682. · 1.61 Impact Factor


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