Multi-body Dynamics Modeling And Its Application In Marine Cable Systems

Based on Huston's method, the concept of low-body-group is introduced andthen a new vectorial modeling method for multi-body system is developed. Applyingflexible multibody system theories, the dynamics of marine cables is deliberated andan improved finite segment model for cable is developed. Planar and spatialmechanical arms containing joint clearance and two kinds of typical marine cablesystems are simulated. The effectiveness and validity of the theories are verified, andsome benefit conclusions were obtained as well.Looking into Huston's method, a more meaningful form of partial velocity isobtained, and then the vector form of Kane's equation in Huston's method ispresented. Then based on the concept of low-body-group, a new vectorial mechanicsmodeling method for multibody systems is developed, and the dynamic equations ofmatrix form are derived from the method. The manner of numbering and describingmethod of topological structure of multibody systems are discussed, and a newprogramming approach for multibody systems is presented. Then dynamic equationswith more efficiency, accuracy, stability for multibody systems containing jointclearance are achieved and applied to dynamic simulation of multibody systemscontaining joint clearance. Low-speed planar and high-speed spatial mechanical armsare simulated and the results are compared with that from software Adams withoutregard to joint clearance;and the method was proved to be correct and effective. Thecomparison also come to the conclusion that with different operating speed, jointclearance has different effects on multibody systems.Based on the analysis for Huston's method from the point of view of vectorialmechanics, cable dynamic equations of universal form for the three spatial discretemethods, lump-mass method, finite element method and finite segment method areobtained. By the comparison of the results of static analysis for cables using differentmethods, the degree of accuracy of spatial discrete methods is discussed . Finitesegment method is less accurate and time-consuming when applying to elastic cables.To overcome these deficiency, a new improved finite segment model is developed.This modeling method regards cables as flexible multibody systems, introducingdescribing technique for displacements of flexible body in FEM. According to cableproperties,fitting generalized coordinates are selected and the governing equationsfor planar and three dimensional marine cables are obtained. For reel-in/pay-outconfiguration of towed and tethered cable systems, improved finite segment modelwith variable topology is studied thoroughly. By changing the length of the segmentwith varying lengths and increasing or decreasing the numbers of segments, theprocess of reel-in or pay-out is simulated. Applying improved finite segment method,two types of simulations are presented: towed system and mooring system. The wholeprocess, including launching, paying-out, stable moving, stopping, are simulated andthe results compare favorably with experimental data. A laboratory test is designedfor a small tethered surface buoy. And the buoy system with elastic mooring line aresimulated using the improved finite segment method too. The comparison validatesthe improved finite segment model and it is instructive for the designs and uses ofcable systems.A new idea for large displacement and nonlinear static analysis for cablestructures is presented. Cable is assumed to move from its initial position toequilibrium position under all loads and stop at equilibrium position by imposingattenuation of kinetic energy or damping. It is appropriate to problems that arehighly nonlinear and sensitive to initial condition. Several cable structures aresimulated and show that the method is effective.