Study On Static And Dynamic Characteristics Of Heavy Floating Crane Under The Action Of Sea Waves

Heavy floating crane is important equipment in the field of ocean engineering. When floating crane operations at sea, it will sway under the action of ocean waves. Sway movements bring harm to the safety of working of crane which is installed on the board of vessel. So, in the design of floating crane, in order to ensure safe working of the floating crane, not only the deformation and stress of floating crane structure are calculated under dead weight and lifting weight,and force condition of wheels in different compression stiffness of rubber pads used in rotary bearing,but also dynamic characteristics and dynamic response of floating crane under ocean waves are studied.Floating crane structure mainly include boom, amplitude varying wire rope, tied back wire rope, truss frame, A-frame, counterweight box, rotating machinery base, and rotary bearing structure. Based on finite element theory, a 3-D finite element model of the floating crane is built by the ANSYS software, and a static analysis of the floating crane is done under dead weight and lifting weight with ANSYS software. Under different compression stiffness of rubber pads used in rotary bearing, uniformity of forces applied on wheels is studied. By a modal analysis and a harmonic response analysis of the floating crane, the vibration characteristics and dynamic response under base excitation are calculated. The base excitation is the motion response of the vessel under the action of regular ocean waves. During the modeling of finite model of the floating crane, parts of the floating crane are effectively simulated by the SHELL63 element, BEAM188 elements, LINK10 elements, COMBIN14 elements, MASS21 elements and MATRIX27 elements. Whether structural strength of the crane is enough is the primary consideration in static analysis. In the study of uniformity of forces applied on wheels in different compression stiffness of rubber pads used in rotary bearing, the variation of the bearings of wheels under different compression stiffness is primary consideration. In Modal analysis, by calculating the load case of the floating crane lifting a 7500t load, the vibration characteristics of the structure are calculated. It is the foundation of the following dynamic analysis and calculation. In Harmonic response analysis, displacement responses and stress responses of the floating crane structure under base excitation are paid the most attention. The base excitation is the motion response of the vessel under the action of regular ocean waves. Through these studies, it is found that, the strength of the floating crane structure is enough in the static state; a relatively large stress is found at connection of the rotating machinery base and truss frame; the smaller of rubber pads'compression stiffness, the better distributed of wheels'force. Through the modal analysis, it is found that main vibration modes of floating crane structure are swing of rope-load system and vibration of boom, and the vibration frequencies are low; first order and second order modes are swing modes of rope-load system, the others are almost vibration modes of the boom. The dynamic responses of the floating crane are large when the wave travels in 90°towards the vessel. When the position of the lifted load is high, the dynamic responses of the floating crane are large. As the amplitude of rocking is larger than that of pitching of the vessel, the lateral displacement response of the floating crane is larger than the longitudinal one, and in addition, the rope-load system swings larger in the lateral direction than in the back-forward direction. The largest dynamic stress appears at the bottom of the boom of the crane and it is below the material strength.These studies are key subjects in design of the floating crane. The studies of the structure strength of the floating crane in static and dynamic state examine rationality of the design of floating crane, provide a prediction of dynamic response of floating crane under the action of the ocean waves, and provide a reference for design of floating crane.