Study On Dynamic Response Of Drilling Rig Derrick

In oilfield drilling, rig derrick is one of the most important equipment in hoist system. People can install crownblock and hang tackle, hoisting hook and special tools on it. During drilling, workers can complete manipulations such as making a trip, casing running and so on. Besides the deadweight as the static load, derrick structure must undergo hookload in tripping, wind load outdoors and vibration load when drilling machine is running. All above are dynamical loads which vary following time. Most research at present lays particular stress on static methods of analysis and research, overlooking the especial situation of longitudinal impaction and periodic loads in work phases. Such traditional static methods are not exact and all-around, so it is more scientific and reasonable in derrick design and safety evaluation for designers to regard the dynamical load as the true load acted on derrick structure to research its dynamic characteristic. This thesis builds the dynamic model of drilling rig derrick by the theory of elastic body and principle of model equivalent, and classifies two operating modes, especial and normal modes, by the structure character and work practice of derrick. At the same time, based on probability statistics and probability model of vertical loads, the thesis establishes the load spectrum in periodic experiment and transient course in time impact,then implements the transient analysis and dynamic response calculation. It draws some conclusions including the changes of deformation and stress of derrick structure under dynamic loads, and the vibration rules and characteristic of time responses in different orientation in the main parts such as top, racking platform and propeller strut of drilling rig derrick. Modal analysis is one kind of latter-day theory on dynamic characteristic research, and now becomes the core of dynamic analysis and design in modern engineering. Natural frequencies and modes of vibration of structure resulted from modal analysis are the important parameters on dynamic design of structure. So it is the start of all dynamic analysis, transient analysis especially. This thesis completes the mode analysis of rig derrick by finite element method, getting the free frequencies of preceding 10 steps and vibration modes. Finally it completes the response spectrum analysis, also getting the characteristic between frequencies and responses of the derrick system.