Damage Identification Study Of Oil Derrick Structure Based On Ambient Excitation

Rig derrick is one of the most important equipment in hoist system. People can install crown block and hang tackle, hoisting hook and special tools on it. Some derricks in using have been used for a long time in the long term bad outside environment the derrick produces partial or whole harm. They are hidden danger of the safety in production. At present, methods of the stress test and the computer simulation have a definite limitation. Research a sort of scientific test method is very important on theory and application to enhance evaluating the carrying capacity of oil derrick and safety evaluation method.Structural modal parameters reflect the main dynamic properties, according to identification the change of the modal parameter's damnification structure is widely studied by scientists. Modal parameter's identification can be obtained by traditional or ambient vibration identification techniques. It is difficult to exert artificial excitation and difficult to measure excitation signal on large oil derrick structures for them having huge volume, mixed material, complex bind condition, etc. Ambient excitation(wind load,earth pulse) has many advantages, such as no excitation equipment needed, no interruption of structural service conditions and less test time, which is more close to the real working conditions of oil derrick structures. The state-of-the-art studies are carried out in this thesis on the damage identification of oil derrick structures under ambient excitation conditions. Two time domain methods of modal identification based on ambient excitation carried through damage recognition to JJ160/41-K oil derrick structural models, and the results also identified a comparison. Completed the major work as follows:1. Several damage identification methods based on ambient excitation are presented. These methods include Peak Picking(for short PP),Frequency Domain Decomposition(for short FDD),Time series method(for short TSM),Stochastic Subspace Identification(for short SSI),Random Decrement (for short RD) and Natural Excitation Technique(for short NExT) .2. JJ160/40-K oil derrick structural finite element modeling was built with ANSYS. Damage was simulated by changing the elasticity modulus. Modal analysis and dynamic response analysis is done at healthy condition and some damage condition.3. Free vibration signal of the measuring points were gained by random decrement technique. Then modal analysis was done by ITD method. The structural damage was judged by identification result.4. The cross-correlation function of the measuring points relative to reference point was gained by the natural excitation technique, taken as impulse response functions. Then modal analysis was done by ITD method. The structural damage was judged by identification result.5. The location of structural damage was judged by the injury index of Coordinate Modal Assurance Criteria.