Anti-vibration Performance Analysis And Optimization For A Logging While Drilling Neutron Instrument

Logging while drilling(LWD) is the rapid rise of the advanced logging technology in recent years, compared with the conventional logging data, data of LWD can reflect the actual geologic characteristics of stratum more objectively. Pulsed neutron logging technology has been an important branch of LWD technology rapidly developed, the core instrument of this technology is the LWD neutron instrument which is installed in the drill collar. During the normal drilling operations, however, the drill string will bear different kinds of vibration while it drills down and the vibration may lead to a decline in electrical performance of the instrument, causing distortion of the measurement information. Therefore, it is of great importance to study how to improve the anti-vibration performance of the LWD neutron instrument to make the pulsed neutron logging technology come true. This thesis aims to improve the anti-vibration performance of the LWD neutron instrument by improve and optimize its weak connections, which are determined by the structural dynamics analysis. The major contributions are outlined as follows:1. The accuracy of the structural dynamics analysis of ANSYS Workbench is verified by some examples. To establish a reasonable finite element model of the LWD neutron instrument, the simplification and modification of CAD/CAE models is studied, the methods to simplify and modify the typical model characteristics are described in detail and the influence of different contact set methods to the results are discussed.2. The key technology related to the optimization design is discussed. The optimization design process based on Solid Works and ANSYS Workbench is explored. To realize the modeling and transferring of parameters, the collaborative simulation technology between Solid Works and ANSYS Workbench is studied and the parametric methods of parts and components are emphasized.3. The anti-vibration performance of the original LWD instrument is analyzed, including the modal analysis, harmonic response analysis and random vibration analysis, the analysis results show the weak connections that influence its anti-vibration performance and provide a theoretical basis of improvement.4. The improved design and optimization of the LWD neutron instrument is completed. The topological form of the instrument is improved based on the analysis result of the original instrument, in order to improve the anti-vibration performance further, the structure of the instrument is optimized based on the Lagrange quadratic programming. The results show that improvement scheme can eliminate the resonance problem while the optimization scheme can improve the natural frequency of the instrument further and this will provide structure security of the smooth implementation of instrument test.