Derrick Safety Assessment Based On Model Updating

In essence, finite element (FE) model updating is the problem of optimization. The purpose of model updating is to identify and correct uncertain parameters of FE model that leads to the better predictions of structural real dynamic and static behavior. In view of the characteristic of derrick structural and the existence flaw, this article proposed the method of the sensitivity-based analysis of the parameters finite element (FE) model. Derrick model for the study of technical amendments to the ideal finite element model tends to actual derrick structure to reflect the true state of derrick structure and actual work performance, and play an important role in the health monitoring of the derrick and safety assessment.The finite element method, the structural dynamics theory and large-scale structural finite element software - ANSYS were used and with the actual structure, the mechanical characteristics as displace, stress, natural frequency and modal shapes are acquired. The analysis offers foundation for model updating and forecast of safety.Based on the low-frequency characteristics of the locale derrick structure and the working conditions characteristic, this subject uses the ambient vibration test method. 1MHz high speed portable data acquisition system which the WaveBook series develops using American IOTECH Corporation and eZ-Analyst portable real-time vibration analysis system of the Zonicbook series carries on the gathering analysis and processing to the derrick dynamic signal. The dynamic characteristic parameter provides the basis for the finite element (FE) model updating.The derrick structure forms and possible presence of several security flaws were briefly introduced, such as corrosion of section, initial flexural deformation of member bars, initial flexural deformation of integral structure, eccentric acting load, the decrease of rigidity of knock-off joints, and base sinkage. The finite element model updating approaches of derrick structures have been constructed. The sensitivity-based analysis of the parameters finite element (FE) model was used to update the real derrick FE models. The relevant design parameters are acquired by the way of sensitivity analysis, the frequency and mode shapes by the dynamic measurement as the key indicators, the parameters are acquired by iterative approach and the function of optimization of the structural finite element software - ANSYS to convergence.This article takes the laboratory derrick model as an example. The vibration testing of the laboratory derrick model based on hammer excitation. Vibration tests to be the first to the natural frequency of third-order frequency as the objective function to updatede the laboratory derrick finite element model. Results demonstrate the method of the sensitivity-based analysis of the parameters finite element (FE) model may update the laboratory derrick model well.Through laboratory derrick model confirmation, the method of the sensitivity-based analysis of the parameters finite element (FE) model is field applied. The ambient vibration testing of the locale JJ162/42-K Derrick, the data of the vibration testing was used to update the derrick. After updating, dynamic characters from FE model agreed well with those from dynamic testing. Establishes the datum finite element model of JJ162/42-K derrick, according to the design parameter after updating. The mode after updating carries on the safety assessment to JJ162/42-K derrick.