Finite Element Model Updating And Security Performance Evaluation Of Derrick Based On Stress And Deformation Testing

The security performance evaluation of oil drilling derrick is often realized by comparison and mutually validation between the results of tests and numerical simulation. Because of complexity of the real derrick structure, it is not possible to build in all the details in finite element model. The defects induced by manufacture and service are generally difficult to be taken into account in the analysis model. The analysis of derrick structure is often based on the regular models that neglect some details and defects. The regular model represents the model in which it neglects some auxiliary details, the connections of the bars are regarded the rigid ones, and it is a structure without defects. The experiments proved that the regular FEM model cannot describe truly loading properties of the structure, as there may be the effects of different defects. It is then necessary to modify the regular FEM model, according to the experimental results, for the purpose to make results of simulation closer to the real structural response.Actually the security performance evaluation of oil drilling derrick is mainly based on the measurement of stress on the derrick legs. Restricted by the condition of measurement locale and measurement cost, the number of measured point is limited. It is then not possible to represent wholly loading properties of the structure by the measured stresses on derrick legs. The method of video measurement is employed to measure and test the deformation properties, when the derrick is loaded. It represents the advantage of global measurement without contact.According to results of measurement on stress and deformation in the derrick, and referring to real structure of the derrick, the truer derrick model is determined and validated to realize the FEM analysis. The modified derrick FEM model is used for numerical simulation. The results of computation are used for security performance evaluation of the derrick.The present thesis includes the following main works:1. By means of MATLAB platform, a camera calibration procedure is programed based on Zhang’s method. A camera calibration method is proposed and realized based on the relative distance of feature points. Zhang’s method represents higher calibration precision, but the procedure calibration relies on the calibration plate. It represents the higher requirement on measurement environment and condition, then not suitable for engineering measurement of the large structures. The method based on relative distance between feature points realizes the camera calibration according to the pixel coordinates of feature points and their relative distance, assuming the knowing of camera’s parameters. This method represents the important value in engineering measurement, but the precision for calibration is lower.2. Measurement on stress and deformation under static loads is effected on the K type derrick model in laboratory and JJ315/45-K drilling derrick in service. The Video measurement method is used to measure deformation of the derrick under loading. The technology for measuring the strain is used to measure distribution of the stress in the loaded derrick. Loading feature of the derrick is analyzed according to the measured data. 3. According to the data of Video and strain measurement, a method to modify the FEM model of derrick is proposed. The Pin connections in derrick model is modified by the LINK10element with "gap" property in ANSYS software. The reduction of stiffness by pin gap is realized by reducing suitably the compressive stiffness in the pined elements. The load applied to modified model should consider eccentricity of the hook load. This method is validated by the measured data on stress and deformation of model derrick in laboratory and JJ315/45-K derrick in service under static loading.4. Based on the modified FEM model, the security performance evaluation is realized for model derrick in laboratory and JJ315/45-K drilling derrick in service.5. The correlation between the stress and deformation of a loaded derrick is preliminarily studied. An empirical formula for estimation of the axial stress in derrick legs is obtained, according to the working load of derrick and its maximum horizontal displacement.6. By means of MATLAB platform,"derrick measurement and evaluation system" is developed and realized. This software can be used for the post processing of image measurement data. It displays graphically the deformation of loaded derrick, provides the facility for analysis of the derrick deformation features. The axial stress in derrick legs can be calculated according to working load and horizontal displacement of the derrick, then the loading feature of derrick can be analyzed. The corrective parameters for FEM model of the derrick can be set by the software. The ANSYS software is called to build the modified model and then realize the numerical simulation. Based on the results of measurement and simulation, the security performance evaluation can be made on the derrick.Verified by experiments, the modified FEM model of derrick is used for simulation. The relative error is within15%between the results of computation and test measurements. Then the results of simulation satisfy the requirement for engineering computation. It represents more truly loading properties of the structure, then can be used for security performance evaluation of the derricks. By means of the stress-deformation empirical formula, proposed by this work, the axial stress in derrick legs can be approximately calculated according to maximum horizontal displacement of the derrick. This work forms the basis for the replacement of strain measurement by Video measurement in security performance evaluation. The former represents heavy work, while the latter is simple and easy. These works exhibit the significance for the studies of loading capacity and security performance evaluation of the drilling derricks.