The Study Of Modal Parameter Identification Technology And Optimal Sensor Placement Of Offshore Platform

To carry out vibration test and accurate recognition the structural dynamic characteristics is the foundation of offshore platform structure health monitoring. The precise degree of the identification information is directly related with the number and accuracy amount of measured information. It needs to collect a large amount of test signals, containing all the information of complete structure as far as possible. But offshore platform structures are often complicated, having many nodes, affected by test conditions (such as rotational degrees of freedom can be measured, the underwater test has high difficulty and cost), a great number of sensors is not decorated in the actual test. Measured data are inevitably contaminated with noise, and the number of modes contributing to our measured signal is not known beforehand, it is necessary to identify modal parameters from complex response signals. So it is every significant to choose the reasonable sensor installation position and modal parameter identification method for identifying the modal parameters of structure accurately. To research the issues mentioned above, the main contents and conclusions as follows:The modal parameter identification of offshore platform structure is researched based on eigensystem realization algorithm, focusing on reject of spurious mode and Spatial Incompleteness. It is verified that the ERA method is applicability and engineering practicability in modal parameter identification of offshore platform structure through physical model test of jacket platform. For complex structure, using ERA method and Guyan method can accurately identify the inherent characteristic information of the target modes.Adopting the right method to select sensor installation position can get a signal data containing all the information of structure, so as to avoid the question and the blindness in the traditional experience sensor installation. To get the modal parameter identification, an optimization method of sensor placement of offshore platform based on different mode is proposed. According to the different mode of structure, how to determine the right number of sensors and installation position is researched. It is verified that this method is through the numerical simulation and physical model test, eigensystem realization algorithm and sensor optimal placement are used in the preliminary study of the offshore platform test. For offshore field test signal data, eigensystem realization algorithm can accurately identified the low mode information of the offshore platform. Research findings, the use of4sensors diagonal arrangement divided on two layers achieves the same recognition as the use of8sensors, to provide a certain reference for sensor placement of other test in the future.