F. Hosseinlou, A. Mojtahedi , M. A. Lotfollahi,
Volume 36, Issue 1 (9-2017)
Abstract
An important requirement in design is to be able to compare experimental results from prototype structures with predicted results from a corresponding finite element model. In this context, updating the model using measured vibration test can lead to proposing a desired finite element model. Therefore, this paper presents indirect and direct based numerical updating study of a reduced scale four-story spatial frame structure of offshore jacket platforms constructed and tested at the Structural Dynamics and Vibration Laboratory. Besides, the selection procedure for inactive degrees of freedom in the process of reduced model is evalated, with a reasonable criterion, by using sensitivity analysis of system response under base excitation. This performance leads to faster convergence of iterative algorithm and also, eliminates spurious modes. Since the significant problem fundamental to dynamic structural analysis is the amount of time and cost required for computation, the use of these methods will save both in time and cost.
F. Hosseinlou,
Volume 40, Issue 2 (1-2022)
Abstract
Today many complex models, typically finite element models, have been employed in the analysis of jacket offshore structures. However, these comprehensive models are not readily adopted in engineering practice, especially during the preliminary design stage. As the dynamic analysis of jacket platforms is very complicated, it will be very advantageous to make a simplified computational method to assess dynamic performance of such structures. In this work a refined simplified model has been utilized to calculate dynamic responses of jacket platforms. In this regard, the model simplification based on the vibration modal data and Timoshenko’s beam equation has been employed to overcome the uncertainty problem in modeling. According to the curve fitting method on the set of frequency response functions to derive modal parameters, the concept of power spectrum density has been also used to confirm the proposed computational model.In this regard, first the behavior of the physical model in the frequency domainhas been presented and compared with the spectral results obtained from the simplified model based on Timoshenko beam. Because the modal test of the physical model was performed under the force of white noise, the dynamic responses of the simplified model were also extracted under the force of white noise using MATLAB software. In this paper, an applied mathematical model has been produced, and it has been demonstrated that the refined simplified model can reflect the real structural features.
