Validation of finite element model of a dish-stirling system by performing experimental modal analysis
Examensarbete för masterexamen
Applied mechanics (MPAME), MSc
The energy consumption in the world is currently higher than ever before and it keeps rising. There is a fast rising demand for renewable energy sources such as solar power, and concentrated solar power systems can be a solution to this. However, in order to have robust systems that can compete with solar photovoltaic technologies, the life span and operational load effects on the structure need to be ensured. This can be done by using a validated finite element model. This thesis describes the experimental modal analysis and finite element analysis of a Dish-Stirling system developed by Cleanergy. The purpose of the thesis is to perform experiments on the structure to compare simulated results with actual tests, in order to validate that model in terms of dynamic response. Testing on the structure was done in two different set-ups, one used for calibration and the other for validation. The structure was excited using a snap-back method, hanging a weight from the structure by a fishing line and burning the line to excite the structure. The structure was allowed to oscillate freely and eigenmodes were excited as the vibrations caused by the excitation were damped out. Data from experiments was processed and system identification of the response was done in the form of state space models. Eigenfrequencies and eigenmodes of the state space models were compared to eigenfrequencies and eigenmodes from the finite element model, which were found by performing modal analysis. Calibration of different parameters was done, changing one parameter at a time, and the calibrated data compared to the finite element results. The calibrated parameter which gave the best correlation between experiments and finite element model was used as input to the validation. Due to the complexity of the model, only the first modes were used for the comparison, as the other modes were too complex, and had frequencies too close to each other to distinguish between them. Comparing the finite element model with the experiments showed that the experiments did manage to capture the eigenfrequencies of interest, however, when comparing the eigenvectors, there were differences in the correlation. Some modes were captured better than others. Calibration of the model led to a marginally better correlation. The validation confirmed the calibration, to some extent. In conclusion, the finite element model corresponds well to the experiments, discrepancies in the results could be due to faults in experiment methodology, such as measurements were made too scarcely in the structure. It could also be due to a poorly calibrated finite element model. In order to further validate the finite element model more extensive experiments would need to be performed, as well as a more complex calibration procedure.
Teknisk mekanik , Energi , Applied Mechanics , Energy