Validation of Equivalent Viscous Damping Methodologies
Tutor / director / evaluatorJoseph Morlier
Document typeMaster thesis (pre-Bologna period)
Rights accessOpen Access
To obtain accurate predictions of the satellite dynamic environment it is therefore essential that the damping of the system is correctly defined and taken into account within the resolution methodologies for the Coupled Loads Analysis (CLA). When working with Finite Element Models, the damping of the materials is characterized by structural damping ratios. In addition, most of the load cases present in the CLA are transient excitations. Consequently, the resolution of the equations of motion must be done in the time domain. Unfortunately, the transient analyses cannot be carried out using structural damping characterization since they cannot be used in the time domain. Therefore, a transformation from a structural to a viscous damping characterization needs to be performed. Nevertheless, this transformation from structural damping to viscous damping models is not trivial. There exist many methodologies that aim at computing an Equivalent Viscous Damping Matrix of the system so it can be used in transient analyses. This document describes the results obtained by the author as well as to evidence his contribution for the European Space Agency as an intern in the Structures Section TEC-MSS in the validation of the Equivalent Viscous Damping methodologies. The project was born when the results on finite element models for one Vega propulsion stages where not correlated to the experimental data from the firing tests. During the course of the internship, the limitations in the Equivalent Viscous Damping methodologies that are used in ESA’s Coupled Loads Analysis Toolbox have been identified. The author implemented an enhanced methodology aiming at improving these limitations. The methodology that is currently implemented in the CLA Toolbox and the enhanced method have been compared to a Reference method for frequency response analyses. From this comparison, we could demonstrate that the Enhanced Method does indeed predict more reliable results than the methodology of the CLA Toolbox. Moreover, the enhanced method has been implemented in transient analyses. We could conclude on the applicability of the enhanced method for a transient load case. In addition, it has been noticed an improvement in the reliability of the results for the enhanced method with respect to the method that is currently implemented in the CLA toolbox. This enhancement is a great step forward on the the accurate characterization of the load environment at the Spacecraft’s interface with the launcher in the Coupled Loads Analysis. Therefore, a future perspective is to implement the enhanced methodology in the ESA’s Coupled Loads Analysis Toolbox. Moreover, this enhanced method could be tested in the correlation of a real Solid Rocket Motor finite element model analysis with experimental data from firing tests. Perhaps, new enhancements will need to be introduced for real cases. Finally, the enhanced method shall also be validated before performing the Coupled Loads Analysis between the launcher and the Spacecraft with this method.