About the evaluation of the natural frequencies of a flight vehicle fin at early design stages
State Engineering Design Bureau “Raduga” named after AY Bereznyak, 2а, Zhukovskogo str., Dubna, Moscow region, 141980, Russia
The prediction of a cantilever flutter for a FV requires a rather precise evaluation of natural torsional and bending frequencies for the fin, which is installed on a FV. However, test data concerning the natural frequencies is not available at the early design stages, which require the creation of the design-production documentation for the fin. So it is necessary to do the appropriate calculations for evaluation of the natural frequencies during these stages.
A finite element (FE) software suite was used to conduct the evaluation of the natural torsional frequency of a fin, which is attached to the frame of a FV via control linkage. At that the modeling required the usage of the solid FE models of the links (levers, rods) of the control system linkage that are conjoined in the lugs with the help of the multipoint constraints (MPCs) and the frame, on which the actuator is fixed. The fin was modeled as a rigid solid body. This analysis allowed to find the upper bound of fin torsional stiffness at early design stages.
The implemented analysis has demonstrated the possibility of evaluation of the natural frequencies of the fin at early design stages. The FE software was employed during the analysis for building the detailed FE model with the usage of solid FE. It was necessary to reduce the computing time due to the need for examination of multiple versions of the structure of the control system linkage at the early design stages. Thus it was deemed rational to use superelements during the conducted evaluation. Such superelements allow to reduce the number of the degrees of freedom in the model. To do this it is possible to use the Craig-Bampton method, which is implemented in some commercial software, or other methods, such as the method of component synthesis for dynamic systems. The latter allows to take into account the required number of oscillation components of the analyzed structure with controllable accuracy during the calculations.
Keywords:stabilizer own frequency, flutter, fluctuations
ReferencesGrigor'ev V.G. Metodologiya issledovaniya dinamicheskikh svoistv slozhnykh uprugikh i gidrouprugikh system (Methodology of research of dynamic properties of composite elastic and fluid elastic systems), Doctor’s thesis, Moscow, 2000, 326 p.