Nonlinear aeroelastic analysis of the folding fin with freeplay under thermal environment

The nonlinear aeroelastic behavior of a folding fin in supersonic flow is investigated in this paper.The finite element model of the fin is established and the deployable hinges are represented by three torsion springs with the freeplay nonlinearity.The aerodynamic grid point is assumed to be at the center of each aerodynamic box for simplicity.The aerodynamic governing equation is given by using the infinite plate spline method and the modified linear piston theory.An improved fixed-interface modal synthesis method,which can reduce the rigid connections at the interface,is developed to save the problem size and computation time.The uniform temperature field is applied to create the thermal environment.For the linear flutter analyses,the flutter speed increases first and then decreases with the rise of the hinge stiffness due to the change of the flutter coupling mechanism.For the nonlinear analyses,a larger freeplay angle results in a higher vibration divergent speed.Two different types of limit cycle oscillations and a multiperiodic motion are observed in the wide range of airspeed under the linear flutter boundary.The linear flutter speed shows a slight descend in the thermal environment,but the effect of the temperature on the vibration divergent speed is different under different hinge stiffnesses when there exists freeplay.

Modeling, measurement and simulation of the disturbance torque generated via solar array drive assembly

The disturbance torque generated via solar array drive assembly(SADA) can significantly degrade the key performance of satellite.The discussed SADA is composed of a two-phase hybrid stepping motor and a set of two-stage straight gear reducer. Firstly, the vibration equation of the two-phase hybrid stepping motor is established via simplifying and linearizing the electromagnetic torque.Secondly, based on the vibration equation established, the disturbance torque model of SADA is created via force analysis and force system simplification. Thirdly, for precisely ground measuring the disturbance torque aroused by SADA, a measurement system,including a strain micro-vibrations measurement platform(SMMP) and a set of gravity unloading device(GUD), is designed.Fourthly, the proposed disturbance torque model is validated by measuring and simulating the disturbance torque produced via SADA driving rigid load through GUD. The results indicate that, the proposed disturbance torque model holds the ability to describe the disturbance torque caused by SADA with high precision. Finally, the disturbance torque emitted by SADA driving a flexible load, designed to simulate solar array, is modeled and simulated via using fixed-interface mode synthesis method(FIMSM). All the conclusions drawn from this article do have a meaningful help for studying the disturbance torque produced by SADA driving solar array on orbit.