Investigation of thrust effect on the vibrational characteristics of flexible guided missiles

摘要

In this paper the effect of thrust on the bending behaviour of flexible missiles is investigated. For this purpose, the governing equations of motion of a flexible guided missile are derived following the Lagrangian approach. The missile is idealized as a non-uniform beam where the bending elastic deflections are modelled using the method of modal substitution. The vehicle (time varying) bending modeshapes and natural frequencies are determined by modelling variable mass and stiffness distributions with thrust and mass burning effects accounted for. To solve this problem the missile is divided into several segments of uniform stiffness, density and axial force distribution. This approach produces a non-linear transcendental equation, which requires an iterative scheme to numerically determine the magnitude of the eigenvalues. Since inertial measuring units (IMU) also sense the local body vibrations, the mass and stiffness non-uniformities plus the thrust action on elastic missiles can potentially influence their measurements and thus must be properly accounted for in an aeroelastic simulation. It is noted that the thrust force reduces the vehicle natural frequency while mass consumption increases it. Thus the modal natural frequencies can either decrease or increase in time. Also the critical buckling thrust, which dynamically causes a zero natural frequency, is obtained and therefore the thrust instability limitations are determined through simulation. With proper modelling of the IMU vibrations effects and engine/thrust fluctuations, the influence of body vibrations on the missile dynamics and controls are investigated with axial thrust effect. (C) 2003 Elsevier Ltd. All rights reserved.