Investigation On Dynamics Problems Of Flexible Spinning Missile

With the development of missile technology,the missile design gradually pursues larger payloads,longer flight distances,faster flight speeds,higher hit accuracy,and greater maneuverability and agility.In order to get better performance,this kind of missile gradually shows lighter structural weight and larger slenderness ratio.Unfortunately,as the weight of the structure decreases and the slenderness ratio increases,the structure shows less structural stiffness,lower natural frequencies,and greater flexible deformation.In the traditional missile design,the coupling between rigid-body motion and structural vibration for the missile is very small,and rigid-body motion and structural vibration can be studied independently,which are called flight dynamics and aeroelasticity,respectively.However,as for the missile with large slenderness ratio,it is necessary to consider aerodynamic coupling between rigid-body motion and structural vibration.For flexible spinning missile with large angular velocity,the coupling mechanism is more complicated.It is necessary to consider not only the aerodynamic coupling,but also the inertial coupling.In this paper,flexible spinning missile with large slenderness ratios is used as research object.Based on mesh generalized motion methods such as rigidmotion mesh and mesh deformation method,computational fluid dynamics(CFD)equations and flight dynamics equations of flexible flight vehicle are coupled to establish numerical virtual flight platform for flexible multi-body flight vehicle.The flight dynamics equations of flexible flight vehicle are an extension and enhancement of the classical rigid-body flight dynamics equations and aeroelasticity equations.The equations can handle large nonlinear rigid-body motion and structural vibration in the linear elastic range of the flight vehicle,furthermore,both aerodynamic coupling and inertial coupling between rigid-body motion and structural vibration are considered.Based on this platform,the dynamics of flexible spinning missile are studied systematically and thoroughly.The main research contents are shown as follows.1)Based on rigid-motion mesh methods such as single mesh motion method and multi-body mesh dynamic chimera method,and mesh deformation methods such as inverse distance weighting(IDW)and data-reduced radial basis function(RBF),a mesh generalized motion method for flexible multi-body is established.The method can simultaneously handle any complex motions between meshes,including spatial translation,spatial rotation around arbitrary axis,spatial Euler angle rotation around fixed-point,chimera mesh,mesh boundary deformation,and so on.The method has strong robustness and applicability,which lays a solid foundation for studying complex motions of flexible flight vehicle.2)Based on mesh generalized motion method for flexible multi-body,computational fluid dynamics method is coupled with rigid-body flight dynamics method,aeroelasticity method,flight dynamics method of flexible flight vehicle considering only aerodynamic coupling,aeroelasticity method considering rotation,and flight dynamics method of flexible flight vehicle considering both aerodynamic coupling and inertial coupling,respectively,and a numerical virtual flight platform for flexible multi-body flight vehicle is established.This platform can be used to study the free flight of rigid/flexible flight vehicle,multi-body separation of rigid/flexible flight vehicle,and rudder deflection of rigid/flexible flight vehicle.3)The longitudinal static trimming method of flight vehicle is studied,and based on the numerical virtual flight platform,a longitudinal static trimming tool is established.The longitudinal static trimming method can quickly obtain a trimming state under different initial conditions,and the trimming result is independent of the initial state,and the method has strong robustness and good convergence.4)The effects of structural flexible deformation and vibration on longitudinal dynamics of missile are studied.The structural flexible deformation and vibration have effects on longitudinal equilibrium angle of attack,amplitude of pitch motion,and period of pitch motion,furthermore,the degree of influence is different under different structural stiffness.The study of the longitudinal dynamics of flexible missile is the premise and basis for studying more complex problems of coupling between rigid-body motions such as pitching and yawing motions and structural longitudinal and lateral modes for flexible spinning missile.5)Based on flight dynamics equations of flexible flight vehicle that consider both aerodynamic coupling and inertial coupling,aeroelastic equations that consider centrifugal force,Coriolis force,and other inertial forces due to rotation are derived.The equation can be used to study aeroelasticity of flexible spinning missile.The effects of rotation on structural damping,structural stiffness,structural generalized force,and structural natural frequency are both analytically and numerically studied based on the control equations.The large angular velocity of rigid-body motion of flexible spinning missile will bring additional inertial forces such as centrifugal and Coriolis forces,and these inertial forces have influence that cannot be ignored on structural flexible deformation and vibration.However,in traditional aeroelastic study for aircraft and missile,the additional inertial forces are usually not considered.6)Numerical simulations of flexible spinning missile in flight were conducted,and the aerodynamic coupling and inertial coupling between rigid-body angular motion and structural vibration were quantitatively studied.For the cases studied in this paper,aerodynamic coupling still plays a major role,but inertial coupling cannot be ignored.The degree of inertial coupling is closely related to the structural deformation and rotational angular velocity,and it is necessary to pay more attention when studying related issues.7)Flight simulation based on aerodynamic model for rigid/flexible spinning/non-spinning missile.The aerodynamic models were obtained by parameter identification method from flight trajectory calculated by CFD method,and the aerodynamic model was used to replace CFD method in the simulation platform to solve flight trajectory and structural flexible deformation and vibration of missile in flight.This method has extremely fast computational speed and can take into account aerodynamic non-linearities.It can be used to study the effect of small disturbance in initial conditions on the flight trajectory and structural flexible deformation and vibration for missile.This method has great engineering significance.The research methods and conclusions of this paper can provide a reference for further research in the future,and also have guiding significance for the design of flexible spinning missile with large slenderness ratio.