Analysis Of Guidance And Corrective Strategy For A Spin-stabilized Projectile Equipped With Fixed Canards

The spin-stablized projectile equipped with decoupled canards(SSPDC)provides an innovative approach for the low-cost and guidance level-up of artillery projectiles and is growing up as a research hotspot.Subjected by the launching platform and the projectile's stability,the maneuverability of the spin-stabilized correction projectile is limited.To fully explore the maneuverability and improve the strike accuracy,the stability properties and design of guidance and control system should be analyzed and optimized further.Moreover,the validity of stability analyzed and guidance system design is dependent on an accurate dynamic model.Therefore,the stability properties,aerodynamic parameters identification and design of guidance and control system for SSPDC are investigated in this dissertation.Firstly,the 7 degrees of freedom(7DOF)rigid body trajectory model is established according to the structural features of SSPDC.As the stability of this projectile is guaranteed by its high rolling speed which is unable to be maintained or enhanced by control system,the flight stability analyse under different control cases is the precondition of the design of SSPDC.The stability criterion of this projectile under different flight and control conditions is deduced by using the 7DOF trajectory model and Herwitz theory.Then the influences of canards' rolling speed and control condition on flight stability are analyzed.Furthermore,to analyze the influence of structure parameters on flight stability,take full use of the potential maneuvability and simplify the multi-platform adaptability of the correction fuze analysis and design,a simplified engineering model for the aerodynamic characteristics theory for wing-body combinations is combined with the stability criterion.In order to enhance the performance of stability analysis and guidance system,the aerodynamic parameter identification is analyzed.Unlike fin-stablized projectile,it is difficult to identificate the parameters in roll,pitch and yaw channels separately for the tight coupling.The nonlinearity of trajectory model is particularly obvious because of the coupling of the three channels and the bending of trajectory,so the identification problem is a multi-extremal optimization problem with higher dimensions.To avoid low efficiency and local optimum caused by high dimension and multiple extremum,a multi-population adaptive search optimization method is proposed.In this method,the samples are divided into several subpopulations automatically by an adaptive density clustering method,and then each subpopulation is randomly searched and updated.To improve the convergence rate and diversity of subpopulation simultaneously,the search step of each generation is a combination of the optimal convergence and random search,whose weights are adaptively adjusted by replacement rate and dispersiver characteristics.In order to verify and assess the performance of this method,it is compared with the modified particle swarm optimization method and genetic algorithm on the aerodynamic parameters identification of SSPDC.The simulations demonstrate that the rate of convergence and optimization accuracy are better than those methods.To further improve the model accuracy,a modified square root unscented Kalman filter is used to identificate parameter online.Spherical unscented transformation is used to decrease the number of Sigma points and increase computation speed;the square root of covariance matrixes and QR decompose are used to avoid algorithm validation caused by indefinite matrix.The effectiveness of this method is verified by the online droppoint prediction of flight test.With the excellent robustness the predictive guidance method has become one of the hotspots in the design of guidance and control system.To ensure the performance and make full use of the maneuverability,the response of droppoint under control and the balance between perdiction accuracy and calculation speed was analyzed deeply.The reliable modelling of control response is the premise of realizing effective guidance and ensuring accuracy.Due to the strong coupling and nonlinearity of the trajectory model,the droppoint response of SSPDC in the range and offset directions are coupled obviously.An equivalent control force method is proposed to analyze the droppoint respose of SSPDC,in which the effect of lateral control force on the projectile's translational motion is decomposed into the direct effect of control force and the indirect effct related to the angular motion caused by control force and moment.Furthermore,the approximate expression of droppoint response respected by the correction and phase angle is derived based on the equivalent control force,and the effectiveness is verified by flight test.As the measurement parameters and onboard computer calculation ability are restricted by space and cost,a piecewise prediction control method based on modified perturbation theory with higher prediction accuracy,lower computational complexity and less testing information is proposed.To improve the practicability of perturbation prediction method and prediction accuracy under different environment conditions and target positions,a repid launch condition and reference trajectory determination method is proposed by combining perturbation and stepwise approximation methods.Moreover,a simplified prediction model parameters calculation method is derived.When the remaining flight is long,the perturbation prediction(PP)can effectively improve the prediction accuracy and calculation speed by avoiding the cumulative effect of model and measurement uncertainties;in the termimal trajectory,the precision of integral prediction model is better.Hence,a piecewise prediction method combining PP and integral prediction is proposed,and verified by Mento Carlo simulations.The trajectory tracking method has obvious advantages,such as simple calculation,feedback architecture and insensitivity of model uncertainty,in the design of guidance and control system.To meet the reduced measurement condition,the transfer function between control input and trajectory motion output is derived according to the modified point-mass trajectory model.In order to make full use of maneuverity,a virtural wizard and virtural line-of-sight(VLOS)angle are designed.Using the back-stepping method and Lyapunov theory,a control law is derived with a sliding mode surface established in the reference path coordinate frame and is proven to converge.Moreover,to enhance the robustness of the system,an extended state observer is designed to estimate the parameters and compensate for the uncertainty online.The feasibility and effectiveness of the path-following controller is verified through closed-loop flight simulations with measurement,control,and condition uncertainties.The results indicate that the designed controller can converge to the reference path and evidently decrease the distance between the impact point and target under different uncertainties.