A tiltrotor aircraft trajectory optimization method, device, equipment and medium

Abstract

The present application relates to a method, device, equipment and medium for optimizing the trajectory of a tiltrotor aircraft. The method comprises: establishing the flight equation of a tiltrotor aircraft with distributed power, formulating the flight criteria for forward transition and backward transition and constructing a dynamic flight feasible domain; within the dynamic flight feasible domain, establishing a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable, and constructing a longitudinal motion model; defining an objective function for optimizing the trajectory of the transition process combining the margin feasible reference line and performance requirements, and defining actuator range constraints and system performance constraints; assigning an initial state to the aircraft, converting the nonlinear dynamic optimal control problem into a Bolza-type optimal control problem, solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints to minimize the objective function. The use of this method can improve the safety of the transition of the tiltrotor aircraft.

Description

Technical Field

[0001] The present application relates to the technical field of aircraft trajectory optimization and control algorithm, and in particular to a tiltrotor aircraft trajectory optimization method, device, equipment and medium. Background Art

[0002] Vertical take-off and landing aircraft have the advantages of vertical take-off and landing of helicopters and high-speed cruising of fixed-wing aircraft. They can take off and land in complex terrains such as mountains and ships, and their transportation costs are lower than those of conventional helicopters and fixed-wing aircraft. Therefore, they have attracted much attention from all walks of life and have broad application prospects in many fields such as aerial reconnaissance and material transportation.

[0003] At present, vertical take-off and landing aircraft are mainly divided into standard compound type, tail-seat type and tilt-rotor type according to the flight mode conversion method. Among them, the standard compound type is relatively easy to control, but the separate hovering / forward flight propulsion system adds extra weight and reduces the efficiency of the entire power system. The tail-seat type does not require additional power and tilt mechanism (tilt angle) and has the smallest actuator unit group, but because the fuselage needs to be tilted as a whole, they have greater uncertainty during mode conversion, and the wind has a greater impact on them during hovering and tilting. For tilt-rotors, due to more control authority, they have a larger control margin during mode conversion and are easier to control than tail-seat rotors when hovering, but the additional tilt mechanism increases the control dimension of the aircraft and increases the complexity of the overall system, especially during mode conversion.

[0004] One of the major challenges in the design of tilt-rotor aircraft is to develop a suitable transition control trajectory to ensure safe and efficient flight operations under various conditions. On the one hand, it is necessary to study the appropriate control strategy for the tilt angle of the tilt mechanism to change with the forward speed, that is, to study the feasible domain of dynamic flight of the tilt-rotor aircraft. Because during the transition flight, the aircraft's flight speed, lift resistance and forward vertical thrust change due to the change in the tilt direction of the propulsion system and the angle of attack of some tilt-rotor wings. The balance between these factors may be destroyed as the propulsion tilt angle changes, resulting in a rapid drop in altitude or failure to reach the required speed. On the other hand, since the feasible domain of the tilt transition generally only contains information such as the aircraft speed and tilt angle at each trim point, it is also necessary to design a motion trajectory that changes with time in the feasible domain of the transition to guide the tilt-rotor aircraft to perform mode transition.

[0005] However, the current calculation of the feasible domain of dynamic flight of tiltrotor aircraft is generally based on balancing calculation, which mainly considers the balance of the longitudinal horizontal force, vertical force and pitch moment of the aircraft, but does not consider the problem of dynamic changes in flight speed and force during the transition process of the tiltrotor aircraft.

[0006] The existing tiltrotor aircraft transition process trajectory design method is mainly based on the transition process trajectory design with the best index. The purpose of the transition process trajectory design based on the best index is clear, but the safety margin of the resulting trajectory (that is, to ensure that the aircraft has a certain control margin to deal with unknown disturbances) is not fully considered. In addition, a key issue in the transition process of the tiltrotor aircraft is the rapid decrease in the backward transition flight speed. At present, the flight kinetic energy of the backward transition of most tiltrotor aircraft is reduced only by the aerodynamic drag and gravity, which leads to an increase in the time consumption of the backward transition and an increase in the risk factor, and the safety of the transition of the tiltrotor aircraft cannot be guaranteed. Summary of the invention

[0007] Based on this, it is necessary to provide a tiltrotor aircraft trajectory optimization method, device, equipment and medium to address the above-mentioned technical problems, which can consider the flight speed and dynamic changes of the tiltrotor aircraft transition process when calculating the dynamic flight feasible domain of the tiltrotor aircraft, thereby improving the accuracy of the dynamic flight feasible domain calculation, and in the process of trajectory optimization design of the tiltrotor aircraft transition process, consider the safety margin of the trajectory and the kinetic energy reduction effect of the reverse tilting of the tilt mechanism, so as to obtain a trajectory that meets high safety margin, smaller control input and shorter backward transition time, thereby improving the safety of the tiltrotor aircraft transition.

[0008] A tiltrotor aircraft trajectory optimization method, the method comprising:

[0009] Step 1, establish the flight equations of forces and torques of the distributed power tilt-rotor aircraft, formulate the flight criteria for the forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints;

[0010] Step 2, within the dynamic flight feasible domain, establish a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable, and construct a longitudinal motion model of the tilt-rotor aircraft;

[0011] Step 3, define the objective function of the transition process trajectory optimization combining the margin feasible reference line and the performance requirements, transform the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft into a nonlinear dynamic optimal control problem including the optimization objective defined in step 2, and clarify the actuator range constraint and system performance constraint of the tilt-rotor aircraft; wherein the optimization objective is to ensure that the trajectory of the transition process of the tilt-rotor aircraft is far away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible;

[0012] Step 4, assigning the initial state of the tiltrotor aircraft, transforming the nonlinear dynamic optimal control problem obtained in step 3 into a Bolza-type optimal control problem, solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3 to minimize the objective function.

[0013] In one embodiment, establishing flight equations for forces and moments of a distributed power tiltrotor aircraft includes:

[0014] The pitch velocity and flight acceleration of the distributed power tilt-rotor aircraft during longitudinal trim are both zero, and the forces and moments acting on the tilt-rotor aircraft are offset. The flight equation established based on this is expressed as

[0015] ;

[0016] in, In the body coordinate system The resultant force on the shaft is In the body coordinate system The resultant force on the shaft is is the pitch channel torque, is the mass of the aircraft, is the acceleration due to gravity, In the body coordinate system The aerodynamic force on the shaft, is the pulling force generated by the propeller in the body coordinate system, i Indicates the propeller number, In the body coordinate system The aerodynamic force on the shaft, is the torque generated by the propeller thrust in the pitch direction, is the moment generated by aerodynamic force in the pitch direction;

[0017] For a tilt-rotor aircraft, the flight equation involves six independent variables, namely: tilt angle , Flight speed v , Pitch angle , Angle of Attack , elevator surface deflection angle , tilt propeller speed (corresponding to propeller speeds 1 and 2) and fixed propeller speed (corresponding to the speed of propellers 3 to 6); when solving the feasible domain of dynamic flight, and v The value of will be specified;

[0018] In the specified and v Next, to calculate the analytical solution to the flight equation , and further use numerical methods to balance, and obtain the simplified flight equation, expressed as

[0019] .

[0020] In one embodiment, flight rules for forward transition and backward transition of a tiltrotor aircraft are formulated, including:

[0021] The flight criteria for forward transition are defined as follows: (1) Acceleration: the horizontal flight speed of the aircraft gradually increases; (2) Pitch attitude limit: the pitch angle of the aircraft changes, and the pitch angle change rate is within a certain range; (3) Vertical motion limit: the height of the aircraft changes slightly, and the vertical acceleration of the aircraft remains within a certain range; (4) Power limit: during the transition process, the difference in motor tension on the same side of the aircraft is kept within a certain range;

[0022] Combining the forces and moments of the tilt-rotor aircraft, the mathematical expression of the forward transition flight criterion is obtained as follows:

[0023] ;

[0024] Among them, the superscript F represents the forward transition process, , and They represent the horizontal force, vertical force and vertical velocity of the aircraft during the forward transition process. for The maximum value of for The maximum value of is the angular velocity in the pitch direction of the forward transition, In the body coordinate system The speed in the axis direction, In the body coordinate system The speed in the axis direction, , , and Respectively represent the thrust coefficients of motors 3 to 6, , , and Respectively represent the speed of motors 3 to 6, is the limit value of the thrust difference of the same-side pylons;

[0025] The flight criteria for the backward transition are defined as follows: (1) deceleration: the horizontal flight speed of the aircraft gradually decreases; (2) pitch attitude limitation: the pitch angle of the aircraft changes, and the pitch angle change rate is within a certain range; (3) vertical motion limitation: the height of the aircraft changes slightly, and the vertical acceleration of the aircraft remains within a certain range; (4) power limitation: during the transition process, the difference in motor tension on the same side of the aircraft is kept within a certain range;

[0026] Combining the forces and moments of the tilt-rotor aircraft, the mathematical expression of the flight criterion for backward transition is obtained as follows:

[0027] ;

[0028] Among them, the superscript B represents the backward transition process, , and They represent the horizontal force, vertical force and vertical velocity of the aircraft during the backward transition process, respectively. for The maximum value of for The maximum value of represents the angular velocity in the pitch direction of the backward transition, for The maximum value of .

[0029] In one embodiment, a dynamic flight feasible domain of a tiltrotor aircraft transition process is constructed by solving a dynamic flight feasible domain state point under multi-objective constraints, including:

[0030] The tilt angle range Divide into and arrange them in reverse order, and set the flight speed range Divide into The feasible domain state points of the dynamic flight of the tilt-rotor aircraft transition process are obtained by arranging them in sequence. , and initialize the dynamic flight feasible domain state point decision matrix is 0; Indicates i The tilt angle, ; Indicates j The flight speed, ; Indicates the maximum flight speed. is the tilt limit value, the forward transition process is 90°, the backward transition process Expanded to 120°;

[0031] Dynamic flight feasible region state point , given the initial value of the decision variable , use the least squares method to find the solution that satisfies the flight equation Decision variables that are 0 ,like Satisfy the flight criteria of the tilt-rotor aircraft transition process and assign the multi-objective constraints ,otherwise ;

[0032] Dynamic flight feasible region state point , given the initial value of the decision variable , use the least squares method to find the solution that satisfies the flight equation Decision variables that are 0 ,like If the flight criteria of the tilt-rotor aircraft transition process are met, then the value ,otherwise ;

[0033] Dynamic flight feasible region state point , given the initial value of the decision variable , use the least squares method to find the solution that satisfies the flight equation Decision variables that are 0 ,like If the flight criteria of the tilt-rotor aircraft transition process are met, then the value ,otherwise ;

[0034] comprehensive Dynamic flight feasible domain state point , forming the dynamic flight feasible domain of the tilt-rotor aircraft transition process.

[0035] In one embodiment, within the dynamic flight feasible domain, a margin feasible reference line is established with the flight speed as the independent variable and the tilt angle as the dependent variable, and a longitudinal motion model of the tilt-rotor aircraft is constructed, including:

[0036] Polynomial fitting is performed on the upper and lower boundaries of the feasible domains of the forward transition dynamic flight and the backward transition dynamic flight of the tilt-rotor aircraft, and a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable is established, which is expressed as

[0037] ;

[0038] in, and They are respectively the margin feasible reference line of the dynamic flight feasible domain of the forward transition process and the margin feasible reference line of the dynamic flight feasible domain of the backward transition process. and are the upper and lower boundary polynomials obtained by fitting the feasible domain of dynamic flight in the forward transition process. and are the upper and lower boundary polynomials obtained by fitting the feasible region of dynamic flight in the backward transition process, and the weight factor and Respectively expressed as

[0039] ;

[0040] in, It is the cruising speed for level flight, and its value can be set as required;

[0041] Assuming that the forces and moments generated by the left and right parts of the tilt-rotor aircraft are the same, the longitudinal motion equation of the tilt-rotor aircraft is expressed as

[0042] ;

[0043] in, is the pitch angle, In the body coordinate system The speed in the axis direction, In the body coordinate system The speed in the axis direction, is the forward flight speed, is the vertical flight speed, is the angular velocity in the pitch direction, is the propeller in the body coordinate system The tension generated by the shaft, is the propeller in the body coordinate system The tension generated by the shaft, is the angular acceleration in the pitch direction, for The moment of inertia of the direction, and They represent the forward and vertical velocities in the inertial system, In the body coordinate system The aerodynamic force on the shaft, In the body coordinate system The aerodynamic force on the shaft, is the torque generated by the propeller thrust in the pitch direction, is the moment generated by aerodynamic force in the pitch direction;

[0044] Among them, the actuators of the tiltrotor aircraft include 2 tilt propellers, 4 fixed propellers, 2 tilt motors and 6 auxiliary control surfaces. Considering that the pitch channel is mainly involved in the tilting process, in order to further simplify the spatial dimension of the longitudinal motion equation, it is assumed that the forces and moments generated by the left and right parts of the tiltrotor aircraft are the same. At this time, only 1 tilt propeller, 2 fixed propellers, 1 tilt motor and 1 pitch control surface need to be considered. In order to make the optimized trajectory more consistent with the actual dynamic characteristics, the dynamics of the actuator are considered, and the first-order inertia link is used to describe the longitudinal motion equation. The obtained first-order inertia equation is expressed as:

[0045] ;

[0046] in, , , , as well as They represent the deflection bandwidth of the tilt propeller, front fixed propeller rotation, rear fixed propeller rotation, tilt motor and elevator respectively. , , , and They represent the reference inputs of the tilt propeller, the front fixed propeller rotation, the rear fixed propeller rotation, the tilt motor, and the elevator, respectively. is the tilt propeller speed, and are the front fixed propeller speed and the rear fixed propeller speed respectively. is the elevator surface deflection angle, is the elevator surface deflection angular velocity, is the tilt angle of the tilt motor, is the tilt angular velocity of the tilt motor, , and They represent the angular acceleration of the tilt propeller, the front fixed propeller and the rear fixed propeller respectively.

[0047] In one embodiment, an objective function of transition process trajectory optimization combining a margin feasible reference line and performance requirements is defined, and the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft is transformed into a nonlinear dynamic optimal control problem including the optimization target defined in step 2, and the actuator range constraint and system performance constraint of the tilt-rotor aircraft are clarified, including:

[0048] According to the longitudinal motion equation and first-order inertia equation of the tiltrotor aircraft, the objective function of the transition process trajectory optimization combining the margin feasible reference line and performance requirements is defined and expressed as:

[0049] ;

[0050] in, is the state vector, is the horizontal moving distance in the inertial system, is the vertical moving distance in the inertial system, Indicates the tilt angle, the superscript T represents transpose;

[0051] Then the expanded nonlinear dynamic equation is expressed as

[0052] ;

[0053] in, is the time derivative of the state vector, is a function that defines the rate of change of the system state over time, To control the amount, Indicates time;

[0054] According to the optimization goal defined in step 2, the composite objective function is further defined as

[0055] ;

[0056] in, is the initial time, is the transition end time, is the initial height, , , , are the weight factors of each term of the composite objective function, , and They represent the changes of the thrust of the tilt propeller, the front fixed propeller and the rear fixed propeller over time, is the change of height with time in the inertial system, and They respectively represent the change of the tilt angle with time and the change of the tilt angle with speed under the margin feasible reference line; the first term of the composite objective function represents the time consumed by the transition process, the second term represents the cost loss of the transition process, the third term represents the height change of the transition process, and the fourth term represents the distance between the actual trajectory of the tilt-rotor aircraft and the margin feasible reference line during the transition process; when the tilt-rotor aircraft switches from fixed-wing mode to rotor mode, that is, when switching in the opposite direction, the composite objective function remain unchanged;

[0057] In order to ensure that the trajectory obtained by optimizing the composite objective function is feasible, the actuator range constraints and system performance constraints of the tiltrotor aircraft are further defined;

[0058] Among them, the actuator range constraints include: Propeller speed constraints:

[0059] ; , , They represent the maximum values ​​of the tilt propeller speed, the front fixed propeller speed and the rear fixed propeller speed respectively;

[0060] Tilt angle constraint: ; is the maximum tilt angle;

[0061] Rudder deflection angle constraint: ; is the maximum deflection angle of the elevator surface;

[0062] Among them, system performance constraints include:

[0063] Angle of attack constraint: ; , and They represent the angle of attack, the minimum angle of attack and the maximum angle of attack during the forward transition process, respectively. , and They represent the angle of attack, minimum angle of attack and maximum angle of attack during the backward transition process respectively;

[0064] Pitch rate constraint: ; and They represent the pitch rate and maximum pitch rate of the forward transition process respectively, and They represent the pitch angle rate and the maximum pitch angle rate during the backward transition process respectively.

[0065] In one embodiment, the initial state of the tiltrotor aircraft is given, the nonlinear dynamic optimal control problem obtained in step 3 is converted into a Bolza type optimal control problem, and the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3 are solved to minimize the objective function, including:

[0066] Given the initial state of the tilt-rotor aircraft, the nonlinear dynamic optimal control problem obtained in step 3 is transformed into a Bolza-type optimal control problem, and the converted composite objective function is obtained, which is expressed as

[0067] ;

[0068] in, Represents a steady-state indicator, Represents a process indicator, For the state quantity Parameters when For the state quantity Parameters when To control the amount;

[0069] At this point, the trajectory optimization problem of the tilt-rotor aircraft transition process is expressed as:

[0070] ;

[0071] in, Represents process constraints, including actuator range constraints and system performance constraints, Represents the difference between the actual final state value and the expected final state value. and Respectively represent the control quantity in as well as Parameters when

[0072] The optimal trajectory of the tiltrotor aircraft transition process is obtained by minimizing the transformed composite objective function by solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3.

[0073] A tiltrotor aircraft trajectory optimization device, the device comprising:

[0074] A feasible domain construction module is used to establish the flight equations of forces and moments of a distributed power tilt-rotor aircraft, formulate flight criteria for forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints;

[0075] The optimization target definition module is used to establish a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable within the dynamic flight feasible domain, and to construct a longitudinal motion model of the tilt-rotor aircraft;

[0076] An objective function definition module is used to define an objective function for optimizing the trajectory of the transition process in combination with a margin feasible reference line and performance requirements, and to transform the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft into a nonlinear dynamic optimal control problem containing the optimization target defined by the optimization target definition module, and to clarify the actuator range constraints and system performance constraints of the tilt-rotor aircraft; wherein the optimization target is to ensure that the trajectory of the transition process of the tilt-rotor aircraft is far away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible;

[0077] The trajectory optimization module is used to assign the initial state of the tilt-rotor aircraft, transform the nonlinear dynamic optimal control problem obtained by the objective function definition module into a Bolza-type optimal control problem, and solve the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints specified by the objective function definition module to minimize the objective function.

[0078] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0079] Step 1, establish the flight equations of forces and torques of the distributed power tilt-rotor aircraft, formulate the flight criteria for the forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints;

[0080] Step 2, within the dynamic flight feasible domain, establish a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable, and construct a longitudinal motion model of the tilt-rotor aircraft;

[0081] Step 3, define the objective function of the transition process trajectory optimization combining the margin feasible reference line and the performance requirements, transform the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft into a nonlinear dynamic optimal control problem including the optimization objective defined in step 2, and clarify the actuator range constraint and system performance constraint of the tilt-rotor aircraft; wherein the optimization objective is to ensure that the trajectory of the transition process of the tilt-rotor aircraft is far away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible;

[0082] Step 4, assigning the initial state of the tiltrotor aircraft, transforming the nonlinear dynamic optimal control problem obtained in step 3 into a Bolza-type optimal control problem, solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3 to minimize the objective function.

[0083] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the following steps:

[0084] Step 1, establish the flight equations of forces and torques of the distributed power tilt-rotor aircraft, formulate the flight criteria for the forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints;

[0085] Step 2, within the dynamic flight feasible domain, establish a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable, and construct a longitudinal motion model of the tilt-rotor aircraft;

[0086] Step 3, define the objective function of the transition process trajectory optimization combining the margin feasible reference line and the performance requirements, transform the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft into a nonlinear dynamic optimal control problem including the optimization objective defined in step 2, and clarify the actuator range constraint and system performance constraint of the tilt-rotor aircraft; wherein the optimization objective is to ensure that the trajectory of the transition process of the tilt-rotor aircraft is far away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible;

[0087] Step 4, assigning the initial state of the tiltrotor aircraft, transforming the nonlinear dynamic optimal control problem obtained in step 3 into a Bolza-type optimal control problem, solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3 to minimize the objective function.

[0088] Compared with the prior art, the above-mentioned tiltrotor aircraft trajectory optimization method, device, equipment and medium have the following technical effects:

[0089] 1. According to the distribution and structural characteristics of the tilt-rotor aircraft, the calculation of the dynamic flight feasible domain changes under the condition of limited tilt power and vertical power is carried out, which is conducive to the generation of a flight feasible domain that is more in line with the structural characteristics of the target aircraft, and prevents the generated feasible domain from having a pseudo-feasible solution (i.e., feasible from a dynamic perspective but not structurally feasible). In addition, the difference in motor tension on the same side of the tilt-rotor aircraft needs to be limited within the allowable range of the body structure. Based on the analysis of the steady-state characteristics of the dynamic flight feasible domain of the transition process, the flight criteria of the dynamic flight feasible domain of the transition process considering power limitation are established, which can well solve the problem of different motor tension limitations in the flight feasible domain and avoid structural problems in distributed power.

[0090] 2. By establishing a margin feasible reference line with flight speed as the independent variable and tilt angle as the dependent variable within the dynamic flight feasible domain, it can be used to solve the dynamic flight feasible domain of the tilt-rotor aircraft, and can solve the problem that the traditional flight feasible domain does not consider the dynamic changes of flight speed and force during the transition process of the tilt-rotor aircraft.

[0091] 3. By defining the transition process trajectory optimization goal that takes into account both safety margin and flight performance, designing the objective function and constraint state variables of the transition process trajectory optimization, and solving the nonlinear dynamic optimal control problem to obtain the optimal solution transfer strategy, the optimal trajectory that meets high safety margin, smaller control input and shorter transition time can be obtained, thereby improving the safety of the tilt-rotor aircraft transition. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Figure 1 A schematic diagram of a process flow of a tilt-rotor aircraft trajectory optimization method in one embodiment;

[0093] Figure 2 is a schematic diagram of a tilt-rotor aircraft in one embodiment; wherein, Figure 2 (a) is a schematic diagram of a tilt-rotor aircraft. Figure 2 (b) is a schematic diagram of a tilt-rotating composite wing aircraft;

[0094] Figure 3 A schematic diagram of a forward transition in an embodiment;

[0095] Figure 4 A schematic diagram of a backward transition in an embodiment;

[0096] Figure 5 FIG. 4 is a diagram showing the internal structure of a computer device in one embodiment. DETAILED DESCRIPTION

[0097] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0098] In one embodiment, Figure 1 As shown, a tilt-rotor aircraft trajectory optimization method is provided, comprising the following steps:

[0099] Step 1, establish the flight equations of forces and torques of the distributed power tilt-rotor aircraft, formulate the flight criteria for the forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints.

[0100] Among them, the tilt-rotor aircraft is an aircraft that combines the characteristics of helicopters and fixed-wing aircraft. It can switch between vertical take-off and landing, low-speed cruising and high-speed cruising. At present, the tilt-rotor aircraft can be divided into: Figure 2 (a) shows a tilt-rotor dual-rotor aircraft, a tilt-rotor quad-rotor UAV, and Figure 2(b) shows a tilt-rotating composite wing UAV. The typical features of a tilt-rotating composite wing aircraft are: it has multiple propulsion devices, and only some of the propulsion devices are tilted during forward flight, while the remaining propulsion devices remain closed during forward flight; when the forward flight ends and enters the rotor mode, the tilt-rotating device tilts in the opposite direction, and the remaining propulsion devices are turned on.

[0101] The flight modes of a tilt-rotor aircraft can be divided into three types: rotor mode, transition mode, and fixed-wing mode. In rotor mode, the aircraft can take off and land vertically and hover in the air like a helicopter; in transition mode, the rotor axis tilts forward and the aircraft enters a low-speed forward flight state; and in fixed-wing mode, the rotor axis tilts completely forward and the aircraft cruises at high speed like an ordinary airplane. Figure 3 As shown in the figure, forward transition refers to the process of the aircraft switching from rotor mode to fixed-wing mode. During this process, the aircraft's rotor gradually tilts forward to generate forward thrust, and the wing begins to generate lift. This process requires precise control of the rotor's tilt angle and speed to ensure the stability and safety of the aircraft. Figure 4 As shown, the backward transition is the process of converting from the fixed-wing mode to the rotary-wing mode, which is the reverse process of the forward transition.

[0102] Among them, during the transition process of the tilt-rotor aircraft, the tilt angle and flight speed will change over a large range. According to experience, when the tilt angle of the aircraft is large, its flight speed is small; and when the tilt angle is small, its flight speed is large. For a given tilt angle, there is a flight speed range within which the forces and moments of the tilt-composite wing aircraft can be balanced. The "tilt angle-flight speed" type flight feasible domain of the transition process of the tilt-composite wing aircraft is defined as the collection of the speed ranges that can be balanced under all variable tilt angles during the transition process.

[0103] Step 2: within the feasible domain of dynamic flight, establish a feasible reference line of margin with flight speed as the independent variable and tilt angle as the dependent variable, and construct a longitudinal motion model of the tilt-rotor aircraft.

[0104] Step 3, define the objective function of optimizing the transition process trajectory combining the margin feasible reference line and performance requirements, transform the optimal trajectory problem of the forward transition and backward transition of the tiltrotor aircraft into a nonlinear dynamic optimal control problem including the optimization objective defined in step 2, and clarify the actuator range constraints and system performance constraints of the tiltrotor aircraft; wherein, the optimization goal is to ensure that the trajectory of the transition process of the tiltrotor aircraft is away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible.

[0105] Among them, trajectory optimization is a complex multi-variable, multi-constrained optimal control problem. Its goal is to find the optimal flight path to achieve the predetermined goals, such as minimizing fuel consumption, maximizing range, reducing flight time or improving the survivability of the aircraft, while satisfying various flight constraints.

[0106] Step 4, assigning the initial state of the tiltrotor aircraft, transforming the nonlinear dynamic optimal control problem obtained in step 3 into a Bolza-type optimal control problem, solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3 to minimize the objective function.

[0107] Step 1 specifically includes the following steps:

[0108] First, the pitch velocity and flight acceleration of the distributed power tilt-rotor aircraft during longitudinal trim are both zero, and the forces and moments acting on the tilt-rotor aircraft are offset. The flight equation established based on this is expressed as

[0109] (1)

[0110] in, In the body coordinate system The resultant force on the shaft is In the body coordinate system The resultant force on the shaft is is the pitch channel torque, is the mass of the aircraft, is the acceleration due to gravity, In the body coordinate system The aerodynamic force on the shaft, is the pulling force generated by the propeller in the body coordinate system, i Indicates the propeller number, In the body coordinate system The aerodynamic force on the shaft, is the torque generated by the propeller thrust in the pitch direction, is the moment generated by aerodynamic force in the pitch direction;

[0111] For a tilt-rotor aircraft, the flight equation involves six independent variables, namely: tilt angle , Flight speed v , Pitch angle , Angle of Attack , elevator surface deflection angle , tilt propeller speed (corresponding to propeller speeds 1 and 2) and fixed propeller speed (corresponding to the speed of propellers 3 to 6); when solving the feasible domain of dynamic flight, and v The value of will be specified;

[0112] Since the system dynamics is highly nonlinear, and v Next, to calculate the analytical solution to the flight equation , and further use numerical methods to balance, and obtain the simplified flight equation, expressed as

[0113] (2)

[0114] Next, we formulate the flight rules for the forward transition and backward transition of the tilt-rotor aircraft. During the transition process, the tilt-rotor aircraft is in an acceleration or deceleration state, and the resultant force it receives is not zero. At the same time, its body is in a rotating state, and the pitch rate is not zero. More importantly, the difference in motor tension on the same side of the rear main wing needs to be limited to the range allowed by the body structure. Based on the analysis of the steady-state characteristics of the feasible domain of dynamic flight during the transition process, the flight rules for the feasible domain of dynamic flight during the transition process considering power limitation are established:

[0115] First, the flight criteria for the feasible domain of forward transition, i.e., vertical-to-horizontal flight, are defined, including: (1) acceleration: the horizontal flight speed of the aircraft gradually increases; (2) pitch attitude restriction: the pitch angle of the aircraft changes, and the pitch angle change rate is within a certain range; (3) vertical motion restriction: the height of the aircraft changes slightly, and the vertical acceleration of the aircraft remains within a certain range; (4) power restriction: during the transition process, the difference in motor tension on the same-side pylon of the aircraft is kept within a certain range;

[0116] Combining the forces and moments of the tilt-rotor aircraft, the mathematical expression of the forward transition flight criterion is obtained as follows:

[0117] (3)

[0118] Among them, the superscript F represents the forward transition process, , and They represent the horizontal force, vertical force and vertical velocity of the aircraft during the forward transition process. for The maximum value of for The maximum value of is the angular velocity in the pitch direction of the forward transition, In the body coordinate system The speed in the axis direction, In the body coordinate system The speed in the axis direction, , , and Respectively represent the thrust coefficients of motors 3 to 6, , , and Respectively represent the speed of motors 3 to 6, is the limit value of the thrust difference of the same-side pylon. The first term of the above equation (3) indicates that the horizontal force of the aircraft is not less than zero, corresponding to the acceleration criterion; the second and third terms of equation (3) indicate that the pitch moment of the aircraft is balanced but the pitch angular velocity can be limited to The fourth and fifth terms of equation (3) indicate that the vertical force and vertical velocity of the aircraft are limited to and The last two terms of equation (3) represent the difference in motor tension on the same side of the bracket, which needs to be limited to Within the corresponding power limitation criteria.

[0119] Then, the flight criteria for the feasible domain of backward transition, i.e., horizontal to vertical flight, are defined, including: (1) deceleration: the horizontal flight speed of the aircraft gradually decreases; (2) pitch attitude limitation: the pitch angle of the aircraft changes, and the pitch angle change rate is within a certain range; (3) vertical motion limitation: the height of the aircraft changes slightly, and the vertical acceleration of the aircraft remains within a certain range; (4) power limitation: during the transition process, the difference in motor tension on the same-side pylons of the aircraft is kept within a certain range.

[0120] Combining the forces and moments of the tilt-rotor aircraft, the mathematical expression of the flight criterion for backward transition is obtained as follows:

[0121] (4)

[0122] Among them, the superscript B represents the backward transition process, , and They represent the horizontal force, vertical force and vertical velocity of the aircraft during the backward transition process, respectively. for The maximum value of for The maximum value of represents the angular velocity in the pitch direction of the backward transition, for The maximum value of .

[0123] Further, according to equations (3) and (4), the state points of the dynamic flight feasible domain under multi-objective constraints are solved, and the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft is constructed, including the following steps:

[0124] The tilt angle range Divide into and arrange them in reverse order, and set the flight speed range Divide into The feasible domain state points of the dynamic flight of the tilt-rotor aircraft transition process are obtained by arranging them in sequence. , and initialize the dynamic flight feasible domain state point decision matrix is 0; Indicates i The tilt angle, ; Indicates j The flight speed, ; Indicates the maximum flight speed. is the tilt limit value, the forward transition process is 90°, the backward transition process Expanded to 120°;

[0125] Dynamic flight feasible region state point , given the initial value of the decision variable , use the least squares method to find the solution that satisfies the flight equation Decision variables that are 0 , if v satisfies the flight criteria of the tilt-rotor aircraft transition process, assign the value of ,otherwise ;

[0126] Dynamic flight feasible region state point , given the initial value of the decision variable , use the least squares method to find the solution that satisfies the flight equation Decision variables that are 0 ,like If the flight criteria of the tilt-rotor aircraft transition process are met, then the value ,otherwise ;

[0127] Dynamic flight feasible region state point , given the initial value of the decision variable , use the least squares method to find the solution that satisfies the flight equation Decision variables that are 0 ,like If the flight criteria of the tilt-rotor aircraft transition process are met, then the value ,otherwise ;

[0128] comprehensive Dynamic flight feasible domain state point , forming the dynamic flight feasible domain of the tilt-rotor aircraft transition process.

[0129] It can be understood that by calculating the change of the dynamic flight feasible domain under the condition of limited tilt power and vertical power in step 1 according to the distribution and structural characteristics of the tilt-rotor aircraft, it is beneficial for the tilt-rotor aircraft to generate a flight feasible domain that is more in line with the structural characteristics of the target aircraft, and to prevent the generated feasible domain from having a pseudo-feasible solution (dynamically feasible but structurally infeasible). In addition, the difference in motor tension on the same side of the tilt-rotor aircraft needs to be limited within the allowable range of the fuselage structure. Based on the analysis of the steady-state characteristics of the transition process balance flight feasible domain, a dynamic flight feasible domain flight criterion for the transition process considering power limitation is established, which can well solve the problem of different motor tension limitations in the dynamic feasible domain and avoid structural problems in distributed power. In addition, during the backward transition of the tilt-rotor aircraft, this method expands the flight feasible domain with a tilt angle greater than 90° during the backward transition.

[0130] Step 2 specifically includes the following steps:

[0131] Firstly, polynomial fitting is performed on the upper and lower boundaries of the feasible domains of the forward transition dynamic flight and the backward transition dynamic flight of the tiltrotor aircraft, and a feasible reference line of margin with flight speed as the independent variable and tilt angle as the dependent variable is established, which is expressed as

[0132] (5)

[0133] in, and They are respectively the margin feasible reference line of the dynamic flight feasible domain of the forward transition process and the margin feasible reference line of the dynamic flight feasible domain of the backward transition process. and are the upper and lower boundary polynomials obtained by fitting the feasible domain of dynamic flight in the forward transition process. and are the upper and lower boundary polynomials obtained by fitting the feasible region of dynamic flight in the backward transition process, and the weight factor and Respectively expressed as

[0134] (6)

[0135] in, It is the cruising speed for level flight, and its value can be set as required;

[0136] Assuming that the forces and moments generated by the left and right parts of the tilt-rotor aircraft are the same, the longitudinal motion equation of the tilt-rotor aircraft is expressed as

[0137] (7)

[0138] in, is the pitch angle, In the body coordinate system The speed in the axis direction, In the body coordinate system The speed in the axis direction, is the forward flight speed, is the vertical flight speed, is the angular velocity in the pitch direction, is the propeller in the body coordinate system The tension generated by the shaft, is the propeller in the body coordinate system The tension generated by the shaft, is the angular acceleration in the pitch direction, for The moment of inertia of the direction, and They represent the forward and vertical velocities in the inertial system, In the body coordinate system The aerodynamic force on the shaft, In the body coordinate system The aerodynamic force on the shaft, is the torque generated by the propeller thrust in the pitch direction, is the moment generated by aerodynamic force in the pitch direction;

[0139] Among them, the actuators of the tiltrotor aircraft include 2 tilt propellers, 4 fixed propellers, 2 tilt motors and 6 auxiliary control surfaces. Considering that the pitch channel is mainly involved in the tilting process, in order to further simplify the spatial dimension of the longitudinal motion equation, it is assumed that the forces and moments generated by the left and right parts of the tiltrotor aircraft are the same. At this time, only 1 tilt propeller, 2 fixed propellers, 1 tilt motor and 1 pitch control surface need to be considered. In order to make the optimized trajectory more consistent with the actual dynamic characteristics, the dynamics of the actuator are considered, and the first-order inertia link is used to describe the longitudinal motion equation. The obtained first-order inertia equation is expressed as:

[0140] (8)

[0141] in, , , , as well as They represent the deflection bandwidth of the tilt propeller, front fixed propeller rotation, rear fixed propeller rotation, tilt motor and elevator respectively. , , , and They represent the reference inputs of the tilt propeller, the front fixed propeller rotation, the rear fixed propeller rotation, the tilt motor, and the elevator, respectively. is the tilt propeller speed, and are the front fixed propeller speed and the rear fixed propeller speed respectively. is the elevator surface deflection angle, is the tilt angle of the tilt motor, is the tilt angular velocity of the tilt motor, , and They represent the angular acceleration of the tilt propeller, the front fixed propeller and the rear fixed propeller respectively.

[0142] It can be understood that by establishing a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable in step 2, it can be used to solve the dynamic flight feasible domain of the tilt-rotor aircraft, and can solve the problem that the traditional flight feasible domain does not take into account the dynamic changes in flight speed and force during the transition process of the tilt-rotor aircraft.

[0143] Step 3 specifically includes the following steps:

[0144] First, according to the longitudinal motion equation (7) and the first-order inertia equation (8) of the tiltrotor aircraft, the objective function of the transition process trajectory optimization combining the margin feasible reference line and performance requirements is defined and expressed as

[0145] (9)

[0146] in, is the state vector, is the horizontal moving distance in the inertial system, is the vertical moving distance in the inertial system, Indicates the tilt angle, the superscript T represents transpose;

[0147] Then the expanded nonlinear dynamic equation is expressed as

[0148] (10)

[0149] in, is the time derivative of the state vector, is a function that defines the rate of change of the system state over time, To control the amount, Indicates time;

[0150] According to the optimization goal defined in step 2, the composite objective function is further defined as

[0151] (11)

[0152] in, is the initial time, is the transition end time, is the initial height, , , , are the weight factors of each term of the composite objective function, , and They represent the changes of the thrust of the tilt propeller, the front fixed propeller and the rear fixed propeller over time, is the change of height with time in the inertial system, and They respectively represent the change of the tilt angle with time and the change of the tilt angle with speed under the margin feasible reference line; the first term of the composite objective function represents the time consumed by the transition process, the second term represents the cost loss of the transition process, the third term represents the height change of the transition process, and the fourth term represents the distance between the actual trajectory of the tilt-rotor aircraft and the margin feasible reference line during the transition process; when the tilt-rotor aircraft switches from fixed-wing mode to rotor mode, that is, when switching in the opposite direction, the composite objective function remain unchanged;

[0153] In order to ensure that the trajectory obtained by optimizing the composite objective function is feasible, the actuator range constraints and system performance constraints of the tiltrotor aircraft are further defined;

[0154] Among them, the actuator range constraints include: Propeller speed constraints:

[0155] ; , , They represent the maximum values ​​of the tilt propeller speed, the front fixed propeller speed and the rear fixed propeller speed respectively;

[0156] Tilt angle constraint: ; is the maximum tilt angle;

[0157] Rudder deflection angle constraint: ; is the maximum deflection angle of the elevator surface;

[0158] Among them, system performance constraints include:

[0159] Angle of attack constraint: ; , and They represent the angle of attack, the minimum angle of attack and the maximum angle of attack during the forward transition process, respectively. , and They represent the angle of attack, minimum angle of attack and maximum angle of attack during the backward transition process respectively;

[0160] Pitch rate constraint: ; and They represent the pitch rate and maximum pitch rate of the forward transition process respectively, and They represent the pitch angle rate and the maximum pitch angle rate during the backward transition process respectively.

[0161] It can be understood that by defining the transition process trajectory optimization goal that takes into account both safety margin and flight performance, designing the objective function and constraint state variables for transition process trajectory optimization, and solving the nonlinear dynamic optimal control problem to obtain the optimal solution transfer strategy, it is possible to obtain the optimal trajectory that meets high safety margin, smaller control input and shorter transition time, thereby improving the safety of the tilt-rotor aircraft transition.

[0162] Step 4 specifically includes the following steps:

[0163] Given the initial state of the tilt-rotor aircraft, the nonlinear dynamic optimal control problem obtained in step 3 is transformed into a Bolza-type optimal control problem, and the converted composite objective function is obtained, which is expressed as

[0164] (12)

[0165] in, Represents a steady-state indicator, Represents a process indicator, For the state quantity Parameters when For the state quantity Parameters when To control the amount;

[0166] At this point, the trajectory optimization problem of the tilt-rotor aircraft transition process is expressed as:

[0167] (13)

[0168] in, Represents process constraints, including actuator range constraints and system performance constraints, Represents the difference between the actual final state value and the expected final state value. and Respectively represent the control quantity in as well as Parameters when

[0169] The optimal trajectory of the tiltrotor aircraft transition process is obtained by minimizing the transformed composite objective function by solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3.

[0170] Specifically, the composite objective function after minimization transformation includes:

[0171] First, the time domain change is performed, which is expressed as

[0172] (14)

[0173] in, is the normalized time parameter. t Normalize to The search domain is reduced and the search is more efficient.

[0174] Then, the state variables and control variables are approximated using N+1-order and N-order Lagrange polynomials, respectively, which are expressed as

[0175] (15)

[0176] in, is the state variable, is the control variable, for The value of the state quantity, for The value of the control quantity, k Represents the order, discrete time point are collocation points of the interpolation polynomial, represents the basis of Lagrange polynomials;

[0177] (16)

[0178] The approximate value of the transformed composite objective function is expressed as

[0179] (17)

[0180] in, , is the Gaussian weight;

[0181] In summary, the continuous optimal control problem of the tiltrotor aircraft is transformed into a discrete nonlinear programming problem by identifying the ideal control sequence that satisfies the discretized state equations and constraints at each coordination point. u To minimize the composite objective function .

[0182] In one embodiment, a tiltrotor aircraft trajectory optimization device is provided, comprising:

[0183] A feasible domain construction module is used to establish the flight equations of forces and moments of a distributed power tilt-rotor aircraft, formulate flight criteria for forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints;

[0184] The optimization target definition module is used to establish a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable within the dynamic flight feasible domain, and to construct a longitudinal motion model of the tilt-rotor aircraft;

[0185] An objective function definition module is used to define an objective function for optimizing the trajectory of the transition process in combination with a margin feasible reference line and performance requirements, and to transform the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft into a nonlinear dynamic optimal control problem containing the optimization target defined by the optimization target definition module, and to clarify the actuator range constraints and system performance constraints of the tilt-rotor aircraft; wherein the optimization target is to ensure that the trajectory of the transition process of the tilt-rotor aircraft is far away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible;

[0186] The trajectory optimization module is used to assign the initial state of the tilt-rotor aircraft, transform the nonlinear dynamic optimal control problem obtained by the objective function definition module into a Bolza-type optimal control problem, and solve the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints specified by the objective function definition module to minimize the objective function.

[0187] For the specific definition of the tilt-rotor aircraft trajectory optimization device, please refer to the definition of the tilt-rotor aircraft trajectory optimization method above, which will not be repeated here. Each module in the above-mentioned tilt-rotor aircraft trajectory optimization device can be implemented in whole or in part by software, hardware and a combination thereof. The above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules.

[0188] In one embodiment, a computer device is provided. The computer device may be a terminal, and its internal structure diagram may be as follows: Figure 5 As shown. The computer device includes a processor, a memory, a network interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The network interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a method for optimizing the trajectory of a tilt-rotor aircraft is implemented. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covering the display screen, or a key, trackball or touchpad set on the computer device housing, or an external keyboard, touchpad or mouse, etc.

[0189] Those skilled in the art will understand that Figure 5 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0190] In one embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the following steps are implemented:

[0191] Step 1, establish the flight equations of forces and torques of the distributed power tilt-rotor aircraft, formulate the flight criteria for the forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints;

[0192] Step 2, within the dynamic flight feasible domain, establish a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable, and construct a longitudinal motion model of the tilt-rotor aircraft;

[0193] Step 3, define the objective function of the transition process trajectory optimization combining the margin feasible reference line and the performance requirements, transform the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft into a nonlinear dynamic optimal control problem including the optimization objective defined in step 2, and clarify the actuator range constraint and system performance constraint of the tilt-rotor aircraft; wherein the optimization objective is to ensure that the trajectory of the transition process of the tilt-rotor aircraft is far away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible;

[0194] Step 4, assigning the initial state of the tiltrotor aircraft, transforming the nonlinear dynamic optimal control problem obtained in step 3 into a Bolza-type optimal control problem, solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3 to minimize the objective function.

[0195] In one embodiment, a computer readable storage medium is provided, on which a computer program is stored, and when the computer program is executed by a processor, the following steps are implemented:

[0196] Step 1, establish the flight equations of forces and torques of the distributed power tilt-rotor aircraft, formulate the flight criteria for the forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints;

[0197] Step 2, within the dynamic flight feasible domain, establish a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable, and construct a longitudinal motion model of the tilt-rotor aircraft;

[0198] Step 3, define the objective function of the transition process trajectory optimization combining the margin feasible reference line and the performance requirements, transform the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft into a nonlinear dynamic optimal control problem including the optimization objective defined in step 2, and clarify the actuator range constraint and system performance constraint of the tilt-rotor aircraft; wherein the optimization objective is to ensure that the trajectory of the transition process of the tilt-rotor aircraft is far away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible;

[0199] Step 4, assigning the initial state of the tiltrotor aircraft, transforming the nonlinear dynamic optimal control problem obtained in step 3 into a Bolza-type optimal control problem, solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3 to minimize the objective function.

[0200] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0201] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0202] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A tilt-rotor aircraft trajectory optimization method, characterized in that: The method comprises: Step 1, establish the flight equations of forces and torques of the distributed power tilt-rotor aircraft, formulate the flight criteria for the forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints; Step 2, within the dynamic flight feasible domain, establish a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable, and construct a longitudinal motion model of the tilt-rotor aircraft; Step 3, defining an objective function for optimizing the trajectory of the transition process in combination with the margin feasible reference line and the performance requirements, converting the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft into a nonlinear dynamic optimal control problem including the optimization objective defined in step 2, and clarifying the actuator range constraint and the system performance constraint of the tilt-rotor aircraft; wherein the optimization objective is to ensure that the trajectory of the transition process of the tilt-rotor aircraft is far away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible; Step 4, assigning the initial state of the tiltrotor aircraft, transforming the nonlinear dynamic optimal control problem obtained in step 3 into a Bolza-type optimal control problem, solving the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3 to minimize the objective function.

2. The method according to claim 1, characterized in that The flight equations for the forces and moments of a distributed powered tiltrotor aircraft are established, including: The pitch velocity and flight acceleration of the distributed power tilt-rotor aircraft during longitudinal trim are both zero, and the forces and moments acting on the tilt-rotor aircraft are offset. The flight equation established based on this is expressed as ； in, In the body coordinate system The resultant force on the shaft is In the body coordinate system The resultant force on the shaft is is the pitch channel torque, is the mass of the aircraft, is the acceleration due to gravity, In the body coordinate system The aerodynamic force on the shaft, is the pulling force generated by the propeller in the body coordinate system, i Indicates the propeller number. In the body coordinate system The aerodynamic force on the shaft, is the torque generated by the propeller thrust in the pitch direction, is the moment generated by aerodynamic force in the pitch direction; For a tilt-rotor aircraft, the flight equation involves six independent variables, namely: tilt angle , Flight speed v , Pitch angle , Angle of Attack , elevator surface deflection angle , Tilt propeller speed and fixed propeller speed ; When solving the feasible domain of dynamic flight, and v The value of will be specified; In the specified and v Next, to calculate the analytical solution to the flight equation , and further use numerical methods to balance, and obtain the simplified flight equation, expressed as 。 3. The method according to claim 2, characterized in that Develop flight criteria for forward transition and backward transition of tiltrotor aircraft, including: The flight criteria for forward transition are defined as follows: (1) Acceleration: the horizontal flight speed of the aircraft gradually increases; (2) Pitch attitude limit: the pitch angle of the aircraft changes, and the pitch angle change rate is within a certain range; (3) Vertical motion limit: the height of the aircraft changes slightly, and the vertical acceleration of the aircraft remains within a certain range; (4) Power limit: during the transition process, the difference in motor tension on the same side of the aircraft is kept within a certain range; Combining the forces and moments on the tilt-rotor aircraft, the mathematical expression of the forward transition flight criterion is obtained as follows: ； Among them, the superscript F represents the forward transition process, , and They represent the horizontal force, vertical force and vertical velocity of the aircraft during the forward transition process. for The maximum value of for The maximum value of is the angular velocity in the pitch direction of the forward transition, In the body coordinate system The speed in the axis direction, In the body coordinate system The speed in the axis direction, , , and Respectively represent the thrust coefficients of motors 3 to 6, , , and Respectively represent the speed of motors 3 to 6, is the limit value of the thrust difference of the same-side pylons; The flight criteria for the backward transition are defined as follows: (1) deceleration: the horizontal flight speed of the aircraft gradually decreases; (2) pitch attitude limitation: the pitch angle of the aircraft changes, and the pitch angle change rate is within a certain range; (3) vertical motion limitation: the height of the aircraft changes slightly, and the vertical acceleration of the aircraft remains within a certain range; (4) power limitation: during the transition process, the difference in motor tension on the same side of the aircraft is kept within a certain range; Combining the forces and moments on the tilt-rotor aircraft, the mathematical expression of the flight criterion for backward transition is obtained as follows: ； Among them, the superscript B represents the backward transition process, , and They represent the horizontal force, vertical force and vertical velocity of the aircraft during the backward transition process, respectively. for The maximum value of for The maximum value of represents the angular velocity in the pitch direction of the backward transition, for The maximum value of .

4. The method according to claim 3, characterized in that By solving the state points of the dynamic flight feasible domain under multi-objective constraints, the dynamic flight feasible domain of the tilt-rotor aircraft transition process is constructed, including: The tilt angle range Divide into and arrange them in reverse order, and set the flight speed range Divide into The feasible domain state points of the dynamic flight of the tilt-rotor aircraft transition process are obtained by arranging them in sequence. , and initialize the dynamic flight feasible domain state point decision matrix is 0; Indicates i The tilt angle, ; Indicates j The flight speed, ; Indicates the maximum flight speed. is the tilt limit value, the forward transition process is 90°, the backward transition process Expanded to 120°; Dynamic flight feasible region state point , given the initial value of the decision variable , use the least squares method to find the solution that satisfies the flight equation Decision variables that are 0 ,like Satisfy the flight criteria of the tilt-rotor aircraft transition process and assign the multi-objective constraints ,otherwise ; Dynamic flight feasible region state point , given the initial value of the decision variable , use the least squares method to find the solution that satisfies the flight equation Decision variables that are 0 ,like If the flight criteria of the tilt-rotor aircraft transition process are met, then the value ,otherwise ; Dynamic flight feasible region state point , given the initial value of the decision variable , use the least squares method to find the solution that satisfies the flight equation Decision variables that are 0 ,like If the flight criteria of the tilt-rotor aircraft transition process are met, then the value ,otherwise ; comprehensive Dynamic flight feasible domain state point , forming the dynamic flight feasible domain of the tilt-rotor aircraft transition process.

5. The method according to claim 4, characterized in that In the feasible domain of dynamic flight, a margin feasible reference line is established with flight speed as the independent variable and tilt angle as the dependent variable, and a longitudinal motion model of the tilt-rotor aircraft is constructed, including: Polynomial fitting is performed on the upper and lower boundaries of the feasible domains of the forward transition dynamic flight and the backward transition dynamic flight of the tilt-rotor aircraft, and a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable is established, which is expressed as ； in, and They are respectively the margin feasible reference line of the dynamic flight feasible domain of the forward transition process and the margin feasible reference line of the dynamic flight feasible domain of the backward transition process. and are the upper and lower boundary polynomials obtained by fitting the feasible domain of dynamic flight in the forward transition process. and are the upper and lower boundary polynomials obtained by fitting the feasible region of dynamic flight in the backward transition process, and the weight factor and Respectively expressed as ； in, It is the cruising speed for level flight, and its value can be set as required; Assuming that the forces and moments generated by the left and right parts of the tilt-rotor aircraft are the same, the longitudinal motion equation of the tilt-rotor aircraft is expressed as ； in, is the pitch angle, In the body coordinate system The speed in the axis direction, In the body coordinate system The speed in the axis direction, is the forward flight speed, is the vertical flight speed, is the angular velocity in the pitch direction, is the propeller in the body coordinate system The tension generated by the shaft, is the propeller in the body coordinate system The tension generated by the shaft, is the angular acceleration in the pitch direction, for The moment of inertia of the direction, and They represent the forward and vertical velocities in the inertial system, In the body coordinate system The aerodynamic force on the shaft, In the body coordinate system The aerodynamic force on the shaft, is the torque generated by the propeller thrust in the pitch direction, is the moment generated by aerodynamic force in the pitch direction; Among them, the actuator of the tilt-rotor aircraft includes 2 tilt-rotor propellers, 4 fixed propellers, 2 tilt-rotor motors and 6 auxiliary control surfaces. Considering that the pitch channel is mainly involved in the tilting process, in order to further simplify the spatial dimension of the longitudinal motion equation, it is assumed that the forces and moments generated by the left and right parts of the tilt-rotor aircraft are the same. At this time, only 1 tilt-rotor propeller, 2 fixed propellers, 1 tilt-rotor motor and 1 pitch control surface need to be considered. In order to make the optimized trajectory more consistent with the actual dynamic characteristics, the dynamics of the actuator are considered, and the first-order inertia link is used to describe the longitudinal motion equation. The obtained first-order inertia equation is expressed as: ； in, , , , as well as They represent the deflection bandwidth of the tilt propeller, front fixed propeller rotation, rear fixed propeller rotation, tilt motor and elevator respectively. , , , and They represent the reference inputs of the tilt propeller, the front fixed propeller rotation, the rear fixed propeller rotation, the tilt motor, and the elevator, respectively. is the tilt propeller speed, and are the front fixed propeller speed and the rear fixed propeller speed respectively. is the elevator surface deflection angle, is the elevator surface deflection angular velocity, is the tilt angle of the tilt motor, is the tilt angular velocity of the tilt motor, , and They represent the angular acceleration of the tilt propeller, the front fixed propeller and the rear fixed propeller respectively.

6. The method according to claim 5, characterized in that Define an objective function for optimizing the trajectory of the transition process in combination with the margin feasible reference line and the performance requirements, transform the optimal trajectory problem of the forward transition and the backward transition of the tiltrotor aircraft into a nonlinear dynamic optimal control problem including the optimization objective defined in step 2, and clarify the actuator range constraints and system performance constraints of the tiltrotor aircraft, including: According to the longitudinal motion equation and the first-order inertia equation of the tilt-rotor aircraft, the objective function of the transition process trajectory optimization combining the margin feasible reference line and the performance requirements is defined and expressed as: ； in, is the state vector, is the horizontal moving distance in the inertial system, is the vertical moving distance in the inertial system, Indicates the tilt angle, the superscript T represents transpose; Then the expanded nonlinear dynamic equation is expressed as ； in, is the time derivative of the state vector, is a function that defines the rate of change of the system state over time, To control the amount, Indicates time; According to the optimization goal defined in step 2, the composite objective function is further defined as ； in, is the initial time, is the transition end time, is the initial height, , , , are the weight factors of each term of the composite objective function, , and They represent the changes of the thrust of the tilt propeller, the front fixed propeller and the rear fixed propeller over time, is the change of height with time in the inertial system, and They respectively represent the change of the tilt angle with time and the change of the tilt angle with speed under the margin feasible reference line; the first term of the composite objective function represents the time consumed by the transition process, the second term represents the cost loss of the transition process, the third term represents the height change of the transition process, and the fourth term represents the distance between the actual trajectory of the tilt-rotor aircraft and the margin feasible reference line during the transition process; when the tilt-rotor aircraft switches from the fixed-wing mode to the rotor mode, that is, when switching in the reverse direction, the composite objective function remain unchanged; To ensure that the trajectory obtained by optimizing the composite objective function is feasible, further defining the actuator range constraints and system performance constraints of the tiltrotor aircraft; Wherein, the actuator range constraints include: Propeller speed constraints: ; , , They represent the maximum values ​​of the tilt propeller speed, the front fixed propeller speed and the rear fixed propeller speed respectively; Tilt angle constraint: ; is the maximum tilt angle; Rudder deflection angle constraint: ; is the maximum deflection angle of the elevator surface; The system performance constraints include: Angle of attack constraint: ; , and They represent the angle of attack, the minimum angle of attack and the maximum angle of attack during the forward transition process, respectively. , and They represent the angle of attack, minimum angle of attack and maximum angle of attack during the backward transition process respectively; Pitch rate constraint: ; and They represent the pitch rate and maximum pitch rate of the forward transition process respectively, and They represent the pitch angle rate and the maximum pitch angle rate during the backward transition process respectively.

7. The method according to claim 6, characterized in that Given the initial state of the tiltrotor aircraft, the nonlinear dynamic optimal control problem obtained in step 3 is transformed into a Bolza-type optimal control problem, and the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints in step 3 are solved to minimize the objective function, including: Given the initial state of the tilt-rotor aircraft, the nonlinear dynamic optimal control problem obtained in step 3 is transformed into a Bolza-type optimal control problem, and the converted composite objective function is obtained, which is expressed as ； in, Represents a steady-state indicator, Represents a process indicator, For the state quantity Parameters when For the state quantity Parameters when To control the amount; At this point, the trajectory optimization problem of the tilt-rotor aircraft transition process is expressed as: ； in, Represents process constraints, including actuator range constraints and system performance constraints, Represents the difference between the actual final state value and the expected final state value. and Respectively represent the control quantity in as well as Parameters when The optimal trajectory of the transition process of the tilt-rotor aircraft is obtained by minimizing the converted composite objective function by solving the longitudinal motion model that meets the flight criteria and the ideal control variables that meet the actuator range constraints and system performance constraints of step 3.

8. A tilt-rotor aircraft trajectory optimization device, characterized in that: The device comprises: A feasible domain construction module is used to establish the flight equations of forces and moments of a distributed power tilt-rotor aircraft, formulate flight criteria for forward transition and backward transition of the tilt-rotor aircraft, and construct the dynamic flight feasible domain of the transition process of the tilt-rotor aircraft by solving the state points of the dynamic flight feasible domain under multi-objective constraints; The optimization target definition module is used to establish a margin feasible reference line with the flight speed as the independent variable and the tilt angle as the dependent variable within the dynamic flight feasible domain, and to construct a longitudinal motion model of the tilt-rotor aircraft; An objective function definition module is used to define an objective function for optimizing the trajectory of the transition process in combination with the margin feasible reference line and the performance requirements, converting the optimal trajectory problem of the forward transition and the backward transition of the tilt-rotor aircraft into a nonlinear dynamic optimal control problem containing the optimization target defined by the optimization target definition module, and clarifying the actuator range constraint and system performance constraint of the tilt-rotor aircraft; wherein the optimization target is to ensure that the trajectory of the transition process of the tilt-rotor aircraft is far away from the boundary area of ​​the dynamic flight feasible domain, while making the transition process time and height changes as small as possible; The trajectory optimization module is used to assign the initial state of the tilt-rotor aircraft, transform the nonlinear dynamic optimal control problem obtained by the objective function definition module into a Bolza-type optimal control problem, and solve the longitudinal motion model that satisfies the flight criteria and the ideal control variables that satisfy the actuator range constraints and system performance constraints specified by the objective function definition module to minimize the objective function.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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