CN115509246A - Cross-medium takeoff longitudinal attitude control method for water-air amphibious unmanned aerial vehicle with buoy - Google Patents
Cross-medium takeoff longitudinal attitude control method for water-air amphibious unmanned aerial vehicle with buoy Download PDFInfo
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Abstract
The invention discloses a cross-medium take-off longitudinal attitude control method for a water-air amphibious unmanned aerial vehicle with a buoy, which comprises the following steps of: s1, dividing a control system of an unmanned aerial vehicle into a power system, a controller and an unmanned aerial vehicle longitudinal motion dynamics model; s2, the power system changes the advancing speed of the unmanned aerial vehicle by means of the virtual force N, and changes the flying attitude through the elevator; s3, controlling the longitudinal posture in the takeoff process by the controller; and S4, controlling the force and the moment acting on the unmanned aerial vehicle according to the output of the power system by the dynamic model, and adjusting the longitudinal attitude of the unmanned aerial vehicle. The invention creatively provides an active disturbance rejection + self-adaptive dynamic inverse control method aiming at the water takeoff nonlinear strong coupling characteristic of the water-air amphibious unmanned aerial vehicle, and has the advantages of easiness in realization, simplicity in control, stable aircraft cross-medium takeoff attitude and the like.
Description
Technical Field
The invention belongs to the technical field of unmanned aerial vehicles, and particularly relates to a cross-medium take-off longitudinal attitude control method for a water-air amphibious unmanned aerial vehicle with a buoy.
Background
As a large country with both sea and land, china has abundant ocean resources and wide development prospects, improves the ocean development, utilization, control and protection capabilities, and has great strategic significance in accelerating the construction of ocean strong countries. However, it is difficult to improve efficiency with only human input, limited by the complicated geographical weather conditions of the ocean. In recent years, the unmanned aerial vehicle technology is rapidly developed and widely applied, and the unmanned aerial vehicle has a unique point for providing support for offshore tasks. On the one hand, the software program control is matched with the special on-board task load to realize soft and hard combination, so that the adaptability and the working efficiency of the unmanned aerial vehicle to the environment can be effectively improved, and on the other hand, the characteristics of the unmanned aerial vehicle make the unmanned aerial vehicle have more advantages when the unmanned aerial vehicle completes tasks with high risk, high difficulty and boring property.
Common unmanned aerial vehicles include fixed-wing unmanned aerial vehicles, multi-rotor unmanned aerial vehicles, flapping-wing unmanned aerial vehicles, and the like. The conventional fixed-wing unmanned aerial vehicle needs a runway with a certain length to run until the takeoff speed is reached, the lift takeoff is provided by utilizing the air pressure difference generated on the upper surface and the lower surface of the wing, and the deployment of the conventional fixed-wing unmanned aerial vehicle is greatly limited by the environment due to the requirement on the field. Many rotor unmanned aerial vehicle provides lift control flight through adjusting the rotor rotational speed, can overcome the place restriction of taking off and land to a certain extent, application range is wider, simple structure easily develops, corresponding technical research and practical development are also comparatively ripe, but rely on when taking off and land four rotor unmanned aerial vehicle of present a large amount of uses to adjust four rotor rotational speeds and the motion of direction of rotation completion six degrees of freedom, belong to typical under-actuated system, the limited condition of flexibility appears easily when in-service use, and it is higher to propose the requirement to controller stability. The existing flapping wing unmanned aerial vehicle has the problems of single driving mode, multiple pneumatic couplings, difficult dynamic modeling, high material requirement, immature control technology and the like, and has larger difference in flight performance compared with a fixed wing unmanned aerial vehicle and a rotor wing unmanned aerial vehicle.
The amphibious tilting rotor unmanned aerial vehicle has the advantages of being long in fast navigation of the fixed-wing unmanned aerial vehicle, hovering in the air of the rotor unmanned aerial vehicle, cruising on the unmanned surface vehicle and the like, and has wide application prospect. However, the advantages of water surface take-off and landing also bring corresponding technical problems, and especially the take-off attitude is unstable in the process of the unmanned aerial vehicle running and taking-off and crossing the medium, so that the application of the rotor unmanned aerial vehicle is greatly limited.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a cross-medium takeoff longitudinal attitude control method of a water-air amphibious unmanned aerial vehicle with a buoy, which is compact in structure, easy to assemble, simple to control and stable in takeoff attitude.
In order to solve the technical problems, the invention adopts the following technical scheme:
a cross-medium takeoff longitudinal attitude control method for a water-air amphibious unmanned aerial vehicle with a buoy comprises the following steps:
s1, dividing a control system of an unmanned aerial vehicle into three parts, namely a power system for controlling the rotating speed of a rotor wing and the deflection angle of an elevator, a controller constructed based on an active disturbance rejection control and adaptive dynamic inverse control method and a water-air amphibious unmanned aerial vehicle longitudinal motion dynamic model with a buoy;
s2, a control elevator module in the power system calculates the deflection angle of the elevator according to the pitch angle rate of the unmanned aerial vehicle, the flight speed component in the longitudinal direction, the flight speed, the virtual rolling moment R and the virtual pitching moment P; a motor rotating speed module in the power system changes the rotating speed of a motor by setting a rotor wing tilting angle and a virtual force N; changing the advancing speed of the unmanned aerial vehicle by virtue of the virtual force N, and changing the flight attitude by virtue of an elevator;
s3, the controller controls the longitudinal attitude in the take-off process according to the expected height, the actual height, the pitch angle of the unmanned aerial vehicle, the pitch angle rate, the take-off speed and the actual speed;
and S4, controlling the force and the moment acting on the unmanned aerial vehicle by the longitudinal motion dynamic model of the water-air amphibious unmanned aerial vehicle with the buoy according to the output of the power system, calculating the state of the unmanned aerial vehicle on the basis of the established longitudinal motion dynamic model, and adjusting the longitudinal attitude of the unmanned aerial vehicle by taking the state as a feedback signal.
As a further improvement of the present invention, in step S3, the process of controlling the longitudinal attitude calculates an expected pitch angle according to the actual altitude difference, compares the expected pitch angle with the actual pitch angle, processes the comparison result to form an expected pitch angle rate, compares the expected pitch angle rate with the actual pitch angle rate, and solves the result to obtain a virtual control quantity after processing the result.
As a further improvement of the invention, the process for establishing the longitudinal motion dynamics model of the water-air amphibious unmanned aerial vehicle with the buoy in the step S1 is as follows: and calculating the water acting force of the buoy when the unmanned aerial vehicle runs on the water surface, perfecting hydrodynamic resistance analysis and finishing the derivation of the total water acting force and moment brought by the buoy.
As a further improvement of the invention, the water-air amphibious unmanned aerial vehicle longitudinal motion dynamic model with the buoy comprises the following steps:
in the formula: m isMass of unmanned plane, u and w being unmanned plane at X b Axis and Z b Velocity component of the shaft, q is pitch angular velocity, I y For unmanned aerial vehicle at Y b The moment of inertia of the shaft is,
and
for unmanned aerial vehicle focus in ground coordinate system plane X g ,Z g Projected coordinates of, N w Being hydrodynamic pressure, D a For aerodynamic resistance, L a For aerodynamic lift, M a For pneumatic pitching moment, M T Pitching moment for motor thrust, theta is a pitching angle, T is thrust provided by two motors, alpha i In order to achieve a deviation of the mounting angle of the motor in the longitudinal direction,
representing pitch angle rate, M w Representing the pitch moment generated by the hydrodynamic force,
the pitch angular acceleration is represented as,
for the angle of attack and the speed of the unmanned plane, alpha is the angle of attack of the unmanned plane, D f As frictional resistance in the action of water, G xa Is the component of the weight G on the X axis, G za Being the component of the weight G on the Z-axis,
is the acceleration of the unmanned aerial vehicle.
As a further improvement of the invention, the water acting force of the buoy when the unmanned aerial vehicle runs on the water surface is shown as follows:
in the formula: n is a radical of w Total hydrodynamic pressure, F b Total water buoyancy, M wd Total hydrodynamic pitching moment, C tr And (4) carrying out hydrodynamic correction on the operator.
As a further improvement of the present invention, the total hydrodynamic pressure is:
in the formula: n is a radical of w0 To stabilize the hydrodynamic pressure, N w1 For acceleration-dependent hydrodynamic pressure coefficients, N w2 For angle-of-attack rate-dependent hydrodynamic pressure coefficient, N w3 The angular acceleration is related to hydrodynamic pressure coefficient of the pitch angle;
the total water buoyancy is:
the total hydrodynamic pitching moment is:
in the formula: m is a group of w0 For stabilising the hydrodynamic pitching moment, M w1 For acceleration-dependent hydrodynamic pitching moment coefficients, M w2 For angle-of-attack rate-dependent hydrodynamic pitch coefficient, M w3 Is the pitch angular acceleration related hydrodynamic pitch coefficient.
As a further improvement of the present invention, the hydrodynamic resistance includes a frictional resistance and a splash resistance, and the frictional resistance is:
in the formula: c f Is a coefficient of resistance, V 1 The water flow speed, re and lambda are Reynolds numbers and the average length-width ratio of wetted length-width of the pontoon, and are related to the width B of the bilge of the pontoon, a pitch angle theta and a transverse inclination angle beta;
the splash resistance is as follows:
in the formula: a is k Is the included angle between the keel and the splash stagnation flow line, lws is the characteristic splash length, RNws is the splash Reynolds number, C fs Is the splash resistance coefficient.
As a further improvement of the invention, the calculation formula of the hydrodynamic pressure gravity center is obtained according to the Savitsky formula as follows:
in the formula: l p The distance of the hydrodynamic pressure center at the broken step of the buoy;
wherein, hydrodynamic pressure calculation does not consider the frictional resistance and the splash resistance that the flotation pontoon produced relative rivers motion and the pitching moment that correspondingly produces, then corresponds total hydrodynamic pitching moment and is:
M w ＝M wd -(D f +Rs·cosθ 0 )·l z
in the formula: l. the z For hydrodynamic pressure center to unmanned aerial vehicle focus at the endDistance of the partial projection.
As a further improvement of the present invention, in the step S1, the method based on the active disturbance rejection control and the adaptive dynamic inverse control specifically includes:
s101, carrying out uncertainty estimation after an uncertain part in an unmanned aerial vehicle control system is observed by using an active disturbance rejection control algorithm;
s102, realizing angular velocity tracking by utilizing self-adaptive dynamic inverse control; the inner ring adopts a self-adaptive dynamic inverse controller to control the speed and the pitch angle speed, the self-adaptive link determines self-adaptive dynamic inverse control law parameters according to the fed back pitch angle speed, and the outer ring adopts an active disturbance rejection controller to control the pitch angle of the unmanned aerial vehicle based on a dynamic model of the unmanned aerial vehicle.
As a further improvement of the present invention, in a system using an active disturbance rejection control algorithm, an uncertain disturbance acting on a controlled object and an output error are regarded as an extended state, an error is estimated using an extended state observer by a method of eliminating the error based on the error, and compensation is given in an active disturbance rejection controller.
Compared with the prior art, the invention has the advantages that:
the invention discloses a takeoff control method of a cross-medium takeoff longitudinal attitude control method of a water-air amphibious unmanned aerial vehicle with a buoy, and creatively provides an active disturbance rejection and self-adaptive dynamic inversion unmanned aerial vehicle cross-medium takeoff longitudinal attitude control method aiming at the characteristic of nonlinear strong coupling of water takeoff of a rotor unmanned aerial vehicle. The self-adaptive dynamic inverse control linearizes the nonlinear feedback quantity and then performs state decoupling, the problem of difficulty in hydrodynamic accurate modeling is further solved by the active disturbance rejection control, the performance of the designed control method is tested through a control simulation test of the cross-medium water surface running takeoff longitudinal attitude of the unmanned aerial vehicle, the feasibility and the effectiveness of the control method are shown, and the unmanned aerial vehicle is ensured to realize stable and safe takeoff on the water surface.
Drawings
Fig. 1 is a schematic diagram of a schematic top view structure of the water-air amphibious unmanned aerial vehicle with the buoy.
Fig. 2 is a schematic side view of the structure principle of the water-air amphibious unmanned aerial vehicle with the pontoon according to the invention.
Fig. 3 is a schematic flow diagram of the cross-medium takeoff longitudinal attitude control method of the water-air amphibious unmanned aerial vehicle with the buoy.
Fig. 4 is a schematic block diagram of the unmanned aerial vehicle angle definition according to the present invention.
FIG. 5 is a functional block diagram of the present invention for buoy slice definition.
FIG. 6 is a diagram showing the simulation result of the overwater stress of the unmanned aerial vehicle under the condition that the takeoff longitudinal attitude control method is not adopted in the invention; in the figure: the A-B-C-D process respectively represents that the aircraft accelerates, the aircraft lifts, the pitching angle is downward due to head-lowering moment generated on the water surface, and the aircraft cannot take off due to out-of-control longitudinal attitude angle.
Fig. 7 is a schematic block diagram of the active disturbance rejection + adaptive dynamic inverse control system according to the present invention.
FIG. 8 is a schematic diagram of the power system of the present invention.
FIG. 9 is a schematic diagram of the controller assembly of the present invention.
Fig. 10 is a schematic view of an unmanned aerial vehicle tiltrotor model according to the present invention.
FIG. 11 is a schematic diagram of a controller solver module of the present invention.
Fig. 12 is a schematic diagram of the height change of the unmanned aerial vehicle during the takeoff process in the invention.
Fig. 13 is a schematic diagram of pitch angle change during take-off of the unmanned aerial vehicle according to the present invention.
Fig. 14 is a schematic diagram of pitch angle rate change during take-off of an unmanned aerial vehicle according to the present invention.
Fig. 15 is a schematic view illustrating a flow simulation for controlling a take-off process of an unmanned aerial vehicle according to the present invention.
Illustration of the drawings: 1. a body; 2. a float bowl; 3. an airfoil; 4. a first rotor; 5. an elevator; 6. a tilting mechanism; 7. a second rotor; 8. a landing gear.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
Examples
As shown in fig. 1 and 2, the water-air amphibious unmanned aerial vehicle with buoys of the present invention includes: fuselage 1, buoy 2, wing 3, rotor 4 and elevator 5. The flotation pontoon 2 is installed in 1 bottom both sides of fuselage through 8 symmetries of undercarriage, and the composite material that flotation pontoon 2 adopted the light prepares to provide stability and water skiing ability, realize that unmanned aerial vehicle slides at the surface of water. Further, the bottom of the undercarriage 8 is connected with the buoy 2 through a bolt, and the top of the undercarriage 8 is connected with the bottom of the airframe 1 through a quick-release assembly. Wings 3 are symmetrically arranged on two side parts of the fuselage 1, the wings 4 are upwards arranged on the wings 3, and the wings 4 can be tilted by an angle; the second rotor 7 of elevator 5 and installation down is installed to 1 afterbody of fuselage to improve the stability that unmanned aerial vehicle takes off and lands.
In the present embodiment, the first rotor 4 is connected to the tilt mechanism 6 and the motor (not shown). The motor is installed on wing 3 up, and the motor is used for driving first rotor 4 rotatory. Mechanism 6 verts fixes on wing 3 to connect first rotor 4, mechanism 6 verts and is used for driving first rotor 4 and verts to satisfy the demand of verting of first rotor 4, avoid the smooth aquatic process splash to produce the influence to the motor, reduced the paddle of first rotor 4 under the sea state complex condition and the possibility of surface of water contact.
In this embodiment, through combining fixed wing unmanned aerial vehicle and rotor unmanned aerial vehicle both, the rotor that will have tilting angle installs additional on fixed wing unmanned aerial vehicle, new rotor unmanned aerial vehicle that verts has been formed, can realize the function that VTOL and fly before fast through the transform rotor mode, both have that the fixed wing cruise fast, long advantage such as time of navigating, it is nimble to have rotor unmanned aerial vehicle take off and land again, require advantages such as low to deployment place. Simultaneously, install the flotation pontoon additional on it and obtain the rotor unmanned aerial vehicle that verts who takes the flotation pontoon, when needs extension duration, can directly utilize the flotation pontoon to float and stop at the surface of water, when needs break away from floating state and make quick response to the circumstances around, adopt different take-off and landing modes to realize quick response through control rotor angle of verting, the angle of verting of control rotor has kept the rotor face up and can accomplish VTOL, can become the fixed wing mode flight with the rotor wing face forward after reaching the predetermined altitude, obtain faster flying speed, also can directly use the fixed wing mode, utilize the flotation pontoon to take off with higher speed in the roll of going on the surface of water, it finishes striding the medium and taking off to reach take off speed.
As shown in fig. 3, the cross-medium takeoff longitudinal attitude control method for the water-air amphibious unmanned aerial vehicle with the buoy, provided by the invention, comprises the following steps:
s1, a control system of the unmanned aerial vehicle is divided into three parts, namely a power system for controlling the rotating speed of a rotor wing and the deflection angle of an elevator, a controller constructed based on an active disturbance rejection control and self-adaptive dynamic inverse control method and a water-air amphibious unmanned aerial vehicle longitudinal motion dynamics model with a buoy. The power system is composed as shown in fig. 8, the controller is composed as shown in fig. 9, and the unmanned aerial vehicle tilt rotor model is composed as shown in fig. 10.
S2, a control elevator module in the power system calculates the deflection angle of the elevator according to the pitch angle rate, the longitudinal flight speed component, the flight speed, the virtual rolling moment R and the virtual pitching moment P of the unmanned aerial vehicle; a motor rotating speed module in the power system changes the rotating speed of a motor by setting a rotor wing tilting angle and a virtual force N; the advancing speed of the unmanned aerial vehicle is changed by means of the virtual force N, and the flight attitude is changed through the elevator.
And S3, the controller controls the longitudinal attitude in the take-off process according to the expected height, the actual height, the pitching angle of the unmanned aerial vehicle, the pitching angle rate, the take-off speed and the actual speed. And further, calculating an expected pitch angle according to the actual altitude difference in the process of longitudinal attitude control, comparing the expected pitch angle with the actual pitch angle, processing a comparison result to form an expected pitch angle rate, comparing the expected pitch angle rate with the actual pitch angle rate, and solving a virtual control quantity after processing the result.
And S4, controlling the force and the moment acting on the unmanned aerial vehicle by the longitudinal motion dynamic model of the water-air amphibious unmanned aerial vehicle with the buoy according to the output of the power system, calculating the state of the unmanned aerial vehicle on the basis of the established longitudinal motion dynamic model, and adjusting the longitudinal attitude of the unmanned aerial vehicle by taking the state as a feedback signal.
Further, the establishing process of the water-air amphibious unmanned aerial vehicle longitudinal motion dynamic model with the buoy in the step S1 is as follows: and calculating the water acting force of the buoy when the unmanned aerial vehicle runs on the water surface, perfecting hydrodynamic resistance analysis and finishing the derivation of the total water acting force and moment brought by the buoy. Specifically, the water acting force of the buoy when the water surface runs off is calculated by using a two-dimensional slice theory, the hydrodynamic resistance analysis is completed through a semi-empirical formula, the derivation of the total water acting force and the moment brought by the buoy is completed, a cross-medium unmanned aerial vehicle kinematics and dynamics model with the buoy is established, and the correctness of the model is verified through CFD simulation.
Aiming at the limited flying height of the air-water amphibious unmanned aerial vehicle, part of factors have less influence on the water movement of the unmanned aerial vehicle, and the following hypothesis can be carried out to reasonably simplify the research problem:
1. the unmanned aerial vehicle and the internal device quality are assumed not to change along with the movement, and the unmanned aerial vehicle is assumed to be a rigid body system.
2. Ignoring the curvature of the earth, the apparent ground coordinate system is an inertial coordinate system.
3. Bilateral symmetry of unmanned aerial vehicle, moment of inertia I xz ＝I yz ＝0。
Ground coordinate system (O) e -X e Y e Z e )：O e Is any point on the ground; x e Pointing to a certain fixed direction in the plane; z is a linear or branched member e Pointing to the center of the earth for being vertical to the ground; y is e : perpendicular X in the plane of the ground e And with X e Axis and Z e The axes are oriented according to the right hand rule.
Body coordinate system (O) b -X b Y b Z b )：O b Is the unmanned aerial vehicle centroid; x b The machine head is pointed in a symmetrical plane of the machine body parallel to the reference horizontal plane; y is b The unmanned plane is vertical to the symmetrical plane of the unmanned plane and points to the right of the fuselage; z b Perpendicular X in the plane of symmetry of the unmanned aerial vehicle b Downwards, follow the right-hand rule, and the coordinate system is fixedly connected with the unmanned aerial vehicle.
Stable coordinate system (O) s -X s Y s Z s )：O s At the unmanned aerial vehicle centroid; x s The direction of the projection of the air speed in the symmetry plane of the unmanned aerial vehicle is shown; y is s The vertical unmanned plane points to the right of the fuselage; z s Perpendicular X in the plane of symmetry of the unmanned aerial vehicle s The pointing direction is downward, the right-hand rule is followed, and the coordinate system is fixedly connected with the unmanned aerial vehicle.
Unmanned aerial vehicle Y b Axis and horizontal plane O e X e Y e The included angle between them is called roll angle phi, i.e. the body is around the fuselage X b The rotating angle of the shaft ranges from-90 degrees to 90 degrees. Unmanned aerial vehicle vertical X b Axis and horizontal plane O e X e Y e The included angle between them is a pitch angle theta, i.e. the body is around the body Y b The rotation angle of the shaft ranges from-180 degrees to 180 degrees. Unmanned aerial vehicle longitudinal theta axis and vertical plane O e X e Z e The included angle between the two is a yaw angle psi and ranges from-180 degrees to 180 degrees.
The attack angle alpha is an airspeed vector on the plane O of the unmanned aerial vehicle b X b Z b Projection and unmanned aerial vehicle X b The included angle of the shaft, the sideslip angle beta is the airspeed vector and the plane O of the unmanned aerial vehicle b X b Y b The angle is defined in the manner shown in fig. 4.
The two buoys of the amphibious unmanned aerial vehicle are basically the same in stress, a single buoy is defined to be a cross section as shown in fig. 5, the buoy is divided into a plurality of thin slices along the longitudinal direction, and the total water acting force of the amphibious tilt rotor unmanned aerial vehicle is equal to the stress on each slice on the two buoys, which is obtained by integrating forward and backward along the bottom of the buoy.
As shown in fig. 5, the water force on the slices includes: hydrodynamic forces due to changes in fluid momentum, buoyancy forces due to slice drainage, and cross-flow resistance due to water flow movement. The embodiment analyzes the slice quality and the water acting force related to each section and deduces and calculates the water acting force of the buoy.
(1) Slicing water power
The flotation pontoon can change because of the rivers impulse when the horizontal plane moves and produce corresponding hydrodynamic force, can take place same process on the section, and the rate of change of the available rivers additional impulse of hydrodynamic force along flotation pontoon distribution condition is derived and is obtained on each section:
in the formula: m is sa For adding mass to the slice, w s For the speed of the slice in the Z-axis of the machine system, u s The speed of the slice in the X axis of the machine system,
the quality of the slices is changed along with time,
is the acceleration of the slice in the Z-axis of the machine,
the distribution of slice mass along the shape of the buoy,
is to w s The derivative of the planar coordinate system is fixed.
According to Newton's second law F = m.a, the change of the speed of the unmanned aerial vehicle in the water motion process can influence the magnitude of the water acting force, the magnitude is directly proportional to the acceleration of the derivative of the speed and is also directly proportional to the mass, namely the additional mass, the additional mass of the slice is closely related to the shape of the slice and the transverse inclination angle thereof, and a calculation method for the slice quality can be directly written out:
in the formula: b s Is a half bilge width of slice, k a The additional mass prime, β, is related to the slice lateral tilt angle.
(2) Buoyancy of slice
Buoyancy of the slice is equal to static buoyancy of the slice and a correction factor C bf Multiplication by multiplication
f b ＝ρgC bf A s (3)
In the formula: a. The s For the section wet area, when the buoy enters the sliding state, the water surface and the buoy surfaceSeparately, the buoyancy generated by the same displacement volume at rest is reduced compared to the buoyancy generated by the same displacement volume at rest, thus correcting the factor C bf Taking 0.5 at this time may better match the experimental results.
(3) Resistance to cross flow of sliced sheets
The cross-flow resistance is expressed as:
in the formula: c D,c Is a cross-flow resistance coefficient, generally denoted as C D,c ＝1.33cosβ。
(4) Total water force of unmanned aerial vehicle
The cross flow resistance, the slice buoyancy and the slice hydrodynamic force of the slice are calculated and analyzed in combination with a two-dimensional slice theory, and the total water acting force in the amphibious unmanned aerial vehicle model is deduced to be equal to the integral of all acting forces on the slice along the buoy, as shown in the following formula:
in the formula: n is a radical of w Total hydrodynamic pressure, F b For total water buoyancy, M wd Total hydrodynamic pitching moment, C tr And (4) carrying out hydrodynamic correction on the operator.
As the water entry depth of all slice break lines is not the same in the water entry process of the wedge-shaped slice, and the structure of the bottom part of the buoy is simplified into the wedge shape, the analysis effect is influenced, the low head moment generated by the hydrodynamic pressure calculated by the slice theory is larger than the actual value, the actual pitch angle is larger than the simulation value, and the error is reduced by introducing a hydrodynamic correction operator in the subsequent simulation.
The total hydrodynamic pressure can be expressed as:
in the formula: n is a radical of hydrogen w0 For stabilising the hydrodynamic pressure, N w1 Is to addVelocity dependent hydrodynamic pressure coefficient, N w2 For the hydrodynamic pressure coefficient, N, of angle of attack rate w3 And the hydrodynamic pressure coefficient related to the pitch angle acceleration.
The total water buoyancy can be expressed as:
the total hydrodynamic pitching moment can be expressed as:
in the formula: m is a group of w0 For stabilising the hydrodynamic pitching moment, M w1 For acceleration-dependent hydrodynamic pitching moment coefficients, M w2 For angle-of-attack rate-dependent hydrodynamic pitch coefficient, M w3 Is the pitch acceleration related hydrodynamic pitch coefficient.
The frictional resistance calculation can be expressed as:
in the formula: c f Is a coefficient of resistance, V 1 The water flow speed, re and lambda are Reynolds numbers and the average length-width ratio of the wetted length-width of the pontoon, and are related to the width B of the bilge of the pontoon, the pitch angle theta and the transverse inclination angle beta.
The splash resistance calculation can be expressed as:
in the formula: a is a k Is the included angle between the keel and the splashing stagnant flow line, lws is the characteristic splashing length, RNws is the splashing Reynolds number, C fs As resistance to splashingAnd (4) the coefficient.
The calculation formula of the hydrodynamic pressure gravity center is obtained according to the Savitsky empirical formula as follows:
in the formula: l p The distance of the hydrodynamic pressure center at the broken steps of the buoy.
The hydrodynamic force calculation of the two-dimensional slice theory does not consider the frictional resistance and the splash resistance generated by the relative water flow movement of the buoy and the correspondingly generated pitching moment, and then the corresponding total water action pitching moment is as follows:
M w ＝M wd -(D f +Rs·cosθ 0 )·l z (13)
in the formula: l z For the projected distance in the bottom of hydrodynamic pressure center to unmanned aerial vehicle focus.
The derivation and analysis of the total water acting force and aerodynamic force of the unmanned aerial vehicle and the corresponding generated moment shows that the stress in the water surface sliding process comprises the influence of gravity, the thrust generated by the blades, the total water acting force, the resultant force of the air acting and the pitching moment,
projecting the total water acting force and the aerodynamic force to a body coordinate system according to the following method:
establishing the following longitudinal motion dynamics model of the unmanned aerial vehicle:
in the formula: m is the mass of the unmanned plane, u and w are unmanned planes at X b Axis and Z b Velocity component of the shaft, q is pitch angular velocity, I y For unmanned aerial vehicle at Y b The moment of inertia of the shaft is,
and
for unmanned aerial vehicle focus in ground coordinate system plane X g ,Z g Projected coordinates of, N w Being hydrodynamic pressure, D a For aerodynamic resistance, L a For aerodynamic lift, M a For pneumatic pitching moment, M T Pitch moment for motor thrust, theta is pitch angle, T is thrust provided by two motors, alpha i For the motor installation angle deviation in the longitudinal direction,
representing pitch rate, M w Representing the pitch moment generated by the hydrodynamic force,
a pitch angle acceleration is represented and,
for angular velocity of attack of the unmanned aerial vehicle, alpha is angle of attack of the unmanned aerial vehicle, D f As frictional resistance in the action of water, G xa Is the component of the weight G on the X axis, G za Being the component of the weight G on the Z-axis,
is the acceleration of the unmanned aerial vehicle.
In this embodiment, unmanned aerial vehicle can receive hydrodynamic force's influence on the flotation pontoon at the stage of taking off and land, need carry out the clear effect that influences of mechanism analysis to striding the medium problem. For the takeoff phase, in the embodiment, fluid distribution in the solution area is observed by using a Navier-Stokes equation describing flow of viscous incompressible fluid by using CFD simulation, so that the distribution condition of a water medium in a gas-liquid two-phase flow on the buoy is obtained, and the total water acting force on the buoy is analyzed by using a VOF method.
The fluid flow process is controlled by conservation laws including momentum conservation law, mass conservation law and energy conservation law, and systems in different states still obey the constraints of other equation sets.
(1) Equation of conservation of momentum
This equation, also known as the Navier-Stokes equation, is commonly used to describe the conservation of viscous incompressible fluid momentum within a boundary layer:
in the formula: p is the static pressure,. Tau ij Is the stress tensor, g i Is the gravitational volume force in the i direction, F i The external volumetric force in the i direction and the model-dependent source term.
(2) Conservation of mass equation
In the formula: s m Mass added to the continuous phase for the dispersed secondary phase.
(3) Energy conservation equation
Fluid energy includes internal energy, kinetic energy and potential energy, and an equation is generally obtained based on a first law of thermodynamics,
in the formula: c. C p Is the specific heat capacity, T is the temperature, k is the heat transfer coefficient, S T Is a viscous dissipation term.
The standard k-epsilon equation for describing the turbulence generated during simulation of high speed motion during actual takeoff is:
in the formula: g k Turbulent kinetic energy, G, for laminar velocity gradient changes b Is the kinetic energy of the buoyancy-generated turbulence, Y M Is a wave generated by diffusion in a compressible turbulent flow, C 1ε 、C 2ε 、C 3ε Is a constant coefficient, σ k 、σ ε Turbulence Prandtl coefficient, S, of k equation and epsilon equation, respectively k 、S ε Is a custom compensation term.
Based on a CFD method, a k-epsilon equation is adopted to express a viscosity equation of water, an enhanced wall surface equation is adopted for wall surface characteristics, a transient method is adopted for simulation, and under the condition that a take-off longitudinal attitude control method is not adopted, the result of simulation of the stress on the unmanned aerial vehicle water is shown in figure 6, wherein: the A-B-C-D process respectively represents that the aircraft accelerates, the aircraft lifts, the pitching angle is downward due to head-lowering moment generated on the water surface, and the aircraft cannot take off due to out-of-control longitudinal attitude angle. As can be seen from fig. 6, it is difficult for an unmanned aerial vehicle without a designed controller to achieve a smooth takeoff from the water.
In order to realize stable water-leaving takeoff of the unmanned aerial vehicle and obtain better control performance, the unmanned aerial vehicle cross-medium autonomous flying controller is designed for control of takeoff longitudinal attitude based on the active disturbance rejection control and the adaptive dynamic inverse control method. The method comprises the following steps of (1) realizing feedback linearization and state decoupling of a complex nonlinear model of the water unmanned aerial vehicle by self-adaptive dynamic inverse control; the active disturbance rejection control observes the complex hydrodynamic part and other unmodeled parts in the system model as the expansion state of the system, and meets the requirement of a self-adaptive dynamic inverse control algorithm on an accurate mathematical model of a controlled object.
In this embodiment, in step S1, the method based on the active disturbance rejection control and the adaptive dynamic inverse control specifically includes:
s101, observing uncertain parts such as total water acting force in an unmanned aerial vehicle control system by using an active disturbance rejection control algorithm, and then carrying out uncertainty estimation;
s102, realizing angular velocity tracking by utilizing self-adaptive dynamic inverse control; the inner ring adopts a self-adaptive dynamic inverse controller to control the speed and the pitch angle speed, the self-adaptive link determines self-adaptive dynamic inverse control law parameters according to the fed back pitch angle speed, and the outer ring adopts an active disturbance rejection controller to control the pitch angle of the unmanned aerial vehicle based on a dynamic model of the unmanned aerial vehicle. The functional block diagram of "active disturbance rejection + adaptive dynamic inverse control" is shown in fig. 6, which showsThe method comprises the following steps: theta.theta. c For desired pitch angle, make outer loop input, theta is actual pitch angle of the drone, q c For desired pitch rate, q is the actual pitch rate as the inner loop input, delta e For elevator rudder angle, omega θ And ω q Respectively represent and error theta d And q is d The associated differentiation element.
Further, in the present embodiment, in the system using the active disturbance rejection control algorithm, the uncertain disturbance acting on the controlled object and the output error are regarded as the extended state, and the error is estimated by using the extended state observer by a method of eliminating the error based on the error, so that compensation is given in the active disturbance rejection controller.
Estimating disturbance caused by unknown factors in a controlled object by using an extended state observer, and assuming the following nonlinear systems exist:
in the formula: x is a radical of a fluorine atom 1 And x 2 To expand the system state variables, f (x) 1 ,x 2 ) Is a nonlinear function of the expansion state of the original system, and b is input gain;
according to the general form of a continuous extended state observer,
in the formula: z is a radical of 1 、z 2 、z 3 Are respectively in the state x 1 、x 2 、x 3 And total disturbance x n+1 Estimate of (n =1,2,3), β 01 、β 02 、β 03 To expand the gain coefficient of the state observer, g i (e) (i =1,2,3) is a specific nonlinear function, which can be constructed according to the system requirements;
the nonlinear continuous extended state observer of the system of the embodiment is designed as follows:
in the formula: e.g. of a cylinder obs Is the error between the state observer input and the original system output.
By choosing the appropriate extended state observer gain factor, the observer's state z can be made 1 、z 2 And z 3 Tracking the state of the dilation System well, and thus achieving z 3 For f (x) 1 ,x 2 ) And (5) observing in real time.
A nonlinear feedback controller:
this part is an important part in the active disturbance rejection system, and the control quantity u is generated by this:
when the unknown disturbance has no estimation error, the dynamic state of the system containing the state of the controlled object and the differential of each level can be converted into a standard type, so that the system is suitable for systems with different designs. The feedback control law in the controller can compensate and eliminate the total disturbance output by the extended state observer, so that the active disturbance rejection function is realized. However, when compensation is carried out, the steady-state error is increased by using linear feedback to improve the gain coefficient, and an integral feedback link for eliminating the steady-state error is introduced, so that the system is slow, oscillation is caused, and the input quantity is saturated due to integral saturation. Aiming at the contradiction between the steady-state error and the gain coefficient, a proper nonlinear feedback controller is constructed to improve the compensation work efficiency of the controller, and the model can be assumed as follows:
in the formula: k is a radical of 1 ,k 2 Is a gain factor, alpha 1 ,δ 1 、α 2 ,δ 2 All are undetermined constants, and adjusting the undetermined constants can change the action process of the control and the performance of the system when the system reaches a steady state.
In this embodiment, the specific composition of the controller resolving module is as shown in fig. 8, wherein the power resolving module resolves aerodynamic force and hydrodynamic force on the unmanned aerial vehicle and aerodynamic moment and hydrodynamic moment generated correspondingly thereof, and enters the state resolving module as input quantities to resolve corresponding state quantities.
From the simulation results of the altitude, the pitch angle and the pitch angle rate of the unmanned aerial vehicle in the water surface running process shown in fig. 12 to 14, it can be known that the whole flight process is ideal for the altitude tracking effect and the accuracy, and because the unmanned aerial vehicle is always in an accelerating state in the running process and has a slight head-lowering tendency, the longitudinal attitude controller designed by the embodiment can obtain a good inhibition effect, and the control on the altitude is very close to the expected altitude. On the tracking effect of the pitch angle rate control performance, the method is smooth and high in precision. And the three curve change moments appearing in the simulation result correspond to the moments when the unmanned aerial vehicle changes the motion state, so that the two controllers can both make correct response, the control method of the active disturbance rejection plus the adaptive dynamic inversion can make faster response when the state changes, the control smoothness, the control effect and the control precision effect are obvious, and the tracking fitting degree of the flying height in the takeoff process is also very high.
Fig. 15 is a schematic diagram of the process of taking off the whole unmanned aerial vehicle on the water surface by using the buoys, wherein a shows the process of accelerating the unmanned aerial vehicle on the water surface; b represents the process that the unmanned aerial vehicle takes off at a certain pitch angle and gradually breaks away from the water surface; c and D show that the unmanned aerial vehicle successfully departs from the water surface to take off under the action of the controller. According to the simulation result shown in fig. 15, CFD simulation is performed by adopting "active disturbance rejection + adaptive dynamic inverse" control based on the pitch angle, the pitch angle of the unmanned aerial vehicle is always controlled by the controller in the roll-off process, the unmanned aerial vehicle of the embodiment has stable control capability of the pitch angle, and successfully takes off from water, so that the control problem of taking off across the medium can be effectively solved by introducing the controller based on the pitch angle. And the control method of 'active disturbance rejection + adaptive dynamic inversion' is adopted, so that the control performance is better.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make many variations and modifications to the disclosed embodiments, or equivalent variations, without departing from the spirit and scope of the invention, using the methods and techniques disclosed above. Therefore, any simple modifications, equivalent substitutions, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention are within the scope of the technical scheme of the present invention.
Claims (10)
1. A cross-medium takeoff longitudinal attitude control method for a water-air amphibious unmanned aerial vehicle with a buoy is characterized by comprising the following steps:
s1, dividing a control system of an unmanned aerial vehicle into three parts, namely a power system for controlling the rotating speed of a rotor wing and the deflection angle of an elevator, a controller constructed based on an active disturbance rejection control and self-adaptive dynamic inverse control method and a water-air amphibious unmanned aerial vehicle longitudinal motion dynamics model with a buoy;
s2, a control elevator module in the power system calculates the deflection angle of the elevator according to the pitch angle rate, the longitudinal flight speed component, the flight speed, the virtual rolling moment R and the virtual pitching moment P of the unmanned aerial vehicle; a motor rotating speed module in the power system changes the rotating speed of a motor by setting a rotor wing tilting angle and a virtual force N; changing the advancing speed of the unmanned aerial vehicle by virtue of the virtual force N, and changing the flight attitude by virtue of the elevator;
s3, the controller controls the longitudinal attitude in the takeoff process according to the expected height, the actual height, the pitching angle of the unmanned aerial vehicle, the pitching angle rate, the takeoff speed and the actual speed;
and S4, controlling the force and the moment acting on the unmanned aerial vehicle by the longitudinal motion dynamic model of the water-air amphibious unmanned aerial vehicle with the buoy according to the output of the power system, calculating the state of the unmanned aerial vehicle on the basis of the established longitudinal motion dynamic model, and adjusting the longitudinal attitude of the unmanned aerial vehicle by taking the state as a feedback signal.
2. The method for controlling the cross-medium takeoff longitudinal attitude of a water-air amphibious unmanned aerial vehicle with a buoy according to claim 1, wherein in the step S3, an expected pitch angle is calculated according to an actual height difference in the process of longitudinal attitude control, the expected pitch angle is compared with an actual pitch angle, an expected pitch angle rate and an actual pitch angle rate are formed after the comparison result is processed, comparison processing is carried out, and a virtual control quantity is solved after the result is processed.
3. The method for controlling the cross-medium takeoff longitudinal attitude of the water-air-amphibious unmanned aerial vehicle with the buoy according to claim 1, wherein the establishing process of the longitudinal motion dynamics model of the water-air-amphibious unmanned aerial vehicle with the buoy in the step S1 is as follows: and calculating the water acting force of the buoy when the unmanned aerial vehicle runs on the water surface, perfecting hydrodynamic resistance analysis and finishing the derivation of the total water acting force and moment brought by the buoy.
4. The cross-medium takeoff longitudinal attitude control method for the water-air-amphibious unmanned aerial vehicle with the buoy as claimed in claim 3, wherein the longitudinal motion dynamics model of the water-air-amphibious unmanned aerial vehicle with the buoy is as follows:
in the formula: m is the mass of the unmanned plane, u and w are unmanned planes at X b Axis and Z b Velocity component of the shaft, q is pitch angular velocity, I y For unmanned aerial vehicle at Y b The moment of inertia of the shaft is,
and
for unmanned aerial vehicle focus in ground coordinate system plane X g ,Z g Projected coordinates of, N w Hydrodynamic pressure, D a For aerodynamic resistance, L a For aerodynamic lift, M a For pneumatic pitching moment, M T For pitch moment of motor thrust, theta for pitch angle, T for both motorsThrust, α i In order to achieve a deviation of the mounting angle of the motor in the longitudinal direction,
representing pitch angle rate, M w Representing the pitch moment generated by the hydrodynamic force,
the pitch angular acceleration is represented as,
for angular velocity of attack of the unmanned aerial vehicle, alpha is angle of attack of the unmanned aerial vehicle, D f As frictional resistance in the action of water, G xa Is the component of the weight G on the X axis, G za Being the component of the weight G on the Z axis,
is the acceleration of the unmanned aerial vehicle.
5. The method for controlling the cross-medium takeoff longitudinal attitude of a water-air amphibious unmanned aerial vehicle with a buoy according to claim 4, wherein the water acting force applied to the buoy when the unmanned aerial vehicle runs on the water surface is as follows:
in the formula: n is a radical of w Total hydrodynamic pressure, F b Total water buoyancy, M wd Total hydrodynamic pitching moment, C tr Is a hydrodynamic correction operator.
6. The method for controlling the cross-medium takeoff longitudinal attitude of a water-air amphibious unmanned aerial vehicle with a buoy as claimed in claim 5,
the total hydrodynamic pressure is:
in the formula: n is a radical of w0 To stabilize the hydrodynamic pressure, N w1 For acceleration-dependent hydrodynamic pressure coefficients, N w2 For angle-of-attack rate-dependent hydrodynamic pressure coefficient, N w3 The angular acceleration is related to a hydrodynamic pressure coefficient;
the total water buoyancy is:
the total hydrodynamic pitching moment is:
in the formula: m is a group of w0 For stabilising the hydrodynamic pitching moment, M w1 For acceleration-dependent hydrodynamic pitching moment coefficients, M w2 For hydrodynamic pitch coefficient, M, related to angle of attack rate w3 Is the pitch acceleration related hydrodynamic pitch coefficient.
7. The method for controlling the cross-medium takeoff longitudinal attitude of a water-air amphibious unmanned aerial vehicle with a pontoon according to claim 5, wherein the hydrodynamic drag comprises a frictional drag and a splash drag,
the frictional resistance is as follows:
in the formula: c f Is a coefficient of resistance, V 1 The water flow speed, re and lambda are Reynolds numbers and the average wetted length-width ratio of the pontoon, and are related to the width B of the bilge of the pontoon, the pitch angle theta and the transverse inclination angle beta;
the splash resistance is as follows:
in the formula: a is a k Is the included angle between the keel and the splashing stagnant flow line, lws is the characteristic splashing length, RNws is the splashing Reynolds number, C fs Is the splash resistance coefficient.
8. The cross-medium takeoff longitudinal attitude control method for the water-air amphibious unmanned aerial vehicle with the buoy as claimed in claim 7, wherein a hydrodynamic pressure gravity center calculation formula obtained according to a Savitsky formula is as follows:
in the formula: l p The distance of the hydrodynamic pressure center at the broken step of the buoy;
wherein, hydrodynamic pressure calculation does not consider the frictional resistance and the splash resistance that the flotation pontoon produced relative rivers motion and the pitching moment that correspondingly produces, then corresponds total hydrodynamic pitching moment and is:
M w ＝M wd -(D f +Rs·cosθ 0 )·l z
in the formula: l. the z The distance from the hydrodynamic pressure center to the center of gravity of the unmanned aerial vehicle in the bottom projection is obtained.
9. The method for controlling the cross-medium takeoff longitudinal attitude of the water-air amphibious unmanned aerial vehicle with the buoy according to any one of claims 1 to 8, wherein in the step S1, the method based on active disturbance rejection control and adaptive dynamic inverse control specifically comprises the following steps:
s101, carrying out uncertainty estimation after observing an uncertain part in an unmanned aerial vehicle control system by using an active disturbance rejection control algorithm;
s102, realizing angular velocity tracking by utilizing self-adaptive dynamic inverse control; the inner ring adopts a self-adaptive dynamic inverse controller to control the speed and the pitch angle speed, the self-adaptive link determines self-adaptive dynamic inverse control law parameters according to the fed back pitch angle speed, and the outer ring adopts an active disturbance rejection controller to control the pitch angle of the unmanned aerial vehicle based on a dynamic model of the unmanned aerial vehicle.
10. The method for controlling the cross-medium takeoff longitudinal attitude of a water-air amphibious unmanned aerial vehicle with a pontoon according to claim 9, wherein in a system adopting an active disturbance rejection control algorithm, uncertain disturbance acting on a controlled object and an output error are regarded as an extended state, and the error is estimated by using an extended state observer based on an error elimination method, and compensated in an active disturbance rejection controller.
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| CN116176193A (en) * | 2023-04-23 | 2023-05-30 | 北京大学 | Cross-medium aircraft |
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| CN116090097A (en) * | 2022-12-30 | 2023-05-09 | 北京机电工程研究所 | Near-water surface fluid-solid coupling finite element efficient calculation method based on equivalent water collision design |
| CN116176193A (en) * | 2023-04-23 | 2023-05-30 | 北京大学 | Cross-medium aircraft |
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