Unmanned aerial vehicle inertial load calculation method

Abstract

The invention provides an unmanned aerial vehicle inertial load calculation method which comprises the following steps: in the same coordinate system, respectively extracting barycentric coordinates and masses of all airborne equipment and structural members of an unmanned aerial vehicle; establishing an unmanned aerial vehicle structure and airborne equipment finite element grid; extracting structural finite element grid point coordinate information; assuming that a virtual beam element exists between structural finite element grid points and all barycentric coordinates to establish beam element related information, and establishing a relational equation of deformation energy and load of the beam; establishing a static equivalent equation of deformation energy and gravity center of a beam between finite element grid points; and establishing an unknown equation of the inertia load of the beam and barycentric coordinates by using a Lagrange multiplier method, and solving the unknown equation, so that the corresponding inertia load can be solved according to the overload nz of the unmanned aerial vehicle at the moment. According to the method, the accuracy of a load calculation result and the accuracy of inertia load distribution are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of aircraft load calculation, and in particular relates to a method for calculating the inertial load of an unmanned aerial vehicle. Background Art

[0002] Aircraft structures are subject to various loads during development, production, transportation and service, including take-off and landing loads, flight loads, transportation loads and launch loads. Loads can be classified into three categories from a mechanical point of view: aerodynamic loads, inertial force loads and thermal loads. When an aircraft is subjected to external forces, in most cases, inertial force exists.

[0003] The traditional load calculation method distributes the mass of the aircraft through the lever principle and simply obtains the inertial load by multiplying the mass by the overload coefficient. This method is relatively rough and has low accuracy, which is not conducive to the detailed design of the aircraft. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for calculating the inertial load of a drone. The solution of the present invention can solve the problems existing in the prior art.

[0005] The technical solution of the present invention:

[0006] A method for calculating the inertial load of a UAV comprises the following steps:

[0007] In the same coordinate system, according to the structure and onboard equipment of the UAV, the center of gravity coordinates and mass of all the onboard equipment and structural parts of the UAV are extracted respectively;

[0008] According to the load calculation requirements, establish the finite element mesh of the UAV structure and airborne equipment;

[0009] Extract the coordinate information of the structural finite element grid points;

[0010] Assume that there is a virtual beam element between the structural finite element grid points and all the centroid coordinates to establish the beam element related information and establish the relationship equation between the beam deformation energy and load;

[0011] According to the mass equivalence principle, the static equivalent equations of the deformation energy and center of gravity of the beam between the finite element grid points are established;

[0012] Establish the Lagrange function, use the Lagrange multiplier method to establish the unknown equations of the inertial load of the beam and the center of gravity coordinates and solve them. According to the overload n of the drone at this time z The corresponding inertia load can be calculated.

[0013] Furthermore, the method of establishing the relationship equation between the deformation energy and the load of the beam comprises the following steps:

[0014] Step 401: Center of gravity Qc i and structure finite element mesh point F j There is a virtual beam between the two sides, which is a cantilever beam with one end at the center of gravity as the fixed end and the structural grid point as the free end. The length of the cantilever beam is l ij , the calculation method is as follows:

[0015]

[0016] in, is the coordinate of the i-th centroid on the x-axis, is the coordinate of the jth structural finite element mesh point on the x-axis, is the coordinate of the i-th centroid on the y-axis, is the coordinate of the jth structural finite element mesh point on the y-axis, is the coordinate of the i-th centroid on the z-axis, is the coordinate of the jth structural finite element grid point on the z-axis;

[0017] Step 402: The bending stiffness of the virtual beam is EJ, and its value is as follows:

[0018]

[0019] Step 403: Assume that the load P is distributed at the finite element point F j at the free end of the cantilever beam. j , the center of gravity Qc i and F j The deformation energy u of the beam ij for:

[0020]

[0021] Furthermore, the method for establishing the static equivalent equation of the deformation energy and center of gravity of the beam comprises the following steps:

[0022] Step 501: For the structural finite element point F j, select a circle with F j as the center without duplication, ml max / 10n is the center of gravity of all the circles with radius;

[0023] Step 502: Assume that the mass assigned to the structural finite element point is M j , the quality equivalence condition should be met, and we can get:

[0024]

[0025] Among them, n1 is the number of centroids, M k is the mass of the kth centroid, is the coordinate of the kth centroid on the x-axis, is the coordinate of the kth centroid on the z-axis;

[0026] Step 503: Multiply all equations in formula (4) by the gravitational acceleration g to obtain the equations where the center of gravity satisfies the static equivalent condition:

[0027]

[0028] Among them, G k is the weight of the kth center of gravity, G j is the weight of the jth structural finite element point.

[0029] Step 504: According to formula (3), if the free end structural point finite element point F j The load distributed is G j , then the deformation energy of this beam is:

[0030]

[0031] Here G j To be determined parameter.

[0032] Furthermore, according to the drone overload n z The method for calculating the corresponding inertial load includes the following steps:

[0033] Step 601: Establish the Lagrange function of the Lagrange multiplier method:

[0034]

[0035] Among them, λ, λ x , z , xx , zz , xz is the Lagrange multiplier as the unknown parameter, m is the total number of structural finite element grid points, X i , Z i are the x-axis and z-coordinates of the i-th finite element mesh;

[0036] Step 602: Find F(λ, λ x ,λ z ,λ xx ,λ zz ,λ xz ) for G j The partial derivative of and set it to 0:

[0037]

[0038] Substituting (2) into the equation, we have:

[0039]

[0040] Step 603: Substitute equation (9) into equation (5) to obtain the following linear equation system:

[0041]

[0042] Step 604: Solve equation (10) to obtain λ, λ x , z , xx , zz , xz Substituting into (9), we can get G j ;

[0043] Step 605: If the drone overload is n z , n z G j This is the inertia load at that point.

[0044] The beneficial effects of the present invention compared with the prior art are as follows:

[0045] The present invention proposes a method for calculating the inertial load of an unmanned aerial vehicle. The method disperses the mass through mass equivalence and static equivalence methods, can refine the load distribution of components, and improve the accuracy of load calculation results; and improves the accuracy of inertial load distribution through the Lagrange multiplier method. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0047] Figure 1 A schematic diagram of a flow chart of a method for calculating an inertial load of a UAV provided in an embodiment of the present invention is shown;

[0048] Figure 2 A comparison chart showing the calculation results of the UAV inertial load calculation method provided by an embodiment of the present invention and the calculation results of the traditional method is shown. DETAILED DESCRIPTION

[0049] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0051] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0052] like Figure 1 As shown, according to an embodiment of the present invention, a method for calculating the inertial load of a drone is provided, comprising the following steps:

[0053] In the same coordinate system, according to the structure and onboard equipment of the UAV, the center of gravity coordinates and mass of all the onboard equipment and structural parts of the UAV are extracted respectively;

[0054] According to the load calculation requirements, establish the finite element mesh of the UAV structure and airborne equipment;

[0055] Extract the coordinate information of the structural finite element grid points;

[0056] Assume that there is a virtual beam element between the structural finite element grid points and all the centroid coordinates to establish the beam element related information and establish the relationship equation between the beam deformation energy and load;

[0057] According to the mass equivalence principle, the static equivalent equations of the deformation energy and center of gravity of the beam between the finite element grid points are established;

[0058] Establish the Lagrange function, use the Lagrange multiplier method to establish the unknown equations of the inertial load of the beam and the center of gravity coordinates and solve them. According to the overload n of the drone at this time z The corresponding inertia load can be calculated.

[0059] The above steps disperse the mass through mass equivalence and static equivalence methods, which can refine the load distribution of the components and improve the accuracy of the load calculation results.

[0060] Further in one embodiment, a method for establishing a relational equation between the deformation energy and the load of a beam comprises the following steps:

[0061] Step 401: Center of gravity Q ci and the structural finite element mesh point F j There is a virtual beam between the two sides, which is a cantilever beam with one end at the center of gravity as the fixed end and the structural grid point as the free end. The length of the cantilever beam is l ij , the calculation method is as follows:

[0062]

[0063] in, is the coordinate of the i-th centroid on the x-axis, is the coordinate of the jth structural finite element mesh point on the x-axis, is the coordinate of the i-th centroid on the y-axis, is the coordinate of the jth structural finite element mesh point on the y-axis, is the coordinate of the i-th centroid on the z-axis, is the coordinate of the jth structural finite element grid point on the z-axis;

[0064] Step 402: The bending stiffness of the virtual beam is EJ, and its value is as follows:

[0065]

[0066] Step 403: Assume that the load P is distributed at the finite element point F j at the free end of the cantilever beam. j , the deformation energy of the beam composed of the center of gravity Qc i and F jj is u ij for:

[0067]

[0068] Furthermore, the method for establishing the static equivalent equation of the deformation energy and center of gravity of the beam comprises the following steps:

[0069] Step 501: For the structural finite element point F j, select a circle with F j as the center without duplication, ml max / 10n is the center of gravity of all the circles with radius;

[0070] Step 502: Assume that the mass assigned to the structural finite element point is M j , the quality equivalence condition should be met, and we can get:

[0071]

[0072] Among them, n1 is the number of centroids, M k is the mass of the kth centroid, is the coordinate of the kth center point on the x-axis, is the coordinate of the kth centroid on the z-axis;

[0073] Step 503: Multiply all equations in formula (4) by the gravitational acceleration g to obtain the equations where the center of gravity satisfies the static equivalent condition:

[0074]

[0075] Among them, G k is the weight of the kth center of gravity, G j is the weight of the jth structural finite element point.

[0076] Step 504: According to formula (3), if the free end structural point finite element point F j The load distributed is G j , then the deformation energy of this beam is:

[0077]

[0078] Here G j To be determined parameter.

[0079] Furthermore, according to the drone overload n z The method for calculating the corresponding inertial load includes the following steps:

[0080] Step 601: Establish the Lagrange function of the Lagrange multiplier method:

[0081]

[0082]

[0083] Among them, λ, λ x, z , xx , zz , xz is the Lagrange multiplier as the unknown parameter, m is the total number of structural finite element grid points, X i , Z i are the x-axis and z-coordinates of the i-th finite element mesh;

[0084] Step 602: Find F(λ, λ x ,λ z ,λ xx ,λ zz ,λ xz ) for G j The partial derivative of and set it to 0:

[0085]

[0086] Substituting (2) into the equation, we have:

[0087]

[0088] Step 603: Substitute equation (9) into equation (5) to obtain the following linear equation system:

[0089]

[0090] Step 604: Solve equation (10) to obtain λ, λ x , z , xx , zz , xz Substituting into (9), we can get G j ;

[0091] Step 605: If the drone overload is n z , n z G j This is the inertia load at that point.

[0092] In order to have a further understanding of the method for calculating the inertial load of a UAV provided by the present invention, a detailed description is given below with reference to specific examples and accompanying drawings.

[0093] A method for calculating the inertial load of an unmanned aerial vehicle is characterized in that the specific steps are as follows:

[0094] Step 1: Establish a global Cartesian coordinate system. In the Cartesian coordinate system, extract the center of gravity coordinates and mass of all the UAV's airborne equipment and structural parts according to the UAV structure and airborne equipment. The coordinate set of these points is recorded as {Qc i=(xQ i,yQ i,zQ i)}, 1≤i≤n, n is the total number of concentrated mass points, and the mass set of these points is recorded as {Qm i=M i},1≤i≤n;

[0095] {Qm i=M i},1≤i≤n,M i The value is the mass of the airborne equipment or structural parts. The mass distribution of airborne equipment or structural parts is usually irregular. When calculating, the mass of the airborne equipment or structural parts is concentrated to the center of gravity of the parts according to the components. Concentrating the airborne equipment or structural parts to the center of gravity can simplify the calculation.

[0096] Step 2: In the Cartesian coordinate system, establish the structural finite element mesh according to the load calculation requirements;

[0097] Step 3: Extract the coordinate information of the structural finite element grid points. The coordinate set of the grid points is {F j = (xF j, yF j, zF j)}, 1≤j≤m, where m is the total number of structural finite element grid points;

[0098] Step 4: Assume that there is a virtual beam element between the structural finite element grid points and all the centroid coordinates to establish the relevant information of the beam element and establish the relationship equation between the deformation energy and load of the beam;

[0099] Step 401: There is a virtual beam between the centroid point Qc i and the structural finite element grid point F j. It is a cantilever beam with one end of the centroid point as the fixed end and the structural grid point as the free end. The length of the cantilever beam is l ij , the calculation method is as follows:

[0100]

[0101] Note ij The maximum value of max By establishing a virtual physical connection between the structural point and the center of gravity through a virtual beam, the deformation-energy relationship can be obtained, and the mass equivalence principle can be easily introduced to establish a set of linear equations with load as the unknown variable.

[0102] Step 402: The bending stiffness of the virtual beam is EJ, and its value is as follows:

[0103]

[0104] Taking 1 / 3 of EJ can make subsequent calculations simpler.

[0105] Step 403: Assume that the load P is distributed at the finite element point F j at the free end of the cantilever beam. j , the deformation energy of the beam composed of the center of gravity Qc i and F j is u ij for:

[0106]

[0107] Step 5: According to the mass equivalence principle, establish a set of static equivalent equations;

[0108] Step 501: For the structural finite element point F j with the label j, select a circle ml with F j as the center without duplication max / 10n is the radius of all the centroid points in the circle, the set of these points is {Cc k=(xc k,yc k,zc k)},1≤k≤n1. Select ml max / 10n is used as the radius, which avoids selecting all the center of gravity points for calculation, reduces the amount of calculation, and ensures that the calculation results have high accuracy.

[0109] Step 502: Assume that the mass assigned to the structural finite element point is M j , the quality equivalence condition should be met, and we can get:

[0110]

[0111] Step 503: Note that the mass M multiplied by the gravitational acceleration g is the gravity G. All equations in formula (4) are multiplied by the gravitational acceleration g on both sides to obtain equations that satisfy the static equivalence condition:

[0112]

[0113] Step 504: Similar to the static equivalent condition, according to formula (3), if the load distributed to the finite element point F j of the free end structure point is G j , then the deformation energy of this beam is:

[0114]

[0115] Here G j To be determined parameter.

[0116] Step 6: Establish the Lagrange function, use the Lagrange multiplier method to establish the unknown equation of the inertial load of the center of gravity coordinate and solve it. According to the overload n of the drone at this time z The corresponding inertia load can be calculated.

[0117] Step 601: Establish the Lagrange function of the Lagrange multiplier method:

[0118]

[0119] Among them, λ, λ x , z , xx , zz , xz is the Lagrange multiplier as the unknown parameter,

[0120] Step 602: Find F(λ, λ x ,λ z ,λ xx ,λ zz ,λ xz ) for G j The partial derivative of and set it to 0:

[0121]

[0122] Substituting (2) into the equation, we have:

[0123]

[0124] Step 603: Substitute equation (9) into equation (5) to obtain the following linear equation system:

[0125]

[0126] Step 604: Solve equation (10) to obtain λ, λ x , z , xx , zz , xz Substituting into (9), we can get G j .

[0127] Step 605: If the drone overload is n z , n z G j This is the inertia load at that point.

[0128] In a specific example:

[0129] The initial aircraft component distribution is shown in the following table:

[0130] name Mass(kg) x(mm) y(mm) z(mm) Component 1 8.4 535.64 -21.42 0 Component 2 7.7 1213.43 0 0 Component 3 8.1 2151.2 -9.25 0 Component 4 10.2 3285.45 72.06 0 Component 5 2.6 4047.23 10.58 0 Component 6 15 2408.36 105.93 0 Component 7 1.5 3914.39 8.02 -410.81 Component 8 1.5 3914.39 8.02 410.81 Component 9 2 3973.07 461.63 0 Component 10 3 3299.9 84.28 0 Component 11 1.351 1324 -113.6 0 Component 12 1.351 3415 -113.6 0 Component 13 9.5 1329 41 0 Component 14 1.3 3383 177 0 Component 15 0.9 3511 201 23 Component 16 0.5 3366 185 65 Component 17 1 2680 0 70 Component 18 20.6 3956 1.13 0 Component 19 2 3055.7 113.2 0 Component 20 3 3336.4 68.8 111.6 Component 21 0.7 2221 119 166 Component 22 0.7 2221 119 -166 Component 23 0.7 3798 -2 223 Component 24 0.7 3798 -2 -223 Component 25 0.7 3876 231 0 Component 26 3.79 1019 -65 0 Component 27 0.27 1156 -114 0 Component 28 0.75 725 -155 0 Component 29 0.251 1103 22 -216 Component 30 0.34 997 135 0 Component 32 4 1000 82 0 Component 33 2.1 1664 105 0 Component 34 1 1825 0 120 Component 35 2 735 0 0 Component 36 3 3250 0 0 Component 37 3 2907 25 41 Component 38 18 738 -6 0 Component 39 7 466 -35 0 Component 40 65 2378 -32 0 Component 41 30.5 3557 -358 0 Component 42 14.8 3557 -358 0

[0131] Establish a finite element mesh and calculate according to the method of the present invention. At this time, the whole machine overload is n z =2, the inertial loads in the z direction of the two methods are shown in the following table (x and y coordinates are omitted for ease of comparison):

[0132]

[0133]

[0134] The comparison results are as follows Figure 2 As shown, from the comparison in the figure, it can be found that the inertial load change of the method of the present invention is smoother than that of the traditional method, and is more in line with the physical characteristics of the load distribution, indicating that the method of the present invention has higher accuracy.

[0135] In summary, the method for calculating the inertial load of a UAV provided by the present invention has at least the following advantages over the prior art:

[0136] The method of the present invention disperses the mass through mass equivalence and static equivalence methods, can refine the load distribution of components, and improve the accuracy of load calculation results; and improves the accuracy of inertial load distribution through the Lagrange multiplier method.

[0137] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for calculating the inertial load of an unmanned aerial vehicle, characterized in that: The following steps are involved: In the same coordinate system, according to the structure and onboard equipment of the UAV, the center of gravity coordinates and mass of all the onboard equipment and structural parts of the UAV are extracted respectively; According to the load calculation requirements, establish the finite element mesh of the UAV structure and airborne equipment; Extract the coordinate information of the structural finite element grid points; Assume that there is a virtual beam element between the structural finite element grid points and all the centroid coordinates to establish the beam element related information and establish the relationship equation between the beam deformation energy and load; According to the mass equivalence principle, the static equivalent equations of the deformation energy and center of gravity of the beam between the finite element grid points are established; Establish the Lagrange function, use the Lagrange multiplier method to establish the unknown equations of the inertial load of the beam and the center of gravity coordinates and solve them. According to the overload n of the drone at this time z The corresponding inertia load can be calculated.

2. The method for calculating the inertial load of an unmanned aerial vehicle according to claim 1, characterized in that: The method of establishing the relationship equation between the deformation energy and the load of the beam includes the following steps: Step 401: There is a virtual beam between the centroid point Qc i and the structural finite element grid point F j. It is a cantilever beam with one end of the centroid point as the fixed end and the structural grid point as the free end. The length of the cantilever beam is l ij , the calculation method is as follows: in, is the coordinate of the i-th centroid on the x-axis, is the coordinate of the jth structural finite element mesh point on the x-axis, is the coordinate of the i-th centroid on the y-axis, is the coordinate of the jth structural finite element mesh point on the y-axis, is the coordinate of the i-th centroid on the z-axis, is the coordinate of the jth structural finite element grid point on the z-axis; Step 402: The bending stiffness of the virtual beam is EJ, and its value is as follows: Step 403: Assume that the load P is distributed at the finite element point F j at the free end of the cantilever beam. j , the deformation energy of the beam composed of the center of gravity Qc i and F jj is u ij for:

3. The method for calculating the inertial load of an unmanned aerial vehicle according to claim 2, characterized in that: The method for establishing the static equivalent equation of the deformation energy and center of gravity of the beam comprises the following steps: Step 501: Finite element point F of the structure j , select F without repetition j is the center of the circle, ml max / 10n is the center of gravity of all the circles with radius; Step 502: Assume that the mass assigned to the structural finite element point is M j , the quality equivalence condition should be met, and we can get: Among them, n1 is the number of centroids, M k is the mass of the kth centroid, is the coordinate of the kth centroid on the x-axis, is the coordinate of the kth centroid on the z-axis; Step 503: Multiply all equations in formula (4) by the gravitational acceleration g to obtain the equations where the center of gravity satisfies the static equivalent condition: Among them, G k is the weight of the kth center of gravity, G j is the weight of the jth structural finite element point. Step 504: According to formula (3), if the free end structural point finite element point F j The distributed load is Gj, then the deformation energy of this beam is: Here G j To be determined parameter.

4. The method for calculating the inertial load of an unmanned aerial vehicle according to claim 3, characterized in that: According to the drone overload n z The method for finding the corresponding inertial load includes the following steps: Step 601: Establish the Lagrange function of the Lagrange multiplier method: Among them, λ, λ x , z , xx , zz , xz is the Lagrange multiplier as the unknown parameter, m is the total number of structural finite element grid points, X i , Z i are the x-axis and z-coordinates of the i-th finite element mesh; Step 602: Find F(λ, λ x ,λ z ,λ xx ,λ zz ,λ xz ) for G j The partial derivative of and set it to 0: Substituting (2) into the equation, we have: Step 603: Substitute equation (9) into equation (5) to obtain the following linear equation system: Step 604: Solve equation (10) to obtain λ, λ x , z , xx , zz , xz Substituting into (9), we can get G j ; Step 605: If the drone overload is n z , n z G j This is the inertia load at that point.

Images