Unmanned aerial vehicle ground risk map construction method based on gridding risk matrix

Abstract

The invention provides an unmanned aerial vehicle ground risk map construction method based on a gridding risk matrix, and the method comprises the steps: dividing a city region into a plurality of grid units, and obtaining unmanned aerial vehicle feature parameters, ground personnel density and city ground surface features; according to the unmanned aerial vehicle characteristic parameters and the ground personnel density, an inherent ground risk matrix of the unmanned aerial vehicle to the ground crowd is determined; obtaining a first mitigation matrix according to the urban surface features; obtaining a second mitigation matrix according to the unmanned aerial vehicle failure protection measures; adopting the first mitigation matrix and the second mitigation matrix to construct an overall ground risk mitigation matrix; obtaining a to-ground risk matrix according to the inherent to-ground risk matrix and the overall to-ground risk mitigation matrix; and according to the to-the-ground risk matrix, constructing a static to-the-ground risk map. According to the method, the unmanned aerial vehicle ground risk is comprehensively considered from multiple angles, the accuracy and reliability of risk assessment are improved, support is provided for the development of the urban unmanned aerial vehicle industry, and the safety and efficiency of unmanned aerial vehicle flight are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of unmanned aerial vehicles, and in particular relates to a method for constructing a ground risk map of unmanned aerial vehicles based on a grid risk matrix. Background Art

[0002] Regarding the research on UAV ground risk assessment, current studies all take the configuration parameters and flight status of UAVs as the starting point, and use probability models (such as probability density function, Bayesian network) to quantify the crash risk of UAVs, and then deduce and calculate the ground risk. Although these studies consider many factors, these factors are cascaded with each other, and there is a lack of a modular evaluation framework that can quantify the actual effects of various risk factors.

[0003] Risk maps are a commonly used method in the field of risk assessment. Current research on UAV-to-ground risk maps aims to assess the ground risk caused by the flight mission or track of a single UAV. These studies reflect the ground risk level of UAVs to a certain extent. They mainly conduct risk assessment based on static obstacles such as ground buildings and no-fly zones, and give less consideration to the complex dynamic factors of cities, resulting in low accuracy and reliability of risk assessment of the established risk maps. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a method and device for constructing a UAV-to-ground risk map based on a grid risk matrix to meet the demand for improving the accuracy and reliability of risk assessment of risk maps.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for constructing a ground risk map of an unmanned aerial vehicle based on a grid risk matrix, comprising: dividing an urban area into a plurality of grid units, and obtaining characteristic parameters of unmanned aerial vehicles, ground personnel density, and urban surface characteristics; determining an inherent ground risk matrix of the unmanned aerial vehicle in each grid unit according to the characteristic parameters of the unmanned aerial vehicle and the ground personnel density; determining a protective effect on ground people according to urban surface characteristics in each grid unit, and obtaining a first mitigation matrix; determining a mitigation degree of the unmanned aerial vehicle impacting the ground in each grid unit according to unmanned aerial vehicle failure protection measures, and obtaining a second mitigation matrix; constructing a ground risk mitigation matrix by using the first mitigation matrix and the second mitigation matrix; obtaining a final ground risk matrix by using the Hadamard product of the inherent ground risk matrix and the ground risk mitigation matrix; and constructing a static ground risk map of the unmanned aerial vehicle according to the final ground risk matrix.

[0007] Optionally, the drone failure protection measure is to install a parachute for the drone, and according to the drone failure protection measure, the degree of mitigation of the drone's impact on the ground in each grid unit is determined to obtain a second mitigation matrix, including: dividing the process of the drone falling into each grid unit into a first stage and a second stage, the first stage is that the drone loses power and the parachute is not opened, and the second stage is to open the parachute and the drone enters a parachute descent state; according to the initial speed of the drone in the first stage, the duration of the first stage and the motion model of the first stage, the vertical and horizontal movement speeds of the drone in the first stage are determined; according to the flight speed of the first stage and the motion model of the second stage, the vertical and horizontal movement speeds of the second stage are determined; The vertical and horizontal movement speeds of the first stage are integrated to obtain the horizontal displacement and vertical displacement of the first stage; the vertical and horizontal movement speeds of the second stage are integrated to obtain the horizontal displacement and vertical displacement of the second stage; the coordinates of the UAV hitting the ground in each grid unit are obtained according to the horizontal displacement and vertical displacement of the first stage and the horizontal displacement and vertical displacement of the second stage; the ground casualty area of ​​the impact ground coordinates and the UAV impact kinetic energy are determined according to the horizontal and vertical speeds of the UAV at the end of the second stage; the second mitigation matrix of each grid unit is determined according to the ground casualty area and impact kinetic energy after the parachute is installed and the pre-calculated ground casualty area and impact kinetic energy without the parachute installed.

[0008] Optionally, the UAV is a multi-rotor UAV, and the vertical and horizontal motion speeds of the UAV in the first stage are determined according to the initial speed of the UAV in the first stage, the duration of the first stage, and the motion model of the first stage, including: the motion state of the multi-rotor UAV in the first stage changes from a uniform horizontal flight state to a ballistic descent state, and the ballistic descent state motion model is constructed as follows:

[0009]

[0010] in, represents the horizontal motion speed in the first stage, C d,u Represents the air resistance coefficient of the drone body, S u represents the effective windward area of ​​the drone body, m is the mass of the drone, and v 0 is the initial speed of the drone in the first stage, ρ is the air density, t is the time, It represents the vertical motion speed in the first stage, and g is the acceleration due to gravity.

[0011] Optionally, the UAV is a fixed-wing UAV, and the vertical and horizontal movement speeds of the UAV in the first stage are determined according to the initial speed of the UAV in the first stage, the duration of the first stage, and the motion model of the first stage, including: the vertical and horizontal movement speeds of the fixed-wing UAV performing gliding flight in the first stage are as follows:

[0012]

[0013] in, represents the horizontal speed of the fixed-wing UAV in the first stage, m is the mass of the UAV, and v 0 is the initial speed of the drone in the first stage, C d,u Represents the air resistance coefficient of the drone body, S u represents the effective windward area of ​​the drone body, ρ is the air density, t is the time, It represents the vertical speed of the fixed-wing UAV in the first stage, and g is the acceleration due to gravity.

[0014] Optionally, the vertical and horizontal movement speeds of the second stage are determined according to the flight speed of the first stage and the motion model of the second stage, including: the second stage is a parachute descent state, and the drone and the parachute are regarded as an ideal motion model as a whole:

[0015]

[0016] in, represents the horizontal movement speed in the second stage, represents the vertical movement speed in the second stage, and Respectively represent t 1 The instantaneous speed of the drone in the horizontal and vertical directions at time t, m is the mass of the drone, ρ is the air density, t is the time, and t 1 represents the end time of the first stage, C d,p The air resistance coefficient of the parachute as a whole, S p It represents the effective windward area of ​​the whole parachute, and g is the acceleration due to gravity.

[0017] Optionally, the protective effect on the ground population is determined based on the urban surface characteristics in each grid cell to obtain a first mitigation matrix, including: determining the shielding parameters of each grid cell based on the proportion of the area occupied by different surface characteristics in each grid cell and the shielding parameters of different surface characteristics; determining the mortality rate of drone impacts on humans in each grid cell based on the shielding parameters of each grid cell and the kinetic energy of the drone impact in each grid cell; and constructing the first mitigation matrix based on the mortality rate of drone impacts on humans in each grid cell.

[0018] Optionally, the inherent ground risk matrix of the drone in each grid cell is determined based on the characteristic parameters of the drone and the density of ground personnel, including: determining the impact distance when the drone hits the ground based on the horizontal speed and vertical speed of the drone in each grid cell; determining the casualty area caused by the drone hitting the ground in each grid cell based on the impact distance when the drone hits the ground; determining the fatality rate curve of the drone hitting humans in each grid cell based on the kinetic energy of the drone hitting in each grid cell; determining the expected casualties caused by the crash of the drone in each grid cell based on the casualty area caused by the drone hitting in each grid cell, the fatality rate curve of the drone hitting humans and the density of ground personnel in the grid cell; and constructing the inherent ground risk matrix of the drone to the ground population based on the expected casualties caused by the crash of the drone in each grid cell.

[0019] Optionally, based on the casualty area caused by the drone collision in each grid cell, the collision human fatality rate curve, and the ground personnel density of the grid cell, the expected casualties caused by the drone crash in each grid cell are determined, including:

[0020] E C,adj =D p (i,j)·A c,b ·P f

[0021] Among them, E C,adj represents the expected casualties caused by a drone crash, D p (i,j) represents the ground personnel density of grid cell (i,j), A c,b represents the casualty area of ​​the drone crash, P f is the fatality rate of drone strikes on humans, A c,b =2(r p +r u )d b +π(r p +r u ) 2 ; r p represents the average radius of a person, r u Denotes the average radius of the largest characteristic dimension of the UAV, d b Indicates the distance of the impact speed of the drone when it hits the ground on the casualty area. and They represent the horizontal and vertical velocities of the drone at the time of impact, h p The average height of a person. When calculating the inherent ground risk, only the fatality rate of 0 or 1 is considered. The parameter β is the energy threshold required for human fatality, E crash is the kinetic energy of the drone when it hits, m is the mass of the drone, v cis the instantaneous speed of the drone when it hits;

[0022] The inherent ground risk matrix R of drones to the ground population is constructed based on the expected casualties caused by drone crashes in each grid cell. i , let R i (i,j)=E C,adj ,include:

[0023]

[0024] Optionally, determining a second mitigation matrix for each grid cell according to the ground casualty area and impact kinetic energy after the parachute is installed and the pre-calculated ground casualty area and impact kinetic energy after the parachute is not installed includes:

[0025]

[0026] Among them, M p (i,j) is the second mitigation matrix of the risk grid, A c,b and A c,p They represent the casualty impact area of ​​the drone without parachute descent model and the casualty impact area of ​​the drone with parachute descent model installed, and P f,b and P f,p Respectively represent the fatality rates of drone crashes under the two models.

[0027] Optionally, the first mitigation matrix and the second mitigation matrix are used to construct a ground risk mitigation matrix, including:

[0028]

[0029] Where M(i,j) represents the ground risk mitigation matrix, E crash,p With E crash,b are the impact kinetic energy of the drone in the parachute descent model and the non-parachute descent model, M s (i,j) represents the first mitigation matrix, M p (i, j) represents the second mitigation matrix, and η represents the success rate of UAV parachute opening.

[0030] Optionally, the Hadamard product of the inherent ground risk matrix and the ground risk mitigation matrix is ​​used to obtain a final ground risk matrix, including:

[0031] R f =R i ⊙M;

[0032] Among them, R f represents the final UAV ground risk matrix, R i represents the inherent ground risk matrix, M represents the ground risk mitigation matrix;

[0033] Based on the final ground risk matrix, a static ground risk map of the drone is constructed, including:

[0034] According to the coordinate conversion algorithm, the final ground risk matrix of the UAV is converted to generate a UAV ground risk map corresponding to the geographic grid;

[0035] The coordinate transformation algorithm is as follows:

[0036] R map (x,y)=R f (i,j);

[0037] Among them, R map (x, y) is the drone-to-ground risk map corresponding to the geographic grid, R f (i,j) is the final ground risk matrix of the UAV.

[0038] The present invention proposes a method for constructing a UAV ground risk map based on a grid risk matrix. Based on the urban population density data and taking the grid unit as the basic unit, the inherent ground risk of the UAV is calculated from the perspective of evaluating the impact effect of the ground population with the UAV. Secondly, based on the three-dimensional geographic information data of the city, the protective effect of different surface features of the city on the ground population and the falling process of the UAV under protective measures are analyzed to evaluate the effect of the UAV ground risk mitigation measures. Finally, through the inherent ground risk matrix and risk mitigation matrix of the UAV, the effect of each influencing factor on the risk during the failure of the UAV is modularly characterized, and the effect of the UAV ground risk mitigation measures is evaluated, providing a scientific basis for the formulation of risk control measures. Combined with the airspace structure and airspace attributes, a ground risk map is generated, and the UAV ground risk is comprehensively considered from multiple angles, which improves the accuracy and reliability of risk assessment. It provides theoretical support for the development of the urban UAV industry, while improving the safety and efficiency of UAV flight, and enables researchers and practitioners to more clearly recognize the relationship between UAV ground risk factors and mitigation measures, and promote the safe application and sustainable development of UAV technology in urban management.

[0039] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art may be taught from the practice of the present invention. The objectives and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0041] Figure 1A specific example flow chart of a method for constructing a UAV-to-ground risk map based on a grid risk matrix in the present invention;

[0042] Figure 2 A coordinate relationship diagram of the ground risk map and the ground risk matrix in the present invention;

[0043] Figure 3 This is the airspace structure diagram of a certain district in Shenzhen City in the present invention;

[0044] Figure 4 It is a schematic diagram of the analysis of the falling process of the multi-rotor UAV after failure in the present invention;

[0045] Figure 5 This is a schematic diagram of the analysis of the falling process of the fixed-wing UAV after failure in the present invention;

[0046] Figure 6 It is a schematic diagram of the final ground risk matrix calculation process in the present invention. DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of 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.

[0048] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0050] The embodiment of the present invention provides a method for constructing a UAV-to-ground risk map based on a grid risk matrix. Figure 1 As shown, including:

[0051] S101, dividing the urban area into multiple grid cells, and obtaining characteristic parameters of drones, ground personnel density, and urban surface characteristics;

[0052] S103, determining the inherent ground risk matrix of the UAV in each grid cell according to the characteristic parameters of the UAV and the density of ground personnel;

[0053] S105, determining the protection effect on the ground population according to the urban surface characteristics in each grid unit, and obtaining a first mitigation matrix;

[0054] S107, determining the mitigation degree of the drone hitting the ground in each grid unit according to the drone failure protection measures, and obtaining a second mitigation matrix;

[0055] S109, constructing a ground risk mitigation matrix using the first mitigation matrix and the second mitigation matrix;

[0056] S1011, using the Hadamard product of the inherent ground risk matrix and the ground risk mitigation matrix to obtain a final ground risk matrix;

[0057] S1013: construct a UAV static ground risk map based on the final ground risk matrix.

[0058] For example, the urban area is divided into multiple grid cells, and the attributes of each grid cell include crowd density, building distribution, etc. These attributes are quantified and analyzed and used as the basic data for risk assessment. Each cell is usually square, and its risk level represents the level of casualties caused by a drone crash in the area, which can be represented by a risk matrix.

[0059] In this embodiment, a risk matrix of size m×n is defined, and R m×n Indicates that each element R(i,j) in the matrix represents the risk value of the corresponding cell. Figure 2 The coordinate relationship between the ground risk map and the ground risk matrix is ​​shown. For any geographic location (x, y) in the risk map with a range of X×Y, the coordinate system can be simply converted to obtain the coordinate system from the geographic cell R map (x,y) to matrix element R mat (i, j), r represents the resolution of the geographic grid, and the coordinate system conversion method is as follows:

[0060]

[0061] The inherent ground risk matrix of drones in each grid cell is determined based on the characteristic parameters of drones and the density of ground personnel, including: determining the impact distance when the drone hits the ground based on the horizontal speed and vertical speed of the drone at the time of impact in each grid cell; determining the casualty area caused by the drone impact in each grid cell based on the impact distance when the drone hits the ground; determining the fatality rate curve of drone impacts with humans in each grid cell based on the kinetic energy of the drone impact in each grid cell; determining the expected casualties caused by drone crashes in each grid cell based on the casualty area caused by drone impacts in each grid cell, the fatality rate curve of drone impacts with humans and the density of ground personnel in the grid cell; and constructing the inherent ground risk matrix of drones to the ground population based on the expected casualties caused by drone crashes in each grid cell.

[0062] Specifically, the inherent ground risk of UAVs is an inherent attribute of UAV operations and is only related to the characteristic parameters of UAVs (maximum characteristic size, maximum take-off mass, cruising speed) and the density of ground personnel in the crash area. The inherent ground risk matrix of UAVs R i It can be expressed as a formula:

[0063]

[0064] When a drone crosses the ground risk buffer zone and crashes in the ground area, the ground risk assessment of its crash is calculated as follows:

[0065] E C,adj =D popavg,adj ·A c,b ·P f

[0066] In the formula, E C,adj represents the expected casualties caused by a drone crash in an adjacent area, D popavg,adj represents the ground personnel density in the adjacent area, A c,b represents the area of ​​casualties caused by the drone crash, P f It is the fatality rate curve of drone strikes against humans.

[0067]

[0068] Where P s is the ground shielding parameter, and the parameter α is when P s =6, the mortality rate P f =50% of the impact energy required, α=34kJ, parameter β is the energy threshold required for human lethality, generally 34J. crash is the kinetic energy of the UAV at the time of impact, calculated by the formula, and k is the correction factor, which is applicable to the case when the instantaneous kinetic energy of the UAV impact is low and can be calculated by the formula.

[0069]

[0070] Where m is the mass of the drone, v c is the instantaneous speed of the drone when it hits. In the absence of protective mitigation measures and when the ground crowd is fully exposed, the shielding parameter P s →0, the fatality rate of drone collision is P f The magnitude of the impact kinetic energy E crash related.

[0071]

[0072] For any risk unit (i, j) in the risk matrix, use R i (i, j) represents the inherent ground risk of the drone hitting the ground people, then R i (i,j)=E C,adj , we can get the formula:

[0073]

[0074] Among them, D p (i,j) represents the population density of the cell corresponding to position (i,j), A c,b It represents the casualty area caused by the drone collision in the drone descent model without parachute. When the drone loses power in the air, the aircraft is only affected by gravity and resistance and falls in a ballistic mode. This model is a standard second-order resistance model. The following method can be used to calculate A c,b :

[0075] A c,b =2(r p +r u )d b +π(r p +r u ) 2

[0076]

[0077] where r p and h p Represent the average radius and height of a person, r u Represents the average radius of the largest characteristic dimension of the UAV. b It indicates the impact distance when the drone hits the ground. It is inversely proportional to the approach angle when it hits the ground. The horizontal speed of the drone when it hits the ground can be modeled using a ballistic descent model. and vertical speed It means that the terminal motion of the drone hitting the ground can be approximated as a straight line motion.

[0078] After calculating the inherent ground risk matrix, in order to reduce the number of people directly exposed to the risk area, this embodiment analyzes the protective effects of different urban surface features on the ground population based on the three-dimensional airspace structure of the city, evaluates the effectiveness of drone ground risk mitigation measures, and analyzes the protective effects of different urban surface features on the ground population as follows:

[0079] The shielding parameters of each grid cell are determined based on the area ratios of different surface features in each grid cell and the shielding parameters of different surface features. The fatality rate of drone impacts on humans in each grid cell is determined based on the shielding parameters of each grid cell and the kinetic energy of the drone impact in each grid cell. The first mitigation matrix is ​​constructed based on the fatality rate of drone impacts on humans in each grid cell.

[0080] The ground shielding parameter quantifies the risk mitigation effect brought by ground shielding in normal situations. The embodiment of the present invention only considers the protection effect brought by the ground shielding parameter. s Through surface factors such as buildings or trees, corresponding shielding parameters are provided for people in the area. These factors can effectively reduce the impact of the impact kinetic energy on people on the ground and reduce the probability of death.

[0081]

[0082] Where P s Provide corresponding shielding parameters for the people in the area, and the value range can be (0, +∞). In order to facilitate analysis and modeling, the value range of the ground shielding parameters is defined to make it closer to the Feinstein average curve, P s i Represents the shielding parameters of different ground features. For any risk cell (i, j), the cell at the current grid resolution will contain a variety of surface features. S represents the surface projection area of ​​the accessible airspace in the grid. For drones flying at different altitudes, not all airspaces are accessible. Buildings at different heights will affect the use of airspace. Figure 3 This is a diagram of the airspace structure of a district in Shenzhen at an altitude of 30 meters. The gray part in the figure is a group of buildings, which is an airspace that drones cannot reach. In the process of calculating the ground risk, the risk corresponding to this part of the area should be represented as 0. i / S represents the area ratio of different ground features in the grid unit. The shielding parameter of each surface feature in the grid is weighted to obtain the shielding parameter of the grid.

[0083] After solving the shielding parameters, the fatality rate of drone collision with humans in each grid cell is determined according to the shielding parameters of each grid cell and the kinetic energy of the drone collision in each grid cell. The fatality rate of each grid cell is used as the mitigation coefficient of each grid cell. The first mitigation matrix is ​​constructed according to the mitigation coefficient of each grid cell. Specifically:

[0084] M s (i,j)=P f,b ;

[0085] P f,b Represents the human fatality rate in drone crashes without parachutes (i.e. ballistic mode).

[0086] In addition to the above-mentioned measures of analyzing the protective effects of different urban surface features on the ground population and evaluating the effectiveness of drone-to-ground risk mitigation measures, this embodiment also proposes to provide failure protection measures for drones in order to reduce the impact of drones hitting the ground. For example, drones are equipped with parachutes. According to the drone failure protection measures, the mitigation degree of drones hitting the ground in each grid unit is determined. The specific method of obtaining the second mitigation matrix is ​​as follows:

[0087] The process of the drone falling into each grid unit is divided into the first stage and the second stage. The first stage is that the drone loses power and the parachute is not opened. The second stage is that the parachute is opened and the drone enters the parachute descent state; according to the initial speed of the drone in the first stage, the duration of the first stage and the motion model of the first stage, the vertical and horizontal movement speeds of the drone in the first stage are determined; according to the flight speed of the first stage and the motion model of the second stage, the vertical and horizontal movement speeds of the second stage are determined; the vertical and horizontal movement speeds of the first stage are integrated to obtain the horizontal displacement and vertical displacement of the first stage; the vertical and horizontal movement speeds of the second stage are integrated to obtain the horizontal displacement and vertical displacement of the second stage; according to the horizontal displacement and vertical displacement of the first stage and the horizontal displacement and vertical displacement of the second stage, the coordinates of the drone hitting the ground in each grid unit are obtained; according to the horizontal and vertical displacement of the drone at the end of the second stage, the ground casualty area of ​​the impact ground coordinates and the drone impact kinetic energy are determined; according to the ground casualty area and impact kinetic energy after the parachute is installed and the pre-calculated ground casualty area and impact kinetic energy without the parachute installed, the second mitigation matrix of each grid unit is determined.

[0088] Specifically, drones can be divided into multi-rotor drones and fixed-wing drones. For multi-rotor drones, Figure 4 As shown in the figure, the falling process of a multi-rotor drone equipped with a parachute after failure is analyzed. Under ideal conditions, it is subject to gravity mg and air resistance F airdragThe influence of can be divided into two stages. In the figure, v represents the speed direction, t 1 is the opening time of the parachute system, t 2 is the time when the drone hits the ground. In the first stage, the drone loses power and changes from a uniform horizontal flight state to a ballistic descent state, at which time the parachute system does not work; in the second stage, the parachute system opens and the drone enters a parachute descent state. By decomposing the air resistance of the drone into horizontal and vertical directions and analyzing its motion process, we can get the formula:

[0089]

[0090] and represents the air resistance in the horizontal and vertical directions, ρ represents the air density, C drag represents the drag coefficient, S air represents the effective frontal area, v x and v y represents the horizontal and vertical speeds of the drone. In the first stage t∈[0,t 1 ] The initial velocity of the drone is v o , its equation of motion:

[0091]

[0092] Among them, C d,u Represents the air resistance coefficient of the drone body, S u Indicates the effective windward area of ​​the drone body. The horizontal speed of the drone in the first stage and vertical speed The expression is:

[0093]

[0094] In t 1 At this moment, the parachute is fully opened, and the UAV enters the second stage of parachute descent. In this stage, t∈(t 1 ,t 2 ]The drone and the parachute are considered as an ideal motion model. The formula is as follows:

[0095]

[0096] Among them, and Respectively represent t 1 The instantaneous speed of the drone in the horizontal and vertical directions at the moment, C d,p The air resistance coefficient of the parachute as a whole, S p represents the effective windward area of ​​the entire parachute. Get the horizontal displacement x of the impact point on the groundd and vertical displacement y d The expression is:

[0097]

[0098] When the drone falls with a parachute descent model, the terminal motion that hits the ground can be approximated as a straight line motion. The ground casualty area A c,p The influence distance d p According to the impact time t 2 The value is used to calculate, let the UAV flight height h u =|y d |, we can find t 2 .use and Representing the horizontal and vertical velocity components of the drone when it hits the ground in the parachute descent model, the formula is:

[0099]

[0100] For fixed-wing drones, Figure 5 As shown in the figure, the falling process of a fixed-wing drone equipped with a parachute after failure is analyzed. Because the power mode is different from that of a multi-rotor drone, the falling process after losing power is also more complicated than that of a multi-rotor drone. Under ideal conditions, the falling model of a fixed-wing drone is still divided into two stages. 1 ] stage, when the power fails, the fixed-wing drone will glide in the horizontal direction. Indicates the horizontal speed of the fixed-wing UAV in the first stage.

[0101]

[0102] In the vertical direction, during the short period from the failure of the UAV power to the opening of the parachute system, the aircraft attitude is stable, mainly due to the lift provided by the wing, and the increase in air resistance is very small and can be ignored. Its motion process can be expressed as the formula:

[0103]

[0104] In the formula, F lift is the lift force on the fixed-wing UAV, and the calculation formula is as follows:

[0105]

[0106] Among them, C L Indicates the lift coefficient of the drone in the current flight state, S W represents the wing area, which can be calculated by force analysis of the UAV in a stable state.

[0107] use Represents the vertical speed of the fixed-wing UAV in the first stage, and the formula is:

[0108]

[0109] At t∈(t 1 ,t 2 ] stage, the parachute system is fully opened. After a short period of overload, the fixed-wing drone loses most of its horizontal speed and the lift provided by the wings. It is mainly affected by gravity and air resistance. The lift effect in the vertical direction can be ignored. In this stage, the motion process analysis of the fixed-wing drone is similar to that of the multi-rotor drone. The motion process expression of the second stage can be used directly. and And the displacement expressions of the impact point relative to the ground in the two stages are and

[0110]

[0111] Expected casualties E of drones in parachute drop model C,p The expression is as follows:

[0112]

[0113] The drone parachute reduces the impact kinetic energy by reducing the speed of the drone hitting the ground, and also reduces the area of ​​casualties, so use A c,b and A c,p They represent the casualty impact area of ​​the drone without parachute descent model (i.e., ballistic mode) and the casualty impact area of ​​the drone with parachute descent model installed, respectively, and P f,b and P f,p Respectively represent the fatality rate of the drone crash under the two models. For any risk unit (i, j), after obtaining the coordinates of the drone hitting the ground, the ground casualty area and the drone impact kinetic energy after the drone hits the ground after the parachute is installed are determined according to the horizontal and vertical velocities of the drone at the end of the second stage. According to the kinetic energy of the drone impact with the parachute installed, its fatality rate is determined. The calculation method of the fatality rate refers to the fatality rate curve formula of drone impact with humans, which will not be repeated here.

[0114] make:

[0115]

[0116] Taking a multi-rotor drone as an example, using E crash,p With E crash,bThey represent the impact kinetic energy of the drone in the parachute descent model and the non-parachute descent model (i.e., ballistic mode), and E crash,b >E crash,p . When E crash,b When ≤β, M s (i,j)=0, then the inherent ground risk R i (i,j)=0; when E crash,b >β≥E crash,p When M p (i,j)=0, that is, the expected casualties E of the drone in parachute descent mode C,p =0; when E crash,p When ≥β, there is the formula:

[0117]

[0118] The first term in the formula is that the parachute reduces the impact casualty area by reducing the speed of the drone hitting the ground, and the second term is that the parachute reduces the impact fatality rate by reducing the kinetic energy of the drone hitting the ground. According to the formula, we can get E C,p .

[0119] E C,p =R i (i,j)·M p (i,j)·M s (i,j)

[0120] The formula can be understood as the risk mitigation measures for the inherent ground risk R of the drone. i The mitigation effect. Establish the matrix M s and M p , M s It represents the protective effect of different urban surface features on the ground population, that is, the first mitigation matrix; M p It indicates that the UAV provides a failure protection measure, which is the mitigation effect of the UAV parachute, i.e., the second mitigation matrix.

[0121] After solving the first mitigation matrix and the second mitigation matrix, the ground risk mitigation matrix is ​​constructed by modularly analyzing the effect of different risk mitigation measures on the ground risk in the form of a matrix, thereby deriving the final ground risk matrix of the drone, and generating a ground risk map by combining the airspace structure and airspace attributes. The operation risk of drones in urban environments is analyzed from a wide-area perspective. Specifically, the ground risk mitigation matrix is ​​constructed using the first mitigation matrix and the second mitigation matrix, including:

[0122]

[0123] Where M(i,j) represents the ground risk mitigation matrix, E crash,p With Ecrash,b are the impact kinetic energy of the drone in the parachute descent model and the non-parachute descent model (i.e., ballistic mode), respectively. s (i,j) represents the first mitigation matrix, M p (i, j) represents the second mitigation matrix, and η represents the success rate of UAV parachute opening.

[0124] The final drone-to-ground risk matrix R after mitigation measures f Equal to the inherent ground risk matrix R i The Hadamard product of the ground risk mitigation matrix M is:

[0125] R f =R i ⊙M

[0126] After calculating the final ground risk matrix of the UAV, according to the coordinate transformation method, such as Figure 6 As shown, the drone-to-ground risk map R corresponding to the geographic grid can be generated map (x,y)=R f (i,j), where R map (x, y) is the drone-to-ground risk map corresponding to the geographic grid, R f (i,j) is the final ground risk matrix of the UAV.

[0127] The present invention proposes a method for constructing a UAV ground risk map based on a grid risk matrix. Based on the urban population density data and taking the grid unit as the basic unit, the inherent ground risk of the UAV is calculated from the perspective of evaluating the impact effect of the ground population with the UAV. Secondly, based on the three-dimensional geographic information data of the city, the protective effect of different surface features of the city on the ground population and the falling process of the UAV under protective measures are analyzed to evaluate the effect of the UAV ground risk mitigation measures. Finally, through the inherent ground risk matrix and risk mitigation matrix of the UAV, the effect of each influencing factor on the risk during the failure of the UAV is modularly characterized, and the effect of the UAV ground risk mitigation measures is evaluated, providing a scientific basis for the formulation of risk control measures. Combined with the airspace structure and airspace attributes, a ground risk map is generated, and the UAV ground risk is comprehensively considered from multiple angles, which improves the accuracy and reliability of risk assessment. It provides theoretical support for the development of the urban UAV industry, while improving the safety and efficiency of UAV flight, and enables researchers and practitioners to more clearly recognize the relationship between UAV ground risk factors and mitigation measures, and promote the safe application and sustainable development of UAV technology in urban management.

[0128] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for constructing a UAV-to-ground risk map based on a grid risk matrix, characterized in that: include: Divide the urban area into multiple grid cells and obtain the characteristic parameters of drones, ground personnel density and urban surface characteristics; According to the characteristic parameters of the UAV and the density of ground personnel, the inherent ground risk matrix of the UAV in each grid cell is determined; According to the urban surface characteristics in each grid cell, the protection effect on the ground population is determined to obtain the first mitigation matrix; According to the drone failure protection measures, the mitigation degree of the drone hitting the ground in each grid unit is determined to obtain the second mitigation matrix; The first mitigation matrix and the second mitigation matrix are used to construct a ground risk mitigation matrix; The final ground risk matrix is ​​obtained by using the Hadamard product of the inherent ground risk matrix and the ground risk mitigation matrix; Based on the final ground risk matrix, a static ground risk map of the drone is constructed.

2. The method for constructing a UAV-to-ground risk map based on a grid risk matrix according to claim 1, characterized in that: The drone failure protection measure is to install a parachute for the drone. According to the drone failure protection measure, the mitigation degree of the drone hitting the ground in each grid unit is determined, and the second mitigation matrix is ​​obtained, including: The process of the drone falling into each grid unit is divided into the first stage and the second stage. The first stage is when the drone loses power and the parachute is not opened. The second stage is when the parachute is opened and the drone enters the parachute descent state. Determine the vertical and horizontal movement speeds of the UAV in the first stage according to the initial speed of the UAV in the first stage, the duration of the first stage and the movement model of the first stage; Determine the vertical and horizontal movement speeds of the second stage according to the flight speed of the first stage and the movement model of the second stage; Integrate the vertical and horizontal movement speeds of the first stage to obtain the horizontal displacement and vertical displacement of the first stage; Integrate the vertical and horizontal movement speeds of the second stage to obtain the horizontal displacement and vertical displacement of the second stage; According to the horizontal displacement and vertical displacement of the first stage and the horizontal displacement and vertical displacement of the second stage, the coordinates of the drone hitting the ground in each grid cell are obtained; Determine the ground casualty area at the impact ground coordinates and the kinetic energy of the drone impact based on the drone impact horizontal and vertical velocities at the end of the second phase; The second mitigation matrix of each grid cell is determined according to the ground casualty area and impact kinetic energy after the parachute is installed and the pre-calculated ground casualty area and impact kinetic energy after the parachute is not installed.

3. The method for constructing a UAV-to-ground risk map based on a grid risk matrix according to claim 2, characterized in that: The UAV is a multi-rotor UAV. The vertical and horizontal movement speeds of the UAV in the first stage are determined according to the initial speed of the UAV in the first stage, the duration of the first stage, and the motion model of the first stage, including: In the first stage, the motion state of the multi-rotor drone changes from a uniform horizontal flight state to a ballistic descent state. The ballistic descent state motion model is constructed as follows: in, represents the horizontal motion speed in the first stage, C d,u Represents the air resistance coefficient of the drone body, S u represents the effective frontal area of ​​the UAV body, m is the mass of the UAV, v0 is the initial speed of the UAV in the first stage, ρ is the air density, and t is the time; It represents the vertical motion speed in the first stage, and g is the acceleration due to gravity.

4. The method for constructing a UAV-to-ground risk map based on a grid risk matrix according to claim 2, characterized in that: The UAV is a fixed-wing UAV. The vertical and horizontal movement speeds of the UAV in the first stage are determined according to the initial speed of the UAV in the first stage, the duration of the first stage, and the motion model of the first stage, including: The fixed-wing drone glides in the first stage, and its vertical and horizontal movement speeds are as follows: in, represents the horizontal speed of the fixed-wing UAV in the first stage, m is the mass of the UAV, v0 is the initial speed of the UAV in the first stage, C d,u Represents the air resistance coefficient of the drone body, S u represents the effective frontal area of ​​the UAV body, ρ is the air density, and t is the time; It represents the vertical speed of the fixed-wing UAV in the first stage, and g is the acceleration due to gravity.

5. A method for constructing a UAV-to-ground risk map based on a grid risk matrix according to claim 3 or 4, characterized in that: According to the flight speed of the first stage and the motion model of the second stage, the vertical and horizontal motion speeds of the second stage are determined, including: The second stage is the parachute descent state, where the drone and the parachute are considered as an ideal motion model: in, represents the horizontal movement speed in the second stage, represents the vertical movement speed in the second stage, and They represent the instantaneous speed of the drone in the horizontal and vertical directions at time t1, m is the mass of the drone, ρ is the air density, t is the time, t1 represents the end time of the first stage, C d,p The air resistance coefficient of the parachute as a whole, S p It represents the effective windward area of ​​the whole parachute, and g is the acceleration due to gravity.

6. A method for constructing a UAV-to-ground risk map based on a grid risk matrix according to claim 1 or 2, characterized in that: According to the urban surface characteristics in each grid cell, the protection effect on the ground population is determined, and the first mitigation matrix is ​​obtained, including: Determine the shielding parameters of each grid cell according to the area ratios of different surface features in each grid cell and the shielding parameters of different surface features; Determine the fatality rate of drone impact on humans in each grid cell based on the shielding parameters of each grid cell and the kinetic energy of the drone impact in each grid cell; The first mitigation matrix is ​​constructed based on the fatality rate of drone collisions with humans in each grid cell.

7. The method for constructing a UAV-to-ground risk map based on a grid risk matrix according to claim 1, characterized in that: According to the characteristic parameters of the drone and the density of ground personnel, the inherent ground risk matrix of the drone in each grid cell is determined, including: The impact distance when the drone hits the ground is determined based on the horizontal speed and vertical speed of the drone at the time of impact in each grid cell; Determine the casualty area caused by the drone impact in each grid cell based on the impact distance when the drone hits the ground; According to the kinetic energy of the drone hitting in each grid cell, determine the fatality rate curve of the drone hitting humans in each grid cell; Determine the expected casualties caused by drone crashes in each grid cell based on the casualty area caused by drone crashes, the human fatality curve caused by impacts, and the ground personnel density of the grid cell; The inherent ground risk matrix of drones to people on the ground is constructed based on the expected casualties caused by drone crashes in each grid cell.

8. The method for constructing a UAV-to-ground risk map based on a grid risk matrix according to claim 7, characterized in that: Based on the casualty area caused by drone collision in each grid cell, the human fatality rate curve of collision, and the ground personnel density of the grid cell, the expected casualties caused by drone crash in each grid cell are determined, including: E C,adj =D p (i,j)·A c,b ·P f Among them, E C,adj represents the expected casualties caused by a drone crash, D p (i,j) represents the ground personnel density of grid cell (i,j), A c,b represents the casualty area of ​​the drone crash, P f is the fatality rate of drone strikes on humans, A c,b =2(r p +r u )d b +π(r p +r u ) 2 ; r p represents the average radius of a person, r u Denotes the average radius of the largest characteristic dimension of the UAV, d b Indicates the distance of the impact speed of the drone when it hits the ground on the casualty area. and They represent the horizontal and vertical velocities of the drone at the time of impact, h p The average height of a person. When calculating the inherent ground risk, only the fatality rate of 0 or 1 is considered. The parameter β is the energy threshold required for human fatality, E crash is the kinetic energy of the drone when it hits, m is the mass of the drone, v c is the instantaneous speed of the drone when it hits; The inherent ground risk matrix R of drones to the ground population is constructed based on the expected casualties caused by drone crashes in each grid cell. i , let R i (i,j)=E C,adj ,include:

9. The method for constructing a UAV-to-ground risk map based on a grid risk matrix according to claim 2, characterized in that: The second mitigation matrix of each grid cell is determined based on the ground casualty area and impact kinetic energy after the parachute is installed and the pre-calculated ground casualty area and impact kinetic energy without the parachute installed, including: Among them, M p (i,j) is the second mitigation matrix of the risk grid, A c,b and A c,p They represent the casualty impact area of ​​the drone without parachute descent model and the casualty impact area of ​​the drone with parachute descent model installed, and P f,b and P f,p Respectively represent the fatality rates of drone crashes under the two models.

10. The method for constructing a UAV-to-ground risk map based on a grid risk matrix according to claim 9, characterized in that: The first mitigation matrix and the second mitigation matrix are used to construct a ground risk mitigation matrix, including: Where M(i,j) represents the ground risk mitigation matrix, E crash,p With E crash,b are the impact kinetic energy of the drone in the parachute descent model and the non-parachute descent model, M s (i,j) represents the first mitigation matrix, M p (i, j) represents the second mitigation matrix, and η represents the success rate of UAV parachute opening.

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