Cross-medium navigation body motion stability assessment method based on dynamic pressure center offset

Abstract

The invention discloses a method for evaluating the motion stability of a cross-medium navigation body based on dynamic pressure center offset. Real-time characterization and stability evaluation of the dynamic offset of the pressure center in the cross-medium process of the navigation body are achieved. Comprising the steps of 1, arranging a pressure sensor on the surface of a navigation body, and establishing pressure distribution on the surface of the navigation body according to the sensor position and a measurement value; 2, carrying out high-precision discretization on the surface pressure of the navigation body, and calculating the pressure of each surface element; and step 3, summing the forces and moments of all the surface elements to obtain a total force and a total moment. And 4, solving the position of the pressure center through moment balance, updating pressure distribution at each time step, and dynamically calculating the change of the pressure center. And 5, evaluating the motion stability of the navigation body according to the offset of the dynamic pressure center relative to the center of mass of the navigation body. According to the invention, the motion stability of the navigation body can be evaluated in real time in a complex fluid environment in a cross-medium process.

Description

Technical Field

[0001] The present invention relates to the field of fluid dynamics and motion stability analysis of cross-media vehicles, and in particular to a method for evaluating the motion stability of cross-media vehicles based on the dynamic characteristics of real-time pressure center offset. Background Art

[0002] Water entry stability is a key factor in determining whether a vehicle can normally perform subsequent tasks such as precision guidance, target strike, or data acquisition. However, the vehicle faces a complex fluid environment during the gas-liquid cross-medium motion process, where cavitation evolution and sudden changes in medium density cause the pressure center position to exhibit significant time-varying characteristics. Traditional motion stability research has mostly focused on a single medium environment, using static stability margin to describe the vehicle's motion stability. This makes it difficult to accurately characterize the unsteady effects of the dynamic flow field evolution on the vehicle's motion during the cross-medium process, and is prone to misjudgment.

[0003] Compared to traditional static stability analysis methods, dynamic stability assessment methods can accurately capture the impact of transient changes in unsteady flow fields on the mechanical and motion characteristics of a vehicle during cross-medium flow. However, using CFD methods to calculate dynamic stability requires high computing resources and efficiency, making it difficult to meet the needs of real-time stability assessment. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for evaluating the motion stability of a cross-medium vehicle based on the dynamic pressure center offset, which can realize real-time characterization of the dynamic offset of the pressure center and motion stability evaluation during the cross-medium process.

[0005] The technical solutions for achieving the purpose of the present invention are:

[0006] A method for evaluating the motion stability of a cross-medium vehicle based on the dynamic pressure center offset, including pitch stability and yaw stability evaluation,

[0007] The pitch stability is:

[0008] The yaw stability is:

[0009] in

[0010]

[0011] M x =y·F z -z·F y , M y =z·F x -x·F z , M z =x·Fy -y·F x

[0012] x CP1 and x CP2 Denotes the center of pressure in pitch and yaw directions, x CG is the center of gravity of the vehicle, L is the length of the vehicle, R is the maximum radius of the vehicle, is the total moment M acting on the vehicle total The components in the x, y, and z directions, is the total force F acting on the vehicle total Components in the x, y, and z directions, M x 、M y 、M z is the component of the torque on each element of the navigation body in the x, y, and z axes, F x 、F y 、F z The components of the force F on each surface element on the vehicle on the x, y, and z axes; the surface element includes: a multi-layer annular array is set on the vehicle, and each layer of the annular array has multiple sensors evenly distributed circumferentially, each sensor corresponds to a main surface element, and two new sub-surface elements are inserted in the two main surface elements.

[0013] Compared with the prior art, the present invention has the following significant advantages:

[0014] (1) The present invention uses pressure sensors distributed in an annular array to establish the pressure distribution on the surface of the vehicle under a complex flow field environment. It can respond in real time to the force changes with strong nonlinear and time-varying characteristics during the vehicle's crossing of the medium, and is suitable for unsteady complex flows.

[0015] (2) By real-time monitoring of the dynamic parameters of the pressure center offset and its rate of change, the transient flow field characteristics of the vehicle during the process of crossing the medium can be accurately captured, and the dynamic evaluation of the vehicle's stability when entering the water across the medium can be realized, providing a scientific basis for the dynamic stability evaluation of the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Flowchart for the implementation of the present invention.

[0017] Figure 2 Schematic diagram of the distribution of pressure sensors on the surface of the vehicle. DETAILED DESCRIPTION

[0018] The implementation process of the present invention is as follows Figure 1 As shown in the figure, by arranging a pressure sensor array on the surface of the vehicle to measure the pressure distribution in real time, the total force and torque are solved after high-precision discrete calculation of the force on each surface element, the position change of the pressure center is dynamically tracked, and finally the motion stability of the vehicle is evaluated by the relative offset between the pressure center and the center of mass.

[0019] Step 1: Arrange a high-precision pressure sensor array on the outer surface of the trans-medium vehicle. The sensor sampling frequency should be no less than 1 kHz to ensure accurate capture of dynamic pressure changes. The sensors are numbered according to the axial and circumferential directions of the vehicle: 1-8 along the axial direction from head to tail, and evenly distributed around the circumference. A schematic diagram of the pressure sensor layout is shown in Figure 2. The specific layout is as follows: three layers of annular arrays are set at the bow, three layers at the tail, and two layers in the middle. Each layer of annular array contains eight piezoresistive sensors evenly distributed around the circumference.

[0020] Establish a body coordinate system with its origin o at the center of the body's head. The ox axis coincides with the body's axis and points to the body's tail. The oy axis lies within the body's longitudinal symmetry plane and is perpendicular to the ox axis. Determine the oz axis using the right-hand screw rule. Calculate the sensor positions and express them in the body coordinate system. Number the sensors, such as P. i,j is the jth sensor S in the i-th section i,j Each sensor corresponds to a main surface element. According to the real-time measurement data of the sensor, the main surface element is assigned a corresponding pressure value, thereby establishing a pressure distribution model on the surface of the vehicle.

[0021] Step 2: To improve the accuracy of pressure distribution calculations, an adaptive bin subdivision strategy is employed. When the pressure difference between two adjacent sensors exceeds a preset threshold, the main bin is subdivided. Two new subbins are inserted between the two main bins. Pressure values ​​are assigned to the new subbins using piecewise cubic Hermite interpolation, and the subbin coordinates and pressure data are recorded simultaneously. This process ensures higher computational resolution in areas with large pressure gradients, thereby improving the accuracy of the overall pressure distribution.

[0022] Adjacent sensor S i,j and S i,j+1 The angular coordinates of the circles on the same section are θ i,j and θ i,j+1 , the pressure values ​​are P i,j and P i,j+1 When the pressure difference between two adjacent sensors exceeds the preset threshold,

[0023] ΔP=|P i,j+1 0P i,j |>0.3·max{P i,j ,P i,j+1}

[0024] Insert two evenly distributed sub-surface elements into the two main surface elements. The central angular coordinates of the two sub-surface elements are

[0025]

[0026] Then the piecewise cubic Hermite interpolation method is used to assign the pressure value to the new sub-surface element. The use of piecewise cubic Hermite interpolation method requires the insertion of subsurface angle θ i,j and θ i,j+1 Perform normalization processing to obtain normalized parameters t1 and t2, and the calculation formula is:

[0027]

[0028] The basis function is calculated using the normalized parameters t1 and t2. The Hermite basis function expression is:

[0029]

[0030] Where k = 1, 2, t1 and t2 represent the normalized parameters of the first and second inserted subsurface elements. 00 (t k ), h 01 (t k ), h 10 (t k ), h 11 (t k ) is used to smoothly combine the function value and the derivative value to construct a piecewise cubic interpolation polynomial, h 00 (t k ) and h 01 (t k ) directly controls the transition of endpoint function values ​​to ensure that the interpolation passes through known points, h 10 (t k ) and h 11 (t k ) The shape of the curve is adjusted by the derivative to avoid unphysical oscillations. In this case, the Hermite basis function has no practical meaning.

[0031] Since the pressure changes with the angle, the pressure gradient in the angle direction needs to be calculated, m i,j and m' i,j is the slope and pressure gradient in the angular direction at the jth sensor in the i-th section, and the calculation formula is:

[0032]

[0033] The subsurface pressure is obtained from this The interpolation formula is:

[0034]

[0035] Step 3: After the pressure distribution of each element is determined, calculate the normal force component of each element. The calculation formula of the normal force is

[0036] F=-P·A·n

[0037] Where P is the pressure of a single surface element, which is obtained directly from the sensor or through the interpolation formula A is the area corresponding to a single surface element, the area size is the effective area of ​​the pressure sensor, and n is the normal vector of the corresponding surface element, pointing to the direction of the fluid. Projecting the normal vector in the missile coordinate system, the component F of the force acting on a single surface element can be obtained. x 、F y 、F z The specific calculation formula is

[0038] F x =-P·A·n x

[0039] F y =-P·A·n y

[0040] F z =-P·A·n z

[0041] Among them, n x 、n y 、n z Represents the projection of the normal vector n in the x, y, and z directions of the missile body coordinate system. Further, calculate the components M of the torque on the x, y, and z axes of a single surface element. x 、M y 、M z The specific calculation formula is

[0042] M x =y·F z -z·F y

[0043] M y =z·F x -x·F z

[0044] M z =x·F y -y·F x

[0045] The total force F acting on the vehicle is obtained by vector summing the force and torque components of all individual surface elements. total and total moment M total , and the total force F total Components in the x, y, and z directions and total moment M total Components in the x, y, and z directions The specific calculation formula is:

[0046]

[0047] Step 4: Dynamically solve the position of the center of pressure using the moment balance equation. Since the fluid has little effect on the rolling motion, the rolling moment can be approximated to zero, so the focus is on the effects of the pitch and yaw moments on the center of pressure. CP1 and x CP2 Denotes the pressure center in the pitch and yaw directions respectively. Calculate the longitudinal moment balance in the missile body coordinate system and solve for the position of the pressure center x CP1 , and then combine the lateral moment balance to solve the position of the pressure center x CP2 The calculation formula for the pressure center is

[0048]

[0049] The pressure distribution is updated after each time step and the position of the pressure center is recalculated to obtain a dynamically changing pressure center trajectory.

[0050] Step 5: Finally, the motion stability is evaluated based on the dynamic offset of the pressure center relative to the center of mass of the navigation body and its changing trend. Indicates that L is the length of the vehicle, x CG is the center of gravity of the vehicle. CP1 When it is a negative value, the vehicle is in an unstable state; when 0≤Δx CP1 When Δx<3%, the pitch stability of the vehicle is poor; when 3%≤Δx CP1 When ≤15%, there is good pitch stability. R is the maximum radius of the navigation body. CP2 ≤15%, with good yaw stability; when Δx CP2 >15%, yaw stability is poor.

[0051] Obviously, the above embodiments of the present invention are only examples to clearly illustrate the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for evaluating the stability of a cross-medium vehicle motion based on the dynamic pressure center offset, characterized in that: Including pitch stability and yaw stability assessment, The pitch stability is: The yaw stability is: in M x =y·F z -z·F y ,M y =z·F x -x·F z ,M z =x·F y -y·F x x CP1 and x CP2 Denotes the center of pressure in pitch and yaw directions, x CG is the center of gravity of the vehicle, L is the length of the vehicle, R is the maximum radius of the vehicle, is the total moment M acting on the vehicle total The components in the x, y, and z directions, is the total force F acting on the vehicle total Components in the x, y, and z directions, M x 、M y 、M z is the component of the torque on each element of the navigation body in the x, y, and z axes, F x 、F y 、F z The components of the force F on each surface element on the vehicle on the x, y, and z axes; the surface element includes: a multi-layer annular array is set on the vehicle, and each layer of the annular array has multiple sensors evenly distributed circumferentially, each sensor corresponds to a main surface element, and two new sub-surface elements are inserted in the two main surface elements.

2. The method for evaluating the stability of a cross-medium vehicle motion based on the dynamic pressure center offset according to claim 1 is characterized in that: Force F is the normal force of each surface element: F=-P·A·n Where P is the pressure of a single surface element, which is obtained directly by the sensor or through the interpolation formula, A is the area corresponding to a single surface element, and n is the normal vector of the corresponding surface element.

3. The method for evaluating the stability of a cross-medium vehicle motion based on the dynamic pressure center offset according to claim 2 is characterized in that: The interpolation formula is: in, is the subsurface pressure, h 00 (t k ), h 01 (t k ), h 10 (t k ), h 11 (t k ) is the Hermite basis function, P i,j is the pressure measured by the jth sensor on the i-th section of the vehicle, θ i,j is the angular coordinate of the jth sensor on the i-th section of the vehicle, m i,j and m' i,j is the slope and pressure gradient in the angular direction at the jth sensor in the i-th section.

4. The method for evaluating the stability of a cross-medium vehicle motion based on the dynamic pressure center offset according to claim 3 is characterized in that: The Hermite basis function expression is: Where k = 1, 2, and are the central angle coordinates of the two sub-surface elements, and t1 and t2 represent the normalized parameters of the two sub-surface elements.

5. The method for evaluating the stability of a cross-medium vehicle motion based on the dynamic pressure center offset according to claim 4 is characterized in that: The angular coordinates of the two subsurface centers are:

6. The method for evaluating the stability of a cross-medium vehicle motion based on the dynamic pressure center offset according to claim 1 is characterized in that: When the pressure difference between two adjacent sensors exceeds the preset threshold, ΔP>0.3·max{P i,j ,P i,j+1 } Insert two evenly distributed sub-surfaces into the two main surface elements; P i,j is the pressure measured by the jth sensor at the i-th section of the vehicle.

7. The method for evaluating the stability of a cross-medium vehicle motion based on the dynamic pressure center offset according to claim 1 is characterized in that: Several layers of annular arrays are arranged at the head, tail and middle of the vehicle.

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