A method for constructing a ship pressure field model in shallow water waves and a target determination method

Abstract

The present invention provides a method for constructing a ship pressure field model in shallow water waves and a target determination method. The method uses ideal incompressible fluid theory to establish the continuity equation and momentum equation satisfied by the ship in the geodetic coordinate system. Based on the shallow water assumption, a depth-averaged perturbation velocity potential is introduced. Combined with the bottom boundary conditions and the free surface boundary conditions, a flow field control equation expressed by the depth-averaged perturbation velocity potential is constructed. The wave source term within the domain is set according to the wave environment, and the moving pressure term is set according to the ship type. The wave source term within the domain and the moving pressure term are substituted into the flow field control equation to simulate the effect of the surface ship disturbance in the wave environment, thereby obtaining the ship pressure field control equation. Based on the ship pressure field control equation, the ship pressure field model is constructed in combination with the initial and boundary conditions of the flow field, as well as the relationship between the flow field pressure and velocity potential. The model is adapted to rapidly calculate the pressure field under different environments, thereby improving the prediction efficiency of the ship pressure field signal.

Description

Technical Field

[0001] The present invention relates to the technical field of ship target physical field characteristic identification, and in particular to a ship pressure field model construction method and a target determination method in shallow water waves. Background Art

[0002] The pressure changes in the flow field caused by a ship's navigation are called the ship's pressure field. Using this pressure field signal to identify targets is a research hotspot in target recognition technology. With the rapid development of the shipbuilding industry and the increasing demand for ship optimization, accurate modeling of the ship's pressure field and determination of target performance have become important technical means in the ship design and optimization process. Pressure field models simulate the pressure distribution generated by the interaction between the fluid and the hull during navigation through computational fluid dynamics methods or experimental testing. An efficient and accurate method for constructing a ship's pressure field model can not only reduce design cycles and testing costs, but also significantly improve the accuracy of ship target identification.

[0003] Existing research on ship pressure fields in shallow waters is typically conducted using commercial software platforms. Some studies based on potential flow theory for rapid algorithms and identification of ship pressure fields are primarily focused on ship pressure fields in still water, without considering the presence of waves and ripples in shallow waters. Meanwhile, some studies have explored wave-object interactions based on shallow water wave theory, but these studies are primarily based on floating ships operating at zero speed, without considering the speed of objects. However, ships sailing in shallow waters, such as shallow seas and nearshore areas, inevitably encounter waves. Compared to simple hull motion in still waters, studying ship pressure fields in wave environments is more complex, requiring consideration of both shallow water wave motion simulation technology and coupled flow field modeling technology under different encounter conditions between shallow water waves and moving ships. Therefore, constructing a ship pressure field model for shallow waters, taking into account the effects of both regular and random waves, is a pressing technical issue that needs to be addressed. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for constructing a ship pressure field model in shallow water waves, comprising the following steps:

[0005] Step S11: Using the ideal incompressible fluid theory, the continuity equation and momentum equation satisfied by the ship's navigation are established in the geodetic coordinate system. Based on the shallow water assumption, the depth-averaged perturbation velocity potential is introduced. Combined with the bottom boundary conditions and the free surface boundary conditions, the flow field control equation expressed by the depth-averaged perturbation velocity potential is constructed;

[0006] Step S12: setting a wave source term within the domain according to the wave environment; setting a moving pressure term according to the ship type; substituting the wave source term within the domain and the moving pressure term into the flow field control equation to simulate the effect of the surface hull disturbance in the wave environment, and obtaining the ship pressure field control equation;

[0007] Step S13: Based on the ship pressure field control equation, combined with the initial conditions and boundary conditions of the flow field, and the relationship between the flow field pressure and velocity potential, a ship pressure field model is constructed.

[0008] Preferably, the flow field control equation in step S11 is expressed as:

[0009] ;

[0010] ;

[0011] ;

[0012] Where, is the wave height, express About time Derivative; For water depth; , is the spatial variable along the direction of hull motion; is the spatial variable along the width of the ship; Parameters that represent improved dispersion performance; is the velocity potential averaged along the depth; express About time Derivative; is the acceleration due to gravity; is the ship-wave combined source term; represents the wave source term in the domain; The moving pressure term represents the hull motion.

[0013] Preferably, the expression of the ship pressure field control equation in step S12 is:

[0014] ;

[0015] Where, express About time Find the derivative twice; express About time Find the derivative.

[0016] Preferably, the wave source term in the domain The expression is:

[0017] ;

[0018] ;

[0019] ;

[0020] ;

[0021] Where, Indicates the number of constituent waves; is the horizontal coordinate of the center of the wave source; is the direction of wave propagation; Indicates the The circular frequencies of the constituent waves; Indicates the characteristics of a wave; is the wavelength; is a constant; Indicates the The wave number of each component wave; Indicates the The random initial phases of the constituent waves; For the wave spectrum.

[0022] Preferably, the ship type in step S12 includes a slender ship type and a wide-body ship type.

[0023] Preferably, when the ship is a slender ship, the moving pressure item The expression is:

[0024] ;

[0025] Where, The draft of the center of the ship; is the longitudinal shape parameter of the ship; for The center position of the ship at the moment; and are the length and width of the ship model respectively; 、 are the transverse shape parameters at the bow and stern, respectively.

[0026] Preferably, when the ship is a wide-body ship, the moving pressure item The expression is:

[0027] ;

[0028] Where, The draft of the center of the ship; is the longitudinal shape parameter of the ship; and are the length and width of the ship model respectively; is the ship's transverse shape parameter.

[0029] The present invention also provides a method for determining a ship target in shallow water waves, which is implemented based on the ship pressure field model constructed by the above-mentioned ship pressure field model construction method, and is characterized in that it includes the following steps:

[0030] Step S21: using the finite difference method to discretize the ship pressure field model in space and time to establish a numerical model;

[0031] Step S22: Based on the numerical model, obtain spatial distribution diagrams of the ship pressure field in shallow water without waves and in shallow water with waves by simulation, and process and obtain longitudinal pressure curves;

[0032] Step S23: Analyze the spatial distribution diagram to obtain the transverse position of the ship; analyze the negative peak of the longitudinal pressure curve to obtain the longitudinal position of the ship.

[0033] Preferably, the passing time of the ship is determined by the following steps: obtaining a pressure fluctuation signal at a specified underwater point, drawing a pressure signal curve, and the moment when the pressure signal curve has a negative peak is the time when the ship appears.

[0034] Preferably, when the ship's speed is at a subcritical speed, the transverse position and longitudinal position located in step S23 correspond to the middle of the hull; when the ship's speed is at a supercritical speed, the transverse position and longitudinal position located in step S23 correspond to the stern of the hull.

[0035] The beneficial effects of the present invention include at least the following: by establishing a control equation for the ship pressure field in shallow water waves including a ship-wave combined source term, the present invention effectively separates wave interference and hull disturbance signals, adapts to rapid calculation of pressure fields in different environments, and significantly improves the prediction efficiency of ship pressure field signals in complex shallow water environments; at the same time, based on the spatial distribution characteristics of the pressure field, such as the symmetry of the negative pressure peak and the mutation characteristics of the time domain signal, it can quickly and flexibly determine the target position and passing time of the hull, providing a high-precision determination basis for ship target position identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of a method flow in an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of a ship sailing into waves according to an embodiment of the present invention;

[0038] Figure 3 Schematic diagram of the spatial distribution of the pressure field of a ship in shallow water without waves according to Example 3 of the present invention;

[0039] Figure 4Schematic diagram of the spatial distribution of the pressure field of a ship in shallow water with waves according to Example 3 of the present invention;

[0040] Figure 5 In the shallow water without waves of embodiment 3 of the present invention = 0 at which the pressure passes longitudinally through the curve;

[0041] Figure 6 In the embodiment 3 of the present invention, there are waves in shallow water = 0 at which the pressure passes longitudinally through the curve;

[0042] Figure 7 This is a schematic diagram of a ship navigation according to Example 4 of the present invention;

[0043] Figure 8 In the wave environment of embodiment 4 of the present invention Pressure coefficient at point over time 's change curve. DETAILED DESCRIPTION

[0044] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, 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. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0045] Example 1

[0046] like Figure 1 As shown, an embodiment of the present invention provides a method for constructing a ship pressure field model in shallow water waves, comprising the following steps:

[0047] Step S11: Adopting the theory of ideal incompressible fluid, the continuity equation and momentum equation satisfied by the ship navigation are established in the geodetic coordinate system, and based on the shallow water assumption, the perturbation velocity potential averaged along the depth is introduced. Combined with the bottom boundary conditions and the free surface boundary conditions, the flow field control equation represented by the perturbation velocity potential averaged along the depth is constructed.

[0048] Specifically, the ship moves at a constant speed Sailing against the waves, Figure 2 As shown, establish the geodetic rectangular coordinate system ,in, The plane coincides with the longitudinal mid-section of the hull. The positive direction points to the direction of the ship's motion. The direction points to the water bank, The axis is vertically upward.

[0049] When the water depth is less than or equal to 0.3 times the length of the ship, , which can be regarded as shallow water. Based on the assumption of ideal incompressible fluid, the continuity equation and momentum equation satisfied by the ship in shallow water are established, and the horizontal velocity averaged along the depth is introduced according to the shallow water assumption. Combined with the boundary conditions such as the bottom and free surface, the dimensional form control equation satisfied by the horizontal velocity averaged along the depth in the geodetic coordinate system is obtained, and the velocity potential averaged along the depth is introduced. , we get the governing equation expressed in terms of velocity potential:

[0050] (1)

[0051] (2)

[0052] Where, is the wave height, express About time Derivative; For water depth; , is the spatial variable along the direction of hull motion; is the spatial variable along the width of the ship; Parameters that represent improved dispersion performance; is the velocity potential averaged along the depth; express About time Derivative; is the acceleration due to gravity; is the combined ship-wave source term, ; represents the wave source term in the domain; The moving pressure term represents the hull motion.

[0053] Step S12: A moving pressure term is introduced into the flow field control equation to simulate the influence of the hull disturbance on the water surface, and the ship pressure field control equation is obtained.

[0054] Specifically, transform Equation (2) to time The free surface condition is derived and linearized, and then combined with Equation (1). At the same time, the shallow water wave environment is simulated based on the in-domain wave generation method, and the influence of the ship's navigation is expressed by the water surface disturbance pressure area. To this end, the wave source term that simulates the wave and the moving pressure term that represents the hull disturbance are introduced, and the flow field control equation under the ship-wave interaction is obtained, namely:

[0055] (3)

[0056] Where, express About time Find the derivative twice; express About time Find the derivative.

[0057] In this embodiment, in order to simulate various working conditions such as a ship sailing in different wave environments, such as facing waves or oblique waves, the following in-domain wave source term is proposed: :

[0058] (4)

[0059] (5)

[0060] (6)

[0061] (7)

[0062] Where, Indicates the number of constituent waves; is the horizontal coordinate of the center of the wave source; is the direction of wave propagation; is a wave source width Related functions, Indicates the The circular frequencies of the constituent waves; Indicates the characteristics of a wave; is the wavelength; is a constant, usually about 0.2 times the wavelength; Indicates the The wave number of each component wave; Indicates time; Indicates the The random initial phases of the constituent waves; represents the characteristics of each component wave in the source term, For the wave spectrum.

[0063] For the moving pressure term, in this embodiment, the ship types are firstly differentiated into equal slender ship types and equal width ship types, and model analysis and construction are performed for different ship types.

[0064] For slender ships such as ships, the pressure term is moved Expressed as:

[0065] (8)

[0066] Where, The draft of the center of the ship; is the longitudinal shape parameter of the ship; for The center position of the ship at the moment; and are the length and width of the ship model respectively; 、 are the transverse shape parameters at the bow and stern, respectively.

[0067] For wide-body ships such as cargo ships, the moving pressure term Q is expressed as:

[0068] (9)

[0069] Where, is the ship's transverse shape parameter.

[0070] Step S13: Based on the ship pressure field control equation, combined with the initial conditions and boundary conditions of the flow field, and the relationship between the flow field pressure and velocity potential, a ship pressure field model is constructed.

[0071] Specifically, if a ship is sailing in shallow water with waves, the initial conditions of the flow field include the initial position conditions of the hull, the initial position of the wave-making source, and the wave direction angle conditions; the boundary conditions include the upstream and downstream radiation conditions of the flow field and the boundary damping and wave elimination conditions.

[0072] If the ship is sailing in shallow water without waves, the initial conditions of the flow field only need to give the initial position conditions of the hull, and the boundary conditions include the upstream and downstream radiation conditions of the flow field and the boundary damping and wave elimination conditions.

[0073] Example 2

[0074] Based on Example 1, this embodiment further provides a method for determining a ship target in shallow water waves, which is implemented by the ship pressure field model constructed in Example 1 and includes the following steps:

[0075] Step S21: The ship pressure field model is discretized in space and time using the finite difference method to establish a numerical model.

[0076] Specifically, if a ship is sailing in shallow, wavy water, a finite computational domain is defined. The grid settings are optimized based on the Runge-Kutta stability conditions, combined with wave parameters, ship speed, and wave angle. The time interval is determined by the grid spacing and ship speed. A numerical model of the ship's pressure field in shallow water waves is constructed using the time second derivatives of the central difference scheme discretized theoretical model using three time layers, the space second derivatives of the three-point central difference scheme discretized theoretical model using the same time layer, the space fourth derivatives of the five-point central difference scheme discretized theoretical model, and the space-time fourth derivatives of the combined explicit and implicit central difference scheme discretized theoretical model.

[0077] It should be noted that, in this embodiment, if the ship is sailing in shallow water without waves, there is no need to consider the influence of waves and construct a numerical model of the ship pressure field in shallow water without waves.

[0078] Step S22: Based on the numerical model, the spatial distribution diagram of the ship pressure field in shallow water without waves and in shallow water with waves is obtained by simulation, and the longitudinal pressure curve is obtained by processing.

[0079] Specifically, for a certain ship speed, two shallow water environments with and without waves are adjusted, and the spatial distribution of seabed pressure in shallow water without waves is simulated by the numerical model of the ship pressure field. Matrix, spatial distribution of seabed pressure in shallow water with waves Matrix and seabed The pressure coefficient of a point changes with time Changing Matrix; where is the spatial variable along the direction of ship motion, is the spatial variable along the width of the ship, is the time variable, is the seabed pressure coefficient.

[0080] Obtain the pressure field signal of the ship in shallow water with waves and without waves. According to the spatial distribution of seabed pressure in shallow water without waves Matrix, the spatial distribution of ship pressure field in shallow water without waves is drawn; according to the spatial distribution of seabed pressure in shallow water with waves The matrix is ​​plotted to obtain the spatial distribution diagram of the ship pressure field in shallow water with waves.

[0081] The spatial distribution of the ship pressure field in shallow water without waves is analyzed, and the pressure field along the ship's mid-axis is obtained based on spatial domain processing. = 0, the seabed pressure coefficient Axis change data , and draw the longitudinal pressure curve. Analyze the spatial distribution of ship pressure field in shallow water with waves, and get the pressure along the ship's mid-axis. = 0, the seabed pressure coefficient Axis change data , and draw the pressure longitudinal curve.

[0082] Step S23: Analyze the spatial distribution diagram to obtain the transverse position of the ship; analyze the negative peak of the longitudinal pressure curve to obtain the longitudinal position of the ship.

[0083] Specifically, by analyzing the spatial distribution diagrams of the ship pressure field in shallow water with and without waves, and observing the rear pressure fluctuations caused by the ship's navigation, it can be seen that there are pressure fluctuations spreading out in a V shape behind the ship, thereby determining that the ship is spatially located at the tip of the V shape, that is, determining the lateral position.

[0084] Then, the longitudinal pressure curves under the two states are analyzed to obtain the negative pressure peak value, that is, to determine its longitudinal position.

[0085] Example 3

[0086] For example, this embodiment is a specific implementation of embodiment 2. Assume that the captain Ships sailing at subcritical speed =0.79 sailing at a water depth of 0.3 Shallow open sea, assuming the wave environment is a wave amplitude of 0.0075 , a regular wave with a period of 1.6s, where is the Froude number for water depth.

[0087] The spatial distribution diagram of the ship pressure field in shallow water without waves obtained by simulation is as follows Figure 3 As shown in the figure, the spatial distribution of ship pressure field in shallow water with waves is as follows Figure 4 At the same time, the processing is done in shallow water without waves. = 0 at the longitudinal pressure through the curve Figure 5 As shown, there are waves in shallow water = 0 at the longitudinal pressure through the curve Figure 6 shown.

[0088] Through Figure 3 and Figure 4 The analysis can determine the tip of the V shape and determine =0 in the range, then Figure 5 and Figure 6 The pressure longitudinal curve is analyzed. According to the fact that the peak characteristics of negative pressure in shallow water without waves and shallow water with waves are similar, it is preliminarily determined that the position of the hull target is =10~12. Then the ship is at subcritical speed ( ) When the pressure field of the ship presents a bow and stern symmetric feature, the target position of the hull in the wave environment can be determined. Based on this, the middle of the hull is located at Figure 6 Peak negative pressure =10.8, it should be noted that when the ship speed is at supercritical speed ( ), the position corresponding to the negative pressure peak is the stern of the hull.

[0089] Example 4

[0090] This embodiment further provides a method for determining whether a ship target passes through the bottom of the water based on embodiment 2. Point of time.

[0091] Specifically, in shallow open sea, if a certain point on the bottom of the water Set up the detector, such as Figure 7As shown in the figure, it is necessary to accurately identify the ship pressure field signal under the interference of the wave environment and determine whether the ship is The time that appears above the point.

[0092] Assume the captain is Ships sailing at supercritical speed =1.37 Navigation depth =0.2 In shallow waters, the wave environment in the local sea area satisfies the following random wave spectrum, namely:

[0093] , ;

[0094] , ;

[0095] Where: is a random wave spectrum; Equally divided frequency intervals, is the cusp factor; is the shallow water factor; is the effective wave height, ,in is the average wave height; is the effective period, .

[0096] Based on the time domain, theoretical and numerical models of ship pressure field in shallow water with waves are established to obtain the pressure field of ships passing through the water in a certain period of time under the secondary sea state. The pressure fluctuation signal of the point is received and processed through the The seabed pressure coefficient of a point changes with time Change data , and draw the pressure signal curve as Figure 8 shown.

[0097] Will The pressure fluctuation amplitude and period of the pressure signal curve above the point are analyzed in different periods. The pressure fluctuation at the point is first caused by the waves, and when the ship reaches After the point is above, the pressure fluctuation caused by the sailing ship and the pressure change caused by the environmental wave are superimposed and coupled. Figure 8 The pressure fluctuation amplitude suddenly changes, especially the negative pressure peak suddenly increases. Based on this, according to the pressure field signal characteristics of supercritical speed ships, it can be determined that the moment when the negative pressure peak suddenly changes is when the stern of the ship passes through The time when the middle of the hull target appears above the point =around 15s.

[0098] Example 5

[0099] This embodiment provides a ship pressure field prediction model in shallow water waves. Based on the above-constructed ship pressure field numerical model, a prediction model with computational stability and high prediction efficiency is established through autonomous programming combined with a finite difference algorithm.

[0100] The forecast model consists of an input module, a discrimination module, a waveless environment calculation module, a wave environment calculation module, and an output module.

[0101] Establish an input module for inputting the main dimensions and speed of the ship The system then calculates the ship's hull parameters, including the initial position, wave spectrum, wave angle, and initial position. The system also calculates the ship's wave spectrum, wave direction, and initial position. The system then determines whether the watershed is a shallow-water wave environment. If so, it executes the wave environment calculation module; otherwise, it executes the non-wave environment calculation module. The system also generates pressure field signals for ships operating in shallow water with or without waves.

[0102] The technical features of the above embodiments may be combined in any manner. To simplify the description, not all possible combinations of the technical features in the above embodiments are described. Only preferred embodiments of the present invention are presented. While the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. As long as there are no contradictions in the combination of these technical features, they should be considered to be within the scope of this specification.

[0103] It should be noted that those skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. A method for constructing a ship pressure field model in shallow water waves, characterized by: The following steps are involved: Step S11: Using the ideal incompressible fluid theory, the continuity equation and momentum equation satisfied by the ship's navigation are established in the geodetic coordinate system. Based on the shallow water assumption, the depth-averaged perturbation velocity potential is introduced. Combined with the bottom boundary conditions and the free surface boundary conditions, the flow field control equation expressed by the depth-averaged perturbation velocity potential is constructed; Step S12: setting a wave source term within the domain according to the wave environment; setting a moving pressure term according to the ship type; substituting the wave source term within the domain and the moving pressure term into the flow field control equation to simulate the effect of the surface hull disturbance in the wave environment, and obtaining the ship pressure field control equation; Step S13: constructing a ship pressure field model based on the ship pressure field control equation, combined with the initial conditions and boundary conditions of the flow field, and the relationship between the flow field pressure and velocity potential; The ship type in step S12 includes a slender ship type and a wide-body ship type; When the ship type is a wide-body ship type, the moving pressure term The expression is: ； Where, The draft of the center of the ship; is the longitudinal shape parameter of the ship; and are the length and width of the ship model respectively; is the transverse shape parameter of the ship; is the spatial variable along the direction of hull motion; is the spatial variable along the width of the ship; for The center of the ship at all times.

2. The method for constructing a ship pressure field model in shallow water waves according to claim 1, characterized in that: The expression of the flow field control equation in step S11 is: ； ； ； Where, is the wave height, express About time Derivative; For water depth; , is the spatial variable along the direction of hull motion; is the spatial variable along the width of the ship; Parameters that represent improved dispersion performance; is the velocity potential averaged along the depth; express About time Derivative; is the acceleration due to gravity; is the ship-wave combined source term; represents the wave-generating source term in the domain; The moving pressure term representing the hull motion.

3. The method for constructing a ship pressure field model in shallow water waves according to claim 2, characterized in that: The expression of the ship pressure field control equation in step S12 is: ； Where, express About time Find the derivative twice; express About time Find the derivative.

4. The method for constructing a ship pressure field model in shallow water waves according to claim 3, characterized in that: The wave source term in the domain The expression is: ； ； ； ； Where, Indicates the number of constituent waves; is the horizontal coordinate of the center of the wave source; is the direction of wave propagation; Indicates the The circular frequencies of the constituent waves; Indicates the characteristics of the wave; is the wavelength; is a constant; Indicates the The wave number of each component wave; Indicates the The random initial phases of the constituent waves; For the wave spectrum.

5. The method for constructing a ship pressure field model in shallow water waves according to claim 1, characterized in that: When the ship is a slender ship, the moving pressure term The expression is: ； Where, The draft of the center of the ship; is the longitudinal shape parameter of the ship; for The center position of the ship at the moment; and are the length and width of the ship model respectively; 、 are the transverse shape parameters at the bow and stern, respectively.

6. A method for determining a ship target in shallow water waves, implemented based on the ship pressure field model constructed by the method for constructing a ship pressure field model in shallow water waves according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step S21: using the finite difference method to discretize the ship pressure field model in space and time to establish a numerical model; Step S22: Based on the numerical model, obtain spatial distribution diagrams of the ship pressure field in shallow water without waves and in shallow water with waves by simulation, and process and obtain longitudinal pressure curves; Step S23: Analyze the spatial distribution diagram to obtain the transverse position of the ship; analyze the negative peak of the longitudinal pressure curve to obtain the longitudinal position of the ship.

7. A method for determining a ship target in shallow water waves according to claim 6, characterized in that: The passing time of the ship is determined by the following steps: obtaining a pressure fluctuation signal at a specified underwater point, drawing a pressure signal curve, and the moment when the pressure signal curve has a negative peak is the time when the ship appears.

8. The method for determining a ship target in shallow water waves according to claim 6, characterized in that: When the ship's speed is at a subcritical speed, the transverse position and longitudinal position located in step S23 correspond to the middle of the hull; when the ship's speed is at a supercritical speed, the transverse position and longitudinal position located in step S23 correspond to the stern of the hull.

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