A vortex-induced force calculation method, system and computer readable storage medium

Abstract

The application discloses a vortex-induced force calculation method and system and a computer readable storage medium, relates to the ship and ocean engineering technical field, and is used for evaluating the influence of a drift wake vortex on the underwater movement posture and track of a wreck target and proposing a corresponding vortex-induced force numerical calculation method. Based on a computational fluid dynamics method, a numerical model of a multi-ocean current scene is established, a falling process of the wreck target in static water and an ocean current environment is simulated, corresponding wake vortex structure characteristics are captured, differences in wake vortex distribution under static water and ocean current conditions are compared and analyzed, an influence mechanism of the ocean current on the evolution of the wake vortex is revealed, and an interference mechanism of the wake vortex on the falling track of the wreck target is clarified. The vortex-induced force is extracted from the wake vortex distribution and quantified as a mathematical expression, so that the influence of the wake vortex on the underwater falling track of the target can be directly predicted, the prediction precision of a falling track envelope and a falling point scattering range is improved, and the success rate of underwater search of the wreck target is improved.

Description

Technical Field

[0001] This invention relates to the field of shipbuilding and marine engineering technology, and more particularly to the field of underwater target drift analysis technology, specifically to a method, system and computer-readable storage medium for calculating vortex-induced forces. Background Technology

[0002] The core challenge in underwater search and salvage of wrecked targets lies in accurately predicting their trajectory from the surface to the bottom. Traditional trajectory prediction models primarily consider gravity, buoyancy, viscous forces, drag, and Magnus lift, often neglecting the influence of vortex-induced forces on the trajectory and attitude. However, when a wrecked target moves in the water at a certain angle of attack or with an asymmetric attitude, complex unsteady vortices will detach behind it, forming wake structures such as the Kármán vortex street. This alters the pressure distribution on the target's surface, generating vortex-induced forces and moments that significantly affect the target's attitude and thus change its path, leading to prediction errors in models that ignore vortex-induced forces.

[0003] While computational fluid dynamics (CFD) methods can simulate flow fields with high accuracy, the computational cost of fully coupled six-degree-of-freedom unsteady CFD is extremely high, making it difficult to meet the urgent time requirements of actual search and rescue operations. Furthermore, the real ocean environment is complex and variable, with ocean current disturbances (such as uniform flow and shear flow) altering wake vortex characteristics. This results in fundamental differences in the generation, evolution, and spatial distribution of wake vortices compared to still water flow fields, causing a sharp decline in the prediction accuracy of vortex-induced force models based on still water assumptions when applied to real ocean environments. Currently, there is a lack of methods to systematically reveal the differences in wake vortex characteristics under ocean current disturbances and to establish mathematical models of vortex-induced forces, becoming a key technical bottleneck restricting high-precision prediction.

[0004] Therefore, there is an urgent need for a method, system, and computer-readable storage medium that can not only deeply reveal the physical nature of the wake vortex, but also efficiently quantify the influence of the vortex and embed it into the prediction model of the trajectory of the crashed target. Summary of the Invention

[0005] The purpose of this invention is to provide a method, system, and computer-readable storage medium for calculating vortex-induced forces, in order to solve the problem that existing crash target trajectory prediction models do not consider the influence of the wake structure on the crash target's falling trajectory or cannot quantify the influence of the wake structure on the crash target's falling trajectory, thus affecting the model's prediction accuracy.

[0006] S1. Construct multi-scenario ocean current interference models, including constructing fluid dynamics models of the crashed target in still water reference scenarios, uniform flow interference scenarios, and shear flow interference scenarios based on computational fluid dynamics methods, constructing stable ocean current models and surface wave-current combined action models, and simulating actual ocean current characteristics;

[0007] S2. Integrate the actual ocean current characteristics simulated in S1 into the fluid dynamics model to construct a numerical model of the target falling in water. Perform parameterized simulation by changing the target's motion parameters and ocean current disturbance parameters, record the target's motion trajectory and transient flow field data, and construct a multi-condition flow field database.

[0008] S3. Extract wake vortex structures under different ocean current scenarios from a multi-condition flow field database, calculate key characteristic parameters, and quantify the differences in the distribution characteristics of wake vortex structures.

[0009] S4. Based on the differences in the distribution characteristics of the quantified wake vortex structure, the vortex-induced force component is separated from the total hydrodynamics. Key independent variables are determined based on key characteristic parameters. A mathematical expression formula between vortex-induced force and key independent variables is established, and a vortex-induced force calculation model is constructed.

[0010] S5. Predict the impact of the wake structure on the trajectory of the crashed target based on the vortex-induced force calculation model.

[0011] In S1, a still water reference scenario with no background ocean current is used to obtain the dynamic characteristics of the crashed target in the most basic fluid environment, serving as a benchmark model for constructing a numerical model of the crashed target falling in water.

[0012] In a uniform flow disturbance scenario, the velocity field is constant and the ocean current velocity does not change with water depth. This is used to analyze the influence of the overall advection effect of the ocean current and to construct the simplest flow disturbance model.

[0013] The fluid dynamics model constructed under the shear flow disturbance scenario is an idealized model, used for the parameterization study of the mechanism of ocean current disturbance, including linear shear flow disturbance scenario and exponential shear flow disturbance scenario. In the linear shear flow disturbance scenario, the ocean current velocity changes linearly with water depth, which is the simplest model for analyzing shear effects. In the exponential shear flow disturbance scenario, the ocean current velocity decreases exponentially with increasing depth, which is used to analyze the characteristics of surface ocean currents.

[0014] Steady ocean current models are used to simulate large ocean currents, reflecting the different hydrodynamic effects of the velocity structure within large ocean currents on different parts of long-sized crash targets.

[0015] The total velocity field of the surface wave-current combined model is a vector superposition of the background ocean current velocity and the wave-induced velocity calculated based on wave theory. It is used to simulate the complex flow field experienced by the crashed target after crossing the air-water interface and to predict the initial attitude of the crashed target.

[0016] S2 includes:

[0017] S2.1, Construct a numerical model of the underwater fall of the crashed target;

[0018] By setting corresponding inlet boundary conditions in the computational domain of computational fluid dynamics, the fluid dynamics model, steady ocean current model, and surface wave-current combined interaction model constructed by S1 are implemented. The actual ocean current characteristics simulated by the steady ocean current model and the surface wave-current combined interaction model are integrated into the fluid dynamics model to construct a numerical model of the target falling in water. For models with stable flow fields, such as steady ocean current models, fluid dynamics models under still water reference scenarios, fluid dynamics models under uniform flow disturbance scenarios, and fluid dynamics models under shear flow disturbance scenarios, the velocity profile formula is directly assigned to the inlet boundary. For wave-current combined models, such as surface wave-current combined models, user-defined functions or wave-current boundary conditions are used to generate the velocity and wave surface evolution corresponding to the waves in real time at the inlet.

[0019] S2.2, Construct a multi-condition flow field database;

[0020] In the numerical model of the underwater fall of the crashed target constructed in S2.1, the key parameters affecting the fall trajectory and wake characteristics of the crashed target are parametrically designed to form a multi-dimensional working condition space.

[0021] Key parameters include the initial angle of attack, initial sinking velocity, initial horizontal velocity, mass and moment of inertia of the crashed target, water density and viscosity, and ocean current disturbance parameters. For uniform flow scenarios, ocean current disturbance parameters include the magnitude and direction of ocean current velocity. For shear flow scenarios, ocean current disturbance parameters include surface velocity, shear law exponent or linear shear coefficient, and main direction of ocean current.

[0022] Based on the key design parameters, an unsteady computational fluid dynamics (CFD) model is established for each working condition. Overlapping mesh technology is used to simulate the rigid body motion of the target. The solver of the unsteady CFD model is coupled with the solver of the six-degree-of-freedom rigid body motion equation to capture the wake vortex structure.

[0023] By changing the motion parameters of the crashed target and the ocean current disturbance parameters in the unsteady computational fluid dynamics model, computational fluid dynamics calculations are performed. During the calculation process, the kinematic data, hydrodynamic data, and flow field characteristic data of the crashed target are monitored and recorded in real time. The recorded data are standardized and stored to construct a structured multi-condition flow field database.

[0024] In S3, wake structures under different ocean current scenarios are extracted from a multi-condition flow field database, and vortex identification criteria are used. The criteria identify and extract wake structures from transient flow field data. For the stable shedding stage of wakes under each working condition, key feature parameters are calculated according to quantification requirements. Based on the key feature parameters, the visual differences in wake distribution under different ocean current scenarios are transformed into quantifiable parameters. The function of ocean current interference parameters is calculated, and relationship curves or three-dimensional maps are plotted to explain the mapping relationship between ocean current characteristics and wake characteristics, providing direct and quantitative input for the vortex-induced force calculation model.

[0025] Key feature parameters include:

[0026] Eddy shedding frequency and Strauhall number By monitoring the time history curves of the lateral velocity or lift coefficient at specific points on the tail of the crashed target, the dominant shedding frequency is extracted based on the Fast Fourier Transform. The Strouhal number reflects the timescale of vortex generation and evolution in the wake, quantifying the visual differences in wake distribution by calculating the Strouhal number. The calculation formula is:

[0027] ;

[0028] in, For characteristic length, For reference speed, through analysis The variation pattern in different ocean current interference scenarios reflects the ratio between fluid inertial force and local acceleration force, links the time scale of vortex shedding with the convective scale of flow, establishes a universal relationship between flow conditions and vortex shedding phenomenon, and the specific point at the tail of the crashed target is the location with the highest transverse velocity signal-to-noise ratio in the development zone of the crashed target's tail vortex.

[0029] Eddy intensity distribution and asymmetry index Eddy intensity distribution is the fundamental factor determining the magnitude, direction, and distribution of vortex-induced forces. The asymmetry of the wake is a key factor leading to visual differences in wake vortex distribution. By integrating the absolute values ​​of positive and negative vorticity on multiple cross-sections perpendicular to the flow direction behind the crashed target, the vortex intensity asymmetry index is calculated to quantify the vertical symmetry of the wake. The calculation formula is:

[0030] ;

[0031] in, This represents vortex flux, equivalent to velocity circulation, reflecting the total rotational intensity of the fluid. The computational domain is divided into upper and lower parts by the cross-section. and These represent the total vorticity of the upper and lower halves of the cross-section, respectively; asymmetry index. The value range is from 0 to 1, when When the value of is 0, the wake vortex structure is completely symmetrical with respect to the cross-section. The vortex-induced force is determined by the pressure distribution and shear stress in the flow field. Asymmetrical vortex shedding will directly lead to asymmetrical pressure distribution, thereby generating lift.

[0032] The spatial curvature of the vortex core trajectory is calculated by tracing the instantaneous center position of the main vortex core in three-dimensional space, fitting the spatial trajectory of the vortex core point, and then calculating the average curvature of the vortex core. The spatial curvature of the vortex core trajectory;

[0033] The influence range of the vortex-induced velocity field is determined by calculating the velocity vector induced by the wake vortex field at the target's center of mass. This allows for a quantitative analysis of the induced velocity generated by the induced force on the crashed target, reflecting the change of the induced velocity over time.

[0034] S4 includes:

[0035] S4.1, Separation and extraction of vortex-induced forces;

[0036] The total hydrodynamic time series acting on the crashed target is directly extracted from the computational fluid dynamics calculations of the unsteady computational fluid dynamics model constructed in S2.2. Based on steady-state Reynolds-averaged simulation, the hydrodynamics of the crashed target under instantaneous attitude and velocity, without vortex shedding, are calculated, equivalent to the steady-state reference force. Subtracting the steady-state hydrodynamics calculated under the same instantaneous conditions through steady-state simulation from the total hydrodynamics, we obtain the unsteady component mainly caused by vortex shedding, which is equivalent to vortex-induced force. ;

[0037] The formula for calculating vortex-induced force is:

[0038] ;

[0039] S4.2, Identification of key independent variables and correlation analysis;

[0040] Vortex-induced force Convert to force coefficient form and calculate the transverse vortex-induced force coefficient. The calculation formula is:

[0041] ;

[0042] in, This indicates the transverse vortex-induced force. For reference area, For fluid density;

[0043] Based on the differences in the distribution characteristics of the quantized wake structure in S3, the key independent variables affecting the transverse vortex-induced force coefficient are identified, a scatter plot of the transverse vortex-induced force coefficient and one or more key independent variables is plotted, correlation analysis is performed, and the expression form of the mathematical expression formula of vortex-induced force is determined.

[0044] Key independent variables include: the instantaneous angle of attack that determines the symmetry of vortex shedding. The Strauhal number, which characterizes the periodicity of eddy shedding. An asymmetric index that directly quantifies the degree of asymmetry in the spatial distribution of wake vortices. The shear rate parameter quantifies the shear intensity of the background flow field. ;

[0045] S4.3, Construct the mathematical expression for vortex-induced force;

[0046] Based on fluid mechanics principles and data analysis, a calculation model for vortex-induced force, including static dependence terms and dynamic modulation terms, is constructed based on key parameters and key characteristic parameters. A mathematical expression formula for the relationship between vortex-induced force and key characteristic parameters is established.

[0047] ;

[0048] in, Indicates the vortex-induced force coefficient. Indicates static dependencies. Indicates dynamic modulation term, Indicates instantaneous angle of attack. This represents the shear rate parameter. Representing the Strauhal number, Indicates time, Indicates the coefficients calculated for static dependencies;

[0049] S4.4: Model coefficient determination and verification;

[0050] The vortex-induced force calculation model is globally optimized and fitted using multivariate nonlinear regression or machine learning algorithms.

[0051] The static dependency reflects the magnitude of the time-averaged eddy current induced force, which is calculated by the time-averaged value of the transverse eddy current induced force coefficient. and will A surface is fitted with the instantaneous angle of attack and shear rate parameters to construct a static dependency term. The formula for calculating the static dependency term is as follows:

[0052] ;

[0053] in, It is the shearing effect amplification factor. , These are the fitting coefficients. , This is the linear correction coefficient.

[0054] The dynamic modulation term reflects the periodic fluctuation characteristics of the vortex-induced force around the time-averaged value of the transverse vortex-induced force coefficient. It is a dimensionless periodic function of time. Subtracting the time-averaged value of the transverse vortex-induced force coefficient from the transverse vortex-induced force coefficient yields the fluctuation signal. The amplitude and phase angle of the wave signal are extracted, and a dynamic modulation term is constructed based on the wave signal. The calculation formula for the dynamic modulation term is as follows:

[0055] ;

[0056] in, Indicates the fluctuation range. Indicates the phase angle. Represents dimensionless time. Indicates reference speed. Indicates the feature length.

[0057] Based on a multi-condition flow field database, data points for each condition are input into the vortex-induced force calculation model. Multiple nonlinear regression or machine learning algorithms are used to globally optimize and fit the undetermined coefficients in the model. The formula for calculating the vortex-induced force in the vortex-induced force calculation model is as follows:

[0058] ;

[0059] If the influence of the dynamic modulation term is less than that of the static dependency term, then the dynamic modulation term is ignored, and the formula for calculating the vortex-induced force in the vortex-induced force calculation model is:

[0060] ;

[0061] The undetermined coefficients in the model include linear correction coefficients, fitting coefficients, fluctuation amplitude, and phase angle.

[0062] To achieve the above objectives, the present invention also provides a vortex-induced force calculation system. Applying the aforementioned vortex-induced force calculation method, the vortex-induced force calculation system includes:

[0063] The model building module is used to build multi-scenario ocean current interference models and underwater falling numerical models of crash targets. This includes building fluid dynamics models of crash targets under various ocean current interference scenarios, including still water reference scenarios, uniform flow interference scenarios, and shear flow interference scenarios, based on computational fluid dynamics methods; building stable ocean current models and surface wave-current combined action models to simulate actual ocean current characteristics; and integrating and modeling the fluid dynamics models based on actual ocean current characteristics to build underwater falling numerical models of crash targets.

[0064] The simulation execution module is used to perform parametric numerical design and simulation of key parameters affecting the trajectory and wake characteristics of crashed targets, execute computational fluid dynamics calculations, monitor and record data during the calculation process, and build a multi-condition flow field database.

[0065] The quantitative analysis module is used to extract and quantify the differences in wake distribution characteristics under different ocean current scenarios from a multi-condition flow field database, calculate key feature parameters, and transform the visual differences in wake distribution under different ocean current scenarios into quantifiable parameters.

[0066] The vortex-induced force generation module is used to determine key independent variables based on the quantified differences in wake characteristics, establish mathematical expressions between vortex-induced force and key independent variables, and construct a vortex-induced force calculation model.

[0067] To achieve the above objectives, the present invention also provides a computer-readable storage medium storing computer-executable instructions, wherein when the executable instructions are run on a computer, the computer's processor executes the vortex-induced force calculation method.

[0068] Compared with the prior art, the present invention has the following advantages:

[0069] This invention establishes a multi-scenario ocean current interference model by gradually increasing the complexity of ocean current interference, starting from a still water reference scenario. Based on this model, a numerical model of the target's descent in water is constructed. The target's trajectory is then parametrically simulated, and a multi-condition flow field database is built. The wake vortex structure is extracted and analyzed, and the differences in its distribution characteristics are quantified. The complex unsteady vortex-induced force effect is separated from the overall hydrodynamics, and an explicit mathematical relationship is established between it and quantifiable wake vortex characteristic parameters. This transforms the elusive vortex-induced physical phenomenon into a computable mathematical expression driven by explicit physical parameters, laying a solid foundation for achieving rapid and high-precision trajectory prediction.

[0070] This invention integrates the obtained universal mathematical expression formula of vortex-induced force into a rapid trajectory prediction program, which can be widely used in probability analysis and search area planning for the search of lost targets. It provides reasonable search strategies and professional suggestions for underwater detection and search of lost targets. The search can be carried out sequentially according to the probability of the landing point of the lost target, thereby rationally allocating search resources, increasing the success rate of deep-sea search, and reducing the cost of deep-sea operations. Attached Figure Description

[0071] Figure 1 This is a flowchart of the process of the present invention;

[0072] Figure 2 Mesh partitioning diagram of the background region in computational fluid dynamics (CFD);

[0073] Figure 3 Mesh partitioning diagram for the overlapping region in computational fluid dynamics (CFD);

[0074] Figure 4 This is a schematic diagram of the free surface in computational fluid dynamics (CFD) mesh generation.

[0075] Figure 5 A schematic diagram of the boundary layer for modeling a crashed target in computational fluid dynamics (CFD) mesh generation;

[0076] Figure 6 The diagram shows the wake vortex evolution characteristics at t=0.4s in a uniform flow disturbance scenario.

[0077] Figure 7 The diagram shows the wake vortex evolution characteristics at t=0.6s in a uniform flow disturbance scenario.

[0078] Figure 8 The diagram shows the wake vortex evolution characteristics at t=0.8s in a uniform flow disturbance scenario.

[0079] Figure 9 for Figure 6 The vorticity diagram identified by the corresponding Q criterion;

[0080] Figure 10 for Figure 7 The vorticity diagram identified by the corresponding Q criterion;

[0081] Figure 11 for Figure 8 The vorticity diagram identified by the corresponding Q criterion;

[0082] Figure 12 A predicted trajectory of a cuboid falling after taking vortex-induced forces into account;

[0083] Figure 13 The underwater scattering pattern of the cuboid after considering vortex-induced forces. Detailed Implementation

[0084] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0085] Example 1

[0086] like Figure 1 The method for calculating vortex-induced force shown includes:

[0087] S1. Construct multi-scenario ocean current interference models, including constructing fluid dynamics models of the crashed target under calm water reference scenarios, uniform current interference scenarios, and shear current interference scenarios based on computational fluid dynamics methods; constructing stable ocean current models and surface wave-current combined action models to simulate actual ocean current characteristics; starting from the most basic calm water reference model, gradually increasing and decreasing the complexity of ocean current interference to construct an ocean current interference numerical model that is as close as possible to the real ocean environment, providing a physical background for high-fidelity numerical simulation; the constructed scenarios gradually transition from ideal models to actual ocean current models.

[0088] S2. Integrate the actual ocean current characteristics simulated in S1 into the fluid dynamics model to construct a numerical model of the target falling in water. By changing the target's motion parameters and ocean current interference parameters, perform parameterized simulation, record the target's trajectory and transient flow field data, and construct a multi-condition flow field database. Through systematic computational fluid dynamics numerical experiments, construct a flow field database covering a multivariable space, providing a data foundation for subsequent analysis of wake vortex characteristic differences and extraction of vortex-induced forces.

[0089] S3. Wake vortex structures under different ocean current scenarios are extracted from a multi-condition flow field database. Key characteristic parameters are calculated to quantify the differences in the distribution characteristics of wake vortex structures. Quantifying the differences in the distribution characteristics of wake vortex structures is a crucial bridge connecting high-fidelity computational fluid dynamics (CFD) simulation and vortex-induced force modeling. Its core lies in transforming the visual differences in wake vortex distribution under different ocean current scenarios into quantifiable, physically meaningful characteristic parameters, thereby clearly revealing the influencing mechanisms. The analysis focuses on scenarios such as still water, uniform flow, shear flow, and combined wave-current interactions.

[0090] S4. Based on the differences in the distribution characteristics of the quantified wake vortex structure, the vortex-induced force component is separated from the total hydrodynamics. Key independent variables are determined based on key characteristic parameters. A mathematical expression formula between the vortex-induced force and the key independent variables is established, and a vortex-induced force calculation model is constructed. The complex unsteady vortex-induced force effect is extracted from the total hydrodynamics, and an explicit mathematical relationship between it and the quantifiable wake vortex characteristic parameters is established, ultimately forming an engineering model that can be used for rapid trajectory prediction.

[0091] S5. Predicting the impact of wake structure on the trajectory of crashed targets based on a vortex-induced force calculation model. The obtained universal mathematical expression formula of vortex-induced force is integrated into a fast trajectory prediction program. By comparing the trajectory predicted under complex ocean current conditions with the results of direct numerical simulation by high-fidelity computational fluid dynamics (CFD), its accuracy is verified. This model can be widely used in probabilistic analysis and search area planning for the search of crashed targets.

[0092] In S1, a multi-scenario ocean current interference model is constructed, including:

[0093] S1.1, Building the basic scenario;

[0094] First, two basic scenarios are constructed as benchmarks and comparisons for the construction of fluid dynamics models;

[0095] A still water reference scenario with no background ocean currents is used to obtain the dynamic characteristics of the crashed target in the most basic fluid environment, serving as a benchmark model for constructing a numerical model of the crashed target falling in water.

[0096] The uniform flow disturbance scenario is an idealized scenario in which the flow velocity field is constant and the ocean current velocity does not change with the water depth. That is, the magnitude and direction of the applied velocity do not change with the water depth. It is used to analyze the influence of the overall advection effect of the ocean current and to construct the simplest flow disturbance model.

[0097] S1.2, Construct an idealized shear flow scenario;

[0098] To construct an idealized shear flow model that is closer to the real situation than uniform flow, and to increase the complexity of ocean current disturbances, this model is mainly used for parameterization studies of mechanistic phenomena, including linear shear flow disturbance scenarios and exponential shear flow disturbance scenarios.

[0099] Linear shear flow scenario: The flow velocity varies linearly with water depth, which is the simplest model for analyzing shear effects. Its velocity profile is as follows: ,in, Surface flow velocity, The shear coefficient is a constant. This represents the water depth (positive for downward direction).

[0100] Exponential shear flow ( (Layer approximation): Simulating surface Ekman flows driven by surface wind stress, the flow velocity decreases exponentially with depth, which better matches the characteristics of ocean surface currents. It is used to analyze the characteristics of surface ocean currents, and its velocity profile is as follows: ,in The depth scale parameter of the Ekman layer. The layer is a layer in which the pressure gradient force, the Coriolis force (geostrophic force), and the turbulent drag force are balanced in the fluid.

[0101] The crash target was modeled as a simplified cuboid with dimensions of 0.7m x 0.3m x 0.2m and a mass of 10kg. Its moment of inertia was calculated based on its geometry. Computational fluid dynamics (CFD) methods were used to construct fluid dynamic models of the crash target under three scenarios: still water reference, uniform flow disturbance, and shear flow disturbance.

[0102] S1.3, Integration and modeling of actual ocean current characteristics;

[0103] To make the model more practical for engineering applications, the following two typical characteristics of actual ocean currents are integrated into the fluid dynamics model;

[0104] Steady ocean current models are used to simulate large ocean currents, reflecting the different hydrodynamic effects of the velocity structure within large ocean currents on different parts of long-sized crash targets.

[0105] Steady ocean current models with vertical velocity profiles: These models simulate large ocean currents such as the Kuroshio Current and the Gulf Stream. They are characterized by stable flow direction within a certain sea area, but significant vertical variations in velocity. Polynomial fitting or piecewise linear functions can be used to describe the complex velocity profiles obtained from actual ocean observation data. This model can more realistically reflect the different hydrodynamic effects of the velocity structure inside large ocean currents on various parts of long-sized crashed targets (such as large aircraft fuselages).

[0106] The overall velocity field of the surface wave-current combined model is a vector superposition of the background ocean current velocity and the wave-induced velocity calculated based on wave theory. It is used to simulate the complex flow field experienced by a lost target after crossing the air-water interface and to predict the initial attitude of the lost target. Real sea surfaces typically contain waves, which cause orbital motion of water particles, thus superimposing a periodic wave-induced flow field on top of the mean current. This model combines the background ocean current (uniform or shear flow) with linear wave theory (… Wave theory) or nonlinear wave theory (such as wave theory) The wave-induced velocity fields calculated by wave propagation are vector-superimposed to obtain the total velocity field. for: ,in, It depends on the horizontal position , water depth and time Changing wave-induced flow velocity, Indicates depth as The ocean current velocity at that time. This model can simulate the complex flow field experienced by a crashed target during the initial descent after crossing the air-water interface with extreme realism, which is crucial for accurately predicting the initial attitude.

[0107] S2 includes:

[0108] S2.1, Construct a numerical model of the underwater fall of the crashed target;

[0109] By setting corresponding inlet boundary conditions in the computational domain of computational fluid dynamics, the fluid dynamics model, steady ocean current model, and surface wave-current combined interaction model constructed by S1 are implemented. The actual ocean current characteristics simulated by the steady ocean current model and the surface wave-current combined interaction model are integrated into the fluid dynamics model to construct a numerical model of the target falling in water. For models with stable flow fields, such as steady ocean current models, fluid dynamics models under still water reference scenarios, fluid dynamics models under uniform flow disturbance scenarios, and fluid dynamics models under shear flow disturbance scenarios, the velocity profile formula is directly assigned to the inlet boundary. For wave-current combined models, such as surface wave-current combined models, user-defined functions or wave-current boundary conditions are used to generate the velocity and wave surface evolution corresponding to the waves in real time at the inlet.

[0110] S2.2, Construct a multi-condition flow field database;

[0111] In the numerical model of the underwater fall of the crashed target constructed in S2.1, the key parameters affecting the fall trajectory and wake characteristics of the crashed target are parametrically designed to form a multi-dimensional working condition space.

[0112] Key parameters include the initial angle of attack, initial sinking velocity, initial horizontal velocity, mass and moment of inertia of the crashed target, water density and viscosity, and ocean current disturbance parameters. For uniform flow scenarios, ocean current disturbance parameters include the magnitude and direction of ocean current velocity. For shear flow scenarios, ocean current disturbance parameters include surface velocity, shear law exponent or linear shear coefficient, and main direction of ocean current.

[0113] Based on the key design parameters, an unsteady computational fluid dynamics (CFD) model is established for each working condition. Overlapping mesh technology is used to simulate the rigid body motion of the target. The solver of the unsteady CFD model is coupled with the solver of the six-degree-of-freedom rigid body motion equation to capture the wake vortex structure.

[0114] By changing the motion parameters of the crashed target and the ocean current disturbance parameters in the unsteady computational fluid dynamics model, computational fluid dynamics calculations are performed. During the calculation process, the kinematic data, hydrodynamic data, and flow field characteristic data of the crashed target are monitored and recorded in real time. The recorded data are standardized and stored to construct a structured multi-condition flow field database.

[0115] In S3, wake structures under different ocean current scenarios are extracted from a multi-condition flow field database, and vortex identification criteria are used. The criteria identify and extract wake structures from transient flow field data. For the stable shedding stage of wakes under each working condition, key characteristic parameters are calculated according to quantification requirements. Based on these key characteristic parameters, the visual differences in wake distribution under different ocean current scenarios are transformed into quantifiable parameters. Functions of ocean current interference parameters are calculated, and relationship curves or three-dimensional maps are plotted to explain the mapping relationship between ocean current characteristics and wake characteristics, providing direct and quantitative input for the vortex-induced force calculation model.

[0116] Key feature parameters include:

[0117] Eddy shedding frequency and Strauhall number By monitoring the time history curves of the lateral velocity or lift coefficient at specific points on the tail of the crashed target, the dominant shedding frequency is extracted based on the Fast Fourier Transform. The Strouhal number reflects the timescale of vortex generation and evolution in the wake, quantifying the visual differences in wake distribution by calculating the Strouhal number. The calculation formula is:

[0118] ;

[0119] in, For characteristic length, For reference speed, through analysis The variation patterns under different ocean current interference scenarios reflect the ratio between fluid inertial force and local acceleration force, linking the time scale of vortex shedding with the convective scale of the flow, and establishing a universal relationship between flow conditions and vortex shedding phenomena. The specific point at the tail of the crashed target is the location with the highest transverse velocity signal-to-noise ratio within the target's wake vortex development zone. Based on the characteristic length of the crashed target and its hydrodynamic characteristics, the wake vortex development zone is selected as the monitoring area. An array of multiple sensors is deployed within the monitoring area to measure the transverse velocity signal in the wake vortex development zone, obtaining the location with the highest transverse velocity signal-to-noise ratio as the specific point at the tail of the crashed target. Transverse velocity is the velocity component of the ocean current velocity perpendicular to the direction of the crashed target's descent. The wake vortex development zone is located downstream of the crashed target, with the origin at a transverse distance of 0.8. Up to 1.2 The downstream distance is 5 Up to 7 The area is defined as follows: The base vortex shedding point is the starting point of vortex shedding, located on the surface of the crashed target, and is used to determine the coordinate range of the monitoring area based on hydrodynamics. The lateral distance is the straight-line distance from the base vortex shedding point along the direction perpendicular to the ocean current flow, and the downstream distance is the straight-line distance from the base vortex shedding point along the direction of the ocean current flow.

[0120] Eddy intensity distribution and asymmetry index Eddy intensity distribution is the fundamental factor determining the magnitude, direction, and distribution of vortex-induced forces. The asymmetry of the wake is a key factor leading to visual differences in wake vortex distribution. By integrating the absolute values ​​of positive and negative vorticity on multiple cross-sections perpendicular to the flow direction behind the crashed target, the vortex intensity asymmetry index is calculated to quantify the vertical symmetry of the wake. The calculation formula is:

[0121] ;

[0122] in, This represents vortex flux, equivalent to velocity circulation, reflecting the total rotational intensity of the fluid. The computational domain is divided into upper and lower parts by the cross-section. and These represent the total vorticity of the upper and lower halves of the cross-section, respectively. Indicates water depth; asymmetry index The value range is from 0 to 1, when When the value of is 0, the wake vortex structure is completely symmetrical with respect to the cross-section. The vortex-induced force is determined by the pressure distribution and shear stress in the flow field. Asymmetric vortex shedding will directly lead to asymmetric pressure distribution, thereby generating lift. The vortex intensity asymmetry index is a key bridge that directly links the flow field topology with the forces acting on the object. It is a tool for diagnosing the symmetry of the wake vortex structure. It can directly predict the average lateral force that the object will be subjected to from the flow field information without first performing complex force integration.

[0123] The spatial curvature of the vortex core trajectory is calculated by tracing the instantaneous center position of the main vortex core in three-dimensional space, fitting the spatial trajectory of the vortex core point, and then calculating the average curvature of the vortex core. The spatial curvature of the vortex core trajectory;

[0124] The influence range of the vortex-induced velocity field is determined by calculating the velocity vector induced by the wake vortex field at the target's center of mass. This allows for a quantitative analysis of the induced velocity generated by the induced force on the crashed target, reflecting the change of the induced velocity over time.

[0125] S4 includes:

[0126] S4.1, Separation and extraction of vortex-induced forces;

[0127] The total hydrodynamic time series acting on the crashed target is directly extracted from the computational fluid dynamics calculations of the unsteady computational fluid dynamics model constructed in S2.2. Based on steady-state Reynolds-averaged simulation, the hydrodynamics of the crashed target under instantaneous attitude and velocity, without vortex shedding, are calculated, equivalent to the steady-state reference force. Subtracting the steady-state hydrodynamics calculated under the same instantaneous conditions through steady-state simulation from the total hydrodynamics, we obtain the unsteady component mainly caused by vortex shedding, which is equivalent to vortex-induced force. ;

[0128] The formula for calculating vortex-induced force is:

[0129] .

[0130] S4.2, Identification of key independent variables and correlation analysis;

[0131] Vortex-induced force Convert to force coefficient form and calculate the transverse vortex-induced force coefficient. The calculation formula is:

[0132] ;

[0133] in, This indicates the transverse vortex-induced force. For reference area, The fluid density is given.

[0134] Based on the differences in the distribution characteristics of the quantized wake structure in S3, the key independent variables affecting the transverse vortex-induced force coefficient are identified, a scatter plot of the transverse vortex-induced force coefficient and one or more key independent variables is plotted, correlation analysis is performed, and the expression form of the mathematical expression formula of vortex-induced force is determined.

[0135] Key independent variables include: the instantaneous angle of attack that determines the symmetry of vortex shedding. The Strauhal number, which characterizes the periodicity of eddy shedding. An asymmetric index that directly quantifies the degree of asymmetry in the spatial distribution of wake vortices. The shear rate parameter quantifies the shear intensity of the background flow field. ;

[0136] S4.3, Construct the mathematical expression for vortex-induced force;

[0137] Based on fluid mechanics principles and data analysis, a calculation model for vortex-induced force, including static dependence terms and dynamic modulation terms, is constructed based on key parameters and key characteristic parameters. A mathematical expression formula for the relationship between vortex-induced force and key characteristic parameters is established.

[0138] ;

[0139] in, Indicates the vortex-induced force coefficient. Indicates static dependencies. Indicates dynamic modulation term, Indicates instantaneous angle of attack. This represents the shear rate parameter. Representing the Strauhal number, Indicates time, This indicates the coefficients calculated for static dependencies.

[0140] S4.4: Model coefficient determination and verification;

[0141] The vortex-induced force calculation model is globally optimized and fitted using multivariate nonlinear regression or machine learning algorithms.

[0142] The static dependency reflects the magnitude of the time-averaged eddy current induced force, which is calculated by the time-averaged value of the transverse eddy current induced force coefficient. and will A surface is fitted with the instantaneous angle of attack and shear rate parameters to construct a static dependency term. The formula for calculating the static dependency term is as follows:

[0143] ;

[0144] in, It is the shearing effect amplification factor. , These are the fitting coefficients. , This is the linear correction coefficient.

[0145] The dynamic modulation term reflects the periodic fluctuation characteristics of the vortex-induced force around the time-averaged value of the transverse vortex-induced force coefficient. It is a dimensionless periodic function of time. Subtracting the time-averaged value of the transverse vortex-induced force coefficient from the transverse vortex-induced force coefficient yields the fluctuation signal. The amplitude and phase angle of the wave signal are extracted, and a dynamic modulation term is constructed based on the wave signal. The calculation formula for the dynamic modulation term is as follows:

[0146] ;

[0147] in, Indicates the fluctuation range. Indicates the phase angle. Represents dimensionless time. Indicates reference speed. Indicates the feature length.

[0148] Based on a multi-condition flow field database, data points for each condition are input into the vortex-induced force calculation model. Multiple nonlinear regression or machine learning algorithms are used to globally optimize and fit the undetermined coefficients in the model. The formula for calculating the vortex-induced force in the vortex-induced force calculation model is as follows:

[0149] ;

[0150] If the influence of the dynamic modulation term is less than that of the static dependency term, then the dynamic modulation term is ignored, and a static model is used. That is, the vortex-induced force is approximated by the static dependency term. The formula for calculating the vortex-induced force in the vortex-induced force calculation model is as follows:

[0151] ;

[0152] The undetermined coefficients in the model include linear correction coefficients, fitting coefficients, fluctuation amplitude, and phase angle.

[0153] Example 2

[0154] A vortex-induced force calculation system, applying the aforementioned vortex-induced force calculation method, the vortex-induced force calculation system includes:

[0155] The model building module is used to build multi-scenario ocean current interference models and underwater falling numerical models of crash targets. This includes building fluid dynamics models of crash targets under various ocean current interference scenarios, including still water reference scenarios, uniform flow interference scenarios, and shear flow interference scenarios, based on computational fluid dynamics methods; building stable ocean current models and surface wave-current combined action models to simulate actual ocean current characteristics; and integrating and modeling the fluid dynamics models based on actual ocean current characteristics to build underwater falling numerical models of crash targets.

[0156] The simulation execution module is used to perform parametric numerical design and simulation of key parameters affecting the trajectory and wake characteristics of crashed targets, execute computational fluid dynamics calculations, monitor and record data during the calculation process, and build a multi-condition flow field database.

[0157] The quantitative analysis module is used to extract and quantify the differences in wake distribution characteristics under different ocean current scenarios from a multi-condition flow field database, calculate key feature parameters, and transform the visual differences in wake distribution under different ocean current scenarios into quantifiable parameters.

[0158] The vortex-induced force generation module is used to determine key independent variables based on the quantified differences in wake characteristics, establish mathematical expressions between vortex-induced force and key independent variables, and construct a vortex-induced force calculation model.

[0159] Example 3

[0160] A computer-readable storage medium storing computer-executable instructions, wherein when the executable instructions are run on a computer, the computer's processor executes the vortex-induced force calculation method.

[0161] Taking the still water reference scenario, the uniform flow disturbance scenario, and the shear flow disturbance scenario as examples, the ocean current disturbance scenario is constructed, and the inlet boundary conditions of the three ocean current scenarios are set in the CFD computation domain.

[0162] Scenario A (Still Water Reference Scenario): The inlet boundary condition is set to a velocity inlet with a velocity of 0 m / s.

[0163] Scenario B (Uniform Flow Disturbance Scenario): The inlet boundary condition is set to a velocity inlet with a velocity magnitude of 0.5 m / s and a horizontal direction (positive X-axis).

[0164] Scenario C (Shear Flow Interference Scenario): Using a user-defined function (UDF), a linear shear flow velocity profile is defined at the inlet. The inlet boundary condition is set to the profile velocity of the linear shear flow, U(z) = 0.7 + 0.1z m / s (z is the water depth, which is negative from 0m downwards from the water surface); that is, the flow velocity is 0.7 m / s at a depth of 0m and -0.3 m / s at a depth of -10m (in the opposite direction).

[0165] The dynamic characteristics of the crashed target in the most basic fluid environment were obtained through scenario A. For scenarios B and C, the initial angle of attack of the cuboid (crashed target) was changed to 0°, 5°, 10°, and 15°, respectively. The initial sinking velocity was set to 1 m / s. A total of 8 sets of unsteady numerical simulations (2 types of ocean currents × 4 angles of attack) were performed.

[0166] like Figures 2 to 5 As shown, a high-quality mesh was generated for the computational domain. A six-degree-of-freedom (6-DOF) solver was activated and coupled with an overlapping mesh model to create a cuboid computational domain with dimensions of 10m × 6m × 8m. A hybrid mesh was generated using mesh generation software. A boundary layer mesh was generated on the surface of the cuboid, with the height of the first layer calculated to ensure y+≈1. Local refinement was applied around the cuboid and in the expected fall path and wake region, resulting in a total mesh size of approximately 5.2 million. Overlapping mesh technology was used to handle the large-scale motion of the cuboid.

[0167] Simulation execution: The Large Eddy Simulation (LES) model was selected, and the WALE model was chosen for the subgrid model to capture unsteady vortex shedding with high accuracy. Each simulation calculation lasted 20 seconds, with a time step of 0.001 seconds to meet the accuracy requirements of the LES model. At each time step, Star-ccm+ updated the position and orientation of the cuboid using a 6-DOF solver.

[0168] Data logging: Monitors and records the displacement, velocity, Euler angles, and other motion parameters of the cuboid, as well as the hydrodynamic forces and torques it experiences. Simultaneously, it outputs transient data (velocity, pressure, vorticity) of the entire flow field every 0.1 seconds. All data is automatically stored, forming a multi-condition flow field database.

[0169] like Figures 6 to 11 As shown, the crash target is simplified to a cuboid with length × width × height = 0.7m × 0.3m × 0.2m. Figures 6 to 8(The white area in the image) uses the vortex identification criterion. The criterion identifies and extracts the wake structure from transient flow field data, plots relationship curves or 3D maps, and applies the Q-criterion to generate isosurfaces, which are then colored to display the magnitude of vorticity. Taking scenario C as an example, the wake evolution characteristics of the crashed target at t=0.4s are as follows: Figure 6 As shown, the vorticity diagram identified by the corresponding Q criterion is as follows: Figure 9 As shown, the wake evolution characteristics of the crashed target at t=0.6s are as follows: Figure 7 As shown, the vorticity diagram identified by the corresponding Q criterion is as follows: Figure 10 As shown, the wake evolution characteristics of the crashed target at t=0.8s are as follows: Figure 8 As shown, the vorticity diagram identified by the corresponding Q criterion is as follows: Figure 11 As shown. (Through) Figures 6 to 8 The color bars at the bottom clearly show that different colors represent different vorticity values. Dark blue corresponds to vorticity values ​​less than -10, indicating that the fluid rotation direction and intensity in these areas are low (negative values); dark red corresponds to vorticity values ​​greater than 25, indicating that the fluid rotation in these areas is relatively strong; the intermediate transition colors correspond to different intensities of vorticity values ​​between -10 and 25. Figures 6 to 11 It can be clearly observed that the wake vortex in scene C exhibits obvious spatial curvature and asymmetry.

[0170] For scenes B and C, extract the time history curves of the lateral force (lift) of the cuboid and perform a fast Fourier transform. ), to obtain the dominant shedding frequency .calculate The results show that the scene of Number ratio scenario There is significant drift. Behind the cuboid. (after doubling the diameter) On a plane, Let represent the diameter of the integration region, bounded by the centerline of the cuboid, and calculate the total vorticity of the upper and lower halves of the region. Substitute this into the formula for the vortex intensity asymmetry index. Calculation formula Calculations show that the scenario of The value is close to 0.1, while the scenario of The value is as high as 0.6, which quantifies its strong asymmetry.

[0171] The mathematical expression for vortex-induced force (primarily static terms) was incorporated as an additional force module into a self-developed six-degree-of-freedom rigid body dynamic trajectory prediction program. The core of this program is solving the rigid body motion equations, with initial sinking velocities set accordingly. Model verification was performed at speeds of 0 m / s, 0.1 m / s, and 0.2 m / s, yielding the falling trajectory considering vortex-induced force, as shown below. Figure 12 As shown. From Figure 12 As can be seen, the horizontal displacement of the crashed target increases with the increase of the initial sinking velocity.

[0172] like Figure 13 As shown, considering the uncertainties in the initial entry attitude and velocity of the cuboid into the water, these input parameters are set to follow a certain probability distribution (such as a Gaussian distribution). One hundred Monte Carlo simulations are performed. After the simulations, the final landing points of all simulations are statistically analyzed, generating an underwater landing point scatter map and trajectory envelope. Compared with the prediction results of traditional models that do not consider eddy-induced forces, the landing point scatter area predicted by this invention is more concentrated and has a very high degree of agreement with the "baseline truth" of a full-process high-fidelity LES simulation. The scatter area predicted by this invention (red area: a 500m × 500m area) is output to the search team. Compared with the area predicted by the traditional model (yellow area: 1000m × 1000m), the search efficiency is expected to be improved by 75%.

[0173] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for calculating vortex-induced force, characterized in that, include: S1. Construct multi-scenario ocean current interference models, including constructing fluid dynamics models of the crashed target in still water reference scenarios, uniform flow interference scenarios, and shear flow interference scenarios based on computational fluid dynamics methods, constructing stable ocean current models and surface wave-current combined action models, and simulating actual ocean current characteristics; S2. Integrate the actual ocean current characteristics simulated in S1 into the fluid dynamics model to construct a numerical model of the target falling in water. Perform parameterized simulation by changing the target's motion parameters and ocean current disturbance parameters, record the target's motion trajectory and transient flow field data, and construct a multi-condition flow field database. S3. Extract wake vortex structures under different ocean current scenarios from the multi-condition flow field database, calculate key characteristic parameters, and quantify the differences in the distribution characteristics of wake vortex structures. S4. Based on the differences in the distribution characteristics of the quantified wake vortex structure, the vortex-induced force component is separated from the total hydrodynamics. Key independent variables are determined based on key characteristic parameters. A mathematical expression formula between vortex-induced force and key independent variables is established, and a vortex-induced force calculation model is constructed. S5. Predict the impact of the wake structure on the trajectory of the crashed target based on the vortex-induced force calculation model; In S3, wake structures under different ocean current scenarios are extracted from a multi-condition flow field database, and vortex identification criteria are used. The criteria identify and extract wake structures from transient flow field data. For the stable shedding stage of wakes under each working condition, key feature parameters are calculated according to quantification requirements. Based on the key feature parameters, the visual differences in wake distribution under different ocean current scenarios are transformed into quantifiable parameters. The function of ocean current interference parameters is calculated, and relationship curves or three-dimensional maps are plotted to explain the mapping relationship between ocean current characteristics and wake characteristics, providing direct and quantitative input for the vortex-induced force calculation model. Key feature parameters include: Eddy shedding frequency and Strauhall number By monitoring the time history curves of the lateral velocity or lift coefficient at specific points on the tail of the crashed target, the dominant shedding frequency is extracted based on the Fast Fourier Transform. The Strouhal number reflects the timescale of vortex generation and evolution in the wake, quantifying the visual differences in wake distribution by calculating the Strouhal number. The calculation formula is: ； in, For characteristic length, For reference speed, through analysis The variation pattern in different ocean current interference scenarios reflects the ratio between fluid inertial force and local acceleration force, links the time scale of vortex shedding with the convective scale of flow, establishes a universal relationship between flow conditions and vortex shedding phenomenon, and the specific point at the tail of the crashed target is the location with the highest transverse velocity signal-to-noise ratio in the development zone of the crashed target's tail vortex. Eddy intensity distribution and asymmetry index Eddy intensity distribution is the fundamental factor determining the magnitude, direction, and distribution of vortex-induced forces. The asymmetry of the wake is a key factor leading to visual differences in wake vortex distribution. By integrating the absolute values ​​of positive and negative vorticity on multiple cross-sections perpendicular to the flow direction behind the crashed target, the vortex intensity asymmetry index is calculated to quantify the vertical symmetry of the wake. The calculation formula is: ； in, This represents vortex flux, equivalent to velocity circulation, reflecting the total rotational intensity of the fluid. The computational domain is divided into upper and lower parts by the cross-section. and These represent the total vorticity of the upper and lower halves of the cross-section, respectively. Indicates water depth; asymmetry index The value range is from 0 to 1, when When the value of is 0, the wake vortex structure is completely symmetrical with respect to the cross-section. The vortex-induced force is determined by the pressure distribution and shear stress in the flow field. Asymmetrical vortex shedding will directly lead to asymmetrical pressure distribution, thereby generating lift. The spatial curvature of the vortex core trajectory is calculated by tracing the instantaneous center position of the main vortex core in three-dimensional space, fitting the spatial trajectory of the vortex core point, and then calculating the average curvature of the vortex core. The spatial curvature of the vortex core trajectory; The influence range of the vortex-induced velocity field is determined by calculating the velocity vector induced by the wake vortex field at the target's center of mass. This allows for a quantitative analysis of the induced velocity generated by the induced force on the crashed target, reflecting the change of the induced velocity over time.

2. The method for calculating vortex-induced force according to claim 1, characterized in that, In S1, a still water reference scenario with no background ocean current is used to obtain the dynamic characteristics of the crashed target in the most basic fluid environment, serving as a benchmark model for constructing a numerical model of the crashed target falling in water. In a uniform flow disturbance scenario, the velocity field is constant and the ocean current velocity does not change with water depth. This is used to analyze the impact of the overall advection effect of the ocean current and to construct the simplest flow disturbance model. The fluid dynamics model constructed under the shear flow disturbance scenario is an idealized model, used for the parameterization study of the mechanism of ocean current disturbance, including linear shear flow disturbance scenario and exponential shear flow disturbance scenario. In the linear shear flow disturbance scenario, the ocean current velocity changes linearly with water depth, which is the simplest model for analyzing shear effects. In the exponential shear flow disturbance scenario, the ocean current velocity decreases exponentially with increasing depth, which is used to analyze the characteristics of surface ocean currents. Steady ocean current models are used to simulate large ocean currents, reflecting the different hydrodynamic effects of the velocity structure within large ocean currents on different parts of long-sized crash targets. The total velocity field of the surface wave-current combined model is a vector superposition of the background ocean current velocity and the wave-induced velocity calculated based on wave theory. It is used to simulate the complex flow field experienced by the crashed target after crossing the air-water interface and to predict the initial attitude of the crashed target.

3. The method for calculating vortex-induced force according to claim 2, characterized in that, S2 include: S2.1, Construct a numerical model of the underwater fall of the crashed target; By setting corresponding inlet boundary conditions in the computational domain of computational fluid dynamics, the fluid dynamics model, steady ocean current model, and surface wave-current combined interaction model constructed by S1 are implemented. The actual ocean current characteristics simulated by the steady ocean current model and the surface wave-current combined interaction model are integrated into the fluid dynamics model to construct a numerical model of the target falling in water. For models with stable flow fields, such as steady ocean current models, fluid dynamics models under still water reference scenarios, fluid dynamics models under uniform flow disturbance scenarios, and fluid dynamics models under shear flow disturbance scenarios, the velocity profile formula is directly assigned to the inlet boundary. For wave-current combined models, such as surface wave-current combined models, user-defined functions or wave-current boundary conditions are used to generate the velocity and wave surface evolution corresponding to the waves in real time at the inlet. S2.2, Construct a multi-condition flow field database; In the numerical model of the underwater fall of the crashed target constructed in S2.1, the key parameters affecting the fall trajectory and wake characteristics of the crashed target are parametrically designed to form a multi-dimensional working condition space. Key parameters include the initial angle of attack, initial sinking velocity, initial horizontal velocity, mass and moment of inertia of the crashed target, water density and viscosity, and ocean current disturbance parameters. For uniform flow scenarios, ocean current disturbance parameters include the magnitude and direction of ocean current velocity. For shear flow scenarios, ocean current disturbance parameters include surface velocity, shear law exponent or linear shear coefficient, and main direction of ocean current. Based on the key design parameters, an unsteady computational fluid dynamics (CFD) model is established for each working condition. Overlapping mesh technology is used to simulate the rigid body motion of the target. The solver of the unsteady CFD model is coupled with the solver of the six-degree-of-freedom rigid body motion equation to capture the wake vortex structure. By changing the motion parameters of the crashed target and the ocean current disturbance parameters in the unsteady computational fluid dynamics model, computational fluid dynamics calculations are performed. During the calculation process, the kinematic data, hydrodynamic data, and flow field characteristic data of the crashed target are monitored and recorded in real time. The recorded data are standardized and stored to construct a structured multi-condition flow field database.

4. The vortex-induced force calculation method according to claim 3, characterized in that, S4 include: S4.1, Separation and extraction of vortex-induced forces; The total hydrodynamic time series acting on the crashed target is directly extracted from the computational fluid dynamics calculations of the unsteady computational fluid dynamics model constructed in S2.

2. Based on steady-state Reynolds-averaged simulation, the hydrodynamics of the crashed target under instantaneous attitude and velocity, without vortex shedding, are calculated, equivalent to the steady-state reference force. Subtracting the steady-state hydrodynamics calculated under the same instantaneous conditions through steady-state simulation from the total hydrodynamics, we obtain the unsteady component mainly caused by vortex shedding, which is equivalent to vortex-induced force. ; The formula for calculating vortex-induced force is: ； S4.2, Identification of key independent variables and correlation analysis; Vortex-induced force Convert to force coefficient form and calculate the transverse vortex-induced force coefficient. The calculation formula is: ； in, This indicates the transverse vortex-induced force. For reference area, For fluid density; Based on the differences in the distribution characteristics of the quantized wake structure in S3, the key independent variables affecting the transverse vortex-induced force coefficient are identified, a scatter plot of the transverse vortex-induced force coefficient and one or more key independent variables is plotted, correlation analysis is performed, and the expression form of the mathematical expression formula of vortex-induced force is determined. Key independent variables include: the instantaneous angle of attack that determines the symmetry of vortex shedding. The Strauhal number, which characterizes the periodicity of eddy shedding. An asymmetric index that directly quantifies the degree of asymmetry in the spatial distribution of wake vortices. The shear rate parameter quantifies the shear intensity of the background flow field. ; S4.3, Construct the mathematical expression for vortex-induced force; Based on fluid mechanics principles and data analysis, a calculation model for vortex-induced force, including static dependence terms and dynamic modulation terms, is constructed based on key parameters and key characteristic parameters. A mathematical expression formula for the relationship between vortex-induced force and key characteristic parameters is established. ； in, Indicates the vortex-induced force coefficient. Indicates static dependencies. Indicates dynamic modulation term, Indicates instantaneous angle of attack. This represents the shear rate parameter. Representing the Strauhal number, Indicates time, Indicates the coefficients calculated for static dependencies; S4.4: Model coefficient determination and verification; The vortex-induced force calculation model is globally optimized and fitted using multivariate nonlinear regression or machine learning algorithms.

5. The method for calculating vortex-induced force according to claim 4, characterized in that, The static dependency reflects the magnitude of the time-averaged eddy current induced force, which is calculated by the time-averaged value of the transverse eddy current induced force coefficient. and will A surface is fitted with the instantaneous angle of attack and shear rate parameters to construct a static dependency term. The formula for calculating the static dependency term is as follows: ； in, It is the shearing effect amplification factor. , These are the fitting coefficients. , This is the linear correction coefficient.

6. The method for calculating vortex-induced force according to claim 5, characterized in that, The dynamic modulation term reflects the periodic fluctuation characteristics of the vortex-induced force around the time-averaged value of the transverse vortex-induced force coefficient. It is a dimensionless periodic function of time. Subtracting the time-averaged value of the transverse vortex-induced force coefficient from the transverse vortex-induced force coefficient yields the fluctuation signal. The amplitude and phase angle of the wave signal are extracted, and a dynamic modulation term is constructed based on the wave signal. The calculation formula for the dynamic modulation term is as follows: ； in, Indicates the fluctuation range. Indicates the phase angle. Represents dimensionless time. Indicates reference speed. Indicates the feature length.

7. The method for calculating vortex-induced force according to claim 6, characterized in that, Based on a multi-condition flow field database, data points for each condition are input into the vortex-induced force calculation model. Multiple nonlinear regression or machine learning algorithms are used to globally optimize and fit the undetermined coefficients in the model. The formula for calculating the vortex-induced force in the vortex-induced force calculation model is as follows: ； If the influence of the dynamic modulation term is less than that of the static dependency term, then the dynamic modulation term is ignored and a static model is used. The formula for calculating the vortex-induced force in the vortex-induced force calculation model is as follows: ； The undetermined coefficients in the model include linear correction coefficients, fitting coefficients, fluctuation amplitude, and phase angle.

8. A vortex-induced force calculation system, using the vortex-induced force calculation method as described in any one of claims 1-7, characterized in that, The vortex-induced force calculation system includes: The model building module is used to build multi-scenario ocean current interference models and underwater falling numerical models of crash targets. This includes building fluid dynamics models of crash targets under various ocean current interference scenarios, including still water reference scenarios, uniform flow interference scenarios, and shear flow interference scenarios, based on computational fluid dynamics methods; building stable ocean current models and surface wave-current combined action models to simulate actual ocean current characteristics; and integrating and modeling the fluid dynamics models based on actual ocean current characteristics to build underwater falling numerical models of crash targets. The simulation execution module is used to perform parametric numerical design and simulation of key parameters affecting the trajectory and wake characteristics of crashed targets, execute computational fluid dynamics calculations, monitor and record data during the calculation process, and build a multi-condition flow field database. The quantitative analysis module is used to extract and quantify the differences in wake distribution characteristics under different ocean current scenarios from a multi-condition flow field database, calculate key feature parameters, and transform the visual differences in wake distribution under different ocean current scenarios into quantifiable parameters. The vortex-induced force generation module is used to determine key independent variables based on the quantified differences in wake characteristics, establish mathematical expressions between vortex-induced force and key independent variables, and construct a vortex-induced force calculation model.

9. A computer-readable storage medium storing computer-executable instructions, characterized in that, When the executable instructions are run on a computer, the computer's processor executes the vortex-induced force calculation method as described in any one of claims 1 to 7.

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