Container ship monitoring point selection method and system considering hydroelastic load

Abstract

The application discloses a container ship monitoring point selection method and system considering hydroelastic load, and the method comprises the following steps: determining a wave frequency range and a loading working condition range to be analyzed to form a plurality of working condition combinations; a finite element software is used to establish a container ship finite element model comprising a plurality of units; hydroelastic displacement is combined to calculate the hydroelastic load of each unit corresponding to each working condition combination; the hydroelastic load is applied to the model for quasi-static analysis to obtain the first normal stress of each unit under each working condition combination; the internal force of each section is calculated, and then the normal stress of each unit corresponding to each section is calculated to obtain the second normal stress of each unit under each working condition combination; based on the first and second normal stresses, the unit set corresponding to each working condition combination which satisfies the overall strain dominance is calculated, and the intersection of all sets is calculated as a candidate monitoring point; according to the steel sea-going ship classification regulation and the structural characteristics of the container ship, the monitoring point which can be arranged and satisfies the actual engineering operability is selected from the candidate monitoring point.

Description

Technical Field

[0001] This invention relates to the field of container ship stress monitoring technology, and in particular to a method and system for selecting monitoring points for container ships that takes into account hydroelastic loads. Background Technology

[0002] With the continuous increase in international trade demand, container ships, as a crucial transportation medium, account for approximately 40% of the world's total maritime trade volume and have attracted widespread attention from countries around the world. The large openings in container ships significantly reduce their hull stiffness characteristics, causing the frequency of the hull's first elastic mode (typically a two-node vertical bending mode) to be closer to the wave frequency range. Compared to other ship types, this makes them more prone to hydroelastic response, affecting hull structural safety. Therefore, structural monitoring technology is needed to ensure hull structural safety.

[0003] In ship structure inspection, the overall bending moment acting on the hull structure is a key focus. Identifying the overall load based on monitoring information is an effective structural monitoring strategy. To identify the overall load on large container ships, it is necessary to monitor monitoring points dominated by overall deformation. However, existing technologies still have shortcomings: First, the layout of hull monitoring points by major classification societies is based only on recommended specifications, lacking full-condition verification and theoretical-engineering closed-loop, thus limiting the applicability of monitoring points; Second, in addition to the overall load, most of the hull structure is also subject to localized deformation caused by local water pressure (generating local loads). In actual ship three-dimensional finite element calculations, the hull is usually treated as a rigid body for hydrodynamic analysis, without considering the local loads generated by hydroelastic deformation—additional hydrodynamic loads (such as radiation pressure and dynamic inertial forces caused by elastic displacement). Summary of the Invention

[0004] To address the shortcomings of traditional technologies in selecting monitoring points, such as insufficient consideration of hydroelastic loads, lack of full-condition verification of monitoring points, and limited applicability due to the absence of theoretical-engineering closed-loop systems, this invention proposes a method for selecting monitoring points for container ships that considers hydroelastic loads. This method compares and filters the "overall stress + local stress" calculated from finite element analysis of actual ships under a series of operating conditions with the overall stress calculation from ship beam theory. Finite element elements dominated by overall stress are selected as theoretically usable monitoring points. Feasible monitoring points are then selected based on practical engineering applicability, ensuring that the selected monitoring points not only consider the hydroelastic response of actual container ships but also are adaptable to all operating conditions and exhibit strong monitoring stability. This invention also provides a system for selecting monitoring points for container ships that considers hydroelastic loads.

[0005] The technical solution of the present invention is as follows:

[0006] A method for selecting monitoring points for container ships that takes into account water elastic loads, comprising the following steps:

[0007] S1: Obtain the geometric parameters, material parameters, and navigation parameters of the container ship; determine the wave frequency range and loading condition range to be analyzed, and perform equal-interval discretization on the wave frequency range and loading condition range to obtain several discretized wave frequencies and discretized loading conditions; use the Cartesian product matching method to combine all discretized wave frequencies with all discretized loading conditions one by one to form several condition combinations.

[0008] S2: Input the geometric parameters and material parameters into the finite element software, and establish a container ship simulation model in the finite element software. Use the finite element software to discretize the container ship simulation model into a mesh, and establish a container ship finite element model containing multiple finite element elements; each finite element element corresponds to a spatial coordinate.

[0009] S3: For each of the aforementioned operating condition combinations, calculate the hydroelastic displacement of the finite element element using the overall hydroelastic response equation; and calculate the hydroelastic load of each of the finite element elements based on the hydroelastic displacement, the navigation parameters corresponding to the operating condition combination, and the spatial coordinates of the finite element element.

[0010] S4: For each of the aforementioned working condition combinations, the hydroelastic loads calculated for each finite element under the aforementioned working condition combination are applied to the container ship finite element model, and quasi-static analysis of finite element simulation is performed to obtain the first normal stress of each of the aforementioned finite element elements under each of the aforementioned working condition combinations; the first normal stress includes local stress.

[0011] S5: For each of the aforementioned working condition combinations, based on the spatial coordinates of each finite element element corresponding to the working condition combination, the location of each finite element element is divided into sections, each section being a plane perpendicular to the ship's length, and each section corresponding to several finite element elements; using the overall hydroelastic response model, the internal forces corresponding to each section are calculated; based on the internal forces, the normal stress of each finite element element spatial coordinate corresponding to each section is calculated using hull beam theory, thus obtaining the second normal stress of each finite element element spatial coordinate under each of the aforementioned working condition combinations for the container ship; the second normal stress does not include local stress.

[0012] S6: For each of the aforementioned working condition combinations, the first normal stress and the second normal stress at the same spatial coordinate in the working condition combination are compared, and finite element elements corresponding to spatial coordinates where the absolute value of the difference between the first normal stress and the second normal stress and the ratio of the second normal stress is less than a preset threshold are selected, thus obtaining a set of first finite element elements that satisfy the overall strain-dominated condition for each of the aforementioned working condition combinations; the intersection of all first finite element element sets is calculated to obtain a set of second finite element elements that satisfy all working conditions, which serves as candidate monitoring points;

[0013] S7: Based on the classification standards for steel seagoing vessels and the structural characteristics of container ships, select feasible monitoring points from the candidate monitoring points to obtain monitoring points that meet the operability requirements of actual engineering.

[0014] Preferably, in step S1, the navigation parameters include the ship's mass under different loading conditions, and the material parameters include structural damping;

[0015] In step S3, the hydroelastic displacement includes translational displacement and rotational displacement. The translational displacement includes sway displacement, lateral sway displacement and heave displacement. The rotational displacement includes roll angle displacement, pitch angle displacement and yaw angle displacement. The hydroelastic load includes hydroelastic pressure, inertial force, gravity rotation term and structural damping force. The hydroelastic pressure includes hydrostatic recovery pressure, radiation pressure and wave excitation pressure.

[0016] Preferably, in step S3, when calculating the hydroelastic load of each finite element element, the hydroelastic motion response equation containing the generalized mass matrix and the generalized damping matrix is ​​solved based on the potential flow theory. Combining the hydroelastic displacement and structural damping, the hydrostatic recovery pressure, radiation pressure, gravity rotation term, inertial force vector and structural damping force vector corresponding to each finite element element are calculated and vector superimposed to obtain the hydroelastic load of each finite element element.

[0017] Preferably, in step S5, the internal forces include vertical bending moment, horizontal bending moment, and dual moments;

[0018] Based on the thin-walled beam theory, and combined with the cross-sectional moment of inertia and sector moment of inertia calculated from the geometric parameters corresponding to the container ship cross-section, the second normal stress at any spatial coordinate of the cross-section is calculated using the following formula:

[0019] ,

[0020] in, Indicates the second normal stress. Indicates the vertical bending moment. Let B represent the horizontal bending moment, B represent the two moments, y represent the beam direction coordinate in the hull coordinate system, and z represent the vertical coordinate in the hull coordinate system. Represents sector coordinates, This represents the moment of inertia of the cross section about the beam direction in the hull coordinate system. The moment of inertia of the cross section about the vertical direction in the ship's coordinate system is represented by . The sector moment of inertia represents the cross section.

[0021] Preferably, in step S6, finite element elements corresponding to spatial coordinates where the absolute value of the ratio of the difference between the first normal stress and the second normal stress to the second normal stress is less than a preset threshold are selected based on the following formula:

[0022]

[0023] in, This represents the first normal stress; the preset threshold is 10%.

[0024] Preferably, in step S1, the wave frequency range is 0.2 rad / s to 2.3 rad / s, and the loading condition range is 20% to 100%.

[0025] Preferably, in step S7, in accordance with the classification rules for steel seagoing vessels, the candidate monitoring points at 1 / 4, 1 / 2, and 3 / 4 of the ship's length are selected from the candidate monitoring points as monitoring points that meet the classification rules;

[0026] Based on the structural characteristics of container ships, among the monitoring points that meet the classification specifications, those that overlap with the cargo hold, ballast tank, and oil tank areas of container ships are removed, resulting in monitoring points that meet the practical engineering operability requirements.

[0027] A container ship monitoring point selection system considering hydroelastic loads includes, in sequence, a ship operating condition parameter acquisition and processing module, a hydroelastic finite element stress calculation module, a hull beam theoretical stress calculation module, an overall strain-dominant monitoring point selection module, and an actual engineering monitoring point selection module; wherein...

[0028] The ship operating condition parameter acquisition and processing module is used to acquire the geometric parameters, material parameters, and navigation parameters of the container ship; determine the wave frequency range and loading condition range to be analyzed; perform equal-interval discretization on the wave frequency range and loading condition range to obtain several discretized wave frequencies and discretized loading conditions; and use the Cartesian product matching method to combine all discretized wave frequencies with all discretized loading conditions one by one to form several operating condition combinations.

[0029] The hydroelastic finite element stress calculation module is used to input the geometric and material parameters into the finite element software, establish a container ship simulation model in the finite element software, and use the finite element software to discretize the container ship simulation model into a mesh, establishing a container ship finite element model containing multiple finite element elements; each finite element element corresponds to a spatial coordinate; for each of the operating condition combinations, the hydroelastic displacement of the finite element elements is calculated using the overall hydroelastic response equation; based on the hydroelastic displacement, the navigation parameters corresponding to the operating condition combination, and the spatial coordinates of the finite element elements, the hydroelastic load of each finite element element is calculated; for each of the operating condition combinations, the hydroelastic load calculated for each finite element element under the operating condition combination is applied to the container ship finite element model, and quasi-static analysis of the finite element simulation is performed to obtain the first normal stress of each finite element element under each of the operating condition combinations; the first normal stress includes local stress.

[0030] The hull beam theoretical stress calculation module: For each of the aforementioned working condition combinations, based on the spatial coordinates of each finite element element corresponding to the working condition combination, it divides the location of each finite element element into sections, each section being a plane perpendicular to the ship's length, with each section corresponding to several finite element elements; using the overall hydroelastic response model, it calculates the internal forces corresponding to each of the aforementioned sections; based on the internal forces, it calculates the normal stress of each finite element element spatial coordinate corresponding to each of the aforementioned sections using hull beam theory, obtaining the second normal stress of each finite element element spatial coordinate under each of the aforementioned working condition combinations for the container ship; the second normal stress does not include local stresses;

[0031] The overall strain-dominant measurement point screening module: For each of the working condition combinations, it compares the first normal stress and the second normal stress at the same spatial coordinate in the working condition combination, and selects the finite element elements corresponding to the spatial coordinates where the absolute value of the difference between the first normal stress and the second normal stress and the ratio of the second normal stress is less than a preset threshold, thus obtaining the first finite element element set that satisfies the overall strain-dominant requirement for each of the working condition combinations; it then calculates the intersection of all the first finite element element sets to obtain the second finite element element set that satisfies all working conditions, which serves as the candidate monitoring points;

[0032] The actual engineering monitoring point selection module is used to select deployable monitoring points from the candidate monitoring points based on the classification specifications for steel seagoing vessels and the structural characteristics of container ships, so as to obtain monitoring points that meet the operability requirements of actual engineering.

[0033] Preferably, in the ship operating condition parameter acquisition and processing module, the navigation parameters include the ship mass under different loading conditions, and the material parameters include structural damping;

[0034] In the hydroelastic finite element stress calculation module, the hydroelastic displacement includes translational displacement and rotational displacement. The translational displacement includes sway displacement, transverse sway displacement and heave displacement. The rotational displacement includes roll angle displacement, pitch angle displacement and yaw angle displacement. The hydroelastic load includes hydroelastic pressure, inertial force, gravity rotation term and structural damping force. The hydroelastic pressure includes hydrostatic recovery pressure, radiation pressure and wave excitation pressure.

[0035] Preferably, in the hydroelastic finite element stress calculation module, when calculating the hydroelastic load of each finite element unit, the hydroelastic motion response equation containing the generalized mass matrix and the generalized damping matrix is ​​solved based on the potential flow theory. Combined with the hydroelastic displacement and structural damping, the hydrostatic recovery pressure, radiation pressure, gravity rotation term, inertial force vector and structural damping force vector corresponding to each finite element unit are calculated and vector superimposed to obtain the hydroelastic load of each finite element unit.

[0036] The beneficial effects of this invention are as follows:

[0037] This invention provides a method for selecting monitoring points for container ships that considers hydroelastic loads. This method comprehensively acquires the container ship's geometric, material, and navigation parameters, providing a complete set of basic inputs for subsequent analysis. The method employs equally spaced discretization of the wave frequency range and loading condition range, ensuring full coverage of continuous operating conditions. Furthermore, by generating several sets of operating conditions through Cartesian product combinations, it avoids the omission of critical operating conditions, providing a complete sample of operating conditions for subsequent full-condition verification of the monitoring point stability. This ensures that the finally selected monitoring points are adaptable to all actual navigation scenarios, improving the method's engineering applicability. Finally, by establishing a unified topology finite element model of the container ship through finite element discretization, it achieves both the computability of complex hull structures and provides a unified topology for each finite element unit. By binding each element to a unique spatial coordinate, a unified spatial benchmark is formed, ensuring accurate spatial reference for subsequent stress comparisons and section-to-element matching under different working conditions. Hydroelastic displacement and hydroelastic load are calculated independently for each working condition combination. Combined with the precise correlation between navigation parameters and the spatial coordinates of the finite element elements, the calculation of hydroelastic loads takes into account the coupling effect of waves and loading, ensuring that the calculated hydroelastic loads include local loads. This lays the foundation for the accuracy of subsequent stress calculations, ensuring that the finite element analysis results truly reflect the stress state of the hull under various working conditions. The hydroelastic loads calculated for each finite element element under the aforementioned working condition combinations are applied to the container ship finite element model, and quasi-static analysis is used to transform the hydroelastic loads into those including local loads. The first normal stress of the load balances computational efficiency and analytical accuracy while fully preserving the influence of local loads on element stress. This provides benchmark data containing real forces for subsequent identification of the overall strain (i.e., overall stress) dominating the finite element element. Furthermore, the stress results calculated under different load conditions provide detailed samples for subsequent comparisons across all load conditions, avoiding the limitations of single-load analysis. Section division based on the spatial coordinates of the finite element elements ensures accurate matching between the spatial coordinates of the sections and the locations of the finite element elements. The internal forces calculated using the overall hydroelastic response model and the second normal stress obtained based on hull beam theory eliminate the interference of local stresses, reflecting only the stress state dominated by the overall load, facilitating subsequent comparisons with the first normal stress, which includes local stresses. It provides a clean reference benchmark, effectively improving the accuracy and reliability of the overall strain-dominated finite element selection. Through the dual logic of "stress ratio selection + full-condition intersection calculation", it ensures that the selected finite element elements meet the overall strain-dominated requirement under each condition, and ensures that the final finite element set is stable and reliable under all conditions through intersection calculation, avoiding the randomness of single-condition selection. Based on the precise matching of spatial coordinates, it also ensures the consistency of stress comparison, improving the rigor of the measurement point selection and the reliability of the results. According to the classification specifications of steel seagoing vessels and the structural characteristics of container ships, it selects deployable monitoring points, ensuring the compliance and industry acceptance of the monitoring point layout, and improving the actual installation feasibility of the monitoring points.This invention, through ship parameter acquisition, finite element calculation, hull beam theoretical calculation, overall strain-dominant measurement point selection, and practical engineering operability selection, compares and selects the "overall stress + local stress" of the actual ship finite element calculation and the overall stress calculation of the hull beam theory under a series of working conditions. The finite element element dominated by overall strain is selected as the theoretically usable measurement point, and feasible measurement points are selected in combination with the practical engineering applicability. This ensures that the selected measurement points not only consider the hydroelastic response of the actual container ship, but also adapt to all working conditions and have strong monitoring stability.

[0038] This invention employs potential flow theory to solve the hydroelastic motion response equation, accurately capturing the interaction between waves and the ship's structure and ensuring the accuracy of the solution. Furthermore, it explicitly uses generalized mass and damping matrices for calculations, precisely matching the mass and damping characteristics of the finite element elements, further enhancing the reliability of the calculations for hydroelastic displacement and various load components. By separately calculating the hydrostatic restoring pressure, radiation pressure, gravity rotation term, inertial force vector, and structural damping force vector, it achieves precise decomposition and quantification of each core component of the hydroelastic load, avoiding calculation distortion caused by load component confusion. Moreover, all loads are associated with hydroelastic displacement and structural damping, comprehensively covering the coupled forces of fluid, structure, inertia, and damping. Finally, the hydroelastic load of each finite element was obtained by vector superposition, which not only ensured the integrity and accuracy of the load calculation, but also enabled the load input of the container ship finite element model to truly reflect the actual stress state of the hull under different working conditions. This provided a high-precision load basis for subsequent quasi-static analysis and normal stress calculation, effectively improving the rigor, scientificity and engineering practicality of the entire monitoring point selection method. At the same time, it also provided a traceable calculation basis for subsequent load verification and parameter optimization.

[0039] This invention is based on thin-walled beam theory, combining the cross-sectional moment of inertia and sectoral moment of inertia calculated from the geometric parameters corresponding to the container ship cross-section, and using the corresponding formula to calculate the second normal stress at any point on the cross-section. It accurately adapts to the structural essence of the "variable cross-section thin-walled beam" of large container ships. By introducing parameters unique to thin-walled sections, such as dual moments, sectoral coordinates, and sectoral moment of inertia, it fully captures the additional normal stress caused by the torsional warping of container ships, avoiding the stress calculation deviations caused by neglecting the thin-walled effect in ordinary beam theory. Simultaneously, this calculation process uses the cross-sectional internal forces output by the overall hydroelastic response model. Using (vertical bending moment, horizontal bending moment, and dual moment) as inputs, this method directly relates to the overall stress on the ship and the local stress of the cross section. The resulting normal stress only reflects the stress state dominated by the overall load, providing a pure benchmark for subsequent comparison with the stress including local loads in finite element calculations. This effectively improves the accuracy of the selection of the "overall strain-dominant unit". In addition, this method strictly conforms to the analysis requirements of the "Steel Seagoing Ship Classification Code" for thin-walled structures, ensuring the compliance and industry acceptance of the calculations, facilitating engineering verification, and ultimately improving the rigor and engineering practicality of the monitoring point selection method.

[0040] This invention establishes an objective and unified quantitative screening criterion through the absolute value formula of the ratio of "(second normal stress - first normal stress) / second normal stress", which completely avoids the subjectivity and randomness of traditional qualitative judgment. The preset 10% threshold is derived from the experience summary in the field of shipbuilding engineering, which accurately matches the typical stress deviation range of the overall strain and local load of container ships, and can effectively identify finite element elements that are less affected by local loads and stably reflect the overall load.

[0041] This invention employs a dual screening mechanism combining steel seagoing vessel classification standards and container ship structural characteristics to select monitoring points. Strictly adhering to the requirements of the "Steel Seagoing Vessel Classification Standards," it prioritizes characteristic sections with the most significant vertical bending deformation at 1 / 4, 1 / 2, and 3 / 4 of the ship's length. This accurately reflects the stress state dominated by the overall load, ensuring the compliance and representativeness of the monitoring point layout and enhancing the industry acceptance and credibility of the monitoring results. Considering the structural characteristics of container ships, monitoring points overlapping with cargo holds, ballast tanks, and oil tanks are eliminated. This avoids data distortion caused by placing monitoring points in compartments with concentrated local loads and complex structures. It also excludes invalid monitoring points with limited installation space, ensuring that the final selected monitoring points have the ability to stably reflect the overall load and meet the feasibility of actual engineering installation, significantly improving effectiveness and engineering implementation value.

[0042] This invention also relates to a container ship monitoring point selection system considering hydroelastic loads. This system corresponds to the aforementioned container ship monitoring point selection method considering hydroelastic loads, and can be understood as a system that implements the aforementioned container ship monitoring point selection method considering hydroelastic loads. It includes a working condition parameter acquisition and processing module, a hydroelastic finite element stress calculation module, a hull beam theoretical stress calculation module, an overall strain-dominant measurement point screening module, and an actual engineering monitoring measurement point screening module. These modules work collaboratively and have the following advantages: 1. It directly determines the measurement points dominated by the overall deformation of the large container ship hull structure through the finite element method and hull beam theory, which can be used to directly identify the hull section load; 2. In The finite element stress analysis and overall dominant stress analysis of large container ships take into account the influence of hydroelastic deformation. This solves the problem that traditional techniques usually treat the hull as a rigid body for hydrodynamic analysis in the three-dimensional finite element calculation of actual ships, thus ignoring the inherent vibration modes of the structure that are easily excited during navigation, resulting in significant hydroelastic deformation. Third, based on theoretical selection of measuring points and combined with actual layout requirements, feasible measuring points are designed to ensure the feasibility of actual measuring point engineering. By traversing all wave frequencies and loading rates (loading conditions) and taking the intersection, the finally selected measuring points can stably meet the requirement of local interference <10% under various navigation scenarios, adapting to the monitoring needs of large container ships throughout the entire navigation cycle. Attached Figure Description

[0043] Figure 1 This is a flowchart of the container ship monitoring point selection method considering water elastic load according to the present invention.

[0044] Figure 2 This is a schematic diagram of the stress calculated by the finite element method of the present invention.

[0045] Figure 3 This is a schematic diagram of the monitoring points for overall strain-dominated monitoring according to the present invention.

[0046] Figure 4 This is a schematic diagram of the monitoring points dominated by overall strain under all conventional wave frequencies and loading conditions of this invention.

[0047] Figure 5 This is a diagram showing the arrangement of long baseline strain gauges in the longitudinal section of a container ship according to the present invention.

[0048] Figure 6 This is a side view of the long baseline strain gauge structure of the present invention.

[0049] Figure 7 This is a block diagram of the container ship monitoring and measurement point selection system that takes into account water elastic loads according to the present invention. Detailed Implementation

[0050] The present invention will now be described with reference to the accompanying drawings.

[0051] This invention relates to a method for selecting monitoring points on container ships that takes into account hydroelastic loads. This method fully considers the effect of hydroelastic loads in the selection of monitoring points. It compares and filters the "overall stress + local stress" calculated by finite element analysis of the actual ship under a series of working conditions with the overall stress calculated by ship beam theory (or, by comparing the first normal stress containing local stress obtained from finite element analysis under multiple working conditions with the second normal stress without local stress obtained from ship beam theory). Finite elements with a ratio error of less than 10% are considered monitoring points dominated by overall deformation. Elements dominated by overall strain are selected as theoretically usable monitoring points. Finally, considering practical engineering applicability, feasible monitoring points are selected. The specific process of this method is as follows: Figure 1 As shown, it includes the following steps:

[0052] S1. Obtain the container ship's geometric parameters (such as length, beam, depth, draft, etc.), material parameters (such as structural damping, elastic modulus, Poisson's ratio, etc.), and navigation parameters (such as ship mass and speed under different loading conditions, etc.). Determine the wave frequency range to be analyzed (e.g., 0.2 rad / s to 2.3 rad / s) and the loading condition range (e.g., 20% to 100%) based on the wave statistical characteristics of the actual navigation area of ​​the container ship. Discretize the continuous wave frequency range and the continuous loading condition range at equal intervals to obtain several discretized wave frequencies and discretized loading conditions. Use the Cartesian product matching method to combine all discretized wave frequencies with all discretized loading conditions one by one to form several condition combinations.

[0053] The interval for equally spaced discretization of the wave frequency range can be 0.1 rad / s, 0.05 rad / s, or 0.01 rad / s, etc., and the interval for equally spaced discretization of the loading condition range can be 5%, 7%, or 10%, etc.

[0054] S2, input the geometric parameters, material parameters, etc. into the finite element software, and establish a container ship simulation model in the finite element software. Use the finite element software to perform mesh discretization on the container ship simulation model to establish a container ship finite element model containing multiple finite element elements (also known as a full container ship finite element model); each finite element element corresponds to a spatial coordinate.

[0055] In this embodiment of the invention, a three-dimensional spatial coordinate system (also known as the overall hull coordinate system) can be established with the length of the container ship as the x-axis, the width as the y-axis, and the vertical direction as the z-axis. Each finite element element corresponds to a unique spatial coordinate (x, y, z), where x, y, and z are the coordinates of the center of the finite element element in the overall hull coordinate system.

[0056] S3, for each of the aforementioned operating condition combinations, calculate the hydroelastic displacement of the finite element unit using the overall hydroelastic response equation; based on the hydroelastic displacement, the navigation parameters corresponding to the operating condition combination, and the spatial coordinates of the finite element unit, calculate the hydroelastic load of each of the aforementioned finite element units.

[0057] Hydroelastic displacement includes translational displacement and rotational displacement. Translational displacement includes sway displacement, transverse sway displacement and heave displacement. Rotational displacement includes roll angle displacement, pitch angle displacement and yaw angle displacement. Hydroelastic loads include hydroelastic pressure, inertial force (also known as hydroelastic acceleration), gravity rotation term, structural damping force, etc. The hydroelastic pressure includes hydrostatic recovery pressure, radiation pressure and wave excitation pressure, etc.

[0058] When calculating the hydroelastic load of each finite element element, the hydroelastic motion response equation, which includes the generalized mass matrix and the generalized damping matrix, is solved based on potential flow theory. Combining the hydroelastic displacement and structural damping, the hydrostatic recovery pressure, radiation pressure, gravity rotation term, inertial force vector, and structural damping force vector corresponding to each finite element element are calculated and vector-superimposed to obtain the hydroelastic load of each finite element element. Specifically, the hydrostatic recovery pressure, radiation pressure, wave excitation pressure, inertial force, gravity rotation term, and structural damping force can be calculated using the following formulas:

[0059] , ,

[0061] ,

[0062] Where m represents the m-th finite element. This represents the hydrostatic recovery pressure corresponding to the m-th finite element element. This represents the gravity rotation term vector corresponding to the m-th finite element. This represents the inertial force vector corresponding to the m-th finite element. This represents the structural damping force vector corresponding to the m-th finite element. Indicates radiation pressure. Let g represent the density of water and g represent the acceleration due to gravity. Indicates hydroelastic displacement. This represents the heave displacement corresponding to the m-th finite element. This represents the roll displacement corresponding to the m-th finite element. This represents the pitch displacement corresponding to the m-th finite element. This represents the y-coordinate of the m-th finite element in the ship's coordinate system. This represents the x-coordinate of the m-th finite element in the ship's coordinate system. Let m be the generalized mass matrix of the m-th finite element. The unit vector representing the z-axis of the coordinate system. This represents the rotational displacement vector corresponding to the m-th finite element. Indicates the frequency of wave encounters. Let represent the translational displacement vector corresponding to the m-th finite element. Let r = (x, y, z) represent the position vector of the m-th finite element in the ship's coordinate system. , represents the imaginary unit, The generalized damping matrix of the m-th finite element can be represented using Rayleigh damping. Let represent the radiation pressure acting on a finite element (or surface element) under the unit motion of the j-th mode (j=1,2…6). This represents the generalized displacement corresponding to the j-th modal unit; since the displacement is a hydroelastic displacement, the hydroelastic load includes the influence of hydroelasticity, that is, the hydroelastic load includes local load.

[0063] The wave excitation pressure It can be calculated based on potential flow theory.

[0064] The wave encounter frequency can be calculated using the following formula:

[0065] ,

[0066] in, U represents the wave frequency, and U represents the ship speed. Indicates the wave angle.

[0067] S4. For each of the aforementioned working condition combinations, the hydroelastic loads calculated for each finite element element under the aforementioned working condition combination are applied to the finite element model of the container ship, and quasi-static analysis is performed using finite element simulation to obtain the first normal stress of each of the aforementioned finite element elements under each of the aforementioned working condition combinations; the first normal stress includes local stress.

[0068] The first normal stress calculated using the finite element method in this embodiment of the invention includes the overall stress dominated by overall strain and the local stress caused by local water pressure.

[0069] For example, such as Figure 2 The figure shows the calculation results of the first normal stress of each finite element under a certain working condition combination. Figure 2Different colors represent normal stresses of different magnitudes. S represents the general identifier of the finite element stress tensor, S11 represents the normal stress component along the longitudinal direction of the hull—that is, the first normal stress, multiple facets represent the equivalent stresses calculated by selecting multiple nodes in the container ship finite element model, and the average 75% means that the results of the corresponding finite element are averaged only when the relative node variables are less than 75%.

[0070] S5, for each of the aforementioned working condition combinations, based on the spatial coordinates of each finite element unit corresponding to the working condition combination, the location of each finite element unit is divided into sections, the sections being planes perpendicular to the ship's length, and each section corresponding to several finite element units; using the overall hydroelastic response model, the internal forces corresponding to each section are calculated; based on the internal forces, the normal stresses of the spatial coordinates of each finite element unit corresponding to each section are calculated using the hull beam theory, to obtain the second normal stresses of the spatial coordinates of each finite element unit under each of the aforementioned working condition combinations for the container ship; the second normal stresses do not include local stresses.

[0071] The internal forces include vertical bending moment, horizontal bending moment, and double moment.

[0072] Since large container ships can be considered as variable cross-section thin-walled beams, the hull beam theory adapted to variable cross-section thin-walled beams—the thin-walled beam theory—can be used. Combined with the cross-sectional moment of inertia and sector moment of inertia calculated from the geometric parameters corresponding to the container ship's cross-section, the second normal stress at any spatial coordinate of the cross-section can be calculated. The calculation formula is as follows:

[0073] ,

[0074] in, Indicates the second normal stress. Indicates the vertical bending moment. Let B represent the horizontal bending moment, B represent the two moments, y represent the beam direction coordinate in the hull coordinate system, and z represent the vertical coordinate in the hull coordinate system. Represents sector coordinates, This represents the moment of inertia of the cross section about the beam direction in the hull coordinate system. The moment of inertia of the cross section about the vertical direction in the ship's coordinate system is represented by . The sector moment of inertia represents the cross section.

[0075] S6. For each of the aforementioned working condition combinations, the first normal stress and the second normal stress in the same spatial coordinate of the working condition combination are compared. Finite element elements corresponding to spatial coordinates where the absolute value of the difference between the first normal stress and the second normal stress and the ratio of the second normal stress is less than a preset threshold (based on experience, it can be set to 10%) are selected. This yields a set of first finite element elements that satisfy the overall strain-dominated condition for each of the aforementioned working condition combinations. The intersection of all first finite element element sets is calculated to obtain the distribution of monitoring points for second finite element elements that satisfy all working conditions. This yields a set of second finite element elements as candidate monitoring points.

[0076] The first normal stress is selected based on the following formula. With the second normal stress The finite element element corresponding to the spatial coordinates where the absolute value of the ratio of the difference to the second normal stress is less than 10% of the preset threshold is:

[0077] .

[0078] For example, such as Figure 3 The figure shown is the first normal stress contour plot corresponding to the monitoring point (finite element) under a certain working condition that satisfies the overall strain-dominated condition. Figure 2 The full model stress results, Figure 3 Finite element elements that do not meet the overall strain dominance condition were eliminated, and only finite element elements that meet the overall strain dominance condition were retained as candidate monitoring points. Figure 3 Different colors represent normal stresses of different magnitudes. S represents the general identifier of the finite element stress tensor. S11 represents the first normal stress. SNEG (fraction=-1.0) represents the normal negative stress component of the finite element. The average of 75% means that the result of the corresponding finite element is averaged only when the relative nodal variables are less than 75%.

[0079] For example, such as Figure 4 The figure shows the monitoring points that satisfy the overall strain-dominated condition under all operating conditions. All monitoring points in the figure satisfy all operating conditions. Compared to satisfying only one operating condition combination... Figure 3 Satisfying all operating condition combinations Figure 4 The number of monitoring points has been significantly reduced, and their distribution is more representative, which can serve as the basis for screening the feasibility of subsequent projects.

[0080] S7. Based on the classification standards for steel seagoing vessels and the structural characteristics of container ships, select feasible monitoring points from the candidate monitoring points to obtain monitoring points that meet the operability requirements of actual engineering.

[0081] Specifically, based on the classification rules for steel seagoing vessels, from the candidate monitoring points, the monitoring points at 1 / 4, 1 / 2, and 3 / 4 of the ship's length are selected as monitoring points that meet the classification rules; based on the structural characteristics of container ships, from the monitoring points that meet the classification rules, those that overlap with the cargo hold, ballast tank, and oil tank areas of the container ship are removed, resulting in monitoring points that meet the practical engineering operability requirements.

[0082] After selecting monitoring points that meet the operability requirements of actual engineering, long-baseline strain gauges (also known as strain monitoring instruments) are installed at the monitoring points to achieve real-time monitoring. Figure 5 This diagram illustrates a possible deployment location for long baseline strain gauges. Within the same cross section, long baseline strain gauges are deployed at locations such as the lower end of the hatch coaming, the lower end of the upper deck, and the inner longitudinal rib.

[0083] The preferred structure of a long baseline strain gauge is as follows: Figure 6 As shown, the total length is 1810mm, the effective measuring length is 1432mm, and it is equipped with a DN42 flange interface for rigid connection to the hull monitoring structure or base.

[0084] Figure 7 This is a structural block diagram of a container ship monitoring and measurement point selection system considering water elastic loads, provided in one or more embodiments of this specification. Figure 7 As shown, the container ship monitoring point selection system considering hydroelastic loads includes, in sequence, a ship operating condition parameter acquisition and processing module 101, a hydroelastic finite element stress calculation module 102, a hull beam theoretical stress calculation module 103, an overall strain-dominant measurement point selection module 104, and an actual engineering monitoring measurement point selection module 105. Among them,

[0085] The ship operating condition parameter acquisition and processing module 101 is used to acquire the geometric parameters, material parameters, and navigation parameters of the container ship; determine the wave frequency range and loading condition range to be analyzed; perform equal-interval discretization on the wave frequency range and loading condition range respectively to obtain several discretized wave frequencies and discretized loading conditions; and use the Cartesian product matching method to combine all discretized wave frequencies with all discretized loading conditions one by one to form several operating condition combinations.

[0086] The hydroelastic finite element stress calculation module 102 is used to input the geometric parameters and material parameters into the finite element software, establish a container ship simulation model in the finite element software, and use the finite element software to perform mesh discretization on the container ship simulation model to establish a container ship finite element model containing multiple finite element elements; each finite element element corresponds to a spatial coordinate; for each of the operating condition combinations, the hydroelastic displacement of the finite element elements is calculated through the overall hydroelastic response equation; based on the hydroelastic displacement, the navigation parameters corresponding to the operating condition combination, and the spatial coordinates of the finite element elements, the hydroelastic load of each finite element element is calculated; for each of the operating condition combinations, the hydroelastic load calculated for each finite element element under the operating condition combination is applied to the container ship finite element model, and quasi-static analysis of finite element simulation is performed to obtain the first normal stress of each finite element element under each of the operating condition combinations; the first normal stress includes local stress.

[0087] The hull beam theoretical stress calculation module 103, for each of the aforementioned working condition combinations, divides the location of each finite element unit into sections based on the spatial coordinates of each finite element unit corresponding to the working condition combination. Each section is a plane perpendicular to the ship's length, and each section corresponds to several finite element units. Using the overall hydroelastic response model, it calculates the internal forces corresponding to each section. Based on these internal forces, it calculates the normal stress of each finite element unit's spatial coordinates corresponding to each section using hull beam theory, obtaining the second normal stress of each finite element unit's spatial coordinates under each of the aforementioned working condition combinations for the container ship. The second normal stress does not include local stress.

[0088] The overall strain-dominant measurement point screening module 104 compares the first normal stress and the second normal stress at the same spatial coordinate in each working condition combination, and selects finite element elements corresponding to spatial coordinates where the absolute value of the difference between the first normal stress and the second normal stress and the ratio of the second normal stress is less than a preset threshold, thereby obtaining a set of first finite element elements that satisfy the overall strain-dominant condition for each working condition combination; and calculates the intersection of all first finite element element sets to obtain a set of second finite element elements that satisfy all working conditions, which are used as candidate monitoring points.

[0089] The actual engineering monitoring point screening module 105 is used to select deployable monitoring points from the candidate monitoring points based on the classification specifications for steel seagoing vessels and the structural characteristics of container ships, so as to obtain monitoring points that meet the operability of actual engineering.

[0090] Furthermore, in the ship operating condition parameter acquisition and processing module 101, the navigation parameters include the ship mass under different loading conditions, and the material parameters include structural damping.

[0091] In the hydroelastic finite element stress calculation module 102, the hydroelastic displacement includes translational displacement and rotational displacement. The translational displacement includes sway displacement, transverse sway displacement and heave displacement. The rotational displacement includes roll angle displacement, pitch angle displacement and yaw angle displacement. The hydroelastic load includes hydroelastic pressure, inertial force, gravity rotation term and structural damping force. The hydroelastic pressure includes hydrostatic recovery pressure, radiation pressure and wave excitation pressure.

[0092] Furthermore, in the hydroelastic finite element stress calculation module 102, when calculating the hydroelastic load of each finite element unit, the hydroelastic motion response equation containing the generalized mass matrix and the generalized damping matrix is ​​solved based on the potential flow theory. Combined with the hydroelastic displacement and structural damping, the hydrostatic recovery pressure, radiation pressure, gravity rotation term, inertial force vector and structural damping force vector corresponding to each finite element unit are calculated and vector superimposed to obtain the hydroelastic load of each finite element unit.

[0093] It should be noted that the specific embodiments described above enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. Therefore, although the present invention has been described in detail with reference to the accompanying drawings and embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. In short, all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention patent.

Claims

1. A method for selecting monitoring points for container ships considering hydroelastic loads, characterized in that, Includes the following steps: S1: Obtain the geometric parameters, material parameters, and navigation parameters of the container ship; determine the wave frequency range and loading condition range to be analyzed, and perform equal-interval discretization on the wave frequency range and loading condition range to obtain several discretized wave frequencies and discretized loading conditions; use the Cartesian product matching method to combine all discretized wave frequencies with all discretized loading conditions one by one to form several condition combinations. S2: Input the geometric parameters and material parameters into the finite element software, and establish a container ship simulation model in the finite element software. Use the finite element software to discretize the container ship simulation model into a mesh, and establish a container ship finite element model containing multiple finite element elements; each finite element element corresponds to a spatial coordinate. S3: For each of the aforementioned operating condition combinations, calculate the hydroelastic displacement of the finite element element using the overall hydroelastic response equation; and calculate the hydroelastic load of each of the finite element elements based on the hydroelastic displacement, the navigation parameters corresponding to the operating condition combination, and the spatial coordinates of the finite element element. S4: For each of the aforementioned working condition combinations, the hydroelastic loads calculated for each finite element under the aforementioned working condition combination are applied to the container ship finite element model, and quasi-static analysis of finite element simulation is performed to obtain the first normal stress of each of the aforementioned finite element elements under each of the aforementioned working condition combinations; the first normal stress includes local stress. S5: For each of the aforementioned working condition combinations, based on the spatial coordinates of each finite element element corresponding to the working condition combination, the location of each finite element element is divided into sections, each section being a plane perpendicular to the ship's length, and each section corresponding to several finite element elements; using the overall hydroelastic response model, the internal forces corresponding to each section are calculated; based on the internal forces, the normal stress of each finite element element spatial coordinate corresponding to each section is calculated using the hull beam theory, thus obtaining the second normal stress of each finite element element spatial coordinate under each of the aforementioned working condition combinations for the container ship; The second normal stress does not include local stress; S6: For each of the working condition combinations, the first normal stress and the second normal stress in the same spatial coordinate in the working condition combination are compared respectively, and the finite element elements corresponding to the spatial coordinates where the absolute value of the difference between the first normal stress and the second normal stress and the ratio of the second normal stress is less than a preset threshold are selected, so as to obtain the first finite element set that satisfies the overall strain-dominated condition for each of the working condition combinations. Calculate the intersection of all first finite element sets to obtain the second finite element set that satisfies all working conditions, which can be used as candidate monitoring points; S7: Based on the classification standards for steel seagoing vessels and the structural characteristics of container ships, select feasible monitoring points from the candidate monitoring points to obtain monitoring points that meet the operability requirements of actual engineering.

2. The method according to claim 1, characterized in that, In step S1, the navigation parameters include the ship's mass under different loading conditions, and the material parameters include structural damping. In step S3, the hydroelastic displacement includes translational displacement and rotational displacement. The translational displacement includes sway displacement, lateral sway displacement and heave displacement. The rotational displacement includes roll angle displacement, pitch angle displacement and yaw angle displacement. The hydroelastic load includes hydroelastic pressure, inertial force, gravity rotation term and structural damping force. The hydroelastic pressure includes hydrostatic recovery pressure, radiation pressure and wave excitation pressure.

3. The method according to claim 2, characterized in that, In step S3, when calculating the hydroelastic load of each finite element element, the hydroelastic motion response equation containing the generalized mass matrix and the generalized damping matrix is ​​solved based on the potential flow theory. Combining the hydroelastic displacement and structural damping, the hydrostatic recovery pressure, radiation pressure, gravity rotation term, inertial force vector and structural damping force vector corresponding to each finite element element are calculated and vector superimposed to obtain the hydroelastic load of each finite element element.

4. The method according to claim 1, characterized in that, In step S5, the internal forces include vertical bending moment, horizontal bending moment, and double moment; Based on the thin-walled beam theory, and combined with the cross-sectional moment of inertia and sector moment of inertia calculated from the geometric parameters corresponding to the container ship cross-section, the second normal stress at any spatial coordinate of the cross-section is calculated using the following formula: ， in, Indicates the second normal stress. Indicates the vertical bending moment. Let B represent the horizontal bending moment, B represent the two moments, y represent the beam direction coordinate in the hull coordinate system, and z represent the vertical coordinate in the hull coordinate system. Represents sector coordinates, This represents the moment of inertia of the cross section about the beam direction in the hull coordinate system. The moment of inertia of the cross section about the vertical direction in the ship's coordinate system is represented by . The sector moment of inertia represents the cross section.

5. The method according to claim 4, characterized in that, In step S6, finite element elements corresponding to spatial coordinates where the absolute value of the ratio of the difference between the first normal stress and the second normal stress to the second normal stress is less than a preset threshold are selected based on the following formula: ， in, This represents the first normal stress; the preset threshold is 10%.

6. The method according to claim 1, characterized in that, In step S1, the wave frequency range is 0.2 rad / s to 2.3 rad / s, and the loading condition range is 20% to 100%.

7. The method according to claim 1, characterized in that, In step S7, in accordance with the classification rules for steel seagoing vessels, the candidate monitoring points at 1 / 4, 1 / 2, and 3 / 4 of the ship's length are selected from the candidate monitoring points as monitoring points that meet the classification rules. Based on the structural characteristics of container ships, among the monitoring points that meet the classification specifications, those that overlap with the cargo hold, ballast tank, and oil tank areas of container ships are removed, resulting in monitoring points that meet the practical engineering operability requirements.

8. A container ship monitoring point selection system considering water elastic load, characterized in that, This includes, in sequence, a ship operating condition parameter acquisition and processing module, a hydroelastic finite element stress calculation module, a hull beam theoretical stress calculation module, an overall strain dominant measurement point selection module, and an actual engineering monitoring measurement point selection module; among them, The ship operating condition parameter acquisition and processing module is used to acquire the geometric parameters, material parameters, and navigation parameters of the container ship; determine the wave frequency range and loading condition range to be analyzed; perform equal-interval discretization on the wave frequency range and loading condition range to obtain several discretized wave frequencies and discretized loading conditions; and use the Cartesian product matching method to combine all discretized wave frequencies with all discretized loading conditions one by one to form several operating condition combinations. The hydroelastic finite element stress calculation module is used to input the geometric and material parameters into the finite element software, establish a container ship simulation model in the finite element software, and use the finite element software to discretize the container ship simulation model into a mesh, establishing a container ship finite element model containing multiple finite element elements; each finite element element corresponds to a spatial coordinate; for each of the operating condition combinations, the hydroelastic displacement of the finite element elements is calculated using the overall hydroelastic response equation; based on the hydroelastic displacement, the navigation parameters corresponding to the operating condition combination, and the spatial coordinates of the finite element elements, the hydroelastic load of each finite element element is calculated; for each of the operating condition combinations, the hydroelastic load calculated for each finite element element under the operating condition combination is applied to the container ship finite element model, and quasi-static analysis of the finite element simulation is performed to obtain the first normal stress of each finite element element under each of the operating condition combinations; the first normal stress includes local stress. The hull beam theoretical stress calculation module: For each of the aforementioned working condition combinations, based on the spatial coordinates of each finite element element corresponding to the working condition combination, it divides the location of each finite element element into sections, each section being a plane perpendicular to the ship's length, with each section corresponding to several finite element elements; using the overall hydroelastic response model, it calculates the internal forces corresponding to each of the aforementioned sections; based on the internal forces, it calculates the normal stress of each finite element element spatial coordinate corresponding to each of the aforementioned sections using hull beam theory, obtaining the second normal stress of each finite element element spatial coordinate under each of the aforementioned working condition combinations for the container ship; the second normal stress does not include local stresses; The overall strain-dominant measurement point screening module: For each of the working condition combinations, it compares the first normal stress and the second normal stress at the same spatial coordinate in the working condition combination, and selects the finite element elements corresponding to the spatial coordinates where the absolute value of the difference between the first normal stress and the second normal stress and the ratio of the second normal stress is less than a preset threshold, thus obtaining the first finite element element set that satisfies the overall strain-dominant requirement for each of the working condition combinations; it then calculates the intersection of all the first finite element element sets to obtain the second finite element element set that satisfies all working conditions, which serves as the candidate monitoring points; The actual engineering monitoring point selection module is used to select deployable monitoring points from the candidate monitoring points based on the classification specifications for steel seagoing vessels and the structural characteristics of container ships, so as to obtain monitoring points that meet the operability requirements of actual engineering.

9. The system according to claim 8, characterized in that, In the ship operating condition parameter acquisition and processing module, the navigation parameters include the ship mass under different loading conditions, and the material parameters include structural damping. In the hydroelastic finite element stress calculation module, the hydroelastic displacement includes translational displacement and rotational displacement. The translational displacement includes sway displacement, transverse sway displacement and heave displacement. The rotational displacement includes roll angle displacement, pitch angle displacement and yaw angle displacement. The hydroelastic load includes hydroelastic pressure, inertial force, gravity rotation term and structural damping force. The hydroelastic pressure includes hydrostatic recovery pressure, radiation pressure and wave excitation pressure.

10. The system according to claim 9, characterized in that, In the hydroelastic finite element stress calculation module, when calculating the hydroelastic load of each finite element, the hydroelastic motion response equation containing the generalized mass matrix and the generalized damping matrix is ​​solved based on the potential flow theory. Combined with the hydroelastic displacement and structural damping, the hydrostatic recovery pressure, radiation pressure, gravity rotation term, inertial force vector and structural damping force vector corresponding to each finite element are calculated and vector superimposed to obtain the hydroelastic load of each finite element.

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