Underwater vehicle cylindrical shell model construction method and system and medium

Abstract

The invention provides an underwater vehicle cylindrical shell model construction method and system and a medium, and relates to the technical field of underwater vehicles, and the method comprises the following steps: selecting a cylindrical shell structure and a constituent material, and setting a strength condition and a stability condition; initial design parameters are set according to the cylindrical shell structure, and a parameterized geometric model is obtained in combination with constituent materials; and generating an axisymmetric finite element model according to the parameterized geometric model, performing structural stress calculation, and correspondingly adjusting the parameterized geometric model by taking the lightest weight as a target according to a structural stress calculation result. According to the method, structural stress is calculated by simplifying a parameterized geometric model into an axial symmetry model, buckling pressure is calculated by establishing a three-dimensional model, optimization adjustment and iteration are carried out with the lightest weight as the target, constraint is carried out according to the strength condition and the stability condition, and a final optimization result is obtained. The rapid generation of an optimization parameter adjustment result is realized, and a target model is obtained.

Description

Technical Field

[0001] This invention relates to the field of underwater vehicle technology, and in particular to a method, system, and medium for constructing a cylindrical shell model of an underwater vehicle. Background Technology

[0002] Since the overall weight of an underwater vehicle directly determines its maneuverability, payload capacity, and endurance, its pressure shell structure must be optimized with the lightest possible weight while ensuring safety. Simultaneously, the internal dimensions of the shell directly affect equipment layout and payload, thus requiring strict control over space occupancy. To balance weight, strength, and space constraints, engineers propose various pressure shell configurations, such as ring-ribbed cylindrical shells, double-shell reinforced structures, and mesh-reinforced structures. For combinations of different configurations and materials (such as high-strength steel, titanium alloys, and composite materials), the mechanical response is complex. A high-fidelity three-dimensional finite element analysis model must be established to accurately simulate the stress distribution, stability performance, and failure modes under deep external pressure, ensuring the design meets stringent strength and stability constraints.

[0003] However, performing multi-parameter optimization directly based on a three-dimensional finite element model faces enormous computational challenges. Design variables (such as shell thickness, rib spacing and dimensions, material distribution, etc.) are often numerous, and the parameter combination space is large. Each set of parameters requires detailed three-dimensional nonlinear static and buckling analysis, and a single simulation calculation can take several hours or even longer. If traditional parameter scanning or iterative optimization strategies are used to explore the entire parameter space, the total computational load will increase exponentially, resulting in extremely high computational costs, severely extending the product development cycle, and making it difficult to meet the design requirements of rapid iteration in modern equipment. Summary of the Invention

[0004] In view of this, the present invention proposes a method, system and medium for constructing a cylindrical shell model of an underwater vehicle. By simplifying the parametric geometric model into an axisymmetric model, the structural stress is calculated. At the same time, by establishing a three-dimensional model, the buckling pressure is calculated. The optimization adjustment and iteration are carried out with the goal of minimizing weight. Constraints are imposed according to strength conditions and stability conditions to obtain the final optimization result. This enables the rapid generation of optimization parameter adjustment results and the acquisition of the target model.

[0005] The technical solution of this invention is implemented as follows: On one hand, the present invention provides a method for constructing a cylindrical shell model of an underwater vehicle, comprising the following steps: Select the column shell structure and constituent materials, and set strength and stability conditions; Based on the initial design parameters of the column shell structure, a parametric geometric model is obtained; An axisymmetric finite element model is constructed based on a parametric geometric model, and structural stress is calculated in conjunction with the constituent materials. The axisymmetric finite element model is a two-dimensional planar model of a single-sided cross-section of a cylindrical shell. A shell element finite element model is constructed based on a parametric geometric model, and buckling pressure is calculated in conjunction with the constituent materials. The shell element finite element model is a simplified three-dimensional model of a cylindrical shell. Based on the structural stress calculation results and buckling pressure calculation results, the strength condition and stability condition are used as constraints, and the parametric geometric model is adjusted accordingly with the goal of minimizing weight.

[0006] Based on the above technical solutions, preferably, the cylindrical shell structure includes one of a ring-ribbed cylindrical pressure-resistant shell structure and a double-layer composite cylindrical pressure-resistant shell structure. The ring-ribbed cylindrical pressure-resistant shell structure includes a cylindrical shell with several annular reinforcing ribs disposed on the inner wall of the shell. The double-layer composite cylindrical pressure-resistant shell structure includes an outer shell plate, an inner shell plate disposed inside the outer shell plate, and several annular ribs disposed between the outer shell plate and the inner shell plate.

[0007] Based on the above technical solutions, preferably, before obtaining the final parametric geometric model, the following steps are also included: The parameterized geometric model that meets the stability condition is used as the intermediate parameterized geometric model; The intermediate parameterized geometric model is combined with the constituent materials to perform ultimate load calculations and update the stability conditions. The intermediate parameterized geometric model was verified using the updated stability conditions; The parametric geometric model is updated and optimized based on the review results.

[0008] More preferably, the step of performing ultimate load-bearing calculations on the intermediate parameterized geometric model in conjunction with the constituent materials and updating the stability conditions includes the following steps: Based on the intermediate parameterized geometric model, the ultimate bearing capacity is calculated according to the bilinear elastoplastic constitutive model of the material and the initial imperfection based on the buckling mode. The nonlinear correction coefficient for instability pressure is obtained from the ultimate bearing capacity calculation results. The stability conditions are updated based on the nonlinear correction coefficient of the instability pressure.

[0009] More preferably, the nonlinear correction coefficient for instability pressure is proportional to the calculation result of ultimate bearing capacity and inversely proportional to the calculation result of buckling pressure.

[0010] More preferably, the intermediate parameterized geometric model is an intermediate optimization model based on the parameterized geometric model, with the goal of minimizing weight and with strength and stability conditions as dual constraints.

[0011] More preferably, the initial design parameters of the double-layer composite cylindrical pressure shell structure include the thickness of the double-layer shell, the number of ribs, the thickness of the inner shell plate, the thickness of the outer shell plate and the thickness of the ribs, and the initial design parameters of the ring-ribbed cylindrical pressure shell structure include the shell plate thickness, the rib height, the web plate thickness, the rib thickness, the web plate width and the rib spacing.

[0012] Based on the above technical solutions, preferably, the step of constructing an axisymmetric finite element model based on a parametric geometric model and performing structural stress calculation includes the following steps: Construct an axisymmetric finite element model based on the parametric geometric model; In the axisymmetric finite element model, the evaluation region is set, and the boundary regions on both sides of the axial interface are removed; The strength of the assessment area is checked to obtain the structural stress calculation results.

[0013] Secondly, this invention proposes an underwater vehicle cylindrical shell model construction system, which incorporates the aforementioned underwater vehicle cylindrical shell model construction method.

[0014] Thirdly, the present invention proposes a medium on which a computer can read an underwater vehicle cylindrical shell model construction program, which, when executed by a processor, implements the above-described underwater vehicle cylindrical shell model construction method.

[0015] The underwater vehicle cylindrical shell model construction method, system, and medium of the present invention have the following advantages over the prior art: By simplifying the parametric geometric model into an axisymmetric model, the structural stress is calculated. Simultaneously, by establishing a three-dimensional model, the buckling pressure is calculated. Optimization and iteration are performed with the goal of minimizing weight. Constraints are imposed based on strength and stability conditions to obtain the final optimization result. This enables the rapid generation of optimization parameter adjustment results and the acquisition of the target model. Initial stability conditions are typically based on ideal linear buckling theory. These initial conditions can be preset as needed. This theory assumes perfect structural geometry and perfectly elastic materials; therefore, the calculated buckling pressure, i.e., the ideal critical load, is often significantly higher than the failure pressure of the actual structure. Real shells exhibit geometric imperfections, residual stresses, and material nonlinearities, which can lead to a decrease in their actual stable load-bearing capacity. By introducing correction coefficients and updating the stability conditions, we ensure that the optimization results possess both theoretical rigor and engineering reliability. The correction coefficients quantitatively characterize the difference in load-bearing capacity between the ideal model and the actual structure. Leveraging the axisymmetric characteristics of the shell-and-column structure, the complex three-dimensional problem is simplified into a computationally efficient two-dimensional axisymmetric model for solution. This model can accurately identify atypical stress concentrations near the model boundaries and the connection areas between the ring ribs and the shell plate, caused by boundary effects and abrupt changes in local stiffness. These stress singularities do not accurately reflect the macroscopic strength performance of the structure far from the boundaries. Therefore, this step deliberately excludes these boundary regions on both sides of the axial interface, focusing instead on a core "evaluation region" with uniform and stable stress distribution, unaffected by edge effects, for strength verification. This effectively filters out local interference signals, ensuring that the extracted "structural stress calculation results" purely represent the principal stress state of the shell plate under uniform external pressure. This makes parameter adjustments and strength optimization aimed at minimizing weight based on these results more scientific, accurate, and efficient, avoiding overly conservative designs due to spurious stress peaks. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart illustrating the underwater vehicle cylindrical shell model construction method of the present invention; Figure 2-4 This is a schematic diagram of the double-layer composite cylindrical pressure shell structure of the underwater vehicle cylindrical shell model construction method of the present invention; Figure 5 This is a schematic diagram of the ring-ribbed cylindrical pressure shell structure of the underwater vehicle cylindrical shell model construction method of the present invention; Figure 6 A flowchart illustrating the two-step optimized double-layer composite cylindrical pressure hull design process of the underwater vehicle cylindrical hull model construction method of the present invention. Figure 7 This diagram illustrates the load and boundary conditions of the axisymmetric stress calculation model and the three-dimensional buckling instability calculation model in the parametric modeling process of the double-layer composite cylindrical pressure-resistant structure of the underwater vehicle cylindrical shell model construction method of the present invention. Figure 8 A flowchart illustrating the one-step optimization of the underwater vehicle cylindrical shell model construction method of the present invention, showing the design process of a double-layer composite cylindrical pressure hull; Figure 9 This is a schematic diagram of the parameters of the ring-ribbed cylindrical pressure shell in the underwater vehicle cylindrical shell model construction method of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0019] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0020] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0021] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided, but those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0024] like Figure 2-5 To facilitate understanding of this embodiment, in addition to the traditional ring-ribbed cylindrical pressure shell, a titanium alloy double-layer composite cylindrical structure is used for the pressure shell design. The double-layer composite cylindrical pressure shell consists of an outer shell plate, an inner shell plate, and ring ribs. External water pressure acts only on the outer shell plate, and the radial load is transferred to the inner shell plate through the ring ribs. At the same time, the ring ribs also play a role in resisting buckling instability for the inner and outer shell plates. Compared with the traditional ring-ribbed cylindrical pressure shell, the double-layer composite cylindrical pressure shell has the following advantages: (1) The load-bearing structure changes from a single shell plate to a joint load-bearing structure of inner and outer shell plates, significantly reducing the required shell plate thickness. Finite element analysis shows that the required forged plate thickness is reduced by at least 35%. (2) Due to the significant reduction in shell thickness, the difficulty of bending and welding large-size titanium alloy shells is significantly reduced, thus reducing the difficulty of construction process; (3) The height of the ring ribs of the double-layer composite cylindrical pressure shell can be significantly reduced compared with the traditional ring rib cylindrical pressure shell, so the overall weight of the pressure shell has a certain space for lightweight design; at the same time, since only the outer shell plate of the double-layer composite cylindrical pressure shell bears water pressure, the interior is enclosed by the inner and outer shell plates and ring ribs, which increases the effective load of the pressure shell, that is, increases the weight of the equipment inside the pressure shell. (4) The double-layer composite pressure shell can meet the requirements of structural strength and stability, and because there is a large enclosed space inside, it can provide conditions for further functional design such as noise reduction.

[0025] As can be seen from the examples above, different cylindrical shell structures have different advantages. However, for most of the cylindrical shell structures designed subsequently, the corresponding parameters cannot be obtained by looking up tables. Based on this, a method for constructing a cylindrical shell model for underwater vehicles is proposed to optimize the design of cylindrical shell parameters.

[0026] like Figure 1-9As shown, the underwater vehicle cylindrical shell model construction method of the present invention simplifies the parametric geometric model into an axisymmetric model, calculates the structural stress, and simultaneously calculates the buckling pressure by establishing a three-dimensional model. It then optimizes and iterates with the goal of minimizing weight, applying constraints based on strength and stability conditions to obtain the final optimization result, thus achieving rapid generation of predicted results during optimization parameter adjustment. Specifically, it includes the following steps.

[0027] First, select the column shell structure and constituent materials, and set the strength and stability conditions. Then, set the initial design parameters according to the column shell structure and construct a parametric geometric model.

[0028] The cylindrical shell structure includes one of a ring-ribbed cylindrical pressure shell structure and a double-layer composite cylindrical pressure shell structure. The ring-ribbed cylindrical pressure shell structure includes a cylindrical shell with several annular reinforcing ribs disposed on the inner wall of the shell. The double-layer composite cylindrical pressure shell structure includes an outer shell plate, an inner shell plate disposed inside the outer shell plate, and several annular ribs disposed between the outer shell plate and the inner shell plate.

[0029] like Figure 2-4 As shown, in a specific embodiment, the constituent material is selected as titanium alloy, and the cylindrical shell structure is selected as a double-layer composite cylindrical pressure shell structure. Its design parameters include: double shell thickness h, number of ribs n, and inner shell plate thickness. outer shell thickness Rib thickness The buckling characteristic value of the double-layer composite pressure-resistant structure was calculated using linear buckling analysis, while the calculation of the instability critical pressure was based on the nonlinear finite element analysis method of geometric defects in the buckling mode, with the geometric defect amplitude set at 0.25%.

[0030] When setting strength conditions, multiple conditions can be selected, such as: a) Range of circumferential stress on the mid-span surface of the inner shell plate between adjacent ribs; b) Range of circumferential stress at the mid-span of the outer shell plate between adjacent ribs; c) Range of longitudinal stress on the inner surface of the inner shell plate spanning between adjacent ribs; d) Range of longitudinal stress on the inner surface of the outer shell plate spanning between adjacent ribs; e) The range of rib stress; When setting the strength conditions, all options can be selected. Accordingly, for the subsequent establishment of a three-dimensional finite element model of the double-layer composite cylinder under pressure, and the nonlinear finite element calculation of the ultimate bearing capacity, the critical pressure for instability satisfies the following strength conditions: a) Critical pressure range for shell plate instability between adjacent ribs; b) The critical pressure range for instability of the compartment between adjacent bulkheads.

[0031] like Figure 7 As shown, after obtaining the parametric geometric model, an axisymmetric finite element model is constructed based on the parametric geometric model, and structural stress is calculated in combination with the constituent materials. Based on the structural stress calculation results, the parametric geometric model is adjusted accordingly with the goal of minimizing weight, while ensuring that the parametric geometric model meets the strength conditions. The axisymmetric finite element model is a two-dimensional planar model of the cross-section of a single side of the cylindrical shell.

[0032] If the adjusted parametric geometric model meets the strength conditions, proceed to the next step. If it does not meet the strength conditions, adjust the initial design parameters iteratively to gradually meet the strength conditions and minimize the increase in weight as much as possible. In this step, since the double-layer composite cylindrical shell structure has axisymmetric characteristics in the circumferential direction, it can be simplified to an axisymmetric model, i.e., an axisymmetric finite element model, when calculating the structural stress in order to save computational costs.

[0033] like Figure 7 As shown, a three-dimensional shell element finite element model is constructed based on the parametric geometric model, and buckling pressure is calculated. Based on the buckling pressure calculation results, the parametric geometric model is adjusted accordingly with the goal of minimizing weight, while ensuring that the parametric geometric model meets the stability conditions. The shell element finite element model is a simplified three-dimensional model of a cylindrical shell.

[0034] The buckling pressure calculation of a double-layer composite cylindrical shell structure requires a focus on the radial instability of the shell plates, thus necessitating the establishment of a three-dimensional model, i.e., a three-dimensional shell element finite element model. However, constructing a three-dimensional model entirely using solid elements would result in an excessive number of elements and unacceptable computational costs. Therefore, to save computational costs, the inner and outer shell plates and ribs are simplified into a shell plate structure.

[0035] During the adjustment of the parametric geometric model, stability conditions are also used as constraints, and the design parameters are iteratively optimized with the goal of minimizing weight. After each optimization, the above two steps need to be re-verified until the final parametric geometric model is obtained.

[0036] It should be noted that structural stress calculation and buckling pressure calculation can be performed simultaneously in the process, but the calculations can be performed sequentially.

[0037] Based on the final parametric geometric model, the final design parameters are output.

[0038] In some embodiments, before the final step, i.e. before obtaining the final parametric geometric model, a preliminary design scheme needs to be formed, and then the final design scheme, i.e. the final parametric geometric model, is obtained based on the preliminary design scheme.

[0039] Specifically, the parametric geometric model that meets the stability condition is first used as the intermediate parametric geometric model.

[0040] like Figure 6 As shown, to be precise, it is not that the parameterized geometric model that only meets the stability condition is used as the intermediate parameterized geometric model, but rather that the parameterized geometric model that has passed the stability and strength conditions and meets the goal of minimizing weight is used as the intermediate parameterized geometric model, which can be directly used as the initial design scheme. In other words, in this embodiment, the optimization process is actually divided into two steps: the first step is to obtain the initial design scheme, and the second step is to optimize to obtain the final design scheme.

[0041] The intermediate parameterized geometric model is combined with the constituent materials to perform ultimate load calculations and update the stability conditions.

[0042] The intermediate parameterized geometric model is checked by updating the stability conditions. If it meets the criteria for composite stability, the final solution can be output directly.

[0043] If the stability condition is not met, the parametric geometric model is updated and optimized based on the verification results, and the process re-enters the generation of the initial design scheme to continue iterative optimization.

[0044] Furthermore, in a specific embodiment, the step of calculating the ultimate bearing capacity and updating the stability conditions by combining the intermediate parameterized geometric model with the constitutive material requires the use of a nonlinear correction coefficient for the buckling pressure. Specifically, firstly, based on the intermediate parameterized geometric model, the ultimate bearing capacity is calculated according to the material's bilinear elastoplastic constitutive model and initial defects based on buckling modes. Then, the nonlinear correction coefficient for the buckling pressure is obtained from the ultimate bearing capacity calculation results, and the stability conditions are updated based on this coefficient.

[0045] The bilinear elastoplastic constitutive model is a simplified mathematical model used to describe the elastoplastic mechanical behavior of metallic materials under load. This model idealizes the stress-strain relationship of the material as two straight line segments: the first segment represents the linear elastic stage, with its slope being Young's elastic modulus (E), following Hooke's law; the second segment represents the plastic stage, with its slope being the tangent modulus (Et) or plastic modulus, typically much smaller than the elastic modulus. The intersection of the two segments is the initial yield stress point of the material. The core assumption of this model is that after reaching the yield strength, the material enters a plastic flow stage with a linearized strengthening effect, whose strengthening law follows the isotropic hardening criterion, i.e., the yield surface expands uniformly in stress space without translation or rotation. For the optimization of the cylindrical shell structure of underwater vehicles, this model can relatively efficiently and accurately simulate the mechanical response, stress redistribution, and subsequent load-bearing capacity of high-strength steel and other materials after the local area of ​​the structure enters a plastic state under enormous hydrostatic pressure. It is a key theoretical basis for conducting nonlinear ultimate bearing capacity analysis to assess the true safety margin of the structure.

[0046] Initial imperfections based on buckling modes are a numerical modeling method used in structural buckling analysis to simulate geometric imperfections present in real structures. The principle is to first calculate the lowest-order buckling mode (i.e., the most likely shape to buckle) of the structure through linear buckling analysis (eigenvalue buckling analysis). Then, the morphology (displacement field) of this mode is scaled down and introduced as an initial geometric imperfection into a perfect ideal geometric model. This scaling ratio (usually a fraction of the shell thickness, such as 0.1t to 0.3t) is determined based on engineering experience, manufacturing tolerances, or experimental data. For column-shell structures, this imperfection may originate from minor wrinkles or shape deviations caused by material inhomogeneity, processing errors, or residual welding stress. Introducing such imperfections into subsequent nonlinear buckling analysis or ultimate bearing capacity analysis can significantly reduce the theoretically calculated critical buckling load, making it closer to the experimental value of the real structure, thereby avoiding the non-conservative (i.e., overly dangerous) design results that may result from using an ideal model. This method is a standard and effective technique for considering "imperfection sensitivity" in numerical simulation and accurately predicting the nonlinear stability of shell structures.

[0047] In this embodiment, the nonlinear correction coefficient for buckling pressure is proportional to the ultimate bearing capacity calculation result and inversely proportional to the buckling pressure calculation result. It can be directly calculated by correction coefficient = ultimate bearing capacity / buckling buckling pressure. By calculating the ultimate bearing capacity of the double-layer composite cylindrical shell model under different design parameters, it was found that due to the existence of material plasticity and geometric defects, the ultimate bearing capacity of the double-layer composite cylindrical shell is reduced to varying degrees compared with the ideal buckling buckling pressure, which can vary in the range of 0.5-0.8. For the sake of conservatism, the ultimate bearing capacity reduction coefficient of the double-layer composite pressure shell, i.e., the initial correction coefficient, can be set to 0.5.

[0048] Introducing correction coefficients and updating stability conditions are crucial steps to ensure that optimization results possess both theoretical rigor and engineering reliability. Initial stability conditions are typically based on ideal linear buckling theory, which can be preset as needed. This theory assumes perfect structural geometry and perfectly elastic materials; therefore, the calculated buckling pressure, i.e., the ideal critical load, is often significantly higher than the failure pressure of the actual structure. Real shells possess geometrical defects, residual stresses, and material nonlinearities, which can lead to a decrease in their actual stable load-bearing capacity.

[0049] Therefore, the scheme, through ultimate bearing capacity calculations, comprehensively considers the material's elastoplasticity (i.e., bilinear constitutive model) and initial geometric imperfections to obtain a nonlinear ultimate buckling pressure that more closely approximates engineering reality. By comparing the nonlinear ultimate buckling pressure with the linear buckling pressure, a nonlinear correction coefficient for the buckling pressure can be obtained. This coefficient quantitatively characterizes the difference in bearing capacity between the ideal model and the actual structure. Using this coefficient to update the original linear stability conditions—for example, updating the allowable stability pressure to: linear buckling pressure multiplied by the correction coefficient, then divided by the safety factor—is equivalent to introducing a more realistic constraint condition derived from advanced nonlinear analysis for the optimized design.

[0050] Finally, by reviewing and re-optimizing the intermediate optimization model with updated and more stringent stability conditions, the design parameters can be further adjusted, resulting in a final design that is still safe and reliable after considering various non-ideal factors, and is the lightest in weight, thus avoiding the radical and dangerous design schemes that may be caused by ideal linear theory.

[0051] It should be noted that the intermediate parameterized geometric model in this embodiment is an intermediate optimization model based on the parameterized geometric model, with the goal of minimizing weight and with strength and stability conditions as dual constraints.

[0052] In some embodiments, the step of constructing an axisymmetric finite element model based on a parametric geometric model and performing structural stress calculation includes constructing an axisymmetric finite element model based on a parametric geometric model, setting an evaluation region in the axisymmetric finite element model, removing the boundary regions on both sides of the axial interface, performing strength verification on the evaluation region, and obtaining the structural stress calculation results.

[0053] In another embodiment, the forces acting on the outer shell, inner shell, and ribs are calculated by setting up a mechanical model.

[0054] Under the action of hydrostatic pressure P and longitudinal force T1, the outer shell plate undergoes axisymmetric compressive deformation. With the rib spacing set as l and the mid-span of the outer shell plate taken as the origin of the coordinate system, its bending differential equation is:

[0055] in, Let be the bending stiffness of the outer shell plate, d be the differential operator, w1 be the deflection of the outer shell plate beam, E be the elastic modulus of the material, μ be the Poisson's ratio of the material, R1 be the radius of the outer shell plate, t1 be the thickness of the outer shell plate, and x be the longitudinal coordinate along the generatrix of the shell.

[0056] The inner shell plate has a similar structure to the outer shell plate, but the inner shell plate does not bear hydrostatic pressure and is subjected to an inward force f1 from the ribs. Its bending differential equation is:

[0057] in, R0 is the bending stiffness of the inner shell plate, w0 is the deflection of the outer shell plate beam, R0 is the radius of the inner shell plate, t0 is the thickness of the inner shell plate, and T0 is the longitudinal force on the inner shell plate.

[0058] The rib is subjected to axisymmetric forces f0 and f1 from the inner and outer shell plates, and is in an axisymmetric plane stress state. According to the axisymmetric plane stress theory of elasticity, the radial displacement u at any radius r of the rib is... r for:

[0059] Where t3 is the thickness of the rib plate.

[0060] The core principle of this step lies in accurately obtaining the stress field representing the overall strength of the structure through scientific finite element modeling and post-processing strategies, thus providing a reliable basis for optimization. Specifically, the axisymmetric characteristics of the column-shell structure are first utilized to simplify the complex three-dimensional problem into a computationally efficient two-dimensional axisymmetric model for solution. Crucially, it can accurately identify atypical stress concentrations near the model boundaries and the connection areas between the ring ribs and the shell plate due to boundary effects and abrupt changes in local stiffness. These stress singularities do not accurately reflect the macroscopic strength performance of the structure far from the boundaries. Therefore, this step deliberately excludes these boundary regions on both sides of the axial interface, focusing instead on a core evaluation region with uniform and stable stress distribution, unaffected by edge effects, for strength verification. This effectively filters out local interference signals, ensuring that the extracted structural stress calculation results purely represent the principal stress state of the shell plate under uniform external pressure. This makes parameter adjustments and strength optimization aimed at minimizing weight more scientific, accurate, and efficient, avoiding overly conservative designs due to false stress peaks.

[0061] like Figure 6 As shown, in a specific and complete embodiment, for the design process of a double-layer composite cylindrical pressure shell, based on the design criteria of the double-layer composite cylindrical pressure shell with dual constraints, a preliminary design process based on two-step optimization is formed. Box ① shows the first step of the initial optimization design process, which aims to minimize weight and uses strength and stability criteria as dual constraints. Then, based on the initial optimization design scheme, combined with the bilinear elastoplastic constitutive model of the material and the initial imperfections based on buckling modes, the ultimate bearing capacity is calculated, and the nonlinear correction coefficient in the stability criterion is updated. Finally, the second step of the optimization design process, shown in box ②, is carried out, which is the optimization design process that aims to minimize weight and uses strength and the updated stability criteria as dual constraints.

[0062] Specifically, the parametric geometric model of the double-layered composite cylindrical shell was implemented using the Python scripting language of the ABAQUS finite element software, such as... Figure 4 As shown, the parametric geometric model has five design parameters: the thickness h of the double shell, the number of ribs n, the thickness of the inner shell plate, etc. outer shell thickness Rib thickness Because the double-layer composite cylindrical shell structure has axisymmetric characteristics in the circumferential direction, it can be simplified to an axisymmetric model when calculating structural stress to save computational costs. The buckling pressure calculation of the double-layer composite cylindrical shell structure requires a focus on the radial instability of the shell plates, necessitating the creation of a three-dimensional model. However, constructing a three-dimensional model entirely using solid elements would result in an excessive number of elements, leading to unacceptable computational costs. Therefore, to save computational costs, the inner and outer shell plates and ribs are simplified to a shell plate structure. Parametric modeling of the above two computational models is implemented using the ABAQUS Python scripting language. The written Python script does not require calling the CAE graphics processing interface; it can automatically call the ABAQUS kernel processing program in the background to automatically complete geometry construction, mesh generation, load and boundary application, model submission, numerical solution, and result viewing, facilitating interactive processing with the optimization software ISIGHT. It should be noted that, in order to eliminate... Figure 4 Regarding the influence of the axial load P2 on the upper and lower sections, according to Saint-Venant's principle, the boundary regions on the upper and lower sides are removed when conducting structural strength assessment, and only the internal regions unaffected by the boundaries are checked for strength.

[0063] like Figure 9 As shown, in another specific and complete embodiment, an optimized design process based on the dual-constraint (strength, stability) design criteria of the traditional ring-ribbed cylindrical pressure-resistant structure was also established for the traditional ring-ribbed cylindrical pressure-resistant shell. The design parameters include 6 design parameters: shell thickness. rib height Web thickness Rib thickness Web width And the rib spacing d. Here, the nonlinear correction coefficient for the instability critical pressure is temporarily taken as 0.8. The traditional optimization design of the ring-ribbed cylindrical pressure shell is an optimization design process with the goal of minimizing weight and with strength and stability criteria as dual constraints. Then, based on the optimized design scheme, the ultimate bearing capacity is calculated and verified by combining the bilinear elastoplastic constitutive model of the material and the initial imperfection based on the buckling mode.

[0064] To further illustrate the reproducibility of this optimization method, a specific and feasible embodiment is used for explanation. First, preparatory work is performed before optimization. An optimization module based on a surrogate model is established in the ISIGHT software, comprising four modules: Optimization, Approximations, Simcode, and Calculator. The Approximations module is placed within the Optimization module, and the surrogate model can be activated or deactivated during optimization via checkboxes. The Simcode module mainly contains an ABAQUS parametric modeling file (…). A command execution file (GoAbaqus.bat), and a strength assessment file ( ) and a stability assessment document ( By defining the transmission process of relevant parameters, the modification and iteration of optimized design parameters can be realized. The Calculator module mainly defines the relationship between optimization objectives (weight, welding quantity, radial displacement of inner shell plate) and parameters.

[0065] The specific parameter optimization process steps are as follows: (1) The optimization parameters are 5 design parameters: double shell thickness h, number of ribs n, inner shell thickness outer shell thickness Rib thickness There are two types of optimization constraints: one is the strength design criterion for the shell plates and ribs of the double-layer composite cylindrical shell, and the other is the design criterion for the critical buckling pressure of the shell plates of the double-layer composite cylindrical shell. Due to the significant difficulty in identifying overall and local buckling, for conservative reasons, the allowable pressure for both is taken as [value missing]. (Multiple optimization calculations show that, because the double-layer composite cylindrical shell has more ribs than the traditional ring-ribbed cylindrical shell, its first-order buckling mode is mostly overall buckling). The optimization design objective is to minimize the structural weight. Considering the construction cost of the double-layer composite cylindrical pressure-resistant structure and the deformation control of the inner shell plate under pressure, the amount of welding and the flatness of the inner shell plate (defined as the difference between the maximum and minimum radial displacement of the shell plate) can be simultaneously used as optimization design objectives.

[0066] (2) The sample points selected by the optimized Latin hypercube experimental design method are made into a design matrix so that the generated sampling points are evenly distributed in the whole space with equal probability, which is suitable for fitting complex relationships of more than second order or higher order. The generated design parameters are associated with the structural parameters in ABAQUS to generate the finite element calculation model corresponding to the sample points.

[0067] (3) The background automatically calls the ABAQUS kernel processing program to automatically complete geometry construction, mesh generation, load and boundary application, model submission, numerical solution and result viewing, and obtain the simulation results corresponding to all sample points.

[0068] (4) After obtaining the simulation results corresponding to all sample points, the sample point-response matrix is ​​fitted by surrogate models such as response surface methodology (RSM), radial basis function (RBF), and Kriging model. The accuracy of the surrogate model is verified by means of average error, maximum error, root mean square error, and R2 error.

[0069] (5) If the fitting accuracy of the surrogate model meets the requirements, then the structural parameters are optimized using global optimization algorithms such as multi-island genetic algorithm (MIGA), adaptive simulated annealing algorithm (ASA), and particle swarm optimization (PSO) based on the surrogate model established above. Finally, the results are used as ABAQUS input for verification.

[0070] Furthermore, in the aforementioned two-step optimization-based design method for double-layer composite cylindrical pressure shells, it is necessary to pre-calculate the ultimate bearing capacity by combining the material's bilinear elastoplastic constitutive model and initial imperfections based on buckling modes, and then define the nonlinear correction coefficient in the stability criterion. Since the nonlinear correction coefficient is closely related to the structural form and specific parameters of the pressure shell, the two-step optimization design method requires selecting a relatively conservative nonlinear correction coefficient. For example, setting it to 0.5 for a double-layer composite cylindrical pressure shell and 0.8 for a ring-ribbed cylindrical shell may result in the inability to find the optimal solution.

[0071] To address this, the ultimate bearing capacity calculation can be directly coupled into the optimization system, and the stability criterion can be replaced by the ultimate bearing capacity instead of the buckling instability pressure. This allows for a "one-step optimization" approach to achieve the design of a double-layer composite cylindrical pressure shell, solving problems such as the need for repeated verification and conservative setting of nonlinear correction coefficients in the "two-step optimization" method. The specific optimization design process is as follows: Figure 8 As shown.

[0072] Optimization calculations show that the nonlinear correction coefficient of the double-layer composite cylindrical pressure shell can vary within the range of 0.42-0.79, and is closely related to the pressure shell parameters. The nonlinear correction coefficient set in the aforementioned two-step optimization method is 0.5, which is near the lower bound of the range. The nonlinear correction coefficient is mainly affected by the thickness h of the double-layer composite shell, decreasing significantly with increasing h. Increasing the rib thickness t3 also leads to a decrease in the nonlinear correction coefficient, but the effect is less than that of h. Conversely, increasing the outer shell rib thickness t2 slightly increases the nonlinear correction coefficient, while the number of ribs n and the inner shell thickness t1 have virtually no effect on the nonlinear correction coefficient.

[0073] The results from the "one-step optimization" method show that the shell weight is reduced by 3.14% compared to the "two-step optimization" method. At this point, the first-order buckling characteristic value is only 26.9 MPa, which is sufficient to achieve the ultimate bearing capacity of 18 MPa. The corresponding nonlinear correction coefficient is 0.67, which is significantly higher than the previous setting of 0.5. The optimized scheme shows a significant improvement compared to the "two-step optimization" method.

[0074] The underwater vehicle cylindrical shell model construction system of the present invention specifically includes a computer system and embeds the above-mentioned underwater vehicle cylindrical shell model construction method.

[0075] The medium of the present invention allows a computer to read an underwater vehicle cylindrical shell model construction program on the medium, which, when executed by a processor, implements the aforementioned underwater vehicle cylindrical shell model construction method.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing a cylindrical shell model of an underwater vehicle, characterized in that, Includes the following steps: Select the column shell structure and constituent materials, and set strength and stability conditions; Based on the initial design parameters of the column shell structure, a parametric geometric model is obtained; An axisymmetric finite element model is constructed based on a parametric geometric model, and structural stress is calculated in conjunction with the constituent materials. The axisymmetric finite element model is a two-dimensional planar model of a single-sided cross-section of a cylindrical shell. A shell element finite element model is constructed based on a parametric geometric model, and buckling pressure is calculated in conjunction with the constituent materials. The shell element finite element model is a simplified three-dimensional model of a cylindrical shell. Based on the structural stress calculation results and buckling pressure calculation results, the strength condition and stability condition are used as constraints, and the parametric geometric model is adjusted accordingly with the goal of minimizing weight. Based on the final parametric geometric model, the final design parameters are output, and the cylindrical shell model is obtained.

2. The method for constructing a cylindrical shell model of an underwater vehicle as described in claim 1, characterized in that, The cylindrical shell structure includes one of a ring-ribbed cylindrical pressure shell structure and a double-layer composite cylindrical pressure shell structure. The ring-ribbed cylindrical pressure shell structure includes a cylindrical shell with several annular reinforcing ribs disposed on the inner wall of the shell. The double-layer composite cylindrical pressure shell structure includes an outer shell plate, an inner shell plate disposed inside the outer shell plate, and several annular ribs disposed between the outer shell plate and the inner shell plate.

3. The method for constructing a cylindrical shell model of an underwater vehicle as described in claim 1, characterized in that, Before obtaining the final parametric geometric model, the following steps are also included: The parameterized geometric model that meets the stability condition is used as the intermediate parameterized geometric model; The intermediate parameterized geometric model is combined with the constituent materials to perform ultimate load calculations and update the stability conditions. The intermediate parameterized geometric model was verified using the updated stability conditions; The parametric geometric model is updated and optimized based on the review results.

4. The method for constructing a cylindrical shell model of an underwater vehicle as described in claim 3, characterized in that, The process of performing ultimate load-bearing calculations on the intermediate parameterized geometric model in conjunction with the constituent materials and updating the stability conditions includes the following steps: Based on the intermediate parameterized geometric model, the ultimate bearing capacity is calculated according to the bilinear elastoplastic constitutive model of the material and the initial imperfection based on the buckling mode. The nonlinear correction coefficient for instability pressure is obtained from the ultimate bearing capacity calculation results. The stability conditions are updated based on the nonlinear correction coefficient of the instability pressure.

5. The method for constructing a cylindrical shell model of an underwater vehicle as described in claim 4, characterized in that, The nonlinear correction coefficient for the instability pressure is proportional to the ultimate bearing capacity calculation result and inversely proportional to the buckling pressure calculation result.

6. The method for constructing a cylindrical shell model of an underwater vehicle as described in claim 3, characterized in that, The intermediate parameterized geometric model is an intermediate optimization model based on the parameterized geometric model, with the goal of minimizing weight and with strength and stability conditions as dual constraints.

7. The method for constructing a cylindrical shell model of an underwater vehicle as described in claim 2, characterized in that, The initial design parameters of the double-layer composite cylindrical pressure shell structure include the thickness of the double shell, the number of ribs, the thickness of the inner shell plate, the thickness of the outer shell plate and the thickness of the ribs. The initial design parameters of the ring-ribbed cylindrical pressure shell structure include the shell plate thickness, the rib height, the web plate thickness, the rib thickness, the web plate width and the rib spacing.

8. The method for constructing a cylindrical shell model of an underwater vehicle as described in claim 1, characterized in that, The process of constructing an axisymmetric finite element model based on a parametric geometric model and calculating structural stress includes the following steps: Construct an axisymmetric finite element model based on the parametric geometric model; In the axisymmetric finite element model, the evaluation region is set, and the boundary regions on both sides of the axial interface are removed; The strength of the assessment area is checked to obtain the structural stress calculation results.

9. A system for constructing a cylindrical shell model of an underwater vehicle, characterized in that, The method for constructing a cylindrical shell model of an underwater vehicle, as described in any one of claims 1-8, is embedded.

10. A medium, characterized in that, A computer can read the underwater vehicle hull model construction program on the medium, and when the underwater vehicle hull model construction program is executed by a processor, it implements the underwater vehicle hull model construction method as described in any one of claims 1-8.

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