A safety evaluation method for deep-sea lightweight cylindrical shell pressure-resistant structure

Abstract

The application discloses a safety evaluation method for a deep-sea light-weight cylindrical shell pressure-resistant structure, which comprises the following steps: step 1) researching the deformation field evolution law of the cylindrical shell structure to obtain a strain expression of the cylindrical shell structure in a deformation-instability process; step 2) on the basis of obtaining the strain of the cylindrical shell structure, researching the fracture failure mode of the cylindrical shell structure to obtain an expression of a local instability mode of the cylindrical shell structure; step 3) confirming that the maximum relative deformation amount of the main shell-rib between adjacent ribs is a characteristic parameter for safety evaluation of the cylindrical shell structure; step 4) deducing and verifying the corresponding relationship between the maximum relative deformation amount of the main shell-rib between adjacent ribs and the local fracture failure of the cylindrical shell structure; and step 5) establishing a fracture criterion model of the cylindrical shell structure, so that the pressure-resistant safety of the cylindrical shell structure can be quickly and accurately evaluated through the fracture criterion model of the cylindrical shell structure.

Description

Technical Field

[0001] This invention relates to the field of deep-sea pressure-resistant structure technology, specifically to a safety assessment method for a deep-sea lightweight cylindrical shell pressure-resistant structure. Background Technology

[0002] As human exploration of deep-sea resources continues to advance, the diving depth of large-scale deep-sea equipment is increasing. Deep-sea pressure-resistant structures are crucial for ensuring the safety of personnel and maintaining the normal operation of core equipment in deep-sea equipment. Therefore, evaluating the load-bearing capacity and safety of deep-sea pressure-resistant structures is essential to ensuring structural integrity.

[0003] The structural weight requirements of deep-sea equipment for carrying out missions dictate that replacing high-strength steel with high-strength lightweight materials with high buoyancy-to-weight ratio is an inevitable trend and has been gradually implemented. Numerous experiments have shown that the failure modes of large-scale deep-sea pressure-resistant structures constructed with different types of materials vary greatly. Existing standards are no longer applicable to new lightweight pressure-resistant structures, necessitating the establishment of new deep-sea pressure-resistant safety assessment methods. Summary of the Invention

[0004] The purpose of this invention is to provide a safety assessment method for a lightweight cylindrical shell pressure-resistant structure for deep-sea applications, which can accurately reflect the critical deflection value of the lightweight cylindrical shell pressure-resistant structure before fracture, thereby solving the technical problems existing in the prior art.

[0005] To address the aforementioned technical problems, this invention specifically provides the following technical solution: a safety assessment method for a deep-sea lightweight cylindrical shell pressure-resistant structure, which assesses the safety of the cylindrical shell pressure-resistant structure by establishing a fracture criterion model; including the following steps:

[0006] Step 1) Study the evolution law of the deformation field of the cylindrical shell structure to obtain the strain expression of the cylindrical shell structure during the deformation-instability process;

[0007] Step 2) Based on the strain of the cylindrical shell structure, study the fracture failure mode of the cylindrical shell structure to obtain the expression of the local instability mode of the cylindrical shell structure;

[0008] Step 3) Confirm that the maximum relative deformation between the main shell and the ribs between adjacent ribs is the characterization parameter for the safety evaluation of cylindrical shell structures;

[0009] Step 4) Derive and verify the correspondence between the maximum relative deformation of the main shell and ribs between adjacent ribs and the local fracture failure of the cylindrical shell structure;

[0010] Step 5) Establish a fracture criterion model for cylindrical shell structures.

[0011] Furthermore, in step 1), by studying the evolution law of the deformation field of the cylindrical shell structure, the expression for the strain on the non-mid-surface of the cylindrical shell structure is obtained:

[0012] (1);

[0013] (2);

[0014] (3);

[0015] in, , and These represent the axial strain, circumferential strain, and shear strain on the non-mid-surface of the cylindrical shell structure, respectively. , and θ represents the strain on the mid-surface of the cylindrical shell structure, x is the generatrix direction, and θ is the circumferential direction.

[0016] Furthermore, in step 1), during the deformation of the cylindrical shell structure, the cylindrical shell structure will become unstable. The expression for the radial deflection after the cylindrical shell structure becomes unstable is:

[0017] (4);

[0018] in, This represents the radial deflection after the cylindrical shell structure becomes unstable. The longitudinal length of the cylindrical shell. Let be the deflection at both ends of the cylindrical shell corresponding to the modal number m. For the deflection corresponding to the modal number m, This represents the amplitude of the deflection curve corresponding to the modal number m.

[0019] Furthermore, the material of the cylindrical shell lightweight pressure-resistant structure is titanium alloy; in step 1), during the deformation process of the cylindrical shell structure, it can be seen from the stability analysis of the titanium alloy structure that the strain caused by the deviation of the middle surface of the cylindrical shell structure from the original equilibrium position is very small and can be ignored.

[0020] During the large deformation stage of instability, the bending strain along the thickness direction of the cylindrical shell structure is much greater than the longitudinal and circumferential compressive strains on the mid-surface of the shell. Therefore, substituting equation (4) into equations (1)-(3) yields the strain expression for the instability process of the cylindrical shell structure:

[0021] (5);

[0022] (6);

[0023] (7).

[0024] Furthermore, in step 2), because the plastic strain is much greater than the elastic strain during the nonlinear large deformation of the cylindrical shell structure, the equivalent plastic strain expression for the cylindrical shell structure is:

[0025] (8);

[0026] Substituting equations (5) to (7) into equation (8), the equivalent plastic strain equation for fracture failure of the cylindrical shell structure can be simplified as follows:

[0027] (9);

[0028] Using the material's plastic strain as the criterion for fracture failure, at this time Where h is the shell thickness; therefore, the expression for the local instability mode of the cylindrical shell structure is:

[0029] (10).

[0030] Furthermore, in step 4), when the cylindrical shell structure becomes unstable due to large deformation, eventually leading to local fracture, the mode m=1 between two adjacent ribs; therefore, from equations (9) and (10), we can obtain:

[0031] (11).

[0032] Furthermore, in step 5), when the radial relative displacement is greater than the net span, The maximum value is 1 / 2 of the net span; therefore, a fracture criterion model for cylindrical shell structures is established:

[0033] (12).

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] The safety assessment method for deep-sea lightweight cylindrical shell pressure-resistant structures provided by this invention establishes a fracture criterion model for cylindrical shell structures by studying the correspondence between strain during deformation and local fracture failure of the cylindrical shell structure. This model enables rapid assessment of the deep-sea pressure-resistant safety of lightweight cylindrical shell pressure-resistant structures, especially those made of titanium alloy. Attached Figure Description

[0036] To more clearly illustrate the embodiments of the present invention or the technical solutions in 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 merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the main shell-rib structure in a cylindrical shell structure.

[0038] Figure 2 This is a schematic diagram of the relative deformation between the main shell and the ribs in a cylindrical shell structure.

[0039] Figure 3 A schematic diagram of the circumferential mode number in a cylindrical shell structure under structural failure modes.

[0040] Figure 4 This is a schematic diagram showing the circumferential mode number and relative displacement under structural failure modes. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] This invention provides a safety assessment method for a deep-sea lightweight cylindrical shell pressure-resistant structure. It mainly involves studying the evolution law of the deformation field of the cylindrical shell structure, which reveals that the cylindrical shell structure undergoes three stages during the pressure resistance process: deformation, instability, and failure. By studying the correspondence between the strain of the lightweight cylindrical shell structure during the deformation process and the local fracture failure of the cylindrical shell structure, a fracture criterion model for the cylindrical shell structure is established to assess the pressure resistance safety of the cylindrical shell structure.

[0043] This invention provides a specific implementation method for establishing a fracture criterion model for cylindrical shell structures. The derivation of the formulas involved is mainly based on theoretical analysis and numerical simulation. The specific steps are as follows:

[0044] Step 1) Study the evolution law of the deformation field of the cylindrical shell structure to obtain the surface strain expression of the cylindrical shell structure during the deformation-instability process.

[0045] When a cylindrical shell is subjected to external loads (such as axial pressure, torque, lateral pressure, etc.), it will undergo elastic deformation. At this stage, its deformation is analyzed based on the basic assumptions and theories of elasticity.

[0046] Obtain the expression for the strain on the non-mid-surface of a cylindrical shell structure:

[0047] (1);

[0048] (2);

[0049] (3);

[0050] in, , and These represent the axial strain, circumferential strain, and shear strain on the non-mid-surface of the cylindrical shell structure, respectively. , and θ represents the axial strain, circumferential strain, and shear strain of the mid-surface of the cylindrical shell structure, respectively, where x is the generatrix direction and θ is the circumferential direction.

[0051] As the external load increases, when a certain critical value is reached, the equilibrium state of the cylindrical shell will change from stable to unstable. This phenomenon is called instability. When instability occurs, the deformation of the cylindrical shell will suddenly increase and no longer follow the laws of the elastic deformation stage.

[0052] Specifically, the instability modes can be analyzed using linear stability theory. For example, in the case of axial compressive instability, the instability modes may manifest as multiple wavy deformations in the circumferential direction of the cylindrical shell, with the wave number related to the number of circumferential modes. This deformation mode leads to a significant change in the stress distribution of the cylindrical shell.

[0053] In this embodiment, the radial deflection expression of the cylindrical shell structure after instability during deformation is as follows:

[0054] (4);

[0055] in, This represents the radial deflection after the cylindrical shell structure becomes unstable. The longitudinal length of the cylindrical shell. Let be the deflection at both ends of the cylindrical shell. For the deflection corresponding to the modal number m, This represents the amplitude of the deflection curve corresponding to the modal number m.

[0056] Furthermore, the instability phenomenon can be verified by gradually increasing the axial pressure and observing the deformation of the cylindrical shell; when the pressure approaches the critical value, the cylindrical shell may exhibit slight lateral deformation, and once the critical pressure is exceeded, the lateral deformation will increase rapidly.

[0057] In this embodiment, the material of the lightweight pressure-resistant cylindrical shell structure is titanium alloy; in step 1), during the deformation process of the cylindrical shell structure, it can be seen from the stability analysis of the titanium alloy structure that the strain caused by the deviation of the middle surface of the cylindrical shell structure from the original equilibrium position is very small and can be ignored.

[0058] During the large deformation stage of instability, the bending strain along the thickness direction of the cylindrical shell structure is much greater than the longitudinal and circumferential compressive strains on the mid-surface of the shell. Therefore, substituting equation (4) into equations (1)-(3) yields the expression for the non-mid-surface strain during the instability process of the cylindrical shell structure:

[0059] (5);

[0060] (6);

[0061] (7).

[0062] Failure of cylindrical shell structures mainly includes material failure and structural failure.

[0063] Material failure is usually caused by yielding or fracture. For example, when the stress exceeds the material's yield strength, the material begins to undergo plastic deformation, and further increases in stress will lead to fracture. Structural failure, on the other hand, may be due to excessive deformation that exceeds the design limits of the structure, causing it to malfunction.

[0064] Step 2) Based on the strain of the cylindrical shell structure, study the fracture failure mode of the cylindrical shell structure to obtain the expression of the local instability mode of the cylindrical shell structure.

[0065] During the nonlinear large deformation of a cylindrical shell structure, the plastic strain is much greater than the elastic strain; therefore, the equivalent plastic strain expression for a cylindrical shell structure is:

[0066] (8);

[0067] Substituting equations (5) to (7) into equation (8), the equivalent plastic strain equation for fracture failure of the cylindrical shell structure can be simplified as follows:

[0068] (9);

[0069] Using the material's plastic strain as the criterion for fracture failure, at this time Where h is the shell thickness; therefore, the expression for the local instability mode of the cylindrical shell structure is:

[0070] (10).

[0071] Step 3) Investigate the structural failure of the cylindrical shell structure and confirm that the maximum relative deformation between the main shell and ribs between adjacent ribs is the characterization parameter for the safety evaluation of the cylindrical shell structure.

[0072] like Figure 1 and Figure 2 As shown, in a cylindrical shell structure, the ribs are components that enhance structural stability and are closely connected to the main shell. The main shell mainly bears external loads and transmits the force to the ribs. When subjected to external loads, there is a difference in the degree of deformation between the ribs and the middle of the span. This difference is the relative deformation of the main shell and the ribs.

[0073] The coordinated work of the main shell and ribs is crucial for the stability of a cylindrical shell structure, and the relative deformation directly reflects their synergy. If the relative deformation is within a reasonable range, it indicates that the main shell and ribs can effectively resist external loads together, and the structure is in good working condition.

[0074] Overall deformation parameters (such as axial shortening and radial shrinkage in cylindrical shell structures) primarily reflect the overall deformation of the structure. However, in many cases, even if the overall deformation is within acceptable limits, problems may have already occurred at the local shell-rib connection points.

[0075] The relative deformation focuses more on local coordinated deformation and can reflect the adverse effects of insufficient local stiffness of the structure. Therefore, the maximum relative deformation between the main shell and the ribs of adjacent ribs is used as a characterization parameter for the safety evaluation of cylindrical shell structures.

[0076] Step 4), derive the correspondence between the maximum relative deformation of the main shell and ribs between adjacent ribs and the local fracture failure of the cylindrical shell structure.

[0077] like Figure 2 As shown, in a cylindrical shell structure, the displacement patterns of the main shell and ribs during deformation under different circumferential modes are illustrated. For example, the main shell undergoes periodic wavy deformation in the circumferential direction (circumferential mode), while the ribs, due to their higher stiffness, deform relatively less. This difference causes the relative deformation of the main shell and ribs to change within a complete modal cycle. Therefore, the relative deformation of the main shell and ribs reaches its maximum value at the peaks and troughs of the mode.

[0078] In this embodiment, during the process of large deformation of the cylindrical shell structure leading to instability and even local fracture, data simulation confirms that the mode m=1 between two adjacent ribs during local instability, and the relative deformation of the main shell and ribs is at its maximum value; therefore, from equations (9) and (10), we can obtain:

[0079] (11);

[0080] This represents the amplitude of the deflection curve corresponding to the modal number m, which is also the maximum deformation of the main shell relative to the rib between adjacent ribs.

[0081] Step 5), establish a fracture criterion model for cylindrical shell structures.

[0082] In a cylindrical shell structure, the distance between adjacent ribs is the net span, and the difference in radial displacement between the main shell and the ribs is the radial relative displacement; when the radial relative displacement is greater than the net span... The maximum value is 1 / 2 of the net span. Under this condition, the deformation of the cylindrical shell structure within this range reaches a limit state.

[0083] Therefore, a fracture criterion model for cylindrical shell structures is established:

[0084] (12).

[0085] like Figure 3 As shown in Table 1, this embodiment also provides the maximum radial relative displacement values ​​corresponding to different circumferential modes during structural fracture under different material fracture strain conditions, in order to expand the application scope of this cylindrical shell structure fracture criterion model.

[0086] Table 1. Maximum radial relative displacement values ​​corresponding to different circumferential modes during structural fracture:

[0087]

[0088] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.

Claims

1. A safety assessment method for a deep-sea lightweight cylindrical shell pressure-resistant structure, characterized in that, The pressure resistance safety of cylindrical shell structures is assessed by establishing a fracture criterion model for cylindrical shell structures. The steps for establishing a fracture criterion model for a cylindrical shell structure are as follows: Step 1) Study the evolution law of the deformation field of the cylindrical shell structure to obtain the strain expression of the cylindrical shell structure during the deformation-instability process; Step 2) Based on the strain of the cylindrical shell structure, study the fracture failure mode of the cylindrical shell structure to obtain the expression of the local instability mode of the cylindrical shell structure; Step 3) Confirm that the maximum relative deformation between the main shell and the ribs between adjacent ribs is the characterization parameter for the safety evaluation of cylindrical shell structures; Step 4) Derive the correspondence between the maximum relative deformation of the main shell and ribs between adjacent ribs and the local fracture failure of the cylindrical shell structure; Step 5) Establish a fracture criterion model for cylindrical shell structures; In step 1), by studying the evolution law of the deformation field of the cylindrical shell structure, the expression for the strain on the non-mid-surface of the cylindrical shell structure is obtained: （1）； （2）； （3）； in, , and These represent the axial strain, circumferential strain, and shear strain on the non-mid-surface of the cylindrical shell structure, respectively. , and These represent the axial strain, circumferential strain, and shear strain on the mid-surface of the cylindrical shell structure, respectively, where x is the generatrix direction and θ is the circumferential direction. In step 1), during the deformation of the cylindrical shell structure, the structure will become unstable. The expression for the radial deflection after the cylindrical shell structure becomes unstable is: （4）； in, This represents the radial deflection after the cylindrical shell structure becomes unstable. The longitudinal length of the cylindrical shell. Let be the deflection at both ends of the cylindrical shell corresponding to the modal number m. For the deflection corresponding to the modal number m, The amplitude of the deflection curve corresponding to the modal number m; In step 5), in a cylindrical shell structure, the distance between adjacent ribs is the net span. In the cylindrical shell structure, the difference in radial displacement between the main shell and the ribs is the radial relative displacement. When the radial relative displacement is greater than the net span... The maximum value is 1 / 2 of the net span; Therefore, a fracture criterion model for cylindrical shell structures is established: （12）。 2. The safety assessment method for the deep-sea lightweight cylindrical shell pressure-resistant structure according to claim 1, characterized in that, The cylindrical shell lightweight pressure-resistant structure is made of titanium alloy. In step 1), during the deformation of the cylindrical shell structure, the stability analysis of the titanium alloy structure shows that the strain caused by the deviation of the middle surface of the cylindrical shell structure from the original equilibrium position is very small and can be ignored. During the large deformation stage of instability, the bending strain along the thickness direction of the cylindrical shell structure is much greater than the longitudinal and circumferential compressive strains on the mid-surface of the shell. Therefore, substituting equation (4) into equations (1)-(3) yields the expression for the non-mid-surface strain during the instability process of the cylindrical shell structure: （5）； （6）； （7）。 3. The safety assessment method for the deep-sea lightweight cylindrical shell pressure-resistant structure according to claim 2, characterized in that, In step 2), because the cylindrical shell structure undergoes large nonlinear deformation, the plastic strain is much greater than the elastic strain; therefore, the equivalent plastic strain expression for the cylindrical shell structure is: （8）； Substituting equations (5) to (7) into equation (8), the equivalent plastic strain equation for fracture failure of the cylindrical shell structure can be simplified as follows: （9）； Using the material's plastic strain as the criterion for fracture failure, at this time Where h is the shell thickness; therefore, the expression for the local instability mode of the cylindrical shell structure is: （10）。 4. The safety assessment method for the deep-sea lightweight cylindrical shell pressure-resistant structure according to claim 3, characterized in that, In step 4), during the process of large deformation of the cylindrical shell structure leading to instability and even local fracture, the mode m=1 between two adjacent ribs, and the maximum relative deformation between the main shell and the rib between adjacent ribs can be obtained from equations (9) and (10): （11）。

Images