An ellipsoidal cabin for deep-sea operations, a cabin manufacturing method, and a method for predicting the ultimate strength of the cabin.

Abstract

This invention discloses an ellipsoidal cabin for deep-sea operations, comprising an outer shell and access ports at both ends of the outer shell. The outer shell is symmetrical along its axial midsection. The outer shell on one side of the midsection comprises at least two outer shell unit groups, each comprising several outer shell units divided along the axial direction of the ellipsoidal cabin. The outer shell units in each unit group have the same thickness, while the outer shell units in different units have different thicknesses, with the units closer to the midsection being thicker. All outer shell units are smoothly connected on their outer surfaces to form a streamlined elliptical arc surface. By adopting a stepped-thickening ellipsoidal cabin structure, the material distribution is more rational, achieving the goal of saving material costs. Compared with a uniformly thickened cabin structure, the stepped thickness of the ellipsoidal cabin is easier to process, greatly reducing processing difficulty and manufacturing costs.

Description

Technical Field

[0001] This invention relates to auxiliary equipment for deep-sea exploration and development, specifically to an ellipsoidal cabin for deep-sea operations, a cabin manufacturing method, and a method for predicting the cabin's ultimate strength. Background Technology

[0002] With the advancement and development of deep-sea technology, there is a growing need for more reliable and safer deep-sea equipment to meet the demands of scientific research, oil extraction, and seabed resource development in the deep-sea environment. Deep-sea pressure chambers are a crucial component of deep-sea equipment and are also key to safety and reliability. Deep-sea ellipsoidal chambers have broad application prospects in areas such as relay compartments, manned compartments, ballast water tanks, and electronic compartments for deep-sea mining equipment or deep-sea submersible equipment.

[0003] For example, deep-sea ellipsoidal hulls can serve as ballast water tanks in application number 202111443104.6 (a deep-sea mining bottom-mounted mineral hoisting system); or as high-pressure silos in application number 202010051500.3 (a deep-sea ore hydraulic hoisting system with a deep-sea single high-pressure silo feeding device). This uniquely shaped hull offers several advantages. First, the ellipsoidal design allows it to maintain structural integrity under high pressure and provides a large internal volume. Its unique shape helps to evenly distribute stress, enhancing the overall strength and safety of the hull. Furthermore, the ellipsoidal hull provides sufficient space to accommodate equipment, systems, and personnel, making it suitable for various applications across industries such as marine vessels and aerospace. The versatility and reliability of deep-sea ellipsoidal hulls make them a preferred choice in many critical environments, performing exceptionally well in environments with high strength requirements and where space optimization is crucial.

[0004] Regarding structural design, international application number PCT / YU2003 / 000022 (ELLIPSOIDAL SUBMARINE) proposes an ellipsoidal chamber and describes its underwater operation. However, the steel plates or lightweight alloys used in the manufacturing of such ellipsoidal chambers are of uniform thickness, leading to underutilization of materials and significant material waste. International application number PCT / US2016 / 020788 (UNDERWATER VEHICLE DESIGN AND CONTROL METHODS) proposes a design and control method for an ellipsoidal underwater vehicle. Its ellipsoidal chamber uses homogeneous thickness materials, making the material cost of such ellipsoidal underwater vehicles expensive and unsuitable for practical engineering applications. Patent number ZL201510073803.4 (A Deep-Sea Bionic Pressure-Resistant Shell) proposes a biomimetic egg-shaped pressure-resistant shell and designs an egg-shaped pressure-resistant shell with uniformly varying thickness based on the principle of equal strength. However, the uniform thickening design of this type of egg-shaped pressure-resistant shell is currently only in the theoretical stage. The actual processing difficulty of its uniform thickening is very high, the manufacturing cost is high, and the patent does not provide a specific processing method.

[0005] Regarding evaluation and analysis, patent number ZL201710233630.7 (A method for estimating the ultimate bearing capacity of a titanium alloy submersible pressure spherical shell) and application number 202011187570.8 (A method for calculating the numerical value of the ultimate bearing capacity of a double-layer cylindrical pressure shell) disclose the evaluation of the shell. However, neither of their ultimate bearing capacity calculation methods considers material hardening during the forming process of the pressure shell, resulting in inaccurate theoretical and numerical calculations. Furthermore, existing methods for calculating the ultimate bearing capacity of pressure shells are all for pressure shells of uniform thickness.

[0006] In conclusion, the following three problems exist:

[0007] 1. Traditional ellipsoidal cabins are manufactured using plates of uniform thickness, and the materials used to manufacture ellipsoidal cabins are relatively expensive. This results in the underutilization of materials, which greatly increases manufacturing costs.

[0008] 2. Currently, a uniform thickness design method has been proposed, but this design method is only at the theoretical stage. Existing manufacturing technology cannot achieve uniform thickness of the cabin, and the actual processing difficulty is very high, and the manufacturing cost is extremely expensive.

[0009] 3. Existing ultimate strength prediction methods do not take into account material hardening during actual processing and manufacturing, resulting in inaccurate theoretical and numerical calculations. Furthermore, these ultimate strength prediction methods are all for cabins with uniform thickness. Summary of the Invention

[0010] Purpose of the invention: To address the above problems, this invention provides a method for manufacturing an ellipsoidal cabin and hull for deep-sea operations that saves materials, reduces processing difficulty and manufacturing costs.

[0011] The present invention also provides a method for predicting the ultimate strength of a cabin to improve prediction accuracy and reliability.

[0012] Technical Solution: To solve the above problems, the present invention adopts an ellipsoidal cabin for deep-sea operations, including a cabin shell and access holes at both ends of the cabin shell. The cabin shell is symmetrical in mid-section along the axial direction. The cabin shell on one side of the mid-section includes at least two cabin shell unit groups. The cabin shell unit group includes several cabin shell units cut along the axial direction of the ellipsoidal cabin. The cabin shell units in each cabin shell unit group have the same thickness. The cabin shell units in different cabin shell unit groups have different thicknesses. The cabin shell units in the cabin shell unit group closer to the mid-section are thicker. The cabin shell units are fixedly connected, and the outer surfaces of all cabin units are smoothly connected to form a streamlined elliptical arc surface.

[0013] This invention also employs a method for manufacturing an ellipsoidal cabin, comprising the following steps:

[0014] (1) Determine the number of cabin shell unit groups, the number of cabin shell units in each shell unit group and the thickness, and convert the cabin shell unit into a frustum to obtain an ellipsoidal cabin prefabricated model, and determine the size of the ellipsoidal cabin prefabricated model;

[0015] (2) The equivalent frustum of each cabin shell unit is unfolded in two dimensions to obtain the corresponding arc plate size;

[0016] (3) Laser cutting is performed on the corresponding material according to the obtained arc plate size to obtain the arc plate;

[0017] (4) The obtained arc-shaped plate is rolled and welded at the joint to obtain a frustum-shaped plate;

[0018] (5) Based on the ellipsoidal cabin prefabrication model, the obtained frustum plates are welded sequentially to obtain the ellipsoidal cabin prefabrication;

[0019] (6) Welded flanges connecting the inlet and outlet holes at both ends of the ellipsoidal cabin prefabrication body;

[0020] (7) Fix the two rigid thick plates to the two connecting flanges respectively by using ring clamps to seal the ellipsoidal cabin prefabrication, and open a water injection hole in one of the rigid thick plates.

[0021] (8) Water is injected and pressurized into the ellipsoidal cabin prefabricated body through the water injection hole and the ellipsoidal cabin shell is obtained by moldless expansion.

[0022] Furthermore, the determination of the dimensions of the ellipsoidal cabin prefabricated model includes the determination of the outer contour and the wall thickness; the formula for determining the outer contour is:

[0023]

[0024]

[0025] λ=b / a≥1.4

[0026] Among them, f i (x) represents the outer contour of the ellipsoidal cabin prefabricated model, and q(x) represents the outer contour of the ellipsoidal cabin shell. i ,y i ) represents the position of the bottom edge of the i-th frustum in the ellipsoidal cabin prefabrication model from the center of the ellipsoidal cabin prefabrication model, a is half of the minor axis of the ellipsoidal cabin, b is half of the major axis of the ellipsoidal cabin, and λ is the axis length ratio;

[0027] The formula for determining wall thickness t is:

[0028]

[0029] Where P is the internal pressure of the ellipsoidal chamber, φ is the angle between the radius of curvature of the ellipsoidal chamber at the current wall thickness location and the central axis of the ellipsoidal chamber, and σ e The equivalent stress of the ellipsoidal cabin.

[0030] This invention also employs a method for predicting the ultimate strength of a cabin shell, comprising the following steps:

[0031] (1) Establish the geometric model of the ellipsoidal cabin prefabrication and the cabin shell, and determine the ideal elastic-plastic material parameters of the cabin shell;

[0032] (2) Based on the geometric model of the ellipsoidal cabin prefabrication body, and according to the principle of volume equivalent transformation during the moldless bulging process of the ellipsoidal cabin prefabrication body, the elastic-plastic hardening mechanical parameters of the cabin shell are calculated, thereby obtaining the elastic-plastic hardening material parameters of the cabin shell.

[0033] (3) Establish a finite element model of the cabin shell and determine the exact number of meshes used in the finite element model through mesh convergence analysis;

[0034] (4) Input the elastic-plastic hardening material parameters, cross-sectional parameters, boundary conditions and uniformly distributed load of the cabin shell into the finite element model, and use the Newton iteration method to perform nonlinear solution calculation to obtain the ultimate strength of the cabin shell.

[0035] Furthermore, the specific steps for calculating the elastoplastic hardening mechanical parameters of the cabin shell in step (2) are as follows:

[0036] (2.1) Based on the principle of volume equivalent transformation, the basic assumptions of the material hardening theoretical analysis model of the cabin shell are established;

[0037] (2.2) Calculate the length of the hypotenuse of each frustum based on the basic assumptions;

[0038] (2.3) Calculate the lateral surface area of ​​the frustum based on the length of its hypotenuse, and at the same time calculate the lateral surface area of ​​the cabin shell unit formed after the frustum is molded without a mold.

[0039] (2.4) Based on the wall thickness and lateral area of ​​the frustum and the lateral area of ​​the outer shell unit, the average wall thickness of the outer shell unit is calculated according to the basic assumption that the material volume remains constant.

[0040] (2.5) Calculate the volume of the frustum and the volume of the cabin shell unit. Based on the volumes of the frustum and the cabin shell unit, calculate the equivalent radius of the frustum and the equivalent radius of the cabin shell unit respectively.

[0041] (2.6) Calculate the radial strain of the cabin shell unit based on the wall thickness of the frustum and the cabin shell unit, and calculate the circumferential strain of the cabin shell unit based on the equivalent radius of the frustum and the cabin shell unit; calculate the meridional strain based on the radial strain and the circumferential strain.

[0042] (2.7) The equivalent strain is calculated based on the radial strain, circumferential strain, and meridional strain. Based on the equivalent strain ε... eq Calculate the average yield stress σ eq :

[0043] σ eq =σ y +Kε eq

[0044] Where, σ y Let K be the yield strength of the material, and K be the strength coefficient.

[0045] Furthermore, the basic assumptions of the material hardening theoretical analysis model for the cabin shell include:

[0046] (1.1) During the moldless bulging process, the weld will not undergo rigid displacement;

[0047] (1.2) The outer shell of the cabin is symmetrical about the coordinate axis, and the ellipsoidal cabin prefabrication and the applied pressure are also symmetrical about the coordinate axis. The coordinate axis includes the x-axis and the y-axis. The x-axis is along the central axis of the outer shell of the cabin, and the y-axis is perpendicular to the x-axis. The origin of the coordinate axis is located at the center point of the outer shell of the cabin.

[0048] (1.3) The material volume remains constant during the moldless bulging process, and the axial height of each frustum does not change before and after the moldless bulging process;

[0049] (1.4) The thickness of the outer shell of the cabin is equal to the nominal thickness before and after moldless bulging;

[0050] (1.5) In moldless bulging, the material is isotropic, continuous, uniform, and elastoplastic, and is not affected by any initial stress;

[0051] (1.7) There is no radial stress;

[0052] (1.8) It will not produce dynamic effects;

[0053] (1.9) Rigid thick plates will not deform.

[0054] Beneficial effects: Compared with the prior art, the significant advantages of this invention are:

[0055] 1. By designing an ellipsoidal cabin structure with progressively thicker walls, material distribution becomes more rational. Adjusting the wall thickness at different locations within the cabin saves on material costs. This structural design significantly improves the cabin's structural utilization rate, allowing it to withstand external pressure more effectively.

[0056] 2. Compared with a uniformly thickened cabin structure, the stepped thickness of the ellipsoidal cabin makes it easier to process, greatly reducing processing difficulty and manufacturing costs.

[0057] 3. A method for predicting the ultimate strength of stepped-thickness ellipsoidal hulls. The influence of material hardening is fully considered during the hull manufacturing process. Compared to methods that do not consider material hardening, this prediction method improves calculation accuracy by at least two times, thus significantly reducing calculation errors. Furthermore, this method is not only applicable to stepped-thickness ellipsoidal hulls but can also be extended to irregularly shaped hulls made of other materials, providing a more accurate basis for the design and strength prediction of deep-sea hulls. Attached Figure Description

[0058] Figure 1 This is a cross-sectional view of the stepped thickening structure of the deep-sea ellipsoidal cabin of the present invention;

[0059] Figure 2 This is a cross-sectional view of the ellipsoidal cabin prefabricated variable-thickness structure of the present invention;

[0060] Figure 3 This is a flowchart of the deep-sea ellipsoidal cabin manufacturing method of the present invention;

[0061] Figure 4 This is a flowchart of the deep-sea ellipsoidal cabin ultimate strength prediction method of the present invention;

[0062] Figure 5 This is a schematic diagram of the deep-sea ellipsoidal cabin and the prefabricated ellipsoidal cabin structure of the present invention;

[0063] Figure 6This is a geometric schematic diagram of the front and rear frustums and the equivalent cylinder of the moldless bulging process of the present invention;

[0064] Figure 7 This is a schematic diagram of the material curves obtained from the theoretical analysis of the elastoplastic hardening model of the present invention;

[0065] Figure 8 This is a schematic diagram of the deep-sea ellipsoidal cabin grid unit model of the present invention;

[0066] Figure 9 This is a schematic diagram of the deep-sea ellipsoidal chamber subjected to uniformly distributed loads and equivalent boundary conditions according to the present invention;

[0067] Figure 10 A schematic diagram of the stepped wall thickness distribution of a deep-sea ellipsoidal chamber, which is an embodiment of the present invention;

[0068] Figure 11 A graph showing the mesh convergence of a deep-sea ellipsoidal chamber, representing an embodiment of the present invention.

[0069] Figure 12 The equilibrium displacement curve of the deep-sea ellipsoidal chamber calculated under the elastoplastic hardening material model is an embodiment of the present invention.

[0070] Figure 13 The equilibrium displacement curve of the deep-sea ellipsoidal chamber calculated under an ideal elastoplastic material model is an example of an embodiment of the present invention.

[0071] Figure 14 A schematic diagram of the dimensions of the ellipsoidal cabin prefabricated arc plate, which is an embodiment of the present invention;

[0072] Figure 15 This is a schematic diagram of a moldless bulging test apparatus according to an embodiment of the present invention;

[0073] Figure 16 This is a schematic diagram of a hydrostatic testing apparatus according to an embodiment of the present invention;

[0074] Figure 17 The water pressure curve of the deep-sea ellipsoidal chamber is an example of an implementation of the present invention. Detailed Implementation

[0075] Example 1

[0076] like Figure 1As shown in the figure, an ellipsoidal cabin for deep-sea operations in this embodiment includes a cabin shell and access ports at both ends of the cabin shell. The access ports are fixedly equipped with connecting flanges, and the ends of the connecting flanges are provided with sealing grooves 1. From top to bottom, the cabin shell consists of sealing groove 1, upper connecting flange 2, cabin shell 3, lower connecting flange 5, and sealing groove 1. The cabin shell 3 is welded and fixed to the upper connecting flange 2 and the lower connecting flange 5 by welding technology. The upper connecting flange 2 and the lower connecting flange 5 can be fitted with hatch covers or observation windows for sealing. Their main function is to serve as access ports to ensure the safe entry and exit of personnel and equipment and to observe the surrounding environment.

[0077] The outer shell 3 is symmetrical along its axial mid-section. The outer shell on one side of the mid-section comprises at least two outer shell unit groups. Each outer shell unit group includes several outer shell units divided along the axial direction of the ellipsoidal cabin. The outer shell units in each unit group have the same thickness, but the thicknesses of the outer shell units in different units vary, with the units closer to the mid-section being thicker. At least two thicknesses are selected to improve the structural utilization of the cabin and save material costs. The outer shell units are fixedly connected, and the outer surfaces of all units are smoothly joined to form a streamlined elliptical arc surface. The outer shell comprises at least eight outer shell units.

[0078] In this embodiment, the first thickness cabin 31 and the second thickness cabin 32 in the outer shell 3 are obtained by connecting and combining prefabricated frustums and forming them without a mold. The first thickness cabin 31 and the second thickness cabin 32 are symmetrical about the y-axis. The first thickness cabin 31 is composed of at least four prefabricated frustums: frustum 31-1, frustum 31-2, frustum 31-3, and frustum 31-4. Similarly, the second thickness cabin 32 is also composed of at least four prefabricated frustums: frustum 32-1, frustum 32-2, frustum 32-3, and frustum 32-4.

[0079] The outer shell 3 is the core component of the stepped, variable-thickness structure of the deep-sea ellipsoidal cabin, primarily responsible for withstanding loads under high pressure. The outer shell 3 requires at least two different wall thicknesses, exhibiting a thicker center and thinner ends. Due to the greater curvature of the sections near the upper connecting flange 2 and the lower connecting flange 5, a smaller wall thickness is sufficient to meet the required operating pressure. Most importantly, this design saves material during cabin construction while maintaining strength, reducing economic costs and improving structural utilization. The organic combination of these components of the deep-sea ellipsoidal cabin makes the entire structure more complete and stable. This structural design effectively distributes loads under various stress conditions, providing higher pressure resistance and safety.

[0080] Example 2

[0081] This embodiment describes a method for manufacturing the ellipsoidal cabin described in Embodiment 1. First, a suitable ductile metal material needs to be selected based on design requirements. The material for the deep-sea ellipsoidal cabin can be chosen according to the specific requirements of the deep-sea environment and operating conditions. Then, according to the design requirements of the stepped thickening structure, precise cutting and processing are performed to form the basic structural element of the stepped thickening region of the deep-sea ellipsoidal cabin: a frustum. Finally, the entire manufacturing process of the deep-sea ellipsoidal cabin is completed through processes such as welding, surface treatment, and moldless bulging.

[0082] like Figure 2 The diagram shows the main schematic of the stepped variable thickness structure design of the ellipsoidal cabin prefabrication. Preliminary processing design is based on this ellipsoidal cabin prefabrication. The ellipsoidal cabin prefabrication is symmetrical about the coordinate axes (x-axis and y-axis). The ellipsoidal cabin prefabrication is designed to be inscribed within the target deep-sea ellipsoidal cabin. According to the general assumption of inscription, within a certain range, the size and geometry of the segmented frustums of the ellipsoidal cabin prefabrication have little impact on the result after forming using the moldless bulging technology. However, the most basic segmented design requirement is that the number of frustum segments must be at least 8; and, according to the principle of symmetry, the number of frustums is generally divided into even numbers. Considering the actual processing and manufacturing cost and feasibility, the wall thickness requirement for the stepped variable thickness ellipsoidal cabin in this embodiment is selected to be at least two thicknesses. In the actual manufacturing process, to improve the operability of the moldless bulging technology, the ellipsoidal cabin prefabrication can be sealed using an upper rigid thick plate 7 and a lower rigid thick plate 8 instead of manholes and observation windows. The upper rigid plate 7 and the lower rigid plate 8 are connected and fixed to the upper connecting flange 2 and the lower connecting flange 5 by annular clamps 6, and sealed by sealing grooves 1 and sealing rings. The upper and lower connecting flanges and each truncated cone are assembled and connected by welding. A water injection port is opened at the center of the upper rigid plate 7 to facilitate water injection and pressurization. The diameter of the water injection port should be no less than 1 / 6 and no more than 1 / 3 of the diameter of the rigid plate. The ellipsoidal prefabrication body is formed into a deep-sea ellipsoidal cabin using moldless bulging technology. After the ellipsoidal prefabrication body is formed into a deep-sea ellipsoidal cabin, the annular clamps 6 are removed, and the upper and lower rigid plates 7 and 8 are removed. Then, the hatch or observation window can be assembled and fixed to the upper and lower connecting flanges respectively. The specific processing and manufacturing process of the ellipsoidal prefabrication body and the deep-sea ellipsoidal cabin is as follows.

[0083] The method of hull manufacturing is as follows Figure 3 As shown, the specific steps include the following:

[0084] Step 1: Design the initial geometric model:

[0085] First, the initial geometric models of the ellipsoidal prefabricated body and the stepped-thickness outer shell are determined in the 3D engineering software based on the outer contour of the model. The outer contours of the ellipsoidal prefabricated body and the outer shell can be defined by formulas (1) and (2), respectively:

[0086]

[0087]

[0088] Among them, f i (x) represents the outer contour of the ellipsoidal cabin prefabricated model, and q(x) represents the outer contour of the ellipsoidal cabin shell. i ,y i ) represents the position of the bottom edge of the i-th frustum in the ellipsoidal prefabricated model from the center of the ellipsoidal prefabricated model, such as... Figure 2 As shown, a is half of the minor axis of the ellipsoidal module, b is half of the major axis of the ellipsoidal module, and λ is the axis-to-length ratio. First, the major axis 2b and minor axis 2a of the target deep-sea ellipsoidal module are determined according to actual engineering requirements, and must meet the basic design requirement: λ=b / a≥1.4.

[0089] This invention designs a stepped, variable-thickness structure for a deep-sea ellipsoidal cabin, therefore it is necessary to determine the thickness distribution of the outer shell. Since the outer shell is a thin-walled structure, its stress state is typically considered to be plane stress. (The last sentence appears to be incomplete and possibly refers to the meridional stress of the deep-sea ellipsoidal cabin.) latitudinal stress and equivalent stress (σ e The following formula can be used to calculate:

[0090]

[0091]

[0092]

[0093] Wherein, the axis length ratio is defined as λ = b / a, and the axis length ratio must be greater than or equal to 1.4; p and t are the internal pressure and wall thickness of the outer shell of the hull, respectively; and φ is the angle between the rotation axis x and the second principal radius of curvature R2. The first principal radius of curvature R1 and the second principal radius of curvature R2 of the deep-sea ellipsoidal hull can be expressed as follows:

[0094] R1=λa[(λ 2 -1)sin 2 φ+1] -3 (6)

[0095] R2=λa[(λ 2 -1)sin 2 φ+1] -1 (7)

[0096] By combining formulas (5)-(7), the wall thickness t can be calculated using the following formula:

[0097]

[0098] Formula (8) can be used to determine the stepped wall thickness of a deep-sea ellipsoidal chamber. For example... Figure 5 As shown, this invention specifies that at least two types of cabin stepped wall thicknesses should be selected, respectively set as thickness t1 and thickness t2, so as to make the moldless bulging process simple and reliable.

[0099] Step 2: Cutting and blanking:

[0100] Based on the three-dimensional geometric model of the ellipsoidal cabin prefabricated body designed in the first step and the stepped wall thickness division, each segment of the frustum is flattened in the three-dimensional modeling software, and then two-dimensional drawings are exported to obtain the specific dimensions of the arc plate corresponding to each segment of the frustum. Then, CNC machining is used to perform laser cutting on the required plate to obtain the actual required arc plate.

[0101] Step 3: Bending the rolled plate:

[0102] Frustums are rolled using a conical plate rolling machine. The model and size of the selected conical plate rolling machine should be determined based on the specific dimensions of the deep-sea ellipsoidal chamber being manufactured and the materials. First, determine the thickness of the material to be rolled and select an appropriate number of rolling rollers, adjusting the gap to ensure proper stress distribution and avoid obvious bulging and wrinkling on the material surface. Second, control the rolling machine's operating speed to be uniform and moderate, smoothly feeding the curved plate into the rolling rollers while preventing misalignment and slippage, ensuring that the rolling direction of each frustum is the same. Note that each curved plate should be rolled at least twice on the rolling machine. After rolling, the frustum should generally have a longitudinal joint gap of no more than 2mm in its natural state, and the longitudinal joint should be slightly concave, not convex. Furthermore, the ellipticity of each formed frustum should be controlled within 1% of the nominal average diameter of each frustum to ensure the quality of the rolled plate. The nominal average diameter t of each frustum... im The following formula can be used for calculation:

[0103]

[0104] Step 4: Assembly and welding:

[0105] First, spot weld the joints of each rolled frustum using a spot welding machine. Depending on the size of the frustum, at least three spot welds are generally required. The misalignment at the longitudinal joint should not exceed 10% of the plate thickness, but must not exceed 3mm. Second, following the bottom-up assembly principle, spot weld the overlapping circumferential edges of adjacent frustums. The misalignment at the overlapping circumferential edges should not exceed 10% of the plate thickness plus 1mm, but must not exceed 4mm. It is important to note that each time the overlapping circumferential edges of two adjacent frustums are spot welded, at least four spot welds are required, with each weld spaced 90° apart in a clockwise direction to ensure concentricity. Furthermore, the longitudinal joints of the two adjacent frustums should be staggered, with a clockwise spacing of at least 45°. For butt welding of steel plates of different thicknesses: for thinner plates less than or equal to 10mm, the thickness difference is 3mm; for thinner plates greater than 10mm, the thickness difference is 4mm. If the thickness difference of the plates exceeds these values, the edges of the thicker plates should be beveled, and the beveling width should be greater than four times the thickness difference. During assembly, two adjacent frustums should be tightly fitted together, and any gaps where they cannot be fitted together should not exceed 3mm.

[0106] After all the tack welds on the truncated cones are completed, seam welding is performed. High-quality low-hydrogen electrodes and low-hygroscopic fluxes should be used for welding the hull. Electrodes and fluxes should be dried according to regulations before use. All circumferential overlapping welds on the hull should be fully penetrated sequentially in a clockwise direction. After visual inspection of all longitudinal and circumferential welds, 100% radiographic testing should be performed to inspect for internal defects. Cracks, lack of fusion, and incomplete penetration are not permitted in any longitudinal or circumferential welds on the hull. If porosity is present, the diameter of dispersed pores should be less than or equal to 1 / 4 of the maximum hull wall thickness; in areas with a diameter not exceeding 12mm within any continuous 300mm weld length, the diameter of dense pores should be less than or equal to 1 / 8 of the maximum hull wall thickness; tubular pores should not protrude from the weld surface, and their diameter should be less than or equal to 1 / 8 of the maximum hull wall thickness. The length of any dot-like or strip-like inclusions should be less than or equal to twice the maximum thickness of the bulkhead wall, with a maximum of 4 mm, and the width should be less than or equal to one-quarter of the maximum thickness of the bulkhead wall.

[0107] Step 5: Flange and plate sealing:

[0108] Similarly, after the prefabricated hull shell is assembled and welded, the connecting flanges are spot-welded to the adjacent frustums at the upper and lower ends, followed by seam welding. The design height of the connecting flanges is at least 1 / 4 of the nominal semi-major axis of the deep-sea ellipsoidal hull, and the maximum design diameter of the connecting flanges is at least 1 / 3 of the nominal major axis of the deep-sea ellipsoidal hull. Then, two rigid thick plates are fixed to the upper and lower ends of the hull with annular clamps to seal it, thus obtaining the prefabricated ellipsoidal hull body. The diameter of the rigid thick plates is the same as the maximum design diameter of the connecting flanges, and the thickness of the rigid thick plates is at least 20 times the maximum wall thickness of the hull. A water injection hole is opened in the center of one of the thick plates to facilitate water injection and pressurization. The diameter of the water injection hole should be no less than 1 / 6 and no more than 1 / 3 of the diameter of the rigid thick plate.

[0109] Step 6: Water injection and pressure molding:

[0110] Connect the prefabricated ellipsoidal chamber from step five to a hand-cranked pump via the water inlet pipe for pressurization. Connect a pressure gauge to a branch pipe of the water inlet pipe to monitor the water pressure in real time. After checking the tightness of the connection between the water inlet and the water inlet pipe, manually apply pressure to the hand-cranked pump slowly and evenly, controlling the average loading rate to not exceed 0.02 MPa / s. It is important to carefully observe the pressure gauge readings and changes in the shape of the chamber. The maximum load applied by the hand-cranked pump should not exceed 5 MPa. Simultaneously, the axial height variation of the entire chamber should be controlled within ±1 mm, and the maximum width variation should be controlled within ±0.5 mm. If the overall axial height of the chamber decreases by 1 mm during the bulging process, pressurization should be stopped immediately to prevent instability, weld cracking, and other issues that could lead to poor forming results. Generally, pressurization can be stopped when the shell shape reaches the ideal state, resulting in the ideal deep-sea ellipsoidal chamber.

[0111] Example 3

[0112] like Figure 4 As shown, this embodiment of the method for predicting the ultimate strength of an ellipsoidal cabin manufactured according to Embodiment 2 specifically includes the following steps:

[0113] Step 1: Establish the initial geometric model of the ellipsoidal cabin prefabrication and the cabin shell with varying thickness.

[0114] The outer contours of the ellipsoidal cabin prefabrication and the cabin shell can be calculated using formulas (1) and (2), respectively. Based on the wall thickness formula (8), the optimal stepped wall thickness used for moldless bulging is calculated, and the thickness boundary line of the cabin is determined. The thickness distribution generally exhibits the characteristics of being thin at both ends and thick in the middle.

[0115] Step 2: Define the ideal elastoplastic material parameters for the deep-sea ellipsoidal chamber.

[0116] In the design of deep-sea ellipsoidal hulls, it is necessary to determine their ideal elasto-plastic material parameters to ensure the normal operation and safety of the hull in the deep-sea environment. These parameters can be determined in detail through uniaxial tensile tests according to relevant standards. These include elastic modulus (E), Poisson's ratio (μ), and buckling strength (σ). y The elastic modulus (E) measures a material's ability to recover from deformation under stress, while Poisson's ratio (μ) describes the expansion and contraction of a material in different directions under stress. Buckling strength (σ) is also important. y The stress coefficient (CFC) refers to the critical stress value at which a material begins to undergo plastic deformation under stress. It is an important parameter for predicting the material's failure capability under compressive conditions. The work hardening coefficient characterizes the work hardening properties of a material during plastic deformation. It should be noted that the determination of material parameters must strictly follow relevant standards and specifications, and be conducted using appropriate experimental equipment and methods. A suitable tensile specimen must be designed before a uniaxial tensile test. Generally, tensile specimens are designed in a common dumbbell shape and must be cut from the base material to ensure that the specimen thickness is consistent with the base material thickness. Specific requirements for tensile specimen design are as follows: It is divided into three regions: the clamping region, the transition region, and the parallel region. The overall length of the tensile specimen should be no less than 160 mm, the overall width no less than 20 mm, the total length of the middle parallel region no less than 75 mm, the transition region is arc-shaped with a radius no less than 20 mm, and the length of the clamping region no less than 30 mm. It should be noted that when conducting a uniaxial tensile test, the tension must be applied along a single axis, that is, the load is applied along the centerline and the specimen is stretched uniformly at the specified speed. The coaxiality of the upper and lower clamps must be ensured to generate uniform tensile stress on the specimen, so that the fracture zone occurs in the middle parallel zone, thus ensuring the accuracy of the measured data.

[0117] Step 3: Calculate the elastoplastic hardening mechanical parameters of the deep-sea ellipsoidal chamber.

[0118] This invention utilizes a moldless bulging technique to bulge a prefabricated ellipsoidal chamber into a deep-sea ellipsoidal chamber. It is noteworthy that material hardening is unavoidable during the moldless bulging process, but it is difficult to quantitatively assess in numerical and experimental analyses. Therefore, based on the principle of equivalent volume transformation, a theoretical analysis model for material hardening of the deep-sea ellipsoidal chamber is constructed, and the elastoplastic hardening mechanical parameters of the stepped-thickness deep-sea ellipsoidal chamber are calculated. The specific steps are as follows:

[0119] Step 3.1: Basic assumptions for establishing the material hardening theoretical analysis model of the deep-sea ellipsoidal chamber:

[0120] (a) During the moldless bulging process, the weld will not undergo rigid displacement.

[0121] (b) The deep-sea ellipsoidal chamber is symmetrical about the coordinate axes (x-axis and y-axis), and the inscribed prefabricated body and the applied pressure are also symmetrical about the coordinate axes (x-axis and y-axis).

[0122] (c) The material volume remains constant during the moldless bulging process, and the axial height (H) of each frustum segment is constant. i It does not change after moldless bulging.

[0123] (d) The thickness of the cabin wall is equal to the nominal thickness before and after moldless bulging.

[0124] (e) In moldless bulging, the material is isotropic, continuous, homogeneous, and elastoplastic, and is not affected by any initial stress.

[0125] (f) There is no radial stress. Since the ratio of thickness to radius is very small, thin film theory can be used, and therefore radial stress can be ignored.

[0126] (g) No dynamic effects will occur. Due to the slow loading of internal moldless bulging pressure, quasi-static analysis can be performed without considering dynamic effects.

[0127] (h) Rigid thick plates do not deform due to their large wall thickness.

[0128] Step 3.2: Calculate the hypotenuse length of the frustum. By applying assumptions (a)-(c), the hypotenuse length of the i-th segment of the ellipsoidal prefabricated body can be determined using the following formula:

[0129]

[0130] Where L i0 H represents the length of the hypotenuse of the frustum before moldless bulging. i It is the axial height of the i-th frustum.

[0131] Step 3.3: Calculate the lateral surface area of ​​the frustum. The lateral surface area of ​​the i-th frustum before and after moldless bulging can be calculated by integration, as shown in the following formula:

[0132] S i0 =π(y i +y i+1 )L i0 ,i=1,2,3…n,n≥8 (11)

[0133] and

[0134]

[0135] Among them, S i0 S represents the lateral surface area of ​​the frustum before moldless bulging. i1 This represents the side area of ​​the outer shell unit after moldless bulging.

[0136] Step 3.4: Calculate the average wall thickness of the frustum (t) i1 Based on the principle of constant material volume, the average wall thickness (t) of the i-th cabin shell unit after moldless bulging can be determined. i1 The calculation formula is as follows:

[0137] t i0 S i0 =t i1 S i1 , i=1,2,3…n,n≥8 (13)

[0138] Among them, t i0 It is the average wall thickness of the i-th frustum of the preformed ellipsoidal chamber without mold expansion.

[0139] Step 3.5: Calculate the volume of the frustum. The volume of the i-th frustum before and after moldless bulging can be calculated by integration, as shown in the following formula:

[0140]

[0141] and

[0142]

[0143] Among them, V i0 V represents the volume of the frustum before moldless bulging. i1 This indicates the volume of the cabin shell unit after moldless bulging.

[0144] Step 3.6: Calculation of equivalent radius. Based on assumption (c), the axial height (H) of the i-th frustum before and after moldless bulging is calculated. i The average strain and average stress remain unchanged. To calculate the average strain and average stress, it can be assumed that before and after moldless bulging, the i-th segment of the frustum can be equivalently represented as a cylinder (e.g., ...). Figure 6 As shown). Therefore, the equivalent volumes before and after (V respectively) i0 and V i1 The values ​​are kept equal, and the calculation formula is as follows:

[0145]

[0146] and

[0147]

[0148] Where r i0 and r i1 It is the equivalent radius of the equivalent cylinder.

[0149] Step 3.7: Calculate radial strain (ε) t ) and circumferential strain Using the fundamental theory and assumptions (d)-(h) of rotating shells, the radial strain (ε) of the i-th frustum after moldless bulging is... t ) and circumferential strain The following formula can be used to calculate:

[0150]

[0151] and

[0152]

[0153] Step 3.8: Calculate meridional strain Based on the constant volume assumption (Equation 20), the meridional strain of the i-th frustum after moldless bulging can be calculated using Equation (21).

[0154]

[0155]

[0156] Step 3.9: Calculate the equivalent radial strain (ε′) t Equivalent latitudinal strain and equivalent meridional strain Combining formulas (13)-(17), the equivalent radial strain (ε′) of the i-th frustum after moldless bulging can be determined respectively. t Equivalent latitudinal strain and equivalent meridional strain The calculation formula is as follows:

[0157]

[0158]

[0159] and

[0160]

[0161] Step 3.10: Calculate the equivalent strain (ε) eq By substituting formulas (22)-(24) into the given equivalent strain formula (25), the equivalent strain (ε) of the i-th frustum after moldless bulging is obtained. eq It can be calculated using the following formula:

[0162]

[0163]

[0164] Step 3.11: Calculate the average yield stress. Based on the material model, the linear constitutive equation (27) can be obtained. This equation allows for the easy calculation of the average yield stress of each frustum after material hardening. A schematic diagram of the material curve obtained from the elastoplastic hardening model is shown below. Figure 7 As shown.

[0165] σ eq =σ y +Kε eq (27)

[0166] Where, σ y Let K be the yield strength of the material, and K be the strength coefficient.

[0167] At this point, all the elastoplastic hardening mechanical parameters of the deep-sea ellipsoidal chamber have been calculated.

[0168] Step 4: Establish a finite element model of the deep-sea ellipsoidal chamber.

[0169] like Figure 8 As shown, the 3D model of the deep-sea ellipsoidal cabin is imported into suitable meshing software. A meshing method using quadrilaterals as the primary element and triangles as the secondary element is adopted, with the number of triangular meshes not exceeding 1% of the total number of meshes. The manholes and observation windows at the top and bottom can be completely replaced by rigid thick plates to simplify finite element modeling and improve computational efficiency. The thickness of the rigid thick plates is at least 20 times the maximum thickness of the cabin wall, and the mesh nodes of the rigid thick plates are connected to the cabin mesh nodes at the edges using a common node method. After meshing, the mesh quality must be checked. The maximum angle of quadrilateral meshes cannot exceed 145°, the maximum angle of triangular meshes cannot exceed 120°, and the total number of quadrilateral and triangular meshes with maximum angles cannot exceed 0.5% of the total number of meshes. After the mesh quality check is completed, it is exported to an input format acceptable to the finite element program used. The finite element model of the deep-sea ellipsoidal cabin is now complete.

[0170] Step 5: Calculate the mesh convergence of the finite element model.

[0171] When creating the mesh using suitable meshing software, gradually decrease the size of the quadrilateral mesh elements and gradually increase the number of meshes in the finite element model in 1mm increments. Once the number of meshes in the finite element model reaches a certain value, and the rate of change in the final calculation result does not exceed 2%, then select the minimum number of meshes that meets the requirements as the actual number of finite element meshes used. Mesh convergence analysis can determine the precise number of meshes used in the finite element model to ensure the highest possible computational accuracy.

[0172] Step 6: Define the elastoplastic hardening material parameters for the deep-sea ellipsoidal chamber.

[0173] Input the material's elastoplastic hardening parameters, including Young's modulus (E), Poisson's ratio (μ), and yield strength (σ), into a suitable finite element program. eq The text discusses the hardening coefficient and the material hardening of the deep-sea ellipsoidal hull. It notes that the hull underwent material hardening after being formed using a moldless bulging technique, meaning its material parameters are no longer the ideal elasto-plastic parameters measured by uniaxial tensile testing, and the yield strength (σ) is affected. eq The yield strength (σ) has also changed. eq The hardening coefficient of the plastic stage is calculated using formula (27). Figure 7 The second linear segment of the elastoplastic hardening curve was fitted. For example... Figure 7 As shown, the equivalent strain is calculated according to formula (26) and used as the abscissa. Then, the corresponding ordinate is found on the elastoplastic hardening curve in the figure. The second half is taken as the new hardening coefficient and input into the finite element program.

[0174] Step 7: Define the cross-sectional parameters of the deep-sea ellipsoidal module model.

[0175] In a suitable finite element program, the cross-sectional properties of the shell elements are established. Based on the design requirements and thickness distribution, the thickness of the portion of the cabin near the top and bottom ends is designated as t1, named the first thickness; the thickness of the portion of the cabin near the central equator is designated as t2, named the second thickness; and the thickness of the rigid plate is at least 20t2, named the third thickness. The elastoplastic hardening material parameters determined in step 6 are assigned to the shell elements of these three thicknesses respectively. The shell elements of the first and second thicknesses are thickened from the top to the bottom, and the shell element of the third thickness is thickened from the bottom to the top, with at least 5 integration points selected.

[0176] Step 8: Define the boundary conditions and uniformly distributed loads for the deep-sea ellipsoidal module model.

[0177] like Figure 9 As shown, in this suitable finite element program, for the rigid thick plate element model at both ends of the deep-sea ellipsoidal cabin, the center is selected, the circumferential degree of freedom is fixed, and the axial degree of freedom is released; for the deep-sea ellipsoidal cabin element model, the equatorial center point of the cabin is selected, the normal degree of freedom perpendicular to that point is released and the remaining degrees of freedom are fixed, and a uniformly distributed load is applied to the entire cabin and the thick plates at both ends to simulate the uniformly distributed external pressure conditions in the deep sea.

[0178] Step 9: Perform nonlinear solution calculations using the Newton-Raphson iteration method.

[0179] In this suitable finite element program, the calculation analysis steps are set as follows: the Riks arc length method in general statics is selected for solution, the initial load increment is generally set to no more than 2% of the applied load, the maximum load increment is generally set to no more than 5% of the applied load, the minimum load increment is generally set to no more than 0.01% of the applied load, and the maximum allowable increment step is generally set to at least 1000 steps.

[0180] Step 10: Extract the calculation results of the deep-sea ellipsoidal chamber.

[0181] In the appropriate finite element program, enter the post-processing module of the program to extract the calculation results of the deep-sea ellipsoidal cabin finite element model, specifically including: ultimate strength, post-buckling mode, etc.

[0182] The following examples illustrate this in detail:

[0183] The following is a detailed description of the design process of the stepped variable thickness structure of the deep-sea ellipsoidal cabin.

[0184] First, the initial geometric models of the ellipsoidal prefabricated body and the stepped thickness of the deep-sea ellipsoidal chamber were determined in the 3D engineering software Creo 4.0 based on the model's outer contour formula. In this implementation example, the major axis 2b = 250 mm and the minor axis 2a = 178 mm of the ellipsoidal pressure tank, so the axis-to-length ratio λ = b / a = 1.404. It is assumed that the internal forming pressure value of the ellipsoidal pressure tank is p = 4 MPa. The hypotenuse length and height dimensions of each frustum are listed in Table 1.

[0185] Table 1. Nominal Dimensions of Deep-Sea Ellipsoidal Compartments

[0186]

[0187]

[0188] Meridional stress of deep-sea ellipsoidal chamber latitudinal stress and equivalent stress (σ e The following formula can be used to calculate:

[0189]

[0190]

[0191]

[0192] Where p and t are the internal pressure and wall thickness of the deep-sea ellipsoidal chamber, respectively. The deep-sea ellipsoidal chamber is manufactured using a moldless bulging technique. It is assumed that the internal forming pressure of the deep-sea ellipsoidal chamber is p = 4 MPa. φ is the angle between the rotation axis x and the second principal radius of curvature R2, with a value ranging from [0°-90°]. The first principal radius of curvature R1 and the second principal radius of curvature R2 of the deep-sea ellipsoidal chamber are calculated using the following formula:

[0193] R1=λa[(λ 2 -1)sin 2 φ+1] -3 =0.712×89×[(0.712) 2 -1)sin 2 φ+1] -3 (33)

[0194] R2=λa[(λ 2 -1)sin 2 φ+1] -1 =0.712×89×[(0.712) 2 -1)sin 2 φ+1] -1 (34)

[0195] Based on the above calculation results, the wall thickness t can be calculated using the following formula:

[0196]

[0197] Figure 10 The diagram shows the stepped wall thickness distribution of the deep-sea ellipsoidal cabin. Using formula (35), the cabin wall thickness distribution is calculated. Combined with the thickness of the 304 stainless steel base plate produced in the market, the uniform and equivalent stepped wall thickness of the deep-sea ellipsoidal cabin can be determined. For example... Figure 10 As shown in Table 1, this embodiment selects two types of cabin step thicknesses, set as thickness t1 = 0.67 mm and thickness t2 = 0.83 mm respectively, and selects moldless bulging technology as the forming method to make the deep-sea ellipsoid cabin forming process relatively simple and reliable.

[0198] Step 2: Cutting and blanking:

[0199] Based on the specific dimensions of the curved plate, a CNC machine tool is used to perform laser cutting on the required sheet material to obtain the actual curved plate. During laser cutting, the deviation between the cut part and the position on the design drawing (positioning error) is typically required to be within ±0.05mm, and the deviation between the actual size of the cut part and the size specified on the design drawing (dimensional error) is required to be within ±0.1mm. Secondly, the flatness should be controlled within 0.1mm / m, which can be adjusted according to the specific sheet material application. Furthermore, forming defects such as burr height should be less than 0.03mm, slag should be less than 0.1mm, and molten slag should be less than 0.2mm, and porosity should not affect the quality of the cut surface. In this implementation example, the positioning and dimensional errors during laser cutting meet the above requirements, the flatness is controlled within 0.1mm / m, and the maximum burr height is 0.02mm, the maximum slag height is 0.1mm, the maximum molten slag is 0.1mm, and no porosity appears. Figure 14 The figure shown is a schematic diagram of the dimensions of the ellipsoidal cabin prefabricated arc plate in this embodiment.

[0200] Step 3: Bending the rolled plate:

[0201] according to Figure 14 The dimensions of the curved plate were determined using a small three-roll conical plate rolling machine to form a frustum. First, the gap of the three-roll conical plate rolling machine was adjusted to within 1mm, and the machine's operating speed was controlled at 5m / min. In this embodiment, each curved plate was rolled twice on the rolling machine. The gap at the longitudinal joint of the rolled frustum in its natural state was 1.5mm, and the ellipticity of each formed frustum was controlled to be 0.8% of the nominal average diameter of each frustum, meeting the design requirements and ensuring the quality of the rolled plate.

[0202] Step 4: Assembly and welding:

[0203] Each frustum was spot-welded three times at its joint. The misalignment at the longitudinal joint was 5% of the plate thickness, and the misalignment at the circumferential overlapping edges was 8% of the plate thickness. Each time two adjacent frustums were assembled, the circumferential overlapping edges were spot-welded four times, with each spot weld spaced 90° apart in a clockwise direction. For the two types of steel plates in this embodiment, the thickness difference was only 0.16mm, therefore no beveling of the plate edges was required. During assembly, the two adjacent frustums were brought close together, with any gaps controlled to approximately 2mm.

[0204] After all the frustums were spot-welded and assembled, they were then seam-welded. All longitudinal and circumferential welds on the hull were inspected for cracks, lack of fusion, and incomplete penetration. The diameter of dispersed pores was controlled within 0.2 mm; in areas with a diameter not exceeding 12 mm within a continuous 300 mm weld length, the diameter of dense pores was controlled within 0.1 mm; no tubular pores were found during seam welding. The length of both dot-like and strip-like slag inclusions was less than 1 mm, and the width was less than 0.2 mm.

[0205] Step 5: Flange and plate sealing:

[0206] After spot welding the connecting flange to the adjacent frustums at the upper and lower ends, seam welding is performed. The design height of the connecting flange is 35mm, and the maximum design diameter of the connecting flange is 90mm. Then, two rigid thick plates are fixed to the upper and lower ends of the cabin with ring clamps to close it and obtain the ellipsoidal cabin prefabrication body. The diameter of the rigid thick plate is the same as the maximum design diameter of the connecting flange, the diameter of the rigid thick plate is 90mm, the thickness of the rigid thick plate is 17mm, and the diameter of the water inlet is 20mm.

[0207] Step 6: Water injection and pressure molding:

[0208] The prefabricated ellipsoidal chamber from step five was connected to a hand-cranked pump via an inlet pipe for pressurization. Pressure was applied manually, evenly, and slowly to the pump, controlling the average loading rate at 0.015 MPa / s. During pressurization, the pressure gauge readings and changes in the chamber's shape were carefully observed. It was observed that the axial height of the entire chamber first increased and then decreased. When the axial height returned to its initial value, the chamber had reached its ideal state, and pressurization was stopped. The change in the axial height of the entire chamber was controlled within ±1 mm. The pressure gauge reading was observed to be 4 MPa. Finally, the ideal deep-sea ellipsoidal chamber was obtained.

[0209] The following is a detailed description of the method for predicting the ultimate strength of a deep-sea ellipsoidal chamber.

[0210] Step 1: Establish the initial geometric model of the ellipsoidal prefabricated body and the stepped thickness of the deep-sea ellipsoidal body.

[0211] Based on the parameters in Table 1, calculate the outer contours of the ellipsoidal prefabricated body and the deep-sea ellipsoidal compartment. In the 3D software Creo 4.0, draw two-dimensional sketches of the ellipsoidal prefabricated body and the deep-sea ellipsoidal compartment with stepped thickness, where the ellipsoidal prefabricated body is inscribed within the deep-sea ellipsoidal compartment. Calculate the optimal stepped wall thickness used for moldless bulging according to the wall thickness formula, and determine the thickness boundary line of the compartment. For example... Figure 10The stepped wall thickness distribution used in this implementation example is shown. Two wall thicknesses were selected for the stepped-thickness ellipsoidal chamber, set as t1 = 0.67 mm and t2 = 0.83 mm respectively. The specific design parameters of the ellipsoidal chamber prefabrication and the stepped-thickness geometric model of the deep-sea ellipsoidal chamber are listed in Table 1.

[0212] Step 2: Define the ideal elastoplastic material parameters for the deep-sea ellipsoidal chamber.

[0213] The material used in this implementation example is 304 stainless steel. To obtain the ideal elastic-plastic material parameters for the cabin, tensile tests were conducted on the specimens using a uniaxial tensile testing machine according to the national standard GB / T 228.1–2010 Metallic Materials – Tensile Testing – Part 1: Tests at Room Temperature. Since two different wall thicknesses were chosen for the cabin in this implementation example, dumbbell-shaped tensile specimens were cut from the two different thicknesses of 304 stainless steel base material. During the uniaxial tensile test, a single axial tension was maintained, i.e., a load was applied along the centerline at a uniform loading rate of 1 kN / min, while ensuring that the coaxiality of the upper and lower clamps did not exceed 0.1 mm, thus generating uniform tensile stress on the specimen. The fracture zone was observed to occur in the middle parallel region during the test; the stress-strain curve was then output and processed. Finally, the elastic modulus E, Poisson's ratio μ, and buckling strength σ of the material were obtained. y The strength coefficient K and hardening coefficient are calculated, and the bilinear model curve of the material is plotted. The bilinear model curve of an ideal elastoplastic material is shown below. Figure 7 As shown in Table 2, the parameters of the ideal elastoplastic material obtained are as follows.

[0214] Table 2. Ideal elastic-plastic model parameters for 304 stainless steel.

[0215]

[0216] E = Young's modulus; μ = Poisson's ratio; σ y = Yield strength; K = Strength coefficient

[0217] Step 3: Calculate the elastoplastic hardening mechanical parameters of the deep-sea ellipsoidal chamber. Based on the basic assumptions, calculate the hypotenuse lengths of the eight frustum segments of the prefabricated ellipsoidal chamber; the results are listed in Table 1. Calculate the lateral surface area of ​​the i-th frustum before and after moldless bulging; the results are listed in the second and third columns of Table 3, respectively. Based on the principle of constant material volume, calculate the average wall thickness (t) of the i-th frustum after moldless bulging. i1 The calculation results are listed in column 7 of Table 3; the volume of the i-th frustum before and after moldless bulging is calculated, and the results are listed in columns 4 and 5 of Table 3, respectively; the equivalent radius (r) of the equivalent cylinder before and after moldless bulging is calculated. i0 and r i1 The calculation results are listed in columns 8 and 9 of Table 3, respectively.

[0218] Table 3. Geometric parameters of each frustum before and after moldless bulging

[0219]

[0220] Calculate radial strain (ε) t Circumferential strain Calculate meridional strain Calculate the equivalent radial strain (ε′) t Equivalent latitudinal strain and equivalent meridional strain The calculation results are listed in the second, third, and fourth columns of Table 4.

[0221] Calculate the equivalent strain (ε) eq The calculation formula is as follows:

[0222]

[0223] Equivalent strain (ε) eq The calculation results are listed in the fifth column of Table 4. Average yield stress (σ) eq The results are listed in the sixth column of Table 4.

[0224] Table 4. Mechanical parameters of each frustum after moldless bulging

[0225]

[0226] At this point, all the elastoplastic hardening mechanical parameters of the deep-sea ellipsoidal chamber have been calculated.

[0227] Step 4: Establish a finite element model of the deep-sea ellipsoidal chamber.

[0228] First, import the 3D model of the deep-sea ellipsoidal chamber into the commercial software HYPERMESH in iges format. Second, right-click the model's "make current" option, then click the "elem types" option in the 2D menu below. Change the quadrilateral mesh type to S4 and the triangular mesh type to S3. Next, select the entire deep-sea ellipsoidal chamber model, including the upper and lower rigid plates and the hull. Connect the mesh nodes of the rigid plates and the hull mesh nodes at the edges using common nodes. Click the "automesh" option in the 2D menu, enter a mesh size of 2mm, and check the number of circumferential and axial nodes. Use a meshing method with quadrilaterals as the primary element and triangles as the secondary element, where the number of triangular meshes does not exceed 1% of the total mesh count, meeting the requirements. Select the "normal" option in the "Tool" menu to check the normal direction of each mesh element. After meshing, check the mesh quality. The maximum angle of quadrilateral meshes should not exceed 145°, the maximum angle of triangular meshes should not exceed 120°, and the total number of quadrilateral and triangular meshes with maximum angles should not exceed 0.5% of the total mesh count, meeting the requirements. After the mesh quality check is completed, export the finite element model as an inp file. The creation of the deep-sea ellipsoidal cabin finite element model is now complete.

[0229] Step 5: Calculate the mesh convergence of the finite element model.

[0230] In the commercial software HYPERMESH, the mesh was generated by gradually decreasing the size of the quadrilateral mesh elements in 1mm increments while gradually increasing the number of mesh elements in the finite element model. For example... Figure 11 The diagram shows the mesh convergence of the finite element model. When the number of shell meshes reaches approximately 50,000, the rate of change in the final calculation result does not exceed 1%. Therefore, the minimum required mesh number is selected as the actual mesh number used. Mesh convergence analysis determines the precise number of meshes used in the finite element model to ensure computational accuracy to the greatest extent possible. After mesh convergence analysis, the precise mesh number used in the deep-sea ellipsoidal cabin finite element model of this implementation example is determined to be 50,436, of which 49,940 are quadrilateral meshes and 496 are triangular meshes. The number of triangular meshes accounts for 0.9% of the total mesh number, which does not exceed 1%, thus meeting the requirement.

[0231] Step 6: Define the elastoplastic hardening material parameters for the deep-sea ellipsoidal chamber.

[0232] In the Property module of the commercial finite element software ABAQUS, create isotropic material parameters and input the elastic-plastic hardening material parameters for 304 stainless steel. The elastic parameters are: Young's modulus E, Poisson's ratio μ; the plastic parameters are: yield strength σ. eq And the hardening coefficient. Yield strength (σeq The specific values ​​are listed in column six of Table 4. The hardening coefficient for the plastic stage is based on... Figure 7 The second linear segment of the elastoplastic hardening curve was fitted. For example... Figure 7 As shown, calculate the equivalent strain as the abscissa, then find the corresponding ordinate on the elastoplastic hardening curve in the figure, and input the latter half as the new hardening coefficient into the commercial finite element software ABAQUS.

[0233] Step 7: Define the cross-sectional parameters of the deep-sea ellipsoidal module model.

[0234] In the Property module of the commercial finite element software ABAQUS, import the HYPERMESH inp file to create a continuous, uniform shell section. The shell thickness near the top and bottom ends is set to t1 = 0.67 mm, named the first thickness; the shell thickness near the middle equator is set to t2 = 0.83 mm, named the second thickness; the thickness of the rigid plate is set to 20t2 = 17 mm, named the third thickness; five integration points are selected in the thickness direction. Using the elastoplastic hardening material parameters determined in step 3, and the mesh element model from step 4, the shell elements with the first and second thicknesses are thickened from the top to the bottom, and the shell element with the third thickness is thickened from the bottom to the top, with five integration points selected in the thickness direction.

[0235] Step 8: Define the boundary conditions and uniformly distributed loads for the deep-sea ellipsoidal module model.

[0236] like Figure 9 As shown, in the Load module of the commercial finite element software ABAQUS, the boundary conditions are first defined: For the rigid thick plate element model at both ends of the deep-sea ellipsoidal cabin, the YZ front view is selected, and the center point is selected respectively, with the degrees of freedom: U2 = U3 = 0; for the deep-sea ellipsoidal cabin element model, the XY front view is selected, and the center point of the surface is selected, with the degrees of freedom: U1 = U2 = 0. Next, a uniformly distributed load is defined: a uniformly distributed load P = 1 MPa is applied to the entire cabin and the thick plates at both ends to simulate the uniformly distributed external pressure conditions in the deep sea.

[0237] Step 9: Perform nonlinear solution calculations using the Newton-Raphson iteration method.

[0238] In the Step module of the commercial finite element software ABAQUS, set the calculation and analysis step as follows: define the Riks arc length method in general statics for solution, enable the nonlinearity button, set the initial load increment to 0.02, the maximum load increment to 0.05, and the minimum load increment to 10. -8 The maximum allowed increment step is set to 1000 steps. Then, in the Job module of the ABAQUS software, a new task is created and submitted for task analysis and calculation.

[0239] Step 10: Extract the calculation results of the deep-sea ellipsoidal chamber.

[0240] After the task calculations are completed, the ultimate strength of the deep-sea ellipsoidal cabin finite element model is extracted using the Visualization module of the commercial finite element software ABAQUS, such as... Figure 12 As shown, according to the calculation results, its ultimate strength is P1 = 1.932 MPa.

[0241] Based on steps 1-10 above, to better illustrate the accuracy and effectiveness of this ultimate strength prediction method, without considering material hardening during the forming process—that is, without going through the theoretical calculation derivation process in step 3—the elastoplastic hardening material parameters of the deep-sea ellipsoidal chamber in step 6 of the implementation example are directly changed to the ideal elastoplastic material parameters of the original material. Specifically, the data in Table 2 is input into the Property module of the commercial software ABAQUS, with other operations remaining unchanged, and steps 3-10 of the implementation example are repeated. Finally, the ultimate strength of the deep-sea ellipsoidal chamber is extracted in the Visualization module of the commercial software ABAQUS, as shown below. Figure 13 As shown, according to the calculation results, its ultimate strength is P2 = 1.731 MPa.

[0242] To verify the accuracy of the above theoretical analysis and numerical calculation methods, experimental verification was conducted. Based on the parameters in Table 1 and... Figure 3 The flowchart shown illustrates the overall fabrication process of the ellipsoidal pressure tank. A stepped, variable-thickness ellipsoidal prefabricated body was actually fabricated, and the ideal ellipsoidal pressure tank was obtained through moldless bulging. Subsequently, a hydrostatic test was conducted on the obtained deep-sea ellipsoidal tank to verify its pressure resistance. Figure 16 This is a schematic diagram of a hydrostatic testing apparatus, including a deep-sea ellipsoidal chamber 3, a data acquisition system 9, a hand-operated pump 10, a deep-sea pressure-resistant device 11, a water inlet 111, a pressure sensor 112, a lifting pneumatic cylinder 113, a drain outlet 114, a stepped heavy-duty end cap 115, and a sealing ring 116. The water inlet at the top of the ellipsoidal pressure-resistant chamber is plugged with a plug to prevent leakage. The deep-sea ellipsoidal chamber is placed in the deep-sea pressure-resistant testing apparatus and completely submerged in water. The pressure is slowly increased using the hand-operated pump, and the hydrostatic pressure curve is recorded by the pressure sensor using the dynamic data acquisition system. Figure 17 As shown. Ultimately, the ultimate strength of the deep-sea ellipsoidal chamber was measured in actual experiments to be P0 = 2.056 MPa.

[0243] A comparison of numerical calculations and experimental results shows that the ultimate strength obtained from numerical calculations and experiments differs by only 6%. Therefore, the ultimate strength calculation method presented herein can play a very good predictive role. However, without using the theoretical calculation derivation of this invention, a comparison of numerical calculations and experimental results shows that the ultimate strength error of the ellipsoidal pressure chamber obtained from numerical calculations and experiments is as high as 16%. Therefore, the ultimate strength prediction method of this invention improves the calculation accuracy by 2.6 times. A comparison of experimental results and numerical calculation results is shown in Table 5.

[0244] Table 5. Experimental and Calculation Results

[0245]

[0246] Therefore, through a series of theoretical calculations of this ultimate strength prediction method, the accuracy of the ultimate strength prediction of deep-sea ellipsoidal hulls has been greatly improved, filling the theoretical gap in the ultimate strength prediction model of stepped variable thickness hulls. Furthermore, this ultimate strength prediction method has high accuracy, small error, and is easy to operate.

Claims

1. A method for manufacturing the hull of an ellipsoidal cabin for deep-sea operations, characterized in that, The device includes an outer shell and access holes at both ends of the outer shell. The outer shell is symmetrical in its mid-section along the axial direction. The outer shell on one side of the mid-section includes at least two outer shell unit groups. Each outer shell unit group includes several outer shell units that are cut along the axial direction of the ellipsoidal cabin. The outer shell units in each outer shell unit group have the same thickness. The outer shell units in different outer shell unit groups have different thicknesses. The outer shell units in the outer shell unit group closer to the mid-section are thicker. The outer shell units are fixedly connected to each other, and the outer surfaces of all the outer shell units are smoothly connected to form a streamlined elliptical arc surface. The method for manufacturing the cabin includes the following steps: (1) Determine the number of cabin shell unit groups, the number of cabin shell units in each shell shell unit group and the thickness, and convert the cabin shell unit into a frustum to obtain an ellipsoidal cabin prefabricated model, and determine the size of the ellipsoidal cabin prefabricated model; (2) The equivalent frustum of each cabin shell unit is unfolded in two dimensions to obtain the corresponding arc plate size; (3) Laser cutting is performed on the corresponding material according to the obtained arc plate size to obtain the arc plate; (4) The obtained arc-shaped plate is rolled and welded at the joint to obtain a frustum-shaped plate; (5) Based on the ellipsoidal cabin prefabrication model, the obtained frustum plates are welded sequentially to obtain the ellipsoidal cabin prefabrication; (6) Welded flanges are used to connect the inlet and outlet holes at both ends of the ellipsoidal prefabricated body; (7) Fix the two rigid thick plates to the two connecting flanges respectively with ring clamps to seal the ellipsoidal cabin prefabrication body, and open a water injection hole in one of the rigid thick plates; (8) Water is injected and pressurized into the ellipsoidal cabin prefabricated body through the water injection hole and the cabin shell of the ellipsoidal cabin is obtained by moldless bulging. The determination of the dimensions of the ellipsoidal cabin prefabricated model includes the determination of the outer contour and the wall thickness; the formula for determining the outer contour is: in, This refers to the outer contour of the ellipsoidal cabin prefabricated model. This refers to the outer contour of the ellipsoidal cabin's outer shell. The first in the ellipsoidal cabin prefabrication model The distance from the bottom edge of each frustum to the center of the ellipsoidal cabin prefabricated model is given by: 'a' represents half the minor axis of the ellipsoidal cabin, and 'b' represents half the major axis of the ellipsoidal cabin. The axis length ratio; Wall thickness The formula is determined as follows: in, The internal pressure of the ellipsoidal chamber, This is the angle between the radius of curvature of the ellipsoidal compartment where the current wall thickness is located and the central axis of the ellipsoidal compartment. The equivalent stress of the ellipsoidal cabin.

2. The method for manufacturing a cabin according to claim 1, characterized in that, The inlet / outlet is fixedly fitted with a connecting flange, and a sealing groove (1) is provided at the end of the connecting flange.

3. The method for manufacturing a cabin according to claim 1, characterized in that, The total number of hull shell units is at least 8.

4. The method for manufacturing a cabin according to claim 1, characterized in that, In step (4), the rolled arc plate is first fixed by electric welding. The misalignment at the longitudinal joint of the arc plate shall not exceed 10% of the plate thickness, but shall not be greater than 3 mm.

5. The method for manufacturing a cabin according to claim 4, characterized in that, In step (5), according to the bottom-up assembly principle, the overlapping edges of two adjacent frustums are spot welded together. The misalignment of the overlapping edges shall not exceed 10% of the plate thickness plus 1 mm, but shall not exceed 4 mm. The longitudinal joints of the two frustums are staggered and assembled at least 45° apart in the clockwise direction. When the difference in plate thickness between two adjacent frustums exceeds the set value, the edge of the thicker frustum is beveled.

6. A method for predicting the ultimate strength of a hull shell manufactured according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Establish the geometric model of the ellipsoidal cabin prefabrication and the cabin shell, and determine the ideal elastic-plastic material parameters of the cabin shell; (2) Based on the geometric model of the ellipsoidal cabin prefabrication body, and according to the principle of volume equivalent transformation during the moldless bulging process of the ellipsoidal cabin prefabrication body, calculate the elastic-plastic hardening mechanical parameters of the cabin shell, and thus obtain the elastic-plastic hardening material parameters of the cabin shell. (3) Establish a finite element model of the cabin shell and determine the exact number of meshes used in the finite element model through mesh convergence analysis; (4) Input the elastic-plastic hardening material parameters, cross-sectional parameters, boundary conditions and uniformly distributed load of the cabin shell into the finite element model, and use the Newton iteration method to perform nonlinear solution calculation to obtain the ultimate strength of the cabin shell.

7. The method for predicting the ultimate strength of a cabin according to claim 6, characterized in that, The specific steps for calculating the elastic-plastic hardening mechanical parameters of the cabin shell in step (2) are as follows: (2.1) Based on the principle of volume equivalent transformation, the basic assumptions of the material hardening theoretical analysis model of the cabin shell are established; (2.2) Calculate the length of the hypotenuse of each frustum based on the basic assumptions; (2.3) Calculate the lateral surface area of ​​the frustum based on the length of its hypotenuse, and at the same time calculate the lateral surface area of ​​the cabin shell unit formed after the frustum is molded without a mold. (2.4) Based on the wall thickness and lateral area of ​​the frustum and the lateral area of ​​the outer shell unit, the average wall thickness of the outer shell unit is calculated according to the basic assumption that the material volume remains constant. (2.5) Calculate the volume of the frustum and the volume of the cabin shell unit. Based on the volumes of the frustum and the cabin shell unit, calculate the equivalent radius of the frustum and the equivalent radius of the cabin shell unit respectively. (2.6) Calculate the radial strain of the cabin shell unit based on the wall thickness of the frustum and the cabin shell unit, and calculate the circumferential strain of the cabin shell unit based on the equivalent radius of the frustum and the cabin shell unit; calculate the meridional strain based on the radial strain and the circumferential strain. (2.7) The equivalent strain is calculated based on the radial strain, circumferential strain, and meridional strain. Calculate the average yield stress : in, The yield strength of the material. This is the strength coefficient.

8. The method for predicting the ultimate strength of a cabin according to claim 7, characterized in that, The basic assumptions of the material hardening theoretical analysis model for the outer shell of the cabin include: (1.1) During the moldless bulging process, the weld will not undergo rigid displacement; (1.2) The outer shell of the cabin is symmetrical about the coordinate axis, and the ellipsoidal cabin prefabrication and the applied pressure are also symmetrical about the coordinate axis. The coordinate axis includes the x-axis and the y-axis. The x-axis is along the central axis of the outer shell of the cabin, and the y-axis is perpendicular to the x-axis. The origin of the coordinate axis is located at the center point of the outer shell of the cabin. (1.3) The material volume remains constant during the moldless bulging process, and the axial height of each frustum does not change before and after the moldless bulging process; (1.4) The outer wall thickness of the cabin is equal to the nominal thickness before and after moldless bulging; (1.5) In moldless bulging, the material is isotropic, continuous, uniform, and elastoplastic, and is not affected by any initial stress; (1.7) There is no radial stress; (1.8) It will not produce dynamic effects; (1.9) Rigid thick plates will not deform.

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