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ObjectivesThis study takes a typical pressure hull segment of an unmanned underwater vehicle (UUV) as the object and explores its load bearing capacity law based on lightweight design technology. MethodsFirst, several typical materials are analyzed using the mechanical properties of the pressure hull, load law and optimal critical load design value (stress strength failure and stability failure occur concurrently). The bearing properties of a typical pressure hull with varying depths are then discussed further in terms of the specific engineering requirements. ResultsThe failure mode of the shell gradually transitions from stability failure to strength failure as the depth increases, and the optimal critical load design value is proportional to the qualities of the material. Taking bearing efficiency and other factors into consideration, aluminum alloy shells should be selected within the 300 m depth range, titanium alloy and glass fiber composite shells within the 300−600 m depth range, and titanium alloy and carbon fiber composite shells within the 600−1 000 m depth range. In the 1 000−3 000 m depth range, a carbon fiber and boron fiber composite shell is the ideal solution. ConclusionsThe findings of this study can be used to guide the design of pressure hulls for UUVs made of various materials.

TC4 ELI alloy is widely used in the marine, medicine, and aviation fields. The failure performance of TC4 ELI alloy is significantly different from that of other metal materials, such as steels. In this paper, a modified Mohr–Coulomb criterion is calibrated based on several kinds of specimens under different stress states and a 3D geometric representation of a modified Mohr–Coulomb fracture locus for TC4 ELI is obtained based on these parameters. The effectiveness of the modified M-C criterion is studied by a ring-stiffened cylinder made of TC4 ELI. The ultimate strength of the cylinder obtained in the simulation with the modified M-C criterion is close to that obtained in an external pressure experiment, which shows that the modified M-C criterion is suitable for predicting failure in pressure hulls made of titanium alloy used in the deep-sea field. [ABSTRACT FROM AUTHOR]

Objectives: In order to withstand the deep water pressure, the cylindrical structure and the coni⁃ cal structure are often used as the submarine pressure hull. The section roundness of the submarine pressure hull needs to be measured during construction and repair. Due to the limitation of environment conditions and the fusion of different survey methods to obtain data, the survey points are often non-uniform. This case would result in the deviation between the results of classical least square circle fitting method and the actual situation, especially to the maximum deflection which is used as the judgment condition of round⁃ ness. Therefore, it is necessary to adopt a method to eliminate the influence of non-uniform distribution of the survey points. Methods: A non-uniform sampling weighted least squares circle fitting method and its weighting rules are proposed based on the classical Pratt circle fitting method. There are three steps in the proposed method. First, the survey points are fitted by the classical Pratt method. Then, the weight of point is calculated according to the corresponding center angle. Finally, the survey points with weight are fitted. Results: Numerical experiments on standard ellipse sampling analysis are carried out. The results show that the maximum deflection is more affected than the fitted center and radius by the non-uniformity of the sampling points. Because the roundness evaluation judgment of the submarine pressure hull is based on the maximum deflection, the fitting results of the proposed method are more accurate and reliable than the classical circle fitting method. Conclusions: The proposed method can eliminate the influence of nonuniform sampling on circle fitting better, and has good accuracy and engineering practical value [ABSTRACT FROM AUTHOR]

The water-drop-shaped pressure hull has a good streamline, which has good application prospect in the underwater observatory. Therefore, this study conducted analytical, experimental and numerical investigation of the buckling properties of water-drop-shaped pressure hulls under hydrostatic pressure. A water-drop experiment was conducted to design water-drop-shaped pressure hulls with various shape indices. The critical loads for the water-drop-shaped pressure hulls were resolved by using Mushtari's formula. Several numerical simulations including linear buckling analysis and nonlinear buckling analysis including eigenmode imperfections were performed. The results indicated that the critical loads resolved by Mushtari's formula were in good agreement with the linear buckling loads from the numerical simulations. This formula can be extended to estimate the buckling capacity of water-drop-shaped pressure hulls. In addition, three groups of pressure hulls were fabricated by using stereolithography, a rapid prototyping technique. Subsequently, three groups of the pressure hulls were subjected to ultrasonic measurements, optical scanning, hydrostatic testing and numerical analysis. The experimental results were consistent with the numerical results. The results indicate that the sharp end of the water-drop-shaped pressure hulls exhibited instability compared with the blunt end. This paper provides a new solution to the limitations of experimental studies on the water-drop-shaped pressure hulls as well as a new configuration and evaluation method for underwater observatories. [ABSTRACT FROM AUTHOR]

ObjectivesThis paper aims to discuss the relationship between the ultimate bearing capacity of a pressure hull and pressure tank under the same strength margin, and obtain a matching design with the equivalent ultimate bearing capacity and strength margins accordingly. MethodsTo this end, a typical external pressure tank is taken as the research object. On the basis of evaluating the stability and ultimate bearing capacity of the initial structural scheme, the influences of the thicknesses of the pressure tank shell, solid floor and transverse bulkhead on the ultimate bearing capacity are studied. The initial scheme is then adjusted to obtain a scheme with the equivalent strength margins of the pressure hull and pressure tank. In this context, the relationship between the ultimate bearing capacity of the pressure hull and pressure tank is discussed. By strengthening the pressure hull to match the ultimate bearing capacities of the pressure tank and pressure hull, the corresponding strength margins are obtained. ResultsThe results show that thinning the pressure tank shell by 30%, solid floor shell by 33.3% and transverse bulkhead shell by 30% reduces the ultimate bearing capacity of the tank by 16.5%, 36.4% and 0.17% respectively. ConclusionsAs further analyses show, under the condition of the same strength margin, the ultimate bearing capacity of the pressure hull is much lower than that of the pressure tank. When the strength margin of the pressure tank is about 25% and that of the pressure hull is about 40%, the ultimate bearing capacities of the pressure hull and pressure tank are roughly the same.

Underwater gliders are a class of ocean observation equipment driven by buoyancy, and their energy consumption source is mainly generated by the active regulation of buoyancy. The periodic elastic deformation of the pressure hull during the upward and downward movement of the underwater glider can have a large impact on its driving buoyancy. This paper relates the optimization problem of the pressure hull with the energy consumption of underwater glider, and the energy improvement factor is taken as the optimization objective. Based on the mechanical theory, the theoretical optimization model and constraint model are derived. A hybrid genetic simulated annealing algorithm (HGSAA) is adopted to optimize the pressure hull of the underwater glider developed by Huazhong University of Science and Technology (HUST). Additionally, the effectiveness of the optimized mathematical model and optimization results were verified by the tests. The sea trial results show that after the pressure hull optimization, the energy consumption of the buoyancy regulation unit decreased by 21.9%, and the total energy carried increased by 12.4%. [ABSTRACT FROM AUTHOR]

In this study, the dieless bulging and nonlinear buckling behaviours of a stainless longan-shaped pressure hull were investigated. According to the Cassini oval equation, the longan shape has a shape index of 0.1. The lengths of the major and minor axes of the designed longan-shaped pressure hull were approximately 400 and 396 mm, respectively. The wall thickness of this pressure hull was 1 mm. The Huber–von Mises stress and first yielding load of the designed longan-shaped shell and its inscribed polyhedral preform were investigated analytically and experimentally. Moreover, the dieless bulging of the designed longan-shaped pressure hull was investigated numerically and experimentally by using the nonlinear finite element method and a hydrostatic test, respectively. The analytical, experimental, and numerical results exhibited good agreement with each other.

Fully-transparent deep-sea pressure hulls have been attracted attention in recent years with the increasing demand for underwater observation. So far, public researches on design rule and failure modes for fully-transparent deep-sea pressure hulls are limited and the relevant experience cannot meet the requirements of new cabin design. In this study, the compression test is carried on, in which the material samples are subjected to quasi-static compressive load until failure in tests at different loading rates, and the hyperelastic finite element model is established in LS-DYNA software to simulate the failure process. Simulation results of material properties in finite element analysis on the cylindrical samples are compared with the experimental data, including the characteristic points of the mechanical properties in elastic stage and hardening stage, the ultimate load and failure mode of the samples. Mesh convergence analysis is conducted, and the appropriate mesh quality is accordingly selected in simulation of fully-transparent deep-sea pressure hulls. An equation for prediction of instability-type failure is described, which is derivation based on the classical analytical expression of elastic instability, thus, when 5 times of safety factor is taken, the wall thickness of the pressure hull is calculated to be t/R0 = 0.0685 at 2,500 m depth. Ultimate strength and failure mode of a typical fully-transparent deep-sea pressure hull are simulated. First, the first-order linear buckling modal analysis is carried out to simulate initial geometric imperfections. Then, simulations for the loading and collapse process of two fully-transparent pressure hulls respectively with one opening and two openings are conducted, and the ultimate load of 126 MPa and 128 MPa for the two kinds of hulls are obtained. Finally, simulation of a scaled pressure hull is carried out and simulation results are compared with the experimental data in reference, which are basically consistent. The calculated failure strength shows that the spherical hulls satisfy the safety factor requirement of 5 times. The provided simulation procedure can be referred for failure analysis of fully-transparent pressure hulls.

With the increasing application and study of lightweight and high strength fiber reinforced polymer composites in ocean industry, the structural failure problem of composite pressure hulls has attracted great attention from many researchers in China and globally. Analysis of the structural failure mechanisms is foundational to the design of deep-sea composite pressure hulls, since nowadays the design rules of pressurized vessels is mostly formulated according to their failure modes. Hence, this paper aims to review the research on the structural failure of composite pressure hulls in deep sea settings. First of all, the applied research status on composite material in marine equipment is analyzed, including inspection modalities for composite pressure hulls. The review then focuses on the three main failure modes, namely overall buckling, material failure and snap buckling of the deep-sea composite pressure hulls. The study identifies further problems of composite pressure hulls to be solved through the application of the deep sea equipment research, aiming to provide a reference for the study of mechanical behavior, ultimate strength computation, and design of thick composite pressure hulls for deep sea equipment. [ABSTRACT FROM AUTHOR]

The spherical pressure hull of deep-sea manned submersible is subjected to the alternating load with high dwell pressure during the cyclic working state of diving, operating and rising. Therefore, the compressive dwell fatigue behavior is a key factor to be considered in the structural safety evaluation of the pressure hull for manned submersibles. In this paper, a structure-grade dwell fatigue test of the pressure hull and a variety of specimen-grade compressive dwell fatigue tests were performed for Ti–6Al–4V ELI and Ti–6Al–2Sn–2Zr–3Mo-X alloys. Results show that no obvious structural deformation occurs in the spherical hull after the dwell fatigue test and no detectable out-of-standard defect is found in the welds when the dwell pressure value is the maximum operating pressure. The cumulative compressive strains of dwell fatigue specimens show that the base metal and welding joint have undergone plastic deformation when the maximum compressive stress value is 0.9 R p0.2. No microcracks or changes in the microstructure characteristics are observed in the specimens. The present results support the structural design and safety assessment of deep-sea manned submersibles for long-term service. • Experimental investigations explore the compressive dwell fatigue behavior of pressure hull. • Strains of measurement points mainly remained unchanged after a small initial increase under maximum operating pressure. • No obvious structural deformation occurs in the spherical hull after the dwell fatigue test. • Base metal and welding joint have undergone plastic deformation when the maximum compressive stress value is 0.9 R p0.2 • No microcracks or changes in the microstructure characteristics are observed in the specimens. [ABSTRACT FROM AUTHOR]

During the fabrication of pressure hulls, plastic processing is indispensable, which is an environmental, highly effective, and economical processing method. However dimensional error is also induced during plastic processing. This kind of error is one type of defection, which makes the hulls in danger, especially when the hulls suffer eternal pressure. Von Mises theory is an effective approach to study failure of pressure hulls. In this paper, numerical simulations are performed to investigate influence of distribution of defections along the axial direction on the ultimate strengths of titanium alloy pressure hulls of long barrel shape with two vessel heads using ABAQUS. The results of numerical simulations show that the ultimate strengths of pressure hulls with defections are relative to the location and distribution of defections, and they are decreasing with reduction of the average ratio and standard deviation when the hull suffers eternal pressure. The method of evaluating degradation of ultimate strength based on simulations can be employed to check the safety of pressure hulls. [ABSTRACT FROM AUTHOR]

To optimally coordinate the operational safety, manoeuvrability, positioning reliability, and space expansibility of deep-sea stations, this study proposed a segmented spiral pressure hull with reference to the geometry of worm snails. The design addresses the disadvantages of existing ring-stiffened cylinder, segmented sphere, and circular toroid structures. This study numerically and experimentally examined the buckling performance of segmented spiral pressure hulls. The numerical, experimental, and analytical data exhibited satisfactory agreement. The proposed pressure hulls exhibited a favourable space expansibility and buckled in a nonlinear manner. The buckling loads varied slightly after the threshold number of segments. All the post buckling modes were local dents. The current findings may serve as a reference for the research and development of original deep-sea stations. [ABSTRACT FROM AUTHOR]

This study investigated the free hydroforming of a stainless-steel egg-shaped shell. An egg-shaped shell is a promising geometry for deep pressure hulls. The length and width of the egg-shaped shell were 512.40 and 356.25 mm, respectively. The wall thickness of the egg-shaped shell were 0.844 mm. The equivalent stress, yielding load, internal capacity, and surface area of the egg-shaped shell and its inscribed segmented preform were investigated analytically and experimentally. The hydroforming performance of the egg-shaped shell was analysed using the nonlinear finite element method, and the results were validated by experimental model tests. The results indicated that free hydroforming can be an effective technique for fabricating egg-shaped pressure hulls and can yield highly symmetric shells of revolution regardless of the large geometric deviation of the segmented preform. [ABSTRACT FROM AUTHOR]

Nowadays, the full ocean depth submersible has become a focus of world marine research, and higher requirements are proposed for the mechanical properties of the pressure hull, the core component of a submersible, in the deep-sea environment. Upgrading the materials is one of the key ways to realize this goal. Due to such superior material properties as high specific strength and corrosion resistance, certain non-metallic materials such as composites, ceramics, glass, etc. are especially suitable for the manufacture of marine equipment, and show great potential for application to the pressure hull. This paper discusses the material requirements of deep-sea submersible pressure hulls, analyzes the advantages of composites, ceramics and glass in their material properties, briefly introduces the global development and application of various non-metallic materials in submersible pressure hulls, summarizes the technical problems currently faced and discusses avenues which deserve further study in this field.

Underwater gliders are a class of ocean observation equipment driven by buoyancy, and their energy consumption source is mainly generated by the active regulation of buoyancy. The periodic elastic deformation of the pressure hull during the upward and downward movement of the underwater glider can have a large impact on its driving buoyancy. This paper relates the optimization problem of the pressure hull with the energy consumption of underwater glider, and the energy improvement factor is taken as the optimization objective. Based on the mechanical theory, the theoretical optimization model and constraint model are derived. A hybrid genetic simulated annealing algorithm (HGSAA) is adopted to optimize the pressure hull of the underwater glider developed by Huazhong University of Science and Technology (HUST). Additionally, the effectiveness of the optimized mathematical model and optimization results were verified by the tests. The sea trial results show that after the pressure hull optimization, the energy consumption of the buoyancy regulation unit decreased by 21.9%, and the total energy carried increased by 12.4%.

With the increasing application and study of lightweight and high strength fiber reinforced polymer composites in ocean industry, the structural failure problem of composite pressure hulls has attracted great attention from many researchers in China and globally. Analysis of the structural failure mechanisms is foundational to the design of deep-sea composite pressure hulls, since nowadays the design rules of pressurized vessels is mostly formulated according to their failure modes. Hence, this paper aims to review the research on the structural failure of composite pressure hulls in deep sea settings. First of all, the applied research status on composite material in marine equipment is analyzed, including inspection modalities for composite pressure hulls. The review then focuses on the three main failure modes, namely overall buckling, material failure and snap buckling of the deep-sea composite pressure hulls. The study identifies further problems of composite pressure hulls to be solved through the application of the deep sea equipment research, aiming to provide a reference for the study of mechanical behavior, ultimate strength computation, and design of thick composite pressure hulls for deep sea equipment.

Pressure hulls are designed to stand the hydro static and dynamic bearing when they operate under water. These structures are also applied to naval submarines, remotely operated vehicle (ROV) and autonomous underwater vehicles (AUV). The underwater vehicle plays an important role in the petroleum industry, ocean engineering, and fishing, etc. To do so, ROV and AUV are studied for design and fabrication. This paper focuses on studying linear and nonlinear buckling analysis of stiffened cylindrical pressure hull under bearing load in Vietnam sea environment. The modeling of this pressure hull structure has been carried out by finite element analysis software packages.

The biological module BINOM is a platform for multi-purpose biomedical space experiments with a wide range of biological objects (bacteria, algae, fungi, plants, multicomponent ecosystems). It was designed as a payload for SamSat nanosatellites and can be easily mounted on any other space vehicle. The module consists of three main blocks a sealed chamber for biological objects, a life support system, a system of control and measurement supporting scientific data acquisition and pre-processing. The BiNOM interacts with the electronic systems of the nanosatellite with the help of a single four-pin connector. The life support system maintains the required temperature, pressure, humidity and gas mixture composition in the chamber of the biological object. The control system makes it possible to carry out biomedical experiments in the automatic mode according to a specified program or by commands from the ground control post. The control system is designed to measure the parameters of the environment and the biological object. The module supports visualization of objects in the UV-VIS-IR spectral range, fluorescence analysis, temperature and humidity measurement at several points, pressure, concentration of oxygen and carbon dioxide. Additional sensors can be used depending on the goals of the experiment. A module prototype was made and a number of tests were carried out to confirm the adequacy of the engineering solutions proposed. In particular, the vacuum chamber tests showed that the pressure loss in the pressure hull does not exceed 20% per year. A number of biological experiments demonstrated the possibility of initialization, growth and life support of various biological objects during a long, up to two months, period.

In the presented paper elastic–plastic buckling of hemispherical heads under external pressure was studied. Five laboratory-scale models with nominal diameter = 120 mm and thickness = 0.4 mm were manufactured and tested. Collapse loads of geometrically perfect and imperfect heads were obtained theoretically and numerically. The nonlinear buckling of hemispherical heads are numerically studied under various wall thicknesses 0.24–0.6 mm, yield strengths 180–230 MPa, and imperfection sizes 0.01–0.05 mm. Proposed analytical formulae predicting nonlinear buckling loads of hemispherical heads were verified experimentally and benchmarked against numerical results. The results of analytical, numerical, and experimental investigations were compared in tables and figures. [ABSTRACT FROM AUTHOR]

The paper focuses on Cassini oval pressure hulls under uniform external pressure. The Cassini oval pressure hull is proposed based on the shape index of Cassini oval. The buckling of a series of Cassini oval pressure hulls with the shape index of 0.09–0.30 and one spherical pressure hull with the diameter of 2 m is devoted. Such hulls are numerically studied in the case of constant volume, material properties, and wall thickness. The results show that Cassini oval pressure hulls with the shape index of 0.10–0.11 can resist about 4% more external pressure than the spherical one. This deviates from the classical mechanics conclusion that spherical shell is the optimal shape for underwater pressure resistant structures. [ABSTRACT FROM AUTHOR]

In the paper, an underwater fishing robot for aquatic products is developed. The finite element analysis method is used to optimize the thickness of the pressure hull of underwater robot, which can prevent hull pressure from being damaged to ensure the normal operation of the underwater vehicle. As an important structural component of underwater fishing machinery, the pressure hull should not only meet the requirements of stability but also require its strength within the allowable range under underwater pressure. The optimized pressure hull structure is more in line with the functional requirements of underwater fishing robots, the weight of the robot overall is reduced, the materials and costs of that are saved, and the reliable reference data for practical forestry engineering applications are provided. [ABSTRACT FROM AUTHOR]

This study employed experiments and numerical simulations to investigate the impact of pressure hulls’ degree of out-of-roundness on their buckling strength and buckling modes. In addition, post-buckling simulations were conducted to analyze the post-buckling behavior of the said pressure hull. Regarding numerical simulations for analyzing pressure hull buckling, the common analysis method is to first calculate the eigenvalue and the eigenmodes of buckling and then introduce an appropriate number of eigenmodes based on the initial defect of the structure before conducting a nonlinear buckling simulation. In addition to employing this common nonlinear analysis method (in which ABAQUS was used), this study adopted the PD-5500/33 specification to measure the circularity of the pressure hull for experimentation to confirm that the circularity satisfied the PD-5500/33 specification. Finally, this study compared the differences in nonlinear buckling strength between two numerical models and compared the numerical simulation results with the experimental results. This study verified that by employing the analysis method of eigenmode superpositioning, the buckling and post-buckling behavior of an out-of-roundness pressure hull could be more accurately simulated. [ABSTRACT FROM AUTHOR]

This paper is devoted to a further investigation on a range of externally pressurised egg-shaped pressure hulls. Hulls are 2.561 m long, 1.767 m wide, and have uniform wall thickness varying from 10 to 80 mm with 5 mm increment. Series of numerical simulations and laboratory scale experiments are performed to systematically study the buckling of egg-shaped pressure hulls, along with the effect of wall thickness on the buckling. Volume and mass equivalent spherical pressure hulls are also proposed to make a like-for-like comparison with egg-shaped pressure hulls. The results show that egg-shaped pressure hulls seem to be applicable to deep sea manned/unmanned submersibles, especially to full ocean depth ones (11,000 m). Also, deep pressure hulls tend to buckle in an elastic–plastic regime, which is strongly affected by the wall thickness. [ABSTRACT FROM AUTHOR]

This paper focuses on the buckling of titanium alloy spherical pressure hulls subjected to uniform external pressure. Hulls were spherical shells with 1000 mm median radius and had uniform wall thickness of 25–80 mm. The linear and nonlinear buckling of geometrically perfect hulls were examined numerically and verified analytically in linear range. The nonlinear buckling of hulls with eigenmode geometrical imperfections were evaluated numerically using the modified Riks method, in which imperfection size ranged from 2 to 10 mm. The critical buckling load of geometrically perfect and imperfect hulls was obtained based on elastic-perfectly plastic material modelling, in which the yield strength varied from 800 to 1300 MPa. A semi-analytical formula to predict the load carrying capacity of hulls was derived based on the numerical computations, which was verified against previous laboratory experiments conducted years ago and numerical benchmark study. Results of analytical, numerical, and experimental investigations were given in tables and figures. [ABSTRACT FROM AUTHOR]

This study presents a combined pressure hull design method with variable-section ribs. This method for determining the length-radius ratio of the pressure hull's bearing unit is derived based on the stiffness-matching characteristic of the shell and stiffener. The bearing mechanism of variable curvature stiffened shell is discussed through theoretical derivation and numerical simulation. The design scheme of variable cross-section and the equal-stiffness rib is proposed to address the limitations of outer envelope size and inner space utilization of the pressure hull. Its buckling load is determined by the energy method. The design approach for a new type of stiffened pressure hull is summarized. In addition, the method is verified by the design example and the experiment. The results revealed that the combined variable curvature shells are a superior pressure hull configuration. Compared to the cylindrical stiffened shell, the buckling load of the pressure hull with variable cross-section ribs can be improved significantly (about 26.7%). At the same time, space utilization remains at the original level. The stiffened design technique described in this research based on elastic buckling theory can accurately determine the length-radius ratio of the bearing unit, relying on the design objective with high feasibility. • It derived the relationship between the length-radius ratio and the mechanical characteristics for stiffened pressure hull. The method of determining the size of cabin and the position for ribs is proposed. Which can be realized by programming software. The design efficiency could be enhanced. • The design scheme of variable cross-section rib is proposed. The bearing capacity and the space utilization of the pressure hull with this typed ribs can be inproved obviously. • Through theoretical derivation, numerical simulation and the experiment, the bearing mechanism of pressure hull with variable curvature shells is discussed. The length-radius ratio of bearing unit is one of the key parameters. • On the basis of the above studies, a new design method of combined stiffened pressure hull with variable curvature shells is established, which has high feasibility. To a certain extent, this method improves the systematic design of stiffened pressure hulls, though there are few researchs in this area. [ABSTRACT FROM AUTHOR]

Spherical shells are presently the most extensively used shapes for pressure hulls in the deep manned submersible. However, it is known that the spherical pressure hull has disadvantages of difficult interior arrangement/low space efficiency, and is highly sensitive to geometric imperfections. These limitations have prevented further developments of the deep manned submersible to some extent. In order to overcome these limitations, two egg-shaped pressure hulls respectively with the constant and variable thickness are proposed in this paper, where the equivalent spherical pressure hull is also presented for comparison. Buckling of these pressure hulls with geometric imperfections are further studied using numerical analyses at a given design load. It is found that, with respect to hull strength, buoyancy reserve, and space efficiency etc., egg-shaped pressure hulls could be optimally coordinated, which appear to be leading to overall better performance than the spherical pressure hull. Especially, the egg-shaped pressure hull is quite less sensitive to the geometric imperfections, making it more convenient and low costly to form the hull in manufacturing or to open holes in applications. It is anticipated that egg-shaped pressure hulls will play a key role in the future development of deep-sea manned submersibles. [ABSTRACT FROM AUTHOR]

During the pressure hull manufacturing, processes like cold bending and welding are often applied. These processes lead to permanent plastic deformations which are associated with residual stresses. The presence of residual stresses is equivalent to the introduction of an initial preload in the structure, which accelerates the plastification process, decreasing pressure hull resistance. To quantify this reduction, a case study that considers residual stresses due to cold bending on hull plates and frame flanges had been performed using finite element models. The study encompasses hull diameters of 6, 8, and 10 m with hull plates and frame flange thickness from 20 to 30 mm, with HY100 steel. Finite element numerical analyses were done considering material and geometric nonlinearities. First, the cold bending residual stresses were determined using finite element models. Then, these cold bending residual stresses were introduced as initial stresses in the submarine pressure hulls' finite element models. In the end, it was possible to verify that the presence of cold bending residual stress reduces the submarine hull collapse pressure up to 4.3%. [ABSTRACT FROM AUTHOR]

Composites are an attractive material for pressure hulls because of their high strength and low density. This paper presents a history of composite pressure vessel hull development over the last 50 years and uses the lessons learnt, to develop a composite pressure hull concept for a shallow diving hull, or buoyancy device. This is done by evaluating several concepts modelled using Finite Element Analysis for weight and other criteria. A converged solution is developed and further analysed for sensitivity to geometric imperfections. These imperfections are shown to have a significant effect on the collapse depth of the composite pressure hull. [ABSTRACT FROM AUTHOR]

Cylindrical pressure hulls are widely used in deep-sea submersibles, but they are affected by limitations imposed by their mechanical characteristics. To improve the bearing capacity of pressure hulls, in this work, variable-curvature shells were proposed. Based on the membrane theory and the non-momental theory, expressions for calculating the stress and buckling load of variable-curvature shells were derived. The generalized equal-strength shell theory was taken as an important index to evaluate the bearing capacity of pressure hulls. Pressure hulls with different geometric configurations were analyzed through numerical simulations. Finally, cylindrical and circular variable-curvature shells were fabricated via additive manufacturing. Furthermore, a comparative experiment was carried out on the two types of shells. The results reveal that variable-curvature shells have better mechanical properties than cylindrical shells, which results in a lower stress in the two main directions and a higher buckling load. Additionally, variable-curvature shells are in better agreement with the equal-strength shell theory and ensure a high material utilization. The expressions for calculating the stress and buckling load in this study are found to be highly accurate. • It derived the calculation formulas of stress and buckling load for unclosed meridian variable-curvature shell, based on the membrane theory and non-momental theory. • The evaluation system of variable-curvature pressure hulls based on generalized equal-strength shell theory has been established. • Combined with the generalized equal-strength shell theory, the spatial arrangement and dimension of the structure, the geometric configuration of the variable-curvature pressure hull is analyzed and optimized. For shells of constant thickness, the first and second radius of curvature R 1 , R 2 are key design variable. • Through additive manufacturing technology, the variable-curvature models have been manufactured, and static experiment is carried out to verify the accuracy and applicability of the results in this manuscript. [ABSTRACT FROM AUTHOR]

The phenomenon of room temperature creep in titanium alloys has drawn great attention for decades. With the increasing application of titanium alloys to the manned submersible pressure hull, the traditional calculation and analysis based on strength and stability cannot meet the requirement of structure design and safety evaluation for the spherical pressure hull completely. In this paper, a series of compressive creep tests were performed to reveal the change rule and distribution characteristics for creep behavior of the spherical pressure hull model. Results show that there is no measurable creep strain for pressure hull under maximum operating pressure and steady-state creep appeared in high stress areas of the pressure hull under 1.25 times maximum operating pressure, with the characteristics of internal creep strain and strain rate being greater than the external counterparts. The stress threshold value of the pressure hull model for steady-state creep is 853.7 MPa (equivalent to 0.88 R p0.2), and a creep constitutive equation is proposed based on improved Norton power law model. The results of this paper can provide support for the safety assessment and optimization design of manned submersibles for long-term service. • Experimental tests explore the compressive creep characteristic of pressure hull. • No measurable creep strain occurs for pressure hull under maximum operating pressure. • Steady-state creep appears under 1.25 times maximum operating pressure. • Stress threshold value is 853.7 MPa for pressure hull model under steady-state creep. • A creep constitutive equation is proposed based on improved Norton power law model. [ABSTRACT FROM AUTHOR]

The manned submersibles of the 1960s look very different to the vehicles being built today. Improvements in materials have allowed deeper diving depths, while the rapid advance in electronics and more compact engineering design have helped to reduce launch weights. The rescue submersible has been developed in the last 15 years, but most noticeable is the increased use of acrylic for working depths down to 1,000 m. This article tracks this evolution by looking at just 10 vehicles that formed important stepping stones along this path. Alvin, the Johnson-Sea-Link (JSL), and the Pisces represent the deep-diving science and working submersibles from the 1960s and early 1970s. Alvin has continued to evolve right up to the present day, and 2 of the 10 Pisces boats are still working. The LR5 saw the start of the current military rescue submersibles operating around the world today, although they were never built for that purpose at the start. Oil industry working subs in the 1970s heyday are represented by the ubiquitous Perry PC-12 and PC-18 boats. Now, the same function and more are fulfilled by the deep worker at a fraction of the size. The acrylic hull revolution started in the 1960s with the Naval Experimental Manned Observatory and the JSL boats but has taken until now to be fully realized. This path from the JSL boats is plotted with the Deep Rovers, Alicia AP6, and the current offerings from Triton and, finally, the Deep Fight, an expression of pure enjoyment of the subsea realm made possible by the designer's lifetime experience working with submersibles. [ABSTRACT FROM AUTHOR]