Pressure Hull Research Articles

Effect of corrosion thinning on depth of operation: Case study of an HY-80 steel submarine pressure hull

The effect of corrosion thinning on the collapse pressure of a submarine pressure hull made of HY-80 steel is investigated. Corrosion experiments on the heat-treated steel were conducted using potentiodynamic polarisation and immersion tests in sampled seawater, and compared to the in-situ measurements of a submarine pressure hull, to establish the annual corrosion thinning rates for the material. A finite element analysis was carried out on the ring-stiffened cylindrical section to determine the collapse pressure over a range of hull thinning, using experimentally obtained stress-strain behaviour of the material. Results on collapse pressures and their associated depth of operation are presented.

Energy Consumption Modeling for Underwater Gliders Considering Ocean Currents and Seawater Density Variation

Energy management is a critical and challenging factor required for efficient and safe operation of underwater gliders (UGs), and the energy consumption model (ECM) is indispensable. In this paper, a more complete ECM of UGs is established, which considers ocean currents, seawater density variation, deformation of the pressure hull, and asymmetry of gliding motion during descending and ascending. Sea trial data are used to make a comparison between ECMs with and without the consideration of ocean currents, and the results prove that the ECM that considers the currents has a significantly higher accuracy. Then, the relationship between energy consumption and multiple parameters, including gliding velocity relative to the current, absolute gliding angle, and diving depth, is revealed. Finally, a simple example is considered to illustrate the effects of the depth-averaged current on the energy consumption.

Numerical Study and Finite Element Analysis of Submerged Cylindrical Pressure Hull

Weight and volume are a direct impact on diving which is an important indicator of the overall performance of the deep-sea submersible structure. In order to increase the payload, improve endurance, reduce energy consumption, improve work efficiency, and therefore must accordingly reduce the total weight of the submersible. The design of underwater vehicles with minimum buoyancy factor is a major requirement from the underwater vehicles design point of view. The composite material pressure hull is a new concept due to the excellent structural performance. Therefore, in the present study, a comparison between three different pressure hulls with the same volume and various materials subjected to the same hydrostatic pressure will be investigated. The first, model was constructed from carbon fibre, while the second one constructed from steel (HY100) and the last one constructed from Titanium alloy. The finite element analysis (FEA) was executed using ANSYS. The results illustrated that the best buoyancy factor and the minimum mass occurred in the case of the pressure hull constructed from carbon fibre.

Research on Acoustic Transfer Performance of Power Cabin of Underwater Craft

In order to study the acoustic performance of underwater vehicle including vibration and noise, two kinds of structure models of an underwater craft cabin in the air medium and in the water medium were analyzed separately by finite element method. Through modal analysis, the impedance ratios of the two kinds of models were calculated. The influence of the thickness of the pressure hull on the impedance ratio of the structure was studied, and the acoustic transfer performance was analyzed and compared between the two kinds of models.

Underwater blast resistance of double cylindrical shells with circular tube stiffeners

Underwater explosion seriously affects the combat performance and vitality of submarines. In order to improve the blast resistance of stiffened double cylindrical shells, a new type of stiffened style that replaces the traditional T-shaped stiffeners with circular tube stiffeners, namely O-shaped stiffeners are studied. A series of comparative underwater explosion tests are carried out on two scaled stiffened double cylindrical shells with O and T-shaped stiffeners. Based on the tests, more detailed numerical simulations are made to explore the influence of the structure parameters on the shock performance of the whole structure. It is shown that the O-shaped stiffeners show more superior crushing performance than T-shaped ones when the large plastic deformation appears on the shells. As the plastic deformation of the T-shaped stiffeners is dominated by harmonic buckling while that of the O-shaped stiffeners is dominated by the flattening deformation of circular tubes, the latter can produce greater plastic deformation and absorb more shock energy to reduce the internal energy of pressure hull and thin hull. The shock response spectrums measuring at pressure hull can also be significantly attenuated at high frequency band. Therefore, the O-shaped stiffeners may be more effective sacrificial connected structures in the submarine.

Buckling properties of bulged barrels under external pressure

This study evaluated the buckling properties of externally pressurised bulged barrels and the bulging performance of internally pressurised cylindrical preforms. Barrels were fabricated from stainless-steel cylindrical preforms through the integral hydro-bulge forming technique. The cylindrical preforms had a thickness-to-radius ratio of 0.0176 and height-to-radius ratio of 1.961. Bulging and buckling were numerically evaluated under several bulging magnitudes. In addition, nonlinear numerical evaluations are well-benchmarked against the experimental data of six tested samples. The results indicate that this forming technique can be extended to fabricate atypical externally pressurised vessels, such as barrelled pressure hulls. In addition, the external pressure-supporting capacity of the bulged vessels was substantially enhanced under material hardening and curvature increasing.

Investigation of the influence of distribution of defections along the axial direction on eternal ultimate strength of titanium alloy pressure hulls of long barrel shape

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.

О создании испытательного оборудования для проверки прочности и герметичности подводных технических средств исследования предельных глубин Мирового океана

Object and purpose of research. The object of study is an upgradation of the unique land-based pressure tank DK-600 of Krylov State Research Centre designed to test underwater technologies for strength and leak under external pressures from 90 to 100 MPа. The purpose is to support acceptance tests of pressure hulls and equipment for advanced manned autonomous submersibles of extreme diving depths to 11 500 m. In accordance with the world practices in development of deepwater submersibles it is required to achieve pressures of about 135–140 МPа. Materials and methods. С использованием современных численных методов Preliminary calculations of strength are performed using up-to-date numerical methods (FE analysis), the choice of structural material is validated as weldable steel forgings, strength category 750–800 МPа. Main results. The procedure and setup are suggested (Capsule DК-600) to provide the said tests by placing a special splittype intermediate Capsule capable to generate 135–140 МPа on the test object inside the pressure tank DК-600 with pressures of 85–90 МPа. The Capsule can accommodate a test object of up to 2400 mm (transverse dimension). Conclusion. Results of an exploratory design study are presented to upgrade the unique land-based pressure tank, which would put the KSRC hydrobaric tank at the world forefront in terms of proof pressures for testing the strength and reliability of extremely deep diving submersibles measuring within 2400 mm (transverse dimension).

Multi-Crack Interaction and Influence on the Spherical Pressure Hull for a Deep-Sea Manned Submersible

Multi-Crack Interaction and Influence on the Spherical Pressure Hull for a Deep-Sea Manned Submersible

The protective mechanism of pyramid lattice on submarine subjected to undex

<p indent=0mm>The pyramid lattice sandwich shell is applied to the non-pressure hull of conventional submarine to reduce the damage when it is attacked by torpedo in close range. The design of pyramid lattice sandwich shell on conventional submarine is put forward. MSC.NASTRAN was used to study the anti-high hydrostatic performance of submarine hull after pyramid lattice sandwich shell was installed. The simulation results show that the improved submarine cabin structure is in a safe range under the designed water depth. Then MSC.DYTRAN was used to study the anti-explosion effect of the pyramid lattice sandwich shell as the outer protective structure of submarine. The results show that when the <sc>100 kg</sc> TNT charge explodes at <sc>3 m</sc> on the side of the submarine cabin, taking the damaged deformation as evaluation parameter, the anti-explosion performance of the submarine’s pressure hull mounted with pyramid lattice sandwich shell is 69.7% better than that of conventional submarine. The anti-explosion performance of the shell plate and upper deck was improved by 49.8% and 55.8%, respectively. Compared with solid plates, when the fluid-solid coupling parameter is greater than 10 and the ratio of core strength to peak pressure of shock wave is less than 0.15, the core layer can reduce the total incident impulse by more than 60%. The pyramid lattice sandwich shell used in submarine can not only meet the conditions of high hydrostatic pressure, but also greatly improve the anti-explosion performance of submarine hull structure, which has significant application value.

Optimal design of trapezoid stiffeners of composite cylindrical shells subjected to hydrostatic pressure

Optimization of a composite cylindrical pressure hull subjected to hydrostatic pressure with trapezoidal stiffeners is considered in this paper. The composite cylindrical shell is fabricated with carbon fiber reinforced epoxy composite while the stiffener is made of aluminum alloy. First of all, the analytical buckling model for composite cylinders with stiffeners subjected to hydrostatic pressure is derived. Subsequently, the finite element method is used to verify the accuracy of the analytical solution through some examples. After verification, the analytical solution is coupled with the genetic algorithm and then used to optimize the cross-sectional shape of the stiffeners of the composite pressure hull to obtain the maximum buckling pressure. During the optimization process, the relationship between the buckling pressure and each geometrical parameter of the stiffener has been analyzed. The inertia moment of the stiffener section is found to have a good linear relationship with the buckling pressure. Therefore, the inertia moment is used as an objective function to optimize the cross-sectional shape of the stiffeners of the composite pressure hull, and the feasibility of this method has been proved by comparing the optimization results. With high efficiency, this method can be applied to the optimal design of the stiffener shape of a composite pressure shell.

Structure-acoustic design of floating foundation in high strength steel cabin

Objectives This paper proposes a design for a floating foundation of a high strength steel cabin which simultaneously meets the requirements of impedance adaptation in acoustics and stiffness matching in mechanics. Methods Typical floating foundations which are not connected with the pressure hull are studied by adjusting the structural parameters of the foundation, analyzing the impedance characteristics and intrinsic modes with the finite element method, and calculating the strength of the pressure structure along with the original and improved foundations. A scheme of a floating foundation which satisfies the design requirements is obtained. Results The results show that the amplitude of the improved foundation is increased, the coupling of the intrinsic modes of the foundation with the mechanical equipment is reduced, the strength of the pressure satisfies the specification requirements, and the added weight is within the acceptable range. Conclusions This floating foundation scheme can provide references for the design of large foundations for high strength steel cabins which take into account both acoustic and mechanical requirements.

APPLYING MODERN PROCESS AUTOMATION AND OPTIMISATION TOOLS TO THE DESIGN OF SUBMARINE STRUCTURES

This paper describes the application of commercially available process automation and optimisation software to the design of submarine pressure hulls. The Isight software provided by Dassault Systemes, which integrates with a range of internal and external tools, including their Abaqus FE software, and provides access to numerous sophisticated design assessment and optimisation routines, was used. Within the Isight environment, disparate tools can be linked in structured workflows and the following case studies are described: • Minimum weight pressure hull design for different operating depths using traditional design formulae. • Design refinement for weight reduction using linear elastic FE. • Sensitivity of pressure hull collapse strength to shape imperfection using elasto-plastic non-linear FE. Automating these processes does lead to an increase in the amount of output, which can require an experienced eye to interpret, but they have produced demonstrable design improvements that just would not have been realised by manual methods.

NUMERICAL ESTIMATION OF DAMAGE CAUSED BY THE IMPACT OF AN EXERCISE TORPEDO ON A SUBMARINE PRESSURE HULL STRUCTURE

Torpedo combat and evasion training exercises using trials torpedoes are valuable but involve significant risks to the target submarine in the event of an accidental impact. This paper presents a study of impacts of a nominal heavyweight torpedo against a nominal submarine pressure hull, simulated using the nonlinear explicit finite element analysis code LS-Dyna. The model is validated against experimental work published by the Australian Defence Science and Technology Organisation, then expanded to a segment of a full-size submarine. Impacts were simulated at torpedo speeds of 30, 40 and 50 knots. It was found that the 30 knot impact produced no plastic deformation in the pressure hull, while the 40 and 50 knot impacts produced permanent dents of several mm depth. Reference is made to DNV GL submarine structures rules to suggest that these dents will not impair operational capability.

The New Sealing Structure Design and Research of Pressure Hull of CRDM With the Special Environmental Conditions

The pressure shell seal structure is an important part of the control rod drive mechanism, and it is also one of the key structures to ensure the normal operation, safety and reliability of the reactor. In this paper, a new type of sealing structure of pressure shell of control rod drive mechanism is proposed to meet the requirements of multiple loading and unloading in special marine environment. Compared with the traditional welding connection structure, it has the advantages of fast and convenient operation, easy replacement of sealing components and so on. It can greatly shorten the loading and unloading time of control rod drive mechanism in the refueling process and avoid damage.

Study of the application of PCM to thermal insulation of UUV hulls using Network Simulation Method

The Unmanned Underwater Vehicles (UUV) designed for the detection and neutralization of naval mines are characterized by their high requirements regarding the reduction of the signatures of a vessel (thermal, acoustic, magnetic, etc.), all of them must be reduced in order not to be detected by the mines during the mission. This research work focuses on the reduction of the thermal signature transmitted by the UUV hull, where the use of phase change materials (PCM) is proposed as thermal insulation, placing it between the internal heat source of the UUV and the pressure hull, with the aim of drastically increasing the time in which the external face of the hull of the UUV is within a range of 3 °C and 5 °C temperature increase, allowing it to perform its mission without being detected by the thermal sensors of current naval mines. The simulation will be carried out using the Network Simulation Method for the resolution of the governing equations, which will allow the optimization of the necessary insulation thickness according to the required mission profile. In addition, it is proposed an expression that relates the PCM thickness and the time needed to reach a certain temperature increase.

Buckling analysis of ring stiffened thin cylindrical shell under external pressure

Submarine pressure hulls, fire-tube boilers, vacuum tanks, oil well casings, submersibles, underground pipelines, tunnels, rocket motor casing, etc., are some of the examples of thin cylindrical shell structures which collapse due to buckling under uniform pressure. To enhance the buckling strength of bare cylindrical shells, one of the best solutions is to stiffen them with ring stiffeners. In this work in order to predict the shell instability failure mode (SIFM) and general instability failure mode (GIFM) FE models are generated and analysed using buckling analysis of general-purpose FE software ANSYS. The numerical results obtained using FE analysis are compared with published analytical and experimental results. Hence in the present study efforts are taken to develop FE models to predict global and shell instability failure modes of externally ring stiffened cylindrical shells by using linear FE analysis. It is proposed to use full/half bare cylindrical shell FE models (L/R ratio upto 200) to determine SIFM and FE models with shell281- Beam189 (for stiffeners) can be used to determine GIFM. The developed FE models are validated by comparing numerical results with experimental results published by Seleim and Roorda [25]. By using both proposed FE models it is possible to predict the failure modes namely SIFM and GIFM, comparing their values of critical buckling pressures. The lower pressure value can indicate the possible failure mode.

Multidisciplinary design optimization of underwater glider for improving endurance

Underwater glider (UG) is widely applied for long-term ocean observation, the gliding range of which is mainly influenced by its design. In this paper, the design parameters that have obvious influence on the gliding range, including the buoyancy factor, compressibility of the pressure hull, hydrodynamic coefficients, and motion parameters, are selected based on the gliding range model of UG. Due to their complicate coupling relationship in the design of the UG, the multidisciplinary optimization (MDO) design framework integrating the collaborative optimization (CO) method and approximate model technology is adopted to optimize the key parameters by taking the gliding range as the optimization target. The results show that the optimization leads to an increase of the gliding range of Petrel-L as much as 83.3% when the hotel load is 0.5 W, which is verified by the sea trial. The optimization is applicable to other types of underwater gliders.

The Opportunity of Modern High-Toughness Technical Ceramics for Undersea Systems

AbstractA confluence of recent developments in the formulation and processing of technical ceramics enables an important opportunity for submersible designers, namely, the reliable use of ceramics having density of near 3 g/cm3, compression strength of &gt;4 GPa, tensile strength of &gt;690 MPa, and fracture toughness (KIc) of 8‐10 MPa-m1/2. Concurrent developments in high-strength brazing of ferrous and nickel-based metals to these tough ceramics enables the integration of pressure envelopes with removable endcaps or ports, as well as optimum stiffener configurations and other internal or external design features. The specific opportunity presented by this confluence of tough ceramics and brazed metallic fittings is the possibility of full-ocean-depth (&gt;6,000 m) dry submersible structures with weight/displacement (W/D) ratio &lt; 0.7, as compared to W/D &gt; 1.0 for metallic structures. Self-buoyant dry hull structures at these depths will greatly expand submersible design options, minimizing the need for full-ocean-depth syntactic foams to float key functionalities. The processing of these ceramics requires a cold isostatic press (CIP) or slip cast “green forming” step, plus sintering to near full density, followed by hot isostatic press (HIP) to final density. Present HIP facilities can support processing of 81-cm diameter × 190-cm-long ceramic vessels and brazing of ceramic/metal assemblies to ~163-cm diameter × 254-cm-long in the United States. If larger ceramic pressure hull components are desired, a “tiled” ceramic structure can be assembled and brazed or bonded together with thin metallic skins in a sandwich structure.

RESPONSE SURFACE MODELING FOR OPTIMIZATION OF RING-STIFFENED POLYMER COMPOSITE PRESSURE HULL

RESPONSE SURFACE MODELING FOR OPTIMIZATION OF RING-STIFFENED POLYMER COMPOSITE PRESSURE HULL