Submersible Structures Research Articles

Underwater cylindrical sandwich meta-structures composed of graded semi re-entrant zero Poisson's ratio metamaterials with pre-strained wave propagation properties

Zero Poisson's ratio (ZPR) mechanical metamaterials can yield no transverse displacements when unidirectionally compressed, and cylindrical sandwich meta-structures composed of semi re-entrant (SRE) ZPR metamaterials are thus explored for applications on cylindrical shells of underwater equipment or submersible structures. A group of ZPR unit cells with specified pre-strained wave propagation characteristics and adequate load-bearing capabilities is optimally designed based on the periodic boundary condition (PBC) and Bloch's Theorem. The sound transmission and pressure-resistant performance of cylindrical sandwich meta-structures comprising the homogeneous and graded SRE ZPR unit cells are then investigated. The results show that the designed meta-structures can perfectly yield better vibroacoustic attenuation behavior within the specified frequency regions corresponding to the pre-strained band gaps and safely bear the hydrostatic pressure equivalent to 1000 m depth with low weight-bulk ratios. In addition, the functionally graded metamaterial core can boost vibroacoustic performance within broader frequency ranges.

Modeling of the Interaction of a Large-Sized Shell with a Ground Environment During Immersion

Large-sized reinforced concrete shells are rationally used in the underground construction of transport and engineering infrastructure facilities. For the defect-free construction of an underground structure, it is necessary to jointly solve complex design and geotechnical tasks. The interaction between the solid structure and the ground environment, as well as the heterogeneity of the medium itself, give rise to the need to control the stress-strain state of the "large-sized body - heterogeneous medium" system. Modeling the interaction of the shell with the ground environment and forecasting stress and strain management provide conditions for a defect-free life cycle of the structure during its construction and operation in difficult soil and man-made conditions. The article offers the basics of the concept of assessing the interaction of large-sized submersible structures in soils with different stability, taking into account the unsteadiness of the immersion mode for engineering and transport infrastructure facilities.

Experimental study on motion response of a submersible spherical model under the action of internal solitary wave propagating over a ridge topography

Experimental investigations are performed to study the motion response of submerged spherical model under internal solitary waves propagating over a ridge topography. This study is based on our previous work, that revealed the motion responses of submerged models under internal solitary waves. The relative initial depth between the model and pycnocline, size of topography and upstream/downstream effect of the topography are considered. The velocity and vorticity of fluid are analyzed following particle image velocimetry (PIV) method, and the motion response of the spherical model is analyzed by using image processing algorithms. The results show that the maximum heave motion amplitude and the maximum surge motion amplitude of the model increases 1.9 times and 2.2 times due to the influence of topography, respectively. The heave motion of model in the downstream direction of the topography is twice as much as that in the upstream direction. The flow field becomes extremely complex near the topography resulting in more intense motion response of the submerged model with maximum heave motion amplitude greater than 1.8 times of amplitude of the incident wave. Therefore, internal solitary waves that propagate over ridge topography could pose a significant threat to submersible structure.

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.

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 >4 GPa, tensile strength of >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 (>6,000 m) dry submersible structures with weight/displacement (W/D) ratio < 0.7, as compared to W/D > 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.

Normalised fatigue and fracture properties of candidate titanium alloys used in the pressure hull of deep manned submersibles

The current available design rules of submersible structures from ship classification societies are based on the philosophy of strength design. Nowadays, higher requirements have been made for improved safe and economic design and operation of the submersibles, and the material selection criterion has paid more attention to the synthetic properties of materials of interest including fatigue and fracture properties of materials. Titanium alloys with relatively high ductility are widely used in pressure hull of deep manned submersibles nowadays. Much work should be devoted to systematic investigation of properties evaluation for candidate titanium alloys for submersible structures. This paper gives experimental results of fatigue and fracture properties of two candidate titanium alloys potentially used in pressure hull of deep manned submersibles. Test results are discussed by normalisation considering strength of the material which is an effective way to evaluate fatigue and crack growth properties of two materials. And to save cost and material test time in the future, an improved crack growth rate model proposed by the authors is used for prediction and unification of wide range of their crack growth rates. The comparisons between test data and prediction curves agree very well, which validate that the improved crack growth rate model can be used for prediction and unification of crack growth property of Ti80 and TC4 ELI at different load ratios.

On fracture resistance parameter from non-standard fracture test specimens of titanium alloy

The current available design rules of submersible structures from ship classification societies are based on the philosophy of strength design. As a supplement, damage tolerant design becomes an important consideration in avoiding the catastrophic failure caused by material defects. Titanium alloys with relatively high ductility are widely used in pressure hull of submersibles nowadays. Much work should be devoted to systematic investigation of the fracture properties evaluation for candidate titanium alloys for submersible structures. Traditional fracture toughness test with normal specimen size may not give reliable fracture resistance value. More applicable non-standard specimens can be designed for engineering purpose. Then the establishment of a reliable fracture resistance parameter from the non-standard fracture test specimen for fracture ductility evaluation is necessary. The present work is to primarily study the potential proper fracture resistance parameters for ductile titanium alloys. Series of non-standard specimens of Ti80 are designed for the test and analysis. Thickness effect is specifically investigated using specimens with similar ligament size. Some fundamental proposals are accordingly brought forward for ductility evaluation of titanium alloys used in submersible structures.)

Review of Pressure Vessels , by Carl T. F. Ross

Though the text was written for individuals involved in the design of submersible structures, the author has made significant contributions to the field of shell analysis considering external pressure loading. It becomes obvious when one looks at the book’s reference listing. Of the 157 references listed, the author has been involved in over 60 items published over the last 30 years. As the reader becomes involved in each chapter, it becomes apparent that the writer has a firm understanding of both the experimental and numerical results and techniques. The book contains eight chapters. Chapter One attempts to relate to thin-shell results considering spherical, cylindrical, and conical under external pressure with and without stiffeners. Four materials are discussed as to their usefulness in pressure hull designs. 1. High strength steels, 2. Aluminum alloys, 3. Titanium alloys, and 4. Composites. Each is considered with listed advantages and disadvantages. Chapter Two describes the equations for the analysis of axisymmetric deformation of ring stiffened circular cylinders, cones, and domes. The differential equation solutions to unequal size rings are carried out. Solutions to cones and domes are shown using a finite-element approach. Comparisons to experiments are also shown. Excellent photographs of collapse modes of shells are shown. A section on plastic analysis is included. Chapter Three relates to shell instability under uniform external pressure. Again, the author does a fine job in relating analysis

On the Nonlinear Analysis Methodologies for Thin Spherical Shells Under External Pressure with Different Finite-Element Codes

Submersible structures consist merely of simple and double curvature thin-walled shells. For this kind of structure, collapse occurs due to the combined nonlinear action of buckling and plasticity of material. Load-carrying capacity may then be assessed mainly by two approaches: experimental investigations and step-by-step numerical procedures. In nonlinear analyses, the results obtained are influenced by the magnitude of the load increment adopted. Solution procedures are then required in order to choose adequate parameters for material failure description as well as elastic nonlinearity. The aim of this paper is to carry out a suitable numerical procedure whose reliability does not depend on the finite-element code adopted.

4708081 Stabilizer for floating and submersible structures

4708081 Stabilizer for floating and submersible structures

Submersible structures for shellfish culture

Recent developments in aquaculture in Atlantic Canada have demonstrated a need for suitable structures for the growing of mussels and oysters. One of the greatest difficulties encountered has been damage to rafts and other equipment caused by winter ice. In order to avoid this damage and some other difficulties, a growing system based on submersible structures has been proposed. Accordingly, four prototype systems made largely of wood with plastic vessels for floatation have been built and tested over a period of 18 months. The results have demonstrated the feasibility of submersible systems based on the prototypes.

Optimal design of ring stiffened cylindrical shells using multiple stiffener sizes

Abstract : This report describes the solution to the singly reinforced discrete stiffener problem by direct use of an optimization scheme employing mathematical programming. The optimization formulation and procedure used here admit a large number of simultaneous buckling modes thus allowing optimization under conditions of mode coalescence, which are usual in this type of problem. This is a preliminary study, the purposes of which are; to develop and evaluate methodology for the treatment of this problem, to develop preliminary insights into how multiple frame sizes may efficiently be employed in submersible structures, to examine the nature of design improvement resulting from use of multiple size frames, and to investigate the nature of such optimal designs. (Author)

A Study of Suction and Scouring of Bottom-Sitting Offshore Structures

Two sources of difficulty with offshore submersible structures are suction and scour. It seems reasonable to suppose that the shape of the structure will influence the effect of these forces and the degree of damage they will inflict. Suction-breaker and scour tests have been conducted on models of five different shapes, and the results are presented here. Introduction When a submersible offshore structure sits on the soft, cohesive soil of the sea bed, it penetrates deeply into the soil. When the structure is freed from the bottom, a great suction force is created that not only makes the freeing operation difficult, but also can wreck or capsize the structure. If the foundation soil is sandy, tidal currents or waves may cause scour around the legs of the structure, causing it to turn over, or may cause great local stress upon the structural members. The purposes of this investigation were to study the characteristics of suction and scouring, to develop an efficient suction breaker, and to examine a preventive method against scouring. Suction and scouring were investigated in an experimental tank, and the practical application of the suction breaker was field tested using a large model in the sea. Laboratory Suction-Breaker Test Models and Testing Soil To study the characteristics of suction and the effectiveness of a suction breaker, we designed and manufactured five types of small models (Fig. 1) made of steel and coated with paint, and having a bottom area of 219 sq ft. Sea silt taken from the bed of Hiroshima Bay was reconsolidated and used as the testing soil. First the silt was agitated with water in a holding tank. Then a sheet of canvas was laid over the surface of the silt, and it was weighted down by perforated steel plates for 1 week. The pressure was approximately plates for 1 week. The pressure was approximately 1.5 psi. According to a Vane shear test, the mean cohesion of this soil was as follows. Cohesion of the soil applied to the suction test: C = 0.56 psi. Cohesion of soil applied to the suction-breaker test: C = 0.53 pk Method of Testing Suction Test. After the model penetrated the soil about 8 in. by means of loading, it was unloaded and leg alone for about 5 minutes. Then it was pulled up at a rate of 0.08 in./min; the pulling pulled up at a rate of 0.08 in./min; the pulling force was continuously measured by a tension meter the displacement gauge was read by a displacement gauge every 5 seconds. Suction-Breaker Test. After the model had been sunk into the soil by means of loading as shown in Fig. 2, it was pulled up. When it had been pulled up about 0.8 in. (that is, when the contact pressure under the weight of the model was about zero), pressurized water was jetted by the pumping of the suction breaker until the model was completely pulled out. Items measured were the pulling force, the displacement, the pressure, and the flow rate of the pump. JPT P. 279

Buckling under external hydrostatic pressure of orthotropic cylindrical shells with evenly spaced equal strength circular ring frames

This report presents an energy method solution for the general instability of orthotropic ring-stiffened cylinders subjected to external hydrostatic pressure. Variations in the longitudinal buckling mode are considered and evaluated. This analysis was instigated by the attractiveness of ring-stiffened fibre-glass cylinders for deep submersible structures for which the general instability mode is a primary design consideration. An energy method solution for unstiffened orthotropic cylinders subjected to external hydrostatic pressure, using the classical buckling deformations for simply supported end conditions, is also presented. Numerical examples are given to illustrate the results of the theory.