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WARSHIP 2021: Future Technologies in Naval Submarines Abstracts

Applying Modern Process Automation and Optimisation Tools to the Design of Submarine Structures

D. Graham, QinetiQ, UK

Formal structural optimisation tools have been around for many years and they have been used successfully with advanced numerical methods, such as Finite Element (FE) analysis, in a wide range of applications. Modern developments are producing ever more integrated and powerful tools for automating and controlling simulation based design processes, an example being the Isight software provided by Dassault Systemes which integrates with their Abaqus FE software. It provides access to numerous sophisticated design assessment and optimisation routines and other bespoke software including Tosca for topology optimisation and fesafe for fatigue analysis. Within the Isight environment these disparate tools can be linked in structured workflows. These workflows can be automated and customised for specific applications 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. The use of topology optimisation for the design of a detailed feature (a large penetration) and the inclusion of fatigue assessment in the design loop are also demonstrated. For FE analysis to be truly integrated into the design process designers will have to have confidence in the accuracy of the method. Steps that have been taken to provide verification against analytical methods and validation against experimental data, specific to the design of submarine pressure vessels are discussed.

The design and hydrodynamic assessment of a submarine concept with off-axis propulsion

P. Crossland, QinetiQ, UK / R. Crocker, BAE Systems, UK / S. Machin, Submarine Delivery Agency, UK

The UK’s approach to submarine design is largely evolutionary, however, whilst future submarine hull form designs are likely to remain relatively conventional, changing naval strategy means that there is still sufficient justification to perform investigations into novel hull forms that have the potential to offer easier integration of required capabilities or provide the ability to incorporate novel technologies. Whatever the design, there will be a requirement to manage the safety of a submarine throughout its lifecycle and the approach adopted in the UK, developed from knowledge of hydrodynamics gained over a number of years assessing submarines with a conventional hull form design, is to provide a validated toolset and process that provides an understanding of the manoeuvring and control performance of that submarine. However, if a submarine hull form design changes radically, the tools and processes for evaluating performance need to be developed, in advance, to ensure the capability to evaluate that design is maintained. This paper describes a challenging design and hydrodynamic assessment exercise, in which BAE Systems – Maritime Submarines were tasked, by the Submarine Delivery Agency, to develop a concept design for evaluation by QinetiQ using their computation fluid dynamics and experimental assessment techniques. This work also provides the opportunity to de-risk novel design features to inform future underwater platform programmes and by undertaking a full manoeuvring and control evaluation of this design, the traditional testing techniques are challenged and developed.

Hydrodynamic loads and flow structure analysis for a surfaced submarine using captive model experiments

A. Conway, Defence Science and Technology Group & Australian Maritime College, Australia / C. Kumar, QinetiQ, Australia A. Rolls, Australian Maritime College, Launceston, Australia / A. Fowler, Defence Science and Technology Group, Australia / A. Cameron, Defence Science and Technology Group & QinetiQ, Australia

Submarines are required to operate on the surface for significant periods of time, for example during transit in shallow waters. However, as they are designed primarily for submerged operations, their surfaced sea-keeping behaviour may be poor. Furthermore, the wave making resistance of the vehicle increases in the surfaced state, substantially impacting on its powering requirements. The bow wave encountered when operating in a surfaced state applies a downward heave force and a bow down pitching moment, impacting the vessel’s sea-keeping performance. These interactions are complex, and a combination of numerical simulations and experimental programs is often employed to provide insight. A captive model experimental program was undertaken at the Australian Maritime College Towing Tank facility to generate data at model scale for a 1.69m BB2 generic submarine geome_try operating on the surface in calm water. The experiments consisted of two stages. Firstly, a new calibration technique was employed to produce high quality loads measurement. Secondly, a series of straight line and static angle of drift measurements were undertaken at two Froude numbers. Force measurements were complemented with surface flow field visualisation of bow wave height and flow structures in the bow region. The data generated included the hydrodynamic loads and detailed, time-averaged flow structures on the surface, which will be used to study the behaviour of the vehicle and validate numerical tools. The force measurements showed highly repeatable loads with well-defined trends in both sway and heave, critical to generate coefficients for submarine manoeuvring simulations.

Submarine Maneuvers in a Simulator

C. E. Guedes do Nascimento, E. Aoun Tannuri, Escola Politécnica da USP, Brazil

The thesis consisted in implementing a numerical model of a submarine in the Numerical Offshore Tank of the University of São Paulo (TPN-USP) based on the concepts of maneuverability of vessels. This thesis consisted, among other studies, of adapting the numerical model of the TPN, making the necessary changes to allow not only surface vessels, but also submersibles and submarines to be simulated. The final product is that the Numerical Offshore Tank is now also capable of simulating submarines, allowing for various tests and analyzes related to maneuverability; in addition to all the possibilities that this new tool offers.

Ancillary Battery Technology – Where it Came from and Where it’s Going

M. Moody, D. Mitchell, BMT, UK

After the commercialization of electricity in the late 1800s, the useful applications of electricity on marine vessels became apparent. In that time the benefit of using electricity, and specifically batteries, to power submarines was exploited due to the fact that no exhaust is required, allowing the submarine to dive without snorting. The modern solid-state power electronics revolution in the 70s and 80s created technology that supported more sophisticated battery charging systems with better control and voltage/current optimization to meet the specific needs of different battery types. In parallel, batteries themselves were continually improving and becoming safer. With the expansion of the renewable energy and electric car industries, more research is being carried out on battery technologies than ever before and so too does the potential for their use on submarines. This paper discusses the use of batteries in auxiliary applications used onboard submarines and the challenges faced when selecting a battery technology and the supporting infrastructure for a given application. The paper concludes that the selection methodology for the optimal battery solution is not only dependent on the technology available but also on its intended use, safety measures required and the economic viability of the solution.

An Innovative UCL Concept Submarine Design for an All-electric Boat

R. Pawling, UCL, UK

The UCL Submarine Design Course is a three-month short course in which groups of students develop a submarine concept design to meet a broad user requirement. The course covers the broad process of submarine design, from the development of a concept of operations and subsequent cost-benefit analyses to the design of primary structure and propulsion and hotel systems. The requirements set each year are notable for a “special feature”, a novel aspect that requires some innovation on the part of the students. This paper will summarise the eight designs developed by the 2019 cohort, and in particular detail an all-electric submarine for use in the Baltic and North sea. Codenamed “Renewable”, this 1500tonne design features battery-only propulsion with the ability to use ROVs to recharge from a dispersed power infrastructure based around existing and expanding offshore wind farms. This paper will cover the general CONOPS behind the design, the technical solution developed by the students, and conclusions regarding the viability of all-electric submarines in the near future.

Design of Delta Wing Autonomous Underwater Gliders for Long Term Sustainable & Stealth Reconnaissance Using Numerical Studies

G. Mukesh, R. Vijayakumar, Indian Institute of Technology, India

Autonomous Underwater Gliders (AUGs) are a unique source of collecting the oceanographic data for varying depths with longer endurance than other types of unmanned underwater vehicles. The buoyancy driven propulsion mechanism assists in diving deep into the ocean, collect data, resurface in saw-tooth and spiral motions. There have been various hull-forms introduced for this purpose starting from (Stommel, 1989) - Torpedo hull, XRay Flying-Wing Glider, etc., all of which have seen an improved understanding of the hydrodynamics associated with the hull-form of the gliders. The saw-tooth motion represents the glider's capacity to cover larger distances with a smaller angle of attack thereby achieving an increased range for the same power included within the hull batteries. In this paper, a design study of delta wing hull-forms, which are proven to have better longitudinal motion characteristics, is proposed to arrive at an optimized hull form which can be used for long term reconnaissance missions without affecting the ambient noise of the ocean, remaining in stealth to assist submarines with valuable data. Delta wing hull forms are varied using different NACA sections and numerical analysis of the obtained hull forms is performed to arrive at the hydrodynamics, namely, the drag, lift forces and coefficients for varying angles of attack, using commercial CFD software – StarCCM+. These results are then compared against each other to derive the optimized hull form which can use less battery for its motion underwater. This is achieved by plotting the longitudinal motion of the glider in Matlab using in-house code.

Estimation of damage caused by the impact of an exercise torpedo on a submarine pressure hull structure

R. Castillo, Chilean Navy, Chile N. Bradbeer, UCL, UK

Realistic training is a key enabler of submarine capabilities; it is difficult to completely simulate a torpedo attack in training without launching a physical weapon. While exercise torpedoes have no warhead, they can run at significant speeds and the uncertain consequences of an accidental collision with the target platform preclude numerous navies from this practice. Recent publications have detailed deformations obtained in laboratory tests when the impact of a scaled model of an exercise torpedo against a scaled submarine structure is simulated in several configurations. In one of them, the empirically obtained response has been successfully numerically modelled using ANSYS. This paper describes the development of a full-scale model. Using LS-DYNA explicit solver, previously performed laboratory tests were modelled for validation, obtaining satisfactory results. Built on this performance, a 1:1 dynamic simulation of an impact of a 533mm exercise torpedo against a submarine hull model was performed, and numerically predicted stresses and deformations recorded. Results suggest that high transient stresses generated by the impact may become the driving safety hazard. However, this type of exercise, conducted under controlled conditions (depth of the attacked submarine and torpedo speed), could lead to an overall risk level deemed as acceptable for its performance.

CAD System Distinctive Features in Submarine Design

R. Perez, SENER Madrid, Spain

Although the object of Surface Ships Building (SS) and Submarine Building (SB) industries is the same (a floating artefact aimed to comply with a particular function), the particularities of this same function, the ways for achieving it, the costs involved, and the metrics used to analyse results are so different that in fact make both industries different, usually considering that tools and processes used in both should also be different. This includes CAD Systems, although in this case the dichotomy was not established in the very beginning, but formed as the processes in SB and SS diverged with the pass of the time.

In fact CAD Systems were first conceived for solving problems in other sectors like aerospace/defence, as this industries had the resources to invest in such advanced technology. Submarines has been often perceived as a product with more similarities with hi-tech industries than with traditional shipbuilding. However, the impressive growth of SS and its requirement for reducing costs and delivery time made shipbuilding CAD Systems suppliers focus their attention in it as a source for obtaining incomes, developing and adapting systems to this particular industry. General CAD Systems took advantage of the situation to implement themselves in SB, where they remained (still remain) for many years. But the requirements for reducing costs also catch up with SB, so in many cases they decided to put forward the replacement of general purpose CAD Systems with shipbuilding specific ones, and this produced an automatic reaction of shipbuilding CAD Systems suppliers that have devoted more effort to try to solve particular SB problems.

In order to check the convenience of the use in SB of shipbuilding CAD Systems, nowadays focused in SS, first of all it should be studied the differences between both SS and SB. Once established them, we would be in position to propose a suitable solution.

Reference Designs: An Aid for Enhanced Engagement in Submarine Procurement

A. Walchester, BMT Global, UK

Submarines are generally regarded as some of the most complicated and expensive systems in the world. Their procurement is characterised by long production timescales, a vast number of requirements and competing stakeholder priorities. This is compounded as a submarine design is relatively intolerant to change, such as requirements change during the design process or new requirements added to an existing design. These changes can quickly lead to an unbalanced design and a divergent design spiral. Correcting an unbalanced design can prove costly, delaying programme timescales and creating issues that last well into the submarine's in-service life. The term 'reference design' used in this context refers to a parallel design process that runs alongside the main procurement efforts. It is used to enable the customer to define a balanced requirement set and make informed decisions as part of a collaborative and affordable procurement process. The design is a bespoke pre-concept or concept design that meets the technical requirements of the submarine procurement. BMT explores the benefits of a reference design, focussing on how it can be used as part of the submarine procurement process.

Sustainable Submarine Design

L. Hammock, BMT Global, UK

We design submarines for a service life of 25 years+ and therefore they need to be designed to meet the needs of tomorrow as well as today. This not only means a flexible operational capability but also means increased importance should be placed on areas such as sustainability and climate resilience in design.  Although submarines, through low signature requirements, often present a lower footprint than their larger ship counterparts there is still a considerable concerted effort required to ensure the platform is environmentally sustainable. This paper will explore the key drivers and factors behind submarine sustainability including but not limited to: Bilge water treatment; Energy Management; Waste Disposal; and the effect of sonar and underwater radiated noise. The talk will also discuss the role of teamwork in achieving this goal, including how designers, shipyards and operators can all work together to maximise the benefits of a sustainable submarine design.

Who Says There Are No Real Choices in Submarine Design? 

D. AndrewsUniversity College London, UK

A paper by the author to the last submarine conference emphasised that submarine design is much more constrained than is the case generally for complex surface ship design. This is because the extent of the submarine solution space is usually considerably less and there is the need to go into more detail and achieve a more precise balance very early in concept design. This applies even when compared to the most complex surface ship designs. However, there is a need also to counter the apparent corollary that the submarine designer is therefore not faced with a host of major design choices as should be the case in a properly conducted concept phase for complex vessels. Interestingly, these choices are both highly interrelated and have to be made very early on, at least in order to achieve the synthesis of any distinct submarine design option. The paper does draw on the more general and extensive exposition presented in the recent Special Edition of the RINA Transaction by the author on the sophistication of early stages of design for complex vessels, pointing out where designs for submarines are subtlety different to that for other complex vessels. This is done before sequentially outlining some twenty significant generic submarine design choices. Finally, the paper points out that that sequential listing has therefore had to necessarily simplify what remains a highly integrated and interactive set of choices.  

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