Submarine Capability Optimisation

Transcription

1 Submarine Capability Optimisation Matthew Tetlow The University of Adelaide Adelaide, Australia Dr. Carl Howard The University of Adelaide Adelaide, Australia Proj J.M. Green Naval Postgraduate School Monterey, CA, USA INTRODUCTION Procurement of high value defence assets, such as ships, submarines and aircraft requires rigorous analysis to ensure the system procured will perform as required in the operation. To achieve this, system and subsystem modelling can be conducted to determine how the subsystem choices affect the whole system performance. This should be linked to a capability analysis to relate the subsystem performance back to the operational requirements. Submarines are highly complex systems that require expertise in nearly every engineering discipline to develop. BMT Design and Technology Pty Ltd have conducted several studies of advanced submarine concept designs, such as Binns (2008), and have reported on specific systems, such as power in Buckingham et al. (2008) and hull form in Mann et al (2012). Warren (1997) describes the hydrodynamic performance of several hull forms and Torkelson (2005) describes a series of empirical models for volume and weight, and how they relate to cost. These publications and numerous text books provide good references for modelling system performance; however, few tie the performance back to the required capability. Pearce and Hause (2012) describe the importance of a rigorous capability analysis, via a model based systems engineering analysis. The paper described a usage-driven analysis to extract the operational requirements. However, their work does not expand into sub-system performance analysis and how this relates to the capability. Several groups have developed analysis techniques that combine sub-system performance and their impact on the capability of submarines and surface vessels. Green (2001) describes how a ship should be designed as a weapon system and how other performance parameters should be assessed in the context of their effect on the ability of the ship to complete its mission. The combat system analysis is based on a series of scenarios, in which the probability of detection, kill and survivability are determined quantitatively. The US Naval Post Graduate School has implemented similar techniques in Torres (2010), Sanabria Gaitan (2011) and Fox (2011). They perform a quantitative analysis of the combat system and link it back to the capability requirements. They include a ship

2 synthesis model in an Excel spreadsheet, which is based on the software ASSET, according to Fox (2011). However, little detail of this model has been found in the publicly available literature. Researchers at Virginia Tech such as Blizzard et al. (2008), Shingler et al. (2005) and Alemayehu et al. (2006) use a process where they perform an initial design space evaluation to determine how different sets of subsystems impact on the capability. The design evaluation process includes a rigorous assessment of the performance of the vessel. However, the performance of the combat system is based on a qualitative analysis by experts, who define fixed measures of performance for sub-systems, based on their subjective experience. The scope of this project is to conduct a capability analysis to determine measures of performance that tie the system performance back to the capability requirements. A submarine synthesis model is then developed to explore the design space and show how design parameters relate to system capability, and hence operational effectiveness. CAPABILITY ANALYSIS A capability analysis was performed using the software Vitech Core8 to determine the measures of performance that relate system performance to the effectiveness of the capability. According to the Australian Defence White Paper 2009, the main objective of the future submarine program is to sustain a force at sea large enough in a crisis or conflict to be able to defend our approaches (including at considerable distance from Australia, if necessary) Figure 1 shows the high level mission and associated operational tasks that form the basis of this capability analysis. It should be noted that the Australian Defence White Paper further constrains the design by specifying that The Government has ruled out nuclear propulsion for these submarines. hier Defend Australia 0 Defend Australia Mission 1 Mobility achieved by achieved by achieved by 2 3 Int. law compliance War fighting Project: Sub1 Organization: The University of Adela... Date: 30 November 2012 Figure 1. High level mission and operational tasks

3 The War Fighting tasks are expanded in the Australian Defence White Paper 2009 by defining several key capabilities: will also be equipped with very secure real-time communications and be able to carry different mission payloads such as uninhabited underwater vehicles. will be capable of a range of tasks such as anti-ship and anti-submarine warfare; strategic strike; mine detection and mine-laying operations; intelligence collection; supporting special forces (including infiltration and exfiltration missions); and gathering battle-space data in support of operations. Figure 2 shows the War Fighting task, which includes six sub-tasks, namely: Anti-surface ship warfare (ASUW), Anti-submarine warfare (ASW), Command and control, Intelligence surveillance and reconnaissance (ISR), Land Strike and Mine countermeasures. hier War fighting 3 War fighting 3.1 includes includes includes includes includes includes ASUW ASW Command and control ISR Land strike Mine countermeasures Project: Sub1 Organization: The University of Adelaide Date: 30 November 2012 Figure 2. War fighting operational tasks in detail The next high level operational task is mobility, which will form the basis of the case study discussed in this paper. The Australian Defence White Paper 2009 was used as a source for the high level requirements namely: will have greater range, longer endurance on patrol, and expanded capabilities compared to the current Collins class submarine. high levels of mobility and endurance low signatures across all spectrums, including at higher speeds Figure 3 shows the operational activities and functions associated with the mobility operational task. It has highlighted five measures of performance: Snorkel range, Snorkel speed, Diving depth, Battery sprint speed and Battery range. The above Capability Analysis provides a method to analyse the capability requirements and extract the Measures of Performance required to conduct a design space analysis. In the literature the measures of performance related to the warfare are generally based on expert opinion. For this reason, different combat systems are not considered in this paper. Only the measures of performance related to mobility and crew complement are considered in this paper.

4 hier Mobility 1 Mobility achieved by achieved by achieved by Evade and avoid threat OperationalActiv... Seamanship and navigation OperationalActiv... Transit efficiently OperationalActiv... implemented by implemented by implemented by Evade and avoid threat Function Seamanship and navigation Function Transit efficiently Function exhibits exhibits exhibits exhibits exhibits Battery range Battery sprint speed Diving depth Snorkel range Snorkel speed Measure of Perf... Measure of Perf... Measure of Perf... Measure of Perf... Measure of Perf... Project: Sub1 Organization: The University of Adelaide Date: 5 December 2012 Figure 3. Mobility operational task SUBMARINE SYNTHESIS MODEL The synthesis model allows the performance characteristics of a specific design to be determined for different sets of subsystems. These variants can be used to build up an understanding of the sensitivity of the performance of the submarine to particular subsystems. The submarine synthesis model was built in the software Phoenix Integration Model Center. It comprises modules that calculate the major design parameters of the submarine, joined by numerous links that carry the common variables between the modules. Figure 4 shows the Model Center implementation, which was broken down into four areas; volume and area, weight and stability, electrical power, and drag and performance. Volume The volume analysis for the majority of the subsystems was based on the methods used in Shingler, et al. (2005), Sewel (2010) and Warren (1997). The volumes and areas of the payload subsystems, including combat systems, power systems and fuel requirements, were listed in an input file. All of the combat systems were assumed to be housed within the pressure hull, while 80% of the fuel was stored outside the pressure hull. The reason for this was to have the weight and volume advantage of 80% of the fuel being outside the pressure hull, while at the same time having enough fuel within the protected pressure hull to get to a safe port after unexpected loss of the outboard fuel. Once all of the subsystem volumes had been summed, a feasibility test was performed to ensure that enough volume was available within the envelope volume to contain the required total submerged volume. This was done by calculating the free flood volume V ff, which is the difference between

5 the submarine envelope volume, calculated from the outer dimensions of the submarine, and the submarine volume, calculate by summing the subsystem volumes. The free flood volume V ff had to be positive and between 5% and 10% of the envelope volume for it to be a feasible design. Weight and Stability The weight and stability model was based on empirical data as well as specific component weights. The models were based on the formulation in Shingler, et al. (2005), which seemed to be based on data from older submarines. This was evidenced by the excessive weight increase with increased diving depth. To make the models relevant to current submarine building methods and materials, it was scaled based on data from Sewel (2010), Alemayehu, et al. (2005) and Burcher and Rydill (1994). The lead ballast weight was calculated from the difference between the normal surface condition weight, which is a function of the ever buoyant volume, and the sum of the subsystem weights. A feasibility check was used to ensure that the lead ballast weight was positive and between 2% and 3% of the normal surface condition weight. The vertical centre of gravity (COG) of each subsystem weight was located at a specific height above the keel line, relative to the hull depth, based on the notional layout of the submarine. From this the total vertical COG could be estimated and compared to the position of the centre of buoyancy, which was taken to be at half the hull depth. This difference was the stability margin. A feasibility check was performed to ensure that the vessel was statically stable. No longitudinal stability was modelled in this analysis. Figure 4. Model Center implementation of the synthesis model Electrical load The electrical load analysis was based on empirical data models as well as specific input data for some components. The base model used was from Shingler, et al. (2005), with scaling applied to match the results in Alemayehu, et al. (2006). The payload electrical

6 load and power system generation capacity was listed in input files from Alemayehu, et al. (2006). The subsystem power requirements were added together and a 10% margin added to the total, representing the maximum use case. The 24 hour average electrical load was calculated based on 50% of the sum of the above component power requirements, with the exception of steering and control. As steering and control is always operating at design capacity, its contribution to the average load was assumed to be 100%. A feasibility check was performed to ensure that the required power did not exceed the available power. Drag and performance The drag analysis was based on the method described in Gillmer and Johnson (1982). This method is based on curve fitted scale model data of frictional resistance of a flat plate in a turbulent boundary layer, and associated correction and correlation coefficients to correct for the shape of the submarine and the scaling to full size. From the bare hull resistance, the power required to push the bare hull through the water at velocity could be determined. The additional resistance of the appendages on the submarine was estimated by adding a conservative 30% drag to the bare hull drag. The appendage drag described in literature is between 25% (Gillmer and Johnson (1982)) and 30%, Shingler, et al. (2005) of the bare hull drag. A transmission efficiency of 93% was (Gillmer and Johnson (1982)) assumed, resulting in a required shaft power. The endurance range under battery power was estimated based on a submerged speed of 6kts. The required propulsion power at 6kts was estimated and added to the 24 hour average electrical load to determine the required power draw. Based on the battery capacity, an operation time in hours at 6kts was determined. The snorkel range under diesel power was estimated using a method described in the Naval Sea Systems Command, Design Data Sheet (2011) and the US Naval Postgraduate School Total Ship Systems Engineering course notes TS 4001 (2002). Effectiveness against capability requirements The Overall Measure Of Effectiveness (OMOE) calculator rates each design against the set of requirements, using a Measure of Performance. The Measures of Performance used were those derived in the Error! Reference source not found. section above. These measures of performance were weighted and summed to determine the Overall Measure of Effectiveness for each design iteration. RESULTS A case study was performed to investigate the sensitivity of the submarine effectiveness to the design parameters. This was achieved by linking the submarine synthesis model to the optimisation engine. As discussed in the Capability Analysis section, the Warfare operational tasks were not considered in this analysis. However, the weight, volume and power requirements of the combat systems need to be included in the submarine synthesis model to create a realistic concept design. The combat system from Alemayehu et al. (2006) was used for all analyses in this case study investigation, which included the following: The sonar system consists of a BQQ-10 bow dome passive/active sonar array; an AN/BQQ-5 wide aperture array; high frequency sail and chin arrays; TB-16 and TB-29A towed arrays and a BSY-2 combat system.

7 The sail contains a BPS-16 radar for navigation and surface surveillance; two AN/BRA-34 masts for navigation and communications; two AN/BVS-1 photonics masts for visual and IR observations; two EHF/SHF multiband antennas; sea sentry UAV for ISR and a OE-315 towed buoy for covert surface observations. The electronic support measures consists of; a WLY-1 acoustic and countermeasures system; AN/BLQ-10 ESM system; two 3 counter measure launchers with reloads and two 6.75 counter measure tubes. Six 21 torpedo tubes with 24 reloads. A four module vertical launch system to carry six Tomahawk land attack missile each. A four person lock-out chamber for special warfare operatives. According to Alemayehu et al. (2006) this system had a weight of 49.9 ltons, an outboard volume of 6778 ft 3, and required 143kW of electrical power. The power system comprised three 1400kW diesel generator sets driving a single propulsion motor. The generator sets weighed 17.7 ltons each and the total machinery room had a volume of 9500ft 3. The cost metric used for this analysis was the normal surface condition weight. This only accounts for roughly half the financial cost of a submarine, with the other half being the cost of the combat system (according to a conversation with an industry expert). As the combat system was not varied in this study, the variation in cost would be largely a function of the normal surface condition weight. Figure 5. Surfaced weigh vs number of crewand Figure 6. Surfaced weigh vs mission duration show the growth in surfaced weight as the crew complement and mission duration increases. The red lines (Concept1) show the results from the present study. The stars on the plots show data points from previous studies: Vidar-36 (Binns 2008) is a BMT design, similar to Concept1, except that it has a 21 day Air Independent Propulsion capability; Vtech SSBMD (Blizzard et al. 2008) is a ballistic missile defence submarine concept developed at Virginia Tech, with a 24 day Air Independent Propulsion capability as well as four Kinetic Interceptor missiles in the sail; Vtech SSGX (Alemayehu 2006) is a guided missile submarine concept design with 26 days of Air Independent Propulsion endurance and a relatively small crew complement; Collins is the Collins Class submarine.

8 Weight surfaced [lton] Weight surfaced [lton] Concept1 Vidar-36 Collins VtechSSGX Crew [-] Figure 5. Surfaced weigh vs number of crew Mission duration [Days] Figure 6. Surfaced weigh vs mission duration

9 Figure 7 shows the overall measure of effectiveness versus the normal surface condition weight, with the colour scale representing the snorkel range. Note that the colour scale extends beyond the range of interest. This seems to be a flaw with Model Center, that the colour scale range cannot easily be set. The results show an area of dense feasible solutions extending along a wide diagonal. The top of this diagonal represents the non-dominated solution line. At around 3220lton surfaced weight, the OMOE is seen to increase followed by a sparse area of non-dominated solutions. This sparse area represents designs with near maximum allowable fuel of 220ltons. The reason that there are only a few of these high fuel load designs is that the weighting was biased towards minimising the normal surface condition weight. The trend clearly shows an increase in overall effectiveness with increasing range capability. Sparse area of non-dominated solutions Non-dominated solution line Figure 7. Overall measure of effectiveness vs surfaced weight with snorkel range colour scale

10 CONCLUSIONS A capability analysis tool was developed and applied to a case study. In its current form the tool could be used to analyse a wide range of scenarios, assuming relevant system data is available. If this tool and method were to be applied to a real system with real requirements, the capability analysis would need to be expanded to include multiple scenarios and associated measures of performance. The synthesis model could be expanded to include longitudinal stability as well as more flexibility in the assumed layout of the submarine. Ideally, a quantitative analysis tool would also be used to objectively evaluate the performance of the combat and weapon systems on the overall effectiveness of the submarine. ACKNOWLEDGEMENTS The authors would like to Acknowledge the Defence Science and Technology Organisation for providing the majority of the funding for this project REFERENCES Alemayehu, D. R. Boyle, E. Eaton, T, Lynch, J. Stepanchick, R. Yon (2006), Guided Missile Submarine SSG(X), Virginia Tech Design Report. Australian Government (2009), Defending Australia in the Asia Pacific Century: Force 2030, Defence White Paper. Binns, S.D (2008), Meeting the current challenges of designing high capability SSKs, Paper presented at Warships 2008: Naval Submarines 9, RINA, Glasgow Blizzard, C.R., K. Colantonio, V. Jones, M Toris, D. Reigel, M. Wichgers (2008), Ballistic Missile Defence Submarine, Virginia Tech Design Report. Buckingham, J., C. Hodge, and T. Hardy (2008), Submarine Power and Propulsion Application of Technology to Deliver Customer Benefit, Paper presented at UDT Europe, Glasgow. Burcher, R. and L. Rydill (1994), Concepts in Submarine Design, Ocean Technology, Series 2, Cambridge University Press. Fox, J.P. (2011), A Capability-based Meta-model Approach to Combatant Ship Design, Masters of Science Thesis, Naval Postgraduate School. Gillmer, T.C and B. Johnson (1982), Introduction to Naval Architecture, McGuire Books. Gomez Torres, J.M (2010), Warship Combat System Selection Methodology Based on Discrete Event Simulation, Masters of Science Thesis, Naval Postgraduate School. Green, J.M. (2001), Modelling the Ship as a Weapon System, AIAA 2nd Biennial National Forum on Weapon System Effectiveness, held at the John Hopkins University/Applied Physics Laboratory, March 2001.

11 Gregor J.A. (2003), Real Options for Naval Ship Design and Acquisition: A Method for Valuing Flexibility under Uncertainty, Masters of Science Thesis, Massachusetts Institute of Technology Mann, J. and T. Gibbs (2012), Optimising SSK Transit Performance Through Hullform, Transit Mode and Diesel Powerplant Selection, Paper presented at Pacific 2012, Sydney Australia Naval Postgraduate School, (2002) Total Ship Systems Engineering course notes TS 4001 (2002) Powering Naval Sea Systems Command, Design Data Sheet (2011). DDS Rev1. October 2011 Pearce, P., and M Hause (2012), ISO-15288, OOSEM and Model Based Submarine Design, Paper presented at SETE APCOSE conference Sanabria Gaitan, G.D (2011), Alternatives Impact in Combatant-ship Design, Masters of Science Thesis, Naval Postgraduate School. Sewell, E.A (2010), Open Architecture for Improved Early Stage Submarine Design, Masters of Science Thesis, Massachusetts Institute of Technology. Shingler, K. D. Goff, D. Schewsbury, J. Borthen, J. Geisbert (2005), Littoral Warfare Submarine, Virginia Tech Design Report. Warren, C.L. (1997), Submarine Design Optimisation Using Boundary Layer Control, Master of Science thesis, Massachusetts Institute of Technology.