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The design phase of a naval vessel is extraordinarily complex. The numerous interactions between design specialties have great potential to result in misunderstandings and confusion among engineers, which can then lead to deadline extensions or unnecessary rework. To overcome the difficulties coordinating ship design specialties, our effort seeks to simulate candidate design processes through the construction of a complete ship design planning tool. This planning tool lays out the effects of resources, requirements, and product quality on the overall design schedule, allowing ship design managers (SDMs) to more efficiently task and control work. The tool specifically includes the impacts of iterations on the overall convergence of the design. As a demonstration we focused on modeling the power and propulsion elements of the ship design.

Power systems with highly flexible architectures (i.e. permitting many configurations) may allow for more economic operation as well as improved reliability and resiliency. The greater number of configurations enable optimization for attaining the former benefit and redundancy for achieving the latter. Flexibility is of great importance in electric ship power systems wherein the system must ensure delivery of power to vital loads. The United States (US) Navy is currently investigating new architectures that enable a greater number of interconnection permutations. Among the new features considered are generators that may supply two buses; this may be done using conventional (single winding set) generators and two rectifiers or a dual wound machine with two rectifiers. In systems supplied by dual-wound machines, buses may not be tied directly but are linked dynamically through the shared generator dynamics. In systems with conventional generation supplying two rectifiers, the two buses are tied through a common AC bus supplying both rectifiers. This paper presents a comparison of these two approaches of supplying two buses from one generator; the evaluation considers issues associated with dynamic coupling through these two candidate architectures, including the coupled response due to faults and systems with pulsed loads. Results are based on analysis, simulation results, and hardware experiment.

Auctioneering diodes are often proposed as a method for providing uninterruptible power to d.c. loads from two sources. Although the basic concept of auctioneering diodes is straight-forward, there are many nuances that should be understood before employing them. In particular, this paper discusses common-mode current issues with asymmetric auctioneering diode configurations as well as potential voltage doubling due to double ground faults in symmetric configurations. The design of snubbers and transient surge suppressors is also detailed.

While electric propulsion for warships has existed for nearly a century, it has only been since the end of the Cold War that modern integrated power systems have been developed and implemented on U.S. Navy warships. The principal enablers have been the products of research and development for rotating machines (generators and propulsion motors), power electronics (power conversion and motor drives), energy storage, and controls. The U.S. Navy has implemented this advanced technology incrementally. Notably, DDG 1000 with its integrated propulsion system and CVN 78 with its electromagnetic aircraft launch system will soon join the fleet and mark another important advance to the electric warship. In the future, the integration of electric weapons such as railguns, high power radars, and lasers will result in the final achievement of the electric warship.

As part of the U.S. Navy’s continued commitment to protecting U.S. interests at home and abroad, the Navy is investing in the development of new technologies that broaden U.S. warship capabilities and maintain U.S. naval superiority. In particular, NAVSEA is supporting the development of power systems technologies that help the Navy realize an all-electric warship. It is recognized that a challenge to fielding an all-electric power system architecture includes minimizing the size of energy storage systems while maintaining the response times necessary to support potential pulsed loads. This work explores the trade-off between energy storage requirements (i.e. size and weight) and performance (i.e. bandwidth and storage) in the context of a power system architecture that meets the needs of the US Navy. To compare energy storage technologies and appropriately size them, it is necessary to specify size and weight requirements and thus consider the energy density of the technology in Wh/kg and specific power density in W/kg. The modelled time domain behaviour for different load types and control delays were used to determine technology and sizing requirements by comparing the total energy and maximum power used in the simulation to a Ragone plot. Simulation results based on operational vignettes were used to identify a range of specific power and energy densities that will meet system requirements. Potential energy storage sizing can be determined by approximating where a selected technology intersects with the energy and power requirements of the system. Another major component necessary to determine energy storage technology is the frequency domain behaviour of the system. In this work, the energy storage control bandwidth is evaluated in simulation for different loading scenarios, and a trade-off between size/weight and response bandwidth is illustrated.

Many candidate power system architectures are being evaluated for the Navy’s next generation all-electric warship. One proposed power system concept involves the use of dual-wound generators to power both the Port and Starboard side buses using different 3-phase sets from the same machine (Doerry, 2015). This offers the benefit of improved efficiency through reduced engine light-loading and improved dispatch flexibility, but the approach couples the two busses through a common generator, making one bus vulnerable to faults and other dynamic events on the other bus. Thus, understanding the dynamics of cross-bus coupling is imperative to the successful implementation of a dual-wound generator system. In (Rashkin, 2017), a kilowatt-scale system was analysed that considered the use of a dual-wound permanent magnet machine, two passive rectifiers, and two DC buses with resistive loads. For this system, dc voltage variation on one bus was evaluated in the time domain as a function of load changes on the other bus. Therein, substantive cross-bus coupling was demonstrated in simulation and hardware experiments. The voltage disturbances were attributed to electromechanical (i.e. speed disturbances) as well as electromagnetic coupling mechanisms. In this work, a 25 MVA dual-wound generator was considered, and active rectifier models were implemented in Matlab both using average value modelling and switching (space vector modulation) simulation models. The frequency dynamics of the system between the load on one side and the dc voltage on the other side was studied. The coupling is depicted in the frequency domain as a transfer function with amplitude and phase and is shown to have distinct characteristics (i.e. frequency regimes) associated with physical coupling mechanisms such as electromechanical and electromagnetic coupling as well as response characteristics associated with control action by the active rectifiers. In addition, based on requirements outlined in draft Military Standard 1399-MVDC, an approach to derive specifications will be discussed and presented. This method will aid in quantifying the allowable coupling of energy from one bus to another in various frequency regimes as a function of other power system parameters. Finally, design and control strategies will be discussed to mitigate cross-bus coupling. The findings of this work will inform the design, control, and operation of future naval warship power systems.

Mirroring the terrestrial power system, naval warships have employed electrical power systems for over 100 years. The design philosophy for naval power systems is expressed well by the Naval Sea Systems Command (NAVSEA) Design Practices and Criteria Manual, Electrical Systems for Surface Ships, Chapter 300

Naval Power (and Energy Systems) Existing Ships MVAC Architectures MVDC Architectures Properties of a Naval Power (and Energy) System Limited rotational inertia — AC frequency is not a constant Lack of Time Scale Separation Load sharing vice Power Scheduling Short electrical distances Load dynamics very important System behavior dominated by controls.

The U.S. Navy is exploring the use of power electronics based Medium Voltage Direct Current (MVDC) power distribution systems to affordably provide power to advanced mission systems. The design of equipment and the system grounding scheme should be designed to limit common mode (CM) currents through the ship's hull. This paper presents a CM model of an MVDC power distribution system and makes recommendations for the design of rotating machines, power electronics, grounding systems, and MVDC bus interfaces to limit CM currents.

The U.S. Navy is tasked within a constrained budget with fulfilling its missions in an environment of evolving threats and a corresponding rapidly evolving mission system technology base. Modular Adaptable Ship (MAS) technologies enable the affordable transformation of a ship over its service life to maintain military relevance. The views expressed in this paper are those of the author and do not reflect the official policy or position of the Department of the Navy, the Department of Defense, or the U.S. Government.

On February 4, 2008, Admiral Paul Sullivan, Commander of the Naval Sea Systems Command, sent out a letter entitled: Ship Design and Analysis Tool Goals. The purpose of the widely distributed memorandum was to state the requirements and high-level capability goals for NAVSEA design synthesis and analysis tools. In this memo, Admiral Sullivan expressed the need for evolving models and analysis tools to be compatible with, among other things, set-based design (SBD). Admiral Sullivan's memo was a major step toward improving ship design programs with new, more powerful analytical support tools but many have asked, “What is Set-Based Design and how does it relate to Naval Ship Design?” SBD is a complex design method that requires a shift in how one thinks about and manages design. The SBD paradigm can replace point-based design construction with design discovery; it allows more of the design effort to proceed concurrently and defers detailed specifications until trade-offs are more fully understood. This paper describes the principles of SBD citing improvements SBD in design practice that have set the stage for SBD, and relating these principles to current Navy ship design issues.

Several recent Analyses of Alternatives (AOAs) have demonstrated issues with the AOA process that have limited the Navy in the pre-Milestone A process. The eventual selection of an AOA preferred alternative that balances mission needs, total ownership cost, and acquisition cost was based on a limited trade space. This paper proposes an improved pre-AOA process to better define a fiscally constrained set of fleet requirements that are allocated to the different ships, aircraft, and systems comprising the battle force over a 40-year time span. The proposed process extends the Capabilities-Based Assessment (CBA) defined in the Joint Capabilities Integration and Development System to apply to the entire fleet design instead of each capability area. In this way, fleet requirements derived from the National Security Strategy and the Department of Defense Strategic Guidance are allocated to different warfare platforms. The required analysis combines physics-based modeling of the individual war fighting units, realistic cost engineering/estimation, and rigorous operations analysis via the Navy SYSCOMs. The fleet planning is done over three time horizons: Long-Range planning of 15-40 years in the future to guide science and technnology development; Mid-Term planning from the end of the Future Year Defense Plan (FYDP) to 15 years to establish architectures, guide technology transition, as well as derive from the Fleet Level CBA the platform level CBAs for the individual programs; and Near-Term planning within the FYDP, where the concerns are reacting to emerging threats, meeting affordability goals, and maintaining the industrial base. The resulting fleet level analysis directly supports force level assessments as part of the Quadrennial Defense Review.

Many naval ship acquisition programs have not been able to effectively implement cost as an independent variable (CAIV). With a CAIV approach, operational requirements provided by the customer are given in terms of threshold and objective values. The range between these two values provides the program manager with trade-space to match the available funds with the capabilities that can be bought for that amount-the total program cost remains a constant. In practice though, much of the final cost of an acquisition program is fixed early in the design process through basic design decisions on architecture and the allocation of operational requirements and derived requirements to systems. Unfortunately, while much of the cost is determined early in the design process, estimating that cost to any degree of certainty is nearly impossible. As the costs of the program are better understood, the remaining design flexibility to adjust to increasing costs may not be sufficient to enable the program manager time to take corrective action when the cost estimates indicate a possible problem. This paper describes the techniques, including the use of modularity, cost contingencies, and set-based design, to provide the program manager with sufficient flexibility to implement CAIV. The views expressed in this paper are those of the author and are not necessarily official policy of the US Navy or any other organization. The intent of this paper is to foster dialogue to gain a better understanding of how to develop an acquisition strategy and systems engineering strategy to enable CAIV.

The primary aim of the design of a shipboard electric power system has traditionally been survivability and continuity of the electrical power supply. Survivability relates to the ability of the power system, when damaged by a threat, to support the ship's ability to continue its missions. Power continuity relates to the ability of the power system to reliably provide power to ship systems under normal operations. This paper proposes new metrics for survivability and continuity of service that enable a better definition of power system requirements linked to the operational needs of the ship. For survivability, the threats for which a ship is designed are its design threats, and the required residual capability following damage from a design threat is the design threat outcome. Quality of service serves as a metric of the continuity of the electrical power supply under normal operation. Quality of service is measured in terms of a mean time between service interruption. A service interruption is defined as any interruption in the supply or deviations outside normal bounds of power quality that prevent a load from performing its assigned function.

In 2014, the Small Surface Combatant Task Force completed an innovative study on alternate proposals to procure a capable and lethal small surface combatant. Modified Littoral Combat Ship (LCS) concepts, new design concepts, and existing design concepts were examined. This paper describes the set-based design approach employed to conduct this study.

MIL-STD-1399-300 and MIL-STD-1399-680 have established AC voltage interface requirements for U.S. naval surface ship electrical power systems. No such interface standards have been established for DC interfaces on U.S. naval surface ships. This paper provides recommendations for specific standard DC interface voltages for naval surface ship applications. These standard interface voltages are intended to facilitate the development and integration of DC loads. In recommending Interface Standards, the following were considered: • Existing commercial and military interface standards should be used to the maximum extent practical. • Different standard voltage levels should differ significantly (greater than 25%) • Higher voltages enable lower currents, and lighter cables. • Standard voltage ratings of available semiconductor devices and insulation ratings should be considered. In addition to nominal voltage levels, power quality requirements and conformance testing requirements are recommended.

The Navy has invested a considerable amount of resources in developing Electric Warship technology in the past twenty years. We have witnessed a number of early technology demonstrations as well as incorporation of Integrated Power System (IPS) technology into ship programs such as LHD 8, T-AKE, DD(X), and CVN 21. Although these early adopters have paved the way for establishing the practice of electric warship design, we are now at a critical point in time for institutionalizing the electric warship. A technology is institutionalized when the following activities have occurred: ▪ Establish a common architecture and interfaces. ▪ Establish a common design processes. ▪ Incorporate the architecture and design processes into design tools. ▪ Codify the practice in government or industry specifications, standards, and guides. ▪ Teach the architecture and design process as part of a typical engineering school curriculum. This article reviews the progress in electric warship technology, describes progress (including ongoing efforts) in institutionalization, and highlights critical near term shortcomings. Some of the shortcomings in design processes and tools include: ▪ Undefined (in authoritative documentation) concepts such as zonal survivability and quality of service. ▪ Obsolete requirement terms such as “sustained speed” and “endurance speed/range” ▪ Conflicting design practices for propulsion and ship service prime mover sizing. ▪ Customized system protection strategies for different classes of ships. ▪ Ambiguous methods for the sizing of zonal distribution system components. ▪ Lack of integration of IPS design algorithms into ship concept tools such as ASSET. ▪ Lack of knowledge as to how to effectively use modeling and simulation to make electric plant design decisions for each stage of ship design. Additionally, the article details progress in updating standards and specifications, such as the Naval Vessel Rules and DOD-STD-1399. Finally, efforts to incorporate Electric Warship design into the curriculum at [RA1] traditional Naval Architecture are described.

Modern ships typically have a number of distributed systems. Distributed systems are used because it's simpler, cheaper, and better to centrally produce a commodity such as electricity or chill water, than to locally produce it with the users of the commodity. For naval warships, in addition to cost, two measures of performance are very important: Survivability and quality of service. Survivability relates to the ability of the distributed system, even when potentially damaged by a threat, to support the ship's ability to continue fulfilling its missions to the degree planned for the particular threat. Quality of service measures the ability of the distributed systems to support the normal, undamaged operation of its loads. This paper defines a number of key terms, details a number of different zonal architectures, describes the situations where the architectures are best suited and proposes a framework for zonal ship design that promises to satisfy survivability performance requirements and quality of service requirements.

Open system interfaces for high power electronics equipment used in zonal electrical distribution systems rated above 100 kW are identified in this standard. The required power, monitoring, information exchange, control, and protection interfaces are based on technological maturity, accepted practices, and allowances for future technology insertions. Also, rigorous assessment mechanisms, interface control management, and proactive conformance testing that shall be used to verify and validate open systems to enable plug-and-play operability independently of the components’ origin are defined. Airports, hospitals, major data processing centers especially those using uninterruptible power supply), broadcast systems, and maritime vessels and platforms are pplications covered by this standard. Existing terrestrial utility power systems that do not yet contain the electronic power interfaces and high-speed communication networks that are essential to use this standard shall be upgraded by its application.

In 2013, the United States Marine Corps (USMC) conducted a study to determine the technical feasibility and affordability of a High Water Speed Amphibious Combat Vehicle, quantify performance, determine capability tradeoffs that can be made to reduce cost and reduce technical risk, and compare capabilities with those of a Low Water Speed variant. This paper describes the organizational structure, the study plan, and the innovative Set-Based Design method used by the ACV Directorate to conduct the study.

The U.S. Navy has invested considerable funds in the research and development of electrical power technologies for future electric warships. One aspect of institutionalizing these technologies is the creation or modification of standards and specifications to incorporate the new technologies. This paper assesses the current state of standards and specifications in support of the design and construction of an all-electric naval warship. These technical documents will be evaluated in terms of the different power systems architectures to include low voltage ac generation, medium voltage ac generation, medium voltage dc generation, and zonal power distribution. Ongoing standards activity, both in industry and in the Navy, are discussed. Finally, the paper presents recommendations for updating existing specifications and standards and the creation of new specifications to cover technical areas where standards do not currently exist.

For the past four years, Advanced Surface Machinery Programs (SEA 03R2) has been developing the Integrated Power System (IPS) to reduce ship acquisition and life cycle costs while still meeting all ship performance requirements. IPS provides electrical power to ship service loads and electric propulsion for a wide range of ship applications including surface combatants, aircraft carriers, amphibious ships, auxiliary ships, sealift and high value commercial ships. IPS consists of an architecture and a family of modules from which affordable and high performance configurations can be developed for the full range of ship applications. Two years ago, the initial IPS concepts were presented at ASNE Day 1994. Since then, much has been learned through the Reduced Scale Advanced Development (RSAD) and Full Scale Advanced Development (FSAD) programs. This paper describes the fundamental IPS architecture, details the evolving family of modules and their interface standards, and outlines the Mass Customization based design process for achieving customer performance requirements with an affordable IPS configuration.

The US Navy has shifted priority from designing systems that offer increased capability, to systems which are more affordable, but enable improved performance. To address the emphasis on affordability, the advanced surface machinery programs and the affordability through commonality program are proposing ship systems composed of common modules employing standardized parts. This paper describes the Integrated Power System (IPS) which provides electrical power for both propulsion and ship service loads for a wide range of ship applications including submarines, surface combatants, aircraft carriers, amphibious ships, auxiliary ships, sealift and high value commercial ships. IPS consists of an architecture and a family of modules from which affordable and high performance configurations can be developed for the full range of ship applications. In most configurations, IPS reduces the number of prime movers and divides ships into electrical zones controlled in a modular fashion. Cost reductions are realized in acquisition, training, manning, maintenance and other logistic support areas.

A major consideration in the design of any Naval ship or craft is its ability to meet the endurance requirements. This Design Data Sheet outlines the procedure to determine the minimum necessary fuel tankage for non-nuclear surface ships and operational presence. These conditions represent three different operational scenarios. Economical transit minimizes the consumption of fuel under normal transits. Surge to theater requires a ship to rapidly travel a specified distance, (such as to an operational area) without having to refuel. Operational presence requires a ship while deployed to remain on station for a specified period of time. The mobility requirements of these scenarios in conjunction with sustained speed requirements can drive the choice of prime movers and their ratings. Historically, the U.S. Navy has specified only the economical transit condition for an endurance speed of 20 knots. Assuming sustained speed requirements can be met, a lower endurance speed of 16 knots could result in a Combined Diesel (electric) and Gas Turbine (electric) plant. An operational presence profile heavily weighted for low speeds with high mission electrical loads will favor selecting power plants with a high degree of load sharing. For auxiliary and amphibious warfare ships with a lower sustained speed, diesel or diesel electric plants will likely be selected. This document uses metric units with the exception of distance which is measured in nautical miles, ship speed which is measured in knots, and temperature which is measured in degrees Fahrenheit. Conversion factors are provided to convert the units used to traditional units (long tons, pounds, and horsepower). This document is organized in a task oriented approach. The General Requirements section details the input and outputs of the Endurance Fuel Calculation Process. The Specific Requirements section provides details on the method to calculate the process outputs based on the inputs.

Quality of Service (QOS) is a measure of the ability of the power system to reliably provide loads electrical power with the power continuity required by the loads. QOS recognizes that different loads can tolerate different power interruption durations. This paper reviews QOS concepts as described in IEEE 1662–2008 and IEEE 1709–2010, describes methods for employing QOS in the design of shipboard power systems, and presents modeling and simulation considerations.

The need for integrated power systems will increase in the coming decades with the increased projected propulsion and ship service power demands for future combatants with advanced sensors and weapons such as railguns and lasers. Integrated propulsion systems will also benefit the signature performance of future submarine classes. For expeditionary warfare ships, combat logistics ships, Maritime Prepositioning Force - Future (MPF(Future)), and support vessels, reduced fuel costs and overall reductions in life cycle cost will continue to drive to integrated power solutions. To meet the need of future ship designs, the Navy is investing in Next Generation Integrated Power (NGIPS) system technology. Additionally, to promote commonality and acquisition efficiency, the Navy plans to implement NGIPS using an Open Architecture Business and Technical model. The four technical architectures are: Medium Volt AC Power Generation (MVAC), High Frequency AC Power Generation (HFAC), Medium Voltage DC Power Generation (MVDC) Zonal Electrical Distribution Systems (ZEDS).

Although the U.S. Navy has decreed that the primary aim of the electric power system design is for survivability and continuity of the electrical power supply, metrics have never been developed for continuity of service. This paper examines design issues associated with providing continuity of service under other than combat damage conditions and proposes a quality of service (QOS) metric to aid shipboard power systems design. This QOS metric is based on the probability that the power system provides the degree of continuity of power that each load needs to support the ship's missions. The major factors impacting QOS are the ratings, reliability and failure modes of the prime movers, power conversion equipment, and load equipment as well as system configuration. Additionally, while design features for QOS often improve system survivability, different failure modes require the designer to consider both survivability and QOS.

The recently commissioned Iwo Jima (LHD 7) is the last ship with conventional steam propulsion that the U.S. Navy plans to build. The LHD 8 is the next ship of the class and will be built as a modified repeat design of the LHD 7. The key modifications are steam propulsion being replaced with a hybrid propulsion system of main gas turbine engines augmented with auxiliary propulsion motors and electric powered auxiliaries replacing those powered by steam. The LHD 8 will also be the first USN surface ship to implement a 4160 VAC Zonal Electrical Distribution System (AC ZEDS) as well as the integrated power system concept for electrical power generation, distribution and propulsion. These modifications embody the intent of the all electric warship concept for the future U.S. Navy. This paper presents the constraints and issues involved in the design process by addressing major design impacts and significant design concerns. This text explores the design options within the available trade space and illustrates specifically how the Fleet/mission requirements, LHD 7 hull design and propulsion shafting constraints, schedule and funding drove the propulsion system design.

An object oriented approach for time domain simulations of shipboard electric power systems is proposed. It offers a flexible, user friendly alternative to conventional simulators, allowing design and operation analysis under a variety of operating conditions and topologies. The most general model of an electric power system consists of a set of nonlinear differential equations subject to algebraic constraints, which describes the evolution of the System, following certain contingencies. The algorithm presented adopts an object oriented approach by decomposing the system into its underlying components/devices, developed and maintained independent of one another. The differential equations are solved on the device level using a waveform representation of variables, which exploit both partitioning and parallel processing features. The ideas presented are tested on different test cases and conclusions are drawn.