Documents

Zonal Ship Design (Paper)

Categories
Published
of 16
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
Share
Description
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.
Transcript
  050120ZonalShipDesign.doc 1 Capt. Norbert Doerry, USN Zonal Ship Design ABSTRACT 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. INTRODUCTION The advantages of zonal systems design have long been recognized and documented (Petry and Rumburg 1993)(Shiffler 1993). Since then, zonal a.c. electrical distribution systems have been used in the DDG 51 class, LPD 17 class, and LHD 8. The next advance in zonal electrical distribution, Integrated Fight Through Power (IFTP) featuring d.c. zonal electrical distribution is being developed for the Navy and is a candidate for future installation on DD(X) and CG(X). (Ciezki and Ashton 1999)(Roberts 2002) (Hiller 2003) (Walsh 2003) (Zgliczynski et. al. 2004) To date, zonal design concepts have been applied to distributed systems (usually just the electrical system) in an ad hoc fashion. A systematic study of zonal architectures has not been published. Likewise, the impact of zonal system design on total ship design has not been adequately addressed. 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. The views expressed in this paper are those of the author and are not necessarily official policy of the U.S. Navy or any other organization. The intent of this paper is to foster dialogue to gain a better understanding of zonal system design and zonal ship design. BACKGROUND 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, 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. The threats for which a ship is designed to are its Design Threats, and the residual capability following exposure to the Design Threats is the Design Threat Outcome. While survivability measures the ability of the ship to continue to function during damage, Quality of Service measures the ability of the distributed systems to support the normal, undamaged operation of its loads. Quality of Service is measured in terms of a Mean Time Between Failure (MTBF) where a failure is defined as any interruption in the supply or deviations outside of normal bounds of commodity characteristics that prevent the load from performing its assigned function. Although survivability and quality of service are usually not the source of design conflicts, design  050120ZonalShipDesign.doc 2 features may impact one more than the other. For example, the routing of cables in an electrical distribution plant will have little impact on Quality of Service, but will have a tremendous impact on Survivability. On the other hand, the reliability of generator sets has a bigger impact on Quality of Service than on Survivability. In the design of distributed systems, cost is always a major consideration. Because the relative costs and capabilities of different distributive system components differ from system to system, a universal zonal design that applies to all cases does not exist. In selecting an architecture, the following strategies for reducing acquisition costs (while still meeting performance requirements) should be considered: a.   Eliminate hardware and software b.   Substitute expensive hardware and software with cheaper hardware and software. This includes increasing cost and capability of device A to enable the reduction in cost and capability of device B as long as there is a net savings. c.   Enable the hardware to be installed more easily d.   Enable the hardware to be tested before installation onboard ship e.   Reduce the engineering effort needed to design the ship Because this paper does not address specific distributed systems, these cost reduction strategies will be addressed only in general terms. DEFINITIONS Zone   A zone is a geographic region of ship. In a general sense, the boundaries of the zone can be arbitrary, but to maximize survivability, the zones of multiple distributed systems as well as damage control zones should be aligned. For shipboard distributed systems, this typically means the zone boundaries are the exterior skin of the ship and selected transverse watertight bulkheads. The zone boundaries may rise above the watertight bulkheads into the superstructure, or the superstructure may be composed of one or more zones independent of the zones within the hull. Adjacent Zones Adjacent Zones are zones that could simultaneously be damaged by a design threat. Zones are typically sized so that usually only 2 zones are simultaneously damaged by a design threat, although in some cases a third zone (such as the superstructure) may also be damaged. Zonal Survivability For a distributed system, zonal survivability is the ability of the distributed system, when experiencing internal faults due to damage or equipment failure confined to adjacent zones, to ensure loads in undamaged zones do not experience a service interruption. Zonal Survivability assures damage does not propagate outside the adjacent zones in which damage is experienced. For many distributed system designs, zonal survivability requires that at least one longitudinal bus remains serviceable, even through damaged zones. At the ship level, zonal survivability facilitates the ship, when experiencing internal faults in adjacent zones due to design threats, to maintain or restore the ships primary missions as required by the Design Threat Outcome. Ship level zonal survivability focuses restoration efforts on the damaged zones, simplifying the efforts required of the ship’s crew to maintain situational awareness and take appropriate restorative actions. Ship level zonal survivability requires sufficient damage control features to prevent the spreading of damage via fire or flooding to zones that were not initially damaged. Compartment Survivability Zonal Survivability only addresses loads outside of the damaged adjacent zones. For some important loads, including those implementing mission systems, providing redundant capability across multiple non-adjacent zones may prove to be infeasible. This situation often arises in the superstructure where the sensor masts are located in the same or adjacent zones. In some cases, these loads may be perfectly functional  050120ZonalShipDesign.doc 3 although damage has reached into its zone. Likewise, maximizing the probability of maintaining loads that support damage control efforts within the damaged adjacent zones also assists in preventing the spread of damage to zones not initially impacted. Examples of such loads include emergency lighting and power receptacles for portable dewatering pumps. In these cases, providing Compartment Survivability for the distributed systems for the specific loads is warranted. Compartment Survivability requires that every distributed system required by a specific load provide independent normal and alternate sources of its commodity (power, cooling water, etc.). For the specific design threat, one of the sources of the commodity should be expected to survive if the specific load is expected to survive. The point at which the in zone distribution of the commodity merge (such as with an Automatic Bus Transfer – ABT) from the normal and alternate sources should be within ½ of the expected damage radius of damage centered at the specific load. Mission System A mission system consists of the hardware and software dedicated to the performance of a Primary or Secondary mission of the ship. Examples of mission systems include aircraft launch and recovery equipment (ALRE), propulsion systems, combat systems, and C4ISR systems. Ideally, the mission systems of a ship should be designed such that the capability to perform the ship’s missions is not lost if mission system equipment in adjacent zones are not operational. Unfortunately, ship design constraints will often preclude the level of redundancy required to ensure continuous capability. If mission capability can not be assured continuously, then the ability to restore capability to achieve the Desired Threat Outcome must be provided. Distributed System A distributed system moves a commodity from one or more sources to multiple loads distributed through-out the ship. Examples of commodities include electrical power, cooling water, firefighting water, and fuel. For a given commodity, distributed systems can generally be described by an architecture consisting of the following functional elements: GENERATION A generation element produces the commodity. Examples include Gas Turbine Generator Sets, firepumps, and chill water plants. Generation elements for one distributed system are generally loads for other distributed systems.  DISTRIBUTION   A distribution element transports the commodity between other functional elements. For zonal distribution systems, the longitudinal buses are instances of distribution functional elements. CONVERSION A conversion element converts the commodity from one form to another. An example of a conversion element is a transformer in an electrical system. A transformer changes the voltage level of it commodity, electrical power.  LOAD A load is a consumer of the commodity. A load for one distributed system can be a generation element for another distributed system. For example, a chill water plant is a load to the electrical distribution system and a generation element for the chill water distribution system. STORAGE A storage element stores the commodity for later use. In some systems, such as fuel systems, storage elements (fuel tanks) functionally replace generation elements. In other systems, such as electrical systems, storage elements (Uninterruptible Power Supplies) serve as buffers to prevent power disturbances from propagating to loads. CONTROL A control element coordinates the other elements of a distributed system to enhance quality of service and to facilitate the restoration of service following a casualty. For new designs, the Control Element typically consists of software that resides within the total ship computing environment.  050120ZonalShipDesign.doc 4 For an example of this architecture as applied to an Integrated Power System, see Doerry and Davis (1994) and Doerry et. al. (1996). Design Threat A design threat is a threat to the ship where a Design Threat Outcome has been defined. Examples of Design Threats could be specific cruise missiles, torpedoes, guns, explosives, weapons of mass destruction as well as accidents such as main space fires, helicopter crashes, collisions, and groundings. Design Threat Outcome The design threat outcome is the acceptable performance of the ship in terms of the aggregate of susceptibility, vulnerability, and recoverability when exposed to a design threat. Possible Design Threat Outcomes include: a.   Ship will likely be lost with the loss of over 25% of embarked personnel. b.   Ship will likely be lost with the loss of 25% or under of embarked personnel. c.   Ship will likely remain afloat and not be capable of performing one or more primary mission areas for a period of time exceeding one day. d.   Ship will likely remain afloat and be capable of performing all of its primary mission areas following restoration efforts not exceeding one day using only that external assistance that is likely available within the projected operating environment. e.   Ship will likely remain afloat and be capable of performing all of its primary mission areas following restoration efforts not exceeding two hours using only organic assets. f.   Ship will likely remain afloat and would be capable of performing all of its primary mission areas following restoration efforts (if needed) not exceeding 2 minutes using only organic assets. g.   Ship will likely remain afloat and would likely be capable of performing all of its primary mission areas without interruption. h.   The threat weapon is not considered a significant threat because the probability that the threat weapon would have been defeated before striking the ship is greater than 98%. Note: The term “likely” should be assigned a specific probability of occurrence. A reasonable choice would be to specify that “likely” refers to a probability of occurrence greater than 86%. The levels of survivability for the design threats can be evaluated using Total Ship Survivability Assessment (TSSA) methods. Yarbrough and Kupferer (2002) provided an example of the TSSA process as applied to a naval ship (JCC(X)) during the concept / feasibility stage of design. Over-Matching Threat An over-matching threat is a design threat where the design threat outcome includes likely loss of the ship. Quality of Service Quality of Service is a metric of how reliable a distributed system provides its commodity to the standards required by the users. It is calculated as a Mean-Time-Between-Failure (MTBF) as viewed from the loads. A failure is defined as any interruption in service, or commodity parameters outside of normal parameters, that results in the load equipment not being capable of performing its function. The time is usually measured over an operating cycle or Design Reference Mission. Quality of Service is a reliability metric, as such the calculation of QOS metrics does not take into account survivability events such as battle damage, collisions, fires, or flooding. Quality of Service does take into account equipment failures and normal system operation transients. A typical cause of normal system operation causing a QOS failure is the shifting of sources for the commodity such as shifting to/from shore power (without first paralleling) or manually changing the source of power using a manual bus transfer (MBT). Also note that not all interruptions in service will cause a QOS failure. Some loads, such as refrigerators and chill boxes, will keep their contents cold even if power is interrupted for several minutes. In this case, a QOS failure will
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks