FAULT TOLERANCE TECHNIQUE EMPLOYED BY SEAWOLF SUBMARINE USED

FAULT TOLERANCE TECHNIQUE EMPLOYED BY SEAWOLF SUBMARINE USED IN SEAWOLF SUBMARINE VIDYADHAR R EE 585 : FAULT TOLERANT COMPUTING EE 585 FAULT TOLERANT COMPUTING 1

SEAWOLF SUBMARINE (SSN 21) • Nuclear powered fast attacking submarine. EE 585 FAULT TOLERANT INSIDE VIEW OF SEAWOLFCOMPUTING SUBMARINE COMPUTING 2

SEAWOLF SUBMARINE n State of the art Control system. n Fault tolerant computer. n Flat panel operator displays. n Automatic modes of control. n combat, gyrocompass inertial sensors and data distribution system. 585 FAULT TOLERANT EE COMPUTING 3

SEAWOLF SUBMARINE (CONT) n n Hardware & PM software operate on failing of ship control electronics, sensors and actuation systems. FL performed on maintenance computer for repair and restoration of full redundancy. n PM software runs on 4 channel FTC, uses sensor voting. n Runs real time diagnostic tests. n PM transfers SCS functions to. TOLERANT systems. back-up EE 585 FAULT COMPUTING 4

SEAWOLF SHIP CONTROL DESCRIPTION n n Interfaces with SCS sensors, actuators using A/D signals processed by I/O modules. Operator interfaced by flat panel displays in SCP & BCP. Redundant MIL-STD-1553 data buses connect displays with SCPU. Interfaces with ship combat, data distribution sys, gyro & separate maintenance computer by means of redundant serial data buses. EE 585 FAULT TOLERANT COMPUTING 5

SEAWOLF SHIP CONTROL DESCRIPTION (CONT) n n Bow plane’s position control actuation hardware also interface with SCPU for control. Redundant pressure sensors allow SCPU to serve as master source of ship’s depth. Controls rudder, stern plane steering & diving, drain pumps. Interfaces with many valves and sensors for depth and remote trim pump control. EE 585 FAULT TOLERANT COMPUTING 6

PERFORMANCE MONITORING (PM) FUNCTIONS n n n n n PM steering and diving support. PM depth control support. PM trim and Drain support. FTC OS detects & reconfigures it when failure occurs. Detection & automatic recovery for ship ctrl failures. Also detects mechanical and hydraulic failures. Allows sys repair without shutting down entire system. Real time notification & status display to indicate what part of ship control has failed. Designed to detect 98% of all failures. EE 585 FAULT TOLERANT COMPUTING 7

FAULT LOCALIZATION (FL) FUNCTIONS n n Runs on separate maintenance computer when requested by the crew to diagnose physical location on failure. Indicates which component has to replaced when it is activated by the crew on occurrence of failure. EE 585 FAULT TOLERANT COMPUTING 8

PM/FL DEVELOPMENT PROCESS The Seawolf PM/FL development process followed steps: 1. 2. 3. 4. 5. System analysis and hardware specifications. Definition of the overall approach to PM/FL. Detailed specification and design of PM software. Full system simulated failure testing. Ship installation and sea trials experience. EE 585 FAULT TOLERANT COMPUTING 9

1. System analysis and hardware specifications Analysis process Req. : 1) 2) 3) PM must compare expected & sensed position of surface and detect hydraulic failures. Req. feedback sensors, sensed position of servo valve, output ’I’ & command signal from I/O module to minimize upset. Details of diving position control system and how PM must interact with Emergency Control System. EE 585 FAULT TOLERANT COMPUTING 10

2. Definition of the overall approach to PM/FL § § A mid-value selection filter was used for masking, detecting and isolating failures of redundant sensor inputs. A state machine algorithm was chosen to detect, isolate failures retractable bow planes. Analog input PM applied to synchro sensors, and measured voltages from ship’s speed log and tank level sensors. Discrete input was applied to valve position limit switches and operator control switches located on SCP. EE 585 FAULT TOLERANT COMPUTING 11

3. Detailed specification & Design of PM/FL software n n n Development process was an iterative one. The req. were tailored to follow an algorithm which reduced run time and complexity the most. Tests were conducted with software running on actual target hardware, but interfaced with simulated I/O signals. EE 585 FAULT TOLERANT COMPUTING 12

4. Full system simulates failure testing § With testing done, PM was integrated with actual ship control operating system. § The ship control machinery and submarine were simulated. § Over 1000 simulated failures were formally tested. § The test discovered PM software problems and several SCPU hardware deficiencies. EE 585 FAULT TOLERANT COMPUTING 13

5. Ship installation & sea trials experience As simulates testing of the system proceeded, the SCS was being installed on the SSN 21. § § § PM correctly located faulty wired sensors and installation and rigging problems with the ship control machinery. Tests of all rudder and diving planes worked correctly during both dockside and at-sea tests. Utility of PM surface prediction was also demonstrated. EE 585 FAULT TOLERANT COMPUTING 14

BENEFITS OF PM/FL n n n n Enhances mission effectiveness of the submarine. Capable of reducing required crew members and training. Reduces required maintenance and operating costs. System can tolerate a second failure in the same area and still retain full functional capability. Out of stock, does not result in aborting a mission, the system is robust enough for repair at a later convenient time. Automatic retest of system after Maintenance computer accurately indicates which component must be replaced to restore full system redundancy. PM automatically halts further operation of machinery when it detects potential damage of equipment due to incorrect operation of some machine. EE 585 FAULT TOLERANT COMPUTING 15

FUTURE SUBMARINE PM/FL The following trends may shape the design of future systems: n n n Seawolf SCS is an evolutionary design towards full fly-by-wire submarine control systems. This leads to elevation of PM functions to higher levels of criticality and making them integral to the safety of the system. Drive for fully automated & completely fault tolerant systems that can operate with minimal crew involvement & that require minimal sea maintenance. Applying fast developing technologies of Fuzzy logic and Adaptive fuzzy logic for performing FL in real time. EE 585 FAULT TOLERANT COMPUTING 16

ADVANCED CLASS OF SUBMARINES EE 585 FAULT TOLERANT COMPUTING 17

REFERENCES n n n http: //www. navsource. org/archives/08/08 0021. htm http: //www. fas. org/man/dod 101/sys/ship/ssn-21. htm http: //www. wikipedia. com EE 585 FAULT TOLERANT COMPUTING 18

QUERIES? ? ? EE 585 FAULT TOLERANT COMPUTING 19