Reliability centered modeling for development of deep water Human Occupied Vehicles

• Reliability modeling for key functions of deep water HOV done for 10 h mission.
• Identified the contribution of batteries, hydraulic systems and water tight seals.
• Battery configuration and hydraulics redundancy reduce PoF from 37.5% to 5.24%.
• Personnel sphere water tight integrity modeled and imperfection sensitivity discussed.
• Results help HOV designers to trade-off between CAPEX needs and required reliability.

Human Occupied Vehicle operations are required for deep water activities such as high resolution bathymetry, biological and geological surveys, search activities, salvage operations and engineering support for underwater operations. As this involves direct human presence, the system has to be extremely reliable. Based on applicable standards, reliability analysis is done on 5 key representative functions with the assumption that the submersible is utilized for ten deep water missions per year. Analysis is done on the results obtained to find the influence of the subsystems on the reliability of the overall submersible. Analysis include, influence of battery technologies and reliability centered battery and hydraulic system configurations. Dependence of seal sizes and seal seat surface finish on the leak tight integrity of the personnel sphere is also discussed. It is found that for submersible housing 75 kWh energy storage batteries, the probability of failure of the hard tank buoyancy ascent function with lead acid batteries configured for 300 V terminal voltages and non-redundant hydraulic configuration is 37.74%. The probability of failure can be reduced to 5.24% with lead acid batteries with terminal voltage configured to 120 V and with redundant hydraulic configuration. The results presented shall serve as a model for designers to arrive at the required trade-off between the capital expenditure and the required reliability.