Conceptual re-design techniques utilised for optimisation of a mine countermeasure towed acoustic generator control system

Abstract

Acoustic replication of a surface vessel is achieved by use of an electrohydraulic towed generator emitting a range of low and audio frequency signal spectra patterns within a specified bandwidth. System performance and endurance inadequacies inherent within the design for over a decade necessitated a complex modelling and simulation exercise for key parameter identification of problematic subsystem failures. Previous system updates were based purely on experimental testing and subsequently proved ineffective when implemented. The system comprises three key areas, each with its own complex transient behaviour. These are the input transmission drive, the hydraulic actuation system and the electronic feedback control system. The complex interaction between these three subsystem could only be assessed using modern computer simulation techniques to assist experimental development. This paper describes the development and application of simulation techniques to overcome the reliability and endurance failures. The paper identifies the process involved in failure categorisation, subsystem optimisation, hardware development and results achieved. In essence, the units problems manifested itself as a destructive resonance which produced excessive pressure oscillation in the system service lines. The main system problem was initially thought to be due to the electrohydraulic actuation and feedback control system; however subsequent instrumentation to obtain torque fluctuations on the input drive to the system demonstrated that the original simulation model did not fully represent the chain of events leading to the problem. The model was improved by the addition of a complex input drive comprising four degrees of freedom with representative stiffness and backlash terms. This was shown to reproduce the observed behaviour and highlight the input drive as the prime cause of system malfunction. The simulation provided precise input drive parameter changes necessary to strengthen the drive members and thus overcome the input resonance problem.