Research Areas
Some Centre’s major research fields are:
» Fluid borne noise
» Vehicle dynamics
» Control of electrohydraulic servosystems
» Control of large flexible structures
» Magnetic bearing systems
» Fluid systems
» Synthesis and control of dynamic systems
Fluid-borne noise
A prime source of noise in hydraulic systems is pump flow ripple, which produces fluid-borne noise or pressure ripple, resulting in vibration and air-borne noise. The Centre is well known for its research in this area, which has led to the development of International Standards for the measurement of flow ripple. A methodology has been developed to measure the noise-related characteristics of a wide range of fluid power components.
Current areas of investigation include:
- active cancellation techniques for fluid-borne noise using piezoelectric actuation,
- pump condition monitoring using fluid-borne noise measurements.
Two software packages have been developed to support this research and for commercial use:
- FBN - for measurement of fluid-borne noise characteristics,
- Prasp – a MATLAB/Simulink® toolbox for modelling the fluid-borne noise characteristics of hydraulic systems.
Vehicle dynamics
The Centre’s major vehicle dynamics research activities include:
- design and simulation of active and passive suspension systems,
- analysis, simulation and measurement of the stability of towed vehicles,
- modelling and subjective/objective evaluation of steering feel,
- design and control of narrow-track tilting vehicles,
- experimental studies using the Centre’s 4 poster test rig.
The narrow-track tilting vehicle research has included CLEVER (Compact Low Emission Vehicle for uRban transport), a multi-partner European project. The prototype vehicle will be used as a test bed for further work on the challenging issues of tilting and steering dynamics, control and safety.
Control of electrohydraulic servosystems
Research into adaptive and robust control of hydraulically actuated systems has been undertaken in many application areas. A recent project applied an adaptive control strategy to the Centre’s MAST (Multi-axis shaker table), allowing improved tracking despite cross-axis interaction.
Other work includes use of adaptive control for improving the performance of injection moulding machines. It has been found that a simple proportional plus integral controller is adequate for closed-loop velocity control during the filling phase, but the adaptive controller is effective at compensating for significant non-linearities and disturbances during the packing phase.
Control of large flexible structures using hydraulic actuation
The movement of large structures, such as bridges, is often achieved using high pressure hydraulics. Although this approach has been used for many years, significant problems are still encountered due to inappropriate control, slip-stick motion and the flexibility of the structure. The Gateshead Millennium Bridge in the UK has a unique rotating bridge design operated by hydraulic actuators at either side of river. The structure is large (100m wide x 45m high) and flexible A simulation study was undertaken at the Centre to assist in the design of the actuation system; this included modelling the hydraulics, the controller and the flexibility of the structure. Fundamental research into control of flexible structures continues, making use of a hydraulically-actuated flexible beam rig in the laboratory. The research includes application of robust control methods to achieve smooth and controlled lift-off and to minimise the vibration induced in a moving structure.
Magnetic bearing systems
Rotor/magnetic bearing systems possess many advantages over passive bearing systems. These include higher operating speeds, no wear under normal operation, the ability to control rotor position and transmitted force, and the elimination of lubrication supply systems. Disadvantages include the need for protective auxiliary bearings and the associated uncertain rotor dynamics, and the lack of a universal controller design method.
Dynamic modelling and advanced control studies of these systems have included:
- active vibration control of a flexible rotor,
- advanced control to compensate for mass loss and base motion,
- use of wavelet analysis for the control of transient rotor vibration.
Recent work at the Centre has focussed on the analysis and control of the contact dynamics with auxiliary bearings due to base motion or events such as sudden shaft unbalance.
Fluid systems
The Centre’s expertise in modelling and simulation of fluid power has been applied to other fluid system fields. One is life support systems. Mathematical models have been developed for diving and submarine escape systems for British Royal Navy, and also for human respiratory and cardiovascular systems. The latter have been used in studies of artificially ventilated patients. Fuel systems for future aircraft is another area. The current research will lead to the development of 'intelligent' components, such as pumps and valves, that will help to reduce system complexity, and ultimately give improved performance during both refuel and fuel-transfer operations.
Synthesis and control of dynamic systems
Work has been undertaken to develop a methodology for the automated generation and analysis of design variants of a dynamic system, given some desired dynamic specifications. The approach used takes advantage of the unified representation of dynamic systems provided by bond graph techniques combined with systems inversion and genetic algorithms. Expertise in the dynamic simulation of multi-physics systems has resulted in the development of a software package, DYSIM. Inverse dynamic modelling for multi-body systems is being used for the synthesis of mechanisms, as well for real-time control of complex mechanical systems.