Projects: noise and vibration

Aircraft cabin noise

Mike Blakemore has considerable experience in the modelling of noise transmission through complex structures, including structure-borne sound transmission in submarines and, more recently, in civilian aircraft. During his time with QinetiQ he carried out research on aircraft cabin noise and was instrumental in the development of the COSINE tool (Cabin Optimisation Software for the Internal Noise Environment) for the prediction of cabin noise resulting from external noise sources, including the engines and the turbulent boundary layer flow over the aircraft. This work formed part of a collaborative programme between QinetiQ and Boeing.

Cambridge Applied Physics continues to work with QinetiQ and Boeing to develop the software further, and is in partnership with QinetiQ to provide both consultancy in aircraft noise issues and licensing of the COSINE software.

Aircraft radiated noise

To predict accurately the noise on the ground due to an aircraft in flight requires a detailed knowledge of the noise radiated from the aircraft, in terms of its frequency content and its directivity, and an accurate model for calculating the effects of geometrical spreading, atmospheric absorption, terrain, meteorology and atmospheric turbulence. Cambridge Applied Physics continues to work with QinetiQ to refine and apply QinetiQ’s source representation and characterisation methods, and its propagation modelling software, which is based on advanced ray tracing and parabolic equation (PE) methods.

Applications of this capability to date include noise characterisation, particularly of military airborne vehicles, mission planning and environmental impact assessments.

Dynamic modelling and analysis

Very strong cross-currents can cause a pipeline laid on the seabed to go into self-excited oscillation, slamming repeatedly against the seabed and eventually damaging the pipe. This little-known phenomenon is not normally a problem for pipeline engineers, since very strong cross-currents are needed for it to be strong enough to lift a pipeline.

However in some areas of the world, cyclonic storms are strong enough and frequent enough for the problem to be taken seriously. Cambridge Applied Physics carried out a thorough analysis of the phenomenon to predict the risk of damage to a specific pipeline offshore Australia.

A numerical analysis of the dynamics was combined with a Monte Carlo analysis based on sea-state statistics to estimate both the fatigue life of the pipeline and the uncertainty in it. On the basis of Cambridge Applied Physics’ recommendations the anchoring arrangements for the 40km line were changed, saving the client several million dollars.

Piling shock

Pipelines are normally assembled onshore, together with switchgear which allows pipeline flows to be controlled remotely. The manifolds carrying the switchgear are piled into the seabed. The contractor must decide whether to attach the delicate switchgear before the assembly is towed out to sea and sunk (and risk shock damage during piling) or after piling (incurring the added costs of using divers to install the switchgear on the submerged manifold).

Cambridge Applied Physics produced a rapid dynamical modelling program to allow the contractor to predict peak shock levels at the switchgear during piling, so that this decision can be made more sensibly.

Wind turbines

Complaints about noise from onshore wind farms are common in the UK, and Cambridge Applied Physics has been involved in noise reduction work for many years. Reducing the noise radiation from a large built-up structure is not straightforward, and requires a proper understanding of the acoustics of the structure. Cambridge Applied Physics has used two different analytic tools for doing this: Noise Transmission Path Audit (TPA), and Statistical Energy Analysis (SEA). Following a detailed analysis, clients have been able to apply noise reduction methods cost-effectively.