Individual Based Modelling
Subacoustech is currently developing a suite of computational techniques which allow planners and engineers to incorporate animal responses into realistic models of piling and anthropogenic noise in general. The technique used for this modelling is Individual Based Modelling.
Individual Based Modelling is a computational approach for simulating the behaviour and interactions of individuals in a population with the goal of assessing the effects on the system or population as a whole. The response of each individual is governed by simple rules, such as maintaining a distance from a neighbour, which when incorporated into the full simulation show complex or emergent behaviours, such as shoaling or schooling.
The INSPIRE model allows for fast and efficient calculation of received sound levels as a consequence of piling. When this is combined with the dBht(Species) concept responses can be inferred which indicate how animals may react to the sound levels received. Hence, when behaviours such as fleeing are incorporated, the overall exposures received by the animals may be modelled.
We are currently developing models to investigate the response of marine mammal and fish populations to the effects of piling in shallow waters, including the full INSPIRE output to investigate how the detailed modelling affects the sound levels to which animals are subjected, and allows planners to consider how the change to various engineering parameters may affect the ecological impact of the effect of piling.
In parallel, research is being conducted into the use of Individual Based Models for fish in river complexes where sound barriers are being used to reduce the number of animals entering power station inlets. Here, the complex interaction of water-dynamics, fish schooling and the behavioural effects of sound can probably only be modelled by an Individual Based Model.
Detailed modelling of sound and vibration
The INSPIRE model has been used extensively to allow planners to assess the effects of piling noise on marine fauna. The model allows a rapid and accurate assessment of the noise field as a function of range and bathymetry for a given diameter of pile and pre-defined blow energy.
Subacoustech is presently working on extending these capabilities to:
- Deliver time dependent 3-dimensional sound fields which incorporate the effects of sound velocity profiles (SVP) and bathymetry;
- Use finite element models to predict the coupling between vibrational waves travelling through the pile, the waterborne acoustic waves and the substrate;
- Incorporate detailed modelling of the sounds waves and vibration carried through the substrate.
The completed model will allow planners to consider how engineering parameters will affect the transmission of sound and vibration through the water and through the substrate into which the pile is being driven. Furthermore, it will allow comprehensive and accurate prediction of how mitigation measures, such as bubble-curtains will affect the transmission of noise.
Such detailed modelling offers the promise of investigating the effects of mitigation and piling techniques in simulation before resorting to full scale in-water measurements with a corresponding, significant reduction in cost.