IN DEPTH ENVIRONMENTAL PROTECTION
URN's impact on mammals includes chronic stress and changes in migration behaviour (image: Talia Cohen, Unsplash)
CFD predictions CFD applications can help identify potential noise sources by modelling cavitation, turbulence and pressure pulses, and simulate how sound propagates These tools also support design optimisation efforts resistance. Additionally, CFD can be used to explore how operational factors such as speed, trim and
Elomatic’s approach combines three key elements: Detached Eddy Simulation (DES), a hybrid CFD model that combines the Reynolds-average Navier- Stokes (RANS) equation and Large Eddy Simulation appendages; and the Schnerr-Sauer model, which is a numerical approach that uses CFD to simulate cavitation in order to calculate vapour fraction using bubble dynamics and mass transfer rates. This method enables accurate predictions of cavitation effects in ship’s propellers or pumps. Lastly, the Williams-Hawkings (W-H) equation – a mathematical model used to predict noise generated by moving – is used to simulate how sound radiates from ship structures into the surrounding marine environment.
Together, these simulations provide detailed insight regarding the likely URN emissions a vessel will generate during the design phase, supporting data-driven decisions related to hull design, propeller geometry, machinery placement and the integration of energy-saving systems.
Incorporating these considerations early in the and help ensure that vessels are better prepared for emerging acoustic regulations.
Several strategies for reducing URN also contribute
reducing vessel speed, applying wind-assisted propulsion or installing air lubrication systems can all help reduce underwater noise while simultaneously lowering fuel consumption. Notably, these solutions are not limited to the design phase to existing ships, broadening their potential impact
These intersections suggest that addressing URN does not necessarily require trade-offs with other performance goals, and can in fact support broader environmental compliance efforts.
measures are expected to account for up to 32% of the industry’s decarbonisation gains by 2050, while also supporting a 5dB reduction in URN, with some estimates reaching as high as 10dB.
With regional limits on underwater noise exposure and voluntary frameworks gaining traction, the momentum toward global regulation is building. The longer shipowners delay in addressing URN, the more expensive and disruptive the transition is likely to become. By acting now, stakeholders can future-proof their assets. ■
IMO: MORE URN DATA REQUIRED
Roel Hoenders, IMO Secretariat head of climate action and clean air, has called on the shipping sector to work towards establishing “a true baseline on URN” to identify “knowledge gaps” when addressing the problem.
Welcoming moves to curb URN as a synergistic complement to efforts to meet IMO’s 2050 decarbonisation targets, Hoenders recently commented: “We have strong data at a local level covering smaller ship types, and insights on global URN impacts; what we need is more data from large ocean-going vessels. There are also ships that we know have energy-saving devices, but the impact on noise is not reported, so it is not possible to estimate how many ships in service merit credit for ‘low noise’.”
THE NAVAL ARCHITECT 27
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