Low Noise Ship Design
Acoustic signatures are of critical importance in the naval domain. The specific requirements depend on the type of vessel and its intended operational use and they pertain to both the permissible underwater radiated noise and the interior noise levels aboard ships. By defining noise budgets to all ship units, individual noise sources and components, it is ensured that the overall design remains acoustically discreet and thereby making the vessel more difficult to detect.
A significant portion of unwanted vibrations and noise originates in the engine room. The decoupling of machinery – such as gensets, marine diesel engines, electric motors, gearboxes and pumps – is a key measure for reducing underwater radiated noise. It prevents vibrations and noise from being transmitted directly from the machinery to the ship’s hull via the foundations, thereby avoiding the propagation of sound waves into the water or within the vessel.
Example of a Component Diagram
The diagram shows the transmission paths of vibrations and noise in a mechanical drive train. The main sources are the engine and transmission, which are connected to the structure via mounts and couplings. The vibrations are transmitted to the foundation and ship structure via the upper and lower mounting levels and the intermediate frame. From there, they can spread further into adjacent areas and ultimately be radiated as underwater sound or airborne sound in cabins. The diagram illustrates the coupling between mechanical components and structural elements, which is relevant for acoustic and dynamic analysis.
The selection of elastic elements – such as couplings and resilient mounts - for isolating noisy, vibration intensive machinery must ensure that required limit levels are met at defined positions i.e. foundations or on (the lower side of) the intermediate frame - without compromising other performance criteria of the system. Comprehensive analysis requires consideration of all relevant noise sources, the dynamic frequency dependent properties of the elastic elements as well as the interaction between components when predicting vibrations and structure-borne noise behavior. It is equally important to consider the impedance of the foundation and, where applicable, the dynamic properties of the intermediate frame, as these significantly influence the overall vibroacoustic response of the system.
The necessary calculations are carried out using the VULKAN Acoustic Toolbox (VAT) in combination with advanced numerical simulations based on the finite element method. The most important input variables are presented on the previous page. A decisive factor for project success is a close, solution-driven collaboration with the customer’s acoustic specialists throughout each stage of the design process.
VULKAN lays the groundwork for optimal system design through precise product characterization conducted on proprietary test benches. In this process, the dynamic transfer-stiffness properties of our rubber mounts are measured in translatory directions in accordance with applicable standards. The standardized measurement procedures that are applied enable precise evaluation of vibro-acoustic and dynamic behavior under operational conditions.
The structure-borne noise characteristics of our highly flexible rubber couplings are determined using a custom-designed test bench at the VULKAN Test Center. Employing a dual shaker system, we can measure both transmission loss and insertion loss in axial, radial, and torsional directions, with dynamic force excitations reaching up to 16 kN.