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. 

Illustration of a submarine in side view, depicted in light blue on a blue background. The submarine is elongated with suggested details such as a tower and tail fins.

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.

Diagram with several horizontal boxes connected by lines. Five boxes side by side at the top, with a vertical row of seven boxes below. A blue line runs from the top left box to the middle of the bottom row.
A diagram with a dashed downward line showing several small spikes and dips. At the top is a text box labelled ‘Sound Transfer Function Gearbox Coupling’. The vertical axis is on the left and the horizontal axis is at the bottom, both without lab
A diagram with a black, jagged line running from the top left to the bottom right, showing several peaks and dips. At the top is a light blue text box with the words ‘Structure-Borne Noise Levels Gearbox’. On the left is the vertical axis, at the bottom is the horizontal axis, both without labels.
Diagram with a blue, sloping line running from top left to bottom right, showing several small deflections at the end. Above it is the text “Sound Transfer Function Engine Coupling”.
Diagram with a black, irregular line pattern on a white background. On the left is a vertical axis, at the bottom is a horizontal axis. At the top is a text box with the inscription “Structure-Borne Noise Levels Engine”.
Diagram with a blue dotted line that initially runs flat and then shows a peak on the right. At the top it says ‘Dynamic Transfer Stiffness Upper Mounts’.
Diagram with blue dotted line that starts flat and shows several upward waves. At the top it says ‘Dynamic Transfer Stiffness Lower Mounts’.
A technical illustration shows several interconnected components in a horizontal arrangement. On the left is an elongated rod or shaft connected to a smaller element. This is followed by a rectangular block with a gear symbol. To the right of this is a larger, elongated component with several parallel lines and small circles, which rests on a rail or platform. Blue, curved lines are shown around the components.
Exploded view of a mechanical component with several individual parts, including cylindrical and spherical components arranged in a line. Thin lines connect the parts with labelling points.
Diagram with a grey line running diagonally downwards from the top left and then continuing horizontally. Vertical axis on the left, horizontal axis at the bottom. Text box at the top labelled “Reference Foundation Impedance”.
Graphic in the form of a circular diagram with several curved arrows arranged around a central element. Text is located in the centre, surrounded by additional text fields along the arrows. On the right is a rectangular area with additional text.
Diagram with several coloured lines running from left to right. Some lines are horizontal, others rise slightly. On the left is a vertical axis, at the bottom a horizontal axis. At the top is a text box labelled “Rigid Body Modes”.
Diagram with three lines: a black dashed line, a red dashed line and a black dotted line, all sloping slightly from left to right. A vertical axis on the left, a horizontal axis at the bottom. A text box at the top labelled “Limits”.

How Vibro-Acoustics Contribute to VULKAN´s Holistic Approach

Four small technical symbols in a row, each consisting of black lines and blue accents. The shapes appear to be stylised representations of mechanical or structural components.

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.

Inhouse Acoustic Measurement

Technical drawing of a machine assembly in simplified form. In the center is a blue cylindrical element, with gray components on the left and right that appear to be brackets or bearings.
Accoustic Test Bench for Couplings
Technical drawing of a machine assembly in simplified form. In the centre is a blue cylindrical element, with grey components on the left and right that appear to be brackets or bearings.
Accoustic Test Bench for Mounts

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.