Consulting in Ship Acoustics

GL Noise Review
The noise review is conducted based on the general arrangement plan (GAP) and main ship’s and machinery data of the new building project. It should preferably be carried out in an early project stage – at best before negotiations are started between owner and shipyard. The client will get a quite clearly picture about the comfort situation to be expected on board. GL experts trustworthily provide advice whether a GL.NoisePredictionAnalysis (GL NPA) should be ordered or not.

GL Noise Prediction Analysis (GL NPA)
A sound pressure level prediction carries out for all relevant crew accommodation and working spaces on board as well as for owner and passenger accommodation and open recreation spaces.
Based on the data of the first design and the structure- and airborne noise source levels of the main noise source the A-weighted overall sound pressure levels will be predicted and compared with the specified sound limits. If necessary, additional noise control measures will be recommended aiming to achieve the sound limits specified.

GL Driving-point impedance analysis
The acoustical behaviour of ship foundation investigates in the frequency range up to 250 Hz. The calculation should be conducted in the early design phase and ensures that the vibration isolators of resiliently mounted engines and ship board equipment can work well.

The coarse FEM-model of the ship foundation is created and delivered by the client according to our standards. The refinement of this FEM-model is done by GL. The driving-point impedance and the static stiffness are normally calculated ‘in air’ and evaluated for each location of vibration isolators of the resiliently mounted unit to be considered.
The driving-point impedance calculation can be offered also for rigidly mounted gear boxes, thrust bearings, shaft bearings, shell structure above propellers etc.

GL Window Acoustics
GL Window Acoustics deals with the calculation of the acoustical behaviour of certain window packages and mainly applies on Mega Yachts and Passenger vessels. The knowledge of the structure-borne sound radiation index is essential to know because it is the key to trustable predict the sound pressure level portion of windows in receiving rooms with high accuracy. Based on the acoustical behaviour of the relevant window package the necessity and importance of other noise control measures to be foreseen can be objectively evaluated and optimized by the acoustic consultant. With the aim to maintain specified overall sound pressure level limits in certain spades GL Window Acoustics should be applied during the basic design stage of a newbuilding, conversion or refitting.

GL Window Acoustics is a well validated service which is based on the application of a special acoustic finite element program combined with our professional experience.

The service aims

• to avoid resonance of natural frequencies of the window package with the basic excitation frequencies of main noise sources expected on board, e.g. the first propeller blade passing frequency
• to calculate the structure-borne sound radiation index of a certain window package induced by the structure-borne sound present in the surrounding ship structure
• to calculate the airborne sound insulation index R of a certain window package

This service can also apply on wheelhouse window constructions of work boats, cargo vessels etc to avoid resonance with relevant main excitation frequencies of main engine or propeller.

GL Room Acoustics
Requirements on the acoustic quality of a receiving room, e.g. owner’s salon, owner’s state room, cinema, restaurants, theatre etc mainly depends on the main dimensions and the utilization of the room. Before room acoustic simulations starts the contemplable utilization of the room is agreed upon with the owner.

The current state of the acoustic quality will be calculated based on the outfitting of the room as planned by the customer. The results of the acoustic simulation will be evaluated according to the acoustic demand of the room or (inter-)national standards. If necessary, proposals can be given to improve the speech intelligibility or the acoustic privacy e.g. in order to allow people to enjoy their dinner and converse in a normal level of voice. A high level of acoustic privacy means that the conversation at any one table cannot be easily understood or even heard at the neighbouring table. The room acoustics simulations should be conducted in the early design phase of a project.

GL Check Exhaust Gas Damping System
The complete exhaust gas system of a diesel engine will be investigated concerning the current stage of the acoustic damping behaviour of the system. The exhaust gas system starts after turbo charger, ends at funnel opening and allows the calculation of the sound pressure level to be expected at funnel top.

Analytical and FEM prediction tools are applied. The calculation should be conducted in the early design phase of the project. If necessary, proposals can be given to improve the sound attenuation of the whole exhaust gas system, e.g. to optimize exhaust gas silencer or to install a well tuned exhaust gas resonator in addition.

GL UW-radiated Noise Package – Navy Surface Vessel
Together with the shipyard, GL’s consulting normally starts in the early project phase selecting machinery and their arrangement as well as optimizing the hull lines aiming to reduce propeller cavitations phenomena and flow noise:

• By means of our professional experience and standardized local simulation models GL provides advice to the shipyard how to design the shell structure to reduce the underwater (UW) radiated noise of local shell structure elements like plate fields, stiffeners and panels.
• Based on the first steel design of the hull GL applies FEM and NoiseFEM calculations to predict the UW-radiated noise below propeller cavitations interception speed and at sonar speed of the vessel. GL conducts FEM driving-point impedance calculations on relevant ship foundation. All prediction results will be compared with the sound limits and discussed in detail with the customer to find out the final noise and vibration concept including noise measurements. Decision should be made before the design phase of the vessel and enter into final negotiation with suppliers.
• At certain steps of the design, construction or building phase of the vessel the UW-radiated noise prediction will be updated on final results of the design e.g. based on FAT of main engine and relevant ship board equipment on supplier’s test bed foundation, driving-point impedance calculations or measurements to be taken on board etc.
• GL’s expert supports the customer during delivery phase, conducts indoor sound level measurements and structure-borne noise measurements top be taken during the UW-radiated noise range measurements.
• At certain steps of the project, like the design, building, delivery phase and FAST test GL provides the customer with noise reports which contain all relevant prediction and measurement results of the step to be considered.

Noise survey on board
Noise surveys will be undertaken together with the client and aim to ensure best possible installation of noise abatement measures on board. Consideration will be given to relevant noise control measures, e.g. floating floors, lining, etc as well as to the relevant main and auxiliary machinery, pipe systems, ventilation etc.

Contact: shipacoustics@gl-group.com