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Thursday, August 22, 2019

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INA Seminar focuses on Sonar dome & Energy efficient ships

Posted to INA Seminar focuses on Sonar dome & Energy efficient ships (by on April 24, 2013

Focus on techniques relating to bow sonar dome and the use of hydrodynamics for designing efficient ships

For the naval architects, the quarterly seminar organized by the Institute of Naval Architects (INA) is an opportunity for advancement - learn more about the latest techniques employed in allied fields, like garnering information on innovative strategies in vogue and enjoying the prospects of up-scaling knowledge and expertise.  The event held on 20 April, 2013 showcased two motivating and value added presentations. The first was on “Structural Integration and Fitment of Bow Sonar dome for a destroyer class ships" being undertaken at the Mazagon Docks where naval vessels are being built. This presentation was made by R. G. Goilkar, Chief Manager, Design Structural) of Mazagon Docks Ltd. The other was by Leif Broberg, Managing Director of FLOWTECH International of Sweden, who revealed a number of applications for energy saving techniques offered by SHIPFLOW.  

Bow sonar dome enclosures are specially designed to house underwater warfare detection systems and sensors. Mr. Goilkar explained the need to cut off noises from different sources considered detrimental to effective sonar usage. “Sonar dome is a streamlined protective covering for sonar equipment such as the transducer, sonar projector or hydrophone and associated equipment, while offering minimum interference to sound from external forces, foreign objects and reduced self noise,” he said. “Dome is designed with respect to sonar acoustics performance and mechanical strength. They generally weigh 6.5 tons. The self noise (namely noise other than that from target reaching sonar system) are generated from machinery, propellers, etc.”

Mr. Goilkar explained various methods employed for reducing self noise including damping, absorption and baffling. Various challenges that are experienced in this regard have been addressed. Techniques that have been developed have been integrated into the system. “The Indian Navy has placed orders for indigenous development of sonar domes,” Mr Goilkar stated. "Interested private manufacturers and others are being encouraged to come forward for supplying these domes for which Mazagon Docks Ltd is ready to assist with R & D and provide all help and information.

Most conventions of the International Maritime Organization coming into force have so far focused mostly on manning, ship operations, etc. But the expenditure on fuel, which is the biggest, had almost got ignored. Now there has been a change and a dramatic shift likely in the coming years. The Energy Efficiency Design Index (EEDI), for new ships, and the Ship Energy Efficiency Management Plan (SEEMP) for all ships are in place. But simultaneously, hectic research is on to bring down the cost for running of ships. The INA showcased some of the better results at the seminar.      

In this regard, Leif Broberg spoke about hydrodynamic design which is an important aspect of the design efficient ships. Hydrodynamics design can for example address selection of basic design parameter including hull lines, energy saving design, vibration, shallow or confined water effect, new design / retrofitting of existing ships or operation – optimal ship routing and optimal positioning. He narrated some case studies to present in-depth details during his presentation.

He referred to some case studies and solutions provided by Flowtech in his presentation. For an ordinary single screw vessel there are substantial rotational energy losses in the propeller slip stream. The pre-swirl stator is one of the most attractive devices to recover that energy since it is based on well proven energy saving mechanisms and it is simple, robust and cost effective. The pre-swirl concept consists of stator blades mounted on the stern boss in front of the propeller so that the flow is re-directed before it enters the propeller disc. The stator does not, on its own, save energy or create a forward thrust; in fact it adds resistance; but its interaction with the propeller blade improves the propulsive efficiency and results in a power reduction. Due to its complex nature, the pre-swirl stator has been both successful and unsuccessful, depending on the application. Therefore, the application of pre-swirl has to be integrated with hull design to find an optimum stator configuration.  

Hull form designers are constantly confronted with the problem of how to modify a given hull geometry to improve hydrodynamic performances. Fore body hull forms can be optimized relatively easily by minimizing wave resistance, but design of aft body hull forms has to be compromise between the conflicting requirements of acceptable wake flow quality and speed performance. 

Shipflow design packages provide very efficient capabilities for selecting the best forebody design based on Lackenby shift and an optimization module. The user interface supports designer work by integrating pre and post processing capabilities. The hull form modification, optimization and CFD tools are combined into one package to create an efficient design environment.

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