Computational Technology Resources - CCP

Keywords: additional systems, excitations, crew comfort, hemi ducts, vibration, wake.

Summary

After the vibration measurements during the sea trials of the HISTRIA PERLA tanker, in full load condition, the values of velocity vibration were found to be within the acceptable limits as required by ISO 6954-1984 standard. The ship is powered by a MAN B&W engine, manufactured in Korea, type 6S50MC-C (9480 kW at 127 rpm); the propeller is a fixed pitch four-blade propeller of 5.80 m diameter.

After the first voyage of the vessel, in heavy ballast condition and rough sea, the ship's crew complained about vibration comfort, especially at the level of upper decks (navigation deck and C deck). The situation required new solutions to avoid crew exposure to these vibrations [1].

The first step was to carry out extended investigations during a voyage of the chemical oil tanker, between Genoa (Italy) - Taranto (Italy) - Odessa (Ukraine). The data recorded during the voyage indicated that the main excitations at the level of navigation deck and C deck were caused by the propeller. The excessive vibrations were generated by the small gap between the superstructure natural frequency and the propeller blade first order excitations. The immediate solution for this ship was to increase the gap between the two frequencies by reducing the propeller rpm in reasonable limits even of this meant to loose speed.

For this sister ship the wake distribution, assumed to be the cause of excitations, was analyzed and it was decided to improve the propeller wake (the incoming propeller flow) for a smoother wake, using additional systems (hemi ducts) to reduce the excitations acting on the ship's aft structure. For this purpose, experimental research was carried out in a towing tank, using a ship model to establish the size and location of the hemi ducts in front of the propeller and the influence on the wake distribution [2,3].

With the new additional systems fitted to the hull of the fifth sister ship MT HISTRIA AGATA, the vibrations were measured in the same points as the first sister ship MT HISTRIA PERLA. The results shown an improvement of the vibration comfort and proved the efficiency of these additional devices [4]. Moreover, no complaints from ship's crew were reported. As expected, according to the towing tank tests, most part of the values recorded onboard the fifth sister ship HISTRIA AGATA was much lower than those recorded onboard MT HISTRIA PERLA Therefore the additional systems proved their efficiency in improving the crew comfort onboard.

References

1: C. Hansen, "Optimisation of active and semi-active noise and vibration systems", University of Adelaide, Australia 2007.
2: A. Jones, C. Norwood, D. Hutt, "Underwater and ship acoustics", Canada, 2007.
3: The Naval Architect, "Eliminating vibration at source", April 2006.
4: J. Lai, Noise, vibration, harshness, Australia, 2006.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £145 +P&P)

	Computational & Technology Resources an online resource for computational, engineering & technology publications
	not logged in - login
Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 88 PROCEEDINGS OF THE NINTH INTERNATIONAL CONFERENCE ON COMPUTATIONAL STRUCTURES TECHNOLOGY Edited by: B.H.V. Topping and M. Papadrakakis Paper 103 The Wake Influence on the Vibration Behaviour of a Ship Structure L. Moraru¹, I. Bosoanca² and R. Pirvulescu³ ¹Physics Department, Science Faculty, University Dunarea de Jos, Galati, Romania ²Diagnose and Measurements Group, Galati, Romania ³DAMEN Shipyard, Galati, Romania doi:10.4203/ccp.88.103 purchase the full-text of this paper Full Bibliographic Reference for this paper L. Moraru, I. Bosoanca, R. Pirvulescu, "The Wake Influence on the Vibration Behaviour of a Ship Structure", in B.H.V. Topping, M. Papadrakakis, (Editors), "Proceedings of the Ninth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 103, 2008. doi:10.4203/ccp.88.103 Keywords: additional systems, excitations, crew comfort, hemi ducts, vibration, wake. Summary After the vibration measurements during the sea trials of the HISTRIA PERLA tanker, in full load condition, the values of velocity vibration were found to be within the acceptable limits as required by ISO 6954-1984 standard. The ship is powered by a MAN B&W engine, manufactured in Korea, type 6S50MC-C (9480 kW at 127 rpm); the propeller is a fixed pitch four-blade propeller of 5.80 m diameter. After the first voyage of the vessel, in heavy ballast condition and rough sea, the ship's crew complained about vibration comfort, especially at the level of upper decks (navigation deck and C deck). The situation required new solutions to avoid crew exposure to these vibrations [1]. The first step was to carry out extended investigations during a voyage of the chemical oil tanker, between Genoa (Italy) - Taranto (Italy) - Odessa (Ukraine). The data recorded during the voyage indicated that the main excitations at the level of navigation deck and C deck were caused by the propeller. The excessive vibrations were generated by the small gap between the superstructure natural frequency and the propeller blade first order excitations. The immediate solution for this ship was to increase the gap between the two frequencies by reducing the propeller rpm in reasonable limits even of this meant to loose speed. For this sister ship the wake distribution, assumed to be the cause of excitations, was analyzed and it was decided to improve the propeller wake (the incoming propeller flow) for a smoother wake, using additional systems (hemi ducts) to reduce the excitations acting on the ship's aft structure. For this purpose, experimental research was carried out in a towing tank, using a ship model to establish the size and location of the hemi ducts in front of the propeller and the influence on the wake distribution [2,3]. With the new additional systems fitted to the hull of the fifth sister ship MT HISTRIA AGATA, the vibrations were measured in the same points as the first sister ship MT HISTRIA PERLA. The results shown an improvement of the vibration comfort and proved the efficiency of these additional devices [4]. Moreover, no complaints from ship's crew were reported. As expected, according to the towing tank tests, most part of the values recorded onboard the fifth sister ship HISTRIA AGATA was much lower than those recorded onboard MT HISTRIA PERLA Therefore the additional systems proved their efficiency in improving the crew comfort onboard. References 1 C. Hansen, "Optimisation of active and semi-active noise and vibration systems", University of Adelaide, Australia 2007. 2 A. Jones, C. Norwood, D. Hutt, "Underwater and ship acoustics", Canada, 2007. 3 The Naval Architect, "Eliminating vibration at source", April 2006. 4 J. Lai, Noise, vibration, harshness, Australia, 2006. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £145 +P&P)
Back to top	©Civil-Comp Limited 2023 - terms & conditions