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PRESS
RELEASE
Baltimore, Maryland
NOISE-CON 2010
2010 April 19-21
Shipboard Structureborne Noise by Resonant Interactions of Two Torsional Vibration Modes, a talk given by J&A's Senior Engineer, Darrell Milburn at the 2010 Noise-Con Conference. He offers this abstract.
In recent years several occurences of similar engine-firing rate structureborne noise resonance were observed in the passenger areas of different ships. All were V-16, four stroke, high speed diesel propulsion systems, including engine vibration isolation mountings and remote reduction gears. The engine-firing rate noise path entered the ship structure through the reduction gear mounting feet. Interactions of two torsional vibration modes with nearly equal natural frequencies caused the noise: one mode with the maximum amplitude in the engine crank shaft, the other in the propeller shaft/reduction gear. Over a narrow range of engine speed, the firing rate energy excited both modes. The resonant torsional vibrations were transmitted to the structure through the reduction gear bearing reactions. In the observed cases, the amplitude of the torsional stresses at resonance were well within the safe limits of the driveline components, raising no concern to vibration analysis assessing only the risk for mechanical failure. The paper outlines the system parameters related to the occurrences of these resonances, permitting noise control engineers to diagnose this problem, or to identify 'at risk' installations during the design phase. Noise control recommendations are presented as case studies with examples of the achieved noise reduction results.
Improvement of Acoustical Comfort within Dwellings
Senior Engineer, Aaron Korby, recently conducted several residential application projects in Massachusetts and Rhode Island, evaluating noise transmission through the floor/ceiling assembly, with noise coming from the restaurants into apartments located above them, or noise transmitted through the walls separating apartments from one another, or noise coming from common areas. Apparent STC rating of floor/ceiling assemblies and walls were evaluated in accordance with ASTM E336-09 (including reverberation time measurments at receiving locations). Comparison of the existing STC ratings to the Massachusetts and Rhode Island Building Codes was done. Recommendations for the improvement of acoustical comfort in the dwellings were outlined.
A survey of outdoor ambient daytime and nighttime noise was done at an expected Dunkin' Donuts construction location in Swampscott, Massachusetts for the purpose of establishing the baseline for predicting the noise impact of a drive-through on the surrounding residential area. Calculations of expected noise which might affect the residents' acoustical comfort were done, and the results were compared for compliance with the Commonwealth of Massachusetts noise regulations governing the noise from the new commercial establishments being built in the mixed commercial / residential areas. J&A has testified at the meeting of the City Hall Building Committee, presenting the results of the noise prediction to the committee and the public.
Upon the completion of the Dunkin' Donuts construction, actual noise impact on the closest residences of Summit Estates was mearsured by J&A and found to be in lilne with the noise prediction.
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J&A Enterprises, Inc., in its capacity as a noise and vibration consulting company, is proud to say that it has been involved in overseeing the noise and vibration specifications and design of M/Y CAKEWALK prior to the boat's construction, as well as engineering oversight during construction.
An announcement of the ship's launching can be found at the following Marinelink URL address,
http://www.marinelink.com/news/cakewalk-largest-yacht335180.aspx. The announcement states,
 "On August 8, Derecktor Shipyards launched the 281-ft motor yacht Cakewalk, the
largest yacht (by volume) ever built in the U.S. The six deck, 2,998 gross ton vessel floated off Derecktor’s new 4000 ton dry-dock into the waters of Bridgeport harbor, after several years and many thousands of skilled labor hours.
Cakewalk was designed by Tim Heywood Designs with Naval Architecture by Azure Naval Architecture. Interior design was by Dalton Designs, Inc. Literally dozens of subcontractors from engineering firms to security specialists participated in the project. “We certainly could not have done it without them” commented Gavin Higgins, VP of Business Development at Derecktor. “Some of the world’s most experienced and skilled specialists put their expertise into this job. You cannot successfully build a yacht of this size and complexity without having that sort of talent available.”
The yacht will remain at Derecktor for the next few weeks undergoing final outfitting and sea trials. She is scheduled to make her much-awaited debut at the Ft. Lauderdale International Boat Show in October."
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2002
- 2003 Large Aluminum MCA Yachts
In
the period June 2002 through Mar 2003, J&A has participated
in the delivery of three large (over 50 m ) aluminum yachts built
to the demanding classification rules for Large Yachts, under MCA.
The yachts: Anson Bell (Palmer Johnson), Aussie Rules (Oceanfast),
and FELICITA West (Perini) are among the first aluminum boats constructed
in strict compliance with the MCA rules for large yachts. All three
boats are constructed to very demanding specifications regarding
noise and vibration, and the finished product is superb, resulting
in very satisfied owners.
J&A
has designed innovative, fire rated insulation systems, meeting
the latest MCA requirements calling for "steel equivalent"
or greater protection of structural elements. Our ground breaking
design has been executed while, at the same time, maintaining the
high degree of excellence of noise and vibration requirements for
which we are noted.
J&A
responsibilities went beyond insulation design, and included machinery
mounting, HVAC, exhaust, and propeller design review.
These,
first large aluminum boats built to MCA, set some of the current
ground rules within the evolving MCA rule interpretation, and J&A
is prepared to do follow-on when aluminum is the preferred material
for large yachts, in sail or power.
High
Speed Current Projects
J&A
are the noise control consultants for the design and construction
of the first large Catamaran Ferry (73m) constructed in the U.S.A.
The vessel in fabrication at Dereckter Shipyard, Bridgeport, CT
must perform to specified noise standards within a very restricted
weight budget. J&A modeling of noise transmission in the hull
and of structural dynamics of machinery mountings and of global
structural elements is helping to achieve the design requirements
in a cost efficient and weight effective fashion.
J&A
engineering has verified methods of weight savings which will allow
the noise and vibration requirements to be met, with great benefit
to the program objectives.
The
Yacht Report, April 2003, Issue 52
To read The Yacht Report's interview with the owner of Aussie Rules
and get Greg Norman's views concerning the developments in the marine
industry in general and Aussie Rules in particular, please click
here.
Mr. Norman states, "I can happily and proudly say that Aussie
Rules is the quietest and smoothest yacht that I have ever cruised
on and I have chartered and owned several yachts including some
of those from the reputed best yacht builders. When anchored in
various atolls in the Pacific she sat perfectly in the water, in
both heavy and light ship conditions. Her stability is incredible
and when sitting in my cabin with the engines at almost full load
she is dead quiet. So all in all, I am very pleased with the end
product."
Project
2002, International Exhibition & Congress Centre, Amsterdam,
FAI in conjunction with METS 2002, hosted by The Yacht Report, November
18th - 20th, 2002. To read Joe Smullin's paper presented to the
international yachting audience entitled, "Noise
and Vibration Specifications for Large Yachts", please
click.
The papers as posted or printed are private property and may not be copied in part or in whole without direct written consent from Joe Smullin.
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