MARINE DESIGN
TESTING
On the high seas
Vibro-Acoustic Testing
CETENA Ship Research Center uses LMS Test Lab for a variety of standard � and not so standard maritime equipment testing. Everything from worst-case scenario shock tests to the acoustic resonant frequency of a Murano chandelier on a mega-cruise ship is subject to the expert scrutiny of the CETENA testing team in Genoa, Italy. And this team counts on the LMS testing solutions that can deliver results in minutes. Like the ocean itself, testing sea-going vessels for vibration and acoustics is an awesome world all its own. Measurement systems and analysis software are much the same as those used in automotive, aerospace and other industries. Obviously, the scale and scope of testing ships is far beyond that of most other applications, since these immense and complex machines are the world's largest moving structures. Room-size on-board equipment such as generators and pumps are likewise massive � and noisy � with structure-borne vibrations traveling throughout the ship's all-metal skeleton and skin unless muffled at the source. Another safety concern is that equipment must continue operating without failure, even under extremely adverse conditions. Qualification tests must be completed quickly and accurately to the strictest of standards. In this business, pressures are unrelenting, stakes are high and there is little room for error. But it's all in a day's work for engineers at CETENA S.p.A. who count on LMS Test.Lab solutions for qualification and vibro-acoustic tests. The research center is a subsidiary of Italy-based Fincantieri S.p.A.The LMS test system at CETENA consists of a 24-channel LMS SCADAS III and LMS 24-channel SCADAS mobile data- acquisition system with LMS Test.Lab software for signal conditioning, data analysis, results display, test control and report generation. With this LMS Test. Lab environment, CETENA performs qualification tests on shipboard equipment such as valves, electrical generators and electronic control systems in its state-of-the-art lab located at Fincantieri's Riva Trigoso Shipyard in Genoa, Italy. The tests validate that components will maintain normal operation while subjected to shipboard shock and vibration.
Studying Worst-Case Scenarios
(Photo courtesy of CETENA/FINCANTIERI)
Shock tests are performed to study the effects of an underwater explosion, a collision or other one-time event involving extreme transient force and displacement loads. A series of six shocks are applied by releasing a 1,500-kg hammer that impacts a heavy steel
In addition to its extensive work on shock and vibration qualification tests and acoustic holography, CETENA uses LMS Test.Lab in rather unconventional ways for the cruise ships designed and built by parent company, Fincantieri. One such project was to verify that an expensive Murano glass chandelier would not break due to vibrations encountered on a cruise ship. With the chandelier fitted with accelerometers and suspended from a fixture mounted on the vibration table, engineers performed a vibration sweep to find the item's resonant frequency and then subjected it to vibrations for several hours. After the ship's interior designers viewed the results of the test, they confidently incorporated the chandelier into the ship's d�cor.
platform on which the equipment specimen is mounted. When the hammer is released, a loud "thud" reverberates through the lab as the platform and equipment are jolted. To examine these shocks, CETENA uses the LMS Test.Lab Shock Response Spectrum module, which accounts for input acceleration over a time step to calculate the shock response spectrum using measured signal data acquired from accelerometers mounted at locations across the test specimen. The analysis consists of two steps: calculation of an impulse correction to account for variations in input loads, followed by primary and residual response calculations in terms of acceleration, velocity and displacement. Integrating signal analysis calculations within the data acquisition system increases test productivity and avoids the limitations of data conversions and interoperability difficulties encountered with multiple systems. Also, the ease with which tests can be set up and executed allows CETENA's engineers to more readily delegate routine tests to a staff of technicians. Interactive worksheets and templates for the various types of qualification tests guide personnel step-by-step through the test process with interactive prompts and numerous default settings. A graphical user interface shows prompts that indicate what's to be done, so for many applications technicians point and click to configure tests. In this way, the group manager can more fully utilize the different skill sets of the testing staff, with technicians running fairly routine tests very quickly and engineers focusing on solving more complex problems and coordinating projects.
38 Maritime Reporter & Engineering News