Six segmented test model


Live testing of fatigue predictions for USCG


One of the core services of MARIN is to carry out


measurement campaigns on board ships at sea and to analyse the collected data for the development and validation of design tools.


Currently, MARIN is carrying out an extensive project


for the United States Coast Guard (USCG), which aims to increase confidence in fatigue lifetime prediction.


Ingo Drummen i.drummen@marin.nl


18 report P


redicting a hull’s fatigue lifetime involves the prediction of hull loading in a seaway. This is then


compared to the structural capacity. This type of prediction requires input from a multitude of disciplines, therefore in July 2007, the USCG decided to initiate the VALID Joint Industry Project, which is also known as the Fatigue Lifetime Assessment Project (FLAP). In order to ensure the best possible results MARIN was keen to involve other stake- holders and eventually the American Bureau of Shipping, BEA Systems, Bureau Veritas, Damen, Defence R&D Canada, DGA hydro- dynamics, Lloyd’s Register, Northrop Grumman Ship Systems and the Office of Naval Research came on board.


The main goals of the project are to forecast the structural maintenance needs of USCG Cutters and to further improve the under- standing of wave loading leading to fatigue damage, and ultimately, to increase the con- fidence level in predicting this phenomenon.


Dedicated trials The first step in the project was the instrumentation of the ship and during 2007/2008 the USCG Cutter


BERTHOLF was heavily instrumented, which included long base strain gauges, unidirec- tional strain gauges, accelerometers, fatigue damage sensors and a wave radar. In total about 150 sensors were eventually installed.


Dedicated trials were then conducted in August 2009 and several tests were carried out. Trials in waves were particularly important with a total of 80 executed. Trial conditions included several speeds and relative headings in waves with a signifi- cant height ranging between 1 m and 3 m. These conditions are very suitable for the validation of numerical tools and model tests used for the purpose of fatigue lifetime assessment.


Flexible model tests In 2010, model tests were carried out in three phases with a flexible model with a scale of 25, resulting in a length of 4.7 m. In order to make the model flexible, it was cut into six segments and each of these was connected to the backbone. The properties of this backbone were tuned in such a way that the two and three node horizontal and vertical global flexural vibration modes match those of the


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