Measurement of global loads on a full-scale SES vessel using networks of fiber optic sensors

A method for measurement of global loads on a vessel, using strain measurem ents from a network of strain sensors and extensive finite-element analyses (FEA) with idealistic load cases, is presented. The sensors are attached a t carefully selected locations at a cross section amidships, where the most significant loads have their maximum values. The finite-element (FE) strai n values are used in precalculations to reduce the computational effort to solve a set of linear algebraic equations in real time. The method has been successfully tried out on the full-scale surface effect ship (SES) KNM Skj old (47 m, 270 tons, and 50 knots) instrumented with a network of fiber opt ic Bragg strain sensors. The seakeeping tests were performed in the North S ea (1999) in sea states 3, 5, and upper 6. Other parameters that were varie d during the test program were the heading, forward speed, and on/off-cushi on. The loads measured during the tests were the sagging/hogging moment, th e horizontal bending moment, and the longitudinal twisting moment. The meas ured loads were compared with respective dimensioning loads based on DNV ru les (HSLC) (1996). The results showed that when the vessel is subjected to bow flare slamming impacts, the sagging moment exceeded the DNV dimensionin g value by a factor of 1.6, indicating that the HSLC rules do not provide c onservative global loads when these extreme events occur. However, the peak loads were well within the design limits.