A novel hybridized metaheuristic technique in enhancing the diagnosis of cross-sectional dent damaged offshore platform members

Offshore jacket platforms are widely used for oil and gas extraction as well as transportation in shallow to moderate water depth. Tubular cross-sectional elements are used to construct offshore platforms. Tubular cross sections impart higher resistance against hydrodynamic forces and have high torsional rigidity. During operation, the members can be partially or fully damaged due to lateral impacts. The lateral impacts can be due to ship collisions or through the impact of falling objects. The impact forces can weaken some members that influence the overall performance of the platform. This demonstrates an urgent need to develop a framework that can accurately forecast dent depth as well as dent angle of the affected members. This study investigates the use of an adaptive metaheuristics algorithm to provide automatic detection of denting damage in an offshore structure. The damage information includes dent depth and the dent angle. A model is developed in combination with the percentage of the dent depth of the damaged member and is used to assess the performance of the method. It demonstrates that small changes in stiffness of individual damaged bracing members are detectable from measurements of global structural motion.     

Characterization of multi-scale porosity in cement paste by advanced ultrasonic techniques

The effectiveness of advanced ultrasonic techniques to quantitatively characterize the capillary porosity and entrained air content in hardened cement paste is examined. Direct measurements of ultrasonic attenuation are used to measure the volume fraction and average size of entrained air voids and to assess variations in intrinsic porosity - as influenced by water-to-cement ratio (w/c) - in hardened cement paste samples. For the air entrained specimens, an inversion procedure based on a theoretical attenuation model is used to predict the average size and volume fraction of entrained air voids in each specimen, producing results in very good agreement with results obtained by standard petrographic methods and by gravimetric analysis. In addition, ultrasonic attenuation measurements are related to w/c to quantify the relationship between increasing porosity (with increasing w/c) and ultrasonic wave characteristics.     

Guided Lamb Wave Propagation in Composite Plate/Concrete Component

This research examines the propagation of guided Lamb waves in fiber-reinforced polymer (FRP) bonded components, establishing the effectiveness of combining laser ultrasonic techniques with a time frequency representation (TFR) to experimentally measure the dispersion curves of a concrete component repaired with a FRP plate. A TFR is used to operate on experimentally measured, guided Lamb waves to resolve a FRP bonded component's individual modes and generate its dispersion curves. The objective of this research is to demonstrate that it is possible to develop the dispersion curves of FRP bonded components from a single, experimentally measured guided Lamb wave. The experimental results show that the stiffer the bond, the more deviation from the behavior of a free plate specimen, and the less modes that are present.     

Characterization of entrained air voids in cement paste with scattered ultrasound

This research develops a technique that uses the attenuation of ultrasonic waves to characterize the average size and volume fraction of entrained air voids in hardened cement paste. Quantitative knowledge of entrained air void size and distribution helps ensure that an adequate design strength is developed, while maintaining resistance to freeze-thaw damage in cement-based materials. Ultrasonic attenuation coefficients obtained from pulse-burst signals are measured in the frequency range of 500 kHz–5 MHz. From these parameters, the average size and the volume fraction of the entrained air voids are determined using a combination of an ultrasonic scattering model and an inversion algorithm. Experiments are performed on specimens produced with and without entrained air voids. There is a good agreement between the model prediction and the experiments in these systems that contained <10% by volume of entrained air voids.