Ultrasound Defect Localization in Shell Structures with Lamb Waves Using Spare Sensor Array and Orthogonal Matching Pursuit Decomposition

Lamb waves have multimodal and dispersion effects, which reduces their performance in damage localization with respect to resolution. To detect damage with fewest sensors and high resolution, a method, using only two piezoelectric transducers and based on orthogonal matching pursuit (OMP) decomposition, was proposed. First, an OMP-based decomposition and dispersion removal algorithm is introduced, which is capable of separating wave packets of different propagation paths and removing the dispersion part successively. Then, two simulation signals, with nonoverlapped and overlapped wave packets, are employed to verify the proposed method. Thereafter, with the proposed algorithm, the wave packets reflected from the defect and edge are all separated. Finally, a sparse sensor array with only two transducers succeeds in localizing the defect. The experimental results show that the OMP-based algorithm is beneficial for resolution improvement and transducer usage reduction.

Assessment Of LNG Bunkering Accidents

The maritime safety is of great concern for the entire maritime community. Ships using LNG for propulsion are already sailing the seas, but the majority of the ports are not yet prepared for this kind of supply. As the process of LNG bunkering is only seemingly similar to traditional oil bunkering or liquid loading, dealing with the technical and safety challenges is much more subject of investigation. In this paper, the dispersion part of the consequences of LNG release, pooling, evaporation and dispersion during the future bunkering operation in the port of Koper, Slovenia, where the populated area (city) is located in close proximity are examined. We follow the comparison of three different tools, namely the Unified Dispersion Model (UDM) implemented by the software PHAST from DNV-GL® and two CFD (FDS – Fire Dynamics Simulator from NIST and Ansys Fluent®) in the same case scenario. Geometry, initial and boundary conditions are assumed to be the same as far as possible, according to the limitations of the respective software tools.