The simulation of ultrasonic imaging in the case of the objects with a complex geometry

The main objective of the ultrasonic non-destructive testing (NDT) applications is to detect dangerous defects in the various constructions. The parameters and geometry of defects is very important information determining lifetime of constructions or components. In conventional ultrasonic NDT methods, based on the measurement of the amplitude and delay time of reflected signal are used. Such an approach enables evaluate size and position of defects only approximately. Most accurate is time – of the flight diffraction (TOFD) technique, which allows measuring depth of defects. Additional application of the SAFT or tomographic algorithms enables to increase accuracy even more [1,2,3]. Nevertheless, practical applications of these methods usually are complicated due to a lack of a sufficiently accurate information about ultrasound propagation conditions, such as the propagation velocity, angle, wave fronts and etc. Additional problem arises due to the fact that basic algorithms of these techniques are developed for the direct reflections only [1,2,3]. On the other hand, due to the object geometry or limited access very widely the signals reflected from the bottom or mode conversion signals are used. The successful application of all these signals in tomographic processing may increase the accuracy essentially. The development of such algorithms using only experimental data is very complicated because it is impossible to determine sensitivity of the technique to the uncertainty of the input parameters. This problem can be solved developing special method and software that enables to simulate NDT data acquisition process, taking into account material parameters, transducer characteristics, diffraction and refraction phenomena. Such models are used in other institutions like CEA (France), BAM (German) and others. Usually they are based on complicated numerical approach, which requires essential computer resources [4,5,6]. The objectives of this work was to develop relatively fast NDT simulation model, which enables to take into account not only direct reflection from defects, but specular reflection from object boundaries also. This task may be divided in some parts: