“学萃讲坛”秉承学名家风范、萃科技精华的理念，以学术为魂，以育人为本，追求技术创新，提升学术品位，营造浓郁学术氛围，共品科技饕餮盛宴！

时间：2016年10月11日上午09:45-10:45

地点：水声楼15楼报告厅

报告题目：Propagation of ultrasonic waves in porous materials saturated by heavy fluid

报告人：Aroune DUCLOS副教授

主办单位：水声工程学院

报告人简介：Aroune DUCLOS, Associate professor, Laboratory of Acoustics of Le Mans University.

报告内容简介：This study deals with sound wave propagation in fluid saturated porous media and interactions with a macroscopic defect inside the media. Porous media under consideration are open-cell media consisting of a solid phase (skeleton) and a continuous fluid phase as it is the case for reticulated foams. Generally, the sound wave propagation in such media is described by the Biot theory accounting for skeleton vibrations interacting with propagation inside the fluid phase. Thus the velocity fields associated to the solid and fluid motions depends on the nature of the porous media but also on the nature of the interface between the media and the ambient fluid. For example, in the case of trabecular bone, pores are connected to the surrounding fluid (as for a sample coming from femoral head) and the slow wave predicted by the Biot theory can be observed. However, this slow wave can be no longer observed when the experiment is reproduced with the same bone having closed pores. The aim of this work is to take advantage of the Biot theory in a Non Destructive Testing and Evaluation (NDTE) context in order to characterize the physical parameters describing the behaviour of the porous media and also to detect and localize a macroscopic volume defect. In the first part, numerical simulations and experimental investigations are performed considering a porous plate having either open pores or sealed pores. This problem has already been tackled by previous authors but their conclusions are conflicted. The numerical simulations allow to study the behaviour of both slow and fast wave potentials independently inside the porous plate for each considered boundary conditions. According to these results, measurements performed in a water tank at ultrasonic range show a strong dependence of both reflection and transmission coefficients on the chosen boundary conditions. The analysis of these two coefficients allows for obtaining some physical parameters of the porous material under consideration. In the second part, we introduce a one dimensional volume defect localized inside a porous material having sealed pores. The changes due to the presence of the volume defect on both reflection and transmission coefficients are obtained theoretically by using a scattering matrix. In this case, the conversion mode phenomenon is one of the main mechanism responsible for the wave attenuation. When defects are present in the medium, the number of interfaces increases leading to an important energy transfer from the fast wave to the slow one. Numerical simulations as well as experimental investigations enables us to characterize the one dimensional volume defect in terms of position and size.

This talk will also include an overview of the research activities of the team Acoustics and Mechanics of Complex Materials.