Liang Jiachen, Chen Bo, Shao Chenfei, Li Jianming, Wu Bangbin
College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China.
Sensors (Basel). 2020 Dec 19;20(24):7318. doi: 10.3390/s20247318.
Underwater cracks in concrete structures are often difficult to detect due to their complexity of the service environment. With numerical and experimental analysis of concrete beams immersed in water, an active monitoring system, based on a cement-based piezoelectric intelligent module array (CPIMA), was developed to locate and quantify the underwater cracks. Time reversal (TR) of the stress wave field is accomplished to focus on the crack area through the concrete beam specimen by the system. First, a piezoelectric actuator is applied to emit the initial propagating wave, which can be reflected, attenuated, and diffracted by the crack, transmitted through water filled in the crack, as well as diffracted by the coarse aggregates. To extract the damage waveforms associated with the crack and analyze the robust time-reversal invariance under the high-order multiple scattering effect, a pair of homogeneous and heterogeneous forward finite element (FE) models is established. Then, the damage waveforms are time-reversed and re-propagated in the inverse numerical model, where an optimal refocusing is achieved on the crack that behaves as an acoustic source. Finally, the damage area is obtained in the form of the stacked energy distribution of each time step. The focus results are represented by cloud images and compared with root-mean-square deviation (RMSD) values. Numerical simulation and experiments show that this method can identify and quantify underwater cracks effectively.
由于混凝土结构所处服役环境的复杂性，水下裂缝往往难以检测。通过对浸在水中的混凝土梁进行数值和实验分析，开发了一种基于水泥基压电智能模块阵列（CPIMA）的主动监测系统，用于定位和量化水下裂缝。该系统通过实现应力波场的时间反转（TR），使波在混凝土梁试件中聚焦于裂缝区域。首先，施加一个压电驱动器发射初始传播波，该波会因裂缝发生反射、衰减和衍射，穿过裂缝中的水传播，同时也会因粗骨料发生衍射。为了提取与裂缝相关的损伤波形，并分析高阶多次散射效应下的稳健时间反转不变性，建立了一对均匀和非均匀的正向有限元（FE）模型。然后，将损伤波形进行时间反转并在逆数值模型中重新传播，在该模型中，裂缝作为声源实现了最佳聚焦。最后，以每个时间步的叠加能量分布形式得到损伤区域。聚焦结果用云图表示，并与均方根偏差（RMSD）值进行比较。数值模拟和实验表明，该方法能够有效地识别和量化水下裂缝。
