Time Reverse Modeling of Damage Detection in Underwater Concrete Beams Using Piezoelectric Intelligent Modules

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.

Morphometric Divergence of Anatolian Honeybees through Loss of Original Traits: A Dangerous Outcome of Turkish Apiculture

Five honeybee subspecies exist naturally in Anatolia. Unfortunately, owing largely to migratory beekeeping and lack of control mechanisms against requeening, the native honey bee subspecies located in Anatolia are facing extinction. Beekeeping activities, especially migratory beekeeping jeopardizes the presence of the naturally evolved indigenous subspecies of Anatolia. The present study examined morphological deformation in three Apis mellifera (L.) subspecies (A. m. caucasica, A. m. carnica, A. m. syriaca) and two ecotypes of A. m. anatoliaca (Muğla and Yığılca) that have been kept all together in a long-term breeding program at the common apiary. Worker bee samples representing each honeybee subspecies and ecotype were collected from the common apiary, and also from their original locations. To demonstrate the potential hybridization effect on variations of the Anatolian native honeybee subspecies and ecotypes, the geometric morphometric method was applied on the samples of honeybees that had been kept together in the same apiary since 2008. The findings showed that the honeybee population of the common apiary and those from their native settings formed two different configurations on the scatter plots. Hybridization and promiscuous mating among the different honeybee races maintained in the common apiary may have led to the loss of a valuable combination of morphometric traits. Hence, there is an urgent need for an active monitoring system and a ban on queen trading and migratory practices as well as for periodic testing of registered apiaries to identify ongoing variations in the gene pool.

Target Strength of Southern Resident Killer Whales (Orcinus orca): Measurement and Modeling

A major criterion for permitting the deployment of tidal turbines in Washington State’s Puget Sound is management of risk of injury to killer whales from collision with moving turbine blades. An active monitoring system is being proposed to detect and track killer whales within proximity of turbines and alert turbine operators of their presence and location to permit temporary turbine shutdown when the risk of collision is high. Knowledge of the target strength (TS) of killer whales is critical to the design and application of active acoustic monitoring systems. In 1996, a study of the TS directivity of a 2.2-m-long bottlenose dolphin at an insonifying frequency of 67 kHz was performed. Noting that killer whales, which are dolphins, are morphologically similar to bottlenose dolphins and then assuming allometry, we estimated the relative broadside and tail aspect TS of a 7.5-m-long adult killer whale at an insonifying frequency of 67 kHz to be −8 and −28 dB, respectively. We used a three-layer model for plane wave reflection of sound at 200 kHz from the lung of killer whales to estimate their TS. We assessed the accuracy of our killer whale TS estimates by comparing them with TS estimates of free swimming killer whales obtained using a split-beam active acoustic system operating at 200 kHz. The killer whale TS estimates based on the preliminary model were in good agreement with those obtained for free swimming killer whales.