A Novel Hybrid Deep Learning Method for Predicting the Flow Fields of Biomimetic Flapping Wings.

The physics governing the fluid dynamics of bio-inspired flapping wings is effectively characterized by partial differential equations (PDEs). Nevertheless, the process of discretizing these equations at spatiotemporal scales is notably time consuming and resource intensive. Traditional PDE-based computations are constrained in their applicability, which is mainly due to the presence of numerous shape parameters and intricate flow patterns associated with bionic flapping wings. Consequently, there is a significant demand for a rapid and accurate solution to nonlinear PDEs, to facilitate the analysis of bionic flapping structures. Deep learning, especially physics-informed deep learning (PINN), offers an alternative due to its great nonlinear curve-fitting capability. In the present work, a hybrid coarse-data-driven physics-informed neural network model (HCDD-PINN) is proposed to improve the accuracy and reliability of predicting the time evolution of nonlinear PDEs solutions, by using an order-of-magnitude-coarser grid than traditional computational fluid dynamics (CFDs) require as internal training data. The architecture is devised to enforce the initial and boundary conditions, and incorporate the governing equations and the low-resolution spatiotemporal internal data into the loss function of the neural network, to drive the training. Compared to the original PINN with no internal data, the training and predicting dynamics of HCDD-PINN with different resolutions of coarse internal data are analyzed on the problem relevant to the two-dimensional unsteady flapping wing, which involves unsteady flow features and moving boundaries. Additionally, a hyper-parametrical study is conducted to obtain an optimal model for the problem under consideration, which is then utilized for investigating the effects of the snapshot and fraction of the coarse internal data on the HCDD-PINN's performances. The results show that the proposed framework has a sufficient stability and accuracy for solving the considered biomimetic flapping-wing problem, and its great potential means that it can be considered as an alternative to accelerate or replace traditional CFD solvers in the future. The interested variables of the flow field at any instant can be rapidly obtained by the trained HCDD-PINN model, which is superior to the traditional CFD method that usually needs to be re-run. For the three-dimensional and optimization problems of flapping wings, the advantages of the proposed method are supposedly even more apparent.

Boundary regularized integral equation formulation of the Helmholtz equation in acoustics.

A boundary integral formulation for the solution of the Helmholtz equation is developed in which all traditional singular behaviour in the boundary integrals is removed analytically. The numerical precision of this approach is illustrated with calculation of the pressure field owing to radiating bodies in acoustic wave problems. This method facilitates the use of higher order surface elements to represent boundaries, resulting in a significant reduction in the problem size with improved precision. Problems with extreme geometric aspect ratios can also be handled without diminished precision. When combined with the CHIEF method, uniqueness of the solution of the exterior acoustic problem is assured without the need to solve hypersingular integrals.

Effect of high-intensity focused ultrasound on Enterococcus faecalis planktonic suspensions and biofilms.

In this study, the effect of high-intensity focused ultrasound (HIFU) on Enterococcus faecalis on both planktonic suspensions and biofilms was investigated. E. faecalis persist in secondary dental infections as biofilms. Glass-bottom Petri dishes with biofilms were centered at the focal point of the HIFU wave generated by a 250-kHz transducer. Specimens were subjected to HIFU exposure at different periods of 30, 60 and 120 s. The viable bacteria, removal effect and bacterial viability of biofilms attached to the Petri dish surface were studied by colony-forming units (CFUs), scanning electron microscopy and confocal microscopy, respectively. The removal and bactericidal effects of HIFU are dependent on the exposure time. A significant reduction in biofilm thickness and CFU was found with the increase in HIFU exposure. The removal or bactericidal effect of HIFU was more significant starting from 60 s of exposure. This study highlighted the potential application of HIFU as a novel method for root canal disinfection.

Delivery of antibacterial nanoparticles into dentinal tubules using high-intensity focused ultrasound.

INTRODUCTION: High-intensity focused ultrasound (HIFU) produces collapsing cavitation bubbles. This study aims to investigate the efficacy of collapsing cavitation bubbles to deliver antibacterial nanoparticles into dentinal tubules to improve root canal disinfection. METHODS: In stage 1, experiments were performed to characterize the efficacy of collapsing cavitation bubbles to deliver the miniature plaster beads into a tubular channel model. In stage 2, experiments were conducted on root-dentin blocks to test the efficacy of HIFU applied at 27 kHz for 2 minutes to deliver antibacterial nanoparticles into dentinal tubules. After the stage 2 experiment, the samples were sectioned and analyzed using field-emission scanning electron microscopy and energy dispersive X-ray analysis. RESULTS: The stage 1 experiment showed that collapsing cavitation bubbles using HIFU delivered plaster beads along the entire length of the tubular channel. It was observed from the stage 2 experiments that the diffusion of fluids alone was not able to deliver antibacterial nanoparticles into dentinal tubules. The collapsing cavitation bubbles treatment using HIFU resulted in significant penetration up to 1,000 microm of antibacterial nanoparticles into the dentinal tubules. The statistical analysis showed a highly significant difference in the depth of penetration of antibacterial nanoparticles between the two groups (<0.005). CONCLUSION: The cavitation bubbles produced using HIFU can be used as a potential method to deliver antibacterial nanoparticles into the dentinal tubules to enhance root canal disinfection.