Different rates of progression have been observed among patients with Alzheimer disease. Risk factors that accelerate deterioration have been identified and some are being discussed, such as genetics, comorbidity, and the early appearance of Alzheimer disease motor signs. Progressive forms of Alzheimer disease have been reported with rapid cognitive decline and disease duration of only a few years. This short review aims to provide an overview of the current knowledge of rapidly progressive Alzheimer disease. Furthermore, we suggest that rapid, in this context, should be defined as a Mini-Mental State Examination score decrease of 6 points per year.

A hybrid aeroacoustic approach was developed for the efficient numerical computation of human phonation. In the first step, an incompressible flow simulation on a three-dimensional (3 D) computational grid, which is capable of resolving all relevant turbulent scales, is performed using STARCCM+ and finite volume method. In the second step, the acoustic source terms on the flow grid are computed and a conservative interpolation to the acoustic grid is performed. Finally, the perturbed convective wave equation is solved to obtain the acoustic field in 3 D with the finite element solver CFS++. Thereby, the conservative transformation of the acoustic sources from the flow grid to the acoustic grid is a key step to allow coarse acoustic grids without reducing accuracy. For this transformation, two different interpolation strategies are compared and grid convergence is assessed. Overall, 16 simulation setups are compared. The initial (267 000 degrees of freedom) and the optimized (21 265 degrees of freedom) simulation setup were validated by measurements of a synthetic larynx model. To conclude, the total computational time of the acoustic simulation is reduced by 95% compared to the initial simulation setup without a significant reduction of accuracy, being 7%, in the frequency range of interest.

In low Mach number aeroacoustics, the well-known disparity of scales allows applying hybrid simulation models using different meshes for flow and acoustics, which leads to a fast computational procedure. The hybrid workflow of the perturbed convective wave equation involves three steps: (1) perform unsteady incompressible flow computations on a subdomain; (2) compute the acoustic sources and (3) simulate the acoustic field, using a mesh specifically suited. These aeroacoustic methods seek for a robust, conservative and computational efficient mesh-to-mesh transformation of the aeroacoustic sources. In this paper, the accuracy and the application limitations of a cell-centroid-based conservative interpolation scheme is compared to the computationally advanced cut-volume cell approach in 2D and 3D. Based on a previously validated axial fan model where spurious artifacts have been visualized, the results are evaluated systematically using a grid convergence study. To conclude, the monotonic convergence of both conservative interpolation schemes is demonstrated. Regarding arbitrary mesh deformation (for example, the motion of the vocal folds in human phonation), the study reveals that the computationally simpler cell-centroid-based conservative interpolation can be the method of choice.

SUMMARY In low Mach number aeroacoustics, the known disparity of length scales makes it possible to apply well‐suited simulation models using different meshes for flow and acoustics. The workflow of these hybrid methodologies include performing an unsteady flow simulation, computing the acoustic sources, and simulating the acoustic field. Therefore, hybrid methods seek for robust and flexible procedures, providing a conservative mesh to mesh interpolation of the sources while ensuring high computational efficiency. We propose a highly specialized radial basis function interpolation for the challenges during hybrid simulations. First, the computationally efficient local radial basis function interpolation in conjunction with a connectivity‐based neighbor search technique is presented. Second, we discuss the computation of spatial derivatives based on radial basis functions. These derivatives are computed in a local‐global approach, using a Gaussian kernel on local point stencils. Third, radial basis function interpolation and derivatives are used to compute complex aeroacoustic source terms. These ingredients are necessary to provide flexible source term calculations that robustly connect flow and acoustics. Finally, the capabilities of the presented approach are shown in a numerical experiment with a co‐rotating vortex pair.

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Functional gaps of cars combined with the underlying volume of air represent Helmholtz resonators that are excited at the Helmholtz frequency by the turbulent flow. Based on a model that describes the spatial coherence of pressure fluctuations beneath a turbulent boundary layer, we present how to compute an extensive synthetic excitation signal without performing computational fluid dynamics (CFD) computations. Moreover, this contribution shows the capabilities of complex fluid models to better predict the resonance behavior of Helmholtz resonators.