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Digital holographic microscopy provides the ability to observe throughout a volume that is large compared to its resolution without the need to actively refocus to capture the entire volume. This enables simultaneous observations of large numbers of small objects within such a volume. We have constructed a microscope that can observe a volume of 0.4 µm × 0.4 µm × 1.0 µm with submicrometer resolution (in xy) and 2 µm resolution (in z) for observation of microorganisms and minerals in liquid environments on Earth and on potential planetary missions. Because environmental samples are likely to contain mixtures of inorganics and microorganisms of comparable sizes near the resolution limit of the instrument, discrimination between living and non-living objects may be difficult. The active motion of motile organisms can be used to readily distinguish them from non-motile objects (live or inorganic), but additional methods are required to distinguish non-motile organisms and inorganic objects that are of comparable size but different composition and structure. We demonstrate the use of passive motion to make this discrimination by evaluating diffusion and buoyancy characteristics of cells, styrene beads, alumina particles, and gas-filled vesicles of micron scale in the field of view.

Abstract: Field‐scale and wind tunnel experiments were conducted in the 2D to 6D turbine wake region to investigate the effect of geometric and Reynolds number scaling on wake meandering. Five field deployments took place: 4 in the wake of a single 2.5‐MW wind turbine and 1 at a wind farm with numerous 2‐MW turbines. The experiments occurred under near‐neutral thermal conditions. Ground‐based lidar was used to measure wake velocities, and a vertical array of met‐mounted sonic anemometers were used to characterize inflow conditions. Laboratory tests were conducted in an atmospheric boundary layer wind tunnel for comparison with the field results. Treatment of the low‐resolution lidar measurements is discussed, including an empirical correction to velocity spectra using colocated lidar and sonic anemometer. Spectral analysis on the laboratory‐ and utility‐scale measurements confirms a meandering frequency that scales with the Strouhal number St = fD/U based on the turbine rotor diameter D. The scaling indicates the importance of the rotor‐scaled annular shear layer to the dynamics of meandering at the field scale, which is consistent with findings of previous wind tunnel and computational studies. The field and tunnel spectra also reveal a deficit in large‐scale turbulent energy, signaling a sheltering effect of the turbine, which blocks or deflects the largest flow scales of the incoming flow. Two different mechanisms for wake meandering—large scales of the incoming flow and shear instabilities at relatively smaller scales—are discussed and inferred to be related to the turbulent kinetic energy excess and deficit observed in the wake velocity spectra. [ABSTRACT FROM AUTHOR]

A series of unsteady, three-dimensional numerical simulations of the incompressible, oscillatory flow around a near-bed pipeline is presented. A flow at Reynolds number equal to Re α o = 20,000 with respect to the oscillatory amplitude and maximum oscillation velocity is considered. The ratio of the pipeline diameter to the oscillatory amplitude examined is in the range of D / α o = 0.1 − 1.0 , with the pipeline located at a distance of G / D = 0.0 − 1.0 . The numerical simulations are conducted by means of Large Eddy Simulation (LES), using Cartesian grids. The presence of solid boundaries is taken into account by means of the Immersed Boundary method. For turbulence modelling, two different subgrid scale models are tested, the classical Smagorinsky and the Filtered Structure Function (FSF) models. The results in terms of vortex shedding are compared against previously reported data demonstrating very good agreement. Vortex shedding patterns are presented, indicating suppression of the boundary layer separation of the lower side of the pipeline for gap lengths G / α o ≤ 1 / 20 . The characteristic values of the hydrodynamic forcing in terms of the drag and lift coefficients and the three significant oscillation frequencies extracted from the temporal variation of the forcing signals are associated with the flow regimes and wall proximity. The pipeline experiences hydrodynamic loading which is found to oscillate with the external flow frequency along the direction of the flow. Along the wall-normal direction, the forces exerted on the pipe oscillate with several frequencies of high power spectral density. However, the three significant oscillation frequencies of the lift coefficient appear to have almost constant values. The presented results can provide trends for design purposes in similar flow conditions for a wide range of engineering applications. [ABSTRACT FROM AUTHOR]

This study investigates the vortices produced between two 2d cylinders, and the relationship between the structures of the vortices produced at both cylinders when one is placed in the wake flow of another. CFD simulations using ANSYS Fluent were used to determine the coefficients of lift and drag, as well as the frequency of vortex shedding and size of vortices at three separate Reynolds numbers of 16000, 32000 and 65000 in different arrangements. Each arrangement of cylinders was compared against controls, which consisted of a single cylinder to determine the alteration of forces produced. Two trip wires at 7 different angles of 40, 45, 50, 55, 60, 65, and 70 degrees were then investigated at a Reynolds number of 65000 which was compared to the smooth cylinder control forces and frequency of vortex shedding. The most optimum angle of trip wires was then combined with linear cylinder arrangements also at a Reynolds number of 65000 for comparison with only the upstream cylinder utilizing the trip wires. [ABSTRACT FROM AUTHOR]

In this paper, we identify a new (acoustic) frequency-stenosis relation whose frequencies lie within the recommended auscultation threshold of stethoscopy (< 120 Hz). We show that this relation can be used to extend the application of phonoangiography (quantifying the degree of stenosis from bruits) to widely accessible stethoscopes. The relation is successfully identified from an analysis restricted to the acoustic signature of the von Karman vortex street, which we automatically single out by means of a metric we propose that is based on an area-weighted average of the Q-criterion for the post-stenotic region. Specifically, we perform CFD simulations on internal flow geometries that represent stenotic blood vessels of different severities. We then extract their emitted acoustic signals using the Ffowcs Williams-Hawkings equation, which we subtract from a clean signal (stenosis free) at the same heart rate. Next, we transform this differential signal to the frequency domain and carefully classify its acoustic signatures per six (stenosis-)invariant flow phases of a cardiac cycle that are newly identified in this paper. We then automatically restrict our acoustic analysis to the sounds emitted by the von Karman vortex street (phase 4) by means of our Q-criterion-based metric. Our analysis of its acoustic signature reveals a strong linear relationship between the degree of stenosis and its dominant frequency, which differs considerably from the break frequency and the heart rate (known dominant frequencies in the literature). Applying our new relation to available stethoscopic data, we find that its predictions are consistent with clinical assessment. Our finding of this linear correlation is also unlike prevalent scaling laws in the literature, which feature a small exponent (i.e., low stenosis percentage sensitivity over much of the clinical range). They hence can only distinguish mild, moderate, and severe cases. Conversely, our linear law can identify variations in the degree of stenosis sensitively and accurately for the full clinical range, thus significantly improving the utility of the relevant scaling laws... Future research will investigate incorporating the vibroacoustic role of adjacent organs to expand the clinical applicability of our findings. Extending our approach to more complex 3D stenotic morphologies and including the vibroacoustic role of surrounding organs will be explored in future research to advance the clinical reach of our findings., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Author(s).)

In this study, a fully unsteady computational fluid dynamics (CFD) model was used and the transient airflow properties during the entire breathing cycle, including inhalation and exhalation in a human nasal cavity, were evaluated. Unsteady particle tracking was performed to find the particle motion and deposition in the nasal airway using a Lagrangian approach. In most of earlier computer simulations, the assumption of quasi-steady or steady airflows averaged over the inhalation cycle were typically used to reduce the computational cost. In the present work particular attention was given to assessing the accuracy of these assumptions and their consequence on particle deposition in a human nasal cavity with paranasal sinuses. The simulation results for the airflow field showed significant differences between the unsteady and quasi-steady cases at low breathing rates near the beginning and end of the inspiration cycle. For breathing under a rest condition with a frequency of 0.25 Hz, the quasi-steady airflow assumption in the nasal cavity was found to be reasonable when the instantaneous Strouhal number was smaller than 0.2. The instantaneous deposition of micro-particles was also studied, and the effects of unsteady accelerating and decelerating flows on the deposition fraction were examined. The simulation results showed that the deposition fractions were affected by the accelerating and decelerating airflows during the inhalation phase. The simulated micro-particle depositions under the cyclic breathing condition were compared with those for steady breathing with an equivalent mean airflow rate. It was found that while the general trend was similar, the steady breathing simulation with the mean airflow rate during inhalation cannot accurately predict the total micro-particle deposition for cyclic breathing, particularly for 1–5 µm particles. Furthermore, the predicted regional depositions by the steady breathing were markedly different from those obtained under cyclic breathing. [ABSTRACT FROM AUTHOR]

Flows around blunt bodies at high Reynolds numbers generate a periodic release of staggered vortices. The dimensionless frequency of vortex shedding, the Strouhal number St , was found successful in describing periodic fluid flows. In fact, several literature datasets proved that the number St ~ 0.16 describes with reasonable (at times, excellent) approximation a large variety of periodic fluid phenomena, many of them having no clear affinity. The first motivation of the present study is to collect under one cover the results disseminated in various sources; the second purpose is to double-check the constancy of Strouhal number in wind turbines as well. The St number is here elaborated in a more informative way for horizontal-axis wind turbines, showing that it includes the tip speed ratio and the number of blades; the law St ~ 0.16 is here corroborated by further findings which includes wake meandering and the flow fields produced by three wind turbines (a two-bladed HAWT; a three-bladed lift-driven Darrieus VAWT; and a two-bladed drag-driven Savonius VAWT). The present findings suggest a design criterion for wind turbines. [ABSTRACT FROM AUTHOR]

SUMMARY With the nonstationary wind-induced acceleration data from full-scale measurements, an approach for estimation of the wind-induced overturning bending moments for super-tall buildings was proposed in this paper. The empirical mode decomposition was employed to decompose the measured acceleration data into a set of intrinsic mode functions and a residual component. To remove the baseline offset, the residual component and the intrinsic mode function components with long-period were eliminated before their integrations into velocity and displacement components. Then, the intrinsic mode function components, which have the same dominant periods as the natural periods of the studied tall buildings, were extracted from the original signals, and the natural frequency and damping ratio for the first vibration mode of the building were identified. Finally, the wind-induced overturning bending moments of the building were obtained from the generalized wind loads for the first vibration mode, which could be obtained from the time history analysis of dynamic equation. The Hilbert spectrum of wind-induced overturning bending moments was utilized to observe its characteristics in both time and frequency domains, and the Strouhal number was thus identified. The proposed scheme and some selected results may be helpful for further understanding of wind effects on super-tall buildings. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this work, we propose a formulation to evaluate aerodynamic forces for flow solutions based on Cartesian grids, penalisation and level set functions. The formulation enables the evaluation of forces on closed bodies moving at different velocities. The use of Cartesian grids bypasses the meshing issues, and penalisation is an efficient alternative to explicitly impose boundary conditions so that the body fitted meshes can be avoided. Penalisation enables ice shedding simulations that take into account ice piece effects on the flow. Level set functions describe the geometry in a non-parametric way so that geometrical and topological changes resulting from physics, and particularly shed ice pieces, are straightforward to follow. The results obtained with the present force formulation are validated against other numerical formulations for circular and square cylinder in laminar flow. The capabilities of the proposed formulation are demonstrated on ice trajectory calculations for highly separated flow behind a bluff body, representative of inflight aircraft ice shedding. [ABSTRACT FROM AUTHOR]

Abstract: An effective method of simulation of multidimensional hydrodynamic problems for small Mach numbers is described. The method is based on utilization of FFT (fast Fourier transform) for solving the Poisson equation on a rectangular grid in domains with complicated geometry (particularly multi-linked). Simulation was performed with zero numerical viscosity. The speed of calculation of the Poisson equation is 1–2 orders of magnitude higher compared to that of the calculation based on standard iteration techniques. Systematic simulations of a 2D flow past a cylinder in the channel with permeable and impermeable boundaries were performed. The critical values of the Re number of the onset of vortex movement (Re0) and loss of stability of steady (Re1) and two-dimensional movement (Re2) are estimated with high accuracy for the two cases mentioned. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic similarity is a widely used concept in the fluid mechanics field, and consists in placing two different-sized systems in equivalent experimental conditions. This enables removal of the effects of size and prediction of the behavior of a full size system from a scale model. The aim of this study was to test whether the Froude number (Nfr) or the Strouhal number (Str) could be used as a criterion for dynamic similarity during running. Fifteen male subjects ran barefoot on a runway in three experimental conditions (i) all subjects ran at the same speed V=3.5ms−1; (ii) the speed was determined from Nfr; (iii) the stride frequency was determined from Str. Antero-posterior (Fy) and vertical (Fz) ground reaction force components were assessed. The similarity between the subjects was analysed from scale factor sets computed from anthropometric and kinetic data. The use of Str implied strong inter-subject similarity for temporal parameters (mean r=0.96, time to Fz peak, time to Fy braking peak, Fy zero fore–aft shear, time to Fy propulsive peak) while Nfr induced fewer and lower similarities (mean r=0.75, Fy zero fore–aft shear, time to Fy propulsive peak, Fy braking impulse) that only concerned antero-posterior parameters. This study brought experimental evidence that neither Nfr nor Str were sufficient for dynamic similarity during running, but that each of them made its own contribution. These findings suggested that the concomitant use of Nfr and Str should be assessed to induce inter-subject dynamic similarity during running. [Copyright &y& Elsevier]

Digital holographic microscopy provides the ability to observe throughout a volume that is large compared to its resolution without the need to actively refocus to capture the entire volume. This enables simultaneous observations of large numbers of small objects within such a volume. We have constructed a microscope that can observe a volume of 0.4 µm × 0.4 µm × 1.0 µm with submicrometer resolution (in xy) and 2 µm resolution (in z) for observation of microorganisms and minerals in liquid environments on Earth and on potential planetary missions. Because environmental samples are likely to contain mixtures of inorganics and microorganisms of comparable sizes near the resolution limit of the instrument, discrimination between living and non-living objects may be difficult. The active motion of motile organisms can be used to readily distinguish them from non-motile objects (live or inorganic), but additional methods are required to distinguish non-motile organisms and inorganic objects that are of comparable size but different composition and structure. We demonstrate the use of passive motion to make this discrimination by evaluating diffusion and buoyancy characteristics of cells, styrene beads, alumina particles, and gas-filled vesicles of micron scale in the field of view. [ABSTRACT FROM AUTHOR]

The article presents a study which aims to develop a contaminant of Froude number (Nfr) and Strouhal number (Str) for an accurate dimensionless human walking and running analysis. It states that a light running track was used to identify the speed of the subjects. Results show that the walk-to-run transition occurs nearly 0.5 value of the Nfr.