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A Study on Hydrodynamic Behavior of Fine Sediment in Retention Structure Using Particle Image Velocimetry
摘要： Detention ponds are one type of stormwater best management practices (BMPs) that can be used for the quantity control of stormwater. The pond works by reducing peak discharge downstream through temporary storage and gradual release. In this paper, a new experimental procedure using particle image velocimetry (PIV) is introduced for a two-dimensional study of the hydrodynamic behavior of fine particles in a specially designed sediment basin. The hydrodynamic behavior of fine particles under different hydraulics parameters was achieved by shifting outlet placement, using different particle-size diameters, varying the distance of the inlet from the water surface, and varying the flow rate. The same inlet and outlet level reduced fine-particle dispersion and a lower flow rate assisted with controlling high siltation. Furthermore, smaller spherical particles had more influence on fine particle suspension. Therefore, controlling the hydraulic parameters can decrease the siltation problem level. Water Environ. Res., 88, 2309 (2016).
关键词： stormwater best management practices (BMPs),fine particle,siltation,particle image velocimetry (PIV),water surface
更新于2025-09-23 15:22:29
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Imaging-Based Nearshore Bathymetry Measurement Using an Unmanned Aircraft System
摘要： An imaging-based method to estimate the nearshore bathymetry in the surf zone is described. The method uses imagery collected by an unmanned aircraft system (UAS), or a consumer drone. The UAS was flown over the area of interest to record video, and a particle image velocimetry (PIV) technique was then applied to analyze the image frames to retrieve the wave celerity. Using the shallow water approximation to the linear-wave dispersion relation, wave celerity from the imagery could be used to deduce the local water depth. After combining the water depth inversion at multiple points from within the area of interest, the bathymetry was constructed. To validate the method, water depths from 25 spatial points were surveyed with a total station during a trial in the nearshore surf zone at Freeport, Texas. The root-mean-square error (RMSE) was estimated as 0.132 m. By minimizing the RMSE, the correction factor that accounts for the wave nonlinearity in estimating wave celerity was estimated as 1.02. This new and simple approach provides simultaneous measurement of bathymetry and surface velocity field mainly in the surf zone, where breaking/broken waves and energetic sediment transport frequently dominate, and does not require a high-end UAS, resulting in greater flexibility in sampling across space and time.
关键词： Particle image velocimetry,Remote sensing,Nearshore bathymetry,Unmanned aircraft system
更新于2025-09-23 15:22:29
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On the improvement of visible-responsive photodegradation through artificial cilia
摘要： Photocatalysts as a semiconductor material are widely used in the field of water and environment cleaning applications as it equips with favorite features such as chemical and physical stability, easy availability, inexpensive, and non-toxic in nature. Additionally, photocatalysts can convert the light energy of the irradiation into the chemical energy of the electron-hole pairs. Most commonly used TiO2 can function as the efficient photocatalysts in the presence of light. However it is a material which majorly requires UV light for its activation, and it is not practically being useful. In this aspect, the proposed study demonstrated that with a combination of SnFe2O4 nanoparticles with magnetic artificial cilia, a highly efficient catalytic activity can be achieved under the visible light due to the rapid and uniform mixing within the microfluidic device with least energy budget. To identify the optimal advanced oxidation process using the selected photocatalyst running with the microfluidics, a micro-particle image velocimetry analysis was carried out through three modes of artificial cilia rotation. The study also determined the evolution curves of the degradation rate with respect to time for all of three modes of cilia rotation, and a superior performance was achieved with a maximum degradation rate of 81.7% in 60 minutes using the presented design concept.
关键词： micro-particle image velocimetry,Photodegradation,photocatalyst,artificial cilia
更新于2025-09-23 15:21:21
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Convection Dynamics Forced by Optical Trapping with a Focused Laser Beam
摘要： Optical trapping dynamics of colloidal particles in solution is essential for understanding laser-induced assembling of molecules and nanomaterials, which contributes to nanofabrication, bioengineering, and microfluidics. In this paper, the importance of the surrounding fluid motion in optical trapping is investigated; that is, we reveal convection fluid dynamics forced by optical trapping with a focused laser beam. The fluid flow in optical trapping is evaluated by both experiments using the particle-image-velocimetry of fluorescent particles in solutions and theoretical consideration based on numerical analysis. A theoretical model consists of Navier?Stokes equations with the Boussinesq approximation that considers the temperature elevation induced by a photothermal effect. Furthermore, the effect of the particle motion induced by the optical force on fluid flow is also included in the analysis by developing a simple one-way homogeneous-type multiphase flow model. From both experimental and theoretical results, it turns out that the fluid flow in optical trapping is caused not only by thermal convection due to the temperature elevation but also by the collective particle motion induced by optical forces. Therefore, the optical forces can induce the large-scale fluid convection, which supports accumulating the target particles to the focal spot.
关键词： thermal convection,fluid dynamics,colloidal particles,photothermal effect,Boussinesq approximation,optical trapping,multiphase flow model,Navier?Stokes equations,particle-image-velocimetry
更新于2025-09-23 15:21:01
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A general approach to evaluate the ensemble cross-correlation response for PIV using Kernel density estimation
摘要： Cross-correlation in particle image velocimetry is well known to behave as a non-linear operator, depending heavily on the distribution of tracer images and image quality. While analytical descriptors of the correlation response have so far been dealt with for simplistic flow cases, in this work a methodology is presented based on Kernel density estimation to retrieve the inherent correlation response to any deterministic flow field. The new approach bypasses the need for Monte-Carlo simulations and its inherent sensitivity to parameter settings make it a more efficient alternative to analyse filtering of the underlying velocity field due to image cross-correlation. The derivation of the underlying equations is presented and a numerical assessment corroborates the suitability of the approach to mimic ensemble correlation.
关键词： Ensemble correlation,Particle image velocimetry,Flow field filtering,Kernel density estimation,Cross-correlation
更新于2025-09-23 15:21:01
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Experimental study on the 3D-flow field of a free-surface vortex using stereo PIV
摘要： In order to analyse the flow characteristics of free-surface vortexes and to validate the Burgers vortex model by using stereo particle image velocimetry, experiments are conducted in a 600 mm diameter vortex tank. Measured axial velocities indicate that 10–25% of the flow is transported through the vortex core. The velocity profiles show that the axial flow is concentrated in a domain bounded by two times the core radius. Despite Burgers’ assumption of radially independent axial velocity profiles, the model quantifies the tangential velocity profile within a relative uncertainty of circa 10%. The measurements show that it seems valid to use Burgers’ model to obtain an estimate for the core radius by taking the average axial velocity over a radial domain of approximately 2.2 times the core radius. The Burgers model quantifies the air core depth with an uncertainty of 20% relative to the measurements. When compared with the magnitude of vorticity diffusion by molecular viscosity, the experiments show that there is no significant diffusion by radial turbulence.
关键词： vortex dynamics,Burgers vortex model,Air core depth,vortex core radius,axial vortex flow,stereo particle image velocimetry (SPIV),experiments
更新于2025-09-19 17:15:36
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Phase-locking particle image velocimetry measurement of unsteady flow behaviors: Online dynamic mode decomposition using field-programmable gate array
摘要： A novel online dynamic mode decomposition (DMD) approach using a field-programmable gate array (FPGA), which takes full advantage of the DMD to extract multiple unsteady events and the FPGA system for signal sampling and fast computation, was developed for phase-locking particle image velocimetry (PIV) measurements of unsteady flow behaviors. The turbulent separated and reattaching flow around a finite blunt plate with a length-to-height-ratio L/D = 6.0 was examined to demonstrate this novel approach. The wall-pressure field and the velocity field were measured using arrayed microphones and the conventional planar PIV setup, respectively. Offline DMD analysis of the wall-pressure fluctuation field was first used to identify the dominant modes corresponding to the energetically unsteady events. For each mode, the eigenmode and its mode coefficient reflected the spatial footprint pattern and temporal strength of the unsteady event, respectively. Next, trained machine learning of the mode coefficient was used to establish a phase prediction strategy. Finally, in the online analysis, the relevant eigenmode was cast into the FPGA device to serve as the reference mode for reconstruction with the sampled wall-pressure data, determining the phase signal to fire the PIV setup. High-resolution spatiotemporal evolutions of the dominant flow structures (i.e., the flapping separation bubble, the impinging leading-edge vortex, and the trailing-edge vortex street) were separately assembled. Further measurements demonstrated a clear panoramic view of the synchronous behavior of the enlarging separation bubble and the impinging leading-edge vortex. The proposed online FPGA-DMD approach can serve as a sophisticated strategy for phase-locking PIV measurements of unsteady flow behaviors.
关键词： phase-locking,dynamic mode decomposition,unsteady flow,particle image velocimetry,field-programmable gate array
更新于2025-09-19 17:15:36
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Revealing the impact of laser-induced breakdown on a gas flow
摘要： Laser-induced breakdown spectroscopy (LIBS) is an optical, and thus non-contact, but not non-invasive, measurement technique. Investigating the impact of laser-induced breakdown on a gas flow, combined LIBS and particle image velocimetry (PIV) measurements are performed. In the considered laminar air flow, the induced velocity field disturbance has an extent of about 0.7 cm with magnitudes up to 0.9 m s?1. As a further result, the combination of LIBS with other measurement techniques or high-speed LIBS measurements are found to require a minimal time delay of about 500 μs in order to ensure influence of the preceding LIBS pulse on the considered gas flow of about 10 % relative velocity deviation. For a reduction to 0 % relative velocity deviation a time delay of about 20 ms is estimated for the investigated flow. Smaller time delays may occur in turbulent flows or flows with higher velocities.
关键词： laser-induced breakdown spectroscopy,Flow diagnostics,particle image velocimetry
更新于2025-09-19 17:13:59
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On the application of a supercontinuum white light laser for simultaneous measurements of temperature and velocity fields using thermochromic liquid crystals
摘要： Simultaneous velocity and temperature measurements using thermochromic liquid crystals (TLC) as tracer particles are discussed, with regard to measuring range, uncertainty and spatial resolution. For the first time, a supercontinuum laser is used to illuminate these particles, which shall later be used for the characterization of the momentum and heat transfer in Rayleigh-Bénard cells with high aspect ratio using particle image velocimetry (PIV) and particle image thermometry (PIT). Light scattered from the TLCs is analyzed by spectrometer measurements, revealing its general scattering characteristics depending on the angle between the light sheet plane and the viewing axis. It is shown that white light sources with continuous spectral characteristic and a slightly higher fraction of light in the red wavelength range perform well, thereby the supercontinuum white light laser can be used, even though it has a cut-in wavelength of about 475 nm. The numerical aperture of the detection optics and chromatic aberrations of the laser light significantly affect the temperature sensitivity and dynamic range of the color of the TLCs. This may cause an effective temperature sensitivity range of about one-tenth of their nominal range, particularly at large angles between light sheet plane and viewing axis, as usually applied in PIV. A simultaneous velocity and temperature measurement in a Rayleigh-Bénard cell experimentally validates that the use of the supercontinuum laser allows for reliable simultaneous PIV and PIT measurements with high spatial resolution of less than 500 μm in out-of-plane direction, on condition that an appropriate two-dimensional calibration is applied.
关键词： Thermochromic liquid crystals,Supercontinuum laser,Rayleigh-Bénard convection,Particle image thermometry,Particle image velocimetry
更新于2025-09-16 10:30:52
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Unsteady pressure estimation and compensation capabilities of the hybrid simulation combining PIV and DNS
摘要： The hybrid unsteady-flow simulation, which has been developed to assimilate the Navier–Stokes simulation into a time-resolved particle image velocimetry (PIV) field by synchronizing the frame rate with the direct-numerical-simulation time step, can simultaneously produce an unsteady pressure field. The hybrid process typically introduces a ‘patch function’, which transplants the PIV fields inside the camera window into a larger computational domain. This study evaluates the pressure fields produced by the hybrid simulation inside the patch function (i.e. estimation) and outside of it (i.e. compensation). We take time-resolved planar PIV data of a separated flow past the NACA 0012 airfoil at an angle of attack of 30° in a water tunnel as an example. First, an unsteady pressure field produced from the hybrid simulation is compared with other existing pressure-estimation methods in two dimensions over the entire domain of the camera window. The results of the two-dimensional (2D) hybrid simulation are found to agree best with those of the sequential-integration method with much lower noise levels in time and space. Next, the domain of the forcing is reduced by truncating the patch function in the hybrid simulation, and the pressure fields in the missing parts of the patch function are compared with those solved using the full patch function. When at least the regions in which 2D vortical structures collapse are included in the patch function downstream, the rest of the pressure fields can be compensated for relatively well. In contrast, the forces acting on the airfoil can be estimated accurately only if it is enclosed by the camera window.
关键词： hybrid simulation,data assimilation,pressure estimation,particle image velocimetry
更新于2025-09-10 09:29:36