Particle Image Velocimetry Results Research Articles

The frost heave characteristics of a coarse-grained volcanic soil quantified by particle image velocimetry

The increasing use of the seasonally frozen and permafrost regions for civil engineering constructions and the effects of global warming on these regions have stimulated research on the behaviors of frozen soils. In the present study, the frost heave characteristics of a coarse-grained soil with volcanic nature was experimentally investigated. A large soil tank model was established in laboratory for this purpose. The effects of temperature boundary, external water supply, and water transfer type on the frost heave characteristics of the volcanic soil were studied, through a series of frost heave tests. The particle image velocimetry (PIV) technique was used to quantify the full field deformation of the soil specimen. The results suggest that temperature gradient inside the soil specimen is the driving force for the migration of pore water and vapor. The largest increment in water content generally agrees well with the frost penetration depth. The contribution of vapor to the frost heave of the soil specimen is typically small. The applied seeding method, selected subset size, image-object space calibration, and calculation processes ensured accurate PIV results. Discussions regarding the presented experimental investigation and the employment of PIV technique for quantifying frozen soil deformation are summarized. These findings and discussions can provide valuable insights into the frost heave behavior of the studied soil in particular, as well as promote the application of PIV for frozen soil engineering.

A 3-D Printed Optically Clear Rigid Diseased Carotid Bifurcation Arterial Mock Vessel Model for Particle Image Velocimetry Analysis in Pulsatile Flow

Abstract In recent years, blood flow analyses of diseased arterial mock vessels using particle image velocimetry (PIV) have been hampered by the inability to fabricate optically clear anatomical vessel models that realistically replicate the complex morphology of arterial vessels and provide highly resolved flow images of flow tracer particles. The aim of this paper is to introduce a novel approach for producing optically clear 3-D printed rigid anatomical arterial vessel models that are suitable for PIV analysis using a common 3-D inkjet printing process (using a Formlabs Form 2 3-D printer) and stock clear resin (RS-F2-GPCL-04). By matching the index of refraction (IOR) of the working fluid to the stock clear resin material, and by printing the part in a 45-deg print orientation, a clear anatomical model that allows clear visualization of flow tracer particles can be produced which yields highly resolved flow images for PIV analyses. However, a 45-deg print orientation increases the need for post-processing due to an increased amount of printed support material. During post-processing, the part must be wet sanded in several steps and surface finished with Novus Plastic Polish 3 Step System to achieve the final surface finish needed to yield high-resolution flow images. The mock arterial vessel model produced in this work is a 3-D printed diseased carotid bifurcation artery developed from CTA scan data. A PIV analysis was conducted on the developed mock arterial vessel model installed in a complex transient flow loop to assess the flow profiles within the model and the clarity of the model. A computational fluid dynamics (CFD) simulation was conducted on the same carotid bifurcation arterial geometry, and the results were used as a benchmark comparison for PIV results. The results obtained in this work show excellent promise for using the developed approach for developing 3-D printed anatomical vessel models for experimental PIV analyses. The fabrication methodology of the clear anatomical models, PIV results, and CFD results is described in detail.

Comparison of the Measurement Results of PIV with Different Tracer

Particle Image Velocimetry (PIV) was used to measure the solenoidal vector field of the Taylor-Couette flow with different tracers. It can be seen that both of them, the polyamide and flocs can be a suitable performance tracer particles for PIV in flow field measurement. The results indicated that the instantaneous velocity vector maps obtained with different tracer particles which could denote the characteristics of the flow structure, the size and the vortex centers of the vortex. At the meantime, the experimental results demonstrated that the velocity vector obtained by the flocs generated in real-time as tracer particles was similar with suitable performance to those obtained by polyamide.

Computational Design Analysis of a Hydrokinetic Horizontal Parallel Stream Direct Drive Counter-Rotating Darrieus Turbine System: A Phase One Design Analysis Study

This paper introduces a phase one computational design analysis study of a hydrokinetic horizontal parallel stream direct-drive (no gear box) counter-rotating Darrieus turbine system. This system consists of two Darrieus rotors that are arranged in parallel and horizontal to the water stream and operate in counter-rotation due to the incoming flow. One of the rotors directly drives an armature coil rotor and the other one a permanent magnet generator. A two-dimensional (2-D) and three-dimensional (3-D) computational fluid dynamic (CFD) simulation study was conducted to assess the hydrokinetic performance of the design. From a high computational cost and time perspective, the simulation setup was reduced from a 3-D to a 2-D analysis. Although useful information was obtained from the 3-D simulations, the output performance could be assessed with the 2-D simulations without compromising the integrity of the turbine output results. A scaled experimental design prototype was developed for static (non-movement of the rotors with dynamic fluid flow) particle image velocimetry (PIV) studies. The PIV studies were used as a benchmark for validating and verifying the CFD simulations. This paper outlines the prototype development, PIV experimental setup and results, computational simulation setup and results, as well as recommendations for future work that could potentially improve overall performance of the proposed design.

Numerical modeling of sneeze airflow and its validation with an experimental dataset.

In this study, we aimed at providing datasets using experimental results to validate the sneeze airflow. In addition, the boundary conditions for the sneeze simulation that could reproduce the sneeze airflow in the experimental results are presented and reviewed. The validation datasets were created by performing ensemble-average analysis with the experimental results of particle image velocimetry, and these were used to explore the boundary conditions to reproduce the sneeze airflow. As a result of the sneeze airflow reproduced by computational fluid dynamics simulation, the magnitude ranges of maximum velocity at the interface were observed to be 21.1-23.9m/s for males and 17.9-20.3m/s for females, which were higher than those of coughing. Compared with the experimental results, the root-mean-square error range for the overall airflow distribution was 0.19-0.23 m/s, whereas the error range for the magnitude of the maximum velocity at a criterion point was 0.03-0.08 m/s. The total sneezing airflow volume was in the range of 0.36-0.48 L, which was relatively low compared with that of coughing. Thus, this study provides important fundamental boundary conditions for computational fluid dynamics analysis, validated by experimental results, to interpret the spread of infectious particles by sneezing.

Examination of Cinnamomum camphora interlocked grain adopting X-ray computed tomography combined with particle image velocimetry

Trees develop wood grain more or less parallel to the tree axis as they grow laterally. However, many tree species also develop interlocked grain that is expressed as a change in the wood grain orientation, periodically switching between left- and right-handed spirals over the years. Wood grain information is critical to determining the wood quality and is an important record of cellular events in a cambium. This study examined the wood grain of axial xylem cells in the semi-ring porous hardwood Cinnamomum camphora by first visualizing the three-dimensional structure using a conventional X-ray computed tomography instrument producing tomography images. We propose the use of particle image velocimetry (PIV) and the two-dimensional fast Fourier transform (2D-FFT) to analyze computed tomography images in obtaining grain angle (δ) information from the vessel deviation. We found undulation on the radial variation of the grain angle (δ) that indicates periodical changes in the wood grain orientation as left- and right-handed spirals ranging from − 25° to 16° and − 22° to 18° using the 2D-FFT and PIV, respectively. Furthermore, despite the major orientation of vessels inclining in the tangential direction, the PIV result revealed a minor deviation with vessels inclining in various orientations along the tree radius.

PIV and IRT measurements of hydrothermal performance in a U-shaped heat exchanger with 3D printed detached curved ribs

Novel detached curved ribs are proposed in this study and their influence on turbulent thermofluidic features in a two-pass U-shaped square channel is experimentally investigated using particle image velocimetry (PIV) and infrared thermography (IRT). Due to their geometric complexity, the ribs are fabricated with the 3D printing technology-fused deposition modeling and mounted in line inside the channel with a hydraulic diameter (DH) of 45.5 mm. Examined parameters include the rib convergence angle (α), divergence angle (β), clearance ratio (C/H), and Reynolds number, which are respectively in the range of (25°, 35°, 45°), (30°, 40°, 50°), (0.25, 0.38, 0.56, 0.75, and 1), and (5,000–20,000). The PIV and IRT results show that that the detached curved ribs accelerate the core flow and significantly strengthen the Dean vortices in the turn region, leading up to 70% enhancement in Nusselt number ratio (Nu¯/Nu∞) in that region compared with previous best results. Further parametric studies reveal that at α=25˚and β = 40°, Nu¯/Nu∞ and Fanning friction factor ratio (f¯/f∞) first increase and then decrease with increasing C/H, with the maximum thermal performance factor (TPF) of 1.4 occurring at C/H = 0.38, slightly higher than the previous highest data for f¯/f∞= 10-50. Finally, empirical formulations of Nu¯/Nu∞ and f¯/f∞ with α, β, C/H, and Re for the present design are proposed with an average difference of 2.24% and 4.95%, respectively.

Development and validation of non-invasive endothelial shear stress (ESS) estimations of coronary artery haemodynamics using computational modelling

Abstract Background Vascular remodelling is influenced by various biomechanical forces such as endothelial shear stress (ESS) and is associated with development and progression of coronary artery disease (CAD). ESS is the parallel frictional force exerted by blood flow on the endothelial luminal surface of the arterial wall. While ESS may not be the only cause of atherosclerosis, it is postulated that low ESS creates a pro-atherogenic environment and high ESS is athero-protective. Computational fluid dynamics (CFD) is an engineering method used to analyse fluid flow and has been increasingly applied to simulate ESS in cardiovascular research. However, current CFD-derived ESS estimates have never been validated and can display significant variability between research groups. Purpose This study aims to provide a comparative analysis of coronary flow using in-silico modelling of coronary flow and particle image velocimetry (PIV). Methods A proximal left anterior descending (pLAD) coronary phantom model was constructed from a patient who had received same day cardiac computed tomography angiography (CTCA) and invasive coronary haemodynamic (Combowire XT) assessment. Patient-specific coronary flow data was applied to CFD boundary conditions and a mock circulatory loop. CFD was validated using PIV under steady flow in a 4-times-scaled model. Same plane velocity field and flow patterns (at mid-luminal of pLAD) from both in-silico and in-vivo data were compared and analysed. Results Mean velocity contours and magnitude were analysed from CFD and PIV. Patient specific average peak velocity obtained from invasive assessment was 0.21m/s. Patient-specific velocity average from CFD was 0.22m/s. The approximated magnitude difference is 4.7%. Both same-axial average cross-sectional velocity estimated by CFD-pLAD and PIV-pLAD are 0.087m/s. Velocity contours and flow patterns simulated in the CFD were also comparable with the PIV results. Conclusion Simulation data from CFD correlate well with experimental PIV results. This early data allows for a non-invasive approach to determine patient-specific coronary haemodynamics (such as velocity profiling and ESS) and form the basis of personalising cardiovascular risk. Insights from this work may aid future development of a novel tool that incorporates CFD-derived ESS estimates with patient-specific risk factors to better predict rapid CAD progression. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): Cardiac Society of Australia and New Zealand Monash Institute of Medical Engineering

Finite-Wing and Sweep Effects on Transonic Buffet Behavior

This study experimentally investigates the effects of the sweep angle and finite wing on transonic buffet, studying two-dimensional (2-D) and three-dimensional wing configurations. Background-oriented schlieren and stereographic particle image velocimetry (PIV) have been used as measurement techniques, performing experiments on an OAT15A airfoil (clamped to both the side windows of the wind tunnel), an unswept wing, and two swept wings with sweep angles of 15 and 30 deg, respectively. The three wings are also based on the OAT15A airfoil and are clamped at the wind tunnel only at their root (free wingtip). All wings have been tested at a constant normal Mach number () with respect to the leading edge. The results show that the buffet oscillations are much stronger for the airfoil than for the three finite-span wings. A large difference in the buffet behavior can be noticed between the airfoil and the unswept wing, as is also seen in oil flow visualizations. This difference is particularly evident in correspondence of the more outboard spanwise locations, suggesting that for the unswept wing, an important role could be played by finite-wing effects: notably, the tip vortex. A spectral analysis has shown that for the swept wings, the classical 2-D buffet peak (occurring at for the present conditions) is substantially attenuated, whereas additional contributions in the range of 450–850 Hz appear. The PIV results showed, for the 30 deg sweep angle wing, a periodical occurrence of a secondary supersonic area downstream of the main shock wave structure, which is absent for the other wing models. The stereographic PIV configuration allowed the reconstruction of the spanwise-oriented velocity component, obtaining, in proximity of the trailing-edge, values of the spanwise velocity component () which are in agreement with the spanwise convection of buffet cells observed in the literature in this region.

Turbulence Structure and Dynamics Investigation of Turbulent Swirl Flow in Pipe Using High-Speed Stereo PIV Data

Turbulent swirl flow, which exists in numerous turbomachinery systems, is the focus of this paper. It consumes a significant amount of energy, so it is a subject of investigation for many researchers. It is even more present in ventilation systems, as numerous axial fans are still installed without guide vanes. The experimental investigation of the turbulent swirl flow behind an axial fan in a pipe, installed in a test rig with a free inlet and ducted outlet, as defined in the international standard ISO 5801, is presented in this paper. Moreover, in this paper, the axially restricted case is studied. A designed axial fan generates a Rankine vortex with a complex structure, and research on the vortex turbulence structure and dynamics is presented. On the basis of the HSS PIV (high-speed stereo particle image velocimetry), measurement results are calculated using invariant maps. All states of turbulence anisotropy are thoroughly analyzed by applying the invariant theory on HSS PIV results. Vortex dynamics is observed on the basis of the total velocity minima positions and their repetitions. Both methods are correlated, and important conclusions regarding vortex behavior are deduced.

Optical Flow Methods For Tracer-Based Imaging Techniques In Fluid Mechanics

This paper is aimed at assessing the performance of Optical Flow methods to estimate flow velocities from images designed for 2D Particle Image Velocimetry (PIV). A benchmark is proposed, based on synthetic tracer images associated to rotation- and deformation-dominated flow configurations. The investigated Optical Flow methods are Lucas-Kanade, Horn-Schunck and Farnebäck, combined them with the Liu-Shen method. The true values of the flow field (ground truth) are compared with the results of PIV and Optical Flow methods. Relative and absolute errors are computed for different combinations of flow type, relative velocity, white noise level, particle spot size and particle concentration. The accuracy of Optical Flow methods varies with the flow type, particle sizes and pre-processing steps. Combination of methods improves accuracy. The most accurate method is (dense) Lucas-Kanade/Liu-Shen. The Farnebäck/Liu-Shen combination is highly accurate for 10 or 12 bit images. The range of applicability of Optical Flow methods seems higher than that of correlation-based PIV.

Influence of Groundwater Depth on Pile–Soil Mechanical Properties and Fractal Characteristics under Cyclic Loading

The analysis of the behavior of soil and foundations when the piles in offshore areas are subjected to long-term lateral loading (wind) is one of the major problems associated with the smooth operation of superstructure. The strength of the pile-soil system is influenced by variations in the water content of the soil. At present, there are no studies carried out analyzing the mechanical and deformational behavior of both the material of the laterally loaded piles and soil with groundwater level as a variable. In this paper, a series of 1-g model tests were conducted to explore the lateral behavior of both soil and monopile under unidirectional cyclic loading, based on the foundation of an offshore wind turbine near the island. The influence of underground water level and cyclic load magnitude on the performance of the pile–soil system was analyzed. To visualize the movements of soil particles during the experimental process, particle image velocimetry (PIV) was used to record the soil displacement field under various cyclic loading conditions. The relationship curves between pile top displacement and cyclic steps, as well as the relationship curves between cyclic stiffness and cyclic steps, were displayed. Combined with fractal theory, the fractal dimension of each curve was calculated to evaluate the sensitivity of the pile–soil interaction system. The results showed that cyclic loading conditions and groundwater depth are the main factors affecting the pile–soil interaction. The cyclic stiffness of the soil increased in all test groups as loading progressed; however, an increase in the cyclic load magnitude decreased the initial and cyclic stiffness. The initial and cyclic stiffness of dry soil was higher than that of saturated soil, but less than that of unsaturated soil. The ability of the unsaturated soil to limit the lateral displacement of the pile decreased as the depth of the groundwater level dropped. The greater the fluctuation of the pile top displacement, the larger the fractal dimension of each relationship curve, with a variation interval of roughly 1.24–1.38. The average increment of the cumulative pile top displacement between each cycle step following the cyclic loading was positively correlated with fractal dimension. Based on the PIV results, the changes in the pile–soil system were predominantly focused in the early stages of the experiment, and the short-term effects of lateral cyclic loading are greater than the long-term effects. In addition, this research was limited to a single soil layer. The pile–soil interaction under layered soil is investigated, and the results will be used in more complex ground conditions in the future.

Infection control measures for public transportation derived from the flow dynamics of obstructed cough jet

During the COVID-19 pandemic, WHO and CDC suggest people stay 1 m and 1.8 m away from others, respectively. Keeping social distance can avoid close contact and mitigate infection spread. Many researchers suspect that suggested distances are not enough because aerosols can spread up to 7–8 m away. Despite the debate on social distance, these social distances rely on unobstructed respiratory activities such as coughing and sneezing. Differently, in this work, we focused on the most common but less studied aerosol spread from an obstructed cough. The flow dynamics of a cough jet blocked by the backrest and gasper jet in a cabin environment was characterized by the particle image velocimetry (PIV) technique. It was proved that the backrest and the gasper jet can prevent the front passenger from droplet spray in public transportation where maintaining social distance was difficult. A model was developed to describe the cough jet trajectory due to the gasper jet, which matched well with PIV results. It was found that buoyancy and inside droplets almost do not affect the short-range cough jet trajectory. Infection control measures were suggested for public transportation, including using backrest/gasper jet, installing localized exhaust, and surface cleaning of the backrest.

Comparison of Flow Behavior in Saccular Aneurysm Models Using Proper Orthogonal Decomposition

Aneurysms are abnormal ballooning of a blood vessel. Previous studies have shown presence of complex flow structures in aneurysms. The objective of this study was to quantify the flow features observed in two selected saccular aneurysm geometries over a range of inflow conditions using Proper Orthogonal Decomposition (POD). For this purpose, two rigid-wall saccular aneurysm models geometries were used (i.e., the bottleneck factor of 1 and 1.6), and the inflow conditions were varied using a peak Reynolds number (Rep) from 50 and 270 and Womersley number (α) from 2 and 5. The velocity flow field data for the studied aneurysm geometries were acquired using Particle Image Velocimetry (PIV). The average flow field from the PIV measurement showed that the model geometry and Rep have more significant impact on the average flow field than the variations in α. The POD results showed that the method was able to quantify the flow field characteristics between the two model geometries. The mode shapes obtained showed different spatial structures for each inflow scenarios and models. The POD energy results showed that more than 80% of the fluctuating kinetic energy were captured within five POD modes for BF=1.0 flow scenarios, while they were captured within ten modes for BF=1.6. The time varying coefficient results showed the complex interplay of POD modes at different inflow scenarios, highlighting important modes at different phases of the flow cycle. The low-order reconstruction results showed that the vortical structure either proceeded outward or stayed within the aneurysm, and this behavior was highly dependent on α, Rep, and model geometry that were not evident in average PIV results.

Performance of a Propeller Coated with Hydrophobic Material

Computational and experimental methods were used to study a propeller coated with hydrophobic material and a propeller with a conventional surface for comparison. In CFD simulations, the blade surface mesh was arranged in a way to set non-slip or free slip wall boundary conditions with different proportions to define the level of surface slip. The conventional and the hydrophobic material propellers defined by different surface slip rates were simulated under different advance speed coefficients and different rotational speeds. Propeller performance results, blade pressure, and the Liutex vorticity distribution were studied. An experimental platform was established to study the velocity field around the propeller using a Particle Image Velocimetry (PIV) device. The CFD calculation results were compared with the PIV results. It was found that the calculation results using a 75% surface slip rate were closer to the experimental results. The calculation results show that the propeller coated with hydrophobic material has improved thrust and efficiency compared with the propeller with conventional material. The hydrophobic material can significantly reduce the low-speed region downstream of the propeller hub. The hub and the tip vortices shown by the Liutex are also significantly reduced. Those changes help to improve the propulsion efficiency.

Validation of Non-Invasive Endothelial Shear Stress (ESS) Estimations of Coronary Artery Haemodynamics via In-Silico and In-Vivo Modelling

Endothelial shear stress (ESS) is parallel frictional force exerted by blood flow on the coronary luminal surface and is associated with the development and progression of atherosclerosis. Computational fluid dynamics (CFD) is an engineering method used to analyse fluid flow and has been increasingly applied to simulate ESS. However, current CFD-ESS estimates have never been validated and can display significant variability between research groups. This study aims to provide a comparative analysis of coronary flow using in-silico modelling of coronary flow and particle image velocimetry (PIV). A proximal left anterior descending (pLAD) coronary phantom model was constructed from a patient who had received same day cardiac computed tomography angiography (CTCA) and invasive coronary haemodynamic (Combowire XT) assessment. Patient-specific coronary flow data was applied to CFD boundary conditions and a mock circulatory loop. CFD via PIV under steady flow in a 4-times-scaled model was validated. Same plane velocity field and flow patterns (at mid-luminal of pLAD) from both in-silico and in-vivo data were compared. Mean velocity contours and magnitude were analysed from CFD and PIV. Patient specific average peak velocity obtained from invasive assessment was 0.21m/s. Patient-specific velocity average from CFD was 0.22m/s. The approximated magnitude difference is 4.7%. Velocity contours and flow patterns simulated in the CFD were also comparable with the PIV results. Simulation data from CFD correlate well with experimental PIV results. This early data allows for a non-invasive approach to determine patient-specific coronary haemodynamics (such as velocity profiling and ESS).

Flow and heat transfer in the wake of a triangular arrangement of spheres

This research work seeks to investigate the influence of spacing and heat transfer on the wake behavior of a triangular arrangement of spheres. Four experimental configurations have been investigated at three Reynolds numbers, Re1 = 350, Re2 = 700, and Re3 = 1050. Two isothermal cases were investigated with spacing between the spheres of zero and one sphere diameter, and two cases were investigated with an applied heat flux at the same spacing conditions. The time resolved particle image velocimetry results revealed various flow phenomena including flow separations, von Karman vortex shedding, and Kelvin–Helmholtz instabilities. The turbulent statistics reveal the effect of proximity and heat transfer on the time averaged values of the wake size, turbulent strengths, and Reynolds shear stress in the wake of each sphere, namely, the laminarization effects from the addition of heat and the suppression of the lead sphere wake from the proximity of the trailing spheres. These results are complemented by the application of proper orthogonal decomposition (POD) to the flow fields, which extracts the coherent structures from the flow. The modes that describe the coherent structures are extracted and described in detail, which provide further insight into effects of the experimental conditions on the temporal behavior of the flow. Many of the low order modes are found to be associated in pairs, corresponding to asymmetric structures or advection of a given structure downstream. The capability of POD to produce reduced order models of the flow is then utilized to facilitate vortex identification analysis. A turbulent kinetic energy based mode truncation criteria, which has been found to enhance vortex identification capability, is applied to select the POD modes and temporal coefficients to be used in the reduced order modeling. The reconstructed velocity fields are then analyzed with vortex identification algorithms to extract the vortex cores and boundaries. The combination of these approaches allows the study of the effect of proximity and heat transfer on the vortex characteristics, such as size, strength, and distribution.

Effects of gradient porous metal foam on the melting performance and energy storage of composite phase change materials subjected to an internal heater: A numerical study and PIV experimental validation

This work aims to explore the effects of gradient porous metal foam on the 3D melting heat transfer as well as the heat storage performance of a latent heat thermal energy storage (LHTES) unit inside an internal heated cubic cavity. A modified structure of metal foam with gradient porosity of three stratification layers is proposed to optimize the melting characteristic of the composite phase change materials. The enthalpy-porosity method is adopted to model melting process, and the Darcy-Forchheimer law and local thermal non-equilibrium model are assumed for metal foam. The numerical code of proposed model is in good consistency with the experimental results of particle image velocimetry (PIV) visualization. The effects of porosity gradient with equal and non-equal stratification heights, as well as pore per inch (PPI) on the melting performance, heat transfer and heat storage are investigated. The results indicate that the competitive relation between the conduction and convection induced by the gradient porosity influences the heat transfer and energy storage. The energy storage of negative gradient is greater than that of positive gradient, but the average rate of energy storage of the former is lower than that of the latter. In the middle melting stage, the total average Nusselt number increases with larger porosity gradient for positive cases and decreases for negative cases. With the increase of the stratification height of middle layer, the heat transfer efficiency of positive cases weakens, while it is enhanced for negative cases. Moreover, the increase of PPI can reinforce the conduction effect and improve the average rate of energy storage of the LHTES unit for both positive and negative cases.

Evaluating the behavior of expandable multi-plate mechanical anchors in granular soils

Many offshore and onshore platforms are constructed widely, especially in the energy supply sector. So far, various anchors with different shapes have been introduced for these applications to reinforce and stabilize the superstructures and related facilities. This study deals with the novel Expandable Multi-plate Mechanical Anchors (EMPMAs) and investigates their performance using physical modeling tests. Previous studies have focused on the behavior of single anchors, and there is no comprehensive experimental research on the multi-plate anchors, which is the subject of the present study. This research examines uplift capacity regarding the effect of five soil densities for loose, medium, and dense conditions and the vertical distance between two plate anchors from 0.5B to 2B. The obtained results were compared with the single plate anchor with equivalent areas. Based on the results, the highest bearing capacity is related to the EMPMA with an optimum distance of 1B in 80% relative density. In addition, by decreasing the distance between two plates, the relative density becomes a more dominant bearing capacity parameter. Furthermore, the Particle Image Velocimetry (PIV) method results are presented, and a new formula is proposed. Eventually, a comparative study is conducted between the results of PIV and an analytical formula.

Laboratory investigation of turbulent dissipation in an internal solitary wave breaking over a submerged Gaussian ridge

Laboratory experiments were conducted to investigate an internal solitary wave breaking over a submerged Gaussian ridge. Particle image velocimetry (PIV) was performed with a high-speed camera to analyze the macro- and microstructures of wave-breaking evolution and subsequent induced turbulence and mixing. Four types of wave breaking, namely, plunging breaking, collapsing breaking, plunging-collapsing breaking, and surging breaking, were identified, along with their different evolutionary processes and breaking mechanisms. The turbulent dissipation rates estimated from the PIV results were on the order of 10−6 to 10−4 m2/s3 during the breaking, with the smallest values in the plunging breaking and the largest in surging breaking. Generally, the intensity of turbulence in plunging breakers seems to be insensitive to the changing wave slope; however, the surging breaker shows an opposite trend.