ORIFICE WALL CAVITATION AND SINGLE STRING CAVITATION IN FUEL INJECTORS

Initiation and displacement of landslide induced by earthquake — a study of shaking table model slope test

The steady and transient internal flows within an automotive fuel injector are studied by solving ensemble-averaged, three-dimensional mass and momentum conservation equations. In the analysis, the effects of operating pressure, orifice size, and needle lift on the static flow rate, and the effect of opening rate on the dynamic flow rate have been parametricly investigated. Pressure drop was varied from 100 kPa to 500 kPa; the orifice diameter and needle lift ranged between 400 μm to 700 μm and 60 μm to 120 μm, respectively. A multiblock moving mesh method was used to simulate the needle motion. Predicted static flow rates provide good agreements with the experimental measurements. Static flow increases as the orifice diameter increases. For a constant orifice diameter, static flow rate is found sensitive to the changes of the needle lift for a large nozzle while relatively insensitive for the smaller one. Dynamic flows under various needle opening rates are calculated and results are presented.

Study question Can ooplasm streaming (OS) velocity anticipate the fertilization outcome before the time for pronuclei appearance (tPNa) and infer the ultrastructural cytoskeleton profile of failed-to-fertilize oocytes? Summary answer Changes in OS-velocity post-ICSI identify normally and failed-to-fertilize (FF) oocytes before tPNa, and reveal an association between specific OS-velocities and different fertilization failure patterns. What is known already The ooplasm is a highly dynamic and fluidic milieu, which enables an efficient redistribution of its components in preparation for fertilization and the subsequent ultrastructural reorganization. Particle Image Velocimetry (PIV) has been employed to study the OS behaviour during oocyte activation and changes in velocity and directionality have been associated with the calcium oscillations triggered by a fertilizing sperm. These observations suggest that the ooplasm undergoes meaningful dynamic shifts during the process of fertilization. The question remains how OS swings in the event of failed fertilization, and whether PIV analysis could anticipate this outcome and shed light on the interpretation. Study design, size, duration This retrospective analysis includes 101 FF-oocytes from 22 patients experiencing ICSI failures (mean fertilization rate 31,4±13,5%). FF-oocytes underwent immunodetection to assess meiotic spindle, sperm nucleus and flagellum configurations. FF-oocytes were grouped based on the sperm nucleus configuration: Intact head, Decondensed nucleus, and Premature chromosome condensation (PCC). The absence or the presence of the second polar body (PB) was annotated revisiting time-lapse videos. PIV analysis was applied to FF-oocytes (Study group) and diploid/euploid zygotes (Control group). Participants/materials, setting, methods For immunocytochemistry (ICC) studies we used Hoechst (DNA), alpha-tubulin (maternal spindle) and acetylated-alpha-tubulin (sperm flagellum) monoclonal antibodies. Microinjected MII-oocytes were cultured under hypoxia (Geri; Genea-Biomedx, AUS) using G-TL (Vitrolife, SWE). PIV analysis (v3.08PIVlab, MATLAB) determined the average OS-velocity (µm/s) per hour post-ICSI (hpi). Further, we calculated the velocity change rate (%) from 1hpi to 8hpi, to compare amongst grouped FF-oocytes and the controls. Main results and the role of chance A total of 87 FF-oocytes (86,1%) were informative after ICC. Informative FF-oocytes were grouped following their sperm nucleus profiles: Intact-head (n = 9; 1stPB 11,1%; 2ndPB 88,9%); Decondensed-nucleus (n = 13; 1stPB 61,5%; 2ndPB 38,5%); PCC (n = 53; 1stPB 39,6%; 2ndPB 60,4%); Other patterns (n = 12). This last group (other patterns) and non-stationary time-lapse images (n = 21) were excluded from PIV analysis. Control-oocytes (n = 14) had an OS-velocity (1hpi) of 9,8±0,7 µm/s, declining by 48% at 8hpi. Intact-Head FF-oocytes (n = 7) showed an OS-velocity (1hpi) of 9,8±0,8 µm/s, with a 16% decrease at 8hpi. Decondensed-nucleus FF-oocytes (n = 7) had an initial OS-velocity of 10,6±0,9 µm/s, declining by 7% at 8hpi. PCC FF-oocytes (n = 40) showed an OS-velocity at 1hpi of 8,8±1,0 µm/s, decreasing by 25% at 8hpi. The results reveal a decline in the OS velocity over time, which is significantly slower in FF-oocytes than in controls (p-value <0,05). The velocity change rate showed significant differences from 4hpi between Intact-Head and Decondensed-Nucleus FF-oocytes and the controls, and from 6hpi in PCC FF-oocytes. These data suggest an association between OS velocities and specific ultrastructural cytoskeleton profiles. No differences were observed in PIV when sub-analysing PCC FF-oocytes by the 2ndPB extrusion. Low sample sizes of Head-Intact and Decondensed-nucleus FF-oocytes restricted similar subgroupings. Limitations, reasons for caution This study is a cohort analysis based on a limited sample size; therefore, the results should be interpreted with caution. Prospective studies are required to validate the present observations. PIV analysis only applies to oocytes that remain focused and stationary within the well during incubation. Wider implications of the findings To the best of our knowledge, this is the first study to establish a correlation between failed-to-fertilize immunodetection data, time-lapse imaging, and PIV analysis. Our findings suggest that PIV analysis could serve as a non-invasive method to infer the underlying causes of fertilization failure after ICSI. Trial registration number No

<div class="htmlview paragraph">An experimental study was conducted to characterize the dynamics and spray behavior of a wide range of minisac and Valve-Covered-Orifice (VCO) nozzles using a high-pressure diesel common-rail system. The measurements show that the resultant injection-rate is strongly dependent on common-rail pressure, nozzle hole diameter, and nozzle type. For split injection the dwell between injections strongly affects the second injection in regards to the needle lift profile and the injected fuel amount. The minisac nozzle can be used to achieve shorter pilot injections at lower common-rail pressures than the VCO nozzle.</div> <div class="htmlview paragraph">Penetration photographs of spray development in a high pressure, optical spray chamber were obtained and analyzed for each test condition. Spray symmetry and spray structure were found to depend significantly on the nozzle type. The minisac class of diesel nozzle definitely exhibits superior characteristics regarding hole-to-hole spray symmetry, whereas the VCO class of diesel nozzles produce a more asymmetric, but more dispersed spray plume, with potentially better fuel-air mixing performance than the minisac nozzle. The dual-guided VCO class of nozzle does not significantly improve the spray symmetry over that of the single-guided nozzle. However measurement of spray tip penetration length shows that the dual-guided VCO nozzle provides higher spray-tip velocities than is achieved for single-guided tips. The results obtained show that the liquid spray tip penetration mainly depends on nozzle type, needle guiding strategy, injection pressure, and ambient gas pressure.</div> <div class="htmlview paragraph">Close to nozzle exit spray dynamics observation was carried out. The microscopic visualization results provide very interesting and dynamic information on spray structure, showing spray angle variations, injection-to-injection variation, and primary breakup processes not observed using conventional macroscopic visualization techniques. The near-field spray behavior is shown to be highly transient, strongly depend on the injector design, nozzle geometry, needle lift and vibration, and injection pressure which is a function of the injection system.</div>

The present dissertation has investigated the influence of injection parameters on air/fuel mixture and combustion processes in a DISI engine, through advanced diagnostics. It is possible to distinguish three parts of the work: the spray macroscopic parameters characterization, the spray break-up investigation and the study of the effects of injection timing and duration on the combustion process. In the first stage, the influence of injection pressure and duration on the fuel mass rate and the spray morphology has been analysed. A fuel injection rate meter based on the Bosch Tube principle has provided useful information about the time resolved behaviour of the delivered mass highlighting both transient, such as needle lift and nozzle closing operation, and quasi steady stages of the injection event. 2D Mie-scattering imaging and Particle Image Velocimetry technique have been used for characterizing the liquid spray morphology in terms of tip penetration, cone angle and velocity vector distribution. Even if the injection parameters affect the overall spray geometry, the characterization of the inner structure of the spray is fundamental for featuring the atomization phenomena which influence the fuel - air interaction. Therefore, Phase Doppler Anemometry (PDA) and Laser Doppler Velocimetry (LDV) have been applied for providing information about the velocity and size of droplets. Trials have been performed at different injection pressures and distances from the nozzle, along two different axes: the first one corresponding to the jet axis, the second one on the jet edge. Especially at the higher injection pressure, accurate tests have been possible only at a certain distance from the nozzle, where the spray is more dilute and the laser beam can cross the jet core. For this reason X-ray absorption measurements have been performed in order to investigate high-dense regions of fuel sprays, immediately downstream of the nozzle, providing quantitative measurements of the fuel. X-rays penetrate the dense part of fuel spray because of its weak interaction with the hydrocarbon chain due to their low atomic number. X-ray radiography and tomography have been used to investigate the spray core and reconstruct the 3D inner structure. The information about the spray development has been used to optimize the injection strategies of an optically accessible DISI engine operating at mid load condition, at a fixed speed of 2000 rpm. UV-visible imaging has been performed on the engine for investigating the influence of the injection duration and timing on the flame front propagation, while natural emission spectroscopy has been applied to characterize the formation and the evolution of the main compounds featuring the spark ignition and combustion processes. Exhaust emission measurements (HC, CO and NOx) have been correlated with pressure related data and optical results.

Aneurysms develop as a result of abnormal dilation of a blood vessel due to vessel disease, trauma or congenital factors. A fully grown aneurysm can rupture and lead to cerebral hematoma and hemorrhage. In this research, lateral aneurysms of cerebral arteries were studied by simulation and experimental particle image velocimetry (PIV) analysis in glass models. Reynolds numbers of 100, 400 and 700 were used to characterize flow of blood in cranial blood vessels. Results indicate that rupture is likely on the dome or at the base of aneurysm that experience the impingement of flow. Higher shear stresses were noticed on distal end walls of the aneurysm in simulation. PIV results in glass models seem to suggest that the neck of an aneurysm acts in a way to redirect the blood towards dome. In-vivo, such redirected flows could influence the aneurysm growth and cause higher shear on the proximal walls. Thus, rupture could be localized on the walls of the aneurysmal dome where the flow velocities are absorbed or at the base region or where there is more shear.

Biomechanics of Plant Roots: estimating Localised Deformation with Particle Image Velocimetry

Conventional, field-based streamflow monitoring in remote, inaccessible locations such as Alaska poses logistical challenges. Safety concerns, financial considerations, and a desire to expand water-observing networks make remote sensing an appealing alternative means of collecting hydrologic data. In an ongoing effort to develop non-contact methods for measuring river discharge, we evaluated the potential to estimate surface flow velocities from satellite video of a large, sediment-laden river in Alaska via particle image velocimetry (PIV). In this setting, naturally occurring sediment boil vortices produced distinct water surface features that could be tracked from frame to frame as they were advected by the flow, obviating the need to introduce artificial tracer particles. In this study, we refined an end-to-end workflow that involved stabilization and geo-referencing, image preprocessing, PIV analysis with an ensemble correlation algorithm, and post-processing of PIV output to filter outliers and scale and geo-reference velocity vectors. Applying these procedures to image sequences extracted from satellite video allowed us to produce high resolution surface velocity fields; field measurements of depth-averaged flow velocity were used to assess accuracy. Our results confirmed the importance of preprocessing images to enhance contrast and indicated that lower frame rates (e.g., 0.25 Hz) lead to more reliable velocity estimates because longer capture intervals allow more time for water surface features to translate several pixels between frames, given the relatively coarse spatial resolution of the satellite data. Although agreement between PIV-derived velocity estimates and field measurements was weak (R2 = 0.39) on a point-by-point basis, correspondence improved when the PIV output was aggregated to the cross-sectional scale. For example, the correspondence between cross-sectional maximum velocities inferred via remote sensing and measured in the field was much stronger (R2 = 0.76), suggesting that satellite video could play a role in measuring river discharge. Examining correlation matrices produced as an intermediate output of the PIV algorithm yielded insight on the interactions between image frame rate and sensor spatial resolution, which must be considered in tandem. Although further research and technological development are needed, measuring surface flow velocities from satellite video could become a viable tool for streamflow monitoring in certain fluvial environments.

<div class="htmlview paragraph">Experiments were performed to better understand the aerodynamic flow field of a flapping-wing micro air vehicle. High-resolution laser sheet flow visualization and particle image velocimetry (PIV) analyses have shown the presence of folded vortex filaments that are trailed from the tip and root of the wing, which are combined with a shed dynamic stall vortex with a strong spanwise flow toward the wing tip. This leading-edge vortex gains strength as the translational motion of the wing accelerates through mid-stroke. There is a subsequent shedding of this vortex, but with the simultaneous formation of another leading-edge vortex. The generation of the second vortex occurs before the first vortex reaches mid-chord, enhancing overall lift. This second vortex moves along the chord during supination, before finally being shed from the trailing-edge of the wing. A starting vortex forms near the trailing-edge as the wing starts to accelerate during the downstroke/upstroke of the flapping cycle. This starting vortex grows larger in size, gaining energy from further shed vortices, until the wing reaches the mid-point of the cycle. The folded root and tip vortices that trail from the flapping wing have been found to be relatively strong, and move inward and axially downward as the wing moves through its flapping cycle. The close proximity of the starting vortex, as well as the trailed root and tip vortices, has a large influence on the downwash over the wing. This suggests that any modeling techniques used to predict the lift on flapping wings must fundamentally take into account the three-dimensional, unsteady effects associated with its complex vortex wake structure.</div>

A new image feature tracking velocimetry is presented and tested on airborne video data available from a previous study at Murg Creek (Canton Thurgau, Switzerland). Here, the seeded flow scenery had been recorded by an off-the-shelf action camera mounted to a low-cost quadcopter, and video frames were ortho-rectified to sizes of 4482×2240 px2 at a scale of 64 px/m. The new velocimetry approach is as follows: An adaptive Gaussian mixture model is used for video background subtraction. Then, scale-invariant keypoints on each remaining binary foreground image frame are determined by a feature detection algorithm, and corresponding feature points in subsequent frame pairs are matched using the iterative random sample consensus method. The related feature shifts in metric space divided by the video frame rate finally give the velocity vectors. The obtained velocimetry fields are compared with findings from both a particle image velocimetry and particle tracking velocimetry analysis in terms of accuracy and needed computational power. Indication is given that the feature tracking algorithm presents slightly less precise results, but clearly outperforms the other two in relation to computational power. Therefore, the new simplified method provides a high potential tool that may enable a future way to real time surface velocity measurements obtained from unmanned airborne vehicles.

The mechanical behavior of loess is highly predicated on variation in its moisture content. While the impacts of the water content on the shearing behavior and collapsibility of loess have been extensively studied, its effect on tensile characteristics has received relatively little attention. In this study, a series of tensile tests were conducted on remolded specimens of a clayey loess that were collected from Ili Valley in China. Two sets of loess specimens with varying water contents were prepared separately using wetting and drying methods. The influence of the water content on the tensile stress–strain response, failure mode and tensile strength was investigated by combining the tensile test results and particle image velocimetry (PIV) analysis. On this basis, a nuclear magnetic resonance (NMR) test and scanning electron microscopy (SEM) observations were implemented in order to assist with the interpretation of the underlying mechanism. The test results indicate that the tensile failure process and the variation of tensile strength with varying water contents differ for specimens that are prepared with wetting and drying methods; a finding which arises from the differences in the soil microstructure, clay–water interaction and the distribution of capillary and adsorbed water. This research has shown that the tensile strength of clayey loess is essentially dominated by the clay’s hydration/cementation and the development of capillary and adsorption suction as well as the microstructural evolution that occurs with the change in the water content. Based on the experimental observations, a conceptual model is proposed in order to interpret the effect of water content on loess’ tensile behavior.

Nuclear power plants are designed to avoid damage to their safety installations because of jet impingement when a pipe is ruptured. We have investigated the evaluation method for the design basis of protection of plants against effects of a postulated pipe rupture using the established standard of the American National Standards Institute (ANSI). The steam jet tests using particle image velocimetry and computational fluid dynamics (CFD) analysis were conducted for this verification. Spread angle of steam jet could be visualized. The jet spread angles were lower than 10 deg which was described in the ANSI standard. The ANSI standard was conservative for evaluations of the jet impact region compared to actual test and CFD results. However, it is desirable to use the conservative angle for evaluation of the jet fluid force. We could adequately evaluate the conservative jet fluid forces by the ANSI standard considering the spread suppression region and jet spread angle of 6 deg.

Centrifuge model test and numerical interpretation of seismic responses of a partially submerged deposit slope

Multiphase flow modeling in centrifugal partition chromatography

An interlocking block pavement (IBP) comprises discrete blocks, joints, bedding sand, and base and subbase layers. The thickness of the bedding sand layer gives significant impact on IBP performance. However, previous laboratory model tests have often overlooked the geotechnical properties of paving materials and the deformation characteristics of the sublayers, leading to conflicting recommendations regarding appropriate thickness. This study performed laboratory tests on IBP models with varying bedding thicknesses (30, 50, and 80 mm), considering the geotechnical properties (relative density, shear strength, and stress–strain behaviour) of the paving materials. In addition, a novel two-dimensional (2D) model chamber with a transparent wall was designed for particle image velocimetry (PIV) analysis to assess the overall deformation of the sublayers. The test results demonstrated that a bedding thickness of 50 mm exhibited higher load-dispersion ability, allowing the blocks to settle and rotate appropriately and achieving a full interlocking effect. Consequently, the deflection in the sublayer was distributed over a wide area at shallow depths. However, a bedding thickness of 30 mm provided a better performance in terms of resistance to deflection, imposing a higher stress on the base layer.