Search Results (113)

Seepage beneath earth dams founded on pervious strata can cause excessive under-seepage, elevated downstream exit gradients, and high phreatic levels, thereby increasing susceptibility to internal erosion and piping. This study presents a Hele–Shaw laboratory investigation of seepage-control efficiency for an upstream impervious blanket used alone and in combination with a vertical cutoff (blanket–cutoff system). The experimental geometry reproduces a zoned earth dam cross-section at a scale of 1:200. Five foundation thickness ratios (T/B = 0.184–1.00) were tested. For the blanket-only system, four blanket length ratios (L_b/B = 0.50–1.25) were examined. For the blanket–cutoff system, cutoff depth ratios (S/T = 0.20–0.80) were investigated using (i) a representative blanket length L_b/B = 0.75 across all foundation depths and (ii) a deep-foundation case T/B = 1.00 across all blanket lengths. Seepage discharge, head loss due to seepage-control measures, maximum exit gradient at the downstream toe, and phreatic line location were measured at steady state and expressed in dimensionless form using the equivalent Hele–Shaw hydraulic conductivity. Relative to the no-measure reference case, the upstream blanket reduced dimensionless discharge by 20.8–70.2%, reduced the exit-gradient indicator by 6.4–50.2%, and reduced the downstream seepage-surface height by 58.9–92.8%. Adding a vertical cutoff provided further reductions relative to the blanket-only configuration, up to 34.4% in discharge and to 29.8% in exit-gradient indicator at L_b/B = 0.75—while increasing head loss across the upstream control system. Regression-based correlations and main-text design maps are proposed for preliminary sizing. The proposed correlations and design maps are intended for screening-level use only within the tested ranges 0.18 ≤ T/B ≤ 1.00, 0.50 ≤ L_b/B ≤ 1.25, and 0.20 ≤ S/T ≤ 0.80. Because the Hele–Shaw model is a two-dimensional viscous-flow analog of saturated seepage, the results provide a physical basis for relative comparison of seepage-control measures rather than a direct substitute for site-specific analysis of heterogeneous three-dimensional foundations. Accordingly, the agreement discussed in this paper is qualitative and trend-based, and the proposed tools are intended to complement rather than replace quantitative FEM for site-specific design. Full article

This study experimentally investigates a compact side-exhaust piezoelectric synthetic jet actuator equipped with outlet flaps and compares its performance with a flap-free baseline design. The flap concept is intended to mitigate hot-air recirculation during the suction phase and thereby improve near-field cooling in confined layouts. Experiments were conducted under a 350 Hz, 60 Vpp driving signal with an exit dimension of 20 mm × 1 mm. An initial screening campaign evaluated 24 flap configurations by varying flap length, thickness, and installation distance; the results showed that overly long flaps impose substantial blockage and momentum loss, and therefore the flow analysis was narrowed to a practical flap length of 29.5 mm. The final velocity characterization focuses on two representative flap thicknesses (0.1 mm and 0.5 mm) and three installation distances (5, 10, and 15 mm from the exit). For heat transfer evaluation, the nozzle-to-target spacing was varied from 5 to 50 mm in 5 mm increments. The modified actuator demonstrates improved near-field cooling performance, with the best case achieved using 0.1 mm flaps installed at 5 mm, yielding a maximum Nusselt number enhancement of 6.24% relative to the baseline at very small spacings. Furthermore, the thermal benefit becomes more pronounced at elevated heat source temperatures, with the strongest improvement observed around 60–80 °C (up to ~13% at 60 °C). These results provide practical design guidance for enhancing localized convective heat transfer in compact electronics cooling applications. Full article

To address the critical challenges of minimizing optical thickness and correcting chromatic aberrations in optically transparent head-mounted displays (HMDs), we propose a folded hybrid design incorporating freeform prisms and a discrete multi-wavelength achromatic metalens. Our approach integrates advanced optical engineering techniques to achieve optimal performance while maintaining compactness. The system leverages a phase-optimized SiNx/SiO₂ metalens combined with ray-tracing-based system optimization, enabling the development of a compact 12 mm thickness OST-HMD featuring an 8 mm exit pupil and a 39° virtual field of view (FOV). Through simulations, we demonstrate that this configuration achieves impressive modulation transfer function (MTF) values exceeding 0.7 at 50 lp/mm for see-through viewing and maintaining MTFs above 0.3 at 30 lp/mm for virtual imaging across wavebands. Simulation results highlight an improvement both in the miniaturization of the HMD while maintaining high resolution and in effective correction of chromatic aberrations, offering a robust solution for lightweight, high-performance AR display systems. This work represents an advancement in optically transparent display technology by providing an optimized design framework that balances compactness with visual fidelity. Full article

Background: Intranasal drug delivery is a preferred route for emergency administration of naloxone in opioid overdose due to its rapid onset of action and ease of use. However, limited knowledge exists on the delivery efficiency and safety of nasal sprays in neonates, particularly in life-threatening situations such as coma states where breathing is compromised. This study presents a physiology-based simulation of spray deposition and runoff loss in a 10-day-old infant nose model. Methods: Spray characteristics, including droplet size distribution, exiting velocity, and plume angle, were measured and implemented in ANSYS Fluent droplet tracking model. Naloxone film thickness was measured on ex vivo porcine nasal mucosa at varying angles and used in the Eulerian Wall-Film model. Simulations were conducted in a 10-day-old nose geometry across multiple doses (0.25, 0.50, 1.0, and 2.0 mL) in supine and 45° inclined postures to quantify regional deposition, liquid film translocation, and pharyngeal runoff. Results: While a 0.25 mL spray was fully retained in the nasal passages, higher doses exceeded the mucosal holding capacity and caused significant runoff. Runoff into the pharynx was 18.5% and 10.1% for the spray volume of 0.50 mL in the 45° back tilt and supine positions, respectively. The 1.0 mL spray caused 55.1% and 53.5% runoff in the 45° back tilt and supine positions, while the 2.0 mL spray caused 77.5% and 76.8% runoff in the 45° back tilt and supine positions, respectively. Conclusions: These findings highlight the critical influence of spray volume on drug delivery outcomes in neonates and provide quantitative guidance for optimizing intranasal naloxone administration in emergency pediatric care. Full article

The high-speed motion of a vehicle underwater induces cavitation, and the resulting cavity alters the surface pressure distribution and flow field characteristics. This study employs a numerical approach combining the $\mathrm{k}-\omega$ SST (Shear Stress Transport) turbulence model, the VOF (Volume of Fluid) multiphase flow model, the Schnerr–Sauer cavitation model, and the overlapping mesh technique. The numerical method is validated through the good agreement between simulation results and experimental data for both cavity shape and vehicle trajectory, with a maximum relative error of 6.1% in vertical displacement. The results indicate that during the launch-tube exit phase, with $\sigma =0.235$ and $\mathrm{Fr}=47.9$, the vehicle acceleration causes the pressure at its shoulder to drop below the saturated vapor pressure, initiating cavitation. Under transverse flow (intensity U = 0.016–0.05), the cavity becomes asymmetric. Specifically, the axial length and radial thickness on the back side are significantly larger than those on the face side, and this asymmetry intensifies with increasing transverse flow intensity. Furthermore, after exiting the launcher, the vehicle’s trajectory and attitude deflect towards the back side and the deflection amplitude increases, with horizontal displacement and attitude angle variation positively correlated with transverse flow intensity. Full article

Extrusion of AlZnMgCu alloys is associated with a very high plastic resistance of the materials at forming temperatures and significant friction resistance, particularly at the contact surface between the ingots and the container. In technological practice, this translates into high maximum extrusion forces, often close to the capacity of hydraulic presses, and the occurrence of surface cracking of extruded profiles, resulting in a reduction in metal exit speed (production process efficiency). The accuracy of mathematical material models describing changes in the plastic stress of a material as a function of deformation, depending on the forming temperature and deformation speed, plays a very important role in the numerical modelling of extrusion processes using the finite element method (FEM). Therefore, three mathematical material models of the tested aluminium alloy were analysed in this study. In order to use the results of plastometric tests determined on the Gleeble device, they were approximated with varying degrees of accuracy using the Hnsel–Spittel equation and then implemented into the material database of the QForm-Extrusion^® programme. A series of numerical FEM calculations were performed for the extrusion of Ø50 × 3 mm tubes made of 7075 aluminium alloy using chamber dies for two different billet heating temperatures, 480 °C and 510 °C, and for three different material models. The metal flow was analysed in terms of geometric stability and dimensional deviations in the wall thickness of the extruded tube and its surface quality, as well as the maximum force in the extrusion process. Experimental studies of the industrial extrusion process of the tubes, using a press with a maximum force of 28 MN and a container diameter of 7 inches, confirmed the significant impact of the accuracy of the material model used on the results of the FEM numerical calculations. It was found that the developed material model of aluminium alloy 7075 number 1 allows for the most accurate representation of the actual conditions of deformation and quality of extruded tubes. Moreover, the material data obtained on the Gleeble simulator made it possible to determine the limit temperature of the extruded alloy, above which the material loses its cohesion and cracks appear on the surface of the extruded profiles. Full article

Burrs are a significant machining defect affecting the quality of precision parts, and tool eccentricity may substantially influence milling burrs. Using AISI 304 stainless steel as the workpiece material, a three-dimensional thermo-mechanical coupled model for slot milling was constructed based on an explicit dynamics model. Combining the Johnson–Cook (J-C) constitutive model with the J-C shear failure criterion, simulations were conducted to obtain burr dimensions, cutting temperature distributions, and cutting force waveforms under different tool eccentricity directions and magnitudes. Results: As the eccentricity increases, the temperature of the top burr rises, and both the width of the top burr and the thickness of the exit side burr significantly increase. Under simulated conditions, the width of the top burr in down milling side increased by up to 70%. The burr dimensions under different eccentricity directions can differ by approximately 40%. Groove milling experiments revealed similar burr shapes between experimental and simulated results. Furthermore, the simulated cutting force waveforms aligned with those in the literature, indicating the reliability of the simulation outcomes. Based on these findings, it can be concluded that tool eccentricity significantly affects the dimensions of top burrs and exit side burrs. The width of top burrs and the thickness of exit side burrs are positively correlated with the tool eccentricity distance, while exit bottom burrs remain unaffected by eccentricity. These research results provide valuable reference for burr suppression in practical machining operations. Full article

The natural frequencies and damping characterisation of a new aerospace grade composite material were investigated using a modified impulse method combined with the half power bandwidth method, which is applicable to the structures with a low damping. The composite material of interest was unidirectional carbon fibre reinforced plastic. The tests were carried out with three identical square 4.6 mm thick plates consisting of 24 plies. The composite plates were clamped along one edge in a SignalForce shaker, which applied a sinusoidal signal generated by the signal conditioner exiting the bending modes of the plates. Laser vibrometer measurements were taken at three points on the free end so that different vibrational modes could be obtained: one measurement was taken on the longitudinal symmetry plane with the other two 35 mm on either side of the symmetry plane. The acceleration of the clamp was also recorded and integrated twice to calculate its displacement, which was then subtracted from the free end displacement. Two material orientations were tested, and the first four natural frequencies were obtained in the test. Damping was determined by the half-power bandwidth method. A linear relationship between the loss factors and frequency was observed for the first two modes but not for the other two modes, which may be related to the coupling of the modes of the plate and the shaker. The experiment was also modelled by using the Finite Element Method (FEM) and implicit solver of LS Dyna, where the simulation results for the first two modes were within 15% of the experimental results. The novelty of this paper lies in the presentation of new experimental data for the natural frequencies and damping coefficients of a newly developed composite material intended for the vibration analysis of rotating components. Full article

This study presents a combined experimental and numerical investigation into the evolution of projectile attitude during oblique penetration into thin concrete targets at non-zero angles of attack. An oblique penetration test system was developed based on a cannon platform, incorporating a planar mirror reflection technique and high-speed imaging to capture the projectile’s spatial orientation. A set of equations was derived to relate the projectile’s three-dimensional attitude angles to its two-dimensional and mirror-reflected projections. The system demonstrated the ability to generate controlled initial angles of attack and accurately measure the projectile’s attitude, with measurement errors primarily within 2° and a maximum error of approximately 5°. Numerical simulations were conducted using the RHT strength model to replicate the experimental process. The simulation results showed good agreement with experimental data, with residual velocity errors less than 5% and attitude angle deviations below 15%. The validated model was further employed to study the effects of initial velocity, impact angle of attack, and target thickness on the evolution of projectile attitude. The findings reveal that, within a velocity range of 550–1000 m/s, the post-perforation attitude angle is negatively correlated with projectile velocity, though the variation remains under 15%. Increasing the target thickness from 90 mm to 240 mm significantly raises the post-perforation attitude angle and angle of attack by more than 70% and 20%, respectively. Under varying initial attitude angles, the final attitude angle increases with the initial value, with the maximum growth rate occurring around 15°, after which the rate gradually decreases. The angle of attack evolution during penetration can be divided into four stages: (1) crater formation, (2) plugging penetration, (3) breakthrough plugging, and (4) post-exit. These results offer valuable insights into projectile dynamics under complex impact conditions and provide theoretical support for the design of protective structures. Full article

The flow and solidification inside the mould are crucial to the quality of the casting billet during continuous casting. In this work, a three-dimensional coupled model of flow and solidification was established, and the flow field and temperature distribution characteristics of molten steel were deeply explored. The results indicated that the molten steel streams out of the SEN at a defined degree and enters the mould in the form of an impact stream, and then impacts the narrow surface. The eddy core position in the upper recirculation region of the flow field is (0.565 m, −0.179 m), and eddy core position in the lower recirculation region is (0.524 m, −0.455 m). Within the range of 100–400 mm from the liquid surface, the main stream and upper ring flow of molten steel have a significant impact on the solidification of the casting billet, and the distribution and longitudinal variation in the liquid phase ratio at different height sections are very obvious. At the exit of the mould, the average thickness of the inner arc and outer arc shells is 15.2 mm and 14.5 mm, respectively. The model can provide guidance for enhancing and optimizing the quality of continuous casting billets. Full article

A new quasi-one-dimensional ejector model for the prediction of ejector performance is carried out, which is based on the theory of ideal gas expansion and free layer development. The model is proposed for calculation of the variable area bypass injector (VABI) and ejector nozzle in the variable cycle engine (VCE), both at the design point and off-design point. The internal structure of ejector nozzle is determined based on an analysis of the flow field of the 2D ejector nozzle Computational Fluid Dynamics (CFD) result. The flow during the expansion section is divided into three parts: primary flow, secondary flow, and mixed layer flow. Combined with the growth rate of mixing layer thickness, the calculation methods of ejector nozzle exit parameters under critical working conditions and blocking working conditions are given, and the calculated results demonstrate a strong consistency with CFD results, maintaining relative errors below 3%. This method is used to evaluate the ejector nozzle capacity quickly in the overall design stage, which provides theoretical support for the design of the main bypass system of a variable cycle engine. Full article

To address the limitations of existing models that typically treat crater formation and shear plugging as independent processes and only consider angle of attack effects during the initial crater phase, this study proposes a dynamic shear _plugging model for projectile penetration into thin concrete targets. The model is built upon the improved three-stage penetration theory and cavity expansion principles, and introduces a coupled cratering, plugging mechanism that captures the simultaneous interaction between these stages. A differential surface force approach is employed to describe the asymmetric stress distribution on the projectile nose under non-zero angle of attack conditions, while free surface effects are incorporated to refine local stress predictions. A series of validation experiments was performed with 30 mm rigid projectiles penetrating 27 MPa concrete slabs under different impact velocities and initial angles of attack. The results show that the proposed model achieves prediction errors of less than 20% for both residual velocity and exit attitude angle, significantly outperforming classical models such as those of Duan and Liu, which tend to underestimate post-impact deflection by treating cratering and plugging separately. Based on this validated framework, parametric studies were conducted to examine the effects of the initial inclination, impact velocity, and target thickness on the evolution of projectile attitude and angle of attack. The findings demonstrate that the dynamic shear plugging mechanism exerts a critical regulatory influence on projectile deflection during thin target penetration. This work, therefore, not only resolves the directional reversal issue inherent in earlier theories but also provides theoretical support for the engineering design of concrete protective structures subjected to angular impact conditions. Full article

High-fidelity replication of compressor exit flow fields is critical for combustor design, yet current simulation facilities lack effective, decoupled control of flow parameters. This study proposes a coordinated optimization strategy combining segmented stationary blade twist with leading-edge baffle configurations. The blades are divided into three spanwise sections with independently optimized twist angles to match airflow deflection. Upstream baffles are redesigned by reducing thickness, shortening horizontal length, and adjusting spanwise position to improve total velocity distribution. The final Plate-T configuration achieves a peak total velocity error of ~3.0% and position error of ~8.5%, while maintaining deflection angle accuracy. Experimental validation confirms improved agreement with compressor outlet flow fields, providing robust support for studies on flame stability, emissions, and combustion performance, as well as guidance for aero-engine experimental facility design. Full article

In gas drilling operations, the blooey line is highly susceptible to erosion-induced leakage. This study focuses on the use of field-welded V-shaped elbows in blooey lines, establishing a numerical method for erosion prediction and validating its accuracy through experimental data. The numerical results reveal that, due to the inclined configuration of the V-shaped elbow, particles from the central inlet flow directly impact the outer wall of the outlet pipe opposite the inlet, and then rebound and strike the inner wall. Meanwhile, solid particles near the pipeline wall on both sides of the inclined plane collide with the outer wall and exit in a helical flow pattern along the outlet pipe. The maximum erosion rate (3.6 × 10⁻⁴ kg/(m²·s)) occurs at the intersection of these spiral particle flows. Based on erosion predictions under various operating conditions, an empirical formula was established to correlate the erosion rate with the gas injection rate at a rate of penetration (ROP) of 1 m/h, along with corresponding conversion relationships for different ROPs. The predicted residual thickness of the V-shaped elbow showed a 6.8% relative error compared to field measurements. The proposed method can be programmed to enable real-time monitoring of the residual wall thickness and the remaining service life of the blooey line before leakage occurs, assisting field operators in determining optimal pipeline replacement schedules to ensure operational safety. Full article

To address the challenges of non-axisymmetric tube spinning, this study employs finite element simulations to validate a novel spinning method for right-angle groove tubes. Three forming schemes with distinct roller path geometries were designed and analyzed using Simufact Forming, with 6063-O aluminum alloy tubes serving as the research material. The simulation results indicate that multi-pass forming (Schemes I and II) significantly enhances wall thickness uniformity compared to single-pass forming (Scheme III). Scheme I exhibits optimal performance due to the minimized equivalent stress in the final forming pass. The maximum stress is concentrated at the groove bottom, leading to wall thinning and springback, while the maximum strain occurs at the roller exit point, where metal accumulation causes local wall thickening. Experimental observations confirm the consistency with the simulation results, validating the model’s reliability. This study deepens the understanding of deformation mechanisms in complex groove forming, highlighting the roller path geometry in controlling stress-strain distribution and final product quality. Full article