Search Results (90)

Contemporary evaluation and surgical approaches in congenital aortic valve disease have yielded limited success. The ability to evaluate and understand detailed flow characteristics surrounding surgical repair may be beneficial. This study explores the feasibility and utility of echocardiographic-based blood speckle imaging (BSI) in assessing pre- and post-operative flow characteristics in those with non-stenotic congenital aortic root disease undergoing aortic valve repair or valve-sparing root replacement (VSRR) surgery. Transesophageal echocardiogram was performed during the pre-operative and post-operative assessment surrounding aortic surgery for ten patients with non-stenotic congenital aortic root disease. BSI, utilizing block-matching algorithms, enabled detailed visualization and quantification of flow parameters from the echocardiographic data. Post-operative BSI unveiled enhanced hemodynamic patterns, characterized by quantified changes suggestive of the absence of stenosis and no more than trivial regurgitation. Rectification of an asymmetric jet and the reversal of flow on the posterior aspect of the ascending aorta resulted in a reduced oscillatory shear index ($OSI$) of $0.0543\pm 0.0207$ (pre-op) vs. $0.0275\pm 0.0159$ (post-op) and $p=0.0044$, increased peak wall shear stress of $1.9423\pm 0.6974$ (pre-op) vs. $3.6956\pm 1.4934$ (post-op) and $p=0.0035$, and increased time-averaged wall shear stress of $0.6885\pm 0.8004$ (pre-op) vs. $0.8312\pm 0.303$ (post-op) and $p=0.23$. This correction potentially attenuates cellular alterations within the endothelium. This study demonstrates that children and young adults with non-stenotic congenital aortic root disease undergoing valve-preserving operations experience significant improvements in flow dynamics within the left ventricular outflow tract and aortic root, accompanied by a reduction in $OSI$. These hemodynamic enhancements extend beyond the conventional echocardiographic assessments, offering immediate and valuable insights into the efficacy of surgical interventions. Full article

The velocity distribution at the deflector jet outlet significantly influences the pressure characteristics of the pilot stage, thereby affecting the dynamic performance of the servo valve. Conventional mathematical models fail to account for the influence of dynamic velocity distribution on pilot stage pressure characteristics, resulting in significant deviations from actual situations. As the deflector shifts, the secondary jet velocity distribution transitions from a symmetric to an asymmetric dynamic profile, altering the pressure within the receiving chambers. To address this, a dynamic skewed velocity distribution model is proposed to more accurately capture the pressure characteristics. The relationship between the skewness coefficient and deflector displacement is established, and the pressure calculation method for the receiving chambers is refined accordingly. A comparative analysis shows that the proposed model aligns most closely with computational fluid dynamics results, achieving a 98% match in velocity distribution and a maximum pressure error of 1.43%. This represents an improvement of 84.98% over the normal model and 82.35% over the uniform model, confirming the superior accuracy of the dynamic skewed model in pilot stage pressure calculation. Full article

Stenosis geometries are constrictions of a biological tube that can be found in many forms in the human body. Capturing the flow field in such geometries is important. For this purpose, simulations were performed using the generalised k-$\omega$ (GEKO) turbulence model to study flow through stenosis geometries with throat constrictions of 75, 50 and 25% area reduction. Laminar flow conditions of Re = 2000 and 1000 were applied and the results were compared with experimental data. The effect of four GEKO parameters ($C_{SEP}$, $C_{NW}$, $C_{JET}$ and $C_{MIX}$) on flow in the post-stenotic region was investigated by simulating a wide range of parameter values. Results showed that the $C_{MIX}$ parameter, combined with a modified GEKO blending function, had the greatest effect on axial velocity, velocity fluctuations and the location of the jet breakdown region. A $C_{MIX}$ value of 0.4 closely matched the experimental results for a 75% area reduction stenosis at $Re=2000$ and showed significant improvements over existing Reynolds-averaged Navier–Stokes models. The GEKO model was also able to closely match the axial velocity results predicted by previously published large-eddy simulation models under the same flow conditions. Furthermore, the GEKO model was applied to a realistic oral-to-tracheal airway model for a Reynolds number of 2000 and produced results consistent with the idealised stenotic tube. Full article

Fontan circulation is a fragile system in which imperfections at any of multiple levels may compromise the quality of life, produce secondary pathophysiology, and shorten life span. Increased inferior vena caval pressure itself may play a role in “Fontan failure”. This study describes a mock flow loop model (MFL) designed to quantitatively estimate pulmonary flow entrainment induced by continuous and pulsed flow injections. A patient generic 3D-printed phantom model of the total cavopulmonary connection (TCPC) with average dimensions matching those of a 2–4-year-old patient was inserted in an MFL derived from a reduced lumped parameter model (LPM) representing cardiovascular circulation. The LPM comprises four 2-element Windkessel compartments (compliance and resistance), approximating the upper and lower systemic circulations and the right and left pulmonary circulations. The prescribed cardiac output is about 2.3 L/min for a body surface area of $0.675{ \mathrm{m}}^2$. The injections originate from an external pump through a 7–9 fr catheter, following a strict protocol suggested by the clinical team, featuring a variation in injection rate (flow rate), injection volume, and injection modality (continuous or pulsed). The key measurements in this study are the flow rates sampled at the distal pulmonary arteries, as well as at the upper and lower body boundaries. These measurements were then used to calculate effective entrainment as the difference between the measured and expected flow rates, as well as jet relaxation (rise and fall time of injection). The results show that for continuous or pulsed injections, varying the total volume injected has no significant influence on the entrainment rate across all injection rates. On the other hand, for both injection modalities, increasing the injection rate results in a reduction in entrainment that is consistent across all injected volumes. This study demonstrates the effectiveness of a high-speed injection jet entraining a slow co-flow while determining the potential for fluid buildup, which could ultimately cause an increase in caval pressure. To avoid the increase in caval pressure due to mass accumulation, we added a fenestration to our proposed injection jet shunt-assisted Fontan models. It was found that for a set of well-defined parameters, the jet not only can be beneficial to the local flow, but any adverse effect can be obviated by careful tuning. These results were also cross-validated with similar in silico findings. Full article

Oxy-fuel combustion is a promising way to avoid process-based CO₂ emissions. In this paper, the operational range of a new semi-industrial oxy-fuel combustion chamber for pulverized biomass is analyzed. This approach is used to gain a deeper understanding of the combustion setup and to examine the differences between air and oxy-fuel combustion on an industrial scale. Both analyzed parameters—flame spread and temperature distribution—have a significant influence on heat transfer in commercial boilers. The stability of various operating conditions is assessed by monitoring the CO content in the flue gas via a gas analyzer unit. For stable operation using walnut shells as fuel in an air atmosphere, an overall air-to-fuel ratio of 1.57–1.75 and a local air-to-fuel ratio of 0.75–0.95 provide the most stable conditions. A high swirl number of $0.9$ is found to be critical for stability, as the increased fuel momentum entering the combustion chamber promotes a fuel jet-dominated swirl flame. For the corresponding oxy-fuel combustion with the same volume flows and three different oxygen concentrations between 27% and 33%, stable combustion behavior is also observed. Using a camera setup to analyze flame shape and spread, it is observed that the flame formed with an oxygen content of 33% most closely resembles the flame shape achieved under air combustion conditions. However, the combustion temperatures most closely match those of the air operating condition when the oxygen content is 27%. Overall, it is shown that the approach for corresponding oxy-fuel conditions features similar flame shapes to oxy-fuel combustion with flue gas recirculation in a semi-industrial combustion chamber. Full article

PolyJet™ 3D printing is an additive manufacturing (AM) technology from Stratasys^TM. It has been used for applications such as tissue mimicking, printing anatomical models, and surgical planning. The materials available from Stratasys^TM have the inherent capabilities of producing a number of PolyJet™ materials with a range of physical properties that can be utilized for representing realistic tissue behavior mechanically. The preset materials available in the PolyJet™ printing software version 1.92.17.44384 GrabCAD^TM Print allow the user to manufacture materials similar to biological tissue, but the combinations of possibilities are limited and might not represent the broad spectrum of all tissue types. The purpose of this study was to determine the combination of PolyJet™ materials that most accurately mimicked a particular biological tissue mechanically. A detailed Design of Experiment (DOE) methodology was used to determine the combination of material mixtures and printing parameters and to analyze their mechanical properties that best matched the biological tissue properties available in the literature of approximately 50 different tissue types. Uniaxial tensile testing was performed according to the ASTM standard D638-14 of samples printed from Stratasys J850 digital anatomy printer to their determined stress–strain properties. The obtained values were subsequently validated by comparing them with the corresponding mechanical properties of biological tissues available in the literature. The resulting model, developed using the DOE approach, successfully produced artificial tissue analogs that span a wide range of mechanical characteristics, from tough, load-bearing tissues to soft, compliant tissues. The validation confirmed the effectiveness of the model in replicating the diverse mechanical behavior of various human tissues. Overall, this paper provides a detailed methodology of how materials and settings were chosen in GrabCAD^TM Print software and Digital Anatomy Creator^TM (DAC) to achieve an accurate artificial tissue material. Full article

Accurate data collection and time series creation are crucial for understanding these changes. However, many areas lack reliable data due to geopolitical issues and government permissions. Urgent action is needed for sustainable water management. This study uses Gravity Recovery and Climate Experiment (GRACE) data to analyze monthly fluctuations in groundwater storage in the Missan region of Iraq from January 2022 to December 2023, using Goddard Space Flight Center (GSFC) mascon, Jet Propulsion Laboratory Downscaled (JPL_D), and Catchment Land Surface Model (CLSM). This study revealed the variability in GWS over the area using RS data and in integration with available monitoring wells. To investigate GWS variability, GSFC, JPL_D, and CLSM observed a downward trend in GWS in 2022; GSFC exhibits the highest negative groundwater trend, while CLSM has the lowest negative trend. Then, from January to June 2023, GSFC had the highest positive trend, while CLSM had the lowest positive trend. Most of the study period has a negative trend for remote sensing that matches the monitoring well data in situ, in which wells 1, 2, and 4 are negative trends of the study period. In conclusion, these results improve the role of remote sensing in groundwater monitoring in small-scale region unconfined aquifers, which supports decision-making in water resource management. The findings illustrated a match between the results derived from the GRACE data and monitoring well data. Full article

Cemented carbides, renowned for their exceptional strength, hardness, elastic modulus, wear resistance, corrosion resistance, low coefficient of thermal expansion, and chemical stability, have long been indispensable tooling materials in metal cutting, oil drilling, and engineering excavation. The advent of additive manufacturing (AM), commonly known as “3D printing”, has sparked considerable interest in the processing of cemented carbides. Among the various AM techniques, Selective Laser Melting (SLM), Selective Laser Sintering (SLS), Selective Electron Beam Melting (SEBM), and Binder Jetting Additive Manufacturing (BJAM) have garnered frequent attention. Despite the great application potential of AM, no single AM technique has been universally adopted for the large-scale production of cemented carbides yet. The SLM and SEBM processes confront substantial challenges, such as a non-uniform sintering temperature field, which often result in uneven sintering and frequent post-solidification cracking. SLS notably struggles with achieving a high relative density of carbides. While BJAM yields WC-Co samples with a lower incidence of cracking, it is not without flaws, including abnormal WC grain growth, coarse WC clustering, Co-rich pool formation, and porosity. Three-dimensional gel-printing, though possessing certain advantages from its sintering performance, falls short in dimensional and geometric precision control, as well as fabrication efficiency. Cemented carbides produced via AM processes have yet to match the quality of their traditionally prepared counterparts. To date, the specific densification and microstructure evolution mechanisms during the AM process, and their interrelationship with the feedstock carbide material design, printing/sintering process, and resulting mechanical behavior, have not been thoroughly investigated. This gap in our knowledge impedes the rapid advancement of AM for carbide processing. This article offers a succinct overview of additive manufacturing of cemented carbides, complemented by an analysis of the current research landscape. It highlights the benefits and inherent challenges of these techniques, aiming to provide clarity on the present state of the AM processing of cemented carbides and to offer insights into potential future research directions and technological advancements. Full article

I identify a point-symmetrical morphology in the core-collapse supernova remnant (CCSNR) W44 compatible with shaping by three or more pairs of jets in the jittering jets explosion mechanism (JJEM). Motivated by recent identifications of point-symmetrical morphologies in CCSNRs and their match to the JJEM, I revisit the morphological classification of CCSNR W44. I examine a radio map of W44 and find the outer bright rim of the radio map to possess a point-symmetric structure compatible with shaping by two energetic pairs of opposite jets rather than an S-shaped morphology shaped by a precessing pair of jets. An inner pair of filaments might hint at a third powerful pair of jets. More pairs of jets were involved in the explosion process. This study adds to the growing evidence that the JJEM is the primary explosion mechanism of core-collapse supernovae. Full article

The Pelton turbine is an ideal choice for developing high-head hydropower resources. However, its cantilever-beam structure exposes the runner to intense alternating loads from high-velocity jets, causing localized high stresses, structural vibrations, and potential bucket fractures, all of which compromise safe operation. This study employs fluid–structure interaction analysis for the numerical investigation of a six-nozzle Pelton turbine to examine its unstable flow characteristics and hydrodynamic excitation under high-velocity jets. Our findings indicate that low-order frequencies primarily induce overall runner oscillations, while high-order frequencies result in oscillation, torsional displacement, and localized vibrations. Torsional displacement at the free end of the bucket induces stress concentrations at the root of the bucket and the splitter, the outflow edge, and the cut-out. The amplitudes of stress and displacement are correlated with the nozzle opening, with displacement typically in phase with torque, while stress fluctuations exhibit a phase lag. The stress and displacement values are higher on the bucket’s front, with maximum stress occurring at the bucket root and maximum displacement at the outflow edge, particularly in regions subjected to prolonged jet impact. The dominant frequency of the stress pulsations matches the number of nozzles. This study elucidates the dynamic response of Pelton turbines under high-velocity jets, correlating fluid load with runner dynamics, identifying maximum stress and deformation points, and providing technical support for performance evaluation. Full article

The stellar initial mass function (IMF) represents a fundamental quantity in astrophysics and cosmology describing the mass distribution of stars from low mass all the way up to massive and very massive stars. It is intimately linked to a wide variety of topics, including stellar and binary evolution, galaxy evolution, chemical enrichment, and cosmological reionization. Nonetheless, the IMF still remains highly uncertain. In this work, we aim to determine the IMF with a novel approach based on the observed rates of transients of stellar origin. We parametrize the IMF with a simple but flexible Larson shape, and insert it into a parametric model for the cosmic UV luminosity density, local stellar mass density, type Ia supernova (SN Ia), core-collapse supernova (CCSN), and long gamma-ray burst (LGRB) rates as a function of redshift. We constrain our free parameters by matching the model predictions to a set of empirical determinations for the corresponding quantities via a Bayesian Markov Chain Monte Carlo method. Remarkably, we are able to provide an independent IMF determination with a characteristic mass $m_c=0.{10}_{-0.08}^{+0.24}{\mathrm{M}}_{\odot }$ and high-mass slope $\xi =-2.{53}_{-0.27}^{+0.24}$ that are in accordance with the widely used IMF parameterizations (e.g., Salpeter, Kroupa, Chabrier). Moreover, the adoption of an up-to-date recipe for the cosmic metallicity evolution allows us to constrain the maximum metallicity of LGRB progenitors to $Z_{max}=0.{12}_{-0.05}^{+0.29}{\mathrm{Z}}_{\odot }$. We also find which progenitor fraction actually leads to SN Ia or LGRB emission (e.g., due to binary interaction or jet-launching conditions), put constraints on the CCSN and LGRB progenitor mass ranges, and test the IMF universality. These results show the potential of this kind of approach for studying the IMF, its putative evolution with the galactic environment and cosmic history, and the properties of SN Ia, CCSN, and LGRB progenitors, especially considering the wealth of data incoming in the future. Full article

Aiming at solving difficulties related to aero-engine classification and identification, two telemetry Fourier transform infrared spectrometers are utilized to measure the infrared spectra of six types of aero-engine hot jets, and create a spectral data set, which is divided into a training set (80%), a validation set (10%), and a prediction set (10%). A peak-finding Siamese convolutional neural network (PF-SCNN) is used to match and classify the spectral data. During the training stage, the Siamese convolutional neural network (SCNN) is designed to extract spectral features and calculate the distance similarity. In order to improve the efficiency of the SCNN, a peak-finding method is introduced to extract the spectral peaks, which are used to train the model instead of the original spectral data. During the prediction stage, the trained model is used to calculate the similarity between the prediction set and the combined set of the training set and validation set, and the label of the most similar training data in each prediction set is used as the prediction label. The performance measures of the classification results include accuracy, precision, recall, confusion matrix, and F1-score. The experimental results show that the PF-SCNN can achieve a high classification accuracy rate of 99% and can complete the task of classifying the infrared spectra of aero-engine hot jets. Full article

The objective of this study is to implement a more realistic integrated analysis model for micro gas turbines by incorporating secondary flow and combustion efficiency into the existing model, which includes main engine components such as the compressor and turbine, and to validate this model by comparing it with test results. The study was based on the JetCat P300-RX, which has a maximum thrust level of 300 N. Simulations were performed using ANSYS CFX, employing the κ-ω SST turbulence model and a mixing plane interface between individual components. The eddy dissipation model (EDM), with a combustion efficiency of 90%, was used as the combustion model. A user subroutine was also applied for the power matching of the compressor and turbine to calculate the fuel flow rate in each iteration. For secondary flow, it was assumed that 3% of the total air flow rate would flow through the secondary path and be applied to the compressor and turbine. Simulations were conducted over a range of 30,000 to 104,000 RPM, with ground conditions evaluated, including altitude-simulated conditions. To validate the analysis model, engine performance metrics such as pressure ratio, air flow rate, fuel flow rate, and exhaust gas temperature (EGT) were compared with test results. The results demonstrated that errors were less than 5% for most engine performance metrics, except for EGT and fuel flow. The discrepancy in EGT was attributed to differences in the sensing methods, while the variation in fuel flow was found to be due to the lubrication system and losses due to the secondary air flow. Consequently, this study confirmed that the integrated simulation model accurately predicts engine performance. The results indicate that the integrated simulation model provides a more realistic prediction of overall engine performance compared to previous studies. Therefore, it can evaluate detailed thermo-fluid properties without the need for component performance maps, enhancing performance evaluation and analysis. Full article

Spray penetration into citrus canopies is critical for adequate coverage and deposition to ensure effective pest control. However, mismatch of air assistance to target canopy characteristics can lead to unintended spraying losses through overpenetration. To evaluate the effect of air assistance on on-target deposition, two sprayers (surrogates for airflow rates) were used to apply a fluorescent tracer dye solution @ a target concentration of 300 ppm to 16 medium-foliage-density tree blocks in a commercial mandarin orchard. The complete factorial experiment in three replications, also designed for validating a model-based spray decision support tool, comprised two forward travel speeds (1.6 and 4.8 km/h), two disc-core nozzles (TeeJet^® D3-25 and D6-45), and either one or two nozzle rows to obtain a wide range of application rates (496 to 9719 L/ha). Dye deposition significantly decreased with canopy depth (p =< 0.001) by nearly seven times across the 3.4 m wide canopies but was not significant over 1.2 to 2.2 m sampling height (p = 0.867). Deposition obtained with the low-airflow-rate sprayer was significantly greater (p =< 0.001) than that obtained with the high-airflow-rate sprayer over the dose range likely due to too much air pushing out spray droplets. This study underscores the importance of matching the air assistance of orchard sprayers to the target canopy. Full article

The metal fibre surface combustion structure has the characteristics of strong thermal matching ability, short response time, and strong shape adaptability. It has more advantages in the thermal test of complex hypersonic vehicle surface inlet, leading edge, etc. In this paper, a method of aerodynamic thermal simulation test based on metal fibre surface combustion is proposed. The aim of the study was to create a uniform target heat flow on the inner wall surface of a cylindrical specimen by matching the gas jet flow rate and the geometry of the combustion surface. The research adopted the optimisation design method based on the surrogate model to establish the numerical calculation model of a metal fibre combustion jet heating cylinder specimen. One hundred sample points were obtained through Latin hypercube sampling, and a database of design parameters and heat flux was established through numerical simulation. The kriging surrogate model and the non-dominated sequencing genetic optimisation algorithm with elite strategy were adopted. A bi-objective optimisation design was carried out with the optimisation objective of the coincidence between the predicted and the target heat flux on the inner wall of the specimen. The results showed that the average relative errors of heat flow density on the specimen surface were 8.8% and 6% through the leave-one-out cross-validation strategy and the validation of six test sample points, respectively. The relative error values in most regions were within 5%, which indicates that the established kriging surrogate model has high prediction accuracy. Under the optimal solution conditions, the numerical calculation results of the heat flow on the inner wall of the specimen were in good agreement with the target heat flow values, with an average relative error of less than 5% and a maximum value of less than 8%. These results show that the optimisation design method based on the kriging surrogate model can effectively match the thermal test parameters of metal fibre combustion structures. Full article