Search Results (974)

CFRP possesses the advantages of lightweight and high strength, but its cost is relatively high, and its ductility is insufficient; aluminum alloys have a relatively low cost and good ductility. This paper develops a CFRP-aluminum alloy laminated tube (CFRP-AL tube), which combines the advantages of CFRP and aluminum alloy. Such composite components have broad application prospects in the field of spatial structures. The CFRP-AL tubes were studied by experimental, numerical, and theoretical research on their axial compression performance in this paper. Firstly, the standard tensile test was carried out on 6061-T6 aluminum alloy. Combining the test results and references, the Johnson–Cook hardening model parameters of aluminum alloy were determined. The tensile test of CFRP was conducted to determine its material parameters. Based on composite material mechanics and fracture mechanics, a composite progressive damage model for the CFRP-AL tube was established. Secondly, axial compression tests were carried out on 27 CFRP-AL tubes and 3 aluminum alloy tubes with a small slenderness ratio. The test results show that the typical failure mode of CFRP-AL tubes with small slenderness ratios is strength failure, and the ultimate bearing capacity rises by 11~31% compared to aluminum alloy tubes. Thirdly, a user material subroutine capable of simulating CFRP failure was developed. Based on the user material subroutine, the effect of the initial imperfection, the fiber layer angle, the fiber layer thickness, the slenderness ratio, the diameter-thickness ratio and the CFRP volume ratio were discussed. And the failure mechanism and response of the CFRP-AL tubes under the axial compression were obtained. Finally, based on the strength theory, the formula predicting the bearing capacity of the strength failure was established, and the results of the formula were in a good agreement with the experimental and numerical results. Full article

Annular flow is a common flow configuration encountered in fields such as food engineering, energy and power engineering, and petroleum engineering. The annular space formed by the inner and outer pipes exhibits unique characteristics, with the distinct curvatures of the inner and outer pipes rendering the annulus fundamentally different from a circular pipe. The complexity of the annular structure complicates the rapid calculation of turbulent statistics in engineering practice, as modeling these statistics necessitates a comprehensive understanding of their peak characteristics. However, current research lacks a thorough understanding of the peak characteristics of turbulent flows in annuli with varying diameter ratios (the ratio of the inner tube’s diameter to the outer tube’s diameter) between the inner and outer pipes. To gain a deeper insight into the turbulent peak characteristics within annular flows, this study employs numerical simulation methods to investigate the first- and second-order turbulent statistics under different diameter ratios resulting from varying curvatures of the inner and outer pipes. These statistics encompass velocity distribution, the position and magnitude of maximum velocity, turbulence intensity, turbulent kinetic energy, and Reynolds stress. The research findings indicate that the contour plots of velocity, turbulence intensity, and turbulent kinetic energy distributions under different diameter ratio conditions exhibit central symmetry. The peaks of the first-order statistical quantities are located in the mainstream region of the annulus, and their positions gradually shift closer to the center of the annulus as the diameter ratio increases. For the second-order statistical quantities, peaks are observed near both the inner and outer walls, and their positions move closer to the walls as the diameter ratio rises. The peak values of turbulent characteristics show significant variations across different diameter ratios. Both the inner and outer wall surfaces exhibit peaks in their second-order statistical quantities. For instance, the maximum value of Reynolds stress near the inner tube is 101.4% of that near the outer tube, and the distance from the wall where the maximum Reynolds stress occurs near the inner tube is 97.2% of the corresponding distance near the outer tube. This study is of great significance for optimizing the diameter combination of the inner and outer pipes in annular configurations and for evaluating turbulent statistics. Full article

The locoweeds Astragalus and Oxytropis in the Americas and China, as well as Swainsona in Australia, harbor swainsonine-producing endophytes responsible for “locoism” or “pea struck” syndromes in grazing animals. Demonstration of Alternaria section Undifilum spp. requires demonstration of morphological characters such as a wavy germ tube and slow growth. While Astragalus wetherilli, A. pubentissimus, Swainsona canescens, and S. galegifolia plants have been shown to contain swainsonine, and fungi isolated from the plants have been partially characterized genetically, the fungi have not been characterized morphologically. This work sought to complete morphological characterization and determine species for those fungi and from fungi associated with Swainsona luteola and S. brachycarpa. The fungi were isolated from their hosts onto media and exhibited slow growth, resulting in a colony diameter of approximately 10 mm after 30 days. Morphological identification revealed production of conidia that produced a wavy germ tube for the endophytes from Astragalus pubentissimus species, Swainsona canescens, and S. galegifolia. Sequence analyses of the ITS region and the swnK-KS and swnK-TR genes of these fungi suggest that the fungi isolated from Astragalus are closely related and distinct from the fungi isolated from Swainsona. Presence of the swnK gene demonstrates that all the fungi have a necessary component to produce swainsonine. Fungi isolated from Astragalus spp. differed in color, growth, and conidium size, and/or their sequences. While the fungi isolated from Swainsona canescens and S. galegifolia endophytes differed in color, growth, and conidium size, those isolated from Swainsona luteola and S. brachycarpa did not produce conidia. Sequences from all Swainsona endophytes were almost identical and were concluded to be the same species. The new species described here are Alternaria wetherii, A. pubentissima, A. pubentissimoides, and A. swainsonii. Full article

This paper presents the results of a numerical study on transient temperature distributions and phase fractions in a thermal energy storage unit containing phase change material (PCM). The latent heat storage unit (LHSU) is a compact shell-and-tube exchanger featuring seven tubes arranged in a staggered layout. Three organic phase change materials are investigated: paraffin LTP 56, fatty acid RT54HC, and fatty acid P1801. OpenFOAM software is utilized to solve the governing equations using the Boussinesq approximation. The discretization of the equations is performed with second-order accuracy in both space and time. The three-dimensional (3D) computational domain corresponds to the inner diameter of the LHSU. Calculations are conducted assuming constant thermal properties of the fluids. The experimental and numerical results indicate that for paraffin LTP56, the charging time is approximately 8% longer than the discharging time. In contrast, the discharging times for fatty acids RT54HC and P1801 exceed their charging times, with time delays of about 14% and 49% for RT54HC and 25% and 30% for P1801, according to experimental and numerical calculations, respectively. Full article

Recycled concrete is widely recognized as favorable for environmental protection and sustainable development. However, recycled concrete, especially containing abandoned brick aggregate, is rarely used in main structural members due to its inherent defects. Concrete-filled double steel tube columns (CFDSTCs), consisting of an outer and an inner steel tube with concrete filling the entire section, are effective in load bearing and deformation resistance. The structural application of abandoned brick aggregate, resulting from urbanization renewal, might be widened through CFDSTCs. This paper presents an experimental and analytical study aiming to investigate the axial compressive behavior of recycled-brick-aggregate-concrete-filled double steel tube columns (RBCDSTs). A total of six specimens were tested under concentric compression, including five RBCDSTs and one concrete-filled single steel tube column. The varied parameters included the replacement ratios (0% and 25%) of brick aggregate and the thickness ratio of the inner and outer steel tubes (0.75, 1, and 1.25). Theoretical analysis was also carried out. A new constitutive model of RBCDST was proposed and used in finite element analysis. The investigation indicated that, under the current conditions, the presence of the inner steel tube only increased the strength by 0.14%. When the inner and outer diameter ratio is 0.73, using a 25% replacement rate of bricks in the entire cross-section or only in the ring area of the cross-section will result in 21.1% and 10.1% strength decreases, respectively. For every 0.6% increase in the diameter-to-thickness ratio of the outer tube, the strength of RBCDST increases 16.3% on average. Full article

The horizontal tube falling film heat exchangers (HTFFHEs), which exhibit remarkable advantages such as high efficiency in heat and mass transfer, low resistance, and a relatively simple structural configuration, have found extensive applications. Complex flow phenomena and the coupled processes of heat and mass transfer take place within it. Given that the heat and mass transfer predominantly occur at the gas-liquid interface, the flow characteristics therein emerge as a significant factor governing the performance of heat and mass transfer. This article elaborates on the progress of experimental and simulation research approaches with respect to flow characteristics. It systematically reviews the influence patterns of various operating parameters, namely parameters of gas, solution and internal medium, as well as structural parameters like tube diameter and tube spacing, on the flow characteristics, such as the flow regime between tubes, liquid film thickness, and wettability. This review serves to furnish theoretical underpinnings for optimizing the heat and mass transfer performance of the horizontal tube falling film heat exchanger. It is further indicated that the multi-dimensional flow characteristics and their quantitative characterizations under the impacts of different airflow features will constitute the focal research directions for horizontal tube falling film heat exchangers in the foreseeable future. Full article

Background: The development of transcatheter mitral valves (TMVs) represents a major advancement in cardiology, driven in part by the growing elderly population. Elderly patients frequently suffer from secondary mitral regurgitation but are often ineligible for surgical valve replacement due to high procedural risks. This study aimed to develop a self-expanding TMV stent fabricated from a single nitinol tube, featuring two distinct central zones: a smaller-diameter valve-containing segment and a larger-diameter anchoring segment for the mitral annulus. Methods: We used the COMSOL Multiphysics 6.0 software package for biotechnical engineering. Prototypes of stents and valves were manufactured in five sizes following a 22 Fr delivery system compatibility assessment and pulsatile-flow testing. Results: We bioengineered a novel stent design with an integrated porcine pericardial valve. The stents were laser-cut from nitinol tubes (4.5 mm outer diameter, 0.45 mm wall thickness) and heat-treated to achieve spatial configurations compatible with fibrous ring diameters of 40, 42, 44, 46, and 48 mm. Pericardial leaflets and coverings were then mounted onto the stents. The resulting valves were successfully loaded into a 24 Fr delivery system and exhibited proper opening and closing function under pulsatile-flow testing. Conclusions: Our findings confirm the feasibility of a single-component, dual-diameter TMV stent, offering a promising solution for high-risk patients with mitral regurgitation. Full article

The natural history of focal non-infected lesions of the abdominal aorta (fl-AA) remains unclear and largely depends on their aetiology. These lesions often involve a focal “tear” or partial disruption of the arterial wall. Penetrating aortic ulcers (PAUs) and intramural hematomas (IMHs) are examples of focal tears in the aortic wall that can either progress to dilatation (saccular aneurysm) or fail to fully propagate through the medial layers, potentially leading to aortic dissection. These conditions typically exhibit a morphology consistent with eccentric saccular aneurysms. The management of focal non-infected pathologies of the abdominal aorta remains a subject of debate. Unlike fusiform abdominal aortic aneurysms, the inconsistent definitions and limited information regarding the natural history of saccular aneurysms (sa-AAAs) have prevented the establishment of universally accepted practice guidelines for their management. As emphasized in the latest 2024 ESVS guidelines, the focal nature of these diseases makes them ideal candidates for endovascular repair (class of evidence IIa—level C). Moreover, the Society for Vascular Surgery just referred to aneurysm diameter as an indication for treatment suggesting using a smaller diameter compared to fusiform aneurysms. Consequently, the management of saccular aneurysms is likely heterogeneous amongst different centres and different operators. Endovascular repair using tube stent grafts offers benefits like reduced recovery times but carries risks of migration and endoleak due to graft rigidity. These complications can influence long-term success. In this context, the use of endovascular bifurcated grafts may provide a more effective solution for treating these focal aortic pathologies. It is essential to achieve optimal sealing regions through anatomical studies of aortic morphology. Additionally, understanding the anatomical characteristics of focal lesions in challenging necks or para-visceral locations is indeed crucial in device choice. Off-the-shelf devices are favoured for their time and cost efficiency, but new endovascular technologies like fenestrated endovascular aneurysm repair (FEVAR) and custom-made devices enhance treatment success and patient safety. These innovations provide stent grafts in various lengths and diameters, accommodating different aortic anatomies and reducing the risk of type III endoleaks. Although complicated PAUs and focal saccular aneurysms rarely arise in the para-visceral aorta, the consequences of rupture in this segment might be extremely severe. Experience borrowed from complex abdominal and thoracoabdominal aneurysm repair demonstrates that fenestrated and branched devices can be deployed safely when anatomical criteria are respected. Elective patients derive the greatest benefit from a fenestrated graft, while urgent cases can be treated confidently with off-the-shelf multibranch systems, reserving other types of repairs for emergent or bail-out cases. While early outcomes of these interventions are promising, it is crucial to acknowledge that limited aortic coverage can still impede effective symptom relief and lead to complications such as aneurysm expansion or rupture. Therefore, further long-term studies are essential to consolidate the technical results and evaluate the durability of various graft options. Full article

To investigate the impact of sand-laden flow on energy loss in Francis turbines, this study integrates entropy generation theory with numerical simulations conducted using ANSYS CFX. The mixture multiphase flow model and the SST k-ω turbulence model are employed to simulate the solid–liquid two-phase flow throughout the entire flow passage of the turbine at the Gengda Hydropower Station (Minjiang River Basin section, 103°17′ E and 31°06′ N). The energy loss characteristics under different off-design conditions are analyzed on the basis of the average sediment concentration during the flood season (2.9 kg/m³) and a median particle diameter of 0.058 mm. The results indicate that indirect entropy generation and wall entropy generation are the primary contributors to total energy loss, while direct entropy generation accounts for less than 1%. As the guide vane opening increases, the proportion of wall entropy generation initially rises and then decreases, while the total indirect entropy generation exhibits a non-monotonic trend dominated by the flow pattern in the draft tube. Entropy generation on the runner walls increases steadily with larger openings, whereas entropy generation on the draft tube walls first decreases and then increases. The variation in entropy generation on the guide vanes remains relatively small. These findings provide technical support for the optimal design and operation of turbines in sediment-rich rivers. Full article

In this work, HNTs@ZIF-67 composites were synthesized using the in situ growth method and incorporated into 6FDA-TFMB to prepare mixed-matrix membranes (MMMs). Scanning electron microscope (SEM) and transmission electron microscope (TEM) proved that the HNTs@ZIF-67 composite not only retained the hollow structure of HNTs, but also formed a continuous ZIF-67 transport layer on the surface of HNTs. The results of gas permeability experiments showed that with the increase in HNTs@ZIF-67 incorporation, the He permeability and He/CH₄ selectivity of MMMs showed a trend of increasing first and then decreasing. When the loading is 5 wt%, the He permeability and He/CH₄ selectivity of MMMs reach 116 Barrer and 305, which are 22.11% and 79.41% higher than the pure 6FDA-TFMB membrane. The results of density functional theory (DFT) and Monte Carlo (MC) calculations reveal that He diffuses more easily inside ZIF-67, HNTs and 6FDA-TFMB than CH₄, and ZIF-67 shows larger adsorption energy with He than HNTs and 6FDA-TFMB, indicating that He is easily adsorbed by ZIF-67 in MMMs. Based on experimental and molecular simulation results, the mechanism of HNTs@ZIF-67 improving the He/CH₄ separation performance of MMMs was summarized. With the advantage of a smaller molecular kinetic diameter, He can diffuse through ZIF-67 on the tube orifice of HNTs@ZIF-67 and enter the HNTs’ hollow tube for rapid transmission. At the same time, He can also be rapidly transferred in the continuous ZIF-67 transport channel layer, which improves the He permeability and the He/CH₄ selectivity of MMMs. Full article

This study innovatively proposes a pipeline-type pneumatic lift sediment removal device for cleaning pollutants at the bottom of fish breeding tanks and conducts hydrodynamic characteristic analysis on its core component, the pneumatic lift pipeline structure, which consists of a horizontal circular tube with multiple micro-orifices at the bottom and an upward-inclined circular tube. The pipeline has an inner diameter of 20 mm and a vertical length of 1.2 m, with the orifice at one end of the horizontal tube connected to the gas supply line. During operation, compressed gas enters the horizontal tube, generating negative liquid pressure that draws solid–liquid mixtures from the tank bottom into the pipeline, while buoyant forces propel the gas–liquid–solid mixture upward for discharge through the outlet. Under a constant gas flow rate, numerical simulations investigated efficiency variations through three operational scenarios: ① different pipeline orifice diameters, ② varying orifice quantities and spacings, and ③ adjustable pipeline bottom clearance heights. The results indicate that in scenario ①, an orifice diameter of 4 mm demonstrated optimal efficiency; in scenario ②, the eight-orifice configuration achieved peak efficiency; and scenario ③ showed that the proper adjustment of the bottom clearance height enhances pneumatic efficiency, with maximum efficiency observed at a clearance of 10 mm between sediment suction pipe and tank bottom. Full article

In order to explore the axial compression performance of external steel rib ring restraint waste-steel-fiber-reinforced concrete-filled steel tubes (ERWCFSTs), 18 short-column axial compression tests were conducted. The effects of the number of rib rings, rib ring spacing, rib ring setting position, and waste steel fiber (WSF) content on the axial compression performance of the columns were analyzed. The results show that the concrete-filled steel tube (CFST) short columns with rib rings were strengthened, the specimens were mainly characterized by drum-shaped failure, and the buckling was concentrated between the rib rings. Without rib ring specimens, the steel tube is unable to resist the rapid increase in lateral expansion, leading to buckling initiation near the bottom of the specimens. The columns with rib rings exhibited a minimum increase of 32.5% and a maximum increase of 53.17% in load-bearing capacity compared to those without rib rings, with an average improvement of 37.78%. The columns achieved the best ductility when the rib ring spacing was 50 mm. When the rib ring spacing remained constant, columns with a number of rib rings no less than the height-to-diameter ratio (H/D) demonstrated more uniform stress distribution and optimal confinement effects. For a fixed number of rib rings, specimens with rib ring spacing between H/8 and H/4 showed significant improvements in both load-bearing capacity and ductility. The confinement effect was better when the rib rings were positioned in the middle of the column height rather than near the ends. The incorporation of WSF resulted in a minimum increase of 2.86% and a maximum increase of 10.49% in column load-bearing capacity, indicating limited enhancement. However, WSF improved the ductility performance of the columns by at least 10%. Combined with theoretical analysis and experimental data, a formula for calculating the bearing capacity of ERWCFSTs was established. Full article

Introduction: Pediatric prosthetic knee joints must be appropriately scaled from adult designs to ensure proper gait biomechanics. However, direct dimensional scaling without considering the biomechanical implications may lead to functional discrepancies. This study aimed to evaluate whether using a linear scaling factor can effectively adapt a knee for pediatric use. The study assessed whether such an approach yields a viable pediatric prosthetic knee joint by applying a fixed scaling factor and analyzing the resultant knee geometry. Methods: The linear scaling factor was determined based on the pylon tube diameter, a key constraint in compact pediatric knee design. Given a pediatric pylon diameter of 22 mm, the length of the tibial link was set to 22 mm, yielding a scaling factor of 0.6875 when compared to the adult-sized knee. This scaling factor was used to determine the dimensions of the pediatric four-bar (scaled) knee joint. Static geometric analysis was conducted using GeoGebra^® to model the lower-body segment lengths. The knee joint’s performance was evaluated based on stance and swing phase parameters. These metrics were compared between the scaled knee and a commercial pediatric knee. Results: The geometric analysis revealed that while using the linear scaling factor maintained proportional relationships, certain biomechanical parameters deviated from the expected pediatric norms. The scaled knee achieved a toe clearance of 13.5 mm compared to 19.7 mm in the commercial design and demonstrated a swing-phase heel clearance of 11.6 mm versus 13.3 mm, maintaining negative x/y ratios at heel contact and showing significant stability in push-off moments, while the stance flexion angle remained within an acceptable range. The heel contact and push-off ratios (x/y) were found to be comparable, with the scaled model achieving values of −1.21 and −0.59, respectively. The stance flexion angle measured 10.6°, closely aligning with the commercial reference. Conclusions: Using a linear scaling factor provides a straightforward method for adapting adult prosthetic knee designs to pediatric use. However, deviations in key biomechanical parameters indicate that further experimental study may be required to validate the applicability of the scaled knee joint for pediatric users. Future work should explore dynamic simulations and experimental validations to refine the design further and ensure optimal gait performance. Full article

In intermittent gas lift (IGL), not all the liquid initially in the tubing is usually produced at the surface in one cycle. This is due to a concept known as fallback, which occurs when some amount of the initial liquid column drops back to join the next slug. We conducted a review of earlier works on IGL and the behavior of the fallback factor. The dependence on the fallback factor on the operational conditions such as slug velocity, valve opening pressure, valve closing pressure, casing–tubing pressure ratio, diameter of tubing, and amount of gas injected during IGL are discussed in this paper. The effect on the shape and stability of the nose of the Taylor bubble on the lifting efficiency of the bubble is also explained. In trying to reduce the fallback factor per cycle, there have been recommendations to combine gas lift with plunger lift. We also present the results of this combination and the effects on the fallback factor in gas-assisted plunger lift (GAPL). More light is shed on the behavior of the velocity of the liquid slug and how it affects the fallback factor during IGL. The behavior of the fallback factor with an increase or decrease in plunger velocity during GAPL is also presented in this paper. This review is categorized into experimental and numerical studies on fallback factor to evaluate their impact on production efficiency in IGL and GAPL. Additionally, different formulas for fallback proposed by different literature are compiled. Full article

To enhance the steam parameters of steam injection boilers during the thermal recovery of heavy oil while ensuring the safe and stable operation of boiler pipelines, this study conducted two-phase flow boiling numerical simulations in a horizontal heated tube with an inner diameter of 65 mm, using water and water vapor as working fluids. The analysis focused on the gas–liquid phase distribution, temperature profiles, near-wall fluid velocity, and pressure drop along both the axial and radial directions of the tube. Furthermore, the effects of heat flux density, mass flow rate, and inlet subcooling on these parameters were systematically investigated. The results reveal that higher heat fluxes intensify the velocity difference between the upper and lower tube walls and enlarge the temperature gradient across the wall surface. A reduction in mass flow rate increases the gas phase fraction within the tube and causes the occurrence of identical flow patterns at earlier axial positions. Additionally, the onset of nucleate boiling shifts upstream, accompanied by an increase and upstream movement of the wall’s maximum temperature. An increase in inlet subcooling prolongs the time required for the working fluid mixture to reach saturation, thereby decreasing the gas phase fraction and delaying the appearance of the same flow patterns. Finally, preventive and control strategies for ensuring the safe operation of steam injection boiler pipelines during heavy oil recovery are proposed from the perspective of flow pattern regulation. Full article