Fluid Characteristics Research Articles

Study of Fluid Flow Characteristics and Mechanical Properties of Aviation Fuel-Welded Pipelines via the Fluid–Solid Coupling Method

The welded pipeline structure of aircraft fuel is a complex and diverse entity, significantly influenced by fluid–solid coupling. The refined aviation fuel-welded pipeline model plays a pivotal role in the investigation of its fluid–solid coupling mechanical properties. However, the mechanical analyses of pipelines with welded structures frequently simplify or ignore the influence of the weld zone (WZ). Consequently, these analyses fail to reveal the complex interactions between different weld zones in detail. In this study, a comprehensive and precise fuel-welded pipeline refinement model is developed through the acquisition of microstructural dimensions and mechanical parameters of the weld zone via metallographic inspection and microtensile testing. Additionally, the influence of clamps and brackets under airborne conditions is fully considered. Furthermore, the numerical simulation results are compared and verified using modal and random vibration tests. This paper addresses the impact of diverse fluid characteristics on the velocity field, pressure field, and stress in disparate areas, and it also conducts an investigation into the random vibration characteristics of the pipeline. The results demonstrate that the fluid pressure and velocity exert a considerable influence on the fluid flow state and structural stress distribution within the pipeline. An increase in flow velocity and alteration to the pipeline geometry will result in a change to the local velocity distribution, which in turn affects the distribution of the fluid pressure field. The highest stresses are observed in the weld zone, particularly at the junction between the weld zone and the heat-affected zone (HAZ). In contrast, the stresses in the bend region exhibit a corrugated distribution in both the axial and circumferential directions. An increase in fluid pressure has a significant impact on the natural frequency of the pipeline. This study enhances our comprehension of the mechanical properties of aircraft fuel lines with fluid–solid coupling and provides a foundation and guidance for the optimal design of fuel-welded lines.

Three-Dimensional Multi-Morphology TPMS-Based Microchannel Design Method for Conformal Cooling in Injection Molding

Abstract Triply periodic minimal surface (TPMS) possesses diverse morphological characteristics, such as pore sizes, porosity, and structural types. Integrating TPMS-based microchannels into micro-cellular cooling structures is advantageous for designing and controlling fluid characteristics within mold cooling channels. However, it is still difficult to design multi-morphology TPMS-based cooling microchannels that conform to the external shapes of injection molds. This work proposes a 3D multi-morphology TPMS-based design method that transforms 3D constraints into a combination of 2D constraints. First, a beta growth algorithm based on closed-loop constraints is proposed to transition different morphologies smoothly on the plane. Subsequently, a transition optimization algorithm along the normal direction of the plane is introduced to smoothly transition multi-morphology TPMS-based microchannels in all directions. With this layered approach, multi-morphology microchannels can be obtained with first-order geometric continuity under complex shape constraints. Finally, several TPMS-based conformal cooling structures are designed for an automotive hood cover. The results of finite element simulations show that the cooling structures generated by the proposed method have a better cooling effect than the conformal channels. It can be concluded that multi-morphology TPMS-based structures perform better by contrast with conformal channels as the average temperature of the cooling surface decreases by 8.48 K, and the standard deviation of temperature distribution decreases by 24.65%.

Comparative analysis of sloshing effects on elevated water tanks’ dynamic response using ANN and MARS

Important infrastructure elements like elevated water tanks are vulnerable to fluid sloshing brought on by earthquakes, which can seriously harm the structure. In order to precisely capture the fluid–structure interaction, this work uses a 3D finite element model based on the Coupled Eulerian–Lagrangian (CEL) approach to investigate the dynamic response of raised water tanks under seismic excitation. Seismic ground motions were applied to the model, and the displacements, accelerations, and stresses that resulted were examined. The results highlight how fluid sloshing significantly affects the dynamic response of the tank because sloshing waves increase structural stresses and deformations by imposing large hydrodynamic pressures on the tank walls. The water tank's performance as a tuned liquid damper (TLD) was also evaluated in the study. Multivariate Adaptive Regression Splines (MARS) and Artificial Neural Network (ANN) models were created and trained in order to further examine and forecast the dynamic response. According to statistical analysis and Taylor diagram evaluation, the ANN model outperformed the MARS model in forecasting the displacement response. The numerical simulations and precise results were made possible by the use of ABAQUS software, a potent finite element analysis tool. The study's conclusions can be used to improve the analysis and construction of elevated water tanks in order to reduce seismic risk. The impact of different tank geometries, fluid characteristics, and seismic ground motions on the dynamic response of raised water tanks may be investigated in future studies. This research innovatively employs ABAQUS software to simulate the stabilizing effect of sloshing in steel structures during earthquakes. By optimizing water levels to 60% capacity, the study explores sloshing as a potential damping mechanism to mitigate structural vibrations. In comparison to empty tanks, this leads to better damping throughout velocity, acceleration, and displacement responses, which speeds up stabilization and lowers dynamic loads. The study also demonstrates how well adjusted liquid dampers (TLDs) reduce vibrations in raised water tanks.

Rheology of Bingham viscoplastic flow triggered by a rotating and radially stretching disk

Purpose This study aims to investigate the flow and heat transfer characteristics of a Bingham viscoplastic fluid subjected to the combined effects of axial rotation and radial stretching of a circular disk. Building upon existing models for Bingham fluids on stationary walls, we extend the formulation to incorporate the effects of a linearly stretching disk using von Kármán similarity transformations. Design/methodology/approach The resulting system of nonlinear ordinary differential equations is solved to characterize the flow and thermal fields. Three dimensionless parameters govern the momentum layer: a swirling number capturing the balance between rotation and stretching, a Bingham number characterizing the fluid’s yield stress and a modified Reynolds number incorporating the disk stretching. The Prandtl number controls the thermal response. Findings For purely stretching flows, a two-dimensional flow structure emerges. However, the introduction of rotation induces three-dimensional flow behavior. Unlike previous studies suggesting that moderate Bingham numbers are sufficient for non-Newtonian effects on purely revolving disks, the findings indicate that significantly higher yield stresses are required to observe non-Newtonian characteristics under radial stretching conditions. This difference can be attributed to the enhancing influence of wall movement on the fluid dynamics. At high Bingham numbers, a two-layer flow structure develops, comprising an unyielded plug region above the disk and a yielded shear layer adjacent to the wall. The von Kármán viscous pump mechanism drives the Bingham flow within this regime. Originality/value Physical quantities such as drag force due to wall shear stress, torque resulting from tangential shear stress and Nusselt number are extracted from the quantitative data.

Computational Fluid Dynamics (CFD) Modeling of Material Transport through Triply Periodic Minimal Surface (TPMS) Scaffolds for Bone Tissue Engineering.

Cell-laden, scaffold-based tissue engineering methods have been successfully utilized for the treatment of bone fractures. In such methods, the rate of scaffold biodegradation, transport of nutrients, and removal of cell metabolic wastes are critical fluid-dynamics factors, affecting tissue regeneration. Therefore, there is a critical need to identify the underlying material transport mechanisms associated with stem cell-driven, scaffold-based bone tissue regeneration. The objective of the work is to establish computational fluid dynamics (CFD) models to identify the consequential mechanisms behind internal and external material transport through/over porous bone scaffolds designed based on the principles of triply periodic minimal surfaces (TPMS). In this study, advanced CFD models were established based on ten TPMS designs for analyzing (i) single-unit internal flow, (ii) single-unit external flow, and (iii) cubic, full-scaffold external flow. The main fluid characteristics influential in bone regeneration, including flow velocity, pressure, and wall shear stress (WSS), were analyzed to assess material transport internally through and externally over the TPMS designs. Schwarz Primitive (P) appeared to have the lowest level of flow pressure and WSS (desirable for development of bone tissues). An analysis of streamline velocity exhibited an increase in velocity togther with a depiction of turbulent motion along the curved surfaces of the TPMS designs. Besides, pressure buildup was observed within the inner channels of almost all the TPMS designs. Overall, the outcomes of this study pave the way for optimal design and fabrication of bone-like tissues with desirable medical properties.

Fabrication of Rubus chingii Hu ellagitannins-loaded W/O and O/W emulsion gels: Structure, stability, in vitro digestion and in vivo metabolism.

Tannin is the main naturally occurring phytochemicals in Rubus chingii Hu with poor digestive stability and low bioavailability. In this study, oil-in-water (O/W) and water-in-oil (W/O) emulsion gels encapsulating Rubus chingii Hu ellagitannins (RCHT) were fabricated and their structure, rheology, stability, in vitro digestion and in vivo metabolism were characterized. The W/O emulsion gel showed smaller particle size, better pH stability, thermal stability, centrifugal stability and storage stability. Regarding rheology, two emulsion gels exhibited characteristics of non-Newtonian fluids. The encapsulation efficiency of W/O emulsion gel was higher, reaching 95.46%. The lower release rate and higher bioaccessibility of RCHT were also observed in the W/O emulsion gel. In vitro fermentation results indicated that W/O emulsion gel could promote the growth of intestinal beneficial bacteria and inhibit the growth of harmful bacteria. Metabolic kinetics in rats showed that the embedding of W/O emulsion gel greatly promoted the absorption and transformation of ellagitannins to urolithins in vivo. Thus, the W/O emulsion gel was quite suitable for the delivery of RCHT.

Optimization using Response Surface Methodology for Eyring-Powell Fluid Flow with Cattaneo-Christov Heat Flux and Cross Diffusion Effects

The optimization of heat transfer in engineering applications has significant implications for product performance and efficiency. This study investigates the flow and heat transfer characteristics of Eyring-Powell fluid over a curved sheet, incorporating complex phenomena such as magnetic dipoles, Cattaneo-Christov heat flux, and cross-diffusion effects. Navier's slip and melting boundary conditions are applied to model realistic physical constraints. The study employs response surface methodology (RSM) and sensitivity analysis to evaluate the parametric influences on skin friction and the Nusselt number, providing statistical insights into their behavior. Using similarity transformations, the governing partial differential equations are converted into ordinary differential equations, which are numerically solved using the Runge-Kutta-Fehlberg 4th-5th order method. Key findings include the reduction in velocity due to higher Eyring-Powell parameters, ferrohydrodynamic interactions, and slip effects. Similarly, increased melting and ferrohydrodynamic interactions lower the fluid temperature, while the Dufour number enhances it. The concentration is positively influenced by higher Soret numbers. Statistical results demonstrate a perfect fit with a squared-R coefficient of 100%, and the Pareto chart identifies critical points at 2 for skin friction and the Nusselt number. Sensitivity analysis reveals negative sensitivity for most parameters across ferrohydrodynamic interaction levels, except for the Prandtl number, which exhibits positive sensitivity at low and medium Eyring-Powell parameter levels but turns negative at higher levels. This work provides a robust framework for understanding and optimizing the thermofluidic behavior of non-Newtonian fluids under complex physical conditions, offering valuable insights for industrial applications.

YKL-40 levels in cerebrospinal fluid serve as a diagnostic biomarker for post-neurosurgical bacterial meningitis in patients with stroke.

Previous studies have reported that YKL-40 can serve as a biomarker of infectious diseases and different stroke types. However, evidence supporting its role in diagnosing post-neurosurgical bacterial meningitis (PNBM) remains lacking. A total of 110 patients with stroke who underwent neurosurgical treatment were recruited. Among these, 36 were diagnosed with PNBM based on the results of bacterial culture/Gram staining or cerebrospinal fluid (CSF) characteristics. CSF levels of YKL-40 and other biomarkers with potential diagnostic utility for PNBM were statistically analysed using univariate and logistic regression models. Receiver operating characteristic (ROC) analysis was performed to investigate diagnostic efficiency. According to univariate analysis, CSF levels of glucose, total protein, white blood cells, polymorphocytes, and YKL-40, as well as the CSF-to-blood glucose ratio, were significantly different between the PNBM and non-PNBM groups. Logistic regression analysis revealed that glucose (p=0.026), total protein (p=0.028), and YKL-40 (p=0.006) levels in the CSF may have independent diagnostic utility for PNBM. Among the three biomarkers, CSF-to-blood glucose (area under the receiver operating characteristic curve [AUC] 0.9208) and YKL-40 (AUC 0.9587) demonstrated strong diagnostic utility. CSF levels of YKL-40, glucose, and total protein played independent roles in the diagnosis of PNBM in patients with stroke.

Size-Dependent Wetting Contact Angles at the Nanoscale Defined by Equimolar Surfaces and Surfaces of Tension

The wetting characteristics of fluids play a crucial role in various fields of interface and surface science. Contact angle serves as a fundamental indicator of wetting behavior. However, accurate quantification of wetting phenomena even at the macroscale often poses challenges, particularly due to the hysteresis between receding and advancing contact angles. The complexity increases further at the nanoscale, where the significant volume of the interphase region causes ambiguity in defining the “dividing surface.” In this study, we use molecular dynamics simulations to investigate the wetting dynamics of a “cylindrical nanodroplet” and an argon nanofilm. Through analysis of microscopic density distribution maps and tension tensor distributions within the Gibbs framework, we identified equimolar and tension surfaces at both liquid-gas and liquid-solid interfaces. Our results show over 10% discrepancies between equilibrium contact angles calculated for equimolar surfaces and those based on tension surfaces in the case of the cylindrical nanodroplet. We observed a clear dependence of wetting contact angles on the cross-sectional radius of cylindrical droplets with a straight three-phase contact line. As the radius decreases, the differences between contact angles at equimolar and tension surfaces increase, while for larger droplets, these differences diminish and become negligible.

Measurement of viscosity during vibroextrusion of fiber concrete

Currently, the rheological properties of cement mortars containing dispersed reinforcement have not been studied enough, so it is important to develop a method for measuring the viscosity of fiber concrete mixtures that would simulate the technological process. To consider the flow process and calculate the rheological characteristics of fiber concrete mixtures during vibroextrusion, hydrodynamic theories were applied due to the fact that these mixtures behave like liquids in a vibration field. When solving flow problems, it is taken into account that vibrating fiber concrete mixtures are Newtonian systems. To obtain objective rheological characteristics of fiber concrete mixtures, it is proposed to measure viscosity directly during vibro-extrusion molding of flat products. The peculiarities of the flow of Newtonian fluids between flat fixed walls, which converge in a flat symmetrical rectangular narrowing channel, are considered. It is proposed to determine the reduction of the flow rate of the mixture in the rectangular channel compared to the flow between the plates by the braking coefficient. A graph of the dependence of the braking coefficient on the ratio of the sides of the cross section of the rectangular channel is plotted. 2 formulas are proposed for calculating the braking coefficient. The comparative analysis of the proposed formulas gives a good convergence of the calculation results, the average approximation error is equal to 0.0126%, which indicates a high level of coincidence of the regression equation with a more complex analytical formula. Taking into account the inhibition of the liquid flow in the end zones of the rectangular channel, a formula was proposed for calculating the viscosity of the fiber concrete mixture during the formation of flat products in the narrowing vibroextruder channel. The calculation formula contains the geometric dimensions of the channel, the density and the flow time of the fiber concrete mixture, and to determine the viscosity of the mixture, it is necessary to measure only the time of its complete flow during vibroextrusion. The proposed formula and methodology for calculating viscosity can be used to determine the rheological characteristics of any Newtonian fluids using a flat symmetrical rectangular narrowing channel. In the future, it is planned to continue researching the properties of fiber concrete mixtures under the influence of vibration.

The Use of "Cancer Ratio" in Differentiating Malignant and Tuberculous Pleural Effusions: Protocol for a Prospective Observational Study.

Differentiating between tuberculosis and malignancy as the cause of an exudative lymphocyte predominant pleural effusion is difficult due to similarities in the cellular and biochemical characteristics of the pleural fluid in both conditions. Microbiological tests in tubercular pleural effusions have a poor diagnostic yield, and the long turnaround time for results prevents an early diagnosis. The diagnosis of malignant pleural effusion (MPE) is hampered by a variable yield of pleural fluid cytology and closed pleural biopsy and the fact that thoracoscopy may not be readily available or feasible in each patient. A key gap in the existing knowledge is the performance of the serum lactate dehydrogenase to pleural adenosine deaminase ratio (ie, "cancer ratio"; CR) in differentiating between tuberculous and MPE in a high tuberculosis prevalence country like India, although its use has been well established in Western literature. The CR may find a practical application in the community health care settings in low-income countries without ready access to biopsy. This study aimed to evaluate the CR as a test to differentiate tubercular and malignant etiology in patients with an exudative lymphocyte predominant pleural effusion. Secondary objectives to be assessed include a comparison of CR to pleural fluid carcinoembryonic antigen in MPE and the association of histologic type of lung carcinoma to the CR positivity. This hospital-based, prospective, observational study will include patients admitted with pleural effusion whose pleural fluid reports indicate a lymphocyte-predominant exudate. The ability of the CR to discriminate between tuberculous and MPE will be evaluated as a primary objective of this study. The performance of CR and pleural fluid carcinoembryonic antigen in the diagnosis of MPE will be compared using the receiver operating characteristics and area under the curve for both tests as a secondary objective. The association between a positive CR and histologic type of lung cancer will be analyzed as well. Data collection began in June 2022. As of March 24, 2024, we have recruited 22 patients. Outcomes of the study are expected at the end of 2024. The results of this study will provide an objective basis for the use of CR in differentiating between tuberculosis and malignancy as the cause of an exudative lymphocyte predominant pleural effusion. DERR1-10.2196/56592.

Magnetohydrodynamic squeeze film characteristics of micropolar fluids with piezo-viscous dependency between wide parallel rectangular plates

The study introduces a novel approach to squeeze film behavior by combining Micropolar fluid, its piezo-viscous dependency, and MHD effects on wide parallel rectangular plates. The Reynolds equation is developed analyticaly by utilising the principles of hydromagnetic flow, Eringen’s microcontinuum theory, the micropolar fluid model and the influence of variable viscosity.The current study seeks to maximize the bearing performance by scrutinizing the pressure, load carrying capacity, and squeezing time. The influence of Hartmann number M, coupling number N, fluid gap interacting number L, and Piezo-Viscous Dependency parameter G are numerically calculated and depicted graphically. Notably, the pressure, the load carrying capability, and squeezing time are enhanced by the presence of the micropolar fluid and the magnetic field compared to their Newtonian and non-magnetic counterparts. Additionally, the piezo-viscous dependency, characterized by the viscosity variation factor, also increases the pressure, load and squeezing time. The study highlights the potential of utilizing couple stress fluid, viscosity variation, and MHD as a means to improve load carrying capability and extend the operational life of squeeze film bearings in various engineering applications. The Reynolds equation is derived by applying theory of hydromagnetic flow and Eringen’s micro continuum theory along with micro polar fluid model.

Numerical simulation study of enhanced heat transfer and flow resistance characteristics of twisted tape and twisted elliptical tube composite

ABSTRACT In this paper, the numerical simulation method is used to explore the effect of wall twisting and twisted tape composite to enhance heat transfer in tubes. Comparative analysis of the flow characteristics of fluids in tubes with different Reynolds numbers between 10,000 and 20,000, and with different length/short axis ratios and twist ratios. The results showed that when the length/short axis ratio of twisted elliptical tubes is increased from 1.30 to 2.15, the Nusselt number of twisted elliptical tubes with inserted twisted tapes increases by 10.5–28.6% and the friction coefficient increases by 101.5–128.8% compared with that of smooth elliptical tubes. When the twist ratio is reduced from 2/3 to 1/6, the Nusselt number of the twisted elliptical tube with inserted twisted tape increases by 9.8–37.7%, and the friction coefficient increases by 101.9–164.7%. Increasing the length/short axis ratio and decreasing twist ratio can help to improve the heat transfer performance of the twisted elliptical tube, but all of them are at the expense of increasing the resistance to flow of the fluid inside the tube.

Electrorheological characterization of complex fluids used in electrohydrodynamic processes: Technical issues and challenges

Abstract The electrorheological (ER) characterization of low-viscosity fluids is paramount for producing micro- and nanoscale products through electrohydrodynamic (EHD) techniques, such as EHD-jet printing, electrospray, and electrospinning. Key properties such as viscosity, surface tension, dielectric properties, electrical conductivity, and relaxation time significantly influence both the quality and properties of the final products and the efficiency of the industrial process. ER characterization is essential for studying the macroscopic effects of the interaction between these physicochemical properties under controlled flow kinematics. Researchers may face several technical challenges in performing rigorous ER characterization of moderate conductive fluids typically used in EHD processes. This characterization is crucial for formulating inks compatible with these processes and for understanding fluid dynamics in EHD processes to ensure stable printing conditions and achieve high-resolution, accurate prints. This work highlights the inherent limitations of current ER cells and proposes methodologies to mitigate their impact on measurement accuracy. Furthermore, we propose the use of microfluidic devices as a solution for the ER characterization of moderate conductive fluids.

Investigation of heat transfer and fluid flow in annular curved tubes in laminar flow using Al2O3–water nanofluid

In the present study, the combination of both the secondary flow and the nanofluids as a passive approach as a method to maximize the effectiveness of heat exchangers, and reducing the size was examined. The thermo-fluid behavior of annular curved tubes was investigated numerically ANSYS-FLUENT 14.5 CFD package. The effects of key design parameters, such as different annular tube designs (helical, spiral, and conical), different annular cross-sectional shapes (circular, elliptical, square, rectangular, and triangular), and different annular cross-sectional areas, were studied to evaluate the best design for annular curved heat exchanger. Furthermore, the effects of Al2O3–water nanofluids were presented to evaluate their superiority over the water. To achieve thermal and fluid characteristics, the coils are the same length and cross-sectional area. The numerical simulations were performed at Reynolds numbers, Re, of 850–6400 for various nanofluid concentrations, φ, of 1%, 3%, and 5%. The numerical findings showed that the annular helical tube design exhibited better performance than both the spiral and conical tube designs by 5.1% and 10.4%, respectively, while the pressure drop, ΔP, growth was almost negligible. A circular cross section achieved better heat transfer enhancement among the elliptical, square, rectangular, and triangular shapes by 13%, 30%, 40.5%, and 52.9%, respectively, for the same cross section area. At an Al2O3/water nanofluid concentration of 5%, the heat transfer augmentation was 31.7% greater than that of water, while the pressure drop was 2.37 times greater than that of water. The maximum thermo-hydraulic performance index, η, reaches 1.1% for Al2O3–water at a nanofluid concentration of 5%.Graphical abstract

Study on the dual-segment arctangent model of magnetorheological damper (MRD)

Abstract Magnetorheological fluid damper (MRD) is a damping device that utilizes the instantaneous variable characteristics of magnetorheological fluid (MRF) in magnetic field to control damping force. At present, there are some problems with the existing mechanical parametric models of MRD, such as the complexity of parameters in the Bouc-Wen model, low model accuracy, and the inability of the Bingham model to accurately capture the hysteresis characteristics of damping force with velocity variation. In response to these issues, on the base of MRD performance testing, a dual-segment arctangent model based on arctangent function is proposed. This model uses the arctangent function to describe the nonlinearity of the damping force output curve. And using piecewise fitting method to accurately capture the hysteresis characteristics of the output curve. Compared with existing parametric models such as the Bingham model, Sigmoid model, Bouc-wen improved model, et.al., the dual-segment arctangent model shows simpler parameters and higher model fitting accuracy. The comparative analysis of the fitting results based on experimental data confirms the effectiveness and accuracy of the proposed model, providing valuable reference for the development of high-precision MRD mechanical models.

Intensity of Intrathecal Total IgG Synthesis in Multiple Sclerosis Correlates with the Degree of Pleocytosis, Diversity of Intrathecal Antiviral Antibody Specificities, and Female Sex.

The presence of intrathecal total IgG production is a hallmark of cerebrospinal fluid (CSF) characteristics in multiple sclerosis (MS). Herein, we systematically analyze how the intensity (instead of mere presence) of intrathecal total IgG production relates to basic CSF parameters in MS. We retrospectively assessed clinical routine CSF findings from 390 therapy-naïve relapsing-remitting MS patients diagnosed according to 2017 revised McDonald criteria. The intensity of intrathecal total IgG synthesis according to Reiber's formula was stratified and correlated to demographics, CSF white cell count (WCC), and diversity of MRZ reaction, defined as a polyspecific intrathecal production of IgG reactive against ≥2 of the 3 viruses; measles (M), rubella (R), and varicella zoster (Z) virus. The higher intensity of intrathecal total IgG production significantly correlated with higher CSF WCC (Spearman's ρ = 0.433, p < 0.001) and with the increasing presence and diversity of positive MRZ reaction (Spearman's ρ = 0.600, p < 0.001). Female patients showed higher intensity of intrathecal total IgG production and higher prevalence of positive MRZ reaction than males. The intensity of intrathecal total IgG production correlates with the degree of CSF WCC and diversity of MRZ reaction in MS. As yet unidentified female sex-related factors increase the intensity and diversity of intrathecal IgG production in MS.

Free Vibration Analysis of Hydraulic Quick Couplings Considering Fluid–Structure Interaction Characteristics

As an important component of the automatic hydraulic quick coupling device (AHQCD) on rescue vehicles, the hydraulic quick couplings (HQCs) are used to rapidly dock hydraulic lines and transport fluid while changing and operating hydraulic working tools. However, during tool operation at rescue sites, pressure pulsations at multiple frequencies in the hydraulic lines can coincide with the natural frequencies of the HQCs, potentially causing resonance that severely affects the stability of fluid conveying and damages the connection of hydraulic lines accidentally. To investigate the natural frequencies of the HQCs with upstream and downstream lines, the characteristics of fluid–structure interaction were considered between the poppets and the fluid in this study, and an equivalent stiffness model of the fluid domain was derived based on the fluid compressibility. A dynamic model, along with 6-DOF equations for the system, was established, and the natural frequencies and mode vectors were determined by free vibration analysis. In addition, the effects of working pressure, air content, and stiffness of the springs on the natural frequency of the HQC system were analyzed. The results show the natural frequency increases with a higher working pressure and lower air content, while the effect of spring stiffness on natural frequencies varies with different modes. Furthermore, the proposed model is validated by experimental pressure signals, showing good agreement, with an average error of 2.7% for the first-order natural frequency. This paper presents a theoretical method for improving the stability of fluid transport when operating various hydraulic tools under complex rescue conditions.

Impact of Anisotropic Permeability on Micropolar Fluid Dynamics and Heat Transfer in Porous Channels

The current study explores the fluid dynamics and heat transfer characteristics of micropolar fluids within a channel filled with anisotropic porous media. The governing equations for the fluid flow, microrotation, and temperature profiles are numerically solved using Spectral Quasi-Linearization Method (SQLM). The research examines the influence of various key parameters such as the anisotropic permeability ratio, anisotropic angle, Darcy number, Reynolds number, Brinkman number, Prandtl number, and coupling number. Key findings indicate that the anisotropic permeability ratio and anisotropic angle significantly affect fluid flow and heat distribution, with increased anisotropy leading to enhanced microrotation and temperature, albeit with reduced velocity at the channel center. Higher Darcy numbers result in less restricted flow, increasing velocity and reducing microrotation effects, while increasing the coupling number contributes to a more uniform temperature profile. These results provide significant insights into the optimization of heat transfer and flow control in engineering applications that involve micropolar fluids in porous media.

Comparing clinical and biochemical characteristics of febrile seizures in children with and without COVID-19: a retrospective study

BackgroundTransmission of COVID-19 is now normalized. There is an association between it and increased incidence of febrile seizures in children. Exploring whether COVID-19 has a specific effect on the clinical and biochemical features of febrile seizures is critical for the development of clinical treatment and prevention strategies. This study is to compare the differences in clinical features, hematological features, and cerebrospinal fluid characteristics between COVID-19 and non-COVID-19 children with febrile seizures and to provide a new perspective for further exploring the impact of COVID-19 on the nervous system of children.MethodsThis was a retrospective case–control study. The cases included children with COVID-19 and non-COVID-19 febrile seizures admitted to Xiamen Children’s Hospital from December 2022 to December 2023. The age, gender, length of hospital stay, peak body temperature, presence or absence of other viral infections, hematological characteristics, and cerebrospinal fluid characteristics were compared between children with COVID-19 febrile seizures and non-COVID-19 febrile seizures.ResultsA total of 50 COVID-19 children with febrile seizures and 192 non-COVID-19 children with febrile seizures were enrolled in this study. Multivariate analysis showed that age (OR = 0.715, P = 0.031), blood urea nitrogen (OR = 0.454, P = 0.029), platelet count (OR = 0.987, P = 0.009) and magnesium ion concentration (OR = 0.109, P < 0.001) were negatively correlated with COVID-19 febrile seizures. Albumin (OR = 1.840, P < 0.001) was positively correlated. The concentration of potassium ion in cerebrospinal fluid (OR = 0.334, P = 0.012) was negatively correlated with COVID-19 febrile seizures, and the concentration of sodium ion (OR = 4.383, P = 0.022) was positively correlated with COVID-19 febrile seizures.ConclusionThere were differences in age, blood urea nitrogen, platelet count, magnesium ion concentration, albumin, potassium ion concentration in cerebrospinal fluid, and sodium ion concentration in the cerebrospinal fluid between children with COVID-19 febrile seizures and non-COVID-19 febrile seizures. This study may provide valuable insights into the potential mechanisms of COVID-19 damage to the nervous system in children, and the long-term neurological prognosis of these children requires long-term follow-up.