Forced Flow Research Articles

Stem cell seeding of decellularised porcine right ventricular outflow tracts to advance repair of congenital heart defects

Abstract Background Replacement of the right ventricular outflow tract (RVOT) is necessary in many critical congenital heart disease subtypes, often when the child is less than one year old. Poor availability of small-diameter cardiac homografts necessitates the use of xenografts in paediatric surgical reconstruction. Currently used xenografts are limited by immunoincompatibility and lack of growth, requiring repeat surgery to replace the defective graft. One approach to tackle acute immune rejection of animal tissue is aldehyde fixation of grafts prior to xenotransplantation. Though masking antigenicity, fixation is associated with multiple issues, including toxicity of fixative remnants and calcification. Decellularisation of biological grafts to remove foreign material is a promising alternative to reduce immunogenicity and dampen the risk of rejection. To combat lack of growth, in vitro cellularisation with stem cells is a promising solution. Purpose Current RVOT substitutes have not proven to be a lifelong solution for paediatric cardiac repair. This research has optimised a novel decellularisation technique for porcine RVOTs to produce a durable and cell-free scaffold with translational capability. Current work is looking to seed mesenchymal stem cells (MSCs) onto the acellular RVOT in vitro to enhance immune tolerance and endow the graft with growth capacity upon implant. Methods First, this decellularisation technique produces acellular RVOT scaffolds by simultaneously utilising three methods: enzymatic, chemical, and mechanical decellularisation. Novel to this method, the latter is realised using a 3D printed flow chamber to utilise the shear forces of continuous fluid flow for cell removal from the external and internal RVOTs structure. Coating the acellular graft with poly-lysine has then enabled recellularisation with MSCs isolated from the umbilical cord. Results Nuclei quantification demonstrates decellularisation of all structures of the RVOT, and elimination of residual nucleic acids is evidenced. Immunohistochemical analysis confirms the xenoantigen Galα1-3Galβ1-4GlcNAc-R is absent from the decellularised tissue. In parallel with removal of typical immunogens associated with the rejection response, the elastin and collagen fibres of the extracellular matrix are maintained, supported by histology and electron microscopy. Importantly, the tensile properties of the decellularised grafts are preserved. Finally, MSCs adhered onto the external pulmonary artery surface in vitro, achieving a uniform monolayer of cells. Conclusion RVOTs have been successfully decellularised and proven to possess seeding potential. Future work aims to characterise the seeded MSCs to assess parameters including proliferative capacity and expression of typical MSC markers. Overall, this work has the potential to produce a non-immunogenic graft possessing growth potential as a surgical alternative for paediatric RVOT replacement.

Non-invasive assessment of left ventricular hemodynamic forces in hypertrophic cardiomyopathy

Abstract Background Hemodynamic force (HDF) analysis allows non-invasive measurement of intraventricular pressure gradients, portraying cyclic spatial-temporal interaction between blood and tissues. Impaired HDFs have been implicated in early detecting of adverse cardiac remodelling and treatment response in various cardiovascular disorders, providing insights into cardiac physiology not offered by traditional cardiovascular imaging (1). Mainly explored in heart failure, HDF analysis has not been previously applied to hypertrophic cardiomyopathy (HCM). Purpose To investigate differences in systo-diastolic function in HCM patients compared to healthy controls using HDF analysis. Methods Forty patients with HCM diagnosis (20 obstructive and 20 non-obstructive) were retrospectively evaluated in comparison with 22 healthy controls. Left ventricular (LV) HDFs were derived from routine transthoracic apical 4-, 2- and 3-chamber views using a dedicated software. Apical-basal HDF curves were generated, where positive deflections represent forces directed from the LV apex to the base, whilst negative ones are directed toward the apex. Amplitude and timing parameters were derived, the latter indexed to total cardiac cycle duration. Results Table 1 shows the demographic, clinical and echocardiographic characteristics of HCM compared to controls. Patients with HCM were older, had a slower heart rate due to treatment with beta-blockers, and showed hypercontractility, as expressed by higher LV ejection fraction. Compared to controls, HCM patients showed reduced LV longitudinal force, i.e. the force during the whole cardiac cycle (4.17% [2.36-5.52] vs. 6.01% [4.73-7.78], p=0.002), shorter time interval to systolic peak (0.15 [0.12-0.16] vs. 0.19 [0.17-0.20], p <0.001), and shorter duration of LV impulse (0.29 [0.27-0.32] vs. 0.34 [0.32-0.37], p <0.001) (Figure 1). However, no differences in terms of systolic force peak (p=0.283) or LV impulse intensity (p=0.689) were detected. During the transition between systole and diastole, LV suction (i.e. the interval including late systolic deceleration and early diastolic suction) was significantly longer (0.26 [0.22-0.29] vs. 0.23 [0.21-0.25], p=0.023) but less pronounced (6.30% [4.56-8.44] vs. 8.72% [6.71-12.59], p=0.005), likely reflecting a relaxation impairment from the very beginning of diastole. Such impairment was maintained during early diastolic filling, where the amplitude of the positive deceleration flow force was severely reduced in HCM compared to controls (2.98% [1.98-4.58] vs. 7.11% [4.55-8.72], p <0.001). Conclusions HDF analysis in HCM patients revealed unique systolic and diastolic changes reflecting faster LV contraction during systole and slower and weaker LV forces during diastole. This analysis deepens our understanding of HCM mechanic abnormalities and may help assess response to innovative treatment options.

Fluid Force Reduction and Flow Structure at a Coastal Building with Different Outer Frame Openings Following Primary Defensive Alternatives: An Experiment-Based Review

A well-constructed tsunami evacuation facility can be crucial in a disaster. Understanding a tsunami’s force and the flow structure variation across various building configurations are essential to engineering designs. Hence, this study assessed the steady-state flow structure at building models (BM) incorporating outer frame openings, including piloti-type designs with a different width-to-spacing ratio of piloti-type columns following an embankment model (EM) with a vegetation model (VM). The experiments also demonstrated the outer frame opening percentage’s impact and orientation toward the overtopping tsunami flow at the BM. The results show that the arrangement of an opening on the outer frame and the piloti-type columns are critical in reducing the tsunami force concerning the experimental setup. Moreover, allowing a free surface flow beneath the BM implies that the correct piloti-pillar arrangement is crucial for resilient structure design. In addition, the three-dimensional numerical simulation was utilized to explain the turbulence intensity of the overtopping flow around the critical BM type. The derived resistance coefficient (CR) defined the drag and the hydrostatic characteristics at the BM due to the overtopping tsunami flow. Furthermore, for the impervious BM, the value CR was consistent with the previous studies, while the CR value for the BMs with an outer frame opening was directly coincident with the percentage of porosity.

Research on the distribution of debris flow impact on the upstream surface of the check dam

The impact force of debris flow is not only an important indicator of the risk assessment of debris flow and the strength impact resistance of buildings against debris flow, but also an important parameter in the design of various debris flow prevention projects (such as the check dam and the drainage channel, etc.). The pressure sensors are arranged at different positions (monitoring points) on the upstream face of the check dam. By changing the slope of the drainage channel, the bulk density of debris flow and the slope gradient of the upstream face of the check dam, the time history curves of the impact force at the monitoring points under different experiment conditions are obtained. The characteristic value of the impact force of debris flow acting on the surface of the sand retaining dam is analyzed, and the evolution law of mean value and maximum value of impact force of debris flow at the same detection location with the above conditions is obtained. The mean value and maximum value of debris flow impact force at different detection locations under the same working condition are analyzed to obtain the evolution law of debris flow impact force at different locations, and then the distribution trend of debris flow impact force on the upstream face of the check dam is obtained. The research results provide scientific and reasonable theoretical basis and technical support for the stability analysis of the check dam, so as to better serve the disaster prevention and reduction of debris flow, which will improve the technical level of the debris flow prevention project to a certain extent.

Exploring the correlation between body mass index and lung function test parameters: a cross-sectional analytical study

PurposeThe correlation between body weight and health is a significant public health concern. While the adverse effects of obesity on pulmonary function are well-known, the impact of being underweight remains debated due to limited research. This study aimed to investigate the correlation between Body Mass Index (BMI) categories and lung function parameters.ResultsA study of 3077 participants found significant differences in gender, age, height, and weight across various Body Mass Index (BMI) categories. The study found non-significant variations in forced expiratory flow (FVC) across BMI categories, with underweight individuals showing lower FVC compared to normal and overweight individuals. BMI significantly impacted mean forced expiratory flow during the middle half of FVC. A significant negative correlation was observed between age and FVC, FEV1, FEV1/FVC ratio, and FEF25-75. A significant positive correlation was observed between weight, height, and lung function parameters. Multiple regression analysis revealed a decrease in lung function with advancing age, while height showed significant positive associations. The study concluded that age, sex, smoking, height, and weight collectively explained 41.0% of the variance in FVC, FEV, and FEF25-75.

Transport behavior of Polymeric Methyl Methacrylate nanoplastics in saturated and unsaturated porous media: Combined influence of electrolyte and organic acids

The migration behavior of Polymeric Methyl Methacrylate (PMMA) nanoplastics in saturated porous media and unsaturated porous media is investigated under conditions of electrolytes in combination with organic acids. In the saturated porous media, the mass recovery rate of PMMA decreases with ionic strength. The inhibition effect of Ca2+ on PMMA transport is stronger than that of Na+. Under the conditions of the coexistence of electrolytes with humic acid (HA), increasing the concentration of HA does not consistently enhance PMMA migration in porous media. However, citric acid (CA) exerts solely an inhibitory effect on PMMA transport. The orthogonal analysis suggests that Ca2+ concentration is the major factor affecting PMMA transport. Extended Darjaguin-Landau-Verwe-Overbeek (XDLVO) interaction energy considering the heterogeneity of HA adsorption on PMMA is calculated to quantify the interactions of PMMA-PMMA and PMMA-quartz sand under different physiochemical conditions. In unsaturated porous media, gravity leads to the creation of dominant channels, and the shear force of water flow in porous media leads to the rapid passage of PMMA through the dominant channels. However, as the water content decreases, the recovery rate of PMMA decreases from 0.99 to 0.71. Significantly, the capillary energy of a colloid retained in a thin film or at the air-water-solid (AWS) interface is several orders of magnitude larger than the XDLVO interaction energy. Findings obtained by this study may improve the current understanding of the environmental fate of nanoplastics in subsurface environments and can provide scientific methods to assess the associated risk of nanoplastics.

Turbulent flow and wall forces in staggered square cylinder porous media: An LES Analysis

Abstract The Wall-Modeled-Large Eddy Simulation (WMLES) technique was used to analyze turbulent flow in a porous medium composed of a staggered arrangement of square cylinders. The study focused on a porosity range of 0.3 to 0.8 at a pore Reynolds number of 10×103. The research provides novel information on pressure and shear force distributions around the cylinders and time-averaged values of particle drag and fluctuating lift coefficients. Results indicate that the flow physics are mainly driven by an expansion region in front of the central particle and another in the rear, where the flow is contracted and strongly accelerated. In the first region, velocities, turbulence kinetic energy (k), and its dissipation rate (e) are attenuated by a sudden pressure increase, while in the contraction region, the effect is the opposite. As porosity decreases, flow gradients and the overall levels of k, e, and Reynolds stresses become more significant. Turbulent anisotropy increases as porosity decreases below 0.6. Hydrodynamic stresses in the last interval present relatively uniform levels, which is a unique feature that may be considered in designing dedicated engineering devices with controlled stresses.

Shear-driven magnetic buoyancy in the solar tachocline: Dependence of the mean electromotive force on diffusivity and latitude

Abstract The details of the dynamo process that is responsible for driving the solar magnetic activity cycle are still not fully understood. In particular, whilst differential rotation provides a plausible mechanism for the regeneration of the toroidal (azimuthal) component of the large-scale magnetic field, there is ongoing debate regarding the process that is responsible for regenerating the Sun’s large-scale poloidal field. Our aim is to demonstrate that magnetic buoyancy, in the presence of rotation, is capable of producing the necessary regenerative effect. Building upon our previous work, we carry out numerical simulations of a local Cartesian model of the tachocline, consisting of a rotating, fully compressible, electrically conducting fluid with a forced shear flow. An initially weak, vertical magnetic field is sheared into a strong, horizontal magnetic layer that becomes subject to magnetic buoyancy instability. By increasing the Prandtl number we lessen the back reaction of the Lorentz force onto the shear flow, maintaining stronger shear and a more intense magnetic layer. This in turn leads to a more vigorous instability and a much stronger mean electromotive force, which has the potential to significantly influence the evolution of the mean magnetic field. These results are only weakly dependent upon the inclination of the rotation vector, i.e. the latitude of the local Cartesian model. Although further work is needed to confirm this, these results suggest that magnetic buoyancy in the tachocline is a viable poloidal field regeneration mechanism for the solar dynamo.

Hydrodynamic optimization and performance verification of fairings for round-ended cofferdams using dam-break wave experiments and numerical simulations

Round-ended cofferdams are crucial for large-scale marine projects but are vulnerable to the complex marine environment, including waves, tides, and storms. Enhancing the hydrodynamic performance of these cofferdams is essential for improving safety and efficiency in marine construction. This study introduces a novel fairing design aimed at reducing water flow resistance during the quasi-stable stage of a tsunami. The flow field is analyzed using computational fluid dynamics (CFD) simulations, and an adaptive surrogate model is employed to optimize the parameterized fairing shape. The results demonstrate that the optimized shape significantly suppresses vortex shedding, leading to a 16.59 % reduction in the drag coefficient and a 44.3 % reduction in the lift coefficient under flow conditions. Experimental and numerical simulations of dam-break waves are conducted for two designs, R1 and R0. By comparing their flow field and force characteristics, it is found that R1 effectively separates waves during the impulse stage, reduces wave climb height, and decreases impact loads. In the quasi-stable stage, R1 mitigates the blockage effect, reducing the liquid level difference between the front and back, and thus lowering flow forces. Experimental data further reveals that when the downstream is a dry riverbed, R1′s load reduction is particularly notable, with maximum reductions of 45.62 % in the impulse stage and 28.75 % in the quasi-stable stage. When the riverbed is wet, the maximum load reduction rates are 18.04 % and 8.72 %, respectively. Therefore, R1 not only reduces the resistance of round-end cofferdams under water currents but also under extreme wave forces, providing valuable insights for advancing ocean engineering design.

Minimizing movements for forced anisotropic curvature flow of droplets

We study forced anisotropic curvature flow of droplets on an inhomogeneous horizontal hyperplane. As in Bellettini and Kholmatov [J. Math. Pures Appl. 117 (2018), 1–58], we establish the existence of smooth flow, starting from a regular droplet and satisfying the prescribed anisotropic Young’s law, and also the existence of a 1/2 -Hölder continuous in time minimizing movement solution starting from a set of finite perimeter. Furthermore, we investigate various properties of minimizing movements, including comparison principles, uniform boundedness, and the consistency with the smooth flow.

Vortex shedding and induced forces in unsteady flow

AbstractThis survey paper is concerned with vortex shedding from bodies in unsteady flow due either to time dependent motion of the body in a still fluid or unsteady motion of the fluid about a fixed body. The fluid is treated as incompressible, and the main emphasis is on starting flows and oscillatory flows. Much of the discussion describes 2D flow around sections of long or slender bodies. The first part of the paper covers the inviscid flow scaling of the forces induced by vortex shedding in time dependent flows which drive the shedding. This is followed by application of Wu’s impulse integral of the moment of vorticity to predict the forces induced by vortex shedding from a body in both inviscid and viscous flows. Vortex shedding phenomena involving small amplitude, high-frequency oscillatory flow such as vortex-induced vibration (VIV) and fluid-structure interaction (FSI) are not included in this discussion as in these cases the unsteady flow controls rather than drives the vortex shedding and they are well covered elsewhere.The second part of the paper describes a vortex force mapping (VFM) method derived by considering the Lamb–Gromyko formulation for the pressure contribution which allows the integral of the vorticity field to be restricted to regions which are not far from the body. It is applied to both inviscid and viscous flows. The section finishes with discussion of application of the VFM to the calculation of forces induced on bodies from flow field measurements, such as particle image velocimetry (PIV).

Research of scale effect on propeller bearing force of a four-screw ship in oblique flow

To study the scale effect on propeller bearing forces in oblique flow, the propeller bearing forces of a fully appended four-screw ship that refers to a vessel propelled by four propellers are calculated and investigated. The findings reveal that scale effects in wake fields lead to an increase in the axial velocity of the propeller disk in the full-scale ship compared to the model, influenced by boundary layer flow. Moreover, asymmetric differences in the impact of oblique flow on the leeward and windward sides result in varied effects of positive and negative drift angles on the wakefield. The disparity in wake fields between inside and outside disks exacerbates unbalanced load distribution, with time-averaged loads showing an increase with drift angle for both propellers at full scale. Additionally, pronounced scale effects lead to variations in blade loads between model and full scale, with drift angles shifting the locations of single-blade load extremums. Unsteady bearing force components exhibit periodic fluctuations, with larger amplitudes at the blade passage frequency for the model scale propeller compared to the full scale, particularly evident under negative drift angles. The aforementioned findings can provide theoretical guidance for load balancing and vibration reduction of the four-screw ships.

دراسة علمية حول العزم الزاوي وعلاقته بالخصائص الميكانيكية لشفرات التوربينات

The general trend now in all countries of the world and all sectors is to achieve sustainability. One of how this sustainability can be achieved is to develop and improve the properties of raw materials, and in the field of turbine-powered power plants, sustainability must be achieved in light of the global crisis facing the energy sector, in this study, which aims to study the effect of angular torque on Mechanical properties of turbine blades, so that we can develop and improve the properties of those blades Angular torque is very important in turbine blades because it drives the turbine to rotate. Angular torque results from a force acting on a rotating body. In the case of turbine blades, the force of the gas flow produces angular torque. Turbine blades typically consist of thin, curved metal sheets. When gas passes through the blades, it exerts a force on the blades. This force forces the blades to rotate around its axis the greater the angular torque it produces. The greater the angular torque, the faster the turbine rotates. This study provides a mathematical model to calculate the angular torque resulting from turbine blades. The model was used to study the effect of various factors on the angular torque, including the gas flow speed, the shape of the blades, and their mechanical properties. Then, a simulation was run using the ANSYS program to determine the relationship between the angular torque and the mechanical properties of the turbine blades. The results indicated a large deviation of the flexible blades and unstable rotation of the rotating blade systems, due to the coupling effect of rotation and vibration, where the mechanical properties of mass/inertia distributions, damping, and stiffness are related to changes in rotational speed and local deformation in rotor blade systems, thus, the harmonic balance must occur and the mechanical properties of the blades be improved. Keywords: Angular Torque, Mechanical Properties, Raw Materials, Turbine blades, mathematical model, flow speed, ANSYS, rotation and vibration, harmonic balance.

Forces of Filtrate Flow on Podocyte Foot Processes Studied by Three-Dimensional and Two-Dimensional Computational Fluid Dynamics

Forces of Filtrate Flow on Podocyte Foot Processes Studied by Three-Dimensional and Two-Dimensional Computational Fluid Dynamics

Fixed Airflow Obstruction in Asthma Can Be Identified Early by Low FEF25-75% and is Associated with Environmental Exposure.

This study aimed to identify environmental risk factors associated with asthmatic fixed airflow obstruction (FAO) and assess the relationship between small airway abnormalities defined by forced expiratory flow at 25-75% (FEF25-75%) and FAO. We analyzed data from 312han Chinese patients with stable asthma on standard treatment. Low FEF25-75% was defined as post-bronchodilator FEF25-75% z-score <-0.8435, and FAO as post-bronchodilator FEV1/FVC z-score <-1.645. Exposure levels were retrospectively analyzed in relation to FAO risk in asthmatics. Asthmatics were grouped by low FEF25-75% and FAO, and lung function, environmental exposure, daily symptoms, and exacerbations in the previous year were compared cross-sectionally across groups. In retrospective analyses, pack-years of smoking in male patients (adjusted odd ratio [95% confidence interval] 1.05 [1.03-1.07], P<0.001), biomass exposure for >20 years (2.65 [1.13-6.43], P=0.027), occupational exposure for >10 years (2.01 [1.06-3.86], P=0.035) and occupational exposure for >20 years (2.67 [1.24-5.91], P=0.013) were associated with asthmatic FAO. In cross-sectional analyses, compared with the normal FEF25-75%/ asthmatics without FAO (NON-FAO) group, the low FEF25-75%/ asthmatics with FAO (FAO) group had lower FEV1 z-scores and FEV1/FVC z-scores, more pack-years and years of biomass and occupational exposure, higher Asthma Control Questionnaire-5 and Chronic Obstructive Pulmonary Disease Assessment Test scores, and more frequent exacerbations. The low FEF25-75%/NON-FAO group showed the same trend, but to a lesser extent. Chronic airway inflammation is not the only driver of asthmatic FAO, and management and treatment targeting environmental risk factors (smoking and biomass and occupational exposures) may slow FAO progression in asthmatics. The FEF25-75% determined by the z-score is a reliable marker of small airway abnormalities, and patients with low FEF25-75% are at greater risk for FAO, requiring more frequent follow-up.

Confined seepage analysis of saturated soils using fuzzy fields

Seepage refers to the flow of water through porous materials. This phenomenon has a crucial role in dam, slope, excavation, tunnel, and well design. Performing seepage analysis usually is a challenging task, as one must cope with the uncertainty associated with the parameters such as the hydraulic conductivity in the horizontal and vertical directions that drive this phenomenon. However, at the same time, the data on horizontal and vertical hydraulic conductivities are typically scarce in spatial resolution. In this context, so-called non-traditional approaches for uncertainty quantification (such as intervals and fuzzy variables) offer an interesting alternative to classical probabilistic methods, since they have been shown to be quite effective when limited information on the governing parameters of a phenomenon is available. Therefore, the main contribution of this study is the development of a framework for conducting seepage analysis in saturated soils, where uncertainty associated with hydraulic conductivity is characterized using fuzzy fields. This method to characterize uncertainty extends interval fields towards the domain of fuzzy numbers. In fact, it is illustrated that fuzzy fields are an effective tool for capturing uncertainties with a spatial component, since they allow one to account for available physical measurements. A case study in confined saturated soil shows that with the proposed framework, it is possible to quantify the uncertainty associated with seepage flow, exit gradient, and uplift force effectively.

Simulation analysis and optimization of pilot type electro-hydraulic proportional directional valve based on multi field coupling

The pilot-operated electro-hydraulic proportional directional valve is widely used in complex and precision engineering fields. Its operational stability and reliability determine the overall performance of the hydraulic system. During the working process of the pilot-operated electro-hydraulic proportional directional valve, the spool is deformed due to the influence of pressure and temperature, resulting in problems such as clamping or stagnation. In order to solve this problem, this study uses the fluid-solid-thermal coupling simulation method to analyze the flow field characteristics and thermal deformation of the spool with different structural throttling grooves, and optimizes the U-shaped throttling groove structure. The results indicate that as the valve opening increases, the front section of the throttling groove becomes the primary region where the maximum radial deformation of the spool occurs. In this paper, the steady-state flow force of the valve core is taken as the measurement standard, the constraint range of the structural parameters is determined, and the radial thermal deformation is included in the optimization analysis of the structural size. It’s verified that the optimized flow characteristics are improved by about 32 % compared with that before optimization, and the maximum steady-state flow force after considering thermal deformation is reduced by about 4N compared with that before optimization. This provides an important design basis and reference for the structural design and optimization of the pilot electro-hydraulic proportional directional valve.

Discretization of Thin-Walled Sections with Variable Wall Thickness

At the stage of designing thin-walled aircraft structures, to simplify calculations, their cross sections are idealized. To do this, the section with the skin and the longitudinal elements reinforcing it is replaced (when determining normal stresses) by a discrete one, consisting of concentrated areas at characteristic points. In this case, the equality of the moments of inertia of the initial and discrete sections is preserved. Such idealization is used in the calculation of thin-walled rods for normal and shear stresses (Wagner model). For sections consisting of a system of rectangular strips of constant thickness, discretization allows to set approximate values of normal and shear stresses and accurately find the locations of the singular points of the bending center (in an open contour) and the center of rigidity (in a closed one). The discrete model of a strip consists of three lumped areas: two at the edges and one in the center. The paper proposes to extend the discrete model to sections in which the skin thickness changes according to a linear law. In addition to the rectangular strip, it is possible to use elongated triangles and trapezoids, replaced by three and four concentrated areas, respectively. The possibility of using a discrete model for calculating some thin-walled sections of open and closed contours is considered. The section of an open contour is studied - the problem of transverse bending without torsion of a channel having flanges with a linearly variable thickness. Differences in the flows of tangential forces calculated from the exact and discrete models are shown. The coincidence of the results in determining the position of the bending center according to two models was established. When studying the application of a discrete model to a closed contour, its simplified option is proposed. The problem of transverse bending without torsion and finding the center of rigidity in a section with a contour line in the form of a trapezoid with front and rear walls of constant thickness and upper and lower skins and a similar section with a contour in the form of a rectangle was considered. Differences in the flows of tangential forces calculated by exact and discrete models are established. For a closed section in the form of a rectangle, the decrease in the moment of inertia for torsion due to the redistribution of material in the cross section was studied separately. It has been established that when finding the position of the center of rigidity, the discrepancy between the results of the exact and discrete models in sections with geometric parameters close to real ones was less than 1% for a rectangular contour, and 4% for a trapezoidal contour. The results indicate the possibility of extending the application of the discrete model of thin-walled cross section to the design calculations of thin-walled rods with variable skin thickness, representing practical structures.

Identifying the mixed and forced convection flow with transverse magnetic field

AbstractOptimal control of the steady, laminar, magnetohydrodynamics (MHD) mixed convection flow of an electrically conducting fluid is considered under the effect of the transverse magnetic field in a square duct. The viscous and Joule dissipations are included and the flow is driven by a constant pressure gradient. The triple nonlinear set of momentum, induction, and energy equations are solved in dimensionless form by using the mixed finite element method (FEM) with the implementation of Newton's method for nonlinearity with the discretize‐then‐linearize approach. Accordingly, FEM solutions are obtained for various values of the problem parameters to ensure the efficiency of the underlying scheme. This study aims to investigate the problem of controlling the steady flow by using the physically significant parameters of the problem as control variables in the case of a mixed convection flow. In this respect, classification of the type of convection, forced or free, is achieved by controlling the Grashof number (Gr). Besides, single and pairwise controls with Hartmann number (M), Prandtl number (Pr), and magnetic Reynolds number (Rm) are also used to regain the prescribed fluid behaviors and required magnetic field. Control simulations are conducted with the sequential‐least‐squares‐programming (SLSQP) algorithm in the optimization.

Toward Stabilizing the Keyhole in Laser Spot Welding of Aluminum: Numerical Analysis.

The inherent instability of laser welding, particularly keyhole instability, poses significant challenges in industrial applications, leading to defects such as porosities that compromise weld quality. Various forces act on the keyhole and molten pool during laser welding, influencing process stability. These forces are categorized into those promoting keyhole opening and penetration (e.g., recoil pressure) and those promoting keyhole collapse (e.g., surface tension, Darcy's damping forces), increasing instability and defect likelihood. This paper provides a comprehensive instability analysis to uncover key factors affecting keyhole and process instability, presenting future avenues for improving laser welding stability. Using a novel numerical method for simulating laser spot welding on aluminum with COMSOL Multiphysics 5.6, we investigated the effect of laser pulse shaping on keyhole and process instability. Our analysis focused on keyhole morphology, fluid flow behaviour, and force analysis. The results indicated that the curvature effect, Marangoni effect, and Darcy's damping force are primary contributors to instability, with the curvature effect and Darcy's damping force being the most dominant. Additionally, erratic and high-velocity magnitudes induce intense fluid flow behaviour, exacerbating keyhole instability. Moreover, single/quadruple peak triangular and variant rectangular ramp-down pulse shapes produced the least instability, while multi-pulse rectangular shapes exhibited intense instability. It was found that combining triangular/rectangular pulse shapes can reduce force and keyhole instability by smoothing spontaneous force spikes, resulting in a more stabilized welding process. Controlling fluid flow and abrupt force changes with appropriate pulse shaping is key to defect-free welded products.