Cross-sectional Geometry Research Articles

Atmospheric-level carbon dioxide gas sensing using low-loss mid-IR silicon waveguides.

Interest in carbon dioxide (CO2) sensors is growing rapidly due to the increasing awareness of the link between air quality and health. Indoor, high CO2 levels signal poor ventilation, and outdoor the burning of fossil fuels and its associated pollution. CO2 gas sensors based on integrated optical waveguides are a promising solution due to their excellent gas sensing selectivity, compact size, and potential for mass manufacturing large volumes at low cost. However, previous demonstrations have not shown adequate performance for atmospheric-level sensing on a scalable platform. Here, we report the clearly resolved detection of 500 ppm CO2 gas at 1 s integration time and an extrapolated 1σ detection limit of 73 ppm at 61 s integration time using an integrated suspended silicon waveguide at a wavelength of 4.2 µm. Our waveguide design enables suspended strip waveguides with bottom anchors while maintaining a constant waveguide core cross-sectional geometry. This unique design results in a low propagation loss of 2.20 dB/cm. The waveguides were implemented in a 150 mm silicon on insulator (SOI) platform using standard optical lithography, providing a clear path to low-cost mass manufacturing. The low CO2 detection limit of our proposed waveguide, combined with its compatibility for high-volume production, creates substantial opportunities for waveguide sensing technology in CO2 sensing applications such as fossil fuel combustion monitoring and indoor air quality monitoring for ventilation and air conditioning systems.

Analytical investigation of residual stress in samples with variable cross-sectional surfaces in the laser powder bed fusion process

One of the primary challenges associated with the laser powder bed fusion process is the presence of residual stress. These residual stresses arise from the significant thermal gradients induced by the rapid heating and cooling of the material, which are inherent to the laser powder bed fusion process. Such stresses can contribute to crack formation, distortion, and, ultimately, failure of the component. Consequently, effective control of residual stress is of paramount importance. In this study, an analytical approach was employed to establish the relationship between the distribution of residual stresses within samples exhibiting two variable cross-sectional geometries. Utilizing the principles of force and moment equilibrium, the distribution of residual stresses in each layer of the sample was determined. To validate the analytical method, experimental measurements of residual stresses in both the surface layer and the interlayer region of Inconel 625 samples were conducted. Additionally, the impact of hatch distance on the residual stress within the experimental samples was examined. Residual stress measurements were performed using a non-destructive X-ray diffraction technique. The results from the experimental analysis indicate that an increase in hatch distance correlates with a reduction in residual stress. Furthermore, a comparison between the residual stress at the center of the surface layer and that at the interface of the variable cross-sectional sample reveals that the residual stress at the interface is approximately halved.

Cross-sectional optimisation of I-shape pultruded FRP beams using search-adaptive micro-population genetic algorithm

Despite the growing utilisation of pultruded fibre-reinforced polymers (PFRP) profiles in infrastructure applications, there is still a scarcity of design tools with a feasible computational cost. Such shortage deprives these profiles of competing with economic cost and optimised performance against other construction materials. This research investigated the numerical optimisation of cross-sectional geometry and anisotropy ratio of I-shape PFRP beams for the design against local buckling of flange under bending and web under transverse compression. A new search-adaptive micro-population genetic algorithm (SA-µP GA) tool was proposed to achieve accurate results with low computational cost. This tool was verified and compared with other GA codes from the literature. The artificial neural networks (ANNs) machine learning tool was used to maximise the use of data and generate practical and economic design charts considering the varying interactions between the design parameters. This optimisation approach represents an efficient design tool to achieve the design requirements of stability, strength, and serviceability (stiffness) limits with minimum cost and optimal structural performance. The optimisation approach was addressed using four case studies from the literature.

Nonlinear Analysis and Optimization of Recycled Aggregate Concrete Cross-Sections Based on Restoring Force Models

This research presents a simplified approach using a uniaxial restoring force model to analyze the seismic response of recycled aggregate concrete (RAC) frames. Nonlinear simulations were conducted to explore how factors like axial compression ratio, reinforcement ratio, and cross-sectional geometry affect the ductility and seismic performance of RAC sections. The findings reveal that a reduction in the axial compression ratio from 0.60 to 0.57 results in a 15% increase in ductility, while a higher reinforcement ratio leads to a 20% enhancement. In addition, rectangular sections were found to be more sensitive to variations in material strength than square sections, offering key insights for structural optimization. The method proposed here also enhances computational efficiency by minimizing resource consumption and improving the convergence of nonlinear iterative procedures. These findings provide a theoretical foundation for optimizing the design and seismic evaluation of RAC structures, promoting their broader application in engineering practice.

Evaluating the Influence of Morphological Features on the Vulnerability of Lipid-Rich Plaques During Stenting.

Lipid-rich atheromas are linked to plaque rupture in stented atherosclerotic arteries. While fibrous cap thickness is acknowledged as a critical indicator of vulnerability, it is likely that other morphological features also exert influence. However, detailed quantifications of their contributions and intertwined effects in stenting are lacking. Therefore, our goal is to assess the impact of plaque characteristics on the fibrous cap stress and elucidate their underlying mechanisms. We analyzed the stent deployment in a three-dimensional patient-specific coronary artery reconstructed from intravascular optical coherence tomography (IVOCT) data using the finite element method. Additionally, we performed sensitivity analysis on 78,000 distinct plaque geometries of two-dimensional arterial cross section for verification. Results from the three-dimensional patient-specific model indicate strong correlations between maximum fibrous cap stress and lipid arc (r=0.769), area stenosis (r=0.550), and lumen curvature (r=0.642). Plaques with lipid arcs >60 deg, area stenosis >75%, and lumen curvatures >5 mm-1 are at rupture risk. While we observed a rise in stress with thicker lipid cores, it was less representative than other features. Fibrous cap thickness showed a poor correlation, with the sensitivity analysis revealing its significance only when high stretches are induced by other features, likely due to its J-shaped stress-stretch response. Contrary to physiological pressure, the stent expansion generates unique vulnerable features as the stent load-transferring characteristics modify the plaque's response. This study is expected to prompt further clinical investigations of other morphological features for predicting plaque rupture in stenting.

Leveraging microchannel cross-sectional geometry for acoustophoretic manipulation of submicron particles

Leveraging microchannel cross-sectional geometry for acoustophoretic manipulation of submicron particles

Associations of Habitual Skeletal Loading with Bone Changes During the Menopausal Transition: A Follow-up Study.

While weight-bearing physical activity (PA) benefits bone health, it remains unclear whether PA can counteract hormone-driven menopausal bone deterioration. This secondary analysis of a population-based prospective follow-up study examined changes in bone health indicators around menopause and evaluated whether accelerometer-measured habitual skeletal loading is associated with these changes. A total of 189 initially perimenopausal women without estrogen therapy (mean age 52 [SD 2] years) were followed until they became postmenopausal (mean follow-up time 15 [9] months). Femoral neck bone mineral density (FN BMD) and bone mineral content (BMC) were measured with dual x-ray absorptiometry (DXA). Femoral and tibial shaft volumetric BMD (vBMD), cross-sectional geometry, and stress-strain index (SSI) were assessed using quantitative computed tomography (QCT) in a subset of 61 women. Habitual skeletal loads (mean daily osteogenic index [OI] and low, medium, and high-intensity impact counts) were evaluated with multiple-day free-living accelerometry records. Longitudinal associations of habitual skeletal loads and bone outcomes were analyzed with GEE models. Consistent decreases were observed in FN BMD and BMC, and femoral and tibial shaft vBMD and SSI (p < 0.001) over the follow-up. Slight decreases over the follow-up were also observed in OI and medium impacts in the full sample, and medium and high impact counts in the subsample (p < 0.05). Medium impacts were associated with tibial shaft vBMD and SSI (β = 0.204, 95% CI [0.018, 0.391] and β = 0.077 95% CI [0.000, 0.154], respectively). High impacts were associated with femoral shaft vBMD (β = 0.186 95% CI [0.006, 0.366]. However, no association was observed between habitual skeletal loads and changes in bone characteristics over the follow-up. We observed a rather uniform skeletal response to the menopausal transition at all measured bone sites. Positive associations were found between medium and high-intensity impacts and bone characteristics at the femoral and tibial shafts. However, habitual skeletal loading did not seem to counteract bone deterioration during the menopausal transition.

Flow characteristics in compound channels with skewed and inclined floodplains

ABSTRACT Understanding the flow characteristics of rivers in both their inbank and overbank flow conditions is an important task for engineers. So far, many studies have been carried out in compound channels with prismatic and non-prismatic floodplains. However, we still don’t understand the effect of the floodplain’s side slope on the flow field in compound channels. This paper presents the results of experiments on compound channels with skewed and inclined floodplains (lateral slope of 0.075). Velocity and boundary shear stress were measured at various experimental sections for different relative depths and two skew angles of 3.81º and 11.31º. Using the measured data, the secondary currents pattern, the apparent shear forces at the vertical interface between the main channel and floodplains, and the discharge distribution in the main channel and the floodplains along the flume have been investigated. The results of the experiments were then compared to the experimental data of the skewed compound channel with flat floodplains. The research shows that due to lateral flow and momentum exchange between flume subsections, the flow velocity, bed shear stress, and percentage discharge on the diverging floodplain are greater than those on the converging floodplain with the same cross-sectional geometry.

Sensitivity of Heat Transfer to the Cross-Section Geometry of Cylinders

Sensitivity of Heat Transfer to the Cross-Section Geometry of Cylinders

Effect of the Cross-Sectional Geometry of the Mixed Particle Zone on the Spiral Separation Process and Its Structural Optimization

Cross-sectional geometry is of significance in determining the flow characteristics and the particles separation in spiral concentrators. The effects of the cross-sectional geometry within the mixed particle zone on the secondary flow and the separation process of hematite and quartz particles with a size of 89.5 μm were investigated via a computational fluid dynamics (CFD) approach. The optimization of the line segment slopes was conducted using response surface methodology (RSM). The results indicate that the peak radial fluxes and average radial velocities of the secondary flow are positively correlated with the corresponding line segment slope. The independent adjustment of line slopes in regions I and II, and the interaction of line slopes in regions I and III, influence the separation efficiency of hematite and quartz particles significantly. The separation performance of the experimental spiral concentrator with a cross-sectional profile of the optimized line segments for a feed of hematite and quartz with a size range of −100 + 75 μm is remarkably improved by nearly 5%. This study provides insights for the cross-section design of spiral concentrators for the effective separation of coarse-grained hematite and quartz.

Vibration analysis of rotating pre-twisted composite beams through isogeometric-based dimensional reduction method

The free vibration analysis of rotating pre-twisted composite beams with arbitrary cross-section geometry is investigated using an isogeometric-based dimensional reduction method. The three-dimensional beam problem is decomposed into a two-dimensional cross-sectional analysis and a one-dimensional beam problem, significantly reducing the numerical cost compared to three-dimensional finite element method. The simultaneous influences of pre-twist and rotational speed are carefully studied for various composite beams. This approach benefits from the numerical advantages of isogeometric analysis, with results showing better agreement with three-dimensional finite element method than other studies in the literature.

Simulation and cross-section design of steel beams under moment gradients

A systematic study into the effect of moment gradients on the cross-section resistance of hot-rolled steel square hollow section (SHS), rectangular hollow section (RHS) and I-section beams has been conducted and is presented in this paper. Finite element (FE) models were first developed and validated against test results from the literature; parametric studies covering different steel grades, cross-section geometries and moment distributions were then carried out. It was found that cross-section bending resistances increase with increasing moment gradient in the low to intermediate range, despite the necessary rise in the level of co-existent shear. Under high moment gradients, the negative impact of the high co-existent shear outweighs the positive influence of the moment gradient, and cross-section bending resistances fall. It was found that the benefits from moment gradients vary with the cross-section slenderness and the aspect ratio of the cross-section, and increase when intermediate web stiffeners are present. A new design method that captures the observed behaviour is devised, featuring a new parameter to describe the local moment gradient in beams under different loading conditions. The proposed design equations are shown to be more accurate than existing provisions in EC3 and to meet the reliability requirements set out in EN 1990. The new method is therefore deemed to be suitable for implementation within the EC3 framework.

Variation in the cross-sectional geometry of hot-rolled I-sections: Measurements, statistics, probabilistic modelling

This paper presents the evaluation of an extensive measurement campaign on the cross-sectional dimensions of hot-rolled I-sections. As a preliminary step, the reliability of the measuring process was quantified as well as checked to what extent the cross-sectional dimensions remain constant along a beam. In the main part of the investigation, a total of 561 statistically independent I-sections with a wide range of different sizes were surveyed and statistically analysed. Overall, the observed variation of the dimensions revealed a good agreement with the characterisation in the new Annex E of EN 1993-1-1. However, a more detailed evaluation showed that there is a certain dependence of these statistical parameters on the nominal size of the dimensions. Furthermore, several other aspects were checked, such as the correlation between the individual dimensions, the compliance with manufacturing tolerances according to EN 10034 and the uniformity of the web and flange thickness at various positions within the cross-section. Subsequently, the measured profiles were also analysed based on the resulting cross-sectional properties. In addition to a statistical evaluation in respect to the corresponding nominal values, the influence of the common shape idealisation to a perfectly double-symmetrical cross-section with constant flange thicknesses was addressed. Finally, a comparison of several options for the probabilistic modelling of the geometric variability was carried out, based on the lower 5%-quantiles of the resulting cross-sectional properties.

Extension of the Continuous Strength Method to the design of steel I-sections in fire

This paper presents an investigation into the extension of the Continuous Strength Method (CSM) to the design of steel I-sections at elevated temperatures. Structural response of 21375 high strength and normal strength steel I-sections at elevated temperatures is considered, taking into account a very broad range of cross-section geometries and cross-section slendernesses as well as different elevated temperature levels and steel grades which include both high strength S690 and S460 steel grades and normal strength S355, S275 and S235 steel grades. The implementation of the CSM for the fire design of steel I-sections is set out. The accuracy of the CSM against that of the provisions of the European structural steel fire design standard EN 1993-1-2 and its upcoming version prEN 1993-1-2 for the ultimate resistance predictions of steel I-sections at elevated temperatures is assessed. It is shown that in comparison to the elevated temperature cross-section design provisions of EN 1993-1-2 and prEN 1993-1-2, the CSM leads to a significantly improved level of accuracy and consistency in the ultimate strength predictions of steel I-sections at elevated temperatures.

Exploring droplet oscillation dynamics in surface tension measurements

This study builds upon prior research by exploring droplet oscillation dynamics for surface tension determination using a drop-on-demand high-temperature droplet generator. Computational fluid dynamics (CFD) simulations were conducted to analyse frequency shifts over time, comparing two different materials with consistent results. The findings suggest potential for developing correction factors for oscillations with larger initial deformations. Additionally, frequency shifts relative to evolving aspect ratios of droplets starting with higher initial deformations were compared. Corrective measures can be applied, particularly beneficial for short-term measurements based on image analysis with minimal overall frequency shift. Slight asymmetry in oscillation with increasing aspect ratio could be accredited to droplet cross-sectional geometry or energy availability for returning prolate droplets to a spherical state. Experimental results indicated minimal frequency shift within a measurement duration of up to 40 ms, affirming the adequacy of using a fitted sine function without a time-dependent frequency term for overall frequency determination. A dimensionless criterion can be used to filter out unsuitable droplets. A temperature-dependent surface tension trend for AlCu10 alloy consistent with literature findings is introduced.

VIV mechanisms of a non-streamlined bridge deck equipped with traffic barriers

Vortex-induced vibration (VIV) has been addressed in the literature mostly for quasi-streamlined and shallow π-deck sections, typical of long-span bridges, since the latter are particularly prone to wind-induced oscillations. In contrast, although full-scale observations demonstrate that even steel-box girder bridges, usually characterized by a shorter span length if compared to suspension and cable-stayed bridges, can experience a violent VIV response, systematic studies for these bluffer cross-section geometries are less frequent. In addition, the aerodynamic optimization of non-structural additions (barriers, screens, fairings) is rarely carried out for this bridge typology. Therefore, a wind tunnel investigation is conducted on a non-streamlined box-girder sectional model (inspired by the Volgograd Bridge, Russia) equipped with two typologies of traffic barriers giving rise to a large ratio of barrier height to deck width. A realistic range of angles of attack (from −3° to 3°) are considered, and static forces, aeroelastic vibrations and wake velocity fluctuations are measured. A large and even unexpected variability in the vibration amplitude and lock-in curve pattern is found, emphasizing the possible existence of competing excitation mechanisms. Indeed, low-porosity barriers can alter the characteristics of vortex shedding, in particular creating a cavity on the upper side of the deck, which is known to foster the impinging-shear-layer instability, as in H-shaped sections. This vortex-shedding mechanism may co-exist with Kármán-vortex shedding and may be responsible for significant anticipation of the VIV onset compared to the predictions based on the Strouhal number measured during static tests. The intensity of a secondary excitation mechanism and its interaction with the dominant mechanism strongly depend on the angle of attack and is largely responsible for profound changes in the VIV bridge response, both in terms of qualitative pattern and peak amplitude. In some cases, the tracks of these competing vortex-shedding mechanisms are even clearly visible in the VIV response curves of the tested bridge model. Finally, the wind tunnel results are also reconsidered based on the quasi-steady theory, highlighting some, even qualitative, discrepancies.

Biomechanical modelling infers that collagen content within peripheral nerves is a greater indicator of axial Young's modulus than structure.

The mechanical behaviour of peripheral nerves is known to vary between different nerves and nerve regions. As the field of nerve tissue engineering advances, it is vital that we understand the range of mechanical regimes future nerve implants must match to prevent failure. Data on the mechanical behaviour of human peripheral nerves are difficult to obtain due to the need to conduct mechanical testing shortly after removal from the body. In this work, we adapt a 3D multiscale biomechanical model, developed using asymptotic homogenisation, to mimic the micro- and macroscale structure of a peripheral nerve. This model is then parameterised using experimental data from rat peripheral nerves and used to investigate the effect of varying the collagen content, the fibril radius and number density, and the macroscale cross-sectional geometry of the peripheral nerve on the effective axial Young's moduli of the whole nerve. Our results indicate that the total amount of collagen within a cross section has a greater effect on the axial Young's moduli compared to other measures of structure. This suggests that the amount of collagen in a cross section of a peripheral nerve, which can be measured through histological and imaging techniques, is one of the key metrics that should be recorded in the future experimental studies on the biomechanical properties of peripheral nerves.

Heat Transfer Investigation Inside Heated Pipes of Different Cross-sections

This research examines the thermal transfer efficiency in pipes including various cross-sectional geometries, such as circular, square, and triangular shapes. A computational fluid dynamics (CFD) methodology was used to model flow conditions and examine heat transfer and turbulence intensities under consistent boundary conditions. The results indicate substantial variations in thermal and flow characteristics across the geometries. Circular pipes provide greater convective heat transfer efficiency and minimum temperature gradients, but square and triangular pipes show more turbulence accompanied by a higher pressure drop. These insights may guide the design of efficient piping systems for many technical applications, including HVAC, chemical processing, and renewable energy systems.

Numerical Prediction of Two-Dimensional Coupled Galloping and Vortex-Induced Vibration of Square Cylinders Under Symmetric/Asymmetric Flow Orientations

This study presents an advanced numerical model for predicting a two-dimensional coupled galloping and vortex-induced vibration (VIV) in cross-flow and in-line directions of square cylinders under symmetric and asymmetric flow orientations. The present model combines the quasi-steady theory for the galloping with the nonlinear structure-wake oscillators simulating VIV, capturing the time-varying drag and lift hydrodynamic forces with the time-averaged and fluctuating components. By placing a flexibly mounted square cylinder in uniform flow at an initial angle of incidence, the cylinder is subject to instantaneous changes in the dynamic angle of attack accounting for relative flow-structure velocities. Modelling of such features in cross-flow and in-line directions for low and high mass ratio systems extends previous studies which have mostly focused on cross-flow responses of square cylinders with high mass ratios at a zero angle of incidence. New sets of empirical coefficients governing the drag and lift fluid forces for both the quasi-steady and wake oscillator approaches are introduced by calibrating with available experimental data in the literature, applicable to predict several flow-induced vibration phenomena under arbitrary flow-structure orientations. Mathematical criteria for the onset of two- and one-dimensional galloping instability are presented, verifying the likelihood of galloping occurrence. Parametric investigations are carried out to highlight the important effects of flow incidence angle, mass-damping ratio (Scruton number) and in-line response on the prediction of galloping and VIV in comparison with experimental results. By varying the reduced velocity parameter, the present model captures key qualitative features of the dominant galloping, interfering galloping-VIV and dominant VIV through the response amplitudes, mean drift displacements, oscillation frequencies, fluid force components and motion trajectories. Contributions from in-line responses are found to be meaningful for the interfering galloping-VIV system with a low mass-damping ratio and for an asymmetric flow orientation. The present model could be further calibrated and applied to other fluid-structure interaction applications with non-circular cross-sectional geometries under omnidirectional flow directions.

Multi-objective optimization of metal foam parameters for enhanced performance of LHTES unit in shell-and-tube configurations

Latent heat thermal energy storage (LHTES) units utilize phase change materials (PCMs) to effectively store thermal energy and address the challenges of solar energy intermittency and instability. Heat transfer characteristics largely influence the thermofluidic efficiency of the LHTES unit during phase transitions. To improve the typically low heat transfer capabilities of PCMs, high-conductivity metal foams are introduced to enhance bulk heat conduction. This study focuses on optimizing the parameters of composite PCM (CPCM) embedded in the LHTES unit, specifically examining metal foam height (H), angle (θ), and porosity (ϵ), primarily affecting the performance of the CPCM. A series of Taguchi-based orthogonal experiments were conducted to analyze the effects of these variables. The results indicate that metal foam height has a notable influence on the CPCM performance, significantly reducing melt fraction variations caused by changes in cross-sectional geometry. ANOVA analysis shows that the metal foam height contributes 49.02% to improve operational time and 73.62% to enhance melt fraction. The study also identifies the optimal values for the metal foam parameters (H, θ, ϵ) that most effectively improve the LHTES unit thermal performance. Based on various indices, an economic assessment of the optimal configuration further supports the proposed design. Overall, the findings provide a recommended configuration to enhance the LHTES unit performance, contributing valuable insights for developing efficient TES systems and supporting sustainable energy management.