Cross-sectional Aspect Ratio Research Articles

The Effect of Cross Sectional Properties of Concrete Column on the Repair Material: A Review

The utilization of Ultra High Performance Fibre Reinforced Concrete (UHPFRC) as a material for repairing concrete structures holds immense promise and potential. UHPFRC usage in concrete has been a significant rise in the interest surrounding the enhancement and renovation of concrete structures, particularly focusing on columns. UHPFRC has showcased remarkable bonding potency with concrete, along with an impressive capacity to renew the load-bearing capability of compromised reinforced concrete columns. However, the limited application of UHPRFC as a repair material for concrete columns is primarily attributable to a lack of comprehension regarding the influence of shape and size effects, particularly as they pertain to square and rectangular columns. In this paper, the factors behind the impact of cross-sectional properties on the effectiveness of UHPFRC as a repair material is presented. Therefore, it can be adopted by researchers to explore the UHPFRC potential in structural rehabilitation applications especially for concrete columns. It is believed that the relationship between the cross-sectional area, aspect ratio, and corner radius ratio of the column and repair material is a vital parameter affecting the performance of repaired columns.

Steady flow of non-Newtonian fluids: Momentum and heat transfer around a rectangular cylinder

This research aims to explore the impact of cross-sectional aspect ratio (AR), power-law index (n), Reynolds number (Re), and Prandtl number (Pr) on convective heat transfer rates using the Nusselt number (Nu) and coefficient of drag (CD) as a key metric. Numerical simulations employ the ANSYS FLUENT solver with the finite volume method. The SIMPLE scheme couples pressure and velocity, and the QUICK differencing scheme discretizes convective terms. This study varies the aspect ratio by adjusting the length-to-width ratio (b/D) to explore different configurations of AR = 1–5 and Pr = 0.7, 1, and 7, which investigate 5 ≤ Re ≤ 10 and 0.2 ≤ n ≤ 1, respectively. An increase in the Reynolds number is observed to diminish the thermal boundary layer thickness, resulting in an escalation of heat transfer rates. Additionally, the Nusselt number exhibits an upward trend with an increase in the Prandtl number. The investigation reveals a decrease in Nu with an increase in both AR and n. Specifically, higher aspect ratios and power-law indices are associated with reduced heat transfer rates. The AR emerges as a significant factor, influencing the coefficient of drag, with CD values showing an increase as AR rises, particularly at low Re. Moreover, CD is found to increase with an elevation in the n value. This study explores new ground by investigating power-law fluid behavior and heat transfer phenomenon across varied aspect ratios. These insights not only enhance the design of heat transfer systems with non-Newtonian fluids but also pave the way for future research in this less explored domain.

Numerical simulation of convective heat transfer behavior of nanofluids in elliptical microchannels

This study employs a numerical simulation approach to investigate the heat transfer performance of elliptical microchannel heat sinks (MCHS) with varying aspect ratios (AR) of the elliptical cross-section. The convective heat transfer behavior of water and water-based nanofluids containing CuO nanoparticles at different volume fractions within the MCHSs is examined. The research results indicate that at Re = 600, as the AR of the elliptical cross-section increases from 1:1 to 1.75:1, the thermal performance of the MCHS improves by 5.33%. Furthermore, with an increase in the volume fraction of nanofluid from 0 to 0.75%, the convective heat transfer coefficient of the nanofluid increases by 11.87%. Compared to the circle MCHS using water as the coolant, the MCHS with an elliptical cross-section with an AR of 1.75:1 and a nanofluid volume fraction of 0.75% can reduce the maximum temperature of the chip by 9.78%.

Parametric study on seismic response modification factor of strap-braced cold-formed steel systems

While cold-formed steel structures have been extensively studied for seismic-resistant construction, existing regulations, and implementation guidelines do not comprehensively address the impact of key design parameters on the seismic behavior of CFS strap-braced shear wall systems. This study investigates the lateral resistance and seismic behavior factor of strap-braced shear walls and compares them with code values, and tries to fully understand the effect of different design parameters on the seismic R-factor of these systems. The effect of parameters such as the strap cross-sectional area, aspect ratio, and distance between the studs is studied using ANSYS finite element software to create datasets for various configurations. The pushover analysis results obtained from this analysis are utilized to perform incremental dynamic analysis, under a set of 22 ground motion records, to evaluate the seismic response modification factor for different residential buildings. For this purpose, one to four-story residential buildings are designed based on four seismic hazard zones: low, moderate, high, and very high and then, they are analyzed. Results of pushover analysis show that increasing the strap cross-sectional area and aspect ratio increases capacity, but changing the distance between studs does not have a significant effect, and the R factor presented by codes is conservative. Incremental dynamic analysis results also indicate that the behavior of studied buildings varies depending on the structure and selected record and the suggested R factor by codes for diagonal straps braced cold-formed steel structures is acceptable for buildings up to three stories in low, medium, and high seismic zones, and for buildings up to two stories in very high seismic zones. Overall, this study shows that strap-braced cold-formed steel shear walls have the potential to achieve higher seismic R-values in comparison to design codes.

Numerical characterisation of FRP curved reinforcement produced by filament winding

Previous studies have demonstrated that an automated filament winding process can conveniently produce shear reinforcement for concrete structures. The method allows the creation of geometrically complex elements suitable for materials optimisation. This is in addition to the advantages of non-metallic reinforcement. On the contrary, the biggest drawback is the anisotropy properties of fibrous materials. Concentrations of stresses and material defects characterise the reinforcement’s curved portions; thus, material efficiency reduction is expected. Generally, the strength of pultruded FRP stirrups is estimated at about 30-40% of the tensile strength in the direction of the fibres. Still, experimental studies have shown that efficiency can be increased due to the manufacturing process and cross-section aspect ratio. This study aims to identify a mechanical model for predicting the bent strength of FRP stirrups fabricated by the filament winding technique. This is here formalised as a non-linear equilibrium problem of a curved Timoshenko beam on an elastic foundation. Numerical results agree with the experimental data available from previous studies, assessing the model’s suitability.

The Physics and Manipulation of Dean Vortices in Single- and Two-Phase Flow in Curved Microchannels: A Review.

Microchannels with curved geometries have been employed for many applications in microfluidic devices in the past decades. The Dean vortices generated in such geometries have been manipulated using different methods to enhance the performance of devices in applications such as mixing, droplet sorting, and particle/cell separation. Understanding the effect of the manipulation method on the Dean vortices in different geometries can provide crucial information to be employed in designing high-efficiency microfluidic devices. In this review, the physics of Dean vortices and the affecting parameters are summarized. Various Dean number calculation methods are collected and represented to minimize the misinterpretation of published information due to the lack of a unified defining formula for the Dean dimensionless number. Consequently, all Dean number values reported in the references are recalculated to the most common method to facilitate comprehension of the phenomena. Based on the converted information gathered from previous numerical and experimental studies, it is concluded that the length of the channel and the channel pathline, e.g., spiral, serpentine, or helix, also affect the flow state. This review also provides a detailed summery on the effect of other geometric parameters, such as cross-section shape, aspect ratio, and radius of curvature, on the Dean vortices' number and arrangement. Finally, considering the importance of droplet microfluidics, the effect of curved geometry on the shape, trajectory, and internal flow organization of the droplets passing through a curved channel has been reviewed.

Effect of radius ratio on the instabilities in a vaneless diffuser

The prominent features of the primary instabilities of a turbulent source flow between finite-span parallel rings with spatially modulated inflow conditions rotating at angular rate Ω are investigated. Two different two-dimensional instabilities that occur at large (αQ≳1.00) and low (αQ≲0.65) flow rates have been traced back to two different physical mechanisms related to jet-wake and mean-core flow, respectively. The effect of the radial aspect ratios Γ on the instability characteristics of the flow between parallel rings is also considered in this paper. Numerical URANS simulations are conducted for three different radial aspect ratios, i.e. Γ=1.25, 1.5, and 2, the corresponding cross-sectional aspect ratios Λ=2(Γ−1)×3.325, and two conceptually different inflow conditions. Their impact on the rotating instabilities in terms of instability mode number and instability frequency is the main focus of this study and is analyzed by fast Fourier transform (FFT) and wavelet analysis. Realistic inflow conditions with a leakage flow are found to overtake the instability for small radius ratios and affect the primary instabilities for large radius ratios.

Performance of round-ended recycled aggregate CFST stub columns after fire exposure

The post-fire performance of round-ended recycled aggregate concrete-filled steel tubular (RE-RACFST) short columns has been investigated experimentally and numerically. The test parameters included cross-section aspect ratios, recycled aggregate replacements and steel ratios. Twelve short columns were first heated for 90 min following ISO 834 standard fire, followed by natural cooling. Subsequently, axial compressive tests were performed to obtain the damage mode, load versus axial deformation, and strain development of the columns. The test results revealed that a higher level of recycled aggregate content resulted in decreased bearing capacity and elastic stiffness of RE-RACFSTs, and an earlier onset of the confining effect. Furthermore, finite element (FE) models were established and benchmarked against the experimental results. Parametric investigations were then conducted to study the effects of key factors on the residual load-carrying capacity. Finally, according to the experimental and FE results, a simplified formula was proposed to estimate the post-fire residual capacity of RE-RACFST stub columns.

Reconsideration of shear strength expressions for CFSTs: Rectangular tubes

Concrete filled steel tubes (CFSTs) are typically circular or rectangular. Circular CFSTs are mostly used as vertical components of deep foundation systems; rectangular sections are more commonly used in building construction such as square CFSTs for columns. Prior work has focused on circular CFSTs with far fewer studies on square or rectangular sections. In addition to being more limited, prior research on square CFST sections has focused on flexural and axial response; there have been far fewerstudies on the shear response. As such, the accuracy of shear-strength equations is uncertain. A research study was undertaken to understand and improve design expressions for the shear design of rectangular CFSTs. First, the research team collectedexperimental data on shear resistance of rectangularCFSTs. Selected experimental data was used to develop and validate an advanced nonlinear finite element model (FEM) to predict the measured response and observed damage of rectangular CFSTs controlled by shear behavior. The validated model was then used to conduct parameter studies to investigate important design parameters of rectangular CFSTs responding primarily in shear including: 1) concrete and steel material properties, 2) cross-sectional aspect ratio, and 3) impact of enhanced bond capacity/composite action through the introduction of a single shear key at each end of the member. The results were used to better understand the importance of each parameter on the shear response and strength. A database was assembled, combining the experimental data with the strength predicted by each FEM, to evaluate existing design equations. The shortcomings of the existing equations included (1) only accounting for the steel or the concrete fill contribution, and (2) overestimating the total shear strength because the behavior of the CFST in shear is not well understood. This paper provides a new approach to assessing the shear strength as the individual contributions of the steel tube and the concrete fill are computed for each model to better understand their interaction. This also permits the development of a new design equation to remedy the shortcomings of existing codified models. In particular, the proposed model accurately estimates the individual contributions of steel tube and concrete fill to the shear resistance for salient design parameters.

Experimental and compactional studies of interface toughening on GFRP by hierarchical distribution of halloysite nanotubes

The incorporation of nano-inclusions into the fiber-matrix interfacial regions to create hierarchical structured fiber reinforced polymers (FRPs) is a novel approach aimed at enhancing mechanical properties. However, the specific toughening mechanism facilitated by the hierarchical structure has not been extensively explored or discussed in detail. This study investigates the mechanical properties of glass fiber reinforced polymers (GFRPs) that have been hierarchically incorporated with natural halloysite nanotubes (HNTs) using experimental, computational, and numerical approaches. The hierarchical distribution of HNTs is achieved through electrophoretic deposition (EPD). The stiffening effect of HNTs incorporation is computed using the random-averaged micromechanical Mori-Tanaka model. Subsequently, stiffness and stress concentration analyses are carried out on mesoscale representative volume elements (RVEs) of GFRPs with periodic boundary condition (PBC) assignments in ABAQUS. Overall, the experimental results are consistent with the numerical and computational results in terms of trend and magnitude. The amorphous HNTs (AHNTs) with larger cross-sectional aspect ratios demonstrate significant enhancement of 45 % in transverse modulus. The in-plane stiffness and strength of GFRPs with hierarchical distribution are slightly inferior to those of GFRPs with random distribution. Nevertheless, the hierarchical distribution of nano-inclusions leads to a substantial improvement in interlaminar strength and toughness, with enhancements exceeding 70 % and 100 % respectively. This can be attributed to the reinforcement and toughening effects on the fiber-matrix interface brought about by the hierarchical distribution.

A Fast, Robust Method for Quantitative Assessment of Collagen Fibril Architecture from Transmission Electron Micrographs.

Collagen is the most abundant protein in mammals; it exhibits a hierarchical organization and provides structural support to a wide range of soft tissues, including blood vessels. The architecture of collagen fibrils dictates vascular stiffness and strength, and changes therein can contribute to disease progression. While transmission electron microscopy (TEM) is routinely used to examine collagen fibrils under normal and pathological conditions, computational tools that enable fast and minimally subjective quantitative assessment remain lacking. In the present study, we describe a novel semi-automated image processing and statistical modeling pipeline for segmenting individual collagen fibrils from TEM images and quantifying key metrics of interest, including fibril cross-sectional area and aspect ratio. For validation, we show first-of-their-kind illustrative results for adventitial collagen in the thoracic aorta from three different mouse models.

Cold-formed stainless steel elliptical hollow sections under combined biaxial bending and axial compression - Numerical modeling and design

This paper aims to investigate the cross-section response of cold-formed stainless steel (CFSS) elliptical hollow sections (EHS) under combined biaxial bending and axial compression. In the present study, an advanced finite element (FE) model was adopted to perform a comprehensive parametric study for CFSS EHS under combined biaxial bending and axial compression, with different stainless steel alloys, as well as a broad range of cross-section sizes, aspect ratios, loading eccentricities and angles. Numerical results obtained from the parametric study were compared with the design strengths calculated by the current design rules in European code EN 1993-1-4, American specification SEI/ASCE 8-02 and Australian/New Zealand standard AS/NZS 4673. In addition, the Continuous Strength Method (CSM) for CFSS circular hollow sections (CHS) under combined actions, was also evaluated for the design of CFSS EHS under combined actions. The comparisons revealed that the current design codes EN 1993-1-4, SEI/ASCE 8-02 and AS/NZS 4673 provided conservative and very scattered predictions for CFSS EHS under combined actions. The existing CSM can provide more accurate predictions than the current design codes (i.e., AS/NZS 4673, EN 1993-1-4 and SEI/ASCE 8-02), but a further improvement is needed. In the present study, a modified CSM is proposed for CFSS EHS under combined actions, which can achieve reliable and accurate design predictions.

Gas transport law in inorganic nanopores considering the influence of cross section shape and roughness

To study the gas transport characteristics in rough inorganic nanopores, the effective pore size models of circular and rectangular nanopores are established, considering the influence of the adsorption water film, rock surface roughness, effective stress and the shape of the nanopore section. On this basis, the gas flow patterns are coupled, and the gas transport models in circular and rectangular rough nanopore are established respectively. The effectiveness of this model is verified by comparing it with experimental data and other scholars' models. At the same time, the effects of roughness, cross-sectional shape, cross-sectional aspect ratio, and humidity on gas migration are analyzed. The results indicate that regardless of the cross-sectional shape, an increase in roughness will lead to varying degrees of reduction in the apparent permeability of micro and nano pores. When the pressure is small, the influence of roughness on the gas permeability of rectangular cross-section nanopores is greater than that of circular cross-section nanopores. As the pressure increases, the influence of roughness on the gas permeability of rectangular and circular cross-section nanopores tends to be the same. The influence of roughness on the water saturation of rectangular cross-section nanopores is less than that on circular cross-section nanopores.

Numerical Simulation and Experimental Study Regarding the Cross-Sectional Morphology of PEEK Monofilament Deposition During FDM-Based 3D Printing.

Polyether-ether-ketone (PEEK) is widely used in the field of biomedical engineering because of its excellent mechanical properties, chemical stability, and biocompatibility. Fused deposition modeling (FDM), which is a typical 3D printing process, can achieve low-cost and high-efficiency printing of complex PEEK structures. However, poor monofilament deposition quality leads to rough surfaces on macroscopic printed parts, low dimensional accuracy, and weak interlayer bonding, which are urgent problems to be solved. In this study, considering the shear thinning characteristic of PEEK, a numerical model for monofilament deposition was constructed by using the finite volume method. This model revealed the influences of process parameters on the monofilament cross-sectional profiles and achieved predictions of monofilament cross-sectional profiles during FDM-based 3D printing of PEEK. The average relative error of the monofilament cross-sectional area predictions was 7.68%. The average relative error of the monofilament cross-sectional aspect ratio predictions was 12.06%. It was also found that there are three typical deposited monofilament cross-sectional profile shapes, i.e., a capsule shape, a bread shape, and a circular shape. These three shapes occurred because of the combined effect of the layer thickness and the extrusion width during the extrusion and deposition of PEEK. These revealed monofilament cross-sectional profiles provide the basis for accurate nozzle motion trajectory planning, and they lay a foundation for surface roughness predictions and dimensional accuracy control during the FDM-based 3D printing of PEEK.

Axial compressive behavior and design-oriented model for large-rupture-strain (LRS) FRP-confined concrete in rectangular columns

Polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) composites, which is a kind of low-carbon production and have a large rupture strain, may have prosperous application outcomes. PET FRP wrap has been explored as confining reinforcement for concrete, and the majority of investigations are limited to PET FRP-confined concrete in circular and square columns, whereas PET FRP-confined rectangular columns have barely been touched. To fill this research gap and gain a fundamental understanding of the confinement mechanism, comprehensive compressive tests on 36 columns were conducted in this study, in which the confinement thickness, cross-section aspect ratio, and specimen size were the focal points. All specimens exhibited a three-segment behavior (i.e., strain hardening-softening-hardening response). In addition, it is demonstrated that specimen size had an insignificant effect on the axial stress-strain response of small and medium columns with a height less than 400 mm, provided that their confinement levels were the same (or similar). Furthermore, the minimum effective confinement stiffness for PET FRP-confined rectangular columns to achieve sufficient confinement was 0.004, which was extracted from all available test results. A design-oriented model with improved performance was proposed and the simulated full axial stress-strain showed close agreements with the test results.

Effects of the direction of rotation axis on turbulent flows in rectangular ducts

The effects of the direction of rotation axis on flows in rectangular ducts are studied using direct numerical simulation. The rotation axis lies in the cross section of the duct. The angle of the rotation axis relative to the bottom edge of the cross section is altered from 0° to 90°. A series of cases are considered, including three Reynolds numbers Reτ = 300, 454, and 900, three rotation numbers Roτ = 2, 4, and 8, and two cross-sectional aspect ratios ar = 1.0 and 2.0. The results show that as the angle increases, the bulk velocity remains almost constant in the square duct while it decreases monotonically in the duct with ar = 2.0. When the angle increases from 0° to 45°, turbulence is significantly or even completely suppressed, while the secondary flow is gradually enhanced. Furthermore, with the same rotation number, turbulence is more strongly suppressed at a lower Reynolds number. As the angle further increases from 45° to 90° in the cases with ar = 2.0, the intensity of turbulence is recovered to some extent and the secondary flow gradually weakens. With the angle increasing from 0°, the Ekman layer is formed above the pressure wall and gradually strengthens, resulting in a drastic wall-normal variation of the mean flow direction and a tilting of the low-speed streaks near the wall, which may cause the weakening of the turbulence. In addition, in the flow fields where turbulence is severely suppressed, periodic structures are observed in the corner of the duct, which needs further study.

Film Cooling Effectiveness on Pressure Surface and Suction Surface of Turbine Guide Vane With Diffusion Slot Holes

Abstract This paper investigated the film-cooling effectiveness of diffusion slot holes in a turbine nozzle guide vane. The pressure-sensitive paint measurement technique was employed to obtain the film-cooling effectiveness at a density ratio of DR = 1.5. The mainstream Reynolds number based on the axial chord length and the exit velocity was 6 × 105. The mainstream turbulence intensity was approximately 3.7%. Three diffusion slot hole geometries with cross-sectional aspect ratios (ASs) of 2.3, 3.4, and 4.9 were tested and compared with a typical fan-shaped hole. The experiments were performed at three typical hole row locations on the pressure surface (PS) and suction surface (SS). The average blowing ratios varied from M = 0.5 to 2.5. The results showed that throughout the blowing ratio range, on the PS, a substantially higher film-cooling effectiveness than the fan-shaped hole is always obtained from the diffusion slot hole with a large aspect ratio (AS = 4.9); on the SS, the diffusion slot hole with a small AS (AS = 2.3). The influence of hole row positioning is inconsistent for diffusion slot holes with different ASs. The diffusion slot hole is less affected by the PS when the AS is moderate and less affected by the SS when the AS is large. The film-cooling effectiveness of the diffusion slot holes is basically the lowest where the PS has a maximum concave curvature and the highest where the SS has a large favorable pressure gradient.

Round-ended concrete-filled steel tube columns under impact loading: Test, numerical analysis and design method

This paper reports experimental and numerical investigations on the behaviours of round-ended concrete filled steel tube (RE-CFST) columns under combined pre-axial and impact loadings. Twelve RE-CFST specimens were tested to assess the influences of the cross-sectional aspect ratio, impact velocity and pre-axial loading on the impact-resisting performance. The failure patterns, impact force and mid-span deflection histories were obtained and analyzed. Test results showed that increasing pre-axial loading led to a decrease in the plateau impact force and an increase in the mid-span deflection. In addition, the finite element (FE) models were developed and calibrated with the experimental data, and then employed for evaluating the working mechanism of typical RE-CFSTs during the whole impact process and performing parametric investigations. According to the experimental and numerical results, empirical formulae were proposed for predicting the plateau impact force of RE-CFST columns subjected to lateral impact.

Axial compression testing of concrete prisms confined by FRP spike anchors and estimation of failure modes

Reinforced concrete (RC) walls can exhibit poor drift capacity and premature concrete crushing if the compression region lacks sufficient confinement. Although fiber-reinforced polymer (FRP) jacketing has been used for confinement, wrapping FRP around the edges becomes challenging when adjacent components obstruct the process. To overcome this issue, a novel solution using FRP spike anchors is proposed in this study. These anchors provide confinement without requiring access to the wall edges, and they are installed by drilling holes through the structures, effectively addressing the obstructions. The study investigates the axially compressive behavior of concrete under this confinement approach. Axial compression tests were conducted on 18 concrete prisms confined with FRP spike anchors in addition to five unconfined concrete prisms. Their height by width by length dimensions were all 360 mm × 150 mm × 150 mm or 360 mm × 150 mm × 200 mm. The variables included anchor spacing and cross-sectional aspect ratio, namely length-to-width ratio. Test results indicate that the strain at peak and the failure strain of the confined concrete was respectively up to 1.85 and 5.28 times the ones of unconfined concrete when anchor spacing was 90 mm. An analytical method was developed to estimate the failure modes of the confined concrete prisms.

Dynamics of bubbles detached from non-circular orifices: Confinement effect of orifice boundary

In practice, gas usually escapes from non-circular orifices due to machining accuracy, plugging, and other reasons, especially gas leakage in the natural environment. Compared to circular orifices, the bubble behavior and dynamics of non-circular orifices have rarely been investigated. This paper presents three-dimensional imaging system results to obtain comprehensive information on bubble dynamics generated from five elliptical orifices with equal cross-sectional areas and different aspect ratios. Computational fluid dynamics studies using the coupled level set and volume of fluid methods were adopted to assist in the flow field analysis. Experimental data were analyzed statistically to study the effects of orifice wall structure on bubble flow pattern, size, trajectory, and other dynamic parameters. The results show that the equivalent bubble diameter increases with increasing orifice aspect ratio, as does the randomness of the bubble flow field, while the bubble flow pattern complexity increases. A force analysis as the bubble is generated is also conducted. The wall structure of the orifice affects the bubble migration effect to some extent. The work presented in this article provides valuable fundamental information for a range of heater and desalination applications in chemical engineering, wastewater treatment, and immersion leakage identification.