Elliptical Section Research Articles

Post-fire bond behaviour in elliptical concrete filled steel tubes: Experiment and simulation

The post-fire bond behaviour between the steel tube and core concrete in elliptical concrete filled steel tubes (ECFST) is studied in this paper. A total of 15 post-fire push-out test specimens, including 9 elliptical, 3 circular and 3 square CFSTs, were designed and tested. The testing parameters included: (a) target temperatures (Ttar = 20 °C, 600 °C and 800 °C); (b) high temperature duration time (td = 30 min, 60 min, 180 min and 300 min); (c) length of long axis of elliptical section (2a = 200 mm and 300 mm); (d) section type (elliptical, circular and square). The test results indicated that the target temperature and high temperature duration time affected the post-fire bond strength of ECFSTs significantly, and the post-fire bond strength of ECFSTs could be increased with the increasing values of the two parameters. Based on the test data, a two-linear stage bond stress versus slip constitutive model considering the influence of both the temperature and fire-exposed surface area was proposed and verified to capture the post-fire bond behaviour in ECFSTs, which could be used in the refined bond behaviour numerical analysis of ECFSTs.

Investigation of the dynamic behavior of three-layer cylindrical shells of elliptical form under internal axisymmetric pulse loading

The results of the assessment of the dynamic behavior of three-layer cylindrical shells of circular and elliptical cross-sections under internal impulse loading are given. The finite-element method was used to calculate the indicators of the stress-strain state (SSS) of such structures by the NASTRAN software complex. The values normal deflections and normal stresses of circular and three elliptical forms of intersection of cylindrical structures are determined. A comparative analysis of the values of these indicators with the results of the dynamic behavior of uneven cylindrical shells was performed.
 The shape and curvature of the cross section of three-layer cylindrical thin-walled composite shells significantly affect their SSS under dynamic impulse loading.
 Replacing the circular shape of the cross section of a cylindrical structure with an elliptical one and increasing the ratio of the semiaxes of the elliptical section leads to an increase in normal deflections and normal stresses of the middle surface of the structure.

Impact of elasticity of polymer filler of three-layer cylindrical structure of elliptical section on its behavior under internal impulse loading

The impact of the elasticity of the polymer filler of a three-layer cylindrical structure of normal elliptical cross-section on its stress-strain state under internal impulse loading was studied. Determined values and distribution of normal deflections and stresses in sections S1 and S2. The finite-element method of calculating the stress-strain state (SSS) of such a structure by the software-calculation complex Fimap with NX Nastran was applied. Conclusions were made regarding the sufficient expediency of considering the elasticity of the filler when optimizing the design of such structures.
 Increasing the elasticity of the polymer filler increases the strength and monolithicity of the layered structure. The use of this method ensures efficiency and is appropriate when the ratio of elasticity of the materials of the layers and filler is Е1.3 /Еt ≤50.

Experimental study on additive manufactured 304L stainless steel tubular sections: Material properties and cross-sectional behavior

This paper presents an experimental investigation on the material properties and cross-sectional behavior of 304L stainless steel tubular sections additively manufactured using selective laser melting (SLM). A total of 76 tensile coupons, 76 hardness test specimens, and 25 stub columns were fabricated from 304L stainless steel powders by the SLM technique. Tension coupon tests and hardness tests were conducted to determine the mechanical properties. Residual stresses and local geometric imperfections of the stub columns were measured. The effects of coupon specimen orientations, thicknesses, and annealing conditions on the measured material properties were explored. In addition, the failure modes, ultimate load-carrying capacities and structural responses of the stub columns with four different cross-sections under axial compression were obtained and analyzed to evaluate the cross-sectional behavior. The test results of ultimate strengths were compared with the predictions calculated from the current design methods. The test results showed that the tensile strength of the coupon perpendicular to the building direction was higher than that of the coupon parallel to the building direction. Moreover, the tensile strength of the coupon increased with the increase of the coupon thickness. Considering the cross-sectional behavior, the square hollow section (SHS) and circular hollow section (CHS) had greater cross-sectional axial capacities than the rectangular hollow section (RHS) and elliptical hollow section (EHS), respectively. The introduction of a single stiffener in SHS and CHS reduced the load-carrying capacities to a certain extent.

Compressive behaviour of elliptical FRP tube-confined concrete columns

Elliptical FRP tube-confined concrete columns (EFCCCs) are an extension of circular FRP tube-confined concrete columns recently proposed at The Hong Kong Polytechnic University. Like their circular counterparts, EFCCCs are corrosion-resistant and can be used in situations where a column is subjected to substantially different loads in the two orthogonal lateral directions. The elliptical section of EFCCCs leads to more effective confinement of the concrete and an easier filament-winding fabrication process for the FRP tube compared with their rectangular counterparts. Existing studies on FRP-confined concrete in elliptical columns have been few. This paper first presents a systematic experimental study on the axial compressive behaviour of EFCCCs, with a focus on the stress–strain behaviour of the confined concrete. The test variables included the concrete strength, the thickness and fibre orientations of the FRP tube, and the aspect ratio of the cross-section. The test results showed that the confinement effectiveness of FRP tubes decreases with the aspect ratio and the concrete strength but increases with the FRP tube thickness. The orientations of fibres in the FRP tube were found to have a significant effect on its confinement effectiveness and the failure mode of EFCCCs. On the basis of the test results, existing stress–strain models for FRP-confined concrete in elliptical columns are evaluated. Furthermore, a new stress–strain model for the concrete in EFCCCs is proposed, which includes a more rigorous treatment of the confinement stiffness of EFCCCs and can provide more accurate predictions for the whole stress–strain curve than the existing models.

Stress–strain model and design strength of cold-formed steel non-slender elliptical tubular stub columns

This paper aims to propose a stress–strain model for the stub column behavior of cold-formed steel non-slender elliptical hollow sections (EHS) under axial compression by considering the post-local buckling behavior and taking into account the effects of local imperfection, material nonlinearity and residual stresses. The proposed model is applicable to the sections of both high strength and normal grade steels; and is mainly defined by four key parameters, including the 0.2% proof stress, the local buckling stress and buckling strain, as well as the post-peak residual strength of a stub column. Equations are also proposed to express these key parameters in terms of the basic input cross-section parameters and virgin material properties. In order to determine these key parameters, existing test and numerical results on the structural behavior of cold-formed steel EHS stub columns were collected and analyzed, which covered a wide range of steel grades (up to 960 MPa) and section sizes. Existing design methods, which have not yet been calibrated for cold-formed high strength steel EHS, were first evaluated by comparing their predicted stub column strengths (i.e., local buckling stresses) with the collected test and numerical data. The Continuous Strength Method (CSM) was found to provide better predictions than other examined design methods. Modified CSM base curves were then developed to further improve the accuracy of the existing CSM for both the local buckling strains and design strengths of cold-formed EHS with steel grades up to 960 MPa. In addition, a theoretical framework is proposed to develop the semi-empirical equations for both the 0.2% proof stresses and local buckling stresses of stub columns by incorporating the modified CSM base curves, whereas one curve based on the conventional equivalent diameter and one curve based on equivalent diameter of the four-arc approximation. A predictive expression of the post-peak residual strengths is also presented. Predictions from the proposed stress–strain model were in a good agreement with the collected test and numerical results, which can demonstrate its accuracy and validity.

Numerical study on hydrodynamic performance of underwater manipulator in the subcritical region

The hydrodynamic performance of an underwater manipulator is critical for establishing a hydrodynamic model for precise positioning or grasping. However, elucidating the variable hydrodynamic performance is difficult owing to the different working attitudes in the usage of underwater manipulators. Therefore, this study aims to investigate the hydrodynamic coefficients and flow field characteristics of the underwater manipulator with different motion attitudes in Cartesian coordinates. The effects of section shape, spacing, and interaction on the hydrodynamic performance are investigated in the subcritical range. Results indicated that the lift and drag coefficient of the elliptical section were 76.15 and 51.30% lower than that of the circular section, respectively. Furthermore, the amplitude of the downstream elliptical section was affected primarily by the spacing. However, when arm 2 was in the upstream, the lift coefficient of arm 1 was 3.4 times greater than that of arm 2. This implied that the underwater manipulator is more stable when arm 2 was in the upstream. This study will provide theoretical guidance to reveal the hydrodynamic performance of the underwater manipulator and other marine equipment, such as risers and submarine cable.

Structural Stability Analysis of Eye of the Yellow Sea, a Large-Span Arched Pedestrian Bridge

To date, scholars’ research on the stability behavior of the arch structure mainly focuses on solid–web section arches, steel tubular truss arches and concrete-filled steel tubular arches, but the stability behavior of the novel spatial grid arch structure, which integrates the characteristics of grid structure and arch structure, is not yet clear. Based on the Eye of the Yellow Sea pedestrian bridge project in Rizhao, China, the stability behavior of this large-span spatial grid arch structure was studied, in this paper, by the project’s structure design team. The project is a glass covered steel arch pedestrian bridge with a span of 177 m, a height of 63.5 m, an elliptical section with a long axis of 18 m, and a short axis of 13.5 m. The elastic and the nonlinear elasto-plastic stability behavior considering different initial geometric imperfections, was analyzed by the ABAQUS finite element model. The buckling modes and the full-range load-displacement curve of the structure were analyzed, and the stress distribution, deformation mode and overall structural performance during the whole loading process were analyzed. The effects of initial imperfections, geometric nonlinearity and material nonlinearity on the ultimate load-carrying capacity of the structure were studied. The stability behavior of large-span spatial grid arch structure was studied in this paper, which provides an important reference for the design and analysis of such structures.

Upgrade of the OSIRIS primary spectrometer

A proposed upgrade is presented for the primary part of the indirect time-of-flight near-backscattering spectrometer OSIRIS at the ISIS Facility. This upgrade comprises a new supermirror guide with non-linear defocusing and focusing sections, a new wavelength bandwidth chopper system and a flexible slit system to adjust the divergence. The new neutron guide has an elliptical defocusing section, a curved section and an elliptical focusing section. The estimated gain factor in intensity is wavelength dependent between 4 and 7 at the sample position with a homogeneous divergence distribution on a smaller beam spot. The divergence will increase by up to a factor 3 compared to the present guide, but can be reduced by up to a factor 5 through the slit system. The increased guide cross section requires a system of two counter-rotating disc choppers with larger disc diameters than the present ones for the selection of the wavelength bandwidth. Estimates for the performance indicate that the proposed upgrade will keep the OSIRIS spectrometer competitive in the years to come.

Characterization of a Superconducting Power Filter for Embedded Electrical Grid Application

Stability issues exist in embedded electrical grids, mainly due to power electronics. One of the solutions is to use a superconducting power filter (SPF), made of a non-inductive superconducting coil. The DC losses are close to zero, the coil being in its superconducting state. The AC losses, proportional to the frequency, are weak but still exist and can be used to increase the stability of the DC grid. In this paper, different SPF prototypes are presented and experimental characterizations are exposed: measurements of the critical current, measurements of AC losses and measurements of AC+DC losses. This AC+DC loss measurement is unusual, tricky and especially developed for SPF application. Experimental results are discussed and compared to calculations obtained with the analytical Norris formulas. Strip model formula underestimates losses and elliptical section formula overestimates losses but both formulas give good approximation of the losses and are therefore useful tools to design a SPF.

Mathematical modeling of the contact interaction of two elastic transversely isotropic half-spaces, one of which contains a near-surface groove of an elliptical section

On the basis of a mathematical model, the problem of compression of two elastic transversely isotropic half-spaces, one of which contains a shallow near-surface groove of an elliptical section, is considered. The solution to the problem is obtained using the Elliott representation for a transversely isotropic body in terms of harmonic functions, classical harmonic potentials and reducing the boundary value problem to considering an integro-differential equation with an unknown domain of integration. As a special case, the obtained analytical expressions yield the basic parameters of the contact of transversely isotropic half-spaces in the presence of an axisymmetric groove in one of them, as well as the parameters of the contact interaction of two elastic isotropic half-spaces, one of which contains an elliptical cross-section groove. Numerical results are obtained, the influence of elastic properties of half-spaces, geometrical parameters of groove and loading on contact interaction and closing of the gap between bodies is studied.

Engineered near- and far-field optical response of dielectric nanostructures using focused cylindrical vector beams

Near- and far-field optical properties of silicon nanostructures under linear polarization (Gaussian beam) and azimuthally or radially focused cylindrical vector beams are investigated by finite-difference time-domain method (FDTD) in Meep open-source software. A python toolkit allowing FDTD simulations in Meep for using those excitation sources is provided. In addition to the preferential excitation of specific electric or magnetic resonance modes as a function of the excitation beam polarization, it is shown in the case of spheroids that shape anisotropy affects the resonance wavelength and the dipole orientation of the magnetic or electric dipole mode. Depending on the spheroid symmetry axis with respect to the electric field orientation, the electric dipole resonance can be split into two peaks, giving quasi-unidirectional scattering, separated by an anapole mode. The optical properties in both far-field (scattering pattern) and near-field (electric and magnetic field hot spots) can be tuned by changing the excitation polarization at a fixed wavelength and selecting properly the spheroid shape and dimensions. These numerical simulations are extended to top-down fabrication-friendly nanostructures such as nanocylinders with circular or elliptic sections.

Bony nasolacrimal duct size and outcomes of nasolacrimal silicone intubation for incomplete primary acquired nasolacrimal duct obstruction.

PurposeTo investigate the association between the bony nasolacrimal duct (NLD) size and outcomes of nasolacrimal silicone intubation for incomplete primary acquired nasolacrimal duct obstruction (PANDO).MethodsPatients who underwent silicone intubation for incomplete PANDO and had undergone facial computed tomography (CT) were included. Surgical success was judged by both epiphora improvement and normalized tear meniscus height (TMH; < 300 μm) on anterior segment optical coherence tomography at 3 months after tube removal. The area, major axis diameter, and minor axis diameter of the elliptic bony NLD sections were measured in 1.0 mm-thick axial CT images. These bony NLD sizes were analyzed for associations with surgical success and TMH normalization.ResultsEighty-one eyes of 48 patients were investigated. The smallest area and the smallest minor axis diameter were significantly larger in the success group (49 eyes), compared with those in the failure group (median smallest minor axis diameter: 4.7 mm vs. 3.8 mm, P = 0.008, Mann–Whitney U test). There was also a tendency for the TMH normalization rate to significantly increase as the smallest area and the smallest minor axis diameter increased (P = 0.028 and 0.037, respectively, Fisher’s 2 × 4 tests). Under multivariable logistic regression analysis using generalized estimating equation, a larger smallest minor axis diameter was associated with success of the nasolacrimal silicone intubation (odds ratio: 2.481, 95% confidence interval: 1.143–5.384).ConclusionSurgical success of the nasolacrimal silicone intubation in incomplete PANDO is associated with a larger smallest minor axis diameter of the bony NLD. This finding will help understand the pathophysiology of surgical failure after nasolacrimal silicone intubation.

EARTH SECTION PATHS. SOLUTION TO THE INVERSE AND DIRECT PROBLEMS, AND WAYPOINTS WITHOUT ITERATIONS

The use of central elliptical sections in the calculation of air and sea routes and normal sections in Geodesy is common. Elliptic sections do not represent the shortest path between two points, although are often used in navigation to replace the geodesic lines. All developments include some kind of iteration to solve one of the problems, direct or inverse. When using vector algebra methods and perturbed series, the problems can be solved using an equidistant circle that represents the path of the elliptical section. This is possible because the flattening of the elliptical section is less than or equal to the Earth’s flattening, which implies that the series calculated for the terrestrial ellipsoid, used in the section, always converge. Three direct methods are described in order to calculate: the distance, the azimuth, the coordinates of a point and intermediate positions of an elliptical section. Those algorithms provide solutions to the inverse and direct algorithms with a consistency of the order of truncation error of double-type numbers.

On the circumferential wave responses of connected elliptical-cylindrical shell-like submerged structures strengthened by nano-reinforcer

This paper is devoted to estimate the dynamic performance related to Connected Elliptical-Cylindrical Shells (CECSs), which can be applicable in submerged structures. Conducive to progress the vibrational behavior associated with the homogenous CECS, nanocomposite materials including Graphene Nano Platelets (GNP) nano-reinforcer are used. It is obvious that the corresponding mechanical criteria of nanocomposite counting polymer and GNP nano-reinforcer are required for obtaining the governing formulation. Halpin-Tsai and the rule of mixture schemes are utilized for predicting the equivalent density, Poisson's ratio, and Young's modulus. Furthermore, various patterns are registered for the distribution of GNP nano-reinforcer along with the thickness of the CECSs. According to the obtained equivalent mechanical characteristics, by means of Hamilton's concept, the governing motion equations of CECSs are achieved as well. Moreover, the effect of shear deformation is considered subject to the First Order Shear Deformation Hypothesis (FOSDH). Afterward, a professional semi-analytical approach, licensed the Generalized Differential Quadrature (GDQ) scheme, is employed for discretizing the differential equations at different separator points throughout the longitudinal (for the cylindrical part) and meridional (for the elliptical section) direction of the structure. By solving an eigenvalue problem, the natural frequencies of CECSs having different types of Boundary Conditions (BCs) can be evaluated numerically. First, a validation study is performed to prove the correctness and accuracy of the proposed formulation. Then, several novel and complex problems are analyzed numerically and the effects of different parameters including boundary conditions, geometric properties, and material characteristics on the frequency parameter of CECSs are also investigated.

Fivefold Helically Corrugated Waveguide for High-Power W-Band Gyro-Devices and Pulse Compression

The design, simulation, manufacture, and measurement of a W-band fivefold (5F) helically corrugated waveguide (HCW) is reported. The 5F HCW is based on the coupling of the traveling TE₃₁ and near cutoff TE₂₁ modes to create an operating eigenwave. The fabricated test structure has circular waveguide ports and features elliptical polarizer sections and broadband TE₁₁ to TE₃₁ mode converters on either side of the 5F HCW. The optimized mode converter design, based on a fourfold (4F) HCW, has a predicted power conversion efficiency greater than 90% from 89 to 102.5 GHz, and 96% peak efficiency at 94 GHz. The optimization of the 5F HCW geometry produced an eigenwave suitable for gyro-devices, but the optimization could equally well have been directed to applications such as pulse compression and microwave undulators. Analysis of simulated electric field profiles showed that the propagating power in the 5F HCW was increased by a factor of 6 over that in the 3F HCW at equivalent peak electric field strength. This is due to the larger diameter of the waveguide. Test structures were manufactured through a combination of precision machining of a sacrificial mandrel, copper growth by electroforming followed by removal of the aluminum mandrel by chemically etching. Measurements of the 5F HCW structure's dispersion showed excellent agreement with the prediction over the design range of 90-98 GHz.

Closed-form expressions of shear deformability tensors associated with a new beam model

The application of a recent beam model requires the evaluation of a suitably defined shear deformability tensor in order to ensure both energetic and geometric consistency with the 3D Saint Venant model subjected to non-uniform flexure and torsion. Actually, whatever is the position of the shearing force, the beam model provides the same elastic energy and the same tip displacement of the barycentric axis of the 3D Saint Venant model. The expression of the shear deformability tensor is rather involved since it depends upon three harmonic functions, namely the warping and the warpage functions associated, respectively, with torsion and shear. For this reason, in order to promote its use and shed some light on its properties, we derive explicit expressions of the shear deformability tensor for circular, elliptical and rectangular sections exploiting the relevant analytical formulas of the warping and warpage functions.

Study on the penetration of elliptical cross-section projectiles into concrete targets: theory and experiment

To better understand the penetration mechanism of the elliptical cross-section projectile (ECSP) into semi-infinite concrete target, penetration experiments using three types of ECSPs with different shape ratios (1, 1.25 and 1.61) and with striking velocities ranged from 550 m/s to 1050 m/s were conducted. Penetration depths, penetration trajectory and mass erosion rates of the projectile were obtained after the experiments. The experiment results show that the penetration performance and ballistic stability of the ECSP are equivalent to those of the circular cross-section projectile (CCSP). Based on the theory of complex variable function and conformal transformation, a semi-analytical model which can calculate the cavity boundary stress distribution of elliptical section cavity controlled by the displacement boundary condition was established and the model was validated by comparing the model degenerate solution with Kirsch problem results. Theoretical calculation results show that the radial stress of elliptical section cavity increases progressively from the minor axis to the major axis. In addition, a formula combining with the semi-analytical theoretical model and the local interaction theory was developed. The predicted penetration depths were compared with 30 groups of experiment data with different projectile parameters and striking velocities and coincide quite well with the corresponding experimental data. Finally, the influence of shape ratio and caliber-radius-head (CRH) on the penetration performance of projectile and the application prospect of ECSPs on hypersonic weapon platform were studied.

On the limits of quasi-static theory in plasmonic nanostructures

The approximated analytical approach of quasi-static theory (QST) is widely used in modelling the optical response of plasmonic nanoparticles. It is well known that its accuracy is remarkable provided that the particle is much smaller than the wavelength of the interacting radiation and that the field induced inside the structure is approximately uniform. Here, we investigate the limits of QST range of validity for gold nanostructures freestanding in air. First, we compare QST predictions of scattering spectra of nanospheres and cylindrical nanowires of various sizes with the exact results provided by Mie scattering theory. We observe a non-monotonic behaviour of the error of QST as a function of the characteristic length of the nanostructures, revealing a non-trivial scaling of its accuracy with the scatterer size. Second, we study nanowires with elliptical section upon different excitation conditions by performing finite element numerical analysis. Comparing simulation results with QST estimates of the extinction cross-section, we find that QST accuracy is strongly dependent on the excitation conditions, yielding good results even if the field is highly inhomogeneous inside the structure.

Normal incidence birefringence in nanoporous alumina

There are many works and interests focused on the development of optical sensors based on porous anodic aluminum oxide membranes (AAO). Normal incidence birefringence (BR) is present in AAO when is obtained from a monocrystalline aluminum substrate but his effect has been largely ignored since it is canceled out in a poly-crystalline substrate. Nevertheless, this averaging of BR limits the optical performance of AAO membranes in optical devices. In this work, we study normal incidence BR in AAO for different crystal orientations of the aluminium substrate using a polycrystalline substrate and a simple thermo-mechanical treatment to obtain millimeter size crystalline regions. We found that normal incidence BR is minimum at [100] and [111] orientations and reaches a maximum of ∼ 1.8 ⋅ 10−3 at intermediate orientations. In this case, the BR can be associated with a slight deformation of the structure perpendicular to the direction of the pores, confirmed through scanning electron microscope images. Furthermore, we propose a simple model of elliptical section pores that quantitatively explain the origin of normal incidence BR in AAO. Considering the effect of BR, the design of sensors could be improved to obtain higher quality factors or to incorporate new optical functionalities to these already versatile membranes.