Elliptical Cross Section Research Articles

TEMPERATURE DISTRIBUTION WITHIN THE RISING PIPE IN FLAT PLATE SOLAR COLLECTOR

In the present study, the effect of increasing absorption area by using two different cross-section shapes of rising pipe namely semi-circle cross-section (model -A-) and elliptic cross-section (model -B-) on the temperature distribution of operating liquid within rising pipe of the FPSC is studied numerically and experimentally. Experimental tests are conducted under weather Baghdad – Iraq, while the numerical results are obtained by using Ansys Fluent CFD. The difference between the experimental findings and numerical findings for the average temperature of the water in the tank and the temperature of the operating liquid at exit rising pipe is 8.12 % and 8.36 % respectively. The results have shown that the temperature distribution for all new models higher than the traditional model. Furthermore, model -B- has higher other models under study. Hence, the best model according to the current study is model -B- increase by (2.4%), (2.2%) and (2.5%) regarding the temperature of the operating liquid at the inlet, center, and outlet respectively compared to the traditional model.

Experimental Investigation of Heat Transfer of Nanofluid in Elliptical and Circular Tubes

The paper presents experimental comparison of forced convection for steady state turbulent flow of nanofluid (Al2O3-distilled water) inside circular and elliptical (aspect ratio of 0.75) cross section tubes of identical circumference and tube surface area. Convection coefficient, pressure change, and fiction factor were compared at different Reynolds number (3,000-9,230) with different nanoparticles volume concentration (0.5%, 1.0%, and 1.5%). The results showed that Nusselt number increases with increasing Reynolds number and nanoparticle volume concentration. The pressure drops and friction factor of nanofluid are higher than the distilled water and are increasing as the volume concentration increases. Furthermore, the elliptical tube provided small increase in Nusselt number compared to that of circular cross sectional tube. However, the friction factor in the elliptical tube was slightly higher.

Numerical Studies on the Stiffness of Arc Elliptical Cross-section Helical Spring Subjected to Circumference Force

Due to its excellent properties, elliptical cross-section helical spring has been widely used in automobile industry, such as valve spring, arc spring used in Dual Mass Flywheel and so on. Existing stiffness formulae of helical spring remain to be tested, and stiffness property of elliptical cross-section arc spring has been little studied. Hence, study on the stiffness of elliptical cross-section helical spring is significant in the development of elliptical cross-section helical spring. This paper proposes a method to study the stiffness property of elliptical cross-section helical spring that the experiment design method is adopted with finite element analysis. Firstly, the finite element analysis method was used to verify the cylindrical (circular cross-section and elliptical cross-section) springs. Then, the regression formula was designed and derived compared with the reference springs’ stiffness formulae by experimental design. Last, regression formula was verified with existing experiment data. The novelty in this paper is that simulation technology of arc spring was investigated and a stiffness regression equation of arc elliptical cross-section spring was obtained using orthogonal regression design, with significance in wide use of the arc elliptical cross-section helical spring promotion.

Understanding and prediction of magnetization state of elliptic cross-section matrices in high gradient magnetic separation

Theoretical prediction of magnetization state of matrices in high gradient magnetic separation is of importance to the separation performance analysis. However, the existing methods are limited to the cases where a magnetic field is parallel or perpendicular to one axis of magnetic elements in matrices. To solve this issue, in this work, we propose an easily understood method to construct the correlation between the magnetization of an elliptic cross-section element and the externally applied magnetic field. On this basis, we develop a simple relation to rapidly determine the demarcation for judging the magnetization sate of the element, which is suitable for the cases with an arbitrary magnetic field direction. Furthermore, we reveal the influence of the shape coefficient of the element on the prediction accuracy of its magnetization process. This work has important theoretical value for understanding the magnetization process of elliptic cross-section matrices under different magnetic fields.

Buckling of Arteries With Noncircular Cross Sections: Theory and Finite Element Simulations.

The stability of blood vessels is essential for maintaining the normal arterial function, and loss of stability may result in blood vessel tortuosity. The previous theoretical models of artery buckling were developed for circular vessel models, but arteries often demonstrate geometric variations such as elliptic and eccentric cross-sections. The objective of this study was to establish the theoretical foundation for noncircular blood vessel bent (i.e., lateral) buckling and simulate the buckling behavior of arteries with elliptic and eccentric cross-sections using finite element analysis. A generalized buckling equation for noncircular vessels was derived and finite element analysis was conducted to simulate the artery buckling behavior under lumen pressure and axial tension. The arterial wall was modeled as a thick-walled cylinder with hyper-elastic anisotropic and homogeneous material. The results demonstrated that oval or eccentric cross-section increases the critical buckling pressure of arteries and having both ovalness and eccentricity would further enhance the effect. We conclude that variations of the cross-sectional shape affect the critical pressure of arteries. These results improve the understanding of the mechanical stability of arteries.

Mathematical modeling of the thermally stressed state of elliptical-section concrete structures

At present, there is an urgent need to determine the level of temperature stresses in super-large concrete structural elements that occur during the manufacture of such products and contain a huge amount of concrete at the same time, which is in fact a heat source that is inaccessible to the control of the exothermic process of the entire mass of concrete. The main task of this work is the mathematical modeling of temperature stresses in concrete structures of elliptical cross-section in order to reduce them. Based on mathematical modeling, it is established that the level of thermal stresses that occur during the transition to an elliptical cross-section decreases.

Numerical Investigation of Short Elliptical Twisted Tube for Reduced Fouling Rate in Steam Cracking Furnaces

In the steam cracking industry of natural gas or naphtha, fouling of tubular heat exchangers by cokes is a major issue. This growing carboneous layer has two major negative effects: 1) it increases pressure drop and 2) reduces heat transfer from the tube wall to the processed fluid. Using the open-source Computational Fluid Dynamics software OpenFOAM, this study numerically investigates wall shear stress, pressure drop and heat transfer performances of swirl decaying flow generated by different elliptical cross-section twisted tube. One of the objectives is to determine if minor modifications of tube geometry can generate swirling flow which could enhance wall shear stress at a reduce pressure drop penalty. For a Reynolds number ranging from 10, 000 to 100, 000, it is shown that the investigated geometries could enhance heat transfer by 90% at an increased pressure drop of 128% which yields a Performance Evaluation Criterion (PEC) of 1.44. The comparison between the performances of the different geometries is carried out using a newly defined PEC based on the bulk temperature, along with the usual PEC.

Superplastic behavior of an in-situ TiB2 particle reinforced aluminum matrix composite processed by elliptical cross-section torsion extrusion

In this work, a severe plastic deformation method, namely elliptical cross-section torsion extrusion ( E -TE), was applied to achieve superplasticity of an in-situ TiB 2 /Al-Zn-Mg-Cu composite by obtaining the optimized microstructure of uniformly distributed particles and equiaxed-fine grains. The superplastic behavior and mechanisms of the E -TE processed composite were comprehensively investigated via tensile tests (at T = 350 °C–500 °C and ε ̇ = 10 −1 s −1 -10 −3 s −1 ) and microstructure characterizations. The tests demonstrated that the composite after a single pass of the E -TE gained a maximum elongation of 420% at 450 °C × 10 −3 s −1 . Even with the strain rate increasing to 10 −2 s −1 , the elongation still reached 360%, which implies a high strain rate superplasticity. Analysis based on the strain rate sensitivity ( m ≈ 0.20–0.35) and microstructure characterizations showed that the deformation and failure mechanisms of the composite vary with the temperature. When the temperature is within 350 °C–400 °C, the composite realizes deformation mainly through intragranular dislocation slip and fails by intragranular fracture. With the temperature of 425 °C–450 °C, the deformation is attributed to cooperative grain boundary sliding (CGBS) accommodated by dislocation activity and liquid phase, where a small fraction of liquid phases observed at the triple junctions of GBs facilitates the composite's superplasticity by reducing the stress concentration and deformation incompatibility. The failure is ascribed to the intergranular fracture by cavity formation/coalescence. For temperature within 475 °C–500 °C, numerous liquid phases formed at GBs and significantly weakened the GBs' strength, deteriorating the composite's superplasticity. The composite's failure is resulted from the intergranular fracture by strength weakening of GBs. • Particle reinforced aluminum matrix composites after elliptical cross-section torsion extrusion (E-TE) show superplasticity. • The E-TE processed composite exhibits an elongation of 360% at 450℃×10 -2 s -1 , implying a high strain rate superplasticity. • The superplastic deformation/failure mechanisms of the E-TE processed composite vary with temperatures. • The composite's superplasticity is facilitated by the appropriate liquid phase at the optimized temperature of 450℃.

Efficient Numerical Algorithm for the Solution of Nonlinear Two-Dimensional Volterra Integral Equation Arising from Torsion Problem

In this article, an effective method is given to solve nonlinear two-dimensional Volterra integral equations of the second kind, which is arising from torsion problem for a long bar that consists of the nonlinear viscoelastic material type with a fixed elliptical cross section. First, the existence of a unique solution of this problem is discussed, and then, we find the solution of a nonlinear two-dimensional Volterra integral equation (NT-DVIE) using block-by-block method (B-by-BM) and degenerate kernel method (DKM). Numerical examples are presented, and their results are compared with the analytical solution to demonstrate the validity and applicability of the method.

Assessment of process parameters and performance enhancement through a novel suction flushing technology in RµEDM

ABSTRACT Reverse micro electro-discharge machining (RµEDM) is a promising and cost-effective technology for fabricating unconventional shaped single and arrayed micro-pins of high aspect ratio. However, dimensional inaccuracies, poor surface finish and long machining time are of great concern. An experiment-based detailed investigation of process parameters for analyzing various machining responses has been performed in this article. Taguchi’s L16 orthogonal array design of experiments has been used to frame out the experimental runs. Discharge voltage, capacitance and feed rate have been considered as process parameters whereas, material removal rate, taper root angle, surface roughness and machining time as responses for the fabrication of a single micro-pin. Additionally, the feasibility of a novel high-pressure suction flushing technology implemented for RµEDM has been demonstrated. The performance of this technology is verified for better surface quality and lesser machining time. It is observed that by using the proposed suction technology, along with the suitable parametric settings, the micromachining time significantly improved (~20%) while fabricating an arrayed micro-pins in elliptical cross-sections profile.

Stress analysis of elliptical composite tubular beams using a meshless dimensional reduction method

In the present paper, a meshless dimensional reduction method is presented for the efficient stress analysis of composite tubular beams with elliptical cross-section. A polynomial based method in polar coordinates in conjunction with an asymptotic variational method were used to carry out cross-sectional analysis. The two-dimensional cross-section strain energy is perturbed by perturbing the warping field to obtain unknown warping of the cross-section. The transverse shear effect is taken into consideration using transformation to Timoshenko-Like beam model. Since the present approach does not use finite element mesh in two-dimensional analysis of the cross-section (such as that used in the software Variational Asymptotic Beam Sectional Analysis (VABS)), it is termed meshless method. The one-dimensional finite element analysis through the length is carried out to determine the transverse deflections and rotations of the beam. This procedure is much faster computationally as compared to the three-dimensional finite element method. It is simple-input, and needs less pre-processing time to prepare the model. The obtained results are compared with literature, strength of materials and VABS tool. In addition, the effect of ellipse diameter ratios and lay-up sequence on the mechanical behavior of elliptical tubular beams are investigated.

Analysis of Digital Images on a Mobile Device to Estimate Surface Area and Volume of Mango Fruit (Mangifera indica L.)

Objective: To develop a technique based on the partition method, to estimate the surface area and volume of mango fruit (Mangifera indica L. cv. “Ataulfo”) using two digital orthogonal images, obtained and processed on a mobile device with the Android® operating system, segmented by different discriminants. Design/Methodology/Approach: A technique was developed to estimate the surface area and volume of “Ataulfo” mango fruit based on digital images and was implemented directly on a smartphone with the Android® operating system. Three discriminants were evaluated for segmentation (red channel, green channel, and HIS intensity) and applied in n=30 fruits. The precision and accuracy of the technique was determined. Results: The surface area and volume of the fruit when estimated using the red channel presented a coefficient of variation of less than 2.0% in both variables and the estimation error was less than 3% for surface area and less than 5% for volume. Study Limitations/Implications: This technique was limited to fruit with an elliptical cross-section and smooth surface. Findings/Conclusions: The proposed technique is a non-destructive alternative to estimate the surface area and volume of “Ataulfo” mango fruit with a reasonable margin of error and can be implemented directly on an Android® device using only the red channel as a segmentation discriminant.

Quasi-3D inverse design of S-shaped diffuser with specified cross-section distribution; super-ellipse, egg-shaped, and ellipse

Recently, an inverse design method called the ball spine algorithm (BSA) is introduced to design S-duct diffusers with elliptic cross-sections. The technique is developed for the 3-D design of S-shaped ducts with special cross-sectional profiles in the present work. The upper and lower lines of the S-duct symmetric section are modified under the BSA. Two types of special cross-section profiles are used to improve the aerodynamic properties of the duct. At the S-duct inlet, the super-ellipse profile is used to minimize the duct inlet height. At the aft part of the duct, the egg-shaped profile is predefined to decrease the pressure difference between the upper and lower lines and to diminish the adverse pressure gradient along the upper line. Finally, the flow through the designed S-duct is numerically analyzed using a viscous flow solver with the SST turbulence model to validate the designed S-duct performance.

Heat transfer characteristics induced by multiple tandem elevated inclined jets sources in cross flows

Consideration is given in this paper to the heat transfer induced in an elevated triplet-jet-group in cross flow numerical configuration. The jets are discharged from inclined, inline and elevated cylindrical ducts. We are particularly concerned with the generated aerothermic mixing, a critical and highly affecting parameter in the protection of turbine blade surfaces subject to high temperature levels, in the optimization of air-fuel mixing, and then combustion within scramjet combustors, in the reduction of noise by means of air curtains, etc. Since the generated heat fluxes are closely related to the interacting flows' dynamics and corresponding turbulent features, we intend to bring here some clearance on the development of the aerothermic mixing of an elevated cascaded jet model within a cross flow. To reach our goal, a finite volume method is adopted to reproduce experimental data relative to three isothermal and 60°-inclined jets, placed three diameters apart, sent at a given height from the wind tunnel ground and discharged from similar elliptical cross-sections, under different injection ratios. A mesh sensibility study and different turbulence modeling tests were carried out to obtain the consistent validation of the jets’ velocities and trajectories. The first-order kωSST and the second-order RSM models gave particularly interesting results. Once a satisfactory agreement was achieved, a temperature difference between the jets and the mainstream was adopted to upgrade the model. We could then account for the induced heat transfer through the analysis of the reduced static temperature, a particularly interesting parameter for its closeness (if not similarity under some circumstances) to the film cooling efficiency.

Semi-Analytical Method for Computing Effective Thermoelastic Properties in Fiber-Reinforced Composite Materials

Effective elastic and thermal properties for isotropic or transversely isotropic thermoelastic fibrous composite materials are obtained. Fibers are distributed with the same periodicity along the two perpendicular directions to the fiber orientation. The periodic cell of the composite has a square or hexagonal distribution. Perfect contact between the fiber and the matrix is presented. The effective properties are calculated using a semi-analytical method. The semi-analytical method consists of obtaining the differential equations that describe the local problems using the Asymptotic Homogenization Method. Then, these equations are solved using the Finite Element Method. Effective elastic coefficient (C¯), effective thermal expansion coefficient (α¯) and the effective thermal conductivity (κ¯) are obtained. The numerical results are compared with the semi-analytical solution and with results reported by other authors. Additionally, the effective properties for a fiber with an elliptical cross section are calculated. Distributions of the fiber’s cross section with different orientations are also studied. A MATLAB program for computing the effective coefficients is presented.

Entropy Analysis of the Peristaltic Flow of Hybrid Nanofluid Inside an Elliptic Duct with Sinusoidally Advancing Boundaries.

Peristaltic flow of hybrid nanofluid inside a duct having sinusoidally advancing boundaries and elliptic cross-section is mathematically investigated. The notable irreversibility effects are also examined in this mathematical research by considering a descriptive entropy analysis. In addition, this work provides a comparison analysis for two distinct nanofluid models: a hybrid model (Cu-Ag/water) and a phase flow model (Cu/water). A comprehensive graphical description is also provided to interpret the physical aspects of this mathematical analysis.

Elliptical plasma-filled waveguide as a new standard short-period undulator.

Undulators as the sources of high-brilliance synchrotron radiation are of widespread interest in new generations of light sources and free-electron lasers. Microwave propagation in a plasma-filled elliptical waveguide can be studied as a standard short-period undulator. This structure as a lucrative insertion device can be installed in the storage ring of third- and fourth-generation light sources to produce high-energy and high-brilliance synchrotron radiation. In this article, the propagation of the transverse electric modes in a plasma-filled waveguide with an elliptical cross-section is investigated, and the field components, the cut-off frequencies and the electron beam trajectory are calculated. With due consideration of the electron beam dynamics and in order to achieve a standard short-period undulator, parameters such as the dimensions of the waveguide elliptical cross-section, the microwave frequency and the plasma density are calculated.

Mode Analysis by the Method of Auxiliary Sources With an Excitation Source

The method of auxiliary sources (MAS) is one of the numerical methods employed for the determination of the cutoff wavenumbers (eigenvalues) of cylindrical waveguides. According to the general scheme of MAS, the eigenvalues are obtained by requiring the square impedance matrix to be singular and therefore its determinant to be zero (or its condition number to be large). For large matrices, such computations are complicated and time-consuming. Additionally, these schemes are frequently contaminated with spurious eigenvalues. To overcome the difficulties, an efficient method based on MAS along with an excitation source has been proposed. The eigenvalues are obtained by measuring the physical response of the waveguide's domain to this source; thus, an interior problem is always solved. This article is a comprehensive presentation of this method and its variants and aims to emphasize fundamental and often unfamiliar attributes. One of the main objectives is to show analytically and numerically that when an internal source is used, the eigenvalues are accurately computed without employing a regularization procedure. The method is applied to hollow simply and multiply connected waveguides with circular, elliptical, and rounded-triangular cross sections. The results are compared with those obtained from COMSOL Multiphysics. Moreover, the phenomenon of divergent and oscillating MAS currents-which may or may not occur depending on the relative position between the auxiliary curve and the excitation source-is discussed. It is emphasized that, with proper care, the phenomenon does not affect the accurate computation of the eigenvalues.

Modeling Interplanetary Expansion and Deformation of Coronal Mass Ejections With ANTEATR‐PARADE: Sensitivity to Input Parameters

AbstractSpace weather predictions related to coronal mass ejections (CMEs) requires understanding how a CME is initiated and how its properties change as it propagates. Most predictions have been limited to the arrival time of a CME and include little to no information about the CME's internal properties. ANother Type of Ensemble Arrival Time Results‐Physics‐driven Approach to Realistic Axis Deformation and Expansion (ANTEATR‐PARADE) represents the most thorough description of the interplanetary evolution of CMEs in a highly computationally‐efficient model (Kay & Nieves‐Chinchilla, 2020, https://doi.org/10.1029/2020JA028911). presents the derivation of this model, where we have added an elliptical cross section to the original arrival time model ANTEATR and introduced internal magnetic and thermal forces that, combined with the drag, can alter the shape of the central axis and cross section. ANTEATR‐PARADE results include the transit time of CMEs, as well as the shape and size, propagation and expansion velocities, density, and magnetic field properties upon impact. We determine the dependence of each output on each of the ANTEATR‐PARADE input parameters. For a fast CME, we see that the parameterization of our thermal and magnetic models tends to be more important than the actual initial temperature or magnetic field strength. We extend to other CMEs and find that the sensitivities change with CME scale with thermal forces being more important for a weaker CME and magnetic forces being more important for a stronger CME. The most critical parameters for space weather predictions are the CME mass, the initial magnetic field strength, the adiabatic index, and the profile of the axial magnetic field strength.

Numerical simulation of the unsteady cavitating flow in a Francis turbine draft tube at Upper-Part-Load (UPL) conditions

At part-load conditions, Francis turbines experience the development of a precessing vortex rope in their draft tube (DT), rotating with a frequency between 0.2 and 0.5 times the runner frequency. It induces pressure pulsations at the precession frequency in the whole hydraulic system, undesirable vibrations and noise putting at risk the stability of the system and the lifetime of the machine components. In specific machines, a dramatic amplification of the noise and vibrations can be observed between 70% and 85% of the design conditions. In these cases, synchronous pressure pulsations with a high frequency, typically between 2 and 4 times the runner frequency, are observed, referred to as the so-called Upper-Part-Load (UPL) pulsations. These pulsations are induced by a self-excitation of the entire hydraulic system including the cavitation vortex rope at one of its high order eigenmodes. Besides, the cavitation vortex rope features an elliptical cross-section rotating around the vortex axis at a high frequency. In this manuscript, unsteady two-phase flow simulations using a Scaled-Adaptive-Simulation (SAS) turbulence model and ZGB cavitation model of a Francis turbine draft tube at 80% of the design condition are performed to clarify the mechanisms responsible for the formation of the elliptical shape of the vortex and the UPL pulsations. However, the numerical simulation with a constant inlet boundary condition cannot reproduce the UPL pulsation phenomenon since it is a self-excited oscillation at one eigenmode of the complete system, which is not considered. Therefore, the UPL pulsations component is extracted from the measured pressure fluctuations data by applying a band-pass filter and is then set as the inlet boundary condition in the numerical simulation. The flow field is therefore artificially excited which aims to confirm whether the same phenomenon can be observed and to compare with the flow field obtained with constant inlet boundary condition. The numerical simulations are validated by experimental results, and the wave propagation in the DT is clarified.