Semi-elliptical Cross-section Research Articles

Novel Cooling Strategy for a Hybrid Photovoltaic/Parabolic Dish Concentrator

In this paper, the thermo-optical performance using novel cooling strategy improvements for a hybrid photovoltaic/parabolic dish concentrator with a conical thermal receiver using a beam splitter filter (PV/PDC-CTR-BSF) is investigated. The study’s main goal is to improve the cooling effectiveness of the serpentine-shaped cooling duct by investigating the effect of the cross-section shape and positioning of the cooling duct under the PV panel. Typical cooling pipes have either a rectangular or circular cross-section and are usually attached to the back sheet of the PV panel using off-the-shelf adhesives that have very low thermal conductivity. With the advent of 3D printing technology, the back sheets could be 3D-printed with integral cooling ducts of different cross-sections at different locations and orientations within the back sheet that allow for increased heat transfer from the back sheet and thus improve PV/PDC-CTR-BSF’s thermos-optical performance. For this purpose, the study investigates and compares the thermal performance of four different cooling duct cross-sections that include: rectangular, semi-circular, semi-elliptical and triangular. For each of the cooling duct cross-sections, several positions and orientations, which include flush below the back sheet layer and embedded inside the back sheet but positioned at the bottom, middle and top of the back sheet, are examined. Numerical simulations using the commercial software ANSYS FLUENT(R2019) are performed to assess the performance of the cooling ducts and, in turn, the thermo-optical performance of the PV/PDC-CTR-BSF system. The semi-elliptical cross-section duct embedded in the middle of the back sheet was found to yield the best cooling performance since its rate of heat removal from the PV back sheet was found to be the highest.

Performance tests on triple composite mesh-groove-powder wicks in a visualizable flat-plate heat pipe

Two types of novel triple composite mesh-groove-powder wicks are proposed and tested in a visualizable flat-plate heat pipe. The powders are only added in the evaporator in the triple composite wicks to increase the capillarity therein. Outside the evaporator is the mesh-groove wick, with a layer of 200-mesh copper screen sintered over parallel grooves, which has been shown to exhibit high permeability and anti-gravity ability. The first type (Triple A) is to add powders in the mesh-groove wick at the evaporator section, while the second type (Triple B) contains an evaporator with only copper powders. The parallel grooves have a semi-elliptic cross-section with a width of 0.18 mm and a depth of 0.075 mm. According to visualization, the powders in the mesh-groove evaporator appear to increase the flow resistance and prompt partial dry-out in some grooves at high heat loads. The experiment results for the Triple B wick with a powder-only evaporator demonstrate a maximum heat load (Qmax) 20 % higher than that for the double mesh-groove wick at the horizontal orientation, with evaporator resistances also slightly higher. However, the Triple A wick, with powders added in the mesh-groove evaporator, displays a slightly lower Qmax than the original mesh-groove evaporator due to the excessive flow resistance associated with powder-filled meshed grooves.

Numerical simulation and experimental verification of fatigue crack propagation in high-strength bolts based on fracture mechanics.

To investigate the fatigue crack propagation behavior of high-strength bolts for high-speed train brake discs, the fatigue crack propagation of high-strength bolts with initial defects under various load ratios was numerically simulated and experimentally verified based on fracture mechanics in this paper. Firstly, the fracture mechanics model of a three-dimensional hexahedral mesh with initial root defects was established using ABAQUS-FRANC3D interactive technology. Then the stress intensity factor (SIF) of the crack front was calculated by the stress superposition of the crack surface to simulate the coupling effect of preload and axial cyclic load. Based on it, fatigue crack propagation was simulated. Finally, the corresponding fatigue experiments on prefabricated crack bolts were carried out. The results show that mode I cracks dominate in the process of crack propagation. The stable crack propagation zones of the fractured high-strength bolts all show a semi-elliptical cross-section. The SIF of the crack front decreases with the increase of the load ratio, thus making the crack propagation life increase with the increase of the load ratio. The experimental outcomes are in great agreement with the simulation results, which verify that the numerical simulation method can effectively and accurately evaluate the fatigue life of high-strength bolts with initial defects and provides an effective means for predicting the fatigue crack propagation life of the same type high-strength bolts in engineering applications.

Experimental study of the core role of GFRP and LDPE on the collapse behavior of absorbers printed with PLA and ABS

Since the advent of polymeric materials, many structures have always been built for engineering purposes. On the one hand, the emergence of composites containing glass fibers has had a significant impact on reducing the weight of structures in various industries. On the other hand, with the advent of 3D printers, many limitations for the geometry of engineering structures were removed. In this research, due to the wide application of these two sciences, a new type of composite absorbers has been introduced. The presented absorbers have glass fiber-reinforced polymer cores (GFRP) or low-density polyethylene cores (LDPE), the shells of each sample are made of PLA or ABS. In this study, 24 different samples were tested under quasi-static loading. The samples were examined in three different groups. In the first group, no cores were used, but in the second group, GFRP cores were used, and in the third group, LDPE cores were used. Triangular, trapezoidal, semielliptical, and square sections were studied, and the results showed that the lowest maximum force was related to samples with semielliptical cross section, then the maximum force increased by changing the cross section from triangular to trapezoidal and then to a square. In addition, the maximum force was higher in the GFRP core than in the LPDE core.

Couette–Poiseuille Flow in Semi-Elliptic Channels

Abstract We present a novel analytical solution for Couette flows of incompressible Newtonian fluids in channels with a semi-elliptical cross section. The flow is steady, unidirectional, satisfies the no-slip condition at the boundaries, and is driven by the movement of the planar wall at constant velocity. The theoretical approach consists of a mapping function to rewrite the problem in an elliptical coordinate system coupled with Fourier's method for the solution of a Laplace equation with Dirichlet-type boundary conditions in the new domain. We then use our new solution together with available results for Poiseuille flows in a similar geometry (Alassar and Abushoshah, 2012, “Hagen–Poiseuille Flow in Semi-Elliptic Microchannels,” ASME J. Fluids Eng. 134(12), p. 124502) to study the so-called Couette–Poiseuille flows, where both pressure-driven and boundary-driven mechanisms act simultaneously. We present a detailed analysis of the flow field in Couette, Poiseuille, and Couette–Poiseuille flows in semi-elliptical channels with cross sections of different aspect ratios. For the latter case, we also determine the critical values of the axial pressure gradient that (i) increase the maximum flow velocity above that of the moving wall and shift its position toward the center of the channel, (ii) mark the onset of flow reversal with the emergence of a backflow region below the static wall, and (iii) eventually lead to a zero net flow rate through the channel.

On the sound fields of oblate and prolate hemispheroids in infinite baffles for directivity control.

The hemispheroid is presented as an apodized form for controlling the beam width of a sound source by varying its height-to-radius ratio. Directivity patterns, on-axis responses, and radiation impedances are calculated for various height-radius ratios of the oblate hemispheroid using spheroidal wave functions. It turns out that, for smaller angles at least, there is a direct relationship between the internal angle of the semi-elliptic cross section and the half-cone angle within which the far-field pressure is largely contained at high frequencies. The hemispheroid is compared with both a spherical cap, which produces a much less regular response, and a high-frequency asymptotic approximation. The high-frequency asymptotic approximation is in the form of a flat circular radiator with a delay that increases radially from the center to the perimeter, as used in some electrostatic loudspeakers. With the almost complete absence of lobes, this appears to be an effective alternative means of apodization to a shaded array and is more efficient because, unlike a shaded array, constant axial velocity is maintained over the whole surface. A high-frequency approximation is also derived for a prolate hemispheroid. Since this may be formed from a planar array, a beam steering option is added.

From thin “coffee rings” to thick colloidal crystals, through drop spreading inhibition by the substrate edge

“Coffee rings” structures formed by the evaporation of a nanosphere colloidal drop which rests on a substrate can be grown as thick, good quality colloidal crystals if the drop is settled onto the flat upper side of a pillar in such a way that its spreading is inhibited by the pillar edge. The colloidal crystal thus obtained has a torus shape of a 6 mm in diameter (~ 19 mm in length), with a semi-elliptical cross section (width ~ 0.7 mm, height ~ 1 mm) and has a shape factor (the ratio between its width and its height) around 1, much lower than that formed in a classical manner, onto a semi-infinite surface, which is usually very flat. These microsphere crystals can be detached from the substrate as free-standing, cut and manipulated without special precaution. Growing thick rings in only few hours, in a simple set-up, the method could be useful for the researchers which currently use these colloidal crystals as sacrificial templates for inverse-opals synthesis.

Modeling the stability of horizontal generations worked in parallel to the front of a uniform slope

Improvement of modern urban infrastructure, expansion of transport networks, creation of innovative engineering communications – as well as other circumstances stimulate the development of underground construction, both in our country and abroad. Like any underground structure, it should have the ability not to collapse when exposed to external loads. For the successful operation of such structures throughout their entire service life, it is necessary to constantly assess the influence degree of all factors’ totality, one way or another, affect its strength. The task, the purpose of which is to conduct the experimental studies on models made of equivalent materials to assess the geometric parameters’ influence of the “slope – underground working space” system on the stability of the latter, has been set. Geometric parameters mean the shape of the underground working space cross-section and its position in the soil massif: the shape of the underground working space cross-section is round and semi-elliptical; the underground working spaces’ bottom is at the level of the slope bottom, the underground working space position is determined by the shortest distance from the transition point of the bottom to the slope to the vertical axis of the cross-section symmetry. The criterion for long-term stability is a criterion, the qualitative feature of which is the absence of inelastic (plastic) deformation zones on the development contours, and the quantitative indicator is the value of the reduced pressure of connectivity σcon. As a result of model experiments, safe distances d were determined, on which underground working spaces should be located in the near-slope area so that the stability of the “slope - underground working space” system is ensured. It turned out that these distances for underground working spaces of both circular and semi-elliptical cross-section are practically the same, that is, the underground working spaces of such a cross-section, all other sections being equal, were equally stable. Practical coincidence of the model experiments’ results and numerical finite element analysis, calculations, allows us to speak about the experimental data reliability.

One piece ceramic heat exchanger for concentrating solar power electric plants

Abstract Using additive manufacturing techniques, a ceramic heat exchanger was optimized for a concentrating solar power (CSP) electric power plant with a corrosive molten salt at atmospheric pressure as the solar field heat transfer fluid and supercritical carbon dioxide at 200 bar as the power block fluid. Temperatures ranged from 750 °C to 540 °C. The plant heat exchanger was optimized for heat transfer and stress using 1 m3 modules arranged in parallel. Heat transfer was optimized using COMSOL Multiphysics software resulting in a unique semi-elliptical cross section for the fluid flow channels in a counter-flow configuration. Counter-flow was made possible through additive manufacturing of the fluid headers as part of each modular heat exchanger thus producing the entire module as a single piece and minimizing cost. Using reasonable parametric values, a heat exchanger module was optimized to 0.5 MW/m3, and a section of it was manufactured including the fluid headers. Parametric studies showed the potential for a module to reach 3.5 MW/m3.

Assessing the feasibility of yttria-stabilized zirconia in novel designs as mandibular anterior fixed lingual retention after orthodontic treatment.

The purpose of this study is to explore the feasibility of yttria-stabilized zirconia (Y-TZP) in fixed lingual retention as an alternative to stainless steel. Exploratory Y-TZP specimens were milled to establish design parameters. Next, the specimens were milled according to ASTM standard C1161-13 and subjected to 4-point flexural tests to determine material properties. Finite elementanalysis was used to evaluate 9 novel cross-sectional designs, which were compared with stainless steel wire. Each design was analyzed under loading conditions to determine von Mises and bond stresses. The most promising design was fabricated to assess the accuracy and precision of current CAD/CAM milling technology. The superior design had a 1.0×0.5mm semielliptical cross-section and was shown to be fabricated reliably. Overall, the milling indicated a maximum percent standard deviation of 9.3 and maximum percent error of 13.5 with a cost of $30 per specimen. Y-TZP can be reliably milled to dimensions comparable with currently available metallic retainer wires. Further research is necessary to determine the success of the bonding protocol and the clinical longevity of Y-TZP fixed retainers. Advanced technology is necessary to connect the intraoral scan to an esthetic and patient-specific Y-TZP fixed retainer.

Effect of the Reynolds number on the aerodynamic forces and galloping instability of a cylinder with semi-elliptical cross sections

The effects of the Reynolds number on the aerodynamic forces and galloping instability of a semi-elliptical cross-section, which are used to simulate the shape of the iced conductors, have not been fully studied. Simultaneous multi-pressure wind tunnel experiments were conducted to explore the aerodynamic forces on cylinder with semi-elliptical cross-sections; the Reynolds number was in the sub-critical and critical regimes. A unified single-degree-of-freedom (SDOF) approach and a three-degree-of-freedom (3-DOF) model were used to analyze the galloping instability with the Reynolds number in the following regime: Re=34k–175k. The variation in the aerodynamic force with the angle of attack is sensitive at the critical Reynolds number; at this critical regime, the sudden decrease in the lift coefficient value with an increasing angle of attack is sufficient to create negative aerodynamic damping. The galloping instability analysis shows that the occurrence of negative aerodynamic damping strongly depends on the critical flow state. In all cases considered in the present work, the critical Reynolds number effects are shown to include aerodynamic forces that could well be responsible for the whole range of translational galloping instabilities and part range of torsional flutter and 3-DOF galloping instabilities for semi-elliptical cylinders.

Dynamics of Rocking Semicircular, Parabolic, and Semi-Elliptical Disks: Equilibria, Stability, and Natural Frequencies

This paper performs a theoretical and experimental investigation of the natural frequency and stability of rocking semicircular, parabolic, and semi-elliptical disks. Horace Lamb's method for deriving the natural frequency of an arbitrary rocking disk is applied to three shapes with semicircular, parabolic, and semi-elliptical cross sections, respectively. For the case of the semicircular disk, the system's equation of motion is derived to verify Lamb's method. Additionally, the rocking semicircular disk is found to always have one stable equilibrium position. For the cases of the parabolic and semi-elliptical disks, this investigation reveals a supercritical pitchfork bifurcation for changes in a single geometric parameter which indicates that the systems can exhibit bistable behavior. Comparisons between experimental validation and theory show good agreement.

Multi-functional lens based on conformal mapping.

Based on conformal mapping method, a two dimensional, multi-functional lens structure is proposed and designed in this work. The lens is an infinitely-long, gradient-index dielectric cylinder with a semi-elliptic cross-section. The lens can first be considered like a flattened Luneburg lens, which produces highly-directive electromagnetic waves by adjusting the feed position along the line connecting the two foci. It also functions like an Eaton lens. When an incoming beam impinges on the same line but outside the two foci, it will be guided through the lens structure and take a U-turn. Besides, if properly shaped, the structure can also be used as a waveguide bend. The lens can be realized using non-resonant metamaterials with inhomogeneous hole arrays. Simulation results demonstrate excellent performance of the lens and agree well with theoretical prediction. The designed lens can be used in the electromagnetic control. And it is especially useful in the real optical lens system.

Check of the methodology for determination of profile of reflector of beam stream

The study of the shape of radiant flux reflector, designed for uniform total irradiation of receiver with semi-elliptical cross-section by a single radiator, was continued. Physical and com­puter experiments were conducted in the paper to verify previously developed analytical methodology for determining the reflector profile based on the solution of inverse problem. Using the experimental apparatus with reflector allows conducting a series of physical experiments to determine the temperature in the working chamber followed by construction of the field of irradiation density using the computer algebra system MathCad. The computer experiment, conducted for the same heat system using the optical analysis software TracePro, allows determining the same parameter. The comparison of heat flux density, produced in accordance with the developed theoretical methodology, by computer simulation and physical experimentation proves the accuracy of the developed methodology for determining the reflector profile ensuring uniform irradiation of receiver with semi-elliptical cross-section. The use of reflectors, profiled in accordance with the proved methodology, will reduce the power capacity of infrared equipment for frying food products, as well as enhance the organoleptic properties of products.

Direct loading of polymer matrices in plastic microchips for rapid DNA analysis: A comparative study

We report the design and performance validation of microfluidic separation technologies for human identification using a disposable plastic device suitable for integration into an automated rapid DNA analysis system. A fabrication process for a 15-cm long hot-embossed plastic microfluidic devices with a smooth semielliptical cross section out of cyclic olefin copolymer is presented. We propose a mixed polymer solution of 95% w/v hydroxyethylcellulose and 5% w/v polyvinylpyrrolidone for a final polymer concentration of 2.5 or 3.0% to be used as coating and sieving matrix for DNA separation. This formulation allows preparing the microchip without pretreatment in a single-loading step and provides high-resolution separation (≈1.2 bp for fragments <200 bp), which is superior to existing commercial matrices under the same conditions. The hot-embossed device performance is characterized and compared to injection-molded devices made out of cyclic olefin copolymer based on their respective injector geometry, channel shape, and surface charges. Each device design is assessed by fluorescence videomicroscopy to evaluate the formation of injection plugs, then by comparing electropherograms for the separation of a DNA size standard relevant to human identification.

Design and Finite Element Analysis of a Hydraulic Excavator Boom

In today’s world of growing competition, all industries are trying their best to give the components of high quality with minimum expenditure. So in present work a new semi-elliptical boom has been selected to replace the conventional boom, which is usually made of rectangular. In particular, the study wants to substitute the rectangular section for Semi-elliptical section. This change lightens the weight of the boom. For this purpose, boom with semi-elliptical cross-section has been modeled using cad software pro/E wildfire 4.0. Using VB program automatic calculation module (UPAS), the static force at different working condition of the boom calculated. Then Finite element analysis has been done to determine the static stress at a given load condition using software ANSYS 12. The result shows that total weight is reduced by 5%. The value of maximum stress and displacement is 115.663MPa and 12.885 mm respectively. Thus the structure is capable of withstanding the maximum stress. The structure is failsafe. In this paper only static stress analysis is done.

Alternative equations to estimate the surface-to-volume ratio of different forest fuel particles

Surface-to-volume ratio is an important fuel descriptor. Surface-to-volume ratio quantification methods currently used are specific and their accuracy varies with fuel types. In this work, we developed a geometric surface-to-volume ratio estimation method based on the perimeter-to-area ratio concept. Dimensions of leaves, twigs and needles of Moroccan tree and shrub species were measured. Our findings are: (i) the thickness of a leaf is variable along its width and length, and its average cross-section is located at its mid-length; (ii) a formula to calculate the ellipse perimeter was established using an elongation coefficient e, determined on the basis of the cross-section thickness and width; and (iii) one general surface-to-volume ratio formula was developed, from which five other equations were derived, according to the specific characteristics of each fuel type, for twigs, leaves, needles with semi-elliptical cross-section, needles with crescent cross-section shape, and needles with cross-section representing half or a sector of a circle respectively. Surface-to-volume ratio values obtained with the developed equations were compared with the currently published data.

Vibration isolation device with load dependent stiffness

A vibration isolation device is disclosed. More specifically the vibration isolation device of the present invention comprises means for decreasing the mount stiffness when loads above a threshold load value are applied to the device. The means for decreasing the mount stiffness comprises a shear pin (30) with shear locations that comprise annular grooves with semielliptical cross sections.

Impedances of azimuthally symmetric irises and cavities with semielliptical profile in a beam pipe

The beam coupling impedances of small axisymmetric obstacles having a semielliptical cross section along the beam in the vacuum chamber of an accelerator are calculated at frequencies for which the wavelength is large compared to a typical size of the obstacle. Analytical results are obtained for both the irises and the cavities with such a shape, which allows simple estimates of their broadband impedances.

Fully developed flow and heat transfer in semi-elliptical ducts

A control volume-based numerical solution is described for the fully developed laminar flow and heat transfer in ducts of semi-elliptical cross section. Both an isothermal and a uniform axial heat flux condition on the duct walls have been considered. Numerical results for velocity and temperature profiles, friction factor, pressure defect, and Nusselt number are presented for a wide range of duct aspect ratios from 0.1 to 0.999. Comparison with earlier numerical results for the limiting case of semicircular duct and with analytical solution for fully elliptical ducts is excellent. For ducts in which the baseplate is on the major axis, friction factor and Nusselt number for the uniform heat flux condition increase as the aspect ratio decreases, with values for the lowest aspect ratio of 0.1 being about 25 percent larger than those for a semicircular duct. For ducts with the baseplate on the minor axis, all characteristics exhibit a nonmonotonic behavior with respect to the aspect ratio. While the maximum velocity and pressure defect exhibit a mild maximum for aspect ratio of 0.6, the friction factor and Nusselt number exhibit a minimum at the same aspect ratio. The ratio of Nusselt number to friction factor is higher for semi-elliptical ducts in comparison to that for other ducts, such as sinusoidal, circular segmental, and isosceles triangular ducts.