Elliptical Hole Research Articles

Shear performance of elliptical head one-sided bolt double-lapped joint with plug-in gasket

One-sided bolts are commonly used for bolted connections between closed section members to address the issue of insufficient space for nut installation. Among them, the elliptical head one-sided bolt uses the difference in length between its long and short axes. This allows the bolt head to be inserted into the elliptical bolt hole and subsequently rotated by 90 degrees, effectively achieving anchoring. But the use of elliptical bolt holes may cause some problems, such as bolt slippage and stress concentration around the bolt holes. In this paper, building upon the elliptical head one-sided bolt concept, a novel structure for one-sided bolted connection is proposed, incorporating a plug-in gasket to improve the mechanical properties of the elliptical one-sided bolted joints. Six sets of steel plate double-lapped joints, connected by elliptical head one-sided bolts and plug-in gaskets, were designed for shear resistance tests. A finite element model was designed using ABAQUS, based on the test specimen parameters. By comparing the simulation results with the experimental findings, the reinforcing effect of the gasket on joint stress was analyzed and validated. The results show that the plug-in gasket effectively resolves the excessive slippage issues and enhances the initial stiffness of the joint. Moreover, when pressure is applied to the bolt hole, the plug-in gasket reduces the stress concentration caused by the extrusion between the bolt hole and the bolt shank, thus preventing local premature failure of the bolt hole.

EXPERIMENTAL STUDY ON FLASH BOILING SPRAY OF HIGH-PRESSURE LIQUID AMMONIA JET WITH ROUND AND ELLIPTICAL HOLE NOZZLES

Ammonia is an ideal alternative fuel for mitigating carbon emissions. High-pressure direct injection of liquid ammonia (LNH<sub>3</sub>) offers significant advantages in enhancing energy efficiency and minimizing emissions. Due to the high saturation vapor pressure, the injection of LNH<sub>3</sub> is susceptible to flash boiling. In this study, we used high-speed micro-imaging technology with backlight lighting to establish a high-pressure common-rail LNH<sub>3</sub> jet experimental platform and investigate the flash boiling spray characteristics of nozzles with round and elliptical holes. The results demonstrated that under non-flash boiling conditions, the residual LNH<sub>3</sub> in the sac chamber and nozzle can rapidly corrode the acrylic material of the nozzle, leading to deformation and failure of the nozzle structure. Under flash boiling conditions, LNH<sub>3</sub> ejected from the hole will produce spherical macroscopic spray morphology. Then, the spray gradually transitions from an elliptical profile to a conical profile as the back pressure increases. Compared to nozzles with round holes, nozzles with elliptical holes exhibit higher flow velocity, which enhances oil-gas mixing and promotes more pronounced flash boiling phenomena. Flash boiling occurs at an earlier stage with an increase in the spray cone angle, thereby improving the atomization characteristics under both flash and non-flash boiling conditions. The tail jet of nozzles with elliptical holes terminates earlier while exhibiting a higher decrease rate in the average gray value, which improves the atomization quality in the tail spray stage and meets the requirements of timing, quantification, and precise control of the fuel injection system.

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ СИМЕТРИЧНОЇ КРАЙОВОЇ ЗАДАЧІ ДЛЯ ПОСЛАБЛЕНОГО НАСКРІЗНИМ ОТВОРОМ ШАРУ З ПОКРИТИМИ ДІАФРАГМОЮ ТОРЦЯМИ

The paper presents a new mathematical model for the solution of a static symmetric boundary-value problem for a layer weakened by a through hole with ends covered with a diaphragm. A new method based on a system of three singular integral equations has been developed and tested numerically. As a result of a high-precision numerical study, it was found that with an increase in the thickness of the layer, an increase in the relative circumferential stress occurs. With a decrease in one of the radii of the elliptical hole, an increase in the relative circumferential stress is also observed. The paper presents the respective dependency graphs. Keywords: three-dimensional boundary-value problems, singular integral equations, numerical experiment, static stretching–compression, a through hole.

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ В СТАТИЧНИХ ТРИВИМІРНИХ КРАЙОВИХ ЗАДАЧАХ — КОСОСИМЕТРИЧНА ЗАДАЧА ДЛЯ ШАРУ, ПОСЛАБЛЕНОГО НАСКРІЗНИМ ОТВОРОМ І КОВЗНИМ ЗАЩЕМЛЕННЯМ ТОРЦІВ

Spatial static boundary-value problems of mathematical physics for a layer with a non-circular cylindrical through hole have hardly been solved using the method of singular integral equations (SIE) despite the fact that numerous fundamental theoretical issues have been developed. Methods for the calculation of spectral characteristics are also absent. The paper provides an overview of the methods for solving these problems. A new mathematical model has been constructed, and a new method based on a system of three SIEs has been developed and tested numerically. As a result of a high-precision numerical study, it was found that with an increase in the thickness of the layer, an increase in the relative circumferential stress occurs. In the case of a circular hole, a shift of the maximum relative circumferential stress from the ends to the depth of the layer is observed. In the case of an elliptical hole, with a decrease in one of the radii, an increase in the relative circumferential stress is also observed. Keywords: three-dimensional boundary-value problems, singular integral equations, numerical experiment, static bending, a through hole.

Numerical study on the effect of optimizing the Trombe wall structure with built-in fins on improving building energy efficiency in severe cold region

In order to save heating energy and reduce carbon emission intensity, a floor heating room with built-in finned Trombe wall in Xining, Qinghai, a severe cold area, was taken as the research object. And ANSYS 2021 R1 was used to numerically investigate the effects of several major factors, such as fin height, fin transverse distance, fin longitudinal distance, fin inclined angle, fin shape, perforated shape and perforation ratio of perforated fin, on the average heat transfer coefficient (h) between the absorptive surface and the air in the interlayer. The results show that for fins with low heights, the enhancement effect of horizontal fins on the convective heat transfer of the absorptive surface of Trombe wall is greater than that of vertical fins. The enhancement effect of vertical fins on the convective heat transfer of the absorptive surface is more affected by fin transverse distance, while the enhancement effect of horizontal fins on the convective heat transfer of the absorptive surface is more affected by fin longitudinal distance. Besides, h shows a trend of first increasing and then decreasing with the increase of fin inclined angle, and reaches its maximum value of 5.89 W/(m2·K) at 45°. The fins with different shapes are equilateral triangular fins, semicircular fins, isosceles triangular fins and rectangular fins in descending order of their enhancement effect on the heat transfer of wall. Compared with solid fins, fins with circular holes can obtain a better convective heat transfer effect only when the open area ratio is 1:6. While fins with equilateral triangular holes can obtain better convective heat transfer effect as long as the open area ratio is greater than 1:7. Fins with elliptical holes do not significantly improve the heat transfer effect. On the basis of optimizing the fin layout and structure, the thermal performance of the improved Trombe wall during the 8:00∼16:00 period and its impact on indoor thermal comfort of the building were studied, and the energy-saving performance of the plan was discussed. Compared with the Trombe wall room with no fins, the improved Trombe wall can improve the heat teransfer efficiency and the building energy saving rate by 68.50 % and 53.57 %, respectively. The improved Trombe wall can only ensure the indoor thermal comfort in limited several hours, in the rest of time, the residents should add clothing to keep warm. These conclusions have an important effect of engineering guidance and great realistic meanings for promoting the process of solar building integration and achieving the “carbon peak and carbon neutrality” target.

On the localization of a new phase domain in the vicinity of an elliptical hole

AbstractGrowth of a new phase domain induced by phase transformations in the vicinity of an elliptical hole as a stress concentrator is considered. An elastic solid is subjected to external strain at which no phase transformations occur in the absence of the stress concentrator. The evolution of the interface is described by a kinetic equation that relates the velocity of the interface with a configurational force equal to the jump of the normal component of the Eshelby stress tensor. Various scenarios of the growth of the new phase domain depending on the material parameters of the phases are demonstrated. It is studied how the parameters (Young's moduli, Poisson‘s ratios, transformation strain) affect the distribution of the configurational force along the interface as well as the localization of the new phase domain. It is studied how the new phase growth causes stress relaxation in a body.

Analysis of inner flow and outflow characteristics of different scramjet elliptical holes

ABSTRACT The elliptical hole has the potential to promote jet breakup and improve atomization and mixing quality. The flow behavior in the nozzle and the outflow characteristics have an important influence on the atomization and mixing process of the downstream fuel. Therefore, the inner cavitation flow processes and outflow characteristics for elliptical holes for scramjet engine at injection pressures of 3 MPa and 5 MPa were investigated using the Volume of Fluid (VOF) method and Large Eddy Simulation (LES). The numerical findings demonstrated that the cavitation region and vortex structures of elliptical holes mainly appeared on the long axial plane. The cavitation intensity of elliptical holes was weaker than that of the circular hole. Compared with the circular hole, the gas phase volume fraction of elliptical hole with the aspect ratio of 4 was reduced by about 22.1 and 21.1% respectively under 3MPa and 5MPa injection pressure. The application of elliptical holes inhibited the generation of cavitation and had large mass flow rate and flow coefficient. The mass flow rate of the elliptical hole with the aspect ratio of 4 was the largest, and the mass flow rate increased by about 5.1% compared with that of the circular hole. Elliptical holes showed a smaller velocity coefficient and a larger area coefficient when cavitation existed. The elliptical hole with the aspect ratio of 4 held the smallest velocity coefficient and largest area coefficient, with the difference of 12.1% and 18.9% respectively from the circular hole. Another important point was that elliptical holes enhanced the turbulent disturbance at the hole outlet, which facilitated the breakup of downstream jet.

Comprehensive evaluation on conjugate heat transfer and thermal stress performance of film cooling

Film cooling is a commonly used cooling technology in gas turbines, which could reduce heat load by spreading cooling air. However, it faces the problem of stress concentration in structures with holes. The present work focuses on conjugate heat transfer and thermal stress characteristics for a flat film cooling plate through an experimentally validated numerical approach. It discusses the effect of three geometry factors: inclination angle, compound angle, and ellipticity. An engine case simulation and a laboratory case simulation are compared to validate the analogy principle of conjugate heat transfer and thermal stress analysis derived from theoretical analysis. According to the analogy principle, the laboratory flat plate film cooling cases are set to conduct numerical studies. The maximum Mises stress of the film hole is equal to the product of the reference stress and the stress concentration factor. The reference Mises stress is proportional to the overall cooling effectiveness. The stress concentration factor is mainly related to the geometry of the film hole. Reducing the inclination angle of the film hole from 90° to 30° increases the overall cooling effectiveness and drastically increases the stress concentration factor from 2.7 to 5.5. Based on a cylinder hole with a 30° inclination angle, increasing the compound angle enhances the overall cooling effectiveness and slightly increases the stress concentration factor. Based on a cylinder hole with a 30° inclination angle, increasing the ellipticity increases the overall cooling effectiveness and reduces the stress concentration factor. With the increase of ellipticity from 0 to 4, the stress concentration factor decreases from 5.5 to 2. Elliptical film holes are ideal for future low-stress, high-cooling-efficiency turbine blades to extend the life of cooling vanes.

Influence of Punch Servo Path on Elliptical Hole Flange Forming

This study investigated the process of forming an elliptical hole flange by using a SPFC780Y high-strength steel sheet with a material thickness of 1 mm. Three servo motion paths on a servo press were compared with a traditional crank motion path on a conventional press. Four punch motion paths were analyzed, namely a crank motion path on a conventional press (type T), a servo motion path with a 3-mm downward motion followed by a 0.5-mm upward motion (type S3), a servo motion path with a 2-mm downward motion followed by a 0.5-mm upward motion (type S2), and a servo motion path with a 1-mm downward motion followed by a 0.5-mm upward motion (type S1). The finished products of an elliptical hole flanging process were evaluated in terms of thickness, force-displacement, stress, strain, and springback. The results reveal that the products produced using the evaluated servo motion paths were superior to those produced using the evaluated crank motion path.

Nominal strength of notched pseudo-ductile specimens

Quasi-brittle materials like composites are notch-sensitive, and the stress concentration factor (Kt) determines their strength knock-down. To alleviate this notch sensitivity, researchers are pursuing pseudo-ductility to stimulate stress redistribution around the notches. However, how such a pseudo-ductile material reduces Kt or improves the nominal strength (σN) in notched sub-components (centre crack, elliptical hole and open hole) is unclear. In this work, we analytically determine the Kt of typical notched specimens made of an idealised pseudo-ductile material and show its accuracy using Finite Element (FE) models. Kt increases after the specimen transitions from localised yielding to net-section yielding. Then, we elucidate the size-effect behaviour of the notched sub-components using FE models. The study reveals that the notched pseudo-ductile specimens recover higher σN than their linear elastic counterparts, in proportion to the Kt. However, pseudo-ductility decreases the σN for smaller specimens, and the notch shape is unimportant in this region.

Wang tiles enable combinatorial design and robot-assisted manufacturing of modular mechanical metamaterials

In this paper, we introduce a novel design paradigm for modular architectured materials that allows for spatially nonuniform designs from a handful of building blocks, which can be robotically assembled for efficient and scalable production. The traditional, design-limiting periodicity in material design is overcome by utilizing Wang tiles to achieve compatibility among building blocks. We illustrate our approach with the design and manufacturing of an L-shaped domain inspired by a scissor-like soft gripper, whose internal module distribution was optimized to achieve an extreme tilt of a tip of the gripper’s jaw when the handle part was uniformly compressed. The geometry of individual modules was built on a 3 × 3 grid of elliptical holes with varying semi-axes ratios and alternating orientations. We optimized the distribution of the modules within the L-shaped domain using an enumeration approach combined with a factorial search strategy. To address the challenge of seamless interface connections in modular manufacturing, we produced the final designs by casting silicone rubber into modular molds automatically assembled by a robotic arm. The predicted performance was validated experimentally using a custom-built, open-hardware test rig, Thymos, supplemented with digital image correlation measurements. Our study demonstrates the potential for enhancing the mechanical performance of architectured materials by incorporating nonuniform modular designs and efficient robot-assisted manufacturing.

Towards reduction of bending-extension coupling in unsymmetrical laminates using multi-objective heat transfer search

The main advantage of composite materials is the ability to tailor the properties of stacking sequences. Unsymmetrical laminate involves an arbitrary even or odd number of fiber layers oriented at different angles wherein identical fiber orientation above and below mid-surface does not exist. In the case of these laminates, the coupling deformation is undesired during mechanical loads and symmetrical laminates may not be the best solution for all cases. In this work, an effort has been made to present the methodology to minimize the end effects of bending-extension coupling in the case of unsymmetrical laminates to make it widely applicable. The infinite plate containing the circular and elliptical hole is studied with various in-plane loading conditions. The end effect of bending-extension coupling is presented by the multi-objective problem of minimization of the normalized tangential force and moment. The non-dominated sorting heat transfer search algorithm is employed to solve this optimization problem wherein TOPSIS decision-making technique is used to obtain the best values from the Pareto solution. The different cluster-based methods are proposed to utilize the unsymmetrical laminates most effectively. The effects of these clusters on the bending-extensional coupling are investigated and results reveal that cluster design presenting each fiber angle value distinctly is the best design among all recommended in the present investigation. More than 70% of the bending-extensional coupling is reduced in most cases. A unique correlation is found between the cluster design and fiber angles of the optimum stacking sequences. The proposed approach and designs will support the potential use of unsymmetrical laminates by improving properties through tailoring stacking sequences.

Modeling the complexity of elliptic black hole solution in 4D using Hamiltonian Monte Carlo with stacked neural networks

In this paper, we study the black hole solution of self-similar gravitational collapse in the Einstein-axion-dilaton system for the elliptic class in four dimensions. The solution is invariant under space-time dilation, which is combined with internal SL(2,R) transformations. Due to the complex and highly nonlinear pattern of the equations of motion in the physics of black holes, researchers typically have to use various numerical techniques to make the equations tractable to estimate the parameters and the critical solutions. To this end, they have to ignore the numerical measurement errors in estimating the parameters. To our knowledge, for the first time in the literature on axion-dilation systems, we propose to estimate the critical collapse functions in a Bayesian framework. We develop a novel methodology to translate the modelling of the complexity of the elliptic black hole to a sampling problem using Hamiltonian Monte Carlo with stacked neural networks. Unlike methods in the literature, this probabilistic approach enables us not only to recover the available deterministic solution but also to explore possibly all physically distinguishable self-similar solutions that may occur due to numerical measurement errors.

Are the direct and indirect BEM/BIEMs equivalent?

For a long time, direct and indirect BEM/BIEMs were always unified and seemed equivalent in real implementation for ensuring the solution. Regarding the solution space and the numerical aspects in linear algebra, it is interesting to find that they are not fully equivalent. To demonstrate this finding, antiplane shear problems containing the elliptical rigid inclusion and hole as well as rigid-line inclusion and line crack were given to demonstrate the non-equivalence between the direct and indirect BEM/BIEMs. It is interesting to find that nonunique boundary densities may yield the unique field solution in both analytical derivation and numerical implementation. The mechanism was analytically studied and numerically performed by using the degenerate kernel and the singular value decomposition technique, respectively. Besides, the Fredholm alternative theorem was employed to examine the solvability condition in both the indirect boundary integral equation method and indirect boundary element method. For continuous system and discrete system, we can explain why the boundary density does not match the exact solution but the field solution is always acceptable when setting ξ0 = 0 in the beginning of the derivation of BIE. Two approaches, direct and indirect BEM/BIEMs, show the non-equivalence of solution in case of degenerate boundary and degenerate scale.

Analytical Solution of the Interference between Elliptical Inclusion and Screw Dislocation in One-Dimensional Hexagonal Piezoelectric Quasicrystal

This study examines the interference problem between screw dislocation and elliptical inclusion in one-dimensional hexagonal piezoelectric quasicrystals. The general solutions are obtained using the complex variable function method and the conformal transformation technique. When the screw dislocation is located outside or inside the elliptical inclusion, the perturbation method and Laurent series expansion are employed to derive explicit analytical expressions for the complex potentials in the elliptical inclusion and the matrix, respectively. Considering four types of far-field force and electric loading conditions, analytical solutions for various specific cases are obtained by using matrix operations. Expressions for the phonon field stress, phason field stress, and electric displacement are given for special cases, including the absence of a dislocation, the presence of an elliptical hole, and the interference between a screw dislocation and circular inclusion, as well as the case of a circular hole. The design and analysis of quasicrystal inclusion structures can benefit from the results of this work.

Evaluation of ultimate bearing capacity of large-scale perforated beams with variable cross-section: Experimental verification and numerical simulation

In order to meet the requirements of outfitting layout and light weight, circular or elliptical holes need to be opened on the web of the hull beam. Excessive opening will lead to stress concentration and reduce the bearing capacity of the beam. For the super-standard openings, the general strengthening method cannot guarantee the ultimate bearing capacity of the beam, and locally increasing the web to form a variable cross-section beam can compensate for the lost bearing capacity. In the present paper, the three-point bending load tests of variable cross-section opening beams and equal cross-section beams are carried out. Combined with the results of nonlinear finite element analysis, the ultimate bearing capacity and failure mode of transverse bending are compared, and it is verified that the ultimate bearing capacity of beams with variable cross-section openings is better than that of beams with equal cross-section. By changing the cross-section size and optimizing the transition form, the variable cross-section perforated beam is further improved and optimized to enhance the ultimate strength.

Mid-infrared water pollutant sensor based on SPR-PCF

In this paper, a highly sensitive water pollutant optical sensor is proposed and analyzed. The suggested sensor consists of photonic crystal fiber with a core surrounded by four elliptical holes infiltrated with the studied analyte (pure/polluted water sample). In addition, two gold nanorods are mounted horizontally at the inner surfaces of two horizontal elliptical holes. The proposed sensor can efficiently detect dissolved pollutants in water such as nitric acid ({mathrm{HNO}}_{3}) with concentrations of 14, 23 and 35% and {mathrm{H}}_{2}{mathrm{O}}_{2} with concentrations of 7, 15 and 30%. The dissolved pollutants in water (analyte) have refractive indices (RIs) in the range of 1.350–1.355 in the mid infrared regime from λ = 2200 nm to λ = 3500 nm. A fully vectorial finite element method (FVFEM) is employed for the modal analysis of the reported structure. The geometrical parameters are studied to maximize the RI sensitivity where a high sensitivity of 36,000 nm/RIU is achieved between the studied RIs of 1.350 and 1.355. The obtained RI sensitivity is higher than those of the recent reported sensors in the literature especially those operating in the mid infrared wavelengths.

Explosion resistance performance of reinforced concrete box girder coated with polyurea: Model test and numerical simulation

To study the anti-explosion protection effect of polyurea coating on reinforced concrete box girder, two segmental girder specimens were made at a scale of 1:3, numbered as G (without polyurea coating) and PCG (with polyurea coating). The failure characteristics and dynamic responses of the specimens were compared through conducting explosion tests. The reliability of the numerical simulation using LS-DYNA software was verified by the test results. The effects of different scaled distances, reinforcement ratios, concrete strengths, coating thicknesses and ranges of polyurea were studied. The results show that the polyurea coating can effectively enhance the anti-explosion performance of the girder. The top plate of middle chamber in specimen G forms an elliptical penetrating hole, while that in specimen PCG only shows a very slight local dent. The peak vertical displacement and residual displacement of PCG decrease by 74.8% and 73.7%, respectively, compared with those of specimen G. For the TNT explosion with small equivalent, the polyurea coating has a more significant protective effect on reducing the size of fracture. With the increase of TNT equivalent, the protective effect of polyurea on reducing girder displacement becomes more significant. The optimal reinforcement ratio, concrete strength, thickness and range of polyurea coating were also drawn.

An Improved Finite Element Model to Study Stress Concentration Around an Elliptical Cutout in Pressure Vessel : Application- Part II

The application of finite element method (FEM) to the solution of cutout and inclusion problems in Filament Wound Fibre Reinforced Plastic (FWFRP) pressure vessel is considered. The analysis of pressurised laminated composite shell, which can be regarded as a heterogeneous body consisting of a finite number of orthotropic layers bonded together, with an elliptical hole is carried out. The influence of uniform shear force distribution along the hole boundary is studied. The numerical results of pressurised laminated composite shell with transverse elliptical hole filled by edge bonded elastic cover are also presented. Predicted stress distribution through the thickness of composite shell with cutout/inclusion at critical locations on the hole boundary is presented in graphical form and discussed.

Metallo-Dielectric Millimeter-Wave Huygens’ Quarter-Wave and Half-Wave Plates

A novel metallo-dielectric Huygens’ unit cell is proposed that can be designed to operate either as a quarter-wave plate (QWP) or as a half-wave plate (HWP). The unit cell is based on a single-layer perforated dielectric, with straight (non-metallized) and 45° (metallized) elliptical holes. The novelty of the unit cell is its suitability for millimeter-wave implementation in printed-circuit board (PCB) fabrication due to the absence of metallic patterns of small line widths and gaps. As an example of their applicability, the wave plates are demonstrated in the near-field of 60-GHz band diffusion-bonded slot array antennas. The unit cell operating as a QWP is demonstrated in full-wave simulations and experimentally for linear-to-circular polarization conversion, whereby the combination of a linearly-polarized (LP) antenna and the QWP produces a circularly-polarized (CP) wave. Measurement results of the antenna and the QWP show ≤ -10-dB reflection from 59 to 63 GHz (6.6%), ≤ 3-dB axial ratio from 59.5 to 61.5 GHz (3.3%), and an overall efficiency ≥ 77% from 59.5 to 61.5 GHz. The unit cell operating as a HWP is demonstrated in full-wave simulations for polarization rotation of the LP antenna, and for changing the sense of rotation of a right-hand CP antenna into left-hand circular polarization.