Single Circular Hole Research Articles

A Review of Flow Field and Heat Transfer Characteristics of Jet Impingement from Special-Shaped Holes

The jet impingement cooling technique is regarded as one of the most effective enhanced heat transfer techniques with a single-phase medium. However, in order to facilitate manufacturing, impingement with a large number of smooth circular hole jets is used in engineering. With the increasing maturity of additive technology, some new special-shaped holes (SSHs) may be used to further improve the cooling efficiency of jet impingement. Secondly, the heat transfer coefficient of the whole jet varies greatly on the impact target surface. The experiments with a large number of single smooth circular hole jets show that the heat transfer coefficient of the impact target surface will form a bell distribution—that is, the Nusselt number has a maximum value near the stagnation region, and then rapidly decreases exponentially in the radial direction away from the stagnation region. The overall surface temperature distribution is very uneven, and the target surface will form an array of cold spots, resulting in a high level of thermal stress, which will greatly weaken the structural strength and life of the equipment. Establishing how to ensure the uniformity of jet impingement cooling has become a new problem to be solved. In order to achieve uniform cooling, special-shaped holes that generate a swirling flow may be a solution. This paper presents a summary of the effects of holes with different geometrical features on the flow field and heat transfer characteristics of jet impingement cooling. In addition, the effect of jet impingement cooling with SSHs in different array methods is compared. The current challenges of jet impingement cooling technology with SSHs are discussed, as well as the prospects for possible future advances.

Buckling analysis of thin plates with circular cut-outs for sustainable ventilated food packaging design

Thin plates with circular cut-outs are widely used in engineering structures such as bridges, construction, and ventilated corrugated paperboard boxes in food packaging. This study investigates the critical buckling loads of thin elastic plates comprised of a single circular hole at different locations and with different sizes. To determine the critical loads, experimental tests and finite element method simulations are conducted. The vertical location and the diameter of the hole impact the buckling results significantly. The results indicate a significant correlation between the experimental and finite element data. The study develops second and third order polynomial formulas that predict buckling loads. In this study, corrugated paperboard plates were used as samples to gain insights into ventilated food packaging designs, aiming to enhance their buckling strength while reducing packaging material consumption for packaging sustainability purposes. The solution proposed in this study can be applied to predict the buckling of other elastic thin plate structures with a circular hole, relevant to industries such as construction and aerospace.

Isogeometric analysis of stress concentrations and failure strength in composite plates with circular holes using RHT-splines

This paper studies the stress concentration factors (SCFs) to predict the first ply failure (FPF) of cross and angle-ply laminate composite plates with single circular holes. The rational splines over hierarchical T-meshes (RHT-splines) were chosen as a surface design methodology for Isogeometric Analysis (IGA) due to their ability to exactly represent the geometry, efficient and simple local refinement algorithm, and reduction of the superfluous control points of the NURBS surface. The Bézier extraction concept was used as an element structure for IGA that allows mapping the Bernstein polynomials basis functions on Bezier elements to be performed on RHT-splines geometries. Several failure criteria and composite materials are employed in numerical examples for different fiber orientation angles through Matlab® implementation. The results obtained by the IGA based on RHT-splines showed very good conformity with those obtained by the analytic approach and finite element method (FEM) published in the literature, which demonstrates the robustness and accuracy of the IGA using RHT-splines and provides an effective and realistic way to determine SCF and failure strength. The Matlab® program for the analytical approach and failure theories is made an open-source and can be downloaded from (Github Website).

Numerical simulation of the effect of internal hole defect size on the mechanical properties of limestone.

To better understand the effect of the size of hole defects on the mechanical properties of a rock mass, the two-dimensional particle flow discrete element code (PFC2D) is applied to establish rock mass models with single circular hole defects of different diameters. Uniaxial compressive strength (UCS) tests are conducted on each model by only taking the defect size (area) as a variable. This study analyzes each model’s stress-strain, contact force chain, crack evolution, meso-damage and failure, and mechanical properties. The results showed that with the size enlargement of the circular hole defects, each model’s UCS and elastic modulus gradually decrease, and the defect size is negatively correlated with the mechanical strength of the rock samples. The size of the hole defects affects the entire process of contact force chain and crack evolution. The larger the aperture dimension of the circular hole defects in each model, the greater the concentration degree of the contact force chain, the earlier the crack initiation, and the higher the degree of crack coalescence in the post-peak stage. The number of cracks decreases as the hole size increases, and the model is more prone to failure. Rock models’ strength and failure characteristics with different numbers and arrangements of hole defects are discussed under the same defect area condition.

Fountain fringe field switching (FFFS) for wide viewing angle LCDs

To reduce or completely remove the viewing angle dependence of liquid crystal (LC) displays and devices, we have recently introduced a new electrode structure for LC displays. This electrode structure has openings (holes) in the pixel electrode (PixE) for generating fringe electric field with azimuthal degenerated distribution of the field lines around each hole, resembling a fountain. Such a field is promoting azimuthally degenerated switching of the LC molecules and thus generation of images with 360° viewing angle constant contrast when a pair of crossed circular polarisers are used. A theoretical model of the fountain fringe field, generated around a single circular hole and plurality of such holes in the PixE, is presented.

Stress analysis of an infinite plate with single hole by using Airy’s stress function

To design the machines and structures for optimum material utilization, analysis is required from stress point of view. Stress analysis is a fascinating subject which deals with finding the stress and strain. Also, the displacement distribution in solid component with external forces acting on it is also determined. Analysis of stresses in components and structure members when loads are applied provide help in determination of the magnitude and direction of stresses at various points. For most engineering components stress distribution is never uniform rather it is frequently complex. The reason may be irregularities in cross section, presence of cracks or opening, other material defects present in the component, etc. The present study deals with analyzing the stress concentration in an isotropic infinite plate with a circular hole in it. The load applied on this plate is biaxial and stress concentration is determined using analytical method and the results obtained are compared with ANSYS 10. For infinite plate with single circular hole, Airy’s stress function is used to calculate the stress concentration.

Applicable Formulas for Shear and Thermal Buckling of Perforated Rectangular Panels

The goal of this study is to create semiempirical formulations for predicting thermal and shear buckling loads of perforated rectangular isotropic panels for eight combinations of boundary conditions. The finite element method (FEM) was used to develop and evaluate empirical formulations. In this study, the influences of plate aspect ratios, boundary conditions, and perforation sizes on the buckling strength of perforated panels subjected to shear and thermal loads are investigated. The proposed formulas will enable consistent and reliable computation of the buckling loads for perforated rectangular panels without the need for complex calculations. The results of the empirical equations were found to be reasonably consistent with the outcomes of finite element analysis (FE) and findings from the literature. Various perforation patterns are investigated, ranging from a single circular hole up to 441 circular holes distributed across the plate. The results show that plates with a single central cutout have lower shear buckling loads than plates with multiple holes and an equal total cutout area.

Numerical Study on Strength and Failure Behavior of Rock with Composite Defects under Uniaxial Compression

The cracks and holes in underground engineering are the critical factors that cause the instability of the surrounding rock. It is helpful to control the stability of surrounding rock to study the samples with combined defects of cracks and holes. In this study, PFC 2D is used to analyze the numerical models. Seven combined models of single circular hole and double cracks with different angles are established, and the fracture angle varies from 0° to 90° with an interval of 15°. First, uniaxial compression experiments and numerical simulations are carried out in the 0° defect combination model, and the microscopic parameters of PFC 2D are determined. Then, the numerical simulations of seven defect models under uniaxial compression are carried out, and the crack development law and acoustic emission characteristics of different defect combination models are studied. The failure modes, mechanical behavior, and stress states are studied. The displacement vector distributions of different defect combination models are analyzed; it is found that there are three main types of macro cracks in the defect combination samples. The results show that the combined defects reduce the strength of the model. Meanwhile, the distributions of the stress and displacement are changed by the cracks with different angles in the defective models.

Machine learning solutions of stress concentration factors in perforated plate with single circular hole

The discontinuities such as holes, grooves, notches and fillets in the structural geometry in structures would lead to significant increase of stress level, which can be represented by stress concentration factor (SCF), and further influence the strength of structures. Therefore, SCF plays a vital role in quantitatively understanding the influence of discontinuities on the peak stress. However, analytical or empirical solutions for predicting localized high-stress around the discontinuities are usually difficult to be derived, owing to the complex interaction of the specific boundary conditions and the discontinuities. In this work, machine learning (ML) solutions of SCF of circular holes in a finite perforated plate under tension are modeled using finite element analysis and back propagation neutral network (BPNN) technique. The locations and sizes of circular holes are input as input variables, and the SCFs are target variable. The feasibility and accuracy of the model are demonstrated through numerical examples. It’s found that the developed ML approach base on BPNN technique can provide accurate prediction of SCF value for each set of structural parameters, and vice versa.

Effect of protective layer deposition in cross-sectional analysis of focused ion beam in germanium substrate

In this work, a single micro-size circular and rectangular holes were fabricated in phosphorus/tin implanted germanium substrate using ion milling of FIB, for potential application in photonic crystal and FINFET. One of the important analysis that need to be done in the future is a cross-sectional analysis in order to evaluate the milling rate of material, redeposition of milled material, and the quality of the milled surface in the pattern structure. However, a well-known practise in preparing a cross-sectional sample for transmission electron microscope analysis using FIB involves a deposition of protective layer on the substrate surface before performing the cross-sectional ion milling, in order to prevent the surface damage. Taking this into consideration, this work performed a preliminary study to analyze the effect of depositing a protective layer onto the hole for performing FIB cross-sectional analysis of the fabricated hole structures. Two-step deposition technique of platinum layer involving electron beam, followed by ion beam was performed on the hole prior to the cross-sectional milling. Hole structure without protective layer was also prepared as a comparison. It is found that although the depth of the milled area can be evaluated in both cross-sectioned holes with/without protective layer, an evaluation on roughness and redeposition are difficult, specifically in the one with protective layer. While the existence of secondary damage might affect the quality of milled surface during the cross-sectional milling in the sample without protective layer.

CFD Assisted Investigation on Adiabatic Film Cooling Effectiveness over a Flat Plate

Abstract The paper examines downstream heat transfer performance of a cooling hole in a flat plate computationally at nil pressure gradients. In the simulation both local and transverse averaged cooling effectiveness in the flat surface were studied for a single circular hole geometry over a range of blowing ratios 0.33, 0.50, 0.83 and 1.0. Four different coolant jet angles namely 900, 600, 450and 300 were chosen for the present study. Commercial FLUENT software has been utilized for the numerical analysis applying standard K-∊ turbulence model. The computational model was validated against benchmark experimental results and found a good match with the existing experimental results. It was observed that the film cooling effectiveness varies directly with increment in blowing ratios up to a specific limit and then reduces. It also indicated that film cooling effectiveness increases upon decrease in coolant jet angle. At higher blowing ratios jet lift off phenomena and intermixing of coolant and mainstream flow deteriorates the effectiveness. The work concludes with optimum angle and blowing ratio for maximum cooling effectiveness.

Pinch-off masses of very viscous fluids extruded from dies of arbitrary shape

The extrusion of slender very viscous fluid cylinders from dies of arbitrary geometry is modeled to approximate the mass of the first drop to pinch off. The model neglects inertia, which, although important to the dynamics near pinch-off, does not have a significant impact on the drop mass. Extrudate swell is also assumed to be negligible. The model is able to compute the pinch-off mass for fluid cylinders with cross-sectional geometries of any connectivity. By way of illustration, pinch-off masses are computed for epicycloidal cross sections, two touching circular rods, and circular cylinders with a single circular hole placed both centrally and off-centre. It is shown that the drop mass may be controlled by altering either the extrusion conditions or the die geometry.

Drainage of liquid from a small circular hole in a vertical wall

In this work, the initiation and cessation of flow from a hole in a vertical wall was examined. Water, ethylene glycol or isopropyl alcohol was slowly added to polypropylene (PP) or fluorinated ethylene propylene (FEP) containers with a single circular hole in their side wall. If the hole was sufficiently small, liquid rose past the hole. No liquid flowed through the hole until a critical height was reached. Flow generally ceased before the level of the liquid reached the bottom of the hole. The onset and cessation of flow was successfully modeled as a balance between the hydrostatic pressure in the bulk liquid and the Laplace pressure of the air-liquid interface bulging from the hole.

Fracture evolution characteristics of sandstone containing double fissures and a single circular hole under uniaxial compression

The uniaxial compression experiments on the sandstone samples containing double fissures and a single circular hole were carried out by using electro-hydraulic servo universal testing machine to investigate the effect of rock bridge angle β and fissure angle α on mechanical properties and evolution characteristics of cracks. The results show that the peak strength, peak strain and elastic modulus of defected specimens decrease comparing with those for intact sample, and show a decreased trend firstly and then increase with β changing from 0° to 90°. The peak strength and elastic modulus achieve the minimum value as the rock bridge angle is 60°, while the peak strain reaches the minimum value with the rock bridge angle of 45°. The crack initiation of tested rock samples occurs firstly in stress concentration areas at tips of prefabricated fissures under uniaxial compression, and then propagates constantly and coalescences with the prefabricated hole. Some secondary cracks initiate and propagate as well until buckling failure happens. The rock bridge angle has a great influence on crack initiation, coalescence, final failure mode, crack initiation stress and transfixion stress. The peak strength varies significantly, while the elastic modulus and peak strain change slightly, and the failure modes are also different due to the influence of fissure angle.

Simple estimation of effective elastic constants for thin plates with regular perforations and an application to the vibration of distillation column trays

The horizontal perforated sheet metal plates are commonly used in the process industries as trays in distillation columns, important internal parts for fractionating the input liquid mixture. Normally, the operating performance of such trays is satisfactory. However, cases have been reported of abnormally high levels of tray vibration during operation at particular conditions. The trays then experienced fatigue cracking accompanied by the loosening of bolts and fixings, which led to expensive failures. The excitation of structural resonance was suspected as a component in flow-induced vibration. Using linear stress superposition, a simple but robust analytical method is developed to provide high-quality predictions for the stress and strain distributions for in-plane loaded thin perforated plates with periodic hole arrangements. This approach is built on the classical solution for the elastic stress field around a single circular hole in a large plate. The perforated plates with square penetration patterns are investigated in this article, although the same approach is applicable to any regular penetration pattern. Stress concentration factors as well as the effective elastic constants, which can be used to describe the bending properties of the perforated plates, are then verified against both the established theoretical solutions and the results from finite element simulations. Excellent agreement to both previously published physical experiments and complex modelling is observed in all cases, with small-to-medium (up to 40%) hole-area fraction. The proposed analytical method is much simpler and computationally efficient than finite element analysis. The computed effective elastic constants are used in a finite element modal analysis to estimate the free vibration frequencies of a stiffened distillation column tray example; the first 30 vibration modes are found to be almost uniformly distributed between 25 and 70 Hz, which matches the vibration frequency range reported from plant operations.

Lattice Approach in Continuum and Fracture Mechanics

This study reveals some aspects of lattice formulations to analyze the strain concentration of a famous classic problem in solid mechanics at two different mechanics perspectives: continuum and fracture. A 2D plane stress square panel with a single circular hole is discretized based on Voronoi tessellation. A superelliptic formulation is used to distribute lattice computational points over the panel. From the perspective of linear elasticity under uniaxial and biaxial loading, translational and rotational degrees-of-freedom are considered at each computational node of the lattice to obtain strain concentration factors (SCFs) around the circular perforation. It is observed that the lattice approach is able to approximate the elastic SCFs of three, four, and two in uniaxial, biaxial shear, and equibiaxial tension loadings, respectively. To study the linear elasticity and fracture mechanic (LEFM) and Griffith energy balance in uniaxial loading, a brittle lattice erosion technique is used to compute the energy release rate determined by change in the global stiffness matrix of the mesh with respect to crack extension. This fracture energy is then used to determine the mode I stress intensity factor of the crack emanating from the hole which is validated by the analytical formulation for the same problem. The comparison shows that both methods give very close results for the mode I stress intensity factor. Being simple in terms of constitutive formulation and failure criterion for erosion of brittle material, and also using a propagating crack extension approach, the lattice formulation is used to determine the fracture properties of cohesive/frictional material.

Defect-controlled vortex generation in current-carrying narrow superconducting strips

We experimentally study the effect of a single circular hole on the critical current Ic of narrow superconducting strip with width W much smaller than Pearl penetration depth Λ. We found non-monotonous dependence of Ic on the location of a hole across the strip and a weak dependence of Ic on the radius of a hole in the case of a hole with (ξ is a superconducting coherence length) which is placed in the center of strip. The observed effects are caused by competition of two mechanisms of destruction of superconductivity—the entrance of vortex via the edge of the strip and the nucleation of the vortex–antivortex pair near the hole. The mechanisms are clearly distinguishable by a difference in dependence of Ic on weak magnetic field.

Local buckling of aluminium and steel plates with multiple holes

This paper considers local buckling of perforated square aluminium plates. Plates of various slenderness with simply supported edges and subjected to uniaxial compression are studied using the finite element method. Different perforation patterns are investigated, from a single circular hole to 25 circular holes distributed over the plate. A number of aluminium alloys are considered and compared to steel grade A36. Results show that the resistance of the plates containing a single central cut-out is higher than that of plates with more holes and of equal total cut-out size. A further refinement beyond 5 holes does not influence the resistance.

Nest Biology and Demography of the Fungus-Growing Ant Cyphomyrmex lectus Forel (Myrmicinae; Attini) at a Disturbed Area Located in Rio Claro, SP, Brazil

Cyphomyrmex ants are a basal group of small fungus-growers (Myrmicinae:Attini), which differ profoundly from their most studied relatives Atta and Acromyrmex. Our objective was to investigate the nest biology and demography of the fungus-growing ant Cyphomyrmex lectus in a transitional area (savanna-forest) disturbed by an annual fire regime, in Southeast Brazil. The colonies of C. lectus were located close to each other (mean distance between nests, 3.38 ± 2.75 m). Its external nest structure consisted of a single circular nest-entrance hole but without a conspicuous nest mound. Nests were relatively simple consisting of a single well-formed chamber and a single gallery connecting to the nest entrance. No relationships were found between ant number per colony and gallery length, as well as chamber volume. Nonetheless, we detected an effect of the ant number per colony on chamber depth. In this sense, a deeper chamber could warrant a better protection against fire, natural enemies and offer favorable micro-conditions to yeast culture. The colonies of C. lectus are small (a mean of 70 ± 49.4 individuals/colony). Alates, larvae and pupae were found only in one out of eight colonies. A single dealate queen per colony was observed strongly suggesting that this species is monogynous. Further studies could evaluate whether (1) nests density differ before and after fire periods, (2) fire occurrence affects the survival and establishment rate of new colonies, as well as (3) the nest microclimatic conditions necessary to yeast culture.

English

Gear drive is used to transmit power from one shaft to another when distance between two shafts is very small. There are several failure mechanisms for spur gears. Bending failure of the teeth is one of the main failure modes. In this research work, various stress relieving features are studied. Single circular holes, two circular holes, one circular hole in combination with elliptical hole are used to study the effect of these features in stress reduction. Modeling is done with drafting software AutoCAD. Finite element based software ANSYS is used for this work. Initially using AGMA method bending stresses were determined analytically. A good agreement was found between analytical & finite element results of bending stress.