Circular Hole Research Articles

Experimental analysis of pressure deviation-induced film cooling effectiveness deviation in pressure sensitive paint measurement

The use of the Pressure Sensitive Paint (PSP) measurement method allows for obtaining dense, completely adiabatic film cooling effectiveness (η) results. In order to adapt to the increasing trend of high-speed and complexity in the application scenarios of film cooling, the pressure deviation-induced film cooling effectiveness deviation in PSP measurements needs to be quantified and corrected. Initially, two different jets of specific materials were injected into a dual-hole flat plate test piece. The pressure difference at corresponding positions of the two jet flows was measured to demonstrate that, compared to air, a ternary oxygen mixed gas better simulated the pressure field of the foreign gas. This illustrates the feasibility of the Test3-OM correction method. Building upon this, the influence of pressure deviation on the accuracy of measurement results was quantitatively evaluated in various scenarios, including a flat circular hole, film holes with a compound angle, a converging slot hole, and film holes at three positions on the blade. The results indicate that the pressure deviation-induced η deviation is non-negligible under conditions of high blowing ratios in most positions. Particularly in the low η region, there is a higher sensitivity to pressure deviation. Generally, there is a negative deviation region near the hole downstream, and a positive deviation region slightly downstream. The generation of deviations stems from variations in density, resulting in different flow patterns of the jet near the wall surface.

Assembly method for curved porous circular workpieces based on multidimensional information fusion: Grid electrode component

To tackle the problems related to the complexities of obtaining depth information for circular workpiece with arc surface and holes, a novel vision guidance method has been introduced to precisely gauge interlayer spacing. The process includes the acquisition and preprocessing of point cloud depth information, along with matching and edge processing. The depth coordinates of the point cloud are subsequently determined. Two-dimensional image processing technology is employed to extract the coordinates of the center of the surface circular hole in the curved porous circular workpiece. The 3D coordinates are generated for guiding the assembly by integrating these datasets. Experiments on grid parts in aviation propulsion systems demonstrate that this method maintains dot matrix spacing within 0.5–1.2 mm, ensures the coaxiality of the center hole, and meets assembly standards. The results confirm the method’s effectiveness for automated assembly of curved porous round workpieces.

The Impact of Circular Holes in Twisted Tape Inserts on Forced Convection Heat Transfer

This study investigated heat transfer and friction characteristics in a forced convection system using wavy twisted tape inserts with circular holes. The inserts, with twist ratios (TR) of 8.5, 7.5, and 6.5, were placed inside a test pipe to create turbulent flow. The tapes measured 700 mm in length and 18 mm in width, while the test pipe had an outer diameter of 35 mm and an inner diameter of 30 mm, with a test section length of 700 mm. Airflow rates were adjusted to achieve different bulk mean temperatures. Experimental data were used to develop new correlations for the Nusselt number and friction factor. The Reynolds number (Re) ranged from 4,000 to 14,000. Comparisons between the wavy twisted tape inserts with varying twist ratios and pitches and a smooth tube showed that the highest heat transfer rate was achieved with a twist ratio of 6.5.

Characteristics of Deformation and Damage and Acoustic Properties of Sandstone in Circular Tunnel Morphology under Varying Inundation Depths

When water damage occurs in a mine, variations in the immersion levels of tunnels at different burial depths can be observed. There is a significant relationship between the stability of the surrounding rock and the depth of immersion. Therefore, studying the deformation and damage characteristics of sandstone with circular holes at varying immersion depths, along with their acoustic properties, plays a crucial role in maintaining the stability of water-rich roadways. The TAW-2000 press and static strain system were utilized to investigate the mechanical properties, crack evolution, and deformation field distribution of sandstone with circular holes at varying immersion depths. Additionally, this study analyzed the impact of immersion depth on the characteristic parameters of acoustic emission. The results indicate that immersion depth is negatively correlated with the compressive strength and modulus of elasticity of sandstone; as immersion depth increases, the duration of the compression and yield phases of the rock samples also increases, while the duration of the elastic phase remains relatively unaffected. Furthermore, greater immersion depths correspond to a decrease in the total number of cracks, although the proportion of tensile cracks increases, making the formation of secondary cracks less likely. The frequency of acoustic emission events (transient elastic waves generated by the formation, extension, or closure of tiny cracks within the rock) shows a closely correlated dynamic with the stress–time curve of the rock sample. The acoustic emission ringing counts generated by rock samples under submerged water conditions tend to stabilize with a slight increase before signs of rupture appear. Additionally, the cumulative total energy of acoustic emissions from the rock samples decreases as the water level rises. These research findings provide significant reference value for addressing issues related to water immersion and the extent of water saturation in roadways within rock engineering.

Study on Mechanical Properties of Steel-Strengthened Bamboo Beams with Webbing Opening

Bamboo beams are often reinforced with built-in steel sections to enhance their strength and load-bearing capacity. In this paper, we studied the effect of different parameters, including the location of the hole, the hole size, and the thicknesses of the steel and bamboo, on the mechanical properties of reinforced beams. The damage patterns, deformation characteristics, and force-transfer mechanisms, as well as the mechanical properties of reinforced beams with different hole shapes, underwent non-linear finite element analysis. The damage sustained by the reinforced bamboo beam differed from that of the traditional bamboo beam; two diagonal points formed a plastic hinge, mainly during the process of shear damage to the hole. It was determined that the hole size and the thickness of the bamboo have the greatest influence on the mechanical properties of the reinforced beam. The damage characteristics of the composited beams with different holes are similar; the bearing capacity of reinforced beams with open square holes is reduced by 10%–25%compared with circular holes.

Extending the Natural Neighbour Radial Point Interpolation Meshless Method to the Multiscale Analysis of Sandwich Beams with Polyurethane Foam Core

This work investigates the mechanical behaviour of sandwich beams with cellular cores using a multiscale approach combined with a meshless method, the Natural Neighbour Radial Point Interpolation Method (NNRPIM). The analysis is divided into two steps, aiming to analyse the efficiency of NNRPIM formulation when combined with homogenisation techniques for a multiscale computational framework of large-scale sandwich beam problems. In the first step, the cellular core material undergoes a controlled modification process in which circular holes are introduced into bulk polyurethane foam (PUF) to create materials with varying volume fractions. Subsequently, a homogenisation technique is combined with NNRPIM to determine the homogenised mechanical properties of these PUF materials with different porosities. In this step, NNRPIM solutions are compared with high-order FEM simulations. While the results demonstrate that RPIM can approximate high-order FEM solutions, it is observed that the computational cost increases significantly when aiming for comparable smoothness in the approximations. The second step applies the homogenised mechanical properties obtained in the first step to analyse large-scale sandwich beam problems with both homogeneous and functionally graded cores. The results reveal the capability of NNRPIM to closely replicate the solutions obtained from FEM analyses. Furthermore, an analysis of stress distributions along the beam thickness highlights a tendency for some NNRPIM formulations to yield slightly lower stress values near the domain boundaries. However, convergence towards agreement among different formulations is observed with mesh refinement. The findings of this study show that NNRPIM can be used as an alternative numerical method to FEM for analysing sandwich structures.

Experimental and numerical research on deformation of square plates with circular holes under blast load

The response and failure of plates under blast loads are critical concerns in engineering. Plates with preformed holes may exhibit significantly different behaviors compared to those without holes, and detailed research on this topic remains limited. In this study, the deformation of square plates with circular holes subjected to blast loads was investigated through experiment and simulation methods. Square plates with circular holes were designed with three hole positions and two hole diameters. Far-field explosion experiments measured the displacement fields of the plates and the overpressure on the plate frame. Subsequently, LS-Dyna simulation models were established using a two-dimensional model to three-dimensional model mapping, with numerical results aligning with experimental results. Additional numerical calculations with larger charge mass supplemented the experimental cases, analyzing the influence of holes on plate response. It was found that the presence of a hole influenced the displacement field, with notable local effects such as significantly increased displacement near the hole. The presence of a hole can shift the position of maximum equivalent plastic strain from the plate edge to the hole edge. The influence of the size and position of a hole on the deformation and equivalent plastic strain were discussed.

Micro-perforated plates constructions with approaching the theoretical limits of its sound absorption performance

Micro-perforated plates resonant absorbers have a considerable theoretical sound absorption bandwidth upper limit. Three types of MPPs with straight holes, including circular holes on thick plate, circular holes on thin plate, and slotted holes on thin plate, are investigated with approaching the theoretical limits of its sound absorption performance. It is demonstrated that thin plates are easy to obtain satisfactory sound absorption performance but hard to get high mechanical strength. Slotted holes are beneficial for extending the sound absorption bandwidth of MPP absorbers. MPPs with straight holes usually require a combination of thin plates, minute holes and high perforation ratios, which is practically difficult to apply on a large scale. Two other types of MPPs with variable cross-sectional holes, fabricated using the subtractive processing method and superposition processing method, are then proposed to achieve perfect sound absorption performance and good engineering feasibility.

Geometrically nonlinear vibrations of plate embedding a large circular acoustic black hole

The concept of acoustic black hole (ABH) designates a decrease in bending stiffness and a localized added damping within a thin structure aiming to localize and efficiently dissipate vibrations. The small thickness results in large amplitude vibrations, which suggests to take into account geometrical nonlinearities. The subject has been previously studied on a beam with a one dimensional ABH. Previous research studied a geometrically nonlinear plate embedding a one dimensional ABH. This study aims at solving the Von Karman equations for a variable thickness plate, via a modal projection using the eigenmodes obtained with a finite element model. The use of a finite element model in this context allows to take into consideration more complex geometries. The methodology is then applied to a rectangular plate embedding a large circular ABH with added damping. The convergence of the nonlinear coefficients is studied and time domain computations show the relative importance of the geometrical nonlinearity.

Experimental study on mechanical and acoustic emission characteristics of red sandstone containing combined flaws of hole-fissure under biaxial compression

To investigate the mechanical behaviour and failure mechanism of flawed rock masses under biaxial stress conditions, a series of biaxial compression experiments are conducted on red sandstone specimens containing combined flaws of the circular hole and perforated symmetric fissure combined with acoustic emission (AE) technology in this work. The results show a close association between the stress-strain curve morphology and confining stress, both the biaxial compression strength and elastic modulus exhibit an upward trend with increasing fissure angle and confining stress. The maximum AE energy and cumulative AE energy both increase with higher confining stress. The crack types in the specimens are identified by analyzing the AF/RA value distribution, revealing a gradual decrease in the percentage of tensile cracks with increasing fissure angle. An AE localization algorithm based on the least absolute value method is applied to pinpoint AE events during biaxial compression, and AE events distribution is analyzed through the Kernel density estimation (KDE). The crack extension behaviour is described based on the movement of the maximum kernel density points, which initially exhibits a progression from both ends of the specimen towards the central region and subsequently from the central fissure tip towards the two ends.

Failure characteristics and pressure relief effectiveness of non-persistent jointed rock mass with holes

In tunnel engineering, the rock mass contains a significant number of irregularly distributed joints, and typically exhibits high energy accumulation, thereby posing a risk of rockburst occurrence. Therefore, it is of paramount importance to investigate the fracture propagation behavior in jointed rock masses and assess the impact of borehole pressure relief on mitigating rockburst occurrences for effective prevention and control measures. This paper focuses on failure characteristics and pressure relief effectiveness of non-persistent jointed rock mass with holes through laboratory testing and numerical simulation. In laboratory experiments, rock samples are prepared to include a range of crack dip angles and circular holes. Then, the crack propagation law of crack inclination and circular hole is studied by AE and DIC technology. The experimental results show that with the increase of fracture dip angle, the peak strength and energy change of the sample decrease first and then increase. Due to the existence of holes, the crack propagation direction of the original crack is changed. After drilling, the strain energy of the sample is obviously reduced, which shows that the drilling pressure relief effect is obvious, which can effectively reduce the energy accumulated inside the rock mass and reduce the risk of rockburst. Finally, the PFC numerical simulation software is used to analyze the micro-failure process and energy change law of the sample from three aspects: the relative position of cracks and holes, the diameter of boreholes and the spacing of boreholes. Further understanding of the energy dissipation law and mechanical behavior characteristics of jointed rock mass provides a reference for exploring the pressure relief effect of rock mass and preventing rockburst.

Investigation of the notch sensitivity of tailorable long fiber discontinuous prepreg composite laminates

Tailorable discontinuous fiber composite laminates provide relative formability beyond that of continuous fiber laminates, while achieving improved mechanical performance over comparable stochastic systems. In this work, the notch sensitivity of engineered prepreg platelet molded composite (PPMC) laminates is investigated using the open-hole tension (OHT) test and compared to available data for stochastic PPMCs and continuous fiber laminates made with the same material. The press-formed thermoplastic composites (AS4/PEKK) were molded with a quasi-isotropic stacking sequence. The discontinuous PPMC laminate was found to be notch insensitive with OHT strengths ranging from 145.4 MPa (CV = 7%) for d/w=0.5 to 229.3 MPa (CV = 9%) for d/w=0.25. The highly ordered meso-structure of the engineered PPMC laminate yields comparatively excellent mechanical properties for relatively thin laminates in contrast to stochastic systems. Both net- and gross-section failures were observed for d/w=0.25, which suggests that the engineered PPMC laminates studied here maintain a degree of inherent, internal stress concentrations that compete with those caused by geometric features such as a circular hole. Computational simulations of the OHT tests with explicitly represented platelets were found to be in good agreement with experimental measurements. The progressive failure analysis was used to conduct a numerical investigation of the stacking sequence and platelet meso-morphology.

The analysis of damage mechanisms and vibration effects caused by cut blasting under various void shapes

The effect of the void shape on cut blasting is investigated by establishing a damage analysis model for a void using an improved calculation formula for stress on the wall of the void. Additionally, an optimization scheme is provided for the “square void cutting theoretical model.” The vibration effect of the rock mass outside the excavation area is simultaneously monitored, and its validity is substantiated through experimental and simulation-based verification. The findings indicate that the variation of q2sinθ over time aligns with the dynamic loading process of wall stress in holes. Under the influence of longitudinal waves, thin-walled circular damage occurs, and tensile effects from reflected waves are influenced by impedance. In a square void cutting model, two-stage stress waves cause tensile shear damage and inward collapse in the rock mass along hole walls. The explosive energy generated by square holes significantly contributes to fragmentation of rock masses. The circular empty-hole cutting model generates significant vibrations in central areas due to resistance. Vibration velocity in 45° direction for circular holes is lower than that for square voids outside cuts while vibration velocity remains equivalent between circular and square holes at 90° direction.

Crack arrest characteristics and dynamic fracture parameters of moving cracks encountering double holes under impact loads

Brittle materials such as rock or concrete contain a large number of micro-cracks, voids, and other defects. Under external impacting loads, the interaction between fissures and holes affects the bearing capacity and stability of Engineering structures. To study the interaction mechanism between moving cracks and circular holes, A large-size semi-circular notched with a fissure and double circular hole (SNFDH) specimen was suggested in this research, and the dynamic fracture tests were carried out on the SNFDH specimens with different double circular hole spacing (35mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, and 70 mm) using a drop hammer impact test device. Crack propagation gauges were employed to track the time and velocity at which the crack propagated along its trajectory. Dynamic Drucker-Prager yield criterion and the cumulative damage failure criterion were used in the numerical simulation of SNFDH concrete materials. The program AUTODYN was employed to simulate the crack growth characteristics when a crack encounters the double hole. The program ABAQUS was applied to calculate the dynamic fracture parameter of cracks. The test results manifest that the crack propagating trajectory has three different characteristics according to the double hole spacing; the double circular hole has an arresting function for a moving crack; the size of the double hole spacing has a significant effect on the crack propagating velocity, crack propagating length, dynamic stress intensity factor and dynamic energy release rate; the configuration of the SNFDH specimen can be used to investigate the crack arrest mechanism when moving crack encountering double holes.

Experimental and numerical study of cold-formed steel beams with web perforations

This study focuses on the experimental and numerical investigation of cold-formed steel (CFS) beams with web perforations to assess their shear performance. Twelve samples were tested, all processed from high-strength, cold-formed steel sheets of grade S235 with a thickness of 1.5 mm. The specimens, designated as CC, were formed by interlocking two C-sections and welded together. Various parameters were analyzed, such as the shear-span ratio, hole depth-to-web height ratio (dh/h), and web height-to-thickness ratio. The experimental setup involved mid-span single-point loading conditions to evaluate the mechanical behavior of the beams. Circular holes with different diameters were strategically placed at the mid-height of the webs in two shear zones. The experimental results were validated using finite element analysis (FEA) conducted in ANSYS, ensuring the accuracy of the finite element model. The findings indicate that the ultimate bearing capacity of the specimens decreases as the hole depth-to-web height ratio increases. When the hole depth-to-web height ratio was small (dh/h ≤ 0.4), the load-deflection curves declined rapidly after reaching the peak. Conversely, for a ratio of 0.5, the curves declined more gradually. Additionally, mid-span deflection decreased as dh/h increased, with significant variation observed for smaller ratios and stabilization for a ratio of 0.5. This research provides a comprehensive understanding of the shear behavior of cold-formed steel beams with web openings. It offers valuable insights into the design and optimization of these structures, contributing to the safe and efficient application of CFS beams in various engineering contexts.

EXPERIMENTAL INVESTIGATION ON THE SHEAR RESISTANCE OF I-SHAPED PERFORATED CONNECTORS IN COMPOSITE BEAMS

Introduction: Steel-concrete composite girders have been widely used in bridges, with the stability of the interface being crucial. Shear connectors and reinforced concrete slabs play a key role as interfaces. Understanding the interaction between the composite beam and slab is essential for predicting the overall system response. It is necessary to optimize the connection between steel beams and reinforced concrete slabs in steel-concrete composite girders and facilitate their assembly and installation on-site, emphasizing their pivotal role in upholding the structural integrity of composite systems. The purpose of the study was to conduct an experimental investigation and a numerical simulation using the finite element method. During the study, the following methods were used: examining the behavior of IPE and IPN perforated shear connectors using push-out tests. The main objective was to analyze how the I-shaped perforated connector, concrete slab, steel beam, and rebar affect the measured slip between the steel beam and concrete slab. To achieve that, specimens with IPE80 or IPN80 shear connectors having circular or long cut holes containing 8 mm or 6 mm diameter steel bars were used to enhance the connector’s resistance against uplift forces. The test setup follows Eurocode 4 guidelines, focusing on hole shape and anti-lift rebar diameter parameters. The predominant failure modes were mainly dictated by the crushing of the concrete slab. As a result, it was found that the hole geometry of IPE and IPN perforated shear connectors significantly impacts shear load capacity and ductility. The long cut hole shape in IPE and IPN perforated shear connectors exhibits superior ultimate load capacity but less interfacial slip compared to the circular hole. The IPE and IPN perforated shear connectors demonstrated satisfactory ductility for all tested hole shapes, and the 3D finite element models are consistent with the test results.

Multiscale Analysis of Sandwich Beams with Polyurethane Foam Core: A Comparative Study of Finite Element Methods and Radial Point Interpolation Method.

This study presents a comprehensive multiscale analysis of sandwich beams with a polyurethane foam (PUF) core, delivering a numerical comparison between finite element methods (FEMs) and a meshless method: the radial point interpolation method (RPIM). This work aims to combine RPIM with homogenisation techniques for multiscale analysis, being divided in two phases. In the first phase, bulk PUF material was modified by incorporating circular holes to create PUFs with varying volume fractions. Then, using a homogenisation technique coupled with FEM and four versions of RPIM, the homogenised mechanical properties of distinct PUF with different volume fractions were determined. It was observed that RPIM formulations, with higher-order integration schemes, are capable of approximating the solution and field smoothness of high-order FEM formulations. However, seeking a comparable field smoothness represents prohibitive computational costs for RPIM formulations. In a second phase, the obtained homogenised mechanical properties were applied to large-scale sandwich beam problems with homogeneous and approximately functionally graded cores, showing RPIM's capability to closely approximate FEM results. The analysis of stress distributions along the thickness of the beam highlighted RPIM's tendency to yield lower stress values near domain edges, albeit with convergence towards agreement among different formulations. It was found that RPIM formulations with lower nodal connectivity are very efficient, balancing computational cost and accuracy. Overall, this study shows RPIM's viability as an alternative to FEM for addressing practical elasticity applications.

Research on the Jet Distance Enhancement Device for Blueberry Harvesting Robots Based on the Dual-Ring Model

In China, most blueberry varieties are characterized by tightly clustered fruits, which pose challenges for achieving precise and non-destructive automated harvesting. This complexity limits the design of robots for this task. Therefore, this paper proposes adding a jetting step during harvesting to separate fruit clusters and increase the operational space for mechanical claws. First, a combined approach of flow field analysis and pressure-sensitive experiments was employed to establish design criteria for the number, diameter, and inclination angle parameters of two types of nozzles: flat tip and round tip. Furthermore, fruit was introduced, and a fluid–structure coupling method was employed to calculate the deformation of fruit stems. Simultaneously, a mechanical analysis was conducted to quantify the relationship between jet characteristics and separation gaps. Simulation and pressure-sensitive experiments show that as the number of holes increases and their diameter decreases, the nozzle’s convergence becomes stronger. The greater the inclination angle of the circular nozzle holes, the more the gas diverges. The analysis of the output characteristics of the working section indicates that the 8-hole 40° round nozzle is the optimal solution. At an air compressor working pressure of 0.5 MPa, force analysis and simulation results both show that it can increase the picking space for the mechanical claw by about 5–7 mm without damaging the blueberries in the jet area. The final field experiments show that the mean distance for Type I (mature fruit) is 5.41 mm, for Type II (red fruit) is 6.42 mm, and for Type III (green fruit) is 5.43 mm. The short and curved stems of the green fruit are less effective, but the minimum distance of 4.71 mm is greater than the claw wall thickness, meeting the design requirements.

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.

Optimization of functionally graded materials to make stress concentration vanish in a plate with circular hole

This paper is devoted to the minimization of the stress concentration factor in infinite plates with circular hole made of functionally graded materials and subjected to a far-field uniform uniaxial tension. Despite the vast literature on the versatility of these materials, the novelty of the results is that the material distribution is not limited to prefixed laws, as in many works available in the literature. Instead, it is assumed to be an unknown piecewise constant function, thus aiming to derive the material distribution by exploiting, at best, the inhomogeneity concept associated with functionally graded materials. After a brief review of the governing equations, the motivation, the statement and the mathematical formulation of the optimization problem are given under the hypothesis of axisymmetric material distribution. Still, the problem could not be solved analytically, therefore a direct transcription approach by the aid of finite difference method has been followed to convert it into a nonlinear programming problem, whose solution has been obtained numerically by dedicated gradient-based solvers. Numerical optimal solutions are reported in graphical forms, thoroughly discussed and validated by means of the finite element method. The developed numerical approach yields a material inhomogeneity obeying a sigmoid-like function and a uniform hoop stress along the radial direction, thus making the stress concentration factor at the rim of the circular hole vanish.