Minimum Section Research Articles

Research on internal flow characteristics of the planar conical tube for valveless piezoelectric micropump

Abstract As the most commonly used driving and executing components in microfluidic systems, valveless piezoelectric micropumps have broad application prospects in numerous fields. The steady and unsteady characteristics of planar conical tubes for valveless piezoelectric micropumps were simulated using CFX software at different pressure amplitudes and driving frequencies. The aim was to obtain the factors affecting the flow performance of the valveless piezoelectric micropump. The results show that the numbers of Remax in both diffusion and contraction directions of the planar conical tube increase with increasing pressure. When the number of Wo is lower, the number of Remax under a steady state is approximately equal to that under an unsteady state, and the maximum relative deviation is only 0.25%. The greater the Wo number, the smaller the velocity on the minimum flow section, and the more significant the velocity change. The rectification efficiency η of the valveless piezoelectric micropump and the efficiency λ of the planar conical tube both increase with increasing pressure under steady conditions, and the maximum values can be reached at 11.2% and 1.56, respectively.

Postsurgical Volumetric Airway Changes in Class III Patients Receiving Bimaxillary Orthognathic Surgery.

The purpose of the present study was to investigate the pharyngeal airway space (PAS) changes in class III patients receiving bimaxillary orthognathic surgery and correlate the PAS volume and minimum axial section changes with the magnitude of the surgical movement. This research involved a retrospective sample composed of 38 patients with class III skeletal occlusions. Three-dimensional measurements of the PAS volume and minimum axial section were conducted. Cephalometric points were used to verify the extent of jaw-hyoid bone movement. No significant differences were found between pre and postoperative total PAS volume (P = 0.280), nasopharyngeal volume (P = 0.545), oropharyngeal volume (P = 0.297), and minimum axial section (P = 0.568). Anterior movement of point A and posterior nasal spine were significantly associated with an increase in total PAS volume, oropharyngeal volume, and minimum axial section (P < 0.05). However, the posterior movement of menton was significantly associated with a decrease in total PAS volume, oropharyngeal volume, and minimum axial section (P < 0.05). The results of the present study indicated that PAS is not negatively affected by bimaxillary surgery in class III patients. However, the planning of class III patients who are prone to the development of airway problems should be done carefully.

Study of the Injection of Secondary Air into the Intake Manifold of the Gas Turbine to Avoid the Compressor Surging Phenomenon

This paper presents part of the research on avoiding or reducing the surging effects that appear in the axial compressor intake manifold of a gas turbine. This research has led to an original solution validated by numerical simulations and experimental investigations. The increased amount of air suddenly required in the transient regime of the gas turbine is introduced into the intake manifold through slits arranged perpendicular to the direction of flow, on an aerodynamic profile at a certain angle to it and a certain distance from the minimum transversal section. The slits are arranged on the opposite sides of the gallery and connect with a transverse channel of the airfoil, in which there is air under pressure, from which the introduction of additional air is ordered. The numerical and experimental results extended to the influence of many geometric and mechanical parameters, proving that the proposed solution is as effective as possible compared to the classic ejector solution.

Flow Conditioner Design and Analysis Based on Computational Fluid Dynamics

To address the issue of uneven gas flow velocity distribution upstream of natural gas pipeline flow meters, a wave-type fin flow conditioner was designed. The Computational Fluid Dynamics (CFD) numerical simulation method was used to analyze the velocity distribution inside the pipe, and the rectification effect of the flow conditioner was measured by using the offset degree and the minimum length of the straight pipe section. The offset degree at a specific downstream section was calculated when the fluid passed through a 90 degrees elbow spoiler component without a flow conditioner with an Etoile conditioner and wave-type flow conditioner. The results show that the wave-type flow conditioner has a better rectification effect, and the minimum straight pipe section length is shortened by 72% compared to without a flow conditioner, greatly reducing the pipeline design cost and improving the accuracy of measurement of the Ultrasonic flowmeter.

Modelling of ductile failure in materials with heterogeneous particle structure using localization analysis

In this study, we evaluate the use of strain localization analysis based on the imperfection band approach to model the effect of heterogeneous particle distribution on the ductile failure of structural metallic materials. To this end, tensile tests are performed on smooth and notched samples made of aluminium alloy AA6110 with an equiaxed grain structure and an inhomogeneous distribution of the constituent particles. The constituent particles are assumed to be the main contributors to the ductile failure of the alloy. By varying the heat treatment of the alloy, three different materials are considered with different strength, work hardening, and ductility, while the grain structure and constituent particle distribution are unaltered. Finite element simulations of the tension tests are conducted using both metal and porous plasticity models and the stress–strain histories of the elements in the minimum section of the specimen are used in strain localization analyses. In these analyses, ductile failure is assumed to occur when the strain rate inside a thin, planar imperfection band becomes infinite. The imperfection band is modelled with porous plasticity, using either a higher initial porosity than in the bulk material or by adding void nucleation. It is found that the ductility of the materials is most accurately captured by modelling the imperfection band by stress-enhanced nucleation.

Fracture behavior analysis of X80 pipelines welded joints with unequal wall thickness

Pipeline transportation is one of the main methods for transporting oil and natural gas worldwide. The structural safety of welded joints of large diameter pipes with cracks and unequal wall thickness has become a research focus due to discontinuous geometrical structure and cracks in weld seams. In this paper, the tensile experiment and analysis of specimens with unequal wall thickness across welding seam based on the digital image correlation technology are carried out. Moreover, the influence of transition length and transition form on fracture behavior of welded joints of unequal wall thickness pipeline is obtained. In addition, a three-dimensional finite element model of welded joint of unequal wall thickness pipe with oblique line transition form and circular arc transition form is established. and the accuracy of the full-scale pipeline finite element model modeling method is verified by small-scale experiment data. On this basis, the influence of geometrical parameters of the transition section and wall thickness ratio, pipe diameter, and weld strength matching coefficient on the crack driving force of welded joints with unequal wall thickness is obtained. From the perspective of strain-based design, a method for obtaining the minimum transition length section and avoiding girth weld fracture is proposed. The research results guide the design and safety evaluation of welded joints with unequal wall thickness.

Оптимизация сжатых деревянных стоек переменного сечения по критерию максимума критической нагрузки

The article presents a numerical and analytical solution to the problem of optimizing compressed rods according to the criterion of the maximum critical load with a possible loss of stability in two planes. We consider a wooden bar of rectangular cross section, the height of which varies according to a linear law, and the width is constant. The calculation is performed in an elastic formulation. A constraint on the constancy of the rod mass is introduced. Variable parameters are the ratio of the minimum section height to the maximum, as well as the ratio of the section width to the maximum height. Numerical search for the optimal solution is performed in the MATLAB environment using the method of sequential quadratic programming. It has been established that the use of rods with a cross-sectional height that varies linearly along the length is effective only if the rod is fixed in at least one of the planes according to the “pinched-free end” scheme. It has been established that the increase in the critical load when using rods with a linearly varying cross-sectional height can be up to 22%.

A Study on Very High Cycle Fatigue Properties of Axle Steel with Induction Hardening on the Surface

Rotating bending fatigue tests were performed to investigate the effect of induction hardening (HQI) on the very high cycle fatigue (VHCF) properties of the axle steel. In addition, finite element analyses (FEA) and scanning electron microscope (SEM) observations were conducted to elucidate the fundamental behavior. The results obtained are summarized as follows; (1) It was found that the fatigue strength of the axle steel was improved by almost 300 MPa in VHCF region by HQI, (2) A lot of specimens of the HQI had fractured in VHCF region, therefore, the consideration of VHCF properties should be taken into account in the design of railway axles, (3) Crack initiation sites can be classified into three forms; the surface of the HQI layer in the minimum section, the base metal beyond the HQI layer in the axial direction, and the internal base material in the minimum section. These can be reconfirmed through the comparison between the local fatigue strength distribution and the bending stress distribution obtained by FEA.

Thermal conductivity detector (TCD)-type gas sensor based on a batch-fabricated 1D nanoheater for ultra-low power consumption

Thermal conductivity detectors (TCDs) are widely used to detect high-concentration gases or identify low-concentration gases in chromatography, owing to their fast response and recovery time for a wide range of gases. However, conventional TCD devices require large power consumption because of their relatively large sizes, which limits their applicability, specifically in IoT. In this study, an ultralow-power TCD was implemented for use as a gas sensor by manufacturing a suspended nanoheater via cost-effective wafer-level microfabrication technology (i.e., carbon-microelectromechanical systems). The aspect ratio of the nanoheater was optimized for a fixed minimum section area (width = 200–300 nm, thickness = 300–400 nm) using simulations and experiments. The small size, high aspect ratio (~ 270, corresponding to a nanoheater length of 80 µm), and suspended architecture allowed the nanoheater-based gas sensor to operate with high sensitivity and ultrafast response/recovery (time constant of less than 1 μs). This fast response enabled the sensor to operate with pulse-width modulation, reducing the power by 1/1000 (240 nW). The nanoheater-based gas sensor exhibited a linear gas response for various high-concentration gases (H2: 1–20 %, Ar: 1–100 %, He: 1–5 %). Moreover, the nanoheater was fabricated using only wafer-level microfabrication processes, ensuring cost-effective sensor manufacturing. Thus, nanoheater-based gas sensors are expected to be used in various portable IoT devices.

Weight-strength optimization of wooden household chairs based on member section size

Weight-strength optimization of wooden household chairs was performed based on the member section size in this study. Member section sizes of the Scotch pine (Pinus sylvestris) and Oriental beech (Fagus orientalis) chairs were optimized and resulting re-manufactured optimized chairs were tested under the cyclic “front to back”, “back to front” and “backrest” loads according to American Library Association (ALA) specification. Finite element method (FEM) and MATLAB nonlinear programming were utilized for the optimization. Firstly, the internal forces and moments acting on each member were analyzed by FEM in order to obtain the maximum critical stresses in each type of member; then, optimized cross-sectional sizes of the members were determined by Gradient Descent method, and all constraints were treated with Logarithmic Barrier Functioning. As a result, the minimum section sizes of members were determined, and cyclic performance tests were performed to determine whether the optimized chairs were strong enough to carry the acceptable loads. According to the results, member section size of both beech and pine chairs could be significantly reduced. The reduction was 32 % in the total weight and volume for beech chairs while 16 % for pine chairs without sacrificing the performance required for domestic usage by ALA. In conclusion, the method used is suitable for the optimization of furniture frames, making it lighter and reducing the material costs.

Constitutive Model and Fracture Criterion of Q345 Steel Welded Joints

Welding joint is a key component in steel structure engineering, which is often subjected to complex stress and becomes the weak link of building structure, and different fracture modes may appear under different stress. In this study, the ductile fracture of Q345 steel welded joint was investigated by selecting the base material and heat‐affected zone (HAZ) material. Based on the J–C (Johnson–Cook) fracture model of stress triaxiality factor, a series of round bar specimens were designed for the tensile test, and the variation of minimum diameter and gauge distance was tracked in real time by digital image correlation (DIC) technology, and the cloud map of strain distribution in the whole loading process was obtained. The constitutive model and fracture criterion model of Q345 steel welded joint base material and HAZ material are established through experimental measurement. The results show that the maximum triaxial stress is at the center root of the minimum diameter of the notched round bar tensile specimen, the sudden change of the notched edge will lead to stress concentration, the stress change of the notch section is the most significant, extending from near the notch, the maximum strain is at the root of the notch, and the fracture position appears at the minimum section of the notch. According to the true stress‐strain curve of a standard tensile specimen and the least square method, the values of parameters A, B, and N of the J–C (Johnson–Cook) constitutive model of base material and HAZ material are 379.80, 452.89, and 0.37 and 392.90, 540.61, and 0.49, respectively. The fracture strains of the base metal and HAZ material under different triaxial stresses were measured experimentally, and the J–C fracture model was fitted. The values of failure criterion parameters D1, D2, and D 3 were 1.025, −0.008, and 3.617 and 0.678, −2.689E‐5, and 7.683, respectively. This provides experimental parameters for mechanical properties and fracture models of welded joints in structural engineering, refined finite element models considering material failure for structural numerical analysis, and basic data for evaluation and design of building structures, which have good social and economic benefits.

Stress Rupture Life Prediction Method for Notched Specimens Based on Minimum Average Von Mises Equivalent Stress

Creep tests were carried out on notched plate specimens of nickel-based superalloy GH4169 with different stress concentration coefficients. It was found that the duration of the first stage of the creep curve increases with the increase of stress concentration coefficient, while the fracture ductility decreases with the increase of stress concentration coefficient. To predict the life of notched plate specimens, four constitutive models were used to analyze the stress and strain of the notches. It was found that the average Von Mises equivalent stress (AVES) on the minimum notch section first decreases and then increases with the creep time, resulting in a minimum value. The minimum average Von Mises equivalent stress (MAVES) is considered as the characteristic stress of notched specimens in this paper. The creep life equation is fitted according to the results of creep tests of smooth specimens, and then the predicted life of notched specimens is obtained by substituting the minimum average Von Mises equivalent stress of notched specimens into the creep equation. The prediction results of the four constitutive models are within 2 times the dispersion band, and the three-stage model is within the 1.5 times dispersion band.

New Applied Problems in the Theory of Acyclic Digraphs

The following two optimization problems on acyclic digraph analysis are solved. The first of them consists of determining the minimum (in terms of volume) set of arcs, the removal of which from an acyclic digraph breaks all paths passing through a subset of its vertices. The second problem is to determine the smallest set of arcs, the introduction of which into an acyclic digraph turns it into a strongly connected one. The first problem was solved by reduction to the problem of the maximum flow and the minimum section. The second challenge was solved by calculating the minimum number of input arcs and determining the smallest set of input arcs in terms of the minimum arc coverage of an acyclic digraph. The solution of these problems extends to an arbitrary digraph by isolating the components of cyclic equivalence in it and the arcs between them.

Study on Calculation of Minimum Separation Distance for Insulation Classification Devices according to Railway Line Condition

In electric railway lines, a dead section is a section in which the power supply is temporarily cut off because of a difference in power-feeding method between two stations. However, owing to the lack of theoretical studies on dead sections and the installation spacing of signals, design changes often occur, such as movements of the signal and various indicators after completion of railway line construction. In this study, the minimum dead section distance between the signal and the coasting indicator according to the tractive car number and track conditions (gradient, slope) was obtained using EL-8500, and the result was verified using TPS based on the tractive force, acceleration, and resistance values of the locomotive. It is expected that a standard can be established with further research through more analysis based on various track conditions and locomotives.

The influence of friction on gas parameters in the minimum section of nozzles

Processes of gas flow in nozzles, accompanied by the release of frictional heat, are presented in the form of polytropic processes. The polytropic process index n determines the degree of irreversibility of the gas flow process caused by the release of frictional heating. Relations are obtained to calculate the flow rate and thermodynamic properties of gas in the minimum section of the Laval nozzle and in the outlet section of the convergent nozzle at a pressure behind the nozzle less than the critical pressure. The gas calculated parameters (pressure, temperature, specific volume, velocity, cross-sectional area) in the minimum cross-section differ from the recommended values in the reference literature [1]. In particular, the gas pressure in the minimum cross section turns out to be higher than the critical pressure recommended in [1].

Study on Coal Pillar Size Design Based on Non-integral Contact Structure of Coal and Rock Under Static and Dynamic Loads

Reasonable coal pillar size of roadway protection is an important guarantee for roadway stability under the action of static-dynamic coupling loadings in deep mines. Coal pillar and roof-floor rock form a non-integral contact structure of coal and rock. However, in the existing literature, there is no research on the size of the coal pillar under static-dynamic coupling loadings based on the non-integral contact structure of coal and rock. In this study, the coal-rock non-integral contact composite specimens are designed, and the coal pillar size is simulated by the radial sizes of the specimens. The failure characteristics of coal-rock under the static-dynamic coupling loadings are studied by the SHPB test, which provides the basis for the design of coal pillar size, and finally determines the reasonable coal pillar size by combining with numerical simulation. The test results show that the strength of the specimens decreases with the decrease of section size of coal and increases with the increase of dynamic load, but there is a critical value for static load. When the coal sections radial sizes are 50, 45, and 40 mm and dynamic loads are applied, the stress-strain curve of the specimens has a plastic stage, but the rest do not exist. The minimum coal section radial size which can ensure the stability of the specimens is 40 mm, and the similar calculation of coal pillar size is 88 m. Combined with numerical simulation, the final coal pillar size is 90 m. This study provides a more accurate and reliable method to determine the size of a coal pillar under the action of static-dynamic coupling loadings.

Ductility coaxing during creep and tensile deformation of high temperature alloys

ABSTRACT Ductilities generated after four types of creep test are compared: (i) constant load, (ii) constant stress (calculated); (iii) constant stress (from direct observation of the minimum section) and (iv) constant strain rate. Supplementary information is obtained from a regularly interrupted plastic deformation test. The materials considered are 2¼Cr1Mo and 9Cr1Mo steels at 550°C, type 304 and 316 alloys at 650°C and 700°C, respectively, and 20Cr25Ni/Nb steel at 750°C. The principal parameter of interest is the ‘uniform ductility’ in the gauge section, that is, that part which has not severely necked. It is shown that uniform ductility is effectively described by the Monkman-Grant relation and this in turn can be used to sum creep damage via the ductility exhaustion method. It is further demonstrated that, assuming constant volume conditions, gauge length behaviour can be modelled by considering a truncated cone rather than a traditional cylindrical shape.

Research on optimization of power grid range and pre-control strategy of power flow in key areas under ty-phoon weather

Typhoons Typhoons are extremely destructive and the route trajectory is ex-tremely uncertain. The power grids in coastal areas are frequently attacked by typhoons, resulting in large-scale power outages. When a typhoon strikes, it is difficult to determine the trajectory, which may cause simultaneous fail-ures of multiple contact lines at the same time and the location of the failure is difficult to predict in advance. Based on the above background, this paper proposes a strategy for optimizing the power supply range of the power grid in key areas and pre-controlling the power flow under typhoon weather. First of all, this article will optimize the scope of key areas. The minimum overhead cable ratio, the optimal generator load capacity ratio and the minimum connection sec-tion power flow between the key area power grid and the external power grid are used as the optimization objective function, and the cuckoo search algo-rithm is used to supply power. Scope is optimized. Based on the above opti-mization results of the power supply range, a power flow pre-control strategy is proposed to ensure that the power flow of the connection section between the power grid in key areas and external power grids is zero by optimizing the output of generators, energy storage equipment, and load shedding, and finally ensure that the key areas under typhoon mode the grid can transition and operate stably.

Research on mechanical behaviour of tapered concrete-filled double skin steel tubular members with large hollow ratio subjected to bending

This paper reports a study on the mechanical behaviour of tapered concrete-filled double skin steel tubular (CFDST) members under bending. A total of twelve specimens with diverse hollow ratios and shear span ratios were tested. The failure mode, the distribution of the deflection curves, the bending moment-curvature curves (M-φ), the longitudinal stress distribution of the cross-section and the strain were investigated, respectively, to understand the bending performance and working mechanism of the specimens. Meanwhile, the finite element (FE) models of tapered CFDST members were developed to investigate the flexural behaviour by ABAQUS software. Finally, the calculation method for predicting the flexural capacity of tapered CFDST members was proposed. The results show that tapered CFDST specimen fails in a very ductile manner and no tensile fracture is observed at the tension region. The maximum deflection of tapered CFDST members occurs at the 3/4L0 section. Moreover, it is found that the flexural capacity is sensitive to the change of taper angle and hollow ratio due to the variation of flexure stiffness. For instance, ultimate bending capacity can be decreased by 62.6% when the taper angle changes from 0° to 1.71°. In addition, it is not reliable to directly select the minimum section of tapered CFDST members as designed section, which will underestimate the flexural capacity of the specimens. Therefore, the concept of equivalent section is proposed to predict the calculation, and the predicted results are satisfactorily in accordance with the measured results, which can provide certain reference for engineering design.

An efficient WN catalyst nitrogenized from morphology-controllable WO3 for oxygen reduction reaction

Tungsten oxide (WO3) as precursor was prepared by one-step hydrothermal method and then nitrogenized under ammonia atmosphere to obtain tungsten nitride (WN) electrocatalyst for oxygen reduction reaction (ORR). Different morphological structures such as rod-like, needle-like and urchin-like of WO3 were carried out by adding morphology control agents and adjusting hydrothermal time. WN catalyst from needle-like WO3 with minimum section diameter emerged outstanding ORR performance (rapid kinetics of oxygen reduction and approach to four-electron reaction) for its nanoscale particles, low agglomeration and nitrogen doping. The low-cost WN possessed fine durability and better methanol resistance compared to commercial Pt/C, which were also crucial issues in fuel cells.