Variable Cross-section Research Articles

Investigating the asymmetric effect of income inequality on financial fragility in South Africa and selected emerging markets: a Bayesian approach with hierarchical priors

PurposeThis study aims to test the validity of the Rajan theory in South Africa and other selected emerging markets (Chile, Peru and Brazil) during the period 1975–2019.Design/methodology/approachIn this study, the researchers used time-series data to estimate a Bayesian Vector Autoregression (BVAR) model with hierarchical priors. The BVAR technique has the advantage of being able to accommodate a wide cross-section of variables without running out of degrees of freedom. It is also able to deal with dense parameterization by imposing structure on model coefficients via prior information and optimal choice of the degree of formativeness.FindingsThe results for all countries except Peru confirmed the Rajan hypotheses, indicating that inequality contributes to high indebtedness, resulting in financial fragility. However, for Peru, this study finds it contradicts the theory. This study controlled for monetary policy shock and found the results differing country-specific.Originality/valueThe findings suggest that an escalating level of inequality leads to financial fragility, which implies that policymakers ought to be cautious of excessive inequality when endeavouring to contain the risk of financial fragility, by implementing sound structural reform policies that aim to attract investments consistent with job creation, development and growth in these countries. Policymakers should also be cautious when implementing policy tools (redistributive policies, a sound monetary policy), as they seem to increase the risk of excessive credit growth and financial fragility, and they need to treat income inequality as an important factor relevant to macroeconomic aggregates and financial fragility.

Effects of Performance and Normalized Parameters on Various Materials Based Multistage Thermoelectric Generator

Abstract Multi-staging and variable cross section greatly improve the performance of thermoelectric generators. Hence, the present theoretical study analyzes a multi-stage-variable-shaped thermoelectric generator (MVS-TEG) for a combination of dissimilar materials. Effects on voltage, power, conversion efficiency, normalized constraints (voltage, power, and conversion efficiency), and second law efficiency with a row number, exhaust inlet temperature, and the coolant flowrate have been investigated. Results reveal that the row number is the most critical input parameter followed by exhaust inlet temperature and coolant flowrate. Also, the work gives optimum values of rows for voltage and power as Nx = 19 for MVS TEG-1, MVS TEG-3, and MVS TEG-4 while Nx = 18 for MVS TEG-2. The exhaust inlet temperature variation increases the voltage and power output by 54–59% and by 53–58% respectively. The coolant flow variation has a greater impact on the conversion efficiency and the average improvement in the efficiency is about 9.23% in the present study. The second law efficiency decreases with the increase in all the input parameters.

Effect of the up-riser pipe diameter discontinuity on the airlift pump performance

The present study was directed towards studying the performance of the airlift pump with variable cross-section up-riser. The effect of one-step and two-step up-riser enlargement and contraction on the performance of the pump was experimentally investigated. The two-phase flow patterns at the region of cross-section change were also visualized and discussed. The results show that for the one-step enlargement up-riser pipe, the minimum air mass flow rate required to start water flow increases as the up-riser total inside volume increases. At high air flow rates, by contrast, as the up-riser pipe average cross-sectional area increases, the pump water capacity increases. Meanwhile, the two performance curves of one-step and two-step enlargement have similar trends, but the two-step enlargement delivers higher water productivity. The preference of using multiple steps in low-to-medium air flow rate range is remarkable, as eddy losses are lower in the gradually reducing pipe. No flow pattern change appears in the expansion section of the two-step expansion riser, while the one-step expansion riser marks a flow transition from slug to churn flow patterns and from annular to churn flow patterns. A comparison between the water productivity of the one-step contraction and the two-step contraction up-risers displays that the two-step contraction exhibits a higher performance. Moreover, comparisons between enlargement and contraction configurations outline that the enlarged pipe configuration lifts larger amounts of water than the contracted configuration.

Effect of Shape Tool Parameters on the Performance of Cold Circular Three-Dimensional Pilger Cross-Section Roll Forming

Compared with other forming processes, Pilger cold rolling exhibits unique process characteristics and a simple production method, making it highly advantageous in terms of high-precision, high-strength, and poor-plasticity alloys. Among them, the design parameters of the rolling mill play a significant role in the rolling results, with the key design parameters being the hole opening angle θ and the hole gap ΔK. In this study, a numerical simulation model for cold rolling an AZ31B magnesium alloy with variable cross-section three-roll Pilger cold rolling was established, and finite element simulation analysis was employed to obtain the comprehensive performance impact law of key design parameters on the cold-rolled AZ31B magnesium alloy. It can be concluded that when the hole opening angle is 10° and the hole gap is 1.2 mm, the equivalent stress and equivalent plastic strain of the billet reach a minimum, and the surface precision is excellent.

Analytical Modeling and Application for Semi-Circular Notch Flexure Hinges

Flexure-based compliant mechanisms can be used to achieve bio-imitability and adaptability in the applications of biomedical engineering. However, a nonlinear load-displacement profile increases the design complexity of this type of compliant mechanism, especially when the cross-section of the flexure hinge is not constant. This paper proposes two general analytical models by analyzing the compliance and stress characteristics of the semi-circular notch flexure hinge undergoing large deflections, which is a typical variable cross-section of a flexure hinge, based on the Castigliano’s second theorem and the finite elements analysis method. As a case study for verification, three compliant four-bar linkage mechanisms are designed based on the proposed design approach, the design method proposed by Howell, and the equations proposed by Lobontiu, respectively. The results show that the design accuracy is improved 36% in comparison with designs from Howell and Lobontiu. Finally, a flexure-based artificial finger is designed and manufactured based on the proposed optimization approach. The performance test of the prototype shows that the artificial finger has good bio-imitability and adaptability with respect to joint movements.

Test Methods for the Mechanical Characterization of Flexure Hinges

BackgroundThe design of compliant mechanisms requires detailed knowledge about the stiffness properties of their flexible segments. However, there are no standardized test methods for flexure hinges, and therefore the influence of manufacturing-specific effects, such as anisotropy, on the stiffness properties cannot be quantified.ObjectiveThis paper presents novel test methods for variable cross-section flexure hinges subjected to large deformations and pure bending loading, which determine the bending stiffness of flexure hinges over their entire deflection range using a universal testing machine.MethodsThe novel test methods for flexure hinges are based on the tensile test, the four-point bending test (FPBT), and the column bending test (CBT). These test methods were initially formulated for constant cross-section specimens, but are adapted in this study to examine variable cross-section specimens. The derived test methods are validated by using isotropic materials with well-known properties and by comparing the calculated deflections with deflections measured by means of image processing.ResultsThe deflection validation shows that the adapted CBT (aCBT) is accurate over the entire deflection range, achieving curvature of up to kappa =0.40;text {mm}^{-1}, whereas the maximum curvature in the adapted FPBT (aFPBT) is limited by the test methodology to about kappa =0.15;text {mm}^{-1}. At small strains, the flexural modulus determined in the aCBT and aFPBT agrees well with the Young’s modulus determined in the tensile test, as would be expected for isotropic materials.ConclusionThe aCBT proves to be a suitable test method for flexure hinges at large deflections, whereas the stiffness characterization at small deflections can be performed with both the aCBT and the aFPBT. The presented test methods validated on isotropic materials form the basis for characterizing anisotropic flexure hinges with geometry-dependent stiffness properties.

Improving the Mechanical Properties of a Lattice Structure Composed of Struts with a Tri-Directional Elliptical Cylindrical Section via Selective Laser Melting.

In recent years, lattice structures produced via additive manufacturing have been increasingly investigated for their unique mechanical properties and the flexible and diverse approaches available to design them. The design of a strut with variable cross-sections in a lattice structure is required to improve the mechanical properties. In this study, a lattice structure design method based on a strut cross-section composed of a mixture of three ellipses named a tri-directional elliptical cylindrical section (TEC) is proposed. The lattice structures were fabricated via the selective laser melting of 316L alloy. The finite element analysis results show that the TEC strut possessed the high mechanical properties of lattice structures. Compression experiments confirmed that the novel lattice structure with the TEC strut exhibited increases in the elastic modulus, compressive yield strength, and energy absorption capacity of 24.99%, 21.66%, and 20.50%, respectively, compared with the conventional lattice structure at an equal level of porosity.

Geometric nonlinear analysis of slender layered non-prismatic beams with interlayer slip

This paper presents a novel model that, for the first time, simultaneously captures the effects of variable cross-section and interlayer slip on the geometrically nonlinear response of slender symmetrically layered beams within the framework of a beam theory. While the central layer has a constant cross-section along its length, the height of the two outer layers can vary arbitrarily. A nonlinear axial strain–displacement relationship captures the influence of moderately large deflections for immovably supported beams. The kinematic hypothesis of the Euler–Bernoulli theory is applied layerwise. The relationship between the interlaminar shear tractions and the interlayer slips is assumed to be linear. The Galerkin method is used to solve the derived initial–boundary value problem. Several application examples demonstrate the influence of the interlayer slip, the variable cross-section, and the geometrically nonlinear formulation of the equations of motion on the static and dynamic response. The results of comparative analyses with a numerically much more computational expensive finite element model discretized by plane stress continuum elements are in excellent agreement with the outcomes of the presented theory.

Experimental investigation on the performance of the variable cross section rotating detonation engine

Optimizing the structure of the rotating detonation engine (RDE) is an effective way of improving its performance. In this paper, a variable cross section RDE with convergent-channel combustor (CC-RDE) is designed and compared with annular-channel combustor (AC-RDE). The operation range, propagation characteristics of rotating detonation waves (RDWs), and working performance were analyzed. In this study, the combustor outlet blockage ratios of both RDEs were equal, both being 0.35. The results show that the CC-RDE increased the propellant flow velocity, thus increasing the chemical reaction rate, and led to a comparative increase in RDW intensity of up to 185.4%. However, the higher the RDW intensity, the more likely the air plenum and the combustor were to be coupled, which shortened the range of stable operation. The RDW position under two RDEs were approximately 100 mm away from the combustor inlet. The percentages of pressure feedback and pressure pulsation in the air plenum were defined to evaluate the extent of pressure feedback. The results show that a higher RDW intensity in the CC-RDE led to a greater pressure pulsation in the air plenum. When the unstable mode appeared, the pressure feedback further increased. The heat flux of the combustor was also measured to assess the thermal environment of the RDE. The rates of chemical reaction and energy release were higher when the CC-RDE was used, and the average heat flux increased by 40.2% compared with that of the AC-RDE. Moreover, the specific thrust of the CC-RDE was increased by 40.3%.

Innovative development of a soft robotic gripper: mathematical modeling and grasping capability analysis

Recently, most soft grippers rely on complex mechanisms or complicated structures, leading to challenging fabrication and mathematical modeling. This study presents an innovative soft-fingered gripper design with an asymmetric tube that has a variable cross-section, providing a simple yet effective solution for gripping tasks. The proposed mathematical modeling and solutions were successfully developed and experimentally validated to analyze the effects of the robot arm’s motion on the gripping capability of the gripper. This innovation represents an improvement over existing designs and has the potential to enhance the design and efficient performance of soft robotic grippers.

Hermite Finite Element Method for Variable Coefficient Damping Beam Vibration Problem

Beam is the most common component in mechanical equipment and construction. The heterogeneous beam and the variable cross-section beam both have good structural performance. In this study, a Hermite finite element method is proposed for variable coefficient damping beam vibration. The first-order time derivative is approximated by the Richardson format, the second-order time derivative is approximated by the central difference method, and the fully discrete scheme is obtained. The variable coefficients are processed, the error estimate is analyzed in detail. Finally, we verify the validity of the scheme by Matlab and observe influence of damping coefficient variation on beam vibration.

Analysis of Dynamic Characteristics of Attached High Rise Risers

The exhaust chimney of third-generation nuclear power units is a typical attached high-rise riser structure. In this paper, the simplified mechanical model and dynamic model of China’s third-generation nuclear power Hualong-1 VNA system, including multiple nonlinear factors, are established for the first time. The DTM (differential transformation method) was first applied to solve the natural vibration characteristics of a multi-point constrained variable cross-section riser structure, and the effects of variable cross-section, variable mass, variable axial force, and different elastic constraint parameters on the natural vibration characteristics of the system were studied. The dynamic behavior of the VNA system under the combined action of internal flow velocity, vortex excitation, and foundation excitation was studied. The results show that the outer diameter function of the VNA system pipeline should be designed as a quadratic function or a near quadratic multi-segment constant value function. The “limiting” effect of constraining large stiffness can force low-order vibration modes with high constraint stiffness to jump to high-order vibration modes with low constraint stiffness. The elastic constraint arrangement scheme with near center symmetry can make the system vibration mode present a half stable and half-curved form. A new optimization design scheme has been proposed regarding the layout and stiffness parameters of the VNA system guide bracket. This can enable the VNA system pipeline to avoid severe oscillations near the response extreme values caused by multiple frequency excitations of seismic loads under design and accident conditions and ensure the service life of the equipment.

Real-Time Vocal Tract Model for Elongation of Segment Lengths in a Waveguide Model

A vocal tract model based on a digital waveguide is presented in which the vocal tract has been decomposed into uniform cylindrical segments of variable lengths. We present a model for the real-time numerical solution of the digital waveguide equations in a uniform tube with the temporally varying cross section. In the current work, the uniform cylindrical segments of the vocal tract may have their different lengths, the time taken by the sound wave to propagate through a cylindrical segment in an axial direction may not be an integer multiple of each other. In such a case, the delay in an axial direction is necessarily a fractional delay. For the approximation of fractional-delay filters, Lagrange interpolation is used in the current model. Variable length of the individual segment of the vocal tract enables the model to produce realistic results. These results are validated with accurate benchmark model. The proposed model has been devised to elongate or shorten any arbitrary cylindrical segment by a suitable scaling factor. This model has a single algorithm and there is no need to make section of segments for elongation or shortening of the intermediate segments. The proposed model is about 23% more efficient than the previous model.

Dependence of the coefficient of restitution on the shape of an impacting body

The effect of the shape possessed by an impacting body on the coefficient of restitution is addressed using the case of low velocity axial impact of axisymmetric bars. We consider bars of a fixed mass but varying shapes that are parameterized by certain non-dimensional parameters. The eigenvalue problems in all such cases are solved analytically, and the obtained eigenfunctions are used to address the problem of impact with a rigid wall. This transient response problem is solved exactly using the method of Laplace transform. The analytical solutions are compared with fully numerical solutions obtained from the impact of three-dimensional axisymmetric bars using the Finite Element Method (FEM), and a very good match is obtained in all cases considered. In each case, the deformation and restitution times are determined for calculating the coefficient of restitution (COR) using Poisson’s definition, which is compared with Newton’s definition of COR. It is observed for variable cross-section bars that the end of deformation phase is not marked by the bar being completely at rest with the energy purely as internal strain energy, as is conventionally thought of. The redistribution of the initial kinetic energy of the bar after impact in the form of gross motion of the bar and its internal motion is studied. It is found that the longitudinal cross-section variation of the bar decides its rebound characteristic, which is observed by the velocity of gross motion of the bar post impact.

Ultrasonic SH guided wave detection of the defects of switch rails with 3D finite element method

A switch rail is an important part of the high-speed railway system, but it is highly susceptible to defects during service, which threat traffic safety. A switch rail has an asymmetric variable cross-section structure, which makes it challenging to detect its defects with ultrasonic testing. In this study, the finite element model of switch rails and the ultrasonic SH guided wave detection of groove defects were explored. The three-dimensional finite element model of switch rails with the same sizes used under working conditions was established. Furthermore, the influences of grid division method, switch mechanism setting method, and root end variable cross-section grid type on guided wave propagation in the model were analyzed in detail. The switch rail model was experimentally validated. The ultrasonic SH guided wave detection of the defects at the rail head and rail bottom was successfully realized and the echo signals from other special structures of switch rail were also obtained. The finite element model calibrated with experimental results could be used to simulate guided wave detection at any location with any defect. The calibrated model could optimize the switch rail guided wave detection scheme and guide signal identification. The study provides an important basis for the inspection and monitoring of switch rails.

Leakage Analysis of PEMFC Sealing System Considering Temperature Cycling

Addressing the leakage rate prediction problem of the PEMFC sealing system is of great importance for its stable operation. The leakage calculation method of the PEMFC sealing system is proposed based on thermal coupling. The parallel plate leakage model is improved to make it applicable to the leakage rate calculation with a variable channel cross-section height. The interface macroscopic contact pressure is solved using a finite element simulation for solid mechanics analysis. The Greenwood–Williamson model is used for contact mechanics analysis to solve for the average height of the leakage channel. The effects of the ambient temperature, compression ratio, bipolar plate misalignment, and gasket size on the cell sealing effect were studied numerically. The data indicated that as the ambient temperature, compression ratio, and gasket size became larger, the volume leakage rate began to be reduced. The leakage rate as a parameter to characterize the sealing performance, considering the influence of gasket size, operating conditions, and other factors on the cell sealing effect, is more meaningful for the durability study and failure analysis of PEMFC.

Effect of variable cross-section electrode on the battery performance of all-vanadium redox flow battery

The global warming can be relieved by the application of the renewable energy, which should be supported by the large-scale energy storage such as the vanadium redox flow battery (VRFB). The charge-discharge reactions mainly take place in the porous electrodes, which can influence the battery performance. In the paper, a variable cross-section electrode with interdigital flow field was proposed to enhance the mass transfer in the porous electrode. The charge-discharge voltage, overpotential, concentration distribution and uniformity factors are predicted by a 3-D numerical model to evaluate the battery performance of different electrodes (the Conventional electrode; Variable coss-section electrode #1: the variable coss-section electrode with the interdigital flow field distributed on one side; Variable coss-section electrode #2: the variable coss-section electrode with the interdigital flow field distributed on both sides). The discharging voltage of the variable coss-section electrode #2 was 1.25% higher than that of the variable coss-section electrode #1. The uniformity factor of the variable coss-section electrode #1 and the variable coss-section electrode #2 was 14.24% and 19.56% higher than that of the conventional electrode, respectively. Considering the machining process and promotion of the battery performance, the variable coss-section electrode#1 was the best design of the three battery models mentioned in this article.

Broaden the sound absorption band by using micro-perforated plate back cavities with different cross-sectional areas

In finite size micro-perforated plate structure, the cross-sectional area size of back cavity will affect the resonant frequency of structure. Based on transfer matrix and the characteristics of acoustic propagation in variable cross-section channel, the sound absorption characteristics of the double-layer micro-perforated plate structure with variable cross-section back cavity are studied and analyzed, and a theoretical analysis model of the variable cross-section back cavity micro-perforated plate structure is established. By comparing the theoretical model with the finite element model, the effect of abrupt changes in the cross-sectional area of the back cavity on the noise reduction performance is obtained. As for the double-layer micro-perforated plate in this paper, the bigger the cross-sectional area of back cavity of inner micro-perforated plate, the lower the frequency of first peak absorption coefficient of structure will be and the higher the frequency corresponding to second absorption coefficient peak of structure. Utilizing this feature, a combined micro-perforated plate structure is designed, which has back cavities with different inner cross-sectional areas, and ultimately broadening the structural sound absorption band. Additionally, through using 3D printing technology to produce samples and conducting experimental tests in the impedance tube. Experiments show that the structure can achieve an absorption coefficient of more than 0.8 within the frequency range of 500–1650 Hz, which further improving the noise reduction performance of the MPP structure. The feasibility of variable-sectional back cavity structure for the design of low-frequency and broadband noise reduction absorber is verified.

Analysis and Optimum Design of Self Supporting Steel Communication Tower

The present study deals with the optimum design of self supporting steel communication towers. A special technique is used to represent the tower as an equivalent hollow tapered beam with variable cross section. Then this method is employed to find the best layout of the tower among prespecified configurations. The formulation of the problem is applied to four types of tower layoutwith K and X brace, with equal and unequal panels. The objective function is the total weight of the tower. The variables are the base and the top dimensions, the number of panels for the tower and member's cross section areas. The formulations of design constraints are based on the requirements of EIA and ANSI codes for allowable stresses in the members and the allowable displacement atantenna position. The Sequential Unconstrained Minimization Technique (SUMT) is used to perform the process. Direct stiffness method is used for the analysis of the structure, with beam elements. The strain energy is used to derive the stiffness matrix for members of unsymmetrical cross section. A computer program in FORTRAN is developed to represent the tower as an equivalent beam, and generate the tower nodes and members, analysis, design and to find the optimum design. Four types of tower are studied with different load cases. The effects of earthquake and wind loadings are taken in two directions and two positions of antenna are considered in the process to seek the optimum design. The tower type of X-brace with unequal panels has the minimum weightcompared with other types of tower and the optimum design is satisfied when the angle of main leg is equal to (87O).

Grinding stress of different diamond abrasive grains based on the variable cross-section beam

Grinding stress of different diamond abrasive grains based on the variable cross-section beam