Variable Cross-section Research Articles

A novel approach to crack modeling using extended finite element and substructures methods

In the present work, a combination of Extended Finite Element Method (XFEM) and substructures methods has been utilized for crack modeling. Structures are divided into several substructures, and XFEM is employed to model the presence of cracks within each substructure. In another method, crack modeling has been carried out without using the Extended Finite Element Method. Instead, cracks are modeled by eliminating boundary constraints from two substructures. The Krylov-Schur algorithm is utilized to accelerate the computation of structural modes by preparing stiffness and mass matrices for eigenvalue and eigenvector calculations related to the superstructure. For evaluating this method, four examples have been considered: In the first example, an experimental L-shaped steel structure comprising a beam and a column was examined. The second example involved an experimental steel beam with a box-shaped cross-section. In the third example, a steel beam with simple supports at both ends and a rectangular cross-section was proposed. In the fourth example, a real two-span bridge (Turtle Mountain Bridge) is also presented to evaluate the proposed method. The method was applied for modeling, and the obtained results were validated using experimental and analytical results. In this work, the Structural Similarity Index Method (SSIM) for mode shape similarity assessment has been employed for crack identification. Based on the results obtained from the modeling and crack identification evaluations, it can be concluded that the current method can model multiple cracks in structures with variable cross-sections, real concrete bridges, frame-shaped structures, and diverse structures by assembling substructures. Despite simplifying the problems, it maintains an acceptable level of accuracy in validation. This advantage enables the identification of cracks through a straightforward comparison of mode shapes.

Effect of SDS Solutions on the Jamin Effect in a Capillary Tube with a Contracted Throat.

With the continuous exploitation of petroleum resources, the distribution and displacement of residual oils have become key issues in enhancing oil recovery. In a reservoir, there are various forms of residual oils caused by the capillary force, viscous force, and some other hydrodynamic effects, which lead to the Jamin effect, and they restrict the oil displacement process. In this study, the morphologies of oil droplets in a capillary tube laden with water and sodium dodecyl sulfate (SDS) solutions are experimentally investigated. The pinning behavior of the oil droplet is observed in the waterflood with a lower velocity, while depinning and rupturing behaviors occur at a higher velocity. Hereto, we build a mechanics model to analyze the evolution of the Jamin effect in a capillary tube with varying cross sections. Using this theoretical model, we obtain the two critical velocities for the depinning and rupture of the oil droplet, which agree with the experimental results. Moreover, we find that oil droplets can more easily pass through the entire capillary tube in SDS solutions compared with water. The time required for oil droplets to pass through the pore throat becomes shorter with the increase of SDS concentration. Therefore, a theoretical model is established to determine the total pressure difference and the minimum applied pressure difference. These findings are beneficial to obtain a deep insight into the detailed oil displacement and achieve a higher oil recovery rate.

Investigation on the improved absolute nodal coordinate formulation for curved shell with variable cross-section

Investigation on the improved absolute nodal coordinate formulation for curved shell with variable cross-section

Development and experimental evaluation of an acoustic flow meter prototype for measuring air flow

This study outlines the development and testing of a flow meter prototype specifically designed for use in nuclear reactor environments. The meter uses flow-induced vibration to measure flow rates and is designed for remote monitoring in harsh environments where radiation can damage electronics. The device generates a vibration signal produced by a feedback system when fluid flows out of an orifice and interacts with a downstream wedge. The frequency of the vibration signal corresponds directly to flow rate and velocity. The study investigates geometric parameters intrinsic to the prototype, such as orifice height, width, edge distance, and chamber length. Different configurations were also tested, including a bypass loop with variable cross-sections around the device. The investigation results reveal the impact of these geometric parameters on the vibration signal output, providing valuable insights for future design improvements and enhancing the effectiveness of flow metering systems used in nuclear reactor applications.

Financial Technology (Fintech) as a Driver for Poverty Reduction in Nigeria

ABSTRACT: The human race has been confronting the issue of poverty which is threatening its continued existence for a long time. Poor access to finance can lead to poverty this breeds health issues, lack of access to social and recreational facilities, social delinquencies, reduced living standard, malnutrition and economic difficulties. The goal of defeating poverty in its various ramification remains a cardinal concern for policy formulators in the Nigerian state and international bodies such as the World Bank and United Nations. Following the thriving emergence of financial technology (fintech) in Nigeria, there exist a dearth in academic researches to examine how fintech can be a driver in the reduction of poverty. This study examined the impact of financial technology on poverty reduction in Nigeria. Data on poverty rate, financial technology, mortality rate, literacy rate and gross domestic products were obtained from the National Bureau of Statistics (NBS) in Nigeria and the Central Bank of Nigeria (CBN) statistical bulletin for the period of 1991 – 2021. This study employed the multiple linear regression estimation technique to analyse collected data as it examines a cross-section of major key independent variables across a time series data, on the premise of a common effect model. Data analysed indicates a negative and significant nexus between poverty rate and financial technology innovation. The result also suggest that literacy rate and poverty rate have a negative and insignificant relationship. The poverty rate was also found to be positively and insignificantly related to mortality rate and gross domestic products respectively. The study findings have several significant policy implications. Firstly, infrastructures that support internet and mobile telephony should be expanded by providing incentives for investment since technology is the backbone of the operations of fintech. Secondly, education on fintech, information communication technology and finance should be increased to fill the gap among citizens who are not technological inclined especially in the rural areas to increase the use of fintech. Lastly, there should be further regulatory interventions through reforms to remove the barriers to credit.

Adjustable stereo path design method based on pin-sculpture acoustic topological insulator with Z-dislocation defect immunity

The field of topological protected wave engineering, inspired by quantum mechanics, has generated significant interest. Acoustic analogs of electronic topological insulators provide new opportunities for manipulating sound propagation with unconventional acoustic edge modes that are immune to backscattering. Numerous reports have been published on the design of two-dimensional acoustic topological insulators (ATIs). However, the sound path of a two-dimensional design is simple, and its ability to control sound waves is limited. On the other hand, the design of 3D ATIs is relatively complex, making it difficult to manufacture and limiting its versatility. Based on the design idea of the 2D ATIs, inspired by the art named 3D pin-sculpture, an adjustable structure of a finite size consisting of spindle-shaped units with a variable cross section is designed to realize flexible path transformation. Furthermore, unlike two-dimensional structural defects, such as cavities and disorder, the analysis of vertical dislocation defects in finite-sized structures allows for the design of local sound propagation along the z-direction, providing a concept for constructing a stereo path. The designed structure also serves two functions: acoustic switch and delay. This idea offers an alternative approach to designing complex sound transmission paths.

Design of the Elastic Modulus of porous lattice structures composed of cells with continuously variable cross section carrying structures

BackgroundPorous bone implants have a wide range of applications for their low elastic modulus and good connectivity. It is necessary to explore an elastic modulus control method that can significantly regulate the elastic modulus under the condition of maintaining a constant porosity. MethodsFor achieving continuously changing elastic modulus of porous lattice structure, the simple cubic lattice structures were selected as research object, and the distribution of cross-sectional sizes of its carrying structures were set as variable continuous curves. The prediction model for the elastic modulus was established based on the elasticity mechanics and the equal mass assumption. Then, the prediction model is enhanced through compression simulation of the unit cell structure. Finally, the accuracy of prediction model is validated by compression experiments. FindingsThe results indicate that the distribution of cross-sectional size of the carrying structures has a significant impact on the elastic modulus of unit cell structures under the constraint of equal mass. By adjusting the characteristic parameters of distribution curves, the elastic modulus can be changed within a large range. InterpretationVariable cross-section can effectively change the elastic modulus of porous structures while ensuring constant porosity. This method has important value in decoupling the influence of geometric parameters on the elastic modulus of porous structures.

Implementation of variable cross-section curved beam in train-turnout dynamic interactions

The abundance of variable cross-section curved rails in railway turnouts emphasizes the necessity of intricately modeling them, which facilitates a more accurate evaluation of train-turnout interactions. This study presents a general formulation for analyzing both free and forced vibrations of a variable cross-section curved Timoshenko beam and its implementation in train-turnout dynamic interactions. First, the natural frequencies and mode shapes for in-plane and out-of-plane free vibrations of the beam are determined through eigenvalue analysis, taking into careful consideration the characteristics of variable cross-section and curvature. Then, the forced vibration solution is derived using modal superposition and orthogonality. Furthermore, comparative analyses using finite element method (FEM) validate the natural frequencies and dynamic responses of a beam under various boundary conditions, confirming the reliability and accuracy of the proposed method. Finally, the developed beam model is then applied to simulate the switch rail and point rail under train-turnout interactions, revealing the differences from existing methods that modeled these components as uniform cross-section straight beams. Numerical analyses provide new insights by comparing wheel-rail forces and rail acceleration. Considering curve and variable cross section characteristics could contribute to a more accurate evaluation of train-turnout dynamic interactions.

The Performance and Fabrication of 3D Variable Cross-Section Channel for Passive Microfluidic Control.

Passive fluid control has mostly been used for valves, pumps, and mixers in microfluidic systems. The basic principle is to generate localized losses in special channel structures, such as branches, grooves, or spirals. The flow field in two-dimensional space can be easily calculated using the typical Stokes formula, but it is challenging in three-dimensional space. Moreover, the flow field with periodic variable cross-sections channeled of polyhedral units has been neglected in this research field due to previous limitations in manufacturing technology. With the continuous progress of 3D printing technology, the field of microfluidic devices ushered in a new era of manufacturing three-dimensional irregular channels. In this study, we present finite analysis results for a periodic nodular-like channel. The experiments involve variations in the Reynold number (Re), periodic frequency, and comparative analyses with conventional structures. The findings indicate that this variable 3D cross-section structure can readily achieve performance comparable to other passive fluid control methods in valve applications. A 3D model of the periodic tetrahedron channel was fabricated using 3D printing to validate these conclusions. This research has the potential to significantly enhance the performance of passive fluid control units that have long been constrained by manufacturing dimensions.

Structural integrity assessment of a solid propellant grain considering confining pressure effect

Confining pressure has a significant effect on the mechanical properties of solid propellant, and it is crucial to develop a refined structural integrity analysis and assessment method considering confining pressure effect and nonlinearity of propellant material for the design of propellant grain of a solid rocket motor (SRM), especially for the design of high charge modulus. In this work, an existing viscoelastic-viscodamage constitutive model considering confining pressure effect was implemented as a user-defined material subroutine and verified using a few experiments under various confining pressures. The mechanical responses and safety factor of a typical variable cross-section propellant charge SRM with various charge modulus under ignition pressurization load and room temperature were analyzed and evaluated. The results show that the user-defined material subroutine can well describe nonlinear mechanical responses of solid propellant under different experimental conditions. The Von Mises stress and minimum safety factor considering the confining pressure effect are higher than the value without considering the confining pressure effect, while the Von Mises strain is opposite. In addition, regardless of whether the confining pressure effect is considered or not, the maximum Von Mises stress and strain show a nonlinear increasing relationship with the charge modulus, and the minimum safety factor decreases with charge modulus. However, when analyzing the structural integrity of high charge modulus, using two evaluation methods will yield completely different evaluation results. It is believed that this research can support structural integrity analysis and design of high charge modulus SRM.

Mach reflection and pressure/heating loads on V-shaped blunt leading edges with variable cross-sections and crotches

The primary Mach Reflection (MR) and pressure/heating loads on V-shaped Blunt Leading Edges (VBLEs) with variable elliptic cross-sections and conic crotches are theoretically investigated in this study. The simplified continuity method is used to forecast the shock configurations. The theoretical predictions and the numerical simulations for the Mach stem and the triple point as well as the curved shock accord well. Based on the theoretical model, an analysis of the impact of the axial ratio a/b of the cross-sectional shape and the eccentricity e of the crotch sweep path on shock structures is carried out. The shock configurations obtained from the theoretical model enable the derivation of the transition boundaries between the primary MR and the same family Regular Reflection (sRR). It is found that the increase of a/b and e can both facilitate the primary MR to sRR transition. The resulting transition and the corresponding generation of the wall pressure and heat flux are then investigated. The results indicate that higher values of the ratio a/b can significantly reduce the wall pressure and heating loads by inducing the primary MR to sRR transition. Conversely, the increase in the eccentricity e results in increased loads, despite causing the same transition.

Nonreflecting Propagation of Internal Waves in an Exchange Flow of a Shallow Two-Layer Medium in a Channel with a Variable Cross Section

Nonreflecting Propagation of Internal Waves in an Exchange Flow of a Shallow Two-Layer Medium in a Channel with a Variable Cross Section

Searching for proton transfer channels in respiratory complex I

We have explored a strategy to identify potential proton transfer channels using computational analysis of a protein structure based on Voronoi partitioning and applied it for the analysis of proton transfer pathways in redox-driven proton-pumping respiratory complex I. The analysis results in a network of connected voids/channels, which represent the dual structure of the protein; we then hydrated the identified channels using our water placement program Dowser++. Many theoretical water molecules found in the channels perfectly match the observed experimental water molecules in the structure; some other predicted water molecules have not been resolved in the experiments. The channels are of varying cross sections. Some channels are big enough to accommodate water molecules that are suitable to conduct protons; others are too narrow to hold water but require only minor conformational changes to accommodate proton transfer. We provide a preliminary analysis of the proton conductivity of the network channels, classifying the proton transfer channels as open, closed, and partially open, and discuss possible conformational changes that can modulate, i.e., open and close, the channels.

Wire-arc directed energy deposition of high performance heat treatment free Al-6Mg-0.3Sc alloy

The release of residual stress during heat treatment of additively manufactured components could lead to significant deformation, particularly for those with thin-wall features and variable cross-sections. In this study, high performance heat treatment free Al-6Mg-0.3Sc alloy components were fabricated using the wire-arc directed energy deposition (DED) technique, achieving a yield strength of 223.0 ± 0.9 MPa, tensile strength of 408.5 ± 3.2 MPa, and elongation of 20.6 ± 1.7 %. The results indicate that compared to the CMT arc mode, the CMT + PA arc mode leads to a more pronounced bimodal microstructure, resulting in improved elongation. The mechanical property enhancement mechanism relies more on solid solution strengthening and grain boundary strengthening than on precipitation strengthening. Additionally, this study establishes for the first time a correlation between droplet transition and microstructure evolution. The research presented herein lays a theoretical foundation for wire-arc DED in the direct manufacturing of large thin-walled components without the need for heat treatment.

Novel optimal sensor placement method towards the high-precision digital twin for complex curved structures

The complex shape of the structure and the new needs for high-precision in digital twin modeling pose challenges for sensor placement optimization. A novel optimal sensor placement towards the high-precision digital twin (OSP-HDT) method is proposed for complex curved structures. It comprises three key aspects. Firstly, leveraging the spatial dimensionality reduction method, the complex curved surface is simplified into a planar representation. Subsequently, candidate sensor placement points can be easily identified by dividing the background mesh in the plane and screening them within the curved surface. These candidate points are then binary encoded to facilitate the subsequent optimization. Secondly, the method collects result data from the finite element model, treating it as virtual sensor data. Using this data, a surrogate model is constructed and then the objective function is formulated based on both the global and local critical areas precision of the surrogate model. Thirdly, the sensor placement optimization model is constructed, followed by optimization design using the efficient multi-objective covariance matrix adaptive evolutionary strategy. Through the steps above, the optimal sensor placement can be identified. To validate the proposed OSP-HDT method, an experiment is conducted on an S-shaped variable cross-section stiffened shell, with the construction of the corresponding digital twin. Compared to the uniform placement with an equivalent number of sensors, the OSP-HDT method demonstrated a significant 9.0% improvement in global precision and a remarkable 62.1% enhancement in local precision of critical areas. Furthermore, when compared to the random sensor placement strategies, the OSP-HDT method exhibited a 20.5% increase in global precision, together with a 44.2% increase in the local precision. Notably, even when compared to the full sensor placement, the OSP-HDT method can maintain comparable local precision, while significantly reducing the number of sensors by 77.6%. The above comparison indicates that the proposed OSP-HDT method can build a digital twin model with higher global and local precision for complex structures.

Free Vibration Analysis of Curvilinearly Tapered Axially Functionally Graded Material Beams

The study focuses on the free vibration analysis of beams made of axially functionally graded materials (AFGM) with curvilinear variable cross-sections along their length. The beams encompass various shapes, including concave and convex conic sections, with axial material properties varying according to polynomial and exponential laws. The equations of motion are derived using Hamilton’s principle within the framework of Timoshenko beam theory. These governing equations, subjected to various boundary conditions, are solved using the differential transform method (DTM). The proposed solution technique is validated by comparing computed natural frequencies with the existing literature and results obtained using three-dimensional finite element analysis in ABAQUS. The incorporation of material gradients into the beam finite element models was achieved using the user-defined material subroutine (UMAT). Additionally, a comprehensive study is conducted to examine the influence of various factors on the natural frequencies of functionally graded beams. These factors include parameters of material laws, types of variable beam shapes, slenderness ratio, and specific boundary conditions. This study provides a thorough understanding of the modal dynamics of the considered beams, offering valuable insights into the behavior of FGM structures.

Model Test Study on the Bearing Mechanism of Inclined Variable Cross-Section Piles Using Transparent Soil

In view of the influence of the inclination and variable section on the pile stability and bearing capacity, this paper introduces particle image velocimetry (PIV) technology, and designs a transparent soil visualization model test. The experimental results show that, when the pile has a variable cross-section and inclination angle, the friction resistance on both sides of the pile increases. The vertical-load-carrying capacity of the 2% and 4% inclined piles with a variable cross-section is greater than that of the piles with inclinations greater than 8%. For model piles with the degrees of inclination of 2% and 4%, the variable-section inclined piles with diameters of 17 mm and 15 mm show significantly less settlement than the equal-section inclined piles. For the model pile with an inclination of 8%, the settlement of the inclined piles with a variable cross-section diameter of 17 mm is slightly smaller than that of the equal cross-section inclined piles. The change in variable cross-section and inclination angle has a large effect on the soil displacement around the pile, and the conclusions of this paper can provide guidance for the engineering application of variable cross-section piles.

A Novel Weak-Form Plane Frame Quadrature Element and its Application to Bridge Analysis

A novel weak-form plane frame quadrature element (WPFQE) is developed. A complex structure can be divided into several non-homogeneous (or homogeneous) elements with large size. The Chebyshev–Lobatto differential quadrature dealing with differentiation and the Gauss–Lobatto quadrature dealing with integration have the same integration points including the ends of each element. Based on the energy variational principle, the diagonal mass matrix and positive definite real symmetric stiffness matrix for the element can be obtained. The unknown quantities at the internal quadrature points of the element can be represented by those at the endpoints of the element based on the principle of static equal effect anterior to the development of global matrices, which significantly reduces the sizes of modified element matrices while maintaining sufficient accuracy, thereby obtaining the small-sized global matrices. Assembly of elements can be performed efficiently just as that in the finite element (FE) method. In the case study, the static and dynamic performances of a three-span high-pier rigid-frame bridge with variable cross-section are studied by applying the proposed method. The results indicate that the orders of structural matrices and calculation time obtained by the WPFQE method are much smaller than those of the FE method.

Modeling of compliant-based support for large aperture rotary prisms with horizontal-axis

In the Thirty-Meter-Telescope (TMT), a pair of wedge prisms with diameters of approximately 1500 mm are proposed to mitigate atmospheric dispersion across different zenith angles. This is achieved through controlled linear and rotary movements of the prisms. However, providing stable support for such large aperture prisms, with variable cross-sections and capable of rotating 360° around a horizontal optical axis, poses a significant challenge. This paper introduces a compliant-based support method tailored for TMT’s large aperture prisms. The methodology involves a mechanical analysis of the wedge prism with push-pull forces combination, followed by the development of the support principle based on degrees of freedom and constraints analysis. Subsequently, numerical modeling is conducted using compliant elements as the fundamental units. Furthermore, an integrated optomechanical analysis is performed to evaluate the performance of the support. The findings demonstrate that employing this support method results in superior optical surface accuracy under the coupled conditions of gravity and temperature, particularly for prisms with large apertures, variable cross-sections, and rotational capabilities.

Aerodynamic study of high-speed railway tunnels with variable cross section utilizing equivalent excavation volume

High-speed railway tunnels, being critical components of transportation infrastructure, are subject to various aerodynamic effects that can impact train operations and passenger comfort. To address these challenges, the concept of tunnels with variable cross sections offers a promising solution, allowing for non-uniform adjustments to tunnel geometry along its length. By employing the notion of equivalent excavation volume, this paper aims to provide a comprehensive aerodynamic analysis of variable cross section tunnels, focusing on different rates of cross section variation (CR). The simulation of high-speed trains (HSTs) passing through tunnels is conducted using the compressible, unsteady Reynolds-Averaged Navier–Stokes model, and the accuracy is confirmed through experimental validation. The transient pressure and peak distribution, slipstream characteristics, micro-pressure waves, and aerodynamic loads acting on trains are fully evaluated. The results indicate that variable cross section tunnels can alleviate the negative pressure on train surface, particularly with streamlined heads and tails exhibiting superior effects, whereas its influence on positive pressure is minimal. The mitigation of both positive and negative pressures on the tunnels is promising, with the maximum peak-to-peak pressures exhibiting a quadratic decrease as the CR increases, resulting in a maximum relief of 17.7%. However, variable cross section tunnels have certain adverse effects on slipstreams and transient loads when HSTs passing through front junctions. Therefore, it is necessary to choose an appropriate CR to control these effects during design process. The findings of this research contribute novel insight for optimizing tunnel design and engineering practices to enhance operational efficiency and passenger comfort.