Axisymmetric Structures Research Articles

Stability of thin-walled axisymmetric coaxial structures containing liquid under multifactor loads

Stability of thin-walled axisymmetric coaxial structures containing liquid under multifactor loads

МОДЕЛИРОВАНИЕ ТЕПЛОВОГО СОСТОЯНИЯ СОПРИКАСАЮЩИХСЯ ТВЕРДЫХ ТЕЛ С УЧЕТОМ ЭНЕРГОВЫДЕЛЕНИЯ В ЗОНЕ КОНТАКТА

The paper describes a numerical model simulating thermal conditions of contacting solids considering heat release in the contact region. The finite-volume model is implemented in the Logos Heat digital product within the Logos software package. Logos Heat serves for numerical simulations of heat transfer processes in solids and in air gaps without convective heat transfer. Its methods and algorithms enable thermal simulations of three-dimensional and two-dimensional (including axisymmetric) structures under steady and unsteady conditions using nonconformal mesh models considering contact energy release. We selected and considered the most common ways to determine the heat partition coefficient for the energy released by two solids being at rest or in sliding contact. The methods and algorithms incorporated in the numerical scheme of the Logos Heat product to consider the contact energy release were assessed using a case with a known exact solution and numerical data reported in. The analysis of the calculated data shows that the maximum error does not exceed 0.1% for the resting model and 8% for the sliding-contact model, which indicates that the methods and algorithms are appropriate for such simulations. However, it should be noted that, within the Logos Heat numerical scheme, the solution calculated by Charron's formula introduces an error, which is one order higher than the error associated with the temperature conduction method, and creates a temperature discontinuity at the contact.

Dynamics of high-rise structures taking into account the viscoelastic properties of the material

The article deals with forced vibrations of a high-rise axisymmetric structure, represented as a viscoelastic beam of an annular section with a variable slope of the generatrices and variable thickness. The research was conducted to analyze the behavior of a high-rise structure for various kinematic effects. The task is to determine the displacements of the points of a high-rise structure at different time points under different kinematic effects. The methods were developed and a computer program was built; forced vibrations of high-rise axisymmetric structures under various kinematic actions, considering viscoelastic properties of the material, were investigated in linear, nonlinear, and viscoelastic formulations. The study of the dynamic behavior of a high-rise structure, taking into account the nonlinear and dissipative properties (different in nature) of the material, shows that the combined consideration of all these properties brings the resulting pattern closer to the one observed in reality. That is, the amplitude of the structure’s oscillations does not grow infinitely, but gradually decreases over time, and the maximum possible consideration of nonlinear and dissipative properties leads to the fastest damping of oscillations.

Health Monitoring of Single-Element Piezoelectric Transducer Using Its Electromechanical Admittance.

The transducer is an essential part of all ultrasonic systems used for applications such as medical diagnostics, therapy, nondestructive evaluation, and cleaning because its health condition is vital to their proper operation. Defects within the active element, backing or other constitutive elements, and loss of adhesion between layers can significantly weaken the performance of a transducer. The objective of this work is to determine procedures to monitor the behavior of a single-element probe during its lifetime and detect degradations before they significantly affect the performance of the system. To achieve this, electromechanical admittance (EMA)-based method is envisaged numerically and experimentally. A simplified single-element transducer consisting of a piezoceramic disk, a bonding layer, and a backing is studied and the influence of bonding delamination on EMA is investigated. This study considers three different types of delaminations, which are named, respectively, "center" (circular delamination from the center of the disk toward the peripheric zone), "peripheric" (annular delamination from the peripheric zone toward the center), and "wedge" (wedge-shaped delamination with a given angle). For each case, a numerical model based on the finite-element (FE) method is developed: a 2-D FE analysis is implemented for the first two types of delaminations, taking advantage of their axisymmetric structure, and "wedge" delamination is modeled in 3-D. Then, transducers with different shapes of 3-D printed backings are mounted and experiments are conducted using an impedance analyzer. Finally, experimental results are found to be in good agreement with numerical solutions and it shows that changes in EMA can particularly reveal the occurrence and extent of delamination in an ultrasound probe.

High-order three-scale computational method for elastic behavior analysis and strength prediction of axisymmetric composite structures with multiple spatial scales

A novel high-order three-scale (HOTS) computational method for elastic behavior analysis and strength prediction of axisymmetric composite structures with multiple spatial scales is developed in this paper. The multiple heterogeneities of axisymmetric composite structures we investigated are taken into account by periodic distributions of representative unit cells on the mesoscale and microscale. First, the new micro–meso–macro coupled HOTS computational model for elastic problems of axisymmetric composite structures is established based on multiscale asymptotic analysis, which breaks through the traditional multiscale assumptions and includes three main components. Two classes of mesoscopic and microscopic auxiliary cell functions are constructed on the mesoscale and microscale, respectively. The macroscopic homogenization problems are defined on global axisymmetric structures by twice up-scaling procedures from microscale to mesoscale and then from mesoscale to macroscale. Moreover, the asymptotic HOTS solutions are constructed for approximating multiscale elastic problems of axisymmetric structures and the numerical accuracy analysis of the HOTS solutions is given in detail. Then, the strength prediction formulas for axisymmetric composite structures with multiple spatial scales are presented based on the high-accuracy elastic behavior analysis from the proposed HOTS computational model. Furthermore, the corresponding HOTS numerical algorithm based on the finite element method (FEM) is presented for analyzing the mechanical behaviors and predicting the strength of axisymmetric composite structures with multiple spatial scales in detail. Finally, some numerical examples are reported to verify the feasibility and effectiveness of the proposed HOTS computational method. In this study, a unified three-scale computational framework is offered, which enables the simulation of mechanical behaviors of axisymmetric composite structures with multiple spatial scales.

2D finite-element modeling of 3D blade structures with axisymmetric and non-axisymmetric shapes

Prediction of the clearance between the components of a rotor and casing of a gas turbine is generally based on the two-dimensional (2D) finite-element analysis of the overall layout, the three-dimensional (3D) finite-element analysis of the local parts, and the deformation of the gas turbine components caused by other, unimportant 3D effects, such as cold-build clearances and ovalization. Using this, the variation of clearance, the minimum clearance, and the contact evaluation between the components with respect to the operation time are evaluated. Detailed 3D modeling of the overall shape for transient thermal-structural analysis for the prediction of clearances between components under the operating conditions of gas turbines with complex components, including both axisymmetric and non-axisymmetric shapes, is not economical in terms of computational time and cost. To address this problem, it is efficient to perform finite-element analysis by means of 2D modeling based on the crosssectional information of the gas turbine components. At this moment, the 2D finite-element modeling for the axisymmetric and non-axisymmetric structures of the gas turbine is important for predicting the correct and accurate deformation. In this paper, we show that 2D modeling can obtain results similar to those of 3D finite-element analysis for the original shape. The proposed 2D finite-element modeling method for rotor and support of a gas turbine that includes both axisymmetric and non-axisymmetric shapes will enable rapid and effective prediction of the components' behavior.

Biconical-dominated Accretion Flow onto Seed Black Holes in a Hyperaccretion Regime

Abstract Hyperaccretion occurs when the gas inflow rate onto a black hole (BH) is so high that the radiative feedback cannot reverse the accretion flow. This extreme process is a promising mechanism for the rapid growth of seed BHs in the early universe, which can explain high-redshift quasars powered by billion solar mass BHs. In theoretical models, spherical symmetry is commonly adopted for hyperaccretion flows; however, the sustainability of such structures on timescales corresponding to the BH growth has not been addressed yet. Here we show that stochastic interactions between the ionizing radiation from the BH and nonuniform accretion flow can lead to the formation of a rotating gas disk around the BH. Once the disk forms, the supply of gas to the BH preferentially occurs via biconical-dominated accretion flow perpendicular to the disk, avoiding the centrifugal barrier of the disk. Biconical dominated accretion flows from opposite directions collide in the vicinity of the BH supplying high-density, low angular momentum gas to the BH, whereas most of the gas with nonnegligible angular momentum is deflected to the rotationally supported outflowing decretion disk. The disk becomes reinforced progressively as more mass from the biconical flow transfers to the disk and some of the outflowing gas from the disk is redirected to the biconical accretion funnels through a meridional structure. This axisymmetric hydrodynamic structure of a biconical-dominated accretion flow and decretion disk continues to provide uninterrupted flow of high-density gas to the BH.

Pulsed Inductively Coupled Plasma Discharge Simulation for Semiconductor Processing in 2D Axisymmetric Structure

Pulsed Inductively Coupled Plasma Discharge Simulation for Semiconductor Processing in 2D Axisymmetric Structure

Mechanical and thermal buckling of functionally graded axisymmetric shells

The buckling analysis of functionally graded materials (FGM) axisymmetric plate-shell type structures under mechanical and termal loading is presented in this work. A numerical solution is obtained by expanding the variables in Fourier series in the circumferential direction and using conical frustum finite elements in the meridional direction. The finite element model, having two nodal circles and ten degrees of freedom per node, is based in the Kirchhoff-Love theory that includes the transverse shear deformations by introducing a penalty function, which corresponds to the first order shear deformation theory (FSDT), is suitable for both thin and thick axisymmetric plate/shell structures. The reduced number of finite elements, which are required to model even complex structures, combined with the use of a small number of discrete layers to model the continuous variation of the mechanical properties through the thickness of the structure, results in an extremely low computational time required for FGM buckling applications. An in-house program has been developed, and applications in a variety of axisymmetric shells are solved, including circular plates. The solutions obtained in mechanical and thermal buckling are discussed and compared with alternative models..

Local vibration mode pairs for damage identification in axisymmetric tubular structures

Tubular structures are widely used in infrastructure, especially for pipes and marine installations. Corrosion is a key damage type for these structures, and if undetected may cause structural deficiency or even collapse. This paper investigates the effects of localised corrosion on the vibration properties of axisymmetric tubular structures and proposes a novel baseline-free damage identification method to overcome the fact that the difference between undamaged and damaged properties is usually small and contaminated by noise. The proposed vibration-based method exploits the phenomenon of repeated mode pairs which is peculiar to axisymmetric tubular structures with non-axisymmetric damage. Unlike intact tubular structures, it is found that each vibration mode of a locally damaged tubular structure comprises of two components: active and passive. The active component is sensitive to the local damage and can be used to infer damage existence while the passive component is retentive of the undamaged pipe's properties. Therefore, the passive component of a damaged pipe’s local vibration mode pair (LVMP) can be used to predict its baseline (undamaged) modal properties, which in this research was achieved within a margin of ±2%, whereas the active component confirms damage existence. The work also establishes the criteria for validation of LVMPs through experimental tests involving various corrosion scenarios ranging from longitudinal strips to through-thickness pits. Based on the obtained results, it is proposed that the properties of LVMPs can be linked to corrosion-like local damage in axisymmetric tubular structures, underpinning a new damage detection and identification approach.

Retroreflective spatial-polarization interferometer.

The interference of the beams reflected from a combination of two deployed cube-corner reflectors with a special interference phase-shifting coating is considered. It is shown that in this case a beam with an axisymmetric polarization structure appears. Particular attention is paid to the various optical vortices, which are formed if polarization of light is circular. It is proposed to use this system to create a retroreflective interferometer, in which the spatial polarization structure sensitivity changes due to the path difference between the beams, reflected from two different corner-cube reflectors. It is installed such that the position of the plane of vector E oscillations rotates with azimuth variation in the transverse plane, while at different angular distances from the beam axis this rotation can occur in opposite directions, i.e., we observed a counter-twisted polarization structure, useful for manipulating small particles.

Heat model of a spindle support of a precesion metal cutting machine

Based on the use of the electrothermal analogy in describing the heat transfer process, an engineering technique has been developed to determine the thermal state of the supports of spindle assemblies, which does not require “heavy” software packages based on the application of the finite element method. The design features of modern control rooms made it possible to reasonably present the thermal model in the form of a flat model. The principles of dividing the blocks of a flat model into enlarged elements are proposed, taking into account the features of the geometry of the calculated structure and heat sources. A technique has been developed for determining the thermal resistance of an element of a calculated thermal model taking into account boundary conditions. The use of enlarged elements of the thermal model makes it easy to assess the influence of technological features of processing and assembly of individual structural parts on its thermal state. The presented methodology for developing a thermal model can be used to estimate stationary thermal processes of any axisymmetric structures with insignificant temperature variations.

Fullwave Maxwell inverse design of axisymmetric, tunable, and multi-scale multi-wavelength metalenses.

We demonstrate new axisymmetric inverse-design techniques that can solve problems radically different from traditional lenses, including reconfigurable lenses (that shift a multi-frequency focal spot in response to refractive-index changes) and widely separated multi-wavelength lenses (λ = 1 µm and 10 µm). We also present experimental validation for an axisymmetric inverse-designed monochrome lens in the near-infrared fabricated via two-photon polymerization. Axisymmetry allows fullwave Maxwell solvers to be scaled up to structures hundreds or even thousands of wavelengths in diameter before requiring domain-decomposition approximations, while multilayer topology optimization with ∼105 degrees of freedom can tackle challenging design problems even when restricted to axisymmetric structures.

Real‐time temperature estimation method for electromagnetic performance improvement of a large axisymmetric radio telescope under solar radiation

The temperature field caused by solar radiation can seriously affect the electromagnetic (EM) performances of large-aperture and high-frequency radio telescopes, and achieving the EM performance improvements under solar radiation is of great importance. In this study, combining temperature simulation and measurement, a fast estimation method of the temperature field is presented. First, a temperature database based on transient temperature field simulation is constructed in advance, and by utilising the telescope's axisymmetric structure, the dimension of the database can be greatly reduced. Then, a small number of temperature sensors are installed and the real-time measured data are applied to correct the simulation temperature field extracted from the above temperature database by the table look-up method, which can ensure the temperature field estimation speed. Thus, based on the real-time estimated temperature field and the telescope's finite element model, thermal deformations can be calculated in real-time and used for deformation compensation. A 7.3 m reflector antenna with 21 temperature sensors is adopted to verify the proposed strategy, and the results show the effectiveness and feasibility of the strategy. This study can provide helpful guidance for the real-time compensation of thermal deformations derived from large axisymmetric telescopes.

Controllable fabrication of solid state nanopores array by electron beam shrinking

Electron beam shrinking is a technique for manufacturing solid-state nanopores with direct visual feedback for better control. The electron beam in scanning electron microscopy (SEM) offers the high-resolution geometry information of nanostructure during the nanopore manufacturing processes. However, the mechanism of electron beam shrinkage is still unclear, which hinders the fabrication of solid-state nanopores array as well as their applications. In this study, Si3N4 nanopores were used as examples to explore the mechanism of electron beam shrinking. The morphology and composition characterization of the Si3N4 nanopores before and after shrinking revealed that the deposition of hydrocarbons dominates the shrinking process, accompanied by some decomposition of Si3N4. Based on this model, the controlled shrinking of nanopores was achieved, which were assembled into solid state nanopores array. The size of the nanopores can be accurately tuned by adjusting the electron beam accelerating voltage, beam current, and magnification. Under the optimal conditions, the smallest diameter of nanopore of 5.3 nm and the fastest shrinkage rate of 2.51 nm/s were obtained. Meanwhile, solid-state nanopores array, including an axisymmetric nanopore array structure, were also created for detecting translocated AuNPs-DNA through the shrunken nanopores. This study demonstrated a facile technique for fine control of the shape and size of nanopores with designed array patterns, which have great applications in producing nanogap electrodes, complex nanostructure, and surface modification or nanostructure repairing on different materials with desired geometries.

A mathematical approach to study fluid-coupled vibration of eccentric annular plates

A mathematical method is proposed to study fluid-coupled vibration of axisymmetric plate structures with asymmetries due to either imperfection or practical reasons, e.g. the weight reduction of structure, natural frequency shifting, and accessibility. The suggested approach makes use of the separation of variables to determine general solutions of the partial differential equation of the plate transverse displacement, whilst defining multiple polar coordinate systems, each of which offers its own formulation of the plate deformation with respect to its coordinate system. Moreover, closed-form geometric equations and the chain rule for determining derivatives are implemented to move from one coordinate system to the other in order to satisfy boundary conditions. The mode shapes of the vibrating plate in the dry condition are determined and in turn used in the Rayleigh–Ritz method to characterize vibrational properties of the fluid-coupled plate structure. While implementing such an energy method, the fluid motion is formulated employing the velocity potential and solved using the separation of variables. Fluid–structure interaction is also taken into account satisfying the compatibility condition on the fluid–plate​ interface. The developed methodology to predict natural frequencies has been validated by comparison with results obtained by a commercial finite element program. It is also found that the eccentricity tends to reduce natural frequencies of the fluid-coupled system for the lower serial mode, but increases them for the higher serial modes regardless of the presence of liquid.

Spatial natural vibrations of viscoelastic axisymmetric structures

Spatial natural vibrations of viscoelastic axisymmetric structures

Study on calculation methods for acoustic radiation of axisymmetric structures in finite water depth

In this paper, a kind of FEM–WSM (Finite Element Method–Wave​ Superposition Method) is used to calculate the acoustic radiation of axisymmetric structures in finite water depth. FEM is used to solve the dry modes of axisymmetric structures, and WSM is applied along with the dry mode method to consider fluid–structure interaction effects and calculate the acoustic radiated field. This method combines the advantages of FEM and WSM. On one hand, it is suitable for complex or large axisymmetric structures on the one hand. On the other hand, it has higher computational efficiency than the FEM, and the computational domain size for the water is not limited. As long as the Green’s function is tailored for the boundary condition, the acoustic radiated field of axisymmetric structures in more complex ocean acoustic environments can be calculated by using this method. Besides, a least-square method is used to reduce the distortion resulting from computational errors of the modal estimates. The influence of the number of source and field points and the finite element mesh density on the calculation accuracy are discussed, eliciting some disciplinary conclusions. Using a spherical shell and a capsule shell as models, the results from the present approach, a semi-analytical method, and the crude FEM are compared to verify the correctness and efficiency. Based on numerical examples, the influence of the sea surface and the seafloor on the acoustic radiated field of structures in finite water depth is also analyzed.

Connecting Technologies for Coaxial Dual Core Optical Fiber

Coaxial dual core optical fiber (CDCF) with a lensed tip can be used for microparticle trapping, shooting, and spectra analyzing. In this paper, we introduce the connection technology of CDCFs. On the one hand, the CDCFs can be fusion spliced easily and quickly by using the single-mode fiber (SMF) splicing machine, because they have a completely axisymmetric structure. On the other hand, a fan-in device based on the principle of “vanishing core” is designed, and the insertion loss due to fabrication process error is analyzed. Fan-in devices are fabricated and tested. The average insertion loss of the annular core and central core is 1.48 dB and 0.76 dB, respectively.

A model for the constant-density boundary layer surrounding fire whirls

Abstract