Layered Cylindrical Structures Research Articles

Three-dimensional finite element simulation of magnetic-mechanical-electrical coupling in layered cylindrical multiferroic structures

The excellent magnetoelectric (ME) performance of multiferroic structures under room temperature has inspired a wide range of applications in smart devices like energy collectors, ME transducers, neo-antennas, etc. Starting from the constitutive equations of ferroelectric and ferromagnetic materials, a three-dimensional (3D) finite element simulation model was set up to investigate the ME behaviors of the cylindrical structures consisting of Terfenol-D and lead zirconate titanate (PZT). Then the solid mechanical module, electrostatic module and the magnetic module are coupled to calculate the mechanical, electrical and magnetic properties of the components and the structures. The calculated ME coefficients were in good agreement with the experimental data. The results show that P/T and T/P structures reach the maximum of ME coefficients at different bias magnetic fields, approximately 2.5×104 A/m for P/T structure and 4.8×104 A/m for T/P structure. The maximum value of αE31 in the P/T structure is twice that of T/P structure. Moreover, the distribution of magnetic, mechanical, and electrical fields of the composites are also analyzed. The results show that the magnetization of the ferromagnetic material exhibits a non-uniform distribution at low magnetic field, the stress concentration occurs at the Terfenol-D and PZT interface, and the electric potential of piezoelectric material is non-uniform in the plane. Finally, the influence of the interface characteristics on the ME effect is also studied. It is found that, the thicker the interface and the lower the Young's modulus, then the smaller the corresponding ME coefficient for the P/T structure.

Theoretical and experimental study on guided wave characteristics in bonded bolts

An analytical integration Legendre polynomial series approach (AILPSA) is proposed to study guided waves in a resin bolt, which is a typical layered cylindrical structure. Compared with the conventional Legendre polynomial series approach, the AILPSA can save the abundant numerical integration calculation time and dramatically improve the computational efficiency. The attenuation and group velocity curves of the resin bolts are calculated. The errors of group velocity between the theoretical and the experimental are analyzed, and the contrast diagrams between amplitude curves of end reflection and attenuation curves are given to illustrate the law between these curves.

Morphing of soft tubes by anisotropic growth

We present a study of smart growth in layered cylindrical structures. We start from the characterization of a compatible growth field in an anisotropic growing tube with the aim to show a small perturbation in the compatible growth field that may produce a controlled deprivation of compatibility and localization of elastic energy storage in a composite structure made up of anisotropic growing tubes.

Guided waves in layered cylindrical structures with sectorial cross-section under axial initial stress

Due to mechanical loads, thermal fields and the limitation of the manufacturing technology, initial stresses in layered cylindrical structures are ineluctable. Accordingly, for the purpose of the guided wave nondestructive testing for the layered cylindrical structure with a sectorial cross-section, an analytical approach, the double-orthogonal polynomial method is utilized to investigate the influence of axial initial stress on wave characteristics. Based on Biot’s “Mechanics of Incremental Deformations”, the dynamic equations for the sectorial cylindrical structures in terms of displacements and axial initial stress are deduced. By virtual of the Heaviside function, the boundary conditions are automatically incorporated into constitutive equations and then into wave equations. The corresponding dispersion curves and displacement distributions of various sectorial cylindrical structures are calculated. Numerical results indicate that the influence of the initial stress applied on the outer layer is much significant at low frequencies, and the influence of the initial stress applied on the inner layer is much significant at high frequencies; the cut-off frequencies have negative relation with the area of the cross-section; the displacements at high frequencies are mainly distributed in the layer with smaller elasticity modulus, especially the layer simultaneously with bigger initial stress.

GENERAL SCALARIZATION METHOD OF DYNAMIC ELASTIC FIELDS IN TRANSVERSALLY ISOTROPIC MEDIA AND ITS NEW APPLICATIONS

Introduction. An efficient technique of tensor field scalarization is successfully used while investigating tensor elastic fields of displacements, stresses and deformations in the layered structures of different materials, including transversally isotropic composites. These fields can be expressed through the scalar potentials corresponding to the quasi-longitudinal, quasi-transverse, and transverse-only waves. Such scalarization is possible if the objects under consideration are tensors relating to the subgroup of general coordinate conversions, when the local affine basis has one invariant vector that coincides with the material symmetry axis of the material. At this, the known papers consider structures where this vector coincides with the normal to the boundary between layers. However, other cases of the mutual arrangement of the material symmetry axis of the material and the boundaries between layers are of interest on the practical side.Materials and Methods. The work objective is further development of the scalarization method application in the boundary value problems of the dynamic elasticity theory for the cases of an arbitrary arrangement of the material symmetry axis relative to the boundary between layers. The present research and methodological apparatus are developed through the general technique of scalarization of the dynamic elastic fields of displacements, stresses and strains in the transversally isotropic media.Research Results. New design ratios for the determination of the displacement fields, stresses and deformations in the transversally isotropic media are obtained for the cases of an arbitrary arrangement of the material symmetry axes of the layer materials with respect to the boundaries between layers. Discussion and Conclusions. The present research and methodological apparatus are successfully used in determining the stress-strain state in the layered structures of transversally isotropic materials, and in analyzing the diagnosis results of the state of the plane-layered and layered cylindrical structures under operation.

Abstract 3209: Numerical modeling of intracellular mechanisms in tumor-treating fields

Abstract Tumor Treating Fields (TTFields) are 100-500 kHz electric fields with intensities of about 1-4 V/cm. They are known to exert an antimitotic effect on cancer cells, most likely by exerting forces on highly polar tubulin dimers, thereby disrupting spindle formation. Calculations show that TTFields-tubulin interaction energy is negligible compared to the thermal energy in the cell (1). Therefore, this interaction is unlikely to disrupt cellular function. Conductivity of polymerized tubulin, microtubules (MTs), was measured to be 20 S/m, which is 400 times higher than that of the ambient cytosol (0.05 S/m) (2). Thus when TTFields penetrate the cytosol, they may induce electric currents along MTs that are strong enough to disrupt key cellular functions. In particular, if the power (energy per unit time) deposited by these currents is on par with that the power consumed by the molecular motor kinesin, then TTFields may disrupt the forces needed for cell division, thereby disrupting mitosis. To test this hypothesis, we performed numerical simulations evaluating the magnitude of the electric current along MTs exposed to TTFields at 200 kHz. Based on studies of MTs and their microenvironment, we model the MT as a layered cylindrical structure (1): Innermost is the lumen (15 nm in thickness), surrounded by 13 strands of alpha-beta tubulin dimers linked in a helix (4.5 nm). C-termini extend out from the helix with a thickness of 3.5 nm. MTs carry net negative charge; thus they are surrounded by a counter-ion layer (2 nm), and an outer nonconductive Bjerrum layer (3 nm). We built a finite element model in COMSOL Multiphysics (tm) incorporating these layers and examined the current density induced in each layer by TTFields for MTs varying in length from 1-10 µm within an ambient 200 kHz AC electric field of 1-4 V/cm. Our model shows that MTs act as electrical "shunts" that conduct electric current within them. The highest current flows through the counter-ion layer surrounding the C-termini. The current density in this layer exceeds the level likely to disrupt the motor protein kinesin "walk" along the C-termini. The current density is highest when both the field and the MTs are aligned with the cell axis, in accord with in vitro experiments (3). Our model is consistent with the hypothesis that when cells are exposed to TTFields, MTs act as cables carrying high-density electric currents strong enough to disrupt the function of molecular motors, ultimately disrupting mitosis.

Method of analysis of asymmetrical thermal field in a double insulated wire

PurposeThe purpose of this article is investigating the impact of the spatially variable heat transfer coefficient on the thermal field in the double insulated wire.Design/methodology/approachThe effect of the air boundary layer was modelled by means of changing the total heat transfer coefficient on the external perimeter of the wire. This leads to an elliptical boundary problem with Hankel’s condition dependent on the angular coordinate. The eigenfunctions of the problem were determined analytically. On the other hand, the unknown coefficients of eigenfunctions and the constants were calculated numerically by solving a respective system of algebraic equations. The steady state current rating was determined with an iterative method.FindingsBy means of the presented method, the thermal field distribution deprived of axial symmetry in the double insulated wire was determined. The obtained results have good physical interpretation and were verified with the finite element method (by means of NISA v. 16 software). The determined values of the steady-state current rating were compared with those calculated by means of the equivalent heat transfer coefficient method and the International Electrotechnical Commission (IEC) standard.Research limitations/implicationsThe method is applied to analyse scalar fields in layered cylindrical structures. This could be expanded to the case of a wire of any number of insulation layers. What is more, one could also consider heat sources without axial symmetry and located within the external area.Originality/valueThe analytical method of determining a thermal field deprived of axial symmetry in heterogeneous cylindrical system (the wire composed of three different materials) was developed.

Efficient vertical mode expansion method for scattering by arbitrary layered cylindrical structures.

A relatively simple and efficient numerical method is developed for analyzing the scattering of light by a layered cylindrical structure of arbitrary cross section surrounded by a layered background. The method significantly extends an existing vertical mode expansion method (VMEM) for circular or elliptic cylindrical structures. The original VMEM and its extension give rise to effective two-dimensional formulations for the three-dimensional scattering problems of layered cylindrical structures. The extended VMEM developed in this paper uses boundary integral equations to handle the two-dimensional Helmholtz equations that appear in the vertical mode expansion process. The method is applied to analyze the transmission of light through subwavelength apertures in metallic films and the scattering of light by metallic nanoparticles.

Cylindrical ferroelectric heat pump

In this article, the feasibility of using ferroelectric materials as a heat pump based on electrocaloric effect has been studied. Alternative switching of the electrocaloric elements generate directed heat flux. The dynamics of temperature variations at the inner boundary of a layered cylindrical structure to an applied periodic electric field have been studied in two different cases. These two different cases are the outer boundary convection condition and the outer boundary constant temperature condition. The inner boundary is insulated in two cases. Results show that different boundary conditions affect the heat pump performance.

Corner Reflector as a Model of Layered Cylindrical Structures of Metallic Circular Rods

Electromagnetic radiation in a corner reflector consisting of metallic circular rods of perfect conductor is formulated using a model of layered cylindrical arrays. Radiation from Hertzian dipole coupled to the uniform and tapered corner reflectors is analyzed. The formulation is rigorous. It is shown that the directivity in forward direction is prominently enhanced in both H-plane and E-plane, when the corner reflector is composed of metallic circular rods with radii linearly increasing from the origin. Comparisons with radiation patterns of conventional two plate corner reflector are also presented.

Electromagnetic Scattering by Layered Cylindrical Arrays of Circular Rods

A semi-analytical approach for analyzing two-dimensional electromagnetic scattering by layered cylindrical arrays of circular rods periodically distributed along concentrically layered circular rings is presented. The method uses the T-matrix of a circular rod in isolation, the reflection and transmission matrices of a cylindrical array expressed in terms of the cylindrical harmonic waves as the basis and the generalized reflection and transmission matrices for a layered cylindrical structure. Using the method, the scattering of plane waves impinging on the cylindrical arrays from the exterior region and the radiation from a line source located inside the cylindrical arrays are numerically investigated. Numerical examples demonstrate that the layered cylindrical arrays are effective for forming a directed beam in the scattered and radiated fields.

Experimental and Computational Study of Acceleration Response in Layered Cylindrical Structure Considering Impedance Mismatch Effect

Electronic devices, especially those having high performance capabilities, are sensitive to mechanical shocks and vibrations. Failure of such devices in smart projectiles caused by vibrations has been observed. The currently accepted methodology to protect electronic devices in smart projectiles is use of stiffeners and dampers. However these methods are not effective in protecting the electronic devices from high frequency accelerations in excess of 5,000 Hz. Therefore, it is important to find more effective methods to reduce high frequency vibrations for smart projectiles. In this study, layered cylindrical structures are studied experimentally and computationally to understand the effect of impedance mismatch in axial acceleration response under an impact loading. Experiments are conducted by applying impact forces at one end of cylindrical structures and measuring accelerations at the other end. Experimental results suggest that high frequency accelerations in layered structures could be less compared to those in homogeneous cylinders if a returning wave from the end of the projectile does not interfere with the applied impact force. Computational studies using finite element analysis (FEA) verified the experimental results of our interference hypothesis.

Experimental and Computational Study of Acceleration Response in Layered Cylindrical Structure Considering Impedance Mismatch Effect

Electronic devices, especially those having high performance capabilities, are sensitive to mechanical shocks and vibrations. Failure of such devices in smart projectiles caused by vibrations has been observed. The currently accepted methodology to protect electronic devices in smart projectiles is use of stiffeners and dampers. However these methods are not effective in protecting the electronic devices from high frequency accelerations in excess of 5,000 Hz. Therefore, it is important to find more effective methods to reduce high frequency vibrations for smart projectiles. In this study, layered cylindrical structures are studied experimentally and computationally to understand the effect of impedance mismatch in axial acceleration response under an impact loading. Experiments are conducted by applying impact forces at one end of cylindrical structures and measuring accelerations at the other end. Experimental results suggest that high frequency accelerations in layered structures could be less compared to those in homogeneous cylinders if a returning wave from the end of the projectile does not interfere with the applied impact force. Computational studies using finite element analysis (FEA) verified the experimental results of our interference hypothesis.

Analysis of Radiation from Line Source Located in Cylindrical Electromagnetic Bandgap Structures with Defects

A semi-analytical approach for analyzing the electromagnetic radiation of a line source in cylindrical electromagnetic bandgap (EBG) structure is presented. The cylindrical structure is composed of circular rods periodically distributed along concentrically layered circular rings. The method uses the T-matrix of a circular rod in isolation, the reflection and transmission matrices of a cylindrical array expressed in terms of the cylindrical waves as the basis, and the generalized reflection and transmission matrices for a layered cylindrical structure. Using the proposed method, the radiated field from a line source placed inside a three-layered cylindrical EBG structure with defects is investigated. The defects are created by removing the particular circular rods from each circular ring. The structure is prominent from the viewpoint of flexible design of the directive antennas. Numerical examples demonstrate that the cylindrical EBG structures are very effective at forming and controlling the directed beam in the radiated fields.

Wave Propagation in Layered Cylindrical Structures Using Finite Element and Wave Tracing Analysis

Abstract : In this study, acceleration responses of layered cylindrical structures are obtained using finite element analysis (FEA) and wave tracing technique. The wave tracing technique implies a direct application of the wave propagation equation which includes propagating wave and its reflections at the interfaces due to effect of impedance differences in layered structure. Wave tracing clearly supported FEA results which had showed that interference between applied impact and reflected waves affects wave propagation both negatively and positively depending on material combinations of the structure. The study showed that structures made in order of high-low-high impedance materials reduce magnitude of acceleration responses compared to homogeneous structures made of only high impedance material when there is no interference. While structures made in the order of lowhigh- low impedance materials reduce magnitude of acceleration responses compared to homogeneous structures made of only low impedance material with and without the interference. Furthermore, FEA results showed that structures made of high-low-high impedance materials reduce high frequency accelerations compared to homogeneous high impedance material structures. These results were experimentally verified with the previously reported results.

Instability of myelin tubes under dehydration: deswelling of layered cylindrical structures.

We report experimental observations of an undulational instability of myelin figures. Motivated by this, we examine theoretically the deformation and possible instability of concentric, cylindrical, multilamellar membrane structures. Under conditions of osmotic stress (swelling or dehydration), we find a stable, deformed state in which the layer deformation is given by deltaR infinity r(square root[B(A)/(hB)]), where B(A) is the area compression modulus, B is the interlayer compression modulus, and h is the repeat distance of layers. Also, above a finite threshold of dehydration (or osmotic stress), we find that the system becomes unstable to undulations, first with a characteristic wavelength of order square root[xi(d)0], where xi is the standard smectic penetration depth and d0 is the thickness of dehydrated region.

Characterization of Layered Cylindrical Structures Using Axially Symmetric Waves

For the characterization of the unknown material properties of a layered cylindrical structure, axially symmetric wave signals transmitted and reflected by the structure have been used. Since only a single wave mode propagates in the structure, the measurement and analysis of the transmitted and reflected signals can be simplified significantly. The evaluation of the material properties of the layers can be achieved with great accuracy. In this paper, we first derive the transmission and reflection coefficients for the layered cylindrical structure sonified axisymmetrically by an incident cylindrical wave. We then relate the spectra of the transmitted and reflected wave signals to the transmission and reflection coefficients as ratio functions. The time-domain signals transmitted and reflected by the structure can then be reconstructed from a routine application of the Fourier integrals. A three-layered aluminum/epoxy/aluminum tube is used to illustrate the application of the expressions for both the forward and inverse problems. The results show that the technique developed in this study can be used very effectively for the characterization of layered cylindrical structures.

Viscoelastic effects in resonant sound scattering from layered cylindrical shells

We consider a layered cylindrical structure consisting of an inner elastic shell supporting an outer viscoelastic layer. The structure is immersed in an outer fluid and it contains a dissimilar fluid in its interior. We study the scattering of sound waves normally incident on the structure utilizing the recently developed resonance theory of sound scattering. The role of the viscoelastic properties of the outer layer in the damping of the scattering resonances is investigated, as well as their effect on the partial wave scattering amplitudes, making up the monostatic cross section of the structure. For the purpose of this investigation, we have isolated the resonances from the composite partial-wave contributions, and we have quantitatively shown to what extent their strength can be effectively reduced, for all modes, by increasing the viscous level of the outer layer. [H. Überall is also at Catholic University, Washington, DC, and was additionally supported by Code 421 of ONR.]