Thin Cylinder Research Articles

Modified Aluminium Tube Profile to Enhance the Performance of Impact Energy Absorption

The use of thin-walled structures as impact energy absorbers are well known. The thin aluminum cylinder tube is a good impact energy absorber. However, the energy-absorbing design must also have sufficient toughness. In this research, we made modifications to improve the performance of the thin aluminum tube. The thin aluminum cylinder's modification is prepared by adding four grooves along the wall in the axial direction. Numerical modeling was carried out using the finite element method. The impact test is carried out by  applying a high  speed of 50 m/s  to a hammer that hits the axial direction's specimen. Explicit dynamic analysis is used in this modeling. The reaction force is obtained by measuring fixed support at the end of the tube. The total energy as a function of time is received in this simulation. The explicit dynamic simulation results show that the toughness of the modified specimens increased compared to the original model. The amount of energy per unit time at the start of the collision appears to be higher. Likewise, the total deformation in the modified specimen is shorter than in the original specimen. Thus, until the collision's end, the modified thin aluminum tube specimen provides better performance and absorption of impact energy.

Puzzling magnetic anomaly in the Barun-Khal valley (Olkhon region, western Gisbaikalia)

The Brun-Khal valley is in the Olkhon region, northwest of the village of Chernorud. Since the end of the 70s. the valley and its surroundings has been studied with geophysical methods. During magnetic survey in the central part of the valley, some round-shaped magnetic anomalies were mapped the nature of which remains unclear. Especially unusual is a negative magnetic anomaly with an amplitude of more than 1200 nT and a width of about 50m. According to the simulation, the anomaly is caused by a vertical, negatively magnetized rod or a thin cylinder, the upper and lower edges of which are located at a depth of 17m and 50m, respectively. Presumably, the anomaly is due to a stock of igneous rocks that intruded into host rocks when the polarity of the geomagnetic field was negative.

Numerical observation and analytical formulation of droplet impact and spreading around the thin vertical cylinder

The dynamic characteristics of a water droplet impact on a thin vertical dry solid cylinder are delineated numerically. Finite volume-based axisymmetric simulations are carried out by employing the volume-of-fluid method to predict complex hydrodynamic behaviors. To simulate the present computational work, the conservation equations of mass, momentum, and volume fraction are solved. The droplet surface undergoes a continuous deformation during impact to the thin cylindrical target by resulting in various crucial stages: free fall, hitting, cap formation, encapsulation, uncovering, and detachment. The range of cylinder-to-droplet diameter ratio (Dc/Do) is considered to be from 0.13 to 0.4 for the present computational study to observe different deformation patterns of the droplet. The influence of contact angle (θ), Dc/Do, We, Oh, and Bo on the maximum deformation factor is elucidated from the numerical results. The findings show that the maximum deformation factor increases with the increasing We and the reducing contact angle. An analytical model has been formulated to elucidate the maximum deformation factor, which shows an excellent agreement with the numerical results. Furthermore, a correlation was developed to predict maximum deformation factors in terms of θ, Dc/Do, We, and Oh, which operates exceptionally well within ±1% of the computational data.

An uncoupled limit model for a high-contrast problem in a thin multi-structure

We investigate a degenerating elliptic problem in a multi-structure \Omega_\varepsilon of \mathbb{R}^3 , in the framework of the thermal stationary conduction with highly contrasting diffusivity. Precisely, \Omega_\varepsilon consists of a fixed basis \Omega^- surmounted by a thin cylinder \Omega_\varepsilon^+ with height 1 and cross-section with a small diameter of order \varepsilon . Moreover, \Omega^+_\varepsilon contains a cylindrical core, always with height 1 and cross-section with diameter of order \varepsilon , with conductivity of order 1 , surrounded by a ring with conductivity of order \varepsilon^2 . Also \Omega^- has conductivity of order \varepsilon^2 . By assuming that the temperature is zero on the top and on the bottom of the boundary of \Omega_\varepsilon , while the flux is zero on the remaining part of the boundary, under a suitable choice of the source term we prove that the limit problem, as \varepsilon vanishes, boils down to two uncoupled problems: one in \Omega^- and one in \Omega^+_1 , and the problem in \Omega^+_1 is nonlocal. Moreover, a corrector result is obtained.

Experimental evidence of the Poisson-like effect for flexural waves in thin metallic plates

This Letter reports the feasibility of a structure specifically designed for the control of flexural waves propagating in thin perforated plates. The structure, here denominated as a redirector device, consists of a square array of free holes that splits the impinging beam and transmits sideways their vibrational energy. This behavior is known as a Poisson-like effect, and it was theoretically described in different acoustic structures. This effect is experimentally demonstrated for flexural waves excited in an aluminum perforated plate, and it is explained in terms of a physical mechanism different to that reported for acoustic waves interacting with thin hollow cylinders embedded in water. In addition, a collimator device based also in free holes is designed and validated with the purpose of providing the beam impinging the redirector device. The measurements indicate that the amount of redirected energy is strongly enhanced when a barrier of two-beam resonators is added at the rear side of the redirector. All the designs are validated by an experimental setup employing 1 mm thick aluminum plates.

Localization of eigenfunctions in a thin cylinder with a locally periodic oscillating boundary

We study a Dirichlet spectral problem for a second-order elliptic operator with locally periodic coefficients in a thin cylinder. The lateral boundary of the cylinder is assumed to be locally periodic. When the thickness of the cylinder ε tends to zero, the eigenvalues are of order ε−2 and described in terms of the first eigenvalue μ(x1) of an auxiliary spectral cell problem parametrized by x1, while the eigenfunctions localize with rate ε.

Polynomial mode approximations for longitudinal wave dispersion in solid and hollow circular cylinders

The characteristic equation for wave dispersion in solid or hollow circular cylinders is a transcendental equation: no closed-form solution exists and it can only be solved numerically. The characteristic equation for a hollow circular cylinder is substantially longer and more complex to solve than the equation for a solid cylinder. This paper examines, at different orders of approximation, two polynomial approximations (Jacobi mode approximation and an approximation by Widehammar, Gradin and Lundberg) which simplify the computation of dispersion curves. We focus on the approximation error for the first four modes of axially symmetric longitudinal waves, for both solid and hollow circular cylinders. The two polynomial approximations yield accurate dispersion curves for a solid cylinder, provided a sufficient order is used. For a hollow circular cylinder, the numerical limits of thinner cylinders prevent the use of the highest orders of approximation, limiting the accuracy of the dispersion curves. Classic theories for thin and thick cylindrical shells (by Naghdi and Cooper, and Herrmann and Mirsky), remain useful alternatives when computing dispersion curves for the first propagation mode for very thin hollow circular cylinders. We find that Widehammar’s approximation yields more accurate dispersion curves than Jacobi mode approximation for hollow cylinders, for a given order of approximation, as well as being more straightforward to program.

Elastic-plastic Buckling Analysis of Q690 High Strength Steel Tubes Under Global Bending

In recent years, high-strength steel has been used extensively for infrastructures because of its many advantages, such as its ductility and strain-hardening properties, which are inferior to those of ordinary structural steel, and the small dimensions of the structural elements, which lead to greater freedom and elegance in design, resulting in lighter structures. In practice, imperfections such as residual stresses due to the welding process and pre-buckling mode imperfections are inevitable in cylindrical structures made of high-strength steel. A small imperfection amplitude can lead to a disproportionate reduction in buckling strength. Therefore, imperfection sensitivity should be considered when studying the buckling behaviour of the shell. The influence of the combined residual stress and pre-buckling mode imperfection on the buckling behaviour of Q690 high strength steel cylindrical shell under global bending has not yet been investigated and described for all dimensions. In this paper, the combined imperfections influences on the buckling behaviour of high-strength steel cylindrical shell in global bending in the elastic-plastic range are investigated. Using the ABAQUS fine elements software, perfect cylinders with a constant length to thickness ratio equal to 7 and a radius to thickness ratio in the range 10≤ r/t ≤700 were considered to perform the linear bifurcation analysis (LBA) and the geometric nonlinear analysis (GNA). The non-linear analysis with imperfections (GNIA) and the geometric and material non-linear analysis with imperfections (GMNIA) were then performed considering imperfection amplitudes between 0.01 and 2 to derive the critical buckling loads known as bifurcation point for the models with different aspect ratio. The influences of the combined imperfections show that moderately and very thin cylinders are very sensitive to the increase of the pre-buckling mode imperfection amplitude and their buckling strength is insensitive to plasticity. For thick cylinders, the effect of plasticity is more consistent, while the buckling strength is not significantly affected by the increase in pre-buckling mode imperfection amplitude. The main objective is to predict the buckling sensitivity of cylinders under the influence of combined residual stress and pre-buckling mode imperfection. The obtained results, comments and conclusions intend to allow for safer.

Scattering of an Electromagnetic Wave by a Structure Consisting of Several Thin, Perfectly Conducting and Dielectric Finite-Length Cylinders

Scattering of an Electromagnetic Wave by a Structure Consisting of Several Thin, Perfectly Conducting and Dielectric Finite-Length Cylinders

Thermoelastic reactions in a long and thin flexible viscoelastic cylinder due to non-uniform heat flow under the non-Fourier model with fractional derivative of two different orders

<abstract> <p>In this paper, a new fractional model of non-Fourier heat conduction is presented that includes phase delays and two fractional orders. To derive the proposed model, the fractional integral Atangana-Baleanu (AB) operator with non-singular and non-local kernels was used. The proposed model has been applied to solve a one-dimensional thermoelasticity problem that includes an annular cylinder of a flexible material whose inner and outer surfaces are subjected to a variable heat flux that depends on time and temperature and is free from traction. The Laplace transform approach was applied to find the general solution to the problem and to obtain the expressions for the different physical fields. To estimate the effects of the fractional-order parameters and instantaneous time on the responses of all thermophysical field variables, comparisons are presented in figures and tables.</p> </abstract>

Нестаціонарний теплообмін у вертикальному циліндричному об’ємі, заповненому рідиною

The paper analyzes the conditions of convective heat transfer in the "limited volume" and in the "large volume". It is established that the process of heat exchange in the elements of the basic experimental setup in the system of experimental calculation method corresponds to heat exchange in a "large volume" under conditions of free convection. An experimental stand for the study of nonstationary heat exchange in the system "environment I ― body II", the main elements of which are two working cavities — the outer filled with water, volume V1, and the inner filled with the studied liquid medium volume V2, and V1 is larger V2 3 times. The results of experimental determination of heat transfer between the inner surface of a thin metal cylinder and the investigated liquid medium in a limited space for the system “environment I — body II” under the conditions of laminar regime of both the environment and the investigated liquid medium are presented. The heat transfer coefficient was investigated using the calculation-experimental method during heating and cooling of refined sunflower oil, distilled glycerin, sugar solution with a concentration of 50 %, 60 % under conditions of free convection. The experimental results are compared with the results of studies by well-known authors for "large volume" conditions. The conditions of the heat exchange process during the experiment at different directions of heat exchange in a "limited volume" (inside a thin-walled metal cylinder with the liquid under study) are described. It is substantiated that at the surface of a cylindrical metal wall in the process of heat exchange a thermal boundary layer is formed, within which the coolant temperature changes and heat transfer within the boundary layer occurs due to thermal conductivity. The criterion equations for determining the heat transfer coefficient during heating and cooling of the investigated liquid medium under free convection conditions are obtained.

Heat Transfer and Flow Characteristics of Pseudoplastic Nanomaterial Liquid Flowing over the Slender Cylinder with Variable Characteristics

The present article investigates heat transfer and pseudoplastic nanomaterial liquid flow over a vertical thin cylinder. The Buongiorno model is used for this analysis. The problem gains more significance when temperature-dependent variable viscosity is taken into account. Using suitable similarity variables, nonlinear flow equations are first converted into ordinary differential equations. The generating structure is solved by the MATLAB BVP4C algorithm. Newly developed physical parameters are focused. It is observed that the heat transfer rate and the skin friction coefficient is increased remarkably because of mixing nano-particles in the base fluid by considering γb=1, 2, 3, 4 and λ=1, 1.5, 2, 2.5, 3. It is found that the temperature field increases by inclining the values of thermophoresis and Brownian motion parameters. It is also evaluated that the velocity field decreases by increasing the values of the curvature parameter, Weissenberg number and buoyancy ratio characteristics.

Optimal identification of cavities in the Generalized Plane Stress problem in linear elasticity

For the Generalized Plane Stress (GPS) problem in linear elasticity, we obtain an optimal stability estimate of logarithmic type for the inverse problem of determining smooth cavities inside a thin isotropic cylinder from a single boundary measurement of traction and displacement. The result is obtained by reformulating the GPS problem as a Kirchhoff–Love plate-like problem in terms of the Airy function, and by using the strong unique continuation at the boundary for a Kirchhoff–Love plate operator under homogeneous Dirichlet conditions, which has recently been obtained in [G. Alessandrini et al., Arch. Ration. Mech. Anal. 231 (2019)].

Method of asymptotic partial decomposition with discontinuous junctions

Method of asymptotic partial decomposition of a domain (MAPDD) proposed and justified earlier for thin domains (rod structures, tube structures consisting of a set of thin cylinders) generates some specific interface conditions between three-dimensional and one-dimensional parts. In the case of the heat equation these conditions ensure the continuity of the solution and continuity in average of the normal flux. However for some computational reasons the strong continuity condition for the solution may be undesirable. It may be preferable to replace it by more flexible condition of continuity in average over the interface cross section. In the present paper we introduce and justify this alternative junction condition allowing such discontinuity of the solution of both stationary and non-stationary problems. The closeness of solutions of these hybrid dimension problems to the solution of the fully three-dimensional setting is proved. At the discrete level, finite volume schemes are considered, an error estimate is established. The new version of the MAPDD is compared to the classical one via numerical tests. It shows better stability of the new scheme.

BRDF Importance Sampling for Linear Lights

AbstractWe introduce an efficient method to sample linear lights, i.e. infinitesimally thin cylinders, proportional to projected solid angle. Our method uses inverse function sampling with a specialized iterative procedure that converges to high accuracy in only two iterations. It also allows us to sample proportional to a linearly transformed cosine. By combining both sampling techniques through suitable multiple importance sampling heuristics and by using good stratification, we achieve unbiased diffuse and specular real‐time shading with low variance outside penumbrae at two samples per pixel. Additionally, we provide a fast method for solid angle sampling.

Monte Carlo analytical-geometrical simulation of piezoresistivity and electrical conductivity of polymeric nanocomposites filled with hybrid carbon nanotubes/graphene nanoplatelets

Piezoresistivity and electrical conductivity of carbon nanotube (CNT)/graphene nanoplatelet (GNP)-filled polymer nanocomposites are investigated using a 3D Monte Carlo analytical-geometrical model. GNPs and CNTs are considered as randomly distributed solid thin rectangular cube and cylinder, respectively. After establishment of a random CNT/GNP network, electrical conductivity and relative resistance change with strain is calculated. Model considers effect of CNT and GNP deformation on filler separation distance as the dominant factor for percolation tunneling. Comparing model results with experimental data of hybrid nanocomposites showed a good agreement for electrical conductivity and piezoresitivity. Analytical model is developed on the basis of geometrical tunneling percolation theory to consider the effect of several parameters like height of barrier potential, GNP side length, CNT orientation and dimensions on electric behavior of nanocomposites. Results revealed that CNT dispersion state and GNP dimensions have significant effects on the percolation threshold and resistivity change ratio of nanocomposites with strain.

Axially compressed thin cylindrical shells: Asymptotic limits for a nonlinear basic state

The work presented here revisits the classical bifurcation problem for an axially compressed thin elastic circular cylinder when the nonlinear pre-buckling bending deformations are taken into account. Suitable scaling arguments and singular perturbation methods enable us to explore the link with the more widely studied classical cases in which the uniform membrane solution was used for describing the basic state. Our novel theoretical results are confirmed by direct numerical simulations of the full boundary-value problems corresponding to the relevant buckling scenarios.

Collision of water drops with a thin cylinder

The collision of water drops with a thin cylinder is studied. The droplet flight trajectory and the cylinder axis are mutually perpendicular. In the experiments, the drop diameter is 3 mm, and the diameter of horizontal stainless-steel cylinders is 0.4 and 0.8 mm. The drops are formed by a liquid slowly pumped through a vertical stainless-steel capillary with an outer diameter of 0.8 mm, from which droplets are periodically separated under the action of gravity. The droplet velocity before collision is defined by the distance between the capillary cut and the target (cylinder); in experiments, this distance is approximately 5, 10, and 20 mm. The drop velocities before the impact are estimated in the range of 0.2–0.5 m/s. The collision process is monitored by high-speed video recording methods with a frame rate of 240 and 960 Hz. The test liquids are water. Experiments and numerical simulation show that, depending on the drop impact height (droplets velocity) different scenarios of a drop collision with a thin cylinder are possible: a short-term recoil of a drop from an obstacle, a drop flowing around a cylindrical obstacle while maintaining the continuity of the drop, the breakup of a drop into two secondary drops, one of which can continue flight and the other one is captured by the cylinder, or both secondary droplets continue to fly, and the drop can be also captured by the cylinder, until the impact of the next drop(s) forces the accumulated drop to detach from the cylinder. Numerical modeling satisfactorily reproduces the phenomena observed in the experiment.

A 3D FBG Accelerometer Based on Two Pairs of Flexible Hinges

A three-dimensional (3D) FBG accelerometer was proposed by installing three FBGs in an integrated oscillator structure which consists of two pairs of flexible hinges, a thin cylinder mass block and a base. The theoretical model of the proposed 3D accelerometer was established, and the dynamic response characteristics of the 3D accelerometer with optimal structural parameters were simulated using finite element software. Lots of sensing tests were finished and the sensing data showed that the sensitivities of the proposed 3D accelerometer in X-, Y-, and Z-directions are 108.7 pm/g, 144.2 pm/g, and 27.9 pm/g respectively, the working frequency range in X- and Y- directions are 40 – 300 Hz, and the acceleration amplitude range is 1 – 10 g. The proposed 3D accelerometer has the advantages of small size (28 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times38$ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times38$ </tex-math></inline-formula> mm), light weight (42 g), and simultaneous measurement of multi-dimensional acceleration.

Entropy-Driven Unconventional Crystallization of Spherical Colloidal Nanocrystals Confined in Wide Cylinders.

The densest packings of identical spherical colloidal nanocrystals in a thin cylinder generally give rise to confinement-induced chiral ordering. Here, we demonstrate that entropy can invalidate Pauling's packing rules for the nanocrystals confined in wide cylinders and novel ordered phases, where chiral ordering is broken, emerge. The nucleation and growth of spherical colloidal nanocrystals in the wide cylinders exhibit unique mechanisms which are distinctly different from that of thin ones. Furthermore, theoretical models which capture the essential physics of the ordering transitions are developed to reproduce the achiral ordering and reveal that the ordered phases are thermodynamically stable and stabilized through confinement-mediated entropic effect. These findings demonstrate that entropy arising from thermal motion can invalidate Pauling's packing rules of spherical colloidal nanocrystals confined in cylinders, which provides new insights into confinement physics of colloidal particles and might inspire nonintuitive design rules for the fabrication of novel ordered phases through confinement.