Circular Shells Research Articles

Fatigue Properties of a T Type Welded Joint in a Small-Sized Single Pass Boiler Header

The design of small-sized single pass boilers is usually based on the construction code for small-sized boilers, in Japan. Design methods in this construction code and other country codes have not been clearly defined, although most of small-sized boiler’s headers are constructed from two concentric circular shells and cover plates. Therefore, Finite Element Analysis (FEA) with a PC and measurement by strain gauges are mainly used in strength design of these boilers. A T type welded joint of SS400 was adopted for the header of small-sized single pass boilers was studied. The stress concentration was evaluated by the FEA, and S-N curves were re-drawn using maximum elastic stress, Ktσmax.

Multifrequency study of the Large Magellanic Cloud supernova remnant (SNR) B0513−692 and new SNR candidate J051327−6911

We present a new multiwavelength study of supernova remnant (SNR) B0513−692 in the Large Magellanic Cloud (LMC). The remnant also has a strong, superposed, essentially unresolved, but unrelated radio source at its north-western edge, J051324−691049. This is identified as a likely compact H ii region based on related optical imaging and spectroscopy. We use the Australia Telescope Compact Array (ATCA) at 4790 and 8640 MHz (λ≃ 6 cm and λ≃ 3.5 cm) to determine the large-scale morphology, spectral index and polarization characteristics of B0513−692 for the first time. We detect a strongly polarized region (49 per cent) in the remnant's southern edge (λ≃ 6 cm) . Interestingly, we also detect a small (∼40 arcsec) moderately bright, but distinct optical, circular shell in our Hα imagery which is adjacent to the compact H ii region and just within the borders of the north-eastern edge of B0513−692. We suggest that this is a separate new SNR candidate based on its apparently distinct character in terms of optical morphology in three imaged emission lines and indicative SNR optical spectroscopy (including enhanced optical [S ii] emission relative to Hα).

Elastic-Plastic Dynamic Response of the Tube with Free Boundary Condition Subjected to Impact

Some experimental results of the free-free tubes laterally impacted by the missile were given and the finite element program LS-DYNA was used to simulate this dynamic response process. The instantaneous deformation of the circular shell given by experiments and computer simulation were compared and discussed. It can be seen that when the impact occur the local dents firstly appear at the beginning of impact. With time increase, the depth of the dents increase, the scope of the deformation of the tube wall is enlarged; the total stiffness of the cross-section of the tube is weaken and decreases at the impact point, the beam-like bending deformation take place and the rigid-body translations occur. Through the computer simulation the exchanged energy between the missile and the tube were acquired. The impact energy of the missile is transferred to internal energy and kinetic energy of the tube. The ratio of the internal energy with the kinetic energy of the tube is great for the weakness rigidity of the tube wall, which is opposite to that of a free-free beam. This research made us deeply understand the character of the response when studying the elastic-plastic behavior of the free circular shell under intense dynamic loading.

Thermoelastic transient response of multilayered conical shells subjected to vapor field

The problems of the three-dimensional axisymmetric quasi-static coupled thermoelastic for the laminated circular conical shells subjected to vapor field. The water vapor temperature and pressure relation assumed for the inner boundary. The water vapor temperature and pressure data were obtained from a thermodynamic steam table. The formulation begins with the basic equations of thermoelasticity in curvilinear circular conical coordinates. Laplace transform and finite difference methods are used to analyze problems. The solution is obtained by using the matrix similarity transformation and inverse Laplace transform. We obtain solutions for the temperature and thermal deformation distributions in a transient and steady state. Moreover, the computational procedures established in this thesis, can solve the generalized thermoelasticity problem for multilayered conical shells with nonhomogeneous materials.

Piezoelectric generator based on torsional modes for power harvesting from angular vibrations

Torsional vibration of a circular piezoelectric shell of polarized ceramics mounted on a rotationally vibrating base is analyzed. The shell is properly electroded and connected to a circuit such that an electric output is generated. The structure analyzed represents a piezoelectric generator for converting mechanical energy from angular vibrations to electrical energy. Analytical expressions and numerical results for the output voltage, current, power, efficiency and power density are given.

Puffed noncommutative nonabelian vortices

We present new solutions of noncommutative gauge theories in which coincident unstable vortices expand into unstable circular shells. As the theories are noncommutative, the naive definition of the locations of the vortices and shells is gauge-dependent, and so we define and calculate the profiles of these solutions using the gauge-invariant noncommutative Wilson lines introduced by Gross and Nekrasov. We find that charge 2 vortex solutions are characterized by two positions and a single nonnegative real number, which we demonstrate is the radius of the shell. We find that the radius is identically zero in all 2-dimensional solutions. If one considers solutions that depend on an additional commutative direction, then there are time-dependent solutions in which the radius oscillates, resembling a braneworld description of a cyclic universe. There are also smooth BIon-like space-dependent solutions in which the shell expands to infinity, describing a vortex ending on a domain wall.

Postbuckling Behavior of Angle-Ply Laminated Joined Circular Conical-Cylindrical Shells

The prebuckling and the postbuckling behaviors of the angle-ply composite laminated joined circular conical-cylindrical shells subjected to torsion, external pressure, axial compression, and thermal loading are studied considering the variation of stiffness coefficients along the meridional direction in the conical section. The analysis is carried out using the semi-analytical finite element method based on the first-order shear deformation theory. The nonlinear governing equations, derived using Sanders-type kinematic relations, are solved using the Newton-Raphson iterative technique coupled with the displacement control method to trace the prebuckling followed by the postbuckling equilibrium path. The presence of asymmetric perturbation in the form of a small magnitude load spatially proportional to the linear buckling mode shape is considered to initiate the bifurcation of the shell deformation. The influences of the semicone angle, the ply angle, and the number of circumferential waves on the prebuckling/postbuckling response of the angle-ply laminated joined circular conical-cylindrical shells are investigated. The critical buckling load shows a decreasing trend for positive semicone angle cases and an increasing one for negative semicone angle cases with the increase in the magnitude of the semicone angle of the mechanically loaded shells. The shells with a positive semicone angle mostly depict asymmetric bifurcation buckling under uniform decrease in temperature whereas the shells with a negative semicone angle depict asymmetric bifurcation buckling under a uniform rise in temperature. The ratio of the minimum load in the postbuckling path and the critical buckling load may significantly be lower than unity depending upon the shell parameters and loading situations.

A Proposed Design Chart to Predict the Inelastic Buckling Pressures for Conical Shells Under Uniform External Pressure

The paper presents the theoretical and experimental results obtained when 15 machined circular section conical shells were tested to destruction under uniform external hydrostatic pressure. Three of the shells buckled elastically, but the other 12 buckled inelastically. Previous research has found that the inelastic buckling of such shells with small initial out-of-circularity has defied exact mathematical analysis, due to the fact that the initial out-of-circularity is very small and also of random distribution about the circumference. In this paper these results are used to provide a design chart that enables the inelastic buckling pressures of these vessels to be successfully determined. This design chart should prove to be more accurate, but less conservative, than existing design charts, so that the factor of ignorance is decreased and more reliability can be placed on the true factor of safety.

Design charts for the general instability of ring-stiffened conical shells under external hydrostatic pressure

The paper describes experimental tests carried out on three ring-stiffened circular conical shells that suffered plastic general instability under uniform external hydrostatic pressure. In this mode of failure, the entire ring–shell combination buckles bodily in its flank. The cones were carefully machined from EN1A mild steel to a very high degree of precision. Using the results obtained from these three vessels, together with the results obtained from elsewhere, the paper also provides two-design charts, which are much easier to use than older design charts. The design charts allow the possibility of obtaining a plastic knockdown factor, so that the theoretical elastic buckling pressures for perfect vessels, can be divided by the plastic knockdown factor, to give the predicted buckling pressures. Although similar design charts have been produced in the past, the design charts presented here are based on using the simpler ring-stiffened circular cylinder, which has been made equivalent to the much more complex ring-stiffened circular conical shell. The advantage of using this method is that it is simpler and the design time is reduced by a factor of about 10 with little loss of precision. This method can also be used for the design of full-scale vessels.

Postbuckling characteristics of angle-ply laminated truncated circular conical shells

The postbuckling characteristics of the angle-ply laminated composite conical shells subjected to the torsion, the external pressure, the axial compression, and the thermal loading considering uniform temperature change are studied using the semi-analytical finite element approach. The finite element formulation is based on the first-order shear deformation theory and the field consistency principle. The variations in the stiffness coefficients along the meridional direction due to the changes in the ply-angle and the ply-thickness of the filament wound conical shells are incorporated in the finite element formulation. The nonlinear governing equations are solved using the Newton–Raphson iteration procedure coupled with the displacement control method to trace the prebuckling followed by the postbuckling equilibrium path. The presence of asymmetric perturbation in the form of a small magnitude load spatially proportional to the linear buckling mode shape is considered to initiate the bifurcation of the shell deformation. The influence of semi-cone angle, ply-angle and number of circumferential waves on the prebuckling/postbuckling response of the anti-symmetric angle-ply laminated circular conical shells is investigated.

Vibration Test of a Cross-ply Laminated Composite Circular Cylindrical Shell Partially Filled with Liquid

The vibration characteristics of laminated composite circular cylindrical shell partially filled with liquid was investigated and compared with the isotropic shell. Especially, the differences of the vibration characteristics between the laminated and isotropic shells and the mass effect of liquid on the vibrations of the shells were clarified experimentally. The laminated composite circular cylindrical shell was made from five cross-ply layers of CFRP prepreg. The isotropic circular cylindrical shell with the same size as the composite shell was made of steel. In the experiment, these circular shells were mounted on a vibration table with a clamped lower end and a free upper end, and excited horizontally by white noise. The vibration displacements of laminated shell were measured by non-contact optical fiber sensor, and those of steel shell was measured by eddy current sensor. The natural frequencies and mode shapes were identified by modal analysis using STAR-system software.As the results, in the case of empty shells, the frequencies of laminated shell is high compared with the ones of isotropic shell in the region of large circumferential wave number. When the shells were filled with liquid and increasing in the liquid height, however, the frequencies of laminated-shell is lower than ones of isotropic shell in that circumferential wave number region. And bulging-type modes of laminated shell having partially filled liquid appeared at small circumferential wave numbers by comparison isotropic shell.

FATIGUE PROPERTIES OF A T TYPE WELDED JOINT IN A SMALL-SIZED SINGLE PASS BOILER HEADER

The design of small-sized single pass boilers is usually based on the construction code for small-sized boilers, in Japan. Design methods in this construction code and other country codes have not been clearly defined, although most of small-sized boiler's headers are constructed from two concentric circular shells and cover plates. Therefore, Finite Element Analysis (FEA) with a PC and measurement by strain gauges are mainly used in strength design of these boilers. In this study, a T type welded joint of SS400 was adopted for the header of small-sized single pass boilers. Fatigue testing and FEA was carried out. The fatigue limit was greater for base metal than for weldment. For the weldment, the S - N curve decreased with decreasing ρ value. The stress concentration at the toe was evaluated by the FEA. S - N curves for different toe curvature radii were re-drawn using maximum elastic stress, Ktσmax. Crack initiation occurred in the vicinity of the toe. Several small cracks were observed on the surface of T type welded joint fatigue specimen at N/N f =0.42. These cracks coalesced together at a crack length of 10mm. Fatigue crack growth rate lineally increased with increasing (crack length)1/2.

Nonlinear thermoelastic stability characteristics of cross-ply laminated oval cylindrical/conical shells

In this work, the thermoelastic stability characteristics of the cross-ply laminated oval cylindrical/conical shells subjected to uniform temperature rise are studied through nonlinear static analysis employing the finite element approach. Geometric nonlinearity is introduced in the formulation considering moderately large deformation effects. The study is carried out to highlight the influences of the noncircularity parameter, number of layers, material properties and semi-cone angle on the nonlinear thermoelastic response/stability characteristics of the laminated oval cylindrical/conical shells. It is brought out from the detailed studies that the circular shells exhibit distinct bifurcation point but the noncircular shells reveal smooth transition from the prebuckling to the postbuckling equilibrium path. The moderately noncircular shell response is found to be sensitive to the type of initial perturbation and the semi-cone angle whereas the highly noncircular shells are insensitive to the presence of small perturbation. It is also brought out that the linear eigenvalue buckling analysis approach may not be appropriate for the estimation of the critical temperature parameter of the highly noncircular shells.

Deformation and reverse snapping of a circular shallow shell under uniform edge tension

In this paper we study the deformation and stability of a shallow shell under uniform edge tension, both theoretically and experimentally. Von Karman’s plate model is adopted to formulate the equations of motion. For a shell with axisymmetrical initial shape, the equilibrium positions can be classified into axisymmetrical and unsymmetrical solutions. While there may exist both stable and unstable axisymmetrical solutions, all the unsymmetrical solutions are unstable. Since the unsymmetrical solutions will not affect the stability of the axisymmetrical solutions, it is concluded that for quasi-static analysis, there is no need to include unsymmetrical assumed modes in the calculation. If the shell is initially in the unstrained configuration, it will only be flattened smoothly when the edge tension is applied. No snap-through buckling is possible in this case. On the other hand, if the shell is initially in the strained position, it will be snapped back to the stable position on the other side of the base plane when the edge tension reaches a critical value. Experiment is conducted on several free brass shells of different initial heights to verify the theoretical predictions. Generally speaking, for the range of initial height H < 10 the experimental measurements of the deformation and the reverse snapping load agree well with theoretical predictions.

FEM free vibration and buckling analysis of stiffened toroidal shells

The finite element method (FEM) is used to predict free vibration and buckling characteristics of complete circular toroidal shells with meridional ring stiffeners. New vibration results are presented in the paper which indicate the effect on the natural frequencies of ‘rigid’ meridional ring stiffeners, and of equatorial lines of support. New buckling results are presented which indicate the effect on the buckling pressure of meridional ring stiffeners, and of equatorial lines of support. Results for the natural frequencies and the critical buckling pressure are given for shells covering a wide range of the geometric parameters. Close agreement of results is observed in comparisons with previously published results.

Analysis of Airway Narrowing Based on Dynamic Buckling Model

In order to elucidate the mechanism of airway narrowing in asthma, dynamic buckling analysis was performed for basement membrane. The basement membrane was treated as two-dimensional circular thin-walled viscoelastic shell of Voigt model and contraction of smooth muscle was replaced by inward transmural pressure applied to the basement membrane. Governing equations for the dynamic buckling was derived and wave number of buckling mode obtained were compared with numerical simulation results by non-linear FEM and with experimental results. The non-dimensional parameters are thickness radius ratio, non-dimensional increasing speed of inward transmural pressure, non-dimensional retardation time and Poisson ratio. Wave number of buckling mode is determined as the number having maximum amplification from initial imperfection mode. The wave number of buckling mode increases with increase in non-dimensional increasing speed of inward transmural pressure and it decreases with increase in non-dimensional retardation time. It has been known that wave number of buckling mode decreases due to thickening and hardening of basement membrane caused by the remodeling in asthma. This fact is originated from decrease in non-dimensional increasing speed of inward transmural pressure due to the remodeling. In the dynamic buckling analysis the damping effect of the basement membrane is necessary to take into consideration, because the primary component of the basement membrane is collagen having damping characteristics.

PECULIARITIES IN THE DIELECTRIC RESPONSE OF NEGATIVE-PERMITTIVITY SCATTERERS

This study analyzes polarizability properties of spherically layered small inclusions that possess negative permittivity. Conditions for invisibility to external electric fields are derived. The complementary principle for two-dimensional scatterers is used to derive special properties of self-complementary inclusions. A singular behavior between the limits of invisibility and infinite response is underlined for a hollow circular shell. A similar,although not as drastic,phenomenon is shown to take place for the three-dimensional hollow sphere.

Optimization of open cross sections of thin‐walled beams with plate‐shell‐flanges

AbstractThe paper is devoted to a monosymetrical cold‐formed thin‐walled beam with open cross section. Its flange consists of plates and circular shells. The beam is under pure bending. The cross section is characterized by dimensionless parameters. The authors are searching for an optimal cross section shape of considered beam. This optimal shape is determined by means of parametric optimization. The dimensionless objective function is so defined as to comprise both cross section area and a maximal allowable bending moment. The constraints follow from the local buckling conditions and geometric restrictions. Moreover, there are optimized cross sections of beams, for which the shear center is located either in the web or in the centroid of the cross section. Results are compared and analyzed. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The Life of Academician A. D. Kovalenko and His Research and Teaching Career

The life and career of Academician A. D. Kovalenko, a prominent Ukrainian mechanician, are briefly described. His achievements in thermomechanics are outlined. Among them are the thermomechanical fundamentals of thermoelasticity theory; exact solutions to various stress-strain problems for circular plates and shells of revolution of varying thickness found using the theory of special functions (in particular, hypergeometric functions of the second kind) as the basic mathematical tool; methods widely used to design turbomachine parts; and linear and nonlinear viscoelasticity theory developed considering the temperature dependence of material properties

Solving Problems of Elasticity of Conical Shells

The problem of a local action of normal pressure on a thin circular shell is solved by the method of asymptotic synthesis. A conical shell under the action of local radial loads is considered as an example.