Thickness Of Cylindrical Shell Research Articles

Improved deep neural network for predicting structural response of stiffened cylindrical shells to far-field underwater explosion

This paper is focused on the application of the machine learning for predicting structural response of ring stiffened cylindrical shells subjected to far-field underwater explosion. Three deep neural network (DNN) models are combined to predict the progressive plastic deformation behaviour of stiffened cylindrical shells subjected to the shock wave produced by a TNT charge. In the DNN regression models, the input variables include the charge mass, stand-off distance, detonation depth, cylindrical shell thickness, stiffener web and flange. These three DNN models composed of multi hidden layers are trained based on the data collection originated from a series of simulations performed by the ABAQUS finite element solver. Grid search is introduced to the hyperparameter tuning for deep learning, improving the prediction performance of machine learning methods. The DNN models are compared to the models trained using another three methods: multiple linear regression, decision tree and k-nearest neighbour. An improved Adam optimisation algorithm is used to increase the accuracy of prediction. The challenges encountered during the predictions are discussed to provide a more comprehensive insight into the advantage of the proposed DNN models. The DNN regression models can well predict the permanent plastic deformation and strain of stiffened cylindrical shells.

Dynamic Analysis of Cylindrical Shells with Flexoelectric Actuation

The converse flexoelectric effect can be utilized to actuate and control flexible structures. Assessing the precision flexoelectric actuation and control effectiveness of cylindrical shells is the main objective of this study. The application of voltage to the line electrode on the external surface of a flexoelectric patch, coupled with the bottom surface electrode layer, causes an inhomogeneous electric field to be generated, which consequently induces internal actuation stresses. The stress-induced membrane control force and bending control moment generate modal control effects, which regulate the cylindrical shell vibration. For an elastic cylindrical shell with flexoelectric actuation, the modal forces and microscopic behaviors are studied to evaluate the flexoelectric actuation effects. For the transverse direction, the electric field gradient drops sharply with increasing distance from the line electrode; thus, the induced internal actuation stresses concentrate on the upper surface. Due to the inhomogeneous electric field gradient distributions, the membrane control force and bending control moment concentrate like spikes. To evaluate the actuation effects, modal force distributions of the elastic cylindrical shell with flexoelectric actuation are analyzed with respect to design parameters, such as the flexoelectric patch thickness, line-electrode radius, cylindrical shell thickness, and shell radius.

The requirements for the design and construction of a gas cylinders aimed for transportation of a compressed and liquefied gases

In this paper a typical requirements for the design and construction, workmanship and tests of a gas cylinders of water capacity between 150 l and 3000 l are described. This type of gas cylinder presents a refillable seamless steel tube aimed for transportation of compressed and liquefied gases exposed to extreme world-wide ambient temperatures. These tubes can be used alone or in batteries to equip trailers or multiple element gas containers (ISO modules or skids). When it comes about design requirements, the main focus is on the cylindrical shell thickness, which is calculated using the Lamé-von Mises formula. For some applications such as tubes assembled in batteries to equip trailers or skids (ISO modules) or MEGCs for the transportation and distribution of gases, it is important to calculate stresses associated with mounting the tube (bending stresses, torsional stresses, dynamic loadings etc.). Special attention must be paid to design of tube ends, which should be approximately hemispherical. To permit internal visual inspection of the tube, an adequate opening must be provided at the neck ends. The tubes are manufactured from seamless steel tubing, typically hot rolled, extended/extruded or forged. The ends of tube are hot formed using either forging or spinning methods. After manufacturing process, each tube must be inspected in terms of surface imperfections. Next, each tube must be ultrasonically examined for internal and external defects and laminar imperfections and to determine wall thickness. Batch tests for checking the quality of tubes includes mechanical testing, such as tensile and impact testing. Beside the batch tests, all tubes must be subjected to the following tests: a hydraulic proof pressure test or a volumetric expansion test, a hardness test, a visual inspection, a visual check of the stamp markings, a dimensional inspection and an ultrasonic non-destructive testing (NDT). At the end of this paper, the most commonly found manufacturing imperfections are pointed out.

Numerical investigations on the large deformation behaviour of ring stiffened cylindrical shell subjected to underwater explosion

Ring stiffened cylindrical shells find wide applications in marine vehicles such as submersibles, submarine, autonomous underwater vehicles (AUV) and torpedoes. The structures used for military applications are susceptible to shock loadings from an underwater explosion. It is imperative to understand the shock damage mechanism of such structures to design for survivability. The problem is quite complex involving explosive-fluid interaction, fluid-structure interaction, material, geometric nonlinearity and strain rate effects. In this paper, an attempt has been made to study the shock response of a ring stiffened cylindrical shell of length 1000 mm, diameter 600 mm and thickness 6 mm shock tested using small explosive charge of 70 gm PEK I. The numerical study is performed using LS-DYNA finite element code considering the fluid-structure interaction, strain rate effects, geometric and material nonlinearity. The stiffened cylinder under consideration is modelled using Belytschko-Tsay shell element and the fluid and explosive using Eulerian solid element. The explosive is modelled using JWL equation of state, the fluid using Gruneisen equation of state and the stiffened cylinder fluid interaction using ALE coupling. The permanent deformation obtained from the numerical study compares well with experimental results within 5% accuracy. Subsequently, parametric investigation has been carried out for various charge weights with different cylindrical shell thickness and the results of permanent deformation, effective plastic strain are presented.

CFRP Effect on the Buckling Behavior of Dented Cylindrical Shells

Considering that the use of thin-walled shells is expanding every day, it is important to examine the problem of instability in this form of structure. Many steel structures such as high-water tanks, water and oil reservoirs, marine structures, and pressure vessels, including shell elements, are under stress tension. In addition, shell elements are subject to instability owing to the loads applied. Ten thin-walled cylindrical shell specimens in two groups with different dent depths of tc and 2tc, and the different dent number subject to uniform external pressure were tested in the present research (tc is the thickness of cylindrical shell). The samples were modified to include either one or two dent line with amplitudes of h/3 in height (h the height of cylinder shell). Moreover, CFRP Strips on the dent depth was used in one of the groups. The results of testing under different theories and codes are compared.

Longitudinal Imperfections on Thin Walled Cylindrical Shells

Buckling and post-buckling are among the most important failure factors in thin walled structures. The loadcarrying behavior of cylindrical thin-walled shell structures under external pressure load is strongly dependent upon the nature and magnitude of the initial imperfections. These imperfections are invariably caused by an assortment of manufacturing processes like installing or welding. One of the most important imperfections caused by welding that has been reported to have an essential detrimental effect on the buckling resistance of these shells under external pressure load is longitudinal imperfections. Buckling and post buckling capacity of the shells depend on the H/R and t/ R ratios (H the height, R the radius and t the thickness of a cylindrical shell). The present work discusses the finiteelement models labeled as SS (Shallow Slim), DS (Deep Slim), ST (Shallow Thick) and DT (Deep Thick). The samples of first group are modified to include a line longitudinal imperfection, amplitudes of 0.5t, 1t, 2t, 3t, 4t and 8t in depth (t is the thickness of cylindrical shell). The results presented are in agreement with international codes and theories concerning buckling.

Analytical study on the buckling of cylindrical shells with stepwise variable thickness subjected to uniform external pressure

ABSTRACTThis article focuses on the buckling of cylindrical shells with stepwise variable thickness subjected to uniform external pressure. First, combining the method of separation of variables, perturbation method, and Fourier series expansion, an analytical method for the buckling analysis of cylindrical shells with axisymmetric thickness variation subjected to external pressure is established. The method is verified by comparing with the previous results. Then, the stepwise variable thickness of cylindrical shells is described exactly by the arc tangent function. Finally, using the presented method, a general formula for the critical buckling load of cylindrical shells with stepwise variable thickness subjected to uniform external pressure is derived. This general formula is compared and discussed with some empirical formulae in the current design standards. This study lays a theoretical foundation for the calculation of the buckling load of cylindrical shells with stepwise variable thickness subjected to uniform external pressure. Moreover, it provides a reference and guidance for the further revision of related standards.

The Application of Hasofer-Lind Method in Reliability Design of Thin-Walled Cylindrical Shell

Hasofer-Lind method was applied to reliability design of cylindrical shell with internal pressure. The respective reliability design thickness of different diameter ratio was obtained in the case and compared with the thickness by the second moment reliability design method. The results showed that the wall thickness of cylindrical shell with internal pressure is the thinnest by using Hasofer-Lind method. And it is closest to the wall thickness of the second moment method in which the performance function was defined as the difference in actual wall thickness and the wall thickness needed for cylindrical shell with internal pressure.

Computer Simulation of Cylindrical Shell Penetrated by Rigid Projectile

Computer simulation of cylindrical shell subject to lateral impact by rigid projectile is carried out. The effects of three kinds of typical rigid projectiles, geometric parameters of cylindrical shell and constraint conditions on critical speed are analyzed. The results indicate that the shape of projectile and size of cylindrical shell have a great influence on penetration, and the tapered projectile has a minimum critical speed. The influence of constraint conditions on penetration has a great relationship with thickness of cylindrical shells; energy distribution varies with different thickness of cylindrical shells.

Determination of the Thickness of Elastic Tube Using the Time-Frequency Analysis of Wigner-Ville

The dimensional characterization of an elastic cylindrical shell can be done thanks to its cut-off frequencies of the acoustic circumferential waves propagating around the circumferential of the shell. The Wigner-Ville time-frequency representation, that take into account both the time and frequency parameters of a signal, is used in this study to access to the sought parameters. In this paper, the Wigner-Ville Distribution is applied to acoustic experimental signals backscattered by an aluminium tube with a radii radio b/a (a: external radius, b: internal radius). The time-frequency images of Wigner-Ville obtained permit to determine the cut-off frequency. From these frequencies we have determined with precision the radii radio b/a and also the aluminium cylindrical shell thickness.

Measurement of the thickness of a cylindrical shell with a focused beam

The acoustic scattering from a cylindrical or spherical object immersed in water and insonified with plane wave has been theoretically and experimentally studied. The backscattering spectra show minima, which are related to the circumferential waves circumnavigating around the object. These waves are identical to the Lamb waves propagating in a plate. Two types of resonances are observed on ultrasonic spectra: the resonances related to the thickness and the resonances related to the stationary state that establish around the cylindrical shell from the circumferential waves. To eliminate the second type of resonances a focused beam is used to excite only the thickness resonances. The cylindrical shell thickness is calculated from these experimentally measured resonance frequencies.

Vibrations of Cylindrical Shells with Varying Thickness

The asymmetric vibrations of cylindrical shells with variable thickness are studied by the improved shell theory and the classical one, The equations of vibration and the boundary conditions are obtained from stationary conditions of the Lagrangian of vibrations of cylindrical shells. The solutions are obtained in such a case that the thickness of cylindrical shells, built in at one end, varies exponentially along its axis. After numerical calculations, all boundary conditions at the other end are discussed, the effects of parameters on vibrations are investigated and the results by the improved theory are compared with those by the classical one.