Shallow Shells Research Articles

Free vibration analysis of functionally graded shallow shells with variable thickness and physical neutral surface effects

The study and manufacture of functionally graded (FG) shallow shells with the variable thickness are essential for the actual application of these types of structures. Previously, many researchers have developed different approaches to analyzing the mechanical behaviors of the FG structures, in which the thickness parameter has been assumed to be constant. Moreover, studies on these types of structures with the variable thickness are still quite limited. For this reason, this paper provides an effective and simple approach via mathematical formulations for analyzing the free vibrational responses of FG shallow shells with the variable thickness. Also, the presence of porosities that can occur during the fabrication of FG materials is considered. One of the highlights here is to consider the influence of the physical neutral surface. Before conducting the analysis of these FG structures, firstly, it is important to establish governing equations based on the classical shell theory. These essential equations are used for the FG shallow shells. Then, by setting the Navier solution with the help of simply supported boundary conditions, the natural frequencies are obtained. Finally, the numerical examples will be given to illustrate the effects of porosity coefficient, material and geometry parameters as well as the physical neutral surface on the natural frequencies. In addition, two numerical examples for verification will also be performed and thereby show the accuracy of the current method and model. It is hoped that the main results of this study can be useful not only to designers and researchers but also to be extended to more complex problems.

A semi-analytical sinusoidal shear deformation theory for nonlinear dynamic response and vibration of CNT–FGM doubly curved shallow shells

A semi-analytical sinusoidal shear deformation theory for nonlinear dynamic response and vibration of CNT–FGM doubly curved shallow shells

On the bifurcation of solutions to Marguerre–von Kármán equations

The objective of this work is to study the bifurcation of solutions of the Marguerre–von Kármán equations, which constitute a mathematical model for the buckling of Marguerre–von Kármán shallow shells. More precisely, we reduce the Marguerre–von Kármán equations to a single equation with a cubic operator; its second member depends on the function that defines the middle surface of the shallow shell and the applied forces. Next, we prove a general existence theorem for the reduced equation, by using the main theorem on pseudomonotone operators. Then we study the bifurcation of solutions in the reduced equation, with a second member, is small, at neighborhood of the simple characteristic value of the linearized problem.

EQUILIBRIUM OF A NORMALLY LOADED ELASTIC SHALLOW CYLINDRICAL SHELL WITH DISLOCATIONS AND DISCLINATIONS

We consider the problem of the equilibrium of a normally loaded elastic shallow rectangular circular cylindrical shell, which contains sources of internal stress in the form of fields of continuously distributed edge dislocations and wedge disclinations or other sources, for example, thermal ones. Based on the modified system of Karman equations for the equilibrium of an elastic plate with dislocations and disclinations, a system of nonlinear equilibrium equations for the shell was constructed. The resulting system of equations differs from the Karman system of equilibrium equations for an elastic shallow cylindrical shell under the action of a normal load by the presence on the right side of the continuity equation of a nonzero function, called the incompatibility function, which is expressed through the densities of edge dislocations and wedge disclinations. The edges of the shell are freely clamped or hinged. In the absence of internal stress sources, this system transforms into a system of equilibrium equations for a shallow shell, and in the case of an infinitely large radius of curvature (and the presence of internal stress sources) into a modified system of Karman equilibrium equations for a flexible elastic plate with dislocations and disclinations. To solve the system of nonlinear shell equilibrium equations, the Newton – Kantorovich method in combination with the difference method is proposed. For the case of small values of the normal load and small values of the incompatibility function, linearization is carried out with respect to the deflection and stress function. As a result, a linear boundary value problem was obtained in the form of a system of differential equations for the deflection and the stress function, which is solved by the difference method. The solution of the linearized system is used as an initial approximation in the implementation of the Newton – Kantorovich method. Examples of numerical calculations of deflection and stress function for given values of normal load and incompatibility function are given, and corresponding graphs are constructed.

On the Problem of Solvability of Nonlinear Boundary Value Problems for Shallow Isotropic Shells of Timoshenko Type in Isometric Coordinates

On the Problem of Solvability of Nonlinear Boundary Value Problems for Shallow Isotropic Shells of Timoshenko Type in Isometric Coordinates

Reliability-based Fracture Analysis for Shallow Shell Structure with the Dual Boundary Element Method

Reliability analysis has gained prominence as a stochastic approach to incorporate uncertainties in structural analysis. This study presents a novel methodology for evaluating the sensitivity of the crack tip stress intensity factor in a shallow shell structure. The work focuses on the reliability analysis of a shallow shell structure containing a crack originating from the corner of a fuselage window. The analysis incorporates uncertainties in both geometrical and loading parameters. The sensitivity of the crack tip stress intensity factors with respect to the considered uncertainties is determined. The Implicit Differentiation Method (IDM)-based First-Order Reliability Method (FORM) is utilized, and the results are compared to the results obtained from Monte Carlo Simulation (MCS), with a maximum difference of 2.99%. The reliability analysis aids in determining an appropriate inspection crack size that satisfies safety requirements, consequently facilitating the selection of the corresponding inspection technique.

Nonlinear Deformation of Flexible Shallow Shells of Complex Shape Made of Materials with Different Resistance to Tension and Compression

Nonlinear Deformation of Flexible Shallow Shells of Complex Shape Made of Materials with Different Resistance to Tension and Compression

Nonconforming Finite Element Methods for Two-Dimensional Linearly Elastic Shallow Shell Model

Nonconforming Finite Element Methods for Two-Dimensional Linearly Elastic Shallow Shell Model

Thermally Induced Vibrations of Functionally Graded Shallow Spherical Shells Under Cooling Shock

Based on the first-order shear deformation theory (FSDT), the large-amplitude vibration behavior of shallow spherical shells made of functionally graded materials (FGMs) due to the rapid decrease of temperature (cooling shock) is investigated. FGM is assumed to be a mixture of stainless steel and low-carbon steel whose properties are considered temperature dependent and are estimated based on the power-law model. According to FSDT and von Kármán assumptions, the governing equations of motion in conjunction with corresponding boundary conditions are obtained using Hamilton’s principle. The temperature distribution is also achieved by means of the 1D Fourier transient heat conduction equation, considering two time-dependent thermal loading scenarios. The considered thermal boundary conditions allow that a temperature difference is created with a time delay for the structure under cooling shock. Also, the results of recent experiments are employed to estimate the temperature-dependent properties of structures. In the solution approach, the generalized differential quadrature method and the Newmark-beta integration scheme are utilized. Selected numerical results are presented to study the effects of thermal load rapidity time, geometry, magnitude of thermal load, and material gradient index on the thermally induced vibrations of spherical shells. Stresses generated in the shell due to the thermally induced vibrations are also investigated.

Nonlinear vibration analysis of a double curved shallow sandwich shell in which the core made of three-phase nanocomposite and the two-outer layer of electromagnetic materials

This paper investigates the nonlinear vibrations of a double curved shallow sandwich shell with a three-phase nanocomposite core and two outer electromagnetic layers considering the thermal environment's influence. Relying on the Halpin–Tsai model, the core is assumed to be made of some composite plies incorporating three constituents: carbon nanotubes (CNTs) or graphene nanoplatelets (GPLs) as nanocomposites, fibers and polymeric matrix (resin). Governing equations calculating the nonlinear vibration of the double curved shallow shell were obtained by combining Reddy's first-order shear deformation theory (FSDT) and the Von Kármán geometrical nonlinearity. Later, this system of equations is transformed into the nonlinear ordinary differential expressions by utilizing the Galerkin procedure. Thus, the effects of material properties, temperature, geometrical properties, elastic foundations to the frequency of linear and nonlinear free vibration, and amplitude–frequency relations of the double curved shallow sandwich shell were discussed. The results demonstrate that the free vibration frequency of the shell increases if the magnetic field enhances, whereas that decreases when the voltage expands in both models as CNTs and GPLs. Simultaneously, the shallow shell has a better ability to force load compared to a plate with the same dimensions. These outcomes can make a profit in the design and manufacturing of new smart structures applied in energy harvesting, and medicine.

On the Optimality Conditions in the Weight Minimization Problem for a Shell of Revolution at a Given Vibration Frequency

We consider shallow elastic shells with a given circular boundary and seek an axisymmetric shell shape minimizing the weight at a given fundamental frequency of shell vibrations. Using the resulting formula for the linear part of the increment of the frequency functional, the multiplicity of the minimum natural frequency of vibrations of the shell is estimated. The Fréchet differentiability of the frequency functional is also established, and optimal conditions for minimizing the weight of the shell at a given fundamental vibration frequency are obtained.

Solvability of Nonlinear Equilibrium Problems for Timoshenko-type Shallow Shells in Curvilinear Coordinates

Solvability of Nonlinear Equilibrium Problems for Timoshenko-type Shallow Shells in Curvilinear Coordinates

Panel Flutter Numerical Study of Thin Isotropic Flat Plates and Curved Plates with Various Edge Boundary Conditions

In this article, supersonic panel flutter analysis of flat plates and curved plates with different edge boundary conditions are studied, using efficient, high precision triangular shallow shell finite elements. The fluid on the underside of the plate was is assumed to be stationary. The linear piston theory can be applied to the top surface of the plate. The linear piston theory was used to evaluate the aerodynamic loads. The solution of a complex eigenvalue problem was formulated according to Hamilton’s principle. Lagrange’s equation of motion was obtained using standard methods for finding eigenvalues. Current finite element analysis ignores aerodynamic damping. For panels, the theory of thin and small deformed shells was taken into account. To validate the developed finite element code, the results of a square and rectangular flat-panels with simply supported edges (S-S-S-S), a square plate with four fixed edges (C-C-C-C), and a square plate with the length side clamps (C-S-C-S) were compared with the published data. The flutter results of other edge boundary conditions (S-C-S-C, C-S-C-S, and C-C-C-C) for square and rectangular flat panels are evaluated for which literature data is limited. It has been found that the fixed condition in the cross-flow direction (S-C-S-C) has a significant effect on the critical flutter pressure parameters and flutter frequencies. Further, to study the aforementioned effect, the current finite element (FE) has been extended to curved plates with S-C-S-C(constrained in the cross-flow direction and exposed to supersonic flow), SS-S-S boundary conditions to find flutter results.

Large deformation analysis of functionally graded revolutionary shallow thin shells with bi-modular effect: Snap-through buckling under different boundary constraints

Functionally graded materials (FGMs) enable structures to achieve a smooth transition between different material properties, providing an optimized combination of functions to meet the diversity of engineering needs. However, the presence of bi-modular effect in FGMs is often neglected due to the complexity in the analysis. In this paper, the curvature correction equivalent method based on the von Kármán theory will be applied to the theoretical study for the large deformation problem and the resulting snap-through buckling of functionally graded revolutionary shallow thin shells with bi-modular effect under different boundary constraints. Furthermore, a bi-modular FGMs user material subroutine (UMAT) is developed for the first time to simulate the real material model, thus validating the theoretical solution. The results show that except for the bi-modular effect of materials, boundary constraints of shells also have important influences on the relationship of load vs. central deflection and snap-through buckling. The research of boundary constraints brings new conclusions to snap-through buckling: the rotation constraint and radial constraint at the shell edge have opposite effects on snap-through buckling. This work will contribute to the analysis of the snap-through buckling of functionally graded revolutionary shallow thin shells with an obvious bi-modular effect and under various boundary constraints.

Buckling of Stiffened Heterogeneous Shells Taking into Account Material Creep

The authors propose a mathematical model of shell structures taking into account the linear theory of hereditary material creep. This model is based on the total potential strain energy functional. Shells are reinforced with stiffeners, and the contact between the stiffener and the shell skin along a strip is taken into account. The Ritz method is applied to the functional, and a system of algebraic or integro-algebraic equations is found. The resulting system is first solved as a linear system (without account for the terms reflecting material creep), and the state of the structure under the specified load is determined. Then the iterative method is used to solve the creep problem for a given value of time. The paper presents the results of studying stiffened shallow shells of double curvature made of reinforced concrete under uniformly distributed load. The buckling of shells occurs over time as a result of the development of creep strains. Values of the buckling load as a result of material creep are found. It is shown that stresses are redistributed over the shell field over time and the maximum stress is observed near the contour of the structure.

Nonlinear vibroacoustic response and sound transmission loss analysis of functionally graded doubly curved shallow shells

This paper presents the semi-analytical nonlinear vibroacoustic and sound transmission loss behaviors of functionally graded doubly curved shallow. The model is developed by considering the simple power law scheme of material distribution in the thickness direction, under thermal load and incident oblique plane sound wave, as well as Donnell’s nonlinear shallow shell theory. By defining the stress function in terms of the force resultants and applying differential operators to these resultants, the coupled compatibility equation and nonlinear equation of motion are obtained only with regard to the stress function and displacement components. The methods of inverse differential operator and average form approach are then utilized to solve the particular and homogeneous solutions of the stress function associated with different boundary conditions. Based on this solution and the use of the Galerkin method with trigonometric mode shape functions, the nonlinear partial differential equation of motion is turned into the Duffing equation. Next, the method of multiple scales is implemented to capture the frequency of the shell corresponding to transverse motion. Finally, the nonlinear vibration and acoustic responses of shells are studied by considering the variation of important parameters such as aspect ratio, dimensionless amplitude, volume fraction power of functionally graded material, phase portrait, sound transmission loss, velocity, average mean square velocity of drive point, and the sound power level of the shells.

A hyperbolic theory for the analysis of laminated shallow shells with double curvature

In this paper, higher-order closed-form analytical solutions to the static bending and free vibration problems of laminated composite shells with double curvature are obtained using a hyperbolic shear deformation theory. The current theory is a modification of the shape function provided by Soldatos [30] in his well-known hyperbolic theory. The distributions of transverse shear stresses through the thickness of the shell are precisely predicted by the current theory satisfying traction free boundary conditions at the top and the bottom surfaces of the shell. Hamilton's principle serves as the foundation for the development of equations of motion. Navier's method is used for the analysis of simply-supported laminated shells under static and free vibration conditions. Displacements, stresses, and natural frequencies are presented for different shells with double curvature. The results from past investigations are compared to verify the accuracy and efficacy of the present hyperbolic shell theory.

Method of Solving Geometrically Nonlinear Bending Problems of Functionally Graded Shallow Shells of Complex Shape

Method of Solving Geometrically Nonlinear Bending Problems of Functionally Graded Shallow Shells of Complex Shape

Computer Simulation of the Stress-Strain State of Functionally Graded Sandwich Plates and Shallow Shells of Complex Shape Resting on the Elastic Foundation

Computer Simulation of the Stress-Strain State of Functionally Graded Sandwich Plates and Shallow Shells of Complex Shape Resting on the Elastic Foundation

Numerical vibroacoustic analysis of multi-layered composite structure under hygrothermal loading using coupled FEM-IBEM micromechanical model

The vibroacoustic responses of multi-layer composite shallow shell panels subjected to harmonic mechanical excitation in hygrothermal environment is numerically investigated. A homogenized micromechanical finite element (FE) based on the higher-order mid-plane kinematics replicating quadratic function as well as the through the thickness stretching effect together with the indirect boundary element (IBE) scheme has been first time employed. The isoparametric Lagrangian element with zero-order Hermitian interpolation function (10 degrees of freedom per node) is used for structural model discretization to attain the hygro-thermo-elastic natural frequencies via Hamilton’s principle. The uniqueness of the model is the incorporation of the effective material properties under combined hygrothermal loading via a micromechanics approach. An IBE method is then implemented to attain structure-surrounding coupling and the Helmholtz wave equation is solved to compute the sound radiation responses. The effectiveness of the model is tested by converging it with the similar analytical/numerical results as well as the experimentally acquired data for vibrational as well as acoustic responses. The present scheme is further hold out for solving diverse numerical illustrations. The geometrical parameters, volume fraction of fiber, layup, and support conditions alongside the hygrothermal load is found to have significant influence on the hygro-thermo-acoustic characteristics. The functional inferences will assist in designing the imminent multi-layered structures that serve under the influence of severe hygrothermal loading during high-performance engineering applications.