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The aim of this study is to determine the fundamental frequencies of laminated double-curved nanocomposite structures considering transverse shear stresses (TSSs) and rotary inertia (RI). The basic equations of laminated double-curved structures composed of CNT patterned layers based on the Donnell type shell theory are derived within TSSs and considering RI. By applying the Galerkin technique, the fundamental equations are transformed into frequency-dependent sixth-order algebraic equations, and this equation is solved numerically to find the fundamental frequency for laminated double curved structures consisting of CNT patterned layers considering TSSs and RI. In addition, when the rotary inertia is neglected, analytical expressions for frequencies are obtained in the framework of shear deformation theory (ST) and classical theory (CT). Finally, the influences of the volume fraction, CNT patterns, array of nanocomposite layers, TSSs and RI on the fundamental frequency are examined.

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Materials endowed with microstructure, such as particle composites, show a peculiar mechanical behavior, where discontinuities and heterogeneities cannot be neglected. In detail, aiming to depict the structural response at the macroscopic scale, a non-local description is required to keep into account the microscopic one [1]. In this contribution materials with anisotropic microstructure are described as micropolar (Cosserat) continua. Compared to classical (Cauchy) continua, the latter encompass more kinematical descriptors, and then more stress and strain measures. These enriched fields can be revealed of pivotal significance when concentrated forces and/or geometric discontinuities are of interest [2]. As discussed in [3], non-classical and non-local continua can be deducted through multi-scale approaches relying on eligible energy equivalence criteria. Here, anisotropic materials with irregular hexagonal microstructure are considered. The proposed model is able to expose the macroscopic effects of particle size and orientation [2,4]. It is a suitable enhancement of the one recently presented by the Authors in [2], where the statics of two dimensional bodies made of hexagonal rigid particles interacting via elastic interfaces has been analyzed. It is shown how the dynamics at the macroscopics scale is driven by the microstructure. The effect of material anisotropy is investigated with the help of numerical sensitivity analyses, showing how an increasing in the level of material anisotropy alters both frequencies and mode-shapes. Some reliability threesholds for the Cosserat- and Cauchy-like homogenized continua are deduced and discussed in order to address further developments on this research line.

In the present paper the Generalized Differential Quadrature Finite Element Method (GDQFEM) is applied to deal with the static analysis of plane state structures with generic through the thickness material discontinuities and holes of various shapes. The GDQFEM numerical technique is an extension of the Generalized Differential Quadrature (GDQ) method and is based on the idea of conventional integral quadrature. In particular, the GDQFEM results in terms of stresses and displacements for classical and advanced plane stress problems with discontinuities are compared to the ones by the Cell Method (CM) and Finite Element Method (FEM). The multi-domain technique is implemented in a MATLAB code for solving irregular domains with holes and defects. In order to demonstrate the accuracy of the proposed methodology, several numerical examples of stress and displacement distributions are graphically shown and discussed.

A theoretical framework based on an Equivalent Single Layer (ESL) approach is proposed in this chapter to develop several Higher-order Shear Deformation Theories (HSDTs) in a unified and compact manner. In particular, the maximum order of kinematic expansion can be arbitrarily chosen in order to define more refined displacement fields. The Murakami’s function can be also included in the model to take into account the so-called zig-zag effect. The proposed theory is employed to describe the mechanical behavior of doubly-curved shell structures made of composite materials. In particular, the differential geometry is used to define accurately the curved surfaces at issue. The strong formulation of the governing equation is solved by means of a numerical approach based on the Generalized Differential Quadrature (GDQ) method. The accuracy of both the theoretical model and the numerical method is shown through some applications, in which the solutions are compared with the results obtained by means of a three-dimensional finite element model.

Tubular Joints play quite a vital role in most marine structures. It is obvious that having full control about the capacity and strength of tubular joints would be very worthy to have good knowledge about the total performance of the structure. In recent years, the application of the finite element method has become very popular in the analyses of different types of welded circular tubular joints and many commercial and open-source FE systems have been profoundly involved in these regards. Most of these software shares so much in common that it is difficult to differentiate them. This study was performed to investigate and report the usefulness of the open-source software programs in implementing finite element modeling for design applications. In this regard, with aid of the open-source finite element package Code_Aster and its user-friendly interface Salome-Meca, the behavior of reinforced and unreinforced T-joint specimens subjected to axial brace load with different geometry and material property has been studied. In addition, different types of shell and solid finite elements with various mesh densities are considered in this research. In order to overlap the outcomes, the numerical results of this research are present in terms of load-ovalization curves along with the results of other references. Due to mesh sizes and the element types, 144 different simulations have been performed on 12 different specimens. The results show that Code_Aster can satisfactorily predict the nonlinear static behavior of reinforced and unreinforced joints under both tension and compression load. Hence, Code_Aster can be used as a reliable tool for the evaluation and analysis and design of complex offshore joints.

This paper describes the dynamic behaviour of offshore structures modelled as discrete dynamic systems with the installation of innovative smart-tuned liquid column dampers (TLCDs). The use of advanced nano-fluids enhances the mechanical properties of the TLCD and allows the conventional passive system to be modified into a semi-active damping system. The magnetic force is modelled as an additional non-linear stiffness applied on the main structure once the magnetic field is activated. This new approach brings novel perspectives in reducing structural vibrations with respect to conventional TLCD systems. The aim of the study is to present a numerical investigation of the parameters involved in the dynamic behaviour of these systems subjected to random forces. In particular, a comprehensive analysis of a simplified structural model as a two-degrees-of-freedom system is given. Mathematical details and procedures using magneto-rheological-TLCD dampers without the need for commercial frameworks are presented. The present coupled system of ordinary differential equations is solved in a Matlab environment by using the built-in Runge–Kutta implementations for the solution of non-linear equations. This allows engineers and designers to obtain an initial estimation of the structural behaviour prior to in-depth simulations and analysis.

The manuscript aims to investigate the static behavior of laminated nanoplates in hygro-thermal environment. The theoretical framework is based on the Kirchhoff hypothesis for thin structures including the effect of material length scales, which is described by a nonlocal model. For this purpose, the plane stress constitutive laws for laminates are enriched by a size-dependent parameter according to the principles of strain gradient theory. The variational form of such a peculiar theoretical formulation is developed to obtain the corresponding finite element (FE) model, due to the lack of similar numerical approaches in the literature. The difficulties arisen by the presence of higher-order derivatives of the displacements are overcome by using Hermite interpolating polynomials. Conforming and nonconforming FE formulations are presented to this aim. A broad validation procedure is carried out in terms of displacement and stress analysis to verify the accuracy of the approach. The comparison is accomplished taking into account the analytical solution given by the Navier methodology for cross-ply and angle-ply simply supported plates in hygro-thermal environment. The general model allows to extend the analysis to various boundary conditions and lamination schemes.

Exposure to ionizing radiation (IR) during diagnostic medical procedures brings certain risks, especially when experiencing recurrent exposures. The fabrication of nano-based composites, doped with different nanoparticles, have been suggested as effective shielding materials to replace conventional lead-based ones in material sciences and nanotechnology. In this study, commercially available fabrics, used to produce scrubs and gowns for clinical staff, are modified utilizing graphene oxide (GO) nanoparticles using a layer-by-layer (LBL) technique. GO was obtained from graphite through environmentally friendly technology by using a modified–improved Hummers’ method without NaNO3. Lightweight, flexible, air- and water-permeable shielding materials are produced that are wearable in all-day clinical practice. The nanoparticles are kept to a minimum at 1 wt%; however, utilizing the LBL technique they are distributed evenly along the fibers of the fabrics to achieve as much shielding effect as possible. The evaluation of samples is accomplished by simulating real-time routine clinical procedures and the radiographic programs and devices used daily. The GO-coated nanocomposite fabrics demonstrated promising results for X-ray shielding.

Thin-walled deployable composite hinges (DCHs) can achieve foldable and deployable functions by storing and releasing strain energy, which have great application potential in deployable structures , such as satellite antennas and solar wings. This paper presented multi-objective optimisation designs for DCHs. Firstly, an optimisation problem was established to obtain three conflicting objectives, minimising the peak folding moment, maximising the peak torsional moment and minimising the mass. Three design variables and one constraint had been considered. Moreover, four surrogate models were employed, including response surface methodology (RSM) and machine learning models. Root mean square error (RMSE), mean absolute error (MAE) and correlation coefficient (R 2 ) were used to determine the surrogate model with the highest accuracy. Furthermore, four state-of-the-art Genetic Algorithms were benchmarked to obtain the optimal designs. The mimicked inverted generational distance (mIGD) was applied to determine the best optimiser. The research results have significance to practical engineering application of DCHs.

Nominal stresses have been used for a long time for the assessment of fatigue resistance of welded joints, however, this approach has strong limitations since the definition of the nominal stress may be subjective for complex welded details and/or complex loading. On the other hand, the hot-spot stress approach has been proposed to overcome these limitations considering the structural geometrical discontinuities. However, the hot-spot stress methods also present certain limitations, and the present study aims at evaluating the available numerical and analytical hot-spot stress methods proposed by DNVGL (2016) and IIW (2014). The particular case of an offshore tubular KT joint has been considered herein and discretized in two planes. It has been studied numerically using the ABAQUS software coupled with the hot-spot stress extrapolation methods described in IIW (2014) and DNVGL (2016). The influence of the weld geometry has been considered and evaluated. In addition to the numerical method, the present study has also considered the analytical approach proposed in DNVGL (2016) derived from the combination of Efthymiou solutions for the stress concentration factor with the method of superposition of stresses. The numerical models according to IIW (2014) have been found to be more conservative when compared with the mesh-size methods proposed by DNVGL (2016), both in numerical modelling without the weld or with weld. For the numerical models with weld cord, the mean values of normalized difference index obtained for all braces together, as a result of comparing numerical results with analytical solutions, are lower, when compared with results obtained from the numerical models without weld cord.

The reliable performance of composite tubes conveying nanofluid is an essential issue for robust design under dynamic loads. Further, the frequency failure mode of these structures is a considerable performance function to provide a balance between mass and stiffness of the structure. The ability of the first-order reliability method (FORM)-based finite-step adaptive length (FAL) is discussed for reliability analysis of composite tubes under frequency failure mode. The performances for efficiency and robustness to evaluate the failure probability FORM formulas are discussed. Therefore, the capability of FAL using the steepest descent sensitivity vector is compared with three FORM formulations that are extended by the steepest descent search direction for nanocomposite tubes conveying nanofluid. In this current work, the Navier scheme is employed for calculating the frequency failure mode. Furthermore, the robustness and efficiency related to the steepest descent FORM formulas of HL-RF, directional stability transformation method (DSTM), and finite-step length (FSL) are compared with FAL. Based on this discussion, FAL contains efficient formula in comparison with other FORM formulas. Moreover, it is found that FSL formulas as well as FAL formulas are more robust than HL-RF and DSTM. This structure's failure probability rises as the fluid velocity and pipe diameter increase.

In this article, a completely new numerical method called the Local Least-Squares Element Differential Method (LSEDM), is proposed for solving general engineering problems governed by second order partial differential equations. The method is a type of strong-form finite element method. In this method, a set of differential formulations of the isoparametric elements with respect to global coordinates are employed to collocate the governing differential equations and Neumann boundary conditions of the considered problem to generate the system of equations for internal nodes and boundary nodes of the collocation element. For each outer boundary or element interface, one equation is generated using the Neumann boundary condition and thus a number of equations can be generated for each node associated with a number of element interfaces. The least-squares technique is used to cast these interface equations into one equation by optimizing the local physical variable at the least-squares formulation. Thus, the solution system has as many equations as the total number of nodes of the present heat conduction problem. The proposed LSEDM can ultimately guarantee the conservativeness of the heat flux across element surfaces and can effectively improve the solution stability of the element differential method in solving problems with hugely different material properties, which is a challenging issue in meshfree methods. Numerical examples on two- and three-dimensional heat conduction problems are given to demonstrate the stability and efficiency of the proposed method.