Free Vibration of Composite Cylindrical Shells Based on Third-Order Shear Deformation Theory

The focus of this study is to analyse the free vibration of cylindrical shells under third-order shear deformation theory (TSDT). The constitutive equations of the cylindrical shells are obtained using third-order shear deformation theory (TSDT). The surface and traverse displacements are expected to have cubic and quadratic variation. Spline approximation is used to approximate the displacements and transverse rotations. The resulting generalized eigenvalue problem is solved for the frequency parameter to get as many eigenfrequencies as required starting from the least. From the eigenvectors, the spline coefficients are computed from which the mode shapes are constructed. The frequency of cylindrical shells is analysed by varying circumferential node number, length dimension, layer number, and different materials. The authenticity of the present formulation is established by comparing with the available FEM results.

STRESS DISTRIBUTION IN THE HOLLOW STIFFENED HYBRID LAMINATED COMPOSITE PANELS IN SHIP STRUCTURES UNDER SINUSOIDAL LOADING

A simplified hollow stiffened hybrid laminated plate model has been developed for the marine structures. The detailed stress analysis through the thickness of the stiffened plate based on the higher order shear deformation theory has been carried out under sinusoidal loading. The hybrid laminates are made by wrapping the GFRP laminates with CFRP at the outermost layers of the stiffened panel. This hybridization technique can be an optimum solution from the point of view of cost reduction as well as enhancement of strength properties. The layer-wise stresses for the stiffened plate have been calculated in the present paper. A 3D polynomial curve fitting technique has been used to obtain higher accuracy and consistency in the computation of stresses. The computer code has been developed using MATLAB considering the plates as eight noded isoparametric plate bending element and the stiffener has been modeled as three noded isoparametric beam element. The stiffened panel has also been analysed using the ANSYS14.0 software package considering 2D model. The results obtained from the present formulation have been compared with those available in the published literature to validate the present formulation. The stiffened panels made of GFRP, CFRP and GFRP-CFRP hybrid laminates have been studied here. An extensive parametric study has been carried out with varying fibre content in the laminates.

A 4-node quadrilateral element with center-point based discrete shear gap (CP-DSG4)

This work aims at presenting a novel four-node quadrilateral element, which is enhanced by integrating with discrete shear gap (DSG), for analysis of Reissner-Mindlin plates. In contrast to previous studies that are mainly based on three-node triangular elements, here we, for the first time, extend the DSG to four-node quadrilateral elements. We further integrate the fictitious point located at the center of element into the present formulation to eliminate the so-called anisotropy, leading to a simplified and efficient calculation of DSG, and that enhancement results in a novel approach named as "four-node quadrilateral element with center-point based discrete shear gap - CP-DSG4". The accuracy and efficiency of the CP-DSG4 are demonstrated through our numerical experiment, and its computed results are validated against those derived from the three-node triangular element using DSG, and other existing reference solutions.

Wave Analysis for In-Plane Vibration of Angular and Curved Frames

In many structural applications like bridges, arches, etc., frames are used, and it is important to study their dynamic behavior. Finite element method (FEM) is usually used for computational simulation of vibration for such frame structures. However, FEM simulations for high frequency are computationally intensive and lack accuracy. This paper proposes a wave propagation-based approach for the vibration analysis of a frame having angular and curved joints. The reflection and transmission matrices for the joints are derived using the kinematic compatibility and equilibrium conditions. Reflection, transmission, and propagation matrices are assembled leading to matrix equation terms of the wave amplitudes. Modal analysis and harmonic analysis of frames having curved and angular joints are performed using the present formulation. The frequency response function for point harmonic forcing acting on such structures is also presented. The formulation and the results are non-dimensionalized for wider applicability. The results obtained using the present formulation are compared with those obtained through FEM simulation in a commercial package. It is found that the results obtained using the two methods are in excellent correlation. The computational efficiency of the present method over FEM simulation is also reported.

Sexual Slavery as a War Crime: A Reform Proposal

For the first time in the history of international criminal law, the ICC Elements of Crimes included a statutory definition of sexual slavery as a war crime and as a crime against humanity. Such definition is derived from, and in fact almost identical to, the definition of enslavement in the same text. In July 2019, that language for the first time was adopted and applied in the conviction of general Bosco Ntaganda, the first ever conviction for sexual slavery as a war crime and as a crime against humanity at the ICC, as part of the situation in the Democratic Republic of Congo. This note argues for a reform in the language of the crime of sexual slavery as present in the ICC Elements of Crimes. The present formulation of such crime fails to correctly provide an independent standing for sexual slavery: that is, it does not adequately characterize the sexual nature of the crime as opposed to the broader category of enslavement. The note will focus on the drafting history that led to the present language, as well as on the problems arising from the Ntaganda decision. The note highlights the theoretical and practical limits of the present formulation, and it will address the academic critiques the language already received. It will then provide for an alternative wording for the first element of the crime, a wording that is more reflective of the purpose arising from the negotiating history at Rome and that emphasizes the sexual nature of the offense.

An Efficient Three Nodded Finite Element Formulation for Free Vibration Analysis of Sandwich Arches with Graded Metallic Cellular Core

An efficient finite element model based on three nodded element has been developed for the vibration analysis of sandwich arches with graded metallic cellular (GMC) core. The present formulation is based on the higher-order shear deformation theory and orthogonal curvilinear coordinate axes. The arch consists of two isotropic face sheets and a GMC core layer. The internal pores in the core layer follow the different types of distributions. The material properties of the GMC core layer of the sandwich arches vary in the thickness direction as a function in terms of porosity coefficient and mass density. Three types of porosity distributions have been considered to accomplish the vibration responses of sandwich arches. The present formulation is validated with limited results available in the literature. Few new results are computed and the effects of different influencing parameters such as porosity coefficient [Formula: see text], porosity distribution type, the thickness-to-length ratio [Formula: see text], boundary conditions and opening angle [Formula: see text] on the free vibration characteristics of sandwich arches with the GMC core are observed. The present finite element model gives better convergence and more accurate results than a conventional two nodded element-based finite element model.

Static analysis of co-cured composite structures with double-layer damping membranes embedded

The purpose of this study is to determine the effects of various parameters on the deflection value and strain energy for the individual stress of a co-cured composite structure with double-layer damping membranes embedded (CCSDDME) simply supported on four edges. To achieve this goal, an analytical solution (double Fourier sine series) was developed for the deflection of an embedded co-cured damping composite plate with double-layer damping membranes embedded. The deflection value and strain energy of each stress component are deduced. The present formulation is validated based on the results obtained using the finite element method and parametric studies are then carried out to illustrate the effects of various parameters on the deflection value and strain energy for an individual stress of CCSDDME.

Structural optimization to maximize loss factor of embedded co-cured damping composite

The purpose of this study is to obtain the maximum loss factor of the embedded co-cure damping composite structure with the boundary condition of four edges clamped. To achieve this goal, the strain energy of each stress component is deduced using the Ritz method, and the loss factor of the structure is calculated. The present formulation is validated based on the results obtained using the finite element method. Finally, the law of loss factor variation with the change in structure thickness and layup angle is obtained. The results obtained show that the loss factor of the structure increases as the thickness of the structure increases; when the total thickness of the structure is constant, the loss factor increases first and then decreases, and there is an optimal value for the design; the optimal lay angle is pi/4.

In vivo feasibility study of the use of porous polyhedral oligomeric silsesquioxane implants in partial laryngeal reconstruction

BackgroundLoss of substantial volumes of laryngeal tissue after trauma or cancer significantly impairs quality of life. We hypothesised that repair of laryngeal defects with a candidate biomaterial, seeded with mesenchymal stem cells (MSC) and epithelial cells, may offer a therapeutic approach to this unmet need.MethodMoulded porous polyhedral oligomeric silsesquioxane polycarbonate-urea (POSS-PCU) scaffolds were seeded with human-derived MSC and epithelial cells, were implanted orthotopically into a defect created in the thyroid cartilage in eight pigs and monitoredin vivofor 2 months.In vivoassessments were performed at 1, 2, 4 and 8 weeks post implantation. Histology was performed following termination.ResultsImplant operations were uncomplicated. One pig was terminated early (2 weeks post-implantation) following expectoration of its implant. No other mortality or morbidity was observed. Endoscopy showed partial extrusion of implants at two weeks and complete extrusion of all implants by termination.ConclusionsPOSS-PCU moulded laryngeal implants, in the present formulation, are extruded from the site of implantation between two- and eight-weeks post-surgery in pigs. In its present formulation and with the present, one-stage, protocol, this material does not appear to provide a suitable scaffold and vehicle for cells intended for partial laryngeal replacement in pigs.

Love waves in a nonlocal elastic media with voids

The propagation of Love-type waves in a nonlocal elastic layer with voids resting over a nonlocal elastic solid half-space with voids has been studied. Dispersion relations are derived using appropriate boundary conditions of the model. It is found that there exist two fronts of Love-type surface waves that may travel with distinct speeds. The appearance of the second front is purely due to the presence of voids in layered media. Both fronts are found to be dispersive in nature and affected by the presence of the nonlocality parameter. The first front is found to be nonattenuating, independent of void parameters and analogous to the Love wave of classical elasticity, while the second front is attenuating and depends on the presence of void parameters. Each of the fronts is found to face a critical frequency above which it ceases to propagate. For a specific model, the variation of the phase speeds of both the fronts with frequency, nonlocality, voids and thickness parameters is shown graphically. Attenuation coefficient versus frequency for the second front has also been depicted separately. Some particular cases are deduced from the present formulation.