Thermoelastic Vibration and Stability of Temperature-Dependent Carbon Nanotube-Reinforced Composite Plates

The present article investigates the thermoelastic vibration and stability characteristics of carbon nanotube-reinforced composite (CNTRC) plates in thermal environment. The CNTRC plates are made up of four different types of uniaxially aligned reinforcements. The single-walled carbon nanotubes (SWCNTs) reinforcement is either uniformly distributed (UD) or functionally graded (FG) according to linear functions of the thickness direction. The material properties, of both matrix and CNTs, are temperature-dependent and the effective elastic coefficients are evaluated by using a micromechanical model. The governing equations (GEs) are derived in their weak-form by using Hamilton’s Principle in conjunction with the method of the power series expansion of the displacement components. The Ritz method, based on highly stable trigonometric trial functions, is used as solution technique. Convergence and stability of the proposed formulation have been thoroughly analyzed by assessing many higher-order plate models. Thermal and mechanical pre-stresses are taken into account. Moreover, the effect of significant parameters such as length-to-thickness ratio, volume fraction, aspect ratio, loading-type, CNTs distribution as well as boundary conditions is discussed

Experimental study on circular eccentric cam-follower pairs

Experimental verifications of cam-follower contacts are very important because of the difficulties for a reliable simulation due to the continuous variation of load, speed and geometry of the lubricated contact. Some experiments have been carried out with a new apparatus, specifically designed and realised for investigation on cam-follower and gear teeth contacts, in order to test its capability to measure film thickness and contact forces. Circular eccentric cams have been used because they feature lower transient effects and comparison of the results with the theoretical/numerical ones is easier. The tests have been performed using cams with two different eccentricities and surface roughness, and two different followers, one made of steel and one made of glass. The behaviour of the cam-follower contacts at several different rotational speeds, ranging from 50 to 500 rpm, and different pre-loads have been investigated. Lubrication regimes ranged from boundary to complete, being most of the tests performed under mixed lubrication conditions. Localised wear has occurred during some tests. Data of all contact force and moment components as well as of the cam shaft driving torque have been acquired at high acquisition frequency. Some methodologies for numerical data elaboration have been identified. Optical interference images have been correctly recorded at the desired frequency. The trends of the normal and friction forces measured in the different tests are presented in the paper, as well as the evaluated trends of the friction coefficient. Some sample optical interference images are also shown. The results furnish encouraging indications about the capabilities of the experimental apparatus

An exact dynamic stiffness element using a higher order shear deformation theory for free vibration analysis of composite plate assemblies

An exact dynamic stiffness method based on higher order shear deformation theory is developed for the first time using symbolic computation in order to carry out free vibration analysis of composite plate assemblies. Hamilton's principle is applied to derive the governing differential equations of motion and natural boundary conditions. Then by imposing the geometric boundary conditions in algebraic form the dynamic stiffness matrix is developed. The Wittrick-Williams algorithm is used as solution technique to compute the natural frequencies and mode shapes for a range of laminated composite plates and stepped panels. The effects of significant parameters such as thickness ratio, orthotropy ratio, step ratio, number of layers, lay-up and stacking sequence and boundary conditions on the natural frequencies and mode shapes are critically examined and discussed. The accuracy of the method is demonstrated by comparing results with those available in the literature

Buckling of composite plate assemblies using higher order shear deformation theory-An exact method of solution

An exact dynamic stiffness element based on higher order shear deformation theory and extensive use of symbolic algebra is developed for the first time to carry out a buckling analysis of composite plate assemblies. The principle of minimum potential energy is applied to derive the governing differential equations and natural boundary conditions. Then by imposing the geometric boundary conditions in algebraic form the dynamic stiffness matrix, which includes contributions from both stiffness and initial pre-stress terms, is developed. The Wittrick–Williams algorithm is used as solution technique to compute the critical buckling loads and mode shapes for a range of laminated composite plates including stiffened plates. The effects of significant parameters such as thickness-to-length ratio, orthotropy ratio, number of layers, lay-up and stacking sequence and boundary conditions on the critical buckling loads and mode shapes are investigated. The accuracy of the method is demonstrated by comparing results whenever possible with those available in the literature

Investigation on cam-follower lubricated contacts

The cam-follower contact is one of the most complex lubricated non-conformal contact due to its continuous variation of load, speed and geometry. The complexity of the phenomena occurring in the camshaft systems make experimental verifications very important. In this work, an already existing versatile experimental apparatus for investigation of non-conformal lubricated contacts, able to measure film thickness using the optical interference method and friction force trough a load cell, has been modified in order to tests cam-follower contacts. Some test have been carried out for investigating the behaviour of some fundamental components of the rig. A theoretical/numerical simulations has been performed to investigate the dynamic behaviour of the system and in order to provide some indications for the interpretation of the experimental results. Purposely developed versions of the programme have been also an important support for the design and of a new apparatus specifically addressed to the cam-follower contact and with increased potentialities capable of more detailed measurement of film thickness and contact forces. The apparatus is able to reproduce a cam-follower mechanism that uses a rocker as a link device between the cam follower set and the valve

Some results on thermal stress of layered plates and shells by using Unified Formulation

This work presents some results on two-dimensional modelling of thermal stress problems in multilayered structures. The governing equations are written by referring to the Unified Formulation (UF) introduced by the first author. These equations are obtained in a compact form, that doesn't depend on the order of expansion of variables in the thickness direction or the variable description (layer-wise models and equivalent single layers models). Classical and refined theories based on the Principle of Virtual Displacements (PVD) and advanced mixed theories based on the Reissner Mixed Variational Theorem (RMVT) are both considered. As a result, a large variety of theories are derived and compared. The temperature profile along the thickness of the plate/shell is calculated by solving the Fourier's heat conduction equation. Alternatively, thermo-mechanical coupling problems can be considered, in which the thermal variation is influenced by mechanical loading. Exact closed-form solutions are provided for plates and shells, but also the applications of the Ritz method and the Finite Element Method (FEM) are presented

Hardware prototyping and validation of a W-ΔDOR digital signal processor

Microwave tracking, usually performed by on ground processing of the signals coming from a spacecraft, represents a crucial aspect in every deep-space mission. Various noise sources, including receiver noise, affect these signals, limiting the accuracy of the radiometric measurements obtained from the radio link. There are several methods used for spacecraft tracking, including the Delta-Differential One-Way Ranging (ΔDOR) technique. In the past years, European Space Agency (ESA) missions relied on a narrowband ΔDOR system for navigation in the cruise phase. To limit the adverse effect of nonlinearities in the receiving chain, an innovative wideband approach to ΔDOR measurements has recently been proposed. This work presents the hardware implementation of a new version of the ESA X/Ka Deep Space Transponder based on the new tracking technique named Wideband ΔDOR (W-ΔDOR). The architecture of the new transponder guarantees backward compatibility with narrowband ΔDOR

A study on text-score disagreement in online reviews

In this paper, we focus on online reviews and employ artificial intelligence tools, taken from the cognitive computing field, to help understanding the relationships between the textual part of the review and the assigned numerical score. We move from the intuitions that 1) a set of textual reviews expressing different sentiments may feature the same score (and vice-versa); and 2) detecting and analyzing the mismatches between the review content and the actual score may benefit both service providers and consumers, by highlighting specific factors of satisfaction (and dissatisfaction) in texts. To prove the intuitions, we adopt sentiment analysis techniques and we concentrate on hotel reviews, to find polarity mismatches therein. In particular, we first train a text classifier with a set of annotated hotel reviews, taken from the Booking website. Then, we analyze a large dataset, with around 160k hotel reviews collected from Tripadvisor, with the aim of detecting a polarity mismatch, indicating if the textual content of the review is in line, or not, with the associated score. Using well established artificial intelligence techniques and analyzing in depth the reviews featuring a mismatch between the text polarity and the score, we find that -on a scale of five stars- those reviews ranked with middle scores include a mixture of positive and negative aspects. The approach proposed here, beside acting as a polarity detector, provides an effective selection of reviews -on an initial very large dataset- that may allow both consumers and providers to focus directly on the review subset featuring a text/score disagreement, which conveniently convey to the user a summary of positive and negative features of the review target.Comment: This is the accepted version of the paper. The final version will be published in the Journal of Cognitive Computation, available at Springer via http://dx.doi.org/10.1007/s12559-017-9496-