Search results for "Elastic"
showing 10 items of 2162 documents
A fractional order theory of poroelasticity
2019
Abstract We introduce a time memory formalism in the flux-pressure constitutive relation, ruling the fluid diffusion phenomenon occurring in several classes of porous media. The resulting flux-pressure law is adopted into the Biot’s formulation of the poroelasticity problem. The time memory formalism, useful to capture non-Darcy behavior, is modeled by the Caputo’s fractional derivative. We show that the time-evolution of both the degree of settlement and the pressure field is strongly influenced by the order of Caputo’s fractional derivative. Also a numerical experiment aiming at simulating the confined compression test poroelasticity problem of a sand sample is performed. In such a case, …
Fractional visco-elastic Euler–Bernoulli beam
2013
Abstract Aim of this paper is the response evaluation of fractional visco-elastic Euler–Bernoulli beam under quasi-static and dynamic loads. Starting from the local fractional visco-elastic relationship between axial stress and axial strain, it is shown that bending moment, curvature, shear, and the gradient of curvature involve fractional operators. Solution of particular example problems are studied in detail providing a correct position of mechanical boundary conditions. Moreover, it is shown that, for homogeneous beam both correspondence principles also hold in the case of Euler–Bernoulli beam with fractional constitutive law. Virtual work principle is also derived and applied to some c…
Demographic change, tourism expenditure and life cycle behavior
2015
Abstract The paper explores how demographic changes in human populations may impact on tourism decision-making of households over their life cycle. By means of hurdle models, the study focuses respectively on the decision to travel domestically or abroad and investigates if statistically significant differences exist as to the impact of age and cohort on the decision to travel and tourism expenditure. Using a vast dataset on Italian Household Expenditures over the period 1997–2007 the empirical results show that demographic aspects do have a strong effect on the tourism behaviour of families and that cohort and age effects act differently on the decision of households to make a trip and on …
Intertemporal Substitution in the Spanish Economy: Evidence from Regional Data*
2018
This paper studies the intertemporal substitution in consumption and leisure for the Spanish economy by estimating the first‐order conditions of an individual optimization model with regional and aggregate data. While first‐order conditions determining intertemporal substitution in consumption show a good econometric fit, and the value we obtain for the intertemporal elasticity of substitution is similar to previously available results, the econometric fit of the intertemporal condition in leisure indicates that the behaviour of the Spanish labour supply over the cycle is more complex than can be explained by the canonical intertemporal choice model.
Is participation in the tourism market an opportunity for everyone? Some evidence from Italy
2016
This paper investigates whether there are differences in tourism consumption behaviour among families by analysing the main determinants of tourism participation at national and international levels. In particular, it explores whether tourism is becoming part of the lifestyle of Italians or whether it is still a luxury good only for the privileged. A Heckman model was used on micro-data on Italian family expenditure over the period 1997–2007, and an income elasticity analysis for different personal and household characteristics was carried out. The results show that participation in the tourism market is strongly affected by the personal characteristics of individuals and that tourism cons…
A Hierarchical Model for Analysing Consumption Patterns in Italy Before and During the Great Recession
2016
The paper aims to explore how the Great Recession of the twenty-first century has impacted on the consumption behaviour of Italian households. Following a hierarchical approach, the study investigates differences in consumption behaviour at both household and regional levels. Using micro data on Italian Household Expenditure for the years 2002, 2006, 2010 and 2012, multilevel and two-step regression models have been estimated. The analysis has been performed for four different consumption categories: food, housing, work-related and leisure. The analysis reveals that the economic crisis led to increasing income elasticity for each category of consumption, especially for food, the most essent…
A Novel Adaptive Sliding Mode Controller for a 2-DOF Elastic Robotic Arm
2022
Collaborative robots (or cobots) are robots that are capable of safely operating in a shared environment or interacting with humans. In recent years, cobots have become increasingly common. Compliant actuators are critical in the design of cobots. In real applications, this type of actuation system may be able to reduce the amount of damage caused by an unanticipated collision. As a result, elastic joints are expected to outperform stiff joints in complex situations. In this work, the control of a 2-DOF robot arm with elastic actuators is addressed by proposing a two-loop adaptive controller. For the outer control loop, an adaptive sliding mode controller (ASMC) is adopted to deal with unce…
The Redesigned Serpens, a Low-Cost, Highly Compliant Snake Robot†
2022
The term perception-driven obstacle-aided locomotion (POAL) was proposed to describe locomotion in which a snake robot leverages a sensory-perceptual system to exploit the surrounding operational environment and to identify walls, obstacles, or other structures as a means of propulsion. To attain POAL from a control standpoint, the accurate identification of push-points and reliable determination of feasible contact reaction forces are required. This is difficult to achieve with rigidly actuated robots because of the lack of compliance. As a possible solution to this challenge, our research group recently presented Serpens, a low-cost, open-source, and highly compliant multi-purpose modular…
Time-harmonic solution for acousto-elastic interaction with controllability and spectral elements
2010
The classical way of solving the time-harmonic linear acousto-elastic wave problem is to discretize the equations with finite elements or finite differences. This approach leads to large-scale indefinite complex-valued linear systems. For these kinds of systems, it is difficult to construct efficient iterative solution methods. That is why we use an alternative approach and solve the time-harmonic problem by controlling the solution of the corresponding time dependent wave equation. In this paper, we use an unsymmetric formulation, where fluid-structure interaction is modeled as a coupling between pressure and displacement. The coupled problem is discretized in space domain with spectral el…
Nonsmooth Mechanics. Convex and Nonconvex Problems
1999
Nonlinear, multivalued and possibly nonmonotone relations arise in several areas of mechanics. A multivalued or complete relation is a relation with complete vertical branches. Boundary laws of this kind connect boundary (or interface) quantities. A contact relation or a locking mechanism between boundary displacements and boundary tractions in elasticity is a representative example. Material constitutive relations with complete branches connect stress and strain tensors, or, in simplified theories, equivalent stress and strain quantities. A locking material or a perfectly plastic one is represented by such a relation. The question of nonmonotonicity is more complicated. One aspect concerns…