Fractional visco-elastic systems under normal white noise
In this paper an original method is presented to compute the stochastic response of singledegree- of-freedom structural systems with viscoelastic fractional damping. The key-idea stems from observing that, based on a few manipulations involving an appropriate change of variable and a discretization of the fractional derivative operator, the equation of motion can be reverted to a coupled linear system involving additional degrees of freedom, the number of which depends on the discretization adopted for the fractional derivative operator. The method applies for fractional damping of arbitrary order a (0 < α < 1). For most common input correlation functions, including a Gaussian white noise, …
On the dynamics of non-local fractional viscoelastic beams under stochastic agencies
Abstract Non-local viscoelasticity is a subject of great interest in the context of non-local theories. In a recent study, the authors have proposed a non-local fractional beam model where non-local effects are represented as viscoelastic long-range volume forces and moments, exchanged by non-adjacent beam segments depending on their relative motion, while local effects are modelled by elastic classical stress resultants. Long-range interactions have been given a fractional constitutive law, involving the Caputo's fractional derivative. This paper introduces a comprehensive numerical approach to calculate the stochastic response of the non-local fractional beam model under Gaussian white no…
Flexural vibrations of discontinuous layered elastically bonded beams
Abstract This paper addresses the dynamic flexural behavior of layered elastically bonded beams carrying an arbitrary number of elastic translational supports and rotational joints. The beams are referred to as discontinuous for the discontinuities of response variables at the application points of supports/joints. The Euler-Bernoulli hypothesis is assumed to hold for each layer separately, and a linear constitutive relation between the horizontal interlayer slip and the interlaminar shear force is considered. Based on the theory of generalized functions to handle the discontinuities of response variables due to supports/joints, exact beam modes are obtained from a characteristic equation b…
Fractional-Order Thermal Energy Transport for Small-Scale Engineering Devices
Fractional-order thermodynamics has proved to be an efficient tool to describe several small-scale and/or high-frequency thermodynamic processes, as shown in many engineering and physics applications. The main idea beyond fractional-order physics and engineering relies on replacing the integer-order operators of classical differential calculus with their real-order counterparts. In this study, the authors aim to extend a recently proposed physical picture of fractional-order thermodynamics to a generic 3D rigid heat conductor where the thermal energy transfer is due to two phenomena: a short-range heat flux ruled by stationary and nonstationary transport equations, and a long-range thermal …
Solution strategies for 1D elastic continuum with long-range interactions: Smooth and fractional decay
Abstract An elastic continuum model with long-range forces is addressed in this study within the context of approximate analytical methods. Such a model stems from a mechanically-based approach to non-local theory where long-range central forces are introduced between non-adjacent volume elements. Specifically, long-range forces depend on the relative displacement, on the volume product between interacting elements and they are proportional to a proper, material-dependent, distance-decaying function. Smooth-decay functions lead to integro-differential governing equations whereas hypersingular, fractional-decay functions lead to a fractional differential governing equation of Marchaud type. …
A Novel Solution to Find the Dynamic Response of an Euler–Bernoulli Beam Fitted with Intraspan TMDs under Poisson Type Loading
This contribution considers a virtual experiment on the vibrational response of rail and road bridges equipped with smart devices in the form of damping elements to mitigate vibrations. The internal damping of the bridge is considered a discontinuity that contain a dashpot. Exact complex eigenvalues and eigenfunctions are derived from a characteristic equation built as the determinant of a 4 x 4 matrix
Oral temozolomide in heavily pre-treated brain metastases from non-small cell lung cancer: phase II study
Introduction: The primary tumour type most likely to metastasize to the brain is lung cancer. In heavily pre-treated patients, limited therapeutic option is available and the results of availability therapies reported in literature are disappointing. The present phase II study was designed to assess the efficacy and safety of temozolomide (TMZ) as palliative treatment for brain metastases (BrM) in NSCLC patients pre-treated with WBRT and at least one line of chemotherapy for metastatic brain disease. Material and methods: Temozolomide was administered orally at 150 mg/mq/day for five consecutive days for the first cycle, doses were increased to 200 mg/mq/day for 5 days every 28 days for sub…
Stationary and non-stationary stochastic response of linear fractional viscoelastic systems
Abstract A method is presented to compute the stochastic response of single-degree-of-freedom (SDOF) structural systems with fractional derivative damping, subjected to stationary and non-stationary inputs. Based on a few manipulations involving an appropriate change of variable and a discretization of the fractional derivative operator, the equation of motion is reverted to a set of coupled linear equations involving additional degrees of freedom, the number of which depends on the discretization of the fractional derivative operator. As a result of the proposed variable transformation and discretization, the stochastic analysis becomes very straightforward and simple since, based on stand…
Advanced materials modelling via fractional calculus: challenges and perspectives.
Fractional calculus is now a well-established tool in engineering science, with very promising applications in materials modelling. Indeed, several studies have shown that fractional operators can successfully describe complex long-memory and multiscale phenomena in materials, which can hardly be captured by standard mathematical approaches as, for instance, classical differential calculus. Furthermore, fractional calculus has recently proved to be an excellent framework for modelling non-conventional fractal and non-local media, opening valuable prospects on future engineered materials. The theme issue gathers cutting-edge theoretical, computational and experimental studies on advanced mat…
Stochastic Analysis of a Nonlocal Fractional Viscoelastic Bar Forced by Gaussian White Noise
Recently, a displacement-based nonlocal bar model has been developed. The model is based on the assumption that nonlocal forces can be modeled as viscoelastic (VE) long-range interactions mutually exerted by nonadjacent bar segments due to their relative motion; the classical local stress resultants are also present in the model. A finite element (FE) formulation with closed-form expressions of the elastic and viscoelastic matrices has also been obtained. Specifically, Caputo's fractional derivative has been used in order to model viscoelastic long-range interaction. The static and quasi-static response has been already investigated. This work investigates the stochastic response of the non…
Approximate analytical mean-square response of an impacting stochastic system oscillator with fractional damping
The paper deals with the stochastic dynamics of a vibroimpact single-degree-of-freedom system under a Gaussian white noise. The system is assumed to have a hard type impact against a one-sided motionless barrier, located at the system's equilibrium. The system is endowed with a fractional derivative element. An analytical expression for the system's mean squared response amplitude is presented and compared with the results of numerical simulations.
Non-local stiffness and damping models for shear-deformable beams
This paper presents the dynamics of a non-local Timoshenko beam. The key assumption involves modeling non-local effects as long-range volume forces and moments mutually exerted by non-adjacent beam segments, that contribute to the equilibrium of any beam segment along with the classical local stress resultants. Elastic and viscous long-range volume forces/moments are endowed in the model. They are built as linearly depending on the product of the volumes of the interacting beam segments and on generalized measures of their relative motion, based on the pure deformation modes of the beam. Attenuation functions governing the space decay of the non-local effects are introduced. Numerical resul…
Stochastic response of beams equipped with tuned mass dampers subjected to Poissonian loads
This contribution deals with the vibrational response of Euler-Bernoulli beams equipped with tuned mass dampers, subjected to random moving loads. The theory of generalised functions is used to capture the discontinuities of the response variables at the positions of the tuned mass dampers, which involves deriving exact complex eigenvalues and eigenfunctions from a characteristic equation built as the determinant of a 4 x 4 matrix, regardless of the number of tuned mass dampers. Building pertinent orthogonality conditions for the deflection eigenfunctions, the stochastic responses, under Poissonian white noise, are evaluated. In a numerical application, a beam with multiple tuned mass dampe…
How Effective and Safe Is Bronchial Thermoplasty in “Real Life” Asthmatics Compared to Those Enrolled in Randomized Clinical Trials?
There is limited information on the efficacy and safety of bronchial thermoplasty (BT) inreal life. We evaluated the outcomes of the randomized clinical trials for BT in severe asthmatics, in whom the exclusion criteria were not strictly controlled. A case series of seven asthmatics (M/F: 4/3; age:54.6±2.9years) is reported. Subjects had a statistically significant improvement in AQLQ (from a mean of3.96±1.1to4.5±1.2and5.5±0.6after 6 and 12 months of treatment;p=0.0007) and in the ACQ score (from2.77±0.8to1.83±1.2and1.5±0.8after 6 and 12 months;p<0.001). In the year after BT, severe exacerbations, salbutamol use, and OCS use were significantly lower compared with the 1-yr pretreatment pe…
Finite element method for a nonlocal Timoshenko beam model
A finite element method is presented for a nonlocal Timoshenko beam model recently proposed by the authors. The model relies on the key idea that nonlocal effects consist of long-range volume forces and moments exchanged by non-adjacent beam segments, which contribute to the equilibrium of a beam segment along with the classical local stress resultants. The long-range volume forces/moments are linearly depending on the product of the volumes of the interacting beam segments, and their relative motion measured in terms of the pure beam deformation modes, through appropriate attenuation functions governing the spatial decay of nonlocal effects. In this paper, the beam model is reformulated wi…
Response Power Spectrum of Multi-Degree-of-Freedom Nonlinear Systems by a Galerkin Technique
This paper deals with the estimation of spectral properties of randomly excited multi-degree-of-freedom (MDOF) nonlinear vibrating systems. Each component of the vector of the stationary system response is expanded into a trigonometric Fourier series over an adequately long interval T. The unknown Fourier coefficients of individual samples of the response process are treated by harmonic balance, which leads to a set of nonlinear equations that are solved by Newton’s method. For polynomial nonlinearities of cubic order, exact solutions are developed to compute the Fourier coefficients of the nonlinear terms, including those involved in the Jacobian matrix associated with the implementation o…
Stochastic dynamic analysis of fractional viscoelastic systems
A method is presented to compute the non-stationary response of single-degree-of-freedom structural systems with fractional damping. Based on an appropriate change of variable and a discretization of the fractional derivative operator, the equation of motion is reverted to a set of coupled linear equations involving additional half oscillators, the number of which depends on the discretization of the fractional derivative operator. In this context, it is shown that such a set of oscillators can be given a proper fractal representation, with a Mandelbrot dimension depending on the fractional derivative order a. It is then seen that the response second-order statistics of the derived set of c…
Physically-Based Approach to the Mechanics of Strong Non-Local Linear Elasticity Theory
In this paper the physically-based approach to non-local elasticity theory is introduced. It is formulated by reverting the continuum to an ensemble of interacting volume elements. Interactions between adjacent elements are classical contact forces while long-range interactions between non-adjacent elements are modelled as distance-decaying central body forces. The latter are proportional to the relative displacements rather than to the strain field as in the Eringen model and subsequent developments. At the limit the displacement field is found to be governed by an integro-differential equation, solved by a simple discretization procedure suggested by the underlying mechanical model itself…
A Mellin transform approach to wavelet analysis
The paper proposes a fractional calculus approach to continuous wavelet analysis. Upon introducing a Mellin transform expression of the mother wavelet, it is shown that the wavelet transform of an arbitrary function f(t) can be given a fractional representation involving a suitable number of Riesz integrals of f(t), and corresponding fractional moments of the mother wavelet. This result serves as a basis for an original approach to wavelet analysis of linear systems under arbitrary excitations. In particular, using the proposed fractional representation for the wavelet transform of the excitation, it is found that the wavelet transform of the response can readily be computed by a Mellin tra…
On the moving load problem in Euler–Bernoulli uniform beams with viscoelastic supports and joints
This paper concerns the vibration response under moving loads of Euler–Bernoulli uniform beams with translational supports and rotational joints, featuring Kelvin–Voigt viscoelastic behaviour. Using the theory of generalized functions to handle the discontinuities of the response variables at the support/joint locations, exact beam modes are obtained from a characteristic equation built as determinant of a (Formula presented.) matrix, for any number of supports/joints. Based on pertinent orthogonality conditions for the deflection modes, the response under moving loads is built in the time domain by modal superposition. Remarkably, all response variables are built in a closed analytical for…
A correction method for dynamic analysis of linear systems
Abstract This paper proposes an analytical method to improve the accuracy of the dynamic response of classically damped linear systems, as given by a standard truncated modal analysis. Upon computing the first m undamped modes of a n-degree-of-freedom system, two sets of equations in the Rn nodal space are built, which are uncoupled and govern the contribution to the response of the m computed modes and the remaining (n−m) unknown modes, respectively. The first set is solved in the Rm modal space by using the m available modes; the second set is solved in a reduced R(n−m) nodal space, without computing additional modes. Specifically, it is shown that the particular solution of the second se…
Random vibration mitigation of beams via tuned mass dampers with spring inertia effects
The dynamics of beams equipped with tuned mass dampers is of considerable interest in engineering applications. Here, the purpose is to introduce a comprehensive framework to address the stochastic response of the system under stationary and non-stationary loads, considering inertia effects along the spring of every tuned mass damper applied to the beam. For this, the key step is to show that a tuned mass damper with spring inertia effects can be reverted to an equivalent external support, whose reaction force on the beam depends only on the deflection of the attachment point. On this basis, a generalized function approach provides closed analytical expressions for frequency and impulse res…
On the vibrations of a mechanically based non-local beam model
The vibration problem of a Timoshenko non-local beam is addressed. The beam model involves assuming that the equilibrium of each volume element is attained due to contact forces and long-range body forces exerted, respectively, by adjacent and non-adjacent volume elements. The contact forces result in the classical Cauchy stress tensor while the long-range forces are taken as depending on the product of the interacting volume elements and on their relative displacement through a material-dependent distance-decaying function. To derive the motion equations and the related mechanical boundary conditions, the Hamilton's principle is applied The vibration problem of a Timoshenko non-local beam …
Finite-Element Formulation of a Nonlocal Hereditary Fractional-Order Timoshenko Beam
AbstractA mechanically-based nonlocal Timoshenko beam model, recently proposed by the authors, hinges on the assumption that nonlocal effects can be modeled as elastic long-range volume forces and moments mutually exerted by nonadjacent beam segments, which contribute to the equilibrium of any beam segment along with the classical local stress resultants. Long-range volume forces/moments linearly depend on the product of the volumes of the interacting beam segments, and on pure deformation modes of the beam, through attenuation functions governing the space decay of nonlocal effects. This paper investigates the response of this nonlocal beam model when viscoelastic long-range interactions a…
Stochastic response of offshore structures by a new approach to statistical cubicization
This study presents a new statistical cubicization approach for predicting the stochastic response of offshore platforms subjected to a Morison-type nonlinear drag loading. Statistics of the original system are obtained from an equivalent nonlinear system, which is constructed by replacing the Morison drag force by a cubic polynomial function of the relative fluid-structure velocity, up to cubic order. A Volterra series expansion with a finite Fourier series representation is used to approximate the response of the equivalent system. Exact solutions are developed to express the Fourier coefficients of the second and third-order response as functions of the Fourier coefficients of the first-…
Prognostic value of two geriatric screening tools in a cohort of older patients with early stage Non-Small Cell Lung Cancer treated with hypofractionated stereotactic radiotherapy
Objectives: To investigatewhether assessmentwith two geriatric screening tools shows a correlationwith clinical outcomes of patients aged 65 years or more, with early-stage Non-Small Cell Lung Cancer (es-NSCLC) treated with hypofractionated stereotactic radiotherapy. Methods: FromMarch 2014 to June 2018we retrospectively evaluated 42 patientswith stage I and II lung tumors. Patients were assessed with Charlson Comorbidity Index (CCI) and G8 screening tool. Median age was 74 years (range, 65–91). Stereotactic radiotherapy was performed with Helical Tomotherapy delivering 50–70 Gray (Gy) in 8–10 fractions. Toxicity was evaluated using Common Terminology Criteria for Adverse Events v4.0 criter…
A phase II study of carboplatin and paclitaxel as first line chemotherapy in elderly patients with advanced non-small cell lung cancer (NSCLC)
Introduction: Lung cancer is the leading cause of tumour-related deaths in the elderly population but the optimal management of advanced NSCLC in older patients has not been defined to date. The present phase II study was planned to evaluate the efficacy and toxicity of the combination of carboplatin and paclitaxel in elderly patients with advanced NSCLC. Patients and methods: Patients (>70 years old) who had pathologically been proven to have a NSCLC and measurable lesions were treated with paclitaxel (175 mg/m2for 3 h) and carboplatin [area under the concentration-time curve (AUC = 5)] on day 1 every 3 weeks. Results: Forty patients were enrolled into the study. The median age was 74 year…
A new displacement-based framework for non-local Timoshenko beams
In this paper, a new theoretical framework is presented for modeling non-locality in shear deformable beams. The driving idea is to represent non-local effects as long-range volume forces and moments, exchanged by non-adjacent beam segments as a result of their relative motion described in terms of pure deformation modes of the beam. The use of these generalized measures of relative motion allows constructing an equivalent mechanical model of non-local effects. Specifically, long-range volume forces and moments are associated with three spring-like connections acting in parallel between couples of non-adjacent beam segments, and separately accounting for pure axial, pure bending and pure sh…
Some properties of multi-degree-of-freedom potential systems and application to statistical equivalent non-linearization
This paper presents some properties of two restricted classes of multi-degree-of-freedom potential systems subjected to Gaussian white-noise excitations. Specifically, potential systems which exhibit damping terms with energy-dependent polynomial form are referred to. In this context, first systems with coupled stiffness terms and damping terms depending on the total energy are investigated. Then, systems with uncoupled stiffness terms and damping terms depending on the total energy in each degree-of-freedom are considered. For these two classes, it is found that algebraic relations among the stationary statistical moments of the energy functions can be derived by applying standard tools of…
A mechanically based approach to non-local beam theories
A mechanically based non-local beam theory is proposed. The key idea is that the equilibrium of each beam volume element is attained due to contact forces and long-range body forces exerted, respectively, by adjacent and non-adjacent volume elements. The contact forces result in the classical Cauchy stress tensor while the long-range forces are modeled as depending on the product of the interacting volume elements, their relative displacement and a material-dependent distance-decaying function. To derive the beam equilibrium equations and the pertinent mechanical boundary conditions, the total elastic potential energy functional is used based on the Timoshenko beam theory. In this manner, t…
A Non-Local Two Dimensional Foundation Model
Classical foundation models such as the Pasternak and the Reissner models have been recently reformulated within the framework of non-local mechanics, by using the gradient theory of elasticity. To contribute to the research effort in this field, this paper presents a two-dimensional foundation model built by using a mechanically based non-local elasticity theory, recently proposed by the authors. The foundation is thought of as an ensemble of soil column elements resting on an elastic base. It is assumed that each column element is acted upon by a local Winkler-like reaction force exerted by the elastic base, by contact shear forces and volume forces due, respectively, to adjacent and non-…
The mechanically-based approach to 3D non-local linear elasticity theory: Long-range central interactions
Abstract This paper presents the generalization to a three-dimensional (3D) case of a mechanically-based approach to non-local elasticity theory, recently proposed by the authors in a one-dimensional (1D) case. The proposed model assumes that the equilibrium of a volume element is attained by contact forces between adjacent elements and by long-range forces exerted by non-adjacent elements. Specifically, the long-range forces are modelled as central body forces depending on the relative displacement between the centroids of the volume elements, measured along the line connecting the centroids. Further, the long-range forces are assumed to be proportional to a proper, material-dependent, dis…
On the Stochastic Response of a Fractionally-damped Duffing Oscillator
A numerical method is presented to compute the response of a viscoelastic Duffing oscillator with fractional derivative damping, subjected to a stochastic input. The key idea involves an appropriate discretization of the fractional derivative, based on a preliminary change of variable, that allows to approximate the original system by an equivalent system with additional degrees of freedom, the number of which depends on the discretization of the fractional derivative. Unlike the original system that, due to the presence of the fractional derivative, is governed by non-ordinary differential equations, the equivalent system is governed by ordinary differential equations that can be readily h…
Stochastic response of a fractional vibroimpact system
Abstract The paper proposes a method to investigate the stochastic dynamics of a vibroimpact single-degree-of-freedom fractional system under a Gaussian white noise input. It is assumed that the system has a hard type impact against a one-sided motionless barrier, which is located at the system’s equilibrium position; furthermore, the system under study is endowed with an element modeled with fractional derivative. The proposed method is based on stochastic averaging technique and overcome the particular difficulty due to the presence of fractional derivative of an absolute value function; particularly an analytical expression for the system’s mean squared response amplitude is presented an…
The mechanically based non-local elasticity: an overview of main results and future challenges
The mechanically based non-local elasticity has been used, recently, in wider and wider engineering applications involving small-size devices and/or materials with marked microstructures. The key feature of the model involves the presence of non-local effects as additional body forces acting on material masses and depending on their relative displacements. An overview of the main results of the theory is reported in this paper.
Exact frequency response of bars with multiple dampers
The paper addresses the frequency analysis of bars with an arbitrary number of dampers, subjected to harmonically varying loads. Multiple external/internal dampers occurring at the same position along the bar, modelling external damping devices and internal damping due to damage or imperfect connections, are considered. In this context, the challenge is to handle simultaneous discontinuities of the response variables, i.e. axial force/displacement discontinuities at the location of external/internal dampers. Based on the theory of generalized functions, the paper will present exact closed-form expressions of the frequency response under point/polynomial loads, which hold regardless of the n…
Spectral Approach to Equivalent Statistical Quadratization and Cubicization Methods for Nonlinear Oscillators
Random vibrations of nonlinear systems subjected to Gaussian input are investigated by a technique based on statistical quadratization, and cubicization. In this context, and depending on the nature of the given nonlinearity, statistics of the stationary response are obtained via an equivalent system with a polynomial nonlinearity of either quadratic or cubic order, which can be solved by the Volterra series method. The Volterra series response is expanded in a trigonometric Fourier series over an adequately long interval T, and exact expressions are derived for the Fourier coefficients of the second- and third-order response in terms of the Fourier coefficients of the first-order, Gaussian…
Mechanically Based Nonlocal Euler-Bernoulli Beam Model
AbstractThis paper presents a nonlocal Euler-Bernoulli beam model. It is assumed that the equilibrium of a beam segment is attained because of the classical local stress resultants, along with long-range volume forces and moments exchanged by the beam segment with all the nonadjacent beam segments. Elastic long-range volume forces/moments are considered, built as linearly depending on the product of the volumes of the interacting beam segments and on generalized measures of their relative motion, based on the pure deformation modes of the beam. Attenuation functions governing the space decay of the nonlocal effects are introduced. The motion equations are derived in an integro-differential …
On the moving multi-loads problem in discontinuous beam structures with interlayer slip
Abstract This contribution proposes an efficient approach to the moving multi-loads problem on two-layer beams with interlayer slip and elastic translational supports. The Euler-Bernoulli hypothesis is assumed to hold for each layer separately, and a linear constitutive relation between the horizontal slip and the interlaminar shear force is considered. It is shown that, using the theory of generalized functions to treat the discontinuous response variables, exact eigenfunctions can be derived from a characteristic equation built as determinant of a 6 x 6 matrix. Building pertinent orthogonality conditions for the deflection eigenfunctions, a closed-form analytical response is established i…
The finite element method for fractional non-local thermal energy transfer in non-homogeneous rigid conductors
Abstract In a non-local fractional-order model of thermal energy transport recently introduced by the authors, it is assumed that local and non-local contributions coexist at a given observation scale: while the first is described by the classical Fourier transport law, the second involves couples of adjacent and non-adjacent elementary volumes, and is taken as proportional to the product of the masses of the interacting volumes and their relative temperature, through a material-dependent, distance-decaying power-law function. As a result, a fractional-order heat conduction equation is derived. This paper presents a pertinent finite element method for the solution of the proposed fractional…
On the moving load problem in beam structures equipped with tuned mass dampers
This paper proposes an original and efficient approach to the moving load problem on Euler–Bernoulli beams, with Kelvin–Voigt viscoelastic translational supports and rotational joints, and in addition, equipped with Kelvin–Voigt viscoelastic tuned mass dampers (TMDs). While supports are taken as representative of external devices such as grounded dampers or in-span supports with flexibility and damping, the rotational joints may model rotational dampers or connections with flexibility and damping arising from imperfections or damage. The theory of generalised functions is used to treat the discontinuities of the response variables, which involves deriving exact complex eigenvalues and eigen…
Stochastic response of linear and non-linear systems to α-stable Lévy white noises
Abstract The stochastic response of linear and non-linear systems to external α -stable Levy white noises is investigated. In the literature, a differential equation in the characteristic function (CF) of the response has been recently derived for scalar systems only, within the theory of the so-called fractional Einstein–Smoluchowsky equations (FESEs). Herein, it is shown that the same equation may be built by rules of stochastic differential calculus, previously applied by one of the authors to systems driven by arbitrary delta-correlated processes. In this context, a straightforward formulation for multi-degree-of-freedom (MDOF) systems is also developed. Approximate CF solutions to the …