Vincenzo Mallardo | Università degli Studi di Ferrara (original) (raw)

Papers by Vincenzo Mallardo

In this paper a novel application of the Boundary Element Method (BEM) to nonlinear acoustic fiel... more In this paper a novel application of the Boundary Element Method (BEM) to nonlinear acoustic field is presented. The resulting integral equations require the evaluation of a domain integral. The Dual Reciprocity Boundary Element Method is used to transfer the domain integral to boundary integrals. Both the linear and nonlinear formulations of the acoustic BEM are described. The proposed nonlinear formulation is tested for different basis functions and compared to analytical solution

The boundary element method (BEM) has been used to solve interior/exterior acoustic problems for ... more The boundary element method (BEM) has been used to solve interior/exterior acoustic problems for many years because of its boundary only discretisation and automatically satisfaction of the radiation condition at infinity. The main drawback is related to the final ...

Cmes-computer Modeling in Engineering & Sciences, Sep 1, 2012

The present paper intends to couple the Fast Multipole Method (FMM) with the Boundary Element Met... more The present paper intends to couple the Fast Multipole Method (FMM) with the Boundary Element Method (BEM) in the 2D scalar wave propagation. The procedure is aimed at speeding the computation of the integrals involved in the governing Boundary Integral Equations (BIEs) on the basis of the distance between source point and integration element. There are three main contributions. First, the approach is of adaptive type in order to reduce the number of floating-point operations. Second, most integrals are evaluated analytically: the diagonal and offdiagonal terms of the H and G matrices by consolidated techniques, whereas the moment Mk by a procedure developed by the authors. Third, the article is enriched by Fortran 90 schemes that, specifically developed by the authors, allow the optimum construction of the quad-tree and of the iterative system of equations. The Generalized Minimal Residual Solver is adopted to improve the overall computational efficiency. Some numerical examples are shown to demonstrate the reliability of the method.

International Journal for Numerical Methods in Engineering, Apr 30, 1998

ABSTRACT In this paper a boundary element formulation for the sensitivity analysis of structures ... more ABSTRACT In this paper a boundary element formulation for the sensitivity analysis of structures immersed in an inviscide fluid and illuminated by harmonic incident plane waves is presented. Also presented is the sensitivity analysis coupled with an optimization procedure for analyses of flaw identification problems. The formulation developed utilizes the boundary integral equation of the Helmholtz equation for the external problem and the Cauchy–Navier equation for the internal elastic problem. The sensitivities are obtained by the implicit differentiation technique. Examples are presented to demonstrate the accuracy of the proposed formulations. © 1998 John Wiley & Sons, Ltd.

Structural durability & health monitoring, 2013

ABSTRACT The optimum location of the sensors is a critical issue of any successful Structural Hea... more ABSTRACT The optimum location of the sensors is a critical issue of any successful Structural Health Monitoring System. Sensor optimization problems encompass mainly three areas of interest: system identiﬁcation, damage identiﬁcation and impact identiﬁcation. The current paper is intended as a review of the state of the art at the year 2012 and going back to 1990. The above topics have been dealt with in separate contexts so far but they contain interesting common elements to be exploited.

International Journal for Numerical Methods in Engineering, Mar 20, 2012

In this paper a novel Boundary Element (BE) formulation for sensitivity analysis of local active ... more In this paper a novel Boundary Element (BE) formulation for sensitivity analysis of local active noise control in a three-dimensional field is presented. The formulation is based on the Helmholtz differential equation and it is valid for internal as well as for scattering wave propagation problems. The primary noise is attenuated within an enclosure, called control volume, by adding a control source modelled as an object with a vibrating surface. Both the optimum position of the control volume and the optimum location/orientation of the secondary source are determined by minimisation of a suitable cost function. The sensitivities are determined by implicit differentiation. A hierarchical adaptive cross approximation approach in conjunction with the GMRES solver is implemented to accelerate the convergence. Four numerical examples are presented to demonstrate accuracy and efficiency of the proposed formulations.

Journal of Sound and Vibration, Sep 1, 1998

In this paper the application of the two-dimensional boundary element method to the scattering of... more In this paper the application of the two-dimensional boundary element method to the scattering of plane sound waves from an infinite cylinder in a fluid is presented. The acoustic equation of the wave motion in a barotropic, inviscid fluid is deduced from the linearized hydrodynamics equations and the linearized equation of state, while the wave motion inside the solid is described by two different models. Two sets of boundary integral equations are presented for modelling the interaction of fluid-fluidlike and fluid-solid problems. Several test examples are presented to demonstrate the accuracy of the proposed formulations. Comparison with available analytical results, as well as numerical results for different sizes and positions of the internal boundary are given. Farfield coefficients and the results of the scattering cross-section demonstrate the different behaviour of the two models and the influence of the internal boundary.

International Journal of Plasticity, Aug 1, 2016

A three-dimensional grain-boundary formulation for small strains crystal plasticity is presented ... more A three-dimensional grain-boundary formulation for small strains crystal plasticity is presented for the first time. The method is developed and implemented for both single grains and polycrystalline aggregates and it is based on the use of a suitable set of boundary integral equations for modelling the individ

International Journal of Non-linear Mechanics, Apr 1, 2013

In the present work a model able to predict the buckling behavior of thin, orthotropic, stiffened... more In the present work a model able to predict the buckling behavior of thin, orthotropic, stiffened plates and shells subject to axial compression is proposed. In the context of the Kirchhoff-Love plate theory and making use of different strain-displacement models-namely the von Ká rmá n model, the Koiter-Sanders shell model, an enhanced von Ká rmá n model and a spurious model commonly adopted in literature-the equilibrium equations have been solved by the Levy-type approach. The results obtained highlight the influence of each non-linear strain-displacement term and show that the von Ká rmá n model can noticeably overestimate the buckling load when the critical mode involves significant in-plane displacements.

Key Engineering Materials, Aug 1, 2018

In this paper the integral equation approach is used to describe the propagation of continuumdama... more In this paper the integral equation approach is used to describe the propagation of continuumdamage in three dimensional solids. The governing equation is of integral type and contains bothboundary and domain integrals. Such integrals are computed with the aid of the NURBS functions.The subvolume involved by the damage is modelled by a special mapping procedure that avoids theuse of the internal cells. The implementation is verified on a test case for which an analytical solutionis available.

In the present paper the Boundary Element Method is developed in the framework of the Computer Ai... more In the present paper the Boundary Element Method is developed in the framework of the Computer Aided Design softwares in two-dimensional elastostatics. The B-splines, commonly used to reproduce the geometry of the model, are here adopted to model the field variables and, thus, to solve the structural model under static loads

Aerospace, Jul 15, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Computer Methods in Applied Mechanics and Engineering, Apr 1, 2018

This is a sequel to a previous paper [1] where a novel approach was presented to the 2-D Boundary... more This is a sequel to a previous paper [1] where a novel approach was presented to the 2-D Boundary Element analysis of steady incompressible viscous flow. Here the method is extended to three dimensions. NURBS basis functions are used for describing the geometry of the problem and for approximating the unknowns. In addition, the arising volume integrals are treated differently to published work and volumes are described by bounding NURBS surfaces instead of cells and only one mapping is used. The advantage of the present approach is that complex boundary shapes can be described with very few parameters and that no generation of cells is required. For the solution of the non-linear equations full and modified Newton-Raphson methods are used. A comparison of the two methods is made on the classical example of a forced cavity flow, where accurate two-dimensional solutions are available in the literature. Finally, it is shown on a practical example of an airfoil how more complex boundary shapes can be approximated with few parameters and a solution obtained with a small number of unknowns.

Engineering Structures, Oct 1, 2020

This paper presents a Genetic Algorithm adaptive homogeneous approach aiming at representing the ... more This paper presents a Genetic Algorithm adaptive homogeneous approach aiming at representing the crack patterns induced by ground settlements on masonry walls. This type of damage is a critical issue since it affects all masonry buildings, including those that are not located in seismic-prone areas. The GA-adaptive homogeneous approach here proposed is meant as a tool that overcomes the usual high computational costs requested by the traditional heterogeneous and homogeneous approaches. Here, the considered masonry wall is discretized into a low number of 2D polygonal elements; its displacement field is then determined through a linear programming problem. The actual position of cracks induced by the applied settlement is identified by modifying the initial mesh through an iterative mesh adaptation procedure performed with a Genetic Algorithm (GA); the iterations are carried on until the absolute minimum of the work performed by the reaction forces is attained. In this way, the computational effort needed for identifying the actual crack patterns is dramatically decreased due to the very few unknowns of the problem. The reliability of the GA-adaptive homogeneous approach here proposed is validated against selected benchmarks that come from experimental and numerical results, and is also compared with the traditional heterogeneous and homogeneous approaches. In all the three benchmarks, the GA-adaptive approach offers a satisfying computational efficiency and identifies the actual crack patterns with good accuracy, despite the low number of elements employed in the discretization of the masonry wall. This may pave the way for a broader use of this approach in the analysis of complex masonry structures affected by settlement-induced damages.

Computer Methods in Applied Mechanics and Engineering, Nov 1, 2017

A novel approach is presented to the Boundary Element analysis of steady incompressible flow. NUR... more A novel approach is presented to the Boundary Element analysis of steady incompressible flow. NURBS basis functions are used for describing the geometry of the problem and for approximating the unknowns. In addition, the arising volume integrals are treated differently to published work, that is, volumes are described by bounding NURBS curves instead of cells and a mapping is used. The advantage of our approach is that non-trivial boundary shapes can be described with very few parameters and that no generation of cells is required. For the solution of the non-linear equations both classical and modified Newton-Raphson methods are used. A comparison of the two methods is made on the classical example of a forced cavity flow, where accurate solutions are available in the literature. The results obtained agree well with published ones for moderate Reynolds numbers using both methods, but it is found that the latter requires a relaxation scheme and considerably more iterations to converge. Finally, it is shown on a practical example of an airfoil how more complex boundary shapes can be approximated with few parameters and a solution obtained with a small number of unknowns.

Journal of Cultural Heritage, Dec 1, 2012

ABSTRACT This paper presents a number of estimates of the structural vulnerability of Bethlehem&a... more ABSTRACT This paper presents a number of estimates of the structural vulnerability of Bethlehem's Nativity Church. Due to a lack of appropriate maintenance of the Church's roof over an extended period of time, a copious infiltration of rainwater caused serious damage to the structure's main elements. A damage survey was carried out for the main walls and grotto, in order to assess their structural vulnerability. The survey was backed by the results of a number of non-destructive tests and of the appropriate numerical analyses.

Computers and Geotechnics, Jun 1, 2021

Abstract The paper outlines some recent developments of the boundary element method (BEM) that ma... more Abstract The paper outlines some recent developments of the boundary element method (BEM) that makes it more user friendly and suitable for a realistic simulation in geomechanics, especially for underground excavations and tunnelling. The innovations refer to the introduction of isogeometric concepts, elasto-plastic analysis and the simulation of ground support. The introduction of isogeometric concepts for the description of the excavation boundaries results in less user and analysis effort, since complex geometries can be modelled with few parameters and degrees of freedom. No mesh generation is necessary. Heterogeneous and inelastic ground conditions are considered via general inclusions and rock bolts via linear inclusions. A comparison of results of test examples with other numerical methods and analytical solutions confirm confirms the efficiency and accuracy of the proposed implementation. A practical example with a complex geometry is presented.

Cmes-computer Modeling in Engineering & Sciences, Dec 1, 2014

ABSTRACT The NURBS based isogeometric analysis offers a novel integration between the CAD and the... more ABSTRACT The NURBS based isogeometric analysis offers a novel integration between the CAD and the numerical structural analysis codes due to its superior capacity to describe accurately any complex geometry. Since it was proposed in 2005, the approach has attracted rapidly growing research interests and wide applications in the Finite Element context. Only recently, in 2012, it was successfully tested together with the Boundary Element Method. The combination of the isogeometric approach and the Boundary Element Method is efﬁcient since both the NURBS geometrical representation and the Boundary Element Method deal with quantities entirely on the boundary of the problem. Actually, there are still some difﬁculties in imposing generic boundary conditions, mainly due to the fact that the NURBS basis functions are not interpolatory functions. In this work it is shown that the direct imposition of the inhomogeneous generic boundary conditions to the NURBS control points may lead to signiﬁcant errors. Consequently an improved formulation is proposed that relates the boundary conditions to the governing unknown variables by developing a transformation strategy. Several elasticity problems evince that higher solution accuracy can be achieved by the present formulation.

International Journal for Numerical Methods in Biomedical Engineering, Jan 27, 2011

This paper presents a two-dimensional numerical procedure based on the boundary integral equation... more This paper presents a two-dimensional numerical procedure based on the boundary integral equations to model acoustic waves of finite-amplitude. The analysis is performed in the frequency domain. By applying the perturbation technique up to the second-order term, the governing differential equations are written as a system of two Helmholtz equations, one is homogeneous and the other one is inhomogeneous. Both are transformed into integral equations, which can be numerically solved without domain discretization by the use of the dual reciprocity boundary element method (DRBEM). To the authors' knowledge, this is the first application of DRBEM to nonlinear acoustics. The numerical procedure can be applied to predict the propagation of finite but of moderate amplitude acoustic waves in domains of any geometry. The final formulation is validated by comparison with an analytical solution derived by the authors.

Annals of Solid and Structural Mechanics, Nov 11, 2020

The focus of the present work is to present an analytical approach for buckling and free vibratio... more The focus of the present work is to present an analytical approach for buckling and free vibrations analysis of thick functionally graded nanoplates embedded in a Winkler-Pasternak medium. The equations of motion are derived according to both the third-order shear deformation theory, proposed by Reddy, and the nonlocal elasticity Eringen's model. For the first time, the equations are solved analytically for plates with two simply supported opposite edges, the solutions also turning helpful as shape functions in the analysis of structures with more complex geometries and boundary conditions. Sensitivity analyses are finally performed to highlight the role of nonlocal parameters, aspect and side-to-thickness ratios, boundary conditions, and functionally graded material properties in the overall response of plates and cylindrical shells. It is felt that the proposed strategy could be usefully adopted as benchmark solutions in numerical routines as well as for predicting some unexpected behaviors, for instance, in terms of buckling load, in thick nanoplates on elastic foundations.