Christos Vasilios Massalas

• Emeritus Professor
• Professor Emeritus at University of Ioannina

Stone arch bridges are part of the cultural heritage for many countries. Their construction was based on materials easily available locally, e.g. stones and mortar. The weak-in-tension material dictated the shape of the structures. Many stone arches still survive and some are even used as pedestrian bridges or bridges for light traffic, therefore a...

In the process of fracture healing, several phases of recovery are observed as the mechanical stability, continuity and normal load carrying capacity are gradually restored. The ultrasonic monitoring and discrimination of different healing stages is a complex process due to the significant microstructure and porous nature of osseous and callus tiss...

The aim of this research is to investigate information systems security in the context of internet banking. In doing so, it adopts a non-technical approach by investigating the interrelationship and effect of culture and risk communication in setting internet banking security goals. The research explores and discusses the theories of group culture,...

The ultimate failure load of stone arch bridges is calculated in this paper. The finite element model consists of contact interfaces which simulate potential cracks. A parametric investigation demonstrates the influence of the geometry on the mechanical behavior. A reduction of the rise of the arch (below the initial, real geometry) generally cause...

The use of guided waves has recently drawn significant interest in the ultrasonic characterization of bone aiming at supplementing the information provided by traditional velocity measurements. This work presents a three-dimensional finite element study of guided wave propagation in intact and healing bones. A model of the fracture callus was const...

A computational scheme for the determination of the interface in a strain-induced phase-transition problem for an elastic bar is proposed. The algorithm is based on the material force notion and more specifically on the simultaneous solution of equilibrium equations for the physical and material forces. The weak form of both equations is derived wi...

A method for the estimation of the limit load and the failure mode of fiber-reinforced polymer (FRP) reinforced stone arch bridges is hereby presented. Unilateral contact interfaces with friction simulating potential cracks are considered in the finite element model of the bridge. FRP strips are then applied to the intrados and/or the extrados of t...

In this paper is studied the ultimate failure (limit) load of stone arch bridges. The proposed model is based on finite element analysis with interfaces, simulating potential cracks, which allow for unilateral contact with friction. Opening or sliding of some interface indicates crack initiation. The ultimate load has been calculated by using a pat...

The theory of elasticity deals with the systematic study of the stress, strain, and displacement fields in an elastic body under the influence of external forces. In this chapter, we deal with elastic materials (i.e., materials in which the deformation and stress disappear with the removal of the external forces). However, equations for other types...

This paper deals with the shape control of beams under general loading conditions, using piezoelectric patch actuators that are surface bonded onto beams to provide the control forces. The mathematical formulation of the model is based on the shear deformation beam theory (Timoshenko theory) and the linear theory of piezoelectricity. The numerical...

The ultimate failure load of stone arch bridges is calculated in this paper by using finite element analysis. Contact interfaces simulating potential cracks are considered. Opening or sliding of a number of the potential interfaces indicates crack initiation [1]. Fiber Reinforced Plastic (FRP) strips are then applied to the stone bridge and the ul...

We consider stone bridges with unilateral mortar joints and elastic or rigid stones [1], [2]. Opening or sliding indicates crack initiation and propagation. The ultimate load has been calculated by using a path - following technique. Lack of a solution at a certain level of loading indicates onset of failure, which can be checked by the solvability...

The present work concerns the investigation of the two-dimensional direct scattering problem of time-harmonic elastic waves from bounded anisotropic components of isotropic media. We obtain a Fourier series expansion for the elastic field in the interior of the anisotropic inclusion based on a suitable diagonalization applied to the underlying diff...

This paper deals with the shape control of beams, using piezoelectric patch ac-tuators that are surface bonded onto beams to provide the control forces. The mathematical formulation of the model is based on the shear deformation beam theory and the linear theory of piezoelectricity. The numerical solution of the model is based on the development of...

Fourier analysis is usually employed for the computation of blood flow in arteries. Although the orthogonality of Fourier eigenfunctions guarantees the accurate mathematical modeling of the blood pressure and flow waveforms, the physics behind this objective function is frequently missing. We propose a new method to account for the blood pressure a...

The ability of the Preisach formalism to model hysteresis processes in antiferromagnetically coupled (AFC) recording media is investigated in this paper. Two modeling approaches are proposed, each one using a weighed mixture of two normal bivariate probability function densities as the characteristic density and either classical or appropriately mo...

In this work, a mathematical analysis of the surface remodeling process initiated in a long bone by the insertion of an endoprosthesis is presented. A poroelastic material description that incorporates the dual (solid plus fluid) phase of bone has been employed based on BiotÕs theory of consolidation. The theory of small-strain adaptive elasticity...

This paper presents simulations of hysteresis processes in thin film media using 1D and 2D Preisach models. In the 2D version, a vector operator and superposition of angularly distributed models are used. The characteristic density of the material being modeled is reconstructed via a curve-fitting least-squares procedure that determines the paramet...

Three different approaches to modeling hysteresis processes in antiferromagnetically coupled (AFC)-media for disk drive recording, employing the Preisach formalism, are presented and compared. The Preisach switching field distribution ρ(a,b) is constructed as a weighed sum of two separate distributions corresponding to the upper and lower layer of...

The class of models presented here, targeting the modelling of hysteresis processes in the magnetic and elastic properties of ferromagnetic composites, is based on the Preisach formalism. The 1D and 2D formulations are equipped with a set of five different local hysteresis operators, to address different hysteretic responses. The resulting algorith...

The continuum theory of electro-elasticity is used in order to describe the large deformations observed in gels endowed with electric properties when they are placed in electric fields. The analytical solution of the properly constructed boundary-value problem agrees quantitatively with available experimental data.

This work deals with the study of an initial-boundary value problem in linear theory of thermo-viscoelastic dielectrics. A variational formulation of this problem is provided and the existence of its solution is proved by an auxiliary Faedo-Galerkin scheme. Finally, the uniqueness of the solution is obtained as a corollary of the existence proof.

The continuum theory, previously developed to quantitatively account for the large deformations observed in gels endowed with electric properties, is extended to magnetic field sensitive gels (ferromagnetic or diamagnetic in origin). The derived analytical formula for the dependence of the gel displacement on the magnetic field can be applied eithe...

Ultrasound wave propagation in fractured long bones is studied using the Finite Element (FE) Method. The 3D long bone model (geometry and material properties) is obtained from CT scans. Callus consolidation is modelled as a series of maturation stages. The numerical results are compared with experimental observations.

In this work, a numerical approach is presented for determining the longshore current modification caused by the presence upon the seabed (boundary) of a submerged groin system. This system consists of several low groins with one end-point inshore and the other resting several tens of meters offshore and aligned perpendicularly to the shoreline. Su...

A least-squares parameter fitting procedure is used in conjunction with one-dimensional (1D) and two-dimensional (2D) formulations of the Preisach formalism. The model can use any operator from a selection of 1D and 2D hysteresis operators appropriate for the modeling of hysteresis in ferromagnets, and shape memory alloys. The performance of the hy...

In this paper a theoretical analysis of the internal bone remodeling process induced by a medullary pin is presented. Bone is treated as a poroelastic material using Biot's formulation. Based on the theory of small-strain adaptive elasticity, a new theoretical approach for internal remodeling is proposed. Our results show that the rate of internal...

In this work, we examine the acoustic scattering problem of spherical waves by a two-layer spheroid simulating the kidney-stone system. Both the theoretical as well as the numerical treatment are presented. The outcome of the analysis is the determination of the scattered field along with its multivariable dependence on the several physical and geo...

Proceedings of the Fifth International Workshop on Mathematical Methods in Scattering Theory and Biomedical Technology Corfu, Greece, 18 – 19 October 2001 Edited by: Dimitrios Fotiadis ( University of Ioannina, Greece), Christos Massalas ( University of Ioannina, Greece) In this study, the finite element method (FEM) is employed to describe the st...

A Preisach model able to adjust to different systems with hysteresis is presented. The related identification scheme involved uses data from a major hysteresis curve and a least-squares error minimization procedure for the parameters of the characteristic density. The output sequence, f ðtÞ; is obtained by integrating the characteristic probability...

In the present work an attempt is made to construct the Navier vector functions in spheroidal geometry in a form convenient for the solution of boundary value problems. The complexity of the problem is moderated by exploiting general properties of the vector operators, the underlying Helmholtz equation kernel functions as well as the symmetries of...

It has been argued that silicone ferrofluid internal tamponade (SFIT) can provide (360°) tamponade of the retina in retinal detachment surgery. Provided that the produced SFIT is biocompatible, exact knowledge is needed of its elastic stability in the magnetic field produced by the semi-solid magnetic silicon band (MSB) used as a scleral buckle. We...

The point source excitation acoustic scattering problem by a multilayer isotropic and homogeneous spheroidal body is presented. The multilayer spheroidal body is reached by an acoustic wave emanated by an external point source. The core spheroidal region is inpenetrable and rigid. The exterior interface and the interfaces separating the interior la...

The static position of single leg stance is a generally accepted worst case scenario for hip joint loading. However, it is essential in particular for investigations including temporal effects such as studies on fracture healing, fatigue, micromotion and remodeling to examine the dynamic loading situation not only at a single moment in time, but du...

Existing solutions of the nucleation fields in inhomogeneous ferromagnets, based on the minimization of the energy equation of a soft magnetic inclusion implanted in a hard magnetic matrix, are reviewed and compared. A macroscopic two-dimensional (2-D) model based on the Preisach formalism is proposed. The properties of the model and the effect of...

We present a review of the modelling approaches for the human head-neck system. The models address two major problems, related to the three-dimensional description and second with the material properties which are largely unknown. All the models converge to a layered description where each component corresponds to a different material of the system...

The dynamic behavior of a dry long bone considered as a piezoelectric cylinder of crystal class 6 with arbitrary cross-section is presented. For the solution of the wave propagation problem we follow the procedure proposed in a previous work (D.I. Fotiadis, G. Foutsitzi, C.V. Massalas, Wave propogation modeling in human long bones, Acta Mechanica 1...

The paper establishes the existence of a nonconstant periodic solution of a general second order nonautonomous Hamiltonian system with discontinuous nonlinearities. The multiplicity of solutions is also studied.

The problem of ferromagnetic resonance in magnetic microspheres is revisited due to related experiments in this size range. The eigenfrequency spectrum is examined more rationally compared to previous numerical computations, due to proper selection of the radial dependence of the solution. The cylindrically symmetric modes studied agree with experi...

The exchange constants A and the g factors for CoxNi1−x microspheres are estimated by comparing theoretical calculations of size-dependent resonance modes with the experimental data of spherical monodisperse Co–Ni particles. Only cylindrically symmetric modes are studied. The deviation from previously reported values is presented.

The present study is concerned with determining the dynamic characteristics of the human head-neck system which is described as a fluid-filled spherical cavity supported by a viscoelastic neck reacting in three dimensions. The material of the skull is assumed to be a homogeneous, isotropic, elastic material, and that of the brain-cerebrospinal flui...

A simple micromagnetic model is presented to study the effect of stress on the magnetization reversal in thin ferromagnetic films (well-known as inverse magnetostrictive effect). To simplify the calculations the plane strains are confined to be uniform. The externally applied magnetic field is oriented either, parallel or perpendicular to the stres...

Previous work on magnetic hysteresis modeling using the Preisach formalism forms the basis of this work which proposes a two-dimensional Preisach-type model for anisotropic inhomogeneous rare-earth-transition-metal magnets. The model deals with the two phases in a statistical sense and is not constrained by the specific geometry or the number of so...

The effect of applied mechanical stresses on the magnetization reversal, well known as inverse magnetostriction effect, is studied for thin ferromagnetic films. The model used, is a micromagnetic one proposed in (Voltairas et al., Int. J. Eng. Sci., in press). Numerical non-uniform (NU) solutions for the Brown’ s magnetoelastic equations are presen...

In this paper a full-dynamic theory for elastic dielectrics is presented by a systematic application of thermomechanical balance laws. Polarization gradient, quadrupole polarization and polarization inertia are taken into account in order for a general theory to be obtained. The constitutive relations are produced by using the second law of thermod...

Cited By (since 1996): 7, Export Date: 14 March 2013, Source: Scopus

The proposed micromagnetic model (Voltairas et al., Int. J. Engng. Sci., accepted for publication) is extended to account for shearing strains. We assume that the ferromagnetic material is a single cubic crystal, the magnetization reverses coherently and the strains are uniform. The equilibrium field equations are derived from the free energy funct...

In this work we present an analysis concerning the mathematical formulation of the general problem of the dynamic loading of the human head. In the proposed analysis the system is assumed to constitute of a stratified spherical medium and a methodology is developed for the study of the dynamic behaviour of the human head. The response of the human...

The eigenvector solution of the spectral Navier equation in cylindrical coordinates is constructed by using the Helmholtz decomposition theorem and the method of separation of variables.

The dynamic behavior of a dry long bone that has been modeled as a piezoelectric hollow cylinder of crystal class 6 is investigated. The solution for the wave propagation problem is expressed in terms of a potential function which satisfies an eighth-order partial differential equation, whose solutions lead to the derivation of the explicit solutio...

An analysis of the unsteady magnetohydrodynamic flow of a viscous and electrically conducting fluid past to a plate by the presence of radiation is considered. The fluid is a gray, absorbing-emitting but nonscattering medium and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. Analytical solutions for...

In the present work we discuss the role of the thickness nonuniformities of the human dry skull on its frequency spectrum. The mathematical modelling is based on the three-dimensional theory of elasticity, the approximation of the skull by an isotropic material occupying the region bounded by two non-concentric spheres and the introduction of the b...

In this paper, we present a solution to the problem of free vibrations of the human head system taking into account the dissipative behaviour of the brain. The mathematical model is based on the three-dimensional theory of viscoelasticity and the representation of the displacement field in terms of the Navier eigenvectors. The frequency equation is...

In the present work we discuss the role of small deviation of the spherical to spheroidal geometry on the frequency spectrum of the human dry-skull. The analysis is based on the three dimensional theory of elasticity, complex analysis techniques and the construction of the Navier eigenvectors for the problem under discussion.

In this work we propose an approach to study the dynamic characteristics of double layered cylindrical rods. The description of the problem is based on the three-dimensional theory of elasticity and the mathematical analysis on the representation of the displacement fields in terms of the constructed Navier eigenvectors in cylindrical coordinates....

In this work we deal with the free vibrations of a viscoelastic skull. The analysis is based on the three-dimensional theory of viscoelasticity and the representation of the displacement field in terms of the Navier eigenvectors. The frequency equation was solved numerically and results are presented for the eigenfrequency and the attenuation spect...

In this work, the dynamic characteristics of the human skull-brain system are studied. For the purpose of our analysis, we adopted a model consisted of a hollow sphere (skull), an inviscid and irrotational fluid (cerebrospinal fluid), and a concentrically located inner elastic sphere (brain). The mathematical analysis is based on the elasticity sol...

A three-dimensional model of human skull-brain system has been extended to include neck support. The model is based on the assumption of having a hollow sphere (skull), the behaviour of which is described by the elasticity solution, filled with an inviscid, irrotational fluid (cerebrospinal fluid), whose motion is described by the wave equation. Th...

Es wird ein Anfangs-Randwertproblem aus der Theorie der linearen Thermoviskoelastizität betrachtet. Nach Formulierung des zugeordneten Variationsproblems werden Existenz und Eindeutigkeit seiner Lösung in einem geeigneten funktionalanalytischen Rahmen studiert. An initial-boundary value problem of the theory of linear thermoviscoelasticity is consi...

In this work an attempt is made to she dynamic characteristics of the human dry skull. The analysis is based on the three-dimensional theory of elasticity and the representation of the displacement field in terms of the Navier eigenvectors. The frequency equation was solved numerically and the results obtained are fairly good, in comparison to the...

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Cited By (since 1996): 7, Export Date: 14 March 2013, Source: Scopus

We are concerned with the influence of magnetostriction on the hysteretic behaviour of ferromagnetic materials. The analysis is based on the theory of micromagnetism, and the continuum theory of elastic ferromagnetic insulators proposed by Maugin and Tiersten. Numerical integration of the Brown's equations lead to estimation of the magnetization, d...

In this work the extended Tiersten's theory of thermoelectroelasticity for materials with memory is presented. Constitutive equations are derived for nonlinear dielectric materials that possess fading memory of past fields. The consequences of the second law of thermodynamics is studied. The analysis is based on Coleman's work, the entropy inequali...

In the present work we deal with the resonance modes in small ferromagnetic spheres. The analysis is based on the theory of micromagnetism, proposed by W. F. Brown and an optimization technique. Numerical results are presented for the resonance field, as well as for the resonance modes and the magnetization configuration in the material. The resona...

In the present work we deal with the size-dependent resonances in small ferromagnetic spheres. The analysis is based on the theory of micromagnetism, the work of Aharoni, and an optimization technique. Numerical results are presented for the resonance field, as well as for the resonances mode and the magnetization configuration in the material. The...

In the present work we present a generalized theory of thermoelastic dielectrics. The analysis is based on Tiersten's theory, the entropy production inequality proposed by Green and Lindsay and the invariance of the first law of thermodynamics under rigid body translation and rotation.

Near, but below Curie's temperature Tc, the magnetization increases with applied field above saturation. Therefore, when we approach Tc in a ferromagnet it becomes no longer possible to neglect the change in magnitude of the local magnetization due to magnetic fields. For the purpose of our problem the Brown's equations are extended by using a vari...

In this work we deal with the phenomenological description of the magnetothermoelastic interactions in ferromagnetic material in the framework of the generalized theory of thermoelasticity, proposed by Green and Laws. The material is supposed to be homogeneous, anisotropic and elastic undergoing large deformations. The analysis is based on the ther...

The mathematical description of the generalized theory of linear thennoelasticity is given by a system of hyperbolic-type equations. The uniqueness, existence, continuous dependence on the initial data, differentiability and the asymptotic stability of the generalized (finite energy) solutions are investigated.

In this work we study the propagation of plane magneto-electro-thermo-elastic harmonic waves in an unbounded isotropic, conducting and initially stressed medium permeated by a primary uniform magnetic field. The formulation of the problem is given in the framework of the quasi-static electromagnetic state and the generalized theory of thermoelastic...

The interaction between elastic wave motions and a magnetic field in initially stressed conductors is discussed. The analysis is based on a linearized theory. The propagation of plane harmonic waves in an infinite perfectly conducting elastic solid as well as the Rayleigh waves in the presence of initial stress-state and a uniform magnetic field ar...

The propagation of thermoelastic waves in a waveguide occupying the Cartesian space x1ϵ [0, L], x2ϵ [− H, + H], x3ϵ [− ∞, + ∞] is discussed. The analysis is based on the generalized theory proposed by Lord and Shulman. The solution of the problem is expressed in terms of the Lamé's scalar and vector potentials and the frequency equations are derive...

In this note a reciprocal theorem is presented for initial mixed boundary conditions in the framework of the linearized isotropic thermoelasticity theory of Lord and Shulman.

An analysis is presented of the propagation of thermoelastic waves in a circular cylinder of an infinite length. The analysis is based on the generalized theory proposed by Lord and Shulman. The solution of the problem under discussion is expressed in terms of the Lamé scalar and vector potentials and analytical expressions are given for the wave m...

The generalized theory of Lord and Shulman is used to study the characteristics of the wave motion in a thin plate of infinite length under plane stress state. The frequency equations of the plate are discussed for mixed boundary conditions and for isothermal and insulated edges. For the limiting frequency analytical expressions for the phase veloc...

In the present work we deal with the propagation of thermoelastic waves in a thin plate occupying the Cartesian space (x 1[–, +],x 2[–, +],x 3[–, +]). The analysis is based on the generalized theory of thermoelasticity proposed by Lord and Shulman modified for plane stress problems. A mathematical analysis is presented to study the wave motion char...

The forced vibrations of a thermoelastic strip (x1 ε [0, l], x2 >= 0) produced by a prescribed heating at the boundary x2 = 0 are considered. The analysis is based on classical coupled thermoelastic theory (plane strain) and finite Fourier transforms. The solution of the problem under discussion is expressed in terms of the Lamé scalar and vector p...

In this paper we deal with the coupled thermoelastic problem of an elastic medium (). The analysis is based on the decoupled field equations and the integral transforms. The dynamic behaviour of an elastic half-space due to a thermal shock on the boundary is also discussed.

The dynamic characteristics of rectangular plates subjected to additional stiffness in the form of rectilinear springs attached at discrete points of the plate, when two or more modes possess the same frequency, are discussed. The mathematical analysis to break the degeneracy is based on a perturbation technique. The formulation of the solution is...

In the present paper we deal with tne dynamic behaviour of a Timoshenko beam subjected to a step heat flux to the surface z = + h/2 at time t = 0+. The mathematical analysis is based on integral transforms, the Muller's method of solving algebraic equations and the Heaviside expansion theorem. From the numericad results presented, one can see the e...

In this paper, the problem of the dynamic stability of a clamped cylindrical shell subjected to the simultaneous action of longitudinal compressive forces and temperature field, both periodical in time, in the case of the temperature-dependent modulus of elasticity, is formulated on the basis of Donnell's linear theory and Galerkin's method. Numeri...

In the present work we deal with the problem related to magnetoelastic waves produced by thermal shock in a half-space medium having finite conductivity. The solution of the problem is obtained in an analytical form which is reduced to that given by Kaliski and Nowacki when the coupling between temperature and strain fields is neglected.

In the present paper we deal with the problem related to magnetothermoelastic waves produced by thermal shock in a perfectly conducting half-space. The solution of the problem is obtained in an analytical form which is reduced to that given by Kaliski and Nowacki when the coupling between temperature and strain fields is neglected.

The paper deals with the influence of a constant heat flux on the static and dynamic response of a simply supported and clamped circular plate with the edge immovably constrained. Results are presented for the static and dynamic response of the plate.

The geometry of the middle surface lines of curvature of a thin conical shell, whose cross-section is bounded by a certain closed convex plane curve, is studied. Then, for such a shell, several sets of linear and nonlinear equations of motion are derived in terms of its middle surface orthogonal line-of-curvature coordinate system. As an applicatio...

In the present work we deal with the influence of a constant heat flux on the static and dynamic response of simply supported and clamped circular plate with edge immovably constrained.

Steady hydromagnetic free convective flow of a conducting fluid through a porous medium bounded by two parallel plates is considered and effects of G (Grashof number) and the K (permeability parameter) on the velocity field are discussed.