Showing papers in "Meccanica in 1985"
TL;DR: In this paper, the effects of free convection on the laminar flow of water through a circular duct having essentially constant wall heat transfer rate per unit length of the duct and circumferentially uniform wall temperature were investigated.
Abstract: This investigation considers the effects of free convection on the laminar flow of water through a circular duct having essentially constant wall heat transfer rate per unit length of the duct and circumferentially uniform wall temperature. The effect of the Reynolds and Rayleigh number variations on heat transfer results has been analysed for both horizontal and inclined pipe. The experiment has covered the range of the inlet Reynolds number from 200 to 2300, and of the Rayleigh number from 6,000 to 70,000. The effect of pipe inclination has been investigated for slope angle values up to 60°, with laminar ascending flow.
74 citations
TL;DR: In this paper, the expressions for the consistent mass and gyroscopic matrices for a constant section shaft element are obtained taking into account both shear deformation and transversal inertia.
Abstract: The expressions for the consistent mass and gyroscopic matrices for a constant section shaft element are obtained taking into account both shear deformation and transversal inertia. The results are compared with closed form solutions, which are available in simple cases. The results obtained show that the study of the dynamic behaviour of the rotor with a model which includes rotational inertia but not shear deformation is, at least in the case examined, misleading. Formulae for matrix condensation and for taking into account the effects of axial load and of a linear unbalance distribution are given. Damped systems can be studied using the same model, provided that damping can be assumed to be of either viscous or hysteretic type. Some formulations found in the literature are however not considered correct. An application of consistent matrices to a model which includes damping and uses matrix condensation is shown.
34 citations
TL;DR: In this paper, the static analysis of elastic cable networks submitted to generic, conservative loads and prescribed dislocations is considered, and the cables are assumed as stress-unilateral (only tensile stresses are admitted), and represented according to a Lagrangian standpoint, under the customary large displacements hypothesis.
Abstract: The static analysis of elastic cable networks submitted to generic, conservative loads and prescribed dislocations is considered in this paper. The cables are assumed as stress-unilateral (only tensile stresses are admitted), and represented according to a Lagrangian standpoint, under the customary large displacements hypothesis. A variational formulation of the problem is given, as the stationary of a saddle functional with respect to displacements and (signconstrained) tractions. Uniqueness properties for the solution are derived from this statement, together with two complementary (constrained) minimum formulations, which correspond to the well-known extremum principles of the total potential energy and the complementary energy. The case of a network loaded only at the nodes is exposed as a specialization.
19 citations
TL;DR: In this article, three truncations of the Navier-Stokes equations on a two-dimensional torus are numerically investigated by making use of techniques based on bifurcation theory.
Abstract: Three truncations of the Navier-Stokes equations on a two-dimensional torus are numerically investigated by making use of techniques based on bifurcation theory. The three truncations, to 12, 14 and 18 modes respectively, are obtained by taking into account all the modes contained in balls of increasing radius. While a comparison of the details of the phenomenologies is meaningless, the three models show common global qualitative features. In fact the behaviour of each model is described by three different stories which start from three distinct fixed points and develop parallely. Two stories are characterized by the presence of fixed points and periodic orbits, the third one involves also two-dimensional tori. The three truncations exhibit a surprisingly rich collection of bifurcations. Breaking of tori and disappearance of strange attractors by crisis seem to be the phenomena of greatest interest, particularly in the framework of dynamical systems.
18 citations
TL;DR: In this paper, the nonlinear behavior of long-span cable-stayed bridges is analyzed by assuming a continuous distribution of the stays along the deck, and the second one is a discrete model which accounts for the actual stays spacing.
Abstract: In this paper the nonlinear behaviour of long-span cable-stayed bridges is analyzed. Two different structural models are presented. The first is obtained by assuming a continuous distribution of the stays along the deck, the second one is a discrete model which accounts for the actual stays spacing. Some numerical results are presented.
18 citations
TL;DR: By comparing experimental records with model solutions, a dispersion relation governing the propagation of pressure pulses in fluid filled distensible tubes was proposed in this article, which contains a single undetermined parameter having the dimension of time.
Abstract: By comparing experimental records with model solutions we are led to propose a dispersion relation governing the propagation of pressure pulses in fluid filled distensible tubes. This relation contains a single undetermined parameter having the dimension of time. We show how this parameter may be interpreted and obtain an estimate of its value. Some comments concerning the speed of propagation of pressure waves in the haemodynamics contest are made.
11 citations
TL;DR: In this paper, the Tolman-Bondi equations of pressure-free spherically symmetric systems of particles in general relativity are applied to the special case of a euclidean initial hypersurface.
Abstract: The Tolman-Bondi equations of pressure-free spherically symmetric systems of particles in general relativity are applied to the special case of a euclidean initial hypersurface.
11 citations
TL;DR: In this article, a penalty formulation of the frictionless unilateral contact problem between an elastic rectangular plate and an elastic half-space is presented, in order to take into account the effects of the shear stress.
Abstract: In this paper a penalty formulation of the frictionless unilateral contact problem between an elastic rectangular plate and an elastic half-space is presented. In order to take into account the effects of the shear stress, the Mindlin plate model is analyzed. Some numerical results, obtained via finite elements, are given.
9 citations
TL;DR: In this paper, a displacement method based formulation is presented to perform the analysis of imperfect elastic space trusses, in the response of which the nonlinear effects developing pre-and post-instabilization of the structure are dominant.
Abstract: A displacement method based formulation is presented to perform the analysis of imperfect elastic space trusses, in the response of which the nonlinear effects developing pre- and post-instabilization of the structure are dominant. Additional forces and deformations are used to preserve symmetry in the lagrangian description of the governing system. Perturbation methods are used to formulate the finite incremental problem. The external work rate is used as control variable in the numerical solution procedure, which is designed to maximize the step length and capable of identifying and solving the occurrence of critical points in the equilibrium path.
9 citations
TL;DR: In this article, the elastodynamic interaction between explosively generated body and surface wave and an edge crack in a quarter-plane was investigated, and the authors employed dynamic photoelasticity to obtain full-field information for data analysis.
Abstract: The elastodynamic interaction between explosively generated body and surface wave and an edge crack in a quarter-plane is investigated. Dynamic photoelasticity was employed to obtain full-field information for data analysis. Measurements of the stress distribution along the free boundaries of the quarter-plane and along the crack walls have been made. Stress intensity distributions at both, the corner and the flaw tip and surface stress distributions for the diffracted and reflected Rayleigh-waves were obtained in the region near the cracked corner.
9 citations
TL;DR: In this article, the Poynting vector flux from a charge at rest in an inertial frame is calculated, on the basis of the standard classical Maxwell-Lorentz theory, in a uniformly accelerated frame, through a suitable set of spherical 2-surfaces.
Abstract: The Poynting vector flux from a charge at rest in an inertial frame is calculated, on the basis of the standard classical Maxwell-Lorentz theory, in a uniformly accelerated frame, through a suitable set of spherical 2-surfaces. The results are also interpreted in the framework of general relativity, and critically discussed in connection with the equivalence principle. In particular, we introduce a «quasi-local» definition of radiation, and conclude that a charge, falling freely in a gravitational field locally approximated by a static homogeneous gravitational field (SHGF), does not radiate in its rest frame, but does radiate in a frame supported in the SHGF. Such a radiation appears as «fictitious», i.e. a coordinate transformation eliminating the gravitational field eliminates at the same time also the radiation.
TL;DR: In this paper, a semi-discrete model of the Boltzmann equation was proposed, such that the velocity distribution is discretized in modulus, but non in direction.
Abstract: This paper deals with a semi-discrete model of the Boltzmann equation, such that the velocity distribution is discretized in modulus, but non in direction. The mathematical model is described in details, then the formulation of the initial value problem is proposed; the mathematical analysis supplies some rigorous results on the global mild solution and on its asymptotic behaviour.
TL;DR: In this article, the authors considered the problem of finding T-periodic solutions of dynamical systems under a resonance assumption, and they found a multiplicity of Tperiodic solution for T large enough.
Abstract: In this paper we look for T-periodic solutions of dynamical systems. Particularly we consider the system
$$ - \ddot x =
abla U(x,t)$$
whereU ɛC
1(ℝ
n
x
x ℝ, ℝ),U(x, t + T)=U(x,t) ∀ x ℝ
n
, ∀t ɛ ℝ T>0. We assume that the problem is asymptotically linear with a bounded nonlinearity. Under a resonance assumption, we find a multiplicity of T-periodic solutions for T large enough.
TL;DR: A brief historical outline and some epistemological suggestions on the scientific debate about the parallelogram of forces are presented in this paper, along with a discussion of epistemology.
Abstract: A brief historical outline and some epistemological suggestions are presented on the scientific debate about the parallelogram of forces.
TL;DR: In this article, an ionized gas whose dynamics is dominated by charge exchange is considered and the following two problems are studied: the time behaviour of sinusoidal waves in a uniform equilibrium; the propagation in a bounded equilibrium of sinnusoidal oscillations forced to the wall.
Abstract: An ionized gas whose dynamics is dominated by charge exchange is considered. The following two problems are studied: the time behaviour of sinusoidal waves in a uniform equilibrium; the propagation in a bounded equilibrium of sinusoidal oscillations forced to the wall. It is shown, in particular, that the equilibria considered, not necessarily thermal equilibria, are stable for any form of the distribution function.
TL;DR: In this article, new paradoxical phenomena in mechanics and physics caused by vibrations are stated, such as: a heavy ball in vibrating fluid can emerge and a light body can sink; an unfixed washer on a vertical vibrating bar with a lower hinge support does not fall while the bar stands almost vertically.
Abstract: In the article new paradoxical phenomena in mechanics and physics caused by vibrations are stated. It is indicated that: a) a heavy ball in vibrating fluid can emerge and a light body can sink; b) an unfixed washer on a vertical vibrating bar with a lower hinge support does not fall while the bar stands almost vertically; c) static stability of elastic systems can be increased with the help of vertical vibrations.
TL;DR: In this paper, the authors describe the buckling of an elastically twisted rod, subjected to axial tension, with cylindrical hinges at both ends, whose axes remain parallel while changing their distance.
Abstract: Helicoidal buckling of an elastically twisted rod, subjected to axial tension, with cylindrical hinges at both ends, whose axes remain parallel while changing their distance.
TL;DR: In this article, a general scheme encompassing expansion methods for the sleeve is presented: one homogeneous condition for each contour portion establishes real eigenvalues ensuring orthogonality to Fourier-Bessel expansions, with summations replaced by integrations.
Abstract: A general scheme encompassing expansion methods for the sleeve is presented: one homogeneous condition for each contour portion establishes real eigenvalues ensuring orthogonality to Fourier-Bessel expansions Solutions by integral equations may be regarded as limiting cases, with summations replaced by integrations Special attention is devoted to the alternative use of complex eigensolutions, subjected to two homogeneous conditions on the cylindrical boundary
TL;DR: In this paper, a continuous model of a multi mass drive system with stepped shafts, loaded by external moments, is proposed and analyzed by means of one dimensional torsional waves.
Abstract: A continuous model of a multi mass drive system with stepped shafts, loaded by external moments, is proposed and analysed by means of one dimensional torsional waves. A procedure is developed for calculation of velocities, strains and displacements in an arbitrary cross-section of the shafts, and some necessary conditions for the stability of angular displacements are formulated.
TL;DR: In this article, the decoupling of a first-order partial differential system of four (3×1)-vectorial equations, governing the free three-dimensional dynamic equilibrium of an arc element of an elastic circular helicoidal bar, is presented.
Abstract: A thorough and rigorous analysis for the decoupling of a first-order partial differential system of four (3×1)-vectorial equations (with constant coefficients), governing the free three-dimensional dynamic equilibrium of an arc element of an elastic circular helicoidal bar, is presented. Through this decoupling procedure the equivalent to the system differential equation, with respect to one of the generalized displacements, results of the twelfth-order. Under the assumption that the general integral of this equation is given and for the most general case of response, the transcendental equation for the determination of the natural frequencies of the system is formulated. Finally, as an application on the method and under some restrictions the general integral of the differential equation of harmonic motions of an elastic helicoidal bar is determined in the form of elementary functions.
TL;DR: In this article, a rotating shaft seal, using ferrofluid between biconical truncated magnetic poles, is analyzed both in static and dynamic conditions, and the magnetic forces acting on the working fluid are obtained.
Abstract: A rotating shaft seal, using ferrofluid between biconical truncated magnetic poles, is analysed both in static and dynamic conditions. After solving Laplace's equation and allowing an approximate expression for the magnetic potential, the magnetic forces acting on the working fluid are obtained. It is thus possible to determine the baric field existing in static conditions and the highest tolerable pressure jump. In the case of dynamic working the flow is schematized by two interior regions, where the azimuthal velocity prevails, and four boundary layers on the walls, where meridional transport of fluid takes place. Assuming laminar motion, by means of a perturbation procedure it is possible to see that in the interior, to a first approximation, two potential vortexes exist, whose circulations, after imposing the rotational equilibrium of the fluid about the symmetry axis, are found to be equal to about one half of the rotating pole peripheral circulation. This allows the determination of the baric field in the rotating fluid and of the friction moment exerted on the shaft.
TL;DR: In this article, the diffusion of stresses in a linear isotropic elastic body coated with a thin elastic shell called the ''crust'' was studied, and the authors showed that this shell can be used to measure the elasticity of the body.
Abstract: This paper studies the diffusion of stresses in a linear isotropic elastic body coated with a thin elastic shell called the «crust».
TL;DR: In this paper, the damping factor is obtained by a simplified theory of small perturbation which evaluates the force at the ceiling on the assumption that the dominant motion of sloshing corresponds with that given by linear theory of a potential flow, when the liquid free surface reaches in some instant during the oscillating period the ceiling of the tank.
Abstract: The sloshing flow, when the liquid free surface reaches in some instant during the oscillating period the ceiling of the tank, is analyzed. The damping factor is obtained by a simplified theory of small perturbation which evaluates the force at the ceiling on the assumption that the dominant motion of sloshing corresponds with that given by linear theory of a potential flow. The experimental investigation is carried out with a rigid tank partially filled by water, fixed to an oscillating table laterally excited by a sinusoidal force of given frequency and amplitude. The liquid velocity, near the free surface, is measured by a laser doppler velocimeter. The damping factor is obtained by the band width tecnique applied to the analysis of the velocity RMS versus the frequency of the acting force.
TL;DR: In this paper, sufficient conditions are given for the stability and instability of the equilibrium position x =y=z=0 in the mechanical system consisting of a material point constrained to move on the moving surface z =−λ(t) (x2+y2) (λ (t)>0) under the action of viscous friction of total dissipation.
Abstract: Sufficient conditions are given for the stability and instability of the equilibrium position x=y=z=0 in the mechanical system consisting of a material point constrained to move on the moving surface z=−λ(t)(x2+y2) (λ(t)>0) in a constant field of gravity (the axis 0z is directed vertically upward) under the action of viscous friction of total dissipation.
TL;DR: In this paper, the convergence to the brownian motion of a stochastic process obtained by a onedimensional mechanical system, subject to random initial conditions, is proven, and the convergence of the system to the Brownian motion is shown.
Abstract: The convergence to the brownian motion of a stochastic process obtained by a onedimensional mechanical system, subject to random initial conditions, is proven.
TL;DR: In this paper, the development of the magnetohydrodynamic Stokes flow field due to the discharge of an electric current from a point into a viscous incompressible fluid bounded by a hemispherical bowl is investigated.
Abstract: The development of the magnetohydrodynamic Stokes flow field due to the discharge of an electric current from a point into a viscous incompressible fluid bounded by a hemispherical bowl is investigated. We also discussed, as a special case, the flow induced for the case when the radius of the hemispherical bowl becomes infinitely large and showed that the time taken to establish the steady state flow in the interior of the hemisphere is reduced by a factor of ten compared with the situation where the flow takes place in a semi-infinite fluid. Our solution is analytic as compared with the existing numerical solution.
TL;DR: In this paper, a rigid heat conductor at rest immersed in an electromagnetic field is considered and the interactions between thermodynamic and electromagnetic fields are decribed in the frame work of the theory proposed by I. Muller.
Abstract: We consider a rigid heat conductor at rest immersed in an electromagnetic field. The interactions between thermodynamic and electromagnetic fields are decribed, in the frame work of the theory proposed by I. Muller [1]. Some properties related to the model equations proposed are pointed out. Specifically we are able to show as the governing equations may be written in symmetric and conservative form so that the Cauchy problem results well posed.
TL;DR: In this article, a mechanism was investigated which might lead to enhancement of the rate of mass transfer in channel flow at relatively low Reynolds numbers, and one of the possible areas of application of this mechanism concerns blood oxigenators.
Abstract: A mechanism is investigated which might lead to enhancement of the rate of mass (or heat) transfer in channel flow at relatively low Reynolds numbers. One of the possible areas of application of this mechanism concerns blood oxigenators.
TL;DR: In this paper, the authors established continuous dependence and uniqueness theorems for classical solutions to the equilibrium problem of finite elasticity, and employed the weight function method and a suitable extension to the non-linear case of a method previously introduced by other authors for the linear case.
Abstract: In connection with a foregoing paper, in the present note we establish some continuous dependence and uniqueness theorems for classical solutions to the equilibrium problem of finite elasticity. The elastic body is supposed to fill an unbounded domain of the physical space. We employ the weight function method and a suitable extension to the non-linear case of a method previously introduced by other authors for the linear case.
TL;DR: In this paper, the angular frequencies of a twisted straigth bar of constant section were determined under seven possible (asymmetric) constraint conditions and corresponding frequency equations were found.
Abstract: In a previous paper concerning the determination of angular frequencies of a twisted straigth bar of constant section, only three simple constraint conditions at the ends had been considered (free end, constrained end). In the present paper the other seven possible (asymmetric) constraint conditions are considered and the corresponding frequency equations are found. A final numerical example with several increasing twisting degrees shows the different influence of this increase upon the frequencies having axial or torsional origin.