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  • Coupling of Underground Pipelines and Slowly Moving Landslides by BEM Analysis
  • Abstract Many sloping areas in the world are affected by slow movements. If they are occupied by settlements or are crossed by roads, pipelines or other infrastructures, a correct evaluation of future displacements is crucial for land management and sometimes for men safety. It is widely recognized that rainfall is the main triggering factor, producing an intermittent and delayed recharge of the groundwater; as a consequence, the displacement rate is cyclic, following a seasonal trend. In Italy this problem is particularly relevant since many exploited sloping areas are affected by slowly moving landslides that interact with man-made works. In present paper…
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  • Boundary Element Stress Analysis of Thick Reissner Plates in Bending under Generalized Loading
  • Abstract In a recent publication, the author has introduced boundary integral equations for thick plate bending problems, for cases with generalized types of loading. Internal bending moments and shear forces, required for stress analysis, were calculated by means of a finite difference procedure, which requires fine boundary element meshes to achieve an acceptable degree of accuracy. In this paper, boundary integral equations for internal bending moments and shear forces are presented for thick Reissner plates in bending. Domain loading terms in those boundary integral equations have also been simplified for a variety of loading types including concentrated loading, linearly-distributed loading, and…
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  • The Effect of a Rotational Spring on the Global Stability Aspects of the Classical von Mises Model under Step Loading
  • Abstract The present work deals with the global stability aspects of a simple two-degrees-of-freedom autonomous initially imperfect damped model, under step (conservative) loading. The proposed system is an extension of the classical limit point one firstly introduced by von Mises, with the addition of a linear rotational spring. The effect of its properties (stiffness and damping) are fully assessed and under certain combinations of the parameters involved a third possibility of postbuckling dynamic response is revealed. This is associated with a point attractor response on a stable prebuckling fixed point, although dynamic buckling has already occurred, a finding validating new relevant…
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  • Three dimensional BEM and FEM stress analysis of the human tibia under pathological conditions
  • Abstract In this paper, a three-dimensional Boundary Element model of the proximal tibia of the human knee is described and stresses and displacements in the tibial plateau under static loading are computed. The geometry is generated via three-dimensional reconstruction of Computerized Tomographies and Magnetic Resonance Imaging. Various models of different lengths from the tibia plateau are calculated. The BEM results are compared with a Finite Element model having the same geometry and tibia FE models available in the literature. Also reported are investigations of some pathological situations, including fractures. The results of the comparisons show that BEM is an efficient and…
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  • Implicit Boundary Conditions for Direct Simulation Monte Carlo Method in MEMS Flow Predictions
  • Abstract A simple implicit treatment for the low speed inflow and outflow boundary conditions for the direct simulation Monte Carlo (DSMC) of the flows in microelectromechanical systems (MEMS) is proposed. The local mean flow velocity, temperature, and number density near the subsonic boundaries were used to determine the number of molecules entering the computational domain and their corresponding velocities at every sample average step. The proposed boundary conditions were validated against micro-Poiseuille flows and micro-Couette flows. The results were compared with analytical solutions derived from the Navier-Stokes equations using first-order and second order slip-boundary conditions. The results show that the implicit…
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  • Structured Adaptive Control for Poorly Modeled Nonlinear Dynamical Systems
  • Abstract Model reference adaptive control formulations are presented that rigorously impose the dynamical structure of the state space descriptions of several distinct large classes of dynamical systems. Of particular interest, the formulations enable the imposition of exact kinematic differential equation constraints upon the adaptation process that compensates for model errors and disturbances at the acceleration level. Other adaptive control formulations are tailored for redundantly actuated and constrained dynamical systems. The utility of the resulting structured adaptive control formulations is studied by considering examples from nonlinear oscillations, aircraft control, spacecraft control, and cooperative robotic system control. The theoretical and computational results provide…
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  • Wave Scattering by 2D Smooth Topographical Elastic Deformations Caused by a Point Blast Source
  • Abstract This paper presents the three-dimensional scattering field obtained when 2D smooth topographical deformations are subjected to a dilatational point load placed at some point in the medium. The solution is formulated using boundary elements for a wide range of frequencies and spatially harmonic line loads, which are then used to obtain time series by means of (fast) inverse Fourier transforms into space-time. The topographical surface is modeled with a number of boundary elements, defined according to the excitation frequency of the harmonic source, and in such a way that the free surface can be discretized along a sufficient distance to…
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  • Damage Analysis for Mixed Mode Crack Initiation
  • Abstract The paper presents a numerical simulation for mixed mode crack initiation based on the concepts of damage mechanics. A model with two scalar damage variables is introduced for characterization of damage in a material element. Then a tangent modulus tensor is derived for damage-coupled constitutive equations. A failure criterion is developed with the concept of damage accumulation not only to identify the location of damaged element where the crack initiation angle but also to determine the critical load for mixed mode fracture. The damage model developed is incorporated in a general-purpose finite element program ABAQUA through its UMAT subroutine. The…
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  • MAADLY Spanning the Length Scales in Dynamic Fracture
  • Abstract A challenging paradigm in the computational sciences is the coupling of the continuum, the atomistic and the quantum descriptions of matter for a unified dynamic treatment of a single physical problem. We described the achievement of such a goal. We have spanned the length scales in a concerted simulation comprising the finite-element method, classical molecular dynamics, quantum tight-binding dynamics and seamless bridges between these different physical descriptions. We illustrate and validate the methodology for crack propagation in silicon.
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  • Simulation of Dynamic Failure Evolution in Brittle Solids without Using Nonlocal Terms in the Strain-Stress Space
  • Abstract To simulate the dynamic failure evolution without using nonlocal terms in the strain-stress space, a damage diffusion equation is formulated with the use of a combined damage/plasticity model that was primarily applied to the case of rock fragmentation. A vectorized model solver is developed for large-scale simulation. Two-dimensional sample problems are considered to illustrate the features of the proposed solution procedure. It appears that the proposed approach is effective in simulating the evolution of localization, with parallel computing, in a single computational domain involving different lower-order governing differential equations.
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