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Alfred Zmitrowicz - One of the best experts on this subject based on the ideXlab platform.

  • Models of kinematics dependent anisotropic and heterogeneous friction
    International Journal of Solids and Structures, 2005
    Co-Authors: Alfred Zmitrowicz
    Abstract:

    Anisotropy and heterogeneity of friction and wear can result from anisotropic roughness of engineering surfaces and from anisotropic and heterogeneous microstructures present in many materials (wood, single crystals, ceramics, composites, layer-lattice materials, polymers, biomaterials, monomolecular layers). In sliding surfaces of some materials, kinematics of sliding initiates microstructural and frictional changes. This research deals with advanced constitutive models, which describe evolutions of frictional anisotropy and heterogeneity induced by the sliding kinematics. First-, second- and higher-order constitutive equations of friction are developed with respect to powers of a sliding Path Curvature. The first-order equation of the friction force has two independent variables: sliding velocity unit vector and its derivative. The second- and higher-order equations are polynomials with respect to odd order tensors composed by the sliding velocity unit vector and the derivative. In the equations, friction tensors of even orders describe anisotropy and inhomogeneity of friction and effects associated with the sliding kinematics. The sliding Path Curvature generates: (a) an additional resistance to sliding, (b) a constraint force normal to the sliding trajectory. The friction constitutive equations satisfy the axiom of objectivity. A condition of dissipated energy restricts the friction tensors and the radius of Curvature. Examples illustrate friction descriptions.

  • An equation of anisotropic friction with sliding Path Curvature effects
    International Journal of Solids and Structures, 1999
    Co-Authors: Alfred Zmitrowicz
    Abstract:

    Anisotropy and inhomogeneity of dry friction can induce a dependence of friction force on a sliding Path Curvature. The objective of this study is to extend mathematical models of anisotropic friction by including the sliding Path Curvature effects. Due to this, a set of independent variables of the friction force constitutive equation is extended, and a derivative of the sliding velocity unit vector is taken into account. The friction description is investigated in a general case and in a particular when non-homogeneous friction properties form concentric circles in a contact surface. It has been found that: the friction constitutive equation and its variables satisfy the axiom of objectivity; the Second Law of Thermodynamics restricts components of tensors in the constitutive equation; there are radial and concentric circular privileged sliding directions. Non-homogeneous friction in the form of concentric circles has the global axial symmetry, while two tensors in the constitutive equation are defined locally and they have orthotropic and anisotropic properties, respectively. The sliding Path Curvature can induce positive and negative additional friction.

  • Illustrative examples of anisotropic friction with sliding Path Curvature effects
    International Journal of Solids and Structures, 1999
    Co-Authors: Alfred Zmitrowicz
    Abstract:

    A constitutive equation of anisotropic friction with sliding Path Curvature effects defined in the preceding companion paper is completed with illustrative examples. Friction coefficients, inclination angles and coefficients of tangent and normal components of the friction force with respect to the sliding direction are given in the case of non-homogeneous friction properties which form concentric circles in a contact surface. Motion of a material point in the surface with non-homogeneous friction is investigated for radial, concentric circular and arbitrary trajectories. Essential changes of sliding trajectories of the material point are observed for various values of coefficients of parametric tensors in the constitutive equation.

  • Models of Anisotropic Friction Depending on a Sliding Path Curvature
    Contact Mechanics, 1995
    Co-Authors: Alfred Zmitrowicz
    Abstract:

    Physical properties of solids and surfaces are very often non-homogeneous, and they can form different field singularities in a contact area between two bodies (concentric circles, ellipses, spirals etc.). The phenomenon refers to complex physical properties of materials (e.g. wood, crystals) or to specific techniques of manufacture and finishing. Non-homogeneous physical properties of solids and surfaces can generate a non-homogeneous anisotropic friction in the contact. This is the case where friction depends on the position of a contact point with respect to a singular field center. Then, the frictional anisotropy follows on the one hand from the physical properties of the surface, on the other hand it can additionally depend on a sliding Path in this surface. This fact should be included in the mathematical formulation of the friction law. In the contact surface with complex properties besides rectilinear particular friction directions also curved particular directions can exist.

Renato Zaccaria - One of the best experts on this subject based on the ideXlab platform.

  • Path Following for Unicycle Robots With an Arbitrary Path Curvature
    IEEE Transactions on Robotics, 2011
    Co-Authors: A. Morro, Antonio Sgorbissa, Renato Zaccaria
    Abstract:

    A new feedback control model is provided that allows a wheeled vehicle to follow a prescribed Path. Differently from all other methods in the literature, the method that is proposed neither requires the computation of a projection of the robot position on the Path, nor does it need to consider a moving virtual target to be tracked. Nevertheless, it guarantees asymptotic convergence to a generic 2-D curve which can be represented through its implicit equation in the form f(x,y)=0, and it puts no bounds on the initial position of the vehicle, provided that ∇f ≠ 0 .

  • 3d Path following with no bounds on the Path Curvature through surface intersection
    Intelligent Robots and Systems, 2010
    Co-Authors: Antonio Sgorbissa, Renato Zaccaria
    Abstract:

    The article proposes a new feedback control model which is suited for Path following in a 3 Dimensional Cartesian space. Differently from other methods in literature, the method proposed neither requires to compute a projection of the robot's position on the Path, nor it needs considering a moving virtual target. In spite of this: i) it guarantees asymptotic stability for every 3D curve which can be represented through a couple of intersecting surfaces f1(X, Y,Z) = 0, f2(X, Y,Z) = 0; ii) it does not put any bounds on the initial position of the vehicle depending on the Path's Curvature.

  • IROS - 3D Path following with no bounds on the Path Curvature through surface intersection
    2010 IEEE RSJ International Conference on Intelligent Robots and Systems, 2010
    Co-Authors: Antonio Sgorbissa, Renato Zaccaria
    Abstract:

    The article proposes a new feedback control model which is suited for Path following in a 3 Dimensional Cartesian space. Differently from other methods in literature, the method proposed neither requires to compute a projection of the robot's position on the Path, nor it needs considering a moving virtual target. In spite of this: i) it guarantees asymptotic stability for every 3D curve which can be represented through a couple of intersecting surfaces f1(X, Y,Z) = 0, f2(X, Y,Z) = 0; ii) it does not put any bounds on the initial position of the vehicle depending on the Path's Curvature.

Antonio Sgorbissa - One of the best experts on this subject based on the ideXlab platform.

  • Path Following for Unicycle Robots With an Arbitrary Path Curvature
    IEEE Transactions on Robotics, 2011
    Co-Authors: A. Morro, Antonio Sgorbissa, Renato Zaccaria
    Abstract:

    A new feedback control model is provided that allows a wheeled vehicle to follow a prescribed Path. Differently from all other methods in the literature, the method that is proposed neither requires the computation of a projection of the robot position on the Path, nor does it need to consider a moving virtual target to be tracked. Nevertheless, it guarantees asymptotic convergence to a generic 2-D curve which can be represented through its implicit equation in the form f(x,y)=0, and it puts no bounds on the initial position of the vehicle, provided that ∇f ≠ 0 .

  • 3d Path following with no bounds on the Path Curvature through surface intersection
    Intelligent Robots and Systems, 2010
    Co-Authors: Antonio Sgorbissa, Renato Zaccaria
    Abstract:

    The article proposes a new feedback control model which is suited for Path following in a 3 Dimensional Cartesian space. Differently from other methods in literature, the method proposed neither requires to compute a projection of the robot's position on the Path, nor it needs considering a moving virtual target. In spite of this: i) it guarantees asymptotic stability for every 3D curve which can be represented through a couple of intersecting surfaces f1(X, Y,Z) = 0, f2(X, Y,Z) = 0; ii) it does not put any bounds on the initial position of the vehicle depending on the Path's Curvature.

  • IROS - 3D Path following with no bounds on the Path Curvature through surface intersection
    2010 IEEE RSJ International Conference on Intelligent Robots and Systems, 2010
    Co-Authors: Antonio Sgorbissa, Renato Zaccaria
    Abstract:

    The article proposes a new feedback control model which is suited for Path following in a 3 Dimensional Cartesian space. Differently from other methods in literature, the method proposed neither requires to compute a projection of the robot's position on the Path, nor it needs considering a moving virtual target. In spite of this: i) it guarantees asymptotic stability for every 3D curve which can be represented through a couple of intersecting surfaces f1(X, Y,Z) = 0, f2(X, Y,Z) = 0; ii) it does not put any bounds on the initial position of the vehicle depending on the Path's Curvature.

Bruce C Garrett - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic solvent effects on activated chemical reactions. I. Classical effects of reaction Path Curvature
    The Journal of Chemical Physics, 1992
    Co-Authors: Gregory K. Schenter, Robin P. Mcrae, Bruce C Garrett
    Abstract:

    In gas phase reactions, dynamical recrossings across a phase space dividing surface induced by nonlinear reaction Path Curvature coupling leads to the breakdown of the fundamental dynamical approximation of classical transition state theory (TST). In the following study, we examine the nature of this breakdown for chemical reaction dynamics occurring in solution. As a model system, we consider the collinear A+BC reaction where reaction Path Curvature increases as the mass of B becomes small compared to the mass of A and C. We use a London–Eyring–Polanyi–Sato (LEPS) potential to describe the solute interaction and model the influence of the solvent by using a generalized Langevin equation that is further represented by a system of coupled harmonic oscillators. Exact classical rate constants are compared to those obtained from conventional TST and canonical variational transition state theory (CVT) as a function of solvent friction coupling. A harmonic TST analysis at the saddle point of the full system (so...

Sharon Hammes-schiffer - One of the best experts on this subject based on the ideXlab platform.

  • Time-dependent self-consistent-field dynamics based on a reaction Path Hamiltonian. II. Numerical tests
    The Journal of Chemical Physics, 1998
    Co-Authors: Jian Yun Fang, Sharon Hammes-schiffer
    Abstract:

    Numerical tests are presented for a method that combines the time-dependent self-consistent-field (TDSCF) method with the reaction Path Hamiltonian (RPH) derived by Miller, Handy, and Adams [J. Chem. Phys. 72, 99 (1980)]. The theoretical basis for this TDSCF-RPH method was presented in a previous paper. The equations of motion were derived for three different cases: (1) zero coupling matrix (i.e., zero reaction Path Curvature and zero coupling between the normal modes); (2) zero reaction Path Curvature and nonzero coupling between the normal modes; and (3) zero coupling between the normal modes and nonzero but small reaction Path Curvature. For these three cases the dynamics can always be reduced to a one-dimensional numerical time propagation of the reaction coordinate. In this paper the TDSCF-RPH methodology for all three cases is tested by comparing the TDSCF-RPH dynamics to exact quantum dynamics based on the exact Hamiltonian for simple model systems. The remarkable agreement indicates that the TDSCF...