Contactmodels.m

classdef Contactmodels < handle
% 'Contactmodel' is a class containing all properties relevant to contact
% models between a rotor and a stator.
% The resulting object is pass-by-reference.

  properties (SetAccess = protected)
    name % Name of the contact model
  end


  properties
    mu_k         % Friction coefficient
    v_0 = 1e-4;  % Lower velocity tolerance [m/s]
    v_1 = 2e-4;  % Upper velocity tolerance [m/s]
    calc_ff
  end


  methods

    function obj = Contactmodels(friction_model)
      % Constructor function.
      % INPUT:
      %   friction_model: Parameter defining which friction model to use

      obj.mu_k = 0.2;

      % Assign function handle for the friction model
      if strcmp(friction_model, 'ambrosio')
        obj.calc_ff = @obj.calc_ff_ambrosio;
      elseif strcmp(friction_model, 'none')
        obj.calc_ff = @(~, ~) 0;
      else
        error('Invalid friction model')
      end
    end


    function Ff = calc_ff_ambrosio(obj, Fn, vt_rel)
      % Implements the friction model set forth in the article:
      %   "Influence of the contact–impact force model on the dynamic response
      %   of multi-body systems"
      %   In: Proc. IMechE, Year 2006, Volume 220.
      %   By: Flores, P. and Ambrósio, J. and Claro, J. C. P. and
      %   Lankarani, H. M.
      %
      % INPUT:
      %   Fn: Normal force (scalar)
      %   vt_rel: Relative tangential velocity

      % Dynamical correction coefficient, this makes the friction force
      % disappear close to 0 velocity, and introduces a linear increase from
      % this 0 niveau to static values
      if (obj.v_1 < norm(vt_rel))
        n_d = 1;
      elseif obj.v_0 < norm(vt_rel) & norm(vt_rel) <= obj.v_1
        n_d = (norm(vt_rel) - obj.v_0)/(obj.v_1 - obj.v_0);
      elseif norm(vt_rel) <= obj.v_0
        n_d = 0;
      end

      % Magnitude of the friction force (notice the sign follows the velocity)
      %           |  ___ + Ff
      %          _|_/
      % - Ff ___/ |
      %      -----|-----  v
      %      -    0    +
      Ff = Fn * obj.mu_k * sign(vt_rel) * n_d;
    end

  end


  methods (Access = protected)

    function print_name(obj)
      % Displays the current contact model in the console.
      fprintf('Using the %s model.\n', obj.name)
    end

  end
end % class