Kinematic characteristics

Introduction

In case of magneto-mechanical coupling it is necessary to define the kinematic characteristics of the moving part and of the coupled load, in order to solve the dynamics equation.

Handling in Flux

The diagram below shows the handling of motion in Flux:

  • the fixed part, the moving part and the compressible area belong to the finite element domain
  • the moving part is mechanically coupled to an external device that is the coupled load, outside the finite element domain

Mechanical and kinematic characteristics

The mechanical and kinematic characteristics necessary to solve the fundamental dynamics equation are the following:

  • mass or moment of inertia of the moving part and of the coupled load
  • resistant force or torque acting on the moving part and on the coupled load
  • initial conditions: initial position and initial speed of the moving part

Resistant force or torque

The resistant force or torque can be described in several ways, such as:

  • predefined formulas: friction force, return force (spring)
  • a varying formula, entered by the user

These two types of formulas are detailed in the following blocks.

Predefined formulas (1)

The force or the resistive torque can be described by means of a predefined formula of friction force or torque type.

(1) Friction force or torque
Translation Rotation

The signs in the equation are defined in the following way:

  • if speed is positive ( or > 0): the sign is replaced by the + sign
  • if speed is negative ( or < 0): the sign is replaced by the – sign

The three coefficients f0, f1 and f2, are as follows:

  • f0: constant friction coefficient, independent of speed (in N or N.m)

  • f1: viscous friction coefficient, function of speed (in N.s/m or in N.m.s/degrees)

  • f2: friction coefficient, function of speed to the second power (in N.s²/m² or in N.m.s²/degrees²)

Note: If there are symmetries and periodicities:

the coefficients f0, f1 and f2 must be defined for the entire device, even if it is not represented entirely. The forces or torques are computed for the entire device.

Predefined formulas (2)

The force or the resistive torque can be described by means of a predefined formula of return force or torque type.

(2) Return force or torque (spring)
Translation Rotation

The coefficient k is the stiffness (or torsion) constant of the spring

(in N/m or N.m/degree).

Formula with I/O parameters

The force or the resistive torque can be described by the intermediary of a formula with I/O parameters.

A formula with I/O parameters is a formula function of kinematic parameters, such as position, speed, acceleration of the mechanical set considered; or a function of other mechanical sets; or a function of any parameters.