Introduction - Human Motion Simulation: Predictive Dynamics - page 1

CHAPTER
1

Introduction

I find that the harder I work, the more luck I seem to have.
Thomas Jefferson (1743

1826)

1.1 What is predictive dynamics?
Predictive dynamics is a term coined to characterize a new methodology for pre-
dicting human motion while considering dynamics of the human and the environ-
ment the laws of physics must be obeyed. Whereas kinematics is the study of

motion (position, velocity, and acceleration) without forces and torques, dynamics
is the study of motion of bodies with all external and internal forces taken into
consideration.
For every motion affected by physics, there are laws that govern that motion.
These laws have undergone the test of time, have sent people to the moon, and
have been implemented into every computer program that calculates the motion
of a given system. Equations that represent motion are called the equations of
motion. For large redundant systems such as the human body, these equations
become very complicated nonlinear coupled differential equations subject to vari-
ous algebraic constraints on the motion; hence the term often used to represent
these equations is differential algebraic equations (DAEs).
For a complicated system of segments, such as for a human being, which is
made up of joints and rigid links (we assume rigidity of human bones), the formu-
lation for multi-body dynamics becomes large and complex. Solving the conse-
quent system of equations is almost impossible. Indeed, for structural systems
with limited number of degrees of freedom, integrators have been developed to
solve the problem iteratively. For a highly nonlinear system with a large number
of degrees of freedom, however, integrators come to a halt.
For many years, our research at the Virtual Soldier Research (VSR) program
has focused on a method that employs optimization with dynamics to predict
human motion. Recent results have demonstrated significant promise for resolving
the problem of predicting human motion while taking into consideration external
forces, obstacles, physiology, and most importantly the equations of motion.
Inducing natural behavior is a natural result of this method.
This method, which we call predictive dynamics (PD), provides a way to
address the issue of predicting human motion in a general manner. It addresses
problems where both the motion of the system and the forces causing the motion

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