A new finite element for modeling pneumatic muscle actuators

Pneumatic Muscle Actuators (PMAs) have recently been used as control devices in parachute soft landing systems and parachute steering control systems. In this paper, a special cable element is developed to model the mechanical behavior of PMAs. The new element provides relationships between the PMA internal pressure, fiber bias angle, PMA radius and length, and resultant axial force, based on the kinematic assumption of inextensible PMA fibers. The principle of virtual work and total Lagrange formulation are used to derive the element internal force vector and tangent stiffness matrix. The PMA element is implemented in a geometrically nonlinear, transient finite element program for simulating the structural dynamics of airdrop systems. Several numerical examples are given to validate the mechanical behavior of the new element. Two large-scale application problems are also presented to demonstrate the capabilities of the new element for simulating PMAs used in airdrop systems.