On the equilibrium of a rigid body suspended by a set of linear springs

Abstract

In this paper an approach is described for determining equilibrium states of a rigid body suspended elastically in space by a set of linear springs. This system is considered as a two-terminal generalized spring with terminal across (translational and rotational velocities, vG, ωG) and terminal through (terminal force and moment, fG, mG) variables. The algorithmic approach used for the solution of six nonlinear and coupled equilibrium equations consists of two major steps. The first step is to assign an initial orientation to the rigid body which is represented by the transformation (rotation) matrix T(θ, n) and reduce the problem to the solution of force equations only through a computer program. This yields the position vector ξ of a preselected point G on the rigid body. Although the terminal force fG becomes zero at this position, the calculated terminal moment mG, in general, is not equal to zero. The second step is to try to determine the correct orientation of the rigid body based on an argument that the terminal moment should vanish. The same argument is also used for the solution of force equilibrium equations. These two steps are repeated several times until both fG and mG vanish simultaneously yielding an equilibrium state (ξ, T(θ, n)). Application of the approach is illustrated through various examples. It is observed that, if there are nonstable equilibrium states of the system, then sometimes all possible physical equilibrium states may not be obtained with this approach. © 2000 John Wiley & Sons, Inc.