By this action, the highly elastic axis
must be bent at the lower extremity, where it is naturally slightly curved; and I imagine it is by this elasticity alone that the zoophyte is enabled to rise again through the mud.
The motion of the profile is described by functions [alpha](t), representing the rotation around the elastic axis TR, and H(t), denoting the vertical displacement; see Figure 2.1.
The symbol F stands for the component of the aerodynamic force acting on the profile in the vertical direction, M is the torsional aerodynamic moment with respect to the elastic axis, [D.sub.HH], [D.sub.H[alpha]], [D.sub.[alpha]H], [D.sub.[alpha][alpha]], are the coefficients of structural damping, [S.sub.[alpha]], [I.sub.[alpha]], m and [k.sub.HH], [k.sub.[alpha][alpha]], [k.sub.H[alpha]], [k.sub.[alpha]H] denote the static moment around the elastic axis TR, the moment of inertia around TR, the mass of the profile and the stiffnesses of the profile elastic support.
[x.sub.1], [x.sub.2] are the coordinates of points on [[GAMMA].sub.Wt], [x.sup.TR.sub.i], i = 1, 2, are the coordinates of the elastic axis [x.sup.TR], and