16-02-2013, 11:46 AM
Flutter of Cantilevered Column under Rocket Thrust
Flutter of Cantilevered.pptx (Size: 979.08 KB / Downloads: 27)
Objective
The aim is to experimentally verify the effect of damping on the flutter of a cantilevered column subjected to a tangential follower thrust
Background
Aerospace structures are subjected to tangential follower forces
These forces are nonconservative and may cause flutter instability
Damping plays a vital role in predicting flutter limit
Only a few experimental investigations have been made on the quantitative effect of damping on flutter limit
Viscoelastic material
Consider a simply supported perfect column subjected to an axially applied load F(t). The equation of motion can be written as
where w(x,t) denotes the lateral deflection, M(x,t) is the bending moment and is the mass per unit length of the column
Pfluger’s column
It is convenient to consider the simplified model - Pfluger’s column with internal damping-for the first theoretical prediction of the flutter thrust
It is assumed that the rocket is a particle instead of a rigid body
Rocket motor
The thrust is assumed to be constant and equal to average thrust (40 kgf) during the entire burning period
The mass of the rocket motor is assumed to be constant and equal to the average mass (14.18kg) during burning.
Stability in finite time interval
From the root locus for the test columns, the critical exponent(σ1) for the finite time stability (τ1) is plotted on a dotted line
The white and black circles represent the root loci for elastic and viscoelastic columns respectively
According to the stability in a finite time interval, critical dimensionless thrust parameter, ρcr , is similar for elastic and viscoelastic columns that is ρcr = 12.61
ρ* represents dimensionless flutter thrust with damping and ρ* is dimensionless flutter thrust with damping.
This means the flutter boundary obtained by neglecting internal damping is similar to the flutter boundary obtained by accounting for damping and by applying the stability criterion during the finite time interval