  In recent years, a new method for experimental nonlinear modal analysis has
been developed, which is based on the extended periodic motion concept. The
method is well suited to experimentally obtain amplitude-dependent modal
properties (modal frequency, damping ratio and deflection shape) for strongly
nonlinear systems. To isolate a nonlinear mode, the negative viscous damping
term of the extended periodic motion concept is approximated by ensuring phase
resonance between excitation and response. In this work, an alternative
approach to isolate a nonlinear mode is developed and analyzed: velocity
feedback. The accuracy of the extracted modal properties and robustness of
velocity feedback is first assessed by means of simulated experiments. The two
approaches phase resonance and velocity feedback are then compared in terms of
accuracy and experimental implementation effort. To this end, both approaches
are applied to an experimental specimen, which is a cantilevered beam
influenced by a strong dry friction nonlinearity. In this work, the discussion
is limited to single-point excitation. It is shown that a robust implementation
of velocity feedback requires the measurement of several response signals,
distributed over the structure. An advantage of velocity feedback is that no
controller is needed. The accuracy of the modal properties can, however, suffer
from imperfections of the excitation mechanism such as a phase lag due to
exciter-structure interactions or gyroscopic forces due to single-point
excitation.
