  Higher-order anisotropic flows in heavy-ion collisions are affected by
nonlinear mode coupling effects. It has been suggested that the associated
nonlinear hydrodynamic response coefficients probe the transport properties and
are largely insensitive to the spectrum of initial density fluctuations of the
medium created in these collisions. To test this suggestion, we explore
nonlinear mode coupling effects in event-by-event viscous fluid dynamics, using
two different models for the fluctuating initial density profiles, and compare
the nonlinear coupling coefficients between the initial eccentricity vectors
before hydrodynamic expansion and the final flow vectors after the expansion.
For several mode coupling coefficients we find significant sensitivity to the
initial fluctuation spectrum. They all exhibit strong sensitivity to the
specific shear viscosity at freeze-out, but only weak dependence on the shear
viscosity during hydrodynamic evolution.
