  Part IA: We present numerical measurements of relativistic scaling relations
in $(2+1)$-dimensional conformal fluid turbulence, which perform favourably
over their non-relativistic versions. As seen with incompressible turbulence in
past studies, we find that the energy spectrum exhibits $k^{-2}$ scaling rather
than the Kolmogorov/Kraichnan expectation of $k^{-5/3}$.
  Part IB: We compute the fractal dimension $D$ of a turbulent anti-deSitter
black brane reconstructed from boundary fluid data using the fluid-gravity
duality. Our value of $D=2.584(1)$ is consistent with the upper bound $D\leq
3$, resolving a recent claim that $D=3+1/3$. We describe how to covariantly
define the fractal dimension of spatial sections of the horizon, and we
speculate on assigning a `bootstrapped' value to the entire horizon.
  Part II: We report progress implementing a fluid code with post-Newtonian
(PN) gravity in spherical symmetry. The PN formalism couples a fluid, its
self-gravity, and a black hole via elliptic equations. This eliminates
radiative modes, allowing larger time steps, which is helpful for studying
systems with very long time scales, eg. tidal disruption events.
  Part III: Asteroseismology of rotating core-collapse supernovae is possible
with a multimessenger strategy. We show an $l=2$, $m=0$, $n\gtrsim 2$,
$f\lesssim 280$ Hz mode of the core is responsible for emission in
gravitational waves and neutrinos. The angular harmonics of the neutrino
emission is consistent with the mode energy around the neutrinospheres, where
$r\sim 70$ km. Thus, neutrinos carry information about the mode in the outer
region of the core, whereas gravitational waves probe the deep inner core $r
\lesssim 30$ km.
