Abstract. Coupled reactive transport simulations are extremely demanding in terms of required computational power, which hampers their
application and leads to coarsened and oversimplified domains. The
chemical sub-process represents the major bottleneck: its
acceleration is an urgent challenge which gathers increasing
interdisciplinary interest along with pressing requirements for
subsurface utilization such as spent nuclear fuel storage,
geothermal energy and CO2 storage. In this context we developed
POET (POtsdam rEactive Transport), a research parallel reactive transport simulator
integrating algorithmic improvements which decisively speed up
coupled simulations. In particular, POET is designed with a
master/worker architecture, which ensures computational efficiency
in both multicore and cluster compute environments. POET does not rely on contiguous grid partitions for the parallelization of
chemistry but forms work packages composed of grid cells distant
from each other. Such scattering prevents particularly expensive
geochemical simulations, usually concentrated in the vicinity of a
reactive front, from generating load imbalance between the available
CPUs (central processing units), as is often the case with classical partitions.
Furthermore, POET leverages an original implementation of the
distributed hash table (DHT) mechanism to cache the results of
geochemical simulations for further reuse in subsequent time steps
during the coupled simulation. The caching is hence particularly
advantageous for initially chemically homogeneous simulations and
for smooth reaction fronts. We tune the rounding employed in the DHT
on a 2D benchmark to validate the caching approach, and we evaluate
the performance gain of POET's master/worker architecture and the DHT speedup on a 3D benchmark comprising around 650 000 grid elements.
The runtime for 200 coupling iterations, corresponding to 960
simulation days, reduced from about 24 h on 11 workers to 29 min
on 719 workers. Activating the DHT reduces the runtime further to
2 h and 8 min respectively. Only with these kinds of reduced
hardware requirements and computational costs is it possible to
realistically perform the long-term complex reactive transport
simulations, as well as perform the uncertainty analyses required
by pressing societal challenges connected with subsurface
utilization.
POET (v0.1): speedup of many-core parallel reactive transport simulations with fast DHT lookups
