39 research outputs found
Emergent eddy saturation from an energy constrained eddy parameterisation
The large-scale features of the global ocean circulation and the sensitivity
of these features with respect to forcing changes are critically dependent upon
the influence of the mesoscale eddy field. One such feature, observed in
numerical simulations whereby the mesoscale eddy field is at least partially
resolved, is the phenomenon of eddy saturation, where the time-mean circumpolar
transport of the Antarctic Circumpolar Current displays relative insensitivity
to wind forcing changes. Coarse-resolution models employing the
Gent--McWilliams parameterisation with a constant Gent--McWilliams coefficient
seem unable to reproduce this phenomenon. In this article, an idealised model
for a wind-forced, zonally symmetric flow in a channel is used to investigate
the sensitivity of the circumpolar transport to changes in wind forcing under
different eddy closures. It is shown that, when coupled to a simple
parameterised eddy energy budget, the Gent--McWilliams coefficient of the form
described in Marshall et al. (2012) [A framework for parameterizing eddy
potential vorticity fluxes, J. Phys. Oceanogr., vol. 42, 539--557], which
includes a linear eddy energy dependence, produces eddy saturation as an
emergent property.Comment: 22 pages, 10 figures, Elsevier template, submitted to Ocean
Modelling; comments welcom
A new gauge-invariant method for diagnosing eddy diffusivities
Coarse resolution numerical ocean models must typically include a
parameterisation for mesoscale turbulence. A common recipe for such
parameterisations is to invoke down-gradient mixing, or diffusion, of some
tracer quantity, such as potential vorticity or buoyancy. However, it is well
known that eddy fluxes include large rotational components which necessarily do
not lead to any mixing; eddy diffusivities diagnosed from unfiltered fluxes are
thus contaminated by the presence of these rotational components. Here a new
methodology is applied whereby eddy diffusivities are diagnosed directly from
the eddy force function. The eddy force function depends only upon flux
divergences, is independent of any rotational flux components, and is
inherently non-local and smooth. A one-shot inversion procedure is applied,
minimising the mis-match between parameterised force functions and force
functions derived from eddy resolving calculations. This enables diffusivities
associated with the eddy potential vorticity and buoyancy fluxes to be
diagnosed. The methodology is applied to multi-layer quasi-geostrophic ocean
gyre simulations. It is found that: (i) a strictly down-gradient mixing scheme
has limited success in reducing the mis-match compared to one with no sign
constraint on the diffusivity; (ii) negative signals of diffusivities are
prevalent around the time-mean jet; (iii) there is some indication that the
magnitude of the diffusivity correlates well the eddy energy. Implications for
parameterisation are discussed in light of these diagnostic results.Comment: 22 pages, 14 figures, Elsevier template, submitted to Ocean
Modelling; comments welcom
Application of homogenization theory to the study of trabecular bone mechanics
It is generally accepted that the strength and stiffness of trabecular bone is strongly affected by trabecular microstructure. It has also been hypothesized that stress induced adaptation of trabecular bone is affected by trabecular tissue level stress and/or strain. At this time, however, there is no generally accepted (or easily accomplished) technique for predicting the effect of microstructure on trabecular bone apparent stiffness and strength or estimating tissue level stress or strain. In this paper, a recently developed mechanics theory specifically designed to analyze microstructured materials, called the homogenization theory, is presented and applied to analyze trabecular bone mechanics. Using the homogenization theory it is possible to perform microstructural and continuum analyses separately and then combine them in a systematic manner. Stiffness predictions from two different microstructural models of trabecular bone show reasonable agreement with experimental results, depending on metaphyseal region, (R2>0.5 for proximal humerus specimens, R2 <0.5 for distal femur and proximal tibia specimens). Estimates of both microstructural strain energy density (SED) and apparent SED show that there are large differences (up to 30 times) between apparent SED (as calculated by standard continuum finite element analyses) and the maximum microstructural or tissue SED. Furthermore, a strut and spherical void microstructure gave very different estimates of maximum tissue SED for the same bone volume fraction (BV/TV). The estimates from the spherical void microstructure are between 2 and 20 times greater than the strut microstructure at 10-20% BV/TV.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29647/1/0000736.pd
Highly-parallelized simulation of a pixelated LArTPC on a GPU
The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype
A posteriori real-time recurrent learning schemes for a recurrent neural network based nonlinear predictor
Radial oscillations of thin cylindrical and spherical shells: investigation of Lie point symmetries for arbitrary strain-energy functions
Comparative Study of Advanced Turboprop Aircraft with Wing and Rear Mounted Propulsion System in the Agile EU project
The present paper describes the comparison of two variantof the sameregionalturboprop aircraftusing the AGILEâs collaborative MDO process. The two turboprop aircraftareboth characterized by the same Top Level Aircraft Requirements,but with a different engine positions.The requirements are provided by the industrial partner (Leonardo âAircraft Division) leading to twoaircraft configurationswith wing and rear mounted propulsion system.A complete aircraft preliminary design is carried out to understand the effect of engine position considering all the main design disciplines. 13 engine design cases related to differentflight conditions and engine ratings are considered to select engine cycle and size. Baseline engine size isdefined by high shaft power requirements at max continuous conditionsand by power and thrustrequirementat other design cases. Improvement of cruise installed SFC of baseline engine by 6-7% is shownto reach given preliminary requirement on cruise SFC level.The results ofthe twoaircraft are obtained and compared, showingthatthe rear mounted engine configuration can reach higher cruise speeds, despiteslight incrementsof on-board systems weight and required mission fuel