334 research outputs found
Large-scale grid-enabled lattice-Boltzmann simulations of complex fluid flow in porous media and under shear
Well designed lattice-Boltzmann codes exploit the essentially embarrassingly
parallel features of the algorithm and so can be run with considerable
efficiency on modern supercomputers. Such scalable codes permit us to simulate
the behaviour of increasingly large quantities of complex condensed matter
systems. In the present paper, we present some preliminary results on the large
scale three-dimensional lattice-Boltzmann simulation of binary immiscible fluid
flows through a porous medium derived from digitised x-ray microtomographic
data of Bentheimer sandstone, and from the study of the same fluids under
shear. Simulations on such scales can benefit considerably from the use of
computational steering and we describe our implementation of steering within
the lattice-Boltzmann code, called LB3D, making use of the RealityGrid steering
library. Our large scale simulations benefit from the new concept of capability
computing, designed to prioritise the execution of big jobs on major
supercomputing resources. The advent of persistent computational grids promises
to provide an optimal environment in which to deploy these mesoscale simulation
methods, which can exploit the distributed nature of compute, visualisation and
storage resources to reach scientific results rapidly; we discuss our work on
the grid-enablement of lattice-Boltzmann methods in this context.Comment: 17 pages, 6 figures, accepted for publication in
Phil.Trans.R.Soc.Lond.
Large-scale lattice Boltzmann simulations of complex fluids: advances through the advent of computational grids
During the last two years the RealityGrid project has allowed us to be one of
the few scientific groups involved in the development of computational grids.
Since smoothly working production grids are not yet available, we have been
able to substantially influence the direction of software development and grid
deployment within the project. In this paper we review our results from large
scale three-dimensional lattice Boltzmann simulations performed over the last
two years. We describe how the proactive use of computational steering and
advanced job migration and visualization techniques enabled us to do our
scientific work more efficiently. The projects reported on in this paper are
studies of complex fluid flows under shear or in porous media, as well as
large-scale parameter searches, and studies of the self-organisation of liquid
cubic mesophases.
Movies are available at
http://www.ica1.uni-stuttgart.de/~jens/pub/05/05-PhilTransReview.htmlComment: 18 pages, 9 figures, 4 movies available, accepted for publication in
Phil. Trans. R. Soc. London Series
Reconfigurable Antenna Systems: Platform implementation and low-power matters
Antennas are a necessary and often critical component of all wireless systems, of which they share the ever-increasing complexity and the challenges of present and emerging trends. 5G, massive low-orbit satellite architectures (e.g. OneWeb), industry 4.0, Internet of Things (IoT), satcom on-the-move, Advanced Driver Assistance Systems (ADAS) and Autonomous Vehicles, all call for highly flexible systems, and antenna reconfigurability is an enabling part of these advances. The terminal segment is particularly crucial in this sense, encompassing both very compact antennas or low-profile antennas, all with various adaptability/reconfigurability requirements. This thesis work has dealt with hardware implementation issues of Radio Frequency (RF) antenna reconfigurability, and in particular with low-power General Purpose Platforms (GPP); the work has encompassed Software Defined Radio (SDR) implementation, as well as embedded low-power platforms (in particular on STM32 Nucleo family of micro-controller). The hardware-software platform work has been complemented with design and fabrication of reconfigurable antennas in standard technology, and the resulting systems tested. The selected antenna technology was antenna array with continuously steerable beam, controlled by voltage-driven phase shifting circuits. Applications included notably Wireless Sensor Network (WSN) deployed in the Italian scientific mission in Antarctica, in a traffic-monitoring case study (EU H2020 project), and into an innovative Global Navigation Satellite Systems (GNSS) antenna concept (patent application submitted). The SDR implementation focused on a low-cost and low-power Software-defined radio open-source platform with IEEE 802.11 a/g/p wireless communication capability. In a second embodiment, the flexibility of the SDR paradigm has been traded off to avoid the power consumption associated to the relevant operating system. Application field of reconfigurable antenna is, however, not limited to a better management of the energy consumption. The analysis has also been extended to satellites positioning application. A novel beamforming method has presented demonstrating improvements in the quality of signals received from satellites. Regarding those who deal with positioning algorithms, this advancement help improving precision on the estimated position
The Murchison Widefield Array: the Square Kilometre Array Precursor at low radio frequencies
The Murchison Widefield Array (MWA) is one of three Square Kilometre Array
Precursor telescopes and is located at the Murchison Radio-astronomy
Observatory in the Murchison Shire of the mid-west of Western Australia, a
location chosen for its extremely low levels of radio frequency interference.
The MWA operates at low radio frequencies, 80-300 MHz, with a processed
bandwidth of 30.72 MHz for both linear polarisations, and consists of 128
aperture arrays (known as tiles) distributed over a ~3 km diameter area. Novel
hybrid hardware/software correlation and a real-time imaging and calibration
systems comprise the MWA signal processing backend. In this paper the as-built
MWA is described both at a system and sub-system level, the expected
performance of the array is presented, and the science goals of the instrument
are summarised.Comment: Submitted to PASA. 11 figures, 2 table
Maximising the Utility of Enterprise Millimetre-Wave Networks
Millimetre-wave (mmWave) technology is a promising candidate for meeting the
intensifying demand for ultra fast wireless connectivity, especially in
high-end enterprise networks. Very narrow beam forming is mandatory to mitigate
the severe attenuation specific to the extremely high frequency (EHF) bands
exploited. Simultaneously, this greatly reduces interference, but generates
problematic communication blockages. As a consequence, client association
control and scheduling in scenarios with densely deployed mmWave access points
become particularly challenging, while policies designed for traditional
wireless networks remain inappropriate. In this paper we formulate and solve
these tasks as utility maximisation problems under different traffic regimes,
for the first time in the mmWave context. We specify a set of low-complexity
algorithms that capture distinctive terminal deafness and user demand
constraints, while providing near-optimal client associations and airtime
allocations, despite the problems' inherent NP-completeness. To evaluate our
solutions, we develop an NS-3 implementation of the IEEE 802.11ad protocol,
which we construct upon preliminary 60GHz channel measurements. Simulation
results demonstrate that our schemes provide up to 60% higher throughput as
compared to the commonly used signal strength based association policy for
mmWave networks, and outperform recently proposed load-balancing oriented
solutions, as we accommodate the demand of 33% more clients in both static and
mobile scenarios.Comment: 22 pages, 12 figures, accepted for publication in Computer
Communication
Reinforcement Learning in Self Organizing Cellular Networks
Self-organization is a key feature as cellular networks densify and become more heterogeneous, through the additional small cells such as pico and femtocells. Self- organizing networks (SONs) can perform self-configuration, self-optimization, and self-healing. These operations can cover basic tasks such as the configuration of a newly installed base station, resource management, and fault management in the network. In other words, SONs attempt to minimize human intervention where they use measurements from the network to minimize the cost of installation, configuration, and maintenance of the network. In fact, SONs aim to bring two main factors in play: intelligence and autonomous adaptability. One of the main requirements for achieving such goals is to learn from sensory data and signal measurements in networks. Therefore, machine learning techniques can play a major role in processing underutilized sensory data to enhance the performance of SONs.
In the first part of this dissertation, we focus on reinforcement learning as a viable approach for learning from signal measurements. We develop a general framework in heterogeneous cellular networks agnostic to the learning approach. We design multiple reward functions and study different effects of the reward function, Markov state model, learning rate, and cooperation methods on the performance of reinforcement learning in cellular networks. Further, we look into the optimality of reinforcement learning solutions and provide insights into how to achieve optimal solutions.
In the second part of the dissertation, we propose a novel architecture based on spatial indexing for system-evaluation of heterogeneous 5G cellular networks. We develop an open-source platform based on the proposed architecture that can be used to study large scale directional cellular networks. The proposed platform is used for generating training data sets of accurate signal-to-interference-plus-noise-ratio (SINR) values in millimeter-wave communications for machine learning purposes. Then, with taking advantage of the developed platform, we look into dense millimeter-wave networks as one of the key technologies in 5G cellular networks. We focus on topology management of millimeter-wave backhaul networks and study and provide multiple insights on the evaluation and selection of proper performance metrics in dense millimeter-wave networks. Finally, we finish this part by proposing a self-organizing solution to achieve k-connectivity via reinforcement learning in the topology management of wireless networks
Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)
Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression
Mesoscale fluid simulation with the Lattice Boltzmann method
PhDThis thesis describes investigations of several complex fluid effects., including
hydrodynamic spinodal decomposition, viscous instability. and self-assembly of a
cubic surfactant phase, by simulating them with a lattice Boltzmann computational
model.
The introduction describes what is meant by the term "complex fluid", and why
such fluids are both important and difficult to understand. A key feature of complex
fluids is that their behaviour spans length and time scales. The lattice Boltzmann
method is presented as a modelling technique which sits at a "mesoscale" level
intermediate between coarse-grained and fine-grained detail, and which is therefore
ideal for modelling certain classes of complex fluids.
The following chapters describe simulations which have been performed using
this technique, in two and three dimensions. Chapter 2 presents an investigation
into the separation of a mixture of two fluids. This process is found to involve several
physical mechanisms at different stages. The simulated behaviour is found to be in
good agreement with existing theory, and a curious effect, due to multiple competing
mechanisms, is observed, in agreement with experiments and other simulations.
Chapter 3 describes an improvement to lattice Boltzmann models of Hele-Shaw
flow, along with simulations which quantitatively demonstrate improvements in both
accuracy and numerical stability. The Saffman-Taylor hydrodynamic instability is
demonstrated using this model.
Chapter 4 contains the details and results of the TeraGyroid experiment, which
involved extremely large-scale simulations to investigate the dynamical behaviour
of a self-assembling structure. The first finite- size-effect- free dynamical simulations
of such a system are presented. It is found that several different mechanisms are
responsible for the assembly; the existence of chiral domains is demonstrated, along
with an examination of domain growth during self-assembly.
Appendix A describes some aspects of the implementation of the lattice Boltzmann
codes used in this thesis; appendix B describes some of the Grid computing
techniques which were necessary for the simulations of chapter 4.
Chapter 5 summarises the work, and makes suggestions for further research and
improvement.Huntsman Corporation Queen Mary University Schlumberger Cambridge Researc
Development of an Intelligent Monitoring and Control System for a Heterogeneous Numerical Propulsion System Simulation
The NASA Numerical Propulsion System Simulation (NPSS) project is exploring the use of computer simulation to facilitate the design of new jet engines. Several key issues raised in this research are being examined in an NPSS-related research project: zooming, monitoring and control, and support for heterogeneity. The design of a simulation executive that addresses each of these issues is described. In this work, the strategy of zooming, which allows codes that model at different levels of fidelity to be integrated within a single simulation, is applied to the fan component of a turbofan propulsion system. A prototype monitoring and control system has been designed for this simulation to support experimentation with expert system techniques for active control of the simulation. An interconnection system provides a transparent means of connecting the heterogeneous systems that comprise the prototype
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