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the University of Sussex, said: ‘Our simulations are aimed at understanding this process, which is inherently multi-scale, from the small scales at which stars form (parsecs) up to very large, cosmological ones (hundreds of megaparsec or more).’ Tis research does not just need to incorporate


such multi-scale processes, but must also model multiple processes, including photoionisation and radiative transfer, gas heating and cooling processes, gas flows, gravity and many others. Iliev added: ‘Te radiative transfer simulations are very computationally expensive, so require very large parallel machines to run efficiently.’ Te researchers are now expanding their work


to incorporate more processes, as Iliev explained: ‘We are currently working on new versions of our radiative transfer code ,which will incorporate not just ionising radiation (as now), but also Lyman-Werner radiative transfer and X-rays. We are also improving our galaxy (sub-grid) modelling and including new physical processes for more detailed and realistic modelling.’


SKA simulations Finding answers to astronomical phenomena like cosmic reionisation in the real world involves the use of radio astronomy. Radio telescopes are large structures spanning hundreds of metres, which are usually comprised of dozens of antenna arranged in an array to capture long-wavelength radio waves and make observations. Te SKA (Square Kilometre Array) facility will


be the world’s largest radio telescope. Once it has been built, SKA will be 50 times more sensitive and 10,000 times faster at mapping the sky than the world’s total current radio astronomy facilities. It is also hoped SKA can be used to answer fundamental astronomical questions, such as: how did the universe form and evolve? Does extraterrestrial life exist? What is dark matter and dark energy?


ONE PARSEC IS


EQUAL TO MORE THAN THREE LIGHT YEARS


Te prospects and possibilities of SKA are


monumental, and the radio telescope is relying on simulation soſtware to analyse its structure and optimise its design before construction begins in 2018. Researchers from the Stellenbosch University


are using simulations to analyse both the electromagnetic systems and the mitigation of Radio Frequency Interference (RFI) between adjacent antennas and other systems for the structural analysis of SKA. Dr. Danie Ludick, electrical and electronic engineer from the Stellenbosch University,


26 SCIENTIFIC COMPUTING WORLD


The on-site processing facility for the data captured by the LOFAR array


said: ‘Te research includes multi-physics simulation; for example, a coupled mechanical- electromagnetic analysis of quantifying environmental effects of sensitive equipment (such as a radio telescope) in the harsh desert environments where these structures are typically used. I am also looking at accelerated simulation methods for the fast, yet accurate simulations of antenna arrays.’ Te team is using Altair’s Hyperwork Suite


for its analyses, including OptiStruct for the structural analysis of SKA and computational electromagnetics soſtware product FEKO for the electromagnetic analysis. Simulation is the only viable option for


studying the interference characteristics of SKA in detail, but this requires considerable computational power to incorporate the extensive verification of the computational electromagnetic (CEM) model and the electrical size of the structure. FEKO features a parallel method of moments (MoM) solver to speed up the simulations so they could be completed in days at the Centre for High Performance Computing in Cape Town. Te simulations sometimes produce surprising results, as Ludick said: ‘For the structural analysis, it was interesting to see the impact of the backing structure for a large reflector dish, specifically when it causes the main reflector to deform slightly.’


Simulation results are also compared with


measurements from the MeerKAT radio telescope to validate the FEKO model and enable the rigorous RFI studies required to optimise the design, layout, shielding and bonding recommendations, to mitigate the interference between these extremely sensitive antennas and systems. New solvers are continually being added


or further improved to continue to address the challenges this massive project poses. Ludick added: ‘We are putting a lot of effort into streamlining the coupled mechanical electromagnetic analysis of large dish reflector antennas, specifically to automate the process – which up to now is a bit manual. We are also looking at improving our CEM analysis using domain decomposition methods where possible.’


Turning the sky on its head For radio telescope projects like SKA to thrive, we also need to improve our understanding of our own planet and its ionosphere, which is a layer of the Earth’s atmosphere that contains a high concentration of ions and free electrons, and is able to reflect radio waves. Te ionosphere is very problematic for radio telescopes that work at low frequencies (< 1 GHz) and, for those telescopes working at frequencies below about 300 MHz, it is probably the single biggest limitation to


@scwmagazine l www.scientific-computing.com





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