Papers

Adaptive mesh simulations of polycrystalline materials using a Cartesian representation of an amplitude expansion of the phase-field-crystal model

Matjaž Berčič and Goran Kugler,

Phys. Rev. E 98, 033303 – Published 11 September 2018

This paper introduces improvements to an amplitude expansion of the phase-field-crystal model. An auxiliary field describing local grain rotation is introduced and used to enable the adaptive mesh to be coarsened in all grains, regardless of their orientation. Only a Cartesian representation of the amplitude equations is used.

Enabling simulations of grains within a full rotation range in amplitude expansion of the phase-field crystal model

Matjaž Berčič and Goran Kugler,

Phys. Rev. E 101, 043309 – Published 27 April 2020

DOI:10.1103/PhysRevE.101.043309, pdf

This paper introduces improvements to the amplitude expansion of the phase-field crystal model that enable the simulation of grains within a full range of orientations. The unphysical grain boundary between grains, rotated by a crystal’s symmetry rotation, is removed using a combination of the auxiliary rotation field described in our previous work and an algorithm that correctly matches the complex amplitudes according to the differences in local rotation.

Unified approach to scale transition in simulations of microstructure evolution using phase-field crystal model

Matjaž Berčič (author), Goran Kugler (advisor)

PhD thesis, University of Ljubljana, Faculty of Natural Sciences and Engineering – Completed April 2019

COBISS.SI-ID:1815135 pdf UniLj repository

The Phase-Field Crystal model (PFC) is a model that is able to describe material on the atomic level across diffusive time scales using a continuous atomic density field. Its amplitude expansion (APFC) reformulates the model in a form suitable for the application of adaptive mesh refinement techniques. This thesis presents improvements to the APFC model that lead to effective use of adaptive mesh refinement techniques. An auxiliary field describing local grain rotation is introduced and used to enable the adaptive mesh to coarsen in all grains, regardless of their orientation. Only a Cartesian representation of the amplitude equations is employed. The introduced algorithm extracts the local grain rotation and exploits the rotational covariance of the amplitude equations to achieve efficient use of computational resources. The auxiliary local rotation field is used to remove an unphysical grain boundary present in the APFC model between grains, which are rotated by the crystal’s symmetry rotation. The unphysical grain boundary is removed by correctly matching the complex amplitudes describing the best aligned density waves. This corrects the grain boundary energies in half of the grain boundaries formed between the randomly rotated grains and enables APFC simulations of processes where grain rotation occurs. Simulations of a single rotating grain using the PFC and APFC models show qualitatively matching results, confirming the effective removal of the unphysical grain boundary under conditions where grains rotate dynamically. Together, the improvements enable microstructure simulations with the APFC model on an adaptive computational mesh, which efficiently distributes computational resources even in simulations of processes where grains rotate.

Maturity assessment of ITER diagnostics plant instrumentation and control design

Stefan Simrock et al.

Fusion Engineering and Design – Volumes 96-97, Oktober 2015

DOI:10.1016/j.fusengdes.2015.06.093,

ITER requires extensive diagnostics to meet the demands for machine operation, protection, plasma control and physics studies. The interfaces between plant instrumentation and control (I&C) and the central control system follow mandatory rules described in the Plant Control Design Handbook (PCDH) [1], while the design strategy for PCDH compliant plant I&C is covered in its guidelines and supported by hardware catalogues. During preliminary and final design review as well as factory and site acceptance testing it is therefore important to determine the maturity of the I&C design and its implementation to ensure its compliance with the PCDH and the diagnostics performance requirements.