Publications
13 results found
Aznavourian R, Guenneau S, Ungureanu B, et al., 2022, Morphing for faster computations with finite difference time domain algorithms, EPJ Applied Metamaterials, Vol: 9, ISSN: 2272-2394
In the framework of wave propagation, finite difference time domain (FDTD) algorithms, yield high computational time. We propose to use morphing algorithms to deduce some approximate wave pictures of their interactions with fluid-solid structures of various shapes and different sizes deduced from FDTD computations of scattering by solids of three given shapes: triangular, circular and elliptic ones. The error in the L2 norm between the FDTD solution and approximate solution deduced via morphing from the source and destination images are typically less than 1% if control points are judiciously chosen. We thus propose to use a morphing algorithm to deduce approximate wave pictures: at intermediate time steps from the FDTD computation of wave pictures at a time step before and after this event, and at the same time step, but for an average frequency signal between FDTD computation of wave pictures with two different signal frequencies. We stress that our approach might greatly accelerate FDTD computations as discretizations in space and time are inherently linked via the Courant–Friedrichs–Lewy stability condition. Our approach requires some human intervention since the accuracy of morphing highly depends upon control points, but compared to the direct computational method our approach is much faster and requires fewer resources. We also compared our approach to some neural style transfer (NST) algorithm, which is an image transformation method based on a neural network. Our approach outperforms NST in terms of the L2 norm, Mean Structural SIMilarity, expected signal to error ratio.
Ungureanu B, Tournat V, Craster R, et al., 2021, Theory and experiments for seismic waves propagating within an array of clamped inclusions in a soft matrix, 15th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), Publisher: IEEE, Pages: X438-X441
Varma TV, Ungureanu B, Sarkar S, et al., 2020, The influence of structure geometry and material on seismic metamaterial performance, Publisher: arXiv
Diverting, and controlling, elastic vibrations impacting upon infrastructureis a major challenge for seismic hazard mitigation, and for the reduction ofmachine noise and vehicle vibration in the urban environment. Seismicmetamaterials (SMs), with their inherent ability to manipulate wavepropagation, provide a key route for overcoming the technological hurdlesinvolved in this challenge. Engineering the structure of the SM serves as abasis to tune and enhance its functionality, and inspired by split rings,swiss-rolls, notch-shaped and labyrinthine designs of elementary cells inelectromagnetic and mechanical metamaterials, we investigate altering thestructure geometries of SMs with the aim of creating large bandgaps\textcolor{black}{in a subwavelength regime}. We show that square stiffinclusions, perform better in comparison to circular ones, whilst keeping thesame filling fraction. En route to enhancing the bandgap, we have also studiedthe performance of SMs with different constituent materials; we find that steelcolumns, as inclusions, show large bandgaps, however, the columns are too largefor steel to be a feasible material in practical or financial terms.Non-reinforced concrete would be preferable for industry level scaling up ofthe technology because, concrete is cost-effective, easy to cast directly atthe construction site and easy to provide arbitrary geometry of the structure.As a part of this study, we show that concrete columns can also be designed toexhibit bandgaps if we cast them within a soft soil coating surrounding theprotected area for various civil structures like a bridge, building, oilpipelines etc.
Ungureanu B, Makwana M, Craster R, et al., 2020, Localising symmetry protected edge waves via the topological rainbow effect, Publisher: arXiv
We combine two different fields, topological physics and metamaterials to design a topological metasurface tocontrol and redirect elastic waves. We strategically design a two-dimensional crystalline perforated elastic platethat hosts symmetry-induced topological edge states. By concurrently allowing the elastic substrate to spatiallyvary in depth, we are able to convert the incident slow wave into a series of robust modes, with differing envelopemodulations. This adiabatic transition localises the incoming energy into a concentrated region where it can thenbe damped or extracted. For larger transitions, different behaviour is observed; the incoming energy propagatesalong the interface before being partitioned into two disparate chiral beams. This “topological rainbow” effectleverages two main concepts, namely the quantum valley-Hall effect and the rainbow effect usually associatedwith electromagnetic metamaterials. The topological rainbow effect transcends specific physical systems, hence,the phenomena we describe can be transposed to other wave physics. Due to the directional tunability of theelastic energy by geometry our results have far-reaching implications for applications such as switches, filtersand energy-harvesters.
Ungureanu B, Guenneau S, Achaoui Y, et al., 2019, The influence of building interactions on seismic and elastic body waves, EPJ Applied Metamaterials, Vol: 6, Pages: 1-12, ISSN: 2272-2394
We outline some recent research advances on the control of elastic waves in thin and thick plates, that have occurred since the large scale experiment [S. Brûlé, Phys. Rev. Lett. 112, 133901 (2014)] that demonstrated significant interaction of surface seismic waves with holes structuring sedimentary soils at the meter scale. We further investigate the seismic wave trajectories of compressional body waves in soils structured with buildings. A significant substitution of soils by inclusions, acting as foundations, raises the question of the effective dynamic properties of these structured soils. Buildings, in the case of perfect elastic conditions for both soil and buildings, are shown to interact and strongly influence elastic body waves; such site-city seismic interactions were pointed out in [Guéguen et al., Bull. Seismol. Soc. Am. 92, 794–811 (2002)], and we investigate a variety of scenarios to illustrate the variety of behaviours possible.
Ungureanu B, Achaoui Y, Brule S, et al., 2019, Seismic wave shield using cubic arrays of split-ball resonators
Metre size inertial resonators located in the ground have been theoreticallyshown to interact with a seismic wave (attenuation, band gaps) to enableprotection of surface structures such as buildings. The challenge for CivilEngineering is to both reduce the size of these resonators and to increasetheir efficiency. Here we explore steel spheres, connected to a concrete bulkmedium, either by a coating of rubber, or rubber and steel ligaments, or airand steel ligaments. We show that for a cubic lattice periodicity of 1 metre,we achieve stop bands in the frequency range 14 to 20 Hz; by splitting spheresin 2 and 8 pieces, we tune down the stop bands frequencies and further increasetheir bandwidth. We thus demonstrate we are able to provide a variety ofinertial resonators with stop bands below 10 Hz i.e., in the frequency range ofinterest for earthquake engineering.
Ungureanu B, Guenneau S, Brule S, et al., 2019, Controlling seismic elastic surface waves via interacting structures, 13th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), Publisher: IEEE, Pages: 438-440
Guenneau S, Brule S, Enoch S, et al., 2018, Some challenges regarding cloaking and earthquake protection, 12th International Congress on Artificial Materials for Novel Wave Phenomena (METAMATERIALS), Publisher: IEEE, Pages: 158-160
Brule S, Ungureanu B, Achaoui Y, et al., 2017, Metamaterial-like transformed urbanism, INNOVATIVE INFRASTRUCTURE SOLUTIONS, Vol: 2, ISSN: 2364-4176
Brule S, Achaoui Y, Ungureanu B, et al., 2017, New composite geomaterials for the mitigation of seismic effects, Pages: 1485-1488
The high density of deep foundation or ground reinforcement techniques in urban area, leads researchers to believe in a significant interaction of these buried structures with a certain component of the seismic signal. A promising way to cause a modification on the seismic disturbance is to create a complete dynamic artificial anisotropy by implementing geometrical elements, full or empty, in the soil. The physical process is the interference of waves (body or surface waves) scattered from surfaces or objects. The effects of the dynamic anisotropy are reinforced by the local resonance of implemented, which are disposed along a grid according to transformation elastodynamics and morphing tools that could theoretically lead to an ideal cloak detouring waves around a protected area. In this periodic or non-periodic media, the desired effects are total reflection (Bragg's effect), band-gaps, wave-path control, attenuation by energy-dissipation, etc.
Achaoui Y, Ungureanu B, Enoch S, et al., 2016, Seismic waves damping with arrays of inertial resonators, EXTREME MECHANICS LETTERS, Vol: 8, Pages: 30-37, ISSN: 2352-4316
Ungureanu B, Achaoui Y, Enoch S, et al., 2016, Auxetic-like metamaterials as novel earthquake protections, EPJ APPLIED METAMATERIALS, Vol: 2, ISSN: 2272-2394
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Ungureanu B, Brule S, Achaoui Y, et al., 2015, Mechanical Waves Deflection/Damping With Seismic Metamaterials, 9th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 310-312
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