256 results found
Choi W, Shi F, Lowe MJS, et al., 2018, Rough surface reconstruction of real surfaces for numerical simulations of ultrasonic wave scattering, NDT and E International, Vol: 98, Pages: 27-36, ISSN: 0963-8695
© 2018 Elsevier Ltd The scattering of waves by rough surfaces plays a significant role in many fields of physical sciences including ultrasonics where failure surfaces are often rough and their accurate identification is critical. The prediction of the strength of scattering can be hampered when the roughness is not adequately characterised and this is a particular issue when the surface roughness is within an order of the incident wavelength. Here we develop a methodology to reconstruct, and accurately represent, rough surfaces using an AutoRegressive (AR) process that then allows for rapid numerical simulations of ultrasonic wave rough surface scattering in three dimensions. Gaussian, exponential and AR surfaces are reconstructed based on real surface data and the statistics of the surfaces are compared with each other. The statistics from the AR surfaces agree well with those from a ctual rough surfaces, taken from experimental samples, in terms of the heights as well as the gradients, which are the two main factors in accurately predicting the wave scattering intensities. Ultrasonic rough surface scattering is simulated numerically using the Kirchhoff approximation, and comparisons with Gaussian, exponential, AR and real sample surfaces are performed; scattering intensities found using AR surfaces show the best agreement with the real sample surfaces.
Puvirajesinghe TM, Zhi ZL, Craster RV, et al., 2018, Tailoring drug release rates in hydrogel-based therapeutic delivery applications using graphene oxide, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 15, ISSN: 1742-5689
Shin S, Chergui J, Juric D, et al., 2018, A hybrid interface tracking - level set technique for multiphase flow with soluble surfactant, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 359, Pages: 409-435, ISSN: 0021-9991
Skelton E, Craster RV, Colombi A, et al., 2018, The multi-physics metawedge: graded arrays on fluid-loaded elastic plates and the mechanical analogues of rainbow trapping and mode conversion, New Journal of Physics, Vol: 20, ISSN: 1367-2630
We consider the propagation and mode conversion of flexural-acoustic waves along a fluid-loaded graded array of elastic resonators, forming a metasurface. The multi-physics nature of the problem, coupling two disparate physical systems, brings both challenges and novel features not previously seen in so-called bifunctional metamaterials. In particular, by using an appropriately designed graded array of resonators, we show that it is possible to employ our metasurface to mode-convert sub-sonic surface flexural waves into bulk acoustic waves and vice-versa; transferring energy between two very different physical systems. Whilst the sub-sonic mechanical surface wave is dispersive, the bulk acoustic wave is dispersionless and radiates energy at infinity. We also show that this bifunctional metasurface is capable of exhibiting the classical effect of rainbow trapping for sub-sonic surface waves.
Achaoui Y, Antonakakis T, Brule S, et al., 2017, Clamped seismic metamaterials: ultra-low frequency stop bands, NEW JOURNAL OF PHYSICS, Vol: 19, ISSN: 1367-2630
Colombi A, Ageeva V, Smith RJ, et al., 2017, Enhanced sensing and conversion of ultrasonic Rayleigh waves by elastic metasurfaces, SCIENTIFIC REPORTS, Vol: 7, ISSN: 2045-2322
Colombi A, Craster R, Clark M, et al., 2017, Slow waves, elastic rainbow and dynamic anisotropy with a cluster of resonant rods on an elastic halfspace, 2017 11th International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS), Publisher: IEEE, Pages: 409-410
Colombi A, Roux P, Miniaci M, et al., 2017, The role of large scale computing behind the development of seismic (and elastic) metamaterials., 2017 11th International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS), Publisher: IEEE, Pages: 406-408
Colquitt DJ, Colombi A, Craster RV, et al., 2017, Seismic metasurfaces: Sub-wavelength resonators and Rayleigh wave interaction, JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, Vol: 99, Pages: 379-393, ISSN: 0022-5096
Craster R, Guenneau S, Hutridurga H, et al., 2017, Regularized transformation optics for transient heat transfer, 2017 11th International Congress on Engineered Material Platforms for Novel Wave Phenomena (METAMATERIALS), Publisher: IEEE, Pages: 127-129
Dubrovina E, Craster RV, Papageorgiou DT, 2017, Two-layer electrified pressure-driven flow in topographically structured channels, JOURNAL OF FLUID MECHANICS, Vol: 814, Pages: 222-248, ISSN: 0022-1120
Haslinger SG, Movchan NV, Movchan AB, et al., 2017, CONTROLLING FLEXURAL WAVES IN SEMI-INFINITE PLATONIC CRYSTALS WITH RESONATOR-TYPE SCATTERERS, QUARTERLY JOURNAL OF MECHANICS AND APPLIED MATHEMATICS, Vol: 70, Pages: 215-247, ISSN: 0033-5614
Lefebvre G, Antonakakis T, Achaoui Y, et al., 2017, Unveiling extreme anisotropy in elastic structured media, Physical Review Letters, Vol: 118, ISSN: 0031-9007
Periodic structures can be engineered to exhibit unique properties observed at symmetry points, such as zero group velocity, Dirac cones, and saddle points; identifying these and the nature of the associated modes from a direct reading of the dispersion surfaces is not straightforward, especially in three dimensions or at high frequencies when several dispersion surfaces fold back in the Brillouin zone. A recently proposed asymptotic high-frequency homogenization theory is applied to a challenging time-domain experiment with elastic waves in a pinned metallic plate. The prediction of a narrow high-frequency spectral region where the effective medium tensor dramatically switches from positive definite to indefinite is confirmed experimentally; a small frequency shift of the pulse carrier results in two distinct types of highly anisotropic modes. The underlying effective equation mirrors this behavior with a change in form from elliptic to hyperbolic exemplifying the high degree of wave control available and the importance of a simple and effective predictive model.
Maling B, Colquitt DJ, Craster RV, 2017, Dynamic homogenisation of Maxwell's equations with applications to photonic crystals and localised waveforms on gratings, WAVE MOTION, Vol: 69, Pages: 35-49, ISSN: 0165-2125
Maling B, Schnitzer O, Craster RV, 2017, RADIATION FROM STRUCTURED-RING RESONATORS, SIAM JOURNAL ON APPLIED MATHEMATICS, Vol: 77, Pages: 1047-1067, ISSN: 0036-1399
O'Neill J, Selsil O, Haslinger SG, et al., 2017, ACTIVE CLOAKING FOR FINITE CLUSTERS OF PINS IN KIRCHHOFF PLATES, SIAM Journal on Applied Mathematics, Vol: 77, Pages: 1115-1135, ISSN: 0036-1399
This paper considers active cloaking of a square array of evenly spaced pins in a Kirchhoff plate in the presence of flexural waves. Active sources, modeled as ideal point sources, are represented by the nonsingular Green's function for the two-dimensional biharmonic operator and have an arbitrary complex amplitude. These sources are distributed exterior to the cluster, and their complex amplitudes are found by solving an algebraic system of equations. This procedure ensures that selected multipole orders of the scattered field are successfully annulled. For frequencies in the zero-frequency stop band, we find that a small number of active sources located on a grid is sufficient for cloaking. For higher frequencies, we achieve efficient cloaking with the active sources positioned on a circle surrounding the cluster. We demonstrate the cloaking efficiency with several numerical illustrations, considering key frequencies from band diagrams and dispersion surfaces for a Kirchhoff plate pinned in a doubly periodic fashion.
Quintanilla FH, Lowe MJS, Craster RV, 2017, The symmetry and coupling properties of solutions in general anisotropic multilayer waveguides, JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, Vol: 141, Pages: 406-418, ISSN: 0001-4966
Sasihithlu K, Pendry JB, Craster RV, 2017, Van der Waals Force Assisted Heat Transfer, Zeitschrift für Naturforschung - Section A Journal of Physical Sciences, Vol: 72, Pages: 181-188, ISSN: 0932-0784
Phonons (collective atomic vibrations in solids) are more effective in transporting heat than photons. This is the reason why the conduction mode of heat transport in nonmetals (mediated by phonons) is dominant compared to the radiation mode of heat transport (mediated by photons). However, since phonons are unable to traverse a vacuum gap (unlike photons), it is commonly believed that two bodies separated by a gap cannot exchange heat via phonons. Recently, a mechanism was proposed [J. B. Pendry, K. Sasihithlu, and R. V. Craster, Phys. Rev. B 94, 075414 (2016)] by which phonons can transport heat across a vacuum gap – through the Van der Waals interaction between two bodies with gap less than the wavelength of light. Such heat transfer mechanisms are highly relevant for heating (and cooling) of nanostructures; the heating of the flying heads in magnetic storage disks is a case in point. Here, the theoretical derivation for modelling phonon transmission is revisited and extended to the case of two bodies made of different materials separated by a vacuum gap. Magnitudes of phonon transmission, and hence the heat transfer, for commonly used materials in the micro- and nano-electromechanical industry are calculated and compared with the calculation of conduction heat transfer through air for small gaps as well as the heat transfer calculation due to photon exchange.
Schnitzer O, Craster RV, 2017, BLOCH WAVES IN AN ARBITRARY TWO-DIMENSIONAL LATTICE OF SUBWAVELENGTH DIRICHLET SCATTERERS, SIAM JOURNAL ON APPLIED MATHEMATICS, Vol: 77, Pages: 2119-2135, ISSN: 0036-1399
Shi F, Lowe M, Craster R, 2017, Diffusely scattered and transmitted elastic waves by random rough solid-solid interfaces using an elastodynamic Kirchhoff approximation, PHYSICAL REVIEW B, Vol: 95, ISSN: 2469-9950
Shi F, Lowe MJS, Skelton EA, et al., 2017, A time-domain finite element boundary integral approach for elastic wave scattering, Computational Mechanics, Pages: 1-13, ISSN: 0178-7675
© 2017 The Author(s) The response of complex scatterers, such as rough or branched cracks, to incident elastic waves is required in many areas of industrial importance such as those in non-destructive evaluation and related fields; we develop an approach to generate accurate and rapid simulations. To achieve this we develop, in the time domain, an implementation to efficiently couple the finite element (FE) method within a small local region, and the boundary integral (BI) globally. The FE explicit scheme is run in a local box to compute the surface displacement of the scatterer, by giving forcing signals to excitation nodes, which can lie on the scatterer itself. The required input forces on the excitation nodes are obtained with a reformulated FE equation, according to the incident displacement field. The surface displacements computed by the local FE are then projected, through time-domain BI formulae, to calculate the scattering signals with different modes. This new method yields huge improvements in the efficiency of FE simulations for scattering from complex scatterers. We present results using different shapes and boundary conditions, all simulated using this approach in both 2D and 3D, and then compare with full FE models and theoretical solutions to demonstrate the efficiency and accuracy of this numerical approach.
Theodorakis PE, Muller EA, Craster RV, et al., 2017, Physical insights into the blood-brain barrier translocation mechanisms, Physical Biology, Vol: 14, ISSN: 1478-3975
The number of individuals suffering from diseases of the central nervous system (CNS) is growing with an aging population. While candidate drugs for many of these diseases are available, most of these pharmaceutical agents cannot reach the brain rendering most of the drug therapies that target the CNS inefficient. The reason is the blood–brain barrier (BBB), a complex and dynamic interface that controls the influx and efflux of substances through a number of different translocation mechanisms. Here, we present these mechanisms providing, also, the necessary background related to the morphology and various characteristics of the BBB. Moreover, we discuss various numerical and simulation approaches used to study the BBB, and possible future directions based on multi-scale methods. We anticipate that this review will motivate multi-disciplinary research on the BBB aiming at the design of effective drug therapies.
Uppal AS, Craster RV, Matar OK, 2017, Dynamics of spreading thixotropic droplets, JOURNAL OF NON-NEWTONIAN FLUID MECHANICS, Vol: 240, Pages: 1-14, ISSN: 0377-0257
Vanel AL, Schnitzer O, Craster RV, 2017, Asymptotic network models of subwavelength metamaterials formed by closely packed photonic and phononic crystals, EPL, Vol: 119, ISSN: 0295-5075
Choi W, Skelton EA, Pettit J, et al., 2016, A Generic Hybrid Model for the Simulation of Three-Dimensional Bulk Elastodynamics for Use in Nondestructive Evaluation, IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Vol: 63, Pages: 726-736, ISSN: 0885-3010
Colombi A, Guenneau S, Roux P, et al., 2016, Transformation seismology: composite soil lenses for steering surface elastic Rayleigh waves, SCIENTIFIC REPORTS, Vol: 6, ISSN: 2045-2322
Colombi A, Roux P, Colquitt D, et al., 2016, Conversion and reflection of Rayleigh waves with the seismic metawedge, 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 313-315
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