scholarly journals Janus acoustic metascreen with nonreciprocal and reconfigurable phase modulations

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yifan Zhu ◽  
Liyun Cao ◽  
Aurélien Merkel ◽  
Shi-Wang Fan ◽  
Brice Vincent ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Sound Absorption ◽  
Inner Core ◽  
Unit Cell ◽  
Beam Splitting ◽  
Phase Modulators ◽  
Unique Material ◽  
Acoustic Focusing

AbstractIntegrating different reliable functionalities in metastructures and metasurfaces has become of remarkable importance to create innovative multifunctional compact acoustic, optic or mechanical metadevices. In particular, implementing different wave manipulations in one unique material platform opens an appealing route for developing integrated metamaterials. Here, the concept of Janus acoustic metascreen is proposed and demonstrated, producing two-faced and independent wavefront manipulations for two opposite incidences. The feature of two-faced sound modulations requires nonreciprocal phase modulating elements. An acoustic resonant unit cell with rotating inner core, which produces a bias by a circulating fluid, is designed to achieve high nonreciprocity, leading to decoupled phase modulations for both forward and backward directions. In addition, the designed unit cell consisting of tunable phase modulators is reconfigurable. A series of Janus acoustic metascreens including optional combinations of extraordinary refraction, acoustic focusing, sound absorption, acoustic diffusion, and beam splitting are demonstrated through numerical simulations and experiments, showing their great potential for acoustic wavefront manipulation.

Arbitrary shaped acoustic omnidirectional absorber based on transformation theory

2020 ◽  
Vol 34 (11) ◽  
pp. 2050111
Author(s):  
Weikai Xu ◽  
Yingchun Tang ◽  
Meng Zhang ◽  
Wuchao Qi ◽  
Wei Wang
Keyword(s):  
Numerical Simulations ◽  
Elastic Waves ◽  
Sound Absorption ◽  
Acoustic Absorption ◽  
Two Dimensional ◽  
Acoustic Path ◽  
Transformation Theory ◽  
Material Parameters ◽  
Arbitrary Geometries ◽  
Transformation Acoustics

In this study, an arbitrary shaped acoustic omnidirectional absorber (AOA) is achieved for absorbing incoming acoustic/elastic waves in the ambient environment. Using the transformation acoustics theory, we present a theoretical framework for two-dimensional acoustic path guidance around arbitrary shapes for which the material parameters in the transformed space can be obtained analytically. Results indicate that the transformed space is distorted rather than compressed; numerical simulations confirm that these absorbers exhibit a remarkably large absorption and that the proposed method can control acoustic absorption for arbitrary geometries of interest. This method can potentially be applied to sound absorption and noise control.

scholarly journals Heat and Mass Transfer during Hydrogen Generation in an Array of Fuel Bars of a BWR Using a Periodic Unit Cell

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
H. Romero-Paredes ◽  
F. J. Valdés-Parada ◽  
G. Espinosa-Paredes
Keyword(s):  
Mass Transfer ◽  
Numerical Analysis ◽  
Fuel Element ◽  
Numerical Simulations ◽  
Heat And Mass Transfer ◽  
Nuclear Reactor ◽  
Hydrogen Generation ◽  
Unit Cell ◽  
Concentration Profiles ◽  
Periodic Unit Cell

This paper presents, the numerical analysis of heat and mass transfer during hydrogen generation in an array of fuel cylinder bars, each coated with a cladding and a steam current flowing outside the cylinders. The analysis considers the fuel element without mitigation effects. The system consists of a representative periodic unit cell where the initial and boundary-value problems for heat and mass transfer were solved. In this unit cell, we considered that a fuel element is coated by a cladding with steam surrounding it as a coolant. The numerical simulations allow describing the evolution of the temperature and concentration profiles inside the nuclear reactor and could be used as a basis for hybrid upscaling simulations.

A simplistic unit cell model for sound absorption of cellular foams with fully/semi-open cells

2015 ◽  
Vol 118 ◽  
pp. 276-283 ◽  
Author(s):  
X.H. Yang ◽  
S.W. Ren ◽  
W.B. Wang ◽  
X. Liu ◽  
F.X. Xin ◽  
...  
Keyword(s):  
Sound Absorption ◽  
Cell Model ◽  
Unit Cell ◽  
Unit Cell Model ◽  
Cellular Foams

scholarly journals The thermal expansion of gold: point defect concentrations and pre-melting in a face-centred cubic metal

2018 ◽  
Vol 51 (2) ◽  
pp. 470-480 ◽  
Author(s):  
Martha G. Pamato ◽  
Ian G. Wood ◽  
David P. Dobson ◽  
Simon A. Hunt ◽  
Lidunka Vočadlo
Keyword(s):  
Thermal Expansion ◽  
Cell Volume ◽  
Computer Simulations ◽  
Point Defects ◽  
Unit Cell Volume ◽  
Inner Core ◽  
Debye Model ◽  
Perfect Crystal ◽  
Unit Cell ◽  
Real Crystal

On the basis ofab initiocomputer simulations, pre-melting phenomena have been suggested to occur in the elastic properties of hexagonal close-packed iron under the conditions of the Earth's inner core just before melting. The extent to which these pre-melting effects might also occur in the physical properties of face-centred cubic metals has been investigated here under more experimentally accessible conditions for gold, allowing for comparison with future computer simulations of this material. The thermal expansion of gold has been determined by X-ray powder diffraction from 40 K up to the melting point (1337 K). For the entire temperature range investigated, the unit-cell volume can be represented in the following way: a second-order Grüneisen approximation to the zero-pressure volumetric equation of state, with the internal energy calculatedviaa Debye model, is used to represent the thermal expansion of the `perfect crystal'. Gold shows a nonlinear increase in thermal expansion that departs from this Grüneisen–Debye model prior to melting, which is probably a result of the generation of point defects over a large range of temperatures, beginning atT/Tm> 0.75 (a similar homologousTto where softening has been observed in the elastic moduli of Au). Therefore, the thermodynamic theory of point defects was used to include the additional volume of the vacancies at high temperatures (`real crystal'), resulting in the following fitted parameters:Q= (V0K0)/γ = 4.04 (1) × 10−18 J,V0= 67.1671 (3) Å3,b= (K0′ − 1)/2 = 3.84 (9), θD= 182 (2) K, (vf/Ω)exp(sf/kB) = 1.8 (23) andhf= 0.9 (2) eV, whereV0is the unit-cell volume at 0 K,K0andK0′ are the isothermal incompressibility and its first derivative with respect to pressure (evaluated at zero pressure), γ is a Grüneisen parameter,θDis the Debye temperature,vf,hfandsfare the vacancy formation volume, enthalpy and entropy, respectively, Ω is the average volume per atom, andkBis Boltzmann's constant.

scholarly journals Bio-Inspired Active Skins for Surface Morphing

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Yujin Park ◽  
Gianmarco Vella ◽  
Kenneth J. Loh
Keyword(s):  
Deformation Mechanism ◽  
Unit Cell ◽  
Material Behavior ◽  
Two Dimensional ◽  
New Class ◽  
Mechanical Metamaterials ◽  
Unique Material ◽  
Out Of Plane ◽  
Unit Cells ◽  
Significant Attention

AbstractMechanical metamaterials that leverage precise geometrical designs and imperfections to induce unique material behavior have garnered significant attention. This study proposes a Bio-Inspired Active Skin (BIAS) as a new class of instability-induced morphable structures, where selective out-of-plane material deformations can be pre-programmed during design and activated by in-plane strains. The deformation mechanism of a unit cell geometrical design is analyzed to identify how the introduction of hinge-like notches or instabilities, versus their pristine counterparts, can pave way for controlling bulk BIAS behavior. Two-dimensional arrays of repeating unit cells were fabricated, with notches implemented at key locations throughout the structure, to harvest the instability-induced surface features for applications such as camouflage, surface morphing, and soft robotic grippers.

scholarly journals Mantle-induced temperature anomalies do not reach the inner core boundary

2019 ◽  
Vol 219 (Supplement_1) ◽  
pp. S21-S32 ◽  
Author(s):  
Christopher J Davies ◽  
Jon E Mound
Keyword(s):  
Heat Flow ◽  
Numerical Simulations ◽  
Inner Core ◽  
Liquid Core ◽  
Temperature Variations ◽  
Temperature Anomalies ◽  
Longitudinal Temperature ◽  
Core Boundary ◽  
Core Conditions ◽  
Heat Flow Variations

SUMMARY Temperature anomalies in Earth’s liquid core reflect the vigour of convection and the nature and extent of thermal core–mantle coupling. Numerical simulations suggest that longitudinal temperature anomalies forced by lateral heat flow variations at the core–mantle boundary (CMB) can greatly exceed the anomalies that arise in homogeneous convection (i.e. with no boundary forcing) and may even penetrate all the way to the inner core boundary. However, it is not clear whether these simulations access the relevant regime for convection in Earth’s core, which is characterized by rapid rotation (low Ekman number E) and strong driving (high Rayleigh number Ra). We access this regime using numerical simulations of non-magnetic rotating convection with imposed heat flow variations at the outer boundary (OB) and investigate the amplitude and spatial pattern of thermal anomalies, focusing on the inner and outer boundaries. The 108 simulations cover the parameter range 10−4 ≤ E ≤ 10−6 and Ra = 1−800 times the critical value. At each Ra and E we consider two heat flow patterns—one derived from seismic tomography and the hemispheric $Y_1^1$ spherical harmonic pattern—with amplitudes measured by the parameter q⋆ = 2.3, 5 as well as the case of homogeneous convection. At the OB the forcing produces strong longitudinal temperature variations that peak in the equatorial region. Scaling relations suggest that the longitudinal variations are weakly dependent on E and Ra and are much stronger than in homogeneous convection, reaching O(1) K at core conditions if q⋆ ≈ 35. At the inner boundary, latitudinal and longitudinal temperature variations depend weakly on Ra and q⋆ and decrease strongly with E, becoming practically indistinguishable between homogeneous and heterogeneous cases at E = 10−6. Interpreted at core conditions our results suggest that heat flow variations on the CMB are unlikely to explain the large-scale variations observed by seismology at the top of the inner core.

scholarly journals A Latent Heat Retrieval and Its Effects on the Intensity and Structure Change of Hurricane Guillermo (1997). Part II: Numerical Simulations

2012 ◽  
Vol 69 (11) ◽  
pp. 3128-3146 ◽  
Author(s):  
Stephen R. Guimond ◽  
Jon M. Reisner
Keyword(s):  
Numerical Simulations ◽  
Tropical Cyclones ◽  
Latent Heat ◽  
Inner Core ◽  
Doppler Radar ◽  
Model Parameters ◽  
Saturation State ◽  
Wind Structure ◽  
Tangential Wind ◽  
Airborne Doppler Radar

Abstract In Part I of this study, a new algorithm for retrieving the latent heat field in tropical cyclones from airborne Doppler radar was presented and fields from rapidly intensifying Hurricane Guillermo (1997) were shown. In Part II, the usefulness and relative accuracy of the retrievals is assessed by inserting the heating into realistic numerical simulations at 2-km resolution and comparing the generated wind structure to the radar analyses of Guillermo. Results show that using the latent heat retrievals as forcing produces very low intensity and structure errors (in terms of tangential wind speed errors and explained wind variance) and significantly improves simulations relative to a predictive run that is highly calibrated to the latent heat retrievals by using an ensemble Kalman filter procedure to estimate values of key model parameters. Releasing all the heating/cooling in the latent heat retrieval results in a simulation with a large positive bias in Guillermo’s intensity that motivates the need to determine the saturation state in the hurricane inner-core retrieval through a procedure similar to that described in Part I of this study. The heating retrievals accomplish high-quality structure statistics by forcing asymmetries in the wind field with the generally correct amplitude, placement, and timing. In contrast, the latent heating fields generated in the predictive simulation contain a significant bias toward large values and are concentrated in bands (rather than discrete cells) stretched around the vortex. The Doppler radar–based latent heat retrievals presented in this series of papers should prove useful for convection initialization and data assimilation to reduce errors in numerical simulations of tropical cyclones.

A Numerical Investigation on Sound Absorption Mechanism of Micro Resonator with Offset Slits

2015 ◽  
Vol 23 (01) ◽  
pp. 1550001 ◽  
Author(s):  
Jun Xu ◽  
Xiaodong Li ◽  
Yueping Guo
Keyword(s):  
Numerical Simulations ◽  
Vortex Shedding ◽  
Sound Absorption ◽  
Numerical Data ◽  
Absorption Mechanism ◽  
Practical Applications ◽  
Acoustic Liners ◽  
Low Dissipation ◽  
Parametric Description ◽  
Micro Resonator

Acoustic liners are widely used in commercial aero-engine to suppress noise. In theoretical investigations, the liner geometry is often assumed as an array of symmetric micro resonator with orifice or slit at the center. However, in real application, orifices or slits distributed in micro resonator are offset. For better understanding of sound absorption mechanism of micro resonator with offset slits under high incident sound pressure level (SPL), direct numerical simulations (DNS) using high order low dispersion and low dissipation computational aeroacoustics (CAA) method are carried out. The simulations are first validated by experimental data, showing good agreement and establishing the relevance of the simulation methodology. Numerical simulations of resonators with single offset slit or two slits are then conducted. The two sound absorption mechanisms, namely viscous dissipation and vortex shedding, are discussed with detailed numerical data and analysis, which lead to quantitative parametric description of the energy partition between the two mechanisms as a function of both frequency and geometry. It is shown that offset slit can reduce vortex shedding and results in less sound absorption. The effects of more than one slit are, however, opposite; more vortex shedding occurs with more slits so that sound absorption is enhanced. This may potentially help guide liner design in practical applications.

Simulation study of acoustic refraction wave manipulation based on sub-wavelength artificial periodic structure

2020 ◽  
pp. 2150082
Author(s):  
Shuai Tang ◽  
Jianning Han
Keyword(s):  
Acoustic Wave ◽  
Steel Plate ◽  
Three Dimensional ◽  
Unit Cell ◽  
Asymmetric Transmission ◽  
Plate Structures ◽  
Coding Method ◽  
Acoustic Focusing ◽  
Unit Cells ◽  
Sub Wavelength

We proposed a kind of unit cell composed of simple steel plate structures in this work. A variety of acoustic phenomena including anomalous refraction, asymmetric transmission, acoustic splitting and acoustic focusing were realized by coding the unit cells with different splicing modes. The transformation from plane acoustic wave to vortex acoustic wave was also realized by using the coding method of three-dimensional rotation. This work increased the functionality of the unit cell and provided a method for the design of sub-wavelength acoustic devices.

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