scholarly journals Frequencies analysis in an infinite beams array

2021 ◽  
Vol 2090 (1) ◽  
pp. 012070
Author(s):  
Hugo Aya Baquero
Keyword(s):  
Elastic Properties ◽  
Periodic Structure ◽  
Brillouin Zone ◽  
Wave Vector ◽  
Geometric Parameters ◽  
Periodicity Condition ◽  
Frequency Bands ◽  
Geometric Configurations ◽  
Mechanical Waves ◽  
Forbidden Regions

Abstract This model consists of a periodic structure formed by solid beams equidistant from each other submerged in a fluid. The beams are clamped at both ends. The distance between the beams, the elastic properties of the solid and the fluid; and the geometric parameters of the beams determine a relationship between the frequencies of the mechanical waves that can propagate through the structure and the wave vector. Analysis within the first Brillouin zone with the Bloch periodicity condition gives rise to frequency bands in which there is the propagation of mechanical waves and bands in which no waves are propagated. Some propagation bands and forbidden regions were found in the examined frequency ranges for various geometric configurations.

Group Theoretical Analysis of Lattice Vibrations in GaSe Polytypes

1974 ◽  
Vol 52 (24) ◽  
pp. 2454-2458 ◽  
Author(s):  
S. Jandl ◽  
J. L. Brebner
Keyword(s):  
Theoretical Analysis ◽  
Raman Scattering ◽  
Brillouin Zone ◽  
Wave Vector ◽  
Lattice Vibrations ◽  
Group Theoretical Analysis

We present here a group theoretical analysis of the lattice vibrations of the ε and γ polytypes of GaSe for different directions of the wave vector in the Brillouin zone. The effect of the interlayer interactions and the assignment of the modes observed in Raman scattering is discussed.

Parametric Experimental and Numerical Study of LP Diffuser and Exhaust Hoods

2016 ◽  
Author(s):  
Derek Taylor ◽  
Gurnam Singh ◽  
Phil Hemsley ◽  
Martin Claridge
Keyword(s):  
Numerical Study ◽  
Design Guidelines ◽  
Geometric Parameters ◽  
Design Tools ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Geometric Configurations ◽  
Last Stage ◽  
Lp Turbine ◽  
The Impact

The design of an effective diffuser for a given last stage blade of an LP turbine is known to be highly dependent on the size and shape of the exhaust hood in which it is located. For retrofit steam turbines in particular, where a new last stage blade and diffuser are fitted into an existing exhaust hood, the shapes and sizes of the exhaust box have been seen to vary significantly from one contract to the next. An experimental parametric study of diffuser lips and exhaust hood configurations has been run on a model test turbine rig at GE Power to investigate the impact of various geometric parameters on the performance of the diffusers. Improved testing and post-processing methodologies means the diffuser performance has been obtained for a greater number of geometric configurations than was previously typically possible. The results of these experiments are compared with numerical calculations and confirm the accuracy of the standard in-house diffuser design tools. Key geometric parameters are identified from the test data and used to generate improved diffuser design guidelines.

scholarly journals Computational Investigation of the Effective Mechanical Behavior for 3D Pre-Buckled Auxetic Lattices

2019 ◽  
Vol 86 (11) ◽  
Author(s):  
Frederic Albertini ◽  
Justin Dirrenberger ◽  
Andrey Molotnikov ◽  
Cyrille Sollogoub
Keyword(s):  
Elastic Properties ◽  
Poisson Ratio ◽  
Periodic Boundary Conditions ◽  
Homogenization Method ◽  
Geometrical Parameters ◽  
Computational Investigation ◽  
Effective Elastic Properties ◽  
Acoustic Damping ◽  
The Past ◽  
Geometric Configurations

Abstract Negative Poisson’s ratio materials, or auxetics, have drawn attention for the past 30 years. The auxetic effect could lead to improved mechanical properties such as acoustic damping, indentation resistance, or crashworthiness. In this work, two 3D auxetic lattices are introduced. Auxeticity is achieved by design through pre-buckling of the lattice struts. The influence of geometrical parameters on the effective elastic properties is investigated using computational homogenization method with periodic boundary conditions. Effective Young’s modulus is 3D mapped to reveal anisotropy and identify spatial orientations of interest. The effective Poisson ratio is computed for various geometric configurations to characterize auxeticity. Finally, the influence of effective elastic properties on energy dissipation under compression is explored for elastoplastic lattices with different loading directions, using finite element simulations. Results suggest that loading 3D auxetic lattices along their stiffest direction maximizes their crashworthiness.

scholarly journals Spatial aliasing and distortion of energy distribution in the wave vector domain under multi-spacecraft measurements

2009 ◽  
Vol 27 (8) ◽  
pp. 3031-3042 ◽  
Author(s):  
Y. Narita ◽  
K.-H. Glassmeier
Keyword(s):  
Energy Distribution ◽  
Brillouin Zone ◽  
Wave Vector ◽  
Flow Direction ◽  
Reciprocal Lattice ◽  
Periodic Pattern ◽  
Lattice Vector ◽  
Model Calculations ◽  
Spatial Aliasing ◽  
Spacecraft Data

Abstract. Aliasing is a general problem in the analysis of any measurements that make sampling at discrete points. Sampling in the spatial domain results in a periodic pattern of spectra in the wave vector domain. This effect is called spatial aliasing, and it is of particular importance for multi-spacecraft measurements in space. We first present the theoretical background of aliasing problems in the frequency domain and generalize it to the wave vector domain, and then present model calculations of spatial aliasing. The model calculations are performed for various configurations of the reciprocal vectors and energy spectra or distribution that are placed at different positions in the wave vector domain, and exhibit two effects on aliasing. One is weak aliasing, in which the true spectrum is distorted because of non-uniform aliasing contributions in the Brillouin zone. It is demonstrated that the energy distribution becomes elongated in the shortest reciprocal lattice vector direction in the wave vector domain. The other effect is strong aliasing, in which aliases have a significant contribution in the Brillouin zone and the energy distribution shows a false peak. These results give a caveat in multi-spacecraft data analysis in that spectral anisotropy obtained by a measurement has in general two origins: (1) natural and physical origins like anisotropy imposed by a mean magnetic field or a flow direction; and (2) aliasing effects that are imposed by the configuration of the measurement array (or the set of reciprocal vectors). This manuscript also discusses a possible method to estimate aliasing contributions in the Brillouin zone based on the measured spectrum and to correct the spectra for aliasing.

ELASTIC PROPERTY PREDICTION OF THE STITCHED MULTI-AXIAL WARP KNIT FABRIC COMPOSITES

2006 ◽  
Vol 20 (25n27) ◽  
pp. 4022-4027 ◽  
Author(s):  
HEOUNG-JAE CHUN ◽  
HYUNG-WOO KIM ◽  
JOON-HYUNG BYUN
Keyword(s):  
Composite Materials ◽  
Elastic Properties ◽  
Cross Sections ◽  
Averaging Method ◽  
Geometric Parameters ◽  
Suggested Model ◽  
Fabric Composites ◽  
Out Of Plane ◽  
Experimental Values ◽  
Good Agreement

In order to improve the resistances to delamination, damage tolerance, some in-plane and out-of-plane properties of composite materials, a through-thickness reinforcement must be provided. This through-thickness reinforcement is achieved by stitching multi-axial warp knit (MWK) fabrics used as preforms for the fabrication of composite materials. The MWK fabrics are constructed with layers of insertion fiber bundles in the warp, weft and bias directions. In order to correlate the microstructure of a preform with the elastic properties of stitched MWK composite, the analytical model for stitched MKW composite is developed. The overall geometry and geometric parameters of a representative volume are determined from the photomicrographs of cross sections of the fabricated composite specimens. The various elastic properties of MWK fabric composites are predicted as functions of various geometric parameters using an averaging method. The experimental results are compared with the predicted results in order to validate the suggested model. It is found that the predicted elastic properties are in reasonably good agreement with the experimental values.

scholarly journals Особенности фокусировки спиновых волн в кристаллах EuO и EuS

2019 ◽  
Vol 61 (2) ◽  
pp. 257
Author(s):  
С.М. Бахарев ◽  
С.П. Савченко ◽  
А.П. Танкеев
Keyword(s):  
Exchange Interaction ◽  
Spin Wave ◽  
Lattice Constant ◽  
Brillouin Zone ◽  
Wave Vector ◽  
Magnetic Moment ◽  
Wave Focusing ◽  
Wave Approximation ◽  
Long Wave ◽  
Long Wave Approximation

AbstractSpecificities of spin wave focusing in EuO and EuS crystals are studied. It is shown that spin wave focusing is absent in the long-wave approximation: it is observed only for wave vectors in the second half of the Brillouin zone ( aq $$ \gtrsim $$ π, where a is the lattice constant and q is the magnitude of the wave vector). It was found that, for EuO and EuS crystals, the directions of spin wave focusing differ due to the different signs of the exchange integrals responsible for the exchange interaction of the magnetic moment with the second neighbors. The directions along which a magnon caustic is formed are determined.

A Comparative Analysis of Mixing Performance of Power-Law Fluid in Cylindrical Microchannels With Sudden Contraction/Expansion

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
A. Banerjee ◽  
A. K. Nayak ◽  
B. Weigand
Keyword(s):  
Pressure Drop ◽  
Power Law ◽  
Flow Behavior ◽  
Geometric Parameters ◽  
Mixing Efficiency ◽  
Flow Behavior Index ◽  
Mixing Performance ◽  
Geometric Configurations ◽  
Wide Range ◽  
Behavior Index

Abstract This paper focuses on the comparative electrokinetic micromixing of non-Newtonian fluid in cylindrical microchannels with surface potential heterogeneity due to sudden constriction/expansion. In numerical simulations, the rheology of the aqueous solution is considered to follow power-law characteristic. Based on the Poisson–Nernst–Planck model, the simulations are performed to investigate the mixing efficiency and pressure drop for constricted and expanded configurations over a wide range of the flow behavior index, potential patch strength, and geometric parameters. The results show that, irrespective of geometric configurations, the mixing efficiency can be improved significantly by increasing the flow behavior index, geometric parameters, and the overpotential patch strength. In addition, it is also revealed that the constricted geometry yields better mixing as compared to the other configuration, but the average pressure drop shows reverse characteristics. Thus, a parametric relationship is tried to be established between mixing efficiency and pressure drop for both these configurations to propose an effective and efficient micromixer, which can produce maximum possible mixing efficiency with minimum pressure drop.

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