scholarly journals Exploring Metamaterials’ Structures Through the Relaxed Micromorphic Model: Switching an Acoustic Screen Into an Acoustic Absorber

2021 ◽  
Vol 7 ◽  
Author(s):  
Gianluca Rizzi ◽  
Manuel Collet ◽  
Félix Demore ◽  
Bernhard Eidel ◽  
Patrizio Neff ◽  
...  
Keyword(s):  
Incident Wave ◽  
Characteristic Length ◽  
Dynamic Properties ◽  
Static Characteristic ◽  
Total Reflection ◽  
Homogeneous Material ◽  
Structural Elements ◽  
Challenging Problem ◽  
Total Transmission ◽  
Extended Frequency

While the design of always new metamaterials with exotic static and dynamic properties is attracting deep attention in the last decades, little effort is made to explore their interactions with other materials. This prevents the conception of (meta-)structures that can enhance metamaterials’ unusual behaviors and that can be employed in real engineering applications. In this paper, we give a first answer to this challenging problem by showing that the relaxed micromorphic model with zero static characteristic length can be usefully applied to describe the refractive properties of simple meta-structures for extended frequency ranges and for any direction of propagation of the incident wave. Thanks to the simplified model’s structure, we are able to efficiently explore different configurations and to show that a given meta-structure can drastically change its overall refractive behavior when varying the elastic properties of specific meta-structural elements. In some cases, changing the stiffness of a homogeneous material which is in contact with a metamaterial’s slab, reverses the structure’s refractive behavior by switching it from an acoustic screen (total reflection) into an acoustic absorber (total transmission). The present paper clearly indicates that, while the study and enhancement of the intrinsic metamaterials’ properties is certainly of great importance, it is even more challenging to enable the conception of meta-structures that can eventually boost the use of metamaterials in real-case applications.

Theory of Short Wave Excitation

1986 ◽  
Vol 30 (03) ◽  
pp. 147-152
Author(s):  
Yong Kwun Chung
Keyword(s):  
Incident Wave ◽  
Characteristic Length ◽  
Finite Depth ◽  
Short Wave ◽  
The Body ◽  
Wave Number ◽  
Floating Body ◽  
Wave Excitation ◽  
Exciting Forces ◽  
Wave Exciting Forces

When the wavelength of the incident wave is short, the total surface potential on a floating body is found to be 2∅ i & O (m-l∅ i) on the lit surface and O (m-l∅ j) on the shadow surface where ~b i is the potential of the incident wave and m the wave number in water of finite depth. The present approximation for wave exciting forces and moments is reasonably good up to X/L ∅ 1 where h is the wavelength and L the characteristic length of the body.

Strengthening and Retrofitting of Motín de Oro II Bridge in Mexico

2020 ◽  
pp. 193-209
Author(s):  
Jose M. Jara ◽  
Bertha A. Olmos ◽  
Guillermo Martínez
Keyword(s):  
Material Properties ◽  
River Flow ◽  
Dynamic Properties ◽  
Flow Characteristics ◽  
Ambient Vibration ◽  
Structural Elements ◽  
Box Girder ◽  
Prone Area ◽  
Scour Protection ◽  
Ambient Vibration Measurements

This chapter presents the studies conducted to retrofit an existing bridge in a seismic prone area of Mexico. The Motín de Oro II Bridge was built in the 1970s with a continuous box girder superstructure and wall-type substructure. From the 1970s to nowadays, the design truck loads in Mexico have been substantially incremented and many bridges built in that period have required to be evaluated and, in some cases, rehabilitated and retrofitted. Firstly, the study presents the results of visual inspections of all parts of the bridge and a description of the preliminary studies conducted to determine the material properties, to evaluate the river flow characteristics and to calculate the scour depth. Secondly, the chapter discusses the initial structural analyses of the bridge subjected to the original gravitational and seismic loads and to the current loads before the intervention. These analyses allow to select the structural elements that require to be retrofitted and the best strategy to follow. Finally, the study presents results of the numerical retrofitted model and the experimental assessment of the dynamic properties based on ambient vibration measurements. Additionally, the scour protection and the general construction procedure are also described.

FEM Analysis of Cylindrical Structural Elements under Local Shock Loading

2014 ◽  
Vol 566 ◽  
pp. 499-504 ◽  
Author(s):  
Leopold Kruszka ◽  
Yu.S. Vorobiov ◽  
N.Yu. Ovcharova
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Strain State ◽  
Shock Loading ◽  
Dynamic Properties ◽  
Fem Analysis ◽  
Finite Deformations ◽  
High Rate ◽  
Structural Elements ◽  
Stress Strain

High rate deformations of structures cylindrical elements are considered 3D formulation. Elastic-plastic finite deformations and dynamic properties of material take into account. The problem become geometrically and physically nonlinear and finite element method is used. The numerical analyses of dynamics stress-strain state of real structures elements is executed.

scholarly journals Study of running engines inertial and gyroscopic properties influence on the dynamic system engine – pylon – wing structural capabilities

2020 ◽  
Vol 23 (3) ◽  
pp. 63-72
Author(s):  
V. V. Ovchinnikov ◽  
Yu. V. Petrov
Keyword(s):  
Dynamic System ◽  
Fatigue Damage ◽  
Dynamic Properties ◽  
Elastic Beam ◽  
Aircraft Engine ◽  
Basic Structure ◽  
Elastic Vibration ◽  
Rigid Bodies ◽  
Practical Implementation ◽  
Structural Elements

A modern large-sized aircraft dynamic properties analysis, determined by the specificity of its layout scheme, demonstrates that the engines on under the wing elastic pylons lightly damped oscillations cause a number of undesirable phenomena, including intense accumulation of fatigue damage of the pylon-to-the-wing attachment, in fact in the area of engine installation in the pylon and the wing. The results of theoretical and experimental research show that with some engine attachment to the pylon structural modification it becomes possible to use the engines inertial and gyroscopic properties to absorb these oscillations. In this case, the motor tones damping coefficients increase by an order of magnitude or even more, so the gyroscopic coupling of elastic vibration tones is realized. With the rational choice of the additional parameters of elastic and dissipative bonds in the engine attachments it is possible to affect the aircraft wing and engines aero elastic vibrations effectively, which has a significant effect on the aircraft elements structural capabilities. A mathematical model of aero elasticity (MMAE) with respect to the kinetic moment of the engine rotors and specially designed units for attaching the engines to the pylons was developed in order to study the influence and the selection of rational elastic-dissipative parameters of the pylons-under-the-wing aircraft engine mounts. The method of predetermined basic forms is used for the aircraft with running engines on the pylons MMAE synthesis. The given forms are considered as the aircraft basic structure forms natural vibrations in the void. This work treats the engine nacelle and the rotor as absolutely rigid bodies, the elasticity of the rotor to the nacelle attachment is neglected. The pylon is modeled by an elastic beam, and the elastic and dissipative properties of the pylon-to-the-wing and the engine-to-the-pylon attachments are correspondingly by elastic-dissipative bonds. Schematic diagrams of the engine to the pylon attachments are proposed. The results of the study devoted to the influence of the proposed attachment points modifications on the load and integral strength characteristics of the main structural elements of the engine – pylon – wing dynamic system on the example of an An-124 aircraft are presented. The practical implementation of the proposed solutions aimed to reduce the level of fatigue damage to structural elements of the aircraft feasibility is proved.

scholarly journals Vibration Response-Based Damage Detection

2021 ◽  
pp. 133-173
Author(s):  
Maria Pina Limongelli ◽  
Emil Manoach ◽  
Said Quqa ◽  
Pier Francesco Giordano ◽  
Basuraj Bhowmik ◽  
...  
Keyword(s):  
Damage Detection ◽  
Health Monitoring ◽  
Material Properties ◽  
Damage Identification ◽  
Dynamic Properties ◽  
Health State ◽  
Structural Elements ◽  
Global Level ◽  
Damage Location

AbstractThis chapter aimed to present different data driven Vibration-Based Methods (VBMs) for Structural Health Monitoring (SHM). This family of methods, widely used for engineering applications, present several advantages for damage identification applications. First, VBMs provide continuous information on the health state of the structure at a global level without the need to access the damaged elements and to know their location. Furthermore, damage can be identified using the dynamic response of the structure measured by sensors non-necessarily located in the proximity of damage and without any prior knowledge about the damage location. By principle, VBMs can identify damage related to changes in the dynamic properties of structures, such as stiffness variations due to modifications in the connections between structural elements, or changes in geometric and material properties. A classification of different VBMs was presented in this chapter. Furthermore, several case studies were presented to demonstrate the potential of these methods.

Total Reflection and Cloaking by Triangular Defects Embedded in Zero Index Metamaterials

2015 ◽  
Vol 7 (2) ◽  
pp. 135-144 ◽  
Author(s):  
Yunqing Huang ◽  
Jichun Li
Keyword(s):  
Wave Propagation ◽  
Total Reflection ◽  
Total Transmission ◽  
Zero Index

AbstractIn this work, we investigate wave propagation through a zero index meta-material (ZIM) waveguide embedded with triangular dielectric defects. We provide a theoretical guidance on how to achieve total reflection and total transmission (i.e., cloaking) by adjusting the defect sizes and/or permittivities of the defects. Our work provides a systematical way in manipulating wave propagation through ZIM in addition to the widely studied dielectric defects with cylindrical and rectangular geometries.

scholarly journals The Usage of Alternative Materials to Optimize Bus Frame Structure

Symmetry ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1010 ◽  
Author(s):  
Tautvydas Pravilonis ◽  
Edgar Sokolovskij ◽  
Artūras Kilikevičius ◽  
Jonas Matijošius ◽  
Kristina Kilikevičienė
Keyword(s):  
Dynamic Properties ◽  
Steel Structure ◽  
Frame Structure ◽  
Structural Elements ◽  
Resonant Frequencies ◽  
Centre Of Gravity ◽  
Alternative Materials ◽  
Structural Frame ◽  
Strength And Stiffness ◽  
Key Indicators

The strength and stiffness of the frame is one of the key indicators of vehicle structures. Insufficient stiffness causes vibration and noise, and is also less comfortable for both the passengers and the driver. Symmetry is required between the strength and comfort of the structural frame, which depends on vibration and noise. This article analyses the frame of the structure of a medium-sized passenger bus and its dynamic properties, when replacing materials of structural elements which do not affect the symmetry of the structure. The conducted theoretical and experimental modal analysis of the bus, allows for evaluating dynamic parameters and validating the theoretical model based on the experimental results. The optimization of the medium-sized passenger bus frame—by replacing the material of the ancillary frame elements with fiberglass—reveals that its dynamic characteristics change by up to 20%, comparing the values of the first three resonant frequencies with those of the steel structure. The obtained results show that replacing the material of ancillary frame elements with fiberglass, while maintaining the symmetrical arrangement of the elements in the structure, does not change the safety characteristics of the structure, reducing the mass of the frame by 11%, and shifting the coordinate of the centre of gravity vertically downwards, which is very important for stability, comfort and fuel consumption.

Acoustic total transmission and total reflection in zero-index metamaterials with defects

2013 ◽  
Vol 102 (17) ◽  
pp. 174104 ◽  
Author(s):  
Qi Wei ◽  
Ying Cheng ◽  
Xiao-jun Liu
Keyword(s):  
Total Reflection ◽  
Total Transmission ◽  
Zero Index
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