scholarly journals Dispersion Analysis and Material Property Identification of a Circular Piezoelectric Ridge Waveguide

2021 ◽  
Author(s):  
Tai-Ho Yu
Keyword(s):  
Elastic Constants ◽  
Simplex Method ◽  
Numerical Approach ◽  
Dispersion Analysis ◽  
Dispersion Curves ◽  
Ridge Waveguide ◽  
Geometric Parameters ◽  
Cross Sectional ◽  
Resonant Frequencies ◽  
Ridge Waveguides

Abstract This study investigates the dispersive properties of ridge waves that travel circumferentially around piezoelectric circular ridge waveguides and investigates their resonant modes. Based on the variable separation method and Hamilton's principle, the displacement of ridge waveguides is represented as the product of a cross-sectional coordinate-dependent function and the propagator along the circumference of a circular ridge waveguide. The dispersion curves of the flexural waves and resonant frequencies corresponding to ridge waveguides are solved numerically by applying the bi-dimensional finite element method (Bi-d FEM) and using the 3D ANSYS package. The estimated impedance curves are compared with the predicted dispersion curves of waves from ridge waveguides to validate the proposed numerical approach. The geometric parameters and elastic constants of the piezoelectric circular ridge waveguide are determined through an inverse scheme that is based on the measured resonant frequencies and uses the modified simplex method. The numerical and experimental results show that, using the modified simplex method to inverse calculate the elastic constants and geometric parameters of the piezoelectric circular ridge waveguides, a good degree of accuracy and sensitivity can be achieved.

scholarly journals Rocking Behaviour of Multi-Block Columns Subjected to Pulse-Type Ground Motion Accelerations

2016 ◽  
Vol 10 (1) ◽  
pp. 150-157 ◽  
Author(s):  
Giovanni Minafò ◽  
Giuseppina Amato ◽  
Lorenzo Stella
Keyword(s):  
Ground Motion ◽  
Numerical Approach ◽  
Structural Members ◽  
Cross Sectional ◽  
Practical Engineering ◽  
Pulse Type ◽  
Single Block ◽  
The Individual ◽  
Acceleration Record ◽  
Rocking Response

Ancient columns, made with a variety of materials such as marble, granite, stone or masonry are an important part of the European cultural heritage. In particular columns of ancient temples in Greece and Sicily which support only the architrave are characterized by small axial load values. This feature together with the slenderness typical of these structural members clearly highlights as the evaluation of the rocking behaviour is a key aspect of their safety assessment and maintenance. It has to be noted that the rocking response of rectangular cross-sectional columns modelled as monolithic rigid elements, has been widely investigated since the first theoretical study carried out by Housner (1963). However, the assumption of monolithic member, although being widely used and accepted for practical engineering applications, is not valid for more complex systems such as multi-block columns made of stacked stone blocks, with or without mortar beds. In these cases, in fact, a correct analysis of the system should consider rocking and sliding phenomena between the individual blocks of the structure. Due to the high non-linearity of the problem, the evaluation of the dynamic behaviour of multi-block columns has been mostly studied in the literature using a numerical approach such as the Discrete Element Method (DEM). This paper presents an introductory study about a proposed analytical-numerical approach for analysing the rocking behaviour of multi-block columns subjected to a sine-pulse type ground motion. Based on the approach proposed by Spanoset al.(2001) for a system made of two rigid blocks, the Eulero-Lagrange method to obtain the motion equations of the system is discussed and numerical applications are performed with case studies reported in the literature and with a real acceleration record. The rocking response of single block and multi-block columns is compared and considerations are made about the overturning conditions and on the effect of forcing function’s frequency.

scholarly journals Influence of Geometric Parameters on Aerodynamic and Acoustic Performances of Bladeless Fans

2019 ◽  
Author(s):  
Ang Li ◽  
Jun Chen ◽  
Yangfan Liu ◽  
Stuart Bolton ◽  
Patricia Davies
Keyword(s):  
Cross Section ◽  
Fluid Dynamic ◽  
Geometric Parameters ◽  
Design Stage ◽  
Air Velocity ◽  
Cross Sectional ◽  
Future Design ◽  
Cross Sectional Profile ◽  
The Cross ◽  
Sectional Profile

Abstract In recent years, the bladeless fan that does not have visible impellers have been widely applied in household appliances. Since the customers are particularly sensitive to noise and the strength of wind generated by the fan, the aerodynamic and acoustic performances of the fan need to be accurately characterized in the design stage. In this study, computational fluid dynamic (CFD) and computational aeroacoustics (CAA) are applied to investigate the performances of different designs of a bladeless fan model. The influence of four parameters, namely the airfoil selection for cross-section of the wind channel, the slit width, the height of cross-section and the location of the slit, is investigated. The results indicate the streamwise air velocity increases significantly by narrowing the outlet, but the noise level increases simultaneously. In addition, the generated noise increases while the height of fan cross-section increases, and a 4mm height of the cross section is optimal for aerodynamic performance. When the slit is closer to the location of maximum thickness, the performances of the bladeless fan increases. Moreover, the performance is not changed significantly by changing the cross-sectional profile. Finally, the optimal geometric parameters are identified to guide the future design of the bladeless fan.

Mechanical properties of cellulose nanofibrils determined through atomistic molecular dynamics simulations

2012 ◽  
Vol 27 (2) ◽  
pp. 282-286 ◽  
Author(s):  
Jukka Ketoja ◽  
Sami Paavilainen ◽  
James Liam McWhirter ◽  
Tomasz Róg ◽  
Juha Järvinen ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Elastic Modulus ◽  
Molecular Dynamics Simulations ◽  
Elastic Constants ◽  
Cellulose Nanofibrils ◽  
Amorphous Cellulose ◽  
Cross Sectional ◽  
Elementary Fibrils ◽  
Dynamics Simulations

Abstract We have carried out atomistic molecular dynamics simulations to study the mechanical properties of cellulose nanofibrils in water and ethanol. The studied elementary fibrils consisted of regions having 34 or 36 cellulose chains whose cross-sectional diameter across the fibril was roughly 3.4 nm. The models used in simulations included both crystalline and non-crystalline regions, where the latter were designed to describe the essentials parts of amorphous cellulose nanofibrils. We examined different numbers of connecting chains between the crystallites, and found out that the elastic constants, inelastic deformations, and strength of the fibril depend on this number. For example, the elastic modulus for the whole fibril can be estimated to increase by 4 GPa for each additional connecting chain.

scholarly journals Evaluation of Effective Elastic Properties of Nitride NWs/Polymer Composite Materials Using Laser-Generated Surface Acoustic Waves

2018 ◽  
Vol 8 (11) ◽  
pp. 2319 ◽  
Author(s):  
Evgeny Glushkov ◽  
Natalia Glushkova ◽  
Bernard Bonello ◽  
Lu Lu ◽  
Eric Charron ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Composite Materials ◽  
Elastic Constants ◽  
Acoustic Waves ◽  
Composite Structures ◽  
Elastic Moduli ◽  
Surface Acoustic Waves ◽  
Dispersion Curves ◽  
Effective Elastic Moduli ◽  
Asymptotic Representations

In this paper we demonstrate a high potential of transient grating method to study the behavior of surface acoustic waves in nanowires-based composite structures. The investigation of dispersion curves is done by adjusting the calculated dispersion curves to the experimental results. The wave propagation is simulated using the explicit integral and asymptotic representations for laser-generated surface acoustic waves in layered anisotropic waveguides. The analysis of the behavior permits to determine all elastic constants and effective elastic moduli of constituent materials, which is important both for technological applications of these materials and for basic scientific studies of their physical properties.

Derivation of seismic cone interval velocities utilizing forward modeling and the downhill simplex method

2002 ◽  
Vol 39 (5) ◽  
pp. 1181-1192 ◽  
Author(s):  
Erick J Baziw
Keyword(s):  
Elastic Constants ◽  
Simplex Method ◽  
Forward Modeling ◽  
S Wave ◽  
Cone Penetration ◽  
Interval Velocity ◽  
Wave Velocities ◽  
Downhill Simplex Method ◽  
Downhill Simplex ◽  
Interval Velocities

The seismic cone penetration test (SCPT) has proven to be a very valuable geotechnical tool in facilitating the determination of low strain (<10–4%) in situ compression (P) and shear (S) wave velocities. The P- and S-wave velocities are directly related to the soil elastic constants of Poisson's ratio, shear modulus, bulk modulus, and Young's modulus. The accurate determination of P- and S-wave velocities from the recorded seismic cone time series is of paramount importance to the evaluation of reliable elastic constants. Furthermore, since the shear and compression wave velocities are squared in deriving the elastic constants, small variations in the estimated velocities can cause appreciable errors. The standard techniques implemented in deriving SCPT interval velocities rely upon obtaining reference P- and S-wave arrival times as the probe is advanced into the soil profile. By assuming a straight ray travel path from the source to the SCPT seismic receiver and calculating the relative reference arrival time differences, interval SCPT velocities are obtained. The forward modeling – downhill simplex method (FMDSM) outlined in this paper offers distinct advantages over conventional SCPT velocity profile estimation methods. Some of these advantages consist of the allowance of ray path refraction, greater sophistication in interval velocity determination, incorporation of measurement weights, and meaningful interval velocity accuracy estimators.Key words: seismic cone penetration testing (SCPT), downhill simplex method (DSM), forward modeling, Fermat's principle, weighted least squares (l2 norm), cost function.

FABRICATION OF SU-8 RIDGE WAVEGUIDES BY OPTICAL LITHOGRAPHY AND THEIR CHARACTERIZATION

2011 ◽  
Vol 10 (04n05) ◽  
pp. 771-775 ◽  
Author(s):  
DIKSHA MAKWANI ◽  
R. VIJAYA
Keyword(s):  
Optical Characterization ◽  
Polished Glass ◽  
Ridge Waveguide ◽  
Optical Lithography ◽  
Far Field ◽  
Ridge Waveguides ◽  
Waveguide Length ◽  
Simulation Results ◽  
Waveguide Design ◽  
Lithography Technique

Planar and ridge waveguides are written on SU-8 thin film, coated on end polished glass substrate, by optical lithography technique at near-UV wavelengths. A significant amount of light from a diode laser at 635 nm is guided down the ridge waveguide in the experiment designed to study optical characterization. The measurement of guiding parameters such as number of modes, depth of the waveguide and refractive index are done using prism coupling technique. Simulation results on beam propagation in the SU-8 ridge waveguide (length of 2.54 cm, width of 10 μm and depth of 6 μm) show an appreciable far-field intensity profile that qualifies the waveguide design.

An Inverse Procedure for Determining the Material Constants of Isotropic Square Plates by Impulse Excitation of Vibration

2006 ◽  
Vol 3-4 ◽  
pp. 287-292 ◽  
Author(s):  
Marco Alfano ◽  
Leonardo Pagnotta
Keyword(s):  
Finite Element ◽  
Numerical Analysis ◽  
Carbon Steel ◽  
Elastic Constants ◽  
Natural Vibration ◽  
Finite Element Code ◽  
Resonant Frequencies ◽  
Material Constants ◽  
Impulse Excitation ◽  
Inverse Procedure

The paper presents a procedure whereby the Poisson’s ratio and dynamic Young’s modulus of isotropic and homogeneous materials are determined using two of the first four frequencies of natural vibration in thin square plates. The procedure is based on suitable approximate relationships relating the resonant frequencies to the elastic constants of the material. These relations were derived from an extensive series of numerical analysis carried out by a finite element code. To measure the fundamental resonant frequencies, inexpensive computerized equipment is proposed. The procedure has been validated on Carbon Steel specimens.

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