scholarly journals The Influence of Voids in the Vibrations of Bodies with Dipolar Structure

Symmetry ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1804
Author(s):  
Marin Marin ◽  
Sorin Vlase ◽  
Adina Chirila
Keyword(s):  
Elastic Material ◽  
Lateral Surface ◽  
Harmonic Excitation ◽  
Excitation Level ◽  
The Other ◽  
Spatial Decay ◽  
Dipolar Structure

In our study we analyse the vibration of a right cylinder which consists of an elastic material with dipolar structure and has pores. One end of this cylinder is subjected to an excitation, harmonically in time. The other end of the cylinder and its lateral surface are free of loads. We prove that the presence of the voids does not affect the spatial decay of effects away from the excited end, if the harmonic excitation level is below a predetermined threshold.

scholarly journals Nonlinear vibration of knitted spacer fabric under harmonic excitation

2020 ◽  
Vol 15 ◽  
pp. 155892502098356
Author(s):  
Fuxing Chen ◽  
Hong Hu
Keyword(s):  
Nonlinear Vibration ◽  
Harmonic Balance Method ◽  
Harmonic Excitation ◽  
Polyurethane Foams ◽  
Excitation Level ◽  
Harmonic Amplitude ◽  
Damping Force ◽  
Spacer Fabric ◽  
Fabric System ◽  
Quadratic Stiffness

Knitted spacer fabrics can be an alternative material to typical rubber sponges and polyurethane foams for the protection of the human body from vibration exposure, such as automotive seat cushions and anti-vibration gloves. To provide a theoretical basis for the understanding of the nonlinear vibration behavior of the mass-spacer fabric system under harmonic excitation, experimental, analytical and numerical methods are used. Different from a linear mass-spring-damper vibration model, this study builds a phenomenological model with the asymmetric elastic force and the fractional derivative damping force to describe the periodic solution of the mass-spacer fabric system under harmonic excitation. Mathematical expression of the harmonic amplitude versus frequency response curve (FRC) is obtained using the harmonic balance method (HBM) to solve the equation of motion of the system. Parameter values in the model are estimated by performing curve fit between the modeled FRC and the experimental data of acceleration transmissibility. Theoretical analysis concerning the influence of varying excitation level on the FRCs is carried out, showing that nonlinear softening resonance turns into nonlinear hardening resonance with the increase of excitation level, due to the quadratic stiffness term and the cubic stiffness term in the model, respectively. The quadratic stiffness term also results in biased vibration response and causes an even order harmonic distortion. Besides, the increase of excitation level also results in elevated peak transmissibility at resonance.

scholarly journals No Directional Scapular Asymmetry among Tamarines of the Genus Saguinus (Primates: Callitrichidae)

2020 ◽  
pp. 7-13
Author(s):  
P. M. Parés- Casanova ◽  
J. F. Vélez- García
Keyword(s):  
Fluctuating Asymmetry ◽  
Lateral Surface ◽  
The Other ◽  
Directional Asymmetry ◽  
Geometric Morphometric ◽  
Terrestrial Locomotion ◽  
Developmental Variation ◽  
Morphometric Methods ◽  
Perfect Symmetry ◽  
Left Scapula

Bilateral asymmetry is defined as a deviation of a whole organism or a part of it from a perfect symmetry, and different categories can be recognized. One is the fluctuating asymmetry, defined as the random developmental variation of a trait (or character) that is expected to be perfectly symmetrical on average, and the other one is directional asymmetry, which occurs when one of the sides shows stronger morphological structures or marks than the other. The aim of this study was to determine the kind of scapula asymmetry in Saguinus scapulae. On lateral surface of each right and left scapula, a set of 5 landmarks and 3 curves with semi-landmarks along the margins, on a sample of 16 pairs from different Saguinus species, were considered. Asymmetries (fluctuating and directional) on size and shape of the scapulae were analysed by means of geometric morphometric methods. Directional asymmetry was not detected, demonstrating no side scapular shape bias. The absence of significant directional asymmetry may indicate a similar contralateral pattern of employment of the shoulder, at least for one-arm vertical suspension, as it needs stronger forces than those for terrestrial locomotion and thus would cause more asymmetry in case side loadings were different. To our knowledge, this is the first investigation on the symmetrical/asymmetrical nature of scapulae in Saguinus. Our findings increase knowledge and understanding of humeral joint and arboreal locomotion in primates.

The Centre of Shear of Aerofoil Sections

1953 ◽  
Vol 57 (508) ◽  
pp. 235-237 ◽  
Author(s):  
John A. Jacobs
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Lateral Surface ◽  
The Other ◽  
Principal Axes ◽  
Unstrained State ◽  
Uniform Cross Section ◽  
Single Force ◽  
The Cross ◽  
Fixed End

Consider a cantilever beam of uniform cross section whose generators are parallel to the z-axis and whose lateral surface is free from surface tractions. The line of centroids of the cross sections in the unstrained state is taken as the z-axis, and the x- and y-axes are the principal axes of the cross section at the centroid of the fixed end z = 0.The other end of the beam (z = l) is subject to forces which reduce to a single force with components (Wx, Wv, 0), transverse to the z-axis, acting through the load point L of this end section (see Fig. 1). The co-ordinates of L are taken as (p, q, l).

Vibro-Impact Dynamics of a Periodically Forced Beam

2000 ◽  
Vol 122 (2) ◽  
pp. 210-221 ◽  
Author(s):  
Jakob Knudsen ◽  
Ali R. Massih
Keyword(s):  
Excitation Frequency ◽  
Harmonic Excitation ◽  
Unilateral Contact ◽  
Contact Forces ◽  
The Other ◽  
Impact Dynamics ◽  
Harmonic Loading ◽  
Model Calculations ◽  
Contact Sites ◽  
The Impact

The vibration and impact dynamics of a periodically forced loosely supported beam are analyzed. The wear work rates at impact points are evaluated. The considered beam is clamped at one end, and constrained against unilateral contact at contact sites, with or without friction, near the other end. In this work, the structure is modeled by a Bernoulli-type beam supported by springs using finite element method. Our model calculations are compared with measurements of contact forces and displacements made on a loosely supported rod that was subjected to harmonic loading. Furthermore, the dynamics of vibro-impacts are characterized by evaluating the impact velocity as a function of harmonic excitation frequency for two idealizations of the aforementioned structure. [S0094-9930(00)01002-7]

scholarly journals D. A. Entin. Experiments with reconstruction of the facial skeleton (a new method of direct prosthetics in resection of the upper jaw). With Prof. S.S. Girgolav, Military Medical Academy., Gos. Izd., 1924, 158 pp., 16 figures and 1 drawing

1925 ◽  
Vol 21 (2) ◽  
pp. 214-215
Author(s):  
P. Glushkov
Keyword(s):  
Elastic Material ◽  
Individual Case ◽  
The Other ◽  
New Method ◽  
Facial Skeleton ◽  
Military Medical Academy ◽  
Dental Technician ◽  
Medical Academy ◽  
Upper Jaw ◽  
The One

On the one hand, Entin aimed to simplify the technique of making direct prostheses for the operation, making it accessible to an ordinary dental technician, and on the other hand, to construct a prosthesis that would meet the principle of exact morphological and anatomical-topographic individualization in each individual case. In pursuit of both these objectives, he developed a prosthesis in a soft, elastic material and made it inflatable and pneumatic according to Schiltski's idea.

An experimental study on vibration isolation performance of weft-knitted spacer fabrics

2016 ◽  
Vol 86 (20) ◽  
pp. 2225-2235 ◽  
Author(s):  
Fuxing Chen ◽  
Yanping Liu ◽  
Hong Hu
Keyword(s):  
Experimental Study ◽  
Vibration Isolation ◽  
Nonlinear Behavior ◽  
Harmonic Excitation ◽  
Excitation Level ◽  
Spacer Fabric ◽  
Spacer Fabrics ◽  
Vibration Isolation Performance ◽  
Isolation Performance ◽  
Load Mass

This paper presents an experimental study on the vibration isolation performance of weft-knitted spacer fabrics under forced harmonic excitation. The weft-knitted spacer fabrics with two different thicknesses were first designed by varying the linking distance of the spacer monofilament and fabricated using an electronic flat knitting machine. Then, their vibration isolation performance was tested under forced vibration condition via sinusoidal sweeps from low to high frequencies. The typical acceleration transmissibility curve and effects of fabric thickness, load mass and excitation level were discussed in detail. The results obtained show that the thicker spacer fabric has a lower resonance frequency than the thinner fabric due to lower stiffness, and thus can isolate the vibration at a lower frequency level. The results also show that changing the load mass and excitation level changes the loading conditions of the fabric structure, and thus also changes fabric stiffness and vibration isolation performance due to nonlinear behavior of spacer fabrics. It is expected that this study could provide some useful information to promote the application of weft-knitted spacer fabrics for vibration isolation.

Plane strain rotation moduli for soft elastic blocks

1979 ◽  
Vol 14 (1) ◽  
pp. 17-21 ◽  
Author(s):  
P B Lindley
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Plane Strain ◽  
Elastic Material ◽  
Analysis Data ◽  
Simple Relation ◽  
Theoretical Solution ◽  
The Other ◽  
Element Analysis ◽  
Poisson's Ratios

Making assumptions similar to these used to obtain compression moduli, a simple relation is developed for the plane strain rotation moduli for blocks of soft elastic material bonded to rigid end plates. The deformation arises when one plate rotates relative to the other plane about an axis along the centre of its width. The approximate theoretical solution compares well with finite-element analysis data for materials with Poisson's ratios of 0.333, 0.483 87 and 0.499 83 and blocks having width-to-thickness ratios between 0.25 and 64.

Luminescence from Germanium and Germanium on Silicon

2013 ◽  
Vol 205-206 ◽  
pp. 383-393 ◽  
Author(s):  
Tzanimir Arguirov ◽  
Martin Kittler ◽  
Michael Oehme ◽  
Nikolay V. Abrosimov ◽  
Oleg F. Vyvenko ◽  
...  
Keyword(s):  
Thin Films ◽  
Room Temperature ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Excitation Level ◽  
The Other ◽  
Photoluminescence Spectra ◽  
Si Substrates ◽  
Similar Dependence ◽  
Direct Band

We present an overview on generation of direct gap photo- and electroluminescence in Ge bulk wafers, Ge thin films deposited on Si, and Ge p-i-n diodes prepared on Si substrates. We analyzed the emission in a spectral range from 0.45 eV to 0.95 eV, covering the radiation caused by direct gap transitions, the indirect one, and also the luminescence related to transition on dislocations. The temperature and excitation level strongly influence the intensities of direct and indirect photoluminescence in bulk samples. As it could be expected, high temperature and excitation favour the generation of direct gap luminescence. Intrinsic bulk Ge shows a quadratic dependence of the direct gap luminescence on the excitation and a sub-quadratic one for the indirect. The photoluminescence spectra taken from intrinsic Ge on Si layers show features related to dislocations. There are two spectral regions associated with dislocation recombination. At room temperature one is at around 0.45 eV and the other at 0.72 eV. We found strong direct gap radiation from the Ge p-i-n diodes with intrinsic, highly dislocated active area (dislocation density of about 108-1010 cm-2). There is a threshold current density of 8 kA/cm2, at which the direct band luminescence becomes a super-quadratic. The dependence of the radiation intensity on the excitation is governed by a power law with exponent of 1.7 before reaching that threshold and 4.5 after exceeding it. Above the threshold the dislocation radiation shows similar dependence on the excitation as the direct band luminescence.

Two Analytical Models to Determine the Stress Singularities in Elastic-Viscoelastic Joints

2013 ◽  
Vol 834-836 ◽  
pp. 1391-1394
Author(s):  
Zhi Xu Gu ◽  
Jian Zheng ◽  
Wei Peng ◽  
Xi Nan Tang
Keyword(s):  
Elastic Material ◽  
The Other ◽  
Analytical Models ◽  
Stress Singularities ◽  
Material Parameters ◽  
Elastic Joints ◽  
The Difference

The stress singularities are obtained by two methods in elastic-viscoelastic joints, one is extending the corresponding solutions for elastic-elastic joints by using elastic-viscoelastic correspondence principles and the other is replacing the elastic material parameters with viscoelastic ones in Dundurs parameters directly. The difference between the two methods and the validity are discussed.

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