Wyniki wyszukiwania - BazTech

1

Mapy środowiska radiowego bazujące na PEM w sieciach FANET

Kryk Michał, Malon Krzysztof, Kelner Jan M.

Przegląd Telekomunikacyjny + Wiadomości Telekomunikacyjne

|

2023

|

nr 4

289--292

PL

Mapa środowiska radiowego to pomocne narzędzie, które jest obecnie wykorzystywane do planowania sieci radiowych i zarządzania nimi. Znajdują one zastosowanie np. w sieciach radia kognitywnego lub mobilnych sieciach doraźnych. W przypadku sieci doraźnych z węzłami rozmieszczonymi na bezzałogowych statkach powietrznych, wykorzystanie dwuwymiarowych map jest niewystarczające. Ten artykuł koncentruje się na generowaniu trójwymiarowej mapy, która jest zbiorem map dwuwymiarowych zdefiniowanych dla dyskretnych wysokości nad poziomem gruntu lub morza. Każda taka mapa jest wyznaczana za pomocą metody równań parabolicznych, która pozwala określić tłumienia dróg propagacyjnych dla wielu profili terenu rozchodzących się promieniście od analizowanego węzła sieci. W artykule przedstawiono opracowany algorytm oraz przykładowe wyniki dla rozległego obszaru.

EN

A radio environment map is a helpful tool currently used to plan and manage radio networks. They are used, e.g., in cognitive radio networks or mobile ad-hoc networks. In the case of flying ad-hoc networks, the use of two dimensional maps is insufficient. This paper focuses on generating a three-dimensional map as a set of two-dimensional maps defined for discrete heights above ground or sea level. Each map is determined using the parabolic equation method, which allows for determining the path losses for many terrain profiles outgoing radially from the analyzed transmitting node. The paper presents the developed algorithm and exemplary results for a large area.

2

Resonance of a structure with soil elastic waves released in non-linear hysteretic soil upon unloading

Kowalczyk Piotr

Studia Geotechnica et Mechanica

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2022

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Vol. 44, nr 4

253--266

EN

High-frequency motion is often observed in small-scale experimental works carried out in flexible containers under simplified seismic loading conditions when single harmonic sine input motions are introduced at the base of a soil specimen. The source of the high-frequency motion has often been sought in experimental inaccuracies. On the other hand, the most recent numerical studies suggested that high-frequency motion in the steady-state dynamic response of soil subjected to harmonic excitation can also be generated as a result of soil elastic waves released in non-linear hysteretic soil upon unloading. This work presents an example of a finite element numerical study on seismic soil–structure interaction representative of an experimental setup from the past. The results show how high-frequency motion generated in soil in the steady-state response, apparently representative of soil elastic waves, affects the steady-state response of a structure, that is, it is presented how the structure in the analysed case resonates with the soil elastic waves. The numerical findings are verified against the benchmark experimental example to indicate similar patterns in the dynamic response of the structure.

3

Probabilistic Liquefaction Analysis Using Standard Penetration Test

Kamel Filali, Badreddine Sbartai

Studia Geotechnica et Mechanica

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2022

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Vol. 44, nr 2

162--174

EN

The Youd etal liquefaction resistance curves developed in 2001 to characterize the cyclic resistance of soil based on SPT test are the most used in the context of the Seed and Idriss simplified procedure as a deterministic model. These curves were developed from a modified database of Seed etal. in 1985 with the assumption that the actual peak shear stress (τd) induced at depth h is always less than that predicted by the simplified procedure (τr) of Seed and Idriss (rd= τd/τr<1). By using a suite of equivalent linear site response analyses to adjust the dynamic and the simplified shear stress at depth h, Filali and Sbartai showed in 2017 that the dynamic peak shear stress for some earthquakes is greater than the simplified peak shear stress (rd>1). As in this case, the assumption of the simplified procedure is not verified, Filali and Sbartai have proposed a corrector factor (RC) in the range where rd>1 to adjust the deformable and rigid body. In this paper, we will present a probabilistic study for the evaluation of the liquefaction potential using a database based on SPT measurement compiled after the Chi-Chi Taiwan earthquake, in which the cyclic stress ratio is evaluated using the proposed corrector factor. The objective of this study is to present a probabilistic shape of the cyclic resistance ratio (CRR) curves based on the original simplified method of Seed and Idriss and the corrected version and a new formulation for computing the probability of liquefaction.

4

Nonlocal state-space strain gradient approach to the vibration of piezoelectric functionally graded nanobeam

Selvamani Rajendran, Loganathan Rubine, Ebrahimi Farzad

Engineering Transactions

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2022

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Vol. 70, iss. 4

319--338

EN

In this work, the state-space nonlocal strain gradient theory is used for the vibration analysis of piezoelectric functionally graded material (FGM) nanobeam. Power law relations are used to describe the computing analysis of FGM constituent properties. The refined higherorder beam theory and Hamilton’s principle are used to obtain the equations of motion of the piezoelectric nanobeam. Besides, the governing equations of the piezoelectric nanobeam are extracted by the developed nonlocal state-space theory, and the analytical wave dispersion method is used to solve wave propagation problems. The real and imaginary solutions for wave frequency, loss factor and wave number are obtained and presented in graphs.

5

Wave propagation and free vibration of FG graphene platelets sandwich curved beam with auxetic core resting on viscoelastic foundation via DQM

Al Mukahal F. H. H., Sobhy Mohammed

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e12, 2022

EN

A novel shear and normal deformations theory is presented in this article to illustrate the wave propagation and free vibration of three-layer sandwich curved beams subjected to elevated temperature and moisture environments and resting on viscoelastic foundation. The upper and lower layers are made of metal matrix reinforced with functionally graded (FG) graphene platelets (GPLs). While, the core layer is made of auxetic honeycomb structures. For the layers to be more bonded, the matrix of the face layers and the auxetic layer are both made of aluminum material. The volume fraction of GPLs is varied through the thickness of the face layers according to a layer-wise rule. The modified Halpin–Tsai model is used to describe the effective material properties of the face layers. Four types of GPLs distribution are considered in the present analysis. The differential quadrature method (DQM) is employed to discretize the equations of motion and then converted to a system of algebraic equations. This system can be solved to obtain the natural frequencies of the sandwich curved beams. Whereas, the wave dispersion relations are determined by solving the motion equations analytically. Convergence and comparison examples are presented to adjust and validate the present solution. In addition, comprehensive parametric studies are performed to investigate the effects of the weight fraction of GPLs, temperature, moisture concentrations, core thickness, boundary conditions, and viscoelastic foundation stiffness on the natural frequency, wave frequency and phase velocity of the honeycomb sandwich curved beams.

6

2D Modeling of Wave Propagation in Shallow Water by the Method of Characteristics

Khalilabadi Mohammad Reza

Archives of Acoustics

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2022

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Vol. 47, No. 3

407--412

EN

In this paper, a 2D numerical modeling of sound wave propagation in a shallow water medium that acts as a waveguide, are presented. This modeling is based on the method of characteristic which is not constrained by the Courant–Friedrichs–Lewy (CFL) condition. Using this method, the Euler time-dependent equations have been solved under adiabatic conditions inside of a shallow water waveguide which is consists of one homogeneous environment of water over a rigid bed. In this work, the stability and precision of the method of characteristics (MOC) technique for sound wave propagation in a waveguide were illustrated when it was applied with the semi-Lagrange method. The results show a significant advantage of the method of characteristics over the finite difference time domain (FDTD) method.

7

Analysis of the harmful influence of parasiteismic vibrations using the example of a failure in the building structure of a school gymnasium

Liszewski Wiesław

Zeszyty Naukowe Politechniki Częstochowskiej. Budownictwo

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2021

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Z. 27 (177)

152-157

EN

This article describes, based on the failure of a public utility building structure, the issues related to the destructive impact of vibrations on the ground in connection with the load-bearing structure of the facility. An external source of wave propagation was identified, located in the immediate vicinity of the analyzed building. Additionally, errors in the interpretation of the behavior of the structure during its operation were presented by performing ineffective construction works related to the attempt to strengthen the ground on which the school sports hall was directly erected. On the basis of the analysis of archival materials and additional tests, the necessary scope of repair works necessary to be performed on the site was determined, along with guidelines for the implementation of the diaphragm in the form of a ground vibro-isolating screen, aimed at minimizing the impact of parasiteismic impacts on the public building.

PL

Na przykładzie awarii konstrukcji budynku użyteczności publicznej, opisano problematykę związaną z destrukcyjnym wpływem drgań na podłoże gruntowe w powiązaniu z ustrojem nośnym obiektu. Ustalono zewnętrzne źródło propagacji fal, zlokalizowane w bezpośrednim sąsiedztwie analizowanego budynku. Dodatkowo przedstawiono błędy w interpretacji zachowania konstrukcji w trakcie jej eksploatacji, poprzez wykonywanie nieskutecznych prac budowlanych związanych z próbą wzmocnieniem podłoża gruntowego, na którym w sposób bezpośredni posadowiono przyszkolną salę sportową. Na podstawie przeprowadzonej analizy materiałów archiwalnych oraz dodatkowych badań określono niezbędny zakres robót naprawczych, koniecznych do wykonania na obiekcie wraz z wytycznymi do realizacji przepony w formie gruntowego ekranu wibroizolacyjnego, mającego na celu zminimalizowanie wpływu oddziaływań parasejsmicznych na budynek użyteczności publicznej.

8

First attempt to model numerically seismically-induced soft-sediment deformation structures : a comparison with field examples

Bronikowska Małgorzata, Pisarska-Jamroży Małgorzata, Loon van Tom

Geological Quarterly

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2021

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Vol. 65, No. 4

s. 216--225

EN

No numerical model has thus far addressed seismites, even though seismites are frequently used for the conditions which have to be fulfilled for the development of seismites have also been estimated only empirically. The present contribution is a first attempt to model numerically the soft-sediment deformation structures caused by the passage of S-waves through near-surface sedimentary layers. The simulations are based on the so-reconstruction of seismic events in the geological past. This is the more remarkable since the boundary called pressure tube model and the iSALE2D program. We modelled a seismic S-wave with six different vertical velocities, ranging from 1.6 to 2.6 m · s-1, passing through sediments with different densities and porosities in a sedimentary succession from the surface down to a depth of 10 m. The modelled soft-sediment deformation structures (load casts, flame structures, injection structures and sedimentary volcanoes) show similar geometries and sizes as those known from laboratory experiments and field studies. The geometry, size and type of these structures depend on the sediment properties and on the initial pressure used as a trigger mechanism, rather than on S-wave velocity. In contrast, the depth of the seismites appears to depend strongly on the S-wave velocity.

9

Effective properties of periodic media in elastodynamic problems

Yera Rolando, Méndez Carlos G., Sánchez Pablo J., Huespe Alfredo E.

Computer Methods in Materials Science

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2021

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Vol. 21, No. 3

139--148

EN

This paper describes a homogenization model for evaluating the effective elastodynamic properties of acoustic metamaterials in problems involving wave propagation. The methodology is based on determining the constitutive equations in terms of averaged quantities observed at the macroscale. In this sense, the approach very closely follows the pioneering ideas introduced by Willis, and afterwards, followed by several authors in the last ten years. The distinctive characteristic of our approach is that we write the microscale equation in the spatial domain. The model is validated with previous results published in the literature, and our results replicate them almost exactly. The resulting homogenization model could be used as an additional tool for the topology design of acoustic metamaterials.

10

Experimental study on fatigue failure evolution in composite plate monitored by wave propagation method

Stawiarski Adam, Barski Marek, Muc Aleksander

Vibrations in Physical Systems

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2020

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Vol. 31, nr 2

art. no. 2020227

EN

In this study, the elastic wave propagation method is used to observe the initiation and evolution of the fatigue failure form in the multilayered composite plate with an elliptical hole. The experimental tests with the use of active, pitch-catch elastic wave measurement techniques are used during the fatigue test of the composite specimens. The fatigue tests were preceded by the numerical, finite element analysis of the elastic wave propagation phenomenon in a composite plate with an elliptical hole. The sequential measurement related to the number of cycles during the fatigue tests was assumed. The time of flight (ToF) and amplitude change was monitored by piezoelectric sensors localized in the area of predictable failure form evolution. The analysis of the dynamic response of the structure under fatigue loading conditions by a relatively small number of piezoelectric transduces allows us to build cost-effective Structural Health Monitoring (SHM) system for damage detection and monitoring of the failure form evolution.

11

Micro-vibrations and wave propagation in biperiodic cylindrical shells

Tomczyk B., Litawska A.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 3

789--807

EN

The objects of consideration are thin linearly elastic Kirchhoff-Love-type circular cylindrical shells having a periodically microheterogeneous structure in circumferential and axial directions (biperiodic shells). The aim of this contribution is to study a certain long wave propagation problem related to micro-fluctuations of displacement field caused by a periodic structure of the shells. This micro-dynamic problem will be analysed in the framework of a certain mathematical averaged model derived by means of the combined modelling procedure. The combined modelling applied here includes two techniques: the asymptotic modelling procedure and a certain extended version of the known tolerance non-asymptotic modelling technique based on a new notion of weakly slowly-varying function. Both these procedures are conjugated with themselves under special conditions. Contrary to the starting exact shell equations with highly oscillating, non-continuous and periodic coefficients, governing equations of the averaged combined model have constant coefficients depending also on a cell size. It will be shown that the micro-periodic heterogeneity of the shells leads to exponential micro-vibrations and to exponential waves as well as to dispersion effects, which cannot be analysed in the framework of the asymptotic models commonly used for investigations of vibrations and wave propagation in the periodic structures.

12

Komputerowe wspomaganie analizy propagacji fali w betonowych konstrukcjach sprężonych

Krzyżyński T., Maciejewski I., Szczurowski K.

Materiały Budowlane

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2018

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nr 11

24--26

PL

Wykorzystywane w praktyce metody oceny stanu konstrukcji sprężonych, które mogą występować w konstrukcjach betonowych, polegają na wykryciu zarysowań, wtrąceń, korozji lub innych uszkodzeń. Na ogół metody te są ukierunkowane na znalezienie miejsca ich występowania. Proponowane w artykule podejście do oceny stanu elementów sprężonych polega na obserwacji charakterystyk dynamicznych elementów konstrukcji pod wpływem zmian w rozkładzie naprężeń. Przedstawiono metodę bazującą na analizie propagacji fali w betonowych konstrukcjach sprężonych na potrzeby predykcji stanu naprężenia w przekrojach poprzecznych belki. Badania eksperymentalne poparte są symulacjami komputerowymi z wykorzystaniem Metody Elementów Skończonych.

EN

Used in practice methods of prestressed concrete state identification which can occurred in the structures base at a detection of cracks, inclusions, corrosion or other small damages. Mostly they are targeted at detecting of their localization. An alternative approach consisting an observation of changes in dynamical characteristics of construction elements, due to a change in a structure of internal stresses. In the present paper an analysis of wave propagation in concrete prestressed structures for needs of stress state prediction in beam cross-sections is presented. Experimental approach is aided by means of computer simulations with a use of Finite Element Method.

13

Sun transits in geo satellite systems in the aspect of radio waves propagation

Wilk-Jakubowski J. Ł.

Informatyka, Automatyka, Pomiary w Gospodarce i Ochronie Środowiska

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2018

|

T. 8, nr 4

56--59

EN

The article includes description of process of Sun transits, including indispensable information on the parameters employed to show their impact on these phenomena. On this basis the date, the start time and the end time and the duration time of Sun transits could be presented for a given location. The main considerations are pertinent to propagation studies. The part of results connected with Sun transits for the limited frequencies of Ku band (downlink) in satellite systems, depending on the antennae, is presented in this article.

PL

Artykuł zawiera opis zjawiska influencji słonecznych, ukazując niezbędne informacje na temat zastosowanych parametrów, aby przedstawić ich wpływ na te zdarzenia. Na tej podstawie data, czasy początku i końca oraz czas trwania influencji słonecznych mogą zostać określone dla danej lokalizacji. Rozważania dotyczą badań propagacyjnych. W artykule dla łącza downlink zamieszczono część wyników, w zależności od zastosowanych anten, dla granicznych częstotliwości pasma Ku powszechnie wykorzystywanego w łączności satelitarnej.

14

Badania nieniszczące i monitoring elementów konstrukcji budowlanych w warunkach laboratoryjnych

Rucka M.

Badania Nieniszczące i Diagnostyka

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2018

|

nr 3

36--41

PL

W artykule przedstawiono wyniki przykładowych badań diagnostycznych elementów konstrukcji inżynierskich w warunkach laboratoryjnych metodą propagacji fal mechanicznych. Testom poddano płytę stalową, zakładkowe połączenie klejone oraz czołowe połączenie śrubowe. Badania ukierunkowano na pozyskiwanie i rozpoznawanie wzorców uszkodzeń dla elementów i defektów o znanej geometrii oraz kontrolowanym sposobie zniszczenia. Przeprowadzone badania laboratoryjne umożliwiły przetestowanie efektywności analizowanych metod oraz wytypowanie wskaźników diagnostycznych.

EN

The paper presents the results of diagnostics of structural elements in laboratory conditions using the mechanical wave propagation method. The tests were carried out on a steel plate, an adhesive lap joint and a bolted flange joint. The research was focused on acquiring and recognizing damage patterns for elements with defects of known geometry and controlled failure. The laboratory tests made it possible to test the effectiveness of the analysed methods and to select diagnostic indicators.

15

Separation of split shear waves based on a hodogram analysis of HTI media

Yang Y., Lu J., Wang Y.

Acta Geophysica

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2018

|

Vol. 66, no. 4

643--658

EN

Although the shear-wave birefringence phenomenon affects the imaging of converted shear waves, it also provides a considerable amount of information on subsurface fracture development. Therefore, it is significant to separate split shear waves before seismic interpretation and reservoir prediction. In this paper, we propose a new method of split shear waves separation based on the polarization directions derived from hodogram analysis. Through the hodogram analysis, we find that the split shear-wave particle motions are within the range of a specific and fixed rectangle, which have relations with the fracture azimuth in strata. In addition, we found that a couple of split shear waves can only be fitted to the unique trajectory rectangle through the theoretical derivation. Based on this, we establish the trajectory rectangle through the wave vector calculation and calculate the fracture azimuth according to the fact that the one edge of the trajectory rectangle is along or perpendicular to the fracture azimuth. Synthetic data analysis shows that the calculation accuracy of fracture azimuth under the constraint of trajectory rectangle is less affected by the time delay between split shear waves than using the method of eigenvector–eigenvalue decomposition (EED). Therefore, we can obtain better results for separation of split shear waves using our method than using EED. Eventually, we propose an approach of layer stripping to deal with the problem that shear wave split several times due to the situation that different strata have different fracture azimuths. Synthetic data test indicates that our method can achieve higher calculation efficiency and faster convergence speed than the conventional eigenvector–eigenvalue decomposition method, even though the data are of a low signal-to-noise ratio. Moreover, field data applications show the effectiveness and potential of our method.

16

Numerical modeling of Gaussian beam propagation and diffraction in inhomogeneous media based on the complex eikonal equation

Huang X., Sun H.

Acta Geophysica

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2018

|

Vol. 66, no. 4

497--508

EN

Gaussian beam is an important complex geometrical optical technology for modeling seismic wave propagation and diffraction in the subsurface with complex geological structure. Current methods for Gaussian beam modeling rely on the dynamic ray tracing and the evanescent wave tracking. However, the dynamic ray tracing method is based on the paraxial ray approximation and the evanescent wave tracking method cannot describe strongly evanescent fields. This leads to inaccuracy of the computed wave fields in the region with a strong inhomogeneous medium. To address this problem, we compute Gaussian beam wave fields using the complex phase by directly solving the complex eikonal equation. In this method, the fast marching method, which is widely used for phase calculation, is combined with Gauss–Newton optimization algorithm to obtain the complex phase at the regular grid points. The main theoretical challenge in combination of this method with Gaussian beam modeling is to address the irregular boundary near the curved central ray. To cope with this challenge, we present the non-uniform finite difference operator and a modified fast marching method. The numerical results confirm the proposed approach.

17

The effect of angle of attack on the generated wave propagation

Javanmardi M., Binns J., Izham M. I. C., Rafieshahraki J.

Zeszyty Naukowe Akademii Morskiej w Szczecinie

|

2017

|

nr 50 (122)

36--41

EN

The presented work is an experimental investigation into the waves generated by a pressure source moving in a straight channel. Wave fields generated by the moving pressure source are described and the effects of angle of attack on the generated wave height, surfable wave quality, drag and vertical forces are presented. The main objective of this study was to investigate the relationship between the angle of attack and the generated wave height across the towing tank width and the surfable wave quality. The investigations were conducted at the Australian Maritime College towing tank on a wavedozer at four different attack angles at various speeds. Three wave probes were installed across the channel to record the generated wave heights. Based on the experimental results, it was concluded that smaller angles of attack produced higher quality surfable waves compared to larger angles of attack, while the height of the generated wave has a direct relationship with the angle of attack. By comparing the forces for different models, it was concluded that the pressure source with the lowest angle of attack has the minimum drag but maximum displacement.

18

The modification of the dynamic properties of cohesive soil resulting from triaxial consolidation

Kogut J., Zięba J.

Technical Transactions

|

2017

|

Vol. 9(114)

75--89

EN

This paper describes the laboratory examination of the dynamic parameters of cohesive soil together with an analysis of these parameters using artificial intelligence. The analysis yielded the propagation velocity of shear wave Vs and the dynamic Kirchhoff modulus G obtained during the soil tests in the triaxial stress apparatus. The investigation was conducted using bender elements. The artificial neural networks trained on data obtained from the test were used for the further analysis.

PL

Artykuł łączy ze sobą badania laboratoryjne parametrów dynamicznych gruntu spoistego wraz z ich analizą z użyciem metod sztucznej inteligencji. Rezultatami analizy są wartości prędkości propagacji fali ścinającej Vs oraz dynamicznego moduł Kirchhoffa G uzyskane podczas badania gruntu w aparacie trójosiowego ściskania. Do otrzymania tych parametrów posłużyło wykorzystanie elementów bender. Do analizy użyto sztucznych sieci neuronowych uczonych na danych pozyskanych z badań.

19

The efficiency of an active generator in the case of a deep foundation location

Herbut A.

Studia Geotechnica et Mechanica

|

2017

|

Vol. 39, nr 1

3--12

EN

This paper presents a concept for vibration-mitigation techniques with the potential to reduce ground vibration amplitudes by applying an additional vibration source. The idea of an additional generator is verified in the case of an impact load for the points located on the ground surface and below it. Equations of motion for the damped transversally isotropic ground model with the absorbing boundary conditions are presented and numerically integrated using FlexPDE software, based on the finite element method. The efficiency of the solution is analyzed in terms of reducing the vertical and horizontal components. Results are presented in the form of a dimensionless amplitude reduction factor. In each case being analyzed, a vibration mitigation effect in a three-story building was achieved.

20

Modeling of axisymmetric waves in a piezoelectric circular fiber coated with thin film

Selvamani R.

Mechanics and Mechanical Engineering

|

2017

|

Vol. 21, nr 3

637--648

EN

Mathematical modeling of axisymmetric waves in a piezoelectric fiber of circular cross section coated with thin film is studied using three-dimensional theory of piezoelectricity. Potential functions are introduced to uncouple the equations of motion, electric conduction equations. The surface area of the fiber is coated by a perfectly conducting gold material. The frequency equations are obtained for longitudinal and flexural modes of vibration and are studied numerically for PZT-4 ceramic fiber. The computed nondimensional frequencies and attenuation for fiber with and without coating are presented in the form of dispersion curves.