Wyniki wyszukiwania - Biblioteka Nauki

1

Hydrodynamics of tsunamis generated by asteroid impact in the Black Sea

100%

Isvoranu D. , Badescu V.

Open Physics

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2012

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tom 10

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nr 2

429-446

EN

Two-dimensional and one-dimensional models are used to evaluate the seashore effects of the tsunami generated by an asteroid hitting the deep water in the Eastern region of the Black Sea. The shallow water theory has been used to describe tsunami propagation. The distance between the impact point and the nearest coast is about 150 km. The effects on the coastal regions depend on many factors among which the most important is asteroid size. The tsunami generated by a 250 m asteroid reaches the nearest dry land location in 20 minutes and needs about two hours to hit all over the Black Sea coast. The horizontal inundation length is also known as run-in or run-off distance, according to the direction of water movement. The run-up values may be up to 39 m in the Eastern basin and a more than ten times smaller in theWestern region. The Northern part of the Black Sea coast is not affected by the tsunami. The run-in values of a tsunami generated by a 1000 m diameter asteroid are sensibly larger than the similar values associated to a 250 m diameter asteroid. The run-in strongly depends on the distance from the impact position to the shore and on coastal topographical profile. For instance, the run-in distance in case of a tsunami generated by a 250 m size asteroid is 0.1 km (at Varna), 0.5 km (Ordu), 0.7 km (Yalta) and 1.4 km (Sochi). In case of the 1000 m diameter asteroid the run-in distance is 0.7 km (at Varna) and 2.9 km (Yalta). The results accuracy is also discussed.

2

On the one-dimensional wave propagation in inhomogeneous elastic layer

100%

Wesołowski Z.

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2007

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tom Vol. 55, nr 4

397-403

EN

The standard approach to the wave propagation in an inhomogeneous elastic layer leads to the displacement in a form of a product of a function of space and a harmonic function of time. This product represents the standing, and not the running wave. The part depending on the space variable is governed by the linear ordinary second order differential equation. In order to calculate the propagation speed in the present paper the inhomogeneous material is separated by a plane into two parts. Between the two inhomogeneous parts the virtual homogeneous elastic extra layer is added. The elasticity modulus and the mass density of the extra layer have the same values as the inhomogeneous material on the separation plane. In further calculations the extra layer is assumed to be infinitesimally thin. The virtual layer allows to decompose the motion into two waves: a wave running to the right and a wave running to the left. Energy conservation equation is derived.

3

Damage detection of a T-shaped panel by wave propagation analysis in the plane stress

89%

Rucka M. , Chróścielewski J. , Witkowski W. , Wilde K. , Rucka M. , Chróścielewski J. , Witkowski W. , Wilde K.

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2012

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nr 1

4

Wave propagation and Landau-type damping in liquids

88%

Molinari V. , Mostacci D.

Open Physics

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2012

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tom 10

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nr 3

669-675

EN

Intermolecular forces are modeled by means of a modified Lennard-Jones potential, introducing a distance of minimum approach, and the effect of intermolecular interactions is accounted for with a self consistent field of the Vlasov type. A Vlasov equation is then written and used to investigate the propagation of perturbations in a liquid. A dispersion relation is obtained and an effect of damping, analogous to what is known in plasmas as “Landau damping”, is found to take place.

5

Micromechanical model of rough contact between rock blocks with application to wave propagation

88%

Misra A. , Marangos O.

Acta Geophysica

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2008

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tom Vol. 56, no. 4

1109-1128

EN

The relationship between effective stiffness of rough contacts of rock blocks and transmission of plane waves is well known. Effective stiffness of a rough contact may be related to the force-deformation behavior of the asperity contacts and the statistical description of rock joint surface topography through micromechanical methods. In this paper, a micromechanical methodology for computing the overall rock contact effective stiffness is utilized along with the imperfectly bonded interface model to investigate how transmitted and reflected wave amplitudes are affected by the incident wave frequency, rock joint closure and the existing rock joint normal stress conditions. As a result, expressions for reflected and transmitted wave amplitudes as well as group time delay of the wave-packets are obtained and parametrically evaluated.

6

Wyznaczanie parametrów dynamicznych podłoża gruntowego na podstawie badań doświadczalnych

75%

Kogut J.

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2007

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tom R. 104, z. 1-Ś

45-53

PL

Przedmiotem niniejszego artykułu jest określenie niektórych cech dynamicznych gruntu wpływających na propagację fali sprężystej. Wykorzystano tutaj informacje uzyskane z dynamicznych badań powierzchniowych, wykonanych w przekroju gruntowym za pomocą różnego typu wymuszeń impulsowych oraz sondowań wgłębnych. Analizowano propagację fal sprężystych w gruncie oraz obliczono, stosując Metodę Elementów Brzegowych, odpowiedzi dynamiczne gruntu dla parametrów uzyskanych z badań.

EN

This paper discusses some dynamic parameters of a soil influenced a wave propagation in this medium. The experimental data is used to assess the dynamic soil profile at the site. Furthermore, numerical predictions of the vertical dynamic response with boundary element model of the soil are performed.

7

Stiffness and mass matrices of FEM applicable dynamic infinite element with united shape basis

75%

Kazakov K.

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2009

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tom Vol. 14, no 1

189-200

EN

This paper is devoted to the construction and evaluation of mass and stiffness matrices of elastodynamic four and five node infinite elements with united shape functions (EIEUSF), recently proposed by the author. Such elements can be treated as family elastodynamic infinite elements appropriate for multi-wave soil-structure interaction problems. The common characteristic of the proposed infinite elements is the so-called united shape function, based on finite number of wave shape functions. The idea and the construction of the united shape basis are described in brief. This element belongs to decay class infinite elements. It is shown that by appropriate mapping functions the formulation of such an element can be easily transformed to a mapped form. The results obtained using the proposed infinite elements are in a good agreement with the superposed results obtained by series of standard computational models. The continuity along the finite/infinite element (artificial boundary) line in two-dimensional substructure models is also discussed in brief. In this type of computational models such a line marks the artificial boundary between the near and the far field of the model.

8

On plane waves in an isotropic linear thermoelastic solid with initial stresses

75%

Singh B.

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2006

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tom Vol. 11, no 4

957-963

EN

The plane wave propagation in a homogenous isotropic, thermally conducting elastic solid under normal initial stresses is studied with two thermal relaxation times. Three types of plane waves, quasi-P, thermal and quasi-SV waves, are shown to exist. The dependence of the velocities of these plane waves on the direction of propagation is shown graphically for different combinations of normal initial stresses.

9

Resonance effects in Beroulli-Fuler beams under traveling load with variable speed

75%

Bogacz R. , Frischmuth K.

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2011

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tom nr 6

EN

Moving loads induce also in Euler-Bernoulli beams traveling waves. For a harmonic force moving at constant speed there exist analytical solutions with well known ranges of validity in the speed/frequency plane, divided by critical resonance curves. Recent applications to railway mechanics require the study of the variable speed case. Due to the lack of analytical solutions, numerical techniques have to be developed. As in the analytical approach, the crucial point is the discussion of the Sommerfeld condition in the case of infinite domains. In this paper, a semi-discretization of the equations is used together with an absorbing boundary condition. The method is verified on solutions to the classical case.

PL

Ruchome siły powodują propagację fal biegnących w belkach nawet w przypadku modelu Bernoulliego-Eulera. Gdy siła harmoniczna przemieszcza się ze stałą prędkością, istnieją rozwiązania analityczne. Znane są zakresy różnych postaci rozwiązań na płaszczyźnie prędkości i częstości, które rozdzielane są krzywymi rezonansowymi. Aktualne zastosowania w mechanice kolejowej wymagają analizy również przypadku zmiennej prędkości. Z braku rozwiązań analitycznych trzeba rozwijać techniki numeryczne. Ważnym punktem w przypadku belek nieograniczonych jest uwzględnienie warunków Sommerfelda. W artykule stosuje się metodę semi-dyskretyzacji z absorbującymi warunkami brzegowymi, która weryfikowana jest porównaniem z rozwiązaniami klasycznymi.

10

Krajowe badania propagacji fal radiowych w systemach radiokomunikacyjnych

75%

Katulski R. , Pawłowski W. , Rauhut-Sobczak B. , Stefański J.

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2009

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tom R. 50 nr 177B

165-172

PL

Na podstawie zebranej literatury dokonano przeglądu krajowych badań propagacji fal radiowych systemach radiokomunikacyjnych. Przedmiotem zainteresowania były badania dotyczące rozchodzenia się fal radiowych w środowiskach niezjonizowanych.

EN

Based on a review of the literature collected national survey of radio wave propagation radio communication systems. Interest was to study the propagation of radio waves in ionized environments.

11

Oszacowanie parametrów dynamicznych podłoża gruntowego

75%

Kogut J.

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2007

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tom R. 104, z. 2-B

55-63

PL

Przedmiotem artykułu jest analiza wpływu własności dynamicznych gruntu na propagację fali sprężystej. Wykorzystano tu informacje, które może dostarczyć badanie dynamiczne wykonane w przekroju gruntowym z zastosowaniem wymuszenia impulsowego. Do dalszych analiz wykorzystano informacje o propagacji fali sprężystej w gruncie, zarejestrowanej w punktach pomiarowych na powierzchni wzdłuż badanego przekroju.

EN

This paper describes a feedforward neural network application to the analysis of the measurements of the soil dynamics. The free field experiment has been performed to determine the soil dynamic properties. An inversion process based on the comparison of the experimental and theoretical phase velocity curves shows the dynamic soil profile.

12

Rheological properties of evolutive materials monitored by an acoustic test

75%

Arnaud L. , Thinet S.

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1999

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tom Vol. 4, no spec.

39-44

EN

The rheological behaviour of setting heterogeneous materials is studied by means of an experimental device. It is based on the propagation of acoustic waves at low frequency (100Hz-1kHz). It enables to follow up material setting, and hardening phases and to quantify by an inverse analysis, the evolution of the complex viscoelastic modulus from the fluid to the solid phase. Different rheological evolutions are presented for various formulations of hydraulic concrete and bituminous mix.

13

Acoustic waves in multi-layered medium perturbation numbers approach

75%

Skrzypczyk J. , Winkler-Skalna A.

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2008

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tom Vol. 1, no. 2

79-83

EN

A layered medium of finite height in which the n layers are assumed to have position dependent properties is considered. In the paper the boundary conditions are considered to be either rigid (Dirichlet-type) or of a reflecting type (mixed-type). The perturbation method based on II-order perturbation numbers is used to obtain the eigenvalues and the eigenfunctions of the height equation in case of both the rigid and reflecting boundaries. The corrections to the eigenvalues and eigen- functions are numerically computed from the perturbation formulae in both cases of interest.

PL

Analizowany jest n-warstwowy ośrodek o skończonej wysokości (grubości), w którym parametry warstw zależą od położenia. Rozpatrywane są warunki brzegowe typu Dirichleta (brzeg sztywny) lub typu mieszanego (brzeg odbijający). Zastosowano metodę perturbacji, która wykorzystuje pojęcie liczb perturbacyjnych II rzędu. Otrzymano perturbacyjne wielkości wartości własnych i wektorów własnych równania opisującego położenie w obu rozpatrywanych przypadkach. Poprawki perturbacyjne dla wartości własnych i wektorów własnych zostały wyliczone numerycznie z równań perturbacyjnych dla rozpatrywanych przypadków.

14

Visualization methods of sound flow in the 3D real-live field

75%

Weyna S.

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2011

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tom Vol. 52, nr 1

16-18

EN

Based on the research with intensity technique and using selected visualizations methods, in the publication are demonstrating few examples of vector space distribution of the real acoustic field, illustrate the application of the Sl measurement for practical problems at the acoustical diagnostic and noise abatement. Analysis of the results makes it possible to obtain much new information about energetic and geometric distributions of the acoustic fields. The measurement technique described, as well as the method of graphical presentation of results, can enrich the knowledge of the mechanism of acoustic energy flux through the real partitions. The article presents the application of Sl technique to graphic visualization of spatial distribution the acoustic energy flow over the barriers of various geometrical shapes structures located in a three-dimensional space.

PL

W oparciu o wyniki badań prowadzonych techniką natężeniową i wykorzystanie metod wizualizacji, w przedstawionej pracy pokazano kilka przykładów rozkładu wektorowych pól akustycznych. Pokazano, jak przydatna staje się technika pomiaru natężenia dźwięku (Sl) w pozyskiwaniu nowych informacji o rozkładach energii w polu akustycznym. Stosując technikę natężeniową do obrazowania przepływów akustycznych, możemy znacznie poszerzyć wiedzę o tych zjawiskach. Artykuł przedstawia zastosowanie techniki Sl do przestrzennej wizualizacji przepływów energii wokół barier o różnej geometrii. Rezultaty badań pokazują rozkłady strumienia natężenia w płaszczyźnie (2D) i w przestrzeni (3D w formie linii strumienia, jako kształty czoła fali, lub izopowierzchnie natężenia.

15

Effect of rotation on Rayleigh waves in an isotropic generalized thermoelastic diffusive half-space

75%

Kumar R. , Kansal T.

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2008

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tom Vol. 60, nr 5

421-443

EN

he present investigation is a study of the effect of rotation on the characteristics of Rayleigh waves propagation in a homogeneous, isotropic, thermoelastic diffusive half-space in the framework of different theories of thermoelastic diffusion, including the Coriolis and Centrifugal forces. The medium is subjected to stress-free, thermally insulated/isothermal and chemical potential boundary conditions and is rotating about an axis perpendicular to its plane. Secular equations of surface wave propagation in the considered media are derived. The phase velocities and attenuation coefficients of surface wave propagation have been computed by using the irreducible case of Cardano's method, with the help of DeMoivre's theorem known from the secular equations. The amplitudes of surface displacements, temperature change, concentration and the specific loss of energy are computed numerically. Rotation effect on the phase velocity, attenuation coefficient, amplitudes of surface wave propagation and specific loss of energy are presented graphically in order to illustrate and compare the analytically obtained results. Some special cases of frequency equation are also deduced from the present investigation.

16

Analysis of wave motion in transversely isotropic generalized thermoelastic diffusive plate

75%

Kumar R. , Kansal T.

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2009

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tom Vol. 50, no 1

17-40

EN

The present investigation deals with the propagation of plane harmonic thermoelastic diffusive waves in a homogeneous, transversely isotropic, thin elastic plate of finite width, in the context of generalized theory of thermoelastic diffusion. Lord and Shulman(L-S) theory, in which thermal and thermo-mechanical relaxation is governed by a time constant and diffusion relaxation is governed by other different time constant, is selected for the study. According to the characteristic equation, three quasi-longitudinal waves, namely: quasi-elastodiffusive(QED-mode), quasi-massdiffusive(QMD-mode) and quasi-thermodiffusive(QTD-mode), can propagate in addition to quasi-transverse waves(QSV-mode), and the purely quasi-transverse motion(QSH-mode), which is not affected by thermal and diffusion vibrations, gets decoupled from the rest of the motion of wave propagation. The secular equations corresponding to the symmetric and skew-symmetric modes of the plate are derived. The amplitudes of displacements, temperature change and concentration for symmetric and skew-symmetric modes of vibration of plate are computed numerically. Anisotropy and diffusion effects on the phase velocity, attenuation coefficient and amplitudes of wave propagation, are presented graphically in order to illustrate and compare the analytical results. Some special cases of frequency equation are also deduced from the present investigation.

17

Models for the high frequency response of active piezoelectric composite beams

75%

Braga A. M. B. , De Barros L. P. F. , Gama A. L.

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2000

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tom Vol. 5, no 1

47-61

EN

The problem addressed in this paper is that of modeling composite beams excited by distributed piezoelectric actuators. A model based on Reddy's layerwise laminate theory is proposed. Through comparisons with exact wave-dispersion analytical results, it is shown that the model may provide an accurate description of the active beam's response in the high-frequency (short-wavelength) range.

18

Viscoelastic changes in the blood and vascular wall in a pulsating circular flow

75%

Beraia M. , Todua F. , Khomeriki I.

Polish Journal of Medical Physics And Engineering

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2010

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tom 16

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nr 1

43-53

EN

Altered flow conditions, such as separation and recirculationg zones, low and oscillatory shear stress, play an important role in the development of arterial disease. Endothelial denudation by the blood flow is the first step in atherosclerosis. The description of blood flow in vivo is complicated due to the viscoelasticity of vessel walls. However, conventional researches of the effect of the blood vessel viscoelasticity on the blood pressure wave propagation using non-linear one-dimensional models do not take into account the viscoelasticity, despite it being importance in the analysis of pulse wave propagation in arteries.The purpose of this paper is to study the impact of the arterial pulse wave on the viscoelastic blood flow and initial factors of atherosclerosis.In 12 healthy men (25-39 years of age) peak velocity, mean velocity, mean flow and net flow in the aorta have been investigated by MR angiography.Initial velocity was registered after 43msec of the ECG-R wave, and it differed from zero at all sites of the aorta, although net flow was equal to zero. Womersley's number from the ascending to the thoracic aorta decreased from 12.5 ± 1.5 to 7.3 ± 1.2; flow modified from inertio-elastic to viscous. Pulse pressure wave move on artery walls fifteen or more times more rapidly than the blood flow. In the aortic arch in protodiastole blood flow separated into the opposite directed streams resulting in wave superposition with the high net flow. At the isthmus area separated waves interferences and reflects to anterograde direction.Pulse oscillation increases strain rate to the contiguous vessel wall flow layers. At the sites with the flow wave negative interference vessel pulse oscillation attenuates and at the boundary reflection flow wave can shift the vessel wall.

19

Fabric dependence of bone ultrasound

63%

Cowin S. C. , Cardoso L.

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tom Vol. 12, no. 2

3-23

EN

Current diagnosis of bone loss and osteoporosis is based on the measurement of the Bone Mineral Density (BMD) or the apparent mass density. Unfortunately, in most clinical ultrasound densitometers: 1) measurements are often performed in a single anatomical direction, 2) only the first wave arriving to the ultrasound probe is characterized, and 3) the analysis of bone status is based on empirical relationships between measurable quantities such as Speed of Sound (SOS) and Broadband Ultrasound Attenuation (BUA) and the density of the porous medium. However, the existence of a second wave in cancellous bone has been reported, which is an unequivocal signature of poroelastic media, as predicted by Biot’s poroelastic wave propagation theory. A fabric-dependent anisotropic poroelastic approach is empolyed as a theoretical framework to describe the microarchitectural-dependent relationship between measurable wave properties and the elastic constants of trabecular bone, and thus represents an alternative for bone quality assessment beyond BMD alone.

20

Numerical modeling of wave propagation and interaction in bars

63%

Jankowiak T. , Klepaczko J. , Łodygowski T.

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2006

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tom No. 7

187-199

EN

In the first part, the paper presents analytical solution of symmetric longitudinal impact of a semi-infinite circular bar. In the second part the Maple code is used in order to solve the differential equations, derived and solved by Skalak [1]. Based on this analytical solution, a verification is performed by Finite Element code. The calibration of parameters like the artificial viscosity and the mesh size is done. The initial FE calibration is used, together with cumulative fracture criterion, to verify the laboratory test results presented by Klepaczko [2,3,4,7]. The finite element solution is focused on the new experimental technique to test semi-brittle materials in dynamic tension via spalling. The technique which is based on Hopkinson pressure bar has been developed in LPMM-Metz [4].