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1
Content available remote Micro-vibrations and wave propagation in biperiodic cylindrical shells
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.
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.
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.
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.
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.
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.
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.
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.
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.
10
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.
PL
Przedstawiono metodę wyznaczania wybranych współczynników opisujących proces transportu wilgoci z wykorzystaniem pomiarów ultradźwiękowych ceramiki budowalnej. W tym celu zaproponowano model propagacji fali ultradźwiękowej i wykonano pomiary czasu propagacji podłużnej fali ultradźwiękowej.
EN
In the paper the method of determining the selected moisture transport coefficients using ultrasonic measurements was presented. For this purpose a model of the wave propagation was proposed and the ultrasonic measurements of time propagation of longitudinal wave were made.
PL
W artykule zaprezentowano sposoby wykorzystania rodzajów polaryzacji fali elektromagnetycznej w konstrukcjach mikrofalowych podzespołów ferrytowych. W nieograniczonym ośrodku ferrytowym namagnesowanym równolegle do kierunku propagacji fali EM, wyjaśniono zjawisko nieodwracalności ośrodka dla fal spolaryzowanych liniowo, kołowo i eliptycznie. Podobne zjawiska występują dla ośrodka ferrytowego namagnesowanego prostopadle do kierunku propagacji fali EM. Ograniczając się do podzespołów zawierających skończonych wymiarów kształtki ferrytowe umieszczone w falowodzie prostokątnym przykładowo pokazano sposób realizacji izolatorów ferrytowych i różnicowych przesuwników fazy.
EN
The papers presents ways to use types of polarization electromagnetic waves (EM) in the construction of microwave ferrite devices. The unlimited ferrite material magnetized parallel to the direction of EM wave propagation, explained the phenomenon of its nonreciprocal properties for different polarized waves: linearly, circular and elliptical. Similar phenomena occur for the unlimited ferrite material magnetized perpendicular to the direction of propagation of EM wave. Limited to components containing the finite dimensions of the shaped ferrite placed in a rectangular waveguide example shows how to implement ferrite isolators and differential phase shifters.
EN
Identification of geotechnical soil conditions often requires execution of laboratory tests, especially if you want to measure dynamic parameters of the soil. At present, the triaxial shear apparatus is widely applied in determination of the parameters of the soil. On the basis of the soil samples analysis, the examination results provide a wide range of data from basic performance parameters, e.g. internal friction angle and cohesion, to most complex ones like Young’s modulus permanent side effective stress of water samples. Furthermore, the Soil Structure Interaction Laboratory of Cracow University of Technology, has carried out the measurements of propagation of shear waves velocity with the use of bender elements tests. This work presents geotechnical conditions and the analysis of the results, which might be found useful to determine the transportation load parameters of designed S-7 and S-52 routes, as well as overall impact on soil/structure and surrounding areas located over the former clay open-pit mine. The landslides existing in the vicinity of the mine have prompted the authors to take that action.
PL
Rozpoznanie warunków geotechnicznych podłoża gruntowego wykonywanego w celu ustalenia parametrów dynamicznych podłoża często wymaga wykonania badań laboratoryjnych. Obecnie jednym z najbardziej popularnych sposobów określania parametrów gruntów jest użycie aparatu trójosiowego ściskania. Wynikami badania próbki gruntowej w aparacie trójosiowym mogą być oprócz podstawowych parametrów wytrzymałościowych czyli kąta tarcia wewnętrznego i spójności, parametry takie jak moduł odkształcenia liniowego przy stałym bocznym naprężeniu efektywnym w próbce w warunkach z odpływem, jak i bez odpływu wody z próbki. Dodatkowo w laboratorium Katedry Współdziałania Budowli z Podłożem Politechniki Krakowskiej, przeprowadzano badania określenia prędkości fali poprzecznej przy wykorzystaniu elementów bender. W pracy przedstawiono warunki geotechniczne, a następnie podsumowano wyniki badań, które w przyszłości posłużą autorom do określenia wpływu obciążeń komunikacyjnych trasy S-7 i S-52 na podłoże gruntowe terenu kopalni i ich okolic. Analiza ta wynika z występowania kilku osuwisk w bezpośredniej otoczeniu kopalni.
EN
The paper deals with numerical simulations of wave propagation in reinforced concrete for damage detection purposes. A novel formulation of a 3D spectral element was proposed. The reinforcement modelled as the truss spectral element was embedded in the 3D solid spectral finite element. Numerical simulations have been conducted on cuboid concrete specimens reinforced with two steel bars. Different degradation models were considered to study the real behaviour of bended beams.
EN
In this study, the wave fields induced by both tensile and shear displacement dislocations in stratified fluid-saturated porous media are computed by using the reflection and transmission matrix method. The components of the source discontinuity vector across the source plane to describe those tensile and shear faults are explicitly displayed by using the surface vector harmonics. Numerical examples for a two layer model subjected to tensile and shear dislocations are provided. From the waveforms of surface displacements, the arrivals of transmitted and converted PS and SP waves at the interface of the two layer model can be clearly observed.
EN
The propagation of thermoelastic waves in a homogeneous, isotropic elastic semi-infinite space is subjected to a gravitational field, which is at temperature T0 initially, and whose boundary surface is subjected to heat source and load moving with finite velocity. Temperature and stress distribution occurring due to heating or cooling and have been determined using certain boundary conditions. Numerical results have been given and illustrated graphically in each case considered. The results indicate that the effect of gravity field is very pronounced. Comparison is made with the results predicted by the theory of thermoelasticity in the absence of gravity. The results indicate that the effect of the gravity is very pronounced.
EN
The wave propagation characteristics of functionally graded (FG) double-beams are investigated by use of Euler-Bernoulli beam theory. Two beams are connected by a Winkler foundation. The wave propagation characteristics like frequency, phase and group velocities are obtained for different wave numbers and material properties. Four frequencies are obtained for functionally graded double-beam system. It is obtained that flexural and axial waves are coupled for FG double-beams.
18
Content available remote Ale fenomenalne w żegludze morskiej
PL
W pracy opisano proces planowania nawigacji w obszarach występowania fal fenomenalnych. Zdefiniowano fale fenomenalne, rejony i przyczyny ich powstawania. Przedstawiono kilka programów badawczych ukierunkowanych na propagację, występowanie i prognozowanie fal fenomenalnych. W zakończeniu wspomniano o konieczności wzmocnienia nowo budowanych kadłubów statków morskich z uwzględnieniem istnienia fal fenomenalnych.
EN
In this paper the passage process have been described in the areas where freak waves occur. The freak wave’s definition has been given and the evidence distributes and generation of the freak waves in different sea areas has shown. Some research programs focused on freak waves propagation occurrence and forecast have been presented. Finally some notes on the new ship design to increase the ship structure in the light of freak wave existence in shipping have been mentioned.
PL
W artykule przedstawiono wyniki analiz doświadczalnych propagacji fal sprężystych w modelu laboratoryjnym połączenia nakładkowego dwuteowego dźwigara blachownicowego. Badano możliwość wykrycia całkowitego poluzowania pojedynczych śrub i grup łączników. Przeanalizowano zmiany jakościowe zarejestrowanych sygnałów, ich wpływ na energię sygnału oraz współczynnik korelacji krzyżowej. Wykazano możliwość zastosowania fal sprężystych do wykrywania uszkodzenia i jego ewolucji.
EN
This article presents results of experimental analyses of elastic wave propagation in a laboratory model of the double-T plate girder splice connection. The possibility of detection of complete loosening of individual fasteners and their groups was examined. The qualitative changes of recorded signals, their influence on the signal energy and the cross-correlation coefficient were analysed. It has been shown, that the elastic waves can be effectively used for damage detection and its evolution.
EN
In this study, the elastic wave propagation phenomenon was used to detect the initiation of fatigue damage in a composite plate with a circular hole. The Structural Health Monitoring (SHM) system based on the active pitch-catch measurement technique was proposed. Two configurations of measuring points location were taken into account. The signals from the intact structure were compared with the dynamic response from a structure having a relatively small, interlaminar defect. The influence of the measuring points (actuators and sensors) location on the effectiveness of the damage detection method was performed to obtain an efficient system which can detect the initiation of fatigue damage in a composite plate with a circular hole.
PL
W pracy wykorzystano metodę propagacji fal sprężystych do wykrywania inicjacji uszkodzeń zmęczeniowych w kompozytowej płycie z otworem. Zaproponowano system SHM (Structural Health Monitoring) oparty na aktywnej, transmisyjno-odbiorczej technice pomiarowej. Uwzględniono dwie konfiguracje rozmieszczenia punktów pomiarowych. Sygnały pochodzące ze struktury wzorcowej porównano z dynamiczną odpowiedzią płyty zawierającej stosunkowo niewielki, międzywarstwowy defekt. Określono wpływ lokalizacji punktów pomiarowych (aktywatorów i sensorów) na skuteczność metody detekcji w celu uzyskania efektywnego systemu umożliwiającego wykrycie inicjacji uszkodzenia zmęczeniowego w kompozytowej płycie z otworem.
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