Wyniki wyszukiwania - BazTech

1

Construction and dynamic identification of aeroelastic test models for flexible roofs

Rizzo Fabio, Sadhu Ayan, Abasi Ali, Pistol Aleksander, Flaga Łukasz, Venanzi Ilaria, Ubertini Filippo

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e16, 2023

EN

The aeroelastic wind tunnel testing of flexible roofs made of hyperbolic paraboloid cable nets is a challenging task for designers and researchers, with very limited documented experiences in the literature. The reduced-scale model construction and its dynamic identification are the main issues to address when approaching this problem, mainly because of (i) the very small mass of the roof, (ii) the strict aeroelastic criteria to satisfy and (iii) a large number of very closely spaced significant natural frequencies. To suggest an approach to follow to investigate the wind-structure interaction for this structural typology, this paper discusses the aeroelastic scaling, the aeroelastic model construction, the dynamic modal identification and the FEM predictive numerical modelling of hyperbolic paraboloid roofs (HPRs) with square, rectangular and circular plan shapes and two different curvatures. Modal identification is especially challenging due to the presence of several closely spaced modes and it is here tackled by different methods such as Welch’s method, random decrement technique (RDT), Empirical mode decomposition with a time-varying filter (TVF-EMD) and frequency domain decomposition method (FDD). The satisfying accuracy of the aeroelastic scaling has been verified by comparing the wind-induced vertical displacements of the prototypes against those of the experimental models. Furthermore, an extensive qualitative investigation of the natural mode shapes has been carried out revealing that test models reproduce most of the prototype modes.

2

Verifying of the finite element model of the bridge based on the vibration monitoring at differente stages of construction

Hernandez W., Viviescas A., Riveros-Jerez C. A.

Archives of Civil Engineering

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2020

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Vol. 66, nr 1

25--40

EN

This paper presents the results of a dynamic response evaluation of a segmental bridge during two construction stages: before connecting the final segment of the bridge and after connecting the final segment of the bridge but prior to opening the bridge to traffic. The vibration signals obtained from Ambient Vibration Testing (AVT) campaigns were processed in order to obtain the modal parameters of the bridge during the two construction stages. Modal parameters experimentally obtained for the first stage were compared with those obtained from Finite Element (FE) models considering different construction loads scenarios. Finally, modal parameters experimentally obtained for the second stage were used to update its corresponding FE model considering two scenarios, before and after the installation of the asphalt pavement. The results presented in this paper demonstrated that a rigorous construction control is needed in order to effectively calibrate FE models during the construction process of segmental bridges.

3

Study on applicability of two modal identification techniques in irrelevant cases

Tomaszewska A., Szafrański M.

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 1

168--178

EN

Study on applicability of two modal identification techniques in irrelevant cases is made in this paper. The following techniques are considered: peak picking based on correlation analysis (PP-CA), dedicated for ambient vibrations and eigensystem realization algorithm (ERA), formulated for free-decay vibrations investigation. Irrelevant cases are found when analyzed signals are different than recommended to a given technique. The study is conducted on examples of two real structures: masonry tower and steel railway bridge. Both cases are diverse in age, material, excitation and vibrations energy. The signals measured on the tower are suitable for the PP-CA technique (ambient vibrations), while the signals measured on the bridge are suitable for the ERA (free-decay vibrations). However, both methods have been applied to both systems. Natural frequencies, mode shapes and damping ratios are identified and the effectiveness of the irrelevant technique is assessed in relation to the results obtained by the relevant method in each case.

4

Dynamic analysis of the railway bridge span under moving loads

Szafrański M.

Roads and Bridges - Drogi i Mosty

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2018

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Vol. 17, no. 4

299--316

EN

The first part of the paper provides a review of the state of knowledge of the dynamic behaviour of railway bridges under moving loads. Particular attention is paid to developments in modelling railway bridge loading and dynamic vehicle-span (structure) interaction. The most important aspects determining the advancements in this area of knowledge are identified. The contemporary techniques for defining bridge span finite element models used in dynamic analyses are also discussed. The second, practical part of the paper presents the results of numerical simulations of the passage of load along the bridge structure. The railway loads are represented by a series of concentrated forces and a series of single-mass oscillators. Vibration of the bridge span centre and the vehicle mass depending on the speed of travel are considered. The loading parameters are adopted to represent a real railway vehicle - EN57 electrical multiple unit. The structure’s parameters were adopted on the basis of a 30 m long load-relieving span. In both cases modal identification techniques were used to obtain all the required dynamic parameters of the span under analysis on the basis of experimental data.

PL

W pierwszej części artykułu dokonano przeglądu obecnego stanu wiedzy z zakresu dynamiki mostów kolejowych pod obciążeniem ruchomym. Szczególną uwagę poświęcono rozwojowi modeli obciążeń kolejowych oraz modelom interakcji dynamicznej przęsło-pojazd. Zwrócono uwagę na najważniejsze aspekty determinujące rozwój tej dziedziny wiedzy. Przeprowadzono dyskusję współczesnych sposobów definiowania modeli MES przęseł mostowych wykorzystywanych w analizach dynamicznych. W drugiej, praktycznej części pracy, przedstawiono wyniki symulacji numerycznych przejazdu obciążenia po konstrukcji mostu. Obciążenie kolejowe odwzorowano w postaci strumienia sił skupionych oraz strumienia oscylatorów jedno- masowych. Rozważono drgania środka przęsła mostowego oraz masy pojazdu w zależności od prędkości ruchu. Parametry obciążenia przyjęto na podstawie rzeczywistego pojazdu szynowego - jednostki trakcyjnej serii EN57. Parametry konstrukcji przyjęto na podstawie mostowego przęsła odciążającego o rozpiętości 30 m. W obu przypadkach wszystkie potrzebne parametry dynamiczne przęsła uzyskano na podstawie badań wykorzystując techniki identyfikacji modalnej.

5

Modal identification of dynamic properties of the cylindrical grinder

Pawłowski W., Kępczak N.

Mechanics and Mechanical Engineering

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2017

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Vol. 21, nr 1

147--156

EN

In the paper the method of model identification of the cylindrical grinder dynamic properties by means of experimental modal test was described. The method application, hardware solution as well as the procedure of carrying out the identification modal test of the cylindrical grinder was presented. The experiment was performed in order to acquire the frequency response function (FRF) of the cylindrical grinder. Having obtained the experimental FRF, the mathematical model of the response function was created. That mathematical model of the machine tool dynamic behavior can be applied in grinder and grinding holistic model. The conclusions regarding the application aspects of experimental modal analysis in order to identify dynamic properties of the machine tool were drawn.

6

Modal measurements and model corrections of a large stroke compliant mechanism

Wijma W, Boer S. E, Aarts R. G. K. M, Brouwer D. M, Hakvoort W. B. J

Archive of Mechanical Engineering

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2014

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Vol. LXI, nr 2

347--366

EN

In modelling flexure based mechanisms, generally flexures are modelled perfectly aligned and nominal values are assumed for the dimensions. To test the validity of these assumptions for a two Degrees Of Freedom (DOF) large stroke compliant mechanism, eigenfrequency and mode shape measurements are compared to results obtained with a flexible multibody model. The mechanism consists of eleven cross flexures and seven interconnecting bodies. From the measurements 30% lower eigenfrequencies are observed than those obtained with the model. With a simplified model, it is demonstrated that these differences can be attributed to wrongly assumed leaf spring thickness and misalignment of the leaf springs in the cross flexures. These manufacturing tolerances thus significantly affect the behaviour of the two DOF mechanism, even though it was designed using the exact constraint design principle. This design principle avoids overconstraints to limit internal stresses due to manufacturing tolerances, yet this paper shows clearly that manufacturing imperfections can still result in significantly different dynamic behaviour.

PL

W modelowaniu mechanizmów opartych na ugięciach na ogół zakłada się, że ugięcia są doskonale wyrównane liniowo i przyjmuje nominalne wartości wymiarów. By sprawdzić zasadność tych założeń dla podatnego mechanizmu o długim suwie i dwu stopniach swobody porównano wyniki pomiarów wartości własnych i kształtu modów z wynikami otrzymanymi na podstawie sprężystego modelu wielu ciał. W mechanizmie występuje jedenaście poprzecznych elementów giętych i siedem wzajemnie powiązanych ciał. Wartości własne wyznaczone pomiarowo były o 30% mniejsze od obliczonych na podstawie modelu. Można wykazać, że w uproszczonym modelu różnice te należy przypisać wadliwie przyjętej grubości sprężyny płytkowej i złemu wyrównaniu sprężyn w poprzecznych elementach sprężystych. Jak stąd wynika, tolerancje wykonania silnie wpływają na zachowanie mechanizmu o dwu stopniach swobody, mimo że był on zaprojektowany przy zachowaniu zasady ścisłych więzów. Taką zasadę projektowania stosuje się, by zapobiec tworzeniu więzów nadmiarowych i ograniczyć naprężenia wewnętrzne powstałe w wyniku niedokładności wykonania. Niemniej, w artykule pokazano wyraźnie, że niedokładności wykonania mogą wciąż powodować istotne zmiany we właściwościach dynamicznych mechanizmu.