Wyniki wyszukiwania - BazTech

1

Assessment of the role of structural nonlinearity in galloping energy harvesters

Sarbinowski Filip, Starosta Roman

Vibrations in Physical Systems

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2021

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Vol. 32, nr 2

art. no. 2021209

EN

The study compares different variants of aeroelastic energy harvesters due to the power they generate. For this purpose, models of devices with different stiffness characteristics were prepared: linear, nonlinear, with combined stiffness and bistable. Then, using the authorial procedure, analytical expressions that describe the power of each system were determined and the influence of individual parameters on this quantity was examined. By way of optimization, the system parameters have been selected in such a way that, regardless of the flow velocity, each of them generates the maximum possible power. Based on the results obtained in this way, the advisability of using a device with combined stiffness and bistable characteristics was rejected. Moreover, it was pointed out that the linear system would provide greater efficiency for lower flow velocities.

2

Limit cycle oscillation prediction based on Finite Element-Modal approach

Ahmad K., Wu Z., Rahman H.

Archive of Mechanical Engineering

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2018

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Vol. LXV, nr 4

497--514

EN

The central theme of this work was to analyze high aspect ratio structure having structural nonlinearity in low subsonic flow and to model nonlinear stiffness by finite element-modal approach. Total stiffness of high aspect ratio wing can be decomposed to linear and nonlinear stiffnesses. Linear stiffness is modeled by its eigenvalues and eigenvectors, while nonlinear stiffness is calculated by the method of combined Finite Element-Modal approach. The nonlinear modal stiffness is calculated by defining nonlinear static load cases first. The nonlinear stiffness in the present work is modeled in two ways, i.e., based on bending modes only and based on bending and torsion modes both. Doublet lattice method (DLM) is used for dynamic analysis which accounts for the dependency of aerodynamic forces and moments on the frequency content of dynamic motion. Minimum state rational fraction approximation (RFA) of the aerodynamic influence coefficient (AIC) matrix is used to formulate full aeroelastic state-space time domain equation. Time domain dynamics analyses show that structure behavior becomes exponentially growing at speed above the flutter speed when linear stiffness is considered, however, Limit Cycle Oscillations (LCO) is observed when linear stiffness along with nonlinear stiffness, modeled by FE-Modal approach is considered. The amplitude of LCO increases with the increase in the speed. This method is based on cantilevered configuration. Nonlinear static tests are generated while wing root chord is fixed in all degrees of freedom and it needs modification if one requires considering full aircraft. It uses dedicated commercial finite element package in conjunction with commercial aeroelastic package making the method very attractive for quick nonlinear aeroelastic analysis. It is the extension of M.Y. Harmin and J.E. Cooper method in which they used the same equations of motion and modeled geometrical nonlinearity in bending modes only. In the current work, geometrical nonlinearities in bending and in torsion modes have been considered.

3

Numerical approach in aeroelasticity

Sloboda O., Korba P., Hovanec M., Pila J.

Zeszyty Naukowe. Transport / Politechnika Śląska

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2016

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z. 93

115--122

EN

Aircraft wing design processes should comprise specific analyses oriented towards aeroelasticity, which is one of the essential factors determining flight envelope boundaries. For such cases, static or dynamic aeroelastic phenomena can be simulated using CFD simulation software. ANSYS software offers the fluid structure interaction (FSI) method for solving this multiphysics problem.

4

Flutter analysis of IV standard configuration cascades, direct integration method

Rządkowski R., Kubitz L.

Mechanics and Mechanical Engineering

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2011

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Vol. 15, nr 3

333-341

EN

A three-dimensional nonlinear time-marching method and numerical analysis for aeroelastic behaviour of oscillating blade row has been presented. The approach is based on the solution of the coupled fluid-structure problem in which the aerodynamic and structural equations are integrated simultaneously in time. Thus providing the correct formulation of a coupled problem, as the interblade phase angle at which a stability (or instability) would occur, is a part of the solution.

5

Entomopter maneuverability exchanged by deformations control of flexible flapping wings

Kowalczyk G., Lewitowicz J., Sibilski K.

Journal of KONBiN

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2008

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No. 5 (8)

93-102

EN

In the background of preparing this paper lies our believe that transferring ideas from the more matured disciple like aircraft technology to emerging animal technology should be beneficial for the later one and vice-versa. One integrated idea, of special interest to both disciplines, is the active flexible wing concept. In this paper we developed aeroelastic analysis for a flexible wing for an imposed harmonic flapping motion about the root chord of the wing. A Matlab code was written based on the analysis. This code was used to find the average lift and thrust of a wing of known aerodynamic and structural properties.

PL

Podstawą podjęcia tej pracy było nasze przekonanie o celowości przeniesienia idei bionicznych do zasad budowy miniaturowych statków powietrznych. Jedną z takich idei jest koncepcja aktywnie odkształcalnych skrzydeł. Na wstępie przedstawiliśmy aeroelastyczne analizy odkształcalnych skrzydeł wykonujących wymuszone ruchy harmoniczne względem cięciwy znajdującej się u ich nasady. Na podstawie tych analiz opracowaliśmy pakiet programów w środowisku Matlab. Następnie pakiet ten zastosowaliśmy do obliczeń średniej wartości siły nośnej i siły ciągu odkształcalnego skrzydła.

6

Stability derivatives cast in the frame of subsonic unsteady aerodynamics

Nowak M.

Engineering Transactions

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1998

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Vol. 46, iss. 1

45-72

EN

On the basis of numerical results and theoretical considerations, a general from of the (unsteady) linear, discretized aerodynamic operator in the Laplace- and in the time-domain, for two- and three-dimensional subsonic flow is proposed. It corresponds to the classical Theodorsen solution for an airfoil in incompressible flow. The model of aerodynamic derivatives uses a polynomial approximation to the transfer functions. There are identified terms, which are neglected in this approach: these are the deficiency function and, in the case of compressible fluid, also the term responsible for the initial pulse. These results clears the limitations and possible improvements of the aerodynamic derivatives model.