Flutter Phenomenon Research Articles

Computational Experiments to Evaluate the Approaches to the Modeling of Viscoelastic Plates Motion Based on Various Theories

Mathematical and computer modeling of the flutter of elements and units of the aircraft design is an actual scientific problem; its study is stimulated by the failure of aircraft elements, parts of space and jet engines. In view of the complexity of the flutter phenomenon of aircraft elements, simplifying assumptions are used in many studies. However, these assumptions, as a rule, turn out to be so restrictive that the mathematical model ceases to reflect the real conditions with sufficient accuracy. Therefore, results of theoretical and experimental studies are in bad agreement.At present, the problem of panel flutter is very relevant. Improvement of characteristics of military and civil aircraft inevitably requires reducing their weight, and consequently, the rigidity of paneling, which increases the possibility of a panel flutter. The concept of creating the aircraft with a variable shape, which would inevitably lead to a reduction in paneling thickness are actively discussed. Finally, the use of new materials and, in particular, composites, changes physical properties of the panels and can also lead to a flutter.The above-mentioned scientific problem gives grounds to assert that the development of adequate mathematical models, numerical methods and algorithms for solving nonlinear integral-differential equations of dynamic problems of the hereditary theory of viscoelasticity is actual.In connection with this, the development of mathematical models of individual elements of aircraft made of composite material is becoming very important.Generalized mathematical models of non-linear problems of the flutter of viscoelastic isotropic plates, streamlined by a supersonic gas flow, are constructed in the paper on the basis of integral models. To study oscillation processes in plates, a numerical algorithm is proposed for solving nonlinear integro-differential equations with singular kernels. Based on the developed computational algorithm, a package of applied programs is created. The effect of the singularity parameter in heredity kernels on the vibrations of structures with viscoelastic properties is numerically investigated. In a wide range of changes in plate parameters, critical flutter velocities are determined. Numerical solutions of the problem of viscoelastic plate flutter are compared for different models. It is shown that the most adequate theory for investigating a wide class of problems of the hereditary theory of viscoelasticity is the geometric nonlinear Kirchhoff-Love theory with consideration of elastic waves propagation. It is established that an account of viscoelastic properties of plate material leads to 40-60% decrease in the critical flutter velocity.

On Flutter Suppression in the Keldysh Model

Studying the phenomenon of flutter and developing the method of its suppression is an outstanding achievement of the famous Soviet scientist, President of the Academy of Sciences of the USSR M.V. Keldysh. In this report we apply modern research tools to the Keldysh model and compare the results obtained with their help with the results of М.V. Keldysh.

Aeroelastic Investigation of a Transonic Compressor Rotor with Multi-Row Effects

According to the modern turbomachinery design trend, blades are getting more and more flexible and loaded, and therefore prone to vibration issues due to forced response and flutter phenomena. For this reason, the flutter stability assessment has become a key aspect to avoid high cycle fatigue (HCF) blade failures. The aim of this paper is to numerically evaluate the influence of unsteady aerodynamic effects, due to upstream and downstream rows, on flutter predictions using an uncoupled method. Both CFD aeroelastic and modal analyses have been carried out for a one and half compressor stage in transonic conditions. Flutter results are reported for the classic single-row approach and then for the multi-row model which includes rotor/stator unsteady interactions: a good agreement with measured data is shown for both cases and also a no negligible impact of adjacent rows can be observed.

Suppression of Resonance Induced Vibration Because of Wind Load at Bridge Structure by Using Passive Damper

Wind load on flexible bridge structure has various structural effects. Catastrophic effect because of wind load which is called flutter phenomenon will make structural failure rapid. Resonance induced vibration is the other wind load phenomenon which not only includes catastrophic failure but has a long-term effect and discomfort effect because of the structural vibration. Vortex is a typical rotational flow in the wake of an obstacle. The flow fluctuates in such a pattern which is known as Von Karman Vortex trails. If the frequency of vortex fluctuation coincides with one of the flexible structure natural frequency, a resonance phenomenon occurs. The phenomenon is called Vortex Induced Vibration (VIV). Vortex induced vibration depends on the natural frequency of the structure, dynamic wind load, and geometry of the structure. VIV can make the bridge vibrate with large amplitude and it can make the structure failure, if the VIV phenomenon occurs in the long period and the structure cannot withstand the dynamic load. It is very important to reduce the vibration when the VIV occurs in the flexible bridge. This paper presents the use of the Tuned Mass Damper (TMD) to reduce vibration because of vortex induced vibration at a flexible bridge. By using wind tunnel test and finite element analysis, the research shows that passive TMD is effective to reduce the vibration at flexible bridge when the VIV occurs. The highest vibration reduction occurs when the frequency of TMD coincides with the frequency of force vibration.

Nuclear Norm-Based Recursive Subspace Identification for Wind Turbine Flutter Detection

Commercial wind turbine blades are progressively becoming longer and more flexible; in order to achieve load reduction, the use of shape modifying devices is currently under research. While such modifications facilitate cost reduction, they also render the blade susceptible to the unstable aeroelastic phenomenon of flutter. To be able to detect the onset of flutter, and to modify the load control algorithm accordingly, it is desirable to perform online identification of system dynamics. In this paper, a recursive subspace identification algorithm is augmented with a nuclear norm-based cost function for the rapid identification of changes in the dominant system behavior. The time-consuming singular value thresholding step involved in the identification is replaced by a fast randomized algorithm. The method developed is used to identify the changes in the dynamics of an experimental wind turbine equipped with shape-modifying actuators, and operated under controlled conditions in a wind tunnel. The proposed identification method shows high sensitivity to changes in system dynamics, and is shown capable of stably and rapidly identifying the onset of aeroelastic flutter.

Half Wing N219 Aircraft Model Clean Configuration for Flutter Test On Low Speed Wind Tunnel

Flutter is a rapid self-feeding motion which is caused by the interaction of aerodynamic, structural and inertial forces. Flutter can cause major damage on aircraft structure which can lead to fatal accident in aviation. Several methods have been evolved to avoid the flutter phenomena occur during the flight envelope of aircraft design. On this study, method was developed by Indonesian Aerospace which consist of Finite Element Method (FEM) analysis, Ground Vibration Test (GVT), and Wind Tunnel Flutter Test (WTT). Based on the study, FEM have similar results toward to Wind Tunnel Flutter Test conjunction the clean configuration of N219 aircraft half wing model.

Analysis of classical flutter in steam turbine blades using reduced order aeroelastic model

In the present paper classical flutter phenomena in LP steam turbine rotor is studied . A reduced order aeroelastic model (ROAM) with acceptable accuracy and fast execution is developed for this purpose. The aerodynamics damping (AD) is estimated using Traveling wave mode (TWM) method. Flow field is modeled using Panel method. For the structural part ROM non-linear beam element method (BEM) based FEM structural solver is used. Partitioned based ( loose) coupling approach is adopted to perform aeroelastic (flutter) cosimulation. Both 2D cascade flow and 3D cascade are modeled.The estimated stability parameters are compared with experimental data. Moreover, present ROAM shows significant reduction in computational time.

Speed control for permanent magnet synchronous motor based on an improved extended state observer

An improved extended state observer is designed to eliminate the influences of speed control for a permanent magnet synchronous motor. The improved extended state observer is designed based on a new nonlinear function. This function exhibits better continuity and derivability than previously available functions and can effectively reduce the high-frequency flutter phenomenon. The nonlinear dynamics, model uncertainty, and external disturbances of the permanent magnet synchronous motor speed control system are extended to a new state. The improved extended state observer is utilized to observe this state. The overtime variation of the permanent magnet synchronous motor speed control system can be predicted and compensated in real time by the improved extended state observer. Therefore, the improved extended state observer, which is designed based on the new nonlinear function, can eliminate the disturbances on the permanent magnet synchronous motor speed control system. Finally, simulation experiments are performed and results show that the permanent magnet synchronous motor speed control system with improved extended state observer exhibits better performances.

Methods for flutter stability analysis of long-span bridges: a review

Predicting the phenomenon of aerodynamic instability is essential for the analysis and design of long-span cable-supported bridges. This paper reviews the history and development of aerodynamic analysis techniques and state-of-the-art numerical and experimental methods for flutter stability analysis. A discussion of the flutter phenomenon is followed by a literature review. This study provides a perspective on self-excited aerodynamic force models, identification of aerodynamic derivatives and methods for determining aerodynamic instability of long-span bridges in two dimensions and three dimensions. Computational fluid dynamics (CFD) techniques for modelling the flow past bluff bodies are also covered. Different model combination techniques are presented, utilising analytical, numerical and experimental approaches to predict the flutter limit. The effect of different parameters on the flutter stability limit is also highlighted. Furthermore, an overview of the complementary relationship between wind tunnel testing and CFD is provided. Finally, this paper also describes the engineering solutions adopted as countermeasures to prevent flutter instabilities.

An efficient iterative model reduction method for aeroviscoelastic panel flutter analysis in the supersonic regime

Abstract The flutter boundary prediction of complex aeroelastic systems is not an easy task. In some cases, these analyses may become prohibitive due to the high computational cost and time associated with the large number of degrees of freedom of the aeroelastic models, particularly when the aeroelastic model incorporates a control strategy with the aim of suppressing the flutter phenomenon, such as the use of viscoelastic treatments. In this situation, the use of a model reduction method is essential. However, the construction of a modal reduction basis for aeroviscoelastic systems is still a challenge, owing to the inherent frequency- and temperature-dependent behavior of the viscoelastic materials. Thus, the main contribution intended for the present study is to propose an efficient and accurate iterative enriched Ritz basis to deal with aeroviscoelastic systems. The main features and capabilities of the proposed model reduction method are illustrated in the prediction of flutter boundary for a thin three-layer sandwich flat panel and a typical aeronautical stiffened panel, both under supersonic flow.

Mathematical Model in Studying the Stability of Dynamic Systems

In this paper, the author investigated the phenomenon of flutter, which may be the cause of instability of construction structure when it is affected by aerodynamics. By analyzing the effect of aerodynamic on the structure via mathematical analysis, the author has established a mathematical model to study the stability of the structure in the aerodynamic flux that moves supersonically.

Pitching axis control for a satellite camera based on a novel active disturbance rejection controller

The pitching axis of a satellite camera is controlled under the weightless environment. A novel active disturbance rejection controller is designed to eliminate the influences of the pitching axis. The novel active disturbance rejection controller is designed based on a new nonlinear function, and thus, this function is first established. The function exhibits better continuity and smoothness than previously available functions, hence, it can effectively improve the high-frequency flutter phenomenon. Therefore, the novel active disturbance rejection controller based on the new nonlinear function can eliminate disturbances of the pitching axis. The novel active disturbance rejection controller is composed of a tracking differentiator, a novel extended state observer, and a novel nonlinear state error feedback. The tracking differentiator is used to arrange the transient process. Nonlinear dynamics, model uncertainty, and external disturbances are extended to a new state. The novel extended state observer is utilized to observe this state. The overtime variation of the system can be predicted and compensated using the novel extended state observer. The novel nonlinear state error feedback is adopted to restrain the residual errors of the system. Finally, simulation experiments are performed, and results show that the novel active disturbance rejection controller exhibits better performance than the traditional active disturbance rejection controller.

Supersonic Panel Flutter Analysis Assuming Effects of Initial Structural Stresses

The work is devoted to study the stability of an elastic plate, in a supersonic gas flow. This problem arises in the study of the phenomenon of panel flutter, buckling and vibration intensity of airplane and missile thin-walled structures, excited by their interaction with the airflow at high-speed flight. Using Bubnov-Galerkin method and aerodynamic model by piston theory in supersonic fluid dynamics, effects of longitudinal and lateral stresses on the divergence speed and flutter characteristics of the panel has been analyzed by MATLAB coding. To this end, by finding the panel vibration natural frequencies and drawing the vibration graphs, divergence (flutter) speed has been determined and stress effects on this speed has been discussed.

Current-Loop Control for the Pitching Axis of Aerial Cameras via an Improved ADRC

An improved active disturbance rejection controller (ADRC) is designed to eliminate the influences of the current-loop for the pitching axis control system of an aerial camera. The improved ADRC is composed of a tracking differentiator (TD), an improved extended state observer (ESO), an improved nonlinear state error feedback (NLSEF), and a disturbance compensation device (DCD). The TD is used to arrange transient process. The improved ESO is utilized to observe the state extended by nonlinear dynamics, model uncertainty, and external disturbances. Overtime variation of the current-loop can be predicted by the improved ESO. The improved NLSEF is adopted to restrain the residual errors of the current-loop. The DCD is used to compensate the overtime variation of the current-loop in real time. The improved ADRC is designed based on a new nonlinear functionnewfal(·). This function exhibits enhanced continuity and smoothness compared to previously available nonlinear functions. Thus, the new nonlinear function can effectively decrease the high-frequency flutter phenomenon. The improved ADRC exhibits improved control performance, and disturbances of the current-loop can be eliminated by the improved ADRC. Finally, simulation experiments are performed. Results show that the improved ADRC displayed better performance than the proportional integral (PI) control strategy and traditional ADRC.

Nonlocal and surface effects on the flutter instability of cantilevered nanotubes conveying fluid subjected to follower forces

On the basis of nonlocal elasticity theory, this paper studies the dynamic structural instability behavior of cantilever nanotubes conveying fluid incorporating end concentrated follower force and distributed tangential load, resting on the visco-Pasternak substrate. In order to improve the accuracy of the results, surface effects, i.e. surface elasticity and residual stresses are considered. Extended Hamilton’s principle is implemented to obtain the nonlocal governing partial differential equation and related boundary conditions. Then, the extended Galerkin technique is used to convert partial differential equations into a general set of ordinary differential equations. Numerical results are expressed to reveal the variations of the critical flow velocity for flutter phenomenon of cantilever nanotubes with the various values of nonlocal parameter, mass ratios, nanotubes thickness, surface effects, various parameters of the visco-Pasternak medium, constant follower force and distributed compressive tangential load. Some numerical results of this research illustrated that the values of critical flutter flow velocity and stable region increase by considering surface effects. Also, critical flutter flow velocity decreases towards zero by increasing the value of the distributed compressive tangential load and constant follower force.

Flutter Phenomenon in Flow Driven Energy Harvester-A Unified Theoretical Model for "Stiff" and "Flexible" Materials.

Here, we report a stable and predictable aero-elastic motion in the flow-driven energy harvester, which is different from flapping and vortex-induced-vibration (VIV). A unified theoretical frame work that describes the flutter phenomenon observed in both “stiff” and “flexible” materials for flow driven energy harvester was presented in this work. We prove flutter in both types of materials is the results of the coupled effects of torsional and bending modes. Compared to “stiff” materials, which has a flow velocity-independent flutter frequency, flexible material presents a flutter frequency that almost linearly scales with the flow velocity. Specific to “flexible” materials, pre-stress modulates the frequency range in which flutter occurs. It is experimentally observed that a double-clamped “flexible” piezoelectric P(VDF-TrFE) thin belt, when driven into the flutter state, yields a 1,000 times increase in the output voltage compared to that of the non-fluttered state. At a fixed flow velocity, increase in pre-stress level of the P(VDF-TrFE) thin belt up-shifts the flutter frequency. In addition, this work allows the rational design of flexible piezoelectric devices, including flow-driven energy harvester, triboelectric energy harvester, and self-powered wireless flow speed sensor.

Vibration reduction of a woven composite fan blade by piezoelectric shunted devices

This study concerns the vibration reduction in the low frequency range of a composite fan blade of a turbojet engine with piezoelectric devices. The interest is to increase lifespan and avoid flutter phenomena by reducing the vibration amplitude. The solution considered in the work consists in using piezoelectric elements connected to a passive electric circuit usually called shunt. The use of woven composite materials for fan blades enables to plan on embedding piezoelectric materials, for instance in the form of patches inserted between the composite and the coating material. The work presented during this conference will illustrate the feasibility of a piezoelectric shunted device integrated in an industrial application that doesn't require electrical supply. For such a structure, it is shown that a purely passive resonant shunt can significantly reduce the level of vibration of the second bending mode and that a good correlation between experiments and simulations validates the best fitting finite element model.

Analysis of a Two-Dimensional Aeroelastic System Using the Differential Transform Method

This paper investigates the nonlinear responses of a typical two-dimensional airfoil with control surface freeplay and cubic pitch stiffness in an incompressible flow. The differential transform (DT) method is applied to the aeroelastic system. Due to the nature of this method, it is capable of providing analytical solutions in forms of Taylor series expansions in each subdomain between two adjacent sampling points. The results demonstrate that the DT method can successfully detect nonlinear aeroelastic responses such as limit cycle oscillations (LCOs), chaos, bifurcation, and flutter phenomenon. The accuracy and efficiency of this method are verified by comparing it with the RK (Henon) method. In addition to ordinary differential equations (ODEs), the DT method is also a powerful tool for directly solving integrodifferential equations. In this paper, the original aeroelastic system of integrodifferential equations is handled directly by the DT method. With no approximation or simplification imposed on the integral terms of aerodynamic function, the resulted solutions are closer to representing the real dynamical behavior.

A CFD analysis of controlled flutter phenomenon

A CFD analysis of controlled flutter phenomenon

Flutter Derivatives of the Kao-Pin Hsi Cable-Supported Bridge

Long-span cable-supported bridges, characterized with low natural frequencies and mechanical damping, are very sensitive to wind effects. Therefore, investigation of the aeroelastic behaviour of bridges is particularly important when designing these complex engineering structures. The focus is on evaluation of dimensionless aeroelastic coefficients, i.e. flutter derivatives, which are considered as indicators of the aeroelastic stability of bridges. A comprehensive experimental study on dynamic wind-induced behaviour of the Kao-Pin Hsi Bridge in Taiwan is carried out in the Climatic Wind Tunnel of the Centre of Excellence Telč (CET), Czech Republic. The bridge-deck section is tested at a multipurpose experimental setup originally developed in the CET. Flutter derivatives are obtained by the means of the free-vibration technique for the double-degree-of-freedom (DDOF) system. The results are compared to those of a thin flat plate with large width to height ratio, which previously proved to be stable with respect to the flutter phenomenon. While the torsional instability is observed for the Kao-Pin Hsi bridge-deck section, the flat plate proves to be aeroelastically stable.