Three-dimensional nonlinear flutter analysis of long-span suspension bridges during erection

In this work, the aerodynamic stability of the Yichang Suspension Bridge over Yangtze River during erection was determined by three dimensional nonlinear flutter analysis, in which the nonlinearities of structural dynamic characteristics and aeroelastic forces caused by large deformation are fully considered. An interesting result obtained was that the bridge was more stable when the stiffening girders were erected in a non symmetrical manner as opposed to the traditional symmetrical erection schedule. It was also found that the severe decrease in the aerodynamic stability was due to the nonlinear effects. Therefore, the nonlinear factors should be considered accurately in aerodynamic stability analysis of long span suspension bridges during erection.

Structural design and modal behaviors analysis of a new swept baffled inflatable wing

Inflatable wing has significant application value in the design of loitering munitions because of its advantages such as lightweight and foldability.However,due to the flexible characteristics,aeroelastic behaviors of inflatable wings such as flutter are nonnegligible in flight.By designing a certain angle between the inflatable beam and the wing span,the structural dynamic and even the aeroelastic performance of the inflatable wing can be effectively improved.Based on the analysis of the mechanical and geometric characteristics of the inflatable structure,a new inflatable wing with sweep arranged inflatable beams is proposed,and the main design variables and methods are analyzed.For purpose of investigating the aeroelastic performance of the swept baffled inflatable wing,the modal behaviors by considering the wet mode are studied.In consideration of the deficiencies of the traditional wet modal analysis method,by introducing the influence on the additional stiffness of flow field,an added massstiffness method is proposed in this paper,and the advantages are verified by ground vibration experiments.On this basis,the effects of baffles sweep angle,pressure,and boundary conditions on the modal parameters and aeroelastic performance of inflatable wing are analyzed.The results show that the aeroelastic performance of the inflatable wing can be designed by changing the baffles sweep angle,which is enlightened for the aeroelastic tailoring design on inflatable wings.

Flutter Analysis of Aircraft Wing Using Equivalent-Plate Models with Orthogonal Polynomials

A method of equivalent simplification,using equivalent-plate models(EPMs),is developed.It is to achieve goals of rapid modeling and effective analysis in structural dynamics and flutter analysis of complex wing structures.It is on the assumption that the wing structures discussed are composed of skin,beams and ribs,and the different plate units(such as skin,beam web,rib web)are not distinguished in modeling,which is to avoid the complex pre-processing and make it more generalized.Taking the effect of transverse shear deformation into consideration,the equivalence is based on the first-order shear deformation theory,and it can import the model files of MSC/NASTRAN and process the information to accomplish the equivalent modeling.The Ritz method is applied with the Legendre polynomials,which is used to define the geometry,structure and displacements of the wing.Particularly,the selection of Legendre polynomials as trial functions brings good accuracy to the modeling and can avoid the ill-conditions.This is in contrast to the EPM method based on the classical plate theory.Through vibration and flutter analysis,the results obtained by using EPM agree well with those obtained by the finite element method,which indicates the accuracy and effectiveness in vibration and flutter analysis of the EPM method.

Robust flutter analysis based on genetic algorithm

Robust flutter analysis considering model uncertain parameters is very important in theory and engineering applications.Modern robust flutter solution based on structured singular value subject to real parametric uncertainties may become difficult because the discontinuity and increasing complexity in real mu analysis.It is crucial to solve the worst-case flutter speed accurately and efficiently for real parametric uncertainties.In this paper,robust flutter analysis is formulated as a nonlinear programming problem.With proper nonlinear programming technique and classical flutter analysis method,the worst-case parametric perturbations and the robust flutter solution will be captured by optimization approach.In the derived nonlinear programming problem,the parametric uncertainties are taken as design variables bounded with perturbed intervals,while the flutter speed is selected as the objective function.This model is optimized by the genetic algorithm with promising global optimum performance.The present approach avoids calculating purely real mu and makes robust flutter analysis a plain job.It is illustrated by a special test case that the robust flutter results coincide well with the exhaustive method.It is also demonstrated that the present method can solve the match-point robust flutter solution under constant Mach number accurately and efficiently.This method is implemented in problem with more uncertain parameters and asymmetric perturbation interval.