Aerodynamic Damping Effects Research Articles

Structures Subjected to Low-Level Blast Loads: Analysis of Aerodynamic Damping and Fluid-Structure Interaction

This paper presents the structural behavior of idealized linear single-degree-of-freedom systems subjected to weak blast loads. The authors derive a new coupling model taking into account fluid-structure interaction (FSI) and aerodynamic damping resulting from the surrounding air. This model contributes to a better understanding of the physical coupling phenomena and can be used for the validation of more complex numerical models. Especially mass and stiffness determine the effects of aerodynamic damping and FSI on the deformations, internal forces, and energy contributions. Although the coupling effects are negligible for stiff or heavy systems (e.g., reinforced concrete structures), they significantly influence the structural response of flexible and light systems (e.g., membrane structures or glazing facades). On the basis of the new coupling model, the authors derive a decoupled model incorporating aerodynamic damping and FSI effects. This decoupled model is derived on the basis of an equivalent viscous damping ratio depending on mass and structural stiffness. Finally, a response spectrum is derived, synthesizing the discussed results.

Analytical modeling of sound transmission across finite aeroelastic panels in convected fluids

An analytical approach is formulated to account for the effects of mean flow on sound transmission across a simply supported rectangular aeroelastic panel. The application of the convected wave equation and the displacement continuity condition at the fluid-panel interfaces ensures the exact handling of the complex aeroelastic coupling between panel vibration and fluid disturbances. To explore the mean flow effects on sound transmission, three different cases (i.e., mean flow on incident side only, on radiating side only, and on both sides) are separately considered in terms of refraction angular relations and sound transmission loss (STL) plots. Obtained results show that the influence of the incident side mean flow upon sound penetration is significantly different from that of the transmitted side mean flow. The contour plot of refraction angle versus incident angle for the case when the mean flow is on the transmitted side is just a reverse of that when the mean flow is on the incident side. The aerodynamic damping effects on the transmission of sound are well captured by plotting the STL as a function of frequency for varying Mach numbers. However, as the Mach number is increased, the coincidence dip frequency increases when the flow is on the incident side but remains unchanged when in the flow is on the radiating side. In the most general case when the fluids on both sides of the panel are convecting, the refraction angular relations are significantly different from those when the fluid on one side of the panel is moving and that on the other side is at rest.

Resonant Response of Mistuned Bladed Disks Including Aerodynamic Damping Effects

A mathematical model is developed to investigate the effects of aerodynamic damping on the maximum amplification factor of mistuned bladed disks. LINSUB, an inviscid linearized unsteady aerodynamic damping code, provides aerodynamic damping influence coefficients that are incorporated into a partial-mistuning model that takes advantage of mode localization. This mistuning analysis is then used to demonstrate the effects of aerodynamic damping on the maximum amplification factor of mistuned bladed disks. The relative importance of aerodynamic effects is determined by a comparison of aerodynamic damping and structural damping factors. It is shown that neglecting unsteady aerodynamics may result in the predicted optimal mistuning pattern not being optimum in the actual operating environment wherein unsteady aerodynamic effects are present.

Resonant Response of Mistuned Bladed Disks Including Aerodynamic Damping Effects

Resonant Response of Mistuned Bladed Disks Including Aerodynamic Damping Effects

Effects of hysteretic and aerodynamic damping on supersonic panel flutter of composite plates

The governing equation for the finite element analysis of the panel flutter of composite plates including structural damping is derived from Hamilton's principle. The first order shear deformable plate theory has been applied to structural modelling so as to obtain the finite element eigenvalue equation. The unsteady aerodynamic load in a supersonic flow is computed by using the linear piston theory. The critical dynamic pressures for composite plates have been calculated to investigate the effects of structural damping on flutter boundaries. The effects are dependent on fiber orientation because flutter mode can be weak or strong in the fiber orientation of composite plates. Structural damping plays an important role in flutter stability with low aerodynamic damping but would not affect the flutter boundary with high aerodynamic damping.

Flow Angle, Temperature, and Aerodynamic Damping on Supersonic Panel Flutter Stability Boundary

The effects of flow yaw angle, temperature, and aerodynamic damping on supersonic flutter of plates are investigated. Quasisteady, first-order piston theory is employed for formulation of aerodynamic forces. The von Karman large-deflection plate theory is adapted for the aerothermal deflection. Two types of thermal effects are considered: 1) plate expansion by uniform temperature and 2) thermal moment induced by temperature gradient across the plate thickness. A finite element modal formulation and a two-step procedure are presented for the predictions of stability boundaries and nonlinear aerothermal deflection and shown to be efficient in solution. Results have shown that flow angle has lesser effect on stability boundaries as compared with temperature for isotropic square plates. However, both flow angle and temperature have a large influence on stability boundaries for rectangular isotropic and laminated composite plates. The presence of the ripple characteristics of stability boundaries for composite plates caused by the frequency coalescence of higher modes and the smaller effect of aerodynamic damping is investigated. The stabilization effects on panel motions induced by variations of flow angle, temperature, and aerodynamic damping are discussed.

Coupled-mode buffeting and flutter analysis of bridges

A numerical method for determining aeroelastic stability and buffeting characteristics of long-span bridges is presented. The method originates from the normal-mode method of structural dynamics, spectral density approach of random vibration theory and flutter derivatives presentation of self-excited aerodynamic forces. Advantages include modal cross-correlation effects due to self-excited aerodynamic forces into the analysis (yielding the method applicable to analysis of classical flutter), from non-iterative method on detection of flutter frequency and flutter velocity, and from ability to include aerodynamic damping effects of secondary structures (e.g. cables and pylons) to the response. The result of the present study is a computer code suited for parametric studies of wind-induced vibrations of long-span bridges and other dimensionally large structures.

Inviscid Rotordynamic Damping Forces due to Nonaxisymmetric Tip Clearance in Turbines

An actuator disk analysis is used to examine dynamic characteristics of destabilizing tip clearance excitation forces that arise in turbines with a whirling rotor. The slope of the cross force vs whirling frequency indicates the amount of direct damping that, together with the cross stiffness, determines rotordynamic stability. Thus, damping characteristics are extracted from the dependence of lateral forces on the whirling velocity. The analysis results reveal an inviscid aerodynamic direct damping effect. Furthermore, the damping effect is seen to be entirely due to the azimuthal pressure asymmetry or azimuthal flow redistribution. In addition, this study explores the sensitivity of such ideal damping effects to turbine design parameters such as flow coefficient and axial blade gap

Nonlinear flutter of two-dimensional simply supported symmetric composite laminated plates

The nonlinear flutter behavior of a two-dimensional simply supported symmetric composite laminated plate at high supersonic Mach number has been investigated. Yon Karman's large deflection plate theory and quasisteady aerodynamic theory have been employed. Galerkin's method has been used to reduce the governing equations to a system of nonlinear ordinary differential equations in time, which are then solved by a direct numerical integration method. Nonlinear flutter results are presented with the effects of aerodynamic damping, in-plane force, static pressure differential, and anisotropic properties. Results show that the anisotropic properties such as fiber orientation and elastic modulus ratio have significant effects on the behavior of both limit cycle oscillation and chaotic motion.

Aerodynamic damping effects of tall building for a vortex induced vibration

The influences which are induced upon the wind-induced response of the plane shape of a super high-rise building with an assumed height of 600m, as well as the dynamic effects of the vibration were studied. For this study, results obtained from the measurements of the wind force using a force balance, the response using a dynamic motion model, and the wind pressure of the face were used. From the result obtained from the response analysis made through the use of the measured result of the aerodynamic force and the result gained from the measurement of the response using the dynamic model, the change of the response, caused by a difference in the shape of a building and by the dynamic effect, have been clarified. Furthermore, as for the square shape which is a representative plane, the change of the pressure properties induced by the vibration of the building has been indicated.

Aerodynamic damping effects of tall building for a vortex induced vibration

The influences which are induced upon the wind-induced response of the plane shape of a super high-rise building with an assumed height of 600m, as well as the dynamic effects of the vibration were studied. For this study, results obtained from the measurements of the wind force using a force balance, the response using a dynamic motion model, and the wind pressure of the face were used. From the result obtained from the response analysis made through the use of the measured result of the aerodynamic force and the result gained from the measurement of the response using the dynamic model, the change of the response, caused by a difference in the shape of a building and by the dynamic effect, have been clarified. Furthermore, as for the square shape which is a representative plane, the change of the pressure properties induced by the vibration of the building has been indicated.

Flutter analysis of anisotropic panels with patched cracks

A finite element approach is developed to analyze the panel flutter problems of thin plate-like composite panels with patched cracks. The panel studied is a compound structure that comprises three layers including a thin cracked panel, an adhesive, and a thin patch. A 48-degree-of-f reedom (DOF) triangular crack patching element is derived for numerically analyzing the compound structure. The aerodynamic pressure acting on the panel is estimated using linearized piston theory with aerodynamic damping effect neglected. By a proper tailoring of the materials, very high flutter and/or divergence boundary could usually be obtained for the composite panels. The existence of a crack usually reduces the aeroelastic stability boundary; however, some exceptions were found for the composite panel within certain range of specific filament orientation. The deterioration in flutter/divergence performance due to a crack can, in general, be cured by means of patching, and anisotropic patching is more effective as compared to the isotropic patching provided that the tailoring of the structural parameters is done correctly. I. Introduction A RELIABLE and accurate flutter analysis is of primary importance in the flight vehicle design. The onset of flutter would quickly develop into either catastrophic structural failure or undesirable limit cycle type oscillation. The local panel flutter of the vehicle could be essential for a global flutter to occur. For instance, the initiation of cracks in wing structure is not unusual as they may be produced by either molding, fatigue, or impact damage.1'2 These defects could induce extremely high stresses around the cracktip regions and, thus, precipitate structural failure. When cracks are present, this local structural problem may have significant influence on the local flutter/divergence of the panel structure. The onset of the local aeroelastic instability may cause the failure of the cracked panel and cumulatively affect the global structure as well as the airload distribution and finally result in

Panel flutter analysis using high precision shear flexible element

A finite element formulation with use of a two-noded shear flexible element with four degrees of freedom oer node is adopted to study the effects of shear deformation and rotary inertia on two-dimensional panel flutter. Exact integration is carried out for all the terms in the element matrix for both thick and thin configurations of the panel. The present study shows good agreement with the previous work for thin panels for all boundary conditions as a result of using the high precision finite element. Shear deformation and rotary inertia effects on the critical dynamic pressure, the effect of aerodynamic damping on the critical dynamic pressure, and the change in flutter mode shapes due to the increase in thickness value of the panel and its end conditions are presented in the form of graphs.

Aerodynamic shape effects of tall building for vortex induced vibration

The effects of building plan shape on aerodynamic forces and displacement response have been studied for super high-rise building with an assumed height of 600 m in a wind tunnel. Experiments have been carried out using rigid models with eight kinds of building plan shapes of equal area ( = 6400 m 2) , equal building height ( = 600 m ), and equal density ( = 125 kg/m 3 ). The measurement model force had been combined analytically with a computer model of the building to provide estimates of the actual building response. The dynamic response behavior of a super high-rise building under strong wind due to vortex shedding and the aerodynamic damping effect of vibration by changing the cross section of building were clarified from these results.

Nonlinear flutter of composite laminated plates

The nonlinear flutter behavior of a two-dimensional simply supported composite laminated plate at high supersonic Mach number has been investigated. Von Karman's large deflection plate theory and qusai-steady aerodynamic theory have been employed. Galerkin's method has been used to reduce the governing equations to a system of nonlinear ordinary differential equations in time which are then solved by a direct numerical integration method. Nonlinear flutter results are presented with the effects of aerodynamic damping, in-plane force, static pressure differential, and anisotropic preperties. Results show that the anisotropic properties such as fiber orientation and elastic modulus ratio have significant effects on the behavior of both limit cycle oscillation and chaotic motion.

Flutter analysis of composite panels using high-precision finite elements

A high-precision 18-degree-of-freedom triangular thin plate finite element procedure is presented for studying the panel flutter of composite thin plates. Classical lamination theory, together with linearized piston theory, is used to study the effects of aerodynamic damping, boundary constraint, flow orientation, composite filament angle, and orthotropic modulus ratio on the flutter characteristics of both isotropic and composite panels. The numerical results indicate that aerodynamic damping, which enlarges the flutter boundary, is generally beneficial. The panels with stronger structural boundary constraint possess a better capacity to resist flutter instability. Alignment of the composite filament and flow orientations results in the best flutter performance for both fully simply supported and fully clamped panels, whereas alternative flutter-divergence type instability, which is not observed in the isotropic cases, takes place as the composite filament angle varies in the cases of cantilevered panels. The orthotropic modulus ratio is shown to be very effective in enlarging the flutter boundary; however, a reverse trend may occur if the instability type is changed from flutter to divergence. Substantial improvement or even complete avoidance of flutter can be attained if the composite panel is properly tailored.

Wind-excited ovalling vibration of a thin circular cylindrical shell

Vibration characteristics and growth mechanisms of wind-excited ovalling vibration of thin circular cylindrical shells which have dimensions like silos were investigated by using model shells made of polyester film in a wind tunnel. In the experiments wind pressure characteristics acting on the shell, static and dynamic responses of the shell and the effect of additional air force induced by the vibration of the shell were measured. The approaching flow used was uniform, with a turbulence intensity of only about 0·8%. In addition four kinds of turbulent flows were used in some experiments. The results obtained from this study suggest than the ovalling vibration of these kinds of shell is excited by an aerodynamic negative damping effect when the turbulence intensity of the approaching flow is small. The ovalling vibration occurred at velocities far lower than that for which the vortex shedding frequency would coincide with a natural frequency of vibration of the shell. The relationship between the inertia force of the shell and the mean lateral force acting on the shell at the onset of ovalling vibration is discussed.

Effects of mechanical and aerodynamic damping on the galloping of overhead lines

This paper examines theoretically the effects that mechanical and aerodynamic (drag) dampers can have on the amplitudes of the bulk galloping oscillations of overhead lines. The oscillation amplitudes are calculated using an energy-balance method and the results are presented in a way that allows the two types of damper to be compared. It is shown that, for lines with small vertical phase spacings, mechanical dampers should be more effective in reducing oscillation amplitudes. For lines with larger vertical phase spacings, aerodynamic dampers should be better, provided that a sufficiently large fraction of the span length can be fitted with dampers.

板翼の超音速フラッター速度の一計算法

A method to calculate the supersonic bendingtorsion flutter speed of cantilever plate wings of low aspect ratio is presented. The deflection mode is assumed in a double power series expansion of spanwise and chordwise variables, and the flutter determinant is derived with the aid of the principle of minimum potential energy of the dynamic problem. The chordwise variable is measured from the midchord line along the stream direction for swept-back wings. For the aerodynamic force, the piston theory including the effect of wing thickness is used. Numerical computation is carried out for a cantilever trapezoid tested at the National Aerospace Laboratory. It has been observed that the ten terms approximation yields a good result in comparison with the twenty terms approximation. It has been clarified that the effect of aerodynamic damping on the flutter speed is very small. Reasonable results are obtained in comparison with the experimental results. Furthermore the present method is extended to cantilever plates partially clamped at the root.

Effect of aerodynamic damping on flutter of thin panels

Effect of aerodynamic damping on flutter of thin panels