Membrane Flutter Research Articles

Study Membrane Solarelasticity Using a Wave Model and a Corpuscular Model of Light

The difference between solarelastic interaction and aeroelastic interaction is illustrated from the perspective of external forces. Membrane solarelastic responses of the solar cell and solar sail are studied through a wave model and a corpuscular model of light, respectively, where the light intensity and phase are considered in the wave model to calculate the solar radiation pressure but the phase of light is neglected in the corpuscular model. The effects of the membrane optical properties, the thickness, and the size on the solarelastic flutter instability are investigated. The solar radiation pressure is divided into a part depending on the sail deformation and a part independent of sail deformation to investigate their respective influences. The results show that the former terms result in membrane flutter and the latter term results in membrane static deflection. A comparison is conducted between the wave model and the corpuscular model on the flutter boundaries and membrane responses. The membrane reflectivity is coupled with membrane stiffness by the membrane thickness in the wave model, but it is uncoupled in the corpuscular model. Therefore, the wave model has an advantage over the corpuscular model when evaluating the thickness effect of membrane reflectivity.

Diagnosis and treatment strategies of 56 cases of middle ear myoclonus

Objective: To analyze the clinical characteristics and treatment of middle ear myoclonus. Methods: Fifty-six cases of middle ear myoclonus were enrolled in Shandong Provincial ENT Hospital, Shandong University from September 2019 to August 2021, including 23 males and 33 females. The age ranged from 6 to 75 years, with a median age of 35 years; Forty-seven cases were unilateral tinnitus, nine cases were bilateral tinnitus. The time of tinnitus ranged from 20 days to 8 years. The voice characteristics, inducing factors, nature (frequency) of tinnitus, tympanic membrane conditions during tinnitus, audiological related tests, including long-term acoustic tympanogram, stapedius acoustic reflex, pure tone auditory threshold, short increment sensitivity test, alternate binaural loudness balance test, loudness discomfort threshold, vestibular function examination, facial electromyography, and imaging examination were recorded. Oral carbamazepine and/or surgical treatment were used. The patients were followed up for 6-24 months and the tinnitus changes were observed. Results: Tinnitus was diverse, including stepping on snow liking sound, rhythmic drumming, white noise, and so on. The inducing factors included external sound, body position change, touching the skin around the face and ears, speaking, chewing and blinking, etc. Forty-four cases were induced by single factor and 9 cases were induced by two or more factors. There was no definite inducing factor in 1 case. One patient had tinnitus with epilepsy. One case of traumatic facial paralysis after facial nerve decompression could induce tinnitus on the affected side when the auricle moved. Tympanic membrane flutter with the same frequency as tinnitus was found in 12 cases by otoscopy, and the waveform with the same frequency as tinnitus was found by long-term tympanogram examination. There were 7 patients with no tympanic membrane activity by otoscopy, the 7 cases also with the same frequency of tinnitus by long-term tympanogram examination, but the change rate of the waveform was faster than that of the patients with tympanic membrane flutter. All patients with tinnitus had no change in hearing. One case of tinnitus complicated with epilepsy (a 6-year-old child) was treated with antiepileptic drug (topiramate) and tinnitus subsided. One case suffered from tinnitus after facial nerve decompression for traumatic facial paralysis was not given special treatment. Fifty-four cases were treated with oral drug (carbamazepine), of which 10 cases were completely controlled and 23 cases were relieved; 21 cases were invalid. Among the 21 patients with no effect of carbamazepine treatment, 8 patients were treated by surgery, 7 patients had no tinnitus after surgery, 1 patient received three times of operation, and the third operation was followed up for 6 months, no tinnitus occurred again. The other 13 cases refused the surgical treatment due to personal reasons. Conclusions: Middle ear myoclonus tinnitus and the inducing factors manifestate diversity. Oral carbamazepine and other sedative drugs are effective for some patients, and surgical treatment is feasible for those who are ineffective for medication.

Membrane flutter in three-dimensional inviscid flow

We develop a model and numerical method to study the large-amplitude flutter of rectangular membranes (of zero bending rigidity) that shed a trailing vortex-sheet wake in a three-dimensional (3-D) inviscid fluid flow. We apply small initial perturbations and track their decay or growth to large-amplitude steady-state motions. For 12 combinations of boundary conditions at the membrane edges we compute the stability thresholds and the subsequent large-amplitude dynamics across the three-parameter space of membrane mass density, pretension and stretching rigidity. With free side edges we find good agreement with previous 2-D results that used different discretization methods. We find that the 3-D dynamics in the 12 cases naturally forms four groups based on the conditions at the leading and trailing edges. The deflection amplitudes and oscillation frequencies have scalings similar to those in the 2-D case. The conditions at the side edges, although generally less important, may have small or large qualitative effects on the membrane dynamics – e.g. steady vs unsteady, periodic vs chaotic or the variety of spanwise curvature distributions – depending on the group and the physical parameter values.

Membrane Flutter in Inviscid Flow

Membrane Flutter in Inviscid Flow

Membrane flutter induced by radiation of surface gravity waves on a uniform flow

Abstract

Large-amplitude membrane flutter in inviscid flow

We study the large-amplitude flutter of membranes (of zero bending rigidity) with vortex sheet wakes in two-dimensional inviscid fluid flows. We apply small initial deflections and track their exponential decay or growth and subsequent large-amplitude dynamics in the space of three dimensionless parameters: membrane pretension, mass density and stretching modulus. With both ends fixed, all the membranes converge to steady deflected shapes with single humps that are nearly fore-aft symmetric, except when the deformations are unrealistically large. With leading edges fixed and trailing edges free to move in the transverse direction, the membranes flutter periodically at intermediate values of mass density. As mass density increases, the motions are increasingly aperiodic, and the amplitudes increase and spatial and temporal frequencies decrease. As mass density decreases from the periodic regime, the amplitudes decrease and spatial and temporal frequencies increase until the motions become difficult to resolve numerically. With both edges free to move in the transverse direction, the membranes flutter similarly to the fixed–free case, but also translate vertically with steady, periodic or aperiodic trajectories, and with non-zero slopes that lead to small angles of attack with respect to the oncoming flow.

A wrinkle in flight: the role of elastin fibres in the mechanical behaviour of bat wing membranes.

Bats fly using a thin wing membrane composed of compliant, anisotropic skin. Wing membrane skin deforms dramatically as bats fly, and its three-dimensional configurations depend, in large part, on the mechanical behaviour of the tissue. Large, macroscopic elastin fibres are an unusual mechanical element found in the skin of bat wings. We characterize the fibre orientation and demonstrate that elastin fibres are responsible for the distinctive wrinkles in the surrounding membrane matrix. Uniaxial mechanical testing of the wing membrane, both parallel and perpendicular to elastin fibres, is used to distinguish the contribution of elastin and the surrounding matrix to the overall membrane mechanical behaviour. We find that the matrix is isotropic within the plane of the membrane and responsible for bearing load at high stress; elastin fibres are responsible for membrane anisotropy and only contribute substantially to load bearing at very low stress. The architecture of elastin fibres provides the extreme extensibility and self-folding/self-packing of the wing membrane skin. We relate these findings to flight with membrane wings and discuss the aeromechanical significance of elastin fibre pre-stress, membrane excess length, and how these parameters may aid bats in resisting gusts and preventing membrane flutter.

Sailing the skies: the improbable aeronautical success of the pterosaurs

Pterosaur wings bore a striking resemblance to sails, having a bony spar at the leading edge, formed by the forelimb and one enormously elongated digit, and an elastic wing membrane. Such simple wings would be expected to have performed badly due to excessive deformation, membrane flutter and poor control characteristics. Here I discuss how certain anatomical features, specifically a forewing membrane in the inner part of the wing and a system of fibres embedded in the distal part, may have countered these shortcomings. The forewing, supported by the unique pteroid bone, would have reduced the wings' geometric twist, and has been shown in wind tunnel tests to improve membrane stability at low angles of attack and dramatically increase the maximum lift coefficient at high angles of attack. The function of the fibres is poorly understood, but it is suggested that they improved membrane stability and optimised twist nearer the wingtips.

A monolithic approach to fluid–structure interaction using space–time finite elements

The paper presents a simultaneous solution procedure for fluid–structure interaction problems. The structural motion is described by geometrically nonlinear elastodynamics. The fluid is modeled by the incompressible Navier–Stokes equations. The space–time finite element method is applied to both continua leading to an almost uniform discretization in which velocity variables are used for fluid and structure. In order to enforce momentum conservation and geometric continuity at the interface, a weighted residual formulation of coupling conditions is introduced. The discretized model equations for fluid, structure and coupling conditions are formulated in a single equation system. The nonlinear system and the fluid mesh movement are solved in a single iteration loop. Two-dimensional examples of membrane flutter and vortex excited plate vibrations demonstrate the efficiency of the methodology.

VISCOUS FLUTTER OF A FINITE ELASTIC MEMBRANE IN POISEUILLE FLOW

Flow-induced vibration in a collapsible tube is relevant to many biomedical applications including the human respiratory system. This paper presents a linear analysis of the coupling between Poiseuille flow and a tensioned membrane of finite length using an eigenvalue approach. The undisturbed state of the channel flow is perfectly parallel. To some extent, this configuration bridges the gap between two types of theoretical models: one for the travelling-wave flutter in an infinite, flexible channel, and the other for the self-induced oscillation of a collapsing section of a Starling-resistor tube. In our study, we focus on the parameter range where the wall-to-fluid mass ratio is high (100), and the Reynolds number based on the maximum flow velocity in the channel is moderately high (200). Eigenmodes representing both static divergence and flutter are found. Particular attention is paid to the energetics of flutter modes. It is shown that energy transfer from the flow to the membrane occurs as a result of unstable, downstream-travelling waves, while the upstream-travelling waves are stable and release most of the transferred energy back to the flow. Coupling between different in vacuo modes offers another view of the origin of energy transfer. In addition, an energy conservation analysis similar to the one used in aeroacoustics is carried out. It is shown that terms directly proportional to fluid viscosity contribute most to the production of fluctuation energy, leading to a special type of dynamic instability which resembles both Tollmien–Schlichting instability in the sense that the fluid viscosity destabilises, and traditional travelling wave flutter since the structural damping plays the role of stabilising. Effects of the membrane mass, length and structural damping are also studied. The characteristics of the membrane flutter are found to depend crucially on the upstream and downstream boundary conditions.

Membrane flutter paradox - An explanation by singular-perturbation methods.

The paradox concerning aeroelastic stability of thin plates exposed to supersonic flow is resolved by the use of singular-perturbation methods. The form of the known solution for a membrane suggests a particular limit process, in which the plate thickness and certain other parameters approach zero, and also provides motivation for two methods of obtaining the desired asymptotic expansions. One procedure involves removal of an appropriate exponential factor from the solution and subsequent use of a boundary-layer approach because of the importance of bending stresses near the edges. The second method is based on a two-variable expansion in terms of the space coordinate. In each case, a Poincare type of distorted time coordinate is introduced. A flutter boundary is obtained for a range of the parameters which has not been studied previously, and the significance of the membrane solution is explained in relation to this result. The approximations used permit substantial simplification in the computations.

A comparison of membrane and panel flutter.

N a recent paper,1 the author presented an analysis of the destabilizing effect of a damping-type term on the flutter of a membrane in supersonic flow. In that paper the form of damping was criticized in the light of known theoretical results for the membrane. However, it should also follow that the results agree with panel results for high enough tensions where the membrane theory is satisfactory. Towards a more complete understanding of the membrane flutter problem, consideration is given herein to the panel stability analysis in the region where membrane results are relevant. The infinite aspect-ratio panel equation with simply supported boundaries, for simplicity and brevity, will be solved (using a Galerkin solution) and the results compared with the membrane results of Ref. 1. Consider the conventional infinite aspect-ratio panel flutter equation for the deflection w using linearized, first-order aerodjmamic theory, in the nondimensional form ,, , . (1 + igT] + Xj>*- +

Approximate solutions of the membrane flutter problem

Approximate solutions of the membrane flutter problem

Graphical technique for analyzing marginally stable dynamic systems

It is shown how important qualitative and quantitative information on the dynamic stability characteristics of a linear system can be extracted rather easily from the Argand diagram of the characteristic equation for sinusoidal motion. This diagram reveals directly whether the system possesses marginally stable eigenvalues and also if violent instability may occur for a system with fluid flow (e.g., flutter). In addition, accurate estimates of marginally stable eigenvalues, including amplification or decay rates, may be obtained from the diagram. The method is applied to a model problem of membrane flutter which previously has been employed in a problem of boundary-layer stability. This model exhibits three essentially different classes of instability which are believed to be basic to all problems involving flowing fluids. Some simple cases of flutter are also considered which demonstrate the practical usefulness of the method and its accuracy.