A Simple Approach to the Wing Flutter Problem

1933 ◽  
Vol 37 (273) ◽  
pp. 783-792 ◽  
Author(s):  
B. Lockspeiser
Keyword(s):  
Elastic Energy ◽  
Simple Approach ◽  
Inertial Forces ◽  
Initial Displacement ◽  
Wing Flutter ◽  
Wing Section ◽  
Air Damping ◽  
Gain Energy ◽  
Wing Structure ◽  
Set Up

Let us first consider the oscillations, in still air, of a monoplane wing whose aileron is supposed locked to the wing in such a way that it behaves as though it were an integral part of the wing structure. When the wing is displaced from its position of equilibrium and released it will, in general, vibrate both in flexure and torsion. The initial displacement may be purely flexural, but if the inertial forces called into play, over any wing section, produce a twisting moment about the centre of twist (i.e., the centre about which the wing section twists on the application of a pure torque at that section) torsional as well as flexural oscillations will be set up. Inertia, in general, robs the two kinds of oscillation of their independence, and, when they are interdependent, we may conveniently speak of “inertial couplings” between the two motions. In still air these vibrations must, of necessity, die down. One part of the wing may gain energy at the expense of another, but the store of elastic energy given to the wing by the initial displacement must grow progressively less as the wing does work against the viscous air damping and structural hysteresis forces.

A Simple Approach to the Theory of Secondary Flows

1954 ◽  
Vol 5 (4) ◽  
pp. 218-234 ◽  
Author(s):  
J. H. Preston
Keyword(s):  
Simple Approach ◽  
Secondary Flows ◽  
Large Deflections ◽  
Simple Method ◽  
Vortex Sheets ◽  
Trailing Edges ◽  
Secondary Motion ◽  
Set Up ◽  
Uniform Stream

SummaryA simple method is developed for computing the trailing vorticity which arises when a non-uniform stream is turned.It is shown that, for a sudden and constant deflection of a non-uniform stream, no net trailing vorticity is set up in the exit flow and hence there is no secondary motion.In the case of an impulse cascade of finite dimensions with constant turning, it is found that the trailing vorticity has three distinct components—the passage vorticity and two components which appear as vortex sheets springing from the trailing edges of the aerofoils. It is shown that for small angles of deflection there is no net circulation associated with the trailing vorticity downstream, of the cascade, and it is inferred that this should still be so for large deflections.

scholarly journals Elastic-instability–enabled locomotion

2021 ◽  
Vol 118 (8) ◽  
pp. e2013801118
Author(s):  
Amit Nagarkar ◽  
Won-Kyu Lee ◽  
Daniel J. Preston ◽  
Markus P. Nemitz ◽  
Nan-Nan Deng ◽  
...  
Keyword(s):  
Symmetry Breaking ◽  
Scaling Laws ◽  
Multiple Scales ◽  
Symmetric Cone ◽  
Simple Approach ◽  
Inertial Forces ◽  
Elastic Instability ◽  
Anisotropic Friction ◽  
Buckling Instability ◽  
Elastic Instabilities

Locomotion of an organism interacting with an environment is the consequence of a symmetry-breaking action in space-time. Here we show a minimal instantiation of this principle using a thin circular sheet, actuated symmetrically by a pneumatic source, using pressure to change shape nonlinearly via a spontaneous buckling instability. This leads to a polarized, bilaterally symmetric cone that can walk on land and swim in water. In either mode of locomotion, the emergence of shape asymmetry in the sheet leads to an asymmetric interaction with the environment that generates movement––via anisotropic friction on land, and via directed inertial forces in water. Scaling laws for the speed of the sheet of the actuator as a function of its size, shape, and the frequency of actuation are consistent with our observations. The presence of easily controllable reversible modes of buckling deformation further allows for a change in the direction of locomotion in open arenas and the ability to squeeze through confined environments––both of which we demonstrate using simple experiments. Our simple approach of harnessing elastic instabilities in soft structures to drive locomotion enables the design of novel shape-changing robots and other bioinspired machines at multiple scales.

scholarly journals The motion of a rotor carried by a flexible shaft in flexible bearings

1933 ◽  
Vol 142 (846) ◽  
pp. 92-118 ◽  
Keyword(s):  
Equilibrium State ◽  
Critical Speed ◽  
Transverse Motion ◽  
Initial Displacement ◽  
Flexible Shaft ◽  
Great Amplitude ◽  
Set Up

1.1.— Scope of Investigation .—This paper discusses the transverse motion of a rotor carried by a flexible shaft rotating in flexibly-supported bearings. The rotor is assumed to consist of one or more rigid bodied mounted on a shaft which is weightless and torsionally rigid. The rotor and shaft are in rotation; in the first place, it is taken that the speed of rotation is maintained constant, driving torques being applied if necessary about the shaft axis. Unsymmetrical flexibility of the bearing supports and unsymmetrical transverse flexibility of the shaft of the flexible members of the system is also considered. The work is mainly analytical, but reference is also made to experiments which have been carried out. 1.2. Definitions . —The flexible members (shaft and bearing supports) are described collectively as the mounting. An unstable speed is a speed of rotation at which a rotor, after receiving a small initial displacement from its equilibrium state of motion, tends to increase its amplitude of vibration beyond all bounds; while a critical speed is a speed at which out-of-balance alone tends to set up vibrations of very great amplitude.

scholarly journals A low-cost method for visible fluorescence imaging

2017 ◽  
Vol 73 (12) ◽  
pp. 657-663 ◽  
Author(s):  
Crissy L. Tarver ◽  
Marc Pusey
Keyword(s):  
Light Emitting Diode ◽  
Low Cost ◽  
Stokes Shift ◽  
Simple Approach ◽  
Protein Crystals ◽  
Smart Devices ◽  
Light Emitting ◽  
Set Up ◽  
Β Lactoglobulin ◽  
Diffraction Quality Crystal

A wide variety of crystallization solutions are screened to establish conditions that promote the growth of a diffraction-quality crystal. Screening these conditions requires the assessment of many crystallization plates for the presence of crystals. Automated systems for screening and imaging are very expensive. A simple approach to imaging trace fluorescently labeled protein crystals in crystallization plates has been devised, and can be implemented at a cost as low as $50. The proteins β-lactoglobulin B, trypsin and purified concanavalin A (ConA) were trace fluorescently labeled using three different fluorescent probes: Cascade Yellow (CY), Carboxyrhodamine 6G (CR) and Pacific Blue (PB). A crystallization screening plate was set up using β-lactoglobulin B labeled with CR, trypsin labeled with CY, ConA labeled with each probe, and a mixture consisting of 50% PB-labeled ConA and 50% CR-labeled ConA. The wells of these plates were imaged using a commercially available macro-imaging lens attachment for smart devices that have a camera. Several types of macro lens attachments were tested with smartphones and tablets. Images with the highest quality were obtained with an iPhone 6S and an AUKEY Ora 10× macro lens. Depending upon the fluorescent probe employed and its Stokes shift, a light-emitting diode or a laser diode was used for excitation. An emission filter was used for the imaging of protein crystals labeled with CR and crystals with two-color fluorescence. This approach can also be used with microscopy systems commonly used to observe crystallization plates.

Analysis of State Dependent Vacation Queues with Threshold Gated Service Policy

2010 ◽  
Vol 1 (2) ◽  
pp. 32-49 ◽  
Author(s):  
Yew Sing
Keyword(s):  
Performance Measures ◽  
Cycle Time ◽  
Busy Period ◽  
Simple Approach ◽  
Second Moment ◽  
State Dependent ◽  
The Mean ◽  
Service Policy ◽  
Set Up ◽  
Number Of Customers

In this article, the authors introduce a simple approach for modeling and analyzing a queue where the server may take repeated vacations. When a busy period ends, the server takes a vacation of random duration. At the end of each vacation, the server may either start a new vacation or resume service. If a queue is found of less than customers, the server will always take a new vacation. If there are at least customers in queue, the server provides services to those customers after a brief set-up time. The authors obtain several performance measures of the system, including the mean and second moment of the cycle time, the number of customers in a cycle of service, and the expected delay experienced by a customer.

Real-time, ongoing employee feedback: the perk that actually retains

2017 ◽  
Vol 16 (3) ◽  
pp. 125-130
Author(s):  
Michael Heller
Keyword(s):  
Performance Management ◽  
Performance Feedback ◽  
Design Methodology ◽  
Feedback Loop ◽  
Simple Approach ◽  
Content Type ◽  
Black And White ◽  
Effective Manner ◽  
Set Up ◽  
The Impact

Purpose The purpose of this paper is to help leaders with their performance management explore how a simple ongoing feedback loop retains employees. Design/methodology/approach This paper is set up in a “to-do, not to-do” format to give busy leaders a clear, black and white view on how this approach works. Findings The “simple” approach of having an ongoing feedback loop is hard for employers to get in the habit of doing, which is understandable. This paper shows them that implementation is not as hard as many anticipate. Research limitations/implications A lot of the “research” comes from daily experiences through practice. Studies have proven that leaders want to deliver more performance feedback to their employees; however, it’s the actual implementation we as leaders must learn to deliver in an effective manner. Originality/value This paper includes actual tried-and-true tactics for leaders to easily implement, and get the feel for how feedback works and the impact it makes on business. The hope is to help leaders in any industry to be able to transform the way they provide feedback.

The Cauchy–Poisson problem for a viscous liquid

1968 ◽  
Vol 34 (2) ◽  
pp. 359-370 ◽  
Author(s):  
John W. Miles
Keyword(s):  
Free Surface ◽  
Gravity Wave ◽  
Viscous Liquid ◽  
Inertial Forces ◽  
The Moon ◽  
Initial Displacement ◽  
Diffusive Motion ◽  
Surface Response ◽  
Viscous Forces ◽  
Poisson Problem

The axisymmetric, free-surface response of a semi-infinite viscous liquid to either a point impulse or an initial displacement of zero net volume is calculated. The asymptotic disturbance is resolved into three components: (i) a damped gravity wave, which represents a primary balance between gravitational and inertial forces with secondary, but cumulative, modification by viscous forces; (ii) a diffusive motion, which represents a balance between viscous and inertial forces; (iii) a creep wave, which represents a balance between gravitational and viscous forces. Van Dorn has suggested that the results may be relevant to the concentric circular ridges that surround the crater Orientale on the Moon.

A Momentum Transfer Measurement Technique Between Contacting Free-Falling Bodies in the Presence of Adhesion

2008 ◽  
Vol 75 (1) ◽  
Author(s):  
M. Benedetti ◽  
D. Bortoluzzi ◽  
S. Vitale
Keyword(s):  
Momentum Transfer ◽  
Inertial Forces ◽  
Noise Sources ◽  
Space Applications ◽  
Interaction Forces ◽  
Measurement Resolution ◽  
Transfer Measurement ◽  
Filtering Technique ◽  
Set Up ◽  
Free Falling

The present paper is aimed at investigating the dynamics of release of objects in free-falling conditions typical of space applications. In the presence of surface interaction forces, a quick separation of the released from the constraining body will result in a momentum transfer, provided that the inertial forces exceed the maximum attractive force. The release conditions as well as the related parameters affecting the momentum acquired by the released body through the adhesion rupture play a fundamental role. Therefore, an analytical model has been set up to predict the imparted momentum in the case of conservative interaction forces. Furthermore, an experimental technique aimed at measuring the momentum transfer has been analyzed. Particular attention has been placed on the capability to accurately reproduce the stress status on the contact patch, on the noise sources affecting the measurement, and on the performances of a noise optimal-filtering technique in terms of achievable measurement resolution.

Analysis of State Dependent Vacation Queues with Threshold Gated Service Policy

2012 ◽  
pp. 274-291
Author(s):  
Yew Sing
Keyword(s):  
Performance Measures ◽  
Cycle Time ◽  
Busy Period ◽  
Simple Approach ◽  
Second Moment ◽  
State Dependent ◽  
The Mean ◽  
Service Policy ◽  
Set Up ◽  
Number Of Customers

In this article, the authors introduce a simple approach for modeling and analyzing a queue where the server may take repeated vacations. When a busy period ends, the server takes a vacation of random duration. At the end of each vacation, the server may either start a new vacation or resume service. If a queue is found of less than customers, the server will always take a new vacation. If there are at least customers in queue, the server provides services to those customers after a brief set-up time. The authors obtain several performance measures of the system, including the mean and second moment of the cycle time, the number of customers in a cycle of service, and the expected delay experienced by a customer.

scholarly journals Examination of polarization coupling in a plucked musical instrument string via experiments and simulations

Acta Acustica ◽  
2020 ◽  
Vol 4 (3) ◽  
pp. 9
Author(s):  
Alexander Brauchler ◽  
Pascal Ziegler ◽  
Peter Eberhard
Keyword(s):  
Initial Conditions ◽  
String Model ◽  
Element Model ◽  
Musical Instrument ◽  
Laser Doppler ◽  
Excitation Mechanism ◽  
Initial Displacement ◽  
Transient Motion ◽  
Set Up ◽  
Good Agreement

In this article, the transient motion of a realistically plucked guitar string is studied experimentally and numerically in both transversal polarizations. The frequency dependent damping and suitable initial conditions are identified in the experiment and used in a simulation. For this reason an experimental set-up consisting of a string, an excitation mechanism and two laser Doppler vibrometers is developed. The excitation mechanism performs a realistic and reproducible plucking motion with a plectrum. Two laser Doppler vibrometers are used to measure the string oscillation transversally in two polarizations. The experimental set-up makes it possible to measure the string’s motion under reproducible conditions and, hence, at different positions for the same oscillation. This capability renders the identification of suitable initial conditions, i.e., initial displacement and velocity as well as the pre-tension, for a string model possible. Furthermore, a finite element model for the string is developed that takes into account the oscillation in both transversal planes of polarization and the coupling between them. Finally, the model results are in good agreement with the measurements. With help of the numerical model it can be vividly shown that the coupling between the polarizations of the oscillation is due to a torsional movement of the string on the saddle.

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