Bifurcation Analysis of Parametrically Excited Moving String With Aerodynamic Forces

2012 ◽  
Author(s):  
Changzhao Qian ◽  
Changping Chen ◽  
Liming Dai
Keyword(s):  
Bifurcation Analysis ◽  
Parametric Analysis ◽  
Aerodynamic Force ◽  
Equation Of Motion ◽  
Stable Region ◽  
Second Law ◽  
Bifurcation Equation ◽  
Aerodynamic Forces ◽  
Average Equation ◽  
Prototypical Model

Considering the large deformation of the string, A prototypical model of a elastic moving string with aerodynamic forces is studied. The equation of motion is obtained by Newton’s second law. Then the Perturbation method is used to obtain the average equation and bifurcation equation. Based on the average equation, the stable region of this system is discussed. Based on the bifurcation equation, the multivalued property of response amplitude is studied. At last, the flutter effects of aerodynamic force are discussed by the parametric analysis.

Bifurcation Control for a Kind of Non-Autonomous System with Time Delay

2010 ◽  
Vol 34-35 ◽  
pp. 1752-1756
Author(s):  
Chang Zhao Qian ◽  
Zhi Wen Wang ◽  
Chuang Wen Dong ◽  
Yang Liu
Keyword(s):  
Time Delay ◽  
Perturbation Method ◽  
Time Delays ◽  
Autonomous System ◽  
Primary Resonance ◽  
Stable Region ◽  
Bifurcation Equation ◽  
Van Der Pol ◽  
Average Equation ◽  
System With Time Delay

A forced van der Pol system with two time-delays is studied. The central aim is analyzing primary resonance of this system. Perturbation method is used to obtain the average equation and bifurcation equation with time-delays. Based on the average equation, the stable region of this system is discussed. Based on the bifurcation equation, the multivalued property of response amplitude is studied. The result indicates that this system can be well controlled with time delays.

Extremely Gusty Winds from a Viewpoint of Aerodynamic Force

2020 ◽  
Author(s):  
Junji Maeda ◽  
Takashi Takeuchi ◽  
Eriko Tomokiyo ◽  
Yukio Tamura
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Rise Time ◽  
Aerodynamic Force ◽  
Step Function ◽  
Object Size ◽  
Aerodynamic Forces ◽  
Wind Force ◽  
Wind Observation

To quantitatively investigate a gusty wind from the viewpoint of aerodynamic forces, a wind tunnel that can control the rise time of a step-function-like gust was devised and utilized. When the non-dimensional rise time, which is calculated using the rise time of the gusty wind, the wind speed, and the size of an object, is less than a certain value, the wind force is greater than under the corresponding steady wind. Therefore, this wind force is called the “overshoot wind force” for objects the size of orbital vehicles in an actual wind observation. The finding of the overshoot wind force requires a condition of the wind speed recording specification and depends on the object size and the gusty wind speed.

scholarly journals An Extension of Newton's Equation of Motion

1979 ◽  
Vol 81 ◽  
pp. 53-56
Author(s):  
Ki Jae Cheon
Keyword(s):  
Charged Particle ◽  
Euclidean Space ◽  
Internal Structure ◽  
Atomic Physics ◽  
Classical Mechanics ◽  
Equation Of Motion ◽  
Second Law ◽  
Mass Variation ◽  
Absolute Mass ◽  
Time Point

Classical mechanics failed to solve two problems in own defensive area, namely the motion of Mercury's perihelion, and the high-velcity motion of a charged particle. Today it is generally believed that the concepts of classical mechanics are completely invalid in a treatment of these problems. In this paper, however, we discuss these problems throughly with the concepts of classical mechanics — Euclidean space-time, point of mass and central force. Thereat we introduce a new concept “absolute mass variation”, with which we extend the Newton's second law of motion. In following chapters we show that this extended equation explains the motion of Mercury's perihelion, and that it throws new light on the atomic physics. We also make a study of reconstruction of internal structure of mechanics. We discuss the possibility of the revival of the principal frame of Newton's mechanics.

scholarly journals Complexity Analysis on the Aerodynamic Performance of the Mega High-Speed Train Caused by the Wind Barrier on the Embankment

Complexity ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-17
Author(s):  
He-xuan Hu ◽  
Wan-xin Lei ◽  
Ye Zhang
Keyword(s):  
Negative Pressure ◽  
High Speed ◽  
Complexity Analysis ◽  
Aerodynamic Force ◽  
Pressure Change ◽  
Aerodynamic Performance ◽  
Head Wave ◽  
High Speed Train ◽  
Aerodynamic Forces ◽  
Negative Wave

With the world development of high-speed railways and increasing speeds, aerodynamic forces and moments acting on trains have been increased further, making trains stay at a “floated” state. Under a strong crosswind, the aerodynamic performance of a train on the embankment is greatly deteriorated; lift force and horizontal force borne by trains will be increased quickly; trains may suffer derailing or overturning more easily compared with the flat ground; train derailing will take place when the case is serious. All of these phenomena have brought risks to people’s life and properties. Hence, the paper establishes an aerodynamic model about a high-speed train passing an air barrier, computes aerodynamic forces and moments, and analyzes pulsating pressures on the train surface as well as those of unsteady flow fields around the train. Computational results indicate that when the train passed the embankment air barrier, the head wave of air pressure full wave is more than the tail wave; the absolute value of negative wave is more than that of the positive wave, which is more obvious in the head train. When the train is passing the air barrier, pressure pulsation values at head train points are more than those at other points, while pressure changes most violently at the train bottom, and pressure values close to the air barrier are more than those points far from the air barrier. Pressure values at the cross section 1 were larger than those of other points. Pressure values at measurement points of the tail train ranked the second place, with the maximum negative pressure of 1253 Pa. Pressure change amplitudes and maximum negative pressure on the train surface are increased quickly, while pressure peak values on the high-speed train surface are in direct ratio to the running speed. With the increased speed of the high-speed train, when it is running in the embankment air barrier, the aerodynamic force and moment borne by each train body are increased sharply, while the head train suffers the most obvious influences of aerodynamic effects.

Method for aerodynamic unsteady forces time calculations on an F/A-18 aircraft

2008 ◽  
Vol 112 (1127) ◽  
pp. 27-32
Author(s):  
D. E. Biskri ◽  
R. M. Botez
Keyword(s):  
Least Squares ◽  
Least Squares Method ◽  
Aerodynamic Force ◽  
Analytical Form ◽  
Original Method ◽  
Aerodynamic Forces ◽  
Unsteady Forces ◽  
Laplace Domain ◽  
Different Types ◽  
Execution Speed

Abstract In this paper, a new original method based on the least squares method is presented for the conversion of unsteady aerodynamic forces from frequency into Laplace domain, in which the error is written in an analytical form as a function of the Laplace variable, similar to the analytical form of the aerodynamic forces calculated by use of the least squares method. This method is applied on an F/A-18 aircraft (14 symmetric and 14 anti-symmetric modes) for one Mach number and for a set of 14 reduced frequencies. Two different types of results are obtained and analysed: aerodynamic force approximations in the Laplace domain and flutter speeds and frequencies values. For a better comparison of these results, different lag term numbers are used. Results obtained by this new method are better in terms of execution speed and precision than the results obtained by use of the least squares method.

Aerodynamic Forces on a Simplified Car Body: Towards Innovative Designs for Car Drag Reduction

2010 ◽  
Author(s):  
Mahmoud Khaled ◽  
Fabien Harambat ◽  
Anthony Yammine ◽  
Hassan Peerhossaini
Keyword(s):  
Drag Reduction ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Cooling System ◽  
Aerodynamic Force ◽  
Lift Coefficient ◽  
Force Measurements ◽  
Vehicle Model ◽  
Aerodynamic Forces ◽  
Aerodynamic Drag Reduction

The present paper exposes the study of the cooling system circulation effect on the external aerodynamic forces. We report here aerodynamic force measurements carried out on a simplified vehicle model in wind tunnel. Tests are performed for different airflow configurations in order to detect the parameters that can affect the aerodynamic torsor and to confirm others previously suspected, especially the air inlets localization, the air outlet distributions and the underhood geometry. The simplified model has flat and flexible air inlets and several types of air outlet, and includes in its body a real cooling system and a simplified engine block that can move in the longitudinal and lateral directions. The results of this research are generic and can be applied to any new car design. Results show configurations in which, with respect to the most commonly adopted underhood geometries, the overall drag coefficient can be decreased by 2%, the aerodynamic cooling drag coefficient by more than 50% and the lift coefficient by 5%. Finally, new designs of aerodynamic drag reduction, based on the combined effects of the different investigated parameters, are proposed.

Computational Analysis of Unsteady Flow in a Partial Admission Supersonic Turbine Stage

2014 ◽  
Author(s):  
Yuki Tokuyama ◽  
Ken-ichi Funazaki ◽  
Hiromasa Kato ◽  
Noriyuki Shimiya ◽  
Mitsuru Shimagaki ◽  
...  
Keyword(s):  
Shock Waves ◽  
Unsteady Flow ◽  
Aerodynamic Force ◽  
Low Frequency ◽  
Frequency Component ◽  
Low Flow ◽  
Tvd Scheme ◽  
Aerodynamic Forces ◽  
Partial Admission ◽  
Unsteady Force

Turbines used in upper stage engine for a rocket are sometimes designed as a supersonic turbine with partial admission. This study deals with numerical investigation of supersonic partial admission turbine in order to understand influences on the unsteady flow pattern, turbine losses and aerodynamic forces on rotor blades due to partial admission configuration. Two-dimensional CFD analysis is conducted using “Numerical Turbine” code. Its governing equation is URANS (Unsteady Reynolds Averaged Navier-Stokes Simulation) and fourth-order MUSCL TVD scheme is used for advection scheme. The unsteady simulation indicates that strongly non-uniform circumferential flow field is created due to the partial admission configuration and it especially becomes complex at 1st stage because of shock waves. Some very high or low flow velocity regions are created around the blockage sector. Nozzle exit flow is rapidly accelerated at the inlet of blockage sector and strong rotor LE shock waves are created. In contrast, at rotor blade passages and Stator2 blade passages existing behind the blockage sector, working gas almost stagnates. Large flow separations and flow mixings occur because of the partial admission configuration. As a result, additional strong dissipations are caused and the magnitude of entropy at the turbine exit is approximately 1.5 times higher than that of the full admission. Rotor1 blades experience strong unsteady aerodynamic force variations. The aerodynamic forces greatly vary when the Rotor1 blade passes through the blockage inlet region. The unsteady force in frequency domain indicates that many unsteady force components exist in wide frequency region and the blockage passing frequency component becomes pronounced in the circumferential direction force. Unsteady forces on Rotor2 blades are characterized by a low frequency fluctuation due to the blockage passing.

Aerodynamic Forces of Stay Cables Incorporating in Flutier Analysis

2013 ◽  
Vol 438-439 ◽  
pp. 894-900
Author(s):  
Ke Jian Ouyang ◽  
Yi Long ◽  
Bi Cao Peng
Keyword(s):  
Aerodynamic Force ◽  
Three Dimensional ◽  
Wind Tunnel Test ◽  
Test Results ◽  
Stay Cable ◽  
Aerodynamic Forces ◽  
Stay Cables ◽  
Stiffness Matrices ◽  
Flutter Analysis ◽  
Sutong Bridge

With the length of stay cables close to 580m, only inclusion in aerodynamic forces of main deck cannot reflect the actual situation during wind-resistant design. The aerodynamic forces of stay cables should be considered in the three-dimensional flutter analysis of cable-stayed bridges. In this paper, mathematic expressions of unsteady aerodynamic force of stay cable were then derived in terms of aerodynamic damping and stiffness matrices. The above procedure is implemented into NACS by an independent module. As an example, the multimode flutter analysis of Sutong Bridge was conducted by using NACS. Fair agreement is achieved between the present numerical simulation and wind tunnel test results.

scholarly journals How oscillating aerodynamic forces explain the timbre of the hummingbird’s hum and other animals in flapping flight

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Ben J Hightower ◽  
Patrick W A Wijnings ◽  
Rick Scholte ◽  
Rivers Ingersoll ◽  
Diana D Chin ◽  
...  
Keyword(s):  
Aerodynamic Force ◽  
Microphone Array ◽  
Flapping Wings ◽  
Acoustic Model ◽  
Acoustic Measurements ◽  
Aerodynamic Forces ◽  
Drag Forces ◽  
Radiated Power ◽  
Lift And Drag

How hummingbirds hum is not fully understood, but its biophysical origin is encoded in the acoustic nearfield. Hence, we studied six freely hovering Anna's hummingbirds, performing acoustic nearfield holography using a 2176 microphone array in vivo, while also directly measuring the 3D aerodynamic forces using a new aerodynamic force platform. We corroborate the acoustic measurements by developing an idealized acoustic model that integrates the aerodynamic forces with wing kinematics, which shows how the timbre of the hummingbird's hum arises from the oscillating lift and drag forces on each wing. Comparing birds and insects, we find that the characteristic humming timbre and radiated power of their flapping wings originates from the higher harmonics in the aerodynamic forces that support their bodyweight. Our model analysis across insects and birds shows that allometric deviation makes larger birds quieter and elongated flies louder, while also clarifying complex bioacoustic behavior.

scholarly journals Numerical Simulation of a Pitching Airfoil Under Dynamic Stall of Low Reynolds Number Flow

2019 ◽  
Author(s):  
Mojtaba Honarmand ◽  
Mohammad Hassan Djavareshkian ◽  
Behzad Forouzi Feshalami ◽  
Esmaeil Esmaeilifar
Keyword(s):  
Reynolds Number ◽  
Stokes Equations ◽  
Aerodynamic Force ◽  
Low Reynolds Number ◽  
Oscillation Amplitude ◽  
Dynamic Stall ◽  
Aerodynamic Forces ◽  
Naca0012 Airfoil ◽  
Reduced Frequency ◽  
Low Reynolds

In this research, viscous, unsteady and turbulent fluid flow is simulated numerically around a pitching NACA0012 airfoil in the dynamic stall area. The Navier-Stokes equations are discretized based on the finite volume method and are solved by the PIMPLE algorithm in the open source software, namely OpenFOAM. The SST k - ω model is used as the turbulence model for Low Reynolds Number flows in the order of 105. A homogenous dynamic mesh is used to reduce cell skewness of mesh to prevent non-physical oscillations in aerodynamic forces unlike previous studies. In this paper, the effects of Reynolds number, reduced frequency, oscillation amplitude and airfoil thickness on aerodynamic force coefficients and dynamic stall delay are investigated. These parameters have a significant impact on the maximum lift, drag, the ratio of aerodynamic forces and the location of dynamic stall. The most important parameters that affect the maximum lift to drag coefficient ratio and cause dynamic stall delaying are airfoil thickness and reduced frequency, respectively.

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