Characterization of typical aeroelastic sections under combined structural concentrated nonlinearities

2021 ◽  
pp. 107754632110001
Author(s):  
José Augusto I da Silva ◽  
Flávio D Marques
Keyword(s):  
Time Integration ◽  
Unsteady Aerodynamics ◽  
Nonlinear Effects ◽  
Free Play ◽  
Control Surface ◽  
Trailing Edge ◽  
Aeroelastic System ◽  
Practical Applications ◽  
Structural Nonlinearities ◽  
The Stability

Structural nonlinearities are usually present in aeroelastic systems. The analysis of this system commonly comprises a study involving only one type of nonlinearity, influencing a particular motion of the airfoil. However, practical applications of aeroelastic systems can be affected by different types of structural nonlinearities. It becomes essential to study the stability of the aeroelastic system under these conditions to assess more real operational flight procedures. In this context, this article presents an investigation of a typical aeroelastic section response with trailing edge control surface subjected to combinations of concentrated structural nonlinearities. Different nonlinear scenarios involving cubic hardening stiffness in pitching and free play, free play with preload, and slip dry friction in the trailing edge control surface motion are analyzed. The mathematical model is based on linear unsteady aerodynamics coupled to a three-dof typical aeroelastic section. Hopf bifurcations diagrams are obtained from direct time integration of the equation of motion. The post-flutter limit cycle oscillations are investigated, revealing supercritical and subcritical bifurcations. A complete parametric study of the nonlinear parameters is carried out, thereby allowing a sensitivity analysis of each nonlinear scenario. The results show that aeroelastic tailoring considering the mild post-flutter behavior can be achieved through an appropriate choice of combined nonlinear effects. Moreover, combined nonlinearities can mitigate the undesired subcritical aeroelastic responses caused by free play.

AEROELASTIC BEHAVIOR OF LIFTING SURFACES WITH FREE-PLAY, AND AERODYNAMIC STIFFNESS AND DAMPING NONLINEARITIES

2008 ◽  
Vol 18 (04) ◽  
pp. 1101-1126 ◽  
Author(s):  
LAITH K. ABBAS ◽  
Q. CHEN ◽  
P. MARZOCCA ◽  
K. O'DONNELL ◽  
D. VALENTINE
Keyword(s):  
Dynamic Instability ◽  
Initial Conditions ◽  
Aerodynamic Force ◽  
Free Play ◽  
Aerodynamic Load ◽  
Aeroelastic System ◽  
Structural Nonlinearities ◽  
System Nonlinearity ◽  
Lifting Surfaces ◽  
Stiffness And Damping

Aeroelastic instabilities are dangerous phenomena, where aerodynamic load interacting with the inertia and elastic structural loads can induce catastrophic failures. In this paper the effects of aerodynamic nonlinearities as well as coupled plunging/pitching structural concentrated cubic type and freeplay nonlinearities in the dynamic of a two-dimensional double-wedge airfoil immersed in supersonic/hypersonic flow has been examined. The unsteady nonlinear aerodynamic force and moment on the airfoil are evaluated using the Piston Theory Aerodynamics modified to take into account the effect of the airfoil thickness. The resulting aeroelastic equations are numerically integrated to obtain time responses and to investigate the dynamic instability of the lifting surface under various initial displacement conditions. Results of the complex nonlinear aeroelastic system are presented in the form of bifurcation diagrams constructed from the response amplitude for various types of the system nonlinearity. It is shown that there exist regions, in which the system exhibit Limit Cycle Oscillations (LCOs), strongly dependent on the initial conditions of the aeroelastic system. Concentrated structural nonlinearities, that are freeplays and cubic type nonlinearities, can have significant effects on the flutter behavior and can cause large amplitude oscillations at lower airspeeds than for a linear system. It is also shown that larger amplitude LCOs occur when a pitching freeplay is considered, as compared with the case when a plunging freeplay is taken into account.

An adaptive controller for nonlinear flutter suppression and free-play compensation

2015 ◽  
Vol 23 (14) ◽  
pp. 2269-2290 ◽  
Author(s):  
Andrea Mannarino ◽  
Earl H Dowell ◽  
Paolo Mantegazza
Keyword(s):  
Limit Cycle ◽  
Initial Conditions ◽  
Adaptive Controller ◽  
Free Play ◽  
Control Surface ◽  
Limit Cycle Oscillations ◽  
Multiple Control ◽  
Highly Nonlinear ◽  
Structural Nonlinearities ◽  
Invariance Control

A technique aimed at neutralizing the presence of free-play effects in a control surface actuation chain is presented. It is based on an adaptive inversion of a function approximating such a nonlinearity. A simple, yet robust, on-line adaptive algorithm is proposed to identify the free-play parameters, i.e. free-play width, the equivalent control stiffness and friction. The procedure is then coupled to an immersion and invariance control law to drastically reduce possible residual closed-loop limit cycle oscillations due to the free-play nonlinearity. Within such a framework, the so chosen compensation technique can be interpreted as a control augmentation, easily extendable to multiple control surfaces. The methodology is then verified on a four-degree-of-freedom airfoil in a transonic regime, characterized by highly nonlinear unsteady aerodynamic loads, producing significant shock motions and large limit cycles, at a relatively high frequency. The presence of both aerodynamic and structural nonlinearities makes such a system bistable, leading to complex responses dependent on the initial conditions and the input used to excite the system. The effective suppression of these auto-induced vibrations becomes even more challenging because the limit cycle oscillations generated by different sources are characterized by differing amplitudes and frequencies.

ℒ1 adaptive control of an aeroelastic system with unsteady aerodynamics and gust load

2016 ◽  
Vol 24 (2) ◽  
pp. 303-322 ◽  
Author(s):  
Keum W Lee ◽  
Sahjendra N Singh
Keyword(s):  
Adaptive Control ◽  
Control System ◽  
Pitch Angle ◽  
Unsteady Aerodynamics ◽  
Projection Algorithm ◽  
Control Surface ◽  
Control Law ◽  
Performance Limits ◽  
Aeroelastic System ◽  
Freestream Velocity

This paper presents the design of an ℒ1 adaptive control system for the stabilization of a two-dimensional aeroelastic system with structural nonlinearities and unsteady aerodynamics, using a single trailing-edge control surface. This model describes the plunge and pitch motion of a prototypical wing. It is assumed that its parameters are unknown and external disturbances are present. The unsteady aerodynamics are modeled with an approximation to Theodorsen's theory. The system exhibits limit cycle oscillations beyond a critical speed. Based on the ℒ1 adaptive control theory, a control law is developed for the trajectory control of the integral of the pitch angle. The control system includes a state predictor, a projection algorithm-based adaptation law designed based on the Lyapunov method, and a stabilizing control law. For the synthesis of the control law only the pitch angle and its derivative are measured. Simulation results show that in the closed-loop system, the aeroelastic vibrations are suppressed, despite parametric uncertainties and gust loads. Furthermore the performance limits of this ℒ1 adaptive law with respect to the freestream velocity and strength of gust load are examined.

Fuzzy control of nonlinear aeroelastic system based on neural network identification

2021 ◽  
pp. 095441002110109
Author(s):  
Bo Zhang ◽  
Jing-Long Han ◽  
Hai-Wei Yun ◽  
Xiao-Mao Chen
Keyword(s):  
Neural Network ◽  
Fuzzy Control ◽  
Control Method ◽  
Free Play ◽  
Control Surface ◽  
Limit Cycle Oscillation ◽  
Identification Algorithm ◽  
Aeroelastic System ◽  
Network Identification ◽  
Cycle Oscillation

This article presents a fuzzy control method for the limit cycle oscillation (LCO) suppression of nonlinear aeroelastic systems based on the neural network identification algorithm. A prototypical 2D wing section with a single control surface at the trailing edge of the main wing, which contains a symmetrical free play nonlinearity in the pitch degree of freedom, is modeled to illustrate the proposed method. A neural network is used to identify the fuzzy control rules from the existing LCO suppression input and output data. A new fuzzy control rate of the nonlinear aeroelastic system is obtained by adjusting the parameters of the fuzzy control surface. Numerical simulations are conducted to verify the effectiveness of the proposed method.

Non-adhesive lotus and other hydrophobic materials

2008 ◽  
Vol 366 (1870) ◽  
pp. 1539-1556 ◽  
Author(s):  
David Quéré ◽  
Mathilde Reyssat
Keyword(s):  
Solid Surface ◽  
Room Temperature ◽  
Water Repellency ◽  
Short Review ◽  
Water Repellent ◽  
Practical Applications ◽  
Hydrophobic Materials ◽  
Volatile Liquid ◽  
Air Cushion ◽  
The Stability

Superhydrophobic materials recently attracted a lot of attention, owing to the potential practical applications of such surfaces—they literally repel water, which hardly sticks to them, bounces off after an impact and slips on them. In this short review, we describe how water repellency arises from the presence of hydrophobic microstructures at the solid surface. A drop deposited on such a substrate can float above the textures, mimicking at room temperature what happens on very hot plates; then, a vapour layer comes between the solid and the volatile liquid, as described long ago by Leidenfrost. We present several examples of superhydrophobic materials (either natural or synthetic), and stress more particularly the stability of the air cushion—the liquid could also penetrate the textures, inducing a very different wetting state, much more sticky, due to the possibility of pinning on the numerous defects. This description allows us to discuss (in quite a preliminary way) the optimal design to be given to a solid surface to make it robustly water repellent.

Numerical Study of Viscous Flows Inside Partially Filled Spinning and Coning Cylinders

1996 ◽  
Vol 118 (2) ◽  
pp. 335-340 ◽  
Author(s):  
Mohamed Selmi
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Center Of Mass ◽  
Steady Motion ◽  
Practical Interest ◽  
Nonlinear Effects ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Practical Applications ◽  
Analysis And Design

This paper is concerned with the solution of the 3-D-Navier-Stokes equations describing the steady motion of a viscous fluid inside a partially filled spinning and coning cylinder. The cylinder contains either a single fluid of volume less than that of the cylinder or a central rod and a single fluid of combined volume (volume of the rod plus volume of the fluid) equal to that of the cylinder. The cylinder rotates about its axis at the spin rate ω and rotates about an axis that passes through its center of mass at the coning rate Ω. In practical applications, as in the analysis and design of liquid-filled projectiles, the parameter ε = τ sin θ, where τ = Ω/ω and θ is the angle between spin axis and coning axis, is small. As a result, linearization of the Navier-Stokes equations with this parameter is possible. Here, the full and linearized Navier-Stokes equations are solved by a spectral collocation method to investigate the nonlinear effects on the moments caused by the motion of the fluid inside the cylinder. In this regard, it has been found that nonlinear effects are negligible for τ ≈ 0.1, which is of practical interest to the design of liquid-filled projectiles, and the solution of the linearized Navier-Stokes equations is adequate for such a case. However, as τ increases, nonlinear effects increase, and become significant as ε surpasses about 0.1. In such a case, the nonlinear problem must be solved. Complete details on how to solve such a problem is presented.

scholarly journals Natural microbial polysaccharides as effective factors for modification of the catalytic properties of fungal cellobiose dehydrogenase

2021 ◽  
Author(s):  
Justyna Sulej ◽  
Magdalena Jaszek ◽  
Monika Osińska-Jaroszuk ◽  
Anna Matuszewska ◽  
Renata Bancerz ◽  
...  
Keyword(s):  
Catalytic Properties ◽  
Cellobiose Dehydrogenase ◽  
Pycnoporus Sanguineus ◽  
Practical Applications ◽  
Control Value ◽  
Electrochemical Parameters ◽  
Optimum Ph ◽  
Stabilization Effect ◽  
Fungal Polysaccharides ◽  
The Stability

AbstractPolysaccharides are biopolymers composed of simple sugars like glucose, galactose, mannose, fructose, etc. The major natural sources for the production of polysaccharides include plants and microorganisms. In the present work, four bacterial and two fungal polysaccharides (PS or EPS) were used for the modification and preservation of Pycnoporus sanguineus cellobiose dehydrogenase (CDH) activity. It was found that the presence of polysaccharide preparations clearly enhanced the stability of cellobiose dehydrogenase compared to the control value (4 °C). The highest stabilization effect was observed for CDH modified with Rh110EPS. Changes in the optimum pH in the samples of CDH incubated with the chosen polysaccharide modifiers were evidenced as well. The most significant effect was observed for Rh24EPS and Cu139PS (pH 3.5). Cyclic voltammetry used for the analysis of electrochemical parameters of modified CDH showed the highest peak values after 30 days of incubation with polysaccharides at 4 °C. In summary, natural polysaccharides seem to be an effective biotechnological tool for the modification of CDH activity to increase the possibilities of its practical applications in many fields of industry.

Dynamic Instability in Quartering Seas—Part III: Nonlinear Effects on Periodic Motions

1997 ◽  
Vol 41 (03) ◽  
pp. 210-223 ◽  
Author(s):  
K. J. Spyrou
Keyword(s):  
Periodic Motion ◽  
Horizontal Plane ◽  
Dynamic Instability ◽  
Parametric Instability ◽  
Nonlinear Effects ◽  
Ship Motions ◽  
Nonlinear Phenomena ◽  
Specific Sequence ◽  
The Stability ◽  
Two Stages

The loss of stability of the horizontal-plane periodic motion of a steered ship in waves is investigated. In earlier reports we referred to the possibility of a broaching mechanism that will be intrinsic to the periodic mode, whereby there will exist no need for the ship to go through the surf-riding stage. However, about this point the discussion was essentially conjectural. In order to provide substance we present here a theoretical approach that is organized in two stages: Initially, we demonstrate the existence of a mechanism of parametric instability of yaw on the basis of a rudimentary, single-degree model of maneuvering motion in waves. Then, with a more elaborate model, we identify the underlying nonlinear phenomena that govern the large-amplitude horizontal ship motions, considering the ship as a multi-degree, nonlinear oscillator. Our analysis brings to light a very specific sequence of phenomena leading to cumulative broaching that involves a change in the stability of the ordinary periodic motion on the horizontal plane, a transition towards subharmonic response and, ultimately, a sudden jump to resonance. Possible means for controlling the onset of such undesirable behavior are also investigated.

A Taxonomy to Aid in the Design of Complex Physical Activities for Older Adults

2017 ◽  
Vol 61 (1) ◽  
pp. 21-25
Author(s):  
Lyndsie M. Koon ◽  
Robert J. Brustad ◽  
Megan Babkes Stellino
Keyword(s):  
Physical Activity ◽  
Older Adults ◽  
Cognitive Function ◽  
Environmental Context ◽  
Physical Activities ◽  
The Body ◽  
Practical Applications ◽  
Aging Adults ◽  
The Stability ◽  
Positive Results

Physical activity participation is a non-pharmaceutical intervention that can be utilized to maintain and improve cognitive function in aging adults. Although simple physical activities yield positive results in regards to cognitive function, cognitively and motorically complex physical activities may have an even greater benefit on neuroplasticity for older adults. Commercially available products such as physical activity apps or exergames offer this population a means to engage in regular physical activity on their own. However, a taxonomy is necessary to help distinguish simpler physical activities from more complex physical activities. The taxonomy proposed in this paper carefully considers the following characteristics: the stability or transport of the body, object manipulation, intertrial variability, the environmental context and the reaction or to others. The dimensions of the taxonomy are operationally defined and practical applications are provided.

Sign in / Sign up

Export Citation Format

Share Document