Advances in experimental techniques and the ever-increasing fidelity of numerical simulations have led to an abundance of data describing fluid flows. This review discusses a range of techniques for analyzing such data, with the aim of extracting simplified models that capture the essential features of these flows, in order to gain insight into the flow physics, and potentially identify mechanisms for controlling these flows. We review well-developed techniques, such as proper orthogonal decomposition and Galerkin projection, and discuss more recent techniques developed for linear systems, such as balanced truncation and dynamic mode decomposition (DMD). We then discuss some of the methods available for nonlinear systems, with particular attention to the Koopman operator, an infinite-dimensional linear operator that completely characterizes the dynamics of a nonlinear system and provides an extension of DMD to nonlinear systems.

Model Reduction for Flow Analysis and Control

Bifurcation control deals with modification of bifurcation characteristics of a parameterized nonlinear system by a designed control input. Typical bifurcation control objectives include delaying t...

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Bifurcation control: theories, methods, and applications

Bifurcation analysis has previously been applied to the NASA Generic Transport Model (GTM) to provide insight into open-loop upset dynamics and also the impact on and sensitivity of such behaviour to closing the loop with a flight controller. However, these studies have not considered time delay in the system: this arises in all feedback controllers and has specific relevance when remotely piloting a vehicle such as the NASA AirSTAR GTM with ground-based controllers. Developments in the AirSTAR programme, in which a sub-scale generic airliner model will be tested for loss-of-control conditions over long ranges, raise the prospect of increased adverse effects of time delay relative to previous testing. This paper utilises bifurcation analysis, supplemented with time histories, on the GTM numerical model with a LQR-PI controller to evaluate the sensitivity of the closed-loop system stability to time delay. In this paper, the impact of time delays in both a fixed-gain and a gain-scheduled version of the controller is presented in terms of stability of nominal and off-nominal solutions.

Sensitivity of the Generic Transport Model upset dynamics to time delay

Synopsis: From the nostalgic remembrance of the first dynamic flight test this Survey Paper traces several milestones in the history of flight vehicle system identification. A comprehensive account of modern system identification techniques is provided. Several challenging examples bring out the fact that these techniques have reached a high level of maturity, making them a sophisticated and powerful tool not only for research purposes, but also to support the needs of the aircraft industry. This survey paper includes 183 references and provides a consolidated list of publications on the subject.

https://dlr.de/ft/en/portaldata/2/resources/dokumente/ft/jategaonkar/evol_sysid.pdf

Evolution of flight vehicle system identification

Bats have long captured the imaginations of scientists and engineers with their unrivaled agility and maneuvering characteristics, achieved by functionally versatile dynamic wing conformations as well as more than 40 active and passive joints on the wings. Wing flexibility and complex wing kinematics not only bring a unique perspective to research in biology and aerial robotics but also pose substantial technological challenges for robot modeling, design, and control. We have created a fully self-contained, autonomous flying robot that weighs 93 grams, called Bat Bot (B2), to mimic such morphological properties of bat wings. Instead of using a large number of distributed control actuators, we implement highly stretchable silicone-based membrane wings that are controlled at a reduced number of dominant wing joints to best match the morphological characteristics of bat flight. First, the dominant degrees of freedom (DOFs) in the bat flight mechanism are identified and incorporated in B2’s design by means of a series of mechanical constraints. These biologically meaningful DOFs include asynchronous and mediolateral movements of the armwings and dorsoventral movements of the legs. Second, the continuous surface and elastic properties of bat skin under wing morphing are realized by an ultrathin (56 micrometers) membranous skin that covers the skeleton of the morphing wings. We have successfully achieved autonomous flight of B2 using a series of virtual constraints to control the articulated, morphing wings.

A biomimetic robotic platform to study flight specializations of bats

Aircraft dynamics at high angles of attack due to loss of stability and control essentially limits its manoeuvrability. Modern control systems implement flight envelope protection at the cost of maneuverability to improve safety in these conditions. Flight envelope boundaries, which are set taking into account deterioration of stability and controllability due to separated flow, can be expanded by appropriate design of control laws. However, such a design requires extensive analysis of the maneuver envelope of the airframe and its utilization by the flight envelope protection laws. The reliability of this analysis depends on the adequate aerodynamic modeling which captures nonlinear unsteady variation of aerodynamic loads in these flight regimes. Two novel models for unsteady aerodynamics at low and high subsonic Mach numbers are described. These models and prototyping control laws are used for closed loop computational analysis. The computational methodology of clearing flight control laws for flight envelope expansion of a Generic Tailless Aircraft (GTA) is addressed.

Flight Envelope Expansion via Active Control Solutions for a Generic Tailless Aircraft

An output from research collaboration with TsAGI, Russia resulting in a revision of unsteady aerodynamics representation in active control alleviation of wind gust loads. The project was funded by ONERA, France in support of experimental tests on the free flight catapult facility in ONERA-Lille, designed for evaluation of unsteady aerodynamic effects during penetration of aircraft scaled model in the short gust (TsAGI Deputy Director V.L. Soukhanov, flight15@tsagi.ru).

On unsteady aerodynamic airfoil loads in the design of a control system for minimizing the effect of wind perturbations using the rudder on the trailing edge of the wing.l

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Evaluation of Unsteady Aerodynamic Effects in Stall Region for a T-Tail Transport Model

AIAA Atmospheric Flight Mechanics Conference, Portland, Oregon

Wind tunnel oscillatory testing is a technique conventionally used for the measurement of dynamic aerodynamic loads on subscale aircraft models. Oscillatory testing is commonly used for identificat...

Mikhail Goman

Papers

Flight Envelope Expansion via Active Control Solutions for a Generic Tailless Aircraft

On unsteady aerodynamic airfoil loads in the design of a control system for minimizing the effect of wind perturbations using the rudder on the trailing edge of the wing.l

Evaluation of Unsteady Aerodynamic Effects in Stall Region for a T-Tail Transport Model

AIAA Atmospheric Flight Mechanics Conference, Portland, Oregon

Self-Induced Roll–Yaw Oscillations of an Aircraft Model in a Wind Tunnel