Cristina Riso

Georgia Institute of Technology | GT · School of Aerospace Engineering

This paper investigates the modal characteristics of a composite panel with an embedded network of fluid-filled microchannels. Embedded microvascular networks allow for integrating additional functionality into load-bearing structures, such as active cooling or self-healing. To understand the impact of the microvascular network on panel modal chara...

Presentation slides associated with the conference paper: Hegde and Riso, "Modal Characteristics of Microvascular Composite Panels," AIAA SciTech Forum, 2025. DOI: https://arc.aiaa.org/doi/abs/10.2514/6.2025-0625

This paper evaluates selected output-based methods for whirl flutter prediction for a system with hardening or softening structural nonlinearities. It considers four conventional methods that estimate modal damping using linear assumptions: logarithmic decrement, exponential fit, matrix-pencil estimation, and moving-block analysis. Additionally, it...

This paper introduces a novel approach to constrain limit-cycle oscillations in design optimization. The approach builds upon a limit-cycle oscillation constraint that bounds the recovery rate to equilibrium, circumventing the need for bifurcation diagrams. Previous work demonstrated the constraint using approximate recovery rates obtained by evalu...

The next generation of aerospace vehicles poses significant aeroelastic challenges, ranging from the large deflections of high-aspect-ratio wings to the unexplored dynamics of unconventional configurations. These challenges require advances in our ability to predict, mitigate, and harness aeroelastic phenomena in the design phase. This keynote high...

This paper investigates an output-based approach for flutter bifurcation analysis of single-bay panels in supersonic flow. The approach leverages bifurcation forecasting, a class of methods to predict bifurcation diagrams using pre-bifurcation output data. This work is the first study into this approach applied to panel limit-cycle oscillations, bu...

This paper compares aeroelastic models for gust response prediction in very flexible wings. The investigations focus on the Pazy wing benchmark developed at Delft University of Technology for gust response experiments in low-speed flow. The comparisons consider two geometrically nonlinear aeroelastic models of the wing, which comprise an equivalent...

This paper investigates inflow model effects on propeller whirl flutter focusing on a propeller-nacelle test case from classical whirl flutter theory. The model is implemented into the Rotorcraft Comprehensive Analysis System framework considering two approaches to capture the inflow on the propeller disk: a uniform inflow model and the viscous vor...

This paper investigates an output-based approach for tiltrotor whirl flutter bifurcation analysis. The approach uses free decay output data for a quantity of interest at various forward speeds to estimate the system's recovery rate to equilibrium while capturing its variation with amplitude. The recovery rate is then extrapolated to predict the bif...

This paper investigates inflow model effects on propeller whirl flutter focusing on a propeller-nacelle test case from classical whirl flutter theory. The model is implemented into the Rotorcraft Comprehensive Analysis System framework considering two approaches to capture the inflow on the propeller disk: a uniform inflow model and the viscous vor...

This paper investigates the feasibility of using machine learning to predict whirl flutter bifurcation diagrams. The machine learning techniques selected for the study are XGBoost and the long short-term memory neural network. These techniques are selected for their suitability for sequential and nonlinear data. The techniques are investigated for...

This paper investigates a sliding-window matrix pencil method for predicting flutter points and limit-cycle oscillation amplitudes of nonlinear aeroelastic systems that experience whirl flutter. The approach applies the matrix pencil method to a short time window that slides along the free decay of a quantity of interest, quantifying the variation...

This paper investigates roll maneuvers of a very flexible, transonic high-aspect-ratio-wing aircraft with flared folding wingtips representing a potential future commercial transport configuration. The computational study leverages a fully coupled nonlinear aeroelastic-flight dynamics framework for simulating roll maneuvers commanded by deflecting...

This paper investigates the impact of system nonlinearities on output-based whirl flutter prediction. The investigation considers four widely-used damping identification and extrapolation methods (logarithmic decrement, exponential fit, matrix-pencil estimation, and moving-block analysis) alongside bifurcation forecasting, a recently proposed metho...

In this paper, collaborative aeroelastic analyses of the Pazy Wing are presented, which support the activities of the Large Deflection Working Group, a subgroup of the 3rd Aeroelastic Prediction Workshop (AePW3). The Pazy Wing is a benchmark for the investigation of nonlinear aeroelastic effects at very large structural deflections. Tip deformation...

This paper investigates an approach for predicting limit-cycle oscillations of supersonic panels using output data from pre-flutter transient responses. The approach involves characterizing the recovery rate to equilibrium in the pre-flutter regime, which is used to predict the bifurcation diagram for a quantity of interest. This work explores the...

This paper presents a new approach for constraining limit-cycle oscillations in aeroelastic design optimization. The approach builds on a gradient-oriented limit-cycle oscillation constraint that bounds the recovery rate to equilibrium, bypassing the need for bifurcation diagrams. Previous work demonstrated the constraint using recovery rates appro...

This paper investigates an output-based approach for predicting multi-dimensional whirl flutter bifurcation diagrams, which illustrate the amplitude variation of limit-cycle oscillations resulting from whirl flutter with multiple parameters. The approach involves characterizing the system's recovery rate to equilibrium based on output data from tra...

This paper investigates an approach to predicting whirl flutter bifurcations using pre-flutter output data. The approach leverages the critical slowing down phenomenon, which makes aeroelastic systems recover to equilibrium from disturbances more slowly closer to the flutter boundary. By quantifying this phenomenon based on output data from pre-flu...

Lightweight, high-aspect-ratio wings make aircraft more energy efficient thanks to their lower induced drag. Because such wings exhibit large deflections, design optimization based on linear flutter analysis of the wing undeformed shape is inadequate. To address this issue, we develop a framework for integrating a geometrically nonlinear flutter co...

This paper investigates geometrically nonlinear effects due to nonlinear kinematics and follower aerodynamics in the aeroelastic dynamics of a very flexible wing. The test case is the Pazy wing, a benchmark model for geometrically nonlinear aeroelastic studies involving large deflections in low-speed flow. The work builds on a low-order model of th...

When designing aircraft, avoiding dynamic aeroelastic instabilities such as flutter is a key requirement. One way to meet this requirement is to use a multidisciplinary design optimization subject to a flutter constraint. Flutter-constrained design optimizations have used geometrically linear detailed models, which do not accurately predict flutter...

This paper introduces a new metric to constrain post-flutter responses of aeroelastic systems in design optimization. The new metric aggregates the recovery rate to equilibrium for a range of operating conditions, modes, and amplitudes, resulting in a scalar constraint that does not involve the bifurcation diagram. By generalizing damping-based flu...

This paper explores an approach for predicting whirl flutter bifurcations using output data in the pre-flutter regime. The approach leverages the critical slowing down phenomenon, which causes aeroelastic systems to recover from disturbances more slowly as they operate closer to the flutter boundary. By quantifying how the recovery rate changes wit...

This paper investigates the ability of low-order structural and aerodynamic models to predict geometrically nonlinear aeroelastic behaviors associated with large wing deflections. The study considers the Pazy wing, a very flexible wing developed at the Technion—Israel Institute of Technology for geometrically nonlinear aeroelastic benchmark studies...

This paper investigates geometrically nonlinear effects associated with nonlinear kinematics and follower aerodynamics in the aeroelastic behavior of a very flexible wing in low-speed flow. The test case is the Pazy wing, a benchmark model for geometrically nonlinear studies developed under the Third Aeroelastic Prediction Workshop Large Deflection...

This paper studies roll maneuvers of a very flexible, high-aspect-ratio-wing transport aircraft with free flared folding wingtips. The maneuvers are commanded by different control surfaces inboard or outboard of the hinge. The computational study is conducted using a fully coupled nonlinear aeroelastic-flight dynamics framework-the University of Mi...

Slides from my presentation at the 2022 International Forum on Aeroelasticity and Structural Dynamics (IFASD) in Madrid. The corresponding journal paper is available at the link below: https://www.researchgate.net/publication/370061901_High-Fidelity_Aerostructural_Optimization_with_a_Geometrically_Nonlinear_Flutter_Constraint

Please see the peer-reviewed version of this paper published in the AIAA Journal, available at: https://www.researchgate.net/publication/370061901_High-Fidelity_Aerostructural_Optimization_with_a_Geometrically_Nonlinear_Flutter_Constraint

Ride qualities measure passenger and/or pilot comfort while aircraft experience vibrations and accelerations during flight. Assessing ride qualities is critical to ensure aircraft meet operational requirements. This paper studies the ride qualities of a transonic high-aspect-ratio-wing aircraft representative of a potential future civil transport c...

The Third Aeroelastic Prediction Workshop Large Deflection Working Group (AePW3-LDWG) revolves around the Pazy wing, a geometrically nonlinear benchmark model for aeroelastic tests in low-speed flow. Previous work by the authors assessed a low-order model of the Pazy wing against higher-order numerical solutions and experimental data. This paper le...

This paper introduces a method for estimating flutter bifurcation diagrams of systems described by time-domain state-space models. The method estimates the bifurcation diagram by quantifying changes in the recovery rate in the pre-flutter regime. The recovery rate is approximated from the state velocity, overcoming the need for transient output dat...

This paper has been superseded by our peer-reviewed journal paper, which can be found at: https://www.researchgate.net/publication/371071869_High-Fidelity_Gradient-Based_Wing_Structural_Optimization_Including_Geometrically_Nonlinear_Flutter_Constraint

Civil transport aircraft typically use trailing-edge control surfaces for gust and maneuver load alleviation. However, wash-out effects due to wing flexibility reduce the effectiveness of these devices and may even result in control reversal. Future aircraft configurations with very flexible, high-aspect-ratio wings may use novel load alleviation s...

The Third Aeroelastic Prediction Workshop Large Deflection Working Group is dealing with the analysis and experimentation of the Pazy wing, a very flexible wing developed for benchmark studies at the Technion-Israel Institute of Technology. This work leverages the Pazy wing as the test case to study the ability of low-order structural and aerodynam...

Considering flutter as a constraint in aircraft design optimization has the potential to enable energy-efficient vehicle designs with high-aspect-ratio wings while meeting flutter requirements early in the design cycle. However, nonlinear aeroelastic effects in high-aspect-ratio wings may cause self-sustained oscillations to arise even before flutt...

High-performance flutter and post-flutter predictions are critical in the design of a vast range of nonlinear fluid-structural systems. However, these predictions are often unfeasible due to their high computational cost. Moreover, traditional methods for flutter and post-flutter predictions are model intrusive and limited to one varying parameter...

The Third Aeroelastic Prediction Workshop Large Deflection Group is invested in validating computational models to analyze geometrically nonlinear wings. The effort is based on the Pazy wing, a wind-tunnel aeroelastic benchmark developed at the Technion-Israel Institute of Technology. To consolidate the techniques for testing the Pazy wing, the Tec...

The need for improving fuel efficiency of civil transport aircraft is leading to design high-aspect-ratio-wing configurations that have high aerodynamic performance. However, these configurations exhibit higher structural flexibility, which degrades aileron effectiveness and roll maneuverability. This paper investigates the influence of aileron spa...

Ensuring adequate flutter margins is a critical step in aircraft design. However, in the presence of nonlinear effects, subcritical limit-cycle oscillations can arise even before flutter occurs. When nonlinear effects are anticipated, post-flutter analyses have to be integrated into aircraft design in addition to flutter computations for preventing...

Next-generation civil transport aircraft may take advantage of high-aspect-ratio wings for lower induced drag. However, these high-aspect-ratio wings are very flexible and may degrade aircraft roll maneuverability. This paper analyzes the roll maneuverability of a high-aspect-ratio-wing civil transport aircraft derived from a contemporary configura...

Significant flexibility in aircraft wings may reduce aileron effectiveness and degrade roll maneuverability. This paper investigates the impact of aileron flexibility on the dynamic response of a generic transport aircraft in free flight. To this purpose, the University of Michigan's Nonlinear Aeroelastic Simulation Toolbox (UM/NAST) is extended to...

Ensuring adequate flutter margins is a critical step in aircraft design. However, geometrically nonlinear configurations may develop limit cycle oscillations even before reaching the flutter boundary. When nonlinear effects are anticipated, post-flutter analyses have to be integrated into design for preventing undesirable subcritical limit cycles....

Research presented at the 2019 Women in Aerospace Symposium Website: https://aeroastro.mit.edu/wia2019/

Flutter is a dynamic aeroelastic instability driven by the interaction of inertial, elastic, and aerodynamic forces. It is an undesirable phenomenon in aircraft because it causes divergent oscillations that may lead to structural damage or failure, performance and ride comfort degradation, or loss of control. If flutter is discovered at the aircraf...

This Paper presents an efficient algorithm for the nonlinear aeroelastic trim analysis of very flexible aircraft described by detailed models. The algorithm is based on a novel inertia relief technique for large displacements and is applicable to fluid–structure iteration frameworks coupling generic structural and aerodynamic solvers, including hig...

This paper presents a geometrically exact semi-analytical approach to model the unsteady aerodynamics of a flexible thin airfoil in incompressible potential flow. The velocity field is described by a complex potential, which is developed by mapping the airfoil boundary onto a circle. This methodology, well established for small disturbances, is her...

In design and certification of spacecraft, payload/launcher coupled load analyses are performed to simulate the satellite dynamic environment. To obtain accurate predictions, the system damping properties must be properly taken into account in the finite element model used for coupled load analysis. This is typically done using a structural damping...

Fully coupled equations of rigid-body and structural dynamics of flexible aircraft are deduced from the weak formulation of Cauchy’s equation for an unconstrained elastic continuum. An appropriate choice of the body coordinate system enables to describe inertial coupling using a reduced set of coefficients, which are estimated for complex configura...

A novel approach is presented to compute nonlinear aeroelastic trim of highly flexible aircraft by coupling off-the-shelf solvers for structures and aerodynamics. The methodology includes an inertia relief algorithm for large displacements to perform nonlinear static analysis of unrestrained bodies, which is currently not possible in commercially a...

This paper focuses on the application of a flexible-aircraft model for the synthesis of a robust full-state control law to suppress the body-freedom flutter instability of a flying-wing vehicle. This phenomenon is typically observed in tailless configurations as a result of the coupling between a relatively high-frequency short-period mode and a lo...

A nonlinear aerodynamic modeling based on conformal mapping is presented to obtain semi-analytical formulas for the unsteady aerodynamic force and pitching moment on a flat-plate airfoil in arbitrary motion. The aerodynamic model accounts for large amplitudes and non-planar wake and is used to study the aeroelastic behavior of a flat-plate airfoil...