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Our Research Vision
Images: Airbus, NASA, and Aurora
Our Research Areas
Modeling, analyzing, and simulating geometrically nonlinear aeroelastic systems
The quest for sustainable flight is driving new aerospace vehicle designs toward increasingly lightweight structures that experience larger aeroelastic deflections. These deflections introduce geometrical nonlinearities that invalidate the conventional linear approaches used for aeroelastic modeling, analysis, and simulation. To address this issue, we must establish trusted computational approaches that capture geometrical nonlinearities and understand their impacts on aeroelastic dynamics.
Our current work in this area seeks to answer the following basic research questions:
What is the appropriate level of model complexity required to capture aeroelastic dynamics in the presence of geometrically nonlinear effects?
How does model complexity impact prediction accuracy and computational cost?
How do geometrically nonlinear effects impact aeroelastic dynamics?
We focus on both assessing the predictive capabilities of existing geometrically nonlinear approaches and developing new approaches to handle geometrically nonlinear effects. Our research in this area aligns with the efforts under the frame of the AIAA Aeroelastic Prediction Workshop.
While we have focused on geometrically nonlinear wings in low-speed or transonic flow, we are expanding our research to panels in high-speed flow.
Related journal publications
Riso and Cesnik, "Geometrically Nonlinear Effects in Wing Aeroelastic Dynamics at Large Deflections," Journal of Fluids and Structures, 2023 [Link]
Riso and Cesnik, "Impact of Low-Order Modeling on Aeroelastic Predictions for Very Flexible Wings," Journal of Aircraft, 2023 [Link]
Related conference publications
Sanghi et al., "Evaluation of Aeroelastic Models for Gust Response Prediction in Very Flexible Wings," IFASD, 2024 [Link]
Ritter et al., "Collaborative Pazy Wing Analyses for the Third Aeroelastic Prediction Workshop," AIAA SciTech Forum, 2024 [Link]
Related presentations
Predicting flutter and limit-cycle oscillations in nonlinear aeroelastic systems
Flutter is a dynamic aeroelastic instability associated with the onset of diverging oscillations. This instability raises a significant concern in the design of aerospace vehicles, which is exacerbated by the push to develop configurations capable of higher speeds, enhanced energy efficiency, or new missions (or all of the above). New aerospace vehicle configurations also present multiple sources of nonlinearity, making their flutter characteristics change with the equilibrium state and introducing the potential for periodic responses known as limit-cycle oscillations (LCOs) even before the flutter onset. Flutter and LCOs of aerospace vehicles that exhibit nonlinear behaviors remain poorly understood due to the challenges in obtaining accurate predictions at a computational cost suitable for extensive parameter space exploration.
Our current work in this area seeks to answer the following basic research questions:
How can we best predict flutter and LCOs in nonlinear aeroelastic systems?
What are the fundamental mechanisms that drive these dynamics in systems relevant to current and future aerospace vehicles?
We focus on developing scalable non-intrusive analysis methods and deploying these methods in fixed-wing and vertical lift applications.
Part of our research in this area is under the frame of the Georgia Tech Vertical Lift Research Center of Excellence.
Related journal publications
Riso, "Evaluation of Whirl Flutter Prediction Methods for a System with Hardening or Softening Structural Nonlinearities," J. of the American Helicopter Society [Link]
de Dominicis and Riso, "Bifurcation Analysis of Single-Bay Supersonic Panels Using Pre-Flutter Output Data," AIAA Journal [Link]
Gali et al., "Fundamental Investigation into Output-Based Prediction of Whirl Flutter Bifurcations," Journal of Fluids and Structures [Link]
Riso et al., "Output-Based Flutter Bifurcation Forecasting in Nonlinear Fluid-Structural Systems with Multiple Varying Parameters," Journal of Fluids and Structures [Link]
Riso*, Ghadami* (equal contribution), et al., "Data-Driven Forecasting of Postflutter Responses of Geometrically Nonlinear Wings," AIAA Journal [Link]
Jonsson et al., "Flutter and Post-Flutter Constraints in Aircraft Design Optimization," Progress in Aerospace Sciences [Link]
Related conference publications
Gatlin and Riso, "Predicting Whirl Flutter Bifurcations Using Machine Learning," VFS 80th Annual Forum [Link]
Gali and Riso, "Output-Based Approach for Tiltrotor Whirl Flutter Bifurcation Analysis," VFS 80th Annual Forum [Link]
Gali et al., "Inflow Model Effects on Propeller Whirl Flutter," VFS 80th Annual Forum [Link]
Warren and Riso, "Sliding-Window Matrix Pencil Method for Whirl Flutter Bifurcation Analysis," VFS 80th Annual Forum [Link]
Riso, "Impact of System Nonlinearities on Output-Based Whirl Flutter Prediction," 6th Decennial VFS Aeromechanics Specialists' Conference [Link]
Related presentations
Integrating dynamic aeroelasticity into design optimization
The aeroelastic characteristics of aerospace vehicles are typically assessed late in the design phase. If undesirable characteristics are discovered at that stage, they require late-stage design changes leading to suboptimal performance, delayed production timelines, and increased costs. The field has made progress in integrating aeroelastic analyses into design optimization in the form of constraints, an emerging approach that holds the promise to mitigate the risk of late-stage design changes while enabling more advantageous tradeoffs between performance, aeroelastic characteristics, and other design requirements. However, considering aeroelastic dynamics as design constraints remains a significant challenge due to the high computational costs of dynamic calculations, especially when nonlinear effects come into play. To address these issues, we must develop scalable aeroelastic constraints for (nonlinear) dynamic phenomena that meet the requirements of computationally efficient gradient-based optimization algorithms. These constraints are crucial to mitigate undesired dynamics early in the design phase and harness nonlinearity for higher performance.
Our current work in this area seeks to answer the following basic research questions:
How can we best consider flutter and LCO requirements as design optimization constraints?
How should an aeroelastic system be designed to mitigate undesired (or produce desired) flutter and LCO characteristics?
We focus on both developing constraint formulations and demonstrating their capabilities for specific fixed-wing and vertical lift applications.
While we currently focus on flutter and LCOs in the presence of geometrical nonlinearities, we are broadening our research to other nonlinear effects.
Related journal publications
Golla et al., "Sliding-Window Matrix Pencil Method for Design Optimization with Limit-Cycle Oscillation Constraints", AIAA Journal [Link]
Riso et al., "Bifurcation-Diagram-Free Post-Flutter Response Constraint for Design Optimization," AIAA Journal [Link]
Jonsson et al., "High-Fidelity Gradient-Based Wing Structural Optimization Including Geometrically Nonlinear Flutter Constraint", AIAA Journal [Link]
Gray et al., "High-Fidelity Aerostructural Optimization with a Geometrically Nonlinear Flutter Constraint," AIAA Journal [Link]
Jonsson et al., "Flutter and Post-Flutter Constraints in Aircraft Design Optimization," Progress in Aerospace Sciences [Link]
Related presentations
Riso, "Advances in Aeroelastic Prediction and Design Optimization for Next-Generation Aerospace Vehicles," IFASD, 2024 [Slides]
Our Journal Publications
Mentees at Georgia Tech are in blue. Former mentees at other institutions are in green.
2025
Sanghi, Riso, and Cesnik, "Ride Quality in Transonic High-Aspect-Ratio-Wing Aircraft," Journal of Aircraft [Preprint]
Riso, "Evaluation of Output-Based Whirl Flutter Prediction Methods for a System with Hardening or Softening Structural Nonlinearities," J. Am. Helicopter Soc. [Link]
2024
de Dominicis and Riso, "Bifurcation Analysis of Single-Bay Supersonic Panels Using Pre-Flutter Output Data," AIAA Journal [Link]
Golla et al., "Sliding-Window Matrix Pencil Method for Design Optimization with Limit-Cycle Oscillation Constraints", AIAA Journal [Link]
Sanghi et al., "Roll Maneuverability of Transonic High-Aspect-Ratio-Wing Aircraft with Flared Folding Wingtips," Journal of Aircraft [Link]
2023
Gali et al., "Fundamental Investigation into Output-Based Prediction of Whirl Flutter Bifurcations," Journal of Fluids and Structures [Link]
Riso and Cesnik, "Geometrically Nonlinear Effects in Wing Aeroelastic Dynamics at Large Deflections," Journal of Fluids and Structures [Link]
Riso et al., "Bifurcation-Diagram-Free Post-Flutter Response Constraint for Design Optimization," AIAA Journal [Link]
Jonsson et al., "High-Fidelity Gradient-Based Wing Structural Optimization Including Geometrically Nonlinear Flutter Constraint", AIAA Journal, [Link]
Gray et al., "High-Fidelity Aerostructural Optimization with a Geometrically Nonlinear Flutter Constraint," AIAA Journal [Link]
Riso and Cesnik, "Impact of Low-Order Modeling on Aeroelastic Predictions for Very Flexible Wings," Journal of Aircraft [Link]
2022
Riso et al., "Estimating Flutter Bifurcation Diagrams Using the State Velocity", AIAA Journal [Link]
2021
Riso et al., "Output-Based Flutter Bifurcation Forecasting in Nonlinear Fluid-Structural Systems with Multiple Varying Parameters," Journal of Fluids and Structures [Link]
2020
Riso*, Ghadami* (equal contribution), et al., "Data-Driven Forecasting of Postflutter Responses of Geometrically Nonlinear Wings," AIAA Journal [Link]
2019
Jonsson et al., "Flutter and Post-Flutter Constraints in Aircraft Design Optimization," Progress in Aerospace Sciences [Link]
Mastroddi et al., "Time- and Frequency-Domain Linear Viscoelastic Modeling of Highly Damped Aerospace Structures," Mechanical Systems and Signal Processing [Link]
2018
Riso et al., "Nonlinear Aeroelastic Trim of Very Flexible Aircraft Described by Detailed Models," Journal of Aircraft [Link]
Riso et al., "Semi-Analytical Unsteady Aerodynamic Model of a Flexible Thin Airfoil," Journal of Fluids and Structures [Link]
Riso et al., "Experimental Validation of Solid Rocket Motor Damping Models," CEAS Space Journal [Link]
2017
Saltari et al., "Finite-Element-Based Modeling for Flight Dynamics and Aeroelasticity of Flexible Aircraft," Journal of Aircraft [Link]
2016
Riso et al., "Nonlinear Aeroelastic Modeling via Conformal Mapping and Vortex Method for a Flat-Plate Airfoil in Arbitrary Motion," Journal of Fluids and Structures [Link]
Our Conference Publications
2025
Hegde and Riso, "Modal Characteristics of Microvascular Composite Panels," AIAA SciTech Forum [Link]
2024
Sanghi et al., "Evaluation of Aeroelastic Models for Gust Response Prediction in Very Flexible Wings," IFASD [Link]
Gatlin and Riso, "Predicting Whirl Flutter Bifurcations Using Machine Learning," VFS 80th Annual Forum [Link]
Gali and Riso, "Output-Based Approach for Tiltrotor Whirl Flutter Bifurcation Analysis," VFS 80th Annual Forum [Link]
Gali et al., "Inflow Model Effects on Propeller Whirl Flutter," VFS 80th Annual Forum [Link]
Warren and Riso, "Sliding-Window Matrix Pencil Method for Whirl Flutter Bifurcation Analysis," VFS 80th Annual Forum [Link]
Riso, "Impact of System Nonlinearities on Output-Based Whirl Flutter Prediction," 6th Decennial VFS Aeromechanics Specialists' Conference [Link]
Riso, "Output-Based Prediction of Whirl Flutter Limit-Cycle Oscillations Considering Multiple Varying Parameters," AIAA SciTech Forum [Link]
Golla et al., "A Sliding-Window Matrix Pencil Method for Aeroelastic Design Optimization with Limit-Cycle Oscillation Constraints," AIAA SciTech Forum [Link]
de Dominicis and Riso, "Limit-Cycle Oscillation Prediction in Supersonic Panels Using Pre-Flutter Transient Responses," AIAA SciTech Forum [Link]
Ritter et al., "Collaborative Pazy Wing Analyses for the Third Aeroelastic Prediction Workshop," AIAA SciTech Forum [Link]
2023
Gali et al., "Predicting Whirl Flutter Bifurcations Using Pre-Flutter Output Data," AIAA SciTech Forum [Link]
Riso and Cesnik, "Investigation of Geometrically Nonlinear Effects in the Aeroelastic Behavior of a Very Flexible Wing," AIAA SciTech Forum [Link]
Sanghi et al., "Analysis of Ride Qualities in Transonic High-Aspect-Ratio-Wing Aircraft," AIAA SciTech Forum [Link]
2022
Riso and Cesnik, "Post-Flutter Analysis of the Pazy Wing Geometrically Nonlinear Benchmark Model," IFASD [Preprint]
Sanghi et al., "Analysis of Ride Qualities in Transonic High-Aspect-Ratio-Wing Aircraft," IFASD [Preprint]
Gray et al., "High-Fidelity Aerostructural Optimization with a Geometrically Nonlinear Flutter Constraint," IFASD [Preprint]
Riso and Cesnik, "Low-Order Geometrically Nonlinear Aeroelastic Modeling and Analysis of the Pazy Wing Experiment," AIAA SciTech Forum [Link]
Jonsson et al., "High-Fidelity Gradient-Based Wing Structural Optimization Including a Geometrically Nonlinear Flutter Constraint," AIAA SciTech Forum [Link]
Sanghi et al., "Conventional and Unconventional Control Effectors for Load Alleviation in High-Aspect-Ratio-Wing Aircraft," AIAA SciTech Forum [Link]
2021
Riso et al., "A Post-Flutter Response Constraint for Gradient-Based Aircraft Design Optimization," AIAA AVIATION Forum [Link]
Riso and Cesnik, "Correlations Between UM/NAST Nonlinear Aeroelastic Simulations and the Pre-Pazy Wing Experiment," AIAA SciTech Forum [Link]
2020
Sanghi et al., "Influence of Aileron Placement on Roll Response of High-Aspect-Ratio-Wing Aircraft," AIAA AVIATION Forum [Link]
Riso et al., "Model-Free Nonlinear Flutter Forecasting in Fluid-Structural Systems with Multiple Varying Parameters," ISFA, canceled due to COVID-19 [Preprint]
Riso et al., "Parametric Roll Maneuverability Analysis of a High-Aspect-Ratio-Wing Civil Transport Aircraft," AIAA SciTech Forum [Link]
Sanghi et al., "Impact of Control-Surface Flexibility on the Dynamic Response of Flexible Aircraft," AIAA SciTech Forum [Link]
2019
Riso et al., "Model-Free Forecasting of Limit Cycle Oscillations in Geometrically Nonlinear Wings," IFASD [Link]
Eugeni et al., "Structural Damping Models for Passive Aeroelastic Control," IFASD [Link]
2018
Riso et al., "Assessment of Grain Damping Models for Finite Element Analysis of Solid Rocket Motors," ECSSMET [Preprint]
Riso et al., "Coupled Flight Dynamics and Aeroelasticity of Very Flexible Aircraft Based on Commercial Finite Element Solvers," AIAA SciTech Forum [Link]
2017
Saltari et al., "On the Control of Aeroelastic/Flight Dynamic Integrated Stability of Maneuvering Aircraft," IFASD [Link]
Riso et al., "A FEM-Based Approach for Nonlinear Aeroelastic Trim of Highly Flexible Aircraft," IFASD [Link]
Riso et al., "Semi-analytical Unsteady Aerodynamic Modeling for a Flexible Thin Airfoil in Arbitrary Motion," IFASD [Link]
2015
Riso et al., "Nonlinear Aeroelastic Modeling via Conformal Mappings for a Typical Section in Arbitrary Motion," IFASD [Preprint]
Selected Invited Talks
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