IFASD2024 Paper Submission & Registration
17 – 21 June 2024, The Hague, The Netherlands

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13:30   Aeroelastic testing 2
Chair: Bret Stanford
30 mins
Flexible aircraft flight dynamics and loads model identification from flight test data in unsteady conditions
Andres Jurisson, Bart Eussen, Coen de Visser, Roeland de Breuker
Abstract: This paper presents a method for identifying flight dynamics models for aircraft that includes effects from the flexible structure and the effects from unsteady aerodynamics. In the time domain, the unsteady aerodynamic effects are often modelled using aerodynamic lag states. The proposed method involves first determining the poles that govern the dynamics for these lag states from flight data. This is followed by reconstructing the time signal histories for these lag states so that they can then be used as part of the model fitting procedure. Flight tests were conducted using a scaled Diana2 glider unmanned aerial vehicle (UAV) in order to collect experimental data for modelling. To be able to measure the response of the aircraft and its structure, the glider was instrumented with a wide range of sensors including accelerometers, gyroscopes and strain gauges placed across the aircraft structure. During the flight, various excitation manoeuvres were conducted by the pilot while the aircraft responses were collected. From these measurements, a full flight dynamics model consisting of both lateral and longitudinal dynamics was then identified. Additionally, a model predicting the tail and wing root loads was also identified. First, a rigid aircraft model was fitted that was then extended with states corresponding to the flexible modes and aerodynamic lags. Comparison between the rigid and extended model showed that the addition of structural modes and aerodynamic lag states to the identified models can lead up to 30% improvement in predicting aircraft responses. In conclusion, the method developed and presented in this paper is able to identify flight dynamics models from flight data that more accurately capture the dynamics of flexible aircraft by including effects from the flexible structure and unsteady aerodynamics.
30 mins
Aeroelastic hybrid testing for industrial applications
Davide Balatti, Hamed Haddad Khodaparast, Shakir Jiffri, Michael Friswell, Sebastiano Fichera, Alessandra Vizzaccaro, Andrea Castrichini
Abstract: Aeronautical structures, due to uncertainties and nonlinearities, require extensive experimental testing for both design and certification, especially concerning their aeroelastic behavior. Such experimental procedures are conducted through both wind tunnel tests and flying prototypes. The latter introduces risks to personnel, entails higher costs, and provides considerably less control over external factors. At the same time, wind tunnel tests offer safety, affordability, repeatability, and control over external variables. However, due to the limitations of the wind tunnel test section, only scaled models or limited portions of the whole structure can be tested, resulting in a lack of interaction with surrounding aero-structural systems. Hybrid Testing (HT) is an advanced experimental technique in structural engineering that combines physical testing with numerical simulations to assess the behavior of complex structures and systems under various loading conditions. In HT, the structure of interest is divided into physical and numerical substructures and then combined to form a hybrid structure reproducing the behavior of the original system. In the existing literature, HT has been primarily applied to academic simplified aeroelastic systems. This work aims to evaluate the feasibility of HT for aeroelastic industrial applications, considering two case studies. In the first case, an aeroelastic straight untapered half-wing is examined. The second case involves a modification of the FFAST (Future Fast Aeroelastic Simulation Technologies) aeroelastic model representing a civil commercial aircraft with hinged wingtips. In this work, both virtual and physical substructures are simulated. A transfer system ensures force and displacement compatibility between the numerical and physical substructures through a control system employing sensors and actuators. For both cases, sensors and actuators are modelled to study the effects of the transfer system delay and limit bandwidth. Additionally, to ensure the correctness of the HT, an innovative combination of an active and passive transfer system is proposed.
30 mins
Elastic wind tunnel model design via eigenvector-based level-set topology optimization
Eisuke Nakagawa, Tomohiro Yokozeki, Natsuki Tsushima
Abstract: The objective of this study is to develop a numerical method for designing elastic wind tunnel models suitable for additive manufacturing. To assess dynamic aeroelastic phenomena in wind tunnels, the scaled model must be elastic and emulate the dynamic characteristics of full-scale aircraft [1]. Realizing structural properties at scaled size based on the scaling law is challenging. When scaling down the full-scale components to the scaled model, changes in some structural properties occur [1]. Also, practical constraints may hinder directly scaling down internal structure of full-scale aircraft. Therefore, redesign of the internal structure is necessary. However, the process of redesigning the internal structure is complicated. In this study, we propose a numerical method for designing the internal structure that can be 3D printed. In this work, a Level-set topology optimization method [2] is developed to generate the internal structure of elastic wind tunnel model, which has equivalent mass, eigenvalues, and eigenvectors to its full-scale aircraft. In this method, the internal structure's boundary is implicitly represented by a level-set function. For structural analysis, an automatic differentiation algorithm is integrated into the extended finite element method [3] to enable gradient-based optimization. The proposed method was tested on a simple geometry case. The result showed that the proposed method can iteratively optimize the structure to satisfy each objective function, i.e., the mass, eigenvalues, and eigenvectors. Future modifications will allow consideration of static deflection and multi-objective optimization. The proposed method can take eigenvectors as the objective function. Although there is some research on topology optimization using eigenvalues as the objective function [4], there are few research using eigenvectors as the objective function. The necessity to calculate all eigenvectors to derive one eigenvector derivative vector in machine precision has traditionally been impractical [5]. This study introduces a new approximation method to efficiently optimize structures to meet eigenvector targets. In conclusion, the proposed method can design the 3D-printable elastic wind tunnel models, considering mass, eigenvalues, and eigenvectors as objective functions. Ongoing modifications aim to integrate static analysis results and handle multi-objective optimization.
30 mins
Shape Identification of a wing model by additive manufacturing for transonic tunnel testing
Natsuki Tsushima, Holger Mai, Marc Braune, Thomas Buete
Abstract: Additive manufacturing with a higher degree of design and manufacturing freedom has the potential to enhance structural performance and capability. The technique may also help to effectively perform wind tunnel testing. This paper aims to explore a structural shape identification technique for additively manufactured wing structures to enhance the capability of additively manufactured wing models for transonic wind tunnel testing. The objectives of this paper are 1) to explore the feasibility and capability of a method for the structural shape identification of additively manufactured solid wing structures based on strain measurements, and 2) to design an integrated structural monitoring system into AM-based transonic wing models, which enables the effective construction and investigation of aeroelastic wing models, and 3) to investigate the prediction accuracy for deformations of such a wing model. Ko’s displacement theory was applied to identify structural deformations of wing structures based on strain measurements in this study. Based on the numerical results, it was shown that Ko’s theory could provide good predictions even for the deformations of a solid swept and tapered wing with an unsymmetric airfoil. The aeroelastic simulation proved that the shape prediction of such a wing model based on the designed strain measurement system and Ko’s theory could provide sufficient accuracy for deformation monitoring.

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