Advanced systems and services for ground vibration testing - Application for a research test on an Airbus A340-600 aircraft

Aerospace manufacturers are faced with the challenge of designing systems and components that have to be safer, more reliable, affordable, offer improved passenger comfort and have less environmental impact than their competitors. In addition, they have to systematically reduce development times in order to get new products to market earlier. In the usual case, only a few prototypes are available for testing and experimental verification, in most cases, only towards the end of the development cycle. To shorten development times while still assuring design critical issues like structural integrity and safety, aircraft development teams are faced with several Ground Vibration Testing (GVT) challenges: (i) ensure identification of all critical modes and assess their non-linear behavior; (ii) manage challenging logistical requirements linked to boundary conditions, structure configurations, the typical usage of high number of sensors with multiple shakers and multi-shift testing teams; (iii) reduce test campaign duration to match development schedule and costs; (iv) deliver accurate, validated and traceable reference data in support of the mathematical model updating and of the flutter certification process. This paper will focus on some recent advances in systems and services that allow testing teams to realize an important testing and analysis time reduction without compromising the accuracy of the results. Emphasis will be put on system performance and openness of the selected industrial GVT platform that allows customization in terms of data acquisition and post-processing. Technical advances include efficient handling of very-high channel count (700) data, new capabilities in Normal Mode Testing, and the possibility to stream userdefined shaker excitation signals for dedicated experimental analysis of structures. The new developments will be illustrated by means of a recently conducted Research Ground Vibration Test on an A340-600 aircraft with ONERA, DLR and Airbus as project partners

Nonlinear dynamic analysis of an F-16 aircraft using GVT data

This paper aims at investigating the nonlinear dynamics of an F-16 aircraft, based upon sine-sweep data collected during a ground vibration test (GVT) campaign. Various analysis techniques, including the mere visual inspection of the time series, the wavelet transform and the restoring force surface method, are utilised and reveal that the F-16 wing-to-payload mounting interfaces exhibit both softening and hardening nonlinearities

Nonlinear ground vibration identification of an F-16 aircraft - Part 2: Understanding Nonlinear Behaviour in Aerospace Structures Using Sine-sweep Testing

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic nonlinearity, is the modelling of the wing-to-payload mounting interfaces. For large amplitudes of vibration, friction and gaps may be triggered in these connections and markedly impact the dynamic behaviour of the complete structure. In this series of two papers, the nonlinear dynamics of an F-16 aircraft is investigated using rigorous methods applied to real data collected during a ground vibration test campaign. The present work focuses on the analysis of sine-sweep measurements in order to get an insightful understanding about the nonlinear behaviour of the aircraft. To this extent, restoring force surface and wavelet transform methods are applied both on the collected GVT data and simulation results performed on a simple numerical model of the F-16 wing and its payload

Virtual Shaker Testing: Simulation Technology Improves Vibration Test Performance

In the field of vibration testing, the interaction between the structure being tested and the instrumentation hardware used to perform the test is a critical issue. This is particularly true when testing massive structures (e.g. satellites), because due to physical design and manufacturing limits, the dynamics of the testing facility often couples with the test specimen one in the frequency range of interest. A further issue in this field is the standard use of a closed loop real-time vibration control scheme, which could potentially shift poles and change damping of the aforementioned coupled system. Virtual shaker testing is a novel approach to deal with these issues. It means performing a simulation which closely represents the real vibration test on the specific facility by taking into account all parameters which might impact the dynamic behavior of the specimen. In this paper, such a virtual shaker testing approach is developed. It consists of the following components: (1) Either a physical-based or an equation-based coupled electro-mechanical lumped parameter shaker model is created. The model parameters are obtained from manufacturer's specifications or by carrying out some dedicated experiments; (2) Existing real-time vibration control algorithm are ported to the virtual simulation environment; and (3) A structural model of the test object is created and after defining proper interface conditions structural modes are computed by means of the well-established Craig-Bampton CMS technique. At this stage, a virtual shaker test has been run, by coupling the three described models (shaker, control loop, structure) in a co-simulation routine. Numerical results have eventually been correlated with experimental ones in order to assess the robustness of the proposed methodology

Nonlinear ground vibration identification of an F-16 aircraft - Part 1: Fast nonparametric analysis of distortions in FRF measurements

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic nonlinearity, is the modelling of the wing-to-payload mounting interfaces. For large amplitudes of vibration, friction and gaps may be triggered in these connections and markedly impact the dynamic behaviour of the complete structure. In this series of two papers, the nonlinear dynamics of an F-16 aircraft is investigated using rigorous methods applied to real data collected during a ground vibration test campaign. The present work focuses on the detection, qualification and quantification of nonlinear distortions affecting frequency response function (FRF) measurements. The key idea of the approach is to excite the structure using a random signal with a user-defined amplitude spectrum, where only a set of well-selected frequencies is different from zero in the band of interest. It is demonstrated that this careful choice of the input frequencies allows, without any further user interaction, to quantify the importance of odd and even nonlinear distortions in the output spectra with respect to the noise level. At high excitation amplitude, the F-16 dynamics is found to exhibit substantial odd nonlinearities and less significant, yet not negligible, even nonlinearities

The Use of Dynamic Strain Sensors and Measurements on the Ground Vibration Testing of an F-16 Aircraft

Ground Vibration Testing (GVT) of aircraft is a measurement campaign performed in the development process of an aircraft, with the objective of obtaining experimental data of the aircraft to validate and update the structural dynamic models, which can in turn be used to predict important behavior, such as flutter. These measurements are usually carried out using standard accelerometers, which lead to the identification of the displacement mode shapes. However, the use of strain sensors in vibration and modal related applications has recently gained popularity, due to some advantages, such as sensor size and the fact that strain relates directly to stress. On the other hand, interpreting the strain mode shapes can sometimes be more complex, so the use of both strain and acceleration sensors can lead to a more complete and understandable dataset. In this paper, the main results of a GVT campaign on an F-16 aircraft will be shown, where the full aircraft was instrumented with accelerometers and one of the wings was also fully instrumented with dynamic strain sensors. The main results of the test campaign will be shown, where both strain sensor and accelerometer measurements are processed simultaneously, resulting in the strain and displacement mode shapes, respectively, and some characteristics and advantages of carrying out the tests this way will be presented.status: accepte

Measuring nonlinear distortions: from test case to an F-16 fighter

What are the similarities and differences between the behavior of a small vibrating test system and an F-16 fighter? To find it out, we compare measurements of the test system to measurements from the bolted connection of the wing and the missile of a F-16 Fighter Falcon from the Belgian air force. These measurements were done during a ground vibration test (GVT) campaign. Essentially, the behavior of these systems match, even though the test system is only the heart of a self-study kit for nonlinear system identification and the F-16 is a complex real life mechanical structure. This clearly shows the added value of an experiment driven nonlinear educational system identification package. It provides safe small-scale toy examples for hands-on exercises that react like real systems. We believe that this practical approach lowers the gap between learning system identification concepts and applying it on real systems