http://popups.lib.uliege.be/2684-6500/index.php?id=299 Issues fr Mon, 17 Nov 2025 16:11:00 +0100 Wed, 06 May 2026 14:26:04 +0200 http://popups.lib.uliege.be/2684-6500/index.php?id=299 0 http://popups.lib.uliege.be/2684-6500/index.php?id=300 Vibration testing of nonlinear structures presents various challenges that are not only related to the nonlinear structure itself but also to the exciter. As the exciter and the structure are coupled, the structure's nonlinear behaviour distorts the exciter force amplitude and frequency content, making the test results more difficult to compare with numerical predictions or even less accurate when isolating and identifying nonlinear normal modes (NNMs). This paper uses an adaptive feedforward cancellation (AFC) real-time control algorithm to track multi-harmonic force reference signals accurately. The controller estimates the disturbance generated by the structure and adjusts the exciter's input to compensate for it, recovering the desired force signal. The advantage of this approach is that it does not rely on the knowledge of the exciter and structure models. It only requires knowledge of the phase at the output of the exciter, which is straightforward to estimate experimentally from the force measurements. The effectiveness of the AFC for exciter force control is demonstrated numerically and experimentally on a cantilever beam structure excited by an electromagnetic shaker. The beam's free tip is attached to a spring mechanism, giving rise to geometric nonlinearities and mode interactions resulting in strong harmonic distortions in the excitation force. The method is further demonstrated on a compressor blade from Roll-Royce's aero-engine. Mon, 17 Nov 2025 16:11:47 +0100 http://popups.lib.uliege.be/2684-6500/index.php?id=300 http://popups.lib.uliege.be/2684-6500/index.php?id=306 An interference fit is a common joining technique used to connect a shaft and a hub. In the presence of dynamic loads and vibrations, characteristic variables such as contact pressure and slippage are load and state-dependent quantities. Such effects have either not been investigated using previous simulation methods or have only been addressed in a simplified manner. The reason for this is the nonlinear contact between the shaft and the hub, which makes a Finite Element simulation with fine meshing, while taking all dynamic effects into account, very demanding and significantly increases the computational effort. This work also offers a new and alternative view of contact modes. This perspective is particularly advantageous for structures with initial stresses that occur in the presence of an interference fit. In this paper, so-called contact modes are applied to interference fits with some modifications. This closes the previously mentioned gap in the simulation landscape because it allows nonlinear, accurate, and fast numerical time integration of finely meshed Finite Element models with interference fits, without the need for simplifications regarding contact, friction, and dynamics due to vibrations and nonlinear rigid body motion. Local plasticity and temperature fields were not taken into consideration. Wed, 07 Jan 2026 09:44:42 +0100 http://popups.lib.uliege.be/2684-6500/index.php?id=306 http://popups.lib.uliege.be/2684-6500/index.php?id=314 Substructuring is an important step in the analysis of complex built-up structures. It is the process by which individual components are mathematically assembled to build a model of a coupled system. In the frequency domain, admittance or FRF-based substructuring has become the preferred approach, especially when considering experimental components for which FRFs are easily obtained from test data. However, FRFs are not the only way to represent a component in the frequency domain. Often, particularly for layered systems, the so-called transfer matrix (TM) representation becomes more convenient; component coupling is achieved by simply multiplying together their respective TMs. In the present paper we develop a hybrid substructuring scheme that allows the coupling of FRF-based components using a TM representation of the interconnecting junction. Such an approach might be beneficial for structures with complex layered connections (well suited to TM-based coupling), and has the potential to provide additional insight into structural transmission through multiple interconnected elements. Thu, 08 Jan 2026 17:03:43 +0100 http://popups.lib.uliege.be/2684-6500/index.php?id=314 http://popups.lib.uliege.be/2684-6500/index.php?id=320 Modal analysis is the primary means of analyzing structural responses to external forcing, informing decision-making or further physical testing of the structure. Nevertheless, most commercially available solutions assume the test article behaves linearly with excitation amplitude. If significant amounts of nonlinear stiffness or damping are present in the structure, large errors in linear analysis may result which could lead to improper decisions that may be costly. Therefore, it is useful to develop experimental techniques or computational models which account for nonlinearity during modal analysis. This paper describes a method of generating frequency response functions at various excitation energy levels to generate a three-dimensional transfer function surface. The resulting transfer function surface is agnostic of drive-point location, allowing excitations at different drive points to be compared directly. This result holds only if the drive point is sufficiently far from node points. The Brake-Reuss beam is used as the experimental exemplar at various levels of impact testing. Best practices learned during experimentation are included. Wed, 25 Feb 2026 12:47:03 +0100 http://popups.lib.uliege.be/2684-6500/index.php?id=320