Control-based continuation of nonlinear structures using adaptive filtering

Control-Based Continuation uses feedback control to follow stable and unstable branches of periodic orbits of a nonlinear system without the need for advanced post-processing of experimental data. CBC relies on an iterative scheme to modify the harmonic content of the control reference and obtain a non-invasive control signal. This scheme currently requires to wait for the experiment to settle down to steady-state and hence runs offline (i.e. at a much lower frequency than the feedback controller). This paper proposes to replace this conventional iterative scheme by adaptive filters. Adaptive filters can directly synthesize either the excitation or the control reference adequately and can operate online (i.e. at the same frequency as the feedback controller). This novel approach is found to significantly accelerate convergence to non-invasive steady-state responses to the extend that the structure response can be characterized in a nearly-continuous amplitude sweep. Furthermore, the stability of the controller does not appear to be affected

Méthodes basées sur le contrôle pour l'indentification de structures non-linéaires

One of the key roles of structural engineering is to describe how a structure vibrates, or "responds", when a dynamic load, or "excitation", is applied to it. Often, the assumption of linear behavior is adopted, meaning that the response to a combination of excitation signals is the combination of the responses to the signals taken individually. When this assumption does not hold, complex dynamical phenomena can arise, including the coexistence of multiple responses for the same excitation, the sudden transition from one such response to another, or responses that are not stable. They render the experimental interrogation of engineering structures particularly challenging. An emerging family of testing methods, termed control-based methods, uses feedback loops and controllers to make the interrogation exhaustive and predictable. In this context, this thesis investigates carefully two recently-introduced methods, namely control-based continuation during which the excitation is corrected or generated by a controller, and phase-locked loop testing which imposes the phase lag between the response and the excitation using feedback control. In the first part of the thesis, we aim to deepen the understanding of control-based methods with the objective to design and tune experiments more systematically, reducing the need for trial and error. In the second part of the thesis, new developments exploiting adaptive filtering are carried out to expand the capabilities of both control-based continuation and phase-locked loop testing, but also to tackle dynamical features that were never identified experimentally before. Finally, this thesis opens the way towards more robust control-based methods and, eventually, to their industrial application.Un des buts premiers de l'ingénierie des structures est de décrire comment une structure vibre, ou "répond", lorsqu'une charge dynamique, ou "excitation", lui est appliquée. Souvent, l'hypothèse de comportement dynamique linéaire est adoptée: la réponse à une combinaison d'excitations est la combinaison des réponses aux excitations prises individuellement. Quand cette hypothèse n'est pas vérifiée, des phénomènes dynamiques complexes peuvent se produire comme, par exemple, la coexistence de plusieurs réponses à la même excitation, la transition subite d'une de ces réponses à une autre ou des réponses qui ne sont pas stables. Ces phénomènes rendent l'interrogation expérimentale des structures particulièrement difficile. De nouvelles méthodes basées sur le contrôle et utilisant des boucles de rétroaction sont apparues pour rendre l'interrogation exhaustive et prévisible. Dans ce contexte, cette thèse étudie en détail deux méthodes récemment introduites: la continuation basée sur le contrôle durant laquelle l'excitation est corrigée ou générée par un contrôleur et les tests en boucle à verrouillage de phase avec une boucle de rétroaction imposant le retard de phase entre la réponse et l'excitation. La première partie de cette thèse vise à approfondir la compréhension de ces méthodes afin de concevoir les expériences plus efficacement, notamment en diminuant le recours à des essais-erreurs. La seconde partie exploite le filtrage adaptatif pour étendre le champ d'action des méthodes ainsi que pour étuider des phénomènes dynamiques qui n'ont jamais été identifiés expérimentalement de cette manière. Finalement, cette thèse ouvre la voie à des méthodes basées sur le contrôle plus robustes et, un jour, à leur application industrielle

Comparison between control-based continuation and phase-locked loop methods for the identification of backbone curves and nonlinear frequency responses

Control-based continuation (CBC) and phase-locked loops (PLL) are two experimental testing methods that have demonstrated great potential for the non-parametric identification of key nonlinear dynamic features such as nonlinear frequency responses and backbone curves. Both CBC and PLL exploit stabilizing feedback control to steer the dynamics of the tested system towards the responses of interest and overcome important difficulties experienced when applying conventional testing methods such as sine sweeps to nonlinear systems. For instance, if properly designed, the feedback controller can prevent the system from exhibiting untimely transitions between coexisting responses or even losing stability due to bifurcations. This contribution aims to highlight the similarities that exist between CBC and PLL and present the first thorough comparison of their capabilities. Comparisons are supported by numerical simulations as well as experimental data collected on a conceptually simple nonlinear structure primarily composed of a thin curved beam. The beam is doubly clamped and exhibits nonlinear geometric effects for moderate excitation amplitudes

Experimental Characterization of Superharmonic Resonances Using Phase-Lock Loop and Control-Based Continuation

Experimental characterization of nonlinear structures usually focuses on fundamental resonances. However, there is useful information about the structure to be gained at frequencies far away from those resonances. For instance, non-fundamental harmonics in the system's response can trigger secondary resonances, including superharmonic resonances. Using the recently-introduced definition of phase resonance nonlinear modes, a phase-locked loop feedback control is used to identify the backbones of even and odd superharmonic resonances, as well as the nonlinear frequency response curve in the vicinity of such resonances. When the backbones of two resonances (either fundamental or superharmonic) cross, modal interactions make the phase-locked loop unable to stabilize some orbits. Control-based continuation can thus be used in conjunction with phase-locked loop testing to stabilize the orbits of interest. The proposed experimental method is demonstrated on a beam with artificial cubic stiffness exhibiting complex resonant behavior. For instance, the frequency response around the third superharmonic resonance of the third mode exhibits a loop, the fifth superharmonic resonance of the fourth mode interacts with the fundamental resonance of the second mode, and the second superharmonic resonance of the third mode exhibits a branch-point bifurcation and interacts with the fourth superharmonic resonance of the fourth mode

Comparison between control-based continuation and phase-locked loop methods for the identification of backbone curves and nonlinear frequency responses

Control-based continuation (CBC) and phase-locked loops (PLL) are two experimental testing methods that have demonstrated great potential for the non-parametric identification of key nonlinear dynamic features such as nonlinear frequency responses and backbone curves. Both CBC and PLL exploit stabilizing feedback control to steer the dynamics of the tested system towards the responses of interest and overcome important difficulties experienced when applying conventional testing methods such as sine sweeps to nonlinear systems. For instance, if properly designed, the feedback controller can prevent the system from exhibiting untimely transitions between coexisting responses or even losing stability due to bifurcations. This contribution aims to highlight the similarities that exist between CBC and PLL and present the first thorough comparison of their capabilities. Comparisons are supported by numerical simulations as well as experimental data collected on a conceptually simple nonlinear structure primarily composed of a thin curved beam. The beam is doubly clamped and exhibits nonlinear geometric effects for moderate excitation amplitudes

Measurement of the bb dijet cross section in pp collisions at √s = 7 TeV with the ATLAS detector

Funded by SCOAP3The dijet production cross section for jets containing a b-hadron (b-jets) has been measured in proton–proton collisions with a centre-of-mass energy of √s = 7 TeV, using the ATLAS detector at the LHC. The data used correspond to an integrated luminosity of 4.2 fb−1. The cross section is measured for events with two identified b-jets with a transverse momentum pT > 20 GeV and a minimum separation in the η–φ plane of R = 0.4. At least one of the jets in the event is required to have pT > 270 GeV. The cross section is measured differentially as a function of dijet invariant mass, dijet transverse momentum, boost of the dijet system, and the rapidity difference, azimuthal angle and angular distance between the b-jets. The results are compared to different predictions of leading order and next-to-leading order perturbative quantum chromodynamics matrix elements supplemented with models for parton-showers and hadronization

Circulating non-coding RNAs in head and neck cancer : roles in diagnosis, prognosis, and therapy monitoring

Head and neck cancer (HNC), the seventh most common form of cancer worldwide, is a group of epithelial malignancies affecting sites in the upper aerodigestive tract. The 5-year overall survival for patients with HNC has stayed around 40-50% for decades, with mortality being attributable mainly to late diagnosis and recurrence. Recently, non-coding RNAs, including tRNA halves, YRNA fragments, microRNAs (miRNAs), and long non-coding RNAs (lncRNAs), have been identified in the blood and saliva of patients diagnosed with HNC. These observations have recently fueled the study of their potential use in early detection, diagnosis, and risk assessment. The present review focuses on recent insights and the potential impact that circulating non-coding RNA evaluation may have on clinical decision-making in the management of HNC

Choroid plexus in the central canal of the spinal cord causing recurrent syringomyelia

Background Syringomyelia is a fluid filled cavitation within the substance of the spinal cord. This condition usually follows a primary pathology that disrupts the normal CSF circulation or disturbs the microcirculation and cytoarchitecture of the spinal cord parenchyma. However, an aetiology of recurrent syringomyelia resulted from an ectopic choroid plexus (CP) has not been discussed. Ectopic CP rests may be found within the central nervous system. Although there has been a single report, describing ectopic intramedullary spinal cord CP, to our knowledge, extra-cranial non-malignant CP in the central canal of the spinal cord has not been reported. Case Description We report CP in the central canal of the spinal cord in a 23-year-old male patient who had developmental delay and diabetes mellitus type I who presented with dissociated sensory changes and muscle wastage predominantly on the right upper and lower limbs. MRI demonstrated a multi-loculated spinal cord syringomyelia stretching from cervical (C3) to the conus medullaris causing recurrent neurological deficits. Central canal spinal cord lesion's biopsy revealed CP. Decompression and syringo-subarachnoid shunt insertion stabilised the patient’s neurology. Conclusion Our illustrative case reveals the presence of CP in the central canal of the spinal cord that may suggest a role in the aetiology of recurrent syringomyelia. While management poses a challenge to neurosurgeons, prompt decompression and shunting of the syringomyelia remains a favourable approach with acceptable outcomes. Further investigation into the pathophysiology of central canal CP ectopic causing recurrent syringomyelia and its correlation with spinal cord development may help future treatments