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Multivariate ARMA Based Modal Identification of a Time-varying Beam Bertha, Mathieu ; Golinval, Jean-Claude in Proceedings of the International Modal Analysis Conference (IMAC) XXXIV (2016) The present paper addresses the problem of modal identification of time-varying systems. The identification is based on a multivariate autoregressive moving-average model in which the time variability of ... [more ▼] The present paper addresses the problem of modal identification of time-varying systems. The identification is based on a multivariate autoregressive moving-average model in which the time variability of the system is caught using a basis functions approach. In this approach, the time-varying regressive coefficients in the model are expended in the chosen basis functions and only the projection coefficients have to be identified. In that way, the initial time-varying problem then becomes a time-invariant one that can be solved. Because a multivariate model is used, in addition to the time-varying poles, the time-varying mode shapes may be identified too. The method is first presented and then applied on an experimental demonstration structure. The experimental structure consists of a supported beam on which a mass is travelling. The mass is chosen sufficiently large to have a significant influence on the dynamics of the primary system. This kind of problem is a classical example commonly used by many authors to test time-varying identification methods. [less ▲] Detailed reference viewed: 21 (6 ULg)Experimental modal analysis of a beam travelled by a moving mass using Hilbert Vibration Decomposition Bertha, Mathieu ; Golinval, Jean-Claude Scientific conference (2014, July) In this paper the problem of modal identification of time-varying system is investigated. To do so, a technique based on the sifting process of the Hilbert Vibration Decomposition (HVD) method is ... [more ▼] In this paper the problem of modal identification of time-varying system is investigated. To do so, a technique based on the sifting process of the Hilbert Vibration Decomposition (HVD) method is presented. The key idea is to estimate the instantaneous frequency of the dominant mode, to extract its corresponding component by demodulation of the recorded signals and then to iterate with the subsequent dominant mode. In the case of multiple recorded signals, a source separation method is used as a preprocessing step to facilitate the identification of the instantaneous frequency for the following demodulation step. To illustrate the method, an experimental set-up consisting in a beam travelled by a non negligible mass is considered. The whole structure is randomly excited during the travel of the mass and some responses on the beam are recorded. [less ▲] Detailed reference viewed: 68 (7 ULg)Identification of a Time-varying Beam Using Hilbert Vibration Decomposition Bertha, Mathieu ; Golinval, Jean-Claude in Proceedings of the International Modal Analysis Conference (IMAC) XXXII (2014, February) The present work is concerned by modal identification of time-varying systems. For this purpose, a method based on instantaneous frequency identification and synchronous demodulation is used to extract ... [more ▼] The present work is concerned by modal identification of time-varying systems. For this purpose, a method based on instantaneous frequency identification and synchronous demodulation is used to extract modal components from recorded signals. The proposed method of iterated sifting process is based on the Hilbert Vibration Decomposition (HVD) technique which is used to extract the instantaneous dominant vibrating component at each iteration. A source separation preprocessing step is introduced to treat multiple degree-of-freedom systems in an optimal way. Sources are used as reference signals to get a single instantaneous frequency of each mode for the demodulation on all the channels. The algorithm is presented and is applied to numerical simulation of a randomly excited time-varying structure for illustration purpose. The investigated structure is made up of a beam on which a non-negligible mass is traveling. The variable location of the mass results in changes in modal parameters. [less ▲] Detailed reference viewed: 72 (18 ULg)Modal identification of time-varying systems using Hilbert transform and signal decomposition Bertha, Mathieu ; Golinval, Jean-Claude Scientific conference (2014) The present work investigates modal identification of time-varying dynamical systems by exploiting the Hilbert transform. The proposed method, initially based on the Hilbert Vibration Decomposition (HVD ... [more ▼] The present work investigates modal identification of time-varying dynamical systems by exploiting the Hilbert transform. The proposed method, initially based on the Hilbert Vibration Decomposition (HVD) method, first identifies the instantaneous frequencies of the system. Their corresponding components and modal deflection shapes are then extracted from a set of dynamic responses of the system. The proposed method is first presented and then is illustrated on an experimental set-up. The system under investigation is a recurrent experiment in the field of time-varying systems consisting in a beam travelled by a non-negligible mass while excited by a random external force. The results highlight the time dependency of the modal parameters of the system due to the variant position of the mass with time. [less ▲] Detailed reference viewed: 104 (6 ULg)Identification modale de systèmes variant dans le temps à partir de réponses simulées sur un exemple d'éoliennes Bertha, Mathieu ; Golinval, Jean-Claude Poster (2012, November) Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems ... [more ▼] Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems, classical identification methods have to be adapted to the non-stationary nature of the recorded signals. In this paper, it is proposed to study the dynamic behavior of an offshore five-megawatt wind turbine. First, a numerical model of the wind turbine is created to serve as reference. Then, the time-varying behavior of the system is evaluated by simulating a large number of possible configurations. To this purpose, time responses are generated from the numerical model submitted to different environmental conditions. The wind is considered as the main non-measured external excitation force on the structure and the responses are recorded at several locations to simulate a real measurement process. Special care is brought to the accessibility of the measurement locations and to the limited number of available sensors in practice. Using these simulated measurements, output-only identification methods are used to extract varying dynamic properties of the structure. The final objective of this work is to pave the way to online condition monitoring of wind turbines. [less ▲] Detailed reference viewed: 145 (34 ULg)Modal identification of time-varying systems using simulated responses on wind turbines Bertha, Mathieu ; Mayorga Rios, Jorge Patricio ; Golinval, Jean-Claude in Sas, P; Moens, D; Jonckheere, S (Eds.) Proceedings of ISMA2012-USD2012 (2012, September) Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems ... [more ▼] Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems, classical identification methods have to be adapted to the non-stationary nature of the recorded signals. In this paper, it is proposed to study the dynamic behavior of an offshore five-megawatt wind turbine. First, a numerical model of the wind turbine is created to serve as reference. Then, the time-varying behavior of the system is evaluated by simulating a large number of possible configurations. To this purpose, time responses are generated from the numerical model submitted to different environmental conditions. The wind is considered as the main non-measured external excitation force on the structure and the responses are recorded at several locations to simulate a real measurement process. Special care is brought to the accessibility of the measurement locations and to the limited number of available sensors in practice. Using these simulated measurements, output-only identification methods are used to extract varying dynamic properties of the structure. The final objective of this work is to pave the way to online condition monitoring of wind turbines. [less ▲] Detailed reference viewed: 57 (15 ULg) |
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