Simone Manzato

Virtual Structural Monitoring of Wind Turbines Using Operational Modal Analysis Techniques

Operational Modal Analysis (OMA), also known as output-only modal analysis, allows identifying modal parameters only by using the response measurements of the structures in operational conditions when the input forces cannot be measured. These information can then be used to improve numerical models in order to monitor the operating and structural conditions of the system. This is a critical aspect both for condition monitoring and maintenance of large wind turbines, particularly in the off-shore sector where operation and maintenance represent a high percentage of total costs. Although OMA is widely applied, the wind turbine case still remains an open issue. Numerical aeroelastic models could be used, once they have been validated, to introduce virtual damages to the structures in order to analyze the generated data. Results from such models can then be used as baseline to monitor the operating and structural condition of the machine.

Advanced identification techniques for operational wind turbine data.

During a field test campaign, Sandia National Laboratories acquired operational data both in parked and rotating conditions on a modified MICON wind turbine with the Sensored Rotor 2 experiment. The objective of the test campaign was to acquire data to develop advanced system identification and structural health monitoring techniques. The data includes wind speed, tower deformations, low and high speed shaft rotational speed measurements as well as accelerations and strains on different locations of the blades. Applying Operational Modal Analysis on such data represents a difficult task due to the strong influence of rotor harmonics on the measured data. Accurately identifying and removing the harmonics is required to perform modal parameter identification. In this paper, data acquired with the turbine in both parked and operating conditions will be analyzed and the modal results compared. Several harmonic removal techniques will be applied on the operational data and their efficiency to solve this specific problem analyzed. In addition, a new enhanced identification technique will be applied, that improves the parameter estimation accuracy in the case of very noisy data and also provides uncertainty bounds of the parameters.

Model updating methodologies for multibody simulation models: application to a full-scale wind turbine model

In the industrial environment, the request for accurate models able to predict the behavior of a structure in different operating conditions is continuously increasing. To analyze the dynamic performances of complex mechanisms, multibody models are widely used, in particular if control laws for these systems need to be defined and tested. Wind turbines represent a typical application in which multibody models are used for control laws development. In this paper, an Experimental Modal Analysis campaign on the CART-3 wind turbine is used as reference to update a tailored multibody model. Standard model updating techniques based on mode shapes and natural frequencies are adapted to be used in a professional CAE environment. The results obtained show a big influence of the correlation indices selected to drive the updating phase.

In-Service Measurement of the Small Wind Turbine Test Stand for Structural Health Monitoring

This paper presents the research activity performed on a Small Wind Turbine (SWT) test stand. Commercially available turbine was modi fie towards incorporation of the sensors system for condition monitoring. Installed sensors measure angular shaft position, torque applied from the wind loads, vibration accelerations and la st but not least rotational speed. All gathered dat a are then transferred and processed in Test.Lab by m eans of automatic in house developed Visual Basic application which afterwards converts TDF fil es to text files and stores them in a desired directory. The numerical simulation is being run in parallel to installed sensors measurements and is as well controlled by the same Visual Basic applica tion. By having actual measurements and numerical simulation results one will be able to co mpare those two outcomes. In particular, if the numerical model is tailored to the physical one, da ta comparison will allow identifying malfunctioning due to component damage or extreme w orking condition.

Uncertainty Quantification in Experimental Structural Dynamics Identification of Composite Material Structures

Aerospace and wind energy structures are extensively using components made of composite materials. Since these structures are subjected to dynamic environments with time-varying loading conditions, it is important to model their dynamic behavior and validate these models by means of vibration experiments. Modal testing results depend on numerous factors introducing uncertainty to the measurement results. Different experimental techniques applied to the same test item or testing numerous nominally identical specimens yields different test results. This paper presents a systematic approach for uncertainty evaluation in experimentally estimated models. Investigated structures are plates, fuselage panels and helicopter main rotor blades as they represent different complexity levels ranging from coupon, through sub-component up to fully assembled structures made of composite materials. To evaluate the variability of the identified parameters, a statistical method is implemented for processing an extensive collection of experimental data.

Virtual Assessment of Damage Detection Techniques for Operational Wind Turbine

Operational Modal Analysis (OMA), also known as output-only modal analysis, allows identifying modal parameters only by using the response measurements of the structures in operational conditions when the input forces cannot be measured. These information can then be used to improve numerical models in order to monitor the operating and structural conditions of the system. This is a critical aspect both for condition monitoring and maintenance of large wind turbines, particularly in the off-shore sector where operation and maintenance represent a high percentage of total costs. Although OMA is widely applied, the wind turbine case still remains an open issue. Numerical aeroelastic models could be used, once they have been validated, to introduce virtual damages to the structures in order to analyze the generated data. Results from such models can then be used as baseline to monitor the operating and structural condition of the machine.

Environmental Testing and Data Analysis for Non-linear Spacecraft Structures: Impact on Virtual Shaker Testing

This paper reports on the results of the environmental testing and data analysis that was performed on a satellite structure that incorporates some typical structural non-linearities present in actual flight hardware. The project coordinator EADS Astrium provided the bread-board satellite model and LMS International was responsible for the execution of the environmental tests including sine and random tests at various vibration levels and in multiple directions. Next to a presentation of the test results with an emphasis on the non-linear behaviour, advanced experimental modal estimation technique were applied on the data.

Tracking the Evolution of Modal Properties of a Solid Propellant Launcher During Static Firing Test

During actual operating conditions, mechanical systems, such as aerospace structures, may exhibit variations in their dynamic properties. Those variations need to be carefully tracked and identified to avoid interaction with excitation sources, leading to unstable behavior or even structural failures. In this paper, signals acquired during a static firing test on a Solid Rocket Motor will be analyzed and processed using Operational modal Analysis. To analyze the evolution of natural frequencies and modal damping as the propellant is burnt, time-histories are cut into shorter segments, which are then analyzed separately. Operational PolyMAX method is applied to identify structural properties of the system and correlation techniques are implemented to track the evolution of the modes. Finally, comparison and correlation with a numerical Finite Element model is also performed to evaluate the analysis.