1,721,035 research outputs found
Compensation of Thermal Effects on Tiltmeter Measurements With Moving Least Squares
Full text linkThis article describes a method for compensating thermal effects on tiltmeter (TM) readings using operating temperature measurements. This practice is necessary when the contribution of thermal effects is comparable with the measurand inclination, which is typical of monitoring applications. In such contexts, several temperature-related phenomena take place concurrently and a customized compensation model is necessary. A tailored moving least square (MLS) approach is presented. This formulation is able to separate the contribution of the unknown measurand signal from the contribution of influence quantities, considered as exogenous inputs. Moreover, this method returns the model coefficients over time. However, the uncertainty in the temperature measurements, used as regressors, may induce bias in coefficient estimates. Therefore, a strategy for a posteriori evaluation and correction of the coefficients is proposed and validated with the Monte Carlo method (MCM). The effectiveness of this method is illustrated on a real case, consisting of the inclination monitoring of a wind-turbine tower
Wind actions on the London Eye cables. Part II: damping device design and field measurements
No full textVibration control with piezoelectric elements: The indirect measurement of the modal capacitance and coupling factor
Full text linkThe knowledge of the modal capacitance and electro-mechanical coupling factor is essential for a proper design of systems with embedded piezoelectric transducers and materials. In light of this, this paper presents two indirect methods for measuring the piezoelectric modal capacitance and a method to estimate the modal electro-mechanical coupling factor. All methods rely on simple vibration measurements of the structure with the piezoelectric transducer connected to a proper shunt impedance, thus avoiding measurements of piezoelectric current and voltage by expensive equipment. For the modal electro-mechanical coupling factor, the proposed method guarantees reduced uncertainty compared to traditional experimental estimation procedures. Upon introduction of the underlying theory, the paper experimentally demonstrates the reliability and effectiveness of the methods by comparison with well-established procedures
The prediction of vibrations for light structures in presence of moving people
No full textRecently, a model to describe the vibration of light structures (e.g. footbridges, staircases) was proposed by the authors of this paper. Such a model was developed with the aim of being accurate with a high number of people occupying the structure for long times. The present paper analyses the behaviour of the same model in the case of transient excitation of the structure. This allows to assess the accuracy of the model also in this further situation
Piezoelectric-shunt-based approach for multi-mode adaptive tuned mass dampers
Full text linkThis paper deals with the design and development of a multi-frequency adaptive tuned mass damper based on a cantilever beam equipped with shunted piezoelectric elements. It is demonstrated that the device is able to independently shift a number of eigenfrequencies equal to the number of piezoelectric elements and that the use of negative capacitances is able to strongly improve the adaptation capability of the device. Mathematical formulations are provided for linking the values of the capacitances used for shunting the piezoelectric elements and the resulting shifts of the eigenfrequencies, and vice versa. Furthermore, being the negative capacitances based on operational amplifiers, the stability of the electro-mechanical system is investigated, giving rules about the tuning of these negative capacitances. The resulting adaptive tuned mass damper can be fruitfully employed for lowering vibrations of a primary system whose eigenfrequencies undergo different frequency shifts, improving the robustness to possible mistuning of non-adaptive classical tuned mass dampers. All the theoretical outcomes are validated through an experimental campaign with a cantilever beam equipped with two piezoelectric patches
COMPARISON OF DIFFERENT SMA-BASED ADAPTIVE TUNED MASS DAMPERS
No full textThe use of smart materials has proven to be an effective strategy in the development of adaptive tuned mass dampers. Among different possible materials, shape memory alloys show specific features which make their use advantageous for building adaptive tuned mass dampers. More in detail, by heating/cooling the shape memory alloy components, it is possible to change the natural frequency of the adaptive tuned mass damper, thus allowing maintaining the adaptive mass damper tuned on the primary system to be damped. The heating/cooling is obtained by changing the amount of electrical current flowing through the shape memory alloy elements and, consequently, the amount of heat produced through Joule's effect. This paper compares the two main layouts for designing adaptive tuned mass dampers based on shape memory alloys in case the primary system to be damped is excited by a disturbance of random nature: cantilever beams and tensioned wires with a central mass. The two layouts, which can be described through detailed and experimentally validated models, are compared in terms of adaptation capability, exerted force and electrical power consumption. It results that the wire-based layout, despite being characterised by a more complicated set-up, is less demanding in terms of power consumption and shows much better adaptation capability
Enhancement of the broadband vibration attenuation of a resistive piezoelectric shunt
Full text linkThis paper shows how to enhance the vibration attenuation obtained by means of piezoelectric resistive shunt coupled to the use of negative capacitances. This improvement is achieved by adding an inductance in the shunt circuit. This additional inductance is not used to the usual purpose of mono-modal control, but to improve the attenuation in a broader frequency range. The benefits offered by the use of the inductance are explained by describing the shunted electro-mechanical system as a feedback control loop. The achievable attenuation improvements are highlighted in the paper at first through numerical analyses and then by means of an experimental campaign which also allows to evidence the reliability of the model employed to describe the electro-mechanical system
Vibration control by means of piezoelectric actuators shunted with LR impedances: Performance and robustness analysis
No full textThis paper deals with passive monomodal vibration control by shunting piezoelectric actuators to electric impedances constituting the series of a resistance and an inductance. Although this kind of vibration attenuation strategy has long been employed, there are still unsolved problems; particularly, this kind of control does suffer from issues relative to robustness because the features of the electric impedance cannot be adapted to changes of the system. This work investigates different algorithms that can be employed to optimise the values of the electric components of the shunt impedance. Some of these algorithms derive from the theory of the tuned mass dampers. First a performance analysis is provided, comparing the attenuation achievable with these algorithms. Then, an analysis and comparison of the same algorithms in terms of robustness are carried out. The approach adopted herein allows identifying the algorithm capable of providing the highest degree of robustness and explains the solutions that can be employed to resolve some of the issues concerning the practical implementation of this control technique. The analytical and numerical results presented in the paper have been validated experimentally by means of a proper test setup
Short-Training Damage Detection Method for Axially Loaded Beams Subject to Seasonal Thermal Variations
No full textVibration-based damage features are widely adopted in the field of structural health monitoring (SHM), and particularly in the monitoring of axially loaded beams, due to their high sensitivity to damage-related changes in structural properties. However, changes in environmental and operating conditions often cause damage feature variations which can mask any possible change due to damage, thus strongly affecting the effectiveness of the monitoring strategy. Most of the approaches proposed to tackle this problem rely on the availability of a wide training dataset, accounting for the most part of the damage feature variability due to environmental and operating conditions. These approaches are reliable when a complete training set is available, and this represents a significant limitation in applications where only a short training set can be used. This often occurs when SHM systems aim at monitoring the health state of an already existing and possibly already damaged structure (e.g., tie-rods in historical buildings), or for systems which can undergo rapid deterioration. To overcome this limit, this work proposes a new damage index not affected by environmental conditions and able to properly detect system damages, even in case of short training set. The proposed index is based on the principal component analysis (PCA) of vibration-based damage features. PCA is shown to allow for a simple filtering procedure of the operating and environmental effects on the damage feature, thus avoiding any dependence on the extent of the training set. The proposed index effectiveness is shown through both simulated and experimental case studies related to an axially loaded beam-like structure, and it is compared with a Mahalanobis square distance-based index, as a reference. The obtained results highlight the capability of the proposed index in filtering out the temperature effects on a multivariate damage feature composed of eigenfrequencies, in case of both short and long training set. Moreover, the proposed PCA-based strategy is shown to outperform the benchmark one, both in terms of temperature dependency and damage sensitivity
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