Modal testing

About: Modal testing is a research topic. Over the lifetime, 4047 publications have been published within this topic receiving 64772 citations.

Balanced Shaker and Sensor Placement for Modal Testing of Large Flexible Structures

Abstract: A systematic analytical approach regarding the location of shakers and sensors for the dynamic testing and modal identification of the Z1 truss substructure of the International Space Station(ISS) is discussed in this paper. It is assumed that every degree of freedom of the finite element model is a possible place for sensor location, but shakers can only be placed at selected locations (not all locations are technically suitable for the shaker placement). From this starting point, a subset of four shaker locations and a subset of about 400 sensor locations were selected for the analytical modal identification test of all the ISS modes below 50 Hz of frequency. The locations were selected based on the shaker and sensor performance in the identification test that is comparable to the performance of the full sets. The performance is defined in terms of the Hankel singular values (HSV) that characterize the joint controllability and observability properties of each shaker and sensor for each natural vibration mode of the structure. The additive property of the structural Hankel singular values was used to locate the shakers and sensors. The placement results show good dynamic performance of the structure with the subset of shaker and sensor locations as compared to the structure with the full set of shakers and with sensors located at all degrees of freedom. The main objective of the paper is to present the sound theoretical background and show its practical advantages.

Design of Modal Transducers by Optimizing Spatial Distribution of Discrete Gain Weights

Abstract: A general method is developed of designing distributed modal transducers, especially for use in the active vibration control of structure. For this purpose, a new two-dimensional modal transducer theory has been developed. This theory is based on the finite element model of the structure, which makes it possible to determine spatial gain distribution of the specific modal transducer without restrictions on the geometry and boundary conditions of the structure. Although the optimal gain distribution can he obtained theoretically, there is no practical means of implementing it. Therefore, two design methods of distributed modal transducer are developed, which optimize available parameters of piezoelectric film to approximate optimal gain distribution best. The first method uses multilayered polyvinylidene fluoride (PVDF) films as a single transducer. The electrode pattern, the lamination angle, and the relative poling direction of each PVDF layer are optimized to obtain the desired transducer. In the second method, the whole electrode area on a single PVDF film is divided into several segments, and the gain weight imposed on each segment by interface circuit is optimized. Sensor/actuator systems for the vibration control of cantilever composite plate are designed using the proposed methods. The performance of the designed transducers is verified experimentally. The real-time vibration control of integrated smart structure has been successfully achieved.

Modeling of wind and temperature effects on modal frequencies and analysis of relative strength of effect

Abstract: Wind and temperature have been shown to be the critical sources causing changes in the modal properties of large-scale bridges. While the individual effects of wind and temperature on modal variability have been widely studied, the investigation about the effects of multiple environmental factors on structural modal properties was scarcely reported. This paper addresses the modeling of the simultaneous effects of wind and temperature on the modal frequencies of an instrumented cable-stayed bridge. Making use of the long-term monitoring data from anemometers, temperature sensors and accelerometers, a neural network model is formulated to correlate the modal frequency of each vibration mode with wind speed and temperature simultaneously. Research efforts have been made on enhancing the prediction capability of the neural network model through optimal selection of the number of hidden nodes and an analysis of relative strength of effect (RSE) for input reconstruction. The generalization performance of the formulated model is verified with a set of new testing data that have not been used in formulating the model. It is shown that using the significant components of wind speeds and temperatures rather than the whole measurement components as input to neural network can enhance the prediction capability. For the fundamental mode of the bridge investigated, wind and temperature together apply an overall negative action on the modal frequency, and the change in wind condition contributes less to the modal variability than the change in temperature.

Effects of False Floors on Vibration Serviceability of Building Floors. I: Modal Properties

Abstract: This is the first of two papers that present the results of a comprehensive and systematic study into the effects of false flooring on the vibration serviceability of long-span concrete floors. In this paper, advanced modal testing technology was utilized to determine modal properties of long-span concrete floors (natural frequencies, modal damping ratios, and mode shapes) before and after the installation of false flooring. It was found that false flooring had the capacity to change modal properties significantly, particularly modal damping ratios, which had increases of up to 89%. Parametric studies using updated finite element models were also performed, which showed that the false flooring contributed also to floor stiffness. However, changes in modal properties were not consistent across all modes of vibration and it was not possible to predict easily which modes would be affected beneficially by the installation of false flooring.

Load Identification Using a Modified Modal Filter Technique

Abstract: In this paper the authors propose a modification to the known force identification procedure based on modal filtration. The modification consists of replacing the modal vectors with the Ritz vectors. The latter seem to be more accurate because they take into account the static deformation of the structure and are less sensitive to truncation error. After the main idea- the algorithm modification- is presented, it is verified and then compared with the original solution. Two sets of data are used for this purpose, firstly simulation data from the numerical model, and then physical data recorded during a laboratory experiment.