Modal testing

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

Active control vibration isolation using dynamic manifold

Abstract: A robust controller for multi-degree-of-freedom active vibration isolation accounts for plant uncertainties and payload disturbances using frequency-shaped sliding control. Modal decomposition is used to rewrite a multi-degree of freedom vibration control problem as a combination of individual modal control problems in modal coordinates. Modal parameters for decomposition and modelling can be extracted from theoretical or experimental modal analysis. The target frequency-domain performance of isolation, for example a skyhook model, is recast as a frequency-shaped sliding surface. Boundary layer approximation is examined. The ideal skyhook effect can be robustly achieved. The frequency-shaped manifold is also extended to adaptive vibration isolation without model reference, which has been verified by experiments, and demonstrated to be very effective for vibration isolation. Nonlinear target dynamics of the same order as the nominal plant can also be attained. Control can be achieved without measuring the excitation, such as ground motion. Further, performance during the transient stage can be guaranteed. Also, control can be achieved even without knowing the values of entries for mass, stiffness and damping matrices. The methods of controller design can be used to design control for plants subject to disturbances other than only vibration. The plant can be mechanical, electrical, thermal, or any that can be described by system equations that are mathematically of the same character as are those that describe mechanical dynamic systems. The target dynamics need not be skyhook dynamics, but can be any dynamics desired, even non-linear.

Updating of the Analytical Models of Two Footbridges Based on Modal Testing of Full-Scale Structures

Abstract: This paper describes the analytical FE modelling, modal testing and FE model updating of two full-scale pedestrian footbridges These procedures are well developed in the fields of mechanical and aerospace engineering, and have just started to be applied successfully to large civil engineering structures The aim of this paper is to describe some of the possible problems that may arise when conducting such experimental exercises, and also to give advice on how these problems may be overcome In addition, the paper describes the authors’ experiences in initially constructing the FE models and conducting the updating itself Finally, the practical meaning of the changes to the assumed model parameters, resulting from the updating, is discussed It has been concluded that a period of manual updating should be conducted prior to implementing the automatic updating, as poor starting values may result in the automatic updating software producing unrealistic results

Characterization of vibration and acoustic noise in a gradient-coil insert

Abstract: High-speed switching of current in gradient coils within high magnetic field strength magnetic resonance imaging (MRI) scanners results in high acoustic sound pressure levels (SPL) in and around these machines. To characterize the vibration properties as well as the acoustic noise properties of the gradient coil, a finite-element (FE) model was developed using the dimensional design specifications of an available gradient-coil insert and the concentration of the copper windings in the coil. This FE model was then validated using experimentally collected vibration data. A computational acoustic noise model was then developed based on the validated FE model. The validation of the finite-element analysis results was done using experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Based on the validated FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient-coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again validated through experimental vibration testing with the gradient-coil insert installed in the MRI scanner and excited using swept sinusoidal time waveforms. The simulation results from the computational acoustic noise model were also validated through experimental noise measurement from the gradient-coil insert in the MRI scanner using swept sinusoidal time waveform inputs. Comparisons show that the FE model predicts the vibration properties and the computational acoustic noise model predicts the noise characteristic properties extremely accurately.