Modal testing

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

The Natural Excitation Technique (NExT) for modal parameter extraction from operating wind turbines

Abstract: The Natural Excitation Technique (NExT) is a method of modal testing that allows structures to be tested in their ambient environments This report is a compilation of developments and results since 1990, and contains a new theoretical derivation of NExT, as well as a verification using analytically generated data In addition, we compare results from NExT with conventional modal testing for a parked, vertical-axis wind turbine, and, for a rotating turbine, NExT is used to calculate the model parameters as functions of the rotation speed, since substantial damping is derived from the aeroelastic interactions during operation Finally, we compare experimental results calculated using NExT with analytical predictions of damping using aeroelastic theory

Modal Sensors/Actuators

Abstract: A piezoelectric laminate theory that uses the piezoelectric phenomenon to effect distributed control and sensing of structural vibration of a flexible plate has been used to develop a class of distributed sensor/actuators, that of modal sensors/actuators. The one-dimensional modal sensors/actuator equations are first derived theoretically and then examined experimentally. These modal equations indicate that distributed piezoelectric sensors/actuators can be adopted to measure/excite specific modes of one-dimensional plates and beams. If constructed correctly, actuator/observer spillover will not be present in systems adopting these types of sensors/actuators. A mode 1 and a mode 2 sensor for a one-dimensional cantilever plate were constructed and tested to examine the applicability of the modal sensors/actuators. A modal coordinate analyzer which allows us to measure any specific modal coordinate on-line real-time is proposed. Finally, a way to create a special two-dimensional modal sensor is presented.

Finite Element Prediction of Damping in Structures with Constrained Viscoelastic Layers

Abstract: An efficient method is described for finite element modelling of three-layer laminates containing a viscoelastic layer. Modal damping ratios are estimated from undamped normal mode results by means of the modal strain energy method. Comparisons are given between results obtained by the MSE method implemented in NASTRAN, by various exact solutions for approximate governing differential equations, and by experiment. Results are in terms of frequencies, modal damping ratios, and mechanical admittances for simple beams, plates, and rings. Application of the finite element -- MSE method in design of integrally damped structures is discussed.

Vibration: Fundamentals and Practice

Abstract: VIBRATION ENGINEERING Introduction Study of Vibration Application Areas History of Vibration Organization of the Book Problems TIME RESPONSE Introduction Undamped Oscillator Heavy Springs Oscillations in Fluid Systems Damped Simple Oscillator Forced Response Problems FREQUENCY RESPONSE Introduction Response to Harmonic Excitations Transform Techniques Mechanical Impedance Approach Transmissibility Functions Receptance Method Problems VIBRATION SIGNAL ANALYSIS Introduction Frequency Spectrum Signal Types Fourier Analysis Random Vibration Analysis Other Topics of Signal Analysis Order Analysis Machine Monitoring and Fault Diagnosis Problems MODAL ANALYSIS Introduction Degrees of Freedom and Independent Coordinates System Representation Modal Vibrations Orthogonality of Natural Modes Static Modes and Rigid Body Modes Other Modal Formulations Forced Vibration Damped Systems State-Space Approach Problems DISTRIBUTED-PARAMETER SYSTEMS Introduction Transverse Vibration of Cables Longitudinal Vibrations of Rods Torsional Vibration of Shafts Flexural Vibration of Beams Damped Continuous Systems Vibration of Membranes and Plates Problems VIBRATION DAMPING Introduction Types of Damping Representation of Damping in Vibration Analysis Measurement of Damping Interface Damping Problems VIBRATION INSTRUMENTATION Introduction Vibration Exciters Control System Performance Specification Motion Sensors and Transducers Torque, Force, and Other Sensors Problems SIGNAL CONDITIONING AND MODIFICATION Introduction Amplifiers Analog Filters Modulators and Demodulators Analog-Digital Conversion Bridge Circuits Linearizing Devices Miscellaneous Signal Modification Circuitry Signal Analyzers and Display Devices Problems VIBRATION TESTING AND HUMAN RESPONSE Introduction Representation of a Vibration Environment Pre-Test Procedures Testing Procedures Some Practical Information Vibration Excitations on Humans Human Response to Vibration Regulation of Human Vibration Problems EXPERIMENTAL MODAL ANALYSIS Introduction Frequency Domain Formulation Experimental Model Development Curve Fitting of Transfer Functions Laboratory Experiments Commercial EMA Systems Problems VIBRATION DESIGN AND CONTROL Introduction Specification of Vibration Limits Vibration Isolation Balancing of Rotating Machinery Balancing of Reciprocating Machines Whirling of Shafts Design through Modal Testing Passive Control of Vibration Active Control of Vibration Control of Beam Vibrations Problems APPENDIX A: DYNAMIC MODELS AND ANALOGIES Model Development Analogies Mechanical Elements Electrical Elements Thermal Elements Fluid Elements State-Space Models Response Analysis and Simulation APPENDIX B: NEWTONIAN AND LAGRANGIAN MECHANICS Vector Kinematics Newtonian (Vector) Mechanics Lagrangian Mechanics APPENDIX C: REVIEW OF LINEAR ALGEBRA Vectors and Matrices Vector-Matrix Algebra Matrix Inverse Vector Spaces Determinants System of Linear Equations Quadratic Forms Matrix Eigenvalue Problem Matrix Transformations Matrix Exponential APPENDIX D: LAPLACE TRANSFORM Introduction Laplace Transform Response Analysis Transfer Function APPENDIX E: DIGITAL FOURIER ANALYSIS AND FFT Unification of the Three Fourier Transform Types Fast Fourier Transform (FFT) Discrete Correlation and Convolution Digital Fourier Analysis Procedures APPENDIX F: SOFTWARE TOOLS SIMULINK MATLAB Control Systems Toolbox LabVIEW APPENDIX G: RELIABILITY CONSIDERATIONS FOR MULTI-COMPONENT UNITS Failure Analysis Bayes' Theorem INDEX