Showing papers on "Modal testing published in 1995"
Book•
1 Jan 1995
TL;DR: In this paper, the authors present a single-degree-of-freedom (SDF) system, which is composed of a mass-spring-damper system and a non-viscous Damping Free Vibration (NFV) system.
Abstract: I. SINGLE-DEGREE-OF-FREEDOM SYSTEMS. 1. Equations of Motion, Problem Statement, and Solution Methods. Simple Structures. Single-Degree-of-Freedom System. Force-Displacement Relation. Damping Force. Equation of Motion: External Force. Mass-Spring-Damper System. Equation of Motion: Earthquake Excitation. Problem Statement and Element Forces. Combining Static and Dynamic Responses. Methods of Solution of the Differential Equation. Study of SDF Systems: Organization. Appendix 1: Stiffness Coefficients for a Flexural Element. 2. Free Vibration. Undamped Free Vibration. Viscously Damped Free Vibration. Energy in Free Vibration. Coulomb-Damped Free Vibration. 3. Response to Harmonic and Periodic Excitations. Viscously Damped Systems: Basic Results. Harmonic Vibration of Undamped Systems. Harmonic Vibration with Viscous Damping. Viscously Damped Systems: Applications. Response to Vibration Generator. Natural Frequency and Damping from Harmonic Tests. Force Transmission and Vibration Isolation. Response to Ground Motion and Vibration Isolation. Vibration-Measuring Instruments. Energy Dissipated in Viscous Damping. Equivalent Viscous Damping. Systems with Nonviscous Damping. Harmonic Vibration with Rate-Independent Damping. Harmonic Vibration with Coulomb Friction. Response to Periodic Excitation. Fourier Series Representation. Response to Periodic Force. Appendix 3: Four-Way Logarithmic Graph Paper. 4. Response to Arbitrary, Step, and Pulse Excitations.Response to Arbitrarily Time-Varying Forces. Response to Unit Impulse. Response to Arbitrary Force. Response to Step and Ramp Forces. Step Force. Ramp or Linearly Increasing Force. Step Force with Finite Rise Time. Response to Pulse Excitations. Solution Methods. Rectangular Pulse Force. Half-Cycle Sine Pulse Force. Symmetrical Triangular Pulse Force. Effects of Pulse Shape and Approximate Analysis for Short Pulses. Effects of Viscous Damping. Response to Ground Motion. 5. Numerical Evaluation of Dynamic Response. Time-Stepping Methods. Methods Based on Interpolation of Excitation. Central Difference Method. Newmark's Method. Stability and Computational Error. Analysis of Nonlinear Response: Central Difference Method. Analysis of Nonlinear Response: Newmark's Method. 6. Earthquake Response of Linear Systems. Earthquake Excitation. Equation of Motion. Response Quantities. Response History. Response Spectrum Concept. Deformation, Pseudo-Velocity, and Pseudo-Acceleration Response Spectra. Peak Structural Response from the Response Spectrum. Response Spectrum Characteristics. Elastic Design Spectrum. Comparison of Design ad Response Spectra. Distinction between Design and Response Spectra. Velocity and Acceleration Response Spectra. Appendix 6: El Centro, 1940 Ground Motion. 7. Earthquake Response of Inelastic Systems. Force-Deformation Relations. Normalized Yield Strength, Yield Strength Reduction Factor, and Ductility Factor. Equation of Motion and Controlling Parameters. Effects of Yielding. Response Spectrum for Yield Deformation and Yield Strength. Yield Strength and Deformation from the Response Spectrum. Yield Strength-Ductility Relation. Relative Effects of Yielding and Damping. Dissipated Energy. Energy Dissipation Devices. Inelastic Design Spectrum. Applications of the Design Spectrum. Comparison of Design and Response Spectra. 8. Generalized Single-Degree-of-Freedom Systems. Generalized SDF Systems. Rigid-Body Assemblages. Systems with Distributed Mass and Elasticity. Lumped-Mass System: Shear Building. Natural Vibration Frequency by Rayleigh's Method. Selection of Shape Function. Appendix 8: Inertia Forces for Rigid Bodies. II. MULTI-DEGREE-OF-FREEDOM SYSTEMS. 9. Equations of Motion, Problem Statement, and Solution Methods. Simple System: Two-Story Shear Building. General Approach for Linear Systems. Static Condensation. Planar or Symmetric-Plan Systems: Ground Motion. Unsymmetric-Plan Building: Ground Motion. Symmetric-Plan Buildings: Torsional Excitation. Multiple Support Excitation. Inelastic Systems. Problem Statement. Element Forces. Methods for Solving the Equations of Motion: Overview. 10. Free Vibration. Natural Vibration Frequencies and Modes. Systems without Damping. Natural Vibration Frequencies and Modes. Modal and Spectral Matrices. Orthogonality of Modes. Interpretation of Modal Orthogonality. Normalization of Modes. Modal Expansion of Displacements. Free Vibration Response. Solution of Free Vibration Equations: Undamped Systems. Free Vibration of Systems with Damping. Solution of Free Vibration Equations: Classically Damped Systems. Computation of Vibration Properties. Solution Methods for the Eigenvalue Problem. Rayleigh's Quotient. Inverse Vector Iteration Method. Vector Iteration with Shifts: Preferred Procedure. Transformation of kA A = ...w2mA A to the Standard Form. 11. Damping in Structures.Experimental Data and Recommended Modal Damping Ratios. Vibration Properties of Millikan Library Building. Estimating Modal Damping Ratios. Construction of Damping Matrix. Damping Matrix. Classical Damping Matrix. Nonclassical Damping Matrix. 12. Dynamic Analysis and Response of Linear Systems.Two-Degree-of-Freedom Systems. Analysis of Two-DOF Systems without Damping. Vibration Absorber or Tuned Mass Damper. Modal Analysis. Modal Equations for Undamped Systems. Modal Equations for Damped Systems. Displacement Response. Element Forces. Modal Analysis: Summary. Modal Response Contributions. Modal Expansion of Excitation Vector p (t) = s p(T). Modal Analysis for p (t) = s p(T). Modal Contribution Factors. Modal Responses and Required Number of Modes. Special Analysis Procedures. Static Correction Method. Mode Acceleration Superposition Method. Analysis of Nonclassically Damped Systems. 13. Earthquake Analysis of Linear Systems.Response History Analysis. Modal Analysis. Multistory Buildings with Symmetric Plan. Multistory Buildings with Unsymmetric Plan. Torsional Response of Symmetric-Plan Buildings. Response Analysis for Multiple Support Excitation. Structural Idealization and Earthquake Response. Response Spectrum Analysis. Peak Response from Earthquake Response Spectrum. Multistory Buildings with Symmetric Plan. Multistory Buildings with Unsymmetric Plan. 14. Reduction of Degrees of Freedom. Kinematic Constraints. Mass Lumping in Selected DOFs. Rayleigh-Ritz Method. Selection of Ritz Vectors. Dynamic Analysis Using Ritz Vectors. 15. Numerical Evaluation of Dynamic Response. Time-Stepping Methods. Analysis of Linear Systems with Nonclassical Damping. Analysis of Nonlinear Systems. 16. Systems with Distributed Mass and Elasticity. Equation of Undamped Motion: Applied Forces. Equation of Undamped Motion: Support Excitation. Natural Vibration Frequencies and Modes. Modal Orthogonality. Modal Analysis of Forced Dynamic Response. Earthquake Response History Analysis. Earthquake Response Spectrum Analysis. Difficulty in Analyzing Practical Systems. 17. Introduction to the Finite Element Method.Rayleigh-Ritz Method. Formulation Using Conservation of Energy. Formulation Using Virtual Work. Disadvantages of Rayleigh-Ritz Method. Finite Element Method. Finite Element Approximation. Analysis Procedure. Element Degrees of Freedom and Interpolation Function. Element Stiffness Matrix. Element Mass Matrix. Element (Applied) Force Vector. Comparison of Finite Element and Exact Solutions. Dynamic Analysis of Structural Continua. III. EARTHQUAKE RESPONSE AND DESIGN OF MULTISTORY BUILDINGS. 18. Earthquake Response of Linearly Elastic Buildings. Systems Analyzed, Design Spectrum, and Response Quantities. Influence of T 1 and r on Response. Modal Contribution Factors. Influence of T 1 on Higher-Mode Response. Influence of r on Higher-Mode Response. Heightwise Variation of Higher-Mode Response. How Many Modes to Include. 19. Earthquake Response of Inelastic Buildings. Allowable Ductility and Ductility Demand. Buildings with "Weak" or "Soft" First Story. Buildings Designed for Code Force Distribution. Limited Scope. Appendix 19: Properties of Multistory Buildings. 20. Earthquake Dynamics of Base-Isolated Buildings. Isolation Systems. Base-Isolated One-Story Buildings. Effectiveness of Base Isolation. Base-Isolated Multistory Buildings. Applications of Base Isolation. 21. Structural Dynamics in Building Codes. Building Codes and Structural Dynamics. International Building Code (United States), 2000. National Building Code of Canada, 1995. Mexico Federal District Code, 1993. Eurocode 8. Structural Dynamics in Building Codes. Evaluation of Building Codes. Base Shear. Story Shears and Equivalent Static Forces. Overturning Moments. Concluding Remarks. Appendix A: Frequency Domain Method of Response Analysis.Appendix B: Notation.Appendix C: Answers to Selected Problems.Index.
5,383 citations
TL;DR: In this article, full-scale forced-vibration tests conducted before and after structural repairs on a multispan reinforced-concrete highway bridge are described in order to investigate any correlation that may exist between repair works and changes in the dynamic characteristics of the bridge.
Abstract: Full-scale forced-vibration tests conducted before and after structural repairs on a multispan reinforced-concrete highway bridge are described in the paper. The tests were conducted to investigate any correlation that may exist between the repair works and changes in the dynamic characteristics of the bridge. The approach adopted is suitable for assessing the structural condition of a bridge using vibration data. A purpose-built hydraulic vibrator was used to artificially excite the bridge, and the dynamic response was measured by accelerometers placed on the bridge deck. A single-degree-of-freedom model was fitted to the response functions in order to extract natural frequencies, modal damping ratios, and mode shapes. It was found that the repair works caused a slight reduction in the natural frequencies but there was no definite trend in the changes to the modal damping ratios. Comparison of the mode shapes before and after repairs using modal analysis procedures was found to give an indication of the ...
262 citations
TL;DR: In this paper, a cantilever plate with a small crack was analyzed using finite element analysis and modal parameters such as natural frequencies, magnitude of frequency response functions, displacement mode shapes and strain mode shapes were calculated against cracking in the plate.
71 citations
TL;DR: This paper investigates structural damage detection using a constrained eigenstructure assignment and makes it possible that the computed feedback gains correspond directly to the structural parameter changes.
Abstract: System health monitoring of aerospace vehicles is important not only for conducting safe operation but also for maintaining system performance. Structural health along with sensor and actuator malfunction must be monitored to perform the system health monitoring. As a step toward developing a system health monitoring scheme, this paper investigates structural damage detection using a constrained eigenstructure assignment. The eigenstructure assignment is selected for the investigation since it may be used not only to perform structural damage detection but also to monitor the sensor and actuator performance in a unified manner. To employ the eigenstructure assignment in the framework of structural modeling and modal testing, a concept of constrained eigenstructure assignment is developed. The constrained eigenstructure assignment makes it possible that the computed feedback gains correspond directly to the structural parameter changes. To demonstrate the capability of the approach, a 20-bay planar truss structure is employed. Modal tests are performed using 11 accelerometers for the undamaged structure and several missing member damage cases. Then the test modes are used to locate the missing member. In spite of incomplete mode shapes and test inaccuracies, accurate damage detection is conducted.
47 citations
31 Dec 1995
TL;DR: In this article, the Natural Excitation Technique (NExT) is used to extract response parameters from large operational structure when subjected to random and unmeasured forces such as wind, road noise, aerodynamics, or waves.
Abstract: A technique called the Natural Excitation Technique or has been developed to response extract response parameters from large operational structure when subjected to random and unmeasured forces such as wind, road noise, aerodynamics, or waves. Six applications of NExT to ambient excitation testing and NExT analysis are surveyed in this paper with a minimum of technical detail. In the first application, NExT was applied to a controlled-yaw Horizontal-Axis Wind Turbine (HAWT). By controlling the yaw degree of freedom an important class of rotating coordinate system effects are reduced. A new shape extraction procedure was applied to this data set with good results. The second application was to a free-yaw HAWT. The complexity of the response has prompted further analytical studies and the development of a specialized visualization package. The third application of NExT was to a parked three-bladed Vertical-Axis Wind Turbine (VAWT) in which traditional modal testing could not excite all modes of interest. The shape extraction process used cross-correlation functions directly in a time-domain shape-fitting routine. The fourth application was to ground transportation systems. Ongoing work to improve driver and passenger comfort in tractor-trailer vehicles and to refine automobile body and tire models will use NExT. NExT has been used to process ambient vibration data for Finite Element Model correlation and is being used to study Structural Health Monitoring with ambient excitation. Shape fitting was performed using amplitude and phase information taken directly from the cross-spectra. The final application is to an offshore structure. This work is on-going, however initial studies have found a high-modal density, high noise content, and sparse data set.
41 citations
TL;DR: In this article, an experimental investigation carried out on square and rectangular plates with various boundary conditions to determine the damping ratios for a few modes of vibration is reported, based on the experimental findings, the Rayleigh damping coefficients can be computed for subsequent use in the modal superposition technique.
40 citations
TL;DR: In this paper, an energy-based representation of modal damping in structural cables is derived in the form of the product of the modal strain energy ratio and loss factor.
33 citations
TL;DR: The modal damping factor is defined as the ratio of the strain energy dissipated per radian of vibration, in the mode of interest, to the total strain energy of the entire laminate at maximum displacement during the same cycle as mentioned in this paper.
Abstract: The present investigation is concerned with the utilisation of the finite element technique for predicting the natural frequencies and the modal damping factor (also called the loss factor) of anisotropic fibre‐reinforced composite laminated plates. The simple definition of the modal damping factor is defined as the ratio of the strain energy dissipated per radian of vibration, in the mode of interest, to the total strain energy of the entire laminate at maximum displacement during the same cycle. Results for the vibration and damping analysis of multi‐layered plates obtained by the present methods are compared with the results obtained by other authors and with the results of experiments.
31 citations
31 Dec 1995
TL;DR: In this paper, several different techniques for damage assessment are demonstrated and compared using experimental modal data from an undamaged and damaged bridge, which are obtained from modal parameters, such as the flexibility matrix, stiffness matrix, and mode shape curvature.
Abstract: Over the past 25 years detecting damage in a structure from changes in dynamic parameters has received a considerable amount of attention from the aerospace, civil, and mechanical engineering communities. The general idea is that changes in the structure`s physical properties (i.e., stiffness, mass, and/or damping) will, in turn, alter the dynamic characteristics (i.e., resonant frequencies, modal damping, and mode shapes) of the structure. Properties such as the flexibility matrix, stiffness matrix, and mode shape curvature, which are obtained from modal parameters, have shown promise for localizing structural damage. In this paper, several different techniques for damage assessment are demonstrated and compared using experimental modal data from an undamaged and damaged bridge.
30 citations
TL;DR: In this article, a technique has been developed, using optical beam deflection, to measure the modal shape of a cantilever non-invasively at each modal frequency.
Abstract: The study of free vibrations of systems such as simple cantilevers has been mainly concerned with the determination of the eigenvalues (frequencies) and eigenfunctions (modal shapes). A technique has been developed, using optical beam deflection, to measure the modal shape of a cantilever non-invasively at each modal frequency. A knowledge of the modal shapes of very small cantilevers incorporating suitable actuators is important in the application of active vibration control to micromechanical structures.
26 citations
Patent•
BMW1
TL;DR: In this article, a process for determining the vibration characteristics of a body by modal analysis is described. But the body is made to vibrate at different frequencies and optical interference images of the body are recorded for the different frequencies.
Abstract: A process is disclosed for determining the vibration characteristics of a body by modal analysis. The body is made to vibrate at different frequencies and optical interference images of the body are recorded for the different frequencies. The interference images are analyzed on the basis of a mathematical/physical model, in view of the vibration characteristics at predetermined points, and the thus obtained information about the vibration characteristics of said points is subjected to a modal analysis.
Journal Article•
TL;DR: In this article, the Integrity Index method was applied to data obtained from testing a structure before and after repairs, and it was possible to identify areas of the structure affected by the repairs.
Abstract: Various non-destructive test methods exist for detailed investigation ofcomponents, relatively small-scale structures and parts oflarger structures. Before detailed investigations, the first stage of any assessment (especially on large structures) involves determining the defective areas of the structure. Most NDT methods are inappropriate or not too efficient for this task. One NDT procedure, called the Integrity Index method, which is suitable for monitoring the global condition of a structure and determining defective areas, is the subject of this paper. The method is based on modal testing and uses measured natural frequencies and mode shapes to compute indices which indicate the existence and location of defects. A brief description of the development of the method is given and its application to a full-scale structure presented. The method was applied to data obtained from testing a structure before and after repairs. From the results, it was possible to identify areas of the structure affected by the repairs. Some details of the structure and the experimental procedure adopted are also given.
1 Jan 1995
TL;DR: The present paper will deduce the SMURF for a one dimensional problem, then two methods for the correction of transducer-loading effects will be developed and extended to a multi dimensional problem.
Abstract: 2 Introduction A transducer mounted on a vibrating system perturbs the dynamics of the system and introduces errors into measured vibrations. For example mass-loading effects cause shifts of natural frequencies. One disadvantage is the loss in accuracy, which can cause unpredictable ~IIOIS when using substructuring techniques. Another drawback is the inconsistency of the database when using series of measurements with moving transducers, because global curve fitting algorithms for modal processing demand strong data consistency. Although this is a well known problem there exist, to the author’s knowledge, publications to solve this basic problem only for the driving point transducer’s mass. This paper developes several methods to correct the transducer-loading effects by using substructuring techniques, especially direct &uctural modification rising experimental frequency response functions (SMURF). Throughout this paper, the focus is put on loading effects from transducers. IIowever, the method devised may equally be applied to any other loading problem. The process of estimating structural modifications directly from experimental frequency response functions (SMURF) was investigated in the early seventies by Klosterman [l]. This method avoids the difficult and time consuming development of a modal model. The present paper will deduce the SMURF for a one dimensional problem. Then two methods for the correction of transducer-loading effects will be developed and extended to a multi dimensional problem. A test of the support of a car engine proves the practicability of the methods.
TL;DR: In this paper, the relationship between pole-residue models for conventional structures and piezostructures is developed and fundamental relationships are developed which reveal that the existing framework of traditional modal analysis approaches can be used to estimate modal parameters which describe the piezstructure dynamics.
Abstract: This paper is motivated by the need for consistency between piezostructure measurements and existing modal analysis approaches. Fundamental relationships are developed which reveal that the existing framework of traditional modal analysis approaches can be used to estimate modal parameters which describe the piezostructure dynamics. The modal analysis technique is a frequency domain method where the relationship between pole-residue models for conventional structures and piezostructures is developed. Since typical arrangements of piezoelectric sensors and actuators for modal testing lead to ambiguous mode shape estimates, the use of sensoriactuator transducers provides critical drive-point response information. Also, the existence of a transformation between the structure's modal matrix and the piezostructure's electromechanical coupling matrix is shown. It is shown that combining the results of a traditional modal test and a piezostructure modal test enables a modal filtering operation which produces experimental measurements of the electromechanical coupling matrix. This method of modal analysis of a piezostructure is demonstrated numerically for a cantilevered beam.
1 Jan 1995
TL;DR: In this paper, the authors apply the force appropriation method on the analytical model of actual aircraft, the tools generally used to extract experimental modal characteristics (frequency, damping, modeshape and modal mass) from test data.
Abstract: Modal parameters of structural systems can be obtained in many different ways. The force appropriation method uses one sine signal to generate forces at different points of a structure and adjusts the relative values of those forces so as to isolate a single mode. Such tests provide very accurate information on the modeshapes which is then complemented by specific tests to determine the mode damping and scaling (modal mass). This approach has been traditionally used for ground vibration testing of aircraft where the use of sine inputs is compatible with the need for large forces at very low frequencies. After a presentation of the theory related to this testing methodology, this study applies, on the analytical model of actual aircraft, the tools generally used to extract experimental modal characteristics (frequency, damping, modeshape and modal mass) from test data. The knowledge of the true answer allows a real evaluation of the difficulties linked to different steps of the appropriation method. Issues addressed in particular are the definition of the actuator and sensor set-up, the determination of the appropriation forces rejecting unwanted modal contributions, and the accuracy of identified modal characteristics.
TL;DR: In this paper, the directivity information of the modes carried in the directional frequency response functions is used in a modal testing method of rotating disks which is proposed for separation of the forward and backward travelling wave modes and identification of the diametrical node numbers associated with modes of interest.
17 Sep 1995
20 Apr 1995
TL;DR: In this article, the effect of prescribed delamination on natural frequencies of laminated composite beam specimens is examined both experimentally and theoretically, and backpropagation neural network models are developed using the results from the simplified beam theory and used to predict delamination size.
Abstract: The effect of prescribed delamination on natural frequencies of laminated composite beam specimens is examined both experimentally and theoretically. Delamination in composite laminate is of particular interest because they can cause catastrophic failure of the composite structure. One consequence of delamination in a composite structure is a change in its stiffness. This change in stiffness will degrade the modal frequencies of the composite structure. Modal testing of perfect beam and beams with different size of delamination is conducted using PVDF sensors and piezoceramic patch with sine sweep actuation. Model testing of beams is also conducted using PVDF sensors and instrumented hammer excitation. The results of instrumented hammer excitation and piezoceramic patch excitation are discussed. The experimental modal frequencies are compared with the results obtained using a simplified beam theory. Also, backpropagation neural network models are developed using the results from the simplified beam theory and used to predict delamination size. The effect of learning rate and momentum rate on neural network performance are discussed. Modal frequencies can be easily and accurately obtained with piezoceramic patch excitation and PVDF sensing. There is good agreement between modal frequencies from modal testing and those from the simplified beam theory. The developed neural network models successfully predict delamination size. Prediction errors varied from 0.25% to 19%.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this article, the use of segmented piezoelectric film sensors for the modal analysis of structures is discussed. And the authors make use of the relation between the charge generated by the piezo-lectric sensors and the modality coordinates, the asymptotic behavior of the eigensolution of structures, and the concept of modal observers to extract modal coordinates and velocities from the sensor output, and conduct sensitivity studies in an effort to determine the optimal coverage area of the piezofilm sensor.
Abstract: This paper is concerned with the use of segmented piezoelectric film sensors for the modal analysis of structures. We make use of the relation between the charge generated by the piezoelectric sensors and the modal coordinates, the asymptotic behavior of the eigensolution of structures, and the concept of modal observers to extract the modal coordinates and velocities from the sensor output. We also conduct sensitivity studies in an effort to determine the optimal coverage area of the piezofilm sensor, and we investigate the effects of noise, unmodeled dynamics, and parameter errors on the accuracy of the modal coordinate and velocity extraction. We analyze implementation of piezoelements on beams as well as on plates.
TL;DR: In this article, the modal analysis method works well regardless of the amount of damping in the system, provided that modal coupling is included in the analysis, and the soundfield produced by a vibrating piston in a tube with an absorptive end is calculated.
Abstract: That the modal analysis method works well regardless of the amount of damping in the system, provided that modal coupling is included in the analysis, is shown. The soundfield produced by a vibrating piston in a tube with an absorptive end is calculated. An exact solution is compared to results computed by modal analysis with and without the inclusion of modal coupling. Recent published results, which did not include the effects of modal coupling, incorrectly concluded that discrepancies were due to limitations of modal analysis, rather than the uncoupling assumption.
1 Jan 1995
TL;DR: In this article, a method is presented to make use of those vakms, each one measured for a pair of response/excitation, in order to extract a// the ten values to characterize the rigid-body behaviour of any unconstrained structure.
Abstract: The determination of the rigid-body dynamic properties of structures is an important task to be performed in the field of structural modification or coupling analyses. In the system representat ion, a modal matr ix which incorporates up to six rigid-body modes may be used to describe the models pertaining to unconstrained structures. In analytical terms, these modes can be easily obtained, a fact that does not happen in the experimental route as, for each FRF measurement of a free/y suppotted structure, a// the rigid body information is condensed to one single value, i.e. to the inertia restraint or mass line value. In this work a method is presented to make use of those vakms, each one measured for a pair of response/excitation, in order to extract a// the ten values to fu//y characterize the rigid-body behaviour of any unconstrained structure. A geometrically simple object, a rectangular cross section beam was used to simulate the measurement responses in different points~and for several excitation conditions. These analytical tests were performed to determine the effects of the measurement and excitation locations on the accuracy of the rigid body properties obtained by using the proposed methodology.
TL;DR: In this article, a specific application of sweep frequency circular input force perturbation testing of rotors rotating in fluid environment is discussed, where the rotors are rotated in a fluid environment.
Abstract: Modal testing of rotating structures has specific aspects, and it requires a specialized approach. Classical modal testing when applied to active (rotating) structures does not provide complete results. These aspects, and specific application of sweep frequency circular input force perturbation testing of rotors rotating in fluid environment, are discussed in this paper.
1 Jan 1995
TL;DR: In this paper, the transformation matrix from displacements to strains, which is constant and independent to time or frequency, is determined based on the displacement and strain mode shapes under modal testing and verified by a simple plate and finally applied to a bicycle when a human rides on a road.
Abstract: The dynamic strain distribution, which is “-Y important consideration for modern machine design, is usually measured under steady state excitation. Besides a huge number of strain gages is necessary due to its local nature. T h e s e requirments a r e difficult to fulfill under operating condition because of non-steady state and of limited number of measurement channel of computer. Therefore, in this paw, first the transformation matrix from displacements to strains, which i s constant and independent to time or frequency , is determined based on the displacement and strain mode shapes under modal testing. Then, under actual operating condition, a small number o f acceleration pickups is used to monitor the actual responses aod the detail dynamic strain distribution can be predicted via the transformation matrix. This technique is verified by a numerical model and a simple plate and finally applied to a bicycle when a human rides on a road.
TL;DR: In this paper, a structural dynamic modification of a fixed-free (cantilever) beam to convert it into a fixed fixed beam with experimental modal data is presented, focusing on incorporating experimental rotational degrees-of-freedom (DOF) measured with a novel laser measurement technique.
Abstract: Structural dynamic modification (SDM) of a fixed-free (cantilever) beam to convert it into a fixed-fixed beam with experimental modal data is presented. The SDM focuses on incorporating experimental rotational degrees-of-freedom (DOF) measured with a novel laser measurement technique. A cantilever beam is tested to develop the experimental modal database including rotational degrees of freedom. A modal database from a finite-element model also is developed for comparison. A structural dynamic modification, with both databases, is performed using a Bernoulli-Euler beam to ground the free end of the cantilever beam. The hardware is then modified and a second experimental modal analysis of the resulting fixed-fixed beam performed. A finite-element model of the fixed-fixed beam also was created. Comparison of results from these four tests are used to assess the effectiveness of SDM using experimental modal rotational data. The evaluation shows that provided high quality experimental rotational modal data can be acquired, SDM work with beam elements can be effective in yielding accurate results.
17 Sep 1995
TL;DR: In this article, an approach to identify modal data as well as reaction forces at the table/structure interface has been introduced, and the verification of the theory using a laboratory test structure has been presented.
Abstract: Base excitation testing is used in industry in order to qualify mechanical systems with respect to specified base acceleration levels. This type of excitation only allows to identify eigenfrequencies, mode shapes and modal damping values of the fixed/free system. Modal masses, mass participation factors and effective masses of the fixed/free system as well as the modal data of the free/free system cannot be identified b ecause the excitation forces are unknown. This paper introduces an approach to identify these modal data as well. For this purpose the reaction forces at the table/structure interface have to be measured also. Furthermore, the verification of the theory using a laboratory test structure will be presented. NOMENCLATURE
1 Jan 1995
TL;DR: Based on the measured data under various excitations and the theory of complex energy, it is found that the modal energy transfer ratio is a very good dynamic signature for structural evaluation and monitoring.
Abstract: Modal testing were conducted for a long steel trnss bridge crossing the Niagara River between the State of New York and the Ontario Province. The purpose of this study is to examine the dynamic signatures of the structure for the evaluation and the development of possible vibration reduction schemes for the bridge. In this study we examined the feasibility of using the modal energy transfer ratios as a parameter for structure evaluations. Based on the measured data under various excitations and the theory of complex energy, it is kno\bn that the modal energy transfer ratio is a very good dynamic signature for structural evaluation and monitoring. This study is jointly supported by the Peace Bridge Authority, PCB Piezotronics, Inc., Twist Technology, Inc. and the National Center for Earthquake Engineering Research.
TL;DR: In this paper, a galvanometer-based laser scanning system for SLDV has been developed for testing and calibration of the scanning system to meet the precision requirements of modal testing.
TL;DR: In this paper, a soil-structure interaction formulation is used based on consideration of the dynamics of the structure with a free, rather than a fixed, base, and it is shown that the damping matrix resulting in equal modal damping values for free-based modes will give a very significantly smaller damping value for the fundamental distortional mode of the feued-base structure.
Abstract: A soil-structure interaction formulation is used here which is based on consideration of the dynamics of the structure with a free, rather than a fixed, base. This approach is shown to give a quite simple procedure for coupling the dynamic characteristics of the structure to those of the foundation and soil in order to obtain a matrix formulation for the complete system. In fixed-base studies it is common to presume that each natural mode of the structure has a given fraction of critical damping, and since the interaction formulation uses a free-base model, it seems natural for this situation to assign the equal modal damping values to free-base modes. It is shown, though, that this gives a structural model which is significantly different than the one having equal modal damping in the fixed-base modes. In particular, it is found that the damping matrix resulting in equal modal damping values for free-based modes will give a very significantly smaller damping value for the fundamental distortional mode of the feued-base structure. Ignoring this fact could lead one to attribute dynamic effects to interaction which are actually due to the choice of damping.
TL;DR: In this paper, a Unified Matrix Polynomial Approach (UMPA) is discussed as a possible method of condensing multiple sets of Perturbed Boundary Condition (PBC) test data into a single modal model of the unmodified system.