Topic

# Modal analysis

About: Modal analysis is a research topic. Over the lifetime, 15114 publications have been published within this topic receiving 192575 citations.

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01 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.

4,683 citations

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TL;DR: In this article, the authors presented an efficient method for digital simulation of general homogeneous processes as a series of cosine functions with weighted amplitudes, almost evenly spaced frequencies, and random phase angles.

Abstract: Efficient methods are presented for digital simulation of a general homogeneous process (multidimensional or multivariate or multivariate-multidimensional) as a series of cosine functions with weighted amplitudes, almost evenly spaced frequencies, and random phase angles. The approach is also extended to the simulation of a general non-homogeneous oscillatory process characterized by an evolutionary power spectrum. Generalized forces involved in the modal analysis of linear or non-linear structures can be efficiently simulated as a multivariate process using the cross-spectral density matrix computed from the spectral density function of the multidimensional excitation process. Possible applications include simulation of (i) wind-induced ocean wave elevation, (ii) spatial random variation of material properties, (iii) the fluctuating part of atmospheric wind velocities and (iv) random surface roughness of highways and airport runways.

1,300 citations

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31 Dec 1999

TL;DR: In this paper, the authors present a modal analysis of power systems and their properties, including the nature of power system oscillations and stabilizers, as well as their properties.

Abstract: 1. Introduction. 2. The Nature of Power System Oscillations. 3. Modal Analysis of Power Systems. 4. Modal Analysis for Control. 5. Power System Structure and Oscillations. 6. Generator Controls. 7. Power System Stabilizers. 8. Power System Stabilizers - Problems and Solutions. 9. Robust Control. 10. Damping by Electronic Power System Devices. A1. Model Data Formats and Block Diagrams. A2. Equal Eigenvalues. Index.

1,264 citations

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01 Apr 1997

TL;DR: An elongated fishing lure includes an elongated body, a head at one end and a tail at the second end, with a series of integral outwardly projecting ribs at closely spaced points along the body to perform multiple significant functions.

Abstract: An elongated fishing lure formed, in the preferred embodiment, entirely of a soft, elastic, flexible and resilient plastic material which results in a lure freely deformable or manipulable under external forces. The lure includes an elongated body, a head at one end and a tail at the second end, with a series of integral outwardly projecting ribs at closely spaced points along the body, which ribs perform multiple significant functions including the selective trapping and release of air, the generation of clear acoustical signals, the increase in the visual bulk of the lure without affecting the flexibility thereof, the provision of means for facilitating movement of the lure over obstacles, etc.

1,214 citations

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TL;DR: By introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode, and close modes can be identified with high accuracy even in the case of strong noise contamination of the signals.

Abstract: In this paper a new frequency domain technique is introduced for the modal identification of output-only systems, i.e. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using this decomposition technique close modes can be identified with high accuracy even in the case of strong noise contamination of the signals. Also, the technique clearly indicates harmonic components in the response signals.

1,084 citations