Chaotic Response of a Hard Duffing Type Vibration Isolator With Combined Coulomb and Viscous Damping

Numerical simulations of the response of a harmonically excited mass on an isolator with a cubic, hard, non-linear restoring force and combined Coulomb and viscous damping are presented. For a base-excited system, the inclusion of a Coulomb damper with a suitable break-loose frequency can suppress the secondary resonances and chaotic motion. However, for a force-excited system, the introduction of Coulomb damping does not alter the bifurcation structure. Transmissibility indices have been defined for the solution obtained by numerical integration and the role of the subharmonic resonances and chaotic motion on the performance of the system is pointed out.

Vibration Control Using Combined Independent Modal Space Control and Fuzzy Logic

Independent Modal Space Control (IMSC) is an established technique in active suppression of vibrations, in which the control law is developed exclusively in the modal space, allowing for independent design of the modal control forces. These forces can be transformed to the physical domain through modal transformation. The resulting controller is fixed-gain, with the active damping introduced to the system determined independently for each mode and is a function of the velocity for the under-damped case. In this work we propose to modify IMSC using fuzzy reasoning. The result is a new non-linear control law, embedding fuzzy reasoning and an implicit fuzzy rule-base that transforms the traditional algorithm from a fixed-gain to a variable-gain controller. The algorithm uses information about the displacement profile across the sensed locations to distribute the active damping rationally among the modal controllers. This new algorithm complements the “local” view of the traditional algorithm in the modal space, with a “global” view of the displacements in the physical space. The results show significant improvement in the settling time as the performance criterion.

Regularization of Some One-Dimensional Inverse Problems for Identification of Nonlinear Surface Phenomena

A simple numerical method for some one-dimensional inverse problems of model identification type arising in nonlinear heat transfer is discussed. The essence of the method is to express the nonlinearity in terms of an integro-differential operator, the values of which are approximated by a linear spline technique. The inverse problems are mildly ill-posed and therefore call for regularization when data errors are present. A general technique for stabilization of unbounded operators may be applied to regularize the process and a specific regularization technique is illustrated on a model problem.

Efficient Numerical Solution of Inverse Heat Conduction Problems

In this contribution we propose new numerical methods for solving inverse heat conduction problems. The methods are constructed by considering the desired heat flux at the boundary as piecewise constant (in time) and then deriving an explicit expression for the solution of the equation for a stationary point of the minimizing functional. In a very special case the well-known Beck method is obtained. For the time being, numerical tests could not be included in this contribution but will be presented in a forthcoming paper.

Identification of Parameters in Hereditary Systems

In this paper we study the numerical performance of a parameter identification technique, based on approximation by equations with piecewise constant arguments, on various classes of hereditary systems. The examples considered here include delay equations with state-dependent delays and neutral equations.

Active Boundary Control of Elastic Cables

Cables are lightweight structural elements used in a variety of engineering applications. This paper introduces an active boundary control approach that damps undesirable vibrations in a cable. Using Hamilton’s principle, the governing nonlinear partial differential equations for an elastic cable are derived, including the natural boundary conditions associated with boundary force control. Based on Lyapunov theory, passive and active vibration controllers are developed. A Galerkin approach generates the linearized, closed loop, modal dynamics equations for out-of-plane vibration. Simulations demonstrate the improved damping provided by the passive and active controllers.

Computer Simulation for Active Control of Vibration in Beam Structures

This paper is concerned with an inverse problem of the active control of non-steady dynamic vibration in elastic beams. A simulation technique based on the boundary element method and the extended Kalman filter or a new filter theory is successfully applied to the inverse problem. The Laplace-transform integral equation method is used for the solution of dynamic bending vibration in elastic beams. Through a Taylor series expansion, the linear system of equations is derived for modification of the unknown parameters, and it is solved iteratively so that an appropriate norm is minimized. The usefulness of the proposed method of inverse analysis is demonstrated through numerical computation of a few examples.

Updating Substructure Models With Dynamic Boundary Conditions

In recent years procedures for updating analytical model parameters have been developed by minimizing differences between analytical and preferably experimental modal analysis results. Provided that the initial analysis model contains parameters capable of describing possible damage these techniques could also be used for damage detection. In this case the parameters are updated using test data before and after the damage. Looking at complex structures with hundreds of parameters one generally has to measure the modal data at many locations and try to reduce the number of unknown parameters by some kind of localization technique because the measurement information is generally not sufficient to identify all the parameters equally distributed all over the structure. Another way of reducing the number of parameters shall be presented here. This method is based on the idea of measuring only a part of the structure and replacing the residual structure by dynamic boundary conditions which describe the dynamic stiffness at the interfaces between the measured main structure and the remaining unmeasured residual structure. This approach has some advantage since testing could be concentrated on critical areas where structural modifications are expected either due to damage or due to intended design changes. The dynamic boundary conditions are expressed in Craig-Bampton (CB) format by transforming the mass and stiffness matrices of the unmeasured residual structure to the interface degrees of freedom (DOF) and to the modal DOFs of the residual structure fixed at the interface. The dynamic boundary stiffness concentrates all physical parameters of the residual structure in only a few parameters which are open for updating. In this approach damage or modelling errors within the unmeasured residual structure are taken into account only in a global sense whereas the measured main structure is parametrized locally as usual by factoring mass and stiffness submatrices defining the type and the location of the physical parameters to be identified. The procedure was applied to identify the design parameters of a beam type frame structure with bolted joints using experimental modal data.

Active Vibration Absorption Using Delayed Resonator With Relative Position Measurement

A novel active vibration absorption technique, the Delayed Resonator, has been introduced recently as a unique way of suppressing undesired oscillations. It suggests a control force on a mass-spring-damper absorber in the form of a proportional position feedback with a time delay. Its strengths consist of extremely simple implementation of the control algorithm, total vibration suppression of the primary structure against a harmonic force excitation and full effectiveness of the absorber in a semi-infinite range of disturbance frequency, achieved by real-time tuning. All this development work was done using the absolute displacements of the absorber in the feedback. These displacement measurements may be difficult to obtain and for some applications impossible. This paper deals with a substitute and easier measurement: the relative motion of the absorber with respect to the primary structure. Theoretical foundations for the Delayed Resonator (DR) are briefly recapitulated and its implementation on a single-degree-of-freedom primary structure disturbed by a harmonic force is introduced utilizing both absolute and relative position measurement of absorber mass. Methods for stability range analysis and transient behavior are presented. Properties acquired for the same system with these two different feedback are compared. Relative position measurement case is found to be more advantageous in most applications of the Delayed Resonator method.

Passive Control of Structural Vibration in Base-Isolated Shear Structures

This paper presents three analytic models for predictions or structural response of oscillating systems with Coulomb and viscous friction. Numeric results were obtained from the models and compared to demonstrate the effects of friction on vibration amplification.