The semi-active variable stiffness tuned mass damper (SAIVS-TMD), developed in this thesis, is capable of continuously varying its stiffness and retuning its frequency due to real time control, and is robust to changes in building stiffness and damping. In comparison, the passive tuned mass damper (TMD) can only be tuned to a fixed frequency, which is the first mode frequency of the building. The building fundamental frequency can change due to damage or other reasons. The developed SAIVS-TMD overcomes the limitations of the TMD by retuning the frequency in real time.
Real time instantaneous frequency identification and control algorithms are developed in this thesis based on time-frequency techniques. Real time tuning algorithms that identify and tune the instantaneous frequency of the SAIVS-TMD are developed based on Hilbert Transform (HT), Short Time Fourier Transform (STFT) and Empirical Mode Decomposition (EMD). A new method for smoothing the end effects of EMD algorithm is proposed and verified through numerical examples.
The mathematical formulation of the linear time varying (LTV) system is developed. A new predictor-corrector algorithm is proposed for the LTV system. The LTV analytical model is developed to study the response of SAIVS-TMD under harmonic...
Semi-active control algorithms are developed and examined for a variety of civil engineering applications subjected to a wide range of excitations. Except two control algorithms based on continuous variable structure control and Lyapunov control, the semi- active controllers developed in this study are based on real-time estimation of instantaneous (dominant) frequency and the evolutionary power spectral density by time-frequency analysis of either the excitation or the response of the structure. Time-frequency analyses are performed by either short-time Fourier transform or wavelet transform.
The semi-active strategies are applied to three categories of structures: (1) smart single- and multi- degree-of-freedom (sSDOF/sMDOF) systems subjected to pulse-type and random ground excitations, (2) single/multiple smart tuned mass dampers (sTMD/sMTMD) subjected to random wind and ground excitations, and (3) smart tuned liquid column dampers (sTLCD) subjected to random wind and ground excitations.
For sMDOF/sMDOF systems, nonlinear control algorithms developed to independently vary stiffness (continuous variable structure control) and damping (Lyapunov control) are examined against near-fault earthquakes and pulse type of excitations fitted to them. Another semi-active (time-frequency) controller is developed based on minimizing the instantaneous H2 norm of the response of the structure.
Two time-frequency controllers (feedforward and feedback) are developed for single/multiple smart tuned mass dampers (sTMD/sMTMD) subjected to either force or base excitation. In the feedforward control...
Fonte: Universidade RicePublicador: Universidade Rice
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By framing the structural health monitoring and control problem as being one
of enhancing structural system intelligence, novel solutions can be achieved through
applications of computational strategies that mimic human learning and attempt
to replicate human response to sensory feedback. This thesis proposes several new
methods which promote adaptive, intelligent decision making by structural systems
relying on sensory feedback and actuator compensation. Four significant contributions
can be found in this thesis study. The first method employs an adaptable subclass of
Artificial Neural Networks (ANNs), called Radial Basis Function Networks (RBFNs)
for robust control in the presence of sensory failure. The second method exploits
this computationally efficient network to detect and isolate system faults in real time.
The third algorithm utilizes an RBFN to effectively linearize the nonlinear actuator
dynamics of a Magnetorheological (MR) damper, thereby improving control of the
semiactive device. Lastly, an open loop observer is implemented experimentally to
both detect damage and act as a trigger for control of the newly developed Adaptive
Length Pendulum-Smart Tuned Mass Damper (ALP-STMD).
Some limitation of existing algorithms in the field of real time structural health
monitoring and control are that they rely heavily on fixed parameter methods...
Current seismic design practice promotes inelastic response in order to reduce the design forces. By allowing the structure to yield while increasing the ductility of the structure, the global forces can be kept within the limited bounds dictated by the yield strength. However, during severe earthquakes, the structures undergo significant inelastic deformations leading to stiffness and strength degradation, increased interstory drifts, and damage with residual drift. The research presented in this thesis has three components that seek to address these challenges.
To prevent the inelastic effects observed in yielding systems, a new concept “apparent weakening” is proposed and verified through shake table studies in this thesis. “Apparent weakening” is introduced in the structural system using a complementary “adaptive negative stiffness device” (NSD) that mimics "yielding” of the global system thus attracting it away from the main structural system. Unlike the concept of weakening and damping, where the main structural system strength is reduced, the new system does not alter the original structural system, but produces effects compatible with an early yielding. Response reduction using NSD is achieved in a two step sequence. First the NSD...
Structural vibration control systems can be divided into four categories: 1) active control; 2) passive control; 3) semi-active control; and 4) hybrid control. It is well established that the semi-active control can provide control effect comparable to that of the active control but requires orders of magnitude smaller external energy. In this regard, researchers in this field have proposed and developed many promising semi-active control methodologies and devices, of which the semi-active or smart tuned mass damper (STMD) is very effective in reducing structural vibrations. In addition, adaptive-passive tuned mass damper (APTMD) which is tuned mechanically provides better reduction than the conventional passive TMD. In the present study, two kinds of TMDs: the smart tuned mass damper (STMD) which has variable frequency and variable damping ratio, and the adaptive passive tuned mass damper (APTMD) are investigated for the control of both linear and nonlinear structures.
Vibration of nonlinear systems is characterized by multiple solution branches and instability, such as bifurcations (the jump phenomenon), and chaos. For a hardening D"uffing oscillator subjected to harmonic excitations, a nonlinear tuned mass damper (NTMD) provides better and more robust control effect than the linear TMD; however...