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Numerical treatment of seismic accelerograms and of inelastic seismic structural responses using harmonic wavelets
The harmonic wavelet transform is employed to analyze various kinds of nonstationary signals common in aseismic design. The effectiveness of the harmonic wavelets for capturing the temporal evolution of the frequency content of strong ground motions is demonstrated. In this regard, a detailed study of important earthquake accelerograms is undertaken and smooth joint time-frequency spectra are provided for two near-field and two far-field records; inherent in this analysis is the concept of the mean instantaneous frequency. Furthermore, as a paradigm of usefulness for aseismic structural purposes, a similar analysis is conducted for the response of a 20-story steel frame benchmark building considering one of the four accelerograms scaled by appropriate factors as the excitation to simulate undamaged and severely damaged conditions for the structure. The resulting joint time-frequency representation of the response time histories captures the influence of nonlinearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event. In this context, the potential of the harmonic wavelet transform as a detection tool for global structural damage is explored in conjunction with the concept of monitoring the mean instantaneous frequency of records of critical structural responses
Technique for Measurement of Weld Resistance for AC Resistance Spot Welding via Instantaneous Phasor Measurement
The resistance measurement in the resistance spot welding (RSW), is an ongoing research topic. The high current flow during the welding process induces an electromagnetic field in the wires which are attached to the electrodes to measure tip voltage. This results an additional voltage drop which is proportional to the derivative of current. Also the presence of silicon controlled rectifier (SCR) in the welding power supply generates harmonics in both supply voltage and current. These issues together complicate the methods for resistance estimation.
A set of simultaneous linear equations is derived for the on-line measurement of dynamic resistance and induced voltage constant by using the dynamic circuit analysis of weld setup. This can be solved to determine the weld resistance using instantaneous phasors measurements for the 1st, 3rd and 5th harmonics of current and measured voltage signals. The instantaneous phasor measurements for these desired harmonics are obtained by employing the following proposed method.
In this thesis, a new method for the measurement of instantaneous phasor is proposed for the narrow band signals. The proposed algorithm is based on the internal model principle (IMP) defined for the cancellation of a sinusoidal disturbance signal. The IMP has two states, exhibiting the properties of being sinusoidal and orthogonal. The instantaneous values of IMP states are defined as real and imaginary components of a complex signal at each time instant. The instantaneous measurements of envelope and phase of a sinusoidal signal are determined from instantaneous values of complex signal by using arithmetic properties of complex numbers. In case of signal comprising of sum of sinusoids of different frequencies, the approach for obtaining instantaneous phasor for each sinusoidal component is presented by connecting multiple internal models in the parallel and open-loop configuration.
The instantaneous phasor measurement of fundamental frequency signal is not only advantageous in detecting faults like short circuiting, harmonic distortion and frequency variations but it can also be applied to protect power system from these faults. In this work, the applicability of the proposed instantaneous phasor measurement algorithm is analyzed for scenarios of power disturbances due to the the harmonic distortion and decaying DC offset. The results are discussed and compared with few existing methods
Optimal greenhouse cultivation control: survey and perspectives
Abstract: A survey is presented of the literature on greenhouse climate control, positioning the various solutions and paradigms in the framework of optimal control. A separation of timescales allows the separation of the economic optimal control problem of greenhouse cultivation into an off-line problem at the tactical level, and an on-line problem at the operational level. This paradigm is used to classify the literature into three categories: focus on operational control, focus on the tactical level, and truly integrated control. Integrated optimal control warrants the best economical result, and provides a systematic way to design control systems for the innovative greenhouses of the future. Research issues and perspectives are listed as well
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