Browsing by Author "Devaraj, D."

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A combined genetic algorithm and Sugeno fuzzy logic based approach for on-line tuning in pH process
(2008) Valarmathi, K.; Devaraj, D.; Radhakrishnan, T.K.
Computing the optimal values of Proportional Integral derivative (PID) control gains is an important task in the design of PID controller. This paper presents the application of Sugeno fuzzy model for on-line tuning of PID controllers in pH process. The optimal PID controller parameters required to develop the Sugeno fuzzy model are estimated by genetic algorithm. The developed fuzzy controller can give the PID parameters on line for different operating conditions. The suitability of the proposed approach has been demonstrated through computer simulation using MATLAB Simulink. Â© 2008 IEEE.
A combined genetic algorithm and Sugeno fuzzy logic based approach for on-line tuning in pH process
(2008) Valarmathi, K.; Devaraj, D.; Radhakrishnan, T.K.
Computing the optimal values of Proportional Integral derivative (PID) control gains is an important task in the design of PID controller. This paper presents the application of Sugeno fuzzy model for on-line tuning of PID controllers in pH process. The optimal PID controller parameters required to develop the Sugeno fuzzy model are estimated by genetic algorithm. The developed fuzzy controller can give the PID parameters on line for different operating conditions. The suitability of the proposed approach has been demonstrated through computer simulation using MATLAB Simulink. � 2008 IEEE.
Joint Time Frequency Analysis Based Synthesis of Acceleration-Time History and Response Spectra for Japanese Earthquakes
(Springer Science and Business Media Deutschland GmbH, 2022) Ramkrishnan, R.; Devaraj, D.; Kolathayar, S.; Sitharam, T.G.
Timeâ€“Frequency Analysis (TFA) techniques help to obtain the ideal time and frequency occurrence characteristics of earthquake motion confined in a seismic recorded signal. Time-histories from recording stations in Japan has been adopted in the present analysis, considering a large number of available data. The seismograms were transformed using Gabor transform, a Linear Joint TFA method, to assess their frequency content by generating their Gabor coefficients. Average Gabor coefficients were estimated for recorded seismograms within a magnitude range of 5.5â€“6.0 and hypocentral distances ranging from 0 to 50Â km. The estimated average Gabor coefficients were used to synthesize a generalized acceleration-time history for the specific distance and magnitude ranges using Gabor Expansion, without compromising the frequency content of the waves. Additionally, it is demonstrated that the response spectra of the synthesized signal and the original signal match very well. These response spectra will be valuable for the nonlinear investigation of structures in this region. Â© 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
RECENT DEVELOPMENTS IN SYNTHESIS OF EARTHQUAKE MOTIONS USING LINEAR JOINT TIME FREQUENCY ANALYSIS TECHNIQUES
(International Association for Earthquake Engineering, 2021) Ramkrishnan, R.; Devaraj, D.; Kolathayar, S.; Sitharam, T.G.
Temporal distribution of the frequency contents of a multi-component signal like seismic motions are not captured and well-represented in Fourier Transform (FT) techniques. Linear Joint Time-Frequency Analysis (LJTFA) addresses this issue and can transform and represent a signal in not only time domain and frequency domain, but in time-frequency domain simultaneously. Considering the better resolution and less spectral spillage when compared to Short Time Fourier Transform (STFT) and less complexity when compared to Wavelet Transform (WT), Gabor Transform (GT) is adopted in the current study. Actual recorded time-histories from recording stations in Japan had been considered for a LJTFA based synthesis of earthquake motions in this study considering the high seismicity of the area and large number of data available. Recorded time-histories of 23 earthquakes throughout Japan has been collected from K-Net and Kik-Net Strong Motion Seismograph Network of Japan and is categorized according to various Magnitude and hypocentral distances. Events of magnitude ranging from 5 to 5.5 and hypocentral distances 0 to 100km is sorted and GT is applied to transform the signals to their time-frequency domain and estimate their Gabor amplitude coefficients. Mean Gabor amplitude coefficients are estimated for different Magnitude (Mx) and Distance (Dy) combinations like M5D0-25, M5D25-50, M5-5.5D0- 25, and M5-5.5D25-50. Using an inverse GT process; Gabor Expansion (GE), the mean transformed Gabor amplitude coefficients are used to reconstruct and synthesize a time-history which doesn’t compromise on the quality of their spectral and frequency contents, thus yielding reliable synthetic seismic motions. Response spectra is developed from the actual and synthesized time-histories and are compared. A statistically good fit in terms of the coefficient of determination factor, R2 is observed between the actual and synthetic response spectrum developed. © 2021, International Association for Earthquake Engineering. All rights reserved.
Study the dynamic behaviour of seven DOF of full car model with semi-active suspension system
(Inderscience Publishers, 2021) Hemanth, H.; Shamanth, S.; Devaraj, D.; Kumar, H.; Gangadharan, K.V.
This paper presents an investigation on the ride comfort and road-holding performance of a vehicle equipped with the semi-active suspension system. The full car semi-active suspension model with 7 degrees of freedom (7 DOF) system is adopted for the study and a fuzzy-logic control strategy is considered for minimising the effect of road disturbance on vehicle performance. The responses of a vehicle have been analysed under the Indian average random road profile (ISO8608) against the conventional passive suspension system. The performance of the semi-active suspension system is evaluated by heave, roll and pitch acceleration of the vehicle body around its centre of gravity. The performance of a vehicle with the semi-active suspension system has been compared with the response conventional passive suspension system. The result specifies that, the semi-active suspension system with a fuzzy-logic controller reduces around 43% of vibration amplitude at the resonance frequency of vehicle than the passive suspension system. © © 2021 Inderscience Enterprises Ltd.
Synthesis of Linear JTFA-Based Response Spectra for Structural Response and Seismic Reduction Measures for North-East India
(World Scientific, 2020) Devaraj, D.; Ramkrishnan, R.; Prabu, T.; Kolathayar, S.; Sitharam, T.G.
North-East India (NEI) has a long history of devastating earthquakes due to the complicated tectonic setting of the region. A shortage of sufficient recorded time-histories from the region calls for a synthesis of accelerograms for dynamic analyses. In this study, a novel Joint Time-Frequency Analysis (JTFA) technique is adopted for the synthesis of accelerograms, considering the non-stationary behavior of earthquake waves. JTFA is used for analyzing the signals in a joint time and frequency domain to better understand its characteristics and synthesize signals without compromising its inherent characteristics like frequency content and amplitude. Synthetic accelerograms are developed using JTFA techniques for different magnitude and distance ranges between 5 to 6.8 and 0-480km and response spectra are developed. Synthesized generalized accelerograms and their response spectra are compared with actual signals in the same magnitude-distance ranges and were found to match. A comparison of the frequency contents of actual and synthetic signals was also carried out using Fourier Transforms and spectrograms (SPs) and was found to be in good agreement. Further, a comparative study of various earthquake reduction measures for NEI is carried out for a scenario earthquake using the synthesized data, and the best suitable structural input for the region is recommended. © 2020 World Scientific Publishing Company.