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Pasala, Dharma Theja Reddy,Nagarajaiah, Satish Techno-Press 2014 Smart Structures and Systems, An International Jou Vol.13 No.2
Due to the shift in paradigm from passive control to adaptive control, smart tuned mass dampers (STMDs) have received considerable attention for vibration control in tall buildings and bridges. STMDs are superior to tuned mass dampers (TMDs) in reducing the response of the primary structure. Unlike TMDs, STMDs are capable of accommodating the changes in primary structure properties, due to damage or deterioration, by tuning in real time based on a local feedback. In this paper, a novel adaptive-length pendulum (ALP) damper is developed and experimentally verified. Length of the pendulum is adjusted in real time using a shape memory alloy (SMA) wire actuator. This can be achieved in two ways i) by changing the amount of current in the SMA wire actuator or ii) by changing the effective length of current carrying SMA wire. Using an instantaneous frequency tracking algorithm, the dominant frequency of the structure can be tracked from a local feedback signal, then the length of pendulum is adjusted to match the dominant frequency. Effectiveness of the proposed ALP-STMD mechanism, combined with the STFT frequency tracking control algorithm, is verified experimentally on a prototype two-storey shear frame. It has been observed through experimental studies that the ALP-STMD absorbs most of the input energy associated in the vicinity of tuned frequency of the pendulum damper. The reduction of storey displacements up to 80 % when subjected to forced excitation (harmonic and chirp-signal) and a faster decay rate during free vibration is observed in the experiments.
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Satish Nagarajaiah,Dharma Theja Reddy Pasala 국제구조공학회 2014 Smart Structures and Systems, An International Jou Vol.13 No.2
Due to the shift in paradigm from passive control to adaptive control, smart tuned mass dampers (STMDs) have received considerable attention for vibration control in tall buildings and bridges. STMDs are superior to tuned mass dampers (TMDs) in reducing the response of the primary structure. Unlike TMDs, STMDs are capable of accommodating the changes in primary structure properties, due to damage or deterioration, by tuning in real time based on a local feedback. In this paper, a novel adaptive-length pendulum (ALP) damper is developed and experimentally verified. Length of the pendulum is adjusted in real time using a shape memory alloy (SMA) wire actuator. This can be achieved in two ways i) by changing the amount of current in the SMA wire actuator or ii) by changing the effective length of current carrying SMA wire. Using an instantaneous frequency tracking algorithm, the dominant frequency of the structure can be tracked from a local feedback signal, then the length of pendulum is adjusted to match the dominant frequency. Effectiveness of the proposed ALP-STMD mechanism, combined with the STFT frequency tracking control algorithm, is verified experimentally on a prototype two-storey shear frame. It has been observed through experimental studies that the ALP-STMD absorbs most of the input energy associated in the vicinity of tuned frequency of the pendulum damper. The reduction of storey displacements up to 80 % when subjected to forced excitation (harmonic and chirp-signal) and a faster decay rate during free vibration is observed in the experiments.
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Kohji Yamaki,Herath Mudiyanselage Theja Herath,Yuko Takano-Ishikawa 한국식품영양과학회 2003 Journal of medicinal food Vol.6 No.4
Certain naturally occurring flavonoids affect immunoregulatory activities in vitroand in vivoagainst cytokineproduction. Since tumor necrosis factor (TNF)-a is one of the major inflammatory cytokines, the effects of various dietaryflavonoids on TNF-a production in lipopolysaccharide (LPS)-stimulated J774.1 cells were evaluated in vitro. Flavones,flavonols, and chalcone are the most potent inhibitors of production of TNF-a. Flavanone, naringenin, anthocyanidin, pelargo-din, and cyanidin exhibit moderate inhibitory activity. In contrast, genistein isoflavone displays weak inhibition, while eri-odictyol flavanone is inactive. It is clear that the double bond between carbons 2 and 3 and the ketone group at position 4 offlavonoids are necessary for potent inhibitory effect. The difference in inhibitory action appears to depend on the categorizedsubclass of flavonoids.
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Preparation of polypyrrole by chemical oxidation: applications for sensor studies
S. Pavithra,R. Thejas,H. N. Anil Rao,B. S. Krishna,G. Nagaraju 한국고분자학회 2024 Macromolecular Research Vol.32 No.1
Polypyrrole has gained more attention in conducting polymer science due to its ease of preparation and many advantages. In this article, by chemical oxidation method, three different polypyrroles were prepared using ferric chloride as an oxidant, including surfactant and natural directing agent, and named the samples PPY-1, PPY-2, and PPY-3. XRD, XPS, EDX, FT-IR, SEM, and electrical conductivity was used to characterize the synthesized polypyrrole. XRD confirms that the prepared samples were polypyrrole by showing peaks in the range of 20°–23°. SEM analysis shows that the sizes are between 120 and 180 nm. The present research work is a modest attempt to demonstrate for the first-time detection of hazardous gas using natural directing agent during polypyrrole synthesis. The prepared samples were used for the sensing of butane. PPY-2 shows a high electrical conductivity of 14 × 10– 3 S cm− 1 and gas sensing with a sensitivity value of 42.03 with lesser response and recovery time. This study reveals the fabrication of low-cost materials for butane sensors.
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Contreras, Michael T.,Pasala, Dharma Theja Reddy,Nagarajaiah, Satish Techno-Press 2014 Smart Structures and Systems, An International Jou Vol.13 No.2
In a companion paper, Pasala and Nagarajaiah analytically and experimentally validate the Adaptive Length Pendulum Smart Tuned Mass Damper (ALP-STMD) on a primary structure (2 story steel structure) whose frequencies are time invariant (Pasala and Nagarajaiah 2012). In this paper, the ALP-STMD effectiveness on a primary structure whose frequencies are time varying is studied experimentally. This study experimentally validates the ability of an ALP-STMD to adequately control a structural system in the presence of real time changes in primary stiffness that are detected by a real time observer based system identification. The experiments implement the newly developed Adaptive Length Pendulum Smart Tuned Mass Damper (ALP-STMD) which was first introduced and developed by Nagarajaiah (2009), Nagarajaiah and Pasala (2010) and Nagarajaiah et al. (2010). The ALP-STMD employs a mass pendulum of variable length which can be tuned in real time to the parameters of the system using sensor feedback. The tuning action is made possible by applying a current to a shape memory alloy wire changing the effective length that supports the damper mass assembly in real time. Once a stiffness change in the structural system is detected by an open loop observer, the ALP-STMD is re-tuned to the modified system parameters which successfully reduce the response of the primary system. Significant performance improvement is illustrated for the stiffness modified system, which undergoes the re-tuning adaptation, when compared to the stiffness modified system without adaptive re-tuning.
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P. Ganeshan,M. S. Ravi Theja,P. Ramshankar,K. Raja 한국고분자학회 2023 폴리머 Vol.47 No.4
Natural rubber/ethylene-propylene-diene monomer (NR/EPDM) rubber blends of composition 75/25 with 0, 2, 4, 6, 8, and 10 phr (parts per hundred rubber) halloysite nanotubes (HNTs) were prepared by two-roll mill. The effect of HNTs on the cure characteristics and mechanical properties of the NR/EPDM nanocomposites were studied. The effect of HNTs loading on the morphological, physical, swelling resistance and compression set of nanocomposites based on NR/EPDM was also investigated. Tensile strength tests revealed that the HNTs-reinforced NR/EPDM composite could resist 84% greater strength to break than the NR/EPDM blend without reinforcement. The introduction of HNTs into the NR/EPDM rubber matrix induced a rough morphology in the fracture surface, and a well-dispersed structure was obtained with the inclusion of up to 8 phr of HNTs, according to the morphological analyses.
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Satish Nagarajaiah,Michael T. Contreras,Dharma Theja Reddy Pasala 국제구조공학회 2014 Smart Structures and Systems, An International Jou Vol.13 No.2
In a companion paper, Pasala and Nagarajaiah analytically and experimentally validate the Adaptive Length Pendulum Smart Tuned Mass Damper (ALP-STMD) on a primary structure (2 story steel structure) whose frequencies are time invariant (Pasala and Nagarajaiah 2012). In this paper, the ALP-STMD effectiveness on a primary structure whose frequencies are time varying is studied experimentally. This study experimentally validates the ability of an ALP-STMD to adequately control a structural system in the presence of real time changes in primary stiffness that are detected by a real time observer based system identification. The experiments implement the newly developed Adaptive Length Pendulum Smart Tuned Mass Damper (ALP-STMD) which was first introduced and developed by Nagarajaiah (2009), Nagarajaiah and Pasala (2010) and Nagarajaiah et al. (2010). The ALP-STMD employs a mass pendulum of variable length which can be tuned in real time to the parameters of the system using sensor feedback. The tuning action is made possible by applying a current to a shape memory alloy wire changing the effective length that supports the damper mass assembly in real time. Once a stiffness change in the structural system is detected by an open loop observer, the ALP-STMD is re-tuned to the modified system parameters which successfully reduce the response of the primary system. Significant performance improvement is illustrated for the stiffness modified system, which undergoes the re-tuning adaptation, when compared to the stiffness modified system without adaptive re-tuning.
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