• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.147-150
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• 2002

For lightweight and flexible structures, it is important to suppress the vibrations induced by interactions between fluid and structures. This paper presents the PPF/Adaptive control of the vortex-induced vibration of composite beam with rigid cylinder in which the fluid force is considered as an external excitation on the structure. For the problems considered here, the excitation frequency (vortex-shedding frequency) is assumed to be equal to the natural frequency of the structure. A pair of piezoceramic devices attached bottom of the composite structure was used as actuators. Simulation and experiment were carried out with the designed controller and effectiveness of the PPF/Adaptive PPF control was verified by both experimental and simulation results.

• Journal of KSNVE
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• v.11 no.1
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• pp.147-155
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• 2001

This paper is concerned with the real-time automatic tuning of the multi-input multi-output positive position feedback controllers for smart structures by the genetic algorithms. The genetic algorithms have proven its effectiveness in searching optimal design parameters without falling into local minimums thus rendering globally optimal solutions. The previous real-time algorithm that tunes a single control parameter is extended to tune more parameters of the MIMO PPF controller. We employ the MIMO PPF controller since it can enhance the damping value of a target mode without affecting other modes if tuned properly. Hence, the traditional positive position feedback controller can be used in adaptive fashion in real time. The final form of the MIMO PPF controller results in the centralized control, thus it involves many parameters. The bounds of the control Parameters are estimated from the theoretical model to guarantee the stability. As in the previous research, the digital MIMO PPF control law is downloaded to the DSP chip and a main program, which runs genetic algorithms in real time, updates the parameters of the controller in real time. The experimental frequency response results show that the MIMO PPF controller tuned by GA gives better performance than the theoretically designed PPF. The time response also shows that the GA tuned MIMO PPF controller can suppress vibrations very well.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.2
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• pp.224-230
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• 2008

This paper is concerned with the active vibration control of building structure by means of the active tuned mass damper and the modified positive position feedback controller. To this end, one-degree-of-freedom spring-mass-damper system equipped with ATMD is considered. The stability condition for the addressed system when applying the proposed PPF controller is derived by Routh-Hurwitz stability criterion. The stability condition shows that the modified PPF controller is absolutely stable if the controller gain is positive. so that the modified PPF controller can be used without difficulty. Theoretical study shows that the modified PPF controller can effectively suppress vibrations as the original PPF controller does in smart structure applications. To investigate the validity of the modified PPF controller, a simple experimental structure with an ATMD system driven by DC motor was built. The modified PPF control algorithm was implemented on Atmel 128 microcontroller. The experimental result shows that the modified PPF controller can also suppress vibrations for the real structure.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.4
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• pp.267-275
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• 2004

This research is concerned with the development of a real-time adaptive PPF controller for the active vibration suppression of smart structure. In general, the tuning of the PPF controller is carried out off-line. In this research, the real-time learning algorithm is developed to find the optimal filter frequency of the PPF controller in real time and the efficacy of the algorithm is proved by implementing it in real time. To this end, the adaptive algorithm is developed by applying the gradient descent method to the predefined performance index, which is similar to the method used popularly in the optimization and neural network controller design. The experiment was carried out to verify the validity of the adaptive PPF controller developed in this research. The experimental results showed that adaptive PPF controller is effective for active vibration control of the structure which is excited by either impact or harmonic disturbance. The filter frequency of the PPF controller is tuned in a very short period of time thus proving the efficiency of the adaptive PPF controller.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.550-555
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• 2007

This paper is concerned with the active vibration control of building structure by means of the active tuned mass damper and the modified positive position feedback controller. To this end, one-degree-of-freedom spring-mass-damper system equipped with ATMD is considered. The stability condition for the addressed system when applying the proposed PPF controller is derived by Routh-Hurwitz stability criterion. The stability condition shows that the modified PPF controller is absolutely stable if the controller gain is positive, so that the modified PPF controller can be used without difficulty. Theoretical study shows that the modified PPF controller can effectively suppress vibrations as the original PPF controller does in smart structure applications. To investigate the validity of the modified PPF controller, a simple experimental structure with an ATMD system driven by DC motor was built. The modified PPF control algorithm was implemented on Atmel 128 microcontroller. The experimental result shows that the modified PPF controller can also suppress vibrations for the real structure.

• Archives of Pharmacal Research
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• v.23 no.4
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• pp.374-380
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• 2000

Propentofylline (PPF, 3-methyl-1-(5-oxohexyl)-7-propylxanthine) has been reported to be a compound for treatment of both vascular dementia and dementia of the Alzheimer type. The short half-life (about 15 min) of PPF at the terminal elimination phase and poor bioavailability after oral administration of PPF to rabbits (Kim et al., 1992) suggest in part that this drug takes the extensive first-pass metabolism in the liver. In addition, the metabolic pathway for PPF remains unclear. The objective of this experiment is to identify urinary metabolites of PPF in rats. For the identification of the metabolites, rat urine was collected after oral administration of 100${m}g/kg$ PPF. PPF metabolite, 3-methyl-1-(5-hydroxyhexyl)-7-propylxanthine, was synthesized and confirmed by gas chromatography/mass spectroscopy (GC/MS) and $^1H$ nuclear magnetic resonance spectroscopy. The urinary metabolites of PPF were extracted with diethyl ether and identified by electron impact and chemical ionization GC/MS. One urinary metabolite was confirmed to be 3-methyl-1-(5-hydroxyhexyl)-7-propylxanthine by synthesized authentic compound. Several metabolites of monohydroxy- and dihydroxy-PPF were identified based on mass fragmentation of both intact and trimethylsilylated derivatives of PPF metabolites and the novel structure of these metabolites is suggested based on mass spectra.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1998.11a
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• pp.122-122
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• 1998

Propentofylline (PPF), a xanthine derivative, has been reported to be effective for the treatment of both vascular dementia and Alzheimer's disease. The elimination half-life of PPF was ranged from 15 to 45 min in rabbit and human, and PPF was rapidly disappeared from the blood. The objective of this experiment is to investigate whether xanthine analogues have effects on the profile of plasma concentration and metabolism of PPF. Caffeine (50 mg/kg, ip) was treated to Sprague-Dawley rats for consecutive 7 days and PPF was intravenously administered to rats 2 hr after the last dose of caffeine. In the other group, PPF was intravenously administered to rats 1 hr after a single dose of pentoxifylline (50 mg/kg, iv). Control group was treated with saline vehicle for the same period as in treatment groups. Blood was withdrawn at specific time intervals. PPF and one of its metabolite (POH) in plasma were determined by gas chromatography/nitrogen phosphorus detector. Plasma concentrations and pharmacokinetic parameters were compared between groups. The area under the curve (AUC) of PPF in rats treated sub chronically with caffeine was significantly decreased compared to control rats. Caffeine treatment results in a significant increase of total body clearance. The AUC of POH was significantly decreased in the caffeine-treated group. A single dose of pentoxifylline has no effect on the phramacokinetics of PPF. Reduction of the AUCs of PPF and POH both suggests that caffeine may increase the excretion of PPF with no affecting the metabolism of PPF to POH.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.3
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• pp.208-213
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• 2004

This paper is concerned with the theoretical estimation of the single-input single-output(SISO) positive position feedback(PPF) controller and the derivation of the stability conditions for the multi-input multi-output (MIMO) PPF controller. Although the stability condition for the SISO PPF controller was derived in the earlier works, the question regarding the performance estimation of the SISO PPF controller has never been studied theoretically. Hence, the SISO PPF controller for the single degree-of-freedom system was first investigated and then control parameters including gain, the filter frequency, and the damping factor of the PPF controller were analyzed in detail thus providing the design methodology for the SISO PPF controller. In the case of real structure. there are infinite number of natural modes so that some modes are to be controlled by a limited number of actuator and sensor. Based on the theoretical results on the SISO PPF controller, the stability condition for the multi-input multi-output PPF controller was derived when only the few number of modes are to be controlled. The control spillover problem is also discussed in detail.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.302-307
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• 2001

This research is concerned with the development of a real-time adaptive PPF controller for the active vibration suppression of smart structure. In general, the tuning of the PPF controller is carried out off-line. In this research, the real-time learning algorithm is developed to find the optimal filter frequency of the PPF controller in real time and the efficacy of the algorithm is proved by implementing it in real time. To this end, the adaptive algorithm is developed by applying the gradient descent method to the predefined performance index, which is similar to the method used popularly in the optimization and neural network controller design. The experiment was carried out to verify the validity of the adaptive PPF controller developed in this research. The experimental results showed that adaptive PPF controller is effective for active vibration control of the structure which is excited by either impact or harmonic disturbance. The filter frequency of the PPF controller can be tuned in a very short period of time thus proving the efficiency of the adaptive PPF controller.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.527-535
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• 2012

This paper reports the active vibration control of plates using positive position feedback controller (PPF). The equations of motion of the plate under force and moment pairs were derived and the equations of PPF controllers were formulated. The effect of the parameters - gain and damping ratio - of the PPF controllers on the open loop transfer function was investigated mainly in terms of the system stability. Increasing the gain of the PPF controller tuned at a mode, the magnitude of the open loop transfer function is increased at all frequencies without changing the phase behavior. The increase of the damping ratio of the PPF controller leads to decrease the magnitude of the open loop transfer function and to modify its phase characteristics to be more stable. Two PPF controllers connected in parallel, Each PPF controller is tuned at the $1^{st}$ and $2^{nd}$ modes, respectively. Their parameters were determined to remain the system to be stable based on the results of the parametric study. A significant reduction in vibration at the 2 modes can be obtained.