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Добірка наукової літератури з теми "Oscillating modulation of the pressure"

Автор: Grafiati

Опубліковано: 30 травня 2022

Оновлено: 31 травня 2022

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Статті в журналах з теми "Oscillating modulation of the pressure"

Staubli, Thomas, and Donald Rockwell. "Pressure fluctuations on an oscillating trailing edge." Journal of Fluid Mechanics 203 (June 1989): 307–46. http://dx.doi.org/10.1017/s0022112089001485.

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Turbulent boundary layers separating from a blunt trailing edge give rise to organized vortical structures in the downstream wake. The perturbation of this inherent flow-instability at f0 by controlled oscillations of the edge at fe produces corresponding, organized components of unsteady surface pressure along the edge. For edge excitation near the ‘natural’ vortex shedding frequency f0, the phase between the local pressure fluctuations and the edge displacement shows large changes for small changes in excitation frequency. Moreover, in this range of excitation, there is quenching (or attenuation) of the surface pressure component at f0 and resonant peaking of the component at fe. These phenomena are related to the change in sign of the energy transfer between the fluid and the body. Integration of the instantaneous pressure distributions along the surfaces of the edge leads to the instantaneous lift at fe and f0 acting upon the oscillating trailing edge. The location of the lift varies as the cotangent of the dimensionless time during an oscillation cycle. When the edge is excited near, or at, the natural vortex shedding frequency, there is a resonant peak in the amplitude of oscillation of the lift location at fe; that at f0 is invariant. Moreover, the mean location of the lift at fe undergoes abrupt changes in this region of excitation. Flow visualization allows determination of the phasing of the organized vortical structures shed from the trailing edge relative to the edge displacement. Modulation of the flow structure at the frequencies f0 and fe, as well as interaction of small-scale vortices at high excitation frequencies, was observed. These aspects of the near-wake structure are related to the instantaneous pressure field.

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Мартынец, Татьяна Викторовна. "Experimental research of oscillating modulation of pressure in hydraulic brake drive." Eastern-European Journal of Enterprise Technologies 2, no. 10(56) (April 1, 2012): 46–49. http://dx.doi.org/10.15587/1729-4061.2012.3893.

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Marsh, Donald J., Olga V. Sosnovtseva, Alexey N. Pavlov, Kay-Pong Yip, and Niels-Henrik Holstein-Rathlou. "Frequency encoding in renal blood flow regulation." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 288, no. 5 (May 2005): R1160—R1167. http://dx.doi.org/10.1152/ajpregu.00540.2004.

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With a model of renal blood flow regulation, we examined consequences of tubuloglomerular feedback (TGF) coupling to the myogenic mechanism via voltage-gated Ca channels. The model reproduces the characteristic oscillations of the two mechanisms and predicts frequency and amplitude modulation of the myogenic oscillation by TGF. Analysis by wavelet transforms of single-nephron blood flow confirms that both amplitude and frequency of the myogenic oscillation are modulated by TGF. We developed a double-wavelet transform technique to estimate modulation frequency. Median value of the ratio of modulation frequency to TGF frequency in measurements from 10 rats was 0.95 for amplitude modulation and 0.97 for frequency modulation, a result consistent with TGF as the modulating signal. The simulation predicted that the modulation was regular, while the experimental data showed much greater variability from one TGF cycle to the next. We used a blood pressure signal recorded by telemetry from a conscious rat as the input to the model. Blood pressure fluctuations induced variability in the modulation records similar to those found in the nephron blood flow results. Frequency and amplitude modulation can provide robust communication between TGF and the myogenic mechanism.

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Teixeira, Luis Augusto, Joane de Figueiredo Serpa Coutinho, and Daniel Boari Coelho. "Regulation of dynamic postural control to attend manual steadiness constraints." Journal of Neurophysiology 120, no. 2 (August 1, 2018): 693–702. http://dx.doi.org/10.1152/jn.00941.2017.

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In daily living activities, performance of spatially accurate manual movements in upright stance depends on postural stability. In the present investigation, we aimed to evaluate the effect of the required manual steadiness (task constraint) on the regulation of dynamic postural control. A single group of young participants ( n = 20) were evaluated in the performance of a dual posturo-manual task of balancing on a platform oscillating in sinusoidal translations at 0.4-Hz (low) or 1-Hz (high) frequencies while stabilizing a cylinder on a handheld tray. Manual task constraint was manipulated by comparing the conditions of keeping the cylinder stationary on its flat or round side, corresponding to low and high manual task constraints, respectively. Results showed that in the low oscillation frequency the high manual task constraint led to lower oscillation amplitudes of the head, center of mass, and tray, in addition to higher relative phase values between ankle/hip-shoulder oscillatory rotations and between center of mass/center of pressure-feet oscillations as compared with values observed in the low manual task constraint. Further analyses showed that the high manual task constraint also affected variables related to both postural (increased amplitudes of center of pressure oscillation) and manual (increased amplitude of shoulder rotations) task components in the high oscillation frequency. These results suggest that control of a dynamic posturo-manual task is modulated in distinct parameters to attend the required manual steadiness in a complex and flexible way. NEW & NOTEWORTHY We evaluated dynamic postural control on a platform oscillating in sinusoidal translations at different frequencies while performing a manual task with low or high steadiness constraints. Results showed that high manual task constraint led to modulation of metric and coordination variables associated with greater postural stability. Our findings suggest that motor control is regulated in an integrative mode at the posturo-manual task level, with reciprocal interplay between the postural and manual components.

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Horsman, H. M., K. C. Peebles, and Y. C. Tzeng. "Interactions between breathing rate and low-frequency fluctuations in blood pressure and cardiac intervals." Journal of Applied Physiology 119, no. 7 (October 1, 2015): 793–98. http://dx.doi.org/10.1152/japplphysiol.00525.2015.

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Evidence derived from spontaneous measures of cardiovagal baroreflex sensitivity (BRS) suggests that slow breathing at 6 breaths/min augments BRS. However, increases in BRS associated with slow breathing may simply reflect the frequency-dependent nature of the baroreflex rather than the modulation of baroreflex function by changes in breathing rate per se. To test this hypothesis we employed a crossover study design ( n = 14) wherein breathing rate and systolic arterial blood pressure (SAP) oscillation induced via the application of oscillating lower body negative pressure (OLBNP) were independently varied at fixed frequencies. Breathing rate was controlled at 6 or 10 breaths/min with the aid of a metronome, and SAP oscillations were driven at 0.06 Hz and 0.1 Hz using OLBNP. The magnitudes of SAP and R-R interval (cardiac period) oscillations were quantified using power spectral analysis, and the transfer function gain between SAP and R-R interval was used to estimate BRS. Linear mixed-effects models were used to examine the main effects and interactions between breathing rate and OLBNP frequency. There was no statistical interaction between breathing and OLBNP frequency ( P = 0.59), indicating that the effect of breathing rate on BRS did not differ according to OLBNP frequency (and vice versa). Additionally, there was no main effect for breathing rate ( P = 0.28). However, we observed a significant main effect for OLBNP frequency ( P = 0.01) consistent with the frequency-dependent nature of baroreflex. These findings suggest that increases in spectral indices of BRS reflect the frequency dependence of the baroreflex and are not due to slow breathing per se.

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Kalashnik, M. V., and S. N. Kulichkov. "On pressure perturbations caused by a moving heat source of the frontal type (hydrostatic mode)." Известия Российской академии наук. Физика атмосферы и океана 55, no. 5 (November 25, 2019): 51–61. http://dx.doi.org/10.31857/s0002-351555551-61.

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The problem of perturbations of the surface pressure caused by a moving nonstationary frontal heat source (localized along one horizontal coordinate) is considered. Pressure disturbances are associated with internal gravity waves (IGWs). It is shown that when a source moves in a finite-height atmospheric layer (atmospheric waveguide) when a discrete set of vertical IGW modes is excited, there are three types of temporal variation of surface pressure at a fixed observation point. These types correspond respectively to the time signal with amplitude modulation, the signal with frequency modulated Doppler type and the signal that occurs only after passing through the source. Each type is implemented for specific values of the oscillation frequency of the source and the Mach number (the ratio of the speed of the source to the phase velocity of the IGW). At Mach numbers less than one, an oscillating source always excites wave precursors disturbances observed before the source arrives. The movement of the source in a semi-infinite atmosphere leads to additional excitation of waves that transfer energy to the upper layers of the atmosphere.

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Chen, C. K., L. Wang, J. T. Yang, and L. T. Chen. "Experimental and Computational Analysis of Periodic Flow Structure in Oscillatory Gas Flow Meters." Journal of Mechanics 22, no. 2 (June 2006): 137–44. http://dx.doi.org/10.1017/s1727719100004433.

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AbstractThe oscillatory characteristics and dynamic structure of periodic flow in an oscillatory gas flow meter were studied experimentally and numerically. The flow oscillations were triggered by the Coanda effect and an universal correlation between Strouhal number and Reynolds number, Str = 1.09 × 10−3 for ReHD >800, was deduced based on spectral analysis of the pressure fluctuations in the flow channel. Numerical simulation indicated that the evolution of the flow patterns was classified into stages of induction and sustainable periodic oscillation. The transformation between the two stages was noticeably affected by the design of the feedback channels. The results further revealed that the development of the main vortex in the oscillating chamber and the small vortices at the entrance of the feedback channels concurrently modulate the mechanism of oscillation. The small vortices located at both entrances of the feedback channels play the role of a pair of modulating valves, which alternatively switch on and off the bypass flow through each feedback channel, thus reinforcing the periodic oscillation.

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Lester, Rosemary A., and Brad H. Story. "Acoustic Characteristics of Simulated Respiratory-Induced Vocal Tremor." American Journal of Speech-Language Pathology 22, no. 2 (May 2013): 205–11. http://dx.doi.org/10.1044/1058-0360(2012/12-0043).

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Purpose The purpose of this study was to investigate the relation of respiratory forced oscillation to the acoustic characteristics of vocal tremor. Method Acoustical analyses were performed to determine the characteristics of the intensity and fundamental frequency (F 0 ) for speech samples obtained by Farinella, Hixon, Hoit, Story, and Jones (2006) using a respiratory forced oscillation paradigm with 5 healthy adult males to simulate vocal tremor involving respiratory pressure modulation. The analyzed conditions were sustained productions of /a/ with amplitudes of applied pressure of 0, 1, 2, and 4 cmH 2 O and a rate of 5 Hz. Results Forced oscillation of the respiratory system produced modulation of the intensity and F 0 for all participants. Variability was observed between participants and conditions in the change in intensity and F 0 per unit of pressure change, as well as in the mean intensity and F 0 . However, the extent of modulation of intensity and F 0 generally increased as the applied pressure increased, as would be expected. Conclusion These findings suggest that individuals develop idiosyncratic adaptations to pressure modulations, which are important to understanding aspects of variability in vocal tremor, and highlight the need to assess all components of the speech mechanism that may be directly or indirectly affected by tremor.

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Amador, Ana, Franz Goller, and Gabriel B. Mindlin. "Frequency Modulation During Song in a Suboscine Does Not Require Vocal Muscles." Journal of Neurophysiology 99, no. 5 (May 2008): 2383–89. http://dx.doi.org/10.1152/jn.01002.2007.

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The physiology of sound production in suboscines is poorly investigated. Suboscines are thought to develop song innately unlike the closely related oscines. Comparing phonatory mechanisms might therefore provide interesting insight into the evolution of vocal learning. Here we investigate sound production and control of sound frequency in the Great Kiskadee ( Pitangus sulfuratus) by recording air sac pressure and vocalizations during spontaneously generated song. In all the songs and calls recorded, the modulations of the fundamental frequency are highly correlated to air sac pressure. To test whether this relationship reflects frequency control by changing respiratory activity or indicates synchronized vocal control, we denervated the syringeal muscles by bilateral resection of the tracheosyringeal nerve. After denervation, the strong correlation between fundamental frequency and air sac pressure patterns remained unchanged. A single linear regression relates sound frequency to air sac pressure in the intact and denervated birds. This surprising lack of control by syringeal muscles of frequency in Kiskadees, in strong contrast to songbirds, poses the question of how air sac pressure regulates sound frequency. To explore this question theoretically, we assume a nonlinear restitution force for the oscillating membrane folds in a two mass model of sound production. This nonlinear restitution force is essential to reproduce the frequency modulations of the observed vocalizations.

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Grisk, Olaf, and Harald M. Stauss. "Frequency modulation of mesenteric and renal vascular resistance." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 282, no. 5 (May 1, 2002): R1468—R1476. http://dx.doi.org/10.1152/ajpregu.00307.2001.

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The hypothesis was tested that low-frequency vasomotions in individual vascular beds are integrated by the cardiovascular system, such that new fluctuations at additional frequencies occur in arterial blood pressure. In anesthetized rats ( n = 8), the sympathetic splanchnic and renal nerves were simultaneously stimulated at combinations of frequencies ranging from 0.075 to 0.8 Hz. Blood pressure was recorded together with mesenteric and renal blood flow velocities. Dual nerve stimulation at low frequencies (<0.6 Hz) caused corresponding oscillations in vascular resistance and blood pressure, whereas higher stimulation frequencies increased the mean levels. Blood pressure oscillations were only detected at the individual stimulation frequencies and their harmonics. The strongest periodic responses in vascular resistance were found at 0.40 ± 0.02 Hz in the mesenteric and at 0.32 ± 0.03 Hz ( P < 0.05) in the renal vascular bed. Thus frequency modulation of low-frequency vasomotions in individual vascular beds does not cause significant blood pressure oscillations at additional frequencies. Furthermore, our data suggest that sympathetic modulation of mesenteric vascular resistance can initiate blood pressure oscillations at slightly higher frequencies than sympathetic modulation of renal vascular resistance.

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Дисертації з теми "Oscillating modulation of the pressure"

Мартинець, Тетяна Вікторівна. "Розширення області застосування антиблокувальних систем легкових автомобілів шляхом спрощення конструкції модуляторів тиску". Thesis, НТУ "ХПІ", 2017. http://repository.kpi.kharkov.ua/handle/KhPI-Press/35084.

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Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.22.02 – автомобілі та трактори. Національний технічний університет "Харківський політехнічний інститут". – Харків, 2017. З метою розширення області застосування АБС за рахунок зниження вартості модулятора тиску досліджено процес осциляційної модуляції тиску. Запропоновано конструкцію осциляційного модулятора, який задовольняє всі висунуті до нього вимоги, та доведено можливість його застосування в якості виконавчого елемента у складі дуальних адаптивних гальмівних системах. Порівняльний аналіз відомих способів модуляції тиску в гідравлічному гальмівному приводі показав, що тільки спосіб осциляційної модуляції не вимагає для своєї реалізації дорогих конструктивних елементів (електромагнітних клапанів, насосів, що підкачують, крокових електродвигунів і т.п.), що дозволяє знизити вартість модуляторів при їх застосуванні. Моделювання процесу осциляційної модуляції та лабораторні випробування осциляційного модулятора показали: – принципову можливість осциляційної модуляції у всьому необхідному діапазоні зміни тиску від 0 до 10 МПа; – працездатність запропонованої конструкції модулятора і його відповідність усім пред’явленим до модулятору АБС вимогам. Дослідження роботи осциляційного модулятора у складі дуальної адаптивної гальмівної системи, виконані шляхом моделювання процесу гальмування автомобіля при різних станах дорожньої поверхні та режимах руху підтвердили, що застосування осциляційного модулятора не погіршують показники ефективності гальмування, стійкості і керованості у порівнянні з відомими.
The dissertation on competition of a scientific degree of candidate of technical sciences, speciality 05.22.02 – cars and tractors. National technical university "Kharkiv polytechnic institute". – Kharkiv, 2017. With the of expanding the field of application of anti-block system by reducing the value of the pressure modulator investigated the process of the oscillating modulation of the pressure. The proposed design of the oscillating modulator that meets all applicable requirements and proved the possibility of its use as an clement in the composition of the dual adaptive brake systems. Comparative analysis of the known methods of modulation of the pressure in the hydraulic brake drive showed that the only way of oscillating modulation does not require expensive structural elements (solenoid valves, booster pumps, stepper motors, etc.) that can reduce the cost of modulators in its application. Modeling of oscillating modulation process and laboratory tests of oscillating modulator showed: – principle possibility of oscillating modulation in all the required range of pressure changes from 0 to 10 МПА; – the efficiency of the proposed design of the modulator and its compliance with all requirements to the anti-block system modulator. Research work of oscillating modulator comprising a dual adaptive brake system, made by modeling the process of deceleration of the vehicle under different conditions of road surface and driving conditions confirmed that the application of an oscillating modulator does not degrade the braking efficiency, stability and controllability with the known.

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Мартинець, Тетяна Вікторівна. "Розширення області застосування антиблокувальних систем легкових автомобілів шляхом спрощення конструкції модуляторів тиску". Thesis, Харківський державний автомобільно-дорожній університет, 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/35082.

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Jeong, Eun S. "Heat transfer with oscillating pressure in reciprocating machinery." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13259.

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Copie, François. "Modulation instabilities in dispersion oscillating passive fiber-ring cavities." Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10111/document.

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Ces travaux de thèse portent sur l’instabilité paramétrique survenant dans les cavités optiques fibrées passives en anneau, induite par une modulation longitudinale de la dispersion chromatique. Dans les cavités optiques, le processus d’instabilité modulationnelle est connu pour être susceptible de déstabiliser l’état stationnaire et de le transformer en un train stable d’impulsions. Nous décrivons dans ce travail comment une variation longitudinale de la dispersion à l’intérieur de la cavité enrichie la dynamique de ce type de dispositif en engendrant un régime d’instabilité paramétrique. Nous détaillons l’étude théorique de ce nouveau mécanisme ce qui nous permet d’en identifier les signatures spectrales et temporelles, parmi lesquels, la génération de multiples pics de résonances dans le spectre optique et l’apparition d’une dynamique de doublement de période dans le domaine temporel. Nous avons réalisé de tels résonateurs afin de confirmer expérimentalement nos prédictions. Le modèle que nous avons retenu consiste à réaliser un anneau en soudant entre elles des fibres uniformes présentant des dispersions différentes. En terme de résultats, nous avons tout d’abord observé pour la première fois l’apparition des instabilités modulationnelle et paramétrique dans un même système, pour ensuite s’intéresser à leur dynamique. Cette dernière est accessible grâce à des méthodes de détection en temps réel à la fois spectrale et temporelle. Nous avons ainsi pu observer avec une précision remarquable l’émergence des instabilités, le doublement de période associé au régime paramétrique ainsi que l’apparition d’un nombre record de résonances paramétriques dans notre système
This thesis work deals with the parametric instability occurring in passive optical fiber-ring cavities, which is induced by a longitudinal modulation of the chromatic dispersion. In optical cavities, the modulation instability process is known to potentially destabilize the stationary state and turn it into a stable train of pulses. We describe in this work how a longitudinal variation of the dispersion inside the cavity enriches the dynamics of this type of device by entailing a regime of parametric instability. We detail the theoretical study of this new mechanism, which allows us to identify its spectral and temporal signatures, among which, the generation of multiple resonance peaks in the optical spectrum and the appearance of a period doubling dynamics in the time domain. We have realized such resonators in order to confirm experimentally our predictions. The model we have chosen simply consists in building a ring by splicing together uniform fibers characterized by different dispersions. In terms of results, we first observed the emergence of both modulational and parametric instabilities in the same system, before investigating their dynamics. The latter is accessible thanks to real-time spectral and temporal detection methods. We thus observed with remarkable precision the emergence of the instabilities, the period doubling associated to the parametric regime and the appearance of a record number of parametric resonances in our system

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Cheng, Peter D. L. (Peter Dien Leung). "Experiments in heat transfer under conditions of oscillating pressure and flow." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/35458.

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Grassmyer, William Alan. "Experiments in heat transfer under conditions of oscillating pressure and flow." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/35981.

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Carroll, Matthew J. "First Order Self-Oscillating Class-D Circuit with Triangular Wave Injection." DigitalCommons@CalPoly, 2021. https://digitalcommons.calpoly.edu/theses/2303.

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An investigation into performance improvements to the modulator stage of a class-D amplifier is conducted in this thesis. Two of the standard topologies, namely class-D open-loop pulse-width modulation (PWM), and the improved self-oscillating feedback system are benchmarked against a topology which includes both a hysteretic comparator in a feedback loop and triangle wave injection. Circuit performance is analyzed by comparing how the triangle injection circuit handles known issues with open-loop and self-oscillating circuits. Using this analysis, it is shown that the triangle injection topology offers an improved power supply rejection ratio relative to open-loop PWM and reduces distortion generated by frequency modulation characteristic of the self-oscillating topology.

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Tziranis, Alexander Konstantinos 1968. "Temperature, heat flux, and velocity measurements in oscillating flows with pressure variations." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12790.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1992.
Vita.
Includes bibliographical references (leaves 99-101).
by Alexander Konstantinos Tziranis.
M.S.

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King, Cameron V. "Time-Resolved PIV And Pressure Measurements Of Oscillating And Pulsating Flow In A Diffuser." DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/106.

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Separating oscillating and pulsating flows in an internal adverse pressure gradient geometry are studied experimentally. Simultaneous velocity-pressure measurements demonstrate that the minor losses associated with oscillating flow in an adverse pressure gradient geometry can be smaller or larger than for steady flow. Separation is found to begin high in the diffuser and propagate downward. Flows are able to remain attached further into the diffuser with larger Reynolds numbers, larger stroke lengths, and smaller diffuser angles. The extent of separation grows with Lo/h. The minor losses grow with increasing displacement amplitude in the range 10 < Lo/h < 40. Losses decrease with Re in the range of 380

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Ma, Jinge. "Design of Frequency Output Pressure Transducer." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc804933/.

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Piezoelectricity crystal is used in different area in industry, such as downhole oil, gas industry, and ballistics. The piezoelectricity crystals are able to create electric fields due to mechanical deformation called the direct piezoelectric effect, or create mechanical deformation due to the effect of electric field called the indirect piezoelectric effect. In this thesis, piezoelectricity effect is the core part. There are 4 parts in the frequency output pressure transducer: two crystal oscillators, phase-locked loop (PLL), mixer, frequency counter. Crystal oscillator is used to activate the piezoelectricity crystal which is made from quartz. The resonance frequency of the piezoelectricity crystal will be increased with the higher pressure applied. The signal of the resonance frequency will be transmitted to the PLL. The function of the PLL is detect the frequency change in the input signal and makes the output of the PLL has the same frequency and same phase with the input signal. The output of the PLL will be transmitted to a Mixer. The mixer has two inputs and one output. One input signal is from the pressure crystal oscillator and another one is from the reference crystal oscillator. The frequency difference of the two signal will transmitted to the frequency counter from the output of the mixer. Thus, the frequency output pressure transducer with a frequency counter is a portable device which is able to measure the pressure without oscilloscope or computer.

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Книги з теми "Oscillating modulation of the pressure"

Piziali, R. A. 2-D and 3-D oscillating wing aerodynamics for a range of angles of attack including stall. Moffett Field, Ca: Ames Research Center, 1994.

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Pfurtscheller, Gert, and Fernando Lopes da Silva. EEG Event-Related Desynchronization and Event-Related Synchronization. Edited by Donald L. Schomer and Fernando H. Lopes da Silva. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780190228484.003.0040.

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Event-related desynchronization (ERD) reflects a decrease of oscillatory activity related to internally or externally paced events. The increase of rhythmic activity is called event-related synchronization (ERS). They represent dynamical states of thalamocortical networks associated with cortical information-processing changes. This chapter discusses differences between ERD/ERS and evoked response potentials and methodologies for quantifying ERD/ERS and selecting frequency bands. It covers the interpretation of ERD/ERS in the alpha and beta bands and theta ERS and alpha ERD in behavioral tasks. ERD/ERS in scalp and subdural recordings, in various frequency bands, is discussed. Also presented is the modulation of alpha and beta rhythms by 0.1-Hz oscillations in the resting state and phase-coupling of the latter with slow changes of prefrontal hemodynamic signals (HbO2), blood pressure oscillations, and heart rate interval variations in the resting state and in relation to behavioral motor tasks. Potential uses of ERD-based strategies in stroke patients are discussed.

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Pressure wave propagation studies for oscillating cascades. [Washington, DC]: National Aeronautics and Space Administration, 1992.

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United States. National Aeronautics and Space Administration., ed. Oscillating-flow regenerator test rig: Final report. [Washington, DC: National Aeronautics and Space Administration, 1994.

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United States. National Aeronautics and Space Administration., ed. Oscillating-flow regenerator test rig: Final report. [Washington, DC: National Aeronautics and Space Administration, 1994.

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United States. National Aeronautics and Space Administration., ed. Oscillating-flow regenerator test rig: Final report. [Washington, DC: National Aeronautics and Space Administration, 1994.

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Szafruga, Janusz. Pressure measurements over a stationary and oscillating rectangular wing. 1993.

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Description of an oscillating flow pressure drop test rig. [Washington, DC]: National Aeronautics and Space Administration, 1988.

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Description of an oscillating flow pressure drop test rig. [Washington, DC]: National Aeronautics and Space Administration, 1988.

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M, Shaw Loretta, and Lewis Research Center, eds. Unsteady pressure measurements on a biconvex airfoil in a transonic oscillating cascade. Cleveland, Ohio: Lewis Research Center, 1985.

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Частини книг з теми "Oscillating modulation of the pressure"

Petříček, Václav, and Michal Dušek. "Modulation and its Crystallographic Methodology." In High-Pressure Crystallography, 139–58. Dordrecht: Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-1-4020-2102-2_10.

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Helvensteijn, B. P. M., A. Kashani, A. L. Spivak, P. R. Roach, J. M. Lee, and P. Kittel. "Pressure Drop over Regenerators in Oscillating Flow." In Advances in Cryogenic Engineering, 1619–26. Boston, MA: Springer US, 1998. http://dx.doi.org/10.1007/978-1-4757-9047-4_203.

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Jeong, S., K. Nam, and J. Jung. "Regenerator Characterization under Oscillating Flow and Pulsating Pressure." In Cryocoolers 12, 531–37. Boston, MA: Springer US, 2003. http://dx.doi.org/10.1007/0-306-47919-2_70.

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Valenza, F., and L. Gattinoni. "Non-invasive Modulation of Intraabdominal Pressure." In Yearbook of Intensive Care and Emergency Medicine 2005, 325–33. New York, NY: Springer New York, 2005. http://dx.doi.org/10.1007/0-387-26272-5_28.

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Fonov, S. D., R. H. Engler, Chr Klein, S. V. Mihailov, V. E. Mosharov, V. P. Kulesh, V. N. Radchenko, and E. Schairer. "Investigations of the pressure fields on the oscillating wings by Pressure Sensitive Paint." In Notes on Numerical Fluid Mechanics (NNFM), 146–53. Wiesbaden: Vieweg+Teubner Verlag, 1999. http://dx.doi.org/10.1007/978-3-663-10901-3_20.

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Takagi, D., S. Ito, K. Takeya, A. Sasoh, K. Nagata, and Y. Sakai. "Post-shock Pressure Modulation through Grid Turbulence." In 28th International Symposium on Shock Waves, 665–70. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-25685-1_101.

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Leone, M., P. Visintini, and C. Martin. "Modulation of Blood Pressure in Traumatic Brain Injury." In Yearbook of Intensive Care and Emergency Medicine, 748–56. Berlin, Heidelberg: Springer Berlin Heidelberg, 2007. http://dx.doi.org/10.1007/978-3-540-49433-1_67.

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Piecha, Felix, and Sebastian Mueller. "Modulation of Liver Stiffness by Arterial and Portal Pressure." In Liver Elastography, 257–64. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-40542-7_24.

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Daniel Raj, D., V. Sundar, and S. A. Sannasiraj. "Influence of Harbour Wall on Pressure Variation in an Oscillating Water Column." In Lecture Notes in Civil Engineering, 751–63. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-3134-3_56.

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Panovsky, J., M. Nowinski, and A. Bölcs. "Flutter of Aircraft Engine Low Pressure Turbine Blades: Oscillating Cascade Experiments and Analysis." In Unsteady Aerodynamics and Aeroelasticity of Turbomachines, 815–29. Dordrecht: Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-5040-8_53.

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Тези доповідей конференцій з теми "Oscillating modulation of the pressure"

Song, Jinkwan, and Jong Guen Lee. "Characterization of Spray Formed by Liquid Jet Injected Into Oscillating Air Crossflow." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43726.

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This paper presents experimental results on the characteristics of spray formed by a liquid (Jet-A) jet injected into an oscillating air crossflow. Ambient air pressure is raised up to 15.86 bar, and the corresponding aerodynamic Weber number and liquid-air momentum flux ratio are up to 1000 and 25, respectively. The level of modulated crossflow velocity is kept up to 20% of its mean value. For limited cases, the air crossflow is preheated. Planar Mie-scattering measurements are utilized to visualize changes of the spray penetration and cross-sectional spray area in the oscillating air crossflow, and PDPA measurements are used to measure the mean drop size and drop size distribution. Phase-synchronized PDPA measurement of droplet size under the modulation of crossflow shows that the modulating crossflow results in preferentially larger amount of smaller and bigger droplets than average-sized droplets. Global spray response of spray to modulating crossflow is characterized by using proper orthogonal decomposition (POD) analysis of Mie-scattering images and collecting (and hence determining gain of) Mie-scattering intensity of droplets at a fixed downstream distance. It is found that the dominant behavior of the spray is convective oscillation in the axial direction and the change of vertical penetration of the spray is almost negligible for the level of crossflow velocity modulation up to 20%. The gain of Mie-scattering intensity with respect to crossflow velocity modulation level gradually decreases as liquid-air momentum flux ratio increases. Also, per given momentum flux ratio and Weber number, the gain hardly varies with respect to crossflow modulation level, suggesting the response of spray increases in proportion to crossflow velocity modulation level.

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Wu, David W., and Hwang Choe. "Effects of Sensor Shape on Oscillating Pressure Measurements With Wind-Tunnel Test Confirmation." In ASME 2006 Pressure Vessels and Piping/ICPVT-11 Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/pvp2006-icpvt-11-93942.

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This paper summarizes the effects of the pressure sensor shape on the dynamic oscillating pressure measurements when the pressure wave modulating along the steam/air flow path is to be characterized. In the study presented in the paper, a three-dimensional CFD model of the external flow around the protruding, dome-shaped sensor was developed to evaluate the effects of the sensor shape on the external flow pattern, and the detailed flow patterns were studied with this protruding, dome-shaped sensors and compared with the flow patterns for the flush mounted sensors. Then, a one-dimensional analysis was done to predict that the dynamic pressures measured with the protruding sensor do not require significant correction, and this was later supported by wind tunnel tests. The amplitude of the dynamic pressure measured on the protruding sensor was determined to be ranging from 0 to 8% higher than measured by a flush mounted pressure sensor. The frequency of the pressure wave is not affected by the presence of the protrusion.

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Boudy, Frédéric, Daniel Durox, Thierry Schuller, and Sébastien Candel. "Nonlinear Flame Describing Function Analysis of Galloping Limit Cycles Featuring Chaotic States in Premixed Combustors." In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-68998.

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Nonlinear prediction of combustion instabilities in premixed systems is undertaken on a generic configuration featuring an adjustable feeding manifold length, a multipoint injector composed of a perforated plate and a flame confinement tube. By changing the feeding manifold or flame tube lengths, the system exhibits different types of combustion regimes for the same flow operating conditions. Velocity, pressure and heat release rate measurements are used to examine oscillations during unstable operation. For many operating conditions, a limit cycle is reached at an essentially fixed oscillation frequency and quasi-constant amplitude. In another set of cases, the system features other types of oscillations characterized by multiple frequencies, amplitude modulation and irregular bursts which can be designated by “galloping” limit cycles or GLC. These situations are explored in this article. Imaging during GLCs indicates that the flame is globally oscillating but that the cycle is irregular. Prediction of these special oscillation states is tackled within the Flame Describing Function (FDF) framework. It is shown that it is possible to predict with a reasonable degree of agreement the ranges where a quasi-constant amplitude limit cycle will be established and ranges where the oscillation will be less regular and take the form of a galloping limit cycle. It is found that the FDF analysis also provides indications on the bounding levels of the oscillation envelope in the latter case.

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Berger, Frederik M., Tobias Hummel, Bruno Schuermans, and Thomas Sattelmayer. "Pulsation-Amplitude-Dependent Flame Dynamics of High-Frequency Thermoacoustic Oscillations in Lean-Premixed Gas Turbine Combustors." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-63997.

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This paper presents the experimental investigation of pulsation-amplitude-dependent flame dynamics associated with transverse thermoacoustic oscillations at screech level frequencies in a generic gas turbine combustor. Specifically, the flame behavior at different levels of pulsation amplitudes is assessed and interpreted. Spatial dynamics of the flame are measured by imaging the OH* chemiluminescence signal synchronously to the dynamic pressure at the combustor’s face plate. First, linear thermoacoustic stability states, modal dynamics, as well as flame-acoustic phase relations are evaluated. It is found that the unstable acoustic modes converge into a predominantly rotating character in the direction of the mean flow swirl. Furthermore, the flame modulation is observed to be in phase with the acoustic pressure at all levels of the oscillation amplitude. Second, distributed flame dynamics are investigated by means of visualizing the mean and oscillating heat release distribution at different pulsation amplitudes. The observed flame dynamics are then compared against numerical evaluations of the respective amplitude-dependent thermoacoustic growth rates, which are computed using analytical models in the fashion of a non-compact flame-describing function. While results show a nonlinear contribution for the individual growth rates, the superposition of flame deformation and displacements balances out to a constant flame driving. This latter observation contradicts the state-of-the-art perception of root-causes for limit-cycle oscillations in thermoacoustic gas turbine systems, for which the heat release saturates with increasing amplitudes. Consequently, the systematic observations and analysis of amplitude-dependent flame modulation shows alternative paths to the explanation of mechanisms that might cause thermoacoustic saturation in high frequency systems.

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Guyot, Daniel, Christian Oliver Paschereit, and Surya Raghu. "A Fluidic Actuator for Active Combustion Control." In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50797.

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In this work the performance of a fluidic actuator in an active combustion control scheme is demonstrated. The actuator was tested in two different burner configurations, a bluff body burner and a generic swirl-stabilized burner, where it modulated parts of the fuel flow. The oscillation frequency was controlled by varying the inlet mass flow of the actuator. Fluidic actuators are of special interest for fuel-based active control schemes featuring high frequency fuel flow modulation, as they are much more durable then conventional valves due to the absence of fast moving parts. Hot wire measurements were performed to investigate the fluidic actuator’s oscillation characteristics without combustion. The actuator was then incorporated into a bluff body burner and a swirl-stabilized burner, respectively, where it modulated parts of the fuel flow blended with nitrogen. Pressure and heat release fluctuations in the combustor were recorded and images of the flame were taken. For both burners the heat release response of the flame to fuel flow modulation was first studied during stable combustion. The spectra of the heat release signals showed a clear peak corresponding to the fluidics’ oscillation frequency, thus validating the ability of the actuator to influence the combustion process. As the next step, each of the two combustors was operated at conditions that featured a strong low-frequency combustion instability when no fuel was modulated. In case of the bluff body burner applying fuel modulation resulted in attenuation of the combustion instability for some oscillation frequencies. The attenuation was highest when modulating the fuel flow in between the fundamental instability frequency and its subharmonic. Modulating the fuel flow at the subharmonic, however, resulted in an amplification of the instable mode. Also when applied to the swirl burner, the fludics’ fuel flow modulation caused a significant reduction of the pressure oscillations, although the actuator could only be operated at oscillation frequencies much lower than the instability frequency due to the attached tubes. The results obtained in this work show that the fluidic actuator in use allows for fuel modulation and hence combustion control without the need for complex and fast moving parts, thus ensuring a long actuator lifetime. This makes the fluidic actuator highly appropriate for application in industrial gas turbines.

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Chishty, Wajid A., Joan Boulanger, and Sangsig Yun. "Experimental and Numerical Investigation of Spatial and Temporal Dispersion of Forced Fuel Oscillations." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-12595.

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In lean premixed combustors of gas turbine engines, fuel-air mixing is considered vital for controlling pollutant emissions as well as combustion instability. Enhancement in mixing may be obtained by modulating the fuel flow rate. Modulation of fuel flow is also a useful technique to actively control combustion instabilities arising from the pressure oscillations in the combustor and thrust augmenters. Effectiveness of the forced oscillations depends on the level of dispersion present in the system. Knowledge of dispersion levels is also important in determining the degree of mixing and therefore, the effectiveness of a premixer. This paper presents the experimental efforts undertaken to study the spatial and temporal dispersion of fuel flow rate oscillation introduced at the premixer inlet. Effects of oscillation amplitude and frequency are investigated at different bulk flow rates and at various locations in the premixer. Also presented is a review of the in-house numerical work done towards this end, using three computational methods. Results show that the degree of dispersion in fuel flow rate oscillations depends on modulation amplitude and frequency as well as advective velocity of the bulk flow.

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Meier, U., J. Heinze, and C. Hassa. "Response of Spray and Heat Release to Forced Air Flow Fluctuations in a Gas Turbine Combustor at Elevated Pressure." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27310.

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The objective of this work was to investigate the response of the heat release and liquid fuel distribution to forced periodic modulations of the primary air flow through diffusion type burners with different exit geometries. The spatial distribution of spray density and heat release at different modulation frequencies was studied using phase-resolved OH chemiluminescence for heat release visualization, and planar Mie scattering of kerosene. Experiments were performed for a variety of operating conditions. It was observed that the exit geometry of the nozzle has a considerable effect on the flame shape and fuel distribution, but also on the amplitude of the response to forcing of the air flow. The expanding and contracting fuel spray cone drives the region of the heat release during a period of the air flow modulation, by establishing favourable flammability conditions at varying locations during the oscillation. The temporal shape of the response of the fuel mass in the combustor, as well as the large modulation depth at low frequencies compared to the changes of air flow velocity, suggest that the fuel feed rate into the combustor is affected by a storage mechanism.

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Guyot, Daniel, and Christian Oliver Paschereit. "Active Control of Combustion Instability Using Symmetric and Asymmetric Premix Fuel Modulation." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27342.

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Active instability control was applied to an atmospheric swirl-stabilized premixed combustor using open loop and closed loop control schemes. Actuation was realised by two on-off valves allowing for symmetric and asymmetric modulation of the premix fuel flow while maintaining constant time averaged overall fuel mass flow. Pressure and heat release fluctuations in the combustor as well as NOx, CO and CO2 emissions in the exhaust were recorded. In the open loop circuit the heat release response of the flame was first investigated during stable combustion. For symmetric fuel modulation the dominant frequency in the heat release response was the modulation frequency, while for asymmetric modulation it was its first harmonic. In stable open loop control a reduction of NOx emissions due to fuel modulation of up to 19% was recorded. In the closed loop mode phase-shift control was applied while triggering the valves at the dominant oscillation frequency as well as at its second subharmonic. Both, open and closed loop control schemes were able to successfully control a low-frequency combustion instability, while showing only a small increase in NOx emissions compared to, for example, secondary fuel modulation. Using premixed open loop fuel modulation, attenuation was best when modulating the fuel at frequencies different from the dominant instability frequency and its subharmonic. The performance of asymmetric fuel modulation was generally slightly better than for symmetric modulation in terms of suppression levels as well as emissions. Suppression of the instability’s pressure rms level of up to 15.7 dB was recorded.

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Shcherbik, D., E. Lubarsky, Y. Neumeier, B. T. Zinn, K. McManus, T. F. Fric, and S. Srinivasan. "Suppression of Instabilities in Gaseous Fuel High-Pressure Combustor Using Non-Coherent Oscillatory Fuel Injection." In ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38103.

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This paper describes the application of active, open loop, control in effective damping of severe combustion instabilities in a high pressure (i.e., around 520 psi) gas turbine combustor simulator. Active control was applied by harmonic modulation of the fuel injection rate into the combustor. The open-loop active control system consisted of a pressure sensor and a fast response actuating valve. To determine the dependence of the performance of the active control system upon the frequency, the fuel injection modulation frequency was varied between 300 and 420 Hz while the frequency of instability was around 375 Hz. These tests showed that the amplitude of the combustor pressure oscillations strongly depended upon the frequency of the open loop control. In fact, the amplitude of the combustor pressure oscillations varied ten fold over the range of investigated frequencies, indicating that applying the investigated open loop control approach at the appropriate frequency could effectively damp detrimental combustion instabilities. This was confirmed in subsequent tests in which initiation of open loop modulation of the fuel injection rate at a non resonant frequency of 300Hz during unstable operation with peak to peak instability amplitude of 114 psi and a frequency of 375Hz suppressed the instability to a level of 12 psi within approximately 0.2 sec (i.e., 75 periods). Analysis of the time dependence of the spectra of the pressure oscillations during suppression of the instability strongly suggested that the open loop fuel injection rate modulation effectively damped the instability by “breaking up” (or preventing the establishment of) the feedback loop between the reaction rate and combustor oscillations that drove the instability.

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Paschereit, Christian Oliver, and Ephraim Gutmark. "Active Control of Combustion Instabilities in Gas Turbine Burners." In ASME Turbo Expo 2006: Power for Land, Sea, and Air. ASMEDC, 2006. http://dx.doi.org/10.1115/gt2006-90186.

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This paper gives an overview of open and closed loop active control methodologies used to suppress symmetric and helical thermoacoustic instabilities in an experimental low-emission swirl-stabilized gas turbine combustor. The controllers were based on fuel (or equivalence ratio) modulations in the main pre-mixed combustion or alternatively in secondary pilot fuel. For the main premix fuel supply two methods of fuel injection modulations were tested: symmetric and asymmetric injection. The tests showed that the closed loop asymmetric modulations were more effective in the suppression of the symmetric mode instability than symmetric fuel excitation. Symmetric excitation was quite efficient in abating the symmetric mode as well, however, at a certain range of phase shift the combustion was destabilized to an extent that caused blow out of the flame. Using premixed open loop fuel modulations the symmetric instability mode responded to symmetric excitation only when the two frequencies matched. The helical fuel injection affected the symmetric mode only at frequencies that were much higher than that of the instability mode. The asymmetric excitation required more power to obtain the same amount of reduction as that required by symmetric excitation. Unlike the symmetric excitation which destabilized the combustion when the modulation amplitude was excessive, the asymmetric excitation yielded additional suppression as the modulation level increased. The NOx emissions were reduced to a greater extent by the asymmetric modulation. Secondary fuel injection in a pilot flame was used to control low frequency symmetric instability and high frequency helical instability. Adding a continuous flow of fuel into the pilot flame controlled both instabilities. However, modulating the fuel injection significantly decreased the amount of necessary fuel. The reduced secondary fuel resulted in a reduced heat generation by the pilot diffusion flame and therefore yielded lower NOx emissions. The secondary fuel pulsation frequency was chosen to match the time scales typical to the central flow recirculation zone which stabilizes the flame in the burner. Suppression of the symmetric mode pressure oscillations by up to 20 dB was recorded.

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Звіти організацій з теми "Oscillating modulation of the pressure"

Lehotay, Steven J., and Aviv Amirav. Fast, practical, and effective approach for the analysis of hazardous chemicals in the food supply. United States Department of Agriculture, April 2007. http://dx.doi.org/10.32747/2007.7695587.bard.

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Background to the topic: For food safety and security reasons, hundreds of pesticides, veterinary drugs, and environmental pollutants should be monitored in the food supply, but current methods are too time-consuming, laborious, and expensive. As a result, only a tiny fraction of the food is tested for a limited number of contaminants. Original proposal objectives: Our main original goal was to develop fast, practical, and effective new approaches for the analysis of hazardous chemicals in the food supply. We proposed to extend the QuEChERS approach to more pesticides, veterinary drugs and pollutants, further develop GC-MS and LC-MS with SMB and combine QuEChERS with GC-SMB-MS and LC-SMB-EI-MS to provide the “ultimate” approach for the analysis of hazardous chemicals in food. Major conclusions, solutions and achievements: The original QuEChERS method was validated for more than 200 pesticide residues in a variety of food crops. For the few basic pesticides for which the method gave lower recoveries, an extensive solvent suitability study was conducted, and a buffering modification was made to improve results for difficult analytes. Furthermore, evaluation of the QuEChERS approach for fatty matrices, including olives and its oil, was performed. The QuEChERS concept was also extended to acrylamide analysis in foods. Other advanced techniques to improve speed, ease, and effectiveness of chemical residue analysis were also successfully developed and/or evaluated, which include: a simple and inexpensive solvent-in-silicone-tube extraction approach for highly sensitive detection of nonpolar pesticides in GC; ruggedness testing of low-pressure GC-MS for 3-fold faster separations; optimization and extensive evaluation of analyte protectants in GC-MS; and use of prototypical commercial automated direct sample introduction devices for GC-MS. GC-MS with SMB was further developed and combined with the Varian 1200 GCMS/ MS system, resulting in a new type of GC-MS with advanced capabilities. Careful attention was given to the subject of GC-MS sensitivity and its LOD for difficult to analyze samples such as thermally labile pesticides or those with weak or no molecular ions, and record low LOD were demonstrated and discussed. The new approach of electron ionization LC-MS with SMB was developed, its key components of sample vaporization nozzle and flythrough ion source were improved and was evaluated with a range of samples, including carbamate pesticides. A new method and software based on IAA were developed and tested on a range of pesticides in agricultural matrices. This IAA method and software in combination with GC-MS and SMB provide extremely high confidence in sample identification. A new type of comprehensive GCxGC (based on flow modulation) was uniquely combined with GC-MS with SMB, and we demonstrated improved pesticide separation and identification in complex agricultural matrices using this novel approach. An improved device for aroma sample collection and introduction (SnifProbe) was further developed and favorably compared with SPME for coffee aroma sampling. Implications, both scientific and agricultural: We succeeded in achieving significant improvements in the analysis of hazardous chemicals in the food supply, from easy sample preparation approaches, through sample analysis by advanced new types of GC-MS and LCMS techniques, all the way to improved data analysis by lowering LOD and providing greater confidence in chemical identification. As a result, the combination of the QuEChERS approach, new and superior instrumentation, and the novel monitoring methods that were developed will enable vastly reduced time and cost of analysis, increased analytical scope, and a higher monitoring rate. This provides better enforcement, an added impetus for farmers to use good agricultural practices, improved food safety and security, increased trade, and greater consumer confidence in the food supply.

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