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Journal articles on the topic 'Damping of pressure pulsations'

Author: Grafiati
Published: 28 June 2021
Last updated: 1 February 2022

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1

Ma, Quyang, Zhenhuan Wu, Guoan Yang, Yue Ming, and Zheng Xu. "Pulsation suppression in a reciprocating compressor piping system using a two-tank element." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 232, no. 4 (June 6, 2017): 427–37. http://dx.doi.org/10.1177/0954408917713436.

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Gas pulsations excited by reciprocating compressors could introduce severe vibrations and noise in piping systems. When pulsating gas flows through the reducers, the changes in flow characteristics, such as velocity and damping coefficient, will affect the pressure pulsations. To circumvent these constraints, a two-tank element is introduced to control the gas pulsation that is still strong in the piping system with a surge tank. Installing another surge tank to form a two-tank element is more flexible and costs lower than replacing the original surge tank with a larger one. In this work, a theoretical model based on the wave theory was proposed to study the transferring mechanism of gas pulsations in the pipeline with the two-tank element. By considering the damping coefficient and the Mach number, the distributions of the pressure pulsations were predicted by the theoretical model and agreed with the three-dimensional fluid dynamics transient analysis. Three experiments were conducted to prove that the suppression capability of the two-tank element is as good as that of a single-tank element (surge tank) with the same surge volume. The volume optimization of the two-tank element is implemented by selecting the best allocations of the two tanks’ volumes to achieve larger reductions of pressure pulsations. Assuming that the total surge volume is constant, we found that the smaller the volume of the front tank (near the cylinder) is, the lower the pulsation levels are. The optimized result proves that in some conditions the two-tank element could control pulsations better than the single-tank element with the same surge volume.
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2

Himr, Daniel, Vladimír Habán, and Simona Fialová. "Influence of Second Viscosity on Pressure Pulsation." Applied Sciences 9, no. 24 (December 12, 2019): 5444. http://dx.doi.org/10.3390/app9245444.

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A mathematical model of pulsating flow is proposed in the paper. The model includes more accurate description of energy dissipation, so it allows, for example, better stability analysis of water power plant control and more effective operation. Flow in a pipeline system is usually treated as a one-dimensional flow. This is also applied for more difficult cases of the Newtonian and non-Newtonian liquids simulations in the rigid or flexible pipes. Computational simulations of pressure pulsations in pipelines often predict lower damping than what the experimental results show. This discrepancy can be caused by neglecting one of the important damping mechanisms. The second viscosity describes the energy losses due to the compressibility of the liquid. Its existence and use in the computations specifies the real pulsations damping descriptions and predictions. A frequency dependent model of pressure pulsations including second viscosity is introduced. The second viscosity is determined from the system eigenvalue. The experiments were performed with water for low frequencies (from 0.1 to 1 kHz). This area is not fully covered by the current available research results.
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3

Himr, Daniel, and Vladimir Haban. "Damping of Self-Excited Pressure Pulsations in Petrodiesel Pipeline." Applied Mechanics and Materials 630 (September 2014): 375–82. http://dx.doi.org/10.4028/www.scientific.net/amm.630.375.

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A pumping station in a fuel storage suffered from pressure pulsations in a petrodiesel pipeline. Check valves protecting the station against back flow made a big noise when disc hit a seat. Due to employees complaints we were asked to solve the problem, which could lead to serious mechanical problems. Pressure measurement in the pipeline showed great pulsations, which were caused by self-excited oscillation of control valves at the downstream end of pipeline. The operating measurement did not catch it because of too low sampling frequency. One dimensional numerical model of the whole hydraulic system was carried out. The model consisted of check valve, pipeline and control valve, which could oscillate, so it was possible to simulate the unsteady flow. When the model was validated, a vessel with nitrogen was added to attenuate pressure pulsations. According to the results of numerical simulation, the vessel was installed on the location. Subsequent measurement proved noticeably lower pulsations and almost no noise.
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4

Ma, Quyang, Zhenhuan Wu, Mengjun Li, and Guoan Yang. "Pulsation attenuation in a reciprocating compressor piping system using a volume-perforated pipe-volume suppressor." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 232, no. 17 (September 11, 2017): 3074–84. http://dx.doi.org/10.1177/0954406217729422.

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A volume-perforated pipe-volume suppressor is introduced to study its performance in attenuating pressure pulsations. On the basis of plane wave theory, the work developed a mathematical model to predict the distribution of pressure pulsations in a reciprocating compressor piping system with the proposed suppressor. The theoretical predictions were verified through experiments and three-dimensional fluid dynamics transient simulations, and good agreements were attained. Results proved that the pressure pulsations were attenuated significantly when the suppressor was used. In the frequency domain, the amplitude at the first pulsation frequency was decreased considerably. Both the perforation and cross-sectional areas of the perforated pipe could influence the attenuating capacity. Given a fixed ratio of perforation area to cross-sectional area, the best damping performance could be obtained by increasing the number of perforated holes and reducing the hole diameter. The geometric recommendations produced in this work are useful to control pulsations and vibrations under different functioning conditions.
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5

Himr, Daniel, Vladimír Habán, and David Štefan. "Inner Damping of Water in Conduit of Hydraulic Power Plant." Sustainability 13, no. 13 (June 25, 2021): 7125. http://dx.doi.org/10.3390/su13137125.

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The operation of any hydraulic power plant is accompanied by pressure pulsations that are caused by vortex rope under the runner, rotor–stator interaction and various transitions during changes in operating conditions or start-ups and shut-downs. Water in the conduit undergoes volumetric changes due to these pulsations. Compression and expansion of the water are among the mechanisms by which energy is dissipated in the system, and this corresponds to the second viscosity of water. The better our knowledge of energy dissipation, the greater the possibility of a safer and more economic operation of the hydraulic power plant. This paper focuses on the determination of the second viscosity of water in a conduit. The mathematical apparatus, which is described in the article, is applied to data obtained during commissioning tests in a water storage power plant. The second viscosity is determined using measurements of pressure pulsations in the conduit induced with a ball valve. The result shows a dependency of second viscosity on the frequency of pulsations.
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6

Lato, T., and A. Mohany. "Passive damping of pressure pulsations in pipelines using Herschel-Quincke tubes." Journal of Sound and Vibration 448 (May 2019): 160–77. http://dx.doi.org/10.1016/j.jsv.2019.02.020.

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7

Lepeshkin, A. A., L. A. Berdnikov, M. G. Korzhachkin, and V. A. Panov. "Damping of pressure pulsations in the fuel system of the motor." IOP Conference Series: Materials Science and Engineering 1086, no. 1 (March 1, 2021): 012011. http://dx.doi.org/10.1088/1757-899x/1086/1/012011.

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8

Lato, T., A. Mohany, and M. Hassan. "A passive damping device for suppressing acoustic pressure pulsations: The infinity tube." Journal of the Acoustical Society of America 146, no. 6 (December 2019): 4534–44. http://dx.doi.org/10.1121/1.5139886.

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9

Britsyn, S. V., M. V. Ryabinin, and S. E. Semenov. "OSCILLATION DAMPER CALCULATION BASED ON THE ELECTRO HYDRAULIC ANALOGY." Spravochnik. Inzhenernyi zhurnal, no. 275 (2020): 17–24. http://dx.doi.org/10.14489/hb.2020.02.pp.017-024.

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The method of the synthesis and the pressure fluctuations damping calculation based on the electro-hydraulic analogy is proposed. The mathematical model describing the processes of unsteady fluid flow through the device is developed. Using the composed transfer function and its approximation, the oscillation damper parameters identification to reduce the outlet pressure pulsations in the triplex plunger pump is carried out.
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10

TEMKIN, S. "Radial pulsations of a fluid sphere in a sound wave." Journal of Fluid Mechanics 380 (February 10, 1999): 1–38. http://dx.doi.org/10.1017/s0022112098003401.

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This paper presents analytical results for the temperature and pressure fluctuations in a droplet or bubble pulsating in a sound wave, the related damping coefficients, as well as the corresponding sound attenuation coefficients for dilute suspensions. The study is limited to small-amplitude motions but includes the effects of compressibility and heat conduction in the fluid outside the particle. Results are obtained for both average and surface values of the particle's temperature and pressure fluctuations that are applicable to droplets in gases and liquids, and to gas bubbles in liquids. In the latter instance, it is found that the bubble's response exhibits a clear resonant peak at the isothermal natural frequency, that acoustic radiation is the dominant dissipation mechanism near resonance, and that the disturbances produced by the bubble in the liquid significantly reduce the thermal damping at most frequencies. Similar conclusions apply for droplets in liquids, except that the effects of resonance are significantly diminished.
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11

HAYASHI, Itsuro, and Shigehiko KANEKO. "817 Damping Characteristics of Pressure Pulsations in Piping Systems Induced by a Centrifugal Compressor." Proceedings of the Dynamics & Design Conference 2007 (2007): _817–1_—_817–6_. http://dx.doi.org/10.1299/jsmedmc.2007._817-1_.

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12

Cyklis, Piotr, and Przemysław Młynarczyk. "Passive pressure pulsation damping using shaped nozzles." Scientific Letters of Rzeszow University of Technology - Mechanics 31, no. 86(3/2014) (2014): 319–26. http://dx.doi.org/10.7862/rm.2014.35.

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13

Hayashi, I., and S. Kaneko. "Pressure pulsations in piping system excited by a centrifugal turbomachinery taking the damping characteristics into consideration." Journal of Fluids and Structures 45 (February 2014): 216–34. http://dx.doi.org/10.1016/j.jfluidstructs.2013.11.012.

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14

Murphy, Simon J., Hideyuki Saio, Masahide Takada-Hidai, Donald W. Kurtz, Hiromoto Shibahashi, Masao Takata, and Daniel R. Hey. "On the first δ Sct–roAp hybrid pulsator and the stability of p and g modes in chemically peculiar A/F stars." Monthly Notices of the Royal Astronomical Society 498, no. 3 (September 4, 2020): 4272–86. http://dx.doi.org/10.1093/mnras/staa2667.

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ABSTRACT Strong magnetic fields in chemically peculiar A-type (Ap) stars typically suppress low-overtone pressure modes (p modes) but allow high-overtone p modes to be driven. KIC 11296437 is the first star to show both. We obtained and analysed a Subaru spectrum, from which we show that KIC 11296437 has abundances similar to other magnetic Ap stars, and we estimate a mean magnetic field modulus of 2.8 ± 0.5 kG. The same spectrum rules out a double-lined spectroscopic binary, and we use other techniques to rule out binarity over a wide parameter space, so the two pulsation types originate in one δ Sct–roAp hybrid pulsator. We construct stellar models depleted in helium and demonstrate that helium settling is second to magnetic damping in suppressing low-overtone p modes in Ap stars. We compute the magnetic damping effect for selected p and g modes, and find that modes with frequencies similar to the fundamental mode are driven for polar field strengths ≲4 kG, while other low-overtone p modes are driven for polar field strengths up to ∼1.5 kG. We find that the high-order g modes commonly observed in γ Dor stars are heavily damped by polar fields stronger than 1–4 kG, with the damping being stronger for higher radial orders. We therefore explain the observation that no magnetic Ap stars have been observed as γ Dor stars. We use our helium-depleted models to calculate the δ Sct instability strip for metallic-lined A (Am) stars, and find that driving from a Rosseland mean opacity bump at ∼5 × 104 K caused by the discontinuous H-ionization edge in bound-free opacity explains the observation of δ Sct pulsations in Am stars.
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15

HAYASHI, Itsuro, and Shigehiko KANEKO. "Pressure Pulsations in Piping Systems Excited by a Centrifugal Compressor (2nd Report, Effect of Operating Conditions on Damping Characteristics)." Transactions of the Japan Society of Mechanical Engineers Series C 74, no. 739 (2008): 650–57. http://dx.doi.org/10.1299/kikaic.74.650.

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16

Młynarczyk, Przemysław, and Piotr Cyklis. "The estimation of the pressure pulsation damping coefficient of a nozzle." Journal of Sound and Vibration 464 (January 2020): 115002. http://dx.doi.org/10.1016/j.jsv.2019.115002.

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17

Zhang, Yanjun, Hongxin Zhang, Jingzhou Yang, Qinghai Zhao, Xiaotian Jiang, Qianchang Cheng, and Qingsong Hua. "Research on Distribution of Flow Field and Simulation of Working Pulsation Based on Rotating-Sleeve Distributing-Flow System." Modelling and Simulation in Engineering 2017 (2017): 1–9. http://dx.doi.org/10.1155/2017/1015494.

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To solve problems of leakage, vibration, and noise caused by disorders of flow field distribution and working pulsation in the rotating-sleeve distributing-flow system, governing equations of plunger and rotating sleeve and computational fluid dynamics (CFD) model are developed through sliding mesh and dynamic mesh technology to simulate flow field and working pulsation. Simulation results show that the following issues exist: obviously periodic fluctuation and sharp corner in flow pulsation, backward flow when fluid is transformed between discharge and suction, and serious turbulence and large loss in kinetic energy around the damping groove in transitional movements. Pressure in the pump chamber rapidly rises to 2.2 MPa involving over 10% more than nominal pressure when the plunger is at the Top Dead Center (TDC) considering changes about damping groove’s position and flow area in two transitional movements. Shortly pressure overshoot gradually decreases to a normal condition with increasing flow area. Similarly, pressure in the pump chamber instantaneously drops to a saturated vapor pressure −98.9 KPa when the plunger is at the Bottom Dead Center (BDC). With increasing flow area the overshoot gradually increases to the normal condition. This research provides foundations for investigating flow field characteristic and structure optimization of rotating-sleeve distributing-flow system.
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18

Shaik Chand Mabhu Subhani and N.Vijay Kumar. "Static and Model Analysis on Pneumatic Suspension by using Ansys Software." International Journal for Modern Trends in Science and Technology 6, no. 12 (December 18, 2020): 384–89. http://dx.doi.org/10.46501/ijmtst061272.

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During the tractor movement, with being attached to the hitch-system working equipment over Rough road surfaces oscillation of the machine take place. These oscillations are a reason of pressure pulsations in the hydraulic hitch-system. The pressure pulse reduction in the tractor Hitch-system is important for increasing of the system components lifetime. Pressure oscillation damping in the tractor hydraulic hitch-system can reduce overall system oscillations and improve the driving control. The design of spring in suspension system is very important. In this project a shock absorber is designed and a 3D model is created using CATIA V5 R20. The model is also changed by changing the thickness of the spring. Structural analysis and modal analysis are done on the suspension system by varying material for spring, Spring Steel and Beryllium Copper. Analysis done in ANSYS 14.5. The analysis is done by considering loads, bike weight, single person and 2 persons. Structural analysis is done to validate the strength and modal analysis is done to determine the displacements for different frequencies for number of modes. Comparison is done for two materials to verify best material for spring in suspension system.
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19

Bach, David, Tom Masselter, and Thomas Speck. "Damping of Pressure Pulsations in Mobile Hydraulic Applications by the Use of Closed Cell Cellular Rubbers Integrated into a Vane Pump." Journal of Bionic Engineering 14, no. 4 (December 2017): 791–803. http://dx.doi.org/10.1016/s1672-6529(16)60444-4.

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20

Houdek, G., M. N. Lund, R. Trampedach, J. Christensen-Dalsgaard, R. Handberg, and T. Appourchaux. "Damping rates and frequency corrections of Kepler LEGACY stars." Monthly Notices of the Royal Astronomical Society 487, no. 1 (May 2, 2019): 595–608. http://dx.doi.org/10.1093/mnras/stz1211.

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ABSTRACT Linear damping rates and modal frequency corrections of radial oscillation modes in selected LEGACY main-sequence stars are estimated by means of a non-adiabatic stability analysis. The selected stellar sample covers stars observed by Kepler with a large range of surface temperatures and surface gravities. A non-local, time-dependent convection model is perturbed to assess stability against pulsation modes. The mixing-length parameter is calibrated to the surface-convection-zone depth of a stellar model obtained from fitting adiabatic frequencies to the LEGACY observations, and two of the non-local convection parameters are calibrated to the corresponding LEGACY linewidth measurements. The remaining non-local convection parameters in the 1D calculations are calibrated so as to reproduce profiles of turbulent pressure and of the anisotropy of the turbulent velocity field of corresponding 3D hydrodynamical simulations. The atmospheric structure in the 1D stability analysis adopts a temperature–optical–depth relation derived from 3D hydrodynamical simulations. Despite the small number of parameters to adjust, we find good agreement with detailed shapes of both turbulent pressure profiles and anisotropy profiles with depth, and with damping rates as a function of frequency. Furthermore, we find the absolute modal frequency corrections, relative to a standard adiabatic pulsation calculation, to increase with surface temperature and surface gravity.
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21

Li, Yelin, Youxin Luo, and Xiao Wu. "Impact System Dynamic Characteristics of Hydraulic Rock Drill Based on an Overlapped Reversing Valve." Shock and Vibration 2018 (September 19, 2018): 1–11. http://dx.doi.org/10.1155/2018/8963750.

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For the phenomenon of a hydraulic rock drill based on an underlapped reversing valve, the mechanical structure of the overlapped reversing form was proposed, which affected the pressure pulsation of the impact system, and motion of the impact piston was analyzed. The model of a hydraulic rock drill was built based on Newton’s laws. The initial lead size of the reversing point was calculated by the equilibrium position of the damping piston and final velocity of the impact piston. The size of the overlapped reversing valve was designed and the best impact interval was calculated, according to pressure characteristic curves in the piston of the front-rear chamber and in the reversing valve of the left-right chamber, and the damping piston floating feature had an impact on initial lead size of the reversing point. The advantages of the overlapped reversing valve were analyzed, by contrasting the pressure pulsation of the impact system and motion of the impact piston with the underlapped reversing valve. The inner mechanism experiment of the hydraulic rock drill was designed to test the pressure characteristic curves in the piston of the front-rear chamber and in the reversing valve of the left-right chamber. The model of the overlapped reversing valve was verified by the experiment.
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22

Cyklis, Piotr, and Przemysław Młynarczyk. "The CFD Based Estimation of Pressure Pulsation Damping Parameters for the Manifold Element." Procedia Engineering 157 (2016): 387–95. http://dx.doi.org/10.1016/j.proeng.2016.08.381.

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23

Cao, Wenbin, Yinshui Liu, Jie Dong, Zhuang Niu, and Youcheng Shi. "Research on Pressure Pulsation Characteristics of Gerotor Pump for Active Vibration Damping System." IEEE Access 7 (2019): 116567–77. http://dx.doi.org/10.1109/access.2019.2936489.

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24

Gogstad, Peter Joachim, and Ole Gunnar Dahlhaug. "Evaluation of runner cone extension to dampen pressure pulsations in a Francis model turbine." IOP Conference Series: Earth and Environmental Science 49 (November 2016): 082019. http://dx.doi.org/10.1088/1755-1315/49/8/082019.

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25

Et al., Navruzov Kuralbay. "Pulsing Flows of a Viscous Incompressible Liquid in a Pipe with Elastic Walls." Psychology and Education Journal 58, no. 2 (February 1, 2021): 1436–44. http://dx.doi.org/10.17762/pae.v58i2.2293.

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As you know, the recent intensive introduction into practice of flexible pipelines made of polymer synthetic materials, pulsating fluid flow in elastic pipes is of great importance. As you know, the recent intensive introduction into practice of flexible pipelines made of polymer synthetic materials, pulsating fluid flow in elastic pipes is of great importance. By solving the problem, the necessary hydrodynamic parameters will be determined, such as pressure distributions, velocities, flow rates, the speed of propagation of the pulse wave pressure and their decay. For the first time in this article, a decrease in hydraulic resistance in a pulsating flow through pipes due to the elasticity of the wall will be determined. The dependence of the dimensionless value of the pressure pulse wave on the vibrational number was investigated .The speed of the pulse wave was compared with the speed of Moens-Korteweg , and significant differences were revealed between them occurring at lower values of the Womersley oscillatory parameter, at large values of which significant differences are not observed. The dependence of the reciprocal damping per wavelength on the vibrational number , was also investigated; it was shown that the damping is free at smaller values of the Womersley vibrational parameter, practically equal to zero, and at large values of which it asymptotically approaches unity.
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26

Druzhinin, A. A., A. P. Kutrakov, and R. V. Zinko. "Silicon whisker pressure sensors for noise reduction in silencers." Технология и конструирование в электронной аппаратуре, no. 1-2 (2021): 28–32. http://dx.doi.org/10.15222/tkea2021.1-2.28.

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The article contains the results of research and development of a system for active noise damping of an automobile engine. The main source of noise from a running engine is exhaust noise. The frequency spectrum of this sound has a pronounced low-frequency character, which explains its weak absorption when the sound is propagating in open spaces. A possible solution to this problem is to use an active system for suppressing the resonant frequencies of the muffler using strain gauges to read the primary information about the dynamic processes that determine the noise level. It is for such active noise suppression systems that the authors develop a high-temperature pressure sensor based on strain gauges made of silicon whiskers. Such strain gauges have unique mechanical properties, are characterized by high sensitivity and the ability to operate in various amplitude-frequency and temperature ranges up to 500℃. The study of the dynamic characteristics of pressure sensors made it possible to confirm the quality of its electromechanical part and determine that the measurement error of the sensor is ±0.5 in the temperature range of 20 to 500℃. The active noise suppression system is a buffer tank whose volume changes in accordance with signals from pressure sensors. This design makes it possible to dynamically change the resonant frequency of the buffer capacitance depending on the operating modes of the engine, which leads to a decrease in its noise characteristics. Using the developed additional resonator chamber with a variable volume in the exhaust muffler of an internal combustion engine made it possible to reduce resonance phenomena in the zone of low-frequency pulsations of the exhaust gas pressure from 57 to 43 Hz with a frequency drift in the range of 310 to 350 Hz, which significantly improved its noise characteristics.
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27

Sun, Fengyong, and Haibo Zhang. "A research on the compressor blade tip pressure modeling and stall detection measure." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 230, no. 14 (August 6, 2016): 2654–60. http://dx.doi.org/10.1177/0954410016629703.

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A new compressor rotational stall detection algorithm is proposed in this paper, and a well monotonicity exists in the correlation coefficient calculated by the algorithm and compressor surge margin. In order to reconstruct the compressor blade pressure, a trustworthy digital compressor blade pressure model is built. Specially, the model consists of three sub-models, the blade duct pressure model, rotational stall pulsation pressure model, and corrected rotational stall damping model. Simulation results indicate the effectiveness of the stall detection algorithm and compressor stochastic pressure model, which means that the correlation coefficient calculated from the algorithm and stochastic pressure model has a high reliability to take the place of surge margin as the flag of compressor stability.
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28

Su, Xin Ping, Shi Tong Liu, Fu Ming Yin, Guang Kun Nie, and Wei Sun. "The Calculation and Simulate Research of the Natural Frequency of Liquid Flow on Piping Networks of Multi-Pulse Sources." Applied Mechanics and Materials 137 (October 2011): 250–55. http://dx.doi.org/10.4028/www.scientific.net/amm.137.250.

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The pressure resonance problem impelled by hydraulic pulsation power in piping networks is studied in this thesis. Through theoretical analyzing and computer simulating to the flow variation of multi-pulse sources accumulation, two concepts: the variable initial angle by equal probability and flow pulsation rare, are introduced. Some useful conclusions are also obtained. Most of piping networks vibration in engineering is aroused by the medium pressure pulsation. Destructive violent vibration is set off by the simulation of pressure pulsation when resonant occurred. In order to reduce the vibration, it is important to restrain pressure pulsation and to avoid the resonance areas determined by piping networks construction. On the basis of the optimized approximate model to meet the need of the practical engineering and fluidic network theory, this thesis is mainly concerned with the natural frequency of internal liquid vibration in pipelines. In this thesis a no-damping piping mathematics model as well as the transfer matrix method is employed, and the computer simulation is used in theoretical researching. The simulation software of pressure fluctuation for the complex fluidic transmission systems is developed. The effects of every structure parameters of simulated hydraulic pipelines on the pressure pulsation performance are analyzed in details by using the software which makes us modify some structure parameters efficiently so as to optimize structure, evade resonant, reduce the amplitude of pressure pulsation and avoid fluid resonance. The experiments verify the conclusion of the computer simulation and show that the software is easy to be widely used in the dynamic optimum design of fluid transmission systems.
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29

TSUKAMOTO, Koji, Masahiro KOIZUMI, and Masato SHINJI. "Estimation of Compressive Strength of Rocks Using Damping Pressure Pulsation of Hydraulic Rock Drill." Journal of the Society of Materials Science, Japan 68, no. 4 (April 15, 2019): 366–73. http://dx.doi.org/10.2472/jsms.68.366.

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30

Carraro, Mattia, Jaina Negandhi, Jafri Kuthubutheen, Evan J. Propst, Lukas Kus, Vincent Y. W. Lin, and Robert V. Harrison. "Attenuating Cardiac Pulsations within the Cochlea: Structure and Function of Tortuous Vessels Feeding Stria Vascularis." ISRN Otolaryngology 2013 (May 19, 2013): 1–7. http://dx.doi.org/10.1155/2013/941757.

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The mammalian ear has an extraordinary capacity to detect very low-level acoustic signals from the environment. Sound pressures as low as a few μPa (−10 dB SPL) can activate cochlear hair cells. To achieve this sensitivity, biological noise has to be minimized including that generated by cardiovascular pulsation. Generally, cardiac pressure changes are transmitted to most peripheral capillary beds; however, such signals within the stria vascularis of the cochlea would be highly disruptive. Not least, it would result in a constant auditory sensation of heartbeat. We investigate special adaptations in cochlear vasculature that serve to attenuate cardiac pulse signals. We describe the structure of tortuous arterioles that feed stria vascularis as seen in corrosion casts of the cochlea. We provide a mathematical model to explain the role of this unique vascular anatomy in dampening pulsatile blood flow to the stria vascularis.
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31

CHATZIDAI, N., Y. DIMAKOPOULOS, and J. TSAMOPOULOS. "Viscous effects on the oscillations of two equal and deformable bubbles under a step change in pressure." Journal of Fluid Mechanics 673 (March 1, 2011): 513–47. http://dx.doi.org/10.1017/s0022112010006361.

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According to linear theory and assuming the liquids to be inviscid and the bubbles to remain spherical, bubbles set in oscillation attract or repel each other with a force that is proportional to the product of their amplitude of volume pulsations and inversely proportional to the square of their distance apart. This force is attractive, if the forcing frequency lies outside the range of eigenfrequencies for volume oscillation of the two bubbles. Here we study the nonlinear interaction of two deformable bubbles set in oscillation in water by a step change in the ambient pressure, by solving the Navier–Stokes equations numerically. As in typical experiments, the bubble radii are in the range 1–1000 μm. We find that the smaller bubbles (~5 μm) deform only slightly, especially when they are close to each other initially. Increasing the bubble size decreases the capillary force and increases bubble acceleration towards each other, leading to oblate or spherical cap or even globally deformed shapes. These deformations may develop primarily in the rear side of the bubbles because of a combination of their translation and harmonic or subharmonic resonance between the breathing mode and the surface harmonics. Bubble deformation is also promoted when they are further apart or when the disturbance amplitude decreases. The attractive force depends on the Ohnesorge number and the ambient pressure to capillary forces ratio, linearly on the radius of each bubble and inversely on the square of their separation. Additional damping either because of liquid compressibility or heat transfer in the bubble is also examined.
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32

Quaal, Susan J. "Quality Assurance in Hemodynamic Monitoring." AACN Advanced Critical Care 4, no. 1 (February 1, 1993): 197–206. http://dx.doi.org/10.4037/15597768-1993-1015.

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Patient care management decisions frequently are based, at least in part, on hemodynamic indices. Accuracy in repeated measurement of hemodynamic parameters is therefore critical. It can be achieved only through a program of quality assurance (QA), which should include the following factors: static, dynamic, and validation of pulmonary artery wedge pressure (PAWP). The static QA factor consists of establishing an accurate reference point from which all subsequent measurements are made. The hemodynamic monitoring system must be able to transmit pulsating physiologic pressures to the transducer with high fidelity, which is validated via the dynamic response or “square wave” test and damping coefficient. Other QA aspects that arc used to validate the accuracy of PAWP include catheter placement into lung zone 3 capillary and comparison of capillary to arterial blood gases. Measurement error also can be introduced because of varying methods to quantify the analog pressure waveforms, such as end-expiratory or pressure averaging techniques. This paper explores each of these domains within a framework of quality assurance
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33

Jiang, Jihai, and Zhongxun Liu. "Pressure characteristics of a novel double rotor hydraulic transformer." Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering 233, no. 9 (January 2, 2019): 1182–94. http://dx.doi.org/10.1177/0959651818822392.

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The hydraulic transformer is the core component when it works with the common pressure rail system, which integrates the functions of the pump and the motor, and thus possesses sensitive pressure characteristics. The rotating speed has significant influence on the pressure characteristics of a hydraulic transformer while it has not been considered previously. In this study, aimed at improving the working performance, a novel double rotor hydraulic transformer is proposed and a comprehensive mathematical model considering the dynamic characteristics of the cylinder block is established. At the same time, a prototype is made and the experiment is conducted. The test results show that the robust rotor structure enables a larger pressure range, and the numerical results exhibit a good match with the test results. The parameter sensitivity study shows that the delivery pressure is mainly subject to the valve plate control angle δ and, under the effects of the resistance torques, pressure loss will occur especially under a large control angle and a high rotating speed. The magnitude of the instantaneous angular velocity fluctuation increases sharply when the speed is lower than 400 r/min, which is the main reason for the serious pressure pulsation at a low speed. As a result of the improved low-speed stability and output flow uniformity, the pressure pulsation rate of the double rotor hydraulic transformer is greatly reduced. However, the pulsation rate is still high at an extremely low speed. In addition, when the rotating speed exceeds the capability of the damping grooves, the pressure undershoot becomes serious at the A-T transition region around the control angle of −30°. Consequently, from the perspective of pressure characteristics, the limitation on the rotating speed under small control angles is suggested for the design of the double rotor hydraulic transformer controller.
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34

Longuet-Higgins, Michael S. "Resonance in nonlinear bubble oscillations." Journal of Fluid Mechanics 224 (March 1991): 531–49. http://dx.doi.org/10.1017/s0022112091001866.

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In two recent papers (Longuet-Higgins 1989a,b) the author showed that the shape oscillations of bubbles can emit sound like a monopole source, at second order in the distortion parameter ε. In the second paper (LH2) it was predicted that the emission would be amplified when the second harmonic frequency 2σn of the shape oscillation approaches the frequency ω of the breathing mode. This ‘resonance’ would however be drastically limited by damping due to acoustic radiation and thermal diffusion. The predictions were confirmed by further numerical calculations in Longuet-Higgins (1990a).Ffowcs Williams & Guo (1991) have questioned the conclusions of LH2 on the grounds that near resonance there is a slow (secular) transfer of energy between the shape oscillation and the volumetric mode which tends to diminish the amplitude of the shape oscillation and hence falsify the perturbation analysis. They have also argued that the volumetric mode never grows sufficiently to produce sound of the stated order of magnitude. In the present paper we show that these assertions are unfounded. Ffowcs Williams & Guo considered only undamped oscillations. Here we show that when the appropriate damping is included in their analysis the secular transfer of energy becomes completely insignificant. The resulting pressure pulse (figure 5 below) is found to be essentially identical to that calculated in LH2, figure 3. Moreover, in the initial-value problem considered in LH2, the excitation of the volumetric mode takes place not by a secular energy transfer but by a resonance during the first few cycles of the shape oscillation. This accounts for the amplification near resonance found in Longuet-Higgins (1990a). Finally, it is pointed out that the initial energy of the shape oscillations is far greater than is required to produce the O(ε2) volume pulsations that were studied in LH2, and which were used for a comparison with field data. This acoustic radiation was not calculated by Ffowcs Williams & Guo.
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35

Banis, Kārlis. "The Effect of separated Expansion Chamber Parameters on Exhaust Pressure Oscillations in Single Cylinder Motorcycle Engine." Rural Sustainability Research 43, no. 338 (August 1, 2020): 42–51. http://dx.doi.org/10.2478/plua-2020-0006.

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AbstractThis paper investigates the effect of separated exhaust expansion chamber parameters on pressure oscillations in spark-ignited internal combustion (IC) gasoline engines. It is known that exhaust expansion chambers are becoming increasingly more popular among both – original equipment (OE) and aftermarket equipment (AE) exhaust system manufacturers for performance-oriented motorcycles equipped with mainly single cylinder engines, but the companies are reluctant to reveal any detailed principles of operation of the mentioned expansion chambers. The subject of this research is the type of expansion chamber (separate) as used on performance-oriented motorcycles, particularly its’ effect on exhaust pressure pulsations as different chamber volumes, locations and passage sizes are tested. Time-dependent computational fluid dynamics (CFD) analysis was carried out in Solidworks Flow Simulation environment on a simplified exhaust header pipe model imitating engine operation at full load and steady speed. Honda CRF450R motorcycle engine was used as the example and fully defined using a 1D engine performance calculator software to determine the combustion chamber pressure and exhaust valve lift at any given crankshaft position. Volume flow rate of exhaust gasses at the header pipe inlet was calculated based on engine parameters and operating speed. The average pressure values with respect to physical time were measured and graphed across the header pipe inlet cross-section. Eight different header pipe and exhaust expansion chamber combinations were modelled, tested, and results compared at low, medium and high engine speeds. It was found that the presence of exhaust expansion chamber tends to dampen the amplitude and decrease the frequency of pressure oscillations generated at the opening of the exhaust valve(s). Observations show that the addition of an expansion chamber as per design of performance-oriented motorcycles helps to decrease the negative effect of engine tuning while also dampening the positive effect.
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36

Chen, Yan-li, Shun-an Liu, Ji-hai Jiang, Tao Shang, Yuan-kun Zhang, and Hang Sui. "Pulsating characteristic of the hydraulic hybrid vehicle system with pipeline effect." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 229, no. 12 (December 8, 2014): 2158–73. http://dx.doi.org/10.1177/0954406214562996.

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The configuration and working principle of hydraulic hybrid vehicle (HHV) based on the hydraulic transformer (HT) were described to extend its energy-regenerated potential. The approximate algorithm of basic elements for pipeline distributed parameter model was summarized to simplify the pipeline model calculation, and the various basic elements of this method were proven to be used in the practical application by comparison with the experimentally validated Zhao and Hullender model. The pressure pulsation characteristics between the HT and accumulator of the HHV by considering Zhao model, Hullender model, and original pipeline approximate model was analyzed to optimize the system structure design by the method of the mathematical model, which mainly includes the series accumulator and parallel accumulator, respectively. The simulation result shows that the series accumulator was better than the parallel accumulator in terms of pulsation damping of hydraulic transformer with considering the pipeline effect. The test-rig result shows that the theoretical analysis of the pulsation between the HT and accumulator with pipeline was very close to the measurement data of the experiment in the curve trend, where the theoretical analysis results of pulsation characteristic for HHV were appropriate and reasonable.
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37

Zinko, R. V., A. P. Kutrakov, S. V. Shybanov, N. M. Zashchepkina, and O. M. Markina. "Active system for reduction of noise parameters of car muffler with the use of pressure sensors based on silicon microcrystals." Archives of Materials Science and Engineering 1, no. 109 (May 1, 2021): 35–41. http://dx.doi.org/10.5604/01.3001.0015.0513.

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Purpose: The article contains the results of research and development of a system for active noise damping of an automobile engine. The proposed system of active noise suppression can significantly reduce the sound pressure level in the frequency band up to 500 Hz. The robotic principle of the developed system is based on the addition of an additional buffer tank with a variable volume in the silencer system. The use of high-temperature sensors with strain gauges based on silicon microcrystals to obtain information on the parameters of sound vibrations arising during the exhaust gas outflow made it possible to create a control system for changing the volume of the buffer tank. The results of testing the proposed system of active noise suppression of an internal combustion engine are presented. Design/methodology/approach: The active noise suppression system based on the Helmholtz resonator used tools to control general noise levels, experimental tests, complex mathematical modelling of acoustic processes in Solidworks, taking into account the conditions of propagation and attenuation of sound energy by intermediate closed volumes. Findings: The use of an additional resonator chamber with variable volume in the exhaust muffler of the internal combustion engine allowed to reduce the resonant phenomena in the zone of low-frequency pulsations of exhaust gas pressure from 57 Hz to 43 Hz at frequency drift in the range of 310… 350 Hz, which significantly improved its noise characteristics. Research limitations/implications: For further research, to improve the characteristics of the active noise suppression system, it is advisable to consider the use of several inadditional cameras of the Helmholtz resonator and to clarify the algorithm of the controller in transient modes of engine operation. Practical implications: The developed design of active noise reduction is simpler in comparison with analogs and allows reducing the noise of exhaust gases in a low-frequency range. Originality/value: To reduce the noise, a variable-volume Helmholtz resonator was used, the efficiency of which is provided by high-temperature sensors of the original design.
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38

Xu, Enle, Xiaofeng Jiang, Zhenya Duan, Lefu Xie, and Shichang Wang. "Effect of rectangular damping groove on flow fluctuation and pressure pulsation for rotary energy recovery device through CFD simulation." DESALINATION AND WATER TREATMENT 115 (2018): 97–105. http://dx.doi.org/10.5004/dwt.2018.22297.

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39

Tu, Shan, Ming Hao Li, Chao Wang, De Dong, and Yue Juan Shi. "Study on Characteristics of Flow-Induced Vibration in Pre-Opening Sleeve Valve." Advanced Materials Research 562-564 (August 2012): 1182–85. http://dx.doi.org/10.4028/www.scientific.net/amr.562-564.1182.

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Flow-induced vibration widely exists in fluid power machinery, and there is a great relation between the vibration and engineering construction. In this paper, prototype valve experiment and three-dimensional simulation has been done on the pre-opening sleeve valve. High-frequency minute dynamic pressure sensors are adopted in the valve in experiment. Vibration data with dynamic pressure in different conditions are collected and measured to find out the pulsation characteristics of the valve disc during the experiment. Meanwhile, three-dimensional numerical simulation and analysis on the internal flow field of the valve has carried out, in order to discover the factors of vibration induced by fluid flow. The result shows that the main cause of flow-induced vibration varies in different conditions. At the condition of large opening and large pressure difference between valve inlet and outlet, it is mainly due to vortex-induced vibration. Several ways such as improving damping, avoiding the resonance frequency and changing the type of the valve profile can be taken to weaken the vortex-induced vibration.
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40

Grushenkova, E. D., L. I. Mogilevich, V. S. Popov, and A. V. Khristoforova. "Mathematical Model of Oscillations of a Three-Layered Channel Wall Possessing a Compressible Core and Interacting with a Pulsating Viscous Liquid Layer." Herald of the Bauman Moscow State Technical University. Series Instrument Engineering, no. 6 (129) (December 2019): 4–18. http://dx.doi.org/10.18698/0236-3933-2019-6-4-18.

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The paper deals with the formulation of a mathematical model to study a dynamics interaction of a three-layered channel wall with a pulsating viscous fluid layer in a channel. The narrow channel formed by two parallel walls was considered. The lower channel wall was a three-layered plate with a compressible core, and the upper one was absolutely rigid. The face sheets of the three-layered plate satisfied Kirchhoff's hypotheses. The plate core was considered rigid taking into account its compression in the transverse direction. Plate deformations were assumed to be small. The continuity conditions of displacements are satisfied at the layers' boundaries of the three-layered plate. The oscillations of the three-layered channel wall occurred under the action of a given law of pressure pulsation at the channel edges. The dynamics of the viscous incompressible fluid layer within the framework of a creeping motion was considered. The formulated mathematical model consisted of the dynamics equations of the three-layered plate with compressible core, Navier --- Stokes equations, and the continuity equation. The boundary conditions of the model were the conditions at the plate edges, the no-slip conditions at the channel walls and the conditions for pressure at the channel edges. The steady-state harmonic oscillations were investigated and longitudinal displacements and deflections of the plate face sheets were determined. Frequency-dependent distribution functions of amplitudes of plate layers displacements were introduced. These functions allow us to investigate the dynamic response of the channel wall and the fluid pressure change in the channel. The elaborated model can be used for the evolution of non-destructive testing of elastic three-layered elements contacting with a viscous fluid layer and being part of the lubrication, damping or cooling systems of modern instruments and units.
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41

KIMURA, Yasumasa, Toshimitsu TANAKA, Kazuhiro UEDA, and Hajime NAKASHIMA. "Development of Measuring Method for Pressure Pulsation Characteristics by Using 3-microphones (Measurement of Damping Characteristics of the Hydraulic Systems)." Transactions of the Japan Society of Mechanical Engineers Series C 70, no. 694 (2004): 1651–56. http://dx.doi.org/10.1299/kikaic.70.1651.

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42

Chan, Gregory S. H., Philip N. Ainslie, Chris K. Willie, Chloe E. Taylor, Greg Atkinson, Helen Jones, Nigel H. Lovell, and Yu-Chieh Tzeng. "Contribution of arterial Windkessel in low-frequency cerebral hemodynamics during transient changes in blood pressure." Journal of Applied Physiology 110, no. 4 (April 2011): 917–25. http://dx.doi.org/10.1152/japplphysiol.01407.2010.

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The Windkessel properties of the vasculature are known to play a significant role in buffering arterial pulsations, but their potential importance in dampening low-frequency fluctuations in cerebral blood flow has not been clearly examined. In this study, we quantitatively assessed the contribution of arterial Windkessel (peripheral compliance and resistance) in the dynamic cerebral blood flow response to relatively large and acute changes in blood pressure. Middle cerebral artery flow velocity (MCAV; transcranial Doppler) and arterial blood pressure were recorded from 14 healthy subjects. Low-pass-filtered pressure-flow responses (<0.15 Hz) during transient hypertension (intravenous phenylephrine) and hypotension (intravenous sodium nitroprusside) were fitted to a two-element Windkessel model. The Windkessel model was found to provide a superior goodness of fit to the MCAV responses during both hypertension and hypotension ( R2 = 0.89 ± 0.03 and 0.85 ± 0.05, respectively), with a significant improvement in adjusted coefficients of determination ( P < 0.005) compared with the single-resistance model ( R2 = 0.62 ± 0.06 and 0.61 ± 0.08, respectively). No differences were found between the two interventions in the Windkessel capacitive and resistive gains, suggesting similar vascular properties during pressure rise and fall episodes. The results highlight that low-frequency cerebral hemodynamic responses to transient hypertension and hypotension may include a significant contribution from the mechanical properties of vasculature and, thus, cannot solely be attributed to the active control of vascular tone by cerebral autoregulation. The arterial Windkessel should be regarded as an important element of dynamic cerebral blood flow modulation during large and acute blood pressure perturbation.
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43

Guo, Bing, Weixiao Tang, and Tianhui Zhen. "Effects of the Wet Steam Non-Equilibrium Condensation on the Dynamics of the Excitation-Relying Bearing-Rotor system." MATEC Web of Conferences 179 (2018): 01005. http://dx.doi.org/10.1051/matecconf/201817901005.

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This paper investigated the effects of the wet steam non-equilibrium condensation on the dynamic characteristics of the bearing as well as the bearing-rotor system by constructing and analyzing a non-linear coupled model of the bearing-rotor system. An excitation-relying dynamic model of bearing is established based on the finite difference method, in which the excitation is converted from the pressure pulsation on the surface of rotor blades generated from the non-equilibrium condensation process. The Raccia transfer matrix method is implemented to analyse the dynamic behavior of this coupled system. Results show that the wet steam non-equilibrium condensation process would greatly reduce the bearing stiffness and damping and result in more intense vibration of the system, besides, its induced pulsed displacement would drive the excitation-relying bearing-rotor system more unstable.
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44

Xiong, D. R., Q. L. Cheng, and L. Deng. "Oscillations of HB Red Variable Stars." Symposium - International Astronomical Union 185 (1998): 401–2. http://dx.doi.org/10.1017/s0074180900239077.

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Using a nonlocal time-dependent theory of convection, we have calculated the linear non-adiabatic oscillations of the Horizontal Branch (HB) stars, with both the dynamic and thermodynamic coupling between convection and oscillations been carefully treated. Turbulent pressure and turbulent viscosity have been included consistently in our equations of non-adiabatic pulsation. When the coupling between convection and oscillations is ignored, for all models with Te ≤ 7350K, the fundamental through the second overtone are pulsationally unstable; while for Te ≤ 6200K all the models are unstable up to (at least) the 9th overtone. When the coupling between convection and oscillations is included, the RR Lyrae instability strip is very well predicted. Within the strip most models are pulsationally unstable only for the fundamental and the first few overtones. Turbulent viscosity is an important damping mechanism. Being exclusively distinct from the luminous red variables (long period variables), the HB stars to the right of the RR Lyrae strip are pulsationally stable for the fundamental and low-order overtones, but become unstable for some of the high-order overtones. This may provide a valuable clue for the short period, low amplitude red variables found outside the red edge of the RR Lyrae strip on the H-R diagram of globular clusters. Moreover, we present a new radiation modulated excitation mechanism functioning in radiation flux gradient regions. The effects of nonlocal convection and the dynamic coupling between convection and oscillations are discussed. The spatial oscillations of the thermal variables in the pulsational calculations have been effectively suppressed.
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45

Umurzakov, Uktam, Bakhtiyor Obidov, Oybek Vokhidov, Furqat Musulmanov, Boyburi Ashirov, and Javlon Suyunov. "Force effects of the flow on energy absorbers in the presence of cavitation." E3S Web of Conferences 264 (2021): 03076. http://dx.doi.org/10.1051/e3sconf/202126403076.

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As the experience of operating high-pressure spillway structures shows, the operating conditions of the downstream extinguishing devices are very difficult. At flow rates, more than 12–15 m/s, downstream damping devices, as a rule, operate in a cavitation mode. First of all, this mode of operation gives rise to erosional destruction of the damper itself and the waters near it. This occurs where the cavitation torch closes on the structure. Attempts to avoid these desirable phenomena by lining erosion sites with steel sheets do not always lead to the desired result since it is not uncommon for the steel lining to be torn off by hydrodynamic forces. The separation of the cladding occurs in two cases: firstly, when the cladding is not in close contact with the concrete to be protected, and secondly, its anchoring is not enough. In both cases, fracture occurs from fatigue phenomena in the metal due to multiple oscillatory cycles from hydrodynamic loads. It is difficult to avoid this in cavitation modes since the spectrum of pressure pulsations, in this case, is very wide, which leads to oscillations of linings at resonant frequencies. Apparently, the strength of the linings is an object of special research, and in the future, it should be dealt with theoretically and experimentally. Hydrodynamic forces at high flow rates in the zone of intense energy extinguishing can reach such values that they can lift and overturn concrete slabs of water walls and water walls. Currently, there are practically no specific and accounting for vertical hydrodynamic loads on slabs of water walls in the presence of cavitation on erosion-free absorbers in the technical literature. To a certain degree of approximation, it is possible to use experimental data obtained on a model of the same structure but operating without cavitation, as data on hydrodynamic loads in the downstream of structures operating in a cavitation mode. The main disadvantage of such comparisons is that there is no guarantee that the amplitude and frequency characteristics of the flow during cavitation do not change (in particular, the amplitudes do not increase) as the cavitation limit is approached.
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46

Bakhtiar, Sadia, and Farid Ullah Khan. "Analytical Modeling and Simulation of an Electromagnetic Energy Harvester for Pulsating Fluid Flow in Pipeline." Scientific World Journal 2019 (August 1, 2019): 1–9. http://dx.doi.org/10.1155/2019/5682517.

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This paper presents the analytical modeling and simulation of an electromagnetic energy harvester (having linear behaviour) that generates power from pulsating fluid flow for pipeline condition monitoring systems. The modeled energy harvester is comprised of a cylindrical permanent magnet and a wound coil attached to a flexible membrane which oscillates due to the pulsating fluid flow in the pipe over which the prototype is considered to be mounted. In the harvester electrical energy is produced due to the relative motion between the coil and magnet. Based on the harvester’s architecture a lumped parameter model (single degree of freedom system) is developed and is simulated at different physical operational conditions. The simulation is performed at pressure amplitude of 625 Pa. When subjected to the operational frequency sweep, at the harvester’s resonant frequency (500 Hz) and damping ratio of 0.01, the devised model predicted the maximum open circuit voltage of 2.55 V and load voltage of 1.27 V. While operating under resonance, the maximum load voltage of 2.45 V is estimated at load resistance of 100 Ω. However, at an optimum load of 4.3 Ω, the simulation shows a production of 188151.2 μW power at a frequency of 500 Hz.
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47

Tsigklifis, Konstantinos, and Anthony D. Lucey. "Asymptotic stability and transient growth in pulsatile Poiseuille flow through a compliant channel." Journal of Fluid Mechanics 820 (May 5, 2017): 370–99. http://dx.doi.org/10.1017/jfm.2017.163.

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The time-asymptotic linear stability of pulsatile flow in a channel with compliant walls is studied together with the evaluation of modal transient growth within the pulsation period of the basic flow as well as non-modal transient growth. Both one (vertical-displacement) and two (vertical and axial) degrees-of-freedom compliant-wall models are implemented. Two approaches are developed to study the dynamics of the coupled fluid–structure system, the first being a Floquet analysis in which disturbances are decomposed into a product of exponential growth and a sum of harmonics, while the second is a time-stepping technique for the evolution of the fundamental solution (monodromy) matrix. A parametric study of stability in the non-dimensional parameter space, principally defined by Reynolds number ($Re$), Womersley number ($Wo$) and amplitude of the applied pressure modulation ($\unicode[STIX]{x1D6EC}$), is then conducted for compliant walls of fixed geometric and material properties. The flow through a rigid channel is shown to be destabilized by pulsation for low $Wo$, stabilized due to Stokes-layer effects at intermediate $Wo$, while the critical $Re$ approaches the steady Poiseuille-flow result at high $Wo$, and that these effects are made more pronounced by increasing $\unicode[STIX]{x1D6EC}$. Wall flexibility is shown to be stabilizing throughout the $Wo$ range but, for the relatively stiff wall used, is more effective at high $Wo$. Axial displacements are shown to have negligible effect on the results based upon only vertical deformation of the compliant wall. The effect of structural damping in the compliant-wall dynamics is destabilizing, thereby suggesting that the dominant inflectional (Rayleigh) instability is of the Class A (negative-energy) type. It is shown that very high levels of modal transient growth can occur at low $Wo$, and this mechanism could therefore be more important than asymptotic amplification in causing transition to turbulent flow for two-dimensional disturbances. Wall flexibility is shown to ameliorate mildly this phenomenon. As $Wo$ is increased, modal transient growth becomes progressively less important and the non-modal mechanism can cause similar levels of transient growth. We also show that oblique waves having non-zero transverse wavenumbers are stable to higher values of critical $Re$ than their two-dimensional counterparts. Finally, we identify an additional instability branch at high $Re$ that corresponds to wall-based travelling-wave flutter. We show that this is stabilized by the inclusion of structural damping, thereby confirming that it is of the Class B (positive-energy) instability type.
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48

Yumoto, K., V. Pilipenko, E. Fedorov, N. Kurneva, and K. Shiokawa. "The Mechanisms of Damping of Geomagnetic Pulsations." Journal of geomagnetism and geoelectricity 47, no. 2 (1995): 163–76. http://dx.doi.org/10.5636/jgg.47.163.

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49

Guelich, J. F., and U. Bolleter. "Pressure Pulsations in Centrifugal Pumps." Journal of Vibration and Acoustics 114, no. 2 (April 1, 1992): 272–79. http://dx.doi.org/10.1115/1.2930257.

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Pressure pulsations in centrifugal pumps are created by the wake flow from the impeller blade trailing edge and by large-scale turbulence and vortices generated by flow separation and flow recirculation at part load. The physical mechanisms causing pressure pulsations and the design parameters having an influence on the level of the pressure pulsations are reviewed. The system in which a pump is operated has a strong impact on the level of pressure pulsations measured, which also depends on the detailed design of the impeller and the diffuser. These effects cannot be predicted theoretically. Therefore, statistical data of 36 tests with different pump configurations are given in order to document the level of pulsations which can be achieved.
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50

Bellucci, V., P. Flohr, C. O. Paschereit, and F. Magni. "On the Use of Helmholtz Resonators for Damping Acoustic Pulsations in Industrial Gas Turbines." Journal of Engineering for Gas Turbines and Power 126, no. 2 (April 1, 2004): 271–75. http://dx.doi.org/10.1115/1.1473152.

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In this work, the application of Helmholtz resonators for damping low-frequency pulsations in gas turbine combustion chambers is discussed. We present a nonlinear model for predicting the acoustic response of resonators including the effect of purging air. Atmospheric experiments are used to validate the model, which is employed to design a resonator arrangement for damping low-frequency pulsations in an ALSTOM GT11N2 gas turbine. The predicted damper impedances are used as the boundary condition in the three-dimensional analysis of the combustion chamber. The suggested arrangement leads to a significant extension of the low-pulsation operating regime of the engine.
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