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Zieliński, Dariusz, i Karol Fatyga. "Attenuation of DC-Link Pulsation of a Four-Wire Inverter during Phase Unbalanced Current Operation". Applied Sciences 11, nr 3 (1.02.2021): 1322. http://dx.doi.org/10.3390/app11031322.
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This paper proposes a control algorithm for a hybrid power electronic AC/DC converter for prosumer applications operating under deep phase current asymmetry. The proposed system allows independent control of active and reactive power for each phase of the power converter without current pulsation on the DC link connected to an energy store. The system and its algorithm are based on a three-phase converter in four-wire topology (AC/DC 3p-4w) with two dual-active bridge (DC/DC) converters, interfaced with a supercapacitor and an energy storage. The control algorithm tests were carried out in a Hardware in the Loop environment. Obtained results indicate that operation with deep unbalances and powers of opposite signs in individual phases leads to current oscillations in the DC link. This phenomenon significantly limits energy storage utilization due to safety and durability reasons. The proposed algorithm significantly reduces the level of pulsation in the DC link which increases safety and reduces strain on lithium-ion storage technology, enabling their application in four-wire converter applications.
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Casoli, Paolo, Carlo Maria Vescovini i Massimo Rundo. "One-Dimensional Fluid Dynamic Modeling of a Gas Bladder Hydraulic Damper for Pump Flow Pulsation". Energies 16, nr 8 (11.04.2023): 3368. http://dx.doi.org/10.3390/en16083368.
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Positive displacement pumps produce pressure ripple that can be reduced with the attenuation of the generated flow ripple. This paper presents the application of a gas bladder hydraulic damper with the aim of reducing the oscillations of the delivery flow rate of positive displacement machines. This work is focused on the development of a 1D fluid dynamic model of the damper, which is based on the fundamental fluid motion equations applied for a mono-dimensional flow. In order to represent the fluid flow inside the damper, a particular evaluation of the sound speed has been implemented. Experimental tests have been performed involving an axial piston pump with the damper installed in the delivery pipe to validate the model; tests were carried out at different pump working conditions and with different gas precharge pressure of the damper. The test results confirmed the effectiveness of the device, and the comparison with numerical results demonstrated a good agreement. Simulations have been carried out to investigate the influence of various parameters on damper effectiveness.
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Narayana, Gopalakrishna, i Saravanan Selvaraj. "Attenuation of pulsation and oscillation using a disk at mid-section of spiked blunt body". Physics of Fluids 32, nr 11 (1.11.2020): 116106. http://dx.doi.org/10.1063/5.0024649.
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Ivanov, D. A. "Investigation of the impact of unsteady air flows on the mechanical and operational properties of aircraft structural elements". Civil Aviation High Technologies 26, nr 2 (2.05.2023): 61–71. http://dx.doi.org/10.26467/2079-0619-2023-26-2-61-71.
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The use of pulsating subsonic gas flow treatment (gas pulse treatment) in the process of maintenance and repair for a duration not exceeding a certain value contributes to the restoration and improvement of mechanical and operational properties of aeronautical equipment structural elements. This article presents the results of a study to determine the optimal duration of gaspulse processing of aircraft parts, as which, the duration of processing was adopted, providing the maximum increase in the properties of material viscosity, which prevents crack development without reducing the strength properties. As a result of the study, the influence of various factors, such as the subsonic airflow velocity and the frequency of oscillations, the material and geometric parameters of the processed product, on both the optimal and leading to a decrease in mechanical properties duration of processing by pulsating airflow of aircraft structural elements during maintenance and repair, was evaluated. It has been established that mechanical waves generated by gas flow pulsations can have a significant impact on the structural strength of aircraft structural elements, which makes it possible to increase their reliability as well as the accuracy of forecasting the technical condition. The harmonic nature of the attenuation of the ratio of residual stresses to their initial values has been experimentally established, depending on the duration of gas pulse treatment, which allows us to control their magnitude and sign. An empirical formula has been obtained to determine the optimal processing time for products of various materials. As an indicator of the duration of gas pulse treatment, an increase in the viscosity of the material was adopted without reducing the strength properties. Graphical dependences of the relative time of gas pulse processing, which provides an increase in the mechanical properties of the relative frequency of the gas flow oscillations, have been constructed.
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Kateryna, Deineka. "INFLUENCE OF SMALL FRACTION OF POLYGRANULAR FILL OF ROTATING DRUM ON SELF-OSCILLATION SWING". Vibrations in engineering and technology, nr 4(95) (20.12.2019): 31–37. http://dx.doi.org/10.37128/2306-8744-2019-4-4.
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The influence of the structure of two-fractional polygranular fill of a rotating drum on the self-oscillation swing is considered. The pulsating mode of flow of such intrachamber fill is used in the self-oscillating grinding process in a tumbling mill. Spherical particles of non-coherent granular material of 2.2 mm size were used as a large fraction modeling the grinding bodies. Cement was used as the small fraction modeling the particles of the crushed material. The factors of experimental studies were accepted: the gaps between particles of large fraction degree of filling at rest dispersed particles of small fraction 0, 25, 50 and 100%, the relative size of particles of large fraction in the drum chamber 0.519, 0.733, 1.04, 1.47, 2.08, 2.93, 4.15 and 5.87% (drum chamber radius 212, 150, 106, 75, 53, 37.5, 26.5 and 18.75 mm), the chamber degree of filling at rest 25, 35 and 45%. The method of visual analysis of fill motion patterns in the cross section of a rotating chamber and measurement of dilatation was applied.Video of the fill pulsating flow was taken. The magnitude of the self-oscillation swing was estimated by the increase in the difference of the maximum and minimum values of the fill dilatation over one period of pulsating. The maximum range of self-oscillation swing reached the value of 1.36. The change of the self-oscillation swing from zero at the beginning of self-excitation of pulsations to the maximum value with the greatest increase of dilatation was revealed. The effect of a decrease in the maximum range of self-oscillation swing with enhanced fill coherent properties has been registered. The attenuation of the spray of particles of large fraction in the chamber due to the coherent effect of the small fraction was established. An increase in the self-oscillation swing of single-grain fill was found with a decrease in the relative particle size and the chamber degree of filling. A decrease in the self-oscillation swing of two-fractional fill was found with an increase in the content of small fraction, a decrease in the relative size of particles of a large fraction, and an increase in the chamber degree of filling.
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Fang, Zhenlong, Qiang Wu, Mengda Zhang, Haoyang Liu, Pan Jiang i Deng Li. "Large Eddy Simulation of Self-Excited Oscillation Pulsed Jet (SEOPJ) Induced by a Helmholtz Oscillator in Underground Mining". Energies 12, nr 11 (5.06.2019): 2161. http://dx.doi.org/10.3390/en12112161.
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Pulsed waterjet can break rocks effectively by taking advantage of the water hammer effect, and is thus widely used in mining, petroleum, and natural gas fields. With the aim to further clarify the flow field characteristics of pulsed jets induced by a Helmholtz oscillator, large eddy simulation was conducted under different operating pressures. The velocity distribution, mean flow field, and the coherent structure were examined using the oscillators of different cavity lengths and diameters. The results clearly showed that the major frequency of jet pulsation gradually increased with the increase of operating pressure. A stable periodic velocity core was formed at the outlet of the Helmholtz oscillator, while the external flow field was subjected to periodic impact. As a result, the ambient fluid was strongly entrained into the jet beam. With the increase of the cavity length, the length of the core segment decreased while the energy loss caused by the cavity increased, which was also accompanied by a rapid attenuation of the axial velocity at the jet outlet. The coherent structure of the jet in the oscillator with small cavity diameter was more disordered near the nozzle outlet, and the vortex scale was larger. The effect of cavity diameter can be reflected in the feedback modulation of the jet in the cavity. Compared with the conical nozzle, the length of the core section of the jet was shorter, but the jet had better bunching, a smaller diffusion angle, and better mixing performance. These results provide a further understanding of the characteristics of pulsed water jet for better utilizations in the fields of energy exploitation.
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Song, Soon H., Susan S. McIntyre, Hasnain Shah, Johannes D. Veldhuis, Peter C. Hayes i Peter C. Butler. "Direct Measurement of Pulsatile Insulin Secretion from the Portal Vein in Human Subjects1". Journal of Clinical Endocrinology & Metabolism 85, nr 12 (1.12.2000): 4491–99. http://dx.doi.org/10.1210/jcem.85.12.7043.
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Insulin is secreted in a high frequency pulsatile manner. These pulses are delivered directly into the portal vein and then undergo extraction and dilution before delivery into the systemic circulation. The reported frequency of these insulin pulses estimated in peripheral blood varies from an interpulse interval of 4–20 min. We postulated that this discrepancy is due to the attenuation of the pulse signal in the systemic circulation vs. the portal circulation. In the present study we measured pulsatile insulin release directly in the portal circulation of human subjects who had indwelling transjugular intrahepatic portasystemic stent shunts (TIPSS) to decompress portal hypertension. We quantitated pulsatile insulin secretion in both the overnight fasted state (fasting) and during a hyperglycemic clamp (8 mmol/L). Direct portal vein sampling established that pulsatile insulin secretion in humans has an interval (periodicity) of approximately 5 min. The amplitude (and mass) of the insulin concentration oscillations observed in the portal vein was approximately 5-fold greater than that observed in the arterialized vein and was similar to that observed in the dog. Increased insulin release during hyperglycemia was achieved through amplification of the insulin pulse mass. In conclusion, direct portal vein sampling in humans revealed that the interpulse interval of insulin pulses in humans is about 5 min, and this frequency is also observed when sampling from the systemic circulation using a highly specific insulin assay and 1-min sampling, but is about 4-fold greater than the frequency observed at this site using single site RIAs. We confirm that enhanced insulin release in response to hyperglycemia is achieved by amplification of these high frequency pulses.
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Yuan, Jun, Hang Jiang, Zheng-yan Fang, Tian-sheng Wang, Zhi Luo, Feng-xian Jiang i Gui-hong Yin. "Design and Characteristic Analysis of a New Type of Hydraulic Pulsation Suppressor". E3S Web of Conferences 293 (2021): 02028. http://dx.doi.org/10.1051/e3sconf/202129302028.
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In order to decrease the pressure pulsation of high-pressure hydraulic system and speed up the process of high-pressure hydraulic system, a new type of hydraulic pulsation suppressor is designed. The hydraulic pulsation suppressor is designed on the basis of the structural characteristics and attenuation performance of the expansion chamber attenuator and H-type muffler. The theoretical model of the modern hydraulic pulsation suppressor is established based on the fluid theory, and the attenuation performance of the new hydraulic pulsation suppressor is analyzed. The results demonstrate that the designed new hydraulic pulsation suppressor can attenuate the pressure pulsation with a pulsation frequency of 20 Hz～2000 Hz, and attenuate the frequency bandwidth; the attenuation effect is above 50dB, and the attenuation effect is ideal.
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Zhou, Shenghao, Hangyu Jiao, Dongxu Liu, Weizhen Liu, Junzhe Lin, Qingkai Han i Zhong Luo. "Numerical and Experimental Analysis of Pressure Pulsation Attenuator Based on Helmholtz Resonator". Applied Sciences 13, nr 14 (20.07.2023): 8381. http://dx.doi.org/10.3390/app13148381.
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Due to the development of aviation hydraulic systems towards high pressure and high flow, the frequency range of pressure pulsation becomes wider, and the amplitude of pulsation increases. This puts higher requirements on the attenuation characteristics of the pressure pulsation attenuator. To reduce the damage caused by pressure pulsation to the pipeline, a Helmholtz-type pulsation attenuator (HTPA) is designed, which works through the Helmholtz resonant chamber. The theoretical model of HTPA is established by the method of lumped parameter method and distribution parametric method. The insertion loss is adopted to evaluate its attenuation characteristics. The internal pressure dynamic characteristics and attenuation effect of the HTPA are analyzed by simulation and experimentation. The results show that the pulsation attenuation rate δ was 40% after the installation of the attenuator. In the frequency range of 0–1000 Hz, the maximum insertion loss is 19 dB, which verifies the validity and correctness of the theoretical model.
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Shang, Yaoxing, Hong Tang, Huawang Sun, Changbin Guan, Shuai Wu, Yuanzhi Xu i Zongxia Jiao. "A novel hydraulic pulsation reduction component based on discharge and suction self-oscillation: Principle, design and experiment". Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering 234, nr 4 (4.09.2019): 433–45. http://dx.doi.org/10.1177/0959651819871775.
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The reduction of fluid ripple in pipes is extremely important for the reliability and safety of aircrafts and ships. Currently, most researches only pay attention to the discharge port and ignore the suction port and the inherent characteristic of the axial pump between both ports, which may cause significant underestimation of fluid ripple especially in the closed-loop hydraulic system. Therefore, the aim of this study is to propose a novel passive fluid ripple attenuator, which can simultaneously reduce discharge and suction pulsation of the axial-piston pump, and adapt to the condition of frequent change of load reversing in closed hydraulic system. First, the phase matching rule is discovered between discharge and suction ripple, and then based on that, the proposed discharge and suction self-oscillation principle is verified through simulation on the phase relationship of the pump internal pistons, instead of considering the two separately as before. The attenuator designed with the concept of the discharge and suction self-oscillation principle is presented, and models of how ripple generates and the attenuator works are represented analytically. The corresponding simulation model is established, and the result indicates that the ripple of both ports of the piston pump is weakened significantly. Moreover, one testing platform is developed, and the experimental study is conducted on the discharge and suction ripple. It proves that the proposed attenuator based on discharge and suction self-oscillation principle can reduce the fluid ripple effectively.
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Yang, Fan, i Bin Deng. "Filtering performance and optimization of double-chamber compound hydraulic attenuators". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 232, nr 18 (28.09.2017): 3250–62. http://dx.doi.org/10.1177/0954406217733293.
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At present, double expansion chamber structures are widely used in the field of acoustic attenuation, and two kinds of double-chamber compound structures for hydraulic attenuators are proposed in this paper. A one-dimensional analytical approach was developed to predict the pressure pulsation attenuation performance of these two structures, and comparisons of insertion loss predictions with experimental results illustrated that the one-dimensional approach is suitable for accurate prediction among the research frequency band. This approach was then used to investigate the effects of porosity and geometrical parameters on the pressure pulsation performance of these two double-chamber compound hydraulic attenuators. To optimize the pressure pulsation attenuation performance at the backwash frequency, parameter optimization was performed for these double-chamber compound structures, and a genetic algorithm based on double-precision floating-point encoding was proposed. The results showed that the range of attenuation frequency bands was widened; however, the effect on low frequency filtering characteristics was limited. The insertion loss of the second structure, which had a partially perforated tube, exhibits a superposition of dome attenuation and axial resonance in the plane wave region. By choosing the length and location of the perforated section to match resonances with the troughs of the pulsation attenuator, a desirable broadband pressure pulsation attenuation can be obtained.
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Reese, D. R., G. M. Mirouh, F. Espinosa Lara, M. Rieutord i B. Putigny. "Oscillations of 2D ESTER models". Astronomy & Astrophysics 645 (styczeń 2021): A46. http://dx.doi.org/10.1051/0004-6361/201935538.
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Context. Recent numerical and theoretical considerations have shown that low-degree acoustic modes in rapidly rotating stars follow an asymptotic formula. In parallel, recent studies have revealed the presence of regular pulsation frequency patterns in rapidly rotating δ Scuti stars that seem to match theoretical expectations. Aims. In this context, a key question is whether strong gradients or discontinuities can adversely affect the asymptotic frequency pattern to the point of hindering its identification. Other important questions are how rotational splittings are affected by the 2D rotation profiles expected from baroclinic effects and whether it is possible to probe the rotation profile using these splittings. Methods. In order to address these questions, we numerically calculate stellar pulsation modes in continuous and discontinuous rapidly rotating models produced by the 2D Evolution STEllaire en Rotation (ESTER) code. This code self-consistently calculates the rotation profile based on baroclinic effects and uses a spectral multi-domain approach, thus making it possible to introduce discontinuities at the domain interfaces without loss of numerical accuracy. The pulsation calculations are carried out using an adiabatic version of the Two-dimensional Oscillation Program (TOP) code. The variational principle is then used to confirm the high numerical accuracy of the pulsation frequencies and to derive an integral formula for the generalised rotational splittings. Acoustic glitch theory, combined with ray dynamics, is applied to the discontinuous models in order to interpret their pulsation spectra. Results. Our results show that the generalised rotational splittings are very well approximated by the integral formula, except for modes involved in avoided crossings. This potentially allows the application of inverse theory for probing the rotation profile. We also show that glitch theory applied along the island mode orbit can correctly predict the periodicity of the glitch frequency pattern produced by the discontinuity or Γ1 dip related to the He II ionisation zone in some of the models. Furthermore, the asymptotic frequency pattern remains sufficiently well preserved to potentially allow its detection in observed stars.
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Christensen-Dalsgaard, Jørgen. "New theoretical developments in stellar pulsation". International Astronomical Union Colloquium 193 (2004): 3–17. http://dx.doi.org/10.1017/s0252921100010277.
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AbstractThe basic properties of stellar oscillations are reasonably well understood, allowing measurements of their frequencies to be used as probes of stellar interiors. The detailed understanding of the processes responsible for the oscillations, in the very broad range of stars observed to pulsate, has improved substantially over the past decade, as have the techniques for asteroseismic investigations on the basis of the observations. Here I provide a brief overview of the theory of stellar oscillations, emphasizing several cases of recent progress, often inspired by new observational developments.
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Cyklis, Piotr, i Przemysław Młynarczyk. "An innovative simulation method for the estimation of the nozzle pressure pulsation attenuation". Journal of Vibration and Control 23, nr 16 (13.12.2015): 2690–703. http://dx.doi.org/10.1177/1077546315619534.
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Pressure pulsations in volumetric compressor manifolds have a high impact on compression power requirement and the reliability of manifold operation. These pulsations induce vibrations, noise, and in some cases, mechanical failure of piping or compressor valves. For pressure pulsation attenuation, different types of mufflers are applied using a design based upon the Helmholtz resonator approach. This design is particularly effective for constant revolution speed compressors. For contemporary applications of variable revolution speed compressors, other pressure pulsation attenuation methods are needed. It is known that different shapes of nozzles can attenuate pressure pulsations, however, they unfortunately increase the compressor power at the same time. The main criterion for nozzle selection is achieving pressure pulsation attenuation that is as high as possible whilst having the lowest possible effect on compressor power. In this paper, innovative computational fluid dynamics (CFD) simulation methodology is applied for the optimisation of nozzle shape and size. The steady flow simulation results correspond with compressor power consumption and impulse flow simulation results are related to pressure pulsation attenuation. This method has been validated on the basis of the experimental results for three different nozzle geometries. For experimental validation, nozzles have been mounted in the variable speed screw compressor discharge manifold.
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Maintz, M., Th Rivinius, D. Baade i S. Štefl. "Astero-Oscillometry: Gauging Stars with Oscillations". International Astronomical Union Colloquium 185 (2002): 222–25. http://dx.doi.org/10.1017/s0252921100016067.
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AbstractAstero-oscillometry is presented as a new method for deriving stellar parameters on the basis of a physical modeling of line profile variability (lpv) caused by nonradial pulsation (nrp). First applications to rapidly rotating B-type stars show that the method is able to yield reasonable stellar parameters. The radii are systematically smaller compared to those derived by conventional methods. This could be attributed to possible effects of rapid rotation on stellar evolution. Since the method requires only one or a few pulsation modes to be excited, it is ideally suited to investigating early-type stars.
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Saio, Hideyuki. "Pulsation of magnetic stars". Proceedings of the International Astronomical Union 9, S301 (sierpień 2013): 197–204. http://dx.doi.org/10.1017/s1743921313014324.
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AbstractSome Ap stars with strong magnetic fields pulsate in high-order p modes; they are called roAp (rapidly oscillating Ap) stars. The p-mode frequencies are modified by the magnetic fields. Although the large frequency separation is hardly affected, small separations are modified considerably. The magnetic field also affects the latitudinal amplitude distribution on the surface. We discuss the properties of axisymmetric p-mode oscillations in roAp stars.
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Shibahashi, H., i M. Takata. "Pulsation of Rotating Magnetic Stars". International Astronomical Union Colloquium 139 (1993): 134. http://dx.doi.org/10.1017/s0252921100117117.
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Recently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of obliquely rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We suppose that the star is rigidly rotating and that the magnetic field is a dipole field and its axis is oblique to the rotation axis. We treat the effects of the rotation and of the magnetic field as perturbations. In doing so, we suppose that the rotation of the star is slow enough so that the effect of the rotation on oscillations is smaller than that of the magnetic field.
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Jin, Faye, Ran Tao, Zhaoheng Lu i Ruofu Xiao. "A Spatially Distributed Network for Tracking the Pulsation Signal of Flow Field Based on CFD Simulation: Method and a Case Study". Fractal and Fractional 5, nr 4 (23.10.2021): 181. http://dx.doi.org/10.3390/fractalfract5040181.
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The pulsating characteristics in turbulent flow are very important physical quantities. There are many studies focused on the temporal characteristics of pulsation. However, the spatial distribution of temporal states with pulsations rarely receives attention. Therefore, the pulsation tracking network (PTN) method is proposed to track the pulsating characteristics of turbulence. Based on the computational fluid dynamics (CFD) simulation result, the PTN is arranged in a specific region of the flow domain. The fast Fourier Transform (FFT) method is used for time-frequency conversion. As shown in the example of trailing-edge vortex-shedding flow over NACA0009 hydrofoil, important pulsation quantities, including the total pulsation intensity, dominant frequencies, amplitude of frequencies, and the phase and phase difference, can be obtained with a high spatial resolution. The source, reason and attenuation of the vortex-shedding frequency fvs and the 2 fvs frequency caused by vortex-interaction are well indicated. The dominant regions of fvs and 2 fvs are shown and analysed. The propagation and attenuation of vortex-shedding induced pulsation are understood in detail. Based on the comparison against traditional analysis, PTN is found to function as a good supplement for the CFD post-processing by tracking unknown temporal and spatial characteristics. These findings represent a potential breakthrough in terms of solving actual pulsation-excited flow problems.
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Liu, Zhan, Junming Cheng, Quanke Feng i Xiaoling Yu. "Effect of a cross-flow perforated tube on pressure pulsation and pressure loss in a reciprocating compressor piping system". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 231, nr 3 (9.08.2016): 473–84. http://dx.doi.org/10.1177/0954406215616981.
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This paper experimentally investigates the effects of a cross-flow perforated tube on the pressure pulsation attenuation and pressure loss in a reciprocating compressor piping network, with particular focus on the structure parameters and installation positions. The results demonstrate that significant pressure fluctuation attenuation and less pressure loss in the whole piping system can be achieved when a well-designed cross-flow perforated tube is installed downstream of the pulsating bottle. The pressure pulsation is reduced as the perforated rate decreases and as the perforated tube length increases, while the hole diameter has little effect upon the pulsation attenuation. In the aspect of reducing pressure loss, the perforated rate should be larger than 0.05 and the hole diameter should be larger than 8 mm. In addition, a pressure pulsation computation model based on the linear acoustic wave theory and transfer matrix method is developed to predict the pulsating pressure in compressor piping systems with an installed cross-flow perforated tube. With favorable agreement between the model prediction and the present experimental results (maximum deviation within 6.8%), the predicted pulsating pressure can be attenuated for the reciprocating compressor piping system with various compressor speeds when a cross-flow perforated tube is reasonably designed and installed.
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Christensen-Dalsgaard, J. "Pulsation Theory and Stellar Structure". International Astronomical Union Colloquium 137 (1993): 483–96. http://dx.doi.org/10.1017/s0252921100018327.
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AbstractObserved periods of pulsating stars provide information about the properties of the stars. As examples I here consider double-mode pulsators, solar-like oscillations and δ Scuti stars. The ongoing expansion in the observational efforts in this area may be expected to lead to increasingly detailed tests of stellar evolution theory.
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Zhang, X. B. "The eclipsing binary IU Per and its intrinsic oscillations". Proceedings of the International Astronomical Union 4, S252 (kwiecień 2008): 429–30. http://dx.doi.org/10.1017/s1743921308023417.
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AbstractThe results of a long-term time-series photometry of the short-period eclipsing binary IU Per are reported. The observation confirms the intrinsic δ Scuti-like pulsation of the star as discovered by previous authors. A photometric solution for the binary system was carried out with the new data. Based on which, the pure oscillation light variations from the mass-accreting primary component were extracted. A Fourier analysis reveals four pulsation modes. Combining with the photometric solution, a preliminary mode identification was given.
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Saio, H. "An Overview of Stellar Pulsation Theory". International Astronomical Union Colloquium 134 (1993): 61–72. http://dx.doi.org/10.1017/s0252921100013932.
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AbstractIn this paper I will give overview of the stellar pulsation theory. Starting with basic equations I will discuss modal properties of oscillations and excitation mechanisms. I also mention briefly the effects of rotation.
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Yang, Fan, i Bin Deng. "Pulsation Attenuation Analysis of Double-Chamber Composite Hydraulic Suppressors with Inserted Conical Tubes". Volume 24, No 3, September 2019 24, nr 3 (wrzesień 2019): 578–85. http://dx.doi.org/10.20855/ijav.2019.24.31401.
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A one-dimensional analytical approach is developed to predict the pulsation attenuation performance of doublechamber compound hydraulic suppressors. The theoretical insertion loss agreed well with experimental results. The need for broadband pressure pulsation attenuation has led to extensive research on the structure improvement. In the present work, the straight-through tube has been replaced by a conical tube and two improved hydraulic attenuator configurations are presented. A parametric study to investigate the effects of different parameters on the research frequencies is included as well. The validity of the models of the improved structures is demonstrated theoretically and experimentally.
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Deng, Xiao Wen, Sun Cai, Yong Xin Feng, Yan Hui Xu i Cong Ma. "Power System Low Frequency Oscillation of Resonance Mechanism Induced by Disturbance of Turbine Governing System". Advanced Materials Research 1008-1009 (sierpień 2014): 441–44. http://dx.doi.org/10.4028/www.scientific.net/amr.1008-1009.441.
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According to the resonance mechanism, power system forced low frequency oscillations can be aroused by power disturbance of prime mover. Therefore, the causes of turbine power disturbance were analyzed. The coupling model between turbine-governing system and power system was established in MATLAB. The possibility of governing system disturbance inducing the variation of control valve position and turbine power was researched in detail. The simulation results indicate that high level variation of control valve can be induced by the rotor speed deviation disturbance, if the speed-droop ratio of turbine-governing system is too small in local running position; power system low frequency oscillations of resonance mechanism might be caused by the disturbance of rotor speed deviation, when it’s frequency is close to power system natural oscillations frequency. Oil-pressure pulsation is easily happened in hydraulic governing system. If the frequency of oil-pressure pulsation is near to power system natural oscillations frequency, power system low frequency oscillations of resonance mechanism can be induced.
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Liu, Yiming, Yueming Gao, Liting Chen, Tao Liu, Jiejie Yang, Siohang Pun, Mangi Vai i Min Du. "A Variable-Volume Heart Model for Galvanic Coupling-Based Conductive Intracardiac Communication". Sensors 22, nr 12 (12.06.2022): 4455. http://dx.doi.org/10.3390/s22124455.
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Conductive intracardiac communication (CIC) has become one of the most promising technologies in multisite leadless pacemakers for cardiac resynchronization therapy. Existing studies have shown that cardiac pulsation has a significant impact on the attenuation of intracardiac communication channels. In this study, a novel variable-volume circuit-coupled electrical field heart model, which contains blood and myocardium, is proposed to verify the phenomenon. The influence of measurements was combined with the model as the equivalent circuit. Dynamic intracardiac channel characteristics were obtained by simulating models with varying volumes of the four chambers according to the actual cardiac cycle. Subsequently, in vitro experiments were carried out to verify the model’s correctness. Among the dependences of intracardiac communication channels, the distance between pacemakers exerted the most substantial influence on attenuation. In the simulation and measurement, the relationship between channel attenuation and pulsation was found through the variable-volume heart model and a porcine heart. The CIC channel attenuation had a variation of less than 3 dB.
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Jeffery, C. S., i H. Saio. "Pulsation in extremely low-mass helium stars". Proceedings of the International Astronomical Union 9, S301 (sierpień 2013): 425–26. http://dx.doi.org/10.1017/s1743921313014877.
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AbstractWe explore the stability of extremely low-mass stars (M < 0.25 M⊙) across a wide range of composition, effective temperature, and luminosity. We identify the instability boundaries associated with radial oscillations. These are a strong function of both composition and radial order (0 ≤ n ≤ 13). The classical blue edge shifts to higher effective temperature and luminosity with decreasing hydrogen abundance. Higher-order modes are more easily excited, and small islands of instability develop. Short-period oscillations have been discovered in the low-mass pre-white dwarf component of the eclipsing binary J0247–25. If its envelope is depleted in hydrogen, J0247–25B is unstable to intermediate-order p modes. Driving is by the classical κ mechanism operating in the second helium ionization zone. The observed periods, temperature and luminosity of J0247–25B require an envelope hydrogen abundance 0.2 ≤ X ≤ 0.3.
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Waelkens, C. "Pulsation and Evolution. An observer’s viewpoint". International Astronomical Union Colloquium 155 (1995): 23–30. http://dx.doi.org/10.1017/s0252921100036733.
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AbstractWe review observational evidence on the interaction between stellar pulsation and evolution. We discuss to what extent observations of pulsating stars with variable amplitudes and pulsation periods have implications on our understanding of stellar structure and evolution. The probable link between mass loss and pulsation in AGB stars and in hot luminous stars appears to be the strongest way in which pulsations affect evolution. We point out the possibility that forced oscillations in the components of binaries may have important consequences on evolution, that could offer an explanation for some classes of peculiar evolved objects.
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Williams, J. E. Ffowcs, i Y. P. Guo. "On resonant nonlinear bubble oscillations". Journal of Fluid Mechanics 224 (marzec 1991): 507–29. http://dx.doi.org/10.1017/s0022112091001854.
Pełny tekst źródłaStreszczenie:
If a bubble were produced with an initial surface distortion, the energy carried by surface modes could be converted to other modes by nonlinear interaction, a conversion that provides a possible mechanism of second generation by bubbles. Longuet-Higgins (1989a,b) has argued that volume pulsation would be excited at twice the frequency of the distortion mode and that the response to such excitation is ‘surprisingly large’ when its frequency is close to the natural resonance frequency of the volumetrical mode. It is shown in this paper that this is feasible only if the driving system is sufficiently energetic to supply the energy involved in those volume pulsations, and that this is not generally the case. In the absence of external sources, the sum of energies in the interacting modes cannot exceed the initial bubble energy; an increase in one mode is always accompanied by a decrease in another. In contrast to any expectation of significant pulsations near resonance, we find that, once modal coupling is admitted, the volumetrical pulsation has very small amplitude in comparison with that of the initial surface distortion. This is because of the constraint of energy, a constraint that becomes more severe once damping is admitted. Our conclusion therefore is that the distortion modes of a bubble are unlikely to be the origin of an acoustically significant bubble response.
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Li, Lei, Kok-Meng Lee, Xiaoping Ouyang i Huayong Yang. "Attenuating characteristics of a multi-element buffer bottle in an aircraft piston pump". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 231, nr 10 (14.12.2015): 1791–803. http://dx.doi.org/10.1177/0954406215622793.
Pełny tekst źródłaStreszczenie:
Pressure pulsation of an aircraft piston pump and accompanying vibrations are often sources of unreliability and fatigue of an aircraft hydraulic energy system. To reduce discharge pressure pulsation, a buffer bottle is usually installed inside the pump for space consideration that generally restricts its chamber volume resulting in a high working frequency range usually well exceeding the pressure pulsation frequencies corresponding to the normal operating speed range of the pump and hard to be adjusted once installed. To meet this challenge, this paper presents a method for designing a multi-element buffer bottle as an integrated fluid filter network formed by sub-elemental circuits (consisting of orifice, pipe and T-off) that can be assembled in an aircraft piston-pump. This design method of a compact fluid filter network is illustrated with a practical example based on a multi-element buffer bottle. Based on impedance models, results of an in-depth numerical investigation analyzing the effects of different buffer-bottle designs, geometrical parameters and adjustable orifice dimensions on pressure pulsation attenuation are discussed. The method for tuning the operating resonant frequency of a multi-element buffer bottle for pressure attenuation using a changeable orifice diameter is demonstrated experimentally confirming the buffer bottle as an attractive alternative to the conventional methods based on large-volume chambers.
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Pinheiro, F. J. G., D. F. M. Folha, M. J. P. F. G. Monteiro, M. Marconi, V. Ripepi i F. Palla. "Oscillations in Young Stellar Objects". International Astronomical Union Colloquium 185 (2002): 352–53. http://dx.doi.org/10.1017/s0252921100016493.
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AbstractWe report the discovery of periodicities in the light curve of the Herbig Ae star V346 Ori. We interpret these variations as the superposition of at least two signals with periods P1=42±6 min and P2=68±12 min resulting from stellar oscillations. The computation of linear non-adiabatic pulsation models for Pre-Main Sequence (PMS) stars reproduces these periods for a 1.5 M⊙ star with Teff= 7300 K and log L/L⊙= 0.74, pulsating in the fundamental and second overtones.
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Berbirenkov, I. A. "Oscillations of a Rotor of the Valve Traction Motor". Izvestiya MGTU MAMI 3, nr 1 (10.01.2009): 12–14. http://dx.doi.org/10.17816/2074-0530-69846.
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The article considers the structure of the valve traction motor with synchronous electromechanical transformer. Oscillations of the rotor of the synchronous motor may be caused by various reasons, e.g.: cyclic work of a traction inverter, pulsation of conductivity of operating air clearance, natural and forced oscillations of the rotor.
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HAN, WEN-BIAO, REMO RUFFINI i SHE-SHENG XUE. "SPACE-TIME EVOLUTION OF ELECTRIC FIELDS IN CORES OF COMPACT STARS". International Journal of Modern Physics: Conference Series 12 (styczeń 2012): 193–97. http://dx.doi.org/10.1142/s201019451200637x.
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Studying the electrodynamics of proton and electron fluids in cores of compact stars, we find oscillations of electron density and electric field around their equilibrium configurations, provided cores undergo a pulsation or trigger of gravitational collapse. These field and density oscillations can possibly lead to observable electromagnetic radiation.
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Kolláth, Zoltán. "Hydrodynamical Modeling of Double-Mode Pulsation". International Astronomical Union Colloquium 176 (2000): 356–61. http://dx.doi.org/10.1017/s0252921100058048.
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AbstractThe hydrodynamical modeling of steady double-mode (DM) pulsations has been a long-standing quest. Recent improvements in turbulent-convective pulsation codes provide a natural way to calculate nonlinear DM oscillations. The eddy viscosity plays a crucial role in these models. We present models both for RRd and beat Cepheid variables and for different chemical compositions. Simple nonresonant amplitude equations capture the DM phenomenon, giving an overview of modal selection on the HR diagram.
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Gautschy, A. "Recent Developments in Stellar Pulsation Theory". International Astronomical Union Colloquium 155 (1995): 31–41. http://dx.doi.org/10.1017/s0252921100036745.
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AbstractA major driving force behind the efforts invested in stellar pulsation calculations in the recent years was certainly the success story of the new generation of opacity data. The new opacities did not only solve old problems but they also increased the complexity of quantitative stellar pulsation studies. Besides surveying the consequences of the new generation of stellar opacities for pulsation theory we also address more formal aspects of dealing with stellar oscillations. The section reviewing recent literature on the application of stellar pulsation theory to different classes of pulsating variables is strongly biased towards the high-luminosity part of the Hertzsprung-Russell (HR) diagram. We finish by mentioning recent changes in our beliefs concerning the envelope structure of oscillating white dwarfs.
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KRESTIN, Evgenyi A. "THE ISSUE OF PULSATING FLOW IN THE SLIT OF VARIABLE HEIGHT CLEARANCES". Urban construction and architecture 6, nr 2 (15.06.2016): 48–55. http://dx.doi.org/10.17673/vestnik.2016.02.10.
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Dynamic liquid layer is obtained in the gap of variable height. It is found total solution as the sum of the discharge currents with a constant pressure drop and oscillating components: Differential pressure pulsation and wall vibrations. The formulas for fluid pulsation rate limiting cases are obtained. The article identifies border of quasistationary model of viscous fluid from the fluid changes the dimensionless frequency of oscillations in a slot gap.
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Antia, H. M., S. M. Chitre i D. O. Gough. "On the excitation of solar five-minute oscillations". Symposium - International Astronomical Union 123 (1988): 371–74. http://dx.doi.org/10.1017/s0074180900158371.
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A simple prescription for the dynamics of convection perturbed by stellar pulsation is used in an estimation of the growth rates of solar five-minute modes. Convection appears to enhance the excitation of the modes, and the maximum in the growth rate versus frequency found previously when oscillatory convective perturbations were ignored is still present.
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Takeuti, Mine, i Yasuo Tanaka. "A Model Oscillator of Irregular Stellar Variability". International Astronomical Union Colloquium 108 (1988): 195–96. http://dx.doi.org/10.1017/s0252921100093805.
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Stellar pulsation is one of the condidates for strong mass loss from red giant stars. Recent investigations have shown sporadic outbursts of the pulsation can eject a considerable mass from the stars. Such a sporadic increase of the amplitudes seems to have a connection with the irregularity found in the pulsations. Recently the iregular propreties in stellar pulsation are investigated in the relation to nonlinear dynamics (see for instance Perdang, 1985). Unfortunately no single model oscillator of a star of which the equilibrium state is dynamically stable had been found. In the present paper, we shall discuss a simple oscillator which shows period-doubling and chaotic, that is, irregular oscillations.
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Lu, Zhaoheng, Ran Tao, Faye Jin, Puxi Li, Ruofu Xiao i Weichao Liu. "The Temporal-Spatial Features of Pressure Pulsation in the Diffusers of a Large-Scale Vaned-Voluted Centrifugal Pump". Machines 9, nr 11 (2.11.2021): 266. http://dx.doi.org/10.3390/machines9110266.
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A large-scale, vaned-voluted centrifugal pump can be applied as the key component in water-transfer projects. Pressure pulsation will be an important factor in affecting the operation stability. This paper researches the propagation and spatial distribution law of blade passing frequency (BPF) and its harmonics on the design condition by numerical simulation. Experimental and numerical monitoring is conducted for pressure pulsation on four discrete points in the vaneless region, which shows that the BPF is dominant. The pulsation tracking network (PTN) is applied to research propagation law and spatial distribution law. It provides a reference for frequency domain information and visualization vaned diffuser. The amplitude of BPF and its harmonics decays rapidly in the vaneless region. BPF and BPF’s harmonics influence each other. BPF has local enhancement in the vaneless region when its harmonics attenuate. In the vaned diffuser, the pulsation amplitude of BPF attenuates rapidly, but the local high-pressure pulsation amplitude can be found on the vane blade concave side because of obstruction and accumulation of the vaned diffuser. In the volute, the pulsation amplitude of BPF is low with the decelerating attenuation. This study provides an effective method for understanding the pressure pulsation law in turbomachinery and other engineering flow cases.
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Motriuk, R. W., i D. P. Harvey. "Centrifugal Compressor Modifications and Their Effect on High-Frequency Pipe Wall Vibration". Journal of Pressure Vessel Technology 120, nr 3 (1.08.1998): 276–82. http://dx.doi.org/10.1115/1.2842058.
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High-frequency pulsation generated by centrifugal compressors, with pressure wavelengths much smaller than the attached pipe diameter, can cause fatigue failures of the compressor internals, impair compressor performance, and damage the attached compressor piping. There are numerous sources producing pulsation in centrifugal compressors. Some of them are discussed in literature at large (Japikse, 1995; Niese, 1976). NGTL has experienced extreme high-frequency discharge pulsation and pipe wall vibration on many of its radial inlet high-flow centrifugal gas compressor facilities. These pulsations led to several piping attachment failures and compressor internal component failures while the compressor operated within the design envelope. This paper considers severe pulsation conditions at an NGTL compression facility which resulted in unacceptable piping vibration. Significant vibration attenuation was achieved by modifying the compressor (pulsation source) through removal of the diffuser vanes and partial removal of the inlet guide vanes (IGV). Direct comparison of the changes in vibration, pulsation, and performance are made for each of the modifications. The vibration problem, probable causes, options available to address the problem, and the results of implementation are reviewed. The effects of diffuser vane removal on discharge pipe wall vibration as well as changes in compressor performance are described.
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Kryuchkov, A. N., M. A. Еrmilov, E. N. Еrmilova, I. V. Balakhonov i A. N. Vidyaskina. "Development of a pulsation dampener for hydraulic systems of power plants". VESTNIK of Samara University. Aerospace and Mechanical Engineering 18, nr 2 (2.07.2019): 146–55. http://dx.doi.org/10.18287/2541-7533-2019-18-2-146-155.
Pełny tekst źródłaStreszczenie:
The article considers the development of a capacitance-type pressure pulsation dampener. The pressure pulsation dampener is used to reduce the noise of hydraulic systems which are subject to increased requirements for vibro-acoustic characteristics. The developed pressure pulsation dampener is a flexible element with negligible hydraulic resistance. This element contains a gas cavity the pressure in which depends on its deformation. Overall dimensions of the dampener under investigation do not exceed the dimensions of a standard pipeline. This property, along with its low hydraulic resistance, is an advantage over its analogues. The article analyzes the known pressure pulsation dampeners and considers two design schemes of the proposed device. The experimental results of analyzing the dampener that showed its high efficiency (5 ... 40 dB) in a wide range of pressure oscillations in the fluid flow (20 ... 3000 Hz) are presented.
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Shan, Chang Ji, Yi Duo Bian i Nan Xu. "The Performance Comparison Analysis on Hydraulic Muffler of Quality Room with Parallel Line". Applied Mechanics and Materials 709 (grudzień 2014): 125–29. http://dx.doi.org/10.4028/www.scientific.net/amm.709.125.
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Though establishing physical modeling of porous hydraulic mufflers, it could derive the transfer matrix. Porous hydraulic muffler attenuation characteristic curve is obtained by MATLAB programming. Through the analysis of characteristic curve, the result showed that the porous hydraulic muffler can effectively absorb fluid pulsation and it is concluded that the change of the structure parameters affect on the attenuation characteristics. It can provide a reference for related research platform.
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Randall, S. K., G. Fontaine, S. Charpinet, V. Van Grootel i P. Brassard. "Origin and pulsation of hot subdwarfs". Proceedings of the International Astronomical Union 9, S301 (sierpień 2013): 289–96. http://dx.doi.org/10.1017/s1743921313014476.
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AbstractWe briefly introduce hot subdwarfs and their evolutionary status before discussing the different types of known pulsators in more detail. Currently, at least six apparently distinct types of variable are known among hot subdwarfs, encompassing p- as well as g-mode pulsators and objects in the Galactic field as well as in globular clusters. Most of the oscillations detected can be explained in terms of an iron opacity mechanism, and quantitative asteroseismology has been very successful for some of the pulsators. In addition to helping constrain possible evolutionary scenarios, studies focussing on stellar pulsations have also been used to infer planets and characterize the rotation of the host star.
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Clement, Maurice J. "Pulsation in Rapidly Rotating Stars". Symposium - International Astronomical Union 162 (1994): 117–27. http://dx.doi.org/10.1017/s0074180900214691.
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The line-profile variables observed on the upper main sequence have been interpreted by some astronomers to be the manifestation of nonaxisymmetric oscillations. More specifically, most of these variables can be modelled by prograde or corotating equatorial waves. In the absence of rotation, these waves have surface velocity distributions which are given simply by spherical harmonics. Unfortunately, the corresponding velocity fields in the presence of rotation are much more difficult to calculate. In this paper, I will summarize what is known about the effect of rapid rotation on the normal mode eigenfunctions of main sequence stars. The principal conclusions are as follows: Low-order, axisymmetric modes couple very strongly to rotation and their velocity distributions are very much different from those of their zero-rotation counterparts. On the other hand, higher-order (shorter wavelength), nonaxisymmetric modes couple only weakly to rotation and, therefore, retain many of the spherical harmonic properties that they possess in the absence of rotation.
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Kalinin, Yevhen, Irina Lebedeva i Dmytro Lysytsia. "Dynamic effects in multi-mass rheonomic systems at high-frequency ripple of "forms" of oscillations". Advanced Information Systems 5, nr 3 (18.10.2021): 137–41. http://dx.doi.org/10.20998/2522-9052.2021.3.18.
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The subject of research in the article is the degeneration of the first form with a monoharmonic change in the form factor and provided that the pulsation frequency of the "forms" of oscillations reaches the second partial frequency. The goal is to assess the possibility of degeneration of the i-th form of oscillations under various laws of change in the exciting effect and to analyze this phenomenon. The objectives of the study are to build principles for assessing the impact of high-frequency pulsations of system parameters on the free oscillations of the latter. Applied methods: description of dynamic models by differential equations; frequency analysis; formation of amplitude-frequency characteristics. The obtained results: for a dynamic model with certain indicators of the leading and driven links, it was determined that with a harmonious change in the motion function with a pulsation frequency that exceeds one, when the ratio of the damping coefficients is greater than one, the effect of degeneration of the first mode of vibration is observed, as a result of which the oscillation frequency of the driven link practically corresponds to the second form. The practical significance of the work lies in the construction of a model for the formation of frequency characteristics of a dynamic model with a high-frequency pulsation of the parameters of the latter. To identify these effects, one has to abandon the traditional ideas about the smallness of inertial components caused by the nonstationarity of vibration modes.
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Yang, Chunxia, Jiawei Wu, Dinge Xu, Yuan Zheng, Xueyuan Hu i Zhe Long. "Analysis of Flow Field Characteristics and Pressure Pulsation in Horizontal Axis Double-Runner Francis Turbine". Water 13, nr 19 (27.09.2021): 2671. http://dx.doi.org/10.3390/w13192671.
Pełny tekst źródłaStreszczenie:
Horizontal axis double-runner Francis turbines have great advantages in the development of small hydropower plants, but the arrangement of double runners aggravates the complexity of the water flow between runners, and the mutual influence of the two runners cannot be ignored. In order to explore the relationship between the performance and the internal flow field and investigate the pressure pulsation characteristics of the double-runner Francis turbine, the steady and unsteady numerical analysis of the full flow channel of a prototype turbine was carried out based on the Realizable k-epsilon model and the polyhedral mesh method. The results show that the relationship between the average efficiency of the two runners and the flow difference between the runners is negatively correlated. As the flow rate difference between the runners on both sides increases, the average efficiency of the runners decreases. The draft tube flow of a horizontal-axis turbine has a profound effect on the flow field characteristics in the runner. When the working conditions change, the turning and converging timing of the mainstream at the outlet of the two runners will change. The movement of the mainstream promotes the change in location of the dead water zone. The existence of the vortex zone makes the pressure distribution at the outlet of the runner uneven, which is an important reason for the asymmetry of the flow in the runner. The analysis of pressure pulsation and its frequency spectrum shows that when the working conditions change, the low-frequency, strong pressure pulsation area on the surface of the guide vane will regularly migrate between the two runners, while the high-frequency pressure pulsation that occurs in the bladeless zone will dissipate in the runner. The doubling of the blade frequency on the pressure surface and back surface of the blades gradually attenuates with the increase of frequency. The pressure pulsation attenuation on the surface of the high-position blade conforms to the linear law, and the attenuation of the pressure pulsation on the surface of the low-position blade conforms to the exponential law. The research in this paper provides a certain reference value for revealing the flow field mechanism and pressure pulsation characteristics of the double-runner Francis turbine.
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Pacheco, Eduardo Janot, Laerte B. P. de Andrade, Marcelo Emilio, Juan Carlos Suárez i Andressa Jendreieck. "Non-radial pulsations in the CoRoT Be Star 102761769". Proceedings of the International Astronomical Union 6, S272 (lipiec 2010): 507–8. http://dx.doi.org/10.1017/s1743921311011203.
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AbstractWe investigate non-radial pulsations of the CoRoT IR1 Be Star 102761769, with a projected stellar rotation estimated to be 120±15 km/s. If the star is a typical galactic Be star it rotates near the critical velocity. We propose an alternative scenario, where the star could be seen nearly equator-on rotating at a relatively moderate velocity say, ≈ 120 km/s and therefore the nonradial oscillations could be modeled. In order to identify the pulsation modes of the observed frequencies, we computed a set of models representative of CoRoT 102761769 by means of the adiabatic pulsation package FILOU. Results indicate that the two frequencies are compatible with a high-g mode as predicted by pulsation models of Be stars.
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Kovacs, G. "Is Delta Scuti Star Seismology Possible?" International Astronomical Union Colloquium 111 (1989): 271. http://dx.doi.org/10.1017/s0252921100011799.
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AbstractThe direct fit of theoretical pulsation frequencies to the observations (i.e. stellar seismology) proved to be a very efficient tool in the study of solar oscillations. In the case of other multiperiodic variables, like δ Scuti stars, Ap stars and white dwarfs the method suffers from the disturbing abundance of possible nonradial modes. Colour and/or radial velocity (or line profile) measurements can narrow down the number of possibilities, but these kinds of data are not often available with the desired accuracy and sampling rate. Since pulsational frequencies are the most readily and accurately computed and measured quantities of pulsation, we address the question of the accurate fit of the nonradial pulsation frequencies to the observations in the case of δ Scuti stars.
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Shibahashi, H. "The Effect of a Close Binary upon Stellar Pulsation". International Astronomical Union Colloquium 185 (2002): 82–83. http://dx.doi.org/10.1017/s0252921100015591.
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AbstractThrough tidal deformation of the equilibrium state, the p-mode oscillations may show apparently complicated features. I discuss the fundamental characteristics of the tidally forced oscillation, and show the possibility that it leads to a triplet fine structure in the frequency spectrum of p-modes.
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Handler, G., L. A. Balona, R. R. Shobbrook, C. Koen, A. Bruch, E. Romero-Colmenero, A. A. Pamyatnykh i in. "Asteroseismology and Forced Oscillations of the Simultaneous p-Mode and g-Mode Pulsator HD 209295". International Astronomical Union Colloquium 185 (2002): 90–93. http://dx.doi.org/10.1017/s0252921100015633.
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AbstractWe report the discovery of both intermediate-order gravity mode and low-order pressure mode pulsation in the same star, HD 209295. It is therefore both a γ Doradus and a δ Scuti star, which makes it the first confirmed member of two classes of pulsating star.This object is located in a close binary system with an unknown, but likely degenerate companion in an eccentric orbit, and some of the γ Doradus pulsation frequencies are exact integer multiples of the orbital frequency. We suggest that these pulsations are tidally excited. HD 209295 may be the progenitor of an intermediate-mass X-Ray binary.
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Shan, Chang-ji, Yi-duo Bian, Ting-ting Dai, Cai Yan, Guo-fang Du i Hai-tao Yang. "The Design of Follow-up Hydraulic Muffler Based on Spring-Damp Regulating Device". E3S Web of Conferences 79 (2019): 01006. http://dx.doi.org/10.1051/e3sconf/20197901006.
Pełny tekst źródłaStreszczenie:
The follow-up hydraulic muffler can make the natural frequency of the muffler equal to systematic pulsation frequency in time by changing the section area of the quality chamber so as to achieve the best attenuation effect. In this paper, a spring-damp regulator is installed on the basis of the hydraulic muffler, and the static and dynamic characteristics of the follow-up hydraulic muffler are analyzed by measuring the rotational speed of the pump with the sensor. The results show that the hydraulic muffler based on the spring-damp regulator can effectively attenuate the pulsation.