Analysis Of Pulsations Research Articles

Dynamic characteristic analysis of pressure pulsations of a pump turbine in turbine mode utilizing variational mode decomposition combined with Hilbert transform

Mastering the dynamic characteristics of the pressure pulsations is necessary to ensure high efficiency and security, and extend the life span of the pump turbine (PT) and the pumped storage system. In this research work, the experimental investigation was conducted with the aid of the high-precision equipment to measure the pressure pulsation signals from a PT in the turbine direction. The variational mode decomposition (VMD) and Hilbert marginal spectrum (HMS) are adopted to improve the extraction capabilities of dynamic characteristics in the signals. Through carrying out the VMD, the pressure pulsation signals can be decomposed into several modes. By calculating the average instantaneous frequencies, energy ratios, and correlation coefficients of these modes, the dominant modes are determined, and the trends of the values of root mean square of them with load at typical monitoring points can reflect the dynamic transition of the internal flow status. To be specific, the entire load range can be segmented into three load areas to analyze different physical sources of pressure pulsations. In the low load area, they are mainly induced by the unstable flows of blade passing frequency (BPF) in the vaneless area (VA) and the low-frequency vortex strips in the draft tube (DT). In the intermediate load area, they are mainly caused by the low-frequency vortex strips in the DT. In the high load area, they are mainly caused by the phenomenon of rotor-stator interaction in the VA. By conducting the HMS based on VMD, it can be found that the head changes will affect the amplitudes of dominant frequencies of pressure pulsation signals. Based on the current signal processing results, the high-sensitivity indexes can be used to characterize the generation and dynamic propagation of pressure pulsations.

Analysis of Pc3 And Pc4 Geomagnetic Pulsations over the Amazon Region

The geomagnetic field produces aeronomic phenomena according to the Earth’s magnetic latitude. In South America, we find two important phenomena: the South America Magnetic Anomaly (SAMA) and the Equatorial Electrojet (EEJ). This study aimed to analyze the amplitudes of continuous magnetic pulsations (Pc3 and Pc4 type) in magnetic stations located between EEJ and SAMA. Based on the Dst index, we acquired data from four monitoring stations on quiet and disturbed days in August 2018. The magnetic pulsations in the equatorial region are related to the type of ionospheric conductivity, such as Cowling’s conductivity, contributing to amplifying the damping of Pcs wavelength. Finally, we found evidence that suggests a potential influence of the EEJ behavior on the amplitudes of Pc3 and Pc4. Therefore, the present study contributes to future research to fully understand the nature and extent of this influence.

Pulsation Analysis of High-Amplitude δ Scuti Stars with TESS

In this work, the pulsation analysis is performed on 83 high-amplitude δ Scuti stars (HADS), which have been observed by the Transiting Exoplanet Survey Satellite. The results show that 49 of these HADS show single-mode pulsation, 27 of them show radial double-modes pulsation (in which 22 of them pulsate with the fundamental and first overtone modes and five of them pulsate with the first and second overtone modes), and seven of them show radial triple-modes pulsation (three of which are newly confirmed triple-mode HADS). The histogram of the fundamental periods and the ratios between the fundamental and first overtone periods show bimodal structures, which might be caused by the stellar evolution in this specific phase. Most of the radial triple-mode HADS have a fundamental amplitude of 41–54 mmag, and 50% of them have similar amplitudes of the fundamental and first overtone pulsation modes. All these hints require further confirmation not only in observations with more HADS samples, but also in theoretical models with suitable treatments of stellar evolution and pulsation.

Time–frequency signal analysis of flow pulsation in siphon outlet conduit based on HHT considering the pump‐conduit interaction

AbstractThe unsteady three‐dimensional numerical simulation calculation of the vertical axial flow pump device is performed based on CFD to examine the pressure pulsation and energy distribution features of the water flow within the siphon outlet conduit (SOC) under the hydraulic coupling of the pump and the flow conduit. The pressure pulsation signals (PPS) of monitoring points are decomposed using the Hilbert–Huang approach via empirical mode decomposition (EMD) and Hilbert spectrum analysis. The results show that the PPS of monitoring points of the SOC has no obvious periodicity. The low‐frequency range below 20 Hz serves as the primary frequency, and the energy ratio of the high‐frequency signal above 700 Hz is less than 1%. Under the condition of a small flow rate 0.3Qbep, there is obvious high‐frequency pulsation above 500 Hz at the inlet of the upstream section of the SOC, and there are periodic components distributed around 200 Hz. The energy of the pressure pulsation is primarily focused in the low‐frequency range below 40 Hz at the SOC outlet section. The PPS at the top and bottom monitoring points of the hump section are consistent, and the pressure pulsation energy (PPE) is mainly concentrated in the low frequency below 40 Hz. In both the big flow condition (1.2Qbep) and the optimal flow condition (1.0Qbep), the PPE of the monitoring points at the top of the hump section is distributed in the middle and low‐frequency band below 40 Hz, and the energy of monitoring points at the bottom of the hump section is concentrated in the low‐frequency band below 20 Hz, accounting for more than 70%. When the flow rate increases from 0.3Qbep to 1.2Qbep, the peak value of the pressure pulsation coefficient at the main frequency of each monitoring point at the top of the hump section changes little, and the peak value of the pressure pulsation coefficient at the main frequency of each monitoring point at the bottom increases first and then decreases. From the upstream section to the hump section of the SOC, the average frequency of each intrinsic mode function (IMF) of the PPS under different flow conditions shows an overall increasing trend. From the hump section of the SOC to its outlet, the average frequency of each IMF of the PPS decreases under the conditions of 1.0Qbep and 1.2Qbep, and there is no obvious change under the condition of 0.3Qbep.

Analysis and treatment of gas pulsation in the pipeline of a hyper compressor

The compressor discharge pressure of a polyethylene plant in Yanshan Petrochemical Company exceeds 170 MPa, and the gas pulsation in some pipe sections is large, which leads to strong vibration of pipeline elements. The acoustic modeling and analysis of gas pulsation characteristics were carried out around the hyper compressor pipeline system of the polyethylene device. The non-invasive strain–pressure method was used to indirectly measure the pressure pulsation data in the high-pressure pipeline, and the test results were in good agreement with the simulations. On this basis, based on the acoustic analysis, the treatment measures to effectively suppress the gas pulsation in the high-pressure pipeline were further proposed.

The Analysis of Cavitation Flow and Pressure Pulsation of Bi-Directional Pump

A bi-directional pump is designed by using S-shaped hydrofoil, is the most convenient way to achieve bi-directional operation. In this paper, high-speed photography is used to visualize the flow field characteristics of the bidirectional pump under different cavitation numbers, and the flow field changes caused by cavitation are quantitatively analyzed in combination with the pressure pulsation sensor. The results show that the operation efficiency of the bidirectional pump in reverse operation is lower than that in forward operation. Tip clearance cavitation occurs on both suction and pressure surfaces of the impeller under reverse operation and large flow. In reverse operation, the influence of guide vane on the main frequency of pressure pulsation in the impeller is obvious. The quasi-periodic vertical cavitation flow phenomenon increases the amplitude of pressure pulsation in the impeller and becomes the main component of the internal flow in the bidirectional axial flow pump.

Analysis of wave propagation and pulsation in an elastic tube using a diaphragm pump

In this research, the flow wave propagation, speed, and pulsation suppression in an elastic tube were studied using a diaphragm pump. The flow fluctuations with shocking pressure fluctuations occur in the elastic tube because the check ball was blocked, thereby preventing reverse flow. Consequently, the check ball is one of the causes of pulsating flows in diaphragm pumps. However, only a few studies have analyzed the relationship among the check ball movement, pressure, and flow fluctuations. In this study, we constructed several elastic tube experiments: (i) single-tube model; (ii) two-tube model. To predict the flow wave propagation and pulsation in an elastic tube, we developed an axisymmetric theoretical model and compared into the experimental results. Based on our study, the main results were as follows: the relationship among the check ball movement, pressure, and flow fluctuations showed that the pressure and flow rate pulsation were caused by the asymmetry of the check ball movement. Additionally, we observed that the theoretical flow wave propagation trend had a good agreement with the experimental results, although the flow wave speed in the urethane-tube experiment differed considerably from the theoretical prediction. Furthermore, the amplitude of the pulsation increased considerably owing to the reflected wave at the tube exit, although it did not increase when the resistance was added at the exit. Finally, we observed that the pulsation reduced more in the silicon tubes compared to the urethane tubes because the deformation of the silicon tubes was larger than that of the urethane tubes.

Time-harmonic analysis of acoustic pulsation in gas pipeline systems using the Finite Element Transfer Matrix Method: Theoretical aspects

Structural vibration of gas pipeline systems can be strongly affected by the response of the acoustic domain represented by the gas being transported through pressurized pipes, cylinders and other related components. The resultant Acoustically Induced Vibration (AIV) can be a cause of failure, for example, in reciprocating compressor systems, where the discharge and suction pulsations are the main source of excitation. The objective of this work is to explore and enhance the use of the Finite Element Transfer Matrix Method (FETM) for solving time-harmonic acoustic problems related to AIV, whose results can be used to analyze pulsation in piping systems. Four different damping models are explored and implemented (apart from the classical undamped model) resulting in five different acoustic elements for the quiescent fluid case. In addition, two different damping models are analyzed for the case of a fluid with mean flow, and implemented through two flow-acoustic elements. The physical behavior of certain typical junctions is also investigated, represented by acoustic and flow-acoustic length corrections, and an FETM formulation is proposed to account for local non-linear effects in transfer impedance elements. Also, a discussion related to the minimum and maximum FETM element sizes is presented. A critical analysis of the effectiveness of the whole FETM strategy is performed using a variety of representative gas pipeline geometries as application examples with a particular set of boundary conditions for quiescent and moving fluid medium. Nodal pressure frequency plots of cases considering all the presented acoustic and flow-acoustic elements, and related damping models, are presented. Coherent results were achieved using the procedure when frequency plots are compared with experimental data and 3D FEM equivalent models.

Alex magnetometer and telluric station in Egypt: First results on pulsation analysis

This study presents the first results of a newly installed ground-based station Alex Magnetometer and Telluric Station (AMTS) located in Alexandria governorate in Egypt (geographic coordinate: 30° 51.68′ N, 29° 33.67′ E). The station consists of a fluxgate digital magnetometer and a two-channel digital Long Period Telluric Recorder (LPTR). The station commenced operation on October 12th, 2021, by providing real-time data of the geoelectric and geomagnetic field components. Despite the low solar activity, the AMTS detected several signatures of geomagnetic storms. An illustrative case study was conducted on the strong geomagnetic storm of November 4th, 2021. The magnetic field components recorded by the station demonstrated a prompt increase synchronized with the Sudden Storm Commencement (SSC) captured by the ACE satellite arriving at 19:42 UT on November 3rd, 2021. The three geomagnetic field components recorded by the AMTS during the storm were consistent with the nearby INTERMAGNET stations. The digital fluxgate magnetometer’s high sampling frequency (400 Hz) and the LPTR with a sampling frequency (1 Hz), allowed us to capture all ULF pulsations. The structural pearl-shaped Pc1 pulsation was obtained in all phases of the geomagnetic storm with repetitive oscillations in the main storm phase. The wavelet analysis of micropulsations recorded at AMTS showed a high coherence with the nearby-four INTERMAGNET stations demonstrating high data integrity and reliability. The magnetometer and telluric measurements at the AMTS will fill the data gap in the northern section of Africa and allow us to study geoelectric and geomagnetic micropulsations in the region.

Statistical Analysis of Pi2 Pulsations Observed by Van Allen Probes

AbstractThe relative importance of propagating and cavity mode waves remains an important question regarding the generation of Pi2 pulsations detected on the ground. To determine the wave mode, we statistically generate spatial maps of magnetospheric oscillations that are coherent with ground Pi2 pulsations. The magnetospheric observations were made by the two Van Allen Probes spacecraft over a 7‐year period. The amount and quality of the spacecraft data allow us to investigate the mode structure of Pi2 pulsation in ways that were not possible in previous studies. We use the H component of low‐latitude ground Pi2 pulsations detected in the 22–02 magnetic local time (MLT) sector as the reference signal to generate L‐MLT and meridional maps of the coherence, amplitude, and phase of the magnetospheric electric and magnetic field components defined in magnetic field aligned coordinates. We identify low‐frequency and high‐frequency components in Pi2 power spectra, and we are able to determine the mode structure of the high‐frequency events for the first time. The maps demonstrate that the poloidal components have higher coherence than the toroidal components. For each frequency component, the maps of the poloidal components agree with those of cavity mode oscillations obtained in a numerical simulation using realistic models for the magnetospheric mass density and magnetic field. This result is conclusive evidence of the cavity mode nature of Pi2 pulsations detected in the inner magnetosphere.

Influence of Guide Vane Profile Change on Draft Tube Flow Characteristics of Water Pump Turbine

In order to study the influence of the change of the guide vane airfoil on the flow characteristics in the draft tube of a reversible hydraulic turbine, a reversible hydraulic turbine was used as the object of study, and the effect of the change on the flow pattern, energy loss, and pressure pulsation in the draft tube area was studied based on the SST k-ω turbulence model. The results show that under low flow conditions, the modified movable guide vane directly affects the direction and speed of water entering the draft tube, reduces the density of vortex in the draft tube area, reduces the impact on the near wall of the draft tube during the rotation of the vortex belt, and improves the stability of the unit operation. The turbulent energy comparison graph shows that the energy loss in the bent elbow section and the diffusion section of the draft tube is reduced, and the energy return coefficient of the draft tube is improved by calculating that the energy recovery level of the draft tube is improved under different operating conditions. A comparative analysis of the pressure pulsation in the draft tube area before and after the modification in combination with the development of the vortex belt shows that the modified movable guide vane effectively reduces the vibration intensity in the draft tube area and improves the stable operation threshold of the unit.

Comprehensive analysis of southern eclipsing systems with pulsating components: The cases of HM Pup, V632 Sco, and TT Vel

This work presents an extensive analysis of the properties of three southern semi-detached eclipsing binaries hosting a pulsating component, namely HM Pup, V632 Sco, and TT Vel. Systematic multi-filtered photometric observations were obtained using telescopes located in Australia and Chile mostly between 2018 and 2021. These observations were combined with data from the Transiting Exoplanet Survey Satellite (TESS) mission for a detailed analysis of pulsations. Spectral types and radial velocities were determined from spectra obtained with the Australian National University’s 2.3 m telescope and Wide Field Spectrograph. The data are modelled and the absolute parameters of all components are derived. The light curve residuals are further analysed using Fourier transformation techniques for the determination of the pulsation frequencies. Using theoretical models, the most probable modes of the principal oscillations are also identified. Eclipse-timing variation analysis is also carried out for all systems and the most likely mechanisms modulating the orbital period are proposed. The physical properties of these systems are compared with other similar cases and the locations of their components are plotted in the Mass-Radius (M−R) and Hertzsprung-Russell diagrams. Finally, the pulsational properties of the oscillating components are compared with currently known systems of this type within the orbital-pulsation period and log g-pulsation period diagrams. These systems are confirmed as oscillating eclipsing Algol-type systems (oEA stars), as the primary components are pulsating stars of δ Scuti type, with evidence of mass flow from the evolved secondary components present in their Na I D spectra.

Hunting for overlooked eccentric eclipsing binaries from ASAS-3 survey

We present the results of searching for new candidates of eclipsing binaries with eccentric orbits in the ASAS Catalog of Variable Stars (ACVS) using publicly available data from the All Sky Automated Survey (ASAS) and the Transiting Exoplanet Survey Satellite (TESS). Unsupervised machine learning techniques were applied to find anomalies among the light curves of eclipsing binaries. The light curves modeling were performed using JKTEBOP code. The pulsation analysis was done with FAMIAS. We identified 19 new eclipsing binary candidates with non-zero eccentricities in the ACVS, including 10 candidates with eccentricities e ≥ 0.1. Estimates of eccentricities are given. We also report on possible presence of the small-amplitude stellar pulsations at least in two of the reported systems.

Pressure pulsation analysis of runner and draft tube of pump turbine under different working conditions

As the core component of pumped storage power station, the pump turbine usually needs to adjust the operating condition point according to the electricity demand during operation. Pressure pulsation is an inevitable phenomenon in the operation of pump turbine, which affects the safe and stable operation of the unit. In this paper, the method of combining numerical simulation and experiment is adopted to carry out three-dimensional full flow channel numerical simulation of the pump turbine by using CFD. The flow pattern and pressure pulsation of the runner and draft tube of the pump turbine were analyzed at the three working conditions of PL (50% maximum load), BEP (70% maximum load) and HL (90% maximum load). It is found that under the three conditions, the pressure pulsation from the leafless area to the downstream of the draft tube shows a weakening trend. Because the flow pattern in the bladed area of the unit is poor, the pressure pulsation in the bladed area is the most obvious. From low load to high load, the pressure pulsation tends to weaken at first and then increase. Combined with flow pattern analysis and vortex analysis, it can be concluded that the number and scale of vortex flow are positively correlated with the pressure pulsation, and the vortex flow inside the unit is an important factor that causes the flow disorder inside the unit, and then becomes an important factor that affects the pressure pulsation inside the pump turbine unit.

Control and Dynamic Characteristics Analysis for the Double-Compound Axial Piston Pump Based on Working Conditions

The periodic flow and pressure pulsation of the axial piston pump can lead to periodic vibration, noise, and even damage to various components in the hydraulic system. Therefore, the dynamic characteristics analysis of the axial piston pump in the hydraulic system is of great significance for reducing vibration and noise in the hydraulic system and improving efficiency. The double-compound axial piston pump is the key component of a high power and large flow hydraulic power system, which has a special power control mode. In this paper, the working and control principles of the double-compound axial piston pump are analyzed, the numerical model of the double-compound axial piston pump is established, and the effectiveness of the model is verified through experimental tests. The constant power control characteristics of the double-compound axial piston pump under different power settings and the variable power control characteristics under the rated load pressure are analyzed. By analyzing the dynamic characteristics of the double-compound axial piston pump, the influence of different working conditions on the dynamic characteristics is investigated. The results show that the output efficiency of the double-compound axial piston pump is higher when the output flow is larger. When the piston chamber works in the closed pre-compression pressure zone and the closed pre-release pressure zone, oil backflow occurs. The oil backflow in the piston chamber seriously intensifies the outlet flow pulsation of the double-compound axial piston pump. The flow pulsation rate is positively correlated with load pressure and power control pilot pressure, while negatively correlated with spindle speed. The paper provides a basis for the analysis and optimization of power control, flow pulsation, fluid vibration, and noise of the double-compound axial piston pump.

Effect of the pressure balance device on the flow characteristics of a pump-turbine

Pump-turbine plays a significant role in the pumped storage station, and it is troubled by unreasonable hydraulic thrust. Some pressure balance devices have been adopted to ensure the safety of the pump-turbine unit, but the effect mechanism has not been numerical studied. This paper establishes the CFD model of the flow passage of a pump-turbine, wherein the crown gap, band gap, pressure balance pipe, and the discharge ostium are considered. Then, the flow characteristics of the pump-turbine at four typical operating conditions in turbine mode are calculated in transient scheme, and the numerical results agree with the experimental results. Finally, the effect of the pressure balance pipe and the discharge ostium on the pressure pulsation and the hydraulic thrust is discussed. The results show that the pressure balance pipe causes the direction of the axial hydraulic thrust to change from downward to upward, and the discharge ostium helps reducing the axial hydraulic thrust to a reasonable range. The pressure balance pipe and the discharge ostium have little effect on the radial hydraulic thrust. The pressure pulsation analysis provides a basis for revealing the mechanism of the hydraulic thrust frequency, and the rotor-stator interaction frequency exists in the axial hydraulic thrust. This paper provides a deeper knowledge of the impact mechanism of the pressure balance pipe and discharge ostium on the flow characteristics of the pump-turbine, which could contribute to future designs of the pump-turbine units, and is helpful for improving the safety of the pumped storage unit.

Determining the seismic age of the young open clusterα Per using δ Scuti stars

ABSTRACTIn this work, we aim at constraining the age of the young open cluster Melotte 20, known as α Per, using seismic indices. The method consists of the following steps: (1) Extract the frequency content of a sample of stars in the field of an open cluster. (2) Search for possible regularities in the frequency spectra of δ Sct stars candidates, using different techniques, such as the Fourier transform, the autocorrelation function, the histogram of frequency differences and the échelle diagram. (3) Constrain the age of the selected stars by both the physical parameters and seismic indices by comparing them with a grid of asteroseismic models representative of δ Sct stars. (4) Find possible common ages between these stars to determine the age of the cluster. We performed the pulsation analysis with MultiModes, a rapid, accurate and powerful open-source code, which is presented in this paper. The result is that the age of α Per could be between 96 and 100 Myr. This is an improvement over different techniques in the past. We therefore show that space astroseismology is capable of taking important steps in the dating of young open clusters.

Pulsation Analysis and Suppression Study of Pump-controlled Motor System Driven by Variable Frequency Permanent Magnet Synchronous Motor

To improve the control accuracy and robustness of variable frequency pump-controlled motor systems, a mathematical model was built to depict the system pulsation caused by the non-uniform magnetic field of a permanent magnet synchronous motor (PMSM), the harmonic current of an inverter and the structure of a plunger pump. At the same time, system pulsations were mitigated by a novel control algorithm based on sliding mode control (SMC) and harmonic suppression compensation. In addition, the performance of the system was analysed under variable load and speed. Under low-speed and heavy-load conditions, the electromagnetic torque of the PMSM and the outlet pressure of the plunger pump fluctuated greatly by traditional controlling, with maximum deviations of 11.719 N•m and 4.63 MPa, respectively. By coordinating SMC and harmonic suppression compensation, the control algorithm reduced the electromagnetic torque and the outlet pressure of the plunger pump to 45% and 40% of the traditional pump-controlled motor system driven by variable frequency PMSM values, respectively. Furthermore, the pulsation coefficient of the PMSM output speed and the hydraulic motor output speed were both controlled within 0.2%.

Stress and Pressure Pulsation Analysis of Low Temperature Compressor Piping System in LNG Vaporizing Station

LNG (Liquefied Natural Gas) vaporizing stations are usually built in the cities and towns, and the BOG (Boiled Off Gas) pressurizing system is a very important element. In the pressurizing system, the severe vibration of the low-temperature reciprocating compressor may lead to a failure of the pipeline system and the equipment. Therefore, this paper analyzes the stress and pressure pulsation of the BOG compressor piping system in the LNG vaporizing station. The beam model was used to establish the pipe model. The static, harmonic and modal analysis were carried out based on the plane-wave theory and the pressure-fluctuation theory, and the influence factors of support spacing, the settlement of the fulcrum foundation, pipe pressure and elbow angle were analyzed. The main conclusions are as follows: (1) the unbalanced excited force caused by pressure pulsation greatly affects the stress of the exhaust pipe and compressor outlet pipe, and has less influence on the stress of the suction pipe and compressor inlet pipe; (2) although unbalanced excited force is generated in the elbow, it also has an impact on the straight pipe stress; (3) adding an expansion joint to the pipe of the BOG compressor can effectively reduce the stress of the pipe its the displacement, and can increase the flexibility of the pipe.

Numerical and Experimental Analysis of Transient Flow Field and Pressure Pulsations of an Axial-Flow Pump Considering the Pump–Pipeline Interaction

The internal flow in a vertical axial-flow pump is a complex unsteady three-dimensional viscous flow. An unstable flow often produces complex flow phenomena such as flow separation, vortices, and secondary reflux, which reduces the operating efficiency of the pump and can endanger safety and stability. In this paper, computational fluid dynamics is used to calculate the flow characteristics in an axial-flow pump using the shear stress transport and curvature correction (SST-CC) model for turbulence modified to account for the rotational curvature. Furthermore, the dependability of the numerical results was confirmed by a test with an actual model of a pump. The transient deviation angle at the impeller inlet of the pump, the stream field attributes in various spanwise parts of the impeller and guide vane, and the velocity distributions at the impeller inlet and outlet were analyzed. The omega method was utilized to recognize the vortex structure inside the guide vane. Moreover, the development of the transient vortex structure inside the guide vane was studied. As the flow rate increased, the scale and turbulent kinetic energy of the vortex structure gradually decreased. The time-domain graph for the impeller inlet is clearly periodic, with three peaks and three troughs in an impeller rotational period. The dominant frequency in the spectrum at each monitoring point was basically the blade frequency, and the secondary dominant frequency was twice the blade frequency.