Pulsation Cycle Research Articles

Temporal Changes in the Infrared Spectra of Magellanic Carbon Stars

A Medium-Resolution Spectrometer on a Mid-Infrared Instrument on the JWST obtained spectra of three carbon stars in the Large Magellanic Cloud. Two of the spectra differ significantly from spectra obtained ∼16–19 years earlier with the Infrared Spectrograph on the Spitzer Space Telescope. The one semi-regular variable among the three has changed little. The long-period Mira variable in the sample shows changes consistent with its pulsation cycle. The short-period Mira shows dramatic changes in the strength of its molecular absorption bands, with some bands growing weaker and some stronger. Whether these variations result from its pulsation cycle or its evolution is not clear.

Quantitative assessment of the nanoanatomy of the contractile vacuole complex in Trypanosoma cruzi.

Trypanosoma cruzi uses various mechanisms to cope with osmotic fluctuations during infection, including the remodeling of organelles such as the contractile vacuole complex (CVC). Little is known about the morphological changes of the CVC during pulsation cycles occurring upon osmotic stress. Here, we investigated the structure-function relationship between the CVC and the flagellar pocket domain where fluid discharge takes place-the adhesion plaque-during the CVC pulsation cycle. Using TcrPDEC2 and TcVps34 overexpressing mutants, known to have low and high efficiency for osmotic responses, we described a structural phenotype for the CVC that matches their corresponding physiological responses. Quantitative tomography provided data on the volume of the CVC and spongiome connections. Changes in the adhesion plaque during the pulsation cycle were also quantified and a dense filamentous network was observed. Together, the results suggest that the adhesion plaque mediates fluid discharge from the central vacuole, revealing new aspects of the osmoregulatory system in T. cruzi.

Numerical simulation analysis of turbulent pulsation drag reduction at different intermittent times

The shear stress generated by wall turbulence is the main cause of wall friction resistance in turbulent flow through pipes. This paper investigates the impact of inserting rest periods (regions of constant Reynolds number) within the pulsating operating cycle of velocity on the fully turbulent flow at large time-averaged Reynolds numbers, using the large eddy simulation (LES) method. The study aims to explore the effect of increasing rest periods within pulsations on drag resistance. The dimensionless shear stress and drag reduction rates during different time periods of rest were analyzed. Numerical simulation results indicate that the pulsating velocity operation mode does not necessarily lead to drag reduction; it may even result in increased resistance. Inserting rest periods within the pulsation cycle can achieve drag reduction effects, with the maximum drag reduction rate reaching 21.8%. This paper utilizes large eddy simulation (LES) to compare and validate the feasibility of LES for pipe pulsating operation modes against experimental results and direct numerical simulation (DNS) results from the literature, providing a rationale and proof of concept for further in-depth studies on other pipe pulsating flows.

Identification of Single-Blade Angle Variation in Axial Flow Pumps Based on the Variational Mode Decomposition Method

Pressure pulsations are crucial data within the flow field of a pump, and the characteristics of these pulsations can reveal changes in the internal flow. Based on model experiments, this paper obtained pressure pulsation data under two blade conditions and compared direct time-domain observations, peak-to-peak value changes, and the VMD decomposition method. The results show that even when it is known that one blade condition has changed, it is not possible to determine this through direct observation of pressure pulsation changes. The peak-to-peak value changes indicate that under special flow conditions, they are easily affected by different operating conditions, which can interfere with the results. In contrast, the VMD method, which decomposes the signal into low-frequency components, can better display anomalies within the pressure pulsation cycle and is less susceptible to the interference of flow conditions, offering some reference significance for diagnosing the blade operating conditions of the main pump.

A new dimension in the variability of AGB stars: Convection patterns size changes with pulsation

Context. Stellar convection plays an important role in atmospheric dynamics, wind formation, and the mass-loss processes in asymptotic giant branch stars. However, a direct characterization of convective surface structures in terms of size, contrast, and lifespan is quite challenging, as spatially resolving these features requires the highest angular resolution. Aims. We aim to characterize the size of convective structures on the surface of the O-rich AGB star R Car to test different theoretical predictions based on mixing-length theory from solar models. Methods. We used infrared low-spectral resolution (R ∼ 35) interferometric data in the H-band (∼1.76 μm) obtained by the instrument PIONIER at the Very Large Telescope Interferometer (VLTI) to image the star’s surface at two epochs separated by approximately six years. Using a power spectrum analysis, we estimated the horizontal size of the structures on the surface of R Car. The sizes of the stellar disk at different phases of a pulsation cycle were obtained using parametric model fitting in the Fourier domain. Results. Our analysis supports that the sizes of the structures in R Car are correlated with variations in the pressure scale height in the atmosphere of the target, as predicted by theoretical models based on solar convective processes. We observed that these structures grow in size when the star expands within a pulsation cycle. While the information is still scarce, this observational finding highlights the role of convection in the dynamics of those objects. New interferometric imaging campaigns with the renewed capabilities of the VLTI are envisioned to expand our analysis to a larger sample of objects.

An empirical view of the extended atmosphere and inner envelope of the asymptotic giant branch star R Doradus

Context. The mass loss experienced on the asymptotic giant branch (AGB) at the end of the lives of low- and intermediate-mass stars is widely accepted to rely on radiation pressure acting on newly formed dust grains. Dust formation happens in the extended atmospheres of these stars, where the density, velocity, and temperature distributions are strongly affected by convection, stellar pulsation, and heating and cooling processes. The interaction between these processes and how that affects dust formation and growth is complex. Hence, characterising the extended atmospheres empirically is paramount to advance our understanding of the dust formation and wind-driving processes. Aims. We aim to determine the density, temperature, and velocity distributions of the gas in the extended atmosphere of the AGB star R Dor. Methods. We acquired observations using ALMA towards R Dor to study the gas through molecular line absorption and emission. We modelled the observed 12CO v = 0, J = 2 − 1, v = 1, J = 2 − 1, and 3 − 2 and 13CO v = 0, J = 3 − 2 lines using the 3D radiative transfer code LIME to determine the density, temperature, and velocity distributions up to a distance of four times the radius of the star at sub-millimetre wavelengths. Results. The high angular resolution of the sub-millimetre maps allows for even the stellar photosphere to be spatially resolved. By analysing the absorption against the star, we infer that the innermost layer in the near-side hemisphere is mostly falling towards the star, while gas in the layer above that seems to be mostly outflowing. Interestingly, the high angular resolution of the ALMA Band 7 observations reveal that the velocity field of the gas seen against the star is not homogenous across the stellar disc. The gas temperature and density distributions have to be very steep close to the star to fit the observed emission and absorption, but they become shallower for radii larger than ∼1.6 times the stellar sub-millimetre radius. While the gas mass in the innermost region is hundreds of times larger than the mass lost on average by R Dor per pulsation cycle, the gas densities just above this region are consistent with those expected based on the mass-loss rate and expansion velocity of the large-scale outflow. Our fits to the line profiles require the velocity distribution on the far side of the envelope to be mirrored, on average, with respect to that on the near side. Using a sharp absorption feature seen in the CO v = 0, J = 2 − 1 line, we constrained the standard deviation of the stochastic velocity distribution in the large-scale outflow to be ≲0.4 km s−1. We characterised two blobs detected in the CO v = 0, J = 2 − 1 line and found densities substantially larger than those of the surrounding gas. The two blobs also display expansion velocities that are high relative to that of the large-scale outflow. Monitoring the evolution of these blobs will lead to a better understanding of the role of these structures in the mass-loss process of R Dor.

The impact of pulsating parameters on particle dynamics in vertical pipe during hydraulic conveying with pulsating inlet flow

This paper presents a numerical investigation of the hydraulic conveying performance of coarse particles with the inlet pulsating fluid velocity in a vertical pipe. The influence of pulsating parameters, in terms of pulsating amplitudes and frequencies, on hydraulic conveying is mainly considered. The pulsations of particle and slip velocity are as periodic and regular as the inlet pulsating velocity. The variation of the normalized force in one pulsating time cycle is also analyzed. Then the laws of particle group distribution with transient time and vertical distance are obtained: the plug phenomenon is more obvious at the larger pulsating amplitude, further leading to pipe blockage, while a larger pulsating frequency is beneficial to the weakening of the plugs. Particle relaxation time is introduced to explain the changes in particle group distribution. Additionally, the temporal variations of flow fields are also used to illustrate the propagation of kinematic waves.

Modified Split Mandrel Method and Equipment to Improve the Fatigue Performance of Structural Components with Fastener Holes

Fastener holes are among the most common natural stress concentrators in metal structures. The life cycles of various structural elements, such as those in aircraft structures, automobiles, and rail-end bolt joints, are limited by fatigue damage around the holes. An effective approach to delay the formation and growth of fatigue macrocracks is to introduce residual hoop compressive stresses around the holes. Two methods have become established in the prestressing of fastener holes in aircraft components, split sleeve and split mandrel, which implement one-sided processes. The common disadvantage of both methods is the complex procedure due to the need for high accuracy of the initial holes. This article presents a new modified split mandrel method providing the same tightness (interference fit) with a wide tolerance of the pre-drilled hole diameters, reducing the number of technological cycle steps and production costs. To implement the new method, a functionally connected tool and a device with a hydraulic drive were developed. An extensive experimental study of 2024-T3 AA specimens was carried out to evaluate the effectiveness of the method under a high scattering of the pre-drilled holes. The new method provided a deep zone of residual hoop compressive stresses on both faces of the specimens after cold working and after hole final reaming. The removal of a plastically deformed layer around the hole of suitable thickness during the final reaming decreased the axial gradient of residual hoop stress distribution. Fatigue tests on a tensile pulsating cycle verified the effectiveness of the modified split mandrel method to significantly increase the fatigue life by 6.6 times based on 106 cycle fatigue strength compared to the conventional case of machining the holes. The obtained S-N curves for three groups of samples with initial hole diameters of 8.0, 8.1, and 8.2 mm, which were cold worked with the same tightness of 0.32 mm and final reamed, aligned well, indicating that the new method can provide constant fatigue strength for a given stress amplitude.

Pulsation modeling of the Cepheid Y Ophiuchi with RSP/MESA

Context. Y Ophiuchi (Y Oph) is a classical Cepheid with a pulsation period of P = 17.12 days. This star is reported to be as dim as a Cepheid of about half its pulsation period and it exhibits a low radial velocity and light-curve amplitude. For these reasons, Y Oph is not used to calibrate period-luminosity (PL) relation and its distance remains uncertain. Aims. Our objective is to conduct hydrodynamical pulsation modeling of Y Oph to derive its distance and provide a physical insight into its low amplitude and luminosity, constrained by an extensive set of observations. Methods. We first performed a linear analysis on a grid of models using the hydrodynamical pulsation code MESA-RSP to find the combinations of mass, metallicity, effective temperature, and luminosity resulting in linear excitation of pulsations with period of about 17 days. Then, we performed non-linear computations to obtain the full-amplitude pulsations of these models. Last, we compare the results to a complete set of observations along the pulsation cycle, including the angular diameter obtained by interferometry, effective temperature, and radial velocity obtained by high-resolution spectroscopy, as well as the light curves in the VJHKSLM bands. We simultaneously adjusted the distance, the color excess and circumstellar envelope (CSE) model to fit the light curves and the angular diameter. Results. We find that all pulsation models at high effective temperatures are in remarkable agreement with the observations along the pulsation cycle. This result suggests that the low amplitude of Y Oph may be explained by proximal location to the blue edge of the instability strip (IS). We also find that a pulsational mass of about 7 − 8 M⊙ is consistent with a non-canonical evolutionary model with moderate overshooting, PL relation and Gaia parallax. However, a much lower mass below 5 M⊙ is required to match Baade-Wesselink (BW) distance measurements from the literature. We show that the combination of the impact of the CSE on the photometry, together with a projection factor of about 1.5, explains the discrepant distance and luminosity values obtained from BW methods. Conclusions. Our findings indicate that the small pulsation amplitude of Y Oph can be attributed to its proximity to the blue edge of the instability strip. Additionally, our analysis reveals that the distances obtained using the BW method are biased compared to Gaia, mainly due to the impact of circumstellar envelope on the photometries and a high p-factor close to 1.5. Despite these unique characteristics, Y Oph is a long-period classical Cepheid that holds potential for calibration of the PL relation in the Galaxy.

Experimental, numerical and deep learning modeling study of heat transfer in turbulent pulsating pipe flow

Pulsating heat transfer is important in many engineering applications but is not fully understood or easily modeled. This work helps understand the phenomenon and demonstrates the efficacy and utility of deep learning modeling for pulsating heat transfer. The convective heat transfer coefficient (HTC) of pulsating flow through a copper tube was experimentally investigated at seventy-seven different operating conditions (500,000 time-series data points were collected at each operating condition) corresponding to different pulsating waveforms, frequencies, mass flow rates and pressures. The intensity of pulsation ranged from mild to strong enough to cause reverse flow. The literature on pulsating HTC is mixed, with several researchers reporting increased heat transfer and several other reporting decreased heat transfer relative to steady flow. The experimental data showed that both could be true depending on the ratio of the amplitude to mean flow velocity (amplitude ratio AR). The enhancement ratio (ER) of pulsating HTC relative to steady-flow HTC was measured to vary between 0.48 and 2.18 for AR ranging from 0.64 to14.42. A numerical study showed that this was only a (positive) correlation; fundamentally the overall pulsating HTC could be approximately explained by the variation of instantaneous Reynold’s number (Re) during the pulsating cycle. The distribution of instantaneous Re and hence the ER is primarily determined by the pulsating waveform, and this explains the disparate observations by different researchers. Long Short-Term Memory (LSTM) networks have been used to model pulsating HTC as a function of pulsating waveforms occuring across a measurement orifice. The ‘Toy Model’ concept where physics-based variables are used to increase generalization was implemented with the LSTMs for increased model robustness. These models could be used to maximize pulsating heat transfer by optimizing the waveform.

Turning kinematics of the scyphomedusa Aurelia aurita

Scyphomedusae are widespread in the oceans and their swimming has provided valuable insights into the hydrodynamics of animal propulsion. Most of this research has focused on symmetrical, linear swimming. However, in nature, medusae typically swim circuitous, nonlinear paths involving frequent turns. Here we describe swimming turns by the scyphomedusa Aurelia aurita during which asymmetric bell margin motions produce rotation around a linearly translating body center. These jellyfish ‘skid’ through turns and the degree of asynchrony between opposite bell margins is an approximate predictor of turn magnitude during a pulsation cycle. The underlying neuromechanical organization of bell contraction contributes substantially to asynchronous bell motions and inserts a stochastic rotational component into the directionality of scyphomedusan swimming. These mechanics are important for natural populations because asynchronous bell contraction patterns are common in situ and result in frequent turns by naturally swimming medusae.

Signal Processing from the Radiation Detector of the Radiometric Density Meter Using the Low-Pass Infinite Impulse Response Filter in the Measurement Path in the Coal Enrichment Process Control System

One of the most common coal preparations is enrichment in a jig using a float regulation system. The latest solutions propose to compensate for significant measurement errors of the float by introducing a radiometric density meter operating on the principle of gamma radiation absorption into the bottom product discharge zone of the jig. The signal from the radiometric density meter detector is in the form of a sequence of pulses with a Poisson time distribution, which are counted by a counter, as a form of digital low-pass filter. The requirement to maintain accuracy at an appropriate level forces the measurement time to be extended, which worsens the dynamic properties. Changes in the density of the coal–water medium have an unsteady, cyclical course, resulting from the principle of operation of the jig. The research goal was to develop an algorithm for processing the signal from the radiation detector using an IIR filter in the measurement path in a way that ensures optimization of the dynamic properties of the radiometric density meter operating in the control system of the coal enrichment process in the jig. For this purpose, a low-pass IIR filter was introduced into the measurement path to process the signal from the pulse counter. The identified course of the medium density for one cycle (the first) served as a reference signal. A first-order IIR filter was proposed, with a constant parameter selected on the basis of the reference signal and a parameter depending on the time derivative of the identified density of the medium. The mean squared error MSE was adopted as an indicator for assessing the dynamic properties of the radiometric density meter. The results of simulation tests showed that introducing an IIR filter into the measurement path gives better results in terms of the adopted criterion than using a counter with a constant measurement time. The best results (MSE = 2.05 × 10−4) were obtained using an IIR filter with a parameter that is a linear function of the derivative of the medium density over time, determined for one air pulsation cycle and applied in four subsequent cycles. These results were obtained for an adaptive first-order filter with a variable parameter a from the designated range from 0.833 to 0.999, for a measurement time of 2 ms.

Survey of Liner Characteristics Used in Japan

Highlights The vacuum during milking causes teat ends to suck into liners by 7 to 10 cm. Liner rubber is classified as hard or soft. Volume changes are greater in round liners than those of other shapes in the pulsation cycle. Non-round liners did not press completely during the closing phase. The liner shape had a greater effect on liner volume change than the material. ABSTRACT. A variety of liner shapes are used in the dairy industry in Japan, and it is not known which is optimal for maintaining teat-end condition, preventing mastitis, ensuring milk quality, and improving dairy cow and milking system performance. Liners can be generally classified into types based on their internal shape: round, round with ribs on the outside of the liner, triangular, clover-shaped, or square. In addition, liners can be characterized based on the position of the air vent. The optimal combination of air vent location and internal shape for the maintenance of good teat end condition has not been clarified. The aim of this study is to survey liners in Japan to determine the characteristics of liners currently in use. The depth to which the teat end is pulled into the liner during milking was investigated. An experimental vacuum device was fabricated to measure the touch-point and closure-point (the vacuum levels at which the opposite sides of the internal liner surface begin to touch, and the level at which the liner bore completely closes, respectively). In addition, the volume change of the pulsation chamber during the pulsator opening and closing phases was also investigated. The internal shape of the liner was molded when the liner was opened and closed, and the cross-sectional area was compared for each liner type. The findings showed that liner hardness could be characterized as being either soft or hard. The change in the borevolume of round liners during a pulsation cycle, i.e., between the pulsation opening phase and the closing phase, was larger than that observed with the other liners. The cross-sectional area of the molded shape tended to be wider for liners of other shapes than for round liners. This study investigated and compared the characteristics of various types of liners and found that the characteristics varied widely. It is not clear what kind of liner shape is best, and further research is needed. Keywords: Liner internal shape, Overpressure, Pulsation, Teat end condition, Teat end position.

Curve of Growth Analysis of SZ Lyn

We present one high-resolution and a time series of 561 low-resolution follow-up spectroscopic observations of SZ Lyn. It is a high-amplitude δ Scuti-type pulsating star in a binary system. The photometric observations reveal the existence of radial and non-radial oscillation modes in SZ Lyn. In spectroscopy, the variation of equivalent width of the line profiles reflects the temperature variations. The equivalent widths of the Balmer lines, Hα, Hβ, and Hγ were measured over the pulsation cycle of SZ Lyn using time sequence spectra. Hence, the temperature profile of SZ Lyn was derived using the curve of growth analysis. Furthermore, the stellar parameters were determined through the best fit analysis of observed and synthetic high-resolution spectral lines. The best fit determines a model of Teff = 6750 K, log g = 3.5 dex, and vrot = 10 km s−1 for solar abundance.

Dynamic Computed Tomography Angiography for capturing vessel wall motion: A phantom study for optimal image reconstruction.

Reliably capturing sub-millimeter vessel wall motion over time, using dynamic Computed Tomography Angiography (4D CTA), might provide insight in biomechanical properties of these vessels. This may improve diagnosis, prognosis, and treatment decision making in vascular pathologies. The aim of this study is to determine the most suitable image reconstruction method for 4D CTA to accurately assess harmonic diameter changes of vessels. An elastic tube (inner diameter 6 mm, wall thickness 2 mm) was exposed to sinusoidal pressure waves with a frequency of 70 beats-per-minute. Five flow amplitudes were set, resulting in increasing sinusoidal diameter changes of the elastic tube, measured during three simulated pulsation cycles, using ECG-gated 4D CTA on a 320-detector row CT system. Tomographic images were reconstructed using one of the following three reconstruction methods: hybrid iterative (Hybrid-IR), model-based iterative (MBIR) and deep-learning based (DLR) reconstruction. The three reconstruction methods where based on 180 degrees (half reconstruction mode) and 360 degrees (full reconstruction mode) raw data. The diameter change, captured by 4D CTA, was computed based on image registration. As a reference metric for diameter change measurement, a 9 MHz linear ultrasound transducer was used. The sum of relative absolute differences (SRAD) between the ultrasound and 4D CTA measurements was calculated for each reconstruction method. The standard deviation was computed across the three pulsation cycles. MBIR and DLR resulted in a decreased SRAD and standard deviation compared to Hybrid-IR. Full reconstruction mode resulted in a decreased SRAD and standard deviations, compared to half reconstruction mode. 4D CTA can capture a diameter change pattern comparable to the pattern captured by US. DLR and MBIR algorithms show more accurate results than Hybrid-IR. Reconstruction with DLR is >3 times faster, compared to reconstruction with MBIR. Full reconstruction mode is more accurate than half reconstruction mode.

Atmospheric dynamics and shock waves in RR Lyr

Context. Although spectroscopic observations of RR Lyrae stars have been underway for almost a century, the fact that the hydrogen line exhibits three successive emissions in each pulsation cycle is still a very recent discovery. Aims. The purpose of the present study is to clarify the physical origin of these three emissions and their connection to atmospheric dynamics and to examine the influence of Blazhko modulation on their intensity. Methods. We used 2437 high-resolution spectra over a total of 81 nights taken by the ELODIE spectrograph (Haute Provence Observatory, France) in the years 1994–1997, rounded out with a 2015 run from Oukaïmeden Observatory (Morocco). We performed a detailed analysis of the line profile variations over the whole pulsation cycle. Results. Based on the blueshift of the main Hα emission, the velocity of the hypersonic shock front was estimated at between 100 and 150 ± 10 km s−1 (Mach number between 10 and 15). It has been established that the shock velocity increases from the minimum Blazhko to its maximum and afterward, it gradually decreases to the Blazhko minimum to start growing again. This observational result is consistent with the shock model proposed in 2013 to explain the Blazhko effect. The intensity of the Hα emission increases with the shock velocity up to a maximum value around 137 km s−1 and then decreases as the shock velocity increases further. This effect would be the consequence of the increasingly important ionization of the atoms in the radiative shock wake. The second (blueshifted) Hα emission is the consequence of an approximately constant supersonic compression (Mach number between 2 and 3) of the upper atmosphere falling onto the photospheric layers, during 3 to 16% of the pulsation period. Finally, the third Hα emission (P-Cygni profile) would be the consequence of the expansion of the high atmosphere induced by the shock wave during its final weakening.

Geometry of the LMC based on multiphase analysis of multiwavelength Cepheid light curves using OGLE-IV and Gaia DR3 data

ABSTRACT The period–luminosity (PL) relation of Cepheids in the Large Magellanic Cloud (LMC) plays a pivotal role in extragalactic distance measurement and the determination of the Hubble constant (H0). In this work, we probe the geometry of the LMC through a detailed study of multiphase PL relations of these Cepheids, leveraging data from the OGLE-IV and Gaia DR3 data bases. We analyse the light curves of a combined sample of ∼3300 fundamental (FU) and first overtone (FO) mode classical Cepheids. We obtain multiphase data with 50 phase points over a complete pulsation cycle from the OGLE (V, I) and Gaia (G, GBP, GRP) photometric bands. We determine the distance modulus and reddening values of individual Cepheids by fitting a simultaneous reddening law to the apparent distance modulus values. We calculate the LMC viewing angle parameters: the inclination angle (i) and position angle of line of nodes (θlon) by fitting a plane of the form z = f(x, y) to the three-dimensional distribution of Cepheids in Cartesian coordinates $(x, y, z)$. The values of LMC viewing angles from multiphase PL relations are found to be: i = 22.°87 ± 0.°43 (stat.) ± 0.°53 (syst.), θlon = 154.°76 ± 1.°16 (stat.) ± 1.°01 (syst.), respectively. The use of multiphase PL relations in multiple bands results in lower uncertainties for the LMC viewing angle parameters as compared to those derived from the mean-light PL relations. This shows that the use of multiphase PL relations with multiwavelength photometry significantly improves the precision of these measurements, allowing better constraints on the morphology and the structure of the LMC.

Simulation of the effect of pulsatile flow on flow features dynamics during abrupt contraction into two parallel rectangular jets

The analysis of the converging region of two parallel jets under unsteady flow conditions is important in its design and safety. Numerical simulation was used to investigate the flow features before the contraction plane. Pulsatile flows with a fixed flow period of 5 s, mean flow velocities between 0.033–0.045 m/s, and flow amplitudes of 0.2–0.4 were simulated in this study. The changes at the contraction were characterized by repeated changes in the velocity profile, recirculation area, and corner vortices. The velocity profile in the contraction region remains axisymmetric throughout the cycle of pulsation. The corner vortices increased with a decrease in the mean velocity when the vortex length was longer than the length from the corner to the stagnation point but began to reduce when the mean velocity started increasing in the pulsation cycle. The results provide more explanation of flow feature characteristics at channel corners and abrupt contraction planes.

Numerical research on dynamic responses of the emulsion pump crankshaft under multiple working conditions

The stability and safety of emulsion pumps are significantly influenced by crankshafts. However, the crankshaft of the emulsion pump bears complex torsional and bending stresses during operation; thus, it is prone to failure. The purpose of this paper is to determine the dynamic response of the crankshaft under various working conditions. The mechanical model of the power end of the emulsion pump is constructed, and the dynamic model is established by LS-DYNA. The stress distribution characteristics of the surface element of the crankpin in the pulsating impact cycle are analysed, and the dynamic response of the crankpin under multiple working conditions is studied. The results show that under the action of pulsating impact, the edge position of the crankpin is more likely to fail, especially at the second crankpin, and the maximum stress can reach 213 MPa. The dynamic impact of the connecting rod on the crankpin is positively correlated with the flow of the emulsion pump and the hydraulic pressure on the plunger, and the crankshaft vibration becomes more noticeable as the flow rate rises. Doubling the flow rate increases the vibration by 73.9 %. Our research results provide a reference for avoiding the failure of the crankshaft and optimizing the design.

Left Ringing: Betelgeuse Illuminates the Connection between Convective Outbursts, Mode Switching, and Mass Ejection in Red Supergiants

Betelgeuse, the nearest red supergiant, dimmed to an unprecedented level in early 2020. The star emerged from this “Great Dimming” episode with its typical, roughly 400 days pulsation cycle halved, and a new dominant period of around 200 days. The dimming event has been attributed to a surface mass ejection, in which rising material drove shocks through the stellar atmosphere and expelled some material, partially obscuring the star as it formed molecules and dust. In this paper, we use hydrodynamic simulations to reveal the connections between Betelgeuse's vigorously convective envelope, the surface mass ejection, and the pulsation mode switching that ensued. An anomalously hot convective plume, generated rarely but naturally in the star's turbulent envelope, can rise and break free from the surface, powering an upwelling that becomes the surface mass ejection. The rising plume also breaks the phase coherence of the star's pulsation, causing the surface to keep expanding even as the deeper layers contract. This drives a switch from the 400 days fundamental mode of pulsation, in which the whole star expands and contracts synchronously, to the 200 days first overtone, where a radial node separates the interior and exterior of the envelope moving in opposite phase. We predict that the star's convective motions will damp the overtone oscillation and Betelgeuse will return to its previous, 400 days fundamental-mode pulsation in the next 5–10 yr. With its resolved surface and unprecedentedly detailed characterization, Betelgeuse opens a window to episodic surface mass ejection in the late-stage evolution of massive stars.