Large Pressure Fluctuations Research Articles

The Determinants of Detrimental Changes in Pulse Pressure During Maintenance Hemodialysis Treatments

Background: Studies indicate that large fluctuations in pulse pressure during hemodialysis are associated with cardiovascular events, cardiovascular mortality, and all-cause mortality. Objective: We investigated the determinants of detrimental changes in pulse pressure (ΔPP) during hemodialysis. Methods: This prospective, observational cohort study was conducted from 1 to 30 April 2023 at Dr. Sardjito Hospital Yogyakarta, involving maintenance hemodialysis patients for ≥ 6 months. Patients were categorized into group 1 (detrimental ΔPP, ΔPP >5 mmHg or <−25 mmHg) and group 2 (stable ΔPP, −25 to 5 mmHg). Mann-Whitney, independent-t, chi-square, Fisher exact tests, and logistic regression were applied to evaluate associations between ΔPP groups and clinical variables. Results: This study involved 136 patients, 75 males (55.1%) with a mean age of 52 (18-87). The most common comorbid was hypertension, present in 85 patients (62.5%). The mean hemodialysis vintage of patients was 47.2 (6.5-330.7) months. We found significant difference between group in post-dialysis systolic blood pressure (SBP) (p=0.003), pre-dialysis diastolic blood pressure (DBP) (p=0.015), post-dialysis DBP (p=0.007), ultrafiltration (p=0.041), pre-dialysis mean-arterial-pressure (MAP) (p=0.013), post-dialysis MAP (p=0.002), and alpha-blocker treatment (p=0.037). Multivariate logistic regression analysis shows a significant association between groups of ΔPP with pre-dialysis DBP (p=0.035; OR=1.153; OR=Exp(10xℬ) =4.137) and post-dialysis SBP (p=0.007; OR=1.052; OR=Exp(10xℬ) =1.6487). Conclusion: Our study demonstrates that group 1, with detrimental changes in pulse pressure during hemodialysis, was found to have higher post-dialysis DBP, pre-dialysis DBP, post-dialysis SBP, pre-dialysis MAP, post-dialysis MAP, alpha-blocker treatment, and ultrafiltration, with significant association with post-dialysis SBP and pre-dialysis DBP.

Evolution of arbitrary temporal ocean floor motion-induced surface waves over a trench

The scattering of surface water waves generated through an arbitrary temporal motion of a portion of the ocean floor within a trench and from the sudden depth change at the wall of the trench is studied under the assumption of linearized water wave theory and a weakly compressible ocean that includes static oceanic background compression. The Fourier transformation and eigenfunction expansion techniques are deployed to find the surface displacement and pressure profiles with the help of appropriate matching conditions between regions of different depths. The difficulties of numerical computation owing to large oscillations of the displacement potential function around specific frequencies are overcome using adequate non-uniform finer meshing. Apart from the time-domain propagation of tsunami waves away from the origin, standing wave formations are observed within the trench region, supported by significantly large pressure fluctuations in time. These standing waves or the pressure fluctuations are higher when the ocean depth is large. The change in tsunami speed due to sudden depth change is readily visible in the time-domain simulations. Ocean compressibility results in fluctuations in the envelope of the propagating wavefront. Both the two-dimensional and axisymmetric three-dimensional solutions are presented. In comparison, the propagating surface wavefront for the latter case evolves with a sharper slope, which is additionally illustrated by the animation movies.

Improved severe slugging modeling and mapping

Improved severe slugging modeling and mapping

Compressible ocean waves generated by sudden seabed rise near a step-type topography

A typical tsunami generation occurs through submarine earthquakes leading to large volume displacement. The corresponding mathematical problem involves modeling surface water waves generated by an arbitrary temporal motion of the ocean floor. The propagation of tsunami wave and the subsequent scattering from a sudden drop in bathymetry away from the ground motion is studied following linearized water wave theory and a weakly compressible ocean, including static oceanic background compression. The Fourier transformation and eigenfunction expansion techniques are employed to find the surface displacement and pressure profiles by leveraging appropriate matching conditions between regions of different depths. A novel energy balance relationship is derived by considering both the pure-gravity and acoustic-gravity modes. The model is validated in the limit that the depth difference approaches zero, showing a vanishing reflection contribution from the depth change. An efficient numerical code is developed that accurately captures the contribution of the cutoff frequencies of acoustic-gravity modes. Apart from the time-domain propagation of tsunami waves away from the origin, standing wave formations are observed within the shallow region, supported by significantly large pressure fluctuations in time. These standing waves or, equivalently, the pressure fluctuations sustain longer for larger ocean depth. The increase in tsunami speed in the deeper region is readily visible in the time-domain simulations. A three-dimensional axisymmetric solution is also developed, and results show a more gradual sloping tsunami wavefront compared to the equivalent two-dimensional solution for shallower depths. Animation movies corresponding to the two- and three-dimensional surface profiles are provided for better visualization.

Relativistic SZ temperatures and hydrostatic mass bias for massive clusters in the FLAMINGO simulations

ABSTRACT The relativistic Sunyaev-Zel’dovich (SZ) effect can be used to measure intracluster gas temperatures independently of X-ray spectroscopy. Here, we use the large-volume FLAMINGO simulation suite to determine whether SZ y-weighted temperatures lead to more accurate hydrostatic mass estimates in massive ($M_{\rm 500c} \gt 7.5\times 10^{14}\, {\rm M}_{\odot }$) clusters than when using X-ray spectroscopic-like temperatures. We find this to be the case, on average. The median bias in the SZ mass at redshift zero is $\left\langle b \right\rangle \equiv 1-\left\langle M_{\rm 500c,hse}/M_{\rm 500c,true} \right\rangle = -0.05 \pm 0.01$, over 4 times smaller in magnitude than the X-ray spectroscopic-like case, $\left\langle b \right\rangle = 0.22 \pm 0.01$. However, the scatter in the SZ bias, $\sigma _{b} \approx 0.2$, is around 40 per cent larger than for the X-ray case. We show that this difference is strongly affected by clusters with large pressure fluctuations, as expected from shocks in ongoing mergers. Selecting the clusters with the best-fitting generalized NFW pressure profiles, the median SZ bias almost vanishes, $\left\langle b \right\rangle = -0.009 \pm 0.005$, and the scatter is halved to $\sigma _{b} \approx 0.1$. We study the origin of the SZ/X-ray difference and find that, at $R_{\rm 500c}$ and in the outskirts, SZ weighted gas better reflects the hot, hydrostatic atmosphere than the X-ray weighted gas. The SZ/X-ray temperature ratio increases with radius, a result we find to be insensitive to variations in baryonic physics, cosmology, and numerical resolution.

Effects of liquid lubricants on the surface characteristics of 3D-printed polylactic acid

In this study, 3D-printed Polylactic acid (PLA) specimens were manufactured and polished using various lubricants to assess their surface, friction, and wear characteristics. After polishing, the surface roughness decreased by approximately 80% compared with that before polishing, except when acetone was used as the lubricant. In particular, under deionized (DI) water and acetone lubrication conditions, the friction coefficient decreased by 63% and 70%, respectively, whereas the specific wear rate decreased by 88% and 83%, respectively, compared with the unpolished specimens. In the case of dry polishing, adhesion, friction, and wear increase owing to surface damage. Ethanol and IPA polishing resulted in hydrolysis and increased friction, but slightly decreased wear rates. The surface of the specimen polished with acetone dissolved and became very rough. Only the surface polished with DI water exhibited hydrophobic properties. When acetone and DI water were used as lubricants, the surface adhesion force, adhesion energy, friction coefficient, and wear rate were lowest. The finite element analysis results showed that the polished surface exhibited stable contact pressure and friction force, while the unpolished surface showed large fluctuations in contact pressure and friction force owing to the laminated pattern. These results suggest that the polishing process is crucial for improving the surface characteristics and mechanical performance of 3D-printed PLA parts.

Investigation of unsteady friction effects in transient two-phase pipe flow

Water hammer and transient cavitating flow may induce large pressure fluctuations in pipelines. Transient events in pipeline may cause a drop in pressure large enough to break liquid homogeneity and continuity (liquid column separation, distributed vaporous cavitation). Trapped air pockets in liquid may be a major problem in piping systems. The paper deals with mathematical tools for modelling unsteady skin friction, transient vaporous cavitation (liquid column separation) and transient gaseous cavitation (trapped air pockets). The method of characteristics transformation of the unsteady liquid pipe flow equations gives the water hammer solution procedure. A convolution-based unsteady skin friction model is explicitly incorporated into the staggered grid of the method of characteristics. Incorporating discrete cavities into the water hammer model leads to the discrete cavity model. An advanced discrete gas cavity model (DGCM) with consideration of unsteady pipe flow friction effects is presented in the paper. The DGCM is capable to simulate vaporous and gaseous cavitation at the same time. Pipeline apparatus for measurement of transient liquid flow (water hammer) and transient two-phase flow (vaporous and gaseous cavitation) is briefly described. The paper concludes with two distinct case studies showing profound effects of unsteady skin friction on pressure histories.

Optimized sulfur curing of pulse-damping rubber tubes

Optimized sulfur curing of pulse-damping rubber tubes

A numerical analysis on the thermal characteristics by filling parameters of high-pressure valve for hydrogen refueling station

A numerical analysis on the thermal characteristics by filling parameters of high-pressure valve for hydrogen refueling station

Study on single-phase and two-phase flow and heat transfer characteristics of HFE-7100 in manifold microchannel heat sink with corrugated bottom

To solve the problem of high heat flux heat dissipation in microelectronic devices, a manifold micro-channel heat sink with corrugated bottom (CB-MMC) is pro-posed on the basis of the manifold microchannel heat sink (MMC). The flow and heat transfer characteristics of HFE-7100 in MMC and CB-MMC are investigated numerically. The results show that CB-MMC reduces the pressure loss and enhances the heat transfer performance in single-phase flow. The orthogonal test method is used to obtain structural design solutions with optimal thermal performance. It is observed that the temperature reduction is always at the expense of the increase of the pressure drop. In addition, the optimization parameters combination obtained through comprehensive evaluation of temperature and pressure drop through weight matrix ? optimized solution 19 (wavelength A = 800 ?m, am-plitude B = 40 ?m, channel depth C = 180 ?m, outlet width D = 300 ?m, channel width E = 25 ?m). Its Tave has decreased by 6.89?C, ?P decreased by 10.27 kPa. Moreover, the subcooled boiling flow and heat transfer performance in MMC and CB-MMC are comparatively studied. The results demonstrate that the dynamic behavior of vapor bubbles causes large pressure fluctuations, which further leads to small temperature fluctuations, and thus reduces the stability of the flow and boiling heat transfer. Compared with MMC, CB-MMC exhibits more stable two-phase flow and better boiling heat transfer.

Numerical analysis on two-phase flow-induced vibrations at different flow regimes in a spiral tube

Numerical analysis on two-phase flow-induced vibrations at different flow regimes in a spiral tube

Aerodynamic noise from a high-speed train bogie with complex geometry under a leading car

Aerodynamic noise from a high-speed train bogie with complex geometry under a leading car

The Correspondence between Large Pressure Fluctuations and Runway Wind Shear: The Event on 12 December 2019 at Songshan Airport, Taipei

In this study, the association of large pressure fluctuations (LPFs) ≥ 0.2 hPa and runway wind shear (RWS) ≥ 12 kt at the Songshan Airport in Taipei, Taiwan, during the event on 12 December 2019 with strong northeasterly winds are analyzed. The goal of the study is to demonstrate that the two phenomena exhibited close correspondence, and the former (LPFs) measured using a single barometer can be useful to detect the latter (RWS), which relies on the low-level wind-shear alert system (LLWAS) at the present time. Concentrated before 1200 UTC and especially during 0100-0800 UTC, both LPFs (52 times) and RWS (62 times) over the runway exhibited close association, and one rarely occurred more than 15–20 min apart in time from the other. Using the 2 × 2 contingency table and categorical scores, our results for LPFs and RWS to both occur at least once or five times within the same hour also suggest high accuracy rates of ≥80% and low miss rate and false alarm ratio of both < 10%, respectively. The two variables are also tested to be statistically dependent on each other to a high confidence level of 95–97.5%. Thus, using LPFs as an auxiliary or additional method to detect RWS at airports appears to be reasonable and feasible. At small and remote airports where the LLWAS is not yet available, this method also provides a good and less expensive alternative and can be helpful to the overall improvement of air traffic safety around the world.

Cross-spectral analysis of cerebral autoregulation after mild traumatic brain injury.

Severe traumatic brain injury (TBI) disrupts cerebral autoregulation (CAR), which may increase the risk of secondary neuronal damage in victims with large fluctuations in blood pressure (BP). CAR is also impaired in mild TBI. Given that mild TBI accounts for up to 70% of cases, this issue needs to be addressed. Physiological and non-invasive methods are now required to study CAR without the sharp fluctuations in blood pressure that underlie CAR tests. The cross-spectral analysis of fluctuations between cerebral blood flow and blood pressure discussed in the article is truly non-invasive and physiological. Forty-eight victims with mild traumatic brain injury were studied. CAR was assessed using two methods. The cuff test was used as a control method to assess autoregulation (RoR). Non-invasive cross-spectral analysis with phase shift (PS) detection was performed. The RoR values were normal, but there were cases within the group with varying severity of symptoms of the acute period of mild TBI. For example, the RoR was significantly higher (p < 0.001) in 32 patients with regression of symptoms than in 16 with persistence of symptoms. Their RoR and PS indicated a violation of the CAR, which required correction of the treatment. It was found that in 1/3 of the patients with mild TBI, a different state of CAR required individual tactics. RoR and PS correlated well.

Experimental study on the influence of maintenance track position on vortex-induced vibration performance of a box girder suspension bridge

To study the influence of maintenance track on the vortex-induced vibration (VIV) performance of main girder, the VIV response and time history of surface pressure data of a section model were obtained by wind tunnel vibration and pressure measurements for a large-span steel box girder suspension bridge. The VIV performance of the main girder was tested at ±5° attack angles of various maintenance track positions, including 1, 2.5, and 5 m away from the outer edge of the girder bottom plate. The mean values, root variances and amplitude spectra of vortex-induced force and the correlation and contribution coefficients of local aerodynamic force to overall aerodynamic force were analyzed. The results show that when the maintenance track is 1 m away from the outer edge of the bottom plate, the main girder exhibits the worst VIV performance with a maximum amplitude of 0.457 m, far beyond the allowable value of the specification. The VIV performance of the main girder was greatly improved by moving the maintenance track inward. The pressure analysis indicates that the large pressure fluctuation at the front and rear parts of the upper surface is attributed to the strong VIV of the main girder. In this sense, the improved VIV performance is mainly contributed by the weakening of pressure fluctuation in these two areas and the reduced local aerodynamic force. When the distance between the maintenance track and bottom plate is adjusted to 2.5 m, a 3.5 m wind barrier with a ventilation rate of 30% effectively inhibits the VIV of the box girder. The main reason for the suppression is that the elimination of pressure fluctuation on the upper surface of the girder disturbs the correlation between local aerodynamic force and overall aerodynamic force, consequently diminishing the contribution of local aerodynamic force to the vortex-induced force.

Gas–droplet–liquid transitions and fluctuations in soft nano-confinement

One permanent characteristic of the thermodynamics of small systems is environment-dependence, also known as ensemble-dependence. Fluid molecules in soft (deformable) nano-confinement offer a special ensemble that acts as a bridge between classical isobaric (NPT) and isochoric (NVT) ensembles. Here, we discuss the gas–liquid transition taking place in a soft nano-confinement where the cell volume is not fixed but changes when the system pressure is changed. The free energy of the system is calculated as a function of the size of the liquid droplet that appears in the gas phase. We discuss how the phase behavior changes when the condition of the confinement changes from rigid confinement to very soft confinement. For the simple fluid model studied, the coexistence and critical phase behaviors are found to be uniquely determined by αK (αK is the dimensionless elasticity constant of the wall of confined space and is proportional to its ability to resist deformation), and the confinement with moderate softness exhibits richer phase behavior. We then study the fluctuations of pressure, volume, and droplet size for fluid in soft confined spaces, which is again closely related to the wall softness. Under moderate softness, large fluctuations in both fluid pressure and volume are seen in the transition region where fluid pressure increases with volume expansion, accompanied by the strengthened fluctuation of droplet size.

Simulation Analysis of Pipeline Detection Robot Motion State

Pipeline transportation has the advantages of safety, reliability and low energy consumption in transporting natural gas, and is an important transportation route for transporting natural gas. Due to the characteristics of natural gas pipelines with large internal pressure fluctuations, plenty of pipeline bending sections and complex pipeline deformation characteristics, pipeline detection robots are required to have higher detection capabilities, and the study of the motion state of natural gas pipeline detection robots in pipeline detection is of practical significance. This paper adopts the CFD numerical simulation method and establishes the model of DN800 pipeline deformation detection robot. Next, by simulating the natural gas pipeline detection robot under different media and different pipeline types respectively, the motion state of the detection robot is analyzed under different conditions. The simulation results verify the reliability of the detection robot working inside the pipeline, which can fully guarantee the safe transportation of natural gas pipeline.

Numerical and Experimental Study on the Process of Filling Water in Pressurized Water Pipeline

As an important working condition in water conveyance projects, the water filling process of pipelines is a complex hydraulic transition process involving water–air two-phase flow with sharp pressure changes that can easily cause pipeline damage. In light of the complex water–air two-phase flow during pipeline water filling, this study explores the water filling process of right-angle elbow pressure pipelines using CFD numerical simulations and physical model experiments, analyzing changes in water phase volume fraction, water-gas two-phase flow patterns, and hydraulic parameters in the pipeline under low flow rate conditions of 0.6 m/s and high flow rate conditions of 1.5 m/s. Results show that under low flow rate conditions, there is more local trapped gas at the top of the pipeline, causing negative pressure at local high points in the pipeline and forming a vacuum. Under high velocity conditions, water-gas two-phase flow changes more frequently in the pipeline, with a large number of bubbles collapsing at the top, resulting in large fluctuations in pipeline pressure. Finally, through physical experiments, the main flow patterns during water filling in right-angle elbows are verified and analyzed. These results have certain reference significance for formulating safe and efficient water filling velocity schemes for pressurized pipelines.

Effect of straight riblets of the underlying surface on wall bounded flow drag

Direct numerical simulations of thin, straight riblets were conducted to investigate the physical mechanisms involved when the inertial effects within the ribs become important. The main parameter that we assess here is the ribs’ height to spacing ratio (a=h/s). In all cases, ‘k’-type behaviour was observed despite the absence of the pressure drag component. This trend also refers to the destruction of the near-wall cycles and was indicated by the shortening of Reynolds stress structures, mimicking the flows over rough walls. Closely-packed ribs with large h/s have a tendency to generate Kelvin–Helmholtz (KH) like structures at the tips, inducing large pressure fluctuations. Conversely, sparser ribs with low h/s trigger the formation of large mean secondary flows that suppress the pressure fluctuations. We further split the drag contribution of these distinct flow features by decomposing the roughness function into the dispersive and the Reynolds-stress terms. This analysis concludes that the fully-rough (logarithmic) scaling within the drag-increasing regime is transitional, and as the Reynolds number increases, deviates to a more gradual power-law scaling due to the drag increasing mechanism of streamwise aligned secondary motions.

Experimental analysis of heat and mass transfer in non-isothermal sloshing using a model-based inverse method

Nonisothermal liquid sloshing in partially filled reservoirs can significantly enhance heat and mass transfer between liquid and ullage gasses. This can result in large temperature and pressure fluctuations, producing thrust oscillations in spacecraft and challenging thermal management control systems. This work presents an experimental characterization of the thermodynamic evolution of a cylindrical reservoir undergoing sloshing-induced thermal de-stratification. We use a 0D model-based inverse method to retrieve the heat and mass transfer coefficients in planar and swirl sloshing conditions from the temperature and pressure measurements in the liquid and the ullage gas. The experiments were carried out in the SHAKESPEARE shaking table of the von Karman Institute in a cuboid quartz cell with a cylindrical cut-out of 80 mm diameter in the centre, filled up to 60 mm with the cryogenic replacement fluid HFE-7200. A thermal stratification with ΔT=25 K difference between the ullage gas and liquid was set as the initial conditions. A pressure drop of 90% in the ullage gas was documented in swirling conditions. Despite its simplicity, the model could predict the system’s thermodynamic evolution once the proper transfer coefficients were derived.