Low Pulsation Research Articles

Hemodynamic Effects of Additional Pulmonary Blood Flow on Glenn and Fontan Circulation.

Additional pulmonary blood flow (APBF) can provide better pulsating blood flow and systemic arterial oxygen saturation, while low blood pulsation and low oxygen saturation are defects of the Fontan and Glenn procedure. Studying the hemodynamic effect of APBF is beneficial for clinical decisions. This study aimed to explore the effect on particle washout, as well as the differences among the sensitivities of both different hemodynamic parameters and different procedures to APBF. The patient-specific clinical datasets of a patient who underwent bilateral bidirectional Glenn (BBDG) with APBF were enrolled in this study, and using these datasets, Glenn- and Fontan-type artery models were reconstructed. A series of parameters, including the total caval flow pulsatility index (TCPI), indexed energy loss (iPL), wall shear stress (WSS), systemic arterial oxygen saturation (Satart), particle washout time (WOT), pressure in the rightsuperior vena cava (PRSVC), pulmonary flow distribution (PFD) and hepatic flow distribution (HFD), were computed from computational fluid dynamic (CFD) simulation to evaluate the hemodynamic effect of APBF. The result showed that APBF led to better iPL and Satart but worse PRSVC and heart load accompanied by a great impact on HFD, making hepatic flow easier to perfuse the side without MPA and APBF. The increase in the APBF rate also effectively results in larger flow pulsation, region velocity, and wall shear stress and lower WOT, and this effect may be more effective for patients with persistent left superior vena cava (PLSVC). However, APBF might have little effect on PFD. Furthermore, APBF might affect WOT, iPL and HFD more significantly than PRSVC and has a greater improvement effect in patients with poorer iPL and WOT. Moderate APBF is not only a measure to promote pulmonary artery growth and systemic arterial oxygen saturation but also an effective method against endothelial dysfunction and thrombosis. However, moderate APBF is patient-specific and should be determined based on hemodynamic preference that leads to desired patient outcomes, and care should be taken to prevent PRSVC and heart load from being too high as well as an imbalance in HFD.

Design of Dissolution Apparatus for the Flow-through Cell Method Based on the Low Pulsation Peristaltic Pump

Design of Dissolution Apparatus for the Flow-through Cell Method Based on the Low Pulsation Peristaltic Pump

Development of a high-quality brushless dc electric drive systems model

When designing electric drives based on brushless DC motors with permanent magnets (BLDC), which have low level torque pulsations, the problem of modelling non-standard topological solutions appears. The known models of BLDC motors are either based on the assumptions about the symmetry of the stator pa-rameters of the electric motor and/or the ideal form of the phase back-EMF waveform, which reduce the accuracy of evaluating the effectiveness of the proposed solutions or prove unusable for modelling an operation of the electric motor with a non-standard semiconductor converter. It is necessary to develop a mathematical model of the BLDC motor-based electric drive that takes into account the structural features of the electric motor and allows for semiconductor converter configuration variability. The model is designed in the Matlab Simulink environment. The verification is carried out by comparing the modelling results with experimental data obtained previously by other researchers. The proposed method for generating phase back-EMF in the BLDC motor model provides the possibility for the user to set the EMF form templates independent for each phase. The proposed method for stator circuit simulating provides the user with access to each of the stator windings leads as well as with the possibility of asymmetric determination of each parameter of the electric motor. Upon verification, it has been shown that the difference in the control points between the simulated and experimental speed-torque curves does not exceed 3,5 %. The developed model allows analyzing the static and dynamic characteristics of operation modes of non-standard topology BLDC motor-based electric drives taking into account the stator pa-rameters asymmetry and the real phase back-EMF waveform. The specified features of the model allow exploring the operation of the designed electric drive, taking into account the BLDC motor and converter design. The model can be applied when checking atypical design decisions and when changing the set parameters of the electric drive and restrictions on working conditions and target functions to refine the control system algorithms and automate the search for optimal parameters of the motor and the semiconductor converter.

Comparison of Designs of a Valve-Inductor Motor of an Electric Spindle Drive

When designing electric machines, in particular, the valve-inductor motor of the electric spindle drive, there is a need to compare several designs of such machines in order to choose the most rational one. Based on the given initial data and preliminary calculations, two design variants of the engine were selected: three-phase and five-phase. For each variant, the FEMM v 4.2 software package has been used to calculate optimal geometric ratios based on the maximum of the average moment value. Then, for the optimal variants of a three-phase and five-phase machine, calculations of the voltage, current, and flow coupling of the stator phase, as well as the electromagnetic moment, were performed. It is shown that in a five-phase electric machine, the total electromagnetic moment has several times lower pulsations compared to the three-phase version.

CFD Simulation of Two-Phase Flow in a Hybrid Pulsed Sieve-Plate Solvent Extraction Column: Prediction of Holdup and Axial-dispersion Coefficients

ABSTRACTTwo-phase computational fluid dynamics (CFD) models for a hybrid pulsed sieve-plate solvent extraction column, as well as a standard pulsed sieve-plate column, have been developed with commercial software ANSYS FLUENT. Hydrodynamic performance including two-phase distribution and velocity fields are generated with the models and comparisons are made between two columns. Important parameters including holdup and axial-dispersion coefficients are studied systematically, and CFD successfully predicts the higher holdup and lower axial-dispersion coefficients for the hybrid pulsed sieve-plate column as measured in the experiments. CFD also gives reasonable predictions for the effect of pulsation intensity, dispersed-phase velocity, and continuous-phase velocity on holdup, except for the effect of pulsation intensity in low pulsation region, and the cause has been discussed from the perspective of droplet breakage and coalescence. Comparison with literature data shows that CFD underestimates the holdup of hybrid pulsed sieve-plate column and standard pulsed sieve-plate column by 23.3% and 31.4%, respectively, and the cause has been discussed from the perspective of drag law. CFD gives good prediction of axial-dispersion coefficients for the hybrid pulsed sieve-plate column and the standard pulsed sieve-plate column with ARD of 12.0% and 14.3%, respectively. This study shows CFD to be a useful tool to predict performance for the novel hybrid pulsed sieve-plate column as well as the standard pulsed sieve-plate column.Abbreviations: CFD: computational fluid dynamics; RDC: rotating-disc contactor; ARD: average relative deviation

On the mechanism of symmetric vortex shedding

In this paper, we study the vortex-shedding mechanism of a square cylinder subjected to a mean flow with a superimposed pulsatile flow, under symmetric vortex shedding conditions. The near-body vortical events are interpreted in accordance with the two-dimensional vorticity transport equation, and the interactions between different vortical regions are quantified by circulation balance for a control volume in the near wake. Strong wake counter flow that splits into two branches, with one branch considerably disrupting the boundary layer while other branch cuts off supply of vorticity to the shear layer, is found to be an essential feature of symmetric vortex shedding. To further clarify the roles of correlated terms contributing to the vorticity generation and transport in the wake, the Reynolds number was varied while keeping other excitation parameters constant. This results in the intensity of symmetric vortex shedding increasing with Reynolds number. The increase in wake counter-flow strength with increased Reynolds number cannot be explained either by a relative velocity between the mean and pulsatile flow components or relative acceleration between bluff body and fluid. Based on the results it is inferred that the brief rolling up of the shear layer to form a wake vortex during a part of the pulsation cycle, together with the associated unsteady tangential pressure gradient around the body, contribute to the stronger wake counter flow at higher Reynolds numbers. At lower pulsation amplitudes, the tendency of the fluid in the wake to form strong counter flow can interact significantly with the transverse entrainment flow to alter the natural vortex-shedding mechanism, to give different vortex-shedding modes.

A High-Power Multiphase Wireless Dynamic Charging System With Low Output Power Pulsation for Electric Vehicles

Wireless dynamic charging (WDC) of electric vehicles (EVs) is a new initiative aimed to increase EV uptake. However, pulsating output power along the driving direction is a major problem with this technology. Moreover, in order to deliver enough driving power for EVs, WDC systems must operate at high power. This article proposes a WDC system that has the capability of providing a low pulsating and high output power to EVs. The proposed WDC utilizes multiple primary windings that guarantee a homogeneous mutual magnetic flux for the receiver along the driving direction. This results in a constant induced voltage across the receiver, and hence, constant output power to charge the EV battery. High output power is realized by using multiple transmitter windings, which have been arranged in a novel winding method. The structure layout of the proposed WDC, including ferrite cores, windings, and resonant tanks, is presented. Furthermore, a theoretical analysis is conducted to determine the conditions of each winding’s current phase and amplitude for achieving constant output power. The crossing mutual inductances between the different transmitter’s phases are compensated by adding small capacitors in series with each transmitter winding. An optimization analysis using Maxwell 3-D simulation for both transmitter and receiver is carried out to achieve the highest coupling factor by using minimum ferrite material. The effectiveness of the proposed system is analytically demonstrated and experimentally verified using a 3-kW laboratory prototype. Finally, the performance of the proposed method is compared with similar systems presented in the literature. The comparison shows that the proposed system has the advantages of using simple control, it also eliminates communications between the primary and secondary side and delivers a normalized power of 2.25, which is 125% higher compared to conventional single-phase systems.

A Novel Spoke-Type PM Motor With Auxiliary Salient Poles for Low Torque Pulsation

This paper proposes a novel spoke-type permanent-magnet (PM) motor with auxiliary salient poles (ASPs). With these ASPs, unequal ASPs and shifted ASPs in the circumferential direction can be realized and combined to reduce the torque pulsation, while their functions are different. Unequal ASPs are employed to eliminate the second-order torque pulsation. Nevertheless, the shifted ASPs are selected to reduce the first-order torque pulsation. Additionally, the relationship between the unequal angle or shifted angle of the ASPs and the order of the torque pulsation is revealed. Furthermore, the revealed principle of the torque pulsation reduction can be extended to other slot–pole combinations. Finally, a prototype is manufactured for experiments to evaluate the low torque pulsation spoke-type PM motor. Through theoretical analysis and experimental testing, it is verified that the proposed motor offers low torque pulsation and that the revealed principle for torque pulsation reduction of different orders is feasible and effective.

Investigation of thermal and magnetic field effects on the dynamic instability of FG Timoshenko nanobeam employing nonlocal strain gradient theory

Dynamic instability of temperature-dependent TIMOSHENKO functionally graded (TFG) nanobeam exposed to an axial excitation load and magnetic field in thermal environment is carried out in the present work. The power-law model is utilized to represent the material variations across the nanobeam thickness. In accordance with nonlocal strain gradient theory (NSGT), the equations of motion are derived through Hamilton's principle. Navier and Bolotin's approaches are here employed in order to specify the dynamic instability region of the FG nanoscale beam. The effects of different factors like length to thickness ratio, temperature variation, nonlocal parameter (NP), power-law index, static load factor, magnetic field as well as length scale parameter (LSP) on the dynamic instability boundary are scrutinized through some parametric studies. Based on the outcomes, with increasing temperature change, power-law index and NP, the instability region will be happened at lower pulsation frequencies whereas LSP and magnetic field effects are on the contrary. The obtained results can be useful as reference solutions for future dynamic stability analysis of FG nanobeams reinforced nanocomposites under thermal and magnetic effects.

Flow and heat transfer characteristics of a pulsed jet impinging on a flat plate

The flow and heat transfer characteristics of a pulsed jet impinging on a flat plate under various excitation conditions were experimentally studied. The flow behaviors and time-averaged velocity fields of the characteristic flow structures were examined using a laser-assisted smoke flow visualization method and particle image velocimetry (PIV). The heat transfer of a pulsed impinging jet was measured by a thermal imaging camera. Two primary flow modes were observed in the domain of the jet pulsation intensity and excitation Strouhal number. The coherent vortices and vortex breakup modes appeared in the regimes of low and high jet pulsation intensities, respectively. In the coherent vortices mode, two submodes (contiguous vortices and discrete vortices) were additionally classified. The vortex ring maintained its coherency before impinging on the flat plate in the coherent vortices mode, while the vortex ring lost its coherency and broke up quickly before impinging on the flat plate in the vortex breakup mode. The increase rates of the axial traveling distance and axial convective velocity of the vortex rings in the vortex breakup mode were greater than those in the coherent vortices mode. Pulsating the impinging jet in vortex breakup mode, the effect of a large convective velocity of the vortex rings caused large mean axial velocities and axial velocity fluctuation intensities. The convective heat transfer was enhanced by increasing the convective velocity of the vortex ring and fluctuation intensity.

Experimental and Calculated Investigation of a Natural Circulation Loop’s Thermal-Hydraulic Characteristics

The results from experimental investigation into hydrodynamics and heat transfer in a two-phase natural circulation loop (NCL) under atmospheric pressure are presented. The experiments were carried out for liquids having essentially different properties: water, ethanol, and perfluorohexane C6F14 (the product trademark is FC-72). The circulation velocity in the NCL is not known in advance but is a complex function of the specified parameters (heat flux and liquid temperature at the heated section inlet) and of the two-phase flow internal characteristics. The liquid temperatures at the heated section inlet, the wall temperature over the section height, and also the circulation velocity were measured in the experiments at a specified heat flux; in addition, the two-phase flow at the loop riser leg outlet was filmed on video. The experiments and analysis have shown that flow hydrodynamic instability (circulation velocity pulsations) is really unavoidable in a two-phase NCL. Hydrodynamic instability with a high circulation velocity amplitude and with the occurrence of backward flows is typical for regimes involving significant liquid subcooling values at the heated section inlet and for NCLs containing an extended part with single-phase convection. This instability, which is characteristic for experiments with water, is due to the displacement of the boiling incipience section over the section height; the instability also persists at small subcooling values but with a low pulsation amplitude. Under the developed saturated liquid nucleate boiling conditions (at high heat flux values), the circulation velocity and wall temperature pulsations have small amplitudes, and the flow can be regarded as stable. In the experiments with perfluorohexane, the smallest wall temperature and circulation velocity pulsations were pointed out, which is attributed to a relatively high value of reduced pressure. In the experiments with ethanol, instability occurs in the developed nucleate boiling region (q > 35 kW/m2); this instability is caused by periodically alternating two-phase flow structure (regime). A procedure for calculating a low-pressure NCL is developed, in which the two-phase flow’s local parameters (void fraction, phase velocities, and pressure) are calculated according to a modified homogeneous model (taking into account the phase distribution factor and phases slip) and a dispersed-annular flow model taking into account the droplet entrainment and deposition phenomena. A comparison of the NCL calculation results with the experimental data obtained for three different liquids has shown that they are in good agreement with each other.

Critical limb ischemia in a patient with systemic lupus erythematosus: a case report

BackgroundPeripheral vascular disease is the rarest vascular complication in systemic lupus erythematosus. Some theories propose that immune complexes may promote inflammation in the vessel, and disrupt it in a manner that may cause ischemia.Case presentationA 14-year-old Asian girl presented with intermittent claudication as the chief complaint followed by discoloration of her left big toe for 2 weeks prior to admission. Her medical history showed that 1 month prior to admission she had photosensitivity, rash, and arthralgia, with positive antinuclear antibody test, positive anti-double-stranded DNA test, positive anti-ribosomal protein P, and complement C4 (7.4 mg/dL); she was diagnosed as having systemic lupus erythematosus and started therapy. A local examination of her left toe showed black discoloration, low pulsation, localized tenderness, and decreased sensation. Laboratory results showed C-reactive protein of 1.16 mg/dL and D-dimer of 2.28 uG/mL. A computed tomography angiogram showed near total occlusion of her popliteal artery; critical limb ischemia was confirmed. Peripheral arteriography was performed with invasive strategy. After the procedure, the flow was improved to distal, but there was inflammation in the vessel, so we decided to stop the procedure because of the risk of dissection. Our patient was given atorvastatin and warfarin, and we maximized her systemic lupus erythematosus therapy with prednisone. There were two follow-ups. The first follow-up was 1 week after the procedure. Our patient attended her first follow-up at our out-patient department with no symptoms and improvement in her toe’s discoloration; warfarin was stopped, and clopidogrel and cilostazol were added for thrombus prevention therapy, she was then scheduled for debridement. The second follow-up was done 2 months after the first follow-up and discoloration was improved. The third follow-up, 5 months after the second follow-up, showed improvement.ConclusionCritical limb ischemia is a rare complication of systemic lupus erythematosus that requires immediate treatment. Due to our limited resources, we improvised a strategy to achieve the best possible outcome in our patient by using a combination of invasive treatment and medication.

Dimensionless numbers and correlations for characterizing heat transfer in a pulsating fluidized bed

Heat transfer behavior in a pulsating gas fluidized bed was investigated using Computational Fluid Dynamics. The average rate of heat transfer from the fluidizing gas to the solids was observed to increase with increasing average velocity at low to moderately high pulsation amplitudes. The temperature homogeneity of the fluidized bed improved with increasing pulsation amplitude but the average rate of heat transfer decreased when the maximum gas velocity at the peak of each pulsation cycle became too high. Temperature homogeneity decreased when high average velocities and high pulsation amplitudes were applied simultaneously. Both average rate of heat transfer and temperature homogeneity of the fluidized bed were high when a low or high pulsation frequency was applied but poorer at an intermediate value of pulsation frequency. The Buckingham Π theorem was applied to derive two dimensionless numbers and to develop two dimensionless correlations which exhibited high goodness of fit with the simulation data obtained in this study.

Francis turbine with tandem runners: a proof of concept

Hydraulic turbines operating at off-design regimes inherently have a large residual swirl at runner outlet. This swirling flow is further ingested by the draft tube and its deceleration in the discharge cone results in self-induced instabilities (e.g. precessing vortex rope, low frequency pressure pulsations, power swing) that may hinder the turbine operation. Moreover, for low head Francis turbines the draft tube losses sharply increase as the operating point departs from the best efficiency one, practically shaping the efficiency hill chart. We arrive at the conclusion that an effective approach to flatten the hill chart, while mitigating the instabilities in the draft tube cone is to adaptively adjust the swirling flow exiting the runner for variable operating regimes. As a result, a novel concept of tandem runners is introduced, whereas the classical Francis runner is conceptually split into a high-pressure runner with a constant speed and a low-pressure runner with variable speed. We explore this concept using realistic Francis turbine tandem cascades, with constant and variable transport speed, respectively.

The approach on reducing the pressure pulsation and vibration of seawater piston pump through integrating a group of accumulators

Seawater piston pump is a key power component for underwater equipment. Low pressure pulsation and vibration have become the key requirements of high quality seawater piston pump in the interest of improving the stability, reliability and stealth of underwater equipment. A new type crankshaft seawater piston pump was studied in this paper. The kinematics of the pistons was analyzed and a simulation model was established. The simulation results indicated that its pressure pulsation rate was as high as 17%. Fortunately, after integrating accumulators and optimizing the precharge pressures, the pressure pulsation rate can be reduced below 5% in the working range. The pump possessed better performance when the accumulators were precharged with optimized multiple pressures than with a single pressure. In addition, experimental analysis was conducted through measuring the pressure pulsation and vibration acceleration under different conditions. The experiment results of the pressure pulsation well agreed with the simulation results. Besides, the vibration acceleration of the seawater piston pump was obviously reduced in wide working range when the accumulators were precharged with the optimized combination multiple parameters. In conclusion, integrating accumulators into pump and optimizing the precharge parameters can reduce the pressure pulsation and vibration acceleration in the working range.

Study of pulsational instabilities in models of δ Scuti pulsators discovered under the Nainital-Cape Survey

Under the Nainital-Cape Survey, eight Scuti type pulsators have been discovered with the pulsation periods in the range of several minutes to few hours. In order to understand these observed pulsational variabilities, we have performed non-adiabatic linear stability analyses of these stars having mass in the range of 1 to 3 Mʘ. Several low order pressure modes (p-modes) are found to be unstable where the pulsation pe-riods associated with these unstable modes are in good agreement with the observed periods. Particularly for HD 118660, HD 113878, HD 102480, HD 98851, and HD 25515, we demonstrate that the observed variabilities can be explained with the low order radial p-mode pulsations.

Development and performance evaluation of low pulsation type water hydraulic motor practicable under a radiation environment

Development and performance evaluation of low pulsation type water hydraulic motor practicable under a radiation environment

Design and development of low pulsation type water hydraulic motor practicable under a radiation environment

Design and development of low pulsation type water hydraulic motor practicable under a radiation environment

The effect of pulsation frequency on transition in pulsatile pipe flow

Pulsatile flows are common in nature and in applications, but their stability and transition to turbulence are still poorly understood. Even in the simple case of pipe flow subject to harmonic pulsation, there is no consensus among experimental studies on whether pulsation delays or enhances transition. We here report direct numerical simulations of pulsatile pipe flow at low pulsation amplitude$A\leqslant 0.4$. We use a spatially localized impulsive disturbance to generate a single turbulent puff and track its dynamics as it travels downstream. The computed relaminarization statistics are in quantitative agreement with the experiments of Xuet al. (J. Fluid Mech., vol. 831, 2017, pp. 418–432) and support the conclusion that increasing the pulsation amplitude and lowering the frequency enhance the stability of the flow. In the high-frequency regime, the behaviour of steady pipe flow is recovered. In addition, we show that, when the pipe length does not permit the observation of a full cycle, a reduction of the transition threshold is observed. We obtain an equation quantifying this effect and compare it favourably with the measurements of Stettler & Hussain (J. Fluid Mech., vol. 170, 1986, pp. 169–197). Our results resolve previous discrepancies, which are due to different pipe lengths, perturbation methods and criteria chosen to quantify transition in experiments.

Hydrodynamic characteristics of sawdust in a pulsed slot-rectangular spouted bed

The effects of the pulsation frequency and slot dimensions on the hydrodynamic characteristics and the particle motion of sawdust of mean diameter 1.29 mm were investigated in a pulsed slot-rectangular spouted bed. Pulsation frequencies ranged from 1 to 5 Hz. The pulsed gas flow helped to mobilize the sawdust particles, regardless of the slot dimensions and initial bed height. The fountain height depended more on the slot dimensions than on the pulsation frequency. The time-average bed pressure drop increased with increasing pulsation frequency, while the maximum bed pressure drop was higher for low pulsation frequencies than for high frequency. A slot fully spanning the column thickness and a 3 Hz pulsation frequency were optimal conditions for spouting of sawdust particles without inert particles.