Maximum Jet Velocity Research Articles

Aortic valve tract dynamics in normal-flow low-gradient and normal-flow high-gradient severe aortic stenosis

Abstract Introduction Aortic stenosis (AS) is the most common valvular heart disease in developed countries. Severe AS is defined as a mean pressure gradient (MG) ≥ 40 mmHg, a maximum aortic jet velocity≥4 m/s and an aortic valve area (AVA)≤1 cm2. However, classification of AS severity may be challenging due to discordant results on echocardiography. The normal-flow low-gradient severe AS (NFLG-AS) is defined as AVA≤1 cm2, MG<40 mmHg, left ventricular ejection fraction ≥ 50%, and stroke volume index (SVi) ≥ 35 ml/m2, whereas in the presence of MG > 40mmHg the condition is described as normal-flow high-gradient AS (NFHG-AS). Purpose The purpose of this study was to seek differences in the dynamic changes of the aortic valve tract throughout the cardiac cycle between the two clinical entities: NFHG-AS (Group 1) and NFLG-AS (Group 2). Methods In total, 130 patients with normal flow severe AS who underwent TAVI and had 3D transoesophageal echocardiographic data sets were screened. 38 patients with NFHG-severe AS and 40 patients with NFLG-severe AS with matching clinical characteristics and aortic valve area were identified. A custom-made semi-automated application developed by SQ was used. The application allows tracking of the aortic valve tract surface throughout the cardiac cycle in 3D transoesophageal echocardiograms and provides measurements of the geometrical planes at 4 levels: left ventricular outflow tract (LVOT), aortic annulus (AoA), sinuses of Valsalva (SoV) and sinotubular junction (STJ). Results The echocardiographic characteristics and the dynamic changes of the aortic valve tract between the two groups are shown in Tables 1 and 2. Both groups had comparable echocardiographic characteristic apart from the mean aortic valve pressure gradient as expected. With regards to the aortic valve tract geometrical dynamic changes, the relative LVOT and AoA area changes were bigger in Group 1 (36.8±15.9% vs 29.1±11.9%; p=0.017 and 21.0±8.39% vs 17.1±6.6%; p=0.028). The SoV and STJ relative changes were similar between the two groups. The same applies to aortic stiffness parameters, namely compliance and distensibility of the ascending aorta, systemic arterial compliance, and valvulo-arterial impedance. Conclusion The LVOT and aortic annulus area demonstrate more prominent dynamic changes in patients with normal-flow high-gradient severe AS compared to individuals with normal-flow low-gradient severe AS. While the SoV and the STJ geometry does not change significantly through the cardiac cycle, a more elastic outflow tract allows larger expansion in systole and higher pressure gradients across the aortic valve, whereas a stiffer outflow tract and annulus result in lower pressure gradients, despite the presence of severe aortic stenosis (AVA<1.0cm2). These differences in dynamic LVOT and aortic annulus changes may explain the discrepancy between aortic valve area and pressure gradients in patients with normal-flow low-gradient AS.

On the transient dynamics of laser-induced cavitation bubbles near the end of a slender cylinder

In this work, we perform high-speed imaging and numerical simulation to investigate the transient dynamics of cavitation bubbles near the end of a slender cylinder. The bubble dynamics can be categorized into four distinct regimes in terms of the types of bubble collapse, corresponding to the regular jet, needle jet, in-phase double jets, and anti-phase double jets, respectively, depending on two dimensionless parameters, the normalized cylinder radius η (=rc/Rmax, where rc is the cylinder radius and Rmax is the spherical bubble radius at maximum expansion), and the dimensionless standoff distance γ (=SD/Rmax, where SD is the standoff distance between the end surface of the cylinder and bubble center). The peak velocity of the liquid jet could easily reach a supersonic state in the regime of the needle jet when the cavitation bubble collapses near a slender cylinder, and the maximum jet velocity can reach up to 635 m/s. Quantitative analysis of the evolution of pressure distribution also indicates that the end surface of the cylinder will have strong hydrodynamic pressure loading, particularly for the case of η=0.3 and γ ranging from 0.5 to 0.83. Additionally, we find that the collapse time of the cavitation bubble near a slender cylinder is close to the Rayleigh collapse time. We believe that our findings can be valuable in mitigating or utilizing cavitation near solid cylinders.

Fluid-structure interaction analysis of a healthy aortic valve and its surrounding haemodynamics.

The opening and closing dynamics of the aortic valve (AV) has a strong influence on haemodynamics in the aortic root, and both play a pivotal role in maintaining normal physiological functions of the valve. The aim of this study was to establish a subject-specific fluid-structure interaction (FSI) workflow capable of simulating the motion of a tricuspid healthy valve and the surrounding haemodynamics under physiologically realistic conditions. A subject-specific aortic root was reconstructed from magnetic resonance (MR) images acquired from a healthy volunteer, whilst the valve leaflets were built using a parametric model fitted to the subject-specific aortic root geometry. The material behaviour of the leaflets was described using the isotropic hyperelastic Ogden model, and subject-specific boundary conditions were derived from 4D-flow MR imaging (4D-MRI). Strongly coupled FSI simulations were performed using a finite volume-based boundary conforming method implemented in FlowVision. Our FSI model was able to simulate the opening and closing of the AV throughout the entire cardiac cycle. Comparisons of simulation results with 4D-MRI showed a good agreement in key haemodynamic parameters, with stroke volume differing by 7.5% and the maximum jet velocity differing by less than 1%. Detailed analysis of wall shear stress (WSS) on the leaflets revealed much higher WSS on the ventricular side than the aortic side and different spatial patterns amongst the three leaflets.

The influence of background co-flow on the propulsive characteristics of starting jets

The influence of uniform background co-flow on the propulsive characteristics of starting jets with stroke ratios (length to diameter ratio, L/D) from 1 to 5 and velocity ratios (ratio of co-flow velocity to maximum jet velocity, Rv) from 0 to 0.6 has been investigated numerically. The total impulse generated increases with increasing Rv for L/D<1.5, but increases initially and then decreases for 1.5≤L/D≤3.5. Furthermore, it decreases with increasing Rv for L/D>3.5. The co-flow affects the generation of total impulse mainly by modifying the development of pressure thrust FP(t). The influence on FP(t) can be divided into three stages. During the initial and final stages, FP(t) decreases with increasing Rv, and increases during the middle stage. These three stages are explained by the influence of co-flow on wake vortex ring, leading vortex ring and stopping vortex ring, respectively. Transition between stages can also be related to the instantaneous velocity ratio Rv(t), which is the ratio of co-flow velocity to instantaneous jet velocity. The negative influence of co-flow on the generation of impulse can be mitigated by the velocity program with faster acceleration and shorter deceleration duration, which is equivalent to reducing the average value of Rv(t).

Simulation of the Effect of Particle-bubble Size Ratio on the Collapsing Dynamics of a Cavitation Bubble Near a Particle

Abstract The synergistic effect of cavitation bubbles and sediment particles on material damage is a significant problem in fluid machinery. The dynamic behavior of a cavitation bubble near a spherical particle were simulated in this study using the Volume of Fluid (VOF) method. The effects of the particle-bubble size ratio δ on the bubble profiles, the collapse time, the micro-jets and the pressure at the particle surface have been investigated under the conditions of three values of stand-off distance γ. The results show that (1) the bubble collapse time rises as the particle-bubble size ratio δ increases; (2) the peak values of the maximum jet velocity and the maximum pressure exerting on the particle appear at γ = 1.0 and δ = 1.2, which are 165.3 m/s and 10.46 MPa, respectively; (3) the influence on the particle caused by the micro-jets cannot be ignored when the stand-off distance is less than 1.5.

On the role of aortic valve architecture for physiological hemodynamics and valve replacement, Part I: Flow configuration and vortex dynamics

Aortic valve replacement has become an increasing concern due to the rising prevalence of aortic stenosis in an ageing population. Existing replacement options have limitations, necessitating the development of improved prosthetic aortic valves. In this study, flow characteristics during systole in a stenotic aortic valve case are compared with those downstream of two newly designed surgical bioprosthetic aortic valves (BioAVs). To do so, advanced three-dimensional fluid–structure interaction simulations are conducted and dedicated analysis methods to investigate jet flow configuration and vortex dynamics are developed. Our findings reveal that the stenotic case maintains a high jet flow eccentricity due to a fixed orifice geometry, resulting in flow separation and increased vortex stretching and tilting in the commissural low-flow regions. One BioAV design introduces non-axisymmetric leaflet motion, which reduces the maximum jet velocity and forms more vortical structures. The other BioAV design produces a fixed symmetric triangular jet shape due to non-moving leaflets and exhibits favourable vorticity attenuation, revealed by negative temporally and spatially averaged projected vortex stretching values, and significantly reduced drag. Therefore, this study highlights the benefits of custom-designed aortic valves in the context of their replacement through comprehensive and novel flow analyses. The results emphasise the importance of analysing jet flow, vortical structures, momentum balance and vorticity transport for thoroughly evaluating aortic valve performance.

One-year initial efficacy and safety outcomes of the premounted dry-pericardium Vienna self-expandable transcatheter aortic valve system: A first-in-human VIVA feasibility study.

The dry-pericardium Vienna transcatheter aortic valve system is repositionable and retrievable, already premounted on the delivery system, eliminating the need for assembly and crimping of the device before valve implantation. The VIVA first-in-human feasibility study, a prospective, nonrandomized, single-center trial, evaluated the Vienna aortic valve in 10 patients with severe symptomatic aortic stenosis, who were at intermediate or high surgical risk. This study, registered at ClinicalTrials.gov (NCT04861805), focused on the safety, feasibility, clinical and hemodynamic performance of the Vienna system up to 1-year follow-up. The mean patient age was 79 ± 5 years, 60% male. Valve sizes used: 26 mm (10%), 29 mm (30%), 31 mm (60%). Key hemodynamic improvements were significant: mean aortic valve pressure gradient (mmHg) decreased from 48.7 to 8.1, aortic valve area (cm2) increased from 0.75 to 1.91, and maximum jet velocity through the aortic valve (m/s) decreased from 4.41 to 1.95 (p < 0.0001). No moderate/severe paravalvular leakage was observed, and computed tomography scans revealed no evidence of hypo-attenuated leaflet thickening. The study recorded one life-threatening bleeding event, two cases requiring postprocedural pacemaker implantation, and three ischemic events, with only one causing lasting neurological impairment. Importantly, there were no cases of cardiovascular mortality and only one noncardiovascular death, which was confirmed as unrelated to the device. The study indicates the Vienna valve as a potential option for severe symptomatic aortic stenosis, designed to streamline the procedure and potentially lower healthcare costs by reducing resource and equipment needs, also procedural errors. Further research is essential to thoroughly evaluate its safety and efficacy.

NUMERICAL INVESTIGATION OF SUBMERGED HYBRID CAVITATION JET NOZZLE BASED ON STRESS-BLENDED EDDY SIMULATION MODEL

Cavitation jet technology is extensively applied in fields such as mechanical processing, rock fragmentation, and energy development. To further enhance the cavitation capability of the nozzle, first a submerged organ pipe-angular hybrid cavitation nozzle model is established using the software SOILDWORKS. Second, the stress blended eddy simulation (SBES) technology is applied, and the jet law of internal and external flow field of submerged cavitation nozzle is studied numerically using FLUENT. Finally, the periodic shedding of cavitation clouds and the velocity characteristics and vapor volume fraction are studied for different expansion or contraction angles. The study revealed that the cavitation first occurs in the expansion section. With the development of cavitation, the asymmetry of the cavitation cloud increases significantly. Under an inlet pressure of 20 MPa, the fluctuation part of velocity is more concentrated. As the pressure increases, the maximum jet distance and velocity also increase.

The impact of resting heart rate on adverse outcomes and haemodynamic progression of aortic stenosis

Abstract Introduction A high resting heart rate (RHR) is an established risk factor for cardiovascular disease, adverse cardiac events, accelerated calcification in coronary artery disease and carotid stenosis, and increased aortic valve calcification in patients with and without a confirmed diagnosis of aortic stenosis (AS). Aortic valve calcification is the most common precursor to AS and is associated with significantly faster disease progression. There are few studies exploring the effects of RHR on the progression of AS, the development of severe stenosis, and the risk of complications and death. Purpose We hypothesised that an elevated RHR would be associated with poorer outcomes and more rapid haemodynamic disease progression in patients with AS and tested this in a large cohort of patients without severe disease. Methods Using the National Echocardiography Database of Australia (NEDA) we undertook a retrospective observational study on patients without severe AS, a bicuspid aortic valve or prior aortic valve replacement. The association between baseline RHR and time to the composite primary endpoint of severe AS, aortic valve replacement or cardiovascular death was tested using Cox proportional hazards regression. In addition, the relationship between baseline RHR and the components of this composite was investigated. Subsequently, the relationship between annualised AS progression rate, defined as change in standard indices of AS severity (maximal jet velocity [Vmax], mean pressure gradient [MPG], and aortic valve area [AVA]), and RHR were analysed using general linear models. Results The initial study cohort comprised 55 585 individuals: 54% male, mean age 63 years and median baseline RHR 70 bpm. The composite primary endpoint, reached by 7 434 patients, was independently associated with RHR (hazard ratio [per 10bpm increase], 1.04; 95% CI, 1.02-1.05; p &amp;lt; 0.001). RHR was also independently associated with time to developing severe AS (hazard ratio [per 10bpm increase], 1.06; 95% CI, 1.01-1.12; p = 0.017) and cardiovascular death (hazard ratio [per 10bpm increase], 1.04; 95% CI, 1.02-1.06; p &amp;lt; 0.001). The event rate was significantly higher in patients with a RHR of at least 70 bpm (the median RHR) compared to those with an RHR less than 70 bpm. In addition, RHR was independently associated with rate of change of each individual measurement index of AS severity including Vmax (β = 0.65 cm/s/year [per 10 bpm increase]; p &amp;lt; 0.001), MPG (β = 0.05 mmHg/ year [per 10 bpm increase]; p&amp;lt;0.001), and AVA (β = -0.01 cm2/year [per 10 bpm increase]; p &amp;lt; 0.001). Conclusions RHR is independently associated with adverse clinical outcomes and haemodynamic progression of AS in patients without severe disease. Future randomised controlled trials should investigate the effect of lowering RHR on clinical endpoints and progression of AS.

Droplet impact on a microhole through a partially wetting surface

In this study, we thoroughly investigate the impact dynamics of water droplets on a partially wetting substrate with a single hole. By conducting experiments using de-ionized water droplets and high-speed imaging, we observe various outcomes, including downward jetting without pinch-off, jetting with single and multiple pinch-offs, and the intriguing emergence of an upward jet during droplet recoil. A regime map is constructed to establish the relationship between the dynamics of the jet and the Weber number. We find the small amount of liquid leakage through the hole has a negligible effect on the maximum spreading of the droplet. We analyze the behavior of the downward jet resulting from droplet impact in terms of its length, speed, and breakup characteristics. The scaling relation between the maximum jet length before its breakup and the Weber number is derived and compared with experimental data. We find that the growth of the downward jet length follows a consistent power-law relationship with time regardless of impact velocity, while the maximum jet velocity scales linearly with the impact velocity, confirming the hydrodynamic focusing theory. The size of the head satellite droplet formed during the jet pinch-off process remains nearly constant across different Weber numbers. Additionally, we investigate the volume of ejected liquid through the microhole, observing an initial increase with the Weber number followed by a saturation point. The occurrence of the upward jet during droplet recoil is a significant finding, and we analyze its diameter, height, and velocity in relation to the Weber number.

Numerical analysis of nonlinear interaction between a gas bubble and free surface in a viscous compressible liquid

Liquid viscosity has a potential effect on bubble dynamics. This paper is concerned with bubble dynamics in a compressible viscous liquid near the free surface. The liquid–gas flow is modeled using the Eulerian finite element method coupled with the volume of fluid method. The numerical results have been shown to be in excellent agreement with those from the spherical bubble theory and experiment. Parametric studies are carried out regarding the Reynolds number Re and the stand-off parameter γd. It clearly demonstrated that the liquid viscosity inhibits bubble pulsation, jet flow, free surface jet, and bubble splitting. Quantitatively, as Reynolds number Re decreases, the maximum bubble volume, jet tip velocity, free surface spike, and crown height decrease, and the toroidal bubble splitting weakens. As the stand-off parameter γd increases, the maximum bubble volume, jet velocity, and bubble average pressure peak increase while the height of the free surface spike decreases. Close observation reveals that the free surface crown tends to disappear at small Re or large γd, further indicating the complex mechanism behind the crown spike evolution.

Local Heat Transfer Measurements for an Impinging Synthetic Jet

Abstract Research results demonstrate the heat transfer effectiveness of an impinging synthetic jet toward cooling a plane normal to it. The utility of the synthetic jet lies in that the supply of coolant comes from the device itself as an alternating jetting flow that emerges from a plenum followed by a sink flow that returns to that same plenum. Experiments reported herein were conducted with the synthetic jet driven by an oscillating diaphragm powered by a rotating cam to expel fluid from the plenum out of a single hole, then return it through the same hole. The frequency of diaphragm oscillation and the distance from the synthetic jet's orifice to the surface being cooled are varied in the test program to determine their effects on cooling performance. A numerical study agrees with the results given by the experiment and flow visualization utilizing a smoke generator supports the data and numerical results. The local, time-average Nusselt numbers were measured in the experiment using the thermochromic liquid crystal technique and air as coolant. The color display of each test case was recorded with a fisheye camera. In the case of the highest frequency and shortest distance from orifice to cooled plate, a Nusselt number of nearly 40 was achieved within the central region of the cooled plate when the Reynolds number based upon jet maximum velocity and orifice diameter was 7500 and the distance from the orifice to cooled plate was 3.2 orifice diameters.

Abstract 14356: Machine Learning for Detection of Presence and Severity of Aortic Stenosis From B-mode Ultrasound Images: Results of a Blinded Clinical Trial

Introduction: Aortic stenosis (AS) is common, with &gt;= moderate severity ~10% above age 75. Despite new therapies, many with AS go undiagnosed due to lack of echo availability and untreated due to improper interpretation. To expand AS diagnosis, we developed an artificial intelligence (AI) algorithm to characterize AS from routine B-mode echo exams without Doppler (AutoAS). Methods: 80,000 de-identified clinical echoes were assembled spanning none, mild, moderate, and severe AS. About 30,000 of these were used to train a convolutional neural network (CNN) using labels derived from a cluster analysis of maximal jet velocity, mean AS gradient, and aortic valve area (AVA). Once labeled, we extracted all available B-mode clips from parasternal long-axis, short axis at aortic level, and apical 5-chamber views, irrespective of image quality. A spatiotemporal CNN was trained to return a probability distribution for none/mild/moderate/severe AS. To assess performance of the model, a hold-out test set of echoes uniformly distributed over patient sex and AS severity was used. Three Level 3 echo trained cardiologists blindly read the complete Doppler echoes and agreed to call AS severity by AVA (&lt; 1 cm2, severe; 1.0-1.5 cm2, moderate; &gt; 1.5 cm2 but restricted, mild; no restriction, none). Results were also dichotomized into none/mild and moderate/severe AS. Results: 40 cases comprised this initial test set. Consistency among the readers was outstanding, with κ = 0.95. The table shows the confusion matrix between AutoAS and panel reads, with excellent accuracy (κ = 0.90). Dichotomous results were also outstanding with sensitivity to detect moderate/severe AS of 91% and specificity of 94%. Conclusions: AI can identify AS from 3 B-mode views and characterize AS severity with accuracy highly congruent to an expert panel using full Doppler data. This may allow AS to be detected in low-resource and screening settings. Further assessment with a larger hold-out test set is planned.

Entropy and exergy analysis of the steam jet condensation in crossflow of subcooled water

The direct contact condensation of steam jet in the liquid is an irreversible process with inevitable energy loss. In this paper, interaction between the subcooled water and gas-liquid two-phase boundary, and influence of thermal hydraulic parameters on the change of entropy and exergy are studied. Because of the crossflow of subcooled water, two-phase heat transfer occurs mainly in four regions of the plume cross-section. With increasing temperature, the growth rate of subcooled water entropy flow increases significantly, and the change in the dissipation ratio and damping ratio of kinetic energy is smoother. With the increase of steam mass flux, the entropy flow of the subcooled water reaches a peak at the end of the plume and the peak continuously increases, and the dissipation ratio of kinetic energy and the subcooled water entropy flow fluctuate more violently. Most energy dissipation occurs between the location of maximum jet velocity and the tail of steam jet.

Flow–structure interaction of a starting jet through a flexible circular nozzle

In the present study, the flow–structure interaction of a starting jet through a flexible nozzle is experimentally investigated, with a focus on the optimal flexibility for thrust generation. Water slug is impulsively accelerated through a cylindrical nozzle, fabricated with silicone rubber of varying flexibility. In general, the flexible nozzle modifies the vortical structure of the jet and augments the thrust of the starting jet. The measurement of nozzle surface deformation revealed that a back-and-forth wave propagation on the nozzle surface is responsible for the jet-vortex evolution augmenting the thrust generation. Combining the hydrodynamic conservation equations and the linearized shell theory, we also formulated the governing equations, dominated by two relevant dimensionless parameters: the effective acceleration time of the jet ( $\varPi _0$ ) and the effective nozzle stiffness ( $\varPi _1$ ). Asymptotic analysis of the equation showed that the dimensionless wave speed ( $\hat {c}$ ) is expressed as $\hat {c}=(\varPi _{0}^{2}\varPi _{1}/2)^{0.5}$ , and the jet momentum is maximized at $\hat {c}=\hat {c}_{crit}$ ( $\simeq 3.0$ ), the condition at which the release of elastic energy stored during nozzle contraction to the jet is synchronized with the instant of termination of jet acceleration. While $\hat {c}=\hat {c}_{crit}$ , the achievable maximum jet velocity decreases with the effective acceleration time of the jet ( $\varPi _0$ ), which is attributed to the reduced speed of the surface wave by the flow inside the nozzle.

Experimental Study on Characteristics of Plasma Synthetic Jet Actuators With Different Insulating Materials

Plasma synthetic jet actuator (PSJA) has a wide application prospect in the high-speed flow control field for its high jet velocity. In this article, Nylon and Teflon were selected as the insulation materials of synthetic jet actuators to make use of the ionization ablation properties of thermoplastic materials to improve the actuator performance. The performance differences between these actuators and traditional ceramic synthetic jet actuator are obtained. Based on electrical measurement and high-speed schlieren image system, the electrical characteristics and jet performance of the three kinds of actuators at different air pressures are studied. The discharge voltage, current waveform, discharge efficiency, and discharge energy of the three kinds of actuators were almost the same under different pressures. However, Nylon and Teflon materials will be ablated after ionization, resulting in higher jet velocity and longer jet duration time than traditional actuator of ceramic. The ablation of Teflon was most serious. The Teflon actuator had the maximum jet velocity up to 447.51 m/s at 20-kPa pressure. Based on the schlieren image processing method, the affected area of the actuator was calculated. It was found that the maximum affected area of the Teflon actuator was 144.84% larger than that of the ceramic actuator at 100 kPa. The synthetic jet actuator of Teflon had larger affected area and higher jet velocity than other actuators, so it has great application value in high-speed flow field control.

Effects of loudspeaker-driven synthetic jet actuator parameters on the characteristics of the synthetic jet

In this study, a method for calculating synthetic jet actuator (SJA) parameters by combining diaphragm boundary conditions based on the laws of particle vibration and geometric parameters of the cavity is proposed to obtain accurate rules of variation in which the characteristics of a synthetic jet (SJ) are affected by actuator parameters. Based on the calculating method,an aeroacoustics simulation model of loudspeaker-driven SJA is established with COMSOL software. Simulation results show that the influence of cavity geometry parameters on the velocity characteristics of SJ is greater than that of exciter parameters under the excitation of Helmholtz resonance frequency. Moreover, changing the cavity parameters can increase the jet velocity and reduce the sound pressure level. The velocity characteristics of SJ are consistent with the experimental results.On the basis of the simulation results, the relationship between the aperture length, the cavity length and the modulus of mechanical impedance is established to achieve the maximum jet velocity. It solves various complicated problems of the cavity geometry parameters caused by excitation frequency.

Factors associated with aortic valve stenosis in Japanese patients with end-stage kidney disease

BackgroundAortic valve stenosis (AS) has a high prevalence and poor prognosis in patients who receive maintenance dialysis. However, few large-scale observational studies in Japan have investigated patients with AS who underwent dialysis. In this study, we investigated the prevalence and factors associated with AS in Japanese patients who underwent dialysis.MethodsIn this cross-sectional analysis, we enrolled patients who underwent dialysis and transthoracic echocardiography between July 1, 2017 and June 30, 2018. Patients with a maximum aortic jet velocity (Vmax) ≥ 2.0 m/s, pressure gradient (PG) between the left ventricle and ascending aorta (mean PG) ≥ 20 mmHg, or aortic valve area (AVA) ≤ 1.0 cm2 were categorized into the AS group (G1). Patients with Vmax ≥ 3.0 m/s, mean PG ≥ 20 mmHg, or AVA ≤ 1.0 cm2 were categorized into the moderate and severe AS groups (G2). We performed multivariate logistic regression analysis and compared G1 and G2 with the non-AS group to determine the risk factors for AS. We also investigated the risk factors for aortic valve calcification, which is a pre-stage for AS.ResultsOf the 2,786 patients investigated, 555 (20.0%) and 193 (6.9%) were categorized into G1 and G2, respectively. Multivariate logistic regression analysis revealed that age, long-term dialysis, and elevated serum phosphorus levels were associated with AS in both the groups (p < 0.05). These factors were converted into ordinal categories, and a multivariate logistic regression analysis was performed. Patients with serum phosphorus levels measuring 5.0–5.9 mg/dL and > 6.0 mg/dL showed a higher risk of AS than those with serum phosphorus levels measuring < 4.0 mg/dL (odds ratio 2.24, p = 0.01 and odds ratio 2.66, p = 0.005, respectively). Aortic valve calcification was associated with age, long-term dialysis, diabetes mellitus, administration of vitamin D receptor activators, elevated serum calcium levels, and anemia (p < 0.05 for all).ConclusionsPatients on dialysis showed a high prevalence of AS, which was associated with age, long-term dialysis, and elevated serum phosphorus levels.Trial registrationUMIN000026756, registered on March 29, 2017.

Numerical simulation and instability analysis of particles in liquid–solid concave‐wall jet using DPM‐RSM

AbstractThe liquid–solid concave‐wall jet existed in the vertical cylinder separator with tangential inlet; the instability near concave‐wall was the key factor for centrifugal separation. The effects of jet flowrate and wall curvature radius on the instability of solid‐particles were explored by experiment and numerical simulation. The results showed that the separation efficiency of particles decreased with the increase of centrifugal separation factor. The liquid–solid concave‐wall jet flow in separator was unstable in this study. The decay rate of jet maximum velocity on the concave‐wall was larger than that on plane‐wall jet. The ratio of half‐width value to wall curvature radius was about 0.08 at the circumferential direction 90°, which coincided with the critical value of centrifugal instability in strongly concave‐wall jet. The pressure, velocity, and vorticity fluctuated periodically along streamwise direction in separator. The fluctuation period was linearly related to the wall curvature, and the radial range of fluctuation was only half of jet width. The paired longitudinal vortices formed along the flow direction, and the longitudinal vortices merged at length 0.74 m from the inlet cross‐section along circumferential direction. After the position of vortices merged, the particle trajectory oscillated obviously.

Numerical research of water jet characteristics in underwater explosion based on compressible multicomponent flows

Owing to the high-speed motion and high-pressure load characteristics of water jet, explosion bubble plays an important influence on the surrounding structures in underwater explosion (UNDEX). Based on interface compression and density correction treatment, an important compressible multicomponent flow model is proposed and its discrete method is briefly introduced in the study. This method shows a great potential in multicomponent flow, especially in the research of water jet characteristics caused by bubble collapse in underwater explosion. The bubble dynamic behavior caused by a weighted of 0.2 kg charge at a depth of 50 m is researched under the condition of different distance to diameter ratio near a rigid wall. It can be observed that when the bubble shrinks to the minimum volume, the collapsed pressure on the center of the wall (coordinate origin) does not reach the maximum, excluding γ = 0.24. Owing to the strong nonlinearity of the water jet, the characteristics of the pressure load on the wall are very complex. For the example in the study, the maximum water jet velocity under different γ conditions is between 140 and 280 m/s, and the maximum pressure of the bubble collapse on the wall is between 13.8 and 48.0 MPa. Under such a high-speed impact, a local high-pressure zone is formed near the wall, indicating that the impact damage caused by the water jet to nearby structures cannot be ignored in the underwater explosion.