Pressure-flow Characteristics Research Articles

Evaluation of Left Ventricular Relaxation in Rotary Blood Pump Recipients Using the Pump Flow Waveform: A Simulation Study

In heart failure, diastolic dysfunction is responsible for about 50% of the cases, with higher prevalence in women and elderly persons and contributing similarly to mortality as systolic dysfunction. Whereas the cardiac systolic diagnostics in ventricular assist device patients from pump parameters have been investigated by several groups, the diastolic behavior has been barely discussed. This study focuses on the determination of ventricular relaxation during early diastole in rotary blood pump (RBP) recipients. In conventional cardiology, relaxation is usually evaluated by the minimum rate and the time constant of left ventricular pressure decrease, dP/dt(min) and τ(P) . Two new analogous indices derived from the pump flow waveform were investigated in this study: the minimum rate and the time constant of pump flow decrease, dQ/dt(min) and τ(Q) . The correspondence between the indices was investigated in a numerical simulation of the assisted circulation for different ventricular relaxation states (τ(P) ranging from 24 to 68 ms) and two RBP models characterized by linear and nonlinear pressure-flow characteristics. dQ/dt(min) and τ(Q) always correlated with the dP/dt(min) and τ(P) , respectively (r>0.97). These relationships were influenced by the nonlinear pump characteristics during partial support and by the pump speed during full support. To minimize these influences, simulation results suggest the evaluation of dQ/dt(min) and τ(Q) at a pump speed that corresponds to the borderline between partial and full support. In conclusion, at least in simulation, relaxation can be derived from pump data. This noninvasively accessible information could contribute to a continuous estimation of the remaining cardiac function and its eventual recovery.

Parameter Identification for Electrohydraulic Valvetrain Systems

We consider an electrohydraulic valve system (EHVS) model with uncertain parameters that may possibly vary with time. This is a nonlinear third order system consisting of two clearly separated subsystems, one for the piston position and the other for the chamber pressure. The nonlinearities involved are flow-pressure characteristics of the solenoid valves, the pressure dynamics of the chamber due to varying volume, and a variable damping nonlinearity. We develop a parametric model that is linear in the unknown parameters of the system using filtering. We deal with a nonlinear parameterization in the variable damping term using the Taylor approximation. We design a parameter identifier, which employs a continuous-time unnormalized least-squares update law with a forgetting factor. This update law exponentially converges to the true parameters under a persistence of excitation condition, which is satisfied due to the periodic regime of operation of EHVS. We present simulation results that show good following of unknown parameters even with the presence of sensor noise.

Parametric characterization of piezoelectric valveless micropump

Experimental investigations are performed to determine the influence of electrical excitation and geometrical parameters on the performance of piezoelectric valveless micropumps fabricated on printed circuit board substrates. Strain gauges and shunt resistor are used in conjunction with a data acquisition system to form an effective transducer, capable of providing magnitude and phase response information pertaining to fluid–structure interaction. Effect of conical diffuser geometry on the displacement response and pressure flow characteristics are studied. With suitable variations in the design of the diffuser element and input excitation parameters, the ability of the valveless micropump can be extended to include forward, reversed and bidirectional flow features. The characteristic signatures of single and two peaks in flowrate or pressure data are captured in the displacement phase response. System identification approach is proposed to model and predict the performance of valveless micropumps.

Intracorporeal neobladder reconstruction: pressure‐flow urodyamic studies in cadaveric orthotopic neobladders

To determine the pressure-flow characteristics of neobladders created in various configurations that may be constructed intra-abdominally. Complete intracorporeal neobladder construction has been previously described but is limited due to excessive operative time and the need for an advanced laparoscopic skill set. Four neobladder configurations were constructed, each using 20 cm of human cadaveric small intestine. The standard hand sewn Studer pouch was compared with a circular loop, W-pouch, and U-pouch with stapled anastamoses. Pressure flow studies were completed using the Aquarius TT UDS system (Laborie Medical Technologies, Toronto, Ontario) and each neobladder was filled to a pressure of 50 cm H2O. Neobladder change in pressure, capacity, and overall compliance were determined. The cystometric capacities of the stapled U-pouch, W-pouch, Circle pouch, and Studer pouch were 167.3 mL, 177.5 mL, 114 mL, and 145.2 mL respectively. The first increase in intravesical pressure was at 90.3 mL, 103 mL, 50 mL, and 85 mL. The greatest compliance of 3.81 mL/cmH2O was demonstrated in the U-pouch, with the W-pouch revealing a compliance of 3.44 mL/cmH2O. The least compliant neobladder was the circle pouch (2.24 mL/cmH20) followed by the standard Studer pouch (2.94 mL/cmH2O). The construction of an orthotopic neobladder must not only be technically feasible but maintain adequate capacity and compliance for optimal functioning. Pressure-flow studies demonstrated equivalent results in alternate neobladder configurations. Additional data is needed to determine feasibility in vivo.

CFD Simulation of Two-Phase Flow in a Downhole Venturi Meter

This work performs an oil-water two-phase flow simulation in a downhole Venturi meter to investigate the flow field and pressure characteristics with different flow and oil-water ratios. The relation between the pressure drop and the feed flow rate in the flowmeter is investigated for its optimal design.

Mechanical Cavopulmonary Assistance of a Patient-Specific Fontan Physiology: Numerical Simulations, Lumped Parameter Modeling, and Suction Experiments

This study investigated the performance of a magnetically levitated, intravascular axial flow blood pump for mechanical circulatory support of the thousands of Fontan patients in desperate need of a therapeutic alternative. Four models of the extracardiac, total cavopulmonary connection (TCPC) Fontan configuration were evaluated to formulate numerical predictions: an idealized TCPC, a patient-specific TCPC per magnetic resonance imaging data, and each of these two models having a blood pump in the inferior vena cava (IVC). A lumped parameter model of the Fontan physiology was used to specify boundary conditions. Pressure-flow characteristics, energy gain calculations, scalar stress levels, and blood damage estimations were executed for each model. Suction limitation experiments using the Sylgard elastomer tubing were also conducted. The pump produced pressures of 1-16 mm Hg for 2000-6000 rpm and flow rates of 0.5-4.5 L/min. The pump inlet or IVC pressure was found to decrease at higher rotational speeds. Maximum scalar stress estimations were 3 Pa for the nonpump models and 290 Pa for the pump-supported cases. The blood residence times for the pump-supported cases were shorter (0.9 s) as compared with the nonsupported configurations (2.5 s). However, the blood damage indices were higher (1.5%) for the anatomic model with pump support. The pump successfully augmented pressure in the TCPC junction and increased the hydraulic energy of the TCPC as a function of flow rate and rotational speed. The suction experiments revealed minimal deformation (<3%) at 9000 rpm. The findings of this study support the continued design and development of this blood pump.

Simulation of Deep-Sea Extremophiles Sampling System and Experimental Study

The Deep-sea Extremophiles Sampling System, which contents plaited filter, is modeled and simulated in high pressure seawater environment by AMESim software. The dynamic performances of the system under different environment pressures are analyzed and some experiments are done to validate the simulation model. According to the simulation and experimental results, the environment pressure has very little influence on the pressure drop and flow characteristics of plaited filter. The plaited filter performs perfectly in high pressure seawater environment. The deep-sea extremophiles sampling system can meet the requirements.

Endotracheal tube resistance and inertance in a model of mechanical ventilation of newborns and small infants—the impact of ventilator settings on tracheal pressure swings

Resistive properties of endotracheal tubes (ETTs) are particularly relevant in newborns and small infants who are generally ventilated through ETTs with a small inner diameter. The ventilation rate is also high and the inspiratory time (ti) is short. These conditions effectuate high airway flows with excessive flow acceleration, so airway resistance and inertance play an important role. We carried out a model study to investigate the impact of varying ETT size, lung compliance and ventilator settings, such as peak inspiratory pressure (PIP), positive end expiratory pressure (PEEP) and inspiratory time (ti) on the pressure–flow characteristics with respect to the resistive and inertive properties of the ETT. Pressure at the Y piece was compared to direct measurement of intratracheal pressure (Ptrach) at the tip of the ETT, and pressure drop (ΔPETT) was calculated. Applying published tube coefficients (Rohrer's constants and inertance), Ptrach was calculated from ventilator readings and compared to measured Ptrach using the root-mean-square error. The most relevant for ΔPETT was the ETT size, followed by (in descending order) PIP, compliance, ti and PEEP, with gas flow velocity being the principle in common for all these parameters. Depending on the ventilator settings ΔPETT exceeded 8 mbar in the smallest 2.0 mm ETT. Consideration of inertance as an additional effect in this setting yielded a better agreement of calculated versus measured Ptrach than Rohrer's constants alone. We speculate that exact tracheal pressure tracings calculated from ventilator readings by applying Rohrer's equation and the inertance determination to small size ETTs would be helpful. As an integral part of ventilator software this would (1) allow an estimate of work of breathing and implementation of an automatic tube compensation, and (2) be important for gentle ventilation in respiratory care, especially of small infants, since it enables the physician to estimate consequences of altered ventilator settings at the tracheal level.

대형 유조선의 저항 및 추진성능에 대한 축척효과의 수치적 연구

This article examines the scale effect of the flow characteristics, resistance and propulsion performance on a 317k VLCC. The turbulent flows around a ship in both towing and self-propulsion conditions are analyzed by solving the Reynolds-averaged Navier-Stokes equation together with the application of Reynolds stress turbulence model. The computations are carried out in both model- and full-scale. A double-body model is applied for the treatment of free surface. An asymmetric body-force propeller is used. The speed performances including resistance and propulsion factors are obtained from two kinds of methods. One is to analyze the computational results in model scale through the revised ITTC’78 method. The other is directly to analyze the computational results in full scale. Based on the computational predictions, scale effects of the resistance and the self-propulsion factors including form factor, thrust deduction fraction, effective wake fraction and various efficiencies are investigated. Scale effects of the streamline pattern, hull pressure and local flow characteristics including x-constant sections, propeller and center plane, and transom region are also investigated. This study presents a useful tool to hull-form and propeller designers, and towing-tank experimenters to take the scale effect into consideration.

Prediction of the pressure–flow characteristic of a Belleville washer-based damper valve

Flow control valves used in automotive suspension dampers are almost universally based upon the restriction of flow using Belleville washers. These washers can best be described as a non-flat washer of conical shape and uniform thickness. They are also known as disc springs and are commonly used for load bearing in which their compactness and ability to produce a wide range of load–deflection characteristics provide an alternative to conventional coil springs. Due to the non-linear behaviour of Belleville washers, and the complex flow paths in an automotive damper valve, it is difficult to predict the resulting pressure–flow characteristic. As a result, damper valve design is often considered to be a ‘black art’ best carried out by an experienced engineer using an experimental-based trial-and-error approach. Clearly, without the aid of an analytical tool to predict the behaviour of prototype systems it is difficult for the designer to fully exploit the functionality of a particular design. The current paper describes theoretical and experimental studies undertaken to investigate the pressure–flow characteristic of a Belleville washer-based damper valve. Existing load–deflection theory was extended to account for the hydraulic pressure acting on the surfaces of the washer. However, poor agreement was obtained between the measured pressure–flow data using a uniform pressure distribution across the washer diameter. For this reason the model was developed further to include the effect of a non-uniform pressure distribution within the valve. Computational fluid dynamics software was used to predict the pressure regime within the valve and this, in turn, was used to calculate the forces acting on the surface of the Belleville washer. The improved model was found to match the experimental behaviour with good accuracy, both for a range of spring pre-load conditions and for applications where several washers are stacked up in parallel. However further work would be required to develop a reliable simulation tool as an element of trial and error was necessary to estimate some simulation parameters.

Shock pattern solutions for viscous-collisional plasma ion acoustic waves in view of the linear theory of the non-equilibrium thermodynamics

In the framework of irreversible thermodynamics, we study nonlinear ion-acoustic waves (IAWs) in viscous and collisional plasmas. Electrons, which form the background, are assumed to be nonthermal. On account of ion viscosity and ion-electron collisions, we investigate using ion fluid equations. We study the effects of the nonthermally distributed electrons β and the temperature ratio σ (= Ti/Te) on the stability, where the stability for Burger’s equation is analyzed by two methods: the phase portrait method and irreversible thermodynamics relations at different values of σ and β. We usa a reductive perturbation technique, where the nonlinear evolution of an IAW is governed by the driven Burger equation. This equation is solved exactly by using two methods: the tanh-function method and the Cole–Hopf transformation. Both methods produce shock wave solutions, their results compared, and good agreement exists in most predictions. The analytical calculations show that an IAW propagates as a shock wave with subsonic speed. The flow velocity, pressure, number density, electrostatic potential, and thermodynamic characteristics are estimated and illustrated as functions of time t and the distance x. It is found via the tanh-function method that the amplitudes of the sought-for functions of the system are suppressed and move towards an equilibrium state at the highest value of β. The tanh-function method reveals an advantage over the Cole–Hopf method in the viscous and collisional cases of IAWs, where it satisfies the stability conditions at the highest value of β with the chosen σ values when applied to evaluate the Onsager relation.

Effects of Pressure Ratio and Rotational Speed on Leakage Flow and Cavity Pressure in the Staggered Labyrinth Seal

Effects of pressure ratio and rotational speed on the leakage flow and cavity pressure characteristics of the rotating staggered labyrinth seal were investigated by means of experimental measurements and numerical simulations. The rotating seal test rig with turbine flowmeter and pressure measuring instruments was utilized to investigate the leakage flow of the staggered labyrinth seal at eight pressure ratios and five rotational speeds. The repeatability of the experimental data was demonstrated by three times measurements at different pressure ratios and fixed rotational speed. The three-dimensional Reynolds-averaged Navier–Stokes equations and standard k-ε turbulent model were also applied to study the leakage flow characteristics of the staggered labyrinth seal at the experimental conditions. The validation of the numerical approach was verified through comparison of the experimental data. The detailed flow field in the staggered labyrinth seal was illustrated according to the numerical simulations. The experimental and numerical results show that the leakage flow coefficient increases with increasing pressure ratio at the fixed rotational speed and is more sensitive to the smaller pressure ratio. The influence of rotational speed on the leakage flow coefficient is not obvious in the present rotational speed limitations. The cavity pressure coefficient in the staggered labyrinth seal decreases and is significantly influenced by the cavity structure along the flow direction.

Double Step Reducing Characteristics Analysis of On-Board High Pressured Hydrogen Transmission

Pressure reducing and control is the key technology in hydrogen transmission for fuel cell cars. A double step system with two direct reducing valves had been provided in this paper. These two valves depressurize the tank hydrogen pressure from 35MPa or 70MPa to 5MPa at first, then to 0.16MPa, adapting the fuel cell demands. The valves static analysis show the flow rate and pressure characteristics are rigid. The dynamic simulation display the valves quick response and pressure control accuracy are satisfied fuel cell working condition. The analogue experiments verify the system reducing performance and the double step reducing system is applicable to fuel cell cars hydrogen transmission.

LPV Model-based Robust Controller Design of Electro-hydraulic Servo Systems

In this paper, a Lyapunov-based control algorithm is developed for position tracking control of a class of electro-hydraulic servo systems driven by double-rod hydraulic actuators. By utilizing the nonlinear servo valve flow-pressure characteristics of the hydraulic system, the electro-hydraulic servo system is firstly described as a linear parameter varying (LPV) model. Then the sufficient strict linear matrix inequality (LMI) conditions for the robust stabilizability of the uncertain systems are proposed in terms of LMIs. By solving those LMIs, a parameter-dependent controller is established for the closed-loop system to be stable with a prescribed level of disturbance attenuation. Finally, the numerical simulations demonstrate the usefulness and advantages of the proposed controllers.

Interaction of an Idealized Cavopulmonary Circulation With Mechanical Circulatory Assist Using an Intravascular Rotary Blood Pump

This study evaluated the performance of an intravascular, percutaneously-inserted, axial flow blood pump in an idealized total cavopulmonary connection (TCPC) model of a Fontan physiology. This blood pump, intended for placement in the inferior vena cava (IVC), is designed to augment pressure and blood flow from the IVC to the pulmonary circulation. Three different computational models were examined: (i) an idealized TCPC without a pump; (ii) an idealized TCPC with an impeller pump; and (iii) an idealized TCPC with an impeller and diffuser pump. Computational fluid dynamics analyses of these models were performed to assess the hydraulic performance of each model under varying physiologic conditions. Pressure-flow characteristics, fluid streamlines, energy augmentation calculations, and blood damage analyses were evaluated. Numerical predictions indicate that the pump with an impeller and diffuser blade set produces pressure generations of 1 to 16 mm Hg for rotational speeds of 2000 to 6000 rpm and flow rates of 1 to 4 L/min. In contrast, for the same flow range, the model with the impeller only in the IVC demonstrated pressure generations of 1 to 9 mm Hg at rotational speeds of 10,000 to 12,000 rpm. Influence of blood viscosity was found to be insignificant at low rotational speeds with minimal performance deviation at higher rotational speeds. Results from the blood damage index analyses indicate a low probability for damage with maximum damage index levels less than 1% and maximum fluid residence times below 0.6 s. The numerical predictions further indicated successful energy augmentation of the TCPC with a pump in the IVC. These results support the continued design and development of this cavopulmonary assist device.

Polymer microvalve with pre-stressed membranes for tunable flow–pressure characteristics

A novel, inexpensive, polymer-based valve approach is presented that offers the combination of a check valve’s rectifying properties with the possibility to actively control the flow rate in the forward (open) direction. An elastic membrane with an incision is clamped between two rigid polymer plates and expands when pressure is applied in the forward direction allowing fluid to pass. In the backward direction, expansion of the membrane is not possible and flow is prevented. Varying the clamping force influences the expansion capability of the membrane due to its elasticity and thus enables control of the flow rate.

주거환기용 시로코홴의 공력 및 소음 특성 연구

This paper presents a procedure for the aerodynamic and aeroacoustic characteristics of a sirocco fan. For the aerodynamic and aeroacoustic analyses of the sirocco fan, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes equations are solved with a shear stress transport turbulence model for turbulence closure. The flow analyses were performed on a hexahedral grid using a finite-volume solver. The validation of the numerical results is performed by comparing with experimental data for the pressure, efficiency and power. The internal flow analyses of the sirocco fan are performed to understand the unstable flow phenomenon on the casing for the wall pressure and internal flow characteristics at each position. It was found that fluctuation of pressure and locally concentrated noise source are observed near the cut-off and expansion regions of the casing.

Flow Force Analysis of a Variable Force Solenoid Valve for Automatic Transmissions

Three-dimensional numerical simulations were carried out to investigate the flow dynamic behavior and pressure characteristics of a variable force solenoid (VFS) valve used in automatic transmissions. To visualize the dynamic movement of the spool, a moving mesh with dynamic layering meshes for varying boundary conditions was employed. Relevant experiment was performed to validate the simulations. The VFS valve was characterized by determining the variation in the equivalent orifice area with the spool displacement. The pressure sensitivity was found to be precisely controlled by the relation between the depth and the area of the notch in the range of the characteristic length of the valve. The results of model C, which takes into account both seal leakage and notches, indicate that there are linear pressure sensitivities in the range of the valve overlap and that there are smooth pressure control characteristics in the range of the two notches. The VFS valve with a spool was shown to have an unavoidable and unique hysteresis, which is caused by the nonlinear electromagnetic forces at the end of strokes of the spool and by the friction forces in the valve overlap. The effects of varying the oil temperature on the pressure sensitivity curves and the seal leakage flow rates were also examined.

Harmonic distortion reduction on seismic vibrators

To improve seismic resolution using vibroseis, vibrators must output the ground-force energy with minimum harmonic distortion. Four main sources within the vibrator system cause the ground force to suffer severe harmonic distortion: the nonlinear servo-valve flow-pressure character-istics, the servo-valve characteristics near null, the fluctuations in the hydraulic pressure, and the nonlinear contact-stiffness between the baseplate and the ground. Modeling was undertaken to investigate and quantify harmonic distortion from each source. As a result, three modifications have been made to reduce the harmonic distortion of the ground force:

Three-dimensional numerical simulations of cross-flow around four cylinders in an in-line square configuration

This paper presents a numerical study of three-dimensional (3-D) laminar flow around four circular cylinders in an in-line square configuration. The investigation focuses on effects of spacing ratio ( L/ D) and aspect ratio ( H/ D) on 3-D flow characteristics, and the force and pressure coefficients of the cylinders. Extensive 3-D numerical simulations were performed at Reynolds number of 200 for L/ D from 1.6 to 5.0 at H/ D=16 and H/ D from 6 to 20 at L/ D=3.5. The results show that the 3-D numerical simulations have remedied the inadequacy of 2-D simulations and the results are in excellent agreement with the experimental results. The relation between 3-D flow patterns and pressure characteristics around the four cylinders is examined and discussed. The critical spacing ratio for flow pattern transformation was found to be L/ D=3.5 for H/ D=16, while a bistable wake pattern was observed at L/ D=1.6 for the same aspect ratio. Moreover, a transformation of flow pattern from a stable shielding flow pattern to a vortex shedding flow pattern near the middle spanwise positions of the cylinders was observed and was found to be dependent on the aspect ratio, spacing ratio, and end wall conditions. Due to the highly 3-D nature of the flows, different flow patterns coexist over different spanwise positions of the cylinders even for the same aspect ratio. It is concluded that spacing ratio, aspect ratio, and the no-slip end wall condition have important combined effects on free shear layer development of the cylinders and hence have significant effects on the pressure field and force characteristics of the four cylinders with different spacing ratios and aspect ratios.