Unstable Pump Research Articles

Regurgitation during the fully supported condition of the percutaneous left ventricular assist device

Objective. A percutaneous left ventricular assist device (PLVAD) can be used as a bridge to heart transplantation or as a temporary support for end-stage heart failure. Transvalvularly placed PLVADs may result in aortic regurgitation due to unstable pump position during fully supported operation, which may diminish the pumping effect of forward flow and predispose to complications. Therefore, accurate characterization of aortic regurgitation is essential for proper modeling of heart-pump interactions and validation of control strategies. Approach. In the present study, an improved aortic valve model was used to analyze the severity of regurgitation produced by different pump position offsets. The link between pump position offset degree and regurgitation is validated in the fixed speed mode, and the influence of pump speed on regurgitation is verified in the variable speed mode, using the mock circulatory loop (MCL) experimental platform. Main results. The greater the pump offset and the more severe the regurgitation, the more carefully the pump speed needs to be managed. To avoid over-pumping, the recommended pump speed in this study should not exceed 30 000 rpm. Significance. The modeling approach provide in this study not only makes it easier to comprehend the impact of regurgitation events on the entire interactive system during mechanical assistance, but it also aids in providing timely alerts and suitable management measures.

Study on model-based pump noise suppression method of mud pulse signal

Mud pulse telemetry system plays a critical role in modern oil drilling engineering. However, the valid signal is complicated to be obtained because of the main disturbing of pump noises, especially in ultra-deep drilling operations. Therefore, four model-based noise suppression plans for the mud pulse signal pump are mainly proposed in this paper. First, three kinds of pump noise state-space models (linear time-invariant model, linear time-varying model, and nonlinear model) are constructed based on the detailed analysis of the pump noise characteristics. Then, the standard Kalman filter based on the linear system and the extended Kalman filter and unscented Kalman filter algorithm adopting the nonlinear system are respectively used to reconstruct and filter the pump noise. Moreover, the wavelet threshold denoising method based on a new power threshold function is specifically adopted to filter residual random noise after the removal of pump noise. Simultaneously, several noise-containing mud pulse signals with different SNRs (Signal-to-Noise Ratios) in the stable/unstable pump noise states were simulated. Besides, the noise suppression capability experiments of the four plans are deeply conducted. The results indicate that all the four plans can suppress and even remove the stable or unstable pump noise from the original signals: plan 1 and plan 2 have similar denoising effect, which can improve the SNR of signals with stable and unstable pump noise of different intensities by approximately 5–25 dB and 5–14 dB; while the plan 3 can increase the SNR of signals by about 4–20 dB and 2–8 dB; and plan 4 can increase that by about 4–20 dB and 1–8 dB, respectively. Under the comprehensive consideration of denoising ability, computation intensity and convergence speed, it is suggested that plan 1 integrating the time-invariant linear model and the standard Kalman filtering reveals superior performance. Furthermore, using the processing method consisting of plan 1 and wavelet threshold denoising method, the SNRs of the denoised signals can reach 6–7 dB even if the original SNR is as low as −30 dB. The proposed method is applied to the actual deep well mud pulse signal processing. The effective downhole pulse transmission waveform is successfully obtained, providing a highly reliable input signal for subsequent data restoration and contributing to an essential and practical significance for improving mud pulse transmission quality.

Numerical modeling of pulse-pumped ultrafast regenerative amplifier with unstable pump laser

A numerical model of a regenerative amplifier based on the Frantz-Nodvik equation with spatially dependent stored energy density in the active medium has been developed. The model was used to investigate the stability of the output energy of the amplifier associated with fluctuations of the pump energy and pump beam position. It was found that, same as in the known case with the fluctuations of the pump energy, the influence of the fluctuations of the pump beam position is much weaker at oversaturated operation of the regenerative amplifier. Opposite to fluctuations of the pump energy, fluctuations of the pump beam position result in highly-asymmetric histogram of the output energy, which is highly skewed to the lower energies.

Parametric study on pump noise processing method of continuous wave mud pulse signal based on dual-sensor

Continuous wave pulse transmission technology has become the forefront development direction of measurement while drilling and logging information transmission with its high transmission rate and strong anti-interference ability. In this paper, the denoising principle of time-domain delay differential method based on two pressure sensors is analyzed in detail. The acquisition signals of two sensors with different sensor intervals and SNRs (Signal-to-Noise Ratio) are constructed. The denoising ability of the time-domain delay differential method in different cases, i.e., stable and unstable pump noise, the amplitude and frequency distortion of the original pulse signal, and the structural change of the original pulse signal, are emphatically studied. Simulations show that this method can effectively suppress the pump noise even when there is a significant fluctuation in the fundamental frequency and amplitude of pump noise. This method can also obtain well-formed reconstructed signal when the pulse signal has high frequency and amplitude distortion. Besides, a general method for deriving an optimal dual-sensor installation interval is discussed for a BFSK (Binary Frequency Shift Keying) transmission signal, which consists of high-frequency and low-frequency carrier waves, and a reference installation interval is given. Finally, this method is applied to denoise the actual dual-sensor acquisition signal, and satisfactory results are obtained.

TESTING THE INTERACTION OF HEART LEFT VENTRICLE AND CONTINUOUS-FLOW PUMP ON A MOCK CIRCULATION MODEL UNDER NORMAL AND PATHOLOGICAL CONDITIONS

Introduction. The preliminary study of new developed pumps for circulatory support on the hydrodynamic circulation model is an important step in the process of their designing. Hydrodynamic circulation models that can closely imitate cardio – vascular system are important to defi ne the range of effective functioning of the pumps under normal and heart disease conditions which is of great importance for defi ning the mode of these pumps in real clinical conditions.The aim of study is to create a new hydrodynamic circulation model of the systemic circulation to study the processes of interaction of heart left ventricle and continuous – fl ow pumps.Materials and methods. The main components of the mock circulation model (arterial and venous blocks) are designed as closed reservoirs with an air bag providing the necessary elasticity value of these reservoirs. The heart left ventricle was simulated with an artifi cial heart ventricle with a pneumatic drive Sinus-IS which allows to change its options in a wide range. As a test pump we used the fi rst native implantable axial pump VISH – 1. In the course of research we made the registration and recording of the basic hemodynamic parameters (pressure, fl ow) with a multichannel module Pumpax for the measurement of pressure parameters.Results. The designed circulation model allows to adequately reproduce the main hemodynamic parameters of the circulatory system in normal (arterial pressure – 110/77 mmHg, left atrium pressure – 7 mmHg and cardiac output – 4.2 l/min) and heart failure conditions (arterial pressure – 79/53 mmHg, left atrium pressure – 15 mmHg and cardiac output – 3.1 l/min). On the circulation model the interaction of heart left ventricle and continuous-fl ow pump in heart failure simulation was studied. The dynamics of the main circulation fi gures is shown under conditions of changing of the pump rotor speed. Meanwhile, the conditions of the closing of aortic valve are identifi ed which is important for theclinical use of this pump. Using a special separately fl exible camera on the pump inlet we modeled phenomena of negative pressure leading to unstable pump operation and reduction of pump fl ow.Conclusion. Characteristics of the developed hydrodynamic circulation model allow us to reproduce parameters of systemic circulation in a wide range and to use it in designing of new pumps for circulatory support.

Dependency on Runner Geometry for Reversible-Pump Turbine Characteristics in Turbine Mode of Operation

Characteristics of a reversible-pump turbine have been measured with five different leading edge profiles in turbine mode. These profiles varied the inlet blade angle and the radius of curvature. Further geometry parameters have been investigated through numerical simulations. The pump turbine tested has much steeper flow-speed characteristics than a comparable Francis turbine. The most obvious geometry difference is the inlet part of the runner blades, where the blade angle for the pump turbine is much smaller than for the Francis turbine. Two different blade angles have been tested on a physical model and computational fluid dynamics (CFD) simulations have been performed on four different angles. Both methods show that a smaller blade angle gives less steep characteristics in turbine mode, whereas the measured s-shape in turbine brake- and turbine pumping mode gets more exaggerated. Long-radius leading edges result in less steep characteristics. The unstable pump turbine characteristics are in the literature shown to be a result of vortex formation in the runner and guide vane channels. A leading edge with longer curvature radius moves the formation of vortices towards higher speed of rotation.

Stability Limits of Reversible-Pump Turbines in Turbine Mode of Operation and Measurements of Unstable Characteristics

Measurements have been performed on a reversible-pump turbine model installed in a closed loop conduit system. The characteristics of the unstable pump turbine in turbine mode show a hysteresis pattern. Hence the output of the system is dependent on the previous state of the flow and not only the input variables. The hysteresis pattern is a characteristic of the whole system, but is caused by the unstable pump turbine. The unstable part of the characteristics was measured by three different methods: 1) by transient sampling of data during the transition between operation modes, 2) by throttling valves that steepens the friction-loss curve, and 3) by switching the causality in the system such that the torque becomes an input parameter and the speed of rotation becomes an output parameter. In the valve throttling measurements a pressure dependency was seen for the characteristics at high nondimensional speeds. This was further investigated by additional measurements of the characteristics at three different pressure levels. A rigid-water-column stability analysis has been conducted. The classic H-Q criterion describes static stability for a pump turbine with constant speed of rotation. With the speed of rotation as a variable, there is a new static stability criterion in addition to the dynamic stability criterion.

Bandwidth and stability enhancement of optical parametric amplification using chirped ferroelectric superlattice

We report a theoretical analysis and numerical simulation of bandwidth and stability enhancement in optical parametric amplification (OPA) when using chirped periodically poled KTiOPO 4. Calculation results show that the bandwidth and stability are enhanced significantly by the use of a chirped grating. Temperature-gradient and fanned gratings are introduced and chirp factors of them are deduced and calculated. The use of a fanned grating flattens the Quasi-phase-matching response and improves the efficiency. Finally, we propose a method to reduce the instability induced by an unstable pump.

Stability of Electrohydrodynamic Induction Pumping of Liquid Film in Vertical Annular Configuration

Instability of electrohydrodynamic (EHD) induction pumps can manifest itself in a sudden drop/jump in pump output. The instability can also result in alternating/bidirectional flow. To understand and avoid this erratic behavior of the pump operation, a nondimensional stability analysis of EHD induction pumping of liquid film in a vertical annular configuration in the presence of an external load (i.e., pressure gradient and gravitational force) for repulsion mode is carried out. A general nondimensional stability criterion is presented, indicating that the stability of the pump depends on the nondimensional geometric parameters of the pump as well as the nondimensional electric properties of the liquid film. A stability map based on dimensionless electric conductivity and liquid-film thickness is presented. The effect of the dimensionless angular velocity on the nondimensional interfacial velocity under the influence of a pressure gradient and gravitational force is investigated. It is also shown that the erratic behavior of the unstable pump can be eliminated by a proper selection of geometric and liquid-film parameters, as well as the traveling electric-wave frequency.

Modulational instability arising from collective Rayleigh scattering.

It is shown that under certain conditions a collection of dielectric Rayleigh particles suspended in a viscous medium and enclosed in a bidirectional ring cavity pumped by a strong laser field can produce a new modulational instability transverse to the wave-propagation direction. The source of the instability is collective Rayleigh scattering i.e., the spontaneous formation of periodic longitudinal particle-density modulations and a backscattered optical field. Using a linear stability analysis a dispersion relation is derived which determines the region of parameter space in which modulational instability of the backscattered field and the particle distribution occurs. In the linear regime the pump is modulationally stable. A numerical analysis is carried out to observe the dynamics of the interaction in the nonlinear regime. In the nonlinear regime the pump field also becomes modulationally unstable and strong pump depletion occurs.

Excitation of zonal flow by drift waves in toroidal plasmas

An analytical dispersion relation is derived which shows that, in toroidal plasmas, zonal flows can be spontaneously excited via modulations in the radial envelope of a single-n coherent drift wave, with n the toroidal mode number. Predicted instability features are verified by three-dimensional global gyrokinetic simulations of the ion-temperature-gradient mode. Nonlinear equations for mode amplitudes demonstrate saturation of the linearly unstable pump wave and nonlinear oscillations of the drift-wave intensity and zonal flows, with a parameter-dependent period doubling route to chaos.

Flow Physics Leading to System Instability in a Centrifugal Pump

The off-design performance in a centrifugal pump is investigated experimentally. The objective is to identify flow features that lead to the onset of surge as the fundamental pumping system instability. Results show that there are primarily two reasons for the onset of surge as the flow is reduced in the pump studied: (a) adverse flow in the tongue region, and (b) destabilizing effect of the pipe diffuser. The former is due to premature diffusion of the flow entering the tongue region, which is manifested by increased flow recirculation through the tongue/impeller gap and flow separation on the volute outer side-wall opposite the tongue. These effects in the tongue region flow coupled with the destabilizing behavior of the pipe diffuser lead to the eventual unstable pump operation.

System instability caused by the dynamic behaviour of a centrifugal pump at partial operation.

The system instability of a centrifugal pump and pipe network is encountered in the high pressure systems of power plant. The frequency of the instability is limited to be very low (4HZ). Judging from the observation that this instability occurs at the pump operating point with a negative gradient of head-flow characteristics (stable characteristics) and with sufficient NPSH (Net Positive Suction Head), it is concluded that this is a new type of system instability, different from classical surging or cavitation surging. A series of experiments to solve the mechanism of this instability was carried out. The research program consisted of the measurement of the dynamic behaviour of the centrifugal pump, a confirmation test using a pipe network similar to that of the plant and the stability analysis of the system. Our result shows that the matching of the frequency of unstable pump impedance and the pipeline's resonant frequency results in this new type of system instability.

The dynamic behaviour of a centrifugal pump at partial operation and its effect on the system instability.

The system instability of a centrifugal pump and pipe network is encountered at a power plant. The frequency of the instability is confined to a very low level (4.0 Hz). Judging from the observation that this instability occurs at the pump operating point with negative gradient of head-flow (stable) characteristics and with sufficient NPSH, it is concluded that this is a new type of system instability, different from the classical surging or the cavitation surge of inducers. A series of experimental research to solve the mechanism of this instability is carried out. The research program consists of the measurement of the dynamic behaviour of the centrifugal pump, the confirmation test using similar pipeline and the stability analysis of the system. Our result shows that the matching of the frequency of unstable pump impedance and the pipeline's resonant frequency result in this new type of system instability.

Chaotic (strange) and periodic behavior in instability saturation by the oscillating two-stream instability

The nonlinear Schrödinger equation with linear growth and damping is truncated to three waves. The resulting system of nonlinear ordinary differential equations describes the excitation of linearly damped waves by the oscillating two-stream instability driven by a linearly unstable pump wave. This system represents a simple model for the nonlinear saturation of a linearly unstable wave. The model is examined analytically and numerically as a function of the dimensionless parameters of the system. It is found that the model can exhibit a wealth of characteristic dynamical behavior including stationary equilibria, Hopf bifurcations to periodic orbits, period doubling bifurcations, chaotic solutions characteristic of a strange attractor, tangent bifurcations from chaotic to periodic solutions, transient chaos, and hysteresis. Many of these features are shown to be explainable on the basis of one-dimensional maps. In the case of chaotic solutions, evidence for the presence of a strange attractor is provided by demonstrating Cantor set-like structure (i.e., scale invariance) in the surface of section.

Stationary solutions of resonant nonlinear three wave interactions involving growing and damped waves

An investigation is made of the existence and stability of stationary solutions of a system describing the resonant interaction between one linearly unstable pump wave and two damped decay waves. An explicit stability criterion is found as well as expressions for the steady state excitation levels.