This article presents the application of model predictive control (MPC) in high-performance drives. A wide variety of machines have been considered: Induction machines, synchronous machines, linear motors, switched reluctance motors, and multiphase machines. The control of these machines has been done by introducing minor and easy-to-understand modifications to the basic predictive control concept, showing the high flexibility and simplicity of the strategy. The second part of the article is dedicated to the performance comparison of MPC with classical control techniques such as field-oriented control and direct torque control. The comparison considers the dynamic behavior of the drive and steady-state performance metrics, such as inverter losses, current distortion in the motor, and acoustic noise. The main conclusion is that MPC is very competitive concerning classic control methods by reducing the inverter losses and the current distortion with comparable acoustic noise.
The application of model predictive control in electrical drives has been studied extensively in the past decade. This article presents what the authors consider the most relevant contributions published in the last years, mainly focusing on three relevant issues: weighting factor calculation when multiple objectives are utilized in the cost function, current/torque harmonic distortion optimization when the power converter switching frequency is reduced, and robustness improvement under parameters uncertainties. Therefore, this article aims to enable readers to have a more precise overview while facilitating their future research work in this exciting area.
This experimental study aims to explore the Lagrangian nature of fluid transport downstream of a bileaflet mechanical aortic valve under different malfunction scenarios that might be encountered clinically. Time-resolved planar particle image velocimetry measurements are performed to extract instantaneous velocity fields downstream of the bileaflet mechanical valve implanted in an elastic aortic model. The results show an increase in particle residence time with the severity of malfunction. This is attributed to the expansion of the recirculation regions downstream of the valve. The time-evolution of Lagrangian coherent structures over one cardiac cycle (using finite-time Lyapunov exponent fields) shows the effect of valve dysfunction on the material transport and its barriers inside the aorta. The unbalanced flow through the dysfunctional leaflets leads to a significant redistribution of the LCS, thus the fluid transport along the ascending aorta. Moreover, a new technique for the evaluation of the highest accumulated shear stresses is applied along the Lagrangian trajectory of particles being released from the extracted Lagrangian coherent structures where the highest stretching occurs. Finally, the induced non-laminar flow behavior by the valve dysfunction is analyzed using the time-frequency spectra of velocity signals at selected points in the ascending aorta.
Purpose—Mitral regurgitation (MR) is the second most common valve disease in industrialized countries. Despite its high prevalence, little is known about its impact on the flow dynamics in the left ventricle (LV). Because of the interdependence between valvular function and hemodynamics in the heart chambers, an exploration of the dynamics in the LV could lead to a diagnosis of MR. This in vitro study aimed to develop an advanced left heart simulator capable of reproducing several conditions of MR and to evaluate their impact on the LV flow dynamics in terms of flow structures and viscous energy dissipation (VED). Methods—A simulator, previously developed to test mechanical and biological valves, was upgraded with an original anatomically-shaped mitral valve made from a hydrogel. The valve can be used in healthy or pathological configurations. The nature and severity of the disease was controlled by applying specific strain to the chordae. In this study, in addition to a healthy condition, two different severities of MR were investigated: moderate MR and severe MR. Planar time-resolved particle image velocimetry measurements were performed in order to evaluate the velocity field in the LV and the VED induced by each condition. Results—Our results showed that MR led to flow disturbances in the LV that were characterized by an increase in mitral inflow velocity and by elevated values of VED. Interestingly VED increased in proportion to the severity of MR and with a dissipation predominating during systole. Conclusion—Considering these results, the introduction of new parameters based on LV VED could provide crucial information regarding the coupling between the mitral valve and the LV and allow for better stratification of patients with MR.
A high-power Y-junction circulator is proposed for radar applications in the Ku-band (12–18 GHz). The design consists of two identical circulators combined using power splitters at all ports. The overall circulator network achieves 20-dB isolation level and return loss over the Ku-band with a peak power level of 14 kW. An internally matched divider is used at one port of the overall system to eliminate the cavity resonances produced by the practical asymmetries between the two circulators. The asymmetry problem is analyzed in detail to understand the consequences of these practical variations fully. Experimental validation is done by a fabricated prototype and shows a good agreement between the simulated and the measured results with differences in the range of ±2 dB.
Despite the availability of in vivo, instantaneous, and three-dimensional intracardiac flow data, their clinical analysis from a Lagrangian perspective remains limited due to their high computational cost. As an example, identifying Lagrangian coherent structures (LCS) in cardiac flows is not routinely performed in clinical settings despite their ability to identify mixing and stagnation regions along with locations of elevated shear stresses. Here, we explore a recently developed approach, “Lagrangian descriptors”, which quantifies the finite time Euclidean arc-length of Lagrangian trajectories released from a grid of initial positions. Through the evaluated arc-lengths of a set of trajectories, signatures of the LCS (computed from the same initial condition) are captured. Notably, the Lagrangian descriptor approach extracts the LCS within the flow at least five times faster than the common geometrical approach (i.e., using finite-time Lyapunov exponents). In this work, we apply, for the first time, the Lagrangian descriptors approach to in vivo 4D-MRI velocity fields inside left ventricles. The results show the ability of this approach to rapidly reveal the LCS within the left ventricle and how their organization can be altered under healthy and pathological conditions.
In cardiovascular flows, blood transport has been revealed using the Lagrangian coherent structures (LCS). Through a geometric approach, the extracted LCS highlight mixing, stagnation, and elevated shear stress regions. In geophysical flows, graph-theoretic approaches are used to represent fluid transport as a complex flow network. By using classical graph measures, one can extract the LCS along with direct measures of local dispersion and mixing. Also, from the adjacency matrix of the flow network, we can identify the coherent sets in the flow where the fluid within each set is minimally mixed with that in other sets. Notably, the geometric approach can only detect the borders of such regions. This study shows the first application of complex networks analysis to instantaneous planar velocity fields (acquired via PIV) downstream different arrangements of healthy and repaired mitral valves. Using the in- and out-degrees of the transport matrix, the instantaneous local mixing and dispersion are highlighted. Moreover, the LCS are revealed by computing the discrete finite time entropy of the network. Finally, the flow transport matrix is partitioned using a fuzzy c-means clustering algorithm to reveal the flow coherent sets which can better reveal fluid transport mechanisms.
Study aims were to compare hemodynamics and viscous energy dissipation (VED) in 3D printed mitral valves–one replicating a normal valve and the other a valve with severe mitral annular calcification (MAC). Patients with severe MAC develop transmitral gradients, without the commissural fusion typifying rheumatic mitral stenosis (MS), and may have symptoms similar to classical MS. A proposed mechanism relates to VED due to disturbed blood flow through the diseased valve into the ventricle.
A silicone model of a normal mitral valve (MV) was created using a transesophageal echocardiography dataset. 3D printed calcium phantoms were incorporated into a second valve model to replicate severe MAC. The synthetic MVs were tested in a left heart duplicator under rest and exercise conditions. Fine particles were suspended in a water/glycerol blood analogue for particle image velocimetry calculation of VED.
Catheter mean transmitral gradients were slightly higher in the MAC valve compared to the normal MV, both at rest (3.2 vs. 1.3 mm Hg) and with exercise (5.9 vs. 5.0 mm Hg); Doppler gradients were 2.7 vs. 2.1 mm Hg at rest and 9.9 vs 8.2 mm Hg with exercise. VED was similar between the two valves at rest. During exercise, VED increased to a greater extent for the MAC valve (240%) versus the normal valve (127%).
MAC MS is associated with slightly increased transmitral gradients but markedly increased VED during exercise. These energy losses may contribute to the exercise intolerance and exertional dyspnea present in MAC patients.
Aortic valve replacement remains the only viable solution for symptomatic patients with severe aortic valve stenosis. Despite their improved design and long history of successful operation, bileaflet mechanical heart valves are still associated with post-operative complications leading to valve dysfunction. Thus, the flow dynamics can be highly disturbed downstream of the dysfunctional valve.
In this in vitro study, the flow dynamics downstream of healthy and dysfunctional bileaflet mechanical heart valves have been investigated using particle image velocimetry measurements. Proper orthogonal decomposition of the velocity field has been performed in order to explore the coherent flow features in the ascending aorta in the presence of a dysfunctional bileaflet mechanical heart valve.
The ability of proper orthogonal decomposition derived metrics to differentiate between heathy and dysfunctional cases is reported. Moreover, reduced-order modeling using proper orthogonal decomposition is thoroughly investigated not only for the velocity field but also for higher order flow characteristics such as time average wall shear stress, oscillatory shear index and viscous energy dissipation.
Considering these results, proper orthogonal decomposition can provide a rapid binary classifier to evaluate if the bileaflet mechanical valve deviates from its normal operating conditions. Moreover, the study shows that the size of the reduced-order model depends on which flow parameter is required to be reconstructed.
