Valve Dynamics Research Articles

Eulerian finite element method for the numerical modeling of fluid dynamics of natural and pathological aortic valves

We present a finite element methodology tailored for the simulation of pulsatile flow in the full aorta and sinus of Valsalva interacting with highly deformable thin leaflets. We describe an extension of the so-called “Resistive Immersed Surface” method. To circumvent stability issues resulting from the bad conditioning of the linear system, especially when flow and geometry become complex after the inclusion of the aorta, we use a Lagrange multiplier technique that couples the dynamics of valve and flow. A banded level set variant allows to address the singularity of the resulting linear system while featuring, in addition to the parallel implementation, higher accuracy and an affordable computational burden. High-fidelity computational geometries are built and simulations are performed under physiological conditions. Several numerical experiments illustrate the ability of the model to capture the basic fluidic phenomena in both healthy and pathological configurations. We finally examine numerically the flow dynamics in the sinus of Valsalva after Transcatheter Aortic Valve Implantation. We show numerically that flow may be subject to stagnation in the lower part of the sinuses. We highlight the far-reaching implications of this phenomenon and we hope inciting adequate studies to further investigate its potential clinical consequences.

Fluid-Structure Interaction Study of Transcatheter Aortic Valve Dynamics Using Smoothed Particle Hydrodynamics.

Computational modeling of heart valve dynamics incorporating both fluid dynamics and valve structural responses has been challenging. In this study, we developed a novel fully-coupled fluid-structure interaction (FSI) model using smoothed particle hydrodynamics (SPH). A previously developed nonlinear finite element (FE) model of transcatheter aortic valves (TAV) was utilized to couple with SPH to simulate valve leaflet dynamics throughout the entire cardiac cycle. Comparative simulations were performed to investigate the impact of using FE-only models vs. FSI models, as well as an isotropic vs. an anisotropic leaflet material model in TAV simulations. From the results, substantial differences in leaflet kinematics between FE-only and FSI models were observed, and the FSI model could capture the realistic leaflet dynamic deformation due to its more accurate spatial and temporal loading conditions imposed on the leaflets. The stress and the strain distributions were similar between the FE and FSI simulations. However, the peak stresses were different due to the water hammer effect induced by the fluid inertia in the FSI model during the closing phase, which led to 13-28% lower peak stresses in the FE-only model compared to that of the FSI model. The simulation results also indicated that tissue anisotropy had a minor impact on hemodynamics of the valve. However, a lower tissue stiffness in the radial direction of the leaflets could reduce the leaflet peak stress caused by the water hammer effect. It is hoped that the developed FSI models can serve as an effective tool to better assess valve dynamics and optimize next generation TAV designs.

Role of vessel-to-prosthesis size mismatch in venous valve performance.

Efforts to treat chronic venous insufficiency have focused on the development of prosthetic venous valves. The role of prosthetic valve-to-vessel size matching has not been determined. The purpose of this investigation was to assess the effect of size mismatching on venous valve function and to establish a mismatch limit that affects valve hemodynamic performance and venous wall stress to improve future valve designs and implants. Flow dynamics of prosthetic venous valves were studied invitro using a pulse duplicator flow loop. Valve performance based on flow rate and pressure measurements was determined at oversizing ratios ranging from 4.2% to 25%. Valve open area ratios at different size mismatching ratios were investigated by image analysis. Finally, a wall stress analysis was used to determine the magnitude of circumferential (hoop) stress in the venous wall at various degrees of oversizing. Our findings indicate that valve regurgitate volume, closing time, and pressure difference across the valve are significantly elevated at mismatch ratios greater than ∼15%. This is supported by increases in regurgitate velocity and open area relative to valves tested at near-nominal diameters. At this degree of size mismatch, the wall stress is increased by a factor of two to three times relative to physiologic pressures. These findings establish a relationship between valve size matching and valve hemodynamic performance, including vessel wall stress, which should be considered in future valve implants. The size of the prosthetic valve should be within 15% of maximum vein size to optimize venous valve hemodynamic performance and to minimize the hoop wall stress.

Reed Valve Dynamics of Reciprocating Compressor – A Review

Reed Valve Dynamics of Reciprocating Compressor – A Review

Application of second order sliding mode algorithms for output feedback control in hydraulic cylinder drives with profound valve dynamics

The application of second order sliding mode algorithms for output feedback control in hydraulic valve-cylinder drives appear attractive due to their simple realization and parametrization, and strong robustness toward bounded parameter variations and uncertainties. However, intrinsic nonlinear dynamic effects of hydraulic valves such as slew rate limitations and time delays arising in the electrical and mechanical amplification stages limits the applicability of such methods, and may lead to partial losses of robustness and limit cycles/oscillations in the outputs, internal states and the valve input signals. The application of some popular second order sliding mode controllers and their smooth counterparts are analyzed and experimentally verified. The controllers are considered for output feedback control and compared with a conventional PI control approach. The controllers under consideration are applied for position tracking control of a hydraulic valve-cylinder drive exhibiting strong variations in inertia- and gravitational loads, and furthermore suffer from profound valve dynamics. Results demonstrate that both the twisting- and super twisting algorithms may be successfully applied for this purpose, when continuous approximations of discontinuous are utilized, and furthermore that excellent performance may be achieved when applying their smooth counterparts directly.

Planar biaxial testing of heart valve cusp replacement biomaterials: Experiments, theory and material constants.

Aortic valve (AV) repair has become an attractive option to correct aortic insufficiency. Yet, cusp reconstruction with various cusp replacement materials has been associated with greater long-term repair failures, and it is still unknown how such materials mechanically compare with native leaflets. We used planar biaxial testing to characterize six clinically relevant cusp replacement materials, along with native porcine AV leaflets, to ascertain which materials would be best suited for valve repair. We tested at least six samples of: 1) fresh autologous porcine pericardium (APP), 2) glutaraldehyde fixed porcine pericardium (GPP), 3) St Jude Medical pericardial patch (SJM), 4) CardioCel patch (CC), 5) PeriGuard (PG), 6) Supple PeriGuard (SPG) and 7) fresh porcine AV leaflets (PC). We introduced efficient displacement-controlled testing protocols and processing, as well as advanced convexity requirements on the strain energy functions used to describe the mechanical response of the materials under loading. The proposed experimental and data processing pipeline allowed for a robust in-plane characterization of all the materials tested, with constants determined for two Fung-like hyperelastic, anisotropic strain energy models. Overall, CC and SPG (respectively PG) patches ranked as the closest mechanical equivalents to young (respectively aged) AV leaflets. Because the native leaflets as well as CC, PG and SPG patches exhibit significant anisotropic behaviors, it is suggested that the fiber and cross-fiber directions of these replacement biomaterials be matched with those of the host AV leaflets. The long-term performance of cusp replacement materials would ideally be evaluated in large animal models for AV disease and cusp repair, and over several months or more. Given the unavailability and impracticality of such models, detailed information on stress-strain behavior, as studied herein, and investigations of durability and valve dynamics will be the best surrogates, as they have been for prosthetic valves. Overall, comparison with Fig. 3 suggests that CC and SPG (respectively PG) patches may be the closest mechanical equivalents to young (respectively aged) AV leaflets. Interestingly, the thicknesses of these materials are close to those reported for porcine and younger human AV leaflets, which may facilitate surgical implantation, by contrast to the thinner APP which has poor handling qualities. Because the native leaflets as well as CC, PG and SPG patches exhibit anisotropic behaviors, from a mechanistic perspective alone, it stands to reason that cardiac surgeons should seek to intraoperatively match the fiber and cross-fiber directions of these replacement biomaterials with those of the repaired AV leaflets.

Invited Commentary

Leonardo da Vinci was a master at blending function of biologic systems into his graphic drawings. His illustrations of aortic flow currents most likely were rendered from the first models that recapitulated the dynamic function of any biologic system [1Gharib M. Kremers D. Koochesfahani M.M. Kemp M. Leonardo’s vision of flow visualization.Exp Fluids. 2002; 33: 219-223Crossref Scopus (52) Google Scholar]. Similarly, ever since echocardiography was developed and expanded in the 1970s and 1980s, cardiologists and surgeons have desired to develop structural models of heart valves. This article by Pouch and associates [2Pouch A.M. Jackson B.M. Lai E. et al.Modeling the myxomatous mitral valve with three-dimensional echocardiography.Ann Thorac Surg. 2016; 102: 703-711Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar] describes a complex imaging and reconstruction method that attempts to characterize both non-diseased and myxomatous mitral valves. This work from the Gorman Laboratory at the University of Pennsylvania is unique; it used three-dimensional echocardiographic reconstructions to study the material properties of non-diseased and myxomatous mitral valves. Moreover, they were able to make transforms that potentially could be printed three-dimensionally into actual solid models of different degenerative mitral lesions. Although the methodology described in the article is beyond the interest or scope of most practicing cardiac surgeons, the message from this work is important. Clearly, improvement in echocardiography has been an iterative process, albeit a rapid one. Future advancements assuredly will allow us to have dynamic models of mitral valves to be created instantaneously in the operating room. With image fusion techniques, the creation of onlay “blueprints” may be possible to guide more perfectly engineered mitral repairs. The complexity of mitral valve stress-strain (pressure versus deformation) relationships is so multifactorial that perfect modeling will be even more difficult than this article describes. The authors had to make assumptions. They were not able to negate the mechanical property alterations of velocity and anisotropy; this means that degenerative valve leaflets often have variable regional thicknesses with variable viscoelastic properties rather than uniform ones. Moreover, multiple areas of prolapse impose additional nonconstant mechanical properties. In the early 1990s, Kunzelman and associates [3Kunzelman K.S. Cochran R.P. Chuong C. Ring W.S. Verrier E.D. Eberhart R.D. Finite element analysis of the mitral valve.J Heart Valve Dis. 1993; 2: 326-340PubMed Google Scholar] first used finite element analysis to determine mitral valve stress strain relationships in an attempt to define what leaflet regions were at highest risk (strain) for failure. Their most recent in vitro modeling studies, using micro computed tomographic images, focuses on stress-strain interactions of normal mitral leaflets, papillary muscles, and chords throughout the cardiac cycle [4Toma M. Bloodworth IV, C.H. Einstein D.R. et al.High-resolution subject-specific mitral valve imaging and modeling: experimental and computational methods.Biomech Model Mechanobiol. 2016 Apr 19; ([Epub ahead of print])Crossref PubMed Scopus (24) Google Scholar]. Recently, Hossien’s group [5Hossien A. Nithiarasuc P. Cheriex E. Maessen J. Sardari Nia P. Ashraf S. A multi-dimensional dynamic quantification tool for the mitral valve.Interact Cardiovasc Thorac Surg. 2015; 21: 481-487Crossref PubMed Scopus (10) Google Scholar] in Maastricht modeled mitral valve dynamics from segmented transesophageal echocardiography data in healthy patients. Subsequently, they have been able to print solid models for teaching minimally invasive mitral repairs for patients with various types of degenerative disease (Personal Communication, Peyman Sardari Nia, MD, University of Maastricht, 2016). The present article brings us much closer to translating image data from degenerative mitral valves into useful models for teaching and aiding in providing tailored mitral repairs for individualized patients. Anyanwu and colleagues [6Anyanwu A. Itagaki S. Chikwee J. El-Eshmawi A. Adams D.H. A complexity scoring system for degenerative mitral valve repair.J Thorac Cardiovasc Surg. 2016; 151: 1661-1670Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar] suggested recently that mitral valve pathologic complexity be categorized with a view toward selecting repair potentials based on a surgeon’s experience and talents. Thus, the information gained from future echocardiographic modeling studies could help surgeons to categorize the pathologic complexities of degenerative valves and to determine the best technique for reattaining the near-perfect leaflet and chord stress-strain relationships. To this end, the authors now must be challenged to develop dynamic operating room models that can be translated contemporaneously. Mitral repair surgeons should stay abreast of this evolving and exciting imaging and modeling technology; it could help us save more mitral valves from the pathologists’ microscope. Modeling the Myxomatous Mitral Valve With Three-Dimensional EchocardiographyThe Annals of Thoracic SurgeryVol. 102Issue 3PreviewDegenerative mitral valve disease is associated with variable and complex defects in valve morphology. Three-dimensional echocardiography (3DE) has shown promise in aiding preoperative planning for patients with this disease but to date has not been as transformative as initially predicted. The clinical usefulness of 3DE has been limited by the laborious methods currently required to extract quantitative data from the images. Full-Text PDF

A laboratory model of the aortic root flow including the coronary arteries

Cardiovascular flows have been extensively investigated by means of in vitro models to assess the prosthetic valve performances and to provide insight into the fluid dynamics of the heart and proximal aorta. In particular, the models for the study of the flow past the aortic valve have been continuously improved by including, among other things, the compliance of the vessel and more realistic geometries. The flow within the sinuses of Valsalva is known to play a fundamental role in the dynamics of the aortic valve since they host a recirculation region that interacts with the leaflets. The coronary arteries originate from the ostia located within two of the three sinuses, and their presence may significantly affect the fluid dynamics of the aortic root. In spite of their importance, to the extent of the authors’ knowledge, coronary arteries were not included so far when modeling in vitro the transvalvular aortic flow. We present a pulse duplicator consisting of a passively pulsing ventricle, a compliant proximal aorta, and coronary arteries connected to the sinuses of Valsalva. The coronary flow is modulated by a self-regulating device mimicking the physiological mechanism, which is based on the contraction and relaxation of the heart muscle during the cardiac cycle. Results show that the model reproduces satisfyingly the coronary flow. The analysis of the time evolution of the velocity and vorticity fields within the aortic root reveals the main characteristics of the backflow generated through the aorta in order to feed the coronaries during the diastole. Experiments without coronary flow have been run for comparison. Interestingly, the lifetime of the vortex forming in the sinus of Valsalva during the systole is reduced by the presence of the coronaries. As a matter of fact, at the end of the systole, that vortex is washed out because of the suction generated by the coronary flow. Correspondingly, the valve closure is delayed and faster compared to the case with no coronary flow.

Validation of an immersed thick boundary method for simulating fluid–structure interactions of deformable membranes

This paper constitutes an extension of the work of Mendez et al. (2014) [36], for three-dimensional simulations of deformable membranes under flow. An immersed thick boundary method is used, combining the immersed boundary method with a three-dimensional modeling of the structural part. The immersed boundary method is adapted to unstructured grids for the fluid resolution, using the reproducing kernel particle method. An unstructured finite-volume flow solver for the incompressible Navier–Stokes equations is coupled with a finite-element solver for the structure. The validation process relying on a number of test cases proves the efficiency of the method, and its robustness is illustrated when computing the dynamics of a tri-leaflet aortic valve. The proposed immersed thick boundary method is able to tackle applications involving both thin and thick membranes/closed and open membranes, in significantly high Reynolds number flows and highly complex geometries.

Global sensitivity analysis of a model for venous valve dynamics

Chronic venous disease is defined as dysfunction of the venous system caused by incompetent venous valves with or without a proximal venous obstruction. Assessing the severity of the disease is challenging, since venous function is determined by various interacting hemodynamic factors. Mathematical models can relate these factors using physical laws and can thereby aid understanding of venous (patho-)physiology. To eventually use a mathematical model to support clinical decision making, first the model sensitivity needs to be determined. Therefore, the aim of this study is to assess the sensitivity of the venous valve model outputs to the relevant input parameters. Using a 1D pulse wave propagation model of the tibial vein including a venous valve, valve dynamics under head up tilt are simulated. A variance-based sensitivity analysis is performed based on generalized polynomial chaos expansion. Taking a global approach, individual parameter importance on the valve dynamics as well as importance of their interactions is determined. For the output related to opening state of the valve, the opening/closing pressure drop (dpvalve,0) is found to be the most important parameter. The venous radius (rvein,0) is related to venous filling volume and is consequently most important for the output describing venous filling time. Finally, it is concluded that improved assessment of rvein,0 and dpvalve,0 is most rewarding when simulating valve dynamics, as this results in the largest reduction in output uncertainty. In practice, this could be achieved using ultrasound imaging of the veins and fluid structure interaction simulations to characterize detailed valve dynamics, respectively.

A new global model to characterise the dynamics of a pneumatic proportional-pressure valve for a biomechatronic application

Traditionally, the pneumatic proportional-pressure valve dynamics has been characterised from its output pressure and input reference voltage relationship. However, in our application about the use of a pneumatic artificial muscle as actuator of a gait rehabilitation exoskeleton, where an adequate valve output pressure control is required to simultaneously attain a smooth joint movement and an efficient interaction force with the patient, it is also important to evaluate the effect on valve output pressure of the input airflow rate disturbance caused by downstream load variations during this actuator operation. In this paper we present a new global linear model for such application, considering the concurrent effect on valve output of both voltage and airflow rate inputs. From data acquired through an experimental setup and for reference inputs in the frequency range of human gait, two transfer functions describing the relationships between valve output pressure and their respective inputs were first obtained. Second, the individual models were combined in a global one, according to the superposition principle. Third, the resultant model was analysed in the time and frequency domains and finally, validated (MSE = 0.0499) and discussed, in the search for clues to design a suitable actuation system for this type of robotic device.

On-X Heart Valve Prosthesis: Numerical Simulation of Hemodynamic Performance in Accelerating Systole.

Numerical simulation of the bileaflet mechanical heart valves (BMHVs) has been of interest for many researchers due to its capability of predicting hemodynamic performance. A lot of studies have tried to simulate this three-dimensional complex flow in order to analyze the effect of different valve designs on the blood flow pattern. However, simplified models and prescribed motion for the leaflets were utilized. In this paper, transient complex blood flow in the location of ascending aorta has been investigated in arealistic model by fully coupled simulation. Geometry model for the aorta and the replaced valve is constructed based on the medical images and extracted point clouds. A 23-mm On-X Medical BMHV as the new generation design has been selected for the flow field analysis. The two-way coupling simulation is conducted throughout the accelerating phase in order to obtain valve dynamics in the opening process. The complex flow field in the hinge recess is captured precisely for all leaflet positions and recirculating zones and elevated shear stress areas have been observed. Results indicate that On-X valve yields relatively less transvalvular pressure gradient which would lower cardiac external work. Furthermore, converging inlet leads to a more uniform flow and consequently less turbulent eddies. However, the leaflets cannot open fully due to middle diffuser-shaped orifice. In addition,asymmetric butterfly-shaped hinge design and converging orifice leads to better hemodynamic performance. Withthe help of two-way fluid solid interaction simulation, leaflet angle follows the experimental trends more precisely rather than the prescribed motion in previous 3D simulations.

Modeling of a Fast Plate Type Hydraulic Check Valve

Check valve dynamics plays an important role in many fluid systems, such as in compressors, hydraulic pumps, and hydraulic switching converters. Plate type check valves are a frequently employed valve type in dynamically challenging cases. Despite the relevancy of plate valve dynamics, only few exhaustive works can be found in the literature, focusing on the behavior of hydraulic check valves for high-frequency applications. This paper presents an in-depth characterization of a plate valve designed as rectifier of a high-frequency oscillation pump working at 300 Hz. The aim is to identify a sufficiently simple mathematical model, which permits to optimize the design of the valve for the considered application. The paper analyses the different phenomena contributing to the dynamics of such a valve and presents the results of simulation and experimental activity. The results show how small details in the design and manufacturing of those valves (namely, the contact surfaces) have important consequences on the dynamics of the pump system. In general, a good agreement between model and reality is achieved.

Modelling and experimental validation of the displacement of a check valve in a hydraulic piston pump

AbstractA variety of methods have previously been applied to modelling hydraulic check valves. While the theoretical framework has been established, robust experimental validation of check valve models is lacking. When present, validation methods typically rely on measurements of pressure differential or flow rates, from which check valve dynamics are inferred. In this paper, a lumped parameter model is constructed for a disc style check valve used to control the inlet and outlet flow of a piston pump. Pressure, spring, contact, stiction, and flow forces are investigated to determine which have a significant effect on the check valve dynamics. An experimental pump circuit is constructed and an acrylic sight glass is installed on the check valve manifolds. A method of directly measuring the check valve position during operation using a Laser Triangulation Sensor (LTS) is developed by applying Snell’s law to the air-acrylic and acrylic-oil interfaces and calculating laser refraction to obtain a relationship...

In silico coronary wave intensity analysis: application of an integrated one-dimensional and poromechanical model of cardiac perfusion.

Coronary wave intensity analysis (cWIA) is a diagnostic technique based on invasive measurement of coronary pressure and velocity waveforms. The theory of WIA allows the forward- and backward-propagating coronary waves to be separated and attributed to their origin and timing, thus serving as a sensitive and specific cardiac functional indicator. In recent years, an increasing number of clinical studies have begun to establish associations between changes in specific waves and various diseases of myocardium and perfusion. These studies are, however, currently confined to a trial-and-error approach and are subject to technological limitations which may confound accurate interpretations. In this work, we have developed a biophysically based cardiac perfusion model which incorporates full ventricular–aortic–coronary coupling. This was achieved by integrating our previous work on one-dimensional modelling of vascular flow and poroelastic perfusion within an active myocardial mechanics framework. Extensive parameterisation was performed, yielding a close agreement with physiological levels of global coronary and myocardial function as well as experimentally observed cumulative wave intensity magnitudes. Results indicate a strong dependence of the backward suction wave on QRS duration and vascular resistance, the forward pushing wave on the rate of myocyte tension development, and the late forward pushing wave on the aortic valve dynamics. These findings are not only consistent with experimental observations, but offer a greater specificity to the wave-originating mechanisms, thus demonstrating the value of the integrated model as a tool for clinical investigation.

Magnetic resonance-compatible model of isolated working heart from large animal for multimodal assessment of cardiac function, electrophysiology, and metabolism.

To provide a model close to the human heart, and to study intrinsic cardiac function at the same time as electromechanical coupling, we developed a magnetic resonance (MR)-compatible setup of isolated working perfused pig hearts. Hearts from pigs (40 kg, n = 20) and sheep (n = 1) were blood perfused ex vivo in the working mode with and without loaded right ventricle (RV), for 80 min. Cardiac function was assessed by measuring left intraventricular pressure and left ventricular (LV) ejection fraction (LVEF), aortic and mitral valve dynamics, and native T1 mapping with MR imaging (1.5 Tesla). Potential myocardial alterations were assessed at the end of ex vivo perfusion from late-Gadolinium enhancement T1 mapping. The ex vivo cardiac function was stable across the 80 min of perfusion. Aortic flow and LV-dP/dtmin were significantly higher (P < 0.05) in hearts perfused with loaded RV, without differences for heart rate, maximal and minimal LV pressure, LV-dP/dtmax, LVEF, and kinetics of aortic and mitral valves. T1 mapping analysis showed a spatially homogeneous distribution over the LV. Simultaneous recording of hemodynamics, LVEF, and local cardiac electrophysiological signals were then successfully performed at baseline and during electrical pacing protocols without inducing alteration of MR images. Finally, (31)P nuclear MR spectroscopy (9.4 T) was also performed in two pig hearts, showing phosphocreatine-to-ATP ratio in accordance with data previously reported in vivo. We demonstrate the feasibility to perfuse isolated pig hearts in the working mode, inside an MR environment, allowing simultaneous assessment of cardiac structure, mechanics, and electrophysiology, illustrating examples of potential applications.

Multiphysics simulation of the effect of leaflet thickness inhomogeneity and material anisotropy on the stress–strain distribution on the aortic valve

This study developed a realistic 3D FSI computational model of the aortic valve using the fixed-grid method, which was eventually employed to investigate the effect of the leaflet thickness inhomogeneity and leaflet mechanical nonlinearity and anisotropy on the simulation results. The leaflet anisotropy and thickness inhomogeneity were found to significantly affect the valve stress–strain distribution. However, their effect on valve dynamics and fluid flow through the valve were minor. Comparison of the simulation results against in-vivo and in-vitro data indicated good agreement between the computational models and experimental data. The study highlighted the importance of simulating multi-physics phenomena (such as fluid flow and structural deformation), regional leaflet thickness inhomogeneity and anisotropic nonlinear mechanical properties, to accurately predict the stress–strain distribution on the natural aortic valve.

Actuator stiction compensation via model predictive control for nonlinear processes

The problem of valve stiction is addressed, which is a nonlinear friction phenomenon that causes poor performance of control loops in the process industries. A model predictive control (MPC) stiction compensation formulation is developed including detailed dynamics for a sticky valve and additional constraints on the input rate of change and actuation magnitude to reduce control loop performance degradation and to prevent the MPC from requesting physically unrealistic control actions due to stiction. Although developed with a focus on stiction, the MPC‐based compensation method presented is general and has potential to compensate for other nonlinear valve dynamics which have some similarities to those caused by stiction. Feasibility and closed‐loop stability of the proposed MPC formulation are proven for a sufficiently small sampling period when Lyapunov‐based constraints are incorporated. Using a chemical process example with an economic model predictive controller (EMPC), the selection of appropriate constraints for the proposed method is demonstrated. The example verified the incorporation of the stiction dynamics and actuation magnitude constraints in the EMPC causes it to select set‐points that the valve output can reach and causes the operating constraints to be met. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2004–2023, 2016

Numerical simulation of the performance of an artificial heart valve

AbstractThe present paper is focused on the mathematical model describing the dynamics of an artificial heart valve and the method of its numerical solution. The results of performance simulation are presented for the tricuspid valve of perfect form and the biological prosthesis ‘Uniline’.

Optimum Design of a Moving Coil Actuator for Fast-Switching Valves in Digital Hydraulic Pumps and Motors

Fast-switching seat valves suitable for digital hydraulic pumps and motors utilize direct electromagnetic actuators, which must exhibit superior transient performance to allow efficient operation of the fluid power pump/motor. A moving coil actuator resulting in a minimum valve switching time is designed for such valves using transient finite-element analysis of the electromagnetic circuit. The valve dynamics are coupled to the fluid restrictive forces, which significantly influence the effective actuator force. Fluid forces are modeled based on transient computational fluid dynamics models. The electromagnetic finite-element model is verified against experimental measurement, and used to design an optimum moving coil actuator for the application considering different voltage–current ratios of the power supply. Results show that the optimum design depends on the supply voltage–current ratio, however, the minimum switching time obtained is nearly independent on this voltage–current ratio. Selecting a suitable power supply based on thermal considerations yields a switching time just above one millisecond for a travel length of 3.5 mm while submerged in oil. The proposed valve has a pressure drop below 0.5 bar at 600 L/min flow rate, enabling efficient operation of digital hydraulic pumps and motors.