Valve Dynamics Research Articles

In vivo analysis of aortic valve dynamics by transesophageal 3-dimensional echocardiography with high temporal resolution

Objectives Knowledge of aortic valve function has been obtained from experimental studies. The aim of the present study was to investigate characteristics of aortic valve motion in humans. Methods Fifty-six patients were studied: 19 with normal valve and good systolic left ventricular function (Group NL), 12 with normal valve and reduced left ventricular function (Group CMP), and 25 with aortic stenosis and good left ventricular function (Group AS). The frame rate was doubled (50 Hz) compared with previous 3-dimensional systems. A mean of 38 ± 9 images were acquired per cardiac cycle, with 14 ± 4 images during the systole. The changes in shape and orifice area were analyzed over time. Results With normal valves, valve movement proceeded in 3 phases: rapid opening, slow closing, rapid closing. Stenotic valves showed a slower opening and closing movement. The times to maximum opening in Groups NL, CMP, AS were 76 ± 30, 88 ± 18 ( P = .06), and 130 ± 29 ( P < .01) ms, respectively. It was inversely correlated to the maximum orifice area (r = −0.59, P < .001). The opening velocities in Groups NL, CMP, AS were 42 ± 23, 28 ± 9 ( P < .05), and 5 ± 2 ( P < .001) cm 2/s, respectively. There was a close correlation between the opening velocity and the maximum orifice area (r = 0.87, P < .001). Slow valve closings occurred at a velocity of 8.0 ± 5.2, 5.3 ± 2.0 ( P = .21), 2.8 ± 1.1 ( P < .01) cm 2/s, respectively, and rapid closings in Groups NL and CMP at 50 ± 23, 29 ± 8 ( P < .01) cm 2/s. The results show good agreement with experimental data. Conclusion Rapid aortic valve movement can be recorded by 3-dimensional echocardiography and analyzed quantitatively. Time and velocity indices of valve dynamics are influenced by valvular and myocardial factors. A comparable in vivo analysis is not possible with any other imaging procedure.

Slug Detection as a Tool for Predictive Control of GLCC© Compact Separators

Current design and performance of the GLCC©1 separator is dependent on the prediction of the upstream inlet flow conditions based on available models. It is expected that early detection of terrain slugging (slug length, slug velocity and holdup) and controlling the liquid level in the GLCC using feed forward mechanism can improve the operational range of the GLCC, by decreasing the gas carry under and liquid carry over, and thereby decreasing the control valve dynamics. The conventional feedback control loops can seldom achieve perfect control considering the impact of huge slugs that are keeping the output of the process continuously away from desired set point value. The reason is simple: a feedback controller reacts only after it has detected a deviation in the value of the level from the set point. Unlike the feedback systems, a feed forward control configuration measures the disturbance directly and takes control action to negate the effect of the disturbance on liquid level in the GLCC. Therefore, a feed forward control system has the theoretical potential for perfect control if the slug detection and characterization are perfect. A strategy for GLCC predictive control has been proposed which integrates the feedback and feed forward loops to compensate for error due to modeling and slug characterization. A model has been developed for predictive control system design and simulated in MATLAB-Simulink®. Experimental results obtained demonstrate that the proposed strategy is a viable approach for GLCC predictive control.

Modeling and Numerical Simulation of the Thermal and Fluid Dynamic Behavior of Hermetic Reciprocating Compressors—Part 1: Theoretical Basis

A detailed numerical simulation of the thermal and fluid dynamic behavior of reciprocating compressors, commonly used in household refrigerators and freezers, has been developed. The model is based on the integration of the transient fluid conservation equations (continuity, momentum, and energy) in the whole compressor domain (compression chamber, valves, manifolds, mufflers, shell, piston, connecting tubes, parallel paths, etc.) using instantaneous local mean values for different variables. Effective flow areas are evaluated considering a multidimensional model based on modal analysis of fluid interaction in the valve. In order to evaluate the instantaneous compression chamber volume, force balances in the crankshaft connecting rod mechanical system are simultaneously solved at each time-step. The thermal analysis of the solid elements is based on global energy balances at each macro-volume considered (shell, muffler, tubes, cylinder head, crankcase, motor, etc.). The resulting governing equations (fluid flow, valve dynamics, conductive heat transfer in solids, etc.) are discretized by means of a fully implicit control volume formulation. The complete set of algebraic equations is coupled using the segregated pressure-based algorithm Semi-Implicit Method for Pressure-Linked Equations (SIMPLEC) extended to compressible flow. A detailed numerical analysis is presented with the aim of verifying the quality of the numerical solution. A comparison between numerical simulation results and experimental data is presented in the companion paper (Part 2).

Acoustical analysis and modeling of reciprocating compressors, noise produced by gas pulsation, using four‐pole method. I

Presented in Paper I are the fluid‐structure interactions, structural dynamics, and thermodynamic analyses of reciprocating compressors (such as air conditioning and refrigeration reciprocating compressors). The compressor performance can be analyzed using the follows criteria: (1) thermodynamic model of the cylinder process, using the polytropic process model for thermodynamic model of cylinder; (2) suction and discharge valves dynamics analysis and modeling; (3) the valves modeling and the cylinder volume calculation; (4) Effective flow area and effective force area models.

P1676 A new three-dimensional echocardiographic system using digital radio frequency data ? visualization and quantitative analysis of aortic valve dynamics with high resolution

P1676 A new three-dimensional echocardiographic system using digital radio frequency data ? visualization and quantitative analysis of aortic valve dynamics with high resolution

A study on the design of electromagnetic valve actuator for VVT engine

Electromagnetic valve (EMV) actuation system is a new technology for improving fuel efficiency and at the same time reducing emissions in internal combustion engines. It can provide more flexibility in valve event control compared with conventional variable valve actuation devices. The electromagnetic valve actuator must be designed by taking the operating conditions and engine geometry limits of the internal combustion engine into account. To help develop a simple design method, this paper presents a procedure for determine the basic design parameters and dimensions of the actuator from the relations of the valve dynamics, electromagnetic circuit and thermal loading condition based on the lumped method. To verify the accuracy of the lumped method analysis, experimental study is also carried out on a prototype actuator. It is found that there is a relatively good agreement between the experimental data and the results of the proposed design procedure. Through the whole speed range, the actuator maintains proper performances in valve timing and event control.

OC254: Dynamics of the flap valve of the foramen ovale in the fetus and false positive diagnosis of coarctation of the aorta

OC254: Dynamics of the flap valve of the foramen ovale in the fetus and false positive diagnosis of coarctation of the aorta

Calculation of Dynamic Behavior of Valves for Reciprocating Compressors (Comparison with Experimental and Field Data)

Authors presented the newly derived governing equations of self-acting valve dynamics and the influence of valve characteristics on the valve behavior(6). This paper describes the validity of the calculation method by comparing with experimental and field data. The calculated results agree well with the experimental results for the movements and impact speed of valves. Design values are obtained through comparison between the calculations of impact speed and the field data of valve damage.

Microflow fields in the hinge region of the CarboMedics bileaflet mechanical heart valve design

Objective: The design of bileaflet mechanical heart valves includes some degree of leakage flow on valve closure for the reverse flow to wash the hinge and pivot region of the valve. It is believed that this reverse flow helps to prevent areas of stasis and inhibit microthrombus formation. However, the magnitude of this retrograde flow may also give rise to unacceptable levels of blood element damage and lead to platelet activation or hemolysis as a result of the increased flow velocities through the hinge region. The purpose of this study was to evaluate the hinge flow dynamics of a 23-mm CarboMedics bileaflet mechanical valve (Sulzer CarboMedics Inc, Austin, Tex) and then to compare the results with those of the St Jude Medical 23-mm Regent (St Jude Medical Inc, Minneapolis, Minn) and Medtronic Parallel (Medtronic, Inc, Minneapolis, Minn) valves studied earlier. This comparison allows new insight into the microflow fields within the hinge region of the CarboMedics bileaflet mechanical valve, which have not been previously assessed during its clinical history. Methods: Two-dimensional laser Doppler velocimetry was used to measure the velocity and turbulent shear stress fields in the hinge regions. To conduct these measurements, exact dimensional models of the bileaflet hinge regions were cast or machined from transparent plastic materials. The experiment was conducted in a pulsatile flow loop with measurements taken at different levels within the pivot and hinge regions. Results: In the 23-mm CarboMedics valve hinge, the phase-averaged forward velocity obtained at the flat level and levels of 190 μm and 390 μm above flat and 1 mm below flat were 0.54 m/s, 0.77 m/s, 0.3 m/s, and 1.0 m/s, respectively. Corresponding values of the peak phase-averaged leakage velocities were 3.17 m/s, 2.91 m/s, 2.52 m/s, and 0.5 m/s, respectively. Corresponding turbulent shear stresses were 5510 dyne/cm2, 5640 dyne/cm2, 4380 dyne/cm2, and 4810 dyne/cm2, respectively. Conclusions: The hinge flow dynamics of the CarboMedics bileaflet design lie somewhere in between those of the St Jude Medical and the Medtronic Parallel valve designs. The fluid dynamics of the investigated valve were found to be similar to those of the St Jude Medical valves, although with slightly higher leakage velocities and turbulent shear stresses. This discrepancy may be a result of the sharper corners associated with the hinge design of the CarboMedics valve. It could also be due to the incremental enlargement of the internal orifice area of the St Jude Medical Regent design.J Thorac Cardiovasc Surg 2002;124:561-74

Modelling and dynamics of single-stage pressure relief valve with directional damping

The dynamics of a direct operated relief valve with directional damping have been studied through Bondgraph simulation technique. The governing equations of the system have been derived from the Bondgraph model. While solving the system equations numerically, the pressure-flow characteristics of the valve port and the damper unit have been taken into consideration. From this study, some significant parameters of the valve response are identified, which can be modified to improve the dynamic characteristics of the valve.

Leonardo's vision of flow visualization

Leonardo's studies of cardiovascular systems, in more than 50 surviving pages from two phases of his research (around 1508–1509 and 1513), are a clear demonstration of his observational genius and progressive deduction of cardiac mechanics and the vascular system. He carried out a detailed hemodynamic study of the aortic valve motion and the role of the Sinus of Valsalva in the closure dynamics of the aortic valve, and he accurately correlated the formation of vortices with the separation of a retarded (shear) layer from the lips of the leaflets. In-vivo verification of vortex formation in the Sinus of Valsalva during the systolic phase awaited the application of modern phase-averaged magnetic resonance imaging techniques. Did Leonardo actually build the glass model he twice mentioned, thus performing the first scientific flow visualization of impulsive vortex formation or other fluid mechanical phenomena? Evidence in support of this possibility can be found in both the unusually schematic style he employed for this suite of drawings and the recent flow imaging results obtained in our laboratory through laser-based imaging techniques.

A hierarchical physical model-based approach to predictive control of a thermal power plant for ef”cient plant-wide disturbance rejection

Extending the work presented in Prasad et al. (IEEE Proceedings on Control Theory and Applications, 147, 523-37, 2000), this paper reports a hierarchical nonlinear physical model-based control strategy to account for the problems arising due to complex dynamics of drum level and governor valve, and demonstrates its effectiveness in plant-wide disturbance handling. The strategy incorporates a two-level control structure consisting of lower-level conventional PI regulators and a higher-level nonlinear physical model predictive controller (NPMPC) for mainly set-point manoeuvring. The lower-level PI loops help stabilise the unstable drum-boiler dynamics and allow faster governor valve action for power and grid-frequency regulation. The higher-level NPMPC provides an optimal load demand (or set-point) transition by effective handling of plant-wide interactions and system disturbances. The strategy has been tested in a simulation of a 200-MW oil-fired power plant at Ballylumford in Northern Ireland. A novel approach is devized to test the disturbance rejection capability in severe operating conditions. Low frequency disturbances were created by making random changes in radiation heat ‘ow on the boiler-side, while condenser vacuum was ‘uctuating in a random fashion on the turbine side. In order to simulate high-frequency disturbances, pulse-type load disturbances were made to strike at instants which are not an integral multiple of the NPMPC sampling period. Impressive results have been obtained during both types of system disturbances and extremely high rates of load changes, right across the operating range. These results compared favourably with those from a conventional state-space generalized predictive control (GPC) method designed under similar conditions.

Modeling and simulation of thermal chlorine etching of gallium arsenide with application to real-time feedback control

A dynamic model for the simulation of thermal chlorine etching of gallium arsenide is developed. The primary motivation for the development of the simulation is the design and testing of real time adaptive feedback controllers which rely upon in-situ optical measurements of etch depth obtained via spectroscopic ellipsometry. The basis for the model is an empirically derived relationship between etch rate, chlorine pressure, and substrate temperature. The chlorine pressure in the chamber is regulated by a throttle valve which determines the effective pumping rate of a turbo-molecular pump which is used to evacuate chlorine pressure dynamics and a second-order damped harmonic oscillator with zero-order hold valve position command inputs is used to model the dynamics of the throttle valve. An output equation is used to model the fact that ellipsometry based etch depth and chamber pressure can be observed at discrete time intervals. Unmeasurable parameters which appear in the model are identified, and the model is validated using experimental data. An adaptive linear-quadratic Gaussian based controller based on our model which forces etching to precede at a desired rate while estimating the often difficult to measure substrate temperature is designed and then tested using our simulation.

An Elementary Model for Control of a Semiconductor Etching Process

A dynamic model for the thermal chlorine etching of gallium arsenide is formulated and validated. The model consists of three ordinary differential equations. One models the chemical reaction between the chlorine gas and the gallium arsenide substrate being etched. The second equation, which is based on an inflow/outflow paradigm, models the dynamics of the pressure in the etching chamber. The third equation models the dynamics of a throttle valve which controls the chamber pressure. The entire model is based upon a combination of empirical and first principle physics-based reasoning, and is formulated using sophomore-level elementary chemistry, physics, and differential equations. Spectroscopic ellipsometry, a nondestructive optically based technique for real-time in-situ characterization of materials, is described. Offline and real-time ellipsometry measurements of sample thickness are used to identify or estimate otherwise unmeasurable parameters which appear in the model and to verify or validate our model via comparison with simulation results based upon the model. The use of the model in the design, implementation, and testing of a feedback control system for the etching process is discussed.

Time delay in a semi-active damper: modelling the bypass valve

Ride comfort and handling of off-road vehicles can be significantly improved by replacing the normal passive dampers in the vehicle suspension system with controllable, two-state, semi-active dampers. The hydraulic valve, which enables the semi-active damper characteristics to be controlled, is a critical component of a semi-active damper and has a marked influence on suspension performance. Models of the dynamics of a hydraulic bypass valve used on semi-active suspension systems for heavy vehicles were investigated. It is envisaged that similar models will eventually be incorporated into a full vehicle, three-dimensional simulation study. Valve response time (or time delay) is used as a measure of model accuracy because it is an important parameter in the performance of a semi-active damper. Models were created with AMESim, a commercial fluid power simulation environment, and MATLAB. AMESim was found to be capable of dealing with detailed and complex fluid power models. Attempts to solve models of similar complexity in the MATLAB environment were unsuccessful due to numerical stiffness. Experimental work was conducted to obtain dynamic performance data with which to validate model integrity. Several external factors influenced the valve behaviour during experiments. Test bench dynamics significantly influences results and obscures the absolute accuracy of the models and the experimental data. The investigation demonstrated an approach to creating fluid power models for this application that can be used in simulation, but also indicated that substantial effort is required in the process. The accuracy of the current model is not sufficient for design purposes.

ELECTROHYDRAULIC SYSTEM FOR HIGH SPEED GAS EXCHANGE VALVE ACTUATION

Diesel engine performance can be improved and emissions reduced by improving the power density and combustion cycle efficiency. It can be done by increasing combustion pressure and engine speed which also necessitates improving the controllability of the engine. One of the key elements in improving overall controllability of the engine is the valvetrain. During recent years various camless valvetrain designs for automotive size engines have been introduced, but in bigger engines camless valve actuation is only applied to low speed two stroke marine diesels. Feasible way to realize camless valve actuation in modern and future medium speed diesels is electrohydraulic valvetrain. It, how ever, has numerous shortcomings and difficulties to overcome.An electrohydraulic valvetrain for experimental engine, having performance characteristics twice the level of current medium speed engines, has been developed. Valvetrain offers significant benefits in comparison to traditional cam actuated valvetrain. Valvetrain is able to operate up to engine speed of 1600 rpm and combustion pressure of 400 bar at speed level twice the tradional cam actuation. Hydraulic peak power of the valvetrain is approx 100 kW and shortest controlled actuation time is approx 6 ms for 18 mm stroke. Main challenges in valvetrain design are are keeping the continuous power consumption at reasonable level, controlling the valve speed, precission of valve timing and dynamics of the system in whole as well as individual components.The paper will introduce the system and component design of the prototype system. System and component performance is discussed on basis of Amesim simulation models. Control system design, realization and valvetrain prototype testing are also discussed.

Opening and closing characteristics of the aortic valve after valve-sparing procedures using a new aortic root conduit

Background. The durability of aortic valve-sparing procedures is negatively affected by increased leaflet stress in the absence of normally shaped sinuses of Valsalva. We compared valve motion after remodeling procedures using a standard conduit and a specifically designed aortic root conduit. Methods. Echocardiographic studies of the aortic valve dynamics were performed in 14 patients after remodeling of the aortic root (7 standard conduits, group A; 7 new conduits, group B) and in 7 controls (group C). Opening and closing leaflet velocities and percent of slow closing leaflet displacement were measured. Root distensibility and the pressure strain of the elastic modulus were measured at all root levels. Results. Root distensibility and the pressure strain of the elastic modulus were different in group A and B only at the sinuses ( p < 0.001). Opening and closing leaflet velocities were not different among groups. Slow closing leaflet displacement was markedly more evident in group B patients (24.2% ± 1.9% versus 2.5% ± 1.9% in group A, p < 0.001) and similar to controls (22.1% ± 7.9%). Conclusions. The new conduit guarantees dynamic features of the aortic valve leaflets superior to those obtained with standard conduits and more similar to normal subjects.

Intracardiac echocardiography: current uses and future directions.

Advances in transducer technology have enabled development of catheter-based ultrasound imaging devices that produce very high resolution images of vessels and cardiac structures. Although the majority of clinical use has been in the evaluation of the coronary and peripheral vasculature, a broad spectrum of cardiac applications continue to develop, including evaluations of the ventricles, valves, and great vessels, as well as the guidance of electrophysiological procedures. Specifically, introduction of the ultrasound catheter into the heart results in dynamic, real-time images for assessment and quantitation of ventricular systolic function, severity of valve stenosis, and extent of regurgitant orifices. The intracardiac applications have the potential to become the gold standard for quantitation of valve dynamics and a critical tool in the ICU for prolonged monitoring of cardiac physiology.

Coordinate-free analysis of mitral valve dynamics in normal and ischemic hearts.

The purpose of this investigation was to study mitral valve 3D geometry and dynamics by using a coordinate-free system in normal and ischemic hearts to gain mechanistic insight into normal valve function, valve dysfunction during ischemic mitral regurgitation (IMR), and the treatment effects of ring annuloplasty. Radiopaque markers were implanted in sheep: 9 in the ventricle, 1 on each papillary tip, 8 around the mitral annulus, and 1 on each leaflet edge midpoint. One group served as a control (n=7); all others underwent flexible Tailor partial (n=5) or Duran complete (n=6) ring annuloplasty. After an 8+/-2-day recovery, 3D marker coordinates were measured with biplane videofluoroscopy before and during posterolateral left ventricular ischemia, and MR was assessed by color Doppler echocardiography. Papillary to annular distances remained constant throughout the cardiac cycle in normal hearts, during ischemia, and after ring annuloplasty with either type of ring. Papillary to leaflet edge distances similarly remained constant throughout ejection. During ischemia, however, the absolute distances from the papillary tips to the annulus changed in a manner consistent with leaflet tethering, and IMR was observed. In contrast, during ischemia in either ring group, those distances did not change from preischemia, and no IMR was observed. This analysis uncovered a simple pattern of relatively constant intracardiac distances that describes the 3D geometry and dynamics of the papillary tips and leaflet edges from the dynamic mitral annulus. Ischemia perturbed the papillary-annular distances, and IMR occurred. Either type of ring annuloplasty prevented such changes, preserved papillary-annular distances, and prevented IMR.

Coordinate-Free Analysis of Mitral Valve Dynamics in Normal and Ischemic Hearts

Background —The purpose of this investigation was to study mitral valve 3D geometry and dynamics by using a coordinate-free system in normal and ischemic hearts to gain mechanistic insight into normal valve function, valve dysfunction during ischemic mitral regurgitation (IMR), and the treatment effects of ring annuloplasty. Methods and Results —Radiopaque markers were implanted in sheep: 9 in the ventricle, 1 on each papillary tip, 8 around the mitral annulus, and 1 on each leaflet edge midpoint. One group served as a control (n=7); all others underwent flexible Tailor partial (n=5) or Duran complete (n=6) ring annuloplasty. After an 8±2-day recovery, 3D marker coordinates were measured with biplane videofluoroscopy before and during posterolateral left ventricular ischemia, and MR was assessed by color Doppler echocardiography. Papillary to annular distances remained constant throughout the cardiac cycle in normal hearts, during ischemia, and after ring annuloplasty with either type of ring. Papillary to leaflet edge distances similarly remained constant throughout ejection. During ischemia, however, the absolute distances from the papillary tips to the annulus changed in a manner consistent with leaflet tethering, and IMR was observed. In contrast, during ischemia in either ring group, those distances did not change from preischemia, and no IMR was observed. Conclusions —This analysis uncovered a simple pattern of relatively constant intracardiac distances that describes the 3D geometry and dynamics of the papillary tips and leaflet edges from the dynamic mitral annulus. Ischemia perturbed the papillary-annular distances, and IMR occurred. Either type of ring annuloplasty prevented such changes, preserved papillary-annular distances, and prevented IMR.