Research On Structure Design And Hemocompatibility Of Hydrodynamic Bearing In Artificial Heart

The dissertation dwells on hydrodynamic bearing in an artificial heart. The structure design and hemocompatibility of hydrodynamic bearing are systematically studied. We research on the structure design of hydrodynamic bearing, the parameter optimization, the rotor displacement measurement under stable and pulsatile conditions and the hemocompatibility of hydrodynamic bearing. It provides some valuable results to the reseaich on structure design and hemocompatibility of hydrodynamic bearing in artificial heart.Firstly, the mathematical model of fluid flow in the levitation gap is developed according to the characteristics of hydrodynamic flow field, based on the equations, the radial and axial bearing structures are preliminary designed. Secondly, the spherical hydrodynamic bearing structure is designed and the corresponding trials are tested; for the conical hydrodynamic bearing, the fluid flow characteristics and load-carrying capacity within different minimum clearance are compared by numerical simulation; for the spiral groove on spindle hydrodynamic bearing, combined with orthogonal experimental design, a set of optimal spiral groove design is given; based on the results, a novel spiral groove structure is proposed for low thrombus, and the upper thrust bearing is simulated. The relationship is analyzed between flowrate, load-carrying capacity and pressure for three typical spiral groove bearing design, and a characteristic plane is originally presented relating to load-carrying capacity and flowrate. Comparisons are made between various kinds of spiral groove bearing designs, and CFD results are plotted on this characteristic plane from which load/flowrate performances can be directly read out. Thirdly, the displacement of rotor is tested under stable and pulsatile conditions for hydrodynamic bearing. The relationship between motion parameters and suspension displacements in the axial and radial directions are given under different conditions, and the corresponding bearing stability is also analyzed. Finally, the hemocompatibility of the hydrodynamic bearing is simulated. The hemocompatibility for different suspension structure and pressure is analyzed, and the antithrombotic property is tested through animal testing.The main contents of this dissertation are briefly stated as followings:1. Research on hydrodynamic bearing.Based on the flow field characteristics analysis for hydrodynamic bearing, the mathematical model of the flow field is established, and the structure designs for radial and thrust bearing are carried out initially. Based on this, the spherical hydrodynamic bearing is designed and corresponding experiments are studied. The artificial heart with conical hydrodynamic bearing and with spiral groove on spindle bearing are designed. Through experiment study, the structure with spherical hydrodynamic bearing is researched on whether it can meet the requirements of suspension; through numerical simulation, the relationship between the minimum gap and load-carrying capacity force is studied for the structure with spherical hydrodynamic bearing, and the structure parameters are given for the hydrodynamic bearing with spiral groove on spindle. The flowrate of the two hydrodynamic bearings are compared through numerical results.2. The spiral groove hydrodynamic bearing design for low thrombus and numerical simulation.A novel spiral groove bearing design is introduced to the artificial heart for rotor supporting aiming for long-term implantation in human body. The characteristics of this spiral groove design is that the width gradually narrows with the radius larger, and thus it can increase the suspending force using dynamic lubrication, and its rotation direction is the same with rotor, which contribute to increasing the flowrate in the gap and to avoiding thrombus. Comparations are taken for this kind of design and the traditional design by three-dimensional numerical simulation and the characterization relating to load-carrying capacity and flowrate is introduced, the load-carrying capacity and flowrate are analyzed and compared for a variety of spiral groove bearing designs. The contrast results are united in the same characteristics plane and the load/flowrate changes can be directly read out.3. Test study on the displacement of hydrodynamic suspension.According to the suspension structure with better load/flowrate characteristics, the test pump with hydrodynamic bearing is designed and fabricated. The test platforms are set up in axial and radial direction under steady and pulsatile conditions. The absolute displacement in axial direction and the clearance changes in radial are obtained. For the displacement test under steady conditions, by studying the relations between speed, spiral groove structure parameters and displacement of rotor suspension, the range of radial movement and the gap changes of rotor radial movement are given for a variety of suspension structures to study the law of rotor radial trajectory variation; for the displacement test under pulsatile conditions, through measuring axial displacement and radial changes of rotor under different pulse pressure variation, the changes of suspending fluid under different conditions are analyzed and compared. The difference changes between radial radius clearance and eccentricity are obtained by calculating. The rotor suspension stability is analyzed and the speed adjustment range is given out for the stable rotor suspension.4. Research on hemocompatibility for hydrodynamic bearing. Using Lagrangian particle tracking method to analyze the blood damage within the bearing gap, according to the empirical formula, the shear stress imposed on red blood cells and the exposure time within the bearing gap for different structures are calculated. According the results, it can be determined that whether the hemolytic estimates of the design for the spiral groove structure can meet the hemolytic performance requirements for the hydrodynamic bearing. On this basis, the antithrombotic evaluation for spiral structure is tested through animal experiment.