Characterization of disturbed hemodynamics due to stenosed aortic jets with a Lagrangian Coherent structures technique

Isfahan University of Technology. The aortic valve is located at left ventricular outlet and is exposed to the highest pressure in the cardiovascular system. Problems associated with the valve leaflet movement can cause complications for the heart. Specifically, aortic stenosis (AS) arises when aortic leaflets do not efficiently open. In the present study, Lagrangian Coherent Structures (LCSs) were utilized by processing a variety of Computational Fluid Dynamics (CFD) models velocity vector data further to identify the characteristics of AS jets. Particularly, effective orifice areas (EOA) for different cases were accurately identified from unstable manifolds of finite time Lyapunov exponent (FTLE) fields. Calcified leaflets were modeled by setting the leaflet's Young modulus to 10 MPa and 20 MPa for moderately and severely calcified leaflets respectively while a healthy leaflet's Young modulus was assigned to be 2 MPa. Increase in calcification degree of the leaflet caused destruction of the vortex structures near the fibrosa layer of the leaflet indicating a malfunctioning for the movement mechanism of the leaflet. Furthermore, when we analyzed stable manifolds, we identified a blockage region at the flow upstream due to the stagnant blood here. Compared to a healthy case, for the calcified valve, this blockage region was enlarged, implying an increase in AS jet velocity and wall shear stress on leaflets. As a conclusion, results from the present study indicate that aortic leaflet malfunctioning could be accurately evaluated when LCS technique was employed by post processing velocity vector data from CFD. Such precise analysis is not possible using the Eulerian CFD approach or a Doppler echocardiography since these methods are based on only analyzing instantaneous flow quantities and they overlook fluid flow characteristics of highly unsteady flows

Kinematic-Kinetic-Rigidity Evaluation of a Six Axis Robot Performing a Task

Six axis serial robots of different sizes are widely used for pick and place, welding and various other operations in industry. Developments in mechatronics, which is the synergistic integration of mechanism, electronics and computer control to achieve a functional system, offer effective solutions for the design of such robots. The integrated analysis of robots is usually used in the design stage. In this study, it is offered that the integrated analysis of robots can also be used at the application stage. SolidWorks, CosmosMotion and ABAQUS programs are used with an integrated approach. Integration software (IS) is developed in Visual Basic by using the application programming interface (API) capabilities of these programs. An ABB-IRB1400 industrial robot is considered for the study. Different trajectories are considered. Each task is first evaluated by a kinematic analysis. If the task is out of the workspace, then the task is cancelled. This evaluation can also be done by robot programs like Robot Studio. It is proposed that the task must be evaluated by considering the limits for velocities, motor actuation torques, reaction forces, natural frequencies, displacements and stresses due to the flexibility. The evaluation is done using kinematic, kinetic and rigidity evaluation charts. The approach given in this work can be used for the optimal usage of robots

Haemodynamic Issues with Transcatheter Aortic Valve Implantation

Transcatheter aortic valves are typically implanted inside the native (or failed bioprosthetic’s) leaflets, permanently forcing the old leaflets open into a pseudo-cylindrical condition. Due to the passive nature of heart valves, the dynamics of the surrounding fluid environment is critical to their optimum performance. Following intervention, the haemodynamics of the region would ideally be returned to their healthy, physiological state, but major alterations are currently inevitable, such as increased peak flow velocity, the presence of stagnation regions, and increased haemolytic fluid environments. These leaflets reduce the volume of and restrict the flow into the Valsalva’s sinuses, and minimise the development of vortices and associated flow structures, which would aid washout and valve closure. Despite these differences to the healthy condition, implantation of these devices offers much improved flow from that of a moderately stenotic valve, with reduced transvalvular systolic pressure drop, peak blood velocity, and shear stress, which normally outweighs the disadvantages highlighted above, especially for high-risk patients