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Numerical Analyses of Idealized Total Cavopulmonary Connection Physiologies with Single and Bilateral Superior Vena Cava Assisted by an Axial Blood Pump
Get PDFOur study evaluated the hemodynamic performance of an axial flow blood pump surgically implanted in idealized total cavopulmonary connection (TCPC) models. This blood pump was designed to augment pressure from the inferior vena cava (IVC) to the pulmonary circulation. Two Fontan procedures with single and bilateral superior vena cava (SVC) were compared to fit the mechanical supported TCPC physiologies. Computational fluid dynamics (CFD) analyses of two Pump-TCPC models were performed in the analyses. Pressure-flow characteristics, energy efficiency, fluid streamlines, hemolysis and thrombosis analyses were implemented. Numerical simulations indicate that the pump produces pressure generations of 1 mm to 24 mm Hg for rotational speeds ranging from 2000 RPM to 5000 RPM and flow rates of 2 LPM to 4 LPM. Two surgical models incorporated with the pump were found to be insignificant in pressure augmentation and energy boost. The risk assessment of blood trauma and thrombosis generation was evaluated representatively through blood damage index (BDI), particle resident time (PRT) and relative resistant time (RRT). The hemolysis and thrombosis analyses declare the advantage of the pump supported bilateral SVC surgical scheme in balancing flow distribution and reducing the risk of endothelial cell destruction and trauma generation
The Study of the Graft Hemodynamics with Different Instant Patency in Coronary Artery Bypassing Grafting
Get PDFIn coronary artery bypass grafting (CABG), graft’s poor instant patency may lead to an abnormal hemodynamic environment in anastomosis, which could further cause graft failure after the surgery. This paper investigates the graft hemodynamics with different instant patency, and explores its effect on graft postoperative efficiency. Six CABG 0D/3D coupling multi-scale models which used left internal mammary artery (LIMA) and saphenous vein (SVG) as grafts were constructed. Different types of grafts were examined in the models, including normal grafts, grafts with competitive flow and grafts with anastomotic stenosis. Simulation results indicated that comparing with SVG grafts, there was a greater difference between normal LIMA graft and non-patent LIMA graft. Also, the backflow occurred even in LIMA systolic flow. The wall shear stress (WSS) in the graft of the competitive flow LIMA model had an appreciable decrease comparing with the normal graft. In addition, the WSS in the stenosis region of the anastomotic stenosis LIMA model was much higher than its adjacent regions. In contrast, the WSS distributions in the SVG models were much smoother than in the LIMA models. For oscillatory shear index (OSI), there was little difference between normal LIMA and SVG. But when the graft had competitive flow or anastomotic stenosis, much higher OSI occurred in some regions in LIMA than SVG. There are significant differences in hemodynamics between normal grafts and non-patent grafts both in LIMA and SVG. The hemodynamic environment in a normal LIMA is better than that in a normal SVG. However, in the situation of the two types of non-patent grafts, the hemodynamics of SVG is better than LIMA
A Fast-Fractional Flow Reserve Simulation Method in A Patient with Coronary Stenosis Based on Resistance Boundary Conditions
Get PDFFractional flow reserve (FFR) is the gold standard to identify individual stenosis causing myocardial ischemia in catheter laboratory. The purpose of this study is to present a fast simulation method to estimate FFR value of a coronary artery, which can evaluate the performance of vascular stenosis, based on resistance boundary conditions. A patient-specific 3-dimensional (3D) model of the left coronary system with intermediate diameter stenosis was reconstructed based on the CTA images. The resistance boundary conditions used to simulate the coronary microcirculation were computed based on anatomical reconstruction of coronary 3D model. This study was performed by coupling the 3D coronary tree model with the lumped parameter model (0D model). The flow rate and pressure of coronary tree were calculated in twenty minutes. In addition, the effect of inlet pressure and myocardial mass on FFRss values has been investigated. The results showed that the effect of myocardial mass was greater than the effect of inlet pressure on FFRss. This FFRss simulation method can quickly and accurately assess the influence of coronary stenosis in aid clinical diagnosis
Individualized Design of the Ventilator Mask based on the Residual Concentration of CO<sub>2</sub>
Get PDFOSAHS (Obstructive Sleep Apnea Hypopnea Syndrome) is a respiratory disease mainly characterized by limited and repeated pauses of breathing in sleep. Currently, the optimal treatment is to apply CPAP (Continuous Positive Airway Pressure) ventilation on the upper airway of the patient through a household respiratory machine. However, if the ventilator mask is designed improperly, it might cause the residue and repeated inhalation of CO2, which will exert an adverse impact on the therapeutic effect. Present research numerically analyzed the CO2 transportation inside a commercial ventilator mask (Mirage SoftGel, ResMed, Australia) based on the reconstructed 3D numerical model of a volunteer's face and performed the improved design of the ventilator mask in terms of the CO2 residual concentration below the nostrils. The fluid dynamic analyses showed that at the end time of expiratory, the CO2 residual concentration below the nostrils is close to 4%. To improve the therapeutic effect, we changed the position of the exhaust holes and found that by moving the exhaust holes to the bottom of the ventilator mask, the CO2 residual concentration below the nostrils would be reduced to no more than 1%. This study established a near physiological computational model and provided a new method for the individualized design of the commercial ventilator mask
Safety Evaluation of Concrete Structures Based on a Novel Energy Criterion
No full textIn this article, the post-peak softening stage of the constitutive relation and the elastic stiffness degradation of concrete are investigated, and a highly reasonable constitutive relation curve is proposed. At the material level, the energy change in the concrete failure process is studied based on the different stress-strain curves of concrete under uniaxial tension and compression. The concrete failure criterion based on elastic strain energy density is deemed suitable and consistent with the experimental phenomena. The hysteresis phenomenon (lags behind the peak strength) is also discussed. At the structure level, the strength reduction method is employed for the stability analysis, the energy change in the failure process of the Long Xi-Kou Dam is examined, and the results show that the dam failure criterion based on elastic strain energy shows a greater significance in practical applications compared with other conventional structural failure criteria in engineering. This criterion is objective and can avoid subjective arbitrariness
Fast Solving the Cauchy Problems of Poisson Equation in an Arbitrary Three-Dimensional Domain
No full textIn this paper we propose a novel two-stage method to solve the three-dimensional Poisson equation in an arbitrary bounded domain enclosed by a smooth boundary. The solution is decomposed into a particular solution and a homogeneous solution. In the first stage a multiple-scale polynomial method (MSPM) is used to approximate the forcing term and then the formula of Tsai et al. [Tsai, Cheng, and Chen (2009)] is used to obtain the corresponding closed-form solution for each polynomial term. Then in the second stage we use a multiple/scale/direction Trefftz method (MSDTM) to find the solution of Laplace equation, of which the directions are uniformly distributed on a unit circle S1, and the scales are determined a priori by the collocation points on boundary. Two examples of 3D data interpolation, and several numerical examples of direct and inverse Cauchy problems in complex domain confirm the efficiency of the MSPM and the MSDTM
Numerical Investigation of the Effect of Sorption Time on Coal Permeability and Gas Pressure
No full textAdsorption deformation significantly affects the seepage characteristics of coal. However, effect of sorption time on coal permeability and gas pressure has not been investigated systematically. In this study, the sorption experiment of coal samples is conducted to elaborate the importance of sorption equilibration time. Then a coupled coal deformation and gas flow model is established considering the sorption characteristic and permeability evolution. This coupled model is implemented through finite element method to analyze the effect of sorption time on coal permeability and gas pressure. The simulation results reveal that the gas pressure of the coal will change with the adsorption time. The fracture pressure maintains a high level while the matrix pressure is relatively low during the adsorption process. The sorption time has a great influence on the distribution of gas pressure. The smaller the adsorption time is, the lower the gas pressure becomes
A Pathway to Explore the Hidden Specialty in the Design of Fifteen Level Inverter in Grid Connected PV System
No full textThis research paper proposes a single phase fifteen level inverter for a grid connected PV system. The proposed inverter is also called cascaded asymmetric multilevel inverter. By adopting appropriate hybrid modulation technique improved output voltage is obtained with minimum number of power electronic switches. By reducing the number of gate triggering circuits of the switches, the size and power consumption of the driving circuits can be reduced. The total harmonic distortion of the output of the inverter is improved by this inverter. The proposed inverter developed by cascading a full bridge inverter with modified H bridge multilevel inverter. The validity of the proposed system is verified through MATLAB simulations
Emission of Electric Dipole Radiation in Between Parallel Mirrors
Get PDFAn oscillating electric dipole in free space emits its energy along straight lines. When the dipole is located in between parallel mirrors, this mechanism is significantly altered. Interference between the electric field of the dipole and the reflected magnetic field by the mirrors leads to a four-vortex structure in the emission pattern. The strength of the vortices depends on the separation between the mirrors and the distance of the dipole to one of the mirrors through a universal function
Novel Butterfly Photonic Crystal Fiber Structure with Negative Dispersion and High Non-Linearity
Get PDFDesign flexibility and enormous optical properties of Photonic Crystal Fiber (PCF) suited for different types of applications have influenced researchers and engineers in enhancing present drawbacks. Photonic crystal fiber is based on periodic morphological microstructure of air-holes where different arrangement of air holes led to different types of structures. Several types of structures with different shapes like Hexagonal, Octagonal, Honeycomb, Circular etc. have been proposed earlier. In this research, a novel PCF structure is proposed with butterfly geometry being inspired by natural form of PCF. To validate the performance of the new design, optical properties like dispersion, confinement loss and high nonlinearity are extracted with satisfactory results. COMSOL Multiphysics is used as modelling and simulation environment. To achieve negative dispersion -1.56x10^4 ps/km.nm at 1550nm, holes diameter and their spacing are considered accordingly. Multiple defect holes as well as elliptical core make the structure asymmetric which exhibits high nonlinearity of 42.