A Model for the Nonlinear Buckling of Human Aorta

2012 ◽  
Author(s):  
Marco Amabili ◽  
Kostas Karazis ◽  
Rosaire Mongrain ◽  
Nastaran Shahmansouri
Keyword(s):  
Blood Flow ◽  
Flow Velocity ◽  
Stokes Equations ◽  
Surrounding Tissue ◽  
Human Aorta ◽  
Critical Flow ◽  
Linear Potential ◽  
Critical Flow Velocity ◽  
Aortic Segment ◽  
The Stability

Human aortas are subjected to large mechanical stresses due to blood flow pressurization and through contact with the surrounding tissue. It is essential that the aorta does not lose stability by buckling for its proper functioning to ensure proper blood flow. A refined reduced-order bifurcation analysis model is employed to examine the stability of an aortic segment subjected to internal blood flow. The structural model is based on a nonlinear cylindrical orthotropic laminated composite shell theory that assumes three aortic wall layers representing the tunica intima, media and adventitia. The fluid model contains the unsteady effects obtained from linear potential flow theory and the steady viscous effects obtained from the time-averaged Navier-Stokes equations. Residual stresses due to pressurization are evaluated and included in the model. The aortic segment loses stability by divergence with deformation of the cross-section at a critical flow velocity for a given static pressure, exhibiting a strong subcritical behaviour with partial or total collapse of the inner wall. Subsequent analyses including the effect of geometric wall imperfections indicate that imperfections in the axial direction have a more profound effect on the stability of the aorta decreasing the critical flow velocity for buckling.

Basic Study on Mitigation of Annular-Flow-Induced Vibration by Considering Variability in Parameters of Structure and Fluid

2013 ◽  
Author(s):  
Atsuhiko Shintani ◽  
Hirokazu Isono ◽  
Tomohiro Ito ◽  
Chihiro Nakagawa
Keyword(s):  
Flow Velocity ◽  
Annular Flow ◽  
Coupled System ◽  
Critical Flow ◽  
Control Input ◽  
Navier Stokes Equation ◽  
Critical Flow Velocity ◽  
Fluid Structure ◽  
The Stability ◽  
Coupled Equation

In this study, the stability of a structure and mitigation of the vibration of a structure subjected to annular flow are investigated when the parameters of the structure and fluid have variability or uncertainty. The equations of motion of the structure and fluid are given by the Euler-Bernoulli-type partial differential equation and the Navier–Stokes equation, respectively. Hence, the fluid–structure coupled system has variability. The fluid–structure coupled equation considering variability is derived from the above-mentioned equations. By drawing the root locus of the coupled equation, the stability of the coupled system with variability is investigated. Because the parameters of structure and fluid have variability, the critical flow velocity also varies. The effect of parameter variability on the critical flow velocity variability is investigated. Furthermore, to reduce the coupled vibration of the system with variability, a control input is used. Through adequate control, the coupled system with variability is stabilized.

Numerical Study of Thermal Effect on the Stability of Carbon Nanotubes Resting on a Viscoelastic Foundation Subjected to Magnetic Field

2021 ◽  
Author(s):  
Zeinab Heidary ◽  
Afsaneh Mojra
Keyword(s):  
Magnetic Field ◽  
Carbon Nanotubes ◽  
Fluid Flow ◽  
Flow Velocity ◽  
Temperature Variation ◽  
Critical Flow ◽  
Viscoelastic Foundation ◽  
Critical Flow Velocity ◽  
The Stability ◽  
The Magnetic Field

Carbon nanotubes (CNTs) have emerged as efficient tools in drug delivery systems; therefore, it is essential to refer to the importance of the magnetic field, in addition to the fluid flow on the dynamic behavior of CNTs. Additionally, in such medical applications, the actual working environment of nanotube often contains temperature changes, and CNTs are surrounded by soft tissues with viscoelastic mechanical properties. In this study, the vibrational behavior of CNTs conveying magnetic-fluid flow and resting on a viscoelastic foundation is investigated under various temperature variations. To incorporate the influence of slip velocity at the nanoscale, a correction factor is employed on the basis of the Beskok–Karniadakis model. The nanotube is modeled by the Euler–Bernoulli beam theory, and governing equations of motion are derived by implementing Hamilton’s principle based on Eringen’s nonlocal elasticity theory. Results indicate that by applying a magnetic field with an intensity of 30[Formula: see text]T, the dimensionless critical flow velocity increases from 4.345 to 12.603. Also, the critical flow velocity shows an increase from 4.345 to 5.854 in the presence of a viscoelastic foundation. Furthermore, a temperature variation equal to 20[Formula: see text]K reduces the critical flow velocity dramatically from 4.345 to 1.802 at low temperatures, while an increase from 4.345 to 5.443 is observed at high temperatures. Consequently, while the magnetic field and the viscoelastic foundation affect the system stability, the temperature variation may improve or deteriorate the stability. Therefore, to plan for a medical application, the inclusion of temperature variation is required.

scholarly journals Hybrid Scour Depth Prediction Equations for Reliable Design of Bridge Piers

Water ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2019
Author(s):  
Hossein Hamidifar ◽  
Faezeh Zanganeh-Inaloo ◽  
Iacopo Carnacina
Keyword(s):  
Flow Velocity ◽  
Critical Velocity ◽  
Depth Estimation ◽  
Hybrid Models ◽  
Velocity Estimation ◽  
Bridge Piers ◽  
Critical Flow ◽  
Scour Depth ◽  
Critical Flow Velocity ◽  
Estimation Equations

Numerous models have been proposed in the past to predict the maximum scour depth around bridge piers. These studies have all focused on the different parameters that could affect the maximum scour depth and the model accuracy. One of the main parameters individuated is the critical velocity of the approaching flow. The present study aimed at investigating the effect of different equations to determine the critical flow velocity on the accuracy of models for estimating the maximum scour depth around bridge piers. Here, 10 scour depth estimation equations, which include the critical flow velocity as one of the influencing parameters, and 8 critical velocity estimation equations were examined, for a total combination of 80 hybrid models. In addition, a sensitivity analysis of the selected scour depth equations to the critical velocity was investigated. The results of the selected models were compared with experimental data, and the best hybrid models were identified using statistical indicators. The accuracy of the best models, including YJAF-VRAD, YJAF-VARN, and YJAI-VRAD models, was also evaluated using field data available in the literature. Finally, correction factors were implied to the selected models to increase their accuracy in predicting the maximum scour depth.

An Analysis of In-Flow Fluidelastic Instability Based on a Physical Insight

2014 ◽  
Author(s):  
Tomomichi Nakamura
Keyword(s):  
Flow Velocity ◽  
Flow Instability ◽  
Pressure Sensors ◽  
Measured Data ◽  
Critical Flow ◽  
Nonlinear Phenomenon ◽  
Critical Flow Velocity ◽  
Fluid Force ◽  
Tube Arrays ◽  
Fluidelastic Instability

Fluidelastic vibration of tube arrays caused by cross-flow has recently been highlighted by a practical event. There have been many studies on fluidelastic instability, but almost all works have been devoted to the tube-vibration in the transverse direction to the flow. For this reason, there are few data on the fluidelastic forces for the in-flow movement of the tubes, although the measured data on the stability boundary has gradually increased. The most popular method to estimate the fluidelastic force is to measure the force acting on tubes due to the flow, combined with the movement of the tubes. However, this method does not give the physical explanation of the root-cause of fluidelastic instability. In the work reported here, the in-flow instability is assumed to be a nonlinear phenomenon with a retarded or delayed action between adjacent tubes. The fluid force acting on tubes are estimated, based on the measured data in another paper for the fixed cylinders with distributed pressure sensors on the surface of the cylinders. The fluid force acting on the downstream-cylinder is assumed in this paper to have a delayed time basically based on the distance between the separation point of the upstream-cylinder to the re-attachment point, where the fluid flows with a certain flow velocity. Two models are considered: a two-cylinder and three–cylinder models, based on the same dimensions as our experimental data to check the critical flow velocity. Both models show the same order of the critical flow velocity and a similar trend for the effect of the pitch-to-diameter ratio of the tube arrays, which indicates this analysis has a potential to explain the in-flow instability if an adequate fluid force is used.

Human Aorta Buckling Related to Dissection

2010 ◽  
Author(s):  
Kostas Karagiozis ◽  
Marco Amabili ◽  
Rosaire Mongrain ◽  
Raymond Cartier ◽  
Michael P. Pai¨doussis
Keyword(s):  
Blood Flow ◽  
Nonlinear Stability ◽  
Shell Theory ◽  
Inviscid Flow ◽  
Mechanical Stresses ◽  
Surrounding Tissue ◽  
Navier Stokes ◽  
Human Aorta ◽  
Navier Stokes Equation ◽  
Viscous Stresses

Human aortas are subjected to large mechanical stresses and loads due to blood flow pressurization and through contact with the surrounding tissue and muscle. It is essential that the aorta does not lose stability for proper functioning. The present work investigates the buckling of human aorta relating it to dissection by means of an analytical model. A full bifurcation analysis is used employing a nonlinear model to investigate the nonlinear stability of the aorta conveying blood flow. The artery is modeled as a shell by means of Donnell’s nonlinear shell theory retaining in-plane inertia, while the fluid is modelled by a Newtonian inviscid flow theory but taking into account viscous stresses via the time-averaged Navier-Stokes equation. The three shell displacements are expanded using trigonometric series that satisfy the boundary conditions exactly. A parametric study is undertaken to determine the effect of aorta length, thickness, Young’s modulus, and transmural pressure on the nonlinear stability of the aorta. As a first attempt to study dissection, a quasi-steady approach is taken, in which the flow is not pulsatile but steady. The effect of increasing flow velocity is studied, particularly where the system loses stability, exhibiting static collapse. Regions of large mechanical stresses on the artery surface are identified for collapsed arteries indicating possible ways for dissection to be initiated.

scholarly journals The Rule of Carrying Cuttings in Horizontal Well Drilling of Marine Natural Gas Hydrate

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1129 ◽  
Author(s):  
Na Wei ◽  
Yang Liu ◽  
Zhenjun Cui ◽  
Lin Jiang ◽  
Wantong Sun ◽  
...  
Keyword(s):  
Particle Size ◽  
Flow Velocity ◽  
Gas Hydrate ◽  
Horizontal Well ◽  
Drilling Fluid ◽  
Test Method ◽  
Critical Flow ◽  
Fluid Density ◽  
Critical Flow Velocity ◽  
Orthogonal Test Method

Horizontal well drilling is a highly effective way to develop marine gas hydrate. During the drilling of horizontal wells in the marine gas hydrate layer, hydrate particles and cutting particles will migrate with the drilling fluid in the horizontal annulus. The gravity of cuttings is easy to deposit in the horizontal section, leading to the accumulation of cuttings. Then, a cuttings bed will be formed, which is not beneficial to bring up cuttings and results in the decrease of wellbore purification ability. Then the extended capability of the horizontal well will be restricted and the friction torque of the drilling tool will increase, which may cause blockage of the wellbore in severe cases. Therefore, this paper establishes geometric models of different hole enlargement ways: right-angle expansion, 45-degree angle expansion, and arc expanding. The critical velocity of carrying rock plates are obtained by EDEM and FLUENT coupling simulation in different hydrate abundance, different hydrate-cuttings particle sizes and different drilling fluid density. Then, the effects of hole enlargement way, particle size, hydrate abundance and drilling fluid density on rock carrying capacity are analyzed by utilizing an orthogonal test method. Simulation results show that: the critical flow velocity required for carrying cuttings increases with the increase of the particle size of the hydrate-cuttings particle when the hydrate abundance is constant. The critical flow velocity decreases with the increase of drilling fluid density, the critical flow velocity carrying cuttings decreases with the increase of hydrate abundance when the density of the drilling fluid is constant. Orthogonal test method was used to evaluate the influence of various factors on rock carrying capacity: hydrate-cuttings particle size > hole enlargement way > hydrate abundance > drilling fluid density. This study provides an early technical support for the construction parameter optimization and well safety control of horizontal well exploitation models in a marine natural gas hydrate reservoir.

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