scholarly journals Fluid–Structure Interaction and In Vitro Analysis of a Real Bileaflet Mitral Prosthetic Valve to Gain Insight Into Doppler-Silent Thrombosis

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Annalisa Dimasi ◽  
Daniela Piloni ◽  
Laura Spreafico ◽  
Emiliano Votta ◽  
Riccardo Vismara ◽  
...  
Keyword(s):  
Prosthetic Valve ◽  
Heart Valves ◽  
Fluid Dynamic ◽  
Fluid Structure Interaction ◽  
Prosthetic Heart Valves ◽  
False Negatives ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Vitro Analysis

Prosthetic valve thrombosis (PVT) is a serious complication affecting prosthetic heart valves. The transvalvular mean pressure gradient (MPG) derived by Doppler echocardiography is a crucial index to diagnose PVT but may result in false negatives mainly in case of bileaflet mechanical valves (BMVs) in mitral position. This may happen because MPG estimation relies on simplifying assumptions on the transvalvular fluid dynamics or because Doppler examination is manual and operator dependent. A deeper understanding of these issues may allow for improving PVT diagnosis and management. To this aim, we used in vitro and fluid–structure interaction (FSI) modeling to simulate the function of a real mitral BMV in different configurations: normally functioning and stenotic with symmetric and completely asymmetric leaflet opening, respectively. In each condition, the MPG was measured in vitro, computed directly from FSI simulations and derived from the corresponding velocity field through a Doppler-like postprocessing approach. Following verification versus in vitro data, MPG computational data were analyzed to test their dependency on the severity of fluid-dynamic derangements and on the measurement site. Computed MPG clearly discriminated between normally functioning and stenotic configurations. They did not depend markedly on the site of measurement, yet differences below 3 mmHg were found between MPG values at the central and lateral orifices of the BMV. This evidence suggests a mild uncertainty of the Doppler-based evaluation of the MPG due to probe positioning, which yet may lead to false negatives when analyzing subjects with almost normal MPG.

Thermo-Fluid-Dynamic Design of Reciprocating Compressor Cylinders by Fluid Structure Interaction (FSI)

2011 ◽  
Author(s):  
Riccardo Traversari ◽  
Alessandro Rossi ◽  
Marco Faretra
Keyword(s):  
High Speed ◽  
Fluid Dynamic ◽  
Fluid Structure Interaction ◽  
Classical Equation ◽  
Flow Coefficient ◽  
Reciprocating Compressor ◽  
Complex Situation ◽  
Fluid Structure ◽  
Associated Gas ◽  
Structure Interaction

Pressure losses at the cylinder valves of reciprocating compressors are generally calculated by the classical equation of the flow through an orifice, with flow coefficient determined in steady conditions. Rotational speed has increased in the last decade to reduce compressor physical dimensions, weight and cost. Cylinder valves and associated gas passages became then more and more critical, as they determine specific consumption and throughput. An advanced approach, based on the new Fluid Structure Interaction (FSI) software, which allows to deal simultaneously with thermodynamic, motion and deformation phenomena, was utilized to simulate the complex situation that occurs in a reciprocating compressor cylinder during the motion of the piston. In particular, the pressure loss through valves, ducts and manifolds was investigated. A 3D CFD Model, simulating a cylinder with suction and discharge valves, was developed and experimentally validated. The analysis was performed in transient and turbulent condition, with compressible fluid, utilizing a deformable mesh. The 3D domain simulating the compression chamber was considered variable with the law of motion of the piston and the valve rings mobile according to the fluid dynamic forces acting on them. This procedure is particularly useful for an accurate valve loss evaluation in case of high speed compressors and heavy gases. Also very high pressure cylinders, including LDPE applications, where the ducts are very small and MW close to the water one, can benefit from the new method.

Fluid–Structure Interaction Models of Bicuspid Aortic Valves: The Effects of Nonfused Cusp Angles

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Karin Lavon ◽  
Rotem Halevi ◽  
Gil Marom ◽  
Sagit Ben Zekry ◽  
Ashraf Hamdan ◽  
...  
Keyword(s):  
Flow Direction ◽  
Fluid Dynamic ◽  
Fluid Structure Interaction ◽  
Jet Flow ◽  
Elastic Behavior ◽  
Principal Stresses ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Biomechanical Models ◽  
Hyper Elastic

Bicuspid aortic valve (BAV) is the most common type of congenital heart disease, occurring in 0.5–2% of the population, where the valve has only two rather than the three normal cusps. Valvular pathologies, such as aortic regurgitation and aortic stenosis, are associated with BAVs, thereby increasing the need for a better understanding of BAV kinematics and geometrical characteristics. The aim of this study is to investigate the influence of the nonfused cusp (NFC) angle in BAV type-1 configuration on the valve's structural and hemodynamic performance. Toward that goal, a parametric fluid–structure interaction (FSI) modeling approach of BAVs is presented. Four FSI models were generated with varying NFC angles between 120 deg and 180 deg. The FSI simulations were based on fully coupled structural and fluid dynamic solvers and corresponded to physiologic values, including the anisotropic hyper-elastic behavior of the tissue. The simulated angles led to different mechanical behavior, such as eccentric jet flow direction with a wider opening shape that was found for the smaller NFC angles, while a narrower opening orifice followed by increased jet flow velocity was observed for the larger NFC angles. Smaller NFC angles led to higher concentrated flow shear stress (FSS) on the NFC during peak systole, while higher maximal principal stresses were found in the raphe region during diastole. The proposed biomechanical models could explain the early failure of BAVs with decreased NFC angles, and suggests that a larger NFC angle is preferable in suture annuloplasty BAV repair surgery.

Numerical Study on Fluid Structure Interaction of Slug Flow in a Horizontal Pipeline

2016 ◽  
Vol 819 ◽  
pp. 319-325
Author(s):  
Abdalellah Omer Mohmmed ◽  
Mohammad Shakir Nasif ◽  
Hussain Hamoud Al-Kayiem ◽  
Zahid Ibrahim Al-Hashimy
Keyword(s):  
Slug Flow ◽  
Maximum Stress ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Fluid Structure Interaction ◽  
Water Velocity ◽  
Design Stage ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Model Code

It is well-known that when slug flow occurs in pipes it may result in damaging the pipe line. Therefore it is important to predict the slug occurrence and its effect. Slug flow regime is unsteady in nature and the pipelines conveying it are indeed susceptible to significant cyclic stresses. In this work, a numerical study has been conducted to investigate the interaction between the slug flow and solid pipe. Fluid Structure Interaction (FSI) coupling between 3-D Computational Fluid Dynamic (CFD) and 3-D pipeline model code has been developed to assess the stresses on the pipe due to slug flow. Time – dependent stresses results has been analyzed together with the slug characteristic along the pipe. Results revealed that the dynamic behavior of the pipelines is strongly affected by slug parameters. The FSI simulation results show that the maximum stresses occurred close to the pipe supports due to slug flow, where the pipe response to the exerted slug forces is extremely high. These stresses will subsequently cause fatigue damage which is likely reduce the total lifetime of the pipeline. Therefore a careful attention should be made during the design stage of the pipeline to account for these stresses. The system has been investigated under multiple water velocities and constant air velocity, the maximum stress was obtained at the water velocity of 0.505 m/s. Moreover, when the water velocity is increased from 0.502 to 1.003 m/s the maximum stress magnitude is decreased by 1.2% and when it is increased to 1.505 m/s the maximum stress is diminished by 3.6%.

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