scholarly journals Particle Based Visualization of Stress Distribution Caused by the Aortic Valve Deformation

1970 ◽  
Vol 6 (1) ◽  
pp. 33-39
Author(s):  
Masashi Nakagawa ◽  
Nobuhiko Mukai ◽  
Kiyomi Niki ◽  
Shuichiro Takanashi
Keyword(s):  
Aortic Valve ◽  
Stress Distribution ◽  
Particle Method ◽  
Blood Stream ◽  
Free Surfaces ◽  
Surgical Simulators ◽  
Virtual Particles ◽  
Pressure Calculation ◽  
Operative Planning ◽  
Moving Particle

Medical and engineering technologies have developed the surgical simulators, which allow users to train for surgical skills. To perform the aortic valve replacement, which is one of the cardiovascular surgeries, it is necessary to examine not only the timing of the heart pulsating but also the stress distribution on the aortic valve. For pre-operative planning, wehave visualized the stress on the aortic valve due to the deformation of the aorta and blood stream. In our research, simulations of the deformation of the aortic valve and blood stream have been performed with 3D aorta and aortic valve models, which are composed of particles. In the simulation, the aortic valve and blood models are treated as an elastic body and Hershel-Bulkley fluid, respectively. We have used MPS (Moving Particle Semi-implicit) as the particle method; however, it is known that MPS method cannot specify the stress because the pressure among the particles on the free surfaces is zero. Then, in this paper, we propose more stable pressure calculation by considering virtual particles. As a result, visualization of the stress distribution on the aortic valve has been achieved.

scholarly journals Study on divergence approximation formula for pressure calculation in particle method

2018 ◽  
Vol 10 (4) ◽  
pp. 159-169
Author(s):  
Zhu Yue ◽  
Jiang Shengyao ◽  
Yang Xingtuan ◽  
Duan Riqiang
Keyword(s):  
Pressure Oscillation ◽  
Particle Method ◽  
Free Surface Flows ◽  
Implicit Method ◽  
Approximation Formula ◽  
Pressure Poisson Equation ◽  
Pressure Calculation ◽  
Approximation Formulas ◽  
Moving Particle ◽  
Dam Breaking

The moving particle semi-implicit method is a meshless particle method for incompressible fluid and has proven useful in a wide variety of engineering applications of free-surface flows. Despite its wide applicability, the moving particle semi-implicit method has the defects of spurious unphysical pressure oscillation. Three various divergence approximation formulas, including basic divergence approximation formula, difference divergence approximation formula, and symmetric divergence approximation formula are proposed in this paper. The proposed three divergence approximation formulas are then applied for discretization of source term in pressure Poisson equation. Two numerical tests, including hydrostatic pressure problem and dam-breaking problem, are carried out to assess the performance of different formulas in enhancing and stabilizing the pressure calculation. The results demonstrate that the pressure calculated by basic divergence approximation formula and difference divergence approximation formula fluctuates severely. However, application of symmetric divergence approximation formula can result in a more accurate and stabilized pressure.

Optimization of Moving Particle Semi-Implicit (MPS) Method and Studying of Flow Instability

2018 ◽  
Author(s):  
Kailun Guo ◽  
Ronghua Chen ◽  
Suizheng Qiu ◽  
Wenxi Tian ◽  
Guanghui Su ◽  
...  
Keyword(s):  
Multiphase Flows ◽  
Flow Instability ◽  
Free Particle ◽  
Particle Method ◽  
Severe Accident ◽  
Particle Methods ◽  
Two Phase ◽  
Mps Method ◽  
Viscosity Term ◽  
Moving Particle

Multiphase flow widely exists in the nature and engineering. The two-phase flow is the highlight of the studies about the flow in the vessel and steam explosion in nuclear severe accidents. The Moving Particle Semi-implicit (MPS) method is a fully-Lagrangian particle method without grid mesh which focuses on tracking the single particle and concerns with its movement. It has advantages in tracking complex multiphase flows compared with gird methods, and thus shows great potential in predicting multiphase flows. The objective of this thesis is to develop a general multiphase particle method based on the original MPS method and thus this work is of great significance for improving the numerical method for simulating the instability in reactor severe accident and two-phase flows in vessel. This research is intended to provide a study of the instability based on the MPS method. Latest achievements of mesh-free particle methods in instability are researched and a new multiphase MPS method, which is based on the original one, for simulating instability has been developed and validated. Based on referring to other researchers’ papers, the Pressure Poisson Equation (PPE), the viscosity term, the free surface particle determination part and the surface tension model are optimized or added. The numerical simulation on stratification behavior of two immiscible flows is carried out and results are analyzed after data processing. It is proved that the improved MPS method is more accurate than the original method in analysis of multiphase flows. In this paper, the main purposes are simulating and discussing Rayleigh-Taylor (R-T) instability and Kelvin-Helmholtz (K-H) instability. R-T and K-H instability play an important role in the mixing process of many layered flows. R-T instability occurs when a lower density fluid is supported by another density higher fluid or higher density fluid is accelerated by lower density fluid, and the resulting small perturbation increases and eventually forms turbulence. K-H instability is a small disturbance for two different densities, such as waves, at the interface of the two-phase fluid after giving a fixed acceleration in the fluid. Turbulence generated by R-T instability and K-H instability has an important effect in applications such as astrophysics, geophysics, and nuclear science.

3D Simulation of Molten Metal Freezing Behaviour Using Finite Volume Particle Method

2010 ◽  
Author(s):  
Rida S. N. Mahmudah ◽  
Masahiro Kumabe ◽  
Takahito Suzuki ◽  
LianCheng Guo ◽  
Koji Morita ◽  
...  
Keyword(s):  
Molten Metal ◽  
Finite Volume ◽  
Particle Method ◽  
Metal Structure ◽  
Freezing Behavior ◽  
Severe Accident ◽  
Particle Methods ◽  
Freezing Process ◽  
Penetration Length ◽  
Moving Particle

Understanding the freezing behavior of molten metal in flow channels is of importance for severe accident analysis of liquid metal reactors. In order to simulate its fundamental behavior, a 3D fluid dynamics code was developed using Finite Volume Particle (FVP) method, which is one of the moving particle methods. This method, which is fully Lagrangian particle method, assumes that each moving particle occupies certain volume. The governing equations that determine the phase change process are solved by discretizing its gradient and Laplacian terms with the moving particles. The motions of each particle and heat transfer between particles are calculated through interaction with its neighboring particles. A series of experiments for fundamental freezing behavior of molten metal during penetration on to a metal structure was also performed to provide data for the validation of the developed code. The comparison between simulation and experimental results indicates that the present 3D code using the FVP method can successfully reproduce the observed freezing process such as molten metal temperature profile, frozen molten metal shape and its penetration length on the metal structure.

scholarly journals Numerical Parametric Study of Paravalvular Leak Following a Transcatheter Aortic Valve Deployment Into a Patient-Specific Aortic Root

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Wenbin Mao ◽  
Qian Wang ◽  
Susheel Kodali ◽  
Wei Sun
Keyword(s):  
Aortic Valve ◽  
Computational Model ◽  
Aortic Root ◽  
Paravalvular Leak ◽  
Patient Specific ◽  
Fe Method ◽  
Transcatheter Aortic Valve ◽  
Operative Planning ◽  
The Difference ◽  
The Impact

Paravalvular leak (PVL) is a relatively frequent complication after transcatheter aortic valve replacement (TAVR) with increased mortality. Currently, there is no effective method to pre-operatively predict and prevent PVL. In this study, we developed a computational model to predict the severity of PVL after TAVR. Nonlinear finite element (FE) method was used to simulate a self-expandable CoreValve deployment into a patient-specific aortic root, specified with human material properties of aortic tissues. Subsequently, computational fluid dynamics (CFD) simulations were performed using the post-TAVR geometries from the FE simulation, and a parametric investigation of the impact of the transcatheter aortic valve (TAV) skirt shape, TAV orientation, and deployment height on PVL was conducted. The predicted PVL was in good agreement with the echocardiography data. Due to the scallop shape of CoreValve skirt, the difference of PVL due to TAV orientation can be as large as 40%. Although the stent thickness is small compared to the aortic annulus size, we found that inappropriate modeling of it can lead to an underestimation of PVL up to 10 ml/beat. Moreover, the deployment height could significantly alter the extent and the distribution of regurgitant jets, which results in a change of leaking volume up to 70%. Further investigation in a large cohort of patients is warranted to verify the accuracy of our model. This study demonstrated that a rigorously developed patient-specific computational model can provide useful insights into underlying mechanisms causing PVL and potentially assist in pre-operative planning for TAVR to minimize PVL.

Proposed percutaneous aortic valve prosthesis made of cryogel

2019 ◽  
Vol 233 (5) ◽  
pp. 515-524 ◽  
Author(s):  
Hadi Mohammadi ◽  
Dylan Goode ◽  
Guy Fradet ◽  
Kibret Mequanint
Keyword(s):  
Aortic Valve ◽  
Heart Valves ◽  
Kidney Injury ◽  
Blood Stream ◽  
Valve Prosthesis ◽  
Element Analysis ◽  
Novel Approach ◽  
Natural Geometry ◽  
Myocardial Infraction ◽  
Aortic Valve Prosthesis

Transcatheter heart valves are promising for high-risk patients. Generally, their leaflets are made of pericardium stented in a Nitinol basket. Despite their relative success, they are associated with significant complications such as valve migration, implantation risks, stroke, coronary obstruction, myocardial infraction, acute kidney injury (which all are due to the release of detached solid calcific pieces in to the blood stream) and expected issues existing with tissue valves such as leaflet calcification. This study is an attempt to fabricate the first ever polymeric percutaneous valves made of cryogel following the geometry and mechanical properties of porcine aortic valve to address some of the above-mentioned shortcomings. A novel, one-piece, tricuspid percutaneous valve, consisting of leaflets made entirely from the hydrogel, polyvinyl alcohol cryogel reinforced by bacterial cellulose natural nanocomposite, attached to a Nitinol basket was developed and demonstrated. Following the natural geometry of the valve, a novel approach was applied based on the revolution about an axis of a hyperboloid shape. The geometry was modified based on avoiding sharp warpage of leaflets and removal of the central opening orifice area of the valve when valve is fully closed using the finite element analysis. The modified geometry was replaced by a cloud of (control) points and was essentially converted to Bezier surfaces for further adjustment. A cavity mold was then designed and fabricated to form the valve. The fabricated valve was sewn into the Nitinol basket which is covered by Dacron cloth. The models presented in this study merit further development and revisions for both aortic and mitral positions.

Simulation of Liquid Jet Breakup of a Swirl-Type Fuel Injector for Automobile Engines

2007 ◽  
Author(s):  
Eiji Ishii ◽  
Toru Ishikawa ◽  
Yoshiyuki Tanabe
Keyword(s):  
Water Column ◽  
Grid Method ◽  
Particle Method ◽  
Engine Fuel ◽  
Fuel Injector ◽  
Free Surfaces ◽  
Scale Free ◽  
Multi Scale ◽  
Jet Breakup ◽  
Automobile Engines

To simulate multi-scale free surfaces, we developed a hybrid particle/grid method by which the free surfaces within sub-grid regions are simulated by the particle method, and other regions are simulated with the grid method. The particle method uses two types of particles to model gas and liquid fluids in order to simulate the interaction between them. We tested the new method on fragmentation of a water column, and the predicted configurations of the water column are consistent with measurements of Koshizuka and Oka. We also simulated the fuel spray near the outlet of an automobile-engine fuel injector and found that this method qualitatively simulated the breakup of the liquid film.

Numerical Study of Pressure Wave Transmission in Liquid Under Different Interface Conditions Using Particle Method

2009 ◽  
Author(s):  
Zhongguo Sun ◽  
Guang Xi
Keyword(s):  
Free Surface ◽  
Pressure Wave ◽  
Numerical Study ◽  
Wave Length ◽  
Particle Method ◽  
Wave Transmission ◽  
Wave Transport ◽  
Moving Particle ◽  
Energy Absorbing ◽  
The Waves

The process of pressure wave transmission in liquid is simulated with the moving particle semi-implicit (MPS) method. The simulation is carried out in a tube full filled with an energy absorbing liquid. Here we studied the shapes and positions of pressure waves and investigated the behavior of the waves under different viscosities and densities of liquids. Some typical parameters of pressure wave, such as peak pressure value, wave length and transport speed are studied. Varying viscosity does not change the wave length and speed of the pressure wave evidently. The effect of interfaces which formed by viscosity difference or density difference is investigated. Reflection is found not always happened on such interfaces. Pressure wave transport to liquid-solid interface and free surface are also simulated. Pressure wave is vanished when closing to free surface. These results give useful qualitative suggestions on controlling the pressure wave in fluid engineering.

Particle Method for Incompressible Flow With Free Surface

2002 ◽  
Author(s):  
S. Koshizuka ◽  
Y. Oka
Keyword(s):  
Solid Mechanics ◽  
Differential Operators ◽  
Incompressible Flows ◽  
Particle Method ◽  
Equation System ◽  
Nucleate Boiling ◽  
Droplet Breakup ◽  
Lagrangian Description ◽  
Free Surfaces ◽  
Mps Method

Moving Particle Semi-implicit (MPS) method is a particle method which has been developed to analyze incompressible flows with free surfaces. Fluids are represented by particles which move in fully Lagrangian description. Since grids are not necessary, complex motion of free surfaces can be calculated without grid tangling or numerical diffusion. In the MPS method, a differential equation system is transformed to particle dynamics using the models representing differential operators. Incompressibility is solved by the Poisson equation of pressure to keep the particle number density constant. Solid mechanics is also modeled by particles and fluid-structure interaction can be solved. Calculation examples are provided in this paper: collapse of a water column, melt droplet fragmentation, sloshing with tank deformation, nucleate boiling and droplet breakup. These examples show that the MPS method is a powerful tool to investigate complex behaviors of free surfaces and multiphase flows.

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