Intracranial aneurysm is a pathological dilatation of the cerebral artery which can lead to high mortality rate upon rupture. The aspect ratio (AR) of an aneurysm, being the ratio of the height to neck width, is an im...
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Intracranial aneurysm is a pathological dilatation of the cerebral artery which can lead to high mortality rate upon rupture. The aspect ratio (AR) of an aneurysm, being the ratio of the height to neck width, is an important factor in estimating the likelihood of aneurysm rupture in clinical practice. AR will generally increase while the aneurysm grows. Clinical observations over the years show that aneurysms with larger AR usually exhibit higher rupture risk. The goal of the current study is to conduct fluid-structure interaction (FSI) analyses to provide quantitative estimates on the importance of AR, wall thickness (t(w)) and hypertension. The effects of varying AR and t(w) on the hemodynamics, wall stress and displacement will be studied based on patient-specific models. Both sidewall and bifurcation aneurysms are investigated. There is a significant increase in the wall stress at the aneurysmal dome (the location in an aneurysm where rupture is commonly observed clinically) when the AR increases and t(w) decreases due to the aneurysm growth process. Furthermore, these investigations are repeated for patients with hypertension (high blood pressure) conditions. The increase in the wall stress due to hypertension for models with higher ARs is more dramatic. The clinically observed feature of higher rupture risk of aneurysms with larger AR is thus supported quantitatively.
Engineering design via CAD software relies on Non-Uniform Rational B-Splines (NURBS) as a means for representing and communicating geometry. Therefore, in general, a NURBS description of a given design can be consider...
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Engineering design via CAD software relies on Non-Uniform Rational B-Splines (NURBS) as a means for representing and communicating geometry. Therefore, in general, a NURBS description of a given design can be considered the exact description. The development of isogeometric methods has made the geometry available to analysis methods Hughes et al. (2005). Isogeometric analysis has been particularly successful in structural analysis;one reason being the wide-spread use of two-dimensional finite elements in this field. For fluid dynamics, where three-dimensional analysis is usually indispensable, isogeometric methods are more complicated, yet of course not impossible, to apply in a general fashion. This paper describes a method that enables the solution of fluid-structure-interaction with a matching spline description of the interface. On the structural side, the spline is used in an isogeometric setting. On the fluid side, the same spline is used in the framework of a NURBS-enhanced finite element method (extension of Sevilla et al. (2011)). The coupling of the structural and the fluid solution is greatly facilitated by the common spline interface. The use of the identical spline representation for both sides permits a direct transfer of the necessary quantities, all the while still allowing an adjusted, individual refinement level for both sides. (C) 2018 Elsevier B.V. All rights reserved.
It is known that atherosclerosis disease can lead to narrowing of human arteries over time. In this research, the flow field in the left external carotid artery is studied numerically considering fluid-structure inter...
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It is known that atherosclerosis disease can lead to narrowing of human arteries over time. In this research, the flow field in the left external carotid artery is studied numerically considering fluid-structure interactions and effect of different activities on the risk of atherosclerosis disease is evaluated. In this research, it is studied as to whether having physical exercise can reduce the risk of this disease to a great extent. The artery's tissue is assumed homogeneous and isotropic hyperelastic in fluid-structure interaction simulations. The normal heart cycle (without physical activity) is considered 0.8s (75bpm), and the effects of normal and high activities (having physical exercise with heart rates of 100, 120 and 150bpm) are studied on the artery's parameters (one healthy subject is studied). It is shown that the results obtained by considering fluid-structure interaction are close to those of rigid wall consideration in low activity. However, when the person has very high activity (i.e., heart rates of 120 and 150bpm), the differences become noticeable, and rigid wall assumption cannot be correct. Wall shear stress is one of the parameters that shows specific reaction to high exercise. Maximum difference between time average wall shear stress in normal activity and very high activity (150bpm) is about 103.7% for FSI simulation. Wall shear stress also shows greater difference between fluid-structure interaction and rigid wall consideration with respect to the other parameters by 36.2% in very high activity.
At present, the numerical simulation on the aerodynamic response and force of the iced conductor are mainly based on the quasi steady criterion, which ignored the interaction between the conductor and the flow field. ...
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At present, the numerical simulation on the aerodynamic response and force of the iced conductor are mainly based on the quasi steady criterion, which ignored the interaction between the conductor and the flow field. This paper presents a numerical study of three kinds of fluid-structure interaction models for D-shape conductor. The effects of reduced velocity, degree of freedom and wind attack angle on aerodynamic response of the iced conductor are discussed. The results show that the rotational freedom has certain influence on the across-wind vibration. The mean value of drag coefficient decreases with the increase of wind attack angle, while the lift and moment coefficient increase with the increase of wind attack angle. When the maximum amplitude of vibration displacement occurs, the corresponding reduced velocity is not entirely consistent with that of the maximum aerodynamic force.
In the SG (steam generator) of PWR (pressurized water reactor) for a nuclear plant, hundreds of U-shaped tubes are used for the heat exchanger system. They interact with primary pressurized cooling water flow, generat...
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In the SG (steam generator) of PWR (pressurized water reactor) for a nuclear plant, hundreds of U-shaped tubes are used for the heat exchanger system. They interact with primary pressurized cooling water flow, generating flow-induced vibration in the secondary flow region. A simplified U-tube model is proposed in this study to apply for experiment and its counterpart computation. Using the commercial code, ANSYS-CFX, we first verified the Moody chart, comparing the straight pipe theory with the results derived from CFD (computational fluid dynamics) analysis. Considering the virtual mass of fluid, we computed the major modes with the low natural frequencies through the comparison with impact hammer test, and then investigated the effect of pump flow in the frequency domain using FFT (fast Fourier transform) analysis of the experimental data. Using two-way fluid-structure interaction module in the CFD code, we studied the influence on mean flow rate to generate the displacement data. A feasible CFD method has been setup in this research that could be applied potentially in the field of nuclear thermal-hydraulics. (C) 2019 Korean Nuclear Society, Published by Elsevier Korea LLC.
In the present study, a numerical model of the injection molding filling stage was developed by combining non-Newtonian behavior, heat transfer, and thermo-elastic behavior in order to precisely predict mold deformati...
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In the present study, a numerical model of the injection molding filling stage was developed by combining non-Newtonian behavior, heat transfer, and thermo-elastic behavior in order to precisely predict mold deformation. In general, local deformation of an injection mold can be caused by two critical factors - elastic compression induced by the plastic melt and thermal expansion due to rapid heat transfer from the plastic melt. As severe mold deformation lowers the dimensional accuracy of the molded product or results in failure of the injection mold, the accurate prediction of mold deformation is critical to the design and manufacture of precision injection mold. In this regard, a numerical model considering the relevant physical behavior was developed and applied to a center-gated disc model. Both the melt flow behavior and effect of heat transfer inside the mold cavity were investigated, which subsequently revealed that the dominant influence is that of thermal expansion due to heat transfer.
This paper presents a numerical method for the simulation of fluid-structure interaction specifically tailored to interactions between Newtonian fluids and a large number of slender viscoelastic Cosserat rods. Because...
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This paper presents a numerical method for the simulation of fluid-structure interaction specifically tailored to interactions between Newtonian fluids and a large number of slender viscoelastic Cosserat rods. Because of their high flexibility and low weight the rods considered here exhibit large deflections, even under moderate fluid loads. Their motion, in turn, modifies the flow so that fluid and structures are strongly coupled to each other which is numerically very challenging. The paper proposes a new coupling approach based on an immersed boundary method which improves upon existing methods for this problem. It is numerically stable and exempt from any global iteration between the fluid part and the structure part, thus yielding high stability and low computational cost of the coupling scheme. The contribution presents the underlying methodology and its algorithmic realization, including an assessment of accuracy and convergence by systematic studies. Various validation cases illustrate performance and versatility of the proposed method. (C) 2020 Elsevier Inc. All rights reserved.
fluid-structure interaction is ubiquitous in nature and occurs at all biological scales. Immersed methods provide mathematical and computational frameworks for modeling fluid-structure systems. These methods, which ty...
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fluid-structure interaction is ubiquitous in nature and occurs at all biological scales. Immersed methods provide mathematical and computational frameworks for modeling fluid-structure systems. These methods, which typically use an Eulerian description of the fluid and a Lagrangian description of the structure, can treat thin immersed boundaries and volumetric bodies, and they can model structures that are flexible or rigid or that move with prescribed deformational kinematics. Immersed formulations do not require body-fitted discretizations and thereby avoid the frequent grid regeneration that can otherwise be required for models involving large deformations and displacements. This article reviews immersed methods for both elastic structures and structures with prescribed kinematics. It considers formulations using integral operators to connect the Eulerian and Lagrangian frames and methods that directly apply jump conditions along fluid-structure interfaces. Benchmark problems demonstrate the effectiveness of these methods, and selected applications at Reynolds numbers up to approximately 20,000 highlight their impact in biological and biomedical modeling and simulation.
Anisotropic distribution of the turbulent kinetic energy and the near-field excitations are the main causes of the steady state Flow-Induced Vibration (FIV) which could lead to fretting wear damage in vertically arran...
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Anisotropic distribution of the turbulent kinetic energy and the near-field excitations are the main causes of the steady state Flow-Induced Vibration (FIV) which could lead to fretting wear damage in vertically arranged supported slender rods. In this article, a combined Computational fluid Dynamics (CFD) and Computational Structural Mechanic (CSM) approach named two-way fluid-structure interaction (FSI) is used to investigate the modal characteristics of a typical rod's vibration. Performance of an Unsteady Reynolds-Average Navier-Stokes (URANS) and Large Eddy Simulation (LES) turbulence models on asymmetric fluctuations of the flow field are investigated. Using the LES turbulence model, any large deformation damps into a weak oscillation which remains in the system. However, it is challenging to use LES in two-way FSI problems from fluid domain discretization point of view which is investigated in this article as the innovation. It is concluded that the near-wall meshes whiten the viscous sub-layer is of great importance to estimate the Root Mean Square (RMS) of FIV amplitude correctly as a significant fretting wear parameter otherwise it merely computes the frequency of FIV. (C) 2018 Korean Nuclear Society, Published by Elsevier Korea LLC.
The purpose of this paper is to investigate the problem of weak parting coupling between incompressible fluids and shell structures that can develop large displacements. For this, a code computational model with formu...
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The purpose of this paper is to investigate the problem of weak parting coupling between incompressible fluids and shell structures that can develop large displacements. For this, a code computational model with formulation based on the finite element method (FEM) for analysis of incompressible flows in arbitrary Lagrangian-Eulerian description (ALE), which is coupled to an existing dynamic analysis program. In this work a positional FEM approach for the dynamic shell modeling considering the geometric nonlinearity was coupled to an FEM based methodology for the simulation of Newtonian fluids in ALE description using quadratic order elements for velocity and linear for pressure. In addition, a coupling proposal without the need of coincidence of the nodes of the domains accompanied by a scheme of dynamic movement of the fluid network based on the use of an auxiliary mesh with cubic order elements was successfully implemented. For the consideration of the geometric nonlinearity of shell structures, a formulation described in positions that does not interpolate rotations as degrees of freedom was employed. This technique proved to be robust and capable of simulating dynamic instability problems. The treatment of the fluid by means of the mixed formulation, or pressure-velocity, with stabilization by means of the Streamline Upwind Petrov-Galerkin (SUPG) technique proved to be quite suitable for the simulation of laminar flows, producing satisfactory results and in accordance with the literature.
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