On the Role and Effects of Uncertainties in Cardiovascular in silico Analyses

The assessment of cardiovascular hemodynamics with computational techniques is establishing its fundamental contribution within the world of modern clinics. Great research interest was focused on the aortic vessel. The study of aortic flow, pressure, and stresses is at the basis of the understanding of complex pathologies such as aneurysms. Nevertheless, the computational approaches are still affected by sources of errors and uncertainties. These phenomena occur at different levels of the computational analysis, and they also strongly depend on the type of approach adopted. With the current study, the effect of error sources was characterized for an aortic case. In particular, the geometry of a patient-specific aorta structure was segmented at different phases of a cardiac cycle to be adopted in a computational analysis. Different levels of surface smoothing were imposed to define their influence on the numerical results. After this, three different simulation methods were imposed on the same geometry: a rigid wall computational fluid dynamics (CFD), a moving-wall CFD based on radial basis functions (RBF) CFD, and a fluid-structure interaction (FSI) simulation. The differences of the implemented methods were defined in terms of wall shear stress (WSS) analysis. In particular, for all the cases reported, the systolic WSS and the time-averaged WSS (TAWSS) were defined.

An efficient, localised approach for the simulation of elastic blood vessels using the lattice Boltzmann method

Many numerical studies of blood flow impose a rigid wall assumption due to the simplicity of its implementation compared to a full coupling with a solid mechanics model. In this paper, we present a localised method for incorporating the effects of elastic walls into blood flow simulations using the lattice Boltzmann method implemented by the open-source code HemeLB. We demonstrate that our approach is able to more accurately capture the flow behaviour expected in elastic walled vessels than ones with rigid walls. Furthermore, we show that this can be achieved with no loss of computational performance and remains strongly scalable on high performance computers. We finally illustrate that our approach captures the same trends in wall shear stress distribution as those observed in studies using a rigorous coupling between fluid dynamics and solid mechanics models to solve flow in personalised vascular geometries. These results demonstrate that our model can be used to efficiently and effectively represent flows in elastic blood vessels.

Effective in-plane elastic properties of honeycomb-polymer composites

Honeycomb composites are now common materials in applications where high specific stiffness is required. Previous research has found that honeycombs with polymer infills in their cells, here referred to as honeycomb-polymer composites (HPCs), exhibit effective stiffnesses greater than the honeycomb or polymer alone. Currently, the state of analytic models for predicting the elastic properties of these composites is limited, and further research is needed to better characterize the behavior of these materials. In this research, a nonlinear finite element analysis was employed to perfor2m parametric studies of a filled honeycomb unit cell with isotropic wall and infill materials. A rigid wall model was created as an upper bound on the deformable wall model’s performance, and an empty honeycomb model was employed to better understand the mechanisms of stiffness amplification. Parametric studies were completed for infill material properties and cell geometry, with the effective Young’s modulus studied in two in-plane material directions. The mechanisms by which the stiffness amplification occurs are studied, and comparisons to existing analytic models are made. It has been observed that both the volume change within the honeycomb cell under deformation and the mismatch in Poisson’s ratios between the honeycomb and infill influence the effective properties. Stiffness amplifications of over 4000 have been observed, with auxetic behavior achieved by tailoring of the HPC geometry. Additionally, the effect of large effective strains up to 10% is explored, where the cell geometry changes significantly. This research provides an important step toward understanding the design space and benefits of HPCs.

Torsional stability of thin-walled cylindrical shells filled with free-flowing aggregate

Экспериментами изучено влияние сыпучего заполнителя на устойчивость при кручении тонкостенных цилиндрических оболочек. Для исследования образцы изготавливались из алюминиевого сплава 3004 глубокой вытяжкой в матрице. Образцы закреплялись консольно к жесткой стенке, на свободный конец прикладывался крутящий момент. Испытывались пустые и заполненные железным порошком образцы. Нагружение образцов выполнялось ступенчато, порциями по 10Н вначале и при приближении к моменту потери устойчивости по 1Н, 0,5Н. На каждой ступени нагружения фиксировались крутящий момент и угол поворота свободного конца образца. Построены графики зависимости угла поворота от крутящего момента. Устойчивость образцов терялась в упругости. Вначале нагружения, на заполненных сыпучим заполнителем образцах, не происходит поворот сечений из-за препятствия сил трения заполнителя. Железный порошок увеличивает значение критического крутящего момента на 20-30%. Experiments have studied the effect of free-flowing aggregate on torsional stability of thin-walled cylindrical shells. For research samples were made of aluminum alloy 3004 deep hood in the matrix. The samples were fixed cantilever to a rigid wall, on torque was applied to the free end. Tested empty and samples filled with iron powder. The loading of the samples was carried out stepwise, in portions of 10N at the beginning and when approaching the moment of loss stability of 1H, 0.5H. At each loading stage, torque and angle of rotation of the free end of the sample. Graphs built the dependence of the angle of rotation on the torque. Stability of samples lost in elasticity. At the beginning of loading, on filled with bulk filler in samples, no rotation of sections occurs due to obstacle forces friction of the aggregate. Iron powder increases the critical value of torque by 20-30 %.

Effect of Different Types of Stenosis on Generalized Power Law Model of Blood Flow in a Bifurcated Artery

This study is focus on generalized power law model of blood flow in a stenosed bifurcated artery under the effect of different types of stenosis. Stenosis can cause the narrowing of the artery that may reduce the flow of blood supply to the heart, and this may lead to the heart attacks. The geometry of the bifurcated artery with different classification of stenosis locations is considered in order to shows four possible morphologies formation of plaque from healthy artery to disease artery. The bifurcated artery is modelled as a two-dimensional rigid wall since the wall of a disease artery is reported to be less flexibility. Few assumptions are considered such as blood are incompressible, laminar, steady and characterized as the generalized power-law model. Simulation results are obtained using COMSOL Multiphysics 5.2, which is a software that based on the finite element method to solve this problem. Results concerning the effect of different locations of stenosis on generalized power law model of the blood flow characteristic such as streamlines pattern are discussed.

AiStudy on the Behavior of an Underwater Explosion Bubble near a Rigid Wall

The dynamic approach to an underwater explosion (UNDEX) is a complex episode that involves shockwave propagation, bubble pulse with high pressure, and water jet impact. This paper proposes linkage of Finite Element Avenue (FEM) and Companion of Eulerian-Lagrangian (CEL) to supply promised data of large deformations and flow simulation of fluid and gas where the bubble interaction is near a stiff wall. To conduct the process, a 7.5 m x 9.0 m Eulerian domain and explosive charges of 10 g, 35 g, and 55 g TNT are built in a free field, respectively. Numerical analysis, as far as a comparison with research from E. Klaseboer, has been given in this study. The important results obtained from the CEL approach imply high expectations. In spite of the fact that this approach is not adequately consistent to totally supplant a live test, it can be utilized as an outline database to anticipate outcomes of managing an UNDEX with a high pressure bubble. The behavioral explosion from an UNDEX bubble near a rigid wall is a prospective contribution in this research. With these results, this technique can be used in further studies to examine UNDEX bubbles in the vicinity of deformable and complex structures.

Numerical Investigation of Interaction between Saccular Abdominal Aortic Aneurysms and Arterial Bifurcations

In order to fully understand the interaction between the Abdominal Aortic Aneurysms (AAAs) and the arterial bifurcations interface it is important to attain more detailed information on blood hemodynamics stresses by using an accurate and real model of the vascular system of the human. In this study, a computer simulation, which integrates dinically acquired of 73-year-old male patient with saccular AAA MR angiograms image is considered. The numerical predictions for 2D of two models (with and without saccular AAA) – axisymmetric, rigid wall Newtonian and non-Newtonian Carreau blood model are presented. The finite volume method performed by ANSYS-Fluent Package was used to model this problem. The blood hemodynamics is considered as steady state condition in two values of Reynolds numbers of laminar flow condition. Blood hemodynamics is calculated for an improved set of dimensionless values pointer parameters include the pressure dimensionless, dimensionless Wall Shear Stress (WSS) and flow velocity. The results show that at the turbulent flow, velocity is with highest fluctuation profile and generate some vortices near the inner wall of AAA. The highest WSS levels are obtained downstream of AAA and at bifurcation apex. The presence of AAA in flow path will increase blood velocity of the distal by 35% for laminar and about 42% for turbulent. Finally, the velocity profile was compared with previous literature and give good agreement at the same computational condition.