Evaluation of dentinal fluid flow behaviours: a fluid-structure interaction simulation

This study uses the fluid-structure interaction (FSI) method to investigate the fluid flow in dental pulp. First, the FSI method is used for the biomechanical simulation of dental intrapulpal responses during force loading (50, 100 and 150 N) on a tooth. The results are validated by comparison with experimental outcomes. Second, the FSI method is used to investigate an intact tooth subjected to a mechanical stimulus during loading at various loading rates. Force loading (0–100 N) is applied gradually to an intact tooth surface with loading rates of 125, 62.5, 25 and 12.5 N/s, respectively, and the fluid flow changes in the pulp are evaluated. FSI analysis is found to be suitable for examining intrapulpal biomechanics. An external force applied to a tooth with a low loading rate leads to a low fluid flow velocity in the pulp chamber, thus avoiding tooth pain.     

计算流体力学在古生物学中的应用——以寒武纪始海百合在COMSOL软件中的模拟为例*

提要关于古生物生态位和功能形态学方面的研究通常是推测性的,而定量分析工作较少。此外由于缺少现生生物做对比等诸多因素,使得有些假说存在争议。计算流体力学CFD (computational fluid dynamics)在验证这些推测性假说上具有极大的潜力,并为了解古生物的生活环境以及解释生物在进化过程中的形态变化提供了新的契机。COMSOL Multiphysics作为一款多物理场仿真软件,适用于对古生物的CFD模拟,本文以凯里组始海百合Globoeocrinus模型在COMSOL中的流体实验为案例,来论证关于Globoeocrinus螺旋的腕会使附近的水体形成湍性流动进而帮助滤食这一假说的可能性。流体模拟结果表明在水流流速0.01–0.5 m/s的范围内,Globoeocrinus腕周围并没有出现湍性流动的涡,而是形成了低流速域。低流速域的形成有利于增加始海百合滤取食物的概率。同时文章详细介绍了在COMSOL中进行案例研究的操作步骤,以期望帮助更多的古生物研究者理解和应用CFD技术。     

How much does nasal cavity morphology matter? Patterns and rates of olfactory airflow in phyllostomid bats

The morphology of the nasal cavity in mammals with a good sense of smell includes features that are thought to improve olfactory airflow, such as a dorsal conduit that delivers odours quickly to the olfactory mucosa, an enlarged olfactory recess at the back of the airway, and a clear separation of the olfactory and respiratory regions of the nose. The link between these features and having a good sense of smell has been established by functional examinations of a handful of distantly related mammalian species. In this paper, we provide the first detailed examination of olfactory airflow in a group of closely related species that nevertheless vary in their sense of smell. We study six species of phyllostomid bats that have different airway morphologies and foraging ecologies, which have been linked to differences in olfactory ability or reliance. We hypothesize that differences in morphology correlate with differences in the patterns and rates of airflow, which in turn are consistent with dietary differences. To compare species, we make qualitative and quantitative comparisons of the patterns and rates of airflow through the olfactory region during both inhalation and exhalation across the six species. Contrary to our expectations, we find no clear differences among species in either the patterns of airflow through the airway or in rates of flow through the olfactory region. By and large, olfactory airflow seems to be conserved across species, suggesting that morphological differences appear to be driven by other mechanical demands on the snout, such as breathing and feeding. Olfactory ability may depend on other aspects of the system, such as the neurobiological processing of odours that work within the existing morphology imposed by other functional demands on the nasal cavity.     

Stratification of a population of intracranial aneurysms using blood flow metrics

Indices of the intra-aneurysm hemodynamic environment have been proposed as potentially indicative of their longitudinal outcome. To be useful, the indices need to be used to stratify large study populations and tested against known outcomes. The first objective was to compile the diverse hemodynamic indices reported in the literature. Furthermore, as morphology is often the only patient-specific information available in large population studies, the second objective was to assess how the ranking of aneurysms in a population is affected by the use of steady flow simulation as an approximation to pulsatile flow simulation, even though the former is clearly non-physiological. Sixteen indices of aneurysmal hemodynamics reported in the literature were compiled and refined where needed. It was noted that, in the literature, these global indices of flow were always time-averaged over the cardiac cycle. Steady and pulsatile flow simulations were performed on a population of 198 patient-specific and 30 idealised aneurysm models. All proposed hemodynamic indices were estimated and compared between the two simulations. It was found that steady and pulsatile flow simulations had a strong linear dependence (r ≥ 0.99 for 14 indices; r ≥ 0.97 for 2 others) and rank the aneurysms in an almost identical fashion (ρ ≥ 0.99 for 14 indices; ρ ≥ 0.96 for other 2). When geometry is the only measured piece of information available, stratification of aneurysms based on hemodynamic indices reduces to being a physically grounded substitute for stratification of aneurysms based on morphology. Under such circumstances, steady flow simulations may be just as effective as pulsatile flow simulation for estimating most key indices currently reported in the literature.     

A simple fluid–structure coupling algorithm for the study of the anastomotic mechanics of vascular grafts

Vascular anastomoses constitute a main factor in poor graft performance due to mismatches in distensibility between the host artery and the graft. This work aims at computational fluid–structure investigations of proximal and distal anastomoses of vein grafts and synthetic grafts. Finite element and finite volume models were developed and coupled with a user-defined algorithm. Emphasis was placed on the simplicity of the coupling algorithm. An artery and vein graft showed a larger dilation mismatch than an artery and synthetic graft. The vein graft distended nearly twice as much as the artery while the synthetic graft displayed only approximately half the arterial dilation. For the vein graft, luminal mismatching was aggravated by development of an anastomotic pseudo-stenosis. While this study focused on end-to-end anastomoses as a vehicle for developing the coupling algorithm, it may serve as useful point of departure for further investigations such as other anastomotic configurations, refined modelling of sutures and fully transient behaviour.