47 research outputs found
Chromo-dynamic multi-component lattice Boltzmann equation scheme for axial symmetry
We validate the chromo-dynamic multi-component lattice Boltzmann equation (MCLBE) simulation for immiscible fluids with a density contrast against analytical results for complex flow geometries, with particular emphasis on the fundamentals of the method, i.e. compliance with inter-facial boundary conditions of continuum hydrodynamics. To achieve the necessary regimes for the chosen validations, we develop, from a three-dimensional, axially-symmetric flow formulation, a novel, two-dimensional, pseudo Cartesian, MCLBE scheme. This requires the inclusion in lattice Boltzmann methodology of a continuously distributed source and a velocity-dependent force density (here, the metric force terms of the cylindrical NavierâStokes equations). Specifically, we apply our model to the problem of flow past a spherical liquid drop in Re = 0, Ca regime and, also, flow past a lightly deformed drop. The resulting simulation data, once corrected for the simulationâs inter-facial micro-current (using a method we also advance herein, based on freezing the phase field) show good agreement with theory over a small range of density contrasts. In particular, our data extend verified compliance with the kinematic condition from flat (Burgin et al 2019 Phys. Rev. E 100 043310) to the case of curved fluidâfluid interfaces. More generally, our results indicate a route to eliminate the influence of the inter-facial micro-current
Personalised parameter estimation of the cardiovascular system: Leveraging data assimilation and sensitivity analysis of the cardiovascular system: Leveraging data assimilation and sensitivity analysis of the cardiovascular system: Leveraging data assimilation and sensitivity analysis
Detailed models of dynamical systems used in the life sciences may include hundreds of state variables and many input parameters, often with physical meanings. Therefore, efficient and unique input parameter identification, from experimental data, is an essential but challenging task for this class of models. This study presents a comprehensive analysis of a nine-dimensional single ventricle lumped-parameter model, representing the systemic circulation. This model is formulated in terms of differential algebraic equations, often found in other areas of the life sciences. We introduce a novel computational algorithm designed to incorporate patient-specific beat-to-beat variability into model investigations, utilising the Unscented Kalman Filter (UKF) for efficient parameter estimation. Our findings demonstrate the exceptional adaptability of the UKF to severe parameter perturbations, representing significant physiological changes. Furthermore, we provide novel insights into the continuous sensitivity of model input parameters, illustrating the robustness and efficacy of UKF. The monitoring of a patientâs physiological state, with minimal delay, becomes feasible, by incorporating patient-specific measurements and leveraging the UKF. The workflow presented in this paper enables prompt identification of pathophysiological conditions and will improve patient care
P83 A pilot study to assess peak systolic velocity as a possible marker of atherosclerotic burden using ultrasound
Introduction: Ischemic heart disease (IHD) has been associated with lower peak systolic velocity (PSV) on penile Doppler measurements [1]. This study establishes whether carotid ultrasound (US) PSV was associated with computational fluid dynamics (CFD) outputs, which in turn may contribute to IHD pathogenesis. Methods: A sample of 57 subjects (with IHD: 27, without IHD: 30) had US velocity profiles (left- common carotid artery) determined between 10e12 equispaced points. Bezier curve fitting was used to fit the profile through the measured velocity points for a normalised diameter. PSV was correlated against CFD results such as wall shear stress (WSS) [2]. Difference in PSV between individuals with/without IHD was studied via t-test. Linear regression was carried out to see if peak systolic velocity was associated with CFD outputs. Any significant associations were analysed within stratified groups (with/without IHD). Results: PSV was significantly lower (p Z 0.042) in subjects with IHD (with IHD: 53.6 17.3 cm/s, without IHD: 62.8 16.1 cm/s). PSV was associated with carotid bulb average pressure drop (p < 0.001), area of average bulb WSS (<1 Pa: p Z 0.016, <2 Pa: p Z 0.006, <3 Pa: p Z 0.001). All the above associations remained significant in individuals with IHD (average bulb pressure drop: p Z 0.001, average bulb WSS (<1 Pa: p Z 0.013, <2 Pa: p Z 0.008, <3 Pa: p Z 0.003). In subjects without IHD, PSV was associated with only average bulb pressure drop (p Z 0.016). Conclusions: This study suggests that further work on PSV and its associations with CFD outputs is required in individuals with and without IHD in various vascular beds
Chromodynamic multirelaxation-time lattice Boltzmann scheme for fluids with density difference
We develop, after Dellar ( P. J. Dellar, Phys. Rev. E. 65, 036309 (2002), J. Comput. Phys.
190, pp351 (2003)), a multiple-relaxation time (MRT), chromodynamic, multi-component lattice
Boltzmann equation (MCLBE) scheme for simulation of isothermal, immiscible fluid flow with a
density contrast. It is based on Lishchukâs method (J. U. Brackbill, D. B. Kothe and C. Zemach, J.
Comp. Phys. 100, 335-354 (1992), S. V. Lishchuk, C. M. Care and I. Halliday, Phys. Rev. E. 67(3),
036701(2), (2003)) and the segregation of dâOrtona et al. (U. DâOrtona, D. Salin, M. Cieplak, R.
B. Rybka and J. R. Banavar Phys. Rev. E. 51, 3718, (1995)). We focus on fundamental model
verifiability but do relate some of our data to that from previous approaches, due to Ba et al. (Y.
Ba, H. Liu, Q. Li, Q. Kang and J. Sun, Phys. Rev. E 94, 023310 (2016)) and earlier Liu et al. (H.
Liu, A. J. Valocchi and Q. Kang, Phys. Rev. E 85, 046309 (2012)), who pioneered large density
difference chromodynamic MCLBE and showed the practical benefits of a MRT collision model.
Specifically, we test the extent to which chromodynamic MCLBE MRT schemes comply with the
kinematic condition of mutual impenetrability and the continuous traction condition by developing
analytical benchmarking flows. We conclude that our data, taken with those of Ba et al., verify the
utility of MRT chromodynamic MCLBE
Three-dimensional single framework multi-component lattice Boltzmann equation method for vesicle hydrodynamics
We develop a three dimensional immersed boundary chromodynamic multi-component lattice Boltzmann method capable of simulating vesicles, such as erythrocytes. The presented method is encapsulated in a single framework, where
the application of the immersed boundary force in the automatically adaptive interfacial region results in correct vesicle
behaviour. We also set-down a methodology for computing the principal curvatures of a surface in a three-dimensional,
physical space which is defined solely in terms of its surface normal vectors. The benefits of such a model are its
transparent methodology, stability at high levels of deformation, automatic-adaptive interface and potential for the simulation of many erythrocytes. We demonstrate the utility of the model by examining the steady state properties, as
well as dynamical behaviour within shear flow. The stability of the method is highlighted through its handling of high
deformations, as well as interaction with another vesicle
Dietary Docosahexaenoic Acid Reduces Oscillatory Wall Shear Stress, Atherosclerosis, and Hypertension, Most Likely Mediated via an ILâ1âMediated Mechanism
Background: Hypertension is a complex condition and a common cardiovascular risk factor. Dietary docosahexaenoic acid (DHA) modulates atherosclerosis and hypertension, possibly via an inflammatory mechanism. ILâ1 (interleukin 1) has an established role in atherosclerosis and inflammation, although whether ILâ1 inhibition modulates blood pressure is unclear.
Methods and Results: Male apoEâ/â (apolipoprotein Eânull) mice were fed either a high fat diet or a high fat diet plus DHA (300 mg/kg per day) for 12 weeks. Blood pressure and cardiac function were assessed, and effects of DHA on wall shear stress and atherosclerosis were determined. DHA supplementation improved left ventricular function, reduced wall shear stress and oscillatory shear at ostia in the descending aorta, and significantly lowered blood pressure compared with controls (119.5±7 versus 159.7±3 mm Hg, P<0.001, n=4 per group). Analysis of atheroma following DHA feeding in mice demonstrated a 4âfold reduction in lesion burden in distal aortas and in brachiocephalic arteries (P<0.001, n=12 per group). In addition, DHA treatment selectively decreased plaque endothelial ILâ1ÎČ (P<0.01).
Conclusions: Our findings revealed that raised blood pressure can be reduced by inhibiting ILâ1 indirectly by administration of DHA in the diet through a mechanism that involves a reduction in wall shear stress and local expression of the proinflammatory cytokine ILâ1ÎČ
Assessment of surface roughness and blood rheology on local coronary hemodynamics: a multi-scale computational fluid dynamics study
The surface roughness of the coronary artery is associated with the onset of atherosclerosis. The study applies, for the first time, the micro-scale variation of the artery surface to a 3D coronary model, investigating the impact on haemodynamic parameters which are indicators for atherosclerosis. The surface roughness of porcine coronary arteries have been detailed based on optical microscopy and implemented into a cylindrical section of coronary artery. Several approaches to rheology are compared to determine the benefits/limitations of both single and multiphase models for multi-scale geometry. Haemodynamic parameters averaged over the rough/smooth sections are similar; however, the rough surface experiences a much wider range, with maximum wall shear stress greater than 6 Pa compared to the approximately 3 Pa on the smooth segment. This suggests the smooth-walled assumption may neglect important near-wall haemodynamics. While rheological models lack sufficient definition to truly encompass the micro-scale effects occurring over the rough surface, single-phase models (Newtonian and non-Newtonian) provide numerically stable and comparable results to other coronary simulations. Multiphase models allow for phase interactions between plasma and red blood cells which is more suited to such multi-scale models. These models require additional physical laws to govern advection/aggregation of particulates in the near-wall region