No abstract

A fundamental study has been conducted to understand the front characteristics and the mixing in the flow of density currents over rough surfaces. A large-eddy simulation (LES) has been performed for lock-exchange release density currents over rough walls to shed light on the unsteady mixing processes. A volume-penalization method, which is a special case of the immersed-boundary method, has been implemented to realize the bottom-mounted rough topology. In this study, the LES has been conducted in a channel with a lower wall covered with three-dimensional cube- and pyramid-shaped roughness elements, such that all cases have the same base area, but differences in the roughness solidity and volume fraction of roughness. Both cases of identical roughness elements and those with randomness in height have been considered. The maximum roughness height for all cases is kept at a constant fraction (10 %) of the total channel height. The study focuses on the instantaneous mixing processes in lock-exchange release currents over rough surfaces. An important contribution of the work is that qualitative and quantitative analysis has been conducted to demonstrate additional mixing mechanisms due to the presence of surface roughness that enhances dilution of the current. Enhanced mixing due to roughness is related to the strength of the shear layer resulting from the roughness, and hence depends on friction Reynolds number ($Re_{\unicode[STIX]{x1D70F}}$). The combined role of current characteristics and $Re_{\unicode[STIX]{x1D70F}}$ together dictate the mixing processes and extent of dilution in density currents over surface roughness.

The objective of this study was to quantify pentagalloyl glucose (PGG) mediated biomechanical restoration of degenerated extracellular matrix (ECM). Planar biaxial tensile testing was performed for native (N), enzyme-treated (collagenase and elastase) (E), and PGG (P) treated porcine abdominal aorta specimens (n = 6 per group). An Ogden material model was fitted to the stress–strain data and finite element computational analyses of simulated native aorta and aneurysmal abdominal aorta were performed. The maximum tensile stress of the N group was higher than that in both E and P groups for both circumferential (43.78 ± 14.18 kPa vs. 10.03 ± 2.68 kPa vs. 13.85 ± 3.02 kPa; p = 0.0226) and longitudinal directions (33.89 ± 8.98 kPa vs. 9.04 ± 2.68 kPa vs. 14.69 ± 5.88 kPa; p = 0.0441). Tensile moduli in the circumferential direction was found to be in descending order as N > P > E (195.6 ± 58.72 kPa > 81.8 ± 22.76 kPa > 46.51 ± 15.04 kPa; p = 0.0314), whereas no significant differences were found in the longitudinal direction (p = 0.1607). PGG binds to the hydrophobic core of arterial tissues and the crosslinking of ECM fibers is one of the possible explanations for the recovery of biomechanical properties observed in this study. PGG is a beneficial polyphenol that can be potentially translated to clinical practice for preventing rupture of the aneurysmal arterial wall.

Pulmonary hypertension (PH) is a progressive disease characterized by elevated pressure and vascular resistance in the pulmonary arteries. Nearly 250,000 hospitalizations occur annually in the US with PH as the primary or secondary condition. A definitive diagnosis of PH requires right heart catheterization (RHC) in addition to a chest computed tomography, a walking test, and others. While RHC is the gold standard for diagnosing PH, it is invasive and posseses inherent risks and contraindications. In this work, we characterized the patient-specific pulmonary hemodynamics in silico for diverse PH WHO groups. We grouped patients on the basis of mean pulmonary arterial pressure (mPAP) into three disease severity groups: at-risk (18mmHg mPAP<25mmHg, denoted with A), mild (25mmHg mPAP<40mmHg, denoted with M), and severe (mPAP ! 40mmHg, denoted with S). The pulsatile flow hemodynamics was simulated by evaluating the three-dimensional Navier-Stokes system of equations using a flow solver developed by customizing OpenFOAM libraries (v5.0, The OpenFOAM Foundation). Quasi patient-specific boundary conditions were implemented using a Womersley inlet velocity profile and transient resistance outflow conditions. Hemodynamic indices such as spatially averaged wall shear stress (SAWSS), wall shear stress gradient (WSSG), timeaveraged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT), were evaluated along with the clinical metrics pulmonary vascular resistance (PVR), stroke volume (SV) and compliance (C), to assess possible spatiotemporal correlations. We observed statistically significant decreases in SAWSS, WSSG, and TAWSS, and increases in OSI and RRT with disease severity. PVR was moderately correlated with SAWSS and RRT at the mid-notch stage of the cardiac cycle when these indices were computed using the global pulmonary arterial geometry. These results are promising in the context of a long-term goal of identifying computational biomarkers that can serve as surrogates for invasive diagnostic protocols of PH.

This work reports a set of numerical experiments to understand flow-induced vibrations of the square columns kept in a tandem arrangement. Results on the coupled force and response dynamics are presented for an isolated column and for a pair of square columns in the tandem configuration where downstream column is elastically mounted and free to oscillate in in-line and transverse directions. We assess the combined wake-induced and sharp-corner based galloping effects on the downstream column by comparing with the isolated square column counterpart. It is known that the circular cylinders undergo vortex-induced motion alone whereas motion of a square column is vortex-induced at low Re and galloping at high Re. The simulations are performed by means of a Petrov-Galerkin based finite-element solver using Arbitrary Lagrangian-Eulerian technique to account for the fluid mesh motion. The predicted results of the isolated column agree well with the available numerical results in the literature. The dimensions of the square columns and the domain are set in order to a have total blockage area of 5 %. The effects of reduced velocity on the fluid forces, wake contours, and the phase angles are analyzed. This work is also an attempt to enhance our understanding on the origin of wake-induced vibrations in a tandem arrangement of bluff bodies. In the case of tandem arrangement, upstream vortex shifts the stagnation point on the downstream column to the lower suction region. Thus a larger lift force is observed for the downstream column as compared to a vibrating isolated column. Phase difference between the transverse load and velocity of the downstream column determines the extent of upstream wake interaction with downstream column. When the column velocity is in-phase with the transverse pressure load component, interaction of wake vortex with the downstream column is minimum. For higher reduced velocities (Ur > 15), the wake downstream is very wide and irregular and the phase angle is consistently close to 180°.