Papers by Mhamad Mahdi Alloush
Cardiovascular Engineering and Technology, Nov 28, 2018
Purpose-Peristaltic pumps (PP) are favored in flow bioreactors for their non-contact sterile desi... more Purpose-Peristaltic pumps (PP) are favored in flow bioreactors for their non-contact sterile design. But they produce pulsatile flow, which is consequential for the cultured cells. A novel pulse damper (PD) is reported for pulsatility elimination. Methods-The PD design was implemented to target static pressure pulsatility and flow rate (velocity) pulsatility from a PP. Damping effectiveness was tested in a macro-scale, closed-loop recirculating bioreactor mimicking the aortic arch at flow rates up to (4 L/min). Time-resolved particle image velocimetry was used to characterize the velocity field. Endothelial cells (EC) were grown in the bioreactor, and subjected to continuous flow for 15 min with or without PD. Results-The PD was found to be nearly 90% effective at reducing pulsatility. The EC exposed to low PP flow without PD exhibited distress signaling in the form of increased ERK1/2 phosphorylation (2.5 folds) when compared to those exposed to the same flow with PD. At high pump flow without PD, the cells detached and did not survive, while they were perfectly healthy with PD. Conclusions-Flow pulsatility from PP causes EC distress at low flow and cell detachment at high flow. Elevated temporal shear stress gradient combined with elevated shear stress magnitude at high flow are believed to be the cause of cell detachment and death. The proposed PD design was effective at minimizing the hemodynamic stressors in the pump's output, demonstrably reducing cell distress. Adoption of the proposed PD design in flow bioreactors should improve experimental protocols.
Flow Measurements in a Matched-Index-of-Refraction Aortic Arch Model for Endothelial Cell Culture
Flow details such as wall shear stress, hemodynamic pressure, and separation can play an importan... more Flow details such as wall shear stress, hemodynamic pressure, and separation can play an important role in the development and progression of inflammation and cardiovascular disease, such as atherosclerosis. Clinical evidence correlating blood vessel locations exhibiting atherosclerosis and plaque buildup to flow disturbances and separation is significant. Prevalence of atherosclerosis in cardiovascular patients is noticed in vessels exhibiting geometric features such as bifurcation, arching, and stenosis. The bending vessel geometry is interesting for the wealth and variety of flow physics that it incorporates. An in vitro flow loop system for the study of cardiovascular disease is described. The system incorporates an aortic arch vessel model that permits endothelial cell culturing, sampling, and imaging on the aortic lumen. The model was designed to allow imaging of the internal flow by choice of the clear model material and the optically compatible working fluid. Particle image velocimetry measurements were acquired at different locations on the arch, for time-averaged inlet Reynolds number range of 2000 to 4400. It was found that the peristaltic pump introduced significant pulsatility to the flow particularly at the low rpm. The flow behavior in the arch is discussed with emphasis on separation and recirculation zones.
Numerical Heat Transfer Part B-fundamentals, Jul 9, 2020
The article deals with an implicit formulation of the pressure far field boundary condition, also... more The article deals with an implicit formulation of the pressure far field boundary condition, also known as the characteristic boundary condition, in a pressure-based coupled solver. This boundary condition applies to compressible flows over the entire Mach regime, and is derived by invoking the Riemann invariants to implicitly express the flow variables at inlets and outlets in terms of their values inside the domain. A set of inviscid an turbulent flow cases that include pressure far field boundary conditions are tested, namely: low subsonic compressible flow past a NACA0012 airfoil at 10 angle of attack; transonic flow over circular bump; supersonic flow over a series of slender bumps; and DLR-F6 Wing-Body-Nacelle-Pylon Aircraft. Predictions using the prescribed coupled solver are in good agreement with similar results obtained with density-based methods and/or experimental data.
A Pressure-Based Fully-Coupled Flow Algorithm for the Control Volume Finite Element Method
Applied sciences, May 5, 2022
A coupled VOF solver for the solution of incompressible free surface flows
INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS ICNAAM 2020, 2022
The Development of a Fully Coupled Solver for the Solution of Free Surface Flows
INTERNATIONAL CONFERENCE OF NUMERICAL ANALYSIS AND APPLIED MATHEMATICS ICNAAM 2020
The current work presents necessary geometric modifications to the coarse grids utilized in a ful... more The current work presents necessary geometric modifications to the coarse grids utilized in a full approximation scheme method (FAS). This work path is a preliminary stage to the development of a robust full approximation scheme method which withstand high distortions in the coarse grids of the grid hierarchy. The hierarchies of coarse grids required by the FAS method are commonly constructed using low-quality agglomeration algorithms that deteriorate performance. This work attempts to resolve the problem by altering the agglomeration procedure through a geometric modification to the coarse cells. While the proposed method does not require any complicated or time-consuming agglomeration techniques, its turnout has enhanced the solver stability.
An implicit bounding formulation for the volume fraction equation in multiphase flows
Numerical Heat Transfer, Part B: Fundamentals, 2021
The solution of the volume fraction equations in multiphase flows has to satisfy geometric conser... more The solution of the volume fraction equations in multiphase flows has to satisfy geometric conservation, that is, the volume fraction fields at each control volume sum to 1. Enforcing this constraint on the volume fraction fields is critical for all multiphase flow applications especially for cases involving mass transfer. This article reviews some of the techniques used to enforce geometric conservation when solving the volume fraction equations for general multiphase flows, including free surface flows. An implicit method is then introduced and applied to a number of multiphase and free surface flow problems. It is compared to the current explicit approaches and its effectiveness in enforcing the geometric conservation demonstrated.
2nd Middle East Conference on Biomedical Engineering, 2014
Hemodynamic forces play an important role in maintaining the function and structure of blood vess... more Hemodynamic forces play an important role in maintaining the function and structure of blood vessels. In this work we discuss the design of an in vitro flow loop mimicking the aortic arch that is aimed at studying the response of endothelial cells to geometric curvature and the resulting flow field. The flow system allows for quantitative flow visualization measurements, and for access to the vessel lumen for cell culturing and sampling.
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Papers by Mhamad Mahdi Alloush