10 research outputs found
CFD simulation of the airflow through the human respiratory tract
No full textThis study compares the effect of extra-thoracic airways (ETA) on the flow field through the lower airways by carrying out simulations of the airflow through the human respiratory tract. Three geometries, consisting of the ETA, CT-derived lower airway, and a combination of the two were utilized in simulations that were performed for transient breathing in addition to constant inspiration/expiration. Physiologically-appropriate regional ventilation for two different flow rates was induced at the distal boundaries by imposing appropriate lobar specific flow rates. Two breathing rates were considered, i.e., 7.5 and 15 breaths per minute with a tidal volume of 0.5 liter. For comparison, the flow rates for constant inspiration/expiration were selected to be identical to the peak flow rates during the transient breathing. Significant differences indicate that simulations that utilize constant inspiration or expiration may not be appropriate for gaining insight into the flow patterns through the human airways
Biomechanics of Breastfeeding: Fluid-Structure Interaction Simulation of Milk Expression
No full textBreastfeeding is a highly dynamic and complex mechanism. There are two theories for the
dynamics of milk expression by the infant. One hypothesis is that milk expression is due
to negative pressure applied by infant sucking; the alternative hypothesis is that the tongue
movement and squeezing of nipple/areola due to mouthing is responsible for the extraction
of milk from the nipple. In this study, a 3-D Fluid-Structure Interaction (FSI) simulation
is conducted to investigate the factors that play the primary role in milk expression from
the nipple. The models include solid deformation and periodic motion of the tongue and
jaw movement. To obtain boundary conditions, ultrasound images of the oral cavity, and
motion of tongue movement during breastfeeding are extracted in parallel to the intra-oral
vacuum pressure. The numerical results are cross-validated with clinical data. The results
show that, while vacuum pressure plays an important role in the volume of milk removal,
the tongue/jaw movement is essential for facilitating this procedure by decreasing the shear
stress within the main duct. The developed model can contribute to a better understanding
of breastfeeding complications that are due to physical infant and/or breast abnormalities
and for the design of medical devices such as artificial teats and breast pumps.
The second part of this study focuses on investigation of the non-Newtonian behavior of the
milk during breastfeeding. The accumulated milk from the nipple varies depending on the
milk properties and transient flow rate during the suckling cycle. The rheological studies
on raw human milk have indicated non-Newtonian shear-thinning flow behavior. There
exists no prior numerical simulation in the area of breastfeeding to study the non-Newtonian
flow behavior inside the milk ducts. The novelty of this study is to investigate the nonNewtonian milk flow through the breast ductal system using fluid-structure interaction (FSI)
simulation. The geometry of an infant’s mouth and breast is used in the 3-D FSI simulations.
The analyses are performed using Newtonian and non-Newtonian models to quantify the
effects of non-Newtonian behavior of milk through the milk duct. The results of the nonNewtonian effects on the surface of milk duct, velocity profiles, and volume of expressed
milk are presented. The non-Newtonian Carreau model provides a promising model to
simulate human milk flow during suckling. The Newtonian model is also acceptable for the
numerical simulation but choosing an adequate Newtonian viscosity from experimental data
is challenging.
The final part discusses the contact pressure distribution on the surface of the breast and
Von-Mises stress as the result of the infant’s suckling. The values of contact pressure on
the nipple/areola complex from simulation are in good agreement with the observation in
clinical data. The finite element analysis (FEA) is performed to study the areas that are
exposed to tension or compression. The study of stresses on the nipple provides a better
understanding of the potential physical sources of nipple pain after natural breastfeeding.
The physical factors of nipple soreness are discussed by studying mouthing only and suckling
only along with natural suckling
CFD Investigation of Human Tidal Breathing through Human Airway Geometry
No full textAbstractThis study compares the effect of the extra-thoracic airways on the flow through the lower airways by carrying out computational fluid dynamics (CFD) simulations of the airflow through the human respiratory tract. In order to facilitate this comparison, two geometries were utilized. The first was a realistic nine-generation lower airway geometry derived from computed tomography (CT) images, while the second included an additional component, i.e., an idealized extra-thoracic airway (ETA) coupled with the same nine-generation CT model. Another aspect of this study focused on the impact of breathing transience on the flow field. Consequently, simulations were carried out for transient breathing in addition to peak inspiration and expiration. Physiologically-appropriate regional ventilation for two different flow rates was induced at the distal boundaries by imposing appropriate lobar specific flow rates. The scope of these simulations was limited to the modeling of tidal breathing at rest. The typical breathing rates for these cases range from 7.5 to 15 breaths per minute with a tidal volume of 0.5 Liter (L). For comparison, the flow rates for constant inspiration/expiration were selected to be identical to the peak flow rates during the transient breathing. Significant differences were observed from comparing the peak inspiration and expiration with transient breathing in the entire airway geometry. Differences were also observed for the lower airway geometry. These differences point to the fact that simulations that utilize constant inspiration or expiration may not be an appropriate approach to gain better insight into the flow patterns present in the human respiratory system. Consequently, particle trajectories derived from these flow fields might be misleading in their applicability to the human respiratory system
Temporal evolution of mechanical stimuli from vascular remodeling in response to the severity and duration of aortic coarctation in a preclinical model
No full textAbstract Coarctation of the aorta (CoA) is one of the most common congenital cardiovascular diseases. CoA patients frequently undergo surgical repair, but hypertension (HTN) is still common. The current treatment guideline has revealed irreversible changes in structure and function, yet revised severity guidelines have not been proposed. Our objective was to quantify temporal alterations in mechanical stimuli and changes in arterial geometry in response to the range of CoA severities and durations (i.e. age of treatment) seen clinically. Rabbits were exposed to CoA resulting in peak-to-peak blood pressure gradient (BPGpp) severities of ≤ 10, 10–20, and ≥ 20 mmHg for a duration of ~ 1, 3, or 20 weeks using permanent, dissolvable, and rapidly dissolvable sutures. Elastic moduli and thickness were estimated from imaging and longitudinal fluid–structure interaction (FSI) simulations were conducted at different ages using geometries and boundary conditions from experimentally measured data. Mechanical stimuli were characterized including blood flow velocity patterns, wall tension, and radial strain. Experimental results show vascular alternations including thickening and stiffening proximal to the coarctation with increasing severity and/or duration of CoA. FSI simulations indicate wall tension in the proximal region increases markedly with coarctation severity. Importantly, even mild CoA induced stimuli for remodeling that exceeds values seen in adulthood if not treated early and using a BPGpp lower than the current clinical threshold. The findings are aligned with observations from other species and provide some guidance for the values of mechanical stimuli that could be used to predict the likelihood of HTN in human patients with CoA
The philosophy of the Mazdayasnian religion under the Sassanids : translated from the French with prefatory remarks, notes, and a brief biographical sketch of the author /
No full textMode of access: Internet
Laser powder-bed fusion of a high entropy alloy with outstanding intrinsic mechanical properties
No full textIn the past few years, laser powder-bed fusion (LPBF) of high entropy alloys (HEAs) has gained significant interest. We investigated a HEA (PdPtRhIrCuNi) elaborated by LPBF, and studied its microstructure and mechanical properties. This alloy has potential applications in luxury industries, as well as in medical technologies. The microstructure consists of two coherent FCC phases behaving as a single-phase structure, with strong segregation of different elements in the dendritic and inter-dendritic regions. It is much finer than that inherited from arc-melting, as reported in the literature, because of the much higher cooling rate of the LPBF process. Two cracking mechanisms were identified: solidification and liquation, and in both of them, the cracks propagate through grain boundaries and inter-dendritic regions. Despite the presence of micro-cracking, the mechanical properties in compression, bending, and wear resistance are outstanding. A new hybrid technique, called 3D laser shock peening (3D LSP), was effective in reducing crack density. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).LMT
2019 UT Dallas Spring Poster Competition
No full textA repository of the 2019 UT Dallas Spring Poster Competition Entries
2019 UT Dallas Spring Poster Competition
No full textA repository of the 2019 UT Dallas Spring Poster Competition Entries
