Computational fluid dynamics
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Úvod: Charakter nosního proudění je zásadní pro bezproblémové nosní dýchání, stejně jako může být patofyziologickým podkladem symptomů nosních onemocnění (nosní neprůchodnost, sekrece, tvorba krust aj.). Je obtížné definovat jeden fyziologický charakter proudění, protože subjektivní potíže nemocných často nejsou v korelaci s objektivním nálezem. Pozornost je proto věnována studiu nosní aerodynamiky, pro které je v současnosti nejvíce využíváno počítačové modelování proudění, tzv. computational fluid dynamics (CFD). Metodika: Pro simulaci nosního proudění byl ve spolupráci s Vysokou školou báňskou (VŠB) vytvořen 3D model dle CT vyšetření nosní dutiny pacientky, která neměla potíže s nosním dýcháním ("fyziologická" nosní dutina). Výsledky: Dle získaných výsledků se liší proudění vzduchu v pravé a levé nosní dutině. Hlavní proud vzduchu lze pozorovat jak v dolním a dolní části společného průduchu, tak i ve středním a střední části společného průduchu. První výsledky se shodují se studiemi uvádějícími značné rozdíly v nosní aerodynamice mezi zdravými jedinci. Závěr: Počítačové modelování proudění vzduchu má potenciál být využíváno v klinické praxi, především ve funkční rinochirurgii.
Introduction: The pattern of the nasal airflow is crucial for normal nasal breathing as well as it can be a pathophysiological underlay of nasal symptoms (nasal obstruction, crusting etc). It is difficult to define one physiological airflow pattern because subjective symptoms of patients do not correlate with objective findings quite often. Nowadays, the computational fluid dynamics (CFD) is dominant way how to simulate and study nasal airflow. Methods: For nasal airflow simulation 3D model of nasal cavity was created according to CT scans of nasal cavity (patient had no problems with nasal breathing). The 3D model was created with the cooperation with Technical University of Ostrava. Results: Our first experience with CFD showed that there is a different airflow pattern between right and left nasal cavity. Major part of airflow was detected in inferior and inferior part of common meatus and also in the middle and in the middle part of common nasal meatus. These results support studies that declare differences in nasal aerodynamics among healthy adults. Conclusion: CFD has a potential to be used in clinical practice especially in functional rhinosurgery.
- Klíčová slova
- nosní proudění,
- MeSH
- konvekce MeSH
- lidé MeSH
- nos * fyziologie MeSH
- počítačová simulace * MeSH
- zobrazování trojrozměrné MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- práce podpořená grantem MeSH
A microfluidic cell capture device was designed, fabricated, evaluated by numerical simulations and validated experimentally. The cell capture device was designed with a minimal footprint compartment comprising internal micropillars with the goal to obtain a compact, integrated bioanalytical system. The design of the device was accomplished by computational fluid dynamics (CFD) simulations. Various microdevice designs were rapidly prototyped in poly-dimethylsiloxane using conventional soft lithograpy technique applying micropatterned SU-8 epoxy based negative photoresist as moulding replica. The numerically modeled flow characteristics of the cell capture device were experimentally validated by tracing and microscopic recording the flow trajectories using yeast cells. Finally, we give some perspectives on how CFD modeling can be used in the early stage of microfluidics-based cell capture device development.
BJR. Supplement, ISSN 0007-1285 Vol. 82, special issue 1, 2009
71 s. : il., tab. ; 30 cm
- MeSH
- aneurysma MeSH
- hemodynamika MeSH
- koronární cévy MeSH
- přesuny tekutin MeSH
- tekutiny a sekrety tělesné MeSH
- Publikační typ
- sborníky MeSH
V posledních letech se rozvinula metodika počítačového modelování toku tekutin v cerebrovaskulární problematice, především pak v oblasti intrakraniálních aneuryzmat. Cílem většiny studií je pochopit patofyziologii vzniku, růstu a ruptury mozkových výdutí a určit ty rizikové hemodynamické parametry, které k těmto procesům vedou. V naší práci shrnujeme současný stav počítačového modelování toku tekutin především z pohledu chirurgie mozkových aneuryzmat a zaměřujeme se na možný přínos pro klinickou praxi.
Computational fluid dynamics have developed in the area of cerebrovascular diseases in recent years, especially in the research of intracranial aneurysms. The goal of most studies is to understand the pathophysiology of the initiation, growth and rupture of brain aneurysms and determine those risk hemodynamic parameters that lead to such processes. In our paper, we summarize the current state of art computational fluid dynamics especially from a surgical point of view of intracranial aneurysms and we focus on its possible contribution in clinical practice.
BACKGROUND: Photosynthetic microalgae have been in the spotlight of biotechnological production (biofuels, lipids, etc), however, current barriers in mass cultivation of microalgae are limiting its successful industrialization. Therefore, a mathematical model integrating both the biological and hydrodynamical parts of the cultivation process may improve our understanding of relevant phenomena, leading to further optimization of the microalgae cultivation. RESULTS: We introduce a unified multidisciplinary simulation tool for microalgae culture systems, particularly the photobioreactors. Our approach describes changes of cell growth determined by dynamics of heterogeneous environmental conditions such as irradiation and mixing of the culture. Presented framework consists of (i) a simplified model of microalgae growth in a culture system (the advection-diffusion-reaction system within a phenomenological model of photosynthesis and photoinhibition), (ii) the fluid dynamics (Navier-Stokes equations), and (iii) the irradiance field description (Beer-Lambert law). To validate the method, a simple case study leading to hydrodynamically induced fluctuating light conditions was chosen. The integration of computational fluid dynamics (ANSYS Fluent) revealed the inner property of the system, the flashing light enhancement phenomenon, known from experiments. CONCLUSION: Our physically accurate model of microalgae culture naturally exhibits features of real system, can be applied to any geometry of microalgae mass cultivation and thus is suitable for biotechnological applications.
Needle-shaped crystals are a common occurrence in many pharmaceutical and fine chemicals processes. Even if the particle size distribution (PSD) obtained in a crystallization step can be controlled by the crystal growth kinetics and hydrodynamic conditions, further fluid-solid separation steps such as filtration, filter washing, drying, and subsequent solids handling can often lead to uncontrolled changes in the PSD due to breakage. In this contribution we present a combined computational and experimental methodology for determining the breakage kernel and the daughter distribution functions of needle-shaped crystals, and for population balance modeling of their breakage. A discrete element model (DEM) of needle-shaped particle breakage was first used in order to find out the appropriate types of the breakage kernel and the daughter distribution functions. A population balance model of breakage was then formulated and used in conjunction with experimental data in order to determine the material-specific parameters appearing in the breakage functions. Quantitative agreement between simulation and experiment has been obtained.
- MeSH
- arteria cerebri anterior diagnostické zobrazování patofyziologie MeSH
- edém mozku diagnostické zobrazování MeSH
- fatální výsledek MeSH
- Glasgowská stupnice kómat MeSH
- intrakraniální aneurysma diagnostické zobrazování patofyziologie MeSH
- lidé středního věku MeSH
- lidé MeSH
- mozková angiografie MeSH
- mozkový krevní oběh MeSH
- počítačová rentgenová tomografie MeSH
- počítačová simulace MeSH
- prasklé aneurysma diagnostické zobrazování patofyziologie MeSH
- subarachnoidální krvácení diagnostické zobrazování patofyziologie chirurgie MeSH
- Check Tag
- lidé středního věku MeSH
- lidé MeSH
- ženské pohlaví MeSH
- Publikační typ
- časopisecké články MeSH
- kazuistiky MeSH
CONTEXT: The increase in the detection of unruptured cerebral aneurysms has led to management dilemma. Prediction of risk based on the size of the aneurysm is not always accurate. There is no objective way of predicting rupture of aneurysm so far. Computational fluid dynamics (CFDs) was proposed as a tool to identify the rupture risk. AIMS: To know the correlation of CFD findings with intraoperative microscopic findings and to know the relevance of CFD in the prediction of rupture risk and in the management of unruptured intracranial aneurysms. SETTINGS AND DESIGN: A prospective study involving nine cases over a period of 6 months as an initial analysis. SUBJECTS AND METHODS: Both males and females were included in the study. Preoperative analysis was performed using computed tomography angiogram, magnetic resonance imaging in all cases and digital substraction angiogram in some cases. Intraoperatively microscopic examination of the aneurysm wall was carried out and images recorded. The correlation was done between microscopic and CFD images. RESULTS: Seven cases were found intraoperatively to have a higher risk of rupture based on the thinning of the wall. Two cases had an atherosclerotic wall. All cases had low wall shear stress (WSS).Only two cases with atherosclerotic wall had a correlation with low WSS. CONCLUSIONS: While the pressure measured with CFD technique is a good predictor of rupture risk, the WSS component is controversial. Multicentric trials involving a larger subset of population are needed before drawing any definite conclusions. On-going development in the CFD analysis may help to predict the rupture chances accurately in future.
- Publikační typ
- časopisecké články MeSH
Passage of nasal airflow during breathing is crucial in achieving accurate diagnosis and optimal therapy for patients with nasal disorders. Computational fluid dynamics (CFD) is the dominant method for simulating and studying airflow. The present study aimed to create a CFD nasal airflow model to determine the major routes of airflow through the nasal cavity and thus help with individualization of surgical treatment of nasal disorders. The three-dimensional nasal cavity model was based on computed tomography scans of the nasal cavity of an adult patient without nasal breathing problems. The model showed the main routes of airflow in the inferior meatus and inferior part of the common meatus, but also surprisingly in the middle meatus and in the middle part of the common nasal meatus. It indicates that the lower meatus and the lower part of the common meatus should not be the only consideration in case of surgery for nasal obstruction in our patient. CFD surgical planning could enable individualized precise surgical treatment of nasal disorders. It could be beneficial mainly in challenging cases such as patients with persistent nasal obstruction after surgery, patients with empty nose syndrome, and patients with a significant discrepancy between the clinical findings and subjective complaints.
- Publikační typ
- časopisecké články MeSH
We consider the properties of free pyrene probes inside gel- and fluidlike phospholipid membranes and unravel their influence on membrane properties. For this purpose, we employ atomic-scale molecular dynamics simulations at several temperatures for varying pyrene concentrations. Molecular dynamics simulations show that free pyrene molecules prefer to be located in the hydrophobic acyl chain region close to the glycerol group of lipid molecules. Their orientation is shown to depend on the phase of the membrane. In the fluid phase, pyrenes favor orientations where they are standing upright in parallel to the membrane normal, while, in the gel phase, the orientation is affected by the tilt of lipid acyl chains. Pyrenes are found to locally perturb membrane structure, while the nature of perturbations in the gel and fluid phases is completely different. In the gel phase, pyrenes break the local packing of lipids and decrease the ordering of lipid acyl chains around them, while, in the fluid phase, pyrenes increase the ordering of nearby acyl chains, thus having an opposite effect. Interestingly, this proposes a similarity to effects induced by cholesterol on structural membrane properties above and below the gel-fluid transition temperature. Further studies express a view that the orientational ordering of pyrene is not a particularly good measure of the acyl chain ordering of lipids. While pyrene ordering provides the correct qualitative behavior of acyl chain ordering in the fluid phase, its capability to predict the correct temperature dependence is limited.
