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3D blood vessels reconstruction based on segmented CT data for further simulations of hemodynamic in human artery branches

Polańczyk A., Strzelecki M., Woźniak T., Szubert W., Stefańczyk L.

Foundations of Computing and Decision Sciences

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2017

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Vol. 42, No. 4

359--371

EN

We aimed at the reconstruction of the branches of human aortic arch for blood perfusion analysis used later in the Computational Fluid Dynamic (CFD). The reconstruction was performed based on segmentation results obtained from CT data. Two segmentation algorithms, region growing and level set were implemented. Obtained binary segmentation results were next evaluated by the expert and corrected if needed. The final reconstruction was used for preparation of a numerical grid and for further calculation of blood hemodynamic. The collected data composed of blood velocity and blood flow rate in function of time were compared with USG-Doppler data. Results demonstrate that proposed algorithm may be useful for initial reconstruction of human cardiac system, however its accuracy needs to be improved as further manual corrections are still needed.

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Przegląd hybrydowych modeli pożaru

Gałaj J., Oleksy M.

Bezpieczeństwo i Technika Pożarnicza

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2013

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Nr 4

79--92

PL

Cel: Celem niniejszego artykułu jest omówienie oraz ocena hybrydowych modeli pożaru, które zostały opracowane na świecie w ostatnich kilkudziesięciu latach. Wprowadzenie: Modelowanie pożarów przy użyciu komputera miało swój początek w latach 80-tych. Od tej pory aż do dzisiaj powstało kilkaset różnych modeli, poczynając od najprostszych integralnych poprzez strefowe do najbardziej złożonych polowych wykorzystujących technikę CFD (Computational Fluid Dynamics). Ze względu na bardzo długi czas obliczeń, jaki jest wymagany w przypadku modeli polowych (przy prostszych obiektach jest to średnio kilkadziesiąt godzin dla jednego scenariusza, przy bardziej złożonych nawet kilkaset), w końcu lat 90-tych zaczęto opracowywać koncepcję modeli, których dokładność byłaby znacznie większa niż modeli strefowych, natomiast czas obliczeń byłby istotnie krótszy. Takim przykładem mogą być hybrydowe modele pożaru. Metodologia: Artykuł zawiera podstawowe informacje na temat aktualnie dostępnych na świecie modeli hybrydowych. Omówiono w nim: model komórkowy Chowa wykorzystujący rozpowszechniony model strefowy CFAST, modele FASIT i FAS3D, które uwzględniają dodatkową warstwę mieszania, model wielowarstwowy Suzuki, w którym zastosowano podział pomieszczenia na n poziomych warstw o tej samej wysokości, model mieszany Hua wykorzystujący kombinację modeli strefowych i polowych. Biorąc pod uwagę ogólne wymagania, jakie powinny spełniać modele pożarów, w pracy zamieszczono ocenę poszczególnych modeli hybrydowych, a także próbę ich porównania ze sobą. Na końcu zamieszczono podsumowanie rozważań i kilka ogólnych wniosków z nich wynikających. Wnioski: Na podstawie przeprowadzonej oceny można stwierdzić, że obecnie istniejące modele hybrydowe nie są w stanie w pełni zastąpić modeli polowych opartych na technice CFD. Aby było to możliwe, należy jeszcze włożyć wiele pracy w ich rozwój, a w szczególności uwzględnić m.in. następujące zagadnienia: zmianę parametrów pożaru w każdej komórce, uniwersalny model gaszenia przy pomocy tryskaczy, dysz mgłowych lub prądownic, wpływ pożaru na konstrukcję budynku, możliwość wpływania użytkownika na dokładność otrzymanych wyników, a tym samym czas obliczeń, określenie bieżącego zapotrzebowania na tlen i wpływu jego stężenia na proces spalania oraz zastosowanie odpowiedniego modelu turbulencji.

EN

Purpose: The main purpose of this article is to describe and evaluate of hybrid fire models which have been developed all over the world in the last several decades. Introduction: Computer modeling of fires was introduced in the early eighties. Several hundred fire models have been created till now from the simplest integral to the most complex field one, using CFD (Computational Fluid Dynamics) technique. Field models require very long time for single simulation (the simpler objects need often about several dozen hours for simple scenario and even hundred hours for more complex scenarios). That was the main reason for appearance of a new idea in modeling of fires. Several hybrid models have been carried out in the end of nineties and in the beginning of this century. Its accuracy was comparable with field models, but time needed for single fire scenario was significantly shorter. Methodology: This article contains basic information on hybrid models and includes their evaluation. One of the first models was a result of work made by Charters and McIntosh on Leeds University (England), which effected in FASIT program created for studying of fires in tunnels and FAS 3D being a three-dimensional version of the first one (fires in compartments). CFD modeling elements were used in this program and each gas layer was divided into the grid of control volumes. For the first time, the mixing zone was separated into upper and lower zone. Obtained model has both main features of the field and zone models, what enables to simulate the gas fire environment in compartments more precisely than with the typical zone model without the need of performing long and expensive calculations. In turn, Chow proposed a method of using the existing CFAST tool for larger compartments. He divided the analyzed volume into several smaller cells (he examined cases with 3, 9 and 15 cells), and then, for each one of them he used the same approach as for single compartment. In 2002, Suzuki et al. proposed a modified multilayer model. He divided single compartments into horizontal layers with equal heights and determined the same parameters for each one of them using the equations following from mass and energy conservation laws. Another approach to the hybrid model was proposed by Hua et al. They used a combination of field and zone models to simulate and analyze the fire smoke propagation in multistorey building. It was assumed that in compartments with more complex fire dynamics, that is, i.e. with a fire source, the calculation mechanism would be consistent with the field model, while in compartments where the hot and cold zones are determined more clearly (i.e. corridors, compartments located farther from the fire source), the zone model should be used. Conclusions: Article presents several characteristics which show time curves of under-ceiling layer thickness achieved for the proposed model and for the typical zone and field models. Last of the mentioned solutions seems to be very interesting, but even in compartments with simpler fire dynamics where the zone model was used, unpredictable processes can occur (i.e. unsteady flows, local whirls). They can result in considerable spatial differences of calculated parameters, such as: temperatures, pressures, gas concentrations, etc. Based on the evaluation and comparison of discussed hybrid models one can claim, that neither of them doesn’t meet all requirements. There is still a lot of work that should be done on these models to improve them by consideration of the following aspects: changes of fire parameters in every cell, turbulence model, application of universal model of extinguishing systems including sprinklers, mist heads and nozzles, affecting of fire on building construction, possibility for user to influence on the calculation accuracy, determining of actual oxygen consumption and influence of different factors on combustion and pyrolysis process.

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Radiation heat transfer modelling and CFD analysis of pulverised-coal combustion with staged air introduction

Filkoski R.

Archives of Thermodynamics

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2009

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Vol. 30, no. 4

97-118

EN

Modelling of fossil fuel utility and industrial boilers has reached a remarkable development in recent years. Particular attention in optimisation of a utility boiler furnace operation, is given to the flame geometry and position. Combustion chamber designers endeavour to achieve optimum operating conditions that give maximum combustion efficiency, as well as minimum pollutant formation rate. The application of computational fluid dynamics (CFD) modelling technique and other advanced mathematical methods offer opportunities for analysis, optimisation and options examination in order to increase the overall efficiency of the energy facilities. The main purpose of the present study was to investigate how the results obtained with two radiative heat transfer methods, the PI approximation method and the discrete ordinates (DO) method, fit temperature field in a boiler furnace on pulverised coal, with implemented over-fire air (OFA) ports. The framework of the CFD modelling approach is described. The numerical modelling results for boiler baseline operating conditions are com-pared with a test matrix of local temperature measurements. An accuracy analysis of the PI and DO methods is done on a basis of a comparison between the numerically obtained and measured temperature profiles.

4

Simulation of dynamic changes of liquid-liquid interface using the CFD technique

Staszak M., Alejski K.

Chemical and Process Engineering

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2007

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Vol. 28, z. 4

1113-1123

EN

The simulation of the forming water drop pushed from the capillary into organic phase (octane) was performed using the CFD technique. The results of the simulation were compared with experimental data: drop geometry at the characteristic stages, forming time and obtained volume. Very good agreement with experimental data was affirmed.

PL

Za pomocą techniki CFD przeprowadzono symulację formowania się kropli wody wypychanej z kapilary do rozpuszczalnika organicznego - oktanu. Wyniki symulacji porównano z danymi eksperymentalnymi: geometrią kropli w charakterystycznych etapach jej formowania, czasem tworzenia oraz uzyskaną objętością. Stwierdzono bardzo dobrą zgodność z wynikami badań eksperymentalnych.