Decision support system for cardiovascular problems

The DISHEART project aims at developing a new computer based decision support system (DSS) integrating medical image data, modelling, simulation, computational Grid technologies and artificial intelligence methods for assisting clinical diagnosis and intervention in cardiovascular problems. The RTD goal is to improve and link existing state of the art technologies in order to build a computerised cardiovascular model for the analysis of the heart and blood vessels. The resulting DISHEART DSS interfaces computational biomechanical analysis tools with the information coming from multimodal medical images. The computational model is coupled to an artificial neural network (ANN) based decision model that can be educated for each particular patient with data coming from his/her images and/or analyses. The DISHEART DSS system is validated in trials of clinical diagnosis, surgical intervention and subject-specific design of medical devices in the cardiovascular domain. The DISHEART DSS also contributes to a better understanding of cardiovascular morphology and function as inferred from routine imaging examinations. Four reputable medical centers in Europe took an active role in the validation and dissemination of the DISHEART DSS as well as the elaboration of computational material and medical images. The integrated DISHEART DSS supports health professionals in taking promptly the best possible decision for prevention, diagnosis and treatment. Emphasis was put in the development of userfriendly, fast and reliable tools and interfaces providing access to heterogeneous health information sources, as well as on new methods for decision support and risk analysis. The use of Grid computing technology is essential in order to optimise and distribute the heavy computational work required for physical modelling and numerical simulations and especially for the parametric analysis required for educating the DSS for every particular application. The four end user SMEs participating in the project benefits from the new DISHEART DSS. The companies COMPASS, QUANTECH and Heartcore will market the DSS among public and private organizations related to the cardiovascular field. EndoArt will exploit the DISHEART DSS as a support for enhanced design and production of clinical devices. The partnership was sought in order to gather the maximum complementary of skills for the successful development of the project Disheart DSS, requiring experts in Mechanical sciences, Medical sciences, Informatic, and FEM technique to grow up the testes.Postprint (published version

Atmosphere Re-Entry Simulation Using Direct Simulation Monte Carlo (DSMC) Method

Aerothermodynamic investigations of hypersonic re-entry vehicles provides crucial information to other key disciplines as structures and materials, assisting the development of efficient and lightweight thermal protection systems (TPS). Under the transitional flow regime, where chemical and thermal nonequilibrium are predominant, the most innovative numerical method for such studies has been the di- rect simulation Monte Carlo (DSMC) numerical technique. In the 50 years since its invention, the acceptance and applicability of the DSMC method have increased signicantly. Extensive verication and validation eorts have led to its greater acceptance, whereas the increase in computer speed has been the main factor behind its greater applicability. As the performance of a single processor reaches its limit, massively parallel computing is expected to play an even stronger role in its future development. In the present work, the Monte Carlo simulator OpenFOAM and Sparta have been studied and benchmarked against experimental, numerical, and theoretical data for inert and chemically reactive ows. The results show the validity of the the data found with the DSMC. The best setting of the fundamental parameters used by a DSMC simulator are presented for each software and they are compared with the guidelines deriving from the theory behind the Monte Carlo method. In particular the number of particle per cell it is found to be the most relevant parameter to have right and op- timized results. It is shown how a simulation with a mean value of one particle per cell give sufficiently good results with very low computational resources. This achievement wants to be a reason to think back to the correct investigation method in the transitional regime were both the direct simulation Monte Carlo (DSMC) and the computational uid-dynamics (CFD) can work but with dier- 1 ent computational eort. In parallel it has been presented the results deriving from this study in terms of vibration/electron/electronic and translation/rotational temperature, pressure, Mach number, specie number density needed to start a design of a thermal shield

Conjugate heat transfer coupling relying on large eddy simulation with complex geometries in massively parallel environments

Progress in scientific computing has led to major advances in simulation and understanding of the different physical phenomena that exist in industrial gas turbines. However' most of these advances have focused on solving one problem at a time. Indeed' the combustion problem is solved independently from the thermal or radiation problems' etc... In reality all these problems interact: one speaks of coupled problems. Thus performing coupled computations can improve the quality of simulations and provide gas turbines engineers with new design tools. Recently' solutions have been developed to handle multiple physics simultaneously using generic solvers. However' due to their genericity these solutions reveal to be ineffective on expensive problems such as Large Eddy Simulation (LES). Another solution is to perform code coupling: specialized codes are connected together' one for each problem and they exchange data periodically. In this thesis a conjugate heat transfer problem is considered. A fluid domain solved by a combustion LES solver is coupled with a solid domain in which the conduction problem is solved. Implementing this coupled problem raises multiple issues which are addressed in this thesis. Firstly' the specific problem of coupling an LES solver to a conduction solver is considered: the impact of the inter-solver exchange frequency on convergence' possible temporal aliasing' and stability of the coupled system is studied. Then interpolation and geometrical issues are addressed: a conservative interpolation method is developed and compared to other methods. These methods are then applied to an industrial configuration' highlighting the problems and solutions specific to complex geometry. Finally' high performance computing (HPC) is considered: an efficient method to perform data exchange and interpolation between parallel codes is developed. This work has been applied to an aeronautical combustion chamber configuration

Mathematical Modeling and Numerical Simulation of Atherosclerosis Based on a Novel Surgeon’s View

This paper deals with the mathematical modeling of atherosclerosis based on a novel hypothesis proposed by a surgeon, Prof. Dr. Axel Haverich (Circulation 135(3):205–207, 2017). Atherosclerosis is referred as the thickening of the artery walls. Currently, there are two schools of thoughts for explaining the root of such phenomenon: thickening due to substance deposition and thickening as a result of inflammatory overgrowth. The hypothesis favored here is the second paradigm stating that the atherosclerosis is nothing else than the inflammatory response of of the wall tissues as a result of disruption in wall nourishment. It is known that a network of capillaries called vasa vasorum (VV) accounts for the nourishment of the wall in addition to the natural diffusion of nutrient from the blood passing through the lumen. Disruption of nutrient flow to the wall tissues may take place due to the occlusion of vasa vasorums with viruses, bacteria and very fine dust particles such as air pollutants referred to as PM 2.5. They can enter the body through the respiratory system at the first place and then reach the circulatory system. Hence in the new hypothesis, the root of atherosclerotic vessel is perceived as the malfunction of microvessels that nourish the vessel. A large number of clinical observation support this hypothesis. Recently and highly related to this work, and after the COVID-19 pandemic, one of the most prevalent disease in the lungs are attributed to the atherosclerotic pulmonary arteries, see Boyle and Haverich (Eur J Cardio Thorac Surg 58(6):1109–1110, 2020). In this work, a general framework is developed based on a multiphysics mathematical model to capture the wall deformation, nutrient availability and the inflammatory response. For the mechanical response an anisotropic constitutive relation is invoked in order to account for the presence of collagen fibers in the artery wall. A diffusion–reaction equation governs the transport of the nutrient within the wall. The inflammation (overgrowth) is described using a phase-field type equation with a double well potential which captures a sharp interface between two regions of the tissues, namely the healthy and the overgrowing part. The kinematics of the growth is treated by classical multiplicative decomposition of the gradient deformation. The inflammation is represented by means of a phase-field variable. A novel driving mechanism for the phase field is proposed for modeling the progression of the pathology. The model is 3D and fully based on the continuum description of the problem. The numerical implementation is carried out using FEM. Predictions of the model are compared with the clinical observations. The versatility and applicability of the model and the numerical tool allow

Three-dimensional Computational Analysis Of The Flow Around An Oscillating Flat-plate

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2009Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2009Son zamanlarda, kanat-çırpma aerodinamiği büyük bir ilgi toplamış ve mikro-hava taşıtlarına uygulanabilirlik açısından büyük bir potansiyel teşkil ettiğinden, konu üzerindeki araştırmalar yoğunlaşmıştır. Düşük hızlar ve düşük en-boy oranları, halen tam anlaşılamamış düşük Reynolds-sayılı akışlar yaratmaktadırlar. . Bu çalışmanın amacı, salınım yapmakta olan düz bir plaka etrafındaki üç-boyutlu akışın HAD (Hesaplamalı Akışkanlar Dinamiği) yöntemiyle incelenmesidir. Reynolds Ortalamalı Navier-Stokes Denklemlerinin çözümü için ticari bir program olan Fluent kullanılmıştır. Hedef, üç boyutlu akış karakteristiklerinin ve bazı kinematik parametrelerin akış ve performans üzerindeki etkilerinin vurgulanmasıdır. Süreksiz akış özelliklerinin çözümlenebilmesi için bir türbülans modelinin kullanılması gerekmektedir. Düşük Reynolds-sayılı akışları da kapsayan bir yöntem olduğundan ve bu tür akışlar için güvenilir sonuçlar verdiği bilindiğinden, k-ω sst modeli kullanılmıştır. Viskozitenin etkili olduğu bölgelerin düzgün olarak çözümlenebilmesi için duvar kenarı modelli bir yaklaşım uygulanmıştır. Çalışma boyunca Reynolds sayısı 60 000’e sabitlenmiş, en-boy oranı, ortalama akış açısı, genlik oranı ve indirgenmiş frekans değerleri birbirlerinden bağımsız olarak değiştirilerek parametrik çalışmalar yapılmıştır. Uç vorteksinin (girdap), hücum-kenarı vorteksini kontrol etmek ve dağılmasını sınırlamak suretiyle, aşağı akış üzerinde olumlu bir etkisi vardır. Yüksek indirgenmiş frekans değerleri için itme sağlayan konfigürasyonlar elde edilebilmiştir.Recently, flapping-wing aerodynamics has generated a great deal of interest and an important research effort is being made due to its potential application to Micro-Air Vehicles (MAVs). The low speed and small aspect ratio generate low Reynolds number flows that are still not well understood. The objective of this study is to perform three-dimensional CFD analyzes of the flow developing around an oscillating flat-plate. The commercial software Fluent is used to carry out the computations based on the Reynolds Averaged Navier-Stokes (RANS) equations. The aim is to highlight the three dimensional flow structure and the effect that some of the kinematics parameters have on the flow and performance parameters. To account for the unsteady flow features a turbulence model had to be incorporated. The kω-sst model was chosen as it includes a treatment of low-Reynolds number flows and proved to provide reliable results for these types of flows. A near-wall modelling approach was adopted since the flow had to be properly resolved throughout the viscosity-affected region. The Reynolds number was fixed to 60 000 and the parametric studies consisted in varying the aspect ratio of the flat-plate, the mean flow angle and the reduced frequency, independently from one another. The results highlighted the presence of an excessive amount of separation, often resulting in drag-producing motions. The tip vortex played a positive role by controlling and limiting the spreading of the leading-edge vortex spanwise. It is at higher reduced frequency values that thrust-producing configurations were achieved.Yüksek LisansM.Sc

Enhancement Of Jet Impingement Heat Transfer Using Shape Modification And Phase Change

The overall goal of the present study is to enhance heat transfer rate performance on high heat flux surfaces while maintaining a uniform and low temperature of the substrate. The specific objectives are to determine shapes which maximize heat transport from heater surfaces when using jet impingement cooling method and to model a two phase jet impingement process which incorporates phase change at the impingement substrate

Advances in Modeling of Fluid Dynamics

This book contains twelve chapters detailing significant advances and applications in fluid dynamics modeling with focus on biomedical, bioengineering, chemical, civil and environmental engineering, aeronautics, astronautics, and automotive. We hope this book can be a useful resource to scientists and engineers who are interested in fundamentals and applications of fluid dynamics

Systematic study of instrumental mass discrimination in multi-collector inductively coupled plasma-mass spectrometry

Multi-collector inductively coupled plasma - mass spectrometry (MC-ICP-MS) has gained substantial importance in isotopic analysis over the last two decades. In the beginning, MC-ICP-MS was almost solely deployed in geo- and cosmochemistry and in nuclear sciences and industry. Nowadays, many other scientific fields make use of the technique, which is mostly based on the high versatility of the ICP ion source and the high sample throughput in comparison to methods with equal or even slightly better precision, such as thermal ionization mass spectrometry (TIMS). The major benefit of MC-ICP-MS is clearly the high ionization power of the ICP, compared to, e.g. that of thermal ionization. A major limitation of MC-ICP-MS is the omnipresent instrumental mass discrimination. It is the effect that light isotopes are discriminated against heavier isotopes during the measurement. The goal of this PhD research project was to identify and possibly quantify the major contributors to instrumental mass discrimination in MC-ICP-MS. Commonly, instrumental mass discrimination is attributed to space-charge effects. Even though this is an easy to comprehend effect at first glance, it becomes more complicated once studied more closely. Firstly, space-charge effects are present in charged particle beams only. Secondly, space-charge effects are most severe for low energetic particle beams with high current. Certainly, the space-charge effects are not the only contributors to mass discrimination. Several other contributors have been identified in the past, namely: collisions, sample introduction and ion formation and energy-selective ion transmission. The effect of the above mentioned processes in terms of mass discrimination were investigated by several strategies. The processes occurring during the ion beam formation were addressed by the Direct Simulation Monte Carlo method. Due to the nature of the ion source, the plasma is extracted from ambient pressure into the vacuum of the mass spectrometer; leading to drastically reduced fluid density. Yet, sufficient collisions between particles take place to possibly contribute to mass discrimination. The modeling results show a significant alteration of the fluid composition after the skimmer cone. Also a radial fractionation of the fluid was found. The ion beam is formed shortly after the plasma is extracted through the skimmer cone, the electrons are lost; a process known as charge-separation. During this phase, the space-charge effects are strongest. Thus a radial dependence of the isotopic composition of the ion beam might occur. This particular effect was investigated by two experiments, one comprising of ion implantation for the subsequent determination of the radial composition of the ion beam, the second experiment with a variable aperture addressing the shortcomings of the ion implantation and provide reliable \emph{in situ} information about the beam composition and diameter. These beam diameters are in contradiction to those expected from typically reported ion beam current. In order to measure the gross beam current, a Faraday cup was placed after the first ion lens of the mass spectrometer. The results reveal a much lower ion current than reported in literature, but are in reasonable agreement with estimations by the Child-Langmuir law for space-charge limited beams. Finally, it has to be pointed out that no dominant contributor to the mass discrimination could be identified. However, the energy-selective transmission can be excluded from the list of contributors, given the low ion beam current with the associated quasi complete beam transport. Since sample introduction a priory can be ruled out, only two contributors remain: collisions and space-charge effects. Both contributors can hardly be separated from one another experimentally, i.e., a higher throughput through the interface will lead to more collisions in the interface and consequently, to a higher ion beam current after charge-separation. Yet, the isolated treatment of both effects in computer simulations might provide a tool to solve this problem. Of course, the same simulator would need to have the capability to model both effects simultaneously, as well as separately, which is not yet possible

Hierarchical modelling of multiphase flows using fully resolved fixed mesh and PDF approaches

Fully–resolved simulations of multiphase flow phenomena and in particular particulate flow simulations are computationally expensive and are only feasible on massively parallel computer clusters. A 3D SIMPLE type pressure correction algorithm is implemented and extensively tested and parallelized to exploit the power of massively parallel computing clusters currently available. Domain decomposition and communication schemes applicable to a general unstructured or structured multi–block CFD codes are discussed and algorithms are proposed, implemented and tested. Several high–performance linear solvers and a multi–grid strategy for the current framework are implemented and the best types of solvers are identified. A 2D CFD code is developed by the author to test several possible fixed–mesh strategies. Variations of immersed boundary (IB) and fictitious domain (FD) methods are implemented and compared. FD methods are identified to have better properties especially if other transport phenomena are also considered. Therefore an FD method is adapted by the author for the SIMPLE type flow solvers and is extended to heat transfer problems. The method is extensively tested for the simulation of flow around stationary in addition to freely moving particles and forced motion where both natural and forced convection are considered. The method is used to study the flow and heat transfer around a stationary cylinder and a new high resolution correlation is devised for the estimation of the local Nusselt number curves. Free fall problem for a single circular cylinder is considered and the effects of internal heat generation and also long term behavior of single cold particle subject to natural convection are also studied in detail. A particle collision strategy is also adapted and tested for the particle–particle collision problems. The FD algorithm is extended to the 3D framework and the flow around single stationary sphere and also free fall of a single sphere are used to validate the FD algorithm in 3D. A unique polydispersed fluid-particle turbulent modelling process is reviewed and the closure problem for this framework is studied in detail. Two methods for the closure of the non–integer moments which results from the polydispersity of the particles are proposed namely PDF reconstruction using Laguerre polynomials and a unique direct method named Direct Fractional Method of Moments (DFMM). The latter is derived using the results of the fractional calculus by writing an equation for the fractional derivatives of the moment generating function. The proposed methods are tested on a number of problems consisting of analytical, experimental and DNS simulations to asses their validity and viability which shows that both methods provide accurate results with DFMM having more desirable properties.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

COUPLED LAGRANGE-EULER MODEL FOR SIMULATION OF BUBBLY FLOW IN VERTICAL PIPES CONSIDERING TURBULENT 3D RANDOM WALKS MODELS AND BUBBLES INTERACTION EFFECTS

Una nueva aproximación euleriana-lagarangiana, en su forma de acople en dos vías, para la simulación de flujo de burbujas, agua-aire es presentada en la tesis, en la que se incluyen los efectos de las colisiones entre burbujas, así como las posibles roturas o coalescencia de burbujas. Esta aproximación utiliza el modelo Continuous Random Walk, CRW, para tener en cuenta las fluctuaciones de la velocidad. Esta aproximación se enmarca dentro de un modelo de turbulencia k-epsilon para la fase continua del líquido. En esta tesis se estudiarán los métodos para realizar el acople entre ambas aproximaciones, el efecto de la fuerza lift y de la dispersión turbulenta sobre la distribución de la fracción de huecos, así como los modelos de coalescencia y rotura de burbujas que puedan ser empleados en este tipo de aproximación. Se ha partido de un código euleriano para simular la parte continua, y sobre él se ha acoplado la aproximación lagrangiana. Para que ese acople afecte a la fase continua sobre su solver ser han añadido fuentes de momento y turbulencia. Además se ha modificado el volumen computacional de cada celda para que tenga en consideración el volumen ocupado por la fase dispersa. El acople en doble vía hace que los perfiles de velocidad y turbulencia de la fase continua se modifiquen notablemente y que se aproximen a los reales, lo que resulta básico para la correcta simulación de las fuerzas interfaciales. La colisión entre burbujas, y burbujas y pared se ha incluido. Este efecto es necesario como paso previo a incluir los procesos de rotura o coalescencia de burbujas, aunque la colisión en sí tenga efectos limitados en la distribución de la fracción de huecos. El proceso de coalescencia se basa en el modelo de Chester ( 1991 ) , el modelo compara el tiempo de colisión con el tiempo de drenaje de la película entre burbujas para determinar si existe o no coalescencia. El modelo de rotura se basa en el modelo de Martínez-Bazán. Uno de los principales hitos deAli Abd El Aziz Essa ., M. (2012). COUPLED LAGRANGE-EULER MODEL FOR SIMULATION OF BUBBLY FLOW IN VERTICAL PIPES CONSIDERING TURBULENT 3D RANDOM WALKS MODELS AND BUBBLES INTERACTION EFFECTS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18068Palanci