Abstract-The paper presents a 3D numerical analysis of the thermal behavior of a small permanent ... more Abstract-The paper presents a 3D numerical analysis of the thermal behavior of a small permanent magnet DC motor, performed by Finite Element Method (FEM). The accuracy of the computed temperatures was confirmed by comparison with experimental results; a prototype of the ...
International Journal of Heat and Mass Transfer, 1994
This paper shows that the hot spot temperature of an electronic module with finned air heat sink ... more This paper shows that the hot spot temperature of an electronic module with finned air heat sink can be reduced by allowing the fin thickness and height to increase in the flow direction X. The hot spot temperature decreases by about 15% if the thickness of a plate fin with constant height increases as .Y"~'. The decrease is approximately 30% if the height of a constant-thickness plate fin increases as x, i.e. if the fin shape is almost like a triangle when viewed from the side. In addition to lowering the hot spot temperature, the fin thickness and height variations recommended by this study lead to considerably more uniform temperature distributions on the module surface on which the fins are installed.
Potentially adverse health effects due to the exposure of living bodies to electromagnetic radiat... more Potentially adverse health effects due to the exposure of living bodies to electromagnetic radiation is still a subject of debate. An engineering perspective on this issue deals with electromagnetic field parameters estimate by computation and measurement and with the certification of the electric and electronic equipment in compliance with exposure standards. The paper presented here describes a 3D computational model, based on the finite element method, for the study of microwaves penetration in the head exposed in the near field of a dipole antenna, in conditions similar to mobile telephony. The head is accurate in its external shape and has an equivalent homogeneous inner structure. The microwaves penetration in human tissue is superficial and the electric field distribution is less sensible to the accuracy of the inner anatomy, than to the body shape. Field parameters, like electric field strength and specific energy absorption rate, are evaluated in order to be compared to values stated in limiting exposure standards.
There is an outstanding growing interest in developing numerical methods and tools to investigate... more There is an outstanding growing interest in developing numerical methods and tools to investigate the hemodynamic of the arterial flow, and to understand its interaction with the anatomic structural system. As arteries morphology is complex and patient-related, medical data based reconstruction of the geometry may be utilized to generate realistic computational domains. Numerical methods and image-based geometry reconstruction have reached the stage where they may be utilized to investigate and predict the hemodynamic flows in arteries. In this paper we report numerical simulation results on arterial blood flow - vessel and muscular mass interaction. The flow patterns and the structural displacements thus obtained may be utilized for vascular surgery training, planning and intervention, to investigate atherosclerosis genesis, in drug targeting, etc.
Contemporary superconductor synchronous motors utilize high current density, high temperature sup... more Contemporary superconductor synchronous motors utilize high current density, high temperature superconductor (HTS) direct current windings that request special cooling technologies. This paper presents a preliminary study in the design phase on several aspects of the thermal stability of a small power prototype of an HTS motor. The model we developed is notional, aimed at investigating the design of the cooling system. We present electromagnetic field and heat transfer mathematical models, and their numerical implementation. The results outline the heat transfer mechanisms, the hot spot regions in the motor, and may provide information useful to the motor design.
A ferrofluid-cooled low power, single-phased electric transformer was designed and prototyped wit... more A ferrofluid-cooled low power, single-phased electric transformer was designed and prototyped with the aim of investigating the performance that such an apparatus may exhibit. The nanometric, colloidal, super-paramagnetic fluid used as coolant has specific electric, magnetic, and thermal properties, and presents an overall better stability and capacity to withstanding electromagnetic and thermal stress. This paper addresses also the electromagnetic and heat transfer processes that occur. First, the physical, mathematical, and numerical models are introduced. Numerical simulation results suggest that the magnetization body forces may add to the thermal, buoyancy body forces in providing for better heat transfer. To outline this, several numerical models that may conveniently be treated numerically within the current hardware and software limits, while still providing for satisfactory accuracy were developed. The results may be utilized also in the design phase of the transformer.
A detailed two-dimensional (2-D) finite element model (FEM) of the electroconductive anatomy of a... more A detailed two-dimensional (2-D) finite element model (FEM) of the electroconductive anatomy of a human thorax was formulated to investigate the fields and currents generated by the on-set of a magnetic field. The 2-D model of the thorax was constructed from archived cross-sectional maps and accounts for eight isotropic tissue conductivities and the anisotropic conductivity of the intercostal muscles. A circular excitation coil that surrounds the anatomic structure is assumed to produce a magnetic field that sources a system of induced currents throughout the thorax. Although cross-sectional too, (eddy) currents that irrigate the heart are shown to differ in pattern from the classic (advection) currents which accompany defibrillation. Our exploratory computational results suggest that magnetic excitation may have a potential value in defibrillation
The cardiac electrical activity is macroscopically manifested as action potentials that travel th... more The cardiac electrical activity is macroscopically manifested as action potentials that travel through atria and ventricles in a synchronized fashion. Cardiac arrhythmias are disorders of the normal electrical rhythm. At high heart rate, the action potential duration follows a long-short-long pattern. This oscillatory electrical rhythm is called alternans and it is believed to be a precursor to the development of severe ventricular arrhythmias. In this computational study we analyze the initiation of alternans in a paced one-dimensional strand of cardiac cells governed by the Beeler-Reuter model. We present results from numerical experiments and a qualitative description of the observed patterns of cardiac activation.
Recently, there is a growing interest in developing numerical methods and tools to investigate th... more Recently, there is a growing interest in developing numerical methods and tools to investigate the hemodynamics of the arterial flow, and to understand its influence on the transport of solutes (e.g., oxygen), nutrients, etc. As arteries morphology is complex and patient-related, medical data based reconstruction of the geometry may be utilized to generate realistic computational domains. The blood flow is then investigated by finite element method (FEM) for a range of flow parameters. The flow patterns thus obtained may be utilized for vascular surgery training, planning and intervention, to investigate atherosclerosis genesis, in drug targeting, etc.
Superior, scalable grid topology that may provide for higher quality of service, survivorship cap... more Superior, scalable grid topology that may provide for higher quality of service, survivorship capacity, and reconfiguration capability is a feature of modern grid architecture. The reported research is aimed at delivering a possible, constructal solution that is based on a minimumredundant, scalable, reconfigurable topology that helps increasing the grid immunity to faults. We assume that a tree network serves nodes of consumption that are evenly distributed throughout the territory. All nodes are equally important and network survivability means delivering electrical energy to as many consumers as possible. The models and loads estimation is based on the load momentum method.
ABSTRACT The study concerns the numerical simulation of the electrical signal propagation in an e... more ABSTRACT The study concerns the numerical simulation of the electrical signal propagation in an excitable tissue that models the electrical activity of the heart. Several objectives are pursued: the response of the dynamical system to the influence of a strong external stimulus, the propagation of the electrical signal in the thoracic volume, and its electrical mapping on the thorax, when the source of the electric activity of the heart is the action potential as described by the complex Landau-Ginzburg equations. The volume conductor - built out of medical images reconstruction techniques out of MRI scans - that models the thorax comprises the heart, the lungs, the spinal cord and the ribs, aiming to evidence the outlining dynamics of the electrical activity of the heart and its echo in the thorax. The numerical simulation results evidence the causal relations that exist between the electrical activity of the heart and the electrical field distribution within the thorax. The model of this direct electrocardiagraphy (ECG) problem may prove useful in studying the associated inverse ECG problems, which consists of investigating the electrical activity of the heart by using available (measured) voltage signals on the thorax - an inverse ECG problem.
The opportunity for the research objectives and results presented in the paper was offered by the... more The opportunity for the research objectives and results presented in the paper was offered by the setup and certification of an electromagnetic compatibility laboratory, targeted on development and compliance testing of mobile communication devices, concerning their ability to provide safe working conditions to the user. The experiments are designed to assess the compliance of the emitted radiation level with the basic restrictions expressed in terms of the dosimetric estimate, i.e. the specific energy absorption rate, physical quantity widely known by its acronym, SAR. A numerical model, based on the implementation of the finite element method was designed in order to replicate, as good as possible, some experimental results. After validation, the numerical model is intended to become a flexible tool, useful for intensive dosimetric analysis, with objectives complementary to the experimental goals and possibilities. The paper introduces the experimental arrangement and the numerical model, both designed accordingly to the current testing standardization in the field. A comprehensive set of results gives data for the comparison between measurements and calculus, with the specific objective of the calibration and validation the numerical model, in conformity with the experimental setup.
This paper reports a mathematical model and numerical, finite element (FEM) experiments performed... more This paper reports a mathematical model and numerical, finite element (FEM) experiments performed on a dipolar superferric magnet for high uniformity (magnetic) field usable in particle accelerators. First, we address the magnetic field problem, as the main purpose of the superconductor magnet is to provide for a highly uniform, high flux density magnetic field. Then, the heat transfer problem is investigated. As radiation heat transfer is of concern in this application twodimensional models may not produce accurate, realistic results. Therefore our study is based on a three dimensional geometry abstracted from the CAD design of the prototype. The numerical simulation results unveil the magnetic field spectrum and the heat transfer paths within the structure that may be valuable in optimizing the magnet's design.
A detailed two-dimensional (2-D) finite element model (FEM) for the electroconductive anatomy of ... more A detailed two-dimensional (2-D) finite element model (FEM) for the electroconductive anatomy of a human thorax was formulated to investigate the unsteady diffusion of the electromagnetic field that occurs during defibrillation. An equivalent electric circuit simulating a defibrillator is solved to generate the analytic form of the defibrillation current, that is further used as input (boundary condition) to the field problem. Specific insights in the defibrillation process, not apparent through an electrokinetic analysis, such as dynamic patterns of current density that irrigates the heart and the important role played in the diffusion process by chest wall, intercostal muscles and interstitial fluid, were evidenced. Our results lead to a deeper understanding of the anatomic structure response to defibrillation and suggest that a different approach to its optimization may be needed
Hyperthermia and coagulation therapies are based on the tissue heating and represent minimally in... more Hyperthermia and coagulation therapies are based on the tissue heating and represent minimally invasive medical procedures; they are recommended for the treatment of tumors in soft tissues (liver, kidney, breast, etc.). The energy is delivered to the tissue through a microwave (MW) thin antenna, inserted transcutaneously. Both procedures require a careful preparation for the intervention; the power and frequency of the MW source, the design of the antenna, the time interval while the energy is delivered are some significant factors that determine the temperature distribution in the target tissue. Numerical modeling of the intervention is a research tool, useful for the optimization of the procedure. The coupled phenomena, electromagnetic and thermal, are analyzed here in a numerical experiment with the finite element method (FEM); electromagnetic field (EMF), absorbed power density and temperature distributions are computed inside the exposed volume of tissue and the energetic efficiency of the applicator is evaluated.
Biomedical engineering distinguished itself as an emerging educational domain during the last 15-... more Biomedical engineering distinguished itself as an emerging educational domain during the last 15-20 years, stimulated in the contemporary developed societies by the growing need for competitive health care facilities and high quality assistance.
Abstract-The paper presents a 3D numerical analysis of the thermal behavior of a small permanent ... more Abstract-The paper presents a 3D numerical analysis of the thermal behavior of a small permanent magnet DC motor, performed by Finite Element Method (FEM). The accuracy of the computed temperatures was confirmed by comparison with experimental results; a prototype of the ...
International Journal of Heat and Mass Transfer, 1994
This paper shows that the hot spot temperature of an electronic module with finned air heat sink ... more This paper shows that the hot spot temperature of an electronic module with finned air heat sink can be reduced by allowing the fin thickness and height to increase in the flow direction X. The hot spot temperature decreases by about 15% if the thickness of a plate fin with constant height increases as .Y"~'. The decrease is approximately 30% if the height of a constant-thickness plate fin increases as x, i.e. if the fin shape is almost like a triangle when viewed from the side. In addition to lowering the hot spot temperature, the fin thickness and height variations recommended by this study lead to considerably more uniform temperature distributions on the module surface on which the fins are installed.
Potentially adverse health effects due to the exposure of living bodies to electromagnetic radiat... more Potentially adverse health effects due to the exposure of living bodies to electromagnetic radiation is still a subject of debate. An engineering perspective on this issue deals with electromagnetic field parameters estimate by computation and measurement and with the certification of the electric and electronic equipment in compliance with exposure standards. The paper presented here describes a 3D computational model, based on the finite element method, for the study of microwaves penetration in the head exposed in the near field of a dipole antenna, in conditions similar to mobile telephony. The head is accurate in its external shape and has an equivalent homogeneous inner structure. The microwaves penetration in human tissue is superficial and the electric field distribution is less sensible to the accuracy of the inner anatomy, than to the body shape. Field parameters, like electric field strength and specific energy absorption rate, are evaluated in order to be compared to values stated in limiting exposure standards.
There is an outstanding growing interest in developing numerical methods and tools to investigate... more There is an outstanding growing interest in developing numerical methods and tools to investigate the hemodynamic of the arterial flow, and to understand its interaction with the anatomic structural system. As arteries morphology is complex and patient-related, medical data based reconstruction of the geometry may be utilized to generate realistic computational domains. Numerical methods and image-based geometry reconstruction have reached the stage where they may be utilized to investigate and predict the hemodynamic flows in arteries. In this paper we report numerical simulation results on arterial blood flow - vessel and muscular mass interaction. The flow patterns and the structural displacements thus obtained may be utilized for vascular surgery training, planning and intervention, to investigate atherosclerosis genesis, in drug targeting, etc.
Contemporary superconductor synchronous motors utilize high current density, high temperature sup... more Contemporary superconductor synchronous motors utilize high current density, high temperature superconductor (HTS) direct current windings that request special cooling technologies. This paper presents a preliminary study in the design phase on several aspects of the thermal stability of a small power prototype of an HTS motor. The model we developed is notional, aimed at investigating the design of the cooling system. We present electromagnetic field and heat transfer mathematical models, and their numerical implementation. The results outline the heat transfer mechanisms, the hot spot regions in the motor, and may provide information useful to the motor design.
A ferrofluid-cooled low power, single-phased electric transformer was designed and prototyped wit... more A ferrofluid-cooled low power, single-phased electric transformer was designed and prototyped with the aim of investigating the performance that such an apparatus may exhibit. The nanometric, colloidal, super-paramagnetic fluid used as coolant has specific electric, magnetic, and thermal properties, and presents an overall better stability and capacity to withstanding electromagnetic and thermal stress. This paper addresses also the electromagnetic and heat transfer processes that occur. First, the physical, mathematical, and numerical models are introduced. Numerical simulation results suggest that the magnetization body forces may add to the thermal, buoyancy body forces in providing for better heat transfer. To outline this, several numerical models that may conveniently be treated numerically within the current hardware and software limits, while still providing for satisfactory accuracy were developed. The results may be utilized also in the design phase of the transformer.
A detailed two-dimensional (2-D) finite element model (FEM) of the electroconductive anatomy of a... more A detailed two-dimensional (2-D) finite element model (FEM) of the electroconductive anatomy of a human thorax was formulated to investigate the fields and currents generated by the on-set of a magnetic field. The 2-D model of the thorax was constructed from archived cross-sectional maps and accounts for eight isotropic tissue conductivities and the anisotropic conductivity of the intercostal muscles. A circular excitation coil that surrounds the anatomic structure is assumed to produce a magnetic field that sources a system of induced currents throughout the thorax. Although cross-sectional too, (eddy) currents that irrigate the heart are shown to differ in pattern from the classic (advection) currents which accompany defibrillation. Our exploratory computational results suggest that magnetic excitation may have a potential value in defibrillation
The cardiac electrical activity is macroscopically manifested as action potentials that travel th... more The cardiac electrical activity is macroscopically manifested as action potentials that travel through atria and ventricles in a synchronized fashion. Cardiac arrhythmias are disorders of the normal electrical rhythm. At high heart rate, the action potential duration follows a long-short-long pattern. This oscillatory electrical rhythm is called alternans and it is believed to be a precursor to the development of severe ventricular arrhythmias. In this computational study we analyze the initiation of alternans in a paced one-dimensional strand of cardiac cells governed by the Beeler-Reuter model. We present results from numerical experiments and a qualitative description of the observed patterns of cardiac activation.
Recently, there is a growing interest in developing numerical methods and tools to investigate th... more Recently, there is a growing interest in developing numerical methods and tools to investigate the hemodynamics of the arterial flow, and to understand its influence on the transport of solutes (e.g., oxygen), nutrients, etc. As arteries morphology is complex and patient-related, medical data based reconstruction of the geometry may be utilized to generate realistic computational domains. The blood flow is then investigated by finite element method (FEM) for a range of flow parameters. The flow patterns thus obtained may be utilized for vascular surgery training, planning and intervention, to investigate atherosclerosis genesis, in drug targeting, etc.
Superior, scalable grid topology that may provide for higher quality of service, survivorship cap... more Superior, scalable grid topology that may provide for higher quality of service, survivorship capacity, and reconfiguration capability is a feature of modern grid architecture. The reported research is aimed at delivering a possible, constructal solution that is based on a minimumredundant, scalable, reconfigurable topology that helps increasing the grid immunity to faults. We assume that a tree network serves nodes of consumption that are evenly distributed throughout the territory. All nodes are equally important and network survivability means delivering electrical energy to as many consumers as possible. The models and loads estimation is based on the load momentum method.
ABSTRACT The study concerns the numerical simulation of the electrical signal propagation in an e... more ABSTRACT The study concerns the numerical simulation of the electrical signal propagation in an excitable tissue that models the electrical activity of the heart. Several objectives are pursued: the response of the dynamical system to the influence of a strong external stimulus, the propagation of the electrical signal in the thoracic volume, and its electrical mapping on the thorax, when the source of the electric activity of the heart is the action potential as described by the complex Landau-Ginzburg equations. The volume conductor - built out of medical images reconstruction techniques out of MRI scans - that models the thorax comprises the heart, the lungs, the spinal cord and the ribs, aiming to evidence the outlining dynamics of the electrical activity of the heart and its echo in the thorax. The numerical simulation results evidence the causal relations that exist between the electrical activity of the heart and the electrical field distribution within the thorax. The model of this direct electrocardiagraphy (ECG) problem may prove useful in studying the associated inverse ECG problems, which consists of investigating the electrical activity of the heart by using available (measured) voltage signals on the thorax - an inverse ECG problem.
The opportunity for the research objectives and results presented in the paper was offered by the... more The opportunity for the research objectives and results presented in the paper was offered by the setup and certification of an electromagnetic compatibility laboratory, targeted on development and compliance testing of mobile communication devices, concerning their ability to provide safe working conditions to the user. The experiments are designed to assess the compliance of the emitted radiation level with the basic restrictions expressed in terms of the dosimetric estimate, i.e. the specific energy absorption rate, physical quantity widely known by its acronym, SAR. A numerical model, based on the implementation of the finite element method was designed in order to replicate, as good as possible, some experimental results. After validation, the numerical model is intended to become a flexible tool, useful for intensive dosimetric analysis, with objectives complementary to the experimental goals and possibilities. The paper introduces the experimental arrangement and the numerical model, both designed accordingly to the current testing standardization in the field. A comprehensive set of results gives data for the comparison between measurements and calculus, with the specific objective of the calibration and validation the numerical model, in conformity with the experimental setup.
This paper reports a mathematical model and numerical, finite element (FEM) experiments performed... more This paper reports a mathematical model and numerical, finite element (FEM) experiments performed on a dipolar superferric magnet for high uniformity (magnetic) field usable in particle accelerators. First, we address the magnetic field problem, as the main purpose of the superconductor magnet is to provide for a highly uniform, high flux density magnetic field. Then, the heat transfer problem is investigated. As radiation heat transfer is of concern in this application twodimensional models may not produce accurate, realistic results. Therefore our study is based on a three dimensional geometry abstracted from the CAD design of the prototype. The numerical simulation results unveil the magnetic field spectrum and the heat transfer paths within the structure that may be valuable in optimizing the magnet's design.
A detailed two-dimensional (2-D) finite element model (FEM) for the electroconductive anatomy of ... more A detailed two-dimensional (2-D) finite element model (FEM) for the electroconductive anatomy of a human thorax was formulated to investigate the unsteady diffusion of the electromagnetic field that occurs during defibrillation. An equivalent electric circuit simulating a defibrillator is solved to generate the analytic form of the defibrillation current, that is further used as input (boundary condition) to the field problem. Specific insights in the defibrillation process, not apparent through an electrokinetic analysis, such as dynamic patterns of current density that irrigates the heart and the important role played in the diffusion process by chest wall, intercostal muscles and interstitial fluid, were evidenced. Our results lead to a deeper understanding of the anatomic structure response to defibrillation and suggest that a different approach to its optimization may be needed
Hyperthermia and coagulation therapies are based on the tissue heating and represent minimally in... more Hyperthermia and coagulation therapies are based on the tissue heating and represent minimally invasive medical procedures; they are recommended for the treatment of tumors in soft tissues (liver, kidney, breast, etc.). The energy is delivered to the tissue through a microwave (MW) thin antenna, inserted transcutaneously. Both procedures require a careful preparation for the intervention; the power and frequency of the MW source, the design of the antenna, the time interval while the energy is delivered are some significant factors that determine the temperature distribution in the target tissue. Numerical modeling of the intervention is a research tool, useful for the optimization of the procedure. The coupled phenomena, electromagnetic and thermal, are analyzed here in a numerical experiment with the finite element method (FEM); electromagnetic field (EMF), absorbed power density and temperature distributions are computed inside the exposed volume of tissue and the energetic efficiency of the applicator is evaluated.
Biomedical engineering distinguished itself as an emerging educational domain during the last 15-... more Biomedical engineering distinguished itself as an emerging educational domain during the last 15-20 years, stimulated in the contemporary developed societies by the growing need for competitive health care facilities and high quality assistance.
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Papers by Mihaela Morega