Igor Fedchenia - Academia.edu (original) (raw)

Papers by Igor Fedchenia

ABSTRACT Fiscal Year (FY) 2011 Objectives Collaborate closely with the Hydrogen Storage • Enginee... more ABSTRACT Fiscal Year (FY) 2011 Objectives Collaborate closely with the Hydrogen Storage • Engineering Center of Excellence (HSECoE) partners to advance materials-based hydrogen storage system technologies. Develop vehicle/power plant/storage system integrated • system modeling elements to improve specification of storage system requirements and to predict performance for candidate designs. Establish detailed heat and mass transfer modeling • and apply to design improved internal heat exchange configurations. Design and evaluate compacted/structured hydride • powder beds including integration into the above heat exchange configurations. Assess the viability of on-board purification for various • storage material classes and purification approaches. Conduct risk assessments during the progression of the • phased HSECoE efforts to evaluate concepts regarding the "Environmental Health and Safety" target.

Apparatus and methods are disclosed for uniformly mixing fluid phases entrained in a porous mater... more Apparatus and methods are disclosed for uniformly mixing fluid phases entrained in a porous material. A mixer may have a vessel and at least one porous material held by the vessel. At least one actuator may be acoustically coupled with at least one wall of the vessel for generating a wave. The wave effects mixing of at least two fluids in the porous material. The actuator may be a linear motor actuated with a control signal of predetermined frequency. The actuator may have a number of actuator pairs each including respective first and second actuators at respective first and second sides of the vessel. The actuators may be hinged for reciprocal movement. The actuators may be actuated to form a compression-expansion wave to effect fluid motion in the porous material.

Molecular Physics, 1995

... Cross-correlation effects in the fluorescence anisotropy r(t) By II FEDCHENIA and P.-O. WESTL... more ... Cross-correlation effects in the fluorescence anisotropy r(t) By II FEDCHENIA and P.-O. WESTLUNDt Department of Physical Chemistry, Umeh University, S-901 87 Ume~, Sweden (Received 28 July 1994; accepted 20 September 1994) ...

The Journal of Chemical Physics, 1998

Results from nonequilibrium molecular-dynamics simulations of collisional energy transfer from vi... more Results from nonequilibrium molecular-dynamics simulations of collisional energy transfer from vibrationally highly excited azulene in compressed CO2 are compared with experimental results from our laboratory obtained under comparable physical conditions. As observed in the experiment, the cooling rates show a purely monoexponential decay of the excess energy. The influence of the microscopic solvent shell structure on these processes is investigated using the full three-dimensional anisotropic CO2 structure around azulene obtained from the simulation. The analysis shows that local heating effects of any kind do not play a role in our model system. Predictions of the pressure dependence of the energy transfer rates by the isolated binary collision model are compared with results from the simulations using two different definitions of the collision frequency in dense fluids.

Molecular Simulation, 1993

ABSTRACT Three different algorithms are presented for Brownian Dynamics simulations of diffusion ... more ABSTRACT Three different algorithms are presented for Brownian Dynamics simulations of diffusion on the unit sphere restricted by the intersection with a symmetric or distorted cone. The second rank time correlation function has been determined. The three algorithms are compared and discussed with respect to computational efficiency and accuracy.

Abstract : In this work we aim developing a novel theoretical framework to evaluate the feasibili... more Abstract : In this work we aim developing a novel theoretical framework to evaluate the feasibility of attaining significant improvement of fuel cells performance and stability by increasing the transport processes in porous partially fluid filled cathode compartment through the application of acoustic and structural waves. We have developed a unified model of structural/acoustic wave propagation in the PEM cathode compartment and coupled it with mass transfer in the porous media. A novel generalized filtration law that accounts for dynamic loadings, varying saturation, and solid structure distortion describing mass transfer in this complex but generic system has been found. It has been demonstrated that vibration gives rise to net change of saturation inside porous medium. Based on the numerical and experimental results number of practical recommendations optimizing material selections and performance regime has been made. Developed methodology is useful for wide range of Fuel Cell problems as well as for wide range of other porous structures and could serve as an important design tool.

Inverse Problems in Science and Engineering, 2014

Physical Review E, 1994

An algorithm is developed in order to solve the stochastic Liouville equation describing energy t... more An algorithm is developed in order to solve the stochastic Liouville equation describing energy transfer between a donor-donor pair of reorienting chromophores. The algorithm requires the fluctuating part of the Liouville equation in the form of trajectories. In this particular case the molecular reorientation of the chromophores was simulated by means of a Brownian dynamic simulation technique where each of the two molecules are allowed to undergo a restricted rotational diffusion in a cone potential. Numerical results are presented for the correlation function (y{t}y{0}), representing the probability that the initially excited donor sti11 is excited at a later time t. Results are given for the weak or Forster regime and for a simple case in the strong or slow motion regime. The time resolved fluorescence anisotropy r (t) is also calculated for different molecular reorientational rates and cone potentials.

2012 IEEE International Conference on Imaging Systems and Techniques Proceedings, 2012

We present a new image reconstruction method for Electrical Capacitance Tomography (ECT). ECT ima... more We present a new image reconstruction method for Electrical Capacitance Tomography (ECT). ECT image reconstruction is generally ill-posed because the number of measurements is small whereas the image dimensions are large. Here, Compressive Sensing is used to provide better reconstruction from the small number of measurements. Given the sparsity of the signal (image), the idea is to apply an efficient and stable algorithm through L1 regularization to recover the sparse signal with sufficient measurements that have cardinality comparable to the sparsity of the signal. In this paper, we present Total Variation (TV) regularization for ECT image reconstruction, and apply an efficient Split-Bregman Iteration (SBI) approach to solve the problem. We propose a joint metric of positive reconstruction rate (PRR) and false reconstruction rate (FRR) to evaluate image reconstruction performance. The results on both synthetic and real data show that the proposed TV-SBI method can better preserve the edges of images and better resolve different objects within reconstructed images, as compared to a representative state-of-the-art ECT image reconstruction algorithm, Projected Landweber Iteration with Linear Back Projection initialization (LBP-PLI).

Flow Measurement and Instrumentation, 2015

We present a new image reconstruction method for Electrical Capacitance Tomography (ECT). ECT ima... more We present a new image reconstruction method for Electrical Capacitance Tomography (ECT). ECT image reconstruction is generally ill-posed because the number of measurements is small whereas the image dimensions are large. Here, we present a sparsity-inspired approach to achieve better ECT image reconstruction from the small number of measurements. Our approach for ECT image reconstruction is based on Total Variation (TV) regularization. We apply an efficient Split-Bregman Iteration (SBI) approach to solve the problem. We also propose three metrics to evaluate image reconstruction performance, i.e., a joint metric of positive reconstruction rate (PRR) and false reconstruction rate (FRR), correlation coefficient, and a shape and location metric. The results on both synthetic and real data show that the proposed TV-SBI method can better preserve the edges of images and better resolve different objects within reconstructed images, as compared to a representative state-of-the-art ECT image reconstruction algorithm, Projected Landweber Iteration with Linear Back Projection initialization (LBP-PLI).

2012 Twenty-Seventh Annual IEEE Applied Power Electronics Conference and Exposition (APEC), 2012

This paper presents a comprehensive study on the wire bond life for Insulated Gate Bipolar Transi... more This paper presents a comprehensive study on the wire bond life for Insulated Gate Bipolar Transistors (IGBT). The main elements are as follows: 1) Substantial non-uniformity in temperature distribution across the chip area was revealed; 2) Additional electrical resistance at the wire bonds was discovered, which can elevate the local temperature and shorten the wire bond life; 3) Thermo-structural simulation

International Journal of Energy for a Clean Environment, 2008

ABSTRACT Power electronics devices based on IGBTs are destined to play a critical role in the sus... more ABSTRACT Power electronics devices based on IGBTs are destined to play a critical role in the sustainable energy economy by providing the efficient interface between lower emissions and renewable primary movers such as wind turbines, microturbines, photovoltaic, fuel cells, etc and local power consumers or electrical distribution system such as microgrids. The designers of Thermal Management Systems (TMS) for power electronics are faced with ever increasing demand of improving efficiency, increased reliability and life time as well as reducing the design cycle time, which requires the capability to quickly analyze and optimize enhanced thermal solutions though accurate prediction of three-dimensional transient temperature fields. A universal training strategy for a state space model is suggested that reproduces temperature responses of power electronic devices with any transient power dissipation profile. Full CFD and FEA transient models of IGBT modules of various structural elements cooled by natural convection and conduction have been created using the ANSYS IcePak software package. It is extremely time-consuming to use this full model for multiple-mission studies therefore a reduced order model in state space form has been developed to significantly reduce design time. The reduced order model has been trained using a single finite element model run with a universal power dissipation profile. This profile consisted of band limited white noise with a magnitude and frequency limit based on the combination of given devices and set of mission profiles. It has been shown that the state space model trained with such a profile reproduces the response to a wide variety of different power dissipation patterns typical for our application with an accuracy of about 2°C. Several different approaches for the choice of the state space model have been studied as well as proper selection of state space size and metrics for estimation of modeling error. It is suggested that the proposed method can be a universal way of extracting a reduced order model from the high fidelity combination of CFD and FEA models typical for power electronics applications, and possibly for a broader range of applications as well.

Pedestrian and Evacuation Dynamics 2008, 2009

... Yiqing Lin1, Igor Fedchenia1, Bob LaBarre1, and Robert Tomastik2 ... In this paper, we presen... more ... Yiqing Lin1, Igor Fedchenia1, Bob LaBarre1, and Robert Tomastik2 ... In this paper, we present an agent-based simulation model developed for a 2-story office building verified using the evacuation data collected using video cameras during fire drills in the building. ...

Physical Review E, 1999

An approximate expression describing the density dependence of vibrational energy relaxation rate... more An approximate expression describing the density dependence of vibrational energy relaxation rates in fluids in terms of thermodynamic and transport parameters of the fluid is developed on the basis of a classical statistical mechanical theory of vibrational energy relaxation of highly excited molecules in polyatomic solvents. The energy relaxation rate is expressed via the friction coefficient, which describes the interaction between solute oscillator and solvent molecules. The corresponding force-force time correlation function is expressed in terms of the dynamic structure factor of the solvent and the force of interaction between solute and solvent molecules. Approximating the dynamic structure factor appropriately leads to expressions for the density dependence of vibrational relaxation rates in terms of thermophysical solvent parameters. Using these expressions the density dependence of vibrational relaxation rates in supercritical ethane and propane both in the vicinity of the critical point and far from it are evaluated and compared with measured relaxation rates obtained under the same physical conditions. ͓S1063-651X͑99͒15710-6͔

ABSTRACT Fiscal Year (FY) 2011 Objectives Collaborate closely with the Hydrogen Storage • Enginee... more ABSTRACT Fiscal Year (FY) 2011 Objectives Collaborate closely with the Hydrogen Storage • Engineering Center of Excellence (HSECoE) partners to advance materials-based hydrogen storage system technologies. Develop vehicle/power plant/storage system integrated • system modeling elements to improve specification of storage system requirements and to predict performance for candidate designs. Establish detailed heat and mass transfer modeling • and apply to design improved internal heat exchange configurations. Design and evaluate compacted/structured hydride • powder beds including integration into the above heat exchange configurations. Assess the viability of on-board purification for various • storage material classes and purification approaches. Conduct risk assessments during the progression of the • phased HSECoE efforts to evaluate concepts regarding the "Environmental Health and Safety" target.

Apparatus and methods are disclosed for uniformly mixing fluid phases entrained in a porous mater... more Apparatus and methods are disclosed for uniformly mixing fluid phases entrained in a porous material. A mixer may have a vessel and at least one porous material held by the vessel. At least one actuator may be acoustically coupled with at least one wall of the vessel for generating a wave. The wave effects mixing of at least two fluids in the porous material. The actuator may be a linear motor actuated with a control signal of predetermined frequency. The actuator may have a number of actuator pairs each including respective first and second actuators at respective first and second sides of the vessel. The actuators may be hinged for reciprocal movement. The actuators may be actuated to form a compression-expansion wave to effect fluid motion in the porous material.

Molecular Physics, 1995

... Cross-correlation effects in the fluorescence anisotropy r(t) By II FEDCHENIA and P.-O. WESTL... more ... Cross-correlation effects in the fluorescence anisotropy r(t) By II FEDCHENIA and P.-O. WESTLUNDt Department of Physical Chemistry, Umeh University, S-901 87 Ume~, Sweden (Received 28 July 1994; accepted 20 September 1994) ...

The Journal of Chemical Physics, 1998

Results from nonequilibrium molecular-dynamics simulations of collisional energy transfer from vi... more Results from nonequilibrium molecular-dynamics simulations of collisional energy transfer from vibrationally highly excited azulene in compressed CO2 are compared with experimental results from our laboratory obtained under comparable physical conditions. As observed in the experiment, the cooling rates show a purely monoexponential decay of the excess energy. The influence of the microscopic solvent shell structure on these processes is investigated using the full three-dimensional anisotropic CO2 structure around azulene obtained from the simulation. The analysis shows that local heating effects of any kind do not play a role in our model system. Predictions of the pressure dependence of the energy transfer rates by the isolated binary collision model are compared with results from the simulations using two different definitions of the collision frequency in dense fluids.

Molecular Simulation, 1993

ABSTRACT Three different algorithms are presented for Brownian Dynamics simulations of diffusion ... more ABSTRACT Three different algorithms are presented for Brownian Dynamics simulations of diffusion on the unit sphere restricted by the intersection with a symmetric or distorted cone. The second rank time correlation function has been determined. The three algorithms are compared and discussed with respect to computational efficiency and accuracy.

Abstract : In this work we aim developing a novel theoretical framework to evaluate the feasibili... more Abstract : In this work we aim developing a novel theoretical framework to evaluate the feasibility of attaining significant improvement of fuel cells performance and stability by increasing the transport processes in porous partially fluid filled cathode compartment through the application of acoustic and structural waves. We have developed a unified model of structural/acoustic wave propagation in the PEM cathode compartment and coupled it with mass transfer in the porous media. A novel generalized filtration law that accounts for dynamic loadings, varying saturation, and solid structure distortion describing mass transfer in this complex but generic system has been found. It has been demonstrated that vibration gives rise to net change of saturation inside porous medium. Based on the numerical and experimental results number of practical recommendations optimizing material selections and performance regime has been made. Developed methodology is useful for wide range of Fuel Cell problems as well as for wide range of other porous structures and could serve as an important design tool.

Inverse Problems in Science and Engineering, 2014

Physical Review E, 1994

An algorithm is developed in order to solve the stochastic Liouville equation describing energy t... more An algorithm is developed in order to solve the stochastic Liouville equation describing energy transfer between a donor-donor pair of reorienting chromophores. The algorithm requires the fluctuating part of the Liouville equation in the form of trajectories. In this particular case the molecular reorientation of the chromophores was simulated by means of a Brownian dynamic simulation technique where each of the two molecules are allowed to undergo a restricted rotational diffusion in a cone potential. Numerical results are presented for the correlation function (y{t}y{0}), representing the probability that the initially excited donor sti11 is excited at a later time t. Results are given for the weak or Forster regime and for a simple case in the strong or slow motion regime. The time resolved fluorescence anisotropy r (t) is also calculated for different molecular reorientational rates and cone potentials.

2012 IEEE International Conference on Imaging Systems and Techniques Proceedings, 2012

We present a new image reconstruction method for Electrical Capacitance Tomography (ECT). ECT ima... more We present a new image reconstruction method for Electrical Capacitance Tomography (ECT). ECT image reconstruction is generally ill-posed because the number of measurements is small whereas the image dimensions are large. Here, Compressive Sensing is used to provide better reconstruction from the small number of measurements. Given the sparsity of the signal (image), the idea is to apply an efficient and stable algorithm through L1 regularization to recover the sparse signal with sufficient measurements that have cardinality comparable to the sparsity of the signal. In this paper, we present Total Variation (TV) regularization for ECT image reconstruction, and apply an efficient Split-Bregman Iteration (SBI) approach to solve the problem. We propose a joint metric of positive reconstruction rate (PRR) and false reconstruction rate (FRR) to evaluate image reconstruction performance. The results on both synthetic and real data show that the proposed TV-SBI method can better preserve the edges of images and better resolve different objects within reconstructed images, as compared to a representative state-of-the-art ECT image reconstruction algorithm, Projected Landweber Iteration with Linear Back Projection initialization (LBP-PLI).

Flow Measurement and Instrumentation, 2015

We present a new image reconstruction method for Electrical Capacitance Tomography (ECT). ECT ima... more We present a new image reconstruction method for Electrical Capacitance Tomography (ECT). ECT image reconstruction is generally ill-posed because the number of measurements is small whereas the image dimensions are large. Here, we present a sparsity-inspired approach to achieve better ECT image reconstruction from the small number of measurements. Our approach for ECT image reconstruction is based on Total Variation (TV) regularization. We apply an efficient Split-Bregman Iteration (SBI) approach to solve the problem. We also propose three metrics to evaluate image reconstruction performance, i.e., a joint metric of positive reconstruction rate (PRR) and false reconstruction rate (FRR), correlation coefficient, and a shape and location metric. The results on both synthetic and real data show that the proposed TV-SBI method can better preserve the edges of images and better resolve different objects within reconstructed images, as compared to a representative state-of-the-art ECT image reconstruction algorithm, Projected Landweber Iteration with Linear Back Projection initialization (LBP-PLI).

2012 Twenty-Seventh Annual IEEE Applied Power Electronics Conference and Exposition (APEC), 2012

This paper presents a comprehensive study on the wire bond life for Insulated Gate Bipolar Transi... more This paper presents a comprehensive study on the wire bond life for Insulated Gate Bipolar Transistors (IGBT). The main elements are as follows: 1) Substantial non-uniformity in temperature distribution across the chip area was revealed; 2) Additional electrical resistance at the wire bonds was discovered, which can elevate the local temperature and shorten the wire bond life; 3) Thermo-structural simulation

International Journal of Energy for a Clean Environment, 2008

ABSTRACT Power electronics devices based on IGBTs are destined to play a critical role in the sus... more ABSTRACT Power electronics devices based on IGBTs are destined to play a critical role in the sustainable energy economy by providing the efficient interface between lower emissions and renewable primary movers such as wind turbines, microturbines, photovoltaic, fuel cells, etc and local power consumers or electrical distribution system such as microgrids. The designers of Thermal Management Systems (TMS) for power electronics are faced with ever increasing demand of improving efficiency, increased reliability and life time as well as reducing the design cycle time, which requires the capability to quickly analyze and optimize enhanced thermal solutions though accurate prediction of three-dimensional transient temperature fields. A universal training strategy for a state space model is suggested that reproduces temperature responses of power electronic devices with any transient power dissipation profile. Full CFD and FEA transient models of IGBT modules of various structural elements cooled by natural convection and conduction have been created using the ANSYS IcePak software package. It is extremely time-consuming to use this full model for multiple-mission studies therefore a reduced order model in state space form has been developed to significantly reduce design time. The reduced order model has been trained using a single finite element model run with a universal power dissipation profile. This profile consisted of band limited white noise with a magnitude and frequency limit based on the combination of given devices and set of mission profiles. It has been shown that the state space model trained with such a profile reproduces the response to a wide variety of different power dissipation patterns typical for our application with an accuracy of about 2°C. Several different approaches for the choice of the state space model have been studied as well as proper selection of state space size and metrics for estimation of modeling error. It is suggested that the proposed method can be a universal way of extracting a reduced order model from the high fidelity combination of CFD and FEA models typical for power electronics applications, and possibly for a broader range of applications as well.

Pedestrian and Evacuation Dynamics 2008, 2009

... Yiqing Lin1, Igor Fedchenia1, Bob LaBarre1, and Robert Tomastik2 ... In this paper, we presen... more ... Yiqing Lin1, Igor Fedchenia1, Bob LaBarre1, and Robert Tomastik2 ... In this paper, we present an agent-based simulation model developed for a 2-story office building verified using the evacuation data collected using video cameras during fire drills in the building. ...

Physical Review E, 1999

An approximate expression describing the density dependence of vibrational energy relaxation rate... more An approximate expression describing the density dependence of vibrational energy relaxation rates in fluids in terms of thermodynamic and transport parameters of the fluid is developed on the basis of a classical statistical mechanical theory of vibrational energy relaxation of highly excited molecules in polyatomic solvents. The energy relaxation rate is expressed via the friction coefficient, which describes the interaction between solute oscillator and solvent molecules. The corresponding force-force time correlation function is expressed in terms of the dynamic structure factor of the solvent and the force of interaction between solute and solvent molecules. Approximating the dynamic structure factor appropriately leads to expressions for the density dependence of vibrational relaxation rates in terms of thermophysical solvent parameters. Using these expressions the density dependence of vibrational relaxation rates in supercritical ethane and propane both in the vicinity of the critical point and far from it are evaluated and compared with measured relaxation rates obtained under the same physical conditions. ͓S1063-651X͑99͒15710-6͔