The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform

Michael Rethmeier - One of the best experts on this subject based on the ideXlab platform.

  • Numerical assessment and experimental verification of the influence of the Hartmann effect in laser beam welding processes by steady magnetic fields
    International Journal of Thermal Sciences, 2016
    Co-Authors: Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier
    Abstract:

    Abstract Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential Equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solid–liquid phase transition was taken into account and the solidification was modelled by the Carman–Kozeny Equation for porous medium morphology. The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics.

  • about the influence of a steady magnetic field on weld pool dynamics in partial penetration high power laser beam welding of thick aluminium parts
    International Journal of Heat and Mass Transfer, 2013
    Co-Authors: Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier
    Abstract:

    Abstract A multi-physics numerical model was developed to investigate the influence of a steady magnetic field aligned perpendicular to the welding direction during partial penetration high power laser beam welding of aluminium in downhand position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential Equations were successfully solved with the finite element differential Equation solver COMSOL Multiphysics 4.2. The implemented material model used temperature-dependent properties up to evaporation temperature. Marangoni convection in the surface region of the weld pool, natural convection due to the gravitational field and latent heat of solid–liquid phase transition were taken into account. Solidification was modelled by the Carman–Kozeny Equation for porous media morphology. The flow pattern in the melt as well as the weld bead geometry were significantly changed by the induced Lorentz force distribution in the liquid metal. It reveals that the application of a steady magnetic field to laser beam welding with corresponding Hartmann numbers Ha2 ≈ 104 allows for a suppression of the characteristic wineglass-shape of the weld cross section caused by thermocapillary flow. The numerical results are in good agreement with experimental results obtained with welding of AlMg3 with a 16 kW disc laser. The steady magnetic field was delivered by permanent magnets mounted on both lateral sides of the weld specimen. The maximum magnetic flux density was around 500 mT. It shows, that the applied magnetic field has a predominant dissipating effect on the weld pool dynamics independently of its polarity.

  • numerical simulation of full penetration laser beam welding of thick aluminium plates with inductive support
    Journal of Physics D, 2012
    Co-Authors: Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier
    Abstract:

    A three-dimensional laminar steady-state numerical model was developed to investigate the influence of an alternating current (ac) magnetic field during high-power full-penetration laser welding on the weld pool dynamics and weld cross section of a 20 mm thick aluminium plate in flat position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential Equations were solved iteratively with the commercial finite element software COMSOL Multiphysics using temperature-dependent material properties up to evaporation temperature. Thermocapillary convection at the weld pool surfaces, natural convection and latent heat of solid–liquid phase transition were taken into account in this model. Solidification was modelled by the Carman–Kozeny Equation for porous media morphology. The ac magnet was mounted on the root side of the weld specimen. The magnetic field was aligned perpendicular to the welding direction. The flow pattern in the melt and thus also the temperature distribution were significantly changed by the application of oscillating magnetic fields. It was shown that the application of an ac magnetic field to laser beam welding allows for a prevention of the gravity drop-out. The simulation results are in good qualitative agreement with the experimental observations.

Christine Lafforgue - One of the best experts on this subject based on the ideXlab platform.

  • Use of fluorescent microorganisms to perform in vivo and in situ local characterization of microbial deposits
    Journal of Membrane Science, 2011
    Co-Authors: Sandra Beaufort, Sandrine Alfenore, Christine Lafforgue
    Abstract:

    This study presents an original method for in situ characterisation of the structure and organization of a microbial deposit accumulated on a membrane surface during filtration operations. The strategy is based on coupling macroscopic measurements (filtration results) and local observations at the microscopic level. This approach has been performed thanks to the use of self-fluorescent microorganisms (modified microorganisms) and the design of a specific filtration cell allowing a direct microscopic visualisation of the deposit to be performed without any treatment which could damage or modify the structure. Indeed the use of living fluorescent cells has allowed a non-destructive, in situ and in vivo, study of the deposits. As an example of application, the influence of microorganism size and morphology on the filtration performances and the deposit characteristics were examined in the case of dead-end microfiltration of model suspensions (yeasts and bacteria) obtained under controlled conditions. For these compact deposits the upper part of the deposits, corresponding to a 30 mu m thickness slice, could be precisely analysed at the microscopic level and for yeasts/bacteria mixed deposit, the local microorganisms organization in the slice could be analysed. For pure yeasts deposit, the porosity obtained by image analysis, 12%, was in agreement with the calculated value by Carman-Kozeny Equation using permeate flow measurements. (C) 2010 Elsevier B.V. All rights reserved.

  • Use of fluorescent microorganisms to perform in vivo and in situ local characterization of microbial deposits
    Journal of Membrane Science, 2010
    Co-Authors: Sandra Beaufort, Sandrine Alfenore, Christine Lafforgue
    Abstract:

    Abstract This study presents an original method for in situ characterisation of the structure and organization of a microbial deposit accumulated on a membrane surface during filtration operations. The strategy is based on coupling macroscopic measurements (filtration results) and local observations at the microscopic level. This approach has been performed thanks to the use of self-fluorescent microorganisms (modified microorganisms) and the design of a specific filtration cell allowing a direct microscopic visualisation of the deposit to be performed without any treatment which could damage or modify the structure. Indeed the use of living fluorescent cells has allowed a non-destructive, in situ and in vivo , study of the deposits. As an example of application, the influence of microorganism size and morphology on the filtration performances and the deposit characteristics were examined in the case of dead-end microfiltration of model suspensions (yeasts and bacteria) obtained under controlled conditions. For these compact deposits the upper part of the deposits, corresponding to a 30 μm thickness slice, could be precisely analysed at the microscopic level and for yeasts/bacteria mixed deposit, the local microorganisms organization in the slice could be analysed. For pure yeasts deposit, the porosity obtained by image analysis, 12%, was in agreement with the calculated value by Carman–Kozeny Equation using permeate flow measurements.

Marcel Bachmann - One of the best experts on this subject based on the ideXlab platform.

  • Numerical assessment and experimental verification of the influence of the Hartmann effect in laser beam welding processes by steady magnetic fields
    International Journal of Thermal Sciences, 2016
    Co-Authors: Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier
    Abstract:

    Abstract Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential Equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solid–liquid phase transition was taken into account and the solidification was modelled by the Carman–Kozeny Equation for porous medium morphology. The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics.

  • about the influence of a steady magnetic field on weld pool dynamics in partial penetration high power laser beam welding of thick aluminium parts
    International Journal of Heat and Mass Transfer, 2013
    Co-Authors: Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier
    Abstract:

    Abstract A multi-physics numerical model was developed to investigate the influence of a steady magnetic field aligned perpendicular to the welding direction during partial penetration high power laser beam welding of aluminium in downhand position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential Equations were successfully solved with the finite element differential Equation solver COMSOL Multiphysics 4.2. The implemented material model used temperature-dependent properties up to evaporation temperature. Marangoni convection in the surface region of the weld pool, natural convection due to the gravitational field and latent heat of solid–liquid phase transition were taken into account. Solidification was modelled by the Carman–Kozeny Equation for porous media morphology. The flow pattern in the melt as well as the weld bead geometry were significantly changed by the induced Lorentz force distribution in the liquid metal. It reveals that the application of a steady magnetic field to laser beam welding with corresponding Hartmann numbers Ha2 ≈ 104 allows for a suppression of the characteristic wineglass-shape of the weld cross section caused by thermocapillary flow. The numerical results are in good agreement with experimental results obtained with welding of AlMg3 with a 16 kW disc laser. The steady magnetic field was delivered by permanent magnets mounted on both lateral sides of the weld specimen. The maximum magnetic flux density was around 500 mT. It shows, that the applied magnetic field has a predominant dissipating effect on the weld pool dynamics independently of its polarity.

  • numerical simulation of full penetration laser beam welding of thick aluminium plates with inductive support
    Journal of Physics D, 2012
    Co-Authors: Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier
    Abstract:

    A three-dimensional laminar steady-state numerical model was developed to investigate the influence of an alternating current (ac) magnetic field during high-power full-penetration laser welding on the weld pool dynamics and weld cross section of a 20 mm thick aluminium plate in flat position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential Equations were solved iteratively with the commercial finite element software COMSOL Multiphysics using temperature-dependent material properties up to evaporation temperature. Thermocapillary convection at the weld pool surfaces, natural convection and latent heat of solid–liquid phase transition were taken into account in this model. Solidification was modelled by the Carman–Kozeny Equation for porous media morphology. The ac magnet was mounted on the root side of the weld specimen. The magnetic field was aligned perpendicular to the welding direction. The flow pattern in the melt and thus also the temperature distribution were significantly changed by the application of oscillating magnetic fields. It was shown that the application of an ac magnetic field to laser beam welding allows for a prevention of the gravity drop-out. The simulation results are in good qualitative agreement with the experimental observations.

Sandra Beaufort - One of the best experts on this subject based on the ideXlab platform.

  • Use of fluorescent microorganisms to perform in vivo and in situ local characterization of microbial deposits
    Journal of Membrane Science, 2011
    Co-Authors: Sandra Beaufort, Sandrine Alfenore, Christine Lafforgue
    Abstract:

    This study presents an original method for in situ characterisation of the structure and organization of a microbial deposit accumulated on a membrane surface during filtration operations. The strategy is based on coupling macroscopic measurements (filtration results) and local observations at the microscopic level. This approach has been performed thanks to the use of self-fluorescent microorganisms (modified microorganisms) and the design of a specific filtration cell allowing a direct microscopic visualisation of the deposit to be performed without any treatment which could damage or modify the structure. Indeed the use of living fluorescent cells has allowed a non-destructive, in situ and in vivo, study of the deposits. As an example of application, the influence of microorganism size and morphology on the filtration performances and the deposit characteristics were examined in the case of dead-end microfiltration of model suspensions (yeasts and bacteria) obtained under controlled conditions. For these compact deposits the upper part of the deposits, corresponding to a 30 mu m thickness slice, could be precisely analysed at the microscopic level and for yeasts/bacteria mixed deposit, the local microorganisms organization in the slice could be analysed. For pure yeasts deposit, the porosity obtained by image analysis, 12%, was in agreement with the calculated value by Carman-Kozeny Equation using permeate flow measurements. (C) 2010 Elsevier B.V. All rights reserved.

  • Use of fluorescent microorganisms to perform in vivo and in situ local characterization of microbial deposits
    Journal of Membrane Science, 2010
    Co-Authors: Sandra Beaufort, Sandrine Alfenore, Christine Lafforgue
    Abstract:

    Abstract This study presents an original method for in situ characterisation of the structure and organization of a microbial deposit accumulated on a membrane surface during filtration operations. The strategy is based on coupling macroscopic measurements (filtration results) and local observations at the microscopic level. This approach has been performed thanks to the use of self-fluorescent microorganisms (modified microorganisms) and the design of a specific filtration cell allowing a direct microscopic visualisation of the deposit to be performed without any treatment which could damage or modify the structure. Indeed the use of living fluorescent cells has allowed a non-destructive, in situ and in vivo , study of the deposits. As an example of application, the influence of microorganism size and morphology on the filtration performances and the deposit characteristics were examined in the case of dead-end microfiltration of model suspensions (yeasts and bacteria) obtained under controlled conditions. For these compact deposits the upper part of the deposits, corresponding to a 30 μm thickness slice, could be precisely analysed at the microscopic level and for yeasts/bacteria mixed deposit, the local microorganisms organization in the slice could be analysed. For pure yeasts deposit, the porosity obtained by image analysis, 12%, was in agreement with the calculated value by Carman–Kozeny Equation using permeate flow measurements.

Vjaceslav Avilov - One of the best experts on this subject based on the ideXlab platform.

  • Numerical assessment and experimental verification of the influence of the Hartmann effect in laser beam welding processes by steady magnetic fields
    International Journal of Thermal Sciences, 2016
    Co-Authors: Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier
    Abstract:

    Abstract Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential Equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solid–liquid phase transition was taken into account and the solidification was modelled by the Carman–Kozeny Equation for porous medium morphology. The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics.

  • about the influence of a steady magnetic field on weld pool dynamics in partial penetration high power laser beam welding of thick aluminium parts
    International Journal of Heat and Mass Transfer, 2013
    Co-Authors: Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier
    Abstract:

    Abstract A multi-physics numerical model was developed to investigate the influence of a steady magnetic field aligned perpendicular to the welding direction during partial penetration high power laser beam welding of aluminium in downhand position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential Equations were successfully solved with the finite element differential Equation solver COMSOL Multiphysics 4.2. The implemented material model used temperature-dependent properties up to evaporation temperature. Marangoni convection in the surface region of the weld pool, natural convection due to the gravitational field and latent heat of solid–liquid phase transition were taken into account. Solidification was modelled by the Carman–Kozeny Equation for porous media morphology. The flow pattern in the melt as well as the weld bead geometry were significantly changed by the induced Lorentz force distribution in the liquid metal. It reveals that the application of a steady magnetic field to laser beam welding with corresponding Hartmann numbers Ha2 ≈ 104 allows for a suppression of the characteristic wineglass-shape of the weld cross section caused by thermocapillary flow. The numerical results are in good agreement with experimental results obtained with welding of AlMg3 with a 16 kW disc laser. The steady magnetic field was delivered by permanent magnets mounted on both lateral sides of the weld specimen. The maximum magnetic flux density was around 500 mT. It shows, that the applied magnetic field has a predominant dissipating effect on the weld pool dynamics independently of its polarity.

  • numerical simulation of full penetration laser beam welding of thick aluminium plates with inductive support
    Journal of Physics D, 2012
    Co-Authors: Marcel Bachmann, Vjaceslav Avilov, Andrey Gumenyuk, Michael Rethmeier
    Abstract:

    A three-dimensional laminar steady-state numerical model was developed to investigate the influence of an alternating current (ac) magnetic field during high-power full-penetration laser welding on the weld pool dynamics and weld cross section of a 20 mm thick aluminium plate in flat position. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential Equations were solved iteratively with the commercial finite element software COMSOL Multiphysics using temperature-dependent material properties up to evaporation temperature. Thermocapillary convection at the weld pool surfaces, natural convection and latent heat of solid–liquid phase transition were taken into account in this model. Solidification was modelled by the Carman–Kozeny Equation for porous media morphology. The ac magnet was mounted on the root side of the weld specimen. The magnetic field was aligned perpendicular to the welding direction. The flow pattern in the melt and thus also the temperature distribution were significantly changed by the application of oscillating magnetic fields. It was shown that the application of an ac magnetic field to laser beam welding allows for a prevention of the gravity drop-out. The simulation results are in good qualitative agreement with the experimental observations.