The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Stefanie Reese - One of the best experts on this subject based on the ideXlab platform.
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Solid‐Shell Finite Elements for Tesselated Geometries
PAMM, 2012Co-Authors: Johannes Wimmer, Stefanie ReeseAbstract:Sandwich structures made of sheets of composite materials are in widespread use, particularly in the transportation industry. Finite Element simulation of the thin, tesselated structures with complex, three-dimensional material behaviour is a challenging task for the underlying Element Technology. In particular, frequently used linear isoparametric approaches exhibit unphysical stiffening phenomena. Recent developments in solid-shell finite Element Technology aim to overcome these undesirable effects. Here, they are applied to an example of a corrugated sandwich core under transversal compression. A study of convergence is conducted with respect to commercially available shell and solid finite Elements, and their ability to reproduce the bending dominated deformation state. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)
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sheet metal forming and springback simulation by means of a new reduced integration solid shell finite Element Technology
Computer Methods in Applied Mechanics and Engineering, 2011Co-Authors: Marco Schwarze, Ivaylo N. Vladimirov, Stefanie ReeseAbstract:Abstract The paper deals with the validation of a recently proposed hexahedral solid-shell finite Element in the field of sheet metal forming. Working with one integration point in the shell plane and an arbitrary number of integration points in thickness direction, highly non-linear stress states over the sheet thickness can be incorporated in an efficient way. In order to avoid volumetric locking and Poisson thickness locking at the level of integration points the enhanced assumed strain (EAS) concept with only one EAS degree-of-freedom is implemented. A key point of the formulation is the construction of the hourglass stabilization by means of different Taylor expansions. This leads to the advantage that the sensitivity with respect to mesh distortion is noticeably reduced. The hourglass stabilization includes the assumed natural strain (ANS) concept and a kind of B-Bar method. So transverse shear locking and volumetric locking are eliminated. The finite Element formulation incorporates a finite strain material model for plastic anisotropy as well as non-linear (Armstrong–Frederick type) kinematic and isotropic hardening. In this context the plastic anisotropy can be modeled by representing the yield surface and the plastic flow rule as functions of so-called structural tensors. The integration of the evolution equations is performed by means of an exponential map exploiting the spectral decomposition. The Element formulation and material model have been implemented into the commercial code ABAQUS/Standard by means of the UEL interface for user-defined Elements. Using an implicit time integration scheme numerical results for classical deep drawing simulations as well as springback predictions are presented in comparison to experimental measurements.
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A reduced integration finite Element Technology based on a thermomechanically consistent stabilisation for 3D problems
Computer Methods in Applied Mechanics and Engineering, 2010Co-Authors: Daniel Juhre, Stefanie ReeseAbstract:In this paper we suggest a new finite Element Technology for thermomechanically fully coupled problems. It is based on the method of reduced integration with hourglass stabilisation. The proposed formulation allows the evaluation of the additional thermal field at one Gauss point, e.g. in the centre of the Element. One crucial aspect is the Taylor expansion of all constitutively dependent variables, as e.g. the heat flux, the internal and the external rates of dissipation, with respect to the centre of the Element. In this way a so-called thermal hourglass stabilisation, analogously to the classical mechanical hourglass stabilisation, is derived. The thermal stabilisation parameters are defined well and the computational efficiency which comes along with the consistent formulation is very high. The new Element formulation is applied on thermomechanically coupled problems of finite elastoplasticity. It can be also easily used in the context of other multi-field problems.
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A new solid‐shell finite Element Technology incorporating plastic anisotropy in forming simulations
AIP Conference Proceedings, 2007Co-Authors: Stefanie Reese, Ivaylo N. Vladimirov, Marco SchwarzeAbstract:In the recent years shell finite Element formulations which include only displacement degrees‐of‐freedom, the so‐called solid‐shells, have been successfully applied in sheet metal forming (see e.g. [1]). A very efficient strategy to deal with the problem of locking which occurs in bending‐dominated problems and in the limit of incompressibility is the method of reduced integration with hourglass stabilization [12]. Further advantages of these finite Element technologies are their robustness with respect to severe mesh distortion and the low computational cost. A disadvantage is, however, the necessity to develop a suitable hourglass stabilization which adapts to both, the changing geometry and the usually highly non‐linear material behaviour. Most earlier finite Element technologies are based on the assumption that the material behaviour is initially isotropic. In the present contribution we develop an approach to include initial and deformation‐induced anisotropy. Prerequisite for that is the development of a suitable material law. In contrast to many other current papers ([10], [13], [2], [7], [14]) we aim at a purely continuum mechanical modelling to arrive at optimal numerical efficiency.
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On a new finite Element Technology for electromagnetic metal forming processes
Archive of Applied Mechanics, 2005Co-Authors: Stefanie Reese, Bob Svendsen, Marcus Stiemer, J. Unger, Marco Schwarze, H. BlumAbstract:The increasing need for lightweight building components has led to the development of new methods to manufacture such components. A promising concept is the systematic application of high-speed metal forming methods. Electromagnetic forming is one such method. Here, the deformation of the workpiece is driven by the Lorentz force which results from the interaction of a current generated in the workpiece with a magnetic field generated by a coil adjacent to the workpiece. This force represents an additional volume- or body-force density contribution in the balance of linear momentum. The numerical treatment of the coupled set of partial differential equations for the mechanical and electromagnetic fields can be made more efficient from the computational point of view by using the finite Element Technology suggested here, which is based on reduced integration and hourglass stabilisation. The main idea behind this new Technology is to expand the constitutive quantities in a Taylor expansion with respect to a point on the local coordinate axis in the thickness direction. The result is a weak system of equations which decomposes into a part to be evaluated in two Gauss points and in addition the so-called hourglass stabilisation to be computed analytically.
Marco Schwarze - One of the best experts on this subject based on the ideXlab platform.
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sheet metal forming and springback simulation by means of a new reduced integration solid shell finite Element Technology
Computer Methods in Applied Mechanics and Engineering, 2011Co-Authors: Marco Schwarze, Ivaylo N. Vladimirov, Stefanie ReeseAbstract:Abstract The paper deals with the validation of a recently proposed hexahedral solid-shell finite Element in the field of sheet metal forming. Working with one integration point in the shell plane and an arbitrary number of integration points in thickness direction, highly non-linear stress states over the sheet thickness can be incorporated in an efficient way. In order to avoid volumetric locking and Poisson thickness locking at the level of integration points the enhanced assumed strain (EAS) concept with only one EAS degree-of-freedom is implemented. A key point of the formulation is the construction of the hourglass stabilization by means of different Taylor expansions. This leads to the advantage that the sensitivity with respect to mesh distortion is noticeably reduced. The hourglass stabilization includes the assumed natural strain (ANS) concept and a kind of B-Bar method. So transverse shear locking and volumetric locking are eliminated. The finite Element formulation incorporates a finite strain material model for plastic anisotropy as well as non-linear (Armstrong–Frederick type) kinematic and isotropic hardening. In this context the plastic anisotropy can be modeled by representing the yield surface and the plastic flow rule as functions of so-called structural tensors. The integration of the evolution equations is performed by means of an exponential map exploiting the spectral decomposition. The Element formulation and material model have been implemented into the commercial code ABAQUS/Standard by means of the UEL interface for user-defined Elements. Using an implicit time integration scheme numerical results for classical deep drawing simulations as well as springback predictions are presented in comparison to experimental measurements.
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A new solid‐shell finite Element Technology incorporating plastic anisotropy in forming simulations
AIP Conference Proceedings, 2007Co-Authors: Stefanie Reese, Ivaylo N. Vladimirov, Marco SchwarzeAbstract:In the recent years shell finite Element formulations which include only displacement degrees‐of‐freedom, the so‐called solid‐shells, have been successfully applied in sheet metal forming (see e.g. [1]). A very efficient strategy to deal with the problem of locking which occurs in bending‐dominated problems and in the limit of incompressibility is the method of reduced integration with hourglass stabilization [12]. Further advantages of these finite Element technologies are their robustness with respect to severe mesh distortion and the low computational cost. A disadvantage is, however, the necessity to develop a suitable hourglass stabilization which adapts to both, the changing geometry and the usually highly non‐linear material behaviour. Most earlier finite Element technologies are based on the assumption that the material behaviour is initially isotropic. In the present contribution we develop an approach to include initial and deformation‐induced anisotropy. Prerequisite for that is the development of a suitable material law. In contrast to many other current papers ([10], [13], [2], [7], [14]) we aim at a purely continuum mechanical modelling to arrive at optimal numerical efficiency.
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On a new finite Element Technology for electromagnetic metal forming processes
Archive of Applied Mechanics, 2005Co-Authors: Stefanie Reese, Bob Svendsen, Marcus Stiemer, J. Unger, Marco Schwarze, H. BlumAbstract:The increasing need for lightweight building components has led to the development of new methods to manufacture such components. A promising concept is the systematic application of high-speed metal forming methods. Electromagnetic forming is one such method. Here, the deformation of the workpiece is driven by the Lorentz force which results from the interaction of a current generated in the workpiece with a magnetic field generated by a coil adjacent to the workpiece. This force represents an additional volume- or body-force density contribution in the balance of linear momentum. The numerical treatment of the coupled set of partial differential equations for the mechanical and electromagnetic fields can be made more efficient from the computational point of view by using the finite Element Technology suggested here, which is based on reduced integration and hourglass stabilisation. The main idea behind this new Technology is to expand the constitutive quantities in a Taylor expansion with respect to a point on the local coordinate axis in the thickness direction. The result is a weak system of equations which decomposes into a part to be evaluated in two Gauss points and in addition the so-called hourglass stabilisation to be computed analytically.
Ivaylo N. Vladimirov - One of the best experts on this subject based on the ideXlab platform.
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sheet metal forming and springback simulation by means of a new reduced integration solid shell finite Element Technology
Computer Methods in Applied Mechanics and Engineering, 2011Co-Authors: Marco Schwarze, Ivaylo N. Vladimirov, Stefanie ReeseAbstract:Abstract The paper deals with the validation of a recently proposed hexahedral solid-shell finite Element in the field of sheet metal forming. Working with one integration point in the shell plane and an arbitrary number of integration points in thickness direction, highly non-linear stress states over the sheet thickness can be incorporated in an efficient way. In order to avoid volumetric locking and Poisson thickness locking at the level of integration points the enhanced assumed strain (EAS) concept with only one EAS degree-of-freedom is implemented. A key point of the formulation is the construction of the hourglass stabilization by means of different Taylor expansions. This leads to the advantage that the sensitivity with respect to mesh distortion is noticeably reduced. The hourglass stabilization includes the assumed natural strain (ANS) concept and a kind of B-Bar method. So transverse shear locking and volumetric locking are eliminated. The finite Element formulation incorporates a finite strain material model for plastic anisotropy as well as non-linear (Armstrong–Frederick type) kinematic and isotropic hardening. In this context the plastic anisotropy can be modeled by representing the yield surface and the plastic flow rule as functions of so-called structural tensors. The integration of the evolution equations is performed by means of an exponential map exploiting the spectral decomposition. The Element formulation and material model have been implemented into the commercial code ABAQUS/Standard by means of the UEL interface for user-defined Elements. Using an implicit time integration scheme numerical results for classical deep drawing simulations as well as springback predictions are presented in comparison to experimental measurements.
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A new solid‐shell finite Element Technology incorporating plastic anisotropy in forming simulations
AIP Conference Proceedings, 2007Co-Authors: Stefanie Reese, Ivaylo N. Vladimirov, Marco SchwarzeAbstract:In the recent years shell finite Element formulations which include only displacement degrees‐of‐freedom, the so‐called solid‐shells, have been successfully applied in sheet metal forming (see e.g. [1]). A very efficient strategy to deal with the problem of locking which occurs in bending‐dominated problems and in the limit of incompressibility is the method of reduced integration with hourglass stabilization [12]. Further advantages of these finite Element technologies are their robustness with respect to severe mesh distortion and the low computational cost. A disadvantage is, however, the necessity to develop a suitable hourglass stabilization which adapts to both, the changing geometry and the usually highly non‐linear material behaviour. Most earlier finite Element technologies are based on the assumption that the material behaviour is initially isotropic. In the present contribution we develop an approach to include initial and deformation‐induced anisotropy. Prerequisite for that is the development of a suitable material law. In contrast to many other current papers ([10], [13], [2], [7], [14]) we aim at a purely continuum mechanical modelling to arrive at optimal numerical efficiency.
Eung Seok Kim - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Runoff According to Application of SWMM-LID Element Technology (II): Parameter Uncertainty Analysis
Journal of the Korean Society of Hazard Mitigation, 2020Co-Authors: Eung Seok KimAbstract:An increase in the ratio of impermeable area due to urban watersheds and industrial development has led to an increase in nonpoint source pollution and floodplains. In order to solve these problems, development and application of low impact development (LID), which is a rainwater management facility, is actively underway. In this study (I), parameters and ranges applied to the Storm Water Management Model-Low Impact Development (SWMM-LID) model are examined. To this end, 100 scenarios were created through the simulation method within the parameter range, and the sensitivity of peak and total runoff to the influence of the parameters of each Element Technology dealing with runoff was analyzed. As a result, bio retention cell, green roof, rain garden, rain barrell, in the given order, showed a sensitive response. However, since the LID Element Technology itself is intended to store low-frequency small-scale rainfall, it is important to understand the degree of rainfall, from low to high frequency. Further, the results of this study can be used as basic data for the design and development of LID Element Technology and performance verification of LID facilities.
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Analysis of Runoff According to Application of SWMM-LID Element Technology (II): Parameter Uncertainty Analysis
Journal of the Korean Society of Hazard Mitigation, 2020Co-Authors: Eung Seok KimAbstract:This study quantitatively analyzed the degree of uncertainty associated with runoff based on the sensitivity analysis of runoff parameters using Low Impact Development (LID) Element Technology of study (I). Uncertainty was analyzed for parameter uncertainty, uncertainty of runoff, and uncertainty about the degree of parameter and runoff. Parameter uncertainty indices showed lower uncertainty indices as a whole and uncertainty indices of peak runoff were higher than that of total runoff in runoff uncertainty. The reason for this is that the LID Element Technology itself is intended to store low-frequency small-scale rainfall, so that the uncertainty index of peak rainfall seems to be highly uncertain. As a result of the analysis of uncertainty degree associated with runoff, it was found that the uncertainty of storage depth of bio retention cell and rain garden was low, while the heaviness parameters of rain barrel had the highest uncertainty index. In future experiments and research, it is necessary to modify the parameter range suitable for Korea, which will be helpful for urban development, reduction of nonpoint source pollution, and designing of low frequency rainfall storage facilities.
Helen L. Reed - One of the best experts on this subject based on the ideXlab platform.
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Experiments on Discrete Roughness Element Technology for Swept-Wing Laminar Flow Control
AIAA Journal, 2019Co-Authors: William S. Saric, David E. West, Matthew W. Tufts, Helen L. ReedAbstract:Micrometer-sized spanwise-periodic discrete roughness Elements (DREs) were applied to and tested on a 30 deg swept-wing model in order to study their effects on boundary-layer transition in flight ...
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Flight Test Experiments on Discrete Roughness Element Technology for Laminar Flow Control
53rd AIAA Aerospace Sciences Meeting, 2015Co-Authors: William S. Saric, David E. West, Matthew W. Tufts, Helen L. ReedAbstract:Micron-sized, spanwise-periodic, discrete roughness Elements (DREs) were applied to and tested on a 30° swept-wing model in order to study their effects on boundary-layer transition in flight where stationary crossflow waves are the dominant instability. Significant improvements have been made to previous flight experiments in order to more reliably determine and control the model angle of attack (α) and unit Reynolds number (Re′) in order to minimize the uncertainties that DREs have on swept-wing, laminar-turbulent transition. Two interchangeable leading-edge surface-roughness configurations were tested: highly polished and painted. The baseline transition location for the painted leading edge (increased surface roughness) was unexpectedly farther aft than the polished. Transport unit Reynolds numbers were achieved using a Cessna O-2A Skymaster. Infrared thermography, coupled with a post-processing code, was used to globally extract a quantitative boundary-layer transition location. Each DRE configuration was compared to curve-fitted baseline data in order to determine increases or decreases in percent laminar flow while accounting for the influence of small differences in Re' and α. Linear Stability Theory (LST) guided the DRE configuration test matrix. In total, 63 flights were completed, where only 30 of those flights resulted in useable data. While the results of this research have not reliably confirmed the use of DREs as a viable laminar flow control technique in the flight environment, it has become clear that significant computational studies, specifically direct numerical simulation (DNS) of these particular DRE configurations on this model geometry and flight conditions, are a necessity in order to better understand the influence that DREs have on laminar-turbulent transition.