bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling and simulation of heat exchange and transport in a geothermal plant
Authors: Koch David , Ehlers Wolfgang 
Published: December 2014

AbstractThe production of energy by use of the high temperature in the earth's mantle has played an increasingly important role in recent years. However, large uncertainties concerning the conditions in the subsurface make it difficult to use power plants efficiently. An appropriate modelling and simulation of the heat exchange and transport provides a promising tool for further investigations of the process and optimisation of the productivity. Starting from the isothermal state at high temperatures, a cold fluid is injected through a borehole into a porous rock by applying a pressure difference between at least two wells. Passing the fractured rock, the water is heated at the crack interfaces. In addition to the convection of the temperature due to the water flow, the conduction of heat in the rock and the water has to be considered. The modelling approach of this coupled process is based on the Theory of Porous Media (TPM). Both, the rock and the water, are assumed to be materially incompressible and the thermal expansion is solely considered for the fluid, since the expansion of the rock is negligible for the occurring temperature differences. Furthermore, it is assumed that the subsurface is saturated with water. To solve the generated initial‐boundary‐value problem, the governing primary variables of the coupled model are spatially approximated by mixed finite elements and the time discretisation is carried out by an implicit Euler time‐integration scheme. Since in the considered problem the convective transport is dominant, a streamline upwinding scheme is used for the numerical stabilisation to obtain non‐oscillatory solutions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model reduction of porous‐media problems using proper orthogonal decomposition
Authors: Otto Davina , Ehlers Wolfgang 
Published: December 2014

AbstractIn the context of finite‐element simulations of porous media, computing time and numerical effort is an important issue because the number of degrees of freedom of such coupled problems can become very large. Following this, model reduction plays an important role. A broad variety of materials exhibit a porous microstructure. In order to evaluate the overall response of these materials, a macroscopic continuum‐mechanical modelling approach is used. Therefore, the complex inner structure of porous media is regarded in a multi‐phasic and multi‐component manner by means of the well‐founded Theory of Porous Media (TPM). The mechanical behaviour of porous media is solved using the Finite‐Element Method (FEM).The basic idea of model reduction is to transform a high dimensional system, in terms of the system's degrees of freedom, to a low dimensional subspace to minimise the computational effort while maintaining the accuracy of the solution. The method of proper orthogonal decomposition (POD) can be seen as a method to approximate a given data set with a low dimensional subspace. Furthermore, the POD method is independent of the type of the model and can be used for nonlinear systems as well as for systems of second order. In several applications, such as consolidation problems of partially saturated soils, commonly occurring motion sequences can be found, which can be used as typical “snapshots” of the system. Therefore, the application of the POD method to the simulation of porous media is discussed in the present contribution. Investigated computations of a biphasic standard problem show that the POD method reduces the numerical effort to solve the linearised system of equations in each iteration step. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Powder compaction. Experiments, modeling and simulation
Authors: Rothe Steffen , Hartmann Stefan 
Published: December 2014

AbstractField‐assisted sintering technology (FAST) is a combined thermal and mechanical loading process to compact and sinter a powder material within one process step. In this short essay a constitutive model of thermo‐viscoplasticity is proposed representing most of the phenomena observed in the experiments. The constitutive model is calibrated to the experimental data and some predicted experiments are compared with constitutive model showing appropriate results. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the necessity of alternative approaches towards finite elastoplasticity
Authors: Schröder Bettina , Kuhl Detlef 
Published: December 2014

AbstractIn order to simulate elastoplasticity within metal forming processes different approaches towards numerical implementation have been realized. Nevertheless, most of them or consider only the quasistatic case or use distinct time discretization schemes for the balance and the evolution equations. In the following, the effects of latter will be outlined on the basis of a numerical example exploiting a conventional ansatz towards finite elastoplasticity. This access should serve as a motivation for identifying why it is still important to investigate the implementation of elastoplastic phenomena beyond the well established methods. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of Self‐Healing phenomena in a Polymer matrix within the Framework of the Theory of Porous Media
Authors: Specht Steffen , Bluhm Joachim , Schröder Jörg 
Published: December 2014

AbstractIn this work, a multiphase material model will be presented in order to simulate self‐healing effects in a polymer. The material model is developed using the Theory of Porous Media (TPM). In order to describe the damage behavior of the polymer, the well known (1 − D)‐approach is included, and for the description of the healing, a phase change between the liquid like healing agents and the solid healed material is considered. This phase change depends on the amount of catalysts inside the polymer matrix. The applicability of the developed model, in order to describe the time dependency of the healing mechanism, will be shown by a virtual experiment of a self‐healing tapered double cantilever beam (TDCB). (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damage model for ferroelectric materials and its applications to multilayer actuators
Authors: Gellmann Roman , Ricoeur Andreas 
Published: December 2014

AbstractIn this paper a damage model for ferroelectric materials is presented. It is implemented in terms of a user element in the commercial FEM‐code Abaqus. The model is based on micromechanical considerations of domain switching and its interaction with microcrack growth and coalescence. Finite element analysis of a multilayer actuator is performed, showing principal stresses leading to crack initiation and damage of the actuator. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A condensed microelectromechanical constitutive and damage model for tetragonal ferroelectrics
Authors: Lange Stephan , Ricoeur Andreas 
Published: December 2014

AbstractA condensed model for ferroelectric solids with tetragonal unit cells is presented. The approach is microelectromechanically and physically motivated, considering discrete switching processes on the level of unit cells and quasi‐continuous evolution of inelastic fields on the domain wall level. To calculate multiple grain interactions an interaction tensor is introduced. Hysteresis loops are simulated for pure electric and electromechanical loading, demonstrating e.g. the influence of a compressive preload on the poling process and interaction between statistically arranged crystallits. The residual stresses and the corresponding principle stresses are used to simulate fatigue damage in ferroelectric materials. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational Based Stability Analysis in Coupled Electro‐Mechanics at Finite Strains
Authors: Vallicotti Daniel , Zäh Dominic , Miehe Christian 
Published: December 2014

AbstractSmart or functional materials are in focus in broad fields of recent research. In particular, electroactive polymers (EAPs) with their large actuator strains are used for innovative design in robotics. These materials become practical as soon as the material is robust, reliable and long lived. However, EAPs suffer from different types of instabilities, such as unstable thinning of actuators, local buckling induced by coexistent states and electrical breakdown. One distinguishes between structural instability, i.e. instabilities in the global structural response like buckling or wrinkling and local or material instability, e.g. the formation of microstructures and phase decompositions. These effects are well known and analyzed for purely mechanical phenomena, but not fully developed in the context of electro‐mechanically coupled problems. To this end, we develop new variational‐based stability criteria in finite electro‐elastostatics, by postulating an electro‐mechanical quasi‐convexity condition for weakly convex energy and weakly convex‐concave energy‐enthalpy formulations. Starting from distinct variational principles, we develop criteria for local and global stability and construct stability checks, which accompany equilibrium paths for the detection of critical points in finite element models. Numerical examples validate the developed concepts for boundary value problems. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A thermodynamically consistent and numerically stable formulation for the description of diffusion in polymeric gels
Authors: Krischok Andreas , Tkachuk Mykola , Linder Christian 
Published: December 2014

AbstractThis work proposes a stable equal‐order element formulation for polymeric gels at finite deformations. From the numerical point of view the description of flow in incompressible elastic media such as gels leads to singularities in the coupled system of equations of the corresponding finite element discretization unless certain requirements are met to satisfy the Ladyženskaja‐Babuška‐Brezzi (LBB) condition. The proposed computationally efficient mixed enhanced assumed strain method allows to satisfy the LBB condition and to account for locking phenomena without the requirement of higher order interpolations for the displacement field. The proposed model can be employed in various fields where the modeling of flow in incompressible media undergoing finite deformations is of interest such as Computational Soil Mechanics or Computational Biomechanics. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of Debonding on Thermal Conduction and Humidity Diffusion at Mesoscale of Concrete
Authors: Wu Tao , Wriggers Peter 
Published: December 2014

AbstractIn order to numerically describe the phenomena that the debonding at interfacial transition zone (ITZ) between hardened cement paset (HCP) and aggregates could affect thermal conduction and humidity diffusion in the concrete, cohesive zone model (CZM) characterized by traction‐separation law combined with micromechanically motivated thermal flux‐separation relation and diffusion flux‐separation relation is established at ITZ. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cardiovascular fluid‐structure interaction: A partitioned approach utilizing the p‐FEM
Authors: Radtke Lars , Larena‐Avellaneda Axel , Kölbel Tilo , Debus Eike Sebastian , Düster Alexander 
Published: December 2014

AbstractIn this paper, we propose a technique for simulating the fluid‐structure interaction in blood vessels. A partitioned approach is used, which allows for an independent discretization of the fluid domain and the structural domain. We choose the finite volume method to solve the Navier‐Stokes equations and the p‐version of the finite element method (p‐FEM) to solve the equations of geometrically nonlinear structural dynamics. The solution strategy can be seen as a first approach towards a comprehensive study of the hemodynamics in vascular substitutes with the goal of improving their long term functionality. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of a long slender structure in turbulent flow
Authors: Tschisgale Silvio , Fröhlich Jochen 
Published: December 2014

AbstractThe dynamic behaviour of a long slender structure in turbulent flow can vary considerably, depending on the particular excitation. Regimes from simple static deformation, over periodic to irregular and chaotic behaviour are observed. An example is the self‐excited periodic motion of a long slender structure in cross flow. In such cases, the fluid flow and the structure movement are strongly coupled. The paper presents a robust partitioned coupling approach based on the Immersed Boundary Method which integrates the geometrically exact Cosserat rod model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Analysis of Heat Transfer for Cooling of Photovoltaic Cells
Authors: Lotfi Abdelhakim 
Published: December 2014

AbstractPhotovoltaic cells are devices which convert solar radiation directly into electricity. However, solar radiation increases the photovoltaic cells temperature [1] [2]. The temperature has an influence on the degradation of the cell efficiency and the lifetime of a PV cell. This work reports on a cooling water technique for cells, whereby the cooling system was placed at the front surface of the cells to dissipate away excess heat and to block unwanted radiation. Using water as a cooling medium for the cells, the overheating of closed panel is greatly reduced without prejudicing luminosity and water acts as a filter to remove a portion of solar spectrum in the infrared band but allows transmission of the visible spectrum most useful for the PV operation. The aims of this study are to develop a 3D thermal model to simulate the cooling and heat transfer in Photovoltaic panel and recommend a cooling technique for the PV panel. In order to have a good estimation for the temperature distribution, the three‐dimensional flow and heat transfer across the cooling block is investigated numerically by solving the continuity, momentum and energy equations using FLUENT. The second objective of this work is to study the influence of the geometrical dimensions of the panel, water mass flow rate and water inlet temperature on the flow distribution and the solar panel temperature. The results obtained by the model are compared with experimental results from testing the prototype of the cooling device. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Assessment of Stabilization Techniques for Coupled Poro‐plastic Analysis using Low‐Order Finite Elements
Authors: Khisamitov Ildar , Alsahly Abdullah , Meschke Günther 
Published: December 2014

AbstractFor the numerical modeling of geomaterials in general, and soft, water saturated soils in particular, the nonlinear constitutive behavior of the skeleton and its strong coupling with the pore fluid must be considered. In the limit of zero compressibility of water and soil grains and very low permeability (which correspond to the classical “undrained” assumption in soil mechanics), the functions used to interpolate displacements and pressures must fulfill either the Ladyženskaja‐Babuška‐Brezzi inf‐sup condition [1] or the much simpler patch test proposed by Zienkiewicz and Taylor. These requirements exclude the use of elements with equal order of linear interpolation for pressures and displacements, for which spurious oscillations may appear. Low‐order elements with linear approximation of displacements and pressure variables may be used if stabilization techniques are employed. The work is concerned with the numerical assessment and investigation of several stabilization techniques and their application to strain localization problems in coupled poro‐plastic analyses of soft, saturated soils [2,3]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of numerical homogenization techniques in BT‐CFO multiferroic particle composites
Authors: Wang Zhibin , Avakian Artjom , Ricoeur Andreas 
Published: December 2014

AbstractThis work is restricted to linear material behavior, i.e. the structure is considered to be in a perfectly poled state. Different numerical homogenization methods are investigated and used to calculate effective properties of a 0‐2 composite modelled in reprensentative volume elements. Bariumtitanate (BT) and cobaltferrite (CFO) are employed in the Finite Element model, where the roles of matrix and inclusion are mutable in principle. Mixed magnetoelectromechanical boundary conditions based on different homogenization theories are applied to the model. The calculated macroscopic behaviors described by the different approaches are compared and presented in the paper. The special focus is on the prediction of coefficients of magnetoelectric coupling with respect to an optimization of the structural arrangement of the composite. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of a viscous soft dielectric elastomer generator operating in an electrical circuit
Authors: Bortot Eliana , Denzer Ralf , Menzel Andreas , Gei Massimiliano 
Published: December 2014

AbstractDielectric Elastomer Generators (DEGs) are able to convert mechanical work into electric energy. A soft dielectric elastomer generator can be modelled as a strain‐dependent variable capacitor undergoing large viscoelastic deformation. In this work we analyze an electrical circuit for energy harvesting in which the DEG is stretched periodically by a source of mechanical work. Since these devices undergo a high number of electro‐mechanical loading cycles at large deformation, it turns out that viscous effects must be carefully taken into account as they strongly affect the generator performance. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of the Crosstalk Phenomenon within Electro‐Magnetic Systems from a Differential‐Algebraic Equations Point of View
Authors: Niroomand Rad Helia , Steinbrecher Andreas 
Published: December 2014

AbstractIn this paper, we consider modeling of the crosstalk phenomenon in electro‐magnetic systems and, in particular, in electrical circuit where electrical devices such as inductors, capacitors, and resistors are located closely together. In principle, we model the crosstalk phenomenon by bilateral coupling of two fundamental components: Electro‐magnetic induction and dynamical behavior of the electrical circuit. First, in order to describe the electro‐magnetic induction the Maxwell equations are presented. Then, to prescribe dynamical behavior of the circuit we introduce the modified nodal analysis system which is derived by the circuit equations. Finally suitable coupling relations will be outlined. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Acceleration methods for the convergence of vector sequences applied to multi‐physics problems
Authors: Erbts Patrick , Düster Alexander 
Published: December 2014

AbstractPartitioned solution approaches are well‐known strategies to solve coupled problems and have demonstrated their applicability in a wide range of multi‐physical simulations. Applying a partitioned approach opens up numerous possibilities, such as connecting different solvers or combining non‐matching meshes and time‐step sizes. On the other hand such a procedure has the drawback of only conditional stability, leading to poor convergence rates or ‐ as a worst case scenario ‐ to divergent behavior. In this contribution, we will give an interpretation of the iterative coupling process as a sequence of vectors converging to an unknown limit, which indeed represents a solution to the coupled problem. In order to improve computational efficiency, there are several practicable methods to accelerate the convergence of vector sequences. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled differential algebraic equations in the simulation of flexible multibody systems with hydrodynamic force elements
Authors: Fiedler Robert , Arnold Martin 
Published: December 2014

AbstractThe mathematical modelling of elastohydrodynamic bearings in combustion engines leads to a coupled system of (partial) differential algebraic equations, which is represented by a flexible multibody system model of the engine including crankshaft and bearing and by the Reynolds equation that describes the non‐linear effects in the fluid film. The hydrodynamic forces depend strongly on the position and the elastic deformation of crankshaft and bearing shell. We discuss the influence of the spatial discretization on accuracy and numerical effort. Since a fine spatial discretization substantially slows down the numerical solution, we propose a semi‐analytical method based on singular perturbation theory to speed‐up time integration. Numerical tests for a simplified benchmark problem illustrate the advantages of this approach. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐local modeling of size effects in amorphous metals
Authors: Klusemann Benjamin , Xiao Tao , Bargmann Swantje 
Published: December 2014

AbstractThe present contribution is concerned with the modeling of lengthscale‐dependent behavior of submicron sized amorphous metal. As these samples reach the size of a few hundred nanometers, the main deformation mechanism changes from catastrophic to a stable shear localization. For the underlying model description, we resort to a thermodynamically consistent approach. Klusemann & Bargmann [1] presented results for a small strain formulation which was extended recently to finite strains by Bargmann et al. [2]. The non‐local material model is formulated with a dual mixed finite element approach. It is shown that the proposed finite deformation model is well suited to predict the stable shear localization process in submicron‐sized metallic glasses and its size effect. The model confirms the experimental observation that with decreasing sample size the shear localization process becomes stable and delayed. The finite deformation model is able to predict the failure process in submicron‐sized metallic glasses as well as the delay of it with decreasing sample size. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydrodynamic Behaviour of Very Large Floating Structures (VLFS) in Waves
Authors: König Marcel , Ferreira González Daniel , Abdel‐Maksoud Moustafa , Düster Alexander 
Published: December 2014

AbstractAn effective way to solve multiphysics scenarios in general and fluid‐structure interaction problems in particular is to rely on a partitioned solution approach, which allows for the use of different discretisation schemes and specialised solvers for each of the individual subdomains. A coupling interface, which manages the transfer of the field quantities between the solvers, has been developed and successfully applied to a great variety of coupled problems. Different predictor and relaxation techniques have been implemented to stabilize the solution algorithm and accelerate its convergence. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bounds and an isotropically self‐consistent singular approximation of the linear elastic properties of cubic crystal aggregates for application in materials design
Authors: Lobos Mauricio , Böhlke Thomas 
Published: December 2014

AbstractFor crystal aggregates, the orientation distribution of single crystals affects the anisotropic linear elastic properties. In the singular approximation for cubic materials, this influence is reflected by a fourth‐order texture coefficient. From this approximation, the statistical bounds of Voigt, Reuss and Hashin‐Shtrikman, and an isotropically self‐consistent singular approximation can be obtained. Here, an approximation is called isotropically self‐consistent, if, for a vanishing texture, it results in the isotropic self‐consistent approximation. The isotropically self‐consistent singular approximation has the following advantages: i) it lies between the bounds of Voigt, Reuss and Hashin‐Shtrikman, ii) it offers a useful approximation of the effective material behavior of textured anisotropic polycrystals, and iii) it can be used for material design purposes tailoring anisotropic properties mainly depending on the crystallographic texture. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)