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Maximum flow of complex manufacturing networks Omar, Yamila ; Plapper, Peter in Procedia CIRP (2019) Detailed reference viewed: 54 (3 UL)Maximum-Entropy Meshfree Method for the Reissner-Mindlin Plate Problem based on a Stabilised Mixed Weak Form Hale, Jack ; Scientific Conference (2012) Meshless methods, such as the Element Free Galerkin (EFG) method, hold various advantages over mesh-based techniques such as robustness in large-deformation problems and high continuity. The Reissner ... [more ▼] Meshless methods, such as the Element Free Galerkin (EFG) method, hold various advantages over mesh-based techniques such as robustness in large-deformation problems and high continuity. The Reissner-Mindlin plate model is a particularly popular choice for simulating thin structures. It is well known in the Finite Element and Meshless literature that the simplest numerical treatments of the Reissner-Mindlin model lead to shear-locking which in turn produces erroneous results. This is due to the inability of the approximation functions to satisfy the Kirchoff constraint in the thin-plate limit. A recent advance in the area of meshless approximation schemes are Maximum-Entropy (MaxEnt) approximants. MaxEnt schemes provide a weak Kronecker-delta property on convex node sets which allows the direct imposition of Dirichlet (essential) boundary conditions. In this work, we derive a shear-locking free meshless method using MaxEnt approximants by consider- ing a stabilised mixed weak form. We include a scalar parameter which splits the energy from the shear bilinear form into two parts; the first is formed from the displacement fields only and the second from the independently interpolated shear strain field and the displacement fields. This splitting greatly eases the satisfaction of the LBB stability condition. We then eliminate the independently interpolated shear strain field using a localised projection operator, related to the “volume-averaged pressure” technique, which produces a final system of equations in the original displacement unknowns only. We show the good performance of the method for a variety of test problems. [less ▲] Detailed reference viewed: 54 (2 UL)Measure and Failure Cost Analysis: Selecting Risk Treatment Strategies Gericke, Kilian ; ; Blessing, Lucienne in Proceedings of the 17th International Conference on Engineering Design (2009) Project Risk Management is used to prevent projects to fail. Despite its proven use, barriers still exist that hinder implementation and use by inexperienced persons. One barrier is the additional effort ... [more ▼] Project Risk Management is used to prevent projects to fail. Despite its proven use, barriers still exist that hinder implementation and use by inexperienced persons. One barrier is the additional effort required by the process of Project Risk Management itself. An additional barrier is the lack of systematic support of important steps like the selection of an appropriate risk treatment strategy. The decision which strategy to select is a challenging task due to the uncertain character of the addressed issue. The trade-off of the perceived additional efforts caused by a method must be addressed by an enhancement of the cost-benefit ratio of the applied methods and implemented risk treatment measures. Decision making using the proposed Measure and Failure Cost Analysis (MFCA) method enables the Risk Manager to compare the arising costs of different risk treatment strategies caused by an occurring risk and risk treatment measures. It is based on a de-escalation principle which analyzes the course of the impact of an event. The method compares the reaction rate of different strategies and proposes the favorite one. [less ▲] Detailed reference viewed: 53 (0 UL)Mechanical failure in microstructural heterogeneous materials Bordas, Stéphane ; ; in Lecture Notes in Computer Science (2007), 4310 LNCS Various heterogeneous materials with multiple scales and multiple phases in the microstructure have been produced in the recent years. We consider a mechanical failure due to the initiation and ... [more ▼] Various heterogeneous materials with multiple scales and multiple phases in the microstructure have been produced in the recent years. We consider a mechanical failure due to the initiation and propagation of cracks in places of high pore density in the microstructures. A multi-scale method based on the asymptotic homogenization theory together with the mesh superposition method (s-version of FEM) is presented for modeling of cracks. The homogenization approach is used on the global domain excluding the vicinity of the crack where the periodicity of the microstructures is lost and this approach fails. The multiple scale method relies on efficient combination of both macroscopic and microscopic models. The mesh superposition method uses two independent (global and local) finite element meshes and the concept of superposing the local mesh onto the global continuous mesh in such a way that both meshes not necessarily coincide. The homogenized material model is considered on the global mesh while the crack is analyzed in the local domain (patch) which allows to have an arbitrary geometry with respect to the underlying global finite elements. Numerical experiments for biomorphic cellular ceramics with porous microstructures produced from natural wood are presented. [less ▲] Detailed reference viewed: 76 (2 UL)Mechanical parameters identification of keloid and surrounding healthy skin using Digital Image Correlation measurements in vivo ; ; Sensale, Marco et al Scientific Conference (2019, December 09) The human skin behaves as an elastic membrane initially prestressed but not uniformly. The presence of anatomical sites favorable to the appearance of some tumors, a keloid in our case, while other sites ... [more ▼] The human skin behaves as an elastic membrane initially prestressed but not uniformly. The presence of anatomical sites favorable to the appearance of some tumors, a keloid in our case, while other sites never develop them attests to the importance of the mechanical environment of the tissue. Thus, a mechanical characterization of the tumored skin is necessary to understand the keloid expansion from a mechanical point of view. Our case study consists in modeling a bi-material structure composed of a keloid skin surrounded by healthy skin located on upper left arm of a young female. From the experimental measurements in vivo, by combining force sensor, displacement sensor and Digital Image Correlation techniques, we perform a mechanical analysis to characterize the mechanical stress fields over the entire area and on the interface ‘healthy skin/keloid skin’. Since the mechanical behavior of the tumorous skin is unknown, many physical models can be implemented and assessed very easily inside the specific digital software to fit with the real data. Once a set of mechanical parameters for both the healthy skin and the keloid skin are identified, the stress fields around the keloid are calculated. Next steps consist in determining matching preferential directions in order to define as precisely as possible the specifications of a device for preventing the growth of keloids. [less ▲] Detailed reference viewed: 21 (2 UL)The mechanical reliability of an electronic textile investigated using the virtual-power-based quasicontinuum method Beex, Lars ; ; et al in Mechanics of Materials (2015), 80 The quasicontinuum (QC) method is a multiscale method for the solution of lattice models that combines coarse-grained regions and fully resolved regions with individual lattice events. QC methodologies ... [more ▼] The quasicontinuum (QC) method is a multiscale method for the solution of lattice models that combines coarse-grained regions and fully resolved regions with individual lattice events. QC methodologies are mainly used to reduce the computational costs of conservative atomistic lattice computations. Recently, a virtual-power-based variant has been proposed that enables its use for non-conservative lattice computations. In this contribution the virtual-power-based QC approach is adopted in combination with a recently proposed mesostructural lattice model for electronic textile in order to investigate its mechanical behaviour. The interactions of the lattice model for electronic textile are modelled elastoplastically and hence, regular conservative QC approaches are not adequate. This article incorporates a modification of a previously defined exact summation rule for QC methods –by sampling the lattice interactions directly instead of via the lattice nodes. This leads to a significant reduction of the computational cost, whereas the accuracy of the summation rule remains unaffected. The presented methodology is used to efficiently investigate the failure envelope of an electronic textile – a woven fabric with embedded electronic components and conductive wires. The dependence of the failure envelope on the locations of the conductive wires and the stiffness of the weft yarns is investigated as well. [less ▲] Detailed reference viewed: 207 (8 UL)Mechanische und thermische Untersuchungen zur Entwicklung eines Wärmedämmsteines aus Leichtbeton Leufgens, Nadine Doctoral thesis (2010) The current discussion about the necessity of sustainable reduction of primary energy for heating of housing structures and of CO2 – emissions led the University of Luxembourg to issue a project to ... [more ▼] The current discussion about the necessity of sustainable reduction of primary energy for heating of housing structures and of CO2 – emissions led the University of Luxembourg to issue a project to develop hybrid light-weight concrete blocks with high heat-insulating properties. Therefore, the demand for wall constructions limiting the heat flow through the outer wall was steadily growing. Because of the progressing standard of national and European Energy Saving Regulations for housing structures and office buildings in the past years, most of the producers of bricks and concrete masonry blocks were forced to develop new, innovative wall materials and constructions. For assessing the real actual state of the art of masonry blocks, 15 different bricks and blocks were taken from European free market as samples. It was shown, that especially for highly-heat insulating masonry lightweight concrete blocks (e.g. Vbl SW 2) with dry densities below 800 kg/m3 an optimization potential still exists. A relevant aspect for a critical estimation of a wall construction is the knowledge of mechanical and thermal lightweight aggregate concrete (LAC) parameters. The present work describes investigations for determining design limit values of the thermal and mechanical properties of LAC. Based on this, a mathematical approach to describe the strength, the thermal conductivity and for e.g. the stress-strain-relationship linked to the dry density in a range between 500 and 2000 kg/m3 was derived. For studying the material behavior of LAC, specimens were produced in laboratory tests as well as in the production line by fabricating solid lightweight concrete blocks without inner air holes. Due to the unsatisfying results of the market study, further investigations had to be done to determine the influence of size and slenderness effects on the strength of solid specimen and masonry blocks with inner air holes made of LAC. Additionally, combined influencing factors were studied on block sections cut out of hollow and solid masonry blocks. In the following, the experimental results were verified by simulations with the Finite-Element-Method using the commercial software ANSYS© for modeling different LAC-specimen geometries and the influence of the kind of load applications by a contact zone between steel plates and specimen. Subsequently, the results of these investigations and the achieved knowledge of the influencing factors on the load carrying capacity of the block structures lead to an analytical model approach for design purpose of masonry blocks based on the elasticity theory. This model allows quantitative predictions of the load bearing strength of hollow and solid masonry blocks with inner air holes arranged in a grid system. The analytical model is verified by comparison of experimental results of different block geometries. Finally, the knowledge of the load carrying behavior of different LAC specimen geometries achieved by various experimental and numerical results contribute to the construction of new prototypes of heat insulating masonry blocks made of LAC. Based on the results of the market study and numerical parameter studies, it is revealed that it is suggestive to separate the load bearing from the thermal function of the block by developing 3-layered Sandwich and composite blocks made of an insulating and load bearing part. [less ▲] Detailed reference viewed: 71 (4 UL)Médias et médiations culturelles au Luxembourg Colas-Blaise, Marion ; Tore, Gian Maria Book published by Binsfeld (2011) Detailed reference viewed: 87 (4 UL)Mensch-Roboter-Kollaboration in der Domäne Refabrikation – State-of-the-Art und Ausblick Groß, Sebastian ; ; Plapper, Peter in Jäkel, Jens; Thiel, Robert (Eds.) Tagungsband AALE 2020 Automatisierung und Mensch-Technik-Interaktion (2020, March 05) Detailed reference viewed: 76 (0 UL)Merging DEMs from VHR Optical Imagery with Drone Data - A High-resolution DEM for Tristan da Cunha Backes, Dietmar ; Teferle, Felix Norman Scientific Conference (2018, December 12) The extraction of high-resolution, Digital Elevation Models (DEM) from very high-resolution (VHR) optical satellite imagery, as well as low altitude drone images by Photogrammetric methods or modern ... [more ▼] The extraction of high-resolution, Digital Elevation Models (DEM) from very high-resolution (VHR) optical satellite imagery, as well as low altitude drone images by Photogrammetric methods or modern Structure from Motion (SFM) engines, has rapidly matured. Today both data sources are representing cost-effective alternatives to dedicated airborne sensors, especially for remote and difficult to access regions. Ever-growing archives of high-resolution Satellite imagery, are providing a rich data source which covers even the most remote locations with high-resolution imagery up to 0.30m ground sample distance multiple times enabling the generation of high-resolution DEMS. Furthermore, low-cost, low weight and easy to use drones can easily be deployed in remote regions and capture limited areas with very high resolution. Dense point clouds derived from this method provide an invaluable data source to fill the gap between globally available low-resolution DEMs and highly accurate terrestrial surveys. The presented case study investigates the use of VHR archive imagery as well as low-cost drone imagery to generate high-quality DEMs using photogrammetric tools over a remote region which is difficult to access by manned airborne platforms. We highlight the potential and limitations of both data sources to provide high resolution, accurate elevation data. [less ▲] Detailed reference viewed: 66 (3 UL)Mesh adaptivity driven by goal-oriented locally equilibrated superconvergent patch recovery ; ; et al in Computational Mechanics (2013) Goal-oriented error estimates (GOEE) have become popular tools to quantify and control the local error in quantities of interest (QoI), which are often more pertinent than local errors in energy for ... [more ▼] Goal-oriented error estimates (GOEE) have become popular tools to quantify and control the local error in quantities of interest (QoI), which are often more pertinent than local errors in energy for design purposes (e.g. the mean stress or mean displacement in a particular area, the stress intensity factor for fracture problems). These GOEE are one of the key unsolved problems of advanced engineering applications in, for example, the aerospace industry. This work presents a simple recovery-based error estimation technique for QoIs whose main characteristic is the use of an enhanced version of the Superconvergent Patch Recovery (SPR) technique previously used for error estimation in the energy norm. This enhanced SPR technique is used to recover both the primal and dual solutions. It provides a nearly statically admissible stress field that results in accurate estimations of the local contributions to the discretisation error in the QoI and, therefore, in an accurate estimation of this magnitude. This approach leads to a technique with a reasonable computational cost that could easily be implemented into already available finite element codes, or as an independent postprocessing tool. © 2013 Springer-Verlag Berlin Heidelberg. [less ▲] Detailed reference viewed: 187 (2 UL)Meshfree methods for shear-deformable structures based on mixed weak forms Hale, Jack Scientific Conference (2014, July 24) Similarly to the finite element method, meshfree methods must be carefully designed to overcome the shear-locking problem when discretising the shear-deformable structural theories. Many successful ... [more ▼] Similarly to the finite element method, meshfree methods must be carefully designed to overcome the shear-locking problem when discretising the shear-deformable structural theories. Many successful treatments of shear-locking in the finite element literature are constructed through the application of a mixed variational form, where the shear stress is treated as an independent variational quantity in addition to the usual displacements. Because of its sound mathematical underpinnings this is the methodology I have chosen to solve the shear-locking problem when using meshfree basis functions. In this talk I will discuss the mathematical origins of the shear-locking problem and the applicability of the celebrated LBB stability condition for designing well-behaved mixed meshfree approximation schemes. I will show results from two new formulations that demonstrate the effectiveness of this approach. The first method is a meshfree formulation for the Timoshenko beam problem that converges to a classic inf-sup stable finite element method when using Maximum- Entropy basis functions. The second method is a generalised displacement meshfree method for the Reissner- Mindlin problem where the shear stress is eliminated prior to the solution of the linear system using a local patch-projection technique, resulting in a linear system expressed in terms of the original displacement unknowns only. Stability is ensured by using a stabilised weak form which is necessary due to the loss of kernel coercivity for the Reissner-Mindlin problem. [less ▲] Detailed reference viewed: 66 (7 UL)Meshfree Point Collocation Schemes for 2D Steady State Incompressible Navier-Stokes Equations in Velocity-Vorticity Formulation for High Values of Reynolds Number Bourantas, Georgios ; ; et al in Computer Modeling in Engineering & Sciences (2010), 59(1), 31-63 A meshfree point collocation method has been developed for the velocity- vorticity formulation of two-dimensional, steady state incompressible Navier-Stokes equations. Particular emphasis was placed on ... [more ▼] A meshfree point collocation method has been developed for the velocity- vorticity formulation of two-dimensional, steady state incompressible Navier-Stokes equations. Particular emphasis was placed on the application of the velocity-correc- tion method, ensuring the continuity equation. The Moving Least Squares (MLS) approximation is employed for the construction of the shape functions, in conjunc- tion with the general framework of the point collocation method. Computations are obtained for regular and irregular nodal distributions, stressing the positivity con- ditions that make the matrix of the system stable and convergent. The accuracy and the stability of the proposed scheme are demonstrated through two representative, well-known, and established benchmark problems. The numerical scheme was also applied to a case with irregular geometry for marginally high Reynolds numbers [less ▲] Detailed reference viewed: 131 (7 UL)Meshfree volume-averaged nodal pressure methods for incompressible elasticity Hale, Jack ; ; Scientific Conference (2014, April 03) We present a generalisation of the meshfree method for incompressible elasticity developed in Ortiz et al. (10.1016/j.cma.2010.02.013). We begin with the classical u-p mixed formulation of incompressible ... [more ▼] We present a generalisation of the meshfree method for incompressible elasticity developed in Ortiz et al. (10.1016/j.cma.2010.02.013). We begin with the classical u-p mixed formulation of incompressible elasticity before eliminating the pressure using a volume-averaged nodal projection technique. This results in a family of projection methods of the type Q_p/Q_p-1 where Q_p is an approximation space of polynomial order p. These methods are particularly robust on low-quality tetrahedral meshes. Our framework is generic with respects to the type meshfree basis function used and includes various types of existing finite element methods such as B-bar and nodal-pressure techniques. As a particular example, we use maximum-entropy basis functions to build a scheme Q_1+/Q_1 with the displacement field being enriched with bubble-like functions for stability. The flexibility of the nodal placement in meshfree methods allows us to demonstrate the importance of this bubble-like enrichment for stability; with no bubbles the pressure field is liable to oscillations, whilst with bubbles the oscillation is eliminated. Interestingly however with half the bubbles removed, a scheme we call Q_1*/_Q_1, certain undesirable tendencies of the full bubble scheme are also eliminated. This has important applications in non-linear hyperelasticity. We also discuss some difficulties associated with moving to second-order maximum entropy shape functions associated with numerical integration errors. [less ▲] Detailed reference viewed: 78 (8 UL)Meshfree volume-averaged nodal projection method for nearly-incompressible elasticity using meshfree and bubble basis functions ; Hale, Jack ; in Computer Methods in Applied Mechanics & Engineering (2015), 285 We present a displacement-based Galerkin meshfree method for the analysis of nearly-incompressible linear elastic solids, where low-order simplicial tessellations (i.e., 3- node triangular or 4-node ... [more ▼] We present a displacement-based Galerkin meshfree method for the analysis of nearly-incompressible linear elastic solids, where low-order simplicial tessellations (i.e., 3- node triangular or 4-node tetrahedral meshes) are used as a background structure for numerical integration of the weak form integrals and to get the nodal information for the computation of the meshfree basis functions. In this approach, a volume- averaged nodal projection operator is constructed to project the dilatational strain into an approximation space of equal- or lower-order than the approximation space for the displacement field resulting in a locking-free method. The stability of the method is provided via bubble-like basis functions. Because the notion of an ‘ele- ment’ or ‘cell’ is not present in the computation of the meshfree basis functions such low-order tessellations can be used regardless of the order of the approximation spaces desired. First- and second-order meshfree basis functions are chosen as a particular case in the proposed method. Numerical examples are provided in two and three dimensions to demonstrate the robustness of the method, its ability to avoid volumetric locking in the nearly-incompressible regime, and its improved performance when compared to the MINI finite element scheme on the simplicial mesh. [less ▲] Detailed reference viewed: 230 (51 UL)Meshless Elasticity Model and Contact Mechanics-based Verification Technique ; ; et al in MICCAI Computational Biomechanics for Medicine (2014, January 01) Mesh-based techniques are well studied and established methods for solving continuum biomechanics problems. When the problem at hand involves extreme deformations or artificial discontinuities, meshless ... [more ▼] Mesh-based techniques are well studied and established methods for solving continuum biomechanics problems. When the problem at hand involves extreme deformations or artificial discontinuities, meshless methods provide sev-eral advantages over the mesh-based methods. This work discusses the Moving Least Square approximation-based meshless collocation method for simulating de-formable objects and presents a verification technique that is based on the Hertzian theory of non-adhesive elastic contact. The effectiveness of the Hertzian contact theory as a means for verification was first tested and proven through a well-established FEM code, FEBio. The meshless method was implemented as a reusable component for the SOFA framework, an open source software library for real-time simulations. Through experimentation, the Hertzian theory has been tested against SOFA hexahedral FEM and the meshless models within the SOFA framework. Convergence studies and L2 error curves are provided for both mod-els. Experimental results demonstrated the effectiveness of the implementation of the meshless method. [less ▲] Detailed reference viewed: 419 (1 UL)A Meshless Method for the Reissner-Mindlin Plate Equations based on a Stabilized Mixed Weak Form Hale, Jack ; Scientific Conference (2013, September) Detailed reference viewed: 37 (1 UL)Meshless Methods for the Reissner-Mindlin Plate Problem based on Mixed Variational Forms Hale, Jack Presentation (2013, October 31) Meshless numerical methods such as the element free Galerkin (EFG) method and $hp$-clouds method rely on a field of particles to construct a basis for the solution of partial differential equations (PDEs ... [more ▼] Meshless numerical methods such as the element free Galerkin (EFG) method and $hp$-clouds method rely on a field of particles to construct a basis for the solution of partial differential equations (PDEs). This is in contrast with methods such as the finite element method (FEM) and finite difference method (FDM) which rely upon a mesh or grid. Because of this increased flexibility, meshfree methods have shown themselves to be effective tools for simulating difficult problems such as those with discontinuities, complex geometries and large deformations. The Reissner-Mindlin problem is widely used by engineers to describe the deformation of a plate including the effects of transverse shear. A well-known problem which must be overcome when designing an effective numerical method for the Reissner-Mindlin problem is shear-locking. Shear-locking is the inability of the constructed approximation space (meshless or otherwise) to richly represent the limiting Kirchhoff mode. This inability manifests itself as an entirely incorrect solution as the thickness of the plate approaches zero. We will demonstrate and explain the shear-locking problem and potential solutions to it using a simple one-dimensional example. The most effective, robust and general approaches to the shear-locking problem developed in the FEM literature are based on mixed variational forms, where a combination of displacements, stresses and strains are approximated directly. In our approach we start with a mixed variational form before eliminating the extra stress unknowns using the local patch projection technique of A Ortiz et. al. We will discuss the issues presented by the well-known LBB stability conditions and present a solution based upon the stabilising properties of both the augmented Lagrangian and additional `bubble' type functions. We will then show the good performance of the method and its shear-locking free properties. [less ▲] Detailed reference viewed: 68 (7 UL)Meshless methods: A review and computer implementation aspects ; ; Bordas, Stéphane et al in Mathematics & Computers in Simulation (2008), 79(3), 763-813 The aim of this manuscript is to give a practical overview of meshless methods (for solid mechanics) based on global weak forms through a simple and well-structured MATLAB code, to illustrate our ... [more ▼] The aim of this manuscript is to give a practical overview of meshless methods (for solid mechanics) based on global weak forms through a simple and well-structured MATLAB code, to illustrate our discourse. The source code is available for download on our website and should help students and researchers get started with some of the basic meshless methods; it includes intrinsic and extrinsic enrichment, point collocation methods, several boundary condition enforcement schemes and corresponding test cases. Several one and two-dimensional examples in elastostatics are given including weak and strong discontinuities and testing different ways of enforcing essential boundary conditions. © 2008 IMACS. [less ▲] Detailed reference viewed: 1085 (4 UL) |
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