Simulation of two- and three-dimensional viscoplastic flows using adaptive mesh refinement

This paper presents a finite element solver for the simulation of steady non-Newtonian flow problems, using a regularized Bingham model, with adaptive mesh refinement capabilities. The solver is based on a stabilized formulation derived from the variational multiscale framework. This choice allows the introduction of an a posteriori error indicator based on the small scale part of the solution, which is used to drive a mesh refinement procedure based on element subdivision. This approach applied to the solution of a series of benchmark examples, which allow us to validate the formulation and assess its capabilities to model 2D and 3D non-Newtonian flows.Postprint (author's final draft

Computational and rheological studies for coating flows.

Coating flows can be defined as a laminar free surface flows, whereby a liquid layer is applied onto a solid substrate. A typical industrial application consists of co-rotating cylindrical rollers, which are used to apply a liquid coating (paint) onto a moving substrate, and depending on the direction of the rollers, can be configured in either forward or reverse mode. These types of coating solution flows are industrially important applications, and convey viscoelastic aspects due to their polymeric content and unsteady polymeric behaviour. The process often possesses localized regions of high shear and extension rates (narrow nip and wetting-line zones), which may cause instabilities on the coated substrate (ribbing, leveling, striping). These non-Newtonian and viscoelastic studies for industrial reverse roll coating focus on the use of computational techniques to model these types of coating flows, alongside the analysis of the fluid flow behaviour and under varied rheological properties. Two flow problem configurations have been considered, a model benchmark problem of mixed combined-separating flow, and the industrial application of reverse roll coating flow. Predictions and corresponding solutions are reported for viscous, inelastic and complex viscoelastic fluid properties. The numerical formulation adopts a Taylor-Galerkin pressure-correction (TGPC) scheme, using a finite element method for viscous, inelastic flows and a hybrid finite element/finite volume method for their viscoelastic counterparts. The research plan is centered around computational fluid dynamics and rheological studies, with the main target focused on industrial roll-coating operations. From simple theory, Newtonian and non-Newtonian coating flows possess specific, yet disparate characteristics. This may lead to distinct and significant differences in their detailed flow behaviour, and in the stressing levels generated, dependent upon the nature of the flow configuration. The study is segmented into several stages: initially, solution was sought for a benchmark flow problem, where a semi- implicit time stepping finite element procedure was employed to simulate a mixed combined- separating flow. Here, both viscous and viscoplastic material approximations have been introduced. Secondly, the industrial application of reverse roll coating flow was addressed for viscous inelastic coating fluids. This incorporated scenarios of inclusion and not of a dynamic wetting line and consideration of the effects of a rubber elastomer-cover upon the applicator roll. Thirdly, viscoelastic paint coatings were addressed for the industrial reverse roll coating flow. Here, a hybrid finite element/finite volume sub-cell method was utilized, and with inclusion of a dynamic wetting line. Of the various viscoelastic material models available, use has been made of the Phan-Thien Taimer (PTT) network class of models, in both linear and exponential variety, and of the FENE class of models, with FENE-CR and FENE-P versions. This has offered a richness in capacity over variation of rheological properties. The choice of computational methods has been justified and the TGPC algorithm was deemed suitable for problem solution. The methodology tested on combined-separating flow provided high-quality numerical results, which compare favorably against experiments, literature and theory. When applied to the reverse roll coating problem, the TGPC algorithm has been coupled to a time-dependent free-surface update procedure, to determine the dynamic movement of the meniscus and the wetting line. Around the nip-region, the flow problem manifests strong flow features, which have been investigated for a range of rheological properties of varying shear and extensional response. The direct impact these have on localized peak nip-pressures and distributional lift levels has been observed, where several relief mechanisms have been successfully identified (important to optimize process control). The influence of solvent fraction, extensional viscosity and increasing elasticity, up to critical stress states have been analysed in considerable detail. In summary, the success of this work indicates optimal flow process settings and preferential Theological coating properties to employ, with respect to this industrial coating process. As such, it lays the foundation and guide towards achieving a stable and consistent coating application - specifically, as high-speed high-gain production is of current demanded

Recent advances and applications of machine learning in metal forming processes

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Recent Advances and Applications of Machine Learning in Metal Forming Processes

Machine learning (ML) technologies are emerging in Mechanical Engineering, driven by the increasing availability of datasets, coupled with the exponential growth in computer performance. In fact, there has been a growing interest in evaluating the capabilities of ML algorithms to approach topics related to metal forming processes, such as: Classification, detection and prediction of forming defects; Material parameters identification; Material modelling; Process classification and selection; Process design and optimization. The purpose of this Special Issue is to disseminate state-of-the-art ML applications in metal forming processes, covering 10 papers about the abovementioned and related topics

Several applications of a model for dense granular flows

This dissertation describes efforts to evaluate a recently proposed continuum model for the dense flow of dry granular materials (Jop, Forterre & Pouliquen, 2006, Nature, 441, 167-192). The model, based upon a generalisation of Coulomb sliding friction, is known to perform well when modelling certain simple free surface flows. We extend the application of this model to a wide range of flow configurations, beginning with six simple flows studied in detailed experiments (GDR MiDi, 2004, Eur. Phys. J. E, 14, 341-366). Two-dimensional shearing flows and problems of linear stability are also addressed. These examples are used to underpin a thorough discussion of the strengths and weaknesses of the model. In order to calculate the behaviour of granular material in more complicated configurations, it is necessary to undertake a numerical solution. We discuss several computational techniques appropriate to the model, with careful attention paid to the evolution of any shear-free regions that may arise. In addition, we develop a numerical scheme, based upon a marker-and-cell method, that is capable of modelling two-dimensional granular flow with a moving free surface. A detailed discussion of our unsuccessful attempt to construct a scheme based upon Lagrangian finite elements is presented in an appendix. We apply the marker-and-cell code to the key problem of granular slumping (Balmforth & Kerswell, 2005, J. Fluid Mech., 538, 399-428), which has hitherto resisted explanation by modelling approaches based on various reduced (shallow water) models. With our numerical scheme, we are able to lift the assumptions required for other models, and make predictions in good qualitative agreement with the experimental data. An additional chapter describes the largely unrelated problem of contact between two objects separated by a viscous fluid. Although classical lubrication theory suggests that two locally smooth objects converging under gravity will make contact only after infinite time, we discuss several physical effects that may promote contact in finite time. Detailed calculations are presented to illustrate how the presence of a sharp asperity can modify the approach to contact.Supported by a Natural Environment Research Council Studentship

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen