3,549 research outputs found
SPH method applied to high speed cutting modelling
The purpose of this study is to introduce a new approach of high speed cutting numerical modelling. A Lagrangian smoothed particle hydrodynamics (SPH)- based model is arried out using the Ls-Dyna software. SPH is a meshless method, thus large material distortions that occur in the cutting problem are easily managed and SPH contact control permits a "natural" workpiece/chip separation. The developed approach is compared to machining dedicated code results and experimental data. The SPH cutting model has proved is ability to account for continuous to shear localized chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Thus, comparable results to machining dedicated codes are obtained without introducing any adjusting numerical parameters (friction coefficient, fracture control parameter)
A limiter-based well-balanced discontinuous Galerkin method for shallow-water flows with wetting and drying: Triangular grids
A novel wetting and drying treatment for second-order Runge-Kutta
discontinuous Galerkin (RKDG2) methods solving the non-linear shallow water
equations is proposed. It is developed for general conforming two-dimensional
triangular meshes and utilizes a slope limiting strategy to accurately model
inundation. The method features a non-destructive limiter, which concurrently
meets the requirements for linear stability and wetting and drying. It further
combines existing approaches for positivity preservation and well-balancing
with an innovative velocity-based limiting of the momentum. This limiting
controls spurious velocities in the vicinity of the wet/dry interface. It leads
to a computationally stable and robust scheme -- even on unstructured grids --
and allows for large time steps in combination with explicit time integrators.
The scheme comprises only one free parameter, to which it is not sensitive in
terms of stability. A number of numerical test cases, ranging from analytical
tests to near-realistic laboratory benchmarks, demonstrate the performance of
the method for inundation applications. In particular, super-linear
convergence, mass-conservation, well-balancedness, and stability are verified
Least-Squares Finite Element Formulation for Fluid-Structure Interaction
Fluid-structure interaction problems prove difficult due to the coupling between fluid and solid behavior. Typically, different theoretical formulations and numerical methods are used to solve fluid and structural problems separately. The least-squares finite element method is capable of accurately solving both fluid and structural problems. This capability allows for a simultaneously coupled fluid structure interaction formulation using a single variational approach to solve complex and nonlinear aeroelasticity problems. The least-squares finite element method was compared to commonly used methods for both structures and fluids individually. The fluid analysis was compared to finite differencing methods and the structural analysis type compared to traditional Weak Galerkin finite element methods. The simultaneous solution method was then applied to aeroelasticity problems with a known solution. Achieving these results required unique iterative methods to balance each domain\u27s or differential equation\u27s weighting factor within the simultaneous solution scheme. The scheme required more computational time but it did provide the first hands-off method capable of solving complex fluid-structure interaction problems using a simultaneous least-squares formulation. A sequential scheme was also examined for coupled problems
Fluid-structure interaction in lower airways of CT-based lung geometries
In this study, the deformability of airway walls is taken into account to study airflow patterns
and airway wall stresses in the first generations of lower airways in a real lung geometry. The
lung geometry is based on CT-scans that are obtained from in-vivo experiments on humans. A
partitioned fluid-structure interaction (FSI) approach, realized within a parallel in-house finite
element code, is employed. It is designed for the robust and eficient simulation of the interaction
of transient incompressible Newtonian flows and (geometrically) nonlinear airway wall behavior.
Arbitrary Lagrangian Eulerian (ALE)-based stabilized tetrahedral finite elements are used for the fluid and Lagrangian-based 7-parametric mixed/hybrid shell elements are used for the airway walls using unstructured meshes due to the complexity of the geometry. Air flow patterns as well as airway wall stresses in the bronchial tree are studied for a number of different scenarios. Thereby, both models for healthy and diseased lungs are taken into account and both normal breathing and mechanical ventilation scenarios are studied
Observations from Preliminary Experiments on Spatial and Temporal Pressure Measurements from Near-Field Free Air Explosions
It is self-evident that a crucial step in analysing the performance of protective structures is to be able to accurately quantify the blast load arising from a high explosive detonation. For structures located near to the source of a high explosive detonation, the resulting pressure is extremely high in magnitude and highly non-uniform over the face of the target. There exists very little direct measurement of blast parameters in the nearfield, mainly attributed to the lack of instrumentation sufficiently robust to survive extreme loading events yet sensitive enough to capture salient features of the blast. Instead literature guidance is informed largely by early numerical analyses and parametric studies. Furthermore, the lack of an accurate, reliable data set has prevented subsequent numerical analyses from being validated against experimental trials. This paper presents an experimental methodology that has been developed in part to enable such experimental data to be gathered. The experimental apparatus comprises an array of Hopkinson pressure bars, fitted through holes in a target, with the loaded faces of the bars flush with the target face. Thus, the bars are exposed to the normally or obliquely reflected shocks from the impingement of the blast wave with the target. Pressure-time recordings are presented along with associated Arbitary-Langrangian-Eulerian modelling using the LS-DYNA explicit numerical code. Experimental results are corrected for the effects of dispersion of the propagating waves in the pressure bars, enabling accurate characterisation of the peak pressures and impulses from these loadings. The combined results are used to make comments on the mechanism of the pressure load for very near-field blast events
Proceedings for the ICASE Workshop on Heterogeneous Boundary Conditions
Domain Decomposition is a complex problem with many interesting aspects. The choice of decomposition can be made based on many different criteria, and the choice of interface of internal boundary conditions are numerous. The various regions under study may have different dynamical balances, indicating that different physical processes are dominating the flow in these regions. This conference was called in recognition of the need to more clearly define the nature of these complex problems. This proceedings is a collection of the presentations and the discussion groups
Numerical methods for the modelling of chip formation
The modeling of metal cutting has proved to be particularly complex due to the diversity of physical phenomena involved, including thermo-mechanical coupling, contact/friction and material failure. During the last few decades, there has been significant progress in the development of numerical methods for modeling machining operations. Furthermore, the most relevant techniques have been implemented in the the relevant commercial codes creating tools for the engineers working in
the design of processes and cutting devices. This paper presents a review on the numerical modeling methods and techniques used for the simulation of machining processes. The main purpose is to identify the strengths and weaknesses of each method and strategy developed up-to-now. Moreover the review covers the classical Finite Element Method covering mesh-less methods, particle-based methods
and different possibilities of Eulerian and Lagrangian approaches.Postprint (author's final draft
Interface Tracking and Solid-Fluid Coupling Techniques with Coastal Engineering Applications
Multi-material physics arise in an innumerable amount of engineering problems. A broadly
scoped numerical model is developed and described in this thesis to simulate the dynamic interaction
of multi-fluid and solid systems. It is particularly aimed at modelling the interaction
of two immiscible fluids with solid structures in a coastal engineering context; however it can
be extended to other similar areas of research. The Navier Stokes equations governing the
fluids are solved using a combination of finite element (FEM) and control volume finite element
(CVFE) discretisations. The sharp interface between the fluids is obtained through the
compressive transport of material properties (e.g. material concentration). This behaviour is
achieved through the CVFE method and a conveniently limited flux calculation scheme based
on the Hyper-C method by Leonard (1991). Analytical and validation test cases are provided,
consisting of steady and unsteady flows. To further enhance the method, improve accuracy, and
exploit Lagrangian benefits, a novel moving mesh method is also introduced and tested. It is
essentially an Arbitrary Lagrangian Eulerian method in which the grid velocity is defined by
semi-explicitly solving an iterative functional minimisation problem.
A multi-phase approach is used to introduce solid structure modelling. In this approach,
solution of the velocity field for the fluid phase is obtained using Model B as explained by
Gidaspow (1994, page 151). Interaction between the fluid phase and the solids is achieved
through the means of a source term included in the fluid momentum equations. The interacting
force is calculated through integration of this source term and adding a buoyancy contribution.
The resulting force is passed to an external solid-dynamics model such as the Discrete Element
Method (DEM), or the combined Finite Discrete Element Method (FEMDEM).
The versatility and novelty of this combined modelling approach stems from its ability to
capture the fluid interaction with particles of random size and shape. Each of the three main
components of this thesis: the advection scheme, the moving mesh method, and the solid interaction
are individually validated, and examples of randomly shaped and sized particles are
shown. To conclude the work, the methods are combined together in the context of coastal engineering
applications, where the complex coupled problem of waves impacting on breakwater
amour units is chosen to demonstrate the simulation possibilities. The three components developed
in this thesis significantly extend the application range of already powerful tools, such
as Fluidity, for fluids-modelling and finite discrete element solids-modelling tools by bringing
them together for the first time
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