1,891 research outputs found
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Scalable computation of thermomechanical turbomachinery problems
A commonly held view in the turbomachinery community is that finite element
methods are not well-suited for very large-scale thermomechanical simulations.
We seek to dispel this notion by presenting performance data for a collection
of realistic, large-scale thermomechanical simulations. We describe the
necessary technology to compute problems with to
degrees-of-freedom, and emphasise what is required to achieve near linear
computational complexity with good parallel scaling. Performance data is
presented for turbomachinery components with up to 3.3 billion
degrees-of-freedom. The software libraries used to perform the simulations are
freely available under open source licenses. The performance demonstrated in
this work opens up the possibility of system-level thermomechanical modelling,
and lays the foundation for further research into high-performance formulations
for even larger problems and for other physical processes, such as contact,
that are important in turbomachinery analysis.The support of Mitsubishi Heavy Industries is gratefully acknowledged. CNR is supported by EPSRC Grant EP/N018877/1
SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES
Crack propagation in thin shell structures due to cutting is conveniently simulated
using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell
elements are usually preferred for the discretization in the presence of complex material
behavior and degradation phenomena such as delamination, since they allow for a correct
representation of the thickness geometry. However, in solid-shell elements the small thickness
leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new
selective mass scaling technique is proposed to increase the time-step size without affecting
accuracy. New ādirectionalā cohesive interface elements are used in conjunction with selective
mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile
shells
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A Material Point Method for Elastoplasticity with Ductile Fracture and Frictional Contact
Simulating physical materials with dynamic movements to photo-realistic resolution has always been one of the most crucial and challenging topics in Computer Graphics. This dissertation considers large-strain elastoplasticity theory applied to the low-to-medium stiffness regime, with topological changes and codimensional objects incorporated. We introduce improvements to the Material Point Method (MPM) for two particular objectives, simulating fracturing ductile materials and incorporation of MPM and Lagrangian Finite Element Method (FEM).Our first contribution, simulating ductile fracture, utilizes traditional particle-based MPM [SSC13, SCS94] as well as the Lagrangian energy formulation of [JSS15] which uses a tetrahedron mesh, rather than particle-based estimation of the deformation gradient and potential energy. We model failure and fracture via elastoplasticity with damage. The material is elastic until its deformation exceeds a Rankine or von Mises yield condition. At that point, we use a softening model that shrinks the yield surface until it reaches the damage thresh- old. Once damaged, the material Lam Ģe coefficients are modified to represent failed material. This approach to simulating ductile fracture with MPM is successful, as MPM naturally captures the topological changes coming from the fracture. However, rendering the crack surfaces can be challenging. We design a novel visualization technique dedicated to rendering the materialās boundary and its intersection with the evolving crack surfaces. Our approach uses a simple and efficient element splitting strategy for tetrahedron meshes to create crack surfaces. It employs an extrapolation technique based on the MPM simulation. For traditional particle-based MPM, we use an initial Delaunay tetrahedralization to connect randomly sampled MPM particles. Our visualization technique is a post-process and can run after the MPM simulation for efficiency. We demonstrate our method with several challenging simulations of ductile failure with considerable and persistent self-contact and applications with thermomechanical models for baking and cooking.Our second contribution, hybrid MPMāLagrangian-FEM, aims to simulate elastic objects like hair, rubber, and soft tissues. It utilizes a Lagrangian mesh for internal force computation and a Eulerian grid for self-collision, as well as coupling with external materials. While recent MPM techniques allow for natural simulation of hyperelastic materials represented with Lagrangian meshes, they utilize an updated Lagrangian discretization and use the Eulerian grid degrees of freedom to take variations of the potential energy. It often coarsens the degrees of freedom of the Lagrangian mesh and can lead to artifacts. We develop a hybrid approach that retains Lagrangian degrees of freedom while still allowing for natural coupling with other materials simulated with traditional MPM, e.g., sand, snow, etc. Furthermore, while recent MPM advances allow for resolution of frictional contact with codimensional simulation of hyperelasticity, they do not generalize to the case of volumetric materials. We show that our hybrid approach resolves these issues. We demonstrate the efficacy of our technique with examples that involve elastic soft tissues coupled with kinematic skeletons, extreme deformation, and coupling with various elastoplastic materials. Our approach also naturally allows for two-way rigid body coupling
Center for Computational Structures Technology
The Center for Computational Structures Technology (CST) is intended to serve as a focal point for the diverse CST research activities. The CST activities include the use of numerical simulation and artificial intelligence methods in modeling, analysis, sensitivity studies, and optimization of flight-vehicle structures. The Center is located at NASA Langley and is an integral part of the School of Engineering and Applied Science of the University of Virginia. The key elements of the Center are: (1) conducting innovative research on advanced topics of CST; (2) acting as pathfinder by demonstrating to the research community what can be done (high-potential, high-risk research); (3) strong collaboration with NASA scientists and researchers from universities and other government laboratories; and (4) rapid dissemination of CST to industry, through integration of industrial personnel into the ongoing research efforts
Large scale Optimal Transportation Meshfree (OTM) Simulations of Hypervelocity Impact
Large scale three-dimensional numerical simulations of hypervelocity impact of Aluminum alloy 6061-T6 plates by Nylon 6/6 cylindrical
projectile have been performed using the Optimal Transportation Meshfree (OTM) method of Li et al. [7] along with the seizing contact
and variational material point failure algorithm [17, 18]. The dynamic response of the Al6061-T6 plate including phase transition in the
high strain rate, high pressure and high temperature regime expected in our numerical analysis is described by the use of a variational
thermomechanical coupling constitutive model with SESAME equation of state, rate-dependent J2 plasticity with power law hardening
and thermal softening and temperature dependent Newtonian viscosity. A polytropic type of equation of state fit to in-house ReaxFF
calculations is employed to model the Nylon 6/6 projectile under extreme conditions. The evaluation of the performance of the numerical
model takes the form of a conventional validation analysis. In support of the analysis, we have conducted experiments over a range of
plate thicknesses of [0.5, 3.0] mm, a range of impact velocities of [5.0, 7.0]km/s and a range of obliquities of [0, 70]Ā° at Caltech's Small
Particle Hypervelocity Range (SPHIR) Facility. Large scale three-dimensional OTM simulations of hypervelocity impact are performed
on departmental class systems using a dynamic load balancing MPI/PThreads parallel implementation of the OTM method. We find
excellent full field agreement between measured and computed perforation areas, debris cloud and temperature field
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