15,962 research outputs found
Modelling Rod-like Flexible Biological Tissues for Medical Training
This paper outlines a framework for the modelling of slender rod-like biological tissue structures in both global and local scales. Volumetric discretization of a rod-like structure is expensive in computation and therefore
is not ideal for applications where real-time performance is essential. In our approach, the Cosserat rod model is introduced to capture the global shape changes, which models the structure as a one-dimensional entity, while the
local deformation is handled separately. In this way a good balance in accuracy and efficiency is achieved. These advantages make our method appropriate for
the modelling of soft tissues for medical training applications
Modelling self-piercing riveted joint failures in automotive crash structures
This paper describes a new model and method to predict Self-Piercing Riveted (SPR) joint interlock failures in aluminium sheet at crash speeds using explicit finite element simulation. SPR interlock failure is dependent on rivet direction, which is included in the model. A mesh independent approach is adopted for connection model which is capable of industrial application at the full vehicle crash analysis level. The paper provides an overview of the approach to validate connection model; typically by developing detailed physics based models of various joint configurations supported with high speed experimental data, through to model capable of industrial application. The framework to validate connection model for use in crash simulation tools is expected to have broader applicatio
Folding Large Antenna Tape Spring
This paper presents a novel concept for a low-mass, 50-m^2-deployable, P-band dual polarization antenna that can measure terrestrial biomass levels from a spacecraft in a low Earth orbit. A monolithic array of feed and radiating patches is bonded to a transversally curved structure consisting of two Kevlar sheets. The first sheet supports the array and the other sheet supports a ground plane. The two sheets are connected by a compliant Kevlar core that allows the whole structure to be folded elastically and to spring back to its original, undamaged shape. Test pieces have been made to demonstrate both the radio frequency and mechanical aspects of the design, particularly the radio frequency performance before and after folding the structure. It is concluded that the proposed design concept has high potential for large, low-frequency antennas for low-cost missions
The application of three-dimensional mass-spring structures in the real-time simulation of sheet materials for computer generated imagery
Despite the resources devoted to computer graphics technology over the last 40 years,
there is still a need to increase the realism with which flexible materials are simulated.
However, to date reported methods are restricted in their application by their use of
two-dimensional structures and implicit integration methods that lend themselves to
modelling cloth-like sheets but not stiffer, thicker materials in which bending moments
play a significant role.
This thesis presents a real-time, computationally efficient environment for simulations
of sheet materials. The approach described differs from other techniques principally
through its novel use of multilayer sheet structures. In addition to more accurately
modelling bending moment effects, it also allows the effects of increased temperature
within the environment to be simulated. Limitations of this approach include the
increased difficulties of calibrating a realistic and stable simulation compared to
implicit based methods.
A series of experiments are conducted to establish the effectiveness of the technique,
evaluating the suitability of different integration methods, sheet structures, and
simulation parameters, before conducting a Human Computer Interaction (HCI) based
evaluation to establish the effectiveness with which the technique can produce credible
simulations. These results are also compared against a system that utilises an
established method for sheet simulation and a hybrid solution that combines the use of
3D (i.e. multilayer) lattice structures with the recognised sheet simulation approach.
The results suggest that the use of a three-dimensional structure does provide a level of
enhanced realism when simulating stiff laminar materials although the best overall
results were achieved through the use of the hybrid model
A parallel interaction potential approach coupled with the immersed boundary method for fully resolved simulations of deformable interfaces and membranes
In this paper we show and discuss the use of a versatile interaction
potential approach coupled with an immersed boundary method to simulate a
variety of flows involving deformable bodies. In particular, we focus on two
kinds of problems, namely (i) deformation of liquid-liquid interfaces and (ii)
flow in the left ventricle of the heart with either a mechanical or a natural
valve. Both examples have in common the two-way interaction of the flow with a
deformable interface or a membrane. The interaction potential approach (de
Tullio & Pascazio, Jou. Comp. Phys., 2016; Tanaka, Wada and Nakamura,
Computational Biomechanics, 2016) with minor modifications can be used to
capture the deformation dynamics in both classes of problems. We show that the
approach can be used to replicate the deformation dynamics of liquid-liquid
interfaces through the use of ad-hoc elastic constants. The results from our
simulations agree very well with previous studies on the deformation of drops
in standard flow configurations such as deforming drop in a shear flow or a
cross flow. We show that the same potential approach can also be used to study
the flow in the left ventricle of the heart. The flow imposed into the
ventricle interacts dynamically with the mitral valve (mechanical or natural)
and the ventricle which are simulated using the same model. Results from these
simulations are compared with ad- hoc in-house experimental measurements.
Finally, a parallelisation scheme is presented, as parallelisation is
unavoidable when studying large scale problems involving several thousands of
simultaneously deforming bodies on hundreds of distributed memory computing
processors
Wrinkling of Orthotropic Viscoelastic Membranes
This paper presents a simplified simulation technique for orthotropic viscoelastic films.
Wrinkling is detected by a combined stress-strain criterion and an iterative scheme searches
for the wrinkle angle using a pseudo-elastic material stiffness matrix based on a nonlinear
viscoelastic constitutive model. This simplified model has been implemented in
ABAQUS/Explicit and is able to compute the behavior of a membrane structure by superposition
of a small number of response increments. The model has been tested against
a published solution for a time-independent isotropic membrane under simple shear and
also against experimental results on StratoFilm 420 under simple shear
Global Energy Matching Method for Atomistic-to-Continuum Modeling of Self-Assembling Biopolymer Aggregates
This paper studies mathematical models of biopolymer supramolecular aggregates that are formed by the self-assembly of single monomers. We develop a new multiscale numerical approach to model the structural properties of such aggregates. This theoretical approach establishes micro-macro relations between the geometrical and mechanical properties of the monomers and supramolecular aggregates. Most atomistic-to-continuum methods are constrained by a crystalline order or a periodic setting and therefore cannot be directly applied to modeling of soft matter. By contrast, the energy matching method developed in this paper does not require crystalline order and, therefore, can be applied to general microstructures with strongly variable spatial correlations. In this paper we use this method to compute the shape and the bending stiffness of their supramolecular aggregates from known chiral and amphiphilic properties of the short chain peptide monomers. Numerical implementation of our approach demonstrates consistency with results obtained by molecular dynamics simulations
Virtual reality training and assessment in laparoscopic rectum surgery
Background: Virtual-reality (VR) based simulation techniques offer an efficient and low cost alternative to conventional surgery training. This article describes a VR training and assessment system in laparoscopic rectum surgery. Methods: To give a realistic visual performance of interaction between membrane tissue and surgery tools, a generalized cylinder based collision detection and a multi-layer mass-spring model are presented. A dynamic assessment model is also designed for hierarchy training evaluation. Results: With this simulator, trainees can operate on the virtual rectum with both visual and haptic sensation feedback simultaneously. The system also offers surgeons instructions in real time when improper manipulation happens. The simulator has been tested and evaluated by ten subjects. Conclusions: This prototype system has been verified by colorectal surgeons through a pilot study. They believe the visual performance and the tactile feedback are realistic. It exhibits the potential to effectively improve the surgical skills of trainee surgeons and significantly shorten their learning curve. © 2014 John Wiley & Sons, Ltd
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