2,695 research outputs found
Linear and non-linear dynamic analyses of sandwich panels with face sheet-tocore debonding
А survey of recent developments in the dynamic analysis of sandwich panels with face sheet-to-core
debonding is presented. The finite element method within the ABAQUSTM code is utilized. The emphasis
is directed to the procedures used to elaborate linear and non-linear models and to predict dynamic response
of the sandwich panels. Recently developed models are presented, which can be applied for structural
health monitoring algorithms of real-scale sandwich panels. First, various popular theories of intact
sandwich panels are briefly mentioned and a model is proposed to effectively analyse the modal dynamics
of debonded and damaged (due to impact) sandwich panels. The influence of debonding size, form and
location, and number of such damage on the modal characteristics of sandwich panels are shown. For
nonlinear analysis, models based on implicit and explicit time integration schemes are presented and dynamic
response gained with those models are discussed. Finally, questions related to debonding progression
at the face sheet-core interface when dynamic loading continues with time are briefly highlighted
Studying Flow Close to an Interface by Total Internal Reflection Fluorescence Cross Correlation Spectroscopy: Quantitative Data Analysis
Total Internal Reflection Fluorescence Cross Correlation Spectroscopy
(TIR-FCCS) has recently (S. Yordanov et al., Optics Express 17, 21149 (2009))
been established as an experimental method to probe hydrodynamic flows near
surfaces, on length scales of tens of nanometers. Its main advantage is that
fluorescence only occurs for tracer particles close to the surface, thus
resulting in high sensitivity. However, the measured correlation functions only
provide rather indirect information about the flow parameters of interest, such
as the shear rate and the slip length. In the present paper, we show how to
combine detailed and fairly realistic theoretical modeling of the phenomena by
Brownian Dynamics simulations with accurate measurements of the correlation
functions, in order to establish a quantitative method to retrieve the flow
properties from the experiments. Firstly, Brownian Dynamics is used to sample
highly accurate correlation functions for a fixed set of model parameters.
Secondly, these parameters are varied systematically by means of an
importance-sampling Monte Carlo procedure in order to fit the experiments. This
provides the optimum parameter values together with their statistical error
bars. The approach is well suited for massively parallel computers, which
allows us to do the data analysis within moderate computing times. The method
is applied to flow near a hydrophilic surface, where the slip length is
observed to be smaller than 10nm, and, within the limitations of the
experiments and the model, indistinguishable from zero.Comment: 18 pages, 12 figure
Virtual Delamination Testing through Non-Linear Multi-Scale Computational Methods: Some Recent Progress
This paper deals with the parallel simulation of delamination problems at the
meso-scale by means of multi-scale methods, the aim being the Virtual
Delamination Testing of Composite parts. In the non-linear context, Domain
Decomposition Methods are mainly used as a solver for the tangent problem to be
solved at each iteration of a Newton-Raphson algorithm. In case of strongly
nonlinear and heterogeneous problems, this procedure may lead to severe
difficulties. The paper focuses on methods to circumvent these problems, which
can now be expressed using a relatively general framework, even though the
different ingredients of the strategy have emerged separately. We rely here on
the micro-macro framework proposed in (Ladev\`eze, Loiseau, and Dureisseix,
2001). The method proposed in this paper introduces three additional features:
(i) the adaptation of the macro-basis to situations where classical
homogenization does not provide a good preconditioner, (ii) the use of
non-linear relocalization to decrease the number of global problems to be
solved in the case of unevenly distributed non-linearities, (iii) the
adaptation of the approximation of the local Schur complement which governs the
convergence of the proposed iterative technique. Computations of delamination
and delamination-buckling interaction with contact on potentially large
delaminated areas are used to illustrate those aspects
Simulation tools for biomechanical applications with PGD-based reduced order models
Cotutela Universitat Politècnica de Catalunya i Università degli Studi di PaviaNumerical simulation tools are generally used in all modern engineering fields, especially those having difficulties in performing large number of practical experiments, such as biomechanics. Among the computational methods, Finite Element (FE) is an essential tool. Nowadays, the fast-growing computational techniques, from the upgrading hardware to the emerging of novel algorithm, have already enabled extensive applications in biomechanics. For applications that require fast response and/or multiple queries, Reduced Order Modelling (ROM) methods have been developed based on existing methods such as FE, and have eventually enabled real-time numerical simulation for a large variety of engineering problems.
In this thesis, several novel computational techniques are developed to explore the capability of Proper Generalised Decomposition (PGD), which is an important approach of ROM. To assess the usability of the PGD-based ROM for biomechanical applications, a real human femur bone is chosen to study its mechanical behaviour as an example. Standard image-based modelling procedure in biomechanics is performed to create an FE model which is then validated with in vitro experimental results.
As a basis of this work, the medical image processing has to be performed, in order to generate an available FE model. This model is validated according to data collected from a previously performed \textit{in vitro} experimental test. The full procedure of image-based model generation and the validation of generated model is described in Chapter 2.
As a major objective of this thesis, a non-intrusive scheme for the PGD framework is developed in Chapter 3. It is implemented using in-house developed Matlab (Mathworks, USA) code to conduct the PGD work flow, and calling Abaqus as an external solver for devised fictitious mechanical problems.
The transformation of data from computed tomography (CT) image set to FE model including inhomogeneous material properties is subjected to some physical constraints, and when applying the load, there are also geometric constraints limiting the locations where load could be applied. These constraints will lead to a constrained parameter space, which possibly has difficulty to be separated in a Cartesian fashion. Therefore, a novel strategy to separate the parameters in a collective manner is proposed in Chapter 4.
Chapter 5 details a comprehensive application in biomechanics, the methodologies proposed in Chapter 3 and 4 are applied on the practical model generated in Chapter 2. As a typical application of the PGD vademecum, a material property identification problem is discussed. Further PGD vademecum is generated using the identified material properties with variable loading locations, and with this vademecum, real-time mechanical response of the femur is available.
In addition, for the purpose of extending the methodologies to orthotropic materials, which is commonly used in biomechanics, in Chapter 6 another linear elastic model is investigated with the non-intrusive PGD scheme. Nowadays, isogeometric analysis (IGA) is a very popular tool in computational mechanics. It is appealing to take advantage of non-uniform rational B-splines (NURBS) to discretise the model. For PGD, using B-splines for the discretisation of the parameter space could improve the quality of vademecum, especially for problems involving sensitivities with respect to the parameters during the online computations.
It is important and necessary to extend the PGD framework to nonlinear solid mechanics, because most biological soft tissues have been observed nonlinear mechanical behaviours. Consequently, in Chapter 7 we have developed a PGD framework for the St.Venant-Kirchhoff constitutive model using the Picard linearisation which is consistent with the fixed-point iteration algorithm commonly used in PGD.
In Chapter 8, conclusive remarks are addressed as well as forecasts of possible future works.Postprint (published version
Development of Viscous Techniques for Application to Weapons Configuration Throughout the Flight Regime. A Review. G.U. Aero Report 9119
This report provides a review of current technology on the prediction of viscous
flows using numerical techniques for applications to weapons configurations. The
work is aimed at aiding the preparation of a strategy for advising a capability for
predicting the aerodynamics of weapon configuration and to eventually bring such a
strategy to fruition. Such a strategy would have to involve a long term research and
development programme
A CFD based procedure for airspace integration of small unmanned aircraft within congested areas
Future integration of small unmanned aircraft within an urban airspace requires an a posteriori understanding of the
building-induced aerodynamics which could negatively impact on vehicle performance. Moving away from generalised
building formations, we model the centre of the city of Glasgow using Star-CCMþ, a commercial CFD package. After
establishing a critical turbulent kinetic energy for our vehicle, we analyse the CFD results to determine how best to
operate a small unmanned aircraft within this environment. As discovered in a previous study, the spatial distribution of
turbulence increases with altitude. It was recommended then that UAVs operate at the minimal allowable altitude within
a congested area. As the flow characteristics in an environment are similar, regardless of inlet velocity, we can determine
areas within a city which will have consistently low or high values of turbulent kinetic energy. As the distribution of
turbulence is dependent on prevailing wind directions, some directions are more favourable than others, even if the wind
speed is unchanging. Moving forward we should aim to gather more information about integrated aircraft and how they
respond to turbulence in a congested area
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