Abstract

Abstract

Self-deployable composite structures are attractive for space applications as they provide lightweight, low cost and simple solutions that can replace mechanical systems. These structures can be folded and use the stored strain energy to promote a self-deployment event. However, these structures present design, manufacture and optimize challenges.

This article describes the process of designing and optimizing an elastic-hinge, for a telecommunication satellite considering both structural and frequency requirements using finite element analysis, manufacturing and experimental testing. Furthermore, the paper details the sequence of optimization algorithms that were used to produce a solution capable of meeting the original design specifications.

The structural assessment consists of the elastic-hinge numerical modelling during the folding process, by means of an explicit formulation. This model correlates well to the experimental test data and was used to evaluate the damage installed in the hinge using a pletfora of damage criteria.

The frequency analysis considers the numerical modelling of a system constituted by the elastic-hinge and a telecommunication satellite antenna. This model was used to estimate the natural frequency of the system.

Results show that a design methodology which uses a genetic algorithm (GA) for a global search, followed by a particle swarm optimization (PSO) method for a local search provides a good approach to the optimization problem. It is also shown that the efficiency of these algorithms can be maximized by tailoring their architecture and internal parameters.

Abstract

Living biological tissues are complex structures that have the capacity of evolving
in response to external loads and environmental stimuli. The adequate modelling
of soft biological tissue behaviour is a key issue in successfully reproducing
biomechanical problems through computational analysis.
This study presents a general constitutive formulation capable of representing
the behaviour of these tissues through finite element simulation. It is based on
phenomenological models that, used in combination with the generalized mixing
theory, can numerically reproduce a wide range of material behaviours.
First, the passive behaviour of tissues is characterized by means of hyperelastic
and finite-strain damage models. A generalized damage model is proposed,
providing a flexible and versatile formulation that can reproduce a wide range of
tissue behaviour. It can be particularized to any hyperelastic model and requires
identifying only two material parameters. Then, the use of these constitutive
models with generalized mixing theory in a nite strain framework is described
and tools to account for the anisotropic behaviour of tissues are put forth.
The active behaviour of tissues is characterized through constitutive models
capable of reproducing the growth and remodelling phenomena. These are built
on the hyperelastic and damage formulations described above and, thus, represent
the active extension of the passive tissue behaviour. A growth model considering
biological availability is used and extended to include directional growth. In addition,
a novel constitutive model for homeostatic-driven turnover remodelling is
presented and discussed. This model captures the stiffness recovery that occurs
in healing tissues, understood as a recovery or reversal of damage in the tissue,
which is driven by both mechanical and biochemical stimuli.
Finally, the issue of correctly identifying the material parameters for computational
modelling is addressed. An inverse method using optimization techniques
is developed to facilitate the identification of these parameters.

Abstract

This work is about the development of a general algorithm for the numerical solution of flow equations: the Navier-Stokes set. This set of differential equations models the time dependent behavior of fluids. It is formed by continuity, linear momentum and an energy transport equations. The algorithm here described is a general one since it can handle equally a great variety of problems, ranging from incompressible to compressible flows, viscous to inviscid, stationary and transient, all of them phisically modeled by the same set of differential equations.

In the present work, a quest for a general algorithm is described, following one of many possible ways to tackle the problem. In general, this is done extending methods either from compressible to incompressible flows or from incompressible to compressible ones.

Abstract

In this paper some results of a wide experimental program are presented and compared with some finite element solution of sheet metal forming problems using a viscous shell formulation.

Abstract

This study proposes a methodology for the calibration of combined sewer overflow (CSO), incorporating the results of the three-dimensional ANSYS CFX model in the SWMM one-dimensional model. The procedure consists of constructing calibration curves in ANSYS CFX that relate the input flow to the CSO with the overflow, to then incorporate them into the SWMM model. The results obtained show that the behavior of the flow over the crest of the overflow weir varies in space and time. Therefore, the flow of entry to the CSO and the flow of excesses maintain a non-linear relationship, contrary to the results obtained in the one-dimensional model. However, the uncertainty associated with the idealization of flow methodologies in one dimension is reduced under the SWMM model with kinematic wave conditions and simulating CSO from curves obtained in ANSYS CFX. The result obtained facilitates the calibration of combined sewer networks for permanent or non-permanent flow conditions, by means of the construction of curves in a three-dimensional model, especially when the information collected in situ is limited.

Abstract

Abstract

Permeable pavements are a common solution for wearing course layers in roads and urban areas. They are composed by highly porous materials with permeability several orders of magnitude above of the natural terrain. This work presents, on one hand, the experimental characterisation of the hydraulic behaviour of a permeable asphalt concrete wearing course layer and, on the other hand, the development and validation of a two-dimensional coupled hydraulic-hydrological distributed numerical model to reproduce the effect of the infiltration in the rainfall-runoff transformation and in the overland flow propagation processes. Experiments show linear and potential trends for permeability-hydraulic head relations when considering constant and variable hydraulic heads, respectively, reaching permeability up to 0.04 m/s for 1 m of hydraulic head. Experiments are reproduced numerically by incorporating new infiltration formulas, which consider the infiltration rate as a function of the hydraulic head, and a specific numerical scheme for properly dealing the mass conservation when negative values of the water depth may occur numerically due to high infiltration rates. This two-dimensional coupled hydraulic-hydrological distributed numerical model is a validated tool for simulating the effect of permeable pavements not only in the rainfall-runoff process, but also for the overland flow propagation.

Abstract

Generally, the effects of suction in fine sands can be evidenced by a stiffening of the material, as the capillary front advances in the granular skeleton. In geotechnical retention structures this effect can be translated in an increasing of earth pressure, which is not normally considered in geotechnical designs. This study analyzes the capillary effects by implementing a physical modelling in centrifuge and a numerical simulation, using different constitutive models that involve suction within the analysis. The modelling is based on a structure of retention in sheetpiles built on a real scale. Some factors that affect both physical and numerical modelling were taken into account and should be considered in the analysis of the results obtained and, in the comparisons, carried out by both methodologies. As a point of interest, numerical modelling showed less dispersion in the results obtained than physical modelling, these and other aspects are analyzed in the document

Abstract