Vol. 19, No 3, 2015 < Volumes
(ISSN 1428-6394)

Contents:

  • Rohan Soman, Pawel Malinowski, Wieslaw Ostachowicz Bi-axial Neutral Axis Tracking for Crack Detection in Wind Turbine Towers   abstract | full text
  • Lara Trapani, Ruben Gatt, Luke Mizzi and Joseph N. Grima Mechanical Properties of 2D Flexyne and Reflexyne Polyphenylacetylene Networks: A Comparative Computer Studies with Various Force-Fields   abstract | full text
  • Yevhen Chaplya, Olha Chernukha and Anastasiia Davydok Mathematical Modeling of Random Diffusion Flows in Two-Phase Multilayered Stochastically Nonhomogeneous Bodies   abstract | full text
  • Yevhen Chaplya, Olha Chernukha and Anastasiia Davydok Simulation of Diffusion Flows in Two-Phase Multilayered Stochastically Nonhomogeneous Bodies with Non-Uniform Distribution of Inclusions   abstract | full text

Abstracts:

hRohan Soman, Pawel Malinowski, Wieslaw Ostachowicz Bi-axial Neutral Axis Tracking for Crack Detection in Wind Turbine Towers

This work concentrates on Structural Health Monitoring (SHM) of a wind turbine tower. The paper investigates the use of a decision level data fusion based on bi-axial tracking of change in the neutral axis (NA) position for damage detection in wind turbine towers. A discrete Kalman Filter (KF) is employed for the estimation of the NA in the presence of measurement noise from the strain sensors. The KF allows data fusion from the strain sensors and the yaw mechanism for the accurate estimation of the NA. Any change in the NA position may be used for detecting and locating the damage. The tan inverse of the ratio of the change in the NA along two perpendicular axes is taken and used for the localization. The study was carried out on a simulated finite element (FE) model of a wind turbine tower with a surface crack. The sensitivity studies carried out on the structure in terms of different crack sizes, crack locations and crack orientations indicate that the methodology is robust enough to detect the crack under different operational loading conditions.

 

hLara Trapani, Ruben Gatt, Luke Mizzi and Joseph N. Grima Mechanical Properties of 2D Flexyne and Reflexyne Polyphenylacetylene Networks: A Comparative Computer Studies with Various Force-Fields

Auxetic materials exhibit the very unusual property of becoming wider when stretched and narrower when compressed, – they have a negative Poisson's ratio. This unusual behaviour is the source of many desired effects in the materials' properties and it is therefore, no wonder that auxetics are described as being superior to conventional materials in many practical applications. Here we make use of force-field based molecular modelling simulations in order to investigate the mechanical properties of polypehyleacetylene systems known as (n, m)-flexyne and (n, m)-reflexyne in an attempt to extend the existing knowledge there is regarding these systems. These systems have already attracted considerable consideration since negative on-axis Poisson's ratios have been discovered for the reflexynes. We first developed a methodology for the modelling and property determination of flexyne and reflexyne network systems which we validated against existing published data. Then, extended the study to prove the simulated results were independent of the modelling methodology or the force-field used. In particular, we showed that on-axis auxeticity in the reflexynes is a force-field independent property, i.e. a property which is not an artefact of the simulations but a property which is likely to be present in the real materials if these were to be synthesised. We also studied and reported the shear behaviour of these systems were we show that the flexynes and reflexynes have very low shear moduli, a property which regrettably limits the prospects of these systems in many practical applications. Finally we examine the in-plane off-axis mechanical properties of the systems and we report that in general, these mechanical properties are highly dependent on the direction of loading. We also find that the auxeticity exhibited by the reflexynes on-axis is lost when these systems are loaded off axis since the Poisson's ratios becomes positive very rapidly as the structure is stretched slightly off-axis (e.g. 238 L. Trapani, R. Gatt, L. Mizzi and J. N. Grima 15deg off-axis). This is once again of great practical significance as it highlights another major limitation of these systems in their use as auxetics.

 

hYevhen Chaplya, Olha Chernukha and Anastasiia Davydok Mathematical Modeling of Random Diffusion Flows in Two-Phase Multilayered Stochastically Nonhomogeneous Bodies

An approach for studying stochastical diffusion flows of admixture particles in bodies of multiphase randomly nonhomogeneous structures is proposed, according to which initialboundary value problems of diffusion are formulated for flow functions and methods of solution construction are adapted for the formulated problems. By this approach the admixture diffusion flow is investigated in a two-phase multilayered strip for the uniform distribution of phases under conditions of constant flow on the upper surface and zero concentration of admixture on the lower surface. An integro-differential equation equivalent to the original initial-boundary value problem is constructed. Its solution is found in terms of the Neumann series. Calculation formulae are obtained for the diffusion flow averaged over the ensemble of phase configurations under both zero and constant nonzero initial concentrations. Software is developed, a dependence of averaged diffusion flows on the medium characteristics is studied and general regularities of this process are established.

 

hYevhen Chaplya, Olha Chernukha and Anastasiia Davydok Simulation of Diffusion Flows in Two-Phase Multilayered Stochastically Nonhomogeneous Bodies with Non-Uniform Distribution of Inclusions

Admixture diffusion flows are investigated in two-phase randomly nonhomogeneous multilayered strips with non-uniform distributions of inclusions. Cases where the most probable disposition of layered inclusions is located near the body boundary on which the mass source acts in the neighborhood of another boundary and in the middle of the body are considered. The initial-boundary value problem is formulated for the function of random mass flow under conditions of a constant flow on the upper surface and zero concentration of the admixture on the lower surface. Calculation formulae are obtained for the diffusion flow averaged over the ensemble of phase configurations in the particular cases of beta-distribution at zero and nonzero initial concentrations. The dependences of the averaged admixture flows on medium characteristics are established. It is shown that if the admixture diffusion coefficient in inclusions is greater than in the matrix, consolidation of inclusions in the middle of the body leads to an increasing diffusion flow. Simulation of the averaged diffusion flows of the admixture in the multilayered strip is performed for different model variants of a probable disposition of phases in the body and their comparative analysis is carried out.

 

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