Aeroelastic Stability of Rotor Blades Using Finite Element Analysis

The flutter stability of flap bending, lead-lag bending, and torsion of helicopter rotor blades in hover is investigated using a finite element formulation based on Hamilton's principle. The blade is divided into a number of finite elements. Quasi-steady strip theory is used to evaluate the aerodynamic loads. The nonlinear equations of motion are solved for steady-state blade deflections through an iterative procedure. The equations of motion are linearized assuming blade motion to be a small perturbation about the steady deflected shape. The normal mode method based on the coupled rotating natural modes is used to reduce the number of equations in the flutter analysis. First the formulation is applied to single-load-path blades (articulated and hingeless blades). Numerical results show very good agreement with existing results obtained using the modal approach. The second part of the application concerns multiple-load-path blades, i.e. bearingless blades. Numerical results are presented for several analytical models of the bearingless blade. Results are also obtained using an equivalent beam approach wherein a bearingless blade is modelled as a single beam with equivalent properties. Results show the equivalent beam model

The representation and consumption of 'Asian culture'

This thesis focuses on the representation and consumption of 'Asian culture' within a context of Western popular culture and specifically, 'British mainstream' and 'British Asian' magazine visual discourses. Through a critical engagement with Edward Said's Orientalism (1978) which charted Western inferiorizing cultural representations of the East as located in historical and material contexts, I aim to explore issues of 'race' and Otherness amidst a background of historical and commodification processes. This has been attempted using multiple methodologies that in addition to engaging with secondary material, has involved a reflexive use of semiotics and discourse analysis to analyse magazine images and written text respectively. Further, I have attempted to go beyond the textual focus of both Orientalism (1978) and many media studies by also gathering contextual reader responses to magazine representations. These have taken the form of the subjective interpretations of 20 British youths (men and women of Asian and white English origin) that have been analysed in conjunction with biographical narratives that I also conducted with each of them. Through the use of this rich and varied empirical data coupled with a thorough review of secondary source material, I aim to add to and question work that has been conducted in the area of 'race' and culture that appears to have moved from a concentration on the 'essential black subject' to an emphasis on ethnic unities within an uncritical celebration of 'diaspora' and 'hybridity'. I also aim to make problematic work that has been conducted in the area of orientalism through drawing attention to the limitations associated with the concept of 'self-orientalism' and practices of 'self-representation' by minorities. Overall, through conducting work on Asian representations within the popular magazine media coupled with its interrelation with varied audiences, I hope to make some inroads into these under-researched areas

Passivity-Based Control of Human-Robotic Networks with Inter-Robot Communication Delays and Experimental Verification

In this paper, we present experimental studies on a cooperative control system for human-robotic networks with inter-robot communication delays. We first design a cooperative controller to be implemented on each robot so that their motion are synchronized to a reference motion desired by a human operator, and then point out that each robot motion ensures passivity. Inter-robot communication channels are then designed via so-called scattering transformation which is a technique to passify the delayed channel. The resulting robotic network is then connected with human operator based on passivity theory. In order to demonstrate the present control architecture, we build an experimental testbed consisting of multiple robots and a tablet. In particular, we analyze the effects of the communication delays on the human operator's behavior

Static dielectric response and Born effective charge of BN nanotubes from {\it ab initio} finite electric field calculations

{\it Ab initio} investigations of the full static dielectric response and Born effective charge of BN nanotubes (BN-NTs) have been performed for the first time using finite electric field method. It is found that the ionic contribution to the static dielectric response of BN-NTs is substantial and also that a pronounced chirality-dependent oscillation is superimposed on the otherwise linear relation between the longitudinal electric polarizability and the tube diameter ($D$), as for a thin dielectric cylinderical shell. In contrast, the transverse dielectric response of the BN-NTs resemble the behavior of a thin (non-ideal) conducting cylindrical shell of a diameter of $D+4$\AA$$, with a screening factor of 2 for the inner electric field. The medium principal component $Z_y^*$ of the Born effective charge corresponding to the transverse atomic displacement tangential to the BN-NT surface, has a pronounced $D$-dependence (but independent of chirality), while the large longitudinal component $Z_z^*$ exhibits a clear chirality dependence (but nearly $D$-independent), suggesting a powerful way to characterize the diameter and chirality of a BN-NT.Comment: submitted to PR

Magnetoresistance of atomic-sized contacts: an ab-initio study

The magnetoresistance (MR) effect in metallic atomic-sized contacts is studied theoretically by means of first-principle electronic structure calculations. We consider three-atom chains formed from Co, Cu, Si, and Al atoms suspended between semi-infinite Co leads. We employ the screened Korringa-Kohn-Rostoker Green's function method for the electronic structure calculation and evaluate the conductance in the ballistic limit using the Landauer approach. The conductance through the constrictions reflects the spin-splitting of the Co bands and causes high MR ratios, up to 50%. The influence of the structural changes on the conductance is studied by considering different geometrical arrangements of atoms forming the chains. Our results show that the conductance through s-like states is robust against geometrical changes, whereas the transmission is strongly influenced by the atomic arrangement if p or d states contribute to the current.Comment: Revised version, presentation of results is improved, figure 2 is splitted to two figure

First-Principle Description of Correlation Effects in Layered Materials

We present a first-principles description of anisotropic materials characterized by having both weak (dispersion-like) and strong covalent bonds, based on the Adiabatic--Connection Fluctuation--Dissipation Theorem within Density Functional Theory. For hexagonal boron nitride the in-plane and out of plane bonding as well as vibrational dynamics are well described both at equilibrium and when the layers are pulled apart. Also bonding in covalent and ionic solids is described. The formalism allows to ping-down the deficiencies of common exchange-correlation functionals and provides insight towards the inclusion of dispersion interactions into the correlation functional.Comment: Accepted for publication in Physical Review Letter