Abstracts of Journal Articles - Accepted for Publication


The Effect of a Movable Mass on the Aeroelastic Stability of Composite Hingeless Rotor Blades in Hover

Authors
MR Amoozgar, AD Shaw, J Zhang & MI Friswell (Swansea University)
Journal
Journal of Fluids and Structures
accepted for publication
Abstract
In this paper, the aeroelastic stability of a composite hingeless rotor blade with a chordwise movable mass is investigated. The point mass is located near the tip of the blade and its chordwise location is variable with respect to the elastic axis and can be moved during the flight. This movable mass is added to the blade to actuate the blade twist during flight. By actuating the mass in the chord direction of the blade during the flight, a bending moment which is the result of the centrifugal force of the mass and its offset is induced on the blade. This bending moment induces twist in the blade, due to bend-twist coupling in the composite lamination. The blade is modelled by using the geometrically exact fully intrinsic beam equations along with the variational asymptotic beam sectional analysis. The aerodynamic loads are simulated by using the two-dimensional strip theory combined with a uniform inflow. The nonlinear partial differential aeroelastic equations are discretized by a time-space scheme, and the converged results are compared with those reported in the literature and a very good match is observed. The results show that by positioning the mass near the tip of the blade, and also by using the ply angle of about 30 degree in this configuration, the highest possible twist change is achieved when the mass moves from the leading edge to the trailing edge of the blade. Moreover, the spanwise location of the mass slightly changes the stability boundaries, while the chordwise movement significantly affects the aeroelastic instability.

Experimental Validation of an Impact Off-resonance Energy Harvester

Authors
G Martinez-Ayuso, MI Friswell, H Haddad Khodaparast & S Adhikari (Swansea University)
Journal
European Physical Journal - Special Topics
accepted for publication
Abstract
Most piezoelectric energy harvesting research has focused on developing on-resonance harvesters that work at low frequencies, even though higher frequencies can generate more power. In addition, conventional resonant harvesters have low efficiency when the excitation frequency is away from resonance. Using mechanical impacts has the potential to improve the overall harvested energy since high frequencies are excited during impacts. Also, the presence of impacts reduces the influence of the base excitation frequency and the requirement to exactly match the resonance frequency. To take advantage of the higher frequency response, an impact energy harvester is designed and validated experimentally. The harvester consists of a cantilever beam with a piezoelectric patch attached to its base which impacts with a stiff object. The harvester is modelled using finite element analysis and a Hertzian contact law. The model is tested and validated in the laboratory using an in-house manufactured demonstrator. Good agreement with the experimental data is obtained, setting the basis for future optimisation of the harvester geometry and piezoelectric properties.

Non-conservative Stability Analysis of Columns with Various Loads and Boundary Conditions using Fully Intrinsic Equations

Authors
SA Fazelzadeh, M Tashakorian, E Ghavanloo (Shiraz University, Iran), MI Friswell & MR Amoozgar (Swansea University)
Journal
AIAA Journal
accepted for publication
Abstract
In this paper, the stability analysis of the elastic columns subjected to seven different types of the non-conservative force is investigated on the basis of fully intrinsic beam equations. The generalized differential quadrature method is used for the discretization of the first-order intrinsic equations and corresponding boundary conditions. Altogether, four important boundary conditions, including simply supported, clamped-simply supported, clamped-free and clamped-clamped conditions, are considered. Furthermore, the effect of the combined action of an end- concentrated force and a distributed tangential follower force is investigated. To confirm the validity of the proposed intrinsic formulations, the present results are compared with those obtained from classical formulations. Our results reveal that the fully intrinsic formulation is a suitable framework to model non-conservative problems.

Composite Rotor Blade Twist Modification in Flight by Using a Moving Mass and Stiffness Tailoring

Authors
MR Amoozgar, AD Shaw, J Zhang & MI Friswell (Swansea University)
Journal
AIAA Journal
accepted for publication
Abstract
In this paper, a new concept for morphing composite blades is proposed, and how this concept changes the twist distribution of the blade is explained. A change in the blade twist is obtained by adding a mass to the blade which produces an extra centrifugal force. This centrifugal force then may produce a moment that can change the blade twist via the extension-twist or bend-twist coupling of the composite lamination. These types of couplings are present in anti-symmetrically and symmetrically laminated beams, respectively. The dynamics of the rotating composite blade is modeled by using the geometrically exact fully intrinsic beam equations. The concentrated mass is considered as a non-structural concentrated mass which has offsets with respect to the beam reference line. The nonlinear partial differential equations are discretized by using a time-space scheme, and the converged results are compared with those reported in the literature and very good agreement is observed. It is found that for an antisymmetric lamination, the spanwise location of the concentrated mass affects the twist while in the symmetric case the chordwise position of the concentrated mass is the source of twist change. It is also found that introducing the concentrated mass to a real blade can change the twist dramatically.