Abstracts of Journal Articles - Accepted for Publication
Improving Wind Tunnel '1-cos' Gust Profiles
D Balatti, H Haddad Khodaparast, MI Friswell (Swansea University) & M Manolesos (City University, London)
Journal of Aircraft
A vane type gust generator has been designed and characterized in the Swansea University wind tunnel to enable the validation of the response of aircraft models to gust loads. The experimental results reveal the complexity of the flow between the gust vanes and the aircraft model location. Previous studies have shown that generating a predetermined gust profile at the desired location in the wind tunnel is a challenging problem. In this work, two techniques to improve the '1-cos' gust have been considered. In the first case, the transfer functions between the vane rotation and the gust produced at the aircraft model location have been identified, and its inverse has been used to calculate the vane rotation. The strong aerodynamics nonlinearity limits the improvements of this method. A parametric study on vane rotation has shown that a more complicated vane rotation function made it possible to obtain '1-cos' gusts at the aircraft model location with a mean square error two orders of magnitude smaller than the initial case. Creating '1-cos' gusts with similar frequency content as the regulations require will help design more efficient gust load alleviation systems.
System Level Optimisation of Passive Energy Balancing
AD Shaw (Swansea University), J Zhang (Beihang University, China), C Wang (Nanjing University of Aeronautics and Astronautics, China), BKS Woods (University of Bristol) & MI Friswell (Swansea University)
A common issue with morphing structures is that the actuators must work against significant structural and aerodynamic stiffness. The concept of Passive Energy Balancing (PEB) aims to ameliorate this, and thereby reduce system mass, by connecting negative stiffness elements to the actuated degrees of freedom. However, these devices can be complex to design and will also add their own mass to the system. It is therefore difficult to determine the potential for system level mass saving without significant detailed design effort. This work treats a PEB device as essentially a local energy storage mechanism. This framework leads to an approach to optimisation that will deliver a lightweight PEB mechanism in addition to reducing actuator requirements. It also allows a high level method to obtain an approximate evaluation of system level benefits with only basic information about the application being considered, by comparing general properties of the actuators used to the energy storage properties of the underlying materials used in the PEB device. The work concludes with a case study that shows how the PEB can potentially reduce system mass both through reduced energy consumption requirements and actuator mass savings, and can work particularly well for actuators with non ideal stroke/force profiles.
Nonlinear Modal Interactions during Rub-Impact of a Rotating Flexible Shaft
A Kartheek, K Vijayan (Indian Institute of Technology Kharagpur, India) & MI Friswell (Swansea University)
Journal of Vibration and Control
An understating on interaction between a rotating flexible member and a stationary element has wide range of industrial application. The focus of this study was to understand the modal interactions using a conceptual model. The conceptual model of the system consists of multiple disc rotor with a localised conduit. A theoretical model of the system was developed using finite element analysis. An eigenvalue analysis was carried out on the system and a Campbell diagram of the system was developed. The Campbell diagram provided information about the rotor speed wherein synchronization with the whirling modes occur. Further a reduced order non-linear contact model was developed. A numerical bifurcation analysis with rotor speed as parameter was carried out on the reduced model. Analysis was carried out using randomized initial condition for each rotation speed. During the bifurcation study certain rotation speed produced high whirling response at speeds different from the critical speed. The increase in response was associated with the internal resonance of whirling modes and rotor speed. The participating modes were identified using the Campbell diagram and full spectrum. The results from the theoretical model was validated using an experimental test rig. The identification of these internal resonance rotor speed can be useful in identifying the rotor speed exclusion zone and thereby improve the rotor life.
Eringen's Nonlocal and Modified Couple Stress Theories Applied to Vibrating Rotating Nanobeams with Temperature Effects
A Rahmani, S Faroughi (Urmia University of Technology, Iran), MI Friswell (Swansea University) & A Babaei (University of Kentucky, USA)
Mechanics of Advanced Materials and Structures
This study develops a comprehensive vibrational analysis of rotating nanobeams on visco-elastic foundations with thermal effects based on the modified couple stress and Eringen's nonlocal elasticity theories. This approach accurately simulates the nonlocal stress and size effects. Higher-order shear deformation beam theory and the generalized differential quadrature method are used to obtain the numerical results. The effects of nonlocal parameters, length scale, Winkler-Pasternak coefficients, thermal gradient, slenderness ratios, rotating velocity and viscoelastic coefficient are demonstrated and discussed in detail. Mode switching and the importance of the correct choice of theory and associated size effect parameters are highlighted.