Computationally-efficient aeroelastic analysis tool for short-wing/propeller configuration on compound helicopters

A time-domain aeroelastic analysis for short-wing/propeller configuration in compound helicopters is presented in this paper. A linear Timoshenko beam is used in conjunction with analytical aerodynamic theories, while propeller effects are simplified as defined velocity profiles in the advancing and vertical directions. A numerical modal analysis approach is used to incorporate the coupling between bending and torsion. The paper focuses on the application of coupled mode shapes and Timoshenko beam in an aeroelasticity context. A Eurocopter X3-liked short-wing/propeller configuration is studied. Differences introduced by coupled mode shapes and Timoshenko beam theory are discussed. The results show that coupled modal analysis gives a better representation of the modal behaviour with less computational power required. While rotary inertia and shear deformation effects result in a higher mean deflection and a smaller amplitude in the steady state, revealing a different energy distribution mechanism compare to Euler-Bernoulli beam in the system studied

Nonlinear electrostatic effects in MEMS ring-based rate sensors under shock excitation

The vibration response of a capacitive ring-based Coriolis Vibrating Gyroscope (CVG) subjected to in-plane shock is modelled and analysed to quantify the effect of shock on angular velocity measurement. The model developed considers a ring resonator with 8 uniformly spaced support legs and describes the in-plane ring response as the sum of the first 3 modes of a perfect ring and the nonlinear electrostatic force as a Taylor series. When a severe in-plane shock is applied, the rigid body response of the ring reduces the electrode gap significantly and a high order expansion is needed to represent the electrostatic force. These nonlinear forces are shown to cause direct and mixed mode coupling to occur, which can significantly modify the response characteristics. Numerical results are presented and interpreted for a range of shock cases to demonstrate the importance of mode coupling, and estimates are made to quantify the angular rate measurement error caused by shock for devices based on 2θ- and 3θ-modes of operation. To aid the design of devices that are more resilient to shock, a parameter study is performed to identify the modal frequency ratios that minimise this coupling

Efficient numerical methods for aeroelastic analysis of wing-propeller configuration compound helicopters

Efficient numerical methods for time-domain aeroelastic analysis of a wing structure under a propeller-wing configuration is described in the paper. A linear beam model with deformable elastic axis under torsion and flapping is considered to simulate a wing structure with a tipmounted propeller, relying on efficient, analytical formulations. The complete aeroelastic system of equations is then solved using Galerkin’s approach, and numerically integrated by the Newmark-beta method. The computational tool developed is able to efficiently predict in the time domain the wing aeroelastic transient behaviour and the wing-propeller interaction effects. The purpose of the tool developed is to provide accurate enough predictions of the system aeroelastic response to be included in structural optimisation and control synthesis procedures. A detailed analysis on the solver used and an aeroelastic case study of a Eurocopter X3-like compound helicopter wing/propeller configuration are demonstrated

Time-domain aeroelastic model for compound helicopter propeller-wing configuration

A simplified numerical model for time-domain aeroelastic analysis of a wing structure in a propeller-wing configuration is described in the paper. A linear beam model with deformable elastic axis under torsional deformation and out-of-plane bending is considered to simulate a wing structure with tip mounted propeller, relying on efficient, analytical formulations. The complete aeroelastic system of equations is solved using Galerkin’s approach, and numerically integrated by the Newmark-beta method. The computational tool developed is able to predict the wing aeroelastic transient behaviour and the wing-propeller interaction effects in the time domain. The purpose of such a tool is to provide accurate enough predictions of the system aeroelastic response to be included in structural optimisation and control synthesis procedures. A complete analysis on the solver used and an aeroelastic analysis of a Eurocopter X3-like compound helicopter wing/propeller configuration are demonstrated

Modal Control of Vibration in Rotating Machines and Other Generally Damped Systems

Second order matrix equations arise in the description of real dynamical systems. Traditional modal control approaches utilise the eigenvectors of the undamped system to diagonalise the system matrices. A regrettable consequence of this approach is the discarding of residual off-diagonal terms in the modal damping matrix. This has particular importance for systems containing skew-symmetry in the damping matrix which is entirely discarded in the modal damping matrix. In this paper a method to utilise modal control using the decoupled second order matrix equations involving non-classical damping is proposed. An example of modal control successfully applied to a rotating system is presented in which the system damping matrix contains skew-symmetric components

Hierarchical Control for Trajectory Generation and Tracking Via Active Front Steering

A new hierarchical model predictive controller for autonomous vehicle steering control is presented. The controller generates a path of shortest distance by determining lateral coordinates on a longitudinal grid, while respecting road bounds. This path is then parameterized by arc length before being optimized to restrict the normal acceleration values along the trajectory's arc length. The optimized tra-jectory is then tracked using a nonlinear model predictive control scheme using a bicycle plant model to calculate an optimal steering angle for the tires. The proposed controller is evaluated in simulation during a double-lane-change maneuver, where it generates and tracks a reference trajectory while observing the road boundaries and acceleration limits. Its performance is compared to a controller without path optimization, along with another that uses a smooth, predetermined, reference path instead of creating its own initial reference. It is shown that the proposed controller improves the tracking compared to a controller without path optimization, with a four-times reduction in average lateral tracking error. The average lateral acceleration is also reduced by 6%. The controller also maintains the tracking performance of a controller that uses a smooth reference path, while showing a much greater flexibility due to its ability to create its own initial reference path rather than having to follow a predetermined trajectory

A phenomenological constitutive model for the viscoelastic deformation of elastomers

This study proposes a one-dimensional constitutive model for elastomeric materials based on recent observations regarding the separation of elastic and viscous contributions in uniaxial cyclic tensile experiments on EPDM rubber. The focus is on capturing the changes in constitutive behaviour and energy dissipation associated with the Mullins effect. In the model, this is achieved through the evolution of both permanent set and hyperelastic parameters of an Edwards-Vilgis function to account for the Mullins effect, and with a viscosity associated with the effective stretch rate of the network to describe the non-linear flow stress. The simulations are able to reproduce the observed constitutive response and its change with increasing levels of pre-deformation. The model is less able to accurately reproduce the virgin loading response, which is achieved via extrapolation to zero pre-strain. However, for practical purposes, where scragging of elastomeric products is the norm, the model is able to predict the cyclic response and the dissipated energy, and their change with different scragging levels in good agreement with experimental data

Modal Control of Vibration in Rotating Machines and Other Generally Damped Systems

Second order matrix equations arise in the description of real dynamical systems. Traditional modal control approaches utilise the eigenvectors of the undamped system to diagonalise the system matrices. A regrettable consequence of this approach is the discarding of residual o-diagonal terms in the modal damping matrix. This has particular importance for systems containing skew-symmetry in the damping matrix which is entirely discarded in the modal damping matrix. In this paper a method to utilise modal control using the decoupled second order matrix equations involving nonclassical damping is proposed. An example of modal control sucessfully applied to a rotating system is presented in which the system damping matrix contains skew-symmetric components

Computationally-efficient aeroelastic analysis tool for short-wing/propeller configuration on compound helicopters

A time-domain aeroelastic analysis for short-wing/propeller configuration in compound helicopters is presented in this paper. A linear Timoshenko beam is used in conjunction with analytical aerodynamic theories, while propeller effects are simplified as defined velocity profiles in the advancing and vertical directions. A numerical modal analysis approach is used to incorporate the coupling between bending and torsion. The paper focuses on the application of coupled mode shapes and Timoshenko beam in an aeroelasticity context. A Eurocopter X3-liked short-wing/propeller configuration is studied. Differences introduced by coupled mode shapes and Timoshenko beam theory are discussed. The results show that coupled modal analysis gives a better representation of the modal behaviour with less computational power required. While rotary inertia and shear deformation effects result in a higher mean deflection and a smaller amplitude in the steady state, revealing a different energy distribution mechanism compare to Euler-Bernoulli beam in the system studied

Recent research on flexible fixtures for manufacturing processes

Fixtures, are used to fixate, position and support workpieces, and form a crucial tool in manufacturing. Their performance influences the manufacturing (and assembly) process of a product. Furthermore, fixturing can form a significant portion of the needed investment and total process planning time for the manufacturing system. Many fixturing concepts, as contribution to increase the flexibility of the manufacturing system, are reported in the literature. The flexible fixturing designs can be classified into the following seven categories: modular fixtures, flexible pallet systems, sensor-based fixture design, phase-change based concepts, chuck-based concepts, pin-type array fixtures and automatically reconfigurable fixtures. It is observed that the more intelligent and automated fixturing systems are designed with the demands for automation in certain industries in mind. Furthermore, different fixturing solutions suit the engineering demands for different manufacturing areas, this means that for the foreseeable future all technologies will remain current. From the self-reconfigurable fixturing techniques a new fixturing capability is emerging: in process reconfigurability for the optimal placement of clamps and supports during the whole process time. These several concepts together with some recent patents are studied here. The paper concludes with some prospective research directions in the field of flexible fixturing