DSpace Collection:
https://dspace.lboro.ac.uk/2134/2397
2015-06-30T03:38:45ZOn the effects of mistuning a force-excited system containing a quasi-zero-stiffness vibration isolator
https://dspace.lboro.ac.uk/2134/18010
Title: On the effects of mistuning a force-excited system containing a quasi-zero-stiffness vibration isolator
Authors: Abolfathi, Ali; Brennan, M.J.; Waters, T.P.; Tang, B.
Abstract: Nonlinear isolators with high-static-low-dynamic-stiffness have received considerable attention in the recent literature due to their performance benefits compared to linear vibration isolators. A quasi-zero-stiffness (QZS) isolator is a particular case of this type of isolator, which has a zero dynamic stiffness at the static equilibrium position. These types of isolators can be used to achieve very low frequency vibration isolation, but a drawback is that they have purely hardening stiffness behavior. If something occurs to destroy the symmetry of the system, for example, by an additional static load being applied to the isolator during operation, or by the incorrect mass being suspended on the isolator, then the isolator behavior will change dramatically. The question is whether this will be detrimental to the performance of the isolator and this is addressed in this paper. The analysis in this paper shows that although the asymmetry will degrade the performance of the isolator compared to the perfectly tuned case, it will still perform better than the corresponding linear isolator provided that the amplitude of excitation is not too large.
Description: This paper is closed access.2015-01-01T00:00:00ZReachability analysis of landing sites for forced landing of a UAS in wind using trochoidal turn paths
https://dspace.lboro.ac.uk/2134/18006
Title: Reachability analysis of landing sites for forced landing of a UAS in wind using trochoidal turn paths
Authors: Coombes, Matthew; Chen, Wen-Hua; Render, Peter M.
Abstract: This paper details a method to ascertain the reachability
of known emergency landing sites for any fixed wing
aircraft in a forced landing due to engine failure in steady
uniform wind conditions. With knowledge of the aircraft’s
state and parameters, and landing site location and landing
direction, the minimum height loss path can be defined. This
uses glide performance calculations and a trajectory planner to
give a minimum height loss to each landing site. Based on the
aircraft’s initial altitude it can calculate if the site is reachable,
and how reachable it is. The path definition takes into account
wind and uses a geometric shape called a trochoid to define
the gliding turns in wind. This method is generic enough for
use by any aircraft in any wind conditions.
Description: This conference paper is closed access.2015-01-01T00:00:00ZMethod to improve catalyst layer model for modelling proton exchange membrane fuel cell
https://dspace.lboro.ac.uk/2134/17950
Title: Method to improve catalyst layer model for modelling proton exchange membrane fuel cell
Authors: Zhang, Xiaoxian; Gao, Yuan; Ostadi, Hossein; Jiang, Kyle; Chen, Rui
Abstract: Correctly describing oxygen reduction within the cathode catalyst layer (CL) in modelling proton exchange membrane fuel cell is an important issue remaining unresolved. In this paper we show how to derive an agglomerate model for calculating oxygen reactions by describing dissolved oxygen in the agglomerates using two independent random processes. The first one is the probability that an oxygen molecule, which dissolves in the ionomer film on the agglomerate surface, moves into and then remains in the agglomerates; the second one is the probability of the molecule being consumed in reactions. The first probability depends on CL structure and can be directly calculated; the second one is derived by assuming that the oxygen reduction is first-order kinetic. It is found that the distribution functions of the first process can be fitted to a generalised gamma distribution function, which enables us to derive an analytical agglomerate model. We also expend the model to include oxygen dissolution in the ionomer film, and apply it to simulate cathode electrodes. The results reveal that the resistance to oxygen diffusion in ionomer film and agglomerate in modern CL is minor, and that the main potential loss is due to oxygen dissolution in the ionomer film.
Description: This article will be in closed access until 1 Sept 2016.2015-01-01T00:00:00ZUAV conflict detection and resolution using probabilistic approach
https://dspace.lboro.ac.uk/2134/17862
Title: UAV conflict detection and resolution using probabilistic approach
Authors: Oh, Hyondong; Park, Jung-Woo; Tahk, Min-Jea
Abstract: This paper presents a real-time conflict detection and resolution algorithm based on a probabilistic method. It is assumed
that aircraft are linked by real time data link like ADS-B. The approach uses a set of probability density functions that describe
uncertainties from ADS-B. To calculate the probability of conflict, we use probabilistic method by using Monte Carlo simulations.
Monte Carlo simulations are often thought of as too slow for real-time usage. However, in this paper, we use geometric based Monte
Carlo simulations which allow for reducing computation time considerably. From the probability of conflict obtained, ‘Threat Level’
is determined between two aircraft, then, one of possible resolution maneuver options is chosen to minimize the probability of
conflict. Resolution maneuver chosen as three-axis acceleration commands is added to the current acceleration and transformed into
the control inputs. While the probability of conflict is in threat level zero, own aircraft is guided to the way-point. For guidance to
the waypoint, proportional navigation guidance law is used. The paper finishes with several multiple-aircraft encounter simulations,
illustrating the performance and properties of the proposed algorithm.
Description: This conference paper is closed access.2008-01-01T00:00:00Z