Empirical assessment of the critical time increment in explicit particulate discrete element method simulations

This contribution considers the critical time increment (〖∆t〗_crit) to achieve stable simulations using particulate discrete element method (DEM) codes that adopt a Verlet-type time integration scheme. The 〖∆t〗_crit is determined by considering the maximum vibration frequency of the system. Based on a series of parametric studies, 〖∆t〗_crit is shown to depend on the particle mass (m), the maximum contact stiffness (Kmax), and the maximum particle coordination number (CN,max). Empirical expressions relating 〖∆t〗_crit to m, Kmax, and CN,max are presented; while strictly only valid within the range of simulation scenarios considered here, these can inform DEM analysts selecting appropriate 〖∆t〗_crit values

SAW torque transducers for disturbance rejection and tracking control of multi-inertia servo-drive systems

The paper proposes a resonance ratio control (RRC) technique for the coordinated motion control of multi-inertia mechanical systems, based on the measurement of shaft torque via a SAW-based torque sensor. Furthermore, a new controller structure, RRC plus disturbance feedback is proposed, which enables the controller to be designed to independently satisfy tracking and regulation performance. A tuning method for the RRC structure is given based on the ITAE index, normalized as a function of the mechanical parameters enabling a direct performance comparison between a basic proportional and integral (PI) controller. The use of a reduced-order state observer is presented to provide a dynamic estimate of the load-side disturbance torque for a multi-inertia mechanical system, with an appraisal of the composite closed-loop dynamics. It is shown that the integrated formulation of the tuning criteria enables lower bandwidth observers to be implemented with a corresponding reduction in noise and computational load. The control structures are experimentally validated via a purpose designed test facility and demonstrate significant improvement in dynamic tracking performance, whilst additionally rejecting periodic load side disturbances, a feature previously unrealisable except by other, high-gain control schemes that impose small stability margins

Observer based tuning techniques and integrated SAW torque transducers for two-inertia servo-drive systems

A controller design and tuning methodology is proposed that facilitates the rejection of periodic load-side disturbances applied to a torsional mechanical system, whilst simultaneously compensating for the disturbance observer's inherent phase delay, thereby facilitating the used of lower bandwidth, practically realisable, disturbance observers. The merits of implementing both a full- and reduced order observer, is investigated, with the latter being implemented with a new low-cost, high-bandwidth torque sensing device based on surface acoustic wave technolog

"So go downtown": simulating pedestrian movement in town centres

Pedestrian movement models have been developed since the 1970s. A review of the literature shows that such models have been developed to explain and predict macro, meso, and micro movement patterns. However, recent developments in modelling techniques, and especially advances in agent-based simulation, open up the possibility of developing integrative and complex models which use existing models as 'building blocks'. In this paper we describe such integrative, modular approach to simulating pedestrian movement behaviour. The STREETS model, developed by using Swarm and GIS, is an agent-based model that focuses on the simulation of the behavioural aspects of pedestrian movement. The modular structure of the simulation is described in detail. This is followed by a discussion of the lessons learned from the development of STREETS, especially the advantages of adopting a modular approach and other aspects of using the agent-based paradigm for modelling

STREETS: an agent-based pedestrian model.

8-11 Septembe

Zebra battery technologies for all electric smart car

This paper describes the operational behaviour and advantages of the high temperature, sodium nickel chloride (Zebra) battery, for use in all electric urban (city) vehicles. It is shown that an equivalent parallel electrical circuit can be employed to accurately simulate the electrochemical behaviour inherent in the most recent generation of Zebra cells. The experimental procedure is outlined and summary attributes of the investigation validated by both simulation studies, and experimentally, via measurements from a prototype battery module intended for use in an all electric smart ca

Improved performance of motor-drive systems by SAW shaft torque feedback

The paper describes the application of a non-contact, high bandwidth, low cost, SAW-based torque measuring system for improving the dynamic performance of industrial process motor-drive systems. Background to the SAW technology and its motor integration is discussed and a resonance ratio control (RRC) technique for the coordinated motion control of multi-inertia mechanical systems, based on the measurement of shaft torque via a SAW-based torque sensor is proposed. Furthermore, a new controller structure, RRC plus disturbance feedback is proposed, which enables the controller to be designed to independently satisfy tracking and regulation performance. A tuning method for the RRC structure is given based on the ITAE index, normalized as a function of the mechanical parameters enabling a direct performance comparison between a basic proportional and integral (PI) controller. The use of a reduced-order state observer is presented to provide a dynamic estimate of the load-side disturbance torque for a multi-inertia mechanical system, with an appraisal of the composite closed-loop dynamics. The control structures are experimentally validated and demonstrate significant improvement in dynamic tracking performance, whilst additionally rejecting periodic load side disturbances, a feature previously unrealisable except by other, high-gain control schemes that impose small stability margins

On the Anomalous Temperature Distribution of the Intergalactic Medium in the NGC 3411 Group of Galaxies

We present XMM, Chandra and VLA observations of the USGC S152 group and its central elliptical NGC 3411. Imaging of the group X-ray halo suggests it is relaxed with little apparent structure. We investigate the temperature and metal abundance structure of the group halo, and find that while the abundance distribution is fairly typical, the temperature profile is highly unusual, showing a hot inner core surrounded by a cool shell of gas with a radius of \~20-40 kpc, at the center of the larger group halo. Spectral mapping confirms an irregular ring of gas ~0.15 keV cooler than its surroundings. We estimate the total mass, entropy and cooling time profiles within ~200 kpc, and find that the cool shell contains ~9x10^9 Msun of gas. VLA observations at 1.4, 5 and 8 GHz reveal a relatively weak nuclear radio source, with a core radio luminosity L_R=2.7x10^38 erg/s, and a diffuse component extended on scales of a few arcseconds (or more). A lack of evidence for activity at optical or X-ray wavelengths supports the conclusion that the central black hole is currently in a quiescent state. We discuss possible mechanisms for the formation of temperature features observed in the halo, including a previous period of AGN activity, and settling of material stripped from the halo of one of the other group member galaxies.Comment: 15 pages, 8 postscript figures, accepted for publication in ApJ version with high resolution figures available at http://hea-www.harvard.edu/~ejos/files/N3411_hires.pd

Empirical assessment of the critical time increment in explicit particulate discrete element method simulations

This contribution considers the critical time increment (〖∆t〗_crit) to achieve stable simulations using particulate discrete element method (DEM) codes that adopt a Verlet-type time integration scheme. The 〖∆t〗_crit is determined by considering the maximum vibration frequency of the system. Based on a series of parametric studies, 〖∆t〗_crit is shown to depend on the particle mass (m), the maximum contact stiffness (Kmax), and the maximum particle coordination number (CN,max). Empirical expressions relating 〖∆t〗_crit to m, Kmax, and CN,max are presented; while strictly only valid within the range of simulation scenarios considered here, these can inform DEM analysts selecting appropriate 〖∆t〗_crit values