Multiple Impacts and Multiple-Compression Process in the Dynamics of Granular Chains

In this paper, we study the dynamics of one-dimensional chains composed of elastoplastic beads. Three uniform chains, which were experimentally studied in the existing literature, are taken as benchmark examples for manifesting wave propagation induced by multiple impacts between particles and by multiple-compression process in a single contact point. We perform simulations using an elastoplastic contact model developed recently for the binary contact of a sphere. Numerical results show good agreement with the experimental observations, including the profile and amplitude of the incident and reflected solitary waves, the travel time of the wave propagation, and the high-frequency oscillations residing in the high-amplitude stress wave. Our simulations also show that the multiple-compression process of the contact between particles is responsible for the oscillations residing in the pulse profile.

VIBRATION OF ROAD BRIDGES UNDER MOVING VEHICLES: A COMPARATIVE STUDY BETWEEN SINGLE CONTACT POINT AND TWO CONTACT POINT MODELS

The study of dynamic response of bridges under the action of moving vehicles provides a tool for structural designing as well as damage identification. Bridge-vehicle interaction is generally modelled through single contact point for mathematical simplicity, although the interaction actually takes place through front and rear wheels. In the present work, dynamic deflection of the bridge modelled through two contact points is investigated for a range of vehicle velocity and wheel to wheel distance. It is observed that for wheelbase to bridge span ratio greater than a certain limit, two contact point model gives significantly different results particularly at higher velocity range. The results, presented in terms of non-dimensional parameters, can be used as a design monograph for any bridge-vehicle-velocity combination.

Analysis and Computation of Two Body Impact in Three Dimensions

A formal impulse-based analysis is presented for the collision of two rigid bodies at single contact point under Coulomb's friction in three dimensions (3D). The tangential impulse at the contact is known to be linear in the sliding velocity whose trajectory, parametrized with the normal impulse and referred to as the hodograph, is governed by a generally nonintegrable ordinary differential equation (ODE). Evolution of the hodograph is bounded by rays in several invariant directions of sliding in the contact plane. Exact lower and upper bounds are derived for the number of such invariant directions, utilizing the established positive definiteness of the matrix defining the governing ODE. If the hodograph reaches the origin, it either terminates (i.e., the contact sticks) or continues in a new direction (i.e., the contact resumes sliding) whose existence and uniqueness, only assumed in the literature, are proven. Closed-form integration of the ODE becomes possible as soon as the sliding velocity turns zero or takes on an invariant direction. Assuming Stronge's energy-based restitution, a complete algorithm is described to combine fast numerical integration (NI) with a case-by-case closed-form analysis. A number of solved collision instances are presented. It remains open whether the modeled impact process will always terminate under Coulomb's friction and Stronge's (or Poisson's) restitution hypothesis.

Supporting Mental Health in the Community: New Systems for General Practice

General practitioners (GPs) manage nearly one-third of Australians seeking help for mental health problems, and frequently express their need for consultant psychiatric support in this work. The introduction of new Medical Benefits Schedule Item Numbers 291 and 293 to provide "one-off" psychiatric assessments on referral from GPs offered the potential for providing this support, and a single point-of-entry scheme was organised to provide ease of access to appointments. The aims were to establish a single point of entry for psychiatrist assessment using Item 291, to evaluate the take-up rates of Item 291 in South Australia (SA) through this service and to evaluate the acceptability to GPs and psychiatrists of a psychiatric primary care consultation-liaison (c-l) model. Results were: 26 psychiatrists joined the project; 64 GPs referred 78 patients for assessment, providing 24% of the Australian take-up rate for Item 291, for 8% of the population; evaluation showed high approval ratings from GPs who particularly appreciated the single contact point; and positive evaluation by psychiatrists of the primary care c-l model. The conclusions were that a single contact point provided ease of access to psychiatrists for GPs; GP and psychiatrist groups evaluated Item 291 very positively; and consumer and carer evaluation are essential for further primary care c-l development.

Manipulator Calibration Using a Single Endpoint Contact Constraint

Most manipulator calibration techniques require expensive and/or complicated pose measuring devices, such as theodolites. This paper investigates a calibration method where the manipulator endpoint is constrained to a single contact point and executes self-motions. From the easily measured joint angle readings, and an identification model, the manipulator is calibrated. Adding a wrist force sensor allows for the calibration of elastic effects due to end-point forces and moments. Optimization of the procedure is discussed. Experimental results are presented, showing the effectiveness of the method.