Cargo scheduling decision support for offshore oil and gas production: a case study

Woodside Energy Ltd (Woodside), Australia’s largest independent oil and gas company, operates multiple oil and gas facilities off the coast of Western Australia. These facilities require regular cargo shipments from supply vessels based in Karratha, Western Australia. In this paper, we describe a decision support model for scheduling the cargo shipments to minimize travel cost and trip duration, subject to various operational restrictions including vessel capacities, cargo demands at the facilities, time windows at the facilities, and base opening times. The model is a type of non-standard vehicle routing problem involving multiple supply vessels—a primary supply vessel that visits every facility during a round trip taking at most 1 week, and other supply vessels that are used on an ad hoc basis when the primary vessel cannot meet all cargo demands. We validate the model via test simulations using real data provided by Woodside

Isotropic compliance in RRP planar manipulators

In the present paper, the isotropic compliance property is investigated, specifically focusing on RRP plane manipulators. The property is achieved by means of active stiffness regulation, considering three different control strategies, dependent on the joint exerting the control action. For each case, the analytical solutions and the corresponding workspace subsets are presented. To compare the three methods, the active and overall stiffness coefficients are evaluated in the postures defining the isotropic compliance subsets. The feasibility of the methods is also evaluated, considering the passive and active stiffness coefficients

Isotropic compliance in E(3): Feasibility and workspace mapping

A manipulator control system, for which isotropic compliance holds in the Euclidean space E(3), can be significantly simplified by means of diagonal decoupling. However, such simplification may introduce some limits to the region of the workspace where the sought property can be achieved. The present investigation reveals how to detect which peculiar subset, among four different classes, a given manipulator belongs to. The paper also introduces the concept of control gain ratio for each specific single-input/single-output joint control law in order to limit the maximum gain required to achieve the isotropic compliance condition

Optimal joint stiffness regulation in a planar robot for packaging operations

In this paper a new method for achieving isotropic compliance at the contact point is applied to a manipulator for packaging operation. Two different manipulators are considered, namely, PR and PPR. The paper discloses some different strategies for stiffness control, with the purpose of contact force optimization. The control system acts on the controlled joint stiffness in such a way that the contact force, in the Cartesian Space, will be parallel to the displacement of the contact point. Such feature minimizes friction and wear during packaging operations and minimize tangential reactions

Analysis of the Driving Seat Vibrations in High Forward Speed Tractors

The transition towards increased forward speeds in agriculture introduces new technical problems related to dynamic behaviour and the exposure of tractor drivers to high levels of whole-body vibration during on-road and off-road transportation and during field operations. In this study, vibrations transmitted from the ground to the driver's seat have been analysed using methods that meet International Organisation for Standardisation (ISO) standards using a four-wheel-drive tractor, equipped with a front suspension axle and a suspended cab, operating at 11.1 and 13.9 m s?1. The test runs simulating the transportation of agricultural implements were conducted on a rectilinear plane tract of a conglomerate bituminous closed track. Two different tyre types, coded ‘A’ and ‘B’, were tested at different forward speeds. Values for the root-mean-square (RMS) accelerations for each measurement axis and the corresponding vector sum av measured on the tractor rear axle were not proportional to the forward speeds 11.1 and 13.9 m s?1 for tyre A. For tyre B, the vector sum av decreased by 18%. No significant difference was found in the acceleration values on the driver's seat. A 1/3 octave band analysis was performed at the frequency range 1–1000 Hz. Accelerations of the tractor rear axle, beyond the forward speed range of 11.1–13.9 m s?1, increased by 48% along the vertical Z-axis in the frequency range 400–1000 Hz for tyre A and decreased by 66% in the frequency range 1–2 Hz along the horizontal X-axis and by 28% along the Y-axis for tyre B. Comparing the two tyres at 11.1 m s?1 forward speed, the average acceleration values for tyre B compared with tyre A were lower along the X-axis (84%) and greater along the Z (74%) and Y (51%) axes. Comparing the two tyres at 13.9 m s?1 forward speed, the acceleration values for tyre B compared with tyre A were lower along the X-axis (78%) and greater (53%) along the Z-axis. The same analysis was also applied to driving seat accelerations at frequencies of 1–80 Hz. Accelerations for tyre A appeared to have similar trends at the two forward speeds except along the vertical Z-axis, for which acceleration decreased by 22% when forward speed increased. For tyre B, the average acceleration along the X-axis increased by 50% in the frequency range 1–2.5 Hz when forward speed increased. On the other hand, accelerations along the Y and Z axes decreased by 27% and 44%, respectively, when forward speed increased. Comparing the two tyres at 11.1 m s?1, average accelerations for tyre B were found. They were lower by 36% along the X-axis in the frequency range 1–2.5 Hz and greater by 14% along the Z-axis compared with tyre A. At 13.9 m s?1 forward speed, the average acceleration for tyre B compared with tyre A was lower by 17% along the Y-axis. Despite the differences in behaviour of the two tyres with respect to forward speed, the performances were the same in the values of limit fatigue that were bounded within the limit of 4 h for all treatments

Complete analytical thermomechanical model of double friction pendulum devices

Friction Pendulum Devices (FPDs) are strongly attracting the attention of both Ac-ademic and Technical Communities of Engineers concerned with the development of strategies for the protection of structures against earthquakes. Several versions of such devices can be found on the market, ranging from the Single, to the Double and up to the so-called Triple Friction Pendulum. Those devices are characterized by an increasing number of kinematic pairs and corresponding sliding plates. Even though their effectiveness has extensively been proven by means of numerous experimental campaigns carried out worldwide, it seems that many aspects concerning their mechanical behavior still need to be clarified. These aspects concern, among others: 1) the sequence of sliding on the several concave surfaces, 2) the in-fluence of temperature on the frictional properties of the coupling surfaces, 3) the possibility of alternation of mechanical sticking and slipping phases, 4) the possibility of impact-induced rupture of some components, and so on. Those aspects are less clear the larger the number of concave surfaces the device is composed of. With the aim to contribute to a better understating of the mechanical behavior of the multiple friction pendulum devices, a new mechanical inter-pretation of their behavior was formulated and the relevant model was developed. Such model is based on a rigorous, though simplified, mechanical approach. Starting from the analysis of a double pendulum device, which comprises two stainless steel concave plates facing each other and a convex-faced pad coated with polytetrafluoroethylene (PTFE), the mechanical model envisages the decomposition of each time-instant of the dynamic time-history in two phases. For each phase the device is modelled by an open kinematic chain of rigid bodies differently constrained between each other. Moreover, the model is based on the fulfillment of 1) geometric compatibility, 2) kinematic compatibility, 3) dynamical equilibrium and 4) thermo-mechanical coupling

A Comprehensive Survey on Microgrippers Design: Mechanical Structure

An atlas of 98 microgrippers that recently appeared in Literature is herein presented by using four different forms: (a) a restyled layout of the original mechanical structure, (b) its corresponding pseudorigid body model (PRBM), (c) its kinematic chain, and finally, (d) its related graph. Homogeneity in functional sketching (a) is assumed to be greatly helpful to understand how these grippers work and what are the most significant differences between them. Therefore, a unified and systematic set of aesthetics and proportionality criteria have been adopted. Analogously, unified criteria for obtaining pseudorigid (b), kinematic (c), and graph (d) representations have been also used, which made the atlas easy to be read and inspected. The distinction among lumped and distributed compliance has been also accepted to develop the structure of the atlas. A companion paper has been prepared to present a survey on the variety of operational strategies that are used in these microgrippers