216,514 research outputs found
An optimization framework for solving capacitated multi-level lot-sizing problems with backlogging
No full textThis paper proposes two new mixed integer programming models for capacitated multi-level lot-sizing problems with backlogging, whose linear programming relaxations provide good lower bounds on the optimal solution value. We show that both of these strong formulations yield the same lower bounds. In addition to these theoretical results, we propose a new, effective optimization framework that achieves high quality solutions in reasonable computational time. Computational results show that the proposed optimization framework is superior to other well-known approaches on several important performance dimensions
A curvilinear abscissa approach for the lap time optimization of racing vehicles
No full textThe optimal control and lap time optimization of vehicles such as racing cars and motorcycle is a challenging problem, in particular the approach adopted in the problem formulation has a great impact on the actual possibility of solving such problem by using numerical techniques. This paper illustrates a methodology which combines some modelling technique which have been found to be numerically efficient. The methodology is based on the 3D curvilinear coordinates technique for the road modelling, the moving frame approach for the derivation of the vehicle equations of motion, the replacement of the time with the position along the track as new independent variable and the formulation and the solution of the minimum lap time problem by means of the indirect approach. The case study of a GT car is presented and simulation examples are given and discussed
Investigating Alternative Phase Planes for Assessing Vehicle Stability
No full textThis paper discusses the possibility of assessing vehicle stability by means of unconventional graphical methodologies and defining a region of stability of the vehicle, using only yaw rate, lateral acceleration and sideslip rate. The three-dimensional β-r-β ̇ phase surface is investigated, relating trajectories in the r-β ̇ plane to their β values. The r-β ̇ phase plane is investigated for different tyre models and tyre-road friction conditions. A new stability region is proposed
Green driving optimization of a series hybrid electric vehicle
No full textThis paper develops an indirect optimal control methodology to achieve green driving optimisation for series hybrid electric vehicles. Starting from a given vehicle mission, specified in terms of a road journey that has to be completed in a given amount of time, the power sharing among the powertrain sources and the vehicle speed profile along the journey are optimised and found. The scheme combines parametric modelling of the vehicle and powertrain together with computationally efficient optimal control software to provide an optimization strategy that works in real-time. Simulation results that demonstrate the success of the method and provide further insight into efficient driving, are presented
Analysis of the Effects of Large Lot Zoning
No full textThis study extends a test for the presence of binding zoning, originally developed to be applied across many adjacent jurisdictions, so that it can be applied within a single jurisdiction. This study also demonstrates how to carry out this test in the presence of spatially correlated OLS residuals by using a mixed effects model whose coefficients are estimated using the maximum likelihood technique. The study examines twenty years of land sales data from a Midwestern county containing two adjacent cities surrounded by rural areas. A thirty-five-acre acre, minimum lot size in the rural area is found to be binding; while a 9,000 square foot minimum lot size in the cities is found to be not binding.
Gyroscopic stabilisers for powered two-wheeled vehicles
No full textThis paper illustrates the potential of a gyroscopic stabiliser for the stabilisation of single-track vehicles, at low and high speed as well as during braking. Alternative systems are considered, including single and twin counter-rotating gyroscopes, spinning and precessing with respect to different axes, either freely (passive stabilisers) or in a controlled way (active stabilisers). A suitable mathematical model has been developed and stability has been investigated both by eigenvalue calculation and time domain simulations. It has been found that the most effective configuration is one where the gyroscope(s) spin with respect to an axis parallel to the wheels' spin axis and swing with respect to the vehicle yaw axis. Passive systems may effectively stabilise both weave and wobble at medium and high speed, but cannot stabilise the vehicle at low and zero speed. On the contrary, actively controlled gyroscopes are capable of stabilising the vehicle in its whole range of operating speed, as well as during braking. The alteration of the original vehicle handling characteristics is negligible when active counter-rotating gyroscopes are used, and still acceptable if a single gyroscope is adopted instead
Optimal torque management strategies for all-wheel-drive electric motorcycles
No full textThe need for more sustainable mobility is fostering the electrification of all types of road vehicles. Electrification has also led to increased interest in multi-motor solutions for all-wheel-drive powertrains, to the benefit of handling and stability, and offering the possibility of reducing energy usage thanks to the optimisation of multi-motor torque management. This paper investigates whether the energy efficiency of a dual-motor, all-wheel-drive electric motorcycle is greater than the efficiency of a standard single-motor, rear-wheel-drive one. A mathematical model for the estimation of the driving losses is presented first. The model is then used to develop an optimal torque management strategy that minimises powertrain losses under propulsion as well as a strategy that maximises energy recovery under braking. A case study is used to quantitatively assess the proposed strategies, which are also compared to the performance of standard rear-wheel-drive motorcycles both in terms of energy efficiency and riding safety. Simulation results highlight that the all-wheel-drive electric motorcycle outperforms the rear-wheel-drive both in terms of energy efficiency and tyre-road friction usage. Overall, the maximisation of energy efficiency or safety–depending on specific driving conditions–is achievable with a feed-forward torque management system
Competition under Capacitated Dynamic Lot Sizing with Capacity Acquisition
No full textLot-sizing and capacity planning are important supply chain decisions, and competition and cooperation affect the performance of these decisions. In this paper, we look into the dynamic lot sizing and resource competition problem of an industry consisting of multiple firms. A capacity competition model combining the complexity of time-varying demand with cost functions and economies os scale arising from dynamic lot-sizing costs is developed. Each firm can replenish inventory at the beginning of each period in a finite planning horizon. Fixed as well as variable production costs incur for each production setup, along with inventory carrying costs. The individual production lots of each firm are limited by a constant capacity restriction, which is purchased up front for the planning horizon. The capacity can be purchased from a spot market, and the capacity acquisition cost fluctuates with the total capacity demand of all the competing firms. We solve the competition model and establish the existence of a capacity equilibrium over the firms and the associated optimal dynamic lot-sizing plan for each firm under mild conditions
Lap time optimization of a sports series hybrid electric vehicle
No full textThis paper illustrates a methodology for the lap time optimization of a race series hybrid electric vehicle based on the indirect optimal control approach. More specifically, for a vehicle with given characteristics running on a given track, the optimal trajectory and powertrain power flow that minimize the lap time are found. The paper presents a parametric model of a sports series hybrid electric vehicle, illustrates the optimization method and discusses simulation results
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