Experimental Characterization of Damping Force in Shock Absorbers with Constant Velocity Excitation

For the characterization of shock absorbers, which are intrinsically non-linear, it was considered advisable to use the 3D representation of force vs velocity-displacement domain rather than traditional force vs velocity or force vs displacement. Experimental apparatus was therefore designed and constructed to measure the damping force produced by shock absorbers. Data were processed with software suitable for fitting the experimental data functions of several variables. Experiments showed that 3D representation of restoring force allows the non-linearity of shock-absorber damping to be examined more thoroughly.     

Direction dependent prices in public transport: A good idea? The back haul pricing problem for a monopolistic public transport firm

Markets for transport are often characterised by unequal demand in both directions: every morning during peak hours the trains are crowded while moving towards the direction of large cities, whereas they may be almost empty in the other direction. In this paper we discuss the implications of these imbalances for price setting of transport firms. From the viewpoint of economic theory, two regimes can be distinguished: one where – owing to price discrimination – the flows are equal, and one where unequal flows are the result. Special attention is paid to the case where the transport firm does not apply price discrimination, as is the case with most railway firms in Europe. We find that in the case of substantial joint costs, the introduction of price discrimination not only leads to an increase of profits, but also to positive effects on consumer surplus. This result differs from the standard result in the literature on industrial economics. The standard result purports that with linear demand functions price discrimination has a negative impact on the welfare of the average consumer and that this negative impact dominates the positive effect on profits of the producer.     

A local model for the simulation of two–dimensional spilling breaking waves

A numerical model for the simulation of two dimensional spilling breaking waves is described. It is derived from a previous model which, in turn, takes its underlying ideas from the Cointe and Tulin theory of steady breakers. With respect to the former model, the present one is local, i.e., the inception, extension, and geometry of the breakers are determined through the local shape of the water surface. The model has been implemented in a RANSE code, which was developed for the simulation of ship flows, through a modification in the boundary conditions. This yields a simple and effective way to reproduce the breakers influence on the underlying flow. The resulting code has been used to simulate the flow past a submerged hydrofoil. The numerical results are compared with those of the previous model and with the experimental data obtained by Duncan.     

Understanding connectivity to international markets: a systematic review

Improving freight connectivity is increasingly a topic at the centre of the international trade and transport policy agendas. An examination of available documents and studies in both the policy-making and the academic fields shows that the concept of freight connectivity has often been defined in different ways, and thus has taken a variety of meanings. This poses the question on what connectivity is and what are its determinants in the context of international trade. We are not aware of any studies that have analysed, in a systematic way, the different perspectives and determinants of freight connectivity so as to increase access to international markets. This paper seeks to fill this gap by performing a systematic literature review that spans disciplines such as Transport Engineering, Transport and International Economics, and Supply Chain Management. The outcome of this examination is a multidisciplinary framework that hopefully will help stakeholders to understand freight connectivity to international markets better, as well as guide future research and analysis in policy-making.     

Estimation of Load-Induced Damage and Repair Cost in Post-Tensioned Concrete Rocking Walls

Post-tensioned concrete rocking walls might be used to avoid severe seismic damage at the base of structural walls, decrease residual drift, and lessen post-earthquake repair costs. The prediction of load-induced damage to the rocking wall resulting from seismic loading can provide an extremely valuable tool to evaluate the status and safety of structural concrete walls following earthquakes. In this study, the behavior and the damage state of monolithic, self-centering, rocking walls, as a new type of concrete rocking wall, are investigated. The nonlinear mechanical behavior of the wall is first modeled numerically, and subsequently the mechanical parameters from the numerical simulation are used to generate the local damage index. The results from the damage index model are compared with the full-scale test results, confirming the viability of the numerically based damage index method for estimating the seismically induced damage in concrete walls. Moreover, the estimated damage can be utilized as a qualitative and quantitative scale to assess the status of the wall following seismic loading events. Finally, an equation is proposed to estimate the repair cost based on the predicted damage state for the studied structural system.     

Safe Platooning in Automated Highway Systems Part II: Velocity Tracking Controller

This paper presents the design of a velocity tracking controller for safe vehicle maneuvering in Automated Highway Systems (AHS) in which traffic is organized into platoons of closely spaced vehicles. The notion of safety is related to the absence of collisions that exceed a given relative velocity threshold. In a companion paper, state dependent safety regions for the platoons are designed in such a way that, whenever the state of a platoon is inside these safety regions, it is guaranteed that platoon maneuvering will be safe and follow the behavior prescribed by the finite state machines that control vehicles maneuvers. Velocity profiles inside these safety regions are derived for all the single lane maneuvers and a nonlinear velocity tracking controller is designed to track these profiles. This controller attempts to complete the maneuvers with comfort in minimum time, whenever safety is not compromised. The control schemes presented in this paper were implemented and tested using AHS simulation software.     

Safety Oriented Maneuvers for IVHS

The IVHS architecture of the California PATH program organizes traffic into platoons of closely spaced vehicles. Platoons are formed and broken up by two longitudinal control maneuvers, the merge and the split. A third longitudinal maneuver, decelerate to change lane, allows a platoon switching from one lane to another to enter its new lane at a safe spacing and speed. The maneuvers, particularly the merge, can be potentially hazardous. In a merge, the cars in the trail platoon are moving faster than those in the lead platoon, while the gap separating the two platoons is smaller than usual. A sudden deceleration by the lead platoon could cause a high-speed collision. If the relative velocities of the merging platoons can be constrained so that they are guaranteed never to collide at a high relative velocity, the merge can be considered safe. A maximum safe velocity for the trail platoon can be found for any given spacing and lead-platoon velocity. This paper presents a merge maneuver in which the velocity of the trail platoon never exceeds the maximum safe velocity. The controller switches among several feedback control laws that keep the velocity of the trail platoon inside a safe region and within comfort limits on jerk and acceleration, under normal circumstances. This merge maneuver can be considered to be the fastest merge strategy mat does not violate bounds on safety and comfort. The controller is also more robust to changes in the vehicles' acceleration capability than those that use a desired open-loop trajectory

The control approach used for the merge maneuver can be applied to the other maneuvers to ensure that they never result in a collision. The switching controllers for the split and decelerate to change lane maneuvers that are safe and yield a more comfortable ride than those that track a timed trajectory are also presented.     

Ship underwater noise assessment by the acoustic analogy,part III: measurements versus numerical predictions on a full-scale ship

The acoustic analogy represents a powerful and versatile approach, able to numerically predict the noise generated by a body moving in a fluid. It is widely used to provide essential indications about the aeroacoustic behavior of aircraft and helicopters (even at a design stage) and, eventually, to pursue effective strategies aimed at desirable reduction and/or control of noise. Nevertheless, applications in the area of hydroacoustics and in the prediction of ship underwater noise are very rare. In this paper, the potential of the acoustic analogy is directly tested on a large ferry, for which a measurement campaign at sea was performed. In spite of the complexity of the tested configuration [the ship mounts two contracted and loaded tip (CLT) propellers located ahead of two rudders, and its hull is characterized by a rather elongated skeg] and the many variables not taken into account in the numerical simulation (such as the contribution from machinery noise and the probable occurrence of tip vortex cavitation), the agreement between the measured and computed noise spectra is quite satisfactory. The analysis suggests many interesting features of the ship hydroacoustic field: the dominant role played by nonlinear sources far from the body and the relevance of scattering effects from the hull surface. Furthermore, the scattered pressure seems to contribute to alter the frequency content of the resulting signatures with respect to the blade passage frequencies. Finally, an overview of future developments and applications of this numerical approach for marine/maritime problems is presented.     

Lap time optimisation of a racing go-kart

The minimum lap time optimal control problem has been solved for a go-kart model. The symbolic algebra software Maple has been used to derive equations of motion and an indirect method has been adopted to solve the optimal control problem. Simulation has been successfully performed on a full track lap with a multibody model endowed with seven degrees of freedom. Geometrical and mechanical characteristics of a real kart have been measured by a lab test to feed the mathematical model. Telemetry recorded in an entire lap by a professional driver has been compared to simulation results in order to validate the model. After the reliability of the optimal control model was proved, the simulation has been used to study the peculiar dynamics of go-karts and focus to tyre slippage dynamics, which is highly affected by the lack of differential.     

Optimizing the demand captured by a railway system with a regular timetable

The railway systems in various European countries adopt regular timetables, in which the trains arrive and depart at constant intervals. In fact, their simple structure provides several advantages both to the passengers and to the management of the service. The design of such timetables has recently received a certain attention in the literature, but the standard model aims to optimize the service for a fixed demand. We relax this unrealistic assumption, taking into account the reciprocal influence between the quality of the timetable and the amount of transport demand captured by the railway. This results into a mixed-integer non linear model with a non-convex continuous relaxation. We solve it by a branch-and-bound algorithm based on a piecewise-linear overestimate of the objective function and a heuristic algorithm which iteratively applies the standard fixed-demand model and a demand-estimation model, feeding each one with data based on the solution obtained from the other one at the previous iteration. The computational results presented concern both random instances and a real-world regional network located in Northwestern Italy.