Control Algorithms for Active Cab Suspensions on Agricultural Tractors

This paper describes active agricultural tractor cab suspensions based on optimal control theory. Control algorithms based on time invariant state feedback and on adaptive control are developed and studied. The influence of different observers and measurement noise levels on the vibration damping capacity are studied as well as the power consumption for the suspensions.

The principle for the adaptive algorithm is based on the parameters in the penalty matrices being varied so that the resulting controller always strives to make optimum use of available travel space. The feedback and observer gains are also changed depending on the characteristics of the vehicle's frame movements.

The results show that it is possible to design an effective active suspension, but that the choice of feedback gains must be dependent on the surface characteristics to reach satisfactory vibration damping performance.     

Hybrid steering cultures in the governance of public transport: A successful way to meet demands?

This paper concerns steering aspects in the governance context of public transport. Various theoretical views of steering have been presented over the years, and it has been argued that a multiple-principal context often leads to fragmented steering. The paper aims to identify steering culture models found among principals operating in the same public transport context, and to explain how a successful procurement outcome is possible, despite the hybrid of steering cultures. The paper is based on an empirical analysis of a Swedish county's planning process that resulted in a very successful procurement outcome that met high environmental and safety standards at a relatively low cost. This procurement was seen as a triumph by principals. The findings presents the existence of various steering cultures among the principals, leading to the conclusion that a “metagovernor,” in this case the PTA, is central to achieving successful outcomes. The metagovernor designed the planning process and formulated a procurement document that satisfied the principals. In this process, the metagovernor negotiated separately with each principal, focusing on the particular characteristics of each principal.     

Solving procurement problems in public transport: Examining multi-principal roles in relation to effective control mechanisms

Despite the EU’s increasing role in regulating public transport procurement, few studies have considered this aspect when analysing procurement problems of public transport. This paper examines how the institutional relationships between different actors, including international governmental bodies, in public transport effects the possibility of exerting control over a county public transport authority (PTA) in a multi-principal setting. The analysis is carried out using empirical material from an infringement process including a Swedish PTA and the EU. The conclusions have clear policy implications for the procedural order when exerting control over the PTA in cases of procurement problems. It is for example shown, that the implementation process would be much more efficient if the regulations allowed the EU to impose sanctions directly towards the local authorities without having to involve the national government when the procurement laws are violated.     

Valuing cargo flexibility in oil transportation

The seaborne oil transportation market is served by two main types of vessels—crude oil tankers and product tankers. Product tankers are designed to move refined oil products, yet they can also opportunistically carry ‘dirty’ products such as crude and heavy fuel oil, subject to the cost of tank cleaning when re-entering the clean products trade. We apply an entry-exit real option model with a stochastic freight rate differential to derive optimal triggers for switching between the two cargo types and estimate the value of the switching option. We show that the value of active switching has grown over time, and generally exceeds the additional construction cost of a product tanker. Our findings are important both from a practical point of view and for our understanding of market integration in the tanker freight market. Specifically, shipowners can use our model as a basis for optimizing chartering policy for clean product tankers. We also show that there are periods where the dirty market is persistently stronger, and discuss the possible reasons for such apparent inefficiencies.