Analysis of dynamic decision-making in a bicycle-sharing auction using a dynamic discrete choice model

For clarifying the usefulness and practical issues of a tradable permit system empirically, we implemented a tradable permit system for a bicycle-sharing service in Yokohama city, Japan. We analyzed both travel and transaction behavior within this system. Many activity factors, such as the amount of free time in each day, home location and travel mode to the bicycle port, were shown to affect the transaction of tradable permits. The results of the pilot program indicated that inefficient allocation of tradable permits occurred when participants postponed their decision-making because of uncertainty. To determine the reason for this effect and the contributing factors, we created a dynamic discrete choice model to describe the choice results and timing. The estimation result indicated that the option value of postponing decision-making caused the transactions to be performed at the last minute, and that this effect blocked the liquidity of the permits trade. In addition, because the result reveals that there was heterogeneity in the time discount factor, the initial allocation of permits was found to be important for efficient allocation.

     

Fatigue strength improvement for ship structures by Ultrasonic Peening

Ultrasonic Peening has attracted recent attention as a fatigue strength improvement method. The main features of Ultrasonic Peening are generation of compressive residual stress and smoothing of weld toe radius. However, for ship structures, various loads act on the hull structure over a ship??s life, including the construction period, and the compressive stress field of structural members generated by Ultrasonic Peening may change. In order to verify the technique's benefits to ship structures, the influence of load history on the improvement effects on fatigue strength by Ultrasonic Peening needs to be clarified. In this paper, the improvement effects on fatigue strength by Ultrasonic Peening for welding joints were confirmed by experiments with several joint type specimens. In addition, fatigue tests modeling launching, when the stress conditions of a ship's structure changes significantly, were carried out in order to clarify the influence of load history in a ship??s life. Consequently, some cases that have the possibility of decreasing or increasing the improvement effects on fatigue strength by Ultrasonic Peening were clarified, and some efficient methods of Ultrasonic Peening for ship structures were suggested.