With a steadily growing number of vehicles, our roads are getting more and more crowded. As a consequence, traffic jams are becoming common. Vehicle platoon systems form a possible solution in the short term. It consists of a number of vehicles automatically following a leader vehicle, in-line, one after another at a short but safe distance. Ideally, all vehicles have to maintain the same speed, so as to have a better usage of the road by minimizing the distance between two vehicles. In this paper we present a timed automata model of a vehicle platoon system with the goal of finding a minimal but guaranteed safe distance between two vehicles under variable speed. Contrary to other models based on cooperative adaptive cruise control, we assume no (Internet) communication among different vehicles or road system. Instead of such global perspective we rather take a local point of view: each vehicle relies on its own sensors to dynamically calculate and maintain a safe distance with the preceding member of the platoon. We use the model checker UPPAAL to verify that the system does not deadlock, and most importantly, that it is safe, avoiding crashes at all time.INDEX TERMS Model checking, vehicle safety, modeling of platoon systems, formal verification.

The Boolean Satisfiability problem (SAT) is a prototypical NP-complete problem, which has been widely studied due to its significant importance in both theory and applications. Stochastic local search (SLS) algorithms are among the most efficient approximate methods available for solving certain types of SAT instances. The quantitative configuration checking (QCC) heuristic is an effective approach for improving SLS algorithms on solving the SAT problem, resulting in an efficient SLS solver for SAT named Swqcc. In this paper, we focus on combining the QCC heuristic with an aspiration mechanism, and then design a new heuristic called QCCA. On the top of Swqcc, we utilize the QCCA heuristic to develop a new SLS solver dubbed AspiSAT. Through extensive experiments, the results illustrate that, on random 3-SAT instances, the performance of AspiSAT is much better than that of Swqcc and Sparrow, which is an influential and efficient SLS solver for SAT. In addition, we further enhance the original clause weighting schemes employed in Swqcc and AspiSAT, and thus obtain two new SLS solvers called Ptwqcc and AspiPT, respectively. The eperimental results present that both Ptwqcc and AspiPT outperform Swqcc and AspiSAT on random 5-SAT instances, indicating that both QCC and QCCA heuristics are able to cooperate effectively with different clause weighting schemes.

As the offshore oil and gas industry seeks to reduce costs, a semi-submersible floatel, which provides the space for crew accommodation and open deck space for the necessary equipment, is used to perform maintenance instead of returning the FPSO to a shipyard. One of the unavoidable challenge we have to cope with is the large amount of shielding effects due to the FPSO in the vicinity. The objective of this study is to understand the hydrodynamic interactions and flow interference between them, which will help to develop a comprehensive numerical tool to predict the motion behavior and help designers increase the operability window. Firstly, the second-order diffraction program is used to evaluate hydrodynamic coefficients for a system composed of a floatel operating close to a turret moored FPSO. The calculation is carried out according to different relative positions and yaw angles between the vessels to assess the second-order nonlinear effects and the shielding effects due to waves. Secondly, CFD (computational fluid dynamics) software is used to determine the drag force coefficients due to current and the shielding effects for the two bodies. Numerical studies of thrusterthruster and thruster-hull interactions on unsteady loads are also conducted based on CFD numerical tools. Thirdly, a PID control scheme is used to control low-frequency relative position and orientation between the two bodies. Finally, using the wave, wind and current force coefficients and feedback of DP control system, the global motions of the two vessels in non-parallel environmental conditions are numerically simulated. By using this numerical tool, the shielding effect between a floatel and a FPSO is studied in detail, and all the nonlinearities of the problem can be assessed. New understanding is created through the parametric study, by which useful physics-based information can be provided to optimize the length requirement of gangway and help the operator to decide on the safe working operational scenario. The number of aging FPSO installations worldwide is increasing every year. These FPSOs are connected with massive permanent riser systems and mooring system and it is very costly to bring them to the dry dock for maintenance. By accurately estimating the interactions and shielding effects, improved predictions models are being developed which can increase the up-time of the floatel by up to 20%. This opens up new opportunities for on-site FPSO maintenance with reduced costs.

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