Station Keeping of a Subsea Shuttle Tanker System Under Extreme Current During Offloading

A subsea shuttle tanker has been proposed as a multipurpose, versatile transport and storage system. This paper presents the station keeping challenge of the subsea shuttle tanker design during underwater loading and offloading at a subsea well under an extreme current environment. Understanding the behaviour of the proposed subsea shuttle tanker during offloading in extreme currents is vital for both the design of the subsea shuttle tanker itself but also the required actuator effort needed to uphold the demanded station keeping abilities. During the offloading process, the hoovering subsea shuttle tanker would current-vane in a water depth of approximately 70 metres. Recent studies have shown that the drag force exerted on the subsea shuttle tanker body is up to 80 times larger for side-ways current compared to the head-on current. With current-waning capabilities, the generated lift forces are low, and thus the subsea shuttle tanker will use less effort to maintain its desired position and water depth. The paper further investigates the movement of the subsea shuttle tanker during offloading with extreme current speeds, i.e., above 1.6 m/s, in the surge, heave, and pitch motions, respectively. The planar model is built up using a Luenberger observer, where the vessel motions are measured and fed into a linear quadratic regulator (LQR) for calculations of the control input. The LQR control’s primary focus is to hold and achieve the target for the subsea shuttle tanker during the offloading process, i.e., minimize the horizontal and vertical motion. Finally, a state-of-the-art probabilistic method is used to predict the maximum potential displacement during offloading, i.e., the Average Exceedance Rate Method

Differential Evolution in Wireless Communications: A Review

Differential Evolution (DE) is an evolutionary computational method inspired by the biological processes of evolution and mutation. DE has been applied in numerous scientific fields. The paper presents a literature review of DE and its application in wireless communication. The detailed history, characteristics, strengths, variants and weaknesses of DE were presented. Seven broad areas were identified as different domains of application of DE in wireless communications. It was observed that coverage area maximisation and energy consumption minimisation are the two major areas where DE is applied. Others areas are quality of service, updating mechanism where candidate positions learn from a large diversified search region, security and related field applications. Problems in wireless communications are often modelled as multiobjective optimisation which can easily be tackled by the use of DE or hybrid of DE with other algorithms. Different research areas can be explored and DE will continue to be utilized in this contex