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In this paper, the design principles of sensor data flow in ship information system (SIS) structure are researched. In order to save communication resources to achieve the practicable maximum without sacrificing the expected performance of system, an observability analysis-based setting method is proposed to shorten the length of each sensor data flow. In addition, according to the determined data flow length, a scheduling algorithm is presented to set the content of data flow as well. This scheduling algorithm is based on a double-index evaluation method, which includes the variation of sensor data during assigned steps, meanwhile the deviation between estimated value and real value of observation is considered as well. Besides these, algorithm and hardware realization examples are provided at the end of this paper. 1. Introduction The past three decades have witnessed the rapid spreading of a ship information system (SIS) architecture in which sensors and actuators exchange information with a Command Control Interface (CCI) through a communication network. Based on such wide-scale networks, ship control/monitoring systems (such as Integrated Bridge System, Standard Machinery Control System) are able to be linked together. These technological advances make it possible to create a highly integrated real-time control architecture in a modern ship (Geer 2009). As a result, several SISs have been widely applied in different types of ships, e.g., RICE (Lister and Rosie 1995), Ship System 2000 (Källberg and Stråhle 2001), GEDMS (Meier and Manfredi 2006), FORCEnet (Waters et al. 2005), and Total Ship Computing Environment (Henry et al. 2009). For most designers, the SIS is more like a special application case of Supervisory Control and Data Acquisition (SCADA) system, the theory research of SIS is scattered and immethodical. However, there also exist several differences in normal SCADA system and SIS. For example, the connection principle between distributed controller units (DCUs) and remote terminal units in SIS is mere proximity instead of task relation, which has reduced the difficulty of planning and laying networks greatly, but increases the complexity of every control processes in SIS, most missions in SIS are designed to be completed by several DCUs cooperatively. Such structure has been summarized briefly by Liu et al. (2014a). Mostly, a SIS could be regarded as a wide-scale sensor/actuator network under a highly integrated structure in the ship environment, which increases the importance of sensor information obtaining ability. In recent years, the U.S. Naval Research Laboratory has developed a multisensory real-time detection system for situational awareness named "Volume Sensor" (Minor et al. 2007). This designed framework can serve as a template for a variety of real-time sensing and situational awareness applications.

In this paper, we apply a CFD computer code to study the hydrodynamic behavior of a stand-alone cylinder and a dual coaxial-cylinder system (DCCS) via free-decay motion tests. The geometric proportions of a stand-alone cylinder and the inner and outer cylinder of the DCCS are chosen to be the same as those in [1] and [2], respectively, as ocean wave-energy converter (WEC) devices. Overset mesh based on the commercial code ‘Star-CCM+ 11’ is used to simulate the free-decay motion of the two systems. Five parameters chosen for the CFD implementation are: turbulence model, initial displacement, time step, number of prism layers and mesh size. Results obtained from using different values of these parameters are compared so as to confirm the validity of choices made. The hydrodynamic performance of the stand-alone cylinder and outer cylinder in the DCCS are compared with the experimental results to assess and validate the CFD models. In addition, the heave hydrodynamic coefficients, namely, the added mass and total damping, and ‘resonance’ frequency of the stand-alone cylinder and those of the inner cylinder of the DCCS, with the outer cylinder being fixed, are obtained by using the CFD procedure. The hydrodynamic coefficients of another stand-alone cylinder with the same dimensions as the inner cylinder of the dual-coaxial cylinder are also obtained by simulations. The vorticity-contour plots for the stand-alone cylinder and the outer cylinder in the DCCS in free-decay motion are presented and analyzed. Finally, the results of the three cases are compared to examine the effect of the outer cylinder on the heave hydrodynamic coefficients of the inner cylinder.