In underwater towing operations, the drag force and vertical offset angle of towropes are important considerations when choosing and setting up towing equipment. The aim of this paper is to study the variation in drag force, vertical offset angle, resistance, and attitude for towing operations with a view to optimizing these operations. An underwater experiment was conducted using a 1:8 scale physical model of a subsea module. A comprehensive series of viscous Computational Fluid Dynamics (CFD) simulations were carried out based on Reynolds-averaged Navier–Stokes equations for uniform velocity towing. The results of the simulation were compared with experimental data and showed good agreement. Numerical results of the vorticity field and streamlines at the towing speeds were presented to analyze the distribution of vortexes and flow patterns. The resistance components were analyzed based on the numerical result. It was found that the lateral direction was a better direction for towing operations because of the smaller drag force, resistance, and offset angle. Similar patterns and locations of streamlines and vortexes were present in both the longitudinal and lateral directions, the total resistance coefficient decreases at a Reynolds number greater than that of a cylinder.

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The dynamic action induced on offshore pipelines by deepwater S-laying is significant, and directly determines how the pipeline structures are designed and installed. Existing research has not fully investigated the benefits of coupling models of pipeline and pipelaying vessel motions. Therefore, this paper presents a coupled time-domain numerical model for examining the effect of coupled dynamic reactions. The coupled model takes into account the motion of the pipelaying vessel, surface waves, ocean currents, wind forces, pipeline dynamics, and contact between the rollers and the pipeline. A proportional, integral, derivative (PID) controller was used for simulating the control of the pipelaying vessel. The hydrodynamic forces that the pipeline experiences were modeled using the Morison equation. The model was solved using Newmark's method and verified using OrcaFlex software. The model was then used to analyze practical operations: the laying of a 22" gas export pipeline on the seabed by the pipelaying vessel HYSY201 in the Pingbei-Huangyan gas fields in the East China Sea. The effects of coupled factors on pipelaying vessel motions and pipeline dynamics were approximated. These effects included configurations, axial tensions, and bending moments. The results show a significant connection between the dynamic responses of the pipelines and pipelaying vessel motions.S-laying method, the pipeline is supported using a stinger and passes over a regular roller sequence forming an S-shaped trajectory before landing on the seabed, as illustrated in Figure 1. The upper curved S-shaped parts that rest on stingers are called overbends and are followed by inflection points where the pipeline curvature is zero. Before approaching the seafloor, the pipeline is reversed into a sagbend. Horizontal tension in the pipeline is maintained by mounted tensioner devices on the top of the pipeline. Consequently, S-laying operations depend on roller configuration and stinger radius. Large plastic deformation occurs when pipes pass over stingers. The plastic deformation is caused by the combined effects of the pipelaying vessel motion, roller reaction forces, axial tensions, and bending moments [5,6].Processes 2018, 6, x FOR PEER REVIEW 2 of 22 the S-laying method, the pipeline is supported using a stinger and passes over a regular roller sequence forming an S-shaped trajectory before landing on the seabed, as illustrated in Figure 1. The upper curved S-shaped parts that rest on stingers are called overbends and are followed by inflection points where the pipeline curvature is zero. Before approaching the seafloor, the pipeline is reversed into a sagbend. Horizontal tension in the pipeline is maintained by mounted tensioner devices on the top of the pipeline. Consequently, S-laying operations depend on roller configuration and stinger radius. Large plastic deformation occurs when pipes pass over stingers. The plastic deformation is caused by the combined effects of the pipelaying vessel motion, roller reaction forces, axial tensions, an...

This paper puts forward a development method of ship motion simulation system that can conduct UDP communication in real time. This system is based on Simulink in order to meet the need of modular and fast ship motion simulation systems. First, the mathematics models of ship motion are set up based on the modular ideology, which includes thruster model and models of wind, wave and current. Then, real time simulation module using S-fun function is developed, and built into executable program. This could realize real time communication between ship motion simulation system and visual simulation system and induce real time communication between ship motion system and ship simulation control system. In this way, it can save time and cost when developing the simulation system. This method has been used successfully in the development of real time simulation system of some engineering ship.

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