Analysis of Hydrodynamic Characteristics in the Process of Autonomous Underwater Vehicle Docking

The successful operation of an Autonomous Underwater Vehicle (AUV) requires the capability to return to a dock. A number of underwater docking technologies have been proposed and tested in the past. The docking allows the AUV to recharge its batteries, download data and upload new instructions, which is helpful to improve the working time and efficiency. During the underwater docking process, unsteady hydrodynamic interference occurs between the docking device and an AUV. To ensure a successful docking, it is very important that the underwater docking hydrodynamics of AUV is understood. In this paper, numerical simulations based on the computational fluid dynamics (CFD) solutions were carried out for a 1.85m long AUV with maximum 0.2 m in diameter during the docking process. The two-dimensional AUV model without fin and rudder was used in the simulation. The mathematical model based on the Reynolds-averaged Navier-Stokes (RANS) equations was established. The finite volume method (FVM) and the dynamic structured mesh technique were used. SIMPLE algorithm and the k-ε turbulence model in the Descartes coordinates were also adopted. The hydrodynamics characteristics of different docking states were analyzed, such as the different docking velocity, the docking device including baffle or not. The drag coefficients of AUV in the process of docking were computed for various docking conditions, i.e., the AUV moving into the docking in the speed of 1m/s, 2m/s, 5m/s. The results indicate that the drag coefficient increases slowly in the process of AUV getting close to the docking device. When the AUV moves into the docking device, the drag coefficient increases rapidly. Then the drag coefficient decreases rapidly. The drag coefficient decreases with the increase of velocity when AUV enters the docking device. It was also found that the drag coefficient can be effectively reduced by dislodging the baffle of docking device.

A Numerical Study of Fluid Structure Interaction of a Flexible Submerged Cylinder Mounted on an Experimental Rig

The aim of the study is to investigate VIV effects, not only on a test cylinder but also on the experimental rig being towed under water at a prescribed depth and operating speeds. For this purpose, a numerical Multi-Physics model was created using one way coupled analysis simultaneously between the Mechanical and Fluent solvers of ANSYS software package. A system coupling was developed in order to communicate force data alternately between the solvers with the help of automatic mapping algorithms within millesimal time periods of a second. Numerical investigation into the dynamic characteristics of pressure and velocity fields for turbulent viscous fluid flow along with structural responses of the system, stressed the significance of time and space scales for convergence and accuracy of our Finite Volume (FV) CFD calculations.

Study and Simulation on the Energy Efficiency Management Control Strategy of Ship Based on Clean Propulsion System

Nowadays, with the higher voice of ship energy saving and emission reduction, the research on energy efficiency management is particularly necessary. Energy efficiency management and control of ships is an effective way to improve the ship energy efficiency. In this paper, according to the new clean propulsion system configurations of 5000 tons of bulk carrier, the energy efficiency management control strategy of the clean propulsion system is designed based on the model of advanced brushless doubly-fed shaft generator, propulsion system using LNG/diesel dual fuel engine and energy consumption of the main engine for reducing energy consumption. The simulation model of the entire propulsion system and the designed control strategy were designed. The influence of the engine speed on the ship energy efficiency was analyzed, and the feasibility of the energy efficiency management control strategies was verified by simulation using Matlab/Simulink. The results show that the designed strategies can ensure the power requirement of the whole ship under different conditions and improve the ship energy efficiency and reduce CO2 emissions.

Numerical Study of Hydrodynamic Impact on Bubbly Water

The phenomenon of slamming on a bubbly liquid has many occurrences in marine and costal engineering. However, experimental or numerical data on the effect of the presence of gas bubbles within the liquid on the impact loads are scarce and the related physical mechanisms are poorly understood. The aim of the present paper is to study numerically the relationship between the void volume fraction and the impact loads. For that purpose, numerical simulations of the impact of a cone on bubbly water have been performed using the finite element code ABAQUS/Explicit. The present results show the diminution of the impact loads with the increase of the void fraction. This effect appears to be related to the high compressibility of the liquid-gas mixture.

A Study on Resistance Performance for Various Trim Conditions and Bulb Shapes on a Container Ship Under Slow Steaming

Hull form had been unavoidably optimized for a single speed condition, normally a contract speed at design draft in the past many years due to various reasons such as limited design period, less advanced data processing capacity of a computer and so on. For this reason, for maximizing present ship’s operating efficiency, additional analysis relevant to resistance performance for slow steaming condition is newly required since the original hull form for this study also was developed about 10 years ago. In this paper, the resistance performances corresponding to various trim conditions are investigated not only for ship’s original contract speed (Fn: 0.255) but for slow speed (Fn: 0.163∼0.183) by slow steaming. Through this study, it can be accomplished to identify the optimum trim condition meeting the objectives of ship operator. Further to the trim optimization, bulbous bow shape renovation was carried out for off design condition (Fn:0.173) and both of CFD results, one is from an original bulbous bow shape, the other is from a reformed bulbous bow shape by us, are compared each other to identify the concrete reason for the improvement of resistance performance. Commercial CFD code of the STAR-CCM+ was utilized to evaluate the ship’s resistance performance on a 6,800 TEU container ship. To validate of the effectiveness of Starccm+, the experimental result of the subject hull form is referred and compared with the result from STAR-CCM+. Form factor prediction method by CFD that is based on extracting form pressure resistance component from difference of two different computational domains is presented. In this study, it is investigated to compare the form factor calculated by CFD with the model test result. This approach allows hull form designer to calculate a form factor corresponding ship’s trim variation by CFD in order to separate total resistance into wave making resistance and viscous resistance for more accurate effective power prediction.

Studies of Extreme Energy Localizations With Smoothed Particle Hydrodynamics

Smoothed particle hydrodynamics (SPH) is used to simulate hydrodynamic waves and wave phenomena including focusing from wave interference. This Lagrangian based method can be used to naturally simulate hydrodynamic free surfaces, including the free surface of a breaking wave. A virtual wave tank is simulated where wave motions can be excited from either side. Wave focusing is observed at the tank center, where the waves interfere. As a measure of the interference, the wave heights that result from focusing are presented. Certain types of wave focusing are thought to lead to large ocean waves. The efficacy of SPH in modeling wave focusing is critical to further understanding and predicting extreme wave phenomena with SPH.

Freak Wave Generation in a Wave Basin With HOSM-WG Method

A method to produce freak waves with arbitrary spectrum in a fully directional wave basin is presented here. This is an extension of Waseda, Houtani and Tanizawa at OMAE 2013[1], which used “HOSM-WG” based on the higher-order spectral method (HOSM). We used the following three methods to improve the HOSM-WG in [1]: “separation of free waves from bound waves,” “using Biesel’s transfer function in wavenumber space” and “using Schaffer’s 2nd-order wave maker control method.” Modulational wave trains, freak waves in unidirectional irregular waves and freak waves in short-crested irregular waves were generated in a wave basin. The experimental results using the improved HOSM-WG were compared to the HOSM simulation, and good agreements were found. The effectiveness of the improved HOSM-WG was ascertained. We showed that the difference between HOSM-WG and HOSM simulations became larger as wave steepness, frequency bandwidth of the spectrum or directional spreading became larger.

The Floating Harbour Transhipper: New-Generation Transhipment of Bulk Ore Products

Bulk products such as iron ore and coal are usually shipped directly from shore facilities using large bulk carriers. This often involves significant cost due to major dredging operations, long jetties, large storage sheds and the acquisition of large tracts of coastal land. The costs of direct shore to an ocean-going export vessel (OGV) loading often run into billions of dollars — prohibitive for small- to medium-scale mining operations, particularly in remote regions with only distant access to deep water ports. The current industry standard for mitigating these issues is transhipping; the bulk cargo is transported from a smaller shore based facility to the export vessel moored in deep water by a small feeder vessel. Transhipment, while mitigating many of these issues, does introduce other concerns with respect to limiting seastate, environmentally harmful dust and potential spillage during materials transfer. The Australian company Sea Transport Corporation and the Australian Maritime College at the University of Tasmania are developing new technology for bulk ore transhipment: the floating harbour transhipper (FHT). The FHT is essentially a large floating warehouse with an aft well dock to support material transfer operations from the feeder vessel. The major advantages to the mining export industry are in the form of environmental and economic improvements, in some cases completely avoiding expensive dredging while minimising the environmentally invasive onshore infrastructure. In addition, the whole process is enclosed, therefore eliminating grab spillage and dust transport issues common to other transhipping methods. This paper presents an overview of the main hydrodynamic issues currently being investigated: primarily the interaction between multiple floating bodies close to one another in a seaway. The two primary ship-to-ship interactions that are being investigated are the effects experienced by the feeder vessel when it is docking or undocking within the FHT well dock and the interactions between the three vessels when operating in close proximity in an open seaway. A combination of physical scale model experiments and numerical techniques is employed, with a significant portion of the experimental program dedicated to the validation of the numerical simulation codes used to investigate the behaviour of the vessels. ShipMo3D is an object based library developed by DRDC for the purpose of analysing the seakeeping performance of vessels operating in a seaway in either the frequency or time domain. The capabilities of ShipMo3D are applied to this novel application in an attempt to provide realistic simulations of the interaction between the vessels of the FHT system. DualSPHysics, an open source Smoothed Particle Hydrodynamics (SPH) code, is being applied to the domain within the very restricted water environment of the FHT well dock to investigate the fluid flow behaviour and the effect that this has on the feeder vessel when entering/exiting.

Distributed Damping of Tsunamis

Tsunamis are a major threat to coastal communities. One of the ways to avoid tsunami disasters is to use breakwaters to attenuate the incident tsunami energy. The incident tsunami energy is expected to be dissipated by induced wave breaking in the shallow water over the structure peak. In this paper, a new method to attenuate the tsunami energy is described and investigated. This new concept dissipates tsunami energy by implementing small barriers into the water before the tsunami reaches the shore. The interaction of tsunami-like solitary waves with new submerged barriers has been investigated and their performance was compared with that of conventional breakwaters. We found that the new structure can be used as a tsunami wave attenuator.