Tae-Hwan Joung

Shape optimization of an autonomous underwater vehicle with a ducted propeller using computational fluid dynamics analysis

ABSTRACT Autonomous Underwater Vehicles (AUVs) provide a useful means of collecting detailed oceano-graphic information. The hull resistance of an AUV is an important factor in determining the power requirements and range of the vehicle. This paper describes a procedure using Computational Fluid Dynamics (CFD) for determining the hull resistance of an AUV under development, for a given propeller rotation speed and within a given range of AUV velocities. The CFD analysis results reveal the distribution of the hydrodynamic values (velocity, pressure, etc.) around the AUV hull and its ducted propeller. The paper then proceeds to present a methodology for optimizing the AUV profile in order to reduce the total resistance. This paper demonstrates that shape optimization of conceptual designs is possible using the commercial CFD package contained in Ansys™. The optimum design to minimize the drag force of the AUV was identified for a given object function and a set of constrained design parameters

A study on the design and manufacture of a deep-sea unmanned underwater vehicle based on structural reliability analysis

The reliability analysis tool provided with the commercial structure-analysis package, ANSYS 9.0, is relatively easy to use and allows solutions to be rapidly obtained. However, the tool cannot guarantee the results of the reliability analysis since it can only provide an outline tendency of the probability of failure without giving an accurate numerical value of the probability of failure at the regions that a designer requires. The independent commercial reliability analysis code, NESSUSS 7.0, also has problems in that it may not necessarily converge and can waste computation time from having to undertake unnecessary repetitive structure analyses for design variables that have little significance to the structural integrity of the object being designed. A design methodology and a software module, which can make up for the current deficiencies in these commercial packages, have been developed by the authors and are presented in this paper. This paper describes how the methodology and the software module were applied to the design and manufacture of a stiffened pressure vessel, which can be mounted on a 6000 m class deep-sea unmanned underwater vehicle.

CFD Simulations and Experimental Tests for Three Different Ducted Propellers

In this study, propeller open water characteristics (,  and ) were compared for three different ducted propellers using a Computational Fluid Dynamics (CFD) analysis, as well as an experimental test at a basin. The best shape of the duct was selected from the three types of specially designed ducts based on the CFD analysis results. The same propeller model (Kaplan type propeller) was used inside all three duct models, and the propeller open water characteristics were compared, predominantly at the design speed for an underwater vehicle. Finally, the results of the CFD test simulations for the selected duct case were verified by experimental open water tests in a towing tank.

Reliability analysis of a load-out support frame in offshore installations

ABSTRACT When an offshore platform topside is constructed in a yard, it should be loaded-out onto a transportation vessel. The load-out operations, however, involves many uncertainties, such as changing the load (weight of the topside platform) on the LSF or possible structural failures. The load on the LSF should be evaluated, as even a small failure in a structural member or a welding connection can lead to structural instability, or even catastrophic structural collapse. This study presents a newly developed method for analyzing the structural reliability of the LSF. The probability of failure is calculated by using AFOSM method assessment along with response surface methods. This proposed approach can provide a better understanding of safety requirements, so that the over-design of structures can be avoided. Furthermore, it can provide the coordinators of load-out operations with a better set of guidelines for determining the probability of failure during the load-out process.

Verification of CFD analysis methods for predicting the drag force and thrust power of an underwater disk robot

ABSTRACT This paper examines the suitability of using the Computational Fluid Dynamics (CFD) tools, ANSYSCFX, as an initial analysis tool for predicting the drag and propulsion performance (thrust and torque) of a concept underwater vehicle design. In order to select an appropriate thruster that will achieve the required speed of the Underwater Disk Robot (UDR), the ANSYS-CFX tools were used to predict the drag force of the UDR. Vertical Planar Motion Mechanism (VPMM) test simulations (i.e. pure heaving and pure pitching motion) by CFD motion analysis were carried out with the CFD software. The CFD results reveal the distribution of hydrodynamic values (velocity, pressure, etc.) of the UDR for these motion studies. Finally, CFD bollard pull test simulations were performed and compared with the experimental bollard pull test results conducted in a model basin. The experimental results confirm the suitability of using the ANSYS-CFX tools for predicting the behavior of concept vehicles early on in their design process.