A streamlined form of underwater towed body is considered here for the experimental and CFD studies to verify its stability when towed in submerged condition. Its physical characteristics lead to different behavior in the hydrodynamic tow conditions. Influence of lifting fins and tow arrangements on the operational depth and stability of the tow body are studied. The main variants associated with the body, and which affect the tow characteristics, are identified as basic body shape, tow point location, fin size for stable tow and dynamic trim due to forward speed. In order not to disturb the flow around the sensor location, the fin is placed further away towards the lower aft end. Additionally, the stable tow is validated and demonstrated in the towing tank at IIT Madras using the scaled model. The drag and lift force values obtained from model tests are extrapolated to the prototype and compared with CFD results.
This paper presents an hardware-in-the-loop (HIL) simulation system tool to test and validate an autonomous free running model system for ship hydrodynamic studies with a view to verification of the code, the control logic and system peripherals. The computer simulation of the plant model in real-time computer does not require the actual physical system and reduces the development cost and time for control design and testing purposes. The HIL system includes: the actual programmable embedded controller along with peripherals and a plant model virtually simulated in a real-time computer. With regard to ship controller design for ship model testing, this study describes a plant model for surge and a Nomoto first order steering dynamics, both implemented using Simulink software suit. The surge model captures a quasi-steady state relationship between surge speed and the propeller rpms, obtained from simple forward speed towing tank tests or derived analytically. The Nomoto first order steering dynamics is obtained by performing the standard turning circle test at model scale. The control logic obtained is embedded in a NI-cRIO based controller. The surge and steering dynamics models are used to design a proportional-derivative controller and an LQR controller. The controller runs a Linux based real-time operating system programmed using LabVIEW software. The HIL simulation tool allows for the emulation of standard ship hydrodynamic tests consisting of straight line, turning circle and zigzag to validate the combined system performance, prior to actual for use in the autonomous free-running tests.
This paper addresses the hydro-elastic performance of two composite marine propellers at operating condition and compares the results with conventional materials. The study involves three stages namely, design and development of a B series propeller, hydrodynamic and structural performance analysis in uniform flow and free vibration test both in dry and wet condition. In order to perform the hydro-elastic based fluid structure interaction (FSI), Co-Simulation method was adopted to couple Reynolds Averaged Navier-Strokes Equation (RANSE) based Computational Fluid Dynamics (CFD) solver and finite element method (FEM) solvers. The open water characteristics such as thrust coefficient (KT), torque coefficient (KQ), and open water efficiency (ηO) were analyzed as a function of advance velocity (J) of the propeller. A detailed study of the various blade materials by varying mechanical properties are presented. The results obtained show the variation of stress and deflection on the blade, along with the influence of the blade deformation on the performance of propeller. The vibration behaviour of the propellers were also analysed by Block-Lanczos method in FEM solver to obtain the natural frequencies and the mode shapes using Acoustic Fluid-Structure Coupling method for both dry and wet condition. Results showed that composite propeller have better hydro-dynamic property and lower vibration than metal propeller.
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