Naval architecture

Towing tank/water flume experiments are conducted to characterize the dynamics
of a Remotely-Piloted Unmanned Underwater Vehicle (RPUUV) propelled by a
vectored-thruster system. Force and torque measurements are used to determine the
coefficients of drag, lift, yaw-moment and thrust of the vehicle as a function of the
vehicle yaw angle and the vectored-thruster rudder angle. Simultaneously, particle Image
Velocimetry (PIV) measurements of the propeller inlet flow are also performed to
examine the variation of flow conditions at the propeller inlet with rudder angle. The tests
are conducted at 0.150 rnls, 0.300 rnls, 0.515 rnls and 0.773 rnls. While the measured
drag coefficient is slightly higher than predicted by theory at low Reynolds number (1.44
x10^5 and 2.88 x10^5), the hydrodynamic coefficients data are expected to be useful in
predicting the response of vehicles in the field. Additionally, the magnitude of the thrust
vector varies nonlinearly with rudder angle and for nonzero rudder angles the thrust
vector does not point in the same direction as the thruster axis.

This thesis presents two-dimensional hydrodynamic analysis of flapping foils for the propulsion of underwater vehicles using a source-vortex panel. Using a simulation program developed in MatLab, the hydrodynamic forces (such as the lift and the drag) as well as the propulsion thrust and efficiency are computed with this method. The assumptions made in the analysis are that the flow around a hydrofoil is two-dimensional, incompressible and inviscid. The analysis is first considered for the case of a deeply submerged hydrofoil followed by the case where it is located in shallow water depth or near the free surface. In the second case, the presence of the free surface and wave effects are taken into account, specifically at high and low frequencies and small and large amplitudes of flapping. The objective is to determine the thrust and efficiency of the flapping –foils under the influence of added effects of the free surface. Results show that the free-surface can significantly affect the foil performance by increasing the efficiency particularly at high Frequencies.

Studies of composite multihull structure under wave loads, extreme loads, and blast loads have been conducted using finite element and computational fluid dynamics (CPF) tools. A comprehensive finite element tool for structural analysis of composite multi-hull structures is developed. Two-way fluid structure interaction (FSI) is implemented by coupling finite element analysis (FEA) and CFD. FEA models have been developed using sandwich construction having composite face sheets and a foam core. Fluid domain was modeled using the CFD code, CFX and a wave motion was simulated based on Sea State 5... In addition to hydrodynamic loads, the simulation of composite ship under extreme loads is performed. Stress analysis was performed and dynamic response of the hull was determined in time domain. In the final analysis, an underwater explosion model was developed to study the composite hull resistance to blast load.

Scale model tests are conducted of a Surface Effect Ship in a near-shore developing sea. A beach is built and installed in a wave tank, and a wavemaker is built and installed in the same wave tank. This arrangement is used to simulate developing sea conditions and a 1:30 scale model SES is used for a series of experiments. Pitch and heave measurements are used to investigate the seakeaping response of the vessel in developing seas. The air-cushion pressure and the vessel speed are varied, and the seakeeping results are compared as functions of these two parameters. The experiment results show a distinct correlation between the air-cushion pressure and the response amplitude of both pitch and heave. The results of these experiments are compared against results of a computer model of a Surface Effect Ship (SES).

The development and experimental testing of the DUKW-Ling amphibious vehicle was performed during the first phase of an autonomous amphibious vehicle system development project. The DUKW-Ling is a 1/7th scale model of a cargo transport concept vehicle. The vehicle was tested in the three regions it is required to operate: land, sea and the surf zone region. Vehicle characteristics such as turning radii, yaw rate and velocities were found for different motor inputs on land and water. Also, because a vehicle navigating the surf zone is a new area of research that lacks experimental data the vehicle was tested in the breaking waves of the surf zone and its motion characteristics were found, as well as the drivetrain forces required to perform this transition. Maneuvering tests provided data that was used to estimate a model for future autonomous control efforts for both land and water navigation.