SHAFT LOADS ON AZIMUTH PROPULSORS IN OBLIQUE FLOW AND WAVES

A range of model experiments have been carried out in calm water and waves for an oil spill vessel model with twin tractor azimuth thrusters at different heading angles and advance coefficients in the large towing tank at the Marine Technology Centre in Trondheim, Norway. Propeller shaft bending loads have been measured using a shaft dynamometer capable of measuring all shaft side force and bending moment components as well as propeller torque and thrust. The results include the loads on the propeller shaft with and without the presence of a ship hull model at the same heading angles and advance velocities in order to study the wake influence from the ship hull on the hydrodynamic loads. Results show that the ship hull wake has a much stronger effect on the propeller loads when the propeller is azimuthed outward from the ship hull centreline than inward. Measurements from the experiments in waves are also presented for the same thruster model in a straight-line course for both the head and following sea states under different wave conditions. Larger bending loads are found in head sea conditions compared with the following sea conditions. Generally it is found that the shaft bending loads and lateral forces are quite large, which is important to consider in the mechanical design layout and for dimensioning of components.

Oblique Stagnation-Point Flow Past a Shrinking Surface in a Cu-Al2O3/H2O Hybrid Nanofluid

To fill the existing literature gap, the numerical solutions for the oblique stagnation-point flow of Cu-Al2O3/H2O hybrid nanofluid past a shrinking surface are computed and analyzed. The computation, using similarity transformation and bvp4c solver, results in dual solutions. Stability analysis then shows that the first solution is stable with positive smallest eigenvalues. Besides that, the addition of Al2O3 nanoparticles into the Cu-H2O nanofluid is found to reduce the skin friction coefficient by 37.753% while enhances the local Nusselt number by 4.798%. The increase in the shrinking parameter reduces the velocity profile but increases the temperature profile of the hybrid nanofluid. Meanwhile, the increase in the free parameter related to the shear flow reduces the oblique flow skin friction.

Analytical solutions describing the oblique flow of a viscous incompressible fluid around a dendritic crystal

This article considers the hydrodynamic problem of an oblique flow of a viscous incompressible fluid around the tip of a dendritic crystal. Approximate analytical solutions of Oseen’s hydrodynamic equations are obtained in 2D and 3D cases using special curvilinear coordinates. It is shown that the projections of the fluid velocity change significantly with a change in the flow slope and Reynolds number. The theory developed in this work has a limiting transition to the previously known solutions for the rectilinear (without tilt) fluid flow around a dendrite.

Determining the acceptable turning circle manoeuvring modes to avoid loss of efficiency of the twin propeller system

Nowadays, a large number of newly built inland and navy vessels are equipped with a twin propeller-twin rudder configuration (TPTR). Observations of the modes of work of each unit of the TPTR system when performing manoeuvres at curvilinear trajectory show asymmetrical loading. The nature and parameters of the phenomenon are not sufficiently studied, which in specific manoeuvres could create overloading and loss of effectiveness. The purpose of the task is to study the effectiveness of the ship’s TP system in manoeuvring, taking into account the specifics of working in oblique flow of the “internal” and “external” propellers, respectively to the trajectory of motion. Appropriate manoeuvring experiments with self-running ship model have been carried out by which the propeller thrust and torque have been measured. In the present paper, based on obtained investigation results, analysis of interaction effects in the TP system has been performed. Coefficients for estimating the asymmetric efficiency of the twin-screw system have been developed, and related conclusions were summarized.