• Journal of the Society of Naval Architects of Korea
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• v.61 no.4
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• pp.236-246
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• 2024

The present study aims to identify the effects of the oblique inflow and vertical acceleration on a marine propeller's hydrodynamic force and moment. Computational Fluid Dynamics analysis is performed for a rotating propeller in open water conditions with heave motion after performing validation against experiment in straightforward conditions. The oblique inflow results in a linear increase of the off-axial component of the hydrodynamic force and moment rather than the axial one. Pitch and yaw moments due to the hull motion are dominated by the heave force and the moment arm of the propeller location. Additionally, the vertical acceleration leads to a linear augmentation of off-axial hydrodynamic force and moment, implying the added mass and moment of inertia. Notably, it is found that the off-axial hydrodynamic force and moment are dominated by the oblique inflow velocity rather than the acceleration.

• Journal of Ocean Engineering and Technology
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• v.29 no.6
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• pp.436-444
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• 2015

A submerged body is sensitive to changes in the roll moment because of the small restoring moment and moment of inertia. Thus, a method for predicting the roll-related hydrodynamic coefficients is important. This paper describes a deduction method for the hydrodynamic coefficients based on the results of a coning motion test. A resistance test, static drift test, and coning motion test were performed to obtain the coefficients in the towing tank of Seoul National University. The sum of the hydrodynamic force, inertial force, gravity, and buoyancy was measured in the coning motion test. The hydrodynamic force was deduced by subtracting the inertial force, gravity, and buoyancy from the measured force. The hydrodynamic coefficients were deduced using the regression method.

• Journal of Ocean Engineering and Technology
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• v.30 no.5
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• pp.374-380
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• 2016

The large drift and angle of attack motion of an ROV (Remotely operated vehicle) cannot be modeled using the typical hydrodynamic coefficients of conventional straight running AUVs and specific slender bodies. In this paper, the ROV hull is divided into several simple-shaped components to model the hydrodynamic force and moment. The hydrodynamic force and moment acting on each component are modeled as the components of added mass force and drag using the known values for simple shapes such as a cylinder and flat plate. Since an ROV is operated under the water, the only environmental force considered is the current effect. The target ROV dealt with in this paper has six thrusters, and it is assumed that its maneuvering motion is determined using a thrust allocation algorithm. Tracking simulations are carried out on the ship’s surface near the stern, bow, and midship sections based on the modeling of the hydrodynamic force and current effect.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.2 s.140
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• pp.98-104
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• 2005

The mathematical models of hydrodynamic force and moment acting on a ship at low speed range should be established differently from the ones at nominal cruising speed range since a ship moves with large drift angle or rotates in a stationary position. We modified widely used Yoshimura's cross flow model in order to apply the system identification method to estimate parameters in the model. The apparatus and the procedure of free running model test were suggested so that the parameters in the model be estimated. The validity of our proposing modified model and test procedure was confirmed by comparison with the results of simulated model test.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.1
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• pp.56-69
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• 2015

This paper presents a numerical study on investigating on hydrodynamic characteristics of a marine propeller in oblique flow. The study is achieved by RANS simulations on an open source platform - OpenFOAM. A sliding grid approach is applied to compute the rotating motion of the propeller. Total force and moment acting on blades, as well as average force distributions in one revolution on propeller disk, are obtained for 70 cases of combinations of advance ratios and oblique angles. The computed results are compared with available experimental data and discussed.

• Journal of Ocean Engineering and Technology
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• v.32 no.5
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• pp.386-392
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• 2018

It is necessary to predict hydrodynamic derivatives when assessing the maneuverability of a submarine. The force and moment acting on the vehicle may affect its motion in various modes. Conventionally, the derivatives are determined by performing captive model tests in a towing tank or applying a system identification method to the free running model test. However, a computational fluid dynamics (CFD) method has also become a possible tool to predict the hydrodynamics. In this study, virtual captive model tests for a full-scale submarine were conducted by utilizing a Reynolds-averaged Navier-Stokes solver in ANSYS FLUENT version 18.2. The simulations were carried out at design speed for various modes of motion such as straight forward, drift, angle of attack, deflection of the rudder, circular, and combined motion. The hydrodynamic force and moment acting on the submarine appended rudders and stern stabilizers were then obtained. Finally, hydrodynamic derivatives were determined, and these could be used for evaluating the maneuvering characteristics of the submarine in a further study.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.3
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• pp.259-269
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• 2018

In this study, the second order bending moment induced by sea waves is calculated using the quadratic strip theory. The theory has the fluid forcing terms including the quadratic terms of the hydrodynamic forces and the Froude-Krylov forces. They are applied to a ship as the external forces in order to estimate the second order ship responses by fluid forces. The sensitivity of the second order bending moment is investigated by implementing the quadratic terms by varying the ship side angle for two example ships. As a result, it was found that the second order bending moment changes significantly by the variation of the ship side angle. It implies that increased flare angles at the bow and the stern of ships being enlarged would amplify their vertical bending moments considerably due to the quadratic terms and may make them vulnerable to the fatigue.

• Ocean Systems Engineering
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• v.6 no.3
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• pp.233-244
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• 2016

Tension Leg Platform (TLP) is a floating structure that consists of four columns with large diameter. The diffraction theory is used to calculate the wave force of floating structures with large dimensions (TLP). In this study, the diffraction and Froude-Krylov wave forces of TLP for surge, sway and heave motions and wave force moment for roll, pitch degrees of freedom in different wave periods and three wave approach angles have been investigated. From the numerical results, it can be concluded that the wave force for different wave approach angle is different. There are some humps and hollows in the curve of wave forces and moment in different wave periods (different wavelengths). When wave incidents with angle 0 degree, the moment of diffraction force for pitch in high wave periods (low frequencies) is dominant. The diffraction force for heave in low wave periods (high wave frequencies) is dominant. The phase difference between Froude-Krylov and diffraction forces is important to obtain total wave force.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.2 no.4
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• pp.208-222
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• 1990

The nonlinear hydrodynamic pressure force and moment on hinged wavemakers of variable-draft are presented. A closed-form solution (correct to second-order) for the nonlinear wavemaker boundary value problem has been obtained by employing the Stokes perturbation expansion scheme. The physical significance of the second-order contributions to the hydrodynamic pressure moment are examined in detail. Design curves are presented which demonstrate both the magnitude of the second-order nonlinearities and the effects of the variable-draft hinge height. The second-order contributions to the total hydrodynamic force and moment consist of a time-dependent and a steady part. The sum of the first and second-order pressure force and moment show a significant increase over those predicted by linear wavemaker theory. The second-order effects are shown to vary with both relative water depth and wave amplitude. The second-order dynamic effects are relatively more important for hinged wavemakers with shallower drafts.

• Journal of Ocean Engineering and Technology
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• v.35 no.2
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• pp.99-112
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• 2021

The prediction of maneuverability is very important in the design process of an underwater vehicle. In this study, we predicted the steady turning ability of a symmetrical underwater vehicle while considering interactions between the yaw rate and drift/rudder angle through a simulation-based methodology. First, the hydrodynamic force and moment, including coupled derivatives, were obtained by computational fluid dynamics (CFD) simulations. The feasibility of CFD results were verified by comparing static drift/rudder simulations to vertical planar motion mechanism (VPMM) tests. Turning motion simulations were then performed by solving 2-degree-of-freedom (DOF) equations with CFD data. The turning radius, drift angle, advance, and tactical diameter were calculated. The results show good agreement with sea trial data and the effects on the turning characteristics of coupled interaction terms, especially between the yaw rate and drift angle.