• Journal of the Society of Naval Architects of Korea
• /
• v.40 no.5
• /
• pp.43-52
• /
• 2003

Two methods which estimate manoeuvring derivatives in the model of hydrodynamic force and moment acting on a manoeuvring ship using sea trial data were compared. One is the widely used parameter estimation method by using the Extended Kalman Filter (EKF), which estimates state variables of linearized state space model at every instant after dealing with the coefficients as the augmented state variables. The other one is the Estimation-Before-Modeling (EBM) technique, so called the two-step method. In the first step, hydrodynamic force of which dynamic model is assumed the third-order Gauss-Markov process is estimated along with motion variables by the EKF and the modified Bryson-Frazier smoother. Then, in the next step, manoeuvring derivatives are identified through the regression analysis. If the exact structure of hydrodynamic force could be known, which was an ideal case, the EKF method would be regarded as being more superior compared to the EBM technique. However the EBM technique was more robust than the EKF method from a realistic point of view where the assumed model structure was slightly different from the real one.

• Journal of Ocean Engineering and Technology
• /
• v.20 no.6 s.73
• /
• pp.93-100
• /
• 2006

This paper is concerned with the dynamic analysis of an underwater tracked vehicle, operating on extremely soft soil of the deep-seafloor. The vehicle is assumed as a rigid-body with 6-dof. The orientation of the vehicle is defined by four Euler parameters. To solve the motion equations of the vehicle, the Newmark numerical integrator is used in the incremental-iterative algorithm. The normalization constraint of Euler parameters is satisfied by using of a sequential updating method. The hydrodynamic force and moment are included in the tracked vehicle's dynamics. The hydrodynamic effects on the performance of tracked vehicles are investigated through numerical simulations.

• Journal of computational fluids engineering
• /
• v.13 no.1
• /
• pp.14-20
• /
• 2008

The flow characteristics around a rudder in open water condition is analyzed by the computational method. Reynolds averaged Navier-Stoke's equation is utilized for the computation. The computational hydrodynamic force coefficients are verified through comparing with the experimental results. The information of these flow characteristics is necessary to predict cavitation and maneuvering performances, to estimate steering gear capacitance, and to get the bending moment which is useful for the structural analysis. The pressure distribution, the three-dimensional flow separation, and the tip vortices are investigated. The pattern of the three-dimensional flow separation is analyzed utilizing a topological rule. The tip vortices are also investigated through a visualization technique.

• Journal of Navigation and Port Research
• /
• v.35 no.3
• /
• pp.197-204
• /
• 2011

The authors adopt the Unmanned Undersea Vehicle(UUV), the shape of which is like a manta. They call here it Manta UUV. Manta UUV has been designed from the similar concept of the UUV called Manta Test Vehicle(MTV), which was originally built by the Naval Undersea Warfare Center of USA(Lisiewicz and French, 2000; Simalis et al., 2001; U.S. Navy, 2004). The present study deals with the effect of Reynolds numbers on hydrodynamic forces acting on Manta UUV at large angles of attack. The large angles of attack cover the whole range of 0 to ${\pm}$ 180 degrees in horizontal plane and in vertical plane respectively. Static test at large attack angles has been carried out with two Manta UUV models in circulating water channel. The authors assume that the experimental results of hydrodynamic forces (lateral force, yaw moment, vertical force and pitch moment) are analyzed into two components, which are lift force component and cross-flow drag component. First of all, Based on two dimensional cross-flow drag coefficient at 90 degrees of attack angle, the cross-flow drag component at whole range of attack angles is calculated. Then the remainder is assumed to be the lift force component. The only cross-flow drag component is assumed to be subject to Reynolds number.entstly the authors suggest the methodology to predict hydrodynamic derivertives acting on the full-scale Manta UUV.

• Journal of Mechanical Science and Technology
• /
• v.17 no.6
• /
• pp.844-853
• /
• 2003

In this paper, a dynamic analysis of the reciprocating compression mechanism of a small refrigeration compressor is performed. In the problem formulation of the mechanism dynamics, the viscous frictional force between the piston and the cylinder wall is considered in order to determine the coupled dynamic behaviors of the piston and the crankshaft. Simultaneous solutions are obtained for the equations of motion of the reciprocating mechanism and the time-dependent Reynolds equations for the lubricating film between the piston and the cylinder wall and for the oil films on the journal bearings. The hydrodynamic forces of the journal bearings are calculated by using a finite bearing model along with the Gumbel boundary condition. A Newton-Raphson procedure is employed in solving the nonlinear equations for the piston and crankshaft. The developed computer program can be used to calculate the complete trajectories of the piston and the crankshaft as functions of the crank angle under compressor-running conditions. The results explored the effects of the radial clearance of the piston, oil viscosity, and mass and mass moment of inertia of the piston and connecting rod on the stability of the compression mechanism.

• International Journal of Fluid Machinery and Systems
• /
• v.3 no.3
• /
• pp.235-244
• /
• 2010

Recent studies on the moment whirl due to leakage flow in the back shroud clearance of hydro-turbine runners or centrifugal pump impellers are summarized. First, destabilizing effect of leakage flow is discussed for lateral vibrations using simplified models. Then it is extended to the case of whirling motion of an overhung rotor and the criterion for the instability is obtained. The fluid moment caused by a leakage clearance flow between a rotating disk and a stationary casing was obtained by model tests under whirling and precession motion of the disk. It is shown that the whirl moment always destabilizes the whirl motion of the overhung rotor while the precession moment destabilizes the precession only when the precession speed is less than half the rotor speed. Then vibration analyses considering both whirl and precession are made by using the hydrodynamic moments determined by the model tests. For larger overhung rotors, the whirl moment is more important and cause whirl instability at all rotor speed. On the other hand, for smaller overhung rotors, the precession moment is more important and cancels the destabilizing effect of the whirl moment.

• Journal of Ship and Ocean Technology
• /
• v.7 no.4
• /
• pp.16-31
• /
• 2003

The finite volume based multi-block RANS code, WAVIS developed at KRISO, is used to simulate the turbulent flows around a submarine with the realizable $\textsc{k}-\varepsilon$ turbulence model. RANS methods are verified and validated at the level of validation uncertainty 1.54% of the stagnation pressure coefficient for the solution of the turbulent flows around SUBOFF submarine model without appendages. Another SUBOFF configuration, axisymmetric body with four identical stem appendages, is also computed and validated with the experimental data of the nominal wake and hydrodynamic coefficients. The hydrodynamic forces and moments for SUBOFF model and a practical submarine are predicted at several drift and pitch angles. The computed results are in extremely good agreement with experimental data. Furthermore, it is noteworthy that all the computations at the present study were carried out in a PC and the CPU time required for 2.8 million grids was about 20 hours to get fully converged solution. The current study shows that CFD can be a very useful and cost effective tool for the prediction of the hydrodynamic performance of a submarine in the basic design stage.

• Journal of Ocean Engineering and Technology
• /
• v.31 no.5
• /
• pp.340-345
• /
• 2017

It is important to predict the hydrodynamic maneuvering derivatives, which consist of the forces and moment acting on a hull during a maneuvering motion, when estimating the maneuverability of a ship. The estimation of the maneuverability of a ship with a change in the stern hull form is often performed at the initial design stage. In this situation, a method that can reflect the change in the hull form is necessary in the prediction of the maneuverability of the ship. In particular, the linear hydrodynamics maneuvering derivatives affect the yaw checking motion as the key factors. In the present study, static drift calculations were performed using Computational Fluid Dynamics (CFD) based on Reynolds Average Navier-Stokes (RANS) for a 40-segment hull. A prediction method for the linear hydrodynamic maneuvering derivatives was proposed using the slender body theory from the distribution of the lateral force acting on each segment of the hull. Moreover, the results of a comparison study to the model experiment for KVLCC1 performed by KRISO are presented in order to verify the accuracy of the static drift calculation. Finally, the linear hydrodynamic maneuvering derivatives obtained from both the model test and calculation are compared and presented to verity the usefulness of the method proposed in this study.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2018.11a
• /
• pp.4-6
• /
• 2018

Traditional methods of research on ship maneuvering performance were estimated in calm water. Ship maneuverability in waves is of vital importance for navigation safety of a ship (ITTC, 2008). The accurate estimation of force and moment acting on the ship and rudder behind propeller are necessary because the rudder, propeller and hull interaction is of key importance. In addition, course-keeping ability and maneuvering performance of a ship can be significantly affected by the presence of wave. In this study, the model test is performed in the regular wave in the square wave tank in Changwon National University and the hydrodynamic force acting on the ship hull and rudder behind the propeller in various wave directions is investigated. The effect of wavelength and wave direction on hydrodynamic force acting on ship and rudder behind propeller in regular waves is discussed.

• Journal of the Korean Institute of Navigation
• /
• v.23 no.2
• /
• pp.29-42
• /
• 1999

An accurate method of estimating ship maneuverability needs to be developed to evaluate precisely and improve the maneuverability of ships according to the water depth. In order to estimate maneuverability by a mathematical model. The hydrodynamic forces acting on a ship hull and the flow field around the ship in maneuvering motion need to be estimated. The ship speed new the berth is very low and the fluid flow around a ship hull is unsteady. So, the transient fluid motion should be considered to estimate the drag force acting on the ship hull. In the low speed and short time lateral motion, the vorticity is created by the body and grow up in the acceleration stage and the velocity induced by the vorticity affect to the body in deceleration stage. For this kind of problem, CFD is considered as a goof tool to understand the phenomena. In this paper, the 2D CFD code is used for basic consideration of the phenomena to solve the flow in the cross section of the ship considering the ship is slender and the water depth is large enough. The flow fields Added and hydrodynamic forces for the some prescribed motions are computed and compared with the preliminary experiment results. The comparison of the force with measurement is shown a fairly good agreement in tendency. The 3D Potential Calculation based on the Hess & Smith Theory is employed to predict the surge, sway added mass and yaw added moment of inertia of hydrodynamic coefficients for M/V ESSO OSAKA according to the water depth. The results are also compared with experimental data. Finally, the sway added mass of hydrodynamic coefficients for T/S HANNARA is suggested in each water depth.