• Journal of the Society of Naval Architects of Korea
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• v.29 no.3
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• pp.45-52
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• 1992

The Mathematical Model, which can describe the maneuvering motion of a ship in low speed, is highly required these days because it is directly related to the safety of ship in confused harbour. Kose has presented a new model for the low speed maneuvering motion, but the usefulness of it is not confirmed widely. Lets of difficulties are revealed in the case of low speed maneuver, The first is the fact that a ship moves the stirred water region for the longer time than in the case of high speed. So, the hydrodynamic forces, exerted on the hull need to be treated strictly, not by the ordinary differential equation with constant coefficients. Another difficulty is arised from the fact the lateral motion is relatively large comparing to the longitudinal motion in low speed. And, by the result the effect of cross-flow drag or vortex sheding effects are dominant. Besides, the captive model tests of low speed motion has lots of problems. For example, the hydrodynamic forces do not converge to a certain values for the long time. And the absolute values of measured forces are very small, so we must expend lots of efforts to raise up the S/N ratio of the experiments. In this paper, a new mathematical model for the maneuvering motion in low speed, is built up, and the usefulness is discussed, comparing with other models, for example, Kose's model or M.M.G. model or Cross-Flow model, The CMT data for a PCC model of 3.00 M length, released from the RR-742 of Japan, are used for the validation of each models.

• Journal of computational fluids engineering
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• v.13 no.1
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• pp.14-20
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• 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 the Society of Naval Architects of Korea
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• v.41 no.1
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• pp.8-14
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• 2004

As the number of offshore structure is glowing in deep waters, there have been increased damages of it. These floating structures in offshore locations exposed to harsh environmental conditions. In recent years, there has been a slowing attention around damages on bow and deck on FPSO caused by waves in steep storm condition. This paper describes a study of the water on deck due to the dynamic behavior of a FPSO with turret mooring system. The nonlinear motions of the FPSO are simulated under external forces due to wave, current, wind, and mooring forces in the time domain. The direct integration method is employed to estimate low frequency drift wave forces. The current forces are calculated by using slow motion maneuvering equations in the horizontal plane. The coefficients of a model for wind forces are calculated from Isherwood's experimental data and the variation of wind speed is estimated by wind spectrum according to the guidelines of API-RP2A.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.601-607
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• 2005

This paper describes a hydrodynamic modelling study based on the Feldman's equation to predict the nonlinear and coupled maneuvering characteristics of high speed submarine. The hydrodynamic coefficients set is obtained from the modeling of the cross flow drag force and sail induced vorticity, and the captive model experiments(VPMM and RA test) results used to improved the accuracy. The results contained in this paper will be helpful to predict the behavior of tight turn maneuver and to improve the SOE(Safety Operational Envelope) analysis in case of emergency maneuver.

• Journal of the Korea Institute of Military Science and Technology
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• v.9 no.2 s.25
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• pp.20-25
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• 2006

Low frequency towed line array with high array gain and beam resolution is a long range surveillance sensor for anti-submarine warfare. The beam characteristics is however deteriorated due to the distorted line array sensor caused by low towing speed, wind, current, and towing ship maneuvering. An adaptive beamforming method is utilized in this paper to enhance the distorted line array beam performance by estimating and compensating the nonlinear array shape. A polynomial curve fitting in the least square sense is used to estimate the array shape iteratively with the distributed heading sensors data along the array. Real time array shape estimation and nonlinear array beam calculation is applied to a very long towed line array sensor system and the beam performance is evaluated and compared to the linear beamformer for the simulation and sea trial data.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.4
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• pp.345-355
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• 2014

This paper focuses on aerodynamic and inertial modeling of the propeller for its applications in flight dynamics analyses of a propeller-driven airplane. Unsteady aerodynamic and inertial loads generated by the propeller are formulated using the blade element method, where the local velocity and acceleration vectors for each blade element are obtained from exact kinematic relations for general maneuvering conditions. Vortex theory is applied to obtain the flow velocities induced by the propeller wake, which are used in the computation of the aerodynamic forces and moments generated by the propeller and other aerodynamic surfaces. The vortex lattice method is adopted to obtain the induced velocity over the wing and empennage components and the related influence coefficients are computed, taking into account the propeller induced velocities by tracing the wake trajectory trailing from each of the propeller blades. Aerodynamic forces and moments of the fuselage and other aerodynamic surfaces are computed by using the wind tunnel database and applying strip theory to incorporate viscous flow effects. The propeller models proposed in this paper are applied to predict isolated propeller performances under steady flight conditions. Trimmed level forward and turn flights are analyzed to investigate the effects of the propeller on the flight characteristics of a propeller-driven light-sports airplane. Flight test results for a series of maneuvering flights using a scaled model are employed to run the flight dynamic analysis program for the proposed propeller models. The simulations are compared with the flight test results to validate the usefulness of the approach. The resultant good correlations between the two data sets shows the propeller models proposed in this paper can predict flight characteristics with good accuracy.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.4
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• pp.356-365
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• 2014

This paper is the second in a series and aims to build a high-fidelity mathematical model for a propeller-driven airplane using the propeller's aerodynamics and inertial models, as developed in the first paper. It focuses on aerodynamic models for the fuselage, the main wing, and the stabilizers under the influence of the wake trailed from the propeller. For this, application of the vortex lattice method is proposed to reflect the propeller's wake effect on those aerodynamic surfaces. By considering the maneuvering flight states and the flow field generated by the propeller wake, the induced velocity at any point on the aerodynamic surfaces can be computed for general flight conditions. Thus, strip theory is well suited to predict the distribution of air loads over wing components and the viscous flow effect can be duly considered using the 2D aerodynamic coefficients for the airfoils used in each wing. These approaches are implemented in building a high-fidelity mathematical model for a propeller-driven airplane. Flight dynamic analysis modules for the trim, linearization, and simulation analyses were developed using the proposed techniques. The flight test results for a series of maneuvering flights with a scaled model were used for comparison with those obtained using the flight dynamics analysis modules to validate the usefulness of the present approaches. The resulting good correlations between the two data sets demonstrate that the flight characteristics of the propeller-driven airplane can be analyzed effectively through the integrated framework with the propeller and airframe aerodynamic models proposed in this study.

• Journal of Navigation and Port Research
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• v.40 no.5
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• pp.241-247
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• 2016

The tracking filter plays a key role in the accurate estimation and prediction of maneuvering a vessel's position and velocity when attempting to enhance safety by avoiding collision. Therefore, in order to achieve accurate estimation and prediction, many oceangoing vessels are equipped with the Automatic Radar Plotting Aid (ARPA) system. However, the accuracy of prediction depends on the tracking filter's ability to reduce noise and maintain a stable transient response. The purpose of this paper is to derive the optimal values of the gain parameters used in tracking a High Dynamic Warship. The algorithm employs a ${\alpha}-{\beta}-{\gamma}$ filter to provide accurate estimates and updates of the state variables, that is, positions, velocity and acceleration of the high dynamic warship based on previously observed values. In this study, the filtering coefficients ${\alpha}$, ${\beta}$ and ${\gamma}$ are determined from set values of the damping parameter, ${\xi}$. Optimization of the damping parameter, ${\xi}$, is achieved experimentally by plotting the residual error against different values of the damping parameter to determine the least value of the damping parameter that results in the optimum smoothing coefficients leading to a reduction in the noise corruption effect. Further investigation of the performance of the filter indicates that optimal smoothing coefficients depend on the initial and average velocity of the target.

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

• Journal of Ocean Engineering and Technology
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• v.29 no.3
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• pp.270-282
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• 2015

A submerged body moving near the free surface needs to maintain its attitude and position to accomplish missions. It is necessary to validate the performance of a designed controller before a sea trial. The hydrodynamic coefficients of maneuvering are generally obtained by experiments or computational fluid dynamics, but these coefficients have uncertainty. Environmental loads such as the wave exciting force and suction force act on the submerged body when it moves near the free surface. Thus, a controller for the submerged body should be robust to parameter uncertainty and environmental loads. In this paper, the six-degree-of-freedom equations of motions for the submerged body are constructed. The suction force is calculated using the double Rankine body method. An adaptive control method based on an artificial neural network and proportional-integral-derivative control are used for the depth controller. Simulations are performed under various depth and speed conditions, and the results show the effectiveness of the designed controller.