• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.104-113
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• 1992

The hydrodynamic problem is treated here when a pressurized bag is submerged partially into water and the end points of it oscillate. SES(Surface Effect Ship)has a bag filled with pressurized air at the stern in order to prevent the air leakage, and the pitch motion of SES is largely affected by the hydrodynamic force of the bag. The shape of a bag can be determined with the pressure difference between inside and outside. Once the hydrodynamic pressure is given, the shape of a bag can be obtained, however in order to calculate the hydrodynamic pressure we should know the shape change of the bag, and vice versa. Therefore the type of boundary condition on the surface of a bag is a moving boundary like a free surface boundary. In this paper, the formulation of this problem was done and linearized. The calculation scheme for the radiation problem of an oscillating bag is shown in comparison with the case that the bag is treated as rigid body. The hydrodynamic forces are calculated for various values of the pressure inside the bag and the submerged depth.

• Journal of Navigation and Port Research
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• v.35 no.3
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• pp.227-233
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• 2011

This paper presents the tracking and stabilization problem of a night vision system for marine surveillance. Both a hardware system and software modules are developed to control azimuth and elevation axes independently with compensation for ship motion. A two degree of freedom(2DOF) PID controller is designed and its parameters are tuned using a real-coded genetic algorithm(RCGA). Simulation demonstrates the effectiveness of the proposed method.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.4
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• pp.61-73
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• 1993

In the present study, sloshing problem is analyzed by the application of Finite Difference Method. SOLA-SURF scheme is applied to the analysis of fluid motion considering free surface. Especially, the concept of impact buffer zone is introduced for the prediction of more realistic impact pressure on tank. Numerical computation is carried out for the typical three models, and the computed results show good agreement with experimental data. The computation is also performed for 300,000 tons VLCC as a real-ship application. From the present study, it is proved that this numerical technique is quite practical to the prediction of sloshing impact pressure.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.169-179
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• 1997

This paper presents a discrete-time sliding mode control of an autonomous underwater vehicle with parameter uncertainties and long sample interval based on discrete variable structure system. Although conventional sliding mode montrol techniques are robust to system uncertainties, in the case of the system with long sample interval, the sliding control system reveals chattering phenomenon and even makes the system unstable. This paper considers the AUV which acquires position informations from a surface ship through an acoustic telemetry system with a certain discrete interval. The control system is designed on the basis of a Lyapunov function and a sufficient condition of the switching gain to make the system stable is give. Each component of the switching gain can be determined separately one another. The controller is robust to the uncertainties, and reaching condition of the control system is satisfied for any initial condition. This control law is a generalized form of the discrete sliding mode control and reduce the chattering problem considerably. Motion control of the AUV in the vertical plane shows the effectiveness of the proposed technique.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.44 no.2
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• pp.148-156
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• 2008

In this study it will be discussed how to solve the problem of discomfort from rolling motion on the fishing boats. Most discomfort is caused by the short cycle of rolling due to the light weight of the boats. The light weight is due to the FRP material which dries a boat. A way to improve the feeling of boarding by using fish hold was researched. The experiment was done on experimental fishing boat made by FRP in Jeju. An existing fish hold was designed and manufactured through the rolling test and that was used for a marine experiment. The rolling condition of the U-tank boat ideally designed was compared to that of an existing fishing boat using the same conditions. The experiments were carried out two times on the stop engine in the outward Sehwa fishing port, which the experimental data had analysed for effects of rolling reduction to compare the U - tank with the of exiting fish hold. The results were confirmed that the U-boat tank in the roll period and GoM were more safe than the existing fish hold and the average amplitude and significant of rolling angles were decreased relatively.

• Journal of Ship and Ocean Technology
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• v.12 no.4
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• pp.1-6
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• 2008

Nowadays, the computational capability and graphical power based on PCs increase very rapidly every year. As a result, the complicated engineering or scientific problems that could have only been handled by supercomputers a couple of decades ago can now be routinely run on PCs. Besides, the PCs can be assembled in parallel to increase its computational capability theoretically without limitation. The Web-based interface and communication tools are also being enhanced very rapidly and the real-time distance learning (E-Learning) and project cooperation on web get increasing attention. Using the-state-of-the-art computational method, a number of complicated and computationally intensive problems are being solved by PCs. The results can be well demonstrated on screen by graphics and animation tools. Those examples include the simulations of fully nonlinear waves, their interactions with floating bodies, global-motion analysis of multi-unit floating production system including complicated mooring lines and risers. Several examples will be presented in this regard. Also, Web and java-applet based educational tools have been developed at Texas A&M University for better understanding of waves and wave-body interactions. The background and examples of such Web-based educational tools published in Kim et al. (2003) are briefly introduced here.

• Journal of Mechanical Science and Technology
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• v.19 no.6
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• pp.1253-1267
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• 2005

Misalignment can be an important problem in the integration of GPS/INS. Observability analysis of the alignment errors in the integration of low-grade inertial sensors and multi-antenna GPS is presented in this paper. A control-theoretic approach is adopted to study the observability of time-varying error dynamics models. The relationship between vehicle motions and the observability of the errors in the lever arm and relative attitude between GPS antenna array and IMU is given. It is shown that alignment errors can be made observable through maneuvering. The change of acceleration makes the components of the relative attitude error that are orthogonal to the direction of the acceleration change observable. The change of angular velocity makes the components of the lever arm error that are orthogonal to the direction of the angular velocity observable. The motion of constant angular velocity has no influence on the estimation of the lever arm.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.73-88
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• 1990

The three dimensional aspects of hydrodynamic impact are discussed. Theoretical and experimental results for a sphere and a cusped body are presented. The cusped body is axisymmetric and resembles the bow profile of a ship with flare. The sphere was subjected to both vertical and oblique impact angles while the cusped body experienced only vertical motion. Three dimensional calculations using normal dipole distributions and an equi-potentioal free surface are compared with experimental results. The theoretical boundary value problem was solved using a known interior flow. This procedure reduced computation times significantly. Comparisons between theory and experiment show that, depending upon the body shape theoretical estimates of the maximum impact force may be larger or smaller than the experimental values. But the theoretical estimate can be used for practical purposes.

• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.2
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• pp.83-90
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• 2010

The hydrodynamic interaction of two floating bodies in waves freely floating or connected by a rigid link is studied by using a boundary element method in the frequency-domain. The exact two-body hydrodynamic coefficients of added mass, wave damping and exciting force are calculated from the radiation-diffraction potential solution of the improved Green integral equation associated with the free surface Green function. The irregular frequencies in the conventional Green integral equation make it difficult to predict the physical resonance of the fluid in the gap between two bodies floating side by side. However, the improved Green integral equation employed in this study is free of irregular frequencies and always yields the exact solution of the multi-body radiation-diffraction potential boundary value problem. The 6 degree-of-freedom motions of two bodies freely floating side by side or connected parallel by a rigid link have been calculated for the incident wave frequencies ranging from 0.1 to 5 radians per second in head, left and right bow quartering seas. The 6-component load of the rigid link have also been presented.

• The Journal of the Acoustical Society of Korea
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• v.27 no.1
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• pp.40-46
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• 2008

Weak target detection and localization in the presence of loud surface ship noise is a critical problem for matched field processing (MFP) in shallow water. For stationary sources, each signal component of received signal can be separated and interference can be suppressed using eigen space analysis schemes. However, source motion, in realistic cases, causes spreading of signal energies in their subspace. In this case, eigenvalues of target and interfere signal components are mixed and hard to be separated with usual phone space eigenvector decomposition (EVD) approaches. Our technique is based on mode space and utilizes the difference in their physical characteristics of surface and submerged sources. Performing EVD for modal cross spectral density matrix, interference components in the mode amplitude subspace can be classified and eliminated. This technique is demonstrated with synthetic data, and results are discussed.