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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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International Journal of Ocean System Engineering
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Korean Society of Ocean Engineers
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Volume 1, Issue 4 - Dec 2011
Volume 1, Issue 3 - Sep 2011
Volume 1, Issue 2 - Jun 2011
Volume 1, Issue 1 - Mar 2011
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A non-linear tracking control scheme for an under-actuated autonomous underwater robotic vehicle
Mohan, Santhakumar ; Thondiyath, Asokan ;
International Journal of Ocean System Engineering, volume 1, issue 3, 2011, Pages 120~135
DOI : 10.5574/IJOSE.2011.1.3.120
This paper proposes a model based trajectory tracking control scheme for under-actuated underwater robotic vehicles. The difficulty in stabilizing a non-linear system using smooth static state feedback law means that the design of a feedback controller for an under-actuated system is somewhat challenging. A necessary condition for the asymptotic stability of an under-actuated vehicle about a single equilibrium is that its gravitational field has nonzero elements corresponding to non-actuated dynamics. To overcome this condition, we propose a continuous time-varying control law based on the direct estimation of vehicle dynamic variables such as inertia, damping and Coriolis & centripetal terms. This can work satisfactorily under commonly encountered uncertainties such as an ocean current and parameter variations. The proposed control law cancels the non-linearities in the vehicle dynamics by introducing non-linear elements in the input side. Knowledge of the bounds on uncertain terms is not required and it is conceptually simple and easy to implement. The controller parameter values are designed using the Taguchi robust design approach and the control law is verified analytically to be robust under uncertainties, including external disturbances and current. A comparison of the controller performance with that of a linear proportional-integral-derivative (PID) controller and sliding mode controller are also provided.
Numerical Simulation of 3D Free-Surface Flows by Using CIP-based and FV-based Methods
Yang, Kyung-Kyu ; Nam, Bo-Woo ; Kim, Yong-Hwan ;
International Journal of Ocean System Engineering, volume 1, issue 3, 2011, Pages 136~143
DOI : 10.5574/IJOSE.2011.1.3.136
In this paper, three-dimensional free-surface flows are simulated by using two different numerical methods, the constrained interpolation profile (CIP)-based and finite volume (FV)-based methods. In the CIP-based method, the governing equations are solved on stationary staggered Cartesian grids by a finite difference method, and an immersed boundary technique is applied to deal with wave-body interactions. In the FV-based method, the governing equations are solved by applying collocated finite volume discretization, and body-fitted meshes are used. A free-surface boundary is considered as the interface of the multi-phase flow with air and water, and a volumeof-fluid (VOF) approach is applied to trace the free surface. Among many variations of the VOF-type method, the tangent of hyperbola for interface capturing (THINC) and the compressive interface capturing scheme for arbitrary meshes (CICSAM) techniques are used in the CIP-based method and FV-based method, respectively. Numerical simulations have been carried out for dam-breaking and wave-body interaction problems. The computational results of the two methods are compared with experimental data and their differences are observed.
Wake Effect on HAT Tidal Current Power Device Performance
Jo, Chul-Hee ; Lee, Kang-Hee ; Lee, Jun-Ho ; Nichita, Cristian ;
International Journal of Ocean System Engineering, volume 1, issue 3, 2011, Pages 144~147
DOI : 10.5574/IJOSE.2011.1.3.144
The rotor that initially converts the flow energy into rotational energy is a very important component that affects the efficiency of the entire tidal current power system. Rotor performance is determined by various design variables. Power generation is strongly dependent on the incoming flow velocity and the size of the rotor. To extract a large quantity of power, a tidal current farm is necessary with a multi-arrangement of devices in the ocean. However, the interactions between devices also contribute significantly to the total power capacity. Therefore, rotor performance, considering the interaction problems, needs to be investigated to maximize the power generation in a limited available area. The downstream rotor efficiency is affected by the wake produced from the upstream rotor. This paper introduces the performance of a downstream rotor affected by wakes from an upstream rotor, demonstrating the interference affecting various gabs between devices.
The Effect of Moisture Absorption and Gel-coating Process on the Mechanical Properties of the Basalt Fiber Reinforced Composite
Kim, Yun-Hae ; Park, Jun-Mu ; Yoon, Sung-Won ; Lee, Jin-Woo ; Jung, Min-Kyo ; Murakami, Ri-Ichi ;
International Journal of Ocean System Engineering, volume 1, issue 3, 2011, Pages 148~154
DOI : 10.5574/IJOSE.2011.1.3.148
Generally, strength degradation is caused by the absorption of moisture in composites. For this reason, a fracture is generated in the composites and traces of glass fiber degrade human health and physical damage is generated. Therefore, in this research, we studied the mechanical properties change of composites by moistureabsorption. The composites were manufactured with and without the Gel-coating process and were immersed in a moisture absorption device at
for more than 100 days. The mechanical properties of the moistureabsorption composites and the composites which dry after moisture-absorption were compared. The mechanical properties degradation of basalt fiber composites according to the result of the measurement of moistureabsorption was smaller than that of glass fiber composites by about 20%. In addition, the coefficient of moisture absorption was lower for the case of Gel-coating processing than the composites without the Gel-coating process by about 2% and it was deduced that Gel-coating did not have a significant effect on the mechanical properties.
Second-order Motion Characteristics of a Semi-submersible Platform in Waves
Hong, Sa-Young ; Nam, Bo-Woo ; Kim, Jin-Ha ; Kim, Young-Shik ; Hong, Seok-Won ; Kim, Young-Soo ;
International Journal of Ocean System Engineering, volume 1, issue 3, 2011, Pages 155~164
DOI : 10.5574/IJOSE.2011.1.3.155
The second-order motion characteristics of a semi-submersible are investigated in regular waves. A higher-order boundary element method in a frequency domain and a finite element method in a time-domain were applied to the numerical analysis of the nonlinear hydrodynamic force and motion characteristics of semi-submersibles in view point of potential flow. Various aspects of nonlinear effects on the heave and roll of a semi-submersible were numerically investigated and some selected cases were compared with the model test data.
Study on AHRS Sensor for Unmanned Underwater Vehicle
Kim, Ho-Sung ; Choi, Hyeung-Sik ; Yoon, Jong-Su ; Ro, P.I. ;
International Journal of Ocean System Engineering, volume 1, issue 3, 2011, Pages 165~170
DOI : 10.5574/IJOSE.2011.1.3.165
In this paper, for the accurate estimation of the position and orientation of the UUV (unmanned underwater vehicle), an AHRS (Attitude Heading Reference System) was developed using the IMU (inertial measurement unit) sensor which provides information on acceleration and orientation in the object coordinate and the initial alignment algorithm and the E-KF (extended Kalman Filter). The initial position and orientation of the UUV are estimated using the initial alignment algorithm with 3-axis acceleration and geomagnetic information of the IMU sensor. The position and orientation of the UUV are estimated using the AHRS composed of 3-axis acceleration, velocity, and geomagnetic information and the E-KF. For the performance test of the orientation estimation of the AHRS, a testbed using IMU sensor(ADIS16405) and DSP28335 coded with an E-KF algorithm was developed and its performance was verified through tests.
Fatigue Design of Mooring Lines of Floating Type Combined Renewable Energy Platforms
Choung, Joon-Mo ; Jeon, Sang-Ik ; Lee, Min-Seong ;
International Journal of Ocean System Engineering, volume 1, issue 3, 2011, Pages 171~179
DOI : 10.5574/IJOSE.2011.1.3.171
This paper presents the concept design procedure of a floating-type combined renewable energy platform based on hydrodynamic analyses and is focused on the fatigue design of taut-type mooring lines of the platform. Two types of combined renewable energy platforms are considered: a combination of wind turbine, wave turbine and photovoltaic energy plant and a combination of wind turbine, current turbine and photovoltaic energy plant. The basic configurations are conceptually determined from the understanding of floating offshore plants, while the main dimensions have been determined based on a hydrostatic calculation. Fully coupled hydrodynamic analyses have been carried out to identify the motion characteristics of the floating body and the tension histories of the mooring lines. The tension history is used for the fatigue life prediction based on the rain-flow cycle counting method. For the fatigue life prediction, tension life curves from API and the Palmgren-Miner rule are employed.