• Journal of the Society of Naval Architects of Korea
• /
• v.40 no.3
• /
• pp.16-21
• /
• 2003

Seakeeping performance of container ships is investigated in view of increase of their size in terms of TEU. Recent appearance of post Panamax class containers resulted in increase of GM, so increase of possibility of resonant motion in waves is expected accordingly. Ship motions of various classes of TEU containers were calculated for various sea states and heading angles in order to assess seakeeping characteristics according to increase of size of the ships. It was found that roll motion of post Panamax containers increase due to resonance as sea state becomes rougher. The possibility of controlling roll motion by changing main particulars such as L, B, and T is investigated as well.

• Journal of Advanced Research in Ocean Engineering
• /
• v.2 no.2
• /
• pp.81-85
• /
• 2016

Nonlinear wave loads can lead to resonant responses of offshore structures in sum or difference frequencies. In this study, the roll motion of an FPSO with a low natural frequency is simulated in the time domain. To generate the time signals of wave loads, the quadratic transfer functions of the second-order excitations are calculated in the frequency domain. The equations of motions based on the time memory functions are used to evaluate the roll responses in irregular waves. The roll damping in empirical form is accounted for in the simulation.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.3
• /
• pp.275-285
• /
• 2003

A visualization study on the effect of forcing amplitude in tone-excited jet diffusion flames has been conducted. Visualization techniques are employed using optical schemes. which are a light scattering photography. Flame stability curve is attained according to Reynolds number and forcing amplitude at a fuel tube resonant frequency. Flame behavior is globally grouped into two from attached flame to blown-out flame according to forcing amplitude: one sticks the tradition flame behavior which has been observed in general jet diffusion flames and the other shows a variety of flame modes such as the flame of a feeble forcing amplitude where traditionally well-organized vortex motion evolves, a fat flame. an elongated flame. and an in-burning flame. Particular attention is focused on an elongation flame. which is associated with a turnabout phenomenon of vortex motion and on a reversal of the direction of vortex roll-up. It is found that the flame length with forcing amplitude is the direct outcome of the evolution process of the formed inner flow structure. Especially the negative part of the acoustic cycle under the influence of a strong negative pressure gradient causes the shapes of the fuel stem and fuel branch part and even the direction of vortex roll-up to dramatically change.

• Journal of Ocean Engineering and Technology
• /
• v.31 no.3
• /
• pp.208-218
• /
• 2017

The performance of a wave energy converter (WEC) that uses the rolling motion of a partially submerged pendulum plate in front of a quay wall was analyzed. The wave exciting moment and hydrodynamic moment were obtained using a matched eigenfunction expansion method (MEEM) based on the linear potential theory, and then the roll motion response of a pendulum plate, time averaged extracted power, and efficiency were investigated. The optimal PTO damping coefficient was suggested to give the optimal extracted power. The peak value of the optimal extracted power occurs at the resonant frequency. The resonant peak and its width increase as the submergence depth of the pendulum plate decreases and thickness of the pendulum plate increases. An increase in the wave incidence angle reduces the efficiency of the wave energy converter. In addition, the WEC using a rolling pendulum plate contributes not only to the extraction of the wave energy, but also to a reduction in the waves reflected from the quay wall, which helps to stabilize ships going near the quay wall.

• Journal of the Society of Naval Architects of Korea
• /
• v.41 no.6
• /
• pp.1-7
• /
• 2004

Recently, very large container ships are emerging as shipment of containers is expected to rapidly increase near future. A possibility of roll resonant motion in a seaway is expected to noticeably increase for large container ships of which capacity ranges 8,000 to 15,000 TEU due to relatively wide breadth and shallow draft comparing to conventional container ships. In this paper, a design and performance evaluation of a fin stabilizer for a 9,000 TEU container ship is carried out. The weak opposed control concept is adopted for the design. Time domain simulations and model tests are performed for performance evaluation. The design prediction, the model tests and the simulations show generally good agreements.

• Journal of Sensor Science and Technology
• /
• v.26 no.4
• /
• pp.235-238
• /
• 2017

In this study, the design of a tri-axis micromachined gyroscope is proposed and the vibration characteristic of the structure is analyzed. Tri-axis vibratory gyroscopes that utilize Coriolis effect are the most commonly used micromachined inertial sensors because of their advantages, such as low cost, small packaging size, and low power consumption. The proposed design is a single structure with four proof masses, which are coupled to their adjacent ones. The coupling springs of the proof masses orthogonally transfer the driving vibrational motion. The resonant frequencies of the gyroscope are analyzed by finite element method (FEM) simulation. The suspension beam spring design of proof masses limits the resonance frequencies of four modes, viz., drive mode, pitch, roll and yaw sensing mode in the range of 110 Hz near 21 kHz, 21173 Hz, 21239 Hz, 21244 Hz, and 21280 Hz, respectively. The unwanted modes are separated from the drive and sense modes by more than 700 Hz. Thereafter the drive and the sense mode vibrations are calculated and simulated to confirm the driving feasibility and estimate the sensitivity of the gyroscope. The cross-axis sensitivities caused by driving motion are 1.5 deg/s for both x- and y-axis, and 0.2 deg/s for z-axis.