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Enhanced structural design and operation of search and rescue craft
Published in Pentti Kujala, Liangliang Lu, Marine Design XIII, 2018
F. Prini, R.W. Birmingham, S. Benson, R.S. Dow, P.J. Sheppard, H.J. Phillips, M.C. Johnson, J. Mediavilla Varas, S. Hirdaris
To investigate the seakeeping of a vessel in real operational conditions, sea trials are necessary. They are nevertheless expensive and time consuming, which is why they are not carried out on a regular basis. If conducted for design purposes they also require a prototype vessel to be built first.
Experimental study on integrated and autonomous conductivity-temperature-depth (CTD) sensor applied for underwater glider
Published in Marine Georesources & Geotechnology, 2021
Bin Lv, Hai-lin Liu, Yi-fan Hu, Cheng-xuan Wu, Jie Liu, Hai-jing He, Jie Chen, Jian Yuan, Zhao-wen Zhang, Lin Cao, Hui Li
The project team performed a sea trial of the underwater glider outfitted with SZQ1-1 in Northern South China Sea aboard the research ship “No.9 Kediao.” The project team had measured the profile temperature, salinity and depth of the underwater glider more than 100 times. The glider carried two sets of CTD at the same time in the sea trial. According to analysis of more than 100 sets of sea trial data, under the action of stable ocean currents and waves (level ≤ 3), the difference value of conductivity of seawater measured by SZQ1-1 and SBE 19plus is within the range of 0.3mS/cm in the similar depth in the same sea trial. The dispersion in the measurements over the whole 100 measurements is 0.5 °C of temperature, 0.3 mS/cm of conductivity in the similar depth. Data of the two CTD sensors in the above experimental method can be compared with each other. The detailed sea trial plan is to release the glider from the research ship, and then the glider will enter the water to dive according to the set program. The maximum underwater glide depth is 500 m, and the glider will surface 2 km away from the water entry point. The tracks of glider with two CTD is marked as profile 1, 2 and 3. The developed glider's average diving speed is 0.5 m/s, and the actual depth of the two is 500.36 m (Figure 8).
Experimental and numerical study on the scale effect of stern flap on ship resistance and flow field
Published in Ships and Offshore Structures, 2020
Ke-wei Song, Chun-yu Guo, Chao Wang, Cong Sun, Ping Li, Ruo-fan Zhong
At present, there exist two methods (Cusanelli and Hundley 1999) to obtain the effect of installation of a stern flap on a full-scale ship, namely, model test extrapolation and sea trial. The extrapolation results of model testing are often remarkably different from those of the sea trial, especially at low speeds. In addition, sea trials often require enormous financial resources, which are not easily achievable in the initial design stage of the ship. To this end, in this study, the DTMB5415 ship was considered as the research object, and the influence of the stern flap on the ship model resistance and sailing attitude was determined based on numerical simulations and the towing tank test. Furthermore, the corresponding full-scale ship performance based on different extrapolation methods was obtained. Numerical simulations of the flow field around the full-scale ship before and after the installation of the stern flap was carried out. In addition, the difference between the simulated and extrapolated drag reduction rates was analysed, and the reasons for this difference were explained from the perspective of the stern flow field.
A 4 DOF simulation model developed for fuel consumption prediction of ships at sea
Published in Ships and Offshore Structures, 2019
Fabian Tillig, Jonas W. Ringsberg
A ship at sea encounters external forces from waves, wind and ocean currents. Traditionally performance analysis and prediction models follow the ITTC recommendations for sea trial tests (ITTC 2014) to estimate the power increase due to the environmental influences. Such an approach neglects side forces, yaw and heel moments from wind and waves, and focusses on the longitudinal forces (i.e. the added resistance). Under sea trial conditions, i.e. calm weather and only head or stern wind, the approach is feasible because the moments and side forces are virtually zero. However, during rougher weather conditions with varying angles of encounter for the wind and waves this is not the case – side forces and yaw moments will have to be compensated with a drift of the vessel and a rudder angle, which both cause more resistance. In some studies, such as in Naaijen et al. (2006) and Kramer et al. (2016), approaches which consider force and moment balances in four degrees-of-freedom (4 DOF), i.e. surge, drift (sway), heel and yaw, were introduced for ships with wind-assisted propulsion. It has not yet been investigated in detail how a 4 DOF simulation model compares with a 1 DOF simulation model with regards to the predictability of the fuel consumption.