Flow structures around trapezoidal cylinders and their hydrodynamic characteristics: Effects of the base length ratio and attack angle

A “bird” is a device usually being used to control the depth and position of marine seismic streamers. Exact position of the streamers can effectively promote the precision, reduce the measured times and save the costs for marine seismic exploitation. So the “birds” have important significance to marine oil exploitation. A Hydrodynamic characters test concerning a new embedded bird has been introduced in this paper. And some useful hydrodynamic character-data of the hydrofoil are obtained, such as lift-attack angle diagram, resistance-attack angle diagram, torque-attack angle diagram. These data and diagrams are more helpful for studying on the embedded bird, including the control method and control strategy etc. Above all, the results of the test have significant reference value for the control of birds and marine seismic streamers.

Download Full-text

Hydrodynamic characteristics and flow structures of pitching hydrofoil with special emphasis on the added force effect

Renewable Energy ◽

10.1016/j.renene.2020.05.081 ◽

2020 ◽

Vol 157 ◽

pp. 560-573

Author(s):

Mengjie Zhang ◽

Taotao Liu ◽

Biao Huang ◽

Qin Wu ◽

Guoyu Wang

Keyword(s):

Flow Structures ◽

Hydrodynamic Characteristics ◽

Force Effect

Download Full-text

Study the influence of ship length ratio on ship to ship interaction on moving in parallel on their hydrodynamic characteristics

MORSKIE INTELLEKTUAL`NYE TEHNOLOGII ◽

10.37220/mit.2021.54.4.068 ◽

2021 ◽

pp. 61-66

Author(s):

Р. Али ◽

Н.В. Тряскин

Keyword(s):

Hydrodynamic Interaction ◽

Turbulence Modeling ◽

Relative Length ◽

Velocity Fields ◽

Length Ratio ◽

Navier Stokes ◽

Hydrodynamic Characteristics ◽

Turbulent Model ◽

Calm Water ◽

Good Agreement

Суда в некоторых случаях эксплуатации могут двигаться в непосредственной близости друг от друга. Такой сценарий обычно связан с изменением полей давления и скорости вблизи корпуса судов, в результате чего возникают гидродинамические силы и моменты взаимодействия, которые сильно зависит от относительной длины. В этой статье была проведена серия систематических расчётов на двух корпусах KVLCC2, движущихся на большой глубине в безветренную погоду с одинаковой постоянной малой скоростью, не превышающей 4 уз., чтобы исследовать влияние отношения длин на силы и моменты гидродинамического взаимодействия. OpenFOAM, пакет CFD с открытым исходным кодом использовался для организации и проведения расчётов. Метод осреднения по Рейнольдсу уравнений Навье-Стокса (RANS) применялся для моделирования турбулентности. Хорошо известная модель турбулентности использовалась для замыкания уравнений Навье-Стокса. Числовые результаты, касающиеся поля скоростей и гидродинамического следа за судами, были обработаны, проанализированы, сопоставлены и показали хорошее согласование с экспериментальными результатами. Ships, during the lightering operations, are forced to sail in a close position to each other, such a scenario generally associates with a change in the pressure and velocity fields surrounding their hulls, as a result, interaction hydrodynamic forces and moments are generated which are strongly related to the relative length of the interacted ships. In this paper, a series of systematic computations were performed on two KVLCС2 hulls advancing in deep and calm water with the same constant low speed (full scale speed 4kt) in order to investigate the influence of the length ratio on the hydrodynamic interaction forces and moments during the lightering operation. OpenFOAM, an open-source CFD packet was used for carrying out the simulations, Reynolds Averaged Navier-Stokes (RANS) method was used for turbulence modeling and the well-known turbulent model k-ω SST was used to close RANS equations. Numerical results have been post-processed, analyzed, compared and found to be of a good agreement with the experimental results. The velocity fields and wake were presented and analyzed.

Download Full-text

Experimental Study on Hydrodynamic Characteristics of Three-Stranded Polyethylene Rope

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.490-491.421 ◽

2014 ◽

Vol 490-491 ◽

pp. 421-429 ◽

Cited By ~ 2

Author(s):

Liu Yi Huang ◽

Lin Zhang ◽

Tian Wei Dong ◽

Rong Wan ◽

Fen Fang Zhao ◽

...

Keyword(s):

Reynolds Number ◽

Drag Coefficient ◽

Lift Coefficient ◽

Flow Speed ◽

Attack Angle ◽

Hydrodynamic Characteristics ◽

Force Coefficient ◽

Force Components ◽

And Performance ◽

Model Region

Three-stranded polyethylene ropes and twines are widely used as one of the main materials for fishery facilities. The shape and performance of the net fishing facilities in water are determined by the hydrodynamic properties of these ropes and twines. In the present work, experiment investigation was made in the flume tank in Tokyo University of Marine Science and Technology. Five kinds of three-stranded polyethylene rope with different sizes of diameter were tested. Drag and lift forces, together with sideways force acting on ropes under various trial conditions were measured by underwater load cells which were independently developed by the authors to record three axial force components. The drag, lift and sideways forces per unit rope length, under various attack angles at several flow velocities were obtained through data analysis. Then the drag coefficient, the lift coefficient and the sideways force coefficient were calculated within the range of Reynolds numberRd= 2.5×103~3.0×104. The following conclusions may be made from the experimental results: (1) At all the three testing attack angles i.e. 45o, 60o and 90o, the drag per unit rope length is proportional to the square of flow speed; (2) As the attack angle equal to 90o, the drag coefficient can be expressed in a power function of Reynolds number as given below: It can be inferred that the drag coefficient is approximately equal to 1.4 in the automatic model region, i.e. 1.2×104<Rd< 3.0×104. (3) As the attack angle equal to 45o or 60o, the lift force per unit rope length is proportional to the 2.5thpower of flow speed and the lift coefficient has a similar trend as the drag coefficient. But the lift coefficient makes smaller fluctuation compared to the drag coefficient when tending to a constant value in the automatic model region, i.e. 1.2×104<Rd<3.0×104.

Download Full-text

Effect of ducts on the hydrodynamic performance of marine propellers

Engineering Computations ◽

10.1108/ec-03-2021-0190 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Yang Liu ◽

Qingwei Gong ◽

Yongning Bian ◽

Qinghui Suo

Keyword(s):

Hydrodynamic Forces ◽

Attack Angle ◽

Hydrodynamic Performance ◽

Hydrodynamic Characteristics ◽

Computational Domain ◽

Content Type ◽

Wide Range ◽

Advance Ratio ◽

Thrust And Torque ◽

Ducted Propellers

PurposeHydrodynamic forces and efficiency of bare propeller and ducted propellers with a wide range of advance ratio (J) and attack angle (θ) are examined. The thrust and torque coefficients and the efficiency are presented and discussed in detail. The present results give a reliable guidance to the improvement of the hydrodynamic characteristics of ducted propellers.Design/methodology/approachThe effect of a duct on the hydrodynamic performance of the KP458 propeller is numerically investigated in this study. Finite volume method (FVM)-based simulations are performed for a wide range of advance ratio J (0 ≤ J ≤ 0.75) and attack angle θ of the duct (15° ≤ θ ≤ 45°). A cubic computational domain is employed in this study, and the moving reference frame (MRF) approach is adopted to handle the rotation of the propeller. Turbulence is accounted for with the RNG k-ε model. The present numerical results are first compared against available experimental data and a good agreement is achieved.FindingsThe simulation results demonstrate that the hydrodynamic forces and efficiency increases and decreases with J, respectively, at the same attack angle. In addition, it is demonstrated that the hydrodynamic forces and efficiency are both improved due to the presence of the duct, which eventually leads a better hydrodynamic performance at high advance ratios. It is further revealed that as the attack angle increases, the pressure difference between the suction- and pressure-surfaces of the propeller is also augmented, which results in a larger thrust. The wake field is more uniform at θ = 30°, suggesting that a higher efficiency can be obtained.Originality/valueThe present study aims to investigate the effect of a duct on the KP458 propeller subjected to uniform inbound flow. The relationship between the uniform incoming flow and the attack angle of the duct is mainly focused, and the design of the ducted propellers for any ship hull can be improved according to this relationship.

Download Full-text