排序方式: 共有6条查询结果,搜索用时 46 毫秒
1
1.
Kazuhiro Fukuda Junichiro Tokunaga Takashi Nobunaga Tatsuo Nakatani Toru Iwasaki Yoshikuni Kunitake 《Journal of Marine Science and Technology》2000,5(3):123-130
This paper presents a new technique for reducing frictional drag using a super-water-repellent surface and air-injection
(called an SWR & A technique). Its effectiveness was examined by carrying out pressure-loss measurements with a tube of rectangular
cross section, along with resistance tests on a horizontal flat plate, a 7.2-m-long tanker model, and a 12-m-long high length-to-beam-ratio
model ship. These test results showed that the new technique can significantly reduce the models' frictional drag; for example,
the frictional resistance on the SWR surface was reduced by 80% at a speed of 4 m/s and 55% at 8 m/s.
Received: October 16, 2000 / Accepted: December 4, 2000 相似文献
2.
CFD simulation of 3-dimensional motion of a ship in waves: application to an advancing ship in regular heading waves 总被引:1,自引:0,他引:1
A new computational fluid dynamics simulation method has been developed for the unsteady motion of a ship advancing in waves.
The objective is to evaluate the added resistance and predict the performance of a ship in waves. In this study, a finite
volume method, in the framework of a boundary-fitted grid system, is employed. The motion of the ship is solved with six degrees
of freedom by using the hydrodynamic forces and moments obtained from the solution of the simulation method. The marker–density–function
method is employed to calculate the nonlinear free surface. This method is applied to the coupled motion problem of heaving
and pitching.
Received for publication on Nov. 15, 1999; accepted on Nov. 18, 1999 相似文献
3.
In order to investigate the biological impacts of the ocean sequestration of CO2 (carbon dioxide), the dilution processes of CO2 were investigated near injection points in the deep ocean. From a combined fluid-dynamics, chemical, and biological approach,
a two-phase computational fluid dynamics (CFD) method with mass transfer was developed to predict droplet plume flow, the
dissolution of CO2 from droplets into seawater, and the advection–diffusion of dissolved CO2 (DCO2) in the deep ocean. Changes in pH due to the concentration of DCO2 were also calculated. In addition, the isomortality concept of Auerbach et al. was incorporated to predict the lethal damage
to marine organisms caused by DCO2. The simulation results suggested that the biological impacts of CO2 sequestration were insignificant in terms of mortality in both small-scale field experiments and the real-life cases we propose.
Received: October 3, 2001 / Accepted: December 14, 2001 相似文献
4.
Plumes of air and carbon-dioxide (CO2) bubbles in stratified water were studied experimentally and numerically. It is important to understand the plume behavior
of droplets or bubbles in the ocean in marine environmental engineering. In sequestration of CO2 in the ocean, liquid CO2 is injected in the form of droplets, and thermal stratification in enclosed seas is possibly destroyed by a bubble generator.
This study focuses on the relationship between intrusion depth and stratification intensity, gas flow rate, and bubble size.
A desktop-sized tank was used to achieve no-background-flow conditions for salt stratification. The results from the air-bubble
experiments indicated that the larger the bubble size, the smaller the intrusion depth. We also observed the behavior of CO2 bubbles. They are different from air in that they dissolve in water and are reduced in volume. Our numerical simulation method
for two-phase flow was validated by comparisons with the experiments.
Received: August 13, 2001 / Accepted: October 9, 2001 相似文献
5.
Numerical tests of various subgrid-scale (SGS) models were conducted for turbulence in thermally stratified homogeneous-shear
flow at a relatively low Reynolds number. Compared with a direct numerical simulation (DNS), we found that nondynamic isotropic
SGS models are not able to represent the energy spectrum very well because the energy decays considerably during the transition
between an initial random stage and a stage of coherent turbulent structures. Dynamic models performed well for simulating
the energy spectrum and the change of GS properties with time; anisotropy is not a necessary feature under the present simulation
conditions, although one of the special features of stratified turbulence is anisotropy. This may be because the present grids
for large-eddy simulation were fine enough to resolve the patches of counter-gradient heat fluxes, which play an important
role in the evolution of turbulent energy in stratified turbulence. With respect to the domain-averaged values of SGS stresses,
only the dynamic two-parameter mixed (DTM) model produced results of the same order of magnitude as those of filtered DNS.
This is because of the terms arising from re-decomposing of the SGS stresses in the DTM model. It was also found that this
incompetence in simulating the SGS stress is not necessary to simulate GS energy evolution, as is known for wall turbulence.
Updated from the Japanese original (J Soc Nav Archit Jpn 2001; 190:27–39) 相似文献
6.
Burak Yıldız Ferdi Çakıcı Toru Katayama Hüseyin Yılmaz 《Journal of Marine Science and Technology》2016,21(1):48-56
It is analytically difficult to calculate roll damping of ships due to the effects of viscosity. Therefore, computational fluid dynamics (CFD) has become a powerful tool in predicting roll damping recently. The unsteady flow around a forced rolling hull section with bilge keels can be calculated using a commercial URANS code which includes the viscous effects. In this study, two-dimensional (2D) roll damping calculations for a S60 midsection with bilge keels including free surface effects are performed for shallow draft case. The first objective of the study is to show whether the URANS code can be used to predict roll damping coefficient correctly. The second one is to show why Ikeda’s estimation method is insufficient at shallow draft case. Sinusoidal forced roll motion calculation method of roll damping moment with the help of a sliding interface and a fixed roll axis is successfully applied to predict roll damping coefficient. The calculations are carried out for different roll motion periods and amplitudes to validate the accuracy of the URANS code for different cases. Numerical results are compared with experiments, which were carried out at the towing tank facility of Osaka Prefecture University (OPU), and Ikeda’s estimation method. The results show that the URANS code is capable of predicting roll damping coefficients in a good agreement with experimental results and can be used further to develop a better model for prediction of roll damping. 相似文献
1