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Takafumi Kawamura Hideaki Miyata Kohji Mashimo 《Journal of Marine Science and Technology》1997,2(4):245-256
A time-marching CFD simulation is performed for self-propelling ships. The flow about the hull is simulated by the finite-volume
method, and the propeller action is approximated as a propeller disk for which the solution is given by a simplified propeller
model. The interaction of two flow models is treated in a time-marching procedure converging towards the steady self-propelling
condition. This method is applied to five tanker models, and detailed comparisons are made between the simulated results and
corresponding experimental results. It is shown that the flow field in the self-propelling condition is qualitatively well
reproduced in the simulation, and the estimated thrust deduction factors for the five hull forms agree well with measured
ones. However, the effective wake factors are underestimated, since the Reynolds number in the simulations differs from that
in the experiment. 相似文献
2.
Takafumi Kawamura 《Journal of Marine Science and Technology》2000,5(3):112-122
Direct numerical simulation (DNS) and large eddy simulation (LES) of turbulent shear flow beneath a flat water surface with
imposed wind shear stress are presented. The results of DNS indicate that there are clear differences, and also similarities,
between wind-driven flow and the flow near a solid wall. The qualitative structures of turbulence are similar in both types
of flow. Low-speed streaks are also present in wind-driven flow. On the other hand, profiles of the mean velocity and turbulence
intensities in wind-driven flow are significantly different from those in flow near a solid wall. The differences are attributed
to the lack of a viscous sublayer, and to the boundary condition which allows fluctuations of the tangential velocity components
at the boundary. LES of the same flow was also carried out to evaluate subgrid-scale models. It was shown that the features
of the flow observed in DNS are well simulated by all models tested, and that the discrepancies between DNS and LES with the
dynamic mixed model are very small.
Received: August 17, 2000 / Accepted: December 22, 2000 相似文献
3.
Hideaki Miyata Akihiro Kanai Takafumi Kawamura Jhong-Chun Park 《Journal of Marine Science and Technology》1996,1(4):183-197
Three-dimensional (3D) wave breaking around bodies of complex geometry has been numerically investigated by use of two types
of Navier-Stokes solvers, namely the finite-difference and the finite-volume methods employing rectangular and curvilinear
coordinate systems, respectively. Both methods employ the density-function technique to capture the free surface location
and can cope with complicated free surface configurations such as breaking waves. The accuracy of the density-function method
is examined through the comparison with experimental results, and it is confirmed to be satisfactory when the grid spacing
and the time increment are sufficiently small.
New computational methods are applied to several problems including 3D breaking waves around ships and wave diffraction around
offshore structures. The computed results show good agreement with experimental results indicating that wave breaking phenomena
are successfully simulated. The qualitative accuracy, however, could be improved by including the dissipating effect of breaking
waves. 相似文献
4.
Yasumi Kawamura Hideomi Ohtsubo Katsuyuki Suzuki 《Journal of Marine Science and Technology》1997,2(1):35-51
In ship structural design, many structural analyses by the finite element method are carried out on models at several different scale levels; for example, a whole ship, cargo hold parts, and detailed structures. However, one serious problem with this design and analysis process is that the generation of the finite element models for a complex configuration is very difficult and laborious. To overcome this problem, an object oriented, finite element modeling system, MODIFY, has been developed by the authors. In this paper, the concept of the finite element modeling system and the techniques for the construction of the system are explained. First, the object oriented data structure of the system, based on the Part-Object concept, is proposed. In this concept, not only the geometry of the domain but also the analytical conditions, such as boundary conditions and material properties, and the finite element model, are represented by the object oriented data structure. By using this data structure, effective finite element model generation can be expected. Second, a mesh generation algorithm based on the frontal method is described. The original frontal method by S.H. Lo was improved for application to three-dimensional curved surfaces. A new inner node placement technique to make quadrilateral elements around stress concentrated areas is also proposed. These techniques are suitable for ship structures, and more accurate results from the finite element analysis can be expected. Moreover, the parallel mesh generation is implemented in MODIFY by using the client-server concept to accelerate mesh generation. Third, a prototype system for the automatic finite element model generation for different analysis levels is proposed. The system is based on the concept of the PD part, which is the part in the design and production stage, and automatic computing of the intersection between PD parts. The validity of this system is demonstrated by some examples. 相似文献
5.
This paper develops a behavioral analysis of freight mode choice decisions that could provide a basis for an acceptable analytical tool for policy assessment. The paper specifically examines the way that truck and rail compete for commodity movement in the US. Two binary mode choice models are introduced in which some shipment-specific variables (e.g. distance, weight and value) and mode-specific variables (e.g. haul time and cost) are found to be determinants. The specifications of the non-selected choice are imputed in a machine learning module. Shipping cost is found to be a central factor for rail shipments, while road shipments are found to be more sensitive to haul time. Sensitivity of mode choice decisions is further analyzed under different fuel price fluctuation scenarios. A low level of mode choice sensitivity is found with respect to fuel price, such that even a 50% increase in fuel cost does not cause a significant modal shift between truck and rail. 相似文献
6.
Simulation of the oil spill processes in the Sea of Japan with regional ocean circulation model 总被引:1,自引:0,他引:1
Sergey M. Varlamov Jong-Hwan Yoon Naoki Hirose Hideyuki Kawamura Ken Shiohara 《Journal of Marine Science and Technology》1999,4(3):94-107
A simulation of the movement of spilled oil after the incident of the Russian tanker Nakhodka in the Sea of Japan, in January 1997, was performed by a particle tracking model incorporating advection by currents, random
diffusion, the buoyancy effect, the parameterization of oil evaporation, biodegradation, and beaching. The currents advecting
spilled oil were defined by surface wind drift superposed on the three-dimensional ocean currents obtained by the Geophysical
Fluid Dynamics Laboratory modular ocean model (GFDL MOM), which was forced by the climatological monthly mean meteorological
data, or by the European Center for Medium Range Weather Forecasts (ECMWF) daily meteorological data, and assimilated sea
surface topography detected by satellite altimeter. A number of experiments with different parameters and situations showed
that the wide geographical spread of oil observed is not explained by wind drift alone, and that including the simulated climatological
currents gives better results. The combination of surface wind drift and daily ocean currents shows the best agreement between
the model and observations except in some coastal areas. The daily meteorological effect on the ocean circulation model results
in a stronger variability of currents that closely simulates some features of the nonlinear large-scale horizontal turbulent
diffusion of oil. The effect of different parameterizations for the size distribution of model oil particles is discussed.
Received for publication on July 26, 1999; accepted on Nov. 17, 1999 相似文献
7.
A study was performed on TMCP (thermo-mechanical control process) - manufactured high-tensile steel plates with yield point of 40 kgf/mm2 (YP40), which were recently developed for use in ship production and whose ease of shop fabrication is almost equal to that of the well-proven ship high-tensile steel plates (HT50) with yield points at 32 and 36 kgf/mm2 levels.
The authors' study addressed the performance required of the YP40 TMCP high-tensile steel for ship applications, including strength characteristics of base metal and high-heat-input welded joints, and also shop fabrication methods suitable to this material. 相似文献
8.
Takafumi Kawamura 《Journal of Marine Science and Technology》2000,5(4):161-175
Large-eddy simulations (LES) of the interactions between turbulent shear flow and surface waves are presented. The formation
mechanism of Langmuir circulation and its contribution to the vertical momentum transport are investigated in detail. The
effect of surface waves is modeled in two ways in the LES runs. One model includes only the phase-averaged effect of the waves
as an added source term in the momentum equation, and the other model includes the full effect of the waves by use of the
fully nonlinear conditions of the air-water interface. Langmuir circulations are clearly indicated in both cases, indicating
that the phase-averaged effect is essential for the formation of this circulation. It is shown that the formation of Langmuir
circulations enhances the vertical transport of momentum. As a result, the mean velocity gradient and the streamwise component
of the turbulence intensity are decreased, while the spanwise and interface normal components are increased. Examination of
the turbulence energy budget equations shows that production is due to the interaction between the vorticity and the Lagrangian
drift as the phase-averaged effect of the wave becomes the dominant source of turbulence.
Received: August 17, 2000 / Accepted: December 22, 2000 相似文献
9.
Takafumi Kawamura Kazuyuki Ouchi Takeo Nojiri 《Journal of Marine Science and Technology》2012,17(4):469-480
Computational fluid dynamics (CFD) analyses of propeller boss cap fins (PBCF) were carried out for two different propellers at model and full scale Reynolds numbers with two different inflow conditions. Computations corresponding to the reverse propeller open test (POT) experiment were confirmed to be in a good agreement with the measurement. The results of computations at different conditions have shown that increased Reynolds number and presence of hull wake both positively influence the effects of PBCF. Due to the combined effect of the Reynolds number and the wake, the gain in the propeller efficiency at the full scale condition was found to be significantly larger than that at the model test condition. The detailed investigation of the results suggested that the fin drag becomes smaller and the reduction of the boss drag becomes larger at the full scale condition. However, the predicted gain is still smaller than the values reported in the sea trial and logbook analysis. The remaining gap may be attributed to the difference in the estimated and actual wake distribution or to other factors such as interactions with hull and rudder, surface roughness, unsteadiness and hub vortex cavitation. 相似文献
10.
Yoshihisa Takekoshi Takafumi Kawamura Hajime Yamaguchi Masatsugu Maeda Norio Ishii Koyu Kimura Tadashi Taketani Akihiko Fujii 《Journal of Marine Science and Technology》2005,10(2):70-81
A new method for designing propeller blade sections is presented. A vortex lattice method is used to evaluate the performance and the time-dependent pressure distribution on the blade surface in a non-uniform flow, while efficient optimization algorithms are used to modify the blade sections. Two different designs were carried out in this study. The first was a design to realize a target pressure distribution in a rotating three-dimensional flow. A two-dimensional wing theory was used to obtain the target pressure distribution. The predicted increase in efficiency and the reduction in the cavity volume were confirmed by model experiments. The second was a design to maximize the propeller efficiency. By this method, the propeller efficiency was improved by 1.2% under the constrains of constant thrust and a prescribed margin for face cavitation. 相似文献
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