| Co-Investigator(Kenkyū-buntansha) |
TAKIZAWA Kenji NMRI, Project team of ship performance evaluation in the actual seas, 実海域性能評価PT, Researcher (60415809)
SHIBATA Kazuya NMRI, Project team of ship performance evaluation in the actual seas, 実海域性能評価PT, Researcher (30462873)
MINAMI Yoshimasa NMRI, Project team of ship performance evaluation in the actual seas, 実海域性能評価PT, Senior researcher (60399516)
KASHIWAGI Masashi Kyushu Univ., Research Institute for applied mechanics, Professor (00161026)
YABE Takashi Tokyo Institute of Technology, Interdisciplinary graduate school of Science and Technology, Professor (60016665)
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| Research Abstract |
The CIP based CCUP method and the adaptive Soroban grid technique were combined for computation of 3D fluid-object and fluid-structure interactions in the presence of free surfaces and fluid-fluid interfaces. The combined technique is extended to ship hydrodynamics computations. The technique has a number of desirable features. The CIP method brings superior accuracy in computation of the advection terms. The Soroban grid technique, because of its unstructured nature, brings geometric flexibility and makes it possible to generate suitable grids around complex shapes. Even with this geometric flexibility, because the Soroban grid techniques has a very simple data structure, the combined technique is computationally efficient. Also, because the Soroban grid technique does not have any elements or cells connecting the grid points, it is free from mesh distortion limitations. The combined technique can accurately resolve the boundary layers near the ship surface and also calculate, in a ro
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bust and accurate fashion, the complex and unsteady free surfaces. We also introduced a new way of calculating the advective terms with increased computational efficiency. The enhanced efficiency makes the combined technique even more competitive in ship hydrodynamics computations. To show the capability of this method, simulations of realistic hydrodynamics of a running container ship in rough seas were conducted.
Next, we have developed the conservative form of the IDO (IDO-CF) scheme, In the IDO-CF scheme, cell-integrated values and point values of the mass, the momentum, and the energy are time-integrated by solving coupled conservation equations. The time integration of the cell-integrated values is described in the flux form and the cell-integrated values are exactly conserved. Fourier analyses for advection, diffusion, and Poisson equations show that the IDO-CF scheme retains as high resolution property as the IDO-NCF scheme. The effectiveness of the proposed scheme in solving compressible fluid dynamics is confirmed in the solutions of Riemann problems. The IDO-CF scheme also provides highly resolved solutions for incompressible fluid dynamics as shown in DNS of turbulent flow and lid-driven cavity flow. In comparison with the IDO-NCF scheme, the IDO-CF scheme has advantages not only in conservation but also in numerical velocity-pressure coupling While the IDO-NCF scheme needs to introduce special discretizations for stable coupling, in the IDO-CF scheme, the automatically staggered configuration between the cell integrated values and the point values provides stable coupling without any special discretizations. These advantages lead to superior results for both the compressible and incompressible flow problems The proposed scheme can be extended to the three-dimensional formulation straightforwardly, where volume integrals are introduced as the conservative cell-integrated values. The exactly conservation, high resolution, and high stability features of the IDO-CF scheme immensely promises in advanced compressible and incompressible fluid dynamics studies.
A new ship motion model by MPS method was also developed for high wave height conditions where green water occurs. Ship was treated as a rigid body. The interaction between the ship and waves was calculated on the basis of weak coupling. The advantages of this model are as follows: (1) The effect of shipping water is considered. (2) Rotation angle is not restricted. (3) Six degrees of freedom motion can be simulated. (4) Moving ship surface can be easily handled. A numerical wave tank was developed to create a series of waves. This numerical wave tank involves inflow and outflow boundaries. It was shown that the numerical wave tank was useful to reduce the calculation cost. The coupling between ship motion and green water on deck was calculated by using the developed ship motion model and numerical wave tank. The calculation was three-dimensional. Ship motions were calculated in five typical wave conditions. The calculated ship motions were compared with the experimental data quantitatively. As the result, it was shown that the MPS results were closer to the experiment than the ordinary linear method, New Strip Method. From these results, it can be said that the MPS method will be able to predict the ship motion in very rough seas where shipping water occurs. Less
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