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11.
Zdravko R. Kishev Changhong Hu Masashi Kashiwagi 《Journal of Marine Science and Technology》2006,11(2):111-122
In this article, a new computational fluid dynamics simulation approach based on the constraint interpolation profile (CIP)
method is applied to tackle the violent sloshing problem. The present study considers two-dimensional sloshing phenomena in
a rectangular tank. By the proposed method, the sloshing problem is viewed as a multiphase problem that includes water and
air flows. A stationary Cartesian grid is used and the free surface is solved by an interface capturing method. The CIP combined
unified procedure (CCUP) scheme was adopted for the flow solver, and both the CIP scheme and the CIP conservative semi-Lagrangian
with cubic interpolation polynomial (CIP-CSL3) scheme were used for interface capturing. For validation of the numerical method,
a physical experiment was conducted with a rectangular tank for several frequencies and filling heights. A convergence check
was first performed for the method. The numerical simulation results on violent sloshing show that the use of the CIP-CSL3
scheme as an interface capturing procedure gives much better results for the pressures and free-surface profiles than the
conventional CIP scheme. 相似文献
12.
Productive efficiency of public and private solid waste logistics and its implications for waste management policy 总被引:1,自引:0,他引:1
This paper measures the productive efficiency of municipal solid waste (MSW) logistics by applying data envelopment analysis (DEA) to cross-sectional data of prefectures in Japan. Either through public operations or by outsourcing to private waste collection operators, prefectural governments possess the fundamental authority over waste processing operations in Japan. Therefore, we estimate a multi-input multi-output production efficiency at the prefectural level via DEA, employing several different model settings. Our data classify the MSW into household solid waste (HSW) and business solid waste (BSW) collected by both private and public operators as separate outputs, while the numbers of trucks and workers used by private and public operators are used as inputs. The results consistently show that geographical characteristics, such as the number of inhabited remote islands, are relatively more dominant factors for determining inefficiency. While the implication that a minimum efficient scale is not achieved in these small islands is in line with the literature suggesting that waste logistics has increasing returns at the municipal level, our results indicate that waste collection efficiency in Japan is well described by CRS technology at the prefectural level. The results also show that prefectures with higher private-sector participation, measured in terms of HSW collection, are more efficient, whereas a higher private–labor ratio negatively affects efficiency. We also provide evidence that prefectures with inefficient MSW logistics have a higher tendency of suffering from the illegal dumping of industrial waste. 相似文献
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14.
利用改进的霍普金森棒法对汽车用钢板的圆弧焊接接头试验片进行了静强度和冲击强度的拉伸试验,得到了三种不同材料试验片的应变率、应力波、冲击破坏变形和破坏速度并对试验结果进行了分析.试验结果为车体材料的选择提供了依据. 相似文献
15.
A B-spline Galerkin scheme for calculating the hydroelastic response of a very large floating structure in waves 总被引:2,自引:2,他引:0
Masashi Kashiwagi 《Journal of Marine Science and Technology》1998,3(1):37-49
This paper presents an effective scheme for computing the wave-induced hydroelastic response of a very large floating structure, and a validation of its usefulness. The calculation scheme developed is based on the pressure-distribution method of expressing the disturbance caused by a structure, and on the mode-expansion method for hydroelastic deflection with the superposition of orthogonal mode functions. The scheme uses bi-cubic B-spline functions to represent unknown pressures, and the Galerkin method to satisfy the body boundary conditions. Various numerical checks confirm that the computed results are extremely accurate, require relatively little computational time, and contain few unknowns, even in the region of very short wavelengths. Measurements of the vertical deflections in both head and oblique waves of relatively long wavelength are in good agreement with the computed results. Numerical examples using shorter wavelengths reveal that the hydroelastic deflection does not necessarily become negligible as the wavelength of incident waves decreases. The effects of finite water depth and incident wave angle are also discussed. 相似文献
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17.
Propeller load fluctuation in rough sea conditions is caused by two components: one is the fluctuating inflow velocity and
the other is the emergence of the propeller disk from the water. Such disturbances cause large fluctuations in engine power
and revolutions, and can lead to the failure of the propulsion plant, which is unacceptable in extreme seas. However, due
to strong nonlinearity in the effect of propeller emergence and nonlinear interactions with the inflow velocity in the propeller
torque fluctuation, the procedure for obtaining the statistical properties of the propeller torque in extreme sea conditions
is not clear. If the statistical properties of propeller torque fluctuation—such as the variance and the probability density
function—are known, the corresponding statistics of the response of the engine can be obtained, allowing the safe operation
of ship propulsion plants in extreme irregular seas to be assessed. 相似文献
18.
A time-domain higher-order boundary element method for 3D forward-speed radiation and diffraction problems 总被引:1,自引:0,他引:1
A time-domain higher-order boundary element method for seakeeping analyses in the framework of linear potential theory is newly developed. Ship waves generated by two modified Wigley models advancing at a constant forward speed in calm water or incident waves and the resultant radiation and diffraction forces are computed to validate this code. A rectangular computational domain moving with the same forward speed as the ship is introduced, in which an artificial damping beach is installed at an outer portion of the free surface except the downstream side for satisfying the radiation condition. The velocity potential on the ship hull and the normal velocity on the free surface are calculated directly by solving the boundary integral equation. An explicit time-marching scheme is employed for updating both kinematic and dynamic free-surface boundary conditions, with an embedding of a second-order upwind difference scheme for the derivative in the x-direction to stabilize the calculation. Extensive results including the exciting forces, added mass and damping coefficients, wave profiles, and wave patterns for blunt Wigley and slender Wigley hulls with forward speed are presented to validate the efficiency of the proposed 3D time-domain approach. The corresponding physical tests of the radiation and diffraction problems in a towing tank are also carried out. Computed numerical results show good agreement with the corresponding experimental data and other numerical solutions. 相似文献
19.
A time-domain mode-expansion method for calculating transient elastic responses of a pontoon-type VLFS 总被引:3,自引:0,他引:3
Masashi Kashiwagi 《Journal of Marine Science and Technology》2000,5(2):89-100
A time-domain calculation method is described for elastic responses to arbitrary time-dependent external loads, on the basis
of a general differential equation of second order including the convolution integral related to memory effects in the hydrodynamic
forces. The time-dependent elastic deflection of a structure is represented by a superposition of mathematical modal functions,
and a Galerkin scheme is employed to obtain a linear system of simultaneous differential equations for the amplitude of modal
functions assumed. Special care is paid to numerical accuracy in computing the memory-effect function and the added mass at
infinite frequency. The validity of the numerical results was confirmed through a comparison with time histories of the vertical
deflection measured in an impulsive weight-drop test conducted at the Ship Research Institute and a comparison with existing
numerical results for the same problem. To check the necessity of memory-effect terms, computations using a constant value
for the hydrodynamic damping coefficient were also performed, and practical measures for reducing the computation time are
discussed.
Received: April 12, 2000 / Accepted: August 24, 2000 相似文献
20.
In the previous paper, one of the authors proposed a new time-domain nonlinear strip method for a rigid body, in which hydrodynamic
forces are evaluated by a convolution integral with the memory function computed for the instantaneous submerged part of the
transverse sections, and the Froude–Krylov and hydrostatic forces are evaluated on the instantaneous wetted hull surface.
In this paper, first, that nonlinear strip method is extended for an elastic body using a method of superposition of elastic
mode functions, which enabled us to investigate whipping phenomena due to impulsive large waves. Second, the influence of
different approximations of the pressure above the still-water surface is investigated, and then the results calculated by
the proposed nonlinear strip method are compared with the experimental ones. Third, whipping phenomena observed for an elastic
body at higher Froude numbers are studied through a comparison between computed and measured results. Higher-frequency vibrations
in the vertical bending moment due to slamming are discussed. Furthermore, the wave load due to green water on deck is calculated
by introducing a practical model, and the effects of the green water on responses of both rigid and elastic bodies are investigated. 相似文献