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891.
Timothy Lilienthal Akihiko Matsuda Giles Thomas 《Journal of Marine Science and Technology》2007,12(2):111-118
This article presents work based on the development of a performance-based stability assessment method. It describes a numerical
method used to determine the survival limit for a dynamic intact stability assessment procedure. The numerical method utilises
a time-domain vessel motion program to assess the limit for a range of vertical centres of gravity (KG). The appropriateness
of the numerical predictions was examined through comparison with model experiment results. Free-running model tests were
conducted in regular following waves at discrete KGs. A comparison between the survival limits determined through the numerical
and experimental methods is presented. The current International Maritime Organisation (IMO) stability criteria are also evaluated
against the numerical and experimental dynamic performance-based stability assessment methods. 相似文献
892.
Two-dimensional numerical analyses were conducted and analyzed to simulate water splash produced by free falling object models
starting from the resting position. The equilateral prism-shaped object models were allowed to fall onto the free surface
of the water. The moving-particle semi-implicit (MPS) method was used to solve the unsteady Navier-Stokes equation for incompressible
fluid flows with and without the surface tension effect. Froude numbers of 0.75, 1.0, and 1.25 were used with different model
sizes for the entry velocity at the free surface. Splashes obtained by numerical computation closely agreed with the experimental
results. The surface tension force, the Froude number, and the Weber number were found in these calculations to play major
roles in determining various types of splash shapes. Model size was found to influence splash phenomena, even if the Froude
number remained the same. The dependencies on these two nondimensional numbers and the fundamental law of similarity on water
splash with and without the surface tension effect were thoroughly investigated in this research. Several two-dimensional
numerical simulations are presented in this article to describe the hydrodynamic behaviors of water splash with and without
the surface tension effect. 相似文献
893.
The probability of capsize of purse seiners in irregular beam seas and the effect of freeboard height and metacentric height
on trapped water on the deck was investigated. The aim was to quantify a safety level that can be achieved by direct stability
assessment for this type of fishing vessel. The amount of trapped water on deck was numerically estimated using a hydraulic
flow assumption. The long-term capsizing probabilities were estimated using a piecewise linear approach together with wave
statistics from major Japanese fishing areas. The estimated safety level of capsizing probability was compared with that obtained
by the IMO weather criterion and by the water-on-deck criterion of the IMO Torremolinos Convention. Numerical results for
four typical Japanese purse seiners indicated that the effect of freeboard, on the amount of trapped water on deck, is more
important than that of the metacentric height. Besides the metacentric height and the freeboard, it was shown that the danger
of capsizing is a function of the rise of floor. The safety level obtained by the capsizing probability approach is generally
higher than that based on the IMO weather criterion. However, the water-on-deck criterion provides a higher safety level than
the capsizing probability approach for ships with a low rise of floor. 相似文献
894.
LUO Wei ZHANG Pan 《船舶与海洋工程学报》2007,6(4):44-47
A new type of self-propelled barge was designed specifically for use on the Chishui River. This paper presents experimental results of its performance from tests in water of different depths,while bearing different loads. For test purposes,one of the best self-propelled barges from the Chishui River was used as a performance reference. The comparison showed that the new design has better maneuvering performance. 相似文献
895.
This research is intended to provide academic reference and design guidance for further studies to determine the most effective means to reduce a ship’s resistance through an air-cavity. On the basis of potential theory and on the assumption of an ideal and irrotational fluid, this paper drives a method for calculating air cavity formation using slender ship theory then points out the parameters directly related to the formation of air cavities and their interrelationships. Simulations showed that the formation of an air cavity is affected by cavitation number, velocity, groove geometry and groove size. When the ship’s velocity and groove structure are given, the cavitation number must be within range to form a steady air cavity. The interface between air and water forms a wave shape and could be adjusted by an air injection system. 相似文献
896.
Hyun Park Nam Hyun An Nicholas Hutchins Kwing-So Choi Ho Hwan Chun Inwon Lee 《Journal of Marine Science and Technology》2011,16(4):390-401
An experimental assessment has been made of the drag reducing efficiency of the outer-layer vertical blades, which were first
devised by Hutchins and Choi (Proceedings of ASME FEDSM’02 2002 ASME Fluids Engineering Division Summer Meeting, Montreal)
and Hutchins (An investigation of larger-scale coherent structures in fully developed turbulent boundary layers, Hutchins
N (2003), PhD thesis, University of Nottingham). The reported drag reduction efficiency, which was as much as 30%, was quantified
only in terms of the reduction in the local skin-friction coefficient. The assessment of the drag reducing efficiency did
not take the side effects of the inclusion of the blades into considerations. Those effects are the increase in the wetted
surface area and the flow disturbances due to the presence of the blades. In the present study, a series of drag force measurements
in towing tank has been performed toward the assessments of the total drag reduction efficiency of the outer-layer vertical
blades. It was found that for the case of h 4.0 × z 4.0 (h/δ = 1.04), the outer-layer vertical blades array achieved about 9.6% drag reduction without considering the increase in the
wetted surface area. A proper scaling method to give collapsed plot of drag reduction efficiency C
F/C
F0 was attempted, but the correlation remained limited. Of the two scaling methods, the outer scaling is found to be relevant
one. 相似文献
897.
Thomas Spenkuch Stephen R. Turnock Matteo Scarponi R. Ajit Shenoi 《Journal of Marine Science and Technology》2011,16(2):115-128
An approach for enhancing the realism of yacht fleet race simulations based on a lifting line method is developed. The wake
of an upwind sailing yacht is represented as a single heeled horseshoe vortex and image system. At each time step, changes
in vortex strength are convected into the wake as a pair of vortex line elements. These subsequently move in accordance with
the local wind, the self-induced velocity and the velocity induced by the presence of the wakes of other yachts. In addition,
the lifting line model has a model for the viscous wake due to the drag associated with the yacht and its sails superimposed
on it. A synthesis of sail yacht wake representations based on detailed 3D Reynolds-averaged Navier–Stokes computational fluid
dynamics calculations with wind tunnel test results is used to capture the initial strength of the combined main-jib vortex
system and its vertical height. The implementation of the lifting line algorithm within Robo-Race, a real-time yacht race strategy analysis tool, is described. Two upwind race interaction case studies are presented, and
these show that the newly implemented wake model makes an important contribution to enhancing the realism of the sailing simulation. 相似文献
898.
The evolution mechanism and characteristics of the submerged laminar round jet in a viscous homogenous shallow water layer are investigated through computational modeling. The laminar mode is used to solve the Navier-Stokes equations. In order to visualize the formation and evolution of the flow pattern, the volume of fluid (VOF) method is adopted to simulate the free surface of the water layer below the air and to trace the jet fluid. The results show that the jet forms a class of quasi-two-dimensional (Q2D) vortex structures in the ambient fluid with unequal influence from the bottom wall and free surface. The time dependence of three parameters, defined for the flow pattern as jet length, spiral radius and pattern length, is investigated quantitatively in their non-dimensional forms. Three different Reynolds numbers and two injection durations are further considered to discuss their influence on the flow pattern. 相似文献
899.
In order to realize high precision of environment parameters detection in irrigation applications, a sensor and sensor network (SSN) ontology based data fusion method is proposed. An SSN sub-ontology for soilstate monitoring is revised, which includes the sensing devices hierarchies and measurement properties selection according to the detection feature interests. As for sensor data processing, a tuning data method by data pool filtering and clustering is adopted, as well as a useful data fusion method for multi-sensor system. The testing results show that both the accuracy and efficiency of the proposed method are higher after related filtering and clustering process, which enables a thorough monitoring for intelligent irrigation systems and can be extended into environment monitoring and control applications. 相似文献
900.
A network plan model of ship erection was established based on the network planning technologyand the work-package breakdown system. The load-oriented production control method was introduced to buildup a throughput diagram model thus it is possible to describe the ship erection process numerically. Based onthe digitaiized models some cases of production balance of ship erection were studied and three balance indexeswere put forward, they are the load balance rate, the input manpower balance rate and the maximum gantrycrane operating times. Such an analytic method based on the balance evaluation is the important foundationfor digitization and intelligentization of shipyard production management. 相似文献