Oka H.,Japan National Maritime Research Institute |
Oka Y.,Yokohama National University
Fire Safety Journal | Year: 2017
Large eddy simulation (LES) of turbulent buoyant plumes formed above an oscillating fire source has been carried out so as to clarify their temperature properties in the offshore environment. For the sake of simplicity, we are concerned here only with a rolling environment among six-degree-of-freedom system of complex ship motion. Furthermore, under the assumption of a small rolling angle, unsteady fire source movement associated with the rolling motion can be approximated by simple harmonic oscillation in the horizontal direction. Numerical results obtained under several sets of oscillation conditions, especially under different amplitude conditions, are compared with temperature variations of conventional axisymmetric and two-dimensional fire plumes above stationary sources. Consequently, it has been clarified that in the case where the amplitude is four times longer than the side length of a square source, the present buoyant plumes exhibit almost the same feature as the two-dimensional fire plume in the lower part of the buoyant plume region. On the other hand, it has been found that for any value of amplitude, the temperature properties are close to those of axisymmetric plumes in the upper part of the buoyant plume region. Based on these findings, a simple theoretical model to estimate the variation in mean excess temperature as a function of elevation has been developed by the use of a well-recognized, semi-analytical solution of the axisymmetric plume formed above a virtual point source. It has been confirmed that this simple model can reasonably reproduce the same plume features as obtained by the LES simulations. © 2016 Elsevier Ltd
Ueno M.,Japan National Maritime Research Institute
Ocean Engineering | Year: 2010
A submersible surface ship (SSS) is based on a novel concept that the SSS goes on surface like conventional ships in moderate seas but goes underwater in rough seas to the depth sufficient to avoid wave effects. The SSS has a wing system that produces downward lift to go underwater with preserving the residual buoyancy for its safety. The SSS is expected to be able to keep both safety and punctuality even if it encounters unexpected bad weather. The motion of the SSS is studied. The equations of motion are formulated and the procedures for estimating hydrodynamic derivatives are presented. The hydrodynamic derivatives are estimated for a SSS having a configuration, a hull with a pair of main wings and a pair of horizontal tail wings. Using these estimated hydrodynamic derivatives, calculation of the SSS motion is carried out. The calculation results show some specific aspects of the SSS especially for effects of the elevator of main wings and horizontal tail wings, aileron of main wings, rudder and propeller revolution. It is confirmed that the existence of static roll restoring moment and having large hull comparing with wing area play important roles in the motion of the SSS. © 2010 Elsevier Ltd. All rights reserved.
Shibata K.,University of Tokyo |
Koshizuka S.,University of Tokyo |
Sakai M.,University of Tokyo |
Tanizawa K.,Japan National Maritime Research Institute
Ocean Engineering | Year: 2012
A three-dimensional ship motion model was developed using the moving particle semi-implicit (MPS) method to calculate a ship motion under high wave height conditions where shipping water occurs. The ship's hull was assumed to be a rigid body, and the interaction between the rigid body and fluid was simulated on the basis of weak coupling. A numerical wave tank was also developed to calculate a ship motion with minimum calculation costs. The numerical wave tank was able to create a series of waves and express the ship's relative forward speed. Using the developed ship motion model and the numerical wave tank, towing tests were numerically performed for five typical wave conditions. The calculated ship motions were compared with the experimental results. As a result, the nonlinear effect of shipping water was successfully simulated by the MPS method, although there quantitative differences between the calculated and experimental results still remained. This study shows the potential of the MPS method as a new simulation tool for calculating a ship motion in high wave height conditions. © 2012 Elsevier Ltd. All rights reserved.
Kaneko F.,Japan National Maritime Research Institute |
Yuzui T.,Japan National Maritime Research Institute
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2014
This paper shows risk profiles of major ship types which were obtained by analyzing IHSF casualty and ship characteristics data-bases aiming at contributing to the step 2 of FSA introduced in the consideration of safety measures in the IMO. Individual risk, PLL and FN diagrams are considered as elemental indices which are components of risk profiles. Considered period is from 1978 to 2011, continuous 34 years. In this paper risk profiles of the former and the latter periods were compared and improvements of safety of such ship types are discussed. And the method for identifying ship groups which need emergent consideration of safety measures to improve safety is dealt with. In addition a method for prioritizing types of casualty when considering safety measures is also shown. Finally a new method for approximation of FN diagrams and also a new method for setting evaluation criteria by applying that are proposed. Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE).
Yamada Y.,Japan National Maritime Research Institute
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2014
The purpose of the present study is to investigate residual Ultimate Longitudinal Strength (ULS) of bulk carriers after ship-ship collision. A series of a large-scale explicit finite element analysis (FEA) as well as simplified analysis (SA) are carried out using a cape size bulk carrier. In order to accurately investigate collapse mechanism of "damaged ships" under vertical bending moment nonlinear FEA are carried out where two steps analysis is adopted. First step is ship-ship collision analysis; Second step is ULS analysis of the damaged ship. Ship-ship collision analysis is carried out assuming the right angle collision at the midship region of the struck ship, and damage extent of the struck ship is estimated with varying collision speed of 3kt, 6kt, 9kt and 12kt. In the second step of analysis, residual ULS analysis is carried out taking into account residual stress and deformation of the struck ship caused by ship-ship collision. Collapse mechanism of the bulk carrier in damaged condition due to sagging moment as well as combination of longitudinal and horizontal bending moment is investigated and discussed in detail. ULS of hull girder of the bulk carrier in intact condition is also estimated and compared with that in damaged condition. The effect of damaged condition on the reduction of ULS is discussed in detail. Finally some of numerical methodologies are summarized in assessing residual ULS of hull girder after collision. Copyright © 2014 by ASME.
Sato Y.,Paul Scherrer Institute |
Hino T.,Yokohama National University |
Ohashi K.,Japan National Maritime Research Institute
Computers and Fluids | Year: 2013
A multi-color ordering method has been developed for the Gauss-Seidel (GS) method in the framework of the unstructured-grid based Navier-Stokes equations solver using OpenMP. The multi-color ordering method is required to avoid the data race condition in do-loop parallelization and to achieve the uniqueness of a solution of GS. A coloring algorithm of painting neighbor cells with different colors is proposed for the multi-color ordering method. The method is tested for four sample simulation cases: one case of two-dimensional simulation and three cases of three-dimensional simulation. Through the sample simulations, the uniqueness of the solution of the Multi-Color ordering Gauss Seidel (MCGS) method is verified, and the convergence ratio of MCGS is found to be in the similar level to that of GS and better than the Jacobi method. The parallel efficiency is examined for workstations with two hexa-core CPUs or two octa-core CPUs. Although the parallel efficiency is dependent on computer systems and simulation cases, the speed up ratio of MCGS reaches 14 using two octa-core CPUs in the maximum case using 14 million cells. © 2013 Elsevier Ltd.
Sekiguchi H.,Japan National Maritime Research Institute |
Funaki T.,Osaka University
IEEE Transactions on Electromagnetic Compatibility | Year: 2014
This paper proposes a measurement method with a high reliability and reproducibility for the transfer impedance of current probe. The measurement method uses a vector network analyzer and a calibration fixture. The advantages of the proposed measurement method are the high reliability and reproducibility of measured results among different measurement systems, and the reduction of measurement error of the used measurement system. From the experimental measurements, it is shown that the proposed measurement method is more effective than the conventional methods. © 2014 IEEE.
Matsuo K.,Japan National Maritime Research Institute
Nihon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C | Year: 2010
This paper discribes a new system for a curved shell plate forming which is usually regarded as a special skilled work in a shipyard. The system has a characteristic to support a workman be engaged in a shell plate forming by indicating the logical way where to perform a press or a gas heating. The system adopts a new method for developing a curved shell plate to its appropriate flat plate by using geometric curvature lines found on the curved shell plate. This method has been translated as a software system, and has been introduced in a production lines by a one of the major Japanese shipyard. The system shows a good performance for an improvement of time consuming and an accuracy of a curved shell plate forming, according to the results of data calculated in the factory. Also, this paper introduces an example of application of the system to other works for a ship construction.
Kaneko F.,Japan National Maritime Research Institute
Collision and Grounding of Ships and Offshore Structures - Proceedings of the 6th International Conference on Collision and Grounding of Ships and Offshore Structures, ICCGS 2013 | Year: 2013
Methods for estimation of frequency of collision candidates have been developed by several researchers, such as Fujii, Pedersen and Kaneko etc. Those methods are thought to be able to deal with wide ranging situations of collision candidates. However the case of small crossing angle has not been dealt with to a satisfactory extent. This paper introduces a method to estimate the number of collision candidates in a crossing between twowater ways which cross with a small angle. Prior to this a holistic formulation for considering collision candidates is made and the existing method is reformulated. The method was examined by comparing its results with the results of traffic simulations. This examination suggests the rationality of the model. © 2013 Taylor & Francis Group.
Matsuo K.,Japan National Maritime Research Institute
RINA, Royal Institution of Naval Architects - International Conference on Computer Applications in Shipbuilding 2015, ICCAS 2015 - Papers | Year: 2015
The paper introduces ow recent research activities on a development of the AR application for a pipe installation work in a shop floor in shipyards. The application assists a worker by indicating various infomiation on pipe installation through AR technologies. Once the worker points a camera with a tablet PC to a marker which is attached on a pipe, the AR system guides the worker which the pipe corresponds to one in the drawing paper, or where the pipe should be installed in the ship by visualiztng its 3D image through AR technologies. As the worker retrieves information on the pipe from the ship floor in real-time, the application also realizes real-titne work monitoring and management of outfitting works in shipyards. n The paper explains general background of the research, especially summarizes benefits and important approaches on the introduction of AR technologies to shipbuilding. Then, a concrete system development on the AR system mentioned above is particularly explained with indicating the concept image of the system. Some demonstration of the system is also be shown in the paper, and the paper finally concludes with a brief review of future perspective on our AR applications development for shipbuilding. © 2015: The Royal Institute of Naval Architects.