Journal of the Society of Naval Architects of Japan 

About: Journal of the Society of Naval Architects of Japan is an academic journal published by The Japan Society of Naval Architects and Ocean Engineers. The journal publishes majorly in the area(s): Hull & Finite element method. It has an ISSN identifier of 0514-8499. Over the lifetime, 2720 publications have been published receiving 8996 citations.

A New Measuring Method of Residual Stresses with the Aid of Finite Element Method and Reliability of Estimated Values

Abstract: In estimation of residual stresses, the existing methods are mainly based on the idea that variation of strains on the surface of the object is measured by sectioning continuously until there is no variation of the measured strains, which corresponds to the residual stresses. In this kind of method, some definite mathematical relation between the variation of stresses and the released surface force is required. This kind of relation was obtained for the cases where the geometry, boundary condition, and pattern of residual stress distribution are simple. This difficulty is solved when numerical analytical methods, such as the finite element method, etc. are applied.In this paper, a general theory is developed based on the finite element method. With this method, three dimensional residual stresses can be measured. Furthermore, reliability of estimated values, of residual stresses by this method is mathematically studied when error is contained in the measured strains.

On the Coupled Motion of Steering and Rolling of a High Speed Container Ship

Abstract: Digital simulation of maneuvering motions and numerical calculation of directional stability indices are carried out on the basis of captive model test of a typical container ship. An emphasis is laid upon yaw-sway-roll-rudder coupled motion. The smaller metacenteric height proved to introduce the better turning performance and the poorer course-keeping characteristics.The yaw-sway-roll-rudder coupling can be a cause of anomalous rolling which is frequently observed at automatically steered, high speed operations in seaways. We introduce a perturbation stability analysis on the problem. It reveals the possibility of an unstable yaw-roll behavior due to roll-induced yaw moment, small GM and inadequate control parameters of autopilot steering system.

On the manoeuvring performance of a ship with the parameter of loading condition

Abstract: When predicting ship manoeuvring performance at the initial design stage, it is considered that the loading condition is one of the important parameters for manoeuvring characteristics. To accurately predict ship manoeuvrability, hydrodynamic forces acting on a ship in any loading condition must be estimated. In this paper, approximate formulae for estimating the hydrodynamic forces acting on ships in any loading conditions such as half loaded, ballast and trim by stern conditions are proposed. These approximate formulae were derived from the results of a model test. Thirteen models were used to obtain the hydrodynamic forces consisting of general cargo, car carrier and RORO ships. The model test was carried out on 13 ships for fully loaded condition, on 11 ships for ballast condition and 5 ships for half loaded condition. The predicted results agreed well with the model test results. Therefore, this method will be useful for practical prediction of manoeuvrability for conventional ships at the initial design stage. However since the approximate formulae were investigated on ship models there still remain some problems to be solved such as a correlation, scale effect and so on, to predict the manoeuvring performance of a full scale ship.

New element models in discrete structural analysis

Abstract: A family of new element models in discrete structural analysis is proposed in this paperThese models consist of finite number of small rigid bodies connected with springs distributed over the contact area of two neighbouring bodies In general size of stiffness matrices of these elements are at most (6 × 6) which are equal to or even smaller than 1/2 of those of conventional finite elements so that considerable reduction of computing time can be expectedEffectiveness of these elements in nonlinear structural analysis will be demonstrated by several numerical examples

A Nonlinear Simulation Method of 3-D Body Motions in Waves (1st Report)

Abstract: A full nonlinear method to simulate three dimensional body motions in waves is presented. This is a time domain method to simulate Euler's equation of ideal fluid motion coupled with the equation of solid body motions. Introducing Prandtl's nonlinear acceleration potential, whose gradient gives acceleration of the fluid, Euler's differential equation of the ideal fluid motion is converted to the integral equation of the acceleration potential. The boundary condition of the acceleration potential on the body surface is systematically derived from the kinematic relation between the acceleration of the solid body and the acceleration of the fluid on the body surface. Since this kinematic boundary condition is a function of the body acceleration, the boundary values on the floating body can not be evaluated explicitly. To overcome this point, the unknown acceleration of the free floating body is eliminated by substituting the equation of body motion into kinematic condition, then implicit body surface boundary condition is derived. This is the kinematic and dynamic condition which guarantees dynamic equilibrium of forces between ideal fluid and the solid body at any instance. With the free-surface boundary condition of the acceleration potential, the formulation of the boundary value problem for the acceleration field is completed. Although this formulation of the acceleration field is mathematically correct, this is not appropriate to numerical computation, because Prandtl's nonlinear acceleration potential does not satisfy Laplace's equation. Therefore, the nonlinear part is shifted from the governing equation to the boundary condition, then the alternative formulation for the numerical computation is derived. The computational flow of the nonlinear simulation method based on this alternative formulation is also given. In order to show the accuracy of this new method, two dimensional numerical results are presented. They show that the conservation of mass, momentum and energy are satisfied excellently.