In the IACS Polar Class Rules, primary structures are required to be assessed with direct calculation methods, which in most cases is either linear or non-linear finite element analysis. For linear analysis a clear set of requirements and acceptance criteria are provided in the rules. This approach is currently the most widely used assessment method although non-linear analysis would provide better insight into the behavior of the structure, giving designers tools to reduce weight and/or improve safety. The current rule requirements for non-linear analysis are high-level in nature and not easily applicable to practical design work. In order to implement non-linear analysis practically, a simple-to-use acceptance criteria is be needed. In this paper, a robust and simple-to-use assessment methodology and acceptance criteria is proposed. The proposed method provides means to ensure proper structural hierarchy. Appropriate safety margins are described through the plastic response of the local frame and the primary structural member. Allowable plastic deformation caused by the design ice load is determined by relating the permanent set of the structure to newbuild vessel production tolerances. An example analysis comparing the proposed method to existing linear and non-linear methods is presented. The proposed method ensures that the structure remains serviceable throughout the lifetime of the vessel. 相似文献
The aim of the work is the definition of a procedure for the numerical simulation of the response of ship structures under accidental loading conditions, which suffer various different modes of failure, such as tension, bending, tearing and crushing and in particular to investigate the effect of material modeling, i.e. material curve and rupture criterion as well as mesh size and strain rate effect on the results. To this end, different material models and simulation techniques were used for the simulation of eighteen indentation tests conducted by different research groups. The simulations were performed using the explicit finite element code ABAQUS 6.10-2. The tests refer to the quasi-static and dynamic transverse and in-plane loading of various thin walled structures which represent parts of a ship structure. Three rupture criteria are incorporated into VUMAT subroutine, which interacts with the explicit finite element code and refers to an isotropic hardening material that follows the J2 flow theory assuming plane stress conditions, in order to investigate the prediction and propagation of rupture. The focus is on investigating whether it is possible to define a unified methodology, which is appropriate for the simulation of all different tests. Consistency in the numerical results is observed with the use of an equivalent plastic strain criterion, in which formulation a cutoff value for triaxialities below −1/3 is included. 相似文献
Shipbuilding industries have started to employ 3D CAD systems to integrate all design and production processes by achieving seamless data transfer and data sharing. The emerging 3D CAD system brings a considerable change in FE analysis field. The availability of 3D geometry increased the recognition of the need for developing automatic FE modeling system consequently.
However, general automatic mesh algorithms developed by academic research field have a limitation. The difficulty in satisfying lots of line constraints and the absence of proper idealization of 3D geometry entities defined in CAD system hinders directly employing the general mesh algorithms.
In this research, an automatic FE modeling system has been developed for cargo hold FE modeling and whole ship FE modeling. The basic concept of the algorithm is to decompose surfaces using stiffener lines into subregions and generate mesh using a rule established based on FE modeling practice of ship structure. Since the decomposed subregions take simple polygon, they can be easily transformed into elements by decomposing the polygon according to the rule defined considering the shape of the polygon and mesh seed on its perimeter. The algorithm is also designed to treat appropriate geometry idealizations for bracket-type surface and stiffener connections. The idealization process is also completely customized based on FE modeling practice. The validity of the developed system is verified through illustrative examples. 相似文献