Analysis of biaxial proportional low-cycle fatigue crack propagation for hull inclined-crack plate based on accumulative plasticity

Fracture failures of ship plates subjected to in-plane biaxial low-cycle fatigue loading are generally the coupling result of accumulative plasticity and biaxial low-cycle fatigue damage. A biaxial low-cycle fatigue crack growth analysis of hull structure that accounts for the accumulative plasticity effect can be more suitable for the actual evaluation of the overall fracture performance of the hull structure in severe sea conditions. An analytical model of biaxial low-cycle fatigue crack propagation with a control parameter for ∆CTOD is presented for hull inclined-crack plate. A test was conducted for cruciform specimens made of Q235 steel with an inclined crack to validate the presented analysis. The biaxial accumulative plasticity behavior and the effects of biaxiality and stress ratios were investigated. The results of this study reveal a strong dependence of biaxial low-cycle fatigue crack propagation on biaxial accumulated plasticity.

FATIGUE RELIABILITY ASSESSMENT OF WELDED JOINTS OF VERY FAST FERRY ACCOUNTING FOR VEHICLE LOADS

This work deals with the fatigue reliability assessment of a welded joint in a longitudinal stiffener of trapezoidal shape in a very fast ferry. Based on the analysis of wave and cargo induced loads the ship hull structure is evaluated. The local structure is represented by a longitudinal stiffener with a trapezoidal transverse section. The critical hot-spots and the stress distributions are defined by FEM. The fatigue damage assessment of considered hot spots is analysed accounting for the combination of wave induced and car-breaking transient loadings. The formulation for the assessment of the welded steel joint is based on the S-N approach and FORM/SORM techniques are applied to evaluate the reliability against fatigue failure accounting for corrosion deterioration. The structural system composed by several hot spots is evaluated as a series system based on second order reliability bounds.

Impact of high strength steels over large ships fore peak structure

The fore area of the ships in extreme conditions is commonly subjected to external impact pressures such as bottom slamming and bow impact. The phenomenon combined with a poor design can lead to local structural damage (cracks, dents, buckling of plate panels) and malfunction to the installations on-board of the ship. In the present article, a comparison study between different steel material grades is performed for a VLCC fore peak structure subjected to external and internal dynamic pressures under the Harmonized Common Structural Rules for Bulk Carriers and Oil Tankers (H-CSR). Three steel grades generally used in the shipbuilding industry, one normal strength and two higher strength, are subjected for the assessment. The hull structure is built based on the benchmark crude oil carrier KVLCC2 surface developed by KRISO (Korea Research Institute for Ships and Ocean Engineering, and modelled with plate finite elements in FEMAP software. The study targets an optimization process to minimize the steel weight of the structural members by plate elements thickness reduction.

Implementation of methods and algorithms for geometric and structural modeling in the problems of parametric design of a ship's hull structure

В работе рассмотрены методология и алгоритмы геометрического и конструктивного моделирования судовых конструкций специализированного программного обеспечения и автоматизированных систем для проектирования конструкции корпуса судна в соответствии с требованиями Правил Российского морского Регистра судоходства и Гармонизированных общих Правил МАКО. Даны понятия геометрического и конструктивного моделирования. Показано место геометрического и конструктивного моделирования в общей структуре системы автоматизированного проектирования судовых конструкций, рассмотрены основы моделирования конструкций в виде плоского конструктивного сечения и трехмерного перекрытия. Описаны возможности специального программного обеспечения – редакторов геометрической и конструктивной модели. Рассмотрена структура специализированного геометрического ядра автоматизированной системы. Приведены примеры использования предлагаемых методов и алгоритмов в разработанном авторами программном обеспечении автоматизированных систем, обоснованы преимущества предлагаемых методов по сравнению с ранее известными решениями. The paper considers the methodology and algorithms for geometric and structural modeling of ship structures, which are used in specialized software of computer-aided systems for the design of the ship's hull structure in accordance with the requirements of the Russian maritime register of Shipping Rules and the IACS Harmonized Common Structure Rules. The concepts of geometric and constructive modeling are given. The place of geometric and structural modeling in the general structure of the computer-aided design of ship structures is shown, the basics of modeling structures in the form of a flat structural section and three-dimensional grillage are considered. The possibilities of special software - editors of geometric and structural models are described. The structure of a specialized geometric kernel of the computer-aided system is considered. Examples of using the proposed methods and algorithms in the developed by authors software of computer-aided systems are given, the advantages of the proposed methods are substantiated in comparison with previously known solutions.

Hull Roughness and its Effects on Planing Boat Performance

The effects of hull roughness on loss of speed at constant power are investigated. Vessel lifetime roughness profiles are postulated based on construction, coatings and maintenance. These are utilized to determine loss of speed and change in running attitude for planing boats. The formulations are directly applicable to any planing boat for which a lifetime roughness profile is constructed as presented. The approach to developing the speed/power predictions and the roughness profile is provided. This approach can be utilized to analyze the effects of roughness due to hull material utilized and quality of construction, roughness from paints and coatings and their method of application as well as damage to the coating during maintenance, deterioration of the hull structure material, as well as biofouling influenced by the type of antifouling paint or coating and method of application. It provides a means for investigating different magnitudes and scenarios of these causes of roughness rather than providing only example results.

Damage Tolerance Assessment of Multi-Hull Aluminum Vessels Using Global Finite Element Methods

As aluminum high-speed multi-hulls continue to grow in size, capacity and operational sea state, a need is growing to understand the damage tolerance of these structures. This paper presents a Linear Elastic Fracture Mechanics (LEFM) approach to performing damage tolerance assessments of aluminum hull structures using the hydrodynamic analysis and global finite element model developed as part of a class Dynamic Loading Approach (DLA) notation. The LEFM approach is used to calculate the stress intensity factor (K) and the critical crack length throughout the model to screen the entire hull structure and identify fracture critical locations. This paper also investigates the use of elastic-plastic fracture mechanics to predict potential critical crack growth locations, rates, and directions. Fracture critical locations identified and visualized through the analysis provide the ship designer with tools to develop damage tolerant structures. The results of the analysis can also assist owners and regulatory bodies in developing structural inspection and repair plans.