Showing 5 results for Crack
Ali Fathi, Ali Akbar Aghakoochak,
Volume 1, Issue 1 (9-2004)
Abstract
In order to predict the residual life of offshore platforms and establish efficient schedule for underwater inspection and repair, it is necessary to estimate the fatigue crack growth rate in tubular joints properly. Linear Elastic Fracture Mechanics and Stress Intensity Factor are applicable tools for evaluating growth rate of existing fatigue cracks in offshore tubular joints. In the past several approaches based on Paris crack growth law, have been proposed in this regard. Each of these approaches use different methods for estimating the Stress Intensity Modification Factor (Y). In this research the capability of Artificial Neural Networks for evaluating the fatigue crack growth rate in offshore tubular T-joints under axial loading is investigated, when the crack depth is more than 20% of chord wall thickness. For this condition the crack growth process is highly affected by joint geometry and loading mode. Two types of artificial neural network are developed for predicting the Y factor: Radial Basis Function (RBF) and Multi Layer Perceptron (MLP) networks. The required input data consist of the crack shape and the percentage of crack penetration through thickness. Experimental data from NDE center in University College London are used for training and testing the networks. The results of this research are compared with other existing theoretical and empirical solutions.
Mohamadreza Ayatollahi, Karo Sedighiani,
Volume 7, Issue 13 (9-2011)
Abstract
Due to the much higher maintenance and replacement expenses of the offshore wind turbine structures, more attention should be paid for a reliable lifetime analysis of them. Meanwhile, the cyclic nature of wave and wind loads together with the corrosive effects from the sea water are major factors for the creation and growth of flaws and cracks in offshore structures. These cracks can be the cause of instantaneous failure in marine structures. The “Tripod” model is one of the favorite support structures which are used for offshore wind turbines particularly in deeper waters. In this paper, a crack is considered in a support structure that can be typically used in the offshore wind turbine constructions. The finite element code ABAQUS is employed to determine the related stress intensity factors for different types of loads. It is shown that the variations of stress intensity factors with crack length differ significantly for various loading types. Also the mode II stress intensity factor is not negligible compared to the mode I stress intensity factor. Therefore, for analyzing the fatigue life or the fracture load of similar cracked offshore structures, appropriate mixed mode crack growth criteria should be employed together with the curves derived in this research for stress intensity factors.
Amir Moghiseh, Abbas Rahi,
Volume 9, Issue 18 (3-2014)
Abstract
The corrosion fracture life of marine riser is investigated. Riser will be modeled as a long beam and the wave and current forces is estimated by short wave theory and modified Morison’s equation. Dynamic equilibrium equations of riser will be obtained on based of Euler theory. After bending stress calculation along the riser that includes effect of riser weight and platform motion, loading history can be obtained in riser cross section. Since risers exposed to seawater and sour crude oil, an initial crack can have destructive effects and corrosion fracture can be occurred. So effect of initial crack in riser cross sections in different depths and at present of corrosive fluid is studied. At the end the effect of seawater and crude oil on crack propagation and corrosion fracture life is investigated. In order to solve riser dynamic equilibrium equation Range-Kutta and finite difference methods will be used.
Majid Jamal-Omidi, Seyed Mehdi Nabavi, Amir Hossienn Parsania Parsania,
Volume 15, Issue 30 (1-2020)
Abstract
In this paper, the effect of composite patch on
cylindrical pipe with circumferential through-wall crack has been investigated under internal pressure. For this purpose, using three-dimensional finite element and
J-integral,
stress intensity factors is determined before and after the repair. In order to ensure the accuracy of modeling, a pipe with circumferential through-wall crack under uniform tension load is simulated and the results are compared with theoretical data. Then, the cracking cylinder is repaired using four composite patches of Boron/Epoxy, Carbon/Epoxy, Kevlar/Epoxy and Glass/Epoxy in a local manner. The results of study are shown the significant effect of composite patches on reducing the
stress intensity factor of cracked cylinder. It is observed that the use of composite patches with higher stiffness has a more decreasing effect on stress intensity factor. Also, the effect of composite patch, properties and thickness of adhesive on stress intensity factors along crack front is evaluated.
Mohammad Reza Zareei, Mehdi Iranmanesh,
Volume 18, Issue 36 (12-2022)
Abstract
Assessing the ultimate strength of the stiffened plates forming the ship structure is the first step in assessing its ultimate strength. Over time and increase the life of the structure, failures such as cracks reduce the load-bearing capacity of the structure. The main purpose of this paper is to present a machine learning method based on XGBoost algorithm to calculate the ultimate compressive strength of stiffened plates with crack failure using the results of multiple finite element analyzes. To achieve the best possible results from the XGBoost algorithm, some of the hyperparameters in this algorithm have been optimized using the Bayesian optimization method. The results of this method show that the accuracy of using the optimized XGBoost algorithm is much higher than conventional methods based on linear regression.
