Nikolaos Athanasopoulos, Evangelos Gavalas and Spyros Papaefthymiou
The purpose of this paper is to present a finite element method (FEM) model that predicts the collapse pressure of the majority of the gas/petroleum pipelines worldwide. More…
Abstract
Purpose
The purpose of this paper is to present a finite element method (FEM) model that predicts the collapse pressure of the majority of the gas/petroleum pipelines worldwide. More specifically, it refers to pipelines with diameter to wall thickness (D/t) ratios between 15 and 45. The model’s results were evaluated on the basis of the DNV-OS-F101 offshore pipeline design code.
Design/methodology/approach
A series of FEM simulations were conducted using a 2D model created in the ANSYS’ software environment considering both the plane strain and the plane stress approach. The corresponding values of the collapse pressure for pipes with different value sets of D/t and ovality were calculated in Python (programming language) according to the DNV equations. Given that the pipeline’s resistance to collapse is governed by geometric imperfections and material properties, amongst others, the influence of other crucial factors, such as ovality, eccentricity, hardening modulus and the chemical composition (pipe’s steel grade) was examined.
Findings
The FE model approaches very closely the DNV calculations. Although the effect of the hardening modulus and pipe’s steel grade, respectively, was found to be insignificant on the pipeline’s collapse, it turned out that the lower the D/t ratio was the bigger the influence of these factors appeared. The D/t ratio does not affect the pipe’s sensitivity in eccentricity, because for a pipe with the same characteristics and eccentricity, but with higher ovality, the decrease in collapse pressure was found to be lower.
Originality/value
A 2D FEM which estimates collapse pressure and simultaneously takes into account the effect of various factors is less time-consuming and costly than the full-scale pipe collapse tests in pressure chambers.
Details
Keywords
Athanassios Mihailidis, George Savaidis, Emmanouil Bouras, Emmanouil Athanasopoulos, Nikolaos Ganavaras, Ioannis Topalidis, Dimitrios Karageorgos and Ilias Rampidis
Large-scale belt-conveyor systems are extensively used in open mines to continuously transport bulk material. Conveyor pulleys are critical components and failures have…
Abstract
Purpose
Large-scale belt-conveyor systems are extensively used in open mines to continuously transport bulk material. Conveyor pulleys are critical components and failures have significant financial consequences due to extended downtime. Aiming at increasing their durability, two critical spots are identified: the drum and the welds between end-plates and drum. Alternative designs have been evaluated. The paper aims to discuss these issues.
Design/methodology/approach
Loads on the driving drum are determined from measurements of the bearing force and the motor power. The friction interaction between belt and drum is described by the creep model and its impact is evaluated by comparing the results obtained for low and typical values of friction coefficient. Alternative designs are analysed using finite element method with optimised variable density mesh. The stress field and the deformations are calculated and evaluated.
Findings
Friction affects the torque transmission capacity and force distribution, but it is shown that in this case it has almost no impact on the maximum von Mises stress which occurs on the inside surface of the drum; therefore fatigue cracks initiated there, cannot be visually detected. A reinforcing diaphragm is added at the mid-plane to reduce the stress. A new, improved design is proposed to eliminate welds between the end-plates and the drum.
Research limitations/implications
The new proposed design has to be tested in the field to ultimately validate its higher durability.
Originality/value
The impact of the friction of the belt on the drum is demonstrated. The reinforcement resulting from a mid-plane diaphragm is quantitatively evaluated and assessed. A new improved pulley design is proposed aiming at significantly increased operational life compared to the one of the current design.
Details
Keywords
Nikolaos Argyropoulos, Konstantinos Angelopoulos, Haralambos Mouratidis and Andrew Fish
The selection of security configurations for complex information systems is a cumbersome process. Decision-making regarding the choice of security countermeasures has to take into…
Abstract
Purpose
The selection of security configurations for complex information systems is a cumbersome process. Decision-making regarding the choice of security countermeasures has to take into consideration a multitude of, often conflicting, functional and non-functional system goals. Therefore, a structured method to support crucial security decisions during a system’s design that can take account of risk whilst providing feedback on the optimal decisions within specific scenarios would be valuable.
Design/methodology/approach
Secure Tropos is a well-established security requirements engineering methodology, but it has no concepts of Risk, whilst Constrained Goal Models are an existing method to support relevant automated reasoning tasks. Hence we bridge these methods, by extending Secure Tropos to incorporate the concept of Risk, so that the elicitation and analysis of security requirements can be complimented by a systematic risk assessment process during a system’s design time and supporting the reasoning regarding the selection of optimal security configurations with respect to multiple system objectives and constraints, via constrained goal models.
Findings
As a means of conceptual evaluation, to give an idea of the applicability of the approach and to check if alterations may be desirable, a case study of its application to an e-government information system is presented. The proposed approach is able to generate security mechanism configurations for multiple optimisation scenarios that are provided, whilst there are limitations in terms of a natural trade-off of information levels of risk assessment that are required to be elicited.
Originality/value
The proposed approach adds additional value via its flexibility in permitting the consideration of different optimisation scenarios by prioritising different system goals and the automated reasoning support.