Investigating the effect of rotational degree of freedom on a circular cylinder at low reynolds number in cross flow

Numerical simulations of Vortex-Induced Vibrations (VIV) of a circular cylinder in cross flow with a rotational degree of freedom about its axis have been carried out by means of a finite-volume method. The study is performed in two dimensions at a Reynolds number of Re D = 100, based on the free stream velocity and the diameter, D, of the cylinder. The effect of the rotational degree of freedom on the cylinder's lift and drag forces are compared with the baseline simulation results of flow around a stationary cylinder. The introduction of a rotational degree of freedom (d.o.f) is observed to cause the lift and drag forces to change. Also, the pattern of vortex shedding behind the cylinder is found to drastically change when the cylinder is allowed to rotate

Numerical derivation of constitutive models for unbonded flexible risers

This is the post-print version of the final paper published in International Journal of Mechanical Sciences. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication.In this paper a new constitutive model for flexible risers is proposed and a procedure for the identification of the related input parameters is developed using a multi-scale approach. The constitutive model is formulated in the framework of an Euler–Bernoulli beam model, with the addition of suitable pressure terms to the generalized stresses to account for the internal and external pressures, and therefore can be efficiently used for large-scale analyses. The developed non-linear relationship between generalized stresses and strains in the beam is based on the analogy between frictional slipping between different layers of a flexible riser and frictional slipping between micro-planes of a continuum medium in non-associative elasto-plasticity. Hence, a linear elastic relationship is used for the initial response in which no-slip occurs; an onset-slip function is introduced to define the ‘no-slip’ domain, i.e. the set of generalized stresses for which no slip occurs; a non-associative rule with linear kinematic hardening is used to model the full-slip phase. The results of several numerical simulations for a riser of small-length, obtained with a very detailed (small-scale) non-linear finite-element model, are used to identify the parameters of the constitutive law, bridging in this way the small scale of the detailed finite-element simulations with the large scale of the beam model. The effectiveness of the proposed method is validated by the satisfactory agreement between the results of various detailed finite-element simulations for a short riser, subject to internal and external uniform pressure and uniform cyclic bending loading, with those given by the proposed constitutive law.Lloyds Register EME

A comparative study of immersed-boundary interpolation methods for a flow around a stationary cylinder at low Reynolds number

The accuracy and computational efficiency of various interpolation methods for the implementation of non grid-confirming boundaries is assessed. The aim of the research is to select an interpolation method that is both efficient and sufficiently accurate to be used in the simulation of vortex induced vibration of the flow around a deformable cylinder. Results are presented of an immersed boundary implementation in which the velocities near nonconfirming boundaries were interpolated in the normal direction to the walls. The flow field is solved on a Cartesian grid using a finite volume method with a staggered variable arrangement. The Strouhal number and Drag coefficient for various cases are reported. The results show a good agreement with the literature. Also, the drag coefficient and Strouhal number results for five different interpolation methods were compared it was shown that for a stationary cylinder at low Reynolds number, the interpolation method could affect the drag coefficient by a maximum 2% and the Strouhal number by maximum of 3%. In addition, the bi-liner interpolation method took about 2% more computational time per vortex shedding cycle in companion to the other methods

Nonlinear multi-scale homogenization with different structural models at different scales

We present an extension of the computational homogenization theory to cases where different structural models are used at different scales and no energy potential can be defined at the small scale. We observe that volumetric averaging, which is not applicable in such cases unless similarities exist in the macro-scale and micro-scale models, is not a necessary prerequisite to carry out computational homogenization. At each material point of the macro-model, we replace the conventional representative volume element with a representative domain element (RDE). To link the large-scale and small-scale problems, we then introduce a linear operator, mapping the smooth part of the small-scale displacement field of each RDE to the large-scale strain field and a trace operator to impose boundary conditions in the RDE. The latter is defined on the basis of engineering judgement, analogously to the conventional theory. A generalized Hill’s condition, rather than being invoked, is derived from duality principles and is used to recover the stress measures at the large scale. For the implementation in a nonlinear finite-element analysis, ‘control nodes’ and constraint equationsare used. The effectiveness of the procedure is demonstrated for three beam-to-truss example problems, for which multi-scale convergence is numerically analysed.Lloyd’s Register EME

A Critical Review of Deep Learning-Based Multi-Sensor Fusion Techniques

In this review, we provide a detailed coverage of multi-sensor fusion techniques that use RGB stereo images and a sparse LiDAR-projected depth map as input data to output a dense depth map prediction. We cover state-of-the-art fusion techniques which, in recent years, have been deep learning-based methods that are end-to-end trainable. We then conduct a comparative evaluation of the state-of-the-art techniques and provide a detailed analysis of their strengths and limitations as well as the applications they are best suited for

Case studies in estimating subsea systems’ readiness level

Copyright © The Author(s) 2020. Systems readiness level (SRL) is a metric defined for assessing progress in the development of systems. The methodologies to estimate SRLs are built on the technology readiness level (TRL), originally developed by NASA to assess the readiness of new technologies for insertion into a system. TRL was later adopted by governmental institutions and many industries, including the American Petroleum Institute (API). The TRL of each component is mathematically combined with another metric, integration readiness level (IRL), to estimate the overall level of readiness of a system. An averaging procedure is then used to estimate the composite level of systems readiness. The present paper builds on the previous paper by Yasseri (2013) and presents case examples to demonstrate the estimation of SRL using two approaches. The objective of the present paper is to show how the TRL, IRL, and SRL are combined mathematically. The performance of the methodology is also demonstrated in a parametric study by pushing the states of readiness to their extremes, namely very low and very high readiness. The present paper compares and contrasts the two major system readiness levels estimation methods: one proposed by Sauser et al. (2006) for defence acquisition based on NASA's TRL scale, and another based on API's TRL scale. The differences and similarities are demonstrated using a case study

The effects of dynamic loading on hysteretic behavior of frictional dampers

During an earthquake excitation, a frictional damper may experience many cycles of dynamic loading. The effects of wear and heat induced by the cyclic loading result in the possible decay of the slippage load which subsequently reduce the energy absorption of the damper. In this paper, the effect of dynamic loading on hysteretic behavior of a special kind of frictional damper, namely, cylindrical frictional damper (CFD), is investigated by experimental means as well as numerical models which also account for coupled thermal-structural interaction. The damper is deemed to be more susceptible to thermal deformations due to the shrink-fit mechanism by which the device is assembled. The numerical models are validated experimentally and may be utilized for simulation of dynamic cyclic loading on frictional dampers. The results demonstrate that the slippage load is reduced gradually when subjected to consecutive cycles. This drift is attributed to thermal deformation. The verified numerical models are used to improve the geometry of the CFD. With the geometrical improvements implemented, the subsequent numerical studies confirmed that almost no degradation of the slippage load occurred. Furthermore, a dimensionless parameter is introduced by the authors which shows the effect of wear on the response of CFDs. © 2014 Hamid Rahmani Samani et al

Development of a constitutive model to simulate unbonded flexible riser pipe elements

The principal objective of this investigation is to develop a constitutive model to simulate the hysteresis behaviour of unbonded flexible risers. A new constitutive model for flexible risers is proposed and a procedure for the identification of the related input parameters is developed using a multi-scale approach. The constitutive model is formulated in the framework of an Euler-Bernoulli beam model, with the addition of suitable pressure terms to the generalised stresses to account for the internal and external pressures, and therefore can be efficiently used for large-scale analyses. The developed non-linear relationship between generalised stresses and strains in the beam is based on the analogy between frictional slipping between different layers of a flexible riser and frictional slipping between micro-planes of a continuum medium in nonassociative elasto-plasticity. Hence, a linear elastic relationship is used for the initial response in which no-slip occurs; an onset-slip function is introduced to define the ‘noslip’ domain, i.e. the set of generalised stresses for which no slip occurs; a nonassociative rule with linear kinematic hardening is used to model the full-slip phase. The results of several numerical simulations for a riser of small-length, obtained with a very detailed (small-scale) non-linear finite-element model, are used to identify the parameters of the constitutive law, bridging in this way the small scale of the detailed finite-element simulations with the large scale of the beam model. The effectiveness of the proposed method is validated by the satisfactory agreement between the results of various detailed finite-element simulations for a short riser, subject to internal and external uniform pressures and cyclic bending and tensile loadings, with those given by the proposed constitutive law. The merit of the present constitutive law lies in the capturing of many important aspects of risers structural response, including the energy dissipation due to frictional slip between layers and the hysteretic response. This privilege allows one to accurately study the cyclic behavior of unbonded flexible risers subject to axial tension, bending moment, internal and external pressures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Grain refinement and nucleation processes in aluminium alloys through liquid shearing

The industrial practice of grain refinement of aluminium alloys involves the addition of inoculant particles to initiate alpha-aluminium grains at small undercoolings. This results in a uniformly fine, equiaxed as-cast microstructure and is commonly achieved using Al-Ti-B additions. The phase responsible for initiation of grains in aluminium melts inoculated with Al-Ti-B was determined during the 1990s; since that time, scientific understanding of grain refinement has advanced rapidly. However, one of the main problems of addition inoculants is impurities which is added to the melt and may affect the desired characteristics of the product. With regards to this problem other methods of refinement and the mechanisms of refining have not been fully understood and prediction of as-cast Microstructures in aluminium alloys has much scope for improvement. In this thesis: 1-Factors in establishing equiaxed microstructure were analysed and the origin of equiaxed grains were explored. Then the nucleation process and the involved mechanisms were investigated in depth and control of nucleation process to achieve a fine and uniform structure was set as target. 2-Refinement of microstructure with introduction of shearing was evaluated and the process of refinement in the mushy zone (semisolid state) as a base line was established. Then introduction of shearing above liquidus as a development was analysed and outstanding refinement was seen with shearing above liquidus which have not been investigated properly elsewhere. 3- The mechanisms of refinement by introducing shearing were investigated and the refining mechanisms below and specifically above liquidus were investigated systematically. As results an appropriate understanding about the mechanisms of nucleation and refinement above liquidus was established. 4- Finally, with simulation the most dominant factor in approaching fine grain size by applying shear was identified and the results of experimental examination was verified by simulation.EThOS - Electronic Theses Online ServiceUK Department of Trade and Industry (DTI)GBUnited Kingdo

Decision-support tools for selection of pipeline corrosion coatings

A suitable coating is one with high performance and durability; low surveillance and maintenance needs; easy application with no health implications and finally is cost effective. It is not difficult to imagine that one type of coating would not be suitable for all situations. Thus, a decision support tool is needed to assist (not replace) the decision maker in choosing the most appropriate coating This paper presents three methods for a pipeline corrosion coating selection process, where judgment of more than one expert can be aggregated to reach consensus. Based on a literature research, sixteen different criteria for the selection of coatings have been identified. Firstly the paper considers a few multi-criteria decision making methods, and then compares three different decision support tools namely: a simple addition of weights, Pugh’s Matrix and Borda’s algorithm, where the judgment of more than one expert can be elicited and combined. Criteria for selection of the coating are then identified, and a panel of experts are asked to rate a number of candidate coatings against these criteria. Their voting is combined using Borda’s algorithm and Pugh’s matrix. An example is presented to demonstrate the application of these methods and what a good compromise might look like; providing the decisionmaker with the ability to weigh options and set priorities