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 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

Coupling XFEM and Peridynamics for Brittle Fracture Simulation - Part II: Adaptive Relocation Strategy

An adaptive relocation strategy for a coupled XFEM–Peridynamic (PD) model is introduced. The motivation is to enhance the efficiency of the coupled model and demonstrate its applicability to complex brittle fracture problems. The XFEM and PD approximation domains can be redefined during the simulation, to ensure that the computationally expensive PD model is applied only where needed. To this end a two-step expansion/contraction process, allowing the PD patch to adaptively change its shape, size and location, following the propagation of the crack, is employed. No a priori knowledge of the crack path or re-meshing is required, and the methodology can automatically switch between PD and XFEM. Three 2D fracture examples are presented to highlight the performance of the methodology and the ability to follow multiple crack tips. Results indicate significant computational savings. Furthermore, the characteristic length scale of PD theory bestows a nonlocal and multiscale component to the methodology

On the computational derivation of bond-based peridynamic stress tensor

The concept of ‘contact stress’, as introduced by Cauchy, is a special case of a nonlocal stress tensor. In this work, the nonlocal stress tensor is derived through implementation of the bond-based formulation of peridynamics that uses an idealised model of interaction between points as bonds. The method is sufficiently general and can be implemented to study stress states in problems containing stress concentration, singularity, or discontinuities. Two case studies are presented, to study stress concentration around a circular hole in a square plate and conventionally singular stress fields in the vicinity of a sharp crack tip. The peridynamic stress tensor is compared with finite element approximations and available analytical solutions. It is shown that peridynamics is capable of capturing both shear and direct stresses and the results obtained correlate well with those obtained using analytical solutions and finite element approximations. A built-in MATLAB code is developed and used to construct a 2D peridynamic grid and subsequently approximate the solution of the peridynamic equation of motion. The stress tensor is then obtained using the tensorial product of bond force projections for bonds that geometrically pass through the point. To evaluate the accuracy of the predicted stresses near a crack tip, the J-integral value is computed using both a direct contour approximation and the equivalent domain integral method. In the formulation of the contour approximation, bond forces are used directly while the proposed peridynamic stress tensor is used for the domain method. The J-integral values computed are compared with those obtained by the commercial finite element package Abaqus 2018. The comparison provides an indication on the accurate prediction of the state of stress near the crack tip

Energy recovery from domestic radiators using a compact composite metal Foam/PCM latent heat storage

© 2020 Elsevier Ltd With the increasing demand for energy consumption in domestic buildings and consequent CO2 emission, there is a need to provide proper products to reduce energy loss. Domestic radiators for space heating can be improved by using a Compact Latent Heat Storage (CLHS) unit mounted on the wall side surface in order to offer energy saving and peak-shaving. The unit offers the potential to save otherwise wasted energy from the back surface of the radiator to the walls in the charging mode of the energy storage system. When the heating system is turned off, the CLHS unit discharges the stored heat towards the room to provide a uniform temperature on the surface of the radiator. An aluminium foam embedded inside the bulk Phase Change Material (PCM) can modify the heat storage/retrieval rate. A PCM is selected depending on the radiator's surface temperature, which is almost equal to the hot water temperature delivered to the radiator. Different metal foam porosities are examined and compared with the PCM-only alternative (i.e. without metal foam enhancement). The results show the porous-PCM CLHS alternative provides an almost constant temperature during the discharging process equal to 54 °C. However, for the PCM-only alternative, the temperature of the surface reduces continuously. Using the porous medium results in a shorter melting time, about 95% of what is needed for the PCM-only alternative. Increasing the metal foam porosity results in shorter charging/discharging time; however, since the surface temperature of the porous-PCM unit is almost constant for different metal foam porosities, a system with higher porosity (97%) is desirable

Modulation-Mode Assignment in SVD-Aided Downlink Multiuser MIMO-OFDM Systems

Multicarrier transmission such as OFDM (orthogonal frequency division multiplexing) is an established technique for radio transmission systems and it can be considered as a promising approach for next generation wireless systems. However, in order to comply with the demand on increasing available data rates in particular in wireless technologies, systems with multiple transmit and receive antennas, also called MIMO (multiple-input multiple-output) systems, have become indispensable for future generations of wireless systems. Due to the strongly increasing demand in high-data rate transmission systems, frequency non-selective MIMO links have reached a state of maturity and frequency selective MIMO links are in the focus of interest. In this field, the combination of MIMO transmission and OFDM can be considered as an essential part of fulfilling the requirements of future generations of wireless systems. However, single-user scenarios have reached a state of maturity. By contrast multiple users' scenarios require substantial further research, where in comparison to ZF (zero-forcing) multiuser transmission techniques, the individual user's channel characteristics are taken into consideration in this contribution. The performed joint optimization of the number of activated MIMO layers and the number of transmitted bits per subcarrier shows that not necessarily all user-specific MIMO layers per subcarrier have to be activated in order to minimize the overall BER under the constraint of a given fixed data throughput

Fatigue crack shielding in plain bearings under large scale yielding

Multi-layered bearing systems used in the automotive industry show shielding and antishielding effects that reduce or amplify the crack driving force under large-scale yielding conditions. Using finite element analysis, it is shown that shielding in such systems results in path deflection and bifurcation despite the absence of mixed-mode loading. As the crack approaches a stiff layer, the tangential strains measured around a blunted crack tip model show a maximum corresponding to the direction of crack propagation. The distribution of such strains indicates the effect of shielding and the likelihood of the tip to deflect or bifurcate.The suitability of bi-layer and tri-layer bearing architectures is assessed through crack path and respective crack driving force prediction

OMAE2008-58014 NONLINEAR DYNAMIC ANALYSIS OF FLEXIBLE RISER STRUCTURES

ABSTRACT An updated Lagrangian finite element formulation of a three-dimensional pipe elbow element is presented for large displacement and large rotation dynamic analysis. In this formulation a particular linearization method is used to avoid inaccuracies normally associated with the linearization schemes. The formulation has been implemented in a nonlinear finite element code and the results are verified. It is shown that the proposed formulation generates improved results over those previously reported in the literature