Numerical study of the dynamic response of Inflatable Offshore Fender Barrier Structures using the Coupled Eulerian–Lagrangian discretization technique

Inflatable Offshore Fender Barrier Structures (IOFBS) are anti-terrorist security structures that function primarily to either stop terror bound vessels from reaching valuable offshore structures, incapacitate its crew or delay the vessel׳s progress until secondary security measures can be put in place. In this study, an advanced and efficient modelling method for impact simulation of the structure and similar multi-physics systems is presented. Numerical implementation of this modelling technique, using Abaqus finite element code is described and used in the impact simulation of the inflatable structure based on its current design as well as an alternative design of the structure. Results from the two designs provisions were compared and from these results, recommendation for improvement of the current design is also reported. This is desirable in ensuring high reliability in application of the structure in meeting its design objectives

Numerical Modeling of Oil/Gas Flow in Pipes in Deep Sea

The poster is on numerical model, and an introductory work on using the Fluid-Structure Interaction Model Of Abaqus To Analyse The Flow Of Oil/Gas In The Pipes In Deep Se

Novel Composite Riser Development for Offshore Deep Water Applications

Due to the increasing energy demand, there is need for a more sustainable conduit for producing and transporting fluids in the oil and gas industry. This is also in response to the increase in exploration activities in offshore deep water, from shallow waters to deep waters. Thus, more length of marine risers and subsea pipelines are required, which increases the weight of the offshore structure. The properties of composites will be harnessed to help reduce the weight of the marine risers. This necessitated the need for the development of composite risers, the studies of the mechanics and hydrodynamics of composite risers. The study shows that composite risers can be applied on offshore structures however, it works most successfully when used as a hybrid composite riser system, and when used as a top tension composite riser system

Active Vibration Control of a Doubly Curved Composite Shell Stiffened by Beams Bonded with Discrete Macro Fibre Composite Sensor/Actuator Pairs

Doubly curved stiffened shells are essential parts of many large-scale engineering structures, such as aerospace, automotive and marine structures. Optimization of active vibration reduction has not been properly investigated for this important group of structures. This study develops a placement methodology for such structures under motion base and external force excitations to optimize the locations of discrete piezoelectric sensor/actuator pairs and feedback gain using genetic algorithms for active vibration control. In this study, fitness and objective functions are proposed based on the maximization of sensor output voltage to optimize the locations of discrete sensors collected with actuators to attenuate several vibrations modes. The optimal control feedback gain is determined then based on the minimization of the linear quadratic index. A doubly curved composite shell stiffened by beams and bonded with discrete piezoelectric sensor/actuator pairs is modeled in this paper by first-order shear deformation theory using finite element method and Hamilton’s principle. The proposed methodology is implemented first to investigate a cantilever composite shell to optimize four sensor/actuator pairs to attenuate the first six modes of vibration. The placement methodology is applied next to study a complex stiffened composite shell to optimize four sensor/actuator pairs to test the methodology effectiveness. The results of optimal sensor/actuator distribution are validated by convergence study in genetic algorithm program, ANSYS package and vibration reduction using optimal linear quadratic control scheme

A unified formulation for circle and polygon concrete-filled steel tube columns under axial compression

Current design practice of concrete-filled steel tube (CFST) columns uses different formulas for different section profiles to predict the axial load bearing capacity. It has always been a challenge and practically important issue for researchers and design engineers who want to find a unified formula that can be used in the design of the columns with various sections, including solid, hollow, circular and polygonal sections. This has been driven by modern design requirements for continuous optimization of structures in terms of not only the use of materials, but also the topology of structural components. This paper extends the authors’ previous work [1] on a unified formulation of the axial load bearing capacity for circular hollow and solid CFST columns to, now, including hollow and solid CFST columns with regular polygonal sections. This is done by taking a circular section as a special case of a polygonal one. Finally, a unified formula is proposed for calculating the axial load bearing capacity of solid and hollow CFST columns with either circular or polygonal sections. In addition, laboratory tests on hollow circular and square CFST long columns are reported. These results are useful addition to the very limited open literature on testing these columns, and are also as a part of the validation process of the proposed analytical formulas

New methodology for optimal placement of piezoelectric sensor/actuator pairs for active vibration control of flexible structures

This paper describes a computationally efficient method to determine optimal locations of sensor/actuator (s/a) pairs for active vibration reduction of a flexible structure. Previous studies have tackled this problem using heuristic optimization techniques achieved with numerous combinations of s/a locations and converging on a suboptimal or optimal solution after multithousands of generations. This is computationally expensive and directly proportional to the number of sensors, actuators, possible locations on structures, and the number of modes required to be suppressed (control variables). The current work takes a simplified approach of modeling a structure with sensors at all locations, subjecting it to external excitation force or structure base excitation in various modes of interest and noting the locations of n sensors giving the largest average percentage sensor effectiveness. The percentage sensor effectiveness is measured by dividing all sensor output voltage over the maximum for each mode using time and frequency domain analysis. The methodology was implemented for dynamically symmetric and asymmetric structures under external force and structure base excitations to find the optimal distribution based on time and frequency responses analysis. It was found that the optimized sensor locations agreed well with the published results for a cantilever plate, while with very much reduced computational effort and higher effectiveness. Furthermore, it was found that collocated s/a pairs placed in these locations offered very effective active vibration reduction for the structure considered

Electro-mechanical dynamics of spiral waves in a discrete 2D model of human atrial tissue

We investigate the effect of mechano-electrical feedback and atrial fibrillation induced electrical remodelling (AFER) of cellular ion channel properties on the dynamics of spiral waves in a discrete 2D model of human atrial tissue. The tissue electro-mechanics are modelled using the discrete element method (DEM). Millions of bonded DEM particles form a network of coupled atrial cells representing 2D cardiac tissue, allowing simulations of the dynamic behaviour of electrical excitation waves and mechanical contraction in the tissue. In the tissue model, each cell is modelled by nine particles, accounting for the features of individual cellular geometry; and discrete inter-cellular spatial arrangement of cells is also considered. The electro-mechanical model of a human atrial single-cell was constructed by strongly coupling the electrophysiological model of Colman et al. to the mechanicalmyofilament model of Rice et al., with parameters modified based on experimental data. A stretch-activated channel was incorporated into the model to simulate the mechano-electrical feedback. In order to investigate the effect of mechano-electrical feedback on the dynamics of spiral waves, simulations of spiral waves were conducted in both the electromechanical model and the electrical-only model in normal and AFER conditions, to allow direct comparison of the results between the models. Dynamics of spiral waves were characterized by tracing their tip trajectories, stability, excitation frequencies and meandering range of tip trajectories. It was shown that the developed DEM method provides a stable and efficient model of human atrial tissue with considerations of the intrinsically discrete and anisotropic properties of the atrial tissue, which are challenges to handle in traditional continuum mechanics models. This study provides mechanistic insights into the complex behaviours of spiral waves and the genesis of atrial fibrillation by showing an important role of the mechano-electrical feedback in facilitating and promoting atrial fibrillation

Initiation and Propagation of Transverse Cracking in Composite Laminates

The matrix cracking transverse to loading direction is usually the one of most common observations of damages in composite laminates. The initiation and propagation of transverse cracks have been a longstanding issue in the last few decades. In this paper, a three-dimensional stress analysis method based on the state space approach is used to compute the stresses, including the inter-laminar stresses near transverse cracks in laminated composites. The stress field is then used to estimate the energy release rate, from which the initiation and propagation of transverse cracking are predicted. The proposed method is illustrated by numerical solutions and is validated by available experimental results. To the best knowledge of the authors, the predictions of crack behaviour for non-symmetrical laminates and laminates subject to in-plane shearing are presented for the first time in the literature

Modeling and Characterization of Novel Deepwater Marine Risers

Offshore explorations has moved from shallow waters to deep waters. This requires longer risers, resulting in significant weight increase. To improve riser technology, composite materials can be used. They offer advantages that can be harnessed. These include high corrosion resistance, fatigue resistance, high strength characteristics and weight savings since they are lightweight with low bending stiffness. Currently, there are approximately 3,400 deep water wells in the Gulf of Mexico (GoM) having depths greater than 150 meters, and a worldwide undiscovered deep water reserves estimated to exceed 200 billion barrels and 25% of the total US reserves (BOEM, 2016), while others are in regions such as Angola, Brazil, Canada, Egypt, India, Morocco and the UK. The application of composite risers in offshore engineering for ultra-deep applications has been facing a lot of challenges, such as in West Africa and Gulf of Mexico. Presently, the steel catenary risers are used for deep water applications requiring large diameter pipes, and both the flexible and top-tensioned risers are used for shallow water applications. Current trend in the industry is the application of composite riser technology used mostly for deep waters, which have over 1000m depth. The first time composite risers were successfully deployed offshore was on Heidrun Platform in 1995 as a composite joint. This started the success in the historical trend of composite riser development. This research involves hydrodynamic loading using ANSYS AQWA. The main research focus on the characterization and the behaviour as regards the fatigue of composite risers. ANSYS APDL & ANSYS ACP are used to model the composite materials, create the composite layers for the materials like AS4/PEEK. This was done considering the mechanical properties of the composite material. Some coupling analysis on a floating platform using the risers and mooring is also being investigated

Modelling and Characterization of Novel Deepwater Composite Risers

Currently, there are approximately 3,400 deepwater wells in the Gulf of Mexico (GoM) having depths greater than 150 meters, and a worldwide undiscovered deepwater reserves estimated to exceed 200 billion barrels and 25% of the total US reserves (BOEM, 2016), while others are in regions such as Angola, Brazil, Canada, Egypt, India, Morocco and the UK. The application of composite risers in offshore engineering for ultra-deep applications has been facing a lot of challenges, such as in West Africa and Gulf of Mexico. Presently, the steel catenary risers are used for deepwater applications requiring large diameter pipes, while the flexible while top-tensioned risers are used for shallow water applications, but composite riser technology used mostly for deepwaters, as this is an exciting frontier in the offshore industry as it provides a potential solution for future riser design challenges. This research involves hydrodynamic loading using ANSYS AQUA and modelling composite riser using Orcaflex to investigate the Riser Installation behaviour. The behaviour of composite risers is compared against the behaviour of top-tensioned steel risers with the main research focus on the motion characterization and the behaviour as regards the fatigue of composite materials, considering that composite materials are light-weight, combustible but not corrosive. ANSYS APDL is used to model the composite materials and AS4/PEEK was first used considering the mechanical properties make it a good composite material for composite material. Some comparison is made with some research done on composite materials, and further studies is done on the fatigue analysis of the composite risers which is ongoing and specific attention is given on the applicability, and to present the design the local and global analysis, in other to reduce installation and maintenance costs. Recommendations from this will enable other industry specifications like ABS, DNV, API, EN and ISO on composite risers as currently they are limited codes and specifications on composite risers