International Journal of Coastal, Offshore and Environmental Engineering
Volume:3 Issue: 1, Winter 2018

​Due to the high investment costs for deep-water subsea production systems of high-value subsea fields, it is crucial to ensure a high availability to recover the investment. The problem is compounded by the cost of recovery, repair and replacement of failed equipment. Testing and reliability analyses are two pillars of reliability assurance; neither of them on their own assures the delivery of a reliable system. Possibly with more imaginative use of reliability methods, it is possible to optimise testing. It is suggested to use reliability analysis as a guide for allocating resources for testing. This paper outlines a Systems Engineering Framework to link the Client’s requirements for equipment reliability, as a means of proving the desired level of performance. This framework allows a better understanding of verification settings and strategies to handle constraints (e.g. costs, expandability, repair-ability, maintainability, intervention procedures, downtime, automation etc.) and performance measures, to achieve highly reliable production systems.  The bilateral links between the Client’s requirements and subsea equipment performance are established using the systems engineering V-model. These links relate equipment performance to one or more of the Client’s requirements, which helps establish verification and validation testing strategies to enhance reliability and reduce project risk. The proposed procedure also assists risk management efforts by feeding the results of reliability analyses, testing and project risk analysis into validation processes, the systems engineering measurement process ensures enhanced reliability. We define reliability assurance as a part of the systems engineering processes to ensure the continued function and resilience of the production system from the downhole valve to the subsea equipment, housed on the topside or at an onshore terminal, in their operating environment and condition using the “Fit-For-Service” notion.

Despite the enormous military threats against the country's military facilities, especially the naval industry, correct understanding of the behavior of these structures in efficacy of explosion, analysis and design of this industry has been much importance than ever before. An important class of these threats, is underwater explosion and its effect on various structures, Floating or submerged. In this paper, the researcher first introduces the underwater explosion phenomena and theories that govern the propagation of fluid hydrodynamics, shock waves from the explosion and its interaction with floating and also submerged structures have been investigated. Finally, numerical studies (FEM) of the behavior of a super submarine subject to underwater explosion have been provided by ABAQUS software and some results have been obtained such as: response with different frequencies, the place of radiation boundary in interaction of water and construction, the effect of added mass and hydrodynamic pressure.

High Strength Concrete (HSC) is a complex type of concrete, that meets the combination of performance and uniformity at the same time. This paper demonstrates the use of artificial neural networks (ANN) to predict the deflection of high strength reinforced concrete deep beams, which are one of the main elements in offshore structures. More than one thousand test data were collected from the experimental investigation of 6 deep beams for the case of study. The data was arranged in a format of 10 input parameters, 2 hidden layers, and 1 output as network architecture to cover the geometrical and material properties of the high strength self-compacting concrete (HSSCC) deep beam. The corresponding output value is the deflection prediction. It is found that the feed forward back-propagation neural network, 15 & 5 neurons in first and second, TRAINBR training function, could predict the load-deflection diagram with minimum error of less than 1% and maximum correlation coefficient close to 1.

Smoothed Particle Hydrodynamic (SPH) is an attractive Lagrangian tool for simulating flows with large displacement at free surface boundary. Two widely used subcategories of this method are Weakly compressible SPH (WCSPH) and truly Incompressible SPH (ISPH) methods. Each method has its individual advantages while there is not yet a global agreement about the preference of one method to another one. In this study, accuracy, stability and efficiency of these methods are compared in simulating dam break flow as a well-known hydraulic problem. To decrease unrealistic particle fluctuation especially at free surface boundary, a practical solution is applied to both methods while keeping their total accuracy. In addition, different solid boundary treatments are studied and their effect on total accuracy and stability of SPH methods are investigated. Based on the results, both ISPH and WCSPH methods can model free surface profiles properly if a proper solid boundary treatment is utilized. Meanwhile, local surface fluctuations can be damped in both methods efficiently by means of the modified surface viscosity. By means of original versions, it is concluded that ISPH method is generally more stable and more accurate particularly in modeling pressure field than WCSPH method. In addition, it is shown that ISPH method is faster than WCSPH method in solving a dam break flow with equal number of particles. On the other hand, ISPH in its original version using the divergence-free velocity scheme suffers from density loss problem. Since a lot of modifications have been introduced till now to overcome defections of both methods, it is not fair to compare methods with different modifications and therefore, similar modifications are applied in this study. Meanwhile, it can be concluded that each method is growing and is going its own way through enhancement.

The dynamic behavior of a very large rectangular floating structure is considered. The structure is modelled as a plate with free edges. Two different thicknesses are considered for the model. The Mindlin plate theory is used to formulate the structure behavior. Natural frequencies, mode shapes, and stress resultants of the structure are predicted by using finite element method. For this purpose, a MATLAB code is written. The same analysis is performed by using the ANSYS software. The results of these two analysis are compared with each other and with the available results in the literature, where close agreement is observed. Therefore, the written finite element code is found to be acceptable for prediction of the dynamic behavior of very large rectangular floating structures in early stages of design.

A three-dimensional primitive equation model has been developed to study wind-driven currents in the Caspian Sea (CS). The equations were solved in the spherical coordinate system with a vertical array of pressure-sigma using a finite difference Method on a staggered modified Arakawa c grid. Simulations showed that there is an anticyclonic eddy over the deep water of South Caspian Basin (SCB), which extended from surface to subsurface and persist throughout the year. The model successfully produced the coastal current along the eastern coast of the Middle Caspian Basin (MCB) with a prevailing southward component, resulting in upwelling on these coasts to compensate the surface drift. The results indicate that the bottom topography has a key role in steering currents and generated a divergence in the surface Ekman layer which balanced by convergence in the frictional bottom Ekman layer in deepest areas of the CS.