International Journal of Coastal, Offshore and Environmental Engineering
Volume:1 Issue: 3, Summer 2016

This article deals with response of cylindrical shell subjected to loading of Under Water Explosion (UNDEX) when water current is introduced to the surrounding environment. Cylindrical shells as one of main basic structural elements in construction of marine and submarine facilities are prone to UNDEX threat. Due to vicissitudes of conducting experiments in this field and also complicated inherent of fluid-solid interaction phenomenon, numerical models can be used as an effective tool for scrutinizing the problem. In this study, a submerged thin walled cylindrical shell and its surrounding water discretized by coupled shell Lagrangian elements and Eulerian cells respectively. Simulations are performed in AUTODYN hydrocode. For better perceiving of phenomenon, studies are done for two various explosive charge stand-off distances. Results show that introduction of flow to water, can tangibly change the symmetrical configuration of flow- less problem. Due to intricate interaction of water flow and explosion bubble, distribution of UNDEX overpressure and impulse is disturbed and this leads to un-symmetric deformation of cylindrical shell. Also amplitudes of deflection are reduced obviously by increasing flow velocity.

There are several global marine forecast systems based on large scale regional data covering Iranian seas which are freely available on their websites. They are also several local marine forecast systems in Iranian waters. This paper performs an inter-comparison among different marine forecasting systems in Iranian seas in order to evaluate the accuracy and difference between them and give a proper ground for further investigation and research in this crucial issue. For this purpose, the results of two forecasting system in several points in the Persian are compared and the reason of differences are investigated.

Free-span in subsea pipelines occur at manmade supports, uneven seabed or pipeline crossing. Free spanning may induce pipeline vibration due to vortex shedding which makes pipeline susceptible to some failures such as fatigue, fracture, etc. Free spanning analysis is an important subject because fatigue is the most effective factor in reducing the pipeline design life. Free spanning analysis includes static analysis and dynamic analysis.
DNV-RP-F105 suggests a methodology of dynamic analysis for long pipeline with multi-mode responses, but the fatigue analysis method for multi-modes is not detailed. In addition, the fatigue analysis of multi-spanning pipeline is not clear. Based on the methodology of DNV-RP-F105 fatigue life relates to natural frequencies of pipeline, the method of determination of effective natural frequencies still is not clear.
In this paper, a fatigue analysis for multi-spanning pipeline in Persian south gas field is performed based on VIV analysis. ABAQUS FE model is developed to obtain the stress distribution and the natural frequency of each vibration mode for spanning pipeline on seabed with three multi-spans, then the fatigue analysis of VIV is carried out for the spanning pipeline based on DNV-RP-F105.

Flow around a circular cylinder near plane wall has been simulated using Open source CFD codes of OpenFOAM in different flow regimes (Re=100, 200, 3900) and different gap ratios (G/D= ∞, 1, 0.5, 0.2). Time-averaged pressure coefficients around a circular cylinder computed and compared with each others in different cases. Other features of flow including drag and lift coefficients, Strouhal number, separation angle and stagnation angle are also computed to describe the state of flow better. It has been shown that pressure distribution around the circular cylinder can be utilized to describe the variations in hydrodynamic force coefficients as well as other features of wake flow such as separation and vortex shedding phenomenon near a plane boundary. Plane wall effects on pressure distribution in different flow regimes investigated and it was found that the inception of vortex shedding suppression can be deduced from pressure distribution pattern, through pressure gradient between free-stream-side and wall-side of cylinder. In addition, a rapid increase in the maximum value of positive pressure coefficient can be concluded.

Nowadays Autonomous Underwater Vehicles (AUVs) are an unavoidable part of marine industries. One of the most important parts of any autonomous vehicle is the control issue to achieve the desired performance. This paper is concerned with speed control of an AUV model respecting the state and control constraints. According to the Newton-Euler method, the 6 DOF kinematic and dynamic models of the AUV are established. A well-defined performance index and constrained finite horizon optimization program in the form of Model Predictive Control (MPC) strategy is proposed to regulate the horizontal speed of AUV to its desired value while the constraints on the states like depth and control signals are considered in finite time horizon optimization program to be satisfied. The main problem for such a situation is the interaction between speed control and depth deviation then quadratic programing technique managed responses to avoid state and control signal constraints. Simulation results show a reliable performance of proposed MPC strategy to control the horizontal speed of AUV while all the constraints on state, control signal and also the variation of the control signal are satisfied.

Today, the rolled products, i.e. sheet, plate and foil is used in marine applications, including platforms, hatch covers, mast, hulls of boats and superstructures on pleasure boats and the bridges and superstructures of passenger ships and merchant ships. In this paper, simulation of asymmetric cold rolling is presented by using explicit analysis procedure. In asymmetric cold rolling, the workpiese if often bent downwards or upwards. A two dimensional explicit dynamic finite element model with adaptive meshing technique has been employed to simulate asymmetrical condition are here due to different roll radii. To validate the simulation, the results of simulation and experiment are compared. Effects of asymmetry due to roll radii ratio and speed ratio mismatch on sheet curvature variations are discussed. Finally, optimum roll speed ratio in various of roll radii ratio could be found to produce flat sheet.