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In this paper, using two different methods, probability of failure is calculated for three offshore platforms in Persian Gulf. In first method, uncertainties are applied as a magnification factor in calculation of failure probability, whereas in the second method these uncertainties are considered directly for uncertainty parameters. The parameters of wave height hazard curve for eight directions of platforms with statistical analysis were obtained. These parameters are necessary for calculation of failure probability. Finally an analytical comparison has been carried out between two mentioned methods. These methods can be used for assessment of existing platforms and capacity analyses of new platforms.

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Incremental Dynamic Analysis (IDA) is a parametric analysis method that has recently emerged in several different forms to estimate more thoroughly structural performance under seismic loads. It involves subjecting a structural model to one (or more) ground motion record(s), each scaled to multiple levels of intensity, thus producing one (or more) curve(s) of response parameterized versus intensity level. Of great interest in Performance-Based Earthquake Engineering (PBEE) is the accurate estimation of the seismic performance of structures, and in particular, the mean annual frequency (MAF) of exceeding a specified structural demand or a certain limit-state capacity. In this study the behavior of a jacket type offshore platform with different characteristics in its two directions, separately and with 3D modeling considering pile-soil-structure interaction is investigated. By obtaining the IDA curves and summarizing the results, the behavior of the jacket is studied. All analyses are performed using OpenSees software. It is observed that the difference of geometry of jacket in two directions due to employing Float Over Deck (FOD) installation method, does not cause similar behavior in both directions and finally in direction with float over installation design requirement is not satisfied.

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Steel offshore platforms are some of those structures which are built to withstand environmental and accidental loads during oil exploitation operation. Particular attention is being paid to earthquake loads in seismic active areas because it directly influences the capacity of the offshore structure installations. The uncertainties available in earthquake loads as well as in strength of structural components and also the need to gain confidence about the performance of the structure, have convinced the engineers to use probabilistic methods for design purposes. To this end, Probabilistic Seismic Demand Analysis (PSDA) is used to compute the mean annual frequency of exceeding a particular structural response parameter. In this paper, the efficiency of advanced scalar ground motion intensity measures (IM), Inelastic Spectral Displacement (Sdi) which, was proposed by Thosong and Cornell (2007) in Stanford University, has been compared for PSDA of Jacket Type Offshore Platforms (JTOP) with conventional scalar intensity measure, Elastic Spectral Acceleration or correspondingly Elastic Spectral Displacement (Sde). An efficient Im is the one which, leads to lower dispersion in response parameter of structure in an arbitrary level of Im. In this paper, the numerical model of a Jacket Type Offshore Platform in accordance with its real behavior was simulated in OpenSees software. The case study platform has been modeled in OpenSees considering buckling and post buckling behavior of bracing members and material low cycle fatigue effects. In order to consider soil-pile-structure interaction effects, the near field soil was modeled using Beam on Nonlinear Winkler Foundation method including Lateral resistance, skin friction resistance and end bearing resistance. In the current research, Incremental Dynamic Analysis (IDA), which is among one of the most recent and capable approaches in evaluating ultimate capacity of structures, has been performed and a brief discussion has been presented about the efficiency of different Edps in indicating various structural response modes of platform. As a consequence, the same Edp as simple building structures – maximum interstory drift angle – has been proposed for case study platform. Furthermore, the multiple Ida curves in terms of two aforementioned Intensity Measures for 40 pulse-like near fault ground motion records have been depicted and the dispersion of Ida curves in dynamic instability range have been computed for these two Ims. Based on lower computed dispersion for inelastic spectral displacement intensity measure, this Im has been chosen as the most efficient intensity measure for case study platform.

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For structural reliability assessment or risk analysis of aging offshore steel structures, it is essential to have a probabilistic model, which contains specific statistical parameters, and predicts long term corrosion loss as a function of time. The aim of this study is to propose such model for offshore jacket platforms in the Persian Gulf. Field measurements for material loss due to uniform corrosion for submerged members in seawater have been collected and statistically analyzed to identify the probability density distribution function for dispersion and variation of corrosion loss value according to the passage of time. To predict the corrosion loss, two probabilistic models with different approaches and time dependent parameters are suggested, based on the statistical analysis results. For a comparative study, the application of aforementioned models on the reliability analysis of a simple plate structure is investigated. Prediction results, obtained from the proposed probabilistic models, are consistent well with filed measurements. 

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This article has reviewed the dynamic equations of naval submarines by considering all parameters affecting them and summarized a complete set of existing equations. Usually, submarine dynamic equations are complicated and difficult due to the multitude of parameters in them, especially in military submarines that have both normal and emergency conditions such as emergency ascent. These parameters include the following, all of which have been compactly reviewed in this article: Weight and buoyancy distribution, load changes and water changes inside the trim and compensation tanks, metacentric height, amount of thrust force and vertical distance between the thrust direction and the center of gravity, the position of the hydroplanes and their moments, the center of pressure and the effects of speed on Submarine dynamic behavior. Also, a speed is defined in the submarine maneuver that the control of the submarine by after hydroplanes is not possible. Due to the importance of this phenomenon, the reverse speed and its formulation are also presented in this article.

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Offshore gas pipelines used in the 12th phase of South Pars Project generally have a small pipe (Piggyback Pipeline) mounted on the main pipe. The task of this small pipe is to transfer MEG (anti-corrosion) materials from Onshore to Platform. Because of their small size, Piggyback Pipelines are exposed to the damages caused by being dragged by the anchors of fishing and/or operational vessels. The main objective of this research is to assess the pressure capacity of small pipelines (prior to becoming torn) and to investigate the ultimate capacity before rupture.
To solve the problem, a three dimensional non-linear dynamic model of the real sample is simulated in ABAQUS software. 27 models are analyzed, where an anchor is hooked to a pipeline and drags it vertically to a specific height and then releases it. Eventually an equation is presented to determine the relation between pipeline remaining capacity and vertical displacement.