فهرست مطالب

Maritime Technology - Volume:7 Issue:12, 2019
  • Volume:7 Issue:12, 2019
  • تاریخ انتشار: 1398/04/10
  • تعداد عناوین: 6
|
  • Vahid Tamimi*, Mohammad Said Seif, Selda Shahvaghar Asl, Seyed Taghi Omid Naeeni, Mostafa Zeinoddini Pages 1-8

    The horizontal kinetic energy of the fluid flow, from on-land wind to ocean tidal stream, is one of the most promising sources of the energy. In the field of renewable energies, power extraction from Flow Induced Vibration (FIV) of bluff bodies is a fast growing research area which has seen a great advancement over the last decade. In this study, the FIV energy harvesting potential of a sharp edge square cylinder in two different flow incidences is investigated. The square cylinder, depending on its orientation with respect to the incident flow, demonstrates VIV or galloping types of responses. The results indicate that the square cylinder with a flat side perpendicular to the flow has a galloping type of response. In contrast, the same cylinder with a sharp vertex pointing the flow (diamond configuration) shows a VIV type of response. The hydroelastic efficiency of the resonating square cylinder is significantly higher than that with the galloping type of response. This shows the great advantages of diamond VIV excavators over square galloping harvesters.

    Keywords: FIV energy harvesting, Hydroelastic efficiency, VIV, Galloping, Square, diamond cylinders
  • Meysam Rezaee, Aliasghar Golshani*, Hosein Mousavizadegan Pages 9-23

    In recent years, determining the rate of shoreline change by its historical trend has been reported frequently. This study has focused on shorelines at the adjacency of Javad Al-Aemmeh port which has undergone successive constructions in its region. The decadal trend of studied shoreline change was determined by the historical trend method. A numerical method was also employed to reduce the probable deficiencies concerned to these constructions. Accordingly, for the first time, a framework was developed to compare the results of historical trend and numerical methods with a field-measured value both spatially and quantitatively and based on this comparison, the most suitable rate of change was assigned to each coastal landform. Finally, it was revealed that among the computed rates, the Linear Regression Rate (LRR) from historical trend method has given the best estimation for the shoreline change rate, but in those parts which the shoreline was directly under influence of human interventions the change rate derived from the numerical method has been more accurate. Besides, results showed that at those parts which the Net Shoreline Movement (NSM) and the Shoreline Change Envelope (SCE) are identical, predicting the future position of shoreline by its past trend is more reliable.

    Keywords: Historical trend, Digital Shoreline Analysis System (DSAS), LITLINE, End Point Rate (EPR), Linear Regression Rate (LRR)
  • Karim Akbari Vakilabadi*, Hosein Khanzadi Pages 25-30

    Aluminum–magnesium alloys are specially used in high speed boats, submarines, desalination systems, etc.  In this re-search the electrochemical impedance spectroscopy technique was utilized to study the flow accele-rated pitting corrosion behavior of this alloy in 3.5% NaCl solution. To do so, impedance spectra of the samples after 20h of exposure to the test solution at a rotation speeds were investigated. SEM (scanning electron microscopy) method was utilized to investigate the changes in the surface of the samples. Results indicated that under static and dynamic con-dition, the surface growth rate of the pits increases with time. Moreover, at -0.9 V upon altering the flow condition from static to dynamic, the surface growth rate of the pits and their surface fraction increases while the corrosion resistance of the passive layer is time dependent.

    Keywords: Pitting Corrosion, Aluminum Alloys, EIS, Mansfeld's Model
  • Hossein Gholami*, Behrouz Asgarian, Farshad Hashemi Rezvani Pages 31-40

    This research aims to present a practical framework to study the structural response of a jacket type offshore platforms subjected to a sudden member removal considering the pile-soil-structure interaction. To this end, a series of nonlinear dynamic analyses are performed, and the progressive collapse resistance of the generic structure is determined. Consequently, the members prone to failure are detected. As a case study, the application of the proposed framework to control the capability of these type of structures for the prevention of progressive collapse occurrence are investigated. In the model structure, some legs and vertical braces in different locations are eliminated, and the effect of each damage case on the performance of the structure is investigated while the environmental wind and wave loads are imposed to the platform. The simulation results demonstrated that although the jacket structure can sustain the loss of primary members safely, it is susceptible to failure progression while a leg and the connected brace are eliminated simultaneously.  The safety margin, in this case, is about 20% only. In addition, it was revealed that in the case in which a leg and the connected brace are eliminated, progressive collapse resistance is about a third in comparison with the case of a leg damaged only.

    Keywords: Progressive Collapse, Jacket Type offshore Platforms, Non-linear Dynamic Analysis, Pile-Soil-Structure Interaction
  • Mohammad Hossein Sharifi*, Abdolrahim Taheri, Mohammad Bagher Faraji Pool Pages 41-48

    Subsea pipelines are used to transport gas and oil around the world. Oil is transported through subsea pipelines at high pressure and high temperature to smooth the way for its flow and to prevent its solidification. The present paper assesses a pipeline located in South Pars Gas Field against lateral buckling. As more and more pipelines operate at higher temperatures (over 100°C), the likelihood of lateral buckling becomes more relevant. The uncertainty in the lateral buckling parameters of the pipeline is a source of error in determining effective axial compressive force. Uncontrolled lateral buckling can cause excessive plastic deformation of the pipeline, which can lead to localized buckling collapse or cyclic fatigue failure during operation due to multiple heat-up and cool-down cycles, if it is not properly managed. This research reports the results of a reliability analysis to study and quantify the variations of the reliability index (β) with the main parameters involved during the lateral buckling of the subsea pipelines. Uncertainty is considered in the geometric parameters of the pipeline. The probability of failure (Pf) and the reliability index (β) can be determined by the reliability methods. The First-Order Reliability Method (FORM), the Second-Order Reliability Method (SORM) and the sampling method are the three main methods used here to determine Pf and β. The results show that the pipelines, in the case of lateral buckling and corrosion, will be in safe condition for up to 30 years after construction.

    Keywords: Subsea Pipeline, Lateral Buckling, Corrosion, Reliability, Probability of failure
  • Farhood Azarsina*, Aria Pirzadeh, Ghasem Darvish Pages 49-56

    Using artificial constructions is one of the most important ways to protect shores against wave actions and the consequent erosion. Due to costly nature of large scale marine projects, it is considered an efficient approach to study small scale model of the structure for simulation of sea conditions, measurement of hydraulic parameters and wave-structure interactions.In present research, construction of a small wave flume has been reported. Water up to 15 cm deep is filled in the flume and a DC motor directly rotates a flap in oscillations as a result of which regular waves of less than 10 cm height are produced. Wave lengths are around one meter, and wave periods are about one second. High quality fast images were analyzed in order to characterize the waves.Test runs were performed with different combinations of the wave parameters and the water depth, on five different revetments including: vertical seawall, simple slope, stepped slope, curved and recurved. Wave discharge with the aid of a small reserve tank at the far end of flume was measured. Results show that the recurved structure for most of the test cases reduce the wave overtopping to zero. The stepped slope has an efficient performance in dissipating the wave energy and reducing the wave run-up and overtopping. Simple slope recorded maximum discharge. Curved structure creates a water column of high speed vertical jet, and lastly the vertical seawall undergoes severe wave impact. Quantitative test results have been compared with well-known Owen’s formula for wave overtopping.

    Keywords: Shore protecting structure, Seawall, Wave-structure interaction, Small wave flume, Wave overtopping, Wave run-up