مهندسی دریا
سال:1395 | دوره:12 | شماره:23 |تعداد مقالات:14

One of the most important items in the field of engineering and design of structures issafety assessment. It is usually complicated, due to uncertainty in determining themost important parameters in the final design. This paper describes a new method forupdating stiffness matrix structure that is capable of identifying the damage toindividual members, when limited modal data is available by using results of theexperiment on physical model of the offshore jacket platforms. We evaluated selectionprocedure inactive degrees of freedom in the process reduced model with a reasonablecriterion by using the sensitivity analysis of system response under base excitation.This performance leads to faster convergence of iterative algorithm. Also, in thisstudy, with using the finite element model updating based on the empirical models, itwas considered during the process as much as possible to overcome the problem ofuncertainty in modeling.

With the increase in the pollution caused by oil industry developments and relatedinfrastructures in the last century, setting priorities for decisions in sensitive coastalareas to oil spills is important. This study uses the reports in the field of environmentalsensitivity index in shorelines and applies the Delphi method to determine the criteriaand sub-criteria allowed for adjusting the effective hazard components of theshoreline to pollution. Finally, using hierarchical analysis and network analysismethods helped in determining the priorities of the indexes in the evaluation of theshoreline hazards to oil spills. This study compares priorities by utilizing ExpertChoice software for hierarchical analysis and Super Decisions software for networkanalysis process within the framework of multi-criteria decision-making methods.Based on this, biological resources, socio-economic resources of pollution, thephysical characteristics of the shorelines, and the related sub-criteria were prioritized.Accordingly the final ANP/AHP maps are produced by using Index Overlay method.

In this study, the results of a direct numerical simulation of turbulent drag reduction ina channel flow by hydrophobic coating at a nominal shear Reynolds number of Re t=180 are reported. Slip condition is imposed on the lower wall whereas the upper wallhas no-slip condition. For this purpose, the use is made of a numerical simulation of three-dimensional, time-dependent Navier-Stokes equations for the incompressibleflow of a Newtonian fluid. Finally, statistical quantities of turbulent flow (specificallythe mean velocity profile, the root-mean-square of velocity fluctuations in differentdirections and the Reynolds shear stress are shown and discussed. The results confirmthat by increasing the amount of slip on the lower wall, the bulk velocity passingthrough the channel increases. Also, the variation of root-mean-square of velocityfluctuations shows a similar behavior in the vicinity of the upper wall. But, theirgeneral trend is different in the proximity of the lower wall. Moreover, a change in theshape of the Reynolds shear stress profile from a minimum close to the lower walltowards a maximum close to the upper wall is observed.