JOURNAL OF MARINE ENGINEERING
Year:2016 | Volume:12 | Issue:23|Papers Count: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.

In this study, two-dimensional flow analysis around cross-section of the surfacepiercing propeller with a linear profile trailing edge is studied in different Webernumbers. Due to collision of the two-dimensional cross section with surface water, aeration zone is created on the suction side that is heavily impact on the results. Theventilation pattern is a function of the geometrical parameters. In this article, inparticular, the effect of surface tension and the Weber number have been investigated.According to the obtained results at low Weber numbers, the surface tension effectincreases the amount of water surface uplift, and water droplets are visible in thetrailing edge of blade section. At Weber numbers higher than critical Weber number, surface tension effect will only cause loss of fluid droplets in the inlet region.

Estimation of siltation depth in harbors and estuaries plays an important role in designof marine structures. In this paper, siltation process at Bushehr estuary as one of themost important water bodies in south of Iran is modeled by so-called MIKE 21mathematical model. To achieve this, at first a large scale hydrodynamic modelcalibrated by IRANSIAM registered water levels is developed while Chabaharregistered tidal levels are considered as its boundary condition. Then, by developing alocal model with fined mesh the dominant flow pattern is captured in the studied area.The local model is developed by hydrodynamic data taken from the large scalehydrodynamic model. Finally, via MIKE-21 MT module pattern of siltation in thestudy area is simulated by calibrating the model with sediment concentrationsregistered at Bushehr channel. Final results showed variation of siltation depth from7cm in front of CPS platform till 22cm net siltation in front of Kosar platform insidethe estuary.

Existence of the coasts in the north and south of Iran cause to create potentialareas to produce electricity by tidal and wave energies. Therefore, increase offluid velocity is required to exploit these areas. A new generation of turbinesis created by designing and building a shroud to increase fluid velocity whichit increases kinetic energy of flow and generates more electricity at coastlinesand riverbeds.Based on airfoils characteristics, a shroud with an airfoil cross-section formwas designed which increases water velocity approximately 2.8 times greaterthan far field flow numerically. The shroud was built and testedexperimentally. Moreover, several propellers were installed in the shroud.Rotational speeds of the propellers in two states of with and without shroudwere compared and they were proportional to increase ratio of flow velocity.Consequently, more power is generated by installing a turbine in the shroud.

Caspian Sea is one of the most low-lying areas of the region which is located betweenlatitudes 36.34 and 47.13 degrees north. Its considerable vast area and depth haveprovided an opportunity to gain renewable energy by different methods. This paperanalyzes the performance and mechanism of a floating wave energy converter knownas WaveStar, in the above-mentioned sea. Different parts of mechanism are examinedunder hydrodynamic forces of waves with certain periods and amplitudes. By usingthe frequency parameters, profile and velocity of the waves; and solving the governingdynamic equations for the model, the vibration response of system has been derived.The main part of this study is the investigation of the effect of changing the armlength, float diameter, wave period and wave amplitude on the structure using regularwave with Froude-Krylov force.

In this study, patterns of water current, sea surface temperature and salinitydistributions over the South Caspian Sea (SCS) have been investigated using ROMSmodel. Appling the most accurate bathymetry data and forces with temporal resolutionof 3-6 hours, and spatial resolution of 0.125 deg is a characteristic of the simulationsused in this study. Results show that there is a barotropic anticyclonic eddy over thedeep water of SCS, which extended from surface to subsurface. A dipoleanticyclonic/cyclonic feature is another structure of SCS that located in northwest (inApsheron sill) / southwest respectively, a nd persist throughout the year. Based onresults, net buoyancy flux of SCS is more affected by thermal buoyancy rather thanhaline buoyancy. In addition, there is a saline front in the east coast of SCS that isseparated from other regions by combining with warm (cold) water during (warm) seasons.

In this research, the effects of foulings on the outer surface of a marine vessel havebeen studied using the Computational Fluid Dynamics (CFD) methods. To this end, aproper turbulence model was considered and validated for the simulations. Thesimulation results for different fouling grades indicated that existing of a thin layer ofslime could make 4.58 % increase in drag force; however, foulings on the outersurface of a marine vessel could make about 40% increase in drag force. In this study, the application of modern coatings (surface covers) for reducing the foulings and theresulting drag force was also investigated and the results were presented. Based on thesimulation results, application of the coatings, the foulings resulted drag force woulddecrease about 37%. In addition, wave patterns, pressure distribution, drag coefficientdistribution, and turbulent distribution profile were investigated on the free surface.

Strain gage mounted on the surface of the shafts with specified directions are one of the common methods for measurement of the torsion in shafts. The most criticalproblem in utilization of this method, particularly in the online monitoring of torsionalvibration and instantaneous torque in rotary systems, is due to its signal transferprocess. In this paper, a simple, practical and feasible method is introduced based on the usage of an unionized fluid medium with adequate electrical conductivity, encapsulated in a cylindrical connector aligned along the shaft, with a rotatingchamber (rotor part) and a stationary one (stator part). In this method, there is no need for installation of the power supply on the shaft and both of the supply voltage and thegenerated electrical signals are transferred via the unionized fluid. Simplicity in designand high signal to noise ratio, may candidate this method for torsional vibrationmeasurement. The efficiency of the measurement system is examined on a test setup, for static and dynamic (transient) torsions. Moreover, the applicability of the device isobserved on a rotating shaft.

Launching method is commonly applied for installation of heavy template (jacket)platforms. One of the important phases in design and construction of offshoreplatforms is launching condition. This will insure the safty of the procedure and willoptimize the weight of the related members of the jacket. In this article, effectivefactors and amount of forces that applied on steel jacket during launching and theminimum distance of jacket to sea bed are studied through a parametric analysis. Forsimulation of the launching procedure the technical softwate of SACS is applied. Theanalyses are applied on two jackets installed in Persian Gulf. The initial tilting angle, draft, and bouyancy are among the parameters which are studied. The results of thestudy show that the tilting angle and bouyancy are the most effective parameterswhich reduce the launching forces up to 20%. The study shows that optimizing theprocedure of launching in the case of the jackets of the present study can reduce theweight up to 4 percent.