فهرست مطالب

  • Volume:6 Issue:10, 2018
  • تاریخ انتشار: 1397/06/05
  • تعداد عناوین: 6
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  • Alireza Soleymani, Mohammad Hossein Sharifi Seyed, Pedram Edalat, Mohammad Mahdi Sharifi Seyed, Samad Karim Zadeh Pages 7-13
    An approach to deal with the phenomenon of maritime fuel smuggling is to control the quantity of fuel that is supplied to vessels. For the same reason, fuel is delivered to marine vessels in Iran in accordance with the ration defined by the National Iranian Oil Products Distribution Company (NIOPDC). The ration is determined by a fuel consumption formula defined by the Food and Agriculture Organization of the United Nations (FAO) which is used to estimate the fuel cost of agricultural and road construction equipment and machinery. The use of this formula for maritime usage renders fuel allocation to vessels inappropriate. This paper makes a database containing the specifications of 452 vessels, including length, width, summer draft, economical speed, engine power and hourly fuel consumption values. Then, a linear model is estimated over the available database. Ordinary least square method is used for regression analysis. Then, the estimated linear model is compared with FAO formula and linear model is selected as the optimum model to estimate vessel fuel consumption as close to the actual value of fuel consumption as possible. This linear model contains three parameters: engines power, economical speed, and immersed volume as defined by multiplying three parameters of length, width, and summer draft. In general, the amount of fuel consumption estimated by FAO formula is about 50% greater than that estimated by the linear model
    Keywords: Marine vessels, Fuel consumption, Linear Modelling, Regression analysis, Cross sectional data
  • Maziar Khosravi, Seyed Mostafa Siadat Mousavi, Vahid Chegini, Ross Vennell Pages 10-16
    The Khuran Channel, Southern Iran (26°45’N), is a topographically complex channel which is open at both ends. Owning to its particular geometry, this narrow channel is subjected to strong tidal currents.Across-channel distribution of the mean and tidal flows were obtained over a semidiurnal tidal cycle in the Khuran Channel where the highest tidal velocity in the third day of the secondary spring tide exceeded 140 cm/s. Velocity profiles were obtained using a 614.4 kHz Teledyne RDI Workhorse Broadband ADCP over 13 repetitions of a cross-channel transect. The 3.1 km long transect ran north/south across the channel.The M2frequencywas separated from the observed current using sinusoidal form functions and the least square regression analysis. Contrary to the previous study in this channel, the mean inflow observed in the deep parts of the channel and mean outflow occurs over the shallow slopes, with the maximum magnitudes (15-20cm/s) near the surface in the north side. The maximum lateral shear and convergence were found over slopes located between the middle and the north side of the channel.
    Keywords: Persian Gulf, Khuran Channel, Tidal Currents, ADCP measurements
  • Mehdi Shafieefar, Pooya Rangbar Pages 15-24
  • Seyyed Mostafa Seyyedi, Rouzbeh Shafaghat, Negin Donyavizadeh Pages 25-35
    Surface-piercing propellers have been widely used in light and high-speed vessels because of their superior performance. One of the major steps in propeller selection algorithm is the determination of thrust as well as torque hydrodynamic coefficients. For the purpose of simplifying design and selection procedure, some relations are presented for determining hydrodynamic coefficients in some studies, precision, and accuracy of which must be validated due to the importance of the issue as well as having high development and operational costs. Therefore, these issues are evaluated in this study by field study and recognizing the presented relation set as well as acquiring experimental test data. The acquired results show lack of full agreement between semi-experimental relations and experimental data. In the following, due to the limitations of the regression relations presented in the determination of hydrodynamic coefficients, the database was developed from experimental data, the number of series is determined by extracting the regression relations for each series, these relations are used to determine the hydrodynamic coefficient of thrust and torque in the propeller selection algorithm. Finally, a suitable algorithm for selecting the surface-piercing propeller was presented and discussed
    Keywords: Surface-piercing propeller, Propeller experimental test, Hydrodynamic coefficients, Regression relations
  • Mohammad Hossein Sharifi Seyed, Reza Soheili Seyed, Ali Shaghaghi Moghaddam, Farhood Azarsina Pages 37-44
    Economical design with sufficient fracture resistance is of high importance in any offshore pipeline projects. Using an Engineering Critical Assessment (ECA), alternate acceptance criteria for pipeline girth weld inspection can significantly reduce the cost of constructing of offshore oil and gas pipeline by minimizing unnecessary repairs. Offshore pipelines consist of short pipeline segments connected by girth welding method. Surface and embedded elliptical cracks due to welding operation are often observed at welding zone which pose a potential threat to the reliability of the offshore pipelines. To derive the acceptance criteria for pipeline girth weld defects and pipeline safety during installation and operation phase, an ECA based on fracture mechanics is required. In this paper, ECA of offshore pipeline with semi elliptical surface crack under pure tension loading is performed according to finite element method and BS7910 guideline. Moreover, a comparison between these two methods is offered. It is concluded that, ECA by BS7910 guideline is more conservative than finite element method, and the difference between the two diagrams increases as strain levels are increased. Also, comparisons of critical crack size curve for various strain levels are studied.
    Keywords: Engineering Critical Assessment, Offshore Pipeline Girth weld, Surface Cracks, Acceptance Criteria, FEM
  • Amir Behshad, Mohammad Reza Shekari Pages 45-54
    In this paper, the sloshing response of liquid in a two dimensional rigid rectangular tank with rigid baffles is investigated using boundary element technique. A baffle is a supplementary structural element which supplies a kind of passive control on the effects of ground shaking. The complicated liquid domain is divided into two simple sub-domains so that the liquid velocity potential in each liquid sub-domain is specified employing Green’s theorem, and the walls and free surface boundary conditions are applied. The liquid region is modeled by internal quadrilateral boundary elements, which reduce the three-dimensional fluid problem into a two-dimensional-surface one. The validity of the present algorithm is assessed through the comparison with the accessible results for the rectangular tank without baffle and then developed to the solution of tanks with rigid baffles. Several parametric studies are performed to show the liquid sloshing effects in terms of the slosh frequencies and free surface displacement by consideration of the effects of baffle parameters such as position and dimension. From these analyses, it may be concluded that in the special case of long-period ground earthquake, the baffle device amplifies the dynamic responses of liquid tank which may be interpreted by the fact that the predominant period of the ground shaking is set at the fundamental natural sloshing periods.
    Keywords: liquid sloshing, baffled tank, boundary element method