فهرست مطالب

Maritime Technology - Volume:4 Issue:5, 2016
  • Volume:4 Issue:5, 2016
  • تاریخ انتشار: 1395/01/30
  • تعداد عناوین: 6
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  • Farhad Hosseinlou, Alireza Mojtahedi Pages 1-11
    Marine industry requires continued development of new technologies in order to produce oil. An essential requirement in design is to be able to compare experimental data from prototype structures with predicted information from a corresponding analytical finite element model. In this study, structural model updating may be defined as the fit of an existing analytical model in the light of measured vibration test. After fitting, the updated model is expected to represent the dynamic behavior of the jacket structure more precisely. In this way, current article presents a direct based updating study of a reduced scale four-story spatial frame jacket structure fabricated and tested at mechanical system and signal processing laboratory. Also, an efficient model updating process is presented with limited modal data, which uses modal data in order to improve the correlation between the experimental and analytical models.
    The proposed technique is computationally efficient since it does not require iterations. It updates the mass and stiffness matrix such that they are compatible with the modal data of the observed modes.
    Keywords: Offshore Jacket Platforms, Model Updating, Signal Processing, Experimental Modal Analysis, Improved Reduction System
  • Mohd Atif Siddiqui, Vishwanath Nagarajan Pages 13-25
    The increasing world demand for fish cannot be met by capture fisheries. Aquaculture production is increasing and nowadays cage culture has an important role in meeting the world’s fish demand. The design of the physical structure of a cage is determined by the oceanographic conditions of the culture site. Each design is site-specific and knowledge of the topography, wind force and direction, prevalence of storms or monsoons, wave loads, current velocity and water depths are important parameters for consideration. Because of all these reasons the design of an aquaculture cage system is very complex and difficult task. Hence, it is essential to select a proper site, ideal construction materials, proper designing, suitable mooring, good management etc. in bringing out a cage culture production more profitable and economical. A six degree of freedom model is considered to find out the motions and forces acting on the cage. The tensions in the mooring chain and the net twine tension were predicted based on numerical simulation.
    Keywords: Marine Aquaculture Cage, Wave loads, Dynamics
  • Hamid Ahmadi, Ali Ziaei Nejad Pages 27-35
    In the present research, data extracted from the stress analysis of 46 finite element models, verified using test results obtained from an experimental investigation, were used to study the effect of geometrical parameters on the chord-side stress concentration factors (SCFs) of central and outer braces in uniplanar tubular KT-joints of offshore structures subjected to four different types of in-plane bending (IPB) loads. Parametric study was followed by a set of the nonlinear regression analyses to develop SCF parametric equations for the fatigue analysis and design of uniplanar tubular KT-joints under IPB loadings.
    Keywords: Fatigue, Offshore jacket structure, Tubular KT, joint, Stress concentration factor (SCF), In, plane bending (IPB)
  • Mohammad Moonesun, Firouz Ghasemzadeh, Yuri Korol, Valeri Nikrasov, Alexi Yastreba, Alexander Ursolov, Asghar Mahdian Pages 41-54
    In this study, the experimental analysis on the bare hull resistance coefficient of submarine at snorkel depth is represented. The experiments are conducted in marine laboratory of Admiral Makarov University. The results are presented for surface condition and snorkel condition. Snorkel depth is regarded equal to one diameter of submarine hull beneath the water surface as usual in submarines. Performing the experiment at the surface condition is a usual practice process but performing the experiment at submerged condition has several technical notes which are evaluated in this paper. One of challenging discussions is estimating the induced resistance between the main hull and struts. For this part of study, CFD method is used. CFD analyses are conducted by Flow-3D (V.10) software based on solving the RANS equations and VOF method. All analyses are performed for still water condition. The results of this research can be used for AUVs, research submersibles and submarines, torpedoes and every submersible who operate near the free surface of water.
    Keywords: Submarine, Resistance, Experimental, CFD, Snorkel depth, Flow, Vision, Flow, 3D
  • Hamid Kazemi Moghadam, Rouzbeh Shafaghat Pages 55-62
    There are different methods to reduce drag in high speed hulls. One of these methods is a change in the shape of the body by adding longitudinal side tunnels. In this paper it has been attempted to determine the influence of the tunnel height on hydrodynamic characteristics of the hull to achieving an optimum shape for the tunnel. To achieve this purpose, numerical simulation of the problem has been done using finite volume method considering moving mesh. For turbulence modeling, k-ε model and to simulate free surface, the Volume of Fluid (VOF) two phase model has been employed. The results show that creating a tunnel in the base mono-hull would lead to reduction of the total drag at high speed as well as decreasing the vessel draft of the hull over the whole range. Furthermore, in the Volumetric Froude number around 4, a reduction in the height of the tunnel could decrease the hull drag. In higher Volumetric Froude numbers, reduction of the tunnel height, to some extent, increases the drag with a slight slope.
    Keywords: High, speed Planing hull, Tunnel height, Dynamic mesh, Drag Reduction, Trimaran
  • Amin Mahmoudi, Habib Hakimzadeh, Mohammad Javad Ketabdari, Amir Etemadshahidi, Nick Cartwright, Hassan Abyn Pages 63-76
    Breaking waves have ability to transport large quantities of sediment and significant impact on coastal structures morphology. Hence, modeling of wave breaking is an important subject in coastal and marine engineering. In this research, the periodic wave breaking process on a plane slope is studied experimentally and numerically. Laboratory experiments were conducted to record water surface elevation and the wave breaking process. For the current study, a space-averaged Navier–Stokes approach together with laboratory experiments has been deployed to investigate time-dependent wave breaking processes. The developed model is based on the Smoothed Particle Hydrodynamic (SPH) method; a pure Lagrangian approach; capable of handling large deformations at free surface with high accuracy. So, a Weakly Compressible version of the Smoothed Particle Hydrodynamics (WCSPH) method together with a large eddy simulation (LES) approach was used to simulate the wave breaking on a plane slope. The results of numerical simulations were compared both qualitative and quantitative with those of laboratory experiments. Overall, good agreement was found between them. Finally, it is shown that the WCSPH method provides a useful tool to investigate surf zone dynamics.
    Keywords: Experimental Model, Numerical Simulation, weakly compressible smoothed particle hydrodynamics, Wave breaking, large eddy simulation model