فهرست مطالب

International Journal of Maritime Technology
Volume:3 Issue: 3, Autumn-Winter 2014

  • تاریخ انتشار: 1393/09/30
  • تعداد عناوین: 6
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  • CFD Analysis on the Bare Hull Form of Submarines for Minimizing the Resistance
    Mohammad Moonesun, Yuri Korol, Hosein Dalayeli Pages 1-16
    In this paper, a CFD analysis on the bare hull form of submarines or torpedoes for minimizing the resistance is represented. There are several parameters in submarine form design which the most important parameter is resistance. All operational characteristics of submarines are related to the resistance, related required power and then, underwater speed and range. Other parameters are only mentioned. In this paper, the bare hull form is only studied without appendages. About seventy percent of the total resistance, is dedicated to the bare hull. The bare hull has three main parts: bow, cylinder and stern. The most real naval submarines and ROVs have parallel middle body form. Thus in this study, the focus is on this type of hull. The equations of bow and stern form are studied, as well. This paper, has studied the several forms by changing the coefficients of equations. CFD analyses are performed on these shapes for achieving the minimum resistance. The ratio of length on diameter (L/D) is another parameter which is studied in this paper. This analysis is conducted by Flow Vision (V.2.3) software based on CFD method and solving the RANS equations. All analyses are performed for underwater navigation, without free surface effect because, the required power is estimated always by submerged mode of navigation.
    Keywords: Submarine, torpedo, hull, form, CFD, hydrodynamic, resistance
  • VIV of Tapered Cylinders: 3D LES Numerical Simulation
    Khosrow Bargi, Vahid Tamimi, Mostafa Zeinoddini Pages 17-31
    In the present study, the author’s previous experimental investigations on the vortex induced vibration of uniform and tapered circular cylinders are numerically simulated. The circular cylinders have medium mass ratios (5.93, 6.1), low mass-damping parameters (0.0275, 0.0279) a mean diameter of 0.028m and an aspect ratio of about 14. A fully coupled two-way fluid-structure interaction (FSI) analysis is used to simulate the phenomena of vortex induced vibration in vicinity of the lock-in range. The 3D computational fluid dynamic (CFD) model is employed to solve the incompressible transient Navier-Stokes equations. LES-Smagorinsky turbulent model is considered within all simulations. Structural displacements are calculated through transient structural analysis in mechanical application (Computational Structural Dynamics-CSD). The transverse vibrations of uniform and tapered cylinders are compared against the experimental results. The comparison reveals that the model is capable to reasonably well predict the initial and upper branches of the responses. It, however, falls short to properly predict the lower branch. The simulation results of the fixed and elastically mounted tapered cylinders indicate that the flow field, in the case of the elastically mounted tapered cylinder, is completely different from that for the equivalent fixed tapered cylinder. For the case of the elastically mounted tapered cylinder no vortex cell fond to be forming in the lock-in region and a single frequency response dominated the entire length of the cylinder.
    Keywords: Vortex induced vibration, Uniform, tapered cylinders, 3D computational fluid dynamic, Fluid structure interaction, Fixed, elastically mounted
  • Prediction of Mean Overtopping Discharge at Vertical Seawalls Using MLR and GLM Statistical Approaches
    Alireza Sadat Hosseini, Hadi Ganji, Roozbeh Panahi Pages 33-40
    Wave overtopping at breakwaters is one of their essential hydraulic characteristics when determining the design crest level. This study concentrates on developing a new practical formula on predicting wave overtopping, by implementing two different statistical models, Multiple Linear Regression model (MLR) and Generalized Linear Regression model (GLM). The models consider dependency of overtopping on a wide variety of quantities and yield to simple forms of prediction. Such statistical analysis are performed on a set of data called CLASH (Crest Level Assessment of Coastal Structures by full scale monitoring, neural network prediction and Hazard Analysis on permissible wave overtopping) the most complete and available database on overtopping phenomena. Proposed equations are compared with most recently extracted as well as successful ones. Comprehensive assessments clearly show more accurate predictions in the case of mean overtopping at vertical seawalls.
    Keywords: Wave overtopping, Dimensionless parameters, Multivariate linear regressio, Generalized linear regression, CLASH
  • Investigation of Keel Curvature Effect on the Hydrodynamic Characteristics of a V-Shaped Planing Surface
    Hashem Moradi, Amir Hossein Nikseresht, Alireza Mostofizadeh Pages 41-48
    In this paper, three-dimensional two phase turbulent free surface flow is solved by an in-house code. The incompressible Reynolds average Navier-Stocks equations (RANS) with k-ε turbulence model are solved by the finite volume method in the non-orthogonal curvilinear coordinates. For the modeling of the free surface effect, Lagrangian propagation volume tracking method (VOF-PLIC) is used. The code is validated solving two-phase turbulent flow through the impact problem of a circular cylinder. Then, the horizontal movement of a NACA standard wedge with 20 degree deadrise angle is simulated. The flow field and generated waves is estimated with different velocities. Numerical results of the average wetted lengths show acceptable compatibilities with the available experimental data. In addition, some modifications on the V-bottom are done to investigate the effect of the keel curvature and deadrise angle on the hydrodynamic forces. In each cases the ratio of the lift and drag coefficient to the conventional wedge with 20 degree deadrise angle is evaluated. It is depicted that the convex curvature doubles the drag coefficient and has not any significant effect on the lift coefficient. The results confirm that the deadrise angle reduction decreases the needed engine power in take-off. However, this reduction has a destructive effect at the time of landing.
    Keywords: Free surface
  • Field Measurements and 3D Numerical Modeling of Hydrodynamics in Chabahar Bay, Iran
    Mohsen Soltanpour, Mohammad Dibajnia Pages 49-60
    As the first phase of a series of monitoring and modeling studies of Iranian coastal areas, Chabahar Bay, located on the north coast of the Gulf of Oman, was under a comprehensive monitoring and modeling study in 2006-2007. The study included an extensive one-year field measurements program to help understanding the ongoing processes in the bay and provide inputs or boundary conditions and validation data for numerical models. An analysis of the collected data and the results of three-dimensional (3D) hydrodynamic numerical modeling are described in this paper. 3D numerical model of MISED was employed to provide a full spatial picture of bay-wide circulations and its sensitivity to environmental factors such as tides and winds. MISED simulations were completed for the months of February and March 2007 and the results were compared with the measurements. It was observed that the simulated tidal currents favorably agree with the measured data at the selected stations. Particle tracking simulations using a Lagrangian Particle Tracking Model showed that the combination of wind-driven and tidal currents generates a self-flushing function that tends to carry suspended material to outside of the bay. The combination of winds and tides has thus a very important assimilative function for water quality of Chabahar Bay.
    Keywords: field Measurements, hydrodynamics, MISED 3D model, particle tracking, Chabahar Bay
  • Persian Abstract A Survey on Precision of Nested Water Level Data Derived From Delft3D Model
    Maryam Rahbani Pages 61-65
    One of the troublesome aspects of numerical modeling is to determine open boundaries for a model and to make sure that the boundary conditions employed at the open boundaries are compatible with physical processes being simulated within the interior of the model domain. In this investigation the accuracy of the water level data derived from delft3D employing nesting procedure were studied. These water level data were prepared to apply at open boundaries of a tidal channel model. This method was employed due to the lack of measuring stations in the proper geographical positions at the site. There was however three gauges inside the area, in which their records were used for the calibration of the model. Primary water level data derived from the model were compared with those derived from the in situ gauge. Observing dissimilarity between these two time series was the reason to search for the possible reasons. The importance of wind and/or bathymetry on the water level results also was studied. It was found that unreliable results were the outcome of using unjustified data at the boundaries. It is therefore, suggested that the boundary conditions to be verified and if necessary to be justified before applying at open boundaries. Several reasons, explaining the necessity of the justification, are presented.
    Keywords: model, nesting, open boundary condition, water level, wind