مهندسی دریا
Ahmad Hajivand; Hesamoddin Ravanbakhsh
Abstract
The extensive development and design of multihull ships began in the second half of the twentieth century. Nowadays, many of these ships are built with different designs. However, less numerical and experimental studies have been conducted on their behavior compared to single hull ships. The length and ...
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The extensive development and design of multihull ships began in the second half of the twentieth century. Nowadays, many of these ships are built with different designs. However, less numerical and experimental studies have been conducted on their behavior compared to single hull ships. The length and distance of the two hulls are the factors influencing the wave pattern created around and between the hulls and, consequently wavemaking resistance. In this study, the effect of geometric parameters including length to diameter ratio and body spacing on the hydrodynamic performance of a vessel with a small water plane area surface has been studied using computational fluid dynamics. To investigate the effect of L/D on the wave pattern around the body, towing test is simulated for two models with different ratios in a wide speed range. Furthermore, to evaluate the effect of two-hull distance on the interference of waves between two bodies, two models have been simulated at different distances at different speeds in the computational fluid dynamics environment. Simulations are performed for two different draft. The effect of Froude number, length to diameter ratio and draft on hydrodynamic behavior of the model has also been studied. The pressure, friction and interference resistance of the two bodies are calculated and the wave pattern surrounding the body and between the two bodies is extracted and compared with experimental data, which indicates the reasonable approximation of numerical and laboratory results.
مهندسی دریا
Ahmad Hajivand; Aghil Daraie
Abstract
The prediction of ship resistance is the most important part of the ship's hydrodynamic design. Nowadays, computational methods are used as a common tool for this purpose. Ship total resistance calculation by using two phase numerical method based on the Reynolds-averaged Naiver–Stokes solution ...
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The prediction of ship resistance is the most important part of the ship's hydrodynamic design. Nowadays, computational methods are used as a common tool for this purpose. Ship total resistance calculation by using two phase numerical method based on the Reynolds-averaged Naiver–Stokes solution requires high computational power. The idea of total resistance decomposition based on the physical cause is a basic principle in the ship hydrodynamic. In the proposed hybrid method, wave making resistance part is calculated by using Michell Integral and viscous part is computed by numerical solution of one phase viscous flow for double body condition. Computations are performed for 10 velocities from Fn = 0.06-0.62 and at each velocity the percentage of every component calculated. Hybrid method reduce computational time. To investigate the results, tow phase simulations are performed for a SWATH vessel. On average, there are 7% difference between the results obtained from hybrid and two phase method and computational time in hybrid method is 97% less than two phase method.
مهندسی دریا
Shahrzad Nikbakht; Ahmad Hajivand; Mostafa Jafarzadeh Khatibani
Abstract
Power requirements increase severely in rough weather because of added resistance induced by water wave. Amplitude of this additional resistance is between 15 to 30 percent of the ship calm water total resistance. Nowadays, one of the important issue in naval architect is to design a ship hull with minimum ...
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Power requirements increase severely in rough weather because of added resistance induced by water wave. Amplitude of this additional resistance is between 15 to 30 percent of the ship calm water total resistance. Nowadays, one of the important issue in naval architect is to design a ship hull with minimum added resistance that produce less greenhouse gas. There are several numerical viscous and non-viscous method like strip theory, panel method and RANS method. With respect to accuracy and cost calculations, 3-D panel method is the best choice for analysis ship behavior in wave. By using frequency domain Green's function 3-D panel method added resistance of S-175 containership is computed by far filed and near field approaches. To investigate the effect of wave incident and wavelength, calculations are performed in different incident angle and wavelength. Also by using an accurate and fast empirical validated method that have recently been proposed, added resistance in head sea are calculated for different wavelength and ship speed. Far field and near field results are consistent with good accuracy. Numerical and empirical results are compared with experimental that shows high accuracy results.
مهندسی دریا
Moloud Ariyan; Ahmad Hajivand; Etemadodin Rabei Gholami
Abstract
Maneuverability is an important quality of marine vehicles. Hydrodynamic coefficients of ship and rudder should be derived to simulate maneuvering tests. These coefficients can be obtained by using captive model test and empirical formula. Accuracy of rudder hydrodynamic coefficients is important to ...
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Maneuverability is an important quality of marine vehicles. Hydrodynamic coefficients of ship and rudder should be derived to simulate maneuvering tests. These coefficients can be obtained by using captive model test and empirical formula. Accuracy of rudder hydrodynamic coefficients is important to calculate rudder force as the most influence force in ship maneuver, precisely. Empirical formula usually are correspond to single rudder ships and for twin rudder ships numerical or experimental method are used. In this paper, by using numerical method and simulation of static towing test in computational fluid hydrodynamic environment for different angles, linear and nonlinear rudder hydrodynamic coefficients are calculated. Also, fluid velocity field around rudder is obtained to investigate separation for high rudder angle. The comparison of simulated results with the available experimental shows a very good agreement among them.