aliasghar moghaddas ahangari

Pre-swirl stators can operate as a device to improve the hydrodynamic performance of the propeller and reduce the excess propeller torque on the underwater vehicle. This excess torque on the underwater vehicle with a circular cross-section can cause harmful rolling motion. The most important and influential parameters in the design of these stators are the chord length, distance from the propeller, and angle of attack. In this paper, these parameters are investigated using the Taguchi method and stator design to simultaneously reduce the underwater vehicle roll motion (reduction of excess propeller torque) and increase propeller efficiency using computational fluid dynamics with the help of commercial software STAR-CCM+. To validate the calculations, the numerical simulation results of a B-series propeller are compared with the existing experimental test, the numerical results are obtained with less than ten error percentages compared to the experimental results.  The Grid Convergence Index has also been used to ensure the independence of the results obtained from the mesh. The final stator designed in this paper reduces the total propulsion torque by 44.47% compared to the non-stator mode and improves efficiency by 2.29%. Also, the designed stator reduces the vortex of the blade tip and the propeller hub.

In this research, by using Experimental and numerical methods, the hydrodynamic parameters of high-speed prismatic vessel including resistance, rise up and trim for two deadrise angles of 20 and 25 have been investigated. In this paper, first, the experimental results with 2 deadrise angles 20 and 25 with David Taylor Towing Tank results are compared and the hydrodynamic parameters including resistance, rise up and trim are investigated. Then, by modeling the vessel by finite volume method and computational fluid dynamics, the hydrodynamic parameters have been validated and compared and the wet surface of the vessel has been computed at two deadrise angles in different forward speeds. In this study, it was found that the amount of floating resistance increases with increasing deadrise angle. Also, the dynamic trim decreases with increasing deadrise angles at different forward speeds.

One of the important goals of designing of planing boats is to achieve higher speeds, one of the major obstacles to this issue is longitudinal instability.In this research, a new method is proposed to solve the longitudinal instability of steped planing boats. In this method, using the transverse curvature or variable deadrise angle of the body, the instability of boat has been corrected. Two bodies, called Nimala1 and Nimala2, were tested in National Iranian Marine Laboratory. The main difference between the two transverse curvature bodies is that Nimala1 has a constant deadrise angle and nimala2 has a variable deadrise angle in a section. To determine the effect of the variable deadrise angle on the longitudinal instability, each of the models has been tested up to longitudinal instability. Due to the equipment installed during the test of the model in the towing tank, it was not possible to measure the movement and therefore numerical analysis is used as a complement to the exprimental test. The results show that the variation in cross-curvature has a significant effect on longitudinal instability. By shifting the center of pressure to Aft, the delay of the porpoising was changed from 5.89 volumetric Fn in the fixed deadrise angle model, to 8.34 volumetric Fn in Variable deadrise angle model. Also, the resistance of this body is not significantly different from that of a body with constant transverse curvature, especially at high speeds.

One of the undesirable phenomena in the achievement of planing vessels at high speeds is the phenomenon of longitudinal instability. This phenomenon, which is in fact an unstable coupling between heave and pitch, causes damage to the vessel, equipment and crew. In order to evaluate and accurately calculate the speed of occurrence of this phenomenon in the design stages, it is necessary to perform numerical analysis or model testing. Therefore, the existence of a valid data set to validate these analyzes, especially numerical analysis is essential.In this paper, by setting the dynamic trim as a criterion for the occurrence of porpoising in a planing boat, the amount of this trim at different speeds is measured on a sample of a cougar boat without steps in the sea. These results show that the dynamic trim has an increasing trend with increasing speed and after the float is in planing mode, it gradually decreases and tends to an almost constant value at high speeds.

Today, with significant advances in the maritime industry, body design and appendages, including Propellers, rudders, and surface control systems, have many changes. One of the topics of interest these days is high-speed vessels, which increase their speed and maneuverability. With the advancement of technology and new designs in the field of Propellers design, today Propellers called Surface piercing Propellers (SPP) are widely used in high-speed vessels. Because high-speed vessels have low levels of contact with water, these propellers cause very high efficiency at high speeds. One example of this butterfly is the Oloffson Propellers, which is available to researchers as a research sample. In this study, the Oloffson Propellers model was used to test the Propeller at different distance from the rudder. In this research, by using of ANSYS-CFX software, the interaction between Propeller and rudder at three different distances from each other were tested, and the thrust and torque produced by the Propeller are calculated in a complete cycle. Also, the effect of force and torque produced by the Propeller on the rudder is examined. The aim of this study is to provide a background for rudder installation optimum position on planing boats.

Man is always looking for ways to do his daily work at a higher speed. The ability to move individuals and objects in the shortest possible time has always been one of the main concerns of humans. The marine industry is not an exception to this requirement. The use of planing boats to increase displacement speed as well as agility has received a lot of attention from industries that have not been excluded. The design and construction of these vessels requires dynamic understanding and control of their instability. One of the most important instabilities in planing boats is porpoising under the influence of various factors. In this paper, we investigate the effect of aspect ratio on the stability of planing boats by studying prismatic body. First, the numerical parameters were selected using numerical analysis results on three models with different ratio and then the effect of the aspect ratio on the occurrence of porpoising was investigated using Mr. Suitsky's regression equation.

Trim control mechanisms and movements of high-speed crafts such as trim tab, flap and interceptor have effectiveness function on resistance and dynamic behavior on these crafts. Effectiveness of interceptor is investigated in stern of high-speed crafts at various speed of vessel by use of experimental method on the 13 m planning high-speed crafts in Persian Gulf laboratory of Imam Hussein University. The results show that resistance reduction by use of interceptor has remarkable effects over the range of Froude numbers. Use of interceptor at high Froude numbers causes reduction of trim and increases resistance. We use a model of 13 m Cougar boat that two interceptor is installed in transom. Thus causes reduction peak of resistance in velocityresistance curve of high-speed crafts.

Measurement of resistance force acting on the underwater vehicles has some methods such as numerical method. Because of economical and equipmental reasons the numerical methods has more users than other methods. When this methods has insurance that the result has been validated by experimental results. In this paper, resistance force of spheral body in STAR CCM software has calculated and compare with experimental results that measured by towing tank tests. According to the sphere size and test speed, the flow is in laminar regime, so The result of the CFD Analysis ant towing tank test has validated in this regime.