نشریه مهندسی دریا
پیاپی 43 (تابستان 1403)

One of the important challenges in the design and construction of planing craft is the occurrence of longitudinal instability at high speeds. Among the methods that can be used to reduce or eliminate these instabilities is the use of hydrofoil stabilizer. In this research, the influence of the dimensions of the hydrofoil stabilizer on the dynamic behavior of the mono-hull planing craft has been investigated. The vessel studied in this research is a planing mono-hull craft, which experimentally has longitudinal instability. The influence of the speed on the effect of porpoising on the planing craft is also studied. The purpose of this study was to analyze the performance of a high-speed planing craft with a hydrofoil stabilizer and determine the best dimensions of the hydrofoil stabilizer. In this research, the parameters of hydrofoil dimensional ratios and middle width ratio in stingray type hydrofoils have been investigated. Each of these parameters is modeled in its position with the help of a CAD software. A computational fluid dynamics solver has been used for the numerical simulation of the problem. In this article, an attempt has been made to understand the importance of each of the design parameters by comparing the results of the simulation and examining the results related to pitch and heave motions of the planing craft. At this stage, in order to check the parameters, the angle of attack is 0 degrees, the depth of the hydrofoil to the transom of the boat is 15 cm, and the longitudinal distance of the hydrofoil from the transom is assumed to be 10 cm. One of the investigated parameters is the width to the chord length ratio of the hydrofoil, which has a fixed cross section. From the comparison of the results between the three ratios of 0.75, 1.33 and 2.083, it was found that at a speed of 30 knots and in a time of 3 seconds, the range of pitch movement has been reduced by 50, 36.6 and 63.3%, respectively, compared to the case without hydrofoil. Therefore, it can be seen that increasing the width to the chord length ratio of the hydrofoil has been effective in reducing the longitudinal instability. Another parameter that was investigated is the middle width of the angular hydrofoil. By comparing the three sizes of 8, 16 and 24 cm for the middle width of the stingray type hydrofoil, it was found that at a speed of 30 knots and in a time of 3 seconds, the range of motion of the pitch diagram has decreased by 63.3, 68.3 and 63.3% respectively compared to the state without hydrofoil. Although the average ratio of 16 cm shows better efficiency; but in general, the change of this parameter did not make a significant difference in the reduction of the longitudinal instability of the boat, and there was a slight difference in the range of the pitch and heave motions between the three cases.

This study simulated long-term sediment transport patterns and shoreline evolutions of Zarabad fishery harbor in Sistan and Baluchestan province using Delft3D software. The model was first calibrated utilizing available field wave and tide data from March 2004 to October 2005 before constructing a groin for the Zarabad port. Calibration parameters included wave and current-related parameters, bed friction, and roughness coefficient. Subsequently, the model was validated using available field data from February 2013 to October 2015, after construction of the groin. With a validated model, the long-term sediment transport was simulated over ten years from October 2014 to October 2024, using input data reduction and coastal 2DH model method. The results indicated that the sediment transport has been effectively reduced. In addition, the progress of the coastline and the change of shoreline angle behind the eastern breakwater of Zarabad port created a stable state. Furthermore, the predicted shoreline evolution suggests minimal sediment transport concerns over the next ten years. Therefore, sediment transport will not pose a significant problem.

With the development of AUVs, accurate calculation of hydrodynamic coefficients in the equations of motion of these vehicles increased significantly, and accurate calculation of hydrodynamic coefficients for predicting maneuverability, dynamic stability, and controller design is of particular importance. One of the effective parameters in the uncertainty of the results obtained from the regression methods for calculating the hydrodynamic coefficients is the clearance between the control surfaces and the body. In this article, to investigate the effect of the clearance on some linear hydrodynamic coefficients of the maneuver, a numerical analysis has been performed on the Suboff benchmark model, and the damping and added mass coefficients have been studied using static and dynamic tests. The vertical clearance of the control surfaces from the body is considered a variable and the analysis has been done at several clearance from the body. The numerical results, after validating with the model results, showed that the hydrodynamic coefficients become independent of the distance between the body and the control surfaces from the distance of 0.06 meters. Also, in the static drift test, with the increase in the clearance of the control surfaces from the body, the hydrodynamic coefficient related to the sway force and the hydrodynamic coefficient related to the yaw moment decrease. However, in the pure sway test, with the increase in the clearance, the hydrodynamic coefficient related to the sway force decreases, and the hydrodynamic coefficient related to the yaw moment first decreases and then increases.

One of the most important issues in designing a submarine is calculating its resistance and power. It is still a scientific challenge to calculate and generalize the results from a scaled model to the main vessel. In this study, the effect of the scale in a numerical method on the resistance coefficients of a submarine, including the total, friction and pressure resistance coefficients, has been investigated by numerical simulation method. Also, the accuracy of the results of the existing empirical relationships for calculating submarine resistance coefficients has been evaluated. The SUBOFF submarine model was used to conduct studies. The results show that the existing empirical relationships enable the calculation of the friction coefficient with an error of less than 10%, the pressure coefficient with an error of less than 30%, and the total drag coefficient with an error of less than 8.5%.

In this article, the role of moorings in the heave and pitch movements of the semi-submersible platform is investigated due to the increasing use of these platforms in deep waters. Improper movements of the platforms can cause instability of the structure and disrupt its performance. In order to analyze the movements of the platform, taking into account the role of moorings, the numerical simulation of Amir-kabir platform with different mooring modes has been performed as a nonlinear analysis in the time domain using Orca-flex software. By examining 52 different mooring compound models in three stages, 5 mooring compound models have been introduced in terms of the motion response of the semi-submersible platform in the heave and pitch. The results show that the independent combination of catenary and tensile moorings, in addition to the overall reduction of the length of the moorings, causes optimal behavior in the heave and pitch movements of the semi-submersible platform.

The Toe is a structure with the function of supporting the armor layer and preventing scouring of the substrate. Due to the location of the toe under water, the safe design of this layer is important. Experiments have been conducted in order to investigate the parameters of wave period, water depth, nominal stone diameter, toe width and berm height. Based on the results of the experiments, the wave period has a great effect on the stability of the Toe. In the next step, the depth of the water above the Toe is important in the amount of damage caused to the Toe. By increasing the nominal diameter of the Toe stone, no significant reduction in the amount of damage was observed. Decreasing the front slope of the toe from 1:1.5 to 1:3 was a solution to achieve stability. By reducing the front slope, the overall width of the berm increases; Therefore, it was decided to implement the Toe with a front slope of 1:1.5 and the width of the berm to be two nominal diameters. In this case, due to the collision of waves; The front slope of the toe is changed and becomes stable.