نشریه مهندسی دریا
پیاپی 44 (پاییز 1403)

Offshore gas pipelines used in the 12th phase of South Pars Project generally have a small pipe (Piggyback Pipeline) mounted on the main pipe. The task of this small pipe is to transfer MEG (anti-corrosion) materials from Onshore to Platform. Because of their small size, Piggyback Pipelines are exposed to the damages caused by being dragged by the anchors of fishing and/or operational vessels. The main objective of this research is to assess the pressure capacity of small pipelines (prior to becoming torn) and to investigate the ultimate capacity before rupture.To solve the problem, a three dimensional non-linear dynamic model of the real sample is simulated in ABAQUS software. 27 models are analyzed, where an anchor is hooked to a pipeline and drags it vertically to a specific height and then releases it. Eventually an equation is presented to determine the relation between pipeline remaining capacity and vertical displacement.

Mooring lines are the main components in the stability of floating structures in the sea. Clump weights and submerged buoys are two types of devices designed to increase the effectiveness of mooring lines. In this article, the effect of clump weights on the motions of a semi-submersible offshore structure has been investigated considering the environmental conditions of the Persian Gulf. For this purpose, the restoring force of the mooring line in calm water conditions, the motions of the floating structure and the top tension of one of its mooring lines in an irregular wave with a return period of 100 years have been investigated. In general, adding clump weights will reduce the movements of the floating structure and increase the tension of the moorings. These two different effects show that the addition of clump weights needs further investigation.

Propellers are considered as the main propellants of vessels and from the beginning until now, engineers have always been trying to increase the performance of propellers, including their thrust and efficiency. Considering that new propellers called Sharrow Propeller have been introduced, The present study is an attempt to design, model and test this propeller. Considering that there is no information available on the performance characteristics of these propellers, including thrust and efficiency; Finally, it should be compared with the propellers of the B-series and the standard series of high-speed vessel with the same diameter and pitch to make sure that the geometry of the modeled propeller can be used as a vessel propeller. For this purpose, modeling was done using SolidWorks software and two propellers with different geometric parameters but with the same diameter and pitch were modeled. To check the performance of the propeller, an open water test was taken in the simulation software (Star CCM +) and data such as the thrust and torque produced by the propeller and the efficiency of the propeller were extracted and these characteries compared with the other mentioned propellers. The result was that Sharrow propeller 1 has much higher thrust and lower efficiency and Sharrow propeller 2 has less thrust but better efficiency and in general both propellers had better thrust than the two standard propellers.

With the advancement of machine learning and algorithms and the establishment of research sites in coastal areas, valuable information has become available that can be utilized in the development of coastal engineering. This study attempts to examine the coastal area of Narrabeen, Australia with a new approach using machine learning. One of the most important factors in understanding coastal behavior is its self-reconstruction under non-stormy and long-term conditions. Recognizing and describing the phenomena affecting the equilibrium performance of the coast is also of great significance. After sorting the initial data, the best behavioral pattern was examined using a regression decision tree algorithm by evaluating the combination of error and model complexity, and the most appropriate scenarios were selected to describe the influencing parameters on objective functions (shoreline changes and coastal platform geometry). Accordingly, to describe shoreline changes, ∆BW, Berm Slope, SLR, and ζ were considered with values of R2=82% and RMSE=3.489 meters; to describe changes in the elevation of the coastal platform, BC Height, ∆x Shoreline, ∆x BC, and P were considered with values of R2=48% and RMSE=0.397 meters; and to describe the horizontal position of the coastal platform crest, BW, Berm Slope, ∆y BC, BC Height, E, and SLR were considered with values of R2=67% and RMSE=9.807 meters. According to the results of the description and the impact of hydrodynamic and morphodynamic phenomena using the regression decision tree method and the obtained error values ​​and coefficient of determination, it can be stated that this method is suitable and reliable for understanding the governing phenomena on coastal features; Based on this, in order to investigate the morphodynamic changes of the coastal platform and to understand its equilibrium behavior, its geometric shape and initial slope play a significant role.

Calculation of the hull resistance is one of the most important parts in the design process. One of the conventional methods for calculating the resistance of the vessel is the experimental tests of the towing tank. The use of towing tank tests requires the construction of an accurate model of the vessel. In this paper, computational fluid dynamics simulation was performed on a military vessel, using Ansys Fluent software, and compared with the results of the towing tank test, which was carried out in this research. To perform the towing tank test, first the geometry of the vessel was modeled in CATIA software, then it was constructed using a 3D printer. Comparing the experimental and numerical resistance results shows that there is a good agreement between the numerical and experimental results. Therefore, it can be concluded that the developed computational fluid dynamics model has a correct performance. Then the simulated model was developed along with Sonar dome. The results show that the presence of Sonar dome causes the hull resistance to increase linearly at speeds of more than 8.74 knots.

In recent decades, the pile-to-sleeve grouted connections has gained significant popularity. Studies have shown that the failure mode of concrete in this connection is shear failure. Considering the failure modes of the connection, it is predicted that improving the performance of the concrete will also enhance the ultimate strength and ductility of the connection. In this research, the performance of the concrete was improved using steel fibers. For this purpose, 1.5% of straight steel fibers have been used in concrete to improve flexural strength and compressive strength. The results demonstrated that the use of 1.5% steel fibers improved the ultimate strength of the connection by up to 22% and also enhanced its ductility. Furthermore, the experimental results were compared with the DNV, API, and HSE standards, with the DNV standard showing the highest consistency with the experimental results.

The wet surface caused by water spray is one of the factors of creating resistance in high-speed floats. On this basis, the effect of the sprayer appendage in reducing the buoyancy resistance has been investigated and the effect of its geometric characteristics, including the bottom angle, width and number of spray rails, on the hydrodynamic components and the buoyancy resistance has been investigated using a numerical method. The results of numerical simulations have been validated with similar laboratory data for the float without appendages. Taguchi's method has proposed 18 test designs, that each test design is simulated in two general positions of spray rails (in line with the chine and parallel to the keel) for the transverse landing number of 1.99 and 3.33. The results show that the two geometric characteristics of the bottom angle and the number of sprays have a direct relationship with the increase in the landing number of the float, so that in the flight mode, the positive bottom angle with the highest number of rail sprays has caused a greater decrease in the resistance of the float, in addition to the optimal value of the width geometric characteristic The rail spray has decreased with the increase of Froud number, as a result, the width of the rail spray has an opposite relationship with the increase of Froud number. Also, spray rails parallel to the keel have a more effective role in reducing floating resistance than spray rails in line with the chine. The amount of trim and rise of the float for the spray of rails parallel to the keel is less compared to the spray of rails parallel to the chine, which reduces the possibility of longitudinal porpoising instability in the float.

Given the increase in marine aquaculture, designing safe and efficient structures for this purpose is important. The triangular frame in vessel-shaped floating fish farming platforms, by being located at the point of wave impact with the cage, causes wave breaking and reduces its energy, thereby reducing vertical accelerations and reducing the tension force of the mooring lines and creating a safer environment than high-density polyethylene cages. In this research, the dynamic of a sample of these cages with a single mooring system has been studied in marine water conditions near Chabahar Port using the Orcaflex software. The numerical model has first been validated with experimental results. The results show that the vertical accelerations of the main platform are significantly lower than the triangular platform located in front of the cage. Increasing the number of floating square platforms reduces the vertical acceleration of the platforms. The maximum vertical acceleration applied to the platform for local waves in Chabahar is 0.9 m/s2 when using a square platform and 0.35 m/s2 when using two square platforms. Also, the Root Mean Square (RMS) values ​​of the vertical acceleration of the cages are 0.21 and 0.13 m/s2, respectively. The low value of vertical accelerations provides a calm environment for activity in the cage and minimizes stress and emotional movements of aquatic animals inside the cage, which is important in the economic efficiency of the cage. Considering the focus of the research on the marine conditions of Chabahar Port, these cages are recommended for installation in the coastal waters of southern Iran

The arrival of unmanned ships will definitely increase the safety of navigation, and as a result, various maritime accidents will decrease dramatically. In this research, the existing infrastructures of Imam Khomeini port for accepting unmanned ships are examined in order to determine the limits and capacities of this port to accept these types of ships. The present research is of the type of applied purpose and in terms of its nature, it is mixed exploratory. Using library studies, 12 factors influencing the adoption of unmanned vessels were identified and examined by 90 maritime and port experts of Imam Khomeini Port Complex. Preliminary analysis using binomial test has revealed 7 limitations and 5 capacities of this port. Hierarchical technique was used in the prioritization section. The results of which showed that among the factors of the capacity group, the factor of the existence of competent operators for navigation and management of these ships with a score of 0.238, and among the factors of the restriction group, the factor of the existence of a competent judicial authority in connection with the legal issues of unmanned ships with a score of 0.267 the most important factors were identified.

The purpose of this article is the numerical hydro acoustic analysis of non-cavitating radiated noise in different geometric pitches using the computational fluid dynamics method. The geometric pitch of the propeller is one of the most important influencing parameters in the design of marine propellers, Therefore, in this article, a sample of the standard underwater propeller series with different number of blades and different geometric pitches has been used and the data related to the vorticity field and the radiated noise level have been extracted and studied. In this numerical analysis, the DES turbulence model has been used, which has solutions with acceptable accuracy in the noise subject with an average grid number, compared to the large eddies method. In order to increase the accuracy of the numerical data, the grid generated around the propeller in the areas of the leading edge, trailing edge, tips of the blades and in the region of the downstream, has been produced with a higher grid density. According to the obtained results, by increasing the geometric pitch angle of the propeller blade, the static pressure on the pressure side of the blade increases, and the vortices caused by the boss and hub become longer, and the amount of change in the sound pressure level in the axial direction at low frequencies is less than 5 dB, but at high frequencies it is oscillating and the changes are more noticeable. The highest amount of change in the sound pressure level in terms of pitch is in the direction perpendicular to the flow direction and reaches up to about 40 db.