Showing 6 results for ebrahimi
Abouzar Ebrahimi, Mohammad Saeed Seif, Ali Nouri-Borujerdi,
Volume 15, Issue 30 (1-2020)
Abstract
The noise emitted by ships is one of the most important noises in ocean and the propeller noise is one of the major components of the ship noise. Measuring the propeller noise in laboratory despite the high accuracy and good reliability, costs a lot, has some complexities and is very time consuming. For this reason, the calculation of propeller noise using numerical methods has been considered in recent years. In this study, the noise of propeller in non-cavitating conditions is calculated by solving the Ffowcs Williams-Hawkings (FW-H) equations. A software for numerical calculation of propeller noise, based on FW-H equations, is developed and results are validated by experimental results. This study show that the results of the FW-H noise code have also good agreement with experimental data.
Mahdi Ebrahimi Mavini, Mahdi Shafieefar,
Volume 18, Issue 35 (5-2022)
Abstract
Shipping route analysis for maritime traffic management depends on equipments to collect information about ship's behavior. For this purpose, the most reliable data is the Automatic Identification System (AIS) data. The complexity and high volume of AIS data enhances traditional surveillance operations and makes maritime traffic analysis more difficult. Therefore, an unsupervised approach is desirable for the effective conversion of raw AIS data into regular shipping route patterns. The proposed model for the shipping route analysis consists of four sections: AIS data preprocessing, structural similarity measurement, shipping route clustering and representative trajectory extraction. Experimental evaluation of the proposed model with real AIS data from the studied area shows that it has performed well visually and the expected result has been achieved. The results will contribute to better understanding of shipping route patterns and help maritime authorities in sustainable management of maritime traffic.
Abouzar Ebrahimi,
Volume 18, Issue 37 (2-2023)
Abstract
Today, marine transportation has a significant role in global trade. The characteristics of the containerized shipping have made the number of container ships grow every day and made significant improvements in the construction and operation of these ships.
In this research, the main dimensions of a container ship are optimized according to different objectives. This optimization aims to reduce both hydrodynamic resistance and the steel weight of the ship. Initially, the information needed for optimization is specified, and the problem's constraints are determined. Then, the optimization is done using the optimization tool of the genetic algorithm toolbox in Matlab software. Also, a software code is developed, and the optimization case is done using this code. The results show that the genetic algorithm can be used as a practical tool for optimizing the dimensions of the ships.
محمدرضا Negahdari, Atallah Gharechahi, Abuzar Ebrahimi, Mohamadreza Babaei,
Volume 20, Issue 42 (4-2024)
Abstract
Several thousand traditional Iranian floating boats of the launch in the Persian Gulf and Oman Sea, which play an important role in the life and livelihood of many people in this coastal area. The construction of traditional vessels is more based on experience and despite modern commercial vessels, they are not built based on advanced engineering calculations, complex computer modeling and laboratory tests;
The construction of traditional vessels is more based on experience and unlike modern commercial vessels, they are not built based on advanced engineering calculations, complex computer modeling and laboratory tests; Therefore, optimizing the hull form and reducing their fuel consumption is important, and if it is possible to increase the efficiency of these types of vessels, this will be a big step towards increasing the efficiency of traditional vessels.
In this research, by considering the sample floating body form and presenting several modified body forms, with numerical modeling in STAR CCM+ software, the optimal body form with the least hydrodynamic resistance was determined.
The results show that the resistance of the vessel is reduced by 10% by modifying the shape of the stern, and this value reaches about 20% by modifying the shape of the chest.Due to the modification of the form of the hull, we see a 13% reduction in fuel consumption, which is the same amount as by modifying the shape of the chest. It reaches about 30%.
Leila Ranjbar Najaf Abad, Mohammad Reza Zareei, Aboozar Ebrahimi,
Volume 20, Issue 44 (10-2024)
Abstract
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.
Abouzar Ebrahimi, Hassan Sirousi, Mohammad Reza Negahdari, Mohammad Reza Zarei,
Volume 21, Issue 45 (3-2025)
Abstract
Dhow vessels are traditional vessels used for fishing or cargo transportation on short and medium routes, and according to statistics, more than 4,000 of these vessels operate in Iranian ports. These vessels use diesel engines and fixed-pitch propellers for propulsion. The design and selection of the propulsion system of these vessels is done entirely empirically, and in most cases, even the resistance and hull form of these vessels are not considered in the design of the propulsion system and propeller, which causes the propulsion system to not operating with optimum efficiency. In this paper, initially, numerical modeling of the resistance of a dhow vessel was performed using the computational fluid dynamics method. Then, by performing a self-propulsion test using the numerical method, the hydrodynamic coefficients of the hull and propeller of the vessel were calculated. The results of this research show that the thrust deduction factor for this vessel is 0.291 and the wake coefficient of a hull is 0.18. Further research on the hydrodynamics of this vessel can help in selecting a propeller and propulsion system with better efficiency and lower fuel consumption.
