Showing 27 results for Ship
Hamid Zeraatgar, Mesbah Saybani,
Volume 1, Issue 1 (9-2004)
Abstract
Dhow (LanJ) is a wooden vessel which is traditionally operating in Persian Gulf and Oman Sea. In contrast of its frequent lost, ordinary people believe that it has very good behavior at waves. In this study, by means of seakeeping computer software, authors have calculated its dynamic behavior in waves. Comparison between dhow performances in waves against seakeeping criteria has been made. Then, its operable sea waves is concluded. Then the reason behind people believe has been discussed, thoroughly. The end result is that the typical wooden dhow may withstand in waves of significant wave height of not more than 1 meter.
Volker Bertram,
Volume 1, Issue 1 (9-2004)
Abstract
In designing for ship production, the production method should be considered and it’s possible to reduce the manufacturing cost in designing procedure. A review of background of ship design that had minimized production costs, shows the principles and problems of these methods. Modern designing methods for manufacturing, considers hydrodynamic efficiency and less manufacturing cost. Quantifying the results of required designing changes in modern methods, is only possible with Bottom-Up method which is described in this paper. This method needs sufficient data and information of production process.
Hamid Zeraatgar, Faranak Abed Hossein Nezhad,
Volume 2, Issue 1 (3-2006)
Abstract
The sea wave causes excess resistance which is out of scope of calm water resistance. The total wave force in horizontal plane is divided into “Added Resistance” and “Drift Force”. In this study, based on Gerritsma and Beuckelman[3] hypothesis a computer program has been developed for calculation of added resistance and drift force at various ship speeds and various heading angles in oblique seas. This program calculates wave force both in regular and irregular waves. After validation of the program, effects of different parameters on wave force imposed on vessel have been studied.
Gholamreza Rashed, Rahmatollah Ghajar, Seyed Jalalodin Hashemi,
Volume 3, Issue 5 (3-2007)
Abstract
During the offshore drilling operations by drillships or semisubmersible vessels the drillstring in its first drilljoint to the Kelly suffers bending due to float vessel roll or pitch. The cyclic bending stress at any point along the drillstring, is a function of the roll or pitch angle, Kelly position in bushing, and hookload. The cumulative fatigue damage of the drillpipe due to cyclic stresses near the drillpipe connection to Kelly has been calculated in this paper. The effects of the cyclic stress amplitude variation are also taken into account. Then five multiaxial fatigue models are evaluated under variable amplitude loading (similar to drillpipe loading) conditions. Comparing the results of the five models predictions by the muliaxial fatigue tests experimental data under variable amplitude axial-torsional loading, show that the combined critical plane and energy models predict the fatigue life better than the others. It works much better for variable amplitude loading than the existing models.
Firouz Bakhtiari Nejed, Mehdi Jabarzadeh,
Volume 4, Issue 6 (9-2007)
Abstract
Transferring patients under critical conditions such as heart attack, stroke or transient ischemic attack (TIA), and head and backbones injuries is very important, specially transportation on sea because of high level of vibration of ship due to the sea waves is very critical. Many injured persons who work on ships or offshore platform with specialist hospitals are under critical dangers of their life because of their transportation with sea vehicles. In this paper a dynamic analysis is presented to investigate the effect of sea wave on the peak acceleration of critically seek persons during transporting them on a sea. With this information equipments can be designed and installed to transfer patients safer and healthier on sea.
Rooholah Hadipour Goudarzi, Ahmad Rahbar Ranji,
Volume 4, Issue 7 (6-2008)
Abstract
Fatigue analysis and estimation of safe life of structures that are subjected to cyclic loadings, such as ships and offshore structures is one of the most important steps of structural design. Fatigue failure in the form of crack will start from details and propagate in structure. In steel structures these cracks will started from welds. Most of the methods for fatigue life assessment in welded connections are based on stress values at critical points, called "hot spot". Determination of hot spot stress is done by finite element analysis with using some empirical relations, which is expected to be the most practical method. These empirical relations are mostly based on linearization of stress through the thickness or extrapolating the stress to the hot spot locations. In this paper, different methods are reviewed for the evaluation of hot spot stress at a typical ship structural detail by finite element analysis and the results are compared with an experimental data. Accuracy and sensitivity of hot spot stress to finite element meshing is investigated, and the best method for calculation of hot-spot stress based on required accuracy, time and money is proposed.
Javad Daraii, Ahmad Reza Mostafa Gharabaghi, Mohammad Reza Chenaghlou,
Volume 5, Issue 9 (9-2009)
Abstract
In this paper, the behavior of a typical jack-up platform under accidental loading of ship collision was investigated. The studied platform was modeled using ANSYS software and analyzed dynamically under ship impact. The platform was also analyzed dynamically under secondary ship impact. The initial collision results showed that the main energy absorption mechanism in impact to jack-up platform is overall deformation of platform it also shown that environmental preloading in some cases causes yielding or fracture of impacted member. The subsequent collision analysis showed that leg chords can resist to a subsequent impact and the platform in both first and second impacts has local damage such as indentation of the chord wall but the rest of the structure remains almost intact. Finally, the platform was modeled in damaged condition and analyzed dynamically under one-year environmental loads and the value of maximum stress and probability of platform failure was investigated. In addition, the value of stress and displacement in the intact and damaged platform has been compared and the results are analyzed.
Hamed Haghighi, Mohammad Reza Jahed-Motlagh,
Volume 8, Issue 15 (10-2012)
Abstract
For stabilization of zero speed ships active anti roll tanks and gyro stabilizers are used. Because of anti roll tank limitations on working frequencies gyro stabilizers are proposed. A nonlinear model for ship is used to simulate hydrodynamic forces. Wave’s disturbances are considered as non-parametric uncertainty. A sliding mode controller is used for roll stabilizing. A nonlinear h infinity controller is designed to reduce the disturbance effects on the ship. The designed sliding mode controller uses more control energy from h infinity controller. Instead roll reduction of the sliding mode controller is grater from the other one. The main concept of the used model in this article was taken from an authority that ship model data estimated from real ship with Halcyon gyro actuator. Roll reduction increases by applying designed controllers in wide range of sea states. In addition nonlinear effects intended in this article. Simulation results based on Jonswap wave spectrum demonstrates the performance of robust system in confrontation with wave perturbations.
Mohammad Saeid Seif, Sirus Zamani Rad,
Volume 9, Issue 17 (9-2013)
Abstract
In the present study the slamming problem is simulated by numerical methods for investigating the hydroelastic effect during the slamming process. Slamming with two viewpoints of rigid and elastic structures (hydroelastic effect) had been modeled. Due to high impact speed of slamming, inertial and kinematic effects are quite evident in hydroelastic model. The results showed that considering hydroelastic effect especially in high impact speeds reduces the structural deformations and stresses in comparison with statically analysis. The effect of hydroelasticity is studied as a function of different parameters such as boundary condition, plate properties, wedge dead rise angle and impact velocity. Comparison of results for aluminum and steel plate showed that plate density and added mass has a determinant role in hydroelasticity. Finally hydroelasticity effect investigated for one high speed craft and observed that in direct design hydroelasticity effect reduces the plate thickness.
Sajad Hajizadeh, Mohammad Saeid Seif, Hamid Mehdigholi,
Volume 11, Issue 21 (9-2015)
Abstract
Ship maneuvering performance evaluation is essential for primary design stages. Ship maneuvering calculations, horizontal plane motion control and development of maneuvering simulators need a mathematical description of ship maneuvering. In the recent years, different mathematical models are suggested for maneuvering of displacement vessels that are capable of estimation of vessel maneuvers with acceptable precision. These mathematical models are based on determined hydrodynamic coefficients and their accuracy depends on the known coefficients used to solve the mathematical model. System identification methods are developed to calculate these coefficients utilizing input and output data obtained from different sources. In this paper different maneuvers are executed through free running model tests of a container ship. The hydrodynamic coefficients in the mathematical model are determined by the Extended Kalman filter method. Then the mathematical model is solved and different maneuvers are simulated by coefficients calculated from the experiments. Simulations are validated by model tests. Finally the influence of rudder angle and advance speed on turning circle is studied. The mathematical model and hydrodynamic coefficients presented in this paper can be applied for optimization of ship maneuvering performance and course control purposes.
Asghar Mahdian, Mohammad Hadi Mortazavi Manesh, Behrooz Shahriari,
Volume 12, Issue 24 (1-2017)
Abstract
Launching pads are among the essential elements of missiles and their main function is to prepare missiles for launch. Tower launchers dimension and configuration depend on effective loads, dimension and weight of the missile. In the majority of tower launchers, two bars connected to each other with crossbar connectors are considered to be the basic parts. Therefore, it is essential to calculate accelerations (forces) applied from ship to structure of the tower launcher. Space frame element is used for designing and a finite element code has been written in MATLAB Software to calculate stress and deformities of the structure. A Genetic algorithm which is codified in MATLAB has been used for optimization. All of the written codes have been compared to experimental data and results confirm the accuracy and exactness of the outcome. In this design weight of the tower launcher was the target equation, displacement and yield stress were constraints and geometrical specifications of the cross section were variables.
Ehsan Esmailian, Behzad Farzanegan, Hamid Malekizadeh, Hassan Ghassemi, Manouchehr Fadavi Ardestani, Mohammad Bagher Menhaj,
Volume 13, Issue 25 (9-2017)
Abstract
In this paper, the main goal is to reduce the heave motion between a surface effect ship (SES) and a wind turbine in order to safely transfer equipment and person to SES. For this purpose, an LQR control system is designed to damp the vertical motion of the surface effect ship in critical sea states including high-frequency and high amplitude regular waves as well as high frequency irregular waves. The simulation results show the high quality of the system control in the studied sea condition. A comparative analysis of LQR and PID approaches demonstrate the high performance of the new designed control system. The proposed controller outperforms the traditional PD.
Siyavash Filom, Roozbeh Panahi,
Volume 14, Issue 27 (7-2018)
Abstract
Marine transportation industry, as the main basis of world trade, is of great importance. Here, collision and grounding are the most frequent ones, threatening the industry. To study collision accident and assessment of its occurrence risk, we need to identify ship routes, in which Automatic Identification Systems introduces the best tool. Here, based on the concept of safety domain applied on traffic, high collision concentration locations are identified. Accordingly, probability of collision occurrence in the high risk locations is examined based on the Bayesian network. This study just show sample result of implementing new approaches in accident analysis, which has no previous record in our country.
Mohammad Said Shamshiri, Mohammad Moonesun,
Volume 17, Issue 33 (5-2021)
Abstract
In commercial ships, wave making resistance is a part of total resistance which to reduce it, a bulbous bow is added to the ship bow. To investigate the effect of bulbous bow on total resistance, a container ship model is simulated with and without the bulbous bow at three Froude Numbers: 0.22, 0.26 and 0.30. Initially, numerical simulation validation has been done, which shows that the results are valid. According to the results, the bulbous bow increases frictional resistance by a maximum of 2%. In these three Froude Numbers, the pressure resistance decreases by 17.1, 31.6 and 25.9%, respectively. At three mentioned Froude Numbers, bulbous bow decreases total resistance by 1.8, 8.9 and 13.3% respectively. In addition, the bulbous bow reduced the height of the wave made on the hull and the free surface. Bulbous bow causes positive effects on the hydrodynamic behavior of the vessel, which increase with increasing Froude Number.
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.
Majid Norouzi Keshtan, Mehdi Raghebi, Majid Malek Jafarian,
Volume 18, Issue 35 (5-2022)
Abstract
One of the most important issues in the design of a vessel structure is the vibrations of the structure and its effect on the comfort of the crew and the life of the equipment. The most important factor about the comfort of the crew in a vessel is the range of free and forced vibrations under various internal and external factors in the structure of the vessel. One of the serious factors in stimulation of vibrations in the hull vessel is the propeller. Excessive vibrations as well as the being the structure in the frequency range of propeller excitation, cause fatigue, components exhaustion, and also the resonance phenomenon. Resonance and vibration of the components are the structural design challenges, so in this paper, vibrations caused by a five-bladed propeller KP505 excitation were investigated using numerical simulation on a container vessel (KCS). First, the free vibrations of the hull vessel in wet mode were investigated. Then, to investigate the forced vibrations caused by the propeller excitation, the pressure distribution on the hull in self-propulsion mode was obtained from the numerical solution of the fluid flow by computational fluid dynamics. To validate the results, the natural frequencies obtained in free vibrations were compared with empirical formulas. Comparing the values of the first, second and, third bending frequencies with the empirical values, showed that the analysis error was 5.5, 26, and 26.6, respectively, which explain the accuracy of the analysis. Comparing the results of forced vibrations with the standard allowable range, it was shown that the vibrations are within the allowable range. Also, the structure has not being within the range of the excitation frequency of the propeller. As a result, the resonance phenomenon has not occurred.
Zahra Bigharaz, Sajad Hajizadeh, Hassan Abyn,
Volume 18, Issue 35 (5-2022)
Abstract
In this paper, the aim is to analyze the interaction of a commercial container vessel with irregular surface water waves by computational fluid dynamics and also to calculate the marine parameters of this structure, namely the response amplitude (RAO) operator, the kinetic response spectrum in the motion of the structure. Analysis tool in this research is STAR CCM + software based on computational fluid dynamics, which is one of the most powerful software in performing simulation and numerical analysis for the above problem. In this paper, after reviewing and analyzing the validation of the numerical model and analysis tools, the various marine and dynamic parameters for a commercial container vessel in the superficial state in different directions of irregular wave collision to the vessel are investigated.
Moein Bozorg Zadeh, Mohammad Reza Zareei,
Volume 18, Issue 36 (12-2022)
Abstract
The main purpose of this paper is to investigate the stochastic roll motion of a ship in irregular waves. To achieve this goal, the differential equation of ship roll motion roll in longitudinal waves with respect to nonlinear damping and restoring arm has been created. Due to the stochastic nature of sea waves, the wave excitation force is generated through stochastic excitation using effective wave theory. To achieve the ship roll motion response, the stochastic differential equation of the roll is converted to the Ito’s stochastic differential equation form. The generated equation is solved several times using the Monte Carlo process to statistically evaluate the roll motion response. Finally, the probability distribution function of the ship's roll motion at irregular waves is calculated for the C11 container ship as a sample ship. Using these results, a better approximation of the maximum angle of roll motion of a ship in irregular waves can be obtained.
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.
, Mehriar Alimohammadi, , ,
Volume 19, Issue 39 (9-2023)
Abstract
Today, navigation systems have become an integral part of the control of the floating unit. Today, ECDIS navigation system is considered as the most important navigation assistance system. The presence of electronic maps in the memory of the Ecdys device, along with the processing ability of this device, has caused the officer guarding the command bridge to navigate the ocean routes without any worries. One of the disadvantages of conventional navigation systems (such as Ecdis and integrated navigation system) is the lack of meteorological data in these systems.In this study, a navigation system has been developed that has calculated the sea route according to the turning points. And performs estimated navigation. In this system, climatic data of wind, temperature, pressure are calculated on estimated points over a period of forty years. Calculating climatic data on estimated points can help navigating officers decide on a seafaring route.
