M. Soltaninejad; F. Azarsina; A.H. Javid
Volume 5, Issue 2 , June 2015, , Pages 65-75
Abstract
Many existing phenomena in nature are considered new design ideas in various fields of industry. Bionics is the application of biological methods and systems found in nature to the study and design of engineering systems and modern technology. By performing bionic review, the researchers found the penguins ...
Read More
Many existing phenomena in nature are considered new design ideas in various fields of industry. Bionics is the application of biological methods and systems found in nature to the study and design of engineering systems and modern technology. By performing bionic review, the researchers found the penguins by delivering air locked under their wings and creating air bubbles, the drag significantly reduces. This motivates to study this factor in the marine industry by researchers and scientists. The overall drag of a marine vessel is directly proportional to the frictional drag. The reduction of frictional drag can be achieved by creating an air layer between vessel`s hull and flow around it. Creation of a cavity and cross channel of air can be easily just in order to reduce hull drag, while the air from a hole is injecting, the drag reduction up to 20 percent might be achieved. Experiments indicate that the pattern of wave drag reduces due to the air using and changes in pressure fields. In this research, by the use of theoretical relationships and the results of experiments, frictional drag reduction with different methods of air injection was investigated and then by the use of numerical software simulation (ANSYS-fluid flow), air injection on the floating model. The achieved results for drag reduction with decrease of wetted surface area at speeds of 4, 6 and 8 m/s are presented. By comparing the results of experiments(Harley high speed craft model) with software analysis and software simulation was validated. Due to high cost of manufacturing a model with air injection accessories and towing tank tests, with the acceptable precision results of this research, numerical software simulation (ANSYS-Fluid Flow) is more quick and efficient.
S.M. Sajadi; F. Azarsina
Volume 5, Issue 2 , June 2015, , Pages 99-113
Abstract
Given the worldwide industry progress in the construction of massive concrete structures, it would be a good idea to use concrete gravity base structures (GBS).In this regard, better understanding of thesestructuresregardingtheiradvantages and disadvantages in offshore areas seems necessary.The present ...
Read More
Given the worldwide industry progress in the construction of massive concrete structures, it would be a good idea to use concrete gravity base structures (GBS).In this regard, better understanding of thesestructuresregardingtheiradvantages and disadvantages in offshore areas seems necessary.The present study employed MacCammy-Fuchs method, which is based on the size of the structure to the wavelength and the range of Keulegan-Carpenter number; in this method, diffraction theory and Bessel functions are used to compute the velocity potential function and consequently compute the hydrodynamic pressure on the components of the structure.The results of this study with regard to the harmonic dynamic response of the rocking motion of the platform under wave loads revealed that (i) the computed torque value converges to a definite value by decreasing the size of elements,and (ii) Bessel functions can be represented by amplitude and phase functions which have identical performance.The time-history response of the gravitybase structure, and the amplitudechanges of rocking motion relative to frequency and the height of the waves are other results obtained in this study. Finally, the stability index of the GBS shows that the platform is within safe limits.
M. Abdoli; F. Azarsina; M.H. Givian Rad
Volume 5, Issue 1 , January 2015, , Pages 15-21
Abstract
Today due to increasing development and importance of petroleum activities andmarine transport as well as due to the mining of seabed, building activities such as construction of docks, platforms and structures as those in coastal areas and oceans has increased significantly. Concrete strength as one ...
Read More
Today due to increasing development and importance of petroleum activities andmarine transport as well as due to the mining of seabed, building activities such as construction of docks, platforms and structures as those in coastal areas and oceans has increased significantly. Concrete strength as one of the most important necessary parameters for designing, depends on many factors such as mixture plan ofconcrete, concrete forming materials, and curing conditions. Since many of these factors are uncertain and cannot have a specific and accurate formulation for concrete strength, therefore, applying a pre-set mathematical formula roughly predicts the strength of concrete. Inthis research,Genetic algorithm optimization for concrete mix plan is presented. Genetic algorithms are searching algorithms that have been established based on mechanism of natural selection and evolution. These algorithms select the most appropriate strings from organized random data.In every generation, a new group of strings by using the best parts of previous and new accidental sequencewill happen to get a proper answer.First a suitable encoding (or representation) must be found for the problem. The most common representation method of chromosomes in genetic algorithms is in the form of binary strings which is the method used in this study. By iteratingthe computation of marine concrete generation, optimized mix concrete design is achieved.Accordingly, with more detailed information of marine-grade concrete and application of genetic algorithm based on generational leap it can be expected that a new generation of marine concrete will be recoverable
M. Atashrazm Jirande; F. Azarsina; M.S. Seif
Volume 5, Issue 1 , January 2015, , Pages 49-54
Abstract
During design spiral of a merchant ship or a naval vessel, it is important to perform towing tank tests in order to measure its performance either in calm water maneuvers or in waves for seakeeping performance. Also, to optimize a hydrodynamic design, towing tank tests are advantageous.This article presents ...
Read More
During design spiral of a merchant ship or a naval vessel, it is important to perform towing tank tests in order to measure its performance either in calm water maneuvers or in waves for seakeeping performance. Also, to optimize a hydrodynamic design, towing tank tests are advantageous.This article presents the results of an applied research project. The objective of this project is to design and manufacture a six-componentbalance dynamometer to measure drag force, lateral force, yaw moment, roll moment, andheave and pitch motions. Various stages of this work are presented in the text. The main steps of this activity are to design, prototype,and install strain gauges, and eventuallycalibratethem. Using this procedure, implementing the relevant criteria, the appropriate measures of the strain were selectedmore on the basis of recommendations of professional bodies.Material selection of suitable metal machining and construction work is done. Next, the strain meters were installed onthe balance. After equipment calibration, dynamometer is ready for the ultimate test in towing tank
P. . Atabak; S. Allahyaribeik; F. Azarsina
Volume 4, Issue 2 , June 2014, , Pages 57-64
Abstract
This study aims to examine the performance of the rock materials in the protective layer of rubble-mound breakwaters in southern Iran, from Rostami Port in Bushehr Province to Beris Port in Sistan and Baluchestan Province. Field inspections were carried out on a great number of rubble-mound breakwaters ...
Read More
This study aims to examine the performance of the rock materials in the protective layer of rubble-mound breakwaters in southern Iran, from Rostami Port in Bushehr Province to Beris Port in Sistan and Baluchestan Province. Field inspections were carried out on a great number of rubble-mound breakwaters built in the Persian Gulf and Oman Sea coastal regions to study the protective layer of these breakwaters under ambient conditions as well as to detect the damage caused by factors affecting the failure of the used materials. Subsequently, samples were taken from these rock materials, the specimens were tested in accordance with various quality assessment criteria, and the results were compared with those obtained from international standard tests. The obtained results showed that in most cases, the physical and chemical properties of the local rock materials did not meet standard requirements. As such, these materials are not recommended for use in the construction of breakwaters. In practice, however, these rocks exhibit an acceptable performance in certain cases depending on the position of each rock group in the structure of the breakwater. For this reason, design, construction, and structural considerations can somehow influence the performance of these rock materials in the respective marine structures.
M. Arabi; F. Azarsina
Volume 4, Issue 2 , June 2014, , Pages 65-76
Abstract
Scour is a phenomenon that occurs as a result of natural erosion by ground water flow and transport of seabed material. In this research, scour around the legs of marine structures is simulated using the FLOW3D.V.9.3™ commercial software. The general scour model consists of two components, namely, ...
Read More
Scour is a phenomenon that occurs as a result of natural erosion by ground water flow and transport of seabed material. In this research, scour around the legs of marine structures is simulated using the FLOW3D.V.9.3™ commercial software. The general scour model consists of two components, namely, the lift and thrust forces. The drag force, that is inserted to the structure, is a combination of those two components. As the sediment concentration equals the volume fraction of cohesion, the drag force that determines the rigidity of the sediment model, is activated. Also, as the sediment concentration changes, the viscosity and density of the fluid changes. The numerical model used in this research is similar to the experimental set-up that was performed in a sedimentation tank two meters long, 1.5 m wide and 0.3 m high; while the sandy sediment particle diameter was 0.084 cm. The numerical model implements an RNG turbulence model. After the studies, the time to reach equilibrium in the model was 100 seconds. The relative error between experimental and numerical scour depth is about 10 percent. Scour depth was determined for legs with circular and elliptic as well as for rectangular base shapes with different aspect ratios. Numerical results indicate that the scour depth decreases for the more streamlined elliptic base shapes. Also, the effect of water depth on scour depth, while all other parameters are kept constant, is a linear relationship. Finally, as sediment particle diameter increases, scour depth decreases.
K. Kashizadeh; A. Sarvghad Moghadam; F. Azarsina
Volume 4, Issue 2 , June 2014, , Pages 77-88
Abstract
Offshore structures such as jacket platforms have to inevitably be designed against sever environmental actions. In seismically active areas these structures also become susceptible to earthquake excitations. Strong ground motions recorded in recent earthquakes, including the 1995 Kobe, ...
Read More
Offshore structures such as jacket platforms have to inevitably be designed against sever environmental actions. In seismically active areas these structures also become susceptible to earthquake excitations. Strong ground motions recorded in recent earthquakes, including the 1995 Kobe, Japan, 1999 Chi-chi, Taiwan and 1999 Kocaeli, Turkey earthquakes, revealed that the dynamic motions in near fields are dominated by a large, narrow band, long period pulse caused by rupture directivity effects. Sever damages have been reported with specific bridges, quay walls and multistory buildings near to the shaking fault. It was been noticed that the dynamic characteristics of these structures were close to the characteristics of the rupture directivity and felling pulses.This paper deals with the behavior of existing jacket platform under near field earthquake loading. As an example seismic assessment of the existing 4 legged service platform placed in Persian Gulf is presented. A finite element approach utilizing “Opensees” Standard software has been chosen for this study. A dynamic non-linear direct integration analysis method has been used. Seven, near and far fault records have been examined. In general it has been found that the far field excitations produce more critical consequence for the jacket offshore platform as compared with those from the corresponding near field excitations. It has been noticed that the correspondence between the dominant frequency of the record and the main natural frequency of the jacket structure can be used as a criteria to decide whether a far or near field Earthquake is more critical.
M. Tajari; F. Azarsina; N. Ashrafi Khorasani
Volume 3, Issue 1 , March 2013, , Pages 33-42
Abstract
Explosion and fire on an offshore rig can lead to its minor or complete damage and sinking which means the loss of life or environmental pollution. Hence the use of techniques such as blast wall is crucial to reduce the detrimental effects. These blast walls are designed for explosion wave of length ...
Read More
Explosion and fire on an offshore rig can lead to its minor or complete damage and sinking which means the loss of life or environmental pollution. Hence the use of techniques such as blast wall is crucial to reduce the detrimental effects. These blast walls are designed for explosion wave of length between 0.1 to 1 of load mainly to protect the personnel and critical sections. In this research, the behavior of an offshore platform jacket under blast wave 0.2 and 0.7of load is studied with the blast wall thickness of 1, 5 and 10 mm. The analysis is performed in both plastic and elastic aspects in which we need to consider the nonlinear geometrical and material properties.
F. Azarsina; R. Panahi
Volume 2, Issue 1 , March 2012, , Pages 91-100
Abstract
This paper assesses the design guidelines of different classification codes for the liquefied natural gas carriers considering the effect of liquid sloshing. With regard the increasing importance of LNG carriers in today’s marine transportation, and also considering that the marine accidents involve ...
Read More
This paper assesses the design guidelines of different classification codes for the liquefied natural gas carriers considering the effect of liquid sloshing. With regard the increasing importance of LNG carriers in today’s marine transportation, and also considering that the marine accidents involve significant loss, classification societies by regulating national and international standards aim to minimize the related risks. On the other hand, currently, industrial projects are being run in Iran for the design and construction of LNG carriers, and thus, the study of the liquid sloshing effect on the maneuvering ability of those ships is of prime importance. The present paper compares the approach of different marine classification codes in dealing with the sloshing effect in the design of LNG tanks. The outcome of this research is to introduce an integrated and complete procedure for the sloshing analysis.
F. Azarsina
Volume 1, Issue 1 , December 2011, , Pages 59-68
Abstract
In this paper, a feasibility study of building a Human Powered Hydrofoil (HPH) vessel is reported. Hydrofoil vessels are a well-known class of high-speed crafts. In addition to high-speed operation, the hydrofoils have a reliable maneuvering capability, good stability and proper operation in waves. Also, ...
Read More
In this paper, a feasibility study of building a Human Powered Hydrofoil (HPH) vessel is reported. Hydrofoil vessels are a well-known class of high-speed crafts. In addition to high-speed operation, the hydrofoils have a reliable maneuvering capability, good stability and proper operation in waves. Also, a human powered vehicle, nowadays is an advancing idea. Different aspects of the design and construction of a HPH is explained. Some ideas are principles and others are ideas, set forth and should be further analyzed and validated theoretically and experimentally.