مهندسی دریا
Sina Gharavi; Seyed Mostafa Siadatmousavi; Ali Khoshk holgh
Abstract
Sedimentation and erosion are among the most significant issues that pose serious challenges in coastal areas. The consequences of these phenomena include reduced lifespan of ports, continuous dredging, and high costs. When ports experience sedimentation, engineering solutions are required. Predicting ...
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Sedimentation and erosion are among the most significant issues that pose serious challenges in coastal areas. The consequences of these phenomena include reduced lifespan of ports, continuous dredging, and high costs. When ports experience sedimentation, engineering solutions are required. Predicting the rate and pattern of sediment deposition in the access channel and the basin of ports enables better cost management. The objective of this study is to numerically model the hydrodynamic and morphological effects using the open-source numerical model TELEMAC in the Strait of Khuran and Shahid Rajaei Port, located in the Persian Gulf. For this purpose, water surface elevations at open boundaries were provided to the model, obtained from a calibrated MIKE21 model. The hydrodynamic model was executed, and the output included velocity and water surface elevation. Additionally, the sediment transport model GAIA was coupled with the hydrodynamic model and executed. The sediment model output includes bed level changes and suspended sediment concentrations. Finally, the simulated model was validated using measurement data, confirming that the dominant flow is tidal, parallel to the coast, and reaches a maximum velocity of 2 meters per second. The water surface elevation modeled by TELEMAC indicates that localized maximum water levels reach up to 4 meters. Wind speeds rarely reach 5 meters per second in the Khuran channel, and therefore, their influence on the currents is minimal. The results from the sediment model demonstrate that the intensity of sediment deposition in the port area and the access channel is higher in the central and eastern parts of the Strait of Khuran, as well as in the western area of Shahid Rajaei Port.
مهندسی دریا
Farnoosh Jahanbakhshi; Mohammad Reza Noorimehr; Mohammad Esmaeildoust
Abstract
Abstract- With growth of technology, the needs for data and information security over communication channels are necessary. One of the most important issues is the establishment of information security in marine communications. The RSA encryption algorithm is one of the most popular and most asymmetric ...
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Abstract- With growth of technology, the needs for data and information security over communication channels are necessary. One of the most important issues is the establishment of information security in marine communications. The RSA encryption algorithm is one of the most popular and most asymmetric algorithms used for secure data transfer. In the RSA encryption system, due to the very long key length, the encryption and decryption step speeds decrease, so it needs to improve its speed. One of the improving ways of RSA is RPrime RSA that includes the highest decryption of speed to RSA. In this paper, the encryption and decryption speed of RPrime RSA algorithm is improved using efficient residual number system. The result of implementation and comparison shows that the proposed method has an average of %22 and %36 improved at the encryption and decryption speed than the RPrime RSA algorithm.
مهندسی دریا
MORTEZA BAKHTIARI; AMIR ASHTARILARKI; Samer adnan
Abstract
Estimation of sediment transportation is one of the significant factors in river engineering. This is especially important in rivers that are used and exploited in many ways. The problem of sediment transport itself has some complexities and will be much more complex in tidal rivers. In the present study ...
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Estimation of sediment transportation is one of the significant factors in river engineering. This is especially important in rivers that are used and exploited in many ways. The problem of sediment transport itself has some complexities and will be much more complex in tidal rivers. In the present study using MIKE 21 model, particle velocity fall, erosion and sedimentation critical shear stress, Transition parameter between layers, Vertical diffusion coefficient and Roughness of bed stream are investigated. The results showed that particle velocity fall and sedimentation critical shear stress has no significant effect on sediment transport and the slope of the suspended load changes at different speeds is approximately the same. The results also show that by increasing the coefficient of transfer between layers, the concentration of suspended charge increases slightly.
مهندسی دریا
Hamid reza Karimi; Etemad odin Rabei Gholami; Nima Shahni Karam Zadeh
Abstract
Development of industrial activities in the offshore areas has led to the importance of safety of helicopters. Understanding the behavior of the wind around Helideck, especially on take-off, approach and landing are essential to enhance the safe operation of helicopters. In this regard, legislators have ...
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Development of industrial activities in the offshore areas has led to the importance of safety of helicopters. Understanding the behavior of the wind around Helideck, especially on take-off, approach and landing are essential to enhance the safe operation of helicopters. In this regard, legislators have imposed restrictions on the operation of helicopters under varying conditions of disturbance through the standards and rules. In this paper based on the Reynolds-averaged Naviere-Stokes theory, the wind current on the SPD19-A offshore platform from the 19th phase of south pars gas field complex in the CFD environment is modeled, taking into account all the effective equipment. Considering variables such as wind direction, the horizontal and vertical direction of the crane boom, 42 scenarios considered to an appropriate insight of turbulence conditions been provided. The Norsok standard has been used to select the assessment criteria and the two criteria "Horizontal velocity deviation" and "Turbulence energy" has been evaluated, also the stream lines from numerical and experimental modeling have been compared. The results indicate that in the East-West wind direction, the increase in the vertical angle of the boom improves the turbulence conditions in the center of the Helideck. In the direction of the northeast-southwest, the increase in the vertical angle of the boom causes the turbulence conditions in the helideck center to become more complicated. Also, based on the turbulence kinetic energy index, the increase of the vertical angle of the boom for both wind directions makes turbulence conditions more complicated.
مهندسی دریا
Abdolrahim Taheri; Mahdi Tasdighi
Abstract
Design with high Confidence over hard costs overwhelms the execution of the project. Also using a low reliability coefficient raises the risk of high project failure. The degree of contribution of each parameter to uncertainty can be detected by sensitivity analysis. In this paper, the effect of uncertainty ...
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Design with high Confidence over hard costs overwhelms the execution of the project. Also using a low reliability coefficient raises the risk of high project failure. The degree of contribution of each parameter to uncertainty can be detected by sensitivity analysis. In this paper, the effect of uncertainty of three parameters of modulus of elasticity, pipeline thickness and diameter of pipe, which are three influential parameters of a pipeline geometry on the vertical buckling of the offshore pipelines are considered. Both the First Order Second Moment and the Second Order Reliability Method analyzes are considered for the pipeline parameter sensitivity analysis. First Order Second Moment have 4 impact vector and Second Order Reliability Method have 1 impact vector. The results show that the diameter of the pipeline is more effective than the other two parameters. The least difference is between the modulus of elasticity and the thickness of the pipeline, in other words, these two parameters are closely related in sensitivity. Two parameters of thickness and diameter of pipeline are resistance variable and modulus of elasticity of is a load resistance variable. Reliability index values in FORM and FOSM are distinct but close to each other, which is lower in FOSM.
مهندسی دریا
Reza Shamsi; Ali Ebrahimi
Abstract
In the last decade, planing crafts are used widely in civil and military sector due to their good performance in high speeds. Due to complex behavior of planing vessels, the hydrodynamic analysis of planning vessels is important. Computational Fluid Dynamics (CFD) is an effective and efficient tool for ...
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In the last decade, planing crafts are used widely in civil and military sector due to their good performance in high speeds. Due to complex behavior of planing vessels, the hydrodynamic analysis of planning vessels is important. Computational Fluid Dynamics (CFD) is an effective and efficient tool for the numerical hydrodynamic analysis of high speed crafts. In the present study, the hydrodynamic performance of a Naples high-speed craft is investigated using CFD and Reynolds-averaged Navier–Stokes equations (RANS). This simulation is three-dimensional, considering free surface effect and turbulent flow. To calculate the resistance and trim, the vessel is considered in two degrees of freedom. In addition to, using the 6-DOF solver and using dynamic mesh, the rigid-body dynamic equations are coupled to the fluid-governing equations. Numerical simulation are performed at Re>3.5×106 for a range of Froude number from 0.52 to 1.65, and then verified by experimental data. Comparison of the numerical and experimental results shows that the average error values for resistance and trim of the vessel are less than 3% and 9%, respectively, which confirm accuracy of RANS method. Wake and wave pattern around the planing hull also analyzed.
مهندسی دریا
Abdolhossein Mohammadrahimi; Mohammadreza Negahdari; Seyed Amin Hosseini; Ehsan Parsaei
Abstract
Extensive studies on cavitation have been conducted for years as an undesirable phenomenon in marine engineering. The cavitation phenomenon causes severe damage to the body of torpedoes, ship's propellers, pump impellers and turbines. It also increases the frictional drag of submarine vessels and ...
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Extensive studies on cavitation have been conducted for years as an undesirable phenomenon in marine engineering. The cavitation phenomenon causes severe damage to the body of torpedoes, ship's propellers, pump impellers and turbines. It also increases the frictional drag of submarine vessels and imposes many limitations on their design and construction. With increasing speed in submarines and increasing of the cavitation, supercavitation occurs which can be used to create a large bubble around the vessel. Because of drag in the water is mostly due to the friction of the body, by the supercavitation, the contact of water with the torpedo is reduced and as a result the friction drag is greatly reduced and the torpedo speed will increase significantly. In this regard, by artificially injecting air into the body in the state of cavitation, the process of creating supercavitation and reaching this stage can be accelerated.In this study, in order to investigate the effect of torpedo nose shape on supercavitation, different types of torpedo bodies have been modeled and studied different nose shapes. After modeling, meshing is performed with ANSYS Fluent software and the analysis of the model in cavitation numbers (0.2, 0.3 and 0.4) will be examined. Finally, the model will be analyzed in air injection mode (artificial supercavitation) with ANSYS CFX software and the results will be presented.
مهندسی دریا
Elham Matori; Mohammad Esmaeildoust
Abstract
The PRINCE lightweight cryptographic algorithm was introduced as a template in 2012. In this paper, we intend to change the structure of the PRINCE encryption algorithm and use a Dynamic S-BOX to increase the complexity and security of the encryption process. In order to show the efficiency of the proposed ...
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The PRINCE lightweight cryptographic algorithm was introduced as a template in 2012. In this paper, we intend to change the structure of the PRINCE encryption algorithm and use a Dynamic S-BOX to increase the complexity and security of the encryption process. In order to show the efficiency of the proposed structure, differential analysis is performed on the algorithm as well as analysis on the optimal number of revolutions for the algorithm. Analyzes and implementations show that the cryptographic structure is more complex. Despite the slight increase in memory and execution time of the algorithm, compared to the PRINCE encryption algorithm with fixed S-BOX, it has more strength against differential attack and as a result, the security in the improved algorithm has increased. Stronger also increases security.
مهندسی دریا
Javad Ahsan; Mohammad Esmaeildoust; Amer Kaabi; vahid Zareii
Abstract
The residue number system has a parallel computational structure with carry-free operations and is widely used in cases such as digital signal processing, cryptography, design of FIR filters, etc. In this paper we design an efficient reverse converter for the four-moduli set {〖2^(n-2)+1,2〗^(n-3)-1,2^(n-3)+1,2^(n-5)-1}. ...
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The residue number system has a parallel computational structure with carry-free operations and is widely used in cases such as digital signal processing, cryptography, design of FIR filters, etc. In this paper we design an efficient reverse converter for the four-moduli set {〖2^(n-2)+1,2〗^(n-3)-1,2^(n-3)+1,2^(n-5)-1}. In this moduli set, due to the selection of well-formed and balanced modulus, it leads to optimal hardware implementation, with minimum area utilization and minimum time delay. The main advantage of this design is the use of a ROM free and adder base hardware structure. The proposed moduli set are relatively prime to most existed moduli sets in literature and as results it can be employed in the implementation of Montgomery multiplication. The proposed reverse converter has a two-level structure. In the first level, the Chinese remainder theorem is used, and in the second level, the Mixed-radix conversion is used to calculate the final weighted number. The results of computational theory show low time latency and minimal hardware space in this design.
مهندسی دریا
Saeid Khaksari Nezhad; Nima Shahni Karam Zadeh; Nassim Ale Ali
Abstract
The power absorption capability of a floating oscillating body depends on the proper wave-structure interaction. A wave energy converter (WEC) device would capture the wave power as the system radiates waves in the opposite direction (phase) to the incoming waves. Hence, in order to evaluate the initial ...
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The power absorption capability of a floating oscillating body depends on the proper wave-structure interaction. A wave energy converter (WEC) device would capture the wave power as the system radiates waves in the opposite direction (phase) to the incoming waves. Hence, in order to evaluate the initial performance of a point absorber wave energy converter, determination of radiation force is crucial to design and optimal control of wave energy absorption. In this paper, once the hydrodynamic parameters are obtained for a heaving vertical-cylinder buoy, the equation of motion for the system has been considered upon the Cummins integro-differential equation. Numerical analysis of this type of equation could be computationally demanding due to the presence of a convolution term. Therefore, a program was written using the high-level language in MATLAB and the expression for the radiation force in the equation of motion has been substituted with a linear state-space model. The results of the frequency domain analysis in the range of 1-2 radians per second are implemented into the model which corresponds to the predominant wave conditions of the offshore region in Persian Gulf. The proposed open source model compared to direct calculation of the convolution integral in the equation of the motion provides highly accurate prediction and maintains system stability. The model would also be computationally cost effective for higher degrees of freedom since other codes are practically not available.
مهندسی دریا
Mehdi Alavinejhad; Madjid Ghodsi Hassanabad; Mohammadjavad Ketabdari; Masoud Nekooei
Abstract
The passage of personnel and the placement of facilities on the access stairs of offshore complexes have made it very important to identify damage to these components. Modal strain energy method is one of the non-destructive and practical methods in which using changes in the dynamic properties of the ...
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The passage of personnel and the placement of facilities on the access stairs of offshore complexes have made it very important to identify damage to these components. Modal strain energy method is one of the non-destructive and practical methods in which using changes in the dynamic properties of the structure to identify the location and determine the severity of damage in the structure. In recent years, modifications have been made to the initial version of this method, one of which is to take into account the natural frequencies in locating the damage. In this paper, using the improved modal strain energy method and considering natural frequencies, a new relationship is presented to more accurately identify the location of damage in the structure and three different damage indices in the offshore platform access bridge structure are studied and compared. The results show that the average error to accurately identify the location of damage in the average Stubbs index, the improved method and the novel method are 3.55, 2.82 and 2.21 percent, respectively, so the novel method is able to more accurately identify the location of damage in the structure. Also, comparing the results of different cases shows that the average damage location error decreases with increasing damage severity. The accuracy of identifying the location of the damage also increases when move away from the supports.
مهندسی دریا
Fatemeh Asadi Talebbeigi; Saeed Jamei
Abstract
Among the wide range of new industrial materials in the design process under-load structures, Honeycomb composites are said to be one of the best substitutes for common materials used in different industries. In the first part of the present work, three different core cell configurations were chosen ...
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Among the wide range of new industrial materials in the design process under-load structures, Honeycomb composites are said to be one of the best substitutes for common materials used in different industries. In the first part of the present work, three different core cell configurations were chosen as the core cells of a sandwich beam. Then, the effect of core cells’ shape on the mechanical behavior of each structure has numerically been investigated. In the first stage, the vibration of each beam has been investigated by taking advantage of Modal analysis. In the second part, by changing the core height in different cases, the effect of core thickness on the mechanical behavior of honeycomb composites has been studied. The results show that natural frequencies, deflections, and the strength-to-weight ratio of configurations: rectangular, honeycomb, and triangular have been in descending order. Deflection and Von-Mises stress were the results obtained from simulating each model as a cantilever beam. By increasing the core thickness even more, despite the weight being increased, the beam deflection decreases, and the load-bearing and strength of the structure get increased. In the case of the similar thickness of the isotropic plate and the honeycomb composite, the bending stiffness can be enhanced to 7 times at the expense of just a 25% volumetric increase. The comparison and validation of the obtained numerical results with the empirical result show that with just a 4% difference, the results do have a close agreement.
مهندسی دریا
Ali Mohammadi; Mehriar Alimohammadi; Ahmad zadegh abadi; Abbas Khazaei
Abstract
The great circle is of special importance as the shortest distance between two points in navigation. Navigating officers must always be able to calculate the path of the great circle and the turning points on that path. One of the drawbacks of calculations in the path of the great circle is the large ...
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The great circle is of special importance as the shortest distance between two points in navigation. Navigating officers must always be able to calculate the path of the great circle and the turning points on that path. One of the drawbacks of calculations in the path of the great circle is the large volume of calculations and the uncertainty of the correct result. In this research, using the method of composite triangles, the path of the great circle is solved and two general methods for calculating the rotation points of the great circle, which include a) calculating the rotation point with equal longitude difference and b) calculating the rotation point with distance difference equal is used. Next, using the method of equal longitude difference in calculating the points of rotation, a fast and reliable relationship has been developed to calculate the points of rotation. The premise of the developed method is that the point of rotation is always equal to the difference in longitude between the origin and destination. The developed method can calculate the width of the turning point only by calculating 5 sentences from Norris book.
مهندسی دریا
Mohammad Taghi Mansouri Kia; Hamid Reza Sheybani; Elham Rajabi
Abstract
The only navigable river is the Karun River in Iran. Karun shipping history dates back to Nasser al-Din Qajar Shah. Climate change and drought, harvests more water and reduce its capacity, the existence of new railways and highways as the main competitors of cargo from the port of Mahshahr and Khorramshahr ...
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The only navigable river is the Karun River in Iran. Karun shipping history dates back to Nasser al-Din Qajar Shah. Climate change and drought, harvests more water and reduce its capacity, the existence of new railways and highways as the main competitors of cargo from the port of Mahshahr and Khorramshahr to Ahvaz due to the boom in river water transport has been falling.There are few studies on water transport in Karun river. In this study, some of their results are discussed in general. Then, based on the acceptance of the latest research, the most important physical barriers to river transportation have been identified and their remediation strategies adapted to the current situation. Then shipping Signs required of navigation and auxiliary's equipment for sailing have also been offered.Previous studies included :(Iranian structural consulting engineers, 2004; Adabdanan Consulting Engineers, 2004) and Especially (Scott Wilson and Piesold, 2005) It has been attributed to the heavy losses of water transportation, especially in the high tonnage of annual freight. The most recent study, ongoing surveys at the Khuzestan Water and Power Organization (Mansouri Kia, 2018) show that the transport medium (in the pessimistic scenario optimistic scenario about 700 thousand tons and 2133 thousand tons in the target year 1425), together with previous studies is the development of tourism can be no economic losses. Water transport is the base year 2020. Heavy financial losses were previously assumed for river transportation. The most important results of recent research suggest that these losses are reduced by modifying the design vessel dimensions.Another important result of the present study is identifying the physical problems for the Iranian rivers transportation and to provide solutions (except for the sediment removal problem that is being investigated at another study). Applying the research results on solving physical barriers and financial support by private investment (or other financing options), revive water transportation in Karun it is possible.
مهندسی دریا
Mohsen Shojaie; Mostafa Jafarzadeh Khatibani; Etemad ODin Rabei Gholami
Abstract
Estimating the required propulsive power of a vessel at early stage of design is important from two aspects, which are estimating the weight of the machinery as a function of required power and estimating the amount of fuel needed to determine the initial capacity of the vessel. This approximation can ...
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Estimating the required propulsive power of a vessel at early stage of design is important from two aspects, which are estimating the weight of the machinery as a function of required power and estimating the amount of fuel needed to determine the initial capacity of the vessel. This approximation can be based on empirical formulas, data of similar ships or diagrams deduced from statistical data for various types and sizes of ships. Current empirical formulas for estimating ship power are only limited to very few general equations and are inaccurate for specific type of vessels. In this study, by using 90 container ship data and multiple linear regression method, several statistical models were prepared and statistically analyzed considering the influence of the main parameters of the vessels on the required amount of power, and finally a suitable formula extracted. Evaluation of the extracted formula indicates acceptable accuracy for the container ships which can be used to estimate the required power of container ships within the range of this formula.
مهندسی دریا
Mohammad Ramezankhani; Ali Moazemi Goudarzi; Fattaneh Morshedsolouk; Seyed Komeil Hashemi Heidari; Ali Hassani
Abstract
In this paper, the quasi-static compressive strength of two different sandwich structure designs in which cores consist of trapezoidal corrugated panels is investigated. In one design, the core consists of a cross-corrugated multilayer structure, while in the other design the core is consists of two ...
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In this paper, the quasi-static compressive strength of two different sandwich structure designs in which cores consist of trapezoidal corrugated panels is investigated. In one design, the core consists of a cross-corrugated multilayer structure, while in the other design the core is consists of two interlocking bidirectional cross-corrugated panels. For each design, three different trapezoidal wave profiles are studied and one of them is constructed and tested. The results of specimens' crushing tests under quasi-static compressive loads are compared with the numerical modeling results. Afterward, the mechanical behavior of the other four designs is evaluated numerically. The results showed that the ultimate strength of the sandwich structures with an interlocked corrugated core is higher than the ultimate strength of the other design. It was also found that, in a given design, the ultimate strength depends on the corrugation profile geometry. These results can be used in the design of high-strength light-weight structures. Measures that can be taken to improve the ultimate strength of sandwich panels include the use of polyurethane foam, which is light in weight but has high strength, or the geometry of the structure be changed.
مهندسی دریا
Esmaeil Hasanvand; Pedram Edalat
Abstract
Offshore oil terminals are used as a cheaper and safer solution than shore terminals for unloading and loading tankers. There are different types of offshore terminals. Therefore, comparing the dynamic response of these terminals will be effective in identifying their strengths and weaknesses. The present ...
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Offshore oil terminals are used as a cheaper and safer solution than shore terminals for unloading and loading tankers. There are different types of offshore terminals. Therefore, comparing the dynamic response of these terminals will be effective in identifying their strengths and weaknesses. The present study is to compare the dynamic response of the structures of three common offshore oil terminals, including CALM, SALM, and CMBM in environmental conditions under the Persian Gulf region. Simulation is used in OrcaFlex software to obtain structural responses including the tension created in the mooring line and hawser, motion the tankers connected to them. The results show that considering the same operating conditions, the maximum tensions created in the SALM terminal mooring are 2.7 and 1.3 times higher than the CALM and CMBM terminals, respectively. Also, the maximum tension in the SALM terminal hawser is 1.5 and 4.3 times higher in the CALM and CMBM terminals, respectively. As the environmental conditions become more critical, the SALM terminal mooring shows the most stability. By increasing the tonnage of the tankers from 45,000 to 320,000 tons, the maximum tension created in the CMBM mooring has the least change; This is while the maximum tension created in the terminal mooring of CALM and SALM increases by 100% and 156%, respectively. Comparing the displacement created in the tankers (during operation), it results that the displacement in the tanker connected to the CMBM terminal has a minimum size and the displacement in the tankers connected to CALM and SALM is almost the same.
مهندسی دریا
Somayyeh Saffar; Mohsen Solimani Babarsad; Mohammad Mahmoodian Shooshtari; Mohammad Hosein Poormohammadi; Roozbeh Riazi
Abstract
Side weirs are used to control water levels as well as water diversion for various uses in canals and rivers. Due to the complexity of flow conditions inside weirs, in this study, in order to simplify the calculations and increase its efficiency, this structure was investigated in convergent channel ...
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Side weirs are used to control water levels as well as water diversion for various uses in canals and rivers. Due to the complexity of flow conditions inside weirs, in this study, in order to simplify the calculations and increase its efficiency, this structure was investigated in convergent channel conditions. To investigate this issue, different geometric parameters of weir and hydraulic currents were investigated. Based on the geometric parameters of the side weir, experimental scenarios were considered. Based on the scenarios, 5 side weir lengths, 4 side weir heights, and 3 downstream channel widths were considered as side weirs that were tested at different discharges. Due to the fact that different geometric and hydraulic parameters were assumed to be variable in these experiments, the effect of each on the structure was analyzed and solutions for selecting the optimal dimensions in the channel were introduced. Based on the experimental results, it was found that for a fixed upstream water height with a 19% reduction in the width of the downstream channel, the ratio of the flow deflection to the lateral channel increases by 30%. It should be noted that the change in the flow section by converging the passage channel causes the longitudinal profile of the water surface to have a minimum height fluctuation along the entire length of the structure.
مهندسی دریا
Mohammad Taghi Serajian; Alireza Masjedi; Mohammad Heidarnejad; Hooshang Hasonizadeh
Abstract
In this study, experiments are carried out to determine the deviation flow into the intake in a 90º convergent bend, aiming to investigate the effect of flow characteristics on deviation flow with and without submerged vanes. The effective variables include Froude number, convergence, and submerged ...
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In this study, experiments are carried out to determine the deviation flow into the intake in a 90º convergent bend, aiming to investigate the effect of flow characteristics on deviation flow with and without submerged vanes. The effective variables include Froude number, convergence, and submerged vanes’ angle. For this research, a Rectangular channel with a 90º arc was used, which was studied using four different discharges, four different angles of submerged vanes and four degrees of convergence of the end of the channel. According to the results, the deviation flow to the intake increases by converging the laboratory flume. As the end of the flume is converged, the deviation flow is further increased. As the flume is converged (b/B) from 0 to 0.75, the deviation flow is increased from 64.9 to 81.4%, showing a 16.5% increase. Deviation flow is decreased by installing submerged vanes. A decrease in submerged vanes’ angle reduces the deviation flow. Compared to the model without a submerged vane, deviation flow is decreased by 14.9, 9.9, 6.8, and 2.3% by installing submerged vanes at angles of 25, 30, 45 and 60º, respectively. Deviation flow is also decreased by increasing the Froude number, such that it decreases by 5.3% with the increase of Froude number from 0.14 to 0.23.
مهندسی دریا
Hesamoddin Ravanbakhsh
Abstract
Calculating the forces acting from the fluid to different structures is a field of interest to many researchers. Lift and drag forces are the most important parameters in the hydrofoil issues. Given that the Newtonian Fluid assumption is common in most studies in this field; in this paper, the forces ...
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Calculating the forces acting from the fluid to different structures is a field of interest to many researchers. Lift and drag forces are the most important parameters in the hydrofoil issues. Given that the Newtonian Fluid assumption is common in most studies in this field; in this paper, the forces imposed on a hydrofoil in a laminar non-Newtonian fluid flow have been investigated. The model is Power law for non-Newtonian fluid, and is simulated for three dilatants, Newtonian and pseudo plastic fluid at angles of attack of zero, 5, 10, 15, 20 and 25 degrees, and behavior indexes of 0.5, 1 and 1.5 is considered. Creating Mesh, Processing, and Post-Processing Computing This research is done by three free and open source softwares, G-Mesh, Open FOAM, and Para view. For validation, the lift and drag coefficients in the behavior index 1, that's mean Newtonian fluid, are consistent with similar results. As the angle increases, the dilatant fluid separation phenomenon occurs earlier; also Lowering lift coefficient for this concentrated fluid occurs at a larger angle of attack.
مهندسی دریا
Mohammad Hosseini; Mohammad Hadi Fattahi; Saeid Eslamian
Abstract
The density current, as a part of the gravity currents, is the flow of one fluid within another caused by the density difference between two fluids. The density current consists of the nose, head, and body regions within the ambient fluid. In the present study, a flume with 8m length, 35cm width, and ...
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The density current, as a part of the gravity currents, is the flow of one fluid within another caused by the density difference between two fluids. The density current consists of the nose, head, and body regions within the ambient fluid. In the present study, a flume with 8m length, 35cm width, and 40cm height was used. The experiments were performed in 28 different states by changing the bed slope, density, and discharge. The results indicated that by increasing the bed slope, the concentration of the density current decreased by 12% and 19% after continuous and local narrowing, respectively, compared to the non-narrowing state. Further, the entrainment ratio increased by narrowing the flume wall, as the Richardson number decreased by 80% and the entrainment ratio increased by 5 times after narrowing. In addition, the profile formation pattern of the current velocity and concentration enhanced by increasing the inlet density and the pattern indicated more scattering in the jet region compared to the wall region.
مهندسی دریا
Seyed Mohammadreza Mousavi Mirkalaei; Masoud Kaveh; Ali Asghar Mehrabi Mahani
Abstract
Recent advances in electronics and wireless communications have enabled the design and manufacture of sensors with low power consumption, small size, reasonable price and various applications. These small sensors, capable of performing functions such as receiving various peripheral information based ...
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Recent advances in electronics and wireless communications have enabled the design and manufacture of sensors with low power consumption, small size, reasonable price and various applications. These small sensors, capable of performing functions such as receiving various peripheral information based on the type of sensor, processing and transmitting that information, have given rise to an idea for the creation and deployment of so-called wireless sensor networks. Due to the unique limitations and unique features of the underwater channel such as low communication bandwidth, high bitrate error, significant propagation delay, etc., these networks can be easily destroyed by malicious attacks. Coordination and transmission of underwater messages between sensors will naturally present security challenges and perspectives. Attack on network protocols, especially communication protocols, can be easily accomplished in underwater wireless sensor networks. Therefore, the purpose of this paper is to present a secure and efficient protocol for communication in underwater sensor networks based solely on lightweight encoder operators with random number generators and cryptographic hash functions. For this purpose, first, a system consisting of a number of sensor nodes and a central node is modeled as receiving information with the presence of nodes or nodes as attackers and then the various steps of the protocol are described in detail. It is further demonstrated that the communication protocol presented in this paper is secure because it is resistant to the all attacks such as message analysis attack, message manipulation attack, relay attack, spoof message injection, insider attack and physical attack. It is also considered as an efficient protocol because it improves communication and computational overheads and memory consumption over previous methods. Statistical tests also show that the encrypted data in the proposed protocol are acceptable randomly and are independent of each other. Finally, in order to make the proposed method more practical in this paper, and to compare the challenges and resources of this method with previous methods for the purpose of hardware implementation, the required cryptographic components are implemented on the FPGA chip.
مهندسی دریا
Leila Jozaee; Sahar Damiri; Nassim Ale Ali; Etemadeddin Rabei
Abstract
In this paper, free vibration of the ship with Timoshenko beam model is investigated and natural frequencies and mode shapes are obtained. Since the frequency equations of Timoshenko beam are nonlinear, for obtaining the frequencies and mode shapes, numerical method, differential quadrature method with ...
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In this paper, free vibration of the ship with Timoshenko beam model is investigated and natural frequencies and mode shapes are obtained. Since the frequency equations of Timoshenko beam are nonlinear, for obtaining the frequencies and mode shapes, numerical method, differential quadrature method with discretization is used. Frequencies of some vessels with different geometers such as length, height and width are obtained and versus length, height and width are compared and effect of these parameters on the frequencies are investigated. These investigations show that by increasing these parameters the frequencies are decreased and for the vessels that have a large ratio of height to length, the Timoshenko beam model should be used for vibration investigation that the shear effect is considered.
مهندسی دریا
Ahmad Hajivand; Hesamoddin Ravanbakhsh
Abstract
The extensive development and design of multihull ships began in the second half of the twentieth century. Nowadays, many of these ships are built with different designs. However, less numerical and experimental studies have been conducted on their behavior compared to single hull ships. The length and ...
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The extensive development and design of multihull ships began in the second half of the twentieth century. Nowadays, many of these ships are built with different designs. However, less numerical and experimental studies have been conducted on their behavior compared to single hull ships. The length and distance of the two hulls are the factors influencing the wave pattern created around and between the hulls and, consequently wavemaking resistance. In this study, the effect of geometric parameters including length to diameter ratio and body spacing on the hydrodynamic performance of a vessel with a small water plane area surface has been studied using computational fluid dynamics. To investigate the effect of L/D on the wave pattern around the body, towing test is simulated for two models with different ratios in a wide speed range. Furthermore, to evaluate the effect of two-hull distance on the interference of waves between two bodies, two models have been simulated at different distances at different speeds in the computational fluid dynamics environment. Simulations are performed for two different draft. The effect of Froude number, length to diameter ratio and draft on hydrodynamic behavior of the model has also been studied. The pressure, friction and interference resistance of the two bodies are calculated and the wave pattern surrounding the body and between the two bodies is extracted and compared with experimental data, which indicates the reasonable approximation of numerical and laboratory results.
مهندسی دریا
ali saedi; ali asareh
Abstract
Due to the simplicity of operation, Stepped Chutes are among the most common water buildings to reduce water flow energy in irrigation systems. So this research has studied the impact of structure slope, the number of stairs and structure height on energy dissipation rate in stepped chutes. Experimental ...
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Due to the simplicity of operation, Stepped Chutes are among the most common water buildings to reduce water flow energy in irrigation systems. So this research has studied the impact of structure slope, the number of stairs and structure height on energy dissipation rate in stepped chutes. Experimental models used in 2, 20 and 30 cm height, 26.5-degree slope channels (1: 2) and 33.3 degrees (1: 1.5) and in 3, 5, and 7 stairs were built. All tests were done in 4 different rate discharges 10, 13, 15 and 20 liters per second in the laboratory flume, Islamic Azad University of Ahvaz. The results showed that by increasing the amount of the energy dissipation rate will be reduced. It can be also seen that for a certain value of Yc/Δz, the increase in the number of stairs reduces the amount of relative energy dissipation. Also Results showed that increasing the slope, the relative energy dissipation rate increases. In this study, the maximum amount of relative energy dissipation for a model with a slope of z = 2 and a height of 30 cm obtained and the minimum amount of energy dissipation for a model with a slope of z = 1.5 and a height of 20 cm obtained. Results showed that increasing the Froude number, the energy dissipation rate will be reduced.