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
Masih Moore; Ahmad Firouzian-nejad; Saeed Ziaei-Rad; Abdollah Eidany-nejad
Abstract
The interest in bi-stable structures comes from their ability that these structures can have two different stable equilibrium configurations to define a discrete set of stable shapes. The geometrical changes occur with no need to continuously consume power, and mechanical hinges to preserve the structure ...
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The interest in bi-stable structures comes from their ability that these structures can have two different stable equilibrium configurations to define a discrete set of stable shapes. The geometrical changes occur with no need to continuously consume power, and mechanical hinges to preserve the structure in each stable shape. In this study, the stability characteristics and thermal response of a bistable composite plate with different asymmetric composition were considered. The non-linear finite element method (FEM) was utilized to determine the response of the laminate. Attention was focused on the temperature dependency of laminate mechanical properties, especially on the thermal expansion coefficients of the composite graphite-epoxy plate. Also the effect of including the resin layers on the stability characteristics of the laminate was investigated. The effect of the temperature on the laminate cured configurations in the range of 25°C to 180°C was examined. The results indicate that the coefficient of thermal expansions has a major effect on the cured shapes. Next, optical microscopy was used to characterize the laminate composition and for the first time the effect of including the resin layers on the actuation loads that causes snapping behavior between two stable shapes was studied. The results obtained from the finite element simulations were compared with experimental results and a good correlation was obtained.
مهندسی دریا
Ataollah Gharechahi; Esmaeil Shafizadeh
Abstract
In this research, the effect of weights that lose their lashing systems and can move freely in line with vessel breadths is investigated on ship roll motions. Therefore, the effect of friction and possible barriers that impeded on free movement of weights are neglected.To study the effects; weights with ...
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In this research, the effect of weights that lose their lashing systems and can move freely in line with vessel breadths is investigated on ship roll motions. Therefore, the effect of friction and possible barriers that impeded on free movement of weights are neglected.To study the effects; weights with different masses are hung on pendulum which is installed on an ocean going trawler model and vessel roll motions is being experimentally tested.The results show that whoever hanging weights can increase the center of gravity of vessel and decrease the vessel stability; but caused increase the period of roll motions. The findings of research also can be used in design of damping systems of roll motions.In addition, the experimental results are compared with numerical results based on the Strip Theory. The results show that the damping coefficient has important role in the accuracy of numerical results.
مهندسی دریا
ahmad rezaie mazyak; mehdi sanayei
Abstract
The main goal of using floating breakwaters is to provide the sheltered area of calm water in the coastal zone. In present research, for analyzing hydrodynamic modeling of pontoon floating breakwaters the AQWA module of ANSYS software has been selected. The main parameters that have been considered in ...
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The main goal of using floating breakwaters is to provide the sheltered area of calm water in the coastal zone. In present research, for analyzing hydrodynamic modeling of pontoon floating breakwaters the AQWA module of ANSYS software has been selected. The main parameters that have been considered in this research are pattern of significant wave height, wave period, and draft and width of floating pontoon. Wave transmission coefficient can be obtained from water surface changes in any point of leeward. Results of numerical modeling demonstrate that a pontoon floating breakwater with relative width greater than 0.4 have appropriate performance. Also it has been found that the transmission coefficient of pontoon floating breakwaters will be in the range of 0.35 to 0.60 if the relative wave period changes in the range of 1.5 to 4.
مهندسی دریا
hossein bahrami; Mehdi ghomeshi; Seyed Mahmoud kashefi por; Seyed Ali Akbar Salehi Neyshabouri
Abstract
Density current is one of the relative motions that occur between two fluid layers, even in fluids with small difference in density. Differences in specific mass may cause of temperature, suspended material, solved material or a combination of them. These currents are so important specially in cases ...
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Density current is one of the relative motions that occur between two fluid layers, even in fluids with small difference in density. Differences in specific mass may cause of temperature, suspended material, solved material or a combination of them. These currents are so important specially in cases such as water containing sediment entering rivers into dam reservoir, seas or lakes and can also have destructive effects such as sedimentation in reservoir and estuaries to the sea and coastal areas as well as changing bedding sets Offshore areas (Kostic & Parker, 2005). The identification of type of move and change in current regime on the characteristics of the flow movement is very important. Investigation of flow movement, require to recognition of velocity profiles. A physical modeling used for this proposes and measurement and investigation of velocity on the body of current carried out. The results showed that the Coefficients of velocity profiles in wall and jet regions were respectively 2.83, 0.87 and 2.08 for sub critical flow and 1.174, 1.062 and 2.09 for super critical flow, also the maximum height of the supercritical flow was lower than sub critical flows. The other results showed that the velocity reduced 14 to 19 percent and the flow depth increased 21 to 32 percent affected by hydraulic jump respectively. Also, in some cases, large differences were observed between the results of the analytical jump relationship and measured data.