جستجوی مقالات مرتبط با کلیدواژه "resistance" در نشریات گروه "مهندسی دریا"

Traditional dhow has been used for years in Iran and other countries in the Persian Gulf and Oman Sea for the transportation of goods and fishing. Today, these vessels are still operational in Iran and play an important role economically. The construction of these vessels is always done traditionally and no scientific research has been done on its design. In the present study, the hydrodynamic resistance, and motions of a dhow model in the towing tank have been investigated experimentally. A model with 95 cm long was made from a real dhow with a length of 21.1 meters and tested in the NIMALA towing tank. Also, the resistance of the dhow model has been calculated using the Holtrop method. The results show that with the increase in speed, the trim of the model increases and reaches 6.8 degrees at a speed of 1.5 m/s. Also, increasing the speed increases the sinkage of the model and at high speeds, the sinkage increases by 2 cm. At the design speed (1.1 m/s), the resistance of the dhow model is 2.476 N, and when the speed increases to 1.5 m/s, the resistance increases sharply and reaches 15.62 N. Also, the results show that the Holtrop method has an acceptable accuracy compared to the experimental results, and this method can be used, in addition to commercial ships, to estimate the resistance of vessels with special bodies such as dhows.

Gliders are new marine vehicles which have research and military uses and they move by sequent diving and climbing. Suitable design of its main body and wings are important for the most advance velocity. hydrodynamic design variables are main body form, wings (cross section, dimensions, shape, longitudinal and vertical position) and hydrostatic parameters (static trim angle, amount of added force). Spray marine glider is selected as the initial design and changing each of its component in numerical simulation show its effects on the glider performance then the appropriate ones are chosen. The glider is simulated by computational fluid dynamics method in Star CCM+ that its error is less than 10% according to a validation. The main body of Spray has the least resistance force. Symmetry sections performance are better for the wings, and NACA 0012 foil is chosen. smaller wings are better. by moving the wings to back of the glider the advance velocity increases. Increasing the static trim angle and the added force causes increasing the advance velocity.

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.

AbstractHydrofoil craft has submerged wings that mounted with struts below of the hull. With the onset of movement and the production of lift by hydrofoils, the craft hull is separated from the water surface, thereby reducing its resistance and increasing its velocity. The position of the hydrofoils along the body have a significant effect on the resistance, hydrodynamic performance and stability. In this paper, are investigated influence of longitudinal position of front hydrofoil on the hydrodynamic resistance of a hydrofoil craft in three modes and at six different speeds through ship model test. Experiments have been carried out in a towing tank of NIMALA. The results showed that the total resistance coefficient curves showed similar physical behavior between 0.27 to 1.64 in all three states. in this range, the lift created by the front and rear hydrofoils of the model causes the body to be uniformly separated from the water surface and to reduce friction resistance, that in general comparison of these situations, the position of the front hydrofoil at a distance of 56 cm from the center of gravity of the model(Position-1) due to the proper distance of the two front and rear hydrofoils relative to the center of gravity and also to each other has less resistance.

This study was carried out to compare the effect of two commercial prebiotics (A-Max concentrate and A-Max Ultra) on growth performance and resistance of common carpfry. This experiment was conducted in a completely random design with a total number of 1080 apparently healthy carp fry (initialaverage weight of 1.3±0.304 g), which were caught and transferred to the laboratory. After 7 days of adaptation to the laboratory conditions, the fish were randomly divided into 9 treatments in 27 polyethylene tank (40 carp fries per tank) in triplicates. The carp fries were fed with four concentrations of 0.3, 0.5, 0.7 and 1 g kg-1 prebiotics in-feed and the control was fed with diet without prebiotic supplementation, for 60 days. At the end of the study the results indicated that growth performance parameters and feed efficiency were highly significantly (p<0.05) different in probiotic A-max concentrate treatment, especially treatment A4 (1 g kg-1 prebiotic), in comparsion with other treatments and control group. The same trend was observed for survival rate (p<0.05). Similarly, significant differences were observed in resistance against environmental stresses in all treatments compared with control group (p>0.05). These results suggested that supplementing diets with commercial feed additives, A-Max concentrate and A-Max Ultra, promotes growth performance, feed efficiency and increased larvae resistance against the challenge tests compared with the control group, but the comparison between them showed that A- max concentrate was more superior at 1g kg-1 in common carp fry diets.