نشریه مهندسی شناورهای تندرو
پیاپی 48 (بهار و تابستان 1395)

Today, the drag reduction in high speed planning hull vessel, in order to achieve higher speeds, is of great importance and there is a considerable interest to it. Drag reduction becomes possible through using various coating methods, installation of various equipments and changes in the hull form. Using step at the bottom of the hull is one of the most efficient methods to reduce drag. So far, most studies have been conducted on the hydrodynamic behavior of stepped planning hull, and wave pattern created around the hull has been less studied. In this paper, wave pattern around a stepped planning hull is investigated by numerical method. For this purpose, the RANS equations with k-ε turbulence model are implemented to simulate the turbulent flow around the hull. The VOF model is also used to model free surface. A comparison between the results of present simulation and Savitsky's empirical formula for wake profile was done, that showed a good agreement between the two methods.

By regarding expensive towing tank experiments and inavailability of appropriate towing carriage for high speed craft, implementation of various software for numerical simulation are intensified. The main purpose of numerical simulation is to achieve a suitable answer in a low expense, good accuracy and reasonable solution in a short time. Therefore, in the current study, numerical simulation of planing trimaran tunneled boat is performed using commercial software STARCCM and resistance, ship waves and pressure distribution on boat’s hull are analyzed. The final results are presented by comparison of numerical data against experimental results and free surface flows around tunneled boat are illustrated. Pressure distributions over the hull bottom at wide range of Froude number from 1.07 up to 8.4 are also presented and variation of waterlines is considered. Obtained results by numerical simulation have a good accuracy in comparison with experimental data.

Biofouling and Biodeterioration has created many environmental consequences on the blue expanse on Earth; because of the economic problems of the country and also against of their causes. Due to the daily increasing industries immersed in the sea and the maritime transportation industry; biological corrosion and ways to combat it, by maintaining of aquatic ecosystem, is taken into consideration of the scientists in developing countries. In view of the environmental consequences of using chemical control methods, each year scientists try to use of biological control methods rather than chemical methods due to the water ecosystem conditions in different regions of the earth. In this study was tried by analyzing the causes of biofouling, causes and economic consequences arising from it, ways to deal with this biological phenomenon, be considered with emphasis on biological control methods which has already been used in developed countries.

Understanding the dynamics and behavior of high speed crafts, in calm water and waves is of vital importance. Determination of coefficients of equations of motion helps recognition of dynamics of high speed crafts and the factors affecting their instabilities which can be useful in controlling these instabilities. The main purposes of this research are determining the coefficients of longitudinal motions of planing catamarans using CFD and evaluating the Interceptor effect on hydrodynamic coefficients of a planing catamaran. Determination of hydrodynamic coefficients using experimental approaches is remarkably expensive, and requires precise laboratory equipment; therefore, using numerical method for hydrodynamic coefficients determination and development of a visual laboratory seems highly efficient. In this research the interceptor effect on hydrodynamic coefficients of a planing catamaran is evaluated. Results indicate most of the coefficients are frequency independence especially for high frequencies. Also, interceptor effect on hydrodynamic coefficients in different frequencies is negligible except for a few cases.

Nowadays, considering the importance of the energy and speed in the world as well as the limited available energy, the optimum condition should be always considered in designing. In the field of marine industry, considering the length of the water constraints of our country and special strategic situation of the region, there should be an ongoing attempt to reduce energy consumption and increase speed of the high speed crafts. In this research, nature has been used as a guide to reach our target. Study of the skin of the fast marine’s faunas such as sharks and dolphins, has generated the idea of riblet covered surfaces. Various riblet surfaces made in the world and currently used has been studied and ANSYS-CFX has been used to study their performance. In this study riblets applied on planning plate and investigated the effects on hydrodynamics parameters. The results has been validated with the experimental results performed in the towing tank. Riblets can reduce the drag up to 6% in the two phase condition.

At the end of first decade of 21st century in IT world, we have seen the dehiscence of a new technology called cloud computing, leading companies in IT industry have tried to apply it as a customer service processes in which nowadays, the most superior of these companies use the cloud computing as an important competitive advantage to their equal companies. In spite of very important challenges, this relatively new technology, is growing and developing fast. At the advent of it, a lot of researchers thought that cloud computing will soon be comprehensive but recent research indicates that security is the biggest barrier facing this technology. In this study, it has been tried to investigate the security challenges of this technology and also why security caused lack of interest in IT managers and users of this technology. At first an introduction and definition of cloud computing will be discussed then the benefits and advantages of its use as well as its flaws and security problems have been expressed and finally a security analysis is submitted for it.