Study of presence of bubble cloud in liquids has been of interest to researchers because of its positive or negative effects in many industrial processes. This paper aims to understand the behavior of a homogeneous mixture of bubbles and liquid. Due to usual simplifications, the equations governing bubble cloud behavior do not offer a complete analysis of this phenomenon. In this research, the works of the other scientists are reviewed especially the studies carried out by Wang and Brennen. In this study, first, the code devised according to numerical algorithm of this research is validated by results of Wang and Brennen. Then, by taking into account the compressibility property at the bubbles boundary for homogeneous mixture of bubbles in liquid, the governing equations are derived. Next, these equations under different applied sound pressure levels to the cloud, and a variety of gas percentage in liquid are numerically solved by the devised code. The severe reduction in maximum growth of bubbles with compressibility considerations, and the occurrence of collapses under some conditions are of the obtained results. Also, when bubble presence ratio is low the behavior of bubble cloud does not relate to compressibility. Some other outcomes of this research are manners of bubbles collapse in outer and inner layers of bubble cloud, serious compressibility effects on intensity and time of collapses, and maximum bubbles growth.

Nowadays computer technology provides different ways to check technical and economical study of DC traction supply systems projects. It is quite possible to simulate the rolling stock transportation based on operation program, also voltage and current calculation and determines the rectifiers and inverters outputs in every moment and position and also it is possible to check the rectifier substation proposed positions. The estimated passenger number, operation program and passenger comfort are necessary parameters in rolling stock selection. It is possible to determine rectifier output in normal and one transformer rectifier unit out of service condition. As well calculation provides the information of energy consumption and rail voltage regarding the earth. Rolling stock data is needed for calculation and SIMULATION. As an example it is necessary to know motor specification at motoring and braking condition, its weight and also track data such as gradient, curve and maximum speed. All contact line, current returning circuit, substation place and operation program data must be defined.The first step to simulate traction supply network is simulating the train dynamic movement in order to specify the position, speed, acceleration and rolling stock power consumption. Therefore this topic was chosen for the present research.In this paper the dynamic train DYNAMICS was taken into account. The train DYNAMICS graph was presented as a key curve in determination of the number of existent trains in return lines and by the SIMULATION process, the moment rates of mechanical parameters such as the location, the consumption rate of trains in each point of the line and the moment velocity of the-return trains are presented.

The study of a two-dimensional (2-D) system started nearly half a century ago when Peierls and Landau showed the lack of long range translational order in a two-dimensional solid. In 1968, Mermin proved that despite the absence of long range translational order, two-dimensional solids can still exhibit a different kind of long range bond orientation. During the last decade, fascinating theories were put forward to explain the role of topological defects in the melting of two-dimensional solids, starting with Kosterlitz and Thouless. Recent surge of interest in melting is also due to the theoretical ideas of Halperin, Nelson and Young. They have suggested that the transition may be fundamentally different from that observed in ordinary three-dimensional systems. Computer SIMULATIONs suggest that the transition is of the usual first-order type observed in a three-dimensional system. A large body of experimental and SIMULATION research into the two-dimensional melting followed the announcement of the KTHNY theory. In spite of all this effort, the question as to the nature of two dimensional melting remains unresolved. Recent experimental work supporting the existence of continuous melting transitions in some two dimensional systems indicates the need for further theoretical and computational work to lead to an understanding of the experimental results.In this paper we intend to summarize and clarify the current situation with regard to research in the two-dimensional melting with an emphasis on computer SIMULATIONs. The paper begins with an overview of the current status of relevant theoretical, experimental and SIMULATION research, then a two-dimensional SIMULATION of an ionic salt system is studied in detail. This SIMULATION has been done by using the molecular DYNAMICS method. The most important parameters that have been determined are: The transition temperature, the total energy of the system, the mean square displacement and the bond angle distribution. The transition temperature of the system has been specified by plotting some of these parameters as a function of temperature and time. The first order transition is observed. It is difficult to distinguish a hexatic phase from a two-phase coexistence region.

In this paper, a particular propulsion system including, liquid rocket engine, fuel and oxidizer tank and related pressurizing system, have been surveyed. The procedure is based on a nonlinear mathematical model which has been simulated in Matlab SIMULATION environment. In propulsion systems, identifying system performance is essential, because if we can accept ability describe the dynamic behavior of the system components in nominal and transient regimes; we can reduce the associated costs during design and development. Following, results of Propulsion system hot test are compared with model that shows acceptable accuracy of simulator code. In addition to leading research, how to use this model to identify the causes of failure is shown. Match analysis and compatibility testing, after disassembling objective observations show considerable performance model for similar applications.