فصلنامه علوم و فناوری دریا
سال شانزدهم شماره 61 (بهار 1391)

Almost every guns produce high speed and great pressure muzzle blast when they start to shoot. They also damage surrounded structures in their vicinity. In heavy weapons with high frequency of firing, the structure around the gun is incurred under the regular impacts of blast waves. On the other hand, these waves can also negatively impress crews, so their efficiency would be reduced.In this paper, a model of muzzle blast is revealed with the aid of scaling approach, and the traits are estimated with the aid of Friedlander wave form. Blast arrival time, maximum pressure, and positive phase duration are used to describe the muzzle blast. In the case of arrival time, Semi-experimental methods are also utilized. Solution of the reflected pressure at low angles has done with the Oblique Shock Theory, and at the bigger angles experimental methods along with Lagrangian Interpolation is utilized. The equations are attained within two ranges of distances. First: 10 to 50 times of barrel diameter, second is 50 to 400 times of the barrel diameter. The results are also validated with the experimental data from a 30 mm caliber gun and a 105 mm caliber tank. Results of arrival time and reflected pressure are appropriately efficient, and Positive Time Duration although shows a little more error from the experimental error, has half error in compare with the last theory.

With the fast and accurate prediction of smoke and fire on ships and submarines can be assigned to a mission well done. So early in the design process and subsurface military vessels must be a way to simulate the spread of fire and smoke. With the spread of fire and smoke simulation can be optimized layout compartments. Also, the type of ventilation system used on military ships and submarines has been affected by the simulation in the design process. This article describes how to simulate the spread of fire on the necessity compartment utilizes a native Software in the field are also studied. Usually, a network model is used to simulate smoke and fire. Smoke simulation Network include of heat transfer (radiation, conduction), fire detection, fire fighting, and a simple control system.

Problem of slamming by high speed vessels is one of the most important structural phenomenon that vessels continually face during their life span. Many researchers, by employing different methods, have investigated this phenonmenon. In this article, problem of slamming of a two-dimensioanl asymetric wedege has been studied. For the analysis of this phenomenon in an asymetric condition, various analytical relations have been utilized. Method of achieving these relationships has been explained in details. The determined relationships are used in order to compute the pressure distributions and to find the maximum pressure. This has been accomplished by different wedge angles. The obtained results indicate favorable agreement compared to earlier findings by other researchers. Finally, by analyzing the acquired results, the effects of geometrical as well as physical variations on pressure distribution during the slamming have been investigated.

Fully developed laminar steady forced convection inside a circular tube filled with saturated porous medium and with uniform heat flux at the wall is investigated on the basis of a Brinkman model which is appropriate for hyperporous materials which are of current practical importance. The “WKB method” is applied for small values of the Darcy number. For the case of large Darcy number, the solution for the Brinkman momentum equation is found in terms of an asymptotic expansion. With the velocity distribution determined, the energy equation is solved using the same asymptotic technique. The results of the study show that the velocity profiles depends strongly on the parameter s. As this parameter increases, the central region containing a relatively uniform velocity distribution spreads further towards the wall.

Sloshing phenomenon is a complicated free surface flow problem. It has a wide range of engineering applications especially in tanker ships and Liquefied Natural Gas (LNG) carriers. This phenomenon from structural point of view can create critical condition for marine structures. It can cause pressure increase on the tank perimeter due to sloshing. Therefore, it is essential to be able to evaluate the fluid dynamic loads on the tank perimeter. In this paper a numerical model is developed based on incompressible and inviscid fluid for liquid sloshing phenomenon in trapezoidal tank using coupled BEM-FEM. The results are validated for rectangular container using available data. The suggested geometric shape reduces the sloshing effects more efficiently than the available rectangular tank.

In this research application Sea surface temperature, sea surface pressure and precipitation in the province Mazendaran was studied. Mean monthly sea surface temperature data in 30-year period has been from NOAA. 30-year average monthly precipitation data is taken from meteorological office for stations Babolsar, Qrakhyl, Noshahr and is Ramsrgrfth. The correlation between sea surface temperature with rainfall in different months in the province has been calculated. In each month and the third degree regression line was used for statistical estimation.In the present study is shown that there is the negative correlation whit 95 percent confidence interval between sea surface temperature Caspian Sea against precipitation and standardized precipitation index in the in Mazandaran province. Can be deduced., decreasing sea surface temperature in the years Precipitation will increase and rising Sea surface temperature Can be reduced rainfall.

In this article we investigate the effect of offshore wind in shallow water on two stations of bushehr and jask in persian gulf and oman sea. one experimental observe show that the offshore wind cause the surface gradient of order 10-6 to be approximate cause of the longshore flow.we obtain linearized depth integrated equations.parametrize the bottom stress and then curl of these equations and using continuity equations,parabolic equations for elevatin (x,y) will be gotten.one model of bottom is linear changing depth with distance and wind operate them.this assumption for studying region have good approximation.solve the equation by the way we draw theree dimensional curves or elevations change in mentioned regions in time of year in which the offshore wind velocity was stronger by using mathematica software and in each case we calculate surface level gradient along shore and discuss about it.researches indicates that where elevation is maximum,winds fade and recognize from curves that elevation change is greater near coast and will be decreased by being far from beach and also elevation change along shore is variable.also we can realize that maximum elevation gradient is much more than 10-7and occur near shore.