JOURNAL OF MARINE ENGINEERING
Year:2017 | Volume:13 | Issue:25 |Papers Count:12

Hydrodynamic analysis of marine propulsors with complex geometry such as podded drive systems، ducted propellers، and waterjet systems are more complicated than conventional propeller systems. This fact has caused the usage and development of numerical methods and techniques. The hybrid method to couple the Blade Element Momentum Theory (BEMT) with Reynolds-Averaged Navier Stokes method (RANS) is a powerful tool to calculate the hydrodynamic characteristics of marine propulsors with rotating and fix parts. The main purpose of this paper is developing a BEM/RANS coupled method and using it for numerical simulation of podded drive systems. In this approach، the flow around propeller is simulated by BEMT and its effects are substituted in RANS method by a set of equivalent forces which called body force. Then the flow around the fixed parts of propulsors are modelled by RANS solver. The results include the propeller thrust، the propeller torque، and the axial force. The results obtained by coupled method are compared to and verified by the experimental data.

For most vessels، the frictional resistance of the hull in the water has the largest share in the total resistance of the ship، so in the past few decades much research have been done on reducing the frictional resistance of ships. Among these، stepped vessels with a significant reduction in the amount of wetted surface have a special place. In this study، the effect of a single transverse-step on a flat plate is investigated in calm water with computational fluid dynamics methods. First، the vessel is modeled as a planing flat plate in a fixed trim and draft. By adding a transverse step to the geometry of the model، the proportion of frictional drag to the lift is calculated and compared with the other results. Also، changing the amount of frictional drag and wetted surface due to the changing of the longitudinal position and height of the step are investigated.

Forecasting of sea level fluctuations is a suitable tool for comprehensive management of the sea and the protection of coastal areas. On the other hand، application of time series analysis for forecasting purposes has been evaluated to be very appropriate. Therefore، two time series consisting monthly measured sea level data were used in the present research. The data have been recorded at two stations of Anzali and Noushahr in the southern part of the Caspian sea for time lengths of 40 and 14 years، respectively. The nonparametric Mann-Kendall test was employed to determine if measurements exhibit an increasing or decreasing trend. In the next step، different methods of forecasting and modeling of time series including Auto Regressive Integrated Moving Average and Multiplicative ARIMA method were fitted to the data. Then، Akaike Information Criterion was applied to assess the ability and accuracy of fitted methods in forecasting of sea level in future months and to determine the best time series model. The results of forecasting in the final models reveal that the performance of the Multiplicative ARIMA method based on time series analysis، to estimate and simulate the stochastic behavior of the Caspian sea level is acceptable. Meanwhile، the length of the forecast period in the models has increased significantly in comparison with previous researches.

Studying the behaviour of supercavitation from the energy aspect can be divided into two sections. Studying the behavior of supercavitation in the flow field and in vicinity of the flow field. A large portion of field energy is kept in the field، and the rest of it distributed as noise (sound) out of the field. In this paper، harmonious structures of the field which are flowing as energy sources are decomposed by POD method (Proper Orthogonal Decomposition) and presented as spatial modes. The behavior of each mode and therefore behavior of supercavitation can be estimated by studying behavior of supercavitation in nearby area by decomposing the spatial modes via Helmholz decomposition to vectorial and Scalar potential function and then modelling of potential section of scalar to spherical harmonics. By investigating spatial modes، the first mode which has the highest energy is known as mean flow and by studying the intensity of spherical harmonic modes it can be shown that dipole source is an appropriate representative for field behavior in the nearby area and as a result supercavitation behavior in far feild.

In this paper، the main goal is to reduce the heave motion between a surface effect ship (SES) and a wind turbine in order to safely transfer equipment and person to SES. For this purpose، an LQR control system is designed to damp the vertical motion of the surface effect ship in critical sea states including high-frequency and high amplitude regular waves as well as high frequency irregular waves. The simulation results show the high quality of the system control in the studied sea condition. A comparative analysis of LQR and PID approaches demonstrate the high performance of the new designed control system. The proposed controller outperforms the traditional PD.

Sound measured at various points around the environment can be evaluated by a series of multi-pole sources and their acoustic strength can be acquired. In this numerical study، a method، called the inverse method، was examined to achieve this goal. A variety of arrangements of different sources were considered and the acoustic strength of these sources was acquired. Through the application of the mismatch criterion، good conformity was observed between these sound models and the original sound. Furthermore، with regard to results، sound was generated via different source arrangements which showed acceptable agreement with the original sound. Finally، an arrangement named ‘ sources vertical arrangement’ was selected as the best approach.

Coefficients or hydrodynamic derivatives of autonomous underwater vehicles play a key role in their development. The most popular way for the estimation of coefficient is to implement captive model tests such as straight line tests and planar motion mechanism tests in towing tanks. In this paper، investigation of hydrodynamic derivatives was performed based on the water tunnel maneuvers. Forces and moments are measured by a six-component strain gauge balance. The developed apparatus was used for performing the planar motion mechanism tests of the water tunnel. By conducting such tests in a water tunnel، the appropriate range of parameters to estimate the hydrodynamic derivatives was provided. Also، by doing such tests in water tunnel، errors related to the time limitation of tests and the effects of surface waves in towing tank of autonomous underwater vehicles، applied in deep seas، are eliminated.

In the marine industries، defects in welded joints are repaired to improve the performance. It is possible that a welded joint is repaired once or twice. In this research، effect of repair on microstructure، mechanical properties and corrosion behavior of welded joints of 5083-H321 aluminum alloy using pulsed MIG process was investigated. The results show that excess heat due to increasing the number of repair causes recrystallization، grain growth and increasing the grain size in the heat affected zone. The results of tensile test and micro hardness show loss of mechanical properties in heat affected zone of the sample that subjected to repair twice. Also، this sample shows a substantially passive region in the weld metal and the heat affected zone and hence more stable resistance to pitting corrosion.

Tidal basins have been formulated by some empirical relations based on field observations. Although empirical relations explain some morphological patterns، they are not applicable to all conditions. This study aims to evaluate the effects of morphological parameters on tidal basin equilibrium by setting up a numerical lab for the case of Musa Tidal Basin (MTB). In order to assess the morphology pattern which is affected by parameter values and to reduce the computational cost of long-term models، efficient scenarios are designed optimize the number of runs. Then the responses are analysed by statistical approaches to define comprehensive effects of those parameters on the simulated morphological equilibrium. This methodology improves the long-term results in different conditions، which is confirmed by the comparison of the output and measured data.

Considering the effect of wave on marine activities in Chabahar، different factors influencing the wave height were considered in the present study. For this purpose، the daily data of the year 2007-2011 and hourly data consisting of two month data of the year 2006 were employed. The results of the proposed method were compared with the results of the fuzzy logic based on PSO algorithm. The Monte Carlo method had a better performance for both hourly and daily data. So that R2، RMSE، d And MAE predict 0. 941، 0. 08، 0. 9822 and 0. 0545 for hourly prediction and 0. 8499، 0. 1878، 0. 9499 and 0. 1199 for daily forecasting respectively. also in prediction by Fuzzy logic based on PSO algorithm، this parameters is 0. 911، 0. 1065، 0. 9647، 0. 0698 for hourly prediction and 0. 8316، 0. 2225، 0. 9109 and 0. 1665 for daily prediction that show the high ability of Monte Carlo in wave height prediction in this Region.

In this study generation، propagation and run-up of tsunami waves caused by submerged landslide are studied in two dimensions. The governing equations، Navier– Stokes equations، are solved in a Lagrangian form using a mesh-less numerical method by the name of Incompressible Smoothed particle hydrodynamics with a prediction– correction step. The Comparison of the result of this study with experimental data indicates that the deviations between the wave amplitudes are less than 5 cm for every different time steps and also، this model simulated run up and Water surface fluctuations more accurately against the Nasa-Vof until to 3 seconds.