فصلنامه علوم و فناوری دریا
سال بیست و ششم شماره 103 (پاییز 1401)

In the present paper, the turbulent flow around the propeller model 4381 under the sinusoidal flow wake is investigated. Numerical analysis is performed by finite volume method, which first performs numerical simulations of fluid flow around the propeller, and characteristic curves of the hydrodynamic performance of the propeller under open water conditions for different progress coefficients. For the extracted data, validation was performed with experimental values, the maximum and minimum error percentages being 2% and 1.4% for the thrust coefficient and for the propeller torque coefficient of 7.1% and 4.7%, respectively. In the results obtained for sinusoidal flow wake, the rate of change of the thrust coefficient in the progress coefficients of 0.6 and 0.8, respectively, 2.04% and 3.75% and also the rate of change of the torque coefficient for the progress coefficients of 0.6 and 0.8, respectively 15 It is 7.7% and 1.79%. The results show that the sinusoidal flow wake increases the length and width of the vortex produced in the hub and also reduces the velocity and pressure in the area farther from the propeller disc than the free water flow mode, which in turn It can be effective in reducing the thrust force produced by the propeller.

Acoustic source separation is considered as one of the challenging issues in the signal enhancement field and it becomes even more problematic when some acoustic sources are mixed in the presence of noise. In this paper, the weighted gaussian mean shift algorithm method for dual-channel systems is generalized to multichannel systems. The source separation mechanism is blind and it has the ability to extract several sources from various mixtures. The proposed method is compared with a number of existing algorithms for acoustic source separation under noisy conditions recorded by multiple hidrophones. The results demonstrate the effectiveness of the proposed method.

In this paper, coupled partial differential equations governing displacement field in longitudinal, circumferential and radial directions of thin/thick-walled cylindrical shell under compressive axial load and external pressure with simply support end boundary conditions based on classic shell theory have been derived. Considering the solutions in series form for displacements, these governing equations converts to three linear algebraic equations with respect to the shapes of buckling modal amplitudes. Applying a written code in MATLAB mathematical software, the critical buckling load in axial direction is calculated from the non-trivial solution of characteristic equation for buckling amplitudes. Then, with modeling crack on outer surface of cylindrical shell subjected to the buckling load and external lateral pressure in ANSYS finite element software, the crack stress intensity factors have been calculated. The effect of changes of angle of crack opening with respect to the longitudinal direction of cylindrical shell on the obtained results for crack stress intensity factors are investigated.

In this paper, a numerical study is performed in order to investigate the effect of the numerical diffusion on simulation of separated two-phase flow of gas-liquid. The governing equations solved by shock capturing method which can provide predicting the interface without the flow field solving. In this work, in order to calculate the numerical flux term, first-order centred scheme (Force scheme) was applied cause of its accuracy and appropriate validation. Analysis approves that the obtained stability range of this research is consistent with the classic kelvin-Helmholtz instability equation only for the long wavelength with small amplitude. Results reveal that when the wavelengths are reduced, the specified range is not consistent and wavelength affects on instability range and it is overpredicted. An algorithm for water faucet problem was developed in Fortran language. Short wavelength perturbations induce unbounded growth rates and make it impossible to achieve converging solutions. The approach taken in this article has been to adding numerical diffusion as a CFD technique is used to remedy this deficiency.

Now there are various models to simulate rainfall runoff. WMS and HEC-HMS models are comprehensive models that by incorporating GIS features can be a powerful tool in the modeling and management of catchment area. The aim of this paper is to estimate maximum flood of Namin catchment at the SCS method with using WMS and GIS by applying probability distributions. First, digital elevation model and catchment waterways network was drawn by using GIS. Then, based on land use maps and properties of soil permeability, catchment store coefficient maps in format of the SCS were obtained and by using WMS software for different return periods of 2, 5, 10, 25, 50 and 100 years, 6 hour rainfall and maximum flood of catchment estimates and are compared with real results. Normal, Gumball and Pearson distributions are used to complete data deficits. Results show that the 6-hours rainfall of the catchment is between 13.7 and 30.1 mm and the maximum flood of the catchment is between 0.2 and 9 m3/s. Comparison of the results show that the log Pearson III distribution has the best fit for real data and the mean relative error for 100 years return period is 0.8 percent that confirm the accuracy of the model.

One of the most important components of power generation in landlocked countries; Is the development of marine science and technology; The growing trend of marine technologies and the creation of scientific and technological leaps in the field of marine environment, requires the implementation of a development model as a roadmap. One of the most important sciences that has been emphasized by the Supreme Leader and has had specific measures in this field; Is the field of marine science and technology; In this regard, the researcher, by examining the theories and statements of the Supreme Leader as the highest official of the country, seeks to provide a model for the development of marine science and technology based on the statements of the Supreme Leader. The research method is qualitative and thematic analysis. The results showed that the main dimensions of the development of marine science and technology in the country are: marine ecology (9 components), values ​​of marine science and technology (10 components), marine science doctrine (11 components), future goals of science And marine technology (12 components) and policies and guidelines in the field of sea (16 components); The findings of this study show the doctrine of "being strong in the sea" for the future of the country's comprehensive development path.