Showing 5 results for Shafaghat
Armin Najarian, Rouzbeh Shafaghat,
Volume 17, Issue 2 (3-2017)
Abstract
Demands for high speed vessels are increasing due to various usages. Reducing the resistance to achieve high speeds is an important objective in design of high speed crafts. Creating longitudinal side tunnels in the hull causes resistance reduction. Designing the boat is not right only for reducing drag force; stability and maneuverability are also important factors. In this paper, high speed tunneled hull performance is evaluated considering numerical simulation of turning circle maneuver as a standard maneuver. The numerical approach is implemented due to high and acceptable accuracy compared with mathematical models and lower cost compared to experimental tests. Among the various techniques, modeling of maneuver of the boat was performed by considering mesh movement with boat and combination of sliding mesh and movement of domain as an effective method. Reducing computation time and increasing the accuracy of solution is of its advantages. Finite volume method and k-ω model is used respectively for discretization equations and simulation of turbulence. In free surface modeling, mixture model was preferred instead of free surface model. Solution methodology was validated using experimental results of a single-hull boat. Path of the boat in various tests was presented in the result section, considering the effect of angle of rudder, thrust and movement mode of the boat on the maneuver parameters. The results show enhancing maneuverability of the boat by approaching the planing mode so that by increasing the speed and closing to planing mode, tactical diameter is reduced up to 7.5% compared to the displacement mode.
L. Hendooie , R. Shafaghat, A. Ramiar, M. Dardel, Q. Esmaili,
Volume 19, Issue 7 (July 2019)
Abstract
One of the most important factors in decreasing the lifetime and inappropriate performance of PEM electrolyzers is the non-uniform current distribution on membrane surface. Since the smoothest distribution of species and water leads to optimal current distribution, in this research, a 1D- 1D model has been developed that explores the distribution of species and water, and finally the current distribution in layers and determines the optimal performance conditions of the high PEM membrane electrolyzers. In this model, the pressure is assumed constant throughout the channel, the cell temperature is constant, and the membrane is fully hydrated. The length of the anode and cathode channels is divided into 20 equal parts. By simultaneously solving the equations along the channel and perpendicular to it in each section, the distribution of species and current are obtained. The result showed that by increasing the average flow density, the flow distribution is smoother along the channel and, with increasing water flow, the current distribution is smoothed, but it has little effect on the polarization curve. Fick's effect on the distribution of species at the interface between the membrane and the gas diffusion layer has been investigated. Finally, the effect of thickness on the polarization curve is determined. By increasing the thickness of the membrane and the electrodes, the function of the system decreases.
Behrad Alizadeh Kharkeshi, Rouzbeh Shafaghat, Omid Jahanian, Kourosh Rezanejad, Rezvan Alamian,
Volume 21, Issue 12 (December 2021)
Abstract
Wave conditions have a significant effect on the hydrodynamic behavior of OWC. As the interactions of the WEC and the incident waves are important, therefore, due to the importance of coefficients in evaluating the performance of the OWC, in this paper, the experimental evaluation of dimensionless hydrodynamic coefficients of a MC-OWC is applied. To define the experimental tests, considering the installation location of the converter on the break water, the conditions of the Caspian Sea implemented. Calibration and uncertainty analysis have performed, experimental tests have been carried out in the wave tank of the BNUT. According to the results, assuming a dimensionless water depth, with increasing dimensionless frequency of the wave, the dimensionless coefficient of transmitted wave, the dimensionless coefficient of reflected wave, dimensionless coefficient of discharge and the dimensionless coefficient of pressure increase. The results showed that due to the change of dimensionless wave number from 1.9 to 3.3, discharge coefficients, reflected wave, pressure and transmitted wave are 1.6 times, 2.2 times, 2.8 times, respectively, are 3.5 times, the dimensionless coefficient of the transmitted wave is highly sensitive to the wave conditions; the dimensional coefficient of discharge will have less changes compared to other coefficients. On the other hand, the results showed that the OWC in this study has an efficiency of 41.8% in the best case. This efficiency occurs at the dimensionless natural frequency of 0.88 and the dimensionless water intake depth of 0.032; under these conditions, the amplitude of water fluctuations inside the OWC reaches 9.6 cm.
Ghazale Sadripour, Rouzbeh Shafaghat, Behrad Alizadeh Kharkeshi, Sina Sadeqi,
Volume 22, Issue 9 (September 2022)
Abstract
Flap-type WECs are used On-Shore to generate electricity and pump. The draft depth and incident wave frequency are parameters affecting the performance of this type of converters. In this paper, the effect of water draft depth and incident wave frequency on the performance of a converter at a scale of 1: 8 investigated experimentally. The power take-off system is hydraulic. The Caspian Sea was also selected as the target sea. After calibration and uncertainty analysis, experimental tests performed in the wave-flume of BNUT by regular waves. Considering the period of the Caspian Sea ([4-8] s), Froud scaling, the tests were performed in the period interval of [1.6-2.5] s, which is equivalent to the frequency interval [0.4-0.63 ] Hz. Also, due to the importance of the converter's draft, the converter's performance was evaluated from the draft of -0.1 (submerged flap) to 0.6 m. According to the results, the best converter performance was at the lowest frequency; the converter performance decreased with increasing frequency. The best converter performance was obtained at the dimensionless draft of 0.43 (equivalent to 0.4 m draft), and the converter power was reduced at larger and smaller draft. It is worth noting that at a negative draft (submerged flap), the converter has the lowest performance. The maximum values of flow, power and pressure on a laboratory scale were 0.14 liters per second, 21.3 watts and 156.8 kPa, respectively, which were measured at 18 liters per second, 22.66 kW, respectively, using Froud scaling method. And will be 1249/61 kPa
Ali Ebrahimi, Rouzbeh Shafaghat, Mahdi Yousefifard, Ali Haji Abadi,
Volume 23, Issue 1 (January 2022)
Abstract
In this study, the effect of transverse steps location on hydrodynamic components and the longitudinal stability of the vessel has been investigated. The vessel studied in this research is a planning catamaran, each demi-hull with two transverse steps. At first, vessel resistance with a weight of 5.3 kg within a range of length Froude number of 0.49 to 2.9 in calm water has been calculated. Then, craft behavior was evaluated at displacements of 5.3, 4.6, and 4 Kg using the numerical method. The numerical simulation results have been validated with similar experimental results. The craft in 4 and 5.3 kg weights, in Froude numbers greater than 2.43 and 2.9, respectively, has a Porpoising instability. In order to improve the longitudinal stability of the vessel, the Taguchi test design has been used to determine the optimal location of the transverse steps. The results showed that by placing the transverse steps in the optimum location, the Porpoising instability in the vessel has been resolved. In planing mode, vessel resistance decreased by 12%, 9.5%, and 6.6% in the optimum state of transverse steps compared to the base state for the mentioned weights. In similar conditions, the lift force on the vessel increased by 15, 10, and 7 percent for the mentioned weights, respectively.
