جستجوی مقالات مرتبط با کلیدواژه « experimental » در نشریات گروه « مهندسی دریا »

Supplying world future energy is tied with renewable energies and wave energy is one of the biggest resources of renewable energy which is somehow untapped. Oscillating Water Column (OWC), one of the most familiar devices in harnessing wave energy, is still not being properly commercialized due to the complicated hydrodynamic behavior. Offshore OWCs are exposed to higher wave energy; however, the researches on this kind of OWCs is limited. Hence, in this paper, a fully nonlinear two phase flow model of a fixed offshore OWC is developed using Ansys Fluent. Unlike the previous studies, the developed numerical model has the merit of being validated against a relatively large scale physical model (1:15). The results of the model are compared by those obtained in experimental campaign conducted by the authors. Results of both free surface elevation and air pressure in the OWC chamber are compared. Generally, the results showed an admissible accordance between numerical and experimental model. Some discrepancies could be detected in the free surface elevation in the chamber especially for short wave period. This can be attributed to the increase of nonlinear effects in the chamber by increase of wave steepness. The developed model can be applied for further researches on OWCs such as optimization or improving OWC performance.

Increasing problems due to supplying energy demand conveyed researchers to find a solution in renewable energy resources and consequently marine engineers drew attentions towards wave energy which has the merit of higher energy density than the other resources. Oscillating Water Column (OWC) is one of the most propitious devices for capturing wave energy. Researchers have studied the device under different wave height and period conditions and they investigated various geometric parameters such as front wall draft and the chamber length. However, the effects of wave spectrum type or shape has not been investigated deeply yet. Different wave spectra have been developed for different places around the world but the focus of this study is on the two well-known spectra called JONSWAP and Pierson-Moskowitz to see how the type of the spectrum can impact on inner chamber fluctuation, pressure variation and reflection response of an offshore OWC. To achieve this goal, a 1:15 scale model of an offshore OWC was constructed in National Iranian Marine Laboratory. The results show that inner chamber free surface spectrum is affected by the type of incident wave spectrum. In another word, energy content at peak frequency was approximately 50% higher when the incident wave spectrum is of JONSWAP type. However, energy corresponding to sloshing frequency and total energy content in the chamber were almost the same for both types of the spectra. Pressure spectra inside the chamber showed a similar trend as free surface elevation. Although there was a little difference in reflection response of an OWC influenced by the type of spectra, this discrepancy was more pronounced in high frequency waves.

In this study, the experimental analysis on the bare hull resistance coefficient of submarine at snorkel depth is represented. The experiments are conducted in marine laboratory of Admiral Makarov University. The results are presented for surface condition and snorkel condition. Snorkel depth is regarded equal to one diameter of submarine hull beneath the water surface as usual in submarines. Performing the experiment at the surface condition is a usual practice process but performing the experiment at submerged condition has several technical notes which are evaluated in this paper. One of challenging discussions is estimating the induced resistance between the main hull and struts. For this part of study, CFD method is used. CFD analyses are conducted by Flow-3D (V.10) software based on solving the RANS equations and VOF method. All analyses are performed for still water condition. The results of this research can be used for AUVs, research submersibles and submarines, torpedoes and every submersible who operate near the free surface of water.