Showing 4 results for Ghasemloo
Volume 13, Issue 7 (Supplementary Issue - 2011)
Abstract
Classification of vegetation according to their species composition is one of the most important tasks in the application of remote sensing in precision agriculture. To prepare an algorithm for such a mandate, there is a need for ground truth. Field operation is very costly and time consuming. Therefore, some other method must be developed, such as extracting information from the satellite images, which is comparatively cheaper and faster. In this study, we first introduced a simple method for Determination of the Vegetation Specie in full cover pixels (DVS) using their laboratory measured spectral reflectance curves. Then, based on these pixels, a hybrid method for vegetation field classification, which we call SCANN (Spectral Characteristics and Artificial Neural Network), is introduced. In this method, different vegetation spectral reflectance characteristics at the three extremes of green, red, and near-infrared along with an artificial neural network method were used. Comparing the results of DVS with those of field collected data showed near 100% accuracy. Based on the results of DVS, the results of SCANN showed an overall accuracy of more than 94%. This method is suggested for unsupervised classification using Hyperspectral images.
Hadiseh Soltani, Sadjad Ghasemloo, Hamid Parhizkar, Hamidreza Talesh Bahrami,
Volume 18, Issue 2 (4-2018)
Abstract
Plume reversion due to missile ascending and related flow expansion and its interaction with missile body especially with missile base has been an important concern of investigators and missile designers. The aim of the current is investigation of effects of different parameters on the interaction of plume and missile body. To do this, heat flux on the missile body at different conditions including different flight conditions, turbulence modeling, base length and nozzle modeling has been studied. In the following, plume induced flow separation is studied. To model flow field, Gambit 2.4.6 and Ansys Fluent 17 are used for grid generation and flow simulation respectively. The results show that with increasing in flight height, plume at the base of missile gradually expands and finally covers the base completely. As well as, it can be seen that plume expands more rapidly in the base region and reduces heat flux when the nozzle is not considered. The reduction of heat flux is different in various parts of the base, ranging from zero to a maximum of 83% in areas far away from or near the nozzle. In the end, the effect of the base length was investigated. The results showed that as the base length is increased, the vortices are further expanded and this expansion leads to increased heat flux so that when the base length is doubled, the heat flux is increased by 20% at most
Arezoo Najafian, Hamid Parhizkar, Sajjad Ghasemlooy, Abbas Tarabi,
Volume 18, Issue 3 (5-2018)
Abstract
In the present study, the numerical solution of the Ansys Fluent software has been used to calculate the sound produced by the high-speed flow on a cylinder using the Lighthill acoustic analogy. The calculations were carried out on a cylinder (part of the landing gear) at a speed of 70 m/s (take-off and landing speeds of airliners). The problem is initially caried out as a regular unsteady numerical solution. During the solution, aerodynamic noise data sources are stored as inputs of acoustic analyzes in files. Then, by solving the acoustic equations, the volume of produced sound (in decibel) is calculated at points that are pre-defined as the microphone in the desired coordinates. The purpose of this study is to study the ability of Fluent solution to calculate the sound generated by the flow, in addition of using a method for estimating the amount of sound increase by increasing the length of the cylinder. In the other words, due to the timing of the numerical solution, one can calculate sound generated by small length cylinder, and then, using engineering approximation, it estimates the sound of the flow around the larger-length cylinder. After the necessary calculations, results are provided as sound pressure level curves using the acoustic analogy and fourier spectral analysis. The results show that large eddy simulation turbulence model is most appropriate model for acoustic simulations. Also, the approximate method for evaluating the effect of increasing the length of the cylinder is in good agreement with the experimental results.
H.r. Talesh Bahrami, H. Parhizkar, S. Ghasemlooy,
Volume 19, Issue 5 (May 2019)
Abstract
one of the key issues in the design of high-speed modern devices such as giant aircraft and high-speed trains. In this regard, it is to design these devices in such a way to have at least aerodynamic noise. The cylinder, as a bluff body, is widely used in the design of various devices, such as a landing gear. Therefore, the reduction of cylinder noise can be widely used. In the present study, numerical solution is used to present a method for reducing the noise generated by flow on the cylinder. This is done by flow suction from the grooves the cylinder. Acoustic numerical calculations were performed, using LightHill's acoustic analog approach in the form of wave equations of Ffowcs-Williams & Hawkings model. The numerical solution is performed in the three-dimensional unsteady form, using the large eddy simulation turbulence model. The characteristics of the grooves, such as their dimensions and distance the generated acoustic noise have been studied. The results show that the active control method presented in this paper is an effective and yet simple way to control noise. The cylinder used in the present study produces a noise of about 110 dB at a speed of 250 km/h. According to the results, it can be said that by optimally arranging the number of slots and creating a proper flow suction, its sound level can be reduced to about 60 dB.
