Time filter

Source Type

Ghazi S.,Islamic Azad University at Parand | Ip K.,University of Brighton
Renewable Energy | Year: 2014

Increasing installation of photovoltaic (PV) systems and demand for more accurate prediction of their operational performance in the UK has prompted the research that aims to establish the relationships between output efficiencies, weather parameters and deposited solid particles on the panel surface. The direct use of efficiency figures quoted by PV manufacturers, normally based on measurements taken in clean laboratory environments of 25°C and at standard air density, is often not appropriate as field studies demonstrated the actual outputs could be reduced by as much as 60% in dusty or polluted climate without regular cleaning. The experimental investigations and case studies took place in the town of Brighton in the southeast of the UK. Experimental simulations of dry dust cover were carried out in the laboratory to establish the effect of dust density to light transmittance. The effect of dust deposit on panels subjected to the climatic elements was studied using a set of outdoor glass units configured at different tilt angles placed on a roof, which were subsequently analysed in the laboratory after exposures between one and four weeks. Effects of climatic parameters on the performance of PV panels were examined through detailed analysis of the performance of two existing PV installations in relation to their weather exposure. Results for the indoor experiments showed that even a small amount of fine particles could reduce light transmittance by as much as 11%. Distribution analysis of dust collected from the exposed glass units revealed particles sizes were smaller than 400 microns with the highest frequency under 20 microns but the impact on solar transmission through the glass was mere 5% after exposure of four weeks due to the frequent rainy days. Amongst a wide range of climatic parameters used in the statistical analysis, high humidity, rain and snow were found to have significant effects to the efficiencies of the two PV installations, which in some cases could annihilated any system output. This study has also revealed the geographical issue of birds in this coastal city as their droppings can create overheated spots on the PV panel and reduce its output. © 2014 Elsevier Ltd. Source

Mirhabibi A.,Islamic Azad University at Parand | Soroush A.,Amirkabir University of Technology
Tunnelling and Underground Space Technology | Year: 2013

Buildings are usually modeled as elastic beams in plane strain finite element (FE) simulation of tunnel-building interaction. However, neither tunnel nor surface buildings behave in a plane strain manner. In order to assess the effect of building modeling type on twin tunneling-induced ground settlement, some full three-dimensional FE models were analyzed and the effect of building modeling type was reviewed. Two dimensional (2D) plane strain interaction and green-field situation models were also analyzed to compare the results with the three dimensional (3D) models and assess the influence of modeling type. Outcomes of the studies showed that three-dimensional modeling has great influence on the results and equivalent surface beam, which is used in common practice of two-dimensional plane strain models, over-estimates the stiffness of building and leads to less settlement prediction in comparison with 3D simulation. © 2013 Elsevier Ltd. Source

Heidari M.R.,Islamic Azad University at Parand
Aerospace Science and Technology | Year: 2016

In the present study, the impacts of embedding belts are experimentally studied for a supersonic flow field around a long axisymmetric body. Also, the longitudinal and circumferential pressure coefficients along with the boundary layer profile are investigated for g-2 to 6 degrees angles of attack. To this end, two conical-cylindrical belts were installed at the middle and end parts of ogival cylinder model. To ensure the turbulent flow around the model, a trip strip causing artificial disturbances is utilized and the acquired results are compared with the acquired results from the model without a trip strip. To study the effects of the cross section variations on the pressure distribution as well as the boundary layer profiles, three different belts with various leading edge angles were installed at different locations along the cylindrical section of the model. These belts significantly affected both the surface pressure distribution and the boundary layer profile. Passing of flow over the belt leads to sudden variations in pressure coefficient distribution on the belt that is due to sudden cross section variations and consequent development of reverse flow or flow separation regions and production of vortices along the flow path. Also, the presence of belt leads to the development of oblique shock wave on the model, which in turn reduces the Mach number downstream the belt. Studying the circumferential pressure distribution reveals that the presence of belt leads to more asymmetric flow downstream the model, which is intensified as the angle of attack increases. © 2016 Elsevier Masson SAS. Source

Forghan B.,Islamic Azad University at Parand
International Journal of Theoretical Physics | Year: 2012

In this paper, considering the photon self energy in Krein space quantization including quantum metric fluctuation, the running coupling constant of QED is calculated and compared with the conventional result in QED theory. © 2012 Springer Science+Business Media, LLC. Source

Molaei S.,Islamic Azad University at Parand
Measurement: Journal of the International Measurement Confederation | Year: 2016

Mechanical properties of thin films, which can be used to improve the quality of products, have an important role in industry. In this study a new optical measurement technique based on secondary laser speckle patterns to extract Young's modulus by changing resonance frequency of specimen was developed. The samples investigated in this non-destructive and non-contact method were low density polyethylene (LDPE) and paperboard (PPR). This simple and highly accurate scheme has all the advantages of previous measurement techniques without any complex set-up and additional processing. © 2016 Elsevier Ltd. All rights reserved. Source

Discover hidden collaborations