Ahmad Sedaghat

Erratum to: Application of extreme learning machine for estimation of wind speed distribution

Unfortunately, the co-author affiliation Dalibor Petković has been incorrectly published in the original publication.

Rated wind speed reality or myth for optimization in design of wind turbines

The rotor design procedure of wind turbines starts first with adopting a rated output power and a rated wind speed. There is lack of modelling to determine an optimized rated wind speed and no evidences are observed to suggest the best rated wind speed to produce maximum output power annually. For example in the market of small wind turbines, it is frequently observed that the rated wind speed is taken from small value of 8 m/s to large value of 20 m/s. To examine overall performance of these wind turbines, it is required to develop mathematical models to relate the annual power production of the wind turbines to the given rated wind speeds. By examining power curves of some small European wind turbines from 100 to 900 Watt with constant speed generators, a simplified mathematical model for power curves is introduced and combined with Weibull distribution of wind speeds. Results of the model based on a capacity factor are presented versus the rated wind speed using wind characteristics of an optional region. It is observed that between the cut-in and cut-out wind speeds, there is an optimum rated wind speed above which the annual output power production of the wind turbine remains unchanged.

Mathematical modelling of the Marsh Funnel for measuring rheological properties of drilling nanofluids for energy efficient environment

The oil and gas industry has recognized the use of nanofluids for improving production rates and also reducing energy demands. Nanofluids function in oil well drilling is to modify rheological and heat transfer properties of the base fluid. Skin friction is reduced by nanofluids which in turn reduces drilling torque and the corresponding power consumption. This also mitigates wear on drilling equipments. The lubrication effects of nanofluids are achieved through enhanced surface energy absorption and ball bearing effects. Marsh Funnel is the practical method to measure viscosity of the drilling fluids with or without nanoparticles. The discharge time is the only measured parameter during operation. In this study, a new mathematical model is introduced for determining discharge flow rate of the Marsh Funnel. Results of the present method are validated against some available experimental data for Newtonian fluids. The present method can be equally applied for nanofluids. Marsh funnel volume discharge rate and the corresponding time are two important measureable parameters that can be used to determine different rheological parameters of nanofluids. The oil well drilling nanolubricants may be promising in an energy efficient operational environment.

External flows on entry of a hybrid wind catcher-wind turbine system

A new concept in wind power harnessing is recently developed under INVELOX (Increasing VELocity) by the company Sheerwind in USA. It is claimed that the new concept can significantly outperforms traditional wind turbines in terms of reducing the diameter of wind turbine, improve aerodynamic characteristics under the same wind conditions, and delivers significantly higher output at reduced cost. The innovative feature of the wind turbine is the elimination of tower-mounted turbines. It is believed that the entry of such systems is crucially important because external flows over nozzle or diffuse devices are different from classically known internal flows. Shrouded wind turbines and wind catcher systems are normally use a diffuser shape at entry, however, the INVELOX concept suggest using a nozzle at entry. In this paper, two different simpler systems than INVELOX are designed with nozzle or diffuser at the entry using general methods in design of blower wind tunnels. In the first phase of this work, CFD (computational fluid dynamics) method is applied to solve external flows around nozzle and diffuser flows by solving the modelled RANS (Reynolds average Navier-Stokes) equations. The initial results indicate that the wind speed retarded at the entry of nozzle while wind speed accelerated at entry of a diffuser device.

Heat losses from human body in weather condition of Amman city

It is wrongly anticipated that the amount of fats burn in human body is related to the amount of sweating, particularly in hot months of the year. In this study, heat losses from human body are studied based on clothing habit, weather condition in Amman city, and the bio-heat transfer mechanisms. The heat losses from human body include breathing (evaporation), conduction, convection, and radiation mechanisms. It is shown that heat losses are largely prevailed by conduction and radiation compared with convection and breathing mechanisms in all months of the year. It is also realized that the heat loss by breathing air is totally depends on the dry bulb temperature of the ambient. The heat loss by convection mechanism depends on many parameters such as clothes temperature, Nusselt number, and heat convection coefficient. The heat loss by radiation mechanism depends mainly on temperature differences between clothes surface and ambient. From the results of this study, the human body losses more heat in spring and winter than summer and autumn. It is also concluded that human body burns more fats during winter and spring seasons than summer and autumn.

Exergy analysis of reactive combustion processes in gas heaters

In this study, exergy analysis and second law efficiency of gas heaters with reactive combustion processes are considered. The reactive combustion of natural gas is modeled via a chain of eight chemical reactions along with first and second law of thermodynamics. The main constitutional elements react in combustion chamber is considered at constant pressure and temperature of the basic elements hydrogen, carbon, oxygen, and nitrogen from the fuel and air. Heat transfer is modeled assuming free convection and radiation mechanisms from gas heater outer surfaces. The governed equations were solved using Engineering Equation Solver (EES) software tool. Results of this study reveal that preheating of air will considerably increase the second law efficiency of combustion process. Excessive air is effective up to 40 percent to prevent incomplete combustion; however, excessive air more than 80 percent is not recommended from exergy stand point of view in gas heaters.

Neural Network usage in structural crack detection

Artificial Neural Network is becoming an efficient tool in online structural health monitoring. ANN enables, due to its promising inherent capabilities, to predict existence of undesirable effects such as cracks within the structure. Natural frequencies of the structure particularly the first three vibration modes are the most pronounced features of the structure to be evaluated for the health monitoring tasks. Crack in the structure make it weaker and under certain loads it may extend to complete fracture and sometimes to catastrophic failure. In this paper, the ANSYS software which employs finite element (FE) techniques is used to generate data for solid cantilever beams and simply supported beams. Natural frequencies are obtained for the first three vibration modes taking into account that the structure is linear for the healthy and the cracked structures. For different crack locations and crack depths, the ANSYS data on natural frequencies and vibration modes show lower values compared with healthy structure. These are good indicators to be used for training the Artificial Neural Network (ANN) tools. Results of ANSYS software is first verified with some available theoretical solutions and then results of the trained artificial neural network (ANN) for defected structure are compared with ANSYS solutions. The findings of this study suggest high accuracy of ANN on structural health monitoring with robust prediction of size and location of cracks.

Analysis of Polychlorinated Biphenyl Wastes Incineration in Rotary Kilns: Model Development and Validation

Polychlorinated Biphenyls (PCBs) are among hazardous wastes that must be incinerated for environmental and health protection. A dynamic model is introduced for the incineration of Polychlorinated Biphenyls (PCBs) in a rotary kiln. The model accounts for variations in composition and process conditions. The effects of excess air and the number of chlorine atoms in the structure of the PCBs are included in the incineration process. A MATLAB code was developed to solve the set of stiff nonlinear equations of PCBs incineration. The proposed incineration model was found to be in good agreement with the experimental data reported in the literature under ordinary feeding conditions for chlorinated compounds.

Computational study on design parameters of a solar chimney

Today, the production of energy and electricity is one of the major concerns of mankind. Electricity generation by solar energy is considered as one of the alternatives to fossil fuels. Solar chimneys mechanism is based on a natural phenomenon. In this process the solar energy heat up the earths surface and the surrounding air. Due to the density difference between cold air and warm air, heated air ascends and causes air circulation. In this study, mathematical modelling of solar chimney and governing equations of this system will be discussed. In order to validate the numerical results, upwind velocity in chimney has been compared with a reliable reference results. As well as, the optimized geometry of chimney has been investigated. Therefore, by the simulation of a solar chimney, performance (output power and efficiency) for changes in geometry and physical parameters such as chimney height, chimney diameter, radius collector and collector height is estimated.