In a vertical wind tunnel, used for testing of aircraft and helicopters spin and simulation of sk... more In a vertical wind tunnel, used for testing of aircraft and helicopters spin and simulation of skydiving, a protective net made of multistrand wires is installed below the flight chamber to prevent the fall of the test models or skydivers to the ground. The drag due to the protective net is significant, which results in pressure drop and subsequent increase in the required power to attain a desired speed in the tunnel. This paper presents the results of an experimental study of drag coefficient of multistrand wires, using (i) a single normal hot-wire anemometer probe (HWA), (ii) a pitot tube, which measures the total pressure downstream of the multistrand wires. Initially, the non-dimensional distance, X/D, at which HWA measurements can be used to determine the drag coefficient of the multistrand wires with acceptable accuracy, was obtained by considering flow velocity profile and turbulence intensity, downstream of a cylindrical rod of diameter D. The distance was determined to be X/D > 30, where X is the distance along the test section downstream of the cylindrical rod. Results of pitot tube and HWA measurements are in good agreement. These results show that at Reynolds number, Re = 2000, drag coefficient of the multistrand wires is greater than the cylindrical rod by approximately 16%. However, the difference in the drag coefficients
Advances in Materials Science and Engineering, 2013
Al-Mg and CuZn34 alloys were lap joined using friction stir welding while the aluminum alloy shee... more Al-Mg and CuZn34 alloys were lap joined using friction stir welding while the aluminum alloy sheet was placed on the CuZn34. In addition, the mechanical properties of each sample were characterized using shear tests. Scanning electron microscopy (SEM) and X-ray diffraction analysis were used to probe chemical compositions. An artificial neural network model was developed to simulate the correlation between the Friction Stir Lap Welding (FSLW) parameters and mechanical properties. Subsequently, a sensitivity analysis was performed to investigate the effect of each input parameter on the output in terms of magnitude and direction. Four methods, namely, the "PaD" method, the "Weights" method, the "Profile" method, and the "backward stepwise" method, which can give the relative contribution and/or the contribution profile of the input factors, were compared. The PaD method, giving the most complete results, was found to be the most useful, followed by the Profile method that gave the contribution profile of the input variables.
The thermal control system must maintain temperatures of satellite components within their allowa... more The thermal control system must maintain temperatures of satellite components within their allowable limits throughout the satellite mission. Active and passive methods are used for satellite thermal control. A passive system uses suitable passive thermal hardware, structural material properties, and satellite spin at an appropriate rate to achieve the required thermal control action 1. Satellite structural designs use different materials, which are chosen based on their thermal performance, properties, manufacturing ease and cost 2. Aluminum alloys are the most widely used metallic materials in spacecraft manufacturing. The advantages include high strength to weight ratios, high ductility and ease of machining. The disadvantages include low hardness and a high
Research in Agricultural Engineering, Dec 31, 2014
Fuel consumption per hectare of tilled land for the conventional or maximum tillage, reduced till... more Fuel consumption per hectare of tilled land for the conventional or maximum tillage, reduced tillage using a multi-task machine, and no-tillage using a direct drill planter has been studied and compared. Time taken and number of tractor trips needed for performing tillage operations were used for comparison. Yield of crop per hectare was also used for the study. Duncan's multiple range test was used to compare and analyse the data. Results of fuel consumption were 59.33, 29.67 and 14.33 l/ha for the max. tillage, reduced tillage, and no-tillage cases, respectively. The corresponding yield of crop for these methods were 8.07, 7.90, and 6.33 t/ha, respectively. Therefore, the reduced and no-tillage methods provide enough energy saving per ton of yield to justify their use as good replacements for the max. tillage method in Iran. Also, considering land conditions in Iran, use of direct drill planters is recommended for dry cultivated or traditionally irrigated farms, and multi-task machinery for all types of irrigation systems and land conditions.
Agricultural Engineering International: The CIGR Journal, Dec 25, 2013
To study the economy of tillage operations and present suitable systems for land preparation and ... more To study the economy of tillage operations and present suitable systems for land preparation and planting, costs of execution of three different tillage operations in irrigated wheat crop were compared for three successive years. The three systems include: conventional or maximum tillage (Max-till), reduced tillage (Red-till) using multitask machine, and using direct planting machinery to represent the no-tillage case (No-till). Costs were composed of rental cost of tractor, the used implements, multitask machine and direct planting machine. For each case, data were compared and analyzed in randomized block design. The variance of wheat yield in the three tillage systems was significant at the 1% level. Total costs per hectare were 109 and 78 and 46 Dollars for Max-till, Red-till and the No-till case, respectively. Since, the test area under cultivation was part of a 200 hectare farm, crop protection and harvesting operations were carried out alike in the whole farm. Accordingly, operations costs were estimated as 445 Dollars ha-1 tare. Average yields of 7.85, 7.68, 5.2 t ha-1 were obtained, respectively, for Max-till, Red-till and No-till systems. Since, the price per kg of wheat was equal to 0.36 Dollars ha-1 , the profits of the harvest was equal to 2,271 Dollars ha-1 for the Max-till, 2,242 Dollars ha-1 for Red-till and 1,384 Dollars ha-1 for the No-till system. In tillage and planting operations, usage of the reduce tillage system is offered as an alternative to the conventional tillage and no-till systems. The Red-till system reduces fuel consumption, operation time, soil compaction due to decrease in the number of tractor trips, which leads to reduced production costs. In addition, less investment in purchasing implements and preparation of the soil, which breaks the soil cohesion, are achieved with the reduced tillage system.
Wind can adversely affect the thermal performance of a dry cooling tower. In this field study, pe... more Wind can adversely affect the thermal performance of a dry cooling tower. In this field study, performance of Heller cooling tower and the use of guide vanes cascade at the intakes of the periphery cooling sectors, which are parallel to the wind direction and have inadequate thermal performance, for enhancement of the cooling tower performance under wind conditions were investigated. Wind velocity around the cooling tower and water flow rates and temperatures at the cooling tower inlet and outlet were measured. It was observed that the air suction through the tower prevented the flow separation at the radiators locations on the tower periphery. Moreover, with increase in wind velocity, the performance of sectors parallel to the wind direction on the tower periphery and those at the back of the tower deteriorated. However, the better airflow distribution over the wind facing cooling sectors resulted in about 20% increase in the thermal efficiency of these sectors with increased wind velocity. Results further showed that the installation of guide vanes cascade caused more uniform temperatures on the surface of the tower radiators and reduced their temperature by 2 ºC, which was translated into 7% enhancement in the thermal performance of the cooling tower.
A test bed has been designed and constructed for measurement of air flow rate, and Ventilation Ef... more A test bed has been designed and constructed for measurement of air flow rate, and Ventilation Efficiency Ratio (VER) of residential exhaust fans. The test bed can provide accurate measurement of air flow rate, fan energy efficiency, and other air flow parameters. The test bed described here will also be useful for improvement of design of residential exhaust fans constructed in the country. Presently, the test bed is being used in an on going project for compilation of standards for consumption and energy labeling of fans in Iran.
Use of Jigs and fixtures can guarantee the proper fixation and positioning of cutting tools with ... more Use of Jigs and fixtures can guarantee the proper fixation and positioning of cutting tools with respect to work piece during the entire manufacturing process, helping in manufacturing of identical parts at required accuracy and production speed. In this paper, parametric modelling of a jig and fixture for drilling a cylindrical part, with mounting surface perpendicular to the cutting tool, has been carried out in CAE. The stability condition of the work piece during the drilling process has been evaluated by studying the forces due to the cutting tool and the clamp on the work piece, using the built-in FEM tools. The plastic deformation of the work piece must be prevented, and the elastic deformation should be such that it does not cause separation of the work piece from the positioner. Results show the high potential of the software in such design and modelling practices. A static analysis of the work piece secured in a jig and fixture has been performed to obtain the applied loads accurately and quickly. This helps prevent the extra cost incurred due to improper design.
Effective mass is a dynamic property of a structure associated with the modal characteristics; na... more Effective mass is a dynamic property of a structure associated with the modal characteristics; natural frequencies and mode shapes. It is a measure used to classify the importance of a mode when a structure is accelerated via its base. Additionally, a structure under acceleration loads can be affected by the distribution of modal effective masses in different frequencies. Hence, cumulating the effective mass in one frequency may cause a considerable reaction force in the structure. In this paper, effect of structural stiffening in a small satellite structure has been studied. Results show that both the dynamic response and equivalent static loads can be affected by characteristic of stiffening, which is a direct consequence of spreading of modal effective masses among more frequencies. Results of analyses performed on access doors of different geometries, with reinforcement frames having different stiffness, show that for the case of constant satellite structure total mass, the equivalent loads due to random vibrations and shock phenomenon change by 33% and 91%, respectively.
Satellite thermal control ensures safe operating temperature ranges for satellite components thro... more Satellite thermal control ensures safe operating temperature ranges for satellite components throughout the mission life. Effects of altitude, spin, and position of satellite radiator(s) on the thermal control of a small Low Earth Orbit (LEO) satellite have been studied. Results show that change in satellite altitude, in the range considered here, does not produce critical thermal conditions. However, satellite spin rate has a marked influence on the satellite temperatures. Also, comparison of results for the satellite configurations considered in this study suggests that a radiator at top provides better thermal design conditions. Results also indicate the adequacy of the discussed considerations for use in the design of satellites of similar configurations, missions and orbital parameters.
Regenerative Fuel Cell (RFC) systems are used for the enhancement of sustainable energy aspect in... more Regenerative Fuel Cell (RFC) systems are used for the enhancement of sustainable energy aspect in conventional fuel cells. In this study, a photovoltaic-electrolyzer-fuel cell integrated cycle has been presented. The proposed system has been designed as a novel approach for alleviating the restrictions on energy streams in the RFC systems. Modeling of the system has been performed from the mass and energy point of view, based on both theoretical and practical procedures. To generate electricity from hydrogen, a proton exchange membrane fuel cell, integrated with an electrolyzer system which works by solar energy, has been used. Optimized results of required photovoltaic area have shown significantdifferences between theoretical and practical approaches. Moreover, all efficiencies of two scenarios including total efficiency have been indicated and analyzed. The main advantage of this system in comparison with single solar systems, is generation of internal energy of about 2.3 kW for...
Launch event imposes critical loading conditions on the space flight hardware. Space structures a... more Launch event imposes critical loading conditions on the space flight hardware. Space structures are exposed to different environments and consequently the space vehicle experiences various loading conditions. The random vibration load, which is inputted mechanically and acoustically from rocket engines, is one of the major loads which must be considered in payload flight hardware structures. In this study two different approaches for calculating the frequency response of a small satellite structure under random vibration acceleration loads have been considered. These approaches are based on frequency response analysis using modal effective modes and effective masses related to these modes, and finite element spectrum analysis. The first approach considers the overall behavior of the structure. On the other hand, the second approach reveals the response of the structure on each desired node. The results of the first approach are dependent on the number of selected modes, and effectiv...
Effects of temperature on electrical parameters of polysilicon solar cells, fabricated using the ... more Effects of temperature on electrical parameters of polysilicon solar cells, fabricated using the phosphorous spin-on diffusion technique, have been studied. The current density–voltagecharacteristics of polycrystalline silicon solar cells were measured in dark at different temperaturelevels. For this purpose, a diode equivalent model was used to obtain saturation current densitiesmeasured at the required temperatures. The experimental results showed that the increase intemperature from 27 to 70˚C produced a rapid increase in the saturation current densities from 0.00003to 0.0005A. The changes in the open circuit voltage and the short circuit current density were found tobe linear with the temperature variations: about 3 mV/˚C reduction in the open circuit voltage wasobserved. Measurements of the short circuit current density revealed a very small dependency of thecurrent density on the temperature variations. Accordingly, the short circuit current density increasedfrom 17.8 to 18.4 ...
In a steam power plant, the temperature of the cooling water leaving the condenser for recyclings... more In a steam power plant, the temperature of the cooling water leaving the condenser for recyclingshould decrease. This is achieved in a cooling tower. The Heller cooling tower does not require waterfor operation, thus, it is a suitable system for use in thermal power plants throughout Iran. Wind is anenvironmental factor that unfavorably affects the performance of a cooling tower. Previous studieshave not considered real prevailing conditions appropriately; their conclusions are incomplete and, attimes, contradictory. The present field study of the cooling tower at Montazer-Ghaem Power Plant inthe city of Karaj in Iran investigated the effect of wind on the thermal performance of the coolingtower. Wind velocity was measured using blade-and-cup type digital anemometers. The direction ofthe wind around the cooling tower was determined using tufts. Ultrasonic flow meters and resistancethermometers were used to measure the flow rates and temperatures of the water at the inlet and outlet,...
This study proposes a comprehensive data processing and modeling framework for building high-accu... more This study proposes a comprehensive data processing and modeling framework for building high-accuracy machine learning model to predict the steam consumption of a gas sweetening process. The data pipeline processes raw historical data of this application and identifies the minimum number of modeling variables required for this prediction in order to ease the applicability and practicality of such methods in the industrial units. On the modeling end, an empirical comparison of most of the state-of-the-arts regression algorithms was run in order to find the best fit to this specific case study. The ultimate goal is to leverage this model to identify the achievable energy conservation opportunity in such plants. The historical data for this modeling was collected from a gas treating plant at South Pars Gas Complex for 3 years from 2017 to 2019. This data gets passed through a multistage data processing scheme that conducts multicollinearity analysis and model-based feature selection. For model selection, a wide range of regression algorithms from different classes of regressor have been considered. Among all these methods, the Gradient Boosting Machines model outperformed the others and achieved the lowest crossvalidation error. The results show that this model can predict the steam consumption values with 98% R-squared accuracy on the holdout test set. Furthermore, the offline analysis demonstrates that there is a potential of 2% energy saving, equivalent to 24 000 metric tons of annual steam consumption reduction, which can be achieved by mapping the underperforming energy consumption states of the unit to the expected performances predicted by the model.
This study proposes a data‐driven operational control framework using machine learning‐based pred... more This study proposes a data‐driven operational control framework using machine learning‐based predictive modeling with the aim of decreasing the energy consumption of a natural gas sweetening process. This multi‐stage framework is composed of the following steps: (a) a clustering algorithm based on Density‐Based Spatial Clustering of Applications with Noise methodology is implemented to characterize the sampling space of all possible states of the operation and to determine the operational modes of the gas sweetening unit, (b) the lowest steam consumption of each operational mode is selected as a reference for operational control of the gas sweetening process, and (c) a number of high‐accuracy regression models are developed using the Gradient Boosting Machines algorithm for predicting the controlled parameters and output variables. This framework presents an operational control strategy that provides actionable insights about the energy performance of the current operations of the unit and also suggests the potential of energy saving for gas treating plant operators. The ultimate goal is to leverage this data‐driven strategy in order to identify the achievable energy conservation opportunity in such plants. The dataset for this research study consists of 29 817 records that were sampled over the course of 3 years from a gas train in the South Pars Gas Complex. Furthermore, our offline analysis demonstrates that there is a potential of 8% energy saving, equivalent to 5 760 000 Nm3 of natural gas consumption reduction, which can be achieved by mapping the steam consumption states of the unit to the best energy performances predicted by the proposed framework.
Spirometry is pivotal in screening, diagnosing and monitoring pulmonary diseases and is increasin... more Spirometry is pivotal in screening, diagnosing and monitoring pulmonary diseases and is increasingly advocated for use in primary care practice. Inspired and expired lung volumes measured by spirometry are useful for detecting, characterizing and quantifying the severity of lung diseases. [1] A variety of techniques have been developed for the measurement of absolute lung volume based on the flow measurement. One such technique can measure flow rate with known orifice geometry and then do the time integral to get the total volume. One of the available operating principles for flow measurement is thermal anemometry. [2] It measures the total heat loss of a heating element and correlates the output signal to the flow rate of the fluid. [3] A flow rate sensor with large dynamic range is very essential in medical applications to measure, for example, the breathing rate of a child in normal conditions or the breathing rate of an adult person in exercise conditions, all with the same sensor. [4] Hot-wire is a delicate and highly sensitive device that provides flow velocity data. Its small size gives it good spatial resolution and high frequency response. [3] In A b s t r A c t Hot-wire spirometer is a kind of constant temperature anemometer (CTA). The working principle of CTA, used for the measurement of fluid velocity and flow turbulence, is based on convective heat transfer from a hot-wire sensor to a fluid being measured. The calibration curve of a CTA is nonlinear and cannot be easily extrapolated beyond its calibration range. Therefore, a method for extrapolation of CTA calibration curve will be of great practical application. In this paper, a novel approach based on the conventional neural network and self-organizing map (SOM) method has been proposed to extrapolate CTA calibration curve for measurement of velocity in the range 0.7-30 m/seconds. Results show that, using this approach for the extrapolation of the CTA calibration curve beyond its upper limit, the standard deviation is about −0.5%, which is acceptable in most cases. Moreover, this approach for the extrapolation of the CTA calibration curve below its lower limit produces standard deviation of about 4.5%, which is acceptable in spirometry applications. Finally, the standard deviation on the whole measurement range (0.7-30 m/s) is about 1.5%.
In a vertical wind tunnel, used for testing of aircraft and helicopters spin and simulation of sk... more In a vertical wind tunnel, used for testing of aircraft and helicopters spin and simulation of skydiving, a protective net made of multistrand wires is installed below the flight chamber to prevent the fall of the test models or skydivers to the ground. The drag due to the protective net is significant, which results in pressure drop and subsequent increase in the required power to attain a desired speed in the tunnel. This paper presents the results of an experimental study of drag coefficient of multistrand wires, using (i) a single normal hot-wire anemometer probe (HWA), (ii) a pitot tube, which measures the total pressure downstream of the multistrand wires. Initially, the non-dimensional distance, X/D, at which HWA measurements can be used to determine the drag coefficient of the multistrand wires with acceptable accuracy, was obtained by considering flow velocity profile and turbulence intensity, downstream of a cylindrical rod of diameter D. The distance was determined to be X/D > 30, where X is the distance along the test section downstream of the cylindrical rod. Results of pitot tube and HWA measurements are in good agreement. These results show that at Reynolds number, Re = 2000, drag coefficient of the multistrand wires is greater than the cylindrical rod by approximately 16%. However, the difference in the drag coefficients
Advances in Materials Science and Engineering, 2013
Al-Mg and CuZn34 alloys were lap joined using friction stir welding while the aluminum alloy shee... more Al-Mg and CuZn34 alloys were lap joined using friction stir welding while the aluminum alloy sheet was placed on the CuZn34. In addition, the mechanical properties of each sample were characterized using shear tests. Scanning electron microscopy (SEM) and X-ray diffraction analysis were used to probe chemical compositions. An artificial neural network model was developed to simulate the correlation between the Friction Stir Lap Welding (FSLW) parameters and mechanical properties. Subsequently, a sensitivity analysis was performed to investigate the effect of each input parameter on the output in terms of magnitude and direction. Four methods, namely, the "PaD" method, the "Weights" method, the "Profile" method, and the "backward stepwise" method, which can give the relative contribution and/or the contribution profile of the input factors, were compared. The PaD method, giving the most complete results, was found to be the most useful, followed by the Profile method that gave the contribution profile of the input variables.
The thermal control system must maintain temperatures of satellite components within their allowa... more The thermal control system must maintain temperatures of satellite components within their allowable limits throughout the satellite mission. Active and passive methods are used for satellite thermal control. A passive system uses suitable passive thermal hardware, structural material properties, and satellite spin at an appropriate rate to achieve the required thermal control action 1. Satellite structural designs use different materials, which are chosen based on their thermal performance, properties, manufacturing ease and cost 2. Aluminum alloys are the most widely used metallic materials in spacecraft manufacturing. The advantages include high strength to weight ratios, high ductility and ease of machining. The disadvantages include low hardness and a high
Research in Agricultural Engineering, Dec 31, 2014
Fuel consumption per hectare of tilled land for the conventional or maximum tillage, reduced till... more Fuel consumption per hectare of tilled land for the conventional or maximum tillage, reduced tillage using a multi-task machine, and no-tillage using a direct drill planter has been studied and compared. Time taken and number of tractor trips needed for performing tillage operations were used for comparison. Yield of crop per hectare was also used for the study. Duncan's multiple range test was used to compare and analyse the data. Results of fuel consumption were 59.33, 29.67 and 14.33 l/ha for the max. tillage, reduced tillage, and no-tillage cases, respectively. The corresponding yield of crop for these methods were 8.07, 7.90, and 6.33 t/ha, respectively. Therefore, the reduced and no-tillage methods provide enough energy saving per ton of yield to justify their use as good replacements for the max. tillage method in Iran. Also, considering land conditions in Iran, use of direct drill planters is recommended for dry cultivated or traditionally irrigated farms, and multi-task machinery for all types of irrigation systems and land conditions.
Agricultural Engineering International: The CIGR Journal, Dec 25, 2013
To study the economy of tillage operations and present suitable systems for land preparation and ... more To study the economy of tillage operations and present suitable systems for land preparation and planting, costs of execution of three different tillage operations in irrigated wheat crop were compared for three successive years. The three systems include: conventional or maximum tillage (Max-till), reduced tillage (Red-till) using multitask machine, and using direct planting machinery to represent the no-tillage case (No-till). Costs were composed of rental cost of tractor, the used implements, multitask machine and direct planting machine. For each case, data were compared and analyzed in randomized block design. The variance of wheat yield in the three tillage systems was significant at the 1% level. Total costs per hectare were 109 and 78 and 46 Dollars for Max-till, Red-till and the No-till case, respectively. Since, the test area under cultivation was part of a 200 hectare farm, crop protection and harvesting operations were carried out alike in the whole farm. Accordingly, operations costs were estimated as 445 Dollars ha-1 tare. Average yields of 7.85, 7.68, 5.2 t ha-1 were obtained, respectively, for Max-till, Red-till and No-till systems. Since, the price per kg of wheat was equal to 0.36 Dollars ha-1 , the profits of the harvest was equal to 2,271 Dollars ha-1 for the Max-till, 2,242 Dollars ha-1 for Red-till and 1,384 Dollars ha-1 for the No-till system. In tillage and planting operations, usage of the reduce tillage system is offered as an alternative to the conventional tillage and no-till systems. The Red-till system reduces fuel consumption, operation time, soil compaction due to decrease in the number of tractor trips, which leads to reduced production costs. In addition, less investment in purchasing implements and preparation of the soil, which breaks the soil cohesion, are achieved with the reduced tillage system.
Wind can adversely affect the thermal performance of a dry cooling tower. In this field study, pe... more Wind can adversely affect the thermal performance of a dry cooling tower. In this field study, performance of Heller cooling tower and the use of guide vanes cascade at the intakes of the periphery cooling sectors, which are parallel to the wind direction and have inadequate thermal performance, for enhancement of the cooling tower performance under wind conditions were investigated. Wind velocity around the cooling tower and water flow rates and temperatures at the cooling tower inlet and outlet were measured. It was observed that the air suction through the tower prevented the flow separation at the radiators locations on the tower periphery. Moreover, with increase in wind velocity, the performance of sectors parallel to the wind direction on the tower periphery and those at the back of the tower deteriorated. However, the better airflow distribution over the wind facing cooling sectors resulted in about 20% increase in the thermal efficiency of these sectors with increased wind velocity. Results further showed that the installation of guide vanes cascade caused more uniform temperatures on the surface of the tower radiators and reduced their temperature by 2 ºC, which was translated into 7% enhancement in the thermal performance of the cooling tower.
A test bed has been designed and constructed for measurement of air flow rate, and Ventilation Ef... more A test bed has been designed and constructed for measurement of air flow rate, and Ventilation Efficiency Ratio (VER) of residential exhaust fans. The test bed can provide accurate measurement of air flow rate, fan energy efficiency, and other air flow parameters. The test bed described here will also be useful for improvement of design of residential exhaust fans constructed in the country. Presently, the test bed is being used in an on going project for compilation of standards for consumption and energy labeling of fans in Iran.
Use of Jigs and fixtures can guarantee the proper fixation and positioning of cutting tools with ... more Use of Jigs and fixtures can guarantee the proper fixation and positioning of cutting tools with respect to work piece during the entire manufacturing process, helping in manufacturing of identical parts at required accuracy and production speed. In this paper, parametric modelling of a jig and fixture for drilling a cylindrical part, with mounting surface perpendicular to the cutting tool, has been carried out in CAE. The stability condition of the work piece during the drilling process has been evaluated by studying the forces due to the cutting tool and the clamp on the work piece, using the built-in FEM tools. The plastic deformation of the work piece must be prevented, and the elastic deformation should be such that it does not cause separation of the work piece from the positioner. Results show the high potential of the software in such design and modelling practices. A static analysis of the work piece secured in a jig and fixture has been performed to obtain the applied loads accurately and quickly. This helps prevent the extra cost incurred due to improper design.
Effective mass is a dynamic property of a structure associated with the modal characteristics; na... more Effective mass is a dynamic property of a structure associated with the modal characteristics; natural frequencies and mode shapes. It is a measure used to classify the importance of a mode when a structure is accelerated via its base. Additionally, a structure under acceleration loads can be affected by the distribution of modal effective masses in different frequencies. Hence, cumulating the effective mass in one frequency may cause a considerable reaction force in the structure. In this paper, effect of structural stiffening in a small satellite structure has been studied. Results show that both the dynamic response and equivalent static loads can be affected by characteristic of stiffening, which is a direct consequence of spreading of modal effective masses among more frequencies. Results of analyses performed on access doors of different geometries, with reinforcement frames having different stiffness, show that for the case of constant satellite structure total mass, the equivalent loads due to random vibrations and shock phenomenon change by 33% and 91%, respectively.
Satellite thermal control ensures safe operating temperature ranges for satellite components thro... more Satellite thermal control ensures safe operating temperature ranges for satellite components throughout the mission life. Effects of altitude, spin, and position of satellite radiator(s) on the thermal control of a small Low Earth Orbit (LEO) satellite have been studied. Results show that change in satellite altitude, in the range considered here, does not produce critical thermal conditions. However, satellite spin rate has a marked influence on the satellite temperatures. Also, comparison of results for the satellite configurations considered in this study suggests that a radiator at top provides better thermal design conditions. Results also indicate the adequacy of the discussed considerations for use in the design of satellites of similar configurations, missions and orbital parameters.
Regenerative Fuel Cell (RFC) systems are used for the enhancement of sustainable energy aspect in... more Regenerative Fuel Cell (RFC) systems are used for the enhancement of sustainable energy aspect in conventional fuel cells. In this study, a photovoltaic-electrolyzer-fuel cell integrated cycle has been presented. The proposed system has been designed as a novel approach for alleviating the restrictions on energy streams in the RFC systems. Modeling of the system has been performed from the mass and energy point of view, based on both theoretical and practical procedures. To generate electricity from hydrogen, a proton exchange membrane fuel cell, integrated with an electrolyzer system which works by solar energy, has been used. Optimized results of required photovoltaic area have shown significantdifferences between theoretical and practical approaches. Moreover, all efficiencies of two scenarios including total efficiency have been indicated and analyzed. The main advantage of this system in comparison with single solar systems, is generation of internal energy of about 2.3 kW for...
Launch event imposes critical loading conditions on the space flight hardware. Space structures a... more Launch event imposes critical loading conditions on the space flight hardware. Space structures are exposed to different environments and consequently the space vehicle experiences various loading conditions. The random vibration load, which is inputted mechanically and acoustically from rocket engines, is one of the major loads which must be considered in payload flight hardware structures. In this study two different approaches for calculating the frequency response of a small satellite structure under random vibration acceleration loads have been considered. These approaches are based on frequency response analysis using modal effective modes and effective masses related to these modes, and finite element spectrum analysis. The first approach considers the overall behavior of the structure. On the other hand, the second approach reveals the response of the structure on each desired node. The results of the first approach are dependent on the number of selected modes, and effectiv...
Effects of temperature on electrical parameters of polysilicon solar cells, fabricated using the ... more Effects of temperature on electrical parameters of polysilicon solar cells, fabricated using the phosphorous spin-on diffusion technique, have been studied. The current density–voltagecharacteristics of polycrystalline silicon solar cells were measured in dark at different temperaturelevels. For this purpose, a diode equivalent model was used to obtain saturation current densitiesmeasured at the required temperatures. The experimental results showed that the increase intemperature from 27 to 70˚C produced a rapid increase in the saturation current densities from 0.00003to 0.0005A. The changes in the open circuit voltage and the short circuit current density were found tobe linear with the temperature variations: about 3 mV/˚C reduction in the open circuit voltage wasobserved. Measurements of the short circuit current density revealed a very small dependency of thecurrent density on the temperature variations. Accordingly, the short circuit current density increasedfrom 17.8 to 18.4 ...
In a steam power plant, the temperature of the cooling water leaving the condenser for recyclings... more In a steam power plant, the temperature of the cooling water leaving the condenser for recyclingshould decrease. This is achieved in a cooling tower. The Heller cooling tower does not require waterfor operation, thus, it is a suitable system for use in thermal power plants throughout Iran. Wind is anenvironmental factor that unfavorably affects the performance of a cooling tower. Previous studieshave not considered real prevailing conditions appropriately; their conclusions are incomplete and, attimes, contradictory. The present field study of the cooling tower at Montazer-Ghaem Power Plant inthe city of Karaj in Iran investigated the effect of wind on the thermal performance of the coolingtower. Wind velocity was measured using blade-and-cup type digital anemometers. The direction ofthe wind around the cooling tower was determined using tufts. Ultrasonic flow meters and resistancethermometers were used to measure the flow rates and temperatures of the water at the inlet and outlet,...
This study proposes a comprehensive data processing and modeling framework for building high-accu... more This study proposes a comprehensive data processing and modeling framework for building high-accuracy machine learning model to predict the steam consumption of a gas sweetening process. The data pipeline processes raw historical data of this application and identifies the minimum number of modeling variables required for this prediction in order to ease the applicability and practicality of such methods in the industrial units. On the modeling end, an empirical comparison of most of the state-of-the-arts regression algorithms was run in order to find the best fit to this specific case study. The ultimate goal is to leverage this model to identify the achievable energy conservation opportunity in such plants. The historical data for this modeling was collected from a gas treating plant at South Pars Gas Complex for 3 years from 2017 to 2019. This data gets passed through a multistage data processing scheme that conducts multicollinearity analysis and model-based feature selection. For model selection, a wide range of regression algorithms from different classes of regressor have been considered. Among all these methods, the Gradient Boosting Machines model outperformed the others and achieved the lowest crossvalidation error. The results show that this model can predict the steam consumption values with 98% R-squared accuracy on the holdout test set. Furthermore, the offline analysis demonstrates that there is a potential of 2% energy saving, equivalent to 24 000 metric tons of annual steam consumption reduction, which can be achieved by mapping the underperforming energy consumption states of the unit to the expected performances predicted by the model.
This study proposes a data‐driven operational control framework using machine learning‐based pred... more This study proposes a data‐driven operational control framework using machine learning‐based predictive modeling with the aim of decreasing the energy consumption of a natural gas sweetening process. This multi‐stage framework is composed of the following steps: (a) a clustering algorithm based on Density‐Based Spatial Clustering of Applications with Noise methodology is implemented to characterize the sampling space of all possible states of the operation and to determine the operational modes of the gas sweetening unit, (b) the lowest steam consumption of each operational mode is selected as a reference for operational control of the gas sweetening process, and (c) a number of high‐accuracy regression models are developed using the Gradient Boosting Machines algorithm for predicting the controlled parameters and output variables. This framework presents an operational control strategy that provides actionable insights about the energy performance of the current operations of the unit and also suggests the potential of energy saving for gas treating plant operators. The ultimate goal is to leverage this data‐driven strategy in order to identify the achievable energy conservation opportunity in such plants. The dataset for this research study consists of 29 817 records that were sampled over the course of 3 years from a gas train in the South Pars Gas Complex. Furthermore, our offline analysis demonstrates that there is a potential of 8% energy saving, equivalent to 5 760 000 Nm3 of natural gas consumption reduction, which can be achieved by mapping the steam consumption states of the unit to the best energy performances predicted by the proposed framework.
Spirometry is pivotal in screening, diagnosing and monitoring pulmonary diseases and is increasin... more Spirometry is pivotal in screening, diagnosing and monitoring pulmonary diseases and is increasingly advocated for use in primary care practice. Inspired and expired lung volumes measured by spirometry are useful for detecting, characterizing and quantifying the severity of lung diseases. [1] A variety of techniques have been developed for the measurement of absolute lung volume based on the flow measurement. One such technique can measure flow rate with known orifice geometry and then do the time integral to get the total volume. One of the available operating principles for flow measurement is thermal anemometry. [2] It measures the total heat loss of a heating element and correlates the output signal to the flow rate of the fluid. [3] A flow rate sensor with large dynamic range is very essential in medical applications to measure, for example, the breathing rate of a child in normal conditions or the breathing rate of an adult person in exercise conditions, all with the same sensor. [4] Hot-wire is a delicate and highly sensitive device that provides flow velocity data. Its small size gives it good spatial resolution and high frequency response. [3] In A b s t r A c t Hot-wire spirometer is a kind of constant temperature anemometer (CTA). The working principle of CTA, used for the measurement of fluid velocity and flow turbulence, is based on convective heat transfer from a hot-wire sensor to a fluid being measured. The calibration curve of a CTA is nonlinear and cannot be easily extrapolated beyond its calibration range. Therefore, a method for extrapolation of CTA calibration curve will be of great practical application. In this paper, a novel approach based on the conventional neural network and self-organizing map (SOM) method has been proposed to extrapolate CTA calibration curve for measurement of velocity in the range 0.7-30 m/seconds. Results show that, using this approach for the extrapolation of the CTA calibration curve beyond its upper limit, the standard deviation is about −0.5%, which is acceptable in most cases. Moreover, this approach for the extrapolation of the CTA calibration curve below its lower limit produces standard deviation of about 4.5%, which is acceptable in spirometry applications. Finally, the standard deviation on the whole measurement range (0.7-30 m/s) is about 1.5%.
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Papers by Foad Farhani