نشریه مهندسی بیوسیستم ایران
سال چهل و یکم شماره 1 (بهار و تابستان 1389)

In conventional tillage systems, uniform depth tillage is applied over the entire field; however, the depth of hardpan layer varies greatly within the field. Site-specific tillage, which modifies physical properties of soil only where the tillage is needed for crop growth, could achieve significant savings in fuel consumption and drawbar power requirements. Site-specific tillage can be implemented either with (1) a pre-tillage map technology, or (2) a real-time sensor. The pre-tillage map technology would be a two-step process in which a sensor such as a soil cone penetrometer would be employed to develop maps showing the existence of hardpan and its depth. This map would then be used in the site-specific tillage equipment control system to control tillage implement location and depth. The real-time sensor would provide a one-step system to control tillage implement location and depth. In this research, a GPS-based variable-depth tillage implement was developed and evaluated. While the tractor is moving, a laptop receives the location of the tractor through the GPS, and then based on the soil compaction map, the controller dictates the depth of tillage implement. The variable-depth tillage implement was first calibrated in the workshop. The response time of the electro-hydraulic system was assessed. Then, the variable-depth tillage implement was evaluated under field conditions. The time required for the implement to reach the set depth under two ground speeds (2.6 and 3.6 km h-1) was determined. Stress analysis of the designed tillage implement, using a finite-element method, showed that the implement benefited from enough strength. The response time was increased linearly with depth, i.e., 3.7 cm depth increase per second. The accuracy and precision of the control system for changing the depth were 1.2 and 0.83%, respectively. The results showed that by considering the response time of the system and the travel speed of the tractor, the control system can be activated such that the variable-depth tillage implement reaches to the desired depth by the time it approaches the next expected depth changing zone.

For a determination of soil characteristics one should have access to instruments that can measure these characteristics, including: soil penetration resistance with high accuracy. One of the accurate instruments commonly employed in soil penetration determinations is cone penetrometer. This apparatus, by measuring soil cone index at different soil depths can provide useful about information about the soil. In this research a digital cone penetrometer was designed and fabricated. For a later evaluation of the apparatus, tests were carried out on grassland with three levels of moisture content (13%, 34% and 86%). The accuracy of the displacement and force measurement setups were recorded as 0.01 mm and 1.96 N, respectively. Based on the results of the experiments, with an increase in grassland (muskeg) moisture content, soil penetration resistance, increased, such that with an increase of a low level of penetration force, penetration increased greatly. Value of critical pressure at a level of moisture content of 13% was more than those at the other levels of moisture contents.

Canola is a prominent oil seed crop with a very high production potential in Iran and the production process of which needs to be optimized. Drying is an important part of the processing of the crop with EMC values playing a vital role in the process. In this research adsorption and desorption experiments were conducted in an environmental chamber for Licord variety of canola. The thin layer experiments were run in three replications at constant air temperature of 55? and relative humidity between 7% and 84% (8 points). The thermodynamic conditions (temperature and relative humidity) were maintained in the environmental chamber. Temperature was kept constant at 55? via an accurate thermostat and relative humidities were controlled using saturated salt solutions. Referring to the isotherm sigmoid shape curves for adsorption and desorption showed that the desorption EMC ones were more than the adsorption EMC values at constant temperature. The hysteresis effect can be clearly shown through adsorption-desorption curves. In order to find the best predictive EMC model, thirteen mathematical models namely, Oswin, Modified Smith, Modified Oswin, Modified Henderson, Modified Halsey, Modified Chung- pfost, Modified BET, Chung-pfost, Kuhn, Henderson, Halsey, GAB and Caurie were selected for fitting the experimental data. The goodness of fit was evaluated by coefficient of determination (R2), chi-square (?2) and root of mean square error (RMSE). The GAB model showed the best results for both desorption and adsorption processes. The values of coefficient of determination (R2), chi-square (? 2) and root of mean square error (RMSE) were 0.997, 0.023 and 0.120 for adsorption and 0.994, 0.031 and 0.140 for desorption processes respectively. The adsorption monolayer moisture content (m0) was evaluated using BET equation. The monolayer moisture content was calculated 1.555 (%d.b.) and the corresponding constant value in the BET equation was found as -10.371.

One of the most conspicuous arguments in industry as well as agriculture is the well being of the operator during work with machines, studied in the field of ergonomics. One of the machines to the hazardous and risks of which, farmers in the northern regions of Iran are exposed is the power tiller. In this work, some effects of the vibrations produced by a power tiller and imposed upon the operator were evaluated. Experiments were conducted in stationary operational conditions. Six engine speeds (1300, 1600, 1800, 2000, 2200, and 2400 rpm), along with four locations of vibration namely: chassis, hand grip, arm, and chest were selected. It was observed that with increase in engine speed, rms (root mean square) of acceleration in the four locations, increased in three directions. Also the dominant frequency through all locations and directions was found to be equal to the number of piston strokes or revolutions per seconds. Comparing acceleration values in the three directions demonstrated that, in all locations, the values are maximized in the vertical directions. Comparing rms acceleration values (three directions) and vibration total value,, in different locations (from chassis to chest) showed that these values reached their maximum levels on the hand grip. The values decrease gradually in transition path from hand grip to the chest due to damping off in operator’s body with all the transmitted vibrations being damped from head to the feet. In other words, they are absorbed within the operator's body. It was also observed that most of the vibrations are transmitted to the operator’s hand through hand grip, so an operator’s wrist bears the most operational severity. The transmissibility of vibration decreased gradually from wrist to the chest.

The present research reports on an optimized pilot project for plant and the production of biodiesel through alkaline-catalyzed transesterification of waste cooking oil. The reaction variables used were methanol/oil molar ratio (3:1–9:1), potassium hydroxide catalyst (concentration 0.25–1.50%), temperature (45–65???????????? °C), and mixing intensity (200–600 rpm). The interaction of these factors on biodiesel conversion was ignored. An evaluation of the transesterification process was followed by gas chromatographic analysis of the cooking oil fatty acid methyl esters (biodiesel) at different reaction times. A factorial experiment in the form of complete randomized design was employed as the analysis method. A study of the factors affecting the biodiesel purity shows that, within the experimental range considered, all exert positive effect on the biodiesel purity with the biodiesel purity increasing when the values of these variables increase. The biodiesel with best purity and quality was produced at methanol/oil molar ratio of 6:1; potassium hydroxide catalyst concentration of 1.0%; mixing intensity, of 600 rpm and reaction temperature of 65 °C. The yield of the biodiesel produced under optimal conditions was 94-95%. As a result of this study, maximum conversion of free fatty acids esterification (95%) was obtained within 2 hours. Finally, changing the performance of the operating units, the constructed plant output was twice that of such a similar plant as BDI-80.

Yield monitoring is one of the essential steps in the implementation of precision farming. Yield maps derived from yield monitoring system, clearly show crop yield variations. Research reports on preparing hay and forage yield maps are fewer in number and extent than those on grain crop. In this research, a method was developed for estimating alfalfa hay yield from a map developed for a small square baler. To obtain the crop yield map, two series of input data are needed namely: location and crop yield. In this research, location of the baler in the field was determined through using a local coordinate system. Since hay into the square baler is gradually accumulated to form the bale, spatial measurement of the hay is done by calculating the fractional volume accumulation. This fractional volume is converted into mass, by using two bulk density scales: bulk density of the forming bale and average bulk density of total field bales. Results of this study revealed that the output of system's shaft encoders were linearly related to the number of shaft revolutions (R2>0.998). By using each bale bulk density to convert volume data into mass, the error of system's yield measuring section was reduced from 22/12% to 1/74%. The error of the coordinate determination system used for length measurement was lower than that of the regular GPS (4.01% versus 14.27%).

Nowadays, remote sensing comes under the title of management method for precision farming. For provision of the land cover and therefore land use map use must be made of satellite images. For an assessment of the type of agricultural crops it is required to have satellite images of high resolution. From specifications of the satellite images one is to produce maps with varied scales. In this research, satellite images of IRS_1C, 1D within panchromatic and multispectral limits were employed. Satellite images were processed through PCI_GEOMATICA software. For an assessment of the types of the agricultural crops Leaf Area Index (LAI) was employed. Based upon the passing time of the satellite, the time for gathering information from the field was determined as 5/9/2006. Taking samples in latitude and longitude was recorded through GPS system. Following the process of exploitation of information the relationships among the bands were estimated and LAI determined. LAI comparison with ground-related information was carried out and analyzed. Then, through an assessment of the type of the agricultural crop corn and soybean were recognized through LAI. The results of this research indicated that LAI (index) could be used for a distinction of filed plant covering. It was proved that LAI could be used as a fruitful management tool in farm management planning and operations.

Orange (Citrus cinensis) is one of the most important among citrus fruits. The thin layer drying kinetics of orange (Thompson variety) slice was here experimentally investigated in a convective dryer and through mathematical modeling and by use of thin layer drying models. Drying characteristics of oranges were determined using heated ambient air at temperatures from 40 to 80 °C and velocities from 0.5 to 2.0 m/s. Beside the effects of drying air temperature and velocity, the effects of slice thickness on the drying characteristics, drying time were also determined. Drying curves obtained from the experimental data were then fitted to the thin layer drying models. The effects of drying air temperature and velocity on the model constants and coefficients were evaluated through a multiple regression technique. The models were compared according to three statistical parameters, i.e. root mean square error, chi-square and modeling efficiency. The results have shown that, increasing the drying air temperature and velocity causes shorter drying times. Midilli et al. model was found to be the most appropriate model for describing the drying curves of oranges. The effects of drying air temperature and velocity on the drying constant and coefficient were also investigated.

In recent years many researches are carried out to develop robots for agricultural applications. One of the main steps in agricultural robot fabrication is the generation of guidance signals. The objective of this research was a feasibility study of ultrasonic sensors in generating guidance signals to determine the position and orientation of a mobile robot for greenhouse applications. A series of experiments were performed to evaluate the accuracy of the ultrasonic sensors to determine the most applicable arrangement of sensors around the chassis of a robot. The most suitable detected distance ranges of the sensors were 15 to 200 cm. In distances less than 15 cm and angles more than 30 degrees the accuracy was found as low. The maximum width of view of the sensors for flat reflected objects was 17.15 and for curved objects 33.20 cm. The final arrangement of sensors was found out too. Experimental results proved that one can use ultrasonic sensors for generating guidance signals of robot inside greenhouses. With the designed averaging algorithm, one can calculate the lateral and heading errors for corrected data of ultrasonic sensors. Also, in comparison with reference sensors, the maximum error and RMSE for positions were 3 and 0.714 cm and for orientation they were 11.23 and 4.036 cm, respectively

Date palm (Phoenix dactylifera L.) with its delicious and nutritious bearing fruit (dates) is an important agricultural core in Iran. To extend the shelf life of date palm fruit, some such methods of preservation as drying are suggested and drying influences physicochemical and quality characteristics of products, thus modeling of drying kinetics is one of the tools for process control. In this research Barhi dates at khalal stage of maturity, after thawing, skinned and skinless, were dried in a laboratory scale hot-air dryer, under air flow of 1.5 m/s and air temperature of 60, 70 and 80? C. On the basis of these data, kinetics of the drying process were assessed and a characteristic drying curve established. The results showed that drying rate of skinless dates at 80? C is higher than that under other conditions. In plot of drying rate versus time, results indicated that drying took place in the falling rate period. The experimental data didnt show the dominating effect of temperature and being skin or not on the rehydration trend of this product. The influence of temperature and being skinned or not on the rehydration can thus be neglected. Results show that temperature and being skinned or not, have dominating effects on color index L,a and b Hunter Lab system. In order to estimate and select the appropriate drying kinetic model, the drying data as the moisture ratio (MR) versus drying time were fitted to a number 13 thin layer drying models. The comparison criteria employed were to evaluate goodness of fit, namely the coefficient of determination (R2), the root mean square error (RMSE) and the reduced chi-square (?2). The Wang model for drying of dates with skin and the Verma model for drying of skinless dates gave higher R2 vs. and lower RMSE and? 2 values than those in the other models.

Date palm (Phoenix dactylifera L.) is an important agricultural crop in Iran. To extend the shelf life of date palm fruit, some methods of preservation are employed, including drying. Drying influences physicochemical and quality characteristics of products, thus modeling of drying kinetics is a tool for process and therefore quality control. In this research Barhi dates at khalal stage of maturity, with and without peel, were dried in a laboratory scale hot-air dryer, under air flow of 1.5 m/s and air temperatures of 60, 70 and 80? C. The experimental shrinkage data showed a linear relationship with moisture content, a reduction in sample volume, and decrease in moisture content. The effect of temperature and the fruit being peeled or not on the shrinkage phenomenon can thus be neglected. A determination of water diffusivity could help in drying simulation for predicting the suitable drying conditions (air temperature and drying durations).Water diffusion coefficient values were assessed. The determined effective water diffusivity values ranged from 1.94×10-9 to 1.18×10-8 m2/s. The results revealed that the effective diffusion coefficient increased with increasing temperature. The results also showed that temperature and the fruit being peeled or not, have dominating effects on effective diffusion coefficient. The evolution of effective water diffusivity coefficient was described as a function of temperature through Arrhenios relation. The experimental diffusivity values were in a good agreement with the predicted values obtained from Arrhenios relation.