Simulation of Uniaxial Compression for Flexible Fibers of Wheat Straw Using the Discrete Element Method

HighlightsSimulation of uniaxial compression was performed with flexible fibers modeled in DEM.Bond-specific DEM parameters were found to be sensitive in uniaxial compression.A calibration technique that is not plunger-dependent is shown and validated.Abstract. To accurately simulate a discrete element method (DEM) model, the material properties must be calibrated to reproduce bulk material behavior. In this study, a method was developed to calibrate DEM parameters for bulk fibrous materials using uniaxial compression. Wheat straw was cut to 100.2 mm lengths. A 227 mm diameter cylindrical container was loosely filled with the cut straw. The material was pre-compressed to 1 kPa. A plunger (50, 150, or 225 mm diameter) was then lowered onto the compressed straw at a rate of 15 mm s-1. This experimental procedure was simulated using a DEM model for different material properties to generate a simulated design of experiment (DOE). The simulated plunger had a travel rate of 40 mm s-1. The contact Young’s modulus, bond Young’s modulus, and particle-to-particle friction DEM parameters were found to be statistically significant in the prediction of normal forces on the plunger in the uniaxial compression test. The DEM calibration procedure was used to approximate the mean laboratory results of wheat straw compression with root mean square (RMS) percent errors of 3.77%, 3.02%, and 13.90% for the 50, 150, and 225 mm plungers, respectively. Keywords: Calibration, DEM, DOE, Flexible DEM particle, Uniaxial compression, Wheat straw.

An Automatic Handheld Device for Firmness Measurement of Fruit with Edible Peel Based on Resistance Sensing: A Case Study of Peaches

HighlightsA handheld device was developed for automatic on-site measurement of fruit firmness.The prototype device achieved better performance than a typical commercial penetrometer.Two commonly used firmness-related parameters could be predicted based on the prototype readings.The distribution and changes of firmness could be visualized based on 3D models of the prototype readings.Abstract. Firmness is an important indicator of fruit quality. The devices for on-site fruit firmness measurement need to be portable, low-cost, lightweight, reliable, and flexible. Existing portable devices can provide firmness-related parameters, but their measurement results cannot be converted to each other. Their measurement results are also susceptible to operator error due to the manual measurement process. To solve this problem, a prototype handheld device was developed based on sensing fruit resistance to achieve automatic on-site firmness measurement of fruit with edible peel and provide commonly used firmness-related parameters. The prototype’s precision was verified by analyzing the repeatability and reproducibility of the measurement results with four Shore hardness blocks. The relative standard deviations (RSDs) of the results obtained by the same operator were less than 0.61%, and there was no significant difference among the results obtained by different operators (p < 0.05), which indicated that the prototype could provide reliable measurement results. A case study of peaches was performed, and the results showed that (1) the prototype had better performance than a commercial penetrometer, (2) two commonly used firmness-related parameters could be predicted based on regression models between a texture analyzer and the prototype readings (R2P = 0.908 and RMSEP = 4.191 N for maximum force; R2P = 0.923 and RMSEP = 1.613 N mm-1 for initial slope), (3) changes in the prototype readings for peaches during growth corresponded with the growth characteristics, and (4) the distribution and changes of peach firmness over time could be visualized based on 3D models of the prototype readings. Keywords: Automatic, Fruit firmness, Handheld device, High precision, Peach.

Chemical Concentration and Spatial Uniformity of a Premixing In-Line Injection System Attached to a Variable-Rate Orchard Sprayer

HighlightsA newly developed premixing in-line injection system attached to a variable-rate orchard sprayer was evaluated.Tests were conducted to verify the in-line injection system performance using a vertical spray patternator.Concentration accuracy and spatial distribution uniformity were determined with a fluorescent tracer.Uniform spray mixtures were obtained for different spray viscosities and duty cycle combinations.Abstract. Pesticide spray application efficiency is highly dependent on the chemical concentration accuracy and spatial distribution uniformity. In this study, the performance of a newly developed premixing in-line injection system was evaluated when it was attached to a laser-guided, pulse width modulated (PWM), variable-rate orchard sprayer. The chemical concentration accuracy was determined with respect to spray deposition with a fluorescent tracer, and the spatial distribution uniformity was determined with spray deposits at different heights on a vertical spray patternator. Outdoor tests were conducted with 27 combinations of target chemical concentration (1.0%, 1.5%, and 2.0%), viscosity of the simulated pesticide (1.0, 12.0, and 24.0 mPa·s), and various spray outputs manipulated with PWM duty cycles. For each injection loop, the amounts of the chemical concentrate and water discharged into the mixing line were measured separately in response to preset target concentrations. The results showed that the measured concentrations were consistent across the patternator heights, spray viscosities, and duty cycle combinations. For all treatments, the mean absolute percentage error (MAPE) of the measured concentration was 6.96%, indicating that the concentration accuracy of the system was acceptable. The mean coefficient of variation was 3.35%, indicating that the spatial distribution uniformity of the system was in the desirable range. In addition, there was little variation in chemical concentration for spray mixtures collected at different heights on the patternator. Thus, the premixing in-line injection system could adequately dispense chemical concentrate and water to produce accurate concentrations and uniform spray mixtures for variable-rate nozzles to discharge to targets. Keywords: Environment protection, Precision pesticide application, Laser-guided sprayer, Tank mixture disposal, Specialty crop.

Reduction of Torsional Vibration in Resonance Phenomena for Tractor Power Take-Off Drivelines Using Torsional Damper

HighlightsRattling of tractor power take-off drivelines can be detrimental to operators.A novel driveline model, which includes a torsional damper, was constructed.The behavior of the model was validated against that of an actual tractor driveline.The validated model was used to determine the optimal torsional damper parameters.These optimal parameters were validated by laboratory tests.Abstract. Rattle noise and high levels of vibration in agricultural tractors lower the productivity of the operators and may cause serious health issues in them. This study examined a method for preventing resonance and reducing the torsional vibration that causes rattling in tractor power take-off (PTO) drivelines in the idle state using a two-stage torsional damper. The PTO driveline was simplified to a 6-DOF model based on the principle of equivalent mass moment of inertia using commercial simulation software. The variations in the angular velocity of the PTO drive shaft in an actual tractor were measured and compared to the simulation results using a single-stage torsional damper to validate the model. Using this validated PTO driveline model, the pre spring of a two-stage torsional damper was investigated to determine its optimal torsional stiffness to minimize torsional vibration. The simulation results showed that the variations in the angular velocity of the PTO drive shaft decreased as the torsional stiffness of the pre spring decreased; accordingly, an appropriate torsional stiffness reduced the variation in the angular velocity delivered to the PTO drive shaft. The optimal torsional stiffness of the pre spring was determined by considering the manufacturing limitations of the torsional damper and the magnitude of the input engine torque. A pre spring with this optimal torsional stiffness was installed on an actual PTO driveline to measure the angular velocity transmissibility, which was the ratio of the variation in the angular velocity of the engine flywheel to the variation in the angular velocity of the PTO drive shaft, and the results were compared with those of the simulation. When the angular velocity of the engine was 850 rpm, the angular velocity transmissibility of the PTO drive shaft was 0.4 in the actual test, similar to the value of 0.29 obtained using the simulation. Thus, the simulation-optimized pre spring was able to avoid the resonance domain, while considerably reducing the torsional vibration that leads to rattling. The results of this study support the safe operation of agricultural tractors and guide the evaluation of torsional damper configurations of different vehicles. Keywords: PTO driveline, Resonance, Simulation model, Torsional damper, Torsional vibration, Tractor rattle.

Modeling the Effects of Crop Rotation and Tillage on Sugarbeet Yield and Soil Nitrate Using RZWQM2

HighlightsFour crop growth modules in RZWQM2 were calibrated for four sugarbeet rotation sequences.Sugarbeet following wheat had a slightly higher yield (3% to 6.5%).Moldboard plow increased sugarbeet yield by 1% to 2%.The difference in N losses under different crop rotations and tillage operations was negligible.Abstract. Sugarbeet (Beta vulgaris) is considered to be one of the most viable alternatives to corn for biofuel production as it may be qualified as the feedstock for advanced biofuels (reducing greenhouse gas emission by 50%) under the Energy Independence and Security Act (EISA) of 2007. Because sugarbeet production is affected by crop rotation and tillage through optimal use of soil water and nutrients, simulation of these effects will help in making proper management decisions. In this study, the CSM-CERES-Beet, CSM-CERES-Maize, CROPSIM-Wheat, and CROPGRO-Soybean models included in the RZWQM2 were calibrated against experimental field data of crop yield, soil water, and soil nitrate from the North Dakota State University Carrington Research Extension Center from 2014 to 2016. The models performed reasonably well in simulating crop yield, soil water, and nitrate (rRMSE = 0.055 to 2.773, d = 0.541 to 0.997). Simulation results identified a non-significant effect of crop rotation on sugarbeet yield, although sugarbeets following wheat resulted in 3% to 6.5% higher yields compared to other crops. Net mineralization and N uptake rates were slightly higher when sugarbeets followed wheat compared to the other crops. Seasonal N and water mass balances also showed lower N and water stresses when sugarbeets followed wheat. The effects of tillage operations on sugarbeet yield were also non-significant. The difference in the N losses to runoff and drainage from the sugarbeet fields under different crop rotations and tillage operations was negligible. As sugarbeet production may be expanded into nontraditional planting areas in the Red River Valley due to potential demand for biofuel production, our findings will help to assess the associated environmental impacts and identify suitable crop rotations and management scenarios in the region. Keywords: Biofuel, Crop rotation, RZWQM2, Sugarbeet, Tillage.

Integrating Daily CO2 Concentrations in SWAT-VSA to Examine Climate Change Impacts on Hydrology in a Karst Watershed

HighlightsWe used SWAT-VSA to assess the effects of climate change with rising CO2 on the water balance of a karst basin.For future climate, SWAT-VSA with rising CO2 yielded 7.1% less ET and 6.3% more runoff than standard SWAT-VSA.Rising CO2 also affected variable source areas, with greater ET declines and runoff increases in the wettest soils.Findings suggest CO2 effects on water balance should be included in future climate change studies with SWAT-VSA.Abstract. Characterizing the effects of climate change on hydrology is important to watershed management. In this study, we used SWAT-VSA to examine the effects of climate change and increasing atmospheric CO2 (CO2) on the water balance of Spring Creek watershed, a mixed land-use karst basin in the Upper Chesapeake Bay watershed. First, we modified the stomatal conductance and leaf area index (LAI) routines of SWAT-VSA’s Penman-Monteith evapotranspiration (ET) procedure and enabled the model to accept daily CO2 data. Using downscaled climate projections from nine global climate models (GCMs), we then compared water balance estimations from baseline SWAT-VSA against two modified versions of SWAT-VSA. One SWAT-VSA version integrated daily CO2 levels (SWAT-VSA_CO2), while another version added flexible stomatal conductance and LAI routines (SWAT-VSA_CO2+Plant) to the dynamic CO2 capacity. Under current climate (1985-2015), the three SWAT-VSA models produced generally similar water balance estimations, with 51% of precipitation lost to ET and the remainder converted to runoff (10%), lateral flow (9%), and percolate (30%). For future climate (2020-2065), water balance simulations diverged between baseline SWAT-VSA and the two modified SWAT-VSA models with CO2. Notably, variable stomatal conductance and LAI routines produced no detectable effects beyond that of CO2. For the 2020-2065 period, baseline SWAT-VSA projected ET increases of 0.7 mm year-1, while SWAT-VSA models with CO2 suggested that annual ET could decline by approximately -0.4 mm year-1 over the same period. As a result, the two CO2-based SWAT-VSA models predicted streamflow increases of almost 1.6 mm year-1 over the 2020-2065 period, which were roughly double the streamflow increases projected by baseline SWAT-VSA. In general, SWAT-VSA models with CO2 effects produced 22.4% more streamflow in 2045-2065 than the SWAT-VSA model without CO2. Results also showed that adding daily CO2 to SWAT-VSA reduced ET in wetter parts of Spring Creek watershed, leading to greater runoff losses from variable source areas compared to baseline SWAT-VSA. Findings from the study highlight the importance of considering increasing atmospheric CO2 concentrations in water balance simulations with SWAT-VSA in order to gain a fuller appreciation of the hydrologic uncertainties with climate change. Keywords: Carbon dioxide, Climate change, Hydrologic model, Water balance, Watershed.

Electrical Properties Predict Wheat Leaf Moisture

HighlightsA non-destructive prediction model for moisture content of wheat leaves was established based on electrical properties.The model based on a single property (capacitance or resistance) was improved by using both properties.The model accurately detected the moisture content of wheat leaves in real-time to avoid irrigation lag.The results provide a basis for real-time and targeted water-saving irrigation of winter wheat in an arid region.Abstract. In this study, we aimed to establish a non-destructive and rapid approach to monitor the moisture content of wheat leaves in Southern Xinjiang, China, and promptly acquire information on the physiological water demand of crops to guide precision irrigation. Wheat leaves were used as the research object. Using a custom-made clamped parallel-plate capacitor and LCR digital bridge meter, we determined the electrical properties (capacitance and resistance) of wheat leaves with various moisture contents within a frequency range from 0.12 to 100 kHz. Moreover, we explored the correlation between leaf moisture content and the electrical properties. Our data showed that leaf moisture exhibited the best correlation with the electrical properties at 50 kHz. Under these optimized conditions, a model for moisture measurement was established using a single-parameter method (capacitance or resistance). However, the estimated standard errors (RMSE) of this method were 3.29% (for resistance) and 3.49% (for capacitance), which were greater than the standard error of the measured moisture content (2%). Therefore, we developed an improved model using a two-parameter method (capacitance and resistance), and the estimated standard error was 2.68%, which was more feasible for predicting moisture content compared with the single-parameter method. The model was validated using eight groups of wheat leaf samples at the turning-green stage and the jointing stage, and the RMSE values were less than 2%. Our findings provide a scientific basis for real-time and targeted water-saving irrigation of wheat in arid areas of Southern Xinjiang. Keywords: Electrical property, Model, Moisture content, Precision irrigation, Wheat leaves.

Effect of Vibration on Rapeseed Header Loss and Optimization of Header Frame

HighlightsThe relationship of vibration and header loss was studied by multi-point vibration measurement and loss collection test.There was an approximately linear positive correlation between total header vibration and total rapeseed header loss.The header frame was analyzed and optimized through modal simulation and testing.The total rapeseed header loss of the improved header was reduced by 33.2% to 46.9%.Abstract. In view of the current large rapeseed header losses of rape combine harvesters, the effects of the header on rapeseed header loss were studied from the perspective of vibration. First, the vibrations at various measuring points on the header during rape harvest were studied using a data acquisition and analysis system while performing collection tests of rapeseed header loss with the sample slot method. The relationships between total header vibration and total rapeseed header loss and between vertical cutter vibration and rapeseed vertical cutter loss were shown to have a positive correlation, and they all increased with the increase in engine speed. Vertical cutter loss accounted for 31.2% to 42.4% of the total rapeseed header loss. Modal analysis and optimization of the header frame were then performed by simulation and test. The natural frequencies of the first-order and second-order modes of the optimized header were increased, and the possibility of resonance with other working parts was eliminated. Finally, the improved header was tested during rape harvest. The results showed that the total vibration of the improved header was reduced by 19.9% to 43.9%, and the total rapeseed header loss was reduced by 33.2% to 46.9%. The vertical cutter vibration was reduced by 30.5% to 49.8%, and the rapeseed vertical cutter loss was reduced by 20.8% to 34.7%. In addition, the vibration and rapeseed loss of the improved header had relatively slow rates of increase with the increase in engine speed. The method of reducing rapeseed loss by reducing the header vibration achieved an obvious and positive effect. Keywords: Frame optimization, Modal analysis, Rape combine harvester, Rapeseed header loss, Vibration.

Microwave Nondestructive Sensing of Moisture Content and Water Activity of Almonds

HighlightsMoisture and water activity were determined nondestructively and in real time from measurement of dielectric properties.Moisture and water activity calibration equations were established in terms of the dielectric properties.Situations in which bulk density was known or unknown were considered.SEC ranged from 0.41% to 0.68% for moisture and from 0.02 to 0.04 for water activity.Abstract. A method for rapid and nondestructive determination of moisture content and water activity of granular and particulate materials was developed. The method relies on measurement of the dielectric constant and dielectric loss factor at a single microwave frequency. For the purpose of illustration, the method was applied to predicting the moisture content and water activity of almond kernels. A free-space transmission technique was used for accurate measurement of the dielectric properties. Samples of Bute Padre almond kernels with moisture content ranging from 4.8% to 16.5%, wet basis (w.b.), and water activity ranging from 0.50 to 0.93 were loaded into a Styrofoam sample holder and placed between two horn-lens antennas connected to a vector network analyzer. The dielectric properties were calculated from measurement of the attenuation and phase shift at 8 GHz and 25°C. The dielectric properties increased linearly with moisture content, while they showed an exponential increase with water activity. Situations in which the bulk density was known and unknown were considered. Linear and exponential growth regressions provided equations correlating the dielectric properties with moisture content and water activity with coefficients of determination (r2) higher than 0.96. Analytical expressions of moisture content and water activity in terms of the dielectric properties measured at 8 GHz and 25°C are provided. The standard error of calibration (SEC) was calculated for each calibration equation. Results show that moisture content can be predicted with SECs ranging from 0.41% to 0.68% (w.b.) and water activity with SECs ranging from 0.02 to 0.04 for almond kernel samples with water activity ranging from 0.5 to 0.9 and moisture contents ranging from 4.8% to 16.5% (w.b.). Keywords: Bulk density, Dielectric constant, Dielectric loss factor, Free-space measurements, Loss tangent, Microwave frequencies, Moisture content, Water activity.