答辩博士：EMMANUEL AWUAH
指导老师：周俊教授
论文题目：PerformanceEvaluation andNumericalOptimization ofVibratoryDiggingShovelforHarvestingJerusalemArtichokeUsingDiscreteElementMethod
答辩委员会
主席：
薛金林教授/博导 南京农业大学
委员：
谢斌教授/博导中国农业大学
苑进教授/博导山东农业大学
陈坤杰教授/博导 南京农业大学
丁启朔教授/博导 南京农业大学
秘书：
顾宝兴 南京农业大学
答辩地点：2023年9月6日15：00
答辩地点：腾讯会议号902-437-366
论文简介：
Jerusalem artichoke (Helianthus tuberosusL.) is a versatile and resilient crop that has gained attention for its agronomic potential in recent years. It has an underground rhizome from which small tubers grow. The tubers are a good source of insulin, and protein, having high mineral content especially rich in iron, calcium, potassium, sodium, phosphorus and vitamin B, C, and B carotene. It has the potential to be used as raw material for green energy production, including ethanol, biogas, gasoline additives, pulp for paper, and fibreboard. In China, the tuber yield is about 4-6 Mg ha-1and 10-15 Mg ha-1for poor and good fertile soils.
Nonetheless, Jerusalem artichoke’s mechanical harvesting in China is less advanced than potato harvesting. Commercial potato harvester is inefficient in harvesting Jerusalem artichokes due to the vast development area of tubers in the soil and the wide-ranging sizes and shapes, some growing up to a depth of about 350 mm. Harvesting artichoke tubers, mainly at such a deep depth, is problematic, necessitating the optimisation of parameters for the harvesting operations to account for the effect of soil-tool dynamics on the digging performance.Research and development of a high-performance harvester are vital to improving the production efficiency of the Jerusalem artichoke industry.
The digging shovel is one of the harvester's main constituents, which directly interacts with soil. Harvesters' performance is largely determined by the interaction between their digging shovels and the soil. An understanding of the mechanics of cutting tool-formation interactions is required for practical and economical excavation.Conditions, such as soil-metal coefficient of friction and soil type, shovel geometry, and operating parameters (e.g., rake angle, cutting depth, and forward speed), have been revealed to impact machine performance substantially.An effective approach to decreasing energy requirements for root-tuber harvesting operations is the application of vibration. In addition to reducing draught and vertical forces, vibration tools help break up clods.
With computing power and memory development, the possibility of optimising soil-engaging implements using numerical methods has emerged. Numerical modelling has proven to be more accurate, more adaptable, and less expensive than experimental and analytical methods. The discrete element method (DEM) is a numerical technique that tracks the motion of individual particles and updates any contact withneighbouringelements using a constitutive contact law.The DEM was explicitly developed for modelling granular materials such as soils.
Even though some field and laboratory studies have been carried out to study the draught and power requirements of oscillating soil tools, there are only a few investigations where the problem was numerically approached. Additionally, there is no indication that these investigations are related to the specific situation of a mixed medium, such as soil with tubers or roots embedded within it. Despite the importance of understanding cutting tool-formation interactions, little progress has been made in this frontier due to the complexity of tool-medium interaction. The study's objective was to determine the optimal parameters for a vibrating digging toolthat could serve as a reference for reducing soil reaction forces online. The specific research items are as follows:
The effect of travel speed, vibration frequency, amplitude, and rake angle and the shovel geometry on soil reaction forces, drawbar power, and Archard wear were studied using the discrete element method (DEM) and response surface methodology (RSM) at a targeted shovel’s operating depth of 350 mm. Laboratory experiments of the static angle of repose and cone penetration tests were successfully used to calibrate the soil model using multi-sphere particles. Also, Design-Expert® Software (2021) version 13 was used to determine the optimised geometry design and operating parameters values from the soil-to-shovel interaction simulation based on numerical optimisation and desirability functions procedure. Two optimal solutions were obtained, with the first one having 2 km h-1speed, 13.86 Hz frequency, 20 mm amplitude, 15˚ rake angle, and S-shape geometry. Contrariwise, the second solution was at the same geometry design with 4 km h-1speed, 20.3 Hz, 20 mm amplitude, and 15˚ rake angle. Analysis of variance showed that all the individual factors influenced draught force, vertical force, and drawbar power. However, only frequency, amplitude, and geometry design significantly influenced Archard wear. Soil reaction forces increased with increasing speed. Vibration significantly affected soil reaction forces by reducing draught and vertical forces by 43.61% and 36.67%. DEM and RSM are effective techniques for designing and optimising soil-engaging implements.
Discrete element method (DEM) and response surface methodology (RSM) were used to determine the optimal combination of factors for harvesting Jerusalem artichoke tubers grown in cohesive soil. The DEM soil model consisted of particles with different radii in three shapes calibrated using the static angle of repose and cone penetration. Compared to data from a soil bin subsoiler evaluation, the DEM model had acceptable relative errors for draught force (6.7%), vertical force (4.5%), and furrow width (9.3%). Based on RSM, the validated DEM model was utilised to examine the effect of forward speed, vibration frequency, and amplitude on three harvesting shovels (S-shape, step-shape, and fork-shape) by quantifying draught and vertical forces, drawbar power, and abrasive wear. Analysis of variance showed that all the factors significantly affected all the response variables (p<0.05). The ratio of vibratory speed to forward speed (velocity ratio,Vr) was used to analyse the combined effect of the factors. At velocity ratios (Vr) greater than one (1.2-3.9), soil reaction forces and drawbar power were reduced. The optimal combination of parameters for minimising soil reaction forces, drawbar power, and wear at a depth of 350 mm was 2.5 km h-1forward speed, 14.5 Hz frequency, 30 mm amplitude, and S-shape shovel (Vr= 3.94), resulting in a draught force of 4636 N, a vertical force of 412 N, drawbar power of 2.64 kW, and an Archard wear depth of 2.36 mm. The vibratory mode of operation reduced draught force by 49% and 54% for the scaled and the full implement, respectively. The vertical force reduced by 81% and 36% for the scaled and the full implement, respectively. These findings suggested thatDEM, combined with RSM and the input parameters employed to model cohesive soils, may be applied confidently to determine harvesting tools’ performance.
The soil-cutting forces produced by root-tuber harvesters and other soil-engaging tools are key indicators of machine performance. The draught and vertical forces involved in digging root and tuber crops during their harvest need to be minimised to improve field operating efficiency, reduce soil disturbance and energy (fuel) use. Two field experiments were conducted on clay and sandy loam soils to evaluate a harvester using different frequencies and travel speeds at a digging depth of 200 mm. Discrete element models (DEM) were developed and subsequently used to replicate the field experiments and evaluate S-shape and fork-shape shovels. The DEM input parameters used for the clay soil were based on the previous study's calibrated model since the soil had similar properties. However, the Jerusalem artichoke crop was incorporated into the sandy-loam model to mimic the field situation. Hence, the input parameters of the sandy loam soil-crop model were determined by measuring the physical and mechanical characteristics of the crop. The soil-crop particles were then calibrated based on the results of the static angle of repose test. Linear regression and ANOVA(p<0.05) were used to analyse the data. Field measurements and DEM simulations showed that draught force increased concurrently with an increase in forward speed, which was observed for both soil textures, and it decreased with an increase in vibration frequency. In clay soil, the draught force decreased by approximately 41% (21176.69 to 12604.87 N) when the harvester was operated between 5 Hz and 14.5 Hz. In sandy loam soil, draught force reduced by approximately 21% (13327.93-10598.26) when the machine was operated between 10 Hz and 12.5 Hz. DEM-predicted draught force and drawbar power had average relative error values of 4% and 4.7% for clay and sandy loam soils, respectively, compared with experimental data. The S-shovel was more efficient at crushing and translocating soil-crop mass to the rear of the harvester than the fork-shape shovel.
The kinematic and dynamic analysis of vibrating digging shovels revealed that forward speed, vibration frequency, vibration amplitude, and rake angle were crucial performance indicators. The simulations accurately represented the soil-shovel interaction. The scaled and full implements showed substantial reductions in draught and vertical forces during vibratory operation.The method employed in this study to develop DEM soil-cropmodels can be confidently applied to assess the efficacy of different root-tuber harvesting tools, thereby expediting the design process of digging shovels. The optimal vibrating parameters identified in this study can serve as a reference for online soil reaction force reduction, laying the foundation for the development of an automated Jerusalem artichoke harvesting machine.
