Abstract
Hydraulic scouring is the most effective approach to harvest lotus roots, but its application is largely restricted by the low harvesting rate. After hydraulic scouring, some mature lotus roots are still partially buried in the soil. Therefore, it is highly necessary to develop an appropriate approach to harvest semi-buried lotus roots. In this work, we for the first time studied the interaction between semi-buried lotus roots and soil, as well as analyzing the pull-out process and the factors affecting the pull-out force of semi-buried lotus roots. Firstly, a simple testing platform was designed based on the virtual prototype technology and the tests on pull-out force were conducted on five lotus roots with similar shape but different weights, with the burial depth and pull-out speed as the experimental factors. The results revealed that the maximum pull-out force is not significantly affected by the pull-out speed, whereas it is significantly influenced by the burial depth and the surface area of lotus roots. The maximum pull-out force increased with increasing lotus root surface area and burial depth. In addition, the discrete element method was employed to simulate the pull-out process of lotus root at different pull-out speeds. The simulation results indicated that a higher pull-out speed would result in a greater pull-out force at the same displacement of the lotus root from the soil. Both experimental and simulation results revealed that soil adhesion contributes the most to the pull-out resistance. It was also observed that a slight loosening of semi-buried lotus roots could drastically reduce the pull-out force. These results suggest that some kind of mechanical structure or improvement of water flow can be applied to the existing lotus root harvester to reduce the adhesion between lotus roots and soil. Overall, our findings provide a novel direction for optimizing hydraulic harvesting machines of lotus roots.
Highlights
Lotus root is one of the largest aquatic vegetables in China
When the pull-out force is greater than the resistance, the semi-buried lotus root can break away from the mud layer, and the instant pull-out force reaches the maximum value at the moment of separation
The maximum pull-out force is not affected by the pull-out speed, but is significantly influenced by the burial depth and surface area of the lotus root: it increases with increasing burial depth and surface area of the lotus root
Summary
Lotus root is one of the largest aquatic vegetables in China. The planting area of lotus root in China in 2014 was about 500,000 to 700,000 hectares [1]. Due to the huge economic benefits, the number of lotus root growers and the planting area have been increasing year by year. Lotus roots are mostly planted in low-lying and rotten fields with deep silt [2]. The special planting environment and growth conditions result in great difficulties in mechanized harvesting. With the rapid decrease in labor resources and increase in labor cost in rural China, the production cost of lotus roots has increased dramatically, which seriously restricts the scale development of the lotus root industry. Some scholars have developed several simple harvesting machines for lotus roots based on the planting characteristics, and the mechanized harvesting of lotus roots has been partly realized
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