In response to the prevalent challenges of high shellfish breakage rate, excessive sediment inclusion, and severe substrate compaction associated with conventional harvesting equipment for the subtidal Manila clam (Ruditapes philippinarum), this study designed and optimized a novel rotary-cutting harvesting apparatus. The research commenced with a critical analysis of the limitations of existing shallow-sea shellfish harvesting equipment—including drag-harrow, hydraulic, rotary-tooth, submerged-paddle, and vibration types—with particular emphasis on the adverse environmental impacts of hydraulic methods, such as sediment resuspension and nutrient release which can lead to eutrophication. Through systematic design and theoretical analysis, the trajectory of the harvesting blade was meticulously modeled, and key operational parameters, including the velocity ratio, soil-cutting interval, and ridge height at the furrow bottom, were calculated to establish a theoretical foundation for the kinematic optimization. Factors influencing the sliding-cutting angle of the blade edge were thoroughly investigated, identifying the blade edge radius, bending angle, and width as the primary design variables. A high-fidelity simulation model was subsequently established using the Discrete Element Method (EDEM), wherein the intrinsic parameters of the substrate and clams were critically defined based on calibrated contact models, incorporating key sediment properties such as moisture content, bulk density, and internal friction angle. Using the blade edge radius, bending angle, and width as experimental factors, and the harvesting tool resistance and clam yield as the evaluation indicators, simulation results demonstrated that the optimal digging performance was achieved with an edge radius of 142 mm, a bending angle of 54°, and a blade width of 57 mm. Building upon these optimized blade parameters, a rotary-cutting harvesting mechanism was designed. Further simulation and Response Surface Methodology (RSM) analysis were conducted to determine the optimal operational parameters. The results indicated that the optimal harvesting performance was achieved with a forward speed of 0.6 m/s, a blade shaft speed of 125 r/min, and a blade spacing of 26 mm. Under these conditions, the clam harvesting rate reached 90.00%, with a mechanical load of 7.16 N exerted on individual clams and a total mechanism resistance of 476.26 N. A bench-scale test platform was constructed to validate the effects of forward speed, blade shaft speed, and blade spacing on harvesting performance and to verify the optimal operational parameters. The experimental results showed a harvesting rate of 93.00% and a blade shaft torque of 9.88 N·m. The relative errors between the bench test results and the simulation predictions were 3.33% for the harvesting rate and 5.40% for the shaft torque, confirming the reliability and accuracy of both the harvesting apparatus and the simulation model. A comprehensive comparative performance evaluation demonstrated the significant advantages of the proposed rotary-cutting apparatus over traditional hydraulic harvesting methods. Specifically, the sediment inclusion rate in the harvested clams was reduced by 61.49%, and the clam breakage rate was substantially lowered by 74.59%. Furthermore, the harvesting efficiency saw a notable improvement of 27.40%. From an ecological perspective, post-harvest substrate compaction measurements showed a 33.53% reduction compared to pre-harvest conditions, indicating a significantly minimized impact on the seabed ecosystem and promoting sustainable harvesting practices by adhering to the "catch-large-retain-small" principle. In conclusion, this study demonstrates that the designed rotary-cutting harvesting apparatus effectively addresses the critical issues of high breakage rate and sediment inclusion in Manila clam harvesting. It successfully achieves a harmonious balance between high harvesting efficiency and minimal environmental disturbance. The research outcomes, including the optimized structural and operational parameters and the validated simulation approach, provide valuable theoretical guidance and a practical reference for the design optimization and development of efficient and eco-friendly mechanized harvesting equipment for subtidal shellfish resources.

The global planting area of arugula (Eruca sativa Mill.) is increasing because of the unique flavor of this species. Excessive application of chemical fertilizers and pesticides is common in open-field cultivation of arugula, which leads to the accumulation of pesticide residue and nitrates in the leaves. Currently, arugula is mostly consumed as raw produce, increasing the importance of pesticide and pest-derived food safety issues. To improve the food safety and yield of arugula, we evaluated the effects of light quality from different LED light sources on the growth characteristics and nutritional quality of arugula plants hydroponically grown in an artificially illuminated plant factory. The arugula plants were grown under artificial LED light sources with different ratios of red and blue LED chips (3:1, 5:1, 7:1, 9:1), a photoperiod of 12 h/d, and a light intensity of 200 μmol/(m²∙s). White light was used as a control. The height, stem thickness, and leaf width of the arugula plants were measured every 5 d to generate curves of growth characteristics at different growth periods and to analyze the dynamic light quality needs of arugula. After 30 d of growth, the arugula plants were harvested, and the patterns of the effects of light quality on the growth characteristics and nutritional quality were examined. The results showed that red light had a significantly positive effect on the height, stem thickness, biomass accumulation, chlorophyll content, and soluble protein content of arugula. The arugula plants were tallest under the light with 9:1 red and blue LED chips ratio, but the effect on the soluble protein content was not significantly different from that under the 7:1 ratio, and the stem thickness and biomass accumulation were lower under the 9:1 ratio. Under the 7:1 red and blue LED chips ratio, arugula presented the greatest values of stem thickness, dry weight, fresh weight ratio, chlorophyll content, and soluble protein content. In addition, blue light promoted the synthesis of vitamin C. The light quality involving a 3:1 red and blue LED chips ratio led to a stocky plant morphology, which improved the storage and transportation ability of arugula plants.