Using the discrete element method (DEM) to simulate the rice machine transplanting operation is important for assessing the plant injury and optimizing the rice transplanter performance, while the DEM flexible model establishment that can accurately reflect the mechanical properties of the rice blanket seedling root blanket is an important foundation. Based on the root blanket's stratification and the root system structure's measurement and statistics, a new method for root blanket flexible modeling was proposed in this study. Firstly, the Hertz-Mindlin with bonding V2 contact model was used to establish substrate I (SI), substrate II (SII), substrate III (SIII), stemroot combination (SRC), and netted layer (NL) flexible models, respectively, and the model parameters were calibrated and determined by angle of repose (AOR), direct shear, and mechanical tests. The calibration results showed that the deviations of AOR simulated values for SI and SII were both less than 1.5 %, and the deviations of shear strength simulated values were both less than 4 %. Secondly, the shear characteristics of SI and SII were determined by direct shear test. The results showed that the physical and simulated shear stress-displacement relationship curves of SI and SII were basically the same; the hair roots mainly relied on the cohesive between them and the substrate to improve the substrate strength; the fitted lines of simulated shear strength and normal stress of SI and SII were in high agreement with these of the measured values; the deviations of the simulated cohesion and internal friction angle were both less than 5 %. After that, the Hertz Mindlin with JKR V2 contact model was used between SRC and substrate. The interfacial surface energy of the root blanket and the bonding parameters of SIII were calibrated by stem, half-SRC, and SRC pulling-out tests layer by layer. The calibration results showed that the deviation of the maximum pulling-out force of SRC was 5.83 %, verifying that the model could accurately simulate the intertwining effect of the crown roots. Finally, the flexible model of the root blanket was verified by cutting, curling, and tensile tests. The simulated test results were consistent with the trends of the physical test results; the deviations of the maximum cutting resistance of front cutting and side cutting were both within 8 %, the error percentage range of the marked points height was 0.35 % to 17.16 %, and the deviation of the maximum tensile force was 9.22 %, indicating the good feasibility of the modeling method and accuracy of the flexible model. The results of this study lay a foundation for the DEM simulation of the rice machine transplanting operation. They can also provide a reference for the numerical simulation of other multiplant root-soil complexes.

The discrete element method (DEM) is proving to be a reliable tool for studying the behavior of granular materials and has been increasingly used in recent years. The accuracy of a DEM model depends heavily on the accuracy of the particle property parameters chosen which is of vital importance for studying the mechanical properties of granular materials. However, the existing DEM parameter calibration methods are limited in terms of applicability, and the trial-and-error method remains the most common way for DEM parameter calibration. This paper presents a novel calibration method for DEM parameters using the multi-objective tree-structured parzen estimator algorithm based on prior physical information (MOTPE-PPI). The MOTPE-PPI does not rely on the training datasets and may optimize with every single test, significantly reducing the computational efforts for DEM simulation. Moreover, MOTPE-PPI is suitable for a variety of contact models and damping parameters in DEM simulation, showing robust applicability and practical feasibility. Taking an example, the DEM parameters of sandy gravel material collected from Dashixia rockfill dam in China are calibrated using MOTPE-PPI in the paper. The prior physical information is obtained through a series of triaxial loading-unloading tests, single-particle crushing tests, and literature research. Seven parameters in the rolling resistance linear contact model and breakage model are considered, and the optimization process takes only 25 iterations. Through quantitative comparison with existing parameter calibration methods, the high efficiency and wide applicability of the DEM parameter calibration method proposed in this study. The calibrated DEM parameters are used to investigate the hysteretic behavior and deformation characteristics of the granular material, revealing that the accumulation of plastic strain and resilient modulus is related to confining pressure, stress level, and the number of cycles.

In order to accurately model the machine-lunar soil simulant interaction, this study combined physical and simulation experiments to calibrate the discrete element simulation parameters of the JLU-H lunar highland simulant. First, the intrinsic parameters and the true angle of repose of the JLU-H were determined through physical tests to provide data for subsequent simulation tests. A Plackett-Burman test was designed to identify and select the parameters that have a significant effect on the angle of repose. The range of values of the significant parameters was then optimized using the steepest climb test. The Box-Behnken test was then utilized to calibrate and obtain the optimal parameter combinations. Finally, a validation test of the angle of repose was conducted using the calibrated DEM parameters. The relative error between the simulation results and the test results was 1.54 %. Then further straight shear tests were conducted to verify the accuracy and validity of the DEM parameters. The results show that the calibrated parameters can provide a reference for the selection of discrete element simulation parameters for lunar soil simulant and the design and optimization of drilling and excavation machinery for lunar exploration. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The forage crop Caragana korshinskii Kom. is of high quality, and the biomechanical properties of its plant system are of great significance for the development of harvesting equipment and the comprehensive utilisation of crop resources. However, the extant research on the biomechanical properties of Caragana korshinskii Kom. is inadequate to enhance and refine the theoretical techniques for mechanised harvesting. In this study, we established a discrete element model of CKS based on the Hertz-Mindlin bonding contact model. By combining physical experiments and numerical simulations, we calibrated and validated the intrinsic and contact parameters. The Plackett-Burman design test was employed to identify the significant factors influencing bending force, and the optimal parameter combination for these factors was determined through response surface analysis. When the shear stiffness per unit area was 3.56x109 Pa, the bonded disk scale was 0.93 mm, the normal stiffness per unit area was 9.68x109 Pa, the normal strength was 5.62x107 Pa, the shear strength was 4.27x107 Pa, the discrete element numerical simulation results for three-point bending, radial compression, axial tension, and shear fracture exhibited a maximum failure force error of 3.32%, 4.37%, 4.87% and 3.74% in comparison to the physical experiments. In the cutting experiments, a smaller radial angle between the tool edge and the stem resulted in less damage to the cutting section, which was beneficial for the smoothness of the stubble after harvesting and the subsequent growth of the stem. The discrepancy in cutting force between the physical and numerical simulations was 3.89%, and the F-x (force versus displacement) trend was consistent. The multi-angle experimental validation demonstrated that the discrete element model of CKS is an accurate representation of the real biomechanical properties of CKS. The findings offer valuable insights into the mechanisms underlying crop-machine interactions.

Existing discrete element method-based simulation analysis of Panax notoginseng root soil separation still has the challenge to get the accurate and reliable basic parameters, which are necessary for discrete element simulation. In this paper, the P. notoginseng roots suitable for harvesting period were taken as the experimental object. Then using 3D scanning reverse modeling technology and EDEM software to establish the discrete element model of P. notoginseng, based on which, the physical and virtual tests were carried out to calibrate the simulation parameters. First, the basic physical parameters (density, triaxial geometric size, moisture content, shear modulus, and elastic modulus) and contact coefficients (static friction coefficient, rolling friction coefficient, and crash recovery coefficient between P. notoginseng roots and 65Mn steel) were measured by physical tests. Furthermore, treating the contact coefficients of P. notoginseng roots as the influence factor, the steepest uphill test, and four factors combing five levels of rotational virtual simulation are conducted. The measured relative error accumulation angle and simulation accumulation angle are set as the performance indices. The results show that the static friction coefficient, rolling friction coefficient, crash recovery coefficient, and surface energy coefficient of P. notoginseng roots are 0.55, 0.35, 0.16, and 19.5 J/m(2), respectively. Using calibration results as parameters of the vibration separation simulation test of P. notoginseng soil, the Box-Behnken vibration separation simulation tests were carried out, in which the vibration frequency, inclination angle, and vibration amplitude of separation device as factors, screening rate and damage rate of P. notoginseng soil complex are regarded as indices. The results show that the optimal operating parameters of the separation device are the vibration frequency of 10 Hz, the inclination angle of 5 degrees, and the amplitude of 6 cm. Based on the optimal operation parameters, the discrete element simulation experiment and field experiment of P. notoginseng roots soil separation are also performed to compare the soil three-dimensional trajectory space coordinates of P. notoginseng roots. From the results, three axis coordinate error is less than 15%. This proves that the calibration results are reliable. It can also provide the theoretical basis and technical support for the further study of the P. notoginseng root soil separation platform.

The tensile -shear interactive damage (TSID) model is a novel and powerful constitutive model for rocklike materials. This study proposes a methodology to calibrate the TSID model parameters to simulate sandstone. The basic parameters of sandstone are determined through a series of static and dynamic tests, including uniaxial compression, Brazilian disc, triaxial compression under varying confining pressures, hydrostatic compression, and dynamic compression and tensile tests with a split Hopkinson pressure bar. Based on the sandstone test results from this study and previous research, a step-by-step procedure for parameter calibration is outlined, which accounts for the categories of the strength surface, equation of state (EOS), strain rate effect, and damage. The calibrated parameters are verified through numerical tests that correspond to the experimental loading conditions. Consistency between numerical results and experimental data indicates the precision and reliability of the calibrated parameters. The methodology presented in this study is scientifically sound, straightforward, and essential for improving the TSID model. Furthermore, it has the potential to contribute to other rock constitutive models, particularly new user -defined models. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

A modified plastic Burgers model considering cohesion decay is proposed for frozen soils. A series of triaxial compression and creep tests were conducted on a kind of frozen silty clay for obtaining the model parameters. According to typical triaxial creep strain curves with only a decaying creep stage, a deformation parameter calibration method for a plastic Burgers model is proposed, and the validity of the method was further verified. When the original plastic Burgers model was incorporated with a cohesion decay function, it was shown that the successive development process of frozen soil creep strain from the decaying to non-decaying stage could be described reasonably. The modified model is applicable to frozen ground engineering cases with non-decaying creep involved.