Discrete element simulation study of mixing process of Guizhi Fuling Capsules: parameter calibration / 中国中药杂志

The mixing process is a critical link in the formation of oral solid preparations of traditional Chinese medicine. This paper took the extract powder of Guizhi Fuling Capsules and Paeonol powder as research objects. The angle of repose, loose packing density, and particle size of the two powders were measured to calibrate discrete element simulation parameters for the mixing process. The discrete element method was used to calibrate the simulated solid density of Paeonol powder and extract powder of Guizhi Fuling Capsules based on the Hertz-Mindlin with JKR V2 contact model and particle scaling. The Plackett-Burman experimental design was used to screen out the critical contact parameters that had a significant effect on the simulation of the angle of repose. The regression model between the critical contact parameters and the simulated angle of repose was established by the Box-Behnken experimental design, and the critical contact parameters of each powder were optimized based on the regression model. The best combination of critical contact parameters of the extract powder of Guizhi Fuling Capsules was found to be 0.51 for particle-particle static friction coefficient, 0.31 for particle-particle rolling friction coefficient, and 0.64 for particle-stainless steel static friction coefficient. For Paeonol powder, the best combination of critical contact parameters was 0.4 for particle-particle static friction coefficient and 0.19 for particle-particle rolling friction coefficient. The best combination of contact parameters between Paeonol powder and extract powder of Guizhi Fuling Capsules was 0.27 for collision recovery coefficient, 0.49 for static friction coefficient, and 0.38 for rolling friction coefficient. The verification results show that the relative error between the simulated value and the measured value of the angle of repose of the two single powders is less than 1%, while the relative error between the simulated value and the measured value of the angle of repose of the mixed powder with a mass ratio of 1∶1 is less than 4%. These research results provide reliable physical property simulation data for the mixed simulation experiment of extract powder of Guizhi Fuling Capsules and Paeonol powder.

Calibration of discrete element simulation parameters of Chinese medicine extract powders / 中草药

Objective: The discrete element method (DEM) was used to simulate the angle of repose of Chinese medicine extract powders. The contact parameters between particles and between particles and geometry were calibrated. Methods: The licorice extract powder, the extract powders of Angelicae Pubescentis Radix (Duhuo), microcrystalline cellulose (MCC) and ethyl cellulose (EC) were taken as the research objects. DEM was performed based on the Hertz-Mindlin with JKR Cohesion contact model and particle scaling. The Plackett-Burman design was used to screen out the critical contact parameters that had significant impact on the simulation measurement of the angle of repose. Then, the steepest climbing design was used to determine the best area of critical contact parameters. After that, a regression model between the contact parameters and the simulated angle of repose was established according to the Box-Behnken test results, and the best contact parameter values were optimized and verified. Results: The critical contact parameters selected were particle-particle rolling friction coefficient, particle-particle restitution coefficient and particle-stainless steel restitution coefficient. The calibration range of the built regression model was from 33.30° to 43.64°. The absolute values of the relative error between the simulated values and the experimental values of the angle of repose for four powders were all less than 2.0%, indicating that the established calibration method was accurate and reliable. Conclusion: This article proved the feasibility of calibrating the DEM micromechanical parameters of the Chinese medicine particle system through the macroscopic physical parameter, and laid the foundation for accurate simulation of Chinese medicine pharmaceutical processes like powder mixing and conveying.

Applicability of Foot-Ground Contact Model at Different Gait Speed / 医用生物力学

Objective To establish the musculoskeletal multi-body dynamic foot-ground contact model and explore its applicability at different speed. Methods The gait data of the subjects at different speed were collected, and the foot-ground contact model was established based on the full body model from the musculoskeletal multibody dynamic software AnyBody. Then the calculated ground reaction forces (GRFs) and ground reaction moments (GRMs) at different speed (slow walking, normal walking, fast walking and jogging) were compared with the measurements from the force plates. Results The predicted GRFs and GRMs correlated well with the experimental measurements at slow, normal and fast speed (stride speed ranged from 0.69 to 1.68 m/s). The correlation coefficients between predicted and measured GRFs were greater than 0.875 and the correlation coefficients for GRMs were greater than 0.9. Conclusions The developed foot-ground contact model could simultaneously predict GRFs and GRMs with good accuracy, thus eliminating the dependency on force plates. The model could be applied to low-speed gait conditions, such as the elderly and pathological gait.