Three-phase Dynamic Model Research Articles

Effect of AES anionic surfactant on the microstructure and wettability of coal

The paper object is high-quality Shenmu bituminous coal modified by fatty alcohol polyoxyethylene ether sodium sulfate (AES) surfactant. The changes in functional groups, free radicals, Zeta potential, and contact angle of coal modified in AES anionic surfactant were analyzed. Based on the molecular structure of Shenmu coal, a coal-AES-water three-phase dynamic model was constructed. The wetting mechanism of coal was studied by molecular dynamics. The research has demonstrated that as the mass fraction of AES surfactant increases, the proportion of polar groups (-OH, C–O–C, –COOH, –CO), free radical content and Zeta potential increased significantly. The size of contact angle displayed a major negative linear correlation with the proportion of polar groups and free radicals, but positively linearly correlated with the Zeta potential. In the coal-AES-water three-phase dynamic model, the AES molecules adhere to coal molecules as hydrophobic group, while hydrophilic groups extended into the water. This increased H2O diffusion coefficient, enhanced action energy between coal and water interface, decreasing surface tension and achieving effective wetting of the coal. This paper supplies s a new idea for selecting efficient surfactants to change the coal microstructure. It is of major importance for improving coal wettability and offers a theoretical foundation for gas drainage and disaster prevention.

Modeling and solution method of gas-liquid-solid three-phase flow mixing

The mixing process of gas-liquid-solid three-phase flow is a complex multi-fluid-structure coupling dynamic problem. The relationship between the particle parameters and the physical spatial scale of the flow channel directly affects the calculation convergence. Numerical modeling and mesh processing of fluid-structure bidirectional interaction in the strong shear zone are difficult. Aiming at the above problems, a method of modeling and solving the gas-liquid-solid three-phase flow mixing is proposed. Based on the volume-of-fluid coupled with discrete-element-method model, a three-phase dynamic model considering particle motion is established. By solving the momentum equation, the bidirectional coupling of two-phase fluid and particle is realized. The user-defined function communication interface is developed independently to obtain the interaction force between fluid and particles, and a porous-interphase coupling solution is proposed to describe the trajectory of particles. Taking the mixing process of three-phase flow with strong shear for example, this method is used to study the influence of different aeration conditions on the free surface, velocity distribution and particle suspension characteristics in the physical space of the flow channel. The results show that strong shear and wall action can convert the tangential velocity of the fluid into axial and radial velocity; choosing an appropriate inflation velocity can eliminate the instability of the free surface and increasing the flow velocity of the fluid has a limited effect on the suspension of particles in some areas. The research results can provide a useful reference for studying the interaction mechanism of complex multiphase flow, and also provide technical support for the mixing production control of gas-liquid-solid three-phase particles.

Motion Analysis and Control of a Single Leg of Hydraulically Actuated Quadruped Robots during Vertical Hopping

To address the requirements of high speed and mobility for quadruped robots under unstructured environments,a structure model of hydraulically actuated single leg is proposed.For vertical hopping,a two-phase kinematic model and a three-phase dynamic model of a single leg are established under the structure model.After that,the state analysis on the vertical hopping is conducted,and the inverse kinematics solution and the simulation of the hopping are also implemented for a single leg mass-center’s instant vertical hopping with 1.5 m/s.Then,the ground impact on the body structure,the operation characteristics and the output force of the hip joint and knee joint’s hydraulic cylinder,as well as the hydraulic system design during vertical hopping are discussed.Meanwhile,taking the periodicity of vertical hopping of a single leg into consideration,a PD(proportional-derivative) iterative learning control algorithm is applied to joint trajectory tracking,based on single leg’s dynamic model with hydraulic offset.The simulation results indicate that rapid and robust convergence is achieved in trajectory tracking using the presented model,which offers the design and control references for the succeeding prototype development.