Search Results (3)

Since the research of $\mu$-synchronization helps to explore how complex networks (CNs) work together to produce complex behaviors, the $\mu$-synchronization task for uncertain time-delayed CNs is studied in our work. Especially, bounded external perturbations and variable delays of unknown bounds containing coupling delays, internal delays, and pulse delays are all taken into consideration, making the model more general. Through the $\mu$-stable theory together with the hybrid impulsive control technique, the problems caused by uncertain inner couplings, time-varying delays, and perturbations can be solved, and novel synchronization criteria are gained for the $\mu$-synchronization of the considered CNs. Different from traditional models, it is not necessary for the coupling matrices to meet the zero-row-sum condition, and the control protocol relaxes the constraint of time delays on impulse intervals. Moreover, numerical experiments and image encryption algorithms are carried out to verify our theoretical results’ effectiveness. Full article

This paper aims to reveal the motion law and collision behaviors of shotcrete particle flow jets. A physical model of the jet flow field composed of a nozzle structure and jet area was constructed and meshes with various sizes were used to mesh the nozzle and jet area. With the basic contact parameters and contact model parameters of the particles set, the CFD-DEM-coupling simulation method was adopted to perform the numerical simulation of concrete-particle-flow-jet impingement. The variation laws of the continuous-phase velocity and pressure drop of the shotcrete, coarse-aggregate motion characteristics, and particle collision behavior under the interaction of the continuous and discrete phases were obtained. The results showed that the velocity field and pressure-drop field of the continuous phase had an ideal symmetry in the XY plane in the stable injection stage, the continuous-phase velocity gradually increased inside the nozzle and gradually decreased after entering the jet area, the continuous-phase pressure drop was the maximum at the nozzle inlet, and the pressure value at the nozzle outlet became atmospheric pressure. The central axis of the particle flow jet was displaced by 0.15 m in the negative direction of the Y-axis under the action of gravity, the diffusion angle of the small particles that exited the nozzle and entered the jet area was larger than that of the large particles, and the large-particle jets were more concentrated and easier to spray into the designated spraying areas. The particle flow reached a stable jet state about 0.3 s after the jet began, and the peak velocity of the 4 mm particles in the flow reached 25 m/s, while the peak velocity of the 12 mm particles was only 19 m/s. The acceleration time for particles of different sizes to reach the peak velocity also varied, and the large particles took longer to reach the maximum velocity: small particles reached their peak within 0.4 m–8 m of the jet area, and large particles reached their peak within 0.8 m–1.2 m of the jet area. The particle velocity peaked within 0.6 m–1 m of the jet area. Particle collision took three forms: particle collision with the inner wall of the nozzle, interparticle collision, and particle collision with the sprayed wall. The collision between the particles and the sprayed wall was the main form leading to the rebound of the wet shotcrete, and the rebound angle after particle collision was uncertain. Full article

Micro-particle manipulation, based solely on the Dean drag force, has begun to be advocated for with the goal of lowering the pumping pressure and simplifying the complexity of the coupling effects of the inertial lift force and the Dean drag force, thus reducing the difficulty of theoretically predicting particle motion. We employed the CFD-DEM two-way coupling method in this work to quantitatively study the lateral (z in axis) motion of particles (7–10 $\mathsf{\mu }\mathrm{m}$), in square or half-circle segment serpentine microchannels, that was only reliant on Dean drag with the blockage ratio $\frac{d}{D_h}=$ 0.04 (the inertial lift effects show at $\frac{d}{D_h}>0.07$). In the square-segment serpentine channel, under the conditions of single-side-wall sheath flow and sedimentation, we discovered that the particles exhibit a twist-type lateral trajectory around each turn, with the larger particles always twisting in the opposite direction of the smaller particles, as a result of the four-grid-pattern distribution of the lateral velocity values at each turn. The large and small particles are separated at the channel’s exit at $Re$ = 56.7, De = 17.8, indicating the likelihood of separation only due to the Dean drag. This separation efficiency decreases as $Re$ and De decreases. The lateral position and velocity values of the particles oscillate, as time passes, due to the twist trajectory, with the oscillation amplitude increasing as $Re$ or De decreases and deflecting toward the inner side of z. In the cases of the two-side-wall-symmetric sheath flow, the particles exhibit only a little lateral deflection, and particle separation is not achieved. The deflection of the oscillation is uncertain and does not change regularly with any physical quantity. Full article