An Efficient Ship Automatic Collision Avoidance Method Based on Modified Artificial Potential Field

A novel collision avoidance (CA) algorithm was proposed based on the modified artificial potential field (APF) method, to construct a practical ship automatic CA system. Considering the constraints of both the International Regulations for Preventing Collisions at Sea (COLREGS) and the motion characteristics of the ship, the multi-ship CA algorithm was realized by modifying the repulsive force model in the APF method. Furthermore, the distance from the closest point of approach-time to the closest point of approach (DCPA-TCPA) criterion was selected as the unique adjustable parameter from the perspective of navigation practice. Collaborative CA experiments were designed and conducted to validate the proposed algorithm. The results of the experiments revealed that the actual DCPA and TCPA agree well with the parameter setup that keeps the ship at a safe distance from other ships in complex encountering situations. Consequently, the algorithm proposed in this study can achieve efficient automatic CA with minimal parameter settings. Moreover, the navigators can easily accept and comprehend the adjustable parameters, enabling the algorithm to satisfy the demand of the engineering applications.

An Improved Dynamic Boundary Condition in SPH Method

Dynamic boundary condition (DBC) has been widely used in SPH method. However, in certain situations, it was found that a few fluid particles could break through the boundary or were not reflected specularly. Of course, these phenomena are unphysical. To improve the performance of DBC, an improved dynamic boundary condition (IDBC) was presented in this paper. To prevent fluid particles from breaking through the boundary, the repulsive force of boundary particles was enhanced by expanding the equation of state into a higher order. To deal with the asymmetry of DBC, a rectangular support domain attached to boundary particles and a corresponding correction factor are proposed. The results of three test cases showed that the performance of IDBC was satisfied.

Coherent and Compact Zinc Electrodeposition Enabled by Compressing the Electric Double Layer of the Deposits

The porous hexagonal-platelet Zinc (Zn) deposits exacerbate the chemical corrosion and deteriorate the reversibility of the Zn electrodes in aqueous electrolytes. Based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, to turn the messy Zn deposits into agglomerate ones, the challenge is to weaken the electric double layer repulsive force, which is the main reason preventing the dense Zn deposits, between the electrodeposited Zn particles. Here, we proposed a strategy to compress the electric double layer and regulate the forces between the electrodeposited Zn particles by introducing inert charges to the surface of the Zn deposits. The results of the electron microscopies revealed dense and coherent electrodeposition of Zn, indicating that the van der Waals attraction between the deposits becomes governing during electrodeposition. Such results could be attributed to the adsorbed inert charges on Zn deposits decrease the net charges and weaken the electric double layer repulsive force. This design enables the Zn||Zn cells a long-term plating/stripping stability for > 1200 h, a high average Coulombic Efficiency of 99.9% for > 2100 h, and steady charge/discharge responses even under a draconian deep-discharge condition of 80% depth of discharge of Zn (DODZn). In addition, the Zn||VS2 full cells demonstrate significantly improved electrochemical reversibility and capacity retention.

Framboid Self-Assembly and Self-Organization

The formation of framboids involves two distinct processes. First, pyrite microcrystals aggregate into spherical groups through surface free energy minimization. The self-assembly of framboid microcrystals to form framboids is consistent with estimations based on the classical Derjaguin-Landau-Verwey-Overbeek (DVLO) theory, which balances the attraction between particles due to the van der Waals forces against the interparticle electrostatic repulsive force. Second, the microcrystals rearrange themselves into ordered domains through entropy maximization. Icosahedral symmetry tends to minimize short-range attractive interactions and maximize entropy. The physical processes which facilitate this rearrangement are Brownian motion and surface interactions. Curved framboid interface enforce deviation from the cubic close packed structure. In the absence of a curved surface, weakly interacting colloidal particles preferentially self-assemble into a cubic close packed structure, and this is observed in irregular, non-framboidal aggregates of pyrite micro- and nanocrystals.