An overview on nonlinear porous flow in low permeability porous media

This paper gives an overview on nonlinear porous flow in low permeability porous media, reveals the microscopic mechanisms of flows, and clarifies properties of porous flow fluids. It shows that, deviating from Darcy＇s linear law, the porous flow characteristics obey a nonlinear law in a low-permeability porous medium, and the viscosity of the porous flow fluid and the permeability values of water and oil are not constants. Based on these characters, a new porous flow model, which can better describe low permeability reservoir~ is established. This model can describe various patterns of porous flow, as Darcy＇s linear law does. All the parameters involved in the model, having definite physical meanings, can be obtained directly from the experiments.

Kinetic study of transverse electron-scale interface instability in relativistic shear flows

Interfacial magnetic field structures induced by transverse electron-scale shear instability(mushroom instability)are found to be strongly associated with electron and ion dynamics,which in turn will influence the development of the instability itself.We find that high-frequency electron oscillations are excited normal to the shear interface.Also,on a larger time scale,the bulk of the ions are gradually separated under the influence of local magnetic fields,eventually reaching an equilibrium related to the initial shear conditions.Wepresent a theoretical model of this behavior.Such separation on the scale of the electron skin depth will prevent different ions from mixing and will thereafter restrain the growth of higher-order instabilities.We also analyze the role of electron thermal motion in the generation of the magnetic field,and we find an increase in the instability growth rate with increasing plasma temperature.These results have potential for providing a more realistic description of relativistic plasma flows.

Digital Twin Implementation of Autonomous Planning Arc Welding Robot System

Industrial robots are currently applied for ship sub-assembly welding to replace welding workers because of the intelligent production and cost savings.In order to improve the efficiency of the robot system,a digital twin system of welding path planning for the arc welding robot in ship sub-assembly welding is proposed in this manuscript to achieve autonomous planning and generation of the welding path.First,a five-dimensional digital twin model of the dual arc welding robot system is constructed.Then,the system kinematics analysis and calibration are studied for communication realization between the virtual and the actual system.Besides,a topology consisting of three bounding volume hierarchies(BVH)trees is proposed to construct digital twin virtual entities in this system.Based on this topology,algorithms for welding seam extraction and collision detection are presented.Finally,the genetic algorithm and the RRT-Connect algorithm combined with region partitioning(RRT-Connect-RP)are applied for the welding sequence global planning and local jump path planning,respectively.The digital twin system and its path planning application are tested in the actual application scenario.The results show that the system can not only simulate the actual welding operation of the arc welding robot but also realize path planning and real-time control of the robot.

THE BUYER＇S PROCURING MECHANISM UNDER OPERATING COST SHARING IN SUPPLY CHAIN

This paper considers a buyer＇s procuring strategy where the buyer purchases products from a supplier in order to minimize his total cost. Assume that the customer arrivals follow a Poisson process, a base-stock policy is implemented by the buyer, and the supplier will afford partial operating cost incurred by the buyer; The cost shared by the buyer includes procuring cost and some operating cost; The supplier does not hold the inventory and her production time is exponentially distributed. The objective of the supplier is to maximize her profit. The buyer designs a contract to minimize his total expected cost. Two different cases are considered： One potential supplier and many competing suppliers. The optimal control approaches are used to design the buyer＇s optimal mechanism and some simple procurement mechanisms are presented.