The droplet transition of electrical arc welding is a complicated process that combines heat, mass and momentum transfer. A high-speed camera system with laser in the background is established to observe the fast changing process of molten droplet transition. A group of high-speed camera pictures which indicate the droplet gravity center is unstable in welding metal transfer process are taken and analyzed. The experimental results show that the electromagnetic force is the unstable root of the droplet gravity center.

The droplet transition of electrical arc welding is a complicated process that combines heat, mass and momentum transfer. A high-speed camera system with laser in the background is established to observe the fast changing process of droplet transition. A group of high-speed camera pictures which indicate that the size and shape of droplet have strong uncertainty are taken and analyzed. The results show that the randomness of droplet size and shape are decided by its internal and external random factors, such as: the changing of the length of welding wire stretched out, the fluctuation of the feed speed of welding wire etc.

Fractured reservoirs simulation has long been challenge to reservoir engineers to handle the complex geometry structure of fractured reservoir and fluid flow processes in it which includes viscous, capillary, gravitational and diffusive effect. In traditional reservoirs simulation, the fractured reservoir is usually divided into matrix and fracture interacting continua such as Dual Porosity model or Dual Permeability model. It is assumed in these models that the fracture system is in a steady state which the width, length, density of the fractures in reservoir does not change during the whole production history, therefore, it is not possible to simulate fractures variation effect with these models.In order to simulate the unsteady state of fracture system, a dynamic hybrid model has been developed in the paper which a dynamic transitivity tensor model is overlapped to Dual Porosity model. It is assumed that the fracture network is the primary continuum for fluid flow, the matrix of low permeability, high storability is considered to be a sink or source to the fracture. The matrix and the fracture communicate through an exchange term which describes the fluid flow between matrix and fracture. The fracture network is considered to be in unsteady state in which fracture has possibility to widen, lengthen, and close during oil production. A transitivity tensor is introduced to describe these processes, which is a function of pressure, stress, density of fractures.The paper will detail the dynamic hybrid model such as its assumptions, equations, mechanisms and also its applications in the fractured reservoirs simulation. The simulation results show that the dynamic hybrid model has high potential to accurately simulate the dynamic fracture network as well as the fluid flow with the capillary, gravitational and diffusive effects between matrix and fracture. TX 75083-3836, U.S.A., fax +1-972-952-9435

Based on the high-speed photography, the effect of phase relations on droplet transfer and welding seam was analyzed. To each TCGMAW (Twin-wire Co-pool Gas-shielded Metal Arc Welding) torch at four-wire welding robot, under the descriptive welding parameters, when the phase relation of the front wire and the back wire was alternate, the arcs of the two wires had no effect on each other basically; the welding seam shaped very well. When the phase relation was synchronized, the arcs attracted each other and the two arcs centralized to the middle of the two wires; the humping bead was formed. When the phase relation was random, now and then the arcs synchronized and attracted each other, and at times the arcs changed alternately and had no effect on each other; the appearance quality of the welding seam was moderate.