The increase of world population has been requiring more and more lands for human activities, which is why the world dredging market has been significantly growing up during the past 20 years. In dredging engineering, underwater excavation process is one of the major procedures which involves complicated physics, no matter it is sand, clay or rock on the seabed. It is important to reasonably estimate the cutting force needed on the excavator blade, which will help to improve the design and reduce the wear of the equipment so that higher working efficiency can be achieved. However, it is known that the cutting force is greatly influenced by the local water pressure especially in deep water. The fluid flow will change the pore pressure distribution and meanwhile apply certain force to the solid particles. Since the experiments to measure the cutting force are expensive, a numerical model is then needed to describe the physics in it. In this paper, the author tends to use the discrete element modeling to describe the solid particle movement and particle-particle interactions, and the finite volume method to calculate the fluid pressure distribution and flow velocity. Besides, a coupling deck is used between the two models to exchange the information to describe the fluid-solid interaction. This research has proven the feasibility of applying such a method in the underwater excavation process. Further calibration and validation are still necessary depends on the soil properties of the seabed.

This paper reports electric properties calculation of a composite housed SF6 insulated bushing based on the finite element method. After introducing different stages of electric field distribution under DC voltage, the finite element method and boundary conditions are described. The electric field distribution, time constant of transmission from conductive distribution to resistive distribution are presented, taking a polarity reversal into consideration. The surface charge formation, its influence of electric distribution, and the influence of polarity reversal are discussed as well. The polarity reversal and its effect on the electric properties of the bushing are focused on in this paper.

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This paper investigates the insulation reliability of 380 kV XLPE cable systems. In order to obtain sufficient service experience of 380 kV XLPE cable systems and detailed failure information, both literature survey and internal interview with several TSO's (Transmission System Operators) in Europe have been carried out. Based on the collected in-service and failure populations regarding insulation, failure rates of 380 kV XLPE cable systems are statistically investigated with a confidence interval, regarding to some uncertainties. The calculated failure rates are compared with those from literatures. It shows that the results that the failure rates from the existing literatures are not suitable for 380 kV XLPE cable systems, because they are dominated by the failures from 220 kV cable systems. The most important consequence for TSO's is forced outage time, therefore these outage time caused by failures is also discussed.

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