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In order to obtain the hydrodynamic characteristics of the unmanned underwater vehicle (UUV) parking on the seabed and the effect of vertical thrusters on it, two kinds of UUV, with and without vertical thrusters respectively, were modeled and meshed using the software ANSYS ICEM in different distances from the seabed and different seabed oblique angles, and the flow fields around these UUVs were simulated by using CFX. From the simulation, the lateral forces and lifts of these two UUVs under different conditions were obtained and the curves of lateral forces and lifts changing with distance from the seabed, oblique angle and water velocity were analyzed. Finally, the effect of vertical thrusters on the hydrodynamic characteristics was analyzed according to the simulation results. The results reveal that the effect of the distance from the seabed on the lateral forces is minor while that on lifts is great; both of the lateral forces and lifts increase rapidly with the increase of water velocity; the lateral forces decease slowly with the increase of the absolute value of seabed oblique angle while lifts increase rapidly; the lateral forces of UUV with vertical thrusters are 5% ~ 15% larger than that if UUV without vertical thrusters while lifts are several times larger. [ABSTRACT FROM AUTHOR]

Deformation and failure of coal is a complex process with damage evolution, so it's important to study the energy mechanism during coal damage process under all kinds of loading conditions. A serial of cyclical loading and unloading tests of coal were conducted under different confining pressures by means of an advanced conventional triaxial compression testing system. The damage process of coal under confining pressure was discussed carefully. Experimental results show that hysteresis loops of coal occurs under cyclical loading and unloading conditions and correspondingly damage dissipation energy increase with increasing stress. Elastic modulus of coal would decrease with increasing cyclical stress under low confining pressure or uniaxial compression, but it would not decrease with increasing cyclical stress under high confining pressure. It indicates that damage mechanism changes due to the effect of confining pressure. So a new definition of coal damage variable was suggested based on energy analysis and the corresponding damage evolution regular was given. Such definition avoids the default of traditional definition of damage variable based on elastic modulus and can well describe the damage content of coal under different confining pressures. [ABSTRACT FROM AUTHOR]