Numerical Investigation of Flow Motion and Performance of A Horizontal Axis Tidal Turbine Subjected to A Steady Current

Horizontal axis tidal turbines have attracted more and more attentions nowadays, because of their convenience and low expense in construction and high efficiency in extracting tidal energy. The present study numerically investigates the flow motion and performance of a horizontal axis tidal turbine with a supporting vertical cylinder under steady current. In the numerical model, the continuous equation and incompressible Reynolds-averaged Navier-Stokes equations are solved, and the volume of fluid method is employed to track free surface motion. The RNG k-ε model is adopted to calculate turbulence transport while the fractional area/volume obstacle representation method is used to describe turbine characteristics and movement. The effects of installation elevation of tidal turbine and inlet velocity on the water elevation, and current velocity, rotating speed and resultant force on turbine are discussed. Based on the comparison of the numerical results, a better understanding of flow structure around horizontal axis tidal turbine and turbine performance is achieved.

Steady motion and spiral patterns in typhoon

By using the equations describing typhoons in the atmosphere, the steady three-dimensional stream fieldand the corresponding pressure and temperature fields are obtained. The three-dimensional velocity fields construct anonlinear autonomuos system in the physical space. It is shown that the center of typhoon is a local minimum pressurewith positive vertical vorticity and horizontal convergence in lower levels and a local maximum pressure with negativevertical vorticity and horizontal divergence in the upper levels. Because there exits two saddle-focus points in the autnomous system, there exist the spiral patterns, in which the winds blow spirally in and out of the center in the lowerand upper levels in the Northern Hemisphere and cause the ascending motion near the center and dascending motionnear the edge, respectively . All these are in fair conformity with the observations. It implies that the rotation of earthand the viscosity of air play an important role in the spiral structure of typhoons.

STEADY STATE MOTIONS OF SHALLOW ARCH UNDER PERIODIC FORCE WITH 1:2 INTERNAL RESONANCEON THE PLANE OF PHYSICAL PARAMETERS

The bifurcation dynamics of shallow arch which possesses initial deflection under periodic excitation for the case of 1:2 internal resonance is studied in this paper. The whole parametric plane is divided into several different regions according to lire types of motions; then the distribution of steady state motions of shallow arch on the plane of physical parameters is obtained. Combining with numerical method, the dynamics of the system in different regions, especially in the Hopf bifurcation region, is studied in detail. The rule of the mode interaction and the route to chaos of the system is also analysed at the end.