ELECTRO-HYDRAULIC SERVO SYSTEM IN THE CENTRIFUGE FIELD

The mechanical characteristics of the electro-hydraulic servo system in thecentrifuge field are analyzed. The hydraulic pressure law in the centrifuge field indicates theexistence of the centrifuge hydraulic pressure. The mechanical characteristics of the slide-valveand the dual nozzle flapper valve are studied, and it is found that the centrifuge field can notonly increase the driving force or moment of the function units, but also decrease the stability ofthe components. Finally by applying Gauss minimum constraint principle, the dynamic model of theelectro-hydraulic vibrator in the centrifuge field is established, and the mechanical restriction ofthe system is also presented. The study will be helpful for the realization of the combinedvibration and centrifuge test system.

PARTICLE DISTRIBUTION IN CENTRIFUGAL ACCELERATING FIELDS

Based on continuum theory and moving law of particles, a model is presentedto obtain gradient distribution of particles in centrifugal accelerating field, by which theparticle distribution in gradient composite material can be predicted. The simulation shows withincreases in rotating time, four regions gradually appear from the internal periphery to theexternal one, they are free region, transition region, steady region and surface reinforced region,and the latest three regions are defined as a rich region. Finally, the steady region disappears,and the rich region only includes transition region and surface reinforced region. The influences ofcentrifugal acceleration coefficient G, primary volume fraction phi_0, pouring temperature theta_pand density difference between the particle and the metal matrix on particles gradient distributionare studied in detail. The results of the theoretical analysis agree with experiment ones. Both ofanalysis and experiment results indicate that with the increase in G and theta_p the particledistribution becomes more centralized and the consistence of particle in the surface peripherybecomes larger.

INFILTRATION KINETICS MODEL OF LIQUID METAL INTO A FIBROUS PREFORM IN CENTRIFUGAL ACCELERATING FIELD

The infiltration kinetics of the metal melt into a fibrous preform in centrifugal accelerating field is analyzed on the basis of Darcy's law and the assumption that the fibrous preform is treated as 'bundle of capillaries' The critical rotating speed is analyzed with the established model The influences of the metal melt mass,the rotating speed of the equipment,the casting height, the original outer radius of the metal melt and the fibrous volume fraction in fibrous preform on infilatration are studied The results show that the critical rotating speed is dependent on critical pressure, casting height, metal melt mass and the character of fibrous preform With the increase in the metal melt mass, rotating speed of the equipment and original outer radius of the metal melt, or the decrease in casting height and fibrous volume fraction in fibrous of the metal melt,or the decrease in casting height and fibrous volume fraction in fibrous preform,infiltration of metal melt for fibrous preform becomes easier.

Numerical Investigation of Submarine Hydrodynamics and Flow Field in Steady Turn

This paper presents numerical simulations of viscous flow past a submarine model in steady turn by solving the Reynolds-Averaged Navier-Stokes Equations（RANSE） for incompressible, steady flows. The rotating coordinate system was adopted to deal with the rotation problem. The Coriolis force and centrifugal force due to the computation in a bodyfixed rotating frame of reference were treated explicitly and added to momentum equations as source terms. Furthermore, velocities of entrances were coded to give the correct magnitude and direction needed. Two turbulence closure models（TCMs）, the RNG k-ε model with wall functions and curvature correction and the Shear Stress Transport（SST） k-ω model without the use of wall functions, but with curvature correction and low-Re correction were introduced, respectively. Take DARPA SUBOFF model as the test case, a series of drift angle varying between 0° and 16° at a Reynolds number of 6.53×10^6 undergoing rotating arm test simulations were conducted. The computed forces and moment as a function of drift angle during the steady turn are mostly in close agreement with available experimental data. Though the difference between the pressure coefficients around the hull form was observed, they always show the same trend. It was demonstrated that using sufficiently fine grids and advanced turbulence models will lead to accurate prediction of the flow field as well as the forces and moments on the hull.

MODAL TEST AND ANALYSIS OF CANTILEVER BEAM WITH TIP MASS

The phenomenon of dynamic stiffening is a research field of general interest for flexible multi-body systems.In fact,there are not only dynamic stiffening but also dynamic softening phenomenon in the flexible multi-body systems.In this paper,a non-linear dynamic model and its linearization characteristic equations of a cantilever beam with tip mass in the centrifugal field are established by adopting the general Hamilton Variational Principle.Then,the problems of the dynamic stiffening and the dynamic softening are studied by using numerical simulations.Meanwhile, the modal test is carried out on our centrifuge.The numerical results show that the system stiffness will be strengthened when the centrifugal tension force acts on the beam (i.e.the dynamic stiffening).However,the system stiffness will be weakened when the centrifugal compression force acts on the beam (i.e.the dynamic softening). Furthermore,the equilibrium position of the system will lose its stability when the inertial force reaches a critical value.Through theoretical analysis,we find that this phenomenon comes from the effect of dynamic softening resulting from the centrifugal compression force.Our test results verify the above conclusions and confirm that both dynamic stiffening and softening phenomena exist in flexible multi-body systems.

Energy dissipation mechanism and experiment of particle dampers for gear transmission under centrifugal loads

As a passive means of vibration reduction, particle damping is mainly applied to the horizontal or vertical steady field. However, it is seldom applied to centrifugal fields. Under high speed and heavy loading, the vibration of tooth surfaces of gear transmissions becomes more severe shortening gear service life and augmenting noise. Under centrifugal loading, the particle system exhibits different characteristics, for example, particles are extruded at the end farthest from the center. We investigated gears with drilled via holes filled with damping particles. Using the discrete-element method, we developed an energy dissipation model for the particle system accounting for friction and inelastic collisions. Energy dissipation and damping characteristics of this system were analyzed. Experiments were also conducted with the gear system having different particle filling rates. The results show that this filling rate is an important parameter associated with particle damping in a centrifugal field. An unsuitable filling rate would significantly reduce damping effectiveness. With changes in rotation speed and load, the gear transmission system has different optimal filling rates. The results provide guidelines for the application of particle damping in centrifugal fields of gear transmissions.