PFC2D数值方法程序.ppt

单位制 操作窗口 谢 谢 */160 MECHANICAL DAMPING Mechanical damping is used in UDEC for static (non-inertial) solutions and for dynamic solutions. For static analysis, the approach is similar to “dynamic relaxation.” The equations of motion are damped to reach a force equilibrium state as quickly as possible under the applied initial and boundary conditions. */160 DYNAMIC RELAXATION In dynamic relaxation blocks (and gridpoints) are moved according to Newton’s law of motion. The equations of motion are damped to reach a force equilibrium state as quickly as possible Damping is velocity-proportional – i.e., the magnitude of the damping force is proportional to the velocity of the blocks. Velocity-proportional damping introduces body forces that can affect the solution. UDEC provides two different types of damping to minimize this problem for static analysis: adaptive global damping (DAMP auto) local damping (DAMP local) */160 ADAPTIVE GLOBAL DAMPING Adaptive global damping is a servo-mechanism used to adjust the damping constant automatically such that the power absorbed by damping is proportional to the rate of change of kinetic energy in the system. Adjustment of the viscosity constant is made by a numerical servo-mechanism that seeks to keep the ratio, R, equal to a given ratio (e.g., 0.5). Damping forces are introduced to the equations of motion: where Fi is the unbalanced force */160 LOCAL DAMPING The damping force, Fd is: In UDEC the unbalanced force ratio (ratio of unbalanced force, Fi , to the applied force magnitude, Fm) is monitored to determine the static state. By default, when Fi / Fm 10-5 in UDEC then the model is considered to be in an equilibrium state. The damping force at a gridpoint is proportional to the magnitude of the unbalanced force with the sign set to ensure that vibrational modes are damped. */160 BASIS OF STATIC SOLUTIONS IN UDEC The unbalanced force ratio (ratio of unbalanced force, Fi ,